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
2002-07-18
2004-06-01
Moore, Margaret G. (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...
C525S903000, C524S730000, C524S731000, C524S862000
Reexamination Certificate
active
06743868
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for making thermoplastic elastomeric compositions wherein a polyamide, a silicone base, a stabilizer, and optional compatibilizer are first mixed, then a hydrosilation catalyst and subsequently an organohydrido silicon compound are added, and the silicone base is dynamically vulcanized.
BACKGROUND OF THE INVENTION
Thermoplastic elastomers (TPEs) are polymeric materials, which possess both plastic and rubbery properties. They have elastomeric mechanical properties but, unlike conventional thermoset rubbers, they can be re-processed at elevated temperatures. This re-processability is a major advantage of TPEs over chemically crosslinked rubbers since it allows recycling of fabricated parts and results in a considerable reduction of scrap.
In general, two main types of thermoplastic elastomers are known. Block copolymer thermoplastic elastomers contain “hard” plastic segments, which have a melting point or glass transition temperature above ambient as well as “soft” polymeric segments which have a glass transition or melt point considerably below room temperature. In these systems, the hard segments aggregate to form distinct microphases and act as physical crosslinks for the soft phase, thereby imparting a rubbery character at room temperature. At elevated temperatures, the hard segments melt or soften and allow the copolymer to flow and to be processed like an ordinary thermoplastic resin.
Alternatively, a thermoplastic elastomer referred to as a simple blend (physical blend) can be obtained by uniformly mixing an elastomeric component with a thermoplastic resin. When the elastomeric component is also cross-linked during mixing, a thermoplastic elastomer known in the art as a thermoplastic vulcanizate (TPV) results. Since the crosslinked elastomeric phase of a TPV is insoluble and non-flowable at elevated temperature, TPVs generally exhibit improved oil and solvent resistance as well as reduced compression set relative to the simple blends.
Typically, a TPV is formed by a process known as dynamic vulcanization, wherein the elastomer and the thermoplastic matrix are mixed and the elastomer is cured with the aid of a crosslinking agent and/or catalyst during the mixing process. A number of such TPVs are known in the art, including some wherein the crosslinked elastomeric component can be a silicone polymer while the thermoplastic component is an organic, non-silicone polymer (i.e., a thermoplastic silicone vulcanizate or TPSiV). Representative examples of TPSiVs are disclosed in U.S. Pat. Nos. 6,013,715, 6,153,691, 6,362,287, and 6,362,288.
The present inventors have unexpectedly found an improved process for preparing polyamide (nylon) based TPSiVs. While U.S. Pat. Nos. 6,362,287, and 6,362,288 disclose polyamide based TPSiVs, the methods taught therein were limited to polyamides that were rheologically stable under mixing conditions. In particular, the methods of U.S. Pat. Nos. 6,362,287, and 6,362,288 were unsuccessful to prepare a TPSiV based on nylon 11. The present invention provides for an improved process for making polyamide TPSiVs and in particular provides a process for preparing nylon 11 based TPSiVs.
SUMMARY OF THE INVENTION
The present invention relates to a method for preparing a thermoplastic elastomer comprising:
(I) first mixing;
(A) a polyamide resin having a melting point or glass transition temperature of 25° C. to 275° C.,
(B) a silicone base comprising,
(B′) 100 parts by weight of a diorganopolysiloxane gum having a plasticity of at least 30 and having an average of at least 2 alkenyl radicals in its molecule and, optionally,
(B″) 5 to 200 parts by weight of a reinforcing filler, the weight ratio of the silicone base to the polyamide resin is from 35:65 to 85:15,
(C) 0.1 to 5 parts by weight of a stabilizer for each 100 parts by weight of the polyamide and the silicone base,
and optionally,
(D) 0.1 to 10 parts of a compatibilizer for each 100 parts by weight of the polyamide resin,
then;
(II) adding
(E) a hydrosilation catalyst,
and subsequently,
(F) an organohydrido silicon compound which contains an average of at least 2 silicon-bonded hydrogen groups in its molecule and components (E) and (F) being present in an amount sufficient to cure the diorganopolysiloxane (B′); and
(III) dynamically curing the diorganopolysiloxane (B′),
wherein at least one property of the thermoplastic elastomer selected from tensile strength or elongation is at least 25% greater than the respective property for a corresponding simple blend wherein the diorganopolysiloxane is not cured.
DETAILED DESCRIPTION OF THE INVENTION
Component (A) of the present invention is a thermoplastic polyamide resin. These resins are well known by the generic term “nylon” and are long chain synthetic polymers containing amide (i.e., —C(O)—NH—) linkages along the main polymer chain. For the purposes of the present invention, the polyamide resin has a melt point (m.p.), or glass transition temperature (T
g
) if the polyamide is amorphous, of room temperature (i.e., 25° C.) to 275° C. The polyamide resin of the present invention is typically dried by passing a dry, inert gas over pellets or powder of the polyamide resin at elevated temperatures. The degree of drying consistent with acceptable properties and processing depends on the particular polyamide and its value is generally recommended by the manufacturer or may be determined by a few simple experiments. It is generally preferred that the polyamide resin contains no more than about 0.1 weight percent of moisture. The polyamide resin, component (A), can be any thermoplastic crystalline or amorphous high molecular weight solid homopolymer, copolymer or terpolymer having recurring amide units within the polymer chain. In copolymer and terpolymer systems, more than 50 mole percent of the repeat units are amide-containing units. Examples of suitable polyamides are polylactams such as nylon 6, polyenantholactam (nylon 7), polycapryllactam (nylon 8), polylauryllactam (nylon 12), and the like; homopolymers of aminoacids such as polypyrrolidinone (nylon 4); copolyamides of dicarboxylic acid and diamine such as nylon 6/6, polyhexamethyleneazelamide (nylon 6/9), polyhexamethylene-sebacamide (nylon 6/10), polyhexamethyleneisophthalamide (nylon 6,I), polyhexamethylenedodecanoic acid (nylon 6/12) and the like; homopolymers of 11-aminoundecanoic acid (nylon 11), and copolymers thereof, polyaromatic and partially aromatic polyamides; copolyamides such as copolymers of caprolactam and hexamethyleneadipamide (nylon 6,6/6), or a terpolyamide (e.g., nylon 6,6/6,6); block copolymers such as polyether polyamides; or mixtures thereof. Typically, the polyamide resins are nylon 6, nylon 12, nylon 6/12 and nylon 6/6, or alternatively nylon 11. Silicone base (B) is a uniform blend of a diorganopolysiloxane gum (B′) and a reinforcing filler (B″).
Diorganopolysiloxane (B′) is a high consistency (gum) polymer or copolymer which contains at least 2 alkenyl groups having 2 to 20 carbon atoms in its molecule. The alkenyl group is specifically exemplified by vinyl, allyl, butenyl, pentenyl, hexenyl and decenyl. The position of the alkenyl functionality is not critical and it may be bonded at the molecular chain terminals, in non-terminal positions on the molecular chain or at both positions. Typically, the alkenyl group is vinyl or hexenyl and that this group is present at a level of 0.001 to 3 weight percent, preferably 0.01 to 1 weight percent, in the diorganopolysiloxane gum.
The remaining (i.e., non-alkenyl) silicon-bonded organic groups in component (B′) are independently selected from hydrocarbon or halogenated hydrocarbon groups which contain no aliphatic unsaturation. These may be specifically exemplified by alkyl groups having 1 to 20 carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl and hexyl; cycloalkyl groups, such as cyclohexyl and cycloheptyl; aryl groups having 6 to 12 carbon atoms, such as phenyl, tolyl and xylyl; aralkyl groups having 7 to 20 carbon
Fournier Frances Marie
Rabe Richard Leroy
Dow Corning Corporation
Zombeck Alan
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