TWI417579B - Polarizing plate having optical compensation film and liquid crystal device using the same - Google Patents

Description

Polarizing plate with optical compensation film and liquid crystal display device using same

The present invention relates to a liquid crystal display device and a polarizing plate with an optical compensation film used therefor.

A display device for an OA (office automation) machine such as a word processor or a notebook personal computer or a personal computer monitor, a portable terminal, a television, etc., because of a thin body, a light weight, and a small power consumption, Liquid crystal display devices have been the most widely used users.

A liquid crystal display device usually has a liquid crystal cell and a polarizing plate. The polarizing plate is usually composed of a protective film and a polarizing film, which is obtained by dyeing a polarizing film composed of a polyvinyl alcohol film with iodine, stretching it, and laminating the protective film on both sides thereof. In the transmissive liquid crystal display device, it is also possible to mount the polarizing plate on both sides of the liquid crystal cell and then arrange one or more optical compensation films. In the reflective liquid crystal display device, a reflector, a liquid crystal cell, and one or more optical compensation films and a polarizing plate are arranged in this order. The liquid crystal cell system is composed of liquid crystal molecules, two substrates required for sealing them, and an electrode layer for applying a voltage to liquid crystal molecules. The liquid crystal cell system performs ON (ON) and OFF (OFF) display according to the difference in the alignment state of the liquid crystal molecules, and its display mode is applicable to any of the transmissive type, the reflective type, and the semi-transmissive type, such as TN. (Twisted Nematic: twisted nematic), IPS (In-Plane Switching), OCB (Optically Compensatory Bend), VA (Vertically Aligned), ECB (Electrically Controlled Birefringence) : Electronically controlled birefringence type), STN (Super Twisted Nematic: Super Twisted Nematic) display mode.

The optical compensation film is used in various liquid crystal display devices to eliminate image coloration or to widen the viewing angle. Optical compensation films have heretofore been used with extended birefringent polymer films. There has been proposed a method of using an optical compensation film having an optically anisotropic layer formed of a low molecular or high molecular liquid crystalline compound on a transparent support instead of an optical compensation film composed of an extended birefringent film. Since the liquid crystalline compound has various alignment modes, it is possible to realize an optical property which cannot be obtained by a conventional extended birefringence polymer film as long as a liquid crystalline compound is used, and has a function as a protective film for a polarizing plate.

The optical properties of the optical compensation film are determined based on the optical properties of the liquid crystal cell, specifically, based on the difference in display modes as described above. When a liquid crystalline compound is used, an optical compensation film having various optical properties capable of coping with various display modes of liquid crystal cells can be produced. An optical compensation film using a liquid crystal compound has been proposed to disclose a person who can cope with various display modes. For example, the optical compensation film for the TN mode liquid crystal cell is optically compensated by applying a voltage liquid crystal molecule, that is, eliminating the twist structure while performing an alignment state inclined with the substrate surface, and the contrast can be improved by preventing oblique light leakage during black display. Viewing characteristics.

The optical compensation film for the TN mode liquid crystal display device is an optical compensation that eliminates the twisted structure by applying a voltage liquid crystal molecule while performing an alignment state inclined with the substrate surface, and can improve the contrast angle by preventing oblique light leakage during black display. characteristic. A representative example of optical compensation is a technique in which a liquid crystalline compound is mixed and aligned to form a film, and a liquid crystalline compound is used as a discotic liquid crystalline compound (see Patent Document 1), or a rugby-like compound is used. Example.

However, even if an optical compensation film in which the discotic liquid crystal compound is uniformly mixed and aligned is used, it is extremely difficult to cause the liquid crystal cell to perform optical compensation without any problem. For example, in a TN mode TFT (Thin Film Transistor) type liquid crystal display panel, although the front contrast ratio is about 300:1, the TN mode is manufactured by using a transparent electrode glass substrate. In the case of a unit cell, the front contrast ratio can be improved to 600:1 or more. This is because the substrate of the TFT display device has a polarization canceling effect, which causes light leakage when displayed in black, and the contrast ratio is lowered. An example of improving the contrast ratio of the TFT liquid crystal display device is to control the scattering characteristics of the color filter substrate (see Patent Document 2).

(Patent Document 1) Japanese Laid-Open Patent Publication No. Hei No. 6-214116 (Invention Patent Document 2) Japanese Laid-Open Patent Publication No. 2001-166126

The present invention has been made in view of the above problems in order to provide a liquid crystal display device having a simple structure and having the same viewing angle characteristics as before and having high contrast. Further, the present invention provides a polarizing plate which contributes to improvement of the contrast of a liquid crystal display device, and can maintain a simple structure and a viewing angle characteristic thereof.

The technical method for solving the above object is as follows.

(1) A pair of polarizing plates are disposed in a liquid crystal display device for holding liquid crystal cells, and at least one side has at least a polarizing film and an optical compensation film, and the degree of polarization is 99.5% or more, and the optical compensation film is The degree of polarization retention is 90% or more.

The polarizing plate of the item (1) has an optical compensation film having a polarization maintaining ratio of the above range, and the degree of polarization is in the above range, thereby contributing to improvement of viewing angle characteristics of the liquid crystal display device and reduction of image coloration, and at the same time High contrast ratio.

(2) The polarizing plate of item (1), wherein the pair of polarizing plates are ±4 or less for the transmitted light hue a and b of the normal incident light.

In the polarizing plate of the item (2), since the effect of the polarizing plate of the item (1) as described above is exhibited, and the hue and a of the transmitted light of the polarizing plate are both ±4 or less, the liquid crystal display using the same is used. The device can make the color of the black display more excellent in achromatic display.

(3) A liquid crystal display device comprising: an electrode having at least one side, and a pair of opposite substrates; a liquid crystal layer disposed between the substrates; and a pair of polarizing plates configured to sandwich the liquid crystal layer And at least one side of the pair of polarizing plates has a polarizing film and an optical compensation film on a side of the liquid crystal layer adjacent to the polarizing film, and the polarizing degree of the pair of polarizing plates is 99.5%. As described above, the polarization maintaining ratio of the pair of substrates is 90% or more, and the polarization maintaining ratio of the optical compensation film is 90% or more.

In the liquid crystal display device of the item (3), since the polarization compensation is in the above range and the optical compensation film having the polarization maintaining ratio in the above range is displayed, it is possible to display an image of a good color tone at a wide viewing angle and to remarkably improve the contrast ratio.

(4) The liquid crystal display device of item (3), wherein the pair of polarizing plates have a polarizing film on both sides thereof and an optical compensation film on a side of the liquid crystal layer adjacent to the polarizing film.

In the liquid crystal display device of the item (4), since the effect of the item (3) can be exhibited and the optical compensation film is provided on both sides of the polarizing plate, optical compensation can be more accurately achieved, and the viewing angle and color tone can be further improved.

(5) The liquid crystal display device of item (3) or (4), wherein the optical compensation film has a degree of polarization maintaining ratio of not less than a degree of polarization maintenance of the pair of substrates.

The liquid crystal display device of the item (5) is particularly preferable in a transmissive type in which a backlight is disposed on a substrate surface on the back side of the display surface. The backlight light is emitted from the display surface through the lower polarizing plate, the lower substrate, the liquid crystal layer, the upper substrate, and the upper polarizing plate. At this time, high contrast can be obtained by increasing the polarization maintaining ratio of the member closer to the polarizing plate. Further, a high contrast ratio can be obtained by increasing the polarization maintaining ratio of the optical compensation film on the side of the pair of substrates for sandwiching the liquid crystal layer adjacent to the light source.

(6) The liquid crystal display device of any one of (3) to (5), wherein the absorption axis of the pair of polarizing plates is substantially orthogonal.

(7) The liquid crystal display device of any one of (3) to (6), wherein at least one of the pair of substrates forms a color filter including each of red, green, and blue patterns, And if the polarization maintaining ratios of the red pattern, the green pattern, and the blue pattern are Pr, Pg, and Pb, respectively, then Pr/Pg ≦ 1.5 and Pb/Pg ≦ 1.5.

The liquid crystal display device of any one of (3) to (7), wherein the electrode is composed of a pixel electrode and a counter electrode, and the pixel electrode and the counter electrode pair are arranged The pixel electrode and the substrate of the opposite electrode generate a slightly parallel electric field.

(9) The liquid crystal display device of item (8), wherein the electrode is disposed on a different layer, and at least one of the electrodes is composed of a transparent electrode.

(10) The liquid crystal display device of (9), wherein a conductive layer to which no voltage is applied is further disposed in the substrate on which the pixel electrode and the counter electrode are disposed.

In the present specification, "45°", "parallel" or "orthogonal" means that it is within a range of ±5° less than an angle. The error with the tight angle is preferably less than 4°, more preferably less than 3°. In addition, regarding the angle, "+" means the counterclockwise direction, and "-" means the clockwise direction. In addition, the "late phase axis" means that the refractive index becomes the largest direction. In addition, "visible light field" means 380 nm to 780 nm. In addition, the measurement wavelength of the refractive index is a value of λ = 550 nm in the visible light region unless otherwise specifically added.

In the present specification, the "polarizing film" is different from the "polarizing plate". The "polarizing plate" means a layer having at least one side of the surface of the "polarizing film" and having at least one layer of a protective film or the like. body.

According to the present invention, it is possible to provide a liquid crystal display device, particularly a TN type or IPS type liquid crystal display device, which can be improved in contrast without impairing the viewing angle characteristics with a simple configuration. Further, according to the present invention, it is also possible to provide a polarizing plate which contributes to improvement of contrast of liquid crystal cells of a TN type or IPS type liquid crystal display device.

[Embodiment of the Invention]

The invention is described in detail below.

[Polarizer]

The present invention relates to a pair of polarizing plates that can be disposed in a liquid crystal display device for clamping liquid crystal cells. One of the polarizing plates of the present invention has at least one side having at least a polarizing film and an optical compensation film. Further, in the polarizing plate of the present invention, the degree of polarization is 99.5% or more, and the degree of polarization retention of the optical compensation film is 90% or more. When the optical compensation film is provided on both sides of the polarizing plate, it is preferable that the optical compensation film on both sides has a polarization maintaining ratio of 90% or more. A TFT (Thin Film Transistor) type liquid crystal display device or the like has a display having high contrast and high image quality, but on the other hand, the contrast ratio thereof largely changes due to its constituent members. In the present invention, the polarization degree of the polarizing plate and the polarization maintaining ratio of the optical compensation film included in the polarizing plate are set to the above-described ranges, and are used as a polarizing plate which contributes to high contrast of the liquid crystal display device.

The "polarization P" of the polarizing plate can be defined as: P = ((T∥ - T⊥) / (T∥ + T⊥)) ^{1 / 2} . In the formula, "T∥" is a parallel transmittance of a polarizing plate, which is a transmittance obtained when a pair of polarizing plates are arranged in a parallel (∥) state with an absorption axis. "T⊥" is the orthogonal transmittance of the polarizing plate, which is a transmittance obtained when a pair of polarizing plates are arranged in an orthogonal (⊥) state with the absorption axis. One of the polarizing plates of the present invention has a degree of polarization of 99% or more, preferably 99.5% or more, and more preferably 99.9% or more. In addition, the polarization maintaining ratio represents the transmittance when the member is incident on the linearly polarized light. In the present invention, the optical compensation film has a polarization maintaining ratio of 90% or more, preferably 95% or more, and more preferably 99% or more. Further, the ideal value of the contrast ratio of the display device is approximately 3,000:1 in terms of the ratio T∥/T of the transmittance of the polarized light. As far as the polarizing plate is concerned, if the polarization maintaining ratio of the optical deflecting film and the optical compensation film is within the above range, the contrast ratio of the liquid crystal display device can be improved to be close to an ideal value.

[Optical compensation film]

One of the present invention is directed to a polarizing plate having at least one optical compensation film on at least one side thereof. The optical compensation film of the present invention has a polarization maintaining ratio of 90% or more. In order to improve the polarization maintaining ratio of the optical compensation film so as to satisfy the above range, it is preferable to suppress the size of the alignment defect or foreign matter in the compensation film to 1 μm or less. The optical compensation film system helps to eliminate image coloration or enlarge the viewing angle. Therefore, the polarizing plate of the present invention also contributes to improving the contrast ratio of the liquid crystal display device while improving the viewing angle characteristics and reducing image coloration. The polarizing plate of the present invention can also use all or a part of the optical compensation film as a protective film for the polarizing film. For example, when the optical compensation film is a birefringent polymer film, the optical compensation film itself can be used as a protective film for a polarizing film, and the optical compensation film is a support composed of a polymer film or the like and a liquid crystal molecule. When the laminated body of the optically anisotropic layer is formed, a polymer film as a support may be used as a protective film of the polarizing film.

The material of the optical compensation film is not particularly limited, and an optically anisotropic layer formed by stretching a birefringent polymer film and liquid crystal molecules can be used. Since the liquid crystal molecules have various alignment modes, it is possible to easily obtain an optical compensation layer which can satisfy the optical characteristics required for the mode of the liquid crystal cell to be compensated or the like by using the liquid crystal molecules. The liquid crystal compound can be classified into a "rod type" and a "disk type" depending on the shape of the molecule, and any type can be used. Also. They can also be classified into "low molecular" and "polymer" types, but any type can be used.

The optical compensation film composed of the optically anisotropic layer formed of liquid crystal molecules is described in detail below based on its preferred characteristics, materials that can be used, and manufacturing methods.

[Optical properties of optical anisotropic layer]

The retardation Re of the optically anisotropic layer formed by the liquid crystalline molecules is preferably a ratio of Re @450 measured at 450 nm to a value of Re @650 measured at 650 nm {Re @650 }/{Re @450} is between 0.8 and 1.2. As long as it is in this range, the color tone can be remarkably improved.

Further, in the present specification, optical characteristics of various members such as an optical anisotropic layer or a polymer film are values measured by the method described below.

〔delay〕

The sample of 30 mm × 40 mm was conditioned at 25 ° C and 60 % RH for 2 hours, and the Re (λ) was made using KOBRA 21ADH (manufactured by Oji Scientific Instruments Co., Ltd.), and the light having a wavelength of λ nm was directed toward the normal direction of the film. Determined by incidence. Rth(λ) is determined by KOBRA 21ADH according to the above Re(λ), the in-plane retardation axis (determinable by KOBRA 21ADH) as the tilt axis (rotation axis), and inclined by +40° toward the film normal direction. The direction is such that the retardation measured by the incident light having a wavelength of λ nm and the late-phase axis in the plane are used as the tilt axis (rotation axis) and the wavelength is λ Na in a direction inclined by -40° toward the normal direction of the film. The total of the delays measured by the incidence of the light of the meter is calculated from the delay measured in the three directions and the assumed value of the average refractive index and the input film thickness value. Among them, the assumed value of the average refractive index can be used in the "Molecular Handbook" (JOHN WILEY & SONS, INC.), and the values of various optical film catalogues. If the value of the average refractive index is not known, it can be measured by an Abbe refractometer. The values of the average refractive index of the main optical film are exemplified as follows: deuterated cellulose (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), polystyrene. (1.59).

As long as the assumed value of the average refractive index and the film thickness are input, KOBRA 21ADH can calculate nx, ny, and nz. From the calculated nx, ny, nz, the value of Nz = (nx - nz) / (nx - ny) can be further calculated.

(molecular alignment axis)

The sample of 70 mm × 100 mm was conditioned at 25 ° C and 65% RH for 2 hours, and was calculated from the phase difference at the incident angle of normal incidence using an automatic birefringence meter (KOBRA 21ADH, manufactured by Oji Scientific Instruments Co., Ltd.). "Molecular alignment axis".

(axis displacement)

In addition, the "axial displacement angle" was measured using an automatic birefringence meter (KOBRA 21ADH, manufactured by Oji Scientific Instruments Co., Ltd.). The measurement was performed at intervals of 20 at equal intervals in the width direction, and the average value of the absolute values was determined. In addition, the range of the "lattice axis angle (axial displacement)" is measured at 20 intervals at equal intervals in the entire width direction, and then the average of the four absolute values from the axial displacement is larger and the smaller four are averaged. Poor.

[optical anisotropic layer]

A preferred embodiment of the optically anisotropic layer composed of a liquid crystalline compound is described in detail below. The optically anisotropic layer is preferably designed to compensate for liquid crystal compounds in the liquid crystal cell of the liquid crystal display device in black display. The alignment state of the liquid crystal compound in the liquid crystal cell at the time of black display differs depending on the mode of the liquid crystal display device. The alignment state of the liquid crystal compound in the liquid crystal cell is disclosed in IDW '00, FMC 7-2, and pages 411 to 414. The liquid crystalline molecules which can be used to form the optically anisotropic layer include rod-like liquid crystalline molecules and discotic liquid crystalline molecules. The rod-like liquid crystal molecules and the discotic liquid crystal molecules may be polymer liquid crystals or low molecular liquid crystals, and also include those in which low molecular liquid crystals are crosslinked to exhibit no liquid crystallinity.

[rod-like liquid crystalline molecules]

As the "rod-like liquid crystalline molecule" which can form the optically anisotropic layer, azomethine, oxyazo, cyanobiphenyl, cyanobiphenyl ester, benzoate or ring can be used. Phenyl hexanecarboxylate, cyanophenylcyclohexane, phenylpyrimidine substituted by cyano group, phenylpyrimidine substituted by alkoxy group, phenyl dioxane, diphenyl Acetylenes, alkenylcyclohexylbenzonitriles. Further, the rod-like liquid crystalline molecules also include metal complexes. In addition, the rod-like liquid crystalline molecules are included in the repeating single Liquid crystal polymers can also be used as rod-like liquid crystalline molecules. In other words, the rod-like liquid crystalline molecules can be bonded to the (liquid crystal) polymer. The column liquid crystal molecular system is described in the "Quarterly Chemicals", Volume 22, "Chemicals of Liquid Crystals" (1994): Chapters 4, 7 and 11 of the Japanese Chemical Society, and "Liquid Crystal Devices" Handbook: Chapter 3 of the 142th Committee of the Japan Society for the Promotion of Science and so on.

The birefringence of the rod-like liquid crystalline molecules is preferably in the range of 0.001 to 0.7. The rod-like liquid crystal molecular system is fixed in an alignment state, and preferably has a polymerizable group. The polymerizable group is preferably a radical polymerizable unsaturated group or a cationically polymerizable group, and is specifically, for example, included in paragraphs (0064) to (0086) of the specification of Japanese Laid-Open Patent Publication No. 2002-62427. A polymerizable group or a polymerizable liquid crystal compound disclosed.

[disc liquid crystal molecules]

Examples of "disc-like (disc) liquid crystalline molecules" which can be used to form the optically anisotropic layer include: a study by C. Destrade et al., Mol. Cryst., vol. 71, p. 111 ( Benzene derivatives, 1981; published in a study by C. Destrade et al., "Mol. Cryst." 122, 141 (1985), Physics lett. A, vol. 78, p. 82 ( 1990) a derivative of sulphonic acid monoamine; disclosed in B. Kohne et al., Angew. Chem. 96, p. 70 (1984) cyclohexane derivatives; JM Lehn et al., J. Chem. Commun., pp. 1,794 (1985), J. Zhang et al., J. Am. Chem. Soc. 116, 2, 655 (1994) Azacrown or phenylacetylene macrocycles.

The discotic liquid crystalline molecule also includes a structure in which a mother nucleus of a molecular center is substituted with a linear alkoxy group, an alkoxy group, a substituted benzamidineoxy group as a mother nucleus side chain, and is substituted into a radial structure. A compound which exhibits liquid crystallinity. Preferably, the aggregate of molecules or molecules has rotational symmetry and can impart a certain alignment compound. The optically anisotropic layer formed of the discotic liquid crystalline molecules, and finally the compound containing the optically anisotropic layer is not necessarily a discotic liquid crystalline molecule, and may also contain, for example, a low molecular group having a group capable of thermal or photoreaction. A discotic liquid crystalline molecule, but as a result, it is a compound which is polymerized or crosslinked by heat and light reaction, so that the polymer is lost and the liquid crystal property is lost. A preferred example of the discotic liquid crystalline molecule is disclosed in Japanese Laid-Open Patent Publication No. 8-50206. In addition, the polymerization of a discotic liquid crystalline molecule is disclosed in Japanese Patent Publication No. 8-27284. The dish-like liquid crystal phase-solid phase transfer temperature of the discotic liquid crystalline molecules is preferably from 70 to 300 ° C, and more preferably from 70 to 170 ° C.

When the discotic liquid crystalline molecule is immobilized by polymerization, it is necessary to bond the polymerizable group as a substituent in the disc-shaped core portion of the discotic liquid crystalline molecule. The disc-shaped core portion and the polymerizable group are preferably a compound which can be bonded by a linking group, whereby the alignment state can be maintained in the polymerization reaction, for example, the specification of Japanese Patent Laid-Open Publication No. 2000-155216 Compounds and the like disclosed in paragraphs (0151) to (0168).

Further, the preferred alignment of the liquid crystal molecules in the optically anisotropic layer differs depending on the optical characteristics desired by the present invention, and the liquid crystal molecules may be an optically anisotropic layer which is fixed in a mixed alignment state. In the mixed alignment, the angle formed by the long axis of the liquid crystalline molecule (the disc surface of the discotic liquid crystalline molecule) and the surface of the polarizing film is in the depth direction of the optical anisotropic layer, and along with the distance The distance of the support interface is increased while increasing or decreasing. The angle is preferably reduced as the distance increases. Moreover, the change in angle may be an increase in continuity, a decrease in continuity, an intermittent increase, an intermittent decrease, a change including continuity increase and continuity decrease, or an intermittent change including increase and decrease. The intermittent change includes an area where the inclination angle does not change in the direction of the thickness direction. The angle is even if the area including the angle is not changed, but the whole is increased or decreased. Further, it is preferable that the angle is a change in continuity.

The average direction of the major axis of the discotic liquid crystalline molecules on the side of the support interface can be generally adjusted by selecting a material of the discotic liquid crystalline molecule or the alignment film or by selecting a rubbing treatment method. Further, in the direction of the long axis (disk surface) of the disk-side liquid crystalline molecules on the surface side (air side), generally, a discotic liquid crystalline molecule or an additive used together with a discotic liquid crystalline molecule is selected. The type can be adjusted. Examples of the additive used together with the discotic liquid crystalline molecule include a plasticizer, a surfactant, a polymerizable monomer, a polymer, and the like. The degree of change in the direction of the long axis alignment can also be adjusted by the selection of liquid crystal molecules and additives as described above.

[Other constituents of the optically isotropic layer]

A plasticizer, a surfactant, a polymerizable monomer, or the like may be used together with the liquid crystal molecule to improve the uniformity of the coating film, the film strength, the alignment of the liquid crystal molecules, and the like. It is preferable to have compatibility with a liquid crystalline molecule, and it is possible to impart a change in the tilt angle of the liquid crystal molecule or not to hinder the alignment.

The "polymerizable monomer" includes a radically polymerizable or cationically polymerizable compound. It is preferably a polyfunctional radical polymerizable monomer, and it is preferably one which is copolymerized with the above-mentioned liquid crystal compound containing a polymerizable group. For example, the paragraphs (0018) to (0020) in the specification of Japanese Laid-Open Patent Publication No. 2002-296423. The amount of the compound to be added is usually in the range of 1 to 50% by mass, and preferably in the range of 5 to 30% by mass based on the discotic liquid crystalline molecule.

The "surfactant" includes conventionally known compounds, but is particularly preferably a fluorine-based compound. Specifically, for example, the compounds disclosed in paragraphs (0028) to (0056) of the specification of Japanese Laid-Open Patent Publication No. 2001-330725.

The polymer which can be used together with the discotic liquid crystalline molecule is preferably one which can impart a change in the tilt angle to the discotic liquid crystalline molecule.

Examples of "polymer" include cellulose esters. Preferred examples of the cellulose ester include those disclosed in the paragraph (0178) of the specification of Japanese Laid-Open Patent Publication No. 2000-155216. The amount of the polymer to be added is preferably in the range of 0.1 to 10% by mass, and more preferably in the range of 0.1 to 8% by mass based on the liquid crystal molecule, so as not to impede the alignment of the liquid crystal molecules.

[Formation of optical anisotropic layer]

The optically anisotropic layer is formed by applying a coating liquid containing a liquid crystal molecule, and optionally an additive such as a polymerizable initiator or a polymerizable monomer, to the surface of the support, and preferably using an alignment film. .

A solvent which can be used to prepare a coating liquid, preferably an organic solvent. Examples of the "organic solvent" include: guanamines (for example, N,N-dimethylformamide), anthracene (for example, dimethylammonium), heterocyclic compounds (for example, pyridine), and hydrocarbons (for example, Benzene, hexane), alkyl halides (such as chloroform, dichloromethane, tetrachloroethane), esters (such as methyl acetate, butyl acetate), ketones (such as acetone, methyl ethyl ketone), Ethers (e.g., tetrahydrofuran, 1,2-dimethoxyethane). Among them, an alkyl halide and a ketone are preferable, and two or more organic solvents may be used in combination.

The application of the coating liquid can be carried out by a known method (for example, a bar coating method, an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, or a die coating method). The amount of coating can be appropriately determined according to the thickness of the optically anisotropic layer which is desired.

The thickness of the optically anisotropic layer is preferably from 0.1 to 20 μm, more preferably from 0.5 to 15 μm, and most preferably from 1 to 10 μm.

[Fixation of alignment state of liquid crystal molecules]

The aligned liquid crystalline molecules can be immobilized while maintaining their alignment. Immobilization is preferably carried out by a polymerization reaction. The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator, and a photopolymerization reaction using a photopolymerization initiator, and is preferably a photopolymerization reaction.

Examples of the "photopolymerization initiator" include: an α-carbonyl compound (disclosed in the specification of the U.S. Patent No. 2,367,661, the entire specification of which is incorporated herein by reference). - a hydrocarbon-substituted aromatic cryptic compound (disclosed in the specification of U.S. Patent No. 2,722,512), a polynuclear ruthenium compound (disclosed in the specification of U.S. Patent No. 3,046,127, the same as No. 2,951,758), triaryl imidazole dimerization a combination of a substance and a p-aminophenyl ketone (disclosed in the specification of U.S. Patent No. 3,549,367), an acridine and a laminating compound (disclosed in Japanese Laid-Open Patent Publication No. 60-105667, U.S. Patent No. 4,239,850 No.), and a oxadiazole compound (disclosed in U.S. Patent No. 4,212,970).

The amount of the photopolymerization initiator to be used is preferably in the range of 0.01 to 20% by mass, more preferably 0.5 to 5% by mass, based on the solid content of the coating liquid.

In order to irradiate light which polymerizes a liquid crystalline molecule, it is preferable to use ultraviolet rays.

The irradiation energy is preferably in the range of 20 mJ/cm ² to 50 J/cm ² , more preferably in the range of 20 to 5,000 mJ/cm ² , and still more preferably in the range of 100 to 800 mJ/cm ² . Further, in order to promote the photopolymerization reaction, light irradiation may be carried out under heating.

A protective layer may be disposed on the optically anisotropic layer.

[alignment film]

As described above, it is preferred to form an alignment film between the support and the optically anisotropic layer, and to align liquid crystal molecules on the surface of the alignment film. The alignment film has a function of an alignment direction of a specific liquid crystalline molecule. The liquid crystal molecules will become the desired alignment state on the alignment film, and after being fixed to the alignment state thereafter, the alignment state can be maintained even without the alignment film. Therefore, after the liquid crystal molecules are aligned on the surface of the alignment film to form an optically anisotropic layer, only the optical anisotropic layer is transferred onto the surface of the support or the surface of the polarizing film. Therefore, the alignment film is not an essential member of the optical compensation film constituent elements.

The alignment film may be, for example, a rubbing treatment of an organic compound (preferably a polymer), an oblique vapor deposition of an inorganic compound, a formation of a layer having a microgroove, or a Langmuir-Blodgett method (LB). A method of laminating a film of an organic compound (for example, ω-trisuccinic acid, dioctadecylmethylammonium chloride, methyl stearate). Further, an alignment film capable of generating an alignment function by imparting an electric field, imparting a magnetic field, or irradiating with light is also known.

The alignment film is preferably formed by a rubbing treatment of a polymer. The polymer used for the alignment film should, in principle, have a molecular structure capable of aligning liquid crystal molecules.

In the present invention, in addition to the function of aligning liquid crystal molecules, a side chain having a crosslinkable functional group (for example, a double bond) is bonded to a main chain, or a function of aligning liquid crystal molecules is preferable. The crosslinkable functional group is introduced into the side chain.

The polymer used for the alignment film, which may be used as the self-crosslinking polymer or the polymer crosslinked by the crosslinking agent, may be used in combination of several of them.

Examples of the polymer include a methacrylate-based copolymer, a styrene-based copolymer, a polyolefin, and a polycondensation disclosed in paragraph (0022) of the paragraph of the specification of Japanese Laid-Open Patent Publication No. 8-338913. Vinyl alcohol and modified polyvinyl alcohol, poly(N-methylol acrylamide), polyester, polyimide, vinyl acetate copolymer, carboxymethyl cellulose, polycarbonate, and the like. A decane coupling agent can be used as the polymer. Preferred are water-soluble polymers (for example, poly(N-methylol acrylamide), carboxymethyl cellulose, gelatin, polyvinyl alcohol, modified polyvinyl alcohol), more preferably gelatin, polyvinyl alcohol and modified Polyvinyl alcohol, and most preferably polyvinyl alcohol and modified polyvinyl alcohol. It is particularly preferable to use two or more kinds of polyvinyl alcohols or modified polyvinyl alcohols having different degrees of polymerization.

The degree of alkalinity of the polyvinyl alcohol is preferably from 70 to 100%, and more preferably from 80 to 100%. The degree of polymerization of the polyvinyl alcohol is preferably from 100 to 5,000.

A side chain having a function of aligning liquid crystal molecules generally has a hydrophobic group as a functional group. The specific type of the functional group is determined depending on the type of the liquid crystal molecule and the alignment state as needed.

For example, the modified base of the modified polyvinyl alcohol can be introduced by copolymerization modification, chain transfer modification or block polymerization modification. Examples of the "modified base" include a hydrophilic group (carboxylic acid group, sulfonic acid group, phosphonic acid group, amine group, ammonium group, decylamino group, thiol group, etc.), and carbon having 10 to 100 carbon atoms. a hydrogen compound group, a hydrocarbon group substituted with a fluorine atom, a thioether group, a polymerizable group (unsaturated polymerizable group, epoxy group, hydrazine) And the like, an alkoxyalkyl group (trialkoxy group, dialkoxy group, monoalkoxy group) and the like. Specific examples of the modified polyvinyl alcohol compound include, for example, paragraph number (0022) to (0145) in the specification of Japanese Patent Laid-Open Publication No. 2000-155216, and paragraph number (0018) in the specification of the same. ~(0022) disclosed by et al.

When a side chain having a crosslinkable functional group is bonded to a main chain of an alignment film polymer, or a side chain having a function of aligning liquid crystal molecules is introduced into a crosslinkable functional group, an alignment film can be used. The polymer is copolymerized with a polyfunctional monomer contained in the optically anisotropic layer. As a result, not only between the polyfunctional monomer and the polyfunctional monomer, between the alignment film polymer and the alignment film polymer, but also between the polyfunctional monomer and the alignment film polymer will be firmly bonded by covalent bonds. Bonding. Therefore, as long as the alignment film polymer is introduced into the crosslinkable functional group, the strength of the optical compensation film can be remarkably improved.

The crosslinkable functional group of the alignment film polymer preferably contains a polymerizable group in the same manner as the polyfunctional monomer. Specifically, for example, those disclosed in paragraphs (0080) to (0100) of the specification of Japanese Laid-Open Patent Publication No. 2000-155216.

The alignment film polymer may be crosslinked by using a crosslinking agent in addition to the above crosslinkable functional group. The "crosslinking agent" includes an aldehyde group, an N-methylol compound, a dioxane derivative, a compound which activates a carboxyl group, a reactive vinyl compound, an active halogen compound, an isoxazole, and a dialdehyde starch. It is also possible to use two or more kinds of crosslinking agents in combination. Specifically, for example, the compounds disclosed in paragraphs (0023) to (0024) of the specification of Japanese Laid-Open Patent Publication No. 2002-62426. An aldehyde having high reactivity is preferred, and glutaraldehyde is particularly preferred.

The amount of the crosslinking agent added is preferably from 0.1 to 20% by mass, and more preferably from 0.5 to 15% by mass, based on the polymer. The amount of the unreacted crosslinking agent remaining in the alignment film is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less. If it is adjusted so that the alignment film can be used in a liquid crystal display device for a long period of time or in a high-temperature, high-humidity atmosphere for a long period of time, sufficient durability can be obtained without causing fine ridges.

The alignment film is basically formed by applying the above-mentioned polymer of the alignment film forming material to a transparent support containing a crosslinking agent, followed by heat drying (crosslinking) and applying a rubbing treatment. The crosslinking reaction can be carried out at any time after application to a transparent support as described above. When a water-soluble polymer such as polyvinyl alcohol is used as the alignment film forming material, the coating liquid is preferably a mixed solvent of an organic solvent (for example, methanol) having a defoaming action and water. The ratio is preferably in terms of mass ratio, and is water: methanol is from 0:100 to 99:1, and more preferably from 0:100 to 91:9. Thereby, the generation of the foam can be suppressed, and the defects of the surface of the layer of the alignment film and the optical heterogeneous layer are remarkably reduced.

The coating method of the alignment film is preferably a spin coating method, a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method or a roll coating method, and particularly preferably a bar coating method. Bufa. Further, the film thickness after drying is preferably from 0.1 to 10 μm. The heat drying system can be carried out at 20 ° C to 110 ° C. In order to form sufficient crosslinking, it is preferably from 60 ° C to 100 ° C, and particularly preferably from 80 ° C to 100 ° C. The drying time can be carried out for 1 minute to 36 hours, but preferably 1 minute to 30 minutes. The pH is preferably set to the value of the most suitable crosslinking agent, and when glutaraldehyde is used, the pH is 4.5 to 5.5, and particularly preferably 5.

The alignment film is disposed on the transparent support or on the coating as described above. The alignment film is obtained by crosslinking the polymer layer as described above and subjecting the surface to rubbing treatment.

The above rubbing treatment can be used as a processing method widely used as a liquid crystal alignment processing step of an LCD. That is, a method of rubbing the surface of the alignment film in a certain direction using paper or cotton yarn, felt, rubber or nylon, polyester fiber or the like to obtain a alignment method. It is generally used to rub a cloth or the like which has a uniform length and a uniform thickness of fibers, and the like, to be rubbed about several times.

Next, the alignment film is allowed to function, and the liquid crystal molecules of the optically anisotropic layer provided on the alignment film are aligned. Thereafter, the alignment film polymer is allowed to react with the polyfunctional monomer contained in the optically anisotropic layer or the alignment film polymer is crosslinked using a crosslinking agent as needed.

The film thickness of the alignment film is preferably in the range of 0.1 to 10 μm.

[support]

An optically anisotropic layer formed of the above liquid crystalline molecules may be formed on the support as an optical compensation film. The support for constituting the optical compensation film may be different from the user when manufacturing the optically anisotropic layer. For example, an optically anisotropic layer obtained by aligning a liquid crystal compound and performing a fixed alignment state may be transferred onto a transparent support to produce an optical compensation film. When the support used for the alignment of the liquid crystal compound is different from the transparent support of the optical compensation film, the support which can be used for the alignment of the liquid crystal compound is not particularly limited.

The support of the present invention is preferably a glass or transparent polymer film, but is more preferably a polymer film. The support preferably has a light transmittance of 80% or more. Examples of polymers which can be used to form a polymer film include: cellulose esters (e.g., mono- and tri-tellurized cellulose), An olefinic polymer and polymethyl methacrylate (PMMA). Commercially available commercial grade polymers can also be used (lower The olefinic polymers are ARTON and ZEONEX: both are trade names)). In addition, even if it is a conventionally known polymer such as polycarbonate or polyfluorene which is susceptible to birefringence, as disclosed in the specification of World Patent No. 00/26705, as long as the molecule is modified to control the manifestation of birefringence, Can be used as a support.

Among these. Preferred is a cellulose ester, more preferably a lower fatty acid ester of cellulose. The "lower fatty acid" means a fatty acid having 6 or less carbon atoms, preferably a cellulose having 2 to 4 carbon atoms, and particularly preferably cellulose acetate. Mixed fatty acid esters such as cellulose acetate-propionate or cellulose acetate-butyrate can also be used.

The cellulose acetate has a viscosity average degree of polymerization (DP) of preferably 250 or more, and more preferably 290 or more. Further, the cellulose acetate is preferably narrowly distributed according to the molecular weight distribution of Mw/Mn (Mw is a mass average molecular weight and Mn is a number average molecular weight) by gel permeation chromatography. The specific value of Mw/Mn is preferably from 1.0 to 1.7, and more preferably from 1.0 to 1.65.

The polymer film is preferably a cellulose acetate having an acetylation degree of 55.0 to 62.5%. The degree of acetylation is preferably 57.0 to 62.0%. The term "acetylation degree" means the amount of bonded acetic acid per unit mass of cellulose. The degree of acetylation can be measured by the measurement and calculation of the degree of acetylation in ASTM: D-817-91 (test method of averaging acetate or the like).

In the cellulose acetate, the hydroxyl groups at the 2nd, 3rd, and 6th positions of the cellulose are not uniformly substituted, and thus the degree of substitution at the 6th position tends to be small. The polymer film used in the present invention is preferably such that the degree of substitution at the 6th order of the cellulose is the same or more than the 2nd order and the 3rd order. The ratio of the substitution degree of the sixth order of substitution with respect to the 2nd order, the 3rd order, and the 6th order is preferably 30 to 40%, more preferably 31 to 40%, and most preferably 32 to 40%. . The degree of substitution at the 6th order is preferably 0.88 or more.

The specific methods for synthesizing sulfhydryl groups and deuterated cellulose are disclosed in detail in the Japanese Invention Association Open Technical Bulletin (public technology number 2001-1745, March 15, 2001, Japan Invention Association). Page 9.

The preferred range of the retardation value of the polymer film differs depending on the liquid crystal cell of the optical compensation film used or the method of use thereof, but a preferred Re retardation value is 0 to 200 nm, and the Rth retardation value is preferably 10~400 nm.

When the liquid crystal display device uses two optically anisotropic layers (that is, when an optical compensation film is formed on both sides of a pair of polarizing plates), the Rth retardation value of the polymer film is preferably from 10 to 250 nm. The scope. When the liquid crystal display device uses one optically anisotropic layer (that is, when only one of the pair of polarizing films has an optical compensation film), the Rth retardation value of the substrate is preferably in the range of 150 to 400 nm. Further, the birefringence (?n:nx-ny) of the base film is preferably in the range of 0.00028 to 0.020. Further, the birefringence ((nx+ny)/2-nz) in the thickness direction of the cellulose acetate film is preferably in the range of 0.001 to 0.04.

Further, in order to maintain the degree of polarization, it is preferable to set the single transmittance of the support for constituting the optical compensation film to 90% or more, the absolute value of the retardation value to 20 nm or less, or the retardation value to 20 nm. In the above case, the angle of intersection between the slow axis of the support and the absorption axis (or transmission axis) of the polarizing plate is set to be less than 10°. Thereby, the polarization maintaining ratio will be 90% or more.

The measurement of the polarization maintaining ratio is carried out by a luminance meter (for example, BM-5 manufactured by Topucon Co., Ltd.) or a spectrophotometer. That is, the support is incident on the linearly polarized light, and the polarized light transmittance in the direction of the transmission axis parallel to the transmission axis of the linearly polarized light is measured, and the ratio is taken as the polarization maintaining ratio. Further, when there is a delay in the medium such as the support, the angle formed by the transmission axis (or the absorption axis) of the incident linearly polarized light and the slow axis of the medium may be set to be less than 10°.

In order to adjust the retardation of the polymer film, a general method is to apply a force other than stretching, but sometimes it is additionally added as a retardation increasing agent for adjusting the optical anisotropy. In order to adjust the retardation of the deuterated cellulose film, it is preferred to use an aromatic compound having at least two aromatic rings as a retardation increasing agent. The aromatic compound is preferably used in an amount of 0.01 to 20 parts by mass based on 100 parts by mass of the deuterated cellulose. Further, two or more kinds of aromatic compounds may be used in combination. The aromatic ring of the aromatic compound includes an aromatic heterocyclic ring in addition to the aromatic hydrocarbon ring, and is preferably, for example, European Patent No. 0911656A2, Japanese Patent Laid-Open No. 2000-111914, and the same. A compound or the like disclosed in Japanese Patent Publication No. 2000-275434.

Further, the hygroscopic expansion coefficient acetate film of the optical compensation film will be used according to the present invention is set to cellulose 30 × 10 ^{- 5} /% RH or less. Hygroscopic expansion coefficient is preferably set at 15 × 10 ^{- 5} /% RH or less, and more preferably 10 × 10 ^{- 5} /% RH or less. Further, the hygroscopic expansion coefficient is preferably smaller but is usually 1.0 × 10 ^{- 5} than the value of RH /%.

The "hygroscopic expansion coefficient" is the amount of change in the length of the sample when the relative humidity is changed at a certain temperature. By adjusting the coefficient of hygroscopic expansion, it is possible to prevent the frame-like transmittance from rising (light leakage due to strain) while maintaining the optical compensation function of the optical compensation film.

The method for measuring the coefficient of hygroscopic expansion is explained below. A sample having a width of 5 mm and a length of 20 mm was cut out from the obtained polymer film, and one end was fixed and suspended under an atmosphere of 25 ° C and 20 % RH (R ⁰ ). At the other end, a weight of 0.5 g was suspended, and the length (L ⁰ ) was measured after standing for 10 minutes. Then, the temperature was still at 25 ° C, and after adjusting the humidity to 80 % RH (R ¹ ), the length (L ¹ ) was measured. The coefficient of hygroscopic expansion is calculated by the following formula. In the measurement system, 10 samples were subjected to the same sample, and the average value thereof was used: hygroscopic expansion coefficient [/% RH] = ((L ^{1 -} L ⁰ ) / L ⁰ ) / (R ^{1 -} R ⁰ ).

In order to reduce the dimensional change of the polymer film due to moisture absorption, it is preferred to add a compound having a hydrophobic group or fine particles or the like. A compound having a hydrophobic group, particularly a material suitable for use in a plasticizer or an anti-deterioration agent having a hydrophobic group such as an aliphatic group or an aromatic group in a molecule. The amount of the compound to be added is preferably in the range of 0.01 to 10% by mass based on the solution (coating liquid) to be adjusted. Further, specifically, the free volume in the polymer film is reduced, so that the amount of residual solvent at the time of film formation by the solvent casting method as described later is small, and the free volume is small. It is preferred to carry out the drying under the condition that the amount of the residual solvent relative to the cellulose acetate film is 0.01 to 1.00% by mass.

The above additives added to the polymer film or additives which can be added for various purposes (for example, an ultraviolet ray inhibitor, a release agent, an antistatic agent, an anti-deterioration agent (for example, an antioxidant, a peroxide decomposer, a radical inhibitor, a metal) An inerting agent, an acid scavenger, an amine, an infrared absorber, etc., which may be a solid or an oil. Further, when the film is formed of a plurality of layers, the type or addition amount of the additives of the respective layers may be different. The details of such details are preferably those disclosed in detail on pages 16 to 22 of the above-mentioned technique No. 2001-1745. The amount of the additives to be used is not particularly limited as long as the amount of each of the materials is exhibited, but it is preferably used in an amount of 0.001 to 25% by mass in the entire composition of the polymer film. .

[Method for Producing Polymer Film]

The polymer film is preferably produced by a solvent casting method. In the solvent casting method, a film (coating liquid) in which a polymer material is dissolved in an organic solvent is used to produce a film.

The coating liquid is cast on a drum or belt, and then the solvent is evaporated to form a film. The coating liquid before casting is preferably adjusted in advance to have a solid content of 18 to 35%. The surface of the drum or belt is preferably pre-finished into a mirrored state.

The coating liquid is preferably cast on a drum or belt having a surface temperature of 10 ° C or less. After casting, it is preferred to carry out blowing for more than 2 seconds to dry. The obtained film may also be peeled off from a drum or a belt, and then dried by a high-temperature air which is successively changed in temperature from 100 ° C to 160 ° C to evaporate the residual solvent. The above method is disclosed in Japanese Patent Application Laid-Open No. 5-17844. According to this method, the time required from the self-flow to the stripping can be shortened. If this method is to be carried out, the coating liquid must be gelled at the surface temperature of the rotating drum or belt.

In the casting step, a deuterated cellulose solution may be cast in a single layer, or two or more deuterated cellulose solutions may be co-cast simultaneously and/or sequentially.

The method of co-casting a plurality of layers of a deuterated cellulose solution as described above includes, for example, a plurality of casting openings provided at intervals from the direction toward the support body to cause deuteration A method in which a solution of cellulose is separately cast by lamination (for example, the method disclosed in Japanese Laid-Open Patent Publication No. H11-198285); a method of casting a cellulose-deposited cellulose solution from two casting openings (Japanese Patent Laid-Open No. Hei 6-113933) Method disclosed in the bulletin; a method for simultaneously decomposing a high-viscosity deuterated cellulose solution with a low-viscosity deuterated cellulose solution containing a high-viscosity deuterated cellulose solution (Specially Opened No. 56) Method disclosed in Japanese Patent Publication No. 162617). The invention is not limited to such methods.

The manufacturing steps of the solvent casting method are described in detail in the above-mentioned public technical number No. 2001-1745, pages 22 to 30, and can be classified into dissolution, casting (including co-casting), metal support. Body, drying, peeling and stretching steps.

The thickness of the film of the present invention is preferably from 15 to 120 μm, and more preferably from 30 to 80 μm.

[surface treatment of polymer film]

The polymeric film is preferably applied to a surface treatment. The surface treatment includes corona discharge treatment, glow discharge treatment, flame treatment, acid treatment, alkali treatment, and ultraviolet irradiation treatment. The details of this are described in the above-mentioned public technical number No. 2001-1745, pages 30-32. Among these, it is particularly alkaline alkaline treatment, which is an extremely effective method for the surface treatment of deuterated cellulose film.

The alkaline alkalizing treatment may be any method in the method of immersing the alkalizing solution or applying the alkalizing solution, etc., but is preferably a coating method. The coating method includes a dip coating method, a curtain coating method, an extrusion coating method, a bar coating method, and an E type coating method. The alkaline alkalizing treatment liquid includes potassium hydroxide and sodium hydroxide, and the equivalent concentration of the hydroxide ions is preferably in the range of 0.1 to 3.0 N. Further, the alkali treatment liquid needs to contain a solvent (for example, isopropyl alcohol, n-butanol, methanol, ethanol, etc.) excellent in wettability to the film, a surfactant, a wetting agent (for example, a glycol, glycerin, etc.). Further, the wettability of the alkalizing solution to the transparent support, the stability over time of the alkalizing solution, and the like can be made excellent. Specifically, it is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2002-82226, and the World Patent No. 02/46809.

Instead of the surface treatment, it is possible to provide a base coat layer in addition to the surface treatment (disclosed in Japanese Laid-Open Patent Publication No. 7-333433), or as a coating layer containing only a hydrophobic group and a hydrophilic group. a first layer of a single layer of a resin layer such as gelatin, and a layer sufficiently adhered to the polymer film (hereinafter referred to as "the first layer of the undercoat layer") is provided as a second layer thereon. A so-called "multilayer method" of coating a hydrophilic resin layer (hereinafter referred to as "base layer second layer") of gelatin or the like which is sufficiently adhered to the alignment film (disclosed, for example, in Japanese Patent Laid-Open No. 11- Method of No. 248940).

[polarized film]

The polarizing film of the polarizing plate of the present invention is not particularly limited, and various conventional polarizing films can be used. In the present invention, the optically anisotropic layer as the optical compensation film (the first optical anisotropic layer on the most polarizing film side when a plurality of optically anisotropic layers are provided) can also be applied to the polarizing film. It is formed by directly forming a composition of a liquid crystal molecule, or forming an alignment film on the surface of the polarizing film, and then applying the above composition to the surface of the alignment film. As a result, it is not necessary to use a polymer film between the polarizing film and the optically anisotropic layer to obtain a polarizing plate having a small and thin stress (strain x sectional area × elastic modulus) accompanying the dimensional change of the polarizing film. When the polarizing plate according to the present invention is disposed in a large liquid crystal display device, an image of high display quality can be displayed without causing any light leakage or the like.

Further, when the optical compensation film is composed of the support and the optically anisotropic layer, the back surface of the support (the surface on the side where the optically anisotropic layer is not provided) can be adhered to the surface of the polarizing film.

The polarizing film is preferably a coating type polarizing film represented by Optiva Inc., or a polarizing film composed of a binder, iodine or a dichroic dye.

The iodine and the dichroic pigment in the polarizing film exhibit alignment performance by performing alignment in the binder. The iodine and the dichroic dye are preferably aligned along the binder molecules or are oriented in a single direction by self-organization of a dichroic dye such as a liquid crystal.

Commercially available commercial grade polarizing films are usually produced by immersing an extended polymer in a bath in a solution of iodine or a dichroic dye to impregnate iodine or a dichroic dye into a binder.

A commercially available commercial grade polarizing film having an iodine or dichroic dyeing system at a distance of about 4 micrometers from the surface of the polymer (total of about 8 micrometers on both sides), in order to obtain sufficient polarizing properties, at least 10 micron thickness. The degree of soaking can be controlled by the concentration of the solution of iodine or a dichroic dye, the temperature of the bath, and the immersion time.

As described above, the lower limit of the thickness of the binder is preferably 10 μm. The upper limit of the thickness is preferably as thin as possible from the viewpoint of light leakage of the liquid crystal display device. It is preferably a commercially available commercial grade polarizing plate (about 30 μm) or less, more preferably 25 μm or less, and still more preferably 20 μm or less. When it is 20 micrometers or less, light leakage is not observed in a 17-inch liquid crystal display device.

The bonding agent of the polarizing film can also be crosslinked.

For the crosslinked binder, a self-crosslinking polymer can be used. A polarizing film can be formed by reacting a polymer having a functional group or a binder obtained by introducing a polymer into a functional group by reacting light, heat or pH between the binders.

Further, the crosslinked structure can be introduced into the polymer by a crosslinking agent. Crosslinking is usually carried out by applying a coating liquid containing a polymer or a mixture of a polymer and a crosslinking agent to a transparent support, followed by heating. Since the durability can be ensured at the stage of the final product, the treatment of applying the crosslinking can be carried out at any stage until the final polarizing plate is obtained.

As the binder of the polarizing film, either a self-crosslinking polymer or a polymer which can be crosslinked by a crosslinking agent can be used. Examples of the polymer include the same as those disclosed in the above-mentioned alignment film section.

Most preferred are polyvinyl alcohol and modified polyvinyl alcohol. The modified polyvinyl alcohol is disclosed in Japanese Laid-Open Patent Publication No. 8-338913, the same as the Japanese Patent Publication No. 9-152509, and the same. Two or more kinds of polyvinyl alcohol and modified polyvinyl alcohol may be used in combination.

The amount of the crosslinking agent added by the binder is preferably from 0.1 to 20% by mass based on the binder. Polarized light The alignment of the parts and the heat and humidity resistance of the polarizing film will tend to be excellent.

After the end of the crosslinking reaction, the alignment film contains some unreacted crosslinking agent. However, the amount of the crosslinking agent remaining is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less in the alignment film. Therefore, even if the polarizing film is incorporated in a liquid crystal display device, it may not cause a decrease in the degree of polarization after being used for a long period of time or in an atmosphere of high temperature and high humidity for a long period of time.

The cross-linking agent is disclosed in the specification of U.S. Reissue Patent No. 23297. In addition, a boron compound (for example, boric acid, borax) can also be used as the crosslinking agent.

As the dichroic dye, an azo dye, a stilbene dye, a dihydropyrazolone dye, a triphenylmethane dye, a quinoline dye, a cacao dye, a thiophene dye or a guanidine system can be used. pigment. The dichroic dye is preferably water soluble. The dichroic dye preferably has a hydrophilic substituent (for example, a sulfo group, an amine group, or a hydroxyl group).

Examples of the dichroic dye include, for example, the compounds disclosed in Japanese Open Art Association, Public Technology No. 2001-1745, page 58 (issued on March 15, 2001).

The polarizing film and the optically anisotropic layer, or the polarizing film and the alignment film may be disposed by an adhesive. As the adhesive, a polyvinyl alcohol-based resin (including a modified polyvinyl alcohol by an ethylene sulfonate group, a sulfonic acid group, a carboxylic acid group, or an alkylene oxide) or an aqueous solution of a boron compound can be used. A polyvinyl alcohol-based resin is preferred. The thickness of the adhesive layer is preferably in the range of 0.01 to 10 μm after drying, and particularly preferably in the range of 0.05 to 5 μm.

Further, in order to further increase the contrast ratio of the liquid crystal display device, the transmittance of the polarizing plate is preferably higher, and the degree of polarization is preferably higher. The transmittance of the polarizing plate is preferably in the range of 30 to 50%, more preferably 35 to 50%, and most preferably in the range of 40 to 50% at a wavelength of 550 nm. The degree of polarization is preferably in the range of 90 to 100%, more preferably 95 to 100%, and most preferably in the range of 99 to 100%, at a wavelength of 550 nm. Thereby, a high contrast ratio can be obtained even if the support or the substrate has a polarization canceling effect.

The transmittance is the ratio of the incident light brightness (or light quantity, light beam) to the brightness of the emitted light. The degree of polarization is assumed to be the transmittance of the two polarizing plates when the absorption axes are parallel to each other, and the parallel transmittance is T∥, and the transmittance is vertical. When T⊥, it can be calculated by P=(T∥-T⊥)/(T∥+T⊥).

[Manufacture of polarizing plate]

From the viewpoint of yield, the polarizing film is preferably extended by an elongation method (extension method) or friction (friction method) by tilting the binder in the longitudinal direction (MD direction) of the polarizing film by 10 to 80 degrees, and iodine, The dye is dyed. The inclination angle is preferably extended so as to be aligned with an angle formed by the transmission axis of the two polarizing plates which are attached to both sides of the liquid crystal cell constituting the LCD and the longitudinal or lateral direction of the liquid crystal cell. Usually the angle of inclination is 45°. However, recently, devices other than 45° have been developed in transmissive, reflective, and semi-transmissive LCDs, so that the extending direction is preferably arbitrarily adjusted in accordance with the design of the LCD.

When the stretching method is carried out, the stretching ratio is preferably 2.5 to 30.0 times, and more preferably 3.0 to 10.0 times. The extension can be a dry extension implemented in air. It can also be wet-extruded in a state of being immersed in water. The stretching ratio of the dry stretching is preferably 2.5 to 5.0 times, and the stretching ratio of the wet stretching is preferably 3.0 to 10.0 times. The extension step can be carried out in several steps, including oblique extension. As long as it is divided into several times, the extension can be uniformly performed even if it is extended by a high magnification. It is also possible to apply several lateral or longitudinal extensions (to prevent the extent of shrinkage in the width direction) before the oblique extension.

The extension may be carried out by a different stretcher stretching step in the left and right directions when extending biaxially. The above biaxial stretching is the same as the stretching method which is usually employed in film formation. In the case of biaxial stretching, since the system is extended by different speeds from left to right, the thickness of the adhesive film before stretching must be such that the left and right sides are different from each other. At the time of casting film formation, the flow rate of the binder solution can be caused to be left and right by imparting a tapered portion to the mold.

A film which is obliquely extended by 10 to 80 degrees in the MD direction of the polarizing film can be obtained by the method described above.

In the rubbing method, a rubbing treatment method widely used as a liquid crystal alignment processing step of an LCD can be applied. That is, the alignment can be obtained by rubbing the surface of the film in a certain direction using paper or cotton yarn, felt, rubber or nylon or polyester fiber. Generally, a cloth having a uniform length and a uniform thickness of fibers is used to apply the friction about several times.

It is preferably carried out using a friction roller having a roundness, a cylinder degree, and a swing (eccentricity) of the roller itself of 30 μm or less. The overlap angle of the film of the rubbing roller is preferably from 0.1 to 90°. However, as disclosed in Japanese Laid-Open Patent Publication No. 8-160430, it is also possible to obtain a stable rubbing treatment by winding 360° or more.

When a friction treatment is applied to a film having a long length, it is preferred to transport the film at a speed of 1 to 100 m/min under a certain tension using a conveying device. The rubbing roller is preferably arranged such that the direction of the film can be rotated in the horizontal direction to facilitate the setting of the rubbing angle. It is preferred to select an appropriate rubbing angle in the range of 0 to 60°. When used in a liquid crystal display device, it is preferably 40 to 50°, and particularly preferably 45°.

It is preferable to dispose a polymer film on the surface opposite to the optically anisotropic layer of the polarizing film (the arrangement of the optical anisotropic layer/polarizing film/polymer film should be adopted). A polymer film disposed on the surface opposite to the optically anisotropic layer of the polarizing film is used as a polarizing film. It is preferred to provide an antireflection film having antifouling property and scratch resistance on the outermost surface thereof.

[Liquid Crystal Display Device]

One of the present invention is to arrange a polarizing plate in a liquid crystal display device for holding liquid crystal cells. A liquid crystal display device having the polarizing plate of the present invention will be described below.

Fig. 1 is a schematic view showing an embodiment of a liquid crystal display device of the present invention. In Fig. 1, the liquid crystal display device has liquid crystal cells 9 to 13, and one pair of polarizing plates 1 to 7 and 14 to 21 disposed on both sides of the liquid crystal cell. The upper polarizing plate has a polarizing film 3, a pair of transparent protective films 1 and 5 for clamping, and an optical anisotropic layer 7 having optical compensation energy; the lower polarizing plate has a polarizing film 18 for One of the pair of transparent protective films 16 and 21 and the optically opposite optical optically directional layer 14 are disposed, and each is disposed at a position opposite to each other with the liquid crystal cell as a center.

The upper polarizing plate lower protective film 5 serves as a support for the upper optically anisotropic layer 7, that is, the upper polarizing plate is incorporated in a liquid crystal display device by a structure in which the members 1 to 7 are laminated. On the other hand, the lower polarizing plate upper protective film 16 serves as a support for the lower optically anisotropic layer 14, that is, the lower polarizing plate is assembled in the liquid crystal by laminating the members 14 to 20 into a single body. In the display device. In the liquid crystal display device of Fig. 1, the laminated body of the optically anisotropic layer 7 on the upper side of the transparent support 5 and the laminated system of the optical anisotropic layer 14 provided on the lower side of the transparent support 16 are provided. Used as an optical compensation film.

Further, in the present invention, a laminate of a polarizing film and an optically anisotropic layer is used for at least one side of the polarizing plate (for example, the upper polarizing plate is a laminated body of 1 to 7 including the optical anisotropic layer 7). It is not necessary to have the polarizing plates on both sides as the laminated body of the above structure as in Fig. 1. In addition, the liquid crystal display device of Fig. 1 shows an embodiment in which a polarizing plate of a layer of an optically anisotropic layer is used. However, the liquid crystal display device of the present invention is only required to have an optically isotropic layer with at least one layer of a polarizing plate. When a structure of one volume layer is used, it is not limited to the above structure.

In the liquid crystal display device of the present invention, since the transparent support of the optical compensation film can also be used as a protective film on one side of the polarizing film, a transparent protective film, a polarizing film, a transparent protective film (which is also used as a transparent support), and A type of polarizing plate in which the layers of the optically anisotropic layer are stacked. The polarizing plate not only has a polarizing function, but also contributes to widening the viewing angle and reducing display non-uniformity. Further, since the polarizing plate is provided with an optically anisotropic layer having optical compensation energy, optical compensation of the liquid crystal display device can be accurately achieved with a simple structure.

Further, it is preferable to laminate the transparent protective film, the polarizing film, the transparent support, and the optically anisotropic layer from the outer side of the device (the far side of the liquid crystal cell) in the liquid crystal display device.

Regarding the absorption axes 4 and 19 of the polarizing films 3 and 18, the transparent protective films 1, 5, 16, 20, and their retardation axes 2, 6, 17, 21, the optically anisotropic layers 7, 14 and their molecular long axes The average direction of the alignment directions of 8, 15 and the alignment directions 10 and 15 of the liquid crystal molecules 11 can be adjusted to an optimum range depending on the materials used in the respective members, the display mode, and the laminated structure of the members. In order to obtain high contrast, the absorption axes 4 and 19 of the polarizing plates 3 and 18 should be arranged to be substantially orthogonal to each other. However, the liquid crystal display device of the present invention is not limited to these structures.

The liquid crystal cells 9 to 13 are composed of an upper substrate 9 and a lower substrate 12, and a liquid crystal layer formed of the liquid crystal molecules 11 sandwiched therebetween. On the surface of the liquid crystal molecules 11 which are in contact with the substrates 9 and 13 (hereinafter also referred to as "inner surface"), an alignment film (not shown) is formed, and by rubbing treatment or the like applied on the alignment film, The alignment of the liquid crystal molecules 11 when no voltage state or low application state is applied is controlled. Further, on the inner surfaces of the substrates 9 and 12, a transparent electrode (not shown) capable of applying a voltage to the liquid crystal layer composed of the liquid crystal molecules 11 is formed.

[TN mode liquid crystal display device]

For example, in a TN mode liquid crystal display device, in a non-driving state in which a driving voltage is not applied to an electrode, liquid crystal molecules 11 in the liquid crystal cell are slightly aligned to the substrate surface, and the alignment direction thereof is twisted by 90° between the upper and lower substrates. . In the case of a transmissive display device, the backlight light can be linearly polarized by passing through the lower polarizing plate. The linear polarized light propagates along the twisted structure of the liquid crystal layer, and the polarizing surface is rotated by 90 degrees while still maintaining the polarized state, and the direct polarizing plate is still directly passed in the state, so that the display device has a "white display".

On the other hand, if the applied voltage is gradually increased, the liquid crystal molecules will eliminate the twist while gradually erecting toward the direction perpendicular to the substrate surface. In the TN mode liquid crystal display device in an ideal high voltage application state, the twist of the liquid crystal molecules is completely eliminated, and the alignment is substantially perpendicular to the substrate surface. At this time, since the linearly polarized light passing through the lower polarizing plate has no twisting structure in the liquid crystal layer, it will propagate without rotating the polarizing surface, and is incident at an angle orthogonal to the absorption axis of the upper polarizing plate, so that the light is received. Blocked and displayed as "black".

Therefore, in the TN mode, the polarized light is blocked or transmitted to achieve the function of the display device. Generally, the ratio of the white display brightness to the black display brightness is defined as the "contrast ratio" as a value representing the display quality. The higher the contrast ratio, the higher the quality of the display device can be made. Therefore, if the contrast is to be improved, it is important to maintain the liquid crystal display device in a polarized state.

The operation of the liquid crystal display device shown in Fig. 1 will be described below by taking the TN mode as an example. In the embodiment of the present invention, an example in which the nematic liquid crystal having positive dielectric anisotropy is used and the active driving is performed is used for the electric field effect type liquid crystal.

In the TN mode, liquid crystal is applied between the upper and lower substrates 9 and 12 with positive dielectric anisotropy, refractive index anisotropy Δn = 0.0854 (589 nm, 20 ° C), and Δ ε = +8.5. Friction alignment to produce liquid crystal cells. The alignment control of the liquid crystal layer can be controlled by the alignment film and the rubbing. The so-called "tilt angle" indicating the index of the alignment direction of the liquid crystal molecules is preferably about 3°. The rubbing direction is applied in a direction orthogonal to the upper and lower substrates, and the magnitude of the tilt angle can be controlled by the strength and the number of rubbing times. The alignment film is formed by coating a polyimide film and curing it. The twist angle of the liquid crystal layer depends on the angle of intersection of the rubbing directions of the upper and lower substrates and the chiral agent added to the liquid crystal material. For example, if the twist angle is to be approximately 90°, a pair of palms having a pitch of about 60 μm may be added. Further, the thickness d of the liquid crystal layer was set to 5 μm.

The liquid crystal material LC is not particularly limited as long as it is a nematic liquid crystal. The dielectric constant anisotropy Δ ε is such that the larger the value, the lower the driving voltage. The refractive index anisotropy Δn is such that the thickness of the liquid crystal layer (gap) is thicker, the sealing time of the liquid crystal is shortened, and the variability of the gap is reduced. Further, Δn is larger, that is, the lattice gap can be reduced to achieve a high-speed reaction (response).

In the liquid crystal display device of the TN mode, the absorption axis 4 of the upper polarizing plate and the absorption axis 19 of the lower polarizing plate are laminated so as to be substantially orthogonal, and the absorption axis 4 and the upper substrate of the upper polarizing plate of the liquid crystal cell can be laminated. The rubbing direction 10 of 9 is substantially parallel, so that the absorption axis 19 of the lower polarizing plate and the rubbing direction 13 of the lower substrate 12 are stacked substantially in parallel. A transparent electrode (not shown) is formed inside each of the alignment films of the upper substrate 9 and the lower substrate 12. However, in a non-driving state in which no driving voltage is applied to the electrodes, the liquid crystal molecules 11 in the liquid crystal cells are substantially opposite to the substrate surface. In parallel alignment, as a result, the light polarization state of the liquid crystal panel propagates along the twisted structure of the liquid crystal molecules, and the polarizing surface is rotated by 90° to be emitted. That is, the liquid crystal display device will realize white display in a non-driving state. On the other hand, in the driving state, the liquid crystal molecules are aligned in a direction at a certain angle to the substrate surface, so that the light passing through the lower polarizing plate is caused by the optical compensation layers 16, 14, 7, and 5, and the like. The retardation is removed so as to pass through the liquid crystal layer 11 while maintaining the polarization state, and the polarizing film 3 is blocked. In other words, an ideal black display can be obtained while the liquid crystal display device is in the driving state.

As described above, the display is performed by the transmission control of the polarized light in the liquid crystal display device. The image quality evaluation of the display device uses a contrast ratio of the ratio of white display brightness to black display brightness. The larger the contrast ratio coefficient value, the better, and a commercially available commercial-grade liquid crystal display device, for example, a liquid crystal TV (television) can obtain a value of 300 or more. If the contrast ratio is to be increased, it is important that the white display brightness is increased and the black display brightness is reduced. In order to increase the white display luminance in the above display device, it is preferable that the upper polarizing plate is emitted without causing the transmittance of the polarized light passing through the lower polarizing plate to be attenuated. Similarly, when displaying in black, it is important that the emitted light is completely blocked as much as possible on the upper polarizing plate. In the present invention, since an optical compensation film having a high polarization maintaining ratio and a polarizing plate having a degree of polarization of 99.5% or more are used, a high contrast image can be displayed. In order to obtain a higher contrast ratio, it is preferable to maintain a polarization state as much as possible when passing through other members such as a polarizing plate protective film, a substrate for holding a liquid crystal layer, or the like, that is, preferably each member The degree of polarization maintenance should also be increased.

As described above, in the display device, in addition to the polarizing plate, a member capable of reducing contrast is also used. When a member having a low polarization maintaining ratio is used, there is a possibility that a polarization component in the transmission axis direction of the upper polarizing plate and the transmission axis direction in the vertical direction is generated, causing light leakage to increase the black transmittance, so that the contrast ratio is lowered. The polarization maintaining ratio of the member is lowered by the decrease in the single transmittance of each member, or the haze (turbidity), the scattering degree, the birefringence, and the like. When the polarization maintaining ratio of each member is to be improved to satisfy the above range, it is preferable to reduce the size of the foreign matter in each member. For example, a color filter or a TFT is formed on the substrate for holding the liquid crystal layer to constitute a factor for lowering the polarization maintaining ratio. If the polarization maintaining ratio of the color filter is not to be impaired, it is preferable to suppress the flatness when the filter is applied within ±0.5 μm. It is also preferred to suppress the particle size in the filter binder to within 1 micron. In addition, if the polarization maintaining ratio of the TFT substrate is not lowered, it is important to increase the transmittance of the substrate, for example, to control the TFT wiring width composed of metal to be within an average of 3 μm, or the insulating film is made of epoxy or An organic insulating film made of an acrylic resin.

Further, in general, a liquid crystal display device currently has a transmission type in which a backlight is disposed on a substrate surface on a back surface side of a display surface, and a backlight is passed through a lower polarizing plate, a lower substrate, a liquid crystal layer, an upper substrate, and a top. The polarizing plate is then emitted from the display surface. In this way, high contrast can be obtained by increasing the polarization maintenance ratio of the member closer to the polarizing plate. Further, by increasing the polarization maintaining ratio of the light source side optical compensation film adjacent to the pair of substrates for holding the liquid crystal layer, high contrast can be obtained. Therefore, it is preferable that the polarization maintaining ratio of the back side optical compensation film (14 to 16 in Fig. 1) located closer to the backlight side is higher than that of the liquid crystal cell (9 and 12 in Fig. 1).

In addition, the liquid crystal display device of the present invention can realize high-contrast display, and particularly, the transmittance and brightness at the time of black display tend to be low. Therefore, as long as the hue a and b of the light transmitted by the polarizing plate are controlled to be less than ±4, the hue of the black display becomes more excellent in achromatic display. The hue a and b are preferably ±5 or less, and more preferably ±4 or less.

In the liquid crystal display device of the present invention, the contrast ratio T ∥ / T ⊥ is preferably about 3,000:1. In general, the display contrast is preferably from 2,000:1 to 100:1, more preferably from about 1,500:1 to 300:1.

[IPS mode liquid crystal display device]

The polarizing plate of the present invention can also be used in a liquid crystal display device of the IPS mode. The IPS mode liquid crystal display device using the polarizing plate of the present invention can realize high contrast image display as in the above-described TN mode liquid crystal display device.

Fig. 2 is a side cross-sectional view showing an embodiment of an IPS mode liquid crystal display device having a polarizing plate of the present invention. The liquid crystal cells of the IPS mode usually have many pixels due to the matrix-shaped electrodes, but in FIG. 2, only one of the pixels is shown. The liquid crystal display device shown in Fig. 2 has a pair of polarizing plates 30 and 42 of the present invention. Further, the pair of polarizing plates 30 and 42 have a protective film, a polarizing film, and an optical compensation film, but the detailed structure thereof is omitted in FIG.

The liquid crystal display device of Fig. 2 has a pair of polarizing plates 30 and 42 and liquid crystal cells of the IPS mode. The liquid crystal cell of the IPS mode has a pair of transparent substrates 32 and 40, and a liquid crystal layer including rod-like liquid crystal molecules 34 sandwiched between the pair of substrates. A linear electrode 38 is formed inside the transparent substrate 40, and an alignment control film (not shown) is formed thereon. The plurality of linear electrodes 38 are arranged apart from each other to constitute a pixel electrode and a counter electrode, and are configured to generate an electric field parallel to the substrate 40. The rod-like liquid crystalline molecules 34 sandwiched between the substrates 32 and 40 are aligned to have a certain angle with respect to the longitudinal direction of the linear electrodes 38 when an electric field is not applied (OFF display). However, in this case, the dielectric anisotropy of the liquid crystal is assumed to be positive. When an electric field 36 in the direction indicated by the arrow mark 36 is applied (ON display), the liquid crystalline molecules 34 will change their direction toward the direction of the electric field. Therefore, by arranging the polarizing plates 30 and 42 at a specific angle with the direction of the transmission axis, the light transmittance can be changed. Further, the angle formed by the surface electric field direction 36 of the substrate 40 is preferably 20 degrees or less, and more preferably 10 degrees or less, that is, substantially parallel. Hereinafter, those below 20 degrees are collectively referred to as "parallel electric fields". In addition, the electrode 38 is formed by dividing the upper and lower substrates, or the substrate is formed only on one side, and the effect remains unchanged.

Fig. 3 is a side cross-sectional view showing another embodiment of the IPS mode liquid crystal display device. This mode is a way to achieve higher speed response and higher transmittance. In addition, the same components as those shown in Fig. 2 are attached with the same The part number is omitted, and the detailed description is omitted. The electrode system is a two-layer structure of the linear electrode 38 and the lower electrode 46 which are separated from the insulating layer 44 (and disposed in different layers), unlike FIG. The lower electrode 46 may be an electrode that is not subjected to the pattern forming step, or an electrode such as a wire. The electrode 38 of the upper layer is preferably linear. However, any shape such as a mesh shape, a spiral shape, or a dot shape may be used as long as it can pass the electric field from the lower layer electrode 46, and the potential may be added to be neutral. Floating electrode. Further, the insulating layer 44 may be an inorganic material such as SiO or a nitride film, or an organic material such as an acrylic or epoxy resin.

In the IPS mode, the electrode structures (38, 38 and 46) and the insulating layer 44 constitute a factor which causes a decrease in the degree of polarization retention. For high contrast, it is preferred to polarize the electrodes and the insulating layer. The degree of maintenance is set to 90% or more, more preferably 95% or more, and still more preferably 99% or more. If the degree of polarization maintenance of the above range is to be obtained, an effective method is to take, for example, set the width and pitch of the linear electrode 38 to be 2 μm or more larger than the wavelength of visible light to suppress the diffraction effect; or to insulate The transmittance of the layer 44 is set to be 80% or more in the visible light wavelength region to suppress the attenuation of the polarized light transmittance.

The liquid crystal material LC of the IPS mode is a nematic liquid crystal in which the dielectric constant anisotropy Δ ε is positive. The thickness (gap) of the liquid crystal layer is preferably greater than 2.8 microns and less than 4.5 microns. When the retardation (Δn.d) is more than 0.25 μm and less than 0.32 μm, it is easier to obtain transmittance characteristics having almost no wavelength dependency in the visible light range. By combining a specific alignment film and the polarizing plate of the present invention, when the liquid crystalline molecules are rotated by 45 degrees from the rubbing direction toward the electric field, the maximum transmittance can be obtained. In addition, the thickness (gap) of the liquid crystal layer can be controlled by polymer beads. Of course, the gap can be obtained in the same manner by the glass beads or the fibers or the columnar spacer made of resin. Further, the liquid crystal material LC is not particularly limited as long as it is a nematic liquid crystal. The dielectric constant anisotropy Δ ε is larger, and the driving voltage can be reduced. The refractive index anisotropy Δn is smaller, and a thicker liquid crystal layer thickness (gap) can be formed and shortened. The sealing time of the liquid crystal is reduced, and the variability of the gap is reduced.

[Other mode liquid crystal display device]

The display mode of the liquid crystal display device used in the present invention is not particularly limited, but may be applied to the OCB mode and the ECB mode in addition to the TN mode and the IPS mode described above. In the present invention, the thickness d (micrometer) of the liquid crystal layer and the product of the refractive index anisotropy Δn Δn. The d system is set to 0.2 to 1.2 microns. △n. The optimum value of d is different depending on the display mode. The optimum value of Δnd of liquid crystal is 0.2~0.5 micron in TN mode, and 0.4~1.2 micron is optimal in OCB mode, and in ECB mode. 0.2 to 0.5 microns is the optimum value. Further, the twist angle of the liquid crystal layer in the TN mode is optimum at around 90 (from 85 to 95). In these ranges, since the brightness of the white display is high and the black display brightness is small, a bright and high-contrast display device can be obtained.

In addition, the optimum values are the values of the transmission mode. In the reflection mode, since the intra-cell optical path will be doubled, the most appropriate value of Δnd will be about 1/2 of the above value. In addition, the torsion angle is 30 ° ~ 70 ° is the optimum value.

The liquid crystal display device which can be used in the present invention can be effectively applied not only to the above display mode but also to the VA mode, the ECB mode, the STN mode, and the like.

The liquid crystal display device of the present invention is not limited to the structure as shown in Fig. 1, and may include other members. For example, a color filter may be disposed between the liquid crystal cell and the polarizing film. In addition, when used as a transmissive type, a cold cathode or a hot cathode fluorescent tube, or a light emitting diode, field emission can be disposed on the back surface. Piece, electroluminescence A backlight such as a light source. Further, the liquid crystal display device of the present invention may be of a reflective type. In this case, the polarizing plate may be disposed only on the observation side, and a reflective film may be provided on the back surface of the liquid crystal cell or the inner surface of the liquid crystal cell. Of course, it is also possible to provide front light using the above-mentioned light source on the liquid crystal cell observation side. Further, the liquid crystal display device of the present invention may be a semi-transmissive type in which a reflection portion and a transmission portion are provided in one pixel of the display device in order to coexist both in a mode of transmission and reflection.

The liquid crystal display device of the present invention includes an image direct view type, an image projection type or a light modulation type. The invention is particularly applicable to 3-terminal or 2-terminal semiconductors such as TFT or MIM The mode of the active matrix type liquid crystal display device. Of course, it is also applicable to a passive matrix type liquid crystal display device represented by the STN type, which is called "time division driving".

The color filter used in the liquid crystal display device of the present invention will be described below.

[Color Filter]

In one of the liquid crystal cells of the liquid crystal display device of the present invention, a color filter including each of red, green, and blue patterns can be formed. The color filter can be manufactured, for example, in the following manner. First, colored pixels of a red, green, blue color, etc., which are suitable for the purpose, are formed on the transparent substrate. A method of forming colored pixels such as red, green, or blue on a transparent substrate may be carried out by applying a coloring photosensitive resin liquid by the above-described dyeing method, printing method, or spin coating method, and then appropriately using a microphotography step. A colored photoresist method, a lamination method, and the like which are applied to the pattern forming step.

When a black photosensitive resin is used to form a black matrix, it is preferably carried out after forming the colored pixels. Since the black matrix is formed at the beginning, since the black photosensitive resin having a high optical density can only harden the surface of the resin, the unhardened resin will be subjected to the development process immediately after application, especially for coloring. The development process repeated by the pixel and being eluted (referred to as "side etching") may even cause the formed matrix to be peeled off.

On the other hand, when a black matrix is formed at the end, the surrounding of the black matrix is surrounded by colored pixels, and the developing liquid is not easily permeated from the cross section, and side etching is not easily caused, and black with high optical density can be formed. The great advantage of the matrix.

Further, when a coloring layer for forming a colored pixel is formed by a lamination method, when a black matrix is preferentially formed, a portion of the colored pixel to be formed is closed in a lattice shape in a black matrix, resulting in easy lamination. The problem of getting involved in bubbles exists.

When the light transmittance of the colored photosensitive resin in the photosensitive wavelength region is greater than 2%, it is preferable to add a light absorber or the like to the colored pixel in advance so as to control the transmittance to 2% or less. The light absorbing agent used at this time may be various conventional compounds. For example, a benzophenone derivative (Miller's ketone or the like), a merocyanine compound, a metal oxide, a benzotriazole compound, a coumarin compound, or the like. Among them, those having excellent light absorptivity and maintaining a light absorption performance of 25% or more after heat treatment at 200 ° C or higher are preferable, and specifically, they include zinc oxide, a benzotriazole compound, and a coumarin compound. . Among these, a coumarin-based compound is preferred from the viewpoint of heat resistance and light absorbability. Further, the above heat treatment at 200 ° C or higher is carried out for the purpose of further curing after forming each pixel.

Then, the black photosensitive resin layer is entirely provided on the transparent substrate by covering the pixel pattern, which may also be applied by a method of applying a black photosensitive resin liquid by a spin coater or a roll coater, or by coating on a dummy support in advance. A black photosensitive resin liquid is prepared to obtain an image forming material, and then the black photosensitive resin layer is transferred onto a pixel pattern.

Then, the black photosensitive resin layer is exposed from the side of the black photosensitive resin layer via the photomask, and the black photosensitive resin layer of the light shielding portion (black matrix) in which the colored pixels are not present is cured. The colored pixels are usually likely to be affected by the alignment error of the exposure machine or the thermal expansion of the substrate to cause some positional shifts, or the pixels themselves may become thicker or thinner, etc., and may not be configured to be spaced or sized according to the design size. . Especially in the case of large-sized substrates, this tendency will become strong. Therefore, if the exposure is performed in accordance with the mask of the design pixel interval, a portion where the black matrix overlaps with the pixel is generated, or conversely, a portion where a gap is formed between the pixel and the pixel. The overlapping portion will constitute a protrusion, and the portion where the gap is generated will cause light leakage, and thus it is not good.

If the red pattern has a polarization maintaining ratio of Pr, a green pattern of Pg, a blue pattern of Pb, and a pixel color filter having a degree of polarization retention of Pr/Pg ≦ 1.5 and Pb/Pg ≦ 1.5, Then, in the case of white display and black display, the display color of the liquid crystal display device becomes achromatic and excellent color reproducibility is obtained. In contrast, if Pr/Pg and Pb/Pg are greater than 1.5, the display will be colored blue or purple.

[Examples]

The invention will now be described more specifically by way of examples. However, the present invention can be appropriately changed without departing from the precise scope of the materials, reagents, mass and ratio, operation, and the like shown in the following examples. Therefore, the invention is not limited to the specific examples.

[Example 1]

A liquid crystal display device having the structure shown in Fig. 1 was produced. That is, the upper polarizing plates 1 to 5, the upper optical anisotropic layer 7, the liquid crystal cells (the upper substrate 9, the liquid crystal layer 11, the lower substrate 12), and the lower optical anisotropic layer are sequentially laminated from the observation direction (upper). 14. The lower polarizing plates 16 to 20, and the backlight of the cold cathode fluorescent lamp is disposed on the lower side of the lower polarizing plate.

The manufacturing method of each member used will be described below.

<Manufacture of TN mode liquid crystal cells>

The liquid crystal cell system has a lattice gap (d) of 4 μm, and a liquid crystal material having a positive dielectric constant different direction layer is sealed between the dropping substrate, and the Δnd of the liquid crystal layer 11 is 410 nm (Δn liquid crystal) The refractive index of the material is different in direction. Further, the twist angle of the liquid crystal cell is set to 90° in the counterclockwise direction by the angle of intersection of the rubbing direction 10 of the upper substrate 7 with the rubbing direction 14 of the lower substrate 12 and the addition of the palmming agent. Further, when the upper and lower polarizing plates are bonded together, the upper and lower substrates of the liquid crystal cell are rubbed in a direction parallel to the slow phase axes (casting direction and parallel direction) 6, 17 of the supporting members 5 and 16. These angles are shown in Figure 4.

<Liquid Crystal Cell Substrate>

The transparent electrode was formed into a film of ITO (indium tin oxide) on a transparent glass "7059" manufactured by Corning Co., Ltd. by a vapor deposition method. The glass was used together with a pair of substrates, and the transmittance of both substrates was 99.9%, and the polarization maintaining ratio was also 99%.

<Manufacture of cellulose acetate film>

The composition shown below was fed into a mixing tank, stirred while heating, and the components were dissolved to prepare a cellulose acetate solution.

<Composition of Cellulose Acetate Solution>

4 parts by mass of cellulose acetate (cotton) having a degree of acetylation of 60.9%, 16 parts by mass of the retardation increasing agent shown below, and 0.5 part by mass of cerium oxide microparticles (particle size of 20 nm, Mo) Moh's hardness is about 7), 87 parts by mass of methylene chloride, and 13 parts by mass of methanol are fed to another mixing tank, and stirred while heating to prepare a delayed riser solution.

36 parts by mass of the delayed riser solution was mixed with 464 parts by mass of the cellulose acetate solution, and the mixture was thoroughly stirred to prepare a coating liquid. The amount of the retardation increasing agent added was 5.0 parts by mass based on 100 parts by mass of the cellulose acetate.

The resulting polymer substrate (PK-1) had a width of 1,340 mm and a thickness of 92 microns. The retardation value (Re) at a wavelength of 590 nm was measured to be 43 nm using an automatic birefringence meter (KOBRA 21ADH, manufactured by Oji Scientific Co., Ltd.). Further, the retardation value (Rth) of the wavelength of 590 nm was measured and found to be 175 nm.

Further, the transmittance of the obtained polymer was 99%, and the polarization maintaining ratio was 98%.

Further, the hygroscopic expansion coefficient measurement results obtained polymer substrate (PK-1) was of ^{12.0 × 10 - 5 /% RH} .

(Manufacture of base coating)

A coating liquid having the composition shown below was applied to the cellulose acetate film support of 28 ml/m ² and dried to coat a 0.1 μm gelatin layer (coating layer).

On the PK-1, an alignment film coating liquid having the composition shown below was applied at a coating amount of 28 ml/m ² using a wire bar coater of #16. It was dried under a warm air of 60 ° C for 60 seconds, and further dried under a warm air of 90 ° C for 150 seconds to form a film. Further, a rubbing treatment was performed in a direction of 45° with respect to the retardation axis of the polymer substrate (PK-1) (measured at a wavelength of 632.8 nm) to form an alignment film.

<Composition of alignment film coating liquid>

<Formation of optical anisotropic layer>

On the alignment film, 46.65 kg of the following liquid crystalline compound (B) and 4.06 kg of ethylene oxide-modified trimethylolpropane triacrylate (V#360, manufactured by Osaka Organic Chemical Co., Ltd.) ), 0.90 kg of cellulose acetate-butyrate (CAB551-0.2, manufactured by Eastman Chemical Co., Ltd.), 0.23 kg of cellulose acetate-butyrate (CAB531-1, manufactured by Eastman Chemical Co., Ltd.) 1.35 kg of a photopolymerization initiator (Irgacure-907, manufactured by Ciba-Geigy Co., Ltd.), a 0.45 kg sensitizer (Kayacure-DETX, manufactured by Nippon Kayaku Co., Ltd.) dissolved in a solution of 102 kg of methyl ethyl ketone The coating liquid was prepared and coated with a #3.4 wire bar coater. This was heated in a constant temperature zone of 130 ° C for 2 minutes to align the discotic liquid crystalline compound. Then, a 120 W/cm high pressure mercury lamp was used in an atmosphere of 60 ° C, and UV (ultraviolet rays) was irradiated for 1 minute to polymerize the discotic liquid crystalline compound, and then allowed to cool to room temperature. The optically anisotropic layer was formed in such a manner as to obtain an optical compensation film (KH-2).

Disc liquid crystalline compound (B)

The optical anisotropic layer Re retardation value measured at a wavelength of 546 nm was 40 nm.

The angle (inclination angle) formed by the disc surface and the transparent protective film in the disc-shaped liquid crystal compound in the obtained optically anisotropic layer is increased from the transparent protective film toward the air interface, and is 11 °~66° is mixed and aligned. The tilt angle is measured by using an automatic birefringence meter KOBRA 21ADH (manufactured by Oji Scientific Instruments Co., Ltd.) and changing the observation angle to determine the retardation, and is assumed to be a refractive index 楕 round body model, and in the design of the dish-shaped negative birefringence compensation film. The method disclosed in the concept ("Design Concepts of the Discotic Negative Birefringence Compensation Films")" SID 98 DIGEST is calculated.

The polarizing plates were arranged in crossed Nicols, and then the variability of the obtained optical compensation film was observed, and as a result, the variability was not detected from the front side and even in the direction inclined from the normal line to 60°. Further, under the observation of a polarizing microscope, an alignment defect or a foreign matter having a diameter of 1 μm or more was not observed, and the polarization maintaining ratio was 95%, which was an excellent value.

<Manufacture of polarizing film>

The iodine was adsorbed on the stretched polyvinyl alcohol film to obtain a polarizing film, and then the obtained optical compensation film was attached to the one side of the polarizing film with a support surface by using a polyvinyl alcohol-based adhesive. Further, a cellulose triacetate film (TD-80U, manufactured by Fuji Photo Film Co., Ltd.) having a thickness of 80 μm was applied with a saponification treatment, and a polyvinyl alcohol-based adhesive was attached to the opposite side of the polarizing film. Shown by liquid crystal in Figure 4 Accompanied by the angle of film adhesion observed. The absorption axis 4 of the upper polarizing film 3 and the slow axis 6 of the support 5 (parallel to the casting direction) are arranged to be slightly parallel, and the absorption axis 19 of the lower polarizing film 18 is delayed from the support 16 The shafts 17 (parallel to the casting direction) are arranged to be slightly parallel.

Thus, one of the polarizing plates produced has a degree of polarization of 99.95%. Further, the polarizing plates have -2 and 3 for the hue a and b of the normally incident light, respectively.

<Optical Measurement of Liquid Crystal Display Device Produced>

A rectangular wave voltage of 60 Hz was applied to the liquid crystal display device manufactured by this method, and a white display mode of white display of 1.5 V and a black display of black of 5 V were set. The contrast ratio of the transmittance ratio (white display/black display) was measured using a measuring machine (EZ-Contrast 160D, manufactured by ELDIM Co., Ltd.). As a result, the front contrast ratio was 3,000:1, the range in which the transmittance in the lower direction was not reversed, and the contrast ratio was 10 or more, and the range was 80° or more in the upper, lower, left, and right directions.

[Comparative Example 1]

In the first embodiment, a TFT substrate and a color filter substrate obtained by disassembling a commercially available commercial-grade liquid crystal panel were attached to the outside of the transparent glass substrate with ITO attached thereto with an adhesive, and the contrast ratio thereof was measured. The other configuration is the same as that of the first embodiment.

The stacking order is an upper polarizing plate from the display surface, a glass substrate with a color filter, a transparent glass with a transparent electrode, a liquid crystal layer, a transparent glass with a transparent electrode, a glass substrate with a TFT, and a lower surface. Side polarizer and backlight. Commercially available commercial-grade liquid crystal panels use a Type 15 PRIUS television set manufactured by Hitachi. Disassemble the same LCD TV and cut out the glass substrate with the TFT and the glass substrate with the color filter attached. The glass substrate with the TFT attached therein had a transmittance of 92% and a polarization retention of 87%. The glass substrate with the color filter had a transmittance of 31% and a polarization retention of 82%. In addition, the polarizing degree of the upper and lower polarizing plates was 99.90%.

The contrast ratio was measured in the same manner as in Example 1. As a result, the front contrast ratio was 300:1.

[Example 2]

In the first embodiment, a Transer color filter manufactured by Fuji Photo Film Co., Ltd. is formed on the transparent glass substrate by the method disclosed in Japanese Laid-Open Patent Publication No. 10-221518, and the same substrate is fixedly laminated with an adhesive. Between the transparent electrode substrate of ITO and the upper polarizing plate. At this time, the surface of the Transer color filter has a convexity and convexity of 0.2 μm, and the particle diameter of the granular material in the binder is an average of 0.1 μm or less for red and blue, and 0.15 μm or less for green. The transmittance was 35% and the degree of polarization retention was 90%. The other structure is the same as that of the first embodiment.

Set the black display voltage to a 5 V rectangular wave voltage of 60 Hz and the white display voltage to 1.5 V to measure the contrast ratio as a result of 1,500:1.

Further, the transmittance of one pixel was subjected to microscopic photometry using a luminance meter SR-3 manufactured by TOPCON Co., Ltd. to measure the degree of polarization retention of each pixel as Pr/Pg = 1.2 and Pb/Pg ≦ 1.3. The hue of transmitted light to normal incident light is a = 2.1, b = 2.8.

[Example 3] <Manufacture of IPS mode liquid crystal cells>

In Fig. 2, a linear electrode is formed on the lower substrate 40 by vapor deposition. The width of the electrode is 16 μm, and the material is not particularly limited as long as the resistance is low, and may be chromium or copper. By forming a metal electrode having a low resistance, the load on the driving LSI (large integrated circuit) can be reduced to reduce the power consumption. Of course, it can also be a linear electrode of ITO. The size of one pixel is 80 x 240 microns, and the spacing between the signal electrode and the common electrode is set to 48 microns. The upper substrate is an electrodeless transparent glass having a thickness of 0.7 μm.

The liquid crystal material LC is a nematic liquid crystal in which the dielectric constant anisotropy Δ ε is positive, the value is 13.2, and the refractive index anisotropy Δn is 0.085 (589 nm, 20 degrees). (MLC9100-100) manufactured by Merk. The thickness (gap) of the liquid crystal layer was set to 3.5 μm. The same as in the first embodiment is used for the polarizing plate.

The transmittance of the liquid crystal display device was 30%, and the degree of polarization retention was 85%. At this time, the black display voltage was set to 60 V for a rectangular wave voltage of 2 V, and the white display voltage was 6 V to measure the contrast ratio as a result of 1,200:1. In the IPS mode liquid crystal display device, the applied electric field direction 36 is as shown in FIG. 2, and is slightly parallel to the substrate surface 40. Of course, an electric field in the vicinity of the linear electrode 38 which is the same as the TN mode in the vertical direction of the substrate surface is generated, but most of the devices are parallel electric field components.

[Example 4]

In the third embodiment, the lower substrate 14 is formed into a total electrode of ITO by vapor deposition, and then the tantalum oxide film (SiO ₂ ) is formed into a thickness of 0.5 μm or less by vapor deposition so that the degree of polarization maintaining ratio can be 99% or more. . Then, a linear electrode was formed with ITO at a width of 10 μm and a distance between electrodes of 5 μm. The other structure is the same as that of the third embodiment.

The transmittance of the liquid crystal display device was 30%, and the degree of polarization retention was 85%. The other configuration is the same as that of the first embodiment. The rectangular display voltage at which the black display voltage is set to 60 Hz is 2 V, and the white display voltage is 6 V to measure the contrast ratio. As a result, the vertical component of the wire electrode is ITO and the electric field direction 36 in Fig. 3 is increased. Therefore, the white display transmittance is increased to 1,500:1.

1. . . Upper polarizer outer protective film

2. . . Upper side polarizer outer protective film slow phase axis

3. . . Upper polarizing film

4. . . Upper polarizing plate polarizing film absorption axis

5. . . Upper polarizing plate liquid crystal cell side protective film (support)

6. . . Upper polarizer liquid crystal cell side protective film (support) slow phase axis

7. . . Upper optical anisotropic layer

8. . . Molecular long axis alignment average direction of the upper optical anisotropic layer

9. . . Liquid crystal cell upper substrate

10. . . The rubbing direction of the liquid crystal alignment of the upper substrate

11. . . Liquid crystal molecule

12. . . Liquid crystal cell side substrate

13. . . Friction direction of liquid crystal alignment of lower substrate

14. . . Lower optical anisotropic layer

15. . . Molecular long axis alignment average direction of the lower side optical compensation layer

16. . . Lower polarizing plate liquid crystal cell side protective film (support)

17. . . Lower side polarizing plate liquid crystal cell side protective film (support) slow phase axis

18. . . Lower polarizer film

19. . . Absorption axis of polarizing film of lower polarizing plate

20. . . Lower polarizer outer protective film

twenty one. . . Lateral polarizer outer protective film slow phase axis

30, 42. . . Polarizer

32, 40. . . Transparent substrate

34. . . Rod-shaped liquid crystalline molecule

36. . . Electric field direction

38. . . Linear electrode

44. . . Insulation

46. . . Lower electrode

Fig. 1 is a view showing an example of a liquid crystal display device of the present invention.

Fig. 2 is a side sectional view showing another example of the liquid crystal display device of the present invention.

Fig. 3 is a side sectional view showing another example mode of the liquid crystal display device of the present invention.

Fig. 4 is a schematic view showing the relationship between the optical axes of the liquid crystal display device produced in the examples.

Claims (10)

A liquid crystal display device comprising: a liquid crystal layer having electrodes disposed on at least one side thereof and a pair of substrates disposed opposite to each other, and a pair of liquid crystal layers disposed to sandwich the liquid crystal layer; and At least one side of the pair of polarizing plates has a polarizing film, and an optical compensation film is disposed on a surface of the polarizing film on a side closer to the liquid crystal layer, and the polarizing degree of the pair of polarizing plates is 99.5% or more. The polarization maintaining ratio of the substrate is 90% or more, and the polarization compensation rate of the optical compensation film is 90% or more; a color filter is formed on at least one of the pair of substrates, and the surface of the color filter is flat. The particle size is 0.5 μm or less, and the particle size of the binder particles contained in the color filter is 1 μm or less. The liquid crystal display device of claim 1, wherein the pair of polarizing plates have a polarizing film on both sides thereof and an optical compensation film on a surface of the polarizing film on a side closer to the liquid crystal layer. The liquid crystal display device of claim 1 or 2, wherein the optical compensation film has a degree of polarization maintaining ratio of not less than a degree of polarization maintenance of the pair of substrates. The liquid crystal display device of claim 1 or 2, wherein the absorption axis of the pair of polarizing plates is substantially orthogonal. The liquid crystal display device of claim 1 or 2, wherein the color filter comprises each of red, green and blue patterns, and if the red pattern, When the polarization maintenance ratios of the green pattern and the blue pattern are Pr, Pg, and Pb, respectively, Pr/Pg ≦ 1.5 and Pb/Pg ≦ 1.5. The liquid crystal display device of claim 1 or 2, wherein the electrode is composed of a pixel electrode and a counter electrode, and the pixel electrode and the counter electrode are disposed with the pixel electrode and the opposite electrode The substrate produces a slightly parallel electric field. The liquid crystal display device of claim 6, wherein the electrode is disposed on a different layer, and at least one of the electrodes is composed of a transparent electrode. The liquid crystal display device of claim 7, wherein a conductive layer to which no voltage is applied is disposed in the substrate on which the pixel electrode and the counter electrode are disposed. The liquid crystal display device of claim 6, wherein the counter electrode is not subjected to an electrode of a pattern forming step. The liquid crystal display device of claim 6, wherein the pixel electrode is a plurality of linear electrodes, and the pixel electrode has a width of 2 μm or more.