Mixing process for a rubber mixture

Abstract

The invention relates to a method for mixing a rubber mixture, in particular for the production of tires, comprising at least the following three steps: - mixing a sulfur-crosslinkable diene rubber, a filler having free OH groups, and a silane coupling agent in a first mixing step; - mixing the first rubber mixture and processing aids in a second mixing step; and - mixing the second rubber mixture and vulcanization chemicals in a third mixing step.

Description

[0001]202203357 - 1 - Description Mixing process for a rubber mixture The invention relates to a mixing process for a rubber mixture for tires or technical rubber articles with comparable conflicting objectives. Since the driving properties of a tire, in particular a pneumatic vehicle tire, depend to a large extent on the nature of the rubber composition of the tire, particularly high demands are placed on this composition. The properties of the rubber composition can be influenced in particular by the selected components and by the mixing process for production. By partially or completely replacing the filler carbon black with silica in rubber mixtures, the driving properties have been brought to an overall higher level in recent years. However, the known conflicting objectives of the opposing tire properties still exist even with silica-containing rubber mixtures.For example, improvements in wet grip and dry braking generally still result in a deterioration in rolling resistance, winter properties, and abrasion behavior. Wet grip and handling behavior also generally behave in contradictory ways, since a softer compound required for good wet grip is usually accompanied by a less stiff compound, which therefore has poorer handling behavior. A variety of approaches have been pursued to resolve the aforementioned conflicting objectives. For example, a wide variety of polymers, including modified ones, have been used in rubber compounds, and attempts have been made to influence the vulcanizate properties by modifying the compound production process. 202203357 - 2 - Some substances used in modern compounds, such as functionalized polymers, increase the viscosity of the compound and thus impair its processing behavior.The mixture crumbles and disintegrates into small pieces, making such mixtures unsuitable for industrial production without further modification. Other substances, such as processing aids, are used to reduce the viscosity of the mixture, but can negatively impact the physical properties of the final product. Prior art regarding rubber mixing processes is disclosed, for example, in publication DE 102017223554 A1. The present invention is based on the object of providing a suitable mixing process for a rubber mixture that preferably leads to improved properties of the resulting mixture.This object is achieved by carrying out at least three mixing steps to produce a rubber mixture: - mixing at least one sulfur-crosslinkable diene rubber, at least one filler with free OH groups and at least one silane coupling agent in a first mixing step to form a first rubber mixture, wherein the OH group-containing filler and the silane coupling agent react chemically with one another, - mixing the first rubber mixture and processing aids such as activators or processing aids which contain at least one fatty acid and a divalent metal oxide such as ZnO, in a second mixing step to form a second rubber mixture, - mixing the second rubber mixture and vulcanization chemicals in a third mixing step to form a third rubber mixture.202203357 - 3 - This prevents the substances added in the second mixing step from influencing the reactions of the substances mixed in the first mixing step. By dividing the mixing process into three mixing steps as described, the process behavior, such as process reliability, of the rubber mixture can be surprisingly improved. Furthermore, the properties of the vulcanizate obtained from a rubber mixture mixed in this way can be surprisingly improved. In particular, greater reinforcement (polymer-filler interaction), lower abrasion, and lower rolling resistance of the resulting vulcanizate can be achieved. For this purpose, the three mixing steps mentioned are preferably carried out in the order mentioned and particularly preferably staggered in time. According to one embodiment, the three mixing steps take place spatially decoupled orare carried out spatially decoupled in different mixing devices, which allows for flexible process control. The three mixing steps can be processed independently of one another with properties favorable for this purpose. The temperature ranges specified in DE 102017223554 A1 advantageously apply to the first mixing step. In particular, a fluid medium of the mix can advantageously be heated to a preparation temperature in the range of 30 °C to 160 °C before mixing with the rubber components. During mixing with the rubber components in the first step, the mixture can be tempered in the range of 40 °C to 160 °C. The first rubber mixture can then be cooled in a cooling phase to a cooling temperature in the range of 4 °C to 60 °C.In the second mixing step, the mix is ​​advantageously processed until it has a temperature in the range of 130°C to 150°C and is then ejected from the mixer. In the third mixing step, the temperature should advantageously not exceed 130°C. 202203357 - 4 - The rubber mixture can be cooled, in particular between the mixing steps. In particular, the third mixing step preferably takes place in a different mixing device than the first and second mixing steps. The third mixing step comprises the final mixing stage, in which the vulcanization chemicals are added. In this way, the start of the vulcanization process can be precisely adjusted. In particular, the second mixing step also takes place in a different mixing device than the first mixing step, so that the start of the second mixing step can be precisely adjusted and is spatially and temporally decoupled from the first mixing step.This better prevents the substances added in the second mixing step from influencing the reactions of the substances mixed in the first mixing step. According to one embodiment, the first and second mixing steps take place in different mixing chambers of a tandem mixing device. The tandem mixing device comprises two mixing chambers, called the upper machine and the lower machine. The upper machine and the lower machine are essentially independent mixing devices that are directly connected to one another, so that the rubber mixture can be conveyed from the upper machine directly to the lower machine without any additional aids. For example, the first mixing step preferably takes place in the upper machine and the second mixing step in the lower machine.The mixing steps remain spatially separated from one another, but any processing problems during transport of the rubber mixture from the first to the second mixing device are reduced or eliminated. For possible configurations of the tandem mixing device, reference is also made to publication DE 102015210342 A. 202203357 - 5 - Preferably, the first rubber mixture is cooled before being fed into the second mixing device so that the reactions between the substances of the first rubber mixture are completely terminated. Preferably, in the first mixing step, the OH-containing filler and the silane coupling agent react completely with one another so that the reactions during the second mixing step do not influence the reaction between the OH-containing filler and the silane coupling agent. The filler is preferably silicic acid or silica, as explained in more detail later.Preferably, at least one of zinc oxide and stearic acid is added in the second mixing step; their properties will be explained in more detail later. The rubber mixture contains at least one diene rubber. Accordingly, several rubbers can also be used in a blend. Diene rubbers are rubbers that are produced by the polymerization or copolymerization of dienes and / or cycloalkenes and thus contain C=C double bonds either in the main chain or in the side groups. The diene rubbers can be, for example, B. natural polyisoprene and / or synthetic polyisoprene and / or polybutadiene (butadiene rubber) and / or styrene-butadiene copolymer (styrene-butadiene rubber) and / or epoxidized polyisoprene and / or styrene-isoprene rubber and / or halobutyl rubber and / or polynorbornene and / or isoprene-isobutylene copolymer and / or ethylene-propylene-diene rubber.The rubbers can be used as pure rubbers or in oil-extended form. Preferably, however, the diene rubber(s) are natural polyisoprene (NR) and / or synthetic polyisoprene (IR) and / or polybutadiene (BR, butadiene rubber) and / or styrene-butadiene copolymer (SBR, styrene-butadiene rubber). 202203357 - 6 - The natural and / or synthetic 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 of > 90 wt. % is preferred. Such a polyisoprene can be obtained by stereospecific polymerization in solution using Ziegler-Natta catalysts or using finely divided lithium alkyls. On the other hand, natural rubber (NR) is such a cis-1,4 polyisoprene; the cis-1,4 content in natural rubber is greater than 99 wt.%.Furthermore, a mixture of one or more natural polyisoprenes with one or more synthetic polyisoprenes is also conceivable. Natural polyisoprene is understood to be 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)). Natural polyisoprene (NR) is understood to mean non-synthetic polyisoprene. The butadiene rubber (BR, polybutadiene) can be all types known to the person skilled in the art with an Mw of 250,000 to 5,000,000 g / mol. These include, among others, the so-called high-cis and low-cis types, with polybutadiene with a cis content of greater than or equal to 90 wt. % being referred to as the high-cis type and polybutadiene with a cis content of less than 90 wt. % being referred to as the 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.%.A high-cis BR achieves particularly good abrasion properties and low hysteresis of the rubber compound. The polybutadiene used can be end-group modified and / or functionalized along the polymer chains. The modifications can include hydroxyl groups, ethoxy groups, epoxy groups, siloxane groups, amino groups, aminosiloxane, carboxyl groups, phthalocyanine groups, and / or silane sulfide groups. However, other modifications known to the expert, also referred to as functionalizations, are also possible. Metal atoms can be part of such functionalizations.202203357 - 7 - The styrene-butadiene rubber (styrene-butadiene copolymer) can be either solution-polymerized styrene-butadiene rubber (SSBR) or emulsion-polymerized styrene-butadiene rubber (ESBR), although 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. In any case, preference is given to styrene-butadiene copolymers with an Mw of 250,000 to 600,000 g / mol (two hundred and fifty thousand to six hundred thousand grams per mole). The styrene-butadiene copolymer(s) used can be end-group modified with modifications and functionalizations and / or functionalized along the polymer chains.The modification may be one with hydroxyl groups and / or ethoxy groups and / or epoxy groups and / or siloxane groups and / or amino groups and / or aminosiloxane and / or carboxy groups and / or phthalocyanine groups and / or silane sulfide groups. However, other modifications known to the person skilled in the art, also referred to as functionalizations, are also possible. Metal atoms may be a component of such functionalizations. According to a preferred embodiment of the invention, the rubber mixture contains more than 70 phr of at least one styrene-butadiene copolymer. This achieves particularly good values ​​with regard to wet grip. The phr (parts per hundred parts of rubber by weight) used in this document is the quantity specification for mixture formulations customary in the rubber industry.The dosage of the parts by weight of the individual substances in this document is based on 100 parts by weight of the total mass of all high-molecular-weight and therefore solid rubbers present in the mixture. To further improve wet grip and handling behavior, it has proven advantageous for the rubber mixture to contain more than 50 phr of at least one solution-polymerized styrene-butadiene copolymer, preferably more than 70 phr. 202203357 - 8 - According to the invention, the rubber mixture further contains at least one filler. In embodiments, the rubber mixture contains various fillers, such as carbon blacks, silicas, aluminosilicates, chalk, starch, magnesium oxide, titanium dioxide, or rubber gels, in conventional amounts, whereby the fillers can be used in combination.Carbon nanotubes (CNTs) including discrete CNTs, so-called hollow carbon fibers (HCFs), and modified CNTs containing one or more functional groups, such as hydroxyl, carboxyl, and carbonyl groups, are also conceivable. Graphite and graphene, as well as so-called “carbon-silica dual-phase fillers,” can also be used as fillers. The amounts of filler are within ranges known to those skilled in the art. The rubber mixture preferably contains more than 50 phr of filler to improve rolling resistance and abrasion behavior. If the rubber mixture contains carbon black, all types of carbon black known to those skilled in the art can be used. The carbon black content is preferably a maximum of 300 phr, more preferably a maximum of 200 phr, and more preferably a maximum of 150 phr.Preference is given to using a carbon black which has an iodine adsorption number according to ASTM D 1510 of 30 to 180 g / kg, preferably 30 to 130 kg / g, and a DBP number according to ASTM D 2414 of 80 to 200 ml / 100 g, preferably 100 to 200 ml / 100 g, particularly preferably 100 to 180 ml / 100 g. This achieves particularly good rolling resistance indicators (rebound resilience at 70°C) for use in vehicle tires, along with good other tire properties. At least one of the fillers used according to the invention has free hydroxyl, i.e., OH, groups. It is preferably a mineral filler. The content of the filler with free hydroxyl groups is preferably 10 to 300 phr, more preferably 30 to 250 phr, particularly preferably 40 to 200 phr. In some embodiments, silicic acid or silica is used as a filler.If the rubber mixture contains silica, a wide variety of silicas, such as "low surface area" or highly dispersible silica, can be used, even in mixtures. It is particularly preferred to use a finely divided, precipitated silica with a CTAB surface area (according to ASTM D 3765) of 30 to 350 m² / g, preferably 80 to 280 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. Silane coupling agents are added to the rubber mixture to improve processability and to bond any polar filler present to the rubber. The silane coupling agents react with the surface silanol groups of the silica or other polar groups during the first mixing step.Such silane coupling agents are bifunctional organosilanes that possess at least one alkoxy, cycloalkoxy, or phenoxy group as a leaving group on the silicon atom and that have, as another functionality, a group that, optionally 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, -NH2, or -Sx- (where x = 2-8). Thus, silane coupling agents that can be used include, for example, 3-mercaptopropyltriethoxysilane, 3-thiocyanatopropyltrimethoxysilane, or 3,3'-bis(triethoxysilylpropyl)polysulfides with 2 to 8 sulfur atoms, such as 3-methyl-3-methyl-2 ... B. 3,3'-bis(triethoxysilylpropyl)disulfide (TESPD), 3,3'-bis(triethoxysilylpropyl)tetrasulfide (TESPT) 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 a silylated core) can also be used, which are described, for example, in US 20080161477 A1 and EP 2114961 B1.202203357 - 10 - The rubber mixture may contain plasticizers in amounts of 1 to 120 phr, preferably 5 to 90 phr, particularly preferably 15 to 80 phr. Plasticizers which may be used include all plasticizers known to the person skilled in the art, such as aromatic, naphthenic, or paraffinic mineral oil plasticizers, such as MES (mild extraction solvate) or RAE (residual aromatic extract) or TDAE (treated distillate aromatic extract), or rubber-to-liquid oils (RTL) or biomass-to-liquid oils (BTL), preferably with a polycyclic aromatics content of less than 3% by weight according to method IP 346, or rapeseed oil or factice, or plasticizer resins, or liquid polymers, such as liquid polybutadiene—also in modified form. The plasticizer(s) are preferably added in at least one basic mixing stage during the production of the rubber mixture according to the invention.Furthermore, the rubber mixture can contain additives and processing aids in conventional parts by weight, which are added according to the invention in various mixing steps during its production. The additives added during the first mixing step for mixing the first rubber mixture include a) mastication aids, such as 2,2'-dibenzamidodiphenyl disulfide (DBD). The additives and processing aids added to the previously mixed first rubber mixture during the second mixing step according to the invention for mixing the second rubber mixture include b) waxes, and c) activators, such as zinc oxide and fatty acids, in particular, for example, stearic acid or zinc complexes such asZinc ethylhexanoate, Additives and processing aids added to control the kinetics of the first mixing step for mixing either the first or second rubber compound include 202203357 - 11 - d) ageing inhibitors, such as. B. 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), 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), e) processing aids, such as fatty acid salts, such as zinc soaps, and fatty acid esters and their derivatives, as well as commercially available mixtures such as Struktol® EF 44. The proportion of the total amount of further additives is 3 to 150 phr, preferably 3 to 100 phr and particularly preferably 5 to 80 phr.The proportion of the total amount of additional additives added during the second mixing step is 3 to 150 phr, preferably 4 to 100 phr, 5 to 80 phr, and particularly preferably 5 to 25 phr. The addition of the aforementioned additives in the second mixing step instead of the first surprisingly leads to an improvement in important tire properties of a tire produced from the rubber mixture and also enables better processability and producibility of the rubber mixture, thereby further increasing production efficiency and quality. In particular, this increases, for example, the reinforcement of the tire (increased tensile strength) or abrasion (reduced abrasion with increased tensile strength), and reduces the rolling resistance of the tire.The vulcanization of the rubber mixture is carried out in a third mixing step in the presence of sulfur and / or sulfur donors with the aid of vulcanization accelerators, whereby some vulcanization accelerators can also act as sulfur donors. The accelerator is selected from the group consisting of thiazole accelerators and / or mercapto accelerators and / or sulfenamide accelerators and / or thiocarbamate accelerators and / or thiuram accelerators and / or 202203357 - 12 - thiophosphate accelerators and / or thiourea accelerators and / or xanthate accelerators and / or guanidine accelerators. The use of a guanidine accelerator, for example N,N'-diphenylguanidine (DPG), is preferred. In one embodiment, the DPG is added to the rubber mixture during the first mixing step.This has the advantage of increasing the process reliability of the mixing process; in particular, it can delay the pre-vulcanization of the rubber mixture before the third mixing step. For example, a sulfenamide accelerator selected from the group consisting of N-cyclohexyl-2-benzothiazolesufenamide (CBS) and / or N,N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) and / or benzothiazyl-2-sulfenemorpholide (MBS) and / or N-tert-butyl-2-benzothiazylsulfenamide (TBBS) can also be used. The rubber mixture can also contain vulcanization retarders. All sulfur-donating substances known to those skilled in the art can be used as the sulfur-donating substance. If the rubber mixture contains a sulfur-donating substance, this is preferably selected from the group consisting of, for example, thiuram disulfides, such as, for example,Tetrabenzylthiuram disulfide (TBzTD), tetramethylthiuram disulfide (TMTD) or tetraethylthiuram disulfide (TETD), thiuram tetrasulfides such as. B. dipentamethylenethiuram tetrasulfide (DPTT), dithiophosphates, such as. B. DipDis (bis-(diisopropyl)thiophosphoryl disulfide), bis(O,O-2-ethylhexyl-thiophosphoryl)polysulfide (e.g. Rhenocure SDT 50®, Rheinchemie GmbH), zinc dichloryldithiophosphate (e.g. Rhenocure ZDT / S®, Rheinchemie GmbH) or zinc alkyldithiophosphate, and 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane and diarylpolysulfides and dialkylpolysulfides. Other network-forming systems, such as those available under the trade names Vulkuren®, Duralink® or Perkalink®, or network-forming systems as described in WO 2010 / 049216 A2, can also be used in the 202203357 - 13 - rubber mixture. The latter system contains a vulcanizing agent which crosslinks with a functionality greater than four and has at least one Vulcanization accelerator.During production, at least one vulcanizing agent selected from the group consisting of sulfur, sulfur donor, vulcanization accelerator, and vulcanizing agents that crosslink with a functionality greater than four is preferably added to the rubber mixture in the final mixing stage. This allows the mixed final mixture to be vulcanized to produce a sulfur-crosslinked rubber mixture for use in pneumatic vehicle tires. The terms "vulcanized" and "crosslinked" are used synonymously within the scope of the present invention. The rubber mixture is produced according to the process customary in the rubber industry, in which a base mixture containing all components except the vulcanization system (sulfur and vulcanization-influencing substances) is first prepared in one or more mixing stages. The final mixture is produced by adding the vulcanization system in a final mixing stage.The finished mixture is further processed, for example, by an extrusion process and formed into the appropriate shape. Further processing then takes place by vulcanization, whereby sulfur crosslinking occurs due to the vulcanization system added within the scope of the present invention. The rubber mixture is used for the production of pneumatic vehicle tires, such as car, truck, or two-wheeler tires, wherein the rubber mixture forms at least the part of the tread that comes into contact with the road surface. The invention will now be explained in more detail with reference to comparative and exemplary embodiments summarized in Table 1. The comparative mixtures are designated C1 to C3, and the mixtures according to the invention are designated E1 to E3.202203357 - 14 - Unless otherwise stated, the compounds V1, V2, and V3 were produced according to the procedures customary in the rubber industry under standard conditions in three stages in a laboratory mixer. In the first mixing stage (basic mixing stage), all components except the vulcanization system (sulfur and vulcanization-influencing substances) were mixed in a first mixing step. In the second mixing stage, the base mix was mechanically mixed again without any further substances being added to the mixture. By adding the vulcanization system in the third stage (final mixing stage), the final mix was produced in a second mixing step, with mixing taking place at 90 to 120 °C. Different silane coupling agents were used in Comparative Examples V1 and V3. In V2, the vulcanization accelerator DPG was added in the basic mixing stage instead of the final mixing stage, in contrast to V1.Unless otherwise stated, the mixtures E1, E2, and E3 were prepared according to processes customary in the rubber industry under standard conditions. According to the invention, mixing was carried out in three stages in a laboratory mixer. In a first mixing step of the basic mixing stage, all components except activators and processing aids such as zinc oxide, stearic acid, and zinc soaps, and except the vulcanization system (sulfur and vulcanization-influencing substances), were mixed to form a first rubber mixture. In a second mixing step of the basic mixing stage, the activators, such as zinc oxide and stearic acid, and processing aids such as Struktol® EF 44, were added to the first rubber mixture to obtain a second rubber mixture whose composition corresponds to the basic mixture of the comparative examples.According to the invention, the second mixing step of the basic mixing stage replaces the second mixing stage of the comparative process, or in further embodiments, can also be carried out in addition to it. The finished mixture was again produced by adding the vulcanization system in the third stage (final mixing stage), with mixing taking place at 90 to 120 °C. In Examples E1 and E3, the same different silane coupling agents were used as in Comparative Examples C1 and C3. In E2, in contrast to E1, the vulcanization accelerator DPG was again added in the first mixing step of the basic mixing stage instead of in the final mixing stage. After the second mixing step, important process parameters were determined for testing purposes and presented in Table 1: The Mooney viscosity was measured using large rotors (L), a preheating interval of 1 min (minutes), and a measurement interval of 4 min at an external temperature of 130 °C.The Mooney viscosity is abbreviated as ML(1+4 / 130 °C). Viscosity is a process parameter that provides information about the further processability of the rubber compound. If the viscosity is very high, the rubber compound is difficult to handle and, for example, to convey into the individual mixing devices. The measured values ​​presented in Table 1 show that the Mooney viscosity of the rubber compounds is not affected by the modified manufacturing process. The Mooney scorch is given as the time in minutes until a Mooney viscosity of ML(1+4 / 130 °C) = 5 is reached. The Mooney scorch is a parameter for process reliability. A high Mooney scorch means that the rubber compound is stable against unwanted spontaneous vulcanization during the mixing process.The measured values ​​shown in Table 1 show that 202203357 - 16 - the Mooney Scorch of the rubber compounds is not affected or is even increased by the modified manufacturing process.Test specimens were produced from all of the mixtures by vulcanization under pressure at 160 °C for 20 minutes. Using these test specimens, typical material properties for the rubber industry were determined using the test methods specified below: - Rebound resilience at 70 °C in accordance with DIN 53512 - Shore A hardness at room temperature using a durometer in accordance with DIN ISO 7619-1 as an indicator of braking behavior - Tensile strength to break in MPa (megapascals) - Ratio M300 / M50 of modulus 300% (necessary mechanical stress to achieve 300% elongation of the vulcanizate) to modulus 50% (necessary mechanical stress to achieve 50% elongation of the vulcanizate) under tensile stress (each measured in MPa) Table 1: Components Unit V1 E1 V2 E2 V3 E3 First mixing step NO. a phr 10 10 10 10 10 10 BR b phr 15 15 15 15 15 15 S-SBR c phr 75 75 75 75 75 75 Carbon black N339 phr 5 5 5 5 5 5 Silica dphr 85 85 85 85 85 85 Plasticizer (TDAE) phr 25 25 25 25 25 25 Silane coupling agent TESPD e phr 6.2 6.2 6.2 6.2 Silane coupling agent NXT® fphr 3.4 3.4 Ozone protection wax phr 2 2 2 2 2 2 Age inhibitor (6PPD, TMQ) phr 3 3 3 3 3 3 DPG phr 2 2 Zinc oxide phr 3 3 3 202203357 - 17 - Stearic acid phr 2 2 2 Processing aid (Struktol® EF 44) phr 4 4 4 Second mixing step Zinc oxide phr 3 3 3 Stearic acid phr 2 2 2 Processing aid (Struktol® EF 44) phr 4 4 4 Third mixing step DPG phr 2 2 2 2 Accelerator phr 2 2 2 2 2 2 Sulphur phr 1.5 1.5 1.5 1.5 1.5 1.5 Process properties ML(1+4 / 130 °C) MU 79 79 69 83 63 63 Mooney Scorch up to 5 MU min 25 37 52 39 41 26 Product properties Rebound resilience at 70 °C % 53 55 54 54 58 58 Shore A hardness at RT ShoreA 62 60 61 59 63 60 RPA delta(G'(1%)-G'(100%)) kPa 1015 790 932 798 730 607 RPA tan delta(10%) 0.150 0.137 0.149 0.141 0.114 0.110 Tensile strength MPa 14.1 15.8 14.1 16.1 16.3 16.8 M300 / M50 MPa / MPa 7.6 8.9 7.3 9.1 7.0 8.3 a) SIR 20 SED, b) EUROPRENE NEOCIS BR 40, c)solution-polymerized styrene-butadiene copolymer, 40% styrene, 24% vinyl, oil extended with 37.5 phr oil per 100 phr rubber, d) Ultrasil ® VN3, Evonik Industries, e) S2-Silane: TESPD, f)Silane NXT®, Momentive. 202203357 - 18 - Table 1 shows that the tensile strength of the vulcanizates increases when produced according to the mixing process according to the invention. Furthermore, it is also evident that when the vulcanizate is subjected to tensile stress, the M300 / M50 ratio increases from modulus 300% to modulus 50% when produced according to the mixing process according to the invention. From this, it can be deduced that the reinforcement of the vulcanizate increases and the abrasion of the vulcanizate during use can be advantageously reduced. Furthermore, the dynamic storage modulus (stiffness) G' of the vulcanized mixture at 1% to 100% elongation was determined in accordance with ASTM D6601 using RPA (rubber process analyzer) from the second elongation run at 1 Hz and 70°C as a measure of the Payne effect of the mixture and plotted as a graph.The difference between the dynamic storage modulus G'(1%) and G'(100%), as well as the tangent delta at 10% elongation at 70°C, serve as measures of the compound's rolling resistance. The narrower hysteresis, expressed numerically as [delta(G'(1%)-G'(100%))] or tan delta(10%), when evaluated from the RPA analysis shows that the rolling resistance of the vulcanizate is advantageously reduced. Furthermore, it can be seen that product properties such as the hardness and rebound resilience of the vulcanizate are not affected by the modified manufacturing process.

Claims

202203357 - 19 - Claims 1. A process for mixing a rubber mixture for tire production, comprising at least the following three steps: - mixing a sulfur-crosslinkable diene rubber, a filler with free OH groups, and a silane coupling agent in a first mixing step to form a first rubber mixture, wherein the filler with free OH groups and the silane coupling agent react chemically with one another; - mixing the first rubber mixture and processing aids containing at least one fatty acid and a divalent metal oxide in a second mixing step to form a second rubber mixture; - mixing the second rubber mixture and vulcanization chemicals in a third mixing step to form a third rubber mixture.

2. The process according to claim 1, wherein the three mixing steps are carried out sequentially in the stated order. 3.Method according to one of claims 1 or 2, wherein the three mixing steps take place spatially decoupled.

4. Method according to claim 3, wherein the third mixing step takes place in a different mixing device than the first and second mixing steps.

5. Method according to one of claims 3 or 4, wherein the second mixing step takes place in a different mixing device than the first mixing step.

6. Method according to one of claims 3 or 4, wherein the first and second mixing steps take place in different mixing chambers of a tandem mixing device.

7. Method according to one of claims 1 to 6, wherein the first rubber mixture is cooled before being fed to the second mixing device. 202203357 - 20 - 8. A process according to any of claims 1 to 7, wherein, in the first mixing step, the filler having free OH groups and the silane coupling agent react completely with each other.

9. A process according to any of claims 1 to 8, wherein the filler is silicic acid.

10. A process according to any of claims 1 to 9, wherein, in the second mixing step, at least one of zinc oxide and stearic acid is added.