JP2000304924A - Phase plate and its continuous manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin phase difference plate which has superior manufacture efficiency and heat resistance and can fully compensate the birefringence by a liquid crystal cell. SOLUTION: This method is a continuous manufacturing method for the phase plate which adhering one or more heat-shrinkable films to one or both surfaces of a long-sized film made of thermoplastic resin and shrinking the long-sized film along the width at A×0.7 to 1.0 scale factor A by making the shrinkage force of the heat-shrinkable film act on the film while it is gripped by a tenter, and then drawing and increasing the width at a drawing rate (%) satisfying <=(100-rate A×10)×0.15, where the film width excluding the grip part after the shrinkage process is 100. Further, -1.0<Nz<0.1 holes for Nz defined by (nx-nz)/(nx-ny), where nx and ny are the main refractive indexes in a plane, nz is the main refractive index in the thickness direction, and nx>ny; and deviation of the optical axis in the plane is <=±3 deg..

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 continuously producing the retardation plate.

[0002]

BACKGROUND OF THE INVENTION For the purpose of preventing a change in contrast or the like due to a viewing angle due to birefringence caused by a liquid crystal, a technique for improving a viewing angle characteristic by compensating optical characteristics based on birefringence by disposing a retardation plate in a liquid crystal cell has been developed. Proposed. Such a compensating retardation plate is usually made of a uniaxially or biaxially stretched film, but no satisfactory film is currently provided.

[0003] In a case where a film made of a thermoplastic resin having negative birefringence such as polystyrene, that is, a film made of a thermoplastic resin having a property of increasing the refractive index in a direction perpendicular to the stretching direction, is biaxially stretched, It is difficult to obtain a material having excellent heat resistance such as use. In addition, the uniaxially stretched film of the resin needs to be laminated by using two or more sheets, and there is a disadvantage that the production efficiency such as control of the optical axis is poor.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin retardation plate which is excellent in manufacturing efficiency and heat resistance and can highly compensate for birefringence caused by a liquid crystal cell.

[0005]

According to the present invention, one or more heat-shrinkable films are bonded to one or both sides of a long film made of a thermoplastic resin, and the heat-shrinkable films are gripped by a tenter under gripping. To shrink the width direction of the long film at a magnification A of 0.7 times or more to less than 1.0 time by applying a contraction force of And the formula: (100−
It is intended to provide a continuous production method of a retardation plate, wherein the width direction is stretched and stretched at a stretching ratio (%) satisfying a ratio of (A × 100) × 0.15 or less.

In the present invention, the in-plane principal refractive index is nx, n.
y, when the main refractive index in the thickness direction is nz and nx> ny, N defined by the formula: (nx-nz) / (nx-ny)
It is an object of the present invention to provide a retardation plate characterized in that z satisfies -1.0 <Nz <0.1 and a deviation of an optical axis in a plane is within ± 3 degrees.

[0007]

According to the method of the present invention, the aforementioned
1.0 <Nz <0.1 is satisfied, and a thin retardation plate having a deviation of the optical axis within ± 3 degrees can be obtained with high manufacturing efficiency, and display using a viewing angle based on birefringence of a liquid crystal cell using the thin retardation plate. It is possible to obtain a liquid crystal display device having excellent visibility such as contrast over a wide viewing angle range by highly compensating for a change in characteristics.
Further, a retardation plate excellent in heat resistance can be obtained by using a film made of a thermoplastic resin having a positive birefringence characteristic.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The continuous production method according to the present invention is characterized in that one or two or more heat-shrinkable films are adhered to one or both sides of a long film made of a thermoplastic resin, and the heat-shrinkable film is gripped by a tenter. After applying the contraction force of the heat-shrinkable film to contract the width direction of the long film at a magnification A of 0.7 times or more to less than 1.0 times, the grip gripping part after the contraction treatment was removed. The film width is stretched and stretched in the width direction at a stretching ratio (%) satisfying the formula: (100−magnification A × 100) × 0.15 or less, with the film width being 100, to continuously obtain a retardation plate. is there.

As a long film to be processed, a stretchable film made of a thermoplastic resin is used.
From the viewpoint of obtaining a retardation plate having excellent heat resistance, a resin made of a thermoplastic resin having a positive birefringence property and having a high refractive index in the stretching direction is preferably used.

There is no particular limitation on the thermoplastic resin having the above-mentioned positive birefringence property, and any suitable thermoplastic resin can be used.
Incidentally, examples thereof include polycarbonate, polyvinyl alcohol, cellulose resin, polyester such as polyethylene terephthalate and polyethylene naphthalate, polyarylate, polyimide, norbornene resin, polyolefin such as polysulfone, polyether sulfone, and polypropylene. Above all, a thermoplastic resin which is amorphous and has excellent heat resistance and excellent transparency, and particularly capable of forming a film having a light transmittance of 80% or more can be preferably used.

The long 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 long film can be appropriately determined depending on the intended retardation and the like, but is generally 10 to 500 μm.
m, especially 20 to 300 μm.

As the heat-shrinkable film, there can be used, for example, an appropriate film made of a uniaxially or biaxially stretched film made of a thermoplastic resin, and is not particularly limited. What consists of a thermoplastic resin excellent in surface smoothness and the shrinkage controllability of the width direction of a long film is used preferably.

The heat-shrinkable film can be adhered to one or both sides of the long film in an appropriate number of one or two or more depending on the shrinkage force or the like. The adhesion treatment is preferably an adhesion treatment with an adhesive layer from the viewpoint of easy releasability after shrinking the long film in its length direction and width direction under the action of shrinkage force due to heating. As the pressure-sensitive adhesive layer, an appropriate material that exhibits a necessary adhesive force at the shrinkage temperature of the heat-shrinkable film can be used.

The heat-shrinkable film adhered to the long film is shrunk under gripping by a tenter through a grip. The processing temperature is preferably in the vicinity of the glass transition temperature of the long film, especially within the range of ± 20 ° C. of the glass transition temperature from the viewpoint of controllability of the processing operation. From this point, it is preferable that the heat-shrinkable film used starts heat-shrinkage at a temperature lower than the processing temperature.

The shrinking process of the long film through the shrinking force of the heat shrinkable film is performed based on the original 0.7 mm width direction.
This is performed so that the magnification A is equal to or more than 2 times and less than 1.0 times. As a result, a retardation plate satisfying the above-mentioned condition of −1.0 <Nz <0.1 can be obtained. If the stretching ratio A is out of the range, it is difficult to satisfy the Nz. The N
z is a formula: (nx−n) where the in-plane main refractive index is nx, ny, the main refractive index in the thickness direction is nz, and nx> ny.
z) / (nx−ny) (the same applies hereinafter).

On the other hand, in the present invention, even after the above-described shrinking treatment, the holding of the long film via the grip by the tenter is continued, and the width direction thereof is stretched and widened. Therefore, in the present invention, after the long film is contracted in the width direction, the width is increased through the stretching process. This makes it possible to obtain a retardation plate that satisfies -1.0 <Nz <0.1 and has a small deviation of the optical axis in the plane, in particular, the deviation is within ± 3 degrees.

That is, when a film made of a thermoplastic resin having a positive birefringence characteristic is gripped at both ends of a film width through a grip of a tenter and shrunk in the width direction, the restricting force of deformation by the grip is long. The transport speed differs in the width direction of the film differently between the direction and the central portion of the film, thereby causing a deviation of the optical axis in the plane. The deviation of the optical axis lowers the contrast of the liquid crystal display device, and the TN
In the TFT driving method including the mode, the OCB mode, the VA mode, and the like, the contrast is more affected than the phase difference unevenness.

In the above, after the long film is shrunk in the width direction and then the width is widened by a stretching process, the contraction / stretching in the length direction and the width direction of the long film are balanced, and the optical axis of the shrinking process is reduced. The deviation has been corrected, resulting in -1.
A retardation plate satisfying 0 <Nz <0.1 and having a small deviation of the optical axis can be obtained.

In the above-mentioned widening process, when the width of the long film excluding the grip gripping portion after the shrinkage process is set to 100, a stretching ratio satisfying the following formula: (100−magnification A × 100) × 0.15 or less. (%).
If the stretching ratio exceeds the above range, bowing distortion occurs, and the deviation of the optical axis becomes rather large.

As described above, the retardation plate according to the present invention has
1.0 <Nz <0.1, and a deviation of the optical axis in the plane is within ± 3 degrees. Such a retardation plate is formed as a single-layered material in terms of thinning and the like. It is preferable that they are formed as a laminate of the same or different retardation plates. Further, it may be protected or reinforced with an isotropic transparent resin layer or glass layer.

The phase difference plate according to the present invention is of a TN type or a TN type, for example, for compensating for the phase difference in the oblique direction in which the contrast is prevented from decreasing in the front direction, and for compensating for the phase difference in the front direction and the oblique direction. It can be preferably used for compensating viewing angle characteristics due to birefringence in various types of liquid crystal cells such as STN type and π type.

The retardation plate can be used as an optical member laminated with an appropriate optical layer such as a polarizing plate, a diffusion plate, an antiglare layer or an antireflection film, a protective layer or a protective plate in practical use. Further, the formation of a liquid crystal display device using such a retardation plate can be performed according to a conventional method.

That is, the liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal cell, a retardation plate for optical compensation, and a polarizing plate and an illumination system as required, and incorporating a driving circuit. However, in the present invention, as described above, there is no particular limitation except that the retardation plate according to the present invention is used for optical compensation and provided on at least one side of the liquid crystal cell, and a configuration similar to the conventional one is used. Liquid crystal display device.

[0024]

EXAMPLE 1 20% by weight of methylene dichloride of polycarbonate having a molecular weight of about 80,000 and comprising a polycondensate of phosgene and bisphenol A
The solution was continuously cast on a steel drum, which was sequentially peeled off and dried to obtain a polycarbonate film having a thickness of 60 μm and a phase difference of almost 0, and a biaxially stretched polyester film was acrylic-coated on both sides of the film. Adhering through a system adhesive layer, 168
1.2% after shrinking the width direction 0.88 times at ℃
The biaxially stretched polyester film is peeled by stretching at a stretching ratio of [(100−0.88 × 100) × 0.1],
A retardation plate was obtained.

Example 2 0.4% after shrinking 0.92 times in the width direction at 162 ° C.
A retardation plate was obtained in the same manner as in Example 1 except that the film was stretched at a stretching ratio of [(100-94) × 0.067].

Comparative Example 1 A retardation film was obtained in the same manner as in Example 1 except that the film was shrunk in the width direction at 164 ° C. by 0.88 times and the subsequent stretching treatment was not performed.

Comparative Example 2 After shrinking 0.9 times in the width direction at 160 ° C., 2.2%
A retardation plate was obtained in the same manner as in Example 1 except that the film was stretched at a stretch ratio of [(100−0.9 × 100) × 0.22].

Evaluation Test For the retardation films obtained in Examples and Comparative Examples, the main refractive indices nx, ny, and nz in the film plane and in the thickness direction were measured using an Abbe refractometer (manufactured by Atago Co., Ltd.) using a sodium D line as a light source. , 4 type), and Nz was calculated, and the deviation of the optical axis in the film plane was examined (ADR-100X, manufactured by Oak Manufacturing Co., Ltd.).
Y).

The above results are shown in the following table. Example 1 Example 2 Comparative Example 1 Comparative Example 2 Nz −0.43 −0.13 −0.61 −0.40 Optical axis shift (degree) ± 2.0 ± 1.0 ± 4.0 ± 6. 0

Polarizing plates were arranged on both sides of the TN type liquid crystal cell via the retardation films obtained in Examples 1 and 2, and the display characteristics due to the contrast in the front direction and the change in the viewing angle were examined. There was no change in the display characteristics over a wide viewing angle range, and the liquid crystal display device was of high 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 Hiroyuki Yoshimi 1-1-2 Shimohozumi, Ibaraki-shi, Osaka No. NITTO DENKO CORPORATION F-term (reference) 2H049 BA06 BB23 BB42 BB54 BC03 BC09 BC22 2H091 FA11X FA11Z FB02 FC07 FD14 LA04 LA12 LA19 4F210 AA24 AA28 AE01 AG01 AH73 QA02 QC03 QG01 QG15 QG18 A01A01 AE03

Claims (3)

[Claims] 1. One or two or more heat-shrinkable films are adhered to one or both sides of a long film made of a thermoplastic resin, and the shrinkage force of the heat-shrinkable film is applied while gripping by a tenter. Then, after shrinking the width direction of the long film at a magnification A of 0.7 times or more to less than 1.0 time, the film width excluding the gripping portion after the shrinking process is set to 100, and the following formula: 100-magnification A × 10
0) A method for continuous production of a retardation plate, wherein the width direction is stretched and stretched at a stretching ratio (%) satisfying 0.15 or less. 2. The continuous production method according to claim 1, wherein the thermoplastic resin forming the long film and the heat-shrinkable film has a positive birefringence characteristic. 3. When the in-plane main refractive index is nx, ny, the main refractive index in the thickness direction is nz, and nx> ny, the following formula is obtained.
Nz defined by (nx-nz) / (nx-ny) is -1.
A retardation plate, wherein 0 <Nz <0.1 is satisfied, and a deviation of an optical axis in a plane is within ± 3 degrees.