Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
1994-12-22
2001-02-20
Yoon, Tae (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S337000, C528S488000
Reexamination Certificate
active
06191251
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to polyamide resins having improved color and processibility and a process for manufacturing these resins. The polyamide resins prepared in accordance with the process of the present invention are particularly useful in molding and extrusion applications and are manufactured in the presence of certain phosphorus compounds in conjunction with certain bases.
An object of the present invention is to provide polyamide resins which initially appear less yellow than the same resins having not been manufactured in accordance with the present invention. A further object of the present invention is to provide polyamide resins which undergo a lesser degree of color build-up (i.e., increase in yellowness) on storage as compared to the same resins having not been manufactured in accordance with the present invention. Furthermore, an object of the present invention is to provide polyamide resins which do not undergo significant molecular weight increases during subsequent melt processing operations.
It is generally known that when polyamide resins are manufactured according to conventionally known processes without the addition of conventional pigments, these resins tend to exhibit varying degrees of yellowness in initial color, with said yellowness increasing over time. The resins also generally exhibit increased yellowness when exposed to high temperatures during subsequent melt processing operations. For example, during molding and extrusion applications, a certain amount of the resin is subjected to repeated melting in the form of regrind, which generally results in the molded or extruded resin exhibiting increased yellowness. Therefore, considering the extended storage time for some of these resins and the repeated melting during molding and extrusion, there exists a need to provide a process for manufacturing improved polyamide resins which initially appear, and continue to appear over time, less yellow than the same resins not prepared in accordance with the present invention.
Polyamide resins and their preparation are well known in the art. They can be obtained, for example, by self-polymerization of monoaminomonocarboxylic acids, or by reacting a diamine with a diacid in substantially equimolar amounts. It is understood that reference herein to the amino acids, diamines, and dicarboxylic acids is intended to include the equivalent amide-forming lactam derivatives thereof. Representative dicarboxylic acids include, for example, adipic acid, azelaic acid, pimelic acid, suberic acid, sebacic acid, dodecanedioic acid, isophthalic acid, and terephthalic acid, while representative diamines include, for example, hexamethylenediamine, octamethylenediamine, tetramethylenediamine, 2-methylpentamethylenediamine, decamethylenediamine, and dodecamethylenediamine. Representative amino acids include 6-aminocaproic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid. For purposes of this patent application, the above-identified compounds shall be referred to as “polyamide-forming reactants” and this term shall include combinations of the compounds, as well as individual compounds, provided the combination or individual compound can be polymerized to form polyamides.
It has now been observed that improved color (i.e., reduced yellowness) can be attained in polyamides by using certain phosphorus compounds. The phosphorus compounds serve as color stabilizers for the polyamides by reducing the degree of oxidative and thermal degradation. However, these phosphorus compounds also serve as polymerization catalysts and in addition, some serve as nucleating agents, as in U.S. Pat. No. 4,237,034. Nucleated polyamides generally have lower toughness compared to polyamides which have not been nucleated and thus, phosphorus compounds which function as nucleating agents are not particularly desirable in applications where a loss in toughness is not desired. To the extent that the phosphorus compounds act as polymerization catalysts, polyamides containing these phosphorus compounds, when remelted in an extruder or molding machine, undergo rapid polymerization resulting in molecular weight (RV) increases, particularly when the remelting is done under conditions of low moisture. These molecular weight increases consequently result in decreased melt flow of the polyamide in a molding machine or other apparatus. In molding and extrusion applications, generally, this decrease and change in melt flow of the polyamide is undesirable.
In the present invention, it has been found that the catalytic effect of certain phosphorus compounds on a polyamide polymerization process can be reduced or stopped completely by the addition therein of certain bases without significantly and adversely affecting the phosphorus compound's desired effect of reducing resin color. The degree to which the phosphorus compound, acting as a catalyst, is deactivated depends on the amounts of phosphorus and base added to the polymerization process or to the polyamide melt. For economical and efficient processing, some degree of catalytic effect is desired for increased throughput, especially when polymerization is conducted by a continuous mode process, which is, generally, a kinetically limited process.
SUMMARY OF THE INVENTION
A process has now been developed wherein certain phosphorus compounds, in conjunction with certain bases, are incorporated into polyamides either during the polymerization process or after, within the ranges described herein, resulting in polyamide resins that not only exhibit improved initial color and color stability on storage, but that also do not undergo significant molecular weight increases during subsequent melt processing operations, as compared to polyamide resins prepared without these phosphorus compounds and bases. Polyamide resins made by the process herein are useful in numerous molding applications (i.e., automobile parts, mechanical parts, electrical and electronic parts, molded gears, sports equipment, appliances, etc.) and extrusion applications (i.e., tubing, rods, filaments, films, etc.).
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a process for manufacturing polyamide resins, said resins being particularly useful in molding and extrusion applications. The polyamide resins prepared in accordance with the process of the present invention, as compared to polyamide resins not so prepared, exhibit improved initial color (i.e., reduced yellowness) and color stability on storage. Furthermore, the polyamide resins prepared in accordance with the process of the present invention do not undergo significant molecular weight increases during subsequent melt processing operations.
More specifically, the process of the present invention comprises polymerizing polyamide-forming reactants in the presence of certain phosphorus compounds in conjunction with certain bases. Alternatively, the process of the present invention comprises compounding into a polyamide melt certain phosphorus compounds in conjunction with certain bases. Polymerization processes are well known and can be, for example, batch or continuous mode processes. The polymerization processes contemplated by the present invention are those processes generally used to manufacture well known polyamides, such as nylons 6, 11, 12, 66, 69, 610, 612, and their copolymers from well known polyamide-forming reactants. The preferred polyamide-forming reactants to be used in the process of the present invention are those polyamide-forming reactants generally used to manufacture nylons 6, 66, 610 and 612.
The phosphorus compounds used in the process of the present invention, and their preparation, are well known in the art. These phosphorus compounds serve as color stabilizers and polymerization catalysts in nylons. They include phosphorous acids, their salts, and their organic esters. Examples of the phosphorous acids include hypophosphorous acid, orthophosphorous acid, pyrophosphorous acid, and diphosphorous acid. The phosphorous acid salts useful in the present invention incl
E. I. Du Pont de Nemours and Company
Yoon Tae
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