JP6793210B2 - Methods for Producing Light Diffusing Particles, Light Diffusing Transmission Sheets, and Light Diffusing Particles - Google Patents

Description

The present invention relates to light diffusing particles, light diffusing and transmitting sheets, and methods for producing light diffusing particles.

With the improvement of the image quality of the liquid crystal display, there is an increasing demand for a light diffusion transmitting sheet having high light diffusion characteristics in order to spatially homogenize the light emitted from the backlight of the liquid crystal display. In addition, from the viewpoint of reducing energy consumption, there is an increasing demand for light diffusing and transmitting sheets having high luminance characteristics.

Patent Document 1 describes a light diffusing and transmitting sheet including a resin as a base material and silica composite particles dispersed in the resin. The silica composite particles contain titanium oxide fine particles having an average particle size of 100 nm or less. The light diffusing transmission sheet described in Patent Document 1 exhibits a high total light transmittance and a haze rate. The refractive index of titanium oxide is larger than that of silica.

Patent Document 2 describes a transmissive screen for visually recognizing an image projected from a projector. The transmissive screen has a light diffusing layer containing light diffusing fine particles and xerogel. It is described that as the light diffusing fine particles, composite particles of organic fine particles and a small amount of inorganic fine particles or composite particles of inorganic fine particles and a small amount of organic polymer can be used. Examples of composite particles of organic fine particles and a small amount of inorganic fine particles include composite particles in which the surface of fine particles such as melamine resin or acrylic resin is coated with inorganic fine particles such as silica. Usually, the refractive index of the melamine resin and the refractive index of the acrylic resin are higher than the refractive index of silica.

Patent Document 3 describes an optical laminate having a light-transmitting base material and an internal scattering layer. Patent Document 3 describes that this optical laminate exhibits excellent contrast and anti-glare effect while maintaining good antiglare properties. The internal scattering layer contains internal scattering particles. The internally scattered particles include fine particles having an average particle size of 5 to 300 nm. The refractive index n _A of the fine particles contained in the internally scattered particles is larger than the refractive index n _B of the components other than the fine particles contained in the internally scattered particles.

Patent Document 4 describes a light diffusing plate provided with a light diffusing layer made of a transparent base material containing a transparent resin. The light diffusing layer contains first light diffusing particles and second light diffusing particles existing inside the transparent substrate. The refractive index of the second light diffusing particles is larger than the refractive index of the first light diffusing particles. The refractive index of the first light diffusing particles is 1.4 to 1.7, and the refractive index of the second light diffusing particles is larger than 2.

JP-A-2014-48427 Japanese Unexamined Patent Publication No. 2013-195548 JP-A-2009-42554 Japanese Unexamined Patent Publication No. 2008-40479

The techniques described in Patent Documents 1 to 4 are not necessarily advantageous in providing high luminance characteristics to a product having a layer or sheet in which particles described in Patent Documents 1 to 4 are dispersed. In addition, in Patent Documents 1 to 4, no study has been made on the water retention of the particle surface.

Therefore, the present invention provides light diffusing particles having a surface that is advantageous for imparting high luminance characteristics to the light diffusing and transmitting sheet and that does not easily retain water.

The present invention
A core formed by a first binder and first fine particles containing low refractive index fine particles having a refractive index lower than that of the first binder and being covered in contact with the first binder.
A shell that contacts the outer surface of the core and covers the core, and has spherical particles having a particle diameter of 50 nm to 450 nm and imparting surface irregularities to the shell, and a second shell that is in contact with the outer surface of the spherical particles. With a shell, including a binder,
Provides light diffusing particles.

In addition, the present invention
With the base material
The above-mentioned light diffusing particles dispersed in the base material are provided.
A light diffusion transmitting sheet is provided.

Furthermore, the present invention
A method for producing light diffusing particles having a core-shell structure.
A first dispersion liquid in which the raw material of the first binder and the first fine particles containing the low refractive index fine particles having a refractive index lower than that of the first binder are dispersed is prepared.
A cross-linking agent for cross-linking the raw material of the first binder is added to the first dispersion liquid to cross-link the raw material of the first binder to form a core.
A second dispersion liquid in which the core and spherical particles having a particle diameter of 50 nm to 450 nm are dispersed is prepared.
Spray-dry the second dispersion.
Provide a method.

The above-mentioned light diffusing particles are advantageous for imparting high brightness characteristics to the light diffusing transmissive sheet in which the light diffusing particles are dispersed, and water does not easily stay on the surface of the light diffusing particles. Further, according to the above method, light diffusing particles having a core-shell structure and a surface that does not easily retain water can be produced by one spray drying.

FIG. 1 is a cross-sectional view schematically showing the structure of light diffusing particles according to an example of the present invention. FIG. 2 is a diagram schematically showing an optical path of light incident on fine particles having a high refractive index. FIG. 3A is a diagram schematically showing an optical path of light incident on fine particles having a low refractive index. FIG. 3B is a diagram schematically showing an optical path of light incident on another low refractive index fine particle. FIG. 4 is a diagram schematically showing light diffusing particles having a surface that easily retains water. FIG. 5 is a diagram schematically illustrating the difficulty of water retention on the surface of the light diffusing particles according to an example of the present invention. FIG. 6A is a diagram schematically illustrating the vicinity of the surface of the light diffusing particles according to an example of the present invention. FIG. 6B is a diagram showing changes in the refractive index in the sections y0 to y2 shown in FIG. 6A. FIG. 7 is a cross-sectional view showing a light diffusion transmitting sheet according to an example of the present invention. FIG. 8 is a scanning electron microscope (SEM) photograph of the light diffusing particles according to Example 3. FIG. 9 is an SEM photograph of the light diffusing particles according to Comparative Example 1.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description relates to an example of the present invention, and the present invention is not limited thereto.

As shown in FIG. 1, the light diffusing particle 10 includes a core 10c and a shell 10s. The core 10c is formed by the first binder 11 and the first fine particles 12. The first fine particles 12 include low refractive index fine particles 12a having a refractive index lower than that of the first binder 11. In addition, the first fine particles 12 are in contact with and covered with the first binder 11. The shell 10s contacts the outer surface of the core 10c and covers the core 10c. The shell 10s contains spherical particles 13 and a second binder 15. The spherical particles 13 have a particle diameter of 50 nm to 450 nm, and impart surface irregularities A to the shell. The second binder 15 is in contact with the outer surface of the spherical particles 13. In addition, in this specification, "particle diameter" means the maximum diameter. The “spherical particle” means a particle having an aspect ratio (ratio of the maximum diameter to the minimum diameter) of 1.3 or less.

The silica composite particles described in Patent Document 1 contain titanium oxide fine particles having an average particle size of 100 nm or less. The refractive index of titanium oxide is higher than that of silica. Therefore, in the silica composite particles, titanium oxide fine particles having a high refractive index are included in silica having a low refractive index. As shown in FIG. 2, when light is incident on the fine particle PH having a high refractive index from a medium having a relatively low refractive index, a part of the light incident on the fine particle PH is repeatedly reflected inside the fine particle PH and inside the fine particle PH. Easy to be trapped in. In the present specification, such a phenomenon is referred to as a "light confinement phenomenon". The light confinement phenomenon is likely to occur inside the silica composite particles described in Patent Document 1, and it cannot be said that the technique described in Patent Document 1 is advantageous for imparting high luminance characteristics to the light diffusion transmitting sheet. The same applies to the techniques described in Patent Documents 2 and 3. Further, although the composite particles are not described in Patent Document 4, since the refractive index of the second light diffusing particles is larger than 2, it is considered that the light confinement phenomenon is likely to occur in the second light diffusing particles.

On the other hand, for example, as shown in FIGS. 3A and 3B, when light is incident on the fine particle PL1 or the fine particle PL2 having a low refractive index from a medium having a relatively high refractive index, the “light confinement phenomenon” occurs in the fine particle PL1 and the fine particle PL2. Is unlikely to occur. In FIG. 3A, the difference obtained by subtracting the refractive index of the fine particle PL1 from the refractive index of the medium around the fine particle PL1 is 0.01, and in FIG. 3B, the refraction of the fine particle PL2 from the refractive index of the medium around the fine particle PL2. The difference after subtracting the rate is 0.1. In the light diffusing particles 10, the low refractive index fine particles 12a have a refractive index lower than that of the first binder 11 and are covered in contact with the first binder 11. Therefore, the light confinement phenomenon is unlikely to occur in the low refractive index fine particles 12a, and the light diffusing particles 10 are advantageous for imparting high brightness characteristics to the light diffusing transmissive sheet in which the light diffusing particles 10 are dispersed.

Next, the reason why water is difficult to stay on the surface of the light diffusing particles 10 will be described. The conditions for capillary condensation are described by the following equation [1]. Here, p, p _s , σ, V, r, R, and T are the vapor pressure when the liquid is flat, the vapor pressure in the capillary, the surface tension, the molecular volume, the radius of the capillary, the gas constant, respectively. And absolute temperature.
log ₁₀ (p / p _s ) = (-2σV / rRT) [1]

From the formula [1], the radius r of the capillary where capillary condensation occurs when the liquid is water in an environment of 25 ° C. and a relative humidity of 50% RH (p / p _s = 0.5) is estimated. In this estimation, σ, V, r, R, and T are 72 × 10 ^-3 [N ・ m ^-1 ], 18 × 10 ^-6 [m ³・ kg ^-1 ], and 8.31 [J ・ mol, respectively. ^-1 K ^-1 ] and 298 [K]. In this case, the radius of the capillary is r = 3.5 nm. Capillary condensation occurs in a standard environment of 25 ° C and 50% RH. Since the radius of the capillary is 3.5 nm, if there is a recess with a width of several nanometers near the surface of the particle, the water vapor in the air will be removed. Capillaries may condense in the recesses.

For example, as shown in FIG. 4, when recesses having a width of several nanometers are densely present near the surface of the particles, a large amount of water W stays on the surface of the particles due to capillary condensation of water vapor in the recesses. In the shell 10s of the light diffusing particles 10, the surface unevenness A is imparted by the spherical particles 13. As shown in FIG. 1, the surface unevenness A reflects the shape of the spherical particles 13. As shown in FIG. 5, the concave portions of the surface unevenness A are sparsely present in the vicinity of the surface of the light diffusing particles 10 because the spherical particles 13 have a particle diameter of 50 nm to 450 nm. Therefore, there are only sparse sites near the surface of the light diffusing particles 10 that cause capillary condensation of water vapor, and the light diffusing particles 10 have a surface that makes it difficult to retain water. As a result, when the light diffusing and transmitting sheet is manufactured using the light diffusing particles 10, it is possible to prevent the quality of the light diffusing and transmitting sheet from being deteriorated due to moisture.

The spherical particles 13 preferably have a particle size of 50 nm to 350 nm. In this case, the convex portion of the surface unevenness A has a width (for example, 50 nm to 350 nm) of about half or less of the upper limit of the wavelength of visible light. As shown in FIG. 6A, consider a case where the shell 10s (refractive index Ns) of the light diffusing particles 10 is in contact with the medium M (refractive index Nm> Ns). In this case, in the radial direction of the light diffusing particles 10, the specific position inside the shell 10s is y0, the position of the medium M near the apex of the convex portion of the surface unevenness A is y1, and the apex of the convex portion of the surface unevenness A is y1. The position of the medium M that is separated from y1 in the radial direction is defined as y2. The ratio of the space occupied by the surface unevenness A in the vicinity of the surface of the light diffusing particles 10 gradually decreases between y0 to y1. As a result, as shown in FIG. 6B, the apparent refractive index in the vicinity of the surface of the light diffusing particles 10 gradually changes in the section of y0 to y1. For example, if the light-diffusing particles do not have such surface irregularities A, the refractive index suddenly changes in steps at the interface between the light-diffusing particles and the medium M, so that the light incident on the light-diffusing particles is emitted. It is easily reflected on the surface of light-diffusing particles. On the other hand, according to the light diffusing particles 10 having a spherical particle 13 having a particle diameter of 50 nm to 350 nm, incident light is less likely to be reflected on the surface of the light diffusing particles 10. Therefore, the light diffusing particles 10 are more advantageous in imparting high luminance characteristics to the light diffusing and transmitting sheet in which the light diffusing particles 10 are dispersed.

The content of the spherical particles 13 in the components other than the second binder of the shell 10s is, for example, 25% by mass to 70% by mass, and preferably 40% by mass to 60% by mass. As a result, the spherical particles 13 tend to appropriately form surface irregularities A on the entire surface of the shell 10s. As a result, the light diffusing particles 10 have a surface that makes it difficult to retain water more reliably. In addition, it is possible to more reliably impart high luminance characteristics to the light diffusion transmission sheet in which the light diffusion particles 10 are dispersed. Further, since the content of the spherical particles 13 in the shell 10s has the above upper limit, it is possible to suppress a decrease in the haze rate of the light diffusion transmitting sheet in which the light diffusion particles 10 are dispersed.

As shown in FIG. 7, the light diffusing and transmitting sheet 100 includes a base material 20 and light diffusing particles 10 dispersed in the base material 20. Since the light diffusing and transmitting sheet 100 includes the light diffusing particles 10, it can exhibit high luminance characteristics.

The base material 20 is not particularly limited, but is, for example, a resin having excellent dispersibility of the light diffusing particles 10 and having transparency to visible light, weather resistance, moisture resistance, and heat resistance. For example, the base material 20 includes polyester polyol, linear polyester, acrylic resin, amino resin, epoxy resin, melamine resin, silicone resin, urethane resin, vinyl acetate resin, norbornene resin, and polycarbonate resin. And other materials can be mentioned. Further, various thermosetting resins and various ultraviolet curable resins can also be used. A curing agent such as an isocyanate and various dispersants may be appropriately added to these resins. In the light diffusion transmission sheet 100, a substrate (not shown) such as a PET (polyethylene terephthalate) film may be further provided, and a base material 20 in which the light diffusion particles 10 are dispersed may be formed in layers on the substrate.

It is desirable that the average particle size of the light diffusing particles 10 is within a predetermined range so that the light diffusing particles 10 can be uniformly dispersed in the base material 20. From this point of view, the average particle size of the light diffusing particles 10 is, for example, 4 μm to 10 μm, preferably 4 μm to 8 μm, and more preferably 4 μm to 7 μm. This makes it possible to prevent spatial variations in the optical characteristics of the light diffusion transmitting sheet 100. Further, it is possible to reduce the light reflection loss due to the light entering the voids between the primary particles generated when the light diffusing particles 10 are aggregated. As a result, the brightness characteristics of the light diffusion transmission sheet 100 can be improved. Further, the interface where light is refracted can be sufficiently secured in the light diffusion transmission sheet 100. Thereby, the light diffusion characteristic of the light diffusion transmission sheet 100 can be enhanced. In the present specification, the "average particle size" is 50 that can be visually recognized when the cross section of the light diffusion transmission sheet 100 or the light diffusion particles 10 is observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It is calculated as the average value of the maximum diameters of one or more particles. Further, the "average particle size" may be a volume-based D50 measured by a laser diffraction method.

The shape of the light diffusing particles 10 is preferably granular having an aspect ratio of 1 to 2 from the viewpoint of imparting spatially uniform light diffusing characteristics to the light diffusing and transmitting sheet 100.

As shown in FIG. 1, the shell 10s covers, for example, the entire outer surface of the core 10c. The light diffusing particles 10 include, for example, one or more cores 10c.

The refractive index of the first binder 11 is, for example, 1.49 to 1.60, preferably 1.50 to 1.55. The refractive index of the low refractive index fine particles 12a is, for example, 1.35 to 1.59, preferably 1.35 to 1.49. Desirably, the difference n _{B −} n _F obtained by subtracting the refractive index n _F of the low refractive index fine particles 12a from the refractive index n _B of the first binder 11 is 0.01 or more. As a result, the difference in refractive index between the first binder 11 and the low refractive index fine particles 12a becomes large, and the light incident on the low refractive index fine particles 12a is likely to be diffused (scattered). Therefore, the light diffusion transmitting sheet 100 has high brightness characteristics and good light diffusion characteristics.

The first binder 11 can cover the outer surface of the first fine particles 12 and has transparency to visible light. The first binder 11 is preferably selected from the group consisting of acrylic resin, polyurethane resin, and nylon from the viewpoint of reducing the hardness of the light diffusing particles 10 and reducing the possibility of damaging the member in contact with the light diffusing transmissive sheet 100. Contains at least one polymer. Above all, it is desirable that the first binder 11 is a polyurethane resin.

The low refractive index fine particles 12a have a particle diameter of, for example, 4 nm to 9 μm. As a result, the light confinement phenomenon is less likely to occur more reliably in the low refractive index fine particles 12a. The average particle size of the low refractive index fine particles 12a is preferably 4 nm to 4 μm, and more preferably 0.1 μm to 4 μm. As a result, the low refractive index fine particles 12a are likely to be uniformly dispersed in the core 10c.

The low refractive index fine particles 12a are made of, for example, a polymer. In this case, the density of the low refractive index fine particles 12a is low, and the weight of the light diffusing particles 10 and the light diffusing and transmitting sheet 100 can be easily reduced. In addition, the light diffusing particles 10 can impart the property that the low refractive index fine particles 12a are easily deformed by an external force and do not easily damage the member in contact with the light diffusing and transmitting sheet 100. The low refractive index fine particles 12a are preferably made of a crosslinked polymer. In this case, the light diffusing particles 10 tend to have heat resistance. The crosslinked polymer is, for example, a crosslinked acrylic resin or a crosslinked styrene resin. The crosslinked acrylic resin also has good solvent resistance. The crosslinked styrene resin has excellent heat resistance. In some cases, the low refractive index fine particles 12a may be made of an inorganic material such as silica or magnesium fluoride.

As shown in FIG. 1, in addition to the spherical particles 13, the shell 10s further contains second fine particles 14 having a particle size of 4 nm to 15 nm or less. Since the second fine particles 14 have a particle diameter smaller than that of the spherical particles 13, a large number of the second fine particles 14 are arranged in the gaps between the spherical particles 13 in the shell 10s. As a result, the number of sites where light scattering occurs increases, so that the light diffusing particles 10 tend to exhibit good light diffusivity.

The content of the second fine particles 14 in the shell 10s is, for example, 20% by mass to 60% by mass, and more preferably 32% by mass to 48% by mass. As a result, the light diffusing particles 10 are more likely to exhibit good light diffusivity more reliably.

The spherical particles 13 have, for example, a refractive index lower than that of the second binder 15. As a result, in the shell 10s, the light confinement phenomenon is less likely to occur in the spherical particles 13, and the light diffusing particles 10 can more reliably impart high luminance characteristics to the light diffusing and transmitting sheet 100. The second binder 15 covers at least a part of the outer surface of the spherical particles 13. The second binder 15 preferably covers the entire outer surface of the spherical particles 13.

The second fine particles 14 have, for example, a refractive index lower than that of the second binder 15. As a result, the light confinement phenomenon is less likely to occur in the second fine particles 14, and the light diffusing particles 10 can more reliably impart high luminance characteristics to the light diffusing and transmitting sheet 100. The second binder 15 covers at least a part of the outer surface of the second fine particles 14. The second binder 15 preferably covers the entire outer surface of the second fine particles 14.

The refractive index of the second binder 15 is, for example, 1.49 to 1.60, preferably 1.50 to 1.55. The refractive index of the second binder 15 is preferably equal to or higher than the refractive index of the first binder 11. As a result, the light diffusing particles 10 tend to exhibit desired optical characteristics. The refractive index of the spherical particles 13 is, for example, 1.35 to 1.59, preferably 1.35 to 1.49. The refractive index of the second fine particles 14 is, for example, 1.35 to 1.59, preferably 1.35 to 1.49.

The second binder 15 is, for example, a resin having transparency to visible light. The second binder 15 is preferably selected from the group consisting of acrylic resin, polyurethane resin, and nylon from the viewpoint of reducing the hardness of the light diffusing particles 10 and reducing the possibility of damaging the member in contact with the light diffusing transmissive sheet 100. Contains at least one polymer. Above all, it is desirable that the second binder 15 is a polyurethane resin.

It is desirable that the spherical particles 13 do not easily aggregate when the spherical particles 13 are mixed with the raw material of the second binder 15. From this point of view, when the second binder 15 is a resin such as a polyurethane resin, the spherical particles 13 are preferably silica.

The content of the light diffusing particles 10 in the light diffusing and transmitting sheet 100 is, for example, 55% by mass or more, preferably 60% by mass or more, and more preferably 64% by mass or more. As a result, the light diffusing and transmitting sheet 100 surely has high luminance characteristics and has good light diffusing characteristics. The content of the light diffusing particles 10 in the light diffusing and transmitting sheet 100 is, for example, 70% by mass or less, preferably 68% by mass or less, and more preferably 66% by mass or less. As a result, the light diffusing particles 10 are well dispersed in the base material 20, and it is possible to prevent the light diffusing particles 10 from being exposed on the surface of the light diffusing transmission sheet 100, for example.

The ratio of the mass of the core 10c to the mass of the light diffusing particles 10 is, for example, 8% to 30%, preferably 9% to 25%, and more preferably 9% to 21%. On the other hand, the ratio of the mass of the shell 10s to the total mass of the light diffusing particles 10 is, for example, 70% to 92%, preferably 75% to 91%, and more preferably 79% to 91%. As a result, the light diffusing and transmitting sheet 100 can more reliably exhibit high luminance characteristics.

The content of the first fine particles 12 in the core 10c is, for example, 50% by mass to 80% by mass, preferably 50% by mass to 75% by mass, and more preferably 50% by mass to 70% by mass. The content of the first binder 11 in the core 10c is, for example, 20% by mass to 50% by mass, preferably 25% by mass to 50% by mass, and more preferably 30% by mass to 50% by mass. As a result, the light diffusing and transmitting sheet 100 can more reliably exhibit high luminance characteristics.

The content of the low refractive index fine particles 12a in the core 10c is, for example, 4% by mass to 80% by mass, preferably 4% by mass to 10% by mass, and more preferably 5% by mass to 7% by mass. As a result, the light diffusing and transmitting sheet 100 can more reliably exhibit high luminance characteristics.

As shown in FIG. 1, the first fine particles 12 may contain fine particles of a type different from the low refractive index fine particles 12a. For example, the first fine particles 12 are at least one selected from the group consisting of silica, silicone, fluororesin, titanium dioxide, zinc oxide, zirconium oxide, calcium carbonate, barium sulfate, zinc sulfide, aluminum hydroxide, glass, and extender pigment. It may further contain fine particles of the seed. This makes it possible to provide a light diffusing and transmitting sheet having higher luminance characteristics or a light diffusing and transmitting sheet having various optical characteristics.

The average particle size of the fine particles other than the low refractive index fine particles 12a contained in the first fine particles 12 is, for example, 4 nm to 500 nm, preferably 4 nm to 20 nm, and more preferably 4 nm to 15 nm. As a result, the fine particles other than the low refractive index fine particles 12a contained in the first fine particles 12 are likely to be uniformly dispersed inside the first binder 11.

The first fine particles 12 preferably contain only fine particles having a refractive index lower than that of the first binder 11. As a result, light is less likely to be trapped inside the first fine particles 12, so that the light diffusion transmission sheet 100 can be more reliably imparted with high luminance characteristics.

Next, an example of a method for manufacturing the light diffusing particles 10 and the light diffusing transmitting sheet 100 will be described. A dispersion liquid in which the raw material of the first binder 11 and the first fine particles 12 containing the low refractive index fine particles 12a are dispersed is prepared. The dispersion is prepared, for example, by mixing an emulsion containing the raw material of the first binder 11 and a dispersion containing the low refractive index fine particles 12a. A fluorescent dye, a fluorescent whitening agent, a dye, or a pigment may be dispersed in the dispersion liquid, if necessary. The core 10c can be obtained by spray-drying the prepared dispersion. By adjusting the content of the solid component in the dispersion liquid and the spraying conditions in spray drying, the aggregation of the primary particles can be suppressed and the particle size of the core 10c can be adjusted to an appropriate range.

Further, instead of spray drying, the raw material of the first binder 11 may be crosslinked by adding a predetermined crosslinking agent to the dispersion and heating to form the core 10c.

Further, the first fine particles 12 containing the low refractive index fine particles 12a are added to the resin which is the raw material of the first binder 11, and if necessary, a fluorescent dye, a fluorescent whitening agent, a dye, or a pigment is added and mixed. Smelt and mix these additives evenly with the molten resin. The core 10c can also be obtained by crushing the resin mass thus obtained and adjusting the particle size to a predetermined size. However, from the viewpoint of uniformly dispersing the first fine particles 12 in the first binder 11 or efficiently producing the core 10c having a desired particle size and shape, the dispersion liquid is prepared and spray-dried or a cross-linking agent is added. It is desirable to make the core 10c.

Next, a dispersion liquid in which the core 10c and the spherical particles 13 are dispersed is prepared. The raw material of the second binder 15 is typically added to this dispersion, and the second fine particles 14 are added as needed. The light diffusing particles 10 having a core-shell structure can be produced by spray-drying the prepared dispersion liquid. By adjusting the content of the solid component in the dispersion liquid and the spraying conditions in spray drying, the light diffusing particles 10 having a desired particle size and desired characteristics can be produced.

When the core 10c is formed by adding a predetermined cross-linking agent, the raw material of the first binder 11 and the first fine particles 12 including the low refractive index fine particles 12a having a refractive index lower than the refractive index of the first binder 11 are dispersed. Prepare the first dispersion. Next, a cross-linking agent for cross-linking the raw material of the first binder 11 is added to the first dispersion liquid to cross-link the raw material of the first binder 11 to form the core 10c. Then, a second dispersion in which the core 10c and the spherical particles 13 are dispersed is prepared, and the second dispersion is spray-dried. In this case, the light diffusing particles 10 having a core-shell structure can be produced. The raw material of the second binder 15 is also typically added to the second dispersion, and the second fine particles 14 are added as needed.

The light diffusing particles 10 produced as described above are uniformly dispersed in a fluid containing the raw material of the base material 20. In this way, an ink containing the raw materials of the light diffusing particles 10 and the base material 20 is prepared. The light diffusion transmission sheet 100 can be manufactured by applying this ink on a substrate such as a PET film and solidifying the ink.

The present invention will be described in detail with reference to examples. However, the present invention is not limited to the following examples. First, the evaluation method of each Example and Comparative Example will be described.

<Measurement of brightness characteristics and chromaticity>
The brightness characteristics and chromaticity of the sample according to each example and the sample according to the comparative example were measured using a brightness measuring device (manufactured by Highland Co., Ltd., product name: RISA-COLOR ONE). I used the backlight of Apple's iPhone 5 as a light source. "IPhone" is a registered trademark of Apple Inc. The brightness and chromaticity measurement positions were located on the opposite side of the sample light source, and the distance between the brightness and chromaticity measurement positions and the sample was 100 cm. The evaluation results of each sample are shown in Table 1. Incidentally, the luminance value when the relative value of the brightness in Table 1 is 100% is 10 ⁴ cd / cm ^2.

<Measurement of haze rate>
Using a spectrophotometer (manufactured by Shimadzu Corporation, product name: UV-3600) and an integrating sphere, the haze rate of the sample according to each example and the sample according to the comparative example with respect to the incident light having a wavelength of 555 nm was measured. The results are shown in Table 1.

<Weight change before and after drying treatment>
The light diffusing particles according to each Example and Comparative Example were allowed to stand under the same conditions (48 hours in an environment of 20 to 30 ° C. and a relative humidity of 30 to 80% RH), and then dried in an environment of 110 ° C. ± 5 ° C. for 1 hour. Processed. The weight change of each light diffusing particle before and after the drying treatment was measured, and the water content was calculated based on the following formula. Here, ΔW and Wb are the weight change of the light diffusing particles before and after the drying treatment and the weight of the light diffusing particles before the drying treatment, respectively. The results are shown in Table 1.
Moisture content [%] = 100 × ΔW / Wb

(Example 1)
An aqueous dispersion of fine particles made of crosslinked acrylic resin (KMR-3TA, KMR-3TA, refractive index: 1.49, average particle size: 3 μm), colloidal silica A (Nissan Chemical Co., Ltd., Snowtex XS, silica). Refractive index of about 1.45, average particle size of silica fine particles: 4 to 6 nm), colloidal silica B (manufactured by Nippon Kagaku Kogyo Co., Ltd., Silica Doll 30S, refractive index of silica: about 1.45, average particles of silica fine particles) Diameter: 7 to 10 nm) and polyurethane emulsion (Takelac W-6020 manufactured by Mitsui Kagaku Co., Ltd .: refractive index 1.50 to 1.55 and Takelac WS-6021: refractive index 1.50 to 1.55) were mixed. As a result, a dispersion liquid for the core was prepared. In the dispersion liquid for the core, the solid content of the fine particles made of crosslinked acrylic resin was adjusted to 6% by mass, and the solid content of the polyurethane was adjusted to 50% by mass.

After adding a cross-linking agent (Carbodilite E-05, manufactured by Nisshinbo Chemical Co., Ltd.) to the above dispersion for the core, the dispersion for the core was heated in an environment of 80 ° C. for 2 hours. As a result, the polyurethane was crosslinked to obtain a dispersion having a core. 20 parts by mass of the cross-linking agent was added with respect to 100 parts by mass of the solid content of polyurethane. Next, the dispersion liquid in which the core was formed, colloidal silica A (manufactured by Nissan Chemical Industries, Ltd., Snowtex XS, refractive index of silica: about 1.45, average particle size of silica fine particles: 4 to 6 nm) and colloidal. Silica C (Nissan Kagaku Kogyo Co., Ltd., Snowtex ZL, refractive index of silica: about 1.45, average particle size of silica spherical particles: 70 to 100 nm) and polyurethane emulsion (Mitsui Kagaku Co., Ltd. Takelac W-6020: refractive index) A dispersion liquid for light diffusing particles was prepared by mixing a ratio of 1.50 to 1.55 and Takelac WS-6021: refractive index of 1.50 to 1.55). The compounding ratio of silica in colloidal silica A and silica in colloidal silica C was 50:50 on a mass basis. Further, in the dispersion liquid for light diffusing particles, the dispersion liquid for light diffusing particles was prepared so that the solid content of the core was 20% by mass and the solid content of the polyurethane other than the core was 20% by mass. The dispersion liquid for light diffusing particles was spray-dried using a micro mist spray dryer (manufactured by Fujisaki Electric Co., Ltd., product name: MDL-050) to obtain light diffusing particles according to Example 1 having a core-shell structure. The average particle size of the light diffusing particles according to Example 1 was 5 μm.

An ink was prepared by dispersing the light diffusing particles according to Example 1 in an acrylic resin. This ink was applied to a PET film having a thickness of 20 μm by a doctor blade method and solidified to prepare a sample according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

(Example 2)
In the preparation of the dispersion liquid for the light diffusing particles, the compounding ratio of the silica in the colloidal silica A and the silica in the colloidal silica C was changed to 75:25 based on the mass, but the same procedure as in Example 1 was applied to Example 2. Such light diffusing particles were prepared. The average particle size of the light diffusing particles according to Example 2 was 5 μm. A sample according to Example 2 was prepared in the same manner as in Example 1 except that the light diffusing particles according to Example 2 were used instead of the light diffusing particles according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

(Example 3)
In the preparation of the dispersion liquid for light diffusing particles, instead of colloidal silica C, colloidal silica D (manufactured by Nissan Chemical Industries, Ltd., MP-2040, silica refractive index: about 1.45, average particle size of silica spherical particles: 170-230 nm) was used, and the blending ratio of silica in colloidal silica A and silica in colloidal silica D was adjusted to 50:50 on a mass basis, but the light diffusing particles according to Example 3 were the same as in Example 1. Was produced. The average particle size of the light diffusing particles according to Example 3 was 5 μm. FIG. 8 shows an SEM photograph of the light diffusing particles according to Example 3. As shown in FIG. 8, the light diffusing particles according to Example 3 had surface irregularities derived from the silica spherical particles contained in the colloidal silica D. A sample according to Example 3 was prepared in the same manner as in Example 1 except that the light diffusing particles according to Example 3 were used instead of the light diffusing particles according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

(Example 4)
In the preparation of the dispersion liquid for light-diffusing particles, instead of colloidal silica C, colloidal silica E (manufactured by Nikki Catalyst Kasei Co., Ltd., Cataloid SS-300J, silica refractive index: about 1.45, average particle size of silica spherical particles) : 280-300 nm) was used to adjust the blending ratio of silica in colloidal silica A and silica in colloidal silica E to 50:50 on a mass basis, but the light diffusion according to Example 4 was the same as in Example 1. Particles were made. The average particle size of the light diffusing particles according to Example 4 was 5 to 6 μm. A sample according to Example 4 was prepared in the same manner as in Example 1 except that the light diffusing particles according to Example 4 were used instead of the light diffusing particles according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

(Example 5)
In the preparation of the dispersion liquid for light diffusing particles, instead of colloidal silica C, colloidal silica F (manufactured by Nippon Kagaku Kogyo Co., Ltd., MP-4540M, silica refractive index: about 1.45, average particle size of silica spherical particles: (450 nm) was used, and the blending ratio of silica in colloidal silica A and silica in colloidal silica F was adjusted to 50:50 on a mass basis, and the solid content of the core was adjusted to 10% by mass. The light diffusing particles according to Example 5 were produced in the same manner as in 1. The average particle size of the light diffusing particles according to Example 5 was 5 to 6 μm. A sample according to Example 5 was prepared in the same manner as in Example 1 except that the light diffusing particles according to Example 5 were used instead of the light diffusing particles according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

(Comparison example)
A dispersion having a core formed was prepared in the same manner as in Example 1. Next, the dispersion liquid in which the core was formed, colloidal silica A (manufactured by Nissan Chemical Industries, Ltd., Snowtex XS, refractive index of silica: about 1.45, average particle size of silica fine particles: 4 to 6 nm) and colloidal. Silica B (Nihon Kagaku Kogyo Co., Ltd., Silica Doll 30S, Refractive index of silica: Approximately 1.45, Average particle size of silica fine particles: 7 to 10 nm) and polyurethane emulsion (Mitsui Kagaku Co., Ltd. Takelac W-6020: Refractive index) 1.50 to 1.55 and Takelac WS-6021: refractive index 1.50 to 1.55) were mixed to prepare a dispersion for light diffusing particles. The compounding ratio of silica in colloidal silica A and silica in colloidal silica B was 22:78 on a mass basis. Further, in the dispersion liquid for light diffusing particles, the dispersion liquid for light diffusing particles was prepared so that the solid content of the core was 20% by mass and the solid content of the polyurethane other than the core was 20% by mass. The dispersion liquid for light diffusing particles was spray-dried using a micro mist spray dryer (manufactured by Fujisaki Electric Co., Ltd., product name: MDL-050) to obtain light diffusing particles according to a comparative example having a core-shell structure. The average particle size of the light diffusing particles according to the comparative example was 5 μm. FIG. 9 shows an SEM photograph of the light diffusing particles according to the comparative example. As shown in FIG. 9, the surface of the light diffusing particles according to Comparative Example was smoother than that of the light diffusing particles according to Example 3.

A sample according to Comparative Example was prepared in the same manner as in Example 1 except that the light diffusing particles according to Comparative Example were used instead of the light diffusing particles according to Example 1. The thickness of the coating film in the sample was 10 to 17 μm, and the content of light diffusing particles in the coating film of the sample was 65% by mass.

As shown in Table 1, the water content of the light diffusing particles according to Examples 1 to 5 was lower than that of the light diffusing particles according to Comparative Example. This suggests that the light diffusing particles according to Examples 1 to 5 have a surface on which water is less likely to stay than the light diffusing particles according to Comparative Example. In addition, the samples according to Examples 1 to 5 showed a relative value of high brightness of 101.6 or more. In particular, the samples according to Examples 1 to 4 showed higher luminance characteristics than the samples according to Comparative Examples.

Claims (11)

A core formed by a first binder and first fine particles containing low refractive index fine particles having a refractive index lower than that of the first binder and being covered in contact with the first binder.
A shell that contacts the outer surface of the core and covers the core, and is in contact with solid spherical particles having a particle diameter of 50 nm to 450 nm and imparting surface irregularities to the shell, and the outer surface of the spherical particles. With a shell, including a second binder,
Light diffusing particles. The light diffusing particle according to claim 1, wherein the spherical particles have a particle diameter of 50 nm to 350 nm. The light diffusing particles according to claim 1 or 2, wherein the content of the spherical particles in a component other than the second binder of the shell is 25% by mass to 70% by mass. The light diffusing particle according to any one of claims 1 to 3, which has an average particle diameter of 4 μm to 10 μm. The light diffusing particles according to any one of claims 1 to 4, wherein the low refractive index fine particles have a particle diameter of 4 nm to 9 μm. The light diffusing particle according to any one of claims 1 to 5, wherein the shell further contains second fine particles having a particle size of 4 nm to 15 nm. The light diffusing particles according to any one of claims 1 to 6, wherein the first binder contains at least one polymer selected from the group consisting of acrylic resin, urethane resin, and nylon. The light diffusing particles according to any one of claims 1 to 7, wherein the spherical particles have a refractive index lower than that of the second binder. The light diffusing particles according to any one of claims 1 to 8, wherein the second binder contains at least one polymer selected from the group consisting of acrylic resin, urethane resin, and nylon. With the base material
The light diffusing particles according to any one of claims 1 to 9 dispersed in the base material.
Light diffusion transmission sheet. A method for producing light diffusing particles having a core-shell structure.
A first dispersion liquid in which the raw material of the first binder and the first fine particles containing the low refractive index fine particles having a refractive index lower than that of the first binder are dispersed is prepared.
A cross-linking agent for cross-linking the raw material of the first binder is added to the first dispersion liquid to cross-link the raw material of the first binder to form a core.
A second dispersion liquid in which the core and solid spherical particles having a particle diameter of 50 nm to 450 nm are dispersed is prepared.
Spray-dry the second dispersion.
Method.

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