JP2020196786A - Rubber composition, vulcanizate thereof, and molded article - Google Patents

Abstract

To provide a sulfur-modified chloroprene rubber which gives a vulcanizate having excellent wear resistance and scorch resistance and reduced heat build-up properties.SOLUTION: A rubber composition contains, based on 100 pts.mass of the sulfur-modified chloroprene rubber, 0.0005-0.01 pt.mass of a sulfenamide which may have an arbitrary substituent and 25-55 pts.mass of carbon black having an average particle diameter of 15-80 nm. The sulfenamide is preferably one represented by the following chemical formula (1) (where R1 and R2 each independently represent hydrogen or a C1-10 alkyl group; and R1 and R2 may be the same as or different from each other).SELECTED DRAWING: None

Description

Chloroprene-based 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 improvement of mechanical properties, ozone resistance and chemical resistance, reduction of heat generation of rubber, scorch resistance and abrasion resistance Sex is also required.

Techniques for reducing the heat generation of rubber include elastomers such as acrylonitrile-butadiene copolymer rubber, 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-generating rubber composition containing an organic peroxide-based cross-linking agent (see Patent Document 1) is known. Further, a rubber composition containing a specific low heat-generating carbon black in the rubber component (see Patent Document 2), a high molecular weight component having a predetermined property, and a low molecular weight component having a predetermined property are mixed. The obtained modified conjugated diene polymer (see Patent Document 3) is known.

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

Japanese Unexamined Patent Publication No. 9-268239 Japanese Unexamined Patent Publication No. 10-130424 Japanese Unexamined Patent Publication No. 2010-121086 Japanese Unexamined Patent Publication No. 2016-141736

However, there is a problem that the techniques described in Patent Documents 1 to 4 alone are excellent in scorch resistance and wear resistance, and cannot reduce heat generation.

Therefore, it is a main object of the present invention to provide a rubber composition, a vulcanized body and a molded product thereof, which can obtain a vulcanized product having excellent scorch resistance and wear resistance and reduced heat generation. ..

As a result of diligent research to solve this problem, the inventors of the present application have made sulfur-modified chloroprene rubber contain a sulfenamide compound, and set the average particle size of carbon black used as a filler to a specific range. By doing so, we succeeded in reducing the heat generation while being excellent in scorch resistance and abrasion resistance, and completed the present invention.

That is, in the present invention, the amount of sulfenamide which may have an arbitrary substituent is 0.0005 to 0.01 parts by mass with respect to 100 parts by mass of the sulfur-modified chloroprene rubber.
It is a rubber composition containing 25 to 55 parts by mass of carbon black having an average particle size of 15 to 80 nm.
As the sulfenamide contained in the sulfur-modified chloroprene rubber composition according to the present technology, a sulfenamide represented by the following chemical formula (1) can be used.
(In the chemical formula (1), R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 10 carbon atoms. Each of R ¹ and R ² may be the same or different.)
The sulfur-modified chloroprene rubber composition according to the present technology contains 0.1 to 1.5 parts by mass of xanthogen disulfide which may have an arbitrary substituent with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. You can also.
In this case, as the xanthate disulfide, a xanthate disulfide represented by the following chemical formula (2) can be used.
(In the chemical formula (2), R ³ and R ⁴ independently represent alkyl groups having 1 to 4 carbon atoms. Each of R ³ and R ⁴ may be the same or different.)
When xanthogen disulfide is used in the sulfur-modified chloroprene rubber composition according to the present technology, the ratio (B / A) of the sulfenamide content (A) to the xanthate disulfide content (B) is 20 to 20 to A. It can be 2000.
The Mooney viscosity of the sulfur-modified chloroprene rubber can be 20 to 80.

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

The present invention provides a vulcanized product obtained by vulcanizing the above-mentioned rubber composition, and a molded product obtained by vulcanizing the rubber composition after or during molding.

According to the present invention, it is possible to obtain a rubber composition, a vulcanized product and a molded product thereof, which can obtain a vulcanized product having excellent scorch resistance and wear resistance and reduced heat generation.

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.

The sulfur-modified chloroprene rubber according to the present invention is a main chain obtained by emulsifying and polymerizing 2-chloro-1,3-butadiene (hereinafter, also referred to as "chloroprene") alone or chloroprene and another monomer in the presence of sulfur. It includes a latex obtained by plasticizing a sulfur-modified chloroprene polymer into which sulfur is introduced using sulfenamide, and a sulfur-modified chloroprene rubber obtained by drying and washing this latex by a general method. Hereinafter, the details will be described along with the manufacturing process of the sulfur-modified 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. A latex obtained by plasticizing the obtained sulfur-modified chloroprene polymer with sulfenamide which may have an arbitrary substituent, and a sulfur-modified chloroprene rubber obtained by drying and washing this latex by a general method. Including. Hereinafter, the details will be described along with the manufacturing process of the sulfur-modified chloroprene rubber.

<Polymerization process>
The sulfur-modified chloroprene rubber is obtained 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, they are preferably used within a range that does not impair the characteristics of the obtained sulfur-modified chloroprene rubber, and are 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 processing characteristics may be deteriorated.

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, sodium dodecylbenzene sulphonate, potassium dodecylbenzene sulphonate, sodium alkyldiphenyl ether sulphonate, potassium alkyldiphenyl ether sulphonate, and polyoxyethylene. Sodium alkyl ether sulphonate, sodium polyoxypropylene alkyl ether sulphonate, potassium polyoxyethylene alkyl ether sulphonate, potassium polyoxypropylene alkyl ether sulphonate and the like. Of these, it is particularly preferable to use rosin acids. Here, the rosin acids mean rosin acid or disproportionate rosin acid, an alkali metal salt of disproportionate rosin acid, or a compound thereof. A preferably used emulsifier is an aqueous alkaline soap solution consisting of a mixture of an alkali metal salt of unbalanced 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 sesquiterpenes, 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 monomer 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 a polymerization inhibitor is added to terminate the polymerization.

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 gel formation that 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>
In the plasticization step, sulfenamide which may have an arbitrary substituent is added to the polymerization solution obtained in the polymerization step, and the polymer in the polymerization solution is plasticized by the sulfenamide. Is.

As the type of sulfenamide to be added, one or more known sulfenamides can be freely used as long as the effects of the present technology are not impaired. In this technique, it is particularly preferable to use sulfenamide represented by the chemical formula (1).

The amount of sulfenamide to be added is 0.2 to 3.0 parts by mass with respect to 100 parts by mass of the polymer in the polymerization solution. By setting the addition amount of sulfenamide to 0.2 parts by mass or more, the wear resistance of the vulcanized product can be improved, and the compression set and heat generation can be reduced. Further, by setting the addition amount of sulfenamide to 3.0 parts by mass or less, the Mooney viscosity of the obtained sulfur-modified chloroprene rubber becomes appropriate, and as a result, the vulcanization moldability can be improved.

In the plasticization step, it is also possible to use xanthogen disulfide which may have an arbitrary substituent in combination. By using xanthogen disulfide, it becomes easy to control the Mooney viscosity of the sulfur-modified chloroprene rubber, and the physical property balance of the obtained vulcanized product with abrasion resistance, compression set, and heat generation becomes good. As the type of xanthogen disulfide to be added, one or more known xanthogen disulfides can be freely used as long as the effects of the present technology are not impaired. In this technique, it is particularly preferable to use the xanthate disulfide represented by the chemical formula (2).

When xanthogen disulfide is used, the amount to be added is not particularly limited, but in the present technology, it is preferable to add 0.3 to 6.0 parts by mass with respect to 100 parts by mass of the polymer in the polymerization solution. By setting the amount of xanthogen disulfide added within this range, it becomes easier to control the Mooney viscosity of the sulfur-modified chloroprene rubber, the wear resistance of the obtained vulcanized product is further improved, and the compression set and heat generation are further improved. It will be reduced.

Further, it is preferable that the ratio (b / a) of the addition amount (a) of sulfenamide to the addition amount (b) of xanthogen disulfide is 0.2 to 30.0. By setting the ratio of the addition amount (b / a) to the above range, the physical property balance of the wear resistance, the compression set, and the heat generation of the vulcanized product is further improved.

The polymer solution 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 0.0005 to 0.01 parts by mass of unreacted sulfenamide with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. By setting the content of sulfenamide within the above range, the scorch resistance and wear resistance of the vulcanized product are improved, which contributes to the reduction of heat generation.

When xanthogen disulfide which may have an arbitrary substituent is used in the plasticizing step, the content of unreacted xanthogen disulfide present in the obtained sulfur-modified chloroprene rubber is not particularly limited. For example, when 0.3 to 6.0 parts by mass of xanthogen disulfide is added to 100 parts by mass of the polymer in the polymerization solution in the plasticization step, the obtained sulfur-modified chloroprene rubber is sulfur-modified. Unreacted xanthogen disulfide is contained in an amount of 0.1 to 1.5 parts by mass with respect to 100 parts by mass of chloroprene rubber. By setting the content of xanthogen disulfide within the above range, the scorch resistance and wear resistance of the obtained vulcanized product are improved, which contributes to further reduction of heat generation.

The ratio (B / A) of the sulfenamide content (A) to the xanthate disulfide content (B) is preferably 20 to 2000. By setting the content ratio (B / A) within the range, the physical property balance of scorch resistance, wear resistance and heat generation of the obtained vulcanized product is further improved.

[Analysis of the content of plasticizers (compounds represented by chemical formulas (1) and (2))]
The content of the compounds represented by the chemical formulas (1) and (2) in the sulfur-modified chloroprene rubber can be quantified by the following procedure.
After 1.5 g of the obtained sulfur-modified polychloroprene rubber is dissolved in 30 ml of benzene, 60 ml of methanol is added dropwise to precipitate the rubber component, separate it from the solvent, and recover the non-rubber component as a solvent-soluble component. Benzene is dissolved and methanol is added dropwise to the precipitated polymer in the same procedure, the rubber component is separated, the non-rubber component is similarly recovered as a solvent-soluble component, and the first and second solvents are mixed. Then, the volume is adjusted to 200 ml, and this is used as a measurement sample. Inject 20 μL of the measurement sample into a liquid chromatograph (LC Hitachi pump: L-6200, L-600 UV detector: L-4250). The mobile phase of LC is used while changing the ratio of acetonitrile and water, and is flowed at a flow rate of 1 ml / min. As the column, Inertsil ODS-3 (φ4.6 × 150 mm, 5 μm, manufactured by GL Science) is used. The peak detection time of sulfenamide (measurement wavelength: 300 nm) and xanthogen disulfide (measurement wavelength: 280 nm) is confirmed with a standard solution, and a quantitative value is obtained from the calibration curve obtained from the peak area. The contents of the chemical formulas (1) and (2) are 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 in 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 a change 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-tersary-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 of the obtained molded product. The carbon black preferably has an average particle size of 15 nm to 80 nm, and more preferably 20 nm to 50 nm, as observed with an electron microscope in accordance with 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 obtained vulcanized product cannot be improved.

Further, the carbon black preferably has an absorption amount of dibutyl phthalate (hereinafter referred to as DBP) of 50 ml / 100 g to 150 ml / 100 g in accordance with the oil absorption amount A method of JIS K6217-4, and more preferably 80 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 is lowered, which causes an increase in heat generation of the rubber composition in a dynamic environment. If the amount of DBP absorbed is less than 50 ml / 100 g, the wear resistance of the obtained vulcanized product is not improved.

In addition, the carbon black preferably has an iodine adsorption amount of 20 ml / g to 150 ml / g in accordance with JIS K6217-1, and more preferably 50 ml / g to 150 ml / g. If the amount of iodine adsorbed is less than 20 ml / g, the wear resistance of the obtained vulcanized product will not be improved.

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 amount of carbon black blended is less than 25 parts by mass, the wear resistance of the obtained vulcanized product is not improved, and if it exceeds 55 parts by mass, the scorch resistance of the obtained vulcanized product is lowered. 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 wear resistance and scorch resistance of the obtained vulcanized product are further improved, which is preferable.

<Vulcanized products / molded products>
For vulcanized products and molded products, the above-mentioned rubber compositions, metal compounds, plasticizers, etc. are mixed with a roll or a Banbury mixer, and then molded into a shape suitable for the purpose, and vulcanized during or after molding. It is obtained by 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 or to adsorb a chlorine source such as hydrogen chloride generated by the dehydrochlorination reaction of the rubber composition to suppress deterioration 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. One of these metal compounds may be used alone, or two or more thereof may be used in combination.

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.

Plasticizers are 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, silicone 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.
(Transmission belt)
A transmission 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. It is widely used in general machinery such as automobiles and general industries because it is lightweight, quiet, and has a degree of freedom in shaft angle. The types of belts are also diversified, and flat belts, conveyor belts, timing belts, V-belts, rib belts, round belts, etc. are used properly according to the machine application. Elastomer materials such as natural rubber, styrene-butadiene rubber, chloroprene rubber, nitrile rubber, and hydride nitrile rubber are used because the belt applied with high tension repeats rotational deformation in order to efficiently transmit power. .. Chloroprene rubber is used for automobiles, general industry, etc. because of its excellent rubber properties, but it is known that chloroprene rubber often causes scorch at the molding stage, and extending scorch time is an important technique. It is an issue. Further, since the belt is continuously used in a dynamic environment, a material having excellent wear resistance and heat resistance is required in order to improve the reliability of the product.

The rubber composition of the present invention can enhance the scorch resistance, wear resistance, and heat resistance of the transmission belt. This makes it possible to manufacture a belt having excellent productivity and durability, which was 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 for air suspension of automobiles, buses, trucks, etc. There are bellows type and three-leaf type (a type of diaphragm type), both of which can invade the piston into the air chamber to increase the air pressure. It is known that chloroprene rubber often causes scorch at the molding stage, and extending the scorch time is an important technical issue. Further, since the air spring is continuously used in a dynamic environment, a material having excellent wear resistance and heat resistance is required in order to improve the reliability of the product.

The rubber composition of the present invention can enhance the scorch resistance, wear resistance and heat generation resistance of the air spring. This makes it possible to manufacture an air spring having excellent productivity and durability, which was difficult with conventional sulfur-modified chloroprene rubber.

(hose)
A hose is a bendable pipe that bends freely when watering, 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 fracture due to deformation, so it is used for pipes in parts with vibration such as automobile pipes. Among them, the most common is the rubber hose. Rubber hoses include high / low pressure hoses for water supply, oil supply, air supply, steam, and hydraulic pressure. Chloroprene rubber is mainly used in high-pressure hoses for flood control because of its good mechanical properties that can withstand the pressure of high-pressure fluids.

The rubber composition of the present invention can enhance the scorch resistance, wear resistance and heat resistance of a hose. This makes it possible to manufacture an air spring having excellent productivity and durability, which was difficult with 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 polymerization 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 disproportionated potassium rosinate (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 sulfonic acid formarin condensate (trade name: Demol 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.

5 parts by mass of chloroprene monomer as a solvent and 1 mass of N-cyclohexylbenzothiazole-2-sulfenamide (trade name "Noxeller CZ" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) as a plasticizer in the obtained polymer solution 2 parts by mass and diisopropylxanthogen disulfide (trade name "Sanbit DIX" manufactured by Sanshin Chemical Industry Co., Ltd.), 0.05 parts by mass of sodium salt of β-naphthalene sulfonic acid formalin condensate as dispersant, sodium lauryl sulfate as emulsifier A plasticizer emulsion consisting of 0.05 parts by mass 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 dispersant used for general purposes, and its stability is improved by adding a small amount, and it is stable without aggregation or precipitation in the manufacturing process. Latex can be produced. 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 to obtain a plasticized latex (hereinafter referred to as “latex”). 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.

<Measurement of Mooney viscosity>
With respect to the sulfur-modified chloroprene rubber obtained above, the Mooney viscosity was measured at a preheating time of 1 minute, a rotation time of 4 minutes, and a test temperature of 100 ° C. of the L-shaped rotor in accordance with JIS K 630-1.

<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: Lubricants / Processing aids 1: Stearic acid 50S manufactured by New Japan Chemical Co., Ltd.
Anti-aging agent: Nocrack AD-F manufactured by Ouchi Shinko Kagaku Kogyo
Magnesium oxide: Kyowa Mug 30 manufactured by Kyowa Chemical Industry Co., Ltd.
Lubricants / Processing Aid 2: Amide AP-1 manufactured by Mitsubishi Chemical Corporation
Wax: Sannock vulcanizer manufactured by Ouchi Shinko Kagaku Co., Ltd .: Zinc oxide type 2 carbon black manufactured by Sakai Chemical Industry Co., Ltd. Asahi # 70 manufactured by Asahi Carbon Co., Ltd. Average particle size 28 nm, iodine adsorption amount 80 mg / g, DBP absorption amount 101ml / 100g

<Examples 2 to 6 and Comparative Examples 1 to 4>
Sulfur-modified chloroprene rubber was obtained by the same method as in Example 1 by the formulation shown in Tables 1 and 2 below.
The materials used in this example are as follows.
N-tert-Butylbenzothiazole-2-sulfenamide: (trade name "Sunceller NS-G" manufactured by Sanshin Chemical Industry Co., Ltd.)
Diethylxanthate disulfide: (manufactured by Sigma-Aldrich)
Tetraethyl thiuram disulfide: (trade name "Noxeller TET" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.)

<Example 7>
Same as 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 diameter 43 nm, iodine adsorption amount 40 mg / g, DBP absorption amount 110 ml / 100 g). An evaluation sample was prepared by the method.

<Example 8>
Same as 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 diameter 17 nm, iodine adsorption amount 150 mg / g, DBP absorption amount 127 ml / 100 g). An evaluation sample was prepared by the method.

<Example 9>
Same as 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 diameter 80 nm, iodine adsorption amount 23 mg / g, DBP absorption amount 63 ml / 100 g). An evaluation sample was prepared by the method.

<Example 10>
Same as 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 diameter 60 nm, iodine adsorption amount 19 mg / g, DBP absorption amount 128 ml / 100 g). An evaluation sample was prepared by the method.

<Example 11>
The same method 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 diameter 80 nm, iodine adsorption amount 24 mg / g, DBP absorption amount 28 ml / 100 g). An evaluation sample was prepared in.

<Example 12>
Same as 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 diameter 38 nm, iodine adsorption amount 55 mg / g, DBP absorption amount 180 ml / 100 g). An evaluation sample was prepared by the method of.

<Comparative example 5>
Same as 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). An evaluation sample was prepared by the method.

<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 20 parts by mass.

<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 60 parts by mass.

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

<Evaluation of scorch resistance>
Each sample prepared above was subjected to a Mooney scorch test in accordance with JIS K 630-1.

<Fever>
The evaluation of exothermic properties was performed by a Goodrich flexometer (JIS K 6265). The Goodrich flexometer is a test method in which a test piece such as vulcanized rubber is dynamically repeatedly loaded to evaluate the fatigue characteristics due to heat generation inside the test piece. Specifically, the test piece is subjected to a constant temperature condition. A static initial load is applied to the test piece, and a sine vibration of a constant amplitude is further applied to measure the heat generation temperature and creep amount of the test piece that change with the passage of time. The test method was based on JIS K 6265, and the calorific value (ΔT) was measured under the conditions of 50 ° C., strain 0.175 inches, load 55 pounds, and frequency 1,800 vibrations per minute.

<Result>
The results of the examples are shown in Table 1 below, and the results of the comparative examples are shown in Table 2 below.

<Discussion>
As shown in Tables 1 and 2, it was confirmed that the evaluation samples of Examples 1 to 12 were excellent in scorch resistance and wear resistance, and the heat generation was reduced. Even when sulfenamide was used, in Comparative Example 2 in which the content in the sulfur-modified chloroprene rubber exceeded 0.01 parts by mass, the Mooney viscosity was too low to prepare an evaluation sample.

Comparing with Examples, Example 3 in which xanthogen was not used was inferior in wear resistance and heat generation property to Example 1, and the ratio (B / A) of the xanthate disulfide content (B) was 2000 or more. Example 4 was inferior in scorch resistance, wear resistance, and heat generation.
Further, in Example 7, the scorch time was longer and the heat generation was further reduced as compared with Example 12 in which the amount of DBP absorbed by the filler carbon black exceeded 150 ml / 100 g. Example 9 was superior in wear resistance as compared with Example 11 in which the amount of DBP absorbed was 50 ml / 100 g or less.
In Example 10, the amount of iodine adsorbed by carbon black, which is a filler, was less than 20 mg / g, so that the wear resistance was inferior to that of Example 1.

Claims (10)

Sulfenamide was 0.0005 to 0.01 parts by mass with respect to 100 parts by mass of sulfur-modified 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. The rubber composition according to claim 1, wherein the sulfenamide is represented by the following chemical formula (1).
(In the chemical formula (1), R ¹ and R ² each independently represent hydrogen or an alkyl group having 1 to 10 carbon atoms. Each of R ¹ and R ² may be the same or different.) The rubber composition according to claim 1 or 2, which contains 0.1 to 1.5 parts by mass of xanthate disulfide with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. The rubber composition according to claim 3, wherein the xanthate disulfide is represented by the following chemical formula (2).
(In the chemical formula (2), R ³ and R ⁴ independently represent alkyl groups having 1 to 4 carbon atoms. Each of R ³ and R ⁴ may be the same or different.) The rubber composition according to claim 3 or 4, wherein the ratio (B / A) of the content (A) of the sulfenamide to the content (B) of the xanthate disulfide is 20 to 2000. The rubber composition according to any one of claims 1 to 5, wherein the sulfur-modified chloroprene rubber has a Mooney viscosity of 20 to 80. The rubber composition according to any one of claims 1 to 6, wherein the amount of DBP absorbed by carbon black is 50 to 150 ml / 100 g. The rubber composition according to any one of claims 1 to 7, wherein the iodine adsorption amount of carbon black is 20 to 150 mg / g. A vulcanized product comprising the rubber composition according to any one of claims 1 to 8. A molded product made of the vulcanized product according to claim 9.