Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1987-12-01
1989-01-17
Short, Patricia
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
428910, C08L 6702
Patent
active
047988754
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a biaxially oriented polyester film. More particularly, the present invention relates to a biaxially oriented polyester film having an excellent dimensional stability and a high elastic modulus, and suitable for use in the production of magnetic tapes and flexible printed circuit boards.
BACKGROUND ART
A biaxially oriented polyester film is used as the base of a magnetic tape or a flexible printed circuit board.
However, to obtain a labor-saving effect at the processing step in the production of a magnetic tape or a flexible printed circuit board, or with an increase of the height of the application object, the demand for a film having an enhanced elastic modulus and a further improved dimensional stability is increasing. However, although the elastic modulus of a biaxially oriented polyester film is increased by drawing in multiple stages in the film-forming process, the dimensional stability is degraded by this multiple-stage drawing. Attempts to improve the mechanical characteristics of the biaxially drawn polyester film by making the film from a blend of a polymer having a rigid polymer chain, such as an aromatic polyester having a melt anisotropy-forming capacity, with a polymer having a flexible polymer chain have been made. However, the mechanical characteristics are not improved because of an insufficient dispersion of the rigid polymer, and because the rigid polymer peels from the interface of the dispersed phase. Utilization can be made only in a product obtained by drawing a fiber made of a blend of a rigid chain polymer with a polyester to form voids in the interface of the dispersed phase, and thereby mat the film surface.
It is an object of the present invention to provide a polyester film having a high elastic modulus, a low thermal shrinkage and an excellent dimensional stability, in which the defects of the conventional biaxially oriented polyester film are overcome by finely dispersing a polymer having a rigid molecule chain in a polyester.
DISCLOSURE OF THE INVENTION
According to the present invention, this object is attained by providing a biaxially oriented polyester film composed mainly of a polyblend comprising [A] a polyester having recurring units of the following general formula (I): ##STR5## wherein n is 2, 4 or 6 and R is at least one member selected from the group consisting of ##STR6## in which X is H or Cl and at least one X is Cl, and [B] a copolyester having units represented by the general formula (I) and units represented by the following general formula (II) and/or the following general formula (III): ##STR7## wherein R.sup.I, R.sup.II and R.sup.III stand for at least one member selected from the group consisting of 1,3-phenylene, 1,4-phenylene, 2,6-naphthalene, 2,7-naphthalene, ##STR8## and having a flow-initiating temperature not higher than 350.degree. C. and a melt anisotropy-forming capacity, the molar ratio of the units represented by the general formula (II) and/or the general formula (III) being 0.5 to 18 mole % based on the total polyblend, wherein one plane of the crystal of the polyester [A] is plane-oriented in the film surface, the in-plane orientation index is 0.75 to 0.95, and the crystal size in said crystal plane direction is 35 to 75 .ANG..
BEST MODE FOR CARRYING OUT THE INVENTION
In the polyester [A] constituting the film of the present invention, which has the recurring units represented by the following general formula (I): ##STR9## n is an integer selected from the group consisting of 2, 4 and 6, but in view of the elastic modulus and thermal shrinkage of the film, a polymer in which n is 2 is especially preferred. In the general formula (I), R is selected from the group consisting of 1,4-phenylene, 2,6-naphthalene, ##STR10##
As specific examples of the structural units of the polyester [A], the following units (a) through (e) can be mentioned, but in view of the film characteristics, polymers having structural units (a), (b) or (c) are preferred: ##STR11## Other components may be copolymeri
REFERENCES:
patent: 4386174 (1983-05-01), Cogswell
patent: 4497865 (1985-02-01), Minami
patent: 4728698 (1988-03-01), Isayer
Horita Norihiro
Itoyama Kuniyoshi
Minami Satoyuki
Seki Shigemi
Miller Austin R.
Short Patricia
Toray Industries Inc.
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