Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-12-10
2004-02-24
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S409000
Reexamination Certificate
active
06696510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of art to which this invention relates is stabilized resin compositions, more particularly, to stabilized thermoplastic polyester compositions that contain antimony trioxide.
2. Description of the Prior Art
A variety of organophosphites, including for example, pentaerythritol phosphites as well as alkyl-, aryl-, arylalkyl- and alkylarylphosphites have been proposed as additives for thermoplastic polyesters and other polymers. These organophosphites (herein referred to as “conventional organophosphites”) generally function as secondary antioxidants and improve thermal-oxidative stability by scavenging hydroperoxides, the decomposition products of which otherwise attack and degrade polymer chains. Many of the conventional organophosphites are also known to function as transesterification inhibitors and, as such, are common additives to compositions containing a thermoplastic polyester and one or more thermoplastic polymers with which it can transesterify, e.g., other polyesters, polycarbonates, polyestercarbonates, and the like.
In the presence of moisture, the conventional organophosphites hydrolyze to an acid form that, in turn, attacks and degrades polymer chains. The acid form of the hydrolyzed phosphite is desirable in terms of promoting transesterification resistance, however, when antimony trioxide is present, the acid form of the hydrolyzed organophosphite can react with antimony trioxide producing what is believed to be a form of elemental antimony. This reduced form of antimony trioxide is gray in color. Thus, in the presence antimony trioxide, hydrolyzed organophosphites can undesirably darken a polymer's color, giving rise to problems with color uniformity, lot-to-lot color consistency, color matching, and the like. Hydrolyzed organophosphites may cause resin discoloration problems when even very low levels, i.e., catalytic amounts, of antimony trioxide are present.
The discoloration caused by many conventional organophosphites has limited their use in compositions in which antimony trioxide is present. Additionally, the hydrolysis products of many organophosphites, for example, stearyl alcohol in the case of distearyl pentaerythritol diphosphites, have been observed to impart a hazy or foggy appearance to thermoplastic polyester compositions, particularly when materials containing residual soaps, e.g., certain composite interpolymers, are present. Although reduced fogging may be achieved by lowering the level of hydrolysis-prone organophosphites, lower levels of such additives may not be sufficient to consistently provide effective transesterification inhibition and/or thermal-oxidative stability.
It is an object of this invention to provide effective thermal-oxidative stability to antimony trioxide-containing thermoplastic polyester compositions while minimizing discoloration and darkening attributable to the reduction of the antimony trioxide in molded parts made from same. It is a further object of this invention to provide effective transesterification resistance to compositions containing a thermoplastic polyester, one or more polymers with which it can transesterify, and antimony trioxide, while minimizing discoloration and darkening attributable to the reduction of antimony trioxide in molded parts made from same. It is a further object of this invention to provide an organophosphite that does not impart a hazy or foggy appearance to thermoplastic polyester compositions.
SUMMARY OF THE INVENTION
It has now been found that thiobisphenol phosphites of the type known as metal deactivators for polyolefins are effective thermal-oxidative stabilizers in antimony trioxide-containing thermoplastic polyester compositions. It has also been found that darkening and discoloration attributable to the reduction of antimony trioxide is minimized when such thiobisphenol phosphites are used in place of conventional organophosphites. These thiobisphenol phosphites have been found to be effective in inhibiting transesterification in compositions containing a thermoplastic polyester and one or more additional polymers with which it can transesterify. Additionally, such thiobisphenol phosphites do not impart a surface haze or fogging to thermoplastic polyester compositions.
In one embodiment this invention relates to a composition comprising:
(A) a thermoplastic polyester;
(B) antimony trioxide; and
(C) a thiobisphenol phosphite comprising at least one stearically hindered tris[(hydroxyphenylthio)phenyl]phosphite.
In another embodiment this invention relates to a composition comprising:
(A) a first polymer that is a thermoplastic polyester;
(B) a second polymer that can transesterify with said first polymer;
(C) antimony trioxide; and
(D) a thiobisphenol phosphite comprising at least one stearically hindered tris[(hydroxyphenylthio)phenyl]phosphite.
DESCRIPTION OF THE INVENTION
The thermoplastic polyesters useful in the subject compositions comprise one or more thermoplastic polymers that are the reaction product of an aromatic dicarboxylic acid and an aliphatic and/or cycloaliphatic diol. The aromatic dicarboxylic acids useful in the preparation of such thermoplastic polyesters include terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, diphenyldicarboxylic acid, and the like. As used herein the term “dicarboxylic acid” is intended to include the condensation polymerization equivalents of dicarboxylic acids, i.e., their esters or ester forming derivatives, such as acid chlorides, anhydrides, or other derivatives which behave substantially like dicarboxylic acids in a polymerization reaction with a diol. Optionally, the aromatic dicarboxylic acids are ring substituted with one or more substituent groups which do not interfere with polyester production such as, for example, C
1
-C
10
alkyl and alkyoxy groups, as well as aryl and halo groups. In one embodiment of interest, at least 80 mole percent of the aromatic dicarboxylic acid will comprise terephthalic acid or its corresponding dialkyl ester, e.g., dimethyl terephathalic acid.
The diols from which the thermoplastic polyesters are derived contain at least two carbon atoms. Such diols include, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,4-butenediol, 1,6-hexamethylene glycol, 1,6-dihydroxycyclohexane, diethylene glycol, triethylene glycol, and the like, and mixtures thereof. The diols can also include polymeric glycols. Equivalent ester-forming derivatives of the diols, e.g., ethylene oxide or propylene oxide or propylene carbonate, are also useful, and the term “diol” is herein understood to include same. Optionally, the diols are substituted with one or more substituent groups that do not interfere with polyester production. In the practice of this invention C
2
to C
15
diols are of particular interest. Preferred diols are ethylene glycol, 1,4-butane diol, and 1,6-hexamethylene glycol.
Preferred thermoplastic polyesters are poly(alkylene terephthalate)s, with poly(ethylene terephthalate) and poly(butylene terephthalate) being of particular interest. If branching is desired, the thermoplastic polyester may contain minor amounts of units derived from a branching agent such as, for example, trimethylol propane, pentaerythritol, trimethyl trimellitate, and the like.
The thermoplastic polyester used herein typically have molecular weights of from about 10,000 to about 100,000, with thermoplastic polyesters having molecular weights of from about 20,000 to about 50,000 being representative of polymers suitable for use in typical injection molding applications.
The thermoplastic polyesters are produced by conventional polymerization techniques such as are described, for example, in U.S. Pat. Nos. 2,465,319 and 3,047,539, which are incorporated herein by reference. Thermoplastic polyesters are available from a variety of sources including G.E. Plastics and Ticona, the engineering resins business of Celanese AG.
Antimony trioxide may be present in the subject compositions for one or more reasons. For example
Golder Michael
Lu Mengshi
Klumas Karen E.
Szekely Peter
Ticona LLC
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