Foams and methods for making the same

Details Foams and methods for making the same Foams and methods for making the same

2002-06-19

2004-03-30

Nutter, Nathan M. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S054000, C521S055000, C525S191000, C525S192000, C525S194000, C525S199000, C525S205000, C525S214000, C525S216000, C525S222000, C525S232000, C525S240000, C525S241000, C525S243000

Reexamination Certificate

active

06713520

ABSTRACT:

TECHNICAL FIELD
This invention is directed toward foams and methods for making foams from thermoplastic vulcanizates.
BACKGROUND OF THE INVENTION
Thermoplastic elastomers are known. They have many of the properties of thermoset elastomers, yet they are processable as thermoplastics. One type of thermoplastic elastomer is a thermoplastic vulcanizate, which may be characterized by finely-divided rubber particles dispersed within a plastic. These rubber particles are crosslinked to promote elasticity. Thermoplastic vulcanizates are conventionally produced by dynamic vulcanization, which is a process whereby a rubber is cured or vulcanized within a blend with at least one non-vulcanizing polymer while the polymers are undergoing mixing or masticating at some elevated temperature, preferably above the melt temperature of the non-vulcanizing polymer.
Some thermoplastic vulcanizates have been foamed to form cellular products. The ability to foam a thermoplastic vulcanizate is dependent upon the amount of plastic within the composition. For example, when employing conventional thermoplastic vulcanizates, about 40 parts of plastic per 100 parts of rubber is required to produce a technologically useful foam.
The ability to produce soft foams, however, is hindered by the amount of plastic that is required. In other words, while a minimum amount of plastic is required to achieve a foam, the hardness of the foam is directly related to the amount of plastic. For example, where 42 parts of plastic are used per 100 parts of rubber, the thermoplastic vulcanizate has a Shore A Hardness (ASTM 2240) of about 68. The resultant foam may be undesirable for many applications because of high hardness, which translates into high compression set and high compression load deflection.
SUMMARY OF INVENTION
In general the present invention provides a foam profile prepared by a process comprising the steps of foaming a thermoplastic vulcanizate, where the thermoplastic vulcanizate is prepared by a process comprising the step of dynamically vulcanizing a rubber within a mixture that includes from about 15 to about 95 percent by weight of the rubber and from about 5 to about 85 percent by weight of a thermoplastic component based upon the total weight the rubber and thermoplastic component combined, where the thermoplastic component includes from about 65 to about 90 percent by weight of a conventional thermoplastic resin and from about 10 to about 35 percent by weight of a random propylene copolymer based upon the total weight of the thermoplastic component.
The present invention also includes a foam profile prepared by a process comprising the steps of foaming a thermoplastic vulcanizate, where the thermoplastic vulcanizate comprises vulcanized rubber and from about 5 to about 85 percent by weight of a thermoplastic component based upon the total weight of the rubber and thermoplastic component combined, and where the thermoplastic component comprises from about 65 to about 90 percent by weight of a conventional thermoplastic resin and from about 10 to about 35 percent by weight of a random propylene copolymer based upon the total weight of the thermoplastic component.
The present invention further includes foam profile comprising a foamed thermoplastic vulcanizate, where the thermoplastic vulcanizate comprises vulcanized rubber and from about 5 to about 85 percent by weight of a thermoplastic component based upon the total weight of the rubber and thermoplastic component combined, and where the thermoplastic component comprises from about 65 to about 90 percent by weight of a conventional thermoplastic resin and from about 10 to about 35 percent by weight of a random propylene copolymer based upon the total weight of the thermoplastic component.
It has surprisingly been discovered that thermoplastic vulcanizates that contain a certain amount of random propylene copolymer can be used to make foams that do not suffer from many of the problems associated with prior art foams produced from thermoplastic vulcanizates. Notably, even though the thermoplastic vulcanizates employed in this invention have a Shore A hardness (ASTM 2250) of about 50 to about 60, the thermoplastic vulcanizates can be foamed to produce technologically useful foams that have advantageously low compression set and advantageously low compression load deflection.
PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION
The thermoplastic vulcanizates employed to make foams according to this invention include at least one cured rubber, at least one random propylene copolymer, and at least one conventional thermoplastic resin. These thermoplastic vulcanizates are foamed by employing a foaming agent.
Any rubber or mixture thereof that is capable of being crosslinked or cured can be used as the rubber component. Reference to a rubber may include mixtures of more than one rubber. Useful rubbers typically contain some degree of unsaturation in their polymeric main chain. Some non-limiting examples of these rubbers include elastomeric copolymers, butyl rubber, natural rubber, styrene-butadiene copolymer rubber, butadiene rubber, acrylonitrile rubber, halogenated rubber such as brominated and chlorinated isobutylene-isoprene copolymer rubber, butadiene-styrene-vinyl pyridine rubber, urethane rubber, polyisoprene rubber, epichlolorohydrin terpolymer rubber, and polychloroprene. The preferred rubbers are elastomeric copolymers and butyl rubber.
The term elastomeric copolymer refers to rubbery copolymers polymerized from ethylene, at least one &agr;-olefin monomer, and optionally at least one diene monomer. The &agr;-olefins may include, but arc not limited to, propylene, 1-butene, 1-hexene, 4-methyl-1 pentene, 1-octene, 1-decene, or combinations thereof. The preferred &agr;-olefins are propylene, 1-hexene, 1-octene or cornbination. thereof. The diene monomers may include; but are not limited to, 5-ethylidene-2-norbornene; 1,4-hexadiene; 5-methylene-2-norbomene; 1,6-octadiene; 5-methyl-1,4-hexadiene; 3,7-dimethyl- 1,6-octadiene; 1,3-cyclopentadiene; 1,4-cyclohexadiene; dicyclopentadiene; 5-vinyl-2-norbornene and the like, or a combination thereof. The preferred diene monomers are 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene. In the event that the copolymer is prepared from ethylene, &agr;-olefin, and diene monomers, the copolymer may be referred to as a terpolymer or even a tetrapolymer in the event that multiple &agr;-olefins or dienes are used.
Elastomeric copolymers are commercially available under the tradenames Vistalon™ (Exxon Mobil Chemical Co.; Houston, Tex.), Keltan™ (DSM Copolymers; Baton Rouge, La.), Nordel™ IP (DuPont Dow Elastomers; Wilmington, Del.), ElastoFlo™ (Union Carbide; Danbury, Conn.), and Buna™ (Bayer Corp.; Germany).
In one embodiment, the elastomeric copolymer is a terpolymer of ethylene, at least one &agr;-olefin monomer, and 5-vinyl-2-norbomene. This terpolymer is advantageous when a peroxide curative is employed as described in U.S. Pat. No. 5,656,693, which is incorporated herein by reference. This terpolymer is also advantageous when a silicon-containing curative is employed in the presence of platinum-containing catalyst as described in International Publication No. WO 98/38226, which is incorporated by reference. The terpolymer preferably includes from about 40 to about 90 mole percent of its polymeric units deriving from ethylene, and from about 0.2 to about 5 mole percent of its polymeric units deriving from vinyl norbornene, based on the total moles of the terpolymer, with the balance comprising units deriving from &agr;-olefin monomer.
The term butyl rubber refers to rubbery amorphous copolymers of isobutylenc and isoprene or an amorphous terpolymer of isobutylene, isoprene, and a divinyl aromatic monomer. These copolymers and terpolymers should preferably contain from about 0.5 to about 10 percent by weight, or more preferably from about 1 to about 4 percent by weight, isoprene. The term butyl rubber also includes copolymers and terpolymers that are halogenated with from about 0.1 to about 10 weight percent, or pre

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