Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1999-12-21
2001-04-10
Hampton-Hightower, P. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S134000, C521S143000, C525S191000, C525S196000, C525S197000, C525S198000, C525S222000, C525S240000, C428S066400, C264S299000, C264S319000
Reexamination Certificate
active
06214894
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to cross-linked polymer blends including single-site initiated polyolefin resins and polyolefins including ethylene and propylene.
Polymer blends that can be formed (i.e., thermoformed or pressure-formed) are useful in a number of applications, particularly, when the polymer blends have good flexibility properties, high thermal stability, and are foamable. For example, these materials can be used as components in floatation devices for water sports or as sealing or gasket components in, e.g., the automotive industry. Traditionally, the physical properties required by these types of applications suggest the use of high density foams.
In general, polymer blends with these properties are based, in part, on cross-linked ethylene-propylene-diene monomer (EPDM) terpolymers or ethylene-vinyl acetate (EVA) copolymers. These materials generally contain other additives, such as plasticizers, to add to their flexibility. Thermal stability is typically achieved by sulfur vulcanization of the compositions. However, plasticizers can leach out of the materials over time which can make the materials less flexible and the sulfur additives can make the material less desirable for environmental reasons.
SUMMARY OF THE INVENTION
The invention features polymer blends which can be used both in foamed and unfoamed states as a replacement for conventional EPDM and other elastomers. The composition of the polymer blend includes a single-site catalyzed polyolefin resin having a density of below 0.878 g cm
−3
and up to 40 weight percent of a polyolefin including ethylene and propylene. The polymer blend is cross-linked. The use of sulfur to vulcanize the polymer blend is not necessary.
In one aspect, the invention features a polymer blend including a single-site initiated polyolefin resin having a density below 0.870 g cm
−3
and up to 40 weight percent of a polyolefin that includes ethylene and propylene. A portion of the polymer blend is cross-linked. In addition, the polymer blend is formable. In preferred embodiments, the polymer blend is foamed.
In another aspect, the invention features a method of making a cross-linked polymer blend including the steps of providing a polymer mixture including a single-site initiated polyolefin resin and up to 40 weight percent of a polyolefin including ethylene and propylene, and cross-linking the polymer mixture.
In preferred embodiments, the step of cross-linking the polymer blend includes reacting the polymer blend with a peroxide. In other preferred embodiments, the method further includes the step of expanding the polymer mixture to form a foam. It is preferred that the step of expanding the polymer mixture include compression molding the polymer mixture at increased temperature and pressure. Preferably, compression molding comprises the steps of pressing the polymer mixture using a high tonnage press at a temperature of between 275 and 320° F. and a pressure of between 250 and 2500 psi for between 20 and 90 minutes followed by heating the polymer mixture at a temperature between 300 and 380° F. The step of heating the polymer mixture further preferably includes pressing the blend using a medium tonnage press at a pressure of between 250 and 1500 psi.
In yet another aspect, the invention features a gasket including a polymer blend including a single-site initiated polyolefin resin having a density below 0.870 g cm
−3
and up to 40 weight percent of a polyolefin including ethylene and propylene. A portion of the polymer blend is cross-linked. The gasket is thermally stable at 120° F.
In another aspect, the invention features a method of making a gasket including the steps of providing a polymer blend including a single-site initiated polyolefin resin having a density below 0.870 g cm
−3
and up to 40 weight percent of a polyolefin including ethylene and propylene, and forming the polymer blend in a mold in the shape of a gasket. A portion of the polymer blend is cross-linked and the gasket is thermally stable at 120° F. In preferred embodiments, the step of forming includes pressing the polymer blend in the mold. Preferably, the step of forming includes heating the polymer blend in the mold.
In preferred embodiments, the polymer blend includes at least 5 percent of the single-site initiated polyolefin resin and at least 5 percent of the polyolefin that includes ethylene and propylene. It is preferred that the polyolefin that includes ethylene and propylene is an ethylene-propylene-diene monomer (EPDM) terpolymer or an ethylene propylene rubber (EPR), most preferably EPDM.
In preferred embodiments, the polymer blend further includes less than about 70 weight percent of a second polyolefin resin. It is preferred that the second polyolefin resin include a polypropylene, a polyethylene, or a copolymer containing ethylene or propylene. The second polyolefin resin can be a blend or mixture of polymer resins. The polyethylene preferably includes a low density polyethylene, a linear low density polyethylene, a medium density polyethylene, or a high density polyethylene. The copolymer preferably includes an ethylene-vinyl acetate copolymer, an ethylene-maleic anhydride copolymer, or an ethylene-ethyl acetate copolymer.
In other preferred embodiments, the polymer blend includes between about 5 and 95 weight percent of the single-site initiated polyolefin resin and about 5 and 40 weight percent of the polyolefin including ethylene and propylene, preferably an ethylene-propylene-diene monomer terpolymer. It is preferred that the polymer blend further include up to about 65 weight percent of a filler. It is preferred that the polymer blend further include up to about 30 weight percent of an oil.
Preferably, the foamed polymer blend has an average foam density between 1.5 and 25 pounds per cubic foot.
Copolymers include polymers resulting from the polymerization of two or more monomeric species, for example, polyolefins including ethylene and propylene. Copolymers including ethylene and propylene can be ethylene-propylene rubbers (EPR). Copolymers include terpolymers resulting from the polymerization of three monomeric species (e.g., as in EPDM), sesquipolymers, and greater combinations of monomeric species.
A polyolefin including ethylene and propylene can be an ethylene-propylene-diene monomer (EPDM) terpolymer. EPDM can be a polyolefin including ethylene, propylene, and a non-conjugated diene that have been polymerized together to afford a copolymer (in this case a terpolymer). The polymerization initiator can be any known initiator, including a single-site initiator. For examples of polyolefins including ethylene and propylene (i.e., EPR or EPDM resins), see Borg, “Ethylene/Propylene Rubber,” in
Rubber Technology,
M. Morton, Ed., Van Nostrand Reinhold Company, N.Y., 1973, pp. 220-248.
Single-site initiated polyolefin resins can be polyolefins prepared from a single-site initiated polyolefin that has controlled molecular weights and molecular weight distributions. The single-site initiated polyolefin resin can be, for example, polyethylene, polypropylene, or a copolymer of ethylene and alpha-unsaturated olefin monomers.
The specific gravities of the polymer resins can be measured using ASTM D-792 methods.
The foams are generally closed-cell foams in which greater than approximately 70% of the form cell volumes have cell walls isolating them from the external atmosphere. One way to determine this is by measuring the amount of water that is absorbed into the foam when the foam is immersed in water.
The invention can have one or more of the following advantages. The polymer blends can have improved flexibility and thermal stability over blends that do not include single-site initiated polyolefin resins. Flexibility can be measured, for example, by compressing the material by 25 percent and measuring the force it takes to compress the foam. Other advantages of the materials include thermoformability, and the ability to laminate to other materials or to itself without adhesives.
The polymer blends,
Bambara John D.
Cagwin Todd
Hurley Robert F.
Kozma Matthew L.
Fish & Richardson P.C.
Hampton-Hightower P.
Sentinel Products Corp.
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