GB2178046A - Rubber compositions for tire treads - Google Patents

Abstract

A rubber composition for tire treads comprising 100 parts by weight of a rubber component, 2 to 30 parts by weight of a copolymer of an aliphatic olefin or diolefin having 4 or 5 carbon atoms and an aromatic olefin having 9 or 10 carbon atoms, and 60 to 110 parts by weight of furnace carbon at least 90m<2>/g in N2SA.

Description

SPECIFICATION Rubber composition for tire treads The present invention relates to a rubber composition fortire treads which comprises a copolymer of an aliphatic olefin or diolefin having 4 or 5 carbon atoms and an aromatic olefin having 9 or 10 carbon atoms, and more particularly to such a rubber composition for producing tire treads which are remarkably improved in steering stability during running and in braking property in fine orwetweatherandwhich are also improved in anti-chipping and anti-cracking properties conventionally involving problems.

In recent years, motor vehicles are available with a higher horsepower and a reduced weight, and with this trend, tires need to meet severer requirements in respect of steering stability and braking property. Especially of importance are the handle responsiveness, for example, when the vehicle changes the lane during driving and the braking property in wet weather. There is a demand fortireswhich are improved in these properties.

To meet these requirements, the tread rubber must have an increased coefficient of friction and an improved wet skid property. In orderto give the tread rubber an increased coefficient of friction and an improved wetskid property, it is generally known (1 )to use large quantities of carbon black and oil, (2) to use a styrene-butadiene copolymer having a higher styrene content, and (3) to use resins. However, use of any of these materials impairs the cracking characteristics and heat generation characteristics, so that the tread rubber composition incorporating such a material, if used, adversely affects the life ofthetire and is therefore undesirable.

An object of the present invention is to provide a tread rubber composition which has a high coefficient of friction and a high wet skid property and which does not impairthe cracking characteristics or heat generation characteristics.

The above and other objects ofthe invention will become apparent from the following description.

The present invention provides a rubbercomposition fortiretreads comprising 100 parts byweight of a rubber component, 2to 30 parts by weight of a copolymerofan aliphaticolefin or diolefin having 4 or 5 carbon atoms and an aromatic olefin having 9 or 10 carbon atoms, and 60to 110 parts by weight offurnace carbon at least90m2/g in N2SA.

The rubber composition to be used forthe present invention is at least one of natural rubber (N R) and synthetic rubbers. Examples of useful synthetic rubbers are polyisoprene rubber (iR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene-isobutylene rubber (lIR), ethylene-propylene-diene rubber (EPDM), modified products of these rubbers, blends of such rubbers, etc.

According to the present invention, a copolymer (hereinafter referred to as "AA copolymer") is used which is prepared from an aliphatic olefin or diolefin having 4 or 5 carbon atoms and an aromatic olefin having 9 or 10 carbon atoms. Examples of useful aliphatic olefins or diolefins having 4 or 5 carbon atoms are butene, isobutene, pentene, methylbutene, butadiene, pentadiene and the like. Examples of useful aromatic olefins having 9 or 10 carbon atoms are a-methylstyrene, (3-methyistyrene, 2-phenyl-2-butene, 1 -phenyl-1 -butene, 3-phenyl-1 -butene, 1 -phenyl-1 ,3-butadiene, divinylbenzene, phenylallene, 2-phenyl-1 ,3-butadiene and the like. These monomers or eithertype are usable singly or in admixture.Preferably, the AA copolymer is in the range of 500 to 1000 in weight average molecularweight. Furtherthe copolymer is preferably BOto 1 200C, more preferably 95 to 105"C, in softening point as measured according to JIS K2207. It is suitable to use 2 to 30 parts (by weight, the same as hereinafter) ofthe AAcopolymer per 100 parts ofthe rubber component. lfthe amount is less than 2 parts, a sufficient effect will not be achieved, whereas if it exceeds 30 parts, the mixture is likely to excessively adhere to rolls orthe rotorofa Banbury mixer and will not always be processed free of trouble.

The furnace carbon to be used in this invention is at least 90m2/g in specific surface area (N2S A) as determined by the nitrogen adsorption method of ASTM D3037. If the N2SAvalue is less than 90m2/g,the compositionfallsto retain a high coefficientoffriction and exhibits reduced abrasion resistance. It is suitable to use 60 to 110 parts furnace carbon per 100 parts of the rubber component.

The rubber composition of the present invention is obtained by kneading the above components by a usual apparatus such as rolls, Banbury mixer, kneaderorthe like. In addition totheforegoing components, it isof course possible to incorporate into the composition a known vulcanizing agent, vulcanization accelerator, auxiliary vulcanization accelerator, vulcanization retarder, organic peroxide, reinforcing agent, filler, antioxidant, tackifier, coloring agent, etc.

The present invention will be described in greater detail with reference to the following examples and comparative examples.

The hardness (Hs) was measured according to JIS K6301 . The coefficient offriction was measured on an asphalt road using a portable skid tester. The result is shown in terms of a index using the composition of Comparative Example 1 as a control. The greater the value, the better is the result.

The anti-cracking property was determined with use of a De Mattia flexing tester by subjecting a test piece, 0.5x2.5x30mm,to 300 cycles/min at400C under the condition of 100% elongation strain. The number of cycles rest ining in a Weibull probability of 50% was determined. The result is expressed relative to that achieved by the composition of Comparative Example 1 which is taken as 100. The greaterthe value, the better. The degree of heat generation was measured with use of a Goodrich flexometer by flexing a test piece for 25 minutes underthe conditions of a stroke of4.4mm, load of 10.9kg, numberoffrequencies of 1800r.p.m. and initial temperature of 40C, and thereafter measuring the surface temperature of the test piece. The result is expressed by the surface temperature minus the initial temperature, i.e. 40.

Examples 1 to 6 and Comparative Examples l to 10 Each of rubber compositions was prepared from specified proportions of the rubber component, carbon black, aromatic oil and resin listed in Table 1, and 3 parts of zine white, 2 parts of stearic acid, 1 partof antioxidant (p-phenylenediamine type), 1 part of vulcanization accelerator (thiazole type), 0.4 part of vulcanization accelerator (guanidinetype) and 2 parts of sulfur; by uniformly kneading the ingredients by a Banbury mixer. Table 1 also shows the properties of the compositions. The reference numerals given in Table 1 represent the following.

(1)....E-SBR, 23.5% in styrene content (2)....E-SBR, 40% in styrene content (3)....S-SBR, 25% in styrene content (4)....furnace carbon, 93 in N2SA and 120 in DBP (5)....furnacecarbon, 113 in N2SAand 1 14 in DBP (6)....furnace carbon,72 in N2SAand 120 in DBP (7)....terpenephenol resin, 145"CinTs (8)....aliphatic resin, 145"C in Ts (9)....alkylphenol resin,70 to 85 C in Ts (1 0)...aromatic hydrocarbon resin, 1 300C in Ts (11 )...AA copolymer, "Tack Ace A -100", product of Mitsui Petrochemical Industries Ltd.

E-SBR given above stands for emulsion-polymerized SBR, S-SBR for solution-polymerized SBR, and DBPfor the amount of dibutyl phthalate absorbed.

Test Example 1 Radial tires, 1 75/70HR1 3 in size, for passenger motor vehicles were prepared using the compositions of Examples and Comparative Examples for the tread. The tires were tested for braking property, steering stabilityandchipping property. Table 2 showsthe results.

The dry and wet skid properties ofthe tire were determined by the method specified in UTQGS, U.S. under the conditions of a load of 336kg and pneumatic pressure of 1.8kg cm2. The result is expressed by an index using the composition of Comparative Example 1 as a control. The greater the value, the better.

The steering stability is determined in terms of a cornering power under a load of 400kg.The result is expressed byan index using the composition of Comparative Example 1 as a control. The greaterthevalue,the better.

The anti-chipping property was determined by using the tire for driving 2500km on an extremely bad road and thereafter observing the appearance of the tread. The resultwas evaluated according to five criteria relative to the result achieved by Comparative Example 1 and evaluated as 3. The criterion "5" means excellent, and "1" poor.

TABLE 1 Example 1 2 3 4 5 6 E-SBR(1) 100 100 100 100 50 100 E-SBR(2) S-SBR (3) 50 NR Carbon N-339 (4) 70 70 70 70 Carbon N-220 (5) 90 90 Carbon N-351 (6) Aromatic oil 30 20 30 20 30 30 Resin (7) Resin (8) Resin (9) Resin (10) AA copolymer (11) 10 10 15 25 10 3 Properties Hs 68 70 72 73 67 68 index 103 105 107 110 104 102 Anti-cracking property 150 150 200 180 180 120 Degree of heat generation 31 31.5 41 43 32 31 Comp. Example 1 2 3 4 5 E-SBR(1) 100 100 100 100 40 E-SBR (2) 60 S-SBR (3) NR Carbon N-339 (4) 70 55 Carbon N-220 (5) 90 90 Carbon N-351 (6) 70 Aromatic oil 30 45 20 30 45 Resin (7) Resin (8) Resin (9) Resin (10) AAcopolymer(11) 10 10 Properties Hs 68 70 63 68 72 index 100 100 95 98 101 Anti-cracking property 100 90 110 80 60 Degree of heat generation 31 40 27 29 36 Comp.Example 6 7 8 9 10 E-SBR(1) 100 100 100 100 50 E-SBR (2) S-SBR (3) 50 NR Carbon N-339 (4) 70 Carbon N-220 (5) 90 90 90 90 Carbon N-351 (6) Aromatic oil 30 30 Resin (7) 15 Resin (8) 15 Resin (9) 15 Resin (10) 15 AA copolymer (11) Properties Hs 74 72 68 73 68 ELindex 102 100 100 102 97 Anit-cracking property 50 85 20 60 120 Degree of heat generation 42 43.5 42 43 31 TABLE2 Ex.3 Com.Ex.1 Com.Ex.2 Com.Ex.5 Dry skid property 110 100 101 102 Wetskidproperty 108 100 101 104 Cornering power 103 100 100 100 Anti-chipping property 5 3 3 2 With reference to Table 1, the AA copolymer is added to the composition of Comparative Example 1 to provide the composition of Example 1, or is partly substituted for the aromatic oil of the comparative composition to provide the composition of Example 2.Examples 1 and 2 are almostcomparableto Comparative Example 1 in heat generation property and are higher in index and improved in anti-cracking property.

Comparative Examples 5to 9 are improved over Comparative Example 2 in index by incorporating SBR having a high styrene content or a resin, but are impaired in anti-cracking property or heat generation property.

The composition of Comparative Example3 contains less than 60 parts of carbon and fails to retain a high index. Comparative Example 4 uses carbon less than 90 in N2SA and is lower in 'i-index than Example 1 and Comparative Example 1. Comparative Example 10 is improved over Comparative Example 1 in anti-cracking property but is lower in 'i-index. In anti-cracking property, Example 1 is higherthan Comparative Example 10.

Table 2 revealsthatthe compositions of the present invention exhibit high braking performance and cornering stability and are satisfactory in chipping property.

Claims (3)

1. A rubber composition for tire treads comprising 100 parts by weight of a rubber component, 2 to 30 parts byweightofa copolymerofan aliphaticolefin ordiolefin having 4or5 carbon atoms and an aromaticolefin having 9 or 10 carbon atoms, and 60to 110 parts by weight offurnacecarbon at least90m2lg in N2SA.

2. A rubber composition as defined in claim 1 wherein the copolymer has a weight average molecular weightof500to 1000.

3. A rubber composition substantially as hereinbefore described.