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
2000-08-22
2002-06-11
Nutter, Nathan M. (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...
C525S213000, C525S219000, C525S232000, C525S233000, C525S238000, C525S240000, C525S241000
Reexamination Certificate
active
06403720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubber composition suitable for use as, for example, a tire, which is obtained by blending a gelled rubber synthesized with an acid anhydride etc., without substantially decreasing abrasion resistance, with the improved wet performance, and with the decreased rolling resistance, and a process for producing the same.
2. Description of the Related Art
In rubber compositions used for automobile tires etc., rubber compositions superior in drivability on wet road and low in rolling resistance are desired. From such a viewpoint, for example, Japanese Unexamined Patent Publication (Kokai) No. 10-204217 proposes to blend an SBR rubber gel to a rubber composition. This SBR rubber gel is synthesized by a method of cross-linking the SBR rubber with a polyfunctional compound such as divinylbenzene during the polymerization or a method of cross-linking of the polymer after polymerization with a peroxide etc.
SUMMARY OF INVENTION
It is known that, when carbon is blended into rubber the tan &dgr; curve with respect to the temperature becomes broad and the viscoelastic properties are deteriorated. The present inventors engaged in research to develop a rubber composition having a superior wet performance, that is, having a high grip on wet road surfaces and having a low rolling resistance, by mixing a rubber having a low glass transition temperature Tg with a gelled rubber having a high glass transition temperature Tg so as to suppress the incorporation of carbon black to high Tg rubber and hopefully to obtain a rubber composition with the balanced values of tan &dgr; at 0° C. and tan &dgr; at 60° C. As a result, we found that, by mixing a gelled rubber obtained by gelation with a cross-linking agent in the diene rubber, the viscoelastic properties of the rubber composition can be improved. Further, we found that a rubber composition prepared by a two-stage mixing method of premixing the carbon black and other compounding agents to a low Tg rubber, and then mixing the resultant mixture with the gelled rubber obtained by gelation of a high Tg rubber further provides the improved viscoelastic properties.
Accordingly, the objects of the present invention is to provide a rubber composition having a superior tan &dgr; balance, without substantially decreasing the abrasion resistance and with the improved wet performance and decreased rolling resistance and a process for producing the same.
In accordance with the present invention, there is provided a rubber composition comprising 50 to 90 parts by weight of a diene rubber and 50 to 10 parts by weight of a gelled rubber having a toluene swelling index of 16 to 150, based upon the total amount of 100 parts by weight of the diene rubber and the gelled rubber.
In accordance with the present invention, there is also provided a process for producing a rubber composition comprising 100 parts by weight of a starting rubber containing 50 to 90 parts by weight of a diene rubber and 50 to 10 parts by weight of a gelled rubber, the glass transition temperature of the diene rubber being at least 10° C. less than the transition temperature of the gelled rubber, and 30 to 120 parts by weight of a filler, comprising the steps of mixing the diene rubber and at least 80% by weight of the total amount of the filler at a temperature of at least 135° C., and then mixing the gelled rubber and the remaining filler with the resultant mixture.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In a tire use rubber composition comprised of a low Tg (i.e. glass transition temperature) polymer and high Tg polymer, the tan &dgr; around 0° C. is affected to a large extent by the compatibility of the two polymers. The tan &dgr; around 0° C. is improved if the two polymers are incompatible. Further, by blending carbon black to the rubber, the tan &dgr; curve is broadened. Therefore, when the carbon black is predominated in the low Tg polymer and then the high Tg polymer is blended thereto, the incorporation of the carbon black into the high Tg polymer side is suppressed and the tan &dgr; around 60° C. is decreased.
In the present invention, a gelled rubber having a toluene swelling index of 16 to 150 is blended, as the high Tg polymer, to a low Tg polymer of a diene rubber the incompatibility of the two polymers is promoted, the tan &dgr; around 0° C. is improved, and the abrasion resistance is not too much impaired or, in some cases, is even improved. Further, according to the present invention, when the filler such as the carbon black is predominated in the low Tg polymer and when the gelled rubber is added thereto, the tan &dgr; around 0° C. is improved and the tan &dgr; around 60° C. is decreased and the abrasion resistance is maintained.
The gelled rubber used in the present invention may be produced by, for example, reacting a diene rubber such as a styrene-butadiene copolymer rubber (SBR) with maleic anhydride and a phenol compound having an aromatic hydroxyl group (e.g., phenol, t-butylphenol, catechol and t-butyl catechol, hydroquinone, and resorcinol etc.) or a peroxide compound (e.g., dicumyl peroxide etc.) or a mercapto compound (e.g., trithiocyanic acid, 1,10-decanethiol, etc.) at a temperature of 80 to 250° C.
Examples of the above phenol compounds are as follows.
Monophenol Compounds
2,6-di-t-butyl-p-cresol butylated hydroxyanisole (BHA)
2,6-di-t-butyl-4-ethylphenol
Stearyl-&bgr;-(3,5-di-t-butyl-4-hydroxyphenyl) propionate
Bisphenol Compounds
2,2′-methylenebis(4-methyl-6-t-butylphenol)
2,2′-methylenebis(4-ethyl-6-t-butylphenol)
4,4′-thiobis(3-methyl-6-t-butylphenol)
4,4′-butylidenebis(3-methyl-6-t-butylphenol)
3,9-bis[1,1-dimethyl-2-[&bgr;-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl]2,4,8,10-tetraoxapyro[5,5]undecane
Phenol Polymer Compounds
1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane
1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl)benzene
Tetrakis-[methylene-3-(3′,5′-di-t-butyl-4-hydroxyphenyl)propionate]methane
Bis[3,3′-bis(4′-hydroxy-
3′-t-butylphenyl)butyric acid]glycol ester
1,3,5-tris(3 ′, 5′-di-t-butyl-4′-hydroxybenzyl)-S-triazine-2,4,6-(1H,3H,5H)trione
Tocopherol(S)
Other Phenol Compounds
2,6-di-tert-butyl-4-methylphenol (BHT)
Mono(or di-or tri-)(&agr;-methylbenzyl)phenol
2,2′-methylenebis(4-methyl-6-tert-butylphenol)
2,2′-methylenebis(4-ethyl-6-tert-butylphenol)
4,4′-butylidenebis(6-tert-butyl-3-methylphenol)
4,4′-thiobis(6-tert-butyl-3-methylphenol)
1,1-bis(4-hydroxyphenyl)-cyclohexane
2,5-di-tert-butylhydroquinone
2,5-di-tert-amylhydroquinone
comprises the phenol compound abstraction of the hydrogen from the benzyl position or allyl position, adding the benzyl radicals or allyl radicals thus formed to the acid anhydride, and adding the radicals to the double bonds of other rubber molecules or radical coupling them with other rubber molecules to form cross-linking.
The gelled rubber according to the present invention has to have a toluene swelling index of 16 to 150, preferably 16 to 100. The “toluene swelling index” in the present invention is determined by immersing 0.1 g of a gelled rubber in 100 ml of toluene at room temperature for 24 hours, weighing the weight of the rubber at that time (wet weight), then drying the rubber in vacuo at room temperature for 24 hours, measuring the dry weight, and finding the swelling index from the wet weight/dry weight. If the toluene swelling index is too small, the abrasion resistance deteriorates, whereas if it is conversely too large, there is no great difference with normally ungelled rubber and no improvement effects in the viscoelastic properties are observed. Further, a gelled rubber containing at least 0.1% by weight, preferably 0.5 to 10% by weight, of an acid anhydride moiety in the molecule, has less deterioration of the abrasion resistance and in some cases is further improved compared with an ordinary rubber. Further, a rubber composition obtained by
Chino Keisuke
Mihara Satoshi
Onoi Hidekazu
Arent Fox Kintner Plotkin & Kahn
Nutter Nathan M.
The Yokohama Rubber Co. Ltd.
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