JP2022185818A - Rubber composition for tread - Google Patents

Abstract

To provide a rubber composition for a tire which reduces rolling resistance at normal temperature and high temperature.SOLUTION: A rubber composition for a tread contains: a rubber component containing an isoprene rubber and a styrene-butadiene rubber and/or a butadiene rubber; a resin component; and pre-hydrophobized silica.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a tread rubber composition and a tire composed of the rubber composition.

In recent years, progress in fuel-efficient tires has been remarkable, and rolling resistance reduction is a performance that will continue to be required in the future. Here, fuel economy performance is required not to exhibit performance only under certain specific temperature conditions, but to exhibit performance over a wide temperature range. In other words, it is desired to reduce rolling resistance in a wide temperature range in order to suppress seasonal fluctuations in fuel efficiency.

BACKGROUND ART Conventionally, it has been known to blend silica into a rubber composition for tires to improve dynamic viscoelastic properties in order to reduce rolling resistance.

Patent Document 1 discloses a method of improving dispersibility of silica and reducing rolling resistance by adding silica and a specific silane coupling agent together in a mixer and then adding and kneading diene rubber. there is Further, Patent Document 2 discloses a rubber composition in which large particle size carbon black is dispersed in a glycerin fatty acid ester to improve rolling resistance.

JP 2019-206642 A WO2015/194591

However, Patent Documents 1 and 2 have room for improvement in reducing rolling resistance over a wide temperature range, especially in reducing rolling resistance at room temperature and high temperature.

An object of the present invention is to provide a rubber composition having reduced rolling resistance over a wide temperature range, especially at room temperature and high temperature.

As a result of intensive studies to solve the above problems, the present inventors have found that by blending a rubber component containing an isoprene rubber and a styrene-butadiene rubber and/or a butadiene rubber with a resin component and prehydrophobized silica, the above After discovering that the problem can be solved, and further studies, the present invention was completed.

That is, the present invention
[1] A tread rubber composition containing a rubber component containing an isoprene rubber and a styrene-butadiene rubber and/or a butadiene rubber, a resin component, and prehydrophobized silica,
[2] The tread rubber composition according to [1] above, which contains 10% by mass or more of isoprene-based rubber in the rubber component;
[3] The tread rubber composition according to [1] or [2] above, which contains 40 to 120 parts by mass of the prehydrophobized silica relative to 100 parts by mass of the rubber component,
[4] The tread rubber composition according to any one of [1] to [3] above, which contains 1 to 50 parts by mass of the resin component with respect to 100 parts by mass of the prehydrophobized silica.
[5] The content (parts by mass) of the resin component with respect to 100 parts by mass of the rubber component is equal to or greater than the 2/3 power of the content (parts by mass) of the prehydrophobized silica with respect to 100 parts by mass of the rubber component. The tread rubber composition according to any one of [1] to [4] above,
[6] The tread rubber composition according to any one of [1] to [5] above, wherein the acetone extraction amount is 10 to 30% by mass;
[7] The tread rubber composition according to any one of [1] to [6] above, wherein the temperature at the peak position of the tan δ temperature curve is −20° C. or lower;
[8] The rubber composition for a tread according to any one of [1] to [7], which contains 12% by mass or more of butadiene rubber in the rubber component;
[9] The tread rubber composition according to any one of [1] to [8] above, wherein the resin component contains at least one selected from the group consisting of petroleum resins, terpene-based resins, and coumarone-based resins. ,
[10] A tire comprising a tread having at least one rubber layer, wherein the tread has land portions partitioned by a plurality of circumferential grooves, and in the tread, at least one rubber layer comprises the above [ 1] A tire composed of the rubber composition according to any one of [9],
[11] A tire having a tread having two or more rubber layers, wherein the tread has land portions partitioned by a plurality of circumferential grooves, and in the tread, a rubber layer constituting at least the tread surface. A tire in which (the cap rubber layer) is composed of the rubber composition according to any one of [1] to [9] above,
[12] The above [ 11] The tire according to
[13] Preliminary hydrophobicity with respect to 100 parts by mass of the rubber component in the rubber composition, where H (mm) is the distance between the extension line of the outermost surface of the land portion and the extension line of the deepest portion of the groove bottom of the circumferential groove The tire according to any one of [10] to [12] above, wherein A/H is 10 or more, where A (parts by mass) is the content of silica.

According to the present invention, it is possible to provide a tread rubber composition exhibiting low rolling resistance at room temperature and high temperature, and a pneumatic tire having a tread composed of the tread rubber composition.

1 is a cross-sectional view of a tread portion showing an embodiment of the present disclosure; FIG.

The tread rubber composition of the present disclosure is a tread rubber composition containing a rubber component containing isoprene rubber and styrene-butadiene rubber and/or butadiene rubber, a resin component, and prehydrophobized silica.

Although not intending to be bound by theory, the mechanism by which the tread rubber composition of the present disclosure reduces the rolling resistance at room temperature and high temperature is thought to be as follows. That is, when silica is blended into a tread rubber composition containing isoprene rubber and styrene-butadiene rubber and/or butadiene rubber for the purpose of reducing the rolling resistance of a tire, silica has a high affinity with isoprene rubber and when mixed, tend to be unevenly distributed. As a result, the domains bounded by silica become uneven within the phase of the rubber component, and the temperature at which the molecular mobility increases in each domain differs, making it impossible to reduce the rolling resistance at room temperature and high temperature. Therefore, by using previously hydrophobized silica (preliminarily hydrophobized silica) and resin, the affinity between the hydrophobic portion of silica and the hydrophobic portion of resin is increased, and the rubber phase of styrene-butadiene rubber and / or butadiene rubber is improved. It is thought that the silica can be dispersed in the particles, the domains are homogenized, and a noteworthy effect is achieved.

The tread rubber composition preferably contains 10% by mass or more of isoprene rubber in the rubber component.

By containing 10% by mass or more of isoprene-based rubber, it is believed that the improvement in dispersibility due to hydrophobization of silica and the resulting effect of low rolling performance are likely to be exhibited.

The tread rubber composition preferably contains 40 to 120 parts by mass of prehydrophobized silica per 100 parts by mass of the rubber component.

By setting the content of the pre-hydrophobized silica within the above range, it is believed that the effect of improving the dispersibility of the pre-hydrophobized silica can be further obtained.

The tread rubber composition preferably contains 1 to 50 parts by mass of a resin component based on 100 parts by mass of prehydrophobized silica.

By setting the content of the resin component within the above range, it is believed that the resin component sufficiently coats the surface of the silica and enhances the dispersibility of the silica in the rubber.

The content (parts by mass) of the resin component with respect to 100 parts by mass of the rubber component is at least the 2/3 power of the content (parts by mass) of the preliminary hydrophobized silica with respect to 100 parts by mass of the rubber component. preferable.

By setting the content of the resin component within the above range, it is believed that the resin component sufficiently coats the surface of the silica and enhances the dispersibility of the silica in the rubber.

The tread rubber composition preferably has an acetone extraction amount of 10 to 30% by mass.

By setting the acetone extraction amount in the above range, the concentration of the organic low-molecular-weight compound in the plasticizer contained in the rubber composition becomes constant, the dispersibility of silica in the rubber increases, and the wet grip performance improves. Conceivable.

The tread rubber composition preferably has a temperature at the peak of the tan δ temperature curve of −20° C. or lower.

Since the peak position of the tan δ temperature curve of the rubber composition is located on the lower temperature side than −20° C., it is believed that tan δ, which contributes to the reduction of rolling resistance at room temperature and high temperature, can be reduced.

The tread rubber composition preferably contains 12% by mass or more of butadiene rubber in the rubber component.

It is believed that containing 12% by mass or more of butadiene rubber facilitates dispersion of silica in the rubber phase of styrene-butadiene rubber and/or butadiene rubber.

The tread rubber composition preferably contains at least one selected from the group consisting of petroleum resins, terpene-based resins, and coumarone-based resins.

Since the hydrophobic part of hydrophobized silica is non-polar, it has a high affinity with petroleum resins, terpene-based resins, and coumarone-based resins. It is considered possible.

A tire that is one embodiment of the present disclosure is a tire that includes a tread having at least one rubber layer, the tread having land portions partitioned by a plurality of circumferential grooves, the tread comprising: A tire in which at least one rubber layer is composed of the rubber composition of the present disclosure.

A tire that is one embodiment of the present disclosure is a tire that includes a tread having two or more rubber layers, the tread having land portions partitioned by a plurality of circumferential grooves, the tread having at least It is preferable that the rubber layer (cap rubber layer) forming the tread surface is made of the rubber composition of the present disclosure.

In one embodiment of the present disclosure, the tire is arranged such that the deepest portion of the groove bottom of the circumferential groove is located radially inward of the outermost rubber layer adjacent to the radially inner side of the cap rubber layer. It is preferably formed in

In the tire that is one embodiment of the present disclosure, the distance between the extension line of the outermost surface of the land portion and the extension line of the deepest portion of the groove bottom of the circumferential groove is H (mm), and A/H is preferably 10 or more, where A (parts by mass) is the content of the prehydrophobized silica with respect to 100 parts by mass of the rubber component.

The deeper the grooves, the greater the movement of the tread surface. At this time, the domains bounded by silica become more non-uniform within the phase of the rubber component, and the temperature difference at which the molecular mobility in each domain increases widens, increasing the temperature dependence of rolling resistance. Therefore, by containing a certain amount of pre-hydrophobized silica according to the groove depth, the affinity between the hydrophobic portion of silica and the hydrophobic portion of the resin is increased, the domain is uniformed, and it can be used at normal temperature and high temperature. It is thought that rolling resistance is further reduced.

<Definition>
"pH"
“pH” is an index that indicates the concentration of hydrogen ions in an aqueous solution. Here, the pH is a value measured by a desktop pH meter (LAQUAact D-71AC) manufactured by Horiba, Ltd. Alternatively, the pH can be measured by a device equivalent to this. For example, it is applied to pre-hydrophobicized silica and the like.

The "SP value of the resin" means a solubility parameter calculated by the Hoy method based on the structure of the compound, and the smaller the difference between the SP values of the two components, the better the compatibility. The Hoy method is, for example, a calculation method described in K. L. Hoy "Table of Solubility Parameters", Solvent and Coatings Materials Research and Development Department, Union Carbites Corp. (1985).

"Oil content" also includes the amount of oil contained in the oil-extended rubber.

A "regular rim" is a rim defined for each tire in a standard system including standards on which tires are based. Standard rims in applicable sizes, ETRTO (The European Tire and Rim Technical Organization) "STANDARDS MANUAL" "Measuring Rim", TRA (The Tire and Rim Association, Inc.) " "Design Rim" described in the YEAR BOOK. In the case of non-standard tires, the smallest rim diameter among rims that can be assembled and can maintain internal pressure, that is, rims that do not cause air leakage from between the rim and the tire, followed by the rim Indicates the narrowest width.

"Regular internal pressure" is the air pressure specified for each tire by each standard in the standard system including the standard that the tire is based on. For example, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and for ETRTO it is "INFLATION PRESSURE". For non-standard tires, the normal internal pressure is 250 kPa.

"Normal state" means a state in which the tire is mounted on a normal rim, inflated to normal internal pressure, and unloaded. In this specification, unless otherwise specified, the dimensions of each portion of the tire are measured in the normal state.
<Measurement method>

"Acetone extractable amount (AE)"
The amount of acetone extraction is based on JIS K 6229-3: 2015, each rubber test piece is immersed in acetone for 72 hours to extract soluble components, the mass of each test piece before and after extraction is measured, and the following formula is obtained. can be obtained by
Acetone extraction amount (% by mass) = {(mass of rubber test piece before extraction - mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} x 100

"tan δ peak temperature"
A rubber composition test piece sample (e.g., length 20 mm x width 4 mm x thickness 1 mm) is subjected to dynamic viscoelasticity evaluation equipment (e.g., GABO's Xplexer series) at a frequency of 10 Hz and an initial strain of 10. %, an amplitude of ±0.5%, and a heating rate of 2° C./min. ).

“Styrene content” is a value calculated by ¹ H-NMR measurement, and is applied to rubber components having repeating units derived from styrene, such as SBR.

"Cis content (cis-1,4-bonded butadiene unit amount)" is a value calculated by infrared absorption spectroscopy in accordance with JIS K 6239-2: 2017. For example, repeats derived from butadiene such as BR Applies to rubber components with units.

"Weight average molecular weight" is gel permeation chromatography (GPC) (for example, GPC-8000 series manufactured by Tosoh Corporation, detector: differential refractometer, column: TSKGEL SUPERMALTIPORE HZ-M manufactured by Tosoh Corporation). It can be obtained by standard polystyrene conversion based on the measured value. For example, it is applied to SBR, BR, resin components, and the like.

"N ₂ SA of carbon black" is measured according to JIS K 6217-2 "Basic properties of carbon black for rubber-Part 2: Determination of specific surface area--Nitrogen adsorption method--single point method".

The "CTAB specific surface area of prehydrophobized silica" is measured in accordance with JIS K 6430:2008 "Rubber compounds-Silica-Test method: Determination of specific surface area by CTAB adsorption method".

"Softening point" is the temperature at which the sphere descends when the softening point specified in JIS K 6220-1:2001 is measured with a ring and ball type softening point measuring device. For example, it is applied to resin components and the like.

[tire]
A tire that is one embodiment of the present disclosure is a tire that includes a tread having at least one rubber layer, the tread having land portions partitioned by a plurality of circumferential grooves, the tread comprising: A tire in which at least one rubber layer is composed of the following rubber composition.

A tire that is an embodiment of the present disclosure is a tire that includes a tread having two or more rubber layers, the tread having land portions partitioned by a plurality of circumferential grooves, the tread comprising: Any rubber layer other than the innermost layer adjacent to the outer side in the tire radial direction of the belt layer is preferably composed of the following rubber composition; It is more preferable that all the rubber layers other than the innermost layer adjacent to the outer side in the tire radial direction of the belt layer are composed of the following rubber composition.

In the tire that is one embodiment of the present disclosure, the deepest part of the groove bottom of the circumferential groove is the outermost part of the rubber layer adjacent to the inner side in the tire radial direction of the rubber layer (cap rubber layer) whose outer surface constitutes the tread surface. It is preferably formed so as to be located on the inner side in the tire radial direction. Moreover, it may be formed so as to be located radially inward of the outermost layer of the innermost layer.

The distance between the extension line of the outermost surface of the land portion and the extension line of the deepest portion of the groove bottom of the circumferential groove is H (mm), and the amount of prehydrophobized silica with respect to 100 parts by mass of the rubber component in the rubber composition. From the viewpoint of the effects of the present disclosure, A/H when the content is A (parts by mass) is preferably 5 or more, more preferably 7 or more, and even more preferably 10 or more. A/H is preferably 30 or less, preferably 20 or less, and more preferably 15 or less.

A tire including a tread that is one embodiment of the disclosure is described in detail below. However, the following description is an example for explaining the present disclosure, and is not intended to limit the technical scope of the present disclosure only to this description range. In this specification, when a numerical range is indicated using "-", the numerical values at both ends are included.

The tread of the present disclosure may be composed of a single rubber layer, or may have two or more rubber layers. Although the structure of the rubber layer is not particularly limited, it has, for example, an innermost layer adjacent to the outer side of the belt layer in the tire radial direction, and one or more rubber layers present between the tread surface and the innermost layer.

FIG. 1 is an enlarged sectional view schematically showing part of the tread of a tire. In FIG. 1, the vertical direction is the tire radial direction, the horizontal direction is the tire width direction, and the direction perpendicular to the plane of the drawing is the tire circumferential direction.

The tread of the present disclosure has a plurality of circumferential grooves 1 continuously extending in the tire circumferential direction. The circumferential groove 1 may extend linearly along the circumferential direction, or may extend zigzag along the circumferential direction.

The tread of the present disclosure has land portions 2 partitioned by circumferential grooves 1 in the tire width direction.

The groove depth H of the circumferential groove 1 is obtained from the distance between the extension line 4 of the land portion 2 and the extension line 5 of the deepest portion of the groove bottom of the circumferential groove 1 in the normal state. In addition, for example, when there are a plurality of circumferential grooves 1, the groove depth H is determined by the extension line 4 of the land portion 2 and the circumferential groove 1 having the deepest groove depth among the plurality of circumferential grooves 1 (Fig. 1 can be the distance from the deepest extension line 5 of the groove bottom of the left circumferential groove 1). Further, the tire of the present disclosure is a tire in which at least one rubber layer in the tread is composed of the following rubber composition, and the cap rubber layer 6 whose outer surface constitutes the tread surface 3 is composed of a predetermined rubber composition. It is preferable that

In the present disclosure, the tread comprises an innermost layer 7 adjacent to the belt layer on the radially outer side of the tire, and a cap rubber layer 6 present between the tread surface 3 and the innermost layer 7, as shown in FIG. ing. One or more rubber layers may be provided between the cap rubber layer 6 and the innermost layer 7 . One circumferential groove 1 shown on the left side of FIG. is formed to be located in Specifically, the innermost layer 7 has a recess that is recessed inward in the tire radial direction with respect to the outer surface, and a portion of the cap rubber layer 6 is formed in the recess of the innermost layer 7 with a predetermined thickness. . The circumferential groove 1 is formed so as to extend beyond the outer surface of the innermost layer 7 and enter the recessed portion of the innermost layer 7 . Note that the circumferential groove 1 may be formed with a groove depth that does not reach the outer surface of the innermost layer 7, like the circumferential groove 1 shown on the right side of FIG.

In FIG. 1, the double arrow t1 indicates the thickness of the cap rubber layer 6, and the double arrow t2 indicates the thickness of the innermost layer 7. As shown in FIG. In FIG. 1 , the midpoint of the land portion 2 in the tire width direction is indicated by symbol P. As shown in FIG. A straight line indicated by the symbol N is a straight line (normal line) that passes through the point P and is perpendicular to the tangent plane at this point P. As used herein, thicknesses t1 and t2 are measured along the normal N drawn from the point P on the tread surface at the location where no grooves are present in the cross-section of FIG.

In the present disclosure, the thickness t1 of the cap rubber layer 6 is not particularly limited, but is preferably 1.0 mm or more, more preferably 1.5 mm or more, and even more preferably 2.0 mm or more. Also, the thickness t1 of the cap rubber layer 6 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

The ratio t1/H of the thickness t1 of the cap rubber layer to the distance H (mm) between the extension line of the outermost surface of the land portion and the extension line of the deepest portion of the groove bottom of the circumferential groove is the effect of the present disclosure. From the viewpoint of, 0.5 or more is preferable, 0.6 or more is more preferable, and 0.7 or more is even more preferable. Also, t1/H is preferably 2.0 or less, preferably 1.5 or less, and more preferably 0.9 or less.

In the present disclosure, the thickness t2 of the innermost layer 7 is not particularly limited, but is preferably 1.0 mm or greater, more preferably 1.5 mm or greater, and even more preferably 2.0 mm or greater. Moreover, the thickness t2 of the innermost layer 7 is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less.

[Rubber composition]
The rubber composition of the present disclosure is used for at least one rubber layer that constitutes the tread. Further, in the case of a tire having a tread having two or more rubber layers, the rubber composition of the present disclosure is used in any rubber layer other than the innermost layer adjacent to the outer side in the tire radial direction of the belt layer. is preferred; at least the outer surface is more preferably used for the rubber layer (cap rubber layer) constituting the tread surface, and further preferably for all rubber layers other than the innermost layer adjacent to the outer side in the tire radial direction of the belt layer. preferable.

The rubber composition of the present disclosure contains a rubber component comprising isoprene-based rubber and styrene-butadiene rubber and/or butadiene rubber, a resin component and prehydrophobized silica.

<Rubber component>
The rubber component used in the present disclosure contains isoprene-based rubber and styrene-butadiene rubber (SBR) and/or butadiene rubber (BR). Further, other rubber components may be blended within a range that does not impair the effects of the present disclosure.

(Isoprene rubber)
As the isoprene-based rubber, for example, isoprene rubber (IR) and natural rubber commonly used in the rubber industry can be used. Of these, natural rubber includes unmodified natural rubber (NR), epoxidized natural rubber (ENR), hydrogenated natural rubber (HNR), deproteinized natural rubber (DPNR), highly purified natural rubber, Also included are modified natural rubbers such as grafted natural rubber. Among them, NR is preferred. These isoprene-based rubbers can be used singly or in combination of two or more.

NR is not particularly limited, and one commonly used in the tire industry can be used, and examples thereof include SIR20, RSS#3, TSR20, and the like.

The content of isoprene-based rubber in the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, more preferably 20% by mass or more, and 30% by mass or more, from the viewpoint of chipping resistance and abrasion resistance. is more preferable, and 40% by mass or more is particularly preferable. The content of the isoprene-based rubber in the rubber component is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

(SBR)
The SBR is not particularly limited, and includes solution-polymerized SBR (S-SBR), emulsion-polymerized SBR (E-SBR), modified SBR (modified S-SBR, modified E-SBR) thereof, and the like, which are oil-extended. It does not have to be oil extended. Examples of modified SBR include terminal and/or main chain modified SBR, tin, modified SBR coupled with a silicon compound (condensate, branched structure, etc.). Among them, unmodified S-SBR is preferable because it can improve fuel economy performance. These SBRs may be used singly or in combination of two or more.

S-SBRs that can be used in the present disclosure include S-SBRs manufactured and sold by JSR Corporation, Sumitomo Chemical Co., Ltd., Ube Industries, Ltd., Asahi Kasei Co., Ltd., Zeon Corporation, and others.

The styrene content of SBR is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, from the viewpoint of grip performance and the effects of the present disclosure. In addition, the styrene content of SBR is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less from the viewpoint of fuel efficiency. In addition, the styrene content of SBR is measured by the said measuring method.

When SBR is contained, the content in the rubber component is preferably 5% by mass or more, more preferably 10% by mass or more, further preferably 15% by mass or less, and 20% by mass or more, from the viewpoint of improving the dispersibility of silica. is more preferable, and 25% by mass or more is particularly preferable. From the viewpoint of wear resistance performance, the content is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less.

(BR)
BR is not particularly limited, and for example, BR having a cis content of less than 50 mol% (low-cis BR), BR having a cis content of 90 mol% or more (high-cis BR), synthesized using a rare earth element-based catalyst Rare earth-based butadiene rubber (rare earth-based BR), BR containing syndiotactic polybutadiene crystals (SPB-containing BR), modified BR (high-cis modified BR, low-cis modified BR), etc., which are commonly used in the tire industry can be used. can. Among these BRs, high-cis BR is preferable because of its excellent wear resistance performance. The cis content of BR is measured by the above measuring method.

Examples of HISIS BR include those manufactured by Zeon Corporation, those manufactured by Ube Industries, Ltd., and those manufactured by JSR Corporation. By containing high-cis BR, low-temperature characteristics and wear resistance performance can be improved. The cis content of high-cis BR is preferably 90 mol% or more, more preferably 95 mol% or more, still more preferably 96 mol% or more, and particularly preferably 97 mol% or more.

The cis content of BR is preferably 90 mol % or more, more preferably 93 mol % or more, and more preferably 95 mol % or more, from the viewpoint of durability and wear resistance performance. It is believed that the higher the cis content, the more regularly the polymer chains are arranged, and the stronger the interaction between the polymers, the higher the rubber strength, and the better the chipping resistance. The cis content of BR is measured by the above measuring method.

The content in the rubber component when BR is contained is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 12% by mass or more, still more preferably 14% by mass or more, and 16% by mass or more. Especially preferred. When BR is contained, the content in the rubber component is preferably 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, and particularly preferably 25% by mass or less.

(Other rubber components)
The rubber component according to the present disclosure may contain a rubber component other than the above isoprene-based rubber, SBR and BR. As other rubber components, crosslinkable rubber components commonly used in the tire industry can be used, such as styrene-isoprene-butadiene copolymer rubber (SIBR), styrene-isobutylene-styrene block copolymer ( SIBS), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile rubber (HNBR), butyl rubber (IIR), ethylene propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM) , acrylic rubber (ACM), hydrin rubber, and the like. These other rubber components may be used singly or in combination of two or more.

<Preliminary hydrophobized silica>
The rubber composition according to the present disclosure contains prehydrophobized silica. Pre-hydrophobized silica is silica that has been previously treated with an organic silane compound to enhance affinity with the resin component described later. The pre-hydrophobized silica is not particularly limited as long as it can achieve the effects of the present disclosure as a result of enhanced affinity with the resin component. Prehydrophobicized silica can be obtained by hydrophobizing silica by treatment with at least one organosilane compound prior to its addition to the rubber composition. Since prehydrophobized silica has a high affinity with resins, it is possible to disperse silica in the rubber phase of styrene-butadiene rubber and/or butadiene rubber.

Examples of organic silane compounds include, but are not limited to, alkylsilanes, alkoxysilanes, alkoxysilylpolysulfides, mercaptoalkoxysilanes, and the like.

Examples of silica (unmodified silica) used in the preparation of prehydrophobized silica include wet silica (hydrous silicic acid), dry silica (anhydrous silicic acid), colloidal silica, precipitated silica, calcium silicate, aluminum silicate, and the like. is mentioned. Precipitated silica is preferably used because it is highly effective in achieving both grip performance and low rolling resistance.

By containing pre-hydrophobicized silica, the affinity between silica and resin increases due to the non-polar hydrophobic portion, so it becomes possible to disperse silica in the rubber phase, and the domains are homogenized. reduces rolling resistance.

The pre-hydrophobized silica is not particularly limited, but commercially available products such as those manufactured by PPG Industries are preferably used.

The CTAB specific surface area of the prehydrophobized silica is preferably 120 m ² /g or more, more preferably 130 m ² /g or more, and even more preferably 135 m ² /g or more, from the viewpoint of dispersibility in the rubber phase. The CTAB specific surface area of the prehydrophobized silica is preferably 350 m ² /g or less, more preferably 300 m ² /g or less, and even more preferably 250 m ² /g or less, from the viewpoint of dispersibility of silica in the rubber phase. Incidentally, the CTAB specific surface area of the prehydrophobized silica is measured by the above measuring method.

From the viewpoint of dispersibility in the rubber phase, the pH of the prehydrophobized silica is preferably 5.5 or higher, more preferably 6.0 or higher, and even more preferably 6.2 or higher. Further, the pH of the prehydrophobized silica is preferably 7.0 or less from the viewpoint of dispersibility in the rubber phase. The pH of the prehydrophobized silica is measured by the above measuring method.

From the viewpoint of the dispersibility of silica in the rubber phase, the content of the prehydrophobized silica is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, and further preferably 60 parts by mass or more with respect to 100 parts by mass of the rubber component. Preferably, 70 parts by mass or more is particularly preferable. From the viewpoints of dispersibility and workability of the preliminary hydrophobic silica, the amount is preferably 120 parts by mass or less, more preferably 110 parts by mass or less, and even more preferably 100 parts by mass or less.

<Filler>
As the filler, other fillers than the prehydrophobized silica may be used. Such fillers are not particularly limited, and include, for example, carbon black, silica other than prehydrophobized silica, alumina (aluminum oxide), calcium carbonate, talc, clay, and the like, which are generally used in this field. can also be used. These fillers may be used individually by 1 type, and may use 2 or more types together.

(Carbon black)
Carbon black is not particularly limited, and those commonly used in the tire industry, such as GPF, FEF, HAF, ISAF, and SAF, can be used as appropriate. For example, furnace black, acetylene black, thermal black, channel black, graphite, etc., can be mentioned. N330, N339, N343, N347, N351, N356, N358, N375, N539, N550, N582, N630, N642, N650, N660, N683, N754, N762, N765, N772, N774, N787, N907, N908, N990, N991 and the like can be preferably used, and in addition to this, in-house synthesized products and the like can also be preferably used. These carbon blacks may be used singly or in combination of two or more.

The nitrogen adsorption specific surface area (N ₂ SA) of carbon black is preferably 80 m ² /g or more, more preferably 90 m ² /g or more, and even more preferably 100 m ² /g or more, from the viewpoint of reinforcing properties. In addition, N ₂ SA is preferably 200 m ² /g or less, more preferably 170 m ² /g or less, and even more preferably 155 m ² /g or less, from the viewpoint of fuel efficiency and workability. The N ₂ SA of carbon black is measured by the measuring method described above.

When carbon black is contained, the content is preferably 1 part by mass or more, preferably 3 parts by mass or more, more preferably 5 parts by mass or more, more preferably 10 parts by mass with respect to 100 parts by mass of the rubber component, from the viewpoint of abrasion resistance performance. Part or more is more preferable, and 15 mass parts or more is particularly preferable. In addition, the upper limit of the content of carbon black is not particularly limited, but from the viewpoint of fuel efficiency and workability, it is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, further preferably 40 parts by mass or less, and 30 parts by mass. Part or less is particularly preferred.

(Silica other than prehydrophobized silica)
Silica other than prehydrophobized silica is not particularly limited, and for example, silica prepared by a wet method (hydrous silica) and the like commonly used in the tire industry can be used. Silicas other than pre-hydrophobized silica may be used singly or in combination of two or more.

When silica other than prehydrophobized silica is contained, the content per 100 parts by mass of the rubber component is preferably less than 30 parts by mass, more preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and less than 1 part by mass. More preferred. Also, it may not contain silica other than pre-hydrophobized silica.

The pre-hydrophobicized silica does not necessarily need to be used in combination with a silane coupling agent, but when used in combination with a silane coupling agent, it reacts with the hydrophilic portion remaining on the silica when pre-hydrophobicized, so the effects of the present disclosure are more pronounced. improves. When blending silica other than pre-hydrophobized silica, it is preferable to use it together with a silane coupling agent.

(Silane coupling agent)
The silane coupling agent is not particularly limited, and any silane coupling agent conventionally used in combination with silica in the tire industry can be used. For example, the following mercapto-based silane coupling agent; -triethoxysilylpropyl)disulfide, bis(3-triethoxysilylpropyl)tetrasulfide and other sulfide-based silane coupling agents; vinyltriethoxysilane, vinyltrimethoxysilane and other vinyl-based silane coupling agents; 3-aminopropyl Amino silane coupling agents such as triethoxysilane, 3-aminopropyltrimethoxysilane, 3-(2-aminoethyl)aminopropyltriethoxysilane; γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropyl glycidoxy-based silane coupling agents such as trimethoxysilane; nitro-based silane coupling agents such as 3-nitropropyltrimethoxysilane and 3-nitropropyltriethoxysilane; 3-chloropropyltrimethoxysilane and 3-chloropropyltriethoxysilane Examples thereof include chloro-based silane coupling agents such as silane. Among these, sulfide-based silane coupling agents and mercapto-based silane coupling agents are preferred. These silane coupling agents may be used singly or in combination of two or more.

The content of the silane coupling agent with respect to 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and still more preferably 1 part by mass or more. Moreover, the content of the silane coupling agent is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less.

The content of the silane coupling agent with respect to 100 parts by mass of the prehydrophobized silica is preferably 0.5 parts by mass or more in order to react with the hydrophilic portion remaining on the silica after the prehydrophobization. 0 parts by mass or more is more preferable, 2.0 parts by mass or more is even more preferable, and 3.0 parts by mass or more is particularly preferable. In addition, the content of the silane coupling agent with respect to 100 parts by mass of the prehydrophobized silica is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and more preferably 10 parts by mass or less from the viewpoint of preventing deterioration in wear resistance performance. More preferred.

<Resin component>
A rubber composition according to the present disclosure contains a resin component. Examples of resin components include petroleum resins, terpene-based resins, coumarone-based resins, rosin-based resins, phenol-based resins and the like commonly used in the tire industry. The resin component may be used singly or in combination of two or more. Among these, petroleum resins, terpene-based resins, and coumarone-based resins are preferred, and petroleum resins are more preferred, from the viewpoint of affinity with the hydrophobic portion of hydrophobized silica.

The petroleum resin is not particularly limited, but includes aliphatic petroleum resins, aromatic petroleum resins, and aliphatic/aromatic copolymer petroleum resins. One type may be used alone, or two or more types may be used in combination. You may Aliphatic petroleum resins include resins obtained by cationic polymerization of unsaturated monomers such as isoprene and cyclopentadiene, which are petroleum fractions (C5 fractions) corresponding to 4 to 5 carbon atoms (also called C5 petroleum resins). ) can be used. Examples of aromatic petroleum resins include resins (C9 petroleum resins Also called.) can be used. As the aliphatic/aromatic copolymer petroleum resin, a resin obtained by copolymerizing the C5 fraction and the C9 fraction (also referred to as C5C9 petroleum resin) is used. Hydrogenated petroleum resins may also be used. Among them, dicyclopentadiene resin (DCPD resin) and C5C9 petroleum resin are preferably used. As the C5C9-based petroleum resin, for example, commercially available products such as those manufactured by LUHUA, Qilong, and Tosoh Corporation are preferably used.

As the aromatic petroleum resin, an aromatic vinyl resin is preferably used. As the aromatic vinyl resin, α-methylstyrene, homopolymers of styrene, or copolymers of α-methylstyrene and styrene are preferable because they are economical, easy to process, and have excellent heat build-up properties. , a copolymer of α-methylstyrene and styrene is more preferred. As the aromatic vinyl resin, for example, those commercially available from Kraton Co., Eastman Chemical Co., etc. can be used.

Terpene-based resins have a lower SP value than other adhesive resins such as aliphatic petroleum resins, aromatic petroleum resins, phenolic resins, rosin-based resins, and coumarone-based resins. 8.9) and BR (SP value: 8.2), which is preferable from the viewpoint of compatibility with the rubber component. Among them, terpene styrene resin is preferably used because it has particularly good compatibility with both SBR and BR, and sulfur can be easily dispersed in the rubber component.

Terpene resin is not particularly limited, polyterpene resin obtained by polymerizing a terpene compound; terpene aromatic resin obtained by copolymerizing an aromatic compound together with a terpene compound; modified terpene resin with an aromatic compound Aromatic modified terpene resins obtained by and hydrogenated products thereof. The terpene aromatic resin is preferably a terpene phenol resin, and the aromatic modified terpene resin is preferably a terpene styrene resin.

The polyterpene resin is a resin made from at least one selected from terpene compounds such as α-pinene, β-pinene, limonene and dipentene. The terpene phenol resin is a resin made from the terpene compound and the phenolic compound. A terpene styrene resin is a resin made from the terpene compound and styrene as raw materials. The polyterpene resin and the terpene styrene resin may be hydrogenated resins (hydrogenated polyterpene resin, hydrogenated terpene styrene resin). The hydrogenation treatment of the terpene-based resin can be carried out by a known method, and commercially available hydrogenated resins can also be used.

The terpene-based resin may be used singly or in combination of two or more of the above-exemplified terpene-based resins. In the present disclosure, commercially available terpene-based resins may be used. Examples of such commercial products are those manufactured and sold by Kraton Co., Yasuhara Chemical Co., Ltd., and the like.

The coumarone-based resin is a resin containing coumarone as a main component, and examples thereof include a coumarone resin, a coumarone-indene resin, and a copolymer resin containing coumarone, indene, and styrene as main components.

Examples of the rosin-based resin include, but are not limited to, natural resin rosin, and rosin-modified resin obtained by modifying it by hydrogenation, disproportionation, dimerization, esterification, and the like.

Phenol-based resins are not particularly limited, but include phenol-formaldehyde resins, alkylphenol-formaldehyde resins, alkylphenol-acetylene resins, oil-modified phenol-formaldehyde resins, and the like.

The content of the resin component with respect to 100 parts by mass of the rubber component is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and 15 parts by mass or more, from the viewpoint of processability, fuel efficiency, wear resistance, and chipping resistance. is more preferable, and 20 parts by mass or more is more preferable. The content of the resin component with respect to 100 parts by mass of the rubber component is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 35 parts by mass or less.

The content of the resin component with respect to 100 parts by mass of prehydrophobized silica is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and 4 parts by mass from the viewpoint of workability, fuel efficiency, wear resistance, and chipping resistance. Part or more is more preferable, and 5 parts by mass or more is even more preferable. The content of the resin component with respect to 100 parts by mass of the prehydrophobized silica is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less.

The content (parts by mass) of the resin component with respect to 100 parts by mass of the rubber component is 2 of the content (parts by mass) of prehydrophobized silica with respect to 100 parts by mass of the rubber component, in order that the resin component sufficiently coats the surface of the silica. It is more preferable that it is equal to or greater than the power of /3.

From the viewpoint of wet grip performance, the softening point of the resin component is preferably 120° C. or lower, more preferably 100° C. or lower, and even more preferably 90° C. or lower. Also, the softening point is preferably 50° C. or higher, more preferably 60° C. or higher, and even more preferably 70° C. or higher. The softening point of the resin component is measured by the measuring method described above.

The weight average molecular weight (Mw) of the resin component is preferably 15,000 or less, more preferably 10,000 or less, and even more preferably 8,000 or less, from the viewpoint of affinity with the hydrophobic portion of the hydrophobized silica. Moreover, the Mw is preferably 300 or more, more preferably 400 or more, and even more preferably 500 or more, from the viewpoint of less volatilization and good wet grip performance.

The SP value of the resin component is preferably in the range of 8 to 11, more preferably in the range of 8 to 10, and further in the range of 8.3 to 9.5, from the viewpoint of excellent compatibility with the rubber component (especially SBR). preferable. By using a resin having an SP value within the above range, compatibility with SBR and BR can be improved, and abrasion resistance and elongation at break can be improved. The SP value of the resin component is measured by the measuring method described above.

<Other ingredients>
In addition to the rubber component, the resin component, and the pre-hydrophobized silica, the rubber composition according to the present embodiment contains compounding agents and additives conventionally used in the tire industry, such as the pre-hydrophobized silica. fillers, silane coupling agents, oils, zinc oxide, anti-aging agents, stearic acid, waxes, vulcanizing agents such as sulfur, vulcanization accelerators and the like can be contained as necessary.

From the viewpoint of ensuring good wear resistance performance, the content relative to 100 parts by mass of the rubber component when oil is contained is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and even more preferably 60 parts by mass or less. From the viewpoint of workability, the amount is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more. In this specification, the content of oil also includes the amount of oil contained in the oil-extended rubber.

When zinc oxide is contained, the content relative to 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of workability. From the viewpoint of wear resistance performance, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

The anti-aging agent is not particularly limited, and those used in the rubber field can be used. Examples thereof include quinoline, quinone, phenol, and phenylenediamine anti-aging agents.

From the viewpoint of the ozone crack resistance of the rubber, the content of the anti-aging agent with respect to 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more. From the viewpoint of wear resistance and grip performance, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

When stearic acid is contained, the content relative to 100 parts by mass of the rubber component is preferably 0.2 parts by mass or more, more preferably 1 part by mass or more, from the viewpoint of workability. From the viewpoint of vulcanization speed, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

From the viewpoint of the weather resistance of the rubber, the wax content relative to 100 parts by mass of the rubber component is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more. From the viewpoint of whitening of the tire due to blooming, the amount is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

Sulfur is preferably used as the vulcanizing agent. As sulfur, powdered sulfur, oil treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur and the like can be used.

When sulfur is contained as a vulcanizing agent, the content per 100 parts by mass of the rubber component is 0.5 parts by mass or more from the viewpoint of ensuring sufficient vulcanization reaction and obtaining good grip performance and wear resistance performance. Preferably, 1.0 parts by mass or more is more preferable. Moreover, from the viewpoint of deterioration, it is preferably 3.0 parts by mass or less, more preferably 2.5 parts by mass or less.

Examples of vulcanizing agents other than sulfur include sulfur atoms such as 1,6-hexamethylene-dithiosulfate sodium dihydrate and 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane. Examples include vulcanizing agents and organic peroxides such as dicumyl peroxide. Specifically, commercially available products manufactured by Taoka Chemical Co., Ltd., Flexis, Lanxess and the like are preferably used.

Examples of vulcanization accelerators include guanidine-based, sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, dithiocarbamic acid-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators. etc. These vulcanization accelerators may be used alone or in combination of two or more. Among these, sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, and guanidine-based vulcanization accelerators are preferred, and sulfenamide-based vulcanization accelerators are more preferred.

Guanidine-based vulcanization accelerators include, for example, 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, di-o-tolylguanidine salt of dicatechol borate. , 1,3-di-o-cumenylguanidine, 1,3-di-o-biphenylguanidine, 1,3-di-o-cumenyl-2-propionylguanidine and the like. Among them, 1,3-diphenylguanidine (DPG) is preferred.

Examples of sulfenamide-based vulcanization accelerators include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N,N -dicyclohexyl-2-benzothiazolylsulfenamide (DCBS) and the like. Among them, N-tert-butyl-2-benzothiazolylsulfenamide (TBBS) and N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) are preferred.

Thiazole vulcanization accelerators include, for example, 2-mercaptobenzothiazole, cyclohexylamine salts of 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide and the like. Among them, 2-mercaptobenzothiazole is preferred.

When the vulcanization accelerator is contained, the content relative to 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, from the viewpoint of vulcanization acceleration. From the viewpoint of workability, the amount is preferably 5 parts by mass or less, more preferably 4 parts by mass or less.

<Production of rubber composition and tire>
The rubber composition of the present disclosure can be produced by known methods. For example, with a known kneader used in the rubber industry such as a Banbury mixer, kneader, open roll, etc., after kneading the components other than the vulcanizing agent and the vulcanization accelerator among the above components, A vulcanizing agent and a vulcanization accelerator are added to the above, further kneaded, and then vulcanized.

The acetone extraction amount (AE amount) of the rubber composition according to the present disclosure is preferably 10% by mass or more, preferably 12% by mass or more, more preferably 14% by mass or more, and even more preferably 16% by mass or more. The upper limit of the acetone extraction amount is preferably 30% by mass or less, more preferably 28% by mass or less, and even more preferably 25% by mass or less. When the acetone extraction amount of the rubber composition after vulcanization is within the above range, the dispersibility of silica is further improved. The acetone extraction amount serves as an indicator of the concentration of organic low-molecular-weight compounds in the softener contained in the vulcanized rubber composition. Incidentally, the acetone extraction amount is measured by the above measuring method.

The tan δ peak temperature of the rubber composition according to the present disclosure is preferably −60° C. or higher, more preferably −50° C. or higher, and even more preferably −40° C. or higher. The tan δ peak temperature is preferably 0° C. or lower, more preferably −10° C. or lower, and even more preferably −20° C. or lower. The peak temperature of tan δ is measured by the above measuring method.

Since the rubber composition of the present disclosure is excellent in reducing rolling resistance at normal temperature and high temperature, it is suitably used for the cap rubber layer of the tread of tires. Moreover, it may be used for the rubber layer radially inward of the cap rubber layer.

The kneading step includes, for example, a base kneading step of kneading compounding agents and additives other than the vulcanizing agent and the vulcanization accelerator, and adding the vulcanizing agent and the vulcanization accelerator to the kneaded product obtained in the base kneading step. and a final kneading (F kneading) step of adding and kneading. Furthermore, the base kneading step can be divided into a plurality of steps as desired.

Although the kneading conditions are not particularly limited, for example, in the base kneading step, kneading is performed at a discharge temperature of 150 to 170° C. for 3 to 10 minutes, and in the final kneading step, kneading is performed at 70 to 110° C. for 1 to 5 minutes. There is a method of kneading. The vulcanization conditions are not particularly limited, and include, for example, vulcanization at 150 to 200° C. for 10 to 30 minutes.

A tire having a tread containing each of the rubber layers described above can be produced by a conventional method using the rubber composition described above. That is, an unvulcanized rubber composition obtained by blending each of the above components with a rubber component as necessary is extruded according to the shape of each rubber layer using an extruder equipped with a die of a predetermined shape, By bonding together with other tire members on a tire building machine and molding by a normal method, an unvulcanized tire is formed, and by heating and pressurizing this unvulcanized tire in a vulcanizer, the present disclosure of tires can be manufactured.

The present disclosure will be specifically described based on Examples, but the present disclosure should not be construed as being limited thereto.

Various chemicals used in Examples and Comparative Examples will be described.
NR: TSR20
SBR: TUFDENE 3830 manufactured by Asahi Kasei Corporation (unmodified S-SBR, styrene content: 33% by mass, containing 37.5 parts by mass of oil-extended oil per 100 parts by mass of rubber solids)
BR: BR150B (Hi-cis BR, cis content: 97 mol%) manufactured by Ube Industries, Ltd.
Prehydrophobized silica: Agilon® 400 from PPG Industries (precipitated silica surface-treated with an organosilane compound, CTAB specific surface area: 140 m ² /g, pH: 6.5)
Silica: ULTRASIL (registered trademark) VN3 (N ₂ SA: 175 m ² /g) manufactured by Evonik Japan Co., Ltd.
Carbon black: N220 (N ₂ SA: 114 m ² /g) manufactured by Cabot Japan Co., Ltd.
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Evonik Japan Co., Ltd.
Resin component 1: SYLVATRAXX4401 manufactured by Kraton (α-methylstyrene resin, Mw: 700, softening point: 85°C, SP value: 9.1)
Resin component 2: SYLVATARAXX4150 manufactured by Kraton (polyterpene resin, Mw: 2500, softening point: 115°C)
Oil: TDAE oil (VivaTec400 manufactured by H&R Co., Ltd.)
Zinc oxide: zinc oxide No. 1 manufactured by Mitsui Mining & Smelting Co., Ltd. Anti-aging agent: Antigen 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Sumitomo Chemical Co., Ltd.
Stearic acid: beads stearic acid manufactured by NOF Corporation Tsubaki wax: Ozoace 355 manufactured by Nippon Seiro Co., Ltd.
Sulfur: Powdered sulfur vulcanization accelerator manufactured by Karuizawa Sulfur Co., Ltd. 1: Noccellar D (DPG, 1,3-diphenylguanidine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noxceler CZ (N-cyclohexyl-2-benzothiazolylsulfenamide) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

<Production of test vulcanized rubber composition>
According to the formulation shown in Tables 1 and 2, a 1.7 L closed Banbury mixer was used to knead chemicals other than sulfur and vulcanization accelerators at a discharge temperature of 160° C. for 4 minutes to obtain a kneaded product. Next, using an open roll, sulfur and a vulcanization accelerator were added to the resulting kneaded material and kneaded for 4 minutes to obtain an unvulcanized rubber composition.

<Manufacturing test tires>
The unvulcanized rubber composition is extruded according to the shapes of the cap rubber layer (thickness: 7.0 mm) and the innermost layer (thickness: 1.5 mm) of the tread using an extruder equipped with a die of a predetermined shape. A raw tire was produced by molding and bonding this together with other members. Next, in the vulcanization step, press molding was performed at 170° C. for 20 minutes to produce each test tire shown in Table 3 (size: 205/65R15, rim: 15×6JJ, internal pressure: 230 kPa). The groove depth H in the tire circumferential direction is 7.5 mm. Here, the value of the tire circumferential groove depth H is a value measured in a normal state.

Each rubber test piece was prepared by cutting out from the inside of the rubber layer of the tread portion of each test tire so that the tire circumferential direction was the long side, and the following evaluations were performed. Evaluation results are shown in Tables 1 and 3.

(Measurement of acetone extraction amount (AE amount))
According to the above measurement method, each rubber test piece cut out from the rubber compositions A1 to A17 constituting the cap rubber layer of each test tire in accordance with JIS K 6229-3:2015 was immersed in acetone for 72 hours. and extract the soluble components. The mass of each test piece before and after extraction was measured, and the amount of acetone extracted was determined by the following formula.
Acetone extraction amount (% by mass) = {(mass of rubber test piece before extraction - mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} x 100

(Measurement of peak temperature of tan δ)
Each rubber test piece, which was prepared by cutting the rubber composition A1 to A17 constituting the cap rubber layer of each test tire into a length of 20 mm, a width of 4 mm, and a thickness of 1 mm, was prepared using the GABO Xplexer series. , a frequency of 10 Hz, an initial strain of 10%, an amplitude of ±0.5%, and a temperature rise rate of 2 ° C./min. was measured. In addition, the thickness direction of the sample was set to the tire radial direction.

(rolling resistance)
Each test tire was tested using a rolling resistance tester under the following conditions: rim (15 x 6 JJ), internal pressure (230 kPa), load (3.43 kN), speed (80 km/h), and drum surface temperature of 25°C or 50°C. The rolling resistance during running was measured, and the reciprocal thereof was expressed as an index (rolling resistance index) with the reference comparative example (Comparative Example 2) being 100. A larger index indicates lower rolling resistance and better fuel efficiency.

(Overall performance of rolling resistance)
The sum of the rolling resistance index at room temperature (25° C.) and the rolling resistance index at high temperature (50° C.) was calculated and defined as the overall performance of rolling resistance. The larger the sum of the rolling resistance indices at room temperature and high temperature, the lower the rolling resistance at room temperature and high temperature, indicating superior fuel efficiency.

From the results in Table 1, the tread rubber composition containing a rubber component containing isoprene rubber and styrene-butadiene rubber and/or butadiene rubber, a resin component, and prehydrophobized silica has reduced rolling resistance at room temperature and high temperature. It can be seen that

Reference Signs List 1 circumferential groove 2 land portion 3 tread surface 4 extended line of land portion 5 extended line of deepest portion of bottom of circumferential groove 6 cap rubber Layer 7... Innermost layer 8... Extension line of the outer surface of the innermost layer N... Straight line passing through point P and perpendicular to the tangential plane at point P P... On the tread surface at a position where no groove exists Point H: Groove depth of circumferential groove t1: Thickness of cap rubber layer t2: Thickness of innermost layer

Claims (13)

A tread rubber composition comprising a rubber component containing isoprene rubber and styrene-butadiene rubber and/or butadiene rubber, a resin component, and prehydrophobized silica. The rubber composition for a tread according to claim 1, wherein the rubber component contains 10% by mass or more of isoprene-based rubber. The rubber composition for a tread according to claim 1 or 2, containing 40 to 120 parts by mass of said pre-hydrophobized silica with respect to 100 parts by mass of said rubber component. The rubber composition for a tread according to any one of claims 1 to 3, comprising 1 to 50 parts by mass of the resin component based on 100 parts by mass of the prehydrophobized silica. The content (parts by mass) of the resin component with respect to 100 parts by mass of the rubber component is a value equal to or greater than the 2/3 power of the content (parts by mass) of the prehydrophobized silica with respect to 100 parts by mass of the rubber component. The rubber composition for treads according to any one of Items 1 to 4. The rubber composition for treads according to any one of claims 1 to 5, which has an acetone extraction amount of 10 to 30% by mass. The tread rubber composition according to any one of claims 1 to 6, wherein the temperature at the peak position of the tan δ temperature curve is -20°C or lower. The rubber composition for a tread according to any one of claims 1 to 7, wherein the rubber component contains 12% by mass or more of butadiene rubber. The rubber composition for a tread according to any one of claims 1 to 8, wherein the resin component contains at least one selected from the group consisting of petroleum resins, terpene-based resins, and coumarone-based resins. A tire comprising a tread having at least one rubber layer, the tread having land portions partitioned by a plurality of circumferential grooves, and in the tread, at least one rubber layer comprising any one of claims 1 to 9. A tire made of the rubber composition according to any one of the above. A tire comprising a tread having two or more rubber layers, the tread having land portions partitioned by a plurality of circumferential grooves, and a rubber layer (cap rubber Layer) is composed of the rubber composition according to any one of claims 1 to 9. 12. The method according to claim 11, wherein the deepest portion of the groove bottom of the circumferential groove is positioned radially inward of the outermost rubber layer of the cap rubber layer adjacent to the radially inner side of the cap rubber layer. tires. The distance between the extension line of the outermost surface of the land portion and the extension line of the deepest portion of the groove bottom of the circumferential groove is H (mm), and the amount of prehydrophobized silica with respect to 100 parts by mass of the rubber component in the rubber composition. The tire according to any one of claims 10 to 12, wherein A/H is 10 or more when the content is A (parts by mass).

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