JP7738290B2 - Method for producing rubber composition - Google Patents

Description

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

Conventionally, rubber compositions containing diene rubber, silica, and a silane coupling agent are known (Patent Document 1). In the examples of Patent Document 1, Si69 (bis(3-triethoxysilylpropyl)tetrasulfide) is used as the silane coupling agent.

JP 2011-57967 A

The present inventors have studied the rubber composition described in Patent Document 1 and found that the dispersibility of silica therein does not necessarily satisfy current demands. Under these circumstances, the present inventors have discovered that the dispersibility of silica can be improved by using a silane coupling agent having a diazo group (diazo group-containing silane coupling agent).
On the other hand, the inventors' investigations have revealed that when a rubber composition is produced by mixing a diene rubber, silica, and a diazo compound (a compound having a diazo group), variations occur in the performance (silica dispersibility, etc.) of the resulting rubber composition. Furthermore, the inventors have discovered that the diazo group (= _N2 ) of the diazo compound (a compound having a diazo group) reacts with the double bond of the diene rubber to form a cyclopropane ring, and that the performance of the rubber composition tends to improve when the reaction rate is high.

In light of the above-mentioned circumstances, the present invention aims to provide a method for producing a rubber composition obtained by mixing a diene rubber, silica, and a diazo compound, which produces a rubber composition with a high reactivity between the diazo compound and the diene rubber.

As a result of extensive research into the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by, for example, making the decomposition starting temperature of a diazo compound in the atmosphere and the maximum temperature during mixing have a specific relationship, and have arrived at the present invention.
That is, the present inventors have found that the above problems can be solved by the following configuration.

(1) A method for producing a rubber composition, comprising mixing a diene rubber, silica, and a diazo compound,
the blending amount of the silica is 5 to 200 parts by mass per 100 parts by mass of the diene rubber,
the amount of the diazo compound is 0.2 to 20% by mass relative to the amount of the silica;
The method for producing a rubber composition, wherein the diazo compound has a decomposition starting temperature in the atmosphere of 170°C or less and is equal to or lower than the maximum temperature during mixing.
(2) The method for producing a rubber composition according to (1) above, wherein the diazo compound has a decomposition initiation temperature of 50° C. or higher in the atmosphere.
(3) The method for producing a rubber composition according to (1) or (2) above, wherein the initiation temperature of the mixing is equal to or lower than the decomposition initiation temperature of the diazo compound in the atmosphere.
(4) The method for producing a rubber composition according to any one of (1) to (3) above, wherein the diene rubber contains natural rubber in an amount of 20% by mass or more.

As described below, the present invention provides a method for producing a rubber composition obtained by mixing a diene rubber, silica, and a diazo compound, which produces a rubber composition with a high reactivity between the diazo compound and the diene rubber.

1 shows the solution ¹ H NMR spectra of NR and the diazo compound. ^1H NMR spectra of solutions of Reference Examples 2 to 4. ^1H NMR spectra of solutions of Reference Examples 2 to 4.

The method for producing the rubber composition of the present invention will be described below.
In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.
Each component may be used alone or in combination of two or more. When two or more components are used in combination, the blending amount or content of the component refers to the total blending amount or content unless otherwise specified.
Furthermore, for a diazo compound, the decomposition initiation temperature in the atmosphere is also simply referred to as the "decomposition initiation temperature." Furthermore, the maximum temperature when the components are mixed is also referred to as the "maximum mixing temperature." Furthermore, the starting temperature when the components are mixed is also referred to as the "mixing initiation temperature."
Furthermore, the rubber composition obtained has a high reactivity (the proportion of the diazo compound that has reacted with the diene rubber), and, when the diazo compound is a silane coupling agent, has excellent silica dispersibility and low heat buildup, which is also referred to as "excellent effects of the present invention."

The method for producing the rubber composition of the present invention (hereinafter also referred to as the "production method of the present invention") includes the steps of:
A method for producing a rubber composition, comprising mixing a diene rubber, silica, and a diazo compound to produce a rubber composition,
the blending amount of the silica is 5 to 200 parts by mass per 100 parts by mass of the diene rubber,
the amount of the diazo compound is 0.2 to 20% by mass relative to the amount of the silica;
In the method for producing a rubber composition, the decomposition starting temperature of the diazo compound in the atmosphere is 170° C. or lower and is equal to or lower than the maximum temperature during mixing.

As described above, the inventors have found that the diazo group (= _N2 ) of a diazo compound (a compound having a diazo group) reacts with the double bond of a diene rubber to form a cyclopropane ring, and that heating accelerates this reaction.
The present inventors produced various rubber compositions by changing the conditions for mixing a diene rubber, silica, and a diazo compound, and investigated the correlation with the reaction rate (the proportion of the diazo compound that has reacted with the diene rubber). They found that the reaction rate can be rapidly improved by setting the decomposition starting temperature of the diazo compound below the maximum temperature during mixing. The present invention is based on this finding.

First, let's explain each ingredient that will be mixed.

[1] Diene Rubber The diene rubber to be mixed in the production method of the present invention is not particularly limited.
One type of diene rubber may be mixed, or two or more types of diene rubber may be mixed.

[Specific examples]
Specific examples of the diene rubber include natural rubber (NR), butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubber, isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), etc. Examples of the aromatic vinyl-conjugated diene copolymer rubber include styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, etc.

[Molecular weight]
The weight average molecular weight (Mw) of the diene rubber is not particularly limited, but for reasons such as the superior effects of the present invention, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000.

In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are values calculated using standard polystyrene obtained by gel permeation chromatography (GPC).

[Preferred embodiment]
The diene rubber preferably contains natural rubber.
When the diene rubber contains natural rubber, the content of natural rubber in the diene rubber is preferably 20% by mass or more, more preferably 50% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass, for reasons such as better effects of the present invention.

The content of diene rubber other than natural rubber in the diene rubber is not particularly limited, but to achieve better effects of the present invention, it is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, and even more preferably 0 to 10% by mass.

[2] Silica The silica to be mixed in the production method of the present invention is not particularly limited, and any conventionally known silica compounded in rubber compositions for tires and the like can be used.

[Specific examples]
Specific examples of the silica include wet silica, dry silica, fumed silica, and diatomaceous earth. Among these, wet silica is preferred because it provides superior effects of the present invention. The silica may be used alone or in combination of two or more types.
The CTAB (cetyltrimethylammonium bromide) adsorption specific surface area of silica is not particularly limited, but is preferably 100 to 300 ^{m 2} /g, and more preferably 150 to 200 m ² /g, for reasons such as better effects of the present invention. Note that in this specification, the CTAB adsorption specific surface area is a value obtained by measuring the amount of CTAB adsorption on the silica surface in accordance with JIS K6217-3:2001 "Part 3: Determination of specific surface area - CTAB adsorption method."

[Amount]
In the production method of the present invention, the blending amount of the silica is 5 to 200 parts by mass per 100 parts by mass of the diene rubber. In particular, the blending amount of the silica is preferably 10 to 150 parts by mass, more preferably 20 to 100 parts by mass, and even more preferably 30 to 70 parts by mass per 100 parts by mass of the diene rubber, for reasons such as the superior effects of the present invention.

[3] Diazo Compound The diazo compound to be mixed in the production method of the present invention is not particularly limited as long as it is a compound having a diazo group (=N ₂ ).

[Diazo Group-Containing Silane Coupling Agent]
The diazo compound is preferably a silane compound having a diazo group and a hydrolyzable group (diazo group-containing silane coupling agent) because this provides better effects of the present invention.
The hydrolyzable group is not particularly limited, and examples thereof include an alkoxy group, a phenoxy group, a carboxyl group, and an alkenyloxy group. Of these, an alkoxy group is preferred because it provides better effects of the present invention. When the hydrolyzable group is an alkoxy group, the number of carbon atoms in the alkoxy group is preferably 1 to 16, and more preferably 1 to 4, because it provides better effects of the present invention. Examples of alkoxy groups having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, and a propoxy group.

The above-mentioned diazo group-containing silane coupling agent is preferably a compound having a diazo group and a hydrolyzable silyl group (particularly an alkoxysilyl group) because it provides better effects of the present invention, and is more preferably compound (I) (specific silane coupling agent) described below.

[Specific silane coupling agent]
The specific silane coupling agent is the following compound (I).

Compound (I)

In compound (I), A represents a divalent aliphatic or aromatic hydrocarbon group having 3 to 26 carbon atoms, which may have a heteroatom or a substituent, and R ₁ , R ₂ and R ₃ each independently represent a substituent, provided that at least one of R ₁ , R ₂ and R ₃ is an alkoxy group.

[A]
As described above, in compound (I), A represents a divalent aliphatic or aromatic hydrocarbon group having 3 to 26 carbon atoms, which may have a heteroatom or may have a substituent.
For reasons such as better effects of the present invention, A is preferably a group represented by -CH ₂ CH ₂ -R-. Here, R represents a divalent aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms, which may have a heteroatom or a substituent. The aliphatic hydrocarbon group may be linear, branched, or cyclic.
The above R is preferably a divalent aliphatic hydrocarbon group (particularly an alkylene group) having 1 to 5 carbon atoms, because this will result in better effects of the present invention.

[R ₁ , R ₂ and R ₃ ]
As described above, in compound (I), R ₁ , R ₂ and R ₃ each independently represent a substituent, provided that at least one of R ₁ , R ₂ and R ₃ is an alkoxy group.

The number of carbon atoms in the alkoxy group is not particularly limited, but it is preferably 1 to 5, as this will provide better effects of the present invention.

Specific examples of the above-mentioned substituent other than an alkoxy group include an aliphatic hydrocarbon group, an aromatic hydrocarbon group, or a group in which these groups are combined.
The aliphatic hydrocarbon group may be linear, branched, or cyclic. Specific examples of the aliphatic hydrocarbon group include linear or branched alkyl groups (particularly having 1 to 30 carbon atoms), linear or branched alkenyl groups (particularly having 2 to 30 carbon atoms), and linear or branched alkynyl groups (particularly having 2 to 30 carbon atoms).
Examples of the aromatic hydrocarbon group include aromatic hydrocarbon groups having 6 to 18 carbon atoms, such as a phenyl group, a tolyl group, a xylyl group, and a naphthyl group.
When the above-mentioned substituent is other than an alkoxy group, it is preferably an aliphatic hydrocarbon group, more preferably an alkyl group (particularly having 1 to 5 carbon atoms), for reasons such as better effects of the present invention.

In compound (I), it is preferred that R ₁ , R ₂ and R ₃ are all alkoxy groups, as this will result in better effects of the present invention.

[Method of producing specific silane coupling agent]
The method for producing the above-mentioned specific silane coupling agent is not particularly limited, but because the low heat buildup of the rubber composition obtained by using the obtained specific silane coupling agent is further improved, the method 1 of the present invention described below and the method 2 of the present invention described below are preferred, and the method 1 of the present invention described below is more preferred.

[Method 1 of the present invention]
Method 1 of the present invention comprises:
a vinyl group introduction step of reacting a compound (III) described below with a compound represented by CH ₂ ═CH—R—OH (wherein R represents a divalent aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms, which may have a heteroatom or a substituent) (hereinafter also referred to as a “specific alcohol”) to synthesize a compound (IV) described below;
a hydrosilylation step of reacting the compound (IV) with a compound (VI) described below to synthesize a compound (VII) described below;
The method for producing a silane coupling agent includes a diazotization step of synthesizing a silane coupling agent (specific silane coupling agent), which is compound (I) described below, by reacting compound (II) described below with compound (VII).

Each process is explained below.

[Vinyl group introduction process]
The vinyl group introduction step is a step of synthesizing the following compound (IV) by reacting the following compound (III) with a specific alcohol.

<Compound (III)>

Compound (III)

In compound (III), X ₁ and X ₂ each independently represent a halogen atom.

As described above, in compound (III), X ₁ and X ₂ each independently represent a halogen atom.
The halogen atom is not particularly limited, but is preferably a bromine atom, because this increases the yield of the specific silane coupling agent and provides a more effective effect of improving the dispersibility of silica in the resulting specific silane coupling agent.

<Specific alcohol>
The specific alcohol is a compound represented by CH ₂ ═CH—R—OH (where R represents a divalent aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms, which may have a heteroatom or a substituent). The aliphatic hydrocarbon group may be linear, branched, or cyclic.
The above R is preferably a divalent aliphatic hydrocarbon group (particularly an alkylene group) having 1 to 5 carbon atoms, because this will result in better effects of the present invention.

<Compound (IV)>

Compound (IV)

In compound (IV), R represents a divalent aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms, which may have a heteroatom or a substituent, and X represents a halogen atom.

Specific examples and preferred embodiments of R are the same as those of the specific alcohols described above.
Specific examples and preferred embodiments of X are the same as those of X in the compound (III) described above.

<Preferred embodiment>
The vinyl group introduction step is preferably carried out in the following manner, because it is more effective in the present invention.
The process is preferably a step of synthesizing the compound (IV) by reacting the compound (III) with the specific alcohol in the presence of sodium hydrogen carbonate and acetonitrile.

[Hydrosilylation step]
The hydrosilylation step is a step of synthesizing the following compound (VII) by reacting the compound (IV) obtained in the vinyl group introduction step described above with the following compound (VI).

<Compound (VI)>

Compound (VI)

In compound (VI), R ₁ , R ₂ and R ₃ each independently represent a substituent, provided that at least one of R ₁ , R ₂ and R ₃ is an alkoxy group.

The number of carbon atoms in the alkoxy group is not particularly limited, but it is preferably 1 to 5, as this will provide better effects of the present invention.

Specific examples of the above substituents other than alkoxy groups include aliphatic hydrocarbon groups, aromatic hydrocarbon groups, and groups combining these groups.
The aliphatic hydrocarbon group may be linear, branched, or cyclic. Specific examples of the aliphatic hydrocarbon group include linear or branched alkyl groups (particularly having 1 to 30 carbon atoms), linear or branched alkenyl groups (particularly having 2 to 30 carbon atoms), and linear or branched alkynyl groups (particularly having 2 to 30 carbon atoms).
Examples of the aromatic hydrocarbon group include aromatic hydrocarbon groups having 6 to 18 carbon atoms, such as a phenyl group, a tolyl group, a xylyl group, and a naphthyl group.
When the above-mentioned substituent is other than an alkoxy group, it is preferably an aliphatic hydrocarbon group, more preferably an alkyl group (particularly having 1 to 5 carbon atoms), for reasons such as better effects of the present invention.

In compound (VI), it is preferred that R ₁ , R ₂ and R ₃ are all alkoxy groups, as this will result in better effects of the present invention.

<Compound (VII)>

Compound (VII)

In compound (VII), A represents a divalent aliphatic or aromatic hydrocarbon group having 3 to 26 carbon atoms, which may have a heteroatom or a substituent; R ₁ , R ₂ , and R ₃ are defined as R ₁ , R ₂ , and R ₃ in compound (VI) above; and X is defined as X in compound (IV) above.

As described above, in compound (VII), A represents a divalent aliphatic or aromatic hydrocarbon group having 3 to 26 carbon atoms, which may have a heteroatom or may have a substituent.
The above A is preferably a group represented by —CH ₂ CH ₂ —R— because this provides better effects of the present invention, etc. Here, the definition, specific and preferred embodiments of R are the same as those of R in the specific alcohol described above.

As described above, in compound (VII), the definitions of R ₁ , R ₂ and R ₃ are the same as those of R ₁ , R ₂ and R ₃ in compound (VI) described above. Specific examples and preferred embodiments of R ₁ , R ₂ and R ₃ are also the same as those of R ₁ , R ₂ and R ₃ in compound (VI) described above.

As described above, the definition of X in compound (VII) is the same as that of X in compound (IV) described above. Specific examples and preferred embodiments of X are also the same as those of X in compound (IV) described above.

<Preferred embodiment>
The hydrosilylation step is preferably carried out in the following manner, because it is more effective in the present invention.
Preferably, this is a step of synthesizing the compound (VII) by subjecting the compound (IV) obtained in the vinyl group introduction step described above and the compound (VI) described above to a hydrosilylation reaction in the presence of an iridium catalyst and dichloromethane at room temperature.

Examples of the iridium catalyst include iridium salts and iridium complexes. Specific examples of the iridium salt include iridium trichloride, iridium tetrachloride, chloroiridic acid, sodium chloroiridate, and potassium chloroiridate. Specific examples of iridium complexes include chloro(1,5-cyclooctadiene)iridium(I) dimer, bromo(1,5-cyclooctadiene)iridium(I) dimer, iodo(1,5-cyclooctadiene)iridium(I) dimer, chloro(2,5-norbornadiene)iridium(I) dimer, bromo(2,5-norbornadiene)iridium(I) dimer, iodo(2,5-norbornadiene)iridium(I) dimer, 1,5-cyclooctadiene(acetylacetonato)iridium(I), chlorobis(cyclooctene)iridium(I) dimer, and chlorocarbonylbis(triphenylphosphine)iridium(I). Chloro(1,5-cyclooctadiene)iridium(I) dimer is particularly preferred due to its superior effects.

[Diazotization step]
The diazotization step is a step of synthesizing a silane coupling agent (specific silane coupling agent), which is the following compound (I), by reacting the following compound (II) with the compound (VII) obtained in the above-mentioned hydrosilylation step.

<Compound (II)>

Compound (II)

In compound (II), Ts represents a tosyl group.

The method for synthesizing compound (II) is not particularly limited, but a method in which p-toluenesulfonyl hydrazide and paratoluenesulfonyl chloride are reacted in the presence of pyridine and dichloromethane is preferred because it provides superior effects of the present invention.

<Compound (I)>

Compound (I)

In compound (I), the definition of A is the same as that of A in the above-mentioned compound (VII), and the definitions of R ₁ , R ₂ and R ₃ are the same as that of R ₁ , R ₂ and R ₃ in the above-mentioned compound (VI).

As described above, the definition of A in compound (I) is the same as that of A in compound (VII) described above. Specific examples and preferred embodiments of A are also the same as those of A in compound (VII) described above.

As described above, in compound (I), the definitions of R ₁ , R ₂ and R ₃ are the same as those of R ₁ , R ₂ and R ₃ in compound (VI) described above. Specific examples and preferred embodiments of R ₁ , R ₂ and R ₃ are also the same as those of R ₁ , R ₂ and R ₃ in compound (VI) described above.

<Preferred embodiment>
The diazotization step is preferably carried out in the following manner, because it is more effective in the present invention.
Preferably, the compound (II) and the compound (VII) obtained in the hydrosilylation step are subjected to a diazotization reaction in the presence of tetramethylguanidine and tetrahydrofuran to synthesize the silane coupling agent, which is the compound (I).

[Method 2 of the present invention]
Method 2 of the present invention is
a vinyl group introduction step of reacting a compound (III) described below with a compound represented by CH ₂ ═CH—R—OH (wherein R represents a divalent aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms, which may have a heteroatom or a substituent) (specific alcohol) to synthesize a compound (IV) described below;
a diazotization step of synthesizing a compound (V) described below by reacting a compound (II) described below with the compound (IV) described above;
The method for producing a silane coupling agent includes a hydrosilylation step of reacting the compound (V) with a compound (VI) described later to synthesize a silane coupling agent (specific silane coupling agent), which is a compound (I) described later.

Each process is explained below.

[Vinyl group introduction process]
The vinyl group introduction step is the same as the vinyl group introduction step in the above-mentioned Method 1 of the present invention.

[Diazotization step]
The diazotization step is a step of synthesizing the following compound (V) by reacting the following compound (II) with the compound (IV) obtained in the vinyl group introduction step described above.

<Compound (II)>
The compound (II) is the same as the compound (II) used in the diazotization step of the above-mentioned Method 1 of the present invention.

<Compound (V)>

Compound (V)

In compound (V), R represents a divalent aliphatic or aromatic hydrocarbon group having 1 to 24 carbon atoms, which may have a heteroatom or a substituent.

Specific examples and preferred embodiments of R above are the same as those for R in the specific alcohols described above.

<Preferred embodiment>
The diazotization step is preferably a step of synthesizing the compound (V) by subjecting the compound (II) and the compound (IV) obtained in the vinyl group introduction step to a diazotization reaction in the presence of diazabicycloundecene and tetrahydrofuran, because this step provides better effects of the present invention.

[Hydrosilylation step]
The hydrosilylation step is a step of synthesizing a silane coupling agent (specific silane coupling agent), which is the following compound (I), by reacting the compound (V) obtained in the above-mentioned diazotization step with the following compound (VI):

<Compound (VI)>
The compound (VI) is the same as the compound (VI) used in the hydrosilylation step of the above-described Method 1 of the present invention.

<Compound (I)>
The above compound (I) (specific silane coupling agent) is the same as the compound (I) (specific silane coupling agent) synthesized in the diazotization step of the above-described method 1 of the present invention.

<Preferred embodiment>
The hydrosilylation step is preferably a step of synthesizing the above-mentioned compound (I) (specific silane coupling agent) by subjecting the compound (V) obtained in the above-mentioned diazotization step and the above-mentioned compound (VI) to a hydrosilylation reaction in the presence of a Karstedt catalyst, for reasons such as better effects of the present invention.

[Decomposition start temperature]
The decomposition starting temperature of the diazo compound is 170° C. or lower and is equal to or lower than the maximum temperature when the diene rubber, the silica, and the diazo compound are mixed.
The decomposition starting temperature of the diazo compound is preferably 50° C. or higher, more preferably 100° C. or higher, and even more preferably 120° C. or higher, for reasons such as better effects of the present invention.

In this specification, the decomposition onset temperature in the atmosphere refers to the decomposition onset temperature in the atmosphere obtained using a thermogravimetric analyzer, and is the intersection of the baseline and the line passing through the inflection point of the weight loss.

[Specific examples]
Specific examples of diazo compounds include the above-mentioned specific silane coupling agents, diethoxymethyldiazosilane (decomposition onset temperature 141°C, decomposition temperature 175°C), and t-butyldiazoacetate (decomposition onset temperature approximately 60°C, decomposition temperature 98°C).

[Amount]
In the production method of the present invention, the amount of the diazo group-containing silane coupling agent is 0.2 to 20 mass % relative to the amount of silica, preferably 1 to 15 mass %, and more preferably 4 to 12 mass %, relative to the amount of silica.

Furthermore, when the diene rubber described above contains natural rubber, the amount of the diazo group-containing silane coupling agent in the manufacturing method of the present invention is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, even more preferably 3 to 12 parts by mass, and particularly preferably 4 to 8 parts by mass, per 100 parts by mass of the natural rubber, for reasons such as the superior effects of the present invention.

[4] Optional Components In the production method of the present invention, other components (optional components) can be further mixed as needed within a range that does not impair the effects or purposes of the method.
Examples of the optional components include various additives commonly used in rubber compositions, such as carbon black, silane coupling agents other than the above-mentioned diazo group-containing silane coupling agents, terpene resins (e.g., aromatic modified terpene resins), thermally expandable microcapsules, zinc oxide (zinc white), stearic acid, antioxidants, waxes, processing aids, oils, liquid polymers, thermosetting resins, vulcanizing agents (e.g., sulfur), vulcanization accelerators, and metal catalysts.

[5] Maximum temperature during mixing In the production method of the present invention, the maximum temperature (maximum temperature during mixing) when mixing the diene rubber, the silica, and the diazo compound is equal to or higher than the decomposition temperature of the diazo compound. For reasons such as the effects of the present invention being more excellent, the maximum temperature during mixing is preferably lower than the decomposition temperature of the diazo compound.
The maximum temperature during mixing is preferably 140 to 200°C, more preferably 150 to 190°C, and even more preferably 160 to 180°C, for reasons such as the superior effects of the present invention.

[6] Mixing Start Temperature In the production method of the present invention, the starting temperature (mixing start temperature) when mixing the diene rubber, the silica, and the diazo compound is not particularly limited, but is preferably equal to or lower than the decomposition start temperature of the diazo compound.

[7] Uses The rubber composition obtained by the production method of the present invention is suitable for use as a rubber material. For example, it is suitable for use in tires (particularly pneumatic tires), conveyor belts, hoses, vibration-proof materials, rubber rolls, outer covers for railway vehicles, etc. Among these, it is particularly suitable for use in tires (particularly treads).

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

[Synthesis of diazo compounds]

<Synthesis of Compound (II)>
A CH ₂ Cl ₂ suspension of p-toluenesulfonyl hydrazide (Tokyo Chemical Industry Co., Ltd., 18.6 g) and p-toluenesulfonyl chloride (Tokyo Chemical Industry Co., Ltd., 28.6 g) was placed in a 300 mL three-neck flask equipped with a thermometer and cooled in an ice bath. A 1:1 pyridine/CH ₂ Cl ₂ mixed solution (25 mL) was added dropwise using a dropping funnel over approximately 10 minutes while maintaining the internal temperature below 20°C. The reaction mixture was stirred at room temperature for 3 hours. Et ₂ O (diethyl ether) (60 mL) was added and the mixture was poured into a 1 L beaker. 60 mL of purified water and 60 mL of Et ₂ O were added in that order, and the mixture was stirred at room temperature for 10 minutes. The white precipitate was collected by filtration, transferred to a 500 mL recovery flask, and dried under reduced pressure.
MeOH (methanol) (260 mL) was added to the crude product, and the mixture was stirred for 3 hours under gentle reflux at a bath temperature of 80° C. After cooling to room temperature, the white precipitate was collected by filtration and washed with MeOH (90 mL) and Et ₂ O (90 mL).
The resulting solid was dried under reduced pressure to give 26.9 g of a white solid.
From ¹ H and ¹³ C NMR spectra, the obtained white solid was confirmed to be Ts-NHNH-Ts (Ts: tosyl group) (corresponding to the above-mentioned compound (II)). The yield was 79%.

<Vinyl group introduction step>
A 1 L three-neck flask equipped with a thermometer was charged with NaHCO ₃ (sodium bicarbonate) (Fujifilm Wako Pure Chemical Industries, Ltd., 39.6 g), 3-butene-1-ol (corresponding to the above-mentioned specific alcohol, where R is —CH ₂ CH ₂ —) (Tokyo Chemical Industry Co., Ltd., 13.5 mL), and acetonitrile (400 mL), and the flask was cooled in an ice bath. To this mixture, bromoacetyl bromide (corresponding to the above-mentioned compound (III), where X ₁ and X ₂ are bromine atoms) (Tokyo Chemical Industry Co., Ltd., 20 mL) was added dropwise using a dropping funnel over a period of about 1 hour while maintaining the internal temperature at 4 to 5°C. After stirring at the same temperature for a further 30 minutes, the disappearance of 3-butene-1-ol was confirmed by TLC (thin layer chromatography).
Pure water (500 mL) was placed in a 3 L beaker, and the resulting reaction solution was poured into it while stirring. The reaction vessel was washed with pure water and then with a small amount of acetonitrile, and the washed solution was added to the mixture. The mixture was stirred at room temperature for approximately 5 minutes, and then extracted with CH ₂ Cl ₂ (600 mL). The mixture was placed in a 2 L separatory funnel and extracted with CH ₂ Cl ₂ (600 mL), and the CH ₂ Cl ₂ layer was washed with brine. The CH ₂ Cl ₂ layer was dried over anhydrous magnesium sulfate, filtered, and concentrated under reduced pressure. The residual oil was dried under reduced pressure to obtain 28.6 g of a colorless oily product.
From the ¹ H and ¹³ C NMR spectra of the reaction product, the obtained oily product was confirmed to be the above-mentioned compound (IV) (wherein R is —CH ₂ CH ₂ — and X is a bromine atom). The yield was 94%.

<Hydrosilylation step>
[IrCl(C ₈ H ₁₂ )] ₂ (0.955 g, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was placed in a 500 mL three-neck flask equipped with a thermometer, and the reaction vessel was reduced in pressure and purged with nitrogen. Anhydrous CH ₂ Cl ₂ (148 mL) was added, and the reaction vessel was cooled in an ice bath. While maintaining the internal temperature at 3-4°C, triethoxysilane (corresponding to the above-mentioned compound (VI), where R ₁ , R ₂ , and R ₃ are ethoxy groups) (Tokyo Chemical Industry Co., Ltd., 32 mL) was added dropwise using a dropping funnel over approximately 30 minutes. Subsequently, a CH ₂ Cl ₂ solution (15 mL) of compound (IV) (28.6 g) synthesized as described above was added dropwise using a dropping funnel over approximately 1 hour. The mixture was stirred at the same temperature for approximately 30 minutes, and the disappearance of compound (IV) was confirmed by TLC.
In a 3-L beaker, SiO ₂ (114 g) was suspended in 500 mL of a mixed solution of AcOEt (ethyl acetate)/n-hexane = 20/80, and cooled in an ice bath while stirring. The reaction solution was slowly and gently poured into the suspension. A 15 cm Kiriyama funnel was attached to a 3-L suction bottle, and Celite (registered trademark) was placed on top of the filter paper of the Kiriyama funnel. The Celite was compressed under suction to form an approximately 1 cm Celite pad. The quenched reaction mixture was filtered through the Celite pad, and SiO ₂ and insoluble matter were separated. The filter cake was washed with 500 mL of a mixed solution of AcOEt/n-hexane = 20/80, followed by 600 mL of a mixed solution of AcOEt/n-hexane = 30/70. The filtrate was concentrated under reduced pressure to obtain approximately 46 g of a crude product as a light brown oil. The crude product was purified by column chromatography to give 42.46 g of a pale yellow oil.

(Column purification conditions)
・Yamazen Smart Flash EPLC AI 580S
・Column Size 4L (SiO ₂ 200g), injection column 2L
・AcOEt/n-hexane=0/100 → 9/91
UV 254nm

From ^{the 1} H, ¹³ C and ²⁹ Si NMR spectra, the oily substance obtained was identified as the above-mentioned compound (VII) (wherein A is —CH ₂ CH ₂ CH ₂ CH ₂ —, R ₁ , R ₂ and R ₃ are ethoxy groups, and X is a bromine atom). The yield was 80%.

<Diazotization step>
Compound (VII) synthesized as described above was placed in a 100 mL three-neck flask equipped with a thermometer, vacuumed, and purged with nitrogen. The compound was dissolved in 12 mL of anhydrous THF (tetrahydrofuran), and Ts-NHNH-Ts (1.59 g) synthesized as described above was added using a powder funnel. The mixture was cooled to -10°C, and a solution of tetramethylguanidine (Tokyo Chemical Industry Co., Ltd., 32 mL) in anhydrous THF (1.3 mL) was added dropwise using a dropping funnel over approximately 20 minutes while maintaining the internal temperature at -5 to -3°C. At the start of the addition, Ts-NHNH-Ts was not completely dissolved and remained as a suspension. However, as the addition continued, it dissolved completely and became a homogeneous solution, after which a white precipitate gradually formed. The mixture was stirred for approximately 20 minutes while cooled to the same temperature, and TLC confirmed that the raw materials had almost completely disappeared. The reaction mixture was removed from the cooling device and stirred for approximately 1 hour while naturally warming to room temperature. The reaction mixture was a yellow solution containing a white precipitate. The disappearance of the compound (VII) product was confirmed by TLC, and Et ₂ O (50 mL) was added to the reaction solution. The reaction mixture was filtered through a Kiriyama funnel lined with SiO ₂ (5 g). The filtered product was washed four times with 15 mL of Et ₂ O. The filtrate and all the washings were combined and concentrated under reduced pressure, and the residue was purified using a SiO ₂ column. 0.674 g of a yellow oil was thus obtained.

(Column purification conditions)
・Yamazen Smart Flash EPLC AI 580S
・Column Size M (SiO ₂ 16g), injection column S
・AcOEt/n-hexane =0/100 → 17/83
UV 254nm

From ¹ H, ¹³ C and ²⁹ Si NMR spectra, the obtained oily substance was identified as the above-mentioned compound (I) (wherein A is —CH ₂ CH ₂ CH ₂ CH ₂ —, and R ₁ , R ₂ and R ₃ are ethoxy groups) (specific silane coupling agent). The yield was 52%. The specific silane coupling agent had a decomposition onset temperature of 132°C and a decomposition temperature of 166°C in the atmosphere.

[Mixing of Diene Rubber and Diazo Compound (Reference Examples 1 to 4)]
The components shown in Table 1 below were blended in the proportions (parts by mass) shown in the same table.
Specifically, the components shown in Table 1 below were placed in a 1.7 liter internal Banbury mixer and mixed for 5 minutes. The mixing start temperature was 80°C, and the maximum temperature during mixing was as shown in Table 1. After mixing, the mixture was discharged from the internal Banbury mixer and cooled to room temperature.

<NMR measurement>
Solution ¹ H NMR measurements (solvent: CDCl ₃ ) were carried out for the NR and diazo compounds in Table 1. The solution ¹ H NMR spectra are shown in FIG.
Furthermore, solution ¹ H NMR measurements (solvent: CDCl ₃ ) were carried out for Reference Examples 1 to 4 in Table 1. The solution ¹ H NMR spectra of Reference Examples 2 to 4 are shown in FIGS.

(NMR peak intensity ratio)
The intensity ratio (h/g) of the peak g (a peak derived from the diazo compound) to the peak h (a peak derived from the cyclopropane ring formed by the reaction of the diazo compound with natural rubber) was determined for the ¹ H NMR spectra of the solutions of Reference Examples 1 to 4. The results are shown in Table 1.

(Response rate)
From the above-mentioned NMR peak intensity ratio (h/g), the proportion of the compounded diazo compound that reacted with the diene rubber (reaction rate) was determined. Specifically, since the peak g described above is a peak corresponding to two protons and the peak h described above is a peak corresponding to three protons, the reaction rate was determined by dividing h/g by 3/2. The results are shown in Table 1.

[Production of Rubber Compositions (Conventional Example, Comparative Examples 1-2, Examples 1-2)]
The components shown in Table 2 below were blended in the proportions (parts by mass) shown in the same table.
Specifically, first, the components shown in Table 2 below, excluding sulfur and vulcanization accelerator, were placed in a 1.7-liter internal Banbury mixer and mixed for 5 minutes. The mixing start temperature was 80°C, and the maximum temperature during mixing was as shown in Table 2. After mixing, the mixture was discharged from the internal Banbury mixer and cooled to room temperature to obtain a masterbatch. Furthermore, sulfur and a vulcanization accelerator were mixed into the obtained masterbatch using the Banbury mixer to obtain each rubber composition.

<Evaluation>
The rubber compositions thus obtained were evaluated as follows.

(tan δ (60°C))
Each of the resulting unvulcanized rubber compositions was press-vulcanized in a mold (15 cm × 15 cm × 0.2 cm) at 150°C for 30 minutes to produce a vulcanized rubber sheet. Next, the tan δ (60°C) of each of the resulting vulcanized rubber sheets was measured in accordance with JIS K6394:2007 using a viscoelasticity spectrometer (manufactured by Toyo Seiki Seisaku-sho, Ltd.) under conditions of an elongation deformation strain rate of 10%±2%, a frequency of 20 Hz, and a temperature of 60°C.
The results are shown in Table 2. The results are expressed as an index with the conventional example being 100. It can be said that the smaller the index, the better the low heat buildup property.

(Amount of bound rubber)
0.3 g of each rubber composition obtained was placed in a wire mesh basket and immersed in 300 mL of toluene at room temperature for 48 hours, then removed and dried. The mass of the sample was measured and the amount of bound rubber was calculated using the following formula.
Bound rubber amount = [(mass of sample after toluene immersion and drying) - (mass of silica)] / (mass of rubber component)
The results are shown in Table 2. The results are expressed as an index with the Conventional Example being 100. The larger the amount of bound rubber, the more bound rubber (rubber that has reacted with silica) there is, and the higher the dispersibility of silica in the rubber composition.

Details of each component in Tables 1 and 2 are as follows:
NR: Natural rubber Silica: ZEOSIL 1165MP (CTAB adsorption specific surface area: 159 m ² /g, manufactured by Rhodia)
Zinc oxide: zinc oxide Vulcanization accelerator: vulcanization accelerator Sulfur: sulfur TESPT: Si69 (bis(3-triethoxysilylpropyl)tetrasulfide, manufactured by Evonik Degussa)
Diazo compound: specific silane coupling agent synthesized as described above Metal catalyst: rhodium (II) acetate (dimer) (manufactured by Tokyo Chemical Industry Co., Ltd.)

The reason the amount of sulfur in Comparative Example 1 is less than in the other examples is to suppress the increase in hardness of the vulcanized rubber caused by the release of sulfur atoms in the TESPT.

As can be seen from Table 1, in Reference Examples 2 and 3 where the decomposition onset temperature (132°C) of the diazo compound was equal to or lower than the maximum mixing temperature, a reaction product of the diazo compound and the diene rubber was obtained. On the other hand, in Reference Example 1 where the decomposition onset temperature of the diazo compound exceeded the maximum mixing temperature, no reaction product of the diazo compound and the diene rubber was obtained.
Comparing Reference Examples 2 and 3, Reference Example 2, in which the difference between the maximum temperature during mixing and the decomposition starting temperature of the diazo compound was 20° C. or more, showed a higher reaction rate.

Furthermore, Table 2 shows that, compared with Comparative Example 2 in which the decomposition starting temperature (132°C) of the diazo compound exceeds the maximum temperature during mixing, Examples 1 and 2 in which the decomposition starting temperature of the diazo compound is equal to or lower than the maximum temperature during mixing have a large amount of bound rubber and exhibit excellent low heat buildup. This means that, compared with Comparative Example 2, Examples 1 and 2 produce a larger amount of the reaction product of the diazo compound and the diene rubber (higher reaction rate).
Comparing Examples 1 and 2, Example 2, in which the difference between the decomposition starting temperature of the diazo compound and the maximum temperature during mixing was 20°C or more, had more bound rubber and exhibited better low heat buildup. This means that, compared to Example 1, Example 2 produced a larger amount of the reaction product between the diazo compound and the diene rubber (higher reaction rate).

Claims (4)

A method for producing a rubber composition, comprising mixing a diene rubber, silica, and a diazo compound to produce a rubber composition,
The diazo compound is the following compound (I):
the blending amount of the silica is 5 to 200 parts by mass per 100 parts by mass of the diene rubber,
the blending amount of the diazo compound is 0.2 to 20 mass % relative to the blending amount of the silica,
The method for producing a rubber composition, wherein the diazo compound has a decomposition starting temperature in the atmosphere of 170°C or less and is equal to or lower than the maximum temperature during mixing.
The decomposition initiation temperature is the decomposition initiation temperature in the air obtained by a thermogravimetric analyzer, and is the intersection of the baseline and the line passing through the inflection point of the weight loss.

Compound (I)
In compound (I), A represents a divalent aliphatic or aromatic hydrocarbon group having 3 to 26 carbon atoms, which may have a heteroatom or a substituent, and R ₁ , R ₂ and R ₃ each independently represent a substituent, provided that at least one of R ₁ , R ₂ and R ₃ is an alkoxy group. The method for producing a rubber composition according to claim 1, wherein the diazo compound has a decomposition initiation temperature in the atmosphere of 50°C or higher. The method for producing a rubber composition according to claim 1 or 2, wherein the mixing initiation temperature is equal to or lower than the decomposition initiation temperature of the diazo compound in the atmosphere. The method for producing a rubber composition according to any one of claims 1 to 3, wherein the diene rubber contains 20% by mass or more of natural rubber.