Method for vulcanizing rubber composition

Abstract

To provide a method for determining the amount of generation of an episulfide structure in a rubber component, and appropriately set a vulcanization condition for a rubber composition with the calculated amount of generation of the episulfide structure as an index.SOLUTION: Provided is a vulcanization method for a rubber composition for adjusting the molar ratio of an episulfide structure to all 1,4-isoprene bonding units in a rubber component to 1.0 mol% or less, wherein the molar ratio is calculated by measuring the solid 13C-NMR of the rubber composition including the rubber component including isoprene rubber, and determining the ratio between the peak area of a carbon peak derived from a carbon atom forming a double bond and the peak area of a carbon peak derived from a carbon atom constituting the episulfide structure, from among carbon atoms constituting the 1,4-isoprene bonding unit of the rubber component in an obtained solid 13C-NMR spectrum.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for vulcanizing a rubber composition. [Background technology]

[0002] When an unvulcanized rubber composition containing a vulcanizing agent such as sulfur is heated and pressurized (vulcanized), rubber molecules are crosslinked via sulfur atoms, but in butadiene rubber, it has been reported that a side reaction occurs in which the 1,4-butadiene bonds that make up the rubber molecules incorporate sulfur atoms to close a ring and form a cyclic sulfide structure 3 (for example, Non-Patent Document 1). Non-Patent Document 1 proposes a mechanism in which such cyclic sulfide structure 3 is formed via an episulfide, which has a smaller number of ring members. [ka] [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Macromolecules 1999, 32, 22, 7521-7529 Summary of the Invention [Problem to be solved by the invention]

[0004] There have been no reports to date of actually detecting episulfide structures in rubber components containing isoprene-based rubber after vulcanization, and no method for quantifying the amount of episulfide structures produced has been known.

[0005] The formation of episulfide structures that do not contribute to cross-linking between rubber molecules can be considered an undesirable side reaction in terms of vulcanization efficiency. Furthermore, because episulfides have a highly reactive molecular structure, if episulfide structures remain in the rubber component after vulcanization, there is concern that rubber products may deteriorate over time.

[0006] An object of the present invention is to provide a method for quantifying the amount of episulfide structures formed in a vulcanized rubber component and appropriately setting the vulcanization conditions for a rubber composition using the calculated amount of episulfide structures formed as a guideline. [Means for solving the problem]

[0007] The present invention provides a method for vulcanizing a rubber composition, which adjusts the molar ratio of episulfide structures to the total 1,4-isoprene bond units in the rubber component to 1.0 mol% or less, and the molar ratio is determined by the solids content of the rubber composition containing a rubber component containing an isoprene-based rubber. 13 C-NMR was measured and the resulting solid 13 The vulcanization method is calculated by determining the ratio of the peak area of ​​a carbon peak derived from carbon atoms forming double bonds among carbon atoms constituting 1,4-isoprene bond units of the rubber component to the peak area of ​​a carbon peak derived from carbon atoms constituting the episulfide structure in a C-NMR spectrum. [Effects of the Invention]

[0008] According to the present invention, the amount of episulfide structures formed in a rubber component containing an isoprene-based rubber is quantified, and the calculated amount of episulfide structures formed is used as a guideline to appropriately set vulcanization conditions such as vulcanization temperature and time. By keeping the amount of episulfide structures formed in the vulcanized rubber component at or below a certain value, an increase in local rigidity can be prevented, and vulcanized rubber products such as tires having excellent physical properties such as ease of elongation and fracture resistance can be produced. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing an NMR spectrum obtained by measuring the vulcanized rubber composition of Example 1 by solid-state 13C-NMR. [Figure 2] FIG. 2 is an enlarged view showing the NMR spectrum obtained by measuring the vulcanized rubber composition of Example 1 by solid-state 13C-NMR. DETAILED DESCRIPTION OF THE INVENTION

[0010] The method for vulcanizing a rubber composition of the present invention is characterized in that the molar ratio of episulfide structures to all 1,4-isoprene bond units in the rubber component is adjusted to 1.0 mol% or less. In addition, the molar ratio is determined by adjusting the solid content of the rubber composition containing a rubber component containing an isoprene-based rubber. 13 C-NMR was measured and the resulting solid 13 It is calculated by determining the ratio of the peak area of ​​the carbon peak derived from the carbon atoms forming the double bond among the carbon atoms constituting the 1,4-isoprene bond units of the rubber component to the peak area of ​​the carbon peak derived from the carbon atoms constituting the episulfide structure in a C-NMR spectrum.

[0011] By adjusting the molar ratio of the episulfide structure to the total 1,4-isoprene bond units in the rubber component to 1.0 mol % or less (preferably 0.7 mol % or less, more preferably 0.5 mol % or less, and even more preferably 0.3 mol % or less), an increase in local rigidity can be prevented, and vulcanized rubber products such as tires having excellent physical properties such as ease of elongation and fracture resistance can be produced.

[0012] Another embodiment of the present invention is a method for producing a tire using the rubber composition produced by the above vulcanization method.

[0013] Another embodiment of the present invention is a tire using a rubber composition containing a rubber component in which the molar ratio of episulfide structures to all 1,4-butadiene bond units is adjusted to 1.0 mol % or less.

[0014] The quantitative determination method according to the present invention and the method for vulcanizing a rubber composition using the quantitative determination method will be described in detail below. However, the following description is merely an example for explaining the present invention, and is not intended to limit the technical scope of the present invention to the described range.

[0015] <Vulcanized rubber composition> Examples of rubber components that can be used in the present invention include isoprene-based rubbers such as natural rubber (NR) and isoprene rubber (IR). Also, diene-based rubbers such as styrene-butadiene rubber (SBR), butadiene rubber (BR), styrene-isoprene-butadiene rubber (SIBR), chloroprene rubber (CR), and acrylonitrile-butadiene rubber (NBR), as well as non-diene rubbers such as butyl rubber (IIR), halogenated butyl rubber (X-IIR), ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber, polynorbornene rubber, silicone rubber, chlorinated polyethylene rubber, fluororubber (FKM), acrylic rubber (ACM), and hydrin rubber may be included. These rubber components may be used alone or in combination of two or more. The content of the isoprene-based rubber (preferably NR) in the rubber component is not particularly limited, but is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass, and may be 100% by mass.

[0016] As the vulcanizing agent, sulfur is preferably used, and examples of sulfur that can be used include powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur.

[0017] When sulfur is contained as a vulcanizing agent, the content per 100 parts by mass of the rubber component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. Furthermore, from the viewpoint of preventing deterioration, the content is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. When oil-containing sulfur is used as the vulcanizing agent, the content of the vulcanizing agent is the total content of pure sulfur contained in the oil-containing sulfur.

[0018] Examples of vulcanizing agents other than sulfur include alkylphenol-sulfur chloride condensate, sodium 1,6-hexamethylene-dithiosulfate dihydrate, 1,6-bis(N,N'-dibenzylthiocarbamoyldithio)hexane, etc. These vulcanizing agents other than sulfur can be commercially available from Taoka Chemical Co., Ltd., Lanxess K.K., Flexis, etc.

[0019] The vulcanization accelerator is not particularly limited, but examples thereof include sulfenamide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamate-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate-based vulcanization accelerators, with sulfenamide-based, thiazole-based, and guanidine-based vulcanization accelerators being preferred. These vulcanization accelerators may be used alone or in combination of two or more.

[0020] The content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 1.0 part by mass or more, more preferably 1.5 parts by mass or more, and even more preferably 2.0 parts by mass or more. The content of the vulcanization accelerator per 100 parts by mass of the rubber component is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, even more preferably 6.0 parts by mass or less, and particularly preferably 5.0 parts by mass or less. By setting the content of the vulcanization accelerator within the above range, breaking strength and elongation tend to be ensured.

[0021] In addition to the above-mentioned components, the rubber composition according to the present invention may contain compounding agents conventionally commonly used in the rubber industry, such as reinforcing fillers such as carbon black, silica, aluminum hydroxide, calcium carbonate, alumina, clay, and talc, silane coupling agents, resin components, liquid polymers, oils, waxes, processing aids, antioxidants, stearic acid, and zinc oxide, as appropriate.

[0022] The carbon black is not particularly limited, and any carbon black commonly used in the rubber industry can be used as appropriate, such as GPF, FEF, HAF, ISAF, SAF, etc. These carbon blacks may be used alone or in combination of two or more.

[0023] The content of carbon black per 100 parts by mass of the rubber component is not particularly limited, and can be, for example, 1 to 150 parts by mass, 5 to 120 parts by mass, or 10 to 100 parts by mass depending on the purpose of compounding. 13 From the viewpoint of preventing the C-NMR signal from broadening, which makes it difficult to quantify the episulfide structure, the amount is preferably 50 parts by mass or less, and more preferably 25 parts by mass or less.

[0024] The silica is not particularly limited, and can be, for example, silica prepared by a dry method (anhydrous silica) or silica prepared by a wet method (hydrated silica), which are commonly used in the rubber industry. Among them, hydrated silica prepared by a wet method is preferred because it contains a large number of silanol groups. These silicas can be used alone or in combination of two or more.

[0025] The content of silica per 100 parts by mass of the rubber component is not particularly limited, and can be, for example, 1 to 150 parts by mass, 5 to 120 parts by mass, or 10 to 100 parts by mass depending on the purpose of compounding.

[0026] Silica is preferably used in combination with a silane coupling agent.The silane coupling agent is not particularly limited, and any silane coupling agent that has been conventionally used in combination with silica in the rubber industry can be used.Such silane coupling agents include, for example, sulfide-based silane coupling agents, mercapto-based silane coupling agents, thioester-based silane coupling agents, amino-based silane coupling agents, and glycidoxy-based silane coupling agents.

[0027] The content of the silane coupling agent relative to 100 parts by mass of silica is preferably 1.0 part by mass or more, more preferably 3.0 parts by mass or more, and even more preferably 5.0 parts by mass or more, from the viewpoint of improving the dispersibility of silica, and is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less, from the viewpoint of preventing a decrease in wear resistance.

[0028] The solid of the present invention 13 The vulcanized rubber composition to be subjected to C-NMR measurement can be produced by a known method, for example, by kneading the above-mentioned components using a rubber kneading device such as an open roll or an internal kneader (e.g., a Banbury mixer or a kneader), followed by vulcanization.

[0029] The kneading step includes, for example, a base kneading step in which compounding ingredients and additives other than the vulcanizing agent and vulcanization accelerator are kneaded, and a final kneading (F kneading) step in which the vulcanizing agent and vulcanization accelerator are added to the kneaded product obtained in the base kneading step and kneaded. Furthermore, the base kneading step can be divided into multiple steps as desired.

[0030] The kneading conditions are not particularly limited, but examples include a method in which the base kneading step involves kneading for 3 to 10 minutes at a discharge temperature of 150 to 170°C, and in the final kneading step, kneading for 1 to 5 minutes at 70 to 110°C.

[0031] The unvulcanized rubber composition obtained by the kneading step can be vulcanized to obtain a vulcanized rubber composition. The vulcanization conditions are not particularly limited, and can be appropriately set so that the molar ratio (mol%) of episulfide structures relative to all 1,4-isoprene bond units in the rubber component and the number of moles of episulfide structures relative to the weight of the rubber component (mol / g) fall within predetermined ranges, as described below. For example, the vulcanization temperature can be in the range of 120 to 200°C, 120 to 180°C, 120 to 160°C, or 130 to 160°C. The vulcanization time can be in the range of 0.5 to 30 minutes, 0.5 to 15 minutes, 0.5 to 10 minutes, 0.5 to 7 minutes, 0.5 to 5 minutes, or 1 to 5 minutes.

[0032] <Quantitative process> The NMR that can be used in the present invention is a solid-state high-resolution NMR. 13 Although there is no particular limitation to C-NMR, NMR is preferred because it provides better resolution and allows for more accurate quantification. 13 The C resonance frequency is preferably 75 MHz or higher, more preferably 100 MHz or higher, and even more preferably 126 MHz or higher.

[0033] solid 13 The measurement conditions for C-NMR can be set, for example, as follows: (Measurement conditions) Equipment: Bruker Avance 400 Probe used: Bruker 7mm MAS BB WB WVT probe 13 C resonance frequency 100.6MHz MAS rotation speed 5kHz (±1Hz) Measurement mode: DD / MAS Wait time: 6 seconds Total number of times: 40960 Observed temperature: 58℃ Sample volume: 1 / 4 of the zirconia rotor capacity External reference substance: Adamantane (chemical shift value: 29.5 ppm)

[0034] MAS spinning rates are chosen because of the elimination of chemical shift anisotropy and the elimination of dipolar interactions. 13 When the C resonance frequency is 100.6 MHz, 5 kHz or more is preferable. The waiting time is preferably 6 to 30 seconds to ensure quantitative determination. The number of integrations is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 20,000 or more, and particularly preferably 40,000 or more, so that peaks derived from carbon atoms constituting the episulfide structure can be more accurately quantified.

[0035] An episulfide structure in which a 1,4-isoprene bond constituting a rubber molecule incorporates a sulfur atom to close a ring is presumed to have a chemical structure as shown in the following formula (2). Note that the episulfide structure according to the present invention encompasses not only the case where x in the following formula (2) is 1, but also cyclic polysulfides in which x is 2 or more. [ka] (wherein x represents an integer of 1 or more)

[0036] In the present invention, "a carbon atom forming a double bond among the carbon atoms constituting the 1,4-isoprene bond unit" refers to the carbon atoms represented by a1 and a2 in the above formula (2). Of these, "a quaternary carbon atom bonded to a methyl group among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component" refers to the carbon atom represented by a1 in the above formula (2), and "a tertiary carbon atom among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component" refers to the carbon atom represented by a2 in the above formula (2).

[0037] In the present invention, "carbon atoms constituting the episulfide structure" refer to the carbon atoms represented by b1 and b2 in the above formula (2). Among these, "a quaternary carbon atom bonded to a sulfur atom and a methyl group among the carbon atoms constituting the episulfide structure" refers to the carbon atom represented by b1 in the above formula (2), and "a tertiary carbon atom bonded to a sulfur atom among the carbon atoms constituting the episulfide structure" refers to the carbon atom represented by b2 in the above formula (2).

[0038] Of the carbon atoms constituting the 1,4-isoprene bond units of the rubber component, the carbon peak derived from the tertiary carbon atom (carbon atom represented by a2 in the above formula (2)) is observed at 123.5 to 128.0 ppm.

[0039] Of the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component, the carbon peak derived from the quaternary carbon atom bonded to a methyl group (carbon atom represented by a1 in the above formula (2)) is observed at 133.0 to 137.5 ppm.

[0040] Of the carbon atoms constituting the episulfide structure, the carbon peak derived from the tertiary carbon atom bonded to the sulfur atom (the carbon atom represented by b2 in the above formula (2)) is observed at 50.8 to 51.7 ppm.

[0041] Among the carbon atoms constituting the episulfide structure, a carbon peak derived from a sulfur atom and a quaternary carbon atom bonded to a methyl group (the carbon atom represented by b1 in the above formula (2)) is observed at 50.0 to 50.8 ppm.

[0042] The obtained solid 13 From the C-NMR spectrum, the molar ratio (mol %) of the episulfide structure to all 1,4-isoprene bond units in the rubber component can be calculated, for example, by the following formula (3). (molar ratio (mol%) of episulfide structures to all 1,4-isoprene bond units in the rubber component) = {(peak area of ​​the carbon peak derived from the tertiary carbon atom bonded to a sulfur atom among the carbon atoms constituting the episulfide structure) + (peak area of ​​the carbon peak derived from the quaternary carbon atom bonded to a sulfur atom and a methyl group among the carbon atoms constituting the episulfide structure)} / {(peak area of ​​the carbon peak derived from the tertiary carbon atom among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component) + (peak area of ​​the carbon peak derived from the quaternary carbon atom bonded to a methyl group among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component)} × 100 (3)

[0043] Note that, although 1,4-isoprene bond units contain cis-1,4 bonds and trans-1,4 bonds (the above formula (1) is shown as a cis-1,4 bond for convenience), both are included in the present invention. Therefore, the peak area of ​​the carbon peak derived from the carbon atom forming the double bond among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component is the sum of the peak area of ​​the carbon peak derived from the carbon atom in the cis-1,4 bond and the peak area of ​​the carbon peak derived from the carbon atom in the trans-1,4 bond. The peak area of ​​the carbon peak derived from the carbon atom bonded to a sulfur atom among the carbon atoms constituting the episulfide structure is the sum of the peak area of ​​the carbon peak derived from the carbon atom in the episulfide structure formed from the cis-1,4 bond and the peak area of ​​the carbon peak derived from the carbon atom in the episulfide structure formed from the trans-1,4 bond.

[0044] Theoretically, the peak area of ​​the carbon peak derived from the tertiary carbon atom (carbon atom represented by a2 in the above formula (2)) among the carbon atoms constituting the 1,4-isoprene bond units of the rubber component is the same as the peak area of ​​the carbon peak derived from the quaternary carbon atom bonded to a methyl group (carbon atom represented by a1 in the above formula (2)) among the carbon atoms constituting the 1,4-isoprene bond units of the rubber component. Furthermore, the peak area of ​​the carbon peak derived from the tertiary carbon atom bonded to a sulfur atom (carbon atom represented by b2 in the above formula (2)) among the carbon atoms constituting the episulfide structure is also the same as the peak area of ​​the carbon peak derived from the quaternary carbon atom bonded to a sulfur atom and a methyl group (carbon atom represented by b1 in the above formula (2)) among the carbon atoms constituting the episulfide structure. Therefore, the molar ratio (mol%) of the episulfide structure to all 1,4-isoprene bond units in the rubber component may be calculated, for example, by the following formula (4): (molar ratio (mol%) of episulfide structures to all 1,4-isoprene bond units in the rubber component) = {(peak area of ​​the carbon peak derived from the tertiary carbon atom bonded to a sulfur atom among the carbon atoms constituting the episulfide structure) × 2} / {(peak area of ​​the carbon peak derived from the quaternary carbon atom bonded to a methyl group among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component) × 2} × 100 (4)

[0045] When a rubber component having a 1,4-butadiene skeleton, such as butadiene rubber or styrene-butadiene rubber, is vulcanized, a carbon peak derived from the carbon atom forming the double bond among the carbon atoms constituting the 1,4-butadiene bond units of the rubber component is observed at 123 to 134 ppm. This carbon peak does not overlap with the carbon peak derived from the carbon atom represented by a1 in the above formula (2). From this, when a rubber component having a 1,4-isoprene skeleton and a rubber component having a 1,4-butadiene skeleton are used in combination, it is also possible to calculate the molar ratio (mol%) of the episulfide structure relative to the total amount of all 1,4-isoprene bond units and all 1,4-butadiene bond units in the rubber component.

[0046] Furthermore, from the calculated molar ratio of the episulfide structure to all 1,4-isoprene bond units in the rubber component, the number of moles (mol / g) of the episulfide structure relative to the weight of the rubber component can be calculated using the following formula (5). The molar mass of the 1,4-isoprene bond unit is 68.12 g / mol. (Number of moles of episulfide structure relative to the weight of rubber component (mol / g)) = {(molar ratio (mol%) of episulfide structures to all 1,4-isoprene bond units in the rubber component) / 100} × {(weight ratio of all 1,4-isoprene bond units in the rubber component (mass%)) / 100} × {1 / (molar mass of 1,4-isoprene bond unit (g / mol)} (5)

[0047] In the present invention, the amount of episulfide structures formed in a vulcanized rubber composition can be quantified by the above-mentioned method, and this makes it possible to obtain information necessary for optimizing the compounding, kneading and vulcanization conditions, which can suppress the amount of episulfide structures formed.

[0048] The molar ratio of episulfide structures to all 1,4-isoprene bond units in the rubber component is preferably 1.0 mol% or less, more preferably 0.7 mol% or less, even more preferably 0.5 mol% or less, and particularly preferably 0.3 mol% or less, from the viewpoint of suppressing performance changes due to chemical reactions over time. The molar ratio can be appropriately adjusted by the rubber component, filler, vulcanization accelerator, accelerator aid such as zinc oxide, vulcanization temperature, vulcanization time, etc.

[0049] The number of moles of episulfide structure relative to the weight of the rubber component is 15 x 10 -3 mol / g or less is preferable, and 10 × 10 -3 mol / g or less is more preferable, and 7.5×10 -3 It is more preferably mol / g or less. [Example]

[0050] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0051] The various chemicals used in the examples are listed below. NR:TSR20 Silica: ULTRASIL® VN3 (N2SA: 175 ml) manufactured by Evonik Degussa 2 / g) Silane coupling agent: Si266 (bis(3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa Oil: Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd. Wax: Ozoace 0355 manufactured by Nippon Seiro Co., Ltd. Antioxidant 1: Nocrac 6C (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Antioxidant 2: Nocrac RD (poly(2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Stearic acid: Camellia stearic acid beads manufactured by NOF Corporation Zinc oxide: Two types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powdered sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. (powdered sulfur containing 5% oil) Vulcanization accelerator 1: Noccela NS (N-tert-butyl-2-benzothiazolyl sulfenamide (TBBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 2: Noccela CZ (N-cyclohexyl-2-benzothiazolyl sulfenamide (CBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd. Vulcanization accelerator 3: Noccelaer D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0052] <Preparation of vulcanized rubber composition> According to the formulation shown in Table 1, chemicals other than sulfur and vulcanization accelerator were kneaded for 1 to 10 minutes using a 1.7 L closed-type Banbury mixer until the discharge temperature reached 150 to 160°C, yielding a kneaded mixture. Next, sulfur and vulcanization accelerator were added to the kneaded mixture using a two-screw open roll mill, and the mixture was kneaded for 4 minutes until the temperature reached 105°C, yielding an unvulcanized rubber composition. The unvulcanized rubber composition was vulcanized at 160°C for 8 minutes to yield a vulcanized rubber composition.

[0053] <Quantitative determination of episulfide structure> The obtained vulcanized rubber composition was subjected to the solidification test under the following conditions. 13 C-NMR measurement of solid 13 The C-NMR spectrum was obtained. 13 From the C-NMR spectrum, the molar ratio (mol%) of the episulfide structure to all 1,4-isoprene bond units in the rubber component was calculated using the above formula (5) based on the ratio of the peak area of ​​the carbon peak derived from a quaternary carbon bonded to a methyl group among the carbon atoms constituting the 1,4-isoprene bond units of the rubber component to the peak area of ​​the peak derived from the carbon atom constituting the episulfide structure. (molar ratio (mol%) of episulfide structures to all 1,4-isoprene bond units in the rubber component) = {(peak area of ​​the carbon peak derived from the tertiary carbon atom bonded to a sulfur atom among the carbon atoms constituting the episulfide structure) × 2} / {(peak area of ​​the carbon peak derived from the quaternary carbon atom bonded to a methyl group among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component) × 2} × 100 (4)

[0054] (solid 13 C-NMR measurement conditions) Equipment: Bruker Avance 400 Probe used: Bruker 7mm MAS BB WB WVT probe Resonance frequency 100.6MHz MAS rotation speed 5kHz (±1Hz) Measurement mode: DD / MAS Wait time: 6 seconds Total number of times: 40960 Observed temperature: 58℃ Sample volume: 1 / 4 of the zirconia rotor capacity External reference substance: Adamantane (chemical shift value: 29.5 ppm)

[0055] [Table 1]

[0056] <Preparation of vulcanized rubber composition> According to the formulation shown in Table 2, a 1.7 L internal Banbury mixer is used to knead the chemicals other than sulfur and the vulcanization accelerator for 1 to 10 minutes until the discharge temperature reaches 150 to 160°C, for example, to obtain a kneaded mixture. Next, using a two-screw open roll, sulfur and the vulcanization accelerator are added to the kneaded mixture, and the mixture is kneaded for 4 minutes until the temperature reaches 105°C, for example, to obtain an unvulcanized rubber composition. The unvulcanized rubber composition obtained can be vulcanized at, for example, 180°C, to obtain a vulcanized rubber composition.

[0057] <Quantitative determination of episulfide structure> The obtained vulcanized rubber composition was 13 C-NMR is measured, and the molar ratio (mol %) of the episulfide structure to all 1,4-isoprene bond units in the vulcanized rubber component can be calculated by the above-mentioned quantitative method.

[0058] <Measurement of acetone extractables and bound sulfur content> According to JIS K 6229:2015, each vulcanized rubber test piece was immersed in acetone for 24 hours to extract the soluble components. The mass of each test piece was measured before and after extraction, and the amount of acetone extracted (mass%) was calculated using the following formula. Furthermore, after the soluble components were extracted, the test piece was placed in an oven and heated at 100°C for 30 minutes to remove the solvent from the test piece. The amount of bound sulfur (mass%) in the test piece was then calculated using the oxygen combustion flask method according to JIS K 6233:2016. Acetone extractable amount (mass%) = {(mass of rubber test piece before extraction - mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} × 100

[0059] <Measurement of toluene swelling index> According to JIS K 6258:2016, the mass of each vulcanized rubber test piece is measured before and after immersion in toluene at 23°C for 24 hours, and the toluene swelling index can be calculated using the following formula. A smaller toluene swelling index indicates a higher crosslink density. (Toluene swelling index) = (weight after immersion) / (weight before immersion) × 100

[0060] <Tensile test> In accordance with JIS K 6251:2017, a tensile test is carried out in an atmosphere of 23°C using No. 3 dumbbell-shaped test pieces made of each vulcanized rubber composition, and the elongation at break EB (%), tensile strength at break TB (MPa), and tensile stress (MPa) at 100% elongation, 200% elongation, and 300% elongation can be measured.

[0061] [Table 2]

[0062] By evaluating vulcanized rubber test pieces obtained by varying the vulcanization time with the same formulation, it is possible to investigate the correlation between the amount of episulfide structure produced and the crosslink density, elongation, fracture resistance, etc.

[0063] <Vulcanization curve> After preparing an unvulcanized rubber composition according to the compounding recipe shown in Example 2, a curing curve of the vulcanized rubber composition can be obtained at temperatures such as 140°C, 160°C, and 180°C using a Curastometer (registered trademark) in accordance with JIS K 6300-2:2001. The maximum torque (Fmax) and minimum torque (Fmin) are measured for each obtained curing curve at each curing temperature. The curing time (seconds) required to reach a torque of {(Fmax-Fmin) x 0.5+Fmin} is defined as T50, the curing time (seconds) required to reach the maximum torque (Fmax) is defined as T100, and three times the time required to reach T100 is defined as T300.

[0064] For each vulcanization curve obtained at each vulcanization temperature, the vulcanization times T50, T100, and T300 are determined, and rubber compositions vulcanized for each vulcanization time are obtained. 13 C-NMR is measured, and the molar ratio (mol %) of the episulfide structure to all 1,4-isoprene bond units in the vulcanized rubber component can be calculated by the above-mentioned quantitative method.

[0065] By using the above method, it is possible to examine the change over time in torque at each vulcanization temperature and the change over time in the molar ratio of episulfide structures to all 1,4-isoprene bond units in the vulcanized rubber component.

[0066] In the present invention, the amount of episulfide structures formed in a vulcanized rubber composition can be quantified by the above-mentioned method, thereby making it possible to obtain information necessary for optimizing the compounding, kneading, vulcanization conditions, etc. of the rubber composition. Furthermore, by keeping the amount of episulfide structures formed in the vulcanized rubber component at a certain value or less, vulcanized rubber products such as tires that are excellent in physical properties such as ease of elongation and fracture resistance can be produced.

[0067] <Embodiment> Examples of embodiments of the present invention are given below.

[0068] [1] A method for vulcanizing a rubber composition, in which the molar ratio of episulfide structures to all 1,4-isoprene bond units in the rubber component is adjusted to 1.0 mol% or less, The molar ratio is determined by the solids content of the rubber composition containing the rubber component containing the isoprene-based rubber. 13 C-NMR was measured and the resulting solid 13 a vulcanization method in which the ratio of the peak area of ​​a carbon peak derived from carbon atoms forming a double bond among carbon atoms constituting a 1,4-isoprene bond unit of the rubber component to the peak area of ​​a carbon peak derived from carbon atoms constituting the episulfide structure in a C-NMR spectrum is calculated. [2] The vulcanization method according to the above [1], wherein a carbon peak derived from a tertiary carbon atom bonded to a sulfur atom among the carbon atoms constituting the episulfide structure is observed at 50.8 to 51.7 ppm. [3] The vulcanization method according to [1] or [2] above, wherein the rubber component contains natural rubber. [4] The vulcanization method according to any one of [1] to [3] above, wherein the content of carbon black in the rubber composition is 50 parts by mass or less per 100 parts by mass of the rubber component. [5] Solid 13 The vulcanization method according to any one of the above [1] to [4], wherein the C-NMR measurement mode is DD / MAS. [6] A method for producing a tire using a rubber composition produced by the vulcanization method according to any one of [1] to [5] above. [7] A tire using a rubber composition containing a rubber component in which the molar ratio of episulfide structures to all 1,4-isoprene bond units is adjusted to 1.0 mol% or less, and the molar ratio is determined by the solids content of the rubber composition containing a rubber component containing an isoprene-based rubber. 13 C-NMR was measured and the resulting solid 13A tire calculated by determining the ratio of the peak area of ​​a carbon peak derived from carbon atoms forming a double bond among carbon atoms constituting a 1,4-isoprene bond unit of the rubber component to the peak area of ​​a carbon peak derived from carbon atoms constituting the episulfide structure in a C-NMR spectrum.

Claims

1. A method for vulcanizing a rubber composition, comprising adjusting a molar ratio of episulfide structures to 1.0 mol % or less relative to all 1,4-isoprene bond units in a rubber component, the method comprising: The molar ratio is determined by the solids content of the rubber composition containing the rubber component containing the isoprene-based rubber. 13 C-NMR was measured, and the obtained solid 13 a vulcanization method in which the ratio of the peak area of ​​a carbon peak derived from carbon atoms forming a double bond among carbon atoms constituting a 1,4-isoprene bond unit of the rubber component to the peak area of ​​a carbon peak derived from carbon atoms constituting the episulfide structure in a C-NMR spectrum is calculated.

2. 2. The vulcanization method according to claim 1, wherein a carbon peak derived from a tertiary carbon atom bonded to a sulfur atom among carbon atoms constituting the episulfide structure is observed at 50.8 to 51.7 ppm.

3. The vulcanization method according to claim 1 or 2, wherein the rubber component comprises natural rubber.

4. 3. The vulcanization method according to claim 1, wherein the content of carbon black in the rubber composition is 50 parts by mass or less per 100 parts by mass of the rubber component.

5. solid 13 The vulcanization method according to claim 1 or 2, wherein the C-NMR measurement mode is DD / MAS.

6. A method for producing a tire using a rubber composition produced by the vulcanization method according to claim 1 or 2.

7. A tire using a rubber composition containing a rubber component in which the molar ratio of episulfide structures to all 1,4-isoprene bond units is adjusted to 1.0 mol% or less, The molar ratio is determined by the solids content of the rubber composition containing the rubber component containing the isoprene-based rubber. 13 C-NMR was measured, and the obtained solid 13 A tire calculated by determining the ratio of the peak area of ​​a carbon peak derived from carbon atoms forming double bonds among carbon atoms constituting 1,4-isoprene bond units of the rubber component to the peak area of ​​a carbon peak derived from carbon atoms constituting the episulfide structure in a C-NMR spectrum.

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