Zinc compounds for use in rubber compositions

Abstract

The present invention relates to rubber compositions comprising a zinc compound of at least one branched, aliphatic C5- to C30-carboxylic acid, wherein the molar ratio of the carboxylic acid to zinc in the zinc compound is from 0.7 to 1 to 1 to 0.7, as well as to processes for preparing the zinc compound and to the use thereof. The present invention further relates to rubber articles in which at least one component has been manufactured at least partially from the rubber composition according to the invention.

Description

[0001] Zinc compounds for use in rubber compositions

[0002] Field of invention

[0003] The present invention relates to rubber compositions comprising zinc compounds of at least one branched, aliphatic C5 to C 30 The present invention comprises a carboxylic acid, wherein the molar ratio of the carboxylic acid to zinc in the zinc compound is 0.7 to 1 to 1 to 0.7, as well as processes for the preparation of the zinc compounds and their use. Furthermore, the present invention relates to rubber articles in which at least one component is at least partially manufactured from the rubber composition according to the invention.

[0004] Background of the invention

[0005] It is known that some rubber compounds exhibit poor reversion stability. Reversion refers to a decrease in the degree of crosslinking and the mechanical properties of vulcanizates (such as tensile strength, tear strength, and elasticity) when vulcanization continues beyond the optimum. Reversion occurs during the vulcanization of diene rubbers, especially natural rubber and synthetic polyisoprene, at high vulcanization temperatures or long vulcanization times. After reaching a certain state of cure, a reaction opposite to crosslinking is initiated: reversion, in which some sulfur bridges are broken. Since natural rubber is used in almost all areas of the rubber industry (in tires, seals, hoses, shock absorbers, conveyor belts, and shoe soles, to name just a few), accounting for approximately...40-45%), preventing reversion is a relevant problem in the rubber industry.

[0006] It is known that soluble zinc compounds based on branched or unsaturated carboxylic acids can positively influence the crosslinking behavior of rubber compounds by improving their reversibility stability. Zinc ethylhexanoate (2:1 and 4:6 complexes) and zinc neodecanoate (2:1 complex) are among the compounds used for this purpose (industrial standard includes STRUKTOL ZEH, STRUKTOL Aktivator 50, WO2023 / 037239 A1).

[0007] However, the well-known zinc ethylhexanoate is liquid, which means it cannot be used in all production facilities without additional technical dosing units. Therefore, zinc ethylhexanoate is often used as a so-called "dry liquid." Further processing of the zinc compound into a dry liquid, as is known to those skilled in the art, is achieved by applying it to porous materials such as silicon dioxide (silica), chalk, layered silicates, or metal-organic frameworks (MOFs) according to standard procedures. However, the use of carrier materials reduces the final zinc concentration in the material used.

[0008] The object of the present invention is the development of a rubber additive that positively influences the final physical properties and processability of the rubber composition and, in particular, increases the reversibility stability of rubber compositions without increasing toxicity. The Mooney test provides an indication of how well the material can be processed.

[0009] At the same time, the rubber additive used should have a solid form at room temperature and normal pressure to ensure easy dosing and good processability. This eliminates the need for carrier materials, which is advantageous due to reduced dust generation and thus improved occupational safety.

[0010] Furthermore, the flexometer properties, such as the heat build-up (HBU) of rubber compounds, should be improved by the rubber additive. Flexometer testing is particularly important for rubber compounds used in tire manufacturing. Energy dissipation becomes a crucial factor when the tire is subjected to stress during driving or rolling on the road; the rubber must not degrade due to excessive heat, as this would compromise driving safety.

[0011] Summary of the invention

[0012] The problem is solved according to the invention by a rubber composition containing a zinc compound consisting of at least one branched, aliphatic C5 to C 30- is produced from carboxylic acid and at least one zinc source, wherein the molar ratio of carboxylic acid to zinc source in the prepared zinc compound is 0.7 : 1 to 1 : 0.7. Surprisingly, it was found that the rubber composition according to the invention exhibits improved reversibility stability as well as improved dynamic mechanical properties.

[0013] In addition to reversion, the state-of-cure and heat build-up (HB1) could be improved using the zinc compound according to the invention. The term "state-of-cure" refers to the number of network nodes in a piece of rubber (elastomer) that form during the crosslinking reaction, or vulcanization. Reversion is the process of these network nodes breaking down, which begins after the maximum state-of-cure is reached and reduces it again. The state-of-cure is linked to all the final physical properties of the rubber composition, such as tensile strength and tear resistance, which are just as relevant for tires as for hoses, conveyor belts, and shoe soles. Using the zinc compound according to the invention increases both the maximum state-of-cure and reduces the rate and extent of reversion.

[0014] Flexometer properties, such as heat build-up (HB1), were also positively influenced. HB1 is a test that assesses how much energy is dissipated within an elastomer test specimen under external, dynamic, mechanical stress. The more energy is dissipated, depending on the value of the loss modulus G, the faster the test specimen heats up and the faster degradation and the so-called "blow-out" or destruction of the test specimen occur.

[0015] By using a zinc compound with a carboxylic acid to zinc source molar ratio of 0.7:1 to 1:0.7, the physical mixing properties of rubber compositions described above could be improved compared to otherwise identical rubber compositions containing a known zinc compound. The zinc compounds known from the prior art exhibit different carboxylic acid to zinc molar ratios (e.g., 1:2 complex and 4:6 complex). (Industrial standards include STRUKTOL ZEH, STRUKTOL Activator 50, WO2023 / 037239 A1).

[0016] Another aspect of the present invention relates to a rubber article in which at least one component is at least partially made from the rubber composition according to the invention.

[0017] Another aspect of the present invention relates to the use of the zinc compound according to the invention as a processing aid in diene rubber(s), wherein the diene rubber(s) is / are selected from butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber and thermoplastic elastomer, preferably natural rubber.

[0018] Another aspect of the present invention relates to the use of the zinc compound according to the invention for increasing the reversibility stability of rubber compositions. Another aspect of the present invention relates to a method for producing a zinc compound, in which the process: i) at least one branched, aliphatic C5 to C 30-carboxylic acid and at least one zinc source selected from zinc hydroxide, zinc oxide, zinc chloride, zinc nitrate, or mixtures thereof, preferably zinc oxide, are mixed, ü) the mixture prepared in i) is heated at a pressure of 1 to 3 atm to temperatures of 25 to 250°C, preferably 80 to 180°C and particularly 100 to 150°C, to obtain a zinc compound with a molar ratio of carboxylic acid to zinc source of 0.7 to 1 to 1 to 0.7 mol, and iü) optionally the zinc compound obtained in ii) is formed into the form of one or more lozenges.

[0019] Preferred embodiments are the subject of the dependent claims. Embodiments of the inventions include the components listed below and may, in particular, consist of these.

[0020] Images

[0021] Figure 1: TGA measurements (measured according to DIN 51006) of various zinc compounds (zinc compound A, zinc compound B, comparison zinc compound 1:2 and comparison zinc compound 4:6).

[0022] Figure 2: DSC measurements (measured according to DIN 51007) of different zinc compounds (zinc compound A, zinc compound B,

[0023] Comparison zinc compound 1:2 and comparison zinc compound 4:6).

[0024] Figure 3: Comparison of the IR spectra of zinc oxide (ZnO), isononanic acid and

[0025] Zinc compound B. The IR spectra are vector normalized.

[0026] Figure 4: Comparison of the IR spectra of zinc oxide (ZnO), isononanic acid and

[0027] Zinc compound A. The IR spectra are vector normalized.

[0028] Figure 5: Comparison of the IR spectra of reference zinc compound 1:2 (stoichiometry: 1 mol zinc oxide to 2 mol isononanic acid) and zinc compound B. The IR spectra are vector normalized. Figure 6: Comparison of the IR spectra of reference zinc compound 1:2 (stoichiometry: 1 mol zinc oxide to 2 mol isononanic acid) and zinc compound A. The IR spectra are vector normalized.

[0029] Figure 7: Comparison of the IR spectra of reference zinc compound 4:6 (stoichiometry: 4 mol zinc oxide to 6 mol isononanic acid) and zinc compound B. The IR spectra are vector normalized.

[0030] Figure 8: Comparison of the IR spectra of reference zinc compound 4:6 (stoichiometry: 4 mol zinc oxide to 6 mol isononanic acid) and zinc compound A. The IR spectra are vector normalized.

[0031] Figure 9: Graphical representation of the crosslinking behavior of the rubber compositions from example 2a) (dashed line 1.1 , solid line 1.2 , dotted line reference without additive), measured using Vulkameter MDR 2000.

[0032] Figure 10: Graphical representation of the crosslinking behavior of the rubber compositions from example 2b) (solid 2.3, dotted 2.2, dashed 2.1 ) measured using Vulkameter MDR 2000.

[0033] Detailed description of the invention

[0034] The inventors have surprisingly discovered that zinc compounds made from at least one branched, aliphatic C5 to C 30 -Carboxylic acid and at least one zinc source, which have a molar ratio of carboxylic acid to zinc of 0.7 to 1 to 1 to 0.7, exhibit positive properties as a rubber additive in rubber compositions.

[0035] It was experimentally demonstrated that the amount of zinc source used is completely converted at a molar ratio of carboxylic acid to zinc source of 0.7:1 to 1:0.7, and in particular, an approximately 1:1 complex is formed. Thus, the molar ratio of carboxylic acid to zinc source used corresponds to the amount of carboxylic acid and zinc (present here as Zn). 2+ ) in the zinc compound.

[0036] The unit phr (parts per hundred parts of rubber by weight) used in this document is the standard unit of measurement for compound formulations in the rubber industry. The dosage of the individual substances by weight is based on 100 parts by weight of the total mass of all high-molecular-weight and therefore solid rubbers present in the mixture.

[0037] Zinc compound

[0038] The rubber composition according to the invention comprises a zinc compound of at least one branched, aliphatic C5 to C 30 -Carboxylic acid, wherein the molar ratio of the carboxylic acid used to zinc in the prepared zinc compound is 0.7 to 1 to 1 to 0.7. The zinc compound can also be referred to as a zinc salt or zinc complex. The zinc compound according to the invention is prepared from at least one zinc source and at least one branched, aliphatic C5 to C 30 -Carboxylic acid in a molar ratio of carboxylic acid to zinc of 0.7 to 1 to 1 to 0.7.

[0039] In a preferred embodiment, the zinc compound used in the rubber composition according to the invention is produced by heating a mixture of at least one zinc source and at least one carboxylic acid, preferably under pressure. In a preferred embodiment, the mixture of zinc source and carboxylic acid is heated at a pressure of 1 to 3 atm to temperatures of 25 to 250°C, preferably 80 to 180°C and particularly 100 to 150°C.

[0040] The zinc source can be selected from the classes of hydroxides, oxides, chlorides or nitrates, or mixtures thereof.

[0041] In one embodiment, the zinc compound is produced from at least one branched, aliphatic C5 to C30 carboxylic acid and a zinc source selected from zinc hydroxide, zinc oxide, zinc chloride, zinc nitrate, or mixtures thereof, preferably zinc oxide.

[0042] The zinc compound comprises a carboxylic acid component, which is based on at least one saturated or unsaturated, branched C5 to C 30 -carboxylic acid. This means that the one or more carboxylic acids have 5 to 30 carbon atoms. It should be noted that carboxylic acids are usually understood to be aliphatic saturated carboxylic acids with a nonlinear carbon chain. According to the invention, "carboxylic acids" also includes acids that exhibit unsaturations. Furthermore, heteroatoms may be present, as long as this does not significantly impair the aliphatic character of the acids.

[0043] In one embodiment of the invention, the zinc compound was produced from a mixture of various carboxylic acids. The carboxylic acid component can contain at least two, as well as at least three, four, or five different C5 to C6 compounds. 30-carboxylic acid. In another embodiment, the carboxylic acid component consists of a mixture of isomeric branched, aliphatic carboxylic acids with the same number of carbon atoms. In another embodiment, the carboxylic acid component consists of only one specific branched, aliphatic C5 to C 30 -Carboxylic acid.

[0044] Typical examples of carboxylic acids that can be used as a carboxylic acid component in the present invention are iso- and neoacids, as well as naphthenic acids and naturally occurring nonlinear carboxylic acids.

[0045] In one embodiment, the at least one carboxylic acid is a C6 to C6 group. 20 -Carboxy acid, preferably a C7 to C 12 -Carboxy acid, such as C8 to C 10 -Carboxylic acid.

[0046] In one embodiment, the at least one carboxylic acid is a saturated C6 to C 20- Carboxylic acid, preferably a saturated C7 to C 12 -Carboxylic acid, such as saturated C8 to C 10 -Carboxylic acid and in particular isononanic acid. Here, isononanic acid refers to a mixture of isomeric, branched-chain carboxylic acids with nine carbon atoms, consisting of more than 85% 3,5,5-trimethylhexanoic acid.

[0047] In one embodiment, the carboxylic acid used consists of isononanic acid.

[0048] In one embodiment, the at least one carboxylic acid is a branched, aliphatic C5 to C 30 -Monocarboxylic acid.

[0049] In another embodiment, the at least one carboxylic acid is a branched, aliphatic C5 to C30 dicarboxylic or tricarboxylic acid. Dimers or trimers of carboxylic acids can also be used.

[0050] In one embodiment of the invention, the zinc compound was produced from a zinc source and isononanic acid.

[0051] In one embodiment, the zinc compound contained in the rubber composition according to the invention consists only of zinc, carbon, hydrogen and oxygen.

[0052] In one embodiment of the invention, the molar ratio of the carboxylic acid used to the zinc source in the prepared zinc compound is 0.70 to 1 to 1 to 0.70.

[0053] In one embodiment of the invention, the molar ratio of carboxylic acid to zinc in the zinc compound is 0.8 to 1 to 1 to 0.8, such as 0.95 to 1 to 1 to 0.95, preferably 1 to 1.

[0054] In one embodiment of the invention, the zinc compound has a zinc cation content of 20 to 33% Zn. 2+ , preferably 20 to 30 wt.% and particularly 23 to 28 wt.%. The zinc content can be determined according to DIN 55908, more precisely DIN 55908 - Part 2.

[0055] In one embodiment of the invention, the zinc compound has a dropping point of 110 to 120°C, such as 110 to 115°C. The dropping point can be measured according to DIN ISO 2176 / 97.

[0056] In one embodiment of the invention, the zinc compound has a softening point (cup and ball) of 90 to 115°C, such as 100 to 110°C. The softening point can be measured, for example, according to DIN 51920.

[0057] In one embodiment of the invention, the zinc compound exhibits a thermogram, measured by differential scanning calorimetry (DSC) according to DIN 51007, which shows an endothermic peak in the temperature range of 60 to 120°C, as well as in the range of 60 to 110°C. The peak is preferably located in the temperature range of 101 to 105°C. Furthermore, the thermogram of the zinc compound preferably does not show any further peak in the temperature range of 30 to 60°C.

[0058] In one embodiment of the invention, the zinc compound has a DSC thermogram which has an endothermic peak in the temperature range of 60 to 120°C, such as 60 to 110°C, and a peak in the temperature range of 101 to 105°C, and no further peak in the temperature range of 30 to 60°C.

[0059] In one embodiment of the invention, the zinc compound has at least two, or all of the following properties:

[0060] • Dropping point of 110 to 120°C, in particular 110 to 115°C, as measured according to DIN ISO 2176 / 97;

[0061] • Softening points of 90 to 115°C, in particular 100 to 110°C, as measured according to DIN 51920;

[0062] • Thermogram, measured by differential scanning calorimetry (DSC) according to DIN 51007, which shows an endothermic peak in the temperature range of 60 to 120°C, such as 60 to 110°C, and in particular a peak in the temperature range of 101 to 105°C, and no further peak in the temperature range of 30 to 60°C. In one embodiment of the invention, the zinc compound is present in solid form at room temperature and normal pressure and is incorporated into the rubber composition in solid form. The zinc compound can be incorporated into the rubber composition in the form of one or more pastilles, the pastilles preferably not comprising a carrier material. In one embodiment, the zinc compound is incorporated into the rubber composition in the form of one or more pastilles comprising at least 95 wt.% zinc compound or at least 98 wt.% zinc compound.In another embodiment, the one or more lozenges consist essentially of the zinc compound, which has a molar ratio of carboxylic acid to zinc of 0.7 to 1 to 1 to 0.7. Several zinc compounds according to the invention may also be present in one lozenge. In all embodiments, the lozenge may be covered externally with a layer of release agent.

[0063] In a further embodiment of the invention, the zinc compound is incorporated into the rubber composition in the form of a powder. In this case, the powder can consist of the zinc compound according to the invention.

[0064] In a further embodiment, the zinc compound is incorporated into the rubber composition in the form of a mixture, wherein the mixture preferably contains one or more solid carrier materials and optionally other components in addition to the zinc compound. Several zinc compounds according to the invention can also be present in one mixture.

[0065] Preferably, inorganic fillers (such as silicas) or waxy materials (such as polyethylene waxes) can be used as the carrier material. Examples of commercially available silicas that can be used in the mixture of the present invention are Sipernat 22 and Sipernat 50 from Evonik. In a preferred embodiment, silica is used as the carrier material. Other components that can be used in the mixture include, for example, amides, amino alcohols, and soaps.

[0066] In one embodiment, the rubber composition according to the invention includes a mixture as a zinc compound, which contains a) one or more solid carrier materials, preferably silica, and b) one or more zinc compounds according to the invention, and c) optionally further components such as amides, amino alcohols and / or soaps. The weight ratio of carrier material to zinc compound in the mixture is, for example, 10 / 90 to 90 / 10, more preferably 20 / 80 to 80 / 20, and particularly preferably about 30 / 70 or 33 / 67.

[0067] Method for producing the zinc compound

[0068] Furthermore, the present invention relates to a process for producing the zinc compound according to the invention in which process: i) at least one branched, aliphatic C5- to C 30-carboxylic acid and at least one zinc source selected from zinc hydroxide, zinc oxide, zinc chloride, zinc nitrate, or mixtures thereof, preferably zinc oxide, are mixed, ü) the mixture prepared in i) is heated at a pressure of 1 to 3 atm to temperatures of 25 to 250°C, preferably 80 to 180°C and particularly 100 to 150°C, to obtain a zinc compound with a molar ratio of carboxylic acid to zinc of 0.7 to 1 to 1 to 0.7, and iü) optionally the zinc compound obtained in ii) is formed into the form of one or more lozenges.

[0069] The reaction can be carried out as a precipitation reaction or in the molten state without the addition of solvent. Furthermore, catalysts such as hypophosphoric acid, methanesulfonic acid, butanesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, alkylbenzenesulfonic acid, sulfosuccinic acid, water, amines and / or mixtures thereof can be added before the start of the reaction in step ii).

[0070] It was experimentally demonstrated that the amount of zinc source used is completely converted at a molar ratio of carboxylic acid to zinc source of 0.7:1 to 1:0.7, and in particular, an approximately 1:1 complex is formed. Thus, the molar ratio of carboxylic acid to zinc source used in step i) corresponds to the amount of carboxylic acid and zinc of the zinc compound obtained in step ii).

[0071] In step iii), the product can then be placed directly onto the cooling belt at 15 to 120 °C to form the zinc compound into pastilles. The pastilles can optionally be dusted with a release agent. Preferably, however, the pastilles do not contain any carrier material. Furthermore, the present invention relates to a rubber composition comprising: a) a larger quantity of rubber, and b) a smaller quantity of a zinc compound, produced by a process in which i) at least one branched, aliphatic C5 to C 30-carboxylic acid and at least one zinc source selected from zinc hydroxide, zinc oxide, zinc chloride, zinc nitrate, or mixtures thereof, preferably zinc oxide, are mixed in a molar ratio of 0.7 to 1 to 1 to 0.7, preferably 0.70 to 1 to 1 to 0.70, ii) the mixture produced in i) is heated at a pressure of 1 to 3 atm to temperatures of 25 to 250°C, preferably 80 to 180°C and particularly 100 to 150°C, and ii) optionally the zinc compound obtained in ii) is formed into the form of one or more lozenges.

[0072] rubber

[0073] The rubber composition according to the invention comprises a significant amount of rubber (i.e., more than 50% by weight, based on the total weight of the composition). One type of rubber or several different types of rubber can be used in the blend.

[0074] Preferred rubbers are diene rubbers. Diene rubbers are defined as rubbers formed by the polymerization or copolymerization of dienes and / or cycloalkenes, thus exhibiting C=C double bonds either in the main chain or in the side chains. Preferred diene rubbers include butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber, and thermoplastic elastomers.

[0075] In one embodiment, at least 80 wt.%, such as 90 wt.% or 95 wt.% of the rubbers used in the rubber composition are diene rubbers.

[0076] In one embodiment, the rubber used in the rubber composition consists of one or more diene rubbers, i.e., all rubbers present in the rubber composition are diene rubbers.

[0077] In one embodiment, the rubber composition comprises at least one natural rubber. In another embodiment, at least 80 wt.%, 90 wt.%, or 95 wt.% of the rubbers used in the rubber composition are natural rubber. In yet another embodiment, all rubbers present in the rubber composition are natural rubber; that is, the rubber composition comprises exclusively one or more natural rubbers as rubber components.

[0078] Polyisoprene 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 > 90 wt% is preferred. Such a polyisoprene can be produced by stereospecific polymerization in solution with Ziegler-Natta catalysts or using finely divided

[0079] Lithium alkylenes can be obtained. Furthermore, natural rubber (NR) is such a cis-1,4-polyisoprene; the cis-1,4-content in natural rubber is greater than 99 wt.%. A mixture of one or more natural polyisoprenes with one or more synthetic polyisoprenes is also conceivable.

[0080] Styrene-butadiene rubber (styrene-butadiene copolymer) can be either solution-polymerized styrene-butadiene rubber (SSBR) or emulsion-polymerized styrene-butadiene rubber (ESBR), and a mixture of at least one SSBR and at least one ESBR can also be used. The terms "styrene-butadiene rubber" and "styrene-butadiene copolymer" are used synonymously within the scope of the present invention. Styrene-butadiene copolymers with a weight-average molar mass (Mw) in the range of 200,000 to 600,000 g / mol and / or a number-average molar mass (Mn) in the range of 100,000 to 250,000 g / mol are preferred.

[0081] The butadiene rubber (BR, polybutadiene) can be any type known to those skilled in the art with a molecular weight (Mw) of 250,000 to 5,000,000 g / mol. This includes, among others, the so-called high-cis and low-cis types, whereby polybutadiene with a cis content greater than or equal to 90 wt.% is referred to as a high-cis type and polybutadiene with a cis content less than 90 wt.% as a low-cis type. An example of a low-cis polybutadiene is Li-BR (lithium-catalyzed butadiene rubber) with a cis content of 20 to 50 wt.%.

[0082] Other rubber components

[0083] In addition to the essential components of the invention already explained in detail, the rubber composition may contain further rubber additives and components commonly used in the rubber industry. Such rubber components are explained below.

[0084] In a preferred embodiment, the rubber composition of the present invention comprises one or more of the following rubber components selected from the group consisting of fillers, or activators for sulfur, peroxide or amine crosslinking, anti-aging agents, waxes, resins, masticating aids, plasticizers, accelerators, retarders and / or processing aids.

[0085] Preferably, the rubber composition contains at least one filler. The rubber composition can contain 5 to 300 phr, preferably 30 to 300 phr, and in particular 50 to 200 phr of at least one filler, where the total amount of all fillers contained is meant.

[0086] This can include any filler materials known to those skilled in the art, such as carbon black, carbon nanotubes, silica, aluminosilicates, layered silicates like kaolin, calcium carbonate (chalk), starch, calcium carbonate, barium sulfate, magnesium oxides, aluminum oxides, titanium dioxide, or rubber gels. Furthermore, carbon nanotubes (CNTs), including discrete CNTs, so-called "hollow carbon fibers" (HCF), and modified CNTs containing one or more functional groups, such as hydroxy, carboxy, and carbonyl groups, are conceivable.

[0087] The rubber compound may contain plasticizers in typical quantities. Any plasticizer known to those skilled in the art, such as aromatic, naphthenic, or paraffinic mineral oil plasticizers, e.g., MES (mild extraction solvate), RAE (residual aromatic extract), or TDAE (treated distillate aromatic extract), or rubber-to-liquid (RTL) or biomass-to-liquid (BTL) oils, preferably with a polycyclic aromatic content of less than 3% by weight according to method IP 346, or rapeseed oil, Faktisse, or plasticizer resins, or liquid polymers, such as liquid polybutadiene – also in modified form – may be used. The plasticizer(s) are preferably added in at least one basic mixing stage during the production of the rubber compound according to the invention.

[0088] The rubber compound can also contain resins. These resins can increase the hardness or influence the mechanical properties of the vulcanized rubber. Adhesion is also improved, referring to both rubber-to-rubber and rubber-to-metal adhesion. Furthermore, resins can modify the hysteresis properties (tan delta) of the final product, thus improving the grip of, for example, a tire on the road. In recent years, for instance, the development of tread compounds for ultra-high-performance (UHP) and summer tires has focused on improving properties such as tire grip, wear resistance, and handling. For this purpose, a high resin content, e.g., based on alpha-methylstyrene and / or coumarone resins, has been added to the rubber compositions used in the manufacture of UHP and summer tires.

[0089] Generally, a distinction is made between plasticizer resins, which increase the flexibility of the rubber compound and the vulcanized rubber, and reinforcing resins, which increase the stiffness and strength of the vulcanized rubber without impairing its flexibility. There are also tackifier resins, which are used to increase the tackiness of unvulcanized rubber compounds. This is important, for example, where different rubber compounds are combined before vulcanization, such as in the tire industry. All resins known to those skilled in the art can be used, such as phenolic or alkylphenolic resins, terpene resins, rosin resins, pentaerythritol ester resins, petroleum resins, epoxidized resins, or even simply hydrocarbon resins.

[0090] The rubber composition preferably also contains substances required for crosslinking; the most commonly used crosslinking systems are sulfur crosslinking and peroxide crosslinking. Sulfur crosslinking requires sulfur itself, as well as accelerators (bases, dithiocarbamates, thiurams, thiazoles, sulfenamides, or guanidines) and / or retarders (acids, nitroso and chlorine compounds, as well as sulfoanilides and phthalimides). Peroxide crosslinking uses organic peroxides that act as radical initiators (such as dicumyl peroxide, dibenzoyl peroxide, or others); these also require additional co-agents that support crosslinking (cyanurates, methylacrylates, or certain imides).

[0091] Zinc oxide and carboxylic acids (e.g., stearic acid) can be used as activators. The zinc oxide provides zinc ions. which form complexes with the accelerators and sulfur, thus "activating" the sulfur for the reaction. The rubber composition according to the invention preferably comprises 0.5 to 10 phr, preferably 2 to 5 phr activators.

[0092] In one embodiment, the rubber composition comprises, in addition to the zinc compound described above with a carboxylic acid to zinc molar ratio of 0.7 : 1 to 1 : 0.7, further zinc compounds and / or carboxylic acid soaps, in particular zinc and / or potassium carboxylic acid soaps, such as zinc stearate and / or zinc-potassium stearate. The zinc carboxylic acid soaps can act as internal lubricants. In this case, the soaps, as smaller, long-chain molecules, lie between the polymer chains and allow these lighter chains to slide relative to one another. This improves the flow properties of the polymers during processing (mixing, rolling, extrusion, etc.).

[0093] Furthermore, the rubber composition may contain common additives in usual proportions by weight, which are preferably added in at least one basic mixing stage during its manufacture. The additives may be selected from the list consisting of antioxidants, activators, waxes, resins, masticating aids, and processing aids, and mixtures thereof.

[0094] For example, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'-ditolyl-p-phenylenediamine (DTPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), and 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) can be used as antioxidants. The rubber composition according to the invention preferably comprises 0.1 to 3 phr of antioxidants.

[0095] The rubber composition according to the invention preferably comprises 0.1 to 3 phr waxes.

[0096] For example, 2,2'-Dibenzamidodiphenyldisulfide (DBD) can be used as a masticating agent. The rubber composition according to the invention preferably comprises 0.1 to 3 phr of masticating agent.

[0097] In particular, the rubber composition contains: a) 0.1 to 3 phr aging protectants, b) 0.5 to 10 phr, preferably 2 to 5 phr activators, c) 0.1 to 3 phr waxes, d) 5 to 100 phr, preferably 15 to 50 phr of plasticizers and / or resins, e) 0.1 to 3 phr masticating aids, f) 0.5 to 10 phr, preferably 2 to 5 phr processing aids, and g) 5 to 300 phr fillers.

[0098] The proportion of the total amount of other additives is 3 to 150 phr, preferably 3 to 100 phr and particularly preferably 5 to 80 phr. Rubber composition

[0099] The rubber composition according to the invention comprises a larger quantity of rubber (i.e., more than 50 wt.%, based on the total weight of the composition) and a smaller quantity of zinc compound (i.e., less than 50 wt.%, based on the total weight of the composition), as well as optionally further rubber components. The rubber composition can be crosslinked in a known manner.

[0100] In one embodiment, the rubber composition comprises 0.5 to 10 phr, preferably 1 to 7 phr, in particular 2 to 5 phr zinc compound, based on the total weight of the rubber composition.

[0101] In one embodiment, the rubber composition comprises a) a larger quantity of rubber, b) 0.5 to 10 phr zinc compound, produced from at least one branched, aliphatic C5 to C 30-Carboxylic acid and at least one zinc source, wherein the molar ratio of carboxylic acid to zinc in the zinc compound is 0.7 : 1 to 1 : 0.7. c) 5 to 300 phr of one or more fillers.

[0102] In one embodiment, the rubber composition comprises 0.5 to 10 phr, preferably 1 to 7 phr, in particular 2 to 5 phr zinc compound, based on the total weight of the rubber composition.

[0103] In one embodiment, the rubber composition comprises: a) a substantial amount of rubber; b) 0.5 to 10 phr of a zinc compound prepared from at least one branched, aliphatic C5 to Cso carboxylic acid and at least one zinc source, wherein the molar ratio of carboxylic acid to zinc in the zinc compound is 0.70 : 1 to 1 : 0.70; c) 5 to 300 phr of one or more fillers.

[0104] In one embodiment, the rubber composition comprises: a) a significant amount of one or more diene rubbers, wherein the diene rubber(s) is / are preferably selected from butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber, and thermoplastic elastomer, in particular natural rubber; b) 0.5 to 10 phr of zinc compound, prepared from at least one branched, aliphatic C7 to C 12 -Carboxylic acid and at least one zinc source, wherein the molar ratio of carboxylic acid to zinc in the zinc compound is 0.8 : 1 to 1 : 0.8; c) 5 to 300 phr of one or more fillers.

[0105] In one embodiment, the rubber composition comprises: a) a significant amount of one or more diene rubbers, wherein the diene rubber(s) is / are preferably selected from butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber, and thermoplastic elastomer, in particular natural rubber; b) 0.5 to 10 phr of zinc compound, prepared from at least one branched, aliphatic, saturated C7 to C12 carboxylic acid and at least one zinc source, wherein the molar ratio of carboxylic acid to zinc in the zinc compound is 0.8 : 1 to 1 : 0.8; c) 5 to 300 phr of one or more fillers, wherein the rubber composition contains exclusively diene rubber(s), preferably natural rubber as rubber components.

[0106] In one embodiment, the rubber composition comprises: a) a significant amount of one or more diene rubbers, wherein the diene rubber(s) is / are preferably selected from butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber, and thermoplastic elastomer, in particular natural rubber; b) 0.5 to 10 phr of zinc compound, prepared from at least one branched, aliphatic C7 to C 12-Carboxylic acid and at least one zinc source, wherein the molar ratio of carboxylic acid to zinc in the zinc compound is 0.7 : 1 to 1 : 0.7; c) 5 to 300 phr of one or more fillers, and at least one, preferably at least 2, 3, 4, 5 or all of: d) 0.1 to 3 phr of aging inhibitors, e) 0.5 to 10 phr, preferably 2 to 5 phr of activators, f) 0.1 to 3 phr of waxes, g) 5 to 100 phr, preferably 15 to 50 phr of resins, h) 0.1 to 3 phr of masticating aids, and f) 0.5 to 10 phr, preferably 2 to 5 phr of processing aids.

[0107] In one embodiment, the rubber composition comprises: a) a significant amount of one or more diene rubbers, wherein the diene rubber(s) is / are preferably selected from butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber, and thermoplastic elastomer, in particular natural rubber; b) 0.5 to 10 phr of zinc compound, prepared from at least one branched, aliphatic C7 to C 12 -Carboxylic acid and at least one zinc source, wherein the molar ratio of carboxylic acid to zinc in the zinc compound is 0.7 : 1 to 1 : 0.7; c) 5 to 300 phr of one or more fillers, d) 0.1 to 3 phr of anti-aging agents, and e) 0.5 to 10 phr, preferably 2 to 5 phr of activators.

[0108] In one embodiment, the rubber composition comprises: a) a significant amount of one or more diene rubbers, wherein the diene rubber(s) is / are preferably selected from butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber, and thermoplastic elastomer, in particular natural rubber; b) 0.5 to 10 phr of zinc compound, prepared from at least one branched, aliphatic C7 to Ci2 carboxylic acid and at least one zinc source, wherein the molar ratio of carboxylic acid to zinc in the zinc compound is 0.7 : 1 to 1 : 0.7; c) 5 to 300 phr of one or more fillers, d) 0.1 to 3 phr of anti-aging agents, e) 0.5 to 10 phr, preferably 2 to 5 phr of activators, wherein the rubber composition contains exclusively diene rubber(s), preferably natural rubber as rubber components.

[0109] In one embodiment, the rubber composition comprises: a) a significant amount of one or more diene rubbers, wherein the diene rubber(s) is / are preferably selected from butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber, and thermoplastic elastomer, in particular natural rubber; b) 0.5 to 10 phr of zinc compound, prepared from at least one branched, aliphatic C7 to Ci2 carboxylic acid and at least one zinc source, wherein the molar ratio of carboxylic acid to zinc in the zinc compound is 0.70 : 1 to 1 : 0.70; c) 5 to 300 phr of one or more fillers, d) 0.1 to 3 phr of anti-aging agents, e) 0.5 to 10 phr, preferably 2 to 5 phr of activators, wherein the rubber composition contains exclusively diene rubber(s), preferably natural rubber as rubber components.

[0110] The zinc compound can be added to an existing rubber composition in a so-called "on top" application.

[0111] The rubber compound can be used for a wide variety of rubber products, such as bellows, conveyor belts, air springs, belts, straps, hoses, rubber bands, or shoe soles. The rubber compound can also be used in vehicle tires, including pneumatic and solid rubber tires, as well as tires for industrial and construction vehicles, trucks, cars, and motorcycles. The rubber compound is primarily used in commercial vehicle tires. Commercial vehicle tires are defined as tires for motor vehicles that, by their design and equipment, are intended for transporting people or goods, or for towing trailers, but are not passenger cars or motorcycles (e.g., buses, trucks, emergency vehicles, tractors, construction vehicles, etc.).

[0112] The rubber composition according to the invention is produced in a conventional manner, whereby, as a rule, a base mixture containing all components except the vulcanization system (sulfur and vulcanization-influencing substances) is first produced in one or more mixing stages, and the finished mixture is then produced by adding the vulcanization system. The general process for producing rubber compositions and their vulcanizates is described in “Rubber Technology Handbook”, W. Hofmann, Hanser Verlag 1994. It is known to those skilled in the art that, depending on the mixture, and in particular on the filler content, further mixing stages may be necessary after the first base mixing stage to achieve a better reduction in viscosity and improved homogenization. Subsequently, the composition can be further processed, e.g., by an extrusion process, and formed into the appropriate shape, e.g.,the shape of a tread strip blank.

[0113] use

[0114] The present invention further relates to the use of the zinc compound according to the invention as a processing aid in diene rubber(s), wherein the diene rubber(s) is / are selected from butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber and thermoplastic elastomer.

[0115] In a preferred embodiment, the zinc compound according to the invention is used in rubber compositions that comprise at least one natural rubber or contain exclusively natural rubber as the rubber component.

[0116] The present invention further relates to the use of the zinc compound according to the invention for increasing the reversibility stability of rubber compositions. The improvement in reversibility stability leads to a higher degree of crosslinking and thus to an improvement in the chemical and physical properties, such as tensile strength, as well as dynamic mechanical properties.

[0117] The present invention further relates to the use of the zinc compound according to the invention in a rubber composition to lower the Mooney viscosity, which enables the person skilled in the art to assess the general processability of the rubber mixture and / or extrusion properties of the rubber composition (flowability of the rubber in the extruder die and in the mold, injection swelling, extrusion rate, material pressure, surface quality, etc.).

[0118] In a preferred embodiment, the uses of the zinc compound according to the invention described above lead to an improvement of one or both of the following properties by at least 5%, preferably at least 10%, compared to an otherwise identical rubber composition containing a zinc compound of at least one branched, aliphatic C5 to C30 carboxylic acid, wherein the zinc compound has a molar ratio of carboxylic acid to zinc outside the range of 0.7 to 1 to 1 to 0.7: • Reversion stability, measured as the time required for a 3% reversion according to DIN 53529,

[0119] • Blow-out test and / or heat build-up, measured according to DIN 53533-3 at 2 MPa static load, chamber temperature of 50 °C and 6.35 mm deformation path.

[0120] In a preferred embodiment of the use according to the invention, at least one of the aforementioned properties is improved compared to a rubber composition that comprises a known rubber additive in an identical amount instead of the rubber additive according to the invention. Materials known in the prior art that are used as rubber additives can be used as known rubber additives. For verification purposes, two otherwise identical rubber compositions are produced and their properties are then compared.

[0121] In a preferred embodiment, at least one of the aforementioned properties is improved by at least 5%, preferably at least 10%, compared to a rubber composition which comprises a known rubber additive in the same quantity instead of the rubber additive according to the invention.

[0122] Examples of execution

[0123] The invention will now be explained in more detail using comparative and exemplary embodiments, without, however, being limited to these examples.

[0124] Example 1 - Preparation of the zinc compounds according to the invention a) Zinc compound A (1819)

[0125] The composition of the produced zinc compound A is listed in the following Table 1.

[0126] Table 1: Composition of zinc compound A 2141 g of isononanic acid (consisting of 3,5,5-trimhetylhexanoic acid and isomers) was placed in a steel autoclave at room temperature and stirred. Subsequently, 0.1 g of defoamer and 862 g of zinc oxide were added. The reaction mixture was inerted with nitrogen, hermetically sealed, and then heated to 130°C at a pressure of 1 to 3 bar. After reaching the reaction temperature, it was maintained for at least 1 hour. The reactor temperature was then reduced to 115°C, and the product was transferred to a cooling belt, where it solidified into a glassy pastille. The resulting pastilles were lightly dusted with an anti-caking agent.

[0127] The zinc content was determined to be 23% according to DIN 55908 (Part 2), and the softening point (C+B) according to DIN 51920 was 110°C. b) Zinc compound B (1816)

[0128] The composition of the produced zinc compound B is listed in the following Table 1.

[0129] Table 2: Composition of zinc compound B

[0130] 1980 g of isononanic acid (consisting of 3,5,5-trimhetylhexanoic acid and isomers (3,5,5-trimhetylhexanoic acid content > 88.5 wt%)) was placed in a steel autoclave at room temperature and stirred. Subsequently, 0.1 g of defoamer and 1022 g of zinc oxide were added. The reaction mixture was inertized with nitrogen, hermetically sealed, and then heated to 130 °C. After reaching the reaction temperature, it was held for 1 h. The reactor temperature was then reduced to 115 °C, and the product was transferred to a cooling belt, where it solidified as a glassy pastille. The resulting pastilles were lightly dusted with an anti-caking agent.

[0131] The zinc content was determined to be 28% and the softening point (C+B, ASTM D36-D36M) was 110°C. The properties of the two prepared zinc compounds are summarized in Table 3 below.

[0132] Table 3: Characterization of the produced zinc compounds c) Production of reference zinc compounds with different stoichiometry

[0133] For comparison purposes, two zinc compounds of isononanic acid with different stoichiometries were prepared and characterized. A stoichiometric ratio of 1 mol zinc to 2 mol isononanic acid (reference zinc compound 1:2) and 4 mol zinc to 6 mol isononanic acid (reference zinc compound 4:6) were used in the preparation of the reference zinc compound. Outside of these ratios, the procedure described above in a) and b) was used to prepare the reference zinc compound. In both cases, viscous liquids were obtained for which a determination of the dropping point and softening point was not possible.

[0134] The analytical comparisons in Figures 1 to 8 show differences to the known zinc compounds with a stoichiometry of 1 :2 or 4:6 (zinc to carboxylic acid) compared to zinc compounds A and B.

[0135] In the TGA measurements (Figure 1), only one peak was observed, whereas multiple peaks would be expected if different compounds were present (e.g., in the case of incomplete reaction or the formation of a mixture of zinc salts with different stoichiometries). In the IR (Figures 3 to 8), the characteristic zinc oxide peak in the fingerprint region is absent, and new peaks have formed. Similarly, in the DSC (Figure 2), different graphene profiles would be expected if different structures were present within a single sample. The combination of the various measurements suggests that all zinc oxide in zinc compounds A and B was reacted, forming an approximately 1:1 complex. The prepared comparison zinc compounds of isononanic acid with different stoichiometries did not exhibit the desired properties (no crystallizable material, lack of long-term stability, insufficient zinc content, etc.).

[0136] Example 2 - Demonstration of the mode of action of the zinc compound according to the invention in model rubber mixtures compared to known zinc compounds with other stoichiometries

[0137] The mixture was produced under normal conditions in one or more mixing stages. It was then further processed, e.g., by extrusion, and formed into the appropriate shape by compression molding.

[0138] The various components of each mixture are listed in the tables below.

[0139] Table 4: Formulation components of the rubber compositions for examples 2a) and b).

[0140] In all mixture examples included in the table, the quantities given (parts by weight) are based on 100 parts by weight of total rubber (phr).

[0141] Test specimens were produced from all mixtures, and material properties typical for the rubber industry were determined using these test specimens and the following test procedures:

[0142] • Mooney measurement (ML 1 +4, 100 °C) and Mooney Scorch MS 135 °C (TS 5), after each mixing stage and after aging, each according to DIN EN ISO 289-1 ,

[0143] • MDR measurement according to DIN 53529-3

[0144] • Tensile strength, elongation at break and tensile strength measured according to DIN 53 504, parameters for stiffness, also for tire abrasion,

[0145] • Stress values ​​at 100 and 300% elongation at room temperature (module 100%, module 300%), according to DIN 53 504,

[0146] • Compression set (compression set, DVR) at RT, 70 °C and 100 °C and for 22 h, 72 h and 168 h according to DIN ISO 815 Part 1 , Type B.

[0147] • Heat build-up according to DIN 53533-3 at 2 MPa static load, chamber temperature of 50 °C and 6.35 mm deformation path.

[0148] • Blow-out test according to DIN 53533-3 at 2 MPa static load, chamber temperature of 100 °C and 6.35 mm deformation path.

[0149] The vulcanization properties were measured using a Vulkameter MDR 2000. a) Reversion stability, state-of-cure and blow-out test in a rubber compound

[0150] In this example, the properties of a rubber formulation containing additive 1 according to the invention (composition 1.1) were compared with the properties of an otherwise identical rubber formulation containing a prior art comparator additive 2 (zinc 2-ethylhexanoate, ZEH) (comparator composition 1.2). In composition 1.1, the zinc compound A prepared in 1 a) was used. The zinc 2-ethylhexanoate used as the comparator additive is present as a 4:6 complex.

[0151] The comparison shows improved reversal stability of the rubber composition according to the invention. The heat build-up and blow-out properties are also significantly improved in the rubber composition according to the invention. Due to the final higher degree of cross-linking of the mixture (state-of-cure), all physical properties are as expected to be altered. Table 5: Overview of formulations and measurement data of the

[0152] Rubber compositions 1.1 and comparison composition 1.2

[0153] The measurement data in Table 5 show that a reduction in reversion was achieved with the additive according to the invention. Although the absolute crosslinking height is not significantly higher at 15.73 dNm compared to 15.51 dNm, the reversion is significantly reduced: 3% reversion is reached only after 7.54 min, and 10% only after 15.00 min, compared to 6.85 min and 12.22 min for the reference composition 1.2. Figure 9 illustrates this situation graphically. The dotted line represents the vulcanization profile of a reference composition without an additive. The dashed line represents the curve of the composition 1.1 according to the invention, and the solid line represents composition 1.2 treated with the known additive 2 (ZEH). It is evident that the reference composition vulcanizes considerably faster but then exhibits pronounced reversion after approximately 3 to 4 min. The curve of the composition according to the invention 1.In contrast, 1 runs much flatter and hardly drops in the area of ​​reversion; which suggests an improvement compared to the comparison composition 1.2.

[0154] The vulcanizate properties are also positively influenced by the zinc compound according to the invention. At a higher final state of cure, it can be assumed that the corresponding material is slightly stiffer and less tear-resistant. Accordingly, the composition 1.2 according to the invention exhibits slightly lower tensile strengths, tear strengths, and modulus. At the same time, however, the elastic modulus increases compared to the loss modulus, which indicates more pronounced elastic properties—as can be seen in the improvement in the compression set. Here, a lower number means that less of a statically imposed deformation remains on the test specimen.

[0155] The composition 1.2 according to the invention also exhibited advantageous properties in the flexometer test and the blow-out test. The time until a test specimen actually undergoes fatal degradation is almost 5 minutes longer with the rubber formulation containing the additive 1 according to the invention; this means that this composition can withstand, for example, a dynamic load (such as a damping load) for a significantly longer time. b) Reversal stability, state-of-cure and blow-out test in a rubber compound

[0156] In this example, the properties of a rubber composition containing the additive 1 according to the invention (composition 2.1) were compared with the properties of two otherwise identical rubber compositions, each containing a prior art additive 2 (ZEH) and additive 3 (zinc neodecanoate (stoichiometry 1:2), commercially available as activator 50) (comparison compositions 2.2 and 2.3). The additives contain different stoichiometric amounts of zinc ions. To ensure comparability of the mixtures in the present study, the amount of additives used was adjusted to keep the amounts of zinc ions in the composition constant. This comparison also shows improved reversal stability of the additive 1 according to the invention, as well as significantly improved heat build-up and blow-out properties in the flexometer test. Due to the ultimately higher crosslinking of composition 2.1 (state-of-cure) the physical properties of composition 2.1 are also changed.

[0157] Table 6: Overview of formulations and measurement data of the rubber compositions 2.1 and comparison compositions 2.2 and 2.3 The measurement data in Table 6 show a similar picture to the measurements presented in Example 2a). Additive 1 according to the invention showed a reversion of 3% only after approximately 17 minutes and a reversion of 10% after 1 hour, whereas the two comparison compositions 2.2 and 2.3 already showed a 3% reversion after 14.4 and 12 minutes, respectively, and a reversion of 10% occurred at 48 minutes and 31 minutes. Additive 3 is therefore only half as effective with regard to reversion as additive 1 according to the invention.

[0158] Figure 10 shows the vulcanization curves (measured with a Vulkameter MDR 2000) of all three mixtures. All three measured compositions (compositions 2.1 to 2.3) initially show a jump to the start of reversal, but the slope of the composition according to the invention with additive 1 (dashed line) is significantly less pronounced than that of the two comparison compositions 2.2 and 2.3.

[0159] In this case, a significantly greater difference in the height of the absolute maxima can also be observed. This value minus the minimum value at approximately 1 minute yields the relative maximum crosslinking, which is highest for composition 2.1 according to the invention. This shows that composition 2.1 according to the invention has the highest state of cure or is most strongly crosslinked.

[0160] The vulcanizate properties also differ slightly in this example: Comparable values ​​were found for composition 2.1 and comparison composition 2.3. However, comparison composition 2.2 shows a lower tensile strength. The compression set could be reduced in composition 2.1 according to the invention due to the comparatively higher proportion of the modulus of elasticity.

[0161] In this study, values ​​were recorded after one week of aging in addition to the values ​​obtained with the fresh vulcanizate. These simulate a more pronounced, prolonged thermal stress, during which reversal processes also occur. For the composition 2.1 according to the invention, a slightly higher tensile strength was measured after aging, while all tear strengths were comparatively lower. Additionally, the higher M100 and M300 values ​​of the composition 2.1 according to the invention are noteworthy; these are typical for a higher state of cure and thus correspond excellently with the vulcanization curves. Thermal degradation is lowest for the composition 2.1 according to the invention, which underscores the improved stability.The flexometer test was performed twice, each time with differently prepared specimens: once cross-linked to "tc100", which corresponds to vulcanization to the maximum cross-linking level measured in the MDR test, and once to "3x tc100", which corresponds to three times this time. This also exposes one sample to above-average thermal stress, resulting in an increased reversion process.

[0162] In both the crosslinking tc100 and 3xtc100, the composition 2.1 according to the invention is best able to withstand heat induced by energy dissipation and the associated degradation. The blow-out time of the composition 2.1 according to the invention withstands the load for approximately 3 minutes longer in both tests compared to the reference composition 2.2, and even 8.5 minutes and 9 minutes compared to the reference composition 2.3, which represents a significant improvement of almost 50% and 53%, respectively.

[0163] In summary, it can be stated that the use of additive 1 according to the invention resulted in improved crosslinking and better physical properties. Since the amount of zinc compound used is tailored to the stoichiometric amount of zinc ions, this means that when using the zinc compound according to the invention, the zinc ions are significantly more available to the vulcanization system (sulfur, accelerator, activator). This results in a further advantage of using the zinc compound according to the invention: a lower requirement for zinc compound with nevertheless improved effectiveness.

Claims

Claims 1. Rubber composition comprising: a) a major quantity of rubber, and b) a minor quantity of zinc compound prepared from at least one branched, aliphatic C5 to C30 carboxylic acid and at least one zinc source, wherein the molar ratio of carboxylic acid to zinc in the zinc compound is 0.7 : 1 to 1 : 0.

7.

2. Rubber composition according to claim 1, wherein the at least one carboxylic acid is a saturated C6 to C 20 -Carboxylic acid, preferably a saturated C7 to C 12 -Carboxylic acid, such as saturated C8 to C 10 -Carboxylic acid and in particular isononanic acid; and / or the zinc source is selected from zinc hydroxide, zinc oxide, zinc chloride, zinc nitrate, or mixtures thereof.

3. Rubber additive according to any of the preceding claims, wherein the zinc compound has a zinc cation content of 20 to 33 wt.% Zn 2+, preferably 20 to 30 wt.% and in particular 23 to 28 wt.%, as determined or calculated according to DIN 55908 (part 2).

4. Rubber composition according to one of the preceding claims, wherein the molar ratio of carboxylic acid to zinc in the zinc compound is 0.70 to 1 to 1 to 0.70, preferably 0.8 to 1 to 1 to 0.8, preferably 1 to 1.

5. Rubber composition according to any of the preceding claims, wherein the zinc compound has at least one, preferably at least two, or all of the following properties: • Dropping point of 110 to 120°C, in particular 110 to 115°C, as measured according to DIN ISO 2176 / 97; • Softening points of 90 to 115°C, in particular 100 to 110°C, as measured according to DIN 51920; • Thermogram, measured using Differential Scanning Calorimetry (DSC) according to DIN 51007, which shows an endothermic peak in the temperature range of 60 to 120°C, such as 60 to 110°C and in particular a peak in the temperature range of 101 to 105°C and no further peak in the temperature range of 30 to 60°C.

6. Rubber composition according to one of the preceding claims, wherein the zinc compound is incorporated into the rubber composition in solid form, preferably in the form of one or more pastilles, the pastille(s) preferably not comprising any carrier material.

7. Rubber composition according to one of the preceding claims, wherein the zinc compound is present in a concentration of 0.5 to 10 phr, preferably 1 to 7 phr, in particular 2 to 5 phr in the rubber composition, based on the total weight of the rubber composition.

8. Rubber composition according to any of the preceding claims, wherein the rubber comprises at least one diene rubber, preferably consisting of one or more diene rubbers.

9. Rubber composition according to claim 8, wherein the diene rubber(s) is / are selected from butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber and thermoplastic elastomer, preferably natural rubber.

10. Rubber composition according to any of the preceding claims, further comprising one or more of the following rubber components selected from the group consisting of fillers, activators for crosslinking with sulfur, catalysts or activators for peroxide or amine crosslinking, anti-aging agents, waxes, resins, masticating aids, plasticizers, accelerators, retarders and / or processing aids. 1 1 . Rubber article in which at least one component is at least partially made from a rubber composition according to any one of claims 1 to 10, wherein the rubber article is preferably a tire.

12. Use of a zinc compound as defined in any one of claims 1 to 7 as a processing aid in diene rubber(s), wherein the diene rubber(s) is / are selected from butadiene rubber, polyisoprene, styrene-butadiene rubber, natural rubber, acrylonitrile butadiene rubber, ethylene propylene diene rubber, fluororubber and thermoplastic elastomer, preferably natural rubber.

13. Use according to claim 12, wherein one or both of the following properties are improved by at least 5%, preferably at least 10%, compared to an otherwise identical rubber composition comprising a zinc compound produced from at least one branched, aliphatic C5 to Cso carboxylic acid and at least one zinc source, which zinc compound has a molar ratio of carboxylic acid to zinc outside the range of 0.7 to 1 to 1 to 0.7: • Reversal stability, measured as the time required for a 3% reversion according to DIN 53529, • Blow-out test and / or heat build-up, measured according to DIN 53533-3 at 2 MPa static load, chamber temperature of 50 °C and 6.35 mm deformation path.

14. Use of the zinc compound as defined in any one of claims 1 to 7 to increase the reversibility stability of rubber compositions.

15. A process for producing a zinc compound as defined in any one of claims 1 to 7, wherein the process: i) mixes at least one branched, aliphatic C5 to C30 carboxylic acid and at least one zinc source selected from zinc hydroxide, zinc oxide, zinc chloride, zinc nitrate, or mixtures thereof, preferably zinc oxide; ü) heats the mixture produced in i) at a pressure of 1 to 3 atm to temperatures of 25 to 250°C, preferably 80 to 180°C and particularly 100 to 150°C, to obtain a zinc salt with a molar ratio of carboxylic acid to zinc of 0.7 to 1 to 1 to 0.7; and iü) optionally forms the zinc compound obtained in ii) into the form of one or more lozenges.

16. Rubber composition comprising: a) a major quantity of rubber, and b) a minor quantity of zinc compound, produced by a process in which i) at least one branched, aliphatic C5 to C 30-carboxylic acid and at least one zinc source selected from zinc hydroxide, zinc oxide, zinc chloride, zinc nitrate, or mixtures thereof, preferably zinc oxide, in a molar ratio of 0.7 to 1 to 1 to 0.7, ii) the mixture produced in i) is heated at a pressure of 1 to 3 atm to temperatures of 25 to 250°C, preferably 80 to 180°C and in particular is heated to 100 to 150°C, and ii) if necessary the zinc compound obtained in ii) is formed into the form of one or more lozenges.

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