JP2022077519A - Vulcanization method of rubber composition - Google Patents

Abstract

To a method for quantitatively determining a production amount of a cyclic sulfide structure in a rubber component, and appropriately setting a vulcanization condition of the rubber component based on the calculated production amount of the cyclic sulfide structure.SOLUTION: A vulcanization method of a rubber composition adjusts a molar ratio of a cyclic sulfide structure to entire 1,4-isoprene binding units in a rubber component to 2.0 mol% or less, in which the molar ratio is calculated by measuring solid 13C-NMR of the rubber composition containing the rubber component containing the isoprene-based rubber, and determining a ratio of a peak area of a carbon peak derived from a carbon atom forming a double bond in carbon atoms constituting the 1,4-isoprene binding units of the rubber component in the obtained 13C-NMR to a peak area of a carbo peak derived from a carbon atom coupled to a sulfur atom in the carbon atoms constituting the cyclic sulfide structure.SELECTED DRAWING: Figure 5

Description

The present invention relates to a method for vulcanizing a rubber composition.

By heating and pressurizing (vulcanizing) an unvulcanized rubber composition containing a vulcanizing agent such as sulfur, rubber molecules are cross-linked via sulfur atoms. It has been reported that the 1,4-butadiene bond constituting the molecule takes in a sulfur atom and closes the ring, causing a side reaction to form a cyclic sulfide structure (for example, Non-Patent Document 1).

Macromolecules 1999, 32, 22, 7521-7529

However, a method for quantifying the amount of cyclic sulfide structure produced in the vulcanized rubber component has not been known so far. Further, it is not clear whether or not such a cyclic sulfide structure is formed when a diene-based rubber other than butadiene rubber is vulcanized. Furthermore, the effect of the formation of the cyclic sulfide structure on the physical properties of the vulcanized rubber composition has not been investigated in detail so far.

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

It is an object of the present invention to provide a method for quantifying the amount of cyclic sulfide structure produced in a rubber component and appropriately setting the vulcanization conditions of the rubber composition using the calculated amount of cyclic sulfide structure as a guideline. And.

As a result of diligent studies, the present inventor has found that the amount of cyclic sulfide structure produced in a rubber component containing isoprene-based rubber can be quantified by the following method using solid ¹³ C-NMR. Furthermore, by setting the molar ratio of the cyclic sulfide structure to the calculated total 1,4-isoprene bond unit to a certain value or less, vulcanized rubber products such as tires having excellent physical properties such as stretchability and fracture resistance can be manufactured. We found that we could do it and completed the present invention.

That is, the present invention
[1] A method for sulphurizing a rubber composition, wherein the molar ratio of the cyclic sulfide structure to all 1,4-isoprene bonding units in the rubber component is adjusted to 2.0 mol% or less, and the molar ratio is isoprene-based. A solid ¹³ C-NMR of a rubber composition containing a rubber component containing rubber was measured, and a double bond among carbon atoms constituting the 1,4-isoprene bond unit of the rubber component in the obtained ¹³ C-NMR spectrum was obtained. It is calculated by calculating the ratio of the peak area of the carbon peak derived from the carbon atom forming the ring 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. , Sulfurization method,
[2] The molar ratio is a solid ¹³ C-NMR of a rubber composition containing a rubber component containing an isoprene-based rubber, and the 1,4-isoprene bonding unit of the rubber component in the obtained ¹³ C-NMR spectrum is measured. The peak area of the carbon peak derived from the quaternary carbon atom bonded to the methyl group among the carbon atoms constituting the above, and the carbon derived from the tertiary carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure. The sulfide method according to the above [1], which is calculated by obtaining the ratio of the peak areas of the peaks.
[3] The sulfide method according to the above [2], wherein a carbon peak derived from a tertiary 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 vulcanization method according to any one of [1] to [3] above, wherein the rubber component contains natural rubber.
[5] The vulcanization method according to any one of [1] to [4] above, wherein the content of carbon black in the rubber composition is 50 parts by mass or less with respect to 100 parts by mass of the rubber component.
[6] The vulcanization method according to any one of [1] to [5] above, wherein the measurement mode of solid ¹³ C-NMR is DD / MAS.
[7] A method for producing a tire using a rubber composition produced by the vulcanization method according to any one of [1] to [6] above.
[8] The present invention relates to a tire using a rubber composition containing a rubber component in which the molar ratio of the cyclic sulfide structure to all 1,4-isoprene binding units is adjusted to 2.0 mol% or less.

According to the present invention, the amount of cyclic sulfide structure formed in the rubber component containing isoprene-based rubber is quantified, and the calculated amount of cyclic sulfide structure formed is used as a guideline to appropriately set vulcanization conditions such as vulcanization temperature and time. By setting the amount of cyclic sulfide structure generated in the vulcanized rubber component to a certain value or less, it is possible to prevent an increase in local rigidity and vulcanize tires with excellent physical properties such as stretchability and fracture resistance. Can manufacture rubber products.

¹³ It is a figure which shows the NMR spectrum obtained by measuring the vulcanized rubber composition of Example 1 by 13 C-NMR. ¹³ It is an enlarged view which shows the NMR spectrum obtained by measuring the vulcanized rubber composition of Example 1 by 13 C-NMR. It is a figure which shows the vulcanization curve when the rubber composition of Example 2 is vulcanized at 140 degreeC. It is a figure which shows the vulcanization curve when the rubber composition of Example 2 is vulcanized at 180 degreeC. It is a figure which shows the correlation of the vulcanization temperature, the vulcanization time, and the amount of formation of a cyclic sulfide structure in the rubber composition of Example 2. FIG.

The vulcanization method of the rubber composition of the present disclosure is characterized in that the molar ratio of the cyclic sulfide structure to all 1,4-isoprene bonding units in the rubber component is adjusted to 2.0 mol% or less. Further, the molar ratio comprises a solid ¹³ C-NMR of a rubber composition containing a rubber component containing an isoprene-based rubber, and constitutes a 1,4-isoprene binding unit of the rubber component in the obtained ¹³ C-NMR spectrum. The peak area of the carbon peak derived from the carbon atom forming the double bond among the carbon atoms to be formed, and 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. It is calculated by finding the ratio. Further, the molar ratio is a solid ¹³ C-NMR of a rubber composition containing a rubber component containing an isoprene-based rubber, and the 1,4-isoprene bonding unit of the rubber component in the obtained ¹³ C-NMR spectrum is used. The peak area of the carbon peak derived from the quaternary carbon atom bonded to the methyl group among the constituent carbon atoms and the carbon peak derived from the tertiary carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure. It is preferable to calculate by obtaining the ratio of the peak areas of.

The molar ratio of the cyclic sulfide structure to all 1,4-isoprene binding units in the rubber component is 2.0 mol% or less (preferably 1.5 mol% or less, more preferably 1.0 mol% or less, still more preferably 0.8 mol%). By adjusting to the following), it is possible to prevent an increase in local rigidity and manufacture a vulcanized rubber product such as a tire having excellent physical properties such as stretchability and fracture resistance.

Another embodiment of the present disclosure is a method for producing a tire using the rubber composition produced by the above-mentioned vulcanization method.

Another embodiment of the present disclosure is a tire using a rubber composition containing a rubber component in which the molar ratio of the cyclic sulfide structure to all 1,4-isoprene binding units is adjusted to 2.0 mol% or less.

A method for quantifying the amount of cyclic sulfide structure produced in the vulcanized rubber component, which is an embodiment of the present disclosure, will be described in detail below. However, the following description is an example for explaining the present invention, and does not mean that the technical scope of the present invention is limited only to this description range. In this specification, when a numerical range is indicated by using "-", the numerical values at both ends thereof are included.

<Vulcanized rubber composition>
Examples of the rubber component that can be used in the present disclosure include isoprene-based 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), and acrylonitrile butadiene rubber (NBR), butyl rubber (IIR), and halogenated butyl rubber. Contains non-diene rubber such as (X-IIR), ethylene propylene diene rubber (EPDM), ethylene propylene rubber, polynorbornene rubber, silicone rubber, polyethylene chloride rubber, fluororubber (FKM), acrylic rubber (ACM), hydrin rubber, etc. You may be doing it. These rubber components may be used alone or in combination of two or more. The content of 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, further preferably 80% by mass or more, and particularly preferably 90% by mass. Preferably, it may be 100% by mass.

Sulfur is preferably used as the vulcanizing agent. As the sulfur, powdered sulfur, oil-treated sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, highly dispersible sulfur and the like can be used.

When sulfur is contained as a vulcanizing agent, the content with respect to 100 parts by mass of the rubber component is preferably 0.1 part by mass or more, more preferably 0.3 parts by mass or more, from the viewpoint of ensuring a sufficient vulcanization reaction. More preferably, 0.5 part by mass or more. From the viewpoint of preventing deterioration, 5.0 parts by mass or less is preferable, 4.0 parts by mass or less is more preferable, and 3.0 parts by mass or less is further preferable. 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.

Examples of the vulcanizing agent other than sulfur include alkylphenol / sulfur chloride condensate, 1,6-hexamethylene-sodium dithiosulfate / dihydrate, and 1,6-bis (N, N'-dibenzylthiocarbamoyldithio). ) Hexane and the like can be mentioned. As these vulcanizing agents other than sulfur, those commercially available from Taoka Chemical Industry Co., Ltd., LANXESS Co., Ltd., Flexis Co., Ltd. and the like can be used.

The vulcanization accelerator is not particularly limited, and is, for example, sulfuramide-based, thiazole-based, thiuram-based, thiourea-based, guanidine-based, dithiocarbamate-based, aldehyde-amine-based or aldehyde-ammonia-based, imidazoline-based, and xanthate. Examples of each vulcanization accelerator of the system include a sulfur amide-based vulcanization accelerator, a thiazole-based vulcanization accelerator, and a guanidine-based vulcanization accelerator. These vulcanization accelerators may be used alone or in combination of two or more.

The content of the vulcanization accelerator with respect 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 further preferably 2.0 parts by mass or more. The content of the vulcanization accelerator with respect 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, further preferably 6.0 parts by mass or less, and 5.0 parts by mass. Part or less is particularly preferable. By setting the content of the vulcanization accelerator within the above range, the fracture strength and elongation tend to be ensured.

In addition to the above-mentioned components, the rubber composition according to the present disclosure is used for reinforcing compounding agents generally used in the rubber industry, such as carbon black, silica, aluminum hydroxide, calcium carbonate, alumina, clay, and talc. It can appropriately contain a filler, a silane coupling agent, a resin component, a liquid polymer, an oil, a wax, a processing aid, an antiaging agent, stearic acid, zinc oxide and the like.

The carbon black is not particularly limited, and those commonly used in the rubber industry can be appropriately used, and examples thereof include GPF, FEF, HAF, ISAF, and SAF. These carbon blacks may be used alone or in combination of two or more.

The content of carbon black with respect to 100 parts by mass of the rubber component is not particularly limited, and may 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 blending. The content of carbon black with respect to 100 parts by mass of the rubber component is preferably 50 parts by mass or less, preferably 25 parts by mass, from the viewpoint of preventing the signal of solid ¹³ C-NMR from widening and making it difficult to quantify the cyclic sulfide structure. The following is more preferable.

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), and the like, which are common in the rubber industry, can be used. Of these, hydrous silica prepared by a wet method is preferable because it has a large number of silanol groups. These silicas may be used alone or in combination of two or more.

The content of silica with respect to 100 parts by mass of the rubber component is not particularly limited, and may 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 blending.

Silica is preferably used in combination with a silane coupling agent. The silane coupling agent is not particularly limited, and any silane coupling agent conventionally used in combination with silica can be used in the rubber industry. Examples of such a silane coupling agent include a sulfide-based silane coupling agent, a mercapto-based silane coupling agent, a thioester-based silane coupling agent, an amino-based silane coupling agent, and a glycidoxy-based silane coupling agent. ..

The content of the silane coupling agent with respect 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 further preferably 5.0 parts by mass or more from the viewpoint of enhancing the dispersibility of silica. preferable. Further, from the viewpoint of preventing deterioration of wear resistance, 30 parts by mass or less is preferable, 20 parts by mass or less is more preferable, and 15 parts by mass or less is further preferable.

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

In the kneading step, for example, a base kneading step of kneading a compounding agent and an additive other than a vulcanizing agent and a vulcanization accelerator, and a vulcanizing agent and a vulcanization accelerator are added to the kneaded product obtained in the base kneading step. It includes a final kneading (F kneading) step of adding and kneading. Further, the base kneading step can be divided into a plurality of steps, if desired.

The kneading conditions are not particularly limited, but for example, in the base kneading step, kneading is performed at a discharge temperature of 150 to 170 ° C. for 3 to 10 minutes, and in the final kneading step, kneading is performed at 70 to 110 ° C. for 1 to 5 minutes. There is a method of kneading.

A vulcanized rubber composition can be obtained by vulcanizing the unvulcanized rubber composition obtained by the kneading step. The vulcanization conditions are not particularly limited, and are the molar ratio (mol%) of the cyclic sulfide structure to all 1,4-isoprene binding units in the rubber component described later and the mole of the cyclic sulfide structure to the weight of the rubber component. It can be appropriately set so that the number (mol / g) is 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, and 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, and 1 to 5 minutes. ..

<Quantitative process>
The NMR that can be used in the present disclosure is not particularly limited as long as it is a solid high resolution ¹³ C-NMR, but the ¹³ C resonance frequency of the NMR is 75 MHz because better resolution can be obtained and more accurate quantification can be obtained. The above is preferable, 100 MHz or more is more preferable, and 126 MHz or more is further preferable.

The measurement conditions for solid ¹³ C-NMR can be set as follows, for example.
(Measurement condition)
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
Waiting time 6 seconds Total number of times 40960 Observation temperature 58 ° C
Sample amount 1/4 volume of zirconia rotor Adamantane (chemical shift value is 29.5 ppm)

The MAS rotation speed is preferably 5 kHz or more in the case of a ¹³ C resonance frequency of 100.6 MHz for the reason of eliminating chemical shift anisotropy and dipole interaction. The waiting time is preferably 6 to 30 seconds because it guarantees quantitativeness. Further, the number of integrations is preferably 5000 times or more, more preferably 10,000 times or more, further preferably 20,000 times or more, and even more preferably 40,000 times so that the peak derived from the carbon atom constituting the cyclic sulfide structure can be quantified more accurately. More than once is particularly preferable.

（式中、ｘは１以上の整数を表す） The cyclic sulfide structure in which the 1,4-isoprene bond constituting the rubber molecule takes in a sulfur atom and closes the ring is presumed to have a chemical structure as shown in the following formula (3) by the reaction mechanism shown below. ..

(In the formula, x represents an integer of 1 or more)

In the present disclosure, "a carbon atom forming a double bond among carbon atoms constituting a 1,4-isoprene bond unit" refers to a carbon atom represented by a1 and a2 in the above formula (3). Of these, the "quaternary carbon atom bonded to the 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 is a "rubber component". Of the carbon atoms constituting the 1,4-isoprene bond unit of No. 1, the tertiary carbon atom refers to the carbon atom represented by a2 of the above formula (3).

The "carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure" in the present disclosure refers to the carbon atom represented by b1 and b2 of the above formula (3). Of these, the "quaternary carbon atom bonded to the sulfur atom and the methyl group among the carbon atoms constituting the cyclic sulfide structure" refers to the carbon atom represented by b1 of the above formula (3) and constitutes the "cyclic sulfide structure". Of the carbon atoms, the "tertiary carbon atom bonded to the sulfur atom" refers to the carbon atom represented by b2 of the above formula (3).

Of the carbon atoms constituting the 1,4-isoprene bond unit of the rubber component, the carbon peak derived from the tertiary carbon atom (carbon atom represented by a2 in the above formula (3)) is 123.5 to 128.0 ppm. Observed.

Among 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 the methyl group (the carbon atom represented by a1 in the above formula (3)) is 133.0. It is observed at ~ 137.5 ppm.

Among the carbon atoms constituting the cyclic sulfide 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 (3)) is observed at 58.2 to 59.3 ppm. To.

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

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 obtained, for example, by the following formula (4).
(Mole ratio (mol%) of cyclic sulfide structure to all 1,4-isoprene binding units in the rubber component) =
{(Peak area of carbon peak derived from tertiary carbon atom bonded to sulfur atom among carbon atoms constituting the cyclic sulfide structure) + (bonded to sulfur atom and methyl group among carbon atoms constituting the cyclic sulfide structure) Peak area of carbon peak derived from quaternary carbon atom)} / {(Peak area of carbon peak derived from tertiary carbon atom among carbon atoms constituting 1,4-isoprene bond unit of rubber component) + (rubber Peak area of carbon peak derived from quaternary carbon atom bonded to methyl group among carbon atoms constituting 1,4-isoprene bond unit of component)} × 100 ・ ・ ・ (4)

The 1,4-isoprene bond unit includes cis-1,4 bond and trans-1,4 bond (the above formula (1) is represented by cis-1,4 bond for convenience). The disclosure shall include both. 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 derived from the carbon atom of the cis-1,4 bond. The peak area of the carbon peak and the peak area of the carbon peak derived from the carbon atom of the trans-1,4 bond shall be added up. 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 peak of the carbon peak derived from the carbon atom of the cyclic sulfide structure generated from the cis-1,4 bond. The area shall be added up with the peak area of the carbon peak derived from the carbon atom of the cyclic sulfide structure generated from the trans-1,4 bond.

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 bond unit of the rubber component, and the carbon component 1, The peak area of the carbon peak derived from the quaternary carbon atom bonded to the methyl group (the carbon atom represented by a1 in the above formula (3)) among the carbon atoms constituting the 4-isoprene bond unit is theoretically the same. .. Further, among the carbon atoms constituting the cyclic sulfide structure, the peak area of the carbon peak derived from the tertiary carbon atom bonded to the sulfur atom (the carbon atom represented by b2 in the above formula (3)) and the cyclic sulfide structure are formed. The peak area of the carbon peak derived from the quaternary carbon atom bonded to the sulfur atom and the methyl group (the carbon atom represented by b1 in the above formula (3)) is also theoretically the same.

However, among the carbon atoms constituting the cyclic sulfide structure, the carbon peak derived from the sulfur atom and the quaternary carbon atom bonded to the methyl group (the carbon atom represented by b1 in the above formula (3)) constitutes the cyclic sulfide structure. It may overlap with a carbon peak derived from a carbon atom bonded to a non-sulfur atom (that is, a carbon atom constituting a cross-linking site). From this, the molar ratio (mol%) of the cyclic sulfide structure to all 1,4-isoprene binding units in the rubber component may be obtained, for example, by the following formula (5).
(Mole ratio (mol%) of cyclic sulfide structure to all 1,4-isoprene binding units in the rubber component) =
{(Peak area of carbon peak derived from tertiary carbon atom bonded to sulfur atom among carbon atoms constituting the cyclic sulfide structure) x 2} / {(Carbon constituting 1,4-isoprene bond unit of rubber component) Peak area of carbon peak derived from quaternary carbon atom bonded to methyl group among atoms) × 2} × 100 ・ ・ ・ (5)

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 similarly produced. In this case, among the carbon atoms constituting the cyclic sulfide structure, the carbon peak derived from the carbon atom bonded to the sulfur atom is observed at 49 to 52 ppm, and the cyclic sulfide structure is observed in the above-mentioned rubber component having a 1,4-isoprene skeleton. A carbon peak derived from a tertiary carbon atom bonded to a sulfur atom (a carbon atom represented by b2 in the above formula (3)) among the carbon atoms constituting the above, and a carbon atom among the carbon atoms constituting the cyclic sulfide structure. It is distinguished from the carbon peak derived from the quaternary carbon atom bonded to the methyl group (the carbon atom represented by b1 in the above formula (3)). Further, among the carbon atoms constituting the 1,4-butadiene bond unit of the rubber component, the carbon peak derived from the carbon atom forming the double bond is observed at 123 to 134 ppm. From this, when the rubber component having a 1,4-isoprene skeleton and the rubber component having a 1,4-butadiene skeleton are used in combination, all 1,4-isoprene bonding units and all 1,4-butadiene in the rubber component are used. It is also possible to calculate the molar ratio (mol%) of the cyclic sulfide structure to the total amount of bond units.

Further, the number of moles (mol / g) of the cyclic sulfide structure with respect to the weight of the rubber component is determined by the following formula (6) from the calculated molar ratio of the cyclic sulfide structure to all 1,4-isoprene binding units in the rubber component. You can ask. The molar mass of the 1,4-isoprene binding unit is 68.12 g / mol.
(Number of moles of cyclic sulfide structure with respect to the weight of the rubber component (mol / g)) =
{(Mole ratio (mol%) of cyclic sulfide structure to all 1,4-isoprene binding units in the rubber component) / 100}
× {(Weight ratio (mass%) of all 1,4-isoprene binding units in the rubber component) / 100}
× {1 / (molar mass (g / mol) of 1,4-isoprene binding unit} ... (6)

In the present disclosure, the amount of cyclic sulfide structure produced in the vulcanized rubber composition can be quantified by the above-mentioned method, whereby the amount of cyclic sulfide structure produced can be suppressed, and the compounding, kneading, and vulcanization conditions can be suppressed. You can get the information you need for optimization.

The molar ratio of the cyclic sulfide structure to all 1,4-isoprene binding units in the rubber component is preferably 2.0 mol% or less, more preferably 1.5 mol% or less, and 1.0 mol% or less from the viewpoint of fracture resistance. More preferably, 0.8 mol% or less is particularly preferable. The molar ratio can be appropriately adjusted by a rubber component, a filler, a vulcanization accelerator, an accelerator such as zinc oxide, a vulcanization temperature, a vulcanization time, and the like.

The number of moles of the cyclic sulfide structure with respect to the weight 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.

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

The various chemicals used in the examples are collectively shown below.
NR: TSR20
Silica: ULTRASIL® VN3 (N ₂ SA: 175m ² / g) manufactured by Evonik Degussa
Silane coupling agent: Si266 (bis (3-triethoxysilylpropyl) disulfide) manufactured by Evonik Degussa
Oil: Diana Process NH-70S manufactured by Idemitsu Kosan Co., Ltd.
Wax: Ozo Ace 0355 manufactured by Nippon Seiro Co., Ltd.
Anti-aging agent 1: Nocrack 6C (N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Anti-aging agent 2: Nocrack RD (Poly (2,2,4-trimethyl-1,2-dihydroquinoline)) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Stearic acid: Beads made by Nichiyu Co., Ltd. Tsubaki Zinc oxide: Zinc oxide type 2 made by Mitsui Metal Mining Co., Ltd .: Sulfur powder manufactured by Tsurumi Chemical Industry Co., Ltd. (powdered sulfur containing 5% oil)
Vulcanization Accelerator 1: Noxeller NS (N-tert-butyl-2-benzothiazolylsulfenamide (TBBS)) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Vulcanization accelerator 2: Noxeller CZ (N-cyclohexyl-2-benzothiazolylsulfenamide (CBS)) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Vulcanization accelerator 3: Noxeller D (1,3-diphenylguanidine (DPG)) manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.

<Preparation of vulcanized rubber composition>
According to the formulation shown in Table 1, a 1.7 L closed-type Banbury mixer is used to knead chemicals other than sulfur and vulcanization accelerator for 1 to 10 minutes until the discharge temperature reaches 150 to 160 ° C, and the kneaded product is kneaded. Got Next, using a twin-screw open roll, sulfur and a 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.

<Quantification of cyclic sulfide structure>
The obtained vulcanized rubber composition was measured for solid ¹³ C-NMR under the following conditions to obtain a ¹³ C-NMR spectrum. From the obtained ¹³ C-NMR spectrum, 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 cyclic sulfide structure are formed. Based on the ratio of the peak derived from the carbon atom to the peak area, the molar ratio of the cyclic sulfide structure to all 1,4-isoprene bond units in the rubber component is calculated (mol%) by the following formula (5). bottom.
(Mole ratio (mol%) of cyclic sulfide structure to all 1,4-isoprene binding units in the rubber component) =
{(Peak area of carbon peak derived from tertiary carbon atom bonded to sulfur atom among carbon atoms constituting the cyclic sulfide structure) x 2} / {(Carbon constituting 1,4-isoprene bond unit of rubber component) Peak area of carbon peak derived from quaternary carbon atom bonded to methyl group among atoms) × 2} × 100 ・ ・ ・ (5)

(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
Waiting time 6 seconds Total number of times 40960 Observation temperature 58 ° C
Sample amount 1/4 volume of zirconia rotor Adamantane (chemical shift value is 29.5 ppm)

<Preparation of unvulcanized rubber composition>
According to the formulation shown in Table 2, a 1.7 L closed-type Banbury mixer is used to knead chemicals other than sulfur and vulcanization accelerator for 1 to 10 minutes until the discharge temperature reaches 150 to 160 ° C, and the kneaded product is kneaded. Got Next, using a twin-screw open roll, sulfur and a 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.

<Vulcanization curve>
After preparing the above-mentioned unvulcanized rubber composition, the vulcanization curves of the vulcanized rubber composition were obtained at 140 ° C. and 180 ° C., respectively, in accordance with JIS K 6300-2: 2001 and using a curast meter. (Figs. 3 and 4). In the obtained vulcanization curve at each vulcanization temperature, the maximum value (Fmax) and the minimum value (Fmin) of the torque are measured, and vulcanization until the torque reaches {(Fmax-Fmin) × 0.5 + Fmin}. The time (seconds) was T50, the vulcanization time (seconds) until the maximum torque value (Fmax) was reached was T100, and the time three times that of T100 was T300.

The vulcanization times T50, T100, and T300 were obtained for the vulcanization curves of FIGS. 3 and 4, respectively, and the rubber compositions vulcanized by the respective vulcanization times were obtained. For the vulcanized rubber composition, solid ¹³ C-NMR is measured, and the molar ratio (mol%) of the cyclic sulfide structure to all 1,4-isoprene bond units in the vulcanized rubber component is calculated by the above-mentioned quantification method. bottom. The results are shown in Table 3 and FIG. In Table 3 and FIG. 5, the molar ratio (mol%) of the cyclic sulfide structure to the total 1,4-isoprene binding unit is expressed as “cyclic sulfide / total 1,4-isoprene (mol%)”.

Even when the vulcanization temperature was increased from 140 ° C. to 180 ° C., the maximum value of torque hardly changed. On the other hand, when the vulcanization temperature was raised from 140 ° C. to 180 ° C., the amount of cyclic sulfide produced increased. In addition, the amount of cyclic sulfide produced increased even after the torque reached the maximum value.

<Tensile test>
Tensile test in a 23 ° C atmosphere using a No. 3 dumbbell type test piece made of a vulcanized rubber composition prepared at a vulcanization temperature of 180 ° C. and vulcanization times T100 and T300 in accordance with JIS K 6251: 2017. EB (%) at break, tensile strength TB (MPa) at break, and tensile stress (MPa) at 100% elongation, 200% elongation, and 300% elongation were measured. The results are shown in Table 4.

Even after the torque reached the maximum value, it was confirmed that the amount of cyclic sulfide produced increased and the rubber became hard and difficult to stretch.

<Measurement of acetone extraction amount and bound sulfur amount>
According to JIS K 6229: 2015, each vulcanized rubber test piece at vulcanization time T100 and T300 is immersed in acetone for 24 hours to extract soluble components. The mass of each test piece before and after extraction can be measured, and the amount of acetone extracted (% by mass) can be determined by the following formula. Further, the test piece after extracting the soluble component is placed in an oven and heated at 100 ° C. for 30 minutes to remove the solvent in the test piece, and then in the test piece by the oxygen combustion flask method according to JIS K 6233: 2016. The amount of bound sulfur (% by mass) can be calculated.
Acetone extraction amount (mass%) = {(mass of rubber test piece before extraction-mass of rubber test piece after extraction) / (mass of rubber test piece before extraction)} x 100

<Measurement of toluene swelling index>
In accordance with JIS K 6258: 2016, the mass of each vulcanized rubber test piece at vulcanization time T100 and T300 before and after immersion in toluene at 23 ° C. for 24 hours is measured, and the toluene swelling index can be obtained by the following formula. can. The smaller the toluene swelling index, the higher the crosslink density.
(Toluene swelling index) = (weight after immersion) / (weight before immersion) x 100

By changing the vulcanization time with the same composition in this way and evaluating the amount of bound sulfur and the toluene swelling index, respectively, it is possible to investigate the correlation between the change over time in the crosslink density of the rubber composition and the amount of cyclic sulfide produced. ..

In the present disclosure, the amount of cyclic sulfide structure produced in the vulcanized rubber composition can be quantified by the above-mentioned method, whereby the amount of cyclic sulfide structure produced can be suppressed, and the compounding, kneading, and vulcanization conditions can be suppressed. You can get the information you need for optimization.

Claims (8)

A method for vulcanizing a rubber composition, wherein the molar ratio of the cyclic sulfide structure to all 1,4-isoprene bonding units in the rubber component is adjusted to 2.0 mol% or less.
The molar ratio comprises a solid ¹³ C-NMR of a rubber composition containing a rubber component containing an isoprene-based rubber, and constitutes a 1,4-isoprene binding unit of the rubber component in the obtained ¹³ C-NMR spectrum. The ratio of the peak area of the carbon peak derived from the carbon atom forming the double bond among the carbon atoms 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 smelting method calculated by obtaining. The molar ratio measures solid ¹³ C-NMR of a rubber composition containing a rubber component containing isoprene-based rubber, and constitutes a 1,4-isoprene binding unit of the rubber component in the obtained ¹³ C-NMR spectrum. The peak area of the carbon peak derived from the quaternary carbon atom bonded to the methyl group among the carbon atoms and the peak of the carbon peak derived from the tertiary carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure. The sulphurization method according to claim 1, which is calculated by obtaining the area ratio. The sulfide method according to claim 2, wherein the carbon peak derived from the tertiary carbon atom bonded to the sulfur atom among the carbon atoms constituting the cyclic sulfide structure is observed at 58.2 to 59.3 ppm. The vulcanization method according to any one of claims 1 to 3, wherein the rubber component contains natural rubber. The vulcanization method according to any one of claims 1 to 4, wherein the content of carbon black in the rubber composition is 50 parts by mass or less with respect to 100 parts by mass of the rubber component. The vulcanization method according to any one of claims 1 to 5, wherein the measurement mode of the solid ¹³ C-NMR is DD / MAS. A method for producing a tire using a rubber composition produced by the vulcanization method according to any one of claims 1 to 6. A tire using a rubber composition containing a rubber component in which the molar ratio of the cyclic sulfide structure to all 1,4-isoprene binding units is adjusted to 2.0 mol% or less.

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