JP3336100B2 - Viewing angle compensator, elliptically polarizing plate and liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

BACKGROUND OF THE INVENTION As liquid crystal display devices have become widespread as various display screens for personal computers, word processors, data terminal devices, televisions, and the like, it has been pointed out that the viewing angle is narrow as a viewing angle range that can be easily viewed. By the way, in the TFT type liquid crystal display device, even if the display quality when viewed from the front can be higher than that of the CRT, the viewing angle from the vertical direction shows asymmetry and one of the upper and lower sides, usually the viewing angle from the upper side is narrower. It is pointed out.

[0003] The problem of the narrow viewing angle becomes a more serious problem, especially when viewed from different angles, such as a television or a large screen display device, as compared with personal use. It has been pointed out that an increase in the viewing angle is strongly desired.

[0004]

2. Description of the Related Art Conventionally, the above-mentioned viewing angle expanding means includes:
The orientation division method and the capacitive coupling pixel division method have been known.
In each of the methods, one pixel is divided into two different regions to compensate for the asymmetry of the viewing angle of each other, and to obtain a symmetric viewing angle characteristic as an area average.

[0005] However, in any of the methods, there is a problem that the contrast ratio is lowered due to the occurrence of disclination (disorder of the alignment) at the interface between the divided regions of the pixels. In addition, since this method adds improvements to the inside of the liquid crystal cell, there are problems such as the necessity of introducing new manufacturing equipment, in addition to the complication of the cell manufacturing process and the reduction of the cell manufacturing yield. there were.

[0006]

SUMMARY OF THE INVENTION According to the present invention, by disposing the liquid crystal cell outside the liquid crystal cell, the asymmetric change in visibility of the liquid crystal cell due to the viewing angle can be compensated, and the viewing angle can be expanded. It is an object of the present invention to develop a technology that can form a liquid crystal display device such as a TFT type, and therefore can use a conventional cell as it is.

[0007]

According to the present invention, there is provided a tilt retardation plate having an anisotropic refractive index having an optical axis in a direction intersecting a plate surface, and a difference in phase difference in a direction perpendicular to the plate surface. and within 50% retardation of the inclined retardation film, Ri Na stacked so slow axis of their plate surface direction is orthogonal, before
The crossing angle of the above-mentioned inclined phase difference plate with respect to the plate surface is 40 degrees.
Of the slow axis direction in a certain direction and a direction that is 140 degrees
Absolute value of retardation difference is greater than 10 nm
Viewing angle compensation plate, wherein Monodea Rukoto, and have elliptically polarizing plate, characterized in that its viewing angle compensation plate consisting of a laminate of a polarizing plate, and the viewing angle compensation plate on at least one side of the liquid crystal cell A liquid crystal display device characterized by the following.

[0008]

With the above arrangement, the phase difference when viewed from the direction perpendicular to the plate surface, that is, from the front, is small or absent, and when viewed from the direction intersecting with the plate surface, that is, from the oblique direction, a phase difference appears. It is possible to obtain a viewing angle compensating plate exhibiting an asymmetric phase difference characteristic in which the phase difference changes depending on the viewing angle, and using the same, compensates for the asymmetric visibility change accompanying the viewing angle change of the liquid crystal cell to improve the viewing angle. be able to.

[0009]

The viewing angle compensating plate of the present invention is characterized in that the difference in the phase difference in the direction perpendicular to the plate surface is different from that of the inclined retardation plate having an optical axis in a direction intersecting the plate surface. It is formed by laminating retardation plates within 50% of the retardation plate such that the slow axes in the plate surface direction are orthogonal to each other.
And the angle of intersection of the inclined retardation plate with the plate surface is 4
Slow axis in the direction of 0 degree and the direction of 140 degree
The absolute value of the difference between the retardation values in the directions is less than 10 nm
Ing from the largest. An example is shown in FIG. this is,
It is obtained by laminating the components composed of the inclined retardation plates 1.

The inclined retardation plate used in the present invention is of an anisotropic refractive index in which the direction of the optical axis intersects the plate surface as shown by the arrow in FIG. For example, it can be obtained as a film made of a nematic-aligned liquid crystal polymer.

As the liquid crystal polymer, those capable of having nematic alignment are used, and the type thereof is not particularly limited. By the way, as an example of such a liquid crystal polymer,
A main chain type or side chain type in which a conjugated linear atomic group (mesogen) for imparting liquid crystal orientation is introduced into the main chain or side chain of the polymer. Specific examples of the main chain type liquid crystal polymer include a nematic-aligned polyester-based liquid crystal polymer.

Specific examples of the side chain type liquid crystal polymer include polysiloxane, polyacrylate, polymethacrylate or polymalonate having a main chain skeleton and a side chain having a mesogen moiety composed of a para-substituted cyclic compound unit capable of imparting nematic alignment. And the like.

The para-substituted cyclic compound unit includes
For example, a low-molecular liquid crystal compound having a nematic liquid crystal property, which is composed of a para-substituted aromatic unit, a para-substituted cyclohexyl ring unit, and 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 liquid crystal compound, and is generally a cyano group, an alkyl group, an alkoxy group, or the like.

The liquid crystal polymer which can be preferably used has a weight average molecular weight of 2,000 to 200,000 based on polystyrene conversion by gel permeation chromatography. If the molecular weight is less than 2,000, it is difficult to obtain a tilted retarder having excellent strength. If the molecular weight is more than 200,000, the viscosity is increased to lower the orientation, and the alignment treatment requires many hours.

The liquid crystal polymer which can be preferably used has a glass transition point higher than the operating temperature in view of the stability of the fixed alignment. By the way, when used at around normal temperature, the liquid crystal polymer having a glass transition point of less than 30 ° C. may cause a change in the immobilized liquid crystal structure and induce a decrease in function.

In order to form an inclined retardation plate composed of a liquid crystal polymer, for example, a solution of the liquid crystal polymer is spread on an alignment treatment surface, heat-treated, the liquid crystal polymer is obliquely aligned, and then cooled to be cooled. It can be carried out by a method of peeling from the alignment treated surface according to the conditions.

The above-mentioned alignment treatment surface may be any as long as it can obliquely align the liquid crystal polymer in a state having a tilt angle. Examples thereof include those obtained by forming a thin film of polyimide or polyvinyl alcohol on an appropriate substrate made of a glass plate or a polymer film and rubbing the surface thereof, and those obtained by obliquely depositing silicon oxide. .

For example, the liquid crystal polymer is developed by dissolving the liquid crystal polymer in an appropriate solvent to form a solution, which is then spin-coated, roll-coated, flow-coated, printed, dip-coated, cast-film-formed. It can be carried out by a method of developing a thin layer by an appropriate method such as a method, and drying it to remove the solvent. Further, the method can also be carried out by a method without using a solvent, such as a method in which a liquid crystal polymer is heated and melted so as to exhibit an isotropic phase, and is developed into a thin layer while maintaining the temperature.

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

When a liquid crystal polymer is spread on a polyimide-based rubbing film and heat-treated, the polymer can be oriented in the rubbing direction.
By performing the treatment at a curing temperature of 200 ° C., especially 100 to 200 ° C., the tilt angle of the liquid crystal polymer can be controlled within a range of about 40 degrees or less. 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-based tilted phase plate having a nematic alignment at a predetermined tilt angle formed after the fixing process by cooling is separated and recovered from the alignment-treated surface as necessary. For example, a method using a rubbing film forming material having a releasable side chain composed of a long-chain alkyl group or the like, or a glass plate having a surface modified with a silane compound having an alkyl chain having 8 to 18 carbon atoms is oriented. An appropriate method such as a method of forming a processing surface can be applied as needed.

The thickness of the tilt retarder is appropriately determined according to the viewing angle characteristics of the liquid crystal cell to be compensated, the phase difference characteristics of the tilt retarder, and the like. In the case of a liquid crystal polymer, the thickness is 50 μm or less, especially 1 to 10 μm from the viewpoint of flexibility and the like. Note that the flexible inclined phase difference plate has an advantage that a viewing angle compensating plate that can be easily applied to a curved surface, a large area surface, or the like is easily obtained.

[0023] The use Iuru inclined retardation plate to expand the viewing angle, such as TFT type liquid crystal display device in the present invention, the slow axis direction in a direction crossing angle with respect to the plate surface is a direction 140 degrees is 40 degrees The absolute value of the difference between the retardation values is larger than 10 nm.

That is, with the vertical direction with respect to the horizontally installed inclined retarder as a reference direction, the inclined retarder is moved ± 40 degrees in the slow axis direction from the horizontal state (ie, 40 degrees and 140 degrees).
Degree) When the retardation value in the reference direction (の nd: the product of the difference between the birefringence and the plate thickness) when inclined is △ nd ₄₀ and △ nd _-40 , respectively, the formula: ┃ △ nd ₄₀ − Δnd _-40 ┃> 10 nm.

In the present invention, the retardation plate used for lamination with the inclined retardation plate has a difference in retardation in the direction perpendicular to the plate surface within 50% of the laminated inclined retardation plate, preferably as much as possible. Less. Accordingly, the phase difference of the inclined phase difference plate in the direction perpendicular to the plate surface can be reduced and the phase difference of the viewing angle compensator in the direction can be reduced or eliminated.

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

That is, a preferable combination of the phase difference plates for lamination forming the viewing angle compensating plate is a combination of the inclined phase difference plates as in the embodiment of the above-mentioned example. By making the combination of the inclined retardation plates, it is possible to combine the difference of the phase difference due to the oblique viewing angle based on each inclined retardation plate,
In addition, the phase difference can be efficiently made different in a state in which the phase difference in the vertical direction and the horizontal direction is combined in combination with the lamination method orthogonal to the slow axis.

In the above, the laminated retardation plate or retardation plate may be formed as a laminate of two or more plate forming units for the purpose of controlling the retardation or the like. The thickness of the birefringent film used for lamination with the inclined retardation plate can be appropriately determined according to the retardation to be compensated, etc., and is generally 500 μm based on a single-layer film in terms of flexibility and the like. Hereinafter, it is particularly 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 such 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. Upon lamination, an appropriate adhesive such as an acrylic-based, rubber-based, or silicone-based adhesive or a hot-melt-based adhesive may be used as necessary. Note that an error of the orthogonal state due to work accuracy and the like is allowed.

The adhesive used is preferably excellent in transparency and weather resistance, and preferably does not require a high-temperature process for curing and drying from the viewpoint of preventing changes in the optical properties of each functional film. Further, it is desirable that a curing treatment and a drying time which do not require a long time are 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 compensating plate of the present invention can be preferably used for expanding the viewing angle of a liquid crystal display device by compensating the change in the visibility of the liquid crystal cell due to the viewing angle. In this case, the viewing angle compensating plate should be used alone. It can also 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 compensating plate of the present invention with a polarizing plate. FIG. 2 shows an example of the elliptically polarizing plate. 2 is a polarizing plate and 4 is a viewing angle compensating plate. Reference numeral 3 denotes an adhesive layer.

As the polarizing plate, an appropriate polarizing plate having a polarizing function can be used, but generally a polarizing plate is used. There is no particular limitation on the polarizing film, and for example, a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, ethylene
A film obtained by adsorbing iodine and / or a dichroic dye on a hydrophilic polymer film such as a vinyl acetate copolymer partially saponified film, a dehydration product of polyvinyl alcohol or a dehydrochlorination product of polyvinyl chloride And a polyene oriented film. The thickness of the polarizing film is usually 5
８０80 μm, but is not limited to this.

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

The polarizing plate and the viewing angle compensating plate may be treated with a UV absorber such as a salicylate compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, and a nickel complex compound. It may have an ultraviolet absorbing ability. Examples of the adhesive include those described above. When the adhesive layer is an adhesive layer, its surface is preferably protected by a separator or the like until practical use.

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

FIG. 3 illustrates a liquid crystal display device of a type in which a viewing angle compensator is disposed on one side of a liquid crystal cell on the viewing side.
Reference numeral 5 denotes a liquid crystal cell, and other symbols are the same as described above. The viewing angle compensating plate and the like can 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 compensator is applied is arbitrary, and may be, for example, an active matrix drive type represented by a thin film transistor type, a simple matrix drive type represented by a twisted nematic type or a super twisted nematic type, or the like. It can be applied to various types of liquid crystal cells.

Reference Example A polymer consisting of the acrylic monomer unit represented by the above formula is dissolved in chloroform, and the solution is spread on a polyimide rubbing film formed on a glass plate by a flow coat method by spin coating, 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 ° is about 2 mm.
The liquid crystal polymer film of μm is transferred from the rubbing film to the triacetyl cellulose film to form a gradient retardation plate having an anisotropic refractive index in which the optical axis crosses the plate surface at an angle of about 20 degrees. The two sheets were laminated via 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, the phase difference in the direction perpendicular to the plate surface of the laminated inclined retardation plates was substantially 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, cured at 100 ° C. for 1 hour, and then rubbed. Things.

Example A According to the reference example , Δnd ₄₀ was 310 nm and Δn was
d _-40 is 220nm, thus the formula: ┃ △ _{nd 40} -
Δnd ₋₄₀ ┃> 10 nm were formed to obtain two viewing angle compensating plates.

COMPARATIVE EXAMPLE Two retardation plates, each of which is obtained by uniaxially stretching a polycarbonate film at 160 ° C. and having substantially the same phase difference in the direction perpendicular to the plate surface, were placed such that their slow axes in the plate surface direction were orthogonal to each other. A viewing angle compensator was obtained by laminating through an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm.

With respect to the viewing angle compensating plates obtained in the evaluation reference example and the comparative example, the change of the phase difference due to the viewing angle in the slow axis direction of one of the retardation plates was examined. The result is shown in FIG. Note that the change in the phase difference of the viewing angle compensator obtained in Example A was substantially similar to that of the reference example .

[0043]

According to the viewing angle compensator of the present invention, by arranging it outside the liquid crystal cell, it is possible to compensate for a change in visibility due to an asymmetric change in phase difference 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, light weight and excellent thinness without having to change the liquid crystal cell.

[Brief description of the drawings]

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

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

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

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

[Explanation of symbols]

 1: tilt retardation plate 2: polarizing plate 3: adhesive layer 4: viewing angle compensator 5: liquid crystal cell

Continuation of the front page (56) References JP-A-7-181325 (JP, A) JP-A-4-204402 (JP, A) JP-A-5-157913 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) G02B 5/30 G02F 1/1335 510

Claims (5)

(57) [Claims] 1. A retardation plate having an anisotropic refractive index having an optical axis in a direction intersecting with a plate surface and a retardation plate having a difference in phase difference in a direction perpendicular to the plate surface being 50. % within a phase difference plate, Ri Na stacked so slow axis of the plates face directions are perpendicular, said inclined retardation plate whose plate surfaces
Direction where the intersection angle with respect to 40 degrees and 140 degrees
Of the retardation value in the slow axis direction
Viewing angle compensation plate pair value and said der Rukoto larger than 10 nm. 2. The viewing angle compensator according to claim 1 , wherein the retarder laminated on the inclined retarder is also an inclined retarder. 3. A viewing angle compensator according to claim 1 or 2 inclined retardation plate is a liquid crystal polymer which is nematic orientation. 4. elliptically polarizing plate characterized by comprising the laminate of the viewing angle compensation plate according to claim 1 to 3 and the polarizing plate. 5. A liquid crystal display device characterized by having at least one side of the liquid crystal cell viewing angle compensator according to claim 1-3.