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
1998-12-22
2003-01-07
Mullis, Jeffrey (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...
C525S074000, C525S078000, C525S086000, C525S087000, C525S192000, C525S197000, C525S198000
Reexamination Certificate
active
06503984
ABSTRACT:
FIELD OF INVENTION
A polyolefin composition and a thermoplastic elastomer based upon a semi-crystalline polyolefin are described which have improved adhesion to polar polymers including textile fibers and metals including wires. A combination of a low flexural modulus (low crystallinity) polypropylene and a maleic anhydride functionalized polypropylene were found to exhibit excellent adhesion to textile fibers. Incorporation of these two components into a TPE (thermoplastic elastomer) imparts excellent adhesion of the TPE to textile fibers.
BACKGROUND OF INVENTION
Polyolefins and thermoplastic elastomers rich in polyolefins have traditionally had poor adhesion to textile fibers. Experiments with thermoplastic vulcanizates (TPV), a subset of thermoplastic elastomers (TPE), using formulations similar to those of U.S. Pat. Nos. 4,130,534 and 4,130,535 resulted in peel strengths of only 0.5 to 1.0 pounds per linear inch (pli) between the TPV and textile fibers after melt processing the TPV to the textile fibers. The industrial hose and belting markets generally require a peel strength of at least 8 to 12 pli for candidate matrix materials for fiber reinforced hoses and belting. While polyolefins and TPVs from polyolefins have benefits over plasticized polyvinyl chloride resin (in terms of chemical resistance and physical properties after aging) and over crosslinked rubbers (in terms of processability and physical properties after aging) their use with textile fibers has been limited due to low adhesion values (low peel strengths).
U.S. Pat. No. 4,957,968 teaches adhesive thermoplastic elastomer blends comprising a) at least a polyolefin modified by a chemically reactive functional group, b) at least one other polymer, and c) at least one olefinic elastomer.
Typically, when a polymer and a fiber exhibit poor adhesion toward each other, the problem is attributed to poor wetting of the fiber with the polymer or a lack of good interactions between the fiber surface and the polymer. If processing aids are not effective in solving the wetting problem, then different fibers or a different polymer is chosen or a sizing, more interactive with the specific polymer, is applied to the fiber.
SUMMARY OF INVENTION
A combination of two polymers was found that improves the interaction of polyolefins and/or thermoplastic vulcanizates (TPV) with more polar polymers and metals, especially various textile fibers and metal wires. More polar polymers are defined as those polymers more polar than polyolefins due to the inclusion of heteroatoms such as oxygen or nitrogen in the repeating groups. The first polymer is a low crystallinity polyolefin with a low flexural modulus (tangent) such as from about 5,000 to about 20,000 psi (34.5 to 138 MPa). It is hypothesized that the low flexural modulus helps reduce stress at the bond line between the polyolefin and the fiber and/or polar polymer. The first polymer may be characterized as a polyolefin polymer or copolymer with only 10 to 30 percent crystallinity. As described later the first polymer with low crystallinity and a low modulus may be a blend (reactor blend, physical blend, etc.) of a very low crystallinity polymer with a conventional semi-crystalline polyolefin. The second polymer is a functionalized polyolefin (e.g. semicrystalline polyolefin) with from about 0.5 to about 3.5 mole percent of functional repeating units. Preferred functional groups are carboxylic acid groups and/or anhydride from a di or poly carboxylic acid. For the purposes of this application the polyolefin can be derived from polymerizing monoolefins or from polymerizing diolefins and then hydrogenating them to obtain similar microstructures to polyolefins. These polyolefins from diolefins can be block copolymers with other monomers such as stryene.
In some embodiments, the functionalized polyolefin and the polyolefin with the low flexural modulus and low crystallinity are the only required components of a hot-melt composition with excellent adhesion to polar polymers and textile fibers.
In another embodiment, a crosslinked rubber is present so that the rubbery properties of a thermoplastic vulcanizate are present.
In yet another thermoplastic vulcanizate embodiment, both a conventional high modulus polyolefin and rubber are present. The high modulus polyolefin can increase the stiffness and/or increase the softening temperature of the composition for uses requiring stiffness or having a higher use temperature requiring a higher softening temperature for the TPV.
Any of the above compositions can be used to adhere to polar polymers, metal, high tensile strength fibers and/or sheets. The excellent adhesion attributed to the combination of functionalized polyolefin and low crystallinity and low flexural modulus polyolefin is well utilized in melt processing a thermoplastic vulcanizate around a fiber or metal (e.g. wire) reinforced assembly.
Hydrosilylation crosslinking is a particularly advantageous type of crosslinking for the rubber phase as it has minimal side reactions with the functionalized polyolefin allowing the functionalized polyolefin to be blended with the other components before crosslinking the rubber phase.
DETAILED DESCRIPTION
The components of the invention vary depending on the requirements of the particular application. Two polymers are common to all applications. They are the low crystallinity, low flexural modulus polyolefin and the functionalized polyolefin. Other components that can be added are a rubber phase (usually crosslinked by dynamic vulcanization), an additional one or more semicrystalline polyolefins with higher flexural modulus, and conventional additives to a hot-melt adhesive or thermoplastic vulcanizate.
The first polyolefin can also be described as a polyolefin with low levels of crystallinity as compared to a highly isotactic semicrystalline polypropylene. Desirably the first polyolefin has from about 10, 12, 14, or 15 to about 20, 25, 26.5, 30, or 32 weight percent crystallinity. The weight percent crystallinity can be determined by dividing the heat of fusion of the sample as received by the heat of fusion of 100% crystalline polypropylene (assumed to be 209 joules/g). The first polyolefin, with low flexural modulus (tangent), can generally be any polyolefin with low polyolefin crystallinity and a flexural modulus desirably from about 5,000 to about 20,000 psi (34.5-138 MPa), more desirably from about 7,500 to about 17,500 psi (51.7-121 MPa) and preferably from about 9,000 to about 16,000 psi (62 to 110.4 MPa). The flexural modulus is measured by ASTM D 790A test method at 23° C.
The first polyolefin can be a homopolymer with low crystallinity due to random or regular variations in tacticity, a copolymer that has low crystallinity due to the comonomer(s) and/or random or regular variations in tacticity (including blockly homo and copolymers), and polymers prepared by blending or grafting together oligomers or polymers. In particular, atactic and isotactic polypropylene (PP), in-situ blends, long isotactic PP sequence metallocene catalyzed ethylene-propylene copolymers (EP's), elastic PPs with stereoblocks of atactic PP and isotactic PP (which can be metallocene catalyzed), isotactic PPs with metallocene catalyzed asymmetrical stereoerrors, isotactic PP and atactic PP combinations by blending or by stereoblocks from mixed metallocenes, and PPs that have an atactic PP backbone with isotactic PP branches using metallocene catalysis. 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 70, 80, or 90 weight percent of the repeat units are from olefin monomers having from 2 to 8 carbon atoms and preferably at least 70, 80, or 90 weight percent are derived from propylene monomer. Examples of operative low flexural modulus, low crystallinity polymers are Rexflex® 101 from Huntsman in Houston, Tex., characterized as a reactor blend of atactic and
Hill Marvin
Johnson Jim
Advanced Elastomer Systems L.P.
Laferty Samuel B.
Mullis Jeffrey
Skinner William A.
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