Adhesive compounds for rubber

Description

[0001] The present invention relates to adhesive mixtures containing resorcinol and / or resorcinol esters, melamine formaldehyde ethers and sulfenamide derivatives as well as silica for their use in rubbers, their preparation, vulcanizates and composite articles produced therefrom and their use.

[0002] Composite products such as tires, conveyor belts, and all types of belts, such as V-belts, reinforced hoses, fire hoses, or coated fabrics, must be both elastic and able to withstand tensile and compressive loads. Since elastomers deform under load, a reinforcement is required to transmit force. Depending on the load, such reinforcements consist of one or more layers of textile or steel cord, sometimes a combination of both.

[0003] In order to achieve a bond or adhesion of the elastomers to the respective reinforcement, a so-called adhesive system can be applied directly to the reinforcement, or the adhesive system can be introduced into the rubber, or both methods can be combined.

[0004] Adhesive systems intended for coating reinforcements are called resorcinol-formaldehyde latex (RFL) or resorcinol-formaldehyde silica (RFS) systems. Both are disperse systems. The key difference between the two systems lies in the polarity of the medium. RFL systems are dispersions in the polar medium of water, while RFS systems can be considered dispersions in the non-polar medium of the rubber compound. A third component, such as silica-based fillers, acts as a carrier.

[0005] Commercially available adhesion promoter systems often use resorcinol or resorcinol resins (so-called RFS adhesion systems), which are used between fabric plies or steel cord and rubber compounds in tire construction. Furthermore, these contain formaldehyde donors and silica in a rubber mixture. Heat treatment of the mixture produces a resorcinol-formaldehyde resin from the resorcinol and formaldehyde donor, which strengthens the bond between the rubber and the reinforcement.

[0006] From JP-A 2008 308632, rubber compositions are known which contain N,N-dibenzyl-2-benzothiazylsulfenamide (DBBS) as a vulcanization accelerator and which have good adhesion to metal materials, using an adhesive system based on cobalt naphthenate.

[0007] The publication by K. Abhitha ET AL: "Non-regulated Accelerator (DCBSIDBBS) Incorporated Natural Rubber Formulations - Cure Characteristics and Mechanical Properties" in the International Journal of Research and Scientific Innovation of June 1, 2017, deals with a comparison of the crosslinking properties and mechanical properties of the accelerators dicyclohexylbenzothiazyl sulfenamide (DCBS) and N,N-dibenzyl-2-benzothiazyl sulfenamide (DBBS) in natural rubber compounds.

[0008] From EP-A 2960278 it is known to use dicyclohexylbenzothiazyl sulfenamide (DCBS) in rubber as well as in rubber-based adhesive mixtures.

[0009] The object of the present invention is to find an effective accelerator that makes it possible to provide both rubber-to-fabric and rubber-to-metal adhesion with an improved property profile for the rubber processing industry, while maintaining the quality of the vulcanizates produced with such preparations. In particular, neither their rubber-technical properties nor their good adhesion properties between the insert or overlay and the vulcanizate should be impaired. Furthermore, the process should be easy to process, thus making the process economical.

[0010] It is known to those skilled in the art that the crosslinking points and the crosslinking density play an important role in vulcanization.

[0011] One advantage of sulfur crosslinking is the ability to create rubber-to-metal adhesion through this vulcanization process. The metal surface must be coated with a brass layer to enable sulfidation. Mechanical anchoring of the rubber to the metal alloy is achieved through Cu-Sx-C structures at the interface between the two materials and depends on the vulcanization rate, the sulfur content, and the type of rubber.

[0012] A widespread belief is that sulfidation on the metal surface competes with the vulcanization rate, and that the slower the vulcanization of the rubber chains, the better the rubber adheres to the metal, while the bond between rubber and metal becomes stronger the more polysulfide crosslinks / node sites are formed. The retarding effect of DCBS has a positive effect on adhesion. Rubber-metal bonds produced using DCBS as a vulcanization accelerator are significantly more stable and durable than those based on CBS.

[0013] The quality of the rubber molded articles is primarily determined by the sulfur bridges as linkages, with a distinction being made between mono-, di-, and polysulfidic linkages. Ideally, the proportion of monosulfidic linkages should be as low as possible.

[0014] It is known that the crosslink structure of commercially available sulfenamides, such as CBS (N-cyclohexyl-2-benzothiazylsulfenamide) or DCBS (N,N-dicyclohexyl-2-benzothiazylsulfenamide), varies greatly.

[0015] CBS is known to form approximately 1 / 3 monosulfidic (S1), 1 / 3 disulfidic (S2) and 1 / 3 polysulfidic (Sx) cross-linking sites in natural rubber (NR) at the same molar concentration.

[0016] In contrast, DCBS forms more polysulfide cross-links than CBS. This is reflected in vulcanizates that exhibit higher tensile strength compared to CBS-based vulcanizates.

[0017] Furthermore, the acceleration factor in rubber bonding compounds should be selected so that the flow time allows sufficient time for the reaction of formaldehyde release and resin formation, allowing the bond to largely develop. Therefore, DCBS, with its delayed vulcanization, has proven particularly effective time and time again. Experts know that the use of DCBS is specifically recommended for rubber-steel cord adhesion.

[0018] Surprisingly, it has now been found that an adhesive mixture containing resorcinol and / or resorcinol esters, melamine formaldehyde ether and at least one di-benzothiazylsulfenamide derivative as well as silica shows excellent adhesive properties.

[0019] The present invention relates to adhesive mixtures containing Resorcinol and / or resorcinol esters of formula (I) wherein all radicals R 1< are identical or different and denote hydrogen (for resorcinol) or a straight-chain or branched C 1 -C 18 alkyl radical or a phenyl radical, preferably methyl or stearyl, and at least one melamine formaldehyde ether of the formula (II) wherein all radicals R 2< are identical or different and denote hydrogen or a straight-chain or branched C 1 -C 4 alkyl radical or a phenyl radical, preferably hydrogen or methyl, particularly preferably methyl, but where not more than 5, preferably not more than 4, particularly preferably not more than 3, very particularly preferably not more than 2 and most preferably not more than 1 radical R 2< represents hydrogen and / or polymers melamine formaldehyde ethers of the formula (III), at least one sulfenamide of the formula (III) with x = 0 and z = 2, where z and x in total = 2 and y = 1, at least one silica-based filler, preferably precipitated silica or pyrogenic silica, particularly preferably precipitated silica.

[0020] Resorcinol esters are compounds of formula (I) with where R 1< is methyl and / or stearyl, is preferred. Resorcinol can be used as a commercially available compound, for example, from LANXESS Deutschland GmbH.

[0021] As melamine formaldehyde ether of formula (II) Preferred are those in which R 2< is methyl, or those in which 2 to 4 of the radicals R 2< are methyl.

[0022] In one embodiment of the present invention, instead of or together with the compounds of the formula (II), polymers, in particular di-, tri- or tetramers thereof, can also be used, which are understood to mean compounds in which one or more of the amino functions of a compound of the formula (II) are linked to another corresponding compound of formula (II) by -CH 2 groups and / or -CH 2 -O-CH 2 - instead of a radical CH 2 ORq (where q can be 3, 4, 5, 6, 7 or 8). In the following description of the various embodiments of the present invention, the compounds of the formula (II) are to be understood to include the polymers, in particular di-, tri- or tetramers of the compounds. These aforementioned polymers are also commercially available.

[0023] As compounds of formula (III) According to the invention, compounds are those in which x = 0, y = 1 and z = 2, ie N,N-dibenzyl-2-benzothiazylsulfenamide (DBzBS)).

[0024] The compounds of formula (III) used according to the invention are commercially available compounds. They can alternatively be prepared by the process described in EP-A-721946, for example, the compound of formula (III) with x = 0, y = 1, and z = 2 by reacting 2,2'-dibenzothiazolyl disulfide with dibenzylamine in an anhydrous alcohol.

[0025] The following is preferably used as a silica-based filler: Silica, in particular precipitated silica or pyrogenic silica, preferably produced by precipitation of silicate solutions or flame hydrolysis of silicon halides with specific surface areas of 5-1000, preferably 20-400 m² / g (BET surface area) and with primary particle sizes of 10-400 nm. The silicas can optionally also be present as mixed oxides with other metal oxides such as Al, Mg, Ca, Ba, Zn, Zr, or Ti oxides; synthetic silicates such as aluminum silicate; alkaline earth metal silicates such as magnesium or calcium silicate, with BET surface areas of 20-400 m² / g and primary particle sizes of 10-400 nm; and / or natural silicates such as kaolin and other naturally occurring silicas.

[0026] In a preferred embodiment of the invention, the adhesive mixture according to the invention additionally contains one or more silica-based fillers in the form that resorcinol and / or resorcinol esters and / or the melamine formaldehyde ether have been applied to them.

[0027] In general, the resorcinol and / or resorcinol esters of formula (I) and melamine formaldehyde ethers of formula (II) can be used in any ratio to one another.

[0028] In a preferred embodiment, the sum of the resorcinol esters of formula (I) and the melamine formaldehyde ethers of formula (II) is at least 20 wt.%.

[0029] Particularly preferred adhesive mixtures are those in which the total proportion of resorcinol or the resorcinol esters of formula (I), melamine-formaldehyde ethers of formula (II) and / or polymers and sulfenamide is 20-80 wt.%, in particular 25-55 wt.%, based on the total adhesive mixture, with the proportion of compounds of formula (III) being 0.1 to 10 wt.%, preferably 0.15 to 1.5 wt.%. Ideally, resorcinol or the resorcinol esters of formula (I) and melamine-formaldehyde ethers of formula (II) are applied to silica as a carrier.

[0030] In the adhesive mixtures according to the invention, the total proportion of resorcinol esters of the formula (I), melamine formaldehyde ethers of the formula (II) and / or polymers is preferably 20 - 80 wt.%, in particular 25 - 55 wt.% and the proportion of sulfenamide of the formula (III) is 0.1 - 10 wt.%, based on the total adhesive mixture with silica.

[0031] In a further embodiment of the present invention, the adhesive mixture according to the invention additionally contains carbon blacks, in particular carbon blacks produced by the lamp black, furnace black and / or gas black process.

[0032] Additional fillers can, of course, be used. Carbon blacks produced by the lamp black, furnace black, or gas black process with BET surface areas of 20–200 m² / g, such as SAF, ISAF, IISAF, HAF, FEF, or GPF, are particularly suitable for this purpose.

[0033] These adhesive mixtures according to the invention are preferably prepared by mixing together the individual components of the mixture, wherein it is preferred to apply resorcinol and / or resorcinol esters of the formula (I) and melamine formaldehyde ether to silica.

[0034] In a further embodiment of the invention, the adhesive mixtures according to the invention additionally contain rubber, crosslinking agents, fillers and optionally further additives.

[0035] Natural rubber (NR) and / or synthetic rubber can be used as the rubber in the context of the invention. Preferred synthetic rubbers are, for example, BR- Polybutadiene ABR- Butadiene / acrylic acid C 1 -C 4 alkyl ester copolymer CR- Polychloroprene IR- Polyisoprene SBR- Styrene / butadiene copolymers with styrene contents of 1 - 60, preferably 20 - 50 wt.% IIR- Isobutylene / isoprene copolymers NBR- Butadiene / acrylonitrile copolymers with acrylonitrile contents of 5-60, preferably 10 - 50 wt.% HNBR- Partially hydrogenated or fully hydrogenated NBR rubber EPDM- Ethylene / propylene / diene copolymers.

[0036] The use of rubbers in the form of commercially available rubbers is possible.

[0037] The invention also relates to processes for producing the adhesive mixtures according to the invention, according to which: first, the silica-based filler is treated with melamine formaldehyde ether(s) of formula (II) and / or polymers thereof and subsequently with resorcinol ester(s) of formula (I), or the silica-based filler is treated simultaneously with melamine formaldehyde ether(s) of formula (II) and / or polymers thereof and resorcinol ester(s) of formula (I), or first, the silica-based filler is treated with resorcinol ester(s) of formula (I) and subsequently with melamine formaldehyde ether(s) of formula (II) and / or polymers thereof, or the silica-based filler is treated with a mixture of melamine formaldehyde ether(s) of formula (II) and / or polymers thereof and resorcinol ester(s) of formula (I), or resorcinol esters of formula (I) and melamine formaldehyde ether(s) of formula (II) and / or polymers thereof are each treated separately with the silica-based filler mixed and then the mixtures are combined and

[0038] This is then mixed into the rubber with the sulfenamide of formula (III).

[0039] If further additives, such as additional fillers, crosslinkers, vulcanization accelerators and rubber auxiliaries or also ageing inhibitors, heat stabilizers, light stabilizers, antioxidants, in particular ozone protection agents, flame retardants, processing aids, impact strength modifiers, plasticizers, tackifiers, blowing agents, dyes, pigments, waxes, extenders, organic acids, retarders, metal oxides and activators, in particular triethanolamine, polyethylene glycol, hexanetriol, silanes and reversion inhibitors, are used in the mixture, these are stirred into the rubber together with the previously mentioned components.

[0040] Furthermore, the additives listed in detail below can be added separately or in any mixture during the mixing process, such as additional fillers, crosslinkers, vulcanization accelerators and rubber auxiliaries, etc.

[0041] An internal mixer with a downstream mixing mill is preferably used to produce the adhesive mix. It is also possible to produce the adhesive mix solely on the mixing mill, at mixing temperatures below 110°C, preferably between 20 and 90°C.

[0042] Furthermore, the adhesive mixtures can contain one or more crosslinkers. Sulfur-based or peroxide crosslinkers are particularly suitable for this purpose, with sulfur-based crosslinkers being particularly preferred.

[0043] Sulfur can be used as a crosslinker in elemental, soluble or insoluble form, or in the form of sulfur donors. Examples of suitable sulfur donors include dimorpholyl disulfide (DTDM), 2-morpholinodithiobenzothiazole (MBSS), caprolactam disulfide, dipentamethylenethiuram tetrasulfide (DPTT), and tetramethylthiuram disulfide (TMTD).

[0044] In principle, the crosslinking of the elastomer mixture can be carried out with sulfur or sulfur donors alone, or in combination with other vulcanization accelerators, for which dithiocarbamates, thiurams, thiazoles, xanthates, bi- or polycyclic amines, guanidine derivatives, dithiophosphates, caprolactams, and thiourea derivatives are particularly suitable. Zinc diamine diisocyanate, hexamethylenetetramine, 1,3-bis(citraconimidomethyl)benzene, and cyclic disulfanes are also suitable.

[0045] The rubber mixtures according to the invention preferably contain sulfur-based crosslinkers and vulcanization accelerators.

[0046] Bis(2,4-dichlorobenzyl)peroxide, dibenzoyl peroxide, bis(4-chlorobenzoyl)peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, tert-butyl perbenzoate, 2,2-bis(t-butylperoxy)butane, 4,4-di-tert-butylperoxynonylvalerate, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butylcumyl peroxide, 1,3-bis(t-butylperoxyisopropyl)benzene, di-tert-butyl peroxide and 2,5-dimethyl-2,5-di(tert-butylperoxy)-3-hexyne are preferably used as peroxidic crosslinkers.

[0047] It may be advantageous to use other additives in addition to these peroxidic crosslinking agents to increase the crosslinking yield: for example, triallyl isocyanurate, triallyl cyanurate, trimethylolpropane tri(meth)acrylate, triallyl trimellitate, ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, zinc diacrylate, zinc dimethacrylate, 1,2-polybutadiene or N, N'-m-phenylenedimaleimide are suitable for this purpose.

[0048] Sulphur, magnesium oxide and / or zinc oxide are particularly preferably used as crosslinking agents.

[0049] The crosslinking agents and vulcanization accelerators are preferably used in amounts of 0.1 to 10 phr, particularly preferably 0.1 to 5 phr.

[0050] The adhesive mixtures may contain further additives, such as reaction accelerators, ageing inhibitors, heat stabilizers, light stabilizers, antioxidants, in particular ozone protection agents, flame retardants, processing aids, impact strength improvers, plasticizers, tackifiers, blowing agents, dyes, pigments, waxes, extenders, organic acids, retarders, metal oxides and activators, in particular triethanolamine, polyethylene glycol, hexanetriol, silanes and reversion inhibitors.

[0051] These additives are used in typical amounts, depending on the intended use of the vulcanizates. Typical amounts are 0.1 to 30 phr.

[0052] Preferred anti-aging agents are alkylated phenols, styrenated phenol, sterically hindered phenols, such as preferably 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol (BHT), 2,6-di-tert-butyl-4-ethylphenol, ester group-containing sterically hindered phenols, thioether-containing sterically hindered phenols, 2,2'-methylene-bis-(4-methyl-6-tert-butylphenol) (BPH) and sterically hindered thiobisphenols.

[0053] If discoloration of the rubber is not important, aminic anti-aging agents, e.g. mixtures of diaryl-p-phenylenediamines (DTPD), octylated diphenylamine (ODPA), phenyl-a-naphthylamine (PAN), phenyl-β-naphthylamine (PBN), preferably those based on phenylenediamine, e.g. N-isopropyl-N'-phenyl-p-phenylenediamine, N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD), N-1,4-dimethylpentyl-N'-phenyl-p-phenylenediamine (7PPD), N,N'-bis-(1,4-dimethylpentyl)-p-phenylenediamine (77PD) can also be used.

[0054] Other antioxidants include phosphites, such as tris(nonylphenyl)phosphite, polymerized 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), 2-mercaptobenzimidazole (MBI), methyl-2-mercaptobenzimidazole (MMBI), and zinc methylmercaptobenzimidazole (ZMMBI), which are usually used in combination with the above-mentioned phenolic antioxidants. TMQ, MBI, and MMBI are primarily used for NBR rubbers that are vulcanized with peroxides.

[0055] Ozone resistance can be improved by antioxidants such as N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine (6PPD), N-1,4-dimethylpentyl-N'-phenyl-p-phenylenediamine (7PPD), N,N'-bis-(1,4-dimethylpentyl)-p-phenylenediamine (77PD), enol ethers or cyclic acetals.

[0056] Ideally, processing aids should act between the rubber particles and counteract frictional forces during mixing, plasticizing, and molding. The adhesive mixtures according to the invention can contain all lubricants commonly used for processing plastics as processing aids, such as hydrocarbons such as oils, paraffins, and PE waxes; fatty alcohols with 6 to 20 carbon atoms; ketones; carboxylic acids such as fatty acids and montanic acids; oxidized PE wax; metal salts of carboxylic acids; carboxylic acid amides; and carboxylic acid esters, for example, with the alcohols ethanol, fatty alcohols, glycerol, ethanediol, pentaerythritol, and long-chain carboxylic acids as the acid component.

[0057] To reduce flammability and smoke development during combustion, the adhesive mixture composition according to the invention may also contain flame retardants. Examples of flame retardants used include antimony trioxide, phosphoric acid esters, chlorinated paraffin, aluminum hydroxide, boron compounds, zinc compounds, molybdenum trioxide, ferrocene, calcium carbonate, or magnesium carbonate.

[0058] Before crosslinking, other plastics can also be added to the vulcanizate, which act, for example, as polymeric processing aids or impact strength improvers. These plastics are preferably selected from the group consisting of homo- and copolymers based on ethylene, propylene, butadiene, styrene, vinyl acetate, vinyl chloride, glycidyl acrylate, glycidyl methacrylate, acrylates and methacrylates with alcohol components of branched or unbranched C 1 to C 10 alcohols, with polyacrylates with identical or different alcohol radicals from the group of C 4 to C 8 alcohols, in particular butanol, hexanol, octanol and 2-ethylhexanol, polymethyl methacrylate, methyl methacrylate-butyl acrylate copolymers, methyl methacrylate-butyl methacrylate copolymers, ethylene-vinyl acetate copolymers, chlorinated polyethylene, ethylene-propylene copolymers, ethylene-propylene-diene copolymers being particularly preferred.

[0059] In a preferred embodiment, the elastomer mixture contains 0.1 to 50 phr of the reversion inhibitor 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane (CAS No. 151900-44-6).

[0060] The adhesive mixtures according to the invention result in good adhesion between rubber and polyamide, viscose, polyester, aramid or steel cord; especially between rubber and textile fibers.

[0061] The present invention also relates to the use of the mixtures according to the invention as adhesion promoters in rubber mixtures, preferably in rubber mixtures crosslinkable with sulfur, particularly preferably in rubber mixtures containing natural and / or synthetic rubbers.

[0062] The invention further relates to vulcanizates obtainable by vulcanization of the rubber-containing adhesive mixtures according to the invention, preferably at melt temperatures of 100 to 200°C, particularly preferably at melt temperatures of 130 to 180°C, and to the related process for producing vulcanizates by vulcanization of the adhesive mixtures according to the invention, preferably at melt temperatures of 100 to 200°C, particularly preferably at melt temperatures of 130 to 180°C.

[0063] The invention also relates to composite articles, preferably in the form of tires, conveyor belts, belts of all kinds, V-belts, reinforced hoses, fire hoses or coated fabrics, containing the vulcanizates according to the invention.

[0064] The following examples serve to illustrate the invention without limiting it. Examples of implementation:

[0065] Examples of the production of the adhesive systems: Mixture Reference, as well as the rubber mixtures 1 and 2 were produced as follows: Table 1: Adhesive Mix 1 (Exp.) Adhesive Mix 2 (Exp.) Silica CAS No. 7631-86-9 12,7 12,7 Melamine formaldehyde ether of formula (II) with R 2< = hydrogen (4x) and methyl (2x), on silica (50%) 4,6 4,6 Resorcinol and stearic acid (2:1) 3,4 3,4 Benzothiazylsulfenamide of formula (III) with x = 0, y = 1 and z = 2 (DBzBS) 0,7 0,9

[0066] For the preparation of rubber mixtures 1 and 2, the silica was first mixed with melamine formaldehyde ether of formula (II) and then treated with resorcinol and stearic acid, with the amounts used and the reactants corresponding to Table 1. Subsequently, these mixtures were each mixed with the sulfenamide of formula (III). Production of the rubber mixture from the adhesive mixtures 1 and 2

[0067] In an internal mixer, Adhesive Compound 1 or Adhesive Compound 2, followed by carbon black and mineral oil, were added successively to the natural rubber. The ingredients and quantities used are shown in Table 2. The internal mixer was operated at a temperature of < 90°C, and the residence time of the adhesive components was less than 5 minutes.

[0068] Depending on the mixture, either dicyclohexylbenzothiazylsulfenamide / sulfur for reference or the benzothiazylsulfenamide of formula (III) with x = 0, y = 1 and z = 2, sulfur and the other components for the rubber mixtures 1 and 2 were then incorporated on the rolling mill in the amounts specified in Table 2.

[0069] The mixing mill had a temperature of less than 40°C. The resulting rolled sheets were used to measure tear resistance and rebound resilience.

[0070] The internal mixer had a temperature of < 90°C. The dwell time of the adhesive components was less than 5 minutes.

[0071] Another portion of the mixtures was vulcanized in an electric hot press. The curing temperature was T = 150°C, the pressure p = 100 bar, and the curing time was t = 3180 seconds at a conversion of t = 95. Table 2 : Rubber recipe Reference according to EP-A-2960278 Rubber Compound 1 (Exp.) Rubber Compound 2 (Exp.) Natural rubber TSR 100 100 100 soot 50 50 50 Silica CAS No. 7631-86-9 12,7 12,7 12,7 mineral oil 4 4 4 zinc oxide 8 8 8 Melamine formaldehyde ether of formula (II) with R 2< = hydrogen (4x ) and methyl (2x), on filler (50 %) 4,6 4,6 4,6 Resorcinol and stearic acid (2:1) 3,4 3,4 3,4 SULFUR 4,5 4,5 4,5 Dicyclohexylbenzothiazyl sulfenamide (SDT) 0,7 Benzothiazylsulfenamide of formula (III) with x = 0, y = 1 and z = 2 (DBzBS) 0,7 0,9 Exp. = according to the invention StdT = state of the art Quantities in phr (parts by weight per 100 parts of rubber) Trade name Manufacturer / Distributor Natural rubber TSR / RSS 3 DEFO 700 Trading house Weber & Schaer soot CORAX N 326 Degussa-Evonik GmbH Silica VULKASIL S LANXESS Germany GmbH 2,2,4-trimethyl-1,2-dihydroquinoline polymerizes VULKANOX HS / LG LANXESS Germany GmbH zinc oxide ZINC OXIDE ACTIVE LANXESS Germany GmbH sulfur GROUND SULFUR 90 / 95 CHANCEL Solvay Germany GmbH mineral oil TUDALEN 1849-TE Hansen&Rosenthal KG Dicyclohexylbenzothiazyl sulfenamide VULKACIT DZ / EGC LANXESS Germany GmbH DBzBS LANXESS Germany Melamine formaldehyde ether as a condensation product of melamine, formaldehyde, methanol on filler (50%) COHEDUR A250 LANXESS Germany GmbH Resorcinol and stearic acid (2:1) COHEDUR RS LANXESS Germany GmbH

[0072] The following measurement methods were used to determine the properties of rubber compounds or vulcanizates: Scorch behavior (scorch time t3 and t5):

[0073] Furthermore, the scorch behavior of a compound can be measured using the same test as described above. The selected temperature was 130°C. The rotor ran until the torque value, after passing through a minimum, had increased to 5 Mooney units relative to the minimum value (t5). The higher the value (in seconds), the slower the scorch time. In practice, a scorch time of more than 300 seconds is usually advantageous, but considering processing reliability and time requirements, this should be less than 1000 seconds. Tear resistance (according to DIN 53515):

[0074] The force that a vulcanizate resists tearing when subjected to a cut is referred to as tear resistance. It is expressed in N / mm and determined using a tensile testing machine using the "Graves angle test" method (DIN 53515).

[0075] The rebound resilience was determined according to DIN 53512.

[0076] The measurement results of the mixtures are summarized in Table 3. Table 3 : Summary of results parameter Unit DIN reference Rubber formulation 1 Rubber formulation 2 Mooney scorch at 130°C (t3) sec DIN 53523-4 753 876 830 Mooney scorch at 130°C (t5) sec DIN 53523-4 841 997 941 Tear resistance N / mm 53515 41,7 45,2 45,9 Rebound resilience at 23°C % 53512 40 40 41

[0077] Table 4 shows the results of the network node structure analysis at the same molar accelerator concentration in natural rubber (tmax, 150°C; 1.7 phr sulfur). Table 4: parameter Unit reference Rubber formulation 1 Mono-sulfidic network nodes % 4 12 Di-sulfidic network nodes % 38 34 Polysulfide network nodes % 58 55

[0078] Network node structure analysis using the thiol-amine method (according to Saville and Watson; 1967) is based on the selective cleavage of the different sulfur bridges using different reagents. To distinguish between the three types of network nodes, two thiols of different selectivity are required. A 0.5 molar solution of i-propanethiol and piperidine in n-heptane was used to cleave exclusively polysulfidic sulfur bridges. A 1 molar solution of n-hexanethiol and piperidine in n-heptane was used to simultaneously cleave di- and polysulfidic network nodes. The monosulfidic linkages did not react with the reagents used during the degradation times.

[0079] The network node structure analysis of the DCBS system showed for the vulcanizate according to the invention with a conversion of 100% (tmax) mainly polysulfidic crosslinking sites (58%) and a proportion of 38% for the disulfidic network nodes as well as 4% monosulfidic network nodes.

[0080] Surprisingly, DBzBS (N,N-dibenzyl-2-benzothiazylsulfenamide) also forms few monosulfidic network sites and a comparable number of di- and polysulfidic network nodes.

[0081] Due to the noticeably longer scorch time of DBBS compared to DCBS (see Table 3), vulcanization and thus the formation of sulfur bridges between the individual rubber chains are slowed, allowing the rubber to bond well to the metal alloy via Cu-Sx-C bridges. This ensures the safe use of DBBS as a vulcanization accelerator in tire production.

[0082] The measurement results show that the adhesive mixture according to the invention exhibits a significant improvement in scorching behavior (longer scorching time at 130°C). This has the particular advantage that the flow time of the mixture allows sufficient time for the reaction of formula aldehyde cleavage and resin formation to ensure that the bond can form.

[0083] Furthermore, physical properties such as rebound resilience and tear resistance were improved while other physical parameters such as modulus 300 and tensile strength were comparable.

Claims

1. Adhesive mixture containing - resorcinol and / or resorcinol ester of formula (I) wherein all radicals R1 are identical or different and represent hydrogen, a straight-chain or branched C1-C18-alkyl radical or a phenyl radical, preferably methyl or stearyl, and - at least one melamine formaldehyde ether of formula (II) wherein all radicals R2 are identical or different and represent hydrogen or a straight-chain or branched C1-C4-alkyl radical or a phenyl radical, wherein however not more than 5 radicals R2 represent hydrogen, and / or polymers of melamine formaldehyde ethers of formula (II), - at least one sulfenamide of formula (III) where x = 0 and z = 2, wherein the sum of z and x = 2 and y = 1, - at least one silica-based filler.

2. Adhesive mixture according to Claim 1, characterized in that the total proportion of resorcinol and / or resorcinol esters of formula (I), melamine formaldehyde ethers of formula (II) and / or polymers is 20-80% by weight and the proportion of sulfenamide of formula (III) is 0.1-10% by weight, based on the total adhesive mixture.

3. Adhesive mixtures according to either of Claims 1 to 2, characterized in that the mixture additionally contains natural and / or synthetic rubbers.

4. Adhesive mixture according to any of Claims 1 to 3, characterized in that the mixture additionally contains natural and / or synthetic rubbers selected from the group containing polybutadiene, butadiene / C1-C4-alkyl acrylate copolymer, polychloroprene, polyisoprene, styrene / butadiene copolymers with styrene contents of 1-60% by weight, isobutylene / isoprene copolymers, butadiene / acrylonitrile copolymers with acrylonitrile contents of 5-60% by weight, partially hydrogenated and fully hydrogenated NBR rubber and ethylene / propylene / diene copolymers, and mixtures thereof.

5. Adhesive mixture according to any of Claims 1 to 4, characterized in that the silica-based filler is precipitated silica or pyrogenic silica.

6. Process for producing the adhesive mixture according to Claim 3, characterized in that - the silica-based filler is treated initially with melamine formaldehyde ether(s) of formula (II) and / or polymers thereof and subsequently with resorcinol and / or resorcinol ester(s) of formula (I), or - the silica-based filler is simultaneously treated with melamine formaldehyde ether(s) of formula (II) and / or polymers thereof and resorcinol ester(s) of formula (I), or - the silica-based filler is initially charged simultaneously with resorcinol ester(s) of formula (I) and subsequently treated with melamine formaldehyde ether(s) of formula (II) and / or polymers thereof, or - the silica-based filler is treated with a mixture of melamine formaldehyde ether(s) of formula (II) and / or polymers thereof and resorcinol ester(s) of formula (I), or - resorcinol esters of formula (I) and melamine formaldehyde ethers of formula (II) and / or polymers thereof are in each case mixed with the silica-based filler separately and the mixtures are subsequently combined and in each case subsequently added to the rubber with the sulfenamide of formula (III).

7. Use of the adhesive mixture according to any of Claims 1 to 5 as an adhesion promoter in rubber mixtures.

8. Use according to Claim 7, characterized in that the rubber mixtures are sulfur-crosslinkable rubber mixtures.

9. Vulcanizates obtainable by vulcanization of adhesive mixture according to Claim 3 at blend temperatures of 100°C to 200°C.

10. Process for producing vulcanizates according to Claim 9, characterized in that an adhesive mixture according to Claim 3 is vulcanized at blend temperatures of 100°C to 200°C.

11. Composite article containing vulcanizates according to Claim 9.

12. Composite article according to Claim 11, characterized in that it is selected from tires, conveyor belts, belts of all kinds, V-belts, reinforced hoses, fire hoses or coated fabrics.