Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2000-06-12
2002-06-11
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S480000, C428S483000, C428S520000, C428S903300, C428S910000, C526S258000, C526S260000, C525S123000, C525S165000, C525S175000, C525S176000, C525S203000
Reexamination Certificate
active
06403224
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a coated film, more particularly, it relates to a stretched polyester film having a novel coating layer with excellent transparency, gross, adhesion to aqueous overcoating and anti-block properties.
Since stretched polyester films have excellent properties such as mechanical strength, dimensional stability, flatness, smoothness, heat resistance, chemical resistance and transparency, they have been widely used as a base film of magnetic recording medium, a film for printing, magnetic card, synthetic paper, etc.
While the polyester films have such excellent properties, they are poor in adhesion, which is a problem common to the plastic films in general. For instance, the polyester films have poor adhesion to printing inks (printing ink for cellophane, chlorinated PP ink, ultraviolet curing ink, magnetic ink, etc.), thermal transfer ink, magnetic coatings, adhesives (laminating adhesives, wood adhesives, etc.), overcoating materials (releaser, ink image receiving layer, gelatin, polyvinyl alcohol, polyvinyl acetal, cellulose acetate, cellulose butyroacetate, methyl cellulose, carboxymethyl cellulose, etc.), and deposited metals and inorganic materials (aluminum, silver, gold, ITO, silicon oxide, aluminum oxide, etc.). In recent years, attention has been focused especially on aqueous overcoatings (including ink) for lessening environmental contamination.
As a method of solving the above problem, it is known to provide a coating layer on the polyester film surface. Especially the method in which coating is conducted in the course of the film forming process is preferable in view of economic and characteristics thereof. This technique is called “in-line coating.” In a typical instance of this method, coating is conducted after longitudinal stretching and before transverse stretching, and then transverse stretching and heat setting are conducted. In-line coating, as compared with the conventional coating method in which coating is conducted outside the film producing process (this method being hereinafter called off-line coating), is capable of thin coating and allows dry heat treatments at high temperatures without impairing flatness of the film. Therefore, even when a coating with high adhesion is achieved, the tendency of the films to stick to each other (so-called blocking or sticking) is attenuated.
Various types of compounds including polyesters, poly(meth)acrylates, polyurethanes, polyvinylidene chloride, polyolefins and silane coupling agents can be used as the coating compounds. Coating with these compounds provides, in many cases, improvement of adhesion in some way or other. However, there are presently available only a few coating formulations which manifest satisfactory adhesion to aqueous overcoatings (including ink). Also, such undercoat tends to absorb moisture to become sticky.
Incorporation of a crosslinking agent in the coating composition is considered an effective way for reducing stickiness or blocking tendency, but generally addition of a crosslinking agent induces hardening of the coat. So, there arises a problem of a stretching conformability of the coating layer especially when the film is stretched after coating such as mentioned above. More specifically, if the coating layer is poor in stretchability, it fails to be stretched uniformly and may be fractured finely in the polyester film stretching step, thus forming microcracks in the coating layer in many cases. Such cracks in the coating layer cause such defects as reduction of adhesion to the overcoats, etc., and clouding of the coating layer due to scattering of light by fine unevenness of the coating layer surface. Thus, the problem arises that even when the base polyester film is not transparent, glossiness of the film surface lowers. No formulation that can satisfy these contradictory requirements—betterment of transparency and reduction of stickiness—has yet been found.
As a result of the present inventors' earnest studies to solve the above problem, it has been found that the above problem can be solved by providing a coated film having a coating layer formed by a coating solution containing a polymer having oxazoline groups. The present invention has been attained on the basis of the above finding.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a polyester film with excellent transparency of the coat, surface gross, adhesion to aqueous overcoating and blocking resistance.
To attain the above aim, in an aspect of the present invention, there is provided a coated film comprising:
a polyester film,
a coating layer on the said polyester film formed by applying a coating solution containing a polymer (A) having oxazoline groups on the surface of said polyester film, then drying and stretching the film, and
a overcoat layer (topcoat layer) on the said coating layer formed by applying an aqueous coating solution.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
The polyester constituting the polyester film of the present invention is the one obtained by using an aromatic dicarboxylic acid or an ester thereof and a glycol as the main starting materials. Examples of the preferable polyester have not less than 70% of the recurring structural units of ethylene terephthalate units, ethylene-2,6-naphthalate units, 1,4-cyclohexane terephthalate units or ethylene isophthalate units, and are especially preferably polyethylene terephthalate and polyethylene-2,6-naphthalate. It may contain other components as far as the above condition is met.
As the aromatic dicarboxylic acid, it is possible to use, for example, terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, phthalic acid, adipic acid, sebasic acid, oxycarboxylic acids (such as p-oxyethoxybenzoic acid) and the like either singly or as a mixture of two or more of them. As the glycol, ethylene glycol, diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, polyalkylene glycol and the like can be used either singly or as a mixture of two or more of them.
The intrinsic viscosity of these polyesters is usually not less than 0.45, preferably in the range of 0.50 to 1.0, more preferably 0.52 to 0.80. When the intrinsic viscosity is less than 0.45, there may arise the problems such as reduced productivity in manufacture of the film and reduced mechanical strength of the produced film. On the other hand, it is preferable that the intrinsic viscosity does not exceed 1.0 in view of melt extrusion stability of the polymer.
In the polyester film of the present invention, it is possible to contain the particles in the polyester so as to form appropriate projections on the film surface to provide proper slip characteristics to the film to thereby improving its handling qualities. Examples of such particles usable in the present invention include the inorganic particles such as the particles of calcium carbonate, calcium phosphate, silica, kaolin, talc, titanium dioxide, alumina, barium sulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, etc., the organic particles such as the particles of crosslinked polymers, calcium oxalate, etc., and the precipitated particles produced in polyester polymerization.
The size and amount of the particles to be contained in the film in the present invention, although variable depending on the purpose of use of the film, are generally as described below. The average particle size is preferably in the range of 0.005 to 5.0 &mgr;m, more preferably 0.01 to 3.0 &mgr;m. When the average particle size exceeds 5.0 &mgr;m, the film surface is roughened to an excess degree. Also, in a thin film, the insulating performance may deteriorate. Further, the particles become liable to fall off the film surface, causing so-called “drop-off of particles” in use of the film. When the average particle size is less than 0.005 &mgr;m, the effect of improving the slip characteristics of the film tends to lower because of insufficient formation of the
Okajima Nariaki
Shimizu Yoshio
Chen Vivian
Edwards & Angell LLP
Mitsubishi Polyester Film Corporation
Neuner George W.
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