Quantitative method for cyclic sulfide structure

Abstract

To provide a method for quantitating a generation amount of a cyclic sulfide structure in a vulcanized rubber component.SOLUTION: There is provided a method for quantitating a generation amount of a cyclic sulfide structure in a rubber component including isoprene rubber in a vulcanized rubber composition, the method comprises: a step for measuring a solid 13C-NMR in a rubber composition including the rubber component, then, calculating a molar ratio of the cyclic sulfide structure with respect to all 1,4-isoprene binding units in the rubber component, on the basis of a ratio of a peak area of a carbon peak derived from a carbon atom which forms a double bond out of carbon atoms forming the 1,4-isoprene binding units in the rubber component in the acquired 13C-NMR spectrum, and a peak area of a carbon peak derived from the carbon atom coupled to a sulfur atom out of the carbon atoms forming the cyclic sulfide structure.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for quantifying the amount of cyclic sulfide structure formed in a vulcanized rubber component.

Background Art

[0002] By heating and pressurizing (vulcanizing) an unvulcanized rubber composition containing a vulcanizing agent such as sulfur, rubber molecules are crosslinked via sulfur atoms. In the case of butadiene rubber, it has been reported that, at the same time, a side reaction occurs in which the 1,4-butadiene bonds constituting the rubber molecules take in sulfur atoms and form a closed ring to form a cyclic sulfide structure (for example, Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, a method for quantifying the amount of cyclic sulfide structure formed in a vulcanized rubber component has not been known so far. Further, it is not clear whether such a cyclic sulfide structure is formed when a diene rubber other than butadiene rubber is vulcanized. Furthermore, the influence of the formation of the cyclic sulfide structure on the physical properties of the vulcanized rubber composition has not been examined in detail so far.

[0005] The formation of a cyclic sulfide structure that does not contribute to the crosslinking of rubber molecules can be said to be an undesirable side reaction in terms of the efficiency of vulcanization. In addition, the cyclic sulfide structure has a rigid molecular skeleton, and there is concern about a decrease in fracture resistance such as tensile strength due to an increase in local rigidity.

[0006] An object of the present invention is to provide a method for quantifying the amount of cyclic sulfide structure generated in a vulcanized rubber component.

Means for Solving the Problems

[0007] As a result of intensive studies, the present inventors have found that the amount of cyclic sulfide structure generated in a rubber component containing an isoprene rubber can be quantified by the following method using solid 13 13C-NMR, and have completed the present invention.

[0008] That is, the present invention is 〔1〕A method for quantifying the amount of cyclic sulfide structure generated in a rubber component containing an isoprene rubber in a vulcanized rubber composition, comprising measuring the solid 13 13C-NMR of the rubber composition containing the rubber component, and calculating the molar ratio of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component from the ratio of the peak area of the carbon peak derived from the carbon atom forming a double bond among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component in the obtained 13 13C-NMR spectrum to the peak area of the carbon peak derived from the carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure. 〔2〕A method for quantifying the amount of cyclic sulfide structure generated in a rubber component containing an isoprene rubber in a vulcanized rubber composition, comprising measuring the solid 13 13C-NMR of the rubber composition containing the rubber component, and calculating the molar ratio of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component from the ratio of the peak area of the carbon peak derived from the quaternary carbon atom bonded to the methyl group among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component in the obtained 13 13C-NMR spectrum to the peak area of the carbon peak derived from the Two carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure. The quantification method according to the above 〔1〕, including the step of calculating the molar ratio. 〔3〕Among the carbon atoms constituting the cyclic sulfide structure, the TwoThe quantification method according to the above [2], in which a carbon peak derived from a primary carbon atom is observed at 58.2 to 59.3 ppm, 〔4〕The quantification method according to any one of the above [1] to [3], wherein the rubber component contains natural rubber, 〔5〕The quantification method according to any one of the above [1] to [4], wherein the content of carbon black with respect to 100 parts by mass of the rubber component in the rubber composition is 50 parts by mass or less, 〔6〕Solid 13 The quantification method according to any one of the above [1] to [5], wherein the measurement mode of solid C-NMR is DD / MAS.

Advantages of the Invention

[0009] According to the present invention, the amount of cyclic sulfide structure generated in a rubber component containing an isoprene-based rubber can be quantified. Further, using the calculated amount of cyclic sulfide structure as a guideline, vulcanization conditions such as vulcanization temperature and time are appropriately set, and by making the amount of cyclic sulfide structure generated in the vulcanized rubber component equal to or less than a certain value, vulcanized rubber products such as tires excellent in physical properties such as elongation and fracture resistance can be produced.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0011] The method for quantifying the amount of cyclic sulfide structure in the rubber component of the present disclosure measures the solid C-NMR of a rubber composition containing the rubber component, and the obtained 13 C-NMR, and the obtained 13A step of calculating a molar ratio of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component from a ratio of a peak area of a carbon peak derived from a carbon atom forming a double bond among carbon atoms constituting a 1,4-isoprene bond unit of the rubber component in a 13C-NMR spectrum and a peak area of a carbon peak derived from a carbon atom bonded to a sulfur atom among carbon atoms constituting the cyclic sulfide structure is included. Further, the solid of the rubber composition containing the rubber component 13 13C-NMR is measured, and the obtained 13 From a ratio of a peak area of a carbon peak derived from a quaternary carbon atom bonded to a methyl group among carbon atoms constituting a 1,4-isoprene bond unit of the rubber component in a 13C-NMR spectrum and a peak area of a carbon peak derived from a Two carbon atom bonded to a sulfur atom among carbon atoms constituting the cyclic sulfide structure, it is preferable to include a step of calculating a molar ratio of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component. The rubber component includes an isoprene rubber.

[0012] A method for quantifying the amount of a cyclic sulfide structure generated in a vulcanized rubber component, which is one embodiment of the present disclosure, will be described in detail below. However, the following description is an exemplification for explaining the present invention, and is not intended to limit the technical scope of the present invention only to this description scope. In this specification, when a numerical range is indicated using "~", both end values thereof are included.

[0013] <Vulcanized rubber composition> Examples of rubber components that can be used in the present disclosure include isoprene rubbers such as natural rubber (NR) and isoprene rubber (IR). Further, diene rubbers such as styrene-butadiene rubber (SBR), butadiene rubber (BR), styrene-isoprene-butadiene rubber (SIBR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and 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 contained. These rubber components may be used alone or in combination of two or more. The content of isoprene 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, further preferably 80% by mass or more, particularly preferably 90% by mass, and may be 100% by mass.

[0014] Sulfur is preferably used as the vulcanizing agent. As sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersed sulfur, etc. can be used.

[0015] When sulfur is contained as the vulcanizing agent, the content thereof with respect to 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and further preferably 0.5 part by mass or more from the viewpoint of ensuring a sufficient vulcanization reaction. Further, from the viewpoint of preventing deterioration, it is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and further preferably 3.0 parts by mass or less. In addition, 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.

[0016] Examples of vulcanizing agents other than sulfur include alkylphenol sulfur chloride condensates, sodium 1,6 - hexamethylene - dithiothiosulfate dihydrate, 1,6 - bis(N,N'-dibenzylthiocarbamoyldithio)hexane, and the like. As these vulcanizing agents other than sulfur, those commercially available from companies such as Tago Chemical Industry Co., Ltd., Rancess Co., Ltd., and Flexsys can be used.

[0017] The vulcanization accelerator is not particularly limited. For example, it includes 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. Sulfenamide - based vulcanization accelerators, thiazole - based vulcanization accelerators, and guanidine - based vulcanization accelerators are preferred. These vulcanization accelerators may be used alone or in combination of two or more.

[0018] The content of the vulcanization accelerator relative to 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 still more preferably 2.0 parts by mass or more. Also, the content of the vulcanization accelerator relative to 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, still 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, the breaking strength and elongation tend to be ensured.

[0019] In addition to the above - mentioned components, the rubber composition according to the present disclosure may appropriately contain compounding agents generally used in the conventional rubber industry, such as reinforcing fillers like carbon black, silica, aluminum hydroxide, calcium carbonate, alumina, clay, talc, silane coupling agents, resin components, liquid polymers, oils, waxes, processing aids, anti - aging agents, stearic acid, zinc oxide, and the like.

[0020] The carbon black is not particularly limited, and those commonly used in the rubber industry can be appropriately used. For example, GPF, FEF, HAF, ISAF, SAF, etc. can be mentioned. These carbon blacks may be used alone or in combination of two or more.

[0021] The content of carbon black relative to 100 parts by mass of the rubber component is not particularly limited, and depending on the purpose of compounding, it can be, for example, 1 to 150 parts by mass, 5 to 120 parts by mass, 10 to 100 parts by mass. The content of carbon black relative to 100 parts by mass of the rubber component is solid 13 From the viewpoint of preventing the broadening of the signal of solid C-NMR and the difficulty in quantifying the cyclic sulfide structure, 50 parts by mass or less is preferable, and 25 parts by mass or less is more preferable.

[0022] The silica is not particularly limited, and for example, silica prepared by a dry method (anhydrous silica), silica prepared by a wet method (hydrous silica), etc., which are common in the rubber industry, can be used. Among them, hydrous silica prepared by a wet method is preferable because of its many silanol groups. These silicas may be used alone or in combination of two or more.

[0023] The content of silica relative to 100 parts by mass of the rubber component is not particularly limited, and depending on the purpose of compounding, it can be, for example, 1 to 150 parts by mass, 5 to 120 parts by mass, 10 to 100 parts by mass.

[0024] The 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, glycidoxy-based silane coupling agents, etc.

[0025] 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 enhancing the dispersibility of silica. Further, from the viewpoint of preventing a decrease in abrasion resistance performance, it 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.

[0026] The solid of the present disclosure 13 The vulcanized rubber composition to be subjected to 13C-NMR measurement can be produced by a known method. For example, it can be produced by kneading each of the above components using a rubber kneading apparatus such as an open roll, a closed kneader (Banbury mixer, kneader, etc.), and then vulcanizing.

[0027] The kneading process includes, for example, a base kneading process of kneading compounding agents and additives other than the vulcanizing agent and the vulcanization accelerator, and a final kneading (F kneading) process of adding the vulcanizing agent and the vulcanization accelerator to the kneaded product obtained in the base kneading process and kneading them. Further, the base kneading process can be divided into a plurality of processes if desired.

[0028] The kneading conditions are not particularly limited. For example, in the base kneading process, kneading is performed at a discharge temperature of 150 to 170°C for 3 to 10 minutes, and in the final kneading process, kneading is performed at 70 to 110°C for 1 to 5 minutes.

[0029] By vulcanizing the unvulcanized rubber composition obtained by the above kneading process, a vulcanized rubber composition can be obtained. The vulcanization conditions are not particularly limited, and can be appropriately set so that the molar ratio (mol%) of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component described later and the number of moles (mol / g) of the cyclic sulfide structure relative to the weight of the rubber component are within a predetermined range. For example, the vulcanization temperature can be in the range of 120 to 200°C, 120 to 180°C, 120 to 160°C, 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, 1 to 5 minutes.

[0030] <Quantitative Engineering> The NMR that can be used in the present disclosure is not particularly limited as long as it is solid high-resolution 13 C-NMR. However, since better resolution can be obtained and more accurate quantification can be achieved, the 13 C resonance frequency of NMR is preferably 75 MHz or more, more preferably 100 MHz or more, and even more preferably 126 MHz or more.

[0031] Solid 13 The measurement conditions of solid (Measurement Conditions) Device: Avance400 manufactured by Bruker Probe used: 7mm MAS BB WB WVT probe manufactured by Bruker 13 C resonance frequency: 100.6 MHz MAS rotation speed: 5 kHz (±1 Hz) Measurement mode: DD / MAS Waiting time: 6 seconds Number of integrations: 40960 times Observation temperature: 58 °C Sample amount: 1 / 4 volume of the zirconia rotor External reference substance: Adamantane (chemical shift value is 29.5 ppm)

[0032] The MAS rotation speed is preferably 5 kHz or more when the 13 C resonance frequency is 100.6 MHz, for the reasons of removing chemical shift anisotropy and dipole interaction. The waiting time is preferably 6 - 30 seconds to ensure quantification. Also, the number of integrations is preferably 5000 times or more, more preferably 10000 times or more, even more preferably 20000 times or more, and particularly preferably 40000 times or more in order to more accurately quantify the peaks derived from the carbon atoms constituting the cyclic sulfide structure.

[0033] The cyclic sulfide structure formed by the 1,4-isoprene bond constituting the rubber molecule incorporating sulfur atoms is presumed to have a chemical structure as shown in the following formula (3) according to the reaction mechanism shown below. [Chemical formula] (In the formula, x represents an integer of 1 or more)

[0034] In the present disclosure, the "carbon atoms 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 (3). Among these, the "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 (3), and the "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 (3).

[0035] In the present disclosure, the "carbon atoms bonded to sulfur atoms among the carbon atoms constituting the cyclic sulfide structure" refers to the carbon atoms represented by b1 and b2 in the above formula (3). Among these, the " Three primary carbon atom bonded to a sulfur atom and a methyl group among the carbon atoms constituting the cyclic sulfide structure" refers to the carbon atom represented by b1 in the above formula (3), and the " Two primary carbon atom bonded to a sulfur atom among the carbon atoms constituting the cyclic sulfide structure" refers to the carbon atom represented by b2 in the above formula (3).

[0036] The carbon peak derived from the tertiary carbon atom (the carbon atom represented by a2 in the above formula (3)) among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component is observed at 123.5 to 128.0 ppm.

[0037] The carbon peak derived from the quaternary carbon atom (the carbon atom represented by a1 in the above formula (3)) bonded to a methyl group among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component is observed at 133.0 to 137.5 ppm.

[0038] Among the carbon atoms constituting the cyclic sulfide structure, the carbon peak derived from the secondary carbon atom bonded to the sulfur atom (the carbon atom represented by b2 in the above formula (3)) is observed at 58.2 to 59.3 ppm. Two

[0039] Among the carbon atoms constituting the cyclic sulfide structure, the carbon peak derived from the secondary carbon atom bonded to the sulfur atom and the methyl group (the carbon atom represented by b1 in the above formula (3)) is observed at 57.8 to 58.2 ppm. Three

[0040] From the obtained 13 C-NMR spectrum, the molar ratio (mol%) of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component can be determined, for example, by the following formula (4). (Molar ratio (mol%) of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component)= {(Peak area of the carbon peak derived from the secondary carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure)+(Peak area of the carbon peak derived from the secondary carbon atom bonded to the sulfur atom and the methyl group among the carbon atoms constituting the cyclic sulfide 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 the methyl group among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component)}×100 ···(4) Two Three

[0041] ​​​​In addition, the 1,4-isoprene bonding units include cis-1,4 bonds and trans-1,4 bonds (the above formula (1) is shown as cis-1,4 bonds for convenience), and both are included in the present disclosure. Therefore, the peak area of the carbon peak derived from the carbon atom forming a double bond among the carbon atoms constituting the 1,4-isoprene bonding unit of the rubber component is the sum of the peak area of the carbon peak derived from the carbon atom of the cis-1,4 bond and the peak area of the carbon peak derived from the carbon atom of the trans-1,4 bond. The peak area of the carbon peak derived from the carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure is the sum of the peak area of the carbon peak derived from the carbon atom of the cyclic sulfide structure generated from the cis-1,4 bond and the peak area of the carbon peak derived from the carbon atom of the cyclic sulfide structure generated from the trans-1,4 bond.

[0042] The peak area of the carbon peak derived from the tertiary carbon atom (the carbon atom represented by a2 in the above formula (3)) among the carbon atoms constituting the 1,4-isoprene bonding unit of the rubber component and the peak area of the carbon peak derived from the quaternary carbon atom (the carbon atom represented by a1 in the above formula (3)) bonded to the methyl group among the carbon atoms constituting the 1,4-isoprene bonding unit of the rubber component are theoretically the same. Also, the peak area of the carbon peak derived from the Two tertiary carbon atom (the carbon atom represented by b2 in the above formula (3)) bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure and the peak area of the carbon peak derived from the Three quaternary carbon atom (the carbon atom represented by b1 in the above formula (3)) bonded to the sulfur atom and the methyl group among the carbon atoms constituting the cyclic sulfide structure are also theoretically the same.

[0043] However, among the carbon atoms constituting the cyclic sulfide structure, those bonded to the sulfur atom and the methyl group ThreeThe carbon peak derived from the cyclic carbon atom (the carbon atom represented by b1 in the above formula (3)) may overlap with the carbon peak derived from the carbon atom bonded to a sulfur atom not constituting a cyclic sulfide structure (i.e., the carbon atom constituting a crosslinking site). For this reason, the molar ratio (mol%) of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component may be calculated, for example, by the following formula (5). (mol ratio (mol%) of cyclic sulfide structures to the total 1,4-isoprene bond units in the rubber component)= (Among the carbon atoms that make up the cyclic sulfide structure, the carbon atom bonded to the sulfur atom Two (peak area of ​​the carbon peaks derived from quaternary carbon atoms bonded to methyl groups among the carbon atoms constituting the 1,4-isoprene bond units of the rubber component) × 2} / {(peak area of ​​the carbon peaks derived from quaternary carbon atoms bonded to methyl groups among the carbon atoms constituting the 1,4-isoprene bond units of the rubber component) × 2} × 100 (5)

[0044] In addition, when a rubber component having a 1,4-butadiene skeleton such as butadiene rubber or styrene-butadiene rubber is vulcanized, a cyclic sulfide structure is also formed. In this case, the carbon peak derived from the carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure is observed at 49 to 52 ppm. Two The carbon peaks derived from the carbon atom (the carbon atom represented by b2 in the above formula (3)) and the carbon atoms bonded to the sulfur atom and methyl group among the carbon atoms constituting the cyclic sulfide structure. Three It is distinguished from the carbon peak derived from the secondary carbon atom (carbon atom represented by b1 in the above formula (3)). In addition, the 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. 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 cyclic sulfide structure to the total amount of all 1,4-isoprene bond units and all 1,4-butadiene bond units in the rubber component.

[0045] Further, from the molar ratio of the cyclic sulfide structure to all 1,4-isoprene bonding units in the calculated rubber component, the number of moles of the cyclic sulfide structure per gram of the rubber component (mol / g) can be determined by the following formula (6). The molar mass of the 1,4-isoprene bonding unit is 68.12 g / mol. (Number of moles of cyclic sulfide structure per gram of rubber component (mol / g)) = {(Molar ratio of cyclic sulfide structure to all 1,4-isoprene bonding units in rubber component (mol%)) / 100} ×{(Weight ratio of all 1,4-isoprene bonding units in rubber component (mass%)) / 100} ×{1 / (Molar mass of 1,4-isoprene bonding unit (g / mol))} ···(6)

[0046] In the present disclosure, by the above method, the amount of the cyclic sulfide structure generated in the vulcanized rubber composition can be quantified, and thereby, information necessary for optimizing the compounding, kneading, and vulcanization conditions to suppress the amount of the cyclic sulfide structure generated can be obtained.

[0047] From the viewpoint of fracture resistance, the molar ratio of the cyclic sulfide structure to all 1,4-isoprene bonding units in the rubber component is preferably 2.0 mol% or less, more preferably 1.5 mol% or less, still more preferably 1.0 mol% or less, and particularly preferably 0.8 mol% or less. The molar ratio can be appropriately adjusted by the rubber component, filler, vulcanization accelerator, promoter aids such as zinc oxide, vulcanization temperature, vulcanization time, etc.

[0048] The number of moles of the cyclic sulfide structure per gram of the rubber component is preferably 0.30×10 -3 mol / g or less, and more preferably 0.15×10 -3 mol / g or less.

Examples

[0049] Hereinafter, the present disclosure will be described based on examples, but the present disclosure is not limited only to these examples.

[0050] The various chemicals used in the examples are summarized below. NR: TSR20 Stearic acid: Bead stearic acid Camellia made by NOF Corporation Zinc oxide: Two types of zinc oxide made by Mitsui Mining & Smelting Co., Ltd. Sulfur: Powder sulfur manufactured by Tsurumi Chemical Industry Co., Ltd. (5% oil-containing powder sulfur) Vulcanization accelerator: Nocceler NS (N-tert-butyl-2-benzothiazolylsulfenamide (TBBS)) manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

[0051] <Preparation of Vulcanized Rubber Composition> According to the formulation shown in Table 1, using a 1.7 L sealed Banbury mixer, the chemicals other than sulfur and the vulcanization accelerator were kneaded for 1 to 10 minutes until the discharge temperature reached 150 to 160 °C to obtain a kneaded product. Next, using a twin-screw open roll, sulfur and the vulcanization accelerator were added to the obtained kneaded product and kneaded for 4 minutes until the temperature reached 105 °C to obtain an unvulcanized rubber composition. The obtained unvulcanized rubber composition was vulcanized at 160 °C for 8 minutes to obtain a vulcanized rubber composition.

[0052] <Quantification of Cyclic Sulfide Structure> For the obtained vulcanized rubber composition, solid 13 13C-NMR was measured under the following conditions, 13 and a 13C-NMR spectrum was obtained. From the obtained 13 13C-NMR spectrum, based on the ratio of the peak area of the carbon peak derived from the quaternary carbon to which the methyl group is bonded among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component and the peak area of the peak derived from the carbon atom constituting the cyclic sulfide structure, the molar ratio (mol%) of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component was calculated by the following formula (5). (Molar ratio (mol%) of cyclic sulfide structure to all 1,4-isoprene bond units in rubber component) = {(Among the carbon atoms constituting the cyclic sulfide structure, the one bonded to the sulfur atom) Two{(Peak area of the carbon peak derived from the primary carbon atom) × 2} / {(Peak area of the carbon peak derived from the quaternary carbon atom bonded to the methyl group among the carbon atoms constituting the 1,4-isoprene bonding units of the rubber component) × 2} × 100 ···(5)

[0053] (Solid 13 C-NMR measurement conditions) Device: Avance400 manufactured by Bruker Probe used: 7mm MAS BB WB WVT probe manufactured by Bruker Resonance frequency: 100.6 MHz MAS rotation speed: 5 kHz (±1 Hz) Measurement mode: DD / MAS Waiting time: 6 seconds Number of integrations: 40960 times Observation temperature: 58 °C Sample amount: 1 / 4 capacity of the zirconia rotor External reference substance: Adamantane (chemical shift value is 29.5 ppm)

[0054]

Table 1

[0055] In the present disclosure, by the above method, the amount of the cyclic sulfide structure generated in the vulcanized rubber composition can be quantified, and thereby, the amount of the cyclic sulfide structure generated can be suppressed, and the information necessary for optimizing the compounding, kneading, and vulcanization conditions can be obtained.

Claims

1. A method for quantifying the amount of cyclic sulfide structure generated in a rubber component containing an isoprene rubber in a vulcanized rubber composition, The solid of the rubber composition containing the rubber component 13 C-NMR is measured, and the obtained 13 From the ratio of the peak area of the carbon peak derived from the carbon atom forming a double bond among the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component in the C-NMR spectrum to the peak area of the carbon peak derived from the carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure, a step of calculating the molar ratio of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component is included, a quantification method.

2. A method for quantifying the amount of cyclic sulfide structure generated in a rubber component containing an isoprene rubber in a vulcanized rubber composition, The solid of the rubber composition containing the rubber component 13 Perform C-NMR measurement on the obtained 13 From the ratio of the peak area of the carbon peak derived from the quaternary carbon atom bonded to the methyl group among the carbon atoms constituting the 1,4-isoprene bonding unit of the rubber component in the C-NMR spectrum and the peak area of the carbon peak derived from the secondary carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure, calculate the molar ratio of the cyclic sulfide structure to all 1,4-isoprene bonding units in the rubber component. The quantification method according to claim 1, comprising this step.

3. The quantification method according to claim 1 or 2, wherein a carbon peak derived from a secondary carbon atom bonded to a sulfur atom among the carbon atoms constituting the cyclic sulfide structure is observed at 58.2 to 59.3 ppm.

4. The quantification method according to any one of claims 1 to 3, wherein a carbon peak derived from a tertiary carbon atom bonded to a sulfur atom and a methyl group among the carbon atoms constituting the cyclic sulfide structure is observed at 57.8 to 58.2 ppm.

5. The quantification method according to any one of claims 1 to 4, wherein the rubber component contains natural rubber.

6. The quantification method according to any one of claims 1 to 5, wherein the content of carbon black with respect to 100 parts by mass of the rubber component in the rubber composition is 50 parts by mass or less.

7. Solid 13 The quantitative method according to any one of claims 1 to 6, wherein the measurement mode of C-NMR is DD / MAS.

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