Stock material or miscellaneous articles – Composite – Of polyester
Reexamination Certificate
2002-08-07
2004-03-09
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyester
C428S480000, C428S482000, C428S910000, C428S341000, C264S288400, C264S289300, C264S289600, C264S290200
Reexamination Certificate
active
06703138
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a laminated polyester film having a coating layer. More particularly, the present invention relates to a laminated polyester film having a coating layer, which has excellent adhesion with a wide range of materials, such as photographic photosensitive layers, diazo photosensitive layers, mat layers, magnetic layers, ink layers, adhesive agent layers, thermosetting resin layers, UV setting resin layers, and vapor deposited layers of metal or inorganic oxides, which has good water resistance and resistance to whitening due to heating, and which, when recovered in the form of scrap film, can be reused as a film raw material.
BACKGROUND OF THE INVENTION
Laminated polyester films which are adhesive find use in a wide range of applications, such as magnetic tape base films, insulating tapes, photographic films, liquid crystal components, antireflective films, tracing films, and food packaging films. Because a polyester film itself does not have sufficient adhesion, its adhesion is generally improved by providing an anchor coat layer to the polyester film.
Many different resins have been proposed as anchor coating resins up to now. For instance, the use of a water-soluble or water-dispersible polyester resin or acrylic resin for a film with relatively high polarity, typically a polyester film, has been proposed in Japanese Unexamined Patent Publication S54-43017, Japanese Examined Patent Publication S49-10243, Japanese Unexamined Patent Publications S52-19787 and S58-124651, and elsewhere. The effect of these prior art techniques, however, was inadequate in terms of improving adhesion.
In order to improve the adhesion of a polyester film, it has been proposed to use various modified polyester resins (mainly involving graft modification) as an anchor coating resin in Japanese Unexamined Patent Publications H2-3307, H2-171243, H2-310048, and H3-273015, Japanese Examined Patent Publication H3-67626, and elsewhere. Nevertheless, while adhesion is indeed increased by using the graft modified polyester resin as an anchor coating resin, a problem is that the adhesion is poor under wet conditions.
Accordingly, it has been proposed to increase adhesion under wet conditions by adding a crosslinking agent in Japanese Examined Patent Publications H5-744633, H6-24765, H6-39154, and H6-39548 and elsewhere.
The use of such crosslinking agents improves adhesion under wet conditions. Nevertheless, during the manufacture of a polyester film when the film which does not become a finished product, i.e., scrap film, is melted and molded into pellets and reused as a film raw material, the resulting film is so low in quality as to make such reuse impractical. Therefore, even though such a coated polyester film has excellent water resistance and adhesion, the scrap film that does not become a finished product during film manufacture is discarded, or used for limited applications or added in a small amount. This increases production cost and also poses a problem from the standpoint of the environmental load imposed by the scrap film.
Other problems are that under the high-temperature environment encountered during or after processing to the film in optical applications and so forth, the film whitens and loses transparency, or microscopic bumps form on its surface. This film whitening and the formation of microscopic surface bumps occur when crystals of polyester oligomer in the film precipitate at the surface.
As a method for suppressing oligomer precipitation at the film surface, it has been proposed to use a polyester with a low oligomer content manufactured by solid phase polymerization (Japanese Unexamined Patent Publications S55-89330 and S55-189331), or to cover a film surface with a polyester having a low oligomer content (Japanese Unexamined Patent Publication H11-300918), etc. However, adhesion, water resistance and recoverability cannot all be improved by these methods alone, and even if these methods are combined with a known coating film technique, it is still impossible to obtain a laminated polyester film whose adhesion, water resistance, recoverability, and resistance to whitening due to heating are all excellent.
Thus, it is an object of the present invention to solve the above-mentioned problems encountered with prior art, and provide a laminated polyester film whose adhesion, water resistance, recoverability, and resistance to whitening due to heating are all excellent.
SUMMARY OF THE INVENTION
The present invention was accomplished in light of the above situation, and the laminated polyester film with which the stated object can be achieved is as follows.
The first invention of the present invention is a laminated polyester film prepared by forming a coating layer comprising as main constituent component a water-soluble or water-dispersible resin on at least one side of a polyester film, the laminated polyester film having a water resistance value of at least 90%, a discoloration value after melt molding of not more than 10, and a haze value change after heating of not more than 20%.
The second invention is the laminated polyester film according to the first invention, wherein the water-soluble or water-dispersible resin is one or more resins or a copolymer resin comprising two or more resins selected from the group consisting of aqueous acrylic resins with an acid value of at least 200 eq/t and aqueous aromatic polyester resins.
The third invention is the laminated polyester film according to the second invention, wherein the water-soluble or water-dispersible resin contains at least 5 wt % of a radical polymer of at least one monomer comprising an acid anhydride containing a double bond.
The fourth invention is the laminated polyester film according to the first, second, or third invention, wherein the coating weight of the coating layer after drying is 0.01 to 1.0 g/m
2
.
The fifth invention is the laminated polyester film according to the first invention, wherein the film is used for printing applications.
The sixth invention is the laminated polyester film according to the first invention, wherein the film is used as a substrate film for an optical component.
Function
The laminated polyester film of the present invention needs to have a water resistance value at the coating layer surface of at least 90%, with 95% or higher being preferable. If the water resistance value is less than 90%, the adhesion under wet conditions would be inadequate when an ink layer is formed on the coating layer surface of the laminated polyester film. The water resistance value is defined as follows in the present invention. The coating layer surface of the laminated film is coated with a UV-cured sealed ink, and after UV curing, a boiling treatment under pressure is performed for 1 hour at 120° C., and then the peel test according to JIS K 5400 is conducted. The water resistance value defined as the percent area (%) of the remaining ink which is not peeled off.
The laminated polyester film of the present invention needs to have a discoloration value after melt molding of not more than 10. If the discoloration value is over 10, there will be a marked drop in film quality when recovered pellets are used as a film raw material.
The “discoloration value after melt molding” as defined in the present invention is a parameter expressed by the difference in the color b value between a pellet obtained by the melt molding of a laminated polyester film, and the laminated polyester film prior to this melt molding.
More specifically, the laminated polyester film is cut into strips and dried under reduced pressure, and the strips are melt extruded at a temperature of 280° C. with a model test apparatus, and the extrudate is cooled in water and then cut into pellets. These pellets will hereinafter be referred to as “recovered pellets”. The color b values of the recovered pellets and of the laminated polyester film prior to the test are measured, and the difference between the two values is defined as the discoloration after melt molding. The “color b value” refers to the b
Higashiura Shinya
Morishige Chikao
Satoh Masayoshi
Taki Hiroshi
Chen Vivian
Kenyon & Kenyon
Toyo Boseki Kabushiki Kaisha
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