WO2015135847A1

WO2015135847A1 - Rubber composition comprising a thiosulphate salt and a zinc oxide

Info

Publication number: WO2015135847A1
Application number: PCT/EP2015/054718
Authority: WO
Inventors: Lionel BELIN
Original assignee: Compagnie Generale Des Etablissements Michelin; Michelin Recherche Et Technique S.A.
Priority date: 2014-03-13
Filing date: 2015-03-06
Publication date: 2015-09-17
Also published as: FR3018520A1

Abstract

The rubber composition comprises a thiosulphate salt, from 2 to 7 phr of a zinc oxide and a salt of an alkaline-earth, alkali or lanthanide metal.

Description

Rubber composition comprising a thiosulfate salt and a zinc oxide

[001] The invention relates to compositions that can be used especially for the manufacture of semi-finished products and tires.

It is known from the state of the art, a semi-finished product comprising a metal reinforcing element embedded in a rubber composition. The metal reinforcing element comprises one or more metal wire reinforcing elements, for example made of steel, comprising a metal core coated with a metal coating, for example brass. The rubber composition comprises natural rubber as a diene elastomer, silica as a reinforcing filler, a vulcanization system including sulfur and zinc oxide, and various additives. The main function of zinc oxide is to activate the vulcanization between the diene elastomer and the sulfur. However, zinc oxide also has the other function of permitting the incorporation of sulfur in an adhesive interface between the metal core of each metallic wire reinforcing element and the rubber composition. This adhesive interface comprises a mixture of zinc oxide, zinc sulphide and copper sulphide resulting from the reaction between the brass and the rubber composition. Thus, a relatively large amount of zinc oxide, for example between 8 and 12 phr, is generally used.

It is also known from JP2009084410, a rubber composition comprising natural rubber as diene elastomer, silica as a reinforcing filler, a vulcanization system including sulfur oxide zinc oxide and various additives such as a plurality of adhesion promoters comprising cobalt acetylacetonate and sodium hexamethylene 1,6-bisthiosulfate (HTSNa). Such a composition provides improved adhesion and limited sensitivity to elevated temperatures and a humid atmosphere compared to a conventional composition free of cobalt acetylacetonate and / or sodium hexamethylene, 1,6-bisthiosulfate such as described in the previous paragraph. The compositions disclosed in JP209084410 comprise between 0.1 and 0.45 phr of cobalt acetylacetonate, between 4 and 10 phr of hexamethylene 1, 6 sodium bis-thiosulphate (HTSNa) dihydrate and 10 phr of zinc oxide. [004] On the one hand, cobalt acetylacetonate, and more generally cobalt salts, are relatively expensive. In addition, it is desired as much as possible to limit the amount to be employed of these cobalt salts to reduce their environmental impact.

The invention aims a composition to replace the cobalt salts while maintaining good rubber properties, especially in fluidity, and high adhesion, especially in hot and humid environment.

For this purpose, the subject of the invention is a rubber composition, comprising a thiosulphate salt, from 2 to 7 phr of a zinc oxide and a salt of an alkaline earth metal, alkali or lanthanide.

[007] The combination of the components of the composition according to the invention makes it possible, on the one hand, to replace the cobalt salts and, on the other hand, to reduce the use of zinc oxide while, in a very surprisingly, improving the adhesion performance with the metal reinforcing element and retaining the rubber properties at a good level, including fluidity. Thus, contrary to what could have been envisaged by a person skilled in the art, that is to say increasing the level of zinc oxide to reinforce the adhesive interface in order to compensate for the reduction or even the elimination of cobalt salts. a low level of zinc oxide is an essential characteristic of the invention making it possible to obtain excellent adhesion in a hot and humid environment, as demonstrated by the test results set out below.

In addition, the thiosulfate salts are relatively inexpensive and relatively neutral vis-à-vis the environment.

It may be envisaged to use various salts of an alkaline earth metal, alkali or lanthanide, for example potassium, magnesium, lithium, calcium or neodymium salts.

[010] In the present application, any range of values designated by the expression "between a and b" represents the range of values from more than a to less than b (i.e., terminals a and b excluded ) while any range of values designated by the expression "from a to b" means the range of values from the terminal "a" to the terminal "b" that is to say including the strict limits " a "and" b ".

[011] In a preferred embodiment, the thiosulfate salt is a hexamethylene 1, 6-bisthiosulfate salt.

[012] Preferably, the thiosulphate salt is sodium hexamethylene 1, 6-bisthiosulfate. Other salts of hexamethylene 1, 6-bisthiosulfate may be used, for example potassium or calcium salts.

[013] Advantageously, the composition comprises from 0.5 to 10 phr, preferably from 0.5 to 4 phr and more preferably from 1 to 3 phr of the thiosulfate salt. [014] The thiosulphate salt may be used in its hydrated form or not.

[015] Advantageously, the composition comprises from 3 to 6 phr of a zinc oxide and more preferably from 3 to 5 phr of a zinc oxide.

[016] Advantageously, the composition comprises at most 0.1 phr, preferably at most 0.05 phr of a salt of a transition metal. Advantageously, the salt of the transition metal is chosen from cobalt salts, nickel salts, iron salts, manganese salts, chromium salts, cadmium salts and copper salts and more preferably is a cobalt salt.

[017] Preferably, the composition is free of cobalt salt, that is to say that it comprises at most 0.01 phr of cobalt salt. In particular, the cobalt salts absent from the composition are chosen from cobalt acetylacetonate, cobalt naphthenate, cobalt resinate, cobalt stearate, cobalt tallate, cobalt benzoylacetonate and boron rosinate. Cobalt Toluate.

[018] Advantageously, the salt of an alkaline earth metal, alkali or lanthanide is an acetylacetonate of an alkaline earth metal, alkali or lanthanide.

[019] In one embodiment, the composition preferably comprises a salt of an alkaline earth metal. Thus, it is possible to preferentially envisage magnesium salts.

[020] Advantageously, the composition comprises from 0.1 to 5 phr, preferably from 0.5 to 4 phr and more preferably from 0.5 to 2 phr of the alkaline earth metal salt, alkali or lanthanide. Such a salt makes it possible to improve the rubber properties of the composition, in particular to lower its hysteresis, without reducing its adhesion properties.

[021] The composition may be in raw form or vulcanized.

[022] By rubber composition is meant that the composition comprises at least one elastomer or a rubber (both terms being synonymous) and at least one other component.

[023] In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are% by weight. The acronym "pce" means parts by weight per hundred parts of elastomer.

[024] Preferably, the composition comprises a diene elastomer.

[025] By elastomer or rubber (both terms being synonymous) of the "diene" type, is generally meant an elastomer derived at least in part (ie a homopolymer or a copolymer) of monomers dienes (monomers carrying two double bonds carbon-carbon, conjugated or not). [026] In a particularly preferred manner, the diene elastomer of the composition is chosen from the group of diene elastomers consisting of polybutadienes (BR), synthetic polyisoprenes (IR), natural rubber (NR), butadiene copolymers , isoprene copolymers and mixtures of these elastomers. Such copolymers are more preferably selected from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene-copolymers of butadiene-styrene (SBIR) and mixtures of such copolymers.

[027] The compositions may contain a single diene elastomer or a mixture of several diene elastomers, the diene elastomer (s) may be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, by example of thermoplastic polymers.

[028] Preferably, the composition comprises a reinforcing filler.

[029] When a reinforcing filler is used, it is possible to use any type of reinforcing filler known for its ability to reinforce a rubber composition that can be used for the manufacture of tires, for example an organic filler such as carbon black, a filler reinforcing inorganic such as silica, or a blend of these two types of filler, including a blend of carbon black and silica.

[030] As carbon blacks are suitable all carbon blacks conventionally used in tires (so-called pneumatic grade black). For example, mention will be made more particularly of reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades).

By "reinforcing inorganic filler" is meant in the present application, by definition, any inorganic or mineral filler (regardless of its color and origin (natural or synthetic), also called "white" filler, "clear" or "non-black filler" as opposed to carbon black, capable of reinforcing on its own, with no other means than an intermediate coupling agent, a rubber composition for manufacturing In other words, it is capable of replacing, in its reinforcing function, a conventional carbon black of pneumatic grade, which load is generally characterized, in a known manner, by the presence of hydroxyl groups (-OH) at its stage. area. [032] The physical state under which the reinforcing inorganic filler is present is indifferent, whether in the form of powder, microbeads, granules, beads or any other suitable densified form. Of course, the term "reinforcing inorganic filler" also refers to mixtures of different reinforcing inorganic fillers, in particular highly dispersible siliceous fillers as described below.

[033] Suitable inorganic reinforcing fillers include mineral fillers of the siliceous type, in particular silica (SiO ₂ ). The silica used may be any reinforcing silica known to those skilled in the art, especially any precipitated or pyrogenated silica having a BET surface and a CTAB specific surface both less than 450 m 2 / g, preferably from 30 to 400 m 2 / boy Wut. As highly dispersible precipitated silicas (referred to as "HDS"), mention may be made, for example, of the "Ultrasil" 7000 and "Ultrasil" silicas 7005 from Evonik, the "Zeosil" 1 165MP, 1,135MP and 1115MP silicas from Rhodia , the "Hi-Sil" silica EZ150G from the company PPG, the "Zeopol" silicas 8715, 8745 and 8755 from the Huber Company, the high surface area silicas as described in the application WO 03/16837.

Those skilled in the art will understand that, as an equivalent load of the reinforcing inorganic filler described in this paragraph, it would be possible to use a reinforcing filler of another nature, in particular an organic filler, provided that this reinforcing filler is covered with a filler. inorganic layer such as silica, or would comprise on its surface functional sites, especially hydroxyl, requiring the use of a coupling agent to establish the bond between the filler and the elastomer.

[034] The total reinforcing filler content (carbon black and / or reinforcing inorganic filler such as silica) is within a range from 0 to 120 phr inclusive, more preferably 0 to 70 phr included terminals, more particularly 5 at 70 pce included terminals and more preferably also from 0 to 60 pce inclusive terminals and very preferably from 5 to 60 pce inclusive, the optimum being of course differ depending on the particular applications targeted.

[035] Of course one can use a single carbon black or a blend of several carbon blacks of different ASTM grades. The carbon black may also be used in blending with other reinforcing fillers and in particular reinforcing inorganic fillers as described above, and in particular silica. [036] When an inorganic filler (for example silica) is used in the composition, alone or in a blend with carbon black, its content is within a range from 0 to 70 phr included limits (preferentially from 0 to 60 pce terminals included), in particular also from 5 to 70 pce inclusive terminals, and even more preferably this proportion varies from 5 to 60 pce inclusive terminals.

[037] Advantageously, the composition comprises at least 30 pce inclusive and preferably at least 40 pce included silica terminal.

The use of the resin and the oxide makes it possible to obtain excellent adhesion, preferably in the case where the composition comprises a reinforcing filler comprising predominantly by weight of the silica. For the most part, it is understood that the proportion by weight of silica is greater than the proportion by weight of the rest of the other reinforcing fillers of the composition, whether these fillers are organic, for example carbon black, or inorganic.

[039] Preferably, the composition comprises various additives.

The compositions may also comprise all or part of the usual additives usually used in elastomer compositions intended for the manufacture of tires, for example plasticizers or extension oils, whether these are aromatic in nature or not. -aromatic, pigments, protective agents such as anti-oxidants, anti-fatigue agents, reinforcing resins such as bismaleimides, acceptors (for example phenolic novolac resin) or methylene donors (for example HMT or H3M).

[041] Among the non-usual additives, and according to the invention, the composition comprises from 0.1 to 5 phr, preferably from 0.5 to 4 phr and more preferably from 0.5 to 2 phr of the metal salt. alkaline earth, alkaline or lanthanide. Preferably, the composition comprises a salt of an alkaline earth metal. Preferably the salt is acetylacetonate. More preferably, the salt is a magnesium acetylacetonate.

[042] Preferably, the composition comprises a crosslinking system, more preferably a vulcanization system. The crosslinking system, here vulcanization comprises sulfur or a sulfur donor agent, a vulcanization activator and a vulcanization accelerator. The system may optionally comprise one of the compounds selected from a peroxide, a bismaleimide and a vulcanization retarder.

[043] The vulcanization system preferably comprises sulfur and an accelerator, in particular of the sulfenamide type, such as chosen from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated "MBTS"), N-cyclohexyl-2-benzothiazyl sulphenamide (abbreviated "CBS"), N, N-dicyclohexyl-2-benzothiazyl sulphenamide (abbreviated "DCBS"), N-tert-butyl-2-benzothiazyl sulphenamide (abbreviated "TBBS" ), N-tert-butyl-2-benzothiazylsulfenimide (abbreviated "TBSI") and mixtures of these compounds.

[044] The vulcanization system optionally comprises other accelerators and vulcanization activators such as stearic acid. The vulcanization system also optionally includes a vulcanization retarder, for example N- (cyclohexylthio) phthalimide (abbreviated "CTP").

[045] The sulfur or sulfur donor agent is used at a preferential rate of between 0.5 and 10 pce inclusive, more preferably between 0.5 and 8.0 pce inclusive. All accelerators, retarders and vulcanization activators are used at a preferential rate of between 0.5 and 15 pce inclusive. The vulcanization activator (s) is or are used at a preferential rate of between 0.5 and 10 pb inclusive. According to the invention, the level of zinc oxide is 2 to 7 phr, preferably 3 to 6 phr and more preferably 3 to 5 phr.

[046] Another object of the invention is a semi-finished product comprising a metal reinforcing element embedded in a rubber composition as defined above.

[047] Examples of semi-finished products are crown reinforcement plies and carcass reinforcement plies.

[048] The rubber composition of the semi-finished product can be in raw or vulcanized form.

[049] Another object of the invention is a tire comprising a metal reinforcing element embedded in a rubber composition as defined above.

[050] The composition of the rubber mass in contact with the metal reinforcing element is uniform, that is to say identical at each point of the rubber mass. The tire can be in raw form and is then generally called a blank, or vulcanized and is then generally called a tire.

[051] The invention further relates to the use of a thiosulfate salt and 2 to 7 phr of a zinc oxide as an adhesion promoter between a rubber composition and a metallic reinforcement element.

[052] The invention will be better understood on reading the description which follows, given solely by way of non-limiting example. [053] COMPARATIVE TESTS

[054] Several gum compositions have been compared whose components and proportions are collated in Tables 1 and 2 below. The amounts of the components of the various compositions are expressed in parts per 100 parts by weight of elastomer (phr). Table 1 collects the composition data T, T01, T02, T03, T04 in which the level of cobalt salt, thiosulphate salt and alkaline earth metal salt, alkaline salt or lanthanide salt was varied without varying the zinc oxide level. Table 2 collects the data of composition T, compositions T05, T06, T07 and M01, identical respectively to compositions T01, T02, T03 and T04 with the exception of the zinc oxide content. Table 2 also gathers the data of a composition M02 according to the invention. The composition M01 is also in accordance with the invention.

[055] The values of the various properties measured (adhesion and rubber properties) are indicated in base 100 with respect to the values of the corresponding properties of the composition T. When the value of the property is greater than 100, the composition tested is more performance that the composition T vis-à-vis the property tested. Conversely, when the value of the property is less than 100, the composition tested is less efficient than the composition T vis-à-vis the property tested.

[056] Compositions tested

[057] The compositions of Tables 1 and 2 all comprise an elastomer, here a natural rubber and a reinforcing filler comprising predominantly by weight of the silica, here at least 30 pce inclusive, and preferably at least 40 pce including silica. The silica is of the "HD" type - "Zeosil 1 165MP" from the company RHODIA in the form of microbeads (BET and CTAB: approximately 150-160 m2 / g). The antioxidant is N-1,3-dimethylbutyl-N-phenyl-para-phenylenediamine ("Santoflex 6-PPD" from FLEXSYS). The organosilane is TESPT ("Si69" from EVONIK). The vulcanization accelerator is N-cyclohexyl-2-benzothiazylsulfenamide ("Santocure CBS" from FLEXSYS). The cobalt salt is cobalt acetylacetonate. The vulcanization retarder of the composition T is N- (cyclohexylthio) phthalimide (CAS No. 17796-82-6). The thiosulphate salt is a hexamethylene 1,6-bisthiosulfate salt (NOCIL MUMBAI company). The salt of an alkaline earth metal, alkaline or lanthanide is here a magnesium acetylacetonate ("NACEM Magnesium" from the company NIHO KAGAKU SANGYO, CAS No. 68488-07-3). [058] Preparation of the compositions tested

[059] The compositions are manufactured in appropriate mixers, using two successive preparation phases well known to those skilled in the art: a first phase of work or thermomechanical mixing (sometimes called "non-productive" phase) to high temperature, up to a maximum temperature (denoted Tmax) between 1 10 ° C and 190 ° C, preferably between 130 ° C and 180 ° C, followed by a second phase of mechanical work (sometimes called phase " productive ") at a lower temperature, typically below 1 10 ° C, for example between 60 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking system or vulcanization; such phases have been described for example in the aforementioned documents EP 501227, EP 735088, WO00 / 05300, WO00 / 05301 or W002 / 083782.

[060] For example, the first (non-productive) phase is conducted in a single thermomechanical step during which is introduced, in a suitable mixer such as a conventional internal mixer, initially all the constituents necessary basic materials (diene elastomer, reinforcing inorganic filler, anti-oxidant, thiosulphate salt, alkaline earth metal salt, alkali or lanthanide), then in a second step, for example after one to two minutes of mixing, the possible agents additional coating or processing and other miscellaneous additives, with the exception of the vulcanization system; when the bulk density of the reinforcing inorganic filler is low (general case of silicas), it may be advantageous to split its introduction into two or more parts. A second thermomechanical work step may be added to this internal mixer, after the mixture has fallen and intermediate cooling (cooling temperature preferably below 100 ° C.), in order to subject the compositions to a complementary thermomechanical treatment, in particular to improve still further, the dispersion in the elastomeric matrix of the reinforcing inorganic filler and its coupling agent. The total mixing time, in this non-productive phase, is preferably between 2 and 10 minutes.

[061] After cooling the mixture thus obtained, then incorporates the low temperature vulcanization system including zinc oxide, usually in an external mixer such as a roller mixer; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 minutes. [062] The final composition thus obtained is then calendered, for example in the form of a sheet, a plate or extruded, for example to form a rubber profile used for the manufacture of semi-finished products such as crown reinforcement plies, carcass reinforcement plies or finished product plies such as a tire in which a metallic reinforcing element is embedded in the rubber composition.

[063] The vulcanization (or cooking) is conducted in a known manner at a temperature generally between 130 ° C and 200 ° C, preferably under pressure, for a sufficient time which may vary depending in particular on the cooking temperature, vulcanization system adopted, the vulcanization kinetics of the composition in question or the size of the tire.

[064] Membership test

[065] The peel test is carried out according to ASTM D-4393-98 on test pieces comprising metal cables interposed between two rubber bands. The metal cables used are 2.30NF structure cables.

[066] The force required to take off or peel the cable / rubber interface between the cables and one of the two strips is measured. The appearance of the peeled interface is evaluated by a representative score of the peel facies.

[067] If, for a given composition, the number of stripped cables is less than the number of stripped cables of the test specimen, the adhesion of the cables to the rubber band is better than that of the test specimen and therefore the facies score is higher (greater than 100), proportionally to the number of non-bare cables. Conversely, if, for a given composition, the number of stripped cables is greater than the number of stripped cables of the test specimen, the adhesion of the cables to the rubber band is less good than that of the test specimen. and therefore the score of facies is smaller (less than 100), proportionally to the number of non-bare cables.

[068] The adhesion test described above is performed with specimens cured and / or aged in two conditions A and B.

[069] Condition A (vapor aging) corresponds to a test performed on a specimen comprising the raw composition and aged a few hours at a temperature above 100 ° C. [070] Condition B (cooked wet aging) corresponds to a test carried out on a specimen fired for a period of less than 1 hour at a temperature above 100 ° C. and aged for several days at a temperature above 30 ° C. and at more than 50% relative humidity.

[071] The compositions T06 and M01 are those which have the best adhesion performance under conditions A and B. The only use of the thiosulphate salt (T02 composition) or the only decrease in zinc oxide content (composition T05 ) does not improve or even degrade adhesion under conditions A and B. On the contrary, the combination of the use of thiosulfate salt and a low level of zinc oxide makes it possible to obtain adhesion in the conditions A and B improved compared to all other compositions.

[072] Rubber Properties

[073] P60

[074] The hysteresis losses, denoted P60, are measured as rebound percentage at the sixth rebound at 60 ° C. in accordance with the ISO R17667 standard.

[075] Tan 5 to 10%

[076] The loss factor is measured on a viscoanalyzer (Metravib VA4000) according to ASTM D 5992-96. The response of a sample of the vulcanized test composition (cylindrical specimen 2 mm in thickness and 79 mm 2 in section) subjected to a sinusoidal stress in alternating simple shear at a frequency of 10 HZ is recorded under normal conditions. temperature. A crest-to-peak deformation amplitude sweep is performed from 0.1% to 100% (forward cycle), then from 100% to 0.1% (return cycle). The value of tan δ at 10% is measured at 10% of deformation.

[077] Traction tests

[078] These tensile tests make it possible to determine the elastic stresses and the properties at break of the gum compositions. Unless otherwise indicated, they are carried out in accordance with the French standard NF T 46-002 of September 1988. A second elongation (Le., After a cycle of accommodation at the extension rate provided for the measurement itself) is measured. Nominal secant modulus (or apparent stress, in MPa) at 10% elongation (denoted MA10), Stress at fracture (in MPa) and elongations at break (in%) are measured at 23 ° C ± 2 ° C, and under normal humidity conditions (50 ± 5% relative humidity).

[079] Mooney Plasticity

[080] Mooney plasticity is achieved using a consistometer according to ASTM D 1646-99. Mooney plasticity measurement is carried out according to the following principle: the generally raw mixture is molded in a cylindrical chamber heated to a given temperature, usually 100 ° C and here 60 ° C. After a minute of preheating, a type L rotor rotates within the test tube at 2 revolutions per minute and the useful torque is measured to maintain this movement after 4 minutes of rotation. Mooney plasticity (ML 1 +4) is expressed in "Mooney unit" (UM, with 1 UM = 0.83 Newton meter).

[081] Even if certain properties of rubber are little impacted, and sometimes even improved, by the use of the salt of thiosulfate and the low level of zinc oxide in the compositions T05, T06 and T07, the fluidity (Mooney) of these compositions are reduced. Conversely, the fluidity (Mooney) of the compositions M01 and M02 in accordance with the invention is maintained at the level of the control. [082] The invention is not limited to the embodiments described above.

[083] The invention can be implemented with single son or cables, for example single-layer cables, multi-layer or strand.

[084] It will also be possible to combine the characteristics of the various embodiments and variants described or envisaged above provided that they are compatible with each other.

Table 1

Table 2

Claims

1. Rubber composition, characterized in that it comprises a salt of thiosulphate, 2 to 7 phr of a zinc oxide and a salt of an alkaline earth metal, alkali or lanthanide.

2. Composition according to the preceding claim, wherein the thiosulphate salt is a hexamethylene 1, 6-bisthiosulfate salt.

3. A composition according to any one of the preceding claims, wherein the thiosulphate salt is sodium hexamethylene 1, 6-bisthiosulfate.

4. Composition according to any one of the preceding claims, comprising from 0.5 to 10 phr, preferably from 0.5 to 4 phr and more preferably from 1 to 3 phr of thiosulphate salt.

5. Composition according to any one of the preceding claims, comprising from 3 to 6 phr of a zinc oxide and more preferably from 3 to 5 phr of a zinc oxide.

6. Composition according to any one of the preceding claims, comprising at most 0.1 phr and preferably at most 0.05 phr of a salt of a transition metal.

A composition according to any one of the preceding claims, wherein the salt of an alkaline earth metal, alkali metal or lanthanide is an acetylacetonate of an alkaline earth metal, alkali metal or lanthanide.

The composition of any one of the preceding claims, wherein the salt is an alkaline earth metal salt.

9. Composition according to the preceding claim, wherein the salt of an alkaline earth metal is a magnesium salt.

10. Composition according to any one of the preceding claims, comprising from 0.1 to 5 phr, preferably from 0.5 to 4 phr and more preferably from 0.5 to 2 phr of the alkaline earth metal salt, alkali or lanthanide.

1 1. Semi-finished product, characterized in that it comprises a metal reinforcing element embedded in a rubber composition according to any one of claims 1 to 10.

Pneumatic tire, characterized in that it comprises a metal reinforcing element embedded in a rubber composition according to any one of claims 1 to 10.

13. Use of a thiosulfate salt, 2 to 7 phr of a zinc oxide and an alkaline earth metal, alkali or lanthanide salt as an adhesion promoter between a rubber composition and a metal reinforcing element.