JP2015232090A - Rubber composition for rim cushion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for rim cushion having enhanced processability, rubber hardness, crack resistance and rim slippage resistance than conventional levels while reducing pyrogenicity.SOLUTION: There is provided a rubber composition by blending 100 pts.wt. of a rubber composition containing a farnesene polymer of 5 to 10 wt.%, 55 to 85 pts.wt. of carbon black having nitrogen absorption specific surface area NSA of 65 to 120 m/g, sulfur and a vulcanization accelerator and having the total of the blended amount of the sulfur (S) and the blended amount of the vulcanization accelerator (A) (S+A) of 2.0 to 5.0 pts.wt. and a ratio between the total (S+A) and the blended amount of the farnesene polymer (F), (S+A)/F of 0.2 to 1.0.

Description

  The present invention relates to a rubber composition for a rim cushion in which processability, rubber hardness, crack resistance and rim displacement resistance are improved to a conventional level or more while reducing heat generation.

  A rim cushion is provided on an outer layer of the bead portion of the pneumatic tire so that the tire is in close contact with the rim when the rim is assembled to the wheel. The rim cushion must be in close contact with the rim flange to prevent rim displacement with respect to the rim and to maintain air sealability. However, the rim cushion has a problem that durability is lowered due to cracking due to compression force or heat generation from the rim, or fatigue due to repeated deformation.

For this reason, Patent Document 1 discloses a rubber composition in which 40 to 60 parts by weight of carbon black having a nitrogen adsorption specific surface area of 90 m ² / g or more is blended with 100 parts by weight of a rubber component and a sulfenamide vulcanization accelerator is blended. It has been proposed to improve crack resistance by using materials. Increasing the amount of carbon black increases cracking resistance as well as rubber hardness and rim displacement resistance, but increases the viscosity and deteriorates workability and increases heat generation. there were.

  When the exothermic property increases, the rim cushion becomes hot and causes a decrease in durability, and the rolling resistance of the pneumatic tire deteriorates. In particular, it is important to reduce the heat generation of the rim cushion because it is required to improve the fuel efficiency with increasing interest in global environmental problems.

  As a method for improving the heat build-up and processability of the rubber composition, increasing the particle size of the carbon black or decreasing the blending amount of the carbon black can be mentioned. However, when such a prescription is adopted for the rubber composition for the rim cushion, there is a conflicting problem that the rubber hardness is lowered and the rim displacement resistance and crack resistance are lowered.

JP 2005-171016 A

  An object of the present invention is to provide a rubber composition for a rim cushion that is improved in workability, rubber hardness, crack resistance, and rim displacement resistance to a conventional level or more while reducing heat generation.

The rubber composition for a rim cushion of the present invention that achieves the above object has a nitrogen adsorption specific surface area N ₂ SA of 65 to 120 m ² / g with respect to 100 parts by weight of a rubber component containing 5 to 10% by weight of a farnesene polymer. While adding 55 to 85 parts by weight of carbon black, sulfur and a vulcanization accelerator, the total (S + A) of the sulfur content (S) and the vulcanization accelerator content (A) is 2.0 to 5 0.0 part by weight, and the ratio (S + A) / F of the total (S + A) to the blended amount (F) of the farnesene polymer is 0.2 to 1.0.

  The rubber composition for a rim cushion of the present invention is a rubber component containing 5 to 10% by weight of a farnesene polymer, 55 to 85 parts by weight of specific carbon black, a sulfur content (S), and vulcanization acceleration. The total amount (S + A) of the blending amount (A) of the agent is 2.0 to 5.0 parts by weight, and the ratio (S + A) / F of the blending amount (F) of this and the farnesene polymer is 0.2 to 1.0. Therefore, while reducing the heat build-up of the rubber composition, it is possible to ensure the rubber hardness and maintain and improve the rim displacement resistance, and to improve the crack resistance and workability to the conventional level or more.

  The rubber component preferably contains butadiene rubber in an amount of 25 to 70% by weight and natural rubber in an amount of 25 to 70% by weight.

  The pneumatic tire in which the rim cushion made of the rubber composition for a rim cushion according to the present invention is arranged has the conventional rubber hardness, crack resistance and rim deviation resistance while reducing rolling resistance and improving fuel efficiency performance during normal driving. It can be improved beyond the level.

  The rubber composition for a rim cushion of the present invention contains a farnesene polymer as a rubber component. By including the farnesene polymer, it is possible to increase the rubber hardness while reducing the exothermic property (tan δ at 60 ° C.) of the rubber composition. Further, the rim displacement resistance and crack resistance can be improved. Furthermore, the viscosity of a rubber composition can be reduced and processability can be improved.

  The farnesene polymer is a polymer of α-farnesene, a polymer of β-farnesene or a copolymer of α-farnesene and β-farnesene, and preferably a polymer of β-farnesene. Further, the polymer of farnesene has a constitutional unit derived from α-farnesene and / or β-farnesene, preferably 90% by weight or more, more preferably 95% by weight or more, more preferably 100% by weight, butadiene, A structural unit derived from another monomer such as isoprene may be included.

  The blending amount of the farnesene polymer is 5 to 10% by weight, preferably 5 to 8 parts by weight, in 100% by weight of the rubber component. If the blending amount of the farnesene polymer is less than 5% by weight, the effect of improving processability and crack growth resistance cannot be sufficiently obtained. When the blending amount of the farnesene polymer exceeds 10% by weight, the rubber hardness and the rim slip resistance are deteriorated. Furthermore, the exothermic property (tan δ at 60 ° C.) of the rubber composition deteriorates.

  The weight average molecular weight of the farnesene polymer is not particularly limited, but is preferably 2000 to 25000, more preferably 2500 to 20000. When the weight average molecular weight of the farnesene polymer is less than 2000, the rubber strength and rubber hardness of the rubber composition are lowered, and further, bleeding out from the rubber composition is facilitated. Moreover, when the weight average molecular weight of a farnesene polymer exceeds 25000, workability will deteriorate.

  The farnesene polymer has the above-mentioned weight average molecular weight and has a vulcanizable molecular structure, so that the rubber composition and the rubber hardness are increased after vulcanization while ensuring good processability of the rubber composition. be able to.

  The molecular weight distribution (Mw / Mn; Mw is the weight average molecular weight, Mn is the number average molecular weight) of the farnesene polymer is preferably 1.0 to 2.0, more preferably 1.0 to 1.5, and even more preferably 1. It is good that it is .0 to 1.3. When the molecular weight distribution of the farnesene polymer is within such a range, variation in viscosity is reduced. In the present specification, the weight average molecular weight Mw and the number average molecular weight Mn of the farnesene polymer are measured by GPC (gel permeation chromatography) and determined by standard polystyrene conversion.

  The melt viscosity of the farnesene polymer is preferably 0.1 to 2200 Pa · s, more preferably 0.1 to 1000 Pa · s, and further preferably 0.1 to 100 Pa · s. When the melt viscosity of the farnesene polymer is within such a range, kneading of the rubber composition becomes easy and processability is improved. In this specification, the melt viscosity of the farnesene polymer is a melt viscosity at 38 ° C. measured by a Brookfield viscometer.

  The farnesene polymer has the above-mentioned weight average molecular weight and melt viscosity, and has a vulcanizable molecular structure, so that the rubber strength and hardness after vulcanization are ensured while ensuring good processability of the rubber composition. Can be made higher.

  The farnesene polymer can be synthesized by an ordinary method, and examples thereof include an emulsion polymerization method and a solution polymerization method, and preferably a synthesis by a solution polymerization method.

  In the rubber composition for a rim cushion of the present invention, a diene rubber is included as a rubber component other than the farnesene polymer. Examples of the diene rubber include natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, and acrylonitrile-butadiene rubber. These rubber components can be used alone or as any blend.

  Of the diene rubbers, natural rubber and butadiene rubber are preferable. By including butadiene rubber, the temperature dependence of hardness is lowered due to the low embrittlement temperature, and the durability performance is excellent. Inclusion of natural rubber increases the rubber hardness, tensile strength at break, and tensile elongation at break due to its high molecular weight.

  The content of butadiene rubber is preferably 25 to 70% by weight, more preferably 30 to 60% by weight in 100% by weight of the rubber component. If the content of butadiene rubber is less than 25% by weight, the exothermic property is deteriorated. On the other hand, when the content of butadiene rubber exceeds 70% by weight, processability deteriorates.

  The content of the natural rubber is preferably 25 to 70% by weight, more preferably 30 to 60% by weight, in 100% by weight of the rubber component. If the content of the natural rubber is less than 25% by weight, processability deteriorates. On the other hand, if the content of natural rubber exceeds 70% by weight, the heat build-up will deteriorate.

  In the rubber composition for a rim cushion of the present invention, carbon black is blended in an amount of 55 to 85 parts by weight, preferably 60 to 80 parts by weight with respect to 100 parts by weight of the rubber component. When the blending amount of carbon black is less than 55 parts by weight, the reinforcing property of the rubber composition cannot be obtained sufficiently. On the other hand, when the blending amount of carbon black exceeds 85 parts by weight, rolling resistance when the tire is formed increases.

The carbon black used in the present invention has a nitrogen adsorption specific surface area N ₂ SA of 65 to 120 m ² / g, preferably 75 to 100 m ² / g. When N ₂ SA is less than 65 m ² / g, mechanical properties such as rubber hardness of the rubber composition are lowered, and rim displacement resistance is lowered. When N ₂ SA exceeds 120 m ² / g, tan δ (60 ° C.) increases. In addition, the effect of improving workability and crack resistance cannot be obtained sufficiently. N ₂ SA shall be measured according to JIS K6217-2. Such carbon black can be appropriately selected from HAF grade to ISAF grade and used.

  The rubber composition for a rim cushion can be mixed with a reinforcing filler other than carbon black. Examples of other reinforcing fillers include silica, clay, mica, talc, calcium carbonate, aluminum oxide, titanium oxide, activated zinc white and the like. Of these, silica and clay are preferable.

  In this specification, the amount of sulfur added to 100 parts by weight of the rubber component is S parts by weight, and the amount of vulcanization accelerator is A parts by weight. The rubber composition for the rim cushion is 2.0 to 5.0 parts by weight of the total (S + A) of the compounding amount of sulfur (S parts by weight) and the compounding amount of vulcanization accelerator (A parts by weight) (S + A). And the ratio (S + A) / F of the blending amount (F) of the farnesene polymer to 0.2 to 1.0.

  The total amount of sulfur and vulcanization accelerator (S + A) is 2.0 to 5.0 parts by weight, preferably 2.5 to 4.5 parts by weight, per 100 parts by weight of the rubber component. When the sum of sulfur and the vulcanization accelerator (S + A) is less than 2.0 parts by weight, the rubber hardness is insufficient and the rim slip resistance is deteriorated. When the sum of sulfur and the vulcanization accelerator (S + A) exceeds 5.0 parts by weight, crack resistance deteriorates.

  The ratio (S + A) / F of the total amount of sulfur and vulcanization accelerator (S + A) and the amount of farnesene polymer (F) is 0.2 to 1.0, preferably 0.3 to 0.8. is there. When the ratio (S + A) / F is less than 0.2, the heat buildup is increased, the rubber hardness is lowered, and the rim displacement resistance is deteriorated. When the ratio (S + A) / F exceeds 1.0, the crack resistance deteriorates.

  As sulfur and a vulcanization accelerator, it can select and mix | blend suitably from what is normally used for the rubber composition for tires.

  In addition to vulcanization or crosslinking agents, vulcanization accelerators, various additives commonly used in rim cushion rubber compositions such as various oils, anti-aging agents, and plasticizers are included in the rim cushion rubber composition. These additives can be compounded and kneaded by a general method to form a rubber composition, which can be vulcanized or crosslinked. 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 a rim cushion of the present invention can be produced by mixing the above components using a normal rubber kneading machine such as a Banbury mixer, a kneader, or a roll.

  The rubber composition for a rim cushion of the present invention can be suitably used for a rim cushion in a pneumatic tire. Since the pneumatic tire using the rubber composition of the present invention reduces heat generation during running, it can reduce rolling resistance and improve fuel efficiency. Further, the crack resistance can be improved to a level higher than the conventional level. At the same time, by improving the rubber hardness of the rubber composition, it is possible to improve the rim displacement resistance when the tire is made to a level higher than the conventional level.

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

  In preparing 13 types of rubber compositions (Examples 1 to 6 and Comparative Examples 1 to 7) having the compounding ingredients shown in Table 3 as common ingredients and the compositions shown in Tables 1 and 2, sulfur and vulcanization acceleration, respectively. The components excluding the agent were weighed and kneaded for 5 minutes with a 1.8 L closed mixer, and then the master batch was discharged and cooled at room temperature. This master batch was subjected to a 1.8 L closed mixer, and sulfur and a vulcanization accelerator were added and mixed to obtain a rubber composition for a rim cushion.

  The Mooney viscosities of the 13 types of rubber compositions obtained were evaluated by the methods shown below.

Mooney viscosity The Mooney viscosity of the rubber composition conforms to JIS K6300, using a Mooney viscometer with an L-shaped rotor (38.1 mm diameter, 5.5 mm thickness), preheating time 1 minute, rotor rotation time 4 minutes , Measured at 100 ° C. and 2 rpm. The obtained results are shown in the column of “Viscosity (100 ° C.)” in Table 1 as an index with the value of Comparative Example 1 as 100. A smaller index means a smaller Mooney viscosity and better workability.

  The obtained 13 types of rubber compositions were press vulcanized at 170 ° C. for 10 minutes in a predetermined mold to prepare vulcanized rubber test pieces made of a rim cushion rubber composition. The obtained vulcanized rubber specimens were evaluated for tan δ (60 ° C.), rubber hardness and crack resistance by the methods shown below.

tan δ (60 ° C)
Using the obtained vulcanized rubber test piece, using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd., the initial strain is 10%, the amplitude is ± 2%, the frequency is 20 Hz, and the dynamic viscoelasticity at a temperature of 60 ° C. is measured. Measured and determined tan δ at 60 ° C. The obtained results are shown in the column of “tan δ 60 ° C.” in Table 1 as an index with the value of Comparative Example 1 as 100. The smaller this index, the smaller the heat generation, which means that the rolling resistance is small and excellent when made into a tire.

Rubber Hardness Using the obtained vulcanized rubber test piece, rubber hardness was measured at a temperature of 20 ° C. with a durometer type A in accordance with JIS K6253. The obtained results are shown in the “Rubber Hardness” column of Table 1 as an index with the value of Comparative Example 1 as 100. The larger this index, the greater the rubber hardness.

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 index, the better the crack resistance and the better the durability of the pneumatic tire.

Rim slip resistance Pneumatic tires having a tire size of 195 / 65R15 were vulcanized and molded so as to form rim cushions using the 13 types of rubber compositions obtained. As an evaluation of the resistance to rim displacement of a tire, the amount of the tire deviating from the rim in the circumferential direction after repeated rapid braking in a vehicle equipped with a tire assembled with a rim at a predetermined air pressure was measured. The obtained results are shown in the column of “rim displacement resistance” as an index with the reciprocal of the result of Comparative Example 1 being 100. The larger the index, the better the resistance to rim displacement.

The types of raw materials used in Tables 1 and 2 are shown below.
NR: natural rubber, STR20
BR: butadiene rubber, Nipol BR1220 manufactured by Nippon Zeon
Farnesene 1: β-farnesene polymer polymerized in Synthesis Example 1 below, weight average molecular weight of 140,000, molecular weight distribution of 1.2, melt viscosity of 69 Pa · s
Farnesene 2: β-farnesene polymer polymerized in Synthesis Example 2 below, weight average molecular weight 10,000, molecular weight distribution 1.1, melt viscosity 0.9 Pa · s
Carbon black 1: Sea SOP made by Tokai Carbon Co., Nitrogen adsorption specific surface area is 40 m ² / g
Carbon black 2: Seast KH manufactured by Tokai Carbon Co., Ltd., nitrogen adsorption specific surface area is 90 m ² / g
Liquid IR: Liquid polyisoprene rubber, Kuraray Kuraprene LIR-50
Oil: Extract 4 S, Showa Shell Sekiyu
Sulfur: Fine powder sulfur with Jinhua seal oil manufactured by Tsurumi Chemical Industry Co., Ltd. (sulfur content is 95.24% by weight)
Vulcanization accelerator: SANTOCURE CBS manufactured by FLEXSYS

Synthesis example 1 (polymerization of farnesene 1)
In a pressure vessel that was purged with nitrogen and dried, 274 g of hexane and 1.2 g of n-butyllithium (17 wt% hexane solution) were charged, and the temperature was raised to 50 ° C., followed by addition of 272 g of β-farnesene and polymerization for 1 hour. . After adding methanol to the obtained polymerization reaction solution, the polymerization reaction solution was washed with water. The farnesene polymer 1 was obtained by separating water and drying the polymerization reaction solution at 70 ° C. for 12 hours.

Synthesis Example 2 (polymerization of farnesene 2)
A pressure-resistant container purged with nitrogen and dried was charged with 241 g of cyclohexane and 28.3 g of sec-butyllithium (10.5 wt% cyclohexane solution), heated to 50 ° C., and then added with 342 g of β-farnesene for 1 hour. Polymerized. After adding methanol to the obtained polymerization reaction solution, the polymerization reaction solution was washed with water. Water was separated, and the polymerization reaction solution was dried at 70 ° C. for 12 hours to obtain farnesene polymer 2.

In addition, the kind of raw material used in Table 3 is shown below.
Zinc oxide: 3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd. Stearic acid: Beads stearic acid anti-aging agent manufactured by NOF Corporation: Antigen 6C manufactured by Sumitomo Chemical Co., Ltd.

  As is apparent from Table 1, the rubber compositions of Examples 1 to 6 have exothermic properties (tan δ at 60 ° C.), processability (viscosity 100 ° C.), rubber hardness, crack resistance and rim deviation resistance that are higher than conventional levels. It was confirmed that it improved.

  As is clear from Table 1, the rubber composition of Comparative Example 2 increased the amount of oil compared to Comparative Example 1, but did not contain a farnesene polymer, so exothermic properties (tan δ at 60 ° C.), rubber hardness and Deterioration of rim slip resistance is deteriorated.

  In the rubber composition of Comparative Example 3, since the liquid polyisoprene rubber was blended in place of the farnesene polymer, the exothermic property (tan δ at 60 ° C.) and the rim deviation resistance were deteriorated.

  In the rubber composition of Comparative Example 4, the total vulcanized compounding agent (S + A) exceeds 5 parts by weight, so that the crack resistance deteriorates.

Since the rubber composition of Comparative Example 5 has a nitrogen adsorption specific surface area of carbon black 1 of less than 75 m ² / g, the rubber hardness and rim deviation resistance deteriorate.

  In the rubber composition of Comparative Example 6, since the content of farnesene polymer 1 exceeds 10% by weight, the exothermic property (tan δ at 60 ° C.) increases, and the rubber hardness and rim deviation resistance deteriorate.

  In the rubber composition of Comparative Example 7, the total vulcanizing compounding agent (S + A) is less than 2 parts by weight, so that the rubber hardness is lowered and the rim slip resistance is deteriorated.

Claims (3)

To 100 parts by weight of a rubber component containing 5 to 10% by weight of a farnesene polymer, 55 to 85 parts by weight of carbon black having a nitrogen adsorption specific surface area N ₂ SA of 65 to 120 m ² / g, sulfur and a vulcanization accelerator The total amount (S + A) of the blending amount (S) of the sulfur and the blending amount (A) of the vulcanization accelerator is 2.0 to 5.0 parts by weight, and the sum (S + A) and the farnesene polymer A rubber composition for a rim cushion, wherein the ratio (S + A) / F of the blending amount (F) is 0.2 to 1.0.   The rubber composition for a rim cushion according to claim 1, wherein the rubber component contains 25 to 70% by weight of butadiene rubber and 25 to 70% by weight of natural rubber.   A pneumatic tire comprising a rim cushion, the rim cushion rubber composition according to claim 1.