JP2000249832A - Polarizing film, polarizing plate and optical member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyvinyl alcohol-base polarizing film excellent in surface smoothness while enhancing light transmittance and the degree of polarization by a high drawing rate. SOLUTION: A polyvinyl alcohol film having 85-150 μm thickness is dyed with a dichroic material and drawn 4-7 times to obtain the objective polarizing film having 35-50% light transmittance, >=80% degree of polarization and <=0.04 μm center line average surface roughness in a direction perpendicular to the drawing axis. A transparent protective layer optionally subjected to hard coating treatment or anti-glaring treatment is formed on one face or both faces of the polarizing film to obtain the objective polarizing plate. The polarizing film or plate and an optical layer having another optical function are laminated to obtain the objective optical member. The polarizing film is excellent in light transmittance and the degree of polarization and fringes that block visibility are hardly seen even in a reflection mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly stretched polarizing film excellent in light transmittance, degree of polarization and surface smoothness, and a polarizing plate and an optical member using the same.

[0002]

BACKGROUND OF THE INVENTION Conventionally, a polarizing film made of a stretched polyvinyl alcohol film has been known. However, as the use of liquid crystal display devices has been expanded, further improvements in light transmittance and polarization degree have been demanded. A polarizing film obtained by subjecting a polyvinyl alcohol film to a stretching treatment at a higher magnification has been proposed.

However, such polarizing films include:
Streaks such as record grooves are generated due to the high stretching ratio, and the streaks are clearly seen in the reflection mode, and there is a problem that visibility is hindered. The streaks are generated in the form of stripes in the stretching axis direction of the polarizing film, and are generally in the direction perpendicular to the stretching axis, and have a center line average roughness of 0.6 to 0.8 m as irregularities of 0.06 μm or more.
Appears at an average spacing of m.

[0004]

An object of the present invention is to develop a polyvinyl alcohol-based polarizing film having excellent surface smoothness while improving the light transmittance and the degree of polarization by a high stretching ratio.

[0005]

The present invention comprises a stretched film obtained by dyeing a polyvinyl alcohol film having a thickness of 85 to 150 μm with a dichroic substance and stretching it 4 to 7 times, and having a light transmittance of 35 to 50%. An object of the present invention is to provide a polarizing film having a degree of polarization of 80% or more and a surface roughness in a direction perpendicular to the stretching axis of 0.04 μm or less based on a centerline average roughness.

The present invention also provides a polarizing plate comprising a polarizing film having a transparent protective layer or a hard coat-treated or anti-glare-treated transparent protective layer on one or both surfaces of the polarizing film, and the polarizing film or the polarizing plate, Another object of the present invention is to provide an optical member comprising a laminate with an optical layer having another optical function.

[0007]

According to the present invention, a stretched film of polyvinyl alcohol having excellent surface smoothness can be formed even at a high stretch ratio of 4 to 7 times, and it is excellent in light transmittance and polarization degree and in a reflection mode. Also, it is possible to obtain a polarizing film in which striped streaks that hinder visual recognition are hardly seen.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A polarizing film according to the present invention comprises a stretched film obtained by dyeing a polyvinyl alcohol film having a thickness of 85 to 150 μm with a dichroic substance and stretching it 4 to 7 times, and having a light transmittance of 35 to 35. 80% polarization at ~ 50%
% Or more and the surface roughness in the direction perpendicular to the stretching axis is 0.04 μm or less based on the center line average roughness.

The polarizing film is, for example, a dichroic dye such as iodine and / or a dichroic dye added to the polyvinyl alcohol film, except that the polarizing film is stretched 4 to 7 times using a polyvinyl alcohol film having a thickness of 85 to 150 μm. It can be formed by an appropriate method according to the related art, such as a method in which a substance is adsorbed by dyeing and stretched by a uniaxial stretching method or the like.

By stretching the polyvinyl alcohol film having a thickness of 85 to 150 μm 4 to 7 times as described above, a high light transmittance of 35 to 50% and a high degree of polarization of 80% or more can be achieved by a high stretching ratio. Thus, a polarizing film having excellent surface smoothness can be obtained.

In the case of a polyvinyl alcohol film having a thickness of less than 85 μm, when the film is processed at the high stretching ratio in order to achieve the above-mentioned high light transmittance and high degree of polarization, stripes such as record grooves are formed in the stretching axis direction. The streaks are formed, and the streaks form surface irregularities in a direction perpendicular to the stretching axis, so that the streaks are clearly seen in the reflection mode and hinder visual recognition. In addition, breakage such as breakage is likely to occur during the processing at the high stretching ratio, and the yield is reduced. On the other hand, a polyvinyl alcohol film with a thickness of more than 150 μm has a large variation in crystallinity in the plane of the film, and requires a long time for the alignment treatment and the dyeing treatment of a dichroic substance required to achieve a high degree of polarization. Efficiency is greatly reduced, alignment unevenness and dyeing unevenness are liable to occur, and quality variation is increased.

In the polarizing film according to the present invention, in addition to the achievement of the light transmittance and the degree of polarization described above, the surface roughness in the direction perpendicular to the stretching axis is 0.04 based on the center line average roughness.
The thickness of the polyvinyl alcohol film that can be preferably used from the viewpoint of achieving surface smoothness that does not cause such visual impairment is 140 μm or less, especially 90 to 130
μm, especially 95-120 μm.

Further, a polarizing film which is preferable from the viewpoint of optical performance and the like has a light transmittance of 38% or more, especially 40% or more, and especially 4% or more.
2 to 50%, a degree of polarization of 85% or more, particularly 90% or more, particularly 95% or more. Based on the center line average roughness, 0.035 µm or less, particularly 0.030 µm or less, particularly The surface roughness is 0.02 μm or less, especially the surface roughness in the direction perpendicular to the stretching axis. The average interval between the irregularities in the direction perpendicular to the stretching axis based on the surface roughness is usually 0.4 to 0.8 mm.

The polarizing film according to the present invention can be put to practical use by providing a transparent protective layer on one or both sides thereof as required. The transparent protective layer is provided for the purpose of, for example, protecting the surface of the polarizing film, and a polymer or glass having excellent transparency, mechanical strength, heat stability, moisture shielding properties, and the like is preferably used for the formation.

Examples of the polymer include cellulose resins such as triacetyl cellulose, polycarbonate resins, polyester resins and polyethersulfone resins, polyamide resins and polyimide resins, polyolefin resins and acrylic resins, or A thermosetting resin such as an acryl-based or urethane-based, acrylurethane-based, epoxy-based, or silicone-based resin, or an ultraviolet-curable resin may be used. Above all, cellulose-based resins, polycarbonate-based resins, polyester-based resins, and the like are preferably used in terms of transparency, protection function, and the like.

The transparent protective layer can be formed by an appropriate method such as a laminating method via an adhesive layer or a pressure-sensitive adhesive layer of a polymer film or a glass plate or a coating method of a polymer liquid. The thickness can be determined as appropriate, but is generally 500
μm or less, especially 1 to 300 μm, particularly 5 to 200 μm. When a transparent protective layer is provided on both surfaces of the polarizing film, the transparent protective layer may be made of a different resin on the front and back sides.

The transparent protective layer may have been subjected to a hard coat treatment or an anti-glare treatment. The hard coat treatment is performed for the purpose of preventing scratches on the surface of the polarizing plate. For example, a hardened film having excellent hardness and slipperiness by the above-described ultraviolet curing resin such as silicone is coated on the surface of the transparent protective layer. Can be formed by a method according to the related art such as a method of adding to the conventional method.

On the other hand, the anti-glare treatment is carried out for the purpose of preventing external light from being reflected on the surface of the polarizing plate and obstructing the visible light transmitted through the polarizing plate when the polarizing plate is viewed. The transparent protective layer can be formed by imparting a fine uneven structure to the surface of the transparent protective layer by an appropriate method such as a roughening method by a method, an embossing method, or a method of blending transparent fine particles.

The above-mentioned transparent fine particles may be made of, for example, silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide or the like having an average particle size of 0.5 to 20 μm. Certain inorganic fine particles, organic fine particles comprising a crosslinked or uncrosslinked polymer or the like are used. The amount of the fine particles used is 2 to 50 parts by weight, preferably 5 to 25 parts by weight, per 100 parts by weight of the transparent resin.
Parts by weight are common.

The antiglare layer containing the transparent fine particles described above can be provided as the transparent protective layer itself or as a coating layer on the surface of the transparent protective layer. Note that the anti-glare layer may also serve as a diffusion layer for expanding the viewing angle by diffusing light transmitted through the polarizing plate.

The polarizing plate according to the present invention can be put to practical use as a reflection type or a semi-transmission type having a reflection layer or a semi-transmission reflection layer as required. Reflective polarizing plates are
This is for forming a liquid crystal display device or the like of a type that reflects incident light from the viewing side (display side) to display.
There is an advantage that the incorporation of a light source such as a backlight can be omitted and the thickness of the liquid crystal display device can be easily reduced. Further, a transflective polarizing plate is used for forming a liquid crystal display device or the like which is used as a reflective type in a place where external light is present, and is used as a type for displaying through a light source such as a backlight in a dark place. Things.

The reflective polarizing plate is formed by, for example, forming a reflective layer by attaching a foil or a vapor-deposited film made of a reflective metal such as aluminum to a transparent protective layer for forming the polarizing plate. It can be performed by an appropriate method such as a method of bonding a reflection plate attached to a base material to a polarizing film or a transparent protective layer thereof. Further, the formation of the transflective polarizing plate may be appropriately performed by a method such as a method in which the reflective layer or the reflective plate is a half mirror or a method in which a pearl pigment or the like is used as a transflective plate that reflects and transmits light. It can be performed in a system.

The reflective layer or semi-transmissive reflective layer to be formed may have a light diffusion function. The formation can be performed by, for example, a method of providing a reflective layer or the like reflecting the fine uneven structure on the transparent resin layer having the fine uneven structure on the surface. The reflective layer is preferably used in a state where its reflective surface is covered with a transparent substrate or the like, from the viewpoint of preventing a decrease in reflectance due to oxidation, and a long-lasting initial reflectance.

The reflection type polarizing plate having the light diffusion function has an advantage that the incident light is diffused by irregular reflection to prevent directivity and glaring appearance, and that unevenness in brightness can be suppressed. Further, the transflective polarizing plate having a light diffusion function has an advantage that the incident light and its reflected light are diffused when transmitted through the plate, so that uneven brightness can be further suppressed.

The formation of the reflective layer having a fine uneven structure reflecting the fine uneven structure on the surface of the transparent resin layer is performed by a suitable method such as a vapor deposition method such as a vacuum deposition method, an ion plating method and a sputtering method, and a plating method. It can be performed by a method of directly attaching a metal to the surface of the transparent resin layer by a method. The reflection plate and the transflective plate can be bonded to the polarizing plate via an adhesive layer or an adhesive layer as necessary.

Further, the polarizing film or the polarizing plate according to the present invention can be used practically as an optical member laminated with an optical layer having another optical function. In the optical layer, for example, a retardation plate or a viewing angle expansion film, a light collector or a brightness enhancement plate,
An appropriate device such as a light diffusion plate used for forming a liquid crystal display device or the like can be used.

The retardation plate as the optical layer is used for various purposes such as compensation for retardation by a liquid crystal cell. Examples thereof include a birefringent film made of a stretched film of various plastics, an oriented film of a liquid crystal polymer such as discotic or nematic, and a film having the oriented liquid crystal layer supported on a film substrate. In that case, as a film substrate supporting the alignment liquid crystal layer,
A film having excellent isotropy such as a cellulosic film can be preferably used.

On the other hand, as a plastic for forming the birefringent film, for example, an appropriate plastic such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefin, polyarylate, polyamide or the like can be used.

The stretched film may be processed by an appropriate method such as uniaxial or biaxial. Further, a birefringent film in which the refractive index in the thickness direction of the film is controlled by a method of applying a contraction force and / or a stretching force while adhering to the heat-shrinkable film may be used. Two or more retardation plates can be used for the purpose of controlling optical characteristics such as retardation.

The viewing angle widening film is used for the purpose of expanding the viewing angle of a liquid crystal display device or the like. For example, a support film for a discotic liquid crystal layer (a commercially available product such as WV film manufactured by Fuji Photo Film Co., Ltd.). It can be formed as such. The light collector is used for the purpose of controlling an optical path, and can be formed as, for example, a prism array sheet, a lens array sheet, or a dot-attached sheet.

The brightness enhancement plate is used for the purpose of improving brightness in a liquid crystal display device or the like, and as an example, a prism array sheet, a lens array sheet, and a plurality of thin film films having different refractive index anisotropies are laminated. Reflection type polarization separating sheet which has anisotropy of reflectance by interference
Examples include an alignment film of a cholesteric liquid crystal polymer and a polarization separation sheet having the alignment liquid crystal layer supported on a film substrate. The light diffusing plate can be obtained as a sheet or the like according to the transparent protective layer having the above-described fine surface uneven structure.

The optical member is composed of two or three or more layers by using one or two or more appropriate optical layers such as a polarizing film or a polarizing plate and the above-mentioned retardation plate in an appropriate combination according to the purpose of use. It can be obtained as a laminate. In this case, two or more optical layers such as a retardation plate may be arranged. In addition, the arrangement position of each optical layer can be appropriately determined according to the purpose of use, and is not particularly limited.

The optical layer for forming the optical member and the reflective layer and the like as necessary for forming the above-mentioned polarizing plate are adhered and integrated through an adhesive layer as necessary. An appropriate adhesive can be used, and there is no particular limitation.
Adhesion treatment with an adhesive layer is preferred from the viewpoint of simplicity of the adhesion work and prevention of generation of optical distortion due to relaxation of internal stress due to temperature difference.

In the formation of the above-mentioned adhesive layer, for example, an adhesive substance or an adhesive having an appropriate polymer such as an acrylic polymer, a silicone polymer, a polyester, a polyurethane, a polyether or a synthetic rubber as a base polymer is used. And there is no particular limitation. Above all, it is excellent in optical transparency like acrylic adhesive, shows moderate wettability, cohesiveness and adhesive properties such as adhesiveness, excellent in weather resistance and heat resistance, etc., under heating and humidifying conditions Those which do not cause a peeling problem such as floating or peeling can be preferably used.

Incidentally, examples of the acrylic pressure-sensitive adhesive include those having a carbon number of 20 such as methyl group, ethyl group and butyl group.
An alkyl monomer of the following (meth) acrylic acid having an alkyl group and an acrylic monomer comprising an improving component such as (meth) acrylic acid or hydroxyethyl (meth) acrylate are used. C. and a copolymer having a weight average molecular weight of 10 or less.
Examples thereof include, but are not limited to, those using 10,000 or more acrylic polymers as a base polymer.

At the time of the above-mentioned adhesion / integration treatment, an adhesive layer can be provided on one or both sides of a polarizing film or a polarizing plate or an optical layer and subjected to the adhesion treatment. The adhesive layer to be provided is
Superimposed layers of different compositions or types may be used.
When providing an adhesive layer on both surfaces, the adhesive layer may have a different composition or type on the front and back of the polarizing film or the polarizing plate or the optical layer.

The attachment of the pressure-sensitive adhesive layer to the polarizing film, the polarizing plate, and the optical layer can be performed by an appropriate method. For example,
For example, an adhesive substance or a composition thereof is dissolved or dispersed in a solvent composed of an appropriate solvent alone or a mixture of appropriate solvents such as toluene and ethyl acetate to prepare an adhesive liquid of about 10 to 40% by weight, and it is cast. A method of directly attaching on a polarizing plate or an optical layer by an appropriate development method such as a method or a coating method, or forming an adhesive layer on a separator according to the above and transferring it to a polarizing film or a polarizing plate or an optical layer. There is a method of wearing.

The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the adhesive strength and the like, and is generally from 1 to 500 μm. The adhesive layer may be provided on the outer surface of a polarizing plate or an optical member, if necessary, for the purpose of bonding to an adherend such as a liquid crystal cell. When such an adhesive layer is exposed on the surface, it is preferable to cover and protect the surface with a separator or the like until practical use.

The pressure-sensitive adhesive layer may be, if necessary, a filler or a pigment made of, for example, natural or synthetic resins, particularly, tackifying resins, glass fibers, glass beads, metal powders, and other inorganic powders. And appropriate additives such as a coloring agent and an antioxidant. Further, the pressure-sensitive adhesive layer may contain fine particles and exhibit light diffusion.

The polarizing film and the transparent protective layer used for forming the polarizing plate and the optical member, the optical layer such as the retardation plate, and the adhesive layer such as the adhesive layer may be formed of, for example, a salicylate compound or a benzophenol compound, if necessary. UV absorbing ability can be provided by an appropriate method such as a method of treating with an ultraviolet absorber such as a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound.

The polarizing film, the polarizing plate, and the optical member according to the present invention can be preferably used for various conventional applications such as formation of a transmission type, a reflection type, or a transmission / reflection type liquid crystal display device. In that case, the polarizing film or polarizing plate or optical member can be disposed on one side or both sides of the liquid crystal cell, and when provided on both sides, the polarizing film or polarizing plate or optical member may be the same or different. It may be. .

The liquid crystal cell to be used is arbitrary. For example, an appropriate type of liquid crystal such as an active matrix driving type represented by a thin film transistor type and a simple matrix driving type represented by a twisted nematic type or a super twisted nematic type is used. Various liquid crystal display devices can be formed using the cells.

[0043]

EXAMPLES Example 1 A 100 μm thick polyvinyl alcohol film (manufactured by Kuraray Co., Ltd., VF-9X100RS, degree of polymerization 2400) was used.
After swelling with water at 0 ° C. for 2 minutes, it is immersed in a dyeing bath containing iodine (30 ° C.) for 2 minutes to carry out a dyeing treatment, and then is immersed in an acid bath (50 ° C.) containing boric acid for 5.5 minutes. The film was uniaxially stretched twice and dried at 50 ° C. for 7 minutes to obtain a polarizing film. A triacetyl cellulose film having a thickness of 80 μm was adhered to both surfaces of the polarizing film via a polyvinyl alcohol-based adhesive layer to obtain a polarizing plate.

Example 2 After swelling in water of 30 ° C. for 2 minutes, dyeing was carried out for 1 minute in a dyeing bath (30 ° C.) containing iodine and potassium iodide, and then the solution was added to an acidic bath containing boric acid (55 ° C.). )), A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that the film was uniaxially stretched 5.5 times.

Example 3 After swelling in water at 30 ° C. for 2 minutes, dyeing treatment was carried out for 1 minute in a dyeing bath (40 ° C.) containing iodine and potassium iodide, and then the solution was added to an acidic bath containing boric acid (50 ° C.). )), A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that the film was uniaxially stretched 5.5 times.

Example 4 After swelling in water at 30 ° C. for 2 minutes, dyeing treatment was carried out for 1 minute in a dyeing bath (40 ° C.) containing iodine and potassium iodide, and then the solution was added to an acid bath containing boric acid (50 ° C.). ), A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that the film was uniaxially stretched 6 times.

Example 5 After swelling in water at 30 ° C. for 2 minutes, dyeing treatment was carried out for 1 minute in a dyeing bath (30 ° C.) containing iodine and potassium iodide, and then the solution was added to an acidic bath containing boric acid (55 ° C.). ), A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that the film was uniaxially stretched 6 times.

Example 6 After swelling in water at 20 ° C. for 2 minutes, dyeing treatment was carried out for 1 minute in a dyeing bath (30 ° C.) containing iodine and potassium iodide, and then the solution was added to an acid bath containing boric acid (60 ° C.). )), A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that the film was uniaxially stretched 6.5 times.

Comparative Example 1 A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 except that a 75 μm-thick polyvinyl alcohol film (manufactured by Kuraray Co., Ltd., VF-9X75RS, degree of polymerization: 2400) was used.

Comparative Example 2 A polarizing film and a polarizing plate were obtained in the same manner as in Example 2 except that a 75 μm-thick polyvinyl alcohol film (VF-9P75RS, manufactured by Kuraray Co., Ltd., degree of polymerization: 2400) was used.

Comparative Example 3 A polarizing film and a polarizing plate were obtained in the same manner as in Example 3 except that VF-9X75RS was used.

Comparative Example 4 A polarizing film and a polarizing plate were obtained in the same manner as in Example 4 except that a 75 μm-thick polyvinyl alcohol film (VF-9P75R, manufactured by Kuraray Co., Ltd., degree of polymerization: 1700) was used.

Comparative Example 5 A polarizing film and a polarizing plate were obtained in the same manner as in Example 5, except that a polyvinyl alcohol film (VF-9P75RH, manufactured by Kuraray Co., Ltd., degree of polymerization: 4000) having a thickness of 75 μm was used.

Comparative Example 6 A polarizing film and a polarizing plate were obtained according to Example 6, except that VF-9P75RS was used.

Evaluation Test Streaks, Center Line Average Roughness (Ra), Streaks Average Spacing (Sm) The polarizing films obtained in Examples and Comparative Examples were visually inspected for the presence or absence of streaks by visual observation. The average roughness (Ra) of the center line in the direction perpendicular to the stretching axis and the average interval (Sm) of the streaks forming the streaks were examined by (manufactured by Tokyo Seimitsu Co., Ltd.).

Light Transmittance and Degree of Polarization The light transmittance and the degree of polarization of the polarizing films obtained in Examples and Comparative Examples were examined.

Visual observation of streaks The polarizing plates obtained in Examples and Comparative Examples were visually observed to check whether the streaks were visible.

The above results are shown in the following table. Muscle Ra Sm Light transmittance Polarization degree Muscle (μm) (mm) (%) (%) Visual example 1 None 0.01 or less Unmeasurable 43.7 99.95 None Example 2 None 0.01 or less 43.8 99.94 None Perform Example 3 None 0.01 or less Unmeasurable 43.5 99.99 None Example 4 None 0.01 or less Unmeasurable 43.8 99.96 None Example 5 None 0.01 or less Unmeasurable 43.9 99.95 None Example 6 None 0.01 or less Unmeasurable 44.2 99.96 No Comparative Example 1 Yes 0.06 0.75 43.5 99.99 Yes Comparative Example 2 Yes 0.06 0.74 43.7 99.96 Yes Comparative Example 3 Yes 0.08 0.81 43.7 99.95 Yes Comparative Example 4 Yes 0.08 0.62 43.8 99.96 Yes Comparative Example 5 Yes 0.09 0.68 44.0 99.95 Yes Comparative Example 6 Yes 0.09 0.67 44.3 99.97 Yes

As can be seen from the table, in all the comparative examples using the 75 μm-thick polyvinyl alcohol film, record groove-like (striped) streaks in the absorption axis direction were generated, and the streaks were visually recognized even through the transparent protective layer. However, in Examples using a polyvinyl alcohol film having a thickness of 100 μm, substantially no streak was generated in all cases, and it was found that no streak was visually observed even through the transparent protective layer.

Claims (5)

[Claims] 1. A stretched film obtained by dyeing a polyvinyl alcohol film having a thickness of 85 to 150 μm with a dichroic material and stretching it 4 to 7 times, and having a light transmittance of 35 to 50.
% And the surface roughness in the direction perpendicular to the stretching axis is 0.04 μm based on the center line average roughness.
A polarizing film characterized by the following. 2. A polarizing plate comprising the polarizing film according to claim 1, having a transparent protective layer or a hard coat-treated or anti-glare-treated transparent protective layer on one or both surfaces. 3. The polarizing plate according to claim 2, having a reflective layer or a transflective layer. 4. An optical member comprising a polarizing film according to claim 1 or a laminate of the polarizing plate according to claim 2 and an optical layer having another optical function. 5. The optical member according to claim 4, wherein the optical layer is a retardation plate or a viewing angle widening film.