JP2011162625A - Rubber composition for tire tread and pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve balance of wet grip property and low temperature performance while suppressing close-adhesion to a roll. <P>SOLUTION: In the rubber composition for the tire tread containing a diene-based rubber as a rubber component, the rubber component contains 10-50 mass% of a polybutadiene rubber and contains a modified styrene-butadiene copolymer rubber in which a functional group including a hetero atom is introduced. Further, an average value of a glass transition temperature (Tg) of the rubber component is -50°C or lower and 0.5-10 pts.mass of a rosin-modified maleic acid resin is formulated based on 100 pts.mass of the rubber component. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a rubber composition for a tire tread used for a tread of a pneumatic tire, and a pneumatic tire using the same.

  Rubber compositions used for pneumatic tires, especially all-season tire treads, not only have excellent grip performance on wet road surfaces (wet grip properties), but also are hard to harden even in winter and do not deteriorate grip performance. Performance is required.

  Conventionally, as a technique for improving wet grip properties, for example, a technique for increasing hysteresis loss by increasing the amount of filler and oil, or a styrene-butadiene copolymer having a high styrene content and a high glass transition temperature (Tg). There are methods using polymer rubber. However, when the blending amount of the filler and oil is increased, or when a polymer having a high Tg is used, wear resistance and low temperature performance are deteriorated. Therefore, these methods cannot achieve both wet grip properties and low temperature performance.

  On the other hand, it is known to add a tackifier to a rubber composition, and as disclosed in Patent Document 1 below, rosin ester as a tackifier has improved the cut resistance of a tire tread. To make it.

  Conventionally, it is also known to add a tackifier to improve grip performance. For example, in Patent Document 2 below, styrene-butadiene copolymer rubber having a styrene content of 10 to 50% by mass is added to styrene. It is disclosed that a hydrogenated styrene butadiene copolymer rubber having a content of 25 to 70% by mass and an adhesive resin such as a rosin resin are blended. In Patent Document 3 listed below, a rubber component containing a styrene-butadiene copolymer rubber having a styrene content of 20 to 60% by mass has a freezing point of −25 ° C. in order to exhibit high grip performance in both a low temperature range and a high temperature range. It is disclosed that the following plasticizer and a resin having a softening point of 50 to 150 ° C. (for example, maleic acid resin) are combined and blended.

  Patent Document 4 below discloses that in a rubber composition used for a studless tire, a diene rubber is blended with a resin having an acid value of 40 or more together with silica and thermally expandable microcapsules. In this document, rosin-modified maleic acid resin is listed as an example of the resin, but the resin is used to improve the deterioration of workability due to shrinkage due to silica compounding.

JP-A-10-287768 JP 2003-253051 A JP 2004-137463 A JP 2006-152021 A

  Although it has been conventionally known to add a tackifier to improve grip properties as described above, a low Tg diene rubber containing polybutadiene rubber and a modified styrene butadiene copolymer rubber is modified with rosin. It has not been known to improve the balance between wet grip properties and low temperature performance while suppressing excessive adhesion to a roll, which is a disadvantage of a tackifier, by using a maleic acid resin.

  The present invention has been made in view of the above points, and provides a rubber composition for a tire tread that can improve the balance between wet grip properties and low temperature performance while suppressing excessive adhesion to a roll. Objective.

  In view of the above problems, the present inventor has been diligently studying the improvement of the balance between wet grip properties and low temperature performance by using a tackifier, and has a low Tg diene system including polybutadiene rubber and modified styrene butadiene copolymer rubber. It has been found that by blending a rosin-modified maleic resin with a rubber compound, the balance between wet grip and low temperature performance can be greatly improved while suppressing excessive adhesion to the roll, which is a disadvantage of the tackifier. It came to complete.

  That is, the rubber composition for a tire tread according to the present invention uses a diene rubber as a rubber component, and the rubber component contains 10 to 50% by mass of polybutadiene rubber and is modified by introducing a functional group containing a hetero atom. The rubber component contains a styrene-butadiene copolymer rubber, the average value of the glass transition temperature (Tg) of the rubber component is −50 ° C. or less, and the rosin-modified maleic resin is 0 with respect to 100 parts by mass of the rubber component. It contains 5 to 10 parts by mass.

  The pneumatic tire according to the present invention includes a tread made using such a rubber composition.

  According to the present invention, the balance between wet grip properties and low temperature performance can be greatly improved while suppressing excessive adhesion to the roll.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  The rubber composition for a tire tread according to the present invention comprises a diene rubber as a rubber component and a rosin-modified maleic acid resin. The rubber component includes polybutadiene rubber (BR) and a hetero atom. And a modified styrene-butadiene copolymer rubber (SBR) into which a functional group is introduced.

  The polybutadiene rubber (BR) is not particularly limited, but it is preferable to use a high cis type polybutadiene rubber having a cis-1,4 bond content of 92% or more. In the high cis type, it is possible to suppress an increase in the rubber elastic modulus due to crystallization of the polymer in a low temperature region, and the low temperature performance can be further improved. The cis-1,4 bond content is a value measured using a nuclear magnetic resonance apparatus (NMR).

  The said polybutadiene rubber is mix | blended in 10-50 mass% as a ratio which occupies in a rubber component. When the ratio of the polybutadiene rubber is less than 10% by mass, it is difficult to ensure low temperature performance. On the other hand, when the ratio of the polybutadiene rubber exceeds 50% by mass, the blending amount of the modified styrene butadiene copolymer rubber may be reduced, or the glass transition temperature may be too low, thereby impairing wet grip properties. The ratio of the polybutadiene rubber in the rubber component is more preferably 20 to 40% by mass.

  The modified styrene butadiene copolymer rubber is a styrene butadiene copolymer rubber (SBR) in which a functional group containing a hetero atom is introduced, and the functional group is introduced into a polymer terminal of the styrene butadiene copolymer rubber. Or may be introduced into the polymer chain. By using such modified SBR, it is presumed that the dispersibility of the rosin-modified maleic acid resin in the matrix rubber is improved by the interaction with the functional group of the rosin-modified maleic acid resin. Balance can be improved.

  The functional group is not particularly limited as long as it contains a hetero atom, but a hydroxyl group (—OH), amino group, carboxyl group (—COOH), alkoxyl group (—OR, where R is an alkyl group), epoxy Group, cyano group (—CN), halogen and the like, and each of these may be introduced alone or in combination of two or more. Among these, particularly preferred functional groups are a hydroxyl group, an amino group, a carboxyl group, and an alkoxyl group. The amino group may be not only a primary amino group but also a secondary or tertiary amino group. Examples of the alkoxyl group include a methoxy group, an ethoxy group, a propoxy group, and a butoxy group. Furthermore, examples of the halogen include fluorine, chlorine, bromine and iodine, with chlorine and bromine being preferred.

  Modified SBR itself having such a functional group is known, and its production method and the like are not limited. For example, the functional group may be introduced by modifying SBR synthesized by anionic polymerization with a modifier. Alternatively, the monomer having the functional group may be replaced with a monomer constituting the base polymer. You may introduce | transduce into a polymer chain by copolymerizing with a certain styrene and butadiene.

Although it does not specifically limit as modified | denatured SBR, It is preferable that it is solution polymerization SBR (S-SBR). Moreover, it is preferable that the glass transition temperature (Tg) is -70 to -10 degreeC, More preferably, it is -60 to -20 degreeC. Furthermore, it is preferable that a styrene content (St) is 5-50 mass%, More preferably, it is 10-40 mass%. The glass transition temperature is a value measured by a differential scanning calorimetry (DSC) method in accordance with JIS K7121 at a rate of temperature increase of 20 ° C./minute (measurement temperature range: −150 ° C. to 50 ° C.). is there. The styrene content is a value calculated by an integration ratio of ¹ HNMR spectrum.

  The ratio of the modified SBR to the rubber component is preferably 10 to 80% by mass, more preferably 20 to 60% by mass. If the ratio of the modified SBR is too small, the effect of improving the balance between the wet grip property and the low temperature performance due to the interaction with the rosin-modified maleic resin may be insufficient.

  In the rubber component, other diene rubbers other than the polybutadiene rubber and the modified SBR described above may be blended as the third polymer component. Examples of such third polymer component include unmodified styrene butadiene copolymer rubber (SBR), natural rubber (NR), polyisoprene rubber (IR), acrylonitrile-butadiene rubber (NBR), chloroprene rubber ( CR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer, or a combination of two or more thereof, and the like, and is not particularly limited. Preferably, unmodified SBR is used.

The rubber component has an average value of glass transition temperature (Tg) of −50 ° C. or lower. By blending a rosin-modified maleic resin into such a soft polymer system having a low average Tg, combined with the above-mentioned effects by using modified SBR, it is advantageous to balance wet grip properties and low-temperature performance. Can be improved. The average value of Tg is preferably −80 to −50 ° C., more preferably −70 to −55 ° C., and still more preferably −65 to −55 ° C. Here, the average value of Tg is a value obtained by the following formula (1).

  As the rosin-modified maleic resin blended with the rubber component, a polyester resin obtained from a rosin-maleic acid adduct and a polyhydric alcohol can be used. More specifically, a polyhydric alcohol is added to an adduct obtained by the Diels-Alder reaction of rosin (natural resin mainly composed of abietic acid, pimaric acid, colophenoic acid, etc.) and maleic acid (generally maleic anhydride). What is obtained by carrying out heat condensation is mentioned. Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, glycerin, pentaerythritol and the like.

  The compounding amount of the rosin-modified maleic resin is 0.5 to 10 parts by mass with respect to 100 parts by mass of the rubber component. If the amount is too small, the effect of improving the balance between wet grip properties and low-temperature performance becomes insufficient, and the effect of improving wet grip properties may be impaired. Conversely, if the amount is too large, the low temperature performance may be impaired. A more preferable blending amount of the rosin-modified maleic resin is 3 to 8 parts by mass with respect to 100 parts by mass of the rubber component.

  The softening point of the rosin-modified maleic resin is not particularly limited, but is preferably in the range of 70 to 150 ° C, more preferably 80 to 120 ° C. If the softening point is too high, it is difficult to sufficiently improve the initial grip performance. Conversely, if the softening point is too low, it is difficult to sufficiently improve the grip performance after heat generation. Here, the softening point is a value measured by a ring and ball dropping method in accordance with JIS K2207.

  Commercially available products of rosin-modified maleic resin include, for example, Harimac R-80 (softening point = 80 to 90 ° C.), Harimac T-80 (softening point = 80 to 90 ° C.), Harimac R-100 (softening point = 100). -110 ° C), Harimac M-453 (softening point = 100-110 ° C), Harimac 145P (softening point = 135-145 ° C) (above, manufactured by Harima Chemical Co., Ltd.) and the like.

  The rubber composition according to the present invention preferably contains silica as a filler. Wet grip properties can be improved by using silica. In particular, in the present invention, since the modified SBR is used for the rubber composition as described above, the dispersibility of the silica can be improved by the interaction between the functional group and the silanol group of the silica. Can be demonstrated.

The silica is not particularly limited, and examples thereof include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), calcium silicate, aluminum silicate, etc. Among them, wet silica is preferable. Colloidal properties of the silica are not particularly limited, those which are nitrogen adsorption specific surface area (BET) 150~250m ² / g by BET method is preferably used, more preferably 180~230m ² / g. The BET of silica is measured according to the BET method described in ISO 5794.

  It is preferable that the compounding quantity of a silica is 40 mass parts or more with respect to 100 mass parts of rubber components, More preferably, it is 40-150 mass parts, More preferably, it is 50-100 mass parts. In addition, when mix | blending a silica, it is preferable to mix | blend a silane coupling agent, and it is preferable to use a silane coupling agent by 5-15 mass parts with respect to 100 mass parts of silica.

  As a filler, in addition to silica, carbon black may be used in combination. Usually, carbon black is used in combination for coloring the tire. Although the compounding quantity of carbon black is not specifically limited, It is preferable that it is 30 mass parts or less with respect to 100 mass parts of rubber components, More preferably, it is 5-15 mass parts.

  The rubber composition according to the present invention includes tire treads such as oil, stearic acid, zinc white, anti-aging agent, wax, vulcanization accelerator, vulcanizing agent, and vulcanizing aid, in addition to the components described above. Various additives generally used in rubber compositions for rubber can be blended.

  The rubber composition can be prepared by kneading using a commonly used Banbury mixer, a mixer such as a roll or a kneader. The obtained rubber composition can be used for treads of various pneumatic tires, and a pneumatic radial tire provided with the treads can be produced by vulcanization molding according to a conventional method. The tires to be applied are not particularly limited, such as tires for passenger cars, heavy duty tires such as trucks and buses, but more preferably for all seasons where excellent wet grip properties and low temperature performance in winter are required. It is used for tires.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Using a Banbury mixer, a rubber composition was prepared according to a conventional method according to the formulation shown in Table 1 below. Specifically, first, in the first mixing stage, other compounding agents excluding sulfur and a vulcanization accelerator are added to the diene rubber and kneaded, and then the obtained kneaded product is subjected to sulfur mixing in the final mixing stage. And a vulcanization accelerator were added and kneaded to prepare a rubber composition. Each component in Table 1 is as follows. Of the following rubber components, for oil-extended rubber, the blending amount in Table 1 is part by mass as the polymer component, and the blending amount of “oil” in Table 1 is the oil blended in the oil-extended portion. It is the total amount including.

BR: “BR01” manufactured by JSR Corporation (Tg = −102 ° C., cis-1,4 bond content = 95%)
Modified SBR1: OH-modified S-SBR, “Toughden E580” manufactured by Asahi Kasei Corporation (Tg = −32 ° C., St = 36 mass%, 37.5 mass parts oil-extended rubber)
Modified SBR2: OH-modified S-SBR, “Nipol NS616” manufactured by ZEON Corporation (Tg = −25 ° C., St = 21% by mass)
Modified SBR3: alkoxy group and amine modified S-SBR, “HPR340” manufactured by JSR Corporation (Tg = −58 ° C., St = 10% by mass)
Unmodified SBR: Emulsion polymerization SBR (E-SBR), “SBR1723” manufactured by JSR Corporation (Tg = −53 ° C., St = 23.5 mass%, 37.5 mass parts oil-extended rubber)

Carbon black: HAF, N339, “Seast KH” manufactured by Tokai Carbon Co., Ltd.
Silica: “Nip Seal AQ” manufactured by Tosoh Silica Co., Ltd. (BET = 205 m ² / g)
Silane coupling agent: “Si69” manufactured by Evonik
・ Oil: “NC140” manufactured by Japan Energy Co., Ltd.
Rosin-modified maleic resin 1: “Harimak R100” manufactured by Harima Kasei Co., Ltd. (softening point = 100 to 110 ° C.)
-Rosin-modified maleic resin 2: "Harimak T80" manufactured by Harima Kasei Co., Ltd. (softening point = 80 to 90 ° C)
・ Phenol-based tackifier: alkylphenol / formaldehyde resin, “TAMANOL 510” manufactured by Arakawa Chemical Industries, Ltd.

・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
・ Zinc flower: “Zinc flower 1” manufactured by Mitsui Mining & Smelting Co., Ltd.
Anti-aging agent: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.
・ Wax: “Sunknock N” manufactured by Ouchi Shinsei Chemical Co., Ltd.
・ Vulcanization accelerator 1: Sanshin Chemical Co., Ltd. “Sunseller DM-G”
・ Vulcanization accelerator 2: "Soccinol CZ" manufactured by Sumitomo Chemical Co., Ltd.
・ Sulfur: “Sulfur Powder” manufactured by Tsurumi Chemical Co., Ltd.

  About each obtained rubber composition, while evaluating roll adhesiveness, a test piece of a predetermined shape was produced by vulcanization at 160 ° C. for 30 minutes, and wet grip properties and low temperature were obtained using the obtained test piece. Performance was evaluated. Each evaluation method is as follows.

-Wet grip property: An Lupke-type rebound resilience test was performed according to JIS K6255, the rebound resilience at 23 ° C. was measured, and the index of the reciprocal of the value of Comparative Example 1 as 100 (“Rebound resilience of Comparative Example 1”) X100 / "Rebound resilience of each test piece"). A larger index indicates a smaller impact resilience. It is well known to those skilled in the art that there is a correlation between the rebound resilience at 23 ° C. and the wet grip property, and the smaller the rebound resilience, the better the wet grip property. Therefore, it means that it is excellent in wet grip property, so that this index | exponent is large.

Low temperature performance: Using a viscoelasticity testing machine manufactured by Toyo Seiki Co., Ltd., measuring storage elastic modulus E ′ at a frequency of 10 Hz, static strain of 10%, dynamic strain of ± 1%, and temperature of −10 ° C., and comparing their reciprocal numbers The value was expressed as an index (“E ′ of Comparative Example 1” × 100 / “E ′ of each test piece”) with the value of Example 1 being 100. The larger the index is, the smaller the storage elastic modulus E 'is, so that the ground contact area at a low temperature is wide and the low temperature performance is excellent.

-Roll adhesion: After mixing the rubber composition, the rubber sheet was roll-kneaded, and the adhesion with the roll at that time was subjected to sensory evaluation. Evaluation is performed in 5 stages of 1 to 5 points, and the larger the number, the lower the adhesion with the roll and the better the workability.

  The results are as shown in Table 1. In Comparative Example 1, although the improvement effect of wet grip property was recognized as compared with Comparative Example 2 in which rosin-modified maleic acid resin was blended, the effect Was small and the low-temperature performance was deteriorated. On the other hand, in Comparative Example 3, BR and modified SBR were used as the rubber component instead of blending the rosin-modified maleic resin. In this case, although the improvement effect was obtained in the low temperature performance, the wet grip property was large. It was damaged. In Comparative Example 4, as a conventional improvement method of wet grip properties, the amount of filler and oil was increased. In this case, although wet grip properties were improved, the low temperature performance was impaired. It was unsatisfactory in terms of improving balance. In Comparative Example 5, a rosin-modified maleic acid resin is blended with a rubber component containing BR and modified SBR, but the Tg average value of the polymer is high, so the low-temperature performance is greatly deteriorated, and wet grip properties There was also a slight improvement. In Comparative Example 6, instead of rosin-modified maleic resin, a highly tacky alkylphenol-formaldehyde resin is blended, and in this case, not only the effect of improving the balance between wet grip property and low-temperature performance is insufficient, Roll adhesion was deteriorated. In Comparative Example 7, a soft polymer system in which BR and SBR are used in combination as a rubber component and a rosin-modified maleic acid resin are further blended, but since modified SBR is not used, the effect of improving the balance between wet grip properties and low-temperature performance is achieved. Was not obtained.

  On the other hand, in the Example which concerns on this invention, the balance of wet grip property and low-temperature performance was improved significantly by mix | blending the rosin modified maleic acid resin with the soft polymer system containing BR and modified SBR. . That is, both wet grip properties and low-temperature performance are improved, or the other performance is remarkably improved while either one is maintained. In particular, in Examples 1 to 3 and 5, the improvement in wet grip property is noticeable, and the deterioration rate of the low temperature performance is small compared to the conventional wet grip property improvement method, rather the low temperature performance is also improved. It was. Moreover, the great deterioration was also suppressed about the adhesiveness to the roll which is a demerit at the time of use of a tackifier. In Example 6, the modified SBR3 is superior in dispersibility of silica compared to other rubber components, so the heat generation is reduced and the wet grip property is reduced as compared with Example 1, but the low temperature performance is greatly improved. It was improving.

Claims (4)

A diene rubber is used as a rubber component, and the rubber component contains a modified styrene butadiene copolymer rubber containing 10-50 mass% of polybutadiene rubber and having a functional group containing a hetero atom introduced therein, and the rubber component The average value of the glass transition temperature (Tg) of -50 ° C. or less,
A rubber composition for a tire tread containing 0.5 to 10 parts by mass of a rosin-modified maleic acid resin with respect to 100 parts by mass of the rubber component.   The rubber composition for a tire tread according to claim 1, further comprising 40 parts by mass or more of silica as a filler with respect to 100 parts by mass of the rubber component.   The rubber composition for a tire tread according to claim 1 or 2, wherein the functional group is at least one selected from a hydroxyl group, an amino group, a carboxyl group, an alkoxyl group, an epoxy group, a cyano group, and a halogen.   The pneumatic tire provided with the tread which uses the rubber composition of any one of Claims 1-3.