Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
1999-10-09
2002-02-19
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S480000, C428S483000, C428S903300, C428S910000, C526S258000, C526S260000
Reexamination Certificate
active
06348267
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a coated film. More particularly, it relates to a stretched polyester film having novel coating layer and showing excellent transparency, gloss, anti-block properties and adhesiveness.
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 adhesiveness, which is a problem common to the plastic films in general. For instance, the polyester films have poor adhesiveness 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.), topcoating 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.).
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. 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 adhesiveness in some way or other, but on the other hand, it is causative of the phenomenon of the films sticking to each other (so-called “blocking”). In order to prevent such blocking and to improve adhesiveness, a crosslinking agent is further added in many cases.
Generally, the coating layer is hardened when a crosslinking agent is added. 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 adhesiveness to the topcoats, 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.
Therefore, in production of the coated and stretched polyester films, there is required incorporation of a crosslinking agent which is capable of satisfying the above-said antagonistic requirements simultaneously. As this type of crosslinking agent, the oxazoline-based crosslinking agents (for instance, those disclosed in Japanese Patent Publication (KOKOKU) No. 8-2979) have generally been known, but the desired properties can not be obtained when these crosslinking agents are simply applied to the method in which coating is performed in the polyester film forming process.
As a result of the present inventors' earnest studies to solve the above problem, it has been found that by forming a coating layer on a polyester film by applying on the film a coating solution containing a copolymer comprising (meth)acrylonitrile, styrene and an oxazoline-containing monomer, the above problem can be solved.
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 which has excellent transparency and glossiness of the coating layer and also is excellent in adhesiveness and anti-block properties.
To attain the above aim, in the first aspect of the present invention, there is provided a coating film comprising:
a polyester film and
at least one coating layer formed by coating a coating solution containing a polymer (A) comprising a copolymer of oxazoline group-containing monomer, (meth)acrylonitrile and styrene, having an equivalent weight of oxazoline group of less than 300 g/equivalent, and drying and stretching thereof.
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 projections by the particles. That is, the effect of improving the slip characteristics may not be provided unless the particles are contained in large quantities, but on the other hand, mechanical properties o
Chen Vivian
Conlin David G.
Dike, Bronstein, et al. of Edwards & Angell
Sharp Kabuhsiki Kaisha
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