Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Utility Patent
1999-05-20
2001-01-02
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S101000
Utility Patent
active
06169145
ABSTRACT:
FIELD OF THE INVENTION
The vulcanization of carbonyl containing elastomers with a hydrosilylation crosslinking agent and a platinum containing catalyst is disclosed. This type of vulcanization is useful to prepare thermoplastic vulcanizates from carbonyl containing elastomers that cannot be crosslinked by more conventional crosslinkers which require the elastomer to have carbon to carbon double bonds. The thermoplastic vulcanizates prepared from such carbonyl containing elastomers tend to have good lubricity and surface properties.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,672,660 discloses an effective method to prepare thermoplastic elastomer by hydrosilylation crosslinking. Its teachings are focused on the rubber being a diene-containing rubber and more preferably an elastomer with sterically unhindered carbon-carbon double bonds (column 2 lines 7-12).
U.S. Pat. No. 5,051,478 discloses a dynamically vulcanized composition, which comprises a polyolefin resin, an elastomer, and an ethylene copolymer resin such as a copolymer of ethylene and vinyl acetate or alkyl acrylate. In this invention, the ethylene copolymer resin is not vulcanized.
SUMMARY OF THE INVENTION
It has been found that hydrosilylation crosslinkers in combination with platinum containing catalysts are effective crosslinkers for elastomers with carbonyl groups and without any carbon to carbon double bonds. The crosslinking reaction is fast and can result in effective crosslinking in dynamic vulcanization reactions. This alternative crosslinking mechanism makes a new class of elastomers available as the crosslinked components of a thermoplastic vulcanizate. Preferred rubbers with carbonyl groups include, but are not limited to, ethylene-vinyl acetate copolymers, ethylene-acrylate copolymers, ethylene-methacrylate copolymers, maleated ethylene-propylene rubber, and ethylene-acrylic acid copolymers. The thermoplastic vulcanizate can also optionally contain conventional rubber with carbon to carbon double bonds as these can also be crosslinked by the same hydrosilylation crosslinking agent. Such rubbers with carbon to carbon double are preferably those with sterically unhindered double bonds as set forth in U.S. Pat. No. 5,672,660 due to their faster cure rate and more complete crosslinking.
The thermoplastic vulcanizates are useful in applications where additional surface lubricity, more contact clarity, or more polar rubber compounds are desired.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to the use of hydrosilylation crosslinking agents and platinum containing catalysts to crosslink carbonyl containing rubber. The preferred carbonyl containing rubbers are those without conventional crosslinking sites e.g. carbon to carbon double bonds. The crosslinking system can be used to form thermoplastic vulcanizates. The thermoplastic vulcanizates can optionally include more conventional rubbers, which have carbon to carbon double bonds, because the hydrosilylation crosslinking agent is also capable of crosslinking the carbon to carbon double bonds. The use of the carbonyl containing rubbers facilitates making thermoplastic elastomers with higher lubricity, better contact clarity and alternative surface properties.
The thermoplastic polymer (or polymers) is desirably from about 15 to about 85 weight percent of the combined thermoplastic and rubber polymers, more desirably from about 30 to about 70 weight percent. The thermoplastic polymer may be a melt processable thermoplastic polymer and preferably is a semi-crystalline polyolefin. The semi-crystalline polyolefins are well known to the art and are generally from about 5 or 10 to about 50 weight percent crystalline as determined by heat of fusion measurements on samples as received. The polyolefin can be a homopolymer or a copolymer. For the purpose of this application, both the terms polymer and copolymer will be interpreted as including copolymers, terpolymers, etc., so that polymer includes copolymer and copolymer includes a polymer from three or more monomers. Desirably, at least 85, 90 or 95 weight percent of the repeat units of the themoplastic olefin are from a single olefin monomer having from 2 to 8 carbon atoms and preferably at least 85, 90, or 95 weight percent are derived from ethylene or propylene monomer. The residual of up to 5, 10, or 15 weight percent of the polymer may be from a different olefin monomer and/or simply a copolymerizable monomer such as an alkyl (alk)acrylate, acrylic acid, vinyl acetate etc. having from about 3 to about 25 carbon atoms. Typically a thermoplastic polyolefin with at least 85 weight percent of a single type of olefin repeating unit has a significant amount of crystallinity and behaves as a thermoplastic rather than an elastomer.
The rubber polymer (or polymers) is desirably from about 20 to about 85 weight percent of the combined weight of the thermoplastic and rubber polymers, more desirably from about 30 to about 70 weight percent. At least one rubber polymer needs to be a carbonyl containing polymer and in some embodiments all the rubber polymers are carbonyl containing polymers. Desirably at least 10, 20, 30, 50 or 75 weight percent of all the rubbers in thermoplastic vulcanizate are rubbers with two or more carbonyl groups per polymer chain. The carbonyl containing rubber(s) can be any elastomer with generally two or more carbonyl groups per polymer. These include a polymer polymerized from at least one monomer that has a carbonyl group. Desirably the carbonyl groups would be from about 0.2 to about 0.85 moles per 100 grams of polymer. Alternatively the polymer could be one that originally did not have any carbonyl groups but which was post polymerization functionalized with carbonyl groups by grafting on a monomer, oligomer or polymer that had carbonyl groups. An example of this would be maleic anhydride functionalized ethylene-propylene rubber. Preferred carbonyl groups are those in anhydrides from dicarboxylic acids, carboxylic acids, and alkyl esters of carboxylic acids.
Examples of carbonyl containing polymers include copolymers of an alpha olefin, such as ethylene, with a carbonyl containing monomer such as vinyl acetals (e.g. vinyl acetate), acrylic acid, (alk)acrylic acid, alkyl ester of acrylic acid or (alk)acrylic acid, unsaturated anhydrides such as maleic anhydride, or unsaturated polycarboxylic acids such as itaconic acid. Preferred ethylene copolymers have less than 85 weight percent repeat units from polymerizing ethylene. Preferred carbonyl containing rubbers include ethylene-vinyl acetate copolymer, ethylene-methacrylate copolymer, ethylene-acrylic acid copolymer, ethylene-butyl acrylate copolymer, ethylene-methyl acrylate-acrylic acid terpolymer, or blends thereof. Polymers from copolymerizing at least ethylene and carbon monoxide or carbon dioxide as disclosed in U.S. Pat. No. 4,791,190 herein incorporated by reference, may also be used. Desirably the polymer would be an elastomer, which would require that the crystallinity be controlled if it were a monoolefin polymer. Monoolefin crystallinity may be controlled by limiting the amount of any single monoolefin repeating unit to less than 85 weight percent of the final polymer.
Another example of carbonyl containing polymer is a polymer, which has been post polymerization functionalized with a carbonyl containing monomer, oligomer, or polymer. There are many commercially available elastomers, such as ethylene-propylene rubber, block copolymers of a diene and a higher Tg monomer such as styrene (e.g. styrene-butadiene copolymers and styrene-isoprene copolymers either as polymerized or partially hydrogenated after polymerization such as sold under the Kraton name), and other copolymers of dienes and/or acrylates (e.g. random copolymers), which can be functionalized with a few percent of a carbonyl containing group, such as maleic anhydride group, by free radical grafting of a carbonyl containing monomer, e.g. maleic anhydride being grafted onto the elastomer.
The rubber polymer can optionally include any rubber suitable for use in a t
Gilbertson Gary W.
Hazelton Donald R.
Medsker Robert E.
Patel Raman
Advanced Elastomer Systems L.P.
Laferty Samuel B.
Moore Margaret G.
Skinner William A.
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