JP2001242461A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a twisted nematic liquid crystal display device superior in display characteristics, such as a contrast characteristic, a visual angle characteristic and the like and in mechanical characteristics. SOLUTION: The twisted nematic liquid crystal display device is provided with a liquid crystal cell for device consisting of a pair of transparent substrate provided with electrodes and a nematic liquid crystal and two polarizing plate disposed at the upper and lower sides of the liquid crystal cell, an optically anisotropic element consisting of an optical anisotropic film (A) which is obtained by fixing the hybrid alignment formed in a liquid crystal state of a liquid crystal substance having an optically negative uniaxial property and an optical diffusion adhesive layer (B), having 50-90% for the ratio of diffusion transmittance/total light bean transmittance is provided between the liquid crystal cell and the upper and/or lower polarizing plate, to improve the display characterstics and the mechanical characteristics of the liquid crystal display device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a twisted nematic liquid crystal display device having significantly improved display characteristics such as contrast characteristics and viewing angle characteristics and also significantly improved mechanical characteristics.

[0002]

2. Description of the Related Art An active drive twisted nematic liquid crystal display device (hereinafter abbreviated as TN-LCD) using a TFT element or an MIM element is thin, lightweight, and thin.
In addition to the low power consumption inherent in LCDs, it has an image quality comparable to a CRT when viewed from the front. For this reason, it is widely used as a display device for notebook computers, portable televisions, portable information terminals, and the like. However, in the conventional TN-LCD, the problem of the viewing angle that the display color changes or the display contrast decreases when viewed obliquely due to the refractive index anisotropy of the liquid crystal molecules can be essentially avoided. However, the improvement is strongly desired, and various attempts have been made for the improvement.

In recent years, various optical compensation films have been proposed for the purpose of solving the viewing angle problem, and the development of TN-LCDs having a wide viewing angle has been remarkably progressed. For example, Japanese Patent Laying-Open No. 10-104611 discloses a liquid crystal display device in which optical compensating means are provided on both sides of a driving liquid crystal cell and a light diffusion layer is provided on the light emitting surface side of the liquid crystal cell portion. In this publication, by providing a light diffusion layer on the light emission side surface of the polarizing plate,
A wide viewing angle is realized by diffusing outgoing light transmitted through the polarizing plate in all directions by a light diffusion layer.
Also, Japanese Patent Application Laid-Open No. 10-142591 proposes a liquid crystal display device provided with an optically anisotropic film exhibiting negative uniaxiality and a light diffusion film.

However, Japanese Patent Application Laid-Open No. H10-104611 discloses
Providing a light diffusion layer on the light emission side surface as shown in FIG. 1 means that the light diffusion layer is located at the outermost layer of the LCD, and therefore, the light diffusion layer has an antireflection treatment such as an anti-glare treatment.
It is necessary to impart a hard coat property to the surface, impart light resistance, and the like, which disadvantageously increases the manufacturing cost. When an optically anisotropic film and a light diffusing film are laminated and used as in JP-A-10-142591, the thickness of the optical member is increased, and the LCD is thin, which is one of the characteristics of the LCD. In addition to the above, there is a problem that when the optical element including the polarizing plate is bonded to the liquid crystal cell, the thickness of the optical element increases, and the processing cannot be performed by the existing bonding machine. When the optical element as described above is provided between the polarizing plate and the liquid crystal cell, when left under high temperature or high temperature and high humidity, between the light diffusing film and the polarizing plate, or between the light diffusing film. Peeling may occur between the film and the optically anisotropic film, and there is a problem in mechanical properties.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an optically anisotropic element having significantly improved display characteristics such as contrast characteristics and viewing angle characteristics, as well as significantly improved mechanical characteristics. And a twisted nematic liquid crystal display device provided with:

[0006]

That is, the first aspect of the present invention is as follows.
Is a driving liquid crystal cell comprising a pair of transparent substrates provided with electrodes and a nematic liquid crystal, and a twisted nematic liquid crystal display device comprising an upper polarizing plate and a lower polarizing plate disposed above and below the liquid crystal cell. Between the liquid crystal cell and the upper polarizer, or between the liquid crystal cell and the lower polarizer, or between the liquid crystal cell and the upper polarizer and between the liquid crystal cell and the lower polarizer. An optically anisotropic film (A) obtained by fixing a hybrid alignment formed in a liquid crystal state by a uniaxial liquid crystal substance and a diffuse transmittance /
The present invention relates to a liquid crystal display device provided with an optically anisotropic element comprising a light diffusion pressure-sensitive adhesive layer (B) having a total light transmittance of 50% to 90%.

[0007] A second aspect of the present invention is that the liquid crystal display element has a light source /
Lower polarizing plate / optically anisotropic film (A) / driving liquid crystal cell / optically anisotropic element (optically anisotropic film (A) / light diffusion adhesive layer (B)) / upper polarizing plate, or Light source / lower polarizing plate / optically anisotropic film (A) / driving liquid crystal cell /
The present invention relates to the liquid crystal display element described above, in which an optically anisotropic element (light diffusion pressure-sensitive adhesive layer (B) / optically anisotropic film (A)) / upper polarizing plate is arranged. A third aspect of the present invention relates to the above-mentioned liquid crystal display device, wherein the product Δnd value of the refractive index anisotropy Δn of the driving liquid crystal cell and the thickness d of the liquid crystal layer is 300 to 500 nm.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquid crystal display device of the present invention comprises a driving liquid crystal cell, an upper polarizing plate and a lower polarizing plate disposed above and below the liquid crystal cell, and a liquid crystal having optically negative uniaxiality. An optically anisotropic film (A) obtained by fixing a hybrid orientation formed in a liquid crystal state of a substance and a light diffusion pressure-sensitive adhesive layer (B) having a diffusion transmittance / total light transmittance of 50% to 90%. An optically anisotropic element is provided.

The optically anisotropic film (A) can be obtained by fixing a hybrid alignment formed in a liquid crystal state by a liquid crystal material having optically negative uniaxiality. A liquid crystal film (optically anisotropic film (A)) in which the hybrid alignment state is fixed can be obtained by forming a liquid crystal material capable of forming a hybrid alignment into a film. Here, the liquid crystal substance is, for example, a disk-shaped molecular shape,
It refers to a liquid crystal compound or a liquid crystal composition that can exhibit optically negative uniaxiality irrespective of low molecular weight or high molecular weight. As these liquid crystal substances, either lyotropic properties or thermotropic properties can be used. Specific examples of the liquid crystal substance include low-molecular liquid crystals such as a triphenylene derivative and a tolcene derivative. In the present invention, a liquid crystal film obtained by hybridizing the liquid crystal molecules and fixing the alignment state by glass fixing or heat / photocrosslinking reaction is used as the optically anisotropic film (A). Is most preferred.

A liquid crystal film having a fixed hybrid alignment is in a form as it is formed on an alignment substrate (alignment substrate /
(Alignment film) / liquid crystal film), liquid crystal film transferred to a transparent substrate film different from the alignment substrate (transparent substrate film / liquid crystal film), or liquid crystal film single layer if the liquid crystal film has self-supporting properties Any configuration of the mode (liquid crystal film) can be used as the optically anisotropic film (A). Examples of the transparent substrate film include triacetyl cellulose films such as Fujitac (manufactured by Fuji Photo Film Co., Ltd.) and Konikatac (manufactured by Konica), TPX film (manufactured by Mitsubishi Kasei), Arton film (manufactured by Nippon Synthetic Rubber Co., Ltd.), ZEONEX film (manufactured by Zeon Corporation), acrylene film (manufactured by Mitsubishi Rayon) and the like.

As a method of transferring to a transparent substrate film, a method of applying an adhesive to a liquid crystal film layer, laminating the transparent substrate film different from the oriented substrate, curing the adhesive, and then peeling the oriented substrate is used. Etc. can be adopted. This transfer can be preferably employed particularly when an optically non-isotropic film such as a rubbing polyimide film or a rubbing polyethylene terephthalate film is used as an alignment substrate, or when an opaque film is used in a visible light wavelength region. . The light diffusion pressure-sensitive adhesive layer (B) has a property of diffusing incident light isotropically or anisotropically, and a haze value defined by diffuse transmittance / total light transmittance is usually 50% to 90%. Is not particularly limited as long as it has adhesiveness. If the haze value is less than 50%, the intended improvement in the viewing angle characteristics may be insufficient. If it exceeds 90%, the viewing angle characteristics can be improved, but the display screen may be blurred and the contrast may be reduced. In the present invention, the total light transmittance of the light diffusion pressure-sensitive adhesive layer (B) is usually 50% or more, preferably 60% or more, and more preferably 70% or more.

The thickness of the light diffusion pressure-sensitive adhesive layer (B) is not particularly limited, but is usually 1 μm to 100 μm, preferably 5 μm to 50 μm, and more preferably 10 μm to 50 μm.
30 μm. Examples of the light diffusion pressure-sensitive adhesive layer (B) include non-self-supporting sheet-like materials and film-like materials in which particles having a refractive index different from that of the matrix are dispersed in an adhesive matrix. Specifically, acrylic adhesive, rubber adhesive, silicone adhesive, ethylene-vinyl acetate copolymer adhesive, urethane adhesive, vinyl ether adhesive, polyvinyl alcohol adhesive, polyacrylamide adhesive Agent and a matrix comprising a mixed adhesive thereof, for example,
Organic fine particles such as polystyrene-based fine particles and polymethacrylic acid-based fine particles having an average particle size of 0.5 to 5 μm, silica, alumina, titania, zirconia, tin oxide, indium oxide,
Examples thereof include those in which appropriate particles such as inorganic fine particles such as cadmium oxide and antimony oxide, hollow fine particles containing gas, and microcapsules containing liquid are dispersed. Among them, acrylic pressure-sensitive adhesives are preferable as a matrix because they are excellent in transparency, weather resistance, heat resistance and the like. When the light diffusion pressure-sensitive adhesive layers are overlapped, the individual light diffusion pressure-sensitive adhesive layers can be of the same type or different types in an appropriate combination.

As the acrylic pressure-sensitive adhesive, any of known materials can be used. For example, methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, amyl, isoamyl, hexyl, heptyl, cyclohexyl, 2
-Having 1 to 18 carbon atoms such as ethylhexyl, octyl, isooctyl, nonyl, isononyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl; Adhesives mainly composed of an acrylic polymer using one or two or more acrylic acid alkyl esters comprising an ester of acrylic acid or methacrylic acid having a linear or branched alkyl group are exemplified.

In the light diffusion pressure-sensitive adhesive layer, for example, a petroleum resin, a rosin resin, a terpene resin, a synthetic petroleum resin, a phenol resin, a xylene resin, an alicyclic ring, as long as the effects of the present invention are not impaired. Tackifiers such as aliphatic petroleum resins, coumarone indene resins, styrene resins, dicyclopentadiene resins, etc., softeners such as phthalate esters, phosphate esters, chlorinated paraffins, polybutenes, polyisobutylenes, and other various fillings Suitable additives such as an agent, an antioxidant and a crosslinking agent can be added.

The driving liquid crystal cell provided in the present invention has a pair of transparent substrates provided with electrodes and a nematic liquid crystal layer inserted between them. As the transparent substrate, a substrate capable of aligning a nematic liquid crystal in a specific alignment direction can be used. Specifically, either a transparent substrate having the property of aligning the nematic liquid crystal itself or a transparent substrate provided with an alignment film or the like having the property of aligning the liquid crystal can be used. By holding two transparent substrates having such a specific orientation direction such that the orientation direction has a twisted relationship and forming a layer of nematic liquid crystal between the transparent substrates, Normal 7
Twist angles in the range of 0 ° to 110 °, preferably 85 ° to 95 ° can be provided. When the twist angle is out of the above range, the optical rotation effect caused by the liquid crystal cell cannot be sufficiently obtained, and good display characteristics cannot be obtained even when the above-described optically anisotropic element is provided. The twist direction of the nematic liquid crystal layer may be either the left or right.

The electrode of the liquid crystal cell can be usually provided on the surface of the transparent substrate in contact with the nematic liquid crystal layer. When a transparent substrate having an alignment film is used, it is provided between the transparent substrate and the alignment film. be able to. As the nematic liquid crystal, various liquid crystals or the like usually used for a TN type liquid crystal display element can be used. Δnd represented by the product of the refractive index anisotropy Δn of the driving liquid crystal cell used in the present invention and the thickness d of the liquid crystal layer of the driving liquid crystal cell is usually 300 nm to 500 nm.
nm, preferably in the range of 300 nm to 400 nm. If it is larger than 500 nm, the effect of improving the viewing angle is poor when the optically anisotropic element is provided, and the response speed may be reduced. If the thickness is smaller than 300 nm, the provision of the optically anisotropic element has the effect of improving the viewing angle, but may lower the brightness and contrast of the front face. Further, as the driving liquid crystal cell, it is desirable to give a pretilt angle to the nematic liquid crystal molecules of the driving liquid crystal cell in advance in order to reduce alignment defects of the nematic liquid crystal molecules in the cell. The pre-tilt angle of the driving liquid crystal cell used in the present invention is usually desirably 5 ° or less.

As the polarizing plate used in the present invention, an appropriate polarizing plate having a polarizing function can be used. Generally, a polarizing film is used. The polarizing film is not particularly limited, and for example, iodine and / or iodine may be added to a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymer-based partially saponified film, and a cellulose-based film. Or a film stretched by adsorbing a dichroic dye, a polyene oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride, and the like. The thickness of the polarizing film is
Usually, it is 5 μm to 80 μm, but is not limited to this. The polarizing plate may be a polarizing film itself or a polarizing film provided with a transparent protective layer on one side or both sides. The transparent protective layer is not particularly limited as long as it is excellent in, for example, transparency, mechanical strength, heat stability, moisture shielding property, and the like.For example, polyester-based resins, polyethersulfone-based resins, polycarbonate-based resins, and polyamides Resin, polyimide resin, polyolefin resin, acrylic resin, acetate resin, cellulose resin, or thermosetting or ultraviolet curable resin such as acrylic, urethane, acrylic urethane, epoxy, silicone, etc. Can be used.

The formation of the liquid crystal display device of the present invention can be performed according to a known technique. That is, it can be formed by appropriately assembling necessary components such as a driving liquid crystal cell, a polarizing plate, and an illumination system and incorporating a driving circuit. In the liquid crystal display element of the present invention, an optically anisotropic element comprising an optically anisotropic film (A) and a light-diffusing adhesive layer (B) is provided between the liquid crystal cell and the upper polarizing plate or between the liquid crystal cell and the lower polarized light. There is no particular limitation, except that it is disposed at least between one of the liquid crystal cells and between the liquid crystal cell and each of the upper polarizing plate and the lower polarizing plate. Above all, from the lower side of the driving liquid crystal cell (light source / lower polarizing plate / optically anisotropic film (A) / driving liquid crystal cell / optically anisotropic element (optically anisotropic film (A) / light diffusion adhesive) Layer (B)) / upper polarizer) or from the lower side of the liquid crystal cell (light source / lower polarizer / optically anisotropic film (A) / driving liquid crystal cell / optically anisotropic element (light diffusion) By arranging in the order of pressure-sensitive adhesive layer (B) / optically anisotropic element (A)) / upper polarizing plate), the effects of the present invention can be more remarkably exhibited.

In the optically anisotropic film (A) constituting the optically anisotropic element in the present invention, the upper and lower sides of the film are not optically equivalent. Therefore, in the present invention, which of the upper and lower sides of the optically anisotropic film is disposed on the side of the driving liquid crystal cell is not particularly limited, but the cell parameters of the liquid crystal display element provided, the required optical performance, etc. Then, it is necessary to provide the liquid crystal display element. When the optically anisotropic film (A) is arranged so as to sandwich the driving liquid crystal cell as in the above example, the film may have the same parameters,
Also, they may be different.

Further, when the liquid crystal display element of the present invention is classified according to the driving method, it can be classified into a simple matrix method and a TFT (Thin Film Transistor) using an active element as an electrode.
or) electrode, MIM (Metal Insulator)
Metal or TFD; Thin Film D
(i) It can be subdivided like an active matrix method using electrodes. The liquid crystal display device of the present invention is effective for any driving method. Also, a halftone gray scale method (pixel division method) which is a known technique,
The domain division method was conceived in an attempt to expand the viewing angle of the LCD from the driving liquid crystal cell side. However, even if such a driving liquid crystal cell having a somewhat improved viewing angle is used, the viewing angle is further increased. It is possible to obtain a liquid crystal display element having an angle expanding effect.

[0021]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

(Example 1) A light diffusion adhesive layer (B) in which polystyrene fine particles are dispersed in an acrylic adhesive on an optically anisotropic film (A) in which a liquid crystal material composed of a triphenylene derivative is hybrid-aligned and fixed. (Total light transmittance 90.1%, haze value 75%) to form an optically anisotropic element. Thereafter, a liquid crystal display device was manufactured in the arrangement shown in FIG. The driving liquid crystal cell used was ZLI-4792 as a liquid crystal material, and the cell parameter was △ nd
Is 470 nm, the twist angle is 90 degrees (left twist), and the pretilt angle is 4 degrees. A voltage of 0 V to 6 V is applied to the liquid crystal cell, and a color luminance system BM-5 manufactured by Topcon Corporation is used.
The transmittance in the vertical direction at each gradation was measured. As a result of the measurement, no gradation inversion occurred even when the liquid crystal cell was viewed at −60 degrees, that is, the angle between the normal line of the liquid crystal cell and the line of sight was 60 degrees from below.

Comparative Example 1 The transmittance in the vertical direction at each gradation was measured in the same manner except that the light diffusion pressure-sensitive adhesive layer of Example 1 was changed to a pressure-sensitive adhesive having a haze value of 1%. As a result of the measurement, gradation inversion occurred at −20 degrees, that is, when the liquid crystal cell was viewed from below at an angle of 20 degrees between the normal of the liquid crystal cell and the line of sight.

Comparative Example 2 The transmittance in the vertical direction at each gradation was measured in the same manner as in Example 1 except that the haze value of the light diffusion pressure-sensitive adhesive layer was 95%. As a result of the measurement,
Even when the liquid crystal cell was viewed at 60 degrees, that is, the angle between the normal line of the liquid crystal cell and the line of sight was 60 degrees from below, no gradation inversion occurred. However, the image viewed from the front was blurred, and the contrast was reduced to 1/5.

Comparative Example 3 The transmittance in the vertical direction at each gradation was measured in the same manner as in Example 1 except that the haze value of the light diffusion pressure-sensitive adhesive layer of Example 1 was changed to 40%. As a result of the measurement, when the liquid crystal cell was viewed at -30 degrees, that is, when the angle between the normal line of the liquid crystal cell and the line of sight was 30 degrees from below, gradation inversion occurred, and the effect was insufficient.

Comparative Example 4 The transmittance in the vertical direction at each gradation was measured in the same manner as in Example 1 except that １nd of the driving liquid crystal cell of Example 1 was changed to 550 nm. As a result of the measurement, when the liquid crystal cell was viewed at -30 degrees, that is, when the angle between the normal line of the liquid crystal cell and the line of sight was 30 degrees from below, gradation inversion occurred, and the effect was insufficient.

Example 2 In order to examine the mechanical properties of the optically anisotropic element obtained in Example 1, an optically anisotropic film (A) and a polarizing plate were interposed via a light diffusion adhesive layer (B). A laminated body in a bonded form was prepared, and the laminated body was bonded to glass via an adhesive layer (FIG. 2). The laminate bonded to the glass was placed in a thermostat in a dry state at a temperature of 90 ° C., and the state of peeling after 500 hours was examined (high temperature test). Similarly, the laminated body bonded to the glass was placed in a thermo-hygrostat at a temperature of 60 ° C. and a relative humidity of 90%, and the state of peeling after 500 hours was examined (high-temperature high-humidity test). Table 1 summarizes the results of the durability test.

Comparative Example 5 The optically anisotropic film (A) and the light diffusing film (ID manufactured by Dai Nippon Printing Co., Ltd.) used in Example 1 were used.
S-21) was bonded using an ultraviolet-curable adhesive, and a polarizing plate was bonded to the light diffusion film surface via a pressure-sensitive adhesive layer. This laminate was bonded to glass via an adhesive layer (FIG. 3). A high-temperature test and a high-temperature and high-humidity test were performed on the laminate bonded to the glass in the same manner as in Example 2. Table 1 summarizes the results of the durability test.

(Comparative Example 6) The optically anisotropic film (A) of Example 1 and a light diffusing film (IDS-2 manufactured by Dai Nippon Printing Co., Ltd.)
1) was bonded using an adhesive, and a polarizing plate was bonded to the light diffusion film surface via an adhesive layer. This laminate was bonded to glass via an adhesive layer (FIG. 4). A high-temperature test and a high-temperature and high-humidity test were performed on the laminate bonded to the glass in the same manner as in Example 2. Table 1 summarizes the results of the durability test.

[0030]

[Table 1]

[0031]

As described above, according to the present invention, a twisted nematic liquid crystal display device having significantly improved not only display characteristics such as contrast characteristics and viewing angle characteristics but also mechanical characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a layout view of each element in a liquid crystal display device of the present invention prepared in Example 1.

FIG. 2 is a layout view of each element of a laminate used in a durability test of Example 2.

FIG. 3 is a layout view of each element of a laminate used in a durability test of Comparative Example 5.

FIG. 4 is an arrangement diagram of each element of a laminate used in a durability test of Comparative Example 6.

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Claims (3)

[Claims] 1. A driving liquid crystal cell comprising a pair of transparent substrates having electrodes and a nematic liquid crystal, and a twisted nematic liquid crystal display comprising an upper polarizing plate and a lower polarizing plate disposed above and below the liquid crystal cell. An optical element between the liquid crystal cell and the upper polarizer, or between the liquid crystal cell and the lower polarizer, or between the liquid crystal cell and the upper polarizer and between the liquid crystal cell and the lower polarizer. Optically anisotropic film (A) obtained by fixing a hybrid alignment formed of a liquid crystal substance having a negative uniaxial property in a liquid crystal state, and light diffusion having a diffusion transmittance / total light transmittance of 50% to 90%. A liquid crystal display device comprising an optically anisotropic element comprising a pressure-sensitive adhesive layer (B). 2. A liquid crystal display element comprising a light source / lower polarizing plate / optically anisotropic film (A) / driving liquid crystal cell / optically anisotropic element (optically anisotropic film (A) / light diffusion adhesive layer) (B)) / upper polarizer or light source / lower polarizer /
2. The optically anisotropic film (A) / driving liquid crystal cell / optically anisotropic element (light diffusion adhesive layer (B) / optically anisotropic film (A)) / upper polarizing plate in this order. Liquid crystal display element. 3. The liquid crystal display device according to claim 1, wherein the product Δnd value of the refractive index anisotropy Δn of the driving liquid crystal cell and the thickness d of the liquid crystal layer is 300 to 500 nm.