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
1998-12-31
2001-03-13
Michl, Paul R. (Department: 1714)
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...
C523S212000
Reexamination Certificate
active
06201054
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rubber composition which is suitable for tire treads having excellent wet grip performance.
A higher stability at high speed has been so far required for tires with the development of a highway network, and particularly enhancement of grip performance on a wet road has been required.
For example, JP-A-6-1882, JP-A-6-240050, JP-A-9-241430 and JP-A-9-241426 disclose that mainly from the viewpoint of enhancing wet skid characteristics, ozone resistance and flexibility, a halogenated butyl rubber and a brominated copolymer of isomonoolefin and paramethylstyrene are used as a rubber component and carbon black is added as a reinforcing material.
Recently from the viewpoint of enhancing wet grip performance, silica is added instead of a part or the whole of carbon black.
In that case, in the rubber composition containing silica, since dispersibility of silica is low, there was a problem that characteristics of silica such as an enhancement of abrasion resistance and wet grip performance cannot be exhibited sufficiently.
An object of the present invention is to obtain a rubber composition for tire treads which comprises a rubber component containing a brominated isobutylene/ paramethylstyrene copolymer and a specific wet silica and has an enhanced wet grip performance.
SUMMARY OF THE INVENTION
The present invention relates to a rubber composition for tire treads which comprises; a polymer containing not less than 30% by weight of a brominated isobutylene/paramethylstyrene copolymer, wet silica having a BET specific surface area of 100 to 250 m
2
/g after allowed to stand at 150° C. for 0.5 hour in nitrogen atmosphere in an amount of 50 to 200 parts by weight on the basis of 100 parts by weight of the polymer, and a silane compound, in an amount corresponding to 1 to 15% by weight based on the wet silica, which is represented by the formula (1): Z—R—S
n
—R—Z, (2): Z—R—SH, (3): Z—R—NH
3
, (4) Z—CH═CH
2
or (5) Z—R—X in which R is a divalent hydrocarbon radical having 1 to 18 carbon atoms, n is an interger of 2 to 8, Z is —Si(R
1
)
2
R
2
, —SiR
1
(R
2
)
2
or —Si(R
2
)
3
provided that R
1
is alkyl having 1 to 4 carbon atoms, cyclohexyl or phenyl, R
2
is alkoxyl having 1 to 8 carbon atoms, cycloalkoxyl having 5 to 8 carbon atoms or aryloxy having 6 to 8 carbon atoms and X is halogen atom.
In that case, it is preferred that tan &dgr; (10 Hz, 0° C., 0.5%) is not less than 0.5 and that when a modulus of shearing elasticity G is measured at dynamic shear amplitudes of 5%, 25%, 50%, 100% and 150% three times each under the conditions of a frequency of 10 Hz and a temperature of 70° C., the modulus of shearing elasticity G(5%) at the third measurement of 5% and the modulus of shearing elasticity G(100%) at the third measurement of 10% satisfy the following equations.
G(5%)/G(100%)≦1.6 Equation (I)
and
G(100%)≧0.6 Equation (II)
Also when the wet silica is heated up from 20° C. to 500° C. at a temperature raising rate of 5° C./min, it is preferable that a percentage of weight reduction of the wet silica at 400° C. to that at 100° C. is not more than 0.70% by weight.
DETAILED DESCRIPTION
The brominated isobutylene/paramethylstyrene copolymer is contained in the polymer components of the present invention in an amount of not less than 30% by weight, and from the viewpoint of sufficiently exhibiting characteristics of each component, the content of the copolymer is preferably from 50 to 100% by weight, particularly preferably from 70 to 100% by weight.
The polymer components other than the brominated isobutylene/paramethylstyrene copolymer may be those which exhibit elasticity at normal temperature after the vulcanization. Examples thereof are, for instance, one or a mixture of two or more of diene rubbers such as styrene-butadiene rubber (SBR), natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR) and ethylene propylene rubber (EPPM), chloroprene rubber (CR), butyl rubber (IIR), fluorine-containing rubber (FKM), epichlorohydrin rubber, and the like. Among them, one or a mixture of two or more of the styrene-butadiene rubber (SBR), natural rubber (NR), butyl rubber (IIR) and the like are preferable from the point that they are excellent in mechanical strength and have fatigue resistance and heat resistance.
The rubber composition for tire treads of the present invention contains wet silica which has a BET specific surface area of from 100 to 250 m
2
/g after allowed to stand at 150° C. for 0.5 hour in nitrogen atmosphere. The BET specific surface area is preferably from 150 to 250 m
2
/g from the viewpoint of an enhancement of the mechanical strength of the vulcanized rubber composition. Particularly in case of the rubber composition obtained by adding a relatively large amount of silica, if the BET specific surface area exceeds 250 m
2
/g, at the time when the silica is added to the polymer, the rubber composition becomes too hard, resulting in poor processability.
Examples of such silica are, for instance, “NIPSIL VN3” available from Nippon Silica Kabushiki Kaisha, “ULTRASIL VN3” available from Degussa Co., “TOKUSIL V” available from Kabushiki Kaisha Tokuyama, “CARPLEX XR” available from Shionogi & Co., Ltd., and the like.
Further in the present invention, when the wet silica is heated up from 20° C. to 500° C. at a temperature raising rate of 5° C./min, it is preferable that a percentage of weight reduction of the wet silica at 400° C. to that at 100° C. (also referred to as “weight reduction percentage”) is not more than 0.70% by weight. Further the weight reduction percentage is preferably from 0.20 to 0.70% by weight from the point that a small amount of water is necessary at the time of chemical bonding of the silane compound and silica.
The wet silica having the weight reduction percentage of not more than 0.70% by weight can be obtained by the method disclosed in JP-A-9-345972. Concretely the wet silica having the BET specific surface area within the above-mentioned range may be heat-treated at 130° to 180° C. under a pressure of 5 to 20 mmHg for 60 to 120 minutes.
An adding amount of the silica in the present invention may be from 50 to 200 parts by weight based on 100 parts by weight of the above-mentioned polymer components. From the viewpoint of maintaining strength of the vulcanized rubber and exhibiting a good processability at kneading, the adding amount is preferably from 50 to 150 parts by weight, particularly preferably from 60 to 120 parts by weight.
In the present invention, the rubber composition contains a silane compound represented by the formulae (1): Z—R—S
n
—R—Z, (2): Z—R—SH, (3): Z—R—NH
3
, (4) Z—CH═CH
2
or (5) Z—R—X in which R is a divalent hydrocarbon radical having 1 to 18 carbon atoms, n is an integer of 2 to 8, Z is —Si(R
1
)
2
R
2
, —SiR
1
(R
2
)
2
or —Si(R
2
)
3
provided that R
1
is alkyl having 1 to 4 carbon atoms, cyclohexyl or phenyl, R
2
is alkoxyl having 1 to 8 carbon atoms, cycloalkoxyl having 5 to 8 carbon atoms or aryloxy having 6 to 8 carbon atoms and X is halogen atom.
In the rubber composition of the present invention, the silane compound functions as a coupling agent to be chemically bonded to both of the silica and polymer for bonding the silica and polymer.
In the formulae (1) to (5), Z is represented by —Si(R
1
)
2
R
2
, —SiR
1
(R
2
)
2
or —Si(R
2
)
3
, R
1
is alkyl having 1 to 4 carbon atoms such as methyl, ethyl, propyl or butyl, cyclohexyl or phenyl, R
2
is alkoxyl having 1 to 8 carbon atoms such as methoxy, ethoxy or buthoxy, cycloalkoxyl having 5 to 8 carbon atoms such as cyclohexyloxy or aryloxy having 6 to 8 carbon atoms such as phenoxy or benzyloxy. R is a divalent hydrocarbon radical having 1 to 18 carbon atoms such as ethylene or propylene.
Examples of the silane compound represented by the formula (1) are, for instance,
and the like. Examples of the commercially available silane compound represented by the formula (1) are Si69 (3,3′-bis(triethoxysilylpropyl)tetrasulfide) a
Hara Seiji
Muraoka Kiyoshige
Birch & Stewart Kolasch & Birch, LLP
Michl Paul R.
Sumitomo Rubber Industries Ltd.
LandOfFree
Rubber composition for tire 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 tire tread, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rubber composition for tire tread will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2442479