JP4098741B2 - Optical film and manufacturing method thereof - Google Patents

Description

  The present invention relates to a liquid crystal display (LCD), plasma display (PDP), CRT having a transparent substrate and a layer in which transparent fine particles are dispersed in an optically anisotropic polymer phase provided on at least one surface thereof. The present invention relates to an optical film suitably used for image display bodies such as EL.

  The image display devices represented by the LCD, PDP, CRT, EL, etc. (hereinafter referred to as “display”) are used in various fields including televisions and computers, and have made remarkable progress. ing. In particular, LCDs are very popular as personal computers, mobile phones, televisions, digital cameras, PDAs, and other various devices as thin, lightweight, and versatile displays.

  When these displays are used outdoors or under relatively bright places such as under fluorescent lights, reflections on the display due to external light such as sunlight or fluorescent lights are a problem. It is common to perform anti-glare treatment that diffusely reflects external light reflected by forming irregularities on the surface.

  This anti-glare treatment can be performed by forming a rough surface on the display surface by sandblasting or the like, coating a transparent resin on the display surface, and then performing a shaping treatment with a shaping film having irregularities, or forming an inorganic in the resin binder. Alternatively, it is carried out by a treatment such as forming an antiglare layer on the display surface by coating with a paint in which organic transparent fine particles are dispersed.

  Among these treatments, the anti-glare treatment using the resin binder and organic transparent fine particles listed last can scatter external light due to the unevenness formed by the fine particles and the refractive index difference between the resin binder and the fine particles. Currently, the most common method is disclosed in Patent Documents 1 to 3, for example.

  However, as described above, the display with anti-glare treatment suppresses the reflection of the surface, but the image information from the inside of the display is also inadvertently scattered, so that the image is blurred or the contrast is lowered. Has occurred.

On the other hand, the inventors have invented an antiglare film that prevents a decrease in image contrast by dispersing an optically anisotropic phase in an optically isotropic polymer phase and controlling the refractive index difference between the two phases. The application was previously filed as Japanese Patent Application No. 2003-094279. However, in this proposal, it is difficult to form unevenness on the surface, and the ability to prevent reflection of external light is insufficient. In addition, since the dispersion of the shape and size of the dispersed optically anisotropic phase is large, image blurring cannot be sufficiently prevented.
Japanese Patent No. 3314965 JP-A-5-162261 JP-A-7-181306

  The present invention has been made for the purpose of solving the above-mentioned problems, and the purpose thereof is an optical film suitable for performing anti-glare treatment and suppressing blurring of an image and a decrease in contrast, and its It is to provide a manufacturing method.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that image blurring and contrast reduction are caused by light rays that are perpendicularly incident on the antiglare layer from the display and light rays that are obliquely incident on the antiglare layer. It has been found that the scattering of the above causes the color of each light beam to mix. Light scattering occurs at the interface between two phases having different refractive indexes, and the intensity of scattering depends on the difference in refractive index. For this reason, in the antiglare layer comprising the resin binder and the organic transparent fine particles, the presence of the interface between the resin binder and the organic transparent fine particles having different refractive indexes causes light scattering. Therefore, the present inventor eliminates or reduces the refractive index difference of the refractive index interface for obliquely incident light while maintaining the refractive index interface for light incident perpendicularly to the antiglare layer. The present invention has been completed by successfully suppressing blurring of the image and a decrease in contrast.

That is, the optical film of the present invention is an optically anisotropic polymer phase comprising a transparent substrate and a polymer liquid crystal compound that is provided on at least one surface thereof and is molecularly oriented by the application of heat, light, or both. A layer in which transparent fine particles are dispersed, and the linear transmittance of light having a wavelength of 550 nm incident at an incident angle of 30 ° with respect to the film surface of the optical film is It is characterized by being higher than the linear transmittance.

The above optical film of the present invention comprises a step of preparing a paint by dissolving and dispersing a polymer liquid crystal compound and transparent fine particles in a solvent, and applying the paint on a transparent substrate to volatilize the solvent to obtain a polymer liquid crystal. forming a compound phase coating layer formed by dispersing transparent fine particles in the light, heat or polymeric liquid crystal compound to impart both a, can be prepared by a step of molecular orientation.

  Since the optical film of the present invention has the above-described configuration, it can suppress blurring of an image and a decrease in contrast, and as an antiglare film, a liquid crystal display (LCD), a plasma display (PDP), a CRT, an EL, or the like. It can be suitably used for an image display body or the like.

Next, preferred embodiments of the present invention will be described in detail.
The optical film of the present invention has a structure having a transparent substrate and a layer in which transparent fine particles are dispersed in an optically anisotropic polymer phase composed of a molecularly oriented polymer liquid crystal compound provided on at least one surface thereof. Is. And this optical film has the characteristic that the linear transmittance | permeability of the light ray of wavelength 550nm which injects with an incident angle of 30 degrees with respect to a film surface is higher than the linear transmittance of the light ray which injects with an incident angle of 0 degree. Yes. In addition, incident at an incident angle of 0 ° means incident from the normal direction of the film surface, and incident at an incident angle of 30 ° means incident from a direction inclined by 30 ° from the normal direction to the film surface. To do.

  As the transparent substrate used in the optical film of the present invention, a known transparent film, glass or the like can be used. Specific examples thereof include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), polymethyl methacrylate (PMMA), polycarbonate (PC), polyimide (PI), polyethylene (PE), polypropylene ( PP), polyvinyl alcohol (PVA), polyvinyl chloride (PVC), cycloolefin copolymer (COC), norbornene resin, various resin films such as polyethersulfone, cellophane, aromatic polyamide, quartz glass, soda glass, etc. A glass base material etc. can be used conveniently. When the optical film of the present invention is used for a plasma display or a liquid crystal display, the transparent substrate is preferably made of PET, TAC, COC, norbornene-containing resin or the like.

On the above transparent substrate, a layer in which transparent fine particles are dispersed in an optically anisotropic polymer phase composed of a polymer liquid crystal compound that is aligned by applying heat, light, or both directly or through another layer. Is provided. Here, “optical anisotropy” means that the refractive index varies depending on the direction to be measured, and specifically, the refractive indices _nx and _{ny in the} film in-plane direction (film in-plane direction). The difference between the maximum refractive index: _nx and the minimum value: _ny ) and the refractive index _{nz in the} normal direction is 0.03 or more.

In general, the linear transmittance of light having a wavelength of 550 nm with respect to a film having a layer in which fine particles are dispersed in a polymer phase is higher at an incident angle of 0 ° than at an incident angle of 30 °. This is because the optical path length in the film is increased by obliquely entering the film, and as a result, light rays pass through many interfaces formed by polymer phases and fine particles having different refractive indexes, respectively. This is because light is strongly scattered. On the other hand, in the optical film of the present invention, by using an optically anisotropic polymer for the polymer phase, the optical film has characteristics opposite to those of a general film. More specifically, an optically anisotropic polymer is used for the polymer phase, and the optically anisotropic polymer is subjected to orientation treatment, whereby the polymer phase and the transparent fine particles when the light beam is incident on the film from 30 ° The difference in refractive index is smaller than that when light enters from 0 °, and the scattering of light entering from 30 ° is weaker than the scattering of light entering from 0 °. It will be higher.

  For this reason, in the optical film of this invention, control of refractive index anisotropy is easy as an optically anisotropic polymer phase, and a polymer liquid crystal compound is used.

  In general, high molecular liquid crystal compounds cannot be aligned by simply forming a film. Therefore, after forming an alignment film for controlling the alignment on the substrate in advance, the film is formed, and an electric field is applied after the film formation. It is necessary to orient by performing the treatment. In order to facilitate the above alignment treatment, it is preferable to use a polymer liquid crystal compound that is aligned by the application of heat, light, or both in the optical film of the present invention. Further, as such a polymer compound, a polymer liquid crystal compound having a structure having a mesogen and a cinnamoyl group in the side chain is particularly preferable. In a polymer liquid crystal compound having such a structure, by first irradiating light, a mesogen in a direction substantially coincident with the direction of the electric field vector of the light is fixed by a photodimerization reaction of the cinnamoyl group, and further heated. This is because the remaining non-fixed mesogen becomes easy to move and is oriented according to the fixed mesogen.

  Next, polymer liquid crystal compounds preferably used in the present invention will be exemplified. These polymer liquid crystal compounds can be obtained by polymerizing a monomer compound having a reactive functional group such as an acryl group or a vinyl group at the terminal of the mesogen (hereinafter referred to as “liquid crystalline low molecular weight compound”). In addition, n in the following structural formula means a degree of polymerization, and the weight average molecular weight of a desirable polymer liquid crystal compound is in the range of 5000 to 1000000.

  In addition to the exemplified polymer liquid crystal compounds, those obtained by copolymerization of two or more liquid crystalline low molecular compounds, those obtained by copolymerization with a monomer compound having no mesogen such as methyl methacrylate (MMA) or styrene, etc. May be used.

  Furthermore, in order to obtain desired characteristics, other components may be added to the optically anisotropic polymer phase as long as the optical anisotropy is not lost. For example, a compound such as polyacrylate, polymethacrylate, or polystyrene may be added to control orientation and improve thermal characteristics.

  In the optical film of the present invention, the transparent fine particles dispersed in the optically anisotropic polymer phase are not particularly limited in shape, particle size, and the like as long as it is transparent. However, those having a spherical shape and an average particle diameter in the range of 0.5 to 10 μm, particularly in the range of 1 to 5 μm are preferable. When the average particle diameter is less than 0.5 μm, good light diffusibility cannot be obtained. On the other hand, when the average particle diameter exceeds 10 μm, the granular feeling of transparent fine particles appears on the optical film, which is not preferable. The value of the particle diameter of the transparent fine particles in the present invention is a value obtained by a Coulter counter method.

 As described above, various transparent fine particles such as the material, shape and particle diameter can be used as the transparent fine particles, but it is preferable to use resin fine particles whose shape and refractive index can be easily controlled. Examples of the material constituting the resin fine particles include acrylic resin, silicone resin, styrene resin, melamine resin, styrene / acrylic copolymer resin, and the like, and it is free depending on the refractive index and affinity for the optically anisotropic polymer phase. It is possible to select. Further, for the purpose of improving dispersibility and further controlling the refractive index, the resin fine particles may be subjected to a surface treatment with an organic or inorganic material such as fats and oils, a silane coupling agent, or a metal oxide.

  In the present invention, the content of the transparent fine particles in the optically anisotropic polymer phase is generally preferably in the range of 0.5 to 20% by weight. The thickness of the layer in which transparent fine particles are dispersed in the optically anisotropic polymer phase is generally set in the range of 0.5 to 50 μm, particularly 1 to 10 μm.

  Moreover, when using the optical film of this invention as an anti-glare film which prevents the reflection of external light, it has an unevenness | corrugation on the surface, The average roughness Ra of the unevenness | corrugation is 0.1-1. The thickness is preferably 0.0 μm, more preferably in the range of 0.1 to 0.5 μm. If Ra is less than 0.1 μm, the prevention of reflection of external light will be insufficient, and if it is more than 1.0 μm, although the prevention of reflection will be sufficient, the image will be blurred.

  In the optical film of the present invention, the layer in which the transparent fine particles are dispersed in the optically anisotropic polymer phase may be provided on the transparent substrate via another layer, but directly without any other layer. It is preferable to provide it. In addition, as another layer said here, the alignment film etc. for controlling the orientation of a liquid crystal are mentioned.

The optical film of the present invention can be produced as follows. First, a coating material is prepared by dissolving and dispersing the above polymer liquid crystal compound and transparent fine particles in an appropriate solvent such as chloroform. Then, the resultant coating was applied onto the transparent substrate, and the solvent evaporated, transparent fine particles to the polymer liquid crystal compound phase to form a coating layer which is dispersed. The formed coating layer is irradiated with light such as ultraviolet rays, heated with a hot plate, or both, and the polymer liquid crystal compound is molecularly oriented to produce the optical film of the present invention.

  In order to form irregularities with an average roughness Ra of 0.1 to 1.0 μm on the surface of the optical film to be formed, the blending ratio of the optically anisotropic polymer and the transparent fine particles and the thickness of the coating layer are determined. Adjustment may be made in consideration of the relationship with the particle size of the transparent fine particles. In particular, the thickness of the coating layer is preferably in the range of 100 to 120% of the particle diameter of the transparent fine particles.

  Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. “Parts” means parts by weight.

[Poly (4-methoxybiphenyloxyhexyl methacrylate)] (weight average molecular weight: 100,000) as a polymer liquid crystal compound , spherical transparent fine particles made of styrene resin having an average particle size of 3.5 μm as transparent fine particles, and chloroform as a solvent The paint was prepared by blending at the following blending ratio and dispersing in a sand mill for 30 minutes.
[Combination ratio]
Polymer liquid crystal compound : 5 parts Transparent fine particles: 0.5 parts Chloroform: 100 parts

The obtained coating material was applied on a transparent substrate made of PET having a film thickness of 74 μm and a transmittance of 92% by a spin coating method and dried to form a coating layer having a layer thickness of 3.7 μm on the transparent substrate.
Next, the film on which the coating layer was formed was heated on a hot plate (heating conditions: 110 ° C., 10 min) to perform an alignment treatment, thereby producing an optical film. Ra was 0.5 μm.

As a polymer liquid crystal compound , [poly (4 ′-(4-methoxycinnamoyl) -4-biphenyloxyhexyl methacrylate)] (weight average molecular weight: 80,000), made of an acrylic resin having an average particle diameter of 3.0 μm as transparent fine particles The coating was prepared by blending the above transparent spherical fine particles, using chloroform as a solvent, and blending them at the following blending ratio and dispersing in a sand mill for 30 minutes.
[Combination ratio]
Polymer liquid crystal compound : 5 parts Transparent fine particles: 0.5 parts Chloroform: 100 parts

The obtained coating material was applied onto a transparent substrate made of PET having a film thickness of 75 μm and a transmittance of 92% by a spin coating method and dried to form a coating layer having a layer thickness of 3.2 μm on the transparent substrate.
Next, the film on which the coating layer is formed is irradiated with non-polarized ultraviolet rays (irradiation conditions: 150 mW / cm ² , 10 sec) from directly above the film with a UV spot light source, and further heated with a hot plate (heating conditions) : 130 [deg.] C., 5 min) to carry out an alignment treatment to produce an optical film. Ra was 0.3 μm.

(Comparative Example 1)
Instead of the polymer liquid crystal compound , PMMA (weight average molecular weight: 40,000) is used, transparent spherical fine particles made of styrene resin having an average particle size of 3.5 μm are used as transparent fine particles, and chloroform is used as a solvent. A paint was prepared by blending and dispersing in a sand mill for 30 minutes.
[Combination ratio]
PMMA: 5 parts Transparent fine particles: 0.5 parts Chloroform: 100 parts The obtained paint is applied on a transparent substrate made of PET having a film thickness of 75 μm and a transmittance of 92% by a spin coating method and dried to be transparent. A coating layer having a layer thickness of 3.7 μm was formed on the substrate to produce a comparative optical film.

(Comparative Example 2)
PMMA (weight average molecular weight: 40,000) is used in place of the polymer liquid crystal compound , transparent spherical fine particles made of acrylic resin having an average particle size of 3.0 μm are used as transparent fine particles, and chloroform is used as a solvent. A paint was prepared by blending and dispersing in a sand mill for 30 minutes.
[Combination ratio]
PMMA: 5 parts Transparent fine particles: 0.5 parts Chloroform: 100 parts The obtained paint is applied on a transparent substrate made of PET having a film thickness of 75 μm and a transmittance of 92% by a spin coating method and dried to be transparent. A coating layer having a layer thickness of 3.2 μm was formed on the substrate to produce an optical film for comparison.

Next, each example and comparative example were evaluated by the following methods.
(Measurement of incidence angle dependence of linear light transmittance)
With a spectrophotometer, the linear transmittance of a 550-nm light beam was measured when the light beam was incident on the optical film in an incident angle range of 0 ° to 60 °. The result is shown in FIG.

  As is clear from FIG. 1, when the linear light transmittances at incident angles of 0 ° and 30 ° are compared, the optical films of Example 1 and Example 2 have a higher linear light transmittance at an incident angle of 30 °. In contrast, the optical films of Comparative Example 1 and Comparative Example 2 have higher linear light transmittance at an incident angle of 0 °.

  When the optical film of the above example and the optical film of the comparative example were attached to the surface of the LCD and the images projected from the LCD were observed, the LCD with the optical film of Example 1 and Example 2 was blurred. A clear image with no contrast was confirmed, but the LCD with the optical film of Comparative Example 1 clearly blurs the image and sinks color, improving blur and contrast. It wasn't. In addition, in the LCD on which the optical film of Comparative Example 2 was pasted, the image was clearly blurred, and the blur was not improved.

The graph which shows the linear transmittance | permeability of the light beam of 550 nm with respect to an incident angle about the optical film of an Example and a comparative example.

Claims (5)

A transparent substrate and a layer in which transparent fine particles are dispersed in an optically anisotropic polymer phase composed of a polymer liquid crystal compound that is molecularly oriented by application of heat, light, or both, provided on at least one surface thereof An optical film having a linear transmittance of light having a wavelength of 550 nm incident on the film surface at an incident angle of 30 ° is higher than a linear transmittance of light incident at an incident angle of 0 °. Optical film. The optical film according to claim 1, wherein the transparent fine particles are spherical particles, and an average particle diameter thereof is 0.5 to 10 μm. The layer in which transparent fine particles are dispersed in the optically anisotropic polymer phase has irregularities on the surface, and the average roughness Ra of the irregularities is 0.1 to 1.0 μm. The optical film according to claim 1. 2. The optical film according to claim 1, wherein a layer in which transparent fine particles are dispersed in the optically anisotropic polymer phase is directly provided on the transparent substrate. A step of preparing a paint by dissolving and dispersing the polymer liquid crystal compound and transparent fine particles in a solvent, and applying the paint onto a transparent substrate to volatilize the solvent to disperse the transparent fine particles in the polymer liquid crystal compound phase. 2. The method for producing an optical film according to claim 1, comprising a step of forming a coating layer and a step of molecularly aligning the polymer liquid crystal compound by applying light, heat, or both.

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