Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Patent
1996-04-24
1998-03-10
Hampton-Hightower, P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
528318, 528322, 528323, 525183, 525184, 525178, 525420, 525424, 525432, 524413, 524538, 524600, 524606, C08L 7700, C08G 7300
Patent
active
057262780
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a process for manufacturing a polyamide resin composition. Specifically, it relates to a manufacturing process which comprises adding a heat stabilizer to improve the heat stability and the weathering resistance of a polyamide and, at the same time, to suppress any significant change in color of the polyamide.
Incorporating an effective copper compound into a polyamide composition for improving the heat resistance and weathering resistance of the polyamide composition is a well-known method for preventing thermal oxidative degradation of said composition. Additives can be added to polyamide compositions at any stage before molding the polyamide composition into molded article. For example, one of the methods used to incorporate an additive into a polyamide composition involves dry blending the polyamide with the additive, followed by melt mixing and extruding the dry-blended product into pellets. Another known method for compounding an additive into a polyamide composition is to prepare master polyamide pellets, followed by blending these master pellets with dilution polyamide pellets.
However, the manufacture of a polyamide composition always requires attention to a reduction of the thermal history. A copper-type heat stabilizer may be incorporated into a polyamide composition by adding the heat stabilizer to a polyamide containing no heat stabilizer via an extruder or by adding the heat stabilizer to the polyamide during its polymerization. A comparison of the two methods shows that the latter provides a product with better color compared to the former so that heat stabilizers are, in general, added to polyamides during the polymerization thereof. With the attention that has been paid to the suppression of any change in the color of polyamide compositions, any post-polymerization additions, including additions to polyamides in the form of master pellets, have not been generally practiced heretofore.
The addition of an organic heat stabilizer to a polyamide composition has been found to not create any serious yellowing problem for the composition, but a copper-type heat stabilizer has been found to create a yellowing problem for the polyamide compositions, depending upon their heat history. It is further known that the addition of a copper-type heat stabilizer to a polyamide composition greatly changes the color thereof, the extent of which depends upon the amount of copper-type heat stabilizer added. Thus, the greater the amount of copper-type heat stabilizer added, the greater the degree of change in color in the resultant polyamide composition. FIG. 1 shows a relationship between the amount of the copper-type heat stabilizer added to a polyamide composition and the yellowing thereof. By "yellowing", it is meant the extent of yellowing experienced by a molded polyamide article, said yellowing being expressed by the value YI-C. The YI-C is measured on a sample of pellets or plates with an area of at least 5 cm.times.5 cm. Pellets in a glass cup are used for measurement. The measurement is possible with an area less than this range, but precision drops. The measurement is made by a differential color meter. The relationship between YI-C and color in terms of the absolute coordinates (X, Y, Z coordinates) is given for the following formula:
Based on the above, it is found that the greater the amount of the copper-type heat stabilizer added to the polyamide composition for improved heat stability, the greater the extent of yellowing thereof. When such a yellowed polyamide composition is used to prepare a molded article, a pigment or coloring agent is normally added for coloring the molded article. However, since the composition of the polyamide resin itself is yellowed with the incorporation of the above stabilizer, coloring the molded article to the desired color will require greater amounts of pigments or coloring agents. If a colored resin as obtained is to be colored in a different color, an inorganic pigment, such as titanium oxide, must be
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E. I. Du Pont de Nemours and Company
Hampton-Hightower P.
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