Rubber composition, vulcanizate, tire tread rubber, and tire

Abstract

The present invention solves the problem of providing a rubber composition having a low environmental load and capable of improving the performance of a tire on ice. The solution to the problem is a rubber composition comprising: a rubber component including diene rubber; an inorganic blowing agent; and a blowing aid, and characterized in that the total content of the inorganic blowing agent and the blowing aid is 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component, and the mass ratio (inorganic blowing agent: blowing aid) between the inorganic blowing agent and the blowing aid is 1:1.1 to 1:3.3.

Description

TECHNICAL FIELD

[0001] The present application relates to a rubber composition, a vulcanized rubber, a tread rubber for a tire, and a tire. BACKGROUND

[0002] In order to improve the braking performance and the driving performance on an icy / snowy road surface (hereinafter, these performances will be collectively referred to as "on-ice performance"), particularly the tread of a tire, intensive studies have been conducted. Due to the frictional heat between the icy / snowy road surface and the tire, a water film tends to be formed on the icy / snowy road surface, and the water film thus formed can reduce the coefficient of friction between the tire and the icy / snowy road surface. Therefore, in order to improve the on-ice performance of the tire, it is necessary to improve the water film-removing capacity of the tread of the tire.

[0003] A possible solution for improving the water film-removing capacity of the tread of the tire is to form micro drainage grooves at the ground contact surface of the tire, so that the micro drainage grooves remove the water film, thereby increasing the coefficient of friction of the tire on the icy / snowy road surface. However, in this case, while the on-ice performance of the tire is improved at the initial stage of use of the tire, the on-ice performance of the tire deteriorates as the tire wears. Therefore, there is a need for a technology that can prevent the deterioration of the on-ice performance even when the tire wears.

[0004] In this regard, a technology of applying foamed rubber to the tread of a tire to impart the water film-removing capacity to the tread of the tire is known. A rubber composition including a rubber component and a blowing agent is generally used for foamed rubber, in which an organic blowing agent is conventionally used as the blowing agent, although in some cases an inorganic blowing agent is also used as the blowing agent (for example, PTL 1 shown below). By effectively using an inorganic blowing agent therein, it is possible to provide a rubber composition having a low load on the environment, because the inorganic blowing agent has a relatively low load on the environment.

[0005] LIST OF CITATIONS

[0006] PATENT LITERATURE

[0007] PTL 1: WO 2017 / 068772 A1 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] However, as a result of studies conducted by the inventors of the present application, it was found that in the case where a rubber composition using an inorganic blowing agent is applied to the tread of a tire, the on-ice performance of the tire is not satisfactory and has room for improvement.

[0010] In view of the foregoing, an object of the present application is to provide a rubber composition capable of solving the above-described problems of the prior art, i.e., a rubber composition having a low environmental load and capable of reliably improving the ice performance of a tire.

[0011] Further, another object of the present application is to provide i) vulcanized rubbers and tire treads for tires each having a low environmental load and capable of reliably improving the ice performance of a tire, and ii) a tire having a low environmental load and capable of reliably improving the ice performance thereof.

[0012] Solution to the problem

[0013] The principal features of the present application for achieving the above object are as follows.

[0014] The rubber composition of the present application is a rubber composition comprising: a rubber component including a diene rubber; an inorganic blowing agent; and a blowing aid, wherein

[0015] The total content of the inorganic blowing agent and the blowing aid is in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component, and

[0016] The mass ratio of the inorganic blowing agent with respect to the blowing aid (inorganic blowing agent : blowing aid) is in the range of 1 : 1.1 to 1 : 3.3.

[0017] The vulcanized rubber of the present application is characterized in that the foaming rate is in the range of 1% to 45% as a vulcanization product of the rubber composition.

[0018] The tire tread for a tire of the present application is characterized by being made of the rubber composition or the vulcanized rubber.

[0019] The tire of the present application is characterized by having the rubber composition or the vulcanized rubber in the tread portion thereof.

[0020] Effects of the invention

[0021] According to the present application, it is possible to provide a rubber composition having a low environmental load and capable of reliably improving the ice performance of a tire.

[0022] Further, according to the present application, it is possible to provide i) vulcanized rubbers and tire treads for tires each having a low environmental load and capable of reliably improving the ice performance of a tire, and ii) a tire having a low environmental load and capable of reliably improving the ice performance thereof. DETAILED DESCRIPTION

[0023] Hereinafter, the rubber composition, the vulcanized rubber, the tire tread for a tire, and the tire of the present application will be described in detail based on embodiments of the present application.

[0024] <Rubber composition>

[0025] The rubber composition of the present application is characterized by comprising: a rubber component including a diene rubber; an inorganic blowing agent; and a blowing aid, wherein the total content of the inorganic blowing agent and the blowing aid is in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component, and the mass ratio of the inorganic blowing agent with respect to the blowing aid (inorganic blowing agent : blowing aid) is in the range of 1 : 1.1 to 1 : 3.3.

[0026] In the rubber composition of the present application, when the rubber composition is vulcanized, the inorganic blowing agent is foamed, thereby forming bubbles (voids) in the rubber composition thus vulcanized (i.e., in the vulcanized rubber). Further, the blowing aid promotes the foaming reaction of the inorganic blowing agent and increases the foaming ratio of the vulcanized rubber thus obtained. Still further, in the rubber composition of the present application, the total content of the inorganic blowing agent and the blowing aid is set in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component, and the mass ratio of the inorganic blowing agent with respect to the blowing aid (inorganic blowing agent : blowing aid) is set in the range of 1 : 1.1 to 1 : 3.3, whereby when the rubber composition is vulcanized, the rubber composition is foamed in a satisfactory manner and the foaming ratio of the vulcanized rubber is increased. The vulcanized rubber having the foaming ratio thus increased is applied to a tire, ensuring good water film removal ability of the tire, thereby improving the drainage performance, and further improving the performance on ice of the tire. In the case where the total content of the inorganic blowing agent and the blowing aid and / or the mass ratio of the inorganic blowing agent with respect to the blowing aid exceeds the above range, the foaming ratio of the vulcanized rubber is decreased, whereby the performance on ice of the tire is improved in an unsatisfactory manner.

[0027] Still further, the inorganic blowing agent of the present application is an inorganic compound having a relatively low load on the environment (harmless to the human body).

[0028] Accordingly, the rubber composition of the present application has a low load on the environment, and when the rubber composition is applied to a tire, the performance on ice of the tire can be improved in a satisfactory manner.

[0029] (Rubber component)

[0030] The rubber component of the rubber composition of the present application includes a diene rubber. The proportion of the diene rubber in the rubber component is preferably ≥ 80 mass%, more preferably ≥ 90 mass%, and particularly preferably 100 mass%. The rubber component can also include a rubber other than the diene rubber, but is preferably composed only of the diene rubber.

[0031] The diene rubber can be natural rubber (NR) or a synthetic diene rubber. Alternatively, the diene rubber can include both natural rubber and synthetic diene rubber. By applying a rubber composition including at least one of natural rubber and synthetic diene rubber to a tire, the ice performance of the tire can be further improved.

[0032] Examples of the synthetic diene rubber include isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), styrene-isoprene rubber (SIR), and chlorobutadiene rubber (CR), and the like. Among the above examples, isoprene rubber, styrene-butadiene rubber, and butadiene rubber are preferable as the synthetic diene rubber. By applying a rubber composition including at least one selected from the group consisting of isoprene rubber, styrene-butadiene rubber, and butadiene rubber to a tire, the ice performance of the tire can be further improved.

[0033] The single kind among the above examples or a combination of two or more kinds as a blend can be used as the diene rubber (rubber component).

[0034] The diene rubber (rubber component) can be unmodified rubber or modified rubber.

[0035] In the case where the diene rubber has been modified, it is preferable that the diene rubber has been modified by at least one selected from the group consisting of a hydrocarbyloxysilane compound represented by the general formula (I) shown below; a hydrocarbyloxysilane compound represented by the general formula (II) shown below; a hydrocarbyloxysilane compound represented by the general formula (III) shown below; a coupling agent represented by the general formula (IV) shown below; a coupling agent represented by the general formula (V) shown below; a lithium amide represented by the general formula (VI) shown below; and a vinylpyridine.

[0036]

[0037] In the general formula (I), q1+q2=3 (q1 is an integer in the range of 0 to 2, and q2 is an integer in the range of 1 to 3),

[0038] R 11 represents a C 1-20 divalent aliphatic / a cycloaliphatic hydrocarbon group or a C 6-18 divalent aromatic hydrocarbon group,

[0039] R 12 and R 13 each independently represents a hydrolyzable group, or a C 1-20 monovalent aliphatic / cycloaliphatic hydrocarbon group, or a C 6-18 aromatic hydrocarbon group,

[0040] R 14represents C 1-20 monovalent aliphatic / a cyclic hydrocarbon group or C 6-18 aromatic hydrocarbon group, wherein when q1 is 2, R 14 may be the same species or different species, and

[0041] R 15 represents C 1-20 monovalent aliphatic / a cyclic hydrocarbon group or C 6-18 aromatic hydrocarbon group, wherein when q2 is 2, R 15 may be the same species or different species.

[0042]

[0043] in General Formula (II), r1 + r2 = 3 (r1 is an integer in the range of 1 to 3, and r2 is an integer in the range of 0 to 2), R 21 represents C 1-20 divalent aliphatic / a cyclic hydrocarbon group or C 6-18 divalent aromatic hydrocarbon group,

[0044] R 22 represents dimethylaminomethyl, or dimethylaminoethyl, diethylaminomethyl, diethylaminoethyl, methylsilyl(methyl)aminomethyl, methylsilyl(methyl)aminoethyl, methylsilyl(ethyl)aminomethyl, methylsilyl(ethyl)aminoethyl, dimethylsilylaminomethyl, dimethylsilylaminoethyl, C 1-20 monovalent aliphatic / a cyclic hydrocarbon group or C 6-18 aromatic hydrocarbon group, wherein when r1 is 2 or more, R 22 may be the same species or different species, and

[0045] R 23 represents C 1-20 hydrocarbonoxy group, or C 1-20 monovalent aliphatic / a cyclic hydrocarbon group or C 6-18 aromatic hydrocarbon group, wherein when r2 is 2, R 23 may be the same species or different species.

[0046]

[0047] in General Formula (III), A 3The term "(thio)epoxide" indicates a monovalent group having at least one functional group selected from the group consisting of: (thio)epoxide, (thio)isocyanate, (thio)ketone, (thio)aldehyde, imine, amide, trialkyl isocyanate, (thio)carboxylic acid ester, metal salt of (thio)carboxylic acid, carboxylic anhydride, carboxylic acid halide, and dialkyl carbonate ester, wherein "(thio)epoxide" represents epoxy and thioepoxide, "(thio)isocyanate" represents isocyanate and thioisocyanate, "(thio)ketone" represents ketone and thioketone, "(thio)aldehyde" represents aldehyde and thioaldehyde, "(thio)carboxylic acid ester" represents carboxylic acid ester and thiocarboxylic acid ester, and "metal salt of (thio)carboxylic acid" represents metal salt of carboxylic acid and metal salt of thiocarboxylic acid.

[0048] R 31 This indicates a single bond or preferably a divalent inactive hydrocarbon group having 1 to 20 carbon atoms, and

[0049] R 32 and R 33 Each represents C independently. 1-20 Monovalent aliphatic hydrocarbon group or C 6-18 Aromatic hydrocarbon groups, where "n" represents an integer in the range of 0 to 2. When multiple R groups exist... 32 At that time, R 32 They can be of the same kind or different kinds, and when multiple ORs exist... 33 At that time, OR 33 They can be of the same kind or different kinds.

[0050] It should be noted that alkyloxysilane compounds represented by general formula (III) do not contain active protons or onium salts in their molecules.

[0051] Regarding A in general formula (III) 3 The functional group of the compound is defined as follows: "imine" refers to ketimines, aldehyde imines, and amidines, and "(thio)carboxylic acid ester" refers to unsaturated carboxylic acid esters such as acrylates and methacrylates. Examples of metals in the metal salts of (thio)carboxylic acids include alkali metals, alkaline earth metals, Al, Sn, and Zn.

[0052] R 31 Preferred examples of divalent inactive hydrocarbon groups include C 1-20 Alkylenes. Although alkylenes can be linear, branched, or cyclic, linear alkylenes are preferred. Examples of linear alkylenes include methylene, ethylene, trimethylene, butylene, pentylene, hexylene, octylene, decylene, and dodecylene.

[0053] R 32 and R 33 Examples include C 1-20 Alkyl, C 2-18 alkenyl, C 6-18 Aryl and C7-18 The alkyl and alkenyl groups can be linear, branched, or cyclic, and examples thereof include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, t-butyl, pentyl, hexyl, octyl, decyl, dodecyl, cyclopentyl, cyclohexyl, ethenyl, propenyl, allyl, hexenyl, octenyl, cyclopentenyl, and cyclohexenyl, and the like. The aryl group can have a substituent such as a lower alkyl group on its aromatic ring, and examples of such aryl group include phenyl, tolyl, xylyl, and naphthyl, and the like. The aralkyl group can have a substituent such as a lower alkyl group on its aromatic ring, and examples of such aralkyl group include benzyl, phenethyl, and naphthylmethyl, and the like.

[0054] R 32 and R 33 "n" which is an integer in the range of 0 to 2 is preferably 0, and it is essential that the molecules of R 32 and R 33 each do not contain an active proton or onium salt therein.

[0055] Preferred examples of the hydrocarbyloxysilane compound represented by General Formula (III) include hydrocarbyloxysilane compounds having a (thio)epoxy group, such as (2- glycidoxyethyl)trimethoxysilane, (2-glycidoxyethyl)triethoxysilane, (2- glycidoxyethyl)methyldimethoxysilane, (3-glycidoxypropyl)trimethoxysilane, (3- glycidoxypropyl)triethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, 2-(3,4- epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 2- (3,4-epoxycyclohexyl)ethyl(methyldimethoxysilane), 2-(3,4-epoxycyclohexyl)trimethoxysilane, and those obtained by substituting the epoxy group of the aforementioned hydrocarbyloxysilane compounds having an epoxy group with a thioepoxy group. Among these examples, (3- glycidoxypropyl)trimethoxysilane and 2-(3,4-epoxycyclohexyl)trimethoxysilane are particularly preferred.

[0056] Preferred examples of alkyloxysilane compounds having an imine group, as alkyloxysilane compounds represented by general formula (III), include: triethoxysilane compounds such as N-(1,3-dimethylbutylene)-3-(triethoxysilyl)-1-propane, N-(1-methylethylene)-3-(triethoxysilyl)-1-propane, N-ethylene-3-(triethoxysilyl)-1-propane, N-(1-methylpropylene)-3-(triethoxysilyl)-1-propane, N-(4-N,N-dimethylaminophenylmethylene)-3-(triethoxysilyl)-1-propane, N-(cyclohexylene)-3-(triethoxysilyl)- 1-Propylamine; trimethoxysilyl compounds obtained by replacing the triethoxy group of the above-mentioned triethoxysilyl compound with a trimethoxy group; methyldiethoxysilyl compounds obtained by replacing the triethoxy group of the above-mentioned triethoxysilyl compound with a methyldiethoxy group; ethyldiethoxysilyl compounds obtained by replacing the triethoxy group of the above-mentioned triethoxysilyl compound with an ethyldiethoxy group; methyldiethoxysilyl compounds obtained by replacing the triethoxy group of the above-mentioned triethoxysilyl compound with a methyldiethoxy group; ethyldiethoxysilyl compounds obtained by replacing the triethoxy group of the above-mentioned triethoxysilyl compound with an ethyldiethoxy group; and so on. In these examples, N-(1-methylpropylidene)-3-(triethoxysilyl)-1-propane and N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propane are particularly preferred.

[0057]

[0058] In general formula (IV), R 41 R 42 and R 43 Each can independently represent a single bond or C. 1-20 Alkylene

[0059] R 44 R 45 R 46 R 47 and R 49 Each represents C independently. 1-20 alkyl,

[0060] R 48 and R 51 Each represents C independently. 1-20 Alkylene

[0061] R 50 Indicate C 1-20 Alkyl / trialkylsilyl

[0062] "m" represents an integer in the range of 1 to 3 and "p" represents 1 or 2,

[0063] Regarding R 41 ~R 51 , when a plurality of R 44 and / or a plurality of R 45 and / or a plurality of R 47 exist together with m and p, each of R 44 , R 45 , and R 47 is independent of each other; and "j" and "k" each independently represent an integer in the range of 0 to 6, where (i + j + k) is an integer in the range of 3 to 10, and

[0064] A 4 represents C 1-20 hydrocarbyl or an organic group having no active hydrogen but having at least one atom selected from the group consisting of an oxygen atom, a nitrogen atom, a silicon atom, a sulfur atom, and a phosphorus atom.

[0065] The coupling agent represented by general formula (IV) is preferably at least one selected from the group consisting of tetra[3-(2,2-dimethoxy-1 -aza-2-silacyclopentane)propyl]-1,3-propanediamine, tetra(3-trimethoxysilylpropyl)-1,3-propanediamine, and tetra(3-trimethoxysilylpropyl)-1,3-bis(aminomethyl)cyclohexane.

[0066] (R 5 ) a ZX b …(V)

[0067] In general formula (V), "Z" represents tin or silicon, "X" represents chlorine or bromine,

[0068] (R 5 ) is selected from the group consisting of C 1-20 alkyl, C 3-20 cycloalkyl, C 6-20 aryl, and C 7-20 aralkyl, and specific examples of (R 5 ) include methyl, ethyl, n-butyl, neophyl, cyclohexyl, n-octyl, and 2-ethylhexyl, etc., and

[0069] 0 < a < 3 and 1 < b < 4, where a + b = 4.

[0070] Preferred examples of the coupling agent represented by general formula (V) include tin chloride, (R 5 )SnCl3, (R 5 )2SnCl2, and (R 5)3SnCl, etc. In these examples, tin chloride is particularly preferred.

[0071] (AM) Li(Q) y ... (VI)

[0072] In general formula (VI), y = 0 or 0.5 < y < 3 and (Q) is a dissolvable component selected from the group consisting of hydrocarbons, ethers, amines, and mixtures thereof,

[0073] (AM) is represented by formula (VII) or formula (VIII) shown below.

[0074]

[0075] (In general formula (VII), R 71 and R 72 each independently represent C 1-12 alkyl / cycloalkyl / aralkyl.

[0076]

[0077] (In general formula (VIII), R 81 represents: an alkylene group having 3 to 16 methylene groups; or a substituted alkylene group having a C 1-12 linear or branched alkyl group / cycloalkyl group / bicycloalkyl group / aryl group / aralkyl group as a substituent; or an oxydiethylene group; or an N-alkylamino-alkylene group.

[0078] The presence of Q in general formula (VI) allows the lithium amide to be soluble in a hydrocarbon solvent. Q can be a diene-based or vinyl-based polymer / copolymer having a degree of polymerization resulting from 3 to about 300 polymerized (monomer) units. Examples of the above-mentioned polymer and copolymer include polybutadiene, polystyrene, polyisoprene, and copolymers thereof. Other examples of Q include polar ligands such as tetrahydrofuran (THF) and tetramethylethylenediamine (TMEDA), etc.

[0079] The lithium amide represented by general formula (VI) can be a mixture of the lithium amide and an organic alkali metal. The organic alkali metal is preferably selected from the group consisting of compounds each represented by the following general formula: (R 91 )M; (R 92 )OM; (R 93 )C(O)OM; (R 94 )(R 95 )NM; and (R 96 )SO3M, wherein (R 91 ), (R 92 ), (R 93 ), (R 94 ), (R 95 ), and (R 96) are each selected from the group consisting of alkyl, cycloalkyl, alkenyl, aryl, and phenyl (each having about 1 to 12 carbon atoms), and the metal component M is selected from the group consisting of Na, K, Rb, and Cs. M is preferably Na or K.

[0080] The above mixture can preferably contain the organic alkali metal in a mixing ratio of about 0.5 to about 0.02 equivalent per one equivalent of lithium in the lithium amide.

[0081] A chelating agent can be used as a polymerization aid in the mixture of the lithium amide and the organic alkali metal, so that the polymerization does not proceed unevenly. Examples of the usable chelating agent include tetramethylethylenediamine (TMEDA), oxolanyl cyclic acetal-based compounds, and cyclic oligomeric oxolanylalkane-based compounds, etc. The cyclic oligomeric oxolanylalkane-based compounds are particularly preferable, and examples thereof include 2,2-bis(2-tetrahydrofuryl)propane.

[0082] Examples of the vinylpyridine include 2-vinylpyridine and 4-vinylpyridine, etc.

[0083] Among the above various modifiers, N,N-bis(trimethylsilyl)-3-[diethoxy(methyl)silyl]propylamine, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, (3-glycidoxypropyl)trimethoxysilane, tetra(3-trimethoxysilylpropyl)-1,3-propanediamine, tin tetrachloride, a reaction product obtained from the reaction between hexamethyleneimine and n-butyllithium, 4-vinylpyridine, and 2-vinylpyridine are preferable.

[0084] More preferably, the rubber composition of the present application contains a styrene-butadiene rubber in which the bound amount of styrene is ≤ 15 mass% as the styrene-butadiene rubber. By applying a rubber composition containing a styrene-butadiene rubber in which the bound amount of styrene is ≤ 15 mass% to a tire, the ice performance of the tire can be significantly improved.

[0085] The bound amount of styrene in the styrene-butadiene rubber can be determined from the integral ratio of the H-NMR spectrum. 1 H-NMR spectrum.

[0086] (Inorganic blowing agent)

[0087] The rubber composition of the present application contains an inorganic blowing agent. The inorganic blowing agent has a low load on the environment because it is an inorganic compound. When the rubber composition is vulcanized, the inorganic blowing agent causes the effect of foaming (due to heating), thereby forming bubbles (voids) in the rubber composition thus vulcanized (i.e., in the vulcanized rubber).

[0088] Examples of the inorganic foaming agent include carbonates and bicarbonates (i.e., bicarbonates), and the like. Among these examples, bicarbonates are preferred.

[0089] Examples of the carbonates include ammonium carbonate, sodium carbonate, and potassium carbonate, and the like. Examples of the bicarbonates include ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate, and the like. Among these examples, ammonium bicarbonate and sodium bicarbonate are preferred as the inorganic foaming agent because each of the ammonium bicarbonate and the sodium bicarbonate as the inorganic foaming agent strongly foams, thereby further increasing the foaming ratio in the resulting vulcanized rubber, and thus improving the ice performance of the tire.

[0090] Either one kind or a combination of two or more kinds among the above examples can be used as the inorganic foaming agent.

[0091] Sodium bicarbonate (NaHCO3) is particularly preferred as the inorganic foaming agent. When the rubber composition contains sodium bicarbonate, the NaHCO3 strongly foams and further increases the foaming ratio of the resulting vulcanized rubber, whereby the ice performance of the tire can be further improved by applying the rubber composition to the tire.

[0092] From the viewpoint of obtaining a satisfactory foaming ratio of the vulcanized rubber and a satisfactory ice performance of the tire, the content of the inorganic foaming agent is preferably in the range of 1 to 12 parts by mass, more preferably in the range of 1 to 10 parts by mass, even more preferably in the range of 2 to 7 parts by mass, and particularly preferably in the range of 4 to 6.5 parts by mass, relative to 100 parts by mass of the rubber component.

[0093] (Foaming aid)

[0094] The rubber composition of the present application contains a foaming aid. The foaming aid has an effect of promoting the foaming reaction of the inorganic foaming agent at the time of vulcanization of the rubber composition, thereby increasing the foaming ratio of the resulting vulcanized rubber.

[0095] Examples of the foaming aid include urea, zinc stearate, zinc benzenesulfinate, and zinc white, and the like. Among these examples, urea is particularly preferred. When the rubber composition contains urea, the inorganic foaming agent strongly foams and further increases the foaming ratio of the resulting vulcanized rubber, whereby the ice performance of the tire can be further improved by applying the rubber composition to the tire.

[0096] The urea can be treated with an oil or the like. By such a treatment, the urea can be made hydrophobic, thereby improving the dispersibility of the urea in the rubber component. The kind of the oil used in the above treatment is not particularly limited, and various oils can be used.

[0097] Either one kind or a combination of two or more kinds among the above examples can be used as the foaming aid.

[0098] In the rubber composition of the present application, the total content of the inorganic blowing agent and the blowing aid is in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component. When the total content of the inorganic blowing agent and the blowing aid is less than 1 part by mass, the rubber composition cannot be foamed in a satisfactory manner upon vulcanization of the rubber composition, whereby the foaming ratio of the resulting vulcanized rubber decreases. When the total content of the inorganic blowing agent and the blowing aid exceeds 20 parts by mass, the foaming rate similarly decreases.

[0099] Further, from the viewpoint of obtaining a satisfactory foaming ratio of the vulcanized rubber, the total content of the above-mentioned inorganic blowing agent and the blowing aid is preferably ≥ 5 parts by mass and more preferably ≥ 7 parts by mass with respect to 100 parts by mass of the rubber component. Still further, from the viewpoint of obtaining a satisfactory foaming ratio of the vulcanized rubber, the total content of the above-mentioned inorganic blowing agent and the blowing aid is preferably ≤ 20 parts by mass and more preferably ≤ 19 parts by mass with respect to 100 parts by mass of the rubber component.

[0100] In the rubber composition of the present application, the mass ratio of the inorganic blowing agent to the blowing aid (inorganic blowing agent : blowing aid) is in the range of 1 : 1.1 to 1 : 3.3. In the case where the mass ratio (inorganic blowing agent : blowing aid) is 1 : < 1.1, the rubber composition cannot be foamed in a satisfactory manner in the rubber composition upon vulcanization of the rubber composition, whereby the foaming ratio of the resulting vulcanized rubber decreases. The foaming rate similarly decreases in the case where the mass ratio (inorganic blowing agent : blowing aid) is 1 : > 3.3.

[0101] From the viewpoint of obtaining a satisfactory foaming ratio of the vulcanized rubber, the above-mentioned mass ratio of the inorganic blowing agent to the blowing aid (inorganic blowing agent : blowing aid) is preferably 1 : ≥ 1.2 and more preferably 1 : ≥ 1.3. From the viewpoint of obtaining a satisfactory foaming ratio of the vulcanized rubber, the above-mentioned mass ratio of the inorganic blowing agent to the blowing aid (inorganic blowing agent : blowing aid) is preferably 1 : ≤ 3.2, more preferably 1 : ≤ 3.1, even more preferably 1 : ≤ 2.9, still more preferably 1 : ≤ 2.7, particularly preferably 1 : ≤ 2.5, and most preferably 1 : ≤ 2.3.

[0102] From the viewpoint of obtaining a satisfactory foaming ratio of the vulcanized rubber and a satisfactory ice performance of the tire, the content of the blowing aid is preferably in the range of 4 to 14 parts by mass and more preferably in the range of 6 to 14 parts by mass with respect to 100 parts by mass of the rubber component.

[0103] (Short fiber)

[0104] The rubber composition of the present application preferably further comprises short fibers (more preferably, hydrophilic short fibers). In the present application, "hydrophilic short fibers" means short fibers of which a contact angle formed by water thereon is 5 to 80°. The contact angle formed by water on the hydrophilic short fibers can be determined by preparing a test piece by molding a hydrophilic resin of a raw material for the hydrophilic short fibers into a flat and smooth plate; and by using an automatic contact angle meter "DM-301" manufactured by Kyowa Interface Science Co., Ltd., placing a water droplet on the surface of the test piece under conditions of temperature: 25°C and relative humidity: 55%, immediately observing the water droplet on the test piece from the right side of the test piece, and measuring the angle between the tangent of the surface of the test piece and the surface of the water droplet.

[0105] In the case where the rubber composition comprises short fibers, when the rubber composition is vulcanized, the gas generated from the inorganic blowing agent enters the inside of the short fibers, thereby forming voids (bubbles) having a configuration corresponding to the shape of the short fibers in the vulcanized rubber obtained by vulcanization of the rubber composition. By applying the vulcanized rubber to the tread of a tire, the tire can be provided with excellent water film removal ability, thereby further improving the performance on ice of the tire, because the voids present in the vulcanized rubber effectively function as drainage microgrooves when the tire is worn.

[0106] Further, in the case where the rubber composition comprises hydrophilic short fibers, when the rubber composition is vulcanized, the gas generated from the inorganic blowing agent enters the inside of the short fibers, thereby forming voids (bubbles) having i) a configuration corresponding to the shape of the hydrophilic short fibers and ii) a hydrophilic wall surface covered with a resin derived from the hydrophilic short fibers. As a result, by manufacturing a tire using the rubber composition comprising the hydrophilic short fibers in the tread of the tire, the tire can be provided with excellent water film removal ability and drainage, and thus the performance on ice of the tire can be significantly improved even when the tire is worn, because the hydrophilic wall surface of the voids is exposed to the surface of the tread as a result of wear, and the voids thus exposed start to effectively drain water, the affinity to water being increased.

[0107] Still further, in the case where the rubber composition comprises hydrophilic short fibers, the length of each void (bubble) in the vulcanized rubber obtained by vulcanization of the rubber composition can be made longer, thereby successfully further improving the performance on ice of the tire.

[0108] Examples of the hydrophilic resin used as a raw material of the hydrophilic short fiber include a resin having a hydrophilic group in its molecule. Specifically, the hydrophilic resin is preferably a resin having an oxygen atom, a nitrogen atom, or a sulfur atom therein, more preferably a resin having at least one functional group selected from the group consisting of -OH, -COOH, -OCOR (R is an alkyl group), -NH2, -NCO, and -SH, and even more preferably a resin having at least one functional group selected from the group consisting of -OH, -COOH, -NH2, and -NCO.

[0109] Various resins can be used as a raw material of the short fiber. Specifically, examples of the hydrophilic resin used as a raw material of the hydrophilic short fiber include an ethylene-vinyl alcohol copolymer, a vinyl alcohol homopolymer, a poly(meth)acrylic acid or ester thereof, a polyethylene glycol, a carboxyvinyl copolymer, a styrene-maleic acid copolymer, a polyvinylpyrrolidone, a vinylpyrrolidone-vinyl acetate copolymer, and mercaptoethanol, etc. Among these examples, an ethylene-vinyl alcohol copolymer, a vinyl alcohol homopolymer, and a poly(meth)acrylic acid are preferred, and an ethylene-vinyl alcohol copolymer is particularly preferred.

[0110] The hydrophilic short fiber can have a coating layer formed of a low-melting point resin on its outer surface, the low-melting point resin having affinity to the rubber component and preferably having a melting point lower than the vulcanization maximum temperature of the rubber composition. The formation of the coating layer having high affinity to the rubber component as described above on the hydrophilic short fiber improves the dispersibility of the short fiber in the rubber component, while effectively maintaining the high affinity of the inner surface of the hydrophilic short fiber to water. Further, the low-melting point resin of the coating layer melts and becomes fluid during vulcanization, thereby significantly contributing to better adhesion between the rubber component and the hydrophilic short fiber, so that a tire having good water drainage and high durability can be easily achieved. The thickness of the coating layer can vary depending on the content, average diameter, etc. of the hydrophilic short fiber, and is generally in the range of 0.001 to 10 μm, and preferably in the range of 0.001 to 5 μm.

[0111] The melting point of the low-melting point resin for the coating layer is preferably lower than the maximum temperature in vulcanization of the rubber composition. The maximum temperature in vulcanization indicates the highest temperature reached by the rubber composition during the vulcanization process of the rubber composition. For example, in the case where the rubber composition is vulcanized in a mold, the maximum temperature in vulcanization indicates the highest temperature reached by the rubber composition during the period from when the rubber composition enters the mold to when the rubber composition is taken out of the mold for cooling. Such a maximum temperature in vulcanization as described above can be measured by, for example, embedding a thermocouple in the rubber composition. The upper limit of the melting point of the low-melting point resin is not particularly limited, but is preferably selected in accordance with the above requirements. In general, the upper limit of the melting point of the low-melting point resin is preferably at least 10°C lower, and more preferably at least 20°C lower, than the maximum temperature in vulcanization of the rubber composition. The industrial vulcanization temperature of the rubber composition is generally at most about 190°C. When the maximum temperature in vulcanization is set to, for example, 190°C as described above, the melting point of the low-melting point resin is generally set to < 190°C, preferably 180°C, and more preferably 170°C.

[0112] The polyolefin-based resin is preferably used as the low-melting point resin, and examples of the polyolefin-based resin include polyethylene, polypropylene, polybutylene, polystyrene, ethylene-propylene copolymer, ethylene-methacrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene-diene terpolymer, ethylene-vinyl acetate copolymer, and ionomer resin thereof, and the like.

[0113] The average length of the short fibers is preferably in the range of 0.1 to 50 mm, and more preferably in the range of 1 to 7 mm, and the average diameter of the short fibers is preferably in the range of 1 µm to 2 mm, and more preferably in the range of 5 µm to 0.5 mm. Setting the average length and the average diameter of the short fibers in the above ranges prevents the fibers from being unnecessarily entangled, thereby ensuring their satisfactory dispersibility.

[0114] The fibrous resin disclosed in WO2018 / 207472, i.e., the short fiber resin (flat resin), in which, in a cross section taken perpendicular to the longitudinal direction thereof, A is the length of the cross section along its long diameter, and B is the length of the cross section along its short diameter perpendicular to the long diameter, A / B is greater than 1, can be selected as the short fiber of the present application. The shape and area of the cross section taken perpendicular to the longitudinal direction of the short fiber resin (flat resin), and the length in the longitudinal direction of the short fiber resin are not particularly limited, as long as A / B is greater than 1.

[0115] The shape of the cross section taken perpendicular to the longitudinal direction of the flat resin can be any one of an ellipse, a triangle, a rectangle, a polygon, and an irregular shape, and is preferably an ellipse or a rectangle, and more preferably an ellipse, from the viewpoint of improving the water absorption capacity of the vulcanized rubber.

[0116] The average area of the cross section taken perpendicular to the longitudinal direction of the flat resin is preferably in the range of 0.000001 mm 2 ~ 0.5 mm 2 and more preferably in the range of 0.00002 mm 2 ~ 0.2 mm 2 The average value of the length C in the longitudinal direction of the flat resin is preferably in the range of 0.1 mm ~ 500 mm and more preferably in the range of 0.1 mm ~ 7 mm. By setting the cross-sectional dimension and the length in the longitudinal direction of the flat resin in the above ranges, not only the water absorption capacity of the vulcanized rubber is improved, but also the short fiber resin is prevented from being unnecessarily entangled, thereby facilitating satisfactory dispersion of the short fiber resin in the rubber composition. It should be noted that each of the average value of the area of the cross section taken perpendicular to the longitudinal direction of the flat resin and the average value of the length C in the longitudinal direction of the flat resin is the average value of the corresponding values of the area / length C of 100 arbitrarily selected flat resin samples.

[0117] The lengths A, B, C of the flat resin can be measured by observing the resin using an optical microscope at a magnification of x20 ~ x400.

[0118] The ratio of A / B is preferably ≥ 1.5 and more preferably ≥ 2.0 from the viewpoint of further improving the water absorption capacity of the vulcanized rubber. The upper limit of A / B is not particularly limited from the viewpoint of further improving the water absorption capacity of the vulcanized rubber, but is preferably ≤ 10 and more preferably ≤ 5.

[0119] The length A of the flat resin determined as the average value of 100 samples thereof is preferably in the range of 0.001 mm ~ 2 mm and more preferably in the range of 0.005 mm ~ 0.5 mm from the viewpoint of further improving the water absorption capacity of the vulcanized rubber.

[0120] The ratio of the length C in the longitudinal direction of the flat resin to the length A of the long diameter of the cross section of the flat resin (C / A) is generally in the range of 10 ~ 4000 and preferably in the range of 50 ~ 2000.

[0121] The content of the short fiber is preferably in the range of 0.1 ~ 100 parts by mass and more preferably in the range of 1 ~ 50 parts by mass with respect to 100 parts by mass of the rubber component. By setting the content of the short fiber in the above range, it is possible to give consideration to both satisfactory ice performance of the tire and satisfactory wear resistance of the tire in a good balance.

[0122] (Organic acid)

[0123] The rubber composition of the present application can further contain an organic acid having an SP value in the range of 9.15 ~ 16.0 (cal / cm 3) 1 / 2 Organic acids fall within a certain range. When the rubber composition is vulcanized, organic acids promote the degradation and foaming reaction of the inorganic foaming agent, thus successfully matching the rate of degradation and foaming of the inorganic foaming agent with the rate of vulcanization of the rubber composition in a well-balanced manner, thereby increasing the foaming rate in the resulting vulcanized rubber. By blending organic acids with the rubber composition, the degradation and foaming reaction of the inorganic foaming agent can be promoted, thus successfully matching the rate of degradation and foaming of the inorganic foaming agent with the rate of vulcanization of the rubber composition in a well-balanced manner, thereby increasing the foaming rate in the resulting vulcanized rubber while maintaining good processability of the rubber composition. Therefore, by applying a rubber composition further containing organic acids to tires, the ice performance of the tires can be further improved.

[0124] When the SP value of organic acid is ≥9.15 (cal / cm³) 3 ) 1 / 2 At this time, the effect of promoting the degradation of inorganic foaming agents is satisfactoryly high. When the SP value of organic acid is ≤16.0 (cal / cm³), 3 ) 1 / 2 When this is done, the adhesiveness of rubber compositions containing organic acids can be reduced, and thus the adhesiveness of the rubber composition to manufacturing equipment such as rollers can be inhibited during the manufacturing process of the rubber composition, thereby improving the processability of the rubber composition.

[0125] The preferred SP value of the organic acid is between 10.5 and 14.3 (cal / cm³). 3 ) 1 / 2 Within the range. When the SP value of organic acid is ≥10.5 (cal / cm³), 3 ) 1 / 2 This further enhances the effect of promoting the degradation of inorganic foaming agents, especially when the SP value of organic acids is ≤14.3 (cal / cm³). 3 ) 1 / 2 At this time, the adhesiveness of rubber compositions containing organic acids can be further reduced, thereby further improving the processability of the rubber composition.

[0126] In this regard, stearic acid, which is commonly used as a vulcanizing aid in rubber compositions, has an SP value of 9.12 (cal / cm). 3 ) 1 / 2 Therefore, it cannot effectively promote the degradation of inorganic foaming agents.

[0127] In this invention, the SP value (solubility parameter) of organic acids is calculated according to the Fedors method.

[0128] The organic acid can be any one of a monocarboxylic acid, a dicarboxylic acid, and a tricarboxylic acid, and can be an aliphatic / aromatic compound. Further, the organic acid can have a functional group other than a carboxyl group, such as a hydroxyl group, a keto group, or an olefinically unsaturated group.

[0129] The organic acid preferably has an aromatic ring, i.e., is preferably an aromatic compound. Further, the organic acid is preferably a monocarboxylic acid. When the organic acid has an aromatic ring, the rubber composition can further reduce adhesion and improve its processability, and thus is even less likely to adhere to manufacturing equipment such as a roll.

[0130] Examples of the aliphatic monocarboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, and lauric acid.

[0131] Examples of the aliphatic dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid.

[0132] Examples of the aromatic monocarboxylic acid include benzoic acid and salicylic acid.

[0133] Examples of the aromatic dicarboxylic acid include phthalic acid.

[0134] Examples of the organic acid having a functional group other than a carboxyl group include tartaric acid, malic acid, maleic acid, glycolic acid, and a-ketoglutaric acid.

[0135] One species or a combination of two or more of these examples can be used as the organic acid.

[0136] Benzoic acid is particularly preferable as the organic acid. When benzoic acid is blended with the rubber composition, the rubber composition can even further reduce adhesion and improve its processability, and thus is even less likely to adhere to manufacturing equipment such as a roll.

[0137] From the viewpoint of obtaining satisfactory processability of the rubber composition, satisfactory foaming ratio of the vulcanizate, and satisfactory ice performance of the tire, the content of the organic acid is preferably in the range of 0.1 to 7 parts by mass, more preferably in the range of 1.5 to 7 parts by mass, and particularly preferably in the range of 3 to 7 parts by mass, relative to 100 parts by mass of the rubber component.

[0138] In the case where the rubber composition of the present application contains an organic acid, from the viewpoint of obtaining satisfactory foaming ratio of the vulcanizate and satisfactory ice performance of the tire, the total content of the inorganic foaming agent and the organic acid is preferably ≥ 3 parts by mass and < 15 parts by mass, more preferably ≥ 5 parts by mass and < 15 parts by mass, and particularly preferably ≥ 7 parts by mass and < 15 parts by mass, relative to 100 parts by mass of the rubber component.

[0139] In the case where the rubber composition of the present application contains an organic acid, the mass ratio of the inorganic blowing agent, the blowing aid, and the organic acid (inorganic blowing agent : blowing aid : organic acid) is preferably in the range of 1 : 1.1 : 0.3 to 1 : 3.3 : 2, more preferably in the range of 1 : 1.1 : 0.6 to 1 : 3.3 : 1.4, and even more preferably in the range of 1 : 1.3 : 0.7 to 1 : 2.7 : 1.3, from the viewpoint of obtaining a satisfactory foaming rate of the vulcanized rubber and satisfactory ice performance of the tire.

[0140] In the case where the rubber composition of the present application contains an organic acid, the total content of the inorganic blowing agent, the blowing aid, and the organic acid is preferably in the range of 5 to 40 parts by mass, more preferably in the range of 9 to 35 parts by mass, and particularly preferably in the range of 12 to 31 parts by mass, with respect to 100 parts by mass of the rubber component, from the viewpoint of obtaining a satisfactory foaming rate of the vulcanized rubber and satisfactory ice performance of the tire.

[0141] In the case where the rubber composition of the present application contains an organic acid, the mass ratio of the inorganic blowing agent, the blowing aid, and the organic acid (inorganic blowing agent : blowing aid : organic acid) is preferably in the range of 1 : 1.1 : 0.3 to 1 : 3.3 : 2, more preferably in the range of 1 : 1.1 : 0.6 to 1 : 3.3 : 1.4, and even more preferably in the range of 1 : 1.3 : 0.7 to 1 : 2.7 : 1.3, from the viewpoint of obtaining a satisfactory foaming rate of the vulcanized rubber and satisfactory ice performance of the tire.

[0142] (Other Components)

[0143] In addition to the rubber component, the inorganic blowing agent, the blowing aid, the short fiber, and the organic acid, compounding agents generally employed in the rubber industry, such as a filler, a softener, stearic acid, an antioxidant, zinc oxide (zinc white), a vulcanization accelerator, and a vulcanizing agent, etc. can also be optionally selected and added to the rubber composition of the present application, unless the addition thereof adversely affects the purpose of the present application. Commercial products can be appropriately used as these compounding agents.

[0144] Examples of the filler include carbon black and silica, etc. A single kind or a combination of two or more kinds of these fillers can be used as the filler. The content of the filler is not particularly limited, and the content of the filler is preferably in the range of 10 to 150 parts by mass, and more preferably in the range of 20 to 100 parts by mass, with respect to 100 parts by mass of the rubber component.

[0145] Examples of the vulcanizing agent include sulfur, etc. The content of the vulcanizing agent is preferably in the range of 0.1 to 10 parts by mass, and more preferably in the range of 1 to 4 parts by mass, with respect to 100 parts by mass of the rubber component, in terms of sulfur content.

[0146] Examples of the vulcanization accelerator include thiazole-based vulcanization accelerators and guanidine-based vulcanization accelerators, etc. A single kind or a combination of two or more kinds of these vulcanization accelerators can be used as the vulcanization accelerator. The content of the vulcanization accelerator is preferably in the range of 0.1 to 5 parts by mass, and more preferably in the range of 0.2 to 3 parts by mass, with respect to 100 parts by mass of the rubber component.

[0147] The rubber composition of the present application can be manufactured, for example, by blending, mixing, and kneading the rubber component, the inorganic blowing agent, the blowing aid, and various compounding agents, which are optionally selected as necessary, by using a Banbury mixer or a roll, etc.; and warming and extruding the mixture thus mixed and kneaded, etc.

[0148] The rubber composition of the present application can be applied to various rubber products such as tires. The rubber composition of the present application is particularly suitable for use in the tread rubber of a tire.

[0149] <Vulcanized Rubber>

[0150] As a vulcanization product of the above-described rubber composition (which can be obtained by vulcanization of the rubber composition), the vulcanized rubber of the present application is characterized in that the foaming rate thereof is in the range of 1% to 45%. The vulcanized rubber of the present application obtained by vulcanization of the above-described rubber composition has a low load on the environment. Further, when the vulcanized rubber is applied to a tire, the ice performance of the tire is significantly improved.

[0151] The foaming rate of the vulcanized rubber ≥ 1% ensures that a good effect of improving the ice performance of a tire is satisfactorily achieved, and the foaming rate of the vulcanized rubber ≤ 45% ensures that the tire has a satisfactorily high wear resistance when the vulcanized rubber is applied to the tire.

[0152] In the present application, the "foaming rate" of the vulcanized rubber indicates the average foaming rate Vs, which is specifically calculated by the formula (1) shown below.

[0153] Vs = (p0 / p1 - 1) x 100 (%)

[0154] In the formula (1), p1 indicates the density (g / cm3) of the vulcanized rubber (i.e., the foamed rubber), and p0 indicates the density (g / cm3) of the solid phase portion of the vulcanized rubber (i.e., the foamed rubber). The density of the vulcanized rubber and the density of the solid phase portion of the vulcanized rubber are respectively calculated from the mass (and the volume) measured in air and the mass (and the volume) measured in ethanol. 3 3 The density of the vulcanized rubber and the density of the solid phase portion of the vulcanized rubber are respectively calculated from the mass (and the volume) measured in air and the mass (and the volume) measured in ethanol.

[0155] The foaming rate of the vulcanized rubber can be optionally adjusted by changing the kind, content, etc. of the above-described inorganic blowing agent, blowing aid, and organic acid.

[0156] ​The vulcanized rubber of the present application preferably has voids each having a length ≥ 1,000 μm therein. The vulcanized rubber having voids each having a length ≥ 1,000 μm therein is applied to a tire, which ensures good water film removal ability and drainage of the tire, thereby improving the ice performance of the tire. The length of each void of the vulcanized rubber is preferably ≥ 1,100 μm, more preferably ≥ 1,120 μm, and particularly preferably ≥ 1,125 μm.

[0157] The upper limit of the length of each void in the vulcanized rubber is not particularly limited, but from the viewpoint of ease of manufacture, it is preferably ≤ 2,000 μm.

[0158] In the present application, the length of the voids of the vulcanized rubber represents the average length of the plurality of voids in the longitudinal direction. In the present application, the "length of the voids of the vulcanized rubber" can be determined by observing the field area (7,240 μm x 5,430 μm) of the surface of the vulcanized rubber by a microscope; subjecting the image thus observed to binaryzation processing, and measuring the length of 20 to 30 voids; and obtaining the average of the lengths of the voids thus measured.

[0159] By varying the average length of the above short fibers, the length of the voids of the vulcanized rubber can be optionally adjusted.

[0160] The vulcanized rubber of the present application can be applied to various rubber products such as tires. The vulcanized rubber of the present application is particularly suitable for use in the tread rubber of a tire.

[0161] < Tread Rubber for Tire >

[0162] The tread rubber for tire of the present application is characterized by being made of the above rubber composition or vulcanized rubber. The tread rubber for tire of the present application made of the above rubber composition or vulcanized rubber has a low load on the environment. Further, when the tread rubber is applied to a tire, the tread rubber significantly improves the ice performance of the tire.

[0163] The tread rubber for tire of the present application can be applied to a new tire or a retreaded tire.

[0164] < Tire >

[0165] The tire of the present application is characterized by having the above rubber composition or vulcanized rubber in the tread portion thereof. The tire of the present application having the above rubber composition or vulcanized rubber in the tread portion thereof not only has a low load on the environment, but also exhibits excellent ice performance.

[0166] The tire of the present application has excellent ice performance, and is particularly suitable for use in a winter tire such as a studless tire.

[0167] The tire of the present application can be manufactured by any one of i) forming the aforementioned rubber composition in an unvulcanized state, and subjecting the resultant green tire to vulcanization, or ii) subjecting the aforementioned rubber composition to a pre-vulcanization step, forming the resultant semi-vulcanized rubber, and subjecting the resultant tire to a main vulcanization step, depending on the kind of the tire. The tire of the present application is preferably a pneumatic tire, wherein examples of the gas for filling include inert gases such as nitrogen, argon, or helium, as well as ambient air and air whose oxygen partial pressure has been adjusted.

[0168] Examples

[0169] The present application will be described in further detail below by way of examples. The present application is not in any way limited to these examples.

[0170] Preparation and evaluation of rubber composition

[0171] The rubber composition samples were prepared by using a conventional Banbury mixer according to the blending formulations shown in Tables 1 to 3. The processability was evaluated during the preparation step of each rubber composition sample.

[0172] The rubber composition samples were vulcanized by a conventional method, whereby vulcanized rubber samples were obtained. For each vulcanized rubber sample thus obtained, the foaming ratio and the void length were measured and the performance on ice was evaluated by the following methods. The results are shown in Tables 1 to 3.

[0173] (1) Processability

[0174] The processability of the rubber composition samples according to the blending formulations shown in Tables 2 and 3 was evaluated during the manufacturing step thereof. Specifically, it was determined whether the rubber composition sample adhered to the manufacturing equipment such as a roll during the manufacturing step thereof or not for the evaluation.

[0175] In Tables 2 and 3, "good" indicates that the rubber composition sample did not adhere to the manufacturing equipment such as a roll, thereby exhibiting good processability, and "adhered to roll" indicates that the rubber composition sample adhered to the roll, thereby exhibiting poor processability.

[0176] (2) Foaming ratio

[0177] The average foaming ratio Vs was calculated as the foaming ratio of each vulcanized rubber sample by Formula (1) shown below. Then, the average foaming rate Vs was evaluated by the following criteria.

[0178] Vs = (p0 / p1 - 1) x 100 (%) (1)

[0179] O (good): The average foaming ratio Vs was in the range of 1% to 45%.

[0180] X1 (poor): The average foaming ratio Vs was less than 1%.

[0181] X2 (difference): Average expansion ratio Vs over 45%.

[0182] In formula (1), p1 represents the density (g / cm3) of the vulcanized rubber (i.e., the foamed rubber). 3 ), p0 represents the density (g / cm3) of the solid phase portion of the vulcanized rubber (i.e., the foamed rubber). 3 The density of the vulcanized rubber and the density of the solid phase portion of the vulcanized rubber are calculated from the mass (and volume) measured in air and the mass (and volume) measured in ethanol, respectively.

[0183] (3) Length of voids

[0184] From each vulcanized rubber sample obtained from the respective rubber composition sample according to the blending formulation shown in Table 1, a test piece was cut out. The field area (7,240 μm x 5,430 μm) on the surface of the test piece was observed by a microscope. Next, the image of the field area thus observed was subjected to a binaryzation process. For each void observed in the image thus subjected to the binaryzation process, the length in the longitudinal direction of the void (the maximum value of the length of the line connecting two arbitrary points on the void) was measured. Then, the average value of the lengths in the longitudinal direction of the voids thus measured was calculated.

[0185] (4) Ice performance (ICE μ)

[0186] The dynamic friction coefficient μ was determined by cutting out a test piece (shape: square of 25 mm x 25 mm, thickness: 2 mm) from each vulcanized rubber sample; pressing the test piece against a fixed ice (-2°C), reciprocally moving the test piece on the ice while constantly pressing the test piece against the ice, and detecting the frictional force received by the test piece during the reciprocating movement of the test piece by a load cell; and calculating the dynamic friction coefficient μ from the frictional force thus detected.

[0187] The dynamic friction coefficient μ value is expressed as an index value relative to the index value of Comparative Example 1-1 in Table 1 being "100".

[0188] The dynamic friction coefficient μ value is expressed as an index value relative to the index value of Comparative Example 2-1 in Table 2 being "100".

[0189] The dynamic friction coefficient μ value is expressed as an index value relative to the index value of Comparative Example 3-1 in Table 3 being "100".

[0190] The larger the index value, the larger the dynamic friction coefficient μ, i.e., the better the ice performance.

[0191] [Table 1]

[0192] [Table 2]

[0193] *1-1NR: Natural rubber

[0194] *1-2BR: Butadiene rubber (high cis BR) manufactured by Zeon Corporation

[0195] *1-3SBR: Solution polymerized styrene-butadiene rubber (styrene bound content = 10% by mass)

[0196] *1-4 Carbon Black: A product manufactured by Asahi Carbon Co., Ltd., with a nitrogen adsorption specific surface area of ​​148 m². 2 / g

[0197] *1-5 Silica: A product manufactured by Tosoh Silica Corporation, with a nitrogen adsorption specific surface area of ​​222 m². 2 / g

[0198] *1-6 Short fibers: Resin 4 (flat resin) used in Example 4 of WO2018 / 207472, produced by ethylene-vinyl alcohol copolymer (trade name "EVAL") manufactured by Kuraray Co., Ltd. TM The surface of the hydrophilic fiber made of F104B is coated with polyethylene (manufactured by Japan Polyethylene Corporation under the trade name "Novatec"). TM The short fibers obtained by coating with HJ360” are provided, wherein, in a cross-section taken perpendicular to the longitudinal direction of the flat resin, A is the length of the cross-section along its major axis, and B is the length of the cross-section along its minor axis perpendicular to the major axis, A / B = 2.7, the average value of length A = 0.05 mm, and the average area of ​​the cross-section taken perpendicular to the longitudinal direction of the flat resin = 0.0007 mm². 2 The average length C of the flat resin in the longitudinal direction is 3 mm.

[0199] *1-7 Vulcanization Accelerator Package: Includes a package containing vulcanization accelerators MBTS and CZ.

[0200] *1-8 Other chemicals: including the antioxidant "Nocrac 6C", waxes, and resins.

[0201] *1-9 Inorganic foaming agent: Baking soda (sodium bicarbonate), manufactured by EIWA CHEMICAL IND.CO.,LTD. under the trade name "Cellborn FE507".

[0202] *1-10 foaming aid: urea, trade name "Cellpaste K5" manufactured by EIWA CHEMICAL IND. CO., LTD.

[0203] [Table 2]

[0204]

[0205] *2-1 NR: natural rubber

[0206] *2-2 BR: butadiene rubber, "BR 150L" manufactured by Ube Industries, Ltd.

[0207] *2-3 SBR: styrene-butadiene rubber, "1500" manufactured by JSR Corporation

[0208] *2-4 carbon black: "N134" manufactured by Asahi Carbon Co., Ltd.

[0209] *2-5 hydrogenated fatty acid: "STEARIC ACID 50S" manufactured by New Japan Chemical Co., Ltd.

[0210] *2-6 antioxidant: includes an antioxidant with trade name "Nocrac 6C" manufactured by Ouchi-Shinko Chemical Industrial Co., Ltd., and the total content of the antioxidant in the rubber composition is 2 parts by mass.

[0211] *2-7 vulcanization accelerator: "Sanceler CZ" manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.

[0212] *2-8 baking soda: sodium bicarbonate, "Cellborn FE507" manufactured by EIWA CHEMICAL IND. CO., LTD.

[0213] *2-9 urea: "Cellpaste K5" manufactured by EIWA CHEMICAL IND. CO., LTD.

[0214]

[0215] *3-1 NR: natural rubber

[0216] *3-2 BR: butadiene rubber, "BR 150L" manufactured by Ube Industries, Ltd.

[0217] *3-3 Modified BR: Modified butadiene rubber, "BR500" manufactured by JSR Corporation

[0218] *3-4 SBR: Styrene-butadiene rubber, "1500" manufactured by JSR Corporation

[0219] *3-5 Modified SBR: Modified styrene-butadiene rubber, synthesized by the following method

[0220] (Synthesis method of modified SBR)

[0221] The modified SBR was obtained by the following:

[0222] A cyclohexane solution of 1,3-butadiene and a cyclohexane solution of styrene were added to a dry, nitrogen-substituted pressure-resistant glass container having a content of 800 mL, so that 67.5 g of 1,3-butadiene and 7.5 g of styrene were in the container;

[0223] Then, 0.6 mmol of 2,2-bistetrahydrofurylpropane and 0.8 mmol of n-butyllithium were added to the glass container, and polymerization was performed at 50°C for 1.5 hours;

[0224] 0.72 mmol of N,N-bis(trimethylsilyl)-3-[diethoxy(methyl)silyl]propylamine as a modifier was added to the polymerization reaction system when the polymerization conversion reached substantially 100%, and a modification reaction was performed at 50°C for 30 minutes;

[0225] A 2 mL of isopropyl alcohol solution of 2,6-di-tert-butyl-4-methylphenol (BHT concentration: 5 mass%) was added to the polymerization reaction system to terminate the polymerization reaction; and

[0226] The resulting product was dried according to a conventional method, thereby obtaining a modified SBR.

[0227] The results of analyzing the microstructure of the modified SBR thus obtained found that, in the modified SBR, the styrene combination amount was 10 mass%, the vinyl bond content in the butadiene portion was 40%, and the peak molecular weight was 200,000.

[0228] *3-6 Carbon black: "N134" manufactured by Asahi Carbon Co., Ltd.

[0229] *3-7 Hydrogenated fatty acid: "STEARIC ACID 50S" manufactured by New Japan Chemical Co., Ltd.

[0230] *3-8 Antioxidant: "Nocrac NS-6" manufactured by Ouchi-Shinko Chemical Industrial Co., Ltd.

[0231] *3-9 Vulcanization accelerator: "Sanceler CZ" manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.

[0232] *3-10 Baking soda: Sodium bicarbonate, "Cellborn FE507" manufactured by EIWA CHEMICAL IND. CO., LTD.

[0233] *3-11 Citric acid: SP value = 16.53 (cal / cm 3 ) 1 / 2 ) of citric acid, manufactured by Kanto Chemical Industry Co., Ltd.

[0234] *3-12 Benzoic acid: SP value = 11.93 (cal / cm 3 ) 1 / 2 ) of benzoic acid, manufactured by FUJIFILM Wako Pure Chemical Corporation

[0235] *3-13 Malonic acid: SP value = 14.03 (cal / cm 3 ) 1 / 2 ) of malonic acid, manufactured by Kanto Chemical Industry Co., Ltd.

[0236] *3-14 Urea: "Cellpaste K5" manufactured by EIWA CHEMICAL IND. CO., LTD.

[0237] From Tables 1 to 3, it can be understood that the rubber compositions of the examples, in which: the total content of the inorganic blowing agent and the blowing aid is in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the rubber component; and the mass ratio of the inorganic blowing agent with respect to the blowing aid (inorganic blowing agent : blowing aid) is in the range of 1 : 1.1 to 1 : 3.3, are consistently excellent in ice performance.

[0238] Industrial applicability

[0239] The rubber composition, the vulcanized rubber, and the tread rubber of the present application are suitable for use in tires, particularly studless tires. The tire of the present application is particularly suitable for use in studless tires.

Claims

1. A rubber composition comprising: Rubber components containing diene-based rubbers; Inorganic foaming agents; Foaming aids; and SP value is 9.15–16.0 (cal / cm³) 3 ) 1 / 2 organic acids, The total content of the inorganic foaming agent and the foaming aid is in the range of 1 to 20 parts by weight relative to 100 parts by weight of the rubber component. The mass ratio of the inorganic foaming agent to the foaming aid (inorganic foaming agent: foaming aid) is in the range of 1:1.1 to 1:3.

3. The foaming agent is urea. The inorganic foaming agent is selected from the group consisting of ammonium bicarbonate and sodium bicarbonate. The diene-based rubber comprises natural rubber and synthetic diene-based rubber, wherein the synthetic diene-based rubber is unmodified. The organic acid is an aromatic monocarboxylic acid.

2. The rubber composition according to claim 1, wherein, The mass ratio of the inorganic foaming agent to the foaming aid to the organic acid (inorganic foaming agent: foaming aid: organic acid) is 1:1.1:0.3 to 1:3.3:

2.

3. The rubber composition according to claim 1, wherein, The content of the organic acid is in the range of 3 to 7 parts by mass relative to 100 parts by mass of the rubber component.

4. The rubber composition according to claim 1, wherein, The organic acid is benzoic acid.

5. The rubber composition according to claim 1, wherein the synthetic diene rubber comprises at least one selected from the group consisting of isoprene rubber, styrene-butadiene rubber, and butadiene rubber.

6. The rubber composition according to claim 5, comprising styrene-butadiene rubber wherein the styrene content is ≤15% by mass as said styrene-butadiene rubber.

7. A vulcanized rubber, which is a vulcanized product of a rubber composition according to any one of claims 1 to 6, wherein the foaming rate of the vulcanized rubber is in the range of 1% to 45%.

8. The vulcanized rubber according to claim 7, wherein the vulcanized rubber has pores with a length ≥ 1,000 μm therein.

9. A tire tread rubber, made from a rubber composition according to any one of claims 1 to 6 or a vulcanized rubber according to claim 7 or 8.

10. A tire having in its tread a rubber composition according to any one of claims 1 to 6 or a vulcanized rubber according to claim 7 or 8.

Images