JPH0659123A - Polarizing plate and liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain the polarizing plate which is applicable without substantially spoiling the high contrast of a liquid crystal cell. CONSTITUTION:The polarizing plate 4 is formed by laminating a polarizing plate (4) which has a transparent protection layer (1) on at least one side of a polarizing film (2), has >=35% visible light transmissivity, and the degree of polarization P satisfies P=sq. rt. (Tp-Tc)/(Tp+Tc)>=0.990 (where Tp is parallel transmissivity and Tc is orthogonal transmissivity) while the size variation rate at the time of 80 deg.C heating is <=0.3% and a polarizing plate 4 formed by laminating at least one phase difference film on one side of the polarizing plate, and the liquid crystal display device is constituted by arranging the polarizing plate 4 on at least one side of a liquid crystal cell. Therefore, the polarizing plate 4 which is superior in thermal stability enough to prevent the disorder of polarized light due to heat, maintains the polarizing characteristics of the polarizing film 2 at high level, and has the high degree of polarization is obtained and the liquid crystal display device which has the superior contrast and superior visual angle characteristics 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 plate having excellent polarization characteristics and a liquid crystal display device using the same, which has excellent contrast.

[0002]

BACKGROUND OF THE INVENTION There is a demand for a polarizing plate which can be applied to a liquid crystal display device having a high contrast such as a TFT type or a gray scale display FSTN type without substantially lowering the contrast. In the conventional polarizing plate, it is not possible to make full use of such high contrast, which causes a decrease in contrast.

[0003]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to develop a polarizing plate which can be applied without substantially impairing the high contrast of a liquid crystal cell. The inventors of the present invention have made intensive studies to overcome the above-mentioned problems, and have determined that the problem in the conventional polarizing plate is based on the contraction of the polarizing plate due to heat and humidity, particularly the contraction of the polarizing film.

That is, the polarizing film is provided with a transparent protective layer for the purpose of improving the durability by preventing the intrusion of moisture, but the stretching type polarizing film having light absorption anisotropy is subjected to the stretching treatment. Shrinks due to heat and humidity during the manufacturing process of liquid crystal display devices. In particular, a polarizing film having a high degree of polarization of 99% or more has a high degree of stretching and a large degree of shrinkage. The shrinkage of the polarizing film affects the photoelastic change of the transparent protective layer and the retardation film provided as necessary, and further the deformation of the liquid crystal cell, which causes a compensation shift or the like and a contrast around the cell peripheral portion or the like. It was clarified that the decrease in brightness and the occurrence of coloration are induced, and the contrast is lowered particularly in a high-contrast liquid crystal cell, and display unevenness is likely to occur.

[0005]

The present invention has a transparent protective layer on at least one side of a polarizing film, has a visible light transmittance of 35% or more, and a degree of polarization P of the formula: P = √ ({Tp −
Tc} / {Tp + Tc}) ≧ 0.990 (where Tp is parallel transmittance and Tc is orthogonal transmittance), and the dimensional change rate at heating at 80 ° C. is 0.3% or less. A polarizing plate characterized by that, and a polarizing plate characterized by laminating at least one retardation film on one side of the polarizing plate, and the polarizing plate arranged on at least one side of a liquid crystal cell. The present invention provides a liquid crystal display device characterized by the following.

[0006]

By controlling the dimensional change rate of the polarizing plate to be 0.3% or less, deterioration of contrast and unevenness are not visually recognized. This is considered to have a small effect on the photoelastic change of the transparent protective layer and the deformation of the liquid crystal cell even if the dimensions are changed, and the decrease in contrast is considered to be below the visual limit.

[0007]

EXAMPLES The polarizing plate of the present invention has a transparent protective layer on at least one side of a polarizing film and has a dimensional change rate of 0.3% or less when heated at 80 ° C. Examples thereof are shown in FIGS. Reference numerals 1 and 3 are transparent protective layers, and 2 is a polarizing film. When the transparent protective layers are provided on both sides of the polarizing film 2 as illustrated in FIGS. 2 and 3, the transparent protective layers on both sides may be the same 1 (FIG. 2) or may be different. Good (Figure 3).

The polarizing film has a visible light transmittance of 3
It is 5% or more, 35 to 48% in particular, and the degree of polarization is 0.990 or more, especially 0.995 or more. Polarization degree P
Is the formula: P = √ ({Tp-Tc} / {Tp + Tc}) (where Tp is parallel transmittance: light transmittance when the absorption axes of a pair of polarizing plates are aligned in parallel, Tc is orthogonal transmission) Ratio: The light transmittance when the absorption axes of the pair of polarizing plates are aligned in the orthogonal state.).

In the above, the transmittance (T) is JI
Based on S Z 8701, T = K∫S (λ) y
(Λ) τ (λ) dλ, where K = 100 /
∫ S (λ) y (λ) dλ, S (λ): Spectral distribution of standard light used for color display, y (λ): Color matching function in XYZ system, τ (λ): Spectral transmittance .

The material of the polarizing film is not particularly limited. Generally, a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, or an ethylene / vinyl acetate copolymer-based partially saponified film, which is stretched by adsorbing iodine and / or a dichroic dye A polarizing film composed of a polyene oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride is used.
The polarizing film typically has a thickness of 5 to 80 μm, but is not limited thereto.

As a material for forming the transparent protective layer, a material excellent in transparency, mechanical strength, thermal stability, moisture shielding property and the like can be preferably used. Typical examples thereof include polymers such as polyester resins, polyether sulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, acrylic resins and acetate resins. When the retardation of the transparent protective layer is not particularly limited, the transparent protective layer may be formed of a uniaxially or biaxially stretched film or the like. Further, functional layers such as an antiglare layer, an antireflection layer, an electromagnetic wave shield layer, an antistatic layer and a hard coat layer can be provided.

The transparent protective layer may be formed, for example, by coating a polarizing film with a polymer solution or by casting a film to prevent optical distortion and then adhering the film to the polarizing film. can give. The thickness of the transparent protective layer is usually 5 to 500 μm, especially 10 to 20.
It is set to 0 μm, but is not limited to this.

When a casting film or the like is used as the material for forming the transparent protective layer, it is bonded to the polarizing film with, for example, a transparent adhesive or pressure sensitive adhesive. The type of the adhesive or the like is not particularly limited, but from the viewpoint of preventing changes in the optical properties of the polarizing film and the transparent protective layer, those that do not require a high temperature process during curing or drying are preferable,
Those that do not require a long curing process or drying time are desirable.

Achieving a polarizing plate having a visible light transmittance of 35% or more, a polarization degree of 0.990 or more, and a dimensional change rate of 0.3% or less when heated at 80 ° C. is achieved by stretching the polarizing film. The thickness and combination of the polarizing film and the transparent protective layer can be appropriately selected. In particular, in order to achieve the above dimensional change rate, it is advantageous to use a transparent protective layer having excellent thermal stability and small dimensional change.

In the polarizing plate, the polarizing film and the transparent protective layer are treated with an ultraviolet absorber such as salicylate compound, benzophenol compound, benzotriazole compound, cyanoacrylate compound, nickel complex salt compound and the like. It can also be made to have the ability to absorb ultraviolet rays depending on the method.

The polarizing plate of the present invention is, for example, an STN cell, a T
It can be preferably used in various optical system devices such as liquid crystal display devices using FT cells, TN cells, FLC cells, SH cells and the like.

In a liquid crystal display device or the like, a retardation film may be arranged in order to compensate for birefringence and the like. In that case, in the present invention, the retardation film is adhered to a polarizing plate in advance if necessary. However, it can also be used as a laminate. FIG. 4 illustrates a polarizing plate of the type in which the retardation film 5 is laminated on one side of the polarizing plate 4. The retardation film may be formed by laminating two or more retardation films in order to control optical properties such as retardation.
It is possible to laminate one or more retardation films.

As the retardation film, a film made of a thermoplastic polymer or the like is uniaxially or biaxially (including completely biaxially) stretched and further polyaxially stretched, or a thermoplastic polymer is pressed by a pressing method. Appropriate films may be used such as those which are internally oriented, those in which the refractive index in the three-dimensional direction is controlled, those in which the liquid crystal polymer is oriented vertically or horizontally, and those in which they are twisted.

As a general polymer other than the liquid crystal polymer forming the retardation film, for example, a polycarbonate resin, a polyester resin, a polyether sulfone resin, a polyamide resin, a polyimide resin, a polyolefin resin, an amorphous polyolefin is used. Resin,
Examples thereof include polymers such as acrylic resins, polystyrene resins, acetate resins, polyarylate resins, and polyvinyl alcohol resins, but are not limited thereto.

In the liquid crystal display device of the present invention, the above-mentioned polarizing plate is arranged on one side or both sides of the liquid crystal cell. Such a liquid crystal display device is illustrated in FIGS. 4 is a polarizing plate
Reference numeral 5 is a retardation film, and 6 is a liquid crystal cell. As is clear from the examples, the required number of polarizing plates and retardation films can be used for one side or both sides of the liquid crystal cell in an appropriate combination. Also, as the liquid crystal cell, two or more liquid crystal cells may be used, such as a combination of display and compensation. The absorption axis of the polarizing plate and the optical axis of the retardation film may be set to any crossing angle, for example, in the range of 0 to 180 degrees.

Example 1 A methylene chloride solution of triacetyl cellulose was uniformly applied on a mirror-finished stainless steel plate, pre-dried at 50 ° C. for 5 minutes, and then peeled off from the stainless steel plate so that the film was not stressed. And dried at 150 ° C. for 10 minutes to obtain a transparent protective film having a thickness of 50 μm. Next, the protective film was placed on both sides of the iodine / polyvinyl alcohol polarizing film having a thickness of 30 μm via acrylic adhesive layers having a thickness of 20 μm so that the optical axis thereof was parallel to the absorption axis of the polarizing film. It adhered and the polarizing plate was obtained.

Comparative Example A polarizing plate was obtained in the same manner as in Example 1 except that a commercially available triacetyl cellulose film having a thickness of 50 μm was used as a protective film.

Evaluation Test The following characteristics of the polarizing plates obtained in Examples and Comparative Examples were examined.

Shrinkage rate A polarizing plate was cut into a size of 120 mm x 120 mm along the absorption axis, placed in a drier at 80 ° C for 4 hours and then taken out, and the dimensional change rate was calculated from the dimensions before and after heating based on the following formula. did. Dimensional change rate = (initial length-length after heating) / initial length x 1
The dimensional change rate was examined in two directions, the absorption axis and the polarization axis, and the one with the larger change rate was defined as the shrinkage rate.

Variation in polarization degree A polarizing plate with a size of 180 mm × 180 mm is 4 with respect to the absorption axis.
A pair of pieces cut out at an angle of 5 degrees and adhered to a glass plate was put in a dryer at 80 ° C for 5 hours and then taken out, 17 points x 1
The parallel transmissivity (Tp) and the orthogonal transmissivity (Tc) at each of the seven points are equally measured at every 10 nm in the region of 380 to 700 nm by the spectrophotometer, and the polarization degree P is calculated based on the above formula. Was calculated and statistically evaluated to examine the variation.

The above results are shown in Table 1. In addition, in Table 1, the characteristics of those not heat-treated are shown as blanks.

[Table 1]

According to the present invention, it is possible to obtain a polarizing plate having a high degree of polarization, which is excellent in thermal stability, can prevent polarization disorder due to heat, and can highly maintain the polarization characteristics of a polarizing film, and is excellent in contrast. A liquid crystal display device having excellent viewing angle characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of a polarizing plate.

FIG. 2 is a cross-sectional view of another polarizing plate example.

FIG. 3 is a cross-sectional view of still another example of a polarizing plate.

FIG. 4 is a sectional view of an example of a polarizing plate in which retardation films are laminated.

FIG. 5 is a cross-sectional view of an example of a liquid crystal display device.

FIG. 6 is a cross-sectional view of another liquid crystal display device example.

FIG. 7 is a cross-sectional view of still another example of a liquid crystal display device.

[Explanation of symbols]

 1, 3: transparent protective layer 2: polarizing film 4: polarizing plate 5: retardation film 6: liquid crystal cell

Claims (3)

[Claims] 1. A polarizing film having a transparent protective layer on at least one side, a visible light transmittance of 35% or more, and a degree of polarization P of the formula: P = √ ({Tp-Tc} / {Tp + Tc}). ≧
A polarizing plate which satisfies 0.990 (where Tp is parallel transmittance and Tc is orthogonal transmittance) and has a dimensional change of 0.3% or less when heated at 80 ° C. 2. A polarizing plate comprising at least one retardation film laminated on one side of the polarizing plate according to claim 1. 3. A liquid crystal display device comprising the polarizing plate according to claim 1 or 2 disposed on at least one side of a liquid crystal cell.