JP2020196785A - Foamed rubber composition, foamed vulcanizate, and molded article - Google Patents

Abstract

To provide a sulfur-modified chloroprene rubber which gives a foam having a high tear strength, a small shrinkage rate and excellent appearance.SOLUTION: A foamed rubber composition contains, based on 100 pts.mass of a sulfur-modified chloroprene rubber, 0.0005-0.01 pt.mass of a sulfenamide which may have an arbitrary substituent and 3-16 pts.mass of a chemical foaming agent. 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 is used as a material for power transmission belts and conveyor belts for general industry, air springs for automobiles, vibration-proof rubber, etc. by taking advantage of its excellent dynamic characteristics. In addition, chloroprene rubber can be made into a chloroprene rubber sponge by blending a foaming agent and heating and foaming, and the obtained chloroprene rubber sponge is used in various fields such as automobile parts, construction fields, and leisure goods. There is.
Since the chloroprene rubber sponge is a molded product having voids, there is a problem that it shrinks due to tear strength and aging. Therefore, there has been a demand for the development of a chloroprene rubber sponge having a high tear strength and a low shrinkage rate.

As a means for obtaining a chloroprene rubber sponge, an organic oxide, a foaming agent, a softening agent, a filler, and a reinforcing agent are mixed with chloroprene rubber and heated and foamed (see, for example, Patent Document 1), or chloroprene. A rubber obtained by blending a butadiene rubber, a softening agent, and a foaming agent, performing pressureless open sulphurization, and foaming (see, for example, Patent Document 2) is known.

Japanese Unexamined Patent Publication No. 2012-067235 Japanese Unexamined Patent Publication No. 10-298328

With the techniques described in Patent Documents 1 and 2, a chloroprene rubber sponge having a high foaming ratio can be obtained. However, the obtained chloroprene rubber sponge had a low tear strength. For this reason, there has been a demand for the development of a chloroprene rubber sponge that can be used for products that require high tear strength, such as wet suits.

An object of the present invention is to provide a foamed rubber composition which is a raw material for a sponge having high tear strength, low shrinkage and excellent appearance, and a foamed vulcanized product and a molded product obtained by using the foamed rubber composition.

As a result of diligent research to solve this problem, the inventors of the present application have added a sulfenamide compound and a specific foaming agent to the sulfur-modified chloroprene rubber to obtain a high tear strength, a low shrinkage rate, and an appearance. Succeeded in obtaining an excellent foamed rubber composition, and completed the present invention.

That is, in the present invention, sulfenamide is 0.0005 to 0.01 parts by mass with respect to 100 parts by mass of sulfur-modified chloroprene rubber.
It is a rubber composition containing 3 to 16 parts by mass of a chemical foaming agent.
As the sulfenamide, 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 may contain 0.1 to 1.5 parts by mass of xanthogen disulfide with respect to 100 parts by mass thereof.
As the xanthate disulfide, 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 xanthate disulfide is used, the ratio (B / A) of the sulfenamide content (A) to the xanthate disulfide content (B) can be 20 to 2000.
The Mooney viscosity of the sulfur-modified chloroprene rubber can be 20 to 80.

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

According to the present invention, a foamed rubber composition, a vulcanized product thereof, and a molded product can be obtained, which can obtain a foamed vulcanized product having high tear strength, low shrinkage rate, and excellent appearance.

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.

<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 sulfenamide, and a sulfur-modified chloroprene rubber obtained by drying and washing the latex by a general method. Hereinafter, the details will be described along with the manufacturing process of the sulfur-modified chloroprene rubber.

<Polymerization process>
In the polymerization step, chloroprene and sulfur, and if necessary, a monomer copolymerizable with chloroprene are emulsion-polymerized to obtain a polymerization solution.

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>
The plasticization step is a step of adding sulfenamide to the polymerization solution obtained in the polymerization step to plasticize the polymer in the polymerization solution.

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 adding the amount of sulfenamide to 0.2 parts by mass or more, the tear strength of the vulcanized product is improved, the shrinkage rate is reduced, and a vulcanized product having an excellent appearance can be obtained. 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, which contributes to the reduction of the shrinkage rate of the obtained vulcanized product. 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 tear strength is improved, the shrinkage rate is reduced, and a vulcanized product having an excellent appearance can be obtained.

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, a vulcanized product having an improved tear strength, a reduced shrinkage rate, and an excellent appearance can be obtained.

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 range, the tear strength of the vulcanized product is improved, which contributes to the reduction of the shrinkage rate.

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 the xanthate disulfide within the above range, a vulcanized product having an improved tear strength, a reduced shrinkage rate and an excellent appearance can be obtained.

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, it contributes to the reduction of the shrinkage rate.

[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.

<Chemical foaming agent>
As the chemical foaming agent, either a chemical foaming agent or an inorganic foaming agent can be used. Examples of the chemical foaming agent include azo compounds, nitroso compounds, sulfonylhydrazide compounds, azide compounds, and carboxylic diamide compounds. More preferably, a sulfonyl hydrazide compound and an azo compound can be mentioned.

The decomposition temperature of the chemical foaming agent is preferably 120 ° C. to 200 ° C., more preferably 130 ° C. to 170 ° C. By setting the decomposition temperature of the chemical foaming agent within such a range, control of chemical foaming and vulcanization becomes easy, the shrinkage rate is reduced, and a vulcanized product having an excellent appearance can be obtained.

The amount of the chemical foaming agent added is 3 to 16 parts by mass with respect to 100 parts by mass of the sulfur-modified chloroprene rubber. If the amount of the chemical foaming agent is less than 3 parts by mass, a sufficient amount of decomposition gas cannot be obtained due to the insufficient amount of the foaming agent, and if it exceeds 16 parts by mass, foaming and vulcanization are balanced. It is difficult to obtain a foam having an excellent appearance, and the tear strength is also inferior.

<Sponge>
The obtained sulfur-modified chloroprene rubber composition is mixed with a metal compound, a plasticizing agent, a filler, etc. in a roll, a Banbury mixer, an extruder, etc., and a foaming agent is added and vulcanized while foaming to form a sponge. can do.

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.
(Wetsuit)
The obtained sponge can be sliced to a desired thickness, and then a jersey cloth made of polyester fiber or nylon fiber can be laminated on at least one surface to obtain a cloth for a wet suit, which is sewn. By doing so, you can get a wet suit. Wetsuits are required to have excellent tear strength, shrinkage, and appearance in order to improve product reliability.

The rubber composition of the present invention can provide a wetsuit having a higher tear strength, a smaller shrinkage rate, and an excellent appearance than a conventional wetsuit using 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.

In the obtained polymer solution, 5 parts by mass of chloroprene monomer as a solvent and N-cyclohexylbenzothiazole-2-sulfenamide as a plasticizer (trade name "Noxeller CZ" manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) 1. 5 parts by mass and diisopropylxanthogen disulfide (trade name "Sanbit DIX" manufactured by Sanshin Chemical Industry Co., Ltd.) 3.2 parts by mass, 0.05 parts by mass of sodium salt of β-naphthalenesulfonic acid formalin condensate as a dispersant, emulsifier As a result, a plasticizer emulsion consisting of 0.05 parts by mass of sodium lauryl sulfate 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 the obtained unvulcanized compound was press-vulcanized twice in accordance with JIS K 6299. I went to make a sponge. The first press vulcanization is referred to as primary vulcanization, and the second press vulcanization is referred to as secondary vulcanization.

In the primary vulcanization, 102 g of unvulcanized compound (filling rate 105%) is placed in a mold having a cavity region of 100 mm in length, 95 mm in width, and 8 mm in height, and the cavity region is pressured at 3.5 Mpa or more and 145 ° C. It was carried out under the conditions for 20 minutes. Then, it was allowed to stand for 10 minutes under the condition of 23 ° C. under atmospheric pressure. The primary vulcanization compound obtained by allowing to stand is placed in a mold having a cavity region of 175 mm in length, 170 mm in width and 16 mm in height, and the cavity region is placed in a mold with a pressure of 3.5 Mpa or more and 155 ° C. for 20 minutes. went.

The compounds listed in Table 1 are as follows: Lubricants / Processing aids 1: Stearic acid 50S manufactured by New Japan Chemical Co., Ltd.
Lubricants / Processing Aids 2: S & S Japan Co., Ltd. Stratktor WB212
Anti-aging agent 1: Nocrack AD-F manufactured by Ouchi Shinko Kagaku Kogyo
Anti-aging agent 2: Nocrack NBC manufactured by Ouchi Shinko Kagaku Kogyo
Magnesium oxide: Kyowa Chemical Industry Co., Ltd. Kyowa Mug 150
Carbon Black: Asahi Thermal Filler manufactured by Asahi Carbon Co., Ltd. 1: Dixiclay Filler manufactured by Shiraishi Calcium Co., Ltd. 2: Crown Clay Plasticizer manufactured by Shiraishi Calcium Co., Ltd.
Plasticizer 2: AH-16 manufactured by Idemitsu Kosan Co., Ltd.
Wax: Paraffin wax 130 ° F manufactured by Nippon Seiro Co., Ltd.
Vulcanizing agent: Zinc oxide type 2 foaming agent manufactured by Sakai Chemical Industry Co., Ltd. 1: Cellmic S (p, p'-oxybisbenzenesulfonyl hydrazide) manufactured by Sankyo Kasei Co., Ltd.

<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>
Evaluation sample by the same method as in Example 1 except that the foaming agent 1 was changed to the foaming agent 2 (trade name "Celmic C" azodicarbonamide manufactured by Sankyo Kasei Co., Ltd.) and the addition amount was 5 parts by mass. Was produced.

<Example 8>
An evaluation sample was prepared in the same manner as in Example 1 except that the amount of the foaming agent 1 added was 4 parts by mass and the amount of the foaming agent 2 added was 2.5 parts by mass.

<Comparative example 5>
An evaluation sample was prepared in the same manner as in Example 1 except that the amount of the foaming agent 1 added was changed from 8 parts by mass to 2 parts by mass.

<Comparative Example 6>
An evaluation sample was prepared in the same manner as in Example 1 except that the amount of the foaming agent 1 added was changed from 8 parts by mass to 20 parts by mass.

<Evaluation of tear strength>
The obtained sponge was used to prepare a No. 4 type non-cut angle type test piece using a punching jig in accordance with JIS K 6400-1, and then the test speed was tested by a constant speed tensile tester in accordance with JIS K 6400-5. The measurement was performed at 500 mm / min, and the maximum tear load shown until the test piece broke was divided by the film thickness.

<Evaluation of shrinkage rate>
The obtained sponge was allowed to stand under atmospheric pressure at 23 ° C. for 168 hours, and then the surface layer of the sponge was sliced to a thickness of 2 mm ± 0.20 mm to prepare a sponge sheet. The vertical and horizontal sizes of the sponge sheet immediately after slicing are measured and used as a reference, and then the vertical and horizontal sizes of the sponge sheet when allowed to stand for 168 hours under the condition of 23 ° C. under atmospheric pressure are measured again. The shrinkage ratio is H0 (mm) for the vertical length of the sponge sheet immediately after slicing, L0 (mm) for the horizontal length, H1 (mm) for the vertical length of the sponge sheet after standing for 168 hours, and horizontal. The length was L1 (mm) and calculated by the following formula.
Shrinkage rate (%) = (H0 × L0-H1 × L1) ÷ (H0 × L0) × 100

<Evaluation of appearance>
The obtained sponge was allowed to stand at 23 ° C. for 24 hours under atmospheric pressure, and then the surface condition thereof was visually observed. Observations were carried out for the following three items, and samples that were evaluated as ○ in all items were evaluated as ○, and those that were not evaluated as ○ were evaluated as Δ.
Item 1 Presence or absence of craters The presence or absence of crater-like irregularities caused by outgassing was confirmed.
Those that were not confirmed at all were marked with a circle.
Item 2 Presence or absence of claw marks The presence or absence of claw marks when the sponge was opened after the nails were raised on the surface of the sponge and lightly pressed was observed.
Those that did not remain at all were marked as ○.
Item 3 Observation of corners Wrinkles due to shrinkage were confirmed at the corners of the sponge.
Those with solid corners were marked as ○.

<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 to 2, it was confirmed that the evaluation samples of Examples 1 to 8 provided vulcanized products having excellent tear strength, shrinkage rate and appearance. 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. In addition, Comparative Example 5 in which the amount of the foaming agent added was less than 3 parts by mass did not foam and an evaluation sample could not be prepared.

Claims (9)

Sulfenamide was 0.0005 to 0.01 parts by mass with respect to 100 parts by mass of sulfur-modified chloroprene rubber.
A foamed rubber composition containing 3 to 16 parts by mass of a chemical foaming agent. The foamed 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 foamed 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 foamed 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 foam 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 foamed 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 foamed rubber according to any one of claims 1 to 6, wherein the chemical foaming agent is at least one selected from the group consisting of an azo compound, a nitroso compound, a sulfonylhydrazide compound, an azide compound and an inorganic foaming agent. Composition. A foamed vulcanized product comprising the foamed rubber composition according to any one of claims 1 to 7. A molded product made of the foamed vulcanized product according to claim 8.