RUBBER FOAM COMPOSITION, FOAM AND MOLDED ARTICLE

Abstract

A rubber foam composition containing a sulfur-modified chloroprene rubber and a chemical foaming agent, in which the sulfur-modified chloroprene rubber has a functional group A represented by specific General Formula (A) and positioned at a molecular terminal, in the sulfur-modified chloroprene rubber, a mass ratio B/A of a content of a functional group B represented by specific General Formula (B) and positioned at a molecular terminal with respect to a content of the functional group A is 12.00 or less, a total amount of the functional group A and the functional group B is 0.10 to 1.00% by mass, and a content of the chemical foaming agent is 3 to 16 parts by mass with respect to a total of 100 parts by mass of the sulfur-modified chloroprene rubber, a thiazole compound, and a dithiocarbamic acid-based compound.

Claims

1. A rubber foam composition comprising: a sulfur-modified chloroprene rubber and a chemical foaming agent, wherein the sulfur-modified chloroprene rubber comprises a functional group A represented by General Formula (A) below and positioned at a molecular terminal, in the sulfur-modified chloroprene rubber, a mass ratio B/A of a content of a functional group B represented by General Formula (B) below and positioned at a molecular terminal with respect to a content of the functional group A is 12.00 or less, a total amount of the functional group A and the functional group B is 0.10 to 1.00% by mass, and a content of the chemical foaming agent is 3 to 16 parts by mass with respect to a total of 100 parts by mass of the sulfur-modified chloroprene rubber, a thiazole compound, and a dithiocarbamic acid-based compound: ##STR00010## wherein R.sup.a1 and R.sup.a2 each independently represent a hydrogen atom, a halogen atom, a hydroxy group, an alkoxy group, a carboxy group, a carboxylate group, a cyano group, an alkyl group which may have a substituent, or an arylthio group which may have a substituent, and R.sup.a1 and R.sup.a2 may bond with each other to form a ring which may have a substituent; ##STR00011## wherein R.sup.b1 and R.sup.b2 each independently represent an alkyl group which may have a substituent or an aryl group which may have a substituent.

2. The rubber foam composition according to claim 1, wherein the mass ratio B/A is more than 0 and 12.00 or less.

3. The rubber foam composition according to claim 1, wherein the functional group A comprises a benzothiazole ring formed by R.sup.a1 and R.sup.a2 bonding with each other.

4. The rubber foam composition according to claim 1, wherein the number of carbon atoms of at least one selected from R.sup.b1 and R.sup.b2 is 7 to 8.

5. The rubber foam composition according to claim 1, wherein the content of the functional group A in the sulfur-modified chloroprene rubber is 0.05 to 0.40% by mass.

6. The rubber foam composition according to claim 1, wherein the content of the functional group B in the sulfur-modified chloroprene rubber is 0.80% by mass or less.

7. The rubber foam composition according to claim 1, wherein a content of the thiazole compound is 0.0005 to 0.0100 parts by mass with respect to 100 parts by mass of the sulfur-modified chloroprene rubber.

8. The rubber foam composition according to claim 1, wherein the thiazole compound comprises at least one compound selected from N-cyclohexyl-2-benzothiazole sulfenamide, N-cyclohexyl-4-methyl-2-benzothiazole sulfenamide, N-cyclohexyl-4,5-dimethyl-2-benzothiazole sulfenamide, N,N-dicyclohexyl-1,3-benzothiazole-2-sulfenamide, N-(tert-butyl)-2-benzothiazole sulfenamide, N,N-diisopropyl-2-benzothiazole sulfenamide, 4,5-dihydrothiazol-2-sulfenamide, N-cyclohexyl-4,5-dihydrothiazol-2-sulfenamide, N-oxydiethyl benzothiazole-2-sulfenamide, 2-(4′-morpholinyldithio)benzothiazole, 2-mercaptobenzothiazole, 4,5-dihydro-2-mercaptothiazole, dibenzylthiazolyl disulfide, and 2-(morpholinodithio)benzothiazole.

9. The rubber foam composition according to claim 1, wherein a content of the dithiocarbamic acid-based compound is 2.00 parts by mass or less with respect to 100 parts by mass of the sulfur-modified chloroprene rubber.

10. The rubber foam composition according to claim 1, wherein the dithiocarbamic acid-based compound comprises at least one compound selected from dibenzyl dithiocarbamic acid, sodium dibenzyl dithiocarbamate, potassium dibenzyl dithiocarbamate, zinc dibenzyl dithiocarbamate, ammonium dibenzyl dithiocarbamate, nickel dibenzyl dithiocarbamate, sodium di-2-ethylhexyl dithiocarbamate, potassium di-2-ethylhexyl dithiocarbamate, calcium di-2-ethylhexyl dithiocarbamate, zinc di-2-ethylhexyl dithiocarbamate, ammonium di-2-ethylhexylcarbamate, tetrabenzylthiuram disulfide, and tetrakis(2-ethylhexyl)thiuram disulfide.

11. The rubber foam composition according to claim 1, wherein a mass ratio D/C of a content D of the dithiocarbamic acid-based compound with respect to a content C of the thiazole compound is 2000 or less.

12. The rubber foam composition according to claim 1, wherein a Mooney viscosity of a mixture of the sulfur-modified chloroprene rubber, the thiazole compound, and the dithiocarbamic acid-based compound is 20 to 80.

13. The rubber foam composition according to claim 1, wherein the chemical foaming agent comprises at least one selected from an azo compound, a nitroso compound, a sulfonyl hydrazide compound, an azide compound, and an inorganic foaming agent.

14. A foamed product of the rubber foam composition according to claim 1.

15. A molded article made of the foamed product according to claim 14.

16. The rubber foam composition according to claim 1, wherein the content of the chemical foaming agent is more than 6 parts by mass and 16 parts by mass or less by mass with respect to a total of 100 parts by mass of the sulfur-modified chloroprene rubber, a thiazole compound, and a dithiocarbamic acid-based compound.

17. The rubber foam composition according to claim 1, wherein the content of the chemical foaming agent is more than 7 parts by mass and 16 parts by mass or less by mass with respect to a total of 100 parts by mass of the sulfur-modified chloroprene rubber, a thiazole compound, and a dithiocarbamic acid-based compound.

18. The rubber foam composition according to claim 1, wherein the chemical foaming agent comprises a sulfonyl hydrazide compound.

19. The rubber foam composition according to claim 1, wherein the chemical foaming agent comprises an azo compound.

Description

EXAMPLES

[0085] Hereinafter, the present invention will be more specifically described on the basis of Examples. Examples described below are only typical exemplary Examples of the present invention and the scope of the present invention is not restricted thereby at all.

[0086] <Preparation of Evaluation Sample>

Example 1

[0087] [Preparation of Sulfur-Modified Chloroprene Rubber]

[0088] To a polymerization tank having an inner volume of 30 L, 100 parts by mass of chloroprene, 0.55 parts by mass of sulfur, 120 parts by mass of pure water, 4.00 parts by mass of disproportionated potassium rosinate (manufactured by Harima Chemicals, Inc.), 0.60 parts by mass of sodium hydroxide, and 0.6 parts by mass of a sodium salt of β-naphthalene sulfonic acid formalin condensate (manufactured by Kao Corporation, trade name “DEMOL N”) were added. The pH of the aqueous emulsion before polymerization initiation was 12.8. 0.1 parts by mass of potassium persulfate was added as a polymerization initiator, and then emulsion polymerization was performed under a nitrogen flow at a polymerization temperature of 40° C. 0.05 parts by mass of diethylhydroxylamine as a polymerization terminator was added at the time point of a conversion rate of 85% to terminate the polymerization, thereby obtaining a polymer solution of chloroprene.

[0089] To the polymer solution thus obtained, 5 parts by mass of chloroprene (solvent), 1 part by mass of N-cyclohexyl-2-benzothiazole sulfenamide (molecular weight adjustor, manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD., trade name “NOCCELER CZ”), 4 parts by mass of tetrabenzylthiuram disulfide (molecular weight adjustor, manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD., trade name “NOCCELER TBzTD”), 0.05 parts by mass of a sodium salt of p-naphthalene sulfonic acid formalin condensate (dispersant), and 0.05 parts by mass of sodium laurylsulfate (emulsifier) were added, thereby obtaining a sulfur-modified chloroprene polymer latex before molecular weight adjustment.

[0090] The sulfur-modified chloroprene polymer latex thus obtained was distilled under reduced pressure to remove unreacted monomers, and then the molecular weight thereof was adjusted at a temperature of 50° C. for 1 hour under stirring, thereby obtaining a crude rubber (latex after molecular weight adjustment) containing the sulfur-modified chloroprene rubber. The “crude rubber” is a mixture containing the sulfur-modified chloroprene rubber and the unreacted molecular weight adjustor.

[0091] {Analysis of Content of Terminal Functional Group}

[0092] The crude rubber was cooled, and then the polymer was isolated by a common freeze-solidification method to obtain a sulfur-modified chloroprene rubber. On the basis of the total amount of the sulfur-modified chloroprene rubber, the content of the terminal functional group derived from N-cyclohexyl-2-benzothiazole sulfenamide represented by Formula (A1) below (thiazole terminal species A1) was 0.13% by mass, and the content of the terminal functional group derived from tetrabenzylthiuram disulfide represented by Formula (B1) below (dithiocarbamic acid terminal species B1) was 0.29% by mass.

##STR00006##

[0093] The content of the terminal functional group in the sulfur-modified chloroprene rubber was quantified by the following procedure. First, the sulfur-modified chloroprene rubber was purified with benzene and methanol and then freeze-dried again to obtain a sample for measurement. .sup.1H-NMR measurement was performed using this sample for measurement according to JIS K-6239. The measurement data thus obtained were corrected on the basis of the peak (7.24 ppm) of chloroform in deuterated chloroform used as a solvent. On the basis of the corrected measurement data, the area of respective peaks having peak tops at 7.72 to 7.83 ppm was calculated to quantify the content of the terminal functional group (thiazole terminal species), and the area of peaks having peak tops at 5.05 to 5.50 ppm was calculated to quantify the content of the terminal functional group (dithiocarbamic acid terminal species).

[0094] {Measurement of Residual Amount of Molecular Weight Adjustor}

[0095] The content (residual amount) of the molecular weight adjustor in the aforementioned crude rubber with respect to 100 parts by mass of the sulfur-modified chloroprene rubber was quantified by the following procedure. First, 1.5 g of the crude rubber thus obtained was dissolved in 30 mL of benzene, and then 60 mL of methanol was added dropwise thereto. Thereby, the rubber component (polymer component) was precipitated and separated from the solvent, and the liquid phase containing a non-rubber component as a solvent-soluble component was recovered. Dissolving with benzene and dropwise addition of methanol were performed again with respect to the precipitate by the same procedures, and thereby the rubber component was separated and the liquid phase containing a non-rubber component as a solvent-soluble component was recovered. The first and second liquid phases were mixed and then fixed to a constant volume of 200 mL to obtain a liquid as a sample for measurement. 20 μL of this sample for measurement was injected to a liquid chromatograph (LC, manufactured by Hitachi, Ltd., pump: L-6200, L-600, UV detector: L-4250). The mobile phase of the liquid chromatograph was used while changing the ratio of acetonitrile and water, and was flowed at a flow rate of 1 mL/min. As a column, Inertsil ODS-3 (4.6×150 mm, 5 μm, manufactured by GL Sciences Inc.) was used. The peak detection time was checked using 0.05 ppm, 0.1 ppm, and 1.0 ppm of standard solutions of the thiazole compound (measurement wavelength: 300 nm) and 10 ppm, 50 ppm, and 100 ppm of standard solutions of the dithiocarbamic acid-based compound (measurement wavelength: 280 nm), and a quantitative value was obtained by a standard curve obtained from the peak area thereof. By comparison between this quantitative value and the amount of the sample used in analysis, the contents of the unreacted thiazole compound and the unreacted dithiocarbamic acid-based compound in the crude rubber were obtained.

[0096] [Preparation of Sample]

[0097] 100 parts by mass of the aforementioned crude rubber, 1 part by mass of a processing aid 1 (lubricant, manufactured by New Japan Chemical Co., Ltd., trade name “Stearic acid 50S”), 2 parts by mass of a processing aid 2 (lubricant, manufactured by S&S Japan Co., LTD., trade name “Struktol WB212”), 1 part by mass of a processing aid 3 (manufactured by Nippon Seiro Co., Ltd., trade name “Paraffin wax 130° F.”), 1 part by mass of an antioxidant 1 (manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD., trade name “NOCRAC AD-F”, octylated diphenylamine), 1 part by mass of an antioxidant 2 (manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD., trade name “NOCRAC NBC”, nickel dibutyldithiocarbamate), 4 parts by mass of magnesium oxide (manufactured by Kyowa Chemical Industry Co., Ltd., trade name “Kyowamag 150”), 10 parts by mass of a filler 1 (manufactured by Asahi Carbon Co., Ltd., trade name “Asahi Thermal”, carbon black), 10 parts by mass of a filler 2 (manufactured by Shiraishi Calcium Kaisha, Ltd., trade name “DIXIE CLAY”), 15 parts by mass of a filler 3 (manufactured by Shiraishi Calcium Kaisha, Ltd., trade name “CROWN CLAY”), 15 parts by mass of a plasticizer 1 (manufactured by Idemitsu Kosan Co., Ltd., trade name “NP-24”, naphthenic mineral oil), 20 parts by mass of a plasticizer 2 (manufactured by Idemitsu Kosan Co., Ltd., trade name “AH-16”, aromatic process oil), 5 parts by mass of a vulcanizing agent (manufactured by SAKAI CHEMICAL INDUSTRY CO., LTD., Zinc oxide II), and 8 parts by mass of a foaming agent 1 (manufactured by SANKYO KASEI CO., LTD., trade name “Cellmic S”, p,p′-oxybisbenzenesulfonylhydrazide) were mixed using an 8-inch roll to obtain an unvulcanized compound. Next, this unvulcanized compound was subjected to press vulcanization described below twice according to JIS K 6299, thereby preparing an evaluation sample (sponge).

[0098] 102 g (filling rate: 105%) of the unvulcanized compound was placed in a mold having a cavity region with a length of 100 mm, a width of 95 mm, and a height of 8 mm, and the cavity region was subjected to primary vulcanization (first press vulcanization) for 20 minutes under the conditions of a pressure of 3.5 MPa or more and 145° C. Thereafter, under the atmospheric pressure, the mold was left to stand still for 10 minutes under the condition of 23° C. to obtain a primary vulcanized compound. Then, this primary vulcanized compound was placed in a mold having a cavity region with a length of 175 mm, a width of 170 mm, and a height of 16 mm, and the cavity region was subjected to secondary vulcanization (second press vulcanization) for 20 minutes under the conditions of a pressure of 3.5 MPa or more and 155° C.

Example 2

[0099] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide was changed from 1 part by mass to 0.5 parts by mass, and the addition amount of tetrabenzylthiuram disulfide was changed from 4 parts by mass to 8 parts by mass.

Example 3

[0100] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide was changed from 1 part by mass to 2 parts by mass, and the addition amount of tetrabenzylthiuram disulfide was changed from 4 parts by mass to 2 parts by mass.

Example 4

[0101] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide was changed from 1 part by mass to 3 parts by mass, and the addition amount of tetrabenzylthiuram disulfide was changed from 4 parts by mass to 2 parts by mass.

Example 5

[0102] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide was changed from 1 part by mass to 0.5 parts by mass, and the addition amount of tetrabenzylthiuram disulfide was changed from 4 parts by mass to 2 parts by mass.

Example 6

[0103] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide was changed from 1 part by mass to 3 parts by mass, and tetrabenzylthiuram disulfide was not added.

Example 7

[0104] A crude rubber was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide was changed from 1 part by mass to 0.3 parts by mass, and the addition amount of tetrabenzylthiuram disulfide was changed from 4 parts by mass to 8 parts by mass.

Example 8

[0105] An evaluation sample was obtained by the same method as in Example 1, except that the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide as a molecular weight adjustor was changed from 1 part by mass to 0.3 parts by mass, and the treatment time during molecular weight adjustment was changed from 1 hour to 3 hours.

Example 9

[0106] An evaluation sample was obtained by the same method as in Example 1, except that the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide as a molecular weight adjustor was changed from 1 part by mass to 1.5 parts by mass, and the treatment time during molecular weight adjustment was changed from 1 hour to 15 minutes.

Example 10

[0107] An evaluation sample was obtained by the same method as in Example 1, except that the addition amount of tetrabenzylthiuram disulfide as a molecular weight adjustor was changed from 4 parts by mass to 8 parts by mass, and the treatment time during molecular weight adjustment was changed from 1 hour to 15 minutes.

Example 11

[0108] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, N-cyclohexyl-2-benzothiazole sulfenamide was changed to N-cyclohexyl-4-methyl-2-benzothiazole sulfenamide providing a terminal functional group represented by Formula (A2) below (manufactured by Chemieliva pharma & Chem Co., LTD.). On the basis of the total amount of the sulfur-modified chloroprene rubber, the content of the terminal functional group derived from N-cyclohexyl-4-methyl-2-benzothiazole sulfenamide (thiazole terminal species A2) was 0.15% by mass, and the content of the terminal functional group derived from tetrabenzylthiuram disulfide represented by Formula (B1) mentioned above (dithiocarbamic acid terminal species B1) was 0.33% by mass.

##STR00007##

Example 12

[0109] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, tetrabenzylthiuram disulfide was changed to tetrakis(2-ethylhexyl)thiuram disulfide providing a terminal functional group represented by Formula (B2) below (manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD., trade name “NOCCELER TOT-N”). On the basis of the total amount of the sulfur-modified chloroprene rubber, the content of the terminal functional group derived from N-cyclohexyl-2-benzothiazole sulfenamide represented by Formula (A1) mentioned above (thiazole terminal species A1) was 0.16% by mass, and the content of the terminal functional group derived from tetrakis(2-ethylhexyl)thiuram disulfide (dithiocarbamic acid terminal species B2) was 0.25% by mass.

##STR00008##

Example 13

[0110] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, N-cyclohexyl-2-benzothiazole sulfenamide was changed to N-cyclohexyl-4-methyl-2-benzothiazole sulfenamide providing a terminal functional group represented by Formula (A2) mentioned above, and tetrabenzylthiuram disulfide was changed to tetrakis(2-ethylhexyl)thiuram disulfide providing a terminal functional group represented by Formula (B2) mentioned above. On the basis of the total amount of the sulfur-modified chloroprene rubber, the content of the terminal functional group derived from N-cyclohexyl-4-methyl-2-benzothiazole sulfenamide (thiazole terminal species A2) was 0.14% by mass, and the content of the terminal functional group derived from tetrakis(2-ethylhexyl)thiuram disulfide (dithiocarbamic acid terminal species B2) was 0.32% by mass.

Example 14

[0111] An evaluation sample was obtained by the same method as in Example 1, except that 8 parts by mass of the foaming agent 1 was changed to 5 parts by mass of a foaming agent 2 (manufactured by SANKYO KASEI CO., LTD., trade name “Cellmic C”, azodicarbonamide).

Example 15

[0112] An evaluation sample was obtained by the same method as in Example 1, except that 8 parts by mass of the foaming agent 1 was changed to 4 parts by mass of the foaming agent 1 and 2.5 parts by mass of the foaming agent 2 (manufactured by SANKYO KASEI CO., LTD., trade name “Cellmic C”, azodicarbonamide).

Comparative Example 1

[0113] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide was changed from 1 part by mass to 3 parts by mass, and the addition amount of tetrabenzylthiuram disulfide was changed from 4 parts by mass to 12 parts by mass.

Comparative Example 2

[0114] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide was changed from 1 part by mass to 0.3 parts by mass, and the addition amount of tetrabenzylthiuram disulfide was changed from 4 parts by mass to 0.5 parts by mass.

Comparative Example 3

[0115] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, the addition amount of N-cyclohexyl-2-benzothiazole sulfenamide was changed from 1 part by mass to 0.5 parts by mass, and the addition amount of tetrabenzylthiuram disulfide was changed from 4 parts by mass to 12 parts by mass.

Comparative Example 4

[0116] An evaluation sample was obtained by the same method as in Example 1, except that, as a molecular weight adjustor, N-cyclohexyl-2-benzothiazole sulfenamide and tetrabenzylthiuram disulfide were changed to tetraethylthiuram disulfide (manufactured OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD., trade name “NOCCELER TET”) providing a terminal functional group represented by formula below, and the addition amount thereof was changed to 2.5 parts by mass. On the basis of the total amount of the sulfur-modified chloroprene rubber, the content of the terminal functional group derived from tetraethylthiuram disulfide was 0.26% by mass.

##STR00009##

Comparative Example 5

[0117] An evaluation sample was obtained by the same method as in Example 1, except that the addition amount of the foaming agent 1 was changed from 8 parts by mass to 2 parts by mass.

Comparative Example 6

[0118] An evaluation sample was obtained by the same method as in Example 1, except that the addition amount of the foaming agent 1 was changed from 8 parts by mass to 20 parts by mass.

[0119] <Evaluation>

[0120] The crude rubber and the evaluation sample (foamed product) mentioned above were evaluated. Results of Examples are shown in Table 1 and Table 2, and results of Comparative Examples are shown in Table 3. In Comparative Example 1, since the Mooney viscosity of the crude rubber was too low so that an evaluation sample could not be prepared, each evaluation was not performed. In Comparative Example 5, since foaming could not be performed so that an evaluation sample could not be prepared, each evaluation was not performed.

[0121] (Mooney Viscosity)

[0122] Regarding the aforementioned crude rubber, the Mooney viscosity (ML.sub.1+4) was measured according to JIS K 6300-1 under conditions of a type-L-rotor-preheating time of 1 minute, a rotation time of 4 minutes, and a test temperature of 100° C. The Mooney viscosity of the crude rubber of Comparative Example 1 was too low and thus was unmeasurable.

[0123] (Tear Strength)

[0124] A No. 4 unnicked angle-type test piece was prepared from the aforementioned evaluation sample by using a punching jig according to JIS K 6400-1. Thereafter, measurement was performed using a constant rate tensile tester at a testing rate of 500 mm/min according to JIS K6400-5, and the tear strength was obtained by dividing the maximum tearing load shown until the test piece was broken by the film thickness.

[0125] (Shrinkage Rate)

[0126] The aforementioned evaluation sample (the evaluation sample immediately after preparation) was left to stand still for 168 hours under the atmospheric pressure under the condition of 23° C., and the surface layer of the evaluation sample was sliced into a thickness of 2 mm±0.20 mm, thereby preparing a sponge sheet. The horizontal and vertical size of the sponge sheet immediately after slicing was measured to be obtained as a reference value, and then the horizontal and vertical size of the sponge sheet when left to stand still for 168 hours under the atmospheric pressure under the condition of 23° C. was measured again. A vertical length and a horizontal length of the sponge sheet immediately after slicing were designated as H0 (mm) and L0 (mm), respectively, a vertical length and a horizontal length of the sponge sheet after being left to stand still for 168 hours were designated as H1 (mm) and L1 (mm), and then the shrinkage rate was calculated from the following expression.

Shrinkage rate (%)=[(H0×L0−H1×L1)÷(H0×L0)]×100

[0127] (Appearance)

[0128] The aforementioned evaluation sample (the evaluation sample immediately after preparation) was left to stand still for 24 hours under the atmospheric pressure under the condition of 23° C., and the surface state of the evaluation sample was observed by visual inspection. The observation was performed for the following three items, a case where all items were in the condition of “A” was evaluated as “A”, and a case where at least one item was not in the condition of “A” was evaluated as “B”.

[Item 1: Presence or Absence of Crater]

[0129] The presence or absence of crater-like irregularity generated by the release of a gas, or the like, was checked. A case where irregularity was not confirmed at all was evaluated as “A”.

[Item 2: Presence or Absence of Fingernail Mark]

[0130] The presence or absence of a fingernail mark when the surface of the evaluation sample was lightly depressed straight with a fingernail and then released was observed. A case where the fingernail mark did not remain at all was evaluated as “A”.

[Item 3: Observation of Corner Part]

[0131] For a corner part (corner) of the evaluation sample, the wrinkle state due to shrinkage was checked. A case where the corner surely remained was evaluated as “A”.

TABLE-US-00001 TABLE 1 Example Unit 2 3 4 S 6 7 Content of terminal Terminal Thiazole terminal % by 0.13 0.07 0.23 0.42 0.12 0.38 0.04 functional group in functional species A1 mass sulfur-modified group A Thiazole terminal — — — — — — — chloroprene rubber species A2 Terminal Dithiocarbamic acid 0.29 0.59 0.14 0.23 0.12 — 0.47 functional terminal species B1 group B Dithiocarbamic acid — — — — — — — terminal species B2 B/A — 2.23 8.43 0.61 0.55 1.00 0 11.75 A + B % by 0.42 0.66 0.37 0.65 0.24 0.38 0.51 mass Content of Thiazole (C) N-Cyclohexy1-2- parts 0.0052 0.0011 0.0048 0.0076 0.0031 0.0085 0.0006 unreacted benzothiazole by molecular weight sulfenamide mass adjustor with N-Cyclohexyl- — — — — — — — respect to 100 4-methyl- parts by mass of 2-benzothiazole sulfur-modified sulfenamide chloroprene rubber Dithiocarbamic Tetrabenzylthiuram 1.02 1.62 0.48 0.88 0.42 — 1.37 acid-based disulfide compound (D) Tetrakis(2- — — — — — — — ethylhexyl) thiuram disulfide D/C — 196 1473 100 116 135 0 2283 Mooney viscosity (ML.sub.1+4 at 100° C.) of crude rubber — 51 44 48 18 84 43 55 Content of chemical Foaming agent 1 parts 8 8 8 8 8 8 8 foaming agent with Foaming agent 2 by — — — — — — — respect to 100 mass parts by mass of crude rubber Evaluation Tear strength N/mm 4.81 5.01 4.31 4.02 5.06 4.07 5.11 Shrinkage rate % 4.5 5.1 4.2 4.0 5.3 3.9 5.2 Appearance — A A A A A A A

TABLE-US-00002 TABLE 2 Example Unit 8 9 10 11 Content of terminal Terminal functional Thiazole terminal species A1 % by 0.08 0.38 0.11 — functional group in group A Thiazole terminal species A2 mass — — — 0.15 sulfur-modified Terminal functional Dithiocarbamic acid terminal species B1 0.42 0.19 0.74 0.33 chloroprene rubber group B Dithiocarbamic acid terminal species B2 — — — — B/A — 5.25 0.50 6.73 2.20 A + B % by 0.50 0.57 0.85 0.48 mass Content of unreacted Thiazole (C) N-Cyclohexy1-2-benzothiazole parts 0.0004 0.0112 0.0068 — molecular weight sulfenamide by adjustor with respect N-Cyclohexyl-4-methyl-2-benzothiazole mass — — — 0.0044 to 100 parts by mass sulfenamide of sulfur-modified Dithiocarbamic Tetrabenzylthiuram disulfide 0.63 1.35 2.13 1.06 chloroprene rubber acid-based Tetrakis(2-ethylhexyl)thiuram disulfide — — — — compound (D) D/C — 1575 121 313 241 Mooney viscosity (ML.sub.1+4 at 100° C.) of crude rubber — 59 24 26 48 Content of chemical Foaming agent 1 parts 8 8 8 8 foaming agent with Foaming agent 2 by — — — — respect to 100 parts mass by mass of crude rubber Evaluation Tear strength N/mm 4.88 4.02 4.32 4.62 Shrinkage rate % 5.2 4.2 5.1 4.4 Appearance — A A A A Example Unit 12 13 14 15 Content of terminal Terminal functional Thiazole terminal species A1 % by 0.16 — 0.13 0.13 functional group in group A Thiazole terminal species A2 mass — 0.14 — — sulfur-modified Terminal functional Dithiocarbamic acid terminal species B1 — — 0.29 0.29 chloroprene rubber group B Dithiocarbamic acid terminal species B2 0.25 0.32 — — B/A — 1.56 2.29 2.23 2.23 A + B % by 0.41 0.48 0.42 0.42 mass Content of unreacted Thiazole (C) N-Cyclohexy1-2-benzothiazole parts 0.0046 — 0.0052 0.0052 molecular weight sulfenamide by adjustor with respect N-Cyclohexyl-4-methyl-2-benzothiazole mass — 0.0032 — — to 100 parts by mass sulfenamide of sulfur-modified Dithiocarbamic Tetrabenzylthiuram disulfide — — 1.02 1.02 chloroprene rubber acid-based Tetrakis(2-ethylhexyl)thiuram disulfide 0.88 1.12 — — compound (D) D/C — 191 350 196 196 Mooney viscosity (ML.sub.1+4 at 100° C.) of crude rubber — 49 43 51 51 Content of chemical Foaming agent 1 parts 8 8 — 4 foaming agent with Foaming agent 2 by — — 5 2.5 respect to 100 parts mass by mass of crude rubber Evaluation Tear strength N/mm 4.81 4.81 5.07 4.07 Shrinkage rate % 4.7 4.6 4.1 4.2 Appearance — A A A A

TABLE-US-00003 TABLE 3 Comparative Example Unit 1 2 3 4 5 6 Content of terminal Terminal functional Thiazole terminal % by 0.32 0.05 0.06 — 0.13 0.13 functional group in group A species A1 mass sulfur-modified Terminal functional Dithiocarbamic acid 0.71 0.04 0.73 — 0.29 0.29 chloroprene rubber group B terminal species B1 Terminal functional group derived — — — 0.26 — — from tetraethylthiuram disulfide B/A — 2.22 0.80 12.17 — 2.23 2.23 A + B % by 1.03 0.09 0.79 — 0.42 0.42 mass Content of unreacted Thiazole (C) N-Cyclohexyl-2- parts 0.0074 0.0010 0.0014 — 0.0052 0.0052 molecular weight benzothiazole sulfenamide by adjustor with respect Dithiocarbamic Tetrabenzylthiuram mass 0.84 0.14 1.44 — 1.02 1.02 to 100 parts by mass acid-based disulfide of sulfur-modified compound (D) chloroprene rubber D/C — 114 140 1029 — 196 196 Mooney viscosity (ML.sub.1+4 — X 165 23 56 51 51 at 100° C.) of crude rubber Content of chemical Foaming agent 1 parts 8 8 8 8 2 20 foaming agent with by respect to 100 parts by mass mass of crude rubber Evaluation Tear strength N/mm — 6.12 5.2 3.95 — 1.35 Shrinkage rate % — 6.3 5.5 5.5 — 5.2 Appearance — — B A B — B

[0132] As shown in Tables 1 to 3, it is confirmed that according to a foamed product obtained using each of the rubber foam compositions of Examples, a foamed product excellent in a tear strength, a shrinkage rate, and appearance is obtainable. In Comparative Example 1, since the Mooney viscosity was too low, an evaluation sample could not be prepared. In Comparative Example 5, since foaming could not be performed, an evaluation sample could not be prepared.