Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Patent
1995-06-05
1998-07-21
Hampton-Hightower, P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
528125, 528128, 528183, 528184, 528185, 528189, 528310, 528321, 528332, C08G 6932, C08G 6936
Patent
active
057836558
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a process for preparing aromatic polyamide pulp. More particulary, the invention relates to a process for the preparation of polyamide pulp having both excellent physical properties and a high degree of polymerization wherein an aromatic diamine is reacted with aromatic diacid dichloride in an amide and/or urea-based polymerization solvent containing inorganic salts, or a mixture of inorganic salts and a Lewis acid compound.
BACKGROUND ART
U.S. Pat. No. 4,511,623 discloses a process for preparing an aromatic polyamide using solvent mixture of comprising inorganic salts wherein a tertiary amine is added into the amide solvent system.
According to this method, polyamide fibers are prepared by adding tertiary amines prior to polymerization and applying a high mechnical shear rate at the moment gelation is achieved, thus rapidly increasing the rate of polymerization and producing a high degree of orientation and a high degree of polymerization.
But, because U.S. Pat. No. 4,511,623 adds the amide solvent and excess tertiary amines simultaneously, and adds the diacid dichloride all at once, the viscosity of the reaction mixture suddenly increases while polymerization is occurring. Accordingly, polymerization is rapidly terminated (within 10 seconds) and control of the process becomes very difficult. In fact, it is impossible to continuously produce fibers, particularly fibers having a high degree of polymerization which can take 5 hours.
In order to overcome the problems of the prior art the present inventors discovered a process for producing pulp comprising extruding a liquid crystalline pre-polymer (LCP) through an orientation unit, spraying, and contact with a tertiary amine solvent system (e.g., Korean published patent 90-4911). However, because gelation of polymer solution in this process is initiated by the wall surface of the orientation unit the orientation unit becomes clogged, and control of the process becomes difficult.
U.S. Pat. No. 5,106,560 discloses a process for the preparation of pulp by providing a polymerization solution of diacid dichloride, diamine and inorganic salts in an amide solvent system, followed by pouring the solution on a inclined support to provide orientation by means of gravity-induced shear forces. However, by using natural gravity molecular orientation it is impossible to produce pulp having a high degree of orientation.
U.S. Ser. No. 07/87,565 (filed Apr. 28, 1992 by the present inventors) discloses a method wherein an anisotropic polymerizing solution is continuously ejected into container, where it remains to mature. Unfortunately, this method has the same drawback as U.S. Pat. No. 5,106,560 which provides orientation by means of gravity-induced shear forces in that a relatively low degree of orientation is achieved.
When an anisotropic polymerization solution having low inherent viscosity is ejected according to U.S. Ser. No. 07/87,565, the properties of the final product are poor, and it takes approximately 0.5.about.5 hrs to increase the inherent viscosity and degree of orientation of the polymerizing solution. Similarly, the degree of molecular orientation obtained by means of gravity shear is lower than that obtained by means of stirring, which results in decreased fibril growth in the final pulp and an increase in the time required for growth of fibrils having acceptable specific surface areas due to the low degree of orientation. Further, the properties of final product (e.g., as friction materials or gaskets) which are made from such a final pulp are poor.
Generally, in the case of friction materials containing fibers, the friction effect applied to a matrix is increased with an increase in the specific surface area of the fiber while the adhesion effect increases as the length of pulp increases; these behaviors are considered to be mutually compromising factors, and lead to the use of powders which have high friction efficiencies due to a high surface area but provide low material reinforcement.
Therefore, whe
REFERENCES:
patent: 5097015 (1992-03-01), Miess et al.
Choe Won Jun
Ji Chang Seop
Kim Du Hyun
Park Young Hwan
Ryu Seock Chul
Hampton-Hightower P.
Kolon Industries Inc.
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