Pneumatic radial tire

Abstract

A pneumatic tire comprising a rubber member containing a short fiber (A′) formed by the fibrillation of a short fiber (A) whose cross section takes a sea-island structure essentially composed of at least two polymers.

What is claimed is:  
     
         1 . A pneumatic tire comprising a rubber member containing a fibrillated short fiber A′ formed by the fibrillation of a short fiber A whose cross section takes a sea-island structure essentially composed of at least two polymers, wherein the fibrillated short fiber A′ has an average diameter of 0.05 to 5.0 μm.  
     
     
         2 . A pneumatic tire according to  claim 1 , which comprises a carcass layer bridging a pair of bead portions, a plurality of belt layers lying in the tread portion on the outside of the carcass layer, and compound sheets lying in both tire widthwise end portions of the belt layers respectively, with the ratio b/a of the tire circumferential modulus b of the compound sheets to the tire radial modulus a thereof being adjusted to 1.2 or above by incorporating a short fiber A′ formed by the fibrillation of the above short fiber A into the rubber constituting the compound sheets in a proportion of 0.5 to 15 parts by weight per 100 parts by weight of the rubber and orienting the fibrillated short fiber A′ in a tire circumferential direction.  
     
     
         3 . A pneumatic tire according to  claim 1 , which comprises a carcass layer bridging a pair of bead portions, a plurality of belt layers lying in the tread portion on the outside of the carcass layer, and compound sheets lying in both tire widthwise end portions of the belt layers respectively, with the ratio of the tire circumferential modulus (b) of the compound sheets to the tire radial modulus (a) thereof (i.e., b/a ratio) being adjusted to 1.2 or above by incorporating a short fiber (A′) formed by the fibrillation of the above short fiber (A) and a composition which comprises a short fiber (B) made of a thermoplastic polymer having amido groups in the main chain and a matrix made of a rubber and/or a polyolefin and wherein the short fiber (B) is dispersed in the matrix and chemically bonded to the matrix into the rubber constituting the compounds sheets in proportions of 0.5 to 10 parts by weight of the fibrillated short fiber (A′) and 1 to 15 parts by weight of the short fiber, (B) per 100 parts by weight of the rubber and orienting the fibrillated short is fiber (A′) and the short fiber (B) in a tire circumferential direction.  
     
     
         4 . A pneumatic tire according to  claim 2 , wherein the fibrillated short fiber (A′) has an average diameter of 0.05 to 5.0 μm.  
     
     
         5 . A pneumatic tire according to  claim 3 , wherein the fibrillated short fiber (A′) has an average diameter of 0.05 to 5.0 μm.  
     
     
         6 . A pneumatic tire according to  claim 5 , wherein the short fiber B has an average diameter of 0.05 to 5.0 μm.  
     
     
         7 . A pneumatic tire according to  claim 2 , wherein the compound sheets have a width of at least 5% of the maximum belt width.  
     
     
         8 . A pneumatic tire according to  claim 2 , wherein the compound sheets have a thickness of 0.3 mm or above.  
     
     
         9 . A pneumatic tire according to  claim 1 , wherein the ratio of the tire circumferential modulus (b) of the tread to the tire radial modulus (a) thereof (i.e., b/a ratio) is adjusted to 1.2 or above by incorporating a short fiber (A′) formed by the fibrillation of the above short fiber (A) into the tread rubber in a proportion of 0.5 to 5 parts by weight per 100 parts by weight of the rubber and, orienting the short fiber (A′) in a tire circumferential direction, and the groove area ratio of the tread is adjusted to 30 to 40%.  
     
     
         10 . A pneumatic tire according to  claim 1 , wherein the ratio of the tire circumferential modulus (b) of the tread to the tire radial modulus (a) thereof (i.e., b/a ratio) is adjusted to 1.2 or above by incorporating a short fiber (A′) formed by the fibrillation of the above short fiber (A) and a composition which comprises a short fiber (B) made of thermoplastic polymer having amido groups in the main chain and a matrix made of a rubber and/or a polyolefin and wherein the short fiber (B) is dispersed in the matrix and chemically bonded to the matrix into the tread rubber in proportions of 0.5 to 10 parts by weight of the fibrillated short fiber (A′) and 1 to 15 parts by weight of the short fiber (B) per 100 parts by weight of the rubber and orienting the fibrillated short fiber (Al) and the short fiber (B) in a tire circumferential direction, while the groove area ratio of the tread is adjusted to 30 to 40%.  
     
     
         11 . A pneumatic tire according to  claim 1 , wherein the tread portion is constituted of at least two layers comprising a cap tread and an under tread, and the ratio of the tire circumferential modulus (b) of the under tread to the tire widthwise modulus (a) thereof (i.e., b/a ratio) is adjusted to 1.5 or above by incorporating a short fiber (A′) formed by the fibrillation of the above short fiber (A) into the rubber constituting the under tread in a proportion the rubber and orienting the fibrillated short fiber (A′) in a tire circumferential direction.  
     
     
         12 . A pneumatic tire according to  claim 1 , wherein the tread portion is constituted of at least two layers comprising a cap, tread and an under tread and the ratio of the tire circumferential modulus (b) of the under tread to the tire widthwise modulus (a) thereof (i.e., b/a ratio) is adjusted to 1.5 or above by incorporating a short fiber (A′) formed by the fibrillation of the above short fiber (A) and a composition which comprises a short fiber (B) made of a thermoplastic polymer having amido groups in the main chain and a matrix made of a rubber and/or a polyolefin and wherein the short fiber (B) is dispersed in the matrix and chemically bonded to the matrix into the rubber constituting the under tread in proportions of 1 to 12 parts by weight of the fibrillated short fiber (A′) and 1 to 10 parts by weight of the short fiber (B) per 100 parts by weight of the rubber and orienting the fibrillated short fiber (A′) and the short fiber (B) in a tire circumferential direction.  
     
     
         13 . A pneumatic tire according to  claim 1 , wherein at least a part of the sidewall is made from a rubber composition containing 0.5to 15 parts by weight of a short fiber (A′) formed by the fibrillation of the above short fiber (A) per 100 part by weight of the rubber.  
     
     
         14 . A pneumatic tire according to  claim 1 , wherein at least a part of the sidewall is made from a rubber composition containing a short fiber (A′) formed by the fibrillation of the above short fiber (A) and a composition which comprises a short fiber (B) made of a thermoplastic polymer having amido groups in the main chain and a matrix made of a rubber and/or a polyolefin and wherein the short fiber (B) is dispersed in the matrix and chemically bonded to the matrix in proportions of 0.5 to 10 parts, by weight of the fibrillated short fiber (A′) and 1 to 15 parts by weight of the short fiber (B) per 100 parts by weight of the rubber.  
     
     
         15 . A pneumatic tire according to  claim 1 , which comprises a carcass layer containing a plurality of carcass cords in a state arranged in the tire radial direction and bridging a pair of bead portions with both tire widthwise end portions of the carcass layer wound up around the bead cores respectively from the tire inner side to the tire outer side, and short fiber reinforced layers lying at least in the wound-up end portions of the carcass layer, with the ratio of the tire circumferential modulus (b) of the short fiber reinforced layers to the tire radial modulus (a) thereof (i.e., b/a ratio) being adjusted to 1.2 or above by incorporating a short fiber (A′) formed by the fibrillation of the above short fiber (A) into the rubber constituting the short fiber reinforced layers in a proportion of 0.5 to 15 parts by weight the fibrillated short fiber (A′) in a tire circumferential direction.  
     
     
         16 . A pneumatic tire according to  claim 1 , which comprises a carcass layer containing a plurality of carcass cords in a state arranged in the tire radial direction and bridging a pair of bead portions with both tire width wise end portions of the carcass layer wound up around the bead cores respectively from the tire inner side to the tire outer side, and short fiber reinforced layer's lying at least in the wound up end portions of the carcass layer, with the ratio of the tire circumferential modulus (b) of the short fiber reinforced layers to the tire radial modulus (a) thereof (i.e., b/a ratio) being adjusted to 1.2 or above by incorporating a short fiber (A′) formed by the fibrillation of the above short fiber (A) and a composition which comprises a short fiber (B) made of a thermoplastic polymer having amido groups in the main chain and a matrix made of a rubber and/or a polyolefin and wherein the short fiber (B) is dispersed in the matrix and chemically bonded to the matrix into the rubber constituting the short fiber reinforced layers in proportions of 0.5 to 10 parts by weight of the fibrillated short fiber (A′) and 1 to 15 parts by weight of the short fiber (B) per 100 parts by weight of the rubber and orienting the fibrillated short fiber (A) and the short fiber (B) in a tire circumferential direction.  
     
     
         17 . A pneumatic tire according to  claim 1 , comprising bead fillers located on the outer peripheral sides of the bead cores respectively, wherein the bead fillers are made of a rubber composition containing a short fiber (A′) formed by the fibrillation of the above short fiber (A) in a proportion of 3 to 15 parts by weight per 100 parts by weight of the rubber in a state oriented in a direction perpendicular to the tire radial direction, whereby the ratio of the storage modulus (b) of the bead fillers in the direction of orientation of the short fiber to the tire radial storage modulus (a) thereof (i.e., b/a ratio) is adjusted to 4 to 10.  
     
     
         18 . A pneumatic tire according to  claim 1 , comprising bead fillers located on the outer peripheral sides of the bead cores respectively, wherein the bead fillers are made of a rubber composition containing a short fiber (A′) formed by the fibrillation of the above short fiber (A) and a composition which comprises a short fiber (B) made of a thermoplastic polymer having amido groups in the main chain and a matrix made of a rubber and/or a polyolefin and wherein the short fiber (B) is dispersed in the matrix and chemically bonded to the matrix in proportions of 3 to 10 parts by weight of the fibrillated short fiber (A′) and 1 to 15 parts by weight of the short fiber (B) per 100 parts by weight in a state oriented in a direction perpendicular to the tire radial direction, whereby the ratio of the storage modulus (b) of the bead fillers in the direction of orientation of the short fiber to the tire radial storage modulus (a) thereof (i.e., b/a ratio) is adjusted to 4 to 10.