WO2003076985A1

WO2003076985A1 - Optically compensating film, polarizing plate and apparatus for displaying images (lcd)

Info

Publication number: WO2003076985A1
Application number: PCT/JP2003/002846
Authority: WO
Inventors: Taku Nakamura; Yoji Ito
Original assignee: Fuji Photo Film Co., Ltd.
Priority date: 2002-03-13
Filing date: 2003-03-11
Publication date: 2003-09-18
Also published as: CN1509416A; AU2003212651A1; TWI282028B; CN1285929C; KR20040089449A; TW200305043A; JP2005520209A

Abstract

An optically compensating film comprising a polymer film having a retardation value Re ( = (nx - ny) x d) of 0 to 100 nm and a retardation value Rth (= {(nx + ny)/2 - nz} x d) of 70 to 500 nm, and an optically anisotropic layer formed by a liquid crystal compound thereon was disclosed. The polymer film is formed of a polymer having a photoelastic coefficient of 10 x 10-12 m2/N or less, and having a water vapor permeability of 1 g/(m2•24hrs) or less measured according to the test method of JIS Z0208, of 70 to 500 nm. A polarizing plate and apparatus comprising the optically compensating film were also disclosed.

Description

DESCRIPTION

OPTICALLY COMPENSATING FILM, POLARIZING PLATE AND APPARATUS FOR DISPLAYING IMAGES (LCD)

Field of the invention

The present invention relates to light weight and durable optically compensating films, and polarizing plates and apparatus for displaying images using them.

Related Art

Since liquid crystal displays (LCD) need thinner thickness, lighter weight or less electricity to work than CRT, they have been used in stead of CRT in various apparatus such as laptops, monitors, televisions, personal digital assistants (PDA) , cell phones, vehicle navigation systems and video cameras. However, TN-mode LCD, which is standard at present, has disadvantages that color or contrast on display varies depending upon viewing direction to a liquid crystal display.

It is disclosed in Japanese Patent No. 2,587,398 that for providing a LCD of high visual quality having improved viewing angles, an optically compensating film, which is formed of a discotic liquid crystal oriented in a hybrid orientation, is inserted between a polarizing plate and a liquid crystal cell. However, this method makes the thickness of LCD thicker due to presences of the optically compensating film and an adhesive.

It is disclosed in JP-A hei 7-191217 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and EP 0911656A2 that the viewing angle of LCD can be improved without increase of thickness by using an elliptically-polarizing plate which comprises a polarizing film and an optically compensating film, which comprises a support and an optically anisotropic layer thereon formed by applying a discotic liquid crystal to the surface of the support, as a protective film for the polarizing film. However, these optical compensating films are easy to raise retardation where stresses and strains occur through use under the sever condition such as high temperature and humidity. It has been found that the frame like light leakage (increase of transmittance) occur due to the retardation, thereby to lower visual quality of images displayed by LCD. Particularly, it is difficult to prevent completely light leakage from large size LCD having 17 inches or more size. It has been provided a LCD having a simple organization in which the liquid crystalline film functions not only as an optically compensating film but also as a protective film for a polarizing film. However, functioning as a protective film, the optically compensating film is permeable by water through use under the condition of high temperature and humidity, and the optical characteristic of the polarizing film is sometimes lowered by the permeating water . Consequently, the optically compensating film also functioning as a protective film is required to have an enough durability not to lower the optical characteristic and not to be permeated by water under the severe condition such as high temperature and humidity. Summary of the invention

The present invention, devised in light of the various above-described problems, has for its object to provide an optically compensating film, when it is used in a LCD, contributing to improvement of viewing angle, to reduction of the degradation in visual quality of displayed images due to light leakage and the like. Another object of the present invention is to provide an optically compensating film and a polarizing plate having excellent durability such that their optical characteristics hardly change even though they are used under the sever condition. And another object of the present invention is to provide a LCD having wide viewing angle and excellent durability such that the degradation in visual quality of images, which is caused by light leakage during used under a sever condition, is reduced.

We had studied about causes of the change in the optical characteristics responsible for light leakage and we came to the conclusion that the two causes as follows are responsible for light leakage. One of them is a change in the optical characteristic occurring due to expansion and contraction of the polymer film when it is used under the sever condition (high temperature and humidity) . Another is a change in the optical characteristic occurring due to thermal deformation of the polymer film when it is subjected to backlight, thereby to yield temperature distribution in the film.

After extensive investigations based on the conclusion, we found out that the changes of optical characters in the optically compensating films are related to their photoelastic coefficients and water vapor permeability, and achieved the present invention.

In one aspect, the present invention provides an optically compensating film comprising: a polymer film having a retardation value Re, defined as the following formula (I) , of 0 to 100 nm, and a retardation value Rth, defined as the following formula (II) , of 70 to 500 nm; and an optically anisotropic layer formed by a liquid crystal compound thereon: wherein the polymer film is formed of a polymer having a photoelastic coefficient of 10 x 10^"12 m²/N or less, and having a water vapor permeability of 1 g/ (m² 24hrs) or less measured according to the test method of JIS Z0208:

(I) Re = (nx - ny) * d

(II) Rth = { (nx + ny) /2 - nz} * d in which nx and ny are refractive indexes of a slow axis and a fast axis in plane of the polymer film and nz is a refractive index of a thickness direction of the polymer film.

As preferred embodiments; there are provided the optically compensating film wherein the polymer has a specific gravity of 1.20 or less; the optically compensating film wherein the polymer is a cyclic polyolefin based polymer; the optically compensating film wherein the polymer is a polymer prepared by ring-opening polymerization of a monomer selected from tetracyclododecenes or a polymer prepared by hydrogenation of ring-opening copolymer of a monomer selected from tetracyclododecenes and a monomer selected from norbornenes; the optically compensating film wherein the polymer film comprises an aromatic compound having at least two aromatic rings; the optically compensating film wherein the aromatic compound is a compound having at least one 1, 3, 5-triazin ring; the optically compensating film wherein the polymer film comprises heat conductive particles and has a heat conductivity of 1 / (m ^• K) or more; the optically compensating film comprising a heat conductive layer comprising heat conductive particles on at least one of surfaces of the polymer film, wherein the polymer film having the heat conductive layer thereon has a heat conductivity of 1 W/(m-K) or more; the optically compensating film wherein the liquid crystal compound is a compound selected from discotic liquid crystal compounds; the optically compensating film wherein the polymer film is a stretched polymer film.

In another aspect, the present invention provides a polarizing plate comprising a polarizing film with two surfaces and two protective films respectively provided on the two surfaces, wherein at least one of the protective films is a polymer film defined above.

In another aspect, the present invention provides an apparatus for displaying images comprising: two polarizing plates, a liquid crystal cell sandwiched between the two polarizing plates, and an optically compensating film defined above sandwiched between one of the polarizing plates and the liquid crystal cell.

Detailed Description of the Invention

The present invention is described in detail below. In the present Description, the symbol "-" indicates a range having as minimum and maximum the two numbers before and after it, inclusive . [Optically Compensating Film]

The optically compensating film according to the present invention comprises a polymer film and an optically anisotropic layer thereon containing a liquid crystal compound. Various examples of materials and method for preparing the optically compensating film of the present invention are described in detail bellow.

The polymer film is formed of a polymer having photoelastic coefficient of 10 _* 10^-12 m²/N or less at wave length of 633 nm, and having a water vapor permeability of 1 g/(m²'24hrs) or less measured according to the test method of JIS Z0208. Using the polymer having such a photoelastic coefficient and a water vapor permeability, the change of optical characteristics occurred in the polymer film through use under the condition of high temperature and humidity can be reduced, and the optically compensating film having such polymer film is excellent in durability. The preferred polymer used in the present invention has a potoelastic coefficient of 7^χl0^~12 m²/N or less and a water vapor permeability of 0.6 g/(m²"24hrs) or less.

For the present invention, the water vapor permeability is measured for a film having 300 μm thickness at 40 °C under RH 90% according to JIS Z0202 test method.

The polymer used in the present invention has preferably a specific gravity of 1.2 or less. Using the polymer having such a specific gravity, the weight of the polymer film can be decrease with no changing of optical characteristic. Consequently, the optically compensating film contributes to weight saving of a polarizing plate or a displaying apparatus having the optically compensating film.

Preferred examples of the polymers having a proper photoelastic coefficient and a proper water vapor permeability include acrylic based polymers (e.g. polymethyl methacrylate) and cyclic polyolefins (e.g. "ARTON G" and "ARTON F" commercially available from JSR; "ZEOROR 1020R", "ZEOROR 1060R", "ZEOROR 1420R", "ZEOROR 1600R", "ZEONEX 480", "ZEONEX 480R", "ZEONEX 280R", "ZEONEX 490R", "ZEONEX E48R", "ZEONEX E28R" and "ZEONEX RS820"commercially available from ZEON CORPORATION) . Among them, cyclic polyolefins are preferred. And among cyclic polyolefins, polymers prepared by ring-opening polymerization of a monomer selected from tetracyclododecenes and polymers prepared by hydrogenation of ring-opening copolymers of a monomer selected from tetracyclododecenes and a monomer selected from norbornenes are especially preferred. In more specifically, polymers prepared by open-ring polymerization of a monomer selected from tetracyclododecenes (otherwise known as dimethano-1, 4,5, 8-octahydro-l, 2,3,4, 4a, 5, 8, 8a-naphtarenes) and polymers prepared by hydrogenation of a ring-open copolymers of a monomer selected from tetracyclododecenes and a monomer selected from norbornenes, which are described in detail in JP-B hei 2-9619 (the term "JP-B" as used herein means an "examined published Japanese patent application") and JP-A hei 9-263627, are especially preferred since they have very small hygroscopic property, a high transparency, an excellent workability and for ability and high water resistance. Such polymers generally comprise fragments based on tetracyclododecen in the ratio of 50 ol % or more, from the viewpoint of heat resistance, more preferably 80 mol % or more, more preferably 90 mol % or more. The polymers have usually molecular weights of 1, 000 to 500, 000, preferably 10, 000 to 100, 000, that may be controlled by addition of an olefin or chloro olefin while ring-open polymerization.

The polymer film may be prepared according to a solvent casting method or a melt extrusion method. The solvent casting method has the advantageous in producing a smooth surface, on the other hand the melt extrusion method without using solvent has advantageous in productivity and production cost.

For the solvent casting method, a solution (a dope) in which a polymer dissolved in an organic solvent is used for preparation of a film. The solvent casting method generally includes two drying processes, one of which is drying on the surface of a drum (or a band) , and the other is drying in the process of conveying the film. Drying on the surface of a drum (or a band) is preferably carried out slowly at the not higher temperature than the boiling point of the solvent since the drying at the higher temperature than the boiling point, bubbles may forms. Drying in the process of conveying the film is preferably carried out at (30 ± Tg of the polymer) °C, more preferably at (20 ± Tg) °C.

Not only an optically anisotropic layer described after, but also the polymer film of the optically compensating film is required to have retardation within a proper range for optically compensating displays. For preventing light leakage from a display due to heat, stress or deformation and maintaining visual quality, a thickness, a heat conductivity and a coefficient of thermal expansion of the polymer film are respectively within a proper range.

The preferred scopes of various characteristics the polymer film has, which can be used for the present invention, are described bellow. As for the polymer films prepared by the solvent casting method, since the characteristics of the polymer films may vary depending on an amount of the residual solvent which is used for preparation of the dope, the preferred scope of the residual amount is also described bellow.

According to the present invention, a retardation of Re is defined by the following formula (I) and a retardation of Rth is defined by the following formula (II) :

(I) Re = (nx - ny) * d

(II) Rth = { (nx + ny) /2 - nz} x d in which nx and ny are refractive indexes of a slow axis and a fast axis in plane of the polymer film, nz is a refractive index of a thickness direction of the polymer film and d is a thickness .

According to the present invention, the polymer film has a Re of 0 - 100 nm and a Rth of 70 - 500nm.

In case that two optically compensating films according to the present invention are applied to a TN mode LCD, Rth' s of the polymer films are preferably 70 - 250 nm. In case that one optically compensating film according to the present invention is applied to a TN mode LCD, Rth of the polymer film is 150 - 400 nm.

In case that two optically compensating films according to the present invention are applied to an OCB mode LCD, the polymer films have preferably Re's of 30 -50 nm and Rth' s of 150 - 200nm. In case that one optically compensating film according to the present invention is applied to an OCB mode LCD, the polymer film has preferably a Re of 50 -100 nm and a Rth of 300 - 500nm.

According to the present invention, controlling retardation agents, which are described bellow, are preferably used for controlling Re's and Rth' s of the polymer films. The controlling retardation agents are incorporated into the polymer films by dissolution and/or dispersion of the agents in the polymers.

As described above, the polymer film of the present invention usually comprises a controlling retardation agent in order to have the proper retardation. The agents are preferable aromatic compounds having two ore more aromatic rings . In the Description, the term of "aromatic ring" is used as a meaning including not only aromatic hydrocarbon rings but also aromatic hetero rings. The aromatic compounds are preferably discotic compounds disclosed in JP-A 2001-166144 as controlling retardation agents for cellulose ester films. The controlling retardation agents have preferably molecular weights of 300 - 800.

The amount of the controlling retardation agent is preferably 0.01 to 20 wt . % of the polymer weight, more preferably 0.05 to 15 wt. %, much more preferably 0.1 to 10 wt. %. One or more kinds of compounds may be used in preparation of the polymer film as the controlling retardation agent.

The polymer film according to the present invention has preferably a heat conductivity of 1 W /(m-K) or more. The heat conductivity being within the range, temperature distribution in the plane of the polymer film is uniform, and thereby it is possible to reduce remarkably the changes in optical characteristics of the polymer film and the light leakage from a LCD. The heat conductivity of the polymer film is preferably high, however, the heat conductivity of the polymer film added heat conductive particles described bellow is usually 10 W/ (m* K) or less.

For the present invention, a heat conductivity of a polymer film means a value measured by the method comprising the following processes: putting a polymer film between a TO-3 model heater case made of copper and a copper plate so as to compress a polymer film by 10 % of the thickness; measuring temperature difference between the heater case and the copper plate with supplying 5 W of electrical power to the heater case for 4 minutes; and calculating a heat conductivity from the following formula with the measured value; heat conductivity {W/(m-K)} = {electrical power (W) X thickness (m) } /{temperature difference (K) x measured area (m²) }.

The polymer filmmay comprise high heat conductor particles in order to control the heat conductivity of the optical compensating film. A heat conductor layer containing high heat conductor particles may be provided on the surface of the polymer film for the same purpose. The heat conductor layer can be prepared by co-casting a polymer added high heat conductor particles with a polymer for the polymer film, or applying a coating solution containing high heat conductor particles on the surface of the polymer film. Examples of the high heat conductor particles include aluminum nitride, silicon nitride, boron nitride, magnesium nitride, 'silicon carbide, aluminum oxide, silicon oxide, zinc oxide, magnesium oxide, carbon, diamond and metals. So as not to lower transparency, transparent particles are preferably used. The high heat conductor particles have preferably an average particle diameter of 0.05 to 80 μm, more preferably 0.1 to 10 μm. The particles may have spherical shapes or needle-like shapes.

The amount of the high heat conductor particles is preferably 5 to 100 wt. % of the polymer weight. When the amount of the particles is less than 5 wt. %, the enough improvement of heat conductivity may not be obtained. On the other hand, when the amount of the particles is more than 100 wt . %, the productivity may lower and obtained polymer film may be brittle .

The polymer film according to the present invention has preferably a moisture absorption swelling index of 30 X 10^~5/%RH or less, more preferably 15 X 10^~5/%RH or less, much more preferably 10 X 10^~5/%RH or less. The moisture absorption swelling index being within the above range, it is possible to prevent deformation of the polymer film under high humidity, thereby to prevent frame-like light leakage (increasing of transparency) from LCD under high humidity. The moisture absorption swelling index of the polymer film is preferably small, however, it is generally 1.0 X 10^~5/%RH or more.

In the Description, a moisture absorption swelling index of a polymer film is variation in length of the polymer film depending on a variation in humidity at a constant temperature. A moisture absorption swelling index of a polymer film is measured by the method comprising the following processes: hanging a polymer film sample, of which width is 5 mm and length is 20 mm, with an end of which is fixed and the other end of which is free, under 20 % RH (R₀) at 25 °C; measuring a length (L₀) of the sample after leaving the sample under the above condition for 10 minutes with hanging a 0.5 g of weight on the free end of the sample; measuring a length (Li) of the sample after leaving the sample under 80 % RH (Ri) at a constant temperature, i.e. at 25 °C; and calculating a moisture absorption swelling index from the following formula with the R₀, Ri, L₀ and Li:

A moisture absorption swelling index [/%RH] = { ( Lι-Lo ) /L₀ } / ( R₁-Ro ) .

We had studied about a variation in dimension of a polymer film due to moisture absorption and we found that the smaller free volume a polymer film has, the less variation in dimension of the film is. For the polymer film prepared according to the solvent casting method, the free volume in the film varies with an amount of the residual solvent, used for preparation of the dope, in the film. The smaller residual amount is, the smaller variation in dimension is . Usual process for reducing the amount of the residual solvent in the film is drying a polymer film at a high temperature for a long period after preparation of the film by a solvent casting method, however, it may be understood that drying for too long period is lowered productivity. The amount of the residual solvent in the polymer film is preferably 0.01 to 1 wt. %, more preferably 0.02 to 0.07 wt%, much more preferably 0.03 to 0.05 wt. %. An amount of a residual solvent in a polymer film can be determined by a gas chromatography spectro etry (e.g. "GC 18A" from ΞHIMAZU CORPORATION) measurement of a sample such as a chloroform solution of the polymer film.

The polymer film according to the present invention has preferably an elastic modulus of 3000 MPa or less, more preferably 2500 MPa or less.

Improving planer orientation of polymer molecules by stretching the film is effective for preventing deformation of the film and also effective for controlling the retardation of the film. Among of various stretching methods, biaxial stretching is preferred for improving planer orientation. There are two types of biaxial stretching process, one of which is a simultaneous biaxial stretching process and the other is a sequential biaxial stretching process, and the latter is preferred for serial production. The sequential biaxial stretching process includes stretching a polymer film along the width direction (or the longitudinal direction) and re-stretching the film at the longitudinal direction (or the width direction) after peeling the polymer film from on the surface of a band or drum. Details of stretching along the width direction are disclosed JP-A syo 62-115035, JP-A hei 4-152125, JP-A hei 4-284211, JP-A hei 4-298310, JP-A hei 11-48271 and the like. Stretching may be carried out at an ambient temperature or with heating. In case of with heating, the hating temperature is preferably not higher than Tg of the polymer.

In case of preparing the polymer film according to a solvent casting method, stretching the polymer film may be carried out during a process for drying the polymer film after a process for forming the polymer film. The stretching in the process of drying is effective for the polymer film containing a residual solvent. Stretching in the longitudinal direction may be carried out continuously by controlling a speed of a conveying roller, as the speed of rolling the film up is faster than the speed of peeling the film off. Stretching a polymer film in the width direction may be carried out in the process of conveying the polymer film by tentering the polymer film with increasing a width of the tenter gradually. After drying the polymer film, stretching may also be carried out by a stretching machine, preferably by a long monoaxial stretching machine. The stretch ratio, a ration of an increase by stretching for an original length, is preferably 5 to 15 %, more preferably 10 to 40 %, much more preferably 15 to 35 % .

These processes from solvent casting to after-drying may be performed under an atmospheric air or an inert gas atmosphere such as a nitrogen atmosphere.

The polymer film according to the present invention may be stored and conveyed with keeping rolled. Conventional winders may be used for rolling the polymer film by a constant tension method, a constant torque method, a taper tension method, a program-controlled tension method with a constant internal stress or the like.

The polymer film used in the present invention is preferably subjected to surface treatment for forming an optically anisotropic layer containing a liquid crystal compound thereon. Examples of surface treatments include corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment and UV irradiation treatment. The polymer film may have an under coating layer as disclosed in JP-A hei 7-333,433.

The polymer film is preferably subjected to such surface treatment at a temperature not greater than Tg (glass transition temperature) of the polymer, practically not greater than 170 °C, for having a smooth surface.

The surface energy of the polymer film is preferably 55 mN/m or more, more preferably 60 to 75 mN/m. A surface energy of a solid may be calculated by a contact angle method, a heat of wetting method or an adsorption method, as described in "Bases and Applications of Wettability (Nure No Kiso to ouyou) " published at December 10, 1989 by SIPEC Corporation (former Realize Corporation) . A contact angle method is proper for the polymer film of the present invention. Specifically, a surface energy of the polymer film according to the present invention can be calculated by a contact angle method with two contact angles of droplets of which surface energies are respectively known. A contact angle of a droplet on the polymer film is defined as an angle between the polymer film surface and a tangent line to the surface curve of the droplet, which is drawn at an intersection point of the droplet surface and the polymer film surface. There are two angles between the polymer film surface and such tangent line, however, a contact angle is an angle at the side containing the droplet.

The optically compensating film according to the present invention can be prepared by laminating an optically anisotropic layer formed of a liquid crystal compound on the polymer film. An alignment layer, which contributes to alignment of the liquid crystal compound, is preferably placed between the optically anisotropic layer and the polymer film which may be subjected to surface treatment. It is possible to prepare the optically compensating film according to the present by the transferring the optically anisotropic layer, formed by setting of the aligned liquid crystal, from on the alignment layer to on the polymer film. Consequently, in despite of being a necessary component for preparation, the alignment layer is not a necessary component of the optically compensating film according to the present invention.

The alignment layer contributes to control of an alignment of the liquid crystal compound. The alignment layer may be prepared by rubbing treatment of an organic compound (preferably polymer) layer, oblique evaporation of an inorganic compound, forming of a layer having micro grooves or developing a Langmuir-Blodgett film of organic compound (e.g. ω-tricosanoic acid, di-octadecyl methylammonium chloride, methyl stearate) . There are some layers have capability in controlling a liquid crystal alignment only after by applied electric field, magnetic field or light, which may also be used as an alignment layer in the present invention. The alignment layers prepared by rubbing polymers are preferred for the present invention.

The alignment layers formed of polyvinylalcohol based polymers are preferred. Among them, denatured polyvinylalcohols having hydrophobic groups are preferred. The alignment layer may be formed of a polymer or two ore more kinds of cross-linked polymers. The alignment layers formed of polymers cross-linked by themselves or polymers cross-linked by cross-linking agents are preferred. The alignment layers formed of the cross-linked polymers may be prepared by a cross-linking reaction induced by light, heat, change of pH or the like, of polymers originally or artificially having functional groups; or by a cross-linking reaction of polymers and cross-linking agents having high activity to introduce bonds based on the cross-linking agents between the polymers.

The alignment layer formed of a cross-linked polymer can be prepared by applying a coating solution containing a polymer and a cross-linking agent to the surface of the polymer film, and carrying out a cross-linking reaction with heating or the like if needed. Cross-linking of the polymer contributes to improvement in durability of the alignment layer. Since it is enough if the durability of an end product, i.e. an optically compensating film, is high, cross-linking for improvement in durability of the alignment layer may be carried out at any step after a process for applying a coating solution of the alignment layer to the surface of the polymer film. Considering an orientation of a layer (an optically anisotropic layer) formed of a liquid crystal compound, cross-linking of the alignment layer is preferably carried out after a process for aligning the liquid crystal compound. Application of heating for drying a layer formed of the oriented liquid crystal compound usually promotes cross-linking of the alignment layer. After drying the aligned liquid crystal layer is carried out at a relatively low temperature, complete cross-linking of the alignment layer is preferably carried out at the same time as heat treatment for setting an optically anisotropic layer, described hereinafter. Preferred examples of the alignment layer used in the present invention include the alignment layers disclosed in Japanese Patent No. 2,587,398.

A thickness of the alignment layer is preferably 0.1 to 10 μm. Drying the alignment layer may be carried out at 20 to 110 °C . For complete cross-linking, drying is preferably carried out at 60 to 100 °C, more preferably 80 to 100 °C. Drying the alignment layer is usually continued for 1 minute to 36 hours, preferably for 5 to 30 minutes. pH of the alignment layer may be within a range proper for a cross-linking agent used. Using glutaraldehyde as a cross-linking agent, pH of the alignment layer is preferably 4.5 to 5.5, more preferably 5.

Rubbing treatment may be carried out according to the conventional method utilized in a process for aligning a liquid crystal compounds for preparing LCD. Rubbing treatment may be carrier out by rubbing the surface of the alignment layer unidirectionally with a paper, gauze, felt, rubber, fiber such as nylon or polyester, or the like, thereby a liquid crystal compound thereon aligned. Usually rubbing treatment is performed by rubbing the surface of the alignment layer several times with a fabric grafted fibers having a uniform length and a uniform thickness.

The optically anisotropic layer according to the present invention is preferably formed on the alignment layer which is placed on the polymer film. Examples of liquid crystal compounds utilized in forming the optically anisotropic layer include both of rod-like and disk-like liquid crystal compounds and both of high and low molecular weight liquid crystal compounds . Additionally, the examples also include compounds no longer exhibiting liquid crystallinity after being cross-linked for formation of layers, in spite of originally exhibiting liquid crystallinity. Among them, disk-like liquid crystal compounds are preferred.

The optically anisotropic layer may be prepared by applying a coating solution, containing a liquid crystal compound and some components such as a monomer and a surfactant if needed, to the surface of the alignment layer and aligning the liquid crystal compound on the alignment layer. A thickness of the optically anisotropic layer is preferably 0.1 to 20 μm, more preferably 0.5 to 15 μm, much more preferably 1 to 10 μm.

The preferred examples of the optically anisotropic layer according to the present invention include those disclosed in Japanese Patent No. 2,587,398.

For preparation of the optically anisotropic layer, liquid crystal compounds having disk-like structures such as discotic liquid crystal compounds are preferred. The optically anisotropic layer may be prepared by applying a composition, containing a discotic liquid crystal compound, a polymerization initiator described hereinafter and optional additives (e.g. plasticizers, monomers, surfactants, cellulose acetates, 1, 3, 5-triazin based compounds and chiral agents) on the alignment layer; and aligning the discotic liquid crystal on the alignment layer.

Example of the discotic liquid crystal compounds include benzene derivatives disclosed in "Mol. Cryst., vol. 71, p. 111(1981), C. Destrade et al."; truxene derivatives disclosed in "Mol. Cryst., vol. 122, p. 141(1985), C. Destrade et al.," and "Physics lett. A, vol.78, p.82 (1990) , C. Destrade et al. , " ; cyclohexane derivatives disclosed in "Angew. Chem. Vol. 96, p. 70(1984), B. Kohne et al."; aza-crown based or phenyl acetylene based macrocycle compounds disclosed in "J. Chem. Commun., p. 1794 (1985) , J. M. Lehn et al . " and "J. Am. Chem. Soc. , vol. 116, p.2655(1994), J. Zhang et al.". Additionally, the examples also include compounds having above mentioned structures as cores and chains, such as linear alkyl groups or alkoxy groups or substituted benzoyl oxide groups, radiating from the cores as side chains, which exhibit liquid crystallinity. The Examples of the liquid crystal compounds used in the present invention are not ^'limited to the above mentioned examples as far having capability of uniaxial homogeneously-aligned by themselves.

The compounds used in the optically anisotropic layers are not desired having such capability after forming the layers . For example, in case of using a discotic liquid crystal low molecular weight compound having a reactive group, it may be polymerized or cross-linked with heating or irradiation of light, thereby to form an optically anisotropic layer in which the compound has no longer liquid crystallinity.

For setting the discotic compounds in the alignment by polymerization, it is needed that the compounds have polymerizable groups as substituents of the discotic cores. However, if polymerizable groups directly bond to the discotic cores, the alignments of the compounds are sometimes out of order. For preventing the alignment from getting out of order, spacers (linking groups) are preferably introduced between polymerizable groups and the discotic cores. Preferred examples of the discotic liquid crystal compounds include those disclosed in JP-A hei 8-50,206, and preferred examples of polymerization of the discotic liquid crystal compounds are disclosed in JP-A hei 8-27,284.

According to the present invention, an angle between a plane of a discotic core of a discotic liquid crystal molecule and a surface plane of an optically anisotropic layer, i.e. an inclined angle, varies depending on the distance in-depth of the layer. The inclined angle varies with increasing of the distance from the bottom of the optically anisotropic layer (from the surface of the alignment layer side) . Examples of variation in the inclined angle include continuous increasing and decreasing, intermittently increasing and decreasing, variation containing continuous increasing and decreasing and intermittent variation containing increasing and decreasing. The intermittent variation contains an area in which the inclined angle does not change between the top surface and the bottom surface of the optically anisotropic layer. Preferably, the inclined angle of the discotic liquid crystal compound is increasing or decreasing as a whole, even though there is some areas of non-varying the inclined angle in the optically anisotropic layer. More preferably, the inclined angle of the discotic liquid crystal compound is increasing as a whole, much more preferably continuously increasing as a whole.

The inclined angle per a discotic plane unit at the surface of the alignment layer side can usually be controlled by selecting proper materials for the optically anisotropic layer and/or the alignment layer, or selecting proper conditions for rubbing treatment of the alignment layer. On the other hand, the inclined angle per a discotic plane unit at the surface of the air side can be controlled by selecting proper materials for the optically anisotropic layer such as a discotic liquid crystal compound or an additive used with a discotic liquid crystal compound. Examples of additives used with discotic liquid crystal compounds include plasticizers, surfactants, polymerizable monomers and polymers. Additionally, the degree of the variation of the inclined angle can be controlled by the above mentioned selection.

The optically anisotropic layer according to the present invention may contain some additives with the discotic liquid crystal compound. Various additives such as plasticizers, surfactants and polymerizable monomers can be used with the discotic liquid crystal compound, if they have compatibility to the crystal compound and have capability of making the inclined angle of the crystal compound vary or no capability disordering the alignment of the crystal compound. Among them, polymerizable monomers (e.g. compounds having vinyl, vinyl oxy, acryloyl or methacryloyl) are preferred. The amount of the additive is preferably 1 to 50 wt. % based on the weight of the discotic liquid crystal compound, more preferably 5 to 30 wt. % . Using a monomer having 4 or more functional groups with the liquid crystal compound, the adhesiveness between the alignment layer and the optically anisotropic layer is improved.

Various polymers can be used with the discotic liquid crystal compounds, if they have compatibility to the crystal compound and have capability of making the inclined angle of the crystal compound vary. Examples such polymers include cellulose esters. Preferred examples of cellulose esters include cellulose acetate, cellulose acetate propionate, hydroxypropyl cellulose, cellulose acetate butylate. Free from disordering the alignment of the liquid crystal compound, the amount of the polymer is preferably 0.1 to 10 % by weight based on the weight of the discotic liquid crystal compound, more preferably 0.1 to 8 %, much more preferably 0.1 to 5 %.

According to the present invention, the optically anisotropic layer may be produced by applying a solution containing the discotic liquid crystal compound dissolved in a solvent, to the surface of the alignment layer, drying the solution on the alignment layer, subsequently heating at a proper temperature for the discotic liquid crystal compound transfering to a discotic nematic phase, and cooling with keeping the alignment (discotic nematic phase) of the discotic liquid crystal compound. Otherwise, the optically anisotropic layer may be produced by applying a solution containing both of the discotic liquid crystal compound and material for polymerization (e.g. a polymerizable monomer and a polymerization initiator) dissolved in a solvent, to the surface of the alignment layer, drying the solution on the alignment layer, subsequently heating at a proper temperature for the discotic liquid crystal compound transferring to a discotic nematic phase, and polymerizing with keeping the alignment (discotic nematic phase) of the discotic liquid crystal compound, under irradiation of UV light or the like if needed, and finally cooling.

The transition temperature from the liquid crystal phase to the solid phase of the discotic liquid crystal compound used in the present invention is preferably 70 to 300 °C , more preferably 70 to 170 °C .

According to the present indention, fixing the aligned liquid crystal is preferred. Fixing the alignment is preferably carried out by polymerization. Polymerizations include thermal polymerizations used thermal polymerization initiators and photo polymerizations with photo polymerization initiators. Among them, photo polymerizations are preferred. Examples of the photo polymerization initiators include α-carbonyl compounds disclosed in US Patent No. 2, 367, 661 and US patent No . 2,367,670, acyloin ethers disclosed in US patent No.2, 448, 828, α-hydrocarbon substituted aromatic acyloin compounds disclosed in US Patent No.2, 722, 512, polynuclear quinon compounds disclosed in US Patent No.3, 046, 127 and US Patent No.2, 951, 758, tri-aryl imidazole dimmers and p-aminophenyl ketones disclosed in US Patent No. 3,549,367, acridine compounds and phenazine compounds disclosed in JP-A syo 60-105,667 and US Patent No. 4,239,850, and oxadiazole compounds disclosed in US Patent No. 4,212,970.

The amount of the photo polymerization initiator is preferably 0.1 to 20 % by weight base on the weight of a solid content in the coating solution for forming the optically anisotropic layer, more preferably 0.5 to 5 % . The polymerization of the liquid crystal compound is preferably induced by UV light irradiation. Energy of the irradiation of UV light is preferably 20 mj/cm² to 50 J/cm², more preferably 20 to 5000 mJ/cm², much more preferably 100 to 800 mJ/cm². For accelerating the polymerization, light irradiation for inducing the polymerization is preferably carried out with heating.

According to the method described above, the optically anisotropic layer can be formed on the alignment layer to prepare the compensating film of the present invention. A protective layer may be formed on the optically anisotropic layer. The optically compensating film according to the present invention may be used as a member of a polarizing plate or as a member of a LCD. Specifically, used as a member of a LCD, the optically compensating layer of the present invention can contribute to improvement of viewing angle of the LCD. Additionally, the optically compensating layer of the present invention can contribute to reduction of degradation in visual quality of the LCD due to light leakage or the like, even when the LCD is used under a sever condition such as continuous load, high temperature or high humidity. Used as a member of a LCD or a polarizing plate, the optically compensating layer of the present invention can contribute to weight saving of the LCD or the polarizing plate. The optically compensating layer of the present invention may be incorporated in a LCD as an independent member or as a dependent member of a polarizing plate in which the optically compensating layer is attached to a polarizing film. Some embodiments of polarizing plate and the apparatus for displaying images according to the present invention are described in detail below. [Polarizing Plate]

One embodiment of the present invention is a polarizing plate comprising a polarizing film and two protective films respectively provided on the surfaces of the polarizing film, wherein at least one of the protective films is the optically compensating film of the present invention. In this embodiment, one of or two of the protective films may be the optically compensating film of the present invention. In the embodiment in which one of the protective films is the optically compensating film of the present invention, another may be a conventional polymer film such as a cellulose acetate film.

The polarizing film used in the present invention may be selected from iodated polarizing films, dyed polarizing films and polyene based polarizing films. Iodated polarizing films and dyed polarizing films are usually made of polyvinylalcohol films .

Durability, particularly a heat and moisture resistance, of the protective film is an important factor for durability of the polarizing film. While the displaying is used under a high humidity, polarizing quality sometimes gets worse due to permeation of moisture into the polarizing film. According to the present invention, the polymer film formed of the polymer having a water vapor permeability within the specified range is used in the optically compensating film. Therefore, the polarizing plate having the optically compensating film of the present invention as a protective film exhibits excellent durability. Since the polymer films formed of polymers prepared by ring-opening polymerization of a monomer selected from tetracyclododecenes and polymers prepared by hydrogenation of ring-opening copolymers of a monomer selected from tetracyclododecenes and a monomer selected fro norbornenes have significantly lowered water vapor permeability, the optically compensating films have such polymer films are especially proper for the protective films of the polarizing plates. [Apparatus for Displaying Images] one embodiment of the present invention is an apparatus for displaying images comprising two polarizing plates, a liquid crystal cell sandwiched between the two polarizing plates, and an optically compensating film of the present invention sandwiched between one of the two polarizing plate and the liquid crystal cell. The preferred embodiments are Liquid crystal displays and more preferred are transmissive type of Liquid crystal displays. The polarizing plate used in the display consists of a polarizing film and two protective films respectively provided on the surface of the polarizing film. One or two of optically compensating film of the present invention may be placed respectively between the liquid crystal cell and each of the polarizing plates.

The liquid crystal cell may have a liquid crystal layer sandwiched between two substrates having electrodes thereon. The liquid crystal cell used in the display of the present invention may be TN-mode or OCB-mode .

Examples

The present invention will further be detailed referring to specific Examples. It is to be noted that any materials, reagents, ratios of use thereof and operations shown in the Examples below can properly be modified without departing from the spirit of the present invention. Thus the present invention is by no means limited to the Examples described below.

[Example 1]

(Preparation of Polymer Film)

A composition containing 100 weight parts of "ZEONOR 1020R" (provided by ZEON CORPORATION) and 200 weight parts of methylene chloride was put in a mixing tank and stirred with heating, thereby resulting a polymer solution. On the other hand, a composition containing 16 weight parts of a retardation controlling agent shown bellow and 100 weight parts of methylene chloride was put in another mixing tank, stirred with heating, thereby resulting a solution of the retardation controlling agent. 474 weight parts of the polymer solution and 63 weight parts of the solution of the retardation controlling agent were added and mixed under sufficient stirring, thereby resulting a dope. The added amount of the retardation controlling agent was 5.5 weight parts based on 100 parts of the polymer ("ZEONOR 1020R") .

Retardation Controlling Agent

The dope was cast on a band of a band casting machine to form a film. When the amount of the solvent remaining in the film was 15 wt. %, the film was subjected to monoaxal stretching along with a width direction at 150 °C with a retardation ration of 120 %, thereby resulting Polymer Film PF-01.

The Re and Rth retardation values at 550 nm of the obtained Polymer Film PF-01 were measured by means of an ellipsometer ("M-150", provided by JASCO) . The results are set forth in Table 1.

The thicknesses at 100 points in a 1 m² (lm X lm) area of the obtained Polymer Film PF-01 were measured by means of a thicknessmeter ("K-402B", provided by Anritsu) . The average thickness was 62.0 μm with a standard variation of 1.5 μm. (Forming Alignment Layer)

A coating solution containing 10 weight parts of a denatured polyvinylalcohol shown bellow, 371 weight parts of water, 119 weight parts of methanol and 0.5 weight parts of glutaraldehyde (a cross-linking agent) was applied to the surface of the obtained polymer film (Polymer Film PF-01) , subjected to corona discharge treatment, by a 16 # wire bar coater, with a spread of 28 mL/m², and dried with warm air of 60 °C for 60 minutes and subsequently with warm air of 90 °C for 150 minutes , Thus, an alignment layer was formed on the polymer film.

Denatured Polyvinylalcohol

—(CH₂-

(Preparation of Optically Compensating Film)

The alignment layer was subjected to a rubbing treatment along with an angle of 45 to the longer axis of the polymer film. A coating solution containing 41.01 g of discotic liquid crystal compound shown bellow, 4.06 g of ethylene oxide-treated trimethylolpropane triacrylate ("V# 360", provided by OSAkA ORGANIC CHEMICAL INDUSTRY LTD.), 0.23 g of cellulose acetate buthylate ("CAB551-0.2", provided by Eastman Chemical Ltd.), 0.90 g of cellulose acetate buthylate ("CAB531-1", provided by Eastman Chemical Ltd.), 1.35 g of a photo polymerization initiator ("IRGACURE 907", provided by Ciba-Geigy) and 0.45 g of a sensitizer ("KAYACURE DETX", provided by NIPPON KAYAKU CO. , LTD.) dissolved in 102 g of methyl ethyl ketone was applied to the rubbed surface by a # 3 wire bar coater with a spread of 5 mL/m².

The polymer film attached to a metal frame was heated at 130 °C for 2 minutes in a temperature-controlled bath to align the discotic liquid crystal compound. Subsequently, the aligned discotic liquid crystal compound was irradiated with an ultraviolet ray for a minute by a high pressure mercury lamp having a power of 120 W/cm, to polymerize the discotic liquid crystal compound. After cooling down to a room temperature, an optically anisotropic layer was formed on the polymer film. Thus, an optically compensating film (Optically Compensating Film KH-01) was prepared.

Discotic Liquid Crystal Compound

[Example 2]

(Preparation of Polymer Film)

A composition containing 150 weight parts of "ZEONOR 1020R" (provided by ZEON CORPORATION) and 350 weight parts of methylene chloride was put in a mixing tank and stirred with heating, thereby resulting a polymer solution. 36 weight parts of the retardation controlling agent as same as used in Example 1 was added to 474 weight parts of the polymer solution, mixed under sufficient stirring, thereby resulting a dope. The added amount of the retardation controlling agent was 3.5 weight parts based on 100 parts of the polymer ("ZEONOR 1020R") . The dope was cast on a band of a band casting machine to form a film. The film was left on the band by the film surface temperature was 40 °C, subsequently dried by a warm air of 70 °C for a minute and peeled from the band. The obtained film was dried by a dried air of 140 °C for 10 minutes . Thus, Polymer Film PF-02, having a thickness of 50 μm and containing 0.3 wt. % of the residual solvent , was prepared.

Various optical characters were measured as well as Example 1. The results are set forth in Table 1. (Forming Alignment Layer)

After the obtained polymer film, Polymer Film PF-02, was subjected to a corona discharge treatment, an alignment layer was formed on the surface of the polymer film in the same manner as Example 1. (Preparation of Optically Compensating Film)

The alignment layer was subjected to a rubbing treatment along with the longer axis of the polymer film. A coating solution containing 41.01 g of discotic liquid crystal compound as same as used in Example 1, 4.06 g of ethylene oxide-treated trimethylolpropane triacrylate ("V# 360", provided by OSAkA ORGANIC CHEMICAL INDUSTRY LTD . ) , 1.35 g of a photo polymerization initiator ("IRGACURE 907", provided by Ciba-Geigy) and 0.45 g of a sensitizer ("KAYACURE DETX", provided by NIPPON KAYAKU CO. , LTD.) dissolved in 102 g of methyl ethyl ketone was applied to the rubbed surface by a # 3.6 wire bar coater with a spread of 6.3 mL/m².

The polymer film was heated at 130 °C for 2 minutes in a temperature-controlled bath to align the discotic liquid crystal compound. Subsequently, the aligned discotic liquid crystal compound was irradiated with an ultraviolet ray for a minute by a high pressure mercury lamp having a power of 120 W/cm, to polymerize the discotic liquid crystal compound. After cooling down to a room temperature, an optically anisotropic layer was formed on the polymer film. Thus, an optically compensating film (Optically Compensating Film KH-02) was prepared.

[Example 3]

(Preparation of Polymer Film)

A composition containing 100 weight parts of "ZEONOR 1020R"

(provided by ZEON CORPORATION) , 300 weight parts of methylene chloride and 30 weight parts of boron nitride powder was put in a mixing tank and stirred with heating, thereby resulting a polymer solution. 36 weight parts of the retardation controlling agent as same as used in Example 1 was added to 474 weight parts of the polymer solution, mixed under sufficient stirring, thereby resulting a dope. The added amount of the retardation controlling agent was 3.5 weight parts based on 100 parts of the polymer ("ZEONOR 1020R") .

Polymer Film PF-03, having a thickness of 50 μm, was prepared in the same manner as Example 2, except that the used dopes were different each other.

The heat conductivity of the obtained polymer film, Polymer

Film PF-03, was 1.2 W/ (m*K) . Various optical characters were measured as well as Example 1. The results are set forth in Table 1.

(Forming Alignment Layer)

After the obtained polymer film was subjected to a corona discharge treatment, an alignment layer was formed on the surface of the polymer film in the same manner as Example 1. (Preparation of Optically Compensating Film)

An optically anisotropic film (Optically Anisotropic Film KH-03) was prepared in the same manner as Example 2, except that the Polymer Film PF-03 was used in place of the Polymer Film PF-02.

[Comparative Example 1] (Preparation of Polymer Film)

A composition of 100 weight parts of polycarbonate ("PUREACE" provided by TEIJIN CHEMICALS LTD.) and 350 weight parts of methylene chloride was put in a mixing tank, stirred with heating, thereby resulting a polymer solution (a dope) .

The dope was cast on a band of a band casting machine to form a film. The film was left on the band by the film surface temperature was 40 °C, subsequently dried by a warm air of 40 °C for a minute and peeled from the band. The film was stretched along with a perpendicular direction to the conveying direction at 150 °C with a tenter by 25%, and dried for 10 minutes. Subsequently, the polymer film containing 7.0 wt. % of the residual solvent was stretched along with the conveying direction by 25%. Thus, Polymer Film PFH-1 (for comparison), having a thickness of 80 μm, was prepared.

After the obtained polymer film was subjected to a corona discharge treatment, an alignment layer was formed on the surface of the polymer film according to the method as same as that of Example 1. (Preparation of Optically Compensating Film)

An optically anisotropic film (Optically Anisotropic Film KHH-1) was prepared in the same manner as Example 1, except that the Polymer Film PFH-1 was used in place of the Polymer Film PF-01.

Table 1

*1 "ZEONOR 1020R" (provided by ZEON CORPORATION) *2 "PUREACE" (provided by TEIJIN CHEMICALS LTD.)

[Example 4]

A polarizing film was prepared by absorption of iodine to a stretched polyvinylalcohol film. Optically Compensating Film KH-01 was subjected to a corona discharge treatment at the surface of Polymer Film PF-01. The treated surface of KH-01 was laminated on one surface of the polarizing film with a polyvinyl alcohol based adhesive. A commercially available cellulose triacetate film ("Fuji-tac TD80UF", provide by Fuji Photo film Co., Ltd.) was subjected to saponification treatment, and then the film was laminated on the other face of the polarizing film with a polyvinyl alcohol based adhesive. Thus, Polarizing Plate PP-01 was prepared.

Polarizing Plate PP-02, PP-03 and PPH-1 (for comparison) were prepared in the same manner as PP-01, except that Polymer Film KH-02, KH-03 and KHH-1 were respectively used in place of KH-01.

[Example 5]

A pair of polarizing plates was removed from a commercially available liquid crystal display ("AQUOS LC-20C1-S", provided by SHARP CORPORATION) . In place of the removed members, the Polarizing Plate PP-02 prepared in Example 4 was respectively laminated on each side (each of the backlight side and the viewing side) of the cell with an adhesive. Thus, TN-mode LCD-02 was prepared. In the LCD, the transmission axes of the two polarizing plates on the viewing side and on the backlight side run at right angles to one another and the rubbing direction of the liquid crystal cell and the rubbing direction of the optically anisotropic layer were anti-parallel to one another.

TN-mode LCD-03 was prepared in the same manner as LCD-02, except that the Polarizing Plate PP-03 prepared in Example 4 was used in place of the Polarizing Plate PP-02.

The viewing angles of the prepared LCD-02 and LCD-03 were measured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM) when each of eight tones of black (LI) to white (L8) was displayed. The results are set forth in Table 2. The viewing angles shown in Table 2 were mean viewing angles giving a contrast ratio of 10 or more without reversing gradation of black color, specifically reversing gradation between Ll and L2.

Table 2

Display Upward Downward Lateral

LCD-02 55° 52° 118° LCD-03 53° 56° 120°

(Evaluation of Frame-Like Light Leakage)

After the back lights of LCd-02 and LCD-03 were on continuously for 5 hours at 25 °C under 60 % RH, the LCd-02 and LCD-03, displaying black whole area, were placed in a darkroom in order that visual observation of frame-like light leakage from them was performed. As a result, any frame-like light leakage from them were not recognized.

[Example 6]

A polyimide alignment layer was formed respectively on the surfaces of a pair of glass substrates having ITO electrodes and the surfaces of polyimide layers were subjected to rubbing treatment. The glass substrates were placed with alignment layers, of which rubbing directions are parallel to one another, facing each other. The gap between the two glass substrates, of which length was 6 μm, was filled with a liquid crystal compound ("ZLI 1132", provided by Merck) , having a Δn of 0.1396 to prepare a liquid crystal cell of bend alignment. A pair of polarizing plates, PP-01, prepared in Example 4 was respectively laminated to both surfaces of the liquid crystal cell of bend alignment with the optically anisotropic layer facing to the surface of the liquid crystal cell and with the rubbing direction of the optically anisotropic layer being parallel to the rubbing direction of the surface of the liquid crystal cell. Thus, OCB-mode LCD-01 was prepared.

OCB-mode LCD-04 was prepared in the same manner as LCD-01, except that the Polarizing Plate PPH-1 was used in place of the Polarizing Plate PP-01.

The viewing angles of the prepared LCD-01 and LCD-04 were measured by means of a measuring apparatus (EZ-Contrast 160D, ELDIM) when each of eight tones of black (Ll; when applied a square wave voltage of 5 V) to white (L8; when applied a voltage of 2 V at 55 Hz) was displayed. The results are set forth in Table 3. The viewing angles shown in Table 2 were mean viewing angles giving a contrast ratio of 10 or more without reversing gradation of black color, specifically reversing gradation between Ll and L2.

Table 3

Display Upward Downward Lateral LCD-01 78° 76° 160° LCD-04 80° 78° 160° (Evaluation of Frame-Like Light Leakage)

After the back lights of LCd-01 and LCD-04 were on continuously for 5 hours at 25 °C under 60 % RH, the LCd-01 and LCD-04, displaying black whole area, were placed in a darkroom in order that visual observation of frame-like light leakage from them was performed. As a result, any frame-like light leakage from LCD-01 were not recognized. On the other hand, some frame-like light leakage from LCD-04 were recognized, especially upwards and downwards, and the image quality of LCD-04 was poor.

Industrial availability

The present invention can provide an optically compensating film and polarizing film contributing to improvement of viewing angle of the LCD and to reduction of the degradation in visual quality of images displayed by a LCD due to light leakage and the like when they are used in the LCD. The present invention can also provide an optically compensating film and polarizing plate having excellent durability such that their optical characteristics hardly change even though they are used under the sever condition. The present invention can also provide a LCD having wide viewing angle and excellent durability such that the degradation in visual quality of images, which is caused by light leakage during used under a sever condition, is reduced.

Claims

1. An optically compensating film comprising: a polymer film having a retardation value Re, defined as the following formula (I) , of 0 to 100 nm, and a retardation value Rth, defined as the following formula (II), of 70 to 500 nm; and an optically anisotropic layer formed by a liquid crystal compound thereon; wherein the polymer film is formed of a polymer having a photoelastic coefficient of 10 X 10^~12 m²/N or less and having a water vapor permeability of 1 g/(m²-24 hrs) or less measured according to the test method of JIS Z0208, of 70 to 500 nm:

(I) Re = (nx - ny) * d

(II) Rth = { (nx + ny) /2 - nz} * d in which nx and ny are refractive indexes of a slow axis and a fast axis in plane of the polymer film, nz is a refractive index of a thickness direction of the polymer film and d is a thickness .

2. The optically compensating film according to claim 1, wherein the polymer has a specific gravity of 1.20 or less.

3. The optically compensating film according to claim 1 or 2, wherein the polymer is a cyclic polyolefin based polymer.

4. The optically compensating film according to claim 3 wherein the cyclic polyolefin based polymer is a polymer prepared by ring-opening polymerization of a monomer selected from tetracyclododecenes or a polymer prepared by hydrogenation of ring-opening copolymer of a monomer selected from tetracyclododecenes and a monomer selected from norbornenes .

5. The optically compensating film according to any one of claims 1 to 4, wherein the polymer film comprises an aromatic compound having at least two aromatic rings .

6. The optically compensating film according to claim 5, wherein the aromatic compound is a compound having at least one 1, 3, 5-triazin ring.

7. The optically compensating film according to any one of claims 1 to 6, wherein the polymer film comprises heat conductive particles and has a heat conductivity of 1 W/(m-K) or more .

8. The optically compensating film according to any one of claims 1 to 6, comprising a heat conductive layer comprising heat conductive particles on at least one of surfaces of the polymer film, wherein the polymer film having the heat conductive layer thereon has a heat conductivity of 1 W/(rtrK) or more.

9. The optically compensating film according to any one of claims 1 to 8, wherein the liquid crystal compound is a compound selected from discotic liquid crystal compounds.

10. The optically compensating film according to any one of claims 1 to 9, wherein the polymer film is a stretched polymer film.

11. A polarizing plate comprising a polarizing film with two surfaces and two protective films respectively provided on the two surfaces, wherein at least one of the protective films is a polymer film defined in any one of claims 1 to 10.

12. An apparatus for displaying images comprising: two polarizing plates, a liquid crystal cell sandwiched between two polarizing plate, and an optically compensating film defined in any one of claims 1 to 10 sandwiched between one of the polarizing plates and the liquid crystal cell.

13. The apparatus according to claim 12, wherein the liquid cell is TN-mode or OCB-mode.