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
1999-09-28
2001-08-28
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S234000
Reexamination Certificate
active
06281293
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a mixture composition of a synthetic resin and a rubber having improved compatibility. More specifically, the present invention relates to a mixture composition having improved properties, said mixture composition containing a thermoplastic or thermosetting resin and a nitrile group-containing highly saturated copolymer rubber having enhanced processibility.
BACKGROUND ART
It is well known that a nitrile group-containing highly saturated copolymer rubber which may be obtained by hydrogenating the carbon-carbon double bonds of an acrylonitrile-butadiene copolymer rubber has good heat resistance, weather resistance and oil resistance. Accordingly, there have been attempts to exploit such desirable properties of the copolymer rubber in the preparation of thermoplastic elastomer compositions by blending said rubber with a synthetic resin such as a polyamide (see Japanese Unexamined Patent Publication Nos. 269138/1990, 191656/1990 and 112656/1988). These compositions possess a good balance of such desirable properties as high impact resistance, resistance against aging by heat, weather resistance and mechanical strength.
However, in case the viscosity of a nitrile group-containing highly saturated copolymer rubber is greatly different from that of a synthetic resin to be blended therewith, a mixture composition results due to the incompatibility between them. Therefore, it is required to improve, in particular, the processibility of the nitrile group-containing highly saturated copolymer rubber.
It is suggested a method for imparting good processibility to a nitrile group-containing highly saturated copolymer rubber through lowering the Mooney viscosity of the rubber by a high shear treatment (Japanese Unexamined Patent Publication No. 122103/1991). This suggested method comprises the step of subjecting a hydrogenated nitrile rubber having a Mooney viscosity of 55 to 100 to high shear conditions in the presence of an oxygen donor, e.g., oxygen or a peroxide, as well as a radical transfer agent. The shearing induces thermal degradation of the rubber, thereby lowering the Mooney viscosity of the rubber to the range of 30 to 50.
In this method, the oxygen donor functions to stabilize free radicals generated during the thermal degradation. However, the Mooney viscosity of the rubber produced by this method is known to increase during storage, even in the process of an added anti-oxidant, due to gelation caused by residual peroxides as well as by carboxyl groups, carbonyl groups and others generated by the high shear treatment.
Accordingly, it is an object of the invention to improve the physical properties of a mixture composition obtained by blending a thermoplastic or thermosetting resin with a nitrile group-containing highly saturated copolymer rubber, by way of enhancing the compatibility of said rubber with the resin.
The present inventors have endeavored to develop polymeric compositions that meet the afore-mentioned objective and found that the impact resistance of a mixture composition of a polyamide resin and a nitrile group-containing highly saturated copolymer rubber can be improved over that of a conventional blend, by way of pretreating the hydrogenated acrylonitrile-butadiene copolymer rubber under high shear conditions in a twin screw extruder in the presence of an anti-oxidant to lower its Mooney viscosity to a specific level.
DISCLOSURE OF THE INVENTION
In accordance with an aspect of the present invention, therefore, there is provided a mixture composition comprising:
(A) 90 to 10% by weight of a thermoplastic or thermosetting resin; and
(B) 10 to 90% by weight of a rubber obtained by subjecting a nitrile group-containing highly saturated copolymer rubber to a high-shear treatment in the presence of an anti-oxidant so as to lower the Mooney viscosity of the copolymer rubber by 15 units or more, having a Mooney viscosity of 5 to 135, a molecular weight distribution (Mw/Mn) of 3.0 to 5.0 and a increase 10 units or less in the Mooney viscosity of said rubber in 30 days storage in air under room temperature after lowering Mooney viscosity.
The present invention is described below in more detail.
The high shear-treated nitrile group-containing highly saturated copolymer rubber employed in the present invention is a rubber having a lowered Mooney viscosity, obtained by the steps of hydrogenating carbon-carbon double bonds of a nitrile group-containing unsaturated copolymer rubber and treating the hydrogenated rubber with a high shear force in the presence of an anti-oxidant. The nitrile group-containing unsaturated copolymer rubber may be a copolymer of an ethylenically unsaturated nitrile such as acrylonitrile, methacrylonitrile and &agr;-chloroacrylonitrile with a conjugated diene such as 1,3-butadiene, isoprene, 1,3-pentadiene and 2,3-dimethyl-1,3-butadiene, or a terpolymer or a multi-component copolymer obtainable by copolymerizing the above two types of monomers with at least one copolymerizable monomer, e.g., vinyl aromatic compounds, acrylic acid, methacrylic acid, alkyl acrylate, alkyl methacrylate, alkoxyalkyl acrylate, alkoxyalkyl methacrylate, cyanoalkyl acrylate, cyanoalkyl methacrylate and the like.
The nitrile group-containing highly saturated copolymer rubber to be treated with a high shear force comprises repeating units derived from an ethylenically unsaturated nitrile monomer in an amount of 10 to 60% by weight, preferably 20 to 50% by weight and has 70% or more, preferably 90% or more, of the hydrogenated carbon-carbon double bonds by the partially hydrogenation. If the content of the nitrile monomer-derived repeating units in the rubber is too small, the oil resistance of the rubber becomes unsatisfactory, and if its content is too great, the elasticity of the rubber is undesirably low. Further, if the degree of hydrogenation of the carbon-carbon double bonds exceed 30% by weight, the impact strength of the rubber deteriorates. The nitrile group-containing highly saturated copolymer rubber of the present invention generally has good oil resistance, heat resistance and weather resistance.
Representative examples of the nitrile group-containing highly saturated copolymer rubber may include a hydrogenated acrylonitrile-butadiene copolymer rubber, hydrogenated acrylonitrile-isoprene copolymer rubber, hydrogenated acrylonitrile-butadiene-acrylate copolymer rubber, and hydrogenated acrylonitrile-butadiene-acrylate-methacrylic acid copolymer rubber.
The nitrile group-containing highly saturated copolymer rubber to be treated with a high shear force generally has a Mooney viscosity (ML
4
) in the range of 60 to 150, and an iodine value below 120, preferably below 60.
Such a nitrile group-containing highly saturated copolymer rubber is treated with a high shear force so that the Mooney viscosity of the rubber decreases by 15 units or more, preferably 30 units or more and more preferably 60 units or more, from the range of 60 to 150, to provide a rubber having a Mooney viscosity ranging from 5 to 135, preferably 20 to 120 and more preferably 20 to 90.
The high shear treatment may be conducted in the substantial absence of an oxygen donor such as oxygen, peroxides, nitrates and the like, at a temperature ranging from 200 to 380° C., preferably 240 to 360° C., typically for 50 to 200 seconds, preferably for 90 to 150 seconds, at a shear rate ranging from 500 to 5000 s
−1
, preferably 800 to 4800 S
−1
. The phrase “the substantial absence of an oxygen donor” used herein means the absence of any of the oxygen donors described in Japanese Unexamined Patent Publication No. 122103/1991, and thus, the shear treatment is not necessarily conducted under an atmosphere of an inert gas such as nitrogen.
The high shear-treated nitrile group-containing highly saturated copolymer rubber having a lowered Mooney viscosity exhibits a increase 10 units or less, preferably 5 units in the Mooney viscosity of said rubber in 30 days storage in air under room temperature after lowering Mooney viscosity; and has a molecul
Armstrong Westerman Hattori McLeland & Naughton LLP
Michl Paul R.
Nippon Zeon Co. Ltd.
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