JP2014177557A - Rubber composition for bead filler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a bead filler which improves further the balance of operation stability, durability and low rolling resistance.SOLUTION: With 100 pts.wt. of a diene type rubber containing natural rubber, 60-80 pts.wt. of a carbon black of a nitrogen adsorption specific surface area of 25-90 m/g, 0.1-5.0 pts.wt. of an S-(aminoalkyl)thiosulfuric acid of formula (1) or its metal salt and 5-20 pts.wt. of a novolak type phenol resin are blended, and a methylene donor is blended additionally in a blend ratio of 5-15 wt.% relative to the blend amount of the novolak type phenol resin. Formula (1): HN-(CH)-SOH, where n is an integer of 1-10.

Description

  The present invention relates to a rubber composition for bead filler which is improved in balance between steering stability, durability and low rolling resistance.

  In recent years, as a required performance for pneumatic tires, it has been demanded that fuel efficiency performance is excellent with increasing interest in global environmental problems. In order to improve fuel efficiency, it is necessary to reduce rolling resistance. For this reason, by suppressing the heat generation of the rubber composition constituting the pneumatic tire, rolling resistance when the tire is made is reduced. Generally, 60 ° C. tan δ by dynamic viscoelasticity measurement is used as an index of exothermic property of the rubber composition. The smaller the tan δ (60 ° C.) of the rubber composition, the smaller the exothermic property.

  As a method for reducing the tan δ (60 ° C.) of the rubber composition, for example, the amount of carbon black is decreased or the particle size of the carbon black is increased. However, such a method has a problem that mechanical properties such as tensile breaking strength and rubber hardness are lowered, and steering stability and durability are lowered when the tire is formed. In particular, a rubber composition part used for a bead filler of a tire is required to have high strength, crack resistance and set resistance and a small tan δ (60 ° C.).

  For example, Patent Document 1 proposes that a rubber composition containing a cashew-modified phenolic resin and its curing agent improves steering stability and rolling resistance. However, the demand for the air retirement performance of consumers is higher, and the rubber composition described in Patent Document 1 does not necessarily have a sufficient level of handling stability, durability and low rolling resistance. Was demanded.

JP 2009-35683 A

  An object of the present invention is to provide a rubber composition for a bead filler in which the balance of steering stability, durability and low rolling resistance is improved to a level higher than that of the conventional level.

（式中、ｎは１〜１０の整数を表す。） The rubber composition for bead fillers according to the present invention that achieves the above object comprises 60 to 80 parts by weight of carbon black having a nitrogen adsorption specific surface area of 25 to 90 m ² / g with respect to 100 parts by weight of a diene rubber containing natural rubber. 0.1-5.0 parts by weight of S- (aminoalkyl) thiosulfuric acid represented by the following formula (1) or a metal salt thereof and 5-20 parts by weight of a novolak type phenol resin are blended, and a methylene donor is used as the novolak. 5 to 15% by weight of the compounding amount of the phenolic resin is blended.

(In the formula, n represents an integer of 1 to 10.)

  The rubber composition for bead filler according to the present invention contains characteristic carbon black, novolac type phenolic resin, methylene donor and specific S- (aminoalkyl) thiosulfuric acid or a metal salt thereof in a diene rubber containing natural rubber. Therefore, while maintaining and improving the rubber strength, crack resistance and set resistance while reducing the tan δ (60 ° C) of the rubber composition, the balance of handling stability, durability and fuel economy performance of the pneumatic tire is balanced. It can be improved over conventional levels. In particular, surprisingly, by adding S- (aminoalkyl) thiosulfuric acid, the rubber strength, crack resistance and set resistance of the rubber composition can be improved to a level higher than the conventional level.

  The novolak type phenolic resin is modified with cashew oil, and the amount of modification of the cashew oil is preferably 35 to 45% by weight in 100% by weight of the novolak type phenolic resin. The methylene donor is preferably hexamethylenetetramine or a melamine derivative.

  The pneumatic tire using the rubber composition for bead fillers of the present invention can improve steering stability and tire durability to a level higher than the conventional level while reducing rolling resistance and improving fuel efficiency.

  In the rubber composition for bead fillers of the present invention, the rubber component is a diene rubber and necessarily contains natural rubber. When the diene rubber contains natural rubber, when the S- (aminoalkyl) thiosulfuric acid or its metal salt is blended, the rubber strength, crack resistance and set resistance of the rubber composition are surely improved. Can do. The content of the natural rubber is preferably 40 to 100% by weight, more preferably 60 to 100% by weight in 100% by weight of the diene rubber. If the content of natural rubber is less than 40% by weight, the desired effect of the present invention may not be sufficiently obtained.

  The rubber composition of the present invention may contain a diene rubber other than natural rubber. Examples of other diene rubbers include isoprene rubber, butadiene rubber, styrene-butadiene rubber, and acrylonitrile-butadiene rubber. Of these, isoprene rubber, butadiene rubber, and styrene-butadiene rubber are preferable. These other diene rubbers can be used alone or as any blend.

  The rubber composition for bead filler of the present invention contains 60 to 80 parts by weight, preferably 65 to 75 parts by weight of carbon black with respect to 100 parts by weight of the diene rubber. By blending carbon black, the strength of the rubber composition can be increased. When the blending amount of carbon black is less than 60 parts by weight, the rubber strength and rubber hardness of the rubber composition are deteriorated. Moreover, when the compounding amount of carbon black exceeds 80 parts by weight, tan δ (60 ° C.) of the rubber composition increases.

The carbon black used in the present invention has a nitrogen adsorption specific surface area of 25 to 90 m ² / g, preferably 35 to 75 m ² / g. When the nitrogen adsorption specific surface area is less than 25 m ² / g, mechanical properties such as rubber strength and rubber hardness of the rubber composition are lowered. When the nitrogen adsorption specific surface area exceeds 90 m ² / g, tan δ (60 ° C.) increases. The nitrogen adsorption specific surface area of carbon black shall be measured according to JIS K6217-2.

  The rubber composition for bead fillers of the present invention necessarily contains a novolac type phenol resin and a methylene donor. By including the novolac type phenolic resin and the methylene donor, the rubber strength, crack resistance and set resistance of the rubber composition can be increased, and the handling stability and durability of the tire can be improved.

  In the present invention, as the novolac type phenolic resin, those usually compounded in a tire rubber composition can be used. Examples thereof include those produced by a condensation reaction of phenol, cresol, resorcin, tert-butylphenol phenols or a mixture thereof with formaldehyde in the presence of an acid catalyst such as hydrochloric acid or oxalic acid. In addition, novolak-type modified phenol resins obtained by modifying novolak-type phenol resins with oils can be mentioned. Examples of the oils used for the modification of novolak-type phenol resins include cashew oil, rosin oil, tall oil, linole. Examples include acids, oleic acid, and linolenic acid. Among these, a novolac type phenol resin modified with cashew oil is preferable. These novolac-type phenol resins can be used alone or in any mixture.

  In the present invention, as the cashew oil-modified novolak type phenolic resin, the amount of cashew oil modification is preferably 35 to 45% by weight, more preferably 37 to 42% by weight in 100% by weight of the novolak type phenolic resin. Good. By setting the modified amount of cashew oil within such a range, the breaking characteristics can be greatly improved.

  A commercial item can be used for these novolak type phenol resins. Examples of the phenol resin include Sumikalol 620 manufactured by Sumitomo Chemical Co., Ltd. Examples of the phenol resin modified with cashew oil include Sumitomo Bakelite's Sumilite Resin PR-YR-170 and PR-150, Dainippon Ink & Chemicals Phenolite A4-1419.

  The compounding amount of the novolac type phenol resin is 5 to 20 parts by weight, preferably 10 to 15 parts by weight, based on 100 parts by weight of the diene rubber. If the compounding amount of the novolac type phenol resin is less than 5 parts by weight, the effect of improving the rubber strength, crack resistance and set resistance of the rubber composition cannot be obtained sufficiently. Moreover, when the compounding amount of the novolac type phenol resin exceeds 20 parts by weight, the rolling resistance when the tire is made deteriorates, and the tire durability further decreases.

  In the present invention, a methylene donor is used as a curing agent for the above-described novolak type phenol resin. Examples of methylene donors include hexamethylenetetramine and melamine derivatives. Examples of melamine derivatives include hexamethoxymethylol melamine, pentamethoxymethylol melamine, hexamethoxymethyl melamine, pentamethoxymethyl melamine, hexaethoxymethyl melamine, hexakis- (methoxymethyl) melamine, N, N ′, N ″ -trimethyl-N, N ', N "-trimethylol melamine, N, N', N" -trimethylol melamine, N-methylol melamine N, N '-(methoxymethyl) melamine, N, N', N "-tributyl-N, N ′, N ″ -trimethylol melamine and the like. Among them, hexamethylenetetramine, hexamethoxymethylol melamine, pentamethoxymethylol melamine, hexamethoxymethyl melamine, and pentamethoxymethyl melamine are preferable. Can be used alone or in combination.

  Examples of hexamethylenetetramine include Sunseller HT-PO manufactured by Sanshin Chemical Industry Co., Ltd. Examples of hexamethoxymethylmelamine (HMMM) include CYREZ 964RPC manufactured by CYTEC INDUSTRIES. Examples of pentamethoxymethylmelamine (PMMM) include BARA CHEMICAL Co. , LTD. An example is Sumikanol 507A manufactured by the company.

  The blending amount of the methylene donor is 5 to 15% by weight, preferably 7 to 12% by weight, based on the blending amount of the novolac type phenol resin. When the amount of methylene donor exceeds 15% by weight of the amount of novolak phenol resin, the methylene donor remains, the cross-linking density of the phenol resin becomes too high, and brittle fracture tends to occur, resulting in poor tire durability. To do. On the other hand, if the blending amount of the methylene donor is less than 5% by weight, the crosslinking density of the phenol resin is too low to be effective.

（式中、ｎは２〜１０の整数を表す。） In the rubber composition for bead filler of the present invention, 0.1 to 5.0 parts by weight of S- (aminoalkyl) thiosulfuric acid represented by the following formula (1) or a metal salt thereof is added to 100 parts by weight of the diene rubber. Is blended.

(In the formula, n represents an integer of 2 to 10.)

  In said formula (1), n represents the integer of 1-10, Preferably it is 2-6, More preferably, it is an integer of 3-4. As S- (aminoalkyl) thiosulfuric acid, S- (aminomethyl) thiosulfuric acid, S- (2-aminoethyl) thiosulfuric acid, S- (3-aminopropyl) thiosulfuric acid, S- (4-aminobutyl) Thiosulfuric acid, S- (5-aminopentyl), S- (6-aminohexyl) thiosulfuric acid, S- (7-aminopeptyl) thiosulfuric acid, S- (8-aminooctyl) thiosulfuric acid, S- (9-aminononyl) ) Thiosulfuric acid, S- (10-aminodecyl) thiosulfuric acid. Of these, S- (3-aminopropyl) thiosulfuric acid and S- (4-aminobutyl) thiosulfuric acid are preferable.

  Examples of the metal salt of S- (aminoalkyl) thiosulfuric acid represented by the above formula (1) include lithium ions, sodium ions, potassium ions, cesium ions, cobalt ions, copper ions, and zinc ions as metal ions. it can.

  The rubber composition for bead fillers of the present invention can reduce tan δ (60 ° C.) of the rubber composition by blending the above-described S- (aminoalkyl) thiosulfuric acid. Furthermore, surprisingly, the rubber strength, crack resistance, and set resistance of the rubber composition can be improved over conventional levels. Such an effect needs to contain natural rubber as a diene rubber, and it is estimated that S- (aminoalkyl) thiosulfuric acid is due to the action of modifying natural rubber. Further, when S- (aminoalkyl) thiosulfuric acid is blended rather than the metal salt of S- (aminoalkyl) thiosulfuric acid, the effect becomes more remarkable. By adding S- (aminoalkyl) thiosulfuric acid to the rubber composition for bead filler made high strength and high elasticity by adding novolak type phenolic resin and melamine donor, rubber strength and crack resistance It is an unexpected effect that the set resistance can be further improved.

  The amount of S- (aminoalkyl) thiosulfuric acid is 0.1 to 5.0 parts by weight, preferably 0.2 to 2.0 parts by weight, based on 100 parts by weight of the diene rubber. When the blending amount of S- (aminoalkyl) thiosulfuric acid is less than 0.1 part by weight, the effect of reducing tan δ (60 ° C.) of the rubber composition and improving rubber strength, crack resistance and set resistance Is not enough. Moreover, when the compounding quantity of S- (aminoalkyl) thiosulfuric acid exceeds 5.0 weight part, crack resistance will deteriorate significantly.

  In the present invention, fillers other than carbon black can be blended. Examples of other fillers include silica, clay, mica, talc, calcium carbonate, aluminum hydroxide, aluminum oxide, and titanium oxide. Of these, silica, calcium carbonate, and aluminum hydroxide are preferable. By blending other fillers, the mechanical properties of the rubber composition can be further improved, and the balance of low rolling resistance, steering stability and processability when made into a tire can be improved.

  In the rubber composition for bead filler, various additives generally used in rubber compositions for tires such as vulcanization or crosslinking agents, vulcanization accelerators, various oils, anti-aging agents, and plasticizers may be blended. Such an additive can be kneaded by a general method to form a rubber composition, which can be used for vulcanization or crosslinking. As long as the amount of these additives is not contrary to the object of the present invention, a conventional general amount can be used. The rubber composition for bead fillers of the present invention can be produced by mixing the above-described components using an ordinary rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  Since the pneumatic tire using the rubber composition for bead filler of the present invention has low heat generation during running, it can reduce rolling resistance and improve fuel efficiency. At the same time, by improving the mechanical properties of the rubber composition, it is possible to maintain and improve steering stability and tire durability at or above conventional levels.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited to these Examples.

  16 types of bead filler rubber compositions (Examples 1 to 9 and Comparative Examples 1 to 7) having the formulations shown in Tables 1 and 2 as common formulations, and sulfur and vulcanization accelerators. The components except for were prepared by adding sulfur and a vulcanization accelerator to a master batch which was kneaded for 5 minutes at 160 ° C. for 5 minutes with a 1.8 L closed mixer and kneaded with an open roll. In addition, the amount of the common compounding agent described in Table 3 was expressed in parts by weight with respect to 100 parts by weight (net amount of rubber) of the diene rubber described in Tables 1 and 2.

  The obtained 16 kinds of bead filler rubber compositions were each vulcanized at 150 ° C. for 15 minutes in a mold having a predetermined shape to prepare test pieces. The tensile breaking strength and dynamic viscosity were determined by the following methods. Elasticity (tan δ at 60 ° C.), crack resistance and set resistance were evaluated.

Tensile strength at break The JIS No. 3 dumbbell-shaped test piece (thickness 2 mm) was punched out from the obtained test piece in accordance with JIS K6251, and the test was performed at a pulling rate of 500 mm / min, and the tensile breaking strength was measured. The obtained results are shown in the column of “Tensile fracture strength” as an index with the value of Comparative Example 1 as 100. The larger the index of tensile strength at break, the better the steering stability when made into a tire.

Dynamic viscoelasticity (tan δ at 60 ° C)
Based on JIS K6394, the obtained test piece was subjected to a loss tangent tan δ at a temperature of 60 ° C. under the conditions of an initial strain of 10%, an amplitude of ± 2%, and a frequency of 20 Hz, using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho. It was measured. The obtained results are shown in the column of “tan δ (60 ° C.)” as an index with the value of Comparative Example 1 being 100. The smaller the index of tan δ (60 ° C.), the smaller the heat generation, and the smaller the rolling resistance when the tire is made, the better the fuel efficiency.

Crack resistance As the crack resistance of the obtained test piece, in accordance with JIS K6260, by using a Demach bending crack tester with a stroke of 57 mm, a speed of 300 ± 10 rpm, and a number of bending times of 100,000. The length of crack growth was measured. The obtained results were calculated by calculating the reciprocal number of each value, and the result was shown in the “crack resistance” column as an index with Comparative Example 1 as 100. The larger the crack resistance index, the better the crack resistance and the better the durability of the pneumatic tire.

Set Resistance With respect to the obtained test piece, the compression set property was measured under the conditions of 70 ° C. × 22 hours and initial strain of 25% in accordance with JIS K6262. The obtained results are shown in the column of “Set resistance” with the value of Comparative Example 1 as 100. The smaller the set resistance index, the better the compression set resistance, which means that the steering stability and durability of the tire are improved.

  Next, a pneumatic tire having a tire size of 195 / 65R15 was vulcanized and molded so as to constitute a bead filler of a pneumatic tire using the obtained 16 kinds of rubber compositions. The steering stability and high load durability of the obtained pneumatic tire were evaluated by the following methods.

Steering stability The tires obtained were assembled on a standard rim (size 15 x 6J wheel) and mounted on a domestic 2.0 liter class test vehicle. The course was run on a real vehicle, and the handling stability at that time was scored by a sensitive evaluation by three expert panelists. The obtained results are shown in the column “Steering stability” as an index with the value of Comparative Example 1 being 100. The larger this index, the better the steering stability performance.

High load durability The obtained tire is mounted on a standard rim (size 15 × 6J wheel), the air pressure is set to JISMA specified air pressure 230 kPa, and the load is applied to an indoor drum tester (drum diameter 1707 mm) in accordance with JIS D4230. The maximum load specified in Y / B is used, and after a preliminary run at a speed of 81 km / h for 2 hours, 150% of the JATMA specified load is applied and a tire failure occurs under the condition of a speed of 81 km / h. The mileage was measured. The obtained results are shown in the “Load durability” column as an index with the value of Comparative Example 1 as 100. The larger the index, the better the tire durability under high load.

The types of raw materials used in Tables 1 and 2 are shown below.
SBR: styrene-butadiene rubber, Nipol 1502 manufactured by Nippon Zeon Co., Ltd., non-oil exhibition carbon black 1: Show Black N339 manufactured by Cabot Japan Co., Ltd., nitrogen adsorption specific surface area of 90 m ² / g
Carbon Black 2: Show Black N550 manufactured by Cabot Japan, nitrogen adsorption specific surface area of 40 m ² / g
Carbon Black 3: Show Black N220 manufactured by Cabot Japan, Nitrogen adsorption specific surface area is 115 m ² / g
Phenol resin 1: Cashew modified novolak type phenol resin, Sumitomo Bakelite Co., Ltd. Sumilite resin PR-YR-170, modified amount of cashew oil is 30% by weight in the resin
Phenol resin 2: Unmodified novolak-type phenol resin, PR7031A manufactured by Sumitomo Bakelite Co., Ltd.
Methylene donor: Hexamethylenetetramine, Nouchira H-PO manufactured by Ouchi Shinsei Chemical Co., Ltd.
Organic thiosulfuric acid 1: S- (3-aminopropyl) thiosulfuric acid (manufactured by Sumitomo Chemical Co., Ltd.)
Organic thiosulfuric acid 2: S- (4-aminobutyl) thiosulfuric acid (manufactured by Sumitomo Chemical Co., Ltd.)

In addition, the kind of raw material used in Table 3 is shown below.
Zinc Hana: Zinc Oxide 3 types manufactured by Shodo Chemical Industry Co., Ltd. Stearic Acid: Beads manufactured by NOF Corporation Stearate Oil: Extract No. 4 S manufactured by Showa Shell Sekiyu K.K.
Sulfur: Fine powder sulfur vulcanization accelerator with Jinhua seal oil manufactured by Tsurumi Chemical Industry Co., Ltd .: SANTOCURE TBBS manufactured by FLEXSYS

  As is clear from Table 2, it was confirmed that the rubber compositions for bead fillers of Examples 1 to 9 improved the balance of tensile breaking strength, tan δ (60 ° C.), crack resistance and set resistance to the conventional level or more. It was done. Further, pneumatic tires molded using these rubber compositions for bead fillers were excellent in handling stability and high load durability.

  Further, as is apparent from Table 1, the rubber composition of Comparative Example 2 does not contain natural rubber, so that the tensile strength at break, tan δ (60 ° C.), crack resistance and set resistance of the rubber composition are deteriorated. To do. Further, the pneumatic tire of Comparative Example 2 is deteriorated in handling stability and high load durability.

  Since the rubber composition of Comparative Example 3 does not contain a methylene donor, the tensile break strength, tan δ (60 ° C.), crack resistance and set resistance of the rubber composition are deteriorated. Further, the pneumatic tire of Comparative Example 3 is deteriorated in handling stability and high load durability.

  In the rubber composition of Comparative Example 4, the blending amount of the methylene copolymer exceeds 1.5% by weight of the blending amount of the novolac-type phenol resin, so that the tensile strength at break is lowered and the crack resistance and the set resistance are deteriorated. To do. Moreover, the high load durability deteriorates in the pneumatic tire of Comparative Example 4.

  In the rubber composition of Comparative Example 5, since the blending amount of carbon black 1 is less than 60 parts by weight with respect to 100 parts by weight of the diene rubber, the tensile strength at break and the set resistance are deteriorated. Moreover, the handling stability of the pneumatic tire of Comparative Example 5 deteriorates.

  In the rubber composition of Comparative Example 6, since the blending amount of carbon black 1 exceeds 80 parts by weight with respect to 100 parts by weight of the diene rubber, the tensile breaking strength, tan δ (60 ° C.), crack resistance and The set resistance deteriorates. Further, the pneumatic tire of Comparative Example 6 is deteriorated in handling stability and high load durability.

In the rubber composition of Comparative Example 7, since the nitrogen adsorption specific surface area of carbon black 3 exceeds 90 m ² / g, the tensile breaking strength, tan δ (60 ° C.), crack resistance and set resistance of the rubber composition are deteriorated. . Further, the pneumatic tire of Comparative Example 7 is deteriorated in handling stability and high load durability.

Claims (4)

60 to 80 parts by weight of carbon black having a nitrogen adsorption specific surface area of 25 to 90 m ² / g, based on 100 parts by weight of diene rubber containing natural rubber, S- (aminoalkyl) thiosulfuric acid represented by the following formula (1) Or 0.1 to 5.0 parts by weight of a metal salt thereof, 5 to 20 parts by weight of a novolac type phenol resin, and 5 to 15% by weight of a methylene donor based on the amount of the novolac type phenol resin. A rubber composition for bead filler.

(In the formula, n represents an integer of 1 to 10.)   The said novolak-type phenol resin is modified | denatured with cashew oil, The modification | denaturation amount of this cashew oil is 35 to 45 weight% in 100 weight% of the said novolak-type phenol resin, The Claim 1 characterized by the above-mentioned. A rubber composition for bead filler.   The rubber composition for bead filler according to claim 1 or 2, wherein the methylene donor is hexamethylenetetramine or a melamine derivative.   A pneumatic tire using the rubber composition for bead filler according to claim 1, 2 or 3.