Polyamide resins and process for producing the same

Details Polyamide resins and process for producing the same Polyamide resins and process for producing the same

2002-07-11

2004-06-15

Hampton-Hightower, P. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

C528S170000, C528S332000, C528S335000, C528S336000, C528S340000, C528S329100

Reexamination Certificate

active

06750318

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to polyamide resins produced by the polycondensation of a dicarboxylic acid component and a diamine component, and more particularly to polyamide resins with the content of specific impurities being reduced so as to have an excellent moldability and processability.
BRIEF DESCRIPTION OF THE PRIOR ART
Polyamide resins generally contain a certain amount of impurities, typically water. Other impurities include cyclic or linear monomers and their oligomers such as dimers and trimers which are by-produced during the polymerization operation and included into resulting polyamide resins. When impurities accompanied with monomers do not take part in the amidation reaction, the impurities remain as such in resulting polyamide resins without being incorporated into the polyamide backbone chains.
These impurities contained in polyamide resins cause various problems upon molding and processing. For example, dirt adhesion on a mold, sink mark on molded articles and surface roughening of molded articles generally called as silver surface occur in injection molding process. In extrusion process, burning of die, surface roughening of molded articles and deposition of low-molecular substances on the surface of molded articles generally called as bleeding are caused. In the production of fibrous articles, yarn breakage and variation in yarn diameter occur.
The impurities cause other inconveniences during the molding and processing steps and adversely affect the resulting molded and processed products by accelerating yellowing during molding and processing steps, accelerating yellowing with time, decreasing the melt viscosity stability, deteriorating properties of molded articles, and contaminating packaged contents by elution. Thus, it has been required to minimize the amount of impurities in polyamide resins.
Water is highly compatible with polyamide resins and can be present in molten polyamide resins at a certain ratio. When the amount of water is controlled to the saturation amount to polyamide resin at the molding temperature or to a lower amount, water does not cause fatal problem to the molding and processing steps while the melt viscosity is slightly affected. Impurities being vaporized around at the molding temperature of polyamide resins, however, are largely responsible for the inconveniences described above, because such impurities are easily separable from polyamide resins. Therefore, it is desirable to minimize the content of such impurities. In particular, impurities such as alcohols, aldehydes and nitrites, which are likely to be accompanied with the starting monomers for polyamide resins, are less reactive with polyamide resins and are separated from polyamide resins without incorporated into the polyamide resin backbone chains during the melt polymerization or melt molding process, resulting in various inconveniences during the molding and processing steps. Therefore, the removal of these impurities should be fully considered.
In the production of polyamide resins of nylon 6 type by the polymerization of aminocarboxylic acids or lactams, an extraction operation for removing cyclic oligomers is conducted after the polymerization, generally using a hot-water extraction column. Polyamide pellets are fed into an upper portion of the extraction column, brought into a counter flow contact with a hot water fed from the bottom thereof, and then continuously removed from a lower portion of the extraction column. After the extraction procedure, the polyamide resins are dried to obtain a final product. By this extraction procedure, a considerable part of linear oligomers and impurities accompanied with monomers are removed together with the cyclic oligomers. Japanese Patent Application Laid-Open No. 60-101120 discloses a method in which the removal of unreacted monomers from nylon 6 resins and the post-polymerization are simultaneously conducted.
Unlike the production of polyamide resins of nylon 6 type, the above extraction procedure is generally not employed in the production of polyamide resins comprising a diamine component and a dicarboxylic acid component because of a smaller amount of low-molecular substances such as cyclic oligomers. Although the extraction procedure for removing impurities as employed in the production of polyamide resins of nylon 6 type is also very effective to improve the quality, such an extraction procedure has been omitted from economical viewpoints.
The impurities accompanied with monomers also can be removed during the preparation of nylon salt solution by a method including the precipitation of nylon salts by the addition of methanol, etc. and the subsequent separation by filtration. This procedure, however, leads to economically large burdens. In addition, with recent improvement in the purity of monomers, this procedure is generally omitted.
Accordingly, it has been demanded to develop polyamide resins with their impurities being efficiently removed, preferably by a low-cost method.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a high-quality polyamide resin produced by the polycondensation of a dicarboxylic acid component and a diamine component mainly comprising m-xylylenediamine and bisaminomethylcyclohexane, which is suitable for various applications such as molding materials, bottles, sheets, films and fibers.
As a result of extensive research, the inventors have found that the above object is achieved by a polyamide resin that is minimized in the content of impurities, especially impurities having a limited boiling point and a limited solubility parameter (SP). The present invention has been accomplished on the basis of this finding.
Thus, the present invention provides a polyamide resin produced by the polycondensation of a dicarboxylic acid component and a diamine component containing xylylenediamine and bisaminomethylcyclohexane in a total amount of 70 mol % or higher, wherein a total content of impurities having a boiling point of from 150 to 300° C. under ordinary pressure and a solubility parameter (SP) of from 8 to 16 is 0.3% by weight or lower based on the weight of the polyamide resin.
DETAILED DESCRIPTION OF THE INVENTION
The diamine component as a starting monomer of the polyamide resin contains xylylenediamine and bisaminomethylcyclohexane in a total amount of 70 mol % or more. Examples of the xylylenediamine include m-xylylenediamine, p-xylylenediamine and o-xylylenediamine. Examples of the bisaminomethylcyclohexane include 1,2-bisaminomethylcyclohexane, 1,3-bisaminomethylcyclohexane and 1,4-bisaminomethylcyclohexane. These diamines may be used alone or in combination of two or more. When the xylylenediamine is predominantly used, the diamine component preferably contains m-xylylenediamine in an amount of 50 mol % or more, more preferably 70 mol % or more from the standpoint of useful properties of the resulting polyamide resins. When the bisaminomethylcyclohexane is predominantly used, the diamine component preferably contains 1,3-bisaminomethylcyclohexane in an amount of 50 mol % or more, more preferably 70 mol % or more from the standpoint of useful properties of the resulting polyamide resins.
Examples of the other diamine components include tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, o-phenylenediamine, m-phenylenediamine and p-phenylenediamine.
Examples of the dicarboxylic acid component include succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, isophthalic acid, terephthalic acid, phthalic acid, and 2,6-naphthalenedicarboxylic acid. These dicarboxylic acids may be used alone or in combination of two or more. From the standpoint of useful properties of the resulting polyamide resins, 70 mol % or more of the dicarboxylic acid component is preferably adipic acid. As the components of the polyamide resins other than the diamine component and the dicarboxylic acid component, there may be used lactams such as caprolactam, v

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