JP2001242320A - Polarizing element and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a polarizing element capable of widely corresponding to characteristics required for optical compensation of a liquid crystal display panel of various modes. SOLUTION: The polarizing element holds a dichroic substance and has the light absorption axis in a state vertical or inclined to the plane of the element. The liquid crystal display device is provided with the polarizing elements on one side or both sides of the liquid crystal display panel. Consequently the polarizing element with the light absorption axis in the thickness direction, etc., is obtained. By combining it with a conventional polarizing plate with the light absorption axis in the plane of the plate, a wide viewing angle polarizing element with a high dichroic ratio and a polarizing characteristics hardly variable concomitant with variation of the viewing angle is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing element capable of forming a liquid crystal display device having excellent viewing angle, contrast and display uniformity.

[0002]

2. Description of the Related Art Heretofore, there has been known a polarizing plate in which iodine and the like are contained in a polyvinyl alcohol-based film and a uniaxially stretched polarizing film is provided with a transparent protective layer, and a retardation plate for optical compensation is laminated on the polarizing plate. (Patent Publication No. 284343
No. 1). This is because the viewing angle characteristics of the polarizing plate whose light absorption axis is in the plane of the plate affect the display characteristics with respect to the viewing angle change of the liquid crystal display device. Is compensated by the phase difference plate.

However, a liquid crystal display panel has, for example, a twisted nematic (TN) mode, a vertical alignment mode,
There are various modes such as horizontal alignment mode, and optical compensation such as expansion of the viewing angle requires compensation characteristics specific to that mode, and a polarizing plate with a laminated phase difference plate must meet those requirements. There was a difficult problem.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to develop a polarizing element which can widely cope with characteristics required for optical compensation of a liquid crystal display panel in various modes.

[0005]

According to the present invention, there is provided a polarizing element comprising a dichroic substance, the light absorption axis of which is in a state perpendicular or inclined with respect to a plane of the element. A liquid crystal display device provided on one or both sides of a liquid crystal display panel is provided.

[0006]

According to the present invention, a polarizing element having a light absorption axis in the thickness direction or the like can be obtained, and by combining it with a conventional polarizing plate having a light absorption axis in the plane of the plate. It is possible to obtain a polarizing element having a high dichroic ratio and a wide viewing angle in which the polarization characteristics are hardly changed by a change in the viewing angle.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A polarizing element according to the present invention comprises a dichroic substance whose light absorption axis is perpendicular or inclined with respect to the element plane, for example, in the thickness direction of the element. Become. Therefore, in the present invention, the light absorption axis via the dichroic substance need not be in the direction of the element plane.

[0008] The polarizing element can be formed by an appropriate method capable of controlling the arrangement state of the dichroic substance that determines the direction of the light absorption axis. By the way, as an example, a dichroic substance such as a dichroic dye or pigment is mixed with a liquid crystal component,
A method of developing the mixed solution to form an alignment layer may, for example, be mentioned. As the liquid crystal component, for example, one or more appropriate ones such as a liquid crystal or a liquid crystal polymer exhibiting various alignment characteristics such as a nematic type, a smectic type, a cholesteric type, a discotic type, a homeotropic type, and a lyotropic type can be used. . Both positive and negative materials may be used.

For the alignment treatment of the liquid crystal component, an appropriate alignment means such as an alignment film, an alignment substrate, an electric field or a magnetic field can be applied. Incidentally, in the case of the homeotropic liquid crystal component, a polarizing element having a light absorption axis in the thickness direction can be obtained by homeotropic alignment through the vertical alignment film. In addition, lyotropic liquid crystals (WO97 / 3938)
No. 0) can be used to obtain a polarizing element having a light absorption axis in the thickness direction. Lyotropic liquid crystals containing a dichroic dye are commercially available, for example, from Optiva.

A transparent protective layer can be provided on one side or both sides of the polarizing element as required. For forming the transparent protective layer, a film made of an appropriate transparent polymer can be used, and the polymer is not particularly limited. In particular, those excellent in transparency, mechanical strength, heat stability, moisture shielding property, and the like can be preferably used. Further, the transparent protective layer may be obtained by subjecting a film to a stretching treatment or an orientation treatment, or may be a film obtained by coating or impregnating a liquid crystal composition.

Examples of the above-mentioned polymers include acetate resins such as triacetyl cellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyether sulfone resins and polycarbonate resins, polyamide resins and polyimide resins. And polysulfone resins, polystyrene resins, acrylic resins and polyolefin resins, norbornene resins and allylate resins, and modified products thereof. The thickness of the transparent protective layer can be appropriately determined according to the strength and the like, but is generally 300 μm or less, preferably 5 to 200 μm, particularly 10 to 150 μm for the purpose of weight reduction or the like. The surface of the transparent protective layer may be formed in a fine uneven structure by the inclusion of fine particles.

The polarizing element according to the present invention can be preferably used for forming a liquid crystal display. In practical use, for example, a form in which an adhesive layer is provided on one or both sides of a polarizing element for the purpose of bonding to another member such as a liquid crystal display panel, or one or two suitable optical layers such as a polarizing plate and a retardation layer It can also be used as a form laminated with more than one layer. Lamination with an optical layer such as a polarizing plate or a retardation layer can also be performed by a method of sequentially laminating sequentially in the manufacturing process of the liquid crystal display device. The liquid crystal display device has advantages such as less variation and excellent assembly efficiency of the liquid crystal display device.

The pressure-sensitive adhesive layer may be made of any suitable material such as acrylic, silicone, polyester, polyurethane, polyether, or rubber, and is not particularly limited. Above all, acrylic ones are preferably used in terms of heat resistance and optical characteristics. In the adhesive layer,
If necessary, for example, appropriate additives such as fillers and pigments made of natural or synthetic resins, glass fibers and glass beads, metal powders and other inorganic powders, and coloring agents and antioxidants are blended. You can also. In addition, an adhesive layer exhibiting light diffusing properties can be formed by incorporating fine particles. An appropriate adhesive can be used for lamination with a polarizing plate, a retardation plate, or the like, but an adhesive layer is preferably used from the viewpoint of maintaining optical characteristics by suppressing thermal stress.

The lamination of the polarizing element according to the present invention, in particular, the polarizing element having a light absorption axis in the thickness direction and a polarizing plate is intended to obtain a polarizing element having a wide viewing angle. Those having a light absorption axis in the plane of the plate are preferably used from the viewpoint of achieving a color ratio. For a polarizing plate whose light absorption axis is in the plane of the plate, for example, a film made of a hydrophilic polymer such as polyvinyl alcohol is dyed with iodine or a dichroic dye and stretched 2 to 10 times in an aqueous boric acid solution or the like. (For example, NPF, manufactured by Nitto Denko Corporation), a polarizing film comprising a dichroic substance-containing liquid crystal and / or a liquid crystal polymer, and a lyotropic liquid crystal. An appropriate material such as a material using the same can be used, and there is no particular limitation.

On the other hand, the lamination of the retardation layers aims at further improving the compensation accuracy and the like. Any suitable retardation layer can be used, and there is no particular limitation. By the way, as an example, a uniaxially or biaxially stretched or oriented product or a liquid crystal composition such as a discotic or nematic system was coated on a resin film by using the transparent protective layer described above as an example. And impregnated ones. A retardation layer that is optically transparent and has little alignment unevenness is preferable.

As the retardation layer, two or more layers can be laminated in an appropriate combination of the above-mentioned stretched film, liquid crystal system and the like. There is no particular limitation on the positional relationship between the light transmission axis of the polarizing element and the fast axis of the retardation layer. In general, the STN type liquid crystal display device is stacked such that the light transmission axis and the fast axis are at different angles, and the TN type liquid crystal display device is stacked such that the light transmission axis and the fast axis are in a parallel or orthogonal relationship. Is common.

In addition to the polarizing plate and the retardation layer, the optical layer includes, for example, an antiglare layer, an antireflection layer, an antistatic layer, a light diffusion layer or a light diffusion control layer, a brightness enhancement layer, a reflection layer or a semi-transmission layer. An appropriate material such as a layer used for forming a liquid crystal display device can be used. Further, each layer such as the transparent protective layer, the adhesive layer, and the optical layer is treated with an ultraviolet absorber such as a salicylate compound, a benzophenone compound, a benzotriazole compound, a cyanoacrylate compound, and a nickel complex salt compound. UV absorption ability can be imparted by such means.

The formation of a liquid crystal display device using a polarizing element can be performed according to a conventional method. That is, a liquid crystal display device is generally formed by appropriately assembling components such as a liquid crystal display panel, a polarizing element, and optional optical layers and an illumination system, and incorporating a drive circuit, and the like. There is no particular limitation except that a polarizing element having a polarizing plate or an optical layer such as a retardation is provided on at least one side of the liquid crystal display panel according to the present invention.

Therefore, a liquid crystal display device in which a polarizing element is arranged on one or both sides of a liquid crystal display panel, or a transmissive or reflective type using a backlight or a reflector or a transflective reflector for an illumination system, or a reflective / transmissive type. An appropriate liquid crystal display device such as a dual-purpose type can be formed. Also, as the liquid crystal display panel, any type such as a TN type, an STN type, a TFT type, and a ferroelectric liquid crystal type can be used.

[0020]

EXAMPLE 1 A solution of a side chain type liquid crystal polymer containing a dichroic dye was applied on a vertical alignment film provided on a triacetyl cellulose film, dried, and polarized light having a light absorption axis in the thickness direction. An element was obtained. Note that the dichroic dyes described above include G
A mixture of -202 / G-207 / G-429 in a weight ratio of 1/2/4 was used. As the side chain type liquid crystal polymer, a homeotropic type having biphenyl benzoate in the side chain was used.

Example 2 A polarizing plate (NPF-G1225DU, manufactured by Nitto Denko Corporation) having a light absorption axis made of a polyvinyl alcohol-based polarizing film in the plane of the plate was laminated on the polarizing element of Example 1 via an adhesive layer. Thus, a polarizing element was obtained.

Comparative Example A polarizing plate (NPF-G1225DU) was used as it was.

Evaluation Test Two polarizing elements of Example 2 or two polarizing plates of Comparative Example were arranged in crossed Nicols to examine the light transmission state, and the viewing angle characteristics in the dark state were examined. . The result is shown in FIG. In the figures, the ratio of the luminance of the illumination light / the luminance at the crossed Nicols was determined, and the numerical value corresponding to the contrast was used. From the figure, it can be seen that in Example 2, a good dark level was maintained in any direction in which the viewing angle was changed, and there was little variation in contrast depending on the direction.

[Brief description of the drawings]

FIG. 1 is a graph showing viewing angle characteristics.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yuichi Nishikoji 1-1-2 Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation (72) Inventor Tomoaki Masuda 1-1-1, Shimohozumi, Ibaraki-shi, Osaka No. 2 Nitto Denko Corporation F term (reference) 2H049 BA02 BA28 BB03 BB33 BB42 BB51 BC02 BC22 2H091 FA09X FA09Z FA11X FA11Z FD10 GA06 GA13 HA07 LA17 LA19 5G435 AA01 AA02 AA04 BB12 FF05 KK05

Claims (7)

[Claims] 1. A polarizing element comprising a dichroic substance and having a light absorption axis perpendicular or inclined with respect to an element plane. 2. The polarizing element according to claim 1, wherein a light absorption axis is in a thickness direction of the element. 3. The polarizing element according to claim 1, wherein the polarizing element comprises an alignment layer of a liquid crystal component containing a dichroic substance. 4. The polarizing element according to claim 1, which has an adhesive layer on one or both sides. 5. The polarizing element according to claim 1, further comprising a polarizing plate having a light absorption axis in a plane of the plate. 6. The polarizing element according to claim 1, further comprising a retardation layer. 7. A liquid crystal display device comprising the polarizing element according to claim 1 on one or both sides of a liquid crystal display panel.