Pneumatic tire

Abstract

A pneumatic tire using as a tread part, a rubber composition containing a high silica-content rubber composition having a difference F-S between an amount of filler F and an amount of a softening agent S of 60 to 90 parts by weight and having a durometer hardness measured at 20 C. of 65 to 76.

Claims

1. A pneumatic tire using, as a tread part, a high silica-content rubber composition consisting essentially of: (a) a rubber, (b) a filler F consisting of silica and carbon black, (c) a softening agent S, (d) stearic acid, (e) zinc oxide (f) an antioxidant (g) a paraffin wax, and (h) a silane coupling agent, wherein the silica is contained in an amount of 40 to 102 parts by weight, based upon 100 parts by weight of the rubber, said composition having a difference F-S between an amount of silica and carbon black filler F and an amount of a softening agent S of 74 to 87 parts by weight and having a durometer hardness, measured at 20 C., of 65 to 76, wherein (i) the rubber comprises 100 to 30 parts by weight, based upon 100 parts of the rubber, of a hydroxyl group end-modified solution polymerized styrene-butadiene copolymer (SBR) having (a) an aromatic vinyl content of 15 to 50% by weight, (b) a 1,2-vinyl bond content of a conjugated diene of 10 to 80% by weight and (c) a glass transition temperature of 50 C. to 10 C., wherein said hydroxyl group end-modified solution polymerized styrene-butadiene copolymer (SBR) is prepared by copolymerization of styrene and butadiene to produce styrene-butadiene copolymer (SBR) having an active metal bonded in the molecule, then reacting the SBR having an active metal bonded in the molecule with a modifying agent selected from the group consisting of ketones, ethers, aldehydes and epoxies to introduce primary, secondary or tertiary hydroxy groups into the SBR thereby providing the hydroxyl group end-modified solution polymerized styrene-butadiene copolymer (SBR); (ii) the softening agent S is contained in an amount of 0.1 to 15 parts by weight, based upon 100 parts by weight of the rubber; (iii) the filler F consists of silica and carbon black; wherein the silica has a nitrogen adsorption specific surface area (BET method) of 50 m.sup.2/g to 400 m.sup.2/g and the carbon black has a nitrogen adsorption specific surface area (BET method) of 50 m.sup.2/g to 180 m.sup.2/g and a dibutyl phthalate (DBP) adsorption of 60 ml/100 g to 150 ml/100 g; and (iv) the softening agent S is selected from the group consisting of a rubber process oil, a low molecular weight polymer having a weight average molecular weight of 1000 to 100000, terpene resin, rosin, modified rosin, coumarone-indene resin, blown asphalt, polystyrene resin, C5-based petroleum resin and C9-based petroleum resin.

Description

EXAMPLES

(1) A standard Example, Examples and Comparative Examples will now be used to further explain the present invention, but the scope of the present invention is, of course, not limited to these Examples.

(2) Test Method

(3) 1) Durometer hardness test: The type A durometer hardness was measured at 20 C., based on JIS K6253 using a rubber composition obtained according to a formulation shown in the following Table I.

(4) 2) Wet braking test: Tires having a size of 205/55R16 using a rubber composition obtained according to the formulation shown in the following Table I for the tread part were fabricated, mounted on a car with a displacement of 2500 cc and equipped with ABS, and tested for wet braking performance on a road surface wet with water. The distance until stopping from the start of braking at an initial speed of 100 km/hour was measured. The results are indicated indexed to the Standard Example as 100. The greater the value, the better the braking performance.

Standard Example, Examples 1 to 4, and Comparative Examples 1 to 3

(5) The results are shown in Table I.

(6) TABLE-US-00001 TABLE I Standard Comp. Comp. Comp. Ex. Ex. 1 Ex. 1 Ex. 2 Ex. 3 Ex. 2 Ex. 3 Ex. 4 Formation SBR1.sup.1) 80 80 80 SBR2.sup.2) 80 80 80 80 80 SBR3(S).sup.3) 24 24 24 24 24 24 24 24 Carbon black (F).sup.4) 8 8 8 8 8 8 8 43 Silica (F).sup.5) 75 75 57 75 92 75 75 40 Stearic acid.sup.6) 1 1 1 1 1 1 1 1 Zinc oxide.sup.7) 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Antioxidant.sup.8) 3 3 3 3 3 3 3 3 Paraffin wax.sup.9) 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Silane coupling agent.sup.10) 2.8 6 6 6 6 6 6 6 Oil(S).sup.11) 27 5 5 5 5 5 5 5 Vulcanization accelerator 1.sup.12) 1.9 1.7 1.7 1.7 1.7 1.7 1.7 1.7 Vulcanization accelerator 2.sup.13) 0.5 2 2 2 2 2 2 2 Sulfur.sup.14) 1.8 1.2 1.2 1.2 1.2 1.2 1.2 1.2 F-S 52 74 56 74 91 74 74 74 Physical Properties/Characteristics Hardness 68 68 66 78 Extrusion 75 65 76 impossible Brake performance (index) 100 105 97 97 Extrusion 101 102 101 impossible Notes .sup.1)NS 616 (made by Nippon Zeon), hydroxy group end-modified SBR, styrene amount = 21% by weight, vinyl amount = 70% by weight, Tg = 22 C.; .sup.2)NS 116 (made by Nippon Zeon), amino group end-modified SBR, styrene amount = 21% by weight, vinyl amount = 70% by weight, Tg = 22 C.; .sup.3)Tufdene 1524 (made by Asahi Kasei Chemicals), styrene amount = 18% by weight, vinyl amount = 10% by weight, Tg = 65 C., 20 parts by weight oil extended; .sup.4)Seast 7HM (made by Tokai Carbon); .sup.5)Zeosil 1165MP (made by Rhodia), wet silica, moisture content 6.6% by weight; .sup.6)Beads Stearic Acid (made by NOF); .sup.7)Zinc White Type 3 (made by Seido Chemical Industry); .sup.8)SANTOFLEX 6PPD (made by FLEXSYS); .sup.9)Sannoc (made by Ouchi Shinko Chemical Industrial); .sup.10)Si 69 (made by Degussa); .sup.11)Process X-140 (made by Japan Energy); .sup.12)Noccelar CZ (made by Ouchi Shinko Chemical Industrial); .sup.13)Sansera D-G (made by Sanshin Chemical Industry); .sup.14)Gold Flower brand oil-treated sulfur powder (made by Tsurumi Chemical)

(7) According to Table I, it is learned that the wet performance is improved in a pneumatic tire using a rubber composition satisfying the requirements according to the present invention.