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
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Manufacturing Materials 
