JP2023119107A - Rubber composition for tires - Google Patents

Abstract

To provide a rubber composition for tires that can meet high standards for both on-ice performance and wear resistance.SOLUTION: A rubber composition for tires includes 100 pts.mass of a diene rubber, blended with 30 pts.mass or more of a white filler, and 0.5-30 pts.mass of particles with a glass transition temperature of -70°C to 0°C. The particles used here include a polymer of a monomer mixture including 80 mass%-99.5 mass% of a monofunctional (meth)acrylate monomer, 0.1 mass%-5 mass% of a diene monomer, and 0.4 mass%-15 mass% of a polyfunctional vinyl monomer.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a tire rubber composition intended primarily for use in the tread portion of studless tires.

In order to improve the on-ice performance of studless tires, it is known to increase the surface roughness (unevenness) of the tread rubber. When the surface roughness of the tread rubber is increased, the concave portions take in the water film existing on the ice surface, and the convex portions come into contact with the ice surface, thereby increasing the contact area with the ice surface compared to the tread rubber with a smooth surface. It is considered effective.

For example, Patent Literature 1 proposes blending resin particles (acrylic resin) having specific properties into a rubber composition that constitutes a tread rubber. In this proposal, fine irregularities are formed on the surface of the tread rubber by blending the resin particles, and performance on ice can be improved. However, if the resin particles are simply blended, the resin particles may fall off from the tread rubber during running, making it impossible to obtain desired performance on ice or ensure wear resistance. Therefore, in ensuring performance on ice by compounding resin particles into a rubber composition, a measure is required to ensure abrasion resistance while exhibiting excellent performance on ice.

JP 2018-123209 A

An object of the present invention is to provide a rubber composition for a tire that makes it possible to achieve a high level of both performance on ice and wear resistance.

The rubber composition for tires of the present invention, which achieves the above objects, contains 30 parts by mass or more of a white filler per 100 parts by mass of a diene rubber, and 0.5 part of particles having a glass transition temperature of -70°C to 0°C. A studless tire rubber composition containing up to 30 parts by mass, wherein the particles are composed of a polymer of a monomer mixture containing the monomer (A), the monomer (B), and the monomer (C), and the monomer ( A) is a monofunctional (meth)acrylate monomer, the monomer (B) is a diene monomer, and the monomer (C) is a polyfunctional vinyl monomer other than the monomer (B). There, the mass ratio of the monomer (A) in the monomer mixture is 80% by mass to 99.5% by mass, and the mass ratio of the monomer (B) in the monomer mixture is 0.1% by mass to 5% by mass. %, and the mass ratio of the monomer (C) in the monomer mixture is 0.4% by mass to 15% by mass.

The rubber composition for studless tires of the present invention comprises a polymer of the above-mentioned monomer mixture and contains particles having a glass transition temperature of -70°C to 0°C. It can be improved even more. In particular, since the particles are made of a polymer of a monomer mixture containing a monofunctional (meth)acrylic acid ester monomer and a polyfunctional vinyl monomer, the flexibility and resistance to crushing of the particles can be ensured. , it is considered that the on-ice performance can be effectively exhibited when used for tires. Furthermore, since the monomer mixture contains not only monofunctional (meth)acrylic acid ester monomers and polyfunctional vinyl monomers but also diene monomers, the resulting particles are It is believed that the affinity is improved, the particles are less likely to drop out of the rubber composition, the performance on ice is reliably exhibited, and the wear resistance performance is improved. The glass transition temperature is measured by differential scanning calorimetry (DSC) under the condition of a temperature increase rate of 20° C./min, and a thermogram is taken as the temperature at the middle point of the transition region.

In the rubber composition for studless tires of the present invention, the diene rubber preferably contains butadiene rubber and natural rubber, and the content of natural rubber is preferably 30 parts by mass or more per 100 parts by mass of butadiene rubber. . Containing a sufficient amount of natural rubber relative to butadiene rubber in this manner is advantageous for achieving both performance on ice and abrasion resistance.

In the rubber composition for studless tires of the present invention, the monomer (B) has at least two (meth)acryloyl groups, has a weight average molecular weight of 500 to 50,000, and is represented by the following general formula (1). It is preferable to have The compound represented by the following general formula (1) has a reactive carbon-carbon double bond like a polybutadiene skeleton in the molecule, so it is advantageous for increasing the affinity for the diene rubber that is the main component of the rubber composition. is. On the other hand, by having a (meth)acryloyl group, which is a more reactive functional group, the above-mentioned reactive carbon-carbon double bond is not used in the polymerization reaction during particle production, so in the rubber composition Affinity for diene rubber can be effectively increased.
R ¹ -OR ² -OR ³ (1)
(In the formula, R ¹ and R ³ are (meth)acryloyl groups, and R ² is a structure containing a polymer chain having a diene as a structural unit.)

In the rubber composition for studless tires of the present invention, the particles preferably have an average particle size of 3 μm to 70 μm. This is advantageous for achieving both on-ice performance and wear resistance performance.

The rubber composition for studless tires of the present invention preferably has a glass transition temperature of −60° C. or lower. This is advantageous for achieving both on-ice performance and wear resistance performance.

The rubber composition for studless tires of the present invention preferably further contains a liquid polymer having a weight average molecular weight of 1,000 to 100,000. Moreover, it is preferable that the rubber composition for studless tires of the present invention further contains a terminal-modified diene rubber. Furthermore, the rubber composition for studless tires of the present invention preferably further contains an aromatic modified terpene resin. Such a blend is advantageous for achieving both performance on ice and abrasion resistance.

The rubber composition for studless tires of the present invention can be used in the tread portion of studless tires. A studless tire having a tread portion molded from the rubber composition for a studless tire of the present invention can effectively exhibit performance on ice and wear resistance due to the physical properties of the rubber composition for a studless tire described above.

In the rubber composition for tires of the present invention, the rubber component is a diene rubber such as natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, styrene-isoprene rubber, styrene-isoprene-butadiene rubber, acrylonitrile-butadiene. Rubber or the like can be used. Among them, natural rubber, butadiene rubber and styrene-butadiene rubber are preferable, and natural rubber and butadiene rubber are particularly preferable.

When natural rubber and butadiene rubber are used, preferably 20% to 80% by mass, more preferably 30% to 70% by mass, of butadiene rubber is contained in 100% by mass of natural rubber and butadiene rubber in total. In addition, natural rubber is preferably contained in an amount of 20% by mass to 80% by mass, more preferably 30% by mass to 70% by mass, based on a total of 100% by mass of natural rubber and butadiene rubber. At this time, the content of natural rubber is preferably 30% by mass or more, more preferably 60% to 300% by mass with respect to 100% by mass of butadiene rubber. By forming the rubber component from the natural rubber and the butadiene rubber in this manner and containing them in a predetermined blend, it is possible to achieve both performance on ice and abrasion resistance. If the natural rubber content is less than 30% by mass with respect to the butadiene rubber content of 100 parts by mass, the abrasion resistance is lowered.

In the rubber composition for tires of the present invention, the diene rubber may contain a terminal-modified diene rubber modified with an organic compound having a functional group at one or both ends of the molecular chain. Examples of terminal-modified diene rubber include terminal-modified butadiene rubber and terminal-modified styrene-butadiene rubber. Examples of functional groups that modify the ends of molecular chains include alkoxysilyl groups, hydroxyl groups (hydroxyl groups), aldehyde groups, carboxyl groups, amino groups, amide groups, imino groups, alkoxyl groups, epoxy groups, amide groups, and thiol groups. groups, ether groups, and siloxane-bonded groups. Among them, siloxane, alkoxysilyl, and hydroxyl group (hydroxyl group) can be preferably used. The siloxane bond group mentioned above is a functional group having an —O—Si—O— structure.

The average glass transition temperature of the diene rubber described above is preferably -50°C or lower, more preferably -100°C to -60°C. By setting the average glass transition temperature of the diene rubber to -50°C or lower, the flexibility of the rubber compound is maintained at low temperatures and the adhesion to the ice surface is increased, making it suitable for the tread of studless tires. can do. The glass transition temperature is defined as the temperature at the middle point of the transition region by measuring a thermogram by differential scanning calorimetry (DSC) under the condition of a temperature increase rate of 20° C./min. When the diene-based rubber is an oil-extended product, the glass transition temperature of the diene-based rubber in a state not containing an oil-extending component (oil) is used. The average glass transition temperature is the sum (weighted average value of the glass transition temperatures) obtained by multiplying the glass transition temperature of each diene rubber by the mass fraction of each diene rubber. Note that the total mass fraction of all diene rubbers is 1.

The rubber composition for studless tires of the present invention always contains a white filler. Examples of white fillers include silica, calcium carbonate, magnesium carbonate, talc, clay, alumina, aluminum hydroxide, titanium oxide, and calcium sulfate. You may use these individually or in combination of 2 or more types. Among them, silica is preferable and can make performance on ice more excellent. Examples of silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. These may be used alone or in combination of two or more.

The amount of the white filler compounded is 30 parts by mass or more, preferably 35 to 80 parts by mass, per 100 parts by mass of the diene rubber. By setting the amount of the white filler to be 30 parts by mass or more, the mechanical properties of the rubber composition can be improved and the wear resistance can be improved. In addition, by adjusting the amount of the white filler to 35 parts by mass to 80 parts by mass, not only the mechanical properties of the rubber composition are improved and the abrasion resistance is improved, but also the suppleness of the rubber composition is maintained. Performance can be effectively ensured. If the amount of the white filler compounded is less than 30 parts by mass, it becomes difficult to sufficiently secure the mechanical properties of the rubber composition.

Although the CTAB adsorption specific surface area of silica is not particularly limited, it is preferably 80 m ² /g to 260 m ² /g, more preferably 140 m ² /g to 200 m ² /g. By setting the CTAB adsorption specific surface area of silica to 80 m ² /g or more, the wear resistance of the rubber composition can be ensured. By setting the CTAB adsorption specific surface area of silica to 200 m ² /g or less, wet performance and low rolling resistance can be improved. In this specification, the CTAB specific surface area of silica is a value measured according to ISO 5794.

In the present invention, it is preferable to blend a silane coupling agent together with silica. By blending the silane coupling agent, the dispersibility of silica in the diene rubber can be improved, and the balance between abrasion resistance and performance on ice can be improved.

The type of silane coupling agent is not particularly limited as long as it can be used in silica-blended rubber compositions. Examples include sulfur-containing silane coupling agents such as triethoxysilylpropyl)disulfide, 3-trimethoxysilylpropylbenzothiazoletetrasulfide, γ-mercaptopropyltriethoxysilane, and 3-octanoylthiopropyltriethoxysilane. .

When a silane coupling agent is blended, the blending amount is preferably 3% by mass to 15% by mass, more preferably 5% to 10% by mass, based on the mass of silica. If the amount of the silane coupling agent is less than 3% by mass of the silica, the dispersion of silica cannot be sufficiently improved. If the amount of the silane coupling agent compounded exceeds 15% by mass of the silica, the silane coupling agents will condense with each other, making it impossible to obtain the desired hardness and strength in the rubber composition.

The rubber composition for tires of the present invention may further contain carbon black in addition to the white filler described above. Examples of carbon black include furnace carbon blacks such as SAF, ISAF, HAF, FEF, GPF, HMF, and SRF, and these may be used alone or in combination of two or more. The amount of carbon black compounded is preferably 3 parts by mass to 70 parts by mass, more preferably 5 parts by mass to 60 parts by mass with respect to 100 parts by mass of the diene rubber. By adding 3 parts by mass or more of carbon black, the mechanical properties of the rubber composition can be improved and the wear resistance can be improved. Also, by setting the amount of carbon black to be 70 parts by mass or less, the flexibility of the rubber composition can be maintained and performance on ice can be ensured. Moreover, when it is made into a tire, an increase in mass can be suppressed.

When carbon black is blended in addition to the white filler, the nitrogen adsorption specific surface area of carbon black is preferably 70 m ² /g to 240 m ² /g, more preferably 90 m ² /g to 200 m ² /g. . By setting the nitrogen adsorption specific surface area of the carbon black to 70 m ² /g or more, the mechanical properties and abrasion resistance of the rubber composition can be ensured. Also, the performance on ice can be improved by setting the nitrogen adsorption specific surface area of the carbon black to 240 m ² /g or less. In this specification, the nitrogen adsorption specific surface area of carbon black shall be measured according to JIS K6217-2.

The rubber composition for tires of the present invention preferably contains a liquid polymer. By blending a liquid polymer, it is possible to make the rubber hardness in a low temperature state more flexible, and to make the performance on ice more excellent. Examples of liquid polymers include liquid polybutene, liquid polyisobutene, liquid polyisoprene, liquid polybutadiene, liquid poly-α-olefin, liquid isobutylene, liquid ethylene-α-olefin copolymer, liquid ethylene-propylene copolymer, and liquid ethylene-butylene copolymer. etc. The liquid polymer may be various modifications of the liquid polymer described above (maleic acid modification, terminal isocyanate modification, epoxy modification, etc.). The liquid polymer used in the present invention is liquid at room temperature (23°C). Therefore, it is distinguished from the aforementioned diene-based rubber, which is solid at this temperature.

When a liquid polymer is blended, it is particularly preferable to use a liquid polymer having a weight average molecular weight of preferably 1,000 to 100,000, more preferably 2,000 to 90,000. If the weight-average molecular weight of the liquid polymer is less than 1,000, the performance on ice after aging cannot be sufficiently obtained. If the weight average molecular weight of the liquid polymer exceeds 100,000, the performance on ice cannot be sufficiently improved. The amount of the liquid polymer compounded is not particularly limited, but it is preferably 3 to 80 parts by mass, more preferably 5 to 60 parts by mass, per 100 parts by mass of the rubber component. If the amount of the liquid polymer is less than 3 parts by mass, the effect of improving performance on ice and snow cannot be sufficiently obtained. If the amount of the liquid polymer to be blended exceeds 80 parts by mass, the tensile strength at break may deteriorate. In addition, a weight average molecular weight means the weight average molecular weight of polystyrene conversion analyzed by a gel permeation chromatography (GPC).

The rubber composition for tires of the present invention preferably contains an aromatic modified terpene resin. Wet performance can be further improved by blending the aromatic modified terpene resin. This is probably because the aromatic modified terpene resin improves the dispersibility of fillers such as silica and carbon black and improves the compatibility between the filler and the rubber component. Aromatic modified terpene resins include aromatic modified resins obtained by polymerizing terpenes such as α-pinene, β-pinene, dipentene and limonene with at least one aromatic compound selected from among styrene, α-methylstyrene and vinyltoluene. A terpene resin can be exemplified.

As the aromatic modified terpene resin, an aromatic modified terpene resin having a softening point of preferably 60° C. to 150° C., preferably 80° C. to 130° C. can be suitably used. If the softening point of the aromatic modified terpene resin is less than 60°C, the effect of improving wet performance cannot be sufficiently obtained. If the softening point of the aromatic modified terpene resin exceeds 150°C, there is a concern that it may remain undissolved during mixing. The softening point of the aromatic modified terpene resin shall be measured based on JIS K6220-1 (ring and ball method). The amount of the aromatic modified terpene resin to be blended is not particularly limited, but it is preferably 2 to 40 parts by mass, more preferably 3 to 35 parts by mass, per 100 parts by mass of the rubber component. If the blending amount of the aromatic modified terpene resin is less than 2 parts by mass, the effect of improving wet performance cannot be sufficiently obtained. If the blending amount of the aromatic modified terpene resin exceeds 40 parts by mass, the ice and snow performance may deteriorate.

The rubber composition for tires of the present invention improves performance on ice and wear resistance by blending the particles described below. Particles having specific properties can be prepared, for example, by polymerizing non-crosslinkable monomers in the presence of crosslinkable monomers by suspension polymerization, seed polymerization or dispersion polymerization. Further, the particles described later are preferably particles incompatible with the diene rubber. Here, "incompatible with diene rubber" does not mean incompatible with all types of rubber components included in diene rubber, but specific It is sufficient if it is incompatible with the diene rubber. The specific particles that are incompatible with the diene rubber form a phase-separated structure with the diene rubber, thereby providing excellent on-ice performance.

The resin that constitutes the particles used in the present invention is a polymer of a monomer mixture containing monomer (A), monomer (B), and monomer (C) described below.

In the present invention, the monomer (A) is a monofunctional (meth)acrylate monomer. A monofunctional (meth)acrylic acid ester monomer means a (meth)acrylic acid ester having one ethylenically unsaturated group in one molecule. Examples of monofunctional (meth)acrylate monomers include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, and (meth)acrylic acid. (Meth)acrylic acid alkyl esters such as n-butyl, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate; cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, etc. (meth)acrylic acid esters of alicyclic alcohols; (meth)acrylic acid aryl esters such as phenyl (meth)acrylate; (meth)acrylates such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate acid alkoxyalkyl and the like. These monofunctional (meth)acrylic ester-based monomers may be used singly or in combination of two or more. Among these, alkyl (meth)acrylates are preferred, alkyl acrylates are more preferred, and n-butyl acrylate, isobutyl acrylate, and 2-ethylhexyl acrylate are particularly preferred. (Meth)acryl means acryl and/or methacryl.

The monomer (A), that is, the monofunctional (meth)acrylic acid ester-based monomer is used in a proportion of 80% by mass to 99.5% by mass in the monomer mixture. By including the monomer (A) in this way, it is possible to ensure the flexibility and resistance to crushing of the particles, and to effectively exhibit performance on ice when used in a tire. When the mass ratio of the monofunctional (meth)acrylic acid ester-based monomer in the monomer mixture is less than 80% by mass, when the particles are added to the rubber composition, the surface feels sticky while maintaining a soft touch. cannot be eliminated. If the mass ratio of the monofunctional (meth)acrylic acid ester-based monomer in the monomer mixture exceeds 99.5% by mass, the particles aggregate during drying, resulting in poor handleability. The mass proportion of monomer (A) in the monomer mixture is preferably 85% to 99% by mass, more preferably 92.5% to 98% by mass.

In the present invention, the monomer (B) is a diene monomer. As the diene-based monomer, those having at least two (meth)acryloyl groups, having a weight-average molecular weight of 500 to 50,000, and represented by the following general formula (1) can be preferably used. The compound represented by the following general formula (1) has a reactive carbon-carbon double bond like a polybutadiene skeleton in the molecule, so it is advantageous for increasing the affinity for the diene rubber that is the main component of the rubber composition. is. On the other hand, by having a (meth)acryloyl group, which is a more reactive functional group, the above-mentioned reactive carbon-carbon double bond is not used in the polymerization reaction during particle production, so in the rubber composition Affinity for diene rubber can be effectively increased.
R ¹ -OR ² -OR ³ (1)
(In the formula, R ¹ and R ³ are (meth)acryloyl groups, and R ² is a structure containing a polymer chain having a diene as a structural unit.)

If the diene-based monomer represented by the general formula (1) has one or less (meth)acryloyl groups, the strength of the particles is reduced. In the diene-based monomer represented by the general formula (1), the compatibility with diene-based rubbers having a weight average molecular weight of less than 500 cannot be improved. If the weight-average molecular weight of the diene-based monomer represented by formula (1) exceeds 50,000, the reactivity of the diene-based monomer decreases. In addition, a weight average molecular weight means the weight average molecular weight of polystyrene conversion analyzed by a gel permeation chromatography (GPC). Moreover, "(meth)acryloyl" means acryloyl and/or methacryloyl. The weight average molecular weight of the diene monomer represented by formula (1) is more preferably 600 to 35,000, still more preferably 1,000 to 30,000, and particularly preferably 1,500 to 25,000.

In the diene-based monomer represented by the general formula (1), the diene which is the structural unit of the polymer chain contained in R ² in the formula includes conjugated dienes such as butadiene, isoprene and chloroprene; 1,4-hexadiene, 5- Non-conjugated dienes such as ethylidene-2-norbornene can be exemplified. These dienes may be used individually by 1 type, and may be used in combination of 2 or more type. Among these, conjugated dienes are preferred, and butadiene is particularly preferred. Examples of the diene-based monomer represented by the general formula (1) include polybutadiene di(meth)acrylate and di(meth)acrylate having polyisoprene in the main chain skeleton. One of these diene-based monomers may be used alone, or two or more thereof may be used in combination. Among these, polybutadiene di(meth)acrylate is preferred. "(Meth)acrylate" means acrylate and/or methacrylate.

Monomer (B), ie, a diene-based monomer, is used in a proportion of 0.1% by mass to 5% by mass in the monomer mixture. Since the diene-based monomer is contained in this way, the particles have a good affinity for the diene-based rubber, which is the main component of the rubber composition, and the particles are less likely to fall out of the rubber composition, ensuring good on-ice performance. and can improve the wear resistance performance. If the mass ratio of the diene monomer in the monomer mixture is less than 0.1% by mass, the affinity for diene rubber cannot be improved. When the weight ratio of the diene monomer in the monomer mixture exceeds 5% by weight, the flexibility of the particles deteriorates. The weight proportion of the diene monomer is preferably 0.3% to 3% by weight, more preferably 0.5% to 1.5% by weight in the monomer mixture.

In the present invention, the monomer (C) is a polyfunctional vinyl-based monomer other than the monomer (B) described above. A polyfunctional vinyl-based monomer means a monomer (crosslinking agent) having at least two ethylenically unsaturated groups in one molecule. Polyfunctional vinyl monomers include aromatic divinyl monomers such as divinylbenzene and divinylnaphthalene; allyl methacrylate, triacrylic formal, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, Butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, PEG#200 di(meth)acrylate, PEG#400 di(meth)acrylate, PEG#600 di(meth)acrylate, trimethylolpropane Bifunctional or higher (meth)acrylate such as tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 2-butyl-2-ethyl 1,3-propanediol di(meth)acrylate Examples include acrylate-based monomers. One of these polyfunctional vinyl monomers may be used alone, or two or more thereof may be used in combination. Among these, trimethylolpropane trimethacrylate and ethylene glycol dimethacrylate are preferred, and ethylene glycol dimethacrylate is particularly preferred.

Monomer (C), ie, polyfunctional vinyl monomer, is used in a proportion of 0.4% by mass to 15% by mass in the monomer mixture. If the mass ratio of the polyfunctional vinyl-based monomer in the monomer mixture is less than 0.4% by mass, the particles tend to agglomerate when drying the particles due to a low degree of cross-linking, resulting in poor handling properties. If the mass ratio of the polyfunctional vinyl-based monomer in the monomer mixture exceeds 15% by mass, the particles become hard and when added to the rubber composition, the soft feel is impaired. The mass ratio of the polyfunctional vinyl monomer is preferably 0.7% by mass to 12% by mass, more preferably 1% by mass to 7.5% by mass in the monomer mixture.

The particles used in the present invention preferably have an average particle size of 3 μm to 70 μm, more preferably 5 μm to 60 μm. When the average particle size of the particles is 3 μm or more, the surface of the tread rubber can be deformed so as to correspond to minute irregularities on the ice surface, thereby improving performance on ice. If the average particle size of the particles exceeds 70 μm, the particles may easily drop off from the surface of the tread rubber, deteriorating wear resistance. In the present specification, the average particle size of particles is the average value obtained by measuring the particle size of at least 100 particles from a microscope observation image taken at a magnification of 1,000 to 5,000. When the image of the particle is not circular, the equivalent circle diameter obtained from the projected area can be used as the particle diameter.

The glass transition temperature of the particles used in the present invention is -70°C to 0°C, preferably -65°C to -10°C, more preferably -60°C to -15°C. By setting the glass transition temperature of the particles to 0°C or lower, it is possible to maintain the suppleness of the rubber compound at low temperatures and increase the adhesion to the ice surface, making it suitable for use in the tread of studless tires. becomes possible. If the glass transition temperature of the particles is less than -70°C, handling stability will be deteriorated. If the glass transition temperature of the particles exceeds 0°C, the performance on ice deteriorates. The glass transition temperature is measured by differential scanning calorimetry (DSC) under the condition of a temperature increase rate of 20° C./min, and a thermogram is taken as the temperature at the middle point of the transition region.

The rubber composition for tires of the present invention includes vulcanizing or cross-linking agents, vulcanization accelerators, anti-aging agents, plasticizers, processing aids, thermosetting resins and the like, which are commonly used in rubber compositions for tires. Various compounding agents can be blended. Such compounding agents can be kneaded in a conventional manner to form a rubber composition and used for vulcanization or cross-linking. The blending amount of these compounding agents can be a conventional general blending amount as long as it does not contradict the object of the present invention. The rubber composition for tires can be produced by kneading and mixing the above components using a common rubber kneading machine such as a Banbury mixer, a kneader, and a roll. The prepared rubber composition can be used for the tread portion of a studded tire and vulcanized by a conventional method.

The rubber composition for a tire of the present invention constructed as described above preferably has a glass transition temperature of -60°C or lower, more preferably -100°C to -65°C. Having such a glass transition temperature is advantageous for improving performance on ice. If the glass transition temperature of the tire rubber composition exceeds −60° C., performance on ice deteriorates. The glass transition temperature is measured by differential scanning calorimetry (DSC) under the condition of a temperature increase rate of 20° C./min, and a thermogram is taken as the temperature at the middle point of the transition region.

As described above, the rubber composition for tires of the present invention can achieve both excellent performance on ice and wear resistance at a high level. Therefore, it can be suitably used for the tread portion of studless tires. A studless tire having a tread portion molded from the rubber composition for studless tires of the present invention can effectively exhibit performance on ice and wear resistance due to the above-described physical properties of the rubber composition for studless tires.

EXAMPLES The present invention will be further described with reference to examples below, but the scope of the present invention is not limited to these examples.

In preparing 16 types of tire rubber compositions (Standard Example 1, Examples 1 to 11, Comparative Examples 1 to 4) having the compositions shown in Tables 1 and 2, sulfur, vulcanization accelerators, and particles were excluded. The ingredients were mixed in a 1.7 L Banbury mixer for 5 minutes and discharged into a masterbatch when 145°C was reached. Sulfur, a vulcanization accelerator, and particles were added to the obtained masterbatch, and the mixture was kneaded with an open roll at 70°C to obtain 16 types of tire rubber compositions.

The obtained tire rubber composition was vulcanized at 170° C. for 10 minutes using a mold of a predetermined shape (inner dimensions: length 150 mm, width 150 mm, thickness 2 mm) to prepare a vulcanized rubber test piece. . Tables 1 and 2 also show the average glass transition temperature (average Tg) and hardness measured using the obtained vulcanized rubber test pieces. The average glass transition temperature was obtained by measuring the thermogram of each vulcanized rubber test piece by differential scanning calorimetry (DSC) under the condition of a temperature increase rate of 20° C./min and obtaining the temperature at the midpoint of the transition zone. value. The hardness is a value measured according to JIS K6253.

Using the obtained vulcanized rubber test pieces, performance on ice and abrasion resistance performance were evaluated by the following test methods.

Performance on ice The obtained vulcanized rubber test piece was attached to a flat columnar rubber base, and was measured using an inside drum type friction tester on ice at a temperature of -1.5°C, a load of 5.5 kg/cm ² , and drum rotation. The coefficient of friction on ice was measured at a speed of 25 km/h. The coefficient of friction on ice thus obtained was indexed with the value of the standard example being 100, and shown in the column of "Performance on ice". The larger the index value, the higher the coefficient of friction on ice and the better the performance on ice.

Abrasion resistance performance The obtained vulcanized rubber test piece was subjected to JIS K6264 using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho) at a temperature of 20 ° C., a load of 39 N, a slip ratio of 30%, and a time of 4 minutes. The amount of wear was measured under the conditions. The obtained results were indexed to 100, which is the reciprocal of the standard example, and shown in the column of "Abrasion resistance". A larger index means better wear resistance.

The types of raw materials used in Tables 1 and 2 are shown below.
・NR: natural rubber, TSR20
・ BR: butadiene rubber, Nipol BR1220 manufactured by Nippon Zeon Co., Ltd.
・Modified BR: Modified butadiene rubber, Nipol BR1250H manufactured by Nippon Zeon Co., Ltd.
・CB: Carbon black, Show Black N339 manufactured by Cabot Japan
· White filler: Silica, Zeosil 1165MP manufactured by Rhodia (CTAB specific surface area: 159 m ² /g)
・Particle 1: Particles obtained by the preparation method described later ・Particle 2: Particles obtained by the preparation method described later ・Particle 3: Particles obtained by the preparation method described later ・Particle 4: Particles obtained by the preparation method described later ・Silane Coupling agent: Si69 manufactured by Evonik Degussa
・ Oil: Extract No. 4 S manufactured by Showa Shell Oil Co., Ltd.
・ Liquid polymer 1: liquid polybutadiene, LBR302 manufactured by Kuraray Co., Ltd. (weight average molecular weight: 5500)
・ Liquid polymer 2: liquid SBR, LSBR841 manufactured by Kuraray Co., Ltd. (weight average molecular weight: 10000)
・ Orange oil: aromatic modified terpene resin, YS resin TO125 manufactured by Yasuhara Chemical Co., Ltd.
· Anti-aging agent: SANTOFLEX 6PPD manufactured by Solutia Europe
・Wax: Paraffin wax manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd. ・Sulfur: Fine sulfur powder containing Kinkain oil manufactured by Tsurumi Kagaku Kogyo Co., Ltd. ・Vulcanization accelerator: Noxcellar CZ-G manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

Preparation method of Particle 1 To 200 parts by mass of ion-exchanged water, 50 parts by mass of sodium chloride, 20 parts by mass of colloidal silica having an effective silica component of 20% by mass, and 0.5 of an aqueous solution of adipic acid-diethanolamine condensate having an effective concentration of 50%. After adding and mixing parts by mass, an aqueous dispersion medium was prepared by adjusting the pH to 2.8 to 3.2. Separately from this, 95 parts by weight of n-butyl acrylate, 3 parts by weight of ethylene glycol dimethacrylate, 1 part by weight of PEG#400 diacrylate, 1 part by weight of polybutadiene diacrylate having a weight average molecular weight of 10,000, di- 3 parts by mass of 2-ethylhexyl peroxydicarbonate was mixed and dissolved to prepare an oily mixture. The aqueous dispersion medium and the oily mixture obtained above were stirred (8000 rpm×1 min) with TK Homomixer Model 2.5 (manufactured by Primix) to prepare a suspension. This suspension was transferred to a pressurized reactor with a capacity of 1.5 liters, and after nitrogen substitution, the initial reaction pressure was set to 0.2 MPa, and polymerization was carried out at a polymerization temperature of 65° C. for 15 hours while stirring at 80 rpm to obtain particles. An aqueous dispersion containing The resulting aqueous dispersion containing particles was filtered and dried to obtain Particles 1 . The obtained particles 1 were spherical particles having an average particle diameter of 25 μm and a glass transition temperature of -39°C.

Preparation method of Particle 2 Particles except that colloidal silica having a silica active ingredient of 20% by mass is changed to 30 parts by mass, n-butyl acrylate is 91 parts by mass, and polybutadiene diacrylate having a weight average molecular weight of 10000 is changed to 5 parts by mass. Particles 2 were obtained by adjusting in the same manner as in 1. The obtained particles 2 were spherical particles having an average particle diameter of 12 μm and a glass transition temperature of -35°C.

Preparation Method of Particle 3 Particle 3 was obtained in the same manner as Particle 1, except that 96 parts by mass of n-butyl acrylate and 0 parts by mass of polybutadiene diacrylate having a weight average molecular weight of 10,000 were used. The obtained particles 3 were spherical particles having an average particle diameter of 28 μm and a glass transition temperature of -40°C.

Preparation Method of Particle 4 Particle 4 was obtained in the same manner as Particle 1 except that 96 parts by mass of n-butyl acrylate and 0 parts by mass of PEG#400 diacrylate were used. The obtained particles 4 were spherical particles having an average particle diameter of 35 μm and a glass transition temperature of -41°C.

The glass transition temperature of the obtained particles is measured by differential scanning calorimetry (DSC) under the condition of a temperature increase rate of 20° C./min in a thermogram, and taken as the temperature at the midpoint of the transition region. The average particle diameter of the obtained particles is the average value obtained by measuring the particle diameters of at least 100 particles from a microscopic observation image taken at a magnification of 1,000 to 5,000.

As is clear from Tables 1 and 2, the rubber compositions for tires of Examples 1 to 11 exhibit better performance on ice than Standard Example 1, while exhibiting excellent performance equal to or greater than that of Standard Example 1 containing no particles. Demonstrates wear resistance performance and achieves a high degree of compatibility between these performances. On the other hand, in Comparative Examples 1 and 2, since the particles 3 containing no monomer (B), that is, the diene-based monomer, were used, the abrasion resistance performance was deteriorated. In Comparative Example 3, since the amount of the white filler mixed was small, the abrasion resistance performance was deteriorated. In Comparative Example 4, since the amount of particles mixed was too large, the abrasion resistance performance was deteriorated.

Claims (9)

A studless tire rubber composition comprising 100 parts by mass of a diene rubber, 30 parts by mass or more of a white filler, and 0.5 to 30 parts by mass of particles having a glass transition temperature of -70°C to 0°C. There is
the particles are composed of a polymer of a monomer mixture containing a monomer (A), a monomer (B), and a monomer (C);
The monomer (A) is a monofunctional (meth)acrylic acid ester-based monomer,
The monomer (B) is a diene-based monomer,
The monomer (C) is a polyfunctional vinyl monomer other than the monomer (B),
The mass ratio of the monomer (A) in the monomer mixture is 80% by mass to 99.5% by mass, and the mass ratio of the monomer (B) in the monomer mixture is 0.1% by mass to 5% by mass. A rubber composition for a studless tire, wherein the mass ratio of the monomer (C) in the monomer mixture is 0.4% by mass to 15% by mass. The studless tire according to claim 1, wherein the diene rubber contains polybutadiene rubber and natural rubber, and the content of natural rubber is 30% by mass or more with respect to 100% by mass of the polybutadiene rubber. Rubber composition for 3. The monomer (B) according to claim 1 or 2, wherein the monomer (B) has at least two (meth)acryloyl groups, has a weight average molecular weight of 500 to 50,000, and is represented by the following general formula (1). A rubber composition for studless tires.
R ¹ -OR ² -OR ³ (1)
(In the formula, R ¹ and R ³ are (meth)acryloyl groups, and R ² is a structure containing a polymer chain having a diene as a structural unit.) The rubber composition for a studless tire according to any one of claims 1 to 3, characterized in that the particles have an average particle size of 3 µm to 70 µm. The rubber composition for studless tires according to any one of claims 1 to 4, characterized by having a glass transition temperature of -60°C or lower. The rubber composition for studless tires according to any one of claims 1 to 5, further comprising a liquid polymer having a weight average molecular weight of 1,000 to 100,000. The studless tire rubber composition according to any one of claims 1 to 6, wherein the diene rubber further contains a terminal-modified diene rubber. The rubber composition for studless tires according to any one of claims 1 to 7, further comprising an aromatic modified terpene resin. A studless tire having a tread portion molded from the rubber composition for a studless tire according to any one of claims 1 to 8.