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
2001-09-18
Short, Patricia A. (Department: 1712)
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...
C524S409000, C524S411000, C524S412000, C524S423000, C524S513000, C525S064000, C525S09200D, C525S09200D
Reexamination Certificate
active
06291574
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to polyester molded articles having enhanced sound and vibration damping.
BACKGROUND OF THE INVENTION
It is desirable to provide enclosures for mechanical devices, such as fans, switches, compressors and other devices, to suppress vibration and sound associated with the operation of the device.
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. 5,441,997 describes polyester molding compositions which have ceramic like qualities, can be molded into relatively thin sections, and have high impact strength. 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 is described as an added ingredient to the composition as well as a fibrous glass reinforcing filler. Although these compositions are suited for applications where ceramic like qualities are desired, compositions having additional enhanced properties are desirable.
Various rubbery modifiers have been added to polyesters to improve impact. U.S. Pat. No. 4,022,748 discloses rubber elastic graft copolymers having a glass transition below −20° C. U.S. Pat. No. 4,034,013 and 4,092,202 disclose multistage polymers having a rubbery interior and a hard outer shell preferably derived from acrylates. U.S. Pat. No. 4,090,966 and 4,271,064 disclose selectively hydrogenated monoalkenyl arene-diene block copolymers as polyester modifiers. U.S. Pat. No. 4,257,937 describes polyester polycarbonate blends with polyacrylate resins. A wide variety of other polyester impact modifiers have been disclosed in the art, but none address the issue of sound and vibration damping along with retention of a good balance of mechanical and rheological properties.
Vibration damping has been addressed through the use of specific styrenic block copolymers in other thermoplastics such as ethylene-polypropylene as described in Jpn. Kokai Tokkyo Koho JP11 80,456[99 804561]: (Chem Abstracts 130: 238309). U.S. Pat. No. 5,886,094 discloses an inorganic filler with a compatibilizer and styrene block copolymer; in a polyphenylene ether polyamide mixture to increase damping.
Despite all prior work combining thermoplastic polyesters and rubbery impact modifiers there still remains the need to provide a crystalline thermoplastic polyester with high heat, solvent resistance and good mechanical and rheological properties having the additional characteristic of sound and vibration damping.
BRIEF SUMMARY OF THE INVENTION
The invention relates to a moldable thermoplastic polyester composition comprising a sound damping amount of a monoalkenyl arene isoprenoid rubber modifier having a high level of 1,2 or 3,4 linkages. The isoprenoid rubber modifiers may be used alone, in combination with other non isoprenoid impact modifiers, or with fillers, reinforcements, flame retardants or other thermoplastics, especially polycarbonate.
DETAILED DESCRIPTION OF THE INVENTION
The sound damping component as used in the compositions of the present invention are rubbery monoalkenyl arene-isoprenoid copolymers of high-molecular weight. Typical isoprenoid natural and synthetic polymeric materials have elasticity at room temperature with a high level of 1,4 linkages a few, if any, 1,2 or 3,4 linked diene units. To enhance sound and vibration damping capability as required for the invention herein described, the majority of isoprene units should be linked primarily though the 1,2 or 3,4 bond. Traditional impact modifiers using diene based rubbers have primarily 1,4 type linkages and show little if any sound and/or vibration damping behavior when used in the blends of the invention. Sound and vibration damping isoprenoid materials may include copolymers, including random, block, radial block, graft and core-shell copolymers as well as combinations thereof.
Sound and vibration damping isoprenoid AB(diblock), ABA (triblock) copolymers of alkenylaromatic and diene compounds comprising isoprene blocks are most effective. The conjugated diene blocks, having a high level of 1,2 or 3,4 linkages, may be partially or entirely hydrogenated. The preferred conjugated diene is isoprene. The preferred vinyl aromatic compounds are styrene and methyl styrene. Examples of triblock copolymers of this type are polystyrene-polyisoprene-polystyrene (SIS). The most preferred isoprene monoalkenyl arene copolymers of the invention will have sufficient monoalkenyl arene content to keep them from agglomerating at room temperature but still have high isoprenoid content for efficient sound and vibration damping. This is achieved with usually greater than 15-30 wt. % monoalkenyl arene content. The remainder of the sound and vibration damping rubber is comprised of 70-85 wt. % poly isoprenoid units. Partially hydrogenated isoprene monoalkenyl copolymers may be preferred for conditions requiring the isoprenoid rubber to withstand higher temperatures.
The sound damping additive is preferably present in the blends of the invention in an amount from about 3 to about 50%, preferably from 5 to about 20 percent by weight.
The most preferred isoprenoid rubber is a styrene isoprene styrene (SIS) or hydrogenated SIS block (hSIS) copolymer where the isoprene linkages are primarily 1,2 or 3,4 linkages. Sound damping rubber of this type is marketed by Kuraray Co. under the HYBRAR trademark. Usually about more than 50% of the isoprene linkages should be 1,2 or 3,4 linkages with the remainder of the isoprene linkages being 1,4 linkages. The preferred SIS or hydrogenated SIS copolymer will have about 20% styrene units with the remainder comprised of poly isoprene units.
Mixtures of different types of sound damping rubbers may be used. The mixtures may be especially useful in extending the temperature range under which the compositions of the invention will show sound or vibration damping capability.
Sound and vibration damping behavior can be seen in the dynamic mechanical performance of the composition as enhanced tan. delta or loss modulus values between −20 to +20° C. as well as by simply dropping the sample on a hard flat surface and rating the sound reduction compared to a control with no sound and vibration damping rubber (SVDR).
Suitable polyester components include crystalline 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 dicarboxylic 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 tere
General Electric Company
Short Patricia A.
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