JP3495399B2 - Viewing angle compensator and liquid crystal display - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a viewing angle (viewing angle) useful viewing angle compensation plate to compensate for the visibility of change in the liquid crystal cell by
A liquid crystal display device using the 及 Bisore.

[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 the TFT type liquid crystal display device, even if the display quality when viewed from the front can be made higher than that of the CRT, the viewing angle from the upper and lower sides, usually from the upper side, is narrow because it shows 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]

The present invention is directed to a single-layer retardation plate and a polarizing plate having an optical axis in a direction intersecting with a plate surface in a state of having a tilt angle and exhibiting anisotropy in birefringence. It shows asymmetrical phase difference characteristics in which a phase difference appears when viewed from an oblique direction and the phase difference changes depending on the viewing angle.
On the phase difference plate side in to elliptic polarizing plate, that a retardation plate to compensate a phase difference in the vertical direction of that phase difference plate slow axis direction of the plate surface direction formed by laminating a state crossing The present invention provides a characteristic viewing angle compensating plate and a liquid crystal display device having the viewing angle compensating plate on at least one side of a liquid crystal cell.

[0008]

By using the above-mentioned birefringent anisotropic retardation plate, the retardation is reduced when viewed from a direction intersecting with the plate surface, that is, an oblique direction because the optical axis intersects with the plate surface. It is possible to form an elliptically polarizing plate exhibiting an asymmetrical retardation characteristic that develops and the retardation changes depending on the viewing angle, and by laminating a retardation plate for compensating the front retardation in the plate surface vertical direction on the elliptically polarizing plate, It is possible to obtain a viewing angle compensator with little or no phase difference in the front direction and a phase difference in the oblique direction that changes depending on the viewing angle, and use it to compensate for asymmetric changes in visibility due to changes in the viewing angle of a liquid crystal cell. Therefore, the viewing angle can be improved.

[0009]

EXAMPLE An elliptically polarizing plate in a viewing angle compensating plate according to the present invention is a single-layer retardation plate having an optical axis in a direction intersecting with a plate surface in a state of having a tilt angle and exhibiting anisotropy in birefringence. And a polarizing plate, and exhibits an asymmetric phase difference characteristic in which a phase difference appears when viewed from an oblique direction and the phase difference changes depending on the viewing angle. An example thereof is shown in FIG. Reference numeral 1 is a polarizing plate, and 2 is a retardation plate having birefringence anisotropy.
The elliptically polarizing plate of the example has a birefringent anisotropic retardation layer directly formed on one side of the polarizing plate.

The retardation plate showing anisotropy in birefringence used in the present invention has an optical axis in a direction intersecting with the plate surface with a tilt angle as shown by an arrow on the side surface side in FIG. However, such a birefringent anisotropic retardation plate is, for example, a film made of a nematically aligned liquid crystal polymer,
It can be obtained as a coating layer or the like as in the above examples. The arrow on the plate plane in FIG. 2 indicates the slow axis in the plate surface direction of the retardation plate.

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. When the molecular weight is less than 20,000, it is difficult to obtain a birefringent anisotropic retardation plate having excellent strength, and when it exceeds 200,000, the viscosity is increased and the orientation property is deteriorated, which requires a lot of time for the orientation treatment.

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.

To form a birefringent anisotropic retardation plate made of a liquid crystal polymer, for example, a solution of the liquid crystal polymer is spread on the alignment treated surface and heat treated to orient the liquid crystal polymer and then Can be cooled and, if necessary, peeled off from the orientation-treated surface. In addition, when an alignment treated surface is provided on the surface of the polarizing plate and a liquid crystal polymer layer having an oblique orientation is formed on the surface, a birefringent anisotropic retardation plate is used as a coating layer of the liquid crystal polymer on the polarizing plate. It is possible to obtain an elliptically polarizing plate directly attached.

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 liquid crystal polymer type birefringent anisotropic retardation plate which is nematically aligned at a predetermined tilt angle and is formed after the fixing treatment by cooling is not directly formed as a coating layer on a polarizing plate. In some cases, it is peeled and collected from the orientation-treated surface as necessary.
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 to form an orientation-treated surface. Appropriate methods such as the method described above can be applied as necessary.

The thickness of the birefringent anisotropic retardation plate is appropriately determined according to the viewing angle characteristics of the liquid crystal cell to be compensated and the retardation characteristics of the birefringent anisotropic retardation plate. In the case of a liquid crystal polymer type, it is set to 500 μm or less, preferably 1 to 100 μm in view of flexibility and the like. The flexible birefringent anisotropic phase difference plate has an advantage that it is easy to obtain a viewing angle compensation plate which can be easily applied to a curved surface, a large area surface, or the like.

As the polarizing plate, an appropriate one having a polarizing function 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.
A hydrophilic polymer film such as a partially saponified film of vinyl acetate copolymer, which is drawn by adsorbing iodine and / or dichroic dye, a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride. 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 elliptically polarizing plate is usually in the form of laminating the birefringent anisotropic retardation plate 2 on one side of the polarizing plate 1 as shown in the drawing. In that case, the arrangement angle between the absorption axis of the polarizing plate and the slow axis of the retardation plate can be appropriately determined such as 45 degrees. The lamination can be performed by a method of directly forming a predetermined liquid crystal polymer layer on the polarizing plate as described above, or by a method of laminating the polarizing plate and the retardation plate via an adhesive layer or the like. It can be carried out. The former direct forming method does not require a laminating process using an adhesive layer or the like, is excellent in manufacturing efficiency, and is advantageous in terms of thinning.

As the above-mentioned adhesive, for example, an appropriate adhesive such as an acrylic-based, rubber-based or silicone-based adhesive or a hot-melt adhesive can be used. The adhesive that can be preferably used is excellent in transparency and weather resistance. Further, from the viewpoint of preventing changes in the optical properties of each functional film, it is preferable that a high temperature process is not required at the time of curing or drying, and it is desirable that a curing process for a long time or a drying time is not required. 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 comprises a retardation plate for compensating the retardation in the vertical direction of the birefringence anisotropic retardation plate side of the elliptically polarizing plate. It is a laminate. An example thereof is shown in FIG. Reference numeral 4 is a retardation plate for compensation, and other symbols are the same as above. In addition, 3 is an adhesive layer.

The retardation plate for compensation has a difference in retardation in the direction perpendicular to the plate surface within 50%, preferably as small as possible, with respect to the birefringent anisotropic retardation plate to be laminated. Is used. This makes it possible to offset and reduce the phase difference of the birefringence anisotropy in the direction perpendicular to the plate surface due to the phase difference plate, and reduce or eliminate the phase difference of the viewing angle compensation plate in that direction. The offset of the phase difference in the vertical direction of the plate surface, and thus the compensation of the phase difference, is performed by the plate in the phase difference plate .
It can be carried out by laminating so that the slow axis directions of the plane directions intersect with each other, preferably in the orthogonal state as much as possible.

[0029] As the retardation plate for the compensation, the phase difference due to the viewing angle from the diagonal in one retardation plate of birefringent anisotropy having an optical axis in a direction crossing the plate surface in the present invention since to have differences, for example, polymethyl methacrylate, polycarbonate, polyvinyl alcohol,
A polypropylene or other polyolefin, polyarylate, or a birefringent film formed by stretching a film made of an appropriate plastic such as polystyrene may be used, but preferably used is a direction crossing the plate surface. It is a retardation plate showing anisotropy in birefringence having an optical axis.

That is, a preferable combination of retardation plates forming the viewing angle compensating plate is a combination of birefringent anisotropic retardation plates having an optical axis in a direction intersecting the plate surface. By the combination of the birefringent anisotropic retardation plates, it is possible to compound the difference in retardation due to the oblique viewing angle based on each birefringent anisotropic retardation plate, and Efficiently differentiates the phase difference in the vertical direction and the horizontal direction in combination with the laminating method of the slow axis crossing of the phase difference plate for compensating the phase difference in the vertical direction. Can have

[0031] Thus to form a visual angle compensating plate Te above odor
Retardation plate that complement償用is a plate forming units for the purpose of control of the phase difference may be those obtained by superimposing two or three layers or more. The thickness of the birefringent film used as the retardation plate for compensation can be appropriately determined depending on the retardation to be compensated, etc., but is generally based on a single layer film from the viewpoint of flexibility and the like. It is 500 μm or less, and especially 100 μm or less.

The elliptically polarizing plate and viewing angle compensator of the present invention are composed of ultraviolet absorbers such as salicylic acid ester compounds, benzophenol compounds, benzotriazole compounds, cyanoacrylate compounds and nickel complex salt compounds. It may have an ultraviolet absorbing ability depending on the treatment method.

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, such a viewing angle compensating plate can be arranged on one side or both sides of the liquid crystal cell to form the liquid crystal display device. The arrangement of the viewing angle compensation plate is generally such that the retardation plate is located between the liquid crystal cell and the polarizing plate. 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. 4 exemplifies a liquid crystal display device of a type in which a viewing angle compensating plate is arranged on one side of a 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 The polymer consisting of the acrylic monomer unit represented by the above formula is dissolved in chloroform, and the solution is spin-coated on the polyimide-based rubbing film formed on the polarizing plate by the flow-coat method, and dried by heating. After that, it is heat-treated at 120 ° C. for 30 minutes and then cooled, and is composed of a liquid crystal polymer layer having a nematic structure with a tilt angle of about 20 degrees and a thickness of about 2 μm. The optical axis intersects the plate surface at the tilt angle. A birefringent anisotropic retardation plate was formed to obtain an elliptically polarizing plate. The crossing angle between the slow axis of the retardation plate and the absorption axis of the polarizing plate was set to 45 degrees.

On the other hand, a birefringent anisotropic retardation film made of a liquid crystal polymer film having a thickness of about 2 μm was formed on a glass plate provided with a polyimide rubbing film in the same manner as above.
The film is transferred from a glass plate onto the liquid crystal polymer layer of the elliptically polarizing plate through an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm so that the slow axes in the plate surface directions are orthogonal to each other, and elliptically polarized light is obtained. A type of viewing angle compensator was obtained. The retardation of the retardation film in the direction perpendicular to the plate surface was almost the same as that of the liquid crystal polymer layer in the elliptical polarizing plate.

In the above, as the polarizing plate, NP
FG1220DUN (manufactured by Nitto Denko Corporation) was used. The polyimide-based rubbing film was spin-coated with a solution of pyromellitic dianhydride and diaminodiphenyl ether dissolved in an n-methylpyrrolidone / dimethylformamide mixed solvent, which was then cured at 100 ° C. for 1 hour and then rubbed. It is a thing.

Comparative Example Polycarbonate films were uniaxially stretched at 160 ° C., and two retardation plates having substantially the same retardation in the vertical direction of the plate surfaces were made so that their slow axes were orthogonal to each other. A compensator was obtained by laminating an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm on one surface of a polarizing plate according to Example 1 to have a thickness of 2 μm.
An elliptically polarized viewing angle compensator was formed by laminating a 0 μm acrylic adhesive layer. The crossing angle between the slow axis of the retardation plate and the absorption axis of the polarizing plate was set to 45 degrees.

Evaluation With respect to the elliptically polarized 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. 5. The vertical axis of the graph represents the retardation value (Δnd: product of difference in birefringence and thickness).

[0040]

According to the present invention, we are possible to obtain an asymmetric retardation viewing angle compensating plate Ru can compensate for changes in visibility due to such change in the liquid crystal cell due to changes in the viewing angle by arranging on the outside of the liquid crystal cell It is possible to obtain a liquid crystal display device having a wide viewing angle, light weight, and thinness without using the conventional liquid crystal cell.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of an elliptically polarizing plate.

FIG. 2 is an explanatory perspective view of a birefringent anisotropic retardation plate.

FIG. 3 is a sectional view of an embodiment of a viewing angle compensation plate.

FIG. 4 is a sectional view of an embodiment of a liquid crystal display device.

FIG. 5 is a graph showing the change in phase difference depending on the viewing angle.

[Explanation of symbols]

1: Polarizing plate 2: Retardation plate showing birefringence anisotropy 3: Adhesive layer 4: Phase difference plate for compensation 5: Liquid crystal cell

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-323274 (JP, A) JP-A-4-123021 (JP, A) JP-A-5-241019 (JP, A) JP-A-3- 276123 (JP, A) JP-A-5-80323 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 5/30

Claims (5)

(57) [Claims] 1. A laminated body of a single-layer retardation plate and a polarizing plate, which has an optical axis in a direction intersecting with a plate surface in a state of having a tilt angle and exhibits anisotropy in birefringence, and is oblique. asymmetric retardation characteristics the position of the shown to elliptic polarizing plate in which the phase difference retardation expressed is changed by the viewing angle when viewed from a direction
On the phase difference plate side, the phase difference in the vertical direction of the phase difference plate
The retardation plate to be compensated has a shape in which the slow axis direction of the plate surface intersects.
A viewing angle compensating plate characterized by being laminated in a state . 2. The viewing angle compensation according to claim 1, wherein the retardation plate in the elliptically polarizing plate is made of a nematically aligned liquid crystal polymer.
Compensation plate . 3. A viewing angle complement 償板 of claim 2 to one side of the retardation plate is a polarizing plate in which is formed directly as a coating layer of the liquid crystal polymer in the elliptically polarizing plate. 4. A retarder laminated to elliptically polarizing plate is also retardation film exhibiting anisotropy in birefringence of the claims above 1-3
The viewing angle compensator according to 1 . 5. A liquid crystal display device characterized by having a viewing angle compensating plate according to one of the claims 1 to 4 above on at least one side of the liquid crystal cell.