CA1123145A - Reversion-free vulcanizates from rubber mixtures and vulcanization process - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides in a formable and vulcan-isable rubber mixture which contains at least one rubber which still contains double bonds and which can be crosslinked with sulphur and a vulcanisation accelerator to form an elastomer from 0.2 to 10 parts by weight of sulphur, from 0.2 to 10 parts by weight of at least one vulcanisation accelerator and from 1 to 10 parts by weight of at least one silane corresponding to the formula (I) in which each of the individual radicals R and R1 represents an alkyl group containing from 1 to 4 carbon atoms, a cycloalkyl group containing from 5 to 8 carbon atoms or the phenyl radical;
n is 0, 1 or 2, Alk is a difunctional straight-chain or branched hydrocarbon radical containing from 1 to 10 carbon atoms, and x is a number of from 2.0 to 8.0, or its hydrolysate and, the improvement in which the silane, vulcanisation accelerator and sulphur, expressed as S8, are present in such a molar ratio that, at the vulcanisation temperature, the rubber mixture has a rever-sion R resulting from the crosslinking isotherm (DIN 53 529) of 0 (+ 5%), R being calculated in accordance with the following formula:
(II) in which Dmax is the maximum Vulcameter torque, Dmin is the mini-mum Vulcameter torque, D(max + 60 mins.) is the Vulcameter torque as measured 60 minutes after appearance of the maximum torque.
The mixture is useful in the preparation of motor vehicle tires.

Description

1:123~:~5 The present invention relates to rubber mixtures givlng reversion free vulcanisates and a vulcani~ation process.
The vulcanisation behaviour of a rubber mix-ture may be represented, for example, by means of a Vulcameter curve. The Vulcameter curve is formed by plotting the torques determined with a Vulcameter (DIN 53 529) on the abseissa of a rectangular co-ordinate system against the vulcanisation time on the ordinate.
The onset of vulcanisation is reflected in an ascending branch of the Vuleameter curve. Thereafter the curve normally reaches a maximum or indicates a maximum value and, in most cases, descends more of less quickly or slowly as vulcanisation continues.
Vulcameter curves recorded at a constant temperature may also be called crosslinking isotherms.
In the vulcanisation of rubber mixtures based on natural or synthetic rubbers in the presence or absence of rubber fillers by means of sulphur and vulcanisation accelerators, as normally practised in -the industry, these crosslinking isotherms normally pass through a maximum which is formed because during the complex ehemical processes oecurring during vulcanisation, the build-up of polysulphidie crosslinks between the rubber moleeules predominates in the initial stage, whereas the degradation of lntermolecular polysulphidie and disulphidie bridge bonds to intramolecular heteroeyelic rings occurs in the final stage. In a crosslinking isotherm obtained by vulcametry these phenomena are reflected in a eontinuous downward trend of the erosslinking isotherm, i.e. in a fall in the torque values and, in practice, in moduli which deerease with increasing vulcanisation time. The change in the relative erosslink density of the vulcanisa-te (level of the torques) and the relative crosslink density present at any stage of the vulcanisat:ion process may be read off from the slope of the vulcametrieally determined crosslinking isotherm. The change in the crosslink densities is accompanied by a ehange in the ~:

31~5 mechanical properties of the vulcanisates (where this property is dependent upon -the crosslink density), such as -their tensile strength, breaking elongation, elasticity, Shore hardness, heat formation, and abrasion.
In practice, the downwardly sloping branch of the Vula-meter curve signifies a deterioration in the above-mentioned properties of the vulcanisate. This phenomenon is technically known as "reversion". Due to the change in the mechanical proper-ties of the vulcanisates with which reversion is accompanied, reversing vulcanisates are generally undesirable. This applies in particular in the production of thick-walled rubber articles because the poor thermal conductivity of articles, such as these in their individual discrete regions (volume elements) can give rise to differing mechanical properties which means that, on completion of vulcanisation, the vulcanisate is not homogeneous with regard to its crosslink density. In the case of thick-walled rubber articles, the appearance of reversion necessitates a distinct reduction in the vulcanisation temperature in order to postpone the onset of reversion. Another no-torious phenomenon is that reversion increases with increasing temperature. Any reduction in temperature during the vulcanisation of thick-walled articles results in a commensurate increase in the heating times.
For example, the heating times for large pneumatic tyres range from about 10 to 14 hours at a vulcanisation temperature of 120C.
A significant problem has been to enable the vulcanisa-tion temperatures to be reduced without any adverse effects on the properties of the vulcanisates, i.e. to avoid unfavourable reversion phenomena and to considerably shorten theheating times (vulcanisation times) so that the production facilities may be distinctly better utilised and a faster output or higher produc-tivity achieved.

It is known that oligosulphidic silanes may be used in ~2314~S

the vulcanisation of rubber mixtures with sulphur to render the mixtures with silicate fillers added -thereto easier to process and to obtain vulcanisates equivalent or superior in quality to vulcanisates obtained from mixtures filled with carbon black (see German Patent No. 2,255,577 or US Patent No. 3,~73,489). A
typical representative of these oligosulphidic silanes is 3,3-bis-(triethoxysilylpropyl)-tetrasulphide or the commercial pro-duct supplied under the trademark Si 69. It is also known (see . . ~ ~bl;shed ~ebr~a~y~7L, /q7~
~ ~ German Offenlegungsschrift No. 2,53~,6744)that rubber mixtures containing silicate fillers can be crosslinked solely with oligo-sulphidic silanes and vulcanisation accelera-tors, i.e. wi-thout elemental sulphur. In this case, mixtures of silica and carbon black are advantageously used as fillers.
Crosslinking agents with which attempts have been made to avoia reversion phenomena, particularly in the case of rever-sion-prone rubbers, such as natural rubber and polyisoprene, have long been known in the rubber-processing industry. These cross-linking agents are, for example, peroxides which lead to -C-C-crosslinking (carbon-carbon crosslinking) or thiuram disulphides ~0 which form -C-S-C-bridge bonds. Accordingly, the development of polysulphidic degradable crosslinks as described above is avoided.
Systems of the type in question also include vulcanisation systems using so-called sulphur donors which, in terms of function, are distinguished by the fact that, once again, no polysulphidic crosslinks are formed in contrast to standard sulphur vulcanisa-tion. They also include crosslinking systems whose function is based on the fact that, where basically crosslinking accelerators are used, crosslinking is controlled by the addition of small quantities of su]phur in such a way that predominantly monosul-phidic bridge bonds, i.e. bridge bonds which cannot be further degraded are formed. However, the avoidance of polysulphidic crosslinks is also associated with changes in the properties of the vulcanisates which are undesirable. For example, the tensile strengths and breaking elongations are reduced for lhe same cross-link density in comparison with sulphur vulcanisates and, what ls more important, the tear initiation and tear propagation resis-tance is dras-tically reduced. One particularly unfavourable aspect of this method of vulcanisation is the increase in damage to vulcanisates, for example in the form of chipping and chunking effects, which seriously restricts the use of systems such as these so that it is better to work at a low vulcanisation temper-ature with conventional sulphur/accelerator systems, i.e. toaccept and minimise the reversion phenomena. The above-mentioned vulcanisation systems which impart resistance to reversion are even less applicable to rubber mixtures containing silicate fillers or mixtures of carbon blacks with silicate fillers. The silicate fillers disrupt in particular the effect of these vul-canisation systems to such an extent that an adequate crosslink density cannot be obtained, even by using the crosslinking agents in very large quantities. Accordingly, the use of the aforesaid crosslinking systems which impart resistance to reversion is severely restricted and confined to special -types of rubber.
They can only be used to a very limited extent, if at all, in the rubbers normally used for a wide range of applications, such as natural rubber and styrene-butadiene rubbers.
Accordingly, the present invention provides a cross-linking system which may be used in as many types of rubber as possible, preferably in natural rubbers and polyisoprenes, to produce therefrom vulcanisates which do not have any of the numerous unfavourable properties associated with reversion.
According to the present invention there is provided in a formable and vulcanisable rubber mixture which contains at least one rubber which still contains double bonds and which can be crosslinked with sulphur and a vulcanisation accelerator to ~123~45 form an elastomer from 0.2 to 10 parts by wel~h-t o~ sulphur, from 0.2 to 10 parts by weigh-t of at least one vulcanisa-tion accelera-tor and from 1 to 10 parts by weight of at ].east one silane cor-responding to the formula [ n(RO)3 nsi Alk ]2Sx (I) in which each of the indivi.dual radicals R and Rl represen-ts an alkyl group containing from 1 to 4 carbon atoms, a cycloalkyl group containing from 5 to 8 carbon atoms or the phenyl radical;
n is 0, 1 or 2, Alk is a difunctional, straight-chain or branched hydrocarbon radical containing from 1 to 10 carbon atoms, and _ is a number of from 2.0 to 8.0, or its hydrolysate, the improve-ment in which the silane, vulcanisation accelerator and sulphur, .expressed as S8, are present in such a molar ratio that, at the vulcanisation temperature, the rubber mixture has a reversion R
resulting from the crosslinking isotherm (DIN 53 529) of 0 (+ 5%), R being calculated in accordance with the following formula:

Dmax ~ D(max + 60 mins.) . 100 (~I) D - D .
max mln in which DmaX is the maximum Vulcameter torque, Dmin is the mini-mum Vulcameter torque, D(maX + 60 mins) is the Vulcameter torque as measured 60 minutes after appearance of the maximum torque.
The present invention also provides a process for vul-canising moulding compositions based on at least one rubber which still contains double bonds and which can be crosslinked with sulphur and a vulcanisation accelerator to form an elastomer using from 0.2 to 10 parts by weight of sulphur, from 0.2 to 10 parts by weight o:E at least one vulcanisation accelerator and from 1 to 10 parts by weight (all parts by weight being based on 100 parts by weight of rubber) of at least one silane correspond-ing to the formula ~L~23~9cS

n )3-n ]2 x (I) in which each of R and Rl individually represent an alkyl group containing from 1 to 4 carbon a-toms, a cycloalkyl group contain-ing from 5 to 8 carbon atoms or the phenyl radlcal; n is 0, 1 or

2, Alk represents a difunctional, s-traight-chain or branched hydrocarbon radical containing from 1 to 10 carbon atoms and x i's a number of from 2.0 to 8.0, or its hydrolysate, the moulding composition being heated to the selected vulcanisation temperature, thoroughly heated at that temperature and cooled -the improvement in which the molar ratio of silane to accelerator to sulphur (expressed as S8) in the moulding composition is selected in such a way that, at the vulcanisation temperature, the reversion R
resulting from the crosslinking isotherm (DIN 53 529) is nil (+ 5%), as determined in accordance with the following formula:

Dmax ~ D(max + 60 mins.) . 100 (II~
D - D

in which DmaX is the maximum Vulcameter torque, Dmin is the mini-mum Vulcameter torque, D(maX + 60 mins) is the Vulcameter torque as measured 60 minutes after appearance of the maximum torque.
Accordingly it is possible for the first time to control vulcanisation in such a way -that a lasting condition of the quasi-constant crosslink density occurs, in o-ther words the number of crosslinks produced per unit of time by the oligo-sulphidic silane is just compensated by the reversion-induced crosslink degradation per unit of time at a constant vulcanisation tempera-ture. The above-mentioned condition is surprisingly achieved by adjusting the molar ratio of silane to accelerator to sulphur and is, as it were, frozen by terminating vulcanisation, i.e. by cooling. The reversion R is determined in percent in accordance with the following formula ~3 Z3~S

R max (max + 60 mins) . 100 (II) D - D .
max mln in which Dmax is the maximum torque, Dmin is the minimum -torque, D(max + 60 mins ) is the torque measured 60 minutes after appear-- ance of the maximum torque.
According to the invention, a reversion R of nil (~ 5~) is achieved. The above-mentioned torques are taken from vulca-metrically measured crosslinking iso-therms. An MPV Rheometer of L0 the type manufactured by Monsanto Europe S.A., B-1150 Brussells, was used as the Vulcameter.
With regard to the expressions "vulcametry" and "cross-linking isotherm", reference is made to the Tentative Standard DIN 53 529 of February, 1971, cf. in particularpage 1. For the rest, vulcanisation is carried out by the methods normally used in the rubber industry. In this connection, reference is made for example -to "Kautschuck-Handbuch" by Dr. Siegfried BOSTROM
(Verlag Berliner Union, Stuttgart, 1959) or to A~S. CRAIG l'Rubber Technology" (London, 1963).
The rubbers (A) which may be used in accordance with the invention include any rubbers which still contain double bonds and which may be crosslinked with sulphur and vulcanisation accelerator(s) to form elastomers and mixtures of such rubbers.
The rubbers in question are in particular the halogen-free rubbers preferably so-called diene elastomers. Rubbers of this type include, for example, optionally oil-extended natural and synthetic rubbersy such as na-tural rubbers, butadiene rubbers, isoprene rubbers, butadiene-styrene rubbers, butadiene-acrylo-nitrile rubbers, butyl-rubbers, terpolymers of ethylene, propylene and for example, non-conjugated dienes. The following additional rubbers (B) may be used for rubber mixtures with the above-mentioned rubbers: carboxyl rubbers, epoxide rubber, trans-~3~L~S

polypentenamer, halogena-ted butyl rubbers, rubbers of 2-chloro-butadiene, ethylene-vinyl acetate copolymers, ethylene-propylene copolymer5 and even chemical derivatives of natural rubber as well as modified natural rubbers. It is preferred to use na-tural rubbers and polyisoprene rubbers either indiviclually or in admix-ture with one ano-ther and/or in admixture with the above-mentioned rubbers.
The silicate fillers which, according to -the inven-tion, optionally form an ingredient of -the mixture (even in the form of a mixture of two or more of these fillers) are fi]lers known per se in rubber technology. The expression "silicate filler" is a broad definition and covers fillers which consist of silicates, contain silicates and/or include silicates in the broadest sense in chemically bound form and which are compatible with rubbers and may be worked into rubber mixtures. These silicate fillers include in particular (a) highly disperse silicas (silicon dioxide) having specific surfaces in the range from about 5 to 1000 m2/g, and preferably in the range from 20 to 400 m2/g (as determined with gaseous nitrogen by the known BET method) and primary particle sizes in the range from about 10 to 400 nm which may be produced for example by precipitation from solutions of silicates, by the -hydrolytic and/or oxydative high-temperature reaction, also known as flame hydrolysis, of volatile silicon halides or by an arc process. These silicas may even be present in the form of mixed oxides or oxide mixtures with oxides of the metals aluminium, magnesium, calcium, barium, zinc, zirconium and/or titanium, (b) i synthetic silicates, for example aluminium silicate, or alkaline-earth metal silicates, such as magnesium or calcium silicate, having specific surfaces of from about 20 to 400 m2/g and primary particle sizes of from 10 to 400 nm; (c) natural silicates, for example kaolins and asbestoses, and natural silicas, such as for example quartz and kieselguhr; and (d) glass fibres and glass fibre products, such as mats, strands, woven cloths and non-woven structures and also glass microbeads.
The silicate fillers are used in qua~tities of from 1 to about 300 parts by weight, based on 100 par-ts by weight of -the rubber polymer. In order -to obtain white rubber mixtures, they can contain one or several silicates as the sole fillers. At least 5 parts by weight of silicate filler are then used per 100 parts by weight of rubber.
Examples of filler mixtures include silica/kaolin or silica/glass fibres/asbestos and also blends of the silicate reinforcing fillers with known rubber-grade carbon blacks, for example silica/ISAF-carbon black, silica/HAF-carbon black or silica/glass fibre cord/HAF-carbon black. Typical representatives of the silicate fillers which may be used in accordance with the invention are, for example, the silicas and silicates manufactured and marketed by DEGUSSA under the trademarks AEROSIL( ), ULTRA-SIL( ), SI~TEG( ), DUROSIL( ), EXTRUSIL( ) and CALSIL( ). Accord-ing to the invention, preferred silicate fillers are the above-mentioned highly disperse or active silicas, particularly the precipitated silicas, used in quantities of from 10 to 250 parts by weight, based on 100 parts by weight of rubber.
Carbon black may be present as filler in the rubber mixtures according to the invention either on its own or in addi-tion to other fillers not only for greying or blackening the vul-canisates, but also for obtaining the well-known, valuable vulcani-sate properties. It is preerred to use the known rubber-grade carbon blacks. Carbon blacks such as these are the commercial products manufactured and marketed by DEGUSSA under the trade mark CORAX(R). The carbon black or mixtures of carbon black are used in quantities of from 0.1 to 300 parts by weight and preferably in quantities of up to 150 parts by weight, based on 100 parts by weight of rubber, in the new rubber mixtures.

g _ ~23~45 Where silicate filler and carbon black are present in the rubber mixtures, the -total filler content, based on 100 parts by weight of rubber, i.s limited to at most 500 parts by weight and preferably to at most 300 parts by weight.

- 9a -~3~L45 The rubber mixtures always contain in addlti.on one or more accelerators. Accelerators are understood -to be the known vulcanisation accelerators, such as the dithiocarbamate, xan-tho-genate and thiuram accelerators, also the thiazole accelerators, ineluding the mercapto and sulphenamide accelerators, amine accelerators and aldehyde amine aecelerators, basie aecelerators, ineluding for example the quanidine accelerators and other basic : aeeelerators; ef. "Vulkanisation und Vulkanisationhilfsmittel (Vulcanisation ana Vulcanisation Aids)", a comprehensive account by Dr. ~. HOFMANN, Leverkusen (Verlag Berliner ~nion, Stuttgart, 1965, pages 14~ et seq, particularly page 122), and - irrespective of the above classification - the general vulcanisation accelera-tor classes of the mercapto, disulphide, polysulphide, sulphen-amide, thiazole and thiourea accelerators. It is preferred to use the sulphenamide accelerators, such as those disclosed in British Patent No. 1,201,862, including 2-diethylamino-4,6-bis-(eyelohexylsulphenamido)-s-triazine and 2-di-n-propylamino-4,6-bis-(N-t-butylsulphenamido)-s-triazine, also N-eyelohexyl-2-benzthiazole sulphenamide, benzthiazole-2-sulphene morpholide, N-t-butyl-2-benzothiazyl sulphenamide, N,N-dieyelohexyl-2-benzo-thiazyl sulphenamide, N-oxydiethylene-2-benzothiazosulphenamide, benzothiazole sulphene-t-oetylamide and N,N-di-i-propyl-2-benzo-- thiazyl sulphenamide. Other suitable aecelerators or co-aeeelera-to~s are the tetra-alkyl and dlalkyl diaryl thiuram mono-, di-and tetra-sulphides, sueh as tetramethyl thiuram monosulphide, tetramethyl thiuram disulphide, tetraethyl thiuram disulphide, dipentamethylene thiuram monosulphide, disulphide, tetrasulphide and hexasulphide, dimethyl diphenyl thi.uram disulphi.de, diethyl .diphenyl thiuram disulphide and similar known thiuram aeeelera-tors. Suitable dithiocarbamate accelerators are the derivatives of dialkyl, alkylcycloalkyl and alkyl aryl dithiocarbamie acids.
Two known representatives of this elass of accelerators are N-L2~ S

pentamethylene ammonium-N-pentamethylene dithiocarbamate and the zinc dialkyl dithiocarbamates. Xanthogenate accelerators are the known deriva-tives of alkyl and aryl xanthogenic acids, such as for example zinc ethyl xanthogenate. Suitable mercapto accelera-tors are, in particular, 2-mercaptobenzthiazole, 2 mercaptoimida-zoline, mercaptothiazoline and a number of monomercapto and di-mercapto triazine derivatves (cf. for example British Patent No.
1,095,219), also mercapto-triazine accelerators such as, for example, 2-diethanolamino-4,6-bis-mercaptotriazine and 2-ethyl-amino-4-diethylamino-6-mercapto-s-triazine. Suitable disulphide accelerators are bis-(2-ethylamino-4-diethylaminotriazin-6-yl)-disulphide, bis-(2-methylamino-4-di-i-propylaminotriazin-6-yl)-disulphide and dibenzothiazyl disulphide, also the polysulphidic or oligosulphidic triazine derivatives and their polymers which are produced in accordance with German Offenlegungsschrift No.
.~ p~bI;sheo~ ~ecerr~e~ 4, /~7/
; ~ 2,02t,635~and which are also aisclosed in British Patent No.
1,353,532. Suitable-aldehyde amine accelerators include conden-sation products of saturated or unsaturated aliphatic aldehydes with ammonia or aromatic amines, such as for example butyralde-hyde aniline and butyraldehyde butylamine. Other basic accelera-tors are, for example, guanidine derivatives, such as diphenyl guanidine and di-o-tolyl guanidine, and hexamethylene tetramine.
Suitable thiourea accelerators are for example thiourea itself and the diaryl thioureas, such as 1,3-diphenyl-2-thiourea.
According to the invention, it is also possible to use mixtures of two, ~hree or more accelera-tors, particularly the accelerator mixtures known in rubber technology, in the new rubbers mixtures, mixtures of sulphenamide accelerators in a predominant quant:ity and thiuram accelerators in a smaller quan-tity being preferred. For example, the quantity of thiuramaccelerator may amount for example to between one fifth and one twentieth of the quantity of sulphenamide accelerator. The vul-~23145 canisation accelerators are present in the rubber mixture in quan-tities of from 0.2 -to 10 parts by weight, based on 100 parts by weight of rubber, and in addition are in the aforesaid molar ratio to the organosilane and the sulphur.
It may be of advantaye for one or more triazine su phen-imides of dicarboxylic acids to be worked into, or to be addition-ally present in, the rubber mixtures. These -triazine sulphen-~ n,6b~,sheOt ~a~ 5~ ~6 imides are disclosed in German Off~nlegungsschrift No. 2,430,143l.
They are dicarboxylic acid imides attached once or twice to the s-triazine ring through a divalent sulphur atom, such as imides of for example succinic acid, glutaric acid, phthalic acid and tetrahydrophthalic acid, and (alkyl) derivatives thereof. Such compounds are, for example, 2-ethylamino-4-diethylamino-6-phthalimido-thiotriazine, 2-diethylamino-4,6-phthalimido-thio-triazine, 2-diethylamino-4,6-bis-(5,5-dimethylhydantoyl)-thio-triazine, 2-diethylaminotriazinyl-4,6-bis-thio-(3,5-dimethyl cyanurate), 2-diethylamino-4,6-bis-succinimido-thiotriazine and inter alia 2-dimethylamino-4,6-bis-succinimido-thiotriazine.
These triazine sulphenimides may be added to the rubber mixtures in quantities of from 0.01 to 10 parts by weight, based on 100 parts by weight of rubber. It is also possible with advantage to use commercial vulcanisation retarders, in some cases even in addition, for example in quantities of from 0.05 to 5 parts by weight, based on 100 parts by weight of rubber. Vulcanisation retarders are, for example, benzoic acid, salicylic acid, phthalic acid anhydride, N--nitrosodiphenylamine and other retarders known per se, preferably N-cyclohexyl thiophthalimide and polynitroso- -2,2,4-trimethyl-1 t 2-dihydroquinoline.
The sulphur, in the aforesaid qu~ntities and in the aforesaid molar ratio to silane and accelerator, is used in the form of elemental sulphur in the usual purity and in powder form or in the form of rubber-active or insoluble sulphur.

1~;231~5 The oligosulphidic organosilanes correspondiny to general formula I above are known per se and may be obtained by known methods (cf. for example Belgian Patent No. 787,691).
Examples of preferred organosilanes are the bis-(trialkoxysilyl-alkyl)-oligosulphides, such as bis-(trimethoxy-, -triethoxy-, -trimethoxyethoxy-, -tripropoxy-, -tributoxy-, -tri-i--propoxy-and -tri-l-butoxy-silylmethyl)-oligosulphides and, in particular, the di-, tri-, tetra-, penta-, hexa-sulphides etc., also bis-(2-trimethoxy, -triethoxy-, -trimethoxyethoxy-, -tripropoxy- and -tri-n- and -i-butoxy-ethyl)-oligosulphides and, in particular, the di-, tri-, tetra-, penta-, hexa-sulphides etc., also the bis-(3-trimethoxy-, -triethoxy-, -trimethoxyethoxy-, -tripropoxy-, -tri-n-butoxy- and -tri-i-butoxy-silylpropyl)- oligosulphides, particularly the di-, tri-, tetra-sulphides etc. up to octasul-phides; the corresponding bis-(3-trialkoxy-silylisobutyl)-oligosulphides, the corresponding bis-(4-trialkoxysilylbutyl)-oligosulphides and so on up to the bis-(8-trialkoxysilyloctyl)-oligosulphides. Of these selected, relatively simple organo-silanes of formula I, it is preferred to use the bis-(3-tri-methoxy-, -triethoxy- and -tripropoxy-silyl-propyl)-oligosulphides, particularly the di-, tri-, tetra- and penta-sulphides and, above all, the triethoxy compounds containing 2, 3 or 4 sulphur atoms and mixtures thereof. In general formula I, Alk represents a difunctional, linear or branched hydrocarbon radical, preferably a saturated alkylene radical having a straight carbon chain with from 1 to 4 carbon atoms which may be interrupted by a phenylene radical.
The silanes are used in quantities of from about 1.0 to 10 parts by weight, based on the quantity of rubber (100 parts by weight), although they are in addition incorporated into the aforesaid molar ratio to accelerator and sulphur. Where silicate filler is present in the rubber mixture, the silane may be used

3:~45 in a quantity of from about 1 to 25 parts by wei~hl per 100 par-ts by weight of silicate filler.
The rubber mixtures preferably also contain antiagers or mixtures of known an-tiagers in the usual quantities, i.e in quantities of from 0.1 to 10 parts by weight, based on 100 parts by weight of rubber.
It may be of advantage to add plasticiser oils, for example highly aromatic or naphthenic plasticiser oils, to the rubber mixtures, particularly for the production of treads for vehicle tyres. For winter tyre treads for example, these plasticiser oils should have a low setting point of from 0C to -60C and preferably from -10C to -55C. The plasticiser oil may be used in quantities of from about 3 to 100 parts by weight, again based on 100 parts by weight of rubber.
Furthermore oxides of polyvalent metal oxides which are known in rubber technology can be added to the rubber mixture in quantities of 0.05 to 10 parts by weight, relative to 100 parts by weight of rubber. These metal oxides comprise primarily zinc oxide and/or magnesium oxide, particularly in a fine-grained and/
or active form. Magnesium oxide and lead oxide as well as the oxides of alkaline earth metals and of other heavy metals can also be used.
The rubber mixture also contains preferably an organic acid, which is solid at room temperature and is used in rubber technology, in quantities from 0.05 to 10 parts by weight, rela-tive to 100 parts by weight of the rubber used. Fatty acids such as stearic acids, palmitic acid, lauric acid or correspond-ing fatty acids of the homologous series of 12 to 24 carbon atoms in the molecule, as well as benzoic acid or salicylic acid are preferably used.
The other optional ingredients of the mixture are auxiliaries known per se in rubber technology and may be used in ~2~ 5 -the usual quantities. Auxiliaries such as -these include inter alia hea-t stabilisers, liyht stabilisers, ozone stabilisers, vulcanisation retarders, processing aids, plasticisers, tacki-fiers, blowing agents, dyes, pigments, waxes, extenders and acti-vators.
For use, the organosilanes, the accelerators and, optionally, other additives may be added beforehand to the rubber mixtures or to a few other constituents or to one constituent of the mixture, for example the filler. In some cases, it may be advisable to hydrolyse the organosilanes or to subject them to partial hydrolysis before use. However, it is better, particu-larly for reasons of easier metering and handling, to add the oligosulphidic silanes to part of the silicate filler to be used which converts the normally liquid organosilanes into a powder-form processing product. A mixture of equal parts by weight of the previously mentioned silane Si 69 (a trademark) and an active silica filler (Ultrasil(R) VN 3) has proved to be very favourable.
This silica filler may even be rePlaced by an equal amount of carbon black. In some cases, it is even possible, although not of any particular advantage, uniformly to apply the organosilanes from their solution to the surface of the filler particles and to use them in this form. The three or even only two of the described modes of application may even be combined.
The rubber mixtures may be produced by the so-called "upside-down" process which is also known as "overhead mixing".
The present invention will be illustrated by the follow-ing Examples in conjunction with the accompanying drawings in which the ingredien-ts of the mixture are measured in parts by `
weight, unless othe:rwise indicated. The mixtures of the Examples were produced as follows. The mixer used was a so-called kneader whose rotor speed was 40 r.p.m. Friction amounted to 1:1.16 and the initial temperature was 80C. In the first stage, all the ~231~5 rubber was introduced over a period of one minute, after which -the first nalf of the filler, the zinc oxide, tlle stearic acid and the silane were added over a period of around 1.5 minutes.
The second half of the filler was then added, again over a period of 1.5 minutes.
The subsequent general cleaning of tl~e kneader elements, including the pestle, took one minute, after which -the antiager(s) and the remaining chemicals were introduced. After a total mix-ing time of 5.5 minutes, the master batch formed was removed.
The master batch was then stored for 24 hours at room temperature.
The second mixing stage was then carried out in the same kneader rotating at the same speed with the same friction and at the same initial temperature, the master batch, the sulphur and the accelerator(s) being combined over a period of 1.5 minutes and processed to form a mixture in which the ingredients were uni-formly dispersed.
In the accompanying drawings, Figures 1 to 4 are graphs of torque Md against preheating time in minutes after a pre-heating time of 1 minute, test temperature 145~C for four of - 20 the mixtures.
EXA~IPLE 1 The following four mixtures are prepared from the mix-; ture ingredients indicated. Mixture No. 3 corresponds to the present invention:
Mixture No. 1 2 3 4 _ Natural rubber (RSS-I, Defo 1000 )~ 100 100 100 100 Rubber-grade carbon black N-220 42 40 40 40 Silica filler VN 3 gran. 2)12 20 20 20 Plasticiser oil (highly aromatic setting point + OaC) 3 3 3 3 Tackifier 3 3 3 3 Stearic acid 2.5 2.5 2.52.5 ,: : .
- .: - : , , - :- :, ~L2314~

Zinc oxide 5 5 5 5 An~i-ozonant wax (paraffin-based)4) N-Isopropyl-N'-phenyl-p-phenylene diamine 2.5 2.5 2.5 2.5 Poly-2,2,4-trimethyl-1,2-dihydro-quinoline l.S 1.5 1.5 1.5 Si 695) _ _ 3 3 Benzothiazyl-N-sulphene morpholide 1.2 1.2 1.2 1.2 Tetramethyl thiuram monosulphide 0.1 0.1 0.1 0.1 N-nitrosodiphenyl amine 0.3 0.3 0.3 0.3 Sulphur 2 2 1.5 0.75 1) Ribbed Smoke Sheets I having a Defo hardness of 1000 2) Precipita-ted active silica containing 87% of SiO2 and having a sET-surface of 210 m /g and a mean primary particle size of 18 micrometers in granulated form 3) A reaction product of p-tert.-butyl phenol and acetylene in the presence of zinc naphthenate: light-brown to dark granu-late melting at 110 to 130C, soluble in hydrocarbons.

4) Solidi~ication point 61-65C (Type G 35, a product of Lune-burger Wachsbleiche GmbH, Luneburg) 0 5) sis-(3-triethoxysilylpropyl)-ollgosulphlde, technical quality, having a sulphur content of at least 22.0% by weight.
Mixture No. 1 is a good standard comparison mixture.
This mixture and mixture No. 2 are prior art mixtures, mixture No. 2 corresponding to mixtures Nos. 3 and 4 in its composition except for the missing silane and the addition of sulphur. The mixture No. 4 shows that unless the rule according to the inven-tion is observed for this example, the desired properties of the mixtures and of the vulcanizates thereof cannot be attained.

According to this rule, at the vulcanization temperature of 145C
the molar ratio of silane to vulcanization accelerator to sulphur (computed as S8) of 1:1:1 must be maintained in order to attain the desired freedom of reversion. This molar ratio of 1:1:1 3~5 applies to -the corresponding mixture no. 3 of Examp]e 1 of the invention. If the composition of the reaction mixture is chan~ed, for example, with respect to quantity and type of the mixture ingredien-ts or if a different vulcanization temperature is desired, then said molar ratio also changes. Thus, the molar ratio changes if, for example, a different rubber, another carbon black/silica ratio, another silane or another vulcanization accelerator are used, or if the corresponding quantitive propor-tions are changed. The molar ratio also changes if only carbon black or only silica is used as the filler. The reversion values of the mixtures no. 1 to 4 were determined by using a Monsanto Rheometer (type MPV), for example, under the following conditions:
test time 2 hours, test temperature 145C, oscillation 3C, test frequency: 3 cycles per minute.

~ '.

.

~L23~L~5 Table I
Mixture No. 1 2 3 4 Reversion R 11.4 25.50.0 ~-S
Mooney Scorch Time in minutes (according to DIN 53 523/24 at 130C) 13.5 13 5 14O0 17.0 Mooney viscosity 72 85 78 76 The reversion value for mixture No. 4 could not be determined because a steadily-increasing torque (clirnbing Vulcameter curve) was observed with increasing vulcanisation time (cf. Figure 4). As shown further below, the w lcanisate resulting from mixture No. 4 cannot be used in practice.
The mixtures were wlcanised at 145C, a w lcanisation time (VT) of 30 minutes being maintained on one occasion and one of 300 minutes on a second occasion in order to be able to make the freedom from reversion of mixture No. 3 according to the invention more evident in the event of prolonged vulcanisation.
The vulcanisates were tested in accordance with DIN 53 504 using the R1 Standard Ring (6 mm). The results obtained were as follows: -Preliminary note: the upper figure represents the outcome ofthe test of the test specimen ~llcanised for 30 minutes, the lower figure corresponds to the 300-minute w lcanisation time.
Table II
of mixture No. 1 2 3 4 . .
Tensile strength in MPa 20.019;3 22.118.0 15.414.9 19.919.6 Modulus 300 in MPa 9.47.6 10.7 7.9 7.25.0 11.29.8 Shock elasticity according to37 37 38 35 DIN 53 512 (233C) in % 32 29 36 33 Resilience according to Healey 62.8 60.0 59.5 58.4 ASTM D 1054 in % 57.453.7 57.455.9 Tear initiation resistance 93 92 106 115 according to ASTM D 624 54 21 79 90 using Die A in N/mm , ~'~ Z 3~ ~ ~

of mixture No. 1 2 3 4 . . . _ .
Shore-A-hardness 63 61 65 60 DIN 53 505 (230C) 58 53 65 62 VT
(exception) Abrasion60 minutes 108 177 89 112 DIN 53 516120 minutes 154 250 96 123 (60 minutes) -Evaluation of the above test values shows that the vulcanisates produced in accordance with the lnvention from mixture No. 3 give the best individual and overall results:
Tensile strength decreases to a lesser extent than that of the comparison vulcanisate (mixtures 1 and 2) with longer vulcanisation time (VT). The exception is the mixture-4-vulcanisate because, as already mentioned, the Vulcameter curve continues to climb, which is also known as the "marching modulus". The modulus 300 (strain value at 300% elongation) shows a high level. By contrast, the moduli of the - -comparison vulcanisate~s show a distinct fall. The exception (from a low level) is the mixture-4-vulcanisate for the reason explained above. The lowest drop in the measured values starting from a high level is also observed in the measurements ~-~of the shock elasticity, resilience and tear initiation values.
The Shore hardness advantageously remaîns at the same level and ; the favourable and best DIN-abrasion value is only slightly impaired when the VT is doubled. Despite all these good properties, complete freedom from reversion (R=0) is only observed in the case of mixture No. 3 and it is this which is crucial to the invention.
Further measured values important to the utility value of the articles produced in accordance with the invention, such as industrial rubber articles or parts of tyres for motor ~231~5 vehicles, aircraft, etc. were obtained from the Go~licl~
Flexometer test carried out in accordance with AS1~ Standard D 623 A under the following conditions: VT 30 minutes;
test temperature = room temperature; load 11 kp; stroke 0.250 inch; test time 60 minutes. The non-aged test speclmens gave the following values:
Table III
of mixture No. 1 _ 2 3 4 Heat formation in oc 100 84 70 105 Static compression in % 10.0 14.5 6.6 12.8 Dynamic compression in % 38.5 40.0 19.5 38.9 Compression set in % 20.2 d 14.7 d The letter "d" means that the test specimen did not withstand the test load, but instead was prematurely destroyed.
- In some cases, the test specimens burst with a bang.
Testing of aged test specimens (lst ageing 3 days at lOOoC in a recirculating air oven, 2nd alternative ageing ` 7 days at lOOoC) in the same way produced equally favourable results for the mixture-3-vulcanisates. The test specimen of mixture No. 1 aged for 7 days failed after 52.5 minutes under test whilst the test specimen of mixture No. 2 failed after only 10.5 minutes (thermal destruction). The mixture-3-test specimen withstood the entire test without damage.
If the Goodrich Flexometer test is repeated after a longer VT of 300 minutes, the very high stability of the mixture-3-vulcanisates under load is again observed. By contrast, the mixture-1-test specimen, which had previously proved to be relatively stable with the shorter VT, failed after 58 minutes (without ageing), after 35 minutes when aged for 3 days (lOOoC) and after 36 minutes when aged for 3~L~5 7 days (lOOoC) as a result of thermal decomposit;ion.
The results of the useful-life-test in the Goodrich Flexometer carried out under otherwise the same conditions are particularly revealing. Heating times (VT) of 60 minutes were selected~and maintained for this test. The mixture~
test specimens (average from three test specimens) were destroyed by thermal decomposition after 78 minutes and the test specimens of mixture No. 2 o~ average after 13 minutes ~hereas the mixture-3-test specimens remained intact for on average 137 minutes and were only mechanically destroyed thereafter. The corresponding values of the test specimens aged for three days at lOOoC were 38 minutes (mixture No. 1), 11 minutes (mixture No. 2) and ~2 minutes (mixture No. 3).
These figures speak for themselves.
Treads were produced from the known standard mixture 1 and mixture No. 3 a ccording to the invention. )75 SR 14 tyres were produced with these treads and tested for w e a r and durability (total number of kilometers covered on motorways, primary roads and the ~urnburgring = 17,581).
The total tread wear index as an overall evaluation standard a~ounted to 119% for the tyres produced in accordance with the invention based on the figure of 100% laid down for t'ne standard tyres. To illustrate these figures, it may oe stated that, under the same conditions as prevail for example in one and the same vehicle, the standard tyres show the same wear after running for 100 days as the new tyres after running for 119 days (19% better useful life).
-The four Figures show the somewhat simplified trend of the Vulcameter curve (torque Md against the heating time t in minutes after a preheating time of 1 minute; test temperature 145C) for the four above-mentioned mixtures: the customary downwardly sloping branch for the known mixtures 1 (Fig. 1) ~3 1~ 5 and 2 (Fig. 2) and tlle undesirable upward slope of the elongate branch of the Vulcameter curve of mixture 4 (Fig. 4).
The Vulcameter curve in Fig. 3 is the curve of the tested mixture 3 obtained in accordance with the invention which ends in an elongate, horizontal section and which slopes neither upwards or downwards, even after a test period of 120 minutes and longer, which reflects the freedom of reversion (R=0) of the mixture or w lcanisates. According to the above formula II, the reversion R is nil when the molar ratio of silane (general formula I) to accelerator to sulphur (expressed as S8) is adjusted at the required vulcanisation temperature in such a way that the Vulcameter curve ends in the same way as the curve in Fig. 3. Since the vulcanisation time for example is also selected in accordance with the trend of the Vulcameter curve in practice, no difficulty or significant extra expense is involved in determining the above-described molar ratio by means of the Vulcameter curve for the particular rubber mixture.
EXA~PLE 2 This Example is intended to demonstrate the influence of the vulcanisation temperature (VTE) on the molar ratio critical to the invention.
In otherwise the same basic mixtures as in Example 1 (mixture 5 corresponds to mixture 1; mixtures 6 and 7 correspond to mixture 3), the parts by weight of the silane, the accelerator and the sulphur (based on 100 parts by weight of - rubber) in mixtures 6 and 7 according to the invention were changed accordingly, the VTE for mixture No. 6 being 1600C
and for mixture No. 7 170~C. Mixture 5 is the comparison mixture. The mixture ingredients which stayed the same as in Example 1 were omitted.

~314S

Table IV
Mixture No. 5 6 7 . .
Silane Si 69 - 3.5 4.0 Accelerator (benzothiazyl-N-sulphene morpholide) 1.2 1.65 1.88 Tetramethyl thiuram monosulphide0.1 - -N-nitrosodiphenyl amine 0.3 Sulphur 2.0 0.84 0.76 As described in Example 1, the mlxtures were tested for 2 hours in a Monsanto Rheometer, mixture 5 at 160C and 1700C, mix~ure 6 at 160C and mixture 7 at 170C. The conditions and the units of the measured values were otherwise the same as in Example 1. The results of the tests for reversion (see formula II) etc. were as follows:
Table V
of mixture No. 5 6 7 Re version 160C 28.6 0 Reversion 1700C 40.6 0 Modulus 300 (1600C) a. for VT 10 and 15 minutes 9.9 10.4 (VT 15 mins.) b. for VT 60 minutes 6.9 11.9 c. for VT 120 minutes 6.5 12.0 Tear initiation resistance (1600C) according to ASTM D 624 DIE A
a. for VT 10 and 15 minutes 105 109 (VT 15 mins.) b. for VT 60 minutes 69 119 c. for VT 120 minutes 43 81 Shore-A-hardness (1600C) a. for VT 10 and 15 minutes 63 65 (VT 15 mins.) b. for VT 60 minutes 59 68 c. for VT 120 minutes 59 68 Wear (DIN 53 516) (1600C) a. for VT 10 and 15 minutes 91 88 (VT 15 minutes) b. for VT 60 minutes 200 85 c. for VT 120 minutes 217 83 ~ 3145 of mixture No. 5 6 7 .~
Modulus 300 (170C) a. for VT 6 and 10 minutes 10.6 VT10:10.8 b. for VT 60 Ininutes 6,5 12.8 c. for VT 120 minutes 6.6 12.0 Shore-A-hardness (1700C) a. for VT 6 and 10 minutes 62 VT10:65 b. for VT 60 minutes 57 68 c. for VT 120 minutes 57 68 Tensile strength (DIN 53 540) (170C) in MPa a. for VT 6 an~ 10 minutes 24.3 VT10:19.7 b. for VT 60 minutes 16.8 19.0 c. for VT 120 minutes 16.7 18.8 The test results again clearly demonstrate the superiority of the invention. Free from reversion (R=0, fo-rrnula II), the vulcanisates produced in accordance with the invention show distinctly better results and hence have superior utility or service properties. The Vulcameter curves of mixtures 6 and 7 also show the characteristi c trend in analogy to the curve in Fig. 3.

Where different vulcanisation accelerators are used, different ratios by weight are required on account of their different molecular weights and under the rule according to the invention.
Accordingly, the basic mixture No. 3 of Example 1 was varied with different accelerators (once again only the changed agents and quantities are indicated):
Table VI
.
Mixture No. 8 9 10 11 12 13 Silane Si 69 3 3 3 3 3 3 Sulphur 1.43 1.43 1.43 1.43 1.43 1.43 2-Mercaptobenzthiazole 0.93 - - - - -Mixture No. 8 9 10 11 12 13 , ._ I
2,2'-dibenzothiazyl-disulphide - 1.85 N,N-dicyclohexyl-2-benzothiazyl sulphenamide - - 1.93 - - -N-Oxydiethylene-2-benzo-thiazole sulphenamide - - - 1.41 N-t-butylbenzothiazyl-sulphenamide - - - - 1.33 N-cyclohexyl-2-benzothiazyl sulphenamide - - - - - 1.47 As in Example 1, mixtures 8 to 13 were tested for 2 hours in a Monsanto Rheometer under the same conditions as in Example 1. The results o~tained were as follows:
Table VII
of mixture No. 8 9 10 11 12 13 .
Reversion (1450C) O 0 4.1 1.6 0 2.0 Mooney Scorch Time t5 7.0 7.2 19.6 16.7 13.6 14.3 Mooney Cure Time t35 10.6 9.9 ,25.7 24.4 18.1 17.9 (Mooney Test according to DIN 53 523/24 at 1300C) Modulus 300 (MPa) 7.6 9.3 11.2 10.5 11.1 10.7 Tensile strength (DIN 53 504. MPa) 17.8 19.9 22.4 22.2 22.1 22.1 For VT (minutes) 30 25 38 25 25 20 Accordingly, the Mooney Scorch and Cure Times may be varied through the choice of the accelerator without any significant change in the properties of the w lcanisates.
This range of variation represents a valuable enrichment so far as industrial practice is concerned.

~Z3~45 EXA~1PI.E 4 ... .. _ I
Two rubber mixtures are prepared from the followlng ingredients in the same way as described a~ove. Mixture No. 14 is the comparison mixture.
- Mixture No. 14 _15 Rubber SMR 5 ) 100100 Rubber-grade carbon black N 330 30 30 Clay 60 60 Silane Si 69 - 3 Zinc oxide 3 3 Stearic acid 2 2 N-cyclohexyl-2-benzothiazole sulphenamide3) 11.47 Sulphur 2 1) Standard Malaysian Rubber containing at most 0.05%
of impurities 2) Suprex Clay, a product of the J.M. Huber Corp., Locust, N.J., U.S.A.
3) Vulcanisation accelerator Whereas mixture No. 14 showed a reversion R of 10.7 in the Monsanto ~heometer Test at 1400C under otherwise the same conditions as in Example 1, a reversion ~ of 1.3 was calculated in accordance with formula II for mixture No. 15, ~hich signifies virtual freedom from reversion of the vulcanisate. ~urther tests showed that, where vulcanisation was carried out at distinctly higher temperatures of 160 and 170C, mixture No. 15 no longer produced reversion-free vulcanisates. After vulcanisation at 1500C, the mixture-15-vulcanisate again showed very good property values, as evidenced by the following figures:

....~ ., ~ .

~3L;23~

Table VIII
of mixture No. 14 15 Modulus 300 (MP~) 13.7 15.0 Shock elasticity (DIN 53 512) in % 45 45 Shore-A-hardness (DIN 53 505) 68 68 In addition to the already repeatedly described advantages associated with freedom from reversion, the mixture-15-vulcanisate according to the inventi.on shows other favourable properties.
EXA~IPLE 5 Mixtures containing solely carbon black as filler may also be processed in accordance with the invention.
Mixture No. 16 17 Rubber-RSS I
Defo 1000 (cf. Example 1) 100 100 Rubber-grade carbon black N 220 (Degussa's CORAX(~)) 50 50 Zinc oxide 3 3 Stearic acid 2 2 Benzothiazyl-N-sulphene morpholide 1 1~41 Sulphur 2 1.0 Comparison mixture 16 showed a reversion R of 11.3 whereas mixture 17 according to the invention showed a reversion R of I.3 which represents virtual freedom from reversion.
The property values of the vulcanisates obtained at a VTE of 1500C for a VT ensuing from the Vulcameter curve (at t90G/) were as follows:

31~

Table IX
of mixture No. 16 17 VT (minutes) 16 30 Tensile strength (DIN 53 504. MPa) 21.3 22.3 Modulus 300 (MPa) 15.8 14.6 Breaking elongation (%) 390 420 Shock elasticity (DIN 53 512. %) 42 42 Shore-A-hardness (DIN 53 505) 68 67 According to the invention, therefore, it is possible to obtain freedom from reversion and, at the same time, favourable vulcanisate properties comparable with those of a conventional carbon-black-filled rubber mixture.

Mixtures of various rubbers are also accessible to the mixtures and the process according to the invention. Mixture No. 18 is a comparison mixture which gives good results.
Mixture No. 18 19 Natural rubber (RSS I, cf. Example 1) 50 50 Polybutadiene rubber with a high cis-1,4-content 50 50 Silica filler VN 3 (cf. Example 1) - 15 `
Rubber-grade carbon black N 375 45 30 Zinc oxide 5 5 Stearic acid 2 2 Plasticiser oil (cf. Example 1) 8 8 Poly-2,2,4-trimethyl-1,2-dihydroquinoline 1.5 1.5 N-isopropyl-N'-phenyl-p-phenylene diamine 0.8 0.8 Silane Si 69 - 2.25 Benzothiazyl-N-sulphene morpholide 0.8 1.06 Sulphur 1 0.75 231~5i Testing of the mixtures in a Monsanto Rheometer at 150C
(under otherwise the same conditions as in Example 1) produced a reversion R of 13.1 for mixture 18 and a reversion R of O for mix-ture 19.
After vulcanisation at 150~C, the vulcanisates produced the following test results Table X
of mixture No. 18 19 _ Tensile strength in MPa 21.6 21.7 ~odulus 300 in MPa 5.2 5.7 Resilience according to ~ealey (ASTM D 1054) in ~ 57.9 61.9 Shore-A-hardness (DIN 53 505) 53 52 These figures show that the mixture No. 19 according to the invention is not only free from reversion, the mixture-l9-vulcanisates are also superior in their service properties.
The new rubber mixtures contain the main rubbers from the above-described group (A), such as preferably natural rubber and/or polyisoprene rubber, best in a predominant quantity down to 50% by weight, in some cases even to as low as 10%, based on the weight of the total amount of rubber.
EXAMP~E 7 The following rubber mixtures show the favourable effects which can be attained from the above-mentioned additional concomitant use of vulcanization retarders inthe mixtures with the preferred N-cyclo hexyl thiophthalimide Mixture No. 20 21 22 _ natural rubber (RSS I) 100 100 100 rubber-carbon blac~ N-220 45 45 45 ` 30 silica filler VN 3 (see Example 1) 17 17 17 zinc oxide 5 5 5 stearic acid 2.5 2.5 2.5 ~23~

N-isopropyl-N~-phenyl-p-phenylene diamine 2.0 2.0 2.0 poly-2,2,4-trimethyl-1,2-dihydro quinoline 0.5 0.5 0-5 ozone-resistant wax (see Example 1) 2.0 2.0 2.0 plasticizer oil (aromatic) (see Example 1) 8.0 8.0 8.0 benzothiazol-2-sulphene morpholide 1.0 benzothiazyl-2-cyclohexyl-sulphene amide - 1.25 1.25 N-cyclohexyl thiophthalimide - - 0.3 sulphur 1.5 1.6 1.6 mixture of equal parts by weight of Si 69 (see Example 1) and rubber-carbon black N 330 ~ 5.1 5.1 The rheometer test (see Example 1) provided the follow-ing characteristic test results for the three mixtures:
Mixture No. 20 21 22 reversion in % at a test temperature of 142C 9.7 2.0 1.2 incubation time (in seconds) 583 542 797 Mixture No. 1 is a comparison mixture which is conven-tionally cross-linked with sulphur and vulcanization accelerators.
The mixtures no. 2 and 3 are according to the invention, mixture 3 additionally containing only the small quantity of 0.3 part by weight of a vulcanizing accelerator. The results of the measure-ments show particularly that the mixture no. 3 has a resistance to reversion which is practically as good as that of mixture no.
2, but additionally has a distinctly longer incubation time caused by the addition of the vulcanization retarder. The incu-bation time is the time from the start of the testing to the moment of the dist:inct rise of the cross-linking isotherm. In practice the incubation time corresponds to the prevulcanization time, i.e. the time up to the start of the vulcanization reaction.

.

~L~Z3~S

The advantages afforded by the invention are significant, particularly in industrial prac-~ice, for example in the manufac-ture of large pneumatic tyres for heavy transport vehicles, for earth-moving machines and the like.
Further applications for the described rubber mixtures and the process according to the invention include in particular technical rubber articles, such as cable sheaths, hoses, drive belts, V-belts, conveyor belts, roller coverings, motor vehicle tyres, particularly car, lorry and cross-country vehicle tyres and treads, carcasses and sidewalls (cross-country vehicle tyres include any large pneumatic tyres for earth-moving machines, transporters, desert vehicles and the like), also damping elements, sealing rings, sole material for shoes and many others. The new rubber mixtures have also proved to be effective for coupling mixtures for more firmly uniting rubber with reinforcing materials and reinforcing inserts, particularly fibres, fibre structures and wires, for example of glass, metals (for example steel cord, etched, zinc-plated or brass-plated) and textile materials (poly-amide or polyester fabrics and the like).

~0 :

, :

Claims (32)

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

1. In a formable and vulcanisable rubber mixture which contains at least one rubber which still contains double bonds and which can be crosslinked with sulphur and a vulcanisation accelera-tor to form an elastomer from 0.2 to 10 parts by weight of sulphur from 0.2 to 10 parts by weight of at least one vulcanisation accel-erator and from 1 to 10 parts by weight of at least one silane corresponding to the formula (I) in which each of the individual radicals R and R1 represents an alkyl group containing from 1 to 4 carbon atoms, a cycloalkyl group containing from 5 to 8 carbon atoms or the phenyl radical;
n is 0, 1 or 2, Alk is a difunctional, straight-chain or branched hydrocarbon radical containing from 1 to 10 carbon atoms, and _ is a number of from 2.0 to 8.0, or its hydrolysate and, the improvement in which the silane, vulcanisation accelerator and sulphur, expressed as S8, are present in such a molar ratio that, at the vulcanisation temperature, the rubber mixture has a rever-sion R resulting from the crosslinking isotherm (DIN 53 529) of 0 (+ 5%), R being calculated in accordance with the following formula:
(II) in which Dmax is the maximum Vulcameter torque, Dmin is the mini-mum Vulcameter torque, D(max + 60 mins) is the Vulcameter torque as measured 60 minutes after appearance of the maximum torque.

2. A mixture as claimed in claim 1 in which the rubber is a halogen free rubber.

3. A mixture as claimed in claim 2 in which the rubber is a diene elastomer.

4. A mixture as claimed in claim 3 in which the rubber is selected from natural rubbers, butadiene rubbers, isoprene rubbers, butadiene-styrene rubbers, butadiene-acrylonitrile rub-bers, butyl rubbers, terpolymers of ethylene, propylene and non-conjugated dienes.

5. A mixture as claimed in claim 1 which contains one or two additional rubbers admixed with one or two of said rubbers.

6. A mixture as claimed in claim 5 in which the addi-tional rubber is selected from carboxyl rubbers, epoxide rubber, trans-polypentenamer, halogenated butyl rubbers, rubbers of 2-chlorobutadiene, ethylene-vinyl acetate copolymers and ethylene propylene copolymers.

7. A mixture as claimed in claim 1 which contains at least one of natural rubbers and polyisoprene rubbers.

8. A mixture as claimed in claim 1 which contains at least one filler selected from a silicate filler in an amount from 1 to 300 parts by weight and a carbon black filler in an amount from 0.1 to 150 parts by weight, the total amount of filler being not more than 3500 parts by weight based on 100 parts by weight of rubber.

9. A mixture as claimed in claim 8 in which the sili-cate filler is selected from butyl dispersed silicas, synthetic silicates, natural silicates and glass fibers and glass fiber products.

10. A mixture as claimed in claim 8 in which the filler consists of a silicate filler in an amount of at least 5 parts by weight per 100 parts by weight of rubber.

11. A mixture as claimed in claim 8 in which the filler is a precipitated silica in an amount from 10 to 250 parts by weight based on 100 parts by weight of rubber.

12. A mixture as claimed in clalm 8 in which the carbon blaak is a rubber grade carbon black.

13. A mixture as claimed in claim 8 in which the carbon black is present in an amount up to 150 parts by weight based on 100 parts by weight of rubber.

14. A mixture as claimed in claim 1 in which the vul-canization accelerator is selected from dithiocarbamate, xantho-genate thiurea, thiazole, mercapto, sulphenamide, amine, aldehyde, and basic accelerators.

15. A mixture as claimed in claim 1 in which the vul-canization accelerator is a sulphenamide accelerator.

16. A mixture as claimed in claim 1 which contains 0.01 to 100 parts by weight based on 100 parts by weight of rubber of at least one triazine sulphenamide of a dicarboxylic acid.

17. A mixture as claimed in claim 1 which contains 0.05 to 5 parts by weight of a vulcanization retarder based on 100 parts by weight of rubber.

18. A mixture as claimed in claim 1 in which in formula I, Alk is a saturated straight chain alkylene radical with 1 to 4 carbon atoms which may be interrupted by a phenylene radical.

19. A mixture as claimed in claim 1 in which the silane is a bis (tri-alkoxysilylalkyl)-oligosulphide.

20. A mixture as claimed in claim 19 in which the alkyl group has 1 to 8 carbon atoms and the alkoxy group is selected from methoxy, ethoxy, n-propoxy, n-butoxy, iso-propoxy and iso-butoxy.

21. A mixture as claimed in claim 10 in which the silane is selected from the bis-(3-trimethoxy-, -triethoxy- and -tripropoxy-silyl-propyl)- di-, tri-, tetra- and penta-sulphides.

22. A mixture as claimed in claim 1 in which the sil-ane is a bis(3-triethoxy silyl propyl)-oligosulphide having 2 to 4 sulphur atoms.

23. A mixture as claimed in claim 1 which contains a silicate filler and the silane is present in an amount from 1 to 25 parts by weight per 100 parts of silicate filler.

24. A mixture as claimed in claim l, 2 or 3 which contains 0.1 to 10 parts by weight based on 100 parts by weight of rubber of an antiager.

25. A mixture as claimed in claim 1, 2 or 3 which contains 3 to 100 parts by weight based on 100 parts by weight of rubber of a plasticizer oil.

26. A mixture as claimed in claim 1, 2 or 3 which contains 0.05 to 10 parts by weight relative to 100 parts by weight of rubber of a polyvalent metal oxide.

27. A mixture as claimed in claim l, 2 or 3 which contains 0.05 to 10 parts by weight relative to 100 parts by weight of rubber of an organic acid.

28. A rubber mixture as claimed in claim l, in which the rubber is at least one of natural rubber and polyisoprene rubber is used, the mixture containing the technical bis(3-triethoxy-silyl propyl)-oligosulphide having a sulphur content of at least 22.0% by weight, a sulphenamide vulcanisation accelera-tor and the sulphur (S8) in a molar ratio of 1:1:1 (deviation +
0.1 in each case) for a vulcanisation temperature of 145°C (+ 3°C).

29. A mixture as claimed in claim 1, 2 or 3 which contains at least one member selected from heat stabilisers, light stabilisers, ozone stabilisers, vulcanisation retarders, process-ing aids, plasticisers, tackifiers, blowing agents, dyes, pigments, waxes, extenders and activators.

30. A process for vulcanising moulding compositions based on at least one rubber which still contains double bonds and which can be crosslinked with sulphur and a vulcanisation accelerator to form an elastomer using from 0.2 to 10 parts by weight of sulphur, from 0.2 to 10 parts by weight of at least one vulcanisation accelerator and from 1 to 10 parts by weight (all parts by weight being based on 100 parts by weight of rubber) of at least one silane corresponding to the formula ( I ) in which each of R and R1 individually represent an alkyl group containing from 1 to 4 carbon atoms, a cycloalkyl group containing from 5 to 8 carbon atoms or the phenyl radical; n is 0, 1 or 2, Alk represents a difunctional, straight-chain or branched hydro-carbon radical containing from 1 to 10 carbon atoms and x is a number of from 2.0 to 8.0, or its hydrolysate, the moulding compo-sition being heated to the selected vulcanisation temperature, thoroughly heated at that temperature and cooled, the improvement in which the molar ratio of silane to accelerator to sulphur (expressed as S8) in the moulding composition is selected in such a way that, at the vulcanisation temperature, the reversion R
resulting from the crosslinking isotherm (DIN 53 529) is nil (+ 5%), as determined in accordance with the following;

(II) in which Dmax is the maximum Vulcameter torque, Dmin is the mini-mum Vulcameter torque, D(max + 60 mins)is the Vulcameter torque as measured 60 minutes after appearance of the maximum torque.

31. A process as claimed in claim 30, in which a mix-ture based on at least one natural and polyisoprene rubber, which contains a silane of the formula [(C2H5O)3Si-(CH2)3-]2Sx, in which x is 3.0 to 4.0 or technical bis(3-triethoxy-silyl propyl)-oligosulphide having a sulphur content of at least 22.0% by weight a vulcanisation accelerator selected from the class of sulphen-amide accelerators and sulphur, expressed as S8, in a molar ratio of 1:1:1 (with a deviation of + 0.1 in each case), is formed, vulcanised at 145°C (+ 3°C) and, on completion of vulcanisation, is cooled.

32. A motor vehicle tyre formed from a mixture of claim 1, 2 or 3.