JP2001059907A - Phase difference sheet and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably, efficiently and continuously produce a phase difference sheet capable of highly compensating changes of display characteristic due to visual angle in accordance with double refractivity of a liquid crystal display cell and forming a liquid crystal display device which is excellent in visibility of contrast, etc., in the broad range of visual angle. SOLUTION: In this phase difference sheet, the formula (nx+ny)/2<nz is satisfied, when nx, ny are the main refractive index in a surface and nz is the main refractive index in the thickness direction, and the azimuth of advance phase axis or lagging phase axis which has one side in a vertical or transverse direction as a standard is in the range of 0±5 deg. or 90±5 deg.. Heat shrinkable films are stuck on one side or both sides of a thermoplastic resin film in such a manner that the maximum heat shrinking direction forms a cross angle in the range within of 90±5 deg. with respect to the width direction or the length direction of the thermoplastic film. By subjecting the thermoplastic film to the action of heat shrinkage force more than 0.03 kg/mm2 by means of the heat shrinking film, the thermoplastic film is shrunk and the phase difference sheet is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a retardation plate suitable for improving viewing angle characteristics by optically compensating a liquid crystal cell, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Hitherto, as a retardation plate which can be used for the purpose of improving a viewing angle characteristic by compensating a change in an optical characteristic such as a contrast due to a change in a viewing angle due to a birefringence of a liquid crystal, polystyrene or the like is used. Known is a thermoplastic resin exhibiting negative birefringence properties, that is, a biaxially stretched film made of a thermoplastic resin exhibiting negative birefringence properties exhibiting a property of increasing the refractive index in a direction perpendicular to the stretching direction. Was. However, the obtained retardation plate has poor heat resistance,
There is a problem that it is difficult to obtain a material having heat resistance that can be used for forming a liquid crystal display device or the like.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to develop a retardation plate having excellent heat resistance and a method for producing the retardation plate stably and efficiently.

[0004]

According to the present invention, the in-plane principal refractive index is nx,
ny and the main refractive index in the thickness direction as nz, the expression: (nx
+ Ny) / 2 <nz, and the azimuth of the slow axis or fast axis with respect to one of the vertical and horizontal directions is within 0 ± 5 degrees or within 90 ± 5 degrees. The phase difference plate, and the heat-shrinkable film on one or both sides of the thermoplastic resin film so that the maximum heat shrinkage direction thereof has an intersection angle within 90 ± 5 degrees with respect to the width direction or the length direction of the thermoplastic resin film. Glue, heat-shrinkable film by 0.03
An object of the present invention is to provide a method for producing a retardation plate, wherein the thermoplastic resin film is shrunk under the action of a heat shrinkage force of kg / mm ² or more.

[0005]

According to the present invention, a liquid crystal display device which is excellent in heat resistance, can highly compensate for a change in display characteristics due to a viewing angle based on birefringence of a liquid crystal cell, and has excellent visibility such as contrast in a wide viewing angle range. Can be obtained. Further, according to the method of the present invention, such a retardation plate can be obtained stably and efficiently, and continuous production is also possible.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The retardation plate according to the present invention satisfies the following formula: (nx + ny) / 2 <nz, where the in-plane main refractive index is nx and ny and the main refractive index in the thickness direction is nz. And the azimuth of the slow axis or the fast axis with respect to one of the vertical and horizontal directions is within 0 ± 5 degrees or within 90 ± 5 degrees.

In the above retardation plate, for example, a heat-shrinkable film is provided on one or both sides of a thermoplastic resin film, the maximum heat shrinkage direction of which is within 90 ± 5 degrees with respect to the width direction or length direction of the thermoplastic resin film. It can be manufactured by a method in which the thermoplastic resin film is adhered so as to have a crossing angle, and the thermoplastic resin film is shrunk under the action of a heat shrinkage force of 0.03 kg / mm ² or more by the heat shrinkable film.

[0008] As the film to be processed, one kind or two kinds
Those comprising at least one kind of appropriate thermoplastic resin can be used.
A resin made of a thermoplastic resin having a positive birefringence property and having a higher refractive index in the stretching direction than a point of obtaining a retardation plate having excellent heat resistance is preferably used.

Incidentally, examples of the above-mentioned thermoplastic resin having a positive birefringence characteristic include polycarbonate, polyvinyl alcohol, cellulose resin, polyester such as polyethylene terephthalate and polyethylene naphthalate, polyarylate, polyimide, norbornene resin, polysulfone. And polyolefins such as polyether sulfone and polypropylene.

[0010] Among them, a thermoplastic resin which is amorphous and has excellent heat resistance and excellent transparency and which can form a film having a light transmittance of 75% or more, especially 80% or more, especially 85% or more is preferable. Can be used. The thermoplastic resin film may be formed by an appropriate method such as a casting method such as a casting method or an extrusion method. A solution casting method such as a casting method is more preferable in that a film having less unevenness in thickness and uneven orientation is obtained.

The thickness of the thermoplastic resin film can be appropriately determined depending on the intended retardation and the like.
500 μm, especially 10 to 400 μm, especially 20 to 300 μm
m thickness. The phase difference can be obtained as the product (Δn × L) of the refractive index difference (Δn) and the optical path length (L).

[0012] The thermoplastic resin film may be formed into a predetermined size for the purpose of manufacturing a retardation plate for each product by batch processing or the like, or may be formed for continuous production of a retardation plate by continuous processing. It may be a film having a length. A long film can be preferably used from the viewpoint of the production efficiency of the retardation plate and the like. The thermoplastic resin film to be treated may be non-oriented, or may be an oriented film that has been subjected to an appropriate orientation treatment such as uniaxial stretching in advance.

A heat-shrinkable film adhered to one or both surfaces of a thermoplastic resin film transmits a shrinkage force due to the heating to the thermoplastic resin film and moves the thermoplastic resin film in the width direction (TD) under the action of the shrinkage force. ) Or length direction (M
D) or by contracting in both directions,
In particular, it aims at controlling the refractive index in the thickness direction.

Accordingly, as the heat-shrinkable film, an appropriate film exhibiting shrinkage by heat treatment can be used, and there is no particular limitation. In general, a uniaxially or biaxially stretched thermoplastic resin film or the like that starts thermal contraction at a temperature lower than the processing temperature of the thermoplastic resin film in terms of the transmission of shrinkage force and the like is used. In this case, the heat shrink force can be made different by changing the type of the thermoplastic resin and the stretching conditions such as the stretching ratio.

The thermoplastic resin forming the heat-shrinkable film includes, for example, polyvinyl chloride, polyethylene, polypropylene, polyester, polystyrene, polyamide and the like. In the above, from the viewpoint of the accuracy of the shrinkage treatment of the thermoplastic resin film, the glass transition temperature around the thermoplastic resin film, especially ±
A heat-shrinkable film exhibiting heat shrinkability in the range of 20 ° C. is preferably used.

An adhesive can be used for bonding the heat-shrinkable film and the thermoplastic resin film. Above all, the transferability of the heat-shrinkable film during the heat-shrinkage of the heat-shrinkable film, and the separation of the heat-shrinkable film after the shrinkage from the obtained retardation plate, that is, the processed product of the thermoplastic resin film after the shrinkage treatment An adhesive is preferably used from the viewpoint of properties and the like.

The pressure-sensitive adhesive may be any suitable one such as acrylic, silicone, polyester, polyurethane, polyether, or rubber, and is not particularly limited. A heat-shrinkable film is preferably used which forms an adhesive layer whose adhesive strength is hardly increased by heat shrinkage treatment.

The above-mentioned pressure-sensitive adhesive layer may be provided on one or both of the bonding surfaces when the thermoplastic resin film and the heat-shrinkable film are bonded, but when the formed retardation plate and the heat-shrinkable film are separated from each other. From the viewpoint of production efficiency and the like, it is preferable to be able to separate the heat-shrinkable film with the adhesive layer accompanying the heat-shrinkable film. Therefore, it is preferable to use the heat-shrinkable film in advance with the adhesive layer attached to the heat-shrinkable film.

The adhesive layer can be attached to the heat-shrinkable film by applying a pressure-sensitive adhesive to the heat-shrinkable film and drying the heat-shrinkable film. A method in which an adhesive layer provided on a separator is transferred to a heat-shrinkable film is more preferable than preventing a change in characteristics.

In the above case, the separator can be used as a protective cover for preventing the adhesive layer from being contaminated until the heat-shrinkable film is put into practical use by adhering the separator as it is. The surface of the heat-shrinkable film provided with the adhesive layer can be subjected to an appropriate surface treatment such as a corona treatment for the purpose of improving the adhesion to the adhesive layer.

In the present invention, the heat-shrinkable film is used in an amount of 0.03 kg / mm ² when shrinking the thermoplastic resin film.
One or two or more appropriate numbers are adhered to one or both surfaces of the thermoplastic resin film so that the above-mentioned heat shrink force acts. When the action of the heat shrinkage force is less than 0.03 kg / mm ^{2, the} force for shrinking (in-plane direction) the thermoplastic resin film is poor, and has the intended retardation characteristic by controlling the refractive index in the thickness direction. A phase difference plate cannot be obtained stably.

The bonding state of the heat-shrinkable film, which is preferable from the viewpoint of providing a desired retardation characteristic stably, is as follows.
0.04 kg / mm ² or more, in which inter alia 0.05 kg / mm ² or more heat shrinking force is to act. On the other hand, there is no particular limitation on the upper limit of the heat shrink force. Generally 5 kg / mm ² or less from the viewpoint of operability or the like during processing, especially 1kg
/ Mm ² or less, especially 0.5 kg / mm ² or less.

In the above, when bonding the heat-shrinkable film to the thermoplastic resin film, the maximum heat shrinkage direction of the heat-shrinkable film is within 90 ± 5 degrees with respect to the width direction or the length direction of the thermoplastic resin film. Are adhered so as to have an intersection angle of. Thereby, it is possible to obtain a retardation plate in which the original orientation angle of the used thermoplastic resin film is favorably maintained while suppressing the variation of the orientation angle due to shrinkage.

The above-mentioned orientation angle is defined as the azimuth angle of the slow axis or the fast axis with reference to one of the longitudinal and transverse directions of the thermoplastic resin film or the retardation plate. Particularly in the case of a thermoplastic resin film, it is defined as the azimuth of the slow axis with respect to the width (lateral) direction. Therefore, the suppression of the fluctuation of the orientation angle due to the shrinkage as described above means to obtain a retardation plate excellent in the uniformity of the orientation angle and having little variation. Incidentally, in the case of a retardation plate having a large variation in the orientation angle, when the retardation plate is combined with the retardation plate and applied to a liquid crystal cell, a problem such as a liquid crystal display device having poor contrast occurs.

In the above case, when the heat-shrinkable film is bonded to both surfaces of the thermoplastic resin film or when multiple layers are bonded to one surface, the heat-shrinkable films on the front and back surfaces and the upper and lower layers may be the same. It may be one having different heat shrinkage characteristics such as heat shrinkage.

The heat shrinkage treatment of the heat shrinkable film adhered to the thermoplastic resin film can be carried out via a suitable stretching machine such as a roll stretching machine, a tenter or a biaxial stretching machine. As described above, the treatment temperature is preferably in the vicinity of the glass transition temperature of the thermoplastic resin film, more preferably in the range of ± 20 ° C., particularly at or above the glass transition temperature, from the viewpoint of controllability of the treatment operation and the like.

The shrinking treatment given to the thermoplastic resin film under the action of the shrinking force of the heat shrinkable film by heating is as follows:
As described above, either one of the width direction and the length direction of the thermoplastic resin film may be used, or both may be used, and can be appropriately determined according to the retardation plate to be formed.

The control of the shrinkage processing direction in the width direction or the length direction can be performed through the difference in the shrinkage ratio between the width direction and the length direction in the heat-shrinkable film. That is, for example, in the width direction (length direction) rather than the length direction (width direction)
By using a heat-shrinkable film having a large shrinkage ratio, the thermoplastic resin film can be shrunk in a direction corresponding to the width direction (length direction).

In the above, when a shrinkage treatment is given in one of the width direction and the length direction, a stretching treatment can be given in the other direction. Further, the shrinking treatment given to the thermoplastic resin film under the action of the shrinking force of the heat shrinkable film can be performed in two or three or more steps.

After the necessary shrinkage treatment for the thermoplastic resin film is completed, the heat-shrinkable film after the shrinkage treatment is peeled off from the formed retardation film and separated therefrom. The obtained retardation plate can be used for practical use as it is, or can be put to practical use as a product obtained by further adjusting the retardation characteristics by adding a stretching treatment or the like.

The production method according to the present invention can be preferably applied to the formation of various retardation plates having retardation characteristics according to various uses. In particular, from the point that the refractive index in the thickness direction can be controlled, the viewing angle can be increased and the contrast can be increased in various display devices such as a TFT type and an MIM type using a liquid crystal cell exhibiting birefringence such as a TN type or an STN type. The present invention can be advantageously applied to the formation of a retardation plate suitable for compensating a phase difference due to birefringence for the purpose of improving the phase difference.

The retardation plate which can be preferably used for the compensation of the above-mentioned retardation has a formula (nx + ny) / 2 <, where the in-plane main refractive index is nx and ny and the main refractive index in the thickness direction is nz. nz is satisfied, and the orientation angle (the azimuth angle of the slow axis or the fast axis based on one of the vertical and horizontal directions) is within 0 ± 5 degrees or 90 ±.
Within 5 degrees.

The variation in the phase difference and the orientation axis (the orientation angle) due to birefringence is as small as possible. In particular, the variation in the phase difference in the transmitted light perpendicular to the film surface (in the front direction) is 10 nm or less. A retardation plate having a thickness of 8 nm or less, particularly 5 nm or less, and a variation in alignment axis of 8 degrees or less, particularly 5 degrees or less, and particularly 3 degrees or less can be preferably used for compensation of a phase difference.

The retardation plate can be used as a single layer or a laminate of the same type or different types. The lamination of the retardation plates is for the purpose of improving the compensation effect and the like, and in that case, the retardation plate according to the present invention and other retardation plates can be used. As the retardation plate, for example, an appropriate one such as a uniaxially or biaxially stretched thermoplastic resin film, a discotic or nematic liquid crystal alignment plate, or the like can be used.

When the retardation plate is put into practical use, for example, a retardation plate provided with an adhesive layer on one or both sides, a polarizing plate or an isotropic transparent resin layer or a glass layer via the adhesive layer It can also be used as an appropriate form such as a protective layer formed by bonding an adhesive layer. Lamination with a polarizing plate or the like can also be performed by a method of sequentially and separately laminating in the manufacturing process of the liquid crystal display device or the like, but by laminating in advance, the liquid crystal display device is excellent in quality stability and laminating workability. There is an advantage that the manufacturing efficiency can be improved.

The layers such as the above retardation plate, other polarizing plates and adhesive layers are made of, for example, an ultraviolet absorbing material such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, a nickel complex compound, or the like. UV absorption can also be imparted by a method of treating with an agent.

[0037]

Example 1 A stretched polyester film having a heat shrinkage of 0.11 kg / mm ² was attached to both sides of a long polyester film 65 μm thick by a belt casting method via an acrylic adhesive layer attached thereto. After adhering so that the maximum heat shrinkage direction of each sheet becomes a crossing angle of 88 degrees with the length direction of the long polyester film (counterclockwise is the positive direction, the same applies hereinafter), it is spread at 160 ° C through a tenter. The stretched polyester film was peeled off by applying a 9% shrinkage treatment in the direction, and the thickness was 71 μm.
m phase difference plates were continuously obtained.

Example 2 A stretched polypropylene film having a heat shrinkage of 0.07 kg / mm ² was applied to both sides of a long polycarbonate film having a thickness of 65 μm by belt casting via an acrylic adhesive layer attached thereto. After adhering so that the maximum heat shrinkage direction has a crossing angle of 93 degrees with respect to the width direction of the long polycarbonate film, it is passed through a 155 ° C. roll stretching machine at a roll speed ratio of 0.96 times in the length direction. The stretched polypropylene film was peeled off by performing a 4% shrinkage treatment, and a retardation plate having a thickness of 77 μm was continuously obtained.

Example 3 One sheet of a stretched polystyrene film having a heat shrinkage of 0.03 kg / mm ² was attached to both sides of a long polyester film having a thickness of 70 μm by a belt casting method via an acrylic adhesive layer attached thereto. Each of them was adhered so that the maximum heat shrinkage direction was at a crossing angle of 91 degrees with respect to the width direction of the long polyester film.
The stretched polystyrene film is subjected to a shrinkage treatment of 4% in the length direction and 5% in the width direction at 50 ° C., and the stretched polystyrene film is peeled off to a thickness of 75 μm.
Were continuously obtained.

Comparative Example 1 A stretched polyester film having a heat shrinkage force of 0.01 kg / mm ² was attached to both sides of a long polyester film having a thickness of 65 μm by a belt casting method via an acrylic adhesive layer attached thereto. Each of them was bonded so that the maximum heat shrinkage direction was at a crossing angle of 88 degrees with the length direction of the long polyester film, and then it was passed through a 155 ° C. roll stretching machine at a roll speed ratio of 0.96 times to lengthen. The stretched polyester film is peeled off by processing to shrink in the direction, and the thickness is 65 μm.
Were continuously obtained.

Comparative Example 2 A retardation having a thickness of 77 μm according to Example 2, except that the stretched polypropylene film was bonded so that the maximum heat shrinkage direction thereof was at an intersection angle of 80 degrees with the width direction of the long polycarbonate film. I got a board.

Evaluation Test The retardation plates obtained in the examples and comparative examples were measured by an automatic birefringence meter (KOBRA-21ADH, manufactured by Oji Scientific Instruments).
x, ny, nz are examined, and the formula: P = (nx + ny) /
The P value was calculated based on 2-nz, and the orientation angle was examined. The orientation angle was defined as a positive direction with a counterclockwise direction based on the azimuth angle with the slow axis, with the length (longitudinal) direction of the long film to be processed as a reference (0 degree).

The results are shown in the following table. nx ny nz P value Orientation angle (degree) Example 1 1.5853 1.5836 1.5860 -0.0016 -1.6 Example 2 1.5848 1.5831 1.5871 -0.0032 -88.1 Example 3 1.5850 1.5838 1.5862 -0.0018 0.5 Comparative Example 1 1.5854 1.5853 1.5843 0.0010 88.5 Comparative Example 2 1.5848 1.5831 1.5871 -0.0032 79.5

In Comparative Example 1, the shrinkage treatment set in Comparative Example 1 was not achieved, and a product satisfying the target characteristic of P <0 was not obtained. In the process of shrinkage treatment, tension between the rolls was not obtained, and the film meandered and running stability was poor. Further, in Comparative Example 2, a film satisfying the characteristics of the orientation angle within 0 ± 5 ° or 90 ± 5 ° was not obtained.

Each of the retardation films obtained in the above embodiments was disposed on both sides of the TN type liquid crystal cell, and a polarizing plate was placed thereon. The contrast in the front direction and the display characteristics due to the change in viewing angle were examined. There was no change in display characteristics over a wide viewing angle range, and the liquid crystal display device was high in display quality and excellent in visibility.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Kondo 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Tomomori Shoda 1-1-1, Shimohozumi, Ibaraki-shi, Osaka No. 2 Nitto Denko Corporation (72) Inventor Shinichi Sasaki 1-1-2 Shimohozumi, Ibaraki-shi, Osaka F-term in Nitto Denko Corporation (reference) BC22 2H091 FA11X FA11Z GA16 KA01 LA04 LA12

Claims (4)

[Claims] When the in-plane main refractive index is nx and ny and the main refractive index in the thickness direction is nz, the following formula is obtained: (nx + ny) / 2 <nz
Wherein the azimuth of the slow axis or the fast axis with respect to one of the vertical and horizontal directions is within 0 ± 5 degrees or within 90 ± 5 degrees. 2. A heat-shrinkable film is provided on one or both sides of a thermoplastic resin film such that the maximum heat shrinkage direction thereof has an intersection angle within 90 ± 5 degrees with respect to the width direction or length direction of the thermoplastic resin film. A method for producing a retardation plate, comprising: adhering and shrinking the thermoplastic resin film under the action of a heat shrink force of 0.03 kg / mm ² or more by the heat shrinkable film. 3. The production method according to claim 2, wherein the retardation plate is continuously obtained by using a long film made of a thermoplastic resin having a positive birefringence property as the thermoplastic resin film. 4. The method according to claim 2, wherein the thermoplastic resin film is shrunk in the width direction, the length direction, or both directions.