JP2008291065A - Rubber composition for bead apex, and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition for a bead apex having sufficient extrusion working property while sufficiently taking into consideration resource-saving and environment protection by further enhancing a content ratio of a material comprising the resource other than petroleum and maintaining excellent rubber hardness and rubber strength, and a pneumatic tire using the rubber composition. <P>SOLUTION: The rubber composition for the bead apex contains 60 pts.mass or more of silica and 4-16 pts.mass of a silane compound represented by (X)<SB>n</SB>-Si-Y<SB>(4-n)</SB>(wherein X represents a methoxy group or an ethoxy group, Y represents a phenyl group or a straight or branched alkyl group, and n represents an integer of 1-3) relative to 100 pts.mass of a rubber component containing any one kind or more selected from the group consisting of a natural rubber, an epoxylated natural rubber and a deproteinized natural rubber. The pneumatic tire provided with the bead apex rubber comprising the rubber composition is provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a rubber composition used for a tire, and more particularly to a rubber composition for a bead apex of a pneumatic tire. Moreover, this invention relates to a pneumatic tire provided with the bead apex rubber which consists of the said rubber composition.

  Conventionally, a rubber composition for tire bead apex has been blended with a large amount of carbon black as a filler in order to improve the strength and hardness of the bead apex rubber. In such a rubber composition containing a large amount of carbon black, the viscosity was relatively good, and the extrusion processability was not a problem.

  However, in recent years, environmental issues have become more important and regulations on carbon dioxide emissions have been strengthened. In addition, since the existing amount of petroleum is limited, the use of raw materials derived from petroleum resources is limited. This environment-oriented orientation is no exception in the field of tires, and a rubber composition for bead apex in which some or all of the raw materials derived from petroleum resources currently used are replaced with raw materials derived from non-petroleum resources. Development is required.

  For example, Patent Document 1 discloses an eco-tire using silica or the like as a non-petroleum resource as an alternative raw material for carbon black.

  However, when a white filler such as silica is used instead of carbon black in the bead apex rubber composition, there is a problem in that the viscosity of the rubber composition increases, resulting in poor extrudability.

  By the way, Patent Documents 2 to 5 disclose techniques for blending a silylating agent into a rubber composition for a tire tread or a rubber composition for a sidewall. However, the addition of the silylating agent in these documents is intended to improve grip properties or water repellency, and the rubber compositions described in these documents can be used as rubber compositions for tire treads or It cannot be applied to a rubber composition for a bead apex that requires different characteristics from the rubber composition for a sidewall. In particular, in the rubber compositions disclosed in these documents, the viscosity and extrusion processability of the rubber composition are not considered.

Thus, in the rubber composition in which the raw material derived from petroleum resources is replaced with the raw material derived from non-petroleum resources, the extrudability is good while maintaining excellent rubber hardness and rubber strength, and bead apex rubber. The present condition is that the rubber composition used suitably for use is not obtained.
JP 2003-63206 A Japanese Unexamined Patent Publication No. 7-118454 JP 7-292158 A JP-A-9-87427 Japanese Patent Laid-Open No. 10-60175

  The present invention has been made in order to solve the above-mentioned problems, and the purpose of the present invention is to sufficiently consider resource saving and environmental protection by increasing the content ratio of materials made of resources other than petroleum. In addition, a rubber composition for bead apex that has low viscosity and good extrudability while maintaining excellent rubber hardness and rubber strength, and a bead apex rubber comprising the rubber composition are provided. It is to provide a pneumatic tire.

In the present invention, silica is added to 100 parts by mass of a rubber component containing at least one selected from the group consisting of natural rubber (NR), epoxidized natural rubber (ENR), and deproteinized natural rubber (DPNR). The following general formula (1): 60 parts by mass or more and 100 parts by mass of the rubber component:
(X) _n -Si-Y _(4-n) (1)
(In the above general formula (1), X represents a methoxy group or an ethoxy group, Y represents a phenyl group or a linear or branched alkyl group, and n represents an integer of 1 to 3).
It is a rubber composition for bead apex containing 4-16 mass parts of silane compounds represented by these.

  Here, the rubber composition for bead apex of the present invention may further contain 5 parts by mass or less of carbon black with respect to 100 parts by mass of the rubber component.

  Moreover, it is preferable that the rubber composition for bead apex of this invention further contains 5-15 mass parts silane coupling agents with respect to 100 mass parts of said silica.

  Furthermore, this invention provides a pneumatic tire provided with the bead apex rubber which consists of the said rubber composition.

  According to the present invention, by increasing the content ratio of the material consisting of non-petroleum resources, consideration for resource saving and environmental protection is sufficient, while maintaining excellent rubber hardness and rubber strength, A rubber composition for a bead apex having a low viscosity and good extrudability and a pneumatic tire provided with a bead apex rubber made of the rubber composition are provided.

The rubber composition for bead apex of the present invention contains 60 parts by mass or more of silica with respect to 100 parts by mass of the rubber component, and the following general formula (1):
(X) _n -Si-Y _(4-n) (1)
(In the above general formula (1), X represents a methoxy group or an ethoxy group, Y represents a phenyl group or a linear or branched alkyl group, and n represents an integer of 1 to 3).
4 to 16 parts by mass of a silane compound represented by the formula: Hereinafter, each component which the rubber composition for bead apex of this invention contains is demonstrated in detail.

<Rubber component>
The rubber composition for bead apex of the present invention includes, as a rubber component, natural rubber (NR), epoxidized natural rubber (ENR), deproteinized natural rubber (DPNR) and other natural rubbers, and diene synthetic rubber. Etc. are blended.

  The rubber composition for bead apex of the present invention preferably contains natural rubber (NR) as a rubber component. When the rubber composition contains natural rubber (NR), the content of natural rubber (NR) in the rubber component is preferably 10% by mass or more, and more preferably 30% by mass or more. When the NR content is less than 10% by mass, the workability tends to deteriorate. It is also preferable that the content of NR in the rubber component is 100% by mass.

  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 KR7 and TSR20.

  The rubber composition for bead apex of the present invention may contain epoxidized natural rubber (ENR) as a rubber component. Epoxidized natural rubber (ENR) is an epoxidized unsaturated double bond of natural rubber, and its molecular cohesive force is increased by epoxy groups that are polar groups. Therefore, the glass transition temperature (Tg) is higher than that of natural rubber, and the mechanical strength, abrasion resistance, and air permeation resistance are excellent. In particular, when silica is compounded in the rubber composition, due to the reaction between the silanol group on the silica surface and the epoxy group of the epoxidized natural rubber, the same degree as when carbon black is compounded in the rubber composition. The mechanical strength and wear resistance can be obtained.

  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 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 formic acid with natural rubber.

  The epoxidation rate of the epoxidized natural rubber (ENR) is not particularly limited, but is preferably 5 mol% or more, and more preferably 10 mol% or more. When the epoxidation rate of ENR is less than 5 mol%, ENR is compatible with NR, and therefore, sufficient rubber strength tends not to be obtained. The epoxidation rate of the epoxidized natural rubber (ENR) is preferably 60 mol% or less, and more preferably 55 mol% or less. When the epoxidation rate of ENR exceeds 60 mol%, the strength of the rubber is not sufficient, and the adhesiveness to general-purpose rubber tends to be low. The epoxidation rate of the epoxidized natural rubber (ENR) means (number of epoxidized double bonds) / (number of double bonds before epoxidation). Specifically, ENR (ENR25) having an epoxidation rate of 25 mol%, ENR (ENR50) having an epoxidation rate of 50 mol%, and the like can be suitably used.

  In the present invention, only one ENR may be used, or two or more ENRs having different epoxidation rates may be used.

  When the rubber composition for bead apex of the present invention contains epoxidized natural rubber (ENR), the content of epoxidized natural rubber (ENR) in the rubber component is 20% by mass or more from the viewpoint of mechanical strength. It is preferable that it is 30 mass% or more. The content of epoxidized natural rubber (ENR) in the rubber component is preferably 80% by mass or less, and more preferably 70% by mass or less. When the ENR content exceeds 80% by mass, the workability tends to deteriorate. The rubber composition for bead apex of the present invention may contain only epoxidized natural rubber (ENR) as a rubber component, or may not contain ENR at all.

  Further, the bead apex rubber composition of the present invention may contain deproteinized natural rubber (DPNR) as a rubber component. Natural rubber (NR) usually contains about 5 to 10% by mass of non-rubber components such as proteins and lipids. These non-rubber components, particularly proteins, are said to cause entanglement of molecular chains and cause gelation. In order to avoid such a problem, it is very advantageous to blend a deproteinized natural rubber (DPNR) from which the non-rubber component in the natural rubber is removed into the rubber composition.

  Here, it is preferable that the weight average molecular weight (gel permeation chromatography (GPC), polystyrene conversion) of deproteinized natural rubber (DPNR) is 1.4 million or more. When the weight average molecular weight is less than 1,400,000, the strength of raw rubber is lowered. The nitrogen content of the deproteinized natural rubber (DPNR) is preferably 0.1% by mass or less, more preferably 0.08% by mass or less, and further preferably 0.05% by mass or less. preferable. When the nitrogen content exceeds 0.1% by mass, it becomes a factor causing gelation.

  When the rubber composition for bead apex of the present invention contains deproteinized natural rubber (DPNR), the content of deproteinized natural rubber (DPNR) in the rubber component is 10% by mass or more from the viewpoint of processability. It is preferable that it is 50% by mass or more. The content of deproteinized natural rubber (DPNR) in the rubber component is preferably 80% by mass or less, and more preferably 70% by mass or less. When the DPNR content exceeds 80% by mass, the cost increases. Note that the bead apex rubber composition of the present invention may contain only deproteinized natural rubber (DPNR) as a rubber component, or may not contain DPNR at all.

Deproteinized natural rubber (DPNR) can be obtained by deproteinizing natural rubber (NR). Examples of the deproteinization treatment of natural rubber (NR) include the following methods.
(1) A method of degrading protein by adding a proteolytic enzyme or bacteria to natural rubber latex,
(2) A method in which alkali is added to natural rubber latex and heated to decompose proteins,
(3) A method for liberating proteins adsorbed on natural rubber latex by a surfactant.

  The natural rubber latex used for the deproteinization treatment is not particularly limited, and field latex, ammonia-treated latex and the like can be used.

  As the proteolytic enzyme used in the above method (1), conventionally known proteolytic enzymes can be used, and are not particularly limited. For example, protease is preferably used. Protease may be derived from bacteria, filamentous fungi, or yeast. Among these, bacteria-derived proteases are preferred. In addition, enzymes such as lipase, esterase, amylase, laccase and cellulase may be used in combination.

  When alkaline protease is used as the proteolytic enzyme, the activity is preferably in the range of 0.1 to 50 APU / g, preferably 1 to 25 APU / g. Here, the activity of the proteolytic enzyme is determined by the Anson-hemoglobin method [Anson. M.M. L. , J .; Gen. Physiol. , 22, 79 (1938)]. That is, after reacting at a temperature of 25 ° C. and a pH of 10.5 for 10 minutes in a solution adjusted so that the final concentration of urea-modified hemoglobin used as a substrate is 14.7 mg / ml, trichloroacetic acid is terminated in the reaction solution. Add to a concentration of 31.25 mg / ml. Subsequently, the soluble content of trichloroacetic acid is colored with a phenol reagent, and the activity per 10 minutes of reaction is obtained by a calibration curve with the coloration degree of 1 mol of tyrosine as 1 APU, and this is converted per 1 minute. Measure. In addition, 1 APU indicates the amount of protease that gives a soluble amount of trichloroacetic acid having the same coloration degree as 1 mol of tyrosine is colored by a phenol reagent in one minute.

  The addition amount of the proteolytic enzyme is appropriately set depending on the enzyme activity, but is usually 0.0001 to 20 parts by mass, preferably 0.001 to 10 parts by mass with respect to 100 parts by mass of the solid content of natural rubber latex. It is. If the amount of the proteolytic enzyme added is less than 0.0001 parts by mass, the protein in the natural rubber latex may not be sufficiently decomposed. If the amount exceeds 20 parts by mass, the activity of the enzyme is reduced and the cost is reduced. Becomes higher.

  The treatment time with the proteolytic enzyme is not particularly limited and can be appropriately set according to the enzyme activity. Usually, it is preferable to perform the treatment for several minutes to one week. During the proteolytic treatment, the natural rubber latex may be agitated or allowed to stand. Moreover, you may adjust temperature as needed, and it is 5-90 degreeC as a suitable temperature, Preferably it is 20-60 degreeC. If the treatment temperature exceeds 90 ° C., the enzyme is rapidly deactivated, and if it is less than 5 ° C., the enzyme reaction is difficult to proceed.

  As the surfactant used in the above method (3), for example, one or more of an anionic surfactant, a nonionic surfactant, and a zwitterionic surfactant can be used. Examples of the anionic surfactant include carboxylic acid type, sulfonic acid type, sulfate ester type, and phosphate ester type. As the nonionic surfactant, for example, polyoxyalkylene ether, polyoxyalkylene ester, polyhydric alcohol fatty acid ester, sugar fatty acid ester, alkyl polyglycoside, and the like are preferably used. Examples of zwitterionic surfactants include amino acid type, betaine type, and amine oxide type.

  In the method (3), the natural rubber latex is washed with a surfactant to liberate proteins adsorbed on the natural rubber latex. As a method for cleaning the natural rubber latex particles with the surfactant, either a method for cleaning the natural rubber latex not treated with enzyme or a method for cleaning the natural rubber latex that has been subjected to the enzyme treatment may be used. Specific cleaning methods include, for example, a method in which a surfactant is added to natural rubber latex that has not been treated with enzyme or natural rubber latex that has been treated with enzyme, and a method in which natural rubber latex particles are aggregated and separated. Can be mentioned. When the natural rubber latex is washed by centrifugation, the centrifugation can be performed once to several times. Usually, a deproteinized natural rubber latex from which protein is highly removed can be obtained by one centrifugation. Moreover, you may perform a centrifugation process, after diluting with water so that the rubber component of a natural rubber latex may be 5-40 mass%, Preferably it is 10-30 mass%.

  The addition amount of the surfactant is 0.001 to 20 parts by mass, preferably 0.001 to 15 parts by mass with respect to 100 parts by mass of the solid content of the natural rubber latex.

  In the above methods (1) and (3), when using a proteolytic enzyme or a surfactant, other additives such as a pH adjusting agent and a dispersing agent may be added.

  Examples of pH adjusters include phosphates such as potassium dihydrogen phosphate, potassium hydrogen phosphate, sodium dihydrogen phosphate, and sodium hydrogen phosphate; acetates such as potassium acetate and sodium acetate; sulfuric acid, acetic acid, hydrochloric acid, Examples thereof include acids such as nitric acid, citric acid and succinic acid or salts thereof; ammonia, potassium hydroxide, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate and the like. The addition amount of the pH adjuster is usually 0.01 to 0.5 parts by mass with respect to 100 parts by mass of the rubber solid content of the natural rubber latex.

  Examples of the dispersant include styrene sulfonic acid copolymer, naphthalene sulfonic acid formalin condensate, lignin sulfonic acid, polycyclic aromatic sulfonic acid copolymer, acrylic acid, maleic anhydride homopolymer and copolymer, isobutylene- Examples thereof include a copolymer of acrylic acid and isobutylene-maleic anhydride.

  The deproteinized natural rubber latex obtained as described above may be coagulated after removing the non-rubber component by centrifugation or the like, or may be coagulated without removing the non-rubber component. The coagulation method is not particularly limited and can be performed by a known method. Usually, a latex rubber particle is destabilized and solidified by adding a coagulant such as formic acid or sulfuric acid or a salt such as sodium chloride. A method of destabilizing and solidifying is used.

  In addition, it is preferable that the gel content rate of deproteinized natural rubber is 10 mass% or less. When the gel content exceeds 10% by mass, the viscosity of the unvulcanized rubber increases and the processability tends to decrease. The gel content is measured as a toluene insoluble matter.

  The rubber composition for bead apex of the present invention may contain modified natural rubber, diene synthetic rubber and the like other than those described above. Examples of the diene-based synthetic rubber include styrene butadiene rubber (SBR), butadiene rubber (BR), styrene isoprene copolymer rubber, isoprene rubber (IR), butyl rubber (IIR), chloroprene rubber (CR), acrylonitrile butadiene rubber ( NBR), halogenated butyl rubber (X-IIR), and halides of copolymers of isobutylene and p-methylstyrene.

  When the rubber composition for bead apex of the present invention contains a diene synthetic rubber, the content of the diene synthetic rubber in the rubber component is preferably 50% by mass or less. In view of resource saving and environmental protection, it is more preferable not to include a diene synthetic rubber from the viewpoint of increasing the content of non-petroleum resources, and the rubber component is natural rubber (NR) or epoxidized natural rubber (ENR). And at least one selected from deproteinized natural rubber (DPNR).

<Silica>
The rubber composition for bead apex of the present invention contains silica. Silica functions as a reinforcing filler, and by blending silica, the hardness of the obtained bead apex rubber can be improved.

  Silica may be prepared by a wet method or may be prepared by a dry method.

The BET specific surface area of silica is preferably 70 m ² / g or more, and more preferably 80 m ² / g or more. If the BET specific surface area of silica is less than 70 m ² / g, sufficient hardness tends not to be obtained. Further, BET specific surface area of silica is preferably 300 meters ² / g or less, more preferably 280m ² / g. When the BET specific surface area of silica exceeds 300 m ² / g, the processability of rubber tends to be lowered. Specifically, Ultrazil VN2 (BET specific surface area: 125 m ² / g) or Ultrazil VN3 (BET specific surface area: 210 m ² / g) manufactured by Degussa can be suitably used.

  The content of silica is 60 parts by mass or more with respect to 100 parts by mass of the rubber component. When the content of silica is less than 60 parts by mass, sufficient rubber hardness tends to be not obtained. As for content of a silica, 65 mass parts or more are more preferable with respect to 100 mass parts of rubber components. Moreover, 100 mass parts or less are preferable with respect to 100 mass parts of rubber components, and, as for content of a silica, 90 mass parts or less are more preferable. If the silica content exceeds 100 parts by mass, the processability tends to deteriorate.

<Silane compound>
The bead apex rubber composition of the present invention contains a silane compound. By adding the silane compound, it is possible to obtain a rubber composition having low extrusion viscosity and good extrudability while maintaining excellent rubber hardness and rubber strength. Such an effect is considered to result from the fact that the silane compound reacts with active hydrogen groups and as a result, the dispersion of the silane compound in the rubber becomes good.

Here, the silane compound in the present invention is the following general formula (1):
(X) _n -Si-Y _(4-n) (1)
(In the above general formula (1), X represents a methoxy group or an ethoxy group, Y represents a phenyl group or a linear or branched alkyl group, and n represents an integer of 1 to 3).
It is a silane compound represented by.

  X in the general formula (1) is more preferably an ethoxy group because it is more compatible with the rubber component. For the same reason, Y in the general formula (1) is more preferably a phenyl group. Moreover, n in the said General formula (1) is an integer of 1-3. When n is 0, X does not exist, and the reactivity of the silane compound tends to increase too much. When n is 4, Y does not exist and the reactivity of the silane compound tends to decrease.

  Specific examples of the silane compound represented by the general formula (1) include, for example, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltrimethoxysilane. Examples include ethoxysilane, diphenyldiethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, decyltrimethoxysilane, and trifluoropropyltrimethoxysilane. These silane compounds may be used alone or in combination of two or more. Phenyltriethoxysilane is preferred because it is compatible with rubber and can reduce costs.

  Content of a silane compound is 4 mass parts or more with respect to 100 mass parts of rubber components, Preferably it is 5 mass parts or more. When the content of the silane compound is less than 4 parts by mass, good extrudability tends to be not obtained. Moreover, content of a silane compound is 16 mass parts or less with respect to 100 mass parts of rubber components, Preferably it is 15 mass parts or less. When the content of the silane compound exceeds 16 parts by mass, the rubber strength tends to decrease.

<Silane coupling agent>
The rubber composition for bead apex of the present invention preferably contains a silane coupling agent together with 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-dimethylthiocarbamoyltetrasulfide, 3-tri 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.

  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.

  5 mass parts or more are preferable with respect to 100 mass parts of silica, and, as for content of a silane coupling agent, 8 mass parts or more are more preferable. When the content is less than 5 parts by mass, sufficient rubber strength tends not to be obtained. Moreover, 15 mass parts or less are preferable with respect to 100 mass parts of silica, and, as for content of a silane coupling agent, 13 mass parts or less are more preferable. Even if an amount exceeding 15 parts by mass is added, the rubber strength corresponding to the amount is not improved, and the cost tends to increase.

<Carbon black>
The bead apex rubber composition of the present invention may contain carbon black. The BET specific surface area of carbon black is preferably 40 m ² / g or more, and more preferably 70 m ² / g or more. When the BET specific surface area of carbon black is less than 50 m ² / g, the reinforcing property tends to be lowered. Further, BET specific surface area of the carbon black is preferably 250 meters ² / g or less, more preferably 200m ² / g. When the BET specific surface area of carbon black exceeds 250 m ² / g, the workability tends to be lowered.

  The DBP (dibutyl phthalate) oil absorption of carbon black is preferably 60 to 120 ml / 100 g, and more preferably 80 to 110 ml / 100 g. When the DBP oil absorption is less than 60 ml / 100 g, the reinforcing property tends to decrease, and when it exceeds 120 ml / 100 g, the workability tends to decrease.

  When the rubber composition for bead apex of the present invention contains carbon black, the content thereof is preferably 5 parts by mass or less, more preferably 3 parts by mass or less with respect to 100 parts by mass of the rubber component. preferable. By adding carbon black, it is possible to further improve rubber strength and rubber hardness. However, from the viewpoint of resource saving and environmental protection, it is preferable not to contain carbon black.

<Other ingredients>
In addition to the above components, the bead apex rubber composition of the present invention contains other additives such as a vulcanizing agent, a vulcanization accelerator, stearic acid, oil, wax, anti-aging agent, zinc white and the like. You may contain.

  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 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 (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. 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 anti-aging agent, amine-based, phenol-based, imidazole-based, carbamic acid metal salts, and the like can be appropriately selected and used.

  As the oil, for example, process oil, vegetable oil and fat, and a mixture thereof can be used. Examples of the process oil include paraffinic process oil, naphthenic process oil, and aromatic process oil. Vegetable oils include castor oil, cottonseed oil, rapeseed oil, rapeseed oil, soybean oil, palm oil, coconut oil, peanut oil, rosin, pine oil, pineapple oil, tall oil, corn oil, rice bran oil, beet flower oil, Sesame oil, olive oil, sunflower oil, palm kernel oil, coconut oil, jojoba oil, macadamia nut oil, safflower oil, tung oil, and the like.

  The pneumatic tire of the present invention is a pneumatic tire provided with a bead apex rubber made of the rubber composition for bead apex of the present invention. Hereinafter, the pneumatic tire of the present invention will be described with reference to FIG. FIG. 1 illustrates 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 thereof, and a bead portion 4 positioned at an inner end of each sidewall portion 3. A carcass 6 is bridged between the bead portions 4 and 4, and a belt layer 7 that reinforces the tread portion 2 with a tagging effect is disposed outside the carcass 6 and in the tread portion 2.

  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 bead apex rubber composition of the present invention is used for the bead apex rubber 8.

  The pneumatic tire of the present invention is produced by a conventionally known method using the rubber composition for bead apex of the present invention. That is, a rubber composition for a bead apex containing the above-described essential components and other additives blended as necessary is kneaded and matched to the shape of the bead apex of the tire at an unvulcanized stage. An unvulcanized tire is formed by extruding and molding together with other members of the tire by a conventional method on a tire molding machine. The tire of the present invention can be obtained by heating and pressurizing the unvulcanized tire in a vulcanizer.

  Such a pneumatic tire according to the present invention has a higher content ratio of materials made of non-petroleum resources to bead apex rubber, sufficient consideration for resource saving and environmental protection, and excellent rubber hardness and rubber strength. In addition, since a rubber composition exhibiting good extrudability is used, it can be suitably used as, for example, a passenger car as an “eco-tyre” that is 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 1-3 and Comparative Examples 1-4>
In accordance with the formulation shown in Table 1, the components other than sulfur and the vulcanization accelerator were kneaded for 3 minutes under the conditions of a rotation speed of 80 rpm and 150 ° C. using a Kobe Steel Banbury mixer. 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 to obtain an unvulcanized rubber composition. . Next, vulcanized rubber sheets of Examples 1 to 3 and Comparative Examples 1 to 4 were produced by vulcanizing the unvulcanized rubber composition at 150 ° C. for 30 minutes.

The details of various blending components used in Examples and Comparative Examples are as follows.
(1) Natural rubber (NR): TSR20
(2) Epoxidized natural rubber (ENR): “ENR25” (epoxidation rate: 25 mol%) manufactured by Kumpoulang Guthrie
(3) Silane compound: “KBE-103” (phenyltriethoxysilane) manufactured by Shin-Etsu Chemical Co., Ltd.
(4) Carbon black: “Show Black N220” manufactured by Showa Cabot (BET: 111 m ² / g, DBP oil absorption 115 ml / 100 g)
(5) Silica: “Ultrasil VN3” manufactured by Degussa (BET specific surface area: 210 m ² / g)
(6) Silane coupling agent: “Si69” (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Degussa
(7) Stearic acid: Stearic acid “Kashiwa” manufactured by NOF Corporation
(8) Zinc flower: “Zinc flower No. 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
(9) Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Co., Ltd. (10) Vulcanization accelerator: “Noxeller NS” (N-tert-butyl-2-benzothiazolylsulfur manufactured by Ouchi Shinsei Chemical Co., Ltd.) Funamide)
The test shown below was implemented about the vulcanized rubber sheet of Examples 1-3 and Comparative Examples 1-4. The results are shown in Table 1.

(Extrudability)
Using a lab extruder, the shape of the extruded rubber sheet was visually confirmed. A case where there was a problem such as a lack of ears was designated as B, and a case where there was no problem in the shape was designated as A.

(Rubber hardness)
In accordance with JIS-K6253, the hardness was measured at room temperature using a type A hardness meter. The numerical values in Table 1 are relative values when the numerical value of Comparative Example 1 is 100. The higher the value, the higher the hardness of the rubber.

(Rubber strength)
A No. 3 dumbbell-shaped test piece was prepared from the vulcanized rubber sample, and a tensile test was carried out according to JIS-K6251 “Vulcanized rubber and thermoplastic rubber-Determination of tensile properties”. The elongation at break (EB) was measured, and the (TB × EB) value was calculated. The numerical values in Table 1 are relative values when the (TB × EB) value of Comparative Example 1 is 100. The higher the value, the higher the strength of the rubber.

  From the evaluation results in Table 1, it can be seen that by adding 4 to 16 parts by mass of the silane compound to 100 parts by mass of the rubber component, extrudability is improved and good rubber hardness and rubber strength are exhibited. On the other hand, when the silane compound was not added and when the addition amount was small, the extrusion processability was poor, and when the addition amount of the silane compound was too large, the rubber strength tended to decrease.

  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.

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

Explanation of symbols

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

Claims (4)

Including 60 parts by mass or more of silica with respect to 100 parts by mass of a rubber component containing any one or more selected from the group consisting of natural rubber, epoxidized natural rubber and deproteinized natural rubber, and
The following general formula (1):
(X) _n -Si-Y _(4-n) (1)
(In the above general formula (1), X represents a methoxy group or an ethoxy group, Y represents a phenyl group or a linear or branched alkyl group, and n represents an integer of 1 to 3).
A rubber composition for bead apex containing 4 to 16 parts by mass of the silane compound represented by the formula:   The bead apex rubber composition according to claim 1, further comprising 5 parts by mass or less of carbon black with respect to 100 parts by mass of the rubber component.   The rubber composition for bead apex according to claim 1 or 2, further comprising 5 to 15 parts by mass of a silane coupling agent with respect to 100 parts by mass of the silica.   A pneumatic tire provided with the bead apex rubber which consists of a rubber composition in any one of Claims 1-3.

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