Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-09-04
2004-05-11
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S143000, C521S150000
Reexamination Certificate
active
06734218
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for producing a lightweight foamed rubber, which has superior compressive permanent strain, surface appearance and shape retaining property; a process for producing a lightweight foamed rubber; and a sealing material for car use comprising any one of the foamed rubbers obtained according to those processes.
BACKGROUND OF THE INVENTION
Since an ethylene-&agr;-olefin-non-conjugated diene copolymer rubber has superior properties such as weather resistance, heat resistance and ozone resistance, it has been used as a car part such as a sealing material (for example, a weather strip). The sealing material can be produced from a foamed rubber obtained by foaming and cross-linking a rubber composition containing said copolymer rubber, a foaming agent and a cross-linking agent.
The foamed rubber used for the sealing material is required to have (1) superior compressive permanent strain, because the sealing material has to keep its high sealing property for a long period of time, (2) a high expansion ratio for achieving low cost and lightweight of the sealing material, and (3) superior surface appearance and shape retaining property from a viewpoint of designing property of the sealing material. And recently, these requirements have become greater and greater.
However, foamed rubbers known in the art do not have sufficient processability, foamability with a high expansion ratio, compressive permanent strain, surface appearance and shape retaining property.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for producing a lightweight foamed rubber, which has superior compressive permanent strain, surface appearance and shape retaining property; and a sealing material for car use comprising the foamed rubber obtained according to said processes.
Another object of the present invention is to provide a process for producing a lightweight foamed rubber; and a sealing material for car use comprising the foamed rubber obtained according to said processes.
The present invention provides a process for producing a foamed rubber having a density of from 0.30 to 0.50 g/cm
3
, which comprises the step of foaming and cross-linking a rubber composition containing (i) an ethylene-&agr;-olefin-non-conjugated diene copolymer rubber satisfying the following conditions (A) to (D), (ii) a vulcanizing agent and (iii) a foaming agent;
(A) a xylene-insoluble part in the copolymer rubber is from 5 to 20% by weight, or a cyclohexane-insoluble part therein is from 5 to 30% by weight,
(B) a weight ratio of an ethylene polymerization unit/an &agr;-olefin polymerization unit in the copolymer rubber is from 73/27 to 40/60,
(C) a content of a non-conjugated diene polymerization unit in the copolymer rubber is from 18 to 36 in terms of an iodine value, and
(D) Mooney viscosity (ML
1+4
(121° C.)) of the copolymer rubber measured according to JIS-K-6300-Mooney viscosity test is from 50 to 120 (the process being hereinafter referred to as “Process 1”).
The present invention also provides a sealing material for car use, which comprises the foamed rubber obtained according to the above-mentioned Process 1.
Further, the present invention provides a process for producing a foamed rubber having a density of less than 0.50 g/cm
3
, which comprises the step of foaming and cross-linking a rubber composition containing (i) an ethylene-&agr;-olefin copolymer rubber, (ii) a vulcanizing agent and (iii) a foaming agent having a particle diameter of not more than 10 &mgr;m in terms of a median diameter, wherein an amount of the foaming agent exceeds 4.0 parts by weight per 100 parts by weight of the ethylene-&agr;-olefin copolymer rubber(the process being hereinafter referred to as “Process 2”).
Still further, the present invention provides a sealing material for car use, which comprises the foamed rubber obtained according to the above-mentioned Process 2.
According to the above-mentioned Process 1, a lightweight foamed rubber having superior compressive permanent strain, surface appearance and shape retaining property, can be obtained; and according to the above-mentioned Process 2, a lightweight foamed rubber can be obtained. The above-mentioned Processes 1 and 2 are called collectively “process in accordance with the present invention” in the present invention.
DETAILED DESCRIPTION OF THE INVENTION
A xylene-insoluble part contained in the ethylene-&agr;-olefin-non-conjugated diene copolymer rubber used in the Process 1 in accordance with the present invention is from 5 to 20% by weight, and preferably from 6 to 11% by weight; and a cyclohexane-insoluble part therein is from 5 to 30% by weight, and preferably from 5 to 15% by weight. When respective insoluble parts are less than 5% by weight, an expansion ratio is so low that any lightweight foamed rubber cannot be obtained, and the obtained foamed rubber does not have superior shape retaining property. When the insoluble parts exceed 20% by weight or 30% by weight, respectively, the rubber composition used in the present invention does not have such a good kneading processability that the obtained foamed rubber does not have superior surface appearance.
A weight ratio of an ethylene polymerization unit/an &agr;-olefin polymerization unit in the ethylene-&agr;-olefin-non-conjugated diene copolymer rubber used in the present invention is from 73/27 to 40/60, and preferably from 67/33 to 45/55. In the present invention, “monomer polymerization unit” such as “ethylene polymerization unit” is referred hereinafter to “monomer unit”. When the weight ratio of the ethylene unit exceeds 73, the obtained foamed rubber does not have superior compressive permanent strain at a low temperature, or does not have superior recovery property. When the weight ratio of the ethylene unit is lower than 27, dispersion of a reinforcing agent such as carbon black and an inorganic filler in the rubber composition used in the present invention is so insufficient that the obtained foamed rubber does not have superior surface appearance.
A content of the non-conjugated diene unit contained in the ethylene-&agr;-olefin-non-conjugated diene copolymer rubber used in the Process 1 is from 18 to 36, and preferably from 20 to 29, in terms of an iodine value. When the iodine value is less than 18, a cross-linking density of the obtained foamed rubber is so low that the obtained foamed rubber does not have superior compressive permanent strain. Even if the iodine value exceeds 36, the obtained foamed rubber does not have any further improved compressive permanent strain.
Mooney viscosity of the ethylene-&agr;-olefin-non-conjugated diene copolymer rubber used in the Process 1 is from 50 to 120, and preferably from 75 to 95. When the Mooney viscosity is less than 50, a gas generated by decomposition of a foaming agent used for foaming the rubber composition is hardly retained in the composition, so that any lightweight foamed rubber cannot be obtained. When the Mooney viscosity exceeds 120, the rubber composition used in the present invention does not have good kneading processability and extrusion processability.
In the present invention, the xylene-insoluble part and the cyclohexane-insoluble part are measured according to a method comprising the steps of:
(1) cutting the ethylene-&agr;-olefin-non-conjugated diene copolymer rubber to obtain pieces, each of which has a size of nearly 1 mm square,
(2) weighing about 0.5 g of the pieces with a precision of 0.1 mg, and assigning the weight to be “A” g,
(3) putting the weighed pieces and 150 ml of xylene (250 ml of cyclohexane when the cyclohexane-insoluble part is measured) containing 0.1% by weight of 2,6-di-tert-buty-4-methyl phenol (antioxidant) in a 300 ml Erlenmeyer flask equipped with a ground stopper (500 ml Erlenmeyer flask equipped with a ground stopper when the cyclohexane-insoluble part is measured),
(4) equipping said Erlenmeyer flask with a reflux condenser, and dipping it in a water bath at 100° C. for 6 hours to reflux (this step is not necessary when th
Foelak Morton
Sumitomo Chemical Company Limited
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