Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-03-27
2004-04-20
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S120000, C525S439000
Reexamination Certificate
active
06723768
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polyester/polycarbonate blends and more particularly, to such blends with reduced yellowness and with increased thermal and melt stability resulting from the catalyst utilized in the production of the polyester.
BACKGROUND OF THE INVENTION
Thermoplastic compositions and articles made from polyester/polycarbonate blends are known. For example, Research Disclosure 22921, May 1983, discloses blends of polycarbonate with polyesters based on terephthalic acid and a mixture of 1,4-cyclohexanedimethanol and ethylene glycol. Similar blends are disclosed in U.S. Pat. Nos. 4,786,692 and 5,478,896. Blends of polycarbonate with another family of polyesters, those based on a mixture of terephthalic and isophthalic acids with 1,4-cyclohexanedimethanol, are disclosed in U.S. Pat. Nos. 4,188,314 and 4,391,954. British Patent Specification 1,599,230 (published Jan. 16, 1980) discloses blends of polycarbonate with polyesters of 1,4-cyclohexanedimethanol and hexacarbocyclic dicarboxylic acid. Mohn et al. reported on thermal properties of blends of polyesters based on 1,4-cyclohexanedimethanol and terephthalic acid or terephthalic/isophthalic acid mixtures with polycarbonate [J. Appl. Polym. Sci., 23, 575 (1979)], concluding that there were only slight differences in behavior between the two systems. U.S. Pat. No. 6,323,291 describes blends of polycarbonate with a melt flow index greater than 18 g/10 min and polyesters derived from phthalic acid and a diol portion of 1,4-cyclohexanedimethanol and ethylene glycol. For the synthesis of polyesters used in the blends, each of the patents above refers solely to U.S. Pat. No. 2,901,466, which teaches the use of ester interchange catalysts in the production of polyesters but does not specify a particular catalyst type or catalyst level. Fifty-four of the polyester examples in the '466 patent show the use of titanium based catalysts. The titanium concentration in these examples is uniformly greater than 35 parts per million (ppm) elemental titanium, typically in the range of 50 to 200 ppm.
U.S. Pat. No. 6,221,556 discloses an article for optical storage from blends containing polycarbonate and polyesters based on a cycloaliphatic diacid and a cycloaliphatic diol. The '556 patent teaches that the polyester is generally produced with a titanium based catalyst system, in a suitable amount, typically 50 to 200 ppm of titanium based upon the final product and refers to U.S. Pat. Nos. 2,465,319 and 3,047,539 for synthesis of polyesters. The '319 patent discloses the production of polyesters with alkali catalyst metals and the '539 patent discloses the production of polyesters using antimony catalyst system, with neither specifying a particular catalyst level.
Interactions occur during melt blending of polyesters and polycarbonates. These interactions may result in changes in melt viscosity, crystallinity, color, and the production of gaseous by-products. In particular, a yellowish color occurs during the melt blending of a colorless polycarbonate and a colorless polyester. These unfavorable interactions are generally controlled through the use of stabilization additives, typically phosphorus based compounds. U.S. Pat. Nos. 4,188,314; 4,391,954; 4,786,692, 5,478,896; 6,221,556 and 6,323,291 teach the use of stabilizers. U.S. Pat. No. 4,786,692 states that blend compositions may contain stabilizers, such as phosphites, phosphates, epoxides, or combination thereof. The use of phosphorus based stabilizers in polyester/polycarbonate blends are additionally disclosed in U.S. Pat. Nos. 3,953,539 and 4,088,709. U.S. Pat. No. 4,981,898 discloses improved polyester/polycarbonate blends stabilized with a metaphosphate fiber. U.S. Pat. No. 5,254,610 discloses improved polyester/polycarbonate blends with combinations of aliphatic and aromatic phosphite compounds. U.S. Pat. No. 5,491,179 claims improved polyester/polycarbonate blends through the addition of specified cyclic ether based phosphites. U.S. Pat. No. 5,502,119 discloses improved polyester/polycarbonate blends stabilized with an organosilicate. U.S. Pat. No. 5,922,816 discloses improved polyester/polycarbonate blends stabilized with a silyl phosphate. U.S. Pat. No. 6,221,556 teaches that blends must contain an effective amount of stabilizer, typically phosphorus based, to prevent color formation resulting in a yellowness index (YI) less than or equal to 5 YI units. However, as discussed in U.S. Pat. No. 5,354,791, high stabilizer concentrations are known to have detrimental effects on the performance of polyester/polycarbonate blends. Thus, reducing the level of stabilization needed for polyester/polycarbonate blends would be advantageous.
While changes in polyester catalyst type and levels for improvements in the neat polyester are noted widely in prior art, for example U.S. Pat. No. 5,886,133, there are few references to the benefits of catalyst type and levels on the properties of subsequent polyester/polycarbonate blends. U.S. Pat. No. 5,239,020 discloses improved polyester/polycarbonate blends, having a Gardner b value less than 6, without the addition of a stabilizer by use of a tin based ester interchange catalyst. The '020 patent teaches that blends of polyesters made with a titanium based catalyst and polycarbonate without a stabilizer typically results in the formation of a yellowish color, having a Gardner b color value generally greater than 20. The polyesters for blending with polycarbonate claimed in the '020 patent are derived from an acid portion of terephthalic and isophthalic acids and a diol portion of aliphatic diols containing 3 to 20 carbons. Interactions between tin based catalysts and ethylene glycol results in color formation in the neat polyester and subsequently blends with polycarbonate, hence the omission of diols with 2 carbons. U.S. Pat. No. 5,453,479 discloses improved polyester/polycarbonate blends relative to increased strength and reduced processing times by the use of a polyester esterification catalyst containing phosphorus and titanium compounds. The catalyst is added prior to polycondensation during esterification of the diacid and diol in the preparation of the polyester. The titanium catalyst is in an amount typical of the prior art of greater than 50 ppm elemental titanium.
Thus, there exists a need in the art for polyester/polycarbonate blends that have reduced yellowness either without the need for stabilization or with a reduced level of stabilization. Accordingly, it is to the provision of such that the present invention is directed.
SUMMARY OF THE INVENTION
Thermoplastic compositions of polyester/polycarbonate blends have reduced yellowness and improved thermal and melt stability. Such unexpected improvements are achieved by preparing the blends utilizing polyesters that have been produced with a reduced level of titanium catalyst. Depending on end use color requirements, the polyester/polycarbonate blends of the present invention can be used in the absence of a conventional stabilizing compound, thereby eliminating the step and cost of incorporating the stabilizing compound. In addition, further reductions in the b* yellow color of such blends, depending on end use requirements, can be achieved by the addition of stabilizing compounds at much lower concentrations than previously used. The low titanium level polyester/polycarbonate blends have reduced yellowness, and if needed require lower levels of stabilization to reduce b* color, compared to equivalent high titanium level polyester/polycarbonate blends of the prior art.
More specifically, in a thermoplastic composition comprising a compounded blend of a polyester and a polycarbonate, the improvement comprises preparing the polyester in the presence of a titanium-containing catalyst compound in an amount of from about 1 to about 30 ppm elemental titanium, with ppm based on the total weight of the polyester. Optionally, an ester exchange catalyst in an amount of from about 1 to about 150 ppm of an active element is utili
Adams Valerie Sue
Crawford Emmett Dudley
Donelson Michael Eugene
McWilliams Douglas Stephens
Boshears B. J.
Buttner David J.
Eastman Chemical Company
Graves Bernie
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