Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-10-28
2004-09-07
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S199000, C525S232000, C525S240000
Reexamination Certificate
active
06787607
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to thermoplastic elastomer (TPE) materials. Thermoplastic elastomers are broadly defined as rubber-like materials that, unlike conventional vulcanized rubbers, can be processed and recycled like thermoplastic materials, yet have properties and performance similar to that of vulcanized rubber at service temperatures. The invention more specifically relates to thermoplastic vulcanizates (TPV), which are thermoplastic elastomers with a cross-linked rubbery phase produced by the process of dynamic vulcanization. The thermoplastic vulcanizates of the invention are foamed materials produced by physical or chemical blowing agents, wherein processing characteristics and foam properties are improved by the inclusion of a modifier derived from polytetrafluoroethylene. The invention also relates to foamed articles obtainable by the process of the invention.
2. Description of the Prior Art
There has been considerable activity on the development of thermoplastic vulcanizate compositions, especially those based on polyolefin thermoplastic resins, which have good foaming properties, and on processes for producing foams having improved properties. U.S. Pat. No. 5,070,111, incorporated herein by reference, discloses a process of foaming thermoplastic elastomer compositions using water as the sole foaming agent. U.S. Pat. Nos. 5,607,629 and 5,788,889, both incorporated herein by reference, describe methods for the production of foamed thermoplastic elastomer profiles by extrusion with a water blowing agent. U.S. Pat. No. 5,824,400 discloses foamed thermoplastic elastomer compositions which incorporate styrenic elastomers. Published European Patent Application No. 0 860 465 teaches a method of foaming thermoplastic elastomers using a water containing chemical compound which releases water at temperatures above the melting point of the thermoplastic elastomer. Published European Patent Application 0 872 516 discloses the use of polypropylene resins having specific rheological properties to enhance the foaming performance of olefinic thermoplastic elastomers.
However, the problems of providing thermoplastic elastomer foams which are soft, with good surface smoothness, low water absorption, improved compression set and compression load deflection, and having fine and uniform cell structure have not been overcome by prior art.
SUMMARY OF THE INVENTION
The present invention is based on the discovery that superior thermoplastic elastomer foams can be produced by incorporating into the thermoplastic elastomer, prior to foaming, an acrylic-modified polytetrafluoroethylene. Incorporation of this additive provides a very soft foam product having a number of desirable attributes, including improved processability, high melt strength, high cell density and uniformity, smooth surface, low water absorption, with improved compression set and compression load deflection.
In detail the present invention relates to a process for foaming a thermoplastic elastomer using a physical or chemical blowing agent, wherein an acrylic-modified polytetrafluoroethylene is incorporated into the thermoplastic elastomer composition prior to foaming. Sufficient acrylic-modified polytetrafluoroethylene is incorporated to be effective in achieving the desired attributes. The invention also encompasses thermoplastic elastomer compositions containing the acrylic-modified polytetrafluoroethylene, and foamed articles prepared therefrom.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Thermoplastic Elastomer
Thermoplastic Resin Component
Thermoplastic resins suitable for use in the compositions of the invention include thermoplastic, crystalline polyolefin homopolymers and copolymers. They are desirably prepared from monoolefin monomers having 2 to 7 carbon atoms, such as ethylene, propylene, 1-butene, isobutylene, 1-pentene, 1-hexene, 1-octene, 3-methyl-1-pentene, 4-methyl-1-pentene, 5-methyl-1-hexene, mixtures thereof and copolymers thereof with (meth)acrylates and/or vinyl acetates. Preferred, however, are monomers having 3 to 6 carbon atoms, with propylene being most preferred. As used in the specification and claims the term polypropylene includes homopolymers of propylene as well as reactor and/or random copolymers of propylene which can contain about 1 to about 30 weight percent of ethylene and/or an alpha-olefin comonomer of 4 to 16 carbon atoms, and mixtures thereof. The polypropylene can have different types of molecular structure such as isotactic or syndiotactic, and different degrees of crystallinity including materials with a high percentage of amorphous structure such as the “elastic” polypropylenes. Further polyolefins which can be used in the invention are high, low, linear-low and very low density polyethylenes, and copolymers of ethylene with (meth)acrylates and/or vinyl acetates.
The polyolefins mentioned above can be made using conventional Ziegler/Natta catalyst systems or by single site catalyst systems. Commercially available polyolefins may be used in the practice of the invention.
The amount of thermoplastic polyolefin resin found to provide useful thermoplastic elastomer compositions is generally from about 8 to about 90 weight percent. Preferably, the thermoplastic polyolefin content will range from about 9 to about 60 percent by weight.
Elastomer Component
Suitable rubbers include non-polar, rubbery copolymers of two or more alpha-monoolefins, preferably copolymerized with at least one polyene, usually a diene. Saturated monoolefin copolymer rubber, for example ethylene-propylene copolymer rubber (EPM) can be used. However, unsaturated monoolefin rubber such as EPDM rubber is more suitable. EPDM is a terpolymer of ethylene, propylene and a non-conjugated diene. Satisfactory non-conjugated dienes include 5-ethylidene-2-norbornene (ENB); 1,4-hexadiene; 5-methylene-2-norbornene (MNB); 1,6-octadiene; 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; 1,3-cyclopentadiene; 1,4-cyclohexadiene; dicyclopentadiene (DCPD); and vinyl norbornene (VNB).
Butyl rubbers are also useful in the thermoplastic elastomer compositions. As used in the specification and claims, the term butyl rubber includes copolymers of an isoolefin and a conjugated monoolefin, terpolymers of an isoolefin with or without a conjugated monoolefin, divinyl aromatic monomers and the halogenated derivatives of such copolymers and terpolymers. Another suitable copolymer within the scope of the olefin rubber of the present invention is a copolymer of a C
4-7
isomonoolefin and a para-alkylstyrene, and preferably a halogenated derivative thereof. The amount of halogen in the copolymer, predominantly in the para-alkylstyrene, is from about 0.1 to about 10 weight percent. A preferred example is the brominated copolymer of isobutylene and para-methylstyrene. Natural rubbers are also olefin rubbers suitable for use in the thermoplastic elastomer composition.
The amount of rubber in the thermoplastic elastomer generally ranges from about 92 to about 10 weight percent. Preferably the olefin rubber content will be in the range of from about 40 to about 91 weight percent.
Additives
The thermoplastic elastomer may optionally contain reinforcing and non-reinforcing fillers, plasticizers, antioxidants, stabilizers, rubber processing oils, extender oils, lubricants, antiblocking agents, antistatic agents, waxes, foaming agents, pigments, flame retardants and other processing aids known in the rubber compounding art. Such additives may comprise up to about 70 weight percent, more preferably up to about 65 weight percent, of the total composition. Fillers and extenders which can be utilized include conventional inorganics such as calcium carbonate, clays, silica, talc, titanium dioxide, carbon black and the like. The rubber processing oils generally are paraffinic, napthenic or aromatic oils derived from petroleum fractions. The oils are selected from those ordinarily used in conjunction with the specific rubber or rubber component present in the composition.
In one particularly preferred
Finerman Terry M.
Ham Sydney
Jacob Sunny
Sahnoune Abdelhadi
Advanced Elastomer Systems L.P.
Muller William G.
Nutter Nathan M.
Skinner William A.
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