JP2000019308A - Light scattering film, its production and double refractive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light scattering film in which the shapes and sizes of microregions are changed in a thickness direction and the optical characteristics hardly change by wavelengths and the optical characteristics hardly dependent upon the wavelengths in spite of a single layer film by comprising the film dispersed and distributed with the microregions different in double refraction characteristics and varying the average values of the sizes of the microregions between the front and rear of the film by the changes in the film thickness direction. SOLUTION: The light scattering film 1 consists of the film dispersed and distributed with the microregions (e) different in the double refraction characteristics and the sizes of the microregions (e) are changed in the film thickness direction, by which their average values are changed between the front and rear of the film. The production of such light scattering film 1 may be executed by a method of varying the curing rate or temp. at the front and rear of a development layer, thereby varying the growth rate of the microregions formed in the development layer between the front and rear directions of the development layer at the time of forming the film by, for example, a casting method to develop a liquid mixture composed of plural polymers varying in the double refraction characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-scattering film in which optical characteristics such as scattering, phase difference and polarization are hardly changed by wavelength, and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Conventionally, a light scattering film in which minute regions having different birefringence characteristics are dispersed and distributed has been known (Japanese Patent Application Laid-Open No. 9-274108). Such a light-scattering film exhibits optical characteristics in which scattering, phase difference, polarization, and the like are partially different, and is used for the purpose of improving visibility such as prevention of image bleeding and blurring in a liquid crystal display device or the like.

However, there has been a problem that the optical characteristics greatly change depending on the wavelength due to the optical path difference due to the shape and size of the minute region, and the wavelength dependence of the optical characteristics is large.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to develop a light-scattering film whose optical properties are hardly dependent on wavelength even in a single-layer film.

[0005]

The present invention comprises a film in which minute regions having different birefringence characteristics are dispersed and distributed, and the size of the minute regions changes in the thickness direction of the film, so that the average value differs between the front and back of the film. And a birefringent film comprising a light-scattering film and a stretched film of the film.

[0006]

According to the present invention, the light scattering is such that the optical characteristics are hardly changed by the wavelength because the shape and the size of the minute region change in the thickness direction, and the optical characteristics are hardly dependent on the wavelength even in a single-layer film. A film can be obtained.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The light-scattering film according to the present invention comprises a film in which minute regions having different birefringence characteristics are dispersed and distributed. The values are different. Examples thereof are shown in FIGS. 1 is a light scattering film, and e is a minute area.

In the production of the light-scattering film according to the present invention, for example, when a film is formed by a casting method in which a mixed solution of a plurality of polymers having different birefringence characteristics is developed, the curing speed or temperature on the front and back of the developed layer is controlled. Alternatively, it can be performed by a method in which the growth rate of the minute region formed in the spread layer is different between the front and back directions of the spread layer.

Further, when a mixed solution containing a plurality of polymers having different birefringence characteristics as components and containing at least one kind of ultraviolet-curable polymer is developed, and when the developed layer is cured by ultraviolet irradiation, the developed The light-scattering film can also be manufactured by a method in which the amount of ultraviolet irradiation on the front and back of the layer is changed so that the growth rate of the minute region formed in the spread layer is different in the front and back directions of the spread layer.

Further, when a mixture of a plurality of polymers having different birefringence characteristics is formed into a film by an extrusion molding method, a temperature difference is provided between the front and back of the film in the molding process, and fine particles formed in the formed film are formed. The light scattering film can also be manufactured by a method in which the growth rate of the region is made different in the front and back directions of the molded film.

Further, when forming a film by a casting method,
Using a mixture of light-scattering particles having a particle size distribution in a polymer liquid containing one or more kinds of polymers as a component, the mixture is developed so that the thickness direction of the developing layer becomes the direction of gravity. The light scattering film is also used in a method of forming a gradient distribution of light scattering particles according to the size due to the particle size distribution in the front and back directions of the spreading layer using the difference in sedimentation velocity due to the difference in particle size of the light scattering particles. Can be manufactured.

[0012] In addition, as in an ultrafiltration membrane obtained by spraying a poor solvent onto a spreading layer during film formation by a casting method, the pores of a porous film in which the shape of the pores changes in the film thickness direction are used. The light scattering film can also be manufactured by a method of filling a polymer having different birefringence characteristics.

Therefore, the production of the light scattering film according to the present invention is carried out by an appropriate method capable of dispersing and forming minute regions having a difference in birefringence characteristics whose shape and size are changed in the film thickness direction in a base film component. Can be. Incidentally, in the casting method, the ultraviolet irradiation method, the extrusion molding method and the light-scattering particle blending method, the micro-area dispersed type as illustrated in FIG. 1 is used, and in the porous film method, as illustrated in FIG. In general, a micro-area dispersed type is easily obtained. It is preferable that the shape and size of the minute region in the film are continuously changed as much as possible in a constant direction in the film thickness direction from the viewpoint of preventing the wavelength dependence of the optical characteristics.

In the above, the formation of the light scattering film includes:
For example, one or two or more of suitable materials having excellent transparency such as polymers and liquid crystals may be used as they are or through a combination capable of forming regions having different birefringence characteristics through appropriate alignment treatment such as stretching treatment. Can be used.

Incidentally, examples of combinations for forming regions having different birefringence characteristics by the above-mentioned alignment treatment include combinations of polymers and liquid crystals, combinations of isotropic polymers and anisotropic polymers, and combinations of anisotropic polymers. And the like. From the viewpoint of the dispersion distribution of the minute region, a combination that separates phases is preferable, and the dispersion distribution can be controlled by the compatibility of the materials to be combined. The phase separation can be performed by an appropriate method such as a method in which an incompatible material is converted into a solution with a solvent, and a method in which a compatible material is mixed while being heated and melted.

Examples of the polymers include polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, styrene polymers such as polystyrene and acrylonitrile-styrene copolymer (AS resin), polyethylene and polypropylene, and cyclo or norbornene structures. Olefin polymers such as polyolefins and ethylene / propylene copolymers, carbonate polymers, acrylic polymers such as polymethyl methacrylate, vinyl chloride polymers, cellulose polymers such as cellulose diacetate and cellulose triacetate, nylon and aromatic Amide polymers such as aromatic polyamides, imide polymers, sulfone polymers, polyethersulfone polymers, polyetheretherketone polymers, Phenylene sulfide-based polymer,
Examples include vinyl alcohol-based polymers, vinylidene chloride-based polymers, vinyl butyral-based polymers, arylate-based polymers, polyoxymethylene-based polymers, and blends thereof. Those which are polymerized by heat treatment, ultraviolet treatment or the like may be used.

Examples of liquid crystals include a nematic phase and a smectic phase at room temperature or high temperature such as cyanobiphenyl, cyanophenylcyclohexane, cyanophenyl ester, phenyl benzoate, phenylpyrimidine, and mixtures thereof. And low-molecular liquid crystals exhibiting a nematic phase or a smectic phase at room temperature or high temperature.

From the viewpoint of obtaining a light-scattering film having excellent uniform distribution of minute regions, it is preferable to form a mixed solution of materials via a solvent by a casting method, a casting method, or the like. In this case, the size and distribution of the minute region can be controlled by the type of the solvent, the viscosity of the mixed solution, the drying speed of the mixed solution developing layer, and the like. Examples of the light-scattering particles having the above-mentioned particle size distribution include those made of the above-mentioned polymers and liquid crystals.

The thickness of the light scattering film can be determined appropriately. In general, the thickness is 1 μm to 3 mm, particularly 5 μm to 1 mm, and particularly preferably 10 to 500 μm from the viewpoint of optical characteristics. When forming the light scattering film, for example, appropriate additives such as a dispersant, a surfactant, an ultraviolet absorber, a color adjusting agent, a flame retardant, a release agent, and an antioxidant can be blended.

When forming micro regions having different birefringence characteristics, an orientation treatment is performed as necessary. The orientation treatment is, for example, a uniaxial or biaxial, sequential biaxial or Z-axis stretching method or a rolling method, and quenching by applying an electric field or a magnetic field at a temperature higher than the glass transition point or the liquid crystal transition point to fix the orientation. One or two or more of appropriate methods that can control the refractive index by alignment, such as a method of performing liquid alignment during film formation, a method of self-aligning liquid crystal based on a slight alignment of an isotropic polymer, and the like. It can be performed using:

It is preferable that the minute regions in the light scattering film are dispersed and distributed as uniformly as possible from the viewpoint of homogeneity of optical characteristics such as scattering. The ratio of the minute region in the light scattering film is not particularly limited, but is generally 1 to 95%, preferably 5 to 80%, particularly 10 to 70% based on the surface area ratio of the minute region on one surface. Is done.

The light-scattering film according to the present invention may be a birefringent film that has been stretched by an appropriate method for the purpose of controlling optical characteristics and the like. Therefore, the light scattering film according to the present invention may be a stretched film or a non-stretched film. When a stretched film is used, a brittle polymer may be used, but a polymer having excellent extensibility can be particularly preferably used.

By the way, the optical properties are given anisotropy by the above-mentioned stretching treatment, so that, for example, the linearly polarized light is scattered based on the refractive index difference between the minute area and the other part (film base), and the light is transmitted without scattering. It is also possible to obtain a light scattering film having an axial direction.

The light scattering film and the birefringent film according to the present invention can be used for various applications such as a diffusion plate, a retardation plate, a polarization control plate, an anti-glare plate, and a display characteristic control plate. In practical use, they can be superimposed or laminated with other appropriate optical components. There is no particular limitation on the optical component to be laminated, for example, a polarizing plate or a retardation plate,
Appropriate devices such as a backlight such as a light guide plate, a reflection plate, a polarization separation plate composed of a multilayer film and a liquid crystal cell can be used.

[0025]

EXAMPLES Example 1 300 parts of poly (methyl methacrylate) (parts by weight, the same applies hereinafter)
Is mixed with 100 parts of a cyano-based nematic liquid crystal (GR-41, manufactured by Chisso Corp.), and the mixture is spread on a water-cooled substrate. Was spray-dried to obtain a light scattering film having a thickness of 50 μm by a casting method.

The light-scattering film is of the type illustrated in FIG. 1 in which fine regions composed of cyano-based nematic liquid crystals are dispersed and distributed in the form of domains in a film base composed of polymethyl methacrylate. The average diameter was about 1 μm on the hot air drying side and about 5 μm on the substrate side, and the change in particle size distribution was approximately linear in the film thickness direction.

By stretching the light-scattering film, the liquid crystal phase was oriented to generate a phase difference, and a birefringent film showing light-scattering properties was obtained from the difference in refractive index from the embedding substance. The wavelength dependence of the scattering properties was less than that of a uniform film in which the average diameter of the microscopic region did not change on the front and back of the film.

Example 2 80 parts of methyl methacrylate, 10 parts of acrylic acid, 3 parts of a photoreaction initiator (Irgacure 184: 2 manufactured by Ciba-Geigy)
Parts, Irgacure 907: 1 part), 2 parts of an ultraviolet absorber (Tinuvin 1130, manufactured by Ciba Geigy), and a reaction initiator (B
PO) and 30 parts of a cyano-based nematic liquid crystal (GR-41, manufactured by Chisso Corporation) were mixed, and the mixed solution was injected into a space between release-treated glass plates (gap: 100 μm), and one of them was irradiated with ultraviolet rays. Then, turbidity (phase separation) was caused by the progress of the polymerization, and then annealing was performed at 80 ° C. for 120 minutes to complete the reaction of the remaining monomers, thereby obtaining a light scattering film.

The light-scattering film is of the type illustrated in FIG. 1 in which fine regions due to phase separation of a cyano-based nematic liquid crystal are dispersed and distributed in a film base made of a methyl methacrylate-acrylic acid copolymer. The average particle size of the fine region was smaller on the ultraviolet irradiation side and larger on the opposite surface side.

By subjecting the light-scattering film to a stretching treatment, the liquid crystal phase was oriented to generate a phase difference, and a birefringent film exhibiting light-scattering properties was obtained from the difference in refractive index from the embedding substance. The wavelength dependence of the scattering properties was less than that of a uniform film in which the average diameter of the microscopic region did not change on the front and back of the film.

Example 3 A polymethyl methacrylate film having a thickness of 500 μm was subjected to supercritical carbon dioxide gas treatment to form a swelling film with carbon dioxide gas, and then returned to normal temperature and normal pressure to have an apparent volume 1.5 times.
Open cells corresponding to 50% of the original volume were generated inside,
A continuous porous film having no skin layer was obtained. In the cross-sectional structure of this film, as shown in FIG. 2, the average diameter of bubbles was larger on the surface side and smaller on the inner side.
Next, a cyano-based nematic liquid crystal (GR-41, manufactured by Chisso Corporation) was absorbed in the porous film in a vacuum to obtain a light scattering film.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an embodiment.

FIG. 2 is an explanatory view of another embodiment.

[Explanation of symbols]

 1: light scattering film e: minute area

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[Procedure amendment]

[Submission date] June 30, 1998 (1998.6.3)
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

The light-scattering film is a cured film.
Although it was difficult to perform the stretching treatment with a film, the wavelength dependence of the scattering characteristics was smaller than that of a uniform film in which the average diameter of the microscopic region did not change on the front and back of the film.

Claims (7)

[Claims] 1. A film formed by dispersing and distributing minute regions having different birefringence characteristics, wherein the size of the minute regions changes in the film thickness direction and the average value differs between the front and back of the film. Light scattering film. 2. The method according to claim 1, wherein when forming a film by a casting method in which a mixed solution of a plurality of polymers having different birefringence characteristics is developed, the curing speed or the temperature on the front and back surfaces of the developed layer is made different. 2. The method for producing a light-scattering film according to 1. 3. When a mixed solution containing a plurality of polymers having different birefringence characteristics as components and containing at least one kind of UV-curable polymer is developed, and the developed layer is cured by UV irradiation, The method for producing a light-scattering film according to claim 1, wherein the ultraviolet irradiation amounts on the front and back of the spreading layer are different. 4. When forming a mixture of a plurality of polymers having different birefringence characteristics into a film by an extrusion molding method,
The method for producing a light-scattering film according to claim 1, wherein a temperature difference is provided between the front and back of the film in the forming process. 5. When forming a film by a casting method, a mixed solution obtained by mixing light scattering particles having a particle size distribution with a polymer liquid containing one or more kinds of polymers is used. The method for producing a light-scattering film according to claim 1, wherein the developing layer is developed so that the thickness direction of the developing layer becomes the direction of gravity. 6. The method for producing a light-scattering film according to claim 1, wherein a polymer having a different birefringence property is filled in the pores of the porous film. 7. A birefringent film, comprising the stretched film of the light scattering film according to claim 1.