JPH09230335A - Optical compensation film and liquid crystal display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical compensation film which is exceedingly widened in the visual field angle of a TN type LCD and is improved in heat resistance, etc., by subjecting the surface on at least one surface of this optical compensation film to at least one kinds of surface treatment selected from a corona discharge treatment, flame treatment and glow discharge treatment. SOLUTION: This optical compensation film has at least the optically anisotropic layer contg. a disk-shaped compd. on the base consisting of a transparent high-polymer film. The direction where the absolute value of the Re value of this layer attains the min. value is not a normal direction nor a surface direction and the direction where the Re value attains 0 does not exist. The outermost layer on at least one side of such optical compensation film, i.e., the optically anisotropic layer and/or the outermost layer on the back of the base is subjected to the surface treatments in order to intensify the tacky adhesive power of the optical compensation film and tacky adhesive. At least one kinds among the glow discharge treatment, corona discharge treatment and flame treatment are used as the surface treatment. In the glow discharge treatment, the highest adhesive effect is obtainable particularly in the case steam is introduced into the atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical compensation film which significantly improves the viewing angle characteristics of contrast and display color of TN-LCD and has higher durability and handleability, and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art As a liquid crystal display device, a plurality of stripe-shaped electrodes facing each other are arranged to intersect with each other via a liquid crystal having a twist angle of 90 ° or more in a molecular arrangement. A pixel electrode for forming a pixel, a simple matrix type, a pixel electrode having a three-terminal type or two-terminal type non-linear active element using a thin-layer transistor or a diode with a twist angle of 90 ° of liquid crystal molecules, and this pixel electrode An active matrix type in which a pixel is formed with a counter electrode and a counter electrode has been proposed. Of these liquid crystal display devices, a word processor, a personal computer, or a T
A display device such as a V monitor is being changed from a mainstream CRT to an active matrix type, which has high image quality and a high response speed, among liquid crystal display devices having the great advantages of thinness, light weight, and low power consumption.

This active matrix type is basically a twisted nematic type (hereinafter referred to as TN type) liquid crystal cell using a nematic liquid crystal having a twist angle of 90 °. As a non-linear element, a three-terminal type is used. TFT-LCDs using thin-layer transistors and MIM-LCDs using two-terminal MIM elements are currently the mainstream.

The TFT-LCD or MIM-LCD is a TFT or MIM for driving at least each pixel.
A TN type liquid crystal cell having an element, a polarizer arranged so that its transmission axis is orthogonal or parallel to the rubbing direction of the light incident side substrate of the liquid crystal cell, and the transmission axis of the light emitting side substrate of the liquid crystal cell. It is composed of an analyzer arranged parallel or orthogonal to the rubbing direction, has a fast response speed (tens of milliseconds), and has a high display contrast, so it is the most effective compared to other methods. It is a method. However, since these liquid crystal display devices use nematic liquid crystal having a twist angle of 90 °, there is a serious problem that the contrast is reduced depending on the viewing angle due to the principle of the display method.

On the other hand, JP-A-4-229828,
As seen in JP-A-4-258923 and the like,
A method has been proposed in which an optical compensation film is arranged between a pair of polarizing plates and a TN type liquid crystal cell to increase the viewing angle. The optical compensation film proposed in the above patent publication has a phase difference in the direction perpendicular to the liquid crystal cell of almost zero, and does not exert any optical action from the front, but when tilted, A phase difference is developed and the phase difference developed in the liquid crystal cell is compensated. However, this method cannot improve the deterioration of the viewing angle, especially the contrast when tilted in the vertical direction or the horizontal direction from the normal direction of the screen, and cannot be used at all as an alternative to the CRT.

JP-A-4-366808 and JP-A-4-3
In Japanese Patent No. 66809, a liquid crystal cell containing a chiral nematic liquid crystal with an inclined optical axis is used as an optical compensation cell to improve the viewing angle, but a two-layer liquid crystal system is expensive and very heavy. .

Further, JP-A-6-75116, EP
In the specification of 0576304A1 and Japanese Unexamined Patent Publication No. 6-214116, the use of an optical compensation film which exhibits optically negative uniaxiality and whose optical axis is inclined makes it possible to obtain a viewing angle of a TN type LCD. Methods have been proposed to improve the properties. According to this method, the viewing angle is improved as compared with the conventional one, but it is still difficult to realize a wide viewing angle enough to consider CRT replacement.

Therefore, the inventors of the present invention have filed Japanese Patent Application No. 7-1570.
No. 28, an optically anisotropic element having an optically negative uniaxial property whose optical axis is inclined from the normal direction of the film, and an optically negative uniaxial device having its optical axis in the normal direction of the film. It has been found that the viewing angle characteristics of the TN type LCD are remarkably improved by the optical compensation film having the characteristics of a certain optical anisotropic element. Further, by using an optical compensation film in which the tilt angle of the discotic compound continuously changes in the thickness direction, it is possible to achieve a higher degree of compensation.

However, the optical compensation film produced by these methods has sufficient durability itself,
When it is incorporated into a liquid crystal display device, it is attached to the glass and polarizing plate via an adhesive, but it lacks the durability to cope with adverse environments such as in-vehicle applications, in particular, the resistance to humidity and heat, so that it can be stored under high temperature and high humidity over time. However, there is a problem in that bubbles and peeling occur at the adhesive interface, and as a result, the effect of improving the viewing angle is deteriorated.

[0010]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical compensatory film capable of remarkably widening the viewing angle of a TN-LCD and having improved durability at the adhesive interface, especially wet and heat resistance. It is to industrially provide a liquid crystal display device using the same.

[0011]

Means for Solving the Problems The above-mentioned problems are (1) having an optically anisotropic layer containing at least a discotic compound on a support composed of a transparent polymer film, the absolute value of the Re value of which is minimum. In the optical compensation film in which there is no direction in which the Re value is 0, which is neither the normal direction nor the surface direction, and a corona discharge treatment, a flame treatment, or a glow treatment is performed on the surface of at least one side of the optical compensation film. An optical compensation sheet, which has been subjected to at least one surface treatment selected from discharge treatments. (2) The transparent polymer film support has negative uniaxial optical characteristics having its optical axis in the normal direction of the film, and the main refractive indices nx and ny in the support surface and the main refraction in the thickness direction. Plane orientation retardation Rt defined by the ratio nz
The optical compensation film of (1), wherein h satisfies the condition of Expression 1. Formula 1 10 ≦ Rth = {(nx + ny) / 2−nz} × d ≦ 100 (nm) (3) The tilt angle of the discotic compound of the optically anisotropic layer is
The optical compensation film according to (1) or (2), which is characterized in that it continuously changes in the thickness direction of the layer. (4) The method is characterized in that after the surface treatment is performed, an adhesive layer is provided on the surface within 10 months (1).
(3) Optical compensation film. (5) The optical compensation film of (1) to (3), which is characterized in that after the surface treatment, a polarizing plate is laminated on the surface of the polarizing plate via an adhesive layer within 10 months. (6) A liquid crystal cell in which a liquid crystal is sandwiched between two electrode substrates, two polarizing plates arranged on both sides of the liquid crystal cell, and at least one optical compensation film between the liquid crystal cell and the polarizing plate. A liquid crystal display device, wherein the optical compensation film is the optical compensation film of (1) to (3). Achieved by

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below step by step. The surface treatment will be described later. The transparent polymer film support of the present invention has a light transmittance of 80% or more and at the same time has an optically negative uniaxial property and its optical axis is in the normal direction of the film, and the main refractive index in the film plane. N
x, ny, the main refractive index in the thickness direction is nz, and the film thickness is d, the relationship between the triaxial main refractive indexes is nz <ny.
= Nx is satisfied and the expression {(nx + ny) / 2−nz} ×
The surface orientation retardation Rth represented by d is 10 nm.
To 100 nm is preferable. However, nx and ny
The values of do not have to be exactly equal, they need to be approximately equal. Specifically, | nx-ny | / | nx-nz | ≦
If it is 0.3, there is no practical problem. | Nx-ny |
The front retardation represented by xd is preferably 50 nm or less, and more preferably 20 nm or less. Regarding the thickness d, if the thickness is 10 μm or less, handling is difficult, and handling during film formation is also difficult. If the thickness d is 150 μm or more, it is difficult to set Rth to 100 nm or less. ,
Coloring due to the viewing angle becomes a problem. Therefore, 10 μm or more, 1
The thickness is preferably 50 μm or less, more preferably 50 μm or more and 100 μm or less.

Specifically, materials having a small intrinsic birefringence such as Zeonex (Nippon Zeon), ARTON (Nippon Synthetic Rubber), and triacetyl cellulose (Daicel), which have a small intrinsic birefringence value, or polycarbonate or polyarylate. A material having a large intrinsic birefringence value such as polysulfone, polyethersulfone, or the like is formed into a film by solution casting, melt extrusion, or the like. By controlling the film forming temperature, tension and the like, the polymer film having the above preferable optical characteristics can be obtained.

Further, it is preferable to provide an undercoat layer of gelatin or the like on the obtained support in order to improve the adhesion to the alignment film described below, and the back layer for handling aptitude and scratch resistance. It is preferable to provide a protective layer in which silica or the like is dispersed in a binder.

In order to provide the discotic compound of the present invention on the above-mentioned polymer film support and orient it, a generally known inorganic or organic orientation film is used. Considering the ease of handling in manufacturing, an organic alignment film which can be coated with a solvent is preferable. As the polymer used as the organic alignment film,
Examples of the polyimide, polystyrene derivative and the like, and water-soluble ones include gelatin, polyvinyl alcohol, carboxymethyl cellulose and the like. By subjecting all of them to rubbing treatment, the discotic compound can be oriented obliquely. A polyimide film, which is widely used as an alignment film for LCDs, is also preferable as the organic alignment film, which is a polyamic acid (for example, manufactured by Hitachi Chemical Co., Ltd.).
LQ / LX series, SE series manufactured by Nissan Chemical Co., Ltd.) is applied to the surface of the substrate and baked at 100 to 300 ° C. for 0.5 to 1 hour and then rubbed. Further, a thin film, such as an LB film made of an azobenzene derivative, which undergoes isomerization by light and in which molecules are uniformly arranged with directionality is also applicable. In addition, it is also possible to use one in which a dielectric substance is oriented by an electric field or a magnetic field.

The alignment layer is preferably hard-crosslinked so as not to be broken or deformed under high temperature and high humidity. For the above-mentioned cross-linking, a method of reacting the alignment film materials with each other by light, heat, change of PH, etc.
There is a method in which a compound having high reaction activity (a so-called cross-linking agent) is added to cross-link the alignment film materials. Next, regarding the timing of cross-linking, it is sufficient if sufficient durability can be obtained at the stage of the final product, so after the orientation film is applied on the transparent film, the cross-linking reaction occurs anywhere between the products. May be. Considering the orientation of the discotic compound described below, it is preferable that sufficient crosslinking be performed after the discotic compound is oriented.

As specific examples of the cross-linking agent, the compounds shown below are preferable for polyvinyl alcohol and its derivatives, which are particularly highly hydrophilic. Specifically, for example, aldehydes (formaldehyde, glyoxer-
, Glutaraldehyde, etc.), N-methylol compounds (dimethylolurea, methylol-dimethylhydantoin, etc.), dioxane derivatives (2,3-dihydroxydioxane, etc.), activating carboxyl groups Compounds that act on (carbenium, 2-naphthalene sulfonate, 1.1-bispyrrolidino-1-chloro-pyridinium, 1-morpholinocarbonyl-3- (sulfonatoaminomethyl), etc.). Active vinyl compounds (1, 3,
5-triacloyl-hexahydro-s-triazine,
Bis (vinylsulfone) methane, N, N′-methylenebis- [β- (vinylsulfonyl) propionamide] and the like). Active halogen compounds (2,4-dichloro-6-hydroxy-s-triazine etc.), isoxazoles, dialdehyde starch, etc. can be used alone or in combination. Considering the production process and the like, aldehydes having high reaction activity, particularly glutaraldehyde, are preferable.

The above-mentioned alignment film can be generally prepared by coating on a support, drying and rubbing. When the above-mentioned water-soluble polymer is used as an alignment film, the coating liquid is preferably a mixed solvent of an organic solvent such as methanol having an antifoaming action and water, and the solvent composition thereof is 50 to 95 vol of water. ． %, Methanol 5 to 50 vo
l. %. Thereby, the generation of bubbles is suppressed, and the planar defects of the alignment film and further the optical compensation film are significantly reduced.

The coating method includes spin coating, dip coating, extrusion coating and bar coating. The film thickness is preferably 0.1 μm to 5 μm. Drying can be carried out at 20 ° C to 110 ° C. It is preferably 60 ° C to 100 ° C. Drying is 1
It can be done in minutes to 36 hours. It is preferably 3 minutes to 30 minutes.

Next, the optically anisotropic layer of the present invention will be described. Examples of the discotic compound include C.I. Destr
ade et al., Mol. Cryst. 71 volumes, 1
The benzene derivative described in p. 11 (1981), B. Kohne et al., Angew. Ch
em. Vol. 96, p. 70 (1984) and cyclohexane derivatives described in J. Am. M. Lehn et al.,
J. Chem. Commun. , P. 1794 (1985).
Year), J.M. Research report by Zhang et al. Am. Che
m. Soc. 116, pp. 2655 (1994), such as azacrown-based and phenylacetylene-based macrocycles. Generally, these are used as the mother nucleus of the molecular center, and straight-chain alkyl groups, alkoxy groups, and substituted It has a structure in which a benzoyloxy group or the like is linearly substituted as its straight chain, exhibits liquid crystallinity, and includes what is generally called discotic liquid crystal. However, the present invention is not limited to the above description as long as the molecule itself has negative uniaxiality and can impart a certain orientation. In the present invention, the term "formed from a discotic compound" does not mean that the final product is required to be the compound. For example, the low-molecular discotic liquid crystal has a group that reacts with heat, light, or the like. As a result, those which are polymerized or cross-linked by a reaction with heat, light or the like to have a high molecular weight and lose liquid crystallinity are also included.

Next, the discotic compound in the present invention refers to a discotic liquid crystal as listed below, or a reaction of a discotic liquid crystal that no longer exhibits liquid crystallinity due to a reaction with another low molecular compound or polymer. It refers to all compounds in which the molecule itself has optically negative uniaxiality, such as products.

[0022]

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[0023]

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[0024]

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[0025]

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When the discotic compound in the present invention is a discotic liquid crystal, the direction in which the Re value of the layer containing them is the minimum is neither the normal direction nor the plane direction of the film,
Moreover, it is preferable that there is no direction (optical axis) in which the Re value becomes 0, but it is further preferable that the tilt angle of the optical axis of the discotic compound is continuously changed in the thickness direction. Processing is required. Generally, in the case of a liquid crystal cell using a nematic liquid crystal, the optical axis of liquid crystal molecules is aligned in a certain direction by sandwiching both sides of the liquid crystal layer with an alignment film subjected to rubbing treatment. That is, the liquid crystal molecules are uniformly aligned in the thickness direction by the alignment regulating force of the alignment films on both sides of the liquid crystal layer, and the alignment regulating force of the alignment film is unbalanced on both sides. , The orientation of molecules can be continuously changed in the thickness direction. This idea can be applied to discotic liquid crystals. Specifically, a discotic liquid crystal is applied to a substrate on which a rubbing-processed organic alignment film or inorganic alignment film is formed, and one side of the liquid crystal layer is in a liquid crystal phase with an open system (air layer), more preferably disconematic. To raise the temperature to the phase formation temperature. However, when the alignment regulating force of the alignment film is sufficiently strong, the tilt angle of the optical axis of the discotic compound in the thickness direction can be obtained even if one side of the liquid crystal layer is left open (air layer). There are cases where they are the same.

As a result, the liquid crystal has an oblique orientation that continuously changes in the thickness direction, and remains in the solid state at room temperature while maintaining the orientation by subsequent cooling. In this case, the tilt angle in the vicinity of the alignment film can be controlled by a discotic liquid crystal material, an alignment film material, rubbing, etc., and the tilt angle is preferably 0 ° to 85 °, and 0 ° to 5 °.
0 ° is more preferable. Also, the tilt angle near the air layer is
It can be controlled with discotic liquid crystal materials, plasticizers, binders, surfactants, etc. Furthermore, with these plasticizers, binders, surfactants, etc., the degree of orientation change in the thickness direction Can also be controlled.

No particular limitation is imposed on the plasticizer as long as it is compatible with the discotic liquid crystal used, and it is preferable to have a reactive substituent from the viewpoint of imparting heat resistance. The weight of the discotic liquid crystal is 0.1 wt% to 50 wt.
% Is preferred. Further, as a preferable example of the binder, there is no particular limitation as long as it does not significantly disturb the alignment of the discotic liquid crystal used, and a commercially available polymer can be used. As a result of diligent research by the present inventor, it was found that a cellulose-based polymer derivative is extremely preferable.

The rubbing treatment is the same as the one widely used as a liquid crystal alignment treatment step for LCDs. The surface of the alignment film is made of paper, gauze, felt, rubber, nylon, polyester fiber, or the like. Rubbing in a certain direction to obtain an orientation. In general, rubbing is performed several times using a cloth in which fibers having a uniform length and thickness are planted on average.

Of the discotic compound thus obtained,
In order to be able to maintain the oblique orientation that continuously changes in the thickness direction even under high temperature and high humidity, a polymerizable unsaturated group, an epoxy group, a hydroxyl group, an amino group, and a carboxyl group are previously added to the discotic compound. Radical polymerization of a polymerizable unsaturated group with a functional group such as heat or a photopolymerization initiator, or ring-opening polymerization of an epoxy group with a photoacid generator,
It is preferable to crosslink the discotic compound itself by a crosslinking reaction with a polyvalent isocyanate or a polyvalent epoxy compound. At this time, another compound having the same functional group may be contained.

Since the optical compensation film of the present invention compensates birefringence due to a liquid crystal cell in a liquid crystal display element, it is preferable that the wavelength dispersion of the optically anisotropic element is equal to that of the liquid crystal cell. That is, the optically anisotropic elements 450 and 55
The retardation by the light of 0 μm is R450,
If R550, then R450 / R55 representing chromatic dispersion
The 0 value is preferably 1.0 or more.

Next, the surface treatment of the present invention will be described. The surface treatment of the present invention is performed on at least one side, namely, in order to strengthen the adhesive force between the optical compensation film and the pressure-sensitive adhesive.
It is applied to the outermost layer of the optically anisotropic layer and / or the outermost layer of the support back. It is preferably the outermost layer of the support back.

As a preferable surface treatment, glow discharge treatment,
Examples thereof include corona discharge treatment and flame treatment. Among these, the glow discharge treatment and the corona discharge treatment are preferable. These treatments may be performed alone or in combination of two or more. These methods will be described in detail below. The glow treatment is a conventionally known method, for example, Japanese Patent Publication Nos. 35-7578 and 36-1033.
No. 6, No. 45-22004, No. 45-22005,
45-24040, 46-43480, JP-A-53-129262, and U.S. Pat. No. 3,057,792.
No. 3,057,795, No. 3,179,482
Issue 3, Issue 3,288,638, Issue 3,309,299
Issue No. 3,424,735 Issue No. 3,462,335
Nos. 3,475,307 and 3,761,299
No. 4,072,769, British Patent 891,469
No. 997,093, etc. can be used. With such a glow treatment, the most excellent adhesion effect can be obtained especially when water vapor is introduced into the atmosphere. In addition, this method suppresses the yellowing of the optical compensation film,
It is also very effective in preventing blocking. The steam partial pressure when performing the glow treatment in the presence of steam is preferably 10% or more and 100% or less, and more preferably 40% or more and 90% or less. If it is less than 10%, it becomes difficult to obtain sufficient tackiness. The gas other than water vapor is air composed of oxygen, nitrogen and the like.

Further, if the vacuum glow treatment is carried out in a state where the support to be surface-treated is heated, the tackiness is improved in a shorter time as compared with the treatment at room temperature, which is effective. The preheating temperature is preferably 50 ° C or higher and Tg or lower, more preferably 60 ° C or higher and T
g or less is more preferable, and 70 ° C. or more and Tg or less is further preferable. If it is preheated at a temperature of Tg or higher, the tackiness deteriorates. The degree of vacuum during the glow treatment is 0.005 to 20 Torr
It is preferred that More preferably, 0.02 to 2 To
rr. Further, the voltage is preferably between 500 and 5000V. More preferably, it is 500-3000V.
The discharge frequency used is, as seen in the prior art, from direct current to several 1000 MHz, preferably 50 Hz to 20 MH.
z, and more preferably 1 KHz to 1 MHz. Discharge treatment intensity is 0.01 KV · A · min / m ^{2 to 5} KV · A
・ Min / m ² is preferable, more preferably 0.15 KV ・
A desired adhesive performance can be obtained at A · min / m ^{2 to 1} KV · A · min / m ² . It is preferable that the temperature of the support thus subjected to the glow treatment is immediately lowered by using a cooling roll.

Corona treatment is the most well-known method, and any conventionally known method, for example, Japanese Patent Publication No. 48-
5043, 47-51905, and JP-A-47-28.
067, 49-83767, 51-41770.
No. 51-131576 and the like. Discharge frequency is 50Hz-500
0 kHz, preferably 5 kHz to several 100 kHz is suitable. The processing strength of the object is 0.001K
V · A · min / m ^{2 to 5} KV · A · min / m ² , preferably 0.01 KV · A · min / m ^{2 to 1} KV · A · min / m ² . The gap clearance between the electrode and the dielectric roll is 0.5 to 2.5 mm, preferably 1.0 to 2.0 m
m is appropriate.

The flame treatment method may be either natural gas or liquefied propane gas, but the mixing ratio with air is important. In the case of propane gas, a preferable mixing ratio of propane gas / air is 1/14 to 1/22, preferably 1/16 to 1/19 by volume ratio. In the case of natural gas, it is 1/6 to 1/10, preferably 1/7 to 1/9. The flame treatment may be performed in the range of 1 to 50 Kcal / m ² , more preferably 3 to 30 Kcal / m ² . Further, it is more effective if the distance between the tip of the internal flame of the burner and the support is less than 4 cm. A frame processing device manufactured by Kasuga Electric Co., Ltd. can be used as the processing device. Further, the backup roll that supports the support during the flame treatment is a hollow roll, and it is preferable that the backup roll is water-cooled by cooling water and always treated at a constant temperature.

In the optically-compensatory film subjected to the above-mentioned surface treatment, the adhesive coated on the release paper (PET with silicone) is first laminated on the outermost layer of the optically anisotropic layer.
When the outermost layer of the optically anisotropic layer is subjected to the surface treatment, its effect decreases with time, so preferably within 1 year,
More preferably, it should be bonded to a release paper with an adhesive within 10 months. The pressure-sensitive adhesive to be used is not limited, but SBR-based, silicon-based, and acrylic-based adhesives are preferable, and acrylic-based adhesives are particularly preferably used from the viewpoint of wet heat resistance.

Next, a polarizing plate with an adhesive is adhered to the back side of the optical compensation film to which the release paper with an adhesive is adhered, punched to a desired angle and a desired size, and then an optical difference is produced. The release paper on the side of the isotropic layer is peeled off and attached to the cell of the liquid crystal display device. When the surface treatment is performed on the back side, its effect decreases with time, so it is necessary to bond it to the polarizing plate preferably within 1 year, more preferably within 10 months. The pressure-sensitive adhesive to be used is not limited, but SBR-based, silicon-based, and acrylic-based adhesives are preferable, and acrylic-based adhesives are particularly preferably used from the viewpoint of wet heat resistance.

The liquid crystal display device of the present invention will be described in more detail. Examples of the color filter include, for example, "Color Liquid Crystal Display" Industrial Book, edited by Shunsuke Kobayashi, p. 172-
Pages 173, 237 to 251 or “Flat Panel Display 1994” edited by Nikkei Microdevices
A dyeing filter obtained by adding dichromate to a substrate such as gelatin, casein, PVA, etc. described in Nikkei BP, page 216 etc. to impart photosensitivity, patterning by a photolithographic method, and then dyeing. , A printing filter, an electrodeposition filter, a pigment dispersion filter and the like are preferable. However, in addition to this, color purity, dimensional accuracy,
Furthermore, if it has high heat resistance, regardless of the method,
Can be used.

As the liquid crystal used in the liquid crystal display device of the present invention, for example, "Liquid Crystal Device Handbook" edited by Japan Society for the Promotion of Science, 142th Committee, Nikkan Kogyo Shimbun, pages 107-2
The nematic liquid crystal described on page 13 is preferable. The major axis of this liquid crystal molecule is twisted by approximately 90 ° between the upper and lower substrates of the liquid crystal cell, and the incident linearly polarized light changes its 90 ° polarization direction depending on the optical rotatory power of the liquid crystal cell when there is no applied electric field. It will be emitted from the liquid crystal cell. When a sufficiently high electric field equal to or higher than the threshold value is applied, the long axis of the liquid crystal molecule turns to the direction of the electric field, is aligned perpendicular to the electrode surface, and the optical rotatory power is almost lost. Therefore, in order to sufficiently bring out the effect of this optical rotation, the twist angle is preferably 70 ° to 100 °, more preferably 80 ° to 90 °.

In order to reduce the defects (disclination) in the alignment of the liquid crystal molecules due to this electric field, it is preferable to give the liquid crystal molecules a pretilt angle in advance. The pretilt angle is preferably 5 ° or less, more preferably 2 ° to 4 °. The twist angle and pretilt angle are described in Koji Okano and Shunsuke Kobayashi, edited by Liquid Crystal Application, Baifukan, p. 16-
It is described on page 28.

Further, the value of the product Δnd of the refractive index anisotropy Δn of the liquid crystal cell and the thickness d of the liquid crystal layer in the liquid crystal cell is, for example, “Liquid Crystal Device Handbook” edited by Japan Society for the Promotion of Science, 142 Committee, Nikkan Kogyo Shimbun. As described on pages 329 to 337, when d is increased, the contrast is improved, but the response speed is slow and the viewing angle is deteriorated. Therefore, the range of 0.3 μm to 1.0 μm is preferable. ,
The range of 0.3 μm to 0.6 μm is more preferable.

The signal applied to the liquid crystal display device of the present invention is, for example, "Liquid Crystal Device Handbook" edited by Japan Society for the Promotion of Science, 142nd Committee, Nikkan Kogyo Shimbun, pp. 387-465.
Page, or “Medical LCD Application” edited by Mitsuharu Okano and Shunsuke Kobayashi
As described in Baifukan, pages 85-105, 5
The voltage is 20 V or less, preferably 8 V or less with an alternating current of Hz to 100 Hz. For example, in the normally white mode, the applied voltage is 0 to 1.5V, bright display, 1.5V to
In many cases, halftone display is performed at 3.0 V and dark display is performed at 3.0 V or more.

[0044]

【Example】

The present invention will be described in detail below based on examples.

Example 1 A mixture of methylene chloride so that triacetyl cellulose made from pulp cotton, manufactured by Daicel Corp., was 17.4 wt%, triphenyl phosphate was 1.7 wt%, and biphenyldiphenyl phosphate was 0.9 wt%. A dope dissolved in a mixed solvent of methanol in a weight ratio of 9: 1 was cast on a stainless steel band having an effective length of 50 m at a speed of 10 m / min so that the dry film thickness was 100 μm, and stripped off. It was dried with hot air at 120 ° C. A gelatin layer (0.5 μm) was applied on one side, and a diacetyl cellulose layer (0.2 μm) containing silica having a particle size of 0.1 μm was applied on the opposite side. The heat shrinkage of the thus obtained support was MD 1.8% and TD 1.0%, and Rth
= 40 nm. The curl value is +2 (1 / m)
And the residual volatile content was 1.7%. Next, 25 cc / m ^{2 of the following} alignment film coating liquid was applied on the coated gelatin layer with a slide coater, and dried with hot air at 60 ° C. for 60 seconds and further with hot air at 90 ° C. for 150 seconds.

Alignment film coating liquid Polymer A (the structural formula is shown below) 10 g Water 371 g Methanol 119 g Crosslinking agent (glutaraldehyde) 0.5 g

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This coating film was rubbed with a diameter of 150 mm, a film conveying speed of 10 m / min and a lapping angle of 6
The rubbing treatment was performed under the following conditions: rubbing roll rotation speed: 1200 rpm, film substrate transport tension: 4 kgf / cm-substrate width.

On this alignment film, 1.8 g of the above-mentioned discotic liquid crystal TE-8 (8) (m = 4), trimethylolpropane EO-modified triacrylate (V # 360,
Shin-Osaka Chemical Co., Ltd.) 0.2 g, cellulose acetate-butyrate
To (CAB551-0.2, Eastman Chemical)
0.04 g, photopolymerization initiator (Irgacure 907, Ciba-Geigy) 0.06 g, sensitizer (Kayacure-DET)
X, Nippon Kayaku Co., Ltd., 0.02 g was dissolved in 3.43 g of methyl ethyl ketone, and the coating liquid was applied with a wire bar (5.
² cc / m ² ), attach it to a metal frame, put the coating in a temperature atmosphere of 120 ° C., heat for 3 minutes to align the discotic liquid crystal, and then maintain 120 ° C. for 120 W.
/ Cm high pressure mercury lamp, illuminance 600mW / cm ²
After irradiating the coated surface with UV for 1 second, the back surface was subjected to corona treatment under the following conditions, and a release paper with an acrylic adhesive was attached to the optically anisotropic layer. After 17 days of corona treatment, a polarizing plate with a pressure-sensitive adhesive was attached to the back surface of the optical compensation film to form the optical compensation film RF of the present invention.
-1 was created. When the angle dependence of the Re value was measured by an ellipsometer AEP-1000, the direction in which the absolute value of the Re value became the minimum was tilted by about 20 ° from the normal line, and the optical axis did not exist.

(1-1) Corona Discharge Treatment Using a solid state corona treatment machine 6KVA model manufactured by Pilar Co., Ltd., both sides of a 30 cm wide support were subjected to 2 at room temperature.
Process at 0 m / min. The support was treated at 0.375 kV · A · min / m ² from the current and voltage readings at this time. The processing frequency at this time is 9.6 kHz,
Gap clearance between electrode and dielectric roll is 1.6m
m.

Example 2 Except that the disk-shaped compound coated surface was irradiated with UV, the back surface was subjected to glow discharge treatment under the following conditions, and after 30 days, it was bonded to a polarizing plate via an adhesive layer. An optical compensation film RF-2 of the present invention was produced in the same manner as in Example 1.

(2-1) Glow Discharging Treatment Four rod-shaped electrodes having a hollow section which has a diameter of 2 cm and a length of 150 cm and which serves as a coolant channel are fixed in an insulating manner at intervals of 10 cm. This electrode was fixed in a vacuum tank, the optical compensation film was run 15 cm away from this electrode so as to face the electrode surface, and the conveying speed was controlled so that the surface treatment was performed for 2 seconds. Before the optical compensation film of the present invention passes through the electrode, the heating roll is arranged so as to come into contact with a heating roll with a temperature controller having a diameter of 50 cm for 3/4 round, and the temperature of the optical compensation film support is set to 115. After the temperature was set to 0 ° C., glow discharge treatment was performed. The degree of vacuum in the tank is 0.
12 Torr, the moisture content of the atmospheric gas is 75%, the discharge frequency is 27 kHz, the output is 2500 W, and the treatment intensity is 0.5.
It was performed at kV · A · min / m ² . The optical compensation film after the discharge treatment was brought into contact with a cooling roll having a diameter of 30 cm and equipped with a temperature controller, and the temperature was raised to 25 ° C. and then wound. The heating roll
The tension between the roll and the cooling roll was 5 kg / m to convey the support.

Example 3 After irradiating the surface coated with the discotic compound with UV, the back surface was subjected to glow discharge treatment under the same conditions as in Example 2, and after 10 months, it was bonded to a polarizing plate via an adhesive layer. Except for the above, in the same manner as in Example 1, the optical compensation film RF- of the present invention
3 was created.

Comparative Example 1 After irradiating the surface coated with the discotic compound with UV, the back surface was laminated with a polarizing plate with an adhesive after 15 months without any surface treatment to give an optical compensation film RF-4. Created.

The product of the difference in refractive index between the extraordinary light and the ordinary light of the liquid crystal and the gap size of the liquid crystal cell is 480 nm, and the twist angle is 90.
The optical compensation film obtained in each of the examples and comparative examples was mounted on a TN type liquid crystal cell at 0 ° as shown in FIG.
The angle dependence of the transmittance (T) in a 40 Hz rectangular wave of -5 V was measured by LCD-5000 manufactured by Otsuka Electronics.
The contrast ratio (T1V /
The angle up to the position at which T5V) shows 10 was defined as the viewing angle, and the viewing angle in the vertical and horizontal directions was obtained. Here, the measurement of only the TN type liquid crystal cell with no optical compensation film attached,
It was set as Comparative Example 2. Further, each liquid crystal cell was put in an oven at 85 ° C. dry and 60 ° C. and 90% for 500 hours, taken out, and the same evaluation was performed again to compare the heat resistance. In FIG. 1, arrows indicate the rubbing direction in the optical compensation film and the rubbing direction in the liquid crystal cell. In FIG. 1, both of the discotic liquid crystal layers of the optical compensation film are present on the liquid crystal cell side.

In the evaluation immediately after mounting the optical compensation film, all of Examples 1, 2, 3 and Comparative Example 1 had a significantly wider viewing angle than Comparative Example 2 and showed good characteristics. However, in the evaluation after the heat resistance test (60 ° C., 95%, 500 hours), the viewing angle of Comparative Example 1 deteriorated, and further, the frame-like color unevenness of 1 cm in the periphery and the adhesive on the polarizing plate side of the optical compensation film. foam,
And peeling was observed. The viewing angles of Examples 1, 2, and 3 show the same good characteristics as immediately after mounting, and the frame-shaped color unevenness,
Neither bubbles nor peeling was observed. Furthermore, Examples 1 and 2 were the best, with no peeling of the peripheral portion even after 750 hours.

[0058]

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to industrially provide an optical compensation film in which the viewing angle of a TN type LCD is remarkably widened and heat resistance, especially moisture resistance is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship among a polarization axis of a polarizing plate, a rubbing direction of a liquid crystal cell, and a rubbing direction of an optical compensation film alignment film when measuring viewing angle characteristics in Examples and Comparative Examples.

[Explanation of symbols]

TNC: TN type liquid crystal cell A, B: polarizing plate PA, PB: polarization axis L0: natural light L1, L5: linearly polarized light L2: modulated light after passing through the liquid crystal cell L3, L4: elliptically polarized light LC: TN type liquid crystal cell State of liquid crystal molecules when sufficient voltage is applied to the electrodes RF1, RF2: Optical compensation film BL: Backlight R1, R2: Rubbing direction of the optical compensation film

Claims (6)

[Claims] 1. An optically anisotropic layer containing at least a discotic compound on a support made of a transparent polymer film, and the direction in which the absolute value of the Re value is the minimum is not the normal direction but the plane direction. Also, in the optical compensation film in which there is no direction in which the Re value becomes 0, at least one selected from corona discharge treatment, flame treatment, and glow discharge treatment on the surface of at least one side of the optical compensation film. An optical compensation sheet characterized by being surface-treated. 2. The transparent polymer film support has negative uniaxial optical characteristics having its optical axis in the normal direction of the film, and has a main refractive index nx, ny in the plane of the support and a thickness direction. The surface orientation retardation Rth defined by the main refractive index nz satisfies the condition of the expression (1).
The optical compensation film described. Formula 1 10 ≦ Rth = {(nx + ny) / 2−nz} × d ≦ 100 (nm) 3. The optical compensation film according to claim 1, wherein the tilt angle of the discotic compound of the optically anisotropic layer continuously changes in the thickness direction of the layer. 4. The optical compensation film according to any one of claims 1 to 3, wherein an adhesive layer is provided on the surface treatment within 10 months after the surface treatment. 5. The optical compensation film according to any one of claims 1 to 3, wherein after the surface treatment, a polarizing plate is laminated on the surface of the polarizing plate via an adhesive layer within 10 months. 6. A liquid crystal cell in which liquid crystal is sandwiched between two electrode substrates, two polarizing plates arranged on both sides of the liquid crystal cell, and at least one optical compensation film between the liquid crystal cell and the polarizing plate. A liquid crystal display device comprising: the liquid crystal display device, wherein the optical compensation film is the optical compensation film according to any one of claims 1 to 3.