DE102024108401A1 - Rubber compound and vehicle tires - Google Patents

Abstract

The invention relates to a sulfur-crosslinkable rubber mixture, in particular for the horn profile of vehicle tires, containing at least the following components:
- at least one diene rubber,
- 40 to 90 phr (parts by weight, based on 100 parts by weight of the total rubber in the mixture) of at least one carbon black, the carbon black or carbon blacks having an average iodine number according to ASTM D 1510 of 55 to 80 g/kg,
- 5 to 20 phr of at least one silicic acid,
- at least one silane coupling agent and
- an efficient vulcanization system containing at least one vulcanization accelerator and elemental sulfur, wherein the mass ratio of vulcanization accelerator to sulfur is 8:1 to 3:1.

Description

The invention relates to a sulfur-crosslinkable rubber mixture, in particular for the horn profile of vehicle tires.

The invention further relates to a vehicle tire having at least one component consisting of such a sulfur-vulcanized rubber mixture.

Different requirements are placed on the various components of a vehicle tire, especially a pneumatic tire. This is due to the fact that very different compound compositions are used for the various components. The compound and vulcanizate properties of these compound compositions, in turn, can be influenced by the type and quantity of the different compound components. However, improving one property by varying the compound components often results in a deterioration of another. Two of these properties, which often behave in contradiction, are rolling resistance and durability.

Rolling resistance and durability can be influenced, for example, by the type and amount of fillers used and the crosslinking system. Rubber compounds in vehicle tires are typically reinforced with fillers, typically carbon black and/or silica. Changing the carbon black type to one with a lower surface area, for example, generally leads to a reduction in hysteresis (correlating with an improvement in rolling resistance), but at the same time to a deterioration in the properties important for durability. Changing from a carbon black type with a lower surface area to one with a higher surface area, on the other hand, leads to poorer hysteresis while improving durability.

A "sulfur-crosslinked rubber mixture" of the type mentioned above refers to a rubber mixture produced from a ready-made rubber mixture (or raw rubber mixture) by sulfur vulcanization. A sulfur-crosslinked rubber mixture is thus a vulcanizate. All statements also apply to the vehicle tire according to the invention, which has at least one rubber mixture according to the invention in at least one component. The description of the individual components refers to the rubber mixture before vulcanization, i.e., the sulfur-crosslinkable rubber mixture, unless otherwise stated. It is clear to those skilled in the art that the components may be present in an altered form after vulcanization, which applies in particular to the rubbers (polymers), sulfur, and other components involved in the vulcanization.

Rubber compounds for vehicle tires are typically crosslinked with sulfur, with the ratio of vulcanization accelerator to sulfur determining the efficiency of the sulfur network. If the ratio of vulcanization accelerator to sulfur is low, i.e., below 1:2, it is referred to as conventional vulcanization, and long sulfur chains are present. A high ratio indicates an efficient vulcanization system, with shorter sulfur chains. Increasing the efficiency of the sulfur network generally improves durability (aging resistance), but rolling resistance decreases.

High durability, especially resistance to aging, is particularly important, especially in the area of the beads of pneumatic vehicle tires, where high mechanical and thermal stresses occur. At the same time, the rolling resistance of tires must be increasingly reduced. Areas of pneumatic vehicle tires that are particularly exposed to stress are the flange profiles, also known as the rim strip or bead protection strip, which are sometimes in direct contact with the outside air.

Rubber compounds for the tire bead area are, for example, from the EP3632975A1 The compounds described therein contain natural rubber, polybutadiene, two different carbon blacks, and a sulfur vulcanization system.

The WO2020065175A1 discloses bead area compounds containing natural rubber, carbon black, more than 30 phr of silica and a conventional sulfur vulcanization system.

The invention is based on the object of providing rubber mixtures which are characterized by improved durability of the vulcanizates and at the same time lower hysteresis and thus, for example, When used in tires, this can lead to an improvement in the trade-off between durability and rolling resistance.

• - zumindest einen Dienkautschuk,
• - 40 bis 90 phr (Gewichtsteile, bezogen auf 100 Gewichtsteile der gesamten Kautschuke in der Mischung) zumindest eines Rußes, wobei der Ruß oder die Ruße im Mittel eine Jodzahl gemäß ASTM D 1510 von 55 bis 80 g/kg aufweist bzw. aufweisen,
• - 5 bis 20 phr zumindest einer Kieselsäure,
• - zumindest ein Silan-Kupplungsagens und
• - ein effizientes Vulkanisationssystem, das wenigstens einen Vulkanisationsbeschleuniger und elementaren Schwefel enthält, wobei das Massenverhältnis von Vulkanisationsbeschleuniger zu Schwefel 8:1 bis 3:1 beträgt.

This object is achieved according to the invention by a sulfur-crosslinkable rubber mixture, in particular for the horn profile of vehicle tires, which contains at least the following components:

• - at least one diene rubber,
• - 40 to 90 phr (parts by weight, based on 100 parts by weight of the total rubber in the mixture) of at least one carbon black, the carbon black or carbon blacks having an average iodine number according to ASTM D 1510 of 55 to 80 g/kg,
• - 5 to 20 phr of at least one silicic acid,
• - at least one silane coupling agent and
• - an efficient vulcanization system containing at least one vulcanization accelerator and elemental sulfur, wherein the mass ratio of vulcanization accelerator to sulfur is 8:1 to 3:1.

Surprisingly, it has been found that the special combination of one or more carbon blacks, whose average iodine value is between 55 and 80 g/kg, with a small amount of silica and a silane coupling agent and with a special efficient vulcanization system, each in the specified amounts in diene rubber compounds, leads to a high durability of the vulcanizates through improved aging resistance, while at the same time reducing hysteresis.

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

According to the invention, the rubber mixture contains at least one diene rubber. Diene rubbers are rubbers produced by 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 functionalized, modified, or coupled.

The diene rubber(s) is/are preferably selected from the group consisting of natural polyisoprene (NR), synthetic polyisoprene (IR), epoxidized polyisoprene (ENR), butadiene rubber (BR), butadiene-isoprene rubber, styrene-butadiene rubber (SBR), in particular solution-polymerized styrene-butadiene rubber (SSBR) and emulsion-polymerized styrene-butadiene rubber (ESBR), styrene-isoprene rubber, liquid rubbers with a molecular weight M _w of greater than 20,000 g/mol, halobutyl rubber, polynorbornene, isoprene-isobutylene copolymer, ethylene-propylene-diene rubber, nitrile rubber, chloroprene rubber, Acrylate rubber, fluororubber, silicone rubber, polysulfide rubber, epichlorohydrin rubber, styrene-isoprene-butadiene terpolymer, hydrogenated acrylonitrile-butadiene rubber and hydrogenated styrene-butadiene rubber.

In particular, nitrile rubber, hydrogenated acrylonitrile-butadiene rubber, chloroprene rubber, butyl rubber, halobutyl rubber, or ethylene-propylene-diene rubber are used in the production of technical rubber articles, such as belts, straps, and hoses, and/or shoe soles. The preferred blend compositions for these rubbers—specific with regard to fillers, plasticizers, vulcanization systems, and additives—are known to those skilled in the art.

According to a particularly preferred embodiment of the invention, the diene rubber(s) is/are selected from the group consisting of natural polyisoprene (NR), synthetic polyisoprene (IR), butadiene rubber (BR), solution-polymerized styrene-butadiene rubber (SSBR), and emulsion-polymerized styrene-butadiene rubber (ESBR). 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 koksaghyz)). Natural polyisoprene (NR) is understood to mean non-synthetic polyisoprene.

The butadiene rubber (= BR, polybutadiene) optionally contained in the rubber mixture according to the invention can be any type known to the person skilled in the art. These include, among others, the so-called high-cis and low-cis grades, with polybutadiene with a cis content greater than or equal to 90 wt.% being referred to as high-cis, and polybutadiene with a cis content less than 90 wt.% being referred to as low-cis. An example of a low-cis polybutadiene is Li-BR (lithium-catalyzed butadiene rubber) with a cis content of 20 to 50 wt.%. High-cis BR achieves particularly good properties and low hysteresis of the rubber compound.

The polybutadiene(s) used can be end-group modified and/or functionalized along the polymer chains. The modifications can be those with hydroxyl groups and/or ethoxy groups and/or epoxy groups and/or siloxane groups and/or amino groups and/or aminosiloxane and/or carboxyl 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 can be a component of such functionalizations.

If at least one styrene-butadiene rubber (styrene-butadiene copolymer) is present in the rubber mixture, it 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 present invention.

The styrene-butadiene copolymer used can be end-group modified with the modifications and functionalizations mentioned above for polybutadiene and/or functionalized along the polymer chains.

For use of the rubber compound in areas close to the bead of a pneumatic vehicle tire, the rubber compound preferably contains 20 to 50 phr of natural rubber (NR) and 50 to 80 phr of at least one butadiene rubber (BR).

The rubber mixture according to the invention contains 40 to 90 phr, preferably 50 to 80 phr, of at least one carbon black, wherein the carbon black or carbon blacks have an average iodine number according to ASTM D 1510 of 55 to 80 g/kg. Accordingly, a carbon black with an iodine number according to ASTM D 1510 of 55 to 80 g/kg can be used in the mixture, for example in carbon black of type N351 (iodine number: 68 g/kg). However, it is also possible to use two or more carbon blacks in the mixture in such a way that an average iodine number according to ASTM D 1510 of 55 to 80 g/kg is obtained. In this case, a mixture (blend) of several carbon blacks is used.

The rubber mixture contains 5 to 20 phr of at least one silica. Any silica known to the person skilled in the art can be used, even as a mixture. Preference is given to using silicas that have a nitrogen surface area (BET surface area) (according to DIN ISO 9277 and DIN 66132) of 35 to 400 ^m² /g and a CTAB surface area (according to ASTM D 3765) of 30 to 400 ^m² /g. Thus, silicas that can be used include, for example, Ultrasil® VN3 (trade name) from Evonik, silicas such as Zeosil® 1115 or Zeosil® 1085 from Solvay, and highly dispersible silicas, so-called HD silicas (e.g. Zeosil® 1165 MP from Solvay).
To improve the sustainability of the mixture, a silica made from rice husk ash (“rice husk ash silica” (RHAS)) is preferably included in the mixture.

To improve processability and to bond the silica to the diene rubber in the mixtures, the mixtures contain at least one silane coupling agent, which is preferably used in amounts of 1-15 phf (parts by weight, based on 100 parts by weight of silica/silica) in the rubber mixture. The silane coupling agents can also be used in the mixture.

The term phf (parts per hundred parts of filler by weight) used in this document is the quantity commonly used in the rubber industry for coupling agents for polar fillers. In the context of this application, phf refers to the silica/silicic acid present, meaning that other fillers that may be present, such as carbon black, are not included in the calculation of the amount of silane coupling agent.

The silane coupling agents react with the surface silanol groups of the silica or other polar groups during mixing of the rubber or rubber mixture (in situ) or even before the addition of the filler to the rubber, in the sense of pretreatment (premodification). Silane coupling agents that can be used are all silane coupling agents known to the person skilled in the art for use in rubber mixtures. Such coupling agents known from the prior art 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 be, for example, the following chemical groups: -SCN, -SH, -NH ₂ , or -S _x - (where x = 2-8). For example, 3-mercaptopropyltriethoxysilane, 3-thiocyanatopropyltrimethoxysilane, or 3,3'-bis(triethoxysilylpropyl)polysulfides with 2 to 8 sulfur atoms, such as 3,3'-bis(triethoxysilylpropyl)tetrasulfide (TESPT), the corresponding disulfide, or mixtures of sulfides with 1 to 8 sulfur atoms with varying contents of the various sulfides, can be used as silane coupling agents. TESPT can also be added, for example, as a mixture with carbon black (trade name X50S from Degussa). Blocked mercaptosilanes, such as those from 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 can contain other fillers such as aluminosilicates, kaolin, chalk, starch, magnesium oxide, titanium dioxide, rubber gels as well as fibers (such as aramid fibers, glass fibers, carbon fibers, cellulose fibers), carbon nanotubes (including discrete CNTs, so-called hollow carbon fibers (HCF) and modified CNTs containing one or more functional groups such as hydroxyl, carboxy and carbonyl groups), graphite, graphene or so-called “carbon-silica dual-phase filler” in usual amounts, whereby the fillers can be used in combination.

Essential to the invention is that the rubber mixture has an efficient vulcanization system containing at least one vulcanization accelerator and elemental sulfur, wherein the mass ratio of vulcanization accelerator to sulfur is 8:1 to 3:1, preferably 7:1 to 3:1, particularly preferably 6:1 to 3.5:1. This enables crosslinking with short sulfur chains to form an efficient network.

The vulcanization accelerators can be selected from all vulcanization accelerators known to those skilled in the art of sulfur vulcanization. Such accelerators include thiazole accelerators, mercapto accelerators, sulfenamide accelerators, sulfenimide accelerators, thiocarbamate accelerators, thiuram accelerators, thiophosphate accelerators, thiourea accelerators, xanthate accelerators, and guanidine accelerators. For particularly good durability with low rolling resistance, the vulcanization accelerator(s) are preferably selected from the group consisting of mercapto accelerators, sulfenamide accelerators, sulfenimide accelerators, and guanidine accelerators.

According to an advantageous embodiment of the invention, the sulfur-crosslinkable rubber mixture contains at least TBSI (N-tert-butyl-2-benzothiazolesulfenimide) and/or TBBS (N-tert-butyl-2-benzothiazylsulfenamide) and/or DCBS (N,N-dicyclohexyl-2-benzothiazolesulfenamide) and/or CBS (N-cyclohexyl-2-benzothiazolesulfenamide) as vulcanization accelerators. All vulcanization accelerators can also be used in mixtures.

To ensure good ageing resistance of the vulcanizates, the rubber compound preferably contains 0.5 to 1.5 phr of sulfur.

The rubber compound may also contain vulcanization retarders.

The terms “vulcanized” and “crosslinked” are used synonymously in the context of the present invention.

The rubber mixture according to the invention may further contain various plasticizers. These are preferably present in the mixture in amounts of up to 50 phr.

Plasticizers that can be used are, for example, those selected from the group consisting of plasticizers made from renewable raw materials such as rapeseed oil or sunflower oil, 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 in particular resin acids or factises or liquid polymers whose average molecular weight (determined by GPC = gel permeation chromatography, based on BS ISO 11344:2004) is between 500 and 20,000 g/mol, mineral oils, phosphoric acid esters such as tri-(2-ethylhexyl) phosphate, and liquid polymers with a weight average molecular weight distribution M _w according to GPC of 60,000 g/mol or less. If additional liquid polymers are used as plasticizers in the rubber mixture according to the invention, they are not included as rubber in the calculation of the composition of the polymer matrix. Preferably, DAE (Distilled Aromatic Extracts), RAE (Residual Aromatic Extracts), TDAE (Treated Distilled Aromatic Extracts), MES (Mild Extracted Solvents), rapeseed oil, and/or liquid diene polymers are used.

1. a) 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), N,N'-Di(1,4dimethylpentyl)-p-phenylendiamin (77PD), N,N'-Di(1-ethyl, 4-methyl-hexyl)-p-phenylendiamin (88PD), N,N'Bis-(1-ethyl-3-methylpentyl)-p-phenylenediamin (DOPD) sowie N,N'-Di-β-naphthyl-p-phenylenediamin (DNPD), 2,2,4-Trimethyl-1,2-dihydrochinolin (TMQ),
2. b) Aktivatoren, wie z. B. Zinkoxid (wie z.B. ZnO-Granulat oder -Pulver; das herkömmlicherweise verwendete Zinkoxid weist in der Regel eine BET-Oberfläche von weniger als 10 m²/g auf. Es kann aber auch ein Zinkoxid mit einer BET-Oberfläche von 10 bis 100 m²/g, wie z.B. so genannte „nano-Zinkoxide“, verwendet werden) und Fettsäuren (z. B. Stearinsäure) oder Zinkkomplexe wie z. B. Zinkethylhexanoat,
3. c) Harze, wie z. B. Phenolharze, insbesondere Klebharze. Als Klebharze können natürliche oder synthetische Harze, wie Kohlenwasserstoffharze, eingesetzt werden, die als Klebrigmacher wirken. Die Kohlenwasserstoffharze können phenolisch, aromatisch oder aliphatisch sein. Bevorzugt sind die Klebharze ausgewählt aus der Gruppe, bestehend aus Kolophoniumharzen und deren Estern, Terpen-Phenol-Harzen, Alkin-Phenol-Harzen, Phenol-Harzen und Cumaron-Inden-Harzen, wobei Phenol-Harze für die vorliegende Erfindung besonders gut geeignet sind.
4. d) Mastikationshilfsmittel, wie z. B. 2,2'-Dibenzamidodiphenyldisulfid (DBD), und
5. e) Verarbeitungshilfsmittel, wie z.B. Fettsäuresalze, wie z.B. Zinkseifen, und Fettsäureester und deren Derivate.

Furthermore, the rubber mixture may contain conventional additives in the usual parts by weight, which are preferably added in at least one basic mixing stage during its production. These additives include

1. a) 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), N,N'-di(1,4-dimethylpentyl)-p-phenylenediamine (77PD), N,N'-di(1-ethyl, 4-methylhexyl)-p-phenylenediamine (88PD), N,N'bis-(1-ethyl-3-methylpentyl)-p-phenylenediamine (DOPD) and N,N'-di-β-naphthyl-p-phenylenediamine (DNPD), 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ),
2. b) Activators, such as zinc oxide (e.g. ZnO granules or powder; the conventionally used zinc oxide usually has a BET surface area of less than 10 m ² /g. However, a zinc oxide with a BET surface area of 10 to 100 m ² /g, such as so-called “nano-zinc oxides”, can also be used) and fatty acids (e.g. stearic acid) or zinc complexes such as zinc ethylhexanoate,
3. c) Resins, such as phenolic resins, especially tackifier resins. Adhesive resins can be natural or synthetic resins, such as hydrocarbon resins, which act as tackifiers. The hydrocarbon resins can be phenolic, aromatic, or aliphatic. The tackifier resins are preferably selected from the group consisting of rosin resins and their esters, terpene-phenol resins, alkyne-phenol resins, phenolic resins, and coumarone-indene resins, with phenolic resins being particularly suitable for the present invention.
4. d) mastication aids, such as 2,2'-dibenzamidodiphenyl disulfide (DBD), and
5. e) processing aids such as fatty acid salts, such as zinc soaps, and fatty acid esters and their derivatives.

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 rubber compound is produced according to a process commonly used in the rubber industry, in which a base compound containing all components except the vulcanization system (sulfur and vulcanization-influencing substances) is first prepared in one or more mixing stages. The finished compound is created by adding the vulcanization system in a final mixing stage. The finished compound is further processed, for example, by an extrusion process, and formed into the appropriate shape. Further processing then takes place by vulcanization, with sulfur crosslinking occurring due to the vulcanization system added within the scope of the present invention.

The rubber compound can be used for a wide variety of rubber products where low hysteresis and high durability and aging resistance are advantageous. It is preferably used in the production of vehicle tires, such as car, van, truck, or two-wheeler tires. It can be used in various components of vehicle tires, particularly pneumatic vehicle tires. These can include compounds in the bead and sidewall areas, such as the apex, parts of the apex, parts of the sidewall, or crescent-shaped inserts in the sidewall area.

The rubber mixture is preferably used as a flange profile for vehicle tires, especially pneumatic tires. Tires with a flange profile made from the mixture according to the invention are characterized by low rolling resistance and high durability.

During the manufacture of the pneumatic vehicle tire, the mixture is formed as a ready-mixed mixture into the shape of the relevant component, for example a horn profile, before vulcanization and is applied as usual during the manufacture of the vehicle tire blank.

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

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 with V, the mixture according to the invention is marked with E.

The compound was manufactured according to standard rubber industry procedures under standard conditions in three stages in a laboratory mixer. Initially, all components except the vulcanization system (sulfur and vulcanization-influencing substances) were mixed in two mixing stages (basic mixing stages). The final compound was created by adding the vulcanization system in the third stage (final mixing stage), which was mixed at 90 to 120 °C.

• - Netzknotenabstand gemäß dynamischer Differenzkalorimetrie: Dabei macht man sich zu Nutze, dass der Phasenübergang flüssig-fest eines Quellmittels innerhalb eines gequollenen polymeren Netzwerkes von der Vernetzungsdichte abhängig ist. Proben der jeweiligen Kautschukmischung werden mit Cyclohexan als Quellmittel aufgequollen; dazu wird die jeweilige Probe mit Cyclohexan extrahiert und anschließend bei Raumtemperatur (RT) zum weiteren Quellen stehen gelassen. Anschließend wird die Gefrierpunktsdepression von Cyclohexan im Netzwerk im Vergleich zu der makroskopisch ausgedehnten Flüssigphase bestimmt: Die vorbereitete Probe wird in der Messapparatur abgekühlt und der Wärmefluss aufgenommen. Es ergeben sich zwei Gefrierpeaks, der Peak des reinen Cyclohexans bei ca. 3°C und ein weiterer Peak des in der gequollenen Probe befindlichen Cyclohexans. Aus der Temperaturdifferenz berechnet sich der Netzknotenabstand.
• - Shore-A-Härte bei Raumtemperatur gemäß ISO 868
• - Rückprallelastizität bei 70 °C gemäß ISO 4662
• - Bruchdehnung bei Raumtemperatur gemäß DIN 53504. Die Proben wurden vor und nach Alterung gemessen: Alterung jeweils an Luft für 14 Tage bei 80 °C
• - Ermüdungsrissbeständigkeit (Ermüdungsbruchlebensdauer) als Anzahl der Lastwechsel in kiloZyklen (kurz kC) bis zum Bruch einer hantelförmigen Probe unter einem sich ständig wiederholenden Dehnungszyklus mit einer Frequenz von 104 ± 8 min-1, bestimmt mit einem Monsanto Fatigue to Failure Tester (abgekürzt: FTF) bei Raumtemperatur (RT, 23 °C ±2 °C). Die Proben wurden vor und nach Alterung gemessen: Alterung jeweils an Luft für 14 Tage bei 80 °C. Die ungealterten Proben wurden bei einer Vorspannung von 89 %, die gealterten Proben bei einer Vorspannung von 61 % gemessen.

Test specimens were prepared from all compounds by vulcanization under pressure at 160 °C for 15 minutes and material properties typical for the rubber industry were determined using these test specimens using the test methods specified below:

• - Network node spacing according to dynamic differential calorimetry: This method utilizes the fact that the liquid-to-solid phase transition of a swelling agent within a swollen polymer network depends on the crosslinking density. Samples of the respective rubber mixture are swollen using cyclohexane as the swelling agent; for this purpose, the respective sample is extracted with cyclohexane and then allowed to stand at room temperature (RT) for further swelling. The freezing point depression of cyclohexane in the network is then determined compared to the macroscopically expanded liquid phase. The prepared sample is cooled in the measuring apparatus, and the heat flow is recorded. Two freezing peaks result: the peak of pure cyclohexane at approximately 3°C and another peak of the cyclohexane present in the swollen sample. The network node spacing is calculated from the temperature difference.
• - Shore A hardness at room temperature according to ISO 868
• - Rebound resilience at 70 °C according to ISO 4662
• - Elongation at break at room temperature according to DIN 53504. The samples were measured before and after aging: aging in air for 14 days at 80 °C
• - Fatigue crack resistance (fatigue fracture life) as the number of load cycles in kilocycles (kC for short) until failure of a dumbbell-shaped specimen under a continuously repeating strain cycle with a frequency of 104 ± 8 min-1, determined using a Monsanto Fatigue to Failure Tester (FTF for short) at room temperature (RT, 23 °C ± 2 °C). The specimens were measured before and after aging: aging in air for 14 days at 80 °C. The unaged specimens were measured at a prestress of 89%, the aged specimens at a prestress of 61%.

High rebound resilience at 70 °C (equivalent to reduced hysteresis) can be correlated with low rolling resistance when the compound is used in pneumatic vehicle tires. Table 1 Components Unit 1(V) 2(V) 3(V) 4(V) 5(V) 6(E) Natural rubber phr 30 30 30 30 30 30 BR ^a phr 70 70 70 70 70 70 Soot N339 ^b phr 70 70 0 62 0 0 Soot N351 ^c phr 0 0 66.5 0 57 57 Silica ^d phrphr 0 0 66.50 10 5710 5710 Silane coupling ^agent phr 0 0 0 0.72 0.72 0.72 plasticizer oil phr 5 5 5 5 5 5 zinc oxide phr 3 3 3 3 3 3 Stearic acid phr 2 2 2 2 2 2 Anti-aging agents phr 3 3 3 3 3 3 Ozone protection wax phr 2 2 2 2 2 2 Adhesive resin phr 5 5 5 5 5 5 TBBS ^f phr 2.5 4.3 2.5 3.5 3.5 5.3 sulfur phr 2.5 1.01 2.5 2.5 2.5 1.01 Characteristics Network node distance nm 4.2 3.7 3.0 3.7 3.6 3.8 Shore hardness at RT ShoreA 73.6 72.3 75.8 75.0 73.9 73.3 Rebound load at 70 °C % 58.6 57.8 64.0 59.7 62.8 61.2 Elongation at break (unweighted) % 225 208 153 204 211 226 Elongation at break (aged) % 106 151 95 93 104 138 Fatigue crack resistance (untreated) kC 69 101 8 25 38 87 Fatigue crack resistance (aged) kC 14 20 1 15 5 70 ^a high-cis polybutadiene rubber ^b Carbon black N339, iodine value: 90 g/kg ^c Carbon black N351, iodine value: 68 g/kg ^d Ultrasil ^® VN3, Evonik, nitrogen surface area = 180 m ² /g, CTAB 165 m ² /g ^e TESPD (3,3'-bis(triethoxysilylpropyl)disulfide), Si266, Evonik ^f N-tert-butyl-2-benzothiazylsulfenamide

The data in Table 1 demonstrate the effects of the individual measures: efficient vulcanization system only (2(V)), carbon black with a medium iodine number only (3(V)), silica with a silane coupling agent only (4(V)), and the combined measure of carbon black with a medium iodine number and silica with a silane coupling agent (5(V)). None of the comparison compounds simultaneously achieves the task of high durability even after aging (as evidenced by the elongation at break values) and low rolling resistance (derivable from the rebound resilience values at 70 °C).

Only the special compound 6(E) can resolve this conflict in a surprising way. Rebound resilience at 70 °C and elongation at break with and without aging behave to a degree that far exceeds the expected effects of the respective individual measures.

A significant improvement in durability is also evident in the significantly improved fatigue crack resistance, especially after aging. The sample from the special compound 6(E) unexpectedly withstood significantly more load cycles than all other samples after aging at 70 kC.

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

• EP 3632975A1 [0008]
• WO 2020065175A1 [0009]
• WO 99/09036 [0027]
• WO 2008/083241 A1 [0027]
• WO 2008/083242 A1 [0027]
• WO 2008/083243 A1 [0027]
• WO 2008/083244 A1 [0027]
• US 20080161477 A1 [0027]
• EP 2 114 961 B1 [0027]

Claims (11)

A sulfur-crosslinkable rubber mixture, particularly for the flange profile of vehicle tires, comprising at least the following components: - at least one diene rubber, - 40 to 90 phr (parts by weight, based on 100 parts by weight of the total rubber in the mixture) of at least one carbon black, wherein the carbon black or carbon blacks have an average iodine number according to ASTM D 1510 of 55 to 80 g/kg, - 5 to 20 phr of at least one silica, - at least one silane coupling agent, and - an efficient vulcanization system containing at least one vulcanization accelerator and elemental sulfur, wherein the mass ratio of vulcanization accelerator to sulfur is 8:1 to 3:1. Sulphur-curable rubber compound according to Claim 1 , characterized in that it contains 50 to 80 phr of at least one carbon black, the carbon black or carbon blacks having or having on average an iodine number according to ASTM D 1510 of 55 to 80 g/kg. Sulphur-curable rubber compound according to Claim 1 or 2 , characterized in that it contains silica produced from rice husk ash (“rice husk ash silica” (RHAS)). Sulfur-crosslinkable rubber mixture according to at least one of the preceding claims, characterized in that it contains 1 - 15 phf (parts by weight, based on 100 parts by weight of silica) of at least one silane coupling agent. Sulfur-crosslinkable rubber mixture according to at least one of the preceding claims, characterized in that the mass ratio of vulcanization accelerator to sulfur is 7:1 to 3:1, preferably 6:1 to 3.5:1. Sulfur-crosslinkable rubber mixture according to at least one of the preceding claims, characterized in that the vulcanization accelerator(s) is/are selected from the group consisting of mercapto accelerators, sulfenamide accelerators, sulfenimide accelerators and guanidine accelerators. Sulfur-crosslinkable rubber mixture according to at least one of the preceding claims, characterized in that it contains at least TBSI (N-tert-butyl-2-benzothiazolesulfenimide and/or TBBS (N-tert-butyl-2-benzothiazylsulfenamide) and/or DCBS (N,N-dicyclohexyl-2-benzothiazolesulfenamide) and/or CBS (N-cyclohexyl-2-benzothiazolesulfenamide) as vulcanization accelerators. Sulfur-crosslinkable rubber mixture according to at least one of the preceding claims, characterized in that it contains 0.5 to 1.5 phr of sulfur. Sulfur-crosslinkable rubber mixture according to at least one of the preceding claims, characterized in that it contains - 20 to 50 phr of natural rubber (NR) and - 50 to 80 phr of at least one butadiene rubber (BR). Vehicle tyres with at least one component made of a sulphur-vulcanised rubber mixture according to one of the Claims 1 until 9 consists. Vehicle tires, in particular pneumatic vehicle tires, according to Claim 10 , whose horn profile is made of a sulphur-crosslinked rubber mixture according to one of the Claims 1 until 9 consists.