RUBBERIZED, METALLIC STRENGTH BEAM AND PNEUMATIC VEHICLE TIRE

Description

[0001] The invention relates to a metallic reinforcement rubberized with a sulfur-crosslinkable, substantially cobalt-free rubberizing mixture, wherein the metallic reinforcement is a steel cord containing one or more filaments, wherein the filaments comprise a filament-like steel substrate and a coating partially or completely covering the filament-like steel substrate, wherein the coating comprises brass consisting of copper and zinc, and wherein the coating is enriched with iron, which is present in the brass as particles with a size between 10 and 10,000 nm.

[0002] Furthermore, the invention relates to a pneumatic vehicle tire having such a metallic reinforcement rubberized with a sulfur-crosslinked rubber compound.

[0003] The adhesion of steel cords to a rubber matrix is achieved via brass (on the steel) and sulfur (from the rubber compound).

[0004] Sulfur-curable rubber lining compounds for brass-coated steel cords typically contain cobalt-based bonding systems, which, for example, also contain methylene acceptor-methylene donor pairs. The cobalt compounds, usually organic cobalt salts, are intended to inhibit the rapid buildup of zinc oxide and copper sulfide layers on the brass layer of the steel cord, which form during the aging of the rubber-steel cord composite. The zinc oxide and copper sulfide layers can become brittle over time, thus leading to reduced adhesion between the steel cord and rubber. The cobalt compounds improve adhesion under stress in humid and hot environments.

[0005] However, the use of cobalt salts in rubber compounds also has some disadvantages. Organic cobalt salts can act as oxidation catalysts and thus lead to undesirable aging processes within the compound layers. Furthermore, cobalt and its salts are classified as harmful to health, and cobalt mining and salt production harm the environment. Furthermore, there is a growing global demand for cobalt in the battery industry. Therefore, the already high prices for cobalt are expected to continue rising in the coming years.

[0006] Efforts are therefore being made to reduce cobalt in rubber compounds.

[0007] To achieve this, steel cords with special alloys on the surface that already contain cobalt have been developed. Such steel cords with cobalt-containing alloys are described, for example, in EP 2 516 729 B1. However, this only reduces cobalt consumption. The cobalt is shifted from the mixture side to the steel cord side.

[0008] Another way to eliminate cobalt from rubber compounds is disclosed in WO 2020 / 156967 A1. This document describes rubberized metallic reinforcements of the type mentioned above, processes for their production, and their use, using a sulfur-crosslinkable, essentially cobalt-free rubber compound. The reinforcements have a brass coating doped with iron particles in the nanometer range. Such reinforcements are compatible with essentially cobalt-free rubber compounds and can be used, for example, in pneumatic vehicle tires.

[0009] However, removing the cobalt compounds from rubber compounds has shown that the compound properties change. In particular, vulcanization times become significantly longer, even if the compound composition remains unchanged. This is often undesirable, since the rubber coating of the reinforcements, such as the belt rubber in pneumatic vehicle tires, is often the area in the rubber product that determines the curing time. Extending the curing time of the rubber compound results in an extension of the curing time for the entire product, with the resulting problems such as over-vulcanization of individual areas and cost-effectiveness disadvantages.If this extension of the vulcanization times is counteracted, for example by using larger amounts of vulcanization accelerator, it can happen that the crosslinking initially proceeds so quickly that no sufficient adhesive layer can form between the reinforcement and the embedding rubber compound.

[0010] The invention is based on the object of providing a metallic reinforcement of the type mentioned above, rubberized with a sulfur-crosslinkable, essentially cobalt-free rubberizing mixture, which is optimized with regard to vulcanization times and at the same time has good reinforcement-rubber adhesion.

[0011] The object is achieved according to the invention in that the rubberizing mixture contains 0.5 to 3 phr (parts by weight, based on 100 parts by weight of the total rubbers in the mixture) of at least one sulfenimide accelerator and / or at least one sulfenamide accelerator based on dibenzylamine.

[0012] A substantially cobalt-free rubber compound is understood to be a rubber compound that is essentially free of cobalt or organic cobalt compounds. The cobalt content in the vulcanized rubber compound, measured by X-ray fluorescence spectroscopy, is less than 0.01 wt.% based on the weight of the vulcanized rubber compound.

[0013] The term phr (parts per hundred parts of rubber by weight) used in this document is the standard quantity used in the rubber industry for compound formulations. The dosage of the parts by weight of the individual substances is always based on 100 parts by weight of the total mass of all rubbers present in the compound. The mass of all rubbers present in the compound adds up to 100.

[0014] Surprisingly, it has been shown that by using a sulfenimide accelerator and / or a special sulfenamide accelerator based on dibenzylamine in the specified amounts, even without the presence of cobalt, an optimal balance between not too fast initial crosslinking (not too short scorching time t 10 ) and not too slow final crosslinking (not too long vulcanization time t 90 ) can be achieved.

[0015] The rubberized, metallic reinforcement according to the invention also has the advantage of good adhesion even after aging, in particular steam aging.

[0016] In addition, the rubberized metallic reinforcement according to the invention offers the ecological and economic advantages of a cobalt-free mixture and a cobalt-free reinforcement.

[0017] The adhesion between the reinforcement and the embedding rubber compound can be further improved if the coating is enriched with iron, which is present in the brass as particles with a size between 20 and 5000 nm.

[0018] According to a preferred embodiment of the invention, the brass of the coating comprises at least 63 wt.% copper, with the remainder being zinc. According to the invention, the amount of iron is not included in the definition of brass. The coating of the reinforcement then comprises brass and iron.

[0019] Preferably, the amount of iron in the coating is greater than or equal to 1 wt% and less than 10 wt%, more preferably greater than or equal to 3 wt% and less than 9 wt%, compared to the total mass of brass and iron.

[0020] If the iron content is more than 10 wt%, problems may arise when drawing the filaments.

[0021] To improve the processability of the filaments, the coating is essentially free of zinc-iron alloys.

[0022] The gumming mixture contains 0.5 to 3 phr, preferably 1 to 2.5 phr, of at least one sulfenimide accelerator and / or at least one sulfenamide accelerator based on dibenzylamine.

[0023] Sulfenimide accelerators are vulcanization accelerators based on primary amines. In contrast, sulfenamide accelerators such as DCBS (N,N'-dicyclohexyl-2-benzothiazole sulfenamide) or MBS (N-oxydiethylene-2-benzothiazole sulfenamide) are based on secondary amines. One or more sulfinimide accelerators may be included in the mixture.

[0024] For a particularly balanced ratio of scorch time t 10 and full cure time t 90, the sulfenimide accelerator used is N-tert-butyl-2-benzothiazolesulfenimide (TBSI, IUPAC name: N,N-bis(1,3-benzothiazol-2-ylsulfanyl)-2-methylpropan-2-amine). The use of the sulfenimide accelerator N-tert-butyl-2-benzothiazolesulfenimide (TBSI) as a vulcanization accelerator in cobalt-containing rubber compounds is known, for example, from US 2010 / 0200141 A1 and US 6,120,911.

[0025] Dibenzylamine-based sulfenamide accelerators are substances derived from 2-mercaptobenzothiazole, in which a dibenzylamine is attached to the mercaptosulfur. One or more dibenzylamine-based sulfenamide accelerators may be present in the mixture.

[0026] According to a preferred embodiment of the invention, the sulfenamide accelerator based on dibenzylamine is N,N'-dibenzyl-2-benzothiazolesulfenamide (DBBS).

[0027] In order to further improve the durability of the rubber-metal adhesion with regard to oxidative aging processes, it has proven advantageous if the rubber coating mixture contains 2 to 10 phr of zinc oxide.

[0028] To further improve adhesion, the rubberizing mixture can contain methylene acceptor-methylene donor pairs in conventional amounts. Resorcinol-based methylene acceptors or special novolak resins, such as Alnovol ®< PN 760 / Past from Allnex Netherlands BV, can serve as methyl acceptors. Etherified melamine resins, for example, can be used as methylene donor / formaldehyde donors. Examples of etherified melamine resins include hexamethoxymethylmelamine (HMMM) and hexamethylenetetramine (HMT).

[0029] In addition, the rubber compound may contain further adhesion stabilizers acting after vulcanization, such as sodium hexamethylene 1,6-bisthiosulfate dihydrate (NaO 3 SS(CH 2 ) 6 SSO 3 Na·2 H 2 O).

[0030] The sulfur-curable rubber compound contains other components commonly used in the rubber industry, in particular at least one rubber.

[0031] Diene rubbers can be used as rubbers. Diene rubbers include all rubbers with an unsaturated carbon chain that are at least partially derived from conjugated dienes.

[0032] The rubberizing mixture can contain polyisoprene (IR, NR) as the diene rubber. This can be either cis-1,4-polyisoprene or 3,4-polyisoprene. However, the use of cis-1,4-polyisoprenes with a cis-1,4 content of > 90 wt.% is preferred. Such a polyisoprene can be obtained by stereospecific polymerization in solution with Ziegler-Natta catalysts or using finely divided lithium alkyls. Natural rubber (NR) is also such a cis-1,4-polyisoprene; the cis-1,4 content in natural rubber is greater than 99 wt.%. Natural rubber is defined as rubber that can be obtained by harvesting sources such as rubber trees (Hevea brasiliensis) or non-rubber tree sources (such as guayule or dandelion (e.g. Taraxacum koksaghyz)).

[0033] If the rubber coating mixture contains polybutadiene (BR) as the diene rubber, it can be cis-1,4-polybutadiene. The preferred material is cis-1,4-polybutadiene with a cis-1,4 content of greater than 90 wt.%, which can be produced, for example, by solution polymerization in the presence of rare earth catalysts.

[0034] Other diene rubbers that can be used include vinyl-polybutadienes and styrene-butadiene copolymers. Vinyl-polybutadienes and styrene-butadiene copolymers can be solution-polymerized (styrene)-butadiene copolymers (S-(S)BR) with a styrene content, based on the polymer, of approximately 0 to 45 wt.% and a vinyl content (content of 1,2-bonded butadiene, based on the total polymer) of 10 to 90 wt.%, which can be produced, for example, using lithium alkyls in an organic solvent. S-(S)BR can also be coupled and end-group modified. However, emulsion-polymerized styrene-butadiene copolymers (E-SBR) and blends of E-SBR and S-(S)BR can also be used. The styrene content of the E-SBR is approximately 15 to 50 wt.% and the types known from the prior art, which were obtained by copolymerization of styrene and 1,3-butadiene in aqueous emulsion, can be used.

[0035] The diene rubbers used in the mixture, especially the styrene-butadiene copolymers, can also be used in partially or fully functionalized form. The functionalization can be carried out with groups that can interact with the fillers used, especially with fillers bearing OH groups. This can, for example, involve functionalization with hydroxyl groups and / or epoxy groups and / or siloxane groups and / or amino groups and / or phthalocyanine groups and / or carboxyl groups and / or silane sulfide groups. The diene rubbers can also be coupled additionally or alternatively.

[0036] In addition to the diene rubbers mentioned, the mixture may also contain other types of rubber, such as styrene-isoprene-butadiene terpolymer, butyl rubber, halobutyl rubber or ethylene-propylene-diene rubber (EPDM).

[0037] Reclaim can also be added to the rubber compound as a processing aid and to reduce the cost of the compound.

[0038] The rubber compound may contain various fillers such as carbon black, silica, aluminosilicates, chalk, starch, magnesium oxide, titanium dioxide or rubber gels in usual quantities, whereby the fillers may be used in combination.

[0039] If carbon black is used in the rubber compound, it is preferable to use grades with a CTAB surface area (according to ASTM D 3765) of more than 30 m 2 / g. These are easy to mix in and ensure low heat buildup.

[0040] If silicas are included in the mixture, they can be those commonly used in tire rubber compounds. It is particularly preferred to use a finely dispersed, precipitated silica with a CTAB surface area (according to ASTM D 3765) of 30 to 350 m² / g, preferably 110 to 250 m² / g. Both conventional silicas such as type VN3 (trade name) from Evonik and highly dispersible silicas, so-called HD silicas (e.g., Ultrasil 7000 from Evonik), can be used as silicas.

[0041] If the rubber coating mixture contains silica or other polar fillers, silane coupling agents can be added to the mixture to improve processability and to bond the polar filler to the rubber. The silane coupling agents react with the surface silanol groups of the silica or other polar groups during mixing of the rubber or rubber mixture (in situ) or even before the filler is added to the rubber as a pretreatment (premodification). All silane coupling agents known to those skilled in the art for use in rubber mixtures can be used as silane coupling agents.Such coupling agents known from the prior art are bifunctional organosilanes which have at least one alkoxy, cycloalkoxy or phenoxy group as a leaving group on the silicon atom and which have as another functionality a group which, if appropriate after cleavage, can enter into a chemical reaction with the double bonds of the polymer. The latter group can, for example, be the following chemical groups: -SCN, -SH, -NH 2 or -S x - (where x = 2-8). Thus, silane coupling agents which can be used include, for example, 3-mercaptopropyltriethoxysilane, 3-thiocyanatopropyltrimethoxysilane or 3,3'-bis(triethoxysilylpropyl)polysulfides having 2 to 8 sulfur atoms, such as e.g. B. 3,3'-bis(triethoxysilylpropyl)tetrasulfide (TESPT), the corresponding disulfide or mixtures of the sulfides with 1 to 8 sulfur atoms with different contents of the various sulfides can be used.The silane coupling agents can also be added as a mixture with industrial carbon black, such as TESPT on carbon black (trade name X50S from Evonik). Blocked mercaptosilanes, such as those known from WO 99 / 09036, can also be used as silane coupling agents. Silanes such as those described in WO 2008 / 083241 A1, WO 2008 / 083242 A1, WO 2008 / 083243 A1, and WO 2008 / 083244 A1 can also be used. Examples of suitable silanes include those marketed under the name NXT in various versions by Momentive, USA, or those marketed under the name VP Si 363 by Evonik Industries. So-called "silated core polysulfides" (SCP, polysulfides with silylated cores) can also be used, which are described, for example, in US 20080161477 A1 and EP 2 114 961 B1.

[0042] Furthermore, the rubber coating mixture can contain conventional additives in the usual parts by weight. These additives include plasticizers such as glycerides, factices, hydrocarbon resins, aromatic, naphthenic or paraffinic mineral oil plasticizers (e.g. MES (mild extraction solvate) or TDAE (treated distillate aromatic extract)), oils based on renewable raw materials (such as rapeseed oil, terpene oils (e.g. orange oils) or factices), so-called BTL oils (as disclosed in DE 10 2008 037714 A1) or liquid polymers (such as liquid polybutadiene)); ageing inhibitors such as B. N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) and other substances, as known for example from J. Schnetger, Lexikon der Kautschuktechnik, 2nd edition, Hüthig Buch Verlag, Heidelberg, 1991, pp. 42-48, activators, such as fatty acids (e.g.stearic acid), waxes, tackifying resins such as hydrocarbon resins and rosin, and masticating agents such as 2,2'-dibenzamidodiphenyl disulfide (DBD).

[0043] Vulcanization is carried out in the presence of sulfur and / or sulfur donors, whereby some sulfur donors can also act as vulcanization accelerators. Sulfur or sulfur donors are added to the rubber compound in the final mixing step in amounts customary in the art (0.4 to 8 phr). Sulfur is preferably used in an amount of 2 to 5 phr. Sulfur is preferably used in oil-extended form. This allows the sulfur to be incorporated and dispersed more easily and evenly.

[0044] Furthermore, in addition to the sulfenimide accelerators and the dibenzylamine-based sulfenamide accelerators, the rubberizing mixture may contain other vulcanization-influencing substances such as other vulcanization accelerators, vulcanization retarders, and vulcanization activators in conventional amounts. Preferably, the rubberizing mixture contains less than 0.5 phr of other vulcanization accelerators in addition to the sulfenimide accelerators and the dibenzylamine-based sulfenamide accelerators.

[0045] The rubber compound is manufactured in a conventional manner, with a base compound containing all components except the vulcanization system (sulfur and vulcanization-influencing substances) being prepared in one or more mixing stages. The final compound is then created by adding the vulcanization system. The mixture is then further processed.

[0046] Rubberized reinforcements can be used in a wide variety of rubber products containing reinforcements. These rubber products can include tires, drive belts, conveyor belts, hoses, rubberized fabrics, or air springs. The tires can be, for example, car, van, truck, industrial, two-wheel, agricultural, or aircraft tires.

[0047] The rubberized, metallic reinforcements are preferably used in pneumatic vehicle tires. Pneumatic vehicle tires are typically used for passenger cars, vans, or trucks.

[0048] The rubberized, metallic reinforcements can be used in a wide variety of tire components, such as the bead core, the bead caps, the bead reinforcements, the belt, the carcass, or the belt bandages. Several components within a tire can also comprise the rubberized, metallic reinforcements according to the invention. The pneumatic vehicle tires according to the invention are manufactured using methods known to those skilled in the art.

[0049] Preferably, the belt and / or carcass of the pneumatic vehicle tire contains rubberized, metallic reinforcements. The good adhesion between the reinforcements and the rubber compound, even under aging, results in a long service life of the pneumatic vehicle tire and allows for cost-effective production.

[0050] The invention encompasses all advantageous embodiments, which are reflected, inter alia, in the patent claims. In particular, the invention also encompasses embodiments that result from the combination of different features, for example, components of the rubber coating mixture, and varying degrees of preference for these features, so that a combination of a first feature designated as "preferred" or described within the scope of an advantageous embodiment with another feature designated, for example, as "particularly preferred" is also encompassed by the invention.

[0051] The invention will now be explained in more detail using the table below.

[0052] Table 1 shows example compounds for rubber coating metallic reinforcements of a pneumatic vehicle tire.

[0053] In the compounds in the table, the vulcanization accelerators and the cobalt stearate were varied.

[0054] The mixture was prepared under standard conditions by producing a base mixture and then the final mixture in a laboratory tangential mixer.

[0055] The conversion times of 10 and 90% conversion (t 10 : scorching time, t 90 : complete vulcanization time) were determined using a rotorless vulcanometer (MDR = Moving Disc Rheometer) according to DIN 53 529 at vulcanization of 160 °C.

[0056] Furthermore, adhesion tests were carried out with the mixtures from Table 1 on conventional brass-plated steel cord A (2x0.3 HT, brass: 63.5 wt.% copper, 36.5 wt.% zinc, iron content of the coating: 0 wt.%) and on the inventive, iron-doped brass-plated steel cord B (2x0.3 HT, where the coating is composed of 64.1 wt.% copper, 32.6 wt.% zinc, 3.3 wt.% iron with a particle size distribution of the iron particles between 20 and 5000 nm) according to ASTM 2229 / D1871 without aging and after five days of aging in saturated steam at 105 °C (test specimen preparation: vulcanization: 30 min, 150 °C, embedding length in the rubber compound: 10 mm, pull-out speed: 125 mm / min). The pull-out force and the coverage were determined. For the pull-out force, the value of mixture 1 was set as 100%; the values of the other mixtures were referred to mixture 1. Table 1 Components Unit 1 2 3 4 Natural rubber (polyisoprene) phr 100 100 100 100 soot phr 63 63 63 63 Plasticizers and anti-aging agents phr 9,6 9,6 9,6 9,6 Cobalt stearate phr 1,3 - - - Methylene acceptor-methylene donor pair phr 7,2 7,2 7,2 7,2 Accelerator DCBS phr 0,75 0,75 - - Accelerator TBSI phr - - 1,0 - Accelerator DBBS phr - - - 2,2 Sulphur, diluted with 33% w / w oil phr 6,75 6,75 6,75 6,75 Characteristics t 10 min 1,09 0,98 0,88 0,85 t 90 min 11,31 18,19 10,75 12,02 Pull-out force (untreated, steel cord A) % 100 97 91 102 Covering (untreated, steel cord A) % 100 95 95 92 Pull-out force (untreated, steel cord B) % 100 99 105 104 Covering (untreated, steel cord B) % 98 96 100 85 Pull-out force (aged, steel cord A) % 80 57 61 58 Covering (aged, steel cord A) % 99 92 94 80 Pull-out force (aged, steel cord B) % 87 91 87 91 Covering (aged, steel cord B) % 96 97 99 90

[0057] The table shows that optimal curing times can be achieved with compounds 3 and 4. In particular, the curing time t 90 with TBSI or DBBS as accelerators is in the range of, or even below, the time of the reference compound. At the same time, these compounds, in combination with iron-doped steel cord B, can achieve very good adhesion results, which are in the range of, or even better than, Reference Compound 1.

Claims

1. Metallic strength member rubberized with a sulfur-crosslinkable, essentially cobalt-free rubberization mixture, wherein the metallic strength member is a steel cord containing one or more filaments, - wherein the filaments comprise a steel substrate filament and a coating that partly or completely covers the steel substrate filament, - wherein the coating comprises brass consisting of copper and zinc, and - wherein the coating is enriched with iron in the form of particles having a size between 10 and 10 000 nm in the brass, characterized in that the rubberization mixture contains 0.5 to 3 phr (parts by weight, based on 100 parts by weight of all rubbers in the mixture) of at least one sulfenimide accelerator and / or at least one dibenzylamine-based sulfenamide accelerator.

2. Rubberized metallic strength member according to Claim 1, characterized in that the coating is enriched with iron in the form of particles having a size between 20 and 5000 nm in the brass.

3. Rubberized metallic strength member according to Claim 1 or 2, characterized in that the brass comprises at least 63% by weight of copper, the balance being zinc.

4. Rubberized metallic strength member according to at least one of the preceding claims, characterized in that the amount of iron in the coating is not less than 1% by weight and less than 10% by weight, preferably not less than 3% by weight and less than 9% by weight, by comparison with the total mass of brass and iron.

5. Rubberized metallic strength member according to at least one of the preceding claims, characterized in that the coating is essentially free of zinc-iron alloys.

6. Rubberized metallic strength member according to at least one of the preceding claims, characterized in that it contains 1 to 2.5 phr of at least one sulfenimide accelerator and / or at least one dibenzylamine-based sulfenamide accelerator.

7. Rubberized metallic strength member according to at least one of the preceding claims, characterized in that the at least one sulfenimide accelerator is N-tert-butyl-2-benzothiazolesulfenimide (TBSI).

8. Rubberized metallic strength member according to at least one of the preceding claims, characterized in that the at least one dibenzylamine-based sulfenamide accelerator is N,N'-dibenzyl-2-benzothiazolesulfenamide (DBBS).

9. Pneumatic vehicle tire including a metallic strength member rubberized with a sulfur-crosslinked rubberization mixture according to Claim 1.

10. Pneumatic vehicle tire according to Claim 9, characterized in that the belt and / or carcass contains the rubberized metallic strength member.