JPH07110406A - Production of optically anisotropic element and liquid crystal display element formed by using the same - Google Patents

Abstract

PURPOSE:To prevent the degradation in the contrast in diagonal incidence and to improve a visual angle characteristic by having plural times of stages for applying a difference in shearing force on both surfaces of a film consisting of a thermoplastic resin and having light transmissivity to apply a film deformation thereto. CONSTITUTION:An optically anisotropic element RF having an optical axis inclined from the normal direction of a liquid crystal cell is arranged between a polarizing plate B and the liquid crystal cell. The optically anisotropic element RF is a double refractive body, of which the double refractions increase with an increase in the angle at which light is made incident on the optical axis. Light L2 which is made incident diagonally at the liquid crystal display element having such constitution and is elliptically polarized by transmitting the liquid crystal is modulated to the original rectilinearly polarized light by a phase delay effect at the time the elliptically polarized light transmits the optically anisotropic element RF. The same transmittance is obtd. even in various diagonal incidences. Then, the good liquid crystal element having no dependency on visual fields is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical anisotropic element used in a liquid crystal display element, and more particularly to a liquid crystal display element using the optical anisotropic element, and particularly to display contrast and display. The present invention relates to a liquid crystal display device in which color viewing angle characteristics are uniformly improved over the entire display screen.

[0002]

2. Description of the Related Art CRTs, which are the mainstream of display devices for OA equipment such as Japanese word processors and desktop personal computers
Has been converted into a liquid crystal display element (hereinafter referred to as LCD) which has the great advantages of thinness, light weight, and low power consumption. Most of the currently popular LCDs use twisted nematic liquid crystals. The display method using such a liquid crystal can be roughly classified into a birefringence mode and an optical rotation mode.

An LCD using a birefringence mode has a twisted angle of 90 ° or more in the alignment of liquid crystal molecules and has steep electro-optical characteristics. Therefore, it is a simple matrix without an active element (thin film transistor or diode). Even with the above electrode structure, a large capacity display can be obtained by time division driving. However, the response speed is slow (hundreds of milliseconds) and gray scale display is difficult, and a liquid crystal display element (TFT-L) using an active element is used.
The display performance of CDs, MIM-LCDs, etc.) is exceeded.

For the TFT-LCD and MIM-LCD, there is used a display system (TN type liquid crystal display element) of optical rotation mode in which the alignment state of liquid crystal molecules is twisted by 90 °. This display method is the most effective method as compared with other LCDs because it has a fast response speed (several tens of milliseconds), can easily obtain a black-and-white table, and has a high display contrast. But,
Since the twisted nematic liquid crystal is used, there is a viewing angle characteristic that the display color and the display contrast change depending on the viewing direction in view of the principle of the display system, and the display performance of the CRT cannot be exceeded.

Japanese Unexamined Patent Publication Nos. 4-229828 and 4-2.
As disclosed in Japanese Patent No. 58923, a method has been proposed in which an optical anisotropic element is arranged between a pair of polarizing plates and a TN liquid crystal cell to increase the viewing angle.

The optical anisotropic element proposed in the above patent publication has a phase difference of substantially zero in the direction perpendicular to the surface of the liquid crystal cell and exerts no optical action from the front. A phase difference appears when tilted, and the phase difference that appears in the liquid crystal cell is compensated. However, even with these methods, the viewing angle of LCD is still insufficient, and further improvement is desired. In particular, when considered as a vehicle-mounted type or as a substitute for a CRT, the current viewing angle cannot support the current situation.

In order to solve the above-mentioned problems, an optical anisotropic element having a negative uniaxial property in the liquid crystal display element, an optical axis which is neither perpendicular nor parallel to the film surface, and which is inclined by 10 to 30 degrees from the normal line to the film is used. We have found that the viewing angle can be greatly expanded by using it and applied for a patent. (Japanese Patent Application No. 4-308377) Further, as a method for producing the optical anisotropic element, there is provided a method which comprises a step of deforming the film by applying a shearing force difference to both of the films. I applied.
(Specification of Japanese Patent Application No. 4-324116)

[0008]

As the above-mentioned optical anisotropic element, a uniform film which can be manufactured at low cost and high productivity and which has substantially no optical axis deviation or retardation deviation is required. To be done. When making a difference in shearing force on both sides of the film, stick-slip occurs between the film and the roll or the influence of the roll driving unevenness causes the optical axis to shake, and uneven thickness or birefringence unevenness easily occurs.
There is a problem that the in-plane retardation becomes uneven and the viewing angle characteristics of the display contrast and the display color are not uniform in the entire screen when arranged in a liquid crystal display device.

[0009]

Means for Solving the Problems The above-mentioned problems are (1) a step of deforming a film made of a thermoplastic resin by imparting a shearing force difference to both surfaces of the film having light transparency at least twice. A method for producing an optical anisotropic element having an optical axis inclined in the plane of a film from a normal direction, which has the above. (2) The method for producing an optical anisotropic element according to (1), wherein the optical anisotropic element having the optical axis inclined from the film normal direction has optically negative uniaxiality. (3) The method for producing an optical anisotropic element according to the above (1), characterized in that the film is sandwiched between rolls having different peripheral speeds, and deformation is imparted by applying a shearing force difference to both surfaces of the film. (4) T with a twist angle of almost 90 ° between the two electrode substrates
A liquid crystal cell sandwiching an N-type liquid crystal, two polarizing elements arranged on both sides of the liquid crystal cell, and the liquid crystal cell and the polarizing element are manufactured by the method described in (1) to (3) above. It was achieved by a liquid crystal display element characterized by arranging at least one optically anisotropic element.

The operation of the present invention will be described below with reference to the drawings, taking a TN type liquid crystal display device as an example. 1, 2, and 3
Shows the polarization state of light propagating in the liquid crystal cell when a sufficient voltage higher than the threshold voltage is applied to the liquid crystal cell. Since the transmittance characteristic of light particularly when a voltage is applied greatly contributes to the viewing angle characteristic of the contrast, a case where a voltage is applied will be described as an example. FIG. 2 is a diagram showing a polarization state of light when light is vertically incident on the liquid crystal cell. When the natural light L0 is vertically incident on the polarizing plate A having the polarization axis PA, the light transmitted through the polarizing plate A becomes the polarized light L1 directly, so that the polarizing plate B almost completely blocks L1.

When a sufficient voltage is applied to the TN liquid crystal cell, the alignment state of the liquid crystal molecules is schematically shown as a model with one liquid crystal molecule, as shown by LC in the schematic diagram. When the molecular long axis of the liquid crystal molecule LC in the liquid crystal cell is parallel to the light path, there is no difference in the refractive index on the incident surface (in the plane perpendicular to the light path), and therefore the ordinary light propagating in the liquid crystal cell The linearly polarized light that has passed through the LC cell without causing the phase difference of the extraordinary light propagates as the linearly polarized light even after passing through the liquid crystal cell. When the polarization axis PB of the polarizing plate B is set to be perpendicular to the polarization axis PA of the polarizing plate A, the linearly polarized light that has passed through the liquid crystal cell cannot pass through the polarizing plate B and is in a dark state.

FIG. 3 is a diagram showing a polarization state of light when the light obliquely enters the liquid crystal cell. Natural light of incident light L
Polarized light L1 transmitted through the polarizing plate A when 0 is obliquely incident
Becomes almost linearly polarized light. (In the actual case, it becomes elliptically polarized due to the characteristics of the polarizing plate). In this case, the refractive index anisotropy of the liquid crystal causes a difference in the refractive index on the incident surface of the liquid crystal cell, and the light L2 transmitted through the liquid crystal cell becomes elliptically polarized light and is not blocked by the polarizing plate B. As described above, in the case of oblique incidence, blocking of light in a dark state becomes insufficient, resulting in a large decrease in contrast, which is not preferable.

A first object of the present invention is to provide a method of manufacturing an optical anisotropic element capable of preventing such a decrease in contrast due to oblique incidence and improving viewing angle characteristics, and an LCD using the same.
Is to provide. FIG. 1 shows an example of the structure of an LCD using the optically anisotropic element according to the present invention. An optical anisotropic element RF having an optical axis inclined from the normal line direction of the liquid crystal cell is arranged between the polarizing plate B and the liquid crystal cell. The optically anisotropic element RF is a birefringent body whose birefringence increases as the angle of incidence of light on the optical axis increases. As in the case of FIG. 3, the elliptically polarized light L2 that is obliquely incident on the liquid crystal display element having such a structure and transmitted through the liquid crystal cell is elliptically polarized by the phase delay action when transmitting through the optically anisotropic element RF. Is modulated into the original linearly polarized light, the same transmittance is obtained even in various oblique incidences, and a good liquid crystal display element having no viewing angle dependency can be realized.

A second object of the present invention is to provide a method for manufacturing an optical element capable of improving the color unevenness of a display color and an LC using the same.
To provide D. Optical anisotropic element RF shown in FIG.
If the optical axis of is changed depending on the location, uneven color and uneven contrast occur when viewed obliquely. Further, if the retardation varies depending on the location, unevenness in color or unevenness in contrast occurs when viewed from the front. As in the production method of the present invention, the film is divided into two or more times to give a shearing force difference to both sides of the film, and by gradually deforming the optical anisotropic element, the optical axis changes (blur) and the retardation change ( It was possible to realize a liquid crystal display device having a good display quality without unevenness in display color.

Next, the present invention will be described in more detail. The light-transmitting film in the present invention means a film or sheet having a light transmittance of 70% or more, more preferably 85% or more. Specifically, polycarbonate, polyarylate, polysulfone, polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyvinyl alcohol, polyamide, polyimide,
Examples thereof include polyolefins, polyvinyl chloride, cellulosic polymers, polyacrylonitrile, polystyrene, and various binary and ternary copolymers of various monomers, graft copolymers, and blends.

In the present invention, the negative uniaxial property in which the optical axis is inclined means that the refractive index in the triaxial direction of a film or sheet having optical anisotropy is nα, nβ, nγ in the ascending order.
Then, there is a relationship of nα <nβ = nγ. Therefore, it has a characteristic that the refractive index in the optical axis direction is the smallest. However, it is not necessary that the values of nβ and nγ be exactly equal, and it is sufficient if they are almost equal. Specifically, if | nβ-nγ | / | nβ-nα | ≦ 0.2, there is no practical problem. Further, as a condition for significantly improving the viewing angle characteristics of the TN liquid crystal cell in the TFT, the optical axis, that is, the direction of the refractive index nα is 10 degrees from the normal line direction of the sheet surface.
It is preferably inclined by 40 degrees, more preferably by 10 to 30 degrees. Further, when the thickness of the sheet is D, 10
It is preferable to satisfy the condition of 0 ≦ (nβ−nα) × D ≦ 400 nm.

The triaxial refractive index characteristics of the film before shearing are not particularly limited and may be optically isotropic or not. However, when the film before shearing is optically isotropic, in order to develop negative uniaxiality, a step of width direction uniaxial stretching or biaxial stretching should be added before or after shearing. Is preferred. Regarding the stretching ratio in the longitudinal direction and the width direction of the biaxial stretching in this case, it is preferable that the stretching ratio in the width direction is slightly larger. In order to omit the stretching after the shear deformation, it is preferable that the triaxial direction refractive index characteristic before the shear deformation is nTD ≧ nMD.

Further, as a method for making a difference in shearing force on both sides of the film, the Tg of the polymer forming the film is
The film is sandwiched between two rolls that heat the film in the vicinity or at a temperature at which thermal deformation of Tg or more is possible, and rotate so that the peripheral speed is different or the film advances in the opposite direction. It is possible by pulling out. The fact that the main refractive index can be inclined by the shearing force is considered to be due to the strain as shown in FIG. In FIG. 4, the assumed cube a inside the film is deformed by the peripheral speed difference between the two rolls, deforms like a solid b, and is further sent out as a solid c. At this time, the molecules inside the cubic are also considered to be tilted.

A detailed description will be given below with reference to embodiments.

【Example】

Example 1 A polycarbonate having a styrene-equivalent weight average molecular weight of 30,000 obtained by condensation of phosgene and bisphenol A was dissolved in methylene dichloride to prepare a 20% solution. This is cast on a steel drum, continuously stripped and dried to a width of 1
A film (F-1) having a thickness of 5 cm and a thickness of 100 μm was obtained.
The film (F-2) having a roll shape of 200 m was produced by sandwiching the film between rolls having different peripheral speeds shown in FIG.

The F-2 molding conditions in the apparatus of FIG. 5 are as follows. R2, R4 peripheral speed: 2.1 m / min R3, R5 peripheral speed: 2.0 m / min R2, R3, R4, R5 surface temperature: 145 ° C Film sandwiched between R2, R3 and R4, R5 Force applied to: 2000 kg R2, R3, R4, R5 roll diameter: 150 mm Next, F-2 was transversely uniaxially stretched by a tenter to obtain a film (F-3). The stretching conditions are as follows. Stretching temperature: 160 ° C. Stretching ratio: 9% Film feeding speed: 3 m / min

<Measurement of Optical Properties of Optically Anisotropic Element> From the optical anisotropic element of F-3 in Example 1, 15 cm × 60 c
A sample of m was sampled and 36 points were evenly selected, and the Re value and its incident angle dependency were obtained by using an ellipsometer AEP-100 manufactured by Shimadzu Corporation in a transmission mode. Also,
The refractive index in the width direction and the film thickness were measured with an Abbe refractometer and a micrometer, respectively. From these average values, the triaxial refractive index of the film and the tilt angle of the main refractive index axis were calculated. Table 1 shows the relationship of the triaxial refractive index calculated. Here, the smallest refractive index is n1, the widthwise refractive index is n2, the other main refractive index orthogonal to n1 and n2 is n3, and the angle at which n1 is inclined from the film normal direction is β.
And The inclination angle deviation (Δβ) is a value (expressed as a percentage) obtained by dividing the difference between the maximum value and the minimum value of the above 36 points by the average value, and the change rate (ΔRe) of the Re value is measured at the adjacent measurement points. The maximum value among the values obtained by dividing the absolute value of the difference between the values by the average value. The results are shown in Table 1.

[0022]

[Table 1]

Comparative Example 1 The film F-1 obtained in Example 1 was used as R4 and R in the apparatus of FIG.
5 was removed and the film (F-
4) was produced. Peripheral speed of R2 and R3: 2.2m / min, 2.0m /
min Surface temperature of R2 and R3: 145 ° C. Force applied to film sandwiched between R2 and R3: 200
Roll diameter of 0kg R2 and R3: 150mm

Next, the stretching conditions for obtaining a film (F-5) by laterally uniaxially stretching F-4 with a tenter are as follows. Stretching temperature: 160 ° C. Stretching ratio: 9% Film feeding speed: 3 m / min The results are shown in Table 1.

Example 2 The film F-1 obtained in Example 1 was sandwiched between rolls having different peripheral speeds shown in FIG. 6 to prepare a film (F-6) in a roll shape of 200 m.

In FIG. 6, a roll R1 is a feed roll, and R2 to R7 are rolls each having a drive system, and the peripheral speed difference can be controlled arbitrarily. Also, depending on the hydraulic pressure, between R2 and R3, between R4 and R5, R6 and R7
It has a structure that can control the pressure between. R8 is a winding roll having a drive system, and the winding speed is controlled by tension control. Each of R2 to R7 has a built-in heater inside the roll, and a temperature sensor is attached to the roll surface. The sensor temperature is fed back to the heater to control the temperature with an accuracy of ± 1 degree by PID control.

The F-6 molding conditions in the apparatus of FIG. 6 are as follows. Peripheral speed of R2, R4, R6: 2.05m / min, 2.1m / min 2.05m /
Peripheral speed of min R3, R5, R7: 2.0 m / min Force applied to the film sandwiched between R2, R3; R4, R5; R6, R7:
Roll diameter of 2000 kg R2 to R7: 150 mm

Next, F-2 was transversely uniaxially stretched by a tenter to obtain a film (F-7). The stretching conditions are as follows. Stretching temperature: 160 ° C. Stretching ratio: 9% Film feeding speed: 3 m / min

Example 3 <Evaluation of viewing angle characteristics> As the optically anisotropic element shown in FIG. 1, F-3, F-5 and F-7 of Examples and Comparative Examples, and optically anisotropic elements were used in a liquid crystal cell. The viewing angle characteristics of 0 V / 5 V contrast in a 30 Hz rectangular wave were measured by LCD-5000 manufactured by Otsuka Electronics for the case and the case where no film was arranged. The angle of the contrast 10 is defined as the viewing angle, and the results of the viewing angle characteristics in the vertical and horizontal directions are shown in Table 2. The product of the difference in refractive index between the extraordinary ray and the ordinary ray of the liquid crystal used in the liquid crystal cell used here and the gap size of the liquid crystal cell is 480n.
The twist angle is 90 degrees at m. In addition, T in this measurement
N liquid crystal cell polarizing plate polarization axis, liquid crystal cell rubbing axis,
The direction of the optical axis of the optical compensation sheet is shown in FIG.

[0030]

[Table 2]

According to the present invention, it is possible to provide a high-quality liquid crystal display device having improved viewing angle characteristics and color unevenness of a TN type liquid crystal display device, excellent in visibility, and having less unevenness on the entire screen. Needless to say, even if the present invention is applied to an active matrix liquid crystal display element using a three-terminal or two-terminal element such as TFT or MIM, excellent effects can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an example of a configuration of a liquid crystal display element of the present invention.

FIG. 2 is a diagram illustrating a configuration of a conventional TN type liquid crystal display element and a diagram for explaining a light transmission state when light is perpendicularly incident on a display surface.

FIG. 3 is a diagram illustrating a configuration of a conventional TN type liquid crystal display element and a light transmission state when light obliquely enters a display surface.

FIG. 4 is a diagram showing a mechanism of film deformation due to shearing.

FIG. 5 is a view of a different peripheral speed roll device used in the present invention.

FIG. 6 is a different peripheral speed roll device used in the present invention.

FIG. 7 is a configuration diagram showing the direction of the optical axis of the liquid crystal display element used in this example.

[Explanation of symbols]

A, B: Polarizing plates PA, PB: Polarizing axes CE: TN type liquid crystal cell RF: Optical anisotropic element L0: Incident light L1: Linearly polarized light passing through polarizing plate A L2: Polarized light passing through TN type liquid crystal cell ( Mainly elliptically polarized light) LC: A model representation of liquid crystal in a TN liquid crystal cell. θ: incident angle of linearly polarized light R1 to R8: rolls n1 to n3: main refractive index of film

Claims (4)

[Claims] 1. A film made of a thermoplastic resin and having a light-transmitting property is provided with a shearing force difference on both sides,
A method for producing an optical anisotropic element having an optical axis neither in the plane of the film nor in the normal direction, characterized in that it comprises a step of deforming the film at least twice. 2. The method for producing an optical anisotropic element according to claim 1, wherein the optical anisotropic element has an optically negative uniaxial property. 3. The method for producing an optical anisotropic element according to claim 1, wherein the film is sandwiched between rolls having different peripheral speeds, and the film is deformed by applying a shearing force difference to both surfaces of the film. 4. The twist angle between the two electrode substrates is approximately 90.
4. A liquid crystal cell sandwiching a TN type liquid crystal of 2 °, two polarizing elements arranged on both sides of the liquid crystal cell, and between the liquid crystal cell and the polarizing element, manufactured by the method according to claim 1. A liquid crystal display element characterized by arranging at least one optically anisotropic element.