JPH063664A - Form releasing film for polarizing plate - Google Patents

Abstract

(57) [Summary] [Object] To provide a release film for a polarizing plate that does not cause interference color when placed between the polarizing plates. [Structure] A release film for a polarizing plate, wherein a release agent layer or a release agent layer and an adhesive layer are formed on the surface of a transparent polymer film having an optical delay of 400 nm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a release film for polarizing plates, which does not generate interference color when two polarizing plates are stacked.

[0002]

2. Description of the Related Art A polarizing film is used for a liquid crystal display device. The polarizing film includes polyvinyl alcohol adsorbing iodine, polyene polymer or dyeable transparent film dyed with a dichroic dye. Most of these polarizing films are used as a polarizing plate by laminating with a transparent polymer such as triacetyl cellulose because of their weak stiffness, lack of self-holding property and poor chemical resistance, water resistance and scratch resistance. Is. An adhesive layer for sticking to the surface of the liquid crystal display element is provided on the back surface of the polarizing plate, and a release film is laminated on the adhesive layer surface.

A biaxially stretched film of polyethylene terephthalate (hereinafter referred to as PET) is used as the release film, but the biaxially stretched film usually exhibits optical anisotropy. That is, the refractive index distribution in the three-dimensional direction forms an elliptical plate, and if the longitudinal refractive index is nx, the lateral refractive index is ny, and the thickness refractive index is nZ, different values are shown in the film plane. . In this case, the product of the birefringence (Δn) and the thickness of the film, which is represented by the difference (Δn = | nx−ny |) in the two directions of the refractive index in the plane of the film, is called the optical delay. Communication
In a conventional biaxially stretched PET film, this optical delay is large, and when the PET film is sandwiched between orthogonal polarizing plates, white light causes an interference color. This interference color is a problem for polarizing plates, and its solution has been strongly demanded.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a film having a small optical delay and exhibiting no interference color even when sandwiched between polarizing plates.

[0005]

As a result of earnest research by the present inventors, they found that interference color was hardly generated when the optical delay of the film was a certain value or less, and reached the present invention. That is, if a release agent layer or a film in which a release agent layer and an adhesive layer are formed on the surface of a transparent polymer film having an optical delay of 400 nm or less is used as a release film for a polarizing plate, an interference color is generated. I found that there is no.

As a method for obtaining such an optical retardation, a substantially amorphous and unoriented film raw material is heated at a temperature not lower than a glass transition point and not higher than a melting point by extrusion molding of a polymer film and simultaneously biaxially stretched. It is possible to obtain a film having a substantially isotropic molecular orientation in the film plane. As another method, it is possible to perform stretching in which the molecular orientation is balanced by successive biaxial stretching. In the sequential biaxial stretching, the draw ratio of the second step is slightly lower than the draw ratio of the first step, that is, 0.3 to more than the draw ratio of the first step.
By setting the size to be 0.6 times smaller, the biaxial molecular orientation is balanced. In order to obtain the dimensional stability of the stretched film, a method of heat setting at a temperature below the melting point of the film after stretching is generally used.

Suitable polymers for the film include polyethylene terephthalate and polyethylene terephthalate.
An isophthalate copolymer, a polyester polymer, a syndiotactic polystyrene polymer, and cellophane are particularly preferable. Films made of these polymers are excellent in transparency, chemical resistance, heat resistance and mechanical properties, and are particularly suitable for this release film for polarizing plates. Examples of the method for forming the release agent layer on the surface of the film include silicone, fluorocarbon, soap, metal soap, higher fatty acid, higher fatty acid ester, higher fatty acid amide, bisamide, organotin fatty acid, higher alcohol wax, carnauba wax, and lanolin. , Vaseline, liquid paraffin, polyethylene glycol, sodium alkylsulfate, ammonium stearate, higher fatty acid amine, a solution of a releasing agent such as fluorinated oil in a solvent, or an aqueous solution as an emulsion is applied to the film, Make it dry. It is also possible to form a release agent layer by spraying the release agent directly or by spraying the solution onto the film and then drying.

Further, as a method for forming the release agent layer and the pressure-sensitive adhesive layer on the surface of the film, it can be obtained by forming the release agent layer and then forming the pressure-sensitive adhesive layer. A pressure sensitive adhesive is preferable as the adhesive. Natural rubber, synthetic isoprene rubber, SBR, polyisobutylene, NBR, polyvinyl ether, polyacrylic ester or its copolymer, styrene isoprene or styrene butadiene block polymer, elastic body such as silicone and polytyl pen, rosin and its derivative, coumarone Tackifying resins and plasticizers such as indene resin and petroleum hydrocarbon resin, fillers,
An antiaging agent may be combined, dissolved in a solvent, coated on a film and dried to form a pressure-sensitive adhesive layer. The film thickness does not significantly affect the optical retardation as long as it is substantially unoriented and isotropic in-plane. The thickness of the film is generally 10 μm to 500 μm from the viewpoint of practical handling and surface protection. The thickness usually used is 20 μm to 100 μm.

Examples Next, examples and comparative examples of the present invention will be shown. The measuring method used in the present invention is shown below.

1) Birefringence of Film The refractive index was measured using an Atsube refractometer manufactured by Atago Optical Co., Ltd. according to ASTM D 542 and calculated from this.

2) Film Thickness The thickness was measured according to JIS-C2318 using an electronic micrometer μ-mate manufactured by Sony Corporation.

3) Haze and light transmittance Nippon Denshoku Industries Co., Ltd. VSG- according to JIS-K6714
It was measured at 1001 DP.

4) Interference color due to optical interference Measurement was performed using an optical strain measuring device manufactured by Japan Geoscience Co., Ltd.

Example 1 200 ppm of silica having an average particle size of 1.8 μm was used as a lubricant.
After drying PET having an intrinsic viscosity of 0.62 dl / g under vacuum, it is extruded into a sheet at a temperature of 290 ° C. using a 40φ extruder and cooled with a cooling drum at a peripheral speed of 15 m / min to a thickness of 48.
A substantially unoriented PET film stock of 0 μm was obtained.
This film stock is stretched at a temperature of 85 ° C. in both the longitudinal and transverse directions by 3.5 times each, and simultaneously biaxially stretched at a ratio of 2 times with a setter.
It was heat set at 15 ° C. On the surface of the obtained film, Shin-Etsu Chemical Co., Ltd., silicon release agent KS705 under was diluted twice with toluene, and used as a catalyst for combined use as Catalyst.
A coating solution prepared by adding 2 parts to 100 parts of PS under KS705 was applied by a reverse roll coater and dried at a temperature of 160 ° C. The coating amount was 0.3 g / m ² as the silicon solid deposition amount. A polarizing film having a thickness of 40 μm was laminated with an adhesive using two films of triacetyl cellulose having a thickness of 80 μm, and an acrylic sensitive adhesive was applied to a thickness of 5 μm on one outer surface of the laminated film. The release film of the release film was laminated on the laminate as an adhesive layer so that the release layer was aligned with the adhesive layer. On the other side of triacetyl cellulose, Sekisui Chemical Co., Ltd.
A polyethylene protective film # 622AX (50 μm) was laminated. No interference color was generated when the two obtained polarizing plates were overlapped and viewed with white light. Simultaneous biaxial stretching P of this example
Table 1 shows the physical properties of the ET film.

Comparative Example 1 Using the PET film original fabric of Example 1, a temperature of 8 was applied in the longitudinal direction.
The film was sequentially biaxially stretched at a temperature of 110 ° C. in a transverse direction at a temperature of 215 ° C. by a setter at a temperature of 215 ° C. In the same manner as in Example 1, two release plates obtained by applying a silicone release agent to one side of this film were laminated in the same manner as in Example 1, and when two polarizing plates were superposed and observed with white light, an interference color was generated. Was. Table 1 shows the physical properties of the sequential biaxially stretched film used in this comparative example.

Example 2 Using the PET film raw fabric of Example 1, biaxially stretching in the longitudinal and transverse directions at a temperature of 90 ° C. to 3.5 times and 3.1 times respectively, and heat at a temperature of 215 ° C. Fixed Similar to Example 1, a silicon release agent layer was formed on the surface of this film, and then a styrene / butadiene block copolymer was further mixed with a plasticizer, an antioxidant and a tackifier to obtain a hot melt pressure-sensitive adhesive. The agent was extrusion-laminated thereon to a thickness of 8 μm to form a pressure-sensitive adhesive layer. The release film having the above-mentioned pressure-sensitive adhesive layer was attached to one surface of the sandwich-like laminate of triacetyl cellulose, polarizing film and triacetyl cellulose of Example 1. The polyethylene protective film of Example 1 was laminated on the other surface. Two sheets of the obtained polarizing plate were overlapped and viewed with white light, but no interference color was generated. Table 2 shows the physical properties of the sequential biaxial PET film of this example.

Comparative Example 2 Using the PET film raw fabric of Example 1, the film was stretched biaxially in the longitudinal and transverse directions at a temperature of 90 ° C. at a draw ratio of 3.5 times, respectively, and heat-set at a temperature of 215 ° C. A polarizing plate was prepared in the same manner as in Example 2, and two polarizing plates were superposed on each other and viewed with white light, but an interference color was generated. Sequential biaxial stretching P used in this comparative example
Table 1 shows the physical properties of the ET film.

Example 3 500 ppm of silica having an average particle size of 0.3 μm was added to polystyrene having a weight-average molecular weight of 450,000 and having a predominantly syndiotactic structure. The film was cooled with a cooling drum at a speed of 120 m / min to obtain a substantially unoriented film original film having a film thickness of 510 μm. This film stock was simultaneously biaxially stretched in both lengthwise and transverse directions at a temperature of 105 ° C. at a draw ratio of 3.2 times, and heat set at 250 ° C. by a setter. The obtained film having a thickness of 50 μm was coated with a silicone release agent in the same manner as in Example 1 and dried, and then a pressure-sensitive film made of an acrylic copolymer of aliphatic alcohol / acrylic acid having a ratio of 98/2 was used. The adhesive was applied to a thickness of 8 μm to form an adhesive layer. A polarizing film made of polyvinyl alcohol having a thickness of 40 μm is made of two films of triacetyl cellulose having a thickness of 80 μm, and the adhesive layer of the release film is attached to a layered product which is laminated in a sandwich form by using an adhesive. I stuck it so that it would fit. The polyethylene protective film of Example 1 was attached to the other side of the triacetyl cellulose. The obtained polarizing plate is 2
No interference color was generated when the sheets were overlapped and viewed with white light.
Table 1 shows the physical properties of the simultaneously biaxially stretched syndiotactic polystyrene film of this example.

Comparative Example 3 The unoriented film raw material of syndiotactic polystyrene used in Example 3 was used, and the temperature was 10 in both longitudinal and transverse directions.
Sequential biaxial stretching was carried out at 5 ° C. and a draw ratio of 3.2 times. Except for this, the pressure-sensitive adhesive layer made of a silicone release agent and an acrylic pressure-sensitive adhesive was prepared in exactly the same manner as in Example 3. In the same manner as in Example 1, a pressure-sensitive adhesive layer of a release film composed of the above-described sequential biaxially stretched film was laminated on a laminate of a polarizing film of polyvinyl alcohol and triacetyl cellulose so as to be combined with triacetyl cellulose. A polyethylene protective film was attached to the other side of the triacetyl cellulose. When two obtained polarizing plates were superposed and observed with white light, an interference color was generated. Table 1 shows the physical properties of the sequential biaxially stretched syndiotactic polystyrene film of this comparative example.

[0020]

EFFECT OF THE INVENTION When two polarizing plates using the release film of the present invention are stacked, no interference color is generated, which is of great industrial significance.

[0021]

[Table 1]

Front Page Continuation (72) Inventor Hideo Miyake 2-2-8 Dojimahama, Kita-ku, Osaka Toyobo Co., Ltd.

Claims (1)

[Claims] 1. A release film for a polarizing plate, wherein a release agent layer or a release agent layer and an adhesive layer are formed on the surface of a transparent polymer film having an optical delay of 400 nm or less.