KR102787082B1 - Curable composition for forming a light scattering layer - Google Patents

Abstract

The curable composition comprises at least one fluoropolymer, at least one monofunctional (meth)acrylate, at least one difunctional (meth)acrylate, and at least one initiator. The curable composition, when cured, forms an optically-scattering layer, the optically-scattering layer comprising a matrix and phase-separated microdomains. The matrix and the phase-separated microdomains have different refractive indices, and the microdomains are on the order of a wavelength of visible light or greater.

Description

Curable composition for forming a light scattering layer

The present invention relates to an optical light scattering layer formed from a curable polymer composition.

Increasingly, optical devices are becoming more complex and involving more and more functional layers. As light travels through the layers of an optical device, the light can be altered by the layers in a wide variety of ways. For example, the light can be reflected, refracted, or absorbed. Frequently, layers are incorporated into an optical device for more than one purpose. For example, a layer that is used as a spacer layer to separate two layers, which is a mechanical function, may also be said to provide an optical function, such as transmitting or diffusing light.

One optical function that utilizes organic layers is the diffusion of light. Optical devices include, for example, information displays, such as liquid crystal displays and rear projection screens. These devices often rely on light-diffusing optical structures for efficient operation and improved readability. Such light-diffusing structures are believed to play an important role in these displays by forward-scattering light from a light source without significant loss of forward-scattered light intensity. This generated light, which is scattered but still has high transmittance, provides a desirable background brightness for such displays by reducing the amount of incident light that is reflected back toward the light source or backscattered. Elimination or limitation of such "backscattered" light is an important factor in designing such light-diffusing structures. Diffusers can be introduced into an optical system by adding additional diffuser components to the optical system, or in some cases by introducing diffusing properties into existing components.

Adding additional components to an optical system has the disadvantage of introducing additional absorption and creating additional interfaces that can reflect light, resulting in loss of illumination and other forms of image degradation. Additionally, in some multilayer systems, adding additional components may be difficult or impossible.

The present invention relates to an optical light scattering layer formed from a curable polymer composition. The curable composition, an article made from the curable composition, and a method for forming the optical article are described herein.

The curable composition of the present invention comprises at least one fluoropolymer, at least one monofunctional (meth)acrylate, at least one difunctional (meth)acrylate, and at least one initiator. As used herein, the terms "curable composition," "curable ink," and "ink" are used interchangeably and refer to a curable composition that can be deposited on a surface and cured. Although the curable composition may be described as an ink, this does not necessarily mean that it has been or needs to be coated by a printing technique. The curable composition is typically solvent-free and has a viscosity of less than 30 centipoise at a temperature of from room temperature to 60° C.

Articles are also disclosed. In some embodiments, the article comprises a substrate having a first major surface and a second major surface, and an optically-scattering layer disposed on the first major surface of the substrate. The optically-scattering layer comprises a matrix and phase-separated microdomains, wherein the matrix and the phase-separated microdomains have different refractive indices, and wherein the microdomains are on the order of a wavelength of visible light or greater.

A method of making an article is also disclosed. In some embodiments, the method comprises providing a substrate having a first major surface and a second major surface, providing a curable composition, forming a layer of the curable composition on at least a portion of the first major surface of the substrate, and curing the layer of the curable composition to form a cured optically-scattering layer. The curable composition comprises at least one fluoropolymer, at least one monofunctional (meth)acrylate, at least one difunctional (meth)acrylate, and at least one initiator. The curable composition typically has a viscosity of less than 30 centipoise at a temperature of from room temperature to 60° C., as described above. The cured optically-scattering layer comprises a matrix and phase-separated microdomains, wherein the matrix and the phase-separated microdomains have different refractive indices, and wherein the microdomains are on the order of a wavelength of visible light or greater.

The present application may be more fully understood in consideration of the following detailed description of various embodiments of the present invention in connection with the accompanying drawings.
Figure 1a illustrates a schematic diagram of a process of the present invention for forming an optical light scattering article.
Figure 1b illustrates a schematic diagram of another process of the present invention for forming an optical light scattering article.
Figure 1c illustrates a schematic diagram of another process of the present invention for forming an optical light scattering article.
FIG. 1d is a schematic diagram of another process of the present invention for forming an optical light scattering article.
FIG. 1e illustrates a schematic diagram of another process of the present invention for forming an optical light scattering article.
FIG. 1f is a schematic diagram of another process of the present invention for forming an optical light scattering article.
Figure 1g illustrates a schematic diagram of another process of the present invention for forming an optical light scattering article.
Figure 1h illustrates a schematic diagram of another process of the present invention for forming an optical light scattering article.
FIG. 1i is a schematic diagram of another process of the present invention for forming an optical light scattering article.
Figure 2 shows a cross-sectional view of an optical microscope photograph of the optical light scattering layer of Example 2.
Figure 3a shows a cross-sectional view of an AFM height image of the optical light scattering layer of Example 2.
Figure 3b shows a cross-sectional view of an AFM-IR map of the optical light scattering layer of Example 2.
Figure 3c shows a cross-sectional view of an AFM-IR map of the optical light scattering layer of Example 2.
Figure 3d shows a cross-sectional view of an AFM-IR image ratio map of the optical light scattering layer of Example 2.
Figure 4 shows a cross-sectional view of an optical microscope image of the optical light scattering layer of Example 1.
Figure 5a shows a cross-sectional view of an AFM height image of the optical light scattering layer of Example 1.
Figure 5b shows a cross-sectional view of an AFM-IR map of the optical light scattering layer of Example 1.
Figure 5c shows a cross-sectional view of an AFM-IR map of the optical light scattering layer of Example 1.
Figure 5d shows a cross-sectional view of an AFM-IR image ratio map of the optical light scattering layer of Example 1.
In the following description of the illustrated embodiments, reference is made to the accompanying drawings, in which various embodiments in which the present invention may be practiced are shown by way of illustration. It should be understood that the embodiments may be utilized and that structural changes may be made without departing from the scope of the present invention. The drawings are not necessarily to scale. Like reference numerals used in the drawings refer to like components. However, it will be understood that the use of a reference numeral to refer to a component in a given drawing is not intended to limit that component in another drawing labeled with the same reference numeral.

As optical devices become more complex, it becomes increasingly difficult to meet the requirements for the materials used in them. In particular, organic polymer materials are widely used in optical devices, but the requirements for these polymer materials are becoming increasingly stringent.

For example, thin organic polymer films are desirable for a wide range of applications as adhesives, protective layers, spacer layers, etc. in optical devices. As articles have become more complex, the physical demands on these layers have increased. For example, as optical devices have become more compact and, at the same time, often contain more layers, the need for thinner layers has increased. At the same time, because these layers are thinner, they also need to be more precise. For example, to be effective as a spacer, a thin spacer layer (on the order of 1 micrometer thick) needs to be flat and free of gaps and holes to provide adequate spacing. This requires that the organic layer be deposited in a precise and consistent manner. Among the methods that have been developed to provide precise and consistent deposition of organic polymer materials are printing techniques. In printing techniques, a polymer or curable composition that forms a polymer upon curing is printed onto a substrate surface to form a layer. In the case of printable polymers, a solvent is typically added to prepare a printable solution or dispersion. When a polymer is used, after printing to produce the desired polymer layer, a drying step is typically required. In the case of a curable composition which forms a polymer upon curing, the curable composition may or may not contain a solvent. The curable composition is then cured, typically by application of heat or radiation (e.g., UV light), and when a solvent is used, the layer may also be dried. A wide variety of printing techniques may be used, with inkjet printing being particularly preferred due to its excellent precision.

In addition, these layers must not only provide their physical function (adhesion, protection, separation, etc.), but they must also provide the necessary optical properties. One optical property that is becoming increasingly important is light diffusion. Typically, light diffusion has been achieved through the use of particles. Light diffusing particles are dispersed in a polymerizable binder to form a curable mixture, and the curable mixture is placed on a surface and cured to form a layer in which the light diffusing particles are suspended in the polymerized matrix.

This approach to producing light diffusing layers has been widely used, but it has serious drawbacks and limitations. The addition of pre-formed particles and fillers can be problematic, not only because of backscattering problems, but also because the addition of such particles and fillers makes the filtration process, which is often desirable to improve the uniformity of the coating, more difficult. Additionally, as layers become thinner and thinner, techniques such as inkjet printing are increasingly used to deposit curable layers on surfaces, and printing of pre-formed particle-filled mixtures can be very difficult because the pre-formed particles tend to clog the printhead nozzles. Additionally, while uniform diffusing layers, i.e., layers having the same diffusing properties over the entire area of the layer, can be produced in this manner, it is very difficult, if not impossible, to produce selectively diffusing layers in this manner. As used herein, a selectively diffusing layer refers to a layer having different diffusing properties in different areas of the layer.

Other techniques have been used to provide scattering layers without the use of preformed particles for optical applications.

Yang et al. (U.S. Patent Application Publication No. 2010/0259825) blend two immiscible monomers to form an emulsion, coat, and then cure to lock in such a morphology. This does not allow for control of the morphology during cure. Rather, control of the morphology is accomplished prior to cure by varying the amount and/or rate of mixing prior to dispensing. Emulsions require stabilizers and other chemical components to maintain stability and control over the size of the microdomains formed, which can reduce the possible difference in refractive index between the two phases, and thus the amount of scattering that can be achieved. Control over the size of these phases beyond initial emulsification has not been demonstrated.

Young et al. (U.S. Patent No. 9,093,666) also describe a phase-separated solution of two different epoxysilicone monomers mixed with a silicon-free cycloaliphatic epoxy monomer and a photoinitiator. One of the epoxysilicone resins used is immiscible with the cycloaliphatic epoxy resin prior to curing, and stirring is used to achieve different particle size distributions in the range of 0.5 to 20 micrometers prior to curing. This layer was applied as an encapsulating layer between two inorganic layers to improve light outcoupling of the OLED device. Control over the degree of phase separation during the curing step is not demonstrated or discussed.

Mazurek et al. (US Pat. No. 8,343,633B2) use a radiation-curable telechelic silicone-containing monomer dissolved in a silicone-free radiation-curable monomer. In this approach, the two phases are miscible with each other prior to curing, but subsequently phase separate upon curing. Some degree of control over the size of the microdomains during the curing step is demonstrated, but since both phases contain cross-linkable (meth)acrylate moieties, cross-linking between the phases is allowed to occur, thereby limiting the extent of diffusion and phase separation.

Another technique that has been used to prepare light diffusing pressure sensitive adhesives without the use of added particles is described in U.S. Patent No. 9,238,762 (Schaffer et al.). In that application, a block copolymer is dissolved in a solvent together with an optically clear pressure sensitive adhesive matrix. The block copolymer phase separates from the polymer used in the pressure sensitive adhesive after drying of the solvent. The block copolymer-formed microdomains are larger than the wavelength of visible light and thus diffuse visible light. Control over the degree of phase separation during the drying step is not discussed or demonstrated, and the distribution of microdomain sizes is the same at all points along the layer.

The present invention differs from these in that a non-polymerizable amorphous fluoropolymer, typically a fluoroelastomer, is dissolved in a mixture of radiation-curable organic monomers to form an initially transparent and miscible solution. Upon curing, the fluoropolymer phase separates from the methacrylate phase, providing a change in refractive index that allows sufficient optical scattering. Since the polymer does not copolymerize with the monomer during curing, this allows for a greater degree of control over the diffusion required for sufficient phase separation. For example, the ability to control particle size during the curing step by varying the light intensity used during curing, thereby influencing the polymerization rate, has been demonstrated. Furthermore, it is surprising that the fluoropolymer can be dissolved in (fluorine-free)(meth)acrylate monomers, since these two materials have very different chemical structures. The use of such chemically different materials allows for a large difference in refractive index between the individual components after phase separation has occurred. Finally, the ability to control phase separation during the curing step allows for the possibility of creating multiple different domain sizes within a single layer using patterning methods well known in the art, which may be beneficial in certain applications.

The present invention provides a curable composition capable of forming a particle-free, light-diffusing layer. The curable composition comprises a fluoropolymer and a (meth)acrylate together with a free radical initiator, and forms a homogeneous single phase prior to curing. Typically, the fluoropolymer has excellent miscibility with the (meth)acrylate monomer, such that the uncured composition layer does not contain fluorocarbon-rich microdomains, but rather the fluoropolymer/(meth)acrylate mixture is essentially homogeneous and transparent. The terms fluoropolymer and fluorocarbon are used interchangeably to refer to the fluorine-containing polymer of the present invention. Upon activation of the photoinitiator by UV irradiation, free radicals are generated within the film, which induce polymerization of the (meth)acrylate monomers, leading to phase separation into distinct domains of the fluoropolymer or poly(meth)acrylate due to a decrease in the entropy of mixing and an increase in the free energy of mixing between the two components, the fluoropolymer and the poly(meth)acrylate. Due to the difference in refractive indices between the poly(meth)acrylate and the fluoropolymer, the formation of the phase separated microdomains leads to an increase in forward scattering of light (also known as "haze"). When light is forward scattered, the light is scattered, but continues in the same general direction of incidence. In backward scattering, the light is directed back in the direction of incidence. Therefore, in backward scattering, some of the light intensity is lost as it is reflected back toward the light source. In forward scattering, most of the light is transmitted in the direction of incidence, and only a small amount of light is lost due to reflection, since it is only scattered. This is desirable when a point light source is used, which will produce a bright spot where light from the point light source is present, and an unlit spot adjacent to it where light is not transmitted. By using a forward-scatter diffuser, the light from the point light source is spread over a larger area, eliminating the bright spot/unlit spot phenomenon. Forward scattering and back scattering are well understood by those skilled in the art.

The light diffusing layer is prepared by disposing a curable composition on a substrate and curing the curable composition to form a cured organic layer having a matrix and phase-separated microdomains, wherein the matrix and the phase-separated microdomains have different refractive indices. This process of curing a miscible composition to form a cured composition having phase-separated domains is sometimes referred to as polymerization-induced phase separation (PIPS). In the present application, the domain sizes are sufficiently large to diffuse visible light, that is, they have an average diameter that is on the order of or greater than the wavelength of visible light (about 400 to 700 nm). The PIPS model suggests that the matrix would be expected to be a crosslinked (meth)acrylate matrix having microdomains of a fluoropolymer. While this does occur, as will be described in more detail below, the cured organic layer formed is much more complex than a simple crosslinked (meth)acrylate matrix having microdomains of a fluoropolymer. What has been discovered is that the cured organic layer comprises at least one of three different composition types or compositional regions. Each of these regions comprises a matrix and phase-separated microdomains. The first region is a region wherein the essentially continuous matrix comprises a cross-linked (meth)acrylate matrix and phase-separated fluorocarbon-rich microdomains, wherein the fluorocarbon-rich microdomains are essentially, but not entirely, fluorocarbon. These embodiment regions are described above. The second region is a region wherein the essentially continuous matrix comprises a cross-linked (meth)acrylate matrix and the phase-separated microdomains comprise a (meth)acrylate material as well as a fluoropolymer. In these embodiments, the microdomains may still be described as fluoropolymer-rich microdomains, but they comprise nanodomains of the fluoropolymer and nanodomains of the cross-linked (meth)acrylate. The third region is an essentially continuous matrix comprising fluorocarbon-rich domains and phase-separated microdomains comprising (meth)acrylate-rich domains, wherein the (meth)acrylate-rich microdomains comprise at least a cross-linked (meth)acrylate material and may also contain a fluoropolymer.

The optical-scattering layer comprises at least one of the aforementioned regions. In some embodiments, the optical-scattering layer is entirely a single region and is essentially uniform throughout. In other embodiments, the optical-scattering layer comprises more than one region. This phenomenon of different regions differs from the selective diffusion characteristics described below and refers to the composition of the matrix and the phase-separated microdomains.

Another feature of the present invention is the ability to produce selectively diffusive layers using selective curing. As used herein, a selectively diffusive layer refers to a layer having different diffusive properties in different regions of the layer. This selectivity is described in more detail below and may be achieved in a wide variety of ways, for example, by using variable intensity light sources and masking techniques.

A curable composition is disclosed herein, the curable composition comprising at least one fluoropolymer, at least one monofunctional (meth)acrylate, at least one difunctional (meth)acrylate, and at least one initiator. The curable composition typically has a viscosity of less than 30 centipoise at a temperature of from room temperature to 60° C. This viscosity allows the curable composition to be printed by techniques such as inkjet printing techniques, although, of course, a wide variety of coating techniques can be used to coat the curable composition.

Also disclosed herein are articles comprising a cured layer prepared from a curable composition, wherein the cured layer comprises a matrix and phase-separated microdomains, wherein the matrix and the phase-separated microdomains have different refractive indices, and at least some of the microdomains are on the order of or greater than a wavelength of visible light and are thus capable of scattering visible light. Additionally, methods of making such articles are described.

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in this specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the above specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. Recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singular forms "a," "an," and "the" include embodiments having plural referents unless the content clearly dictates otherwise. For example, reference to "a layer" includes embodiments having one, two, or more layers. As used in this specification and the appended claims, the term "or" is generally adopted to include "and/or" in its meaning, unless the content clearly dictates otherwise.

As used herein, the term "adjacent" refers to two layers that are in close proximity to one another. The adjacent layers may be in direct contact with each other, or there may be intervening layers. There is no void space between the adjacent layers.

The curable ink composition is "substantially solvent free" or "solvent free." As used herein, "substantially solvent free" refers to a curable ink composition having less than 5 wt %, 4 wt %, 3 wt %, 2 wt %, 1 wt %, and 0.5 wt % of a nonpolymerizable (e.g., organic) solvent. The concentration of solvent can be determined by known methods, such as gas chromatography (as described in ASTM D5403). The term "solvent free" literally implies that no solvent is present in the composition. It should be noted that whether the curable ink composition is solvent free or substantially solvent free, no solvent is intentionally added.

Typically, curable ink compositions are described as "100% solids". As used herein, "100% solids" refers to a curable ink composition that does not contain volatile solvents, so that all of the material deposited on a surface remains there and no volatile material is lost from the coating.

As used herein, the term "polymer" refers to a material that is a macromolecule, and may be a homopolymer or a copolymer. As used herein, the term "homopolymer" refers to a polymer material that is the reaction product of one monomer. As used herein, the term "copolymer" refers to a polymer material that is the reaction product of at least two different monomers.

The terms "Tg" and "glass transition temperature" are used interchangeably. When measured, unless otherwise indicated, the Tg values are determined by differential scanning calorimetry (DSC) at a scan rate of 10°C/min. As will be appreciated by those skilled in the art, typically, the Tg values for copolymers are not measured, but are calculated using the well-known Fox Equation, using the monomer Tg values provided by the monomer supplier.

The terms "room temperature" and "ambient temperature" are used interchangeably and have their usual meanings, referring to a temperature of 20 to 25°C.

The term “organic” as used herein to refer to a cured layer means that the layer is made from organic materials and is free of inorganic materials.

The terms "fluoropolymer" or "fluorinated polymer" are used interchangeably and refer to fluorocarbon-based polymers having a large number of carbon-fluorine bonds. Fluoropolymers are hydrocarbon polymers in which hydrogen atoms, typically many hydrogen atoms, or even all hydrogen atoms, are replaced by fluorine atoms. An example of a fluoropolymer is a "fluoroelastomer". Fluoroelastomers are special purpose fluorocarbon-based synthetic rubbers that do not contain significant amounts of crystallinity.

The term "(meth)acrylate" refers to a monomeric acrylic acid ester or methacrylic acid ester of an alcohol. Acrylate and methacrylate monomers or oligomers are collectively referred to herein as "(meth)acrylates". As used herein, the term "(meth)acrylate-based" refers to a polymer composition comprising at least one (meth)acrylate monomer and may contain additional (meth)acrylate or non-(meth)acrylate copolymerizable ethylenically unsaturated monomers. A (meth)acrylate-based polymer comprises a majority (i.e., greater than 50 wt %) of a (meth)acrylate monomer.

The terms "free radical polymerizable" and "ethylenically unsaturated" are used interchangeably and refer to reactive groups containing carbon-carbon double bonds that can be polymerized via a free radical polymerization mechanism.

As used herein, the term "hydrocarbon group" refers to any monovalent group containing primarily or exclusively carbon and hydrogen atoms. Alkyl and allyl groups are examples of hydrocarbon groups.

The term "alkyl" refers to a monovalent group which is a radical of an alkane, a saturated hydrocarbon. Alkyl groups can be linear, branched, cyclic, or combinations thereof and typically have from 1 to 20 carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl, n-heptyl, n-octyl, and ethylhexyl.

The term "aryl" refers to a monovalent group that is aromatic and carbocyclic. An aryl can have from 1 to 5 rings connected or fused to an aromatic ring. Other ring structures can be aromatic, non-aromatic, or a combination thereof. Examples of aryl groups include, but are not limited to, phenyl, biphenyl, terphenyl, anthryl, naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl, pyrenyl, perylenyl, and fluorenyl.

The term "alkylene" refers to a divalent group which is a radical of an alkane. Alkylenes can be straight-chain, branched, cyclic, or combinations thereof. Alkylenes often have from 1 to 20 carbon atoms. In some embodiments, the alkylene contains 1 to 18, 1 to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. The radical centers of the alkylene can be on the same carbon atom (i.e., alkylidene), or can be on different carbon atoms.

The term "heteroalkylene" refers to a divalent group comprising at least two alkylene groups joined by thio, oxy or -NR- (wherein R is alkyl). Heteroalkylenes can be linear, branched, cyclic, substituted with alkyl groups or combinations thereof. Some heteroalkylenes are polyoxyalkylenes in which the heteroatom is oxygen, for example

-CH ₂ CH ₂ (OCH ₂ CH ₂ ) _n OCH ₂ CH ₂ -.

As used herein, the term "cycloaliphatic" refers to a group that is both essentially aliphatic and cyclic, containing one or more all-carbon rings, which may be saturated or unsaturated but are not aromatic in nature, and which may be substituted with one or more alkyl groups.

Unless otherwise indicated, “optically transparent” refers to a layer, film, or article having high light transmittance across at least a portion of the visible light spectrum (from about 400 nm to about 700 nm). Typically, an optically transparent layer, film, or article has a light transmittance of at least 90%.

Unless otherwise indicated, "optically clear" refers to a layer, film, or article having high light transmittance and low haze across at least a portion of the visible light spectrum (from about 400 nm to about 700 nm). Typically, an optically clear layer, film, or article has a visible light transmittance value of at least 90%, often at least 95%, and a haze value of 5% or less, often 2% or less. Light transmittance and haze can be measured using the techniques described in the Examples section.

Disclosed herein are curable compositions, articles made using the curable compositions, and methods of making articles using the curable compositions. The curable compositions of the present invention provide methods of selectively forming an optically-scattering layer. Optically-scattering means that the layer forward-scatters visible light. As described above, the optically-scattering layer acts to diffuse visible light. The diffusion of visible light occurs because the curable composition forms phase-separated microdomains within the matrix when cured, and the matrix and the phase-separated microdomains have different refractive indices. As used herein, the phase-separated microdomains are of the same order of magnitude as or greater than the wavelength of visible light. Since visible light is generally characterized as having a wavelength of 400 to 700 nanometers, the phase-separated microdomains are generally at least 100 nm or greater, often 100 to 4,000 nm. The microdomains are either "fluoropolymer-rich" or "(meth)acrylate-rich", where "fluoropolymer-rich" means that they have a high concentration of fluoropolymer within a (meth)acrylate matrix, but are not necessarily composed entirely of fluoropolymer, and "(meth)acrylate-rich" means that they have a high concentration of (meth)acrylate within a fluoropolymer-rich matrix, but are not necessarily composed entirely of (meth)acrylate. The presence of the microdomains having a different refractive index than the surrounding matrix means that when visible light passing through the matrix encounters the microdomains, the light will be refracted or scattered due to this refractive index mismatch, as described by Snell's Law. This scattering is often referred to as forward scattering or haze. As described above, forward scattering is desirable because it produces diffused light with little loss of light intensity.

In the present disclosure, curable compositions are provided which contain a fluoropolymer and a curable (meth)acrylate monomer. These curable compositions are optically transparent or even optically clear because the fluoropolymer has a high miscibility with the (meth)acrylate monomer. The curable compositions also have a relatively low viscosity, which allows them to be coated by a variety of methods, including inkjet printing. Upon curing of the curable composition, the curable composition forms a cured organic layer having a matrix and phase-separated microdomains, wherein the matrix and the phase-separated microdomains have different refractive indices, and wherein at least some of the phase-separated microdomains have a wavelength of visible light (400 to 700 nm) or greater. In some embodiments, the phase-separated microdomains have a wavelength in the range of 100 to 4,000 nm. Methods for making articles having an optically-scattering layer are also disclosed herein.

Disclosed herein are curable compositions. The curable compositions comprise at least one fluoropolymer, at least one monofunctional (meth)acrylate, at least one difunctional (meth)acrylate, and at least one initiator. The curable compositions typically have a viscosity of less than 30 centipoise at a temperature of from room temperature to 60° C. Typically, the curable compositions are solvent-free. In many embodiments, the curable compositions are optically transparent or even optically clear. An advantage of these relatively low viscosity compositions is that they are inkjet printable. The term "inkjet printable" means that the composition can be inkjet printed, but does not mean that the composition must be inkjet printed or that the composition has been inkjet printed. In this way, the term "inkjet printable" is a composition limitation of the curable composition and not a process limitation. The inkjet printable material can be coated in a variety of ways.

The curable composition comprises at least one fluoropolymer. Fluoropolymers are fluorocarbon-based polymers having a large number of carbon-fluorine bonds. They are characterized by high resistance to solvents, acids, and bases. Fluoropolymers are hydrocarbon polymers in which hydrogen atoms, typically many hydrogen atoms, or even all hydrogen atoms, are replaced by fluorine atoms.

Fluoropolymers share the properties of fluorocarbons in that they are not as susceptible to van der Waals forces as hydrocarbons. Thus, like fluorocarbons, fluoropolymers are very stable because of the strength of the carbon-fluorine bond, which is one of the strongest in organic chemistry. Its strength is a result of the electronegativity of fluorine, which imparts partial ionic character through partial charges on the carbon and fluorine atoms, which shortens and strengthens the bond through favorable covalent interactions. Additionally, multiple carbon-fluorine bonds increase the strength and stability of other nearby carbon-fluorine bonds on the same geminal carbon, because the carbon has a higher partial positive charge. Furthermore, multiple carbon-fluorine bonds also strengthen the "backbone" carbon-carbon bond from inductive effects. Thus, saturated fluorocarbons are chemically and thermally more stable than their corresponding hydrocarbon counterparts, and indeed any other organic compound. They are generally incompatible with most organic solvents (e.g., ethanol, acetone, ethyl acetate, and chloroform), but are miscible with some hydrocarbons (e.g., hexane in some cases). They typically have low refractive indices of less than 1.45.

The curable composition of the present invention comprises at least one fluoropolymer, which constitutes from 1 to 20 wt %, based on 100 wt % of the total curable composition. Examples of suitable fluoropolymers are amorphous fluoropolymers having a fluorine content of from 60 to 70 wt %. By fluorine content is meant that from 60 to 70 % of the substitutable hydrogen atoms are replaced by fluorine groups. A particularly suitable class of fluoropolymers are fluoroelastomers. Fluoroelastomers are special purpose fluorocarbon-based synthetic rubbers that are amorphous and do not contain significant amounts of crystallinity. They have broad chemical resistance and superior performance, particularly in high temperature applications in different media. Fluoroelastomers are classified as FKM under the ASTM D1418 and ISO 1629 notations. Elastomers of this class include copolymers of hexafluoropropylene (HFP) and vinylidene fluoride (VDF or VF2), terpolymers of tetrafluoroethylene (TFE), vinylidene fluoride (VDF) and hexafluoropropylene (HFP), as well as specialties containing perfluoromethyl vinyl ether (PMVE). Particularly suitable fluoroelastomers are copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), such as those commercially available from 3M Company, St. Paul, Minn., under the trade names FC 2145, FC 2178, and FC 2211.

As mentioned above, fluoropolymers generally have poor miscibility with organic solvents and fluids. In the present disclosure, the fluoropolymer in the curable compositions was observed to have high miscibility with the (meth)acrylate monomer containing a cyclic moiety. In fact, in many embodiments, the curable compositions are optically transparent. Other fluoropolymers that may be used are described in Jing et al. (U.S. Patent Application Publication No. 2006/0147177 A1).

One desirable feature of the fluoropolymers is that they have a refractive index that is different from the (meth)acrylate matrix formed by polymerizing the (meth)acrylate monomers described below. The fluoropolymers typically have a refractive index in the range of 1.40 to 1.41. This refractive index is different from the refractive index of the (meth)acrylate matrix, which is typically in the range of 1.48 to 1.50.

The curable composition also comprises at least one monofunctional (meth)acrylate. A variety of monofunctional (meth)acrylates are suitable. In some embodiments, the monofunctional (meth)acrylate comprises a monofunctional methacrylate. In some embodiments, methacrylates are preferred over acrylates because methacrylates polymerize more slowly, allowing for a more controlled reaction rate and thus more control over the diffusion characteristics of the resulting film. Examples include, but are not limited to, acrylamides such as acrylamide, methacrylamide, N-methyl acrylamide, N-ethyl acrylamide, N-hydroxyethyl acrylamide, diacetone acrylamide, N,N-dimethyl acrylamide, N,N-diethyl acrylamide, N-ethyl-N-aminoethyl acrylamide, N-ethyl-N-hydroxyethyl acrylamide, N,N-dihydroxyethyl acrylamide, t-butyl acrylamide, N,N-dimethylaminoethyl acrylamide, and N-octyl acrylamide. Examples of suitable monofunctional (meth)acrylates include alicyclic methacrylates. Alicyclic compounds are organic compounds that are aliphatic and are also cyclic. They contain one or more all-carbon rings, which may be saturated or unsaturated but do not have aromatic character. Alicyclic compounds can have one or more aliphatic side chains attached to them. In some embodiments, the alicyclic compounds can include one or more heteroatoms. Monocyclic cycloalkanes and cycloalkenes include cyclopentane, cyclopentene, cyclohexane, cyclohexene, cycloheptane, cycloheptene, cyclooctane, cyclooctene, and the like. Bicyclic alkanes and alkenes include norbornane, norbornene, and norbornadiene. Examples of suitable cycloaliphatic (meth)acrylates include 3,3,5-trimethyl cyclohexyl acrylate and methacrylate, 1-adamantyl acrylate and methacrylate, 3,5-dimethyl adamantyl acrylate and methacrylate, and isobornyl acrylate and methacrylate. Examples of heteroatom-functional cycloaliphatic (meth)acrylates include tetrahydrofurfuryl acrylate and methacrylate. The monofunctional (meth)acrylates can be present in a wide range of amounts. In some embodiments, the monofunctional (meth)acrylate comprises from 60 to 95 parts by weight, based on the total weight of the curable components of the curable composition.

It is also possible to use monomers containing unsaturations in the form of vinyl groups. These are well known in the art to chemically react with and crosslink with the (meth)acrylate matrix. Preferred examples of vinyl-containing monomers which also contain a cyclic moiety include n-vinyl pyrrolidone and n-vinyl caprolactam. Suitable ranges of vinyl-containing monomers comprise 1 to 20 parts by weight, based on the total weight of the curable components of the curable composition.

The curable composition also comprises at least one multifunctional (meth)acrylate. In some embodiments, the multifunctional (meth)acrylate comprises a difunctional (meth)acrylate. In some embodiments, the difunctional (meth)acrylate comprises a difunctional methacrylate. Again, as with the monofunctional (meth)acrylates, difunctional methacrylates may be particularly suitable because they polymerize more slowly than the corresponding acrylates, allowing for more control over the polymerization rate. Examples of suitable difunctional (meth)acrylates include aliphatic (meth)acrylates of the general formula I:

[Chemical Formula I]

H ₂ C=CR2-(CO)-OAO-(CO)-R2C=CH ₂

Here, R2 is hydrogen or methyl, (CO) is a carbonyl group C=O, and A is a divalent group comprising an alkylene or heteroalkylene group. Examples of alkylene groups include those having 4 to 20 carbon atoms and may include cyclic groups. Examples of heteroalkylene groups include polyethylene oxide groups, polypropylene oxide groups, and the like. Examples of useful multifunctional (meth)acrylates include 1,6-hexanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, propylene glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, hydroxy pivalic acid neopentyl glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, bisphenol A di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, poly(ethylene glycol) di(meth)acrylate, polybutadiene di(meth)acrylate, polyurethane di(meth)acrylate, and glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, pentaerythritol. Tri- and tetra(meth)acrylates, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ethoxylated and propoxylated versions and mixtures thereof.

The multifunctional (meth)acrylate or crosslinker can be present in a wide range of amounts. In some embodiments, the multifunctional (meth)acrylate comprises from 1 to 20 parts by weight, based on the total weight of the curable components of the curable composition. The amount and identity of the crosslinker or crosslinkers can vary, but typically the total amount of crosslinkers is present in an amount of at least 5 weight percent. By weight percent is meant the % weight of the total curable components of the curable ink composition.

The curable composition also comprises at least one initiator. Typically, the initiator is a photoinitiator, meaning that the initiator is activated by light, typically ultraviolet (UV) light. Photoinitiators are well understood by those skilled in the art of (meth)acrylate polymerization.

Useful photoinitiators include those known to be useful for photocuring polyfunctional (meth)acrylates via free radicals. Exemplary photoinitiators include benzoin and its derivatives, such as alpha-methylbenzoin; alpha-phenylbenzoin; alpha-allylbenzoin; alpha-benzylbenzoin; benzoin ethers, such as benzyl dimethyl ketal (e.g., OMNIRAD BDK from IGM Resins USA Inc., St. Charles, IL), benzoin methyl ether, benzoin ethyl ether, benzoin n-butyl ether; Acetophenone and its derivatives, such as 2-hydroxy-2-methyl-1-phenyl-1-propanone (available, e.g., from IGM Resins USA, Inc., St. Charles, IL, under the tradename Omnirad 1173) and 1-hydroxycyclohexyl phenyl ketone (available, e.g., from IGM Resins USA, Inc., St. Charles, IL, under the tradename Omnirad 184); 2-methyl-1-[4-(methylthio)phenyl]-2-(4-morpholinyl)-1-propanone (available, e.g., from IGM Resins USA, Inc., St. Charles, IL, under the tradename Omnirad 907); 2-Benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-butanone (e.g., available from IGM Resins USA, Inc., St. Charles, IL under the tradename Omnirad 369) and phosphine oxide derivatives, such as ethyl-2,4,6-trimethylbenzoylphenyl phosphinate (e.g., available from IGM Resins USA, Inc., St. Charles, IL under the tradename TPO-L), and bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (e.g., available from IGM Resins USA, Inc., St. Charles, IL under the tradename Omnirad 819).

Other useful photoinitiators include, for example, pivaloin ethyl ether, anisoin ethyl ether, anthraquinones (e.g., anthraquinone, 2-ethylanthraquinone, 1-chloroanthraquinone, 1,4-dimethylanthraquinone, 1-methoxyanthraquinone, or benzanthraquinone), halomethyltriazines, benzophenones and their derivatives, iodonium salts and sulfonium salts, titanium complexes such as bis(eta-2,4-cyclopentadien-1-yl)-bis[2,6-difluoro-3-(1H-pyrrol-1-yl) phenyl]titanium (available, e.g., from BASF, Florham Park, NJ, under the tradename CGI 784DC); Halomethylnitrobenzenes (e.g., 4-bromomethylnitrobenzene), and combinations of photoinitiators wherein one component is a mono- or bis-acylphosphine oxide (e.g., available from BASF, Florham Park, NJ, USA under the trade names IRGACURE 1700, IRGACURE 1800, and IRGACURE 1850 and from IGM Resins USA, Inc., St. Charles, IL, USA under the trade name Omnirad 4265).

Typically, the photoinitiator is used in an amount of 0.01 to 5 parts by weight, more typically 0.1 to 0.5 parts by weight, per 100 parts by weight of total reactive components.

The curable composition may include additional optional additives. The optional additives may be reactive or non-reactive. A higher difference in refractive index (Δn) between the minority phase and the majority phase will increase the haze and scattering power of the film. This will allow for the use of less fluoropolymer to achieve the same optical effect as a larger amount of fluoropolymer with a smaller (Δn). Less fluoropolymer will allow for lower viscosity ink formulations, which will also be beneficial for inkjet performance. Metal oxide nanoparticles will be particularly useful for increasing the refractive index of the poly(meth)acrylate matrix.

While a wide range of metal oxide nanoparticles are suitable, as noted above, metal oxide nanoparticles having a high refractive index are preferred, since the purpose is to increase the refractive index of the curable ink composition. Examples of suitable metal oxide nanoparticles include metal oxides of titanium, aluminum, hafnium, zinc, tin, cerium, yttrium, indium, antimony, and zirconium, as well as mixed metal oxides, such as indium tin oxide. In this regard, high refractive index refers to a refractive index of 2.0 or greater. Among the more preferred metal oxide nanoparticles are those of titanium, aluminum, and zirconium. Titanium oxide nanoparticles, commonly referred to as titania nanoparticles, are particularly suitable due to their high refractive index. In many cases, a single type of metal oxide nanoparticle is used, although mixtures of metal oxide nanoparticles may also be used.

As mentioned above, the size of such particles is selected to avoid significant visible light scattering. The surface-treated metal oxide nanoparticles can be particles having a primary particle size (e.g., unassociated) or an associated particle size greater than 1 nm, 5 nm or 10 nm. The primary or associated particle size is generally less than 100 nm, 75 nm or 50 nm. Typically, the primary or associated particle size is less than 40 nm, 30 nm or 20 nm. It is desirable that the nanoparticles are unassociated and remain unassociated over time. Their measurements can be based on transmission electron microscopy (TEM) or dynamic light scattering (DLS).

The zirconia and titania nanoparticles can have a particle size of from 5 to 50 nm, or from 5 to 15 nm, or from 8 to 12 nm. Suitable zirconia (nanoparticles of zirconium dioxide) are available from Nalco Chemical Co. under the trade designation "Nalco OOSSOO8" and from Buhler AG, Oudzwil, Switzerland, under the trade designation "Buhler zirconia Z-WO sol". Titania nanoparticles (nanoparticles of titanium dioxide) are particularly suitable. Titania nanoparticles containing a mixture of anatase and brookite crystal structures are commercially available from Showa Denko Corp., Japan, under the designation "NTB-1".

The nanoparticles are preferably surface treated to improve compatibility with the organic matrix material and to maintain the nanoparticles in a non-associative, non-agglomerated, or combined state in the curable ink composition. The surface treatment agent used to produce the surface-treated nanoparticles comprising at least two silane-functional surface treatment agents is a silane surface treatment agent.

Another particularly suitable optional additive is an adhesion promoter. An adhesion promoter is used as an additive to promote adhesion of a coating, ink, or adhesive to a substrate of interest or as a primer. The adhesion promoter typically has an affinity for the substrate and the applied coating, ink, or adhesive. Suitable adhesion promoters include silane-functional compounds, titanates, and zirconates. Examples of suitable titanates and zirconates include titanium or zirconium butoxide. Typically, when used, the adhesion promoter comprises a silane-functional compound. Sometimes silane-functional adhesion promoters are called coupling agents because they have different functional groups at each end of the compound and thus can act to bond different surfaces, such as inorganic surfaces and organic surfaces. A wide variety of silane adhesion promoters are suitable, such as the (meth)acrylate-functional alkoxy silane SILQUEST A-174 from Momentive Performance Materials. For this type of adhesion promoter, the alkoxy silane functionality interacts with the inorganic surface and the (meth)acrylate functionality copolymerizes with the curable ink composition. Other examples of suitable silane coupling agents include octadecyltrimethoxysilane, isooctyltrimethoxysilane, hexadecyltrimethoxysilane, hexyltrimethoxysilane, methyl trimethoxysilane, hexamethyldisilazane, hexamethyldisiloxane, aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, and the like.

Useful additives can include polymers containing functional groups known in the art, such as epoxide groups, allyloxy groups, (meth)acrylate groups, (meth)acrylamide groups, epoxides, episulfides, vinyls, hydroxyls, cyanoesters, acetoxyls, thiols, silanols, carboxylic acids, aminos, phenols, aldehydes, alkyl halides, cinnamates, azides, aziridines, alkenes, carbamates, imides, amides, alkynes, ethylenically unsaturated groups, vinyl ether groups, and any derivatives and any combinations thereof. Alternatively, the polymeric additives can be non-reactive, such as, for example, poly(methyl methacrylate), poly(vinyl butyral), poly(acrylic acid), poly(vinyl alcohol), and others. These polymers can also include copolymers, which are, so to speak, polymers made from more than one type of monomer unit during polymerization. Copolymers may contain different structures such as linear, star, graft, random, or block copolymers.

Other optional additives include heat stabilizers, UV stabilizers, free radical scavengers, chain transfer agents, photosensitizers, and combinations thereof. Examples of suitable commercially available UV stabilizers include benzophenone-type UV light absorbers, which are available from BASF Corp., Parsippany, NJ, USA, under the trade designation "UVINOL 400"; and from BASF, Tarrytown, N.Y., USA, under the trade designations "TINUVIN 900" and "TINUVIN 1130". Suitable concentrations of the UV stabilizer in the polymerizable precursor are in the range of about 0.1 wt % to about 10 wt %, with particularly suitable total concentrations being in the range of about 1 wt % to about 5 wt %, based on the total weight of the polymerizable precursor.

Examples of suitable free radical scavengers include hindered amine light stabilizers (HALS) compounds, hydroxylamines, sterically hindered phenols, and combinations thereof. Examples of suitable commercially available HALS compounds include those available from BASF under the trade names "Tinuvin 123" and "Tinuvin 292." An example of a suitable concentration of the free radical scavenger in the polymerizable precursor is in the range of about 0.05 wt % to about 0.25 wt % of the precursor solution.

An article is also disclosed herein. The article comprises a substrate having a first major surface and a second major surface; and an optically-scattering layer on the first major surface of the substrate. The optically-scattering layer scatters visible light. The optically-scattering layer is prepared by curing the curable composition described above. The optically-scattering layer is described in more detail below.

A wide range of substrates are suitable for the articles of the present invention. The substrates included in the articles may contain polymeric materials, glass materials, ceramic materials, metal-containing materials (e.g., metals or metal oxides), or combinations thereof. The substrates may include multiple layers of materials, such as a backing layer, a primer layer, a hard coat layer, a decorative design, and the like. The substrates may be permanently or temporarily attached to an adhesive layer. For example, a release liner may be temporarily attached and then removed for attachment of an adhesive layer to another substrate.

The substrate may have a variety of functions, such as providing flexibility, encapsulation, barrier, rigidity, strength or support, reflectivity, antireflectivity, polarization, or transmissivity (e.g., selectively to different wavelengths). That is, the substrate may be flexible or rigid; reflective or non-reflective; visibly transparent, colored but transmissive, graphical (i.e., having printed images or indicia), or opaque (e.g., not transmissive); polarizing or non-polarizing.

Exemplary substrates include, but are not limited to, an exterior surface of an electronic display, such as a liquid crystal display, an inorganic light emitting diode (LED) display, or an organic light emitting diode (OLED) display, an exterior surface of a window or glazing, an exterior surface of an optical component, such as a reflector, polarizer, diffraction grating, mirror, or lens, or other films, such as graphic or decorative films or other optical films.

Representative examples of polymer substrates include those containing polycarbonates, polyesters (e.g., polyethylene terephthalate and polyethylene naphthalate), polyurethanes, poly(meth)acrylates (e.g., polymethyl methacrylate), polyvinyl alcohol, polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyimides, cellulose triacetate, acrylonitrile-butadiene-styrene copolymers, and the like.

The substrate may also include an inorganic layer. The inorganic layer may be manufactured from a variety of materials including metals, metal oxides, metal nitrides, metal oxynitrides, metal carbides, metal oxyborides, and combinations thereof. A wide range of metals are suitable for use in the metal oxides, metal nitrides, and metal oxynitrides, particularly suitable metals include Al, Zr, Si, Zn, Sn, and Ti. One particularly suitable inorganic barrier layer material is silicon nitride. In some embodiments, the inorganic layer provides encapsulation and barrier functions to prevent water and oxygen from entering the display device.

Articles of the present invention may be incorporated into larger articles and devices. In some embodiments, the substrate having the light-scattering coating may be incorporated into a display device.

The article of the present invention comprises an optically-scattering layer. The optically-scattering layer is prepared by curing the curable composition described above. The cured optically-scattering layer comprises a matrix having microdomains of a material different from that of the matrix. The compositions of the matrix and microdomains have been found to be more complex than predicted by the PIPS (Polymerization-Induced Phase Separation) model. In the PIPS model, a curable composition comprising a fluoropolymer and a (meth)acrylate monomer which are miscible with each other and are therefore an optically clear fluid would be expected to form microdomains of the fluoropolymer within the crosslinked (meth)acrylate matrix upon curing. This does occur upon curing, but the compositions of the resulting matrix and microdomains are much more complex.

The optically-scattering layer has at least one of three different types of regions. Each of these regions comprises a matrix and phase-separated microdomains, wherein the matrix and the phase-separated microdomains have different refractive indices, and wherein the microdomains are on the order of a wavelength of visible light or greater. Typically, the wavelength of visible light is in the range of 400 to 700 nanometers. Typically, the average diameter of the phase-separated microdomains is in the range of 100 to 4,000 nanometers, or 400 to 2,000 nanometers, or 400 to 1,000 nanometers, or even 400 to 700 nanometers. The first type of region is a region wherein the essentially continuous matrix comprises a cross-linked (meth)acrylate matrix and phase-separated fluorocarbon-rich microdomains. A second type of region is one in which the essentially continuous matrix comprises a crosslinked (meth)acrylate matrix and the phase-separated microdomains comprise a (meth)acrylate material as well as a fluoropolymer. In these embodiments, the microdomains may still be described as fluoropolymer-rich microdomains, but they comprise nanodomains of the fluoropolymer and nanodomains of the crosslinked (meth)acrylate. A third type of region is one in which the essentially continuous matrix comprises fluorocarbon-rich domains and phase-separated (meth)acrylate-rich microdomains, wherein the (meth)acrylate-rich microdomains comprise at least a crosslinked (meth)acrylate material and may also contain a fluoropolymer.

The optical-scattering layer comprises at least one of the types of regions described above. In some embodiments, the optical-scattering layer comprises only one type of region and is essentially uniform throughout. In other embodiments, the optical-scattering layer comprises more than one type of region.

In some embodiments, the optically-scattering layer comprises a cured crosslinked (meth)acrylate matrix having fluoropolymer-rich microdomains. In some embodiments, the fluoropolymer-rich microdomains comprise essentially all fluoropolymer (type 1 regions). In other embodiments, the fluoropolymer-rich microdomains comprise fluoropolymer as well as (meth)acrylate material (type 2 regions). In these embodiments, the fluoropolymer-rich microdomains comprise nanodomains of fluoropolymer and nanodomains of crosslinked (meth)acrylate. In some embodiments, the optically-scattering layer can comprise types 1 and types 2 regions.

In another embodiment, the cured optically-scattering layer comprises an essentially continuous matrix of fluorocarbon-rich and phase-separated microdomains of (meth)acrylate-rich regions (regions of type 3). Typically, when regions of type 3 are present, regions of type 1, regions of type 2, or a combination of types 1 and type 2 are also present. Since the fluorocarbon is present as a minor component (less than 50 wt %) of the curable composition, there is not enough fluorocarbon to form continuous domains throughout the entire cured organic layer, but rather the regions of type 3 are present in localized regions of the cured optically-scattering layer.

As mentioned above, the formation of three different types of domains within the cured optically-scattering layer was unexpected. The PIPS model would suggest a relatively simple process for forming a cured optically-scattering layer from a curable composition containing a fluorocarbon and a (meth)acrylate material. Since fluorocarbon polymers and (meth)acrylate polymers are largely immiscible with each other, it was somewhat surprising that the fluorocarbon polymer and the (meth)acrylate monomer were miscible. However, since these two materials are miscible with each other prior to the formation of the crosslinked poly(methacrylate) matrix, but the fluoropolymer is not miscible with the crosslinked poly(meth)acrylate) matrix, it was assumed that the fluoropolymer domains would form upon formation of the (meth)acrylate matrix by polymerization. It is expected that the domain size can be controlled to have microdomains with an average diameter of 100 to 4,000 nanometers, or 400 to 2,000 nanometers, or 400 to 1,000 nanometers, or even 400 to 700 nanometers. As mentioned above, the cured optical-scattering layer is much more complex than the PIPS model would suggest.

The cured optically-scattering layer was found to be an optically-scattering layer, whether it contained just one type of domain or more than one type of domain. That the optically-scattering layer can forward-scattering visible light as desired is evidenced by the fact that the cured optically-scattering layer had a haze value of greater than or equal to 5% when measured as described in the Examples section.

The complexity of the hardened optical-scattering layer, i.e. the presence of up to three different domain types within the layer, has been detected by a relatively new technique combining atomic force microscopy (AFM) with infrared spectroscopy (IR). This new technique is abbreviated as AFM-IR. AFM-IR, a technique based on the photothermal induced resonance effect (PTIR), is a combination of atomic force microscopy (AFM) and infrared spectroscopy (IR) for nanoscale characterization. It provides simultaneous topographical and chemical information of sub-50 nm features. The AFM-IR technique uses a sharp gold-coated AFM tip to detect the rapid thermal expansion of the sample caused by the absorption of short (10 nanoseconds) pulses of IR radiation. When the monochromatic laser radiation approaches the IR frequency that excites molecular vibrations within the sample, the light is absorbed, inducing a rapid thermal expansion of the sample in contact with the AFM tip. This causes a simultaneous deflection of the AFM tip, which causes the cantilever to "ring down" at its natural deflection resonance frequency as the heat dissipates. These movements of the cantilever are "detected" by a second laser beam reflected from the top of the cantilever, and this signal is measured using a position-sensitive photodetector. The resonance amplitude induced in the cantilever is directly proportional to the amount of IR radiation absorbed by the sample. In this way, an AFM-IR spectrum is generated by measuring the ring-down amplitude while tuning the IR laser across the IR fingerprint region. Furthermore, the IR laser can be tuned to a fixed wavenumber, so that the IR absorption can be measured as a function of position as the AFM tip scans across the sample. The result is a chemical composition map, which shows the distribution of chemical constituents across the sample.

Methods of making articles are also disclosed herein. In some embodiments, the method comprises providing a substrate having a first major surface and a second major surface, providing a curable composition, forming a layer of the curable composition on at least a portion of the first major surface of the substrate, and curing the layer of the curable composition to form a cured crosslinked optically-scattering layer. The curable composition is as described above and comprises at least one fluoropolymer, at least one monofunctional (meth)acrylate, at least one difunctional (meth)acrylate, and at least one initiator, wherein the curable composition typically has a viscosity of less than 30 centipoise at a temperature of from room temperature to 60° C. The cured crosslinked layer comprises a (meth)acrylate matrix and fluoropolymer-rich microdomains, wherein the microdomains are on the order of a wavelength of visible light or greater. Typically, the microdomains range from 100 to 4,000 nanometers, and in some embodiments from 400 to 2,000 nanometers, from 400 to 1,000 nanometers, or even from 400 to 700 nanometers.

The formation of the layer of the curable composition can be accomplished by a wide variety of coating, printing or other patterning techniques. Printing techniques are particularly suitable because these techniques provide excellent control over the formation of the layer. Examples of suitable printing techniques include screen printing, inkjet printing, flexographic printing, gravure printing, offset printing, needle dispensing, and patch coating. In some embodiments, the curable composition is coated by inkjet printing. Typically, the formed layer has a thickness of from 1 to 76 micrometers, in some embodiments from 1 to 51 micrometers, or even from 1 to 25 micrometers.

Curing of the curable composition is accomplished by activating an initiator present in the curable composition to initiate free radical polymerization. Typically, the initiator is a photoinitiator that is generally activated by UV light or visible light. The UV light can be supplied by a variety of different light sources, such as lamps. The source of radiation used for curing can be an "internal" source (e.g., if the coating is coated on a display, the display subpixels themselves can be used for curing) or an external source (e.g., a laser, a bank of UV blacklight bulbs, a UV-LED lamp, etc.). If an internal light source is used, a red, green, or blue photosensitive agent can be added to the resin along with a standard free radical initiator. Assuming non-overlapping absorbances of the visible light photosensitive agent, a series of red, green, or blue flashes on the display can be used to cure the ink over each subpixel. Each color flash can have a different intensity corresponding to the curing rate required for each subpixel scattering layer. Blanket UV flood exposure can be used to complete curing of areas of the coating that are not directly over subpixels.

When an external light source is used, raster scanning, direct-write laser, or UV flood exposure techniques using a photomask may be used. When a laser is used for patterning, the laser may have different wavelengths or intensities as needed to create the scattering layer. The laser may be used to irradiate the film at an angle to create a cone of scattering particles within the film, rather than a column of scattering particles. In the UV flood exposure, three different photomasks may be used, each containing open windows corresponding to the positions of the red, green, or blue subpixels, respectively. Perhaps the same fine metal mask used for evaporation of the three different emission dyes in the OLED display may also be used as the photomask for the phase separation inks. Then, as needed, different radiation intensities may be used for each exposure.

Curing may be performed in selective subsections of the layer, or the entire layer may be cured. In some embodiments, curing comprises pattern-wise curing of selected regions of the layer such that the layer comprises a range of microdomains. Such pattern-wise curing may be performed by selective irradiation, or through the use of a mask. Selective irradiation may be performed in a variety of ways. For example, irradiation with different intensities at different spots may provide variable irradiation, or irradiation of a selective region with a irradiation source may be performed in a selective region using a laser or similar light source, followed by curing of the remainder of the surface region using a conventional light source. One layer of the curable composition formulation may be used as a single film over the entire area of the device, or three different inkjet print heads may deposit three different ink formulations, for example, over each of the R, G, and B subpixels. Each of the three formulations may be tuned to compensate for imperfections at each of the emission wavelengths.

After deposition of the curable composition, a first (low) radiation intensity pulse can be used to form scattering domains and anchor them into the crosslinked matrix. A second (much higher intensity) radiation pulse can be used to complete the curing of the remaining acrylate monomer. Likewise, a higher intensity will also lead to phase separated fluoropolymer domains, but these domains will be so small that they may be considered optically insignificant. Other uses for such multimodal or gradient distributions of domain sizes may also be envisaged, including for some degree of light steering or optical focusing.

At the initiation of polymerization, an optically-scattering layer is formed. As noted above, three different types of regions can be formed within the layer. The optically-scattering layer comprises a matrix and phase-separated microdomains. The microdomains can be fluoropolymer-rich or (meth)acrylate-rich. Without being bound by theory, since the formation of the microdomains is believed to be diffusion-limited, the rate at which the crosslinked poly(meth)acrylate matrix is formed can directly affect the size of the microdomains. Since the rate of curing of the poly(meth)acrylate matrix can be directly affected by varying the intensity of the curing radiation, the ability to pattern distinct levels of scattering using different light intensities is anticipated. For example, a low light intensity can be used to create large fluoropolymer or acrylate microdomains in one region of the layer, while a high light intensity can be used to create small fluoropolymer or (meth)acrylate microdomains in another region of the layer. The different domain sizes will lead to changes in the haze and optical scattering in each region of the layer. According to Mie theory, the intensity of the scattered light is proportional to the square of the difference in refractive indices between the two phases and to the sixth power of the radius of the disperse phase, assuming that the particles are smaller than the wavelength of light. Other methods of influencing the cure rate include varying the functionality, viscosity, and molecular weight of the (meth)acrylate monomers used in the resin mixture. In this way, when curing is selectively performed, i.e., when different regions of the curable composition layer are exposed to different radiation, the formation of the microdomains is likewise different. In other words, selective curing can create a light-diffusing layer having different microdomains at different points on the layer. Such selectivity is not possible with particle-based light diffusing layers or with the light diffusing layers described in U.S. Pat. No. 9,238,762 (Shaffer et al.), because these light diffusing layers are identical at all points in the layer.

The method of the present invention can be further understood by reference to FIGS. 1A-1I, which illustrate a wide range of curing methods that may be utilized to produce the optically-scattering layer of the present invention. It should be noted that these drawings are intended to be illustrative and are not drawn to scale.

Figure 1a illustrates a curable layer comprising a substrate layer (10A) having a curable composition (20A) disposed thereon. The curable composition is exposed to actinic radiation (30A). The actinic radiation is typically UV light, which causes the curable composition (20A) to cure to form a cured matrix (50A) having phase-separated microdomains (40A).

FIG. 1B illustrates a curable layer comprising a substrate layer (10B) having a curable composition (20B) disposed thereon. The curable composition is exposed to actinic radiation (31B, 32B, 33B) of different intensities (indicated by I ₁ , I ₂ , I ₃ ). The actinic radiation (31B) has an intensity (I ₁ ), the actinic radiation (32B) has an intensity (I ₂ ), and the actinic radiation (33B) has an intensity (I ₃ ), and the relative intensities of the actinic radiation are I ₁ < I ₂ < I ₃ . The actinic radiation is typically UV light, which cures the curable composition (20B) to form a cured matrix (50B) having phase-separated microdomains (41B, 42B, 43B). The sizes of the phase-separated microdomains (41B, 42B, 43B) are shown to be different. It should be noted that although the separated microdomains (41B, 42B, 43B) are different, their sizes are representative and not drawn to scale.

FIG. 1C illustrates a curable layer comprising a substrate layer (10C) having a curable composition (20C) disposed thereon. The curable composition is exposed to actinic radiation of different intensities (31C, 32C, 33C). The actinic radiation (31C) has an intensity lower than that of the actinic radiation (32C), the actinic radiation (33C) has an intensity lower than that of the actinic radiation (32C), and can be the same as or different from the intensity of the actinic radiation (31C). The actinic radiation is typically UV light, which causes the curable composition (20C) to cure to form a cured matrix (50C) having phase-separated microdomains (41C, 42C, 43C). The sizes of the phase-separated microdomains (41C, 42C, 43C) are shown to be different. It should be noted that although the separated microdomains (41C, 42C, 43C) are different, their sizes are representative and not drawn to scale.

FIG. 1D illustrates a curable layer comprising a substrate layer (10D) having a curable composition layer disposed thereon, wherein the curable composition sublayers (21D, 22D, 23D) comprise curable compositions. In this embodiment, the curable composition sublayers may represent, for example, curable compositions of different viscosities. Although three sublayers are shown for clarity, it should be understood that a wide range of sublayers are possible. These sublayers may be created by a gradient in the intensity of light received throughout the bulk of the film. For example, a film containing molecules that absorb ultraviolet radiation, such as ultraviolet absorbers, may receive a higher intensity of light on the top portion of the film compared to the bottom portion of the film. The curable composition is exposed to actinic radiation (30D). The actinic radiation is typically UV light, which causes the curable composition sublayers (21D, 22D, 23D) to cure to form a cured matrix (50D) having phase-separated microdomains (41D, 42D, 43D). The sizes of the separated microdomains (41D, 42D, 43D) are shown to be different. It should be noted that although the separated microdomains (41D, 42D, 43D) are different, these sizes are representative and are not drawn to scale.

FIG. 1E illustrates a curable layer comprising a substrate layer (10E) having a curable composition layer disposed thereon, the curable composition sublayers (21E, 22E). In this embodiment, the curable composition sublayers are different because the surface sublayer (22E) is exposed to an oxygen atmosphere since the curable article is not present in an inert atmosphere such as nitrogen. The curable composition is exposed to actinic radiation (30E). The actinic radiation is typically UV light, which causes the curable composition sublayers (21E, 22E) to cure to form a cured matrix (50E) having phase-separated microdomains (41E, 42E). The presence of oxygen in the surface sublayer (22E) is expected to impede the polymerization rate in such sublayers. The sizes of the phase-separated microdomains (41E, 42E) are shown to be different. It should be noted that although the separated microdomains (41E, 42E) are different, their sizes are representative and not drawn to scale.

FIG. 1F illustrates a curable layer comprising a substrate layer (10F) having a curable composition (20F) disposed thereon. A portion of the curable composition (20F) is blocked by a mask (60F). The curable composition is exposed to actinic radiation (30F). Due to the mask (60F), only a portion of the curable composition (20F) is exposed to the actinic radiation (30F). The actinic radiation is typically UV light, which causes the curable composition (20F) to cure to form a cured matrix (50F) having phase-separated microdomains (40F) within the regions exposed to the radiation (30F). The mask (60F) is removed, and the composition is exposed to actinic radiation (30F'). The actinic radiation (30F') may be the same as or different from the actinic radiation (30F). The actinic radiation is typically UV light, which cures the uncured curable composition to form a cured matrix (51F) having phase-separated microdomains (41F, 42F) within the areas exposed to radiation (30F').

FIG. 1g illustrates a curable layer comprising a substrate layer (10G) having a curable composition (20G) disposed thereon. A portion of the curable composition (20G) is exposed to actinic radiation (70G). The actinic radiation (70G) may be, for example, a laser. Due to the narrowness of the light source (70G), only a portion of the curable composition (20G) is exposed to the actinic radiation. The actinic radiation causes the curable composition (20G) to cure, thereby forming a cured matrix (50G) having phase-separated microdomains (40G) within the region exposed to the radiation (70G). The composition is exposed to actinic radiation (30G). Actinic radiation (30G) is typically a flood exposure of UV light, which cures the uncured curable composition to form a cured matrix (51G) having phase-separated microdomains (41G, 42G) within the areas exposed to radiation (30G).

FIG. 1H illustrates a curable layer comprising a substrate layer (10H) having a curable composition (20H) disposed thereon. The curable composition (20H) contains nanoparticles (80H). The curable composition (20H) is exposed to actinic radiation (30H). The actinic radiation is typically UV light, which cures the curable composition (20H) to form a cured matrix (50H) having phase-separated microdomains (40H). The surfaces of the nanoparticles may be engineered to act as seeds to nucleate phase separation, or they may be used for other functions, such as modifying refractive index.

FIG. 1i illustrates a curable layer comprising a substrate layer (10I) having a curable composition (20I) disposed thereon. A tool film (90I) has a microstructured pattern on one surface. In step (100), the tool film (90I) is contacted with the curable composition (20I) to form a laminate structure. The curable composition is exposed to actinic radiation (30I). The actinic radiation is typically UV light, which cures the curable composition (20I) to form a cured matrix (50I) having phase-separated microdomains (40I). The tool film (90I) is then removed in step (110) to produce a structured cured layer having a cured matrix (50I) and phase-separated microdomains (40I).

The present invention includes the following embodiments.

Among the embodiments are curable compositions. Embodiment 1 comprises a curable composition, the curable composition comprising at least one fluoropolymer; at least one monofunctional (meth)acrylate; at least one difunctional (meth)acrylate; and at least one initiator.

Embodiment 2 is a curable composition according to Embodiment 1, which is solvent-free and has a viscosity of less than 30 centipoise at a temperature of room temperature to 60° C.

Embodiment 3 is a curable composition according to Embodiment 1 or Embodiment 2, wherein at least one monofunctional (meth)acrylate comprises a monofunctional cycloaliphatic (meth)acrylate.

Embodiment 4 is a curable composition according to any one of Embodiments 1 to 3, wherein at least one monofunctional (meth)acrylate comprises a monofunctional cycloaliphatic methacrylate.

Embodiment 5 is a curable composition according to any one of Embodiments 1 to 4, wherein at least one bifunctional (meth)acrylate comprises a bifunctional aliphatic (meth)acrylate.

Embodiment 6 is a curable composition according to any one of Embodiments 1 to 5, wherein at least one bifunctional (meth)acrylate comprises a bifunctional aliphatic methacrylate.

Embodiment 7 is a curable composition according to any one of Embodiments 1 to 6, wherein the bifunctional (meth)acrylate constitutes 1 to 20 parts by weight based on the total weight of the curable components of the curable composition.

Embodiment 8 is a curable composition according to any one of Embodiments 1 to 7, wherein at least one fluoropolymer comprises 1 to 20 wt %, based on 100 wt % of the total curable composition.

Embodiment 9 is a curable composition according to any one of Embodiments 1 to 8, wherein at least one fluoropolymer comprises an amorphous fluoropolymer having a fluorine content of from 60 to 70%.

Embodiment 10 is a curable composition according to any one of Embodiments 1 to 9, wherein at least one fluoropolymer comprises a fluoroelastomer.

Embodiment 11 is a curable composition according to any one of Embodiments 1 to 10, further comprising at least one copolymerizable vinyl monomer.

Embodiment 12 is a curable composition according to Embodiment 11, wherein the copolymerizable vinyl monomer comprises N-vinyl pyrrolidone or N-vinyl caprolactam monomer.

Embodiment 13 is a curable composition according to any one of Embodiments 1 to 12, further comprising at least one additive selected from metal oxide nanoparticles, an adhesion promoter, a functional polymer, a heat stabilizer, an ultraviolet light stabilizer, a free radical scavenger, a chain transfer agent, a photosensitizer, and combinations thereof.

Articles are also disclosed. Embodiment 14 includes an article comprising a substrate having a first major surface and a second major surface; and an optically-scattering layer on the first major surface of the substrate, the optically-scattering layer being formed from a curable composition, the curable composition comprising: at least one fluoropolymer; at least one monofunctional (meth)acrylate; at least one difunctional (meth)acrylate; and at least one initiator; wherein the optically-scattering layer comprises a matrix and phase-separated microdomains, wherein the matrix and the phase-separated microdomains have different refractive indices, and wherein the microdomains are on the order of a wavelength of visible light or greater.

Embodiment 15 is an article of embodiment 14, wherein the optical-scattering layer has at least one of three types of regions, a first type of region comprising a (meth)acrylate matrix having fluorocarbon-rich phase-separated microdomains; a second type of region comprising a (meth)acrylate matrix having fluorocarbon-rich phase-separated microdomains, wherein the fluorocarbon-rich phase-separated microdomains further comprise (meth)acrylate-rich nanodomains; and a third type of region comprising a fluorocarbon-rich matrix having (meth)acrylate-rich phase-separated microdomains.

Embodiment 16 is an article according to embodiment 15, wherein the optical-scattering layer comprises at least two of the three types of regions.

Embodiment 17 is an article according to embodiment 15, wherein the optical-scattering layer comprises three types of regions.

Embodiment 18 is an article according to any one of Embodiments 14 to 17, wherein at least some of the separated microdomains comprise fluorocarbon-rich microdomains.

Embodiment 19 is an article according to any one of Embodiments 14 to 18, wherein the separated microdomains are 100 to 4,000 nanometers in size.

Embodiment 20 is an article according to any one of Embodiments 14 to 18, wherein the separated microdomains are 400 to 2,000 nanometers.

Embodiment 21 is an article according to any one of Embodiments 14 to 18, wherein the separated microdomains are 400 to 1,000 nanometers in size.

Embodiment 22 is an article according to any one of Embodiments 14 to 18, wherein the separated microdomains are 400 to 700 nanometers.

Embodiment 23 is an article according to any one of Embodiments 14 to 22, wherein the optically-scattering layer comprising phase-separated microdomains comprises regions having different concentrations of phase-separated microdomains, different sizes of phase-separated microdomains, or a combination thereof.

Embodiment 24 is an article according to embodiment 23, wherein the optically-scattering layer comprises regions having phase-separated microdomains of different concentrations, phase-separated microdomains of different sizes, or a combination thereof, and comprising a difference in concentration through the thickness of the layer.

Embodiment 25 is an article according to embodiment 23, wherein the optically-scattering layer comprises regions having phase-separated microdomains of different concentrations, phase-separated microdomains of different sizes, or a combination thereof, and comprising differences in concentration across the length and width of the layer.

Embodiment 26 is an article according to any one of Embodiments 14 to 25, wherein the optical-scattering layer has a thickness of 1 to 76 micrometers.

Embodiment 27 is an article according to any one of Embodiments 14 to 25, wherein the optical-scattering layer has a thickness of 1 to 51 micrometers.

Embodiment 28 is an article according to any one of Embodiments 14 to 25, wherein the optical-scattering layer has a thickness of 1 to 25 micrometers.

Embodiment 29 is an article comprising a display article according to any one of Embodiments 14 to 28.

Embodiment 30 is an article according to any one of Embodiments 14 to 29, wherein the optical-scattering layer comprises a structured surface.

Embodiment 31 is an article according to embodiment 30, wherein the structured surface comprises a microstructured surface.

A method of making an article is also disclosed. Embodiment 32 includes a method of making an article, comprising: providing a substrate having a first major surface and a second major surface; providing a curable composition, the curable composition comprising at least one fluoropolymer; at least one monofunctional (meth)acrylate; at least one difunctional (meth)acrylate; and at least one initiator; forming a layer of the curable composition on at least a portion of the first major surface of the substrate; curing the layer of the curable composition to form a cured optically-scattering layer, the cured optically-scattering layer comprising an optically-scattering layer on the first major surface of the substrate, wherein the optically-scattering layer comprises a matrix and phase-separated microdomains, the matrix and the phase-separated microdomains having different refractive indices, and the microdomains are on the order of a wavelength of visible light or greater.

Embodiment 33 is a method according to Embodiment 32, wherein the curable composition is solventless and has a viscosity of less than 30 centipoise at a temperature of room temperature to 60° C.

Embodiment 34 is a method according to Embodiment 32 or Embodiment 33, wherein the step of forming a layer of the curable composition on at least a portion of the first major surface of the substrate comprises printing the curable composition.

Embodiment 35 is a method according to embodiment 34, wherein the printing comprises inkjet printing.

Embodiment 36 is a method according to any one of Embodiments 32 to 35, wherein the separated microdomains are 100 to 4,000 nanometers in size.

Embodiment 37 is a method according to any one of Embodiments 32 to 35, wherein the separated microdomains are 400 to 2,000 nanometers in size.

Embodiment 38 is a method according to any one of Embodiments 32 to 35, wherein the separated microdomains are 400 to 1,000 nanometers in size.

Embodiment 39 is a method according to any one of Embodiments 32 to 35, wherein the separated microdomains are 400 to 700 nanometers.

Embodiment 40 is a method according to any one of Embodiments 32 to 39, wherein curing comprises pattern-wise curing of selected regions of the layer such that the layer comprises a predetermined range of phase-separated microdomains.

Embodiment 41 is the method of embodiment 40, wherein the pattern-wise curing comprises exposing different regions of the layer to irradiation of different intensities.

Embodiment 42 is a method of embodiment 40, wherein the pattern-wise curing comprises the steps of using a photomask across a portion of the layer and exposing the layer to radiation.

Embodiment 43 is a method according to embodiment 42, further comprising the steps of removing the photomask and exposing the layer to radiation, wherein the radiation is different from the radiation used when the photomask was in place.

Embodiment 44 is a method of embodiment 40, wherein the pattern-wise curing comprises the step of curing selected regions of the layer using a laser.

Embodiment 45 is the method of embodiment 44, further comprising the step of curing the remainder of the layer by exposure to the radiation.

Embodiment 46 is a method according to any one of Embodiments 32 to 45, wherein the cured optical-scattering layer has a thickness of 1 to 76 micrometers.

Embodiment 47 is a method according to any one of Embodiments 32 to 45, wherein the cured optical-scattering layer has a thickness of 1 to 51 micrometers.

Embodiment 48 is a method according to any one of Embodiments 32 to 45, wherein the cured optical-scattering layer has a thickness of 1 to 25 micrometers.

Example

A curable ink composition was prepared. The material was applied to a substrate and the physical, optical and mechanical properties were evaluated as set forth in the examples below. These examples are for illustrative purposes only and are not intended to limit the scope of the appended claims. Unless otherwise stated, all parts, percentages, ratios, etc. in the examples and the remainder of this specification are by weight. Unless otherwise indicated, the solvents and other reagents used were obtained from Sigma-Aldrich Chemical Company, St. Louis, MO. The following abbreviations are used herein: nm = nanometer; mm = millimeter; cm = centimeter; um = micrometer; m = meter; N = Newton; mW = milliwatt; min = minute; K = 1,000 (i.e., 15 KDa = 15,000 dalton molecular weight); Hz = hertz; cP = centipoise; mol = mole; ℃ = degree Celsius; T = transmittance; H = turbidity; C = clarity; avg = mean; and stdev = standard deviation. The terms "weight percent" and "weight basis percent" are used interchangeably.

[Table 1]

Test method

Sample manufacturing

Coatings for optical testing were prepared on substrate S1 using a wire-wound rod (Model: RDS10, RDS Specialties, Webster, NY). Ultraviolet (UV) curing of the films was performed immediately after coating using a CA-3200 UV-LED curing chamber with an integrated N ₂ purge (λ = 365-400 nm, Clearstone Technologies Inc., Hopkins, MN).

Samples were prepared by sandwiching the resin between two pieces of primed PET (S1) substrate. The S1/resin/S1 laminate was then placed on top of a photomask (IG1) patterned with chrome of varying thicknesses so that multiple discrete intensity levels were achieved across the sample as UV radiation passed through the mask. Another piece of bare glass was placed on top of the S1/resin/S1 laminate and the entire structure was then clamped tightly using binder clips. A piece of thick black plastic was placed on top of the clamped structure to prevent back reflection of UV from the top of the curing chamber during curing. Curing through the photomask was performed for 30 minutes followed by a flood exposure without the photomask for 15 minutes using a UV intensity of 95.6 mW/cm2. The intensity of light passing through each area of the photomask was measured using a radiometer (UV PowerPuck II, Electronic Instrumentation and Technology Inc., Sterling, VA) as reported in Tables 4 and 5.

Test Method 1: Measurement of Transmittance, Turbidity, Clarity, and b*

Measurements of average % transmittance, turbidity, clarity and b* were performed using a turbidimeter (BYK Gardner, Columbia, MD, USA, trade name “BYK HAZEGARD Plus”) based on ASTM D1003-13. The results are reported in Table 5.

Test Method 2: Viscosity Measurement

17 mL of each ink formulation was loaded into a 25 mm diameter double gap coaxial concentric cylinder device (DIN 53019) on a viscometer (BOHLIN VISCO 88, Malvern Instruments Ltd, Malvern, UK). A heat jacket fitted to the double gap cell allowed the flow of recirculating water heated to 25 °C and 35 °C, respectively. The system was allowed to equilibrate for 30 min before each measurement. The shear rate was ramped from 100 to 1000 Hz in steps of 100 Hz and the measurements were repeated in triplicate. The mean and standard deviation over all data points were taken as the viscosity in centipoise. The results are reported in Table 3.

Test Method 3: Atomic Force Microscopy (AFM) Measurements

Samples of the cured resin between substrates S1 were cross-sectioned at room temperature using a Leica EM UC6 Microtome. Cross sections of the phase-separated ink coatings were imaged using atomic force microscopy. Imaging was performed on a Bruker Dimension Icon microscope (Bruker Nano Inc., 112 Robin Hill Rd., Santa Barbara, CA 93117, USA) operated in tapping mode under ambient conditions in air. Bruker OTESPA silicon cantilever tips with aluminum backcoating were used during operation (nominal spring constant = 40 N/m, nominal frequency = 300 kHz, nominal tip radius = 8 nm). Image size was 20 μm × 20 μm with 1024 × 1024 data points. At each light intensity, domain size analysis was performed on three images per sample. Precise measurements of the domain size for each measurement were obtained using the Nanoscope Analysis v1.7 (Brooker, Santa Barbara, CA) software. The mean and standard deviation were reported and tabulated in Table 4.

Test Method 4: Atomic Force Microscopy-Infrared Spectroscopy (AFM-IR)

Samples were cryo-microtomed to obtain 250 nm cross-section slides for AFM-IR studies. Cryo-microtoming was performed using a Leica Ultramicrotome EM UC7 unit at -40 °C. The cross-section slices were then transferred onto a flat 10 mm × 10 mm ZnS single crystal for AFM-IR examination.

AFM-IR experiments were performed using a NanoIR2-FS platform (Bruker Anasys, Santa Barbara, CA, USA). Thin cross-section slices were examined in contact mode using a gold-coated SiN AFM tip with a nominal tip radius of 20 nm (Anasys Instruments). The repetition rate of the IR laser was adjusted to match the second contact resonance of the AFM cantilever to enhance sensitivity. All measurements were performed under ambient conditions.

A cross-section of the film sample was IR-mapped at two characteristic laser frequencies, 1730 cm ^-1 and 1210 cm ^-1 , which are characteristic IR absorption bands for methacrylate and fluoroelastomer, respectively.

Example

Formulation

A stock solution of neat fluoroelastomer was prepared for each methacrylate monomer. A piece of fluoroelastomer was cut from a larger block into small 2 mm × 2 mm squares and added to each neat methacrylate monomer in an amber vial. The vial was placed on a roller for 2 days or until a clear homogeneous solution was formed. An aliquot was withdrawn from the stock solution vial and mixed with the remaining other ingredients. For most examples, an 80:20 mol:mol ratio of monofunctional monomer:difunctional monomer was used for the photocurable portion of the formulation. The photoinitiator (PH1) and spacer beads (B1) were added based on the total weight of the fluoropolymer/monomer solution. The solution was sonicated for 30 minutes or until a homogeneous blend was formed. See Table 2 for the formulations used for each example.

[Table 2]

[Table 3]

[Table 4]

[Table 5]

AFM and AFM-IR images

FIGS. 2 and 4 show optical micrographs of cross-sections of films produced in Examples 2 and 1, respectively, and analyzed by 'Test Method 3: Atomic Force Microscopy'. The AFM IR mapping clearly shows the spatial distribution of methacrylate and fluoropolymer, which confirms distinct phase separation. While the frequency of the IR laser was fixed at 1730 cm ^-1 and 1210 cm ^-1 , respectively, the chemical components were mapped on a 30 μm × 30 μm region of the cross-section using the AFM-IR technique. The IR mapping at 1730 cm ^-1 and 1210 cm ^-1 is shown in FIGS. 3b and 3c. FIG. 3a shows the AFM topographic mapping acquired simultaneously with the IR mapping. FIGS. 3b and 3c clearly show distinct chemical separation between the fluoropolymer phase and the methacrylate phase. The matrix of the image in Fig. 3b is lighter in color on the data scale, indicating a higher IR absorption in this region at 1730 cm ^-1 corresponding to the C=O (carbonyl chemical moiety) stretching mode in the methacrylate phase. In Fig. 3c, these microdomains are shown to have a higher IR absorption at 1210 cm ^-1 corresponding to the CF stretching mode in the fluoroelastomer phase. This color inversion between Figs. 3b and 3c suggests that the matrix is rich in methacrylate, while the microdomains are rich in fluoroelastomer. Furthermore, a closer look inside the fluoroelastomer-rich microdomains shows nanodomains in the methacrylate phase, indicating more complex phase separation phenomena. To remove topography-induced image artifacts, the absorption intensity ratio of the IR mapping was calculated. The absorption intensity ratio of the IR mapping was calculated using the built-in software of the NanoIR2-FS instrument (Brooker Anasys, Santa Barbara, CA, USA). The ratio of absorption at the two IR laser frequencies was calculated for every single pixel on the mapping. Figure 3d shows the absorption intensity ratio of the 1210 cm ^-1 mapping to the 1730 cm ^-1 mapping. The greatly improved contrast clearly indicates the phase-separated morphology of the methacrylate and the fluoroelastomer. Similarly, Figure 5 shows the topographic and chemical mapping of Example 1. As shown in the two IR mappings (Figures 5b and 5c) and the image ratio (Figure 5d), the spherical methacrylate-rich domains are dispersed in the fluoroelastomer-rich matrix, which is exactly the opposite of the phase-separated morphology in Figure 3 .

Claims (24)

At least one non-polymerizable fluoropolymer; and
Radiation-curable organic monomer mixture
A curable composition comprising:
A mixture of radiation-curable organic monomers
At least one monofunctional cycloaliphatic (meth)acrylate;
At least one bifunctional (meth)acrylate; and
At least one initiator
wherein the curable composition is solvent-free, and the curable composition forms a cured organic layer having a matrix and phase-separated microdomains, wherein the matrix and the phase-separated microdomains have different refractive indices, and at least some of the phase-separated microdomains have a diameter of about 400 to 700 nm or greater.
A curable composition. a substrate having a first main surface and a second main surface; and
An optically-scattering layer on the first surface of the substrate
As an article containing,
The optical-scattering layer is prepared from a curable composition, the curable composition comprising:
At least one non-polymerizable fluoropolymer; and
Radiation-curable organic monomer mixture
, and a mixture of radiation-curable organic monomers
At least one monofunctional cycloaliphatic (meth)acrylate;
At least one bifunctional (meth)acrylate; and
At least one initiator
, wherein the curable composition is solvent-free, the optically-scattering layer comprises a matrix and phase-separated microdomains, wherein the matrix and the phase-separated microdomains have different refractive indices, and the microdomains have a wavelength of visible light or greater.
article. In the second paragraph, the optical-scattering layer has at least one of three types of regions,
The first type of region comprises a (meth)acrylate matrix having fluorocarbon-rich phase-separated microdomains;
A second type of domain comprises a (meth)acrylate matrix having fluorocarbon-rich phase-separated microdomains, wherein the fluorocarbon-rich phase-separated microdomains further comprise (meth)acrylate-rich nanodomains;
A third type of region is an article comprising a fluorocarbon-rich matrix having (meth)acrylate-rich phase-separated microdomains. In the third paragraph, the article comprises an optical-scattering layer comprising at least two of three types of regions. An article in the second aspect, wherein the phase-separated microdomains are 100 to 4,000 nanometers. In the second aspect, the optical-scattering layer comprising phase-separated microdomains comprises regions having phase-separated microdomains of different concentrations, phase-separated microdomains of different sizes, or a combination thereof. In the second paragraph, the article has an optical-scattering layer having a thickness of 1 to 76 micrometers. As a method of manufacturing a product,
A step of providing a substrate having a first main surface and a second main surface;
Step of providing a curable composition - the curable composition comprises:
At least one non-polymerizable fluoropolymer; and
Radiation-curable organic monomer mixture
, and a mixture of radiation-curable organic monomers
At least one monofunctional (meth)acrylate;
At least one bifunctional (meth)acrylate; and
At least one initiator
, wherein the curable composition is solvent-free, and the curable composition has a viscosity of less than 30 centipoise at a temperature of room temperature to 60° C.
A step of forming a layer of a curable composition on at least a portion of a first main surface of a substrate;
A step of curing a layer of a curable composition to form a cured optical-scattering layer, wherein the cured optical-scattering layer
A method comprising: an optically-scattering layer on a first surface of a substrate, wherein the optically-scattering layer comprises a matrix and phase-separated microdomains, wherein the matrix and the phase-separated microdomains have different refractive indices, and wherein the microdomains have a wavelength of visible light or greater. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete

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