Rubber composition for tyre tread

Abstract: A rubber composition for a tyre tread, which has decreased rolling resistance without decreased abrasion resistance comprising 100 parts by weight of a rubber component, 0.5 to 1 part by weight of N,N-bis (2-methyl-2-nitropropyl)-1,6-hexane-diamine, 1 to 1.5 parts by weight of sulfur and 1 to 3 parts by weight of a vulcanisation accelerator, wherein the amount X of sulfur and the amount Y of the vulcanisation accelerator satisfy the equation: 2X-1 ≤ Y ≤ 2X.

Description: The present invention relates to a rubber composition for a tyre tread having low fuel consumption. Recently low fuel consumption of vehicles has been socially demanded, and tyres for low fuel consumption have been widely developed with decreased rolling resistance. In order to decrease the rolling resistance, it is general to lower the hysteresis of the rubber composition of the tyre tread. Proposals are to decrease the amount of carbon black in a rubber composition for the tyre tread or to employ silica as a reinforcing agent. However it is undesirable to decrease the amount of carbon black particularly in tread compounds for a truck or bus tyre, since the abrasion resistance becomes lower with decreasing amount of carbon black. Also there is another problem made by using silica as it give an inferior abrasion property under severe running conditions with heavy load. On the other hand Japanese Examined Patent Publication No 62093/1995, for example, discloses a rubber composition which is excellent in properties such as tread cut resistance without a poor abrasion property, which uses a particular mixing ratio of sulfur and a vulcanisation accelerator. However the rubber composition obtained by that technology still has a problem of high rolling resistance and low abrasion property. US 5 002 829 discloses a rubber composition for a vibration isolator or a tyre including a diamene compound which is N,N'-bis(2-methyl-2-nitropropyl)-1,6-hexane diamene which is added directly to the other components in liquid form. This is to provide not only high heat resistance and high durability but excellent dynamic spring characteristics. However this results in great difficulties in obtaining uniform dispersion of the diamene compound and only very limited improvement to properties of the compound when used in a tyre. The object of the present invention is to provide a rubber composition for a tyre tread, the rolling resistance of which is decreased without decreasing abrasion resistance. Accordingly the present invention provides a rubber composition as set out in Claim 1. There is no particular limitation for the rubber component employed in the present invention, as long as it has been conventionally employed in tyre treads. Examples thereof are natural rubber, butadiene rubber, isoprene rubber, and styrenebutadiene rubber. These can be employed solely or in a combination of two or more thereof. In the present invention 0.5 to 1 part by weight of N,N'-bis(2-methyl-2-nitropropyl)-1,6-hexane-diamine based on 100 parts by weight of the rubber component is mixed and acts to control increase of loss tangent and to decrease heating. From the viewpoint of lowering cost, 0.5 to 0.8 part by weight thereof is preferably mixed. In the present invention 1 to 1.5 parts by weight of sulfur based on 100 parts by weight of the rubber component is mixed in order to provide necessary cross-linking points and to prevent blooming occurring on the surface of the rubber in the presence of unnecessary sulfur. If there are many polysulfide bonds in a rubber composition after vulcanisation, they change to monosulfide bonds due to heat of runningthe tyre, and changes of physical properties such as hardness of the resultant tread are promoted. Therefore, 1 to 1.4 parts by weight thereof is preferably mixed in order to improve durability of a tyre. There is no particular limitation for the vulcanisation accelerator. Examples thereof are, for instance, sulfenamides, thiazoles, thiurams, guanidines, dithiocarbamate salts and the like. In the present invention 1 to 3 parts by weight of the vulcanisation accelerator based on 100 parts by weight of the rubber component is mixed from the viewpoint of controlling physical property change and achieving low fuel consumption. From the viewpoint of balance of the above-mentioned properties, 1.5 to 2.5 parts by weight thereof is preferably mixed. In this case if the amount of the vulcanisation accelerator is too small, physical property change becomes large. On the other hand, if the amount is too large, abrasion property and tread cut resistance become small. From the viewpoint of these reasons, sulfur and a vulcanisation accelerator are mixed under the condition that an amount of sulfur X parts by weight and an amount of a vulcanisation accelerator Y parts by weight satisfy the following equation: 2X-1 ≤ Y ≤ 2X. In the rubber composition of the present invention, carbon black is preferably mixed from the viewpoint of abrasion resistance, reinforcement and low cost. There is no particular limitation for the kind of carbon black, as long as it has been conventionally employed in tyres. Preferably the specific surface area for nitrogen adsorption thereof is 30 to 200 and the adsorption amount of compressed dibutyl phthalate (DBP) is 30 to 150 ml/100g. If the specific surface area for nitrogen adsorption is below 30m 2 /g or the adsorption amount of compressed DBP is below 30ml/100ml, it is inferior in dispersion property and reinforcement of carbon black to a rubber composition. On the other hand, if the specific surface area for nitrogen adsorption is above 200m 2 /g or the adsorption amount of compressed DBP is above 150ml/100g, it is inferior in dispersion property of carbon black to a rubber composition and a heat amount thereof becomes large. Examples of the kind of carbon black are, for instance, HAF, ISAF and SAF, but there is no particular limitation for it. The amount of carbon black is preferably 25 to 60 parts by weight from the viewpoint of balance between reinforcement (abrasion resistance) and low fuel consumption, and it is more preferably 30 to 50 parts by weight from the viewpoint of low fuel consumption. To the rubber composition of the present invention, there can be suitably added, except for the above-mentioned components, for instance, filler, an additive such as process oil, an anti-oxidant, stearic acid or zinc oxide in quantities so as not to effect the object of the present invention. There is no particular limitation for filler. Examples therefor are, for instance, silica, clay, calcium carbonate, aluminum hydroxide and the like. There is no particular limitation for an anti-oxidant. Examples thereof are, for instance, aromatic oil, naphthene oil, paraffin oil, castor oil and the like. There is no particular limitation for the anti-oxidant. Examples thereof are, for instance, reaction products of aldehyde, ketone and amine, amines, derivatives of amines, imidazoles, phenoles and the like. The rubber composition for a tyre tread of the present invention obtained therefrom can be applied to a tyre tread by the conventional method. EXAMPLES The present invention is further explained in details based on the Examples concretely, but is not limited thereto. "Parts" in Examples means "parts by weight" unless otherwise specified. EXAMPLES 1 TO 5 The basic combination is the composition comprising 100 parts of a natural rubber, 50 parts of carbon black, 3 parts of process oil, 2 parts of an anti-oxidant, 2 parts of stearic acid, 1 part of a wax and 5 parts of zinc oxide based on 100 parts of the rubber. According to the mixing ratio shown in Table 1, the component except for sulfur and a vulcanisation accelerator were first mixed at 150°C for four minutes by employing a Banbury mixer. To the obtained mixture were added sulfur and a vulcanisation accelerator and the mixture thenwas kneaded at 80°C for five minutes by employing an open roll with twin screws to obtain the rubber compositions 1 to 5 for a tyre tread of the present invention. The following materials were employed in the Examples: Carbon black - Diablack I (N220) of ISAF class available from Mitsubishi Chemical Corporation; Process oil - Diana process PS32 available from Idemitsu Kosan Co., Ltd.; Wax - Sannowax available from Ohuchi Shinko Kagaku Kogyo Co., Ltd.; Anti-oxidant - Ozonone 6C available from Seiko Chemical Co., Ltd.; Stearic acid - Kiri available from NOF Corporation; Zinc oxide - Ginrei R available from Toho Zinc Co., Ltd.; Sulfur - Sulfur available from Tsurumi Chemical Co., Ltd.; Accelerator - NOCCELER NS available from Ohuchi Shinko Kagaku Kogyo Co., Ltd.; and Sumifine 1162 available from Sumitomo Chemical Co., Ltd., comprising calcined clay containing 33% by weight of N,N'-bis(2-methyl-2-nitropropyl)-1,6-hexanediamine was employed as N,N'-bis(2-methyl-2-nitropropyl)-1,6-hexanediamine The rubber compositions then were applied to green tyres of 10.00R20 to prepare tyres for a truck or a bus with divided tread by vulcanisation at 150°C for 45 minutes. The obtained tyres were evaluated by the following tests (1) to (4). Evaluation Tests (1) Loss tangent (viscoelasticity test) Loss tangent (tan δ (60°C)) was measured at the condition of temperature 60°C and dynamic strain 1.0% by employing a viscoelasticity spectrometer VES made by Iwamoto Seisakusyo Co., Ltd. Rolling resistance an fuel efficiency become low with decreasing tan δ (60°C)). Tan δ (20°C)) described in the above-mentioned prior arts was employed as an index of heating, but the temperature condition of the present invention (60°C) showed higher correlation between fuel efficiency and heating. (2) Hardness (JIS-A) A 10 tone truck was equipped with the above-mentioned tyres, and the truck was run 150,000 km. The hardness of the tread before and after running was measured by employing a JIS-A hardness meter, and the increase (change) of hardness was compared. If the change of increase is small, the change of property becomes small and the performance becomes excellent. (3) Abrasion resistance The abrasion amount of tyre tread after running was measured, and the results were shown employing an index based on the abrasion amount of the tyre tread comprising the rubber composition obtained in the following Comparative Example 1 as 100. The larger the index becomes, the more excellent the abrasion resistance becomes. (4) Tread cut resistance The number of cut parts on the tread surface after running was measured. The smaller the number becomes, the more excellent the tread cut resistance was. Mooney scorch times (t 10 ) (min) at 130°C of the obtained rubber compositions 1 to 5 besides the compositions applied to a tyre were measured by employing a Mooney viscometer according to HIS K 6200. The larger the time thereof becomes, the more excellent the property thereof becomes, since the composition is not vulcanised early. COMPARATIVE EXAMPLES 1 TO 7 Except for the amount shown in Table 1, comparative rubber compositions 1 to 7 were obtained and evaluated in the same manner as in Example 1. By the present invention there can be provided a rubber composition fore a tyre tread which decreases rolling resistance without decreasing abrasion resistance.

Claims: A rubber composition for a tyre tread comprising 100 parts by weight of a rubber component, 0.5 to 1 part by weight of N,N'-bis(2-methyl-2-nitropropyl)-1,6-hexane-diamine contained in calcined clay, 1 to 1.5 parts by weight of sulfur and 1 to 3 parts by weight of a vulcanisation accelerator based on 100 parts by weight of the rubber component, wherein the amount X of sulfur and the amount Y of the vulcanisation accelerator satisfy the equations: 2X-1 ≤ Y ≤ 2X. A rubber composition for the tyre tread according to claim 1, characterised by comprising 25 to 60 parts by weight of carbon black.

Inventors: MATSUO TOSHIRO, MIZUNO YOICHI, MATSUO, TOSHIRO, MIZUNO, YOICHI
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1999
Main classification: C08K5
IPC codes: C08K5, C08K3, B60C1, C08L21