Zinc complex of hydrazide compound and reversion inhibitor for rubber

Abstract

To provide a zinc complex of hydrazide compound added to a rubber composition, and a rubber reversion inhibitor containing the zinc complex of hydrazide compound.SOLUTION: The present invention provides a zinc complex of hydrazide compound, and a rubber reversion inhibitor containing the zinc complex of hydrazide compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a zinc complex of a hydrazide compound and a reversion inhibitor for rubber. [Background technology]

[0002] Large tires (especially extra-large tires used in mining) generally use natural rubber, which has excellent strength.

[0003] Due to the size of the tires, the vulcanization of large tires requires a long vulcanization time. For this reason, the vulcanization of large tires can cause a phenomenon called reversion, which is not a problem for small passenger car tires that are mainly made from synthetic rubber. This reversion can cause the polymer backbone or sulfur crosslinks formed during vulcanization to break during long vulcanization periods, resulting in a decrease in tire strength and durability.

[0004] In the production of large tires, it is required to suppress reversion during vulcanization molding, and there is a demand for the production of rubber compositions that are less susceptible to reversion.

[0005] Patent Document 1 discloses a rubber composition containing 100 parts by weight of a rubber component consisting of at least one rubber selected from natural rubber and synthetic rubber, 0.05 to 5 parts by weight of sodium 1,6-hexamethylenedithiosulfate dihydrate (HTS), and 0.05 to 5 parts by weight of a hydrazone compound, wherein the hydrazone compound is at least one selected from 3-hydroxy,N'-(1,3-dimethylbutylidene)-2-naphthoic acid hydrazide (BMH) and N'-(1,3-dimethylbutylidene) salicylic acid hydrazide (BMS). However, the technology of Patent Document 1 does not have sufficient reversion resistance.

[0006] Prior art rubber compositions require further improvement in reversion resistance to meet the demand for increased durability in automobiles. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4608076 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a zinc complex of a hydrazide compound to be added to a rubber composition, and a reversion inhibitor for rubber containing the zinc complex of a hydrazide compound. [Means for solving the problem]

[0009] As a result of extensive research conducted by the present inventors to achieve the above object, they have found that by incorporating a zinc complex of a hydrazide compound having a specific structure into a rubber composition, it is possible to suppress scission of sulfur crosslinks formed by vulcanization in the rubber composition due to reversion (improved reversion resistance) compared to conventional techniques that use hydrazide compounds.

[0010] Based on this finding, the present inventors have conducted further research and have completed the present invention.

[0011] That is, the present invention provides the following zinc complex of a hydrazide compound and a reversion inhibitor for rubber containing the zinc complex of a hydrazide compound.

[0012] Section 1. A zinc complex of a hydrazide compound represented by the following formula (1):

[0013] [ka] [In formula (1), R 1 , and R 2 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A represents a phenyl group or a naphthyl group and has at least one polar group. Section 2. Item 2. The zinc complex according to item 1, wherein the hydrazide compound represented by formula (1) is 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide or 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide.

[0014] Section 3. A reversion inhibitor for rubber, comprising a zinc complex of a hydrazide compound represented by the following formula (1):

[0015] [ka] [In formula (1), R 1 , and R 2 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A represents a phenyl group or a naphthyl group and has at least one polar group. Section 4. Item 4. The reversion inhibitor for rubber according to Item 3, wherein the hydrazide compound represented by formula (1) is 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide or 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide. [Effects of the Invention]

[0016] The zinc complex of a hydrazide compound of the present invention and the reversion inhibitor for rubber containing the zinc complex of a hydrazide compound can, by being contained in a rubber composition, suppress scission of sulfur crosslinks formed by vulcanization in the rubber composition due to reversion. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below.

[0018] In this specification, the terms "comprise" and "contain" are concepts that encompass all of "comprise," "consist essentially of," and "consist only of."

[0019] In this specification, when a numerical range is indicated as "A to B," the numerical range means A or more and B or less (from the numerical value of A to the numerical value of B).

[0020] [1] A hydrazide compound represented by formula (1) that constitutes a zinc complex The hydrazide compound represented by formula (1) constituting the zinc complex of the hydrazide compound of the present invention is represented by the following structural formula.

[0021] [ka] [In formula (1), R 1 , and R 2 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A represents a phenyl group or a naphthyl group and has at least one polar group. In formula (1), R 1 , and R 2 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

[0022] The alkyl group having 1 to 6 carbon atoms is preferably a linear, branched, or cyclic alkyl group. The alkyl group having 1 to 6 carbon atoms preferably has 1 to 4 carbon atoms.

[0023] In formula (1), A represents a phenyl group or a naphthyl group and has at least one polar group.

[0024] In formula (1), the polar group contained in A is not particularly limited. The polar group is preferably an amino group, an aminoalkyl group, an alkoxycarbonyl group, an acyl group, an acyloxy group, an amide group, a carboxyl group, a carboxyalkyl group, a formyl group, a nitrile group, a nitro group, a hydroxyalkyl group, a hydroxyl group, an alkoxy group, an aryloxy group, a heterocyclic group, a thiol group, an alkylthio group, an arylthio group, or the like.

[0025] The number of polar groups may be preferably 1 to 4, and more preferably 1 to 3, at substitutable positions.

[0026] The amino group is preferably an amino group represented by -NH2.

[0027] The amino group is preferably a linear or branched monoalkylamino group (substituted amino group) having 1 to 6 carbon atoms, such as methylamino, ethylamino, n-propylamino, isopropylamino, n-butylamino, isobutylamino, s-butylamino, t-butylamino, 1-ethylpropylamino, n-pentylamino, neopentylamino, n-hexylamino, isohexylamino, or 3-methylpentylamino.

[0028] The amino group is preferably a dialkylamino group (substituted amino group) having two linear or branched alkyl groups having 1 to 6 carbon atoms, such as a dimethylamino, ethylmethylamino, or diethylamino group.

[0029] Among these polar groups, a hydroxyl group, an amino group, etc. are preferred, and a hydroxyl group is more preferred.

[0030] Preferably, at least one of these polar groups is substituted on the carbon atom adjacent to the carbon atom to which the carbohydrazide group is bonded.

[0031] In the rubber composition of the present invention, the hydrazide compound represented by formula (1) constituting the zinc complex of the hydrazide compound is preferably 3-Hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide:

[0032] [ka] 2-Hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide:

[0033] [ka] is.

[0034] In the rubber composition of the present invention, the zinc complex of the hydrazide compound represented by formula (1) is preferably a zinc complex of 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide or a zinc complex of 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide.

[0035] The zinc complex of the hydrazide compound represented by formula (1) of the present invention is formed from 1 mole of zinc atoms per 2 moles of the hydrazide compound represented by formula (1).

[0036] [2] Reversion inhibitor for rubber The reversion inhibitor for rubber of the present invention is a zinc complex of a hydrazide compound represented by the following formula (1):

[0037] [ka] [In formula (1), R 1 , and R 2 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A represents a phenyl group or a naphthyl group and has at least one polar group. Includes:

[0038] The zinc complex of the hydrazide compound represented by formula (1) is described in detail in the above. (1) A hydrazide compound represented by formula (1) that constitutes a zinc complex As stated above.

[0039] In the reversion inhibitor for rubber of the present invention, the zinc complex of the hydrazide compound represented by the formula (1) is preferably a zinc complex of 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide or a zinc complex of 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide.

[0040] The zinc complex of a hydrazide compound of the present invention and the reversion inhibitor for rubber containing the zinc complex of a hydrazide compound can be incorporated into a rubber composition to suppress scission of sulfur crosslinks formed by vulcanization in the rubber composition due to reversion, i.e., to improve the reversion resistance of the rubber composition.

[0041] [3] A component that can be used as a reversion inhibitor for rubber Components that can be applied to the reversion inhibitor for rubber of the present invention include diene rubber components, fillers, etc. The reversion inhibitor for rubber containing the zinc complex of the hydrazide compound represented by formula (1) can be applied to a rubber composition containing a diene rubber component and a filler.

[0042] [3-1] Diene rubber component The diene rubber component is preferably natural rubber (NR), synthetic diene rubber, a mixture of natural rubber and synthetic diene rubber, or the like.

[0043] From the viewpoint of improving the durability of the rubber composition containing the diene rubber component, natural rubber is preferably used. The natural rubber is preferably contained in an amount of 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass to 100% by mass, based on 100% by mass of the diene rubber component.

[0044] The natural rubber is preferably natural rubber such as natural rubber latex, technically graded rubber (TSR), smoked sheet (RSS), gutta percha, eucommia-derived natural rubber, guayule-derived natural rubber, Russian dandelion-derived natural rubber, etc. The natural rubber is preferably modified natural rubber such as epoxidized natural rubber, methacrylic acid-modified natural rubber, styrene-modified natural rubber, etc.

[0045] The synthetic diene rubber is preferably styrene-butadiene copolymer rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), nitrile rubber (NBR), chloroprene rubber (CR), ethylene-propylene-diene terpolymer rubber (EPDM), styrene-isoprene-styrene triblock copolymer (SIS), styrene-butadiene-styrene triblock copolymer (SBS), or modified synthetic diene rubbers thereof.

[0046] The modified synthetic diene rubber is preferably a diene rubber modified by a modification technique such as main chain modification, one end modification, or both ends modification.

[0047] The modified functional group of the modified synthetic diene rubber is preferably a functional group containing a hetero atom such as an epoxy group, an amino group, an alkoxy group, or a hydroxyl group, and preferably contains one or more of these functional groups.

[0048] There are no particular limitations on the cis / trans / vinyl ratio of the diene moiety, and any ratio is preferred.

[0049] There are no particular limitations on the weight average molecular weight and molecular weight distribution of the diene rubber, but the weight average molecular weight is preferably 150,000 to 1,400,000.

[0050] The method for producing the synthetic diene rubber is not particularly limited, and is preferably a synthesis method such as emulsion polymerization, solution polymerization, radical polymerization, anionic polymerization, or cationic polymerization.

[0051] The synthetic diene rubber is preferably IR, SBR, BR, or a mixture of two or more selected from these, more preferably SBR, BR, or a mixture of two or more selected from these. The synthetic diene rubber is particularly preferably a diene rubber containing a structure obtained by polymerizing 1,3-butadiene.

[0052] The glass transition temperature of the synthetic diene rubber (preferably a diene rubber containing a structure obtained by polymerizing 1,3-butadiene) is preferably in the range of -110°C to -20°C, more preferably in the range of -70°C to -20°C, from the viewpoint of achieving both abrasion resistance and braking characteristics.

[0053] [3-2] Amount of zinc complex of hydrazide compound In a rubber composition containing a diene rubber component, the blending ratio of the zinc complex of the hydrazide compound represented by formula (1) to the diene rubber component is preferably 0.05 to 30 parts by mass, more preferably 0.1 to 10 parts by mass, even more preferably 0.15 to 5 parts by mass, and particularly preferably 0.5 to 2 parts by mass, per 100 parts by mass of the diene rubber component.

[0054] When a rubber reversion inhibitor containing a zinc complex of a hydrazide compound represented by formula (1) is used in a rubber composition containing a diene rubber component, the compounding ratio of the zinc complex of the hydrazide compound represented by formula (1) to the diene rubber component can be adjusted to the above ratio based on the content of the zinc complex of the hydrazide compound represented by formula (1) contained in the rubber reversion inhibitor.

[0055] In the rubber composition of the present invention, by blending the zinc complex of the hydrazide compound represented by formula (1) with the diene rubber component in the above ratio, the rubber composition is prevented from cleaving the sulfur crosslinks formed by vulcanization due to reversion, i.e., it exhibits excellent reversion resistance.

[0056] The rubber composition of the present invention exhibits excellent reversion resistance, and therefore, when the rubber composition of the present invention is used in a tire, it is possible to produce a tire that exhibits excellent durability.

[0057] [3-3] Filler The filler (reinforcing material) is preferably a conventional filler used in the rubber industry.

[0058] The filler is preferably an inorganic filler such as silica, carbon black, or the like.

[0059] The inorganic filler is preferably silica or alumina (Al2O3) such as γ-alumina or α-alumina.

[0060] The inorganic filler is preferably alumina monohydrate (Al2O3·H2O) such as boehmite or diaspore.

[0061] The inorganic filler is preferably aluminum hydroxide [Al(OH)3] such as gibbsite or bayerite.

[0062] The inorganic filler is preferably aluminum carbonate [Al2(CO3)3], magnesium hydroxide [Mg(OH)2], magnesium oxide (MgO), magnesium carbonate (MgCO3), talc (3MgO·4SiO2·H2O), attapulgite (5MgO·8SiO2·9H2O), titanium dioxide (TiO2), titanium dioxide (TiO2), titanium dioxide (TiO 2n-1), calcium oxide (CaO), calcium hydroxide [Ca(OH)2], magnesium aluminum oxide (MgO·Al2O3), clay (Al2O3·2SiO2), kaolin (Al2O3·2SiO2·2H2O), pyrophyllite (Al2O3·4SiO2·H2O), bentonite (Al2O3·4SiO2·2H2O), aluminum silicate (Al2SiO5, Al4·3SiO4·5H2O, etc.), magnesium silicate (Mg2SiO4, MgSiO3, etc.) ), calcium silicates (e.g., Ca2·SiO4), calcium aluminum silicates (e.g., Al2O3·CaO·2SiO2), calcium magnesium silicate (CaMgSiO4), calcium carbonate (CaCO3), zirconium oxide (ZrO2), zirconium hydroxide [ZrO(OH)2·nH2O], zirconium carbonate [Zr(CO3)2], and crystalline aluminosilicates containing hydrogen, alkali metals, or alkaline earth metals to compensate for the charge, such as various zeolites.

[0063] In order to improve the affinity with the rubber component, the inorganic filler may preferably be an inorganic filler whose surface has been organically treated.

[0064] silica From the viewpoint of damping characteristics, the inorganic filler is preferably silica.

[0065] The BET specific surface area of the silica is not particularly limited, but is preferably 40 m 2 / g~350m 2 / g range. Silica having a BET specific surface area in this range has the advantage of being able to provide both rubber reinforcement and dispersibility in the rubber component.

[0066] The BET specific surface area is measured in accordance with ISO 5794-1.

[0067] The BET specific surface area of the silica is preferably in the range of 40 m 2 / g~350m 2 / g, more preferably 100m 2 / g~270m 2 / g, and particularly preferably 110m 2 / g~270m 2 / g.

[0068] Commercially available silica products include, for example, the product name "HD165MP" (BET specific surface area = 165 m) manufactured by Quechen Silicon Chemical Co., Ltd. 2 / g), "HD115MP" (BET specific surface area = 115m 2 / g), "HD200MP" (BET specific surface area = 200m 2 / g), "HD250MP" (BET specific surface area = 250m 2 / g), and the product name "Nipsil AQ" manufactured by Tosoh Silica Corporation (BET specific surface area = 205 m 2 / g), "Nipsil KQ" (BET specific surface area = 240 m 2 / g), and the product name "Ultrasil VN3" manufactured by Degussa (BET specific surface area = 175 m 2 / g), etc.

[0069] carbon black The carbon black is not particularly limited, and examples thereof include commercially available carbon black and carbon-silica dual phase filler.

[0070] The carbon black is preferably a high, medium or low structure SAF, ISAF, IISAF, N110, N134, N220, N234, N330, N339, N375, N550, HAF, FEF, GPF, SRF grade carbon black, or the like.

[0071] The carbon black is preferably a carbon black of the SAF, ISAF, IISAF, N134, N234, N330, N339, N375, HAF, FEF grade.

[0072] The range of DBP absorption of carbon black is not particularly limited, and is preferably within 60 cm 3 / 100g~200cm 3 / 100g, more preferably 70cm 3 / 100g~180cm 3 / 100g, and particularly preferably 80cm 3 / 100g~160cm 3 / 100g.

[0073] The nitrogen adsorption specific surface area (NSA, measured in accordance with JIS K 6217-2:2001) of the carbon black is preferably in the range of 30 m 2 / g~200m 2 / g, more preferably 40m 2 / g~180m 2 / g, and particularly preferably 50m 2 / g~160m 2 / g.

[0074] The filler may be used alone or in combination of two or more kinds.

[0075] Filler blend amount The amount of the filler mixed is preferably 10 to 160 parts by mass, more preferably 20 to 100 parts by mass, and even more preferably 30 to 70 parts by mass, per 100 parts by mass of the diene rubber component.

[0076] [3-4] Other ingredients The components that can be applied to the reversion inhibitor for rubber of the present invention are a diene rubber component, a filler, and preferably compounding agents that are commonly used in the rubber industry.

[0077] The compounding agents are preferably antioxidants, antiozonants, softeners, processing aids, waxes, resins, foaming agents, oils, stearic acid, zinc oxide (ZnO), vulcanization accelerators, vulcanization retarders, vulcanizing agents (sulfur), etc., and are appropriately selected and compounded.

[0078] When silica is used as a filler, a silane coupling agent is preferably blended in order to enhance the reinforcing properties of the rubber composition by silica and to enhance the low heat buildup and wear resistance of the rubber composition. The silane coupling agent is preferably a sulfide-based, polysulfide-based, thioester-based, thiol-based, olefin-based, epoxy-based, amino-based, or alkyl-based silane coupling agent.

[0079] [4] Tires The zinc complex of a hydrazide compound of the present invention and the reversion inhibitor for rubber containing the zinc complex of a hydrazide compound, when contained in a rubber composition, can suppress scission of sulfur crosslinks formed by vulcanization in the rubber composition due to reversion, i.e., exhibit excellent reversion resistance.

[0080] By incorporating the zinc complex of a hydrazide compound of the present invention and a reversion inhibitor for rubber containing the zinc complex of a hydrazide compound into a rubber composition and using this rubber composition to produce a tire, it is possible to produce a tire that exhibits excellent durability.

[0081] The tire of the present invention is preferably used as a tire for trucks, buses, heavy loads, winter tires, etc.

[0082] In the tire of the present invention, the rubber composition is preferably used in at least one member selected from the tread portion, sidewall portion, bead area portion, belt portion, carcass portion, and shoulder portion.

[0083] In the tire (pneumatic tire) of the present invention, more preferably, components such as the tread portion, bead area portion, belt portion, and carcass portion are formed from the rubber composition of the present invention.

[0084] In the tire of the present invention, the rubber composition is particularly preferably used in the tread portion. The tread portion has a tread pattern and is the outer shell portion of the tire that directly contacts the road surface, protecting the carcass and preventing wear and damage. The tread portion refers to the cap tread that constitutes the ground contact portion of the tire and / or the base tread disposed inside the cap tread.

[0085] In the tire of the present invention, the rubber composition is preferably used in other parts such as a bead area, a belt, a carcass, and a shoulder.

[0086] The bead area secures both ends of the carcass cord and at the same time secures the tire to the rim. The bead is made of bundled high-carbon steel. The belt is a reinforcing band stretched circumferentially between the radially structured tread and carcass. It tightly fastens the carcass like the hoops of a barrel, increasing the rigidity of the tread. The carcass is the cord layer that forms the skeleton of the tire, and is responsible for withstanding the load, impact, and air pressure that the tire receives. The shoulder is the shoulder of the tire, and serves to protect the carcass.

[0087] In the tire of the present invention, the rubber composition is preferably used in the sidewall portion, which is the portion of a pneumatic radial tire extending from the lower side of the shoulder portion to the bead portion. The sidewall portion protects the carcass and is the portion that is most subject to bending during running.

[0088] The tire of the present invention is preferably manufactured according to a method known in the field of tires. The gas to be filled into the tire is preferably normal air or air with an adjusted partial oxygen pressure, or an inert gas such as nitrogen, argon, or helium.

[0089] [5] Method for producing rubber composition The method for producing the rubber composition is not particularly limited, and preferably, the rubber composition can be produced by mixing the compound, the rubber component, the filler, and other components as required.

[0090] The mixing method is not particularly limited, and preferably, the compound, rubber component, filler, and other components as required are kneaded using a kneader or the like.

[0091] Although the embodiments of the present invention have been described above, the present invention is not limited to these examples and can be embodied in various forms without departing from the spirit of the present invention. [Example]

[0092] The embodiments of the present invention will be described more specifically based on Production Examples and Examples.

[0093] The present invention is not limited to these.

[0094] [1] Preparation of hydrazide compounds Compound 1: 3-Hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide A 500 mL four-neck flask equipped with a Dean-Stark apparatus was charged with 41 g of 3-hydroxynaphthalene-2-carbohydrazide (Tokyo Chemical Industry Co., Ltd.) and 138 mL of 4-methyl-2-pentanone to form a suspension, which was then heated to approximately 116°C and refluxed for 3 hours while removing the generated water using a Dean-Stark apparatus.

[0095] The reaction solution was cooled at a rate of 1.7°C / min while stirring at 250 rpm, and crystals were precipitated at 80°C, after which the solution was immediately cooled to 5°C at a rate of 1.7°C / min. The precipitated crystals were collected by filtration and dried under reduced pressure to obtain 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide as pale brown crystals.

[0096] Melting point: 157.4°C 1H NMR (300 MHz, CDCl3) δ: 0.8-1.1 (6H), 1.8-2.4 (6H), 7.2-7.8 (5H), 8.4-8.5 (1H), 10.2-11.0 (1H). No hydrogen atoms of hydroxyl groups were detected.

[0097] 1 The 1 H NMR spectrum showed a mixture of isomers.

[0098] Compound 2: 2-hydroxy-N ' -(4-Methylpentan-2-ylidene)benzoic acid hydrazide In a 300 mL recovery flask equipped with a condenser, 5.00 g of salicylic acid hydrazide (manufactured by Tokyo Chemical Industry Co., Ltd.) and 100 mL of methanol were added to form a suspension, and 3.95 g of 4-methyl-2-pentanone was added and heated under reflux overnight.

[0099] The reaction mixture was concentrated under reduced pressure, and the precipitated solid was filtered and washed with a mixed solvent of hexane and ethyl acetate. The resulting solid was dried under reduced pressure to obtain 7.50 g (yield 97%) of 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide as a white solid.

[0100] Melting point: 158°C 1 H NMR(500MHz,CDCl3)δ:0.9~1.1(6H),1.8~2.4(6H),6.8~6.9(1H),7.0(1H),7.4~7.5(2H),8.7~9.2(1H),10.3~13.0(1H) 1 The 1 H NMR spectrum showed a mixture of isomers.

[0101] [2] Preparation of zinc complexes of hydrazide compounds Zinc complex of compound 1: Zinc complex of 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide (compound 3) A 300 mL recovery flask equipped with a condenser was charged with 10 g of 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide and 200 mL of methanol to form a solution, and a solution of 7.72 g of zinc acetate dihydrate in 90 mL of methanol was added dropwise.

[0102] The reaction mixture was heated and stirred at 50°C for 5 hours, and then stirred at room temperature overnight. The precipitated solid was filtered and washed with 50 mL of methanol. The resulting solid was dried under reduced pressure to obtain 10.38 g (93% yield) of a zinc complex of 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide as a yellow solid.

[0103] Melting point 250℃ or higher The change in melting point and color confirmed that a zinc complex of 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide had been produced.

[0104] Zinc complex of compound 2: Zinc complex of 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide (compound 4) A 200 mL recovery flask equipped with a condenser was charged with 3.00 g of 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide and 40 mL of methanol to form a solution, to which a solution of 2.81 g of zinc acetate dihydrate in 30 mL of methanol was added dropwise, followed by heating and stirring at 50°C overnight.

[0105] The reaction mixture was allowed to cool to room temperature, and the precipitated solid was filtered and washed with 20 mL of methanol. The resulting solid was dried under reduced pressure to obtain 1.72 g (yield 51%) of a zinc complex of 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide as a white solid.

[0106] Melting point 250℃ or higher The change in melting point confirmed that the zinc complex of 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide was produced.

[0107] [3] Measurement of hydrazide and zinc contents in zinc complexes of hydrazide compounds [3-1] Hydrazide content (mass) in zinc complexes of hydrazide compounds It was measured by HPLC analysis.

[0108] Zinc complex of compound 1: Zinc complex of 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide (compound 3) Preparation of test sample solution: 10 mg of zinc complex was dissolved in 10 mL of tetrahydrofuran, and the solution was diluted to volume with methanol.

[0109] HPLC analysis conditions: Column: GL Sciences Inc., Inertsil® ODS-3 4.6 mm x 250 mm, 5 μm Injection volume: 5 μL Detection wavelength: 254 nm Column temperature: 40℃ Mobile phase: methanol / phosphate buffer = 60 / 40 (Vol) Phosphate buffer was prepared by dissolving 6 mmol of disodium hydrogen phosphate and 6 mmol of potassium dihydrogen phosphate in 1 L of distilled water.

[0110] Flow rate: 1mL / min Retention time: Detected as 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide at approximately 10 minutes.

[0111] Zinc complex of compound 2: Zinc complex of 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide (compound 4) Preparation of test sample solution: 10 mg of zinc complex was dissolved in 10 mL of tetrahydrofuran, and the solution was diluted to volume with methanol.

[0112] HPLC analysis conditions: Column: GL Sciences Inc., Inertsil® ODS-3 4.6 mm x 250 mm, 5 μm Injection volume: 5 μL Detection wavelength: 254 nm Column temperature: 40℃ Mobile phase: methanol / phosphate buffer = 55 / 45 (Vol) Phosphate buffer was prepared by dissolving 6 mmol of disodium hydrogen phosphate and 6 mmol of potassium dihydrogen phosphate in 1 L of distilled water.

[0113] Flow rate: 1mL / min Retention time: Detected as 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide at approximately 15 minutes.

[0114] [3-2] Zinc content (mass) in zinc complexes of hydrazide compounds It was measured by chelate titration.

[0115] Zinc complex of compound 1: Zinc complex of 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide (compound 3) Chelatometric titration conditions: Approximately 100 mg of zinc complex was accurately weighed, dissolved in 2 mL of N,N-dimethylformamide, and diluted with 10 mL of methanol. 40 mL of water, 10 mL of pH 5 acetic acid / sodium acetate buffer, and 0.5 mL of XO reagent were added to form a pink suspension. A chelate titration was performed by adding 0.1 mol / L EDTA disodium solution dropwise until the pink color of the suspension changed to yellow.

[0116] Zinc complex of compound 2: Zinc complex of 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide (compound 4) Chelatometric titration conditions: The zinc complex of 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide was titrated in the same manner.

[0117] Table 1 shows the hydrazide content, zinc content, and content ratio (mass ratio) in the zinc complexes of various hydrazide compounds.

[0118] Compound 1: 3-Hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide Compound 2: 2-Hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide Compound 3: Zinc complex of Compound 1 Compound 4: Zinc complex of compound 2

[0119] [Table 1]

[0120] [4] Examples 1-2 and Comparative Examples 1-2: Production of rubber compositions The components shown in Table 2 were mixed in the proportions (parts by mass) and kneaded in a plastomill to prepare rubber compositions. Each prepared rubber composition was evaluated for reversion resistance by the following method.

[0121] Resistance to reversion The unvulcanized rubber obtained by kneading in a Plastomill was subjected to a vulcanization curve measurement at 150°C for 60 minutes using a vulcanization tester (manufactured by M&K Co., Ltd.). The maximum torque during vulcanization was designated "MH," and the torque after 60 minutes was designated "M60." The reversion resistance was quantified using the following formula.

[0122] Reversion resistance=(MH-M60) / MH The reversion resistance was expressed as an index, which is a numerical value of the reversion resistance. The reversion resistance index of the Examples (zinc complexes of hydrazide compounds) was expressed relative to the reversion resistance index of the Comparative Examples (hydrazide compounds) that were used for comparison.

[0123] Reversion resistance index of example (zinc complex of hydrazide compound) =Reversion resistance of Example (zinc complex of hydrazide compound) / Reversion resistance of comparative example (hydrazide compound) x 100 Reversion resistance index of Example 1 (Compound 3) =Reversion resistance of Example 1 (Compound 3) / Reversion resistance of Comparative Example 1 (Compound 1)×100 Reversion resistance index of Example 2 (Compound 4) =Reversion resistance of Example 2 (Compound 4) / Reversion resistance of Comparative Example 2 (Compound 2)×100 The smaller the index value of reversion resistance, the lower the rate of reduction from the maximum torque, indicating that severance of sulfur crosslinks due to reversion has occurred less frequently, and thus indicating better reversion resistance.

[0124] The evaluation results are shown in Table 2.

[0125] [Table 2] *1: N234 grade *2: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) *3: N-cyclohexyl-2-benzothialylsulfenamide (CBS) *4: Compound 1 *5: Compound 2 *6: Compound 3 (zinc complex of Compound 1) *7: Compound 4 (zinc complex of Compound 2) [Industrial Applicability]

[0126] The zinc complex of a hydrazide compound of the present invention and the reversion inhibitor for rubber containing the zinc complex of a hydrazide compound exhibit excellent reversion resistance when contained in a rubber composition.

[0127] By incorporating the zinc complex of a hydrazide compound of the present invention and a reversion inhibitor for rubber containing the zinc complex of a hydrazide compound into a rubber composition and using this rubber composition to produce a tire, it is possible to produce a tire that exhibits excellent durability.

Claims

1. A zinc complex of a hydrazide compound represented by the following formula (1): 【Chemical 1】 [In formula (1), R 1 , and R 2 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A represents a phenyl group or a naphthyl group and has at least one polar group selected from the group consisting of an amino group, an aminoalkyl group, an alkoxycarbonyl group, an acyl group, an acyloxy group, an amido group, a carboxyl group, a carboxyalkyl group, a formyl group, a nitrile group, a nitro group, a hydroxyalkyl group, a hydroxyl group, an alkoxy group, an aryloxy group, a heterocyclic group, a thiol group, an alkylthio group, and an arylthio group. However, the formula (1) excludes hydrazide compounds in which both R 1 and R 2 are methyl groups.

2. 2. The zinc complex according to claim 1, wherein the hydrazide compound represented by formula (1) is 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide or 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide.

3. A reversion inhibitor for rubber, comprising a zinc complex of a hydrazide compound represented by the following formula (1): 【Chemistry 2】 [In formula (1), R 1 , and R 2 are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. A represents a phenyl group or a naphthyl group and has at least one polar group selected from the group consisting of an amino group, an aminoalkyl group, an alkoxycarbonyl group, an acyl group, an acyloxy group, an amido group, a carboxyl group, a carboxyalkyl group, a formyl group, a nitrile group, a nitro group, a hydroxyalkyl group, a hydroxyl group, an alkoxy group, an aryloxy group, a heterocyclic group, a thiol group, an alkylthio group, and an arylthio group.

4. 4. The reversion inhibitor for rubber according to claim 3, wherein the hydrazide compound represented by formula (1) is 3-hydroxy-N'-(4-methylpentan-2-ylidene)naphthalene-2-carbohydrazide or 2-hydroxy-N'-(4-methylpentan-2-ylidene)benzoic acid hydrazide.

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