JP7315411B2 - Rubber composition, vulcanizate and molded article of said rubber composition - Google Patents

Description

Chloroprene rubber has excellent mechanical properties, ozone resistance, and chemical resistance, and is used in a wide range of fields such as automobile parts, adhesives, and various industrial rubber parts, taking advantage of these properties. In addition, in recent years, the performance required for industrial rubber parts has increased significantly, and in addition to the above-mentioned improvements in mechanical properties, ozone resistance, and chemical resistance, reduction in rubber heat build-up, scorch resistance, and abrasion resistance are also required.

Known techniques for reducing the heat build-up of rubber include elastomers such as acrylonitrile-butadiene copolymer rubbers, metal salts of α,β-ethylenically unsaturated carboxylic acids, magnesium oxide having a BET specific surface area of 25 m ² /g or less, and a low heat build-up rubber composition containing an organic peroxide cross-linking agent (see Patent Document 1). Further, a rubber composition containing a specific low-heat-generating carbon black in a rubber component (see Patent Document 2), and a modified conjugated diene-based polymer obtained by mixing a high-molecular-weight component having predetermined properties and a low-molecular-weight component having predetermined properties (see Patent Document 3) are known.

On the other hand, development of chloroprene rubber excellent in scorch resistance and wear resistance is also desired. As a technique for improving scorch resistance, a rubber composition containing 1 to 10 parts by weight of an amine salt of dithiocarbamic acid and 0.1 to 5 parts by weight of at least one compound selected from the group consisting of thiuram-based vulcanization accelerators, guanidine-based vulcanization accelerators, thiazole-based vulcanization accelerators and sulfenamide-based vulcanization accelerators is known per 100 parts by weight of chloroprene rubber (see Patent Document 4). Also, the aforementioned Patent Document 3 also describes a technique for improving the abrasion resistance of rubber.

JP-A-9-268239 JP-A-10-130424 JP 2010-121086 A JP 2016-141736 A

However, the techniques described in Patent Documents 1 to 4 alone have the problem that the scorch resistance and wear resistance are excellent and the heat buildup cannot be reduced.

Accordingly, the main object of the present invention is to provide a rubber composition, a vulcanized product thereof, and a molded product from which a vulcanized product having excellent scorch resistance and wear resistance and reduced heat build-up can be obtained.

As a result of intensive research to solve such problems, the inventors of the present application introduced a specific structure to the molecular end of the sulfur-modified chloroprene rubber, and made the average particle size of the carbon black used as a filler within a specific range. By doing so, they succeeded in achieving excellent scorch resistance and wear resistance, and reduced heat build-up, and completed the present invention.

That is, the present invention provides a sulfur-modified chloroprene rubber having at least one of the structures represented by chemical formulas 1 and 2 at the molecular end, wherein the mass ratio (B/A) of the terminal functional group (A) represented by chemical formula 1 and the terminal functional group (B) represented by chemical formula 2 is 0 to 6, and the total mass amount (A+B) of the terminal functional group (A) and the terminal functional group (B) in 100 parts by mass of the sulfur-modified chloroprene rubber is 0.1 to 0.6 parts by mass. 100 parts by mass of chloroprene rubber;
A rubber composition containing 25 to 55 parts by mass of carbon black having an average particle size of 15 to 80 nm.
(In the formula, R ₁ and R ₂ each represent a hydrogen atom, a halogen atom, a hydroxy group, a cyano group, an optionally substituted alkyl group, or an optionally substituted arylthio group. R ₁ and R ₂ may be the same or different, and R ₁ and R ₂ may combine with each other to form a ring having a substituent.)
(In the formula, R ₃ represents a hydrogen atom or an optionally substituted alkyl group having 1 to 4 carbon atoms.)

The amount of the terminal functional group (A) in 100 parts by mass of the sulfur-modified chloroprene rubber is preferably 0.05 to 0.4 parts by mass, and the amount of the terminal functional group (B) in 100 parts by mass of the sulfur-modified chloroprene rubber is preferably 0 to 0.4 parts by mass.

The rubber composition preferably contains 0.0005 to 0.01 parts by mass of thiazole with respect to 100 parts by mass of sulfur-modified chloroprene rubber.
Thiazoles include N-cyclohexyl-2-benzothiazolesulfenamide, N-cyclohexyl-4-methyl-2-benzothiazolesulfenamide, N-cyclohexyl-4,5-dimethyl-2-benzothiazolesulfenamide, N,N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide, N-(tert-butyl)-2-benzothiazolesulfenamide, N,N-diisopropyl-2-benzothiazolesulfenamide. , 4,5-dihydrothiazole-2-sulfenamide, N-cyclohexyl-4,5-dihydrothiazole-2-sulfenamide, N-oxydiethylbenzothiazole-2-sulfenamide, 2-(4′-morpholinyldithio)benzothiazole, 2-mercaptobenzothiazole, 4,5-dihydro-2-mercaptothiazole, dibenzylthiazolyl disulfide, and 2-(morpholinodithio)benzothiazole. is preferred.

The rubber composition preferably contains 0 to 1.5 parts by mass of alkylxanthogen disulfide per 100 parts by mass of sulfur-modified chloroprene rubber.
The alkylxanthogen disulfide is preferably at least one compound selected from dimethylxanthogen disulfide, diethylxanthogen disulfide, dipropylxanthogen disulfide, diisopropylxanthogen disulfide, and dibutylxanthogen disulfide.

The mass ratio (D/C) of thiazole (C) and alkylxanthogen disulfide (D) contained in the rubber composition is preferably adjusted to 0-1,000. The Mooney viscosity of the sulfur-modified chloroprene rubber contained in the rubber composition is preferably adjusted to 20-80.

The carbon black preferably has a DBP absorption of 50 to 150 ml/100 g and an iodine adsorption of 20 to 150 mg/g.

The present invention provides a vulcanizate obtained by vulcanizing the rubber composition described above, and a molded article obtained by vulcanizing the rubber composition after or during molding.

ADVANTAGE OF THE INVENTION According to this invention, the rubber composition from which a vulcanizate with excellent scorch resistance and abrasion resistance and reduced heat build-up can be obtained, its vulcanizate and molded article are obtained.

Preferred embodiments for carrying out the present invention will be described below. It should be noted that the embodiments described below are examples of representative embodiments of the present invention, and the scope of the present invention should not be construed narrowly.

The rubber composition of the present invention contains a sulfur-modified chloroprene rubber having a specific molecular end structure and carbon black having a specific average particle size.

<Sulfur modified chloroprene rubber>
Sulfur-modified chloroprene rubber includes a latex obtained by plasticizing a sulfur-modified chloroprene polymer obtained by emulsion-polymerizing 2-chloro-1,3-butadiene (hereinafter also referred to as "chloroprene") alone or chloroprene and other monomers into the main chain to introduce sulfur into the main chain in the presence of sulfur, and a sulfur-modified chloroprene rubber obtained by drying and washing this latex by a general method. The manufacturing process of the sulfur-modified chloroprene rubber will be described in detail below.

<Polymerization process>
A sulfur-modified chloroprene rubber is obtained by emulsion polymerization of chloroprene, sulfur, and, if necessary, a monomer copolymerizable with chloroprene to obtain a polymerization liquid.

Monomers copolymerizable with chloroprene include, for example, 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, styrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, methacrylic acid and esters thereof, and two or more thereof can be used in combination. When these monomers are used, they are preferably used within a range that does not impair the properties of the resulting sulfur-modified chloroprene rubber, and the amount is preferably 10% by mass or less based on the total monomers including chloroprene. If the amount of these monomers used exceeds 10% by mass, the heat resistance of the resulting sulfur-modified chloroprene rubber may not improve, or the workability may deteriorate.

Among these monomers, use of, for example, 2,3-dichloro-1,3-butadiene can slow down the crystallization rate of the obtained sulfur-modified chloroprene rubber. Sulfur-modified chloroprene rubber with a slow crystallization rate can maintain rubber elasticity even in a low-temperature environment, and can improve, for example, low-temperature compression set.

In emulsion polymerization, the amount of sulfur (S ₈ ) added is preferably 0.01 to 0.6 parts by mass, more preferably 0.1 to 0.5 parts by mass, with respect to 100 parts by mass of the total monomers to be polymerized. If the amount of sulfur (S ₈ ) is less than 0.01 parts by mass, the obtained sulfur-modified chloroprene rubber may not have sufficient mechanical properties and dynamic properties. On the other hand, if the amount of sulfur (S ₈ ) exceeds 0.6 parts by mass, the resulting sulfur-modified chloroprene rubber may have too strong adhesion to metals and may not be processed.

As the emulsifier used in the emulsion polymerization, one or more of known emulsifiers and fatty acids that can be used in the emulsion polymerization of chloroprene can be freely selected and used. Specific examples of emulsifiers include rosin acids, metal salts of aromatic sulfonic acid formalin condensates, sodium dodecylbenzene sulfonate, potassium dodecylbenzene sulfonate, sodium alkyldiphenyl ether sulfonate, potassium alkyldiphenyl ether sulfonate, sodium polyoxyethylene alkyl ether sulfonate, sodium polyoxypropylene alkyl ether sulfonate, potassium polyoxyethylene alkyl ether sulfonate, and potassium polyoxypropylene alkyl ether sulfonate. Among these, it is particularly preferable to use rosin acids. Here, rosin acids mean rosin acid, disproportionated rosin acid, alkali metal salts of disproportionated rosin acid, or compounds thereof. A suitable emulsifier is an aqueous alkaline soap solution comprising a mixture of an alkali metal salt of disproportionated rosin acid and a saturated or unsaturated fatty acid having 6 to 22 carbon atoms. Examples of disproportionated rosin acid constituents include sesquiterpene, 8,5-isopimaric acid, dihydropimaric acid, secodehydroabietic acid, dihydroabietic acid, deisopropyldehydroabietic acid, demethyldehydroabietic acid and the like.

The pH of the aqueous emulsion at the start of emulsion polymerization is desirably 10.5 or higher. Here, the aqueous emulsion is a mixture of chloroprene, a monomer copolymerizable with chloroprene, an emulsifier, sulfur (S ₈ ), and the like, immediately before emulsion polymerization is started. A case in which the composition is changed by post-addition or divisional addition of these monomers, sulfur (S ₈ ), etc. is also included. By adjusting the pH to 10.5 or higher, when rosin acids are used as emulsifiers, it is possible to prevent polymer precipitation during polymerization and to stably control polymerization. The pH of the aqueous emulsion can be adjusted by adjusting the amount of alkaline components such as sodium hydroxide and potassium hydroxide present during emulsion polymerization.

The polymerization temperature for emulsion polymerization is 0 to 55°C, preferably 30 to 55°C, from the viewpoint of polymerization controllability and productivity.

As the polymerization initiator, potassium persulfate, benzoyl peroxide, ammonium persulfate, hydrogen peroxide, etc., which are used in ordinary radical polymerization, can be used. Polymerization is carried out at a rate of polymerization of 60 to 95%, preferably 70 to 90%, and then terminated by adding a polymerization inhibitor.

From the viewpoint of productivity, the polymerization rate is preferably 60% or more. Moreover, from the viewpoint of suppressing the development of branched structures and the formation of gels that affect the processability of the obtained sulfur-modified chloroprene rubber, the polymerization rate is preferably 95% or less. Polymerization inhibitors include, for example, diethylhydroxyamine, thiodiphenylamine, 4-tert-butylcatechol, 2,2'-methylenebis-4-methyl-6-tert-butylphenol and the like. A polymerization inhibitor may be used individually by 1 type, and may use 2 or more types together.

<Plasticization process>
In the plasticizing step, thiazole is added to the polymerization solution obtained in the polymerization step, and the added thiazole reacts with the polysulfide bonds (S ₂ to S ₈ ) present in the main chain of the sulfur-modified chloroprene polymer in the polymerization solution, thereby forming the terminal functional group (A) represented by the chemical formula 1 derived from the added thiazole, and cutting and depolymerizing the sulfur-modified chloroprene polymer. Hereinafter, a chemical used for cutting and depolymerizing the sulfur-modified chloroprene polymer is referred to as a plasticizer.

As for the type of thiazole to be added, one or two or more known thiazoles can be freely used. In the present invention, in particular N-cyclohexyl-2-benzothiazolesulfenamide, N-cyclohexyl-4-methyl-2-benzothiazolesulfenamide, N-cyclohexyl-4,5-dimethyl-2-benzothiazolesulfenamide, N,N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide, N-(tert-butyl)-2-benzothiazolesulfenamide, N,N-diisopropyl-2-benzothiazolesulfenamide, 4 ,5-dihydrothiazole-2-sulfenamide, N-cyclohexyl-4,5-dihydrothiazole-2-sulfenamide, N-oxydiethylbenzothiazole-2-sulfenamide, 2-(4'-morpholinyldithio)benzothiazole, 2-mercaptobenzothiazole, 4,5-dihydro-2-mercaptothiazole, dibenzylthiazolyl disulfide, and 2-(morpholinodithio)benzothiazole. is preferred.

The amount of thiazole to be added is preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the sulfur-modified chloroprene polymer in the polymerization liquid. By adding 0.2 parts by mass or more of thiazole, the scorch resistance and abrasion resistance of the obtained vulcanizate can be improved. Also, by setting the amount of thiazole to be added to 3 parts by mass or less, a sulfur-modified chloroprene rubber having an appropriate Mooney viscosity can be obtained, and as a result, vulcanization moldability can be improved.

In the plasticizing step, an alkylxanthogen disulfide can also be used in combination as a plasticizer. In the polymerization solution, the alkylxanthogen disulfide reacts with thiazole to form a reactant having higher reactivity with polysulfide bonds than thiazole or alkylxanthogen disulfide alone, thereby facilitating Mooney viscosity adjustment. The reactant reacts with the polysulfide bond of the sulfur-modified chloroprene polymer to form the terminal functional group (A) and the terminal functional group (B) represented by the chemical formula 2 derived from the added alkylxanthogen disulfide. The vulcanizate of the sulfur-modified chloroprene rubber obtained by the plasticizing step has good scorch resistance, and the resulting vulcanizate has a good balance of physical properties such as wear resistance and heat build-up. As the alkylxanthogen disulfide to be added, one or more known alkylxanthogen disulfides can be freely used, and in particular, it is preferable to use at least one compound selected from dimethylxanthogen disulfide, diethylxanthogen disulfide, dipropylxanthogen disulfide, diisopropylxanthogen disulfide, and dibutylxanthogen disulfide.

When alkylxanthogen disulfide is used, the amount added is not particularly limited, but it is preferably added in an amount of 0 to 6 parts by mass, more preferably 0.5 to 3 parts by mass, per 100 parts by mass of the polymer in the polymerization liquid. By setting the amount of the alkyl xanthogen disulfide within this range, it becomes easier to control the Mooney viscosity of the resulting rubber composition, the scorch resistance and abrasion resistance of the resulting vulcanizate are further improved, and the heat buildup is further reduced.

The polymerized liquid that has undergone the plasticizing step is subjected to cooling, pH adjustment, freezing, drying, and the like by a general method to obtain a sulfur-modified chloroprene rubber. The obtained sulfur-modified chloroprene rubber is characterized by containing 0.05 to 0.4 parts by mass of the terminal functional group (A) represented by the chemical formula 1 in 100 parts by mass. The content of the terminal functional group (A) can be adjusted by adjusting the amount of thiazole added in the plasticizing step and the plasticizing time and plasticizing temperature in the plasticizing step. By setting the content of the terminal functional group (A) within this range, the scorch resistance and abrasion resistance of the obtained vulcanizate are improved, which contributes to the reduction of heat build-up.

By leaving 0.0005 to 0.01 parts by mass of unreacted thiazole with respect to 100 parts by mass of the obtained sulfur-modified chloroprene rubber, the resulting vulcanizate has improved scorch resistance and abrasion resistance, which contributes to a reduction in heat build-up. The amount of unreacted thiazole remaining can be adjusted by adjusting the amount of thiazole added in the plasticizing step and the plasticizing time and plasticizing temperature in the plasticizing step.

When alkylxanthogen disulfide is used in the plasticizing step, the content of the terminal functional group (B) represented by Chemical Formula 2 present in the resulting sulfur-modified chloroprene rubber is not particularly limited. For example, in the plasticizing step, when 0 to 6 parts by mass of alkyl xanthogen disulfide is added to 100 parts by mass of the polymer in the polymerization liquid, the resulting sulfur-modified chloroprene rubber contains 0 to 0.4 parts by mass of the terminal functional group (B) and 0 to 1.5 parts by mass of unreacted alkyl xanthogen disulfide per 100 parts by mass of the polymer. The content of the terminal functional group (B) and the amount of unreacted alkylxanthogen disulfide can be adjusted by adjusting the amount of alkylxanthogen disulfide added and the time and temperature of the plasticizing step. By setting the content of the terminal functional group B within this range, the scorch resistance and abrasion resistance of the resulting vulcanizate are improved, contributing to further reduction of heat buildup.

The mass ratio (B/A) of the content of the terminal functional group (A) to the content of the terminal functional group (B) is 0 to 6, and the total mass (A+B) of the content of the terminal functional group (A) and the terminal functional group (B) is 0.1 to 0.6. If the mass ratio (B/A) exceeds 6, the scorch resistance and heat generation resistance of the resulting vulcanizate will be reduced. If the total mass (A+B) is less than 0.1, the resulting sulfur-modified chloroprene rubber has reduced scorch resistance, abrasion resistance, and heat resistance.

The content of terminal functional groups (A) and terminal functional groups (B) in the sulfur-modified chloroprene rubber can be quantified by the following procedure.
The resulting sulfur-modified chloroprene rubber was purified with benzene and methanol, and freeze-dried again to obtain a sample for measurement. The obtained sample for measurement was subjected to ¹ H-NMR measurement according to JIS K-6239. The obtained measurement data is corrected based on the peak (7.24 ppm) of chloroform in deuterated chloroform used as a solvent, and based on the corrected measurement data, the area of the peak having the peak top at 7.72 to 7.83 ppm and 1.30 to 1.45 ppm is calculated.

Furthermore, the ratio (D/C) of the unreacted thiazole content (C) to the unreacted alkylxanthogen disulfide content (D) is preferably 0-1,000. By setting the content ratio (D/C) within this range, the resulting vulcanizate has a better balance of physical properties such as wear resistance, scorch resistance, and heat build-up.

The unreacted thiazole content (C) and the unreacted alkylxanthogen disulfide content (D) contained in the sulfur-modified chloroprene rubber can be quantified by the following procedures.
After 1.5 g of the obtained sulfur-modified chloroprene rubber was dissolved in 30 ml of benzene, 60 ml of methanol was added dropwise to separate the rubber component from the solvent and recover the non-rubber component as a solvent-soluble component. The precipitated polymer portion was again dissolved in benzene and added dropwise to methanol in the same procedure to separate the rubber component, and the non-rubber component was similarly recovered as a solvent-soluble component. 20 μL of the sample for measurement was injected into a liquid chromatograph (LC manufactured by Hitachi Ltd., pump: L-6200, L-600 UV detector: L-4250). The mobile phase of LC was used while changing the ratio of acetonitrile and water, and flowed at a flow rate of 1 ml/min. Inertsil ODS-3 (φ4.6×150 mm, 5 μm, manufactured by GL Sciences) was used as a column. The peak detection times of thiazole (measurement wavelength: 300 nm) and alkylxanthogen disulfide (measurement wavelength: 280 nm) were confirmed with standard solutions, and quantitative values were obtained from calibration curves obtained from the peak areas. The contents of unreacted thiazole and unreacted alkylxanthogen disulfide contained in the sulfur-modified chloroprene rubber were determined by comparing this quantitative value with the sample amount used for analysis.

Although the Mooney viscosity of the sulfur-modified chloroprene rubber is not particularly limited, it is preferably adjusted in the range of 20-80. By adjusting the Mooney viscosity of the sulfur-modified chloroprene rubber to this range, the processability of the obtained sulfur-modified chloroprene rubber can be maintained.
In order to adjust the Mooney viscosity of the sulfur-modified chloroprene rubber, the addition amount of the plasticizer, the plasticizing process time and the plasticizing temperature may be adjusted.

The sulfur-modified chloroprene rubber may also contain a small amount of stabilizer to prevent Mooney viscosity change during storage. As for the type of stabilizer that can be used in the present invention, one or two or more known stabilizers that can be used for chloroprene rubber can be freely selected and used. Examples include phenyl-α-naphthylamine, octylated diphenylamine, 2,6-di-tert-butyl-4-phenylphenol, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), and 4,4'-thiobis-(6-tert-butyl-3-methylphenol). Among these stabilizers, 4,4'-thiobis-(6-tert-butyl-3-methylphenol is preferred.

<Carbon Black>
Carbon black is added to the sulfur-modified chloroprene rubber in order to improve the abrasion resistance of the resulting molded article. The carbon black preferably has an average particle size of 15 nm to 80 nm, more preferably 20 nm to 50 nm, as observed with an electron microscope according to JIS Z8901. If the average particle size is out of the above range, a sufficient reinforcing effect cannot be obtained and the wear resistance of the resulting vulcanizate cannot be improved.

Carbon black preferably has a dibutyl phthalate (hereinafter referred to as DBP) absorption of 50 ml/100 g to 150 ml/100 g, more preferably 80 ml/100 g to 140 ml/100 g, as measured according to JIS K6217-4. When the DBP absorption exceeds 150 ml/100 g, the scorch resistance of the rubber composition is lowered, causing an increase in heat build-up of the rubber composition under dynamic environments. If the DBP absorption is less than 50 ml/100 g, the resulting vulcanizate will not have improved abrasion resistance.

In addition, the carbon black preferably has an iodine adsorption amount of 20 ml/g to 150 ml/g, more preferably 50 ml/g to 150 ml/g, according to JIS K6217-1. If the iodine adsorption amount is less than 20 ml/g, the wear resistance of the resulting vulcanizate will not improve.

The amount of carbon black added is 25 to 55 parts by mass with respect to 100 parts by mass of sulfur-modified chloroprene rubber. If the amount of carbon black is less than 25 parts by mass, the wear resistance of the resulting vulcanizate will not be improved, and if it exceeds 55 parts by mass, the scorch resistance of the resulting vulcanizate will be reduced. The amount of carbon black added is preferably 25 to 45 parts by mass, more preferably 30 to 40 parts by mass. These ranges are preferable because the wear resistance and scorch resistance of the resulting vulcanizates are further improved.

<Vulcanized product/molded product>
The vulcanizate and molded article are obtained by mixing the rubber composition, the metal compound, the plasticizer, etc. described above with a roll or a Banbury mixer, molding the mixture into a desired shape, and vulcanizing during or after molding. The molding method is not particularly limited, but press molding, injection molding, extrusion molding, and the like can be applied. For example, when the molded article is a power transmission belt, conveyor belt, air spring, seal, packing, anti-vibration material, hose, rubber roll, etc., it can be formed by press molding, injection molding, or extrusion molding.

The metal compound is added to adjust the vulcanization speed of the rubber composition and to adsorb chlorine sources such as hydrogen chloride generated by the dehydrochlorination reaction of the rubber composition to suppress deterioration of the rubber composition. Examples of metal compounds that can be used include oxides and hydroxides of zinc, titanium, magnesium, lead, iron, beryllium, calcium, barium, germanium, zirconium, vanadium, molybdenum, and tungsten. These metal compounds may be used individually by 1 type, and may use 2 or more types together.

The amount of the metal compound added is not particularly limited, but is preferably in the range of 3 to 15 parts by mass with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. By adjusting the amount of the metal compound to be added within this range, the mechanical strength of the obtained rubber composition can be improved.

A plasticizer is added to reduce the hardness of the rubber composition and improve its low temperature properties. In addition, when the rubber composition is used to manufacture a sponge, the feel of the sponge can be improved. Examples of plasticizers include dioctyl phthalate, dioctyl adipate {bis(2-ethylhexyl) adipate}, white oil, silicone oil, naphthenic oil, aromatic oil, triphenyl phosphate, and tricresyl phosphate. These plasticizers may be used alone or in combination of two or more.

The amount of the plasticizer to be added is not particularly limited, but is preferably in the range of 50 parts by mass or less with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. By adjusting the amount of the plasticizer to be added within this range, the above effects can be exhibited while maintaining the tear strength of the resulting rubber composition.

Application examples of the rubber composition are described below.
(transmission belt)
A transmission belt is a mechanical element used in a winding transmission, and is a component that transmits power from a driving wheel to a driven wheel. It is often used over a pulley set on the shaft. It is widely used in general machinery such as automobiles and general industries because it is lightweight, quiet, and has excellent degrees of freedom in terms of shaft angle. The types of belts are also diversified, and flat belts, conveyor belts, timing belts, V-belts, ribbed belts, round belts, etc. are used according to machine applications. Elastomer materials such as natural rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, and hydrogenated nitrile rubber are used because belts under high tension undergo repeated rotational deformation in order to efficiently transmit power. Due to its excellent rubber physical properties, chloroprene rubber is used in automobiles and general industrial applications, but it is known that chloroprene rubber often causes scorching during the molding process, and extending the scorch time is an important technical issue. In addition, since belts are used continuously in a dynamic environment, there is a demand for materials with excellent wear resistance and heat resistance in order to improve product reliability.

The rubber composition of the present invention can improve the scorch resistance, wear resistance, and heat build-up resistance of transmission belts. As a result, it is possible to manufacture a belt with excellent productivity and durability, which has been difficult with conventional sulfur-modified chloroprene rubber.

(air spring)
An air spring is a spring device that utilizes the elasticity of compressed air. It is used in air suspensions for automobiles, buses and trucks. There are bellows type and sleeve type (a type of diaphragm type), both of which can increase the air pressure by inserting the piston into the air chamber. It is known that chloroprene rubber often causes scorching during molding, and extending the scorch time is an important technical issue. In addition, since air springs are continuously used in dynamic environments, there is a demand for materials with excellent wear resistance and heat resistance in order to improve product reliability.

The rubber composition of the present invention can improve the scorch resistance, wear resistance and heat build-up resistance of air springs. As a result, it is possible to manufacture an air spring with excellent productivity and durability, which has been difficult with conventional sulfur-modified chloroprene rubber.

(hose)
A hose is a bendable tube that bends freely when watering or the like, and is used for work that requires portability and mobility. In addition, compared to hard pipes such as metal pipes, it is less likely to cause fatigue failure due to deformation, so it is used for piping in parts that are subject to vibration, such as automobile piping. Among them, rubber hoses are the most common. Rubber hoses include water, oil, air, steam, and high/low pressure hoses for hydraulic pressure. Chloroprene rubber is mainly used in hydraulic high pressure hoses because of its good mechanical properties to withstand the pressure of high pressure fluids.

The rubber composition of the present invention can improve the scorch resistance, wear resistance and heat build-up resistance of hoses. As a result, it is possible to manufacture an air spring with excellent productivity and durability, which has been difficult with conventional sulfur-modified chloroprene rubber.

The present invention will be described in more detail below based on examples. It should be noted that the examples described below are examples of representative examples of the present invention, and the scope of the present invention should not be construed narrowly.

<Example 1>
<Sulfur modified chloroprene rubber>
To a polymerization can having an internal volume of 30 liters, 100 parts by mass of chloroprene, 0.55 parts by mass of sulfur, 120 parts by mass of pure water, 4.00 parts by mass of disproportionated potassium rosinate (manufactured by Harima Chemicals Co., Ltd.), 0.60 parts by mass of sodium hydroxide, and 0.6 parts by mass of β-naphthalenesulfonic acid formalin condensate sodium salt (trade name Demol N: manufactured by Kao Corporation) were added. The pH of the aqueous emulsifier before initiation of polymerization was 12.8. 0.1 part by mass of potassium persulfate was added as a polymerization initiator, and polymerization was carried out at a polymerization temperature of 40° C. under a nitrogen stream. When the conversion rate reached 85%, diethylhydroxyamine as a polymerization inhibitor was added to terminate the polymerization to obtain a chloroprene polymerization solution.

To the resulting polymerization solution, 5 parts by mass of a chloroprene monomer as a solvent, 1 part by mass of N-cyclohexylbenzothiazole-2-sulfenamide (trade name "Noccellar CZ" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) and 2 parts by mass of diisopropyl xanthogen disulfide (trade name "Sanbit DIX" manufactured by Sanshin Chemical Industry Co., Ltd.) as a plasticizer, 0.05 parts by mass of sodium salt of β-naphthalenesulfonic acid formalin condensate as a dispersant, and 0 part by mass of sodium lauryl sulfate as an emulsifier. 05 parts by mass of a plasticizer emulsion was added to obtain a sulfur-modified chloroprene polymer latex before plasticization.

Here, the sodium salt of the β-naphthalenesulfonic acid formalin condensate is a dispersant used for general purposes, and the stability is improved by adding a small amount, and the latex can be stably produced without aggregation or precipitation during the production process. Further, in this example, a plasticizer was added to the polymerization liquid after emulsion polymerization. At that time, in order to enable more stable plasticization, an emulsified state was added by adding sodium lauryl sulfate to a plasticizer liquid obtained by dissolving the plasticizer in chloroprene added as a solvent.

The resulting sulfur-modified chloroprene polymer latex was distilled under reduced pressure to remove unreacted monomers, and the mixture was plasticized by holding at a temperature of 50° C. for 1 hour while stirring to obtain a plasticized latex (hereinafter, this plasticized latex is abbreviated as “latex”).

The resulting latex was cooled, and the polymer was isolated by a conventional freeze-coagulation method to obtain a sulfur-modified chloroprene rubber.
Regarding the terminal functional groups of the obtained sulfur-modified chloroprene rubber, 0.15 parts by mass of the terminal functional group (A) derived from N-cyclohexylbenzothiazole-2-sulfenamide represented by chemical formula 3 and 0.14 parts by mass of the terminal functional group (B) derived from diisopropylxanthogen disulfide represented by chemical formula 4 were found with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. Moreover, the mass ratio (B/A) of terminal functional groups was 0.93, and the total mass amount (A+B) was 0.29.

<Measurement of Mooney viscosity>
The Mooney viscosity of the sulfur-modified chloroprene rubber (crude rubber) obtained above was measured according to JIS K 6300-1 with an L-type rotor preheating time of 1 minute, a rotation time of 4 minutes, and a test temperature of 100°C.

<Preparation of sample for evaluation>
The sulfur-modified chloroprene rubber obtained above and the compounds listed in Table 1 were mixed using an 8-inch roll and press-crosslinked at 160° C. for 20 minutes to prepare samples for evaluation.

The compounds listed in Table 1 are as follows: lubricant/processing aid 1: stearic acid 50S manufactured by New Japan Chemical Co., Ltd.
Antiaging agent: Nocrac AD-F manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Magnesium oxide: Kyowamag 30 manufactured by Kyowa Chemical Industry Co., Ltd.
Lubricant/processing aid 2: Amide AP-1 manufactured by Mitsubishi Chemical Corporation
Wax: manufactured by Ouchi Shinko Kagaku Co., Ltd. Sannok vulcanizing agent: manufactured by Sakai Chemical Industry Co., Ltd. Type 2 zinc oxide Carbon black A: manufactured by Asahi Carbon Co., Ltd. Asahi #70 average particle size 28 nm, iodine adsorption amount 80 mg / g, DBP absorption amount 101 ml / 100 g

<Examples 2 to 8 and Comparative Examples 1 to 3>
An evaluation sample was prepared in the same manner as in Example 1, except that a sulfur-modified chloroprene rubber obtained by changing the amount of plasticizer added was used.

<Example 9>
An evaluation sample was prepared in the same manner as in Example 1, except for using a sulfur-modified chloroprene rubber obtained by changing the amount of N-cyclohexylbenzothiazole-2-sulfenamide, which is a plasticizer, from 1 part by mass to 0.3 parts by mass and changing the holding time of plasticization from 1 hour to 3 hours.

<Example 10>
An evaluation sample was prepared in the same manner as in Example 1, except for using a sulfur-modified chloroprene rubber obtained by changing the amount of N-cyclohexylbenzothiazole-2-sulfenamide, which is a plasticizer, from 1 part by mass to 1.5 parts by mass and changing the holding time of plasticization from 1 hour to 15 minutes.

<Example 11>
An evaluation sample was prepared in the same manner as in Example 1, except that a sulfur-modified chloroprene rubber obtained by changing the addition amount of diisopropylxanthogen disulfide as a plasticizer from 2 parts by mass to 4 parts by mass and changing the holding time of plasticization from 1 hour to 15 minutes was used.

<Example 12>
An evaluation sample was prepared in the same manner as in Example 1, except that a sulfur-modified chloroprene rubber obtained by changing N-cyclohexylbenzothiazole-2-sulfenamide as a plasticizer to N-cyclohexyl-4-methyl-2-benzothiazolesulfenamide: (manufactured by Chemieliva Pharma & Chem Co., Ltd.) was used. The terminal functional groups of the obtained sulfur-modified chloroprene rubber included 0.17 parts by mass of xanthogen terminal species A derived from diisopropyl xanthogen disulfide represented by chemical formula 4, and 0.15 parts by mass of thiazole terminal species B derived from N-cyclohexyl-4-methyl-2-benzothiazolesulfenamide represented by chemical formula 5.

<Example 13>
An evaluation sample was prepared in the same manner as in Example 1, except that a sulfur-modified chloroprene rubber obtained by changing diisopropylxanthogen disulfide as a plasticizer to diethylxanthogen disulfide (manufactured by Sigma-Aldrich) was used. The terminal functional groups of the obtained sulfur-modified chloroprene rubber were 0.16 parts by mass of thiazole terminal species A derived from N-cyclohexylbenzothiazole-2-sulfenamide represented by chemical formula 3 and 0.13 parts by mass of xanthogen terminal species B derived from diethylxanthogen disulfide represented by chemical formula 6.

<Example 14>
An evaluation sample was prepared in the same manner as in Example 1, except that a sulfur-modified chloroprene rubber obtained by changing N-cyclohexylbenzothiazole-2-sulfenamide to N-cyclohexyl-4-methyl-2-benzothiazolesulfenamide as a plasticizer and changing diisopropylxanthogen disulfide to diethylxanthogen disulfide was used. The terminal functional groups of the obtained sulfur-modified chloroprene rubber were 0.14 parts by mass of thiazole terminal species B derived from N-cyclohexyl-4-methyl-2-benzothiazolesulfenamide represented by Chemical Formula 5 and 0.16 parts by mass of xanthogen terminal species B derived from diethylxanthogen disulfide represented by Chemical Formula 6.

<Comparative Example 4>
An evaluation sample was prepared in the same manner as in Example 1, except that a chloroprene rubber obtained by changing N-cyclohexylbenzothiazole-2-sulphenamide and diisopropylxanthogen disulfide as plasticizers to tetraethylthiuram disulfide and changing the amount added to 2.5 parts by mass was used. The terminal functional groups of the obtained sulfur-modified chloroprene rubber were 0.26 parts by mass of terminal functional groups derived from tetraethylthiuram disulfide represented by Chemical Formula 7.

<Example 15>
An evaluation sample was prepared in the same manner as in Example 1 except that carbon black A was changed to carbon black B (trade name “Asahi #60UG” manufactured by Asahi Carbon Co., Ltd., average particle size 43 nm, iodine adsorption amount 40 mg / g, DBP absorption amount 110 ml / 100 g).

<Example 16>
An evaluation sample was prepared in the same manner as in Example 1 except that carbon black A was changed to carbon black C (trade name “Asahi #95” manufactured by Asahi Carbon Co., Ltd., average particle size 17 nm, iodine adsorption amount 150 mg / g, DBP absorption amount 127 ml / 100 g).

<Example 17>
An evaluation sample was prepared in the same manner as in Example 1 except that carbon black A was changed to carbon black D (trade name “Asahi #50” manufactured by Asahi Carbon Co., Ltd., average particle size 80 nm, iodine adsorption amount 23 mg / g, DBP absorption amount 63 ml / 100 g).

<Example 18>
An evaluation sample was prepared in the same manner as in Example 1 except that carbon black A was changed to carbon black E (trade name “Asahi #52” manufactured by Asahi Carbon Co., Ltd., average particle size 60 nm, iodine adsorption amount 19 mg / g, DBP absorption amount 128 ml / 100 g).

<Example 19>
An evaluation sample was prepared in the same manner as in Example 1 except that carbon black A was changed to carbon black F (trade name “Asahi Thermal” manufactured by Asahi Carbon Co., Ltd., average particle size 80 nm, iodine adsorption amount 24 mg / g, DBP absorption amount 28 ml / 100 g).

<Example 20>
An evaluation sample was prepared in the same manner as in Example 1 except that carbon black A was changed to carbon black G (trade name “Asahi F-200GS” manufactured by Asahi Carbon Co., Ltd., average particle size 38 nm, iodine adsorption amount 55 mg / g, DBP absorption amount 180 ml / 100 g).

<Comparative Example 5>
An evaluation sample was prepared in the same manner as in Example 1, except that the amount of carbon black A added was changed from 40 parts by mass to 20 parts by mass.

<Comparative Example 6>
An evaluation sample was prepared in the same manner as in Example 1, except that the amount of carbon black A added was changed from 40 parts by mass to 60 parts by mass.

<Comparative Example 7>
An evaluation sample was prepared in the same manner as in Example 1 except that carbon black A was changed to carbon black H (trade name “Asahi #15” manufactured by Asahi Carbon Co., Ltd., average particle size 122 nm, iodine adsorption amount 11 mg / g, DBP absorption amount 41 ml / 100 g).

<Abrasion resistance evaluation>
Each sample prepared above was subjected to a DIN abrasion test in accordance with JIS K 6264-2.

<Evaluation of scorch resistance>
A Mooney scorch test was performed on each of the samples prepared above in accordance with JIS K 6300-1.

<Pyrogenicity>
Pyrogenicity was evaluated using a Goodrich Flexometer (JIS K 6265). The Goodrich flexometer is a test method that applies a dynamic repeated load to a test piece such as vulcanized rubber and evaluates the fatigue characteristics due to heat generation inside the test piece. Specifically, a static initial load is applied to the test piece under constant temperature conditions, and a sinusoidal vibration of a constant amplitude is applied to measure the heat generation temperature and creep amount of the test piece that change over time. The test method conforms to JIS K 6265, and the calorific value (ΔT) was measured under the conditions of 50° C., strain of 0.175 inches, load of 55 pounds, and frequency of vibration of 1,800 times per minute.

<Results>
The results of Examples are shown in Table 1 below, and the results of Comparative Examples are shown in Table 2 below.

<Discussion>
As shown in Tables 1 to 3, it was confirmed that the evaluation samples of Examples 1 to 20 were excellent in scorch resistance and abrasion resistance and had reduced heat build-up. Even if thiazole was used, the Mooney viscosity was too low for Comparative Example 1, in which the total content (A+B) of the terminal functional groups in the raw rubber exceeded 0.6 parts by mass, and an evaluation sample could not be prepared.

When comparing the examples, Example 1 in which the terminal functional group (A) is 0.4 parts by mass or less has excellent wear resistance and heat build-up compared to Example 4 in which the terminal functional group (A) exceeds 0.4 parts by mass. In addition, Example 1 had a longer scorch time, excellent wear resistance, and lower heat build-up than Example 5, in which the terminal functional group (B) exceeded 0.4 parts by mass.
Example 2, in which the mass ratio (D/C) of the content of thiazole (C) and the content of alkylxanthogen disulfide (D) in the sulfur-modified chloroprene rubber is 1000 or less, had a longer scorch time, excellent wear resistance, and lower heat buildup than Example 8, in which the mass ratio (D/C) exceeded 1000.
Moreover, in Example 15, the scorch time was longer and the heat build-up was further reduced than in Example 20, in which the DBP absorption of carbon black as a filler exceeded 150 ml/100 g. Example 17 was superior in wear resistance to Example 19, which had a DBP absorption of 50 ml/100 g or less.
In Example 18, the iodine adsorption amount of the carbon black used as the filler was less than 20 mg/g, so the wear resistance was inferior to that in Example 1.

Claims (12)

A sulfur-modified chloroprene rubber having at least a structure represented by Chemical Formula 1 among the structures represented by Chemical Formula 1 and Chemical Formula 2 at the molecular end, wherein the mass ratio (B/A) of the terminal functional group (A) represented by Chemical Formula 1 and the terminal functional group (B) represented by Chemical Formula 2 is 0 to 6, and the total amount (A + B) of the terminal functional group (A) and the terminal functional group (B) in 100 parts by mass of the sulfur-modified chloroprene rubber is 0.1 to 0.6 parts by mass. 100 parts by mass of len rubber;
A rubber composition containing 25 to 55 parts by mass of carbon black having an average particle diameter of 15 to 80 nm ,
The rubber composition, wherein the carbon black has an iodine adsorption amount of 40 to 150 mg/g .
(In the formula, R ₁ and R ₂ each represent a hydrogen atom, a halogen atom, a hydroxy group, a cyano group, an optionally substituted alkyl group, or an optionally substituted arylthio group, or R ₁ and R ₂ may be bonded to each other to form a ring . R ₁ and R ₂ may be the same or different.)
(In the formula, R ₃ represents a hydrogen atom or an optionally substituted alkyl group having 1 to 4 carbon atoms.) The rubber composition according to claim 1, wherein the amount of the terminal functional group (A) is 0.05 to 0.4 parts by mass in 100 parts by mass of the sulfur-modified chloroprene rubber. 3. The rubber composition according to claim 1, wherein the amount of the terminal functional group (B) in 100 parts by mass of the sulfur-modified chloroprene rubber is 0 to 0.4 parts by mass. 4. The rubber composition according to any one of claims 1 to 3, further comprising 0.0005 to 0.01 parts by mass of thiazole with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. thiazole is N-cyclohexyl-2-benzothiazolesulfenamide, N-cyclohexyl-4-methyl-2-benzothiazolesulfenamide, N-cyclohexyl-4,5-dimethyl-2-benzothiazolesulfenamide, N,N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide, N-(tert-butyl)-2-benzothiazolesulfenamide, N,N-diisopropyl-2-benzothiazolesulfenamide, at least one compound selected from 4,5-dihydrothiazole-2-sulfenamide, N-cyclohexyl-4,5-dihydrothiazole-2-sulfenamide, N-oxydiethylbenzothiazole-2-sulfenamide, 2-(4′-morpholinyldithio)benzothiazole, 2-mercaptobenzothiazole, 4,5-dihydro-2-mercaptothiazole, dibenzylthiazolyl disulfide, and 2-(morpholinodithio)benzothiazole; A rubber composition according to claim 4. 6. The rubber composition according to any one of claims 1 to 5, further comprising 0 to 1.5 parts by mass of an alkylxanthogen disulfide with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. 7. The rubber composition according to claim 6, wherein the alkylxanthogen disulfide is at least one compound selected from dimethylxanthogen disulfide, diethylxanthogen disulfide, dipropylxanthogen disulfide, diisopropylxanthogen disulfide and dibutylxanthogen disulfide. 8. The rubber composition according to claim 6, wherein the mass ratio (D/C) of thiazole (C) and alkylxanthogen disulfide (D) contained in the sulfur-modified chloroprene rubber is 0-1000. The rubber composition according to any one of claims 1 to 8, which has a Mooney viscosity of 20 to 80 measured at a test temperature of 100° C. at a test temperature of 100° C. with an L-type rotor preheating time of 1 minute and a rotation time of 4 minutes in accordance with JIS K 6300-1 for sulfur-modified chloroprene rubber. 10. The rubber composition according to any one of claims 1 to 9, wherein the carbon black has a DBP absorption of 50 to 150 ml/100 g . A vulcanizate comprising the rubber composition according to any one of claims 1 to 10 . A molded article made from the vulcanizate according to claim 11 .