Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1998-12-21
2001-02-06
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S559000, C524S560000, C524S601000, C525S168000, C525S315000, C528S176000, C528S272000, C152S209100
Reexamination Certificate
active
06184283
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rubber composition for tire tread.
Recently because of increasing social demand for reduction of fuel consumption of cars, in the development of low fuel consumption tires which have decreased rolling resistance, it has been generally attempted to decrease hysteresis loss of a rubber composition for tread. In the method to decrease the hysteresis loss, it is known that reduction of an amount of carbon black in the rubber composition for treads and use of silica as a filler are effective.
However decreasing the amount of carbon black increases the electric resistance of the rubber composition for treads, and thus an electric resistance of a tire obtained by using such a rubber composition for treads also becomes high. As a result, static electricity accumulates on the car body and tire, which causes radio noise and sparking at the time of filling fuel oil. Therefore, with respect to a rubber composition containing silica, in which the amount of carbon black is small, how the electric resistance is decreased is important.
The present inventors have found that the electric resistance can be decreased effectively when a specific diester of adipic acid is mixed to a rubber composition prepared by adding silica, and have completed the present invention.
For example, JP-A-60-223840, JP-A-61-66733, JP-A-63-43937, JP-A-1-242644 and JP-A-7-292154 disclose techniques to add an adipic acid ester as a plasticizer to a rubber composition. However, since only carbon black is used as a filler, a technique for decreasing electric resistance is not discovered and there is no disclosure and teaching with respect to the use of a diester of adipic acid for decreasing the electric resistance.
Namely, an object of the present invention is to obtain a rubber composition for treads which contains silica and has a low electric resistance. A further object of the present invention is to obtain a rubber composition for treads which contains silica and has well-balanced characteristics such as a low rolling resistance, abrasion resistance and good wet performance.
SUMMARY OF THE INVENTION
The present invention relates to a rubber composition for treads which comprises 40 to 90 parts by weight of silica and 5 to 40 parts by weight of a diester of adipic acid based on 100 parts by weight of a diene rubber.
In this case, it is preferred that 1 to 5 parts by weight of a metal salt is added further based on 100 parts by weight of the diester of adipic acid.
DETAILED DESCRIPTION
In the present invention, diene rubbers which have been used in the field of tires may be used without any limitation. Examples of the diene rubber are, for instance, natural rubber NR), styrene-butadiene rubber (SBR), isoprene rubber (IR), ethylene propylene diene rubber (EPDM), isoprene-butadiene rubber (IBR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR) and the like. These diene rubbers are used alone or in optional combinations thereof. Among them, the diene rubbers using NR, BR, SBR or IR are preferable from the point that they are general purpose rubbers for tires.
In the present invention, silica which has been used in the field of tires may be used without any limitation. Example of the preferred silica is, for instance, one which has a BET specific surface area of from 150 to 250 m
2
/g and a DBP oil absorption amount of from 190 to 280 ml/ 100 g from the viewpoints of an effect of reinforcing a rubber and a rubber processability.
Examples of such silica which is commercially available are, for instance, NIPSIL VN3 and NIPSIL AQ which are available from Nippon Silica Kabushiki Kaisha, Z1165MP and Z165Gr which are available from Rhône-Poulenc Co., Ultrasil VN3 available from Degussa Co., and the like.
An amount of silica added in the present invention may be from 40 to 90 parts by weight based on 100 parts by weight of the above-mentioned diene rubber, preferably from 60 to 90 parts by weight from the point of securing wet performance.
In the present invention, a diester of adipic acid is added, which decreases an electric resistance of the obtained rubber composition for treads. It can be considered that the existence of free electrons on oxygen atom of an ester bond can decrease the electric resistance of the obtained rubber composition for treads.
Examples of such diester of adipic acid are, for instance, di(polyethylene glycol) adipate (a reaction product of adipic acid and polyethylene glycol) represented by the formula (1): HO—(CH
2
—CH
2
—O)
m
—OOC—(CH
2
)
4
—COO—(O—CH
2
CH
2
)
m
—OH, in which m is an integer of from 10 to 20, di(diethylene glycol monoalkyl ether) adipate (a reaction product of adipic acid and ether) represented by the formula (2): C
n
H
2n+1
—O—C
2
H
4
—O—C
2
H
4
—OOC—(CH
2
)
4
—COO—C
2
H
4
—O—C
2
H
4
—O—C
n
H
2n+1
, in which n is 1, 2 or 4, and the like. From the viewpoint of high electric conductivity, it is preferred to use a compound represented by the formula (1).
The amount of the diester of adipic acid may be from 5 to 40 parts by weight based on 100 parts by weight of the above-mentioned diene rubber, preferably from 15 to 30 parts by weight from the point of balancing of electric resistance and abrasion resistance.
Also, the diester of adipic acid used in the present invention can be prepared, for example, from polyethylene glycol and adipic acid through usual method.
Further in the present invention, it is preferred to add a metal salt, particularly a perchloric acid salt of metal. This is because in the obtained rubber composition for treads, a metal ion forms a network with oxygen atom in the molecule of the diester of adipic acid to cause an ion conductivity and thus an electric resistance of the obtained rubber composition for treads can be decreased.
Such a metal salt may be one which can provide a metal ion in the rubber composition of the present invention. Examples thereof are, for instance, perchloric acid salts such as LiClO
4
, KClO
4
, NaClO
4
and Mg(ClO
4
)
2
, and particularly a lithium salt is preferred. Among them, LiClO
4
is preferred from the points of being free from a risk of an explosion and being safe and enhancing abrasion resistance of the obtained tread.
An adding amount of the metal salt may be from 1 to 5 parts by weight based on 100 parts by weight of the above-mentioned diester of adipic acid, preferably from 3 to 5 parts by weight from the viewpoint of high electric conductivity.
Further in the present invention, it is preferred to add a silane coupling agent. This is because the addition of the silane coupling agent results in chemical bonding of the above-mentioned diester of adipic acid and a diene rubber through the silane coupling agent, and further the rolling resistance can be reduced and wet performance can be enhanced to reduce dependency of hardness on a temperature.
Silane coupling agents which have been used in the field of tires may be used without any limitation. Examples of the preferred silane coupling agent are, for instance, vinyltrimethoxysilane, vinyltriethoxysilane, N-(2-aminoethyl) -3-aminopropylmethyldimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and the like.
The amount of added silane coupling agent may be the minimum which is necessary for reducing rolling resistance and enhancing wet performance, and can be optionally selected by a person skilled in the art.
In addition to the above-mentioned components, if necessary, to the rubber composition of the present invention optionally be added a filler such as talc, clay or carbon black; a softening agent such as a paraffinic, aromatic or naphthenic process oil; a tackifier such as a cumarone-indene resin, rosine resin or cyclopentadiene resin; a vulcanizing agent such as sulfur or peroxide; a vulcanization accelerator; an activator aid such as a stearic acid or zinc oxide; a rubber antioxidant; and the like, in a range not impairing effects of the present invention.
A method for preparing the rubber composition for treads of the present inv
Komatsuki Masato
Kunisawa Tetsuya
Tsumori Isamu
Asinovsky Olga
Birch & Stewart Kolasch & Birch, LLP
Seidleck James J.
Sumitomo Rubber Industries Ltd.
LandOfFree
Rubber composition for tread does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rubber composition for tread, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rubber composition for tread will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2582065