JPS60159705A - Polarizing plate - Google Patents

Abstract

PURPOSE:To obtain a polarizing plate having superior heat resistance, water resistance and moisture resistance and suitable for liq. crystal display or the like by adhering a cellulose acetate film having a transparent thin film of magnesium oxide formed on the surface to the surface of a polarizing film. CONSTITUTION:A polarizing element such as iodine or Direct Blue 1 is adsorbed on a hydrophilic polymer film such as a polyvinyl alcohol film, and the film is stretched to orient the polarizing element. By the orientation, polarizing performance is provided to form a polarizing film. A transparent thin film of magnesium oxide is formed on at least one side of a cellulose acetate film such as a cellulose triacetate film by vacuum deposition or other method. The cellulose acetate film is adhered to at least one side of the polarizing PVA film so that the magnesium oxide layer contacts with the polarizing film. Thus, the desired polarizing plate is obtd.

Description

[Detailed Description of the Invention] Technical Field The present invention is used for applications such as liquid crystal displays, particularly for water resistance,
This invention relates to a polarizing plate with improved moisture resistance.

Prior Art Recently, liquid crystal displays using polarizing plates have begun to be used in a wide variety of applications, such as automobile display panels and other applications that require durability under high temperature and high humidity conditions. As attempts have been made, the demand for polarizing plates with better heat resistance and moisture resistance is increasing.

And as a polarizing plate, polyvinyl alcohol (hereinafter referred to as PV
A thread polarizing film (referred to as A) is widely used, but this film has poor moisture resistance, and particularly in a high temperature and humidity environment, the polarizing performance is significantly reduced. This is thought to be caused by orientation relaxation due to water absorption of the t/1 PVA film.

For this reason, it is common practice to protect the polarizing film by laminating a transparent film such as triacetic acid cellulose, which does not have birefringence, on the surface of the PVA polarizing film, but the moisture resistance of the PVA film itself is Due to its poor properties and the poor moisture permeability of cellulose triacetate, it does not provide a significant protective effect. For example, in an environment of 80° C. and 95% RH, even if the S-retaining layer is provided, the degree of discoloration and polarization decreases due to orientation relaxation due to water absorption of PVA, resulting in insufficient mixing resistance.

In addition, in order to eliminate such drawbacks, for example,
No. 12050 discloses that 5i is applied directly to the surface of a polarizing film.
Oxide layer such as ser Tidy or S i s
JP-A No. 11 [55-114563] discloses a method of improving moisture resistance by applying ItTIf to a nitride layer such as N4. @Sin via one layer of anchor on the surface of the cellulose triacetate.

A method of improving moisture resistance by providing an oxide layer such as Tto, l Zrot, etc. has been proposed, but even though this improves moisture resistance at room temperature, discoloration at high temperatures,
In view of the above-mentioned current situation, research was conducted with the aim of providing a polarizing plate with excellent heat and moisture resistance, which is not sufficient to prevent a decrease in the degree of polarization, and which further improves heat resistance and moisture resistance. As a result, a transparent thin film layer of magnesium oxide has the conventionally known properties of Sin' and Sin'.
I was disappointed when I discovered that this film has much better moisture permeability than other layers, and that by applying it to the protective film of a polarizing plate, a polarizing plate with excellent performance can be obtained.

Summary and Structure of the Invention The subject matter of the present invention is to provide a polarizing plate in which a cellulose acetate film is adhered to at least one surface of a polarizing film in which a polarizing element is adsorbed and oriented on a hydrophilic polymer film. The present invention relates to a polarizing plate characterized in that a transparent thin film layer of magnesium oxide is closely formed on at least one surface.

The polarizing film used in the present invention is a hydrophilic polymer film made of PVA 9, iodine or a dichroic dye such as Direct Black 17.19.20. direct blue 1.6
．． A polarizing element such as Direct Red 28 is adsorbed, and the adsorbing film is stretched or the like to orient the polarizing element to impart polarizing properties.

Cellulose acetate films include cellulose diacetate and cellulose triacetate, and cellulose triacetate is preferably used.

In order to form a transparent thin film layer of magnesium oxide on the surface of a cellulose acetate film, vapor deposition methods such as vacuum vapor deposition, reactive vapor deposition, ion blasting, or sputtering can be used. A thin layer can be formed in close contact with the surface of a cellulose acetate film.

To explain this vapor deposition method in more detail, for example, when a vacuum vapor deposition method is adopted, heat treatment, etc. A deposited film with good adhesion that does not require post-treatment can be obtained. Vacuum deposition is preferably performed under a pressure of 2×10-” torr or less.Alternatively, a transparent magnesium oxide film can also be formed by a reactive deposition method in which magnesium is heated and evaporated in a vacuum container into which oxygen gas is introduced. Furthermore, the transparent film can also be formed by ion blasting or sputtering, in which case a transparent thin film layer with better adhesion can be formed due to the high energy of the evaporated particles compared to the vacuum evaporation method. You can.

The thickness of the transparent thin film layer is preferably in the range of 100 to 5000 mm in order to improve the moisture resistance of the polarizing plate.

In addition, even if the thickness of the transparent thin film layer exceeds 50,000 mm, the transparency will not be impaired, but due to the stress inside the transparent thin film layer, the curling property of the cellulose acetate film may become a problem, and cracks and peeling may easily occur. It may happen. Furthermore, if the thickness of the transparent thin film layer is less than 100X, the film may form an island-like structure, resulting in insufficient moisture permeability. Although sufficient moisture permeation resistance can be achieved just by providing a material layer, it may of course be formed on both surfaces if necessary.

The polarizing plate of the present invention is formed by adhering to at least one surface of the polarizing film a cellulose acetate film in which a transparent FV film of magnesium oxide is formed in close contact with at least one surface. Urethane-based, acrylic-based, and epoxy-based adhesives can be used as adhesive materials.

When a cellulose acetate film with a transparent thin film layer formed on only one side is adhered to a polarizing film, the thin film layer may be placed in contact with the polarizing film, or the thin film layer may be attached to a polarizing film. Although it may be arranged opposite to the film side, the transparent thin film layer is prevented from being damaged by contact with other objects, and the thin film layer has excellent adhesion with adhesives. It is preferable to bond the thin film layer so that it is in contact with the polarizing film.

The polarizing plate of the present invention has the above-mentioned structure, and the transparent thin film layer of magnesium oxide closely formed on at least one surface of the cellulose acetate film used therein has excellent moisture resistance under high temperature and high humidity conditions. Because of this, it can be used in applications that require moisture resistance under harsh conditions, such as liquid crystal display panels for automobiles, and can exhibit excellent effects.

Example The present invention will be explained below based on embodiments.

Example 1 After washing an unstretched PVA film with a degree of saponification of 99.8% with water at room temperature, it was dyed by passing it through an aqueous dyeing solution at about 40°C containing dichroic dye Direct Blue 15. was dried with hot air at 80°C. This film is 14
Dry heat stretching is carried out in the uniaxial direction by about 4 times at 0°C, followed by heating at 1170°C for 5 minutes while keeping the tensioned rock, and then 55°C.
A PVA polarizing film was prepared by immersing it in a 3% by weight aqueous boric acid solution for 10 minutes while maintaining tension.

On the other hand, a magnesium oxide transparent film with a thickness of 1030× was formed on a cellulose triacetate film with a thickness of 80 μm by vacuum evaporation under the following conditions.

Film formation method: Vacuum deposition method (electron gun heating method) Evaporation source: 99% pure magnesium oxide Vacuum degree: 2X1
Film thickness: 1030i (measured with a crystal oscillation monitor) Film formation surface: One side of the film Next, the magnesium oxide layer of the vapor-deposited film prepared above was in contact with the PVA polarizing film surface. PV
A vapor deposited film was adhered to both sides of the polarizing film using a urethane adhesive. The adhesion between the PVA polarizing film and the magnesium oxide vapor-deposited surface of the vapor-deposited film was extremely good.

Regarding the polarizing plate thus prepared, 8G'C, 95%R
A moisture resistance test was conducted under the conditions of The results shown were obtained.

In addition, it was determined based on the following equation for the degree of polarization PFi.

Parallel transmittance (λ = 610 nm) when two polarizing plates are stacked with their polarization axes parallel to T: Orthogonal transmittance (λ = 61 nm) when two polarizing plates are stacked with their polarization axes perpendicular to T
0nm) Comparative Examples 1 to 3 Using Stow + TtOg + ZrO* as an evaporation source, each was vapor-deposited on one side of a cellulose triacetate film (thickness 80μ) in the same manner as in HP Example 1. SiOx thin film with a thickness of 980X (Comparative Example 1
), thickness 1015 x OTilt thin vS (comparative example 2) and thickness 1080 x f) ZrO, thin film (comparative example 3)
A cellulose triacetate film provided with the following was prepared.

These vapor-deposited films were adhered to both sides of the same PVA polarizing film prepared in Example 1 in the same manner as in Example 1, to produce three types of polarizing plates.

The three types of polarizing plates thus prepared were subjected to the same moisture resistance test as in Example 1, and the results shown in Table @1 were obtained.

@1 Table T(4): Single plate transmittance at wavelength 610 nmK P@4:
Polarization degree at wave 1c610 nmK Patent applicant Mototoshi Fujinuma, Representative of Sekisui Chemical Co., Ltd.

Claims (1)

[Scope of Claims] L A polarizing plate made by adhering a cellulose acetate film to at least seven sides of a polarizing film in which a polarizing element is adsorbed and oriented on a hydrophilic polymer film, and the cellulose acetate film has at least A polarizing plate characterized in that a transparent thin film layer of magnesium oxide is closely formed on one surface. 2. The polarizing plate according to claim gg1, wherein the hydrophilic polymer film is a polyvinyl alcohol film.