DE3910482A1 - Cobalt compounds, their preparation and use as adhesives for rubber articles which contain metal constituents - Google Patents

Abstract

Compounds of the formula R1(-O-Co-O-R2)n, in which R1 is an element selected from amongst Al, B, Ca, Cu, Fe, Mg, Na, P, S, Si, Sn, Ti, Zn and Zr and n is a number between 1 and 5 which corresponds to the valency of the atom R1 and in which R2 is a phenol radical of optionally substituted mono- and polynuclear phenols of the formula <IMAGE> where R3, R4, R5, R6 and R7 are identical or different and are hydrogen, hydroxyl, amino, C1-C18-alkyl, C5-C12-cycloalkyl, C1-C16-alkylthio, C6-C14-aryl, C6-C14-aryl-C1-C4- alkyl, C1-C18-alkylamino, C1-C18-alkoxy, C6-C14-aryloxy, C6-C14-aryl-C1-C4- alkoxy, halogen or a hydrocarbon radical containing 2 to 18 carbon atoms and having one or more double bonds, can be used as adhesives for improving the adhesion between steel cord and rubber mixtures. Also disclosed is a process for the preparation of the novel compounds according to the invention.

Description

The present invention relates to adhesives which in the manufacture of rubber articles, metallic Contain ingredients, the adhesion of the rubber increase the metal component.

To increase the mechanical strength, be technical rubber articles often with reinforcing inserts made of steel cords. For a good performance and a sufficient life of the objects can be ensured is a strong and permanent bond between metal and rubber essential.

Frequently, the metal is a post-treated, high-carbon Steel cord used. This one is common with a few microns thick layer of brass Provided. In this case, the metals are copper and  Zinc involved in the detention process. Such a equipped Cord is vulcanised into the rubber compound.

To improve the binding power can be additive, the hereinafter referred to as "adhesives" added become. These can be broken down according to their chemical Divide structure into two groups.

The first group are adhesives that only work as multi-component systems. These contain on the one hand highly active silicas and on the other hand Resorcinol or resorcinol-formaldehyde condensation products and formaldehyde-releasing compounds such as hexamethylenetetramine, etherified or esterified methylolmelamines with different degrees of etherification or degrees of esterification and their condensation products.

Although such adhesive systems provide good adhesion values, however, the vulcanization produces fumes and a unpleasant odor nuisance. The resulting Formaldehyde raises problems because the allowable concentration not a certain value in the workplace may exceed. This value is in accordance with the MAK List (1987 edition) 0.6 mg / m³. Since formaldehyde is skin-sensitizing and mucous membrane irritant and above addition to the list of substances with a reasoned Suspected carcinogenic potential is listed it is for reasons of job security and the Avoidance of environmental pollution desirable, these adhesives the first group no longer to use.

In addition, such adhesives also in the Processing in the mixing machines disadvantages, since the Resorcinol, especially at temperatures near the Melting point, tends to sublimation, what the usability especially affected in roll mixers.  

There is also a second group of adhesives known comprising organometallic compounds. In different References will be the use of heavy metals disclosed as adhesion promoters.

In FR-PS 13 23 934 different cobalt salts described, wherein the salts of organic acids are preferred.

US-PS 32 96 242 describes Metallacyloxy compounds, the aluminum or boron and another bivalent one Contain metal that is connected via an oxygen atom are. The divalent metal atom has other substituents still an organic acid residue.

The cobalt-boron compounds of the European patent application 1 02 023 have two cobalt and two per molecule Boron atoms, wherein the two boron atoms via an oxygen atom connected to each other.

Compared to the first group of adhesives, the organometallic compounds and in particular the cobalt adhesives have various advantages. They can be processed as one-component systems in a mixing and weighing process. Since they are also effective in silicic acid-free mixtures, the cold running properties of the tires are improved. As a rule, compared to the resorcinol-formaldehyde-silicic acid systems (RFS systems), a greatly improved metal-rubber adhesion on vulcanization is determined in accordance with the t ₉₀ value of the mixture. The t ₉₀ value is the time at which 90% of the maximum achievable degree of vulcanization result. The value is temperature dependent. As heavy metal compounds, they act like a masticating agent. Cobalt compounds provide a certain, albeit weak bond between bare steel and rubber with positive effects on the cut-end problem in tire belts.

Furthermore, it is often observed that the disturbing influence from moisture to adhesion when using  Cobalt adhesives is reduced. By cobalt compounds is also the corrosion behavior of the steel cord favorably influenced, because the corrosion sustained delayed becomes.

But the adhesives of the second group still show serious disadvantages that need improvement are.

At high temperature vulcanization (180-240 ° C) reduced the adhesion significantly. Furthermore cause cobalt overdoses in such Test additional reduction in adhesion. It can be a loss of separation up to over 90% occur. Other essential Disadvantages of the known adhesives of the second group are the rapid loss of adhesion during aging, the caused by temperature / water vapor load be, a low resistance of the rubber-metal bond during reheating and a general vulnerability against heat and humidity.

Object of the present invention is therefore, a Adhesive of the second group described above create, on the one hand has the known advantages and on the other hand avoids their disadvantages.

The advantageous adhesives of the invention must So contain an organometallic compound, wherein especially metals with a high redox potential such as Cobalt, manganese, iron, etc. the degradation double bond containing accelerate organic compounds, even if only in very low concentrations available. Therefore, such metal ions are called rubber sticks. normally not appreciated in rubber compounds. On the other hand, because the cobalt compounds Excellent adhesion enhancers between brassicated Steel cord and rubber pose is the presence desired by Cobalt in the adhesives. It forms  namely in the vulcanization of sulfur-containing rubber mixtures with the brass surface through Implementation of copper with sulfur an adhesion-promoting Layer. The cobalt compound uses positive, an encouraging way. Since the liability causing Contact zone particularly sensitive to moisture and heat is, it is an object of the present invention to create an adhesive that has the above advantages having the organometallic adhesive. In this case, the disadvantageous sensitivity to Moisture and heat can be avoided.

The adhesives of the present invention have the following Formula on:

R₁ (-O-Co-O-R₂) _n (I)

wherein R₁ is a monovalent to pentavalent element bonded through an oxygen atom selected from Al, B, Ca, Cu, Fe, Mg, Na, P, S, Si, Sn, Ti, Zn and Zr. The number n of radicals (-O-Co-O-R₂) corresponds to the valency of the central atom.

In a preferred embodiment, R₁ is aluminum, Boron, titanium or phosphorus, with phosphorus being especially is preferred.

The substituent R₂ of the formula (I) is a phenol radical of optionally substituted mono- and polynuclear phenols the formula:

wherein R₃, R₄, R₅, R₆ and R₇ are the same or different and hydrogen, hydroxy, amino, C₁-C₁₈-alkyl, C₅-C₁₂- Cycloalkyl, C₁-C₁₆-alkylthio, C₆-C₁₄-aryl, C₆-C₁₄-aryl C₁-C₄alkyl, C₁-C₁₈alkylamino, C₁-C₁₈alkoxy, C₆-C₁₄- Aryloxy, C₆-C₁₄-aryl-C₁-C₄-alkoxy, halogen or a 2 to 18 carbon atoms hydrocarbon radical mean with one or more double bonds.  

Preferably, in the phenol radical R₂, the substituents R₃, R₄, R₆ and R₇ are hydrogen, wherein R₅ is nonyl or butyl, with nonyl being especially is preferred.

Ideally, the ratio of phenolic radical R₂ to Cobalt about 1: 1. For technical reasons, cobalt adhesion promoters with a melting range of 70 to 150 ° C required. By appropriate variation of the radicals R₁ and R₂ this is controllable.

The compounds according to the invention are prepared by that one first

• a) Cobaltcarbonsäuresalze and
• b) reacting phenolic compounds, the thereby formed by-products removed and the reaction product this first implementation with
• c) reacting metal alcoholates or acid esters.

In the Cobaltcarbonsäuresalzen (compounds a)) is they are saturated aliphatic carboxylic acid salts with a chain length of 1 to 10 carbon atoms. The salts of acetic acid are preferably used. If it is assumed that other cobalt compounds, must the synthesis route via the corresponding intermediate run off the carboxylic acid salts.

The phenolic compounds (component b)) used are preferably those which are effective as antioxidants. Examples of phenolic, convertible antioxidants are:
Di-tert-butylphenol, di-tert-butyl-methyl-phenol, tri-tert-butylphenol, di-tert-butylnonyl-phenol, tert-butyl-dimethyl-phenol, tert-butyl Dimethylphenol, dimethyl-nonyl-phenol, dimethyl (phenyl-ethyl) phenol, dimethyl (methyl-cyclohexyl) -phenol, di-octadecyl-methyl-phenol, tert-butyl-hydroxy-methyl-benzyl-malonic acid di-n-octodecyl esters, styrenated phenols, di-tert-butyl-hydroxybenzyl alcohol, di-tert-butylmethoxy-phenol, octadecyl- (di-tert-butyl-hydroxyphenyl) propionate, Butylphenol, propylphenol, octylphenol, nonylphenol, benzylphenol, dodecylphenol and tolylcresol, methylenebis (butylmethylphenol), trimethyltris (butylhydroxybenzyl) benzene, catechol, methoxyphenol, di-butylmethoxy phenol, di-butyl-hydroquinone, naphthol, butyrylamino-phenol, nonanoyl-amino-phenol, dodecanoyl-amino-phenol, octadecanoyl-amino-phenol, butyl-dimethylamino-methyl-phenol, thio-bis (methyl-phenol), thio bis (methyl-butyl-phenol).

Preferably, the phenolic compounds butyl phenol and nonylphenol.

The metal alcoholates (component c)) can be simple or condensed present. Preferably, it is Alcoholates of the elements Na, Mg, Ca, Al, Ti, Si, Zr, V and Sn.

Suitable acid esters (component c)) are neutral compounds, or substituted acid esters, wherein the Acid esters of elements B, P and S are preferred. Especially preferred are the acid esters of P.

The alkyl radicals of the metal alcoholates or acid esters have a chain length of C₁-C₁₀, wherein one chain length of 2 to 6 carbon atoms is preferred. exemplary mention may be made of the following compounds which can preferably be used: Al isopropylate, Al-isobutylate, tributyl borate, calcium ethylate, Magnesium ethylate, sodium methylate, phosphoric acid isopropyl ester, Isobutyl phosphoric acid, butyl toluenesulfonate, Tetraethyl silicate, tetrabutyl titanate, polybutyl titanate, Vanadium triisobutylate, zinc butylate, zirconium tetramethylate and tin tetraethylate.  

In the method according to the invention is first the Cobaltcarbonsäuresalz and thus to be reacted phenolic Heated compound, the reaction being preferred is carried out in an organic solvent. A particularly suitable solvent for this reaction is xylene.

The by-product formed in this first reaction is removed, preferably applying a vacuum becomes. In a preferred embodiment, the at The resulting water by an azeotropic reaction Distillation are removed.

Another preferred embodiment of the invention Process is that the by-product the first reaction removed by vacuum distillation becomes. The temperatures in this first reaction are between 80 and 200 °, with a range between 90 and 160 ° C is preferred. After the removal of the by-product the first reaction becomes the corresponding metal alcoholate or the corresponding acid ester added. The reaction according to this second reaction is running at a temperature of 110 to 160 °, with a Temperature of 120 to 140 ° C is preferred. For separation the by-product of this second reaction becomes again increases the temperature, with temperatures between 140 and 220 ° C are preferred. Preference is given at At this distance also the pressure is lowered, so that the Separation of the by-products takes place in vacuo.

The process for the preparation of the invention Compounds are exemplified by the following Examples 1 to 5 explained.

example 1

In an apparatus with distillation, reflux and vacuum connection 300 g of xylene, 747 g Cobalt acetate tetrahydrate and 450 g p.-tert. butylphenol  brought in. While stirring and heating to the boiling point of the azeotropic mixture xylene / water is first dragged the bulk of crystal water. Thereafter, switched to vacuum distillation and the Temperature increased to 90-180 ° C. The distillate consists of xylene-acetic acid-water.

After completion of the vacuum distillation and reduction the temperature in the reaction vessel to 140 ° C are 230 g Borsäuretributylester added and after good homogenization held at 145 ° C at reflux for about 3 hrs. at The reaction forms butyl acetate. This distillate is first at 220 ° -240 ° C via normal distillation away. The last residues of organic solvent are separated at 160 ° -190 ° C in vacuo. This results in about 680 g of a solid at room temperature homogeneous deep blue cobalt compound with a metal content of 25.9%. The other elementary analytical Data is:

C | 52.6% H 5.8% O 14.1% B 1.6%

Example 2

In an apparatus according to Example 1, 661 g of nonylphenol and 747 g of cobalt acetate tetrahydrate are introduced. Under temperature increase and stirring becomes water of crystallization cleaved. Initially, at normal pressure up to 200 ° C heated, later the material at 140 ° -160 ° C over held for several hours in vacuo and further distilled.

After completion of the vacuum distillation is heated to 140 ° C. cooled and added 224 g of phosphoric acid tripropyl ester. After good homogenization and temperature increase Propyl acetate is formed. This is made by distillation away. The temperature can be increased up to 220 ° C become. The last residues of organic solvent  are separated at 160 ° -190 ° C in vacuo.

This results in about 930 g of a solid at room temperature, homogeneous deep blue cobalt compound having a metal content of 19.0%. The other elementary analytical data are
C 58.2% / H 7.5% / O 12.0% / P 3.3%.

Example 3

In an apparatus according to Example 1, 661 g of nonylphenol and 360 g of acetic acid. At room temperature are added with stirring 279 g of cobalt hydroxide. It forms in the first reaction step cobalt acetate. The forming water / acetic acid mixture becomes by raising the temperature to 200 ° C at atmospheric pressure later away. Further distillate is used in the vacuum distillation at 140 ° -160 ° C away.

Analogously to Example 2, with 224 g of phosphoric acid tripropyl ester added and removed with distillation propyl acetate.

This results in about 930 g of a cobalt compound with 19.0% Metal. The remaining composition corresponds to that in the Example 2 described.

Example 4

In an apparatus according to Example 1, 300 g of xylene, 748 g of 4-nonylaminophenol and 747 g of cobalt acetate tetrahydrate brought in. While stirring and heating Xylene / water / acetic acid removed by distillation. Finally, a vacuum distillation at 160 ° C. operated to last residues of volatile matter remove. Traces of water must be avoided.

After cooling the material to 120 ° C with stirring 492 g aluminum butylate (50% solution in xylene) entered. When the temperature increases, butyl acetate forms, which by distillation / vacuum distillation  Will get removed.

This results in about 910 g of a solid at room temperature, blue cobalt compound having a metal content of 19.4% cobalt. The other elementary analytical data are:
C 51.2%, H 6.0%, O 15.8%, N 4.6%, Al 3.0%.

Example 5

In an apparatus according to Example 1, 881 g of nonylphenol and 996 g of cobalt acetate tetrahydrate are introduced. With stirring and distillation at atmospheric pressure to 200 ° C, water of crystallization is split off. Subsequently, further distillate is removed in vacuo at 140 ° -160 ° C. The intermediate thus formed must be absolutely anhydrous. After cooling the material to 120 ° C 680 g of a 50% solution of mono-butyl titanate are introduced into xylene and well homogenized with stirring. By increasing the temperature and distillation / vacuum distillation xylene and butyl acetate is removed. The result is a solid at room temperature compound with the following elemental analytical composition:
C 58.8%, H 7.6%, O 10.5%, Ti 3.9%, Co 19.2%.
The yield is 1225 g.

The compounds according to the invention can be used in the preparation of rubber products with metal inserts advantageously be used.

Surprisingly, it was found that the inventive Connections to the compounds, which are known from the prior art, improved Have adhesion values, the liability in particular above the average for workloads and retirement is well preserved. The reversion will as well reduced.  

The adhesive according to the invention is used as sole Adhesion promoter in an amount of 0.1 to 20%, preferably in an amount of 0.3 to 5%, based on Rubber used.

Furthermore, it has been found that the compounds of the invention of the formula R₁ (-O-Co-O-R₂) _{n can be used} with a formaldehyde donating compound, the latter in an amount of 0.01-10%, preferably in a rubber Amount between 1 and 3%, based on rubber is used.

Furthermore, the compounds of the invention used together with resorcinol and its derivatives become. The dosage of these compounds is thereby 0.01 to 10%, preferably 0.5-5%, based on rubber. The resorcinol compound may be separate or in Combination with the formaldehyde donating compound be used. The adhesives of the invention, the either alone or in combination with resorcinol or Formaldehyde releasing compounds are used, Typical of rubbers are the products diene type, such as natural rubber, chloroprene rubber, Polybutadiene, styrene-butadiene copolymers, polyisoprene, Acrylonitrile butadiene rubber, EPDM (ethylene-propylene Diene elastomer) and mixtures of these types are used.

Before the vulcanization process, the rubber mixture the usual recipe ingredients, such as reinforcing Carbon blacks, inactive and active fillers, such as silica and zinc oxide, sulfur, processing aids and Vulkanisationsbeschleuniger added. For the exam were the compounds of the invention and the test substances in a practical way, d. H. between 120 and 220 ° C, preferably at 140 ° to 180 ° C, vulcanized.  

For the testing of adhesives, the recipe is the rubber compound from the following components together, where the numbers are the corresponding percentage specify:

natural rubber 54.8 Carbon black N 539 11.7 Carbon black N 326 21.3 stearic acid 0.6 rosin 1.4 zinc oxide 5.3 sulfur 3.7 Phenyl- β- naphthylamine 0.8 N, N-Dicyclohexylthiobenzthiazol 0.4

The accelerator and sulfur-free masterbatch was premixed in a mixer at 70 ° C. Subsequently, the addition of accelerator and sulfur and optionally of adhesive in the mixer at a roller temperature of 60 ° C. The cobalt-containing adhesive was used in the tests in an amount of 0.1% cobalt, based on rubber. The rubber composition thus obtained was vulcanized with brass cores at 150 ° C. in accordance with the t ₉₀ value.

To determine the effect on aging, were the rubber mixtures thus obtained with steel cords subjected to artificial aging, while at 120 ° C for several days treated with superheated steam or at 180 ° C were vulcanized over.

With the help of a pulling device, the adhesion of the steel cords to the rubber mixture was determined. The adhesion was determined by pulling out the steel cords from the rubber samples. The required maximum force was defined in N / 20 mm. At least five test specimens were used for the measurement, the median value (X) being determined from the individual values in accordance with standard DIN 53 598. As a measure of the scattering applies the span R , ie the difference between the highest and lowest individual value. The examination of the covering of the steel cord with the rubber compound takes place visually.

Various compounds were tested according to the Table 1.

Table 2 shows the adhesion values of the rubber compounds on brass-plated steel cord without a treatment, which simulates the aging of the rubber compound.

Table 3 shows how the adhesion of the rubber mixtures on the brassed brass cords changed after hot steam aging. this table clearly shows that the adhesives of the prior art Technique (compounds 13 and 14) after hot steaming have lower liability values.

Table 4 shows the change in the adhesion values of Rubber mixtures on brass-plated steel cord a temperature treatment at 180 ° C.

Table 5 shows the effect of hot steam aging on a multi-component system.

In summary, it can be stated that the use the compounds of the invention destruction of the adhesive structure during aging processes (moisture and temperature) sustainably delayed. The improvement the compounds of the invention does not show up only at one due to humidity and elevated temperature simulated aging, but also at a thermal Aging. Again, the compounds of the invention provide significant advantages over the prior art. When the adhesives of the invention come together used with formaldehyde donating multicomponent systems can be, additional beneficial effects be achieved in the aging processes.  

Table 1

The compounds listed in Table 1 can also be represented by the following structural formulas.

Table 2

Table 3

Steam aging

Table 4

temperature aging

Table 5

Multicomponent system

Steam aging

Claims (13)

1. Compounds of formula R₁ (-O-Co-O-R₂) _n (I) wherein R₁ is selected from Al, B, Ca, Cu, Fe, Mg, Na, P, S, Si, Sn, Ti, Zn and Zr, wherein the valency of this element corresponds to the value of n , which may have a value between 1 and 5, and wherein R₂ is the phenol radical of optionally substituted mono- and polynuclear phenols of the meaning: in which R₃, R₄, R₅, R₆ and R₇ are the same or different and are hydrogen, hydroxy, amino, C₁-C₁₈-alkyl, C₅-C₁₂-cycloalkyl, C₁-C₁₆-alkylthio, C₆-C₁₄-aryl, C₆-C₁₄ aryl C₁-C₄ alkyl, C₁-C₁₈ alkylamino, C₁-C₁₈ alkoxy, C₆-C₁₄ aryloxy, C₆-C₁₄ aryl-C₁-C₄ alkoxy, halogen or a 2 to 18 carbon atoms Has hydrocarbon radical having one or more double bonds. 2. Compounds according to claim 1, wherein R₁ Al, B, Ti or P means and wherein in the phenol radical R₂ the substituents R₃, R₄, R₆ and R₇ are hydrogen and R₅ Butyl or nonyl means. 3. A compound according to claim 1, wherein R₁ is P has and the substituents of the phenol radical R₃, R₄, R₆ and R₇ are hydrogen and R₅ is nonyl. 4. A process for the preparation of compounds according to claim 1, characterized in that one

• a) Cobaltcarbonsäuresalze and
• b) reacting phenolic compounds with each other, removing the by-products formed during the reaction and reacting the product of the first reaction step with metal alcoholates or acid esters containing the element R₁.

5. The method according to claim 4, characterized in that the temperature of the first reaction step 100-200 ° C is. 6. The method according to claim 4 or 5, characterized that the by-product of the first reaction step is removed by vacuum distillation. 7. The method according to any one of claims 4 to 6, characterized characterized in that in the first reaction step the cobalt carboxylic acid salts in a molar excess used against the phenolic compounds become. 8. The method according to any one of claims 4 to 7, characterized in that the reaction product of the first reaction of Cobaltcarbonsäuresalzen and phenolic compounds is used at least in a molar ratio of n : 1 to the metal alcoholates or acid esters in the second reaction step, wherein the n Value of R₁ corresponds. 9. Use of compounds according to claim 1 to 3 at the production of rubber articles, the metal components as an adhesive for improvement the contact of metal and rubber. 10. Use of compounds according to claim 1 to 3 as Adhesive for improving the contact of metals and rubber, characterized in that 0.1 to 20%, based on rubber used.   11. Use of compounds according to claim 1 to 3 as Adhesive for improving the contact of metals and rubber, characterized in that 0.3 to 5% the compound, based on rubber. 12. Use of compounds according to claim 1 to 3 as Adhesive for improving the adhesion between metal and rubber in the manufacture of tires. 13. Use of compounds according to claim 1 to 3 as Adhesive for improving the adhesion between metal and rubber, characterized in that these compounds together with a formaldehyde donating Connection can be used.