JPH0675221A - Optical compensation film, polarizing plate and liquid crystal display device - Google Patents

Abstract

(57) [Abstract] [Purpose] A birefringent liquid crystal display device such as STN type which is thin, light and excellent in viewing angle by obtaining a film-shaped compensator that can compensate not only birefringence but also optical rotation. To obtain an optical compensation film or a polarizing plate capable of forming a film. An optical compensatory film comprising a heat-resistant birefringent film (2), which is formed by rubbing the surface of the film, and provided with an optical rotation layer (1) made of a liquid crystalline polymer having a twisted nematic alignment on the alignment-treated surface. And a polarizing plate in which the optical compensation film is laminated on one side of the polarizing film, and a liquid crystal display device having the optical compensation film between a birefringent liquid crystal cell and the polarizing plate. [Effect] A thin optical compensation film that can arbitrarily set the optical rotatory power and birefringence can be easily obtained, and the rotation angle and the rotation direction of the polarization direction can be freely set. It is possible to obtain a liquid crystal display device that is easy and achieves excellent color prevention and contrast.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin optical compensation film capable of coping with optical rotatory power and birefringence, a polarizing plate and a liquid crystal display using the same, and a birefringent liquid crystal display of STN type or the like. It is intended to prevent coloring and improve contrast.

[0002]

BACKGROUND OF THE INVENTION A birefringent liquid crystal display device of STN type or the like, which has a high contrast and a wide viewing angle and can easily display a large screen by a multiplex drive dot matrix system, has been replaced with a personal computer or a conventional TN type. It is used for various screen displays such as word processors and data terminal devices.

In such a liquid crystal display device, due to the birefringence of the liquid crystal cell, there is a problem that it is colored in a blue system or a green or yellow-red system when an electric field is applied or not applied. Induce problems that interfere. Therefore, various coloring preventing means have been proposed in order to realize monochrome display.

[0004]

2. Description of the Related Art Conventionally, as a coloration preventing means, a super twist nematic (ST) having an opposite twist angle has been used.
A double cell structure method has been known in which N) type liquid crystal cells are superposed and compensated. However, in addition to the problems of bulkiness and weight increase, the viewing angle was narrowed, the display was still colored from an oblique perspective, and it was difficult to obtain a compensation cell for the reversal relationship, resulting in poor yield. .

In view of the above, attempts have been made to develop a single-layer film exhibiting optical characteristics equivalent to those of a compensating cell, but this has not been realized yet, and an FTN system in which a retardation plate made of a stretched film is used instead is realized. It has only been done. However, this method has a problem in that it can deal with the phase difference due to the birefringence of the liquid crystal cell and has a poor compensation effect and a poor contrast.

[0006]

SUMMARY OF THE INVENTION The present invention provides a film-like compensator capable of compensating for optical rotation in addition to birefringence, and is thin and light, and has excellent viewing angle. It is an object to develop an optical compensation film or a polarizing plate that can obtain a refractive liquid crystal display device.

[0007]

According to the present invention, an optical rotation layer made of a twisted nematically oriented liquid crystalline polymer is provided on an alignment treated surface formed by rubbing the surface of a heat resistant birefringent film. An optical compensation film characterized by the above, and a polarizing plate characterized in that the optical compensation film is laminated on one side of the polarizing film, and the optical compensation film between the birefringent liquid crystal cell and the polarizing plate. The present invention provides a liquid crystal display device characterized by having.

[0008]

[Function] A liquid crystalline polymer is directly spread on the orientation-treated surface of a heat-resistant birefringent film, and heat-treated and then cooled, whereby the birefringent film is excellent in uniformity without impairing its optical characteristics. It is possible to form a large-area optical rotation layer made of a liquid crystalline polymer having a twisted nematic alignment structure in a monodomain state. As a result, it is possible to obtain an optical compensation film which is thin and has a thickness substantially equal to the sum of the thickness of the birefringent film and the thickness of the optical rotation layer, and which can cope with the optical rotatory power and the birefringence.

[0009]

EXAMPLE The optical compensation film of the present invention comprises a heat-resistant birefringent film having a surface directly provided with an optical rotatory layer comprising a twisted nematically oriented liquid crystalline polymer. An example is shown in FIG. 1 is an optical rotatory layer made of a liquid crystalline polymer, and 2 is a birefringent film.

The optical rotatory layer, for example, exhibits good orientation by heat treatment on the orientation-treated surface to form a monodomain state with excellent uniformity, and has no crystal phase below the temperature range where it exhibits a nematic phase. It can be obtained by using a liquid crystalline polymer capable of stably fixing a monodomain state of a twisted nematic structure by showing the temperature dependence of a phase state of taking a glass state, or a combination of the liquid crystalline polymer and an optically active compound.

Examples of such a liquid crystalline polymer include a main chain type or a side chain type in which a conjugated linear atomic group (mesogen) for imparting liquid crystal orientation is introduced into the main chain or side chain of the polymer. Can be given. Specific examples of the main chain type liquid crystalline polymer include liquid crystallinity such as nematic oriented polyester type, polyamide type, polycarbonate type, polyester imide type, etc. having a structure in which a mesogen group is bonded by a spacer portion that imparts flexibility. Polymers and the like.

Specific examples of the side chain type liquid crystalline polymer include polysiloxane, polyacrylate, polymethacrylate or polymalonate as a main chain skeleton, and nematic orientation is imparted through a spacer portion composed of a conjugated atomic group as a side chain. And the like having a mesogenic moiety composed of a para-substituted cyclic compound unit.

As the above-mentioned para-substituted cyclic compound unit,
For example, a low molecular weight liquid crystal compound having a nematic liquid crystallinity, which is composed of a para-substituted aromatic unit, a para-substituted cyclohexyl ring unit, or the like, can be given. More specifically, for example, azomethine type, azo type, azoxy type, ester type, biphenyl type, phenylcyclohexane type, bicyclohexane type and the like can be mentioned. The terminal substituent at the para position in the para-substituted cyclic compound unit may be a usual substituent in a low molecular weight liquid crystal compound, and is generally a cyano group, an alkyl group, an alkoxy group or the like. The optimum number of methylene chains in such an alkyl group or alkoxy group exists depending on the core structure of the mesogen part, but usually 1
Is in the range of ~ 9 carbon chains.

Examples of the spacer portion include polymethylene chain-(CH ₂ ) _n- , polyoxymethylene chain-(CH ₂ CH ₂ O) _m- , which exhibits flexibility. The repeating number of structural units forming the spacer part has an optimum number depending on the chemical structure of the mesogen part. Incidentally, in the case of a polymethylene chain, n is 2 to 11, and in the case of a polyoxymethylene chain, m is 1 to 3. Outside the above range, the nematic orientation is lowered, and the smectic phase is likely to be exhibited below the temperature range where the nematic phase is exhibited, and it becomes difficult to fix the twisted nematic state.

The preparation of the main chain type liquid crystalline polymer is carried out, for example, by
It can be performed by a method of copolymerizing the component monomers. The side chain type liquid crystalline polymer is prepared, for example, by polymerizing a monomer in which a mesogenic group is introduced into a vinyl-based main chain-forming monomer such as an ester of acrylic acid or methacrylic acid via a spacer group by a radical polymerization method. Addition polymerization method and S of polyoxymethylsilylene
It can be carried out by a method of addition-reacting a vinyl-substituted mesogenic monomer in the presence of a platinum catalyst through an i-H bond.

Further, a method of introducing a mesogenic group by an esterification reaction using a phase transfer catalyst via a functional group imparted to a main chain polymer, and a monomer in which a mesogenic group is introduced into a part of malonic acid via a spacer group The side chain type liquid crystalline polymer can also be prepared by a method such as polycondensation reaction with a diol.

The liquid crystal polymer which can be preferably used has a weight average molecular weight of 20,000 to 200,000 based on polystyrene conversion by gel permeation chromatography. If the molecular weight is less than 20,000, it is difficult to obtain a light-rotating layer having excellent strength, and if it exceeds 200,000, the viscosity is increased and the orientation property is deteriorated, which requires a lot of time for the orientation treatment.

The liquid crystalline polymer that can be preferably used has a glass transition point higher than the operating temperature in view of the stability of the fixed alignment. By the way, when used near room temperature, a liquid crystal polymer having a glass transition point of lower than 30 ° C. may change the immobilized liquid crystal structure to induce a functional decline.

Examples of a combination of a liquid crystalline polymer and an optically active compound include, for example, a mixture of a main chain type or side chain type liquid crystalline polymer and an optically active compound, or a main chain type liquid crystalline polymer in the main chain. Examples include those in which an optically active group based on an optically active compound is introduced, and those in which an optically active compound composed of a liquid crystalline atomic group having an optically active group in the side chain of a side chain type liquid crystalline polymer is introduced via a spacer portion. To be The combination with the optically active compound is intended to control the twist angle and the twist pitch in the nematic orientation.

The optically active compound to be mixed with the main chain type or side chain type liquid crystalline polymer may be any compound having optical activity, and may be a low molecular weight compound or a polymer. Those which can be preferably used are those having liquid crystallinity with good compatibility with the liquid crystalline polymer.

Examples of the liquid crystal low molecular weight compound having good compatibility are the following in addition to cholesterol derivatives. The carbon marked with * in the chemical formula means optically active carbon (hereinafter the same).

Examples of the liquid crystalline polymer having good compatibility with the above-mentioned liquid crystalline polymer include liquid crystalline polyacrylate, polymethacrylate, polymalonate, polysiloxane, polyester having an optically active group.
Polyamide, polyesteramide, polycarbonate,
Examples include polypeptides and cellulose. Above all, an aromatic-based polymer having the following structural units is preferable.

[0023]

[0024]

[0025]

The liquid crystalline polymer and the optically active compound can be mixed by an appropriate method such as mixing with a powder, mixing with a solvent, and mixing by melting. The mixing ratio of the optically active compound may be appropriately determined depending on the optical activity and the force of imparting twist, but in general, the liquid crystalline polymer 1
It is 0.1 to 100 parts by weight per 00 parts by weight.

The liquid crystal polymer obtained by introducing an optically active group based on an optically active compound into the main chain of a main chain type liquid crystalline polymer is one in which the following optically active groups are introduced by a copolymerization method or the like. And so on. The introduction ratio is usually 20 mol% or less.

[0028]

[0029]

The liquid crystal polymer obtained by introducing an optically active compound composed of a liquid crystal atomic group having an optically active group into the side chain of a side chain type liquid crystal polymer through a spacer portion is as follows. And the like. Examples of the spacer portion include those similar to the liquid crystalline polymer. The introduction ratio is usually 20 mol% or less.

[0031]

As the birefringent film, a film which is optically transparent, capable of orienting a liquid crystalline polymer, and having heat resistance so as not to lose the birefringence at the time of forming the optical rotation layer is used. Examples thereof include those obtained by heating a film made of a plastic such as polymethylmethacrylate, polycarbonate, polyvinyl alcohol, polypropylene and other polyolefins, polyarylate, and polystyrene at an appropriate temperature such as a glass transition point and subjecting to stretching treatment. To be The birefringence or retardation can be easily controlled by changing the stretching conditions such as the stretching ratio.

The thickness of the birefringent film can be appropriately determined according to the retardation to be compensated. Generally, it is 500μm based on a single layer film in terms of flexibility.
Hereafter, it is set to 100 μm or less. The birefringent film may be formed as a laminate of stretched films for the purpose of controlling retardation and the like.

The optical compensation film can be formed, for example, by developing a liquid crystal polymer on the surface of the rubbing-treated birefringent film by an appropriate method to form an optical rotation layer directly on the birefringent film. . The rubbing treatment can be performed by, for example, a method of rubbing the surface of the birefringent film with a fiber such as polyester or polyamide or a cloth.

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

The optical rotatory layer can be formed by, for example, a method of heat-treating the liquid crystalline polymer spread on the alignment treated surface to align it to form a monodomain state, and then cooling it. The heat treatment for orientation can be performed by heating within a temperature range from the glass transition point of the liquid crystalline polymer to a molten state exhibiting an isotropic phase. The cooling conditions for fixing the orientation state are not particularly limited, and the heat treatment described above can be generally performed at a temperature of 200 ° C. or less, and thus the natural cooling method is generally adopted.

The thickness of the optical rotatory layer can be appropriately determined within a range where the function based on the twisted nematic structure is exerted as an optical waveguide, but generally 50 from the viewpoint of flexibility and the like.
The thickness is 0 μm or less, preferably 100 μm or less, more preferably 2 μm or more, and especially 3 μm or more, especially 5 μm or more in terms of strength. The twist angle of the nematic orientation in the optical rotatory layer is arbitrary and can be adjusted to the twist angle as needed.

The polarizing plate of the present invention comprises a polarizing film having a laminated structure conforming to the above optical compensation film on one side. Examples thereof are shown in FIGS. 2, 3 and 4. 4 is a polarizing film, and 1 and 2 are the same as above. 3 is a transparent adhesive layer. As is clear from FIGS. 2 and 3, the optical rotation layer 1 and the birefringent film 2 may be arranged at any positions, and any of them may be on the polarizing film 4 side. When two or more birefringent films 2 are used, those birefringent films can be arranged on the same side with respect to the optical rotatory layer 1, or can be arranged on both sides of the optical rotatory layer 1 as illustrated in FIG. Alternatively, the number of birefringent films to be arranged is arbitrary.

As the polarizing film, an appropriate one can be used without any particular limitation. Generally, a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, or an ethylene / vinyl acetate copolymer-based partially saponified film, which is stretched by adsorbing iodine and / or a dichroic dye A polarizing film composed of a polyene oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride is used. The thickness of the polarizing film is usually 5
800 μm, but is not limited to this.

The polarizing film used may have a transparent protective layer on one side or both sides thereof. As a material for forming the transparent protective layer, a material excellent in transparency, mechanical strength, thermal stability, moisture shielding property and the like can be preferably used. Typical examples thereof include polymers such as polyester resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, acrylic resins and acetate resins. The transparent protective layer can also serve as the above-mentioned birefringent film.

The type of transparent adhesive or pressure-sensitive adhesive for adhering the optical compensation film and the polarizing film, etc. is not particularly limited, but in order to prevent changes in the optical characteristics of each functional film, curing or drying is preferable. In this case, those which do not require a high temperature process are preferable, and those which do not require a long curing treatment or a drying time are desirable.

In the polarizing plate of the present invention, the polarizing film or transparent protective layer is provided with an ultraviolet absorber such as salicylate compound, benzophenol compound, benzotriazole compound, cyanoacrylate compound, nickel complex salt compound and the like. It can also be made to have the ability to absorb ultraviolet rays by a method of treating with.

The liquid crystal display device of the present invention comprises a birefringent liquid crystal cell such as an STN type and a polarizing plate having a laminated structure conforming to the above optical compensation film. The example is shown in FIG. 5 is a liquid crystal cell, and 1, 2, 3, 4 are the same as above. The laminated structure according to the optical compensation film is
It is provided on at least one side of the liquid crystal cell. The optically active layer and the birefringent film which can be preferably used are those which prevent optical rotation and birefringence due to the liquid crystal cell used in combination to prevent coloring and reduce the contrast.

[0044]

According to the present invention, it is possible to easily obtain a thin optical compensation film in which optical rotatory power can be easily set with high accuracy and which has desired characteristics in birefringence. In addition, the rotation angle and direction of the polarization direction can be set freely, and it is easy to form a large area body of an optical compensation film or polarizing plate that is excellent in flexibility, light weight, thin film property, and handleability. It is possible to obtain a birefringent liquid crystal display device of STN type or the like, which is excellent in display quality such as achievement degree, contrast, and viewing angle.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of an optical compensation film.

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

FIG. 3 is a sectional view of another embodiment of the polarizing plate.

FIG. 4 is a sectional view of yet another embodiment of the polarizing plate.

FIG. 5 is a sectional view of an embodiment of a liquid crystal display device.

[Explanation of symbols]

 1: Optical rotation layer 2: Birefringent film 3: Adhesive layer 4: Polarizing film 5: Birefringent liquid crystal cell

Claims (3)

[Claims] 1. An optical compensation film, characterized in that an optical rotation layer comprising a twisted nematically aligned liquid crystalline polymer is provided on an alignment treated surface formed by rubbing the surface of a heat resistant birefringent film. . 2. A polarizing plate comprising the polarizing film, and the optical compensation film according to claim 1 laminated on one side of the polarizing film. 3. A liquid crystal display device comprising the optical compensation film according to claim 1 between a birefringent liquid crystal cell and a polarizing plate.