JP4591895B2 - Rubber composition for clinch and pneumatic tire using the same - Google Patents

Description

  The present invention relates to a rubber composition for clinch and a pneumatic tire provided with a clinch apex made of the rubber composition for clinch.

  Conventionally, clinch rubber is provided in a chafing portion with a rim of a pneumatic tire. The clinch rubber has a function of transmitting a driving force from the rim to the tire during traveling, and a function of holding the tire load. Therefore, the clinch rubber needs to have high hardness and excellent heat aging characteristics. Further, in order to reduce wear caused by rubbing with the rim due to repeated deformation of the tire during traveling, the clinch rubber is also required to have predetermined wear resistance. Further, physical properties such as rigidity, hardness and mechanical strength of the clinch rubber have a great influence on the steering stability performance during traveling, and it is also required to set these performances within an appropriate range.

  On the other hand, in recent years, methods for reducing the amount of raw materials derived from petroleum resources have been studied in various technical fields due to increasing interest in environmental problems. 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, and the like, so that about 50% by mass or more of the entire tire is derived from raw materials of petroleum resources. It is configured. Accordingly, it is desired to develop a rubber for tires using a raw material derived from a natural resource that satisfies the same or more required characteristics as when using a raw material derived from a petroleum resource.

Examples of the rubber composition having improved processability include a rubber composition containing a synthetic polyisoprene rubber having a predetermined cis 1,4-bond content and Mooney viscosity ML _{1 + 4} (100 ° C.) and natural rubber. A natural rubber obtained by deproteinizing natural rubber latex and adjusted to have a total nitrogen content of 0.12 to 0.30% by weight and a rubber composition using the same have been proposed. However, with the above-described technology, it is difficult to reduce the amount of raw material derived from petroleum resources and to achieve both physical properties desired for clinch rubber and processability during production.

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

  The present invention solves the above-mentioned problems, and reduces the amount of raw materials derived from petroleum resources, while maintaining the physical properties such as rigidity, hardness, and mechanical strength and improving the workability, a clinching rubber It aims at providing a composition and a pneumatic tire using the same.

The present invention contains a rubber component and silica compounded within a range of 40 to 80 parts by mass with respect to 100 parts by mass of the rubber component, and the silica has a BET specific surface area of 150 m ² / g or less. The component provides a rubber composition for clinch containing a natural rubber component consisting of at least one of natural rubber and epoxidized natural rubber in a range of 20 to 100% by mass.

  In the rubber composition for clinch of the present invention, carbon black can be further blended at 5 parts by mass or less with respect to 100 parts by mass of the rubber component.

  In the rubber composition for clinch of the present invention, the rubber component is preferably composed of the natural rubber component.

  The present invention also provides a pneumatic tire provided with a clinch apex comprising any one of the above-described clinch rubber compositions.

  According to the present invention, there is provided a rubber composition for clinch capable of maintaining both physical properties such as rigidity, hardness, and mechanical strength and improving processability while reducing the amount of raw materials derived from petroleum resources. A pneumatic tire using the tire is provided.

The rubber composition for clinch of this invention contains a rubber component and the silica mix | blended within the range of 40-80 mass parts with respect to 100 mass parts of this rubber component. Moreover, the BET specific surface area of the silica mix | blended in this invention shall be 150 m < ² > / g or less. The rubber component used in the present invention contains a natural rubber component (hereinafter also simply referred to as a natural rubber component) composed of at least one of natural rubber and epoxidized natural rubber within a range of 20 to 100% by mass.

<Rubber component>
In the rubber composition for clinch of the present invention, the rubber component contains a natural rubber component composed of at least one of natural rubber (NR) and epoxidized natural rubber (ENR).

  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.

  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 glass transition temperature of the epoxidized natural rubber (ENR) is low, so the rubber hardness of the clinching rubber composition is low, and the clinching rubber The durability and fatigue resistance of pneumatic tires using the composition as clinch rubber tend to be reduced. 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 clinching rubber composition 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%.

  In the present invention, the content of the natural rubber component in the rubber component is 20% by mass or more. If the content is less than 20% by mass, the effect of reducing the amount of the raw material derived from petroleum resources cannot be sufficiently obtained. The content of the natural rubber component is more preferably 40% by mass or more, and further preferably 50% by mass or more. The content of the natural rubber component is preferably 100% by mass from the viewpoint that the effect of reducing the amount of raw material derived from petroleum resources is good. For example, the content is 80% by mass or less, and further 70% by mass. In the following, rubber other than the natural rubber component may be blended as the balance in the rubber component.

  In addition to the natural rubber component defined above, the rubber component of the present invention can contain modified natural rubber such as hydrogenated natural rubber, for example, as rubber derived from non-petroleum resources.

  Further, the rubber component may contain a petroleum resource-derived rubber as long as the effects of the present invention are not impaired. Examples of rubbers derived from petroleum resources include styrene butadiene rubber (SBR), butadiene rubber (BR), styrene isoprene copolymer rubber, isoprene rubber (IR), butyl rubber (IIR), chloroprene rubber (CR), and acrylonitrile butadiene rubber. Examples thereof include (NBR), halogenated butyl rubber (X-IIR), and halides of copolymers of isobutylene and p-methylstyrene. Among these, SBR, BR, and IR are preferable in that the hardness of the clinching rubber composition can be increased and particularly good durability and fatigue resistance can be imparted to the pneumatic tire.

  The content of natural rubber (NR) in the rubber component is preferably 30% by mass or more. When the content of natural rubber (NR) is less than 30% by mass, the mechanical strength of the rubber composition for clinch 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 the natural rubber (NR) exceeds 80% by mass, the abrasion resistance of the rubber composition for clinch 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.

  The content of 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. If the content of epoxidized natural rubber (ENR) exceeds 70% by mass, the rubber hardness tends to be too high, and the mechanical strength of the clinching 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.

<Silica>
The BET specific surface area of the silica compounded in the present invention is 150 m ² / g or less. 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, by using a silica BET specific surface area of 150 m ² / g or less, the amount of raw material derived from petroleum resources is reduced, and physical properties such as rigidity, hardness and mechanical strength of the rubber composition for clinch 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 BET specific surface area of silica is low. For example, when the BET specific surface area is less than 50 m ² / g, the hardness of the rubber composition for clinching 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.

  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 40-80 mass parts with respect to 100 mass parts of rubber components. When the blending amount of silica with respect to 100 parts by mass of the rubber component is less than 40 parts by mass, the reinforcing effect and hysteresis reduction effect due to the blending of silica cannot be secured sufficiently, and when it exceeds 80 parts by mass, good processability cannot be obtained. . The compounding amount of silica is more preferably 45 parts by mass or more, and further preferably 50 parts by mass or more, more preferably 75 parts by mass or less, and even more preferably 70 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 series such as 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane; Vinyl series such as vinyltriethoxysilane and 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.

  Among these, Si69 (bis (3-triethoxysilylpropyl) tetrasulfide), Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Degussa are preferably used because of 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. When the amount exceeds 20% by mass, the effect of improving the workability is small, 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 clinch of the present invention may further contain carbon black as a reinforcing agent as long as the effects of the present invention are not impaired. By blending carbon black, good mechanical strength is imparted to the rubber composition for clinch, but since carbon black is generally derived from petroleum resources, in order to reduce the amount of raw materials derived from petroleum resources, The compounding amount of carbon black is preferably 5 parts by mass or less, further 4 parts by mass or less, and further 3 parts by mass or less with respect to 100 parts by mass of the rubber component. On the other hand, when carbon black is blended, the carbon black is blended in an amount of 1 part by mass or more and 1.5 parts by mass with respect to 100 parts by mass of the rubber component in that the effect of improving the mechanical strength by the blending of carbon black is obtained. It is preferable that it is 2 parts by mass or more.

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

<Other ingredients>
The rubber composition for clinch of the present invention includes, in addition to the above components, other compounding agents conventionally used in the rubber industry, such as vulcanizing agents, stearic acid, vulcanization accelerators, vulcanization acceleration aids, 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, 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 group 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 (tetramethylthiuram disulfide), tetraethylthiuram disulfide, tetramethylthiuram monosulfide, dipentamethylenethiuram disulfide, dipentamethylenethiuram monosulfide, dipentamethylenethiuram tetrasulfide, dipentamethylenethiuram 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. Examples of guanidine-based compounds include guanidine-based compounds such as diphenylguanidine, diortolylguanidine, triphenylguanidine, orthotolylbiguanide, and diphenylguanidine phthalate. 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 or aldehyde-ammonia system compound such as acetaldehyde-aniline reaction product, butyraldehyde-aniline condensate, hexamethylenetetramine, acetaldehyde-ammonia reaction product, etc. 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 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. As vegetable oils and fats, 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.

  The present invention also provides a pneumatic tire provided with a clinch apex comprising the rubber composition for clinch of the present invention as described above. Hereinafter, the pneumatic tire of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing an example of the pneumatic tire of 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. Prepare. A carcass 6 is bridged between the bead portions 4 and 4, and a belt layer 7 is provided outside the carcass 6 and inside the tread portion 2 to reinforce the tread portion 2 with a tagging effect.

  The carcass 6 is formed of one or more carcass plies 6a 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 6a extends from the tread portion 2 to the sidewall portion. 3, the periphery of the bead core 5 of the bead portion 4 is folded back and locked from the inner side to the outer side in the tire axial direction.

  The belt layer 7 is composed of two or more belt plies 7a in which the belt cord is arranged at an angle of, for example, 40 ° or less with respect to the tire equator CO. It is location. If necessary, a band layer (not shown) for preventing lifting at both ends of the belt layer 7 may be provided at least outside the belt layer 7. At this time, the band layer is formed of a low modulus organic fiber. The cord is formed of a continuous ply spirally wound substantially parallel to the tire equator CO.

  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. The rubber composition for clinch of the present invention is used for the clinch rubber 4G.

  Although FIG. 1 illustrates a pneumatic tire for a passenger car, the present invention is not limited to this, and air used for various vehicles such as a passenger car, a truck, a bus, and a heavy vehicle. Provide filled tires.

  The pneumatic tire of the present invention is manufactured by a conventionally known method using the rubber composition for clinch of the present invention. That is, the rubber composition for clinch containing the above-described essential components and other compounding agents blended as necessary is kneaded and extruded in accordance with the shape of the tire clinch at the unvulcanized stage, An unvulcanized tire is formed by molding in a normal manner on a tire molding machine together with other members of the tire. The tire of the present invention can be obtained by heating and pressurizing the unvulcanized tire in a vulcanizer.

  In the pneumatic tire of the present invention, the content ratio of components derived from petroleum resources in clinch rubber is further reduced, sufficient consideration is given to resource saving and environmental protection, and good physical characteristics are maintained and processability is improved. Since a rubber composition that is compatible with improvement is used, it is an “eco-tyre” that is friendly to the global environment, and has good durability and steering stability performance.

  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 to 3 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, the lower the tan δ and the better the rolling resistance.

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: Silane coupling agent is “Si69” 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 and Comparative Example 2 having a high silica content, good processability is obtained by increasing the Mooney viscosity of the unvulcanized rubber composition. In contrast, in Examples 1 to 3, in which the BET specific surface area and 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. It was. In Examples 1 to 3, E * and tan δ of the test rubber sheet after vulcanization showed good values. From the above results, it can be seen that according to the present invention, a rubber composition for clinch capable of improving processability while maintaining good mechanical strength and rolling resistance characteristics is 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 clinch of the present invention is suitably applied to clinch rubber for pneumatic tires for various uses such as passenger cars, trucks, buses, heavy vehicles, etc., and the pneumatic tire of the present invention is used for the above various uses. It can be suitably applied.

It is a schematic sectional drawing which shows an example of the pneumatic tire of this invention.

Explanation of symbols

  1 tire, 2 tread part, 3 sidewall part, 4 bead part, 5 bead core, 6 carcass, 6a carcass ply, 7 belt layer, 7a belt ply, 8 bead apex rubber, 9 inner liner rubber, 3G side wall rubber, 4G clinch rubber.

Claims (3)

Containing a rubber component composed of a natural rubber component and silica compounded within a range of 60 to 70 parts by mass with respect to 100 parts by mass of the rubber component;
The silica has a BET specific surface area of 150 m ² / g or less,
The rubber component for clinch, wherein the rubber component contains a natural rubber component composed of at least one of natural rubber and epoxidized natural rubber within a range of 20 to 100% by mass.   The rubber composition for clinch according to claim 1, wherein carbon black is further blended at 5 parts by mass or less with respect to 100 parts by mass of the rubber component. A pneumatic tire comprising a clinch apex made of the rubber composition for clinch according to claim 1 or 2 .

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