JPH0531122B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polarizing plate that has excellent transparency, moist heat resistance, dimensional stability, and heat resistance. BACKGROUND ART In recent years, polarizing plates used in liquid crystal display devices such as desktop computers and digital watches generally have a surface protective layer formed on both sides of the polarizing film to maintain a long service life. Until now, literature and patent publications have stated that many glass or plastic films can be used as materials that can form a surface protective layer, as long as they have optical transparency. Only cellulose films or polyacrylic resins have been put into practical use. This is due to not only excellent optical transparency but also the fact that there is little orientation and it is easy to paste or cure the coating. However, the cellulose-based or polyacrylic-based materials that have been put into practical use do not necessarily have sufficient dimensional stability or moisture and heat resistance as polarizing plates, and are particularly suitable for use under harsh conditions such as automobile instruments or outdoor displays. There is a problem in that it is difficult to use at lower temperatures. On the other hand, for the purpose of improving such heat and humidity resistance, it has been proposed that a non-axial or axial moisture-proofing film is bonded to the surface of a polarizing plate in which a surface protective layer is formed on both sides of the polarizing film as described above. There is. However, laminating another film on the surface of the polarizing plate in this way not only goes against the trend of technology that is trying to make liquid crystal display devices, etc. that incorporate this film thinner, but also increases the lamination process. However, it has not been put into practical use so far because it is expensive and the display lacks clarity due to the difference in refractive index between the protective layer and the moisture-proof film. In view of these circumstances, the present inventors developed a plastic material as a surface protective layer that has excellent heat resistance, heat and humidity resistance, and dimensional stability, and does not exhibit colored properties due to retardation when combined with a polarizing film. As a result of intensive research on film layers,
The inventors have discovered that a polyester film stretched in only one direction and having a retardation value of 0.5 to 200 μm is suitable as a surface protective layer, leading to the present invention. That is, in the present invention, on at least one surface of a polarizing film, a polyester film stretched only in one direction and having a retardation value δ of the following formula of 0.5 to 200 μm is arranged so that the absorption axis of the polarizing film and the stretching axis of the polyester film The present invention provides a polarizing plate in which the two are bonded to each other substantially orthogonally and (or in parallel) via an adhesive layer. Formula δ=Δn・d (In the formula, δ is the retardation value when the angle between the incident polarization plane and the longitudinal axis of the film is set to 45 degrees, Δn is the birefringence value, and d is the thickness) Polarizing plate of the present invention According to , it is a liquid crystal that has excellent heat resistance, humidity and heat resistance, and dimensional stability, as well as excellent mechanical strength, so its polarization properties do not deteriorate even when used under harsh conditions such as in automobile instruments and outdoor displays. A display device is obtained. The polarizing film used in carrying out the present invention is a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or a saponified ethylene-vinyl acetate copolymer (EVOH).
A polarizing element such as iodine and/or dichroic dye is adsorbed and oriented on a hydrophilic polymer film such as a film, and an iodine and/or dichroic dye polarizing film or a polyvinyl alcohol film is dehydrated. Alternatively, there may be a polyene polarizing film made by subjecting a polyvinyl chloride film to a desalting hydrochloric acid treatment to form and orient polyene. A polyester film stretched only in one direction and bonded to one or both sides of the polarizing film via an adhesive layer is a film made of polyester such as polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, etc. or at least 5 in the horizontal direction only
%, preferably 50-800%, practically 100-600
% stretched and heat set at 100°C for 60 minutes to 240°C for 5 minutes, with a thickness of about 15 to 1500 μm, and the birefringence value measured by the S'enarmont method. It is necessary that the value of the phase difference expressed as the product of the film thickness and the film thickness is 0.5 to 200 μm, preferably 1 to 150 μm. The phase difference value is determined by the product of δ=Δn.d (Δn is the birefringence value and d is the thickness). A polyester film stretched in only one direction is bonded to one or both sides of the polarizing film via an adhesive layer, but in the case of only one side, the absorption axis of the polarizing film and the polyester film are bonded to each other. The films are bonded together so that the stretching axis of the film is perpendicular or parallel to each other, or even in the case of both sides, the absorption axis and the stretching axis are perpendicular or parallel to each other, or the upper and lower polyester films are laminated so that the stretching axes of the upper and lower polyester films are orthogonal to each other. Ru. In the case of a type in which a polyester film is attached to only one side, a plastic film stretched in no direction or in only one direction other than polyester can be attached to the other side, if necessary. It should be noted that the absorption axis of the polarizing film and the stretching axis of the polyester film are bonded together almost orthogonally and/or in parallel as described above, but the bonding deviation angle is in the range of 1.5 minutes to 5 degrees. That is,
This is preferable in terms of polarization properties and mechanical properties. In addition to adhesive properties, the adhesive composition used for bonding a polarizing film and a polyester film has optical transparency at a thickness of about 2 to 50 μm, and depending on the components contained, the adhesive composition can affect the polarizing properties of the polarizing film. It is necessary that the adhesive does not disappear or deteriorate, and suitable examples include polyester adhesives, polyacrylic adhesives, epoxy adhesives, cyanoacrylate adhesives, polyurethane adhesives, and spirane adhesives. I can do it. Therefore, in order to obtain sufficient adhesive strength when bonding both films together, it is desirable to perform a surface treatment on the bonding interface side of both films. As a surface treatment method for polyester film, puttering method, oxidation fire method, primer treatment method, alkali treatment method, etc. can be used.
As a surface treatment method for the polarizing film, a primer treatment method using a silane coupling agent, a polyisocyanate compound, etc. can be used. The surface of the polyester film (exposed surface)
In addition, coating the polarizing plate with a silicone resin to provide scratch resistance, or forming magnesium fluoride through vapor deposition to improve transparency will extend the life of the polarizing plate and improve its polarizing properties. This is preferable. Since the polarizing plate of the present invention uses a polyester film having a retardation value of 0.5 to 200 μm as a surface protective layer, it has excellent optical transparency, as well as heat resistance, moist heat resistance, and dimensional stability. Moreover, since the polarizing plate of the present invention has a single protective layer, it is possible to obtain a product with a thickness equal to or less than that of the conventional one, and there is no increase in the number of steps and there is no decrease in visibility, which is practical. has advantages. Examples of the present invention will be shown below. The polarizing film used in the following examples is either A or B below. A: An iodine polarizing film made by adsorbing iodine to a polyvinyl alcohol film and stretching it approximately 4 times for orientation. Transmittance 40%, degree of polarization 89%. B: A polyene polarizing film obtained by dehydrating a polyvinyl alcohol film to form polyene and orienting it. Transmittance 40%, degree of polarization 90%. Example 1 Both sides of the polarizing film (A) are surface-treated with a polyisocyanate compound. On the other hand, a polyester adhesive solution is applied (thickness: 20 μm) on one side of a polyester film (thickness: 100 μm, stretching ratio: 200%) having a retardation value of 1.1 μm. Next, the film (A) is bonded to the treated surfaces (both sides) via the adhesive layer so that the absorption axis of the film and the stretching axis of the polyester film intersect at an angle of 5 minutes. Get a board. Example 2 A polarizing plate was obtained in the same manner as in Example 1, except that the absorption axis of the film (A) and the stretching axis of the polyester film were bonded to each other at right angles. Example 3 An epoxy adhesive solution was applied to a polyester film stretched in only one direction having the retardation value, thickness, and stretching ratio shown in Table 1 (thickness: 20 μm)
Then apply this to both sides of the polarizing film (B).
The polarizing plate of the present invention is obtained by bonding so that the absorption axis of (B) and the stretching axis of the polyester film intersect at an angle of 3 minutes.

[Table] Reference Example A non-oriented triacetate film (thickness 100 μm) is attached to both sides of the polarizing film (A) using an epoxy adhesive to obtain a polarizing plate. The test results of Examples 1 to 3 and Reference Examples are shown in Table 2.

[Table] The degree of polarization in Table 2 was determined by calculating the light transmittance in parallel and perpendicular times in the light beam region of 400 to 700 nm every 50 nm, and using the average value thereof based on the formula below. (However, in the formula, H ₀ is the average parallel transmittance and H ₉₀ is the average orthogonal transmittance.)

Claims (1)

[Scope of Claims] 1. On at least one surface of the polarizing film, a polyester film stretched only in one direction and having a retardation value δ of the following formula of 0.5 to 200 μm is arranged between the absorption axis of the polarizing film and the polyester film. A polarizing plate in which the stretching axis of the film is bonded to each other through an adhesive layer so that the stretching axis is substantially perpendicular or parallel to the film. Formula δ=Δn・d (In the formula, δ is the retardation value when the angle between the incident polarization plane and the longitudinal axis of the film is set at 45 degrees, Δn is the birefringence value, and d is the thickness) 2. The adhesive layer is polyester Claim No. 1, comprising at least one adhesive composition selected from the group of adhesives, polyacrylic adhesives, epoxy adhesives, cyanoacrylic adhesives, polyurethane adhesives, and spiran adhesives. Polarizing plate according to item 1.