JPH07294732A - Polarizing plate and liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the generation of light leakage due to the deviation of the optical axis at the time of performing the reliability test by using a high polymer film having a specified coefficient of photoelasticity as the substrate of a polarizing element film of the polarizing plate. CONSTITUTION:In this polarizing plate, as the substrate of the polarizing element film a high polymer film having a <=25.0X10<-13>cm<2>/dye, preferably (5.0 to 25.0)X10<03>cm<2>/dyne coefficient of photoelasticity is used. The high polymer film having such property is a synthetic high polymer film preferably having about 50 to 150mum thickness and its examples are an amorphous polyolefin film such as 'Zeonex (R)' (manufacture: NIPPON ZEON K.K.), etc., and a polymethyl methacrylate film such as 'Acryprene (R)' (manufacturer: MITSUBISHI RAYON K. K.), etc. Also, the polarizing element film is preferably a processed polyvinyl alcohol based film which is obtained e.g. by dyeing a polyvinyl alcohol based film with iodine or a dichroic dyestuff, orienting the dyed film while esterifying it in a boric acid aq. solution and heating and drying the resulting film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing plate and a liquid crystal display device.

[0002]

2. Description of the Related Art In a liquid crystal display element, liquid crystal is sealed between two electrode substrates, and a voltage is applied to the electrodes of the electrode substrates to change the optical properties of the liquid crystal display device. You get the pattern. Such a liquid crystal display element has a thin element thickness, a display pattern can be freely selected, power consumption is extremely low, low voltage driving is possible, and a C-MOS IC can be directly driven. It is used as a display element in most display parts such as air conditioners and telephones.

On the other hand, the twisted nematic type liquid crystal display element is an element having a polarizing plate outside the above two upper and lower electrode substrates, and a switching element (TF) is provided for each dot of this element.
A display body that is driven by attaching T) and combined with a color filter is used in a liquid crystal television and a liquid crystal movie.

Most of the polarizing plates used in this liquid crystal display device are polarizing devices obtained by adsorbing or dispersing iodine or a dichroic dye in a polyvinyl alcohol film (PVA) and stretching the film in a certain direction. Uses a membrane. This polarizing element film is a very thin film,
Further, since it is weak against the tensile force in the direction perpendicular to the stretching axis, it is generally attached to a support. For this support, a non-axially stretched cellulose-based film such as cellulose triacetate, cellulose butyrate, or cellulose acetate is generally used.

[0005]

However, in the conventional polarizing plate using the conventional cellulose film as the support, the optical axis is shifted in the reliability test, and the optical axis of the support corresponding to the upper and lower electrode substrates is formed. It was found that the deviation causes light leakage in the black display state and causes in-plane contrast variation. An object of the present invention is to prevent light leakage due to the deviation of the optical axis in the reliability test of the polarizing plate, and in particular, to prevent light leakage in the black display state due to the optical axis deviation of the support corresponding to the upper and lower electrode substrates. It is to prevent light leakage from occurring in a liquid crystal display device having a polarizing plate attached to a glass electrode via a leakage adhesive layer after a reliability test.

[0006]

The inventors of the present invention have found that light leakage (light leakage that occurs in a black display state after a reliability test) occurs in a liquid crystal display element having a polarizing plate attached to a glass electrode via an adhesive layer. As a result of diligent examination of the cause and mechanism of the phenomenon, the cellulose triacetate film used as the support (or protective film) of the polarizing plate under the reliability test condition performed under high temperature or high temperature and high humidity condition is the polarizing element film. It was confirmed that the optical axis was partially displaced by the stress caused by the dimensional change of the optical axis, and that light leakage was caused by the phase difference of 3 to 8 nm of cellulose triacetate itself. There is a difference depending on the size of the photoelastic coefficient of the polymer film used in the body, and it has a mutual relationship with the dimensional change of the polarizing element film and the fixing force of the adhesive layer, but the photoelastic coefficient has a large value. One Hodohikarijiku off easily, the value of photoelastic coefficient in order to suppress the light leakage is 25.0 × 10 ^-13 cm ²
By using a polymer film having a value of / dyne or less as a support corresponding to the electrode substrate side, it is possible to suppress the deviation of the optical axis caused by the stress caused by the dimensional change of the polarizing element film under the reliability test conditions, It turns out that leakage can be prevented. That is, according to the present invention, (1) the support for the polarizing element film has a photoelastic coefficient of 25.0.
A polarizing plate using a polymer film having a value of × 10 ^-13 cm ² / dyne or less. (2) The polarizing plate according to (1) above, wherein the polarizing element film is a polyvinyl alcohol-based film, and (3) a liquid crystal display element comprising polarizing plates on the outer sides of two electrode substrates arranged facing each other. The photoelastic coefficient is 25.0 × 10 on the support corresponding to the electrode substrate side of the plate.
^A liquid crystal display device comprising a polymer film having a value of ^-13 cm ² / dyne or less, (4) the polarizing plate is a polyvinyl alcohol type polarizing plate, and the liquid crystal display device is a twisted nematic liquid crystal display device. The present invention relates to the liquid crystal display device according to the above (3).

The support used in the present invention has, for example, a photoelastic coefficient of 25.0 × 10 ^-13 cm ² / dyne or less, preferably 5.0 × 10 ^{-13 to} 25.0 × 10 ^-13.
A polymer film having a value of cm ² / dyne can be mentioned. Examples of the polymer film having such properties include an amorphous polyolefin film such as Zeonex (manufactured by Nippon Zeon Co., Ltd.) and a synthetic polymer film such as polymethylmethacrylate film such as Acryprene (manufactured by Mitsubishi Rayon Co., Ltd.). . The thickness of these films is preferably about 50 to 150 μm.

In the polarizing plate of the present invention, at least one side of a polarizing element film (polarizing film) is laminated and adhered (adhered) with a support made of the above-mentioned polymer film, and the opposite surface is made of a transparent polymer film (for example, the above-mentioned high polymer film). It is manufactured by laminating and adhering (adhering) with a molecular film or the above-mentioned cellulose film. The polarizing film used here is not particularly limited, but for example, a polyvinyl alcohol film is dyed with iodine or a dichroic dye, and while being esterified in an aqueous solution of boric acid, it is uniaxially increased to about 3 to 5 times. It can be obtained by stretching and heating and drying. The dichroic dye, for example, can be arbitrarily selected from acid dyes and direct dyes, azo dyes, stilbene dyes, anthraquinone dyes,
Examples include methine dyes and cyanine dyes. Also,
Adhesives (adhesives) used for laminating adhesives (adhesives) are, for example, highly transparent epoxy-based, polyester-based, vinyl acetate-based solvent-based adhesive (adhesive) agents, or alkyl acrylate-based, polyvinyl ether-based adhesives. Examples thereof include pressure-sensitive adhesive (adhesive) agents such as resins, and adhesive (adhesive) resins that can be cured by a polymerization reaction such as acrylic polymer resins and urethane resins.

In the liquid crystal display device of the present invention, the polymer film surface of the polarizing plate manufactured as described above is laminated and adhered to one surface of two electrode substrates which are arranged facing each other using an adhesive. It is manufactured by Examples of the adhesive used here include butyl acrylate, acrylic acid, and 2
Examples thereof include an acrylic pressure-sensitive adhesive such as a hydroxyethyl acrylate copolymer, a rubber-based pressure-sensitive adhesive, a vinyl-based pressure-sensitive adhesive, and a silicon-based pressure-sensitive adhesive, and the acrylic-based pressure-sensitive adhesive is preferable. As this acrylic pressure-sensitive adhesive, one obtained by copolymerizing a main component (meth) acrylic acid ester with a compound having a carboxyl group or a hydroxyl group capable of being copolymerized therewith is used, if necessary. Then, a polyisocyanate curing agent or an epoxy curing agent may be added immediately before coating to form a crosslinked structure.

[0010]

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

Example 1 A polyolefin film having a photoelastic coefficient of 6.3 × 10 ^-13 cm ² / dyne (ZEONEX (manufactured by Zeon Corporation)) was used as a support, and an acrylic adhesive was applied to at least one side of a polarizing element film. It adhere | attached with the agent and manufactured the polarizing plate. A laminated liquid crystal display device is obtained by interposing an adhesive layer so that this polyolefin film is arranged on the glass electrode side. This polarizing plate has an absorption axis of 45 ° (or 135 °) and 120 m
A piece cut into a size of mx 90 mm was attached to a glass plate, and two pieces each were tested under each of the reliability test conditions of 60 ° C / 90% RH and 100 ° C, and after 100 hours, a crossed Nicol state was obtained. The transmittance at the measurement position (A, B) shown in FIG. 1 was measured, and the light leakage was expressed by the lightness index ratio (L _b / L _a ). The results are shown in Table 1.

Example 2 Example 1 was repeated except that the reliability test conditions were 40 ° C./95% RH and 90 ° C., and the results are shown in Table 1.

Example 3 A polarizing plate was prepared by using a polymethylmethacrylate film having a photoelastic coefficient of 6.0 × 10 ^-13 cm ² / dyne as a support and adhering it to at least one side of a polarizing element film with an acrylic adhesive. Manufactured. A laminated liquid crystal display device is obtained by interposing an adhesive layer so that the polymethylmethacrylate film is arranged on the glass electrode side. Example 1 except that the reliability test conditions were 60 ° C./90% RH and 80 ° C.
Was carried out in the same manner as above, and the results are shown in Table 1.

Comparative Example 1 Cellulose triacetate, which is generally used as a support for a polarizing plate, was adhered to a polarizing element film with a polyvinyl alcohol adhesive to manufacture a polarizing plate. This polarizing plate is attached to a glass electrode via an adhesive layer to obtain a liquid crystal display device. 60 ° C
/ 90% RH and 90 ° C. under the respective reliability test conditions, the same procedure as in Example 1 was carried out, and the results are shown in Table 1. The photoelastic coefficient of cellulose triacetate is 30.0 × 10 ^-13 cm ² / d
It was yne.

Comparative Example 2 A polarizing plate was manufactured by bonding a polycarbonate having a photoelastic coefficient of 72 × 10 ^-13 cm ² / dyne to at least one side of a polarizing element film with an acrylic adhesive. This polarizing plate is attached to a glass electrode via an adhesive layer to obtain a liquid crystal display device.
It carried out like Example 1 under each reliability test condition of 60 degreeC / 90% RH, and 90 degreeC, and the result was described in Table 1.

[0016]

[Table 1]

[0017]

By using a polymer film having a photoelastic coefficient of 25.0 × 10 ⁻¹³ or less as a support for a polarizing element film, a liquid crystal display element free from in-plane contrast variations due to light leakage. And the display quality can be improved.

[Brief description of drawings]

FIG. 1 shows the measurement positions A and B of the transmittance. Here, the arrow indicates the absorption axis of the polarizing plate.

Claims (4)

[Claims] 1. A photoelastic coefficient of 2 as a support for a polarizing element film.
A polarizing plate using a polymer film having a value of 5.0 × 10 ⁻¹³ cm ² / dyne or less. 2. The polarizing plate according to claim 1, wherein the polarizing element film is a polyvinyl alcohol film. 3. In a liquid crystal display device comprising a polarizing plate on the outer side of two electrode substrates arranged opposite to each other, a support corresponding to the electrode substrate side of the polarizing plate has a photoelastic coefficient of 25.0 × 10 5.
^A liquid crystal display device comprising a polymer film having a value of ^-13 cm ² / dyne or less. 4. The liquid crystal display device according to claim 3, wherein the polarizing plate is a polyvinyl alcohol type polarizing plate, and the liquid crystal display element is a twisted nematic liquid crystal display element.