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
1999-01-14
2001-04-03
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...
C524S493000, C524S495000, C152S905000
Reexamination Certificate
active
06211281
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pneumatic tire for heavy duty use. More particularly, the present invention pertains to a pneumatic tire for heavy duty use which is particularly well suited for constructional vehicles and the like and in which a carbon black-reinforced rubber composition is employed in a tread of the tire, said rubber composition being excellent in abrasion resistance and heat buildup performance (property of exhibiting low heat-buildup).
2. Description of the Related Arts
In order to improve the abrasion resistance of tread rubber of pneumatic tires, such improvements have heretofore been made by calling attention to the colloidal characteristics of reinforcing carbon black such as its particle diameter and structure (aggregates) For the improvement in carbon black for pneumatic tires, there is adopted in general, a method in which the interaction between carbon black and a polymer is enhanced by using carbon black having small particle sizes and high structures, and thus the reinforcing property is improved by the enhanced interaction therebetween. There is also adopted a method in which the blending amount of carbon black is increased to improve the abrasion resistance of the tread ruber.
In general, however, fine graining of carbon black is liable to deteriorate the low heat-buildup property, that is, heat buildup performance of a rubber composition. Thus, fine-grained carbon black gives rise to a serious problem when used for a heavy duty pneumatic tire such as a tire for a truck and a bus that are in use under severe conditions in many cases. In addition, the use of excessively fine-grained carbon black in a rubber composition brings about such problems as an increase in the amount of the phase wherein carbon black and a polymer are bound to each other, namely so-called carbon gel, accompanied by an increase in the viscosity of an unvulcanized rubber composition, and the resultant marked deterioration of the processability thereof. The use of the said carbon black further causes such a problem that the carbon black is poorly dispersed in a rubber composition with the result that the abrasion resistance thereof is adversely decreased.
In addition to the foregoing, when carbon black as a reinforcer is added to rubber in an excessive amount, there are raised a problem that the resultant rubber composition is unreasonably hardened, thereby making it difficult to carry out industrial processing, and at the same time, a problem in the physical properties of the rubber composition including inferior dispersion of the carbon black in the rubber composition and a failure to contrive enhancement of the abrasion resistance.
On the one hand, the use of carbon black having a high structure causes such a problem as unreasonable increase in the elastic modulus of the rubber composition, accompanied with deterioration of its fatigue resistance.
It follows from what has been mentioned hereinbefore, that the conventional methods for enhancing the abrasion resistance of a rubber composition by means of carbon black exert evil influences upon its low heat-buildup property, and particularly in the case of a heavy duty pneumatic tire, there has been an inevitable limit to the effect on improvement in its abrasion resistance.
On the other hand, there has recently been proposed as well a method for decreasing the proportion of large-diameter components of the aggregate that are considered to be the factors of inhibiting rubber enhancement, by sharpening the aggregate distribution of the primary particles of carbon black (refer to Japanese Patent Application Laid-Open Nos. 264647/1988 (Sho-63), 279624/1994 (Hei-6), etc.
SUMMARY OF THE INVENTION
Under such circumstances, a general object of the present invention is to provide a pneumatic tire for heavy duty use which is remarkably improved in low heat-buildup property without worsening the abrasion resistance of a tread rubber.
In view of the above, intensive research and investigation were accumulated by the present inventors in order to develop a pneumatic tire for heavy duty use which has the above-mentioned favorable properties. As a result, it has been found that although further enhancement of abrasion resistance of a tread rubber is not expectable from the use of merely fine-grained carbon black owing to the deteriorated low heat-buildup property of the rubber and also the worsened dispersibility of carbon black, such deterioration of low heat buildup property of the rubber as well as the worsening of dispersibility of carbon black can favorably be suppressed and at the same time, the abrasion resistance of the tread rubber can markedly be improved by expanding the width of aggregates distribution simultaneously with the fine-graining of carbon black. Further it has been found that the object of the present invention can be achieved by a pneumatic tire for heavy duty use employing a specific rubber composition which comprises an isoprene-based rubber and carbon black having specific properties, and as the case may be, silica having specific properties, each of the components being blended at a prescribed proportion. The present invention has been accomplished on the basis of the above-mentioned findings and information.
That is to say, the present invention provides a pneumatic tire for heavy duty use having a tread which is composed of a rubber composition comprising 100 parts by weight of an (A) isoprene-based rubber and 30 to 70 parts by weight of (B) carbon black which has a nitrogen-adsorption specific surface area (BET) of 120 to 160 m
2
/g; a dibutyl phthalate absorption amount (DBP) of 80 to 130 ml/100 g; a most frequent value of aggregate diameter distribution (D
st
) of 60 to 70 nm; and a half peak width (&Dgr;D
50
) of 65 to 80 nm; and as the case may be, 3 to 20 parts by weight of (C) silica which has a nitrogen-adsorption specific surface area (BET) of 210 to 260 m
2
/g; and an oil absorption amount of 200 to 260 ml/100 g.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the rubber composition to be employed as a tread in the pneumatic tire for heavy duty use according to the present invention, the isoprene-based rubber to be used as the component (A) is exemplified by natural rubber and polyisoprene (IR) which is obtained by the polymerization of isoprene monomer. Among the polyisoprene which is a synthetic rubber, the polyisoprene in which cis 1,4-bond occupies about 98% of all the bonds has a molecular structure extremely similar to that of natural rubber, and thus has fundamental characteristics akin to those of natural rubber.
In the above-mentioned rubber composition, the carbon black to be used as the component (B) needs to have the characteristics as described in the following.
In the first place, the nitrogen-adsorption specific surface area (BET) of the component (B) as measured in accordance with ASTM D-3037-88, should be in the range of 120 to 160 m
2
/g. The BET value, when being less than 120 m
2
/g, results in failure to assure sufficient abrasion-resistance of a tread rubber, whereas the BET value, when being more than 160 m
2
/g, leads to deterioration of low heat-buildup property. Taking into consideration both the abrasion resistance and the low heat-buildup property, the BET value is preferably in the range of 125 to 145 m
2
/g.
In addition, the aforesaid dibutyl phthalate absorption amount (DBP) thereof as measured in accordance with JIS K 6221-1982 (Method A), should be in the range of 80 to 130 ml/100 g. The DBP value, when being less than 80 ml/100 g, results in failure to assure sufficient abrasion-resistance of a tread rubber, whereas the DBP value, when being more than 130 ml/100 g, leads to deterioration of low heat-buildup property. Taking into consideration both the abrasion resistance and the low heat-buildup property, the DBP value is preferably in the range of 85 to 120 ml/100 g.
Moreover, the most frequent value of aggregate diameter distribution (D
st
) thereof should be in the range of 60 to 70 nm. The D
st
value, when be
Bridgestone Corporation
Rajguru U. K.
Seidleck James J.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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