Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2002-12-06
2004-05-04
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...
C521S150000, C523S218000, C523S219000
Reexamination Certificate
active
06730710
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rubber composition having a superior friction performance on ice, which is suitable for use especially for a tire tread and can be obtained by compounding, into a diene rubber, a foaming (or blowing) agent-containing resin having a resin ingredient mainly composed of a polyolefin resin which is not crosslinkable with a diene rubber, and also relates to a process for production thereof.
2. Description of Related Art
Numerous methods are being studied for improving the frictional force on the ice. For example, a hard foreign matter (e.g., see Japanese Unexamined Patent Publication (Kokai) No. 60-258235, Japanese Unexamined Patent Publication (Kokai) No. 2-274740, Japanese Unexamined Patent Publication (Kokai) No. 2-281051, etc.), a foaming agent (e.g., see Japanese Unexamined Patent Publication (Kokai) No. 62-283001), a porous substance (e.g., see Japanese Unexamined Patent Publication (Kokai) No. 8-003373, Japanese Unexamined Patent Publication (Kokai) No. 9-302153, Japanese Unexamined Patent Publication (Kokai) No. 10-973614, Japanese Unexamined Patent Publication (Kokai) No. 2000-044732, Japanese Unexamined Patent Publication (Kokai) No. 2001-072802, etc.), hollow particulates (e.g., see Japanese Unexamined Patent Publication (Kokai) No. 2-170840, Japanese Unexamined Patent Publication (Kokai) No. 2-208336, Japanese Unexamined Patent Publication (Kokai) No. 11-35736, etc.), or expandable graphite (e.g., see Japanese Unexamined Patent Publication (Kokai) No. 2001-279020) are compounded into a rubber to form microroughness (or microrelief) on the surface of the rubber after vulcanization, whereby the film (or micro layer) of water generating on the contact surface of rubber and ice is removed.
Among these methods, the simplest method capable of forming the desired surface roughness by formation of relatively large spherical voids inside the rubber is the compounding of the above-mentioned hollow particulates. According to this method, not only the micro film (or layer) of water between the rubber and ice can be removed by the formation of roughness on the rubber surface, but also the frictional force on ice can be improved by the ice scraping effect of the shell-like substance of the spheres exposed at the rubber surface. Further, since the reinforcing effect on the rubber matrix is derived from the shells possessed by the spheres, there is no drop in rigidity of the rubber matrix due to the occurrence of voids inside the rubber. However, this method has the disadvantage that the hollow particulates are destroyed by the shear force generating inside the rubber during the mixing and extrusion steps of the rubber. To prevent the destruction at these processing steps, the size of the hollow particulates has to be made sufficiently small. However, if this is done, the size of the hollow particulates inside the rubber after vulcanization also becomes smaller and, as a result, there is the problem that sufficient surface roughness cannot be formed. In the case of thermally expansible hollow particulates, since the hollow bodies are fine particles, before expansion the particles are not destroyed during the processing if the ingredients are designed to expand at curing stage. During the vulcanization, the particles expand and grow in size, and therefore surface roughness suitable for removing the micro film (or layer) of water between the rubber and the ice is formed. However, since a low boiling point hydrocarbon is used as the foaming agent in the temperature region above the boiling point of the hydrocarbon, even if below the melting point of the substance of the shell, the behavior of the particles becomes unstable. Therefore, all of the expansible particles compounded are difficult to expand to a desired size at the time of vulcanization. Further, with expansion by a small amount of a low boiling point hydrocarbon, the expansion pressure is not sufficient for expanding the particles inside the highly packed rubber matrix. Therefore, there are limits to the further increase of the expansion for greatly improving the frictional force on ice.
In the method of forming foams in the rubber after vulcanization by the compounding of a foaming agent, there is none of the problem of destruction of the particles during processing as with the blending of hollow particulates, it is possible to easily form spherical voids at the time of vulcanization by addition of a compounding agent of a suitable size, and the microroughness is advantageously formed on the rubber surface. Further, the foam expansion pressure with a chemical foaming agent is sufficiently large, and therefore, sufficiently large bubble-like voids can be formed in the rubber after the vulcanization. However, the bubbles obtained by compounding just a chemical foaming agent do not possess the shells surrounding the bubbles such as those shown in spherical voids obtained by compounding the above hollow particulates, and therefore, the scraping effect by the shells at the contact surface of the rubber and the ice cannot be expected. Further, since there are no shells around the bubbles, the hardness of the rubber matrix greatly falls with increase in the foaming ratio. When used for the tread part of a winter tire, there is the disadvantage that the steering stability on non-snow covered road surfaces is remarkably impaired.
Another disadvantage of a rubber composition using a foaming agent is that gas is easily escaped from the bubbles at the rubber surface contacting the vulcanization mold at the time of vulcanization and foaming, and therefore, it is not possible to form as large a number of bubbles near the surface of the vulcanized rubber as at the inside. When using such a rubber composition for a tire for an ice- and snow-covered road surface, there is the problem that the desired effect cannot be obtained until the tire is abraded to a certain extent. This type of problem can also be solved by giving shells to the foamable bubbles.
As the techniques for forming a resin-like film which acts as the role of shells around bubbles formed by a foaming agent, the compounding of a foaming agent-containing fiber (Japanese Unexamined Patent Publication (Kokai) No. 1999-60770 and Japanese Unexamined Patent Publication (Kokai) No. 2001-2832), the compounding of a foaming agent-containing water-soluble fiber (Japanese Unexamined Patent Publication (Kokai) No. 2000-191831 and Japanese Unexamined Patent Publication (Kokai) No. 2000-191832), etc. have been proposed. However, the size of the foamable bubbles is restricted by the size of the staple fibers, long foamable bubbles are difficult to be dispersed well in rubber, and it is difficult to replace the effects of ordinary compounding of a foaming agent by just this compounding alone. Further, techniques for obtaining bubble-shaped voids coated with resin films by the simultaneous compounding of a resin co-crosslinkable with a diene rubber and a foaming agent have been proposed (Japanese Unexamined Patent Publication (Kokai) No. 1997-188775 and Japanese Unexamined Patent Publication (Kokai) No. 1997-302133). However, when a resin co-crosslinkable with a rubber is compounded, the resin is diffused in the rubber molecules when heating. In a practical use, it is difficult to obtain desired resin-coated bubbles. Further, even if the resin and foaming agent are simultaneously compounded, the probability that the both components will encounter each other and merge during the mixing of the rubber is low, and therefore either resin-coated bubbles will not be formed or the thickness of the resin-coated layer formed is not enough to improve the frictional force on the ice. Thus, the scraping effect on ice as shown in the case of the presence of shells of hollow particles cannot be expected. Japanese Unexamined Patent Publication (Kokai) No. 1997-188775 and Japanese Unexamined Patent Publication (Kokai) No. 1997-302133 describe that use of a co-crosslinkabile resin with rubber can prevent detachment of the re
Hotaka Takeshi
Mori Makio
Shirokawa Takashi
Foelak Morton
Rader Fishman & Grauer
The Yokohama Rubber Co, Ltd.
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