JP2021172696A - Rubber composition, and vulcanizate and molding of rubber composition - Google Patents

Abstract

To provide a sulfur-modified chloroprene rubber that can provide a vulcanizate having excellent permanent compression set and scorching resistance and reduced heat build-up.SOLUTION: A rubber composition contains a sulfur-modified chloroprene rubber having a specific terminal structure of 100 pts.mass, carbon black with an average particle size of 70 nm or less of 25-55 pts.mass, and a diene rubber, excluding chloroprene rubber, of 4-12 pts.mass.SELECTED DRAWING: None

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 by taking advantage of its properties. Further, in recent years, the performance required for industrial rubber parts has been remarkably increased, and in addition to the above-mentioned improvements in mechanical properties, ozone resistance, and chemical resistance, rubber scorch resistance, tensile strength, and compression set resistance are permanent. Improvement of properties and wear resistance is required.

As a technique for improving the scorch resistance of rubber, as described in Patent Document 1, 1 to 10 parts by mass of an amine salt of dithiocarbamic acid and a thiuram-based vulcanization accelerator, guanidine, are added to 100 parts by mass of chloroprene rubber. A rubber composition containing 0.1 to 5 parts by mass of at least one compound selected from the group consisting of a system vulcanization accelerator, a thiazole system vulcanization accelerator and a sulfenamide system vulcanization accelerator is known.

As a technique for improving the tensile strength of rubber, as described in Patent Document 2, 100 parts by mass of chloroprene rubber contains 5 to 20 parts by mass or more of a saturated aliphatic carboxylic acid having a molecular weight of 300 or more. There are known rubber compositions characterized by

In addition, the development of rubber having excellent compression set resistance and abrasion resistance is also desired. As a technique for improving the compression resistance and permanent strain resistance, 100 parts by mass of chloroprene rubber and natural rubber described in Patent Document 3 in total, 0.1 to 10 parts by mass of a copolymer of styrene and butadiene, and 0.1 to 10 parts by mass of a copolymer of styrene and butadiene are used. A chloroprene rubber composition containing 0.1 to 3 parts by mass of ethylene thiourea and 0.1 to 3 parts by mass of dipentamethylene thiuram tetrasulfide is known, and as a technique for improving wear resistance, a patent has been obtained. A modified conjugated diene polymer obtained by mixing a high-mass component having a predetermined property and a low-molecular-weight component having a predetermined property described in Document 4 is known.

Japanese Unexamined Patent Publication No. 2016-141736 Japanese Unexamined Patent Publication No. 2013-249409 Japanese Unexamined Patent Publication No. 2012-11189 Japanese Unexamined Patent Publication No. 2010-121086

However, there is a problem that the techniques described in Patent Documents 1 to 4 alone are excellent in scorch resistance and tensile strength, and cannot improve compression set resistance and wear resistance.

Therefore, it is a main object of the present invention to provide a rubber composition, a vulcanized product and a molded product thereof, which can obtain a vulcanized product having excellent scorch resistance and excellent tensile strength, compression set resistance and abrasion resistance. do.

As a result of diligent research to solve this problem, the present inventors have introduced a specific structure at the molecular terminal of the sulfur-modified chloroprene rubber, and set the average particle size of carbon black used as a filler in a specific range. The above-mentioned problems were achieved by containing a specific amount of a diene polymer other than chloroprene rubber, and the present invention was completed.

（化学式１中、Ｒ_１、Ｒ_２はそれぞれ水素原子、ハロゲン原子、ヒドロキシ基、シアノ基又は置換基を有しても良いアルキル基、置換基を有しても良いアリールチオ基を示す。Ｒ_１、Ｒ_２はそれぞれ同一のものでもよく、異なるものでも良い。また、Ｒ_１、Ｒ_２は互いに結合して、置換基を有する環を形成しても良い。）

（化学式２中、Ｒ_３、Ｒ_４は置換基を有しても良い炭素数７〜８のアルキル基を示す。Ｒ_３、Ｒ_４はそれぞれ同一のものでもよく、異なるものでも良い。） That is, the present invention is a sulfur-modified chloroprene rubber having at least one of the structures represented by the chemical formula 1 and the chemical formula 2 at the molecular terminal, and the terminal functional group (A) represented by the chemical formula 1 and the chemical formula 2. The mass ratio (B / A) of the represented terminal functional group (B) is 0 to 12.0, and the total mass of the terminal functional group (A) and the terminal functional group (B) in 100 parts by mass of the sulfur-modified chloroprene rubber. With 100 parts by mass of sulfur-modified chloroprene rubber having (A + B) 0.1 to 1.0 parts by mass,
25 to 55 parts by mass of carbon black with an average particle size of 70 nm or less,
It is a rubber composition containing 4 to 12 parts by mass of a diene rubber other than chloroprene rubber.

(In Formula 1, R _1, R ₂ are each a hydrogen atom, a halogen atom, hydroxy group, .R ₁ showing a cyano group or an optionally substituted alkyl group, an arylthio group which may have a substituent , R ₂ may be the same or different, and R ₁ and R ₂ may be bonded to each other to form a ring having a substituent.)

(In the chemical formula 2, R ₃ and R ₄ indicate an alkyl group having 7 to 8 carbon atoms which may have a substituent. R ₃ and R ₄ may be the same or different, respectively.)

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 0.8 parts by mass.

The rubber composition preferably contains 0.005 to 0.2 parts by mass of imidazole with respect to 100 parts by mass of the sulfur-modified chloroprene rubber contained.
Examples of imidazole include 2-mercaptoimidazole, 2-mercaptobenzimidazole, N-cyclohexyl-1H-benzimidazol-2-sulfeneamide, 2-methoxycarbonylamino-benzimidazole, 2-mercaptomethylbenzimidazole, 2-mercapto- 5-methoxybenzimidazole, 2-mercapto-5-carboxybenzimidazole, 2-mercaptobenzimidazole-5-sodium sulfonate dihydrate, 2-mercapto-5-nitrobenzimidazole, 2-mercapto-5-aminobenz At least one compound selected from imidazoles is preferred.

The rubber composition further contains 0 to 2 parts by mass of tetraalkylthiuram disulfide or dialkyldithiocarbamate (hereinafter collectively referred to as dithiocarbamic acid-based compound) with respect to 100 parts by mass of the sulfur-modified chloroprene rubber contained therein. It is preferable to include it.
Examples of the dithiocarbamic acid-based compound include dibenzyldithiocarbamic acid, sodium dibenzyldithiocarbamate, potassium dibenzyldithiocarbamate, zinc dibenzyldithiocarbamate, ammonium dibenzyldithiocarbamate, nickel dibenzyldithiocarbamate, and sodium di-2-ethylhexyldithiocarbamate. , Di-2-ethylhexyl dithiocarbamate potassium, di-2-ethylhexyl dithiocarbamate calcium, di-2-ethylhexyl dithiocarbamate zinc, di-2-ethylhexylcarbamate ammonium, tetrabenzylthiuram disulfide, tetrakis (2-ethylhexyl) thiuram disulfide At least one compound selected from the above is preferred.

The mass ratio (D / C) of the imidazole (C) and the dithiocarbamic acid-based compound (D) contained in the rubber composition is preferably adjusted to 0 to 120, and the Mooney viscosity of the sulfur-modified chloroprene rubber is 20 to 80. It is preferable to adjust.

The diene-based rubber other than the chloroprene rubber contained in the rubber composition is not particularly limited, and known butadiene rubber, styrene-butadiene rubber, and nitrile rubber can be used.

The carbon black contained in the rubber composition preferably has a DBP absorption amount of 80 to 150 ml / 100 g, and an iodine adsorption amount of 40 to 150 mg / g.

The present invention further provides a vulcanized product obtained by vulcanizing these rubber compositions and a molded product thereof. The molded product can be used, for example, as a conveyor belt.

According to the present invention, it is possible to provide a rubber composition, a vulcanized body and a molded product thereof, which can obtain a vulcanized product having excellent scorch resistance, tensile strength, compression set resistance and wear resistance. ..

Hereinafter, suitable embodiments for carrying out the present invention will be described. It should be noted that the embodiments described below show an example of typical embodiments of the present invention, and the scope of the present invention is not narrowly interpreted by this.

<Rubber composition>
The rubber composition of the present invention has a sulfur-modified chloroprene rubber having a specific structure, carbon black having a specific average particle size, and a diene-based rubber other than the chloroprene rubber.

<Sulfur-modified chloroprene rubber>
Sulfur-modified chloroprene rubber introduces sulfur into the main chain by emulsion polymerization of 2-chloro-1,3-butadiene (hereinafter also referred to as "chloroprene") alone or chloroprene and other monomers in the presence of sulfur. It includes a latex obtained by plasticizing the sulfur-modified chloroprene polymer obtained by using imidazole, and a sulfur-modified chloroprene rubber obtained by drying and washing the latex by a general method. Hereinafter, a detailed description will be given along with the manufacturing process of the sulfur-modified chloroprene rubber.

<Polymerization process>
The polymerization step is a step of obtaining a polymerization solution by emulsion polymerization of chloroprene and sulfur, and if necessary, a monomer copolymerizable with chloroprene.

Examples of the monomer copolymerizable with chloroprene include 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, styrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, and methacryl. There are acids and esters thereof, and two or more of them can be used in combination. When these monomers are used, it is preferable to use them within a range that does not impair the characteristics of the obtained sulfur-modified chloroprene rubber, and it is preferably 10% by mass or less of all the monomers containing chloroprene. If the amount of these monomers used exceeds 10% by mass, the heat resistance of the obtained sulfur-modified chloroprene rubber may not be improved, or the processability may be lowered.

Among these monomers, for example, 2,3-dichloro-1,3-butadiene can be used to slow down the crystallization rate of the obtained sulfur-modified chloroprene rubber. Sulfur-modified chloroprene rubber, which has a slow crystallization rate, can maintain rubber elasticity even in a low-temperature environment, and can improve, for example, low-temperature compression permanent strain.

_{The amount of sulfur (S 8} ) added during emulsion polymerization is preferably 0.01 to 0.6 parts by mass, preferably 0.1 to 0.5 parts by mass, based on 100 parts by mass of the total amount of the monomers to be polymerized. Is more preferable. If the amount of sulfur (S ₈ ) is less than 0.01 parts by mass, the mechanical properties and dynamic properties of the obtained sulfur-modified chloroprene rubber may not be obtained. On the other hand, if _{the amount of sulfur (S 8} ) exceeds 0.6 parts by mass, the obtained sulfur-modified chloroprene rubber may become too adhesive to the metal and cannot be processed.

As the emulsifier used for emulsion polymerization, one or more known emulsifiers and fatty acids that can be used for emulsion polymerization of chloroprene can be freely selected and used. Specific examples of the emulsifier include logoic acids, metal salts of aromatic formalin sulphonate condensate, sodium dodecylbenzene sulphonate, potassium dodecylbenzene sulphonate, sodium alkyldiphenyl ether sulphonate, potassium alkyldiphenyl ether sulphonate, and polyoxyethylene. There are alkyl ether sodium sulphonate, polyoxypropylene alkyl ether sodium sulphonate, polyoxyethylene alkyl ether potassium sulphonate, polyoxypropylene alkyl ether potassium sulphonate and the like. Of these, it is particularly preferable to use rosin acids. Here, the rosin acids mean a rosin acid or a disproportionate rosin acid, an alkali metal salt of the disproportionate rosin acid, or a compound thereof. A preferably used emulsifier is an alkaline soap aqueous solution consisting of a mixture of an alkali metal salt of disproportionate logonic acid and a saturated or unsaturated fatty acid having 6 to 22 carbon atoms. Examples of the constituents of the disproportionate rosinic acid include sesquiterpen, 8,5-isopimaric acid, dihydropimaric acid, secodehydroabietic acid, dihydroabietic acid, deisopropyldehydroabietic acid, and demethyldehydroabietic acid.

The pH of the aqueous emulsion at the start of emulsion polymerization is preferably 10.5 or higher. Here, the aqueous emulsion, the emulsion polymerization immediately before the start of, chloroprene and chloroprene monomers copolymerizable with a mixture of emulsifier, sulfur (S ₈₎ or the like. Added after such these monomers and sulfur (S _8), it is also encompassed If dividing the composition varies by addition or the like. By setting the pH to 10.5 or higher, when rosin acids are used as emulsifiers, it is possible to prevent polymer precipitation during polymerization and stably control polymerization. The pH of the aqueous emulsion can be adjusted by the amount of alkaline components such as sodium hydroxide and potassium hydroxide present at the time of emulsion polymerization.

The polymerization temperature of 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 and the like, which are used in ordinary radical polymerization, can be used. The polymerization is carried out in a polymerization rate of 60 to 95%, preferably 70 to 90%, and then the polymerization is stopped by adding a polymerization stop.

From the viewpoint of productivity, the polymerization rate is preferably 60% or more. Further, the polymerization rate is preferably 95% or less from the viewpoint of suppressing the development of a branched structure and the formation of gel, which affect the processability of the obtained sulfur-modified chloroprene rubber. Examples of the polymerization inhibitor of the polymer include thiodiphenylamine, 4-tert-butylcatechol, 2,2'-methylenebis-4-methyl-6-3-butylphenol and the like. One type of polymerization inhibitor may be used alone, or two or more types may be used in combination.

<Plasticization process>
The plasticizing step, the sulfur-modified chloroprene polymer solution obtained in the polymerization step, was added imidazole, that polysulfide is present in the main chain bond were added and _(S 2 _{~S 8)} imidazole is reacted, This is a step of cleaving and depolymerizing the polymer in the polymerization solution while forming the terminal functional group (A) represented by the chemical formula 1 derived from the added imidazole. Hereinafter, a chemical used for cleaving and depolymerizing the polymer will be used as a plasticizer.

As the type of imidazole to be added, one or more known imidazoles can be freely used. In the present invention, in particular, 2-mercaptoimidazole, 2-mercaptobenzimidazole, N-cyclohexyl-1H-benzimidazole-2-sulfeneamide, 2-methoxycarbonylamino-benzimidazole, 2-mercaptomethylbenzimidazole, 2-mercapto- 5-methoxybenzimidazole, 2-mercapto-5-carboxybenzimidazole, 2-mercaptobenzimidazole-5-sodium sulfonate dihydrate, 2-mercapto-5-nitrobenzimidazole, 2-mercapto-5-aminobenz It is preferably at least one compound selected from imidazoles.

The amount of imidazole to be added is preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the polymer in the polymerization solution. By adding imidazole in an amount of 0.2 parts by mass or more, the scorch resistance of the obtained rubber composition, the compression resistance to permanent strain of the vulcanized product, and the wear resistance can be improved. Further, by setting the amount of imidazole added to 3 parts by mass or less, 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, a dithiocarbamic acid-based compound can also be used in combination as a plasticizing agent. In the polymer solution, the dithiocarbamic acid-based compound reacts with imidazole to form a reactant having higher reactivity with the polysulfide bond as compared with imidazole or the dithiocarbamic acid-based compound alone, facilitating the adjustment of Mooney viscosity. The reaction product reacts with the polysulfide bond in the sulfur-modified chloroprene rubber main chain to form the terminal functional group (A) and the terminal functional group (B) represented by the chemical formula 2 derived from the added dithiocarbamic acid-based compound. do. The rubber composition obtained by the plasticization step has good scorch resistance, and also has a good balance of physical properties of tensile strength, compression set resistance, and wear resistance of the obtained vulcanized product. As the dithiocarbamic acid-based compound to be added, one or more known dithiocarbamic acid-based compounds can be freely used, and in particular, dibenzyldithiocarbamic acid, sodium dibenzyldithiocarbamate, potassium dibenzyldithiocarbamate, and dibenzyl. Zinc dithiocarbamate, ammonium dibenzyldithiocarbamate, nickel dibenzyldithiocarbamate, sodium di-2-ethylhexyl dithiocarbamate, potassium di-2-ethylhexyl dithiocarbamate, calcium di-2-ethylhexyl dithiocarbamate, di-2-ethylhexyldithiocarbamate It is preferable to use at least one compound selected from zinc, ammonium di-2-ethylhexylcarbamate, tetrabenzylthiuram disulfide, and tetrakis (2-ethylhexyl) thiuram disulfide.

When a dithiocarbamic acid-based compound is used, the amount thereof is not particularly limited, but it is preferably added in an amount of 0 to 8 parts by mass, more preferably 0.5 to 4 parts based on 100 parts by mass of the polymer in the polymerization solution. be. By setting the addition amount of the dithiocarbamic acid-based compound within the above range, it becomes easier to control the Mooney viscosity of the obtained sulfur-modified chloroprene rubber, and the scorch resistance of the obtained rubber composition, the tensile strength of the vulcanized product, and the compression resistance Permanent strain resistance and wear resistance are further improved.

The latex of the polymer that has undergone the plasticization step is cooled, adjusted in pH, frozen, dried, etc. 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 thereof. In order to adjust the content of the terminal functional group (A), the amount of imidazole added in the plasticization step, the plasticization time in the plasticization step, and the plasticization temperature may be adjusted. By setting the content of the terminal functional group (A) within the range, it contributes to the improvement of the tensile strength, the compression set resistance and the wear resistance of the obtained vulcanized product.

The obtained sulfur-modified chloroprene rubber has 0.0005 to 0.01 parts by mass of unreacted imidazole remaining with respect to 100 parts by mass of the rubber composition to obtain scorch resistance and vulcanization thereof. Contributes to improving the tensile strength, compression set resistance and abrasion resistance of objects. In order to adjust the residual amount of unreacted imidazole, the amount of imidazole added in the plasticization step, the plasticization time and the plasticization temperature of the plasticization step may be adjusted.

When a dithiocarbamic acid-based compound is used in the plasticization step, the content of the terminal functional group (B) represented by the chemical formula 2 present in the obtained sulfur-modified chloroprene rubber is not particularly limited. For example, in the plasticization step, when 0 to 8 parts by mass of a dithiocarbamic acid-based compound is added to 100 parts by mass of the polymer in the polymer solution, the obtained sulfur-modified chloroprene rubber has 100 parts by mass of the dithiocarbamic acid-based compound. The terminal functional group (B) is contained in an amount of 0 to 0.8 parts by mass, and the unreacted alkylxanthogen disulfide is contained in an amount of 0 to 2 parts by mass. In order to adjust the content of the terminal functional group (B) and the amount of the unreacted dithiocarbamate-based compound, the amount of the dithiocarbamate-based compound added, the time of the plasticization step, and the plasticization temperature may be adjusted. By setting the content of the terminal functional group B within the above range, it contributes to the improvement of the scorch resistance of the obtained rubber composition and the tensile strength, compression permanent strain resistance and abrasion resistance of the vulcanized product.

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 12.0, and the terminal functional group (A) and the terminal functional group ( The total mass (A + B) of the content of B) is 0.1 to 1.0 parts by mass. If the mass ratio (B / A) exceeds 12, the scorch resistance of the obtained rubber composition and the tensile strength, compression set resistance and wear resistance of the vulcanized product are lowered. The scorch resistance of the rubber composition obtained when the total mass (A + B) is less than 0.1, and the tensile strength, compression set resistance and abrasion resistance of the vulcanized product are reduced, and the total mass (A + B) If it exceeds 1 part by mass, the decrease in Mooney viscosity of the obtained sulfur-modified chloroprene rubber is extremely impractical.

The content of the terminal functional group (A) and the terminal functional group (B) in the sulfur-modified chloroprene rubber can be quantified by the following procedure.
The obtained sulfur-modified chloroprene rubber was purified with benzene and methanol, and freeze-dried again to prepare a sample for measurement. The obtained measurement sample was subjected to ¹ H-NMR measurement according to JIS K-6239. The obtained measurement data was corrected based on the peak of chloroform (7.24 ppm) in deuterated chloroform as a solvent, and based on the corrected measurement data, 6.99 to 7.23 ppm and 5.05- Calculate the area of the peak having the peak top at 5.50 ppm.

Further, the ratio (D / C) of the content (C) of the unreacted imidazole to the content (D) of the unreacted dithiocarbamic acid-based compound is preferably 0 to 120. By setting the content ratio (D / C) within the range, the physical property balance of the scorch resistance of the obtained rubber composition and the tensile strength, compression set resistance and abrasion resistance of the vulcanized product can be improved. It will be even better.

The content (C) of unreacted imidazole in the sulfur-modified chloroprene rubber and the content (D) of the unreacted dithiocarbamic acid-based compound can be quantified by the following procedure.
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 precipitate a rubber component, which was separated from the solvent, and the non-rubber component was recovered as a solvent-soluble component. Benzene is dissolved and methanol is added dropwise to the precipitated polymer again in the same procedure to separate the rubber component, the non-rubber component is similarly recovered as a solvent-soluble component, and the first and second solvents are mixed. Then, the volume was adjusted to 200 ml, and this was used as a sample for measurement. 20 μL of the measurement sample was injected into a liquid chromatograph (LC Hitachi 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. The column used was Inertsil ODS-3 (φ4.6 × 150 mm, 5 μm, manufactured by GL Science). The peak detection time of imidazole (measurement wavelength: 300 nm) and dithiocarbamic acid-based compound (measurement wavelength: 280 nm) was confirmed with a standard solution, and a quantitative value was determined by a calibration curve obtained from the peak area. The contents of unreacted imidazole and unreacted dithiocarbamic acid-based compound in the sulfur-modified chloroprene rubber were determined by comparing this quantitative value with the amount of the sample used for the analysis.

The Mooney viscosity of the sulfur-modified chloroprene rubber is not particularly limited, but is preferably adjusted to the range of 20 to 80. By adjusting the Mooney viscosity of the sulfur-modified chloroprene rubber within 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 amount of the plasticizer added, the time of the plasticizing step, and the plasticizing temperature may be adjusted.

The sulfur-modified chloroprene rubber can also contain a small amount of stabilizer in order to prevent changes in Mooney viscosity during storage. As the type of stabilizer that can be used in the present invention, one or more known stabilizers that can be used for chloroprene rubber can be freely selected and used. For example, phenyl-α-naphthylamine, octylated diphenylamine, 2,6-di-terrary-butyl-4-phenylphenol, 2,2'-methylenebis (4-methyl-6-terrary-butylphenol), and 4, There are 4'-thiobis- (6-terriary-butyl-3-methylphenol) and the like. Of these stabilizers, 4,4'-thiobis- (6-tertiary-butyl-3-methylphenol) is preferred.

<Carbon black>
Carbon black is added to sulfur-modified chloroprene rubber in order to improve the wear resistance and tensile strength of the obtained vulcanized product. The average particle size of carbon black observed with an electron microscope in accordance with JIS Z8901 is preferably 70 nm or less, and more preferably 20 nm to 50 nm. If the average particle size is out of the above range, a sufficient reinforcing effect cannot be obtained and the tensile strength and wear resistance of the vulcanized product cannot be improved.

Further, the carbon black preferably has an absorption amount of dibutyl phthalate (hereinafter referred to as DBP) of 80 ml / 100 g to 150 ml / 100 g in accordance with the oil absorption amount A method of JIS K6217-4, and more preferably 100 ml / 100 g to 140 ml /. It is 100 g. If the amount of DBP absorbed exceeds 150 ml / 100 g, the scorch resistance of the rubber composition and the tensile strength of the vulcanized product are lowered. If the amount of DBP absorbed is less than 80 ml / 100 g, the wear resistance of the vulcanized product will not be improved.

In addition, the carbon black preferably has an iodine adsorption amount of 40 ml / g to 150 ml / g, more preferably 50 ml / g to 150 ml / g, in accordance with JIS K6217-1. If the iodine adsorption amount exceeds 150 ml / g, the scorch resistance of the rubber composition and the compression permanent strain resistance of the vulcanized product decrease, and if it is less than 40 ml / g, the wear resistance and tensile strength of the vulcanized product improve. do not.

The amount of carbon black added is 25 to 55 parts by mass with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. If the blending amount of carbon black is less than 25 parts by mass, the wear resistance and tensile strength of the obtained vulcanized product will not be improved, and if it exceeds 55 parts by mass, the scorch resistance of the obtained rubber composition will be lowered. It ends up. The amount of carbon black added is preferably 25 to 45 parts by mass, more preferably 30 to 40 parts by mass. Within these ranges, the scorch resistance of the obtained rubber composition, the wear resistance of the vulcanized product, and the tensile strength are further improved, which is preferable.

<Diene rubber>
Diene-based rubbers other than chloroprene rubber are added in order to improve the wear resistance of the obtained vulcanized product. The diene rubber used in the present invention is not particularly limited, and a known diene rubber can be used. Among them, a diene rubber selected from at least one of butadiene rubber, styrene-butadiene rubber, and nitrile rubber is used. It is preferable to use it.

In the present invention, a diene rubber other than the chloroprene rubber is contained in an amount of 4 to 16 parts by mass with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. If the content is less than 4 parts by mass, a sufficient effect of improving wear resistance cannot be obtained, and if it exceeds 16 parts by mass, a sufficient reinforcing effect cannot be obtained and the tensile strength cannot be improved.

<Vulcanized products / molded products>
The vulcanized product and the molded product are prepared by mixing the above-mentioned rubber composition with a metal compound, a thermoplastic agent, etc. with a roll or a Banbury mixer, and then molding the vulcanized product into a shape according to the purpose, during or after molding. It is obtained by vulcanization. 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 body is a transmission belt, a conveyor belt, an air spring, a seal, a packing, a vibration-proof material, a hose, a rubber roll, or the like, it can be formed by press molding, injection molding, extrusion molding, or the like.

The metal compound is added to adjust the vulcanization rate of the rubber composition and to suppress deterioration of the rubber composition by adsorbing a chlorine source such as hydrogen chloride generated by the dehydrochloric acid reaction of the rubber composition. Is. As the metal compound, for example, oxides and hydroxides such as zinc, titanium, magnesium, lead, iron, beryllium, calcium, barium, germanium, zirconium, vanadium, molybdenum, and tungsten can be used. These metal compounds may be used alone or in combination of two or more.

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 added within this range, the mechanical strength of the obtained rubber composition can be improved.

The plasticizer is added to reduce the hardness of the rubber composition and improve its low temperature properties. Further, when a sponge is produced using the rubber composition, its texture can be improved. Examples of the plasticizer include dioctyl phthalate, dioctyl adipate {bis (bis (2-ethylhexyl) adipate}), white oil, silicon oil, naphthenic oil, aroma oil, triphenyl phosphate, and tricresyl phosphate. .. These plasticizers may be used alone or in combination of two or more.

The amount of the plasticizer 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 added within this range, the above-mentioned effects can be exhibited while maintaining the tear strength of the obtained rubber composition.

Hereinafter, application examples of the rubber composition will be described.
(Conveyor belt)
A conveyor belt is a mechanical element used in a winding transmission device, and is a component that transmits power from a prime mover to a driven vehicle. It is often used over a pulley set on a shaft. Since belts are continuously used in a dynamic environment, materials with excellent wear resistance, tensile strength, and compression set resistance are required in order to improve product reliability.

The rubber composition of the present invention can enhance the scorch resistance and wear resistance, tensile strength and compression set resistance of the conveyor belt. This makes it possible to manufacture a conveyor belt having excellent productivity and durability as compared with the conventional sulfur-modified chloroprene rubber.

Hereinafter, the present invention will be described in more detail based on Examples. It should be noted that the examples described below show an example of a typical example of the present invention, and the scope of the present invention is not narrowly interpreted by this.

<Example 1>
<Sulfur-modified chloroprene rubber>
In a polymer can with 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 potassium disproportionate (manufactured by Harima Kasei Co., Ltd.), 0 parts of sodium hydroxide .60 parts by mass and 0.6 parts by mass of a sodium salt of β-naphthalene sulfonate formarin condensate (trade name: Demor N: manufactured by Kao Co., Ltd.) were added. The pH of the aqueous emulsifier before the start 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%, a polymerization terminator, diethylhydroxyamine, was added to terminate the polymerization to obtain a chloroprene polymerization solution.

In the obtained polymer solution, 5 parts by mass of chloroprene monomer as a solvent, 1 part by mass of 2-mercaptobenzimidazole (trade name "Nocrack MB" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) as a plasticizer, and tetrabenzylthium disulfide. (Product name "Noxeller TBzTD" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) From 4 parts by mass, 0.05 parts by mass of sodium salt of β-naphthalene sulfonate formalin condensate as emulsifier, 0.05 parts by mass of sodium lauryl sulfate as emulsifier A plasticizer emulsion was added to obtain a sulfur-modified chloroprene polymer latex before plasticization.

Here, the sodium salt of the β-naphthalene sulfonic acid formalin condensate is a general-purpose emulsifier, and the stability is improved by adding a small amount, and the latex is stable without agglutination or precipitation in the manufacturing process. Can be manufactured. Further, in this example, a plasticizer is added to the polymerization solution after emulsion polymerization. At that time, in order to enable more stable plasticization, the plasticizer is dissolved in chloroprene added as a solvent. An emulsified state was added by adding sodium lauryl sulfate to the plasticizer solution.

The obtained sulfur-modified chloroprene polymer latex was distilled under reduced pressure to remove unreacted monomers, and the latex was held at a temperature of 50 ° C. for 1 hour with stirring to plasticize the latex (hereinafter, the latex after plasticization). This plasticized latex is abbreviated as "latex").

The obtained latex was cooled, and the polymer was isolated by a conventional freeze-coagulation method to obtain a sulfur-modified chloroprene rubber.
The terminal functional group of the obtained sulfur-modified chloroprene rubber contains 0.13 parts by mass of the terminal functional group (A) derived from 2-mercaptobenzimidazole represented by Chemical Formula 3 with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. , The terminal functional group (B) derived from tetrabenzylthium disulfide represented by Chemical Formula 4 was 0.29 parts by mass. The mass ratio (B / A) of the terminal functional groups was 2.2, and the total mass (A + B) was 0.42 parts by mass.

<Measurement of Mooney viscosity>
The sulfur-modified chloroprene rubber (raw rubber) obtained above was measured for Mooney viscosity at a preheating time of 1 minute, a rotation time of 4 minutes, and a test temperature of 100 ° C. of an L-shaped rotor in accordance with JIS K 630-1. rice field.

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

The compounds listed in Table 1 are as follows: Butadiene rubber: BR01 manufactured by JSR Corporation
Lubricants / processing aids 1: Stearic acid 50S manufactured by NEW JAPAN CHEMICAL CO., LTD.
Anti-aging agent 1: Nocrack AD-F manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Anti-aging agent 2: Nocrack 810-NA manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Magnesium oxide: Kyowa Mug 30 manufactured by Kyowa Chemical Industry Co., Ltd.
Filler: Shiraishi Calcium Co., Ltd. Crown Clay Flame Retardant 1: Showa Denko Co., Ltd. Heidi Light H-42M
Flame Retardant 2: Ajinomoto Fine Techno Co., Ltd. Empara 70
Flame Retardant 3: Ajinomoto Fine Techno Co., Ltd. Empara 40
Vulcanizing agent: Zinc oxide type 2 vulcanization accelerator manufactured by Sakai Chemical Industry Co., Ltd. 1: Accelerator 22S manufactured by Kawaguchi Chemical Industry Co., Ltd.
Vulcanization accelerator 2: Noxeller DM manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.
Carbon Black A: 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 the sulfur-modified chloroprene rubber obtained by changing the addition amount of the plasticizer was used.

<Example 9>
A sulfur-modified chloroprene rubber obtained by changing the addition amount of 2-mercaptobenzimidazole as a plasticizing agent from 1 part by mass to 0.3 part by mass and changing the holding time of plasticization from 1 hour to 3 hours was used. An evaluation sample was prepared in the same manner as in Example 1 except for the above.

<Example 10>
A sulfur-modified chloroprene rubber obtained by changing the addition amount of 2-mercaptobenzimidazole as a plasticizing agent from 1 part by mass to 1.5 parts by mass and changing the retention time of plasticization from 1 hour to 15 minutes was used. An evaluation sample was prepared in the same manner as in Example 1 except for the above.

<Example 11>
Except for using sulfur-modified chloroprene rubber obtained by changing the addition amount of diisopropylxanthogen disulfide, which is a plasticizing agent, from 2 parts by mass to 4 parts by mass, and changing the retention time of plasticization from 1 hour to 15 minutes. An evaluation sample was prepared in the same manner as in Example 1.

<Example 12>
An evaluation sample was prepared in the same manner as in Example 1 except that the butadiene rubber was changed to styrene-butadiene rubber (trade name "Nipol 1502" manufactured by Nippon Zeon Corporation).

<Example 13>
An evaluation sample was prepared in the same manner as in Example 1 except that the butadiene rubber was changed to nitrile rubber (trade name "Nipol 1041" manufactured by Nippon Zeon Corporation).

<Example 14>
Except for using sulfur-modified chloroprene rubber obtained by changing 2-mercaptobenzimidazole to 2-mercapto-5-carboxybenzimidazole: (trade name "2MB5C" manufactured by Kawaguchi Chemical Industry Co., Ltd.) as a plasticizing agent. An evaluation sample was prepared in the same manner as in Example 1. The terminal functional groups of the obtained sulfur-modified chloroprene rubber are 2-mercapto-5 represented by the chemical formula 5 in addition to 0.33 parts by mass of the dithiocarbamic acid terminal species A derived from the tetrabenzyl thiuram disulfide represented by the chemical formula 4. -Imidazole terminal species B derived from carboxybenzimidazole was 0.14 parts by mass.

<Example 15>
As a plasticizer, sulfur-modified chloroprene rubber obtained by changing tetrabenzyl thiuram disulfide to tetrakis (2-ethylhexyl) thiuram disulfide: (trade name "Noxeller TOT-N" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) was used. An evaluation sample was prepared in the same manner as in Example 1 except for the above. The terminal functional groups of the obtained sulfur-modified chloroprene rubber contained 0.15 parts by mass of imidazole terminal species A derived from 2-mercaptobenzimidazole represented by the chemical formula 3 and tetrakis (2-) represented by the chemical formula 6. Dithiocarbamic acid terminal species B derived from (ethylhexyl) thiuram disulfide was 0.25 parts by mass.

<Example 16>
Except for the use of sulfur-modified chloroprene rubber obtained by changing 2-mercaptobenzimidazole to 2-mercapto-5-carboxybenzimidazole and tetrabenzyl thiuram disulfide to tetrakis (2-ethylhexyl) thiuram disulfide as a plasticizing agent. , An evaluation sample was prepared in the same manner as in Example 1. The terminal functional group of the obtained sulfur-modified chloroprene rubber is represented by the chemical formula 6 with 0.15 parts by mass of the imidazole terminal species B derived from 2-mercapto-5-carboxybenzimidazole represented by the chemical formula 5. Dithiocarbamic acid terminal species B derived from tetrakis (2-ethylhexyl) thiuram disulfide was 0.32 parts by mass.

<Comparative example 4>
Examples except that sulfur-modified chloroprene rubber obtained by changing 2-mercaptobenzimidazole and diisopropylxanthogen disulfide to tetraethylthiuram disulfide and changing the addition amount to 2.5 parts by mass was used as a plasticizing agent. An evaluation sample was prepared in the same manner as in 1. The terminal functional group of the obtained sulfur-modified chloroprene rubber had 0.26 parts by mass of the terminal functional group derived from tetraethylthiuram disulfide represented by Chemical Formula 7.

<Example 17>
Examples except that carbon black A was changed to carbon black B (trade name "Asahi # 60UG" manufactured by Asahi Carbon Co., Ltd., average particle diameter 43 nm, iodine adsorption amount 40 mg / g, DBP absorption amount 110 ml / 100 g) as a filler. An evaluation sample was prepared in the same manner as in 1.

<Example 18>
Examples except that carbon black A was changed to carbon black C (trade name "Asahi # 95" manufactured by Asahi Carbon Co., Ltd., average particle diameter 17 nm, iodine adsorption amount 150 mg / g, DBP absorption amount 127 ml / 100 g) as a filler. An evaluation sample was prepared in the same manner as in 1.

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

<Example 20>
Implemented except that carbon black A was changed to carbon black E (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) as a filler. An evaluation sample was prepared in the same manner as in Example 1.

<Example 21>
Examples except that carbon black A was changed to carbon black F (trade name "Asahi # 70L" manufactured by Asahi Carbon Co., Ltd., average particle diameter 27 nm, iodine adsorption amount 85 mg / g, DBP absorption amount 75 ml / 100 g) as a filler. An evaluation sample was prepared in the same manner as in 1.

<Comparative example 5>
An evaluation sample was prepared in the same manner as in Example 1 except that the amount of butadiene rubber added was changed from 8 parts by mass to 16 parts by mass.

<Comparative Example 6>
An evaluation sample was prepared in the same manner as in Example 1 except that butadiene rubber was not added.

<Comparative Example 7>
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 8>
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 9>
Example 1 except that carbon black A was changed to carbon black G (trade name "Asahi Thermal" manufactured by Asahi Carbon Co., Ltd., average particle diameter 80 nm, iodine adsorption amount 24 mg / g, DBP absorption amount 28 ml / 100 g) as a filler. An evaluation sample was prepared in the same manner as in the above.

<Evaluation of scorch resistance>
The sulfur-modified chloroprene rubber (raw rubber) produced above was subjected to a Mooney scorch test in accordance with JIS K 630-1.

<Measurement of tensile strength>
For the evaluation sample prepared above, a test piece was prepared based on JIS K 6250 (vulcanization conditions: 160 ° C. x 20 minutes), and a tensile test was performed based on JIS K 6251 to determine the tensile strength of each vulcanized product. It was measured.

<Measurement of compression set>
The evaluation sample prepared above was measured at 100 ° C. for 72 hours in accordance with JIS K 6262.

<Evaluation of wear resistance>
The evaluation sample prepared above was subjected to a DIN wear test in accordance with JIS K 6264-2.

<Result>
The results of Examples and Comparative Examples are shown in Tables 1 to 3 below.

<Discussion>
As shown in Tables 1 to 3, it was confirmed that the evaluation samples of Examples 1 to 21 were excellent in scorch resistance, tensile strength, compression set resistance, and abrasion resistance.
Even if imidazole is used, the Mooney viscosity is too low for Comparative Example 1 in which the total content (A + B) of the terminal functional groups in the raw rubber exceeds 0.6 parts by mass, and an evaluation sample can be prepared. There wasn't.

Claims (14)

A sulfur-modified chloroprene rubber having at least one of the structures represented by the chemical formulas 1 and 2 at the molecular end, the terminal functional group (A) represented by the chemical formula 1 and the terminal functional group represented by the chemical formula 2. The mass ratio (B / A) of (B) is 0 to 12.0, 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. With 100 parts by mass of sulfur-modified chloroprene rubber, which is ~ 1.0 parts by mass,
25 to 55 parts by mass of carbon black with an average particle size of 70 nm or less,
A rubber composition containing 4 to 12 parts by mass of a diene rubber other than chloroprene rubber.

(In Formula 1, R _1, R ₂ are each a hydrogen atom, a halogen atom, hydroxy group, .R ₁ showing a cyano group or an optionally substituted alkyl group, an arylthio group which may have a substituent , R ₂ may be the same or different, and R ₁ and R ₂ may be bonded to each other to form a ring having a substituent.)

(In the chemical formula 2, R ₃ and R ₄ indicate an alkyl group having 7 to 8 carbon atoms which may have a substituent. R ₃ and R ₄ may be the same or different, respectively.) The rubber composition according to claim 1, wherein the amount of the terminal functional group (A) in 100 parts by mass of the sulfur-modified chloroprene rubber is 0.05 to 0.4 parts by mass. The rubber composition according to claim 1 or 2, wherein the amount of the terminal functional group (B) in 100 parts by mass of the sulfur-modified chloroprene rubber is 0 to 0.8 parts by mass. The rubber composition according to any one of claims 1 to 3, further containing 0.005 to 0.2 parts by mass of imidazole with respect to 100 parts by mass of sulfur-modified chloroprene rubber. The imidazoles are 2-mercaptoimidazole, 2-mercaptobenzimidazole, N-cyclohexyl-1H-benzimidazol-2-sulfeneamide, 2-methoxycarbonylamino-benzimidazole, 2-mercaptomethylbenzimidazole, 2-mercapto-5. −methoxybenzimidazole, 2-mercapto-5-carboxybenzimidazole, 2-mercaptobenzimidazole-5-sodium sulfonate dihydrate, 2-mercapto-5-nitrobenzimidazole, 2-mercapto-5-aminobenzimidazole The rubber composition according to claim 4, which is at least one compound selected from. The rubber composition according to any one of claims 1 to 5, further comprising 0 to 2 parts by mass of tetraalkylthiuram disulfide or dialkyldithiocarbamate with respect to 100 parts by mass of sulfur-modified chloroprene rubber. Tetraalkyl thiuram disulfide is at least one compound selected from tetrabenzyl thiuram disulfide and tetrakis (2-ethylhexyl) thiuram disulfide, and dialkyl dithiocarbamate is dibenzyl dithiocarbamic acid, sodium dibenzyl dithiocarbamate, dibenzyl dithiocarbamic acid. Potassium, zinc dibenzyldithiocarbamate, ammonium dibenzyldithiocarbamate, nickel dibenzyldithiocarbamate, sodium di-2-ethylhexyl dithiocarbamate, potassium di-2-ethylhexyl dithiocarbamate, calcium di-2-ethylhexyl dithiocarbamate, di-2 The rubber composition according to claim 6, which is at least one compound selected from zinc ethylhexyldithiocarbamate and ammonium di-2-ethylhexylcarbamate. The rubber composition according to claim 6 or 7, wherein the mass ratio (D / C) of thiazole (C) and alkylxanthate disulfide (D) contained in the rubber composition is 0 to 120. The rubber composition according to any one of claims 1 to 8, wherein the diene-based rubber other than the chloroprene rubber is at least one diene-based rubber selected from butadiene rubber, styrene-butadiene rubber, and nitrile rubber. The rubber composition according to any one of claims 1 to 9, wherein the DBP absorption amount of the carbon black is 80 to 150 ml / 100 g. The rubber composition according to any one of claims 1 to 10, wherein the carbon black has an iodine adsorption amount of 40 to 150 mg / g. The rubber composition according to any one of claims 1 to 11, wherein the sulfur-modified chloroprene rubber has a Mooney viscosity of 20 to 80. A vulcanized product comprising the rubber composition according to any one of claims 1 to 12. A molded product made of the vulcanized product according to claim 13.