CA1064245A - Processing aids for natural and synthetic rubber compounds - Google Patents

Abstract

Abstract Compositions containing salts of aromatic sulfonic acids, long chain fatty acids and thioethers are useful in the processing of natural and synthetic rubber by permitting the usual peptizing atop of such processing to be omitted.

Description

Crude natural rubber is generally quite high in viscosity and therefore does not mix easily and quickly with the many additives used during ~; .. ..
processing. To facilitate the additions of these additives, the rubber usually is softened by under-going a preliminary step called mastication.
The rubber is placed into a usual mixer, such as the Banbury*, and is subjected to heat and a plasticiser (peptizer), while being mixed for several minutes. The resulting mixture is then dumped, sheeted on a roll mill and cooled. The softened rubber then undergoes the mixing step.
The processing aids of U.S. Patent No.
3,787,341 issued January 22, 1974 were developed to eliminate the need for the mastication step. These compositions are added directly to the crude rubber in the mixing cycle along with the other additives. ` ~ --In addition to facilitating the breaking of the polymer and the elimination of the need for both the mastication step and the peptizer, these compositions ~ -have other beneficial effects in rubber compounding. .
They reduce the mixing time required for rubber compounding and provide for better dispersal of additives than traditional methods. In addition, ~
they enable the use of lower mixing temperatures and ~ -provide for improved flow, improved physical properties, improved mixing and extruding characteristics, and improved physical characteristic8 of the rubber.
Hence, even the coumpounding of the synthetic rubber requiring no premastication ~ill be enhanced by the *Trade Mark 2 .
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10~4;~45 use of these formulation~
The compositions of U.S. Patent No. 3,882,062 are homoseneous mixtures of:
1) alkali or amine saltq of aromatic sulfonic acids having the general formula:
Q

Xn ~ ~ OH

wherein X can be either hydrogen or a branched ;;-or straight chain alkyl group having from 4 to 14 carbon atoms, and preferably about 8 to 12 carbon atoms; and n has a value of from 1 to 5, and prefer-ably 1; and

2) long chain fatty acids having a maximum of about 22 carbon atoms in the chain, such as, but not limited to, stearic acid, palmitic acid, ~
oleic acid, neodecanoic acid and mixtures of such `~; -acid~. The fatty acids should be present in amounts at least about equal to the amount of sulfonates but may be present in substantial excess if deqired.
It then was found in accordance with the invention of U.S. Patent No. 3,882,062 and U.S.
Patent No 3, 787,341, that thioethers catalyze the action of the compositions. In particular, they promote further reduction in the viscosity of the rubber compound. Thi~ results in a reduced energy -;
input to effect compounding. In addition, it enables -mixing of the rubber compound at lower temperatures, thereby minimizing the danger of scorching the rubber compound.

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It now has been found in accordance with the present invention, that the thioethers not only catalyze the action of the prior sulfonate salt/fatty acid compositions, but they permit a reduction, and even the elimination of the fatty acid without adverse effect on the properties or processing of the rubber compound. This reduction or elimination of the fatty acid represents a signi- -ficant saving in the cost of the processing aids of this invention.
Thus, the compositions of this invention, unlike those of U.S. Patent No. 3,882,062 are homo-geneous mixtures of:
1. An alkali salt of aromatic sulfonic acids as defined above;
2. optionally, a fatty acid as defined above, provided the amount of fatty acid is less than that of the sulfonic acid salt; and

3. a thioether.

A preferred class of thioethers which are employed in accordance with this invention are those of the formula: ~-Rl _y_R2 ~ `

wherein Y is sulfur or dithioalkylene, i.e. -SCXH2xS - wherein x has a value of from 1 to about 5, and preferably is 1; and each of Rl and R2 is alkyl, aryl, alkaryl, aralkyl as well as substitu-ted alkyl, aryl, alkaryl and aralkyl. The precise nature of Rl and R2 i8 not highly critical, provided the thioether is sufficiently non-volatile to remain . ' ,. .

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in the rubber compound for a sufficient period of time to provide effective catalyzing action. In general, thioethers having boiling points in excess of about 130C are sufficiently non-volatile to be useful in accordance with the invention. In addition, the size of the compound should be such that sufficient catalytic activity can be imparted with relatively small amounts of thioether. Accor-dingly, each of Rl and R2 preferably contains no more than about 12 carbon atoms. Lastly, substi-tuents, if any, should be inert and compatible with the compounds of this invention as well as with the ultimate rubber compound into which they will be incorporated. Suitable substituents include ether 15 oxygen, carbonyl oxygen (i.e., keto, ester and ~;
carboxyl groups), cyano, amine nitrogen (primary, secondary or tertiary), amide groups and the like.
An especially preferred class of thioethers comprise thiodicarboxylic acids and their lower alkyl ethers of the formula:
YlrCzH2z_a (C 2 )1~a~2 wherein Y is as defined above; z is a number having a ;
value of from 1 to about 2; a is a number having a value from about 0 to about 1; and R3 is hydrogen or lower alkyl of up to about 3 carbons. Typical thioethers include thio-diglycolic acid, thiodipropionic acid, methylene bis (thioacetic acid), dimethyl thiodi-propionate, thiodisuccinic acid, thiodipropionitrile, and dibenzyl sulfide.
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The thioether is believed to act as a catalyst. In particular, it is believed that the alkali metal sulfonate component of my prior composi-tion is converted in part into the correspondin~
sulfonic acid which acts as a peptizer durlng the compounding process, and that the thioether catalyzes the peptizing action of the sulfonic acid. Thi~
theory is offered solely by way of explanation, however, and it is not intended to limit the inven- -tion to this theory.
Regardless of theory, the amount of thio-ether sufficient to achieve a reduction in compound viscosity and mixing temperature is small, generally not more than 25 per cent of the sulfonate salt.
The thioether preferably is employed in amounts of from about 5 to about 10 percent, based upon the weight of the sulfonate salt, or from about 1 to about 3 percent based upon the combined weight of sulfonate salt and fatty acid, when the fatty acid is present.
The resulting composition is blended E
with the rubber at the beginning of the mixing cycle. -~
The amount of the composition necessary to achieve improved compounding ordinarily is from about 0.5 to about 2 percent, and preferably about 0.9 to about 1.5 percent, based upon the weight of the rubber in the compound. As a result, the thioether is present in the compound at levels of only 0.005 to about 0.06 percent, based upon the rubber. Nonetheles9, the incorporation of such small amounts of the thioether has a material effect on reducing compound viscosity _6-~O~i4'~:45 and co~pounding temperatures.
The sulfonate salts which are disclosed in U.S. Patent No. 3,882,062 are the alkali metal and amine salts. It now has been found that other ~alts of the sulfonic acids may be employed, including salts of alkaline earth metals such as magnesium, calcium and barium, as well as other bivalent metalq such as zinc.
The composition of this invention preferably is mixed with suitable materials to facilitate its introduction into the rubber. Such materials include esters and ethers of aromatic alcohols, polyglycols, etc. Suitable additional materials include these comprising the compositions of the invention of U.S.
Patent No. 3,855,165 issued December 17, 1974. These generally comprise aromatic esters, compounds with ~--alcoholic and glycolic hydroxyl groups, potassium or sodium soaps of fats or fatty acids, metal soaps of zinc, magnesium, calcium or barium, and a paraffin.
Specifically, these additional materials may comprise: 't.
a. From about 5g to 15% aromatic esters selected from groups consisting of (1) di-aryl- and di-arylalkyl phthalates, -(2) di-aryl- and arylalkyl mono-glycol-ether phthalates, (3) phthalates from polyglycol mono-ethers of aryl, aralkyl and alkaryl compounds wherein the polyglycol chain oontains from 2 to 6 ethylene oxide groups in the chain, (4) di-benzoates of glycol and 4~

propyleneglycol, and their di- and tri-mers; and (5) mixtures of the above.
b. From about 5% to about 30% of com-pounds with alcoholic or glycolic hydroxyl groups selected from (1) straight or branched chain aliphatic alcohols having from about 8 to about 20 carbons in the chain, (2) alkyl-phenoxy ethers of glycols or polygly-cols wherein the alkyl group is limited to about 12 carbons in the chain, and the polyglycol grouping does not contain more than about 6 ~ -(CH2-CH2-0-) groups, (3) polypropylene glycol of about three propylene oxide groups in the molecule, and (4) mixtures of the above. ~ `
c. From about 5% to about 15% of potas-sium or sodium soaps made from commer-cial mixtures of fats or fatty acids -containing from about 12 to about 18 carbon atoms in the chain, said chains having only a small degree of unqatur- - - -ation, with more than 50~ of them having 18 carbon atoms in the chain.
d. From about 10% to about 30~ of fatty ,~
acids having from about 12 to about 18 carbon atoms in the chain, said chains having only a small degree of unsatur-:, , : ... . . ;. . . : .

iO64;~4S
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ation, with more than 50% Or them havine 18 carbon atoms in the chain.
e. From about 5% to about 10% of a metal soap where the metal is selected from the group consisting of zinc, magnesium, calcium or barium; and the fatty acid part of the soap has from about 12 to about 18 carbon atoms in the chain and contains a high percent-age of chains with a single double bond in the chain.
f. From about 15% to about 60% of hydro-carbons selected from the group consisting of mineral oil, mineral waxes, and petrolatum, or mixtures of them.
Preferably the potassium or sodium soaps of ~`
(c) above or the fatty acids of (d) above are com-pounds which have iodine values in the range of from about 5 to about 15. The metal soaps of (e) above are more unsaturated and have iodine values in the range of ~;
about 80 to aboùt 95.
Typical aromatic esters of (a) above which may be used in the compositions of this invention are dibenzyl phthalate; diphènyl phthalate; bis t2-phen-oxyethyl) phthalate; bis (nonylphenoxyethyl) phthalate;
bis (nonylphenoxytetraethyleneglycol) phthalate; ~
benzyl dodecylphenoxyhexaethyleneglycol phthalate; ~ -bis (octylphenoxy) hexaethyleneglycol phthalate; `
diethyleneglycol dibenzoate; dipropyleneglycol _9_ ;

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dibenzoate; and triethyleneglycol dibenzoate.
Illustrative of the compounds with alcohollc or glycolic hydroxyl groups referred to in (b) above which may be employed are 2-ethylhexanol, cetyl alcohol, stearyl alcohol, nonylphenoxyglycol, nonyl-phenoxdiglycol, nonylphenoxytetraethyleneglycol, dodecylhexaethyleneglycol, dipropyleneglycol, tri-propyleneglycol.
Among the potassium or sodium soaps referred to in (c) above are sodium and potassium soaps of hydrogenated tallow, hydrogenated oils of vegetable or marine origin, and soaps of potassium or sodium made with fractions prepared from oils and fats, such fractions having iodine values from about 5 to about 15 15. `
Typical fatty acids which may be employed are those derived from hydrogenated tallow and hydrogenated oils of vegetable or marine origin.
Illustrative of the fatty acids part of the metal soaps referred to in (e) above are oils of vegetable origin or fractions of animal fatty acids such as red oil.
Among the petroleum jellies, mineral oils, ;~
and mineral waxes, which may be employed in the . ~
25 compositions of this invention, are waxes having ~ - -melting points of about 120 to 170F.
However, compositions of this invention are not limited to use in combination with the above additional materials and any similar chemcals will suffice. All ingredients may be of technical grade ...

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-, - : . . - .. ,, : , :. .- :~, . : . , 10~4'~45 and may contain varylng amounts of related materlals, by-products, etc. The novel rubber proce~slng aid~
of this invention can ~e made by melting the ingred~-ents together, mixing and cooling, forming a waxy 5 solid. ~he additional materials may be added together with the sulfonic acid salt, fatty acid and thioether and all components heated until a clear melt is obtained. The alkali soaps and soaps of the bivalent metals can also be made in ~ as ls well known in the art, from the oxide, hydroxide or carbonate of the metal and the desired acids or acid anhydrides, followed by the evaporation or boiling off of the ~ ;
resulting water.
Formulations for solid balanced processing aids of this invention contain the following appro-priate percentages by weight of compounds which are typical of their class:
3% to 50% alkali salt of aromtic sulfonic acid 0% to 50% fatty acid ~-0.5% to 5% thioether t -0% to 15% diphenylphthalate .
0% to 20% tetraethyleneglycol mono-nonyl-phenol ether 0% to 10S tripropyleneglycol 0% to 20% potassium stearate -0% to 10% zinc oleate 0% to 5% cetyl alcohol -`
0% to 40% petrolatum ` ~ -In general, the above-described compositions ~ ~
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are solids. It i9 deslrable that they be ln llquld form to facilitate mixing of the compositlon with the rubber compound. Such liquid compositions can be achieved by the use of amine salts of the aromatic sulfonic acids disclosed above. The salts are those of amines of the formula:

and H ~NHCH2CH2~ nNH2 Wherein R4 is alkyl or hydroxyalkyl, each of R5 or R6 is hydrogen alkyl or hydroxyalkyl, and n is a -number having a value of from 2 to 5. Preferred ~
amines are those having a molecular weight of at ~ ; -least 149 which are themselves liquid and react with 15 the aromatic sulfonic acid to ~orm a liquid salt. i- -Preferred amines are tertiary amines, with triethanol-amine being especially preferred. ~ ~
The aromatic sulfonic acid amine salt can ~ ; -be preformed or it can be formed in situ by adding the acid and the amine separately. In the latter case, the aromatic sulfonic acid and the amine are added in ~ -approximately equivalent amounts. ;~ `
The amine salt of the sulfonic acid, the ~ -carboxylic acid and the thioether can be mixed with 25 certain of the ingredients (a-f) discussed above and -~ ;
still afford a liquid formulation. In particular, ~
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one or more of the aromatic esters (a), the alcoholic ~~

compounds (b), and the hydrocarbon (f) can be employed. ~`-However, the metal soaps (c) and (e) are to be avolded if a liquid formulation 19 de9ired. As a re~ult, the 10~4;~45 proportions of the additional materials are appropri-ately adjusted to reflect the ommission Or these components.
Preferred liquid formulations are those including one or more of a liquid fatty acid, a liquid aromatic ester or a liquid polyglycol. Such llquid formulations may contain:
20~ to 50~ salt of aromatic sulfonic acid 0~ to less than 50% fatty acid 0.5% to 5% thioether 0% to 35% dipropylene glycol dibenzoate ;- -0% to 25% tetraethyleneglycol mono-nonyl-phenol ether ; -0~ to 25% tripropyleneglycol 0~ to 20% mineral oil Especially preferred liquid compositions contain. - - -20% to 50% salt of aromatic sulfonic acid 0.5% to 5% thioether ;-0~ to less than 50% fatty acid % to 35~ dipropyleneglycol dibenzoate Y
0~ to 30% tripropylene glycol -As noted above, the compositions of this - ~ -invention generally are added to the rubber at the beginning of the mixing cycle. The usual additives, such as pigments, filters, vulcanizing agents, etc., can then be added and the entire compounding performed in one operation. They may be added to any type ~ -rubber, whether it is of a natural, synthetic or ;, ,- , "". "

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~0~4;~45 reclalmed type.
The following Examples are illuqtrative of the present invention. The processing aids employed in the Examples are summarized in Table I.

Component, wt% 'A C O U N E _ G H I
Dodecylbenzene ~ 33 33 33 33 33 33 33 33 sulfonic acid Triethanol 1515 15 15 15 15 15 15 __ -;

10 zinc oxide __ __ __ __ __ __ __ 4 2-Ethylhexylacid 3o27 22.5 15 7.5 3 1. 5 0 __ Oleic acid ____ __ __ __ __ __ 3 itrile 3 3 3 3 3 3 3 3 3 Dipropyleneglycol 911 13 .0 17 20. 5 2323. 5 24. 5 33 15 dibenzoate .. ~ -~
tripropylene 101 11 13. 5 17 21. 0 2324. 0 24. 5 - -glycol ~ ~ -~._ _ _ _ .
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Each of Compounds A-I was evaluated in a natural rubber tread stock consisting of Component Pts by Wt No. 3 RSS Rubber (1)100 Stearic Acid 2.5 I SAF - N - 219 (2) 55 K - Stay* - G (3) 4 Tarene* - 20 (4) 9 Zinc Oxide 5 -~
Agerite* Superflex (5) Agerite Dipar (6) Amax* (7) 0.65 Sulfur 2.50 , ~ :

(1) Ribbed smoked sheet rubber.
(2) Intermediate super abrasion furnace black. ~- :
(3) A mixture of a high molecular weight sulfonic acid and a paraffin oil sold as a plasticizer -and processing aid for rubber by RTVanderbilt Co., Inc. --;
(4) A pine tar sold as a rubber softener and extruder by National Rosin Oil & Size Co.
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(5) A diphenylamine-acetone reaction product sold as an antioxidant by RTVanderbilt Co., Inc.

(6) A mixture of phenyl-I-~ -naphthylamine, isopro-poxydiphenyl amine and diphenyl-p-phenylenedia- ;
mine sold as an antioxidant by RTVanderbilt Co., Inc.

(7) N-oxydiethylene benzothiazole-2-sulfenamide sold as an accelerator by RTVanderbilt Co., Inc.
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1064~45 The above stock was mlxed wlthout the additive of this lnventlon or with 1.80 part~ of one of the compounds of this invention and the mixing time, dump temperature and Mooney viscosity (ML4 at 212F) of the resulting rubber compounds where recorded.
The result of these tests are summarized in Table II :~
below.

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Each of the compounds of A-l was evaluated in an ethylene-propylene-diene terpolymer rubber (EDPM) compound having the following composition.
Component Pts by Wt EPDM Vistalon*-5600 (1) 100 Stearic Acid 1.5 Paraffin wax 5 Clay 180 10 Mistron* Vapor (2) 190 Sunpar* 2280 (3) 130 zinc Oxide 5 Diethylene glycol 3 MBTS t4) 1.5 ZDBDC (5) 2.5 TM TDS (6) 0.8 Sulfur 2.0 ~
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(1) Ethylene-propylene-diene modified rubber sold by -Exxon Chemical Co.
(2) Talc sold by Sierra Talc & Clay Co. -(3) High viscosity paraffin oil sold by Sun Oil Co.
(4) Dibenzthiazyldisulfide. -(5) Zinc dibutyldithiocarbamate.
(6) Tetramethyl thiuram disulfide.
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1064~4S -The above stock was mixed wlthout the additives of this invention or wlth 6.26 part~ by weight of one of Compounds A-I, and the mixing time, dump temperature and Mooney viscosity (ML4 at 212F) of the resulting compounds were recorded. The results of these tests are ~ummarized in Table II
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From ~he data presented in Table II, it is evident that, when a thioether is present the fatty acid may be omittèd from the composition of this invention without materially adversely affecting the process of compounding rubber or the rubber obtained thereby.
Still other useful formulations within the scope of this invention include:
COMPOUND J
1.0 Parts thiodiglycolic acid -10.0 " tripropylene glycol .
23.0 " tetraethyleneglycol mono-nonylphenoxyether 10.0 " dipropyleneglycol di-benzoate 14.0 " paraffinic mineral oil 100/100 20.0 " neodecanoic acid .
15.0 " dodecylphenylsulfonic acid 7.0 " triethanolamine 99%
COMPOUND K .~ -1.2 Parts thiodipropionic acid 9.8 " tripropylene glycol 23.0 " tetraethyleneglycol m~no-nonyl- `
phenoxyether 10.0 " dipropyleneglycol di-benzoate 14.0 " paraffinic mineral oil 100/100 ~
20.0 " neodecanoic acid -15.0 " dodecylphenylsulfonic acid 7.0 " triethanolamine 99% -`
COMPQU~
1.3 Parts methylene bis (thioacetic acld) - . , ., . :: .:
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~of~4'~45 7 Parts trlpropylene glycol 22 " tetraethyleneglycol mono-nonyl-phenol ether 13.4 " dipropyleneglycol dibenzoate 12 " paraffinic mineral oil 100/100 18 " neodecanoic acid 18 " dodecylphenylsulfonic acid

8.4 " triethanolamine 99%
COMPOUND M
1.5 Parts dimethyl thiodipropionate

9 " tripropylene glycol 24 " tetraethyleneglycol mono-nonyl-phenol ether 14 " dipropyleneglycol dibenzoate 13.5 " paraffinic mineral oil 100/100 :
18 " neodecanoic acid :.
14 " dodecylphenylsulfonic acid 6 " triethanolamine 99%
COMPOUND N
2.0 Parts thiodisuccinic acid 9 " tripropylene glycol : 24 " tetraethyleneglycol mono- `;
nonylphenol ether 14 " dipropyleneglycol dibenzoate 13 " paraffinic mineral oil 100/100 18 " neodecanoic acid 14 " dodecylphenylsulfonic acid 6.6 " triethanolamine 99%
COMPOUND O
1.0 Parts thiodlpropionitrile ^ , . . ' ~ . - . :

10~;4;~45 9 Parts trlpropylene glycol 25 " tetraethyleneglyCOl mono-nonyl-phenol ether 14.5 " dipropyleneglycol dibenzoate 14 " paraffinic mineral oil 100/100 18 " neodecanoic acid 14 " dodecylphenylsulfonic acid 6.5 " triethanolamine 99%
COMPQUND P
1.5 Parts dibenzyl sulfide 9 " tripropylene glycol " tetraethyleneglycol mono-nonyl-phenol ether .
14 " dipropyleneglycol dibenzoate 14 " paraffinic mineral oil 100/100 :.
18 " neodecanoic acid :
14 " dodecylphenylsulfonic acid 6.5 " triethanolamine 99% :- ~
EXAMPLE ~ : .
Two rubber compounds were prepared in a ;-Banbury mixer by first mixing crude natural rubber, and after 1 minute Compound J and K were added. ~.
Subsequently, other additives were charged to the .-.
: mixer. `~
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10~;4;~45 Compound NO.
Compound Component 1 2 Natural Rubber (crude, #3 Rib Smoked Sheet) 100 100 Compound J. 2.0 --Compound K -- 2.0 Activated zinc salt of pentachlorothiophenol (ENDOR) 0.80 0.80 Mercaptobenzothiozole (CAPTAX*) 1.46 1.46 Benzothiazyl-disulfide (ALTAX*) .66 .66 ~

Zinc dimethyldithiocarbamate ~ - -(METHYL ZIMATE~) .025 .025 ~ .

Tetraethylthiuram disulfide (ETHYL TUADS*) .150 .150 Zinc oxide 5.00 5.00 Stearic acid 1.00 1.00 20 Petrolatum 2.00 2.00 - Whiting 82.50 82.50 Sulphur 2.00 2.00 For each formulation three measurements of Mooney viscosity were mzde after 10 minutes of ~ - :
mixing and the values were averaged. The average vi.~cosities achieved with Compounds J and K were 8.5 -and 9.5 respectively.
It has been found that the thioethers also have an effect upon the accelerators employed in the rubber compound, causing increasing curing. Accor~
dingly, the amount of accelerator can be reduced by from about 10% to about 50% t~ avoid the risk of over-curing. To take advantage of this effect, it * Trade Marks -23~

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~' ' ~'', ' ' ' ' ~064Z45 may sometimes be deslrable to 1ncrea~e the amount of thioether to up to 25%, based upon the sulfonate i3alt.

Employing procedures similar to those described in Example 3, seven crepe rubber comounds were prepared employing Compounds J, ~, L, M, N, 0 and P. The mixing time and dump temperatures were recorded and the Mooney viscosity and the radiograph dispersion rating for each of the resulting rubber compounds were determined. The data for these experiments are summarised as follows: ~ ;

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10~4;~45 COMPOUND NO.
COMPOUND COMPONENT 1 2 _ 4 5 6 7 Pale crepe, pts 300 300 300 300 300 300 300 Stearic acid, pts 15 15 15 15 15 15 15 5 Zinc oxide, pts 15 15 15 15 15 15 15 Fine clay, pts 450 450 450 450 450 450 450 a-Pinene resin, pts25 25 25 25 25 25 25 Sulfur, pts 9 9 9 9 9 9 9 Dibenzthiazyldisulfide, pts 3.3 3.3 3.3 3.3 3.3 3.3 3.3 10 Compound J, pts 8 Compound K, pts - 8 Compound L, pts - - 8 Compound M, pts - - - 8 Compound N, pts - - - - 8 15 Compound O, pts - - - - - 8 -Compound P, pts - - - - - - 8 .
TFST DATA
Mixing Time, Minutes 8 8 9 9 10 7 8 Dump Temperature, F 210 210 215 212 215 210 215 20 Mooney Viscosity 6 6 4 5 5 4 4 Radiograph Dispersion :.
Rating 22.721.9 22.2 27.517.8 14.5 24.2 . .

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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED
AS FOLLOWS:

1. An improved rubber processing aid comprising:
a. an alkali or amine salt of an aromatic sulfonic acid having the formula:
where X is hydrogen or alkyl of from 4 to 14 carbon atoms and n has a value of from 1 to 5, and b. optionally a long chain fatty organic acid having a maximum of about 22 carbon atoms in the chain the improvement wherein the amount by weight of said fatty acid present is less than the amount by weight of said sulfonic acid salt and said processing aid includes a thioether in an amount sufficient to catalyze the peptizing action of said salt.

2. A composition according to claim 1 wherein said thioether is a thiodicarboxylic acid or an ether thereof of the formula wherein Y is sulfur or -SCxH2xS-; x has a value of from 1 to 5; z has a value of from 1 to 2; a has a value of from 0 to 1; and R3 is hydrogen or lower alkyl.

3. A composition according to claim 1 wherein said thioether is thiodipropionitrile.

4. A composition according to claim 1 comprising 20% to 50% salt of aromatic sulfonic acid, 0.5% to 5% thioether, 0% to less than 50% fatty acid; 0% to 35% dipropylene glycol dibenzoate, and 0%
to 30% tripropylene glycol.

5. A composition according to claim 4 which is free of fatty acid.

6. A composition according to claim 5 wherein said thioether is thiodipropionitrile.

7. An improved rubber composition compri-sing a rubber base and rubber additives, wherein the improvement comprises a small but effective amount of a composition according to claim 1.

8. An improved method for compounding rubber comprising admixing rubber with an additive of the class consisting of pigments, fillers and vulcani-zing agents, wherein the improvement comprises admixing a composition according to claim 1 with rubber at the beginning of the mixing cycle prior to mastication of the rubber and no later than the time when said rubber is admixed with said additive.