Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-11-18
2001-10-09
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S439000, C524S440000
Reexamination Certificate
active
06300399
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to filled polyester molding compositions having very high specific gravity and enhanced properties.
BACKGROUND OF THE INVENTION
Filled crystalline resin blends typically have less than desirable impact properties. In addition it is difficult to prepare materials with a specific gravity greater than or equal to about 3.0 g./cc with good mechanical properties. In order to mimic articles made of heavy metals, such as zinc or steel, with a very heavily filled polyester resin it is also important that molded crystalline resin part have a smooth surface which can be easily plated using standard plating processes.
Holub et al, U.S. Pat. No. 4,122,061 describes polyester reinforced blends of poly(1,4-butylene terephthalate) and poly(ethylene terephthalate) impact modified with the addition of a polyolefin or olefin based copolymer resin. The polyolefinic resin is dispersed into the polyester blend and used for injection molding. Workpieces molded from such polyester resins are described as having a high degree of surface hardness and abrasion resistance, high gloss, and lower surface friction. It is desirable to provide further enhancements to the properties of resins of the type described in Holub et al.
U.S. Pat. No. 5,132,353 to Wallace describes a blend of thermoplastic polyester with from 50-75% zinc oxide. While the blends have useful mechanical properties and good surface appearance, specific gravity is below 3.0 g./cc. Similarly U.S. Pat. No. 5,149,734 to Fisher et al. describes polyester blends with 30-75% barium sulfate with ceramic like feel and density. In this case again specific gravity is below 3.0 g./cc, well below that of most metals. In both of the above patents no mention is made of metal plating.
U.S. Pat. No. 5,441,997 describes polyester molding compositions which have ceramic like qualities and high impact strength which can be easily molded. The composition is directed to a polybutylene terephthalate and/or polyethylene terephthalate and an aromatic polycarbonate with inorganic fillers selected from the group consisting of barium sulfate, strontium sulfate, zirconium oxide and zinc sulfate. If desired, a styrene rubber impact modifier can be added to the composition as well as a fibrous glass reinforcing filler. Although these compositions are suited for applications where ceramic like qualities are desired, it is desirable to achieve even higher densities while retaining desirable properties for molding.
Metal plating of plastics has been an area of study for many years and metal plated plastic articles are sold in a variety of applications: for instance, truck and automobile parts, appliances, electronic equipment, toys, handles, lighting reflectors and personal grooming equipment. As seen in U.S. Pat. Nos. 5,503,94 and 5,885,497 small changes in polymer structure, described as the presence of some aryl ester units in a polycarbonate copolymer, can have a major effect on plating. Plating and metalization of plastic articles still has a large element of unpredictability.
It is desirable to obtain an impact resistant polyester resin having a high specific gravity and enhanced plating properties. Additionally, it is desirable to achieve a smooth surface important to the final appearance of a metal plated article. Hence, it is desirable to provide improved resins containing additional ingredients which can enhance the above properties without detracting from desirable surface properties which can contribute to good appearance and plateability.
SUMMARY OF THE INVENTION
In the compositions of the present invention it is desirable have high specific gravity with enhanced impact resistance as well as desirable surface properties.
According to the present invention, there is provided a filled polyester molding composition, based on the weight of the total composition, comprising (a) from about 5 to about 40 weight percent of a polyester resin; (b) from about 60 to about 95% weight percent of tungsten metal filler; and (c) optionally from 0 to 20 weight percent of an impact modifier.
The composition of the present invention desirably has a relatively high specific gravity as compared to other materials having similar additions of other filler materials. Preferably, the resulting specific gravity is greater than 3.0 g./cc. With the molded part having good melt processability, good practical impact, a smooth surface as molded and good metal plateability.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A high specific gravity molding composition preferably comprises (a) from about 5 to about 40 weight percent of a thermoplastic polyester resin; (b) from about 60 to about 95 percent of tungsten metal filler; and (c) optionally from 1 to 10 weight percent of an impact modifier. Polyester components include crystalline thermoplastic polyesters such as polyesters derived from an aliphatic or cycloaliphatic diol, or mixtures thereof, containing from 2 to about 10 carbon atoms and at least one aromatic dicarboxylic acid. Preferred polyesters are derived from an aliphatic diol and an aromatic dicarboxylic acid having repeating units of the following general formula:
wherein n is an integer of from 2 to 6. R is a C6-C20 aryl radical comprising a decarboxylated residue derived from an aromatic dicarboxylic acid.
Examples of aromatic dicarboxcylic acids represented by the decarboxylated residue R are isophthalic or terephthalic acid, 1,2-di(p-carboxyphenyl)ethane, 4,4′-dicarboxydiphenyl ether, 4,4′ bisbenzoic acid and mixtures thereof. All of these acids contain at least one aromatic nucleus. Acids containing fused rings can also be present, such as in 1,4-1,5- or 2,6-naphthalene dicarboxylic acids. The preferred dicarboxylic acids are terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid or mixtures thereof.
The most preferred polyesters are poly(ethylene terephthalate) (“PET”), and poly(1,4-butylene terephthalate), (“PBT”), poly(ethylene naphthanoate) (“PEN”), poly(butylene naphthanoate), (“PBN”), (polypropylene terephthalate) (“PPT”) and poly(cyclohexanedimethanol terephthalate) (“PCT”).
Also contemplated herein are the above polyesters with minor amounts, e.g., from about 0.5 to about 5 percent by weight, of units derived from aliphatic acid and/or aliphatic polyols to form copolyesters. The aliphatic polyols include glycols, such as poly(ethylene glycol). Such polyesters can be made following the teachings of, for example, U.S. Pat. Nos. 2,465,319 and 3,047,539.
The preferred poly(1,4-butylene terephthalate) resin used in this invention is obtained by polymerizing a glycol component at least 70 mol %, preferably at least 80 mol %, of which consists of tetramethylene glycol and an acid component at least 70 mol %, preferably at least 80 mol %, of which consists of terephthalic acid, and polyester-forming derivatives thereof.
The polyesters used herein have an intrinsic viscosity of from about 0.4 to about 2.0 dl/g as measured in a 60:40 phenol/tetrachloroethane mixture or similar solvent at 23-30° C. VALOX Registered TM 315 polyester is particularly suitable for this invention.
The preferred polyester of the invention will be crystalline polyesters having a melting point from 150 to 300° C. with the most preferred polyester melting between 180 and 250° C.
In order to improve the as molded surface of an article of the invention it is preferred to combine a fast crystallizing resin like PBT with a slower crystallizing resin like PET. In these type of polyester blends the most preferred compositions have a 1:1 to 3:1 ratio of PBT to PET.
The tungsten metal filler comprises particles of tungsten metal. Tungsten powder is typically produced by carbon reduction techniques known in the art. Tungsten is an especially useful filler for this invention due to its very high gravity. Other key attributes are its low toxicity, compared to lead, mercury, uranium and cadmium, which allows its use without harmful emissions to the environment or costly manufacturing measures to prevent its potential release to the environment. Tun
Gallucci Robert R.
Georgieva Galina D.
Sastri Vinod R.
Cain Edward J.
General Electric Company
Wyrozebski-Lee Katarzyna
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