JP2019183032A - Rubber composition for studless tire, and studless tire using the same - Google Patents

Abstract

To overcome a trend in a studless tire of deterioration with time by migration to under tread less in oil amount by blending a large amount of plasticizer to soften a rubber under a situation that on-ice performance and small degradation with time are required.SOLUTION: The above described problem is solved by a rubber composition for studless tire containing a natural rubber and a polybutadiene rubber, in which the polybutadiene rubber contains 1 to 40 pts.mass of liquid polyester (A) having weight average molecular weight of 10000 to 30000 and 1 to 40 pts.mass of a plasticizer component (B) based on 100 pts.mass of a diene rubber containing 30 pts.mass of the polybutadiene rubber, and the liquid polyester (A) is 20 mass% or more based on total amount of the liquid polyester (A) and the plasticizer component (B).SELECTED DRAWING: None

Description

  TECHNICAL FIELD The present invention relates to a rubber composition for studless tires and a studless tire using the same, and more particularly, to a rubber composition for studless tires that can improve performance on ice and suppress physical property changes over time, and studless using the rubber composition. It relates to tires.

Studless tires are expected to have little deterioration over time because they are expected to be used across multiple seasons as well as on-ice performance at the initial use.
However, since studless tire compounds increase the adhesion to the ice surface and improve the frictional force on ice, it is common practice to add a larger amount of plasticizer such as oil to soften the rubber than summer tires. The tread rubber hardness tends to increase due to a change with time due to the oil flowing out to the outside by running or migrating to an under tread with a small amount of oil.

Patent Document 1 below discloses a ricinoleic acid ester copolymer that satisfies specific requirements. However, Patent Document 1 discloses or suggests a technical idea for adding a specific amount of the ricinoleic acid ester copolymer to a rubber composition for studless tires to improve performance on ice and suppress changes in physical properties over time. Not.
Patent Document 2 below discloses a rubber composition in which a ricinoleic acid copolymer having a specific molecular weight is blended with a diene rubber. However, with the rubber composition disclosed in Patent Document 2, it is impossible to simultaneously improve the performance on ice of the studless tire and to suppress changes in physical properties over time.

International Publication WO2017 / 038734 Pamphlet Japanese Patent No. 5458006

  Accordingly, an object of the present invention is to provide a rubber composition for studless tires that can improve performance on ice and at the same time suppress changes in physical properties over time, and a studless tire using the same.

As a result of intensive studies, the present inventors have found that the above-mentioned problems can be solved by blending liquid polyester and a plasticizer component in specific amounts with a diene rubber having a specific composition, thereby completing the present invention. I was able to.
That is, the present invention is as follows.

1. Including 100 parts by mass of diene rubber containing natural rubber and polybutadiene rubber, wherein the polybutadiene rubber occupies 30 parts by mass or more,
1-40 parts by mass of liquid polyester (A) having a weight average molecular weight of 10,000-30000 and 1-40 parts by mass of plasticizer component (B),
The rubber composition for studless tires, wherein the liquid polyester (A) accounts for 20% by mass or more based on the total amount of the liquid polyester (A) and the plasticizer component (B).
2. 2. The rubber composition for studless tires according to 1 above, wherein the liquid polyester (A) has a glass transition temperature of −60 ° C. or lower.
3. 3. The rubber composition for studless tire according to 1 or 2 above, wherein the constituent component of the liquid polyester (A) contains a fatty acid having a hydroxyl group in the molecule.
4). 4. The rubber composition for studless tires according to 3 above, wherein the fatty acid having a hydroxyl group in the molecule is ricinoleic acid.
5. The liquid polyester (A) includes a structural unit (a) derived from ricinoleic acid, a structural unit (b) derived from an aliphatic dicarboxylic acid, and a structural unit (c) derived from a diol having 2 to 10 carbon atoms. The rubber composition for studless tires as described in any one of 1 to 4 above, which comprises:
6). The rubber composition for studless tires according to any one of 1 to 5, further comprising 0.5 to 20 parts by mass of thermally expandable microcapsules with respect to 100 parts by mass of the diene rubber.
7). The rubber composition for studless tires according to any one of 1 to 6, further comprising 20 parts by mass or more of an inorganic filler with respect to 100 parts by mass of the diene rubber.
8). A studless tire using the rubber composition according to any one of 1 to 7 as a tread.

The rubber composition of the present invention includes natural rubber and polybutadiene rubber, and 1 part of liquid polyester (A) having a weight average molecular weight of 10,000 to 30,000 is 100 parts by mass of the diene rubber in which the polybutadiene rubber occupies 30 parts by mass or more. 1 to 40 parts by mass and 1 to 40 parts by mass of the plasticizer component (B), and the total amount of the liquid polyester (A) and the plasticizer component (B) is 20% by mass or more of the liquid polyester (A). Therefore, the rubber composition is useful as a rubber composition for a studless tire that can improve performance on ice and at the same time suppress changes in physical properties over time.
Moreover, the studless tire using the rubber composition of the present invention for the tread has a high on-ice performance, and the tread rubber is caused by oil flowing out to the outside by traveling or migrating to the under tread. Changes in physical properties over time can also be suppressed.

  Hereinafter, the present invention will be described in more detail.

The diene rubber used in the present invention includes natural rubber (NR) and polybutadiene rubber (BR) from the viewpoint of improving the performance on ice, and the polybutadiene rubber when the total amount of the diene rubber is 100 parts by mass. Needs to occupy 30 parts by mass or more. A preferable blending ratio is 70 to 30 parts by mass of NR and 30 to 70 parts by mass of BR in 100 parts by mass of the diene rubber. In addition to NR and BR, any diene rubber that can be blended into the rubber composition can be used as necessary, for example, styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer. Polymer rubber (NBR), ethylene-propylene-diene terpolymer (EPDM) or the like may be blended. In the diene rubber used in the present invention, its molecular weight and microstructure are not particularly limited, and it may be terminally modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group, or epoxidized. Good.
The synthetic isoprene rubber (IR) is included in the NR referred to in the present invention.

  In addition, the diene rubber used in the present invention preferably has an average glass transition temperature (average Tg) of −60 ° C. or less from the viewpoint of enhancing performance on ice.

(Liquid polyester (A))
The liquid polyester (A) used in the present invention is liquid at room temperature (23 ° C.) and is not particularly limited as long as the weight average molecular weight is 10,000 to 30,000, and further improves the performance on ice, and From the viewpoint that the change in physical properties over time can be further suppressed, the constituent component preferably contains a fatty acid having a hydroxyl group in the molecule, and more preferably the fatty acid having a hydroxyl group in the molecule is ricinoleic acid. Specifically, the liquid polyester (A) is particularly preferably a ricinoleic acid ester copolymer (A1).

(Ricinolic acid ester copolymer (A1))
The ricinoleic acid ester copolymer (A1) used in the present invention may be composed of a structural unit derived from ricinoleic acid and a monomer copolymerizable therewith.
In the present invention, the ricinoleic acid ester copolymer (A1) is composed of a structural unit (a) derived from ricinoleic acid, a structural unit (b) derived from an aliphatic dicarboxylic acid, and a diol having 2 to 10 carbon atoms. The derived structural unit (c) is preferably included.

  The structural unit (a) derived from ricinoleic acid in the present invention (hereinafter sometimes simply referred to as “structural unit (a)”) is ricinoleic acid (12-hydroxy-cis-9-octadecenoic acid) or ricinol. It is a structural unit derived from an acid derivative.

  Examples of derivatives of ricinoleic acid include condensates of ricinoleic acid, esterified products of ricinoleic acid and carboxylic acid, esterified products of ricinoleic acid and alcohols (for example, ricinoleic acid methyl ester), and a reaction product of ricinoleic acid and an epoxy compound. 12-hydroxystearic acid hydrogenated from ricinoleic acid and its condensates, esterified products of 12-hydroxystearic acid and carboxylic acids or alcohols (for example, 12-hydroxystearic acid methyl ester), etc. Examples thereof include various compounds that give the derived structural unit (a).

  Thus, since the derivative of ricinoleic acid includes 12-hydroxystearic acid and its ester, the structural unit (a) in the present invention is specifically represented by the following formula (1) or It is a structural unit represented by Formula (2).

  Here, the ratio of the total of the structural units derived from 12-hydroxystearic acid and its ester derivatives in all the structural units (a), that is, the structure represented by the above formula (2) in all the structural units (a). The proportion of the total of the units is not particularly limited, and the total of the structural units (a) derived from ricinoleic acid (that is, the structural unit represented by the above formula (1) and the structural unit represented by the above formula (2)) Is 100 mol%, the structural unit derived from ricinoleic acid (a) includes the structural unit represented by the above formula (1). It is preferable. In that sense, the above ratio is preferably 0 to 80 mol%, and more preferably 0 to 60 mol%.

  The structural unit (b) derived from an aliphatic dicarboxylic acid (hereinafter sometimes simply referred to as “structural unit (b)”) is derived from an aliphatic dicarboxylic acid or an aliphatic dicarboxylic acid ester. Specifically, the structural unit (b) referred to in the present invention is a structural unit having a structure in which —OH is excluded from two carboxyl groups contained in the aliphatic dicarboxylic acid.

  The aliphatic dicarboxylic acid is not particularly limited as long as it has no other functional group having reactivity in the system in which the ester polymerization reaction is performed, for example, a hydroxyl group, and may be used alone or in combination of two or more. Specifically, malonic acid (3 carbon atoms), dimethyl malonic acid (5 carbon atoms), succinic acid (4 carbon atoms), glutaric acid (5 carbon atoms), adipic acid (6 carbon atoms) 2-methyladipic acid (7 carbon atoms), trimethyladipic acid (9 carbon atoms), pimelic acid (7 carbon atoms), 2,2-dimethylglutaric acid (7 carbon atoms), 3,3- Examples include diethyl succinic acid (8 carbon atoms), suberic acid (8 carbon atoms), azelaic acid (9 carbon atoms), sebacic acid (10 carbon atoms), and the like. On the other hand, examples of the aliphatic dicarboxylic acid ester include various esters of the above aliphatic dicarboxylic acid.

  Of these, aliphatic dicarboxylic acids having 6 to 12 carbon atoms are preferred, and sebacic acid is particularly preferred.

  In the present specification, the monomer component corresponding to the structural unit (b), that is, the aliphatic dicarboxylic acid and the aliphatic dicarboxylic acid ester may be referred to as “aliphatic dicarboxylic acid component (b ′)”. .

  Specifically, the structural unit (c) derived from the diol having 2 to 10 carbon atoms (hereinafter sometimes simply referred to as “structural unit (c)”) has 2 to 10 carbon atoms in terms of form. It is a structural unit having a structure obtained by removing -H from two hydroxyl groups contained in the diol. As the diol having 2 to 10 carbon atoms for leading the structural unit (c), one kind may be used alone, or two or more kinds may be used in combination. Specific examples include the following compounds.

  Examples of the diol having 2 to 10 carbon atoms include aliphatic diols having 2 to 10 carbon atoms. Examples of such aliphatic diols include 1,2-ethanediol (ethylene glycol: 2 carbon atoms), 1,3-propanediol (trimethylene glycol: 3 carbon atoms), 1,2-propanediol ( Propylene glycol: 3 carbon atoms, 1,4-butanediol (tetramethylene glycol: 4 carbon atoms), 2,2-dimethylpropane-1,3-diol (neopentyl glycol: 5 carbon atoms), 1 , 6-hexanediol (hexamethylene glycol: 6 carbon atoms), 1,8-octanediol (octamethylene glycol: 8 carbon atoms), 1,9-nonanediol (nonamethylene glycol: 9 carbon atoms), etc. Is mentioned.

  Among these aliphatic diols, side chain alkyl group-containing glycols include 2-methyl-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-hexyl-1,3-propanediol, 2-hexyl-1,6-propanediol, neopentyl glycol, 2-ethyl-2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-methyl-2-n -Butyl-1,3-propanediol, 1,3-nonanediol, 2-methyl-1,8-octanediol, and the like.

  Among the above diols, 1,4-butanediol is particularly preferable.

  The ricinoleic acid ester copolymer (A1) used in the present invention is preferably composed only of the structural units (a) to (c). However, the structural unit is not limited as long as the effects of the present invention are not impaired. A structural unit that does not fall under any of (a) to (c) (hereinafter referred to as “other structural unit”) may be further included. Other structural units include furandicarboxylic acid such as 2,5-furandicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, alicyclic dicarboxylic acid such as 1,3-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, 2 A structural unit derived from various dicarboxylic acids and carboxylic acid esters not corresponding to the aliphatic dicarboxylic acid component (b ′), such as aromatic dicarboxylic acids such as methyl terephthalic acid and naphthalenedicarboxylic acid, and having 11 or more carbon atoms A structural unit derived from an aliphatic diol, a structural unit derived from an aromatic diol, a trihydric or higher polyhydric alcohol such as trimethylolethane or glycerin, a trivalent or higher polyvalent carboxylic acid such as butanetricarboxylic acid or trimellitic acid Examples include acids and oxydicarboxylic acids such as 4-hydroxyphthalic acid.

  When the total of the structural units (a), (b) and (c) is 100 mol%, the content of the structural unit (a) is 20 to 90 mol%, and the content of the structural unit (b) is 5 to 5 mol%. It is preferable that the content of the structural unit (c) is 40 to 40 mol% and 5 to 40 mol%.

Moreover, it is preferable that molar ratio ((b) / (c)) of the said structural unit (b) and the said structural unit (c) is 0.9-1.1.
When other structural units are included, the total of the structural units (a) to (c) and the other structural units is 100 mol%, and the other structural units are preferably 20 mol% or less, more preferably It is 10 mol% or less, particularly preferably 5 mol% or less.

The contents of the structural units (a) to (c) and “other structural units” in the ricinoleic acid ester copolymer (A1) can be determined by an appropriate technique such as NMR.
Moreover, the manufacturing method of a ricinoleic acid ester copolymer (A1) is well-known, For example, it is disclosed by international publication WO2017 / 038734 pamphlet.

  The liquid polyester (A) used in the present invention, particularly the ricinoleic acid ester copolymer (A1), preferably has a glass transition temperature (Tg) of −60 ° C. or lower. When Tg exceeds −60 ° C., the hardness of rubber at low temperatures increases, and the performance on ice may deteriorate. Further preferable Tg is −65 ° C. or less.

Moreover, it is preferable that the weight average molecular weights (GPC method) of the liquid polyester (A) used by this invention used by this invention, especially a ricinoleic acid ester copolymer (A1) are 10,000-30000. If the weight average molecular weight is less than 10,000, the performance on ice over time may be deteriorated. Conversely, if it exceeds 30000, the rubber becomes hard and the performance on ice may be deteriorated.
In addition, the weight average molecular weight of the ricinoleic acid ester copolymer (A1) used in the present invention is preferably 12000 to 19500 from the viewpoint of further improving the performance on ice and further suppressing the change in physical properties with time.
Since the ricinoleic acid ester copolymer (A1) used in the present invention has the specific weight average molecular weight range as described above, it can be stably dispersed in the diene rubber, and the hardness of the rubber , And the performance on ice can be improved, and it can be prevented that it flows out to the outside by traveling and migrates to an undertread with a small amount of oil.

  The compounding quantity of liquid polyester (A) is 1-40 mass parts with respect to 100 mass parts of diene rubbers, Preferably it is 3-35 mass parts. When the blending amount of the liquid polyester (A) is less than 1 part by mass, the blending amount is too small to obtain the effect of the present invention. Conversely, when it exceeds 40 mass parts, the on-ice performance will deteriorate.

(Plasticizer component (B))
Examples of the plasticizer component (B) used in the present invention include oils, plasticizers, softeners, processing aids, petroleum resins, and aromatic resins. These plasticizer components may be contained singly or in combination. The oil may be an oil-extended component added when producing a diene rubber, or an oil added when preparing a rubber composition.

  In this specification, petroleum-based resins are aromatic hydrocarbon resins produced by polymerizing components obtained by treating crude oil by distillation, decomposition, reforming, etc., or saturated or unsaturated aliphatic carbonization. Hydrogen resin. Examples of petroleum resins include C5 petroleum resins (aliphatic petroleum resins obtained by polymerizing fractions such as isoprene, 1,3-pentadiene, cyclopentadiene, methylbutene, and pentene), C9 petroleum resins (α-methylstyrene, o -Aromatic petroleum resin obtained by polymerizing fractions such as vinyltoluene, m-vinyltoluene, p-vinyltoluene), C5C9 copolymerized petroleum resin, and the like.

  The aromatic resin is a polymer having at least one segment composed of an aromatic hydrocarbon, such as coumarone resin, phenol resin, alkylphenol resin, terpene resin, rosin resin, novolac resin, resole resin, etc. Can be mentioned.

  The average glass transition temperature of the plasticizer component (B) is, for example, −45 ° C. or less, preferably −48 ° C. to −65 ° C. By setting the average glass transition temperature of the plasticizer component to −45 ° C. or less, it is possible to maintain the flexibility of the rubber compound at a low temperature, increase the adhesion force to the ice surface, and improve the performance on ice.

  The average glass transition temperature mentioned in the present specification is a value calculated based on the sum of products obtained by multiplying the glass transition temperature of each component by the weight fraction of each component, that is, a weighted average. In the calculation, the total of the weight fractions of each component is 1.0. The glass transition temperature is determined by differential scanning calorimetry (DSC) by measuring a thermogram under a temperature increase rate condition of 20 ° C./min and setting it as the midpoint temperature of the transition region.

  The compounding quantity of a plasticizer component (B) is 1-40 mass parts with respect to 100 mass parts of diene rubbers, Preferably it is 3-35 mass parts. If the blending amount of the plasticizer component (B) is less than 1 part by mass, the blending amount is too small to obtain the effects of the present invention. Conversely, if it exceeds 40 parts by mass, the performance on ice will deteriorate over time.

  In this invention, it is necessary for the said liquid polyester (A) to occupy 20 mass% or more with respect to the total amount of the said liquid polyester (A) and the said plasticizer component (B). If the ratio of the liquid polyester (A) is less than 20% by mass, the effects of the present invention cannot be achieved.

(Thermal expansion microcapsule)
In the present invention, the thermally expandable microcapsule has a structure in which a thermally expandable substance is encapsulated in a shell material formed of a thermoplastic resin. The shell material of the thermally expandable microcapsule can be formed of a nitrile polymer.
In addition, the thermally expandable substance encapsulated in the shell of the microcapsule has a property of being vaporized or expanded by heat, and examples thereof include at least one selected from the group consisting of hydrocarbons such as isoalkane and normal alkane. Examples of isoalkanes include isobutane, isopentane, 2-methylpentane, 2-methylhexane, 2,2,4-trimethylpentane, and examples of normal alkanes include n-butane, n-propane, n-hexane, Examples thereof include n-heptane and n-octane. These hydrocarbons may be used alone or in combination. As a preferable form of the thermally expandable substance, a substance obtained by dissolving a hydrocarbon which is gaseous at normal temperature in a hydrocarbon which is liquid at normal temperature is preferable. By using such a mixture of hydrocarbons, a sufficient expansion force can be obtained from the low temperature region to the high temperature region in the vulcanization molding temperature range (150 ° C. to 190 ° C.) of the unvulcanized tire.
Examples of such thermally expandable microcapsules include trade names “EXPANCEL 091DU-80” and “EXPANEL 092DU-120” manufactured by EXPANSEL, Sweden, or trade names “Matsumoto Micros Co., Ltd. “Fair F-85D” or “Matsumoto Microsphere F-100D” or the like can be used.
The compounding quantity of a thermally expansible microcapsule is 0.5-20 mass parts with respect to 100 mass parts of diene rubbers, Preferably it is 1-18 mass parts.

(Inorganic filler)
Examples of the inorganic filler used in the present invention include silica, clay, mica, talc, shirasu, calcium carbonate, magnesium carbonate, aluminum hydroxide, barium sulfate and the like.
The compounding quantity of an inorganic filler is 20 mass parts or more with respect to 100 mass parts of diene rubbers, Preferably it is 30-120 mass parts.

(Carbon black)
In the present invention, carbon black can also be used. From the viewpoint of improving the effect of the present invention, the nitrogen adsorption specific surface area (N ₂ SA) is preferably 50 to 250 m ² / g. The nitrogen adsorption specific surface area (N ₂ SA) is a value determined in accordance with JIS K6217-2.
The compounding quantity of carbon black is 3-70 mass parts with respect to 100 mass parts of diene rubbers, Preferably it is 5-60 mass parts.

  In the rubber composition of the present invention, in addition to the above-described components, various types of rubber compositions such as vulcanization or cross-linking agents, vulcanization or cross-linking accelerators, various fillers, anti-aging agents, etc. An additive can be blended, and the additive can be kneaded by a general method to form a composition, which can be used for vulcanization or crosslinking. The blending amounts of these additives can be set to conventional general blending amounts as long as the object of the present invention is not violated.

  The rubber composition of the present invention is suitable for producing a pneumatic tire according to a conventional method for producing a pneumatic tire, and is preferably applied to a tread of a studless tire, particularly a cap tread.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, this invention is not restrict | limited to the following example.

Standard example, Examples 1 to 3 and Comparative Examples 1 to 7
Sample preparation In the formulation (parts by mass) shown in Table 1, the components except the vulcanization accelerator and sulfur were kneaded for 5 minutes in a 1.7 liter closed Banbury mixer, then the rubber was discharged outside the mixer and cooled to room temperature. I let you. Next, the rubber, vulcanization accelerator and sulfur were added to the Banbury mixer and further kneaded to obtain a rubber composition. Next, the obtained rubber composition was press vulcanized in a predetermined mold at 170 ° C. for 10 minutes to obtain a vulcanized rubber test piece, and the physical properties of the vulcanized rubber test piece were measured by the following test method.

Migration Evaluation: Rubber from which a compound of a vulcanized rubber test piece having a diameter of 45 mm and a thickness of 6 mm and a vulcanized sheet piece (A), a ricinoleic acid ester copolymer (A1) and a plasticizer component (B) is omitted. A circular vulcanized sheet piece (b) having a diameter of 45 mm and a thickness of 6 mm similarly produced from the composition was superposed, a load of 40 g / cm ² was applied thereto, and the temperature was kept at 20 ± 2 ° C. and humidity. Left in a 65% room for 5 weeks. The weight of the vulcanized sheet piece (B) before and after being left was measured, and the increase rate was calculated. The results are shown as an index with the standard example being 100. A smaller index value indicates less migration.
Performance on ice: Pneumatic tires of tire size 215 / 60R16 with various vulcanized rubber test pieces incorporated in the tread are assembled into a 16 × 7J rim, filled with air pressure (220 [kPa]), and tested vehicle (domestic 2 liters) It was mounted on a sedan FF vehicle. Subsequently, the braking distance from the initial speed of 40 [km / h] to the complete stop was measured by the test vehicle on the test course which is an ice board road. The results are shown as an index with the standard example being 100. A larger index means better performance on ice.
The results are shown in Table 1.

* 1: NR (Tg = -65 ° C)
* 2: BR (Nipol BR1220 manufactured by Nippon Zeon Co., Ltd., Tg = −105 ° C.)
* 3: Carbon black (N339 manufactured by Cabot Japan Co., Ltd.)
* 4: Silica (ZEOSIL 1165MP manufactured by Rhodia)
* 5: Silane coupling agent (Si69 manufactured by Evonik Japan Co., Ltd.)
* 6: Oil (Extract No. 4 S manufactured by Showa Shell Sekiyu KK)
* 7: Ricinoleic acid ester copolymer 1 (copolymer composed of ricinoleic acid, sebacic acid and 1,4-butanediol synthesized by the method disclosed in the pamphlet of International Publication No. WO2017 / 038734. Tg = −74 ° C, weight average molecular weight = 20000)
* 8: Ricinoleic acid ester copolymer 2 (copolymer composed of ricinoleic acid, sebacic acid and 1,4-butanediol synthesized by the method disclosed in International Publication WO2017 / 038734 pamphlet. Tg = −73 ° C, weight average molecular weight = 6000)
* 9: Ricinoleic acid ester copolymer 3 (copolymer composed of ricinoleic acid, sebacic acid and 1,4-butanediol, synthesized by the method disclosed in the pamphlet of International Publication No. WO2017 / 038734. Tg = −70 ° C, weight average molecular weight = 50000)
* 10: Thermally expandable microcapsules (Matsumoto Microsphere F-100D manufactured by Matsumoto Yushi Seiyaku Co., Ltd.)
* 11: Sulfur (Tsurumi Chemical Industry Co., Ltd. Jinhua Indian Oil Fine Powdered Sulfur, Sulfur content = 95.24% by mass)
* 12: Vulcanization accelerator (CBS) (SANSYS CBS manufactured by Flexsys)
* 13: Vulcanization accelerator (DPG) (Sokucinol DG manufactured by Sumitomo Chemical Co., Ltd.)

As apparent from Table 1 above, in the rubber compositions prepared in Examples 1 to 3, the polybutadiene rubber accounts for 30 parts by mass or more, and 100 parts by mass of the diene rubber containing natural rubber is liquid polyester ( Since the ricinoleic acid ester copolymer (A1) which is A) is blended in the range of 1 to 40 parts by mass and the plasticizer component (B) in the range of 1 to 40 parts by mass, the migration is compared with the rubber composition of the standard example. It can be seen that both evaluation and performance on ice can be improved.
In contrast, in Comparative Example 1, the ratio of the component (A) is less than the lower limit defined in the present invention with respect to the total amount of the ricinoleic acid ester copolymer (A1) and the plasticizer component (B). Both evaluation and performance on ice have not improved.
In Comparative Example 2, since the plasticizer component (B) was not blended, the performance on ice deteriorated.
Since the comparative example 3 did not mix | blend the ricinoleic acid ester copolymer (A1), the on-ice performance deteriorated.
In Comparative Example 4, the weight average molecular weight of the ricinoleic acid ester copolymer (A1) was less than the lower limit specified in the present invention, and the plasticizer component (B) was not blended, so the migration evaluation deteriorated.
Since the weight average molecular weight of the ricinoleic acid ester copolymer (A1) exceeded the upper limit prescribed | regulated by this invention and the plasticizer component (B) was not mix | blended with the comparative example 5, performance on ice deteriorated.
In Comparative Example 6, since the weight average molecular weight of the ricinoleic acid ester copolymer (A1) was less than the lower limit specified in the present invention, the migration evaluation was deteriorated.
Since the weight average molecular weight of the ricinoleic acid ester copolymer (A1) exceeded the upper limit prescribed | regulated by this invention, the comparative example 7 deteriorated on-ice performance.

Claims (8)

Including 100 parts by mass of diene rubber containing natural rubber and polybutadiene rubber, wherein the polybutadiene rubber occupies 30 parts by mass or more,
1-40 parts by mass of liquid polyester (A) having a weight average molecular weight of 10,000-30000 and 1-40 parts by mass of plasticizer component (B),
The rubber composition for studless tires, wherein the liquid polyester (A) accounts for 20% by mass or more based on the total amount of the liquid polyester (A) and the plasticizer component (B).   The rubber composition for a studless tire according to claim 1, wherein the liquid polyester (A) has a glass transition temperature of -60 ° C or lower.   The rubber composition for studless tire according to claim 1 or 2, wherein the constituent component of the liquid polyester (A) contains a fatty acid having a hydroxyl group in the molecule.   The rubber composition for studless tire according to claim 3, wherein the fatty acid having a hydroxyl group in the molecule is ricinoleic acid.   The liquid polyester (A) includes a structural unit (a) derived from ricinoleic acid, a structural unit (b) derived from an aliphatic dicarboxylic acid, and a structural unit (c) derived from a diol having 2 to 10 carbon atoms. The rubber composition for studless tires according to any one of claims 1 to 4, characterized by comprising:   The rubber composition for studless tires according to any one of claims 1 to 5, further comprising 0.5 to 20 parts by mass of thermally expandable microcapsules with respect to 100 parts by mass of the diene rubber.   The rubber composition for studless tires according to any one of claims 1 to 6, further comprising 20 parts by mass or more of an inorganic filler with respect to 100 parts by mass of the diene rubber.   A studless tire using the rubber composition according to claim 1 for a tread.