JPH07159614A - Production of optically anisotropic element and liquid crystal display element using the same - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display element improved in display contrast and the visual angle characteristic of display colors uniformly over the entire surface of a screen by applying a polymer soln. on one surface of a film substrate, then imparting a difference in shearing force on both surfaces to apply a deformation to a film. CONSTITUTION:This process for production has a stage for applying the polymer soln. on at least one surface of the film substrate consisting of a thermoplastic resin and having light transmittability, then applying the difference in the shearing force on both surfaces to apply the deformation to the film and produces the optically anisotropic element having the optical axis neither in the film plane nor in the normal direction. The optically anisotropic element RF having the optical axis inclined from the normal direction of the liquid crystal cell is arranged between a polarizing plate B and a liquid crystal cell CE. Light is made incident diagonally on the liquid crystal cell CE and the light L2 which is elliptically polarized by transmitting this cell is modulated to the original linearly polarized light by a phase delay action at the time of transmitting the optically anisotropic element RF. The same transmittance is obtd. even at various diagonal incidences. The good liquid crystal display element having no dependency on visual angles is obtd.

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 active elements (thin transistors and diodes). Even with the above electrode structure, a large capacity display can be obtained by time division driving. However, it has a drawback that the response speed is slow (several hundreds of milliseconds), and gradation display is difficult.
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 it is considered as a vehicle-mounted type or as a substitute for a CRT, the current viewing angle cannot support the situation at all.

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 including a step of deforming the film by applying a shearing force difference to both sides of the film. I applied. (Japanese Patent Application No. 4-32411
(Specification 6)

[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 problems are (1) to apply a shearing force to both surfaces of a film substrate made of a thermoplastic resin and having a light-transmitting property, after applying a polymer solution to at least one surface of the film substrate. A method for producing an optical anisotropic element having an optical axis neither in the plane of the film nor in the direction of the normal, characterized in that it has a step of deforming the film. (2) Using a co-casting die having a plurality of manifolds, a film is deformed by imparting a shearing force difference to both sides of a light-transmitting film obtained by co-extruding a plurality of polymer solutions. A method for producing an optical anisotropic element having an optical axis neither in the plane of the film nor in the direction of the normal, characterized by having steps. (3) The method for producing an optically anisotropic element as described in (2) above, wherein in the co-extrusion using the co-casting die, a plurality of polymer solutions have different viscosities. (4) The method for producing an optical anisotropic element according to the above (1) to (3), wherein the optical anisotropic element has an optically negative uniaxial property. (5) Insert the film between rolls with different peripheral speeds,
The method for producing an optical anisotropic element according to any one of (1) to (4) above, wherein the film is deformed by applying a shearing force difference to both sides thereof. (6) TN with a twist angle of about 90 ° between two electrode substrates
A liquid crystal cell sandwiching a type liquid crystal, two polarizing elements arranged on both sides of the liquid crystal cell, and an optical element manufactured by the method described in (1) to (5) between the liquid crystal cell and the polarizing element. This has been achieved by a liquid crystal display element characterized by arranging at least one 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 changes depending on the case, color unevenness and uneven contrast occur even when viewed from the front. As in the production method of the present invention, before imparting a shearing force difference to both surfaces of the film, by applying a polymer solution to at least one surface of the film or performing co-casting, the surface condition of the film is improved. In addition, the thickness unevenness may be reduced, and the change of the optical axis (blur) and the change of the retardation (unevenness) of the optical anisotropic element can be remarkably improved, and the display quality without the display color unevenness is excellent. A liquid crystal display device was realized.

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. As the polymer used on the mainstream side of the film substrate or co-casting when coating, polycarbonate, polyarylate, polysulfone, polyethylene terephthalate, polyethylene naphthalate, polyether sulfone, polyphenylene sulfide, polyphenylene oxide, polyallyl sulfone, polyvinyl alcohol. , Polyamide, polyimide, polyolefin, polyvinyl chloride, cellulose-based polymer, polyacrylonitrile, polystyrene, and various binary and ternary copolymers of various monomers, graft copolymers, blends and the like. The polymer used on the side of the side stream of coating or co-casting on the film substrate may be the same as or different from the above, but a polymer having good adhesion with the above polymer is preferable.

Further, it is preferable that the viscosity of the dope on the side of the co-casting is smaller than that of the dope on the side of the main flow because streaks and unevenness caused at the lip during casting are less. Here, the main flow is the one having the largest flow rate and the largest film thickness after drying, and the ones other than the main flow are called the substreams. In the case of two-layer casting, it is preferable that the main stream is cast on the casting substrate and the substream is cast on the air side. In case of 3 layers or more, at least 2 as shown in FIG.
It is preferable that the side stream of the layer is cast so as to sandwich the main stream of one layer. The solvent used for the coating liquid may be the same as or different from the solvent for the film, but when the same solvent is used, a method such as slide coating or roll coating is suitable.

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 order of decreasing value.
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 express negative uniaxiality, uniaxial stretching of a stretching ratio of several% in the width direction before or after shearing is performed, It is preferable to add a step of biaxial stretching. Regarding the stretching ratio in the longitudinal direction and the width direction of the biaxial stretching in this case, the stretching ratio in the width direction is preferably a few percent higher. In order to omit the stretching after shear deformation, it is preferable that the triaxial direction refractive index characteristic before shear deformation is nTD ≧ nMD.

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. The details will be described below with reference to examples.

[0020]

【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,
A 7% methylene dichloride solution of the same polycarbonate was applied by slide coating to a solid content of 3 mg / m ² and dried to give a width of 15
A film having a thickness of cm and a thickness of 80 μm was obtained. The film is shown in FIG.
The film (F-
1) was manufactured in a roll shape for 200 m.

In FIG. 5, the roll R ₁ is a feed roll, and R _{2 to} R ₅ are rolls each having a drive system, and the peripheral speed difference can be arbitrarily controlled. Further, the structure is such that the pressure between R ₂ and R _{3, and} between R ₄ and R ₅ can be controlled by hydraulic pressure. R ₆ is a winding roll having a drive system, and the winding speed is controlled by tension control. From R ₂ R ₅ has a built-in heater inside the roll, and the temperature sensor is attached to the roll surface, and a feedback sensor temperature to the heater PID
The temperature is controlled with an accuracy of ± 1 degree by control.

The F-1 molding conditions in the apparatus of FIG. 5 are as follows. Peripheral speed of the _{R 2, R 4: 1,005m /} min R 3, the peripheral speed of _{R 5: 1,000m / min R 2} , R 3, R 4, R 5 a surface temperature: 145 ℃ R _2, R ₃ And force applied to the film sandwiched between R ₄ and R ₅ : 2000 kg Roll diameter of R ₂ , R ₃ , R ₄ and R ₅ : 150 mm Next, F-1 was transversely uniaxially stretched by a tenter (F- 2) was obtained. The stretching conditions are as follows. Stretching temperature: 150 ° C Stretching ratio: 3% Film feeding speed: 3 m / min

<Measurement of Optical Properties of Optically Anisotropic Element> A 15 cm × 60 cm sample was taken from the optical anisotropic element of F-2 in Example 1, and 36 points were evenly selected, and the ellipsometer AEP- manufactured by Shimadzu Corporation was used. 100 was used in the transmission mode, and the Re value and its incident angle dependence were determined. The refractive index in the width direction and the thickness of the film were measured with an Appe's 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 n ₁ , the refractive index in the width direction is n ₂ , the other main refractive index orthogonal to n ₁ and n ₂ is n ₃ , and the angle at which n ₁ is inclined from the normal direction of the film. Was defined as β. The inclination angle deviation (Δβ) is a value obtained by dividing the difference between the maximum value and the minimum value of the 36 points by the average value, and the rate of change of the Re value (ΔRe) is the absolute difference between the measured values at adjacent measurement points. The maximum value among the values obtained by dividing the value by the average value. The results are shown in Table 1.
Shown in.

[0024]

[Table 1]

Example 2 A 20% methylene dichloride solution (dope A) and a 15% methylene dichloride solution (dope B) of the polycarbonate used in Example 1 were prepared. The viscosities at 25 ° C. were 700 for dope A respectively. Poise and Dope B were 220 poise. The dope A is fed from the liquid feed port 1a and the dope B is fed from the liquid feed ports 1b and 1c of the co-casting die shown in FIG. 6, co-extruded on a steel band, continuously peeled, and dried 1a, The film thickness after drying of the dope fed from 1b and 1c is 60 μm and 10 μm, respectively.
A film having a thickness of 10 μm and a width of 15 cm was obtained. A roll film obtained by molding the film in the same manner as in Example 1 by the apparatus shown in FIG. 5 was subjected to transverse uniaxial stretching with a tenter to obtain a film (F-3). The results are shown in Table 1.

Comparative Example 1 Only the dope A used in Example 2 was cast on a steel band, continuously peeled and dried, and the width was 15 cm and the thickness was 80 μm.
m film was obtained. A roll film obtained by molding the film in the same manner as in Example 1 by the apparatus shown in FIG. 5 was subjected to transverse uniaxial stretching with a tenter to obtain a film (F-4). The results are shown in Table 1.

Example 3 <Evaluation of viewing angle characteristics> When optically anisotropic elements F-3 and F-4 of Examples and Comparative Examples were used in the liquid crystal cell as the optically anisotropic element shown in FIG. With no arrangement, 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. 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 480 nm, and the twist angle is 90 degrees. The directions of the polarization axis of the polarizing plate of the TN liquid crystal cell, the rubbing axis of the liquid crystal cell, and the optical axis of the optical compensation sheet in this measurement are shown in FIG.

[0028]

[Table 2]

According to the present invention, it is possible to provide a liquid crystal display device of high quality display, in which the viewing angle characteristics and color unevenness of the TN type liquid crystal display device are improved, the visibility is excellent, and the unevenness on the entire screen is small. 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 sectional view of a co-casting die used in the present invention, taken along a plane perpendicular to the width direction.

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 R _{1 to} R ₈ : roll n _{1 to} n ₃ : main refractive index of the film 1a, 1b, 1c: dope feed port 2a, 2b, 2c: manifold 3: lip

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[Procedure amendment]

[Submission date] May 27, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0027

[Correction method] Change

[Correction content]

Example 3 <Evaluation of viewing angle characteristics> When the optically anisotropic element of Examples F-2 and F-3 as the optically anisotropic element shown in FIG. 1 was used in a liquid crystal cell and no film was arranged. , 30Hz
The viewing angle characteristics of a 0 V / 5 V contrast in a rectangular wave were measured by LCD-5000 manufactured by Otsuka Electronics. 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 480 nm, and the twist angle is 90 degrees. The directions of the polarization axis of the polarizing plate of the TN liquid crystal cell, the rubbing axis of the liquid crystal cell, and the optical axis of the optical compensation sheet in this measurement are shown in FIG.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

[0028]

[Table 2]

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

According to the present invention, it is possible to provide a liquid crystal display device of high quality display, in which the viewing angle characteristics and color unevenness of the TN type liquid crystal display device are improved, the visibility is excellent and the unevenness is small on the entire screen. In addition, the present invention can be applied to 3 such as TFT and MIM.
It goes without saying that excellent effects can be obtained even when applied to an active matrix liquid crystal display element using a terminal and a two-terminal element.

Claims (6)

[Claims] 1. A method comprising: applying a polymer solution to at least one surface of a film substrate made of a thermoplastic resin and having a light-transmitting property, and then applying a shearing force difference to both surfaces to deform the film. A method of manufacturing an optical anisotropic element whose optical axis is neither in the film plane nor in the normal direction. 2. A film is deformed by applying a shearing force difference to both sides of a light-transmissive film obtained by co-extruding a plurality of polymer solutions using a co-casting die having a plurality of manifolds. A method for producing an optical anisotropic element having an optical axis neither in the plane of the film nor in the normal direction, which comprises a step of providing 3. The optical anisotropic element according to claim 2, wherein in the co-extrusion using the co-casting die, the viscosity of the polymer solution on the side stream side is smaller than the viscosity of the polymer solution on the side stream. Manufacturing method. 4. The method for producing an optical anisotropic element according to claim 1, wherein the optical anisotropic element has an optically negative uniaxial property. 5. The deformation is given by sandwiching the film between rolls having different peripheral speeds and applying a shearing force difference to both surfaces of the film.
A method for manufacturing the optically anisotropic element described. 6. The twist angle between the two electrode substrates is approximately 90.
6. 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 comprising at least one optically anisotropic element.