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
1999-10-12
2001-09-25
Nutter, Nathan M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S216000, C525S240000
Reexamination Certificate
active
06294611
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an olefin thermoplastic elastomer composition which has excellent balance among softness, tensile properties and low-temperature impact resistance and, at the same time, has excellent heat resistance, and a process for producing the same.
BACKGROUND ART
In recent years, thermoplastic elastomers, such as styrene, olefin, polyester, polyamide, and polyurethane thermoplastic elastomers, which are rubbery soft materials, require no vulcanization step, and have the same moldability as thermoplastic resins, have drawn attention from the viewpoints of the rationalization of the process, recycling and the like, and have been extensively used in fields, such as parts for automobiles, parts for domestic electric appliances, parts for medical equipment, electric wires, sundries, civil engineering sheets, building materials and the like. Among others, olefin thermoplastic elastomers comprising mixtures of crystalline propylene polymer resin with an olefin copolymer rubber, such as an ethylene/propylene copolymer rubber or an ethylene/propylene
on-conjugated diene copolymer rubber, are relatively inexpensive and hence have drawn attention as cost-effective materials.
This type of olefin thermoplastic elastomers, however, because they are in the form of a mixture, are likely to cause coarse dispersion or heterogeneous dispersion of the rubber. Therefore, as compared with other thermoplastic elastomers or conventional vulcanized rubber, they are inferior in balance between softness and tensile properties, such as tensile breaking strength and elongation, and balance between softness and low-temperature impact resistance, and, for example, involve a problem that, on substantially the same level of softness, they are inferior in tensile properties and low-temperature impact resistance. In addition, the above type of olefin thermoplastic elastomers have unsatisfactory heat resistance.
In order to solve these problems, processes for producing a composition comprising a crystalline propylene polymer resin and an ethylene/propylene copolymer rubber by polymerization have been proposed. For example, Japanese Patent Laid-Open Publication No. 2054139/1991 discloses an elastoplastic polypropylene composition, produced by successive polymerization, comprising: (A) 10 to 60 parts by weight of a crystalline homopolymer or copolymer of propylene; (B) 10 to 40 parts by weight of a crystalline propylene/ethylene copolymer component insoluble in xylene at room temperature; and (C) 30 to 60 parts by weight of a noncrystalline propylene/ethylene copolymer component soluble in xylene at room temperature and having an ethylene content of 40 to 70% by weight, and Japanese Patent Laid-Open Publication No. 25367/1994 discloses an elastoplastic polypropylene composition, produced by successive polymerization, comprising: (A) 10 to 50 parts by weight of a crystalline homopolymer or copolymer of propylene; (B) 5 to 20 parts by weight of a crystalline propylene/ethylene copolymer component insoluble in xylene at room temperature; and (C) 40 to 80 parts by weight of a noncrystalline propylene/ethylene copolymer component soluble in xylene at room temperature and having an ethylene content of less than 40% by weight.
According to studies conducted by the present inventors, however, although the former composition has excellent balance between softness and low-temperature impact resistance, the balance between softness and tensile properties is poor, while the latter composition has excellent balance between softness and tensile properties, but is poor in balance between softness and low-temperature impact resistance. That is, it has been found that, in both compositions, a simultaneous improvement in balance between softness and tensile properties and balance between softness and low-temperature impact resistance could have not been achieved, and, in addition, the heat resistance is still unsatisfactory.
DISCLOSURE OF THE INVENTION
In view of the above prior art, the present invention has been made. Accordingly, it is an object of the present invention to provide an olefin thermoplastic elastomer composition which has excellent balance between softness and tensile properties and balance between softness and low-temperature impact resistance and, at the same time, has excellent heat resistance, and a process for producing the same.
According to one aspect of the present invention, there is provided an olefin thermoplastic elastomer composition comprising the following components (A) and (B), said composition having been produced by first polymerizing a monomer of the component (A) and then polymerizing monomers of the component (B), said composition having such fractionation properties that, in temperature rising elution fractionation in the temperature range of 0 to 140° C. using o-dichlorobenzene as a solvent, the eluate obtained at 0° C. is 35 to 60% by weight based on the total elution weight and the eluate obtained at 80 to 100° C. is 1 to 5% by weight based on the total elution weight:
(A) 30 to 60% by weight, based on the whole composition, of a propylene homopolymer component having an isotactic index of not less than 90%; and
(B) 40 to 70% by weight, based on the whole composition, of a copolymer of propylene with other &agr;-olefin having 2 to 8 carbon atoms, said copolymer comprising propylene and ethylene as essential components.
According to another aspect of the present invention, there is provided a process for producing the above olefin thermoplastic elastomer composition, said process comprising subjecting a monomer of the component (A) and monomers of the component (B) to successive polymerization in the presence of a catalyst comprising an organoaluminum compound and a solid component, said solid component comprising a titanium atom, a magnesium atom, a halogen atom, and an electron-donating compound as essential components.
BEST MODE FOR CARRYING OUT THE INVENTION
The component (A) as one of the components constituting the olefin thermoplastic elastomer composition according to the present invention is a homopolymer of propylene having an isotactic index of not less than 90%, preferably an isotactic index of not less than 95%. When the isotactic index of the component (A) is less than 90% by weight, the composition as the thermoplastic elastomer has poor balance between softness and tensile properties and poor heat resistance.
The component (B) as the other component constituting the olefin thermoplastic elastomer composition according to the present invention is a copolymer of propylene with other &agr;-olefin having 2 to 8 carbon atoms, the copolymer comprising propylene and ethylene as indispensable components (monomer units). Among others, a copolymer of propylene with ethylene is preferred as the component (B).
&agr;-olefins having 4 to 8 carbon atoms usable herein include, for example, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, and 1-octene.
Further, the component (B) may contain as a comonomer 0.5 to 10% by weight of a nonconjugated diene, such as 1,4-hexadiene, 5-methyl-1,5-hexadiene, 1,4-octadiene, cyclohexadiene, cyclooctadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, 5-butylidene-2-norbornene, or 2-isopropenyl-5-norbornene.
The thermoplastic elastomer composition according to the present invention should be such that, in temperature rising elution fractionation in the temperature range of 0 to 140° C. using o-dichlorobenzene as a solvent, the eluate obtained at 0° C. is 35 to 60% by weight based on the total elution weight and the eluate obtained at 80 to 100° C. is 1 to 5% by weight based on the total elution weight.
When the eluate obtained at 0° C. in the composition is less than the lower limit of the above range and when the eluate obtained at 80 to 100° C. exceeds the upper limit of the above range, the composition as the thermoplastic elastomer has poor balance between softness and tensile properties. On the other hand, when the eluate obtained at 0° C. in the composition is more than the upper limit o
Gotoh Shiroh
Mizukami Shigeo
Takayanagi Kenjiro
Tsuji Tatsumi
Mitsubishi Chemical Corporation
Nutter Nathan M.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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