NO121118B - - Google Patents

Description

Procedure for vulcanizing rubber.

The present invention relates to an improved vulcanization method for rubber. The invention relates to improved accelerator-inhibitor combinations for rubber. More particularly, the invention relates to a method for preventing premature vulcanization of rubber materials.

In the manufacture of vulcanized rubber products, raw rubber is combined with various other ingredients such as fillers, accelerators and anti-degradants to modify and improve the processing of the rubber and to improve the properties of the final product. The raw rubber goes through several steps in the manufacture before it is ready for the final step, vulcanization. In general, rubber is mixed with carbon black and the other ingredients, including the vulcanizing agent and the accelerator. Then vulcanization is added

. and the accelerators to the remainder of the charge in a "Banbury" mixer or

a mill. Unvulcanization, i.e. premature vulcanization, can occur at this stage of manufacture, during storage before vulcanization and during the vulcanization itself. After the vulcanizing and accelerating agents have been added, the mixture of raw rubber is ready for calendering or extrusion and vulcanization. If premature vulcanization occurs during the storage of the raw mixture or during the processing during vulcanization, the processing operations cannot be performed because the unvulcanized rubber is uneven and lumpy and therefore unusable. Premature vulcanization is a major problem in the rubber industry and must be prevented to allow the rubber treatment to preform and shape before it is cured or vulcanized.

There are several reasons for premature vulcanization. The discovery of the thio-azolesulfenamide accelerators represented a major advance in the field of vulcanization because the thiazolesulfenamides delayed the onset of the vulcanization process, but once it began, the built-in amine activation<:>of the thiazole led to strong and rapid curing. Mercaptobenzothiazole is a valuable organic vulcanization accelerator, but according to the current requirements would be considered unvulcanizing. It has largely been replaced by the delayed-action accelerators, but further improvements have not taken place in the subject. The development of "furnace blacks" with high pH which lack the inherent inhibitory effect of the acidic "channel blacks", and the popularity of certain phenylenediamine antidegradants, which promote vulcanization, have led to increasingly stringent requirements for the accelerator system.

Retardants have long been available to rubber manufacturers. These include N-nitrosodiphenylamine, coniferous resin and salicylic acid and a dispersant. See "Editors of Rubber World, Compounding Ingredients for Rubber," 91-94 (3rd Ed., 1961). Acids are generally ineffective with thiazolesulfenamide accelerators or adversely affect the vulcanization process. Nitrosamines have only limited activity with thiazole sulfenamides derived from primary amines. Certain sulfenamides which are not in themselves accelerators have been shown to slow down mercaptobenzothiazole and other vulcanizing accelerators, but the effect on another sulfenamide incorporated as the main accelerator has been minimal. Likewise, mixtures of accelerating sulfenamides have been proposed as a way to improve treatment safety, but none of these new features have particularly improved a good delayed action accelerator.

An aim of the present invention is to provide a method for effectively preventing the premature vulcanization of rubber. A further aim of the invention is to provide a method at a faster curing rate for vulcanizable rubbers without premature vulcanization. A further aim of the invention is to provide a method for increasing the available processing time before the actual vulcanization of rubber. A further object according to the invention is to provide a method for preventing the premature vulcanization of raw rubber during storage, containing a vulcanizing and accelerating agent. A further aim of the invention is to provide a method for preventing the premature vulcanization of rubber during the vulcanization step itself. A further object of the invention is to prevent the premature vulcanization of rubber at any time.

Another aim according to the invention is to provide a safer method for the production and vulcanization of rubber. These goals are achieved by using a sulfenamide derived from an amine or imide in the preparation of vulcanized rubber.

A class of sulfenamides has been found which are very valuable inhibitors of premature vulcanization. These are characterized by the presence of the carbonyl group next to the sulfenamide nitrogen. The characteristic core

Q

is R-S-N-C- where the free bond on the nitrogen may be attached to a further carbonyl, alkyl, aryl, alkaryl, aralkyl, haloaryl, nitroaryl, cycloalkyl, hydrogen, alkylene or arylene and R is alkyl, aryl, alkaryl, aralkyl, cycloalkyl, haloaryl or nitroaryl. The term alkyl includes alkyl hydrocarbons of 1-20 carbon atoms. Primary, secondary and tertiary alkyl hydrocarbons are included in the term, e.g. straight or branched chains. However, primary and secondary alkyl hydrocarbons are the preferred alkyl compounds according to the invention. The term cycloalkyl includes cycloalkyl groups of 5-8 carbon atoms. Some of the inhibitors according to the invention have vulcanizing and accelerating properties in themselves. The sulfur vulcanizing agents, accelerators and anti-degradation agents used in the combinations according to the invention do not include the inhibitors according to the invention.

A combination of an accelerator and an inhibitor according to the present invention is an improved rubber additive that allows longer and safer manufacturing times for rubber.

The present invention relates to a method by inhibiting

for early vulcanization of a vulcanizable diene rubber containing a vulcanizing agent and an organic vulcanization accelerating agent, preferably N-t. butyl-2-benzothiazole-sulfenamide or 2-(morpholinothio)-benzothiazole, and possibly an anti-degradation agent, which method is characterized by the fact that a compound with the formula is used as an inhibitor:

r»

where

a) R is hydrogen, N1-(halogenar ylthio)-carbamoyl, N'-(aralkylthio)-carbamoyl, N'-(alkarylthio)-carbamoyl, N'-(alkylthio)-carbamoyl, N'-(cycloalkylthio)-carbamoyl , N'-arylcarbamoyl, N'-alkylcarbamoyl, N'-aralkylcarbamoyl, N'-nitroarylcarbamoyl, N'-cycloalkylcarbamoyl, N'-haloarylcarbamoyl or alkarylcarbamoyl, and R" is aralkyl, haloaryl, alkyl, alkaryl, nitroaryl, cycloalkyl or aryl, or^ b) R and R' with the carbonyl group and the N atom are 1-phthalimidyl, 1-succinimidyl, 1,4,5,6,7,7-hexachlorbicyclo^2. 2. J_7-hept-5- en-2, 3-dicarboximid-1 - yl, 5, 5-dimethyl-3-hydantoinyl, 5, 5-diphenyl-3-hydantobinyl, 1 -maleimidyl, 4-cyclohexen-1, 2-dicarboximid-1 -yl, 2-benzimidazolinon-1 -yl, 2-benzo-thiazolinon-N-yl, 3-halogenarylthio-2-benzimidazolidinon-1 -yl, 3-arylthio-2-benzimidazolidinon-1 -yl, 3-aralkylthio-2-benzimidazolinone - 1 - yl, 3-nitro-arylthio-2-benzimidazolinon-1 -yl, 3-alkylthio-2-benzimidazolinon-1 -yl, 3-cycloalkylthio-2-benzimidazolinon-1 -yl, 3-alkarylthio-2-benzimidazo linon-1 1-yl, 2-imidazolinon-1-yl, 3-arylthio-2-imidazolinon-1-yl, 3-halogenarylthio-2-imidazolinon-1-yl, 3-aralkylthio-2-imidazolinon-1-yl , 3-alkarylthio-2-imidazolinon-1-yl, 3-alkylthio-2-imidazolinon-1-yl, 3-cycloalkylthio-2-imidazolinon-1-yl, bicyclo^2. 2. \ J- h. ept-b-ei\- 2, 3-dicarboximid-1-yl, alkyl-bicyclo^2. 2. J^-hept-5. en-2, 3-dicarboximid-1-yl, N-(arylthio)-1,2,4,5-benzenetetracarboxylic acid-1,2:4,5-diimid-N1-yl, N-(aralkylthio)-1, 2,4,5-benzenetetracarboxylic acid-1,2:4,5-diimid-N'-yl, N-(halogenarylthio)-1,2,4,5-benzenetetracarboxylic acid-1,2:4,5-diimid-N '-yl, N-(nitroarylthio)-1,2,4,5-benzenetetracarboxylic acid-1,2:4,5-diimid-N1-yl, N-(cycloalkylthio)-1,2,4,5-benzenetetracarboxylic acid- 1,2:4,5-diimid-N'-yl,N-(alkylthio)-1,2,4,5-benzenetetra|-carboxylic acid-1,2:4,5-diimid-N'-yl-N -(alkarylthio)-1,2,4,5-benzenetetracarboxylic acid-1,2:4,5-diimid-N'-ylr1-naphthalimidyl or 1-(3,4,5,6-tetrahalophthalimidyl), and R" is aryl, alkaryl, haloaryl, nitroaryl, aralkyl, cycloalkyl or alkyl. In particular, it should be emphasized that favorable results are obtained when the in inhibitor is used a compound where

is N'-(phenylthio)-

carbamoylrNV(chlorophenylthio)-carbamoyl, N'-(benzylthio)-carbamoyl, N'-(tolylthio)-carbamoyl, N1 -(alkylthio)-carbamoyl, N'-(cyclohexylthio)-carbamoyl, N<1->phenylcarbamoyl, N '-alkylcarbamoyl, N-cyclohexylcarbamoyl, N'-^ benzylcarbamoyl, N'-nitrophenylcarbamoyl, N'-chloro£enylcarbamoyl or tolylcarbamoyl and R" is phenyl, benzyl, chlorophenyl, nitrophenyl, tolyl, primary alkyl, secondary alkyl or cyclohexyl , or a compound where R and R' with car-

the bonyl group and the N atom have the meanings given in claim 1 under b), and R" is phenyl, benzyl, chlorophenyl, nitrophenyl, tolyl, cyclohexyl, primary alkyl or secondary alkyl.

Of particularly applicable inhibitors, the following should be highlighted:

N-(phenylthio)-succinimide,

N-(cyclohexylthio)-phthalimide, and

N-(n-butylthio)-phthalimide.

Known compounds that are useful as inhibitors against premature vulcanization in the present process include, e.g. N, N'-di-(nitrophenylthio)-urea, N-(phenylthio)-phthalimide, N-(p-chloro-phenylthio)-phthalimide, N-(o-tolylthio)-phthalimide, N-(m- tolylthio)-phthalimide, N-(o-nitrophenylthio)-phthalimide, N-(p-chlorophenylthio)-succinimide, N-(o-to'lylthio)-succinimide, N-(m-tc4ylthio)-succinimide, N -(p-tolylthio)-succinimide, N-(t-butylthio)-succinimide, N-(phenylthio)-succinimide, N-(nitrophenylthio)-succinimide, N-(n-dodecylthio)-succinimide and N-(benzylthio)-succinimide -succinimide.

Further examples of compounds useful as inhibitors against premature vulcanization according to the present invention are N-(naphthylthio)-phthalimide, N-(n-butylthio)-succinimide, N-(methylthio)-succinimide, N-(ethyl-thio) )-succinimide, N-(propylthio)-succinimide, N-(isopropylthio)-succinimide, N-(cyclohexylthio)-succinimide. and N-(cyclooctylthio)-succinimide; 1,3-bis-(n-hexylthio)-1, 3-dicyclohexylurea, N-phenyl-N'-(phenylthio)-urea, N-phenyl-N<1->

(methylthio)-urea, N-phenyl-N'-(ethylthio)-urea, N-phenyl-N<1->(propylthio)-urea, N-phenyl-N'-(isopropylthio)-urea, N-phenyl -N<1->(t-butylthio)-urea, N-phenyl-N'-(n-dodecylthio)-urea, N-phenyl-N'-(cyclohexylthio)-urea, N-phenyl-N'-( cyclo-octylthio)-urea, N-methyl-N'-(phenylthio)-urea, N-ethyl-N'-(phenylthio)-urea, N-propyl-N'-(phenylthio)-urea, N-isopropyl- N'-(phenylthio)-urea, N-t-butyl-N' -

(phenylthio)-urea, N-cyclooctyl-N'-(phenylthio)-urea, N-cyclohexyl-N'-(phenyl-thio)-urea, N-n-dodecyl-N'-(phenylthio)-urea and variations thereof.

Rubber materials containing accelerators with a delayed effect can be used in the present method. Cheaper, more vulcanizing accelerators can also be used with excellent improvement. Present improved vulcanization method can be used with advantage when treating materials containing "furnace black" as well as materials containing other types of "carbon blacks" and fillers used in rubber production. The invention is also applicable to natural resin materials.

The present invention is applicable to rubber compounds containing sulfur vulcanizers, peroxide vulcanizers, organic accelerators for vulcanization and antidegradation agents, none of which is the inhibitor used. The term "sulfur vulcanizing agent" is used to denote elemental sulfur or sulfur-containing vulcanizing agents, e.g. an amine disulfide or a polymeric polysulfide. The present invention is applicable with vulcanization accelerators of different classes. For example, rubber compounds containing the aromatic thiazole accelerators which include benzothiazyl-2-monocyclohexyl-sulfenamide, 2-mercaptobenzothiazole, N-tert-butyl-2-benzothiazole-sulfenamide, 2-benzothiazolyl-diethyl-dithiocarbamate and 2-(morpholinothio)-benzothiazole can , is used. Amine salts of mercaptobenzothiazole accelerators, e.g. The t-butylamine salt of mercaptobenzothiazole, and similar salts of morpholine and 2,6-dimethylmorpholine can be used according to the invention. Thiazole accelerators other than aromatic can be used. Materials containing accelerators, e.g. tetramethylthiuram disulfide, tetramethylthiuram monosulfide, aldehyde-amine condensation products, thiocarbamylsulfenamides, thioureas, xanthates and guanidine derivatives are considerably improved by application of the present invention. Examples of thiocarbamylsulfenamide accelerators are found in U.S. Pat. patents 2,381,393, 2,388,236 and 2,424,921. The invention is applicable to materials containing amine anti-degradants. Rubber compounds containing anti-degradation agents, e.g. N-1, 3-dimethylbutyl-N'-phenyl-p-phenylenediamine, N,N'-bis-(1,4-dimethylpentyl)-p-phenylenediamine and other phenylenediamines, ketone, ether and hydroxy anti-degradants , and mixtures thereof, are considerably improved by the application of the present method. Mixtures of anti-degradants, e.g. a mixture of N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine and N,N'-bis-(1,4-dimethylpentyl)-p-phenylenediamine gives a much improved end product when used with the inhibitors of the present invention.

The inhibitors according to the invention can be used in natural and synthetic rubbers and mixtures thereof. Synthetic rubbers that can be improved by the present process include cis-4-polybutadiene, butyl rubber, ethylene-propylene terpolymers, polymers of 1,3>butadiene, for example 1,3-butadiene itself and of isoprene copolymers of 1,3-butadiene with other monomers, for example styrene, acrylonitrile, isobutylene and methyl methacrylate. The invention relates to diene gums and the terms rubber and diene gums are used here synonymously.

The production of the new compounds that can be used according to the invention is described in the widely available Norwegian patent application no. 4116/69

The following tables illustrate the invention in more detail and the best way of carrying it out. For all rubber materials tested and described below as examples of the invention, Mooney vulcanization times at 121°C and 135°C were determined using a Mooney plastometer. The time in minutes (tj) required for the Mooney reading to rise five points above the minimum viscosity is noted. Longer times are indicative of the activity of the inhibitor. Longer times in the Mooney vulcanization test are desirable because this indicates greater production reliability. Percentage increases in vulcanization delay are calculated by dividing the Mooney vulcanization time of the material containing the inhibitor against premature vulcanization by the Mooney vulcanization time of the control material, multiplying by 100 and subtracting 100. These increases show the percent improvement in vulcanization delay over to the control material containing no inhibitor. Also, cure rates are calculated from the time required to cure the materials at 144°C and in some cases 153°C. Cure properties are determined using the Monsanto Oscillating Dise Rheometer described by Decker, Wise and Guerry in Rubber World, December 1962, page 68. From rheometer data, RMT is the maximum modulus distortion in rheometer units, t^ or t^ is the time in minutes for an increase on three and two rheometer units, respectively, above the minimum reading and t^Q is the time required to obtain a modulus of 90% of the maximum.

The trademarks of some compounds used in the practice of the present invention are "Santocure MOR", "Santoflex 77", "Santocure NS", "DPG", "Thiofid" and "Vultrol". "Santocure MOR" is the accelerator 2-(morpho-linothio)-benzothiazole. "Santoflex 77" is the anti-degradant N,N'-bis-(1,4-dimethylpentyl)-p-phenylenediamine. "Santocure NS" is the accelerator N-tert-butyl-2-benzothiazolesulfenamide. "DPG" is an accelerator stated to be diphenylguanidine. "Thiofide" is an accelerator stated to be benzo-thiazyl disulfide. "Vultrol" is a vulcanization sink stated to be N-nitrosodiphenylamine.

Table I shows the results of using N-(phenylthio)-succinimide and N-(benzylthio)-succinimide as inhibitors of premature vulcanization in natural rubber materials containing the antioxidant "Santoflex 77" and the accelerator "Santocure MOR". From the data in Table I, it will be seen that N-(phenylthio)-succinimide and N-(benzylthio)-succinimide are quite active in the presence of the accelerator as inhibitors of premature vulcanization. From the periodic ozone test there does not seem to be any effect on the ozone resistance of

the vulcanizates containing the inhibitors.

Table II shows that N-(phenylthio)-succinimide acts as an inhibitor

in natural rubber with "Santocure NS" as well as it did with the accelerator "Santocure MOR". It also appears from table II that 0.25 parts per 100 N-(phenylthio)-succinimide with "Santocure NS" has approximately the same vulcaniz-

in

ing properties such as 1.0 parts per 100 of the well-known retarder, "Vultrol" with "Santocure MOR". It appears that increasing concentrations of N-(phenyl-thio)-succinimide with "Santocure NS" do not inhibit the rate of cross-link formation as measured by the specific rate constant k^. The parameter actually increases with increasing amounts of N-(phenylthio)-succinimide in the presence of the phenylenediamine antidegradants. Materials containing N-(phenylthio)-succinimide and "Santocure NS" also show an excellent cure rate after vulcanization has begun.

The code for Table II is as follows. The materials contain:

Twelve materials were tested. The materials contained the following:

Material no.

Rheometer at 144°C

Mooney vulcanization

at 121°C

Rheometer at 144°C

Results comparable to the natural rubber preparations in Table II are obtained by using cis-4-polybutadiene, butyl rubber, ethylene-propylene terpolymers, polymers of 1,3-butadiene, e.g. 1,3-butadiene itself, and of isoprene and copolymers of 1,3-butadiene with other monomers, e.g. styrene, acrylonitrile, isobutylene and methyl methacrylate, as starting material and N-(phenylthio)-succinimide and N-(benzylthio)-succinimide as the inhibitor. For example, Table III shows the properties of N-(phenylthio)-succinimide as an inhibitor of premature vulcanization, in a styrene-butadiene rubber B-5 charge. The compound is compared to "Vultrol" in several systems. The code for Table III is as follows. A B-5 charge consists of:

Material no.

"Vultrol", the known inhibitor, shows only an 11% increase in vulcanization delay with "Santocure MOR" and no increased delay with "Santocure NS". However, the compound according to the invention shows, at the same concentrations, a 45% increase in the vulcanization delay with "Santocure MOR" and a 50% increase with "Santocure NS" in styrene-butadiene rubber.

Table IV shows the N-(phenylthio)-succinimide's inhibitor properties against premature vulcanization in natural rubber when a peroxide vulcanizing agent is used. N-(phenylthio)-succinimide shows a 57% increase in vulcanization delay with the vulcanizing agent dicumyl peroxide. The basic charge in table IV consisted of:

Table V illustrates the excellent results obtained using N-(cyclohexylthio)-phthalimide as an inhibitor against premature vulcanization in materials of natural rubber, oil-modified styrene-butadiene rubber and a natural rubber/cis-4-polybutadiene blend cover material. consisted of the following:

The oil-modified styrene-butadiene rubber tire material consisted of the following:

Oil-modified styrene-butadiene-rubber covering material

Natural rubber/cis-4-polybutadiene mixture cover material consisted of the following:

1, 3-bis-(cyclohexylthio)-2-benzimidazolinone shows a 411% increase in vulcanization delay compared to natural rubber material containing "Santocure MOR" alone. These results are calculated from the Mooney vulcanization time, t , at 121°C.

Table VI shows the results of the use of N-(benzylthio)-phthali-:

mid and N-(dodecylthio)-phthalimide in oil-modified styrene-butadiene rubber. The rubber material is the same as the oil-modified styrene-butadiene rubber material described in Table V above.

Table VII shows the results of experiments with N-(phenylthio)-succinimide, N-(t-butylthio)-phthalimide, N,N'-di-(phenylthio)Turea, 1,3-bis-(phenylthio)-2-imidazolinone and N-(phenylthio)-maleimide as inhibitors of premature vulcanization in rubber. N-(phenylthio)-maleimide gave a 174% increase in vulcanization delay compared to the control sample. The rubber compound in the experiment was an A-6 base charge. An A-6 basic charge is composed as follows:

All materials contained three parts "Santoflex 77", 0.5 parts "Santocure MOR" and 2.5 parts sulphur.

Similar results were obtained when the accelerator "Santocure NS" and the anti-degradant, N-1,3-dimethylbutyl-N'-phenyl-p-phenyldiamine or a mixture of this anti-degradant and "Santoflex 77" were used. Table VIII shows N-(phenylthio)-maleimide as a vulcanization inhibitor in a B-5 base charge of styrene-butadiene rubber.

Table IX shows the useful properties against premature vulcanization in an A-6 rubber base mixture of N-(isopropylthio)-phthalimide and N-(n-butylthio)-phthalimide. The materials contained 2.0 parts N-1, 3-dimethylbutyl-N1 -phenyl-p-phenylenediamine, 0.5 parts "Santocure MOR" and 2.5 parts sulfur.

In similar samples, N-(sec-butylthio)-naphthalimide shows a 212% increase in vulcanization retardation and 1,3-bis-(n-dodexylthio)-benzimidazolinone shows a 52% increase in vulcanization retardation.

In an A-6 base charge containing 0.5 parts "Santocure MOR", 2.5 parts sulfur and 3 parts "Santoflex 77", the known compound N-(phenyl-thio)-phthalimide shows a 108% increase in vulcanization delay. N-(phenylthio)-phthalimide is difficult to disperse in rubber, presumably because of its high

'melting point (163 - 165°C).

Table X shows the properties of a mixture of ortho-, meta- and para-N-(tolylthio)-phthalimide as an inhibitor of premature vulcanization in an A-6 base charge using the anti-degradants "Santoflex 77" and N- 1, 3-dimethylbutyl-N'-phenyl-p-phenylenediamine. An 82% increase in vulcanization delay occurs with "Santoflex 77" and a 140% increase is obtained with N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine. All materials contained 0.5 parts "Santocure NS" and 2.5 parts sulfur. Similar results are obtained with other anti-degradation agents.

1, 3-bis-(phenylthio)-2-benzimidazolinone is an excellent inhibitor of premature vulcanization. In an A-1 base charge, this connection increases the vulcanization delay by 170% as shown in Table XI.

An A-1 basic charge consists of:

Corresponding results are obtained by using the accelerator "Santocure NS".

1, 3-bis-(phenylthio)-2-benzimidazolinone and N-(phenylthio)-succinimide

are inhibitors of premature vulcanization in cis-4-polybutadiene as shown in Table XII. 1, 3-bis-(phenylthio)-2-benzimidazolinone shows a 47% increase in vulcanization delay and N-(phenylthio)-succinimide shows a 31% increase. The base charge for Table XII consisted of:

1,3-bis-(phenylthio)-2-benzimidazolinone and N-(phenylthio)-succinimide are inhibitors of premature vulcanization in ethylene-propylene terpolymers as shown in Table XIII. Ethylene-propylene terpolymer is the accepted and commonly used name for the polymerized product from the polymerization of ethylene, propylene and a small amount of a non-conjugated diene. The terpolymer used in Table XIII is known commercially as "Nordel 1070". N-(phenylthio)-succinimide shows a 28% increase in vulcanization delay and 1,3-bis-(phenylthio)-2-benzimidazolinone shows an 80% increase when used as inhibitors of premature vulcanization in ethylene-propylene terpolymers. The base charge in Table XIII consists of: 1,3-bis-(o-nitrophenylthio)-p-benzimidazolinone shows a 57% increase in vulcanization delay in an A-6 base charge. The results appear in table XIV.

Similar results are obtained with the inhibitor 1, 3-bis-(chlorophenylthio)-2-benzimidazolinone.

An ortho-, meta- and para-mixture of 1, 3-bis-(tolylthio)-2-benzimidazolinone gives a 163% increase in vulcanization delay compared to the control sample and 1, 3-bis-(m-tolylthio)-2- benzimidazolinone increases exposure by 142%. These data appear in table XV.

The ortho, meta and para mixture of 1,3-bis-(tolylthio)-2-benzimidazolinone was tested in a B-5 base charge of styrene-butadiene rubber. A 113% increase in vulcanization delay compared to the control sample was obtained with an accelerator mixture of "DPG" and "Thiofide" and the inhibitor. The inhibitor provides an 80% increase in vulcanization delay when used with "Santocure NS" in styrene-butadiene rubber. These results appear in the table

XVI.

N-phenyl-N'-(phenylthio)-urea was tested in an A-6 base charge as an inhibitor against premature vulcanization and showed a 97% increase in vulcanization delay compared to the control sample. The results appear in table XVII.

Similar results are obtained when other unsymmetrical ureas according to the invention are tested as inhibitors of premature vulcanization.

Corresponding results to those in the above tables which show the applicability, are obtained with the inhibitors according to the invention which are not illustrated.

Concentration studies show that the inhibitors according to the invention are effective in rubber at concentrations of 0.25 to 5.0 parts per 100. Concentrations from 0.25 to 3.0 parts per 100 is preferred.

A wide range of combinations of "Santocure NS" and N-(phenylthio)-succinimide show storage stability in an eight week oven burn test at 50°C. These combinations are improved vulcanization accelerators in rubber whereby premature vulcanization is effectively inhibited. Effective inhibitor concentrations for the combinations range from 1 to 9 parts inhibitor. Corresponding results are obtained when other accelerator and inhibitor combinations according to the invention are tested for stability.

Claims (9)

1. Method for inhibiting premature vulcanization of a vulcanizable diene rubber containing a vulcanizing agent and an organic vulcanization-accelerating agent, preferably N-t-butyl-2-benzothiazole-sulfenamide or 2-(morpholinothio)-benzothiazole, and optionally an anti-degradation agent; characterized whereby a compound with the formula is used as an inhibitor: where a) R is hydrogen, is N'-(arylthio)-carbamoyl, N'-(halogenarylthio)-carbamoyl, N'-(aralkylthio)-carbamoyl, N'-(alkarylthio)-carbamoyl, N'-(alkylthio)-carbamoyl, N'-( cycloalkylthio)-carbamoyl, N'-arylcarbamoyl, N'-alkylcarbamoyl, N'-aralkylcarbamoyl, N'-nitroarylcarbamoyl, N'-cycloalkylcarbamoyl, N'-halogenarylcarbamoyl or alkarylcarbamoyl, and R" is aralkyl, haloaryl, alkyl, alkaryl , nitroaryl, cycloalkyl or aryl, or b) R and R<1>with the carbonyl group and the N atom is 1-phthalimidyl, 1-succinimidyl, 1, 4, 5, 6, 7, 7-hexachlorobicyclo^2. 2. l7 -hept-5-en-2, 3-dicarboximid-1 -yl, 5, 5- dimethyl-3-hydantoinyl, 5,-5-diphenyl-3-hydantoinyl, 1-maleimidyl, 4-cyclohexen-1, 2- di-carboximid-1-yl, 2-benzimidazolinon-1-yl, 2-benzothiazdli-non-N-yl, 3-halogenarylthio-2-benzimidazolinon-1-yl, 3-arylthio-2-benzimidazolinon-1-yl, 3-aralkylthio-2-benzimidazolinon-1-yl, 3-nitroarylthio-2-benzimidazolinon-1-yl, 3-alkylthio-2-benzimidazolinon-1-yl, 3-cycloalkylthio-2-benzimidazolinon-1-yl, 3- alkarylthio-2-benz imidazolinon-1-yl, 2-imidazolinon-1-yl, 3-arylthio-2-imidazolinon-1-yl, 3-halogenarylthio-27 imidazolinon-1-yl, 3-a r alkylthio-2-imidazolinon-1-yl, 3-alkarylthio-2-imidazolinon-1-yl, 3-alkylthio-2-imidazolinon-1-yl, 3-cycloalkylthio-2-imidazolinon-1-yl, bicyclo^2. 2.1_7-hept-5-en-2, 3-dicarboximid-1-yl, alkyl-bicyclo^~2. 2. y-hept-5-en-2, 3-dicarboximid-1-yl, N-(arylthio)-1,2,4,5-benzenetetracarboxylic acid-1, 2:4, 5-diimid-N'-yl , N-(aralkylthio)-1,2,4,5-benzenetetracarboxylic acid-1,2:4,5-diimid-N1-yl, N-(halogenarylthio)-1,2,4,5-benzenetetracarboxylic acid-1,2 :4,5-diimid-N'-yl,N-(nitroarylthio)-1,2,4,5-benzenetetracarboxylic acid-1,2:4,5-diimid-N'-yl,N-(cycloalkylthio) -1,2,4,5-benzenetetracarboxylic acid-1,2:4,5-diimid-N'-yl,N-(alkylthio)-1,2,4,5-benzenetetracarboxylic acid-1,2:4,5- diimid-N'-yl, N-(alkarylthio)-1,2,4,5-benzenetetracarboxylic acid-1,2:4,5-diimid-N'-yl,1-naphthalimidyl or l-(3,4,5 , 6-tetrahalophthalimidyl), and R" is aryl, alkaryl, haloaryl, nitroaryl, aralkyl, cycloalkyl or alkyl. 2. Method according to claim 1, characterized in that where inhibitor, a compound is used where 1 under a) is N'-(phenyl - thio)-carbamoyl, N'-(chlorophenylthio)-carbamoyl-, N'-(benzylthio)-carbamoylrN' - (tolylthio) - carbamoyl, N' - (alkylthio) - carbamoyl, N' - (cycloalkylthio) - carbamoyl, N '-phenylcarbamoyl, N'-alkylcarbamoyl, N'-cycloalkylcarbamoyl, N'-benzylcarbamoyl, N'-nitrophenylcarbamoyl, N'-chlorophenylcarbamoyl or tolylcarbamoyl and R" is phenyl, benzyl, chlorophenyl, nitrophenyl, tolyl, primary alkyl, secondary alkyl or cyclohexyl, or a compound where R and R' with the carbonyl group and the N atom have the meanings given in claim 1 under b), and R" is phenyl, benzyl, chlorophenyl, nitrophenyl, tolyl, cyclohexyl, primary alkyl or secondary alkyl. 3. Method according to claim 1 or 2, characterized in that N-(phenylthio)-succinimide is used as inhibitor. 4. Method according to claim 1 or 2, characterized in that N-(cyclohexylthio)-phthalimide is used as inhibitor. 5. Method according to claim 1 or 2, characterized in that N-(n-butylthio)-phthalimide is used as inhibitor. 6. An accelerator-inhibitor combination for carrying out the method according to claims 1-5, characterized in that it includes an organic vulcanization accelerator and a compound in an amount effective to inhibit premature vulcanization of a vulcanizable diene rubber, which compound has the formula: where R, R<1>and R" are as stated in claim 1. 7. Accelerator-inhibitor combination according to claim 6, characterized in that the inhibitor is N-(phenylthio)-succinimide. 8. Accelerator-inhibitor combination according to claim 6, characterized in that the inhibitor is N-(cyclohexylthio)-phthalimide. 9. Accelerator-inhibitor combination according to claim 6, characterized in that the inhibitor is N-(n-butylthio)-phthalimide.