DE102024201548A1 - Mixing process for a rubber compound - Google Patents

Abstract

The invention relates to a method for mixing a rubber mixture, in particular 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
- Mixing the first rubber compound and process aids in a second mixing step
- Mixing the second rubber compound and vulcanization chemicals in a third mixing step.

Description

The invention relates to a mixing process for a rubber mixture for tires or technical rubber articles with comparable conflicting objectives.

Since the driving characteristics of a tire, especially a pneumatic tire, depend to a large extent on the properties of the tire's rubber composition, particularly stringent requirements are placed on this composition. The properties of the rubber composition can be influenced, in particular, by the selected components and the mixing process used for its production.

By partially or completely replacing the carbon black filler with silica in rubber compounds, driving characteristics have been improved overall in recent years. However, the well-known conflicting objectives of opposing tire properties still exist, even with silica-containing rubber compounds.

For example, improvements in wet grip and dry braking generally result in a deterioration in rolling resistance, winter performance, and abrasion behavior. Wet grip and handling behavior also generally behave in opposite directions, as a softer compound for good wet grip is usually accompanied by a less stiff compound, which therefore results in poorer handling.

To resolve the aforementioned conflicting objectives, a variety of approaches have been pursued. For example, a wide variety of polymers, resins, plasticizers, and highly dispersed fillers have been used in rubber compounds, including modified ones. Attempts have been made to influence the vulcanizate properties by modifying the compounding process.

Some substances used in modern blends, such as functionalized polymers, increase the viscosity of the blend, thus impairing its processing behavior. The blend crumbles and disintegrates into small pieces, making such blends impossible to produce on an industrial scale without further modification.

Other substances such as processing aids are used to reduce the viscosity of the mixture, but can negatively affect the physical properties of the final product.

The state of the art in relation to rubber mixing processes is described, for example, in the publication DE 10 2017 223 554 A1 revealed.

The present invention is based on the object of providing a suitable mixing process for a rubber mixture, which preferably leads to improved properties of the resulting mixture.

• - Mischen mindestens eines schwefelvernetzbaren Dienkautschuks, mindestens eines Füllstoffs mit freien OH-Gruppen und mindestens eines Silan-Kupplungsagens in einem ersten Mischschritt zu einer ersten Kautschukmischung, wobei der OH-Gruppen haltige Füllstoff und das Silan-Kupplungsagens miteinander chemisch reagieren,
• - Mischen der ersten Kautschukmischung und von Prozesshilfsmitteln wie z.B. Aktivatoren oder Verarbeitungshilfsmitteln, die zumindest eine Fettsäure und ein zweiwertiges Metalloxid wie zum Beispiel ZnO enthalten, in einem zweiten Mischschritt zu einer zweiten Kautschukmischung,
• - Mischen der zweiten Kautschukmischung und von Vulkanisierungschemikalien in einem dritten Mischschritt zu einer dritten Kautschukmischung.

This task is solved 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 each other,
• - Mixing the first rubber mixture and processing aids such as activators or processing aids containing 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 compound and vulcanization chemicals in a third mixing step to form a third rubber compound.

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 the process reliability, of the rubber compound can be surprisingly improved. Furthermore, the properties of the vulcanizate obtained from such a mixed rubber compound can be surprisingly improved. In particular, higher 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 at different times.

According to one embodiment, the three mixing steps take place spatially separated or are carried out spatially separated in different mixing devices, which allows for flexible process control. The three mixing steps can be processed independently of one another with favorable properties.

For the first mixing step, the following advantageously apply: DE 10 2017 223 554 A1 mentioned temperature ranges. In particular, a fluid medium of the mixture 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. Subsequently, the first rubber mixture can 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 mixture 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 ideally not exceed 130 °C.

The rubber mixture can be cooled, especially between 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. This allows the start of the vulcanization process to be precisely adjusted.

In particular, the second mixing step continues to take 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 system 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 each other, allowing the rubber compound to be transferred directly from the upper machine to the lower machine without any additional equipment.

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, but potential processing problems during transport of the rubber mixture from the first to the second mixing device are reduced or eliminated.

For possible designs of the tandem mixing device, please refer to the publication DE 10 2015 210 342 A referred to.

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-group-containing filler and the silane coupling agent react completely with each other, so that the reactions during the second mixing step do not influence the reaction of the OH-group-containing filler and the silane coupling agent.

The filler is preferably silicic acid or silica as will be explained in more detail later.

Preferably, in the second mixing step, at least one of zinc oxide and stearic acid is added, the properties of which will be explained in more detail later.

The rubber compound contains at least one diene rubber. Therefore, several rubbers can be used in blends.

Diene rubbers are rubbers that are produced by polymerization or copolymerization of dienes and/or cycloalkenes and thus have C=C double bonds either in the main chain or in the side groups.

The diene rubbers can be, for example, 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).

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 with Ziegler-Natta catalysts or using finely divided lithium alkyls. Natural rubber (NR) is also such a cis-1,4-polyisoprene; the cis-1,4 content in natural rubber is greater than 99 wt.%.

Furthermore, a mixture of one or more natural polyisoprenes with one or more synthetic polyisoprenes is also conceivable. Natural polyisoprene is defined as rubber that can be obtained by harvesting from sources such as rubber trees (Hevea brasiliensis) or non-rubber tree sources (such as guayule or dandelion (e.g., Taraxacum)). Natural polyisoprene (NR) is defined as non-synthetic polyisoprene.

The butadiene rubber (BR, polybutadiene) can be any type known to the person skilled in the art with a 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. %. With a high-cis BR, particularly good abrasion properties and low hysteresis of the rubber mixture are achieved. The polybutadiene used can be end-group modified with modifications and functionalizations and/or functionalized along the polymer chains. The modification may involve 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 known as functionalizations, are also possible. Metal atoms may be a component of such functionalizations.

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 in the context of the present invention. In each case, styrene- Butadiene copolymers with a 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 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 skilled person, also referred to as functionalizations, are also possible. Metal atoms can 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 wet grip values.

The term phr (parts per hundred parts of rubber by weight) used in this document is the standard quantity used in the rubber industry for compound formulations. The dosage of the parts by weight of the individual substances 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 compound.

In order to further improve wet grip and handling behavior, it has proven advantageous if the rubber mixture contains more than 50 phr of at least one solution-polymerized styrene-butadiene copolymer, preferably more than 70 phr.

According to the invention, the rubber mixture further contains at least one filler.

The rubber mixture contains various fillers, such as carbon black, silica, aluminosilicates, chalk, starch, magnesium oxide, titanium dioxide, or rubber gels, in typical amounts. 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 "carbonsilica 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 compound 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 even more preferably a maximum of 150 phr. Preference is given to using a carbon black that 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 contains free hydroxyl, i.e., OH, groups. This 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, and particularly preferably 40 to 200 phr.

In some embodiments, silicic acid or silica is used as a filler.

If the rubber compound 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 dispersed, 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.

To improve processability and to bond any polar filler to the rubber, silane coupling agents are added to the rubber mixture. 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 which have at least one alkoxy, cycloalkoxy or phenoxy group as a leaving group on the silicon atom and which have as another functionality a group which, after cleavage, can enter into a chemical reaction with the double bonds of the polymer. The latter group can be, for example, the following chemical groups: -SCN, -SH, -NH2 or -Sx- (where x = 2-8). For example, silane coupling agents can be: B. 3-mercaptopropyltriethoxysilane, 3-thiocyanatopropyltrimethoxysilane or 3,3'-bis(triethoxysilylpropyl)polysulfides with 2 to 8 sulfur atoms, such as 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. 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 from the WO 99/09036 can be used as silane coupling agents. Silanes, such as those used in WO 2008/083241 A1 , the WO 2008/083242 A1 , the WO 2008/083243 A1 and the WO 2008/083244 A1 can be used. Examples of suitable silanes are those marketed under the name NXT® in various versions by Momentive, USA, or those marketed under the name VP Si 363 by Evonik Industries. Also suitable are so-called "silated core polysulfides" (SCP), which are used, for example, in the US 20080161477 A1 and the EP 2 114 961 B1 be described.

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 that can 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.

1. a) Mastikationshilfsmittel, wie z. B. 2,2'-Dibenzamidodiphenyldisulfid (DBD). Zu den Zusatzstoffen und Prozesshilfsmitteln, die während des erfindungsgemäßen zweiten Mischschritts zum Mischen der zweiten Kautschukmischung zur zuvor gemischten ersten Kautschukmischung zugegeben werden, zählen
2. b) Wachse, und
3. c) Aktivatoren, wie z. B. Zinkoxid und Fettsäuren, insbesondere zum Beispiel Stearinsäure oder Zinkkomplexe wie z. B. Zinkethylhexanoat, Zu den Zusatzstoffen und Prozesshilfsmitteln, die zur Steuerung der Kinetik des ersten Mischschritts entweder zum Mischen der ersten oder zweiten Kautschukmischung zugegeben werden, zählen
4. d) Alterungsschutzmittel, wie z. B. N-Phenyl-N'-(1,3-dimethylbutyl)-p-phenylendiamin (6PPD), N,N'-Diphenyl-p-phenylendiamin (DPPD), N,N'-Ditolyl-p-phenylendiamin (DTPD), N-Isopropyl-N'-phenyl-p-phenylendiamin (IPPD), 2,2,4-Trimethyl-1,2-dihydrochinolin (TMQ),
5. e) Verarbeitungshilfsmittel, wie z.B. Fettsäuresalze, wie z.B. Zinkseifen, und Fettsäureester und deren Derivate, sowie im Handel erhältliche Mischungen wie zum Beispiel Struktol® EF 44.

Furthermore, the rubber mixture may contain additives and processing aids in conventional parts by weight, which are added in various mixing steps during its production according to the invention. The additives added during the first mixing step for mixing the first rubber mixture include:

1. 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
2. b) waxes, and
3. c) Activators, such as zinc oxide and fatty acids, in particular, for example, stearic acid or zinc complexes such as zinc ethylhexanoate. The additives and processing aids added to control the kinetics of the first mixing step, either for mixing the first or second rubber compound, include
4. d) Anti-aging agents such as 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),
5. 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 other 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 further 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 above-mentioned additives in the second mixing step instead of the first surprisingly leads to an improvement in important tire properties of a tire made from the rubber compound and also enables better processability and producibility of the rubber compound, thereby further increasing production efficiency and quality.

In particular, this increases 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 compound is carried out in a third mixing step in the presence of sulfur and/or sulfur donors using vulcanization accelerators, whereby some vulcanization accelerators can also act as sulfur donors. The accelerator is selected from the group consisting of thiazole accelerators, mercapto accelerators, sulfenamide accelerators, thiocarbamate accelerators, thiuram accelerators, thiophosphate accelerators, thiourea accelerators, 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 initial 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) may also be used.

The rubber compound may also contain vulcanization retarders.

All sulfur-donating substances known to the person skilled in the art can be used as the sulfur-donating substance. If the rubber mixture contains a sulfur-donating substance, it is preferably selected from the group consisting of, for example, thiuram disulfides, such as tetrabenzylthiuram disulfide (TBzTD), tetramethylthiuram disulfide (TMTD) or tetraethylthiuram disulfide (TETD), thiuram tetrasulfides, such as 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-building systems, such as those sold under the trade names

Vulkuren®, Duralink® or Perkalink®, or network-forming systems as used in the WO 2010/049216 A2 can be used in the rubber compound. The latter system contains a vulcanizing agent that crosslinks with a functionality greater than four and at least one vulcanization accelerator.

During the final mixing stage, 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 during its production. 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 in the context of the present invention.

The rubber compound is manufactured according to the process commonly used in the rubber industry, in which a base compound is first produced in one or more mixing stages, containing all components except the vulcanization system (sulfur and vulcanization-influencing substances). The finished compound is created by adding the vulcanization system in a final mixing stage. The 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 compound is used for the manufacture of pneumatic vehicle tires, such as car, truck or two-wheel tires, whereby the rubber compound 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 using comparative and exemplary embodiments, which are summarized in Table 1.

The comparison mixtures are marked V1 to V3, the mixtures according to the invention are marked E1 to E3.

Unless otherwise stated, the compounding of V1, V2 and V3 was carried out according to the procedures customary in the rubber industry under normal conditions in three stages in a laboratory mixer in which all components except the vulcanization system (sulfur and vulcanization-influencing substances) were mixed in a first mixing step in the first mixing stage (basic mixing stage).

In the second mixing stage, the base mixture was mixed mechanically again without adding any further substances to the mixture.

By adding the vulcanization system in the third stage (finished mix stage), the finished mix was produced in a second mixing step, mixing at 90 to 120 °C.

In comparative examples V1 and V3, different silane coupling agents were used.

In V2, in contrast to V1, the vulcanization accelerator DPG was added in the basic mixing stage instead of in the final mixing stage.

Unless otherwise stated, the compounding of E1, E2 and E3 was carried out according to the procedures customary in the rubber industry under standard conditions.

According to the invention, the mixing was carried out in three stages in a laboratory mixer in which, 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 other embodiments, can also be carried out in addition to it.

By adding the vulcanization system in the third stage (finished mixing stage), the finished mixture was again produced, 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 V1 and V3.

In E2, in contrast to E1, the vulcanization accelerator DPG was added in the first mixing step of the basic mixing stage instead of in the final mixing stage.

• Die Mooney-Viskosität wurde bei Verwendung von großen Rotoren (L), einem Vorheizintervall von 1 min (Minuten) und einem Messintervall von 4 min bei einer Außentemperatur von 130 °C gemessen. Die Mooney-Viskosität wird als ML(1+4/130 °C) abgekürzt. Die Viskosität ist ein Prozessparameter, der Auskunft über die Weiterverarbeitbarkeit der Kautschukmischung gibt. Ist die Viskosität sehr hoch, lässt sich die Kautschukmischung schwer händeln und z.B. in die einzelnen Mischvorrichtungen fördern.

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 outside temperature of 130 °C. The Mooney viscosity is abbreviated as ML(1+4/130 °C). Viscosity is a process parameter that 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 shown in Table 1 show that the Mooney viscosity of the rubber compounds is not affected by the modified manufacturing process.

The Mooney scorch is expressed 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 presented in Table 1 show that the Mooney scorch of the rubber compounds is not affected or even increased by the modified manufacturing process.

• - Rückprallelastizität bei 70°C gemäß DIN 53 512
• - Shore-A-Härte bei Raumtemperatur mittels Durometer gemäß DIN ISO 7619-1 als Indikator für das Bremsverhalten
• - Zugfestigkeit bis zum Bruch in MPa (Megapascal)
• - Verhältnis M300/M50 von Modulus 300 % (notwendige mechanische Spannung um eine Dehnung der Länge des Vulkanisats um 300 % zu erreichen) zu Modulus 50 % (notwendige mechanische Spannung um eine Dehnung der Länge des Vulkanisats um 50 % zu erreichen) bei Beanspruchung auf Zug (jeweils gemessen in MPa)

Tabelle 1: Bestandteile Einheit V1 E1 V2 E2 V3 E3 Erster Mischschritt NR^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 Ruß N339 phr 5 5 5 5 5 5 Kieselsäure^d phr 85 85 85 85 85 85 Weichmacher (TDAE) phr 25 25 25 25 25 25 Silan-KupplungsagensTESPD^e phr 6,2 6,2 6,2 6,2 Silan-KupplungsagensNXT®^f phr 3,4 3,4 Ozonschutzwachs phr 2 2 2 2 2 2 Alterungsschutzmittel(6PPD, TMQ) phr 3 3 3 3 3 3 DPG phr 2 2 Zinkoxid phr 3 3 3 StearinsäureVerarbeitungshilfsmittel phr 2 2 2 (Struktol® EF 44) phr 4 4 4 Zweiter Mischschritt Zinkoxid phr 3 3 3 Stearinsäure phr 2 2 2 Verarbeitungshilfsmittel(Struktol® EF 44) phr 4 4 4 Dritter Mischschritt DPG phr 2 2 2 2 Beschleuniger phr 2 2 2 2 2 2 Schwefel phr 1,5 1,5 1,5 1,5 1,5 1,5 Prozesseigenschaften ML(1+4/130 °C) MU 79 79 69 83 63 63 Mooney Scorch bis 5 MU min 25 37 52 39 41 26 Produkteigenschaften Rückprallelastizität bei 70 °C % 53 55 54 54 58 58 Shore A-Härte bei RTRPA ShoreA 62 60 61 59 63 60 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 Zugfestigkeit 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) lösungspolymerisiertes Styrol-Butadien-Copolymer, 40% Styrol, 24% Vinyl,ölverstreckt mit 37,5 phr Öl pro 100 phr Kautschuk, ^d) Ultrasil^® VN3, Evonik Industries, ^e) S₂-Silan: TESPD, ^f) Silane NXT®, Momentive. Test specimens were prepared from all compounds by vulcanization under pressure at 160 °C for 20 minutes and material properties typical for the rubber industry were determined using these test specimens using the test methods specified below:

• - Rebound resilience at 70°C according to DIN 53 512
• - Shore A hardness at room temperature using a durometer according to DIN ISO 7619-1 as an indicator of braking performance
• - Tensile strength at break in MPa (megapascals)
• - Ratio M300/M50 of modulus 300% (necessary mechanical stress to achieve a length extension of the vulcanizate by 300%) to modulus 50% (necessary mechanical stress to achieve a length extension of the vulcanizate by 50%) under tensile stress (each measured in MPa)

Table 1: Components Unit V1 E1 V2 E2 V3 E3 First mixing step NR ^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 Soot N339 phr 5 5 5 5 5 5 Silica ^d phr 85 85 85 85 85 85 Plasticizers (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® ^f phr 3.4 3.4 Ozone protection wax phr 2 2 2 2 2 2 Anti-aging agents (6PPD, TMQ) phr 3 3 3 3 3 3 DPG phr 2 2 zinc oxide phr 3 3 3 Stearic acid processing aid phr 2 2 2 (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 sulfur 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 features Rebound resilience at 70 °C % 53 55 54 54 58 58 Shore A hardness at RTRPA ShoreA 62 60 61 59 63 60 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) S ₂ -Silane: TESPD, ^f) Silane NXT®, Momentive.

Table 1 shows that the tensile strength of the vulcanizates increases when produced according to the mixing process of the invention.

Furthermore, it is evident that when the vulcanizate is subjected to tensile stress, the ratio M300/M50 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 compound at 1% to 100% elongation was determined according to 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 compound and plotted as a graph.

The difference between dynamic storage modulus G'(1%) and G'(100%) as well as the tangent delta at 10% elongation at 70°C serve as measures for the rolling resistance of the compound.

The narrower hysteresis, numerically expressed by [delta(G'(1%)-G'(100%))] or tan delta(10%), when evaluating the RPA analysis shows that the rolling resistance of the vulcanizate advantageously decreases.

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.

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10 2017 223 554 A1 [0008, 0015]
• DE 10 2015 210 342 A [0024]
• WO 99/09036 [0048]
• WO 2008/083241 A1 [0048]
• WO 2008/083242 A1 [0048]
• WO 2008/083243 A1 [0048]
• WO 2008/083244 A1 [0048]
• US 20080161477 A1 [0048]
• EP 2 114 961 B1 [0048]
• WO 2010/049216 A2 [0061]

Claims (10)

A method 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 chemically react 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. Procedure according to Claim 1 , whereby the three mixing steps are carried out one after the other in the order mentioned. Method according to one of the Claims 1 or 2 , whereby the three mixing steps take place spatially decoupled. Procedure according to Claim 3 , wherein the third mixing step takes place in a different mixing device than the first and second mixing steps. Method according to one of the Claims 3 or 4 , wherein the second mixing step takes place in a different mixing device than the first mixing step. Method according to one of the Claims 3 or 4 , wherein the first and second mixing steps take place in different mixing chambers of a tandem mixing device. Method according to one of the Claims 1 until 6 , wherein the first rubber mixture is cooled before being fed into the second mixing device. Procedure a Claims 1 until 7 , wherein in the first mixing step the filler with free OH groups and the silane coupling agent react completely with each other. Procedure a Claims 1 until 8 , where the filler is silica. Procedure a Claims 1 until 9 , wherein in the second mixing step at least one of zinc oxide and stearic acid is added.