Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Composite having voids in a component
Reexamination Certificate
1997-12-23
2001-10-23
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Composite having voids in a component
C428S319700, C428S336000, C428S341000, C428S480000, C428S910000
Reexamination Certificate
active
06306492
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a laminated polyester film having an improved adhesive property. More particularly, the present invention relates to a laminated polyester film exhibiting superior adhesive property as magnetic recording material, heat transfer recording material, sublimation transfer recording material, insulating material, photographic film, OHP film, mold releasing film, heat-sensitive recording material, heat transfer image receiving material, sublimation transfer image receiving material, ink jet image receiving material, offset printing plate, material for offset printing, pressure-sensitive recording paper, label, sticker, poster, card, various receiving materials for printers, various packaging materials, form printing paper, map, dust-free paper, display board, white board, electronic white board, printing paper, bottom label, wall paper, building material, bill, mold releasing paper, folding paper, calendar, magnetic card, tracing paper, slip, courier delivery slip, pressure-sensitive recording paper, copying paper, paper for clinical testing, parabolic antenna reflector, display reflector and the like.
BACKGROUND OF THE INVENTION
Biaxially stretched polyester films are superior in mechanical strength, heat resistance, chemical resistance and dimensional stability, so that they have been used in a wide range of applications, such as a base film for magnetic tape, an insulating tape, a photographic film, a tracing film, a food packaging film and the like. On the other hand, since polyester films generally have poor adhesive property, it is a common practice to subject a polyester film to a corona discharge surface treatment and to further form an anchor coating layer, when laminating thereon a layer of magnetic agent, photosensitive agent, mat agent and the like. As such anchor coating agent, a number of materials have been proposed, among which are water soluble or water dispersible polyester or acrylic resin to be used for a film having comparatively higher polarity, which is typically a polyester film (Japanese Patent Unexamined Publication Nos. 54-43017, Japanese Patent Examined Publication No. 49-10243 and U.S. Pat. No. 4,098,952). The above-mentioned polyester resin is defective in that a film having a layer made therefrom is susceptible to blocking when rolled, and the above-mentioned acrylic resin is defective in that it sometimes shows insufficient adhesion to a layer to be formed on the anchor coating layer. In an attempt to overcome these drawbacks, it is proposed to use the above-mentioned polyester resin and acrylic resin in mixture (Japanese Patent Unexamined Publication No. 58-124651), though such method does not always satisfactorily compensate for the drawbacks.
It has been also proposed to use various modified polyesters typically represented by one modified by grafting. For example, Japanese Patent Unexamined Publication Nos. 2-3307, 2-171243 and 2-310048 teach that a resin obtained by grafting a compound having an unsaturated bond to a water soluble or water dispersible polyester resin having a hydrophilic group is suitable as an anchor coating agent for a polyester film. Nevertheless, such a graft-modified resin, which has been made to have a hydrophilic group in advance in the polyester resin by, for example, copolymerization, is devoid of high adhesive property or water resistance.
In addition, Japanese Patent Unexamined Publication No. 3-273015 and U.S. Pat. No. 5,015,169 disclose that a graft-modified polyester resin is useful as an anchor coating agent for a polyester film. While such resin shows improved adhesive property in a dry state, it has poor cohesion, such that adhesive property under humidity becomes less and the film increasingly suffers from peeling off of a layer, development of flaws and the like, as the number of process increases.
It is therefore an object of the present invention to resolve the above-mentioned problems and provide a laminated polyester film having superior adhesive property, water resistance and resistance to blocking.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides the following laminated polyester films.
(1) A laminated polyester film comprising a polyester base film and a layer comprising a polyester graft copolymer and which is formed at least on one surface of said polyester base film, said polyester graft copolymer comprising a hydrophobic copolymerizable polyester resin and an acid anhydride having at least one double bond grafted to said polyester resin.
(2) A laminated polyester film comprising a polyester base film and a layer comprising a polyester graft copolymer and which is formed at least on one surface of said polyester base film, said polyester graft copolymer comprising a hydrophobic copolymerizable polyester resin and at least one polymerizable unsaturated monomer grafted to said polyester resin, wherein said layer has a hydrogen bonding component of the surface energy (&ggr;s
h
) of not more than 35 erg/cm
2
.
(3) The film of (1) or (2) above, wherein the polyester graft copolymer comprises a maleic anhydride.
(4) The film of (1) or (2) above, wherein the polyester graft copolymer comprises a maleic anhydride and a styrene.
(5) The film of (1) or (2) above, wherein the polyester graft copolymer has a glass transition temperature of not more than 30° C.
(6) The film of (1) or (2) above, which is formed by applying, to the base film, a coating solution comprising a polyester graft copolymer, thereby forming the layer comprising the graft copolymer, and then at least monoaxially stretching and thermally curing.
(7) The film of (2) above, wherein the &ggr;s
h
is not more than 20 erg/cm
2
.
(8) The film of (1) or (2) above, wherein the polyester base film is opaque white and has a light transmittance of less than 50%.
(9) The film of (8) above, wherein the opaque white polyester film has voids and an apparent specific gravity of not more than 1.3.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, by “being grafted” is meant introduction of a branched polymer distinct from the main chain polymer into the polymer main chain.
(Polyester Graft Copolymer)
The graft polymerization is generally performed by dissolving a hydrophobic copolymerizable polyester resin in an organic solvent, and allowing reaction of at least one kind of polymerizable unsaturated monomer by the use of a radical initiator with the polyester resin in the solution. The reaction product after completion of graft polymerization contains the desired graft copolymer of hydrophobic copolymerizable polyester and polymerizable unsaturated monomer, as well as ungrafted hydrophobic copolymerizable polyester resin and polymer of the above-mentioned unsaturated monomers that did not graft to the hydrophobic copolymerizable polyester. The polyester graft copolymer in the present invention means not only the above-mentioned polyester graft copolymer but also reaction mixture containing, in addition to said graft copolymer, unreacted hydrophobic copolymerizable polyester and polymer of unsaturated monomers that did not undergo grafting.
In the present invention, the polyester graft copolymer obtained by graft polymerization of at least one kind of polymerizable unsaturated monomer to hydrophobic copolymerizable polyester resin has an acid value of preferably not less than 600 eq/10
6
g, more preferably not less than 1200 eq/10
6
g. When the graft copolymer has an acid value of less than 600 eq/10
6
g, the adhesion between the layer containing the objective graft copolymer and a layer to be coated thereon becomes insufficient.
The weight ratio of hydrophobic copolymerizable polyester resin to polymerizable unsaturated monomer, which affords a desirable graft copolymer suitable for the object of the present invention, is preferably polyester/polymerizable unsaturated monomer=40/60-95/5, more preferably 55/45-93/7, and most preferably 60/40-90/10.
When the weight ratio of the hydrophobic copolymerizable polyester resin is less than 40 wt %, the obtai
Higashiura Shinya
Morishige Chikao
Sasaki Yasushi
Suzuki Toshitake
Yamada Koji
Morrison & Foerster / LLP
Thibodeau Paul
Toyo Boseki Kabushiki Kaisha
Zacharia Ramsey
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