Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K13/00—Use of mixtures of ingredients not covered by one single of the preceding main groups, each of these compounds being essential
  • C08K13/02—Organic and inorganic ingredients
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
  • C08K3/22—Oxides; Hydroxides of metals
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/16—Nitrogen-containing compounds
  • C08K5/17—Amines; Quaternary ammonium compounds
  • C08K5/19—Quaternary ammonium compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L7/00—Compositions of natural rubber

Definitions

• the present invention relates to crosslinked rubber and tires using the crosslinked rubber.
• Metal oxides are commonly used in the sulfur vulcanization of rubber.
• metal oxides especially zinc oxide
• reducing the amount of metal oxide in the rubber composition makes it difficult for metal oxide aggregates to form in the vulcanized rubber, suppressing fractures originating from aggregates and improving fracture resistance. is expected to do so.
• Patent Documents 1 to 3 propose rubber compositions in which a eutectic compound is blended into the rubber component.
• Patent Document 3 discloses a rubber composition in which more than 4 parts by mass of a metal oxide is blended with respect to polyisoprene rubber, and a eutectic compound that is a mixed product of an onium salt and a hydrogen bond donor is blended. are doing.
• the eutectic compounds used in Patent Documents 1 to 3 have the problem that the eutectic compounds must be prepared by heating and mixing, making the process complicated. Furthermore, with regard to crosslinked rubbers whose main rubber component is rubber having an isoprene skeleton, an optimal formulation capable of suppressing reversion while reducing the amount of metal oxide compounded has not been proposed.
• airplane tires and ORR (off-road radial) tires need to be vulcanized for a long time, so they tend to be prone to re-vulcanization. Therefore, it is required to ensure a sufficient internal vulcanization reaction without causing overvulcanization.
• An object of the present invention is to provide a crosslinked rubber in which reversion due to overvulcanization is suppressed while reducing the amount of metal oxide compounded, and a tire using the crosslinked rubber.
• the present invention provides the following ⁇ 1> to ⁇ 12>.
• ⁇ 1> A rubber component containing 65% by mass or more of rubber having an isoprene skeleton; filler and At least one compound (A) selected from quaternary ammonium salts, phosphates, guanidine compounds, sulfonium salts, and amine compounds; metal oxide and A crosslinked rubber obtained by crosslinking a rubber composition containing
• the filler is at least one selected from carbon black and silica,
• the content of the silica is 0 parts by mass or more and less than 20 parts by mass with respect to 100 parts by mass of the rubber component,
• the content of the compound (A) is more than 0.5 parts by mass and 2 parts by mass or less based on 100 parts by mass of the rubber component,
• a crosslinked rubber in which the content of the metal oxide is 4 parts by mass or less based on 100 parts by mass of the rubber component.
• ⁇ 3> The crosslinked rubber described in ⁇ 1> or ⁇ 2>, in which the proportion of styrene-butadiene copolymer rubber in the rubber component is 30 mass% or less.
• ⁇ 4> The crosslinked rubber according to any one of ⁇ 1> to ⁇ 3>, wherein the proportion of butadiene rubber in the rubber component is less than 15% by mass.
• ⁇ 5> The crosslinked rubber according to any one of ⁇ 1> to ⁇ 4>, wherein the rubber component contains 90% by mass or more of rubber having an isoprene skeleton.
• ⁇ 6> The crosslinked rubber according to any one of ⁇ 1> to ⁇ 5>, wherein the content of the compound (A) is 1.5 parts by mass or less based on 100 parts by mass of the rubber component.
• the compound (A) contains at least a quaternary ammonium salt,
• R 1 , R 2 , and R 3 are each independently a hydrogen atom or a hydrocarbon group having 1 to 36 carbon atoms
• R 4 is a hydroxyl group, an alkyl group having 1 to 36 carbon atoms, or an alkyl group having 1 to 36 carbon atoms.
• n is an integer from 1 to 36.
• X ⁇ is any one of an inorganic acid ion, an organic acid ion, and a halogen ion.
• ⁇ 9> Further containing a thiuram compound, The crosslinked rubber according to any one of ⁇ 1> to ⁇ 8>, wherein the amount of the thiuram compound is 0.1 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the rubber component.
• ⁇ 11> The crosslinked rubber according to any one of ⁇ 1> to ⁇ 10>, wherein the proportion of polysulfide bonds in all the sulfide bonds is 55.0% or more and 75.0% or less.
• ⁇ 12> A tire using the crosslinked rubber described in any one of ⁇ 1> to ⁇ 11>.
• a to B indicating a numerical range represents a numerical range that includes the endpoints A and B, and is either "A or more and B or less” (if A ⁇ B), or "A or less and B”. or more” (in the case of A>B).
• parts by mass and % by mass have the same meaning as parts by weight and % by weight, respectively.
• the compounds described herein may be partially or entirely derived from fossil resources, may be derived from biological resources such as plant resources, or may be derived from recycled resources such as used tires. It's okay. Moreover, it may be derived from a mixture of any two or more of fossil resources, biological resources, and recycled resources.
• the crosslinked rubber of the present invention is A rubber component containing 65% by mass or more of rubber having an isoprene skeleton; filler and At least one compound (A) selected from quaternary ammonium salts, phosphates, guanidine compounds, sulfonium salts, and amine compounds; metal oxide, A crosslinked rubber obtained by crosslinking a rubber composition containing The filler is at least one selected from carbon black and silica, The content of the silica is 0 parts by mass or more and less than 20 parts by mass with respect to 100 parts by mass of the rubber component, The content of the compound is more than 0.5 parts by mass and 2 parts by mass or less based on 100 parts by mass of the rubber component, The content of the metal oxide is 4 parts by mass or less based on 100 parts by mass of the rubber component.
• the metal oxide and the compound (A) behave differently during the vulcanization reaction, it is thought that they have different effects on the formation of the network structure constituting the crosslinked rubber.
• the crosslinked rubber contains a metal oxide, it is thought that excessive radical generation is suppressed by metal ions generated within the system. Therefore, if the amount of metal oxide compounded is reduced, excessive radicals will be released, sulfide bonds in the crosslinked rubber will be severed, and reversion will likely occur.
• an ionic intermediate is produced during the vulcanization reaction. These ionic intermediates exhibit the effect of promoting the formation of a network structure by vulcanization without contributing to the cleavage of sulfide bonds in the rubber.
• the crosslinked rubber of the present invention contains a rubber component mainly composed of rubber having an isoprene skeleton, and has a low metal oxide content of 4 parts by mass or less, but the above-mentioned compound (A) assists vulcanization. Acts as an activator. Therefore, in the crosslinked rubber of the present invention, even if the metal oxide content is reduced, reversion due to overvulcanization is suppressed.
• the rubber component in the present invention is required to contain 65% by mass or more of rubber having an isoprene skeleton.
• the influence of metal oxides, which will be described later, upon overvulcanization differs depending on the rubber component.
• the rubber having an isoprene skeleton is a rubber whose main skeleton is an isoprene unit, and specific examples thereof include natural rubber (NR), polyisoprene rubber (IR), and the like.
• the rubber component may contain rubber other than rubber having an isoprene skeleton.
• Rubbers other than rubber having an isoprene skeleton include butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), butyl rubber (IIR), ethylene-propylene-diene copolymer (EPDM), and acrylonitrile-butadiene copolymer. Examples include combination (NBR).
• BR butadiene rubber
• SBR styrene-butadiene copolymer rubber
• IIR butyl rubber
• EPDM ethylene-propylene-diene copolymer
• acrylonitrile-butadiene copolymer examples include combination (NBR).
• the rubber component contains styrene-butadiene copolymer rubber
• its proportion in the rubber component is preferably 30% by mass or less, more preferably 20% by mass or less, and 10% by mass or less. It is more preferable that
• the proportion of the rubber having an isoprene skeleton in the rubber component is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more.
• the metal oxide contained in the crosslinked rubber of the present invention serves as an activator to assist in the vulcanization of the rubber.
• metal oxides include zinc oxide, calcium oxide, magnesium oxide, etc. Among these, zinc oxide is preferred.
• the metal oxide may also be an organic acid metal formed in situ by reaction or interaction with an organic acid (eg, a fatty acid such as stearic acid). Preferred examples of the organic acid metal include organic acid zinc.
• a metal oxide and an organic acid metal may be used in combination.
• the metal oxide content must be 4 parts by mass or less per 100 parts by mass of the rubber component. By making the metal oxide content 4 parts by mass or less, it is possible to ensure the mechanical strength of the crosslinked rubber, such as fracture resistance and abrasion resistance.
• the metal oxide content is preferably 3.5 parts by mass or less per 100 parts by mass of the rubber component, and more preferably 3 parts by mass or less. Note that the present invention also includes cases in which the crosslinked rubber does not contain a metal oxide, but from the viewpoint of vulcanization speed, the metal oxide content is preferably 1 part by mass or more per 100 parts by mass of the rubber component.
• the crosslinked rubber of the present invention contains at least one compound (A) selected from quaternary ammonium salts, phosphates, guanidine compounds, sulfonium salts, and amine compounds. These compounds produce ionic intermediates during the vulcanization reaction, and these ionic intermediates have the function of assisting the vulcanization of rubber. Even when the proportion of rubber having an isoprene skeleton is as high as 65% by mass and the content of metal oxides is low, the ionic intermediate produced from the above compound (A) contributes to the vulcanization reaction of the rubber. Therefore, reversion due to overvulcanization can be suppressed while ensuring a sufficient vulcanization reaction.
• compound (A) selected from quaternary ammonium salts, phosphates, guanidine compounds, sulfonium salts, and amine compounds.
• the content of the compound (A) is required to be more than 0.5 parts by mass and 2 parts by mass or less based on 100 parts by mass of the rubber component. If the content of the compound (A) is 0.5 parts by mass or less, the amount of ionic intermediates that contribute to crosslinking will be reduced, making it impossible to obtain sufficient mechanical strength. Moreover, when the content of the compound (A) exceeds 2 parts by mass, the breaking strength of the crosslinked rubber decreases due to poor dispersion of the compound.
• the content of the compound (A) is preferably 1.5 parts by mass or less, more preferably 1 part by mass or less, based on 100 parts by mass of the rubber component. Further, the content of the compound (A) is preferably 0.6 parts by mass or more, more preferably 0.7 parts by mass or more, based on 100 parts by mass of the rubber component.
• the quaternary ammonium salt is preferably a compound represented by the following formula (I).
• R 1 , R 2 , and R 3 are each independently a hydrogen atom or a hydrocarbon group having 1 to 36 carbon atoms
• R 4 is any one selected from a hydroxyl group, an alkyl group having 1 to 36 carbon atoms, an oxyalkyl group having 1 to 36 carbon atoms, and an oxycarbonylalkyl group having 1 to 36 carbon atoms
• n is an integer from 1 to 36.
• X ⁇ is any one of an inorganic acid ion, an organic acid ion, and a halogen ion.
• X in formulas (I) to (III) is preferably at least one selected from halogen elements, SO 3 H and CH 3 COO. Among these, it is preferable that X is a halogen element, and chlorine is particularly preferable because it is useful as a crosslinking promoter when sulfur is used as a crosslinking agent.
• Quaternary ammonium salts include choline chloride, acetylcholine chloride, lauroylcholine chloride, ⁇ -methylcholine chloride, carbamylcholine chloride, metacholine chloride, trimethylacetohydrazide ammonium chloride, benzoylcholine chloride, etc.
• Choline chloride is particularly preferred as a quaternary ammonium salt.
• the phosphate is preferably a compound represented by the following formula (IV).
• R 1 , R 2 , R 3 , and R 4 each independently represent a hydrogen atom, a hydrocarbon group having 1 to 36 carbon atoms, a phenyl group, an oxyalkyl group having 1 to 36 carbon atoms, and a C 1 to 36 oxyalkyl group. is any one selected from the oxycarbonyl alkyl groups.
• X ⁇ is any one of an inorganic acid ion, an organic acid ion, and a halogen ion.
• quaternary phosphate is preferred.
• Specific examples of quaternary phosphates include tetrabutylphosphonium chloride, tetrahexylphosphonium chloride, tetraoctylphosphonium chloride, triethylmethylphosphonium chloride, tributylethylphosphonium chloride, trimethyldecylphosphonium chloride, and tributyl(2-methoxyethyl)phosphonium chloride.
• triphenyl(tetradecyl)phosphonium chloride tetrabutylphosphonium bromide, tetrahexylphosphonium bromide, tetraoctylphosphonium bromide, triethylmethylphosphonium bromide, tributylethylphosphonium bromide, trimethyldecylphosphonium bromide, tributyl(2-methoxyethyl)phosphonium bromide, tri- Examples include phenyl(tetradecyl)phosphonium bromide.
• guanidine compound examples include diphenylguanidine (DPG), 1,3-di-o-tolylguanidine (DOTG), and 1-o-tolyl biguanide (OTBG).
• DPG diphenylguanidine
• DPG 1,3-di-o-tolylguanidine
• OTBG 1-o-tolyl biguanide
• diphenylguanidine is preferred as the guanidine compound.
• the amine compound is preferably a compound represented by the following formula (V).
• Possible forms in which the compound represented by formula (V) can become an ionic intermediate include when it reacts with a fatty acid or the like contained in a rubber composition, or when it undergoes a nucleophilic reaction with sulfur.
• R 1 is any one selected from a hydrocarbon group having 1 to 36 carbon atoms, an oxyalkyl group having 1 to 36 carbon atoms, and an aminoalkyl group having 1 to 36 carbon atoms.
• amine compounds include 1,5-diaminopentane, 2-methyl-5-diaminopentane, 1-aminononane, and dodecylamine.
• the sulfonium salt is preferably a compound represented by the following formula (VI).
• R 1 , R 2 , and R 3 each independently represent a hydrogen atom, a hydrocarbon group having 1 to 36 carbon atoms, an oxyalkyl group having 1 to 36 carbon atoms, and an oxycarbonylalkyl group having 1 to 36 carbon atoms.
• X ⁇ is any one of an inorganic acid ion, an organic acid ion, and a halogen ion.
• sulfonium salt tertiary sulfonium salts are preferred.
• Specific examples of sulfonium salts include tributylsulfonium chloride, trihexylsulfonium chloride, diethylmethylsulfonium chloride, dibutylethylsulfonium chloride, dimethyldecylsulfonium chloride, tributylsulfonium bromide, trihexylsulfonium bromide, diethylmethylsulfonium bromide, dibutylethylsulfonium bromide , dimethyldecylsulfonium bromide and the like.
• the crosslinked rubber of the present invention contains a filler that is at least one selected from carbon black and silica.
• a filler that is at least one selected from carbon black and silica.
• inorganic fillers other than carbon black and silica may be included.
• Carbon black As carbon black, those commonly used in the rubber industry can be used. As the carbon black, various grades of carbon black such as SAF, HAF, ISAF, FEF, SRF, and GPF can be used alone or in combination.
• the nitrogen adsorption specific surface area (N 2 SA, measured according to JIS K 6217-2:2001) of carbon black is preferably 110 to 145 m 2 /g from the viewpoint of fracture resistance, and 115 to 140 m 2 /g. 2 /g is more preferable, and even more preferably 120 to 135 m 2 /g.
• the carbon black preferably has a cetyltrimethylammonium bromide adsorption specific surface area (CTAB) of 110 to 140 m 2 /g, more preferably 115 to 135 m 2 /g, from the viewpoint of fracture resistance. More preferably, it is 120 to 130 m 2 /g.
• CTAB cetyltrimethylammonium bromide adsorption specific surface area
• One type of carbon black from those mentioned above may be used alone, or two or more types may be used in combination.
• the content of carbon black is preferably 30 parts by mass or more, more preferably 35 parts by mass or more, and 38 parts by mass, based on 100 parts by mass of the rubber component, from the viewpoint of maintaining the reinforcing properties of carbon black. It is more preferable that the amount is more than 1 part. Further, from the viewpoint of low heat generation, the content of carbon black is preferably 60 parts by mass or less, more preferably 55 parts by mass or less, and even more preferably 50 parts by mass or less.
• silica that can be used in the present invention is not particularly limited, and wet silica, dry silica, colloidal silica, etc. can be used. These can be used alone or in combination.
• the specific surface area of silica measured by the BET method is preferably 180 to 290 m 2 /g, more preferably 200 to 270 m 2 /g, from the viewpoint of fracture resistance. Note that the BET specific surface area of silica can be measured in accordance with the method of JISK 6430:2008.
• the content of silica is 0 parts by mass or more and less than 20 parts by mass with respect to 100 parts by mass of the rubber component. That is, the crosslinked rubber of the present invention may not contain silica.
• the content of silica is preferably 0 parts by mass or more, more preferably 1.5 parts by mass or more, based on 100 parts by mass of the rubber component. Further, the content of silica is preferably 14 parts by mass or less, more preferably 12 parts by mass or less, based on 100 parts by mass of the rubber component.
• Inorganic filler Inorganic fillers other than carbon black and silica that can be used in the present invention include inorganic compounds represented by the following general formula (VII). nM xSiO y zH 2 O (VII)
• M is at least one selected from the group consisting of metals selected from the group consisting of aluminum, magnesium, titanium, calcium and zirconium, oxides or hydroxides of these metals, and hydrates thereof, or carbonates of these metals, and n, x, y and z are respectively integers from 1 to 5, integers from 0 to 10, integers from 2 to 5 and integers from 0 to 10. These fillers may be used alone or in combination of two or more.
• Examples of the inorganic compound represented by formula (VII) include alumina (Al 2 O 3 ) such as ⁇ -alumina or ⁇ -alumina, alumina monohydrate ( Al 2 O 3 .H 2 O) such as boehmite or diaspore, aluminum hydroxide (Al(OH) 3 ) such as gibbsite or bayerite, aluminum carbonate (Al 2 (CO 3 ) 3 ), magnesium hydroxide (Mg(OH) 2 ), magnesium oxide (MgO), magnesium carbonate (MgCO 3 ), talc (3MgO.4SiO 2 .H 2 O), attapulgite (5MgO.8SiO 2 .9H 2 O), titanium white (TiO 2 ), titanium black (TiO 2n-1 ), calcium oxide (CaO), calcium hydroxide (Ca(OH) 2 ), aluminum magnesium oxide (MgO.Al 2 O 3 ), clay (Al 2 O 3 .2SiO 2 ), kaolin (A
• the rubber composition used in the present invention may contain various ingredients commonly used in the rubber industry, such as stearic acid, anti-aging agents, and vulcanization accelerators, as necessary, to the extent that the effects of the present invention are not impaired. , a vulcanizing agent, a resin, a process oil, etc. As these various components, commercially available products can be suitably used.
• sulfur is preferably blended as a vulcanizing agent.
• the content of sulfur is preferably 1 part by mass or more, more preferably 1.5 parts by mass or more based on 100 parts by mass of the rubber component.
• the content of sulfur is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, based on 100 parts by mass of the rubber component.
• the crosslinked rubber of the present invention preferably contains a thiuram compound as a vulcanization accelerator.
• thiuram compounds include tetrakis(2-ethylhexyl)thiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram disulfide, tetrabutylthiuram disulfide, tetramethylthiuram monosulfide, dipentamethylenethiuram tetrasulfide, tetrabenzylthiuram disulfide, etc. .
• a commercially available product may be used as the thiuram compound.
• the content of the thiuram compound is preferably 0.1 part by mass or more and 0.5 parts by mass or less based on 100 parts by mass of the rubber component.
• Thiuram compounds tend to generate short sulfide bonds such as monosulfide bonds and disulfide bonds. As described later, monosulfide bonds are difficult to break, so the more monosulfide bonds there are, the more reversion tends to be suppressed.
• the content of the thiuram compound is more preferably 0.1 part by mass or more and 0.3 parts by mass or less based on 100 parts by mass of the rubber component.
• the crosslinked rubber may contain a sulfenamide compound as a vulcanization accelerator.
• sulfenamide compounds include N-cyclohexyl-2-benzothiazolylsulfenamide, N-(tert-butyl)-2-benzothiazolesulfenamide, and N-oxydiethylene-2-benzothiazolylsulfenamide. etc.
• Sulfenamide compounds have the effect of generating sulfide bonds during the vulcanization reaction and re-cleaving the formed sulfide bonds during long-term vulcanization.
• the blending balance between the sulfenamide compound and the metal oxide influences the likelihood of reversion.
• the ratio of the molar amount (Mm) of metal ions (metal ions derived from metal oxides) in the crosslinked rubber to the molar amount (Mb) of the sulfenamide compound ( Mm/Mb) of 10 or less is preferable because revulcanization can be effectively suppressed.
• Mm/Mb is more preferably 5 or more, and even more preferably 7 or more.
• the molar amount of metal ions derived from the metal oxide is determined by the following formula (1).
• Mm/Mb (Nm/Lm+Nf/Lf)/(Nb/Lb)...(1)
• Nb is the amount of sulfenamide compound in the crosslinked rubber
• Lb is the molecular weight of the sulfenamide compound
• Nm is the amount of metal oxide in the crosslinked rubber
• Lm is the amount of metal oxide in the crosslinked rubber.
• Nf is the amount of fatty acid metal in the crosslinked rubber
• Lf is the molecular weight of the fatty acid metal.
• a monosulfide bond is a sulfide bond in which one sulfur atom is linked
• a disulfide bond is a sulfide bond in which two sulfur atoms are linked
• a polysulfide bond is a sulfide bond in which three or more sulfur atoms are linked.
• the proportion of monosulfide bonds in all sulfide bonds is preferably 5.0% or more and 25.0% or less.
• total sulfide bonds is the sum of monosulfide bonds, disulfide bonds, and polysulfide bonds. Since monosulfide bonds are strong bonds, they are difficult to break even in an overvulcanized state. On the other hand, disulfide bonds and polysulfide bonds tend to be easily broken by overvulcanization. That is, when there are more monosulfide bonds, reversion tends to be less likely to occur even if vulcanization is performed for a long time to promote the vulcanization reaction to the inside. On the other hand, when there are many monosulfide bonds, impact resistance improves, but crack resistance tends to decrease.
• the proportion of monosulfide bonds in all sulfide bonds is preferably 5.0% or more and 22.0% or less, and 10 More preferably, it is .0% or more and 20.0% or less.
• the crosslinked rubber has a proportion of monosulfide bonds in the above range, and a proportion of polysulfide bonds in all sulfide bonds is 55.0% or more and 75.0% or less.
• the proportions of monosulfide bonds, disulfide bonds, and polysulfide bonds in the total sulfide bonds can be determined by the swelling and compression method.
• the proportions of each bond are calculated according to the following procedure in accordance with the swelling and compression method described in Journal of the Society of Rubber Science and Technology of Japan, Vol. 75, No. 2 (2002), p. 73.
• a solution containing an excess amount of piperidine relative to thiol selectively cleaves disulfide bonds and polysulfide bonds in the crosslinked rubber, but does not cleave monosulfide bonds.
• a solution containing equimolar amounts of thiol and piperidine kinetically cleaves only polysulfide bonds. From this, the amount and proportion of each sulfide bond can be determined by utilizing the differences in the effects of the reagents.
• the total amount of sulfide bonds is referred to as ⁇ T
• the amount of monosulfide bonds among all sulfide bonds is referred to as ⁇ M
• the amount of disulfide bonds among all sulfide bonds is referred to as ⁇ D
• the amount of polysulfide bonds among all sulfide bonds is referred to as ⁇ P .
• the total amount of sulfide bonds ( ⁇ T ) can be determined by swelling the crosslinked rubber with the same solvent containing no reagent.
• ⁇ M and ( ⁇ M + ⁇ D ) are directly measured using the following method.
• ⁇ D can be calculated from ( ⁇ M + ⁇ D ) ⁇ M
• ⁇ P can be calculated from ⁇ T ⁇ ( ⁇ M + ⁇ D ).
• the type of solvent is not limited as long as it can sufficiently swell the crosslinked rubber sample and does not cause side reactions.
• ⁇ M + ⁇ D a mixed solution containing 1-decanethiol and piperidine is used. Note that this mixed solution was prepared using the above-mentioned mixed solvent of toluene and THF as a solvent, and the concentrations of each of piperidine and 1-decanethiol were adjusted to be about 0.4 mol/L.
• ⁇ M a mixed solution adjusted so that the molar ratio of piperidine to 1-decanethiol is about 8.73 is used.
• the solvent the above-mentioned mixed solvent of toluene and THF is used.
• a sample (cubic shape with each side of about 2 mm) is cut out from the crosslinked rubber, and the length of each side is precisely measured.
• This sample is immersed in the above-mentioned mixed solvent of toluene and THF and each mixed solution, and left at 30° C. for 20 hours to swell the sample. Next, the immersed sample is washed with the above-mentioned mixed solvent. For this swollen sample, the relationship between compressive stress and strain is determined using a TMA device.
• the proportions of monosulfide bonds, disulfide bonds, and polysulfide bonds can be adjusted by adjusting the blending amount of each component of the rubber composition for forming the crosslinked rubber, vulcanization conditions, etc. For example, if the amount of vulcanization accelerator is greater than the amount of sulfur, the total amount of crosslinking will increase, and the proportion of monosulfide will tend to increase. Furthermore, when a thiuram compound is included, the proportion of monosulfide bonds tends to increase as the content of the thiuram compound increases.
• the crosslinked rubber of the present invention can be applied to tires, conveyor belts, etc.
• the crosslinked rubber of the present invention is preferably applied to tires. It is preferable that the crosslinked rubber of the present invention is used in a region of a tire where thickness is required.
• the crosslinked rubber of the present invention is suitably used for tires for large vehicles such as ORR (off-road radial) tires, truck tires, and even tires for airplanes. Since the crosslinked rubber of the present invention can suppress reversion, when forming thick rubber (for example, 70 mm or more in thickness) such as tires for large vehicles, long-term vulcanization is required to ensure sufficient crosslinking reaction. It is possible to do so.
• the crosslinked rubber of the present invention can be produced by the following method. First, each component constituting the crosslinked rubber of the present invention (specifically, at least a rubber component, a metal oxide, a filler, and the above-mentioned compound) is blended and kneaded to prepare a rubber composition. For kneading, a kneading machine such as a Banbury mixer, a roll mixer, an internal mixer, etc. can be used. The kneading of each component may be carried out in one step or may be carried out in two or more stages. Thereafter, the obtained rubber composition is vulcanized to obtain a crosslinked rubber.
• a kneading machine such as a Banbury mixer, a roll mixer, an internal mixer, etc.
• the tire When the rubber article of the present invention is applied to a tire, the tire is manufactured by laminating the rubber article of the present invention together with other rubber members to form a green tire, and vulcanizing the green tire.
• the vulcanization temperature is preferably 130 to 150°C.
• Examples 1 to 4 Each component was kneaded according to the composition shown in Table 1 below to prepare a rubber composition.
• the units of numerical values in the formulations in Table 1 are parts by mass.
• the blending amounts in Table 1 are expressed in two significant digits.
• the prepared rubber compositions were vulcanized at 145°C to obtain crosslinked rubbers of Examples and Comparative Examples.
• the details of the components in Table 1 are as follows.
• NR Natural rubber, RSS#1 Carbon black: manufactured by Asahi Carbon Co., Ltd., Asahi #100L Silica: Manufactured by Tosoh Silica Co., Ltd., Nip Seal KQ Silane coupling agent: ABC-865, manufactured by Shin-Etsu Chemical Co., Ltd. Choline chloride: Manufactured by Kanto Kagaku Co., Ltd.
• Diphenylguanidine Manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
• Noxela D Vulcanization accelerator 1: Tetrabenzylthiuram disulfide, manufactured by Sanshin Kagaku Kogyo Co., Ltd.
• Supercellar TBZTD Vulcanization accelerator 2: N-cyclohexyl-2-benzothiazolylsulfenamide, “Noxela CZ” manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
• Sulfur Hosoi Chemical Industry Co., Ltd., HK200-5
• Fatty acid zinc Manufactured by LANXESS Corporation
• Actiplast PP Zinc white Manufactured by Seido Chemical Industry Co., Ltd.
• the total amount of zinc in Table 1 was calculated using the following formula (2).
• Nz is the blending amount of zinc white
• Nf is the blending amount of fatty acid zinc.
• Formula (2) uses zinc stearate as fatty acid zinc, converts the amount of zinc in the zinc fatty acid into zinc oxide, and sums the amount with the zinc white content.
• Zinc white equivalent amount Nf ⁇ 81.41/632.32+Nz...(2)
• Torque increase rate, reversion resistance Using the rubber compositions of each example and comparative example, the results were measured using a curelast meter (Toyo Seiki Model RLR-4 rotorless rheometer) in accordance with JIS K6300-2. , maximum torque time at 145°C (tc (max), unit: minute), maximum torque value (Fmax, unit: dN m), minimum torque value (Fmin, unit: dN m), 45 minutes from maximum torque time The subsequent torque value (Fx, unit: dN ⁇ m) was measured. Induction time and reversion (reversion) were defined as follows.
• the torque increase amount of each example and comparative example was expressed as an index, with the torque increase amount of Comparative Example 1 being 100.
• the results are shown in Table 1.
• the larger the index value the larger the amount of network structure formed.
• the reversion of each Example and Comparative Example was expressed as an index, with the reversion of Comparative Example 1 set as 100. The smaller the index value, the smaller the reversion (reversion) and the better the reversion resistance.
• Comparative Examples 2 and 3 are examples in which the amount of zinc oxide is reduced compared to Comparative Example 1. In both Comparative Examples 2 and 3, the torque increase rate was low, indicating that the mesh structure was not sufficiently formed. Further, Comparative Examples 2 and 3 have large reversion values, indicating that reversion is likely to occur. In Examples 1 and 3, when compared with Comparative Example 2, the torque increase rate is improved and the reversion value is decreased. Further, in Examples 1 and 3, the proportion of monosulfide bonds is higher and the proportion of polysulfide bonds is lower than that of Comparative Example 2.
• Comparative Examples 1 and 2 A comparison between Comparative Examples 1 and 2 and Comparative Example 3 also shows that by adding tetrabenzylthiuram disulfide, the proportion of monosulfide bonds and disulfide bonds tends to increase, and the proportion of polysulfide bonds tends to decrease. . That is, the results of Examples 2 and 4 show that by further adding a thiuram compound, a short crosslinked structure is formed, and as a result, reversion can be suppressed more effectively.

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