JP2007277411A - Rubber composition and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rubber composition which promotes interaction of silica with rubber molecules to improve the reinforcing property of the silica and gives excellent balance between rolling resistance characteristics and wet performance without deteriorating abrasion resistance. <P>SOLUTION: This rubber composition comprising 100 pts.wt. of a dienic rubber and 20 to 120 pts.wt. of silica is characterized by containing a polymer obtained by polymerizing a compound having at least one acrylamide group and at least one hydroxy group in the molecule with a radical polymerization initiator. The compound includes a compound represented by the general formula (1): CH<SB>2</SB>=CHCONH-R-OH (R is one of an alkyl, an alkenyl and an aryl). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a rubber composition, and more specifically, in a rubber composition containing silica, by improving the dispersibility of silica, rolling resistance characteristics and braking performance on a wet road surface are obtained without impairing wear resistance. The present invention relates to a rubber composition capable of achieving both balance and a pneumatic tire using the rubber composition for a tread.

  Rubber compositions used in treads for pneumatic tires are strongly demanded to reduce rolling resistance due to market needs for low fuel consumption, and braking performance and handling stability (hereinafter referred to as wet) on wet roads in terms of safety. The improvement in performance) is required, and in addition, excellent wear resistance is required in terms of durability and economy.

  By the way, the above-mentioned rolling resistance characteristics and wet performance are characteristics related to the hysteresis loss of rubber.Generally, increasing the hysteresis loss increases wet performance and improves braking characteristics, but also increases rolling resistance and reduces fuel consumption. Bring. Thus, the rolling resistance characteristics and the wet performance are in a trade-off relationship, and many rubber compositions have been studied to satisfy both characteristics at the same time.

  In recent years, instead of carbon black, which is used as a rubber reinforcing agent, a rubber composition containing silica that can easily achieve a balance between the rolling resistance characteristics and wet performance has been used for tire treads. .

  However, the silica surface has a low affinity with rubber molecules having hydrophilicity and hydrophobicity, and there is a problem in dispersibility in rubber. This is because the silica surface is covered with highly polar silanol groups, so that it has strong self-aggregation properties, weak interaction with rubber molecules having different polarities, and silica particles tend to aggregate. For this reason, the rubber characteristic inherent in silica blending is not sufficiently exhibited.

  In order to improve this silica dispersibility, silane coupling agents that chemically bond silica and rubber molecules have been used in the past, but in reality the reinforcing performance of silica is not as good as that of carbon black. It is.

In order to solve the above-mentioned problem of silica compounding, improvement of the polymer, for example, utilization of emulsion polymerization-derived terpolymer rubber containing hydroxyl side group (Patent Document 1), specific polyether and its derivatives, α- It has been proposed to use various additives such as copolymer resins with terpene phenols such as pinene, β-pinene, and dipentene, or ethylene / vinyl acetate copolymers for blending with silica (Patent Documents 2 to 4). .
JP 2002-293994 A JP 2005-343963 A JP 2005-47968 A Japanese Patent Laid-Open No. 2005-220212

  However, although the effect of the above technical improvement is recognized, even if the silane coupling agent and the above various additives are used, the reinforcing property of silica is still not sufficient compared to carbon black, and the characteristics of the silica-containing rubber composition There is still room for improvement.

  In addition, since the silane coupling agent itself has a low molecular weight, there are points to be improved in rubber properties such as hardness reduction of the rubber composition. Silica compounding has problems in processing such as kneadability and scorch, and rolling resistance properties. Further improvement is demanded for a good balance between the wet performance and the wet performance, or for improving rubber properties such as strength and modulus.

  Therefore, the present invention has been made in view of the above points, and improves the reinforcing property of silica by improving the interaction between silica and rubber molecules in the silica compounding, and rolling resistance without impairing wear resistance. An object is to provide a rubber composition having an excellent balance between properties and wet performance.

  The present inventor has also known that the use of a polymer compound having a functional group for silica compounding in the above-mentioned patent document, but among these, a highly polar high molecular weight that can remarkably enhance the interaction between silica and rubber molecules. A molecular compound has been found.

  That is, the invention of claim 1 is based on radical polymerization of a compound having at least one acrylamide group and one hydroxyl group in a molecule in a rubber composition containing 20 to 120 parts by weight of silica with respect to 100 parts by weight of diene rubber. A rubber composition comprising a polymer compound obtained by polymerization using an initiator.

The invention according to claim 2 is the rubber composition according to claim 1, wherein the compound is a compound represented by the following general formula (1).
_{CH 2 = CHCONH-R-OH} ··· (1)
In the formula, R is an alkyl group, an alkenyl group, or an aryl group.

  The invention according to claim 3 is the rubber composition according to claim 2, wherein the compound represented by the general formula (1) is N (2-hydroxyethyl) acrylamide.

  Invention of Claim 4 contains 0.5-10 weight part of said high molecular compounds with respect to 100 weight part of said diene rubbers, The rubber composition in any one of Claims 1-3 characterized by the above-mentioned. It is.

  The invention according to claim 5 is the rubber composition according to any one of claims 1 to 4, further comprising 0.5 to 5 parts by weight of polyethylene glycol with respect to 100 parts by weight of the rubber component. is there.

  A sixth aspect of the present invention is a pneumatic tire characterized by using the rubber composition according to any one of the first to sixth aspects in a tread.

  According to the rubber composition of the present invention, a polymer compound having a specific highly polar group is used for blending silica, thereby imparting excellent plasticity to silica particles and improving its dispersibility, thereby interacting with rubber molecules. Can be improved. As a result, it is possible to provide a rubber composition suitable for a tire tread that improves the reinforcing property of silica and has an excellent balance between rolling resistance characteristics and wet performance without impairing wear resistance.

  The present invention is a rubber composition containing silica in a diene rubber, and can be obtained by polymerizing a compound having at least one acrylamide group and one hydroxyl group in the molecule using a radical polymerization initiator. The main point is to contain a high molecular compound.

  As the diene rubber used in the present invention, natural rubber, isoprene rubber (IR), styrene butadiene rubber (SBR), butadiene rubber (BR), nitrile rubber (NBR), ethylene propylene diene rubber (EPDM), etc. can be used. These diene rubbers may be used alone or in combination of two or more in any ratio.

  Synthetic rubbers such as SBR and BR are not particularly limited in terms of their polymerization method (emulsion polymerization, solution polymerization, etc.), molecular weight (distribution), microstructure, presence or absence of oil expansion, etc. It can be arbitrarily selected depending on the application.

  Examples of the silica used in the rubber composition of the present invention include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, and aluminum silicate. Wet silica is preferable because it has both an improvement effect and a low rolling resistance characteristic and wet performance, and is also excellent in terms of productivity.

The silica preferably has a nitrogen adsorption specific surface area (BET) of 100 to 300 m ² / g and a DBP oil absorption of 150 to 300 ml / 100 g. When the BET is less than 100 m ² / g, a silica reinforcing effect is obtained. When it exceeds 300 m ² / g, the dispersibility of silica is remarkably lowered, and the processability (mixing, extrudability) tends to deteriorate. Moreover, a dispersibility can be favorably maintained by making DBP oil absorption amount 150-300 ml / 100g. As such silica, commercially available products such as Nipsil AQ and VN3 manufactured by Tosoh Silica Industry Co., Ltd., Tocsil UR and U-13 manufactured by Tokuyama Co., Ltd., and Ultrazil VN3 manufactured by Degussa Corporation can be used. The BET of silica is measured according to the BET method described in ISO 5794, and the DBP oil absorption is measured according to the method described in JIS K6221.

  Furthermore, as the silica, surface-treated silica that has been surface-treated with amines or organic polymers to improve the affinity with rubber molecules may be used.

  The amount of the silica is 20 to 120 parts by weight with respect to 100 parts by weight of the rubber component. If the amount of silica is less than 20 parts by weight, the effects of the present invention such as reinforcement and low heat build-up due to the silica are not achieved and the object of the present invention cannot be achieved. Even so, the Mooney viscosity and hardness of the rubber are increased, the workability is deteriorated, and the wear resistance is also lowered.

  The polymer compound used in the rubber composition of the present invention is obtained by polymerizing a compound having at least one acrylamide group and one hydroxyl group in the molecule using a radical polymerization initiator.

  As said compound, the compound represented by following General formula (1) is mentioned.

_{CH 2 = CHCONH-R-OH} ··· (1)
In the formula, R is an alkyl group, an alkenyl group, or an aryl group.

  Examples of the alkyl group include methyl, ethyl, propyl, isopropyl, butyl, and isobutyl groups.

  Examples of the alkenyl group include vinyl, allyl, and propenyl groups.

  Examples of the aryl group include phenyl, toluyl, and xylyl groups.

  In the general formula (1), R is preferably an alkyl group or alkenyl group having 2 to 8 carbon atoms. Among them, N (2-hydroxyethyl) acrylamide (may be abbreviated as “HEAA”) is a preferred example.

  The HEAA can be synthesized by a known method. For example, a method such as a reaction between ethanolamine and an acrylate ester, a reaction between ethanolamine and acrylate chloride, or the like can be used.

  The polymer compound contained and used in the rubber composition of the present invention is synthesized by polymerizing a compound represented by the formula (1) having an acrylamide group and a hydroxyl group in the molecule, such as HEAA, with a radical polymerization initiator. Is.

  The radical polymerization initiator is not particularly limited as long as it can be generally used for radical polymerization, and examples thereof include an azo polymerization initiator, an organic peroxide, and a redox polymerization initiator.

  Specific preferred radical polymerization initiators include 2,2′-azobis (isobutyronitrile) (AIBN), 2,2′-azobis (2-methylbutyronitrile) (AMBN), 2,2 An azo compound such as' -azobis (2,4-dimethylvaleronitrile) (ADVN) and an organic peroxide such as benzoyl peroxide, t-butyl hydroperoxide, and dicumyl peroxide are preferable. These polymerization initiators are preferably used in an amount of 0.001 to 5% by weight, particularly 0.01 to 2% by weight, based on the amount of the compound. Moreover, you may add polymerization chain transfer agents, such as an octyl mercaptan and n-dodecyl mercaptan, as needed.

  The polymerization is usually carried out by thermal polymerization at 80 to 120 ° C., preferably 90 to 110 ° C., for 1 to 10 hours, and is appropriately selected depending on the type of radical polymerization initiator, compound, and solvent to be used. The polymerization is preferably performed in an inert gas atmosphere such as nitrogen.

  The polymer compound according to the present invention thus obtained has a structure represented by the following formula (2), and its weight average molecular weight is preferably 1000 to 50000, more preferably 1000 to 30000. . The larger the molecular weight, that is, the longer the repeating unit of the vinyl group portion, the more the portion that comes into contact with the silica, and it becomes easier to impart plasticity to the silica. When the molecular weight exceeds 50000, the polymerization reaction time becomes long and the synthesis becomes difficult.

_{- (CH 2 -CH) n -} ··· (2)
｜
C = O
｜
H-N-R-OH
n is the number of repeating vinyl groups.

  Content of the said high molecular compound is 0.5-10 weight part with respect to 100 weight part of diene rubbers, Preferably it is 1-5 weight part. If the content is less than 0.5 parts by weight, the effect of the present invention is not sufficiently achieved, and if the content exceeds 10 parts by weight, no further effect can be obtained, and if it is further increased, it becomes foreign matter and wear resistance, rolling resistance, etc. It will deteriorate the rubber properties.

  In the present invention, polyethylene glycol having a molecular weight of 100 to 3000 may be further contained. The polyethylene glycol is conventionally known to increase the affinity between silica and rubber molecules by the action of a surfactant, but when used in combination with the polymer compound according to the present invention, it is The rubber properties of the blend can be improved.

  The content is 0.5 to 5 parts by weight with respect to 100 parts by weight of the rubber component. If the amount is less than 0.5 parts by weight, the synergistic effect is not sufficiently achieved. If the amount exceeds 5 parts by weight, the rubber hardness is lowered, and the wear resistance and wet performance are lowered.

  In the present invention, rubber silane coupling agents conventionally used for silica compounding may be used in combination. Examples of the silane coupling agent include sulfur-containing silane coupling agents such as bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide, and 3-trimethoxysilylpropylbenzothiazole tetrasulfide. Etc.

  The content of these silane coupling agents is preferably 1 to 20% by weight, more preferably 2 to 15% by weight, based on the amount of silica. If the content of the silane coupling agent is less than 1% by weight, the coupling effect by the silane coupling agent cannot be obtained, and if it exceeds 20% by weight, no further effect can be obtained, resulting in an increase in cost.

  In addition to the rubber component, silica, and polymer compound, the rubber composition of the present invention includes a reinforcing agent such as carbon black ordinarily used in the rubber composition, a vulcanizing agent such as sulfur, a vulcanization accelerator, and a process. Various compounding agents such as oil, anti-aging agent, zinc white, stearic acid, and vulcanization aid can be appropriately blended and used as needed within the range not impairing the effects of the present invention.

  The rubber composition of the present invention can be prepared according to a conventional method using various kneading machines such as a Banbury mixer, a roll, a kneader and the like by blending various compounding agents with the raw rubber and the above essential components, including tire treads. Can be used for tire parts such as sidewalls and bead parts, but especially by making the dispersion state of silica uniform, the tire has an excellent balance of rolling resistance characteristics and wet performance without impairing wear resistance Suitable as tread rubber.

  Next, although an example and a comparative example explain the present invention, the present invention is not limited to these examples.

The polymer compound according to the present invention used in the examples was prepared by reacting ethanolamine with acrylate, N (2-hydroxyethyl) acrylamide (HEAA) as a radical polymerization initiator, and AIBN as HEAA. thermal polymerization using 0.1 wt% relative to the amount _{(N 2} atmosphere, the reactor temperature 100 ° C. × 4 hours polymerization) is then obtained resultant polymer compound (referred to P-HEAA).

  The obtained P-HEAA had a weight average molecular weight of 5,000 as measured by GPC.

  The above P-HEAA, the following styrene butadiene rubber (SBR), silica and compounding ingredients are blended in the blending amounts (parts by weight) shown in Table 1, and using a Banbury mixer with a capacity of 20 liters, rubber compositions of Examples and Comparative Examples A product was prepared.

[Composition ingredients]
・ SBR: Emulsion polymerization SBR, JSR Corporation "SBR1502"
Silica: Tosoh Silica Industry Co., Ltd. “Nipseal VN3” (BET: 210 m ² / g)
・ Silane coupling agent: Degussa "Si69"
・ Zinc oxide: Mitsui Mining & Smelting Co., Ltd.
・ Stearic acid: Kao Corporation “Lunac S-20”
・ Aroma oil: Japan Enajie "Process X-140"
・ Sulfur: Hosoi Chemical Co., Ltd. “Powder sulfur 150 mesh for rubber”
・ Vulcanization accelerator CZ: Ouchi Shinsei Chemical Co., Ltd. “Noxeller CZ”
-Polyethylene glycol: Daiichi Kogyo Seiyaku "PEG400"

[Evaluation]
Each rubber composition obtained was applied to a cap tread of a tire having a tread having a cap / base structure, and a 205 / 65R159H pneumatic radial tire was produced according to a conventional method. And about each obtained tire, rolling resistance characteristics, wet performance, and abrasion resistance were evaluated. Each evaluation method is as follows. The results are shown in Table 1.

[Rolling resistance characteristics]
The tire was mounted with a rim of 15 × 6.5 JJ, and the rolling resistance was measured when running at 80 km / h at 23 ° C. with a uniaxial drum tester for measuring rolling resistance at an air pressure of 230 kPa and a load of 450 kgf. . It was displayed as an index with the value of Comparative Example 1 being 100. The smaller the index, the smaller the rolling resistance and thus the better the fuel efficiency.

[Wet performance]
Measure the braking distance when decelerating to 20 km / h by installing four tires on a 2000cc domestic FF car, running on asphalt road surface watered at a depth of 2-3 mm, operating ABS at 90 km / h did. It displays with the index | exponent which set the value of the comparative example 1 to 100, and shows that it is excellent in wet performance, so that an index | exponent is large.

[Abrasion resistance]
Four tires were mounted on a 2000 cc domestic FF vehicle, and the amount of wear was determined from the tread remaining groove depth after running 20,000 km while rotating every 5,000 km on the general road surface of dry asphalt. The results are shown in Table 1 as indices with Comparative Example 1 as 100. The higher the index, the better.

  As shown in the results of Table 1, each Example containing the polymer compound P-HEAA according to the present invention can improve and improve the rolling resistance characteristics and the wet performance while improving the wear resistance. it can. However, when the content of P-HEAA is 0.3 parts by weight (Comparative Example 2), the effect is small, and when 10 parts by weight (Example 4), each tire characteristic tends to decrease, and the upper limit of the content is 10 parts by weight. It turns out that it is a grade. Furthermore, at 20 parts by weight (Comparative Example 3), P-HEAA is excessive, so that it becomes a foreign substance and the tire performance is reduced. Moreover, in Example 5 which used polyethylene glycol together, the clear synergistic effect of both is recognized.

  The rubber composition of the present invention is suitable for a tread rubber of a pneumatic tire excellent in fuel efficiency, safety and durability, and can be used for a tire for passenger cars, a large tire for trucks and buses, and a studless tire. it can.

Claims (6)

In a rubber composition containing 20 to 120 parts by weight of silica with respect to 100 parts by weight of diene rubber,
A rubber composition comprising a polymer compound obtained by polymerizing a compound having at least one acrylamide group and one hydroxyl group in a molecule using a radical polymerization initiator. The rubber composition according to claim 1, wherein the compound is a compound represented by the following general formula (1).
_{CH 2 = CHCONH-R-OH} ··· (1)
In the formula, R is an alkyl group, an alkenyl group, or an aryl group. The rubber composition according to claim 2, wherein the compound represented by the general formula (1) is N (2-hydroxyethyl) acrylamide. The rubber composition according to any one of claims 1 to 3, wherein the polymer compound is contained in an amount of 0.5 to 10 parts by weight with respect to 100 parts by weight of the diene rubber. Furthermore, 0.5-5 weight part of polyethylene glycol is contained with respect to 100 weight part of said rubber components. The rubber composition in any one of Claims 1-4 characterized by the above-mentioned. A pneumatic tire using the rubber composition according to claim 1 for a tread.