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
1998-05-27
2002-11-05
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...
C525S093000, C525S095000, C525S098000, C525S309000, C525S310000, C524S504000, C524S505000
Reexamination Certificate
active
06476129
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel thermoplastic elastomer composition with superior oil resistance along with elastomeric flexibility, creep resistance at high temperature, superior mechanical strength and moldability. The invented composition can be applied as a material for various molded parts.
2. Background Art
Recently, thermoplastic elastomer has been widely used in various fields such as automobile, electric appliances, wire and cables, medical goods, consumer products and footwear because it has rubber like elasticity without vulcanization and can be molded just like thermoplastics.
A typical example of the thermoplastic elastomer, a block copolymer of a vinyl aromatic compound and a conjugated diene compound, such as styrene-butadiene-styrene block copolymer, however, is inferior in heat resistance, weather resistance and oil resistance, which have limited application fields.
In order to improve these properties, many compositions have been proposed such as a composition between hydrogenated vinyl aromatic-conjugate diene block copolymer and polyolefin as described in Japanese Laid-open Patent Application Specifications Nos. Sho 50-14742 and Sho 52-65551. These compositions have improved weather resistance and heat resistance, however, their oil resistance are still poor and equivalent to that of the above thermoplastic elastomer.
In order to improve the defect of oil resistance, a dynamic-vulcanization method with an organic peroxide for a composition made of a hydrogenated block copolymer, hydrocarbon oil, polyolefin and inorganic fillers are proposed as described in Japanese Laid-open Patent Application Specifications Nos. Sho 58-13203, Sho 58-145751, Sho 59-53548, Sho 59-131613 and Sho 62-48757. These compositions have improved elasticity at high temperature, however, organic peroxide included in the composition may often cause polymer chain scission which lowers mechanical strength of the composition and oil resistance itself is not necessarily enough.
SUMMARY OF THE INVENTION
In these situations, the inventors have made extensive and intensive studies in order to develop a thermoplastic elastomer composition, which not only has superior flexibility, weather and heat resistance, low temperature properties, mechanical strength, moldability typical of hydrogenated block copolymer but also exhibits excellent oil resistance. As a result, it has unexpectedly been found that, when a partially crosslinked thermoplastic elastomer composed of polyolefin and polyacrylate is blended to a hydrogenated block copolymer, the composition exhibits oil resistance equivalent to that of CR and has typical characteristics of the hydrogenated block copolymer itself.
The foregoing object, features and advantages of the present invention will be apparent to those skilled in the art from the appended claims and detailed description.
According to a first embodiment, the present invention comprises a thermoplastic elastomer composition obtainable by melt blending of a compound comprising:
(a) 100 parts by weight of a hydrogenated block copolymer obtained by hydrogenating a block copolymer comprising at least two A polymer blocks comprised mainly of a vinyl aromatic compound and at least one B polymer block comprised mainly of a conjugated diene compound; and
(b) 30-300 parts by weight of a partially crosslinked thermoplastic elastomer obtained by polymerizing an acrylate monomer absorbed in a polyolefin.
According to another embodiment, the invention comprises a thermoplastic elastomer composition obtainable by melt blending of a compound comprising:
(a) 100 parts by weight of a hydrogenated block copolymer obtained by hydrogenating a block copolymer comprising at least two A polymer blocks comprised mainly of a vinyl aromatic compound and at least one B polymer block comprised mainly of a conjugated diene compound;
(b) 30-300 parts by weight of a partially crosslinked thermoplastic elastomer obtained by polymerizing an acrylate monomer absorbed in a polyolefin.
(c) 40-300 parts by weight of non-aromatic rubber use oil; and
(d) 5-70 parts by weight of polyolefin resin.
Preferably, in a thermoplastic elastomer composition according to the first or second embodiment above, said vinyl aromatic compound is styrene and the said conjugated diene compound is butadiene or isoprene.
Further, in a thermoplastic elastomer composition according to the second embodiment above, said polyolefin resin is a propylene homopolymer and/or a copolymer of propylene with ethylene or C
4
-C
8
&agr;-olefin.
In a thermoplastic elastomer composition according to the second embodiment above, said non-aromatic rubber use oil is a oil with kinematic viscosity of 20-800 cSt at 40° C., fluidity point of 0 to −40° C. and flash point of 200-400° C.
DETAILED DESCRIPTION OF THE INVENTION
For easy understanding of the present invention, the essential features and various embodiments of the present invention are enumerated below.
Examples of a vinyl aromatic compound contained in the hydrogenated block copolymer as a (a) component include styrene, &agr;-methylstyrene, vinyltoluene, p-tert-butylstyrene and the like. They can be used individually and in combination. Among these compounds, styrene is preferred.
Examples of a conjugated diene compound include butadiene, isoprene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and the like. They can be used individually and in combination. Among these compounds, butadiene, isoprene and their combination are preferred. Microstructure of B polymer block before hydrogenation can be arbitrarily selected. For example, in the case of polybutadiene block, the content of 1,2-vinyl bond in the block is preferably from 20 to 50%, more preferably 25 to 45%. In the case of polyisoprene block, the content of 1,4 bond in the block is preferably more than 80%, more preferably more than 90%.
As mentioned above, the structure of the block copolymer before the hydrogenation, is comprised of at least two A polymer blocks comprised mainly of a vinyl aromatic compound and at least one B polymer block comprised mainly of a conjugated diene compound. Examples of the block structure include A—B—A, B—A—B—A, A—B—A—B—A, (A—B)
4
—Si, (B—A—B)
4
—Si, (B—A—B)
4
—Sn and the like.
The term “comprised mainly of” used herein in connection with the polymer block means that 50% by weight or more, preferably 70% by weight or more of all monomer units constituting the polymer block are specified monomer units which are main constituents for the respective polymer block. As examples of the remaining monomer units for each of A and B polymer blocks, there should be mentioned conjugated diene and vinyl aromatic compounds can be arranged in random, tapered, block structure or any combination of them. The term “tapered” structure means that the concentration of certain monomer units contained in the polymer block increasingly or decreasingly changes along the polymer chain. With respect to each of the polymer blocks A and B, when the number of the blocks contained before the hydrogenation is two or more, the structures of the blocks may be the same or different.
In the present invention, the hydrogenated block copolymer has a number average molecular weight of from 30,000 to 800,000, preferably from 50,000 to 500,000, and still more preferably from 100,000 to 400,000. When the number average molecular weight of the hydrogenated block copolymer is less than 30,000, mechanical strength and heat resistance of the thermoplastic elastomer composition are disadvantageously lowered. On the other hand, when the number average molecular weight of the hydrogenated block copolymer is more than 800,000, moldability (fluidity) of the thermoplastic elastomer composition becomes low and so surface appearance of the molded articles disadvantageously becomes poor (flow marks occur).
The hydrogenated block copolymer contains A blocks in an amount of from 10 to 45% by weight, preferably from 20 to 40% by weight. When the amount of A blocks is less than 10% by weight, mechanical s
Asahi Kasei Kogyo Kabushiki Kaisha
Mullis Jeffrey
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