Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Patent
1997-02-03
1999-02-23
Hampton-Hightower, P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
528322, 528332, 528335, 528336, 528348, 428357, 428364, 428395, 4284745, 264184, 264212, 264216, C08G 7310
Patent
active
058745190
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a shaped article made of a para-oriented aromatic polyamide (hereinafter called "para-aramid") of which a representative material is poly(para-phenyleneterephthalamide) (hereinafter called "PPTA") and the preparation thereof, and it particularly relates to para-aramid shaped articles having improved hygroscopic properties and the preparation of the same.
BACKGROUND OF THE INVENTION
A para-aramid is a polymeric material with excellent crystallinity and excellent resistance to heat. Preparations of para-aramid and PPTA films are disclosed PPTA films in U.S. Pat. No. 4,857,255 and U.S. Pat. No. 4,752,643, and para-aramid films composed of a para-aramid consisting of aromatic rings having a nuclear substituting radical are disclosed in Japanese Unexamined Patent Publications No. 58-42649, No. 59-45124, and No. 62-70421.
In the meantime, there are proposed preparations of para-aramid fibers in U.S. Pat. No. 3,819,587, No. 3,767,756, No. 3,869,429, No. 4,016,236, No. 4,419,317, and No. 4,374,978. These known para-aramid shaped articles have generally excellent mechanical properties and heat resistance properties. Accordingly, applications of the shaped articles have been attempted in various fields of use. It has been a problem, however, that para-aramid shaped articles exhibit a great moisture absorption and a high hygroscopic expansion coefficient. A para-aramid shaped article tends to suffer a dimensional change due to moisture absorption (hygroscopic absorption). Problems are encountered in various applications of the shaped articles; for example, a composite material made of PPTA fiber will exhibit crack formation, which results from a repetition of moisture absorption-desorption cycles, and applications of the film as a high-density magnetic recording medium, high-density printed circuit, or the like, will exhibit problems, because the film is required to exhibit dimensional stability.
There have been proposed attempts to obtain PPTA films having improved hygroscopic properties by promoting orientation and crystallization of PPTA by means of extensive heat treatment and/or stretching in Japanese Unexamined Patent Publications No. 62-246719 and No. 6-136156. In Japanese Unexamined Patent Publication No. 62-246719, for example, a process for preparing a film is described where a raw film obtained through coagulation and washing is treated by heating under tension at 300.degree.-500.degree. C. Although application of heat-treatment at high temperature in the known processes can produce films having a low coefficient of hygroscopic expansion, the heat treated films have excessively reduced elongation and tend to become brittle. Satisfactory improvement of films in hygroscopic expansion coefficient cannot be obtained by these known processes when elongation of the films must be maintained at a desired level.
In order to prevent deterioration of the mechanical properties of film during heat-treatment, an acid component contained in a shaped article after coagulation should be removed as completely as possible, not only in the case where a film is cast directly from a polymerization reaction mixture obtained by polymerizing a diacid chloride with a diamine, but also in the case where a film is cast from a dope prepared by dissolving a polymer separated from the reaction mixture in a strong inorganic acid, such as concentrated sulfuric acid. It is noted that satisfactory removal of an acid component in a shaped article cannot be successfully accomplished only by conventional washing with water or warm water. In Japanese Unexamined Patent Publication No. 50-102650, for an example, there is described a preparation of a film containing 500 ppm or less of an ionic inorganic compound by washing. However, deterioration of the mechanical properties of the film tends to occur when heat is applied to the film during film making or in the event of application, since a minute amount of acid, either derived from the acid generated during polymerization or introduced into a
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Kasatani Hideo
Nishimura Satomi
Asahi Kasei Kogyo Kabushiki Kaisha
Hampton-Hightower P.
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