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
2001-06-07
2002-11-05
Short, Patricia A. (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...
C525S054440, C525S126000
Reexamination Certificate
active
06476134
ABSTRACT:
The invention generally involves a polymer material comprising a mixture of two different polymers and its preparation. One of the two polymers is modified by at least one reactive additive during mixture preparation. The reactive additive(s) alter(s) physical property(ies) of the polymer, such as hardness, plasticity and viscosity. The physical property alterations can lead, in turn, to an improvement in dispersion of the modified polymer in a matrix of the other polymer. The modified polymer is usually at least partially crosslinked or vulcanized during preparation of the polymer material. Such crosslinking preferably occurs by way of dynamic vulcanization.
Flexible, single-phase or two-phase thermoplastic elastomeric polymer materials are used today in place of traditional materials in several industrial applications. For example, the thermoplastic elastomeric polymer materials may displace typical rubber materials for any of several reasons. One reason stems from limited recyclability of rubber materials. A second reason lies in a requirement to use more expensive production technology to convert a rubber raw material into finished product than is required for a typical thermoplastic material. Typical finished products that may be formed from such thermoplastic elastomer materials include shaped structures such as shock absorbers, seals or other profiled structures, boots, shoe soles, and cover sheets (“synthetic leather”/decorative sheets).
Plasticized poly(vinyl chloride) (PVC-P) and durably crosslinked rubber materials are predominantly used today for a number of mass-produced articles such as flexible tubing, wire insulation, and consumer goods that require highly flexible polymer materials. A significant disadvantage of flexible PVC products is that one must usually add a considerable quantity of plasticizer to PVC in order to achieve a desired level of flexibility. Unfortunately, plasticizers tend to diffuse from, or exude to external surfaces of, PVC-P articles. Exposure to elevated temperatures (e.g., in excess of 35° Centigrade (°C.)), solvents or both may accelerate such diffusion or exudation. Some allege that plasticizer diffusion from articles such as toys for infants may constitute a health hazard. In the case of automobiles, plasticizer diffusion leads to a phenomenon known as fogging, an undesirable clouding of the windows. In addition, the PVC from which the plasticizer diffuses hardens over time, thereby more or less losing its functional capability. Furthermore, PVC-P in wire applications does not fulfill certain test criteria, such as hot set, due to its low softening temperature range (55-70° centigrade (°C.)). On the other hand, crosslinked rubber materials are generally used only where crosslinking of molecular chains is required for thermal, chemical, and/or mechanical reasons (for example, tubing/seals in motors or chemical installations, rollers, and durable elastic bearings.).
Polyethylenes crosslinked with silane are known as high dielectric strength wire insulation materials, primarily for medium and high voltage ranges. They also fulfill high temperature specifications (such as hot set) for this application and in addition, do not contain plasticizer (see, for example, DE-OS 23 50 876, 22 55 116, and 24 06 844). Silane-crosslinked polyethylenes with a good property profile nevertheless have a disadvantage in that silane crosslinking creates a three dimensional macromolecular spatial structure in a finished part that renders the crosslinked material resistant to remelting. As such, the crosslinked material is not recyclable. In addition, preparation of the crosslinked material involves reactive compounding, and extrudate shaping is very labor and cost intensive.
A series of other flexible and thermoplastically processible polymer materials suggested as alternatives to PVC-P may be summarized under the term “thermoplastic elastomers” (TPE). TPE materials are disclosed, for example, in European Patent Application EP 0 325 573, wherein a synthetic rubber component is used in admixture with polyethylene. TPEs have disadvantages such as their relatively high cost compared to alternate materials, potentially inadequate resistance to certain chemicals and petroleum products, and, when used for soft applications, a need for an undesirably high level of physically admixed plasticizers such as 40 to 80 parts of plasticizer per 100 parts of polymer.
Thermoplastic polyurethanes (TPE-U or TPU) are a subclass of the TPE family. They have outstanding mechanical properties that make them suitable for use in fabricating shaped structures that are subject to significant mechanical stresses, such as shoe soles, roller coverings, and conveyor rollers. TPUs may not be suitable for use in certain applications due to high cost relative to alternate materials, difficult processing when used in soft applications, and a lower hardness scale limit of 70 Shore A when used without plasticizers.
The above disadvantages help define a need or pose a problem to be solved. The need is for a highly flexible, economically produced, thermoplastically processible, soft material that is based on TPU and includes a second polymer. The material desirably avoids most of the above disadvantages of known molding materials. As an example, when the second polymer is an ethylene/vinyl ester polymer, “highly flexible” refers to a Shore A hardness (American Society for Testing and Materials (ASTM) Test D-2240) within a range of 45 to 75, preferably 45-70, and a 100% modulus (tensile modulus at an elongation of 100%) within a range of 0.5 to 2.5 megapascals (MPa). Skilled artisans can readily determine comparable properties for other ethylene copolymers, such as ethylene/(meth)acrylic acid esters, deemed suitable for use as the second polymer.
The present invention addresses this need by providing a two-phase polymer material that comprises a continuous matrix polymer phase and a co-crosslinked, microdispersed soft phase, the continuous matrix polymer phase comprising a thermoplastic polyurethane (TPU) (A) selected from the group consisting of thermoplastic polyether urethanes, thermoplastic polyester urethanes and mixtures thereof, and the dispersed soft phase comprises a product of a reaction between an ethylene copolymer (B) selected from the group consisting of ethylene/vinyl ester copolymers with a vinyl ester content within a range of 5-50% by weight of the copolymer and ethylene/(meth)acrylic acid ester copolymers with a methacrylic acid ester content within a range of 5-50% by weight of the copolymer and an additive combination (C) that comprises a reactive plasticizer and an organic peroxide. The term “(meth)acrylic” is a generic term for both acrylic and methacrylic. “Soft” refers to a Shore A hardness of 45-70. The TPU is desirably present in an amount of more than 30 percent by weight, and the reaction product is desirably present in an amount of is at least 25 percent by weight, the percentages being based on total polymer material weight and selected to total 100 percent.
The organic peroxide, when activated, yields peroxide radicals that initiate hydrogen abstraction and promote formation of carbon-carbon crosslinks in the ethylene copolymer. The reactive plasticizer contains epoxy groups that react with hydroxyl groups in the ethylene copolymer and form covalent linkages or couplings between the plasticizer and the ethylene copolymer. This reaction tends to fix the plasticizer in place, thereby reducing its ability to migrate and weaken the TPU matrix.
The two-phase materials of the present invention polymer materials are desirably prepared by (a) melt mixing a TPU (A) with ethylene copolymer (B), (b) adding additive combination (C) during melt mixing of (A) and (B) and (c) effecting both dynamic crosslinking of ethylene copolymer (B) by way of peroxide contained in additive combination (C) and co-crosslinking between ethylene copolymer (B) and the reactive plasticizer contained in additive combination (C). As an alternative, ethylene copolymer (B) may be coated with additive
Bolz Uwe
Fritz Han Gerhard
DuPont Dow Elastomers LLC
Short Patricia A.
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