Rubber composition for tires

Abstract

The rubber composition for tires contains a rubber component and a tackifier. The tackifier is a polymer that contains structural units derived from isopropenyltoluene and does not substantially contain structural units derived from the C5 fraction. The softening point of the tackifier is 85 DEG C or more and 136 DEG C or less. The tackifier has a weight-average molecular weight of 1910 or less. The z average molecular weight of the tackifier is less than 4000.

Description

TECHNICAL FIELD

[0001] The present application relates to a rubber composition for tires. BACKGROUND

[0002] Conventionally, it is known that a rubber composition for tires containing a rubber component and a tackifier is used to manufacture a tire.

[0003] As such a rubber composition for tires, for example, a racing tire tread rubber composition containing SBR (styrene-butadiene copolymer rubber) and a copolymer resin of an aromatic vinyl compound and a C5 fraction is proposed (for example, refer to Example 2 of Patent Document 1).

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 10-195238 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] On the other hand, in terms of safety, tires are required to improve wet grip (braking performance on a wet road) which indicates braking performance.

[0009] The present application provides a rubber composition for tires, which is used to manufacture a tire having excellent wet grip by using a tackifier having a softening point and a z-average molecular weight in a prescribed ratio, the tackifier being a polymer containing a structural unit derived from isopropenyl toluene and substantially not containing a structural unit derived from a C5 fraction.

[0010] METHOD FOR SOLVING THE PROBLEMS

[0011] The present application [1] is a rubber composition for tires containing a rubber component and a tackifier, the tackifier being a polymer containing a structural unit derived from isopropenyl toluene and substantially not containing a structural unit derived from a C5 fraction, the softening point of the tackifier being 85°C or higher and 136°C or lower, the weight average molecular weight of the tackifier being 1910 or lower, and the z-average molecular weight of the tackifier being less than 4000.

[0012] The present application [2] is the rubber composition for tires described in the above [1], wherein the polymer contains a structural unit derived from indene, and the structural unit derived from indene in the polymer is 35 mol% or lower.

[0013] EFFECTS OF THE INVENTION

[0014] The rubber composition for tire according to the present application contains a tackifier. The tackifier is a polymer containing a structural unit derived from isopropenyl toluene and substantially not containing a structural unit derived from a C5 fraction. The softening point of the tackifier is 85°C or higher and 136°C or lower. The weight average molecular weight of the tackifier is 1910 or lower. The z average molecular weight of the tackifier is less than 4000. Therefore, a tire having excellent wet grip performance can be produced. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a graph showing the relationship of the peak temperature shift value with respect to the peak of the rubber composition for tire not containing the tackifier to the ratio of the peak temperature shift value with respect to the peak of the rubber composition for tire not containing the tackifier. DETAILED DESCRIPTION

[0016] The rubber composition for tire contains a rubber component and a tackifier.

[0017] < Rubber Component >

[0018] As the rubber component, for example, diene rubbers can be cited.

[0019] As the diene rubbers, for example, natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), butyl rubber (IIR), acrylonitrile butadiene rubber (NBR), ethylene propylene diene rubber (EPDM), and chloroprene rubber (CR) can be cited.

[0020] As the rubber component, styrene butadiene rubber (SBR) can be preferably cited.

[0021] The rubber component can be used alone or in combination of two or more.

[0022] The content ratio of the rubber component is, for example, 70 parts by mass or more, preferably 80 parts by mass or more, and, for example, 95 parts by mass or less, preferably 90 parts by mass or less, with respect to 100 parts by mass of the total amount of the rubber component and the tackifier.

[0023] < Tackifier >

[0024] The tackifier is a polymer containing a structural unit derived from isopropenyl toluene and substantially not containing a structural unit derived from a C5 fraction.

[0025] Such a polymer is obtained by polymerizing a polymerization component.

[0026] The polymerization component contains isopropenyl toluene as an essential component.

[0027] Further, the polymerization component substantially does not contain a C5 fraction.

[0028] The C5 fraction is obtained by refining and / or decomposing petroleum. In addition, the C5 fraction is a fraction having a boiling point range of generally -15°C or higher and 45°C or lower under normal pressure, and contains, for example, unsaturated aliphatic hydrocarbons having 5 carbon atoms not containing a conjugated double bond and unsaturated aliphatic hydrocarbons having 5 carbon atoms containing a conjugated double bond.

[0029] As the unsaturated aliphatic hydrocarbons having 5 carbon atoms not containing a conjugated double bond, for example, 1-pentene, 2-methyl-l-butene, 3-methyl-l-butene and 2-pentene can be given.

[0030] As the unsaturated aliphatic hydrocarbons having 5 carbon atoms containing a conjugated double bond, for example, isoprene, 1,3-pentadiene and cyclopentadiene can be given.

[0031] The polymerization component can also contain other components (components other than the isopropenyltoluene and the C5 fraction). As the other components, for example, α-methylstyrene, indene, vinyltoluene and unsaturated aliphatic hydrocarbons (other than the C5 fraction) can be given.

[0032] The unsaturated aliphatic hydrocarbons (other than the C5 fraction) are components capable of copolymerizing with the isopropenyltoluene, the α-methylstyrene, the indene and the vinyltoluene, and, for example, a C4 fraction can be given.

[0033] The C4 fraction is obtained by refining and / or decomposing petroleum. In addition, the C4 fraction is a fraction having a boiling point range of generally -15°C or higher and 45°C or lower under normal pressure, and contains, for example, unsaturated aliphatic hydrocarbons having 4 carbon atoms not containing a conjugated double bond and unsaturated aliphatic hydrocarbons having 4 carbon atoms containing a conjugated double bond.

[0034] As the unsaturated aliphatic hydrocarbons having 4 carbon atoms not containing a conjugated double bond, for example, 1-butene, isobutene and 2-butene can be given.

[0035] As the unsaturated aliphatic hydrocarbons having 4 carbon atoms containing a conjugated double bond, for example, 1,3-butadiene can be given.

[0036] As the other components, indene is preferably given. That is, as the polymer, a copolymer of the isopropenyltoluene and the indene is preferably given.

[0037] The other components can be used alone or in combination of two or more.

[0038] In addition, all or a part of the monomers constituting the polymerization component can be derived from fossil fuels or from biomass.

[0039] The fossil fuels can include petroleum, coal, natural gas, shale gas or a combination thereof. The biomass refers to all renewable natural raw materials derived from plants including fungi, yeasts, algae and bacteria, and animals, and the like, and residues thereof.

[0040] Further, the polymer is obtained by polymerizing the polymerization component in the presence of a Friedel-Crafts catalyst.

[0041] As the Friedel-Crafts catalyst, for example, a phenol complex (for example, a boron trifluoride phenol complex) can be given.

[0042] The complexing ratio of the Friedel-Crafts catalyst is, for example, 0.01 parts by mass or more and, further, for example, 1 part by mass or less with respect to 100 parts by mass of the polymerization component.

[0043] As the polymerization conditions, the polymerization temperature is, for example, -50°C or more and, further, for example, 50°C or less. The polymerization time is, for example, 10 minutes or more and, further, for example, 10 hours or less.

[0044] Further, the above reaction is performed in the presence of a solvent or without a solvent. The above reaction is preferably performed in the presence of a solvent.

[0045] As the solvent, for example, aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ketones, and alkyl esters can be given. As the solvent, aromatic hydrocarbons are preferably given. As the aromatic hydrocarbons, for example, toluene and xylene can be given. As the aromatic hydrocarbons, toluene is preferably given.

[0046] The solvent can be used alone or in combination of two or more.

[0047] By this, a polymer (a solution of the polymer) is obtained. As such a polymer, a homopolymer of isopropenyltoluene and a copolymer of isopropenyltoluene and indene are preferably given. As the polymer, a copolymer of isopropenyltoluene and indene is more preferably given.

[0048] In the solution of the polymer, the solid content concentration is, for example, 5% by mass or more, preferably 10% by mass or more, and, further, for example, 70% by mass or less, preferably 60% by mass or less.

[0049] In such a polymer, the structural unit from isopropenyltoluene is, for example, 65% by mole or more, preferably 70% by mole or more, more preferably 80% by mole or more, further preferably 90% by mole or more, and, further, for example, 100% by mole or less, preferably 95% by mole or less.

[0050] Further, in such a polymer, the structural unit from other components (components other than isopropenyltoluene and the C5 fraction) is, for example, 0% by mole or more, preferably 5% by mole or more, and, further, for example, 35% by mole or less, preferably 30% by mole or less, more preferably 20% by mole or less, further preferably 10% by mole or less.

[0051] The polymer contains structural units derived from indene, particularly in the case where the other component is indene. The structural units derived from indene in the polymer are, for example, 35 mol% or less, preferably 30 mol% or less, more preferably 20 mol% or less, further preferably 10 mol% or less, and additionally, for example, 1 mol% or more, preferably 5 mol% or more, from the viewpoint of improving wet grip.

[0052] Further, as described above, the polymer substantially contains no structural units derived from the C5 fraction. Specifically, the structural units derived from the C5 fraction in the polymer are, for example, 3 mol% or less, preferably 1 mol% or less, more preferably 0.1 mol% or less.

[0053] Note that the proportion of the above structural units can be determined by 13 C-NMR spectroscopy.

[0054] The softening point of the polymer is 85°C or more, and additionally, 136°C or less, more preferably 130°C or less, further preferably 110°C or less, and particularly preferably 90°C or less.

[0055] If the above softening point is within the above range, wet grip can be improved.

[0056] On the other hand, if the above softening point is outside the above range, wet grip is reduced.

[0057] Note that the above softening point can be determined by the ring and ball method (according to JIS K2207).

[0058] The number average molecular weight (Mn) of the polymer is, for example, 400 or more, preferably 500 or more, and additionally, for example, 2000 or less, preferably 1200 or less, more preferably 1000 or less, further preferably 900 or less, and particularly preferably 700 or less, in terms of a standard polystyrene based on gel permeation chromatography (GPC).

[0059] If the above number average molecular weight (Mn) is within the above range, wet grip can be improved.

[0060] Further, the weight average molecular weight (Mw) of the polymer is, for example, 500 or more, preferably 800 or more, and additionally, 1910 or less, preferably 1700 or less, more preferably 1500 or less, and further preferably 1000 or less, in terms of a standard polystyrene based on gel permeation chromatography (GPC).

[0061] If the above weight average molecular weight (Mw) is within the above range, wet grip can be improved.

[0062] In addition, the z-average molecular weight (Mz) of the polymer is less than 4,000, preferably 3,000 or less, more preferably 2,600 or less, further preferably 2,000 or less, particularly preferably 1,500 or less, most preferably 1,200 or less, and, for example, 500 or more, preferably 700 or more, more preferably 1,000 or more, in terms of a standard polystyrene equivalent determined by gel permeation chromatography (GPC).

[0063] If the above z-average molecular weight (Mz) is within the above range, wet grip can be improved.

[0064] On the other hand, if the above z-average molecular weight (Mz) is above the above upper limit, wet grip is reduced.

[0065] In addition, the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw / Mn) in the polymer is, for example, 1.10 or more, preferably 1.30 or more, and, for example, 2.00 or less, preferably 1.80 or less, more preferably 1.60 or less, further preferably 1.40 or less.

[0066] If the above ratio is within the above range, wet grip can be improved.

[0067] The tackifier can be used alone or in combination of two or more.

[0068] The tackifier can be contained in a proportion of, for example, 5 parts by mass or more, preferably 15 parts by mass or more, and, for example, 35 parts by mass or less, preferably 25 parts by mass or less, with respect to 100 parts by mass of the rubber component.

[0069] <Additives>

[0070] The rubber composition for tires can contain additives as needed in an appropriate proportion. As the additives, there can be mentioned antioxidants, ultraviolet absorbers, antistatic agents, anti-aging agents, pigments, fillers, antifungal agents, and processing aids.

[0071] As the fillers, there can be mentioned, for example, silica (also referred to as white carbon), carbon black, activated calcium carbonate, light calcium carbonate, heavy calcium carbonate, talc, silicic acid, and clay.

[0072] As the fillers, from the viewpoints of uniform dispersibility in a rubber matrix and excellent reinforcing properties and general usability (cost), there can be preferably mentioned silica. In other words, the fillers preferably contain silica.

[0073] The silica is not particularly limited, and there can be mentioned any silica conventionally known to be incorporated in rubber compositions for use in tires and the like.

[0074] As such silicon dioxide, for example, fumed silica, calcined silica, precipitated silica, pulverized silica, fused silica, and colloidal silica can be given.

[0075] In addition, the filler preferably contains carbon black together with the silicon dioxide.

[0076] As the carbon black, for example, SAF, ISAF, HAF, FEF, GPE, SRF, and the like can be given.

[0077] The filler can be used alone or in combination of two or more.

[0078] <Preparation of the rubber composition for tire>

[0079] The rubber composition for tire is obtained by compounding and kneading a rubber component, a tackifier, and an additive as necessary.

[0080] In addition, the rubber composition for tire can also be diluted with a known solvent. In addition, in the polymerization of the above-mentioned polymer, when the polymerization component is polymerized in the presence of a solvent, the solvent can also be used directly.

[0081] In the case where the rubber composition for tire is diluted, the solid component concentration is, for example, 5% by mass or more, preferably 10% by mass or more, and, for example, 70% by mass or less, preferably 60% by mass or less.

[0082] <Effects>

[0083] The rubber composition for tire contains a tackifier. The tackifier is a polymer containing a structural unit derived from isopropyltoluene and substantially not containing a structural unit derived from a C5 fraction. The softening point of the tackifier is 85°C or higher and 136°C or lower. The weight average molecular weight of the tackifier is 1910 or lower. The z average molecular weight of the tackifier is less than 4000. Therefore, a tire having excellent wet grip performance can be manufactured.

[0084] In detail, even if the tackifier is compounded in the rubber composition for tire, if the dispersibility of the tackifier is insufficient, the wet grip performance cannot be improved.

[0085] On the other hand, the rubber composition for tire has a prescribed formulation, a prescribed softening point, and a prescribed z average molecular weight, and thus the dispersibility can be improved. As a result, from the viewpoint that the mobility of rubber is hindered at the time of dynamic deformation of the tire and energy loss can be increased, the wet grip performance can be improved.

[0086] Note that, regarding the evaluation of the above-mentioned dispersibility, detailed description is given in the examples described later.

[0087] Furthermore, according to such a rubber composition for tire, a tire having excellent wet grip performance can be manufactured.

[0088] Examples

[0089] Next, the present application is explained based on examples and comparative examples, but the present application is not limited by the following examples. Note that "parts" and "%" are on a mass basis unless otherwise specified. Also, the specific numerical values of compounding ratio (content ratio), physical property values, parameters, etc. used in the following description can replace the upper limit values (values defined as "or less," "less than") or lower limit values (values defined as "or more," "more than") of the compounding ratio (content ratio), physical property values, parameters, etc. described in the above "DETAILED DESCRIPTION" to which they correspond.

[0090] <Details of Components>

[0091] The details of the abbreviations used in the following description of each example and each comparative example are as follows.

[0092] SSBR: Solution-polymerized polystyrene butadiene rubber (manufactured by ENEOS MATERIALS CO., LTD., trade name "SL552")

[0093] IPT: Isopropenyl toluene

[0094] IND: Indene

[0095] aMS: a-Methylstyrene

[0096] St: Styrene

[0097] C5: C5 fraction

[0098] <Production of Tackifier (Polymer)>

[0099] Production Example 1

[0100] A mixture of polymerization components (isopropenyl toluene and indene) and dehydrated and purified toluene (polymerization components / toluene = 1 / 1 (volume ratio)) and a Friedel-Crafts catalyst (boron trifluoride phenol complex (phenol 1.7 times the equivalent amount) diluted 10 times with dehydrated and purified toluene) was continuously supplied to the first stage of a high-pressure vessel having a stirring blade with an actual capacity of 1270 ml, and a polymerization reaction was performed at 25°C. The mass ratio of isopropenyl toluene and indene (isopropenyl toluene / indene) was 75 / 25, the supply amount of the mixture of polymerization components and toluene was 1.0 liters / hour, and the supply amount of the Friedel-Crafts catalyst was set to 90 milliliters / hour. Thus, a reaction mixture was obtained.

[0101] Next, the reaction mixture was transferred to a second-stage autoclave, and the polymerization reaction was continued at 25°C. Then, at the time when the total residence time in the first-stage and second-stage autoclaves became 2 hours, the reaction mixture was continuously discharged from the autoclave, and at the time when the residence time became 3 times, 1 liter of the reaction mixture was collected, and the polymerization reaction was ended. After the polymerization was ended, 1 equivalent of an aqueous NaOH solution was added to the collected reaction mixture, and the catalyst residue was deashed. Further, the reaction mixture was washed with a large amount of water 5 times, and then the solvent and unreacted polymerization components were removed by distillation under reduced pressure using an evaporator, and a polymer (adhesive) as a copolymer of isopropenyl toluene and indene was obtained.

[0102] Production Example 2

[0103] A polymer (adhesive) as a copolymer of isopropenyl toluene and indene was obtained based on the same procedure as in Production Example 1. Therein, the polymerization temperature was changed to 5°C, the mass ratio of isopropenyl toluene to indene (isopropenyl toluene / indene) was changed to 60 / 40, and the supply amount of the Friedel-Crafts catalyst was changed to 120 ml / hour.

[0104] Production Example 3

[0105] A polymer (adhesive) as a homopolymer of isopropenyl toluene was obtained based on the same procedure as in Production Example 1. Therein, the polymerization temperature was changed to 5°C, the polymerization component was changed only to isopropenyl toluene, and the supply amount of the Friedel-Crafts catalyst was changed to 82 ml / hour.

[0106] Production Example 4

[0107] A polymer (adhesive) as a copolymer of α-methylstyrene and styrene was obtained based on the same procedure as in Production Example 1. Therein, the polymerization temperature was changed to 25°C, the polymerization component was changed to α-methylstyrene and styrene (α-methylstyrene / styrene = 60 / 40 (mass ratio)), and the supply amount of the Friedel-Crafts catalyst was changed to 75 ml / hour.

[0108] Production Example 5

[0109] A polymer (adhesive) as a copolymer of α-methylstyrene and styrene was obtained based on the same procedure as in Production Example 1. Therein, the polymerization temperature was changed to 5°C, the polymerization component was changed to α-methylstyrene and styrene (α-methylstyrene / styrene = 60 / 40 (mass ratio)), and the supply amount of the Friedel-Crafts catalyst was changed to 56 ml / hour.

[0110] Production Example 6

[0111] A polymer (adhesion promoter) as a homopolymer of α-methylstyrene was obtained based on the same procedure as in Production Example 1. Therein, the polymerization temperature was changed to 5°C, the polymerization component was changed only to α-methylstyrene, and the supply amount of the Friedel-Crafts catalyst was changed to 56 ml / hour.

[0112] Production Example 7

[0113] A polymer (adhesion promoter) as a homopolymer of α-methylstyrene was obtained based on the same procedure as in Production Example 1. Therein, the polymerization temperature was changed to 5°C, the polymerization component was changed only to α-methylstyrene, and the supply amount of the Friedel-Crafts catalyst was changed to 56 ml / hour.

[0114] Production Example 8

[0115] A polymer (adhesion promoter) as a homopolymer of α-methylstyrene was obtained based on the same procedure as in Production Example 1. Therein, the polymerization temperature was changed to 5°C, the polymerization component was changed only to α-methylstyrene, and the supply amount of the Friedel-Crafts catalyst was changed to 56 ml / hour.

[0116] Production Example 9

[0117] A polymer (adhesion promoter) as a copolymer of isopropenyltoluene and C5 fraction was obtained based on the same procedure as in Production Example 1. Therein, the polymerization component was changed to isopropenyltoluene and C5 fraction, and the supply amount of the Friedel-Crafts catalyst was changed to 105 ml / hour.

[0118] Production Example 10

[0119] A polymer (adhesion promoter) as a copolymer of isopropenyltoluene and indene was obtained based on the same procedure as in Production Example 1. Therein, the polymerization temperature was changed to 5°C, the mass ratio of isopropenyltoluene to indene (isopropenyltoluene / indene) was changed to 60 / 40, and the supply amount of the Friedel-Crafts catalyst was changed to 108 ml / hour.

[0120] Production Example 11

[0121] A polymer (adhesion promoter) as a copolymer of isopropenyltoluene and indene was obtained based on the same procedure as in Production Example 1. Therein, the polymerization temperature was changed to 25°C, the mass ratio of isopropenyltoluene to indene (isopropenyltoluene / indene) was changed to 75 / 25, and the supply amount of the Friedel-Crafts catalyst was changed to 72 ml / hour.

[0122] Production Example 12

[0123] Based on the same steps as Production Example 1, a polymer (adhesion promoter) was obtained as a copolymer of isopropenyltoluene and indene. Among these, the polymerization temperature was changed to 25°C, the mass ratio of isopropenyltoluene to indene (isopropenyltoluene / indene) was changed to 75 / 25, and the supply amount of the Friedel-Crafts catalyst was changed to 200 mL / hour.

[0124] <Preparation of Rubber Composition for Tire>

[0125] Examples 1 to 5 and Comparative Examples 1 to 8

[0126] According to the description of Table 2, the rubber component and the adhesion promoter were compounded, and kneaded for about 5 minutes at a temperature of 160°C and a rotor rotation speed of 40 rpm using a LABO PLASTIC MILL (Model 4C150, manufactured by TOYOJIKKISHO Co., Ltd.). Thereby, a rubber composition for tire was prepared.

[0127] <Assessment>

[0128] [Structural units of each component]

[0129] Based on the following conditions, the structural units of each component in the polymer of each production example were found by 13 The structural units of each component in the polymer of each production example were found by analyzing the C-NMR spectrum. The results thereof are shown in Table 1.

[0130] {Conditions}

[0131] Apparatus: AVANCE III cryo-500 type nuclear magnetic resonance apparatus manufactured by Bruker BioSpin Co.

[0132] Measurement nucleus: 13C (125 MHz)

[0133] Measurement mode: Single pulse proton broadband decoupling

[0134] Pulse width: 45° (5.00 μsec)

[0135] Number of points: 64k

[0136] Measurement range: 250 ppm (-55 to 195 ppm)

[0137] Repetition time: 5.5 seconds

[0138] Number of accumulations: 128 times

[0139] Measurement solvent: o-dichlorobenzene / benzene-d6 (4 / 1 (by volume))

[0140] Sample concentration: 60 mg / 0.6 mL

[0141] Measurement temperature: 120°C

[0142] Window function: exponential (BF: 1.0 Hz)

[0143] Chemical shift reference: δ δ signal 29.73 ppm

[0144] [softening point]

[0145] For each of the polymers of the production examples, the ring and ball method was measured in accordance with JIS K2207. The results thereof are shown in Table 1.

[0146] [Number average molecular weight (Mn), weight average molecular weight (Mw), z average molecular weight (Mz), and Mw / Mn]

[0147] For each of the polymers of the production examples, the number average molecular weight (Mn), the weight average molecular weight (Mw), and the z average molecular weight (Mz) based on gel permeation chromatography (GPC) measured on the basis of the following measurement conditions, and in addition, Mw / Mn was calculated. The results thereof are shown in Table 1.

[0148] {Measurement conditions}

[0149] Apparatus: GPC HLC-8320 (manufactured by Tosoh Corporation)

[0150] Solvent: Tetrahydrofuran

[0151] Column: TSKgel G7000x1, TSKgel G4000x2, TSKgel G2000x1 (all manufactured by Tosoh Corporation)

[0152] Flow rate: 1.0 ml / minute

[0153] Sample: 20 mg / mL tetrahydrofuran solution

[0154] Column temperature: 40°C

[0155] Detector: Differential refractive index detector

[0156] Injection amount: 50 μl

[0157] [Viscoelasticity]

[0158] A prescribed amount of each of the tire rubber compositions of the examples and the comparative examples was filled in a SUS mold frame, and using a manual hot press (PEWR-30 manufactured by Kamo Metal Industry) set to a heating plate 150°C, after pressurization at 9 MPa of gage pressure for 4 minutes, it was transferred to a cooling plate set to 20°C, and compression was performed at 9 MPa of gage pressure, and cooling was performed for 3 minutes. Thereby, a measurement tablet having a length of 65 mm x width of 65 mm x thickness of 2 mm was produced. Next, from the measurement tablet, a test piece was produced by blanking processing to a width of 3 mm.

[0159] For the test pieces, using a rheometer (DVA-225 manufactured by IT Measurement Control Co., Ltd.), the tan δ peak temperature, tan δ peak, and tan δ peak at -30°C were measured at a temperature dispersion of -100 to 200°C under conditions of a tensile mode, a frequency of 1 Hz, a strain setting of 0.05%, and a temperature increase rate of 3°C / minute. The results thereof are shown in Table 2.

[0160] Meanwhile, the change in the tan δ peak temperature and tan δ peak of the examples and comparative examples in which the tackifier was compounded, relative to the tire rubber composition in which no tackifier was compounded (hereinafter, sometimes referred to as no addition), was calculated. Specifically, the peak temperature shift value relative to no addition (the tan δ peak temperature of each example and each comparative example - the tan δ peak temperature of Comparative Example 1) and the ratio relative to the peak of no addition (the tan δ peak of each example and each comparative example / the tan δ peak of Comparative Example 1) were calculated. The results thereof are shown in Table 2.

[0161] <Investigation>

[0162] Figure 1 The relationship between the peak temperature shift value relative to no addition and the ratio relative to the peak of no addition is shown.

[0163] In Figure 1 , the more to the right, the greater the peak temperature shift value relative to no addition. When the peak temperature shift value relative to no addition becomes greater, then if the dispersibility is uneven, a wide tan δ peak from the tackifier monomer is observed on the high temperature side. Therefore, it is known that, in the case where the dispersibility is uneven, the peak temperature shift value corresponding to the amount of addition decreases, and thus the dispersibility of the tackifier is excellent.

[0164] In addition, in Figure 1 , the more to the upper side, the closer the ratio relative to the peak of no addition to 1. If the dispersibility is uneven, a wide tan δ peak from the tackifier monomer is observed on the high temperature side. Therefore, it is known that the ratio relative to the peak of no addition decreases depending on the proportion thereof, and thus if the ratio relative to the peak of no addition is close to 1, the dispersibility of the tackifier is excellent.

[0165] That is, in Figure 1 , it is known that the more to the upper right side (specifically, if in the area indicated by the diagonal line portion in Figure 1 , the dispersibility of the tackifier is improved.

[0166] Furthermore, if the dispersibility of the tackifier is improved, from the viewpoint of hindering the mobility of the rubber at the time of dynamic deformation of the tire and increasing the energy loss, the wet grip performance can be improved.

[0167] According to Figure 1It is understood that Examples 1 to 5 using the prescribed tackifier having a prescribed formulation, a prescribed softening point, a prescribed weight average molecular weight, and a prescribed z average molecular weight are on the right upper side compared to Comparative Examples 1 to 8 not using the prescribed tackifier. It is understood that Examples 1 to 5 using the prescribed tackifier have improved dispersibility of the tackifier compared to Comparative Examples 1 to 8 not using the prescribed tackifier, and can improve wet grip.

[0168] In addition, it is known that 10 4 (10th power) to 10 6 (10th power) Hz corresponds to deformation due to fine irregularities of the road surface. This frequency region is considered to be on the low temperature side when temperature conversion is performed in the time / temperature conversion law of viscoelasticity. In addition, it is reported in documents that tan δ around -30 to -15°C is related to the frictional force on a wet road surface of a tire. Therefore, if the tan δ peak value at -30°C is high, wet grip can be improved.

[0169] Furthermore, the tan δ peak value at -30°C is high in Examples 1 to 5 using the prescribed tackifier compared to Comparative Examples 1 to 6 not using the prescribed tackifier. It is understood that Examples 1 to 5 have excellent wet grip compared to Comparative Examples 1 to 8.

[0170] [Table 1]

[0171]

[0172] [Table 2]

[0173]

Claims

1. A rubber composition for a tire, comprising a rubber component and a tackifier, The tackifier is a polymer containing a structural unit derived from isopropenyltoluene and substantially not containing a structural unit derived from a C5 fraction, The softening point of the tackifier is 85°C or higher and 136°C or lower. The weight average molecular weight of the tackifier is 1910 or less, The z-average molecular weight of the tackifier is less than 4,000.

2. The tire rubber composition according to claim 1, wherein The polymer comprises structural units derived from indene, In the polymer, the content of structural units derived from indene is 35 mol% or less.

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