JP2012180449A - Rubber composition for coating organic fiber reinforcing material, and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for coating an organic fiber reinforcing material in which fracture resistance and fatigue resistance are improved with well balance while maintaining low heat buildup, and which becomes a raw material of a chafer excellent in bead durability, and to provide a pneumatic tire.SOLUTION: The rubber composition for coating an organic fiber reinforcing material includes carbon black that satisfies the following (1)-(4): (1) the dibutyl phthalate (DBP) absorbed amount (ml/100g) is 90-180; (2) the difference between a BET specific surface area (BET5) (m/g) and an outer specific surface area (STSA) (m/g) is 5≤(BET5)-(STSA)≤12; (3) the ratio of a Stokes diameter (Dst) to a Stokes diameter distribution (ΔD-50 (half value width)) of the carbon black is 0.70≤(ΔD-50)/(Dst)≤1.10, and (4) the ratio of the BET specific surface area (BET5) (m/g) to an iodine absorbed amount (IA) (mg/g) is 1.05≤(BET5)/(IA)≤1.35.

Description

  The present invention is a rubber composition for covering an organic fiber reinforcing material, which contains a rubber component and carbon black and is useful as a raw material for a chafer of a pneumatic tire. The present invention relates to a rubber composition for coating an organic fiber reinforcing material and a pneumatic tire, which is a raw material for a chacher with improved fatigue and adhesion in a well-balanced manner and excellent bead durability.

  In the heavy-duty pneumatic tire shown in FIG. 1, as a reinforcing material for the bead wire 1 and the bead filler 2, a chacher 7 in which an organic fiber reinforcing material made of organic fiber is covered with rubber so as to cover the winding end of the carcass ply 5. It is arranged. Although not shown, a steel chacher in which a steel cord is covered with rubber may be disposed together with the chacher 7 on the outer side or the inner side of the chacher 7 in the tire width direction. Since such a chafer is repeatedly subjected to a load while the tire is running, separation is likely to occur between the organic fiber reinforcing material made of organic fibers and the covering rubber, or between the covering rubbers. Therefore, in order to enhance the reinforcement effect of organic fiber reinforcement made of organic fibers and prevent the occurrence of failure such as separation, the coated rubber has high adhesion to organic fibers, excellent low heat generation, and fracture resistance Fatigue resistance is required.

  Examples of a technique for improving the adhesion between the coating rubber and the organic fiber include a method of blending an organic acid metal salt in a coating rubber composition, or a methylene acceptor such as resorcin that can form a strong adhesive layer. A method of blending a methylene donor such as hexamethylenetetramine has been conventionally used (for example, Patent Document 1 below). By these methods, the adhesion between the organic fiber and the coated rubber is improved. However, in these methods, since the fracture resistance of the coated rubber is lowered, it is difficult to say that the durability of the pneumatic tire is sufficiently improved, and there is still room for improvement.

  On the other hand, carbon black blended with organic fiber coating rubber used for chachers, etc., has a relatively large particle size carbon black (in order to suppress heat generation of the coating rubber (that is, to improve low heat generation)) ( For example, HAF class) is used. However, when carbon black having a relatively large particle size is blended in the coated rubber, the low heat build-up is improved, but it is difficult to say that the fracture resistance is sufficiently improved. Therefore, the actual situation is that there is a demand in the market for a coating rubber for an organic fiber reinforcing material containing carbon black, which can improve the fracture resistance while maintaining low exothermic properties.

In the following Patent Document 2, the loss on heating from 150 ° C. to 450 ° C. is 0.87% by mass or more, the toluene coloring permeability is 90% or more, and the nitrogen adsorption specific surface area (N ₂ SA) (m ² / g) and iodine A rubber composition containing carbon black having a ratio of 1.10 to 1.30 with the amount of adsorption (IA) (mg / g) and a processing aid that is at least one of a fatty acid ester and a fatty acid metal salt. In addition, it describes that it is possible to achieve both fracture resistance and low heat build-up. In Patent Document 3 below, the specific surface area (m ² / g) of cetyltriammonium (CTAB) is 115 to 145, and the ratio of DBP absorption (24M4DBP) (ml / 100 g) to CTAB is 0.75 to 0.00. 92, a rubber composition containing carbon black in which the ratio of CTAB to IA is 0.97 to 1.25 and the specific coloring amount TINT (%) ≧ −46.787 (24M4DBP / CTAB) +168 is It describes that both characteristics and low heat build-up can be achieved. In Patent Document 4 below, a rubber composition containing carbon black in which the ratio of N ₂ SA to IA is 1.20 to 1.30 and the difference between N ₂ SA and CTAB is adjusted to 5 or less is It describes that both fracture characteristics and low heat build-up can be achieved. Furthermore, in the following Patent Document 5, carbon having a CTAB of 120 or more, a compressed DBP absorption amount of 90 (ml / 100 g) or more, and an amount occupied by a pore diameter of 25 to 30 nm in the inter-aggregate pore volume is 30 ml / 100 g or more. It describes that a rubber composition containing black can achieve both fracture resistance and low heat build-up.

  However, as a result of intensive studies by the present inventor, it is difficult to accurately grasp the degree of pores on the surface of the carbon black aggregate only by optimizing each index of carbon black noted in the above document. found. The degree of pores on the surface of the carbon black aggregate has a significant effect on the low heat buildup and fracture resistance, so the carbon black used in the above documents has a particularly low heat buildup and fracture resistance in the coated rubber. It was found that there is room for further improvement when trying to achieve both.

JP-A-11-263102 JP 2009-40904 A JP 2000-344945 A JP 2007-231179 A JP-A-2005-334063

  The present invention has been made in view of the above circumstances, and its purpose is to maintain a low exothermic property while improving fracture resistance, fatigue resistance and adhesiveness in a well-balanced manner, and to make Chaher excellent in bead durability. The object is to provide a rubber composition for covering an organic fiber reinforcing material and a pneumatic tire as raw materials.

  In order to solve the above-mentioned problems, the present inventors diligently studied a method for accurately grasping the degree of pores on the surface of the carbon black aggregate. As a result, in the carbon black in which the difference between the BET specific surface area (BET5) and the external specific surface area (STSA) is within a specific range, the degree of pores on the surface of the carbon black aggregate is low exothermic property and fracture resistance. It has been found that it is particularly preferable for achieving both fatigue resistance and adhesion. Further, in addition to BET5 and STSA, dibutyl phthalate (DBP) absorption amount, iodine adsorption amount (IA), and Stokes diameter (Dst) of carbon black, which have been conventionally used as indicators of carbon black characteristics, and An organic fiber reinforcing material is manufactured using a rubber composition containing carbon black that is optimal in relation to the Stokes diameter distribution (ΔD-50 (half width)) as a covering rubber, and a chacher is manufactured using the organic fiber reinforcing material as a raw material. As a result, it has been found that the low exothermic property, the fracture resistance and the fatigue resistance of the chacher can be improved in a well-balanced manner. The present invention has been made as a result of the above-described studies, and achieves the above-described object with the following configuration.

That is, the present invention is an organic fiber reinforcement covering rubber composition containing a rubber component and carbon black, and the carbon black satisfies the following (1) to (4),
(1) Dibutyl phthalate (DBP) absorption (ml / 100 g) is 90 to 180,
(2) The difference between the BET specific surface area (BET5) (m ² / g) and the external specific surface area (STSA) (m ² / g) is 5 ≦ (BET5) − (STSA) ≦ 12,
(3) The ratio between the Stokes diameter (Dst) of the carbon black and the Stokes diameter distribution (ΔD-50 (half-value width)) is 0.70 ≦ (ΔD-50) / (Dst) ≦ 1.10. 4) The ratio of BET specific surface area (BET5) (m ² / g) to iodine adsorption amount (IA) (mg / g) is 1.05 ≦ (BET5) / (IA) ≦ 1.35, at least the carbon The compounding amount of the reinforcing filler containing black is 40 to 70 parts by mass with respect to 100 parts by mass of the rubber component, and the ratio of the carbon black in the reinforcing filler is 70% by mass or more. The present invention relates to a rubber composition for coating an organic fiber reinforcing material.

  In the rubber composition according to the present invention, the carbon black has a (1) dibutyl phthalate (DBP) absorption amount (ml / 100 g) of 90 to 180. Therefore, low heat build-up and fracture resistance, fatigue resistance and adhesion are obtained. Can be balanced in a balanced manner. The DBP absorption amount is an index of the structure of the carbon black aggregate, and if the DBP absorption amount is below the range described in (1), the structure of the carbon black aggregate is too low, so that the rubber reinforcement is It tends to decrease and durability deteriorates. On the other hand, when the DBP absorption amount exceeds the range described in (1), the structure of the carbon black aggregate is too high, and thus the low heat build-up tends to deteriorate.

Further, the rubber composition according to the present invention has a difference between the carbon black (2) BET specific surface area (BET5) (m ² / g) and the external specific surface area (STSA) (m ² / g) of 5 ≦ ( BET5) − (STSA) ≦ 12. Since the BET specific surface area (BET5) and the external specific surface area (STSA) are both indices related to the specific surface area calculated based on the nitrogen absorption amount, the difference between the two is calculated, so that the carbon black aggregate surface The degree of pores can be accurately grasped.

  Since rubber molecules cannot enter the pores on the surface of the carbon black aggregate, the more pores, the weaker the bond between carbon black and rubber molecules. In the present invention, since the relationship of (BET5)-(STSA) of carbon black satisfies the above (2), the degree of binding between carbon black and rubber molecules is optimized, and as a result, low heat buildup and fracture resistance, Both fatigue resistance and adhesiveness can be balanced.

  In the rubber composition according to the present invention, (3) the ratio of the Stokes diameter (Dst) of carbon black to the Stokes diameter distribution (ΔD-50 (half width)) is 0.70 ≦ (ΔD-50) / Since (Dst) ≦ 1.10, it is possible to improve the low exothermic property, the fracture resistance, the fatigue resistance and the adhesiveness in a well-balanced manner. When (ΔD-50) / (Dst) is less than the range described in (3), the low heat build-up tends to deteriorate. On the other hand, when (ΔD-50) / (Dst) exceeds the range described in (3), the fracture resistance and fatigue resistance tend to deteriorate.

Furthermore, in the rubber composition according to the present invention, the ratio of (4) BET specific surface area (BET5) (m ² / g) and iodine adsorption amount (IA) (mg / g) of carbon black is 1.05 ≦ Since (BET5) / (IA) ≦ 1.35, the degree of binding between carbon black and rubber molecules is optimized, and low heat buildup and fracture resistance can be improved in a well-balanced manner. (BET5) / (IA) is an index of the surface activity of the carbon black particles. When (BET5) / (IA) is below the range described in (4), the low heat build-up tends to deteriorate. is there. On the other hand, when (BET5) / (IA) exceeds the range described in (4), the fracture resistance and fatigue resistance tend to deteriorate.

  In the rubber composition according to the present invention, a blending amount of the reinforcing filler containing at least the carbon black is 40 to 70 parts by mass with respect to 100 parts by mass of the rubber component, and the reinforcing filler is in the reinforcing filler. The ratio of carbon black is set to 70% by mass or more. By setting the blending amount of the reinforcing filler containing carbon black within such a range, it is possible to improve the low exothermic property, the fracture resistance, the fatigue resistance and the adhesiveness in a well-balanced manner.

In the rubber composition, the carbon black preferably has an external specific surface area (STSA) (m ² / g) of 75 to 170. STSA is an index of the specific surface area (particle size) of carbon black particles. When STSA is less than 75, the fracture resistance tends to deteriorate, and when it exceeds 170, low heat build-up tends to deteriorate. is there.

  In the said rubber composition, it is preferable to contain 2-5 mass parts of sulfur in conversion of a sulfur content with respect to 100 mass parts of said rubber components. In the rubber composition, the resorcin derivative is 0.5 to 2.5 parts by mass and the melamine resin is 0.5 to 2 times the content of the resorcin derivative with respect to 100 parts by mass of the rubber component. It is preferable to contain within. According to these configurations, it is possible to improve the adhesion of the vulcanized rubber while improving the low heat generation property, the fracture resistance, and the fatigue resistance in a well-balanced manner.

  Moreover, this invention relates to a pneumatic tire provided with the chacher formed by coat | covering an organic fiber reinforcement with the rubber composition for organic fiber reinforcement coating in any one of the said. As described above, the vulcanized rubber of the rubber composition according to the present invention is improved in a well-balanced manner in terms of low heat buildup, fracture resistance, fatigue resistance, and adhesion. Therefore, a pneumatic tire provided with a chacher formed by coating an organic fiber reinforcing material with such a rubber composition is particularly excellent in bead durability.

Tire meridian cross-sectional view showing an example of a pneumatic tire according to the present invention For each carbon black, a graph in which (BET5) / (IA) is plotted on the horizontal axis and (BET5)-(STSA) is plotted on the vertical axis.

  The rubber composition for covering an organic fiber reinforcing material according to the present invention contains a rubber component and carbon black. In the present invention, it is preferable to contain a diene rubber as a rubber component.

  Examples of the diene rubber include natural rubber (NR), polyisoprene rubber (IR), styrene butadiene rubber (SBR), polybutadiene rubber (BR), butadiene rubber (SPB) containing syndiotactic-1,2-polybutadiene, A chloroprene rubber (CR), a nitrile rubber (NBR), etc. are mentioned, These can each be used individually or as a 2 or more types of blend. These exemplified diene rubbers are those having terminal modified as required (for example, terminal modified BR, terminal modified SBR, etc.), or modified to give desired characteristics (for example, modified). NR) can also be used. Regarding polybutadiene rubber (BR), in addition to those synthesized using a cobalt (Co) catalyst, a neodymium (Nd) catalyst, a nickel (Ni) catalyst, a titanium (Ti) catalyst, and a lithium (Li) catalyst, WO2007 What was synthesize | combined using the polymerization catalyst composition containing the metallocene complex as described in -129670 can also be used. In order to improve the low heat buildup, fracture resistance and fatigue resistance of the vulcanized rubber in a well-balanced manner, it is preferable to use natural rubber as a main component among the diene rubbers. Specifically, when the total amount of the rubber component is 100 parts by mass, the natural rubber is preferably contained in an amount of 60 parts by mass or more, more preferably 80 parts by mass or more. Is particularly preferably 100 parts by mass.

In the present invention, the greatest feature is that the carbon black to be used satisfies the following (1) to (4).
(1) Dibutyl phthalate (DBP) absorption (ml / 100 g) is 90 to 180,
(2) The difference between the BET specific surface area (BET5) (m ² / g) and the external specific surface area (STSA) (m ² / g) is 5 ≦ (BET5) − (STSA) ≦ 12,
(3) The ratio between the Stokes diameter (Dst) of the carbon black and the Stokes diameter distribution (ΔD-50 (half-value width)) is 0.70 ≦ (ΔD-50) / (Dst) ≦ 1.10. 4) The ratio of the BET specific surface area (BET5) (m ² / g) to the iodine adsorption amount (IA) (mg / g) is 1.05 ≦ (BET5) / (IA) ≦ 1.35.

  The carbon black satisfying the above (1) to (4) has a smaller degree of pores on the surface of the carbon black aggregate than the ISAF class (ASTM grade) carbon black usually used in the tire industry. The carbon black has a special aggregate distribution. In the present invention, by using such a rubber composition containing carbon black as a raw material, low heat build-up, fracture resistance, fatigue resistance and adhesion are improved in a well-balanced manner. More specifically, it achieves fracture resistance and fatigue resistance comparable to rubber compositions containing ISAF class carbon black and low heat build-up comparable to rubber compositions containing HAF class carbon black. be able to.

The rubber composition according to the present invention preferably contains carbon black having an external specific surface area (STSA) (m ² / g) of 75 to 170. In this case, the fracture resistance and the low heat buildup can be achieved in a balanced manner.

In particular, in the present invention, the carbon black dibutyl phthalate (DBP) absorption (ml / 100 g) is preferably 120 to 150, and the BET specific surface area (BET 5) (m ² / g) and the external specific surface area ( STSA) (m ² / g) is preferably 7 ≦ (BET5) − (STSA) ≦ 10, and the Stokes diameter (Dst) and Stokes diameter distribution (ΔD-50 (half width)) of carbon black )) Is preferably 0.75 ≦ (ΔD-50) / (Dst) ≦ 0.95, or the BET specific surface area (BET5) (m ² / g) and iodine adsorption amount (IA) ( mg / g) is preferably 1.10 ≦ (BET5) / (IA) ≦ 1.30. Moreover, in this invention, it is preferable that the external specific surface area (STSA) (m < ² > / g) of carbon black is 90-120.

Among the characteristic evaluation items of the carbon black, dibutyl phthalate (DBP) absorption (ml / 100 g) is JIS K6217-4, BET specific surface area (BET5) (m ² / g) and external specific surface area (STSA) (m ² / G) is JIS K6217-7, Stokes diameter (Dst) and Stokes diameter distribution (ΔD-50 (half-value width)) is JIS K6217-6, and iodine adsorption amount (IA) (mg / g) is JIS K6217-1. Measured according to the above.

  In the rubber composition according to the present invention, the amount of the reinforcing filler containing carbon black satisfying the above (1) to (4) is 40 to 70 parts by mass with respect to 100 parts by mass of the rubber component, and the reinforcement is performed. The proportion of carbon black in the filler for use is 70% by mass or more. In order to improve the low heat build-up and fracture resistance, fatigue resistance and adhesion in a well-balanced manner, the blending amount of the reinforcing filler containing carbon black is preferably 45 to 65 parts by mass. More preferably, it is 45-55 mass parts.

  In the present invention, silica, calcium carbonate, magnesium carbonate, magnesium oxide, titanium oxide, talc, clay, alumina, sericite, or the like can be used as a filler other than carbon black. In addition, when using a silica, it is preferable to use a silane coupling agent together.

  Moreover, in the rubber composition according to the present invention, it is preferable to blend a methylene acceptor and a methylene donor in order to improve the adhesion to organic fibers. Adhesiveness with organic fibers can be enhanced by a curing reaction between the hydroxyl group of the methylene acceptor and the methylene group of the methylene donor.

  As the methylene acceptor, a phenolic compound or a phenolic resin obtained by condensing a phenolic compound with formaldehyde is used. Such phenolic compounds include phenol, resorcin or alkyl derivatives thereof. Alkyl derivatives include methyl group derivatives such as cresol and xylenol, and derivatives with long chain alkyl groups such as nonylphenol and octylphenol. The phenol compound may contain an acyl group such as an acetyl group as a substituent.

  In addition, phenolic resins obtained by condensing phenolic compounds with formaldehyde include resorcin-formaldehyde resins, phenolic resins (phenol-formaldehyde resins), cresol resins (cresol-formaldehyde resins), and formaldehyde composed of a plurality of phenolic compounds. Resin etc. are included. These are uncured resins that have liquid or heat fluidity.

  Among these, from the viewpoint of compatibility with the rubber component and other components, the denseness of the resin after curing, and the reliability, the methylene acceptor is preferably resorcin or a resorcin derivative, and resorcin or resorcin-alkylphenol- Formalin resin is more preferred. In particular, in order to improve the adhesion and the low heat build-up in a well-balanced manner, it is preferable to blend 0.5 to 2.5 parts by mass of the resorcin derivative with respect to 100 parts by mass of the rubber component. It is more preferable to blend 0 parts by mass.

  As the methylene donor, hexamethylenetetramine or melamine resin is used. As such a melamine resin, for example, methylol melamine, a partially etherified product of methylol melamine, a condensate of melamine, formaldehyde, and methanol is used, and among them, hexamethoxymethyl melamine is particularly preferable. In particular, in order to improve the adhesion and low heat build-up in a well-balanced manner, it is preferable to blend the melamine resin within a range of 0.5 to 2 times the content of the resorcin derivative. It is more preferable to mix within a range of 5 times.

  The rubber composition according to the present invention includes the rubber component, fillers such as carbon black and silica, organic acid metal salt, methylene acceptor and methylene donor, sulfur, silane coupling agent, zinc white, stearic acid, Additives usually used in the rubber industry, such as vulcanization accelerators, vulcanization accelerators, vulcanization retarders, anti-aging agents, softeners such as waxes and oils, and processing aids, impair the effects of the present invention. It can be blended and used as appropriate within the range not included.

  Sulfur should just be normal sulfur for rubber | gum, For example, powder sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur etc. can be used. When the rubber physical properties and durability after vulcanization are taken into consideration, the amount of sulfur to 100 parts by mass of the rubber component is preferably 0.5 to 5 parts by mass, more preferably 1 to 3 parts by mass in terms of sulfur content.

  As the vulcanization accelerator, sulfenamide vulcanization accelerator, thiuram vulcanization accelerator, thiazole vulcanization accelerator, thiourea vulcanization accelerator, guanidine vulcanization, which are usually used for rubber vulcanization. Vulcanization accelerators such as accelerators and dithiocarbamate vulcanization accelerators may be used alone or in admixture as appropriate. When the rubber physical properties and durability after vulcanization are taken into consideration, the blending amount of the vulcanization accelerator with respect to 100 parts by mass of the rubber component is preferably 0.1 to 5 parts by mass.

  As an anti-aging agent, an aromatic amine-based anti-aging agent, an amine-ketone anti-aging agent, a monophenol anti-aging agent, a bisphenol anti-aging agent, a polyphenol anti-aging agent, dithiocarbamic acid, which are usually used for rubber Anti-aging agents such as a salt-based anti-aging agent and a thiourea-based anti-aging agent may be used alone or in an appropriate mixture. In consideration of rubber physical properties and durability, the blending amount of the anti-aging agent with respect to 100 parts by mass of the rubber component is preferably 0.1 to 5 parts by mass.

  The rubber composition according to the present invention includes the rubber component, fillers such as carbon black and silica, organic acid metal salts, methylene acceptors and methylene donors, if necessary, sulfur, silane coupling agents, zinc white, Compounding ingredients usually used in the rubber industry such as stearic acid, vulcanization accelerator, vulcanization accelerator, vulcanization retarder, anti-aging agent, softener such as wax and oil, processing aid, Banbury mixer, It can be obtained by kneading using a kneader used in a normal rubber industry such as a kneader or a roll.

  In addition, the blending method of each of the above components is not particularly limited, and a blending component other than a vulcanizing component such as sulfur and a vulcanization accelerator is previously kneaded to obtain a master batch, and the remaining components are added and further kneaded. , Rubber component and carbon black only in advance as a kneading masterbatch, the remaining components are added and further kneaded, each component is added in any order and kneaded, all components are added simultaneously and kneaded, etc. Either of these may be used. In addition, when making a rubber component and carbon black into a masterbatch beforehand, you may use the wet masterbatch obtained by mixing carbon black in rubber latex.

  As shown in FIG. 1, the pneumatic tire according to the present invention includes a pair of bead wires 1, a bead filler 2 disposed on the outer side of the bead wire 1 in the tire radial direction, a bead wire 1 and a bead filler 2. A sidewall 3 extending radially outward; a tread 4 connected to each tire radial outer end of the sidewall 3; and a carcass ply 5 whose ends are wound up from the inner side in the tire width direction by a pair of bead wires 1; And a belt 6 composed of a plurality of belt plies (four in FIG. 1, 6 a to 6 d) disposed on the outer peripheral side (outer side in the tire radial direction) of the carcass ply 5. The tread 4 may be composed of a single rubber portion, or may be composed of two layers of a cap tread on the ground contact surface side and a base tread on the inner side in the tire radial direction.

  On the inner side in the tire radial direction of the bead wire 1 and the bead filler 2, a chacher 7 and a rim strip 8 are arranged via a carcass ply 5, and the rim strip 8 sits in contact with a tire rim (not shown). On the outer side of the bead filler 2 in the tire radial direction, a chacher pad 9 is disposed so as to sandwich the chacher 7. On the other hand, an inner liner 10 for maintaining air pressure is disposed on the inner peripheral side of the carcass ply 5. A shoulder pad 11 is disposed on the end side of the belt 6 and on the inner side in the tire radial direction, and a belt edge filler 12 is disposed between the belt plies 6b and 6c.

  The chacher 7 is configured by coating an organic fiber reinforcing material made of organic fibers with the rubber composition according to the present invention. Examples of organic fibers include nylon, polyester, rayon, and aramid. In addition to the chacher 7, a steel chacher in which a steel cord is covered with rubber may be disposed on the outer side or the inner side of the chacher 7 in the tire width direction. Using the rubber composition according to the present invention, an organic fiber reinforcing material made of organic fibers is manufactured by a known facility such as a rubber extruder, and an unvulcanized tire provided with this as a chacher is molded. By vulcanizing according to the method, it is possible to produce a pneumatic tire equipped with a chafer with excellent balance of fracture resistance, fatigue resistance and adhesion while maintaining low heat build-up and with good balance of bead durability. .

  Hereinafter, examples and the like specifically showing the configuration and effects of the present invention will be described. The evaluation items in Examples and the like were evaluated based on the following evaluation conditions for rubber samples obtained by heating and vulcanizing each rubber composition at 150 ° C. for 30 minutes.

(1) Rubber hardness According to JIS K6253, the rubber hardness (durometer A type) at 23 ° C. is measured, and the measured value of Comparative Example 1 is indicated by index evaluation. The larger the value is, the rubber hardness (rigidity) is. Means high and good.

(2) Breaking strength (breaking resistance)
In accordance with JIS K6251, a sample was prepared using dumbbell No. 3 and subjected to a tensile test, and the breaking strength at the time of breaking the sample was measured. The measured value of the breaking strength of Comparative Example 1 is expressed as an index evaluation with the value 100, and the larger the value, the better the fracture resistance.

(3) Bending fatigue resistance Bending fatigue resistance was evaluated according to JIS K6260. The measured value of Comparative Example 1 is set to 100 and displayed by index evaluation, and the larger the value, the better.

(4) Low exothermic property (tan δ)
The tan δ value at an initial strain of 10%, a dynamic strain of 2%, a frequency of 50 Hz, and a temperature of 60 ° C. was measured using a viscoelastic spectrometer manufactured by UBM. The measured value of Comparative Example 1 is indicated by index evaluation with 100, and the smaller the value, the better the low heat buildup.

(5) Tire durability An indoor drum testing machine including a pneumatic tire (11R22.5) including a belt using each rubber composition as a raw material for a belt edge filler and provided with a steel drum having a diameter of 1.7 m. Use air pressure as specified in JIS D4230 100%, speed 40km / h, tire load load starting from JIS specified 140%, increase load 10% every 150 hours until tire breaks down A test was conducted. When the travel distance until the failure occurrence of the pneumatic tire of Comparative Example 1 is used as a reference, the case where the travel distance until the failure occurrence is 10% or more shorter than the travel distance of Comparative Example 1 is “× (inferior)”, % (Long) was evaluated as “◯ (good)” and less than ± 10% was evaluated as “Δ (equivalent)”.

(Preparation of rubber composition)
According to the formulation of Table 1 and Table 2, the rubber compositions of Examples 1 to 7 and Comparative Examples 1 to 5 were blended and kneaded using a normal Banbury mixer to prepare a rubber composition. Each compounding agent described in Table 1 and Table 2 is shown below (in Tables 1 and 2, the compounding amounts of carbon black and each compounding agent are shown in terms of parts by mass with respect to 100 parts by mass of the rubber component). Carbon black was produced by the following production method.

a) Rubber component
Natural rubber (NR) "RSS # 3"
Styrene butadiene rubber (SBR) "SBR1502" (manufactured by JSR)
b) Silica “Nipseal AQ” (manufactured by Nippon Silica Industry Co., Ltd.)
c) Resorcin-alkylphenol-formalin resin (resorcin derivative) “SUMIKANOL 620” (manufactured by Sumitomo Chemical Co., Ltd.)
d) Hexamethoxymethylmelamine (melamine resin) “Cyretz 963L” (Mitsui Cytec)
e) Oil "Process P200" (manufactured by Japan Energy)
f) Insoluble sulfur "Muclon HS OT-20" (manufactured by Flexis)
g) Zinc Hana “Zinc Hana 1” (Mitsui Mining & Mining Co., Ltd.)
h) Stearic acid (manufactured by NOF Corporation)
i) Anti-aging agent “Sant Flex 6PPD” (manufactured by Flexis)
j) Vulcanization accelerator “Sunseller CM (CBS)” (manufactured by Sanshin Chemical Co., Ltd.)

(Method for producing carbon black)
A combustion chamber having a tangential air supply port at the furnace head and a combustion burner mounted in the furnace axis direction, a multistage narrow-diameter reaction chamber having a feed oil injection nozzle coaxially connected to the combustion chamber, and a wide chamber The carbon black mixed gas temperature is 1000 to 2200 ° C., and the ratio of the air amount (Nm ³ / h) to the raw material introduction amount (kg / h) is 2.0 using an oil furnace having a diameter reaction chamber. ~ 6.0, the ratio of the air amount and the fuel introduction amount (kg / h) is appropriately adjusted within the range of 15.0 to 30.0, and the ratio of the raw material introduction amount and the fuel introduction amount is within the range of 3.0 to 8.0. In order to obtain carbon black having a specified specific surface area, structure, surface activity, aggregate distribution, and degree of pores, the following i) to iv):
i) Split introduction of feedstock,
ii) oxygen gas addition,
iii) reaction time 0.002 to 0.05 (seconds),
iv) Drying temperature 180-250 (° C),
Were used alone or in combination to produce carbon blacks (A) to (E) shown in Tables 1 and 2. Table 3 shows the carbon black characteristics of the carbon blacks (A) to (E). Moreover, about carbon black (A)-(E), the graph which plotted (BET5) / (IA) on the horizontal axis and (BET5)-(STSA) on the vertical axis | shaft is shown in FIG.

Moreover, the carbon black commercial item as described below was used as carbon black (F)-(G). Table 3 shows the carbon black characteristics of carbon blacks (F) to (G). Moreover, about carbon black (F)-(G), the graph which plotted (BET5) / (IA) on the horizontal axis and (BET5)-(STSA) on the vertical axis | shaft is shown in FIG.
g) Carbon Black (F) “Seast 300 (HAF-LS)” manufactured by Tokai Carbon Co., Ltd. h) Carbon Black (G) “Seast 3 (HAF)” manufactured by Tokai Carbon Co., Ltd.

  From the results of Table 1, in Examples 1 to 7 containing any one of carbon blacks (A) to (E), the low exothermic property, fracture resistance, and fatigue resistance are improved in a well-balanced manner and the durability is improved. It turns out that it is excellent. On the other hand, from the results of Table 2, in Comparative Examples 1 to 3 containing carbon black (F) or (G), the used carbon black does not satisfy any of the above conditions (1) to (4). It can be seen that any of the low exothermic properties, fracture resistance, fatigue resistance and durability deteriorates. In Comparative Example 4, which contains carbon black (A) but its content is low, the fracture resistance is deteriorated, and in Comparative Example 5 where the content of carbon black (A) is high, the low heat build-up property is deteriorated. I understand that.

Claims (5)

A rubber composition for covering an organic fiber reinforcement containing a rubber component and carbon black,
The carbon black satisfies the following (1) to (4),
(1) Dibutyl phthalate (DBP) absorption (ml / 100 g) is 90 to 180,
(2) The difference between the BET specific surface area (BET5) (m ² / g) and the external specific surface area (STSA) (m ² / g) is 5 ≦ (BET5) − (STSA) ≦ 12,
(3) The ratio between the Stokes diameter (Dst) of the carbon black and the Stokes diameter distribution (ΔD-50 (half-value width)) is 0.70 ≦ (ΔD-50) / (Dst) ≦ 1.10. 4) The ratio of the BET specific surface area (BET5) (m ² / g) to the iodine adsorption amount (IA) (mg / g) is 1.05 ≦ (BET5) / (IA) ≦ 1.35,
The amount of the reinforcing filler containing at least the carbon black is 40 to 70 parts by mass with respect to 100 parts by mass of the rubber component, and the proportion of the carbon black in the reinforcing filler is 70% by mass or more. A rubber composition for coating an organic fiber reinforcing material. ^{2. The} rubber composition for coating an organic fiber reinforcement according to claim 1, wherein the carbon black has an external specific surface area (STSA) (m ² / g) of 75 to 170. 3.   The rubber composition for covering an organic fiber reinforcement according to claim 1 or 2, comprising 0.5 to 5 parts by mass of sulfur in terms of sulfur content with respect to 100 parts by mass of the rubber component.   The resorcin derivative is contained in an amount of 0.5 to 2.5 parts by mass and the melamine resin is contained in a range of 0.5 to 2 times the content of the resorcin derivative with respect to 100 parts by mass of the rubber component. 4. The rubber composition for covering an organic fiber reinforcing material according to any one of 3 above.   A pneumatic tire provided with the chacher formed by coat | covering an organic fiber reinforcement with the rubber composition for organic fiber reinforcement covering in any one of Claims 1-4.

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