JP4896826B2 - Rubber composition for tread and pneumatic tire using the same - Google Patents

Description

  The present invention relates to a rubber composition for a tread and a pneumatic tire using the rubber composition for a tread in a tread portion.

In recent years, environmental issues have become more important and regulations on CO ₂ emissions have been strengthened. In addition, oil resources are limited, and in the future, it may become difficult to supply raw materials derived from petroleum resources such as carbon black, and oil prices are expected to rise due to a decrease in supply volume year after year. Is done. Therefore, it is required to replace raw materials derived from petroleum resources with raw materials derived from resources other than petroleum.

  Currently, commercially available tires are composed of raw materials in which more than half of the total weight is petroleum resources. For example, a general tire for a passenger car contains about 20% by mass of synthetic rubber, about 20% by mass of carbon black, a softener, a synthetic fiber, etc., so that about 50% by mass or more of the entire tire is a raw material derived from petroleum resources. It is composed of Therefore, development of rubber for tires using raw materials derived from natural resources is desired. However, even when using raw materials derived from natural resources, for example, tread rubber forming the tread portion of the tire is required to maintain grip performance while reducing rolling resistance of the tire, Basic performance according to the applied member is required.

  Low fuel consumption while reducing the amount of raw materials derived from petroleum resources and suppressing an increase in tire rolling resistance due to an increase in rubber hysteresis loss due to heat generation during travel, specifically loss tangent (tan δ) In order to achieve this, it has also been proposed to replace the filler compounding with a silica compound instead of adding a large amount of carbon black. A rubber composition that gives rubber having relatively good durability can be obtained by blending silica. However, when silica is blended, a problem of deterioration in workability due to an increase in viscosity is likely to occur during the preparation of the rubber composition. Tend. There is a method of using a surfactant-based processing aid for silica or the like in order to improve processability. However, there is a problem that such processing aid is derived from petroleum resources.

As a rubber composition containing silica, for example, Patent Document 1 discloses that 30 parts by mass or more of silica having a BET specific surface area of less than 150 m ² / g and 100 parts by mass of carbon black with respect to 100 parts by mass of a rubber component made of natural rubber. A rubber composition for an inner liner containing 5 parts by mass or less has been proposed. However, this technique is intended to improve the rolling resistance characteristics of the inner liner, and Patent Document 1 does not consider any tread rubber and performance required for it.
JP 2006-249147 A

  The present invention solves the above problems, and uses a rubber composition for treads that has high rigidity, low hysteresis loss, and excellent workability during preparation, while reducing the amount of raw materials derived from petroleum resources. An object of the present invention is to provide a pneumatic tire excellent in durability and rolling resistance characteristics.

The present invention contains 100 parts by mass of a rubber component, 25-60 parts by mass of silica having a BET specific surface area of 150 m ² / g or less, and 5 parts by mass or less of carbon black, and the rubber component is natural rubber or modified natural rubber. A tread rubber composition comprising at least one of the above is provided.

  In the rubber composition for a tread of the present invention, the modified natural rubber is preferably an epoxidized natural rubber.

  The present invention also provides a pneumatic tire in which any of the above-described tread rubber compositions forms at least a part of a tread portion.

  In the pneumatic tire of the present invention, the tread portion has a cap tread portion and a base tread portion, and the base tread portion can be made of the rubber composition for a tread of the present invention.

  According to the present invention, a rubber composition for a tread that reduces the use amount of raw materials derived from petroleum resources, has high rigidity, low hysteresis loss, and excellent workability during preparation, and durability and rolling using the rubber composition. It becomes possible to provide a pneumatic tire having excellent resistance characteristics.

The present invention contains 100 parts by mass of a rubber component, 25-60 parts by mass of silica having a BET specific surface area of 150 m ² / g or less, and 5 parts by mass or less of carbon black, and the rubber component is natural rubber or modified natural rubber. A tread rubber composition comprising at least one of the above is provided.

<Rubber component>
In the rubber composition for a tread of the present invention, the rubber component is composed of at least one of natural rubber and modified natural rubber.

  As the natural rubber (NR), those conventionally used in the rubber industry can be used, and examples thereof include natural rubber of grades such as RSS # 3 and TSR. Examples of the modified natural rubber include epoxidized natural rubber (ENR) and hydrogenated natural rubber. Each of the natural rubber and the modified natural rubber may be a single type or a combination of two or more types.

  In the present invention, the modified natural rubber is preferably an epoxidized natural rubber (ENR) from the viewpoint that both the effect of reducing the amount of the raw material derived from petroleum resources and the securing of rubber properties can be easily achieved.

  As the epoxidized natural rubber (ENR), a commercially available product may be used, or an epoxidized natural rubber (NR) may be used. The method for epoxidizing natural rubber (NR) is not particularly limited, and examples thereof include a chlorohydrin method, a direct oxidation method, a hydrogen peroxide method, an alkyl hydroperoxide method, and a peracid method. Examples of the peracid method include a method of reacting an organic peracid such as peracetic acid or performic acid as an epoxidizing agent with an emulsion of natural rubber.

  Here, the epoxidation rate of the epoxidized natural rubber (ENR) is preferably 5 mol% or more, and more preferably 10 mol% or more. Here, the epoxidation rate means a ratio of the number of epoxidized out of the total number of double bonds in the natural rubber before epoxidation, and is obtained by, for example, titration analysis or nuclear magnetic resonance (NMR) analysis. . When the epoxidation rate of the epoxidized natural rubber (ENR) is less than 5 mol%, the rubber hardness of the tread rubber composition is low because the glass transition temperature of the epoxidized natural rubber (ENR) is low, and the tread rubber There is a tendency that durability and fatigue resistance of a pneumatic tire using the composition as a tread rubber are lowered. The epoxidation rate of the epoxidized natural rubber (ENR) is preferably 60 mol% or less, and more preferably 50 mol% or less. When the epoxidation rate of the epoxidized natural rubber (ENR) exceeds 60 mol%, the mechanical strength tends to decrease due to the rubber composition for tread becoming too hard.

  More typical examples of the epoxidized natural rubber (ENR) include an epoxidized natural rubber having an epoxidation rate of 25 mol% and an epoxidized natural rubber having an epoxidation rate of 50 mol%.

  The content of natural rubber (NR) in the rubber component is preferably 30% by mass or more. When the content of the natural rubber (NR) is less than 30% by mass, the mechanical strength of the tread rubber composition tends to be low. The content of the natural rubber (NR) is more preferably 40% by mass or more, and further preferably 50% by mass or more. The content of natural rubber (NR) in the rubber component is preferably 80% by mass or less. When the content of natural rubber (NR) exceeds 80% by mass, the wear resistance of the tread rubber composition tends to be low. The content of the natural rubber (NR) is more preferably 70% by mass or less, and further preferably 60% by mass or less.

  In the present invention, when the modified natural rubber is an epoxidized natural rubber, the content of the epoxidized natural rubber (ENR) in the rubber component is preferably 20% by mass or more. When the content of epoxidized natural rubber (ENR) is less than 20% by mass, the effect of improving wear resistance tends to be low. The content of the epoxidized natural rubber (ENR) is more preferably 25% by mass or more, and further preferably 30% by mass or more. The content of epoxidized natural rubber (ENR) in the rubber component is preferably 70% by mass or less. When the content of epoxidized natural rubber (ENR) exceeds 70% by mass, the rubber hardness tends to be too high, so that the mechanical strength of the tread rubber composition tends to be low. The content of epoxidized natural rubber (ENR) is more preferably 65% by mass or less, and further preferably 60% by mass or less.

  Note that part or all of the natural rubber (NR) may be deproteinized natural rubber (DPNR), or part or all of the modified natural rubber may be modified rubber of the deproteinized natural rubber (DPNR). good.

<Silica>
In the present invention, silica having a BET specific surface area of 150 m ² / g or less is blended. When silica is blended in the rubber composition, an effect as a reinforcing agent for improving the mechanical strength of the rubber and an effect of reducing hysteresis loss can be obtained. In addition, since silica is derived from non-petroleum resources, the amount of raw material derived from petroleum resources in the rubber composition is reduced compared to the case where a reinforcing agent derived from petroleum resources such as carbon black is blended as a main reinforcing agent. Can be reduced. However, when silica is blended, the Mooney viscosity of the unvulcanized rubber composition is likely to increase during the production of the rubber composition, for example, compared with blending carbon black or the like as the main reinforcing agent. It is often difficult to ensure sex.

In the present invention, the amount of the raw material derived from petroleum resources is reduced by setting the BET specific surface area of silica to 150 m ² / g or less, and the physical properties such as rigidity, hardness and mechanical strength of the rubber composition for treads are reduced. It is possible to improve the processability by reducing the Mooney viscosity of the unvulcanized rubber composition while maintaining the desired characteristics. The BET specific surface area of silica is more preferably 140 m ² / g or less, and further preferably 130 m ² / g or less.

From the viewpoint of improving processability, it is preferable that the silica has a lower BET specific surface area. However, for example, when the BET specific surface area is less than 50 m ² / g, the hardness of the rubber composition for tread is lowered and the mechanical strength is lowered. Tend. Therefore, the BET specific surface area of silica is preferably 50 m ² / g or more, more preferably 80 m ² / g or more, and further preferably 100 m ² / g or more.

  Silica may be of one type or a combination of two or more types, and the BET specific surface area when two or more types of silica are combined is determined as a number average of the entire silica.

  In the present invention, since the processability can be improved by using the specific silica as described above, for example, the need for a petroleum-derived processing aid usually used when blending silica is reduced. The effect that it is possible is also acquired.

  The compounding quantity of a silica shall be in the range of 25-60 mass parts with respect to 100 mass parts of rubber components. When the blending amount of silica is less than 25 parts by weight with respect to 100 parts by weight of the rubber component, the reinforcing effect due to the blending of silica and the effect of reducing hysteresis loss cannot be secured sufficiently, and when it exceeds 60 parts by weight, good workability is obtained. I can't. The compounding amount of silica is more preferably 30 parts by mass or more, and further preferably 35 parts by mass or more. Further, the blending amount of silica is more preferably 50 parts by mass or less, and further preferably 45 parts by mass or less.

Silica may be prepared by a wet method or may be prepared by a dry method. Moreover, as a preferable commercial item, "Ultrasil VN2" (BET specific surface area 125m < ² > / g) made from Degussa etc. can be illustrated, for example.

<Silane coupling agent>
In this invention, it is preferable to mix | blend a silane coupling agent with a silica. As the silane coupling agent, a conventionally known silane coupling agent can be used. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4- Triethoxysilylbutyl) tetrasulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl) tetrasulfide, bis (4-trimethoxysilylbutyl) tetrasulfide, bis (3-triethoxy Silylpropyl) trisulfide, bis (2-triethoxysilylethyl) trisulfide, bis (4-triethoxysilylbutyl) trisulfide, bis (3-trimethoxysilylpropyl) trisulfide, bis (2-trimethoxysilylethyl) ) Resulfide, bis (4-trimethoxysilylbutyl) trisulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) disulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3 -Trimethoxysilylpropyl) disulfide, bis (2-trimethoxysilylethyl) disulfide, bis (4-trimethoxysilylbutyl) disulfide, 3-trimethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxy Ethoxysilylpropyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N, N-dimethylthiocarbamoyl tetrasulfide, 2-trimethoxysilylethyl-N, N-dimethylthio Sulfide systems such as rubamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazolyl tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-trimethoxysilylpropyl methacrylate monosulfide; 3-mercaptopropyltrimethoxysilane Mercapto type such as 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; Vinyl type such as vinyltriethoxysilane, vinyltrimethoxysilane; 3-aminopropyltriethoxysilane 3-aminopropyltrimethoxysilane, 3- (2-aminoethyl) aminopropyltriethoxysilane, 3- (2-aminoethyl) aminopropyltrimethoxy Amino systems such as silane; glycidoxy systems such as γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropylmethyldimethoxysilane Nitro compounds such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 2-chloroethyltrimethoxysilane, 2-chloroethyltri Chloro-based compounds such as ethoxysilane; These silane coupling agents may be used alone or in combination of two or more.

  Of these, Si69 (bis (3-triethoxysilylpropyl) tetrasulfide), Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa are preferably used because of their good processability. It is done.

  The blending amount of the silane coupling agent when the blending amount of silica is 100% by mass is preferably 2% by mass or more, and more preferably 3% by mass or more. When the blending amount of the silane coupling agent is less than 2% by mass, the mechanical strength tends to decrease. Moreover, it is preferable that this compounding quantity of a silane coupling agent is 20 mass% or less, and 18 mass% or less is more preferable. If the blending amount exceeds 20% by mass, no significant improvement in workability can be expected even if the blending amount is increased, but the cost increases, which is not economical. On the other hand, when the amount of the silane coupling agent exceeds 20% by mass, the mechanical strength tends to decrease.

<Carbon black>
The rubber composition for a tread of the present invention contains 5 parts by mass or less of carbon black as a reinforcing agent. By blending carbon black, good mechanical strength is imparted to the rubber composition for tread, but carbon black is generally derived from petroleum resources. If the blending amount of carbon black with respect to 100 parts by mass of the rubber component exceeds 5 parts by mass, the effect of reducing the amount of raw material derived from petroleum resources cannot be obtained sufficiently, and the rolling resistance is reduced and the fuel-efficient pneumatic tire is reduced. It is difficult to achieve a sufficient reduction in the hysteresis loss of the tread rubber composition necessary to obtain the toner, specifically, the reduction in tan δ. The blending amount of carbon black is preferably 4 parts by mass or less, and more preferably 3 parts by mass or less. On the other hand, in terms of achieving both good mechanical strength and good workability at the time of preparation, the blending amount of carbon black is 1 part by mass or more, further 1.5 parts by mass or more with respect to 100 parts by mass of the rubber component, It is preferably 2 parts by mass or more.

  The DBP oil absorption of carbon black is preferably in the range of 70 to 120 ml / 100 g. When the DBP oil absorption of carbon black is less than 70 ml / 100 g, the reinforcing effect tends to be small, and when it exceeds 120 ml / 100 g, the processability during the preparation of the rubber composition for tread tends to be lowered. The DBP oil absorption of carbon black is more preferably 75 ml / 100 g or more, more preferably 80 ml / 100 g or more, more preferably 115 ml / 100 g or less, and even more preferably 100 ml / 100 g or less.

  As a preferable commercial product of carbon black, for example, “Show Black N220” manufactured by Showa Cabonet can be exemplified.

<Other ingredients>
In addition to the components described above, the rubber composition for treads of the present invention includes other compounding agents conventionally used in the rubber industry, such as vulcanizing agents, stearic acid, vulcanization accelerators, vulcanization accelerators, oils. Curing resin, wax, anti-aging agent, etc. may be blended.

  As the vulcanizing agent, an organic peroxide or a sulfur-based vulcanizing agent can be used. Examples of the organic peroxide include benzoyl peroxide, dicumyl peroxide, and di-t-butyl peroxide. , T-butyl cumyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoyl) Peroxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 or 1,3-bis (t-butylperoxypropyl) benzene, di-t-butylperoxy- Diisopropylbenzene, t-butylperoxybenzene, 2,4-dichlorobenzoyl peroxide, 1,1-di t- butyl peroxy-3,3,5-trimethyl siloxane, and the like can be used n- butyl-4,4-di -t- butyl peroxy valerate. Of these, dicumyl peroxide, t-butylperoxybenzene and di-t-butylperoxy-diisopropylbenzene are preferred. Moreover, as a sulfur type vulcanizing agent, sulfur, morpholine disulfide, etc. can be used, for example. Of these, sulfur is preferred. These vulcanizing agents may be used alone or in combination of two or more.

  Vulcanization accelerators include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, aldehyde-amine or aldehyde-ammonia, imidazoline, or xanthate vulcanization accelerators. Those containing at least one of them can be used. Examples of the sulfenamide system include CBS (N-cyclohexyl-2-benzothiazylsulfenamide), TBBS (N-tert-butyl-2-benzothiazylsulfenamide), N, N-dicyclohexyl-2- Sulfenamide compounds such as benzothiazylsulfenamide, N-oxydiethylene-2-benzothiazylsulfenamide, and N, N-diisopropyl-2-benzothiazolesulfenamide can be used. Examples of the thiazole type include MBT (2-mercaptobenzothiazole), MBTS (dibenzothiazyl disulfide), sodium salt of 2-mercaptobenzothiazole, zinc salt, copper salt, cyclohexylamine salt, 2- (2,4-dinitro). Thiazole compounds such as phenyl) mercaptobenzothiazole and 2- (2,6-diethyl-4-morpholinothio) benzothiazole can be used. Examples of thiurams include TMTD (tetramethyl thiuram disulfide), tetraethyl thiuram disulfide, tetramethyl thiuram monosulfide, dipentamethylene thiuram disulfide, dipentamethylene thiuram monosulfide, dipentamethylene thiuram tetrasulfide, dipentamethylene thiuram hexasulfide. Further, thiuram compounds such as tetrabutylthiuram disulfide and pentamethylenethiuram tetrasulfide can be used. As the thiourea series, for example, thiourea compounds such as thiacarbamide, diethylthiourea, dibutylthiourea, trimethylthiourea, diortolylthiourea and the like can be used. As the guanidine-based compound, for example, guanidine-based compounds such as diphenylguanidine, diortolylguanidine, triphenylguanidine, orthotolylbiguanide, diphenylguanidine phthalate can be used. Examples of dithiocarbamate include zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc diamyldithiocarbamate, zinc dipropyldithiocarbamate , Complex salt of zinc pentamethylenedithiocarbamate and piperidine, zinc hexadecyl (or octadecyl) isopropyldithiocarbamate, zinc dibenzyldithiocarbamate, sodium diethyldithiocarbamate, piperidine pentamethylenedithiocarbamate, selenium dimethyldithiocarbamate, tellurium diethyldithiocarbamate, diamyl Di, such as cadmium dithiocarbamate And the like can be used Okarubamin acid compound. As the aldehyde-amine system or aldehyde-ammonia system, for example, an aldehyde-amine system such as an acetaldehyde-aniline reaction product, butyraldehyde-aniline condensate, hexamethylenetetramine, an acetaldehyde-ammonia reaction product, or an aldehyde-ammonia system compound is used. can do. As the imidazoline-based compound, for example, an imidazoline-based compound such as 2-mercaptoimidazoline can be used. As the xanthate type, for example, a xanthate type compound such as zinc dibutylxanthate can be used. These vulcanization accelerators may be used alone or in combination of two or more.

As the vulcanization acceleration aid, for example, zinc oxide, stearic acid and the like can be used.
As the anti-aging agent, amine-based, phenol-based, imidazole-based, carbamic acid metal salts, and the like can be appropriately selected and used.

  Examples of the oil include process oil, vegetable oil and fat, or a mixture thereof. Examples of the process oil include paraffinic process oil, naphthenic process oil, and aromatic process oil. Vegetable oils include castor oil, cottonseed oil, sesame oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut oil, rosin, pine oil, pineapple, tall oil, corn oil, rice bran oil, beet flower oil, sesame oil, Examples include olive oil, sunflower oil, palm kernel oil, cocoon oil, jojoba oil, macadamia nut oil, safflower oil, tung oil, and the like.

<Pneumatic tire>
The present invention also provides a pneumatic tire in which the rubber composition for a tread as described above forms at least a part of the tread portion. In particular, it is preferable that the tread portion has a cap tread portion and a base tread portion, and the base tread portion is made of any one of the above-described tread rubber compositions. The pneumatic tire of this invention should just be provided with said tread part, especially a base tread part.

  FIG. 1 is a cross-sectional view illustrating the left half of a pneumatic tire according to the present invention. The pneumatic tire 1 includes a tread portion 2, a pair of sidewall portions 3 extending inward in the tire radial direction from both ends of the tread portion 2, and a bead portion 4 positioned at an inner end of each sidewall portion 3. It is common to have a structure with. A carcass 6 is bridged between the bead portions 4, and a belt layer 7 that reinforces the tread portion 2 with a tagging effect is disposed outside the carcass 6 and inside the tread portion 2. .

  The carcass 6 is formed of one or more carcass plies in which the carcass cord is arranged at an angle of, for example, 70 to 90 ° with respect to the tire equator CO. The carcass ply extends from the tread portion 2 to the sidewall portion 3. After that, the periphery of the bead core 5 of the bead portion 4 is folded back from the inner side in the tire axial direction to be locked.

  The belt layer 7 is composed of two or more belt plies in which the belt cords are arranged at an angle of, for example, 40 ° or less with respect to the tire equator CO. The belt layers 7 are stacked in different directions so that the belt cords cross each other. is doing.

  Further, a bead apex rubber 8 extending radially outward from the bead core 5 is disposed in the bead portion 4, and an inner liner rubber 9 forming a tire lumen surface is adjacent to the inside of the carcass 6. The outside of the carcass 6 is protected by clinch rubber 4G and sidewall rubber 3G.

  As shown in FIG. 1, the pneumatic tire of the present invention can include a cap tread portion 2a and a base tread portion 2b. In this case, the base tread portion is preferably made of the rubber composition for treads of the present invention.

  By using the rubber composition for a tread of the present invention, it is possible to form a tread portion capable of ensuring good durability and reducing rolling resistance while reducing the amount of a raw material derived from petroleum resources. Moreover, when forming a base tread part using the rubber composition for treads of this invention, even if a cap tread part is worn out, a favorable rolling resistance characteristic can be provided.

  The pneumatic tire of the present invention is produced by a conventionally known method using the tread rubber composition of the present invention. That is, the rubber composition for a tread of the present invention is kneaded and extruded in accordance with the shape of the tread portion of the tire, particularly the base tread portion, at an unvulcanized stage, and on the tire molding machine together with other members of the tire. An unvulcanized tire is formed by molding in a conventional manner. The pneumatic tire of the present invention can be obtained by heating and pressurizing the unvulcanized tire in a vulcanizer.

  Since the pneumatic tire of the present invention includes a tread portion obtained by using the rubber composition for a tread according to the present invention, particularly a base tread portion, the pneumatic tire has good durability and rolling resistance characteristics. The amount of resource-derived raw materials used is reduced, and it is possible to prepare for a future reduction in oil supply.

  The pneumatic tire provided by the present invention can be suitably applied to various applications such as for passenger cars, trucks, buses, and heavy vehicles as “eco-tires” that are friendly to the global environment.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited to these.

<Examples 1 and 2 and Comparative Examples 1 and 2>
In accordance with the formulation shown in Table 1, using a 1.7L Banbury mixer manufactured by Kobe Steel, the components other than sulfur and vulcanization accelerator were filled so that the filling rate would be 58%, and the rotational speed was 80 rpm. And kneading for 3 minutes until reaching 140 ° C. Next, sulfur and a vulcanization accelerator were added to the obtained kneaded material in the amounts shown in Table 1, and then kneaded at 80 ° C. for 5 minutes using an open roll, according to each example and each comparative example. A blended unvulcanized rubber composition was obtained.

(Mooney viscosity index)
According to JIS K6300, the Mooney viscosity of the unvulcanized rubber composition was measured at 130 ° C., and the Mooney viscosity of Comparative Example 1 was taken as 100.
Mooney viscosity index = (Mooney viscosity of Comparative Example 1) ÷ (Mooney viscosity of each Example and each Comparative Example) × 100
The index is indicated by. The larger the index, the lower the viscosity and the easier the processing.

(Processability of unvulcanized rubber sheet)
Using the unvulcanized rubber composition, an unvulcanized rubber sheet having a thickness of 1.0 mm was extruded with a roll, the state of the fabric of the unvulcanized rubber sheet was visually confirmed, and evaluated according to the following criteria.
A: No ear breaks occur, there is no problem with the background, and the processability is good.
B: At least one of the problem of ear cut and background occurs, and the processability is poor.

(E * (complex modulus) index)
Using the unvulcanized rubber composition, an unvulcanized rubber sheet having a thickness of 2 mm was extruded by a calender with a roll and vulcanized at 150 ° C. for 30 minutes to prepare a test rubber sheet. A measurement sample having a width of 4 mm and a length of 40 mm was prepared from the test rubber sheet using a punching machine. For the measurement sample, E * was measured under the conditions of a temperature of 70 ° C., an initial strain of 10%, and a dynamic strain of 2% using a viscoelastic spectrometer VES (manufactured by Iwamoto Seisakusho Co., Ltd.). Assuming E * = 100, the following formula:
E * index = (E * of each Example or each Comparative Example) ÷ (E * of Comparative Example 1) × 100
The index is indicated by. A larger index indicates higher E * (complex elastic modulus) and better mechanical strength.

(Tan δ index)
Under the same method and conditions as the above E * (complex elastic modulus) measurement, tan δ of the test rubber sheet according to each example and each comparative example was measured.
tan δ index = (tan δ of Comparative Example 1) ÷ (tan δ of each Example or each Comparative Example) × 100
The index is indicated by. The larger the index is, the lower tan δ is, and the smaller the hysteresis loss, the better the rolling resistance characteristics.

Note 1: Natural rubber (NR) is TSR20.
Note 2: Carbon black is “Show Black N220” manufactured by Showa Cabonet.
Note 3: Silica A is Ultrazil VN3 (BET: 210 m ² / g) manufactured by Degussa.
Note 4: Silica B is Ultrazil VN2 (BET: 125 m ² / g) manufactured by Degussa.
Note 5: The silane coupling agent is “Si266” manufactured by Degussa.
Note 6: The anti-aging agent is “NOCRACK 6C” (N- (1,3-dimethylbutyl) -N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Note 7: Stearic acid is “stearic acid” manufactured by NOF Corporation.
Note 8: Zinc oxide is “Zinc Hana 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
Note 9: Sulfur is “powder sulfur” manufactured by Tsurumi Chemical Co., Ltd.
Note 10: The vulcanization accelerator is “Noxeller NS” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

  From the results shown in Table 1, in Comparative Example 1 using silica having a large BET specific surface area, good processability cannot be obtained due to an increase in Mooney viscosity of the unvulcanized rubber composition, and the comparative example has a low silica content. In No. 2, E * of the test rubber sheet after vulcanization was remarkably low.

  On the other hand, in Examples 1 and 2 in which the BET specific surface area and the blending amount of silica were within the scope of the present invention, the Mooney viscosity of the unvulcanized rubber composition was kept low and good processability was obtained. In Examples 1 and 2, tan δ showed a low value without a decrease in E * of the test rubber sheet after vulcanization. From the above results, it can be seen that according to the present invention, a rubber composition for a tread having high rigidity, small hysteresis loss, and good workability during preparation can be obtained.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The rubber composition for a tread of the present invention is suitably applied to a tread rubber of a pneumatic tire for various uses such as for passenger cars, trucks, buses, heavy vehicles, and the like. It can be suitably applied to.

It is sectional drawing which illustrated the left half of the pneumatic tire which concerns on this invention.

Explanation of symbols

  1 tire, 2 tread part, 3 sidewall part, 4 bead part, 5 bead core, 6 carcass, 7 belt layer, 8 bead apex rubber, 9 inner liner rubber, 2a cap tread part, 2b base tread part, 3G sidewall Rubber, 4G clinch rubber.

Claims (3)

100 parts by mass of the rubber component, BET specific surface area and contains a 150 meters ² / g or less of silica 40-60 parts by weight, carbon black 1-5 parts by weight, and
The rubber composition for a tread, wherein the rubber component is made of natural rubber.   A pneumatic tire, wherein the tread rubber composition according to claim 1 forms at least a part of a tread portion. The tread portion has a cap tread portion and a base tread portion;
The pneumatic tire according to claim 2 , wherein the base tread portion is made of the rubber composition for tread.

Images