Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2001-04-03
2003-09-30
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S451000, C428S483000, C428S910000
Reexamination Certificate
active
06627308
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a release film, and more particularly, it relates to a release film for protecting an adhesive layer of a polarizing plate used in a liquid crystal display (hereinafter occasionally referred to merely as “LCD”).
Hitherto, release films made of a polyester film as a base material have been used to protect an adhesive layer of a polarizing plate used in LCD. However, these release films tend to cause various inconveniences upon use due to oligomers precipitated on the surface of a release layer thereof when exposed to a high temperature during the production process.
The oligomers precipitated on the surface of the release layer are readily transferred to the surface of an adhesive layer formed on a counterpart member to which the release film is attached, e.g., a polarizing plate. When the polarizing plate having such an adhesive layer on which the oligomers are transferred, is attached onto a glass plate, the obtained LCD tends to cause problems such as deteriorated brightness.
The production process of the polarizing plate for LCD includes steps of attaching the polarizing plate and the release film through the adhesive layer and winding up the resultant laminate into a roll, or the like. In the production process of the polarizing plate, it is considered that the oligomers are precipitated during the drying step after applying an adhesive thereonto.
In recent years, there is a tendency that the brightness of a display surface of LCD is increased in order to enhance a visibility thereof. As a result, the above problems more significantly affect the performance of LCD.
Further, in order to increase the productivity and reduce the production costs, it has been demanded to conduct the production process at a high speed. For this reason, a higher temperature tends to be used in the drying step, so that the above precipitation of oligomers is more likely to occur.
On the other hand, in the inspection step of the polarizing plate for LCD which is accompanied with optical evaluations of display performance, color tone, contrast, inclusion of foreign materials or the like, it has been conventionally attempted to prevent overlooking or detection error of defective products when inspected visually or by a magnifying glass. However, in such a case, there tend to be caused problems such as failure to detect foreign materials contained in the release film due to the optical anisotropy of the polyester base film thereof. Therefore, it has been required to temporarily peel the release film from the polarizing plate upon inspection, and attaching the release film again thereonto after the inspection.
As a result of the present inventors' earnest studies to solve the above problems, it has been found that by using a polyester film which is successively provided on the surface thereof with a coating layer and a release layer, and which exhibits a specific oligomer content, retardation value and total light transmittance, the obtained release film is free from the above-described problems. The present invention has been attained based on the above finding.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a release film which is excellent in handling property when used for protecting an adhesive layer of a polarizing plate for LCD, is capable of minimizing an amount of oligomers precipitated and exhibiting a good transparency, and allows facilitated inspection including optical evaluations.
To attain the above aim, in a first aspect of the present invention, there is provided a release film comprising:
a polyester film;
a coating layer formed on one surface of said polyester film; and
a release layer formed on a surface of said coating layer which exhibits a residual adhesion rate of not less than 80%,
said release film satisfying all of the conditions represented by the following formulae (1) to (3):
OL≦0.6 (1)
TL≧80 (2)
TL(H)≦8 (3)
wherein OL is an amount (mg/m
2
) of oligomers extracted with dimethylformamide from a surface of said release layer after the release film is heat-treated at a temperature of 180° C. for 10 minutes; TL is a total light transmittance (%) of said release film; and TL(H) is a total light transmittance (%) of a laminate prepared by interposing said release film between two polarizing plates disposed in a perpendicular relation to each other.
In a second aspect of the present invention, there is provided a release film for the protection of an adhesive layer formed on a polarizing plate for a liquid crystal display, comprising:
a biaxially stretched polyester film having a thickness of 9 to 50 &mgr;m;
a coating layer containing polyvinyl alcohol which is formed on one surface of said polyester film; and
a release layer formed on a surface of said coating layer,
said release film satisfying all of the conditions represented by the following formulae (1) to (3):
OL≦0.6 (1)
30≦Re≦10,000 (2)
TL≧80 (3)
wherein OL is an amount (mg/m
2
) of oligomers extracted with dimethylformamide from a surface of said release layer after the release film is heat-treated at a temperature of 150° C. for 10 minutes; Re is a retardation value (nm) of said biaxially stretched polyester film; and TL is a total light transmittance (%) of said release film.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
In the present invention, polyesters used for the biaxially stretched polyester film may be either homopolyesters or copolyesters.
As the homopolyesters, there may be exemplified those obtained by the polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acids may include terephthalic acid, 2,6-naphthalene dicarboxylic acid or the like. Examples of the aliphatic glycols may include ethylene glycol, diethylene glycol, 1,4-cyclohexane dimethanol or the like. Typical examples of the homopolyesters may include polyethylene terephthalate (PET), polyethylene-2,6-naphthalene dicarboxylate (PEN) or the like.
As the copolyesters, there may be exemplified copolymers containing, in addition to the above components, a third component in an amount of not more than 30 mol %. Examples of the dicarboxylic acid components of the copolyesters may include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalene dicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acids such as, e.g., p-oxybenzoic acid, or the like. These dicarboxylic acid components may be used alone or in the form of a mixture of any two or more thereof. Examples of the glycol components of the copolyesters may include ethylene glycol, diethylene glycol, propylene glycol, butane diol, 1,4-cyclohexane dimethanol, neopentyl glycol or the like. These glycol components may be used alone of in the form of a mixture of any two or more thereof.
The polyesters described herein may involve polyethylene terephthalates containing ethylene terephthalate units in an amount of usually not less than 80 mol %, preferably not less than 90 mol %, polyethylene-2,6-naphthalates containing ethylene-2,6-naphthalate units in an amount of usually not less than 80 mol %, preferably not less than 90 mol %, or the like.
The biaxially stretched polyester film preferably contains particles in order to mainly impart a good sliding property thereto. The kinds of particles blended are not particularly restricted as long as the particles added is capable of imparting a good sliding property to the polyester film. Specific examples of the particles blended may include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, silicon oxide, kaolin, aluminum oxide, titanium oxide or the like.
Further, the heat-resistant organic particles described in Japanese Patent Publication (KOKOKU) No. 59-5216(1984), Japanese Patent Application Laid-Open (KOKAI) No. 59-217755(1984), etc., may also be blended in the polyest
Inagaki Masashi
Isaki Kimihiro
Conlin David G.
Edwards & Angell LLP
Mitsubishi Polyester Films Corporation
Nakarani D. S.
O'Day Christine C.
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