JPH09230141A - Production of optical compensation film, optical compensation film and liquid crystal display element formed by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the smoothness of a film surface, to lessen unequal orientation and to accelerate the deorientation of molecular chains by applying specified tension on a film in the direction perpendicular to the major axis direction of the refractive index ellipse within the film plane and heat treating the film is a temp. atmosphere below the glass transition point (Tg) temp. SOLUTION: The major axis direction of the refractive index ellipse within the film plane is fixed in parallel with the fixed ends by jigs which uniformly press only a pair of both ends facing each other of the thermoplastic film. The film is then heat treated by applying specified tension thereon in the direction perpendicular to the fixed ends under the conditions under which the spacing LMD at both ends of the fixed film and the spacing LTD at both ends not subjected to the restriction by the jigs attains LMD/LTD>1.0. The major axis direction of the refractive index ellipse in the plane is, therefore, changed 90 deg.. As a result, the optical compensation film which is 5nm<=|nx -ny |×d<=80nm when the main refractive index are defined as nx , ny and the thickness is defined as d, is <=10% in the deflection width thereof and has excellent smoothness and the liquid crystal display element formed by using the same are obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensation film, and more particularly to improvement of display contrast of a liquid crystal display device and high definition of display.

[0002]

2. Description of the Related Art CRTs, which are the mainstream of display devices for office automation equipment such as word processors and desktop personal computers, have been converted into liquid crystal display elements having the great advantages of thinness, light weight, and low power consumption. Most of the liquid crystal display devices that are currently popular use twisted nematic liquid crystals. Display methods using such a liquid crystal can be roughly classified into two methods, a birefringence mode and an optical rotation mode.

A liquid crystal display element using a birefringence mode is a super twisted nematic (hereinafter referred to as STN)
A mode is a mode in which the twist angle of the liquid crystal molecule array is twisted by 90 ° or more. Since STN has steep electro-optical characteristics,
A large capacity display can be obtained even with a simple matrix electrode structure. However, it has a drawback that the response speed is slow and gradation display is difficult, and it does not exceed the performance of a liquid crystal display device using a thin film transistor or a diode.

A liquid crystal display element (TFT-LCD, MIM-LCD) using a thin film transistor or a diode is an optical rotation mode display element in which the molecular alignment state of liquid crystal molecules is twisted by 90 ° and has a high response speed and gradation display. Since it is possible and the display contrast is high, it is considered to be the most effective method as a liquid crystal display element.

A liquid crystal display element utilizing an optical rotation mode (hereinafter referred to as TN) is composed of a liquid crystal cell in which TN liquid crystal is sealed between two substrates and polarizing plates arranged on both sides thereof. Furthermore, there are two types of TN type liquid crystal display devices depending on the arrangement of polarizing plates. A method of making two polarizing plates parallel is called a normally black (NB) mode, and a method of making two polarizing plates orthogonal is normally. It is called the white (NW) mode. NW for high-definition / high-quality display elements and projection display devices
Modes are often used. This is because the NB mode has a problem that the chromaticity change easily occurs in the vicinity of black display, and the NW mode does not have such a problem. Although the chromaticity change occurs in the vicinity of white display, it is not so noticeable. Is.

When displaying black in the NW mode, when natural light enters the incident side polarization plate, only linearly polarized light is emitted and enters the liquid crystal cell. When a driving voltage is applied to the liquid crystal cell, the liquid crystal molecules near the center of the liquid crystal layer rise almost vertically to the substrate, but the liquid crystal molecules near the substrate interface do not rise completely because the anchoring effect of the substrate is strong. In this case, since there is a slight birefringence in the liquid crystal cell,
Light emitted from the liquid crystal cell becomes elliptically polarized light. For this reason, a slight amount of light leaks from the exit side polarization plate disposed orthogonal to the entrance side polarization plate, and the black display level is lowered. From the above results, the contrast is deteriorated, and the display performance of the CRT is not exceeded even in the promising TFT-LCD.

A method of optically compensating the birefringence generated when the liquid crystal of the TN type liquid crystal cell is driven by a retardation plate (for example,
JP-A-6-148628) has been proposed,
In order to optically compensate the retardation generated by the liquid crystal cell, it is necessary to make the thickness unevenness of the retardation plate and the orientation unevenness of the molecular chains uniform, but since the phase difference caused by the liquid crystal cell is very small, The film that compensates for the phase difference needs to have a low birefringence to the extent that it can be called a non-birefringent film, and it is very difficult to obtain a retardation plate with a uniform in-plane birefringence state in a large area. . Due to the problems in manufacturing the retardation plate as described above, the contrast on the entire surface of the panel is not sufficiently improved.

As a method for making the in-plane retardation uniform, a method for producing a retardation film stretched by a tenter transverse uniaxial stretching machine (for example, JP-A-2-42406 and JP-A-6-51118). Although it has been proposed, it has not yet been possible to uniformly manufacture a slight phase difference.

[0009]

The object of the present invention is to set the main refractive index to n _x and n _y and the thickness to d to be 5 nm.
≦ | n _x -n _y | × is in its amplitude is 10% or less by d ≦ 80 nm, there is provided an optical compensation film excellent in smoothness and liquid crystal display device using the same.

[0010]

According to the present invention, (1) a jig for uniformly pressing only a pair of opposite ends of a thermoplastic resin film is used to fix the long-axis direction of a refractive index ellipsoid in the film plane at a fixed end. And the distance L _MD between both ends of the fixed film and the distance L _TD between both ends of the film, which is not restricted by a jig, are L _MD / L _TD > 1.0, and A method for producing an optical compensation film, characterized in that the longitudinal direction of the in-plane refractive index ellipsoid is converted by 90 ° by applying a constant tension in the direction perpendicular to the heat treatment, and (2) the heat treatment temperature is The method for producing an optical compensation film according to item (1), wherein the temperature is equal to or higher than the temperature at which the linear expansion coefficient of the thermoplastic resin film increases and lower than the glass transition point of the thermoplastic resin, (3) item (1) or The optical compensation filter described in item (2). Obtained by the production method of the beam, the main refractive indices n _x in the plane of the optical compensation film, n _y, the thickness d
And 5 nm ≦ | n _x −n _y | × d ≦ 80 nm, and the deflection width is 10% or less, (4) Item (1) or (2) Obtained by the method for producing an optical compensation film, the deflection width of the optical principal axis of the in-plane refractive index ellipsoid of the optical compensation film is ± 1.0 °.
An optical compensation film characterized by being (5)
The thermoplastic resin according to item (1) or (2) is triacetate, diacetate, cellophane, polyether sulfone, polyether ether sulfone, polysulfone,
Item (3) which is one or more thermoplastic resins selected from the group consisting of polyetherimide, polycarbonate, polyester, polyvinyl alcohol, polyarylate, polymethylmethacrylate, vinylidene fluoride, and polystyrene. (4) The optical compensation film according to item (4), (6) a liquid crystal cell in which a TN type liquid crystal is sandwiched between two electrode substrates, two polarizing elements arranged on both sides of the liquid crystal cell, and a polarizing element of the polarizing element. In between, at least one or more (3)
A liquid crystal display device, comprising the optical compensation film according to any one of items (1) to (5).

In the present invention, the relationship between the principal in-plane refractive indices n _x and n _y of the thermoplastic resin film is as follows: the refractive index in the film width direction is n _x and the refractive index in the film stretching direction is n _y.
At that time, by applying a constant tension in a direction perpendicular to the long axis direction of the in-plane refractive index ellipsoid, and heat-treating,
n _x> (90 ° in the major axis direction transformation plane refractive index ellipsoid) converting the refractive index relationship of n _y in the refractive index relationship of n _x <n _y and, 5 nm ≦ when the thickness was d | n _x -n _y | × is in its amplitude is 10% or less by d ≦ 80 nm, it is possible to produce a good optical compensation film smoothness.

Further, in the present invention, when the thermoplastic resin film is fixed by a jig that uniformly presses only opposite ends of the thermoplastic resin film, and a constant tension is applied in a direction perpendicular to the fixed end, the film is fixed. When the distance between both ends is L _MD and the distance between both ends of the film which is not restricted by a jig is L _TD , L _MD / L _TD > 1.0, and the temperature at which the coefficient of linear expansion increases from the glass transition point. By heat treatment under conditions of a low temperature range, to control the magnitude of the birefringence index in the film plane and the long axis direction of the refractive index ellipsoid without impairing the smoothness of the film,
When the thickness is d, 5 nm ≦ | n _x −n _y | × d ≦ 80 nm, the deflection width is 10% or less, and the deflection width of the optical principal axis of the index ellipsoid in the film plane is ± 1. An optical compensation film of 0 or less can be produced.

Further, in the present invention, the distance L _MD between both ends of the fixed film is set sufficiently long with respect to the distance L _TD between the free ends and the film is heated so that the film to be heat treated is not biaxially stretched. Glass is applied from the temperature (hereinafter abbreviated as Tg-) at which tension is applied within the range where the film is not deformed, and the molecular chains that make up the film thermoplastic resin start micro Brownian motion and the linear expansion coefficient of the film starts to increase. By heat-treating at a temperature lower than the transition point (Tg), preferably 10 ° C. to 30 ° C. lower than the glass transition point, the appearance is not impaired and the birefringence of the film and the refractive index ellipsoid of the film are reduced. controls longitudinally, 5 nm ≦ when the thickness was d | n _x -n _y | its amplitude at × d ≦ 80 nm is 10
% Or less, and further, an optical compensation film having a deflection width of the optical main axis of ± 1.0 ° or less can be manufactured.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A method for producing the optical compensation film of the present invention will be described. The process of manufacturing the optical compensation film is performed by film formation and stretching. The method for forming a thermoplastic resin film includes a melt film forming method and a solution film forming method, but if film thickness unevenness and orientation unevenness that affect the optical characteristics of the optical compensation film do not occur, the film forming method according to the present invention There are no restrictions on the membrane. However, in melt film formation, during film cooling, in solution film formation, during film drying,
Due to the strain due to the tension applied to the film during the film transport process, a phase difference of more than 80 nm occurs, and the film of the present invention cannot be obtained.

When the thermoplastic resin film exhibits a retardation, the formed film can be thermally relaxed at Tg or higher to remove the birefringence, but the molecular chain constituting the film is deorientated with high mobility. Due to the behavior, the smoothness of the film surface is lost.

Further, in the film transporting process during film formation, even if the retardation is suppressed by suppressing the tension as much as possible, the uniaxial stretching in the longitudinal direction or the uniaxial stretching in the transverse direction in a temperature atmosphere of Tg or higher gives a highly accurate stretching. be used, the molecular chains constituting the film is rich in fluidity, the phase difference is 5 nm ≦ as in the present invention | it is difficult to obtain a × optical compensation film of d ≦ 80nm | n _x -n _y .

According to the present invention, in a thermoplastic resin film, a constant tension is applied in a direction perpendicular to the long axis direction of the in-plane refractive index ellipsoid of the film, and heat treatment is performed in an atmosphere at a temperature lower than Tg. The index ellipsoid is gently stretched in the minor axis direction. This acts on the effect of reducing the anisotropy of the refractive index in the film plane, and therefore reduces the in-plane alignment unevenness while maintaining the smoothness of the film surface and promotes the deorientation of the molecular chains. Further, when a constant tension is continuously applied in an atmosphere of a temperature lower than Tg, the molecular difference exhibits a gentle flow orientation in the tension direction, so that birefringence occurs. By continuously performing the disorientation and reorientation of the molecular chains at an ambient temperature of less than Tg as described above, 5 nm ≦ of the present invention | n _x -n _y
An optical compensation film having a characteristic of | × d ≦ 80 nm can be obtained.

When the thermoplastic resin film is heat-treated under the setting of L _MD / L _TD ≦ 1.0, not when L _MD / L _TD > 1.0 of the present invention, the fixed interval is short. Even when the tension is applied only in one direction, biaxially oriented tensile stress is generated in the film plane.
Therefore, the ideal uniaxial orientation of the polymer chain is suppressed, and the orientation angle distribution of the polymer chain is developed in the width direction of the film. Since the optical principal axis of the index ellipsoid largely depends on the molecular chain orientation angle, the degree of freedom of molecular chain orientation is not controlled in one direction under the condition of L _MD / L _TD ≦ 1.0 for the film. The optical principal axis is not made uniform.

The thermoplastic resin that becomes the film is L _MD / L _TD
When the heat treatment is performed at a temperature higher than 1.0 when the heat treatment is performed under the condition of> 1.0, the polymer chains constituting the film have a high fluidity, so that the molecular chain orientation in the film flow direction easily occurs and the optical Although the main axis is made uniform, an increase in birefringence occurs due to film stretching, and the 5n
m ≦ | n _x -n _y | it is difficult to obtain an optical compensation film having characteristics × d ≦ 80 nm.

Further, even if the temperature of the heat treatment is lower than the temperature range from Tg- of the film to less than Tg, the micro-Brownian motion of the molecular chain is frozen and only local molecular vibration occurs. Chain orientation is less likely to occur,
In some cases, homogenization of the optical principal axis is not confirmed.

The deflection width of the optical principal axis shows a variation in molecular chain orientation and is ± 1.0 ° or less, preferably ± 0.1 ° or less. However, if the deflection width of the optical principal axis is too large,
Since the phase difference generated from the liquid crystal cell is not uniformly compensated on the entire panel surface, deviation occurs in the compensation performance of the optical compensation film and partial light leakage occurs.
As a result, deviation of black display occurs in the TN type liquid crystal display element, resulting in uneven contrast, which is not preferable.

As the thermoplastic resin in the present invention, triacetate, diacetate, cellophane, polyether sulfone, polyether ether sulfone, polysulfone, polyetherimide, polycarbonate, polyester, polyvinyl alcohol, polyarylate, polymethyl methacrylate, Examples thereof include vinylidene fluoride, polystyrene, and resins obtained by blending these.
The resin in the present invention may contain a small amount of stabilizers, lubricants, dyes and the like as additives.

The thickness of the optical compensation film in the present invention is preferably 10 μm to 500 μm, more preferably 50 μm to 400 μm from the viewpoint of workability and flexibility. Further, the surface roughness of the film in the present invention is preferably 0.5 μm or less, and more preferably 0.1 μm or less. When the surface roughness is larger than 0.5 μm, optical phase unevenness occurs and display unevenness of the liquid crystal display element is remarkably confirmed.

According to the present invention, a thermoplastic resin film is continuously dealigned with a refractive index anisotropic material under constant tension at a temperature of L _MD / L _TD > 1.0 and lower than the glass transition point. And re-orientation, 5nm ≦ | n _x without losing the smoothness of the film.
-N _y | has characteristics of × d ≦ 80 nm, it is possible distribution of the optical principal axis to produce a small optical compensation film, further, by applying to the TN-type liquid crystal display device,
A liquid crystal display device having high contrast and no display unevenness can be obtained. The heating time, heating temperature and tension of the heat treatment are determined by the material and thickness of the synthetic resin used for the film substrate.

[0025]

The present invention will be described below with reference to examples and comparative examples. The optical properties of the film of the present invention were measured by the following methods. (1) Birefringence Using a polarizing microscope BH2 manufactured by Olympus Optical Co., Ltd. and a Berek compensator, the optical phase difference at a wavelength of 550 nm was measured. (2) Optical principal axis After measuring the photoelastic sensitivity with a photoelasticity measuring device, the optical principal axis was measured by examining the phase increasing axis and slow axis of the index ellipsoid using a Berek compensator.

Example 1 Polyethersulfone resin of Sumitomo Chemical Co., Ltd .: Victorex PES4100G
(Tg = 226 ° C.) was formed into a film by the melt extrusion method. The obtained film had a Tg- of 180 ° C., an in-plane retardation of the film of 15 nm, a film thickness of 95 μm, and an optical axis swing range of ± 23 °. The apparatus used was a hot-air dryer in which a film was uniformly chucked and a fixing jig having only one end movable was attached. The film was fixed so that the major axis direction of the index ellipsoid was orthogonal to the direction in which a constant tension was applied, and the heat treatment was performed with a weight applied to one of the movable film fixing parts and a constant tension applied to the film. . The film was attached with L _MD / L _TD = 3, and heat-treated for 4 minutes under the conditions that the processing temperature was 216 ° C. and the film tension due to weighting was 6.3 gf / mm. The polyether sulfone film after the heat treatment had a retardation of 17 nm in which the retardation was developed in the tension direction, and the deflection width of the optical principal axis was ± 0.5 ° or less, and the appearance was good.

Example 2 By the same method as in Example 1, the in-plane retardation of the film was 15 nm, the film thickness was 95 μm,
A polyether sulfone having an optical axis deflection range of ± 23 ° was produced. This film was attached with L _MD / L _TD = 10, processing temperature was 216 ° C, and film tension due to loading was 7.2 gf.
/ Mm, a tension was applied in a direction orthogonal to the major axis direction of the refractive index ellipsoid of the film, and heat treatment was performed for 4 minutes.
After heat treatment, the polyether sulfone film has a phase difference of 19 nm in the tension direction, and the deflection range of the optical axis is ±
The appearance was good at 0.1 ° or less.

Example 3 By the same method as in Example 1, the in-plane retardation of the film was 15 nm, the film thickness was 95 μm,
A polyether sulfone having an optical axis deflection range of ± 23 ° was produced. This film was attached with L _MD / L _TD = 10, processing temperature was 216 ° C, and film tension due to loading was 11.1 g.
Under the condition of f / mm, tension was applied in a direction orthogonal to the major axis direction of the refractive index ellipsoid of the film, and heat treatment was performed for 4 minutes. The polyether sulfone film after the heat treatment had a phase difference of 30 nm in which the retardation was developed in the tension direction, and the deflection width of the optical principal axis was ± 0.1 ° or less, and the appearance was good.

Example 4 By the same method as in Example 1, the in-plane retardation of the film was 15 nm, the film thickness was 95 μm,
A polyether sulfone having an optical axis deflection range of ± 23 ° was produced. This film was attached with L _MD / L _TD = 10, the processing temperature was 216 ° C, and the film tension due to loading was 24.1 g.
Under the condition of f / mm, tension was applied in a direction orthogonal to the major axis direction of the refractive index ellipsoid of the film, and heat treatment was performed for 4 minutes. The polyether sulfone film after the heat treatment had a phase difference of 64 nm in the tension direction, and the deflection width of the optical principal axis was ± 0.1 ° or less, and the appearance was good.

Comparative Example 1 By the same method as in Example 1, the in-plane retardation of the film was 15 nm, the film thickness was 95 μm,
A polyether sulfone having an optical axis deflection range of ± 23 ° was produced. This film was attached with L _MD / L _TD = 3, the processing temperature was 236 ° C, and the film tension due to loading was 6.3 gf.
/ Mm, a tension was applied in a direction orthogonal to the major axis direction of the refractive index ellipsoid of the film, and heat treatment was performed for 4 minutes.
The polyether sulfone film after the heat treatment had a deflection of the optical main axis of ± 0.1 ° or less and a good appearance, but a retardation was developed in the tension direction and was 158 nm.

Comparative Example 2 By the same method as in Example 1, the in-plane retardation of the film was 15 nm, the film thickness was 95 μm,
A polyether sulfone having an optical axis deflection range of ± 23 ° was produced. This film was heat-treated for 4 minutes under the conditions of L _MD / L _TD = 1, treatment temperature of 216 ° C. and film tension of 6.3 gf / mm. The heat-treated polyether sulfone film had a phase difference of 18 nm in the tension direction and a good appearance, but the deflection of the optical principal axis was ± 24 °.

When the optical compensation films of Examples 1 to 4 and Comparative Examples 1 and 2 are arranged at an optimum angle for a NW mode TN type liquid crystal display element, the result of measuring the white illuminance / black illuminance ratio as contrast is shown. It shows in Table 1.

[0033]

[Table 1] * 1 Contrast of TN type liquid crystal display element only. * 2 The TN-type liquid crystal display element was provided with the film of the present invention which was not heat-treated.

[0034]

According to the present invention, the phase difference is 5 nm ≦ | n _x −n
An optical compensation film characterized in that _y | × d ≦ 80 nm and its deflection width is 10% or less, and the deflection width of the optical principal axis is ± 1.0 ° or less can be produced. By applying to active drive TN type liquid crystal display element,
A high-contrast and high-definition liquid crystal display device can be provided.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication // C08J 5/18 C08J 5/18

Claims (6)

[Claims] 1. A fixed film in which the major axis direction of the refractive index ellipsoid in the film plane is fixed in parallel to the fixed end by a jig that uniformly presses only a pair of opposite ends of the thermoplastic resin film. The distance L _MD between both ends and the distance L _TD between both ends of the film that is not restricted by the jig are L _MD / L _TD
The optics characterized in that the major axis direction of the in-plane ellipsoid of the in-plane is converted by 90 ° by applying a constant tension in a direction perpendicular to the fixed end and performing heat treatment under the condition of> 1.0. Compensation film manufacturing method. 2. The method for producing an optical compensation film according to claim 1, wherein the temperature for the heat treatment is not less than the temperature at which the linear expansion coefficient of the thermoplastic resin film increases and less than the glass transition point of the thermoplastic resin. 3. The optical compensatory film obtained by the method for producing an optical compensatory film according to claim 1 or 2, wherein the in-plane main refractive indices are n _x and n _y , and the thickness is d, 5 nm ≦ | n _x −
An optical compensation film, characterized in that n _y | × d ≦ 80 nm and the deflection width is 10% or less. 4. The deflection width of the optical principal axis of the in-plane refractive index ellipsoid of the optical compensation film obtained by the method for producing an optical compensation film according to claim 1 or 2, is ± 1.0 ° or less. An optical compensation film characterized by: 5. The thermoplastic resin according to claim 1 or 2, wherein the thermoplastic resin is triacetate, diacetate, cellophane, polyether sulfone, polyether ether sulfone, polysulfone, polyetherimide, polycarbonate, polyester, polyvinyl alcohol, polyarylate, The optical compensation film according to claim 3, which is one or more thermoplastic resins selected from the group consisting of polymethyl methacrylate, vinylidene fluoride, and polystyrene. 6. A liquid crystal cell in which a TN type liquid crystal is sandwiched between two electrode substrates, two polarizing elements arranged on both sides of the liquid crystal cell, and at least one or more elements are provided between the polarizing elements. Item 3. A liquid crystal display device comprising the optical compensation film according to item 4 above.