JPH09318815A - Production of optical film, laminated polarizing plate and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the lowering of visibility caused by the change of a visual angle in a liquid crystal display device in bearings in a wide range and to easily and stably form optical film having large area by bringing specified heat shrinkable film into contact with the front and back surfaces of light transmissive film through adhesive and drawing-processing the film. SOLUTION: This optical film is obtained by bringing the heat shrinkable film whose heat shrinkage factor in the vicinity of the glass transition temperature of the light transmissive film is different between the front and back surfaces of the light transmissive film into contact with the front and back surfaces of the light transmissive film through the adhesive and drawing-processing the light transmissive film under the heat shrinkage condition of the heat shrinkable film. The film whose difference between the maximum value and the minimum value of the phase difference of vertically transmitted light is <=10nm is desired as the optical film. Thus, the optical film having the large difference of the phase difference by double refraction in right and left obliquely transmitted light with a normal plane on either or both of a phase lagging axis and a phase advancing axis as reference and showing phase difference characteristic asymmetric right and left is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical film suitable for improving the display contrast and the viewing angle characteristics of a display color of a liquid crystal cell, and a laminated polarizing plate and a liquid crystal display device using the optical film.

[0002]

2. Description of the Related Art A liquid crystal display device such as a TFT type or MIM type using a twisted nematic (TN) type or a super twisted nematic (STN) type liquid crystal cell is used as a word processor because of its response speed and display contrast. It is widely used as a display means for various devices such as OA equipment such as a personal computer and a personal computer, but the visibility is deteriorated due to a decrease in contrast at a viewing angle (viewing angle), particularly at an oblique viewing angle and a coloring of a screen. However, there is a strong demand for improvement in the viewing angle characteristics.

Conventionally, as a method of improving the viewing angle characteristics, a method of arranging a retardation film has been known (Japanese Patent Laid-Open No. Hei 4).
No. 229828 and Japanese Patent Laid-Open No. 4-258923). However, it is difficult to improve the viewing angle characteristics in all directions, and the effect of improving the viewing angle characteristics in a certain direction is poor.

On the other hand, a method of arranging a retardation plate in which the main refractive index direction of the index ellipsoid is tilted with respect to the normal direction so as to cope with the tilt of liquid crystal molecules has been proposed (Japanese Patent Laid-Open No. 6-58242). -75116). However, there is a problem that it is difficult to form the retardation plate. Further, a method has also been proposed in which an extruded rod is obliquely cut out along a central axis to dispose retardation plates having different three-refractive indexes in the main axis direction (JP-A-6-174920). However,
There is a problem that it is difficult to obtain a liquid crystal display device having a required area.

Further, there has been proposed a method of disposing a retardation plate having an optical axis inclined with respect to the normal direction, which is formed by stretching with a shearing force through rolls having different peripheral speeds (Japanese Patent Laid-Open No. 6-58242).
-222213). However, the shearing force and the stretch orientation temperature that can be applied are poor, the inclination angle of the optical axis is small, and the variation in the angle is large and the effect of improving the viewing angle characteristics is poor, and contact scratches with the roll are likely to occur on the surface. There were problems such as deterioration of display quality.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a manufacturing method capable of preventing deterioration of visibility in a liquid crystal display device due to a change in viewing angle in a wide range of directions and easily and stably forming a large-area optical film having excellent quality. Therefore, it is an object to obtain a liquid crystal display device having excellent visibility such as contrast and monochrome display in a wide viewing angle range.

[0007]

According to the present invention, a heat-shrinkable film having different heat shrinkage rates at the glass transition temperature of the light-transmissive film is attached to the front and back surfaces of the light-transmissive film with an adhesive. The present invention provides a method for producing an optical film, which comprises subjecting a light-transmitting film to a stretching treatment under the heat-shrinking condition of the heat-shrinkable film.

[0008]

As described above, a large difference in the phase difference due to birefringence in the left and right obliquely transmitted light with respect to the normal plane on one or both of the slow axis and the fast axis is asymmetric. It is possible to obtain an optical film exhibiting excellent retardation characteristics, and it is possible to highly compensate for the change in visibility due to the viewing angle due to the birefringence of the liquid crystal cell over a wide range of orientations, though the mechanism of action is unknown using the optical film. It is possible to obtain a liquid crystal display device having excellent visibility such as contrast and monochrome display. Also, a large-area optical film having excellent quality can be easily and stably formed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The production method of the present invention comprises a heat-shrinkable film having different heat shrinkage rates on the front and back sides of the light-transmitting film near the glass transition temperature of the light-transmitting film via an adhesive. An optical film is obtained by bringing them into close contact with each other and stretching the light-transmitting film under the heat-shrinking condition of the heat-shrinkable film.

As the light-transmitting film, an appropriate light-transmitting film can be used without any particular limitation. A film having a light transmittance of 70% or more, especially 80% or more, and particularly 85% or more, which is excellent in translucency, can be preferably used. Among them, polycarbonate, polyarylate, polysulfone, polyethylene terephthalate, polyether sulfone, polyvinyl alcohol, polyolefins such as polyethylene or polypropylene, cellulosic polymers, polystyrene, polymethylmethacrylate, polyvinyl chloride, polyvinylidene chloride, polyamide, etc. A light-sensitive film can be preferably used.

The translucent film used for forming the optical film may be formed by an appropriate method such as a solution film forming method such as a casting method or an extrusion method, and may be uniaxially stretched with a free end or a fixed end. It may be an oriented film obtained by a stretching treatment such as a product, a biaxially stretched product, a film oriented in the thickness direction, or the like.

The thickness of the translucent film can be appropriately determined according to the retardation characteristics of the desired optical film. The phase difference can be obtained as the product (Δn × d) of the refractive index difference (Δn) of birefringence and the film thickness (d). The general thickness of the transparent film or the optical film is 5 to 500 μm, especially 10 to 350 μm, especially 20 to
It is 200 μm.

The heat-shrinkable film adhered to the front and back surfaces of the translucent film via an adhesive is intended to control the retardation property of the translucent film by transmitting the contracting force. Therefore, as the heat-shrinkable film, a film exhibiting heat-shrinkability at a temperature at which the light-transmissive film can be subjected to orientation treatment, that is, at a glass transition temperature of the light-transmissive film or higher and lower than the melting temperature is used.

Further, in the present invention, a combination of heat-shrinkable films having different heat-shrinkage rates near the glass transition temperature of the light-transmitting film is adhered to the front and back surfaces of the light-transmitting film.
Thereby, when the translucent film is stretched under the heat-shrinkable condition of the heat-shrinkable film, the heat-shrinkable force of the heat-shrinkable film acts in different states on the front and back sides of the translucent film, and thus the translucency Optical that affects the orientation of the film, and the phase difference due to birefringence in obliquely transmitted light with reference to the normal line on one or both of the slow axis and the fast axis is different on the left and right sides of the normal line. A film can be obtained.

The difference in heat shrinkage between the heat-shrinkable film and the heat-shrinkable film on the front and back of the light-transmitting film can be appropriately determined depending on the retardation characteristics of the desired optical film, etc., but is generally 1% or more, preferably 3% or more. In particular, it is a combination that causes a difference in thermal shrinkage of 5% or more. A combination of a heat shrinkable film having a heat shrinkage rate of 5% or more near the glass transition temperature of the light transmissive film and a heat shrinkable film of 2% or less is particularly preferable from the viewpoint of stable stretching processability of the light transmissive film. . Therefore, as one of the heat-shrinkable films, a film that does not exhibit heat-shrinkability may be used.

The heat-shrinkable film can be obtained as a stretched product of a plastic film or the like, and as the plastic, an appropriate one can be used depending on the treatment temperature of the target light-transmitting film, and the like. There is no limit. The difference in the heat shrinkage force in the heat shrinkable film can be brought about by changing the kind of plastic, the drawing conditions such as the draw ratio, and the like. A heat-shrinkable film whose heat-shrinkage force is as uniform as possible over the entire surface of the film is preferably used because it gives a uniform orientation to the translucent film.

As the above-mentioned adhesive for adhering the heat-shrinkable film to the front and back surfaces of the translucent film,
During the heat-shrinking treatment of the heat-shrinkable film, its shrinking force is transmitted to the light-transmitting film well, and after the heat-treatment, the optical properties of the heat-shrinkable film are not changed as much as possible. Those that can separate the shrinkable film are preferably used.

From the above points, a pressure sensitive adhesive or the like is preferably used. As the pressure sensitive adhesive, for example, an acrylic, silicone, polyester, polyurethane, polyether, rubber or other suitable adhesive can be used, and the type thereof is not particularly limited.

The stretching treatment of the translucent film having heat-shrinkable films adhered on the front and back surfaces can be carried out by an appropriate method such as uniaxial or biaxial under the above-mentioned orientation temperature of the translucent film. The retardation characteristics of the stretched product of the translucent film can be controlled by the stretching conditions such as the stretching ratio.

The optical film can be obtained as a stretched product of the above-mentioned light-transmitting film, and the stretched product is further stretched by an appropriate method such as uniaxial or biaxial to control the phase difference characteristics and the like. Can also be obtained as In the present invention, the optical film which is more preferable in view of the improvement of the viewing angle characteristics and the width of the azimuth is based on the normal line 11 on one or both of the slow axis and the fast axis as illustrated in FIG. When the tilt angle (θ) is 40 degrees, the difference in phase difference due to birefringence in the obliquely transmitted lights 12 and 13 on the left and right of the normal line is 50.
It is more than nm. If the difference in phase difference is less than 50 nm, the effect of improving the viewing angle characteristics, particularly the effect of enlarging the improved azimuth, may be poor. In the figure, 1 is an optical film.

Further, in the present invention, an optical film which is preferable from the viewpoint of preventing display unevenness and deterioration of contrast is the difference between the maximum value and the minimum value of the phase difference of transmitted light perpendicular to the film surface (in the front direction). Is less than 10 nm, especially less than 7 nm, especially less than 5 nm.

The optical film of the present invention can be preferably used as a monolayer or a laminate of the same kind or different kinds for compensating the viewing angle characteristics due to the birefringence of the liquid crystal cell. In practical use,
It can be used in an appropriate form such as a laminate with a polarizing plate or a retardation plate, a laminate with a protective layer made of an isotropic transparent resin layer, a glass layer or the like. Lamination with a polarizing plate or the like can be formed by sequentially laminating an optical film or a polarizing plate or the like separately in the manufacturing process of a liquid crystal display device, but by preliminarily laminating as described above, stability of quality and lamination There are advantages such as excellent workability and the like, which can improve the manufacturing efficiency of the liquid crystal display device.

FIG. 2 illustrates a laminated polarizing plate in which the optical film 1 and the polarizing plate 3 are bonded and laminated with the pressure sensitive adhesive 2 interposed therebetween. As the polarizing plate, an appropriate one may be used, and examples thereof include a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, an ethylene / vinyl acetate copolymer partially saponified film, and iodine. And / or a polarizing film formed by adsorbing a dichroic dye and stretched, a polyene oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride, and the like.

The polarizing plate, especially the polarizing film may have a transparent protective layer on one side or both sides thereof. Further, the polarizing plate may be a reflective type having a reflective layer. The reflective polarizing plate is used to form a liquid crystal display device of a type that reflects incident light from the viewing side (display side) to display, and it is possible to omit the built-in light source such as a backlight and to use a liquid crystal. It has an advantage that the display device can be easily thinned.

The above-mentioned transparent protective layer may be appropriately formed as a plastic coating layer, a laminate of protective films, or the like. For its formation, transparency, mechanical strength, thermal stability, moisture shielding property and the like are required. Excellent plastics are preferably used. Examples include polyester resins, acetate resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins and acrylic resins, acrylic resins, urethane resins, and acrylic urethane resins. Examples thereof include thermosetting resins such as epoxy resins and silicone resins, and ultraviolet curing resins. The surface of the transparent protective layer may be formed into a fine uneven structure by containing fine particles.

The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is attached to one surface of the polarizing plate via a transparent resin layer or the like, if necessary. Specific examples thereof include a transparent resin layer such as a protective film that has been subjected to a mat treatment as required, and a foil or vapor-deposited film made of a reflective metal such as aluminum provided on one surface, or a surface containing fine particles of the transparent resin layer. An example in which a metal reflective layer is provided on a fine uneven structure by an appropriate method such as a vapor deposition method or a plating method is exemplified.

As the retardation plate which may be laminated with the above-mentioned optical film, a film made of polycarbonate, polyvinyl alcohol, polystyrene, polymethylmethacrylate, polypropylene or other polyolefin, or a suitable plastic such as polyarylate or polyamide is used. Examples include a birefringent film formed by stretching.

The retardation plate is a uniaxially stretched film or a film oriented in the thickness direction, and has a refractive index in the slow axis direction of n _x ,
A biaxially stretched film showing characteristics such as n _x > n _y > n _z , where n _y is in the fast axis direction and n _z is in the thickness direction, and n _x = n _y > _nz and n _x = n _y <may be those indicating the proper retardation characteristics, such as uniaxial stretching optical ellipsoid showing the characteristics such as n _z.

In the above, for the lamination of the optical film and the polarizing plate and the like, an appropriate adhesive such as the transparent pressure sensitive adhesive exemplified above can be used, and the kind thereof is not particularly limited. From the viewpoint of preventing changes in optical properties of optical films and the like, those that do not require a high temperature process at the time of curing or drying are preferable, and those that do not require a long curing treatment or drying time are desirable. Further, those which do not cause peeling under heating or humidifying conditions can be preferably used.

From these points, the weight average molecular weight of a monomer such as butyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate or (meth) acrylic acid is 100,000 or more, and the glass An acrylic pressure-sensitive adhesive composed of an acrylic polymer having a transition temperature of 0 ° C. or lower can be particularly preferably used. Acrylic pressure-sensitive adhesives are more preferable than those having excellent transparency, weather resistance and heat resistance. When layers having different refractive indices are laminated, an adhesive or the like having an intermediate refractive index is preferably used from the viewpoint of suppressing reflection loss.

If necessary, the adhesive may be, for example, a resin or a natural or synthetic resin, a filler or a pigment comprising a glass fiber or a glass bead, a metal powder or other inorganic powder, a coloring agent or an antioxidant. Can be added.
Further, an adhesive layer exhibiting light diffusing properties can be formed by incorporating fine particles.

Each layer such as the optical film, the polarizing plate, the retardation plate, the transparent protective layer, the adhesive layer and the like is, for example, a salicylic acid ester compound or a benzophenol compound,
It is also possible to impart the ultraviolet ray absorbing ability by a method of treating with an ultraviolet ray absorbing agent such as a benzotriazole type compound, a cyanoacrylate type compound or a nickel complex salt type compound.

The liquid crystal display device using the optical film of the present invention can be formed in a conventional manner. That is, a liquid crystal display device is generally formed by appropriately assembling a liquid crystal cell, an optical film for optical compensation, and components such as a polarizing plate and an illumination system, if necessary, and incorporating a drive circuit. In the invention, there is no particular limitation except that the optical film of the present invention is used for optical compensation and it is provided on at least one side of the liquid crystal cell, and it can follow conventional methods.

Therefore, it is possible to form an appropriate liquid crystal display device such as a liquid crystal display device in which a polarizing plate is disposed on one side or both sides of a liquid crystal cell, or a backlight system or a reflection plate is used for an illumination system. In the case of a liquid crystal display device using a polarizing plate, it is preferable to arrange the optical film for optical compensation between the liquid crystal cell and the polarizing plate, especially the polarizing plate on the viewing side from the viewpoint of compensation effect. When arranging it, the laminated polarizing plate described above can be used.

3 and 4 show examples of the structure of a liquid crystal display device using a polarizing plate. 4 is a liquid crystal cell, 5 is a backlight system, and 6 is a reflective layer. Reference numeral 7 denotes a light diffusion plate.
In FIG. 3, the illumination system in which optical films for optical compensation are arranged on both sides is a backlight type, and in FIG. 4, the illumination system in which optical films for optical compensation are arranged on only one side. Is a reflective type.

In the above, the forming parts of the liquid crystal display device are as follows:
They may be laminated and integrated, or may be in a separated state. In forming a liquid crystal display device, for example, appropriate optical elements such as a diffusion plate, an antiglare layer, an antireflection film, a protective layer and a protective plate can be appropriately arranged.

The optical film of the present invention is a TN type or STN type.
TFT or MIM using liquid crystal cell exhibiting birefringence
It can be preferably used for various display devices such as molds. In that case,
The arrangement relationship of the optical film, the polarizing plate, and the optical axes such as the absorption axis and the slow axis of the retardation plate can be arbitrarily set to, for example, a parallel relationship, an orthogonal relationship, or other cross relationship.

[0038]

【Example】

Example 1 A transparent polycarbonate film having a thickness of 100 μm has a biaxially stretched polyester film having a heat shrinkage of 5% at 160 ° C. on one side and a polyarylate film having a heat shrinkage of 2% having a thickness of 20 μm on the other side. Was bonded via an acrylic pressure-sensitive adhesive layer and stretched to 1.12 times in an oven at 160 ° C., and the heat-shrinkable film was peeled off together with the acrylic pressure-sensitive adhesive layer to obtain an optical film. .

Comparative Example 1 A transparent polycarbonate film having a thickness of 100 μm was used as 16
In an atmosphere of 0 ° C., the film was passed between rolls having different peripheral speeds and stretched by 1.15 times to obtain an optical film.

Comparative Example 2 A transparent polycarbonate film having a thickness of 100 μm was supplied between rolls having a driving system and sheared. One of the rolls had a surface temperature of 150 ° C. and a peripheral speed of 2.8 m / min, and the other had a surface temperature of 150 ° C. and a peripheral speed of 1.9 m / min.

Evaluation Test The following characteristics of the optical films obtained in Examples and Comparative Examples were examined. Phase difference The phase difference when tilted by ± 40 degrees in the front direction and the slow axis direction was examined (Oak Co., ADR-100XY).

Dispersion The phase difference in the front direction within 100 mm square is 100 at 10 mm intervals.
The point was measured and the difference between the maximum value and the minimum value was obtained.

Scratch The appearance of the optical film was visually observed to check for scratches.

The above results are shown in the following table.

As can be seen from the table, in Example 1, the difference in the phase difference between the left and right obliquely transmitted light with respect to the normal plane is large and the asymmetry is excellent, the variation in the phase difference in the plane is small, and the quality is good. On the other hand, in Comparative Example 1, there is no difference in the phase difference between the left and right obliquely transmitted light, and the characteristics of a normal uniaxially stretched product are shown.
In Comparative Example 2, it can be seen that the difference in the phase difference between the left and right obliquely transmitted light is small, the variation in the phase difference in the plane is large, and the scratches are caused by the contact with the roll.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an example of an optical film.

FIG. 2 is a sectional view of an example of a laminated polarizing plate.

FIG. 3 is a cross-sectional view of an example of a liquid crystal display device.

FIG. 4 is a cross-sectional view of another example of a liquid crystal display device.

[Explanation of symbols]

 1: Optical film 2: Adhesive layer 3: Polarizing plate 4: Liquid crystal cell

Claims (5)

[Claims] 1. A heat-shrinkable film comprising: a heat-shrinkable film having different heat shrinkage ratios on the front and back surfaces of the light-transmissive film, the heat-shrinkage films having different heat-shrinkage ratios near the glass transition temperature of the light-transmissive film. A method for producing an optical film, which comprises subjecting a translucent film to a stretching treatment under heat shrinking conditions of the film. 2. The manufacturing method according to claim 1, wherein the difference between the maximum value and the minimum value of the phase difference of the vertically transmitted light of the optical film is 10 nm or less. 3. A laminated polarizing plate comprising a laminated body of one or more optical films produced by the manufacturing method according to claim 1 or 2 and a polarizing plate via a pressure-sensitive adhesive. 4. The laminated polarizing plate according to claim 3, wherein the pressure-sensitive adhesive has a glass transition temperature of 0 ° C. or lower. 5. A liquid crystal display device comprising the laminated polarizing plate according to claim 3 or 4 on at least one side of a liquid crystal cell.