RUBBER COMPOSITION COMPRISING CARBON BLACK HAVING SURFACE TREATED WITH SILICA

Abstract: A rubber composition containing at least one rubber component containing a diene rubber and a rubber reinforcing carbon black having silica deposited on the surface thereof.

Description: TECHNICAL FIELD The present invention relates to a rubber composition for tire use containing carbon black having silica deposited on the surface thereof (hereinafter referred to as "silica surface-treated carbon black") and a process for its preparation as well as specific uses thereof. More specifically, it relates to a rubber master batch composition containing a diene rubber and a surface-treated carbon black for rubber reinforcement having amorphous silica deposited on the surface thereof. Such a rubber composition containing silica surface-treated carbon black may be used for various types of rubber products such as cap treads, side treads, and belt cord covering rubber of tires, and other tire materials and also belt conveyors, rubber rolls for industrial use, hoses, etc. BACKGROUND ART In the rubber industries, such as tire industry, carbon black for reinforcing the rubber is mixed with rubber in advance by a wet carbon black master batch method whereby the process of kneading the carbon black into the rubber has been attempted to be simplified and improvements in the dispersibility of the carbon black in the rubber have been attempted (for example, see Japanese Unexamined Patent Publication (Kokai) No. 59-49247 and Japanese Unexamined Patent Publication (Kokai) No. 63-43937). Rubber compounds for tire use are usually used for applications where repeated deformation is applied. If the tan δ of the rubber compound in the high temperature region (for example, at 60°C) is high, however, the amount of heat generated during use etc. becomes high, which is liable to lead to early breakage of the product such as tire. Therefore there has been a need for lowering the tan δ in the high temperature region, while maintaining the grip on wet roads, the wear resistance, the breakage strength, and other performances. For example, in tire compounds, improvement of the fuel consumption, durability, etc. requires that the tan δ be lowered in the high temperature region (40°C to 100°C), in particular at 60°C, but in general the braking performance (for example, wet grip), which is a contradictory property, falls as well. Thus, it becomes necessary to maintain this property. In recent years, however, the appearance of superior silane coupling agents has led to the formulation of silica instead of carbon black. Silica has a lower tan δ at high temperatures (about 60°C) compared with carbon black and a higher tan δ at low temperatures (about 0°C), and therefore, when used for example for a rubber composition for a tire tread has the advantage of enabling production of a tire having a low rolling resistance and a high grip. As this prior art, for example, Japanese Unexamined Patent Publication (Kokai) No. 3-239737 proposes blending a silica filler with an SBR obtained by the solution polymerization method or a blend thereof and a diene rubber. Further, Japanese Unexamined Patent Publication (Kokai) No. 3-252431 proposes the blending of a silica filler and silane coupling agent into an SBR obtained by the solution polymerization method or a blend thereof with a diene rubber. Further, Japanese Unexamined Patent Publication (Kokai) No. 3-253433 proposes the blending of a silica filler and silane coupling agent with solution polymerization BR or SBR having silane modified terminals. While, according to the above-mentioned proposals the tan δ at the high temperature region can be reduced, without lowering the braking performance and other properties, however, the addition of the silica means that the wear resistance is inferior to that when just adding carbon black. Further, silica tends to make a high degree of self agglomeration, and therefore, is not easy to disperse. Thus the problem of inferior processability is caused. Further, silica is nonconductive, therefore, when silica is used alone for tire use, in particular tire tread use, without the use of a sufficient amount (normally about 40 parts by weight) of carbon black, results in insufficient flow of static electricity to the road surface and, as a result, charging and static discharge. The resultant discharge causes noise in the radio and other electronic apparatuses and in some cases causes erroneous operation of the same. Further, the vulcanization rate is slower, and therefore, a vulcanization promoter becomes necessary and the cost becomes higher. Covering the surface of the pigment etc. with silica etc. to improve the dispersibility and improve the weather resistance has been proposed, for example, in Japanese Examined Patent Publication (Kokoku) No. 50-14254, Japanese Examined Patent Publication (Kokoku) No. 7-30269, etc. but none of these alludes to the deposition of silica on the surface of the carbon black for rubber reinforcement. EP-A-0 711 805 represents prior art in the sense of Article 54(3) EPC and relates to a rubber composition containing a cross-linkable rubber component and a carbon black having silica adhered to the surface thereof. As seen from all examples of this document, the rubber compositions were prepared by mixing and adding under dry conditions. US-3,317,458 relates to a wet method for preparing a rubber composition containing carbon black and silicon dioxide. Further it is stated that the silicon dioxide preferentially precipitates upon the carbon black particles. The ratio of light filler, that is silicon dioxide and/or silicates to carbon black ranges from 1:2 to 1:5, i.e. 20% to 50% silica. DE-A-3 502 494 is concerned with the modification of carbon black with various metal oxides, including silica. This document exclusively discloses a dry method for mixing carbon black and silica. Neither the deposition of silica on the surface of the carbon black particle nor a wet coagulation method for producing a rubber composition is disclosed. US-4,211,578 is concerned with a method of producing a combined carbon black silica pigment. From the preparation method (i.e. spray drying the silica slurry of a carbon black exhaust gas) it cannot be concluded that the silica is deposited on the surface of the carbon black particles. Further, this document does not teach a wet preparation method for a rubber composition, wherein a mixture of a rubber latex and a slurry of the carbon black (having silica deposited on the surface thereof) is coagulated in the presence of a coagulation agent. Further the weight proportion of silica is at least 28%. On the other hand, when blending silica with a rubber composition, it is difficult to cause the dispersion of the silica during the kneading and therefore a large amount of labor becomes necessary for the kneading. Thus, the preparation of master batches has been desired for silica like carbon black. Silica, however, has a different agglomeration pH (about 4 to 7) than the agglomeration pH region of carbon black (about 2.5 to 3), and therefore, in the past a satisfactory wet type silica master batch has not been able to be obtained. DISCLOSURE OF INVENTION Accordingly, an object of the present invention is to provide a rubber composition containing silica surface-treated carbon black which gives a rubber composition having the superior tan δ temperature dependency of silica and an excellent wear resistance and also free from the problems derived from a low electroconductivity. Another object of the present invention is to provide a rubber composition for a tire which gives a rubber superior in wet grip and rolling resistance compared with use of carbon black alone, superior in wear resistance and with a smaller electrical resistance compared with use of silica alone, and therefore, free from the problem of noise in the radio and other electronic apparatuses, and which is superior in the dispersibility as well. A further object of the present invention is to provide a rubber composition which has a superior effect in lowering the rolling resistance and improving the cut resistance of rubber for use for side treads and improving the cord adhesion and improving the hardness of rubber for use in covering belt cords. In accordance with the invention, there is provided a process for the preparation of a rubber composition comprising at least one rubber component containing a diene rubber and a rubber reinforcing carbon black having silica deposited on the surface thereof, comprising the step of coagulating in the presence of a coagulating agent a mixture of (a) 100 parts by weight, in terms of solid content, of a rubber latex containing a diene rubber and (b) 10 to 250 parts by weight, in terms of solid content, of a slurry of a rubber reinforcing carbon black having amorphous silica deposited on the surface thereof, wherein the amount of deposition of the silica in the silica surface treated carbon black is 0.1 to 15% by weight, based on the weight of the silica surface treated carbon black, and a rubber composition obtainable by this process. According to a preferred embodiment, there is further provided a rubber composition for tire use comprising at least one rubber component-containing a diene rubber to which is blended surface-treated carbon black composed of rubber reinforcing carbon black having a nitrogen specific surface area (N 2 SA) of 25 to 250 m 2 /g and a DBP oil absorption of 70 to 180 ml/ 100 g on the surface of which is deposited with 0.1 to 15% by weight of silica. BEST MODE FOR CARRYING OUT THE INVENTION The present inventors, as explained above, succeeded in obtaining a rubber master batch composition containing silica by a wet method providing a rubber having the superior tan δ temperature dependency of silica, having an excellent wear resistance, and free from the problems derived from a low electroconductivity by causing a completely novel rubber reinforcement surface-treated carbon black to coagulate with a diene rubber latex. According to the present invention, as explained above, carbon black having silica deposited (or precipitated) on the surface thereof (i.e., silica surface-treated carbon black) is blended with at least one rubber ingredient containing a diene rubber. The amount of deposition of the silica in the silica surface-treated carbon black is 0.1 to 15% by weight, preferably, 0.3 to 15% by weight. If the content of the silica is too small, the balance between the tan δ in the high temperature region (40°C to 100°C) and the tan δ in the low temperature region (about 0°C) is liable not to be improved, while conversely if the content of the silica is too large, the electroconductivity will be decreased, the agglomerating force of the filler will become stronger, and dispersibility during the kneading may become insufficient. As the rubber reinforcement carbon black usable as the starting substance for manufacture of silica surface-treated carbon black for the rubber reinforcement used in the present invention, any carbon black generally used as carbon for reinforcement of rubber for tires etc. in the past can be used. A preferable carbon black is a GPF to SAF grade of rubber reinforcement carbon black produced by the oil furnace method. The type may be determined depending upon the application or utility of the rubber composition and blends of two or more types may be used as well. The silica surface-treated carbon black according to the present invention may be produced, for example, as follows. That is, the rubber reinforcing carbon black is first dispersed in water. To improve the dispersibility of the carbon black, a suitable dispersant, for example, methanol or various types of surfactants, is added to make a homogeneous slurry. Next, an amount of sodium silicate corresponding to the amount of silica to be deposited on the surface of the carbon black is added, under stirring, in the form of an aqueous solution, for example, to the aqueous slurry of carbon black thus obtained. Note that the amount of silica to be deposited on the surface of the carbon black is 0.1 to 15% by weight based on the weight of the silica surface-treated carbon black. If the amount of deposition of silica is too great, there is a tendency for difficulty in coagulation with the rubber latex. On the other hand, at the same time as the aqueous solution of the sodium silicate, to neutralize the sodium silicate added, an acid, for example, sulfuric acid, hydrochloric acid, nitric acid, etc., is added with stirring. It is preferable to perform the addition of the aqueous solution of the acid and the addition of the sodium silicate simultaneously and in substantially the same amounts. The preferable feed rate of the sodium silicate is 0.001 to 0.110 g/min, in terms of the amount of silica, based upon 100 parts by weight of carbon black. The pH of the reaction system at the stage of the above surface-treatment reaction is preferably 6 to 12, and the reaction temperature is preferably from 50° to 95°C from a practical viewpoint. In the stage of the above surface treatment reaction, after the amorphous silica is deposited on the surface of the carbon black, it is possible to adjust the pH of the system to not more than 7, allow the mixture to stand at a temperature of 50° to 95°C, with stirring, to cause aging and thereby obtain a slurry of the desired silica surface-treated carbon black. However, the silica surface-treated carbon black according to the present invention is not limited to this process of production. It may also be produced by placing carbon black produced by the oil furnace method etc. into an atmosphere for producing white carbon so as to cause silica to deposit on the surface of the carbon black. The total amount of the silica in the rubber reinforcer produced by this method is not necessarily physically or chemically bonded to the surface of the carbon black, but observation by a transmission type electron microscope (about 600,000X) confirms that there is silica deposited on the carbon black. Further, observation of the silica surface-treated carbon black obtained by kneading once with rubber, then pyrolyzing the rubber ingredient in nitrogen also shows silica deposited on the carbon black, and therefore, it is considered that the deposited silica and carbon have bonds of a certain degree of strength. The silica surface-treated carbon black according to the present invention has a nitrogen specific surface area (N 2 SA), measured according to ASTM D 3037, of 20 to 250 m 2 /g, preferably 55 to 250 m 2 /g in the case of the rubber composition for a cap or under tread, 25 to 120 m 2 /g in the case of the rubber composition for a side tread and 70 to 150 m 2 /g, in the case of the rubber composition for a tire belt cord covering. With a nitrogen specific area of less than 20 m 2 /g, the reinforcement of the rubber is insufficient and the breaking strength and wear resistance may decrease, while conversely if the nitrogen specific area is more than 250 m 2 /g, kneading into the rubber becomes difficult and the dispersibility is liable to become poor. The silica surface-treated carbon black according to the present invention preferably has a DBP oil absorption, measured according to JIS K 6221, of 70 to 180 ml/100 g, 70 to 180 ml/100 g in the case of the rubber composition in particular for a cap or under tread, 70 to 150 ml/100 g in the case of the rubber composition for a side tread, and 70 to 150 ml/100 g in the case of the rubber composition for a tire belt cord covering. The rubber ingredient which is blended into the rubber composition according to the present invention may be a rubber ingredient containing a diene rubber - alone or a mixture or two or more types. The blending of the silica surface-treated carbon black improves its wear resistance, grip performance, rolling resistance, etc. As the diene rubber, any rubber which has been used for tires in the past can be used. For example, natural rubber (NR), various types of butadiene rubbers (BR), various types of styrene-butadiene copolymer rubbers (SBR), polyisoprene rubber (IR), butyl rubber (IIR), acrylonitrile butadiene rubber, chloroprene rubber, styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymer rubber, isoprene-butadiene copolymer rubber, etc. may be mentioned. As other rubbers, ethylenepropylene copolymer rubber, ethylene-propylene-diene copolymer rubber, chlorosulfonated polyethylene, acryl rubber, epichlorohydrin, polysulfide rubber, silicone rubber, fluororubber, urethane rubber, etc. may be used. When mixtures of two or more types are used, the ratio of the blend is not particularly limited. According to the present invention, the silica surface-treated carbon black is preferably added in 10 to 250 parts by weight, more preferably 15 to 200 parts by weight, particularly preferably 10 to 100 parts by weight, to 100 parts by weight of the rubber ingredient. If the amount of formulation is too small, the desired effect cannot be obtained, while conversely if the amount is too large, the hardness becomes too high, the processability declines, and the practical value as a rubber material may otherwise become unpreferably poor. The rubber composition of the present invention may contain, in addition to the above-mentioned silica surface-treated carbon black, any carbon black and/or silica usually blended into a rubber composition. The amount of the ordinary carbon black and/or silica blended at this time must be no more than 10 times the silica surface-treated carbon black in weight, preferably no more than 8 times. If the amount of the carbon black blended is too large, the desired effect cannot be obtained. In preferable embodiments of the rubber composition of the present invention, there are provided rubber compositions for tire cap tread, under tread, side tread, and tire belt cord covering. In the tire tread and under tread rubber compositions, the preferable rubber for inclusion as the rubber ingredient may be rubbers selected from natural rubber (NR), polyisoprene rubber (IR), styrenebutadiene copolymer rubber (SBR), polybutadiene rubber (BR), butyl rubber (IIR), acrylonitrile butadiene rubber (NBR), etc. As opposed to this, the rubber composition, for the tire side tread the preferable rubber for inclusion as the rubber ingredient may be one or more types of diene rubbers selected from NR, IR, BR, SBR, BR including 1,2-syndiotactic polybutadiene, NR or BR including microfilaments (e.g., nylon etc.) This is because the rubber for side tread requires particularly superior flex fatigue resistance and damage resistance. In the rubber composition for tire belt cord covering, the rubber included as the rubber ingredient is preferably NR, IR, SBR, or BR. This is because toughness and bondability with steel cord or organic cord are required. The rubber compositions according to the present invention for tire cap tread, under tread, side tread, and tire belt cord covering, as explained above, include as fillers 10 to 200 parts by weight or 10 to 100 parts by weight of a silica surface-treated carbon black based upon 100 parts by weight of a rubber ingredient containing a diene rubber. If the amount of the filler blended is too small, the tensile strength etc. of the rubber composition are decreased, while conversely if the amount is too large, the hardness and the heat generated along with deformation will increase too much and exceed the practical range. In addition, the viscosity of the rubber composition when still unvulcanized will become too hign. None of these is desirable. In the present invention, the silica surface-treated carbon black preferably has a nitrogen specific surface area of 55 to 250 m 2 /g and a DBP oil absorption of 70 to 180 ml/100 g in the case of tire cap tread and under tread. If the value of the nitrogen specific surface area of the silica surface-treated carbon black is too low, the wear resistance, tensile strength, etc. are decreased, which are not desirable, while if the value is too high, the dispersibility at the time of kneading of the rubber becomes difficult, which is also not desirable. On the other hand, in the case of a rubber composition for a side tread, the silica surface-treated carbon black preferably has a nitrogen specific surface area of 25 to 120 m 2 /g and a DBP oil absorption of 70 to 150 ml/100 g. If this value is too low, the tensile strength, modulus, etc. again become low, while if the value is too high, in the nitrogen specific surface area, the heat generation becomes large, which is again not desirable, and, in the DBP oil absorption, when a DBP oil absorption is less than 70 ml/100 g, the cut resistance is decreased, while when the DBP oil absorption is more than 150 ml/l00 g, the crack resistance is decreased. In the case of the rubber composition for a tire belt cord covering, the silica surface-treated carbon black preferably has a nitrogen specific surface area of 70 to 150 m 2 /g and a DBP oil absorption of 70 to 150 ml/100 g. If this value is too low, the modulus becomes low, while conversely if the value is too high, the viscosity of the unvulcanized rubber at the time of rolling becomes high and the processing becomes difficult. The properties of the carbon black other than that surface treated with silica, which is sometimes mixed into the rubber composition for tire tread, under tread, side tread and belt cord covering according to the preferable embodiments of the present invention are not particularly limited, but preferably the carbon is one which is usually used for rubber, that is, as a particle size grade, the FEF to SAF grades. According to the preferable embodiment of the present invention, a silane coupling agent is further blended into the above-mentioned rubber composition. The amount of the silane coupling agent blended is not particularly limited, but one of the features of silica surface-treated carbon black is that it displays an effect in smaller amounts than in the case of use of a usual silica. For example, it is possible to blend this in 0.1 to 8% based upon the weight of the silica surface-treated carbon black blended. Of course, it is also possible to blend in a greater amount. If the amount of the silane coupling agent blended is too large, not only is there no particular improvement in the physical properties, but also it is not preferable that the costs is increased and the scorch time is shortened, etc. As the silane coupling agent which may be used in the preferable embodiment of the present invention, any silane coupling agent which has been blended into conventional rubber compositions together with a silica filler may be blended. As such a silane coupling agent, for example, vinyltrichlorosilane, vinyltrimethoxy-silane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy) silane, β-(3,4-ethoxycyclohexyl)ethylktrimethoxysilane, γ-glycydoxypropyltrimethoxysilane, γ-glycydoxypropylmethyldiethoxysilane, γ-glycydoxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, N-β(aminoethyl) γ-aminopropylmethyldimethoxysilane, N-β(aminoethyl) γ-aminopropylmethyldimethoxysilane, N-β(aminoethyl) γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, Γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γγ-chloropropyltrimethoxysilane, bis-(3-[triethoxysilyl]-propyl)-tetrasulfan, etc. may be mentioned. The rubber composition of the present invention may suitably contain, in addition to the above-mentioned rubber, carbon black having silica deposited on the surface thereof, and optional silane coupling agent, any compounding agent which is normally used in the rubber industry, for example, sulfur, an organic peroxide, a softening agent, an antioxidant, a vulcanization accelerator, a filler, a plasticizer, etc., if necessary, in the normally used range. Further, for the process of production of the rubber composition of the present invention, the kneading method, vulcanization method, and the like normally used in the rubber industry may be used. Further, the rubber composition containing silica surface-treated carbon black according to the present invention may be produced by the same method as the normal wet type carbon black master batch method. In the above method, a slurry of carbon black having silica deposited on the surface thereof is produced then this is mixed with a diene rubber latex (e.g., SBR latex), in a suitable ratio. Next, in accordance with the conventional method of production of a carbon black master batch, sulfuric acid or another acid is added to cause coagulation. Further, a conventional coagulation agent (for example, high molecular weight coagulant, NaCl, etc.) may be used. Next, the coagulated rubber composition is separated from the aqueous phase and is cleared of moisture by, for example, drying with hot air so as to obtain the desired rubber master batch composition. Note that in the above process, it is possible to added an antioxidant, process oil, silane coupling agent, or other additive if necessary. The silica surface-treated carbon black used in the present invention, as explained above, is produced by causing amorphous silica to deposit on the surface of carbon black by a reaction of sodium silicate, sulfuric acid, etc. in, for example, a carbon black slurry, and therefore the surface-treated carbon black exists in a slurry state. Therefore, the rubber composition of the present invention can be produced even if this slurry is directly mixed with the rubber latex. This enables the elimination of the labor in the kneading of the silica into the rubber and also results in an excellent dispersibility of the silica in the rubber. Further, the step of recovering the surface-treated carbon black from the slurry and drying it is eliminated - which contributes further to the reduction of the manufacturing costs. In a preferable embodiment of the present invention, when performing the above wet type mixing, it is possible to blend 10 to 200 parts by weight of other ingredients generally used in formulations of rubber in the past, such as aroma oil, paraffinic oil, naphthenic oil, and other process oils and/or synthetic plasticizers, liquid rubber, and other liquids, based upon 100 parts by weight of the diene family rubber. EXAMPLES The present invention will now be further illustrated by, but is by no means limited to, the following Examples. Example I-1 to I-5 and Comparative Examples I-1 to I-3 Preparation of Silica Surface Treated Carbon Black As the carbon black, the rubber reinforcement carbon black shown in Table I-1 was used. 200 g of a 10 wt% aqueous solution of a carbon black dispersant (i.e., methanol) was well mixed into 100 g of carbon black (CB), then 1.8 liters of water was added while stirring to obtain a homogeneous carbon black slurry. Next, since the desired amount of the silica to be deposited on the surface of the carbon black was, here, 10 wt%, the corresponding amount of sodium silicate, that is, 33.3 g, was weighed and diluted with 0.2 liter of water. The carbon black slurry obtained above was heated to 90°C and adjusted to pH 9. To this slurry was dropwise added the aqueous solution of sodium silicate obtained above at a rate of 0.060 g/min with sufficient stirring. At the same time, the pH of the system was adjusted to 9 by adding a 2.0 wt% aqueous solution of sulfuric acid. When the addition of the aqueous solution of sodium silicate was completed, the mixture was allowed to stand, while maintaining a pH 10 and a temperature of 90°C, while stirring for about 30 minutes (aging) to obtain the desired slurry-like substance (solid content of 4.0 wt%) including the surface-treated carbon black. Measurement of Silica Content Surface Treated Carbon Black A sample of the surface-treated carbon black was pyrolyzed in an electric furnace at 600°C, then the ash was treated with hydrofluoric acid and the reduction in weight expressed as the silica content as a percentage of the weight of the original surface-treated carbon. The results are shown in Table I-1. Preparation of Rubber Composition Containing Surface-Treated Carbon Black Next, the surface-treated carbon black obtained above was made into a slurry (concentration of 12.5 wt%). 200 g of this slurry and 125 g of SBR1502·latex (concentration of 41 wt%) were mixed. 1000 g of saline water (concentration of 3 wt%) was added to this as a coagulant, then the mixture was stirred at a temperature of 50°C for 0.5 hour to obtain the rubber reinforcing rubber composition containing silica surface-treated carbon black. Methods of Measurement of Physical Properties of Rubber The physical properties of rubber were evaluated for a rubber composition of the present invention, that is, Example I-1 of Table I-1, in comparison with a case of kneading by the usual dry blend method and a case of use of carbon black. Various types of rubber compositions were prepared by ordinary methods by kneading the following formulations by a Bambury mixer and roll machine (vulcanization conditions: 160°C × 30 minutes). The results are shown in Table I-2. Formulation Table Diene rubber (SBR1502) 100 parts by weight Reinforcing filler (see Table I-1) 50 parts by weight Silane coupling agent 3 parts by weight Zinc oxide (JIS No. 3) 3 parts by weight Stearic acid 2 parts by weight Antioxidant 2 parts by weight Powdered sulfur 2 parts by weight Vulcanization accelerator 1 part by weight Example I-1 to II-14 and Comparative Example II-1 to II-19 Preparation of Silica surface-Treated Carbon Black The silica surface-treated carbon black was prepared by the following method. That is, carbon black slurry was prepared according to an ordinary method and warmed to 90°C, then diluted JIS No. 1 sodium silicate was added by a constant feed pump, while maintaining a pH of 5 to 10 with dilute sulfuric acid and an aqueous solution of sodium hydroxide so as to cause silica to deposit on the carbon surface. Next, the pH was made 6 and the mixture was allowed to stand for 1 hour, then was filtered, washed with water, and dried to obtain the desired substance. The change of the silica content was performed by adjusting the amount of addition of the sodium silicate and the pH of the system. The silica content in the silica surface-treated carbon black (CB) was found by pyrolyzing the silica surface-treated carbon black in an electric furnace at 600°C, then performing fluorination and the following processing and then finding the content by the following formula: Silica content (%)=[Loss of weight due to fluorination/Weight of surface-treated carbon black]×100 Fluorination: About 200 mg of the sample was weighed with and placed in a polyethylene beaker. This was moistened with distilled water, then 5 mg of hydrofluoric acid was added. This was stirred and allowed to stand for 5 minutes, then was suction filtered, washed well with water, and dried. The properties of the prepared silica surface-treated carbon black are shown in Table II-1. The methods of measurement are as explained below. Nitrogen specific surface area: ASTM D3037 DBP oil absorption: JIS K6221 "Test Methods for Carbon Black for Rubber" The basic formulations (parts by weight) of the various rubber compositions used in the following Examples and Comparative Examples are shown in Table II-2 (Formulation 1), Table II-3 (Formulation 2), and Table II-4 (Formulation 3). SBR1502 100 Reinforcing filler Carbon black, silica, surface-treated carbon suitably used Silane coupling agent q.s. Vulcanization promoter q.s. zinc white 3 Stearic acid 2 Antioxidant 2 Wax 1 Sulfur 1.8 Vulcanization accelerator 0.8 Solution polymerization SBR 35 Natural rubber 65 Reinforcing filler Carbon black, silica, surface-treated carbon suitably used Silane coupling agent q.s. Vulcanization promoter q.s. Zinc white 3 Stearic acid 2 Antioxidant 2 Wax 1 Sulfur 2 Vulcanization accelerator 1 Solution polymerization SBR 65 BR 35 Reinforcing filler Carbon black, silica, surface-treated carbon suitably used Silane coupling agent q.s. Vulcanization promoter q.s. Zinc white 3 Stearic acid 2 Antioxidant 3 Wax 1.5 Aroma oil 30 Sulfur 1.7 Vulcanization accelerator 0.8 Various rubber compositions were prepared by the formulations of Table II-5 (Examples II-1 to II-7 and Comparative Examples II-1 to II-10), Table II-6 (Examples II-8 to II-9 and Comparative Examples II-11 to 14), Table II-7 (Example II-10 to II-11 and Comparative Examples II-15 to II-18), and Table II-8 (Examples II-12 to II-13 and Comparative Examples II-19 to II-20) (using the above Formulation 1) ( parts by weight) by an ordinary method by mixing and kneading by a Bambury mixer and kneading roller. These rubber compositions were vulcanized by pressing at 160°C for 20 minutes to prepare the target test pieces which were then subjected to various types of tests to measure their physical properties. The results are shown in Table II-5 to Table II-8. Note that the test methods were as follows: Comp. Ex. II-19 Ex. II-12 Comp. Ex. II-20 Ex. II-13 Carbon black N 110 60 - 80 - Surface-treated carbon 8 - 60 - 80 Silane coupling agent - 3 - 4 Aroma oil 20 20 30 30 Wear resistance index 100 107 112 117 Wet braking performance 100 100 122 121 Rolling resistance index 100 93 129 116 Electrical resistance (Ωcm) 5.0E+0 5.75+0 8.7E+1 9.4E-1 Vulcanization acceleration index 100 108 98 110 Methods of Measurement of Various Types of Physical Properties Vulcanization Acceleration Index A sample of unvulcanized rubber was tested by a rheometer at 160°C to find the T95. The result was shown as an index using one of the carbon black formulations as 100. The smaller the figure, the less a delay in vulcanization shown. Wear Resistance A Lambourn wear tester was used to measure the wear resistance under conditions of a room temperature, a slip ratio of 35%, and a load of 5 kg. The result was shown as an index using one of the carbon black formulations as 100. The larger the figure, the better the wear resistance. Wet Braking Performance A viscoelasticity spectrometer made by Toyo Seiki Seisakusho Co. was used and the tan δ measured under conditions of a temperature of 0°C, a static stress of 10%, a dynamic stress of ±2%, and a frequency of 20 Hz. The results are shown as an index using one of the carbon black formulations as 100. The larger the figure, the better the wet braking performance shown. Rolling Resistance Index A viscoelasticity spectrometer made by Toyo Seiki Seisakusho Co. was used and the tan δ was measured under conditions of a temperature of 60°C, a static stress of 10%, a dynamic stress of ±2%, and a frequency of 20 Hz. The results are shown as an index using one of the carbon black formulations as 100. The smaller the figure, the smaller the rolling resistance. Electrical Resistance The volume specific resistance was measured by ASTM D991 or JIS K6911. As clear from the results of Table II-5 to Table II-8, compared with the rubber compositions of Comparative Examples II-1 to II-20 where ordinary carbon black or silica was blended rather than blending the surface-treated carbon black, the rubber compositions of Examples II-1 to II-13 where surface-treated carbon black was blended gave rubber with an excellent wet braking performance and low rolling resistance while maintaining an excellent wear resistance. Further, with the examples of the invention, it was possible to reduce the electrical resistance compared with formulations of silica. Examples to II-14 to II-15 and Comparative Examples II-21 to II-23 Various rubber compositions were prepared by the formulations (parts by weight) shown in the above Table II-3 and Table II-9 by an ordinary method by mixing and kneading by a Bambury mixer and kneading roller. These rubber compositions were vulcanized by pressing at 160°C for 20 minutes to prepare test pieces which were then subjected to various tests. The results are shown in Table II-9. Note that the characteristic value of the reinforcing agent is a value including carbon black and silica. As is clear from the results of Table II-9, when the silica surface-treated carbon black of the present invention is blended instead of the usual carbon black (Examples II-14 to II-15), as compared with the case where just carbon black is blended (Comparative Example II-21) and the case where just silica is blended (Comparative Example II-22), the rolling resistance index is vastly improved, without detracting from the other properties. Note that in the case where silica was used, (Comparative Example II-22), the rolling resistance was improved, but the wear resistance became poor and, further, as expected, the vulcanization rate became slower. Accordingly, the Examples of the present invention can be said to improve the important properties of the wear resistance, wet braking performance, rolling resistance index, electrical resistance, vulcanization rate, etc. with a good balance. Example II-16 and Comparative Examples II-24 to II-25 Various rubber compositions were prepared by the formulations (parts by weight) shown in Table II-4 and Table II-10 by an ordinary method by mixing and kneading by a Bambury mixer and kneading roller. These rubber compositions were vulcanized by pressing at 160°C for 20 minutes to prepare test pieces for cap treads which were then subjected to various tests. The results are shown in Table II-10. Comp. Ex. II-24 Comp. Ex. II-25 Ex. II-16 Carbon black N 220 80 - - Silica - 80 - Surface-treated carbon 6 - - 80 Silane coupling agent - 8 4 Vulcanization promoter - 4 - Wear resistance index 100 79 103 Wet braking performance 100 103 104 Rolling resistance index 100 71 76 Electrical resistance (Ωcm) 8.1E-1 2.1E+14 1.1E+0 Vulcanization acceleration index 100 131 13.0 As is clear from the results of Table II-10, by blending in the surface-treated carbon black of the present invention, it is possible to obtain a rubber composition having an improved wear resistance and wet braking performance and having a low electrical resistance and an extremely low rolling resistance. INDUSTRIAL APPLICABILITY As is clear from the results of Table I-1 and Table I-2, the rubber composition containing silica surface-treated carbon black according to the present invention can be produced by a method the same as with an ordinary carbon master batch. The resultant composition also gives a rubber having a lower tan δ at a high temperature region (60°C) compared with one with regular carbon black and does not fall in wear resistance. According to the present invention, further, by blending the silica surface-treated carbon black, it is possible to give a rubber which is superior to one with regular carbon black and has a wet grip and low rolling resistance equal to or better than one with just silica. Further, compared with a conventional silica filler, the resultant electrical resistance is small, and therefore, there is no problem of generation of noise in the ratio or other electronic devices. Also, the dispersibility in a compound is good. In addition, the wear resistance is superior than with silica alone and the vulcanization rate is not slow, and therefore, addition of a vulcanization accelerator etc. is not required.

Claims: Process for the preparation of a rubber composition comprising at least one rubber component containing a diene rubber and a rubber reinforcing carbon black having silica deposited on the surface thereof, comprising the step of coagulating in the presence of a coagulating agent a mixture of (a) 100 parts by weight, in terms of solid content, of a rubber latex containing a diene rubber and (b) 10 to 250 parts by weight, in terms of solid content, of a slurry of a rubber reinforcing carbon black having amorphous silica deposited on the surface thereof, wherein the amount of deposition of the silica in the silica surface treated carbon black is 0.1 to 15% by weight, based on the weight of the silica surface treated carbon black. Process according to claim 1, wherein the surface-treated carbon black used is obtained by depositing amorphous silica on a GPF to SAF grade carbon black produced by the oil furnace method. Process as defined in claim 1, wherein the surface-treated carbon black used is obtained by depositing amorphous silica on carbon black having a nitrogen specific surface area (N 2 SA) of 25 to 250 m 2 /g and a DBP oil absorption of 70 to 180 ml/100g. Process as defined in claim 3, wherein the amount of the surface-treated carbon black is 10 to 200 parts by weight, based upon 100 parts by weight of the rubber, and the surface-treated carbon black used is obtained by depositing amorphous silica on carbon black having a nitrogen specific surface area (N 2 SA) of 55 to 250 m 2 /g. Process as defined in claim 3, wherein the amount of the surface-treated carbon black is 10 to 100 parts by weight, based upon 100 parts by weight of the rubber, and the surface-treated carbon black used is obtained by depositing amorphous silica on carbon black having a nitrogen specific surface area (N 2 SA) of 25 to 120 m 2 /g and a DBP oil absorption of 70 to 150 ml/100 g. Process as defined in claim 3, wherein the amount of the surface-treated carbon black is 10 to 100 parts by weight, based upon 100 parts by weight of the rubber, and the surface-treated carbon black used is obtained by depositing amorphous silica on carbon black having a nitrogen specific surface area (N 2 SA) of 70 to 150 m 2 /g and a DBP oil absorption of 70 to 150 ml/100 g. Rubber composition obtainable according to any of the processes defined in claims 1 to 6. Rubber composition as defined in claim 7, further comprising 5 to 150 parts by weight of an aromatic process oil and/or high viscosity oil. Use of a rubber composition obtainable according to the process defined in claim 3 for tires. Use of a rubber composition obtainable according to the process defined in claim 4 for a tire cap tread or under tread. Use of a rubber composition obtainable according to the process defined in claim 5 for tire side tread. Use of a rubber composition obtainable according to the process defined in claim 6 for covering tire belt cords.

Inventors: HASHIMURA YOSHIAKI, IKAI KOUICHI, ISHIKAWA KAZUNORI, KAWAZOE MASAYUKI, KAWAZURA TETSUJI, YATSUYANAGI FUMITO, HASHIMURA, YOSHIAKI, IKAI, KOUICHI, ISHIKAWA, KAZUNORI, KAWAZOE, MASAYUKI, KAWAZURA, TETSUJI, YATSUYANAGI, FUMITO
Applicants: YOKOHAMA RUBBER CO LTD, THE YOKOHAMA RUBBER CO., LTD.
Application year: 1996
Main classification: C08L21
IPC codes: C08K9, C09C1