Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2000-02-11
2001-10-16
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
Reexamination Certificate
active
06303741
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a solid phase-polymerized polyamide suitable for various applications such as bottles, sheets, films, fibers or the like. More particularly, the present invention relates to a solid phase-polymerized polyamide produced by a step of melt-polycondensing a diamine component composed mainly of m-xylylenediamine with a dicarboxylic acid component composed mainly of adipic acid, and a subsequent step of heating the resultant polyamide while keeping it in solid phase. The solid phase-polymerized polyamide according to the present invention is a medium- to high-viscosity polyamide containing gels or fish eyes in extremely small amount, in which the increase in the molecular weight (increase in viscosity) is achieved by linear molecular growth mainly due to amide bond formation during the solid phase polymerization. Also, the solid phase-polymerized polyamide according to the present invention is a medium- to high-viscosity polyamide containing gels or fish eyes in extremely small amount and having a uniform polymerization degree, which is produced using a batchwise heating apparatus.
BACKGROUND OF THE INVENTION
Generally, polyamides for molding materials have been molded into shaped articles by injection molding or the like. Therefore, polyamides have been required to have a high fluidity upon melting, i.e., low viscosity polyamides have been used as the molding materials. However, when applied to production of bottles, sheets, films, fibers or the like, polyamides are molded into shaped by extrusion in addition to injection molding. Therefore, the polyamides for use in these applications are required to have a lower fluidity than those of the polyamide for use as the molding materials, and medium- to high-viscosity polyamides have been used.
As low-viscosity polyamides to be used mainly as the molding materials, polyamides obtained by melt-polycondensation have been used directly or after drying. However, when it is intended to obtain medium- to high-viscosity polyamides applicable to production of bottles, sheets, films, fibers or the like by the melt-polycondensation, a special polymerization reactor is needed to keep the contents in a polymerization reactor in uniform molten state, because ordinary agitators cannot produce agitating force sufficient for maintaining the uniform molten state. Further, when the polycondensation is continued until a low-viscosity polyamide is converted to a medium- to high-viscosity polyamide, the time required for maintaining the molten state (reaction time) is considerably prolonged. As a result, there arises damage of polyamide molecules (deteriorated polymer molecules due to generation of radicals), or occurrence of aberrant reactions such as non-linear molecular growth (production of three-dimensional polymers), thereby increasing the amount of gels and fish eyes which causes disadvantages in practical use. If such polyamides containing a large amount of gels and fish eyes are used for production of bottles, sheets, films, fibers or the like, defective products occur with extremely high frequency, resulting in deteriorated productivity. Even though a filter is used upon molding, it is difficult to completely remove gels and fish eyes from polyamides. Further, the filter must be replaced with new ones more frequently, this reducing the continuous production run. Therefore, it is desirable that the amount of gels and fish eyes in polyamides is as small as possible.
It is known that medium- to high-viscosity polyamide containing gels or fish eyes in small amount can be obtained by producing low-viscosity polyamide by melt-polycondensation, and then heat-treating the resultant low-viscosity polyamide in solid phase (so-called solid phase polymerization). The difference in the amounts of gels or fish eyes between melt-polycondensation and solid phase polymerization is attributable to the difference in the frequency of occurrence of damages to polyamide molecules and aberrant reactions due to different reaction temperatures. Thus, medium- to high-viscosity polyamide obtained by solid phase polymerization contain gels or fish eyes in smaller amount as compared with those obtained only the melt-polycondensation. However, in the production of bottles, sheets, films, fibers or the like, the productivity of these products is considerably affected even when gels or fish eyes are present in slight amounts. Therefore, it has been demanded to further reduce the amounts of gels or fish eyes in solid phase-polymerized polyamides.
Gels or fish eyes are formed not only during the production of polyamides but also during the melting for molding polyamides into shaped articles. Even though polyamides show no considerable difference in the amounts of gels or fish eyes, molded articles contain, in some cases, different amounts of gels or fish eyes. One reason therefor may be that slight differences in damages to polyamide molecules and slight differences in the occurrence of aberrant reactions, which are not detected just after the production of polyamides, are increased by stagnation of polyamides in filter, molding die, etc. during the molding process. Thus, to obtain molded articles containing gels or fish eyes in small amounts, it is necessary to design a special molding apparatus having few stagnating portions where polyamides are retained not flowing. Simultaneously, it is essentially required to produce high-quality polyamides by preventing damages to molecules and aberrant reactions in melt-polymerization and solid phase polymerization.
Amorphous polyamide granules, i.e., granules of poly-m-xylylene adipamide having a crystallinity of not more than 13% transfer from amorphous state to crystalline state when heated to a temperature higher than a glass transition temperature. The amorphous polyamide granules abruptly become tacky when heated to near the glass transition temperature, and remain tackiness until the polyamide is crystallized. Solid phase polymerization is effected by the heat transferred from a heating medium kept at a temperature higher than that of the polyamide. When polyamide granules fail to move freely and stagnate in the vicinity of heat transfer surface of inner wall of a heating apparatus, the polyamide granules tackifiedly stick to the wall surface of the heating apparatus. Also, the polyamide granules tackifiedly stick to each other to form massive granules. When the tackifiedly stuck granules are crystallized without disintegration, there arises disadvantage of solidified sticking of the granules. If solid phase polymerization is continued after crystallization without disintegration of the solidified sticky massive granules, solid phase-polymerized polyamides having a uniform degree of polymerization cannot be obtained. In addition, damages to polyamide molecules and aberrant reactions are likely to occur due to partial heating, thereby inducing the formation of gels or fish eyes.
To avoid the above disadvantages, there have been generally employed the following processes in subjecting amorphous polymers to solid phase polymerization:
(a) Batchwise process where polymer is heated gently in a batchwise heating apparatus such as a rotary drum in an inert gas atmosphere or under reduced pressure, thereby crystallizing the polymer while avoiding the tackified sticking of the polymer granules, and then further heating the polymer in the same heating apparatus to carry out solid phase polymerization;
(b) Continuous process where the polymer is heated in a channel stirring heating apparatus in an inert gas stream to crystallize the polymer (pre-crystallization), and then the crystallized polymer is subjected to solid phase polymerization in a hopper heating apparatus in an inert gas stream.
(c) Semi-continuous process where the polymer is crystallized in a channel stirring heating apparatus, and then the crystallized polymer is subjected to solid phase polymerization in a batchwise heating apparatus such as a rotary drum.
The following problems arise when solid phase polymerization of an
Antonelli Terry Stout & Kraus LLP
Hampton-Hightower P.
Mitsubishi Gas Chemical Company Inc.
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