Cross-linked polyolefin tape

Details Cross-linked polyolefin tape Cross-linked polyolefin tape

1997-05-05

2002-10-29

Morris, Terrel (Department: 1771)

Coating processes

Coating remains adhesive or is intended to be made adhesive

C427S208400

Reexamination Certificate

active

06472015

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to cross-linked polyolefin resins used to carry adhesives, as in a tape.
In general, tape is useful in joining applications and can be formed from polymer resins with good flexibility properties that are coated with adhesives. Tapes can include foamed or non-foamed polymer resins.
Foamed tape is a useful in applications where cushioning or gap-filling is important. Gap-filling is particularly important when the surface of the substrate is not uniform; the tape is capable of filling the surface irregularities and provide good contact of the adhesive surface with the substrate surface. Foamed tapes are useful for joining rough and irregular surfaces. It is important for the foamed tape to be flexible.
In tape applications, the surface of the polymer resin should be easily coated with a film of the adhesive. It is also important that the polymer resin adhere well to the adhesive in order to bond well to a substrate surface. Generally, desirable foams for making foamed tapes have low densities, decreasing the cost of material and weight while maintaining good foam properties. Foamed tapes can also have good insulating qualities.
In general, foamed tapes with these properties contain foams based on polyvinylchlorides (PVC), ethylene-propylene-diene monomer (EPDM) terpolymers, polyurethanes, or radiation cross-linked polyolefin materials. These materials generally contain other additives, such as plasticizers, to add to their flexibility. Polyolefins alone are typically limited in their application to adhesive tapes because of their limited flexibility. However, plasticizers can leach out of the materials over time which can make the materials less flexible and degrade the properties of the adhesives. In some circumstances, foams for use in tape applications should have good weatherability and flame resistance.
SUMMARY OF THE INVENTION
In general, the invention features polymer tapes that are blends of a polymer resin and a silane-grafted single-site initiated polyolefin resin. The silane-grafted single-site initiated polyolefin resin generally is a copolymer of ethylene and a C
3
-C
20
alpha-olefin that has a molecular weight distribution between about 1.5 and about 3.5. The polymer tapes can be foamed to form foamed polymer tapes.
In one aspect, the invention features a polyolefin tape including a polyolefin sheet and an adhesive on at least one face of the sheet, the polyolefin including a silane-grafted single-site initiated polyolefin resin. It is preferred that the tape have a thickness of less than about {fraction (5/16)} inch.
In other preferred embodiments, the polyolefin is foamed. It is preferred that the foam have a 25% compression resistance of less than 75 psi, more preferably less than 25 psi, and an elongation greater than 100 percent, more preferably greater than 250 percent.
In another aspect, the invention features a polymer tape including an adhesive and a silane-grafted polymer blend containing at least one single-site initiated polyolefin resin, the polymer tape having a tensile strength greater than 20 psi, a 25% compression resistance greater than 3 psi, more preferable between 3 and 150 psi, and an elongation greater than 100 percent, more preferably greater than 250 percent.
In preferred embodiments, the polymer blend is foamed. Preferably, the foam has a density between 1.5 and 50 pounds per cubic foot.
In preferred embodiments, the silane-grafted single-site initiated polyolefin resin is a copolymer of ethylene and a C
3
-C
20
alpha-olefin having a density between about 0.85 and 0.91 g cm
−3
and a molecular weight distribution between about 1.5 and about 3.5. In other preferred embodiments, the polymer blend is foamed. It is preferred that a portion of the single-site initiated polyolefin resin be silane-grafted.
In preferred embodiments, a portion of the polyolefin, or polymer blend, is cross-linked. In other preferred embodiments, the polyolefin, or polymer blend, contains greater than about 20 percent silane-grafted single-site initiated polyolefin resin. It is preferred that the silane-grafted single-site polyolefin resin contain between about 0.1 and 3 percent silane.
In preferred embodiments, the tape further includes a polyethylene resin or an ethylene-vinyl acetate copolymer resin. It is preferred that the polyolefin tape contain between 20 and 50 percent ethylene-vinyl acetate copolymer resin. It is preferred that the ethylene-vinyl acetate copolymer resin contains between 5 and 25 percent vinyl acetate.
In other preferred embodiments, the silane includes a vinyl silane with 2 or 3 hydrolyzable groups. It is preferred that the adhesive include a rubber adhesive or an acrylate adhesive.
In yet another aspect, the invention features a method of making a polymer tape including the steps of: providing a cross-linkable polymer mixture including at least one single-site initiated polyolefin resin and a chemical foaming agent; extruding the polymer mixture; and applying an adhesive to the polymer mixture.
In preferred embodiments, the method further includes the step of silane-grafting the polymer mixture. In other preferred embodiments, the method further includes the step of silane-grafting the single-site initiated polyolefin resin.
It is preferred that the method further include the step of expanding the polymer mixture to form a foam. Preferably, the method also includes the step of cross-linking the polymer mixture. It is preferred that the step of cross-linking the polymer mixture include exposing the polymer mixture to moisture.
The term “short-chain branching,” as used herein, means a branch of a polymer backbone of 6 carbon atoms or less which can be distinguished by
13
C NMR spectroscopic methods.
The term “copolymer,” as used herein, means a polymer resulting from the polymerization of two or more monomeric species, including terpolymers (e.g., resulting from the polymerization of three monomeric species), sesquipolymers, and greater combinations of monomeric species. Copolymers are generally polymers of ethylene with C
3
-C
20
alpha-olefins.
The densities, or specific gravities, of the polymer resins can be measured using ASTM D-792 methods.
The phrase “single-site initiated polyolefin resin,” as used herein, means a polyolefin prepared from a single-site initiated polyolefin that has controlled molecular weights and molecular weight distributions. The polyolefin can be polyethylene, polypropylene, or a copolymer of ethylene and alpha-unsaturated olefin monomers. One class of a single-site initiators of particular interest are the metallocene initiators which are described, for example, in J. M. Canich, U.S. Pat. No. 5,026,798, in J. Ewen, et al., U.S. Pat. No. 4,937,299, in J. Stevens, et al., U.S. Pat. No. 5,064,802, and in J. Stevens, et al., U.S. Pat. No. 5,132,380, each of which are incorporated herein by reference. These initiators, particularly those based on group 4 transition metals, such as zirconium, titanium and hafnium, are extremely high activity ethylene polymerization initiators.
The single-site initiators are versatile. The polymerization conditions such as a initiator composition and reactor conditions can be modified to provide polyolefins with controlled molecular weights (e.g., in a range from 200 g mol
−1
to about 1 million or higher g mol
−1
) and controlled molecular weight distributions (e.g., M
w
/M
n
in a range from nearly 1 to greater than 8, where M
w
is the weight average molecular weight and M
n
is the number average molecular weight). Molecular weights and molecular weight distributions of polymers can be determined, for example, by gel permeation chromatography.
The polyolefins provided by these initiators are essentially linear, meaning that the polymers can contain uniformly distributed, highly controlled short chain branching sites. As used herein, the term “essentially linear” means that the polymers have less than about one long-chain branch for every ten thousand carbon atoms in the backbone of the polymer. As described above

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