JP2003302532A - Polarizing plate and manufacturing method thereof - Google Patents

Abstract

(57) [Problem] To provide a polarizing plate capable of achieving an effect of improving transmittance regardless of wavelength, and a method of manufacturing the same. A polarizing plate having a moth-eye structure on the surface of at least one layer solves the above problem. The surface having the moth-eye structure is JISB0601
^When the arithmetic average height of the contour curve defined in ²⁰⁰¹ is Ra ( ³ ) and the average length of the contour curve element is RSm ( ³ ), 0.001 μm <
Ra ( ³ ) <5.0 μm, 0.001 μm <RSm ( ³ ) <0.5 μm and 0.01
It is preferable to satisfy the relationship of <Ra ( ³ ) / RSm ( ³ ) <5.0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate and a method of manufacturing the same, and more particularly to a polarizing plate having a moth-eye structure and improved transmittance and a method of manufacturing the polarizing plate.

[0002]

2. Description of the Related Art A polarizing plate uses iodine or a dichroic dye,
It is an optical film that produces linearly polarized light from natural light, and has been used for various applications such as liquid crystal displays (LCD). For example, a liquid crystal display (LCD) is used for a personal computer, a liquid crystal television, a liquid crystal movie, and the like, and a polarizing plate is an indispensable element because of the requirements of the operating principle of the LCD. An LCD has a layered structure formed of many members, and its light utilization efficiency is low. Therefore, a bright and highly visible LCD is required.
Therefore, it is required to supply a polarizing plate that is brighter and has a high light transmittance also as a polarizing plate that is one component.

[0003]

Usually, a polarizing plate is prepared by adding iodine or a dichroic dye to polyvinyl alcohol (PVA).
It is formed so as to produce linearly polarized light from natural light by impregnating the same with and then stretching it to orient the iodine or dye to develop a dichroic effect. Figure 2
Figure 1 shows an example of the structure of a conventional polarizing plate as a schematic cross-sectional view. However, since the polarizing element layer using iodine is weak against heat, humidity, etc., triacetyl cellulose (TA
A cellulose-based protective film such as C) is laminated. Further, a hard coat layer such as an organosiloxane type or a polyfunctional acrylate type may be laminated. Since each layer has a different refractive index, reflection occurs at the interface between adjacent layers, which is a significant factor that reduces the transmittance.

The conventional polarizing plate is provided with an antireflection film as shown in FIG. 2 in order to prevent reflection and increase transmittance. As an antireflection method, CaF ₂ , ZnS, a method of vapor-depositing a thin film of an inorganic compound such as SiO ₂ to form a multilayer film, which lowers the reflectance due to the interference effect to improve the transmittance, has a lower refractive index than the base material. A method has been adopted in which a material having a high refractive index is applied onto a substrate to reduce the reflectance. However, the former method using a multilayer film cannot avoid the problem that the transmittance depends on the wavelength, and the latter method using a low refractive index material has a problem that a sufficient antireflection effect cannot be obtained. A method for improving the transmittance has been required.

[0005]

As a result of various studies made by the present inventors in view of such conventional problems, the effect of improving the transmittance can be achieved regardless of the wavelength by providing a polarizing plate with a so-called moth-eye structure. The present invention has been accomplished by finding that a polarizing plate and a manufacturing method thereof can be provided. That is, the first gist of the present invention resides in a polarizing plate characterized by having a moth-eye structure on the surface of at least one layer.

The second gist is that the surface having a moth-eye structure has the arithmetic mean height of the contour curve defined by JIS B 0601 ²⁰⁰¹ as Ra ( ³ ) and the mean length of the contour curve element as RSm ( ³ ). , 0.001 μm <Ra ( ³ ) <5.0 μm and 0.001 μm <RSm ( ³ ) <0.5 μm and 0.01 <Ra ( ³ ) / RSm ( ³ ) <5.0. In the above-mentioned polarizing plate characterized by the above.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The present invention is characterized by having a moth-eye structure on the surface of at least one layer of a polarizing plate. Since the moth-eye structure can be formed on the surface of a resin or the like by a known method, it is possible to improve the transmittance of the polarizing plate without separately providing an antireflection film which has been conventionally provided for improving the transmittance. it can.

In the present invention, the "moth-eye structure" means
As a result of the concentration of protrusions having a structure with a wavelength of incident electromagnetic waves (eg, visible light) or less on the surface of a substance, the reflectance of the surface is reduced. This is a structure found in certain types of moths, so it is called moth's eye
It is called an h-eye) structure and is known to be used as an antireflection film for screens, displays and the like (see, for example, Japanese Patent Publication No. 2001-517319).

The effect of the moth-eye structure will be briefly described with reference to FIG. FIG. 3 shows the relationship when light is incident from a medium having a refractive index n _{1 to} a medium having a refractive index n ₂ and having fine irregularities on the surface. Is the incident light, is the zero-order reflected light, is the reflected + first-order light, is the reflected −first-order light, is the transmitted zero-order light, is the transmitted + first-order light, and is the transmitted −first-order light. In addition to these, there are high-order diffracted lights such as ± 2nd order and ± 3rd order. When light is incident on a medium having a smooth interface, the relationship between incident light, reflected light, and transmitted light (refracted light) only needs to be discussed. However, when there are fine irregularities on the surface, The existence of such diffracted light will be discussed. When the period of this fine structure is Λ, the height is h, and the wavelength of the incident light is λ, the X component k _ix of the wave number vector of the i-th diffracted light is the period Λ of the fine structure and the wavelength λ of the incident light. Is determined as follows.

[0010]

[Expression 1] k _ix = (2πn ₁ / λ) sin α-i 2π / Λ (α: incident angle, i: order of diffracted light) X component of diffracted light wave vector exceeds absolute value of incident light wave vector Then, the component perpendicular to the boundary surface of the diffracted light (Z direction component in FIG. 3) becomes a pure imaginary number. This diffracted light becomes an evanescent wave, and the phenomenon that the amplitude of the electric field in the Z direction is rapidly attenuated occurs. At that time, the redistribution of the amplitude occurs among the diffracted lights.

When L <(λ / 2), the diffracted light of transmission and reflection other than the 0th order becomes an evanescent wave. At this time, the reflectance depends on the aspect ratio h / Λ, and the surface has no moth-eye structure and is smooth. It is confirmed that the reflectance is reduced as compared with the case. From theoretical calculation, it is known that a good antireflection effect can be obtained when the aspect ratio is 0.5 <h / Λ <5.0. At the same time, a phenomenon in which the transmittance increases compared with the transmitted light when the surface has no moth-eye structure and is smooth is observed. Such a phenomenon is called the "moth eye effect".

Based on the above theoretical background, as the moth-eye structure of the polarizing plate of the present invention, the degree of unevenness in the uneven structure of the surface is the arithmetic average height of the contour curve described in JIS B 0601 ^2001. Is Ra ( ³ ) and the average length of the contour curve element is RSm ( ³ ), 0.001 μm <Ra ( ³ ) <5.0 μm and 0.001 μm <RSm ( ³ ) <0.5 μm and 0.01 <Ra ( ³ ) / It is preferable to satisfy the relationship of RSm ( ³ ) <5.0, and further, 0.05 μm <Ra ( ³ ) <0.5 μm and 0.05 μm <RSm ( ³ ) <0.5 μm and 0.5 <Ra ( ³ ) / It is desirable to satisfy the relationship of RSm ( ³ ) <2.0. Further, the moth-eye structure may be a periodic structure or a random structure. In the case of a one-dimensional or two-dimensional periodic diffraction grating structure, when the period is Λ and the depth is H, 0.05 μm <Λ <2.0
μm and 0.05 μm <H <5.0 μm and 0.2 <
It is preferable to satisfy H / Λ <5.0.

In the present invention, the use of the polarizing plate,
A moth-eye structure may be provided at any interface of the layers forming the polarizing plate, depending on the material forming the polarizing plate, the structure of the polarizing plate, and the like. Preferred resins for providing a moth-eye structure on the surface of the resin layer include triacetyl cellulose, which is widely used as a protective film for iodine-based polarizing plates, styrene-based resins, acrylic-based resins, aromatic polycarbonate resins, and amorphous materials. Polyolefin resin, polyamide resin, aromatic polyester resin, plastic resin consisting of polyphenylene ether resin and polyarylene sulfite resin, or phenol resin, urea resin, melamine resin, unsaturated polyester, epoxy resin, diallyl phthalate resin, polyurethane resin, silicon The main component is one or more selected from the group consisting of non-plastic resins such as resins and polyimide resins, and synthetic resins can be both ordinary thermoplastic resins and crosslinked resins. It is preferable that the layer having the moth-eye structure contains as a main component (for example, 50 wt% or more) a resin having a transmittance of 30% or more, particularly 40% or more in the entire wavelength range of 400 nm to 800 nm. When the inorganic layer is used, it is necessary to use a transparent or transparent material for the inorganic layer, and glass is preferably used.

In order to prevent reflection and improve transmittance by the moth-eye structure, the material forming the moth-eye structure is not selected, and the shape is not particularly limited. Therefore, a thin film, a rigid plate, or the thickness thereof is not limited. But usually 1 μm
It is selected from ~ 1000 μm. Preferred methods for forming a moth-eye structure include transfer molding with a stamper, blasting by spraying fine particles, a method of processing the substrate surface such as etching with chemicals, inorganic particles on the substrate surface by sticking fine particles, resin, etc. Of organic particles,
Examples include a method in which fine particles such as are projected as convex portions from a relatively smooth substrate surface. The method of forming the structure may be appropriately selected according to the type of the substrate made of the resin that forms the moth-eye structure.

When a moth-eye structure is provided at the interface of layers,
The transmission of the layer is improved. For example, polymethylmethacrylate
A moth-eye structure is formed on the surface of resin by a stamper
The formed structure with an atomic force microscope (NANOSCO
PE-III. Measured by Digital Instruments)
As a result, the unevenness of the surface structure was determined according to JIS B 0601.
²⁰⁰¹The arithmetic mean height of the contour curve defined by³),ring
The average length of the contour curve element is RSm (³) Ra (³) Is 0.15
μm, RSm (³) Was about 0.25 μm. Transmission of this sample
Fig. 4 shows the results of measuring the rate by changing the wavelength of light, and the horizontal axis shows the wave.
The length is shown in nm and the vertical axis shows the transmittance in%. 1 is moss
Transmittance of film with eye structure on the surface, 2 is moss
The transmittance of a film that does not have an eye structure on its surface.
It As you can see from this graph, the reflection from the moth eye
Preventive treatment 1 has a higher transmittance than 2
I understand.

Although the case where a polymethylmethacrylate resin is used is shown as an example, the same effect can be expected by using TAC generally used for a polarizing plate and other materials. FIG. 1 shows an example of the structure of a polarizing plate having a moth-eye structure according to the present invention. A protective layer made of a cellulosic resin such as TAC was laminated on both surfaces of the polarizing element layer (for example, PVA impregnated with iodine) by a conventional method. In this example, one protective layer, one surface opposite to the polarizing element layer, has a moth-eye structure, and a hard coat layer is formed on the moth-eye structure, and the hard coat layer surface also has a moth-eye structure to realize low reflection characteristics. As a method of forming a moth-eye structure in a cellulose-based protective layer such as TAC, among others, a TAC coated with a photo-curing resin under a stamper roll having a moth-eye structure is brought into contact, and a curing transfer method is performed while irradiating with ultraviolet light. It is preferable to manufacture it by. In this case, the hard coat layer is preferably formed of the synthetic resin described above, and the thickness of this layer is preferably 0.01 μm to 100 μm. As a method of forming the hard coat layer on the protective layer, a method of laminating a film formed in advance with an adhesive or the like is also possible, but in order to increase the reproducibility of the moth-eye structure of the protective layer in the hard coat layer. A die coat in which molten resin is supplied from a die in a predetermined thickness is preferable.

The polarizing plate of the present invention is not limited to the structure shown in FIG. 1 as long as the surface of at least one layer constituting the polarizing plate has a moth-eye structure. For example, (1) the surface of the protective layer is Without the moth-eye structure, only the surface of the hard coat layer (interface between the polarizing plate and the other) has the moth-eye structure,
(2) It is possible to provide a moth-eye structure only on the outer surface of the protective layer without providing a hard coat layer.

[0018]

As described above, the polarizing plate of the present invention can improve the transmittance of the polarizing plate without providing an antireflection film which has been conventionally provided for improving the transmittance.
Further, according to the present invention, it is possible to supply a polarizing plate having a smaller angle dependence of reflection characteristics and a smaller wavelength dependence as compared with an antireflection film realized by an interference method using a conventional multilayer film. .

[Brief description of drawings]

FIG. 1 is a diagram showing an example of the configuration of a polarizing plate having a moth-eye structure according to the present invention.

FIG. 2 is a schematic sectional view showing the structure of a conventional polarizing plate.

FIG. 3 is a diagram for explaining the antireflection effect of the moth-eye structure, and is a schematic cross-sectional view of a concavo-convex boundary surface.

FIG. 4 is a schematic diagram showing the transmittance for each wavelength of a film having a moth-eye structure and a film having no moth-eye structure.

[Explanation of symbols]

1 incident light 2 Zero-order reflected light 5 Zero-order transmitted light

Claims (7)

[Claims] 1. A polarizing plate having a moth-eye structure on the surface of at least one layer. 2. The moth-eye structure according to claim 1 is JI
The arithmetic mean height of the contour curve defined in SB 0601 ²⁰⁰¹
When Ra ( ³ ) and the average length of the contour curve element are RSm ( ³ ), 0.001 μm <Ra ( ³ ) <5.0 μm and 0.001 μm <RSm ( ³ ) <0.5 μm and 0.01 <Ra ( ³ ) / RSm ( ³ ) <5.0 is satisfied, The polarizing plate according to claim 1. 3. A polarizing plate has a polarizing element layer, a protective layer laminated on both sides of the polarizing element layer, and a hard coat layer laminated on the outside of one protective layer, and on the surface of the hard coat layer. The polarizing plate according to claim 1, which has a moth-eye structure. 4. The polarizing plate according to claim 1, wherein the layer forming the moth-eye contains triacetyl cellulose as a main component. 5. The polarizing plate according to claim 1, wherein the layer forming the moth eye is made of glass. 6. A resin in which a layer having a moth-eye structure is formed of a resin, and the transmittance when a film made of the resin and having a thickness of 100 μm is formed is 30% or more in a wavelength range of 400 nm to 800 nm. The polarizing plate according to claim 1, which comprises a main component. 7. The moth-eye structure is obtained by at least one method of transfer molding by a stamper, blasting by spraying fine particles, etching by a chemical agent, and sticking of fine particles.
A method for manufacturing a polarizing plate according to any one of 1.