Bonding agent for vulcanizable polymers and metallic reinforcements

The invention relates to an adhesive substance for improved adhesion between a vulcanizable polymer and a metallic reinforcing carrier, a process for Applying a bonding substance and the use of Adhesive substance.

In order to produce a sufficient and long-lasting adhesion of rubber to metal, many parameters must be considered. Thus, the surface of the metallic must Reinforcement carrier be modified so that adhesion of the rubber is possible. These were hitherto metallic reinforcing members (generally steel cord), with in Sulfur vulcanizable rubber mixtures should be embedded, with a Brass layer plated. Further developments were directed, the brass by replace zinc-cobalt or zinc-nickel alloys (EP 536 545). The Brass layer or zinc alloy is used during vulcanization through education an intermediate layer, a mechanical interlock with the rubber compound produce. A disadvantage, however, lies in the fact that the intermediate layer to the metallic Reinforcements (steel cord) not covered at all points, so that these bodies constitute weak points of adhesion. In addition, for the intermediate layer formation sulfur addition is required, which is also added to the rubber mixture additionally must become. To produce a resistant adhesion between rubber and metal, it is That the rubber compound is highly resistant to aging still required. But were Mixtures suggested that contain cobalt salts. This had rubber compounds in turn, the disadvantage of having a poor durability. Further, for Stahlcordgummierungen known that the addition of resorcinol-formaldehyde Condensation products should increase the aging resistance of the rubber compound. These condensation products are of toxicological concern but what their processing difficult.

So there are already a variety of attempts have been made to increase the adhesion optimizing between rubber and metal. However, it is usually always nor necessary, the strength element and the rubber composition of the adhesive mix in tune narrow limits on each other. This in turn has the disadvantage that in the Combination of another adjoining rubber layer, the composition of this at the detention mixture must be adjusted and therefore varied only within narrow limits can be. A variation of the rubber composition affects but on the Properties of the rubber product, so that this set also not optimal can be. The need to establish a permanent and stable adhesion to the steel cord to achieve, therefore restricts the freedom, other desirable mixture properties to optimize.

From DE 44 44 994 A1 it is known alkoxysilanes without Benzen- and / or Thiophene unit for connection of a specific polymer having a dissimilar Material, such as. For example, a metallic material to use.

In Journal of Electrochemical Analytical Chemisty, 1995, 399, p 61-70 describes that for improved connection of metals on conductive polymers such as polypyrrole, Polythiophenes or polyanilines, which are not vulcanizable by thiols Electrodeposited on the metal can be abgschieden. The metals with the conductive polymers in the manufacture of electronic devices or Batteries.

The US 5,113,004 discloses organosilicon compounds with acrylic or Methacrylresten and phenyl group as an adhesion promoter substances for better adhesion between resins and inorganic materials.

The invention has for its object to provide an improved adhesion between rubber and produce metallic reinforcements, which achieved procedurally low can be.

This object is achieved according to the invention in that the adhesive substance has the structure:

X- (R)_n- (Ar)_i- (R)_m-Y, Wherein

X: SH; -Si (Cl)₃; -Si [R₁(Cl)₂]; -COOH; COClwith R₁: Alkyl (branched or unbranched),R: -CH₂-; --CF₂-; -CH₂-CO-NH-CH₂-; --CF₂-CO-NH-CF₂-; -CH₂-CO-NH-CF₂-; --CF₂-CO-NH-CH₂-with 1 ≦ n ≦ 16 and 0 ≦ m ≦ 16,Ar: benzene and / or thiophene with 1 ≦ i ≦ 6 wherein on that aromatic and / or heteroaromatic system the electron-donating substituent -NH₂ or -OCH₃ or the electron-withdrawing substituent is -CN or -NO₂ may be located, andY: unsaturated hydrocarbon radical containing a double or triple bonds, which in is capable, during vulcanization with the polymer, a covalent bond respond.

The invention is based on the finding that the above class of compounds by having the functionality X a large adsorption to metal surfaces and at the same time by the functionality Y during the vulcanization of the rubber a covalent bond to this is manufactured. This bifunctional Class of compounds as an adhesion promoter is a strong adhesion of the rubber on metallic reinforcing carrier allows.

Through the above-mentioned X functionalities will adsorb a strong bond scored for metallic or metal oxide surface. Metal substrates Conventional pure metals such as. for example, aluminum, in particular the elements the subgroups of the Periodic Table (for. example, platinum, titanium, silver, copper, nickel, Zinc, iron), alloy materials such as. For example, steel, brass, as well as metal oxides such. B. Aluminum oxide, iron oxide, are used. Due to the strong adsorption of the X- Functionality to the metallic surface, it is possible to obtain a monomolecular Cover of adhesive substance on the metallic surface apply. Consequently, little is Haftvermi ttlersubstanz needed, which is cost effective. As particularly advantageous has been found that the adhesion to the metallic substrate toward the Adhesion promoter substance having a thiol group (-SH) as X, one in the best case, covalent binding to the metal surface is formed. It has been found that especially in these compounds, a largely spontaneous adsorption to the metal surface occurs, which leads to a monomolecular coverage of the metallic surface.

Another structural element of the class of compounds of the invention is R (Alkyl, fluorinated alkyl, alkyl or fluorinated alkyl group with or without Säureamidgruppierung between) as "spacer". Depending on the size of n and m, the Chain length of R can be varied. Thereby, the mechanical stability (Chain mobility) affected the binding, so that an optimum adaptation to the type the metallic surface or by varying m to the curable polymer can take place.

As the aromatic and / or heteroaromatic systems can Benzene or thiophenes, are used in particular as oligophenyls and Oligothiophenes. Here, 1 to 6 aromatic units present. Preferably located at this aromatic and / or heteroaromatic system substituents significantly electron oppressive, such. as the NH₂Grouping or OCH₃Moiety, or else electron-withdrawing groups such. as the CN-moiety or NO₂- Grouping. Depending on the nature of the substituents, these can in turn influence on the exhibit binding to the metallic surface or to the vulcanizable polymer.

Be favorable an aromatic and / or heteroaromatic system (Ar) has proven, the thiophene contains. The Thiophenbaustein of the adhesive substance, as already mentioned in general for the aromatic and / or heteroaromatic system, also be provided with suitable substituents. The thiophene ring may directly be bound to R. but it is also possible to form the thiophene ring with or without a suitable to tie substituents on an already existing aromatic system.

Advantageously, in particular for the thiophene as a "connection method" on an already existing aromatic system, the process of electrodeposition proven. In this electrochemical process, it is assumed that the thiophene under the be deprived of influence of an electric voltage electrons. The resulting Thiophenradikal is able to be with elimination of a hydrogen proton with the to connect existing aromatic system. Since the voltage to is needed to snatch the thiophene an electron is relatively low, is the Thiophene for a connection to an existing aromatic system by Electrodeposition ( "grafting") is particularly suitable. In principle, however, other Systems z. B. other monomeric or oligomeric building blocks, by this method be bound.

As already mentioned, the adhesive substance according to the invention a Functionality Y, which makes it possible, with the vulcanizable polymer is a covalent enter into binding. Y may, for. Example, an unsaturated hydrocarbon residue containing Double or Dreichfachbindungen such. B. CH = CH₂; CH = CHCl; -CH═CH-D with D = branched or unbranched alkyl, be.

Depending on the type of polymer to be vulcanized, the functionality Y can be selected so be that it and during vulcanization to form a solid bond between the polymer The adhesive substance and thus comes to strengthening support. As vulcanizable polymers can both elastomers and thermoplastic elastomers be used. Elastomers can include, for example, natural rubber, styrene-butadiene Rubber, butadiene rubber, butyl rubber, acrylonitrile-butadiene rubber, ethylene- Propylene-diene copolymer or ethylene-propylene copolymer are used. As thermoplastic elastomer may be selected from the prior art known polymers be used. By applying the bonding agent to the invention metallic reinforcing carrier, it is possible, an excellent bond at least between the elastomer block of the thermoplastic elastomer and the bonding agent produce on its functionality Y. It is already so sufficient adhesion achieved between the thermoplastic elastomer and the reinforcing members.

It is possible to activate the vulcanization by sulfur or peroxides. Particularly in the case of sulfur vulcanization has the functionality Y of the having the adhesive substance double or triple bonds to the Polymer to form a bond.

For preparing a composite of metallic reinforcing members, Adhesive substance investigators and vulcanizable polymer, it is advantageous if the Adhesive substance is dissolved in an organic solvent and metallic reinforcing carrier is drawn through this solution (dip process). In this case, the adhesive substance already all functionalities (X, Y), both to adhere to the reinforcing members and to the vulcanizable polymer are required have. The surface coated with the adhesive substance metallic reinforcing carriers can are then coated with a vulcanizable polymer and then the Vulcanization undergo. However, it is also possible to the dip solution, a admitting adhesive substance that is not the complete structure of having adhesive substance according to the invention, so that the metallic reinforcing carrier first with him awarded functionality (X) of the adhesive substance is at least covered. Subsequently, then z. B. the electrodeposited remaining structural part of the adhesive substance at least with the functionality (Y) to the adhesive already on metallic reinforcing carrier part of the adhesive substance be tethered. Thereafter, as already mentioned, the vulcanizable polymer be applied and cured.

In principle, however are also other conventional application possibilities of Bonding agent available on the metallic reinforcing carrier such. B. transferring the adhesive substance into a gaseous phase and subsequent deposition of the substance on the metallic reinforcing carrier.

The use of the adhesive substance according to the invention, which generally a monomolecular coating of the adhesive substance on the metallic Reinforcements sufficient is obtained that little is required of this substance, to the strength element to completely cover, so that the through the use Adhesion promoter according to the invention is also a cost-effective production of a metal-reinforced rubber product is possible. By varying the components and R Ar and n and m, it is possible X and Y act on the functionalities so that a variation of the bond strengths of the adhesive substance to the metallic is Reinforcements guarantees or the vulcanizable polymer. Accordingly, can various metallic reinforcing members with different vulcanizable are coated polymers excellent adhesion between each other exhibit. In principle, is not even a monomolecular coating of Adhesive substance on the metallic reinforcing carrier is required (eg. As in thermoplastic elastomers). effect by the functionalities X and Y. Adsorption or covalent bonds a fixed connection. The bond strength a covalent bond is much greater than in a mechanical gearing, which causes the adhesion in conventional brass coatings, so that is achieved according to the invention a firmer grip. Moreover, the disadvantage of the mechanical gearing, namely a lack of aging resistance Network through the use of the adhesive substance according to the invention switched off. According to the invention of rubber products now that with metallic Reinforcing members are reinforced, are produced that are more resistant to corrosion and have better mechanical properties. vulcanizable case with sulfur Polymers, it is now no longer necessary, a further addition of sulfur in the bring rubber mixture, which previously for a sufficient adhesive layer formation was required for brass-strength carrier. By using the Adhesion promoter according to the invention can even be on a separate adhesive mixture be waived.

The adhesion promoter of the invention can for all rubber products with metallic reinforcing elements are reinforced, are used as such. as for conveyor belts, Air springs, belts, hoses, and in particular for vehicle tires. With the latter in the core wires (generally solid rubber tires and pneumatic tires) and / or belt plies and / or carcass made of steel, were through the use of the adhesion promoter obtained special advantages. By omitting the adhesive mixtures may be obtained at Preparation of the vehicle tire, the individual rubber mixtures successive optimal be coordinated, so that it is now also inventively z. B. possible Tread compound directly onto the belt. Thus, the tire be produced cost-effectively and simultaneously optimized in its running properties will. Furthermore, the tire has a longer service life.

An exemplary embodiment is illustrated by a drawing.

It shows:

<b>Fig.</b> 1 shows a schematic flow of the production of a vulcanized composite of Steel cord and a rubber composition using as adhesion promoter the Substance of the invention is used.

<b>Fig.</b> 2 is a radial cross section through a pneumatic vehicle tire.

In the scheme <b>Fig.</b> 1 it is shown that a cord of any type of steel (z. B. 0.8% Carbon, trace elements) in step <b>1</b> with a solution, in the simplest case Phenylmethanethiol (phenylethanthiol, etc.) is treated in toluene. In principle, instead of a thiol Alkylsiliziumchlorid such. B. Trichloromethylsilane, or organic acid or organic Acid chloride are used. The concentration of the thiol in the solvent toluene z. B. 0.1 molar. In step<b>2</b> is excess thiol from steel cord with z. B. a washed alcoholic solution and in step <b>3</b> a drying process at about 60 ° C subjected. In the steel cord there is now a block of The adhesive substance according to the invention, by a covalent bond sulfur adheres to the metal (steel cord). By electrodeposition (step<b>4</b>) Is now part of of the adhesive substance (Y) at the block of the previously located The adhesive substance bonded to the reinforcing members. For this purpose, the treated Steel cord in a three-electrode cell in which a 0.1 molar bath solution thiophene (Z. B. vinylthiophene in acetonitrile) is guided, wherein the steel cord as one of this is poled. A further electrode is used as a reference (Silver / silver nitrate electrode) and the working electrode is a platinum crystal. The Voltage is increased from 0 to 0.75 V at 500 mV per second increments. By applied voltage is the thiophene removes an electron from, and the remaining Thiophenradikal is able to adhere to the first block of the adhesive substance, which are already on the strength carrier (steel cord) is under an abstraction to store the hydrogen atom, the mechanism of the addition is not yet clear is.

The steps <b>1</b> and <b>4</b> are briefly summarized below:

After the electrode position (step <b>4</b>) Followed by a further washing process (step <b>5</b>) With z. B. water and a drying process (step <b>6</b>) At about 60 ° C. The steps<b>4</b> to <b>6</b> can also be omitted if the dip process (step <b>1</b>) Already sufficiently reactive adhesive substance can be applied to the steel cord. For this purpose, the X and Y functionality of the adhesive substance must already exist be. As an example, the following compounds are suitable:

After coating the steel cord with the adhesive substance is followed by step <b>7</b>. namely applying the unvulkaniserten rubber layer. These runs in a Calender of covered with adhesive steel cord and is a calendered Rubber sheet (z. B. natural rubber mixture) covered. This composite of steel cord, The adhesive substance and rubber plate, in a next processing step <b>8th</b> be processed for the particular product manufacturing on. For the manufacture of a pneumatic vehicle tire, for. example, the composite could the belt package represent, which is placed on the carcass ply during tire building. In the further tire manufacturing is on the belt package, the uncured tread applied. After completing the green tire of this is in the set vulcanizing press and cured at elevated pressure and elevated temperature.

In the <b>Fig.</b> 2 is a pneumatic vehicle tire having a tread strip <b>1</b>, Metallic bead core <b>2</b>, Located in the bead area <b>3</b> is, a chipper <b>4</b>, A carcass <b>5</b>. sidewalls <b>6</b> and a metallic belt <b>7</b> shown. The bead core<b>2</b> and the belt <b>7</b> are generally made of metal reinforcements. But the carcass<b>5</b> may be made of steel cord. In particular, those tires for use are in Lorries used. By using the invention Adhesive substance tires can be produced at lower cost since a additional adhesive mixture can be dispensed with for metallic reinforcing carrier. Of Furthermore, the individual rubber mixtures can be better matched , so that the running characteristics of the tire can be optimized. Due to the be good adhesion between the metallic reinforcing carrier and rubber Corrosion problems are largely avoided, so that the tire higher mechanical Loads holds and thus has a longer life.