JPH07198943A - Visual angle compensation plate, ellipse polarizing plate and liquid crystal display device - Google Patents

Abstract

PURPOSE:To form a thin and light liquid crystal display device such as a TFT type, etc., excellent for view angle capable of compensating the change in asymmetrical visibility of a liquid crystal cell according to a visual angle by arranging it outside the liquid crystal cell and enlarging the view angle without revising the conventional liquid crystal cell. CONSTITUTION:A visual angle compensation plate laminates an inclined phase difference plate l with refractive index anisotropy provided with an optical axis in the direction intersecting with a plate surface and a phase difference plate whose difference of a phase difference in the vertical direction of the plate surface is within 50% for the inclined phase difference plate so that these lagging axes in the direction of the plate surface intersect orthogonally. An ellipse polarizing plate is constituted of a laminated body between the visual angle compensation plate and a polarizing plate. Then, the liquid crystal display device is provided with the visual angle compensation plate on at least one side of the liquid crystal cell.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a viewing angle compensating plate suitable for compensating a change in visibility of a liquid crystal cell depending on a viewing angle (viewing angle),
The present invention also relates to an elliptical polarizing plate and a liquid crystal display device using the same.

[0002]

BACKGROUND OF THE INVENTION With the widespread use of liquid crystal display devices as various display screens for personal computers, word processors, data terminal devices, televisions, etc., it has been pointed out that the viewing angle is narrow as a visually recognizable viewing angle range. By the way, in a TFT type liquid crystal display device, even if the display quality when viewed from the front can be set to CRT or higher, the viewing angle from the upper and lower sides, usually from the upper side, is narrow due to asymmetry from the viewpoint in the vertical direction. It has been pointed out.

The problem of the narrow viewing angle becomes a more serious problem than those for personal use, particularly in those viewed from various angles such as televisions and large-screen display devices. It has been pointed out that widening the viewing angle is strongly desired.

[0004]

2. Description of the Related Art Conventionally, as the viewing angle expanding means,
The orientation division method and the capacitive coupling pixel division method have been known.
In any of the methods, one pixel is divided into two different regions to compensate for the asymmetry of the viewing angles of each other, so that a viewing angle characteristic having symmetry as an area average can be obtained.

However, in any of the methods, there is a problem that the contrast ratio is lowered due to the occurrence of disclination (disorder of orientation) at the interface of the areas where the pixels are divided. In addition, since it is a method of improving the inside of the liquid crystal cell, there are problems that the cell manufacturing process is complicated and the cell manufacturing yield is reduced, and it is necessary to introduce new manufacturing equipment. there were.

[0006]

According to the present invention, by arranging the liquid crystal cell outside the liquid crystal cell, it is possible to compensate for the asymmetrical change in the visibility of the liquid crystal cell depending on the viewing angle and to widen the viewing angle, which is thin, light and excellent in the viewing angle. An object is to develop a technique capable of forming a liquid crystal display device such as a TFT type, and thus using a conventional cell as it is.

[0007]

According to the present invention, there is provided a tilted phase difference plate having a refractive index anisotropy having an optical axis in a direction intersecting with a plate surface and a difference in phase difference in a direction perpendicular to the plate surface. A viewing angle compensating plate and a viewing angle compensating plate characterized by laminating a retardation film within 50% of an inclined retardation plate so that their slow axes in the plate surface direction are orthogonal to each other. The present invention provides an elliptical polarizing plate comprising a laminate with a polarizing plate, and a liquid crystal display device comprising the viewing angle compensating plate on at least one side of a liquid crystal cell.

[0008]

With the above configuration, there is little or no phase difference when viewed in the vertical direction of the plate surface, that is, when viewed from the front, and there is a phase difference when viewed in the direction that intersects the plate surface, that is, in the oblique direction, and It is possible to obtain a viewing angle compensator exhibiting an asymmetrical phase difference characteristic in which the phase difference changes depending on the viewing angle, and by using it, the viewing angle is improved by compensating for the asymmetrical change in visibility due to the viewing angle change of the liquid crystal cell. be able to.

[0009]

EXAMPLE A viewing angle compensating plate of the present invention comprises a tilted phase difference plate having a refractive index anisotropy having an optical axis in a direction intersecting the plate surface,
The retardation plate has a retardation difference of 50% or less with respect to the inclined retardation plate in the vertical direction of the plate surface, and is laminated such that the slow axes in the plate surface direction are orthogonal to each other. An example thereof is shown in FIG. This is one in which the tilted phase difference plates 1 are stacked.

The tilted phase difference plate used in the present invention has a refractive index anisotropy in which the direction of the optical axis intersects the plate surface as shown by the arrow in FIG. 1. For example, it can be obtained as a film made of a nematically aligned liquid crystal polymer.

As the above-mentioned liquid crystal polymer, a liquid crystal polymer having a nematic orientation is used, and its kind is not particularly limited. By the way, as an example of such liquid crystal polymer,
Examples thereof include a main chain type or side chain type in which a conjugated linear atomic group (mesogen) that imparts liquid crystal orientation is introduced into the main chain or side chain of a polymer. Specific examples of the main chain type liquid crystal polymer include polyester liquid crystal polymers having nematic orientation.

As a specific example of the side chain type liquid crystal polymer, a mesogen moiety having a main chain skeleton of polysiloxane, polyacrylate, polymethacrylate or polymalonate and a para-substituted cyclic compound unit having a nematic orientation imparting property as a side chain is used. The thing which has is mentioned.

As the above-mentioned para-substituted cyclic compound unit,
For example, a low molecular weight liquid crystal compound having a nematic liquid crystallinity, which is composed of a para-substituted aromatic unit, a para-substituted cyclohexyl ring unit, or the like, can be given. More specifically, for example, azomethine type, azo type, azoxy type, ester type, biphenyl type, phenylcyclohexane type, bicyclohexane type and the like can be mentioned. The terminal substituent at the para position in the para-substituted cyclic compound unit may be a usual substituent in a low molecular weight liquid crystal compound, and is generally a cyano group, an alkyl group, an alkoxy group or the like.

The liquid crystal polymer that can be preferably used has a weight average molecular weight of 20,000 to 200,000 based on polystyrene conversion by gel permeation chromatography. If the molecular weight is less than 20,000, it is difficult to obtain a tilted phase difference plate having excellent strength.

A liquid crystal polymer that can be preferably used has a glass transition point higher than the use temperature in view of the stability of the fixed alignment. By the way, when it is used at around room temperature, a liquid crystal polymer having a glass transition point of less than 30 ° C. may change the immobilized liquid crystal structure and induce a functional decline.

The formation of a tilted retardation plate made of a liquid crystal polymer is required, for example, by developing a solution of the liquid crystal polymer on the alignment treated surface and heat-treating it to orient the liquid crystal polymer obliquely and then cooling it. It can be performed by a method such as peeling from the orientation-treated surface.

Any surface can be used as the above-mentioned orientation-treated surface as long as it can orient the liquid crystal polymer obliquely in a state having a tilt angle. For example, a well-known surface can be used for the orientation treatment of the low-molecular liquid crystal compound. Examples thereof include those obtained by forming a thin film of polyimide, polyvinyl alcohol, or the like on a suitable substrate such as a glass plate or a polymer film, and rubbing the surface thereof, or those obtained by oblique vapor deposition of silicon oxide. .

The liquid crystal polymer is developed, for example, by dissolving the liquid crystal polymer in an appropriate solvent to prepare a solution, which is then spin-coated, roll-coated, flow-coated, printing, dip-coated, cast film-formed. The method can be carried out by a method of developing a thin layer by an appropriate method such as a method and then drying it to remove the solvent. It can also be carried out by a method that does not use a solvent, such as a method in which a liquid crystal polymer is heated and melted in a state of exhibiting an isotropic phase, and a temperature is maintained while developing a thin layer.

The heat treatment for aligning the developed liquid crystal polymer can be carried out by heating within a temperature range from the glass transition point of the liquid crystal polymer to a molten state exhibiting an isotropic phase. The cooling conditions for fixing the orientation state are not particularly limited, and the heat treatment described above is usually performed at 200 ° C.
The natural cooling method is generally adopted because it can be performed at the following temperature.

By the way, when a liquid crystal polymer is spread on a polyimide-based rubbing film and heat-treated, it can be oriented in the rubbing direction.
The tilt angle of the liquid crystal polymer can be controlled within a range of about 40 degrees or less by performing the treatment at a curing temperature of 200 ° C., especially 100 to 200 ° C. The tilt angle of the liquid crystal polymer is appropriately determined according to the viewing angle characteristics of the liquid crystal cell to be compensated.

The nematically aligned liquid crystal polymer tilted phase difference plate formed by finishing the immobilization treatment by cooling and having a predetermined tilt angle is peeled and collected from the alignment treated surface as needed. For example, for example, a method using a rubbing film forming material having a releasable side chain composed of a long-chain alkyl group or a glass plate having a surface modified with a silane compound having an alkyl chain having 8 to 18 carbon atoms is aligned. An appropriate method such as a method of forming a processing surface can be applied as necessary.

The thickness of the tilted phase difference plate is appropriately determined according to the viewing angle characteristics of the liquid crystal cell to be compensated, the phase difference characteristics of the tilted phase difference plate, and the like. In the case of a liquid crystal polymer type, the thickness is 50 μm or less, preferably 1 to 10 μm in view of flexibility and the like. The flexible tilted phase difference plate has an advantage that it is easy to obtain a viewing angle compensation plate that can be easily applied to a curved surface, a large area surface, or the like.

In the present invention, the tilted phase difference plate which can be preferably used for expanding the viewing angle of the TFT type liquid crystal display device or the like has a slow axis direction in a direction having a crossing angle of 40 ° with respect to the plate surface and a direction having a crossing angle of 140 °. The absolute value of the difference in retardation value is larger than 10 nm.

That is, the vertical direction with respect to the horizontally installed tilted phase difference plate is set as a reference direction, and the tilted phase difference plate is ± 40 degrees (ie 40 degrees and 140 degrees) in the slow axis direction from the horizontal state.
When the retardation values (Δnd: product of difference in birefringence and plate thickness) in the reference direction when tilted are Δnd ₄₀ and Δnd _-40 , respectively, the formula: ┃ Δnd ₄₀ − It satisfies Δnd ₋₄₀ ┃> 10 nm.

In the present invention, the retardation plate used for laminating with the inclined retardation plate has a difference in retardation in the direction perpendicular to the plate surface within 50% of that of the laminated retardation plate, preferably as much as possible. Very few. As a result, the phase difference of the tilted phase difference plate in the direction perpendicular to the plate surface can be offset and reduced, and the phase difference of the viewing angle compensation plate in the direction can be reduced or eliminated.

In the present invention, as the laminated retardation plate, even one inclined retardation plate can be provided with a difference in the retardation depending on the oblique viewing angle. Therefore, for example, polymethyl methacrylate, polycarbonate, polyvinyl. Alcohol, polypropylene and other polyolefins, polyarylate, those made of a birefringent film obtained by stretching a film made of a suitable plastic such as polystyrene can be used, but preferably used is a retardation plate. .

That is, a preferable combination of the laminated retardation plates forming the viewing angle compensating plate is a combination of inclined retardation plates as in the embodiment of the above-mentioned FIG. By combining the tilted phase difference plates, it is possible to compound the difference in phase difference due to the oblique viewing angle based on each tilted phase difference plate,
Further, in association with the laminating method orthogonal to the slow axis, the phase difference can be efficiently made different in a state in which the difference in the phase difference between the vertical direction and the horizontal direction is combined.

The inclined retardation plate or retardation plate to be laminated in the above may be formed by laminating two or more plate forming units for the purpose of controlling the retardation. The thickness of the birefringent film used for lamination with the tilted retardation plate can be appropriately determined according to the retardation to be compensated, etc., and generally 500 μm based on the single layer film from the viewpoint of flexibility and the like. Hereafter, it is 100 μm or less.

The viewing angle compensating plate of the present invention is formed by laminating an inclined retardation plate and a predetermined retardation plate so that their slow axes in the plate surface direction are orthogonal to each other as shown by the arrow in FIG. It can be carried out. When laminating, an appropriate adhesive such as an acrylic-based, rubber-based, or silicone-based pressure-sensitive adhesive or a hot-melt adhesive may be used if necessary. It should be noted that the conventional error in the orthogonal state due to the work accuracy and the like is allowed.

The adhesive used is preferably one that is excellent in transparency and weather resistance, and preferably one that does not require a high temperature process during curing and drying from the viewpoint of preventing changes in the optical properties of each functional film. Further, it is desirable to use one that does not require a long curing treatment or a drying time. The attachment of the adhesive layer may be performed by an appropriate method such as a coating method or a transfer method of the one provided on the separator.

The viewing angle compensator of the present invention can be preferably used for expanding the viewing angle of a liquid crystal display device by compensating for the change in the visibility of the liquid crystal cell depending on the viewing angle. In that case, the viewing angle compensator is used alone. Alternatively, it can be used in an appropriate form as a laminate with a polarizing plate.

An elliptically polarizing plate can be obtained by laminating the viewing angle compensation plate of the present invention with a polarizing plate. An example of the elliptically polarizing plate is shown in FIG. Reference numeral 2 is a polarizing plate, and 4 is a viewing angle compensation plate. In addition, 3 is an adhesive layer.

As the polarizing plate, an appropriate polarizing plate can be used, but a polarizing film is generally used. The polarizing film is not particularly limited, and examples thereof include polyvinyl alcohol-based film, partially formalized polyvinyl alcohol-based film, and ethylene.
Polyvinyl acetate copolymer partially saponified hydrophilic polymer film such as iodine and / or dichroic dye adsorbed and stretched, polyvinyl alcohol dehydrated product, polyvinyl chloride dehydrochlorinated product, etc. Examples include polyene oriented films. The thickness of the polarizing film is usually 5
˜80 μm, but not limited to this.

The polarizing plate may be the polarizing film itself or a polarizing film provided with a transparent protective layer on one side or both sides. For forming the transparent protective layer, those having excellent transparency, mechanical strength, thermal stability, moisture shielding property, etc. are preferably used, and examples thereof include polyester resins, polyether sulfone resins, polycarbonate resins, Examples thereof include polymers such as polyamide resins, polyimide resins, polyolefin resins, acrylic resins and acetate resins, and those having excellent light transmittance and strength such as polyester and triacetyl cellulose are preferable.

The polarizing plate and the viewing angle compensator may be treated with an ultraviolet absorber such as salicylate compound, benzophenol compound, benzotriazole compound, cyanoacrylate compound, nickel complex salt compound. It may have an ultraviolet absorbing ability. Examples of the adhesive include the above. When the adhesive layer is a pressure-sensitive adhesive layer, it is preferable to protect the surface with a separator or the like until practical use.

The viewing angle compensator of the present invention can be preferably used for expanding the viewing angle of a liquid crystal display device as described above. In that case, the viewing angle compensator is used for forming a liquid crystal display device in a liquid crystal cell. It can be arranged on one or both sides. The viewing angle compensator may be arranged as an elliptically polarizing plate. The visual angle compensation plate is generally arranged between the liquid crystal cell and the polarizing plate, but is not limited to this. A wide viewing angle can be achieved by disposing a viewing angle compensating plate that compensates for the asymmetry of the viewing angle characteristics in the liquid crystal cell.

FIG. 3 illustrates a liquid crystal display device of the type in which a viewing angle compensator is arranged on one side of the liquid crystal cell on the viewing side.
Reference numeral 5 is a liquid crystal cell, and other reference numerals are the same as above. The viewing angle compensator and the like may be fixed to the main body of the device via an adhesive layer or the like. The liquid crystal cell to which the viewing angle compensation plate is applied is arbitrary, and for example, an active matrix drive type represented by a thin film transistor type, a simple matrix drive type represented by a twist nematic type or a super twist nematic type is appropriately used. It can be applied to various types of liquid crystal cells.

Example 1 A polymer composed of acrylic monomer units represented by the above formula is dissolved in chloroform, and the solution is spin-coated on a polyimide-based rubbing film formed on a glass plate by a flow coating method, and dried by heating. After that, it is heat-treated at 120 ° C. for 30 minutes and then cooled, and the thickness of the formed nematic structure having a tilt angle of about 20 degrees is about 2
A liquid crystal polymer film of μm was transferred from a rubbing film to a triacetyl cellulose film to form a tilted retardation plate with anisotropy of refractive index in which the optical axis intersects the plate surface at an angle of about 20 degrees. Two sheets were laminated with an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm so that their slow axes in the plate surface direction were orthogonal to each other to obtain a viewing angle compensation plate.

In the above description, the phase difference in the vertical direction of the plate surfaces of the laminated tilted phase difference plates was almost the same. The polyimide-based rubbing film was spin-coated with a solution of pyromellitic dianhydride and diaminodiphenyl ether dissolved in a mixed solvent of n-methylpyrrolidone / dimethylformamide, and cured by rubbing at 100 ° C. for 1 hour. It is a thing.

Example 2 According to Example 1, Δnd ₄₀ was 310 nm and Δn
d- ₄₀ is 220 nm, and therefore the formula: ┃Δnd ₄₀ −Δn
Two tilted phase difference plates satisfying d _-40 ┃> 10 nm were formed to obtain a viewing angle compensation plate.

Comparative Example Two pieces of retardation plates obtained by uniaxially stretching a polycarbonate film at 160 ° C. and having substantially the same retardation in the direction perpendicular to the plate surface were made so that their slow axes in the plate surface direction were orthogonal to each other. A 20-μm-thick acrylic pressure-sensitive adhesive layer was laminated to obtain a viewing angle compensation plate.

Evaluation With respect to the viewing angle compensators obtained in Example 1 and Comparative Example, changes in the phase difference depending on the viewing angle in the slow axis direction of one of the retardation plates were examined. The results are shown in Fig. 4. The change in the phase difference of the viewing angle compensation plate obtained in Example 2 was substantially the same as that in Example 1.

[0043]

According to the viewing angle compensating plate of the present invention, by arranging the viewing angle compensating plate outside the liquid crystal cell, it is possible to compensate for a change in visibility due to an asymmetrical phase difference change of the liquid crystal cell due to a change in viewing angle. It is possible to obtain a liquid crystal display device having a wide viewing angle, excellent lightness, and thinness without changing the liquid crystal cell.

[Brief description of drawings]

FIG. 1 is an explanatory perspective view of an embodiment of a viewing angle compensation plate.

FIG. 2 is a sectional view of an example of an elliptically polarizing plate.

FIG. 3 is a sectional view of an embodiment of a liquid crystal display device.

FIG. 4 is a graph showing a change in phase difference depending on a viewing angle.

[Explanation of symbols]

 1: Tilt phase difference plate 2: Polarizing plate 3: Adhesive layer 4: Viewing angle compensating plate 5: Liquid crystal cell

Claims (6)

[Claims] 1. A tilted phase difference plate having a refractive index anisotropy having an optical axis in a direction intersecting with the plate surface and a difference in phase difference in the direction perpendicular to the plate surface is 50 with respect to the tilted phase difference plate. %, And a retardation plate having a phase difference of not more than 100% is laminated so that their slow axes in the plate surface direction are orthogonal to each other. 2. The absolute value of the retardation value difference in the slow axis direction between the direction in which the crossing angle with respect to the plate surface is 40 degrees and the direction in which the crossing angle with respect to the plate surface is 140 degrees is 10 nm.
The viewing angle compensator according to claim 1, which is larger than the above. 3. The viewing angle compensation plate according to claim 1, wherein the retardation plate laminated on the inclined retardation plate is also an inclined retardation plate. 4. The viewing angle compensation plate according to claim 1, wherein the tilted phase difference plate is made of a nematically aligned liquid crystal polymer. 5. An elliptically polarizing plate comprising a laminated body of the viewing angle compensating plate according to claim 1 and a polarizing plate. 6. A liquid crystal display device comprising the viewing angle compensating plate according to claim 1 on at least one side of a liquid crystal cell.