Rubber compound, its use, and vulcanized product

Abstract

Rubber compound for the manufacture of vehicle tires containing at least the following components: - 50 to 100 phr of at least one styrene-butadiene rubber and - 0 to 50 phr of at least one other diene rubber and - 40 to 130 phr of at least one soot and - 0.25 to 0.95 phr sulfur and - 1 to 3 phr N-tert.Butyl-2-benzothiazylsulfenamide (TBBS) and - 1 to 4 phr Tetrabenzylthiuram disulfide (TBzTD), characterized in that the rubber mixture contains 0.01 to 0.15 phr of the accelerator 2-mercaptobenzothiazole.

Description

[0001] The invention relates to a rubber mixture, in particular for treads of vehicle tires, its use, and a vulcanized product.

[0002] The subject matter of the invention is defined in the appended claims.

[0003] The rubber composition of the tread largely determines the driving characteristics of a tire, especially a pneumatic vehicle tire. In this document, the term vehicle tire refers to pneumatic vehicle tires, solid rubber tires, and two-wheel tires.

[0004] Likewise, the rubber compounds used in belts, hoses, and straps, especially in areas subject to high mechanical stress, are largely responsible for the stability and durability of these rubber products. Therefore, these rubber compounds for pneumatic vehicle tires, belts, and hoses are subject to very high demands.

[0005] To influence the compound and vulcanizate properties, a wide variety of additives are added to the mixtures and / or special polymers are used. Examples of additives include fillers (e.g., carbon black), plasticizers, anti-aging agents, and crosslinking systems made of sulfur, accelerators, and activators. However, if one property is improved by varying the mixture, this is often accompanied by a deterioration of another property, resulting in certain conflicting objectives. In compounds for vehicle tire treads, such conflicting objectives exist, for example, with regard to abrasion behavior and increased heat buildup, which leads to poorer rebound resilience and, consequently, poorer rolling resistance.To resolve these conflicting objectives, variations in the mix composition are used, in particular the modification or adaptation of the aggregates, in order to achieve an improved level of the properties that usually behave contrary to one another.

[0006] An important group of additives that influences the vulcanization rate and the physical properties of the vulcanizates is the group of vulcanization accelerators. For the vulcanization of rubber compounds used in the production of vehicle tires, various vulcanization accelerator groups known to those skilled in the art are available. These can also be used in combination, potentially resulting in synergistic effects.

[0007] The vulcanization accelerators serve to activate the sulfur used as a vulcanizing agent. The dosage of sulfur and vulcanization accelerator is individually adjusted to the desired properties of the tire rubber compound. These desired properties are determined by the network formed during vulcanization, e.g., between the polymer and fillers, so the type and degree of crosslinking can be considered significant with regard to the physical properties of the vulcanizates.

[0008] The state of the art regarding vulcanization and crosslinking systems will now be described in more detail using the following publications: DE 2536674 A1 describes a crosslinkable rubber mixture containing silicate fillers and a process for crosslinking. This very generally claims a crosslinkable rubber mixture containing at least 1 to 300 parts by weight of a silicate filler, 0 to 300 parts by weight of carbon black, at least one vulcanization accelerator known per se for rubber vulcanization in amounts of 0.02 to 10 parts by weight, and at least one organosilane.

[0009] DE 4036420 A1 discloses vulcanizates for technical rubber articles without nitrosamine toxicity, which contain a medium or low activity carbon black in combination with special thiuram and mercapto vulcanizing agents, whereby small amounts of elemental sulfur are still required for vulcanization or crosslinking.

[0010] EP 0530590 B1 discloses a process for producing diene rubber vulcanizates with very high aging and reversion stability. The diene rubber vulcanizates contain 1 to 2.5 parts of mercapto accelerator, or 0.2 to 0.8 parts of sulfenamide accelerator, or 0.3 to 2.5 parts of mercapto accelerator and 0.1 to 0.8 parts of sulfenamide accelerator. 0.1 to 0.2 parts of sulfur are also added per 100 parts of rubber, preferably an oil-extended diene rubber.

[0011] WO 2009 / 147006 A1 and US 2009 / 0306267 A1 disclose a rubber compound containing a vulcanization system consisting of sulfur donors and sulfur and vulcanization accelerators, as well as predominantly silica as a filler. Such a rubber compound exhibits improved abrasion properties, but the resulting compromised rolling resistance properties deteriorate.

[0012] DE 69330261 T2 relates to the vulcanization of diene elastomers, in particular to an accelerator composition for the vulcanization of diene elastomers and to a process for vulcanization therewith.

[0013] The present invention is based on the object of providing a rubber mixture which, compared to the prior art, has a further improvement in abrasion behavior and, at the same time, improved wet braking properties, without the other tire properties, such as, in particular, the rolling resistance behavior, being significantly adversely affected.

[0014] This task is solved by a rubber mixture that contains at least the following components: - 50 to 100 phr of at least one styrene-butadiene rubber and - 0 to 50 phr of at least one other diene rubber and - 40 to 130 phr of at least one carbon black and - 0.25 to 0.95 phr sulfur and - 1 to 3 phr N-tert.butyl-2-benzothiazylsulfenamide (TBBS) and - 1 to 4 phr tetrabenzylthiuram disulfide (TBzTD) and - 0.01 to 0.15 phr of the accelerator 2-mercaptobenzothiazole.

[0015] Surprisingly, the rubber compound exhibits improved wet grip properties and improved abrasion behavior compared to the prior art due to the combination of the above-mentioned components, whereby the rubber compound in particular has a higher abrasion resistance and thus shows a lower material loss under corresponding stress compared to the prior art.

[0016] According to the invention, the rubber mixture contains at least one styrene-butadiene rubber,

[0017] The styrene content of the styrene-butadiene rubber is 5 to 70 wt.%, preferably 12 to 70 wt.%, based on the total mass of the styrene-butadiene rubber.

[0018] The solution-polymerized styrene-butadiene rubber preferably has a vinyl content of 5 to 70 wt.%, particularly preferably 10 to 70 wt.%.

[0019] The determination of the styrene content and the vinyl content of the polymers discussed in the present invention is carried out by means of 13 C-NMR (solvent: deuterochloroform CDCl3; NMR: nuclear magnetic resonance) and comparison with infrared spectrometry (IR; FT-IR spectrometer from Nicolet, KBr window 25 mm diameter x 5 mm, 80 mg sample in 5 mL 1,2-dichlorobenzene). The determination of the glass transition temperature (T g) is carried out using Dynamic Scanning Calorimetry (DSC according to DIN 53765: 1994-03 or ISO 11357-2: 1999-03, calibrated DSC with low temperature device, calibration according to device type and manufacturer's specifications, sample in an aluminum crucible with an aluminum lid, cooling to temperatures lower than -120 °C at 10 °C / min).

[0020] 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.

[0021] The styrene-butadiene rubber can be produced by emulsion polymerization or solvent polymerization. It is preferably an ESBR or an ESBR blend.

[0022] The rubber mixture according to the invention contains at least one styrene-butadiene rubber in amounts of 50 to 100 phr, preferably 80 to 100 phr.

[0023] The rubber mixture according to the invention also contains 0 to 50 phr of at least one further rubber.

[0024] The at least one further rubber is selected from the group consisting of natural polyisoprene and / or synthetic polyisoprene and / or butadiene rubber and / or solution-polymerized styrene-butadiene rubber and / or emulsion-polymerized styrene-butadiene rubber and / or liquid rubbers and / or halobutyl rubber and / or polynorbornene and / or isoprene-isobutylene copolymer and / or ethylene-propylene-diene rubber and / or nitrile rubber and / or chloroprene rubber and / or acrylate rubber and / or fluororubber and / or silicone rubber and / or polysulfide rubber and / or epichlorohydrin rubber and / or styrene-isoprene-butadiene terpolymer and / or hydrogenated acrylonitrile-butadiene rubber and / or Isoprene-butadiene copolymer and / or hydrogenated styrene-butadiene rubber.

[0025] 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.

[0026] Particularly preferably, the additional diene rubber is selected from the group consisting of synthetic polyisoprene, natural polyisoprene, and polybutadiene. The additional diene rubber is preferably natural polyisoprene. This achieves particularly good processability (extrudability, miscibility, etc.) of the rubber mixture according to the invention.

[0027] According to an advantageous embodiment of the invention, the rubber mixture contains 1 to 10 phr, preferably 2 to 6 phr of at least one natural polyisoprene.

[0028] The rubber mixture according to the invention contains 40 to 130 phr, preferably 70 to 130 phr, particularly preferably 70 to 110 phr, and most particularly preferably 80 to 90 phr, of at least one carbon black as filler. All types of carbon black known to the person skilled in the art are conceivable.

[0029] However, preference is given to using a carbon black having an iodine adsorption number according to ASTM D 1510 of 80 to 180 g / kg, preferably 80 to 140 g / kg, particularly preferably 80 to 100 kg / g, and a DBP number according to ASTM D 2414 of 115 to 200 ml / 100 g, preferably 118 to 200 ml / 100 g, particularly preferably 118 to 150 ml / 100 g. Thus, preference is given to using a so-called high-activity carbon black whose DBP number is greater than 118 ml / 100 g. This achieves particularly good abrasion and wet grip properties for use in vehicle tires, while the other properties, such as rolling resistance and dry braking, remain at approximately the same level and / or are even improved.

[0030] In addition to carbon black, the rubber mixture according to the invention may also contain other known polar and / or non-polar fillers.

[0031] Preferably, the rubber mixture according to the invention contains carbon black as the sole filler or as the main filler, meaning that the amount of carbon black is significantly greater than the amount of any other fillers present. If a further filler is present in addition to carbon black, this is preferably silica. Thus, it is also conceivable for the rubber mixture according to the invention to contain carbon black and silica, such as 40 to 130 phr of carbon black in combination with 0.1 to 10 phr of silica.

[0032] The silicas can be those known to those skilled in the art and suitable as fillers for tire rubber compounds. However, it is particularly preferred to use a finely divided, precipitated silica with a nitrogen surface area (BET surface area) (according to DIN ISO 9277 and DIN 66132) of 35 to 350 m². 2 / g, preferably from 35 to 260 m 2 / g, particularly preferably from 100 to 260 m 2 / g and most preferably from 130 to 235 m 2 / g, and a CTAB surface area (according to ASTM D 3765) of 30 to 400 m 2 / g, preferably from 30 to 250 m 2 / g, particularly preferably from 100 to 250 m 2 / g and most preferably from 125 to 230 m 2 / g. Such silicas, for example, lead to particularly good physical properties of the vulcanizates in rubber compounds for tire treads. Furthermore, they can offer advantages in compound processing by reducing mixing times while maintaining consistent product properties, leading to improved productivity. Thus, both Ultrasil® VN3 (trade name) from Evonik and highly dispersible silicas, so-called HD silicas (e.g., Zeosil® 1165 MP from Rhodia), can be used as silicas.

[0033] Silane coupling agents can be used in rubber compounds to improve processability and to bond the silica and any other polar fillers present to the diene rubber. The silane coupling agents react with the surface silanol groups of the silica or other polar groups during mixing of the rubber or rubber compound (in situ) or even before the filler is added to the rubber as a pretreatment (premodification). Silane coupling agents that can be used are any silane coupling agents known to those skilled in the art for use in rubber compounds.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, -NH2, or -S. x - (with x = 2 to 8).

[0034] 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 (TESPD), 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 Evonik).

[0035] Preference is given to using a silane mixture which contains 40 to 100% by weight of disulfides, more preferably 55 to 85% by weight of disulfides, and most preferably 60 to 80% by weight of disulfides. Such a mixture is available, for example, under the trade name Si 261® from Evonik, which is described, for example, in DE 102006004062 A1. Blocked mercaptosilanes, as known, for example, from WO 99 / 09036, can also be used as silane coupling agents. Silanes as described in WO 2008 / 083241 A1, WO 2008 / 083242 A1, WO 2008 / 083243 A1 and WO 2008 / 083244 A1 can also be used. The following can be used, for example: B. Silanes, which are marketed under the name NXT in various variants by Momentive, USA, or those which are marketed under the name VP Si 363® by Evonik Industries.

[0036] However, the rubber mixture is particularly preferably free of additional fillers, meaning that in this preferred embodiment, the rubber mixture contains 0 phr of an additional filler. Thus, in this embodiment, no addition of a second filler is necessary.

[0037] Zinc oxide is not considered a filler in the context of the present invention.

[0038] The rubber mixture may also contain 0 to 70 phr, preferably 0.1 to 60 phr, preferably 10 to 50 phr, of at least one plasticizer. This plasticizer is selected from the group consisting of mineral oils and / or synthetic plasticizers and / or fatty acids and / or fatty acid derivatives and / or resins and / or factices and / or glycerides and / or terpenes and / or biomass-to-liquid oils (BTL oils) and / or rubber-to-liquid oils (RTL oils) and / or liquid polymers, with mineral oils being particularly preferred.

[0039] When using mineral oil, this is preferably selected from the group consisting of DAE (Distilled Aromatic Extracts) and / or RAE (Residual Aromatic Extract) and / or TDAE (Treated Distilled Aromatic Extracts) and / or MES (Mild Extracted Solvents) and / or naphthenic oil.

[0040] Furthermore, the rubber mixture according to the invention may contain conventional additives in conventional parts by weight. These additives include 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), 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), b) Activators, such as zinc oxide and fatty acids (e.g. stearic acid), c) waxes, d) resins, in particular adhesive resins, and e) mastication aids such as 2,2'-dibenzamidodiphenyl disulfide (DBD).

[0041] In particular, when using the rubber mixture according to the invention for the inner components of a tire or a technical rubber article which have direct contact with existing reinforcements, a suitable adhesive system, often in the form of adhesive resins, is generally added to the rubber mixture.

[0042] 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.

[0043] The total amount of other additives also contains 0.1 to 10 phr, preferably 0.2 to 8 phr, particularly preferably 0.2 to 4 phr, of zinc oxide (ZnO).

[0044] This can be any type of zinc oxide known to the person skilled in the art, such as ZnO granules or powder. The zinc oxide commonly used usually has a BET surface area of ​​less than 10 m 2 / g. However, so-called nano-zinc oxide with a BET surface area of ​​10 to 60 m 2 / g can be used.

[0045] According to the invention, the vulcanization is carried out in the presence of comparatively small amounts of elemental sulfur in combination with tetrabenzylthiuram disulfide (TBzTD) as sulfur donor with the aid of at least N-tert-butyl-2-benzothiazylsulfenamide (TBBS) as vulcanization accelerator.

[0046] The amount of added elemental sulfur, also called free sulfur, is 0.25 to 0.95 phr, preferably 0.35 to 0.7 phr, particularly preferably 0.35 to 0.6 phr.

[0047] The amount of added sulfur donor TBzTD is 1 to 4 phr, preferably 1.5 to 4 phr, particularly preferably 1.5 to 3 phr.

[0048] The amount of added N-tert.butyl-2-benzothiazylsulfenamide (TBBS) as vulcanization accelerator is 1 to 3 phr, preferably 1 to 2.5 phr, particularly preferably 1.3 to 2.4 phr.

[0049] According to the invention, the rubber mixture of the invention contains comparatively small amounts of the accelerator 2-mercaptobenzothiazole, at 0.01 to 0.15 phr. This results in economically viable heating kinetics of the rubber mixture of the invention during vulcanization.

[0050] According to a preferred embodiment of the invention, several accelerators are contained in the rubber mixture.

[0051] The use of the accelerator TBBS in combination with diphenylguanidine (DPG) is particularly preferred.

[0052] The rubber compound according to the invention is produced according to the process customary 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 final compound is created by adding the vulcanization system, consisting of sulfur and sulfur donors, as well as the aforementioned accelerators, in a final mixing stage. The final compound is further processed, for example, by an extrusion process, and molded into the appropriate shape.

[0053] A further object of the present invention is to provide a vehicle tire characterized by improved abrasion behavior and improved wet grip properties. This object is achieved by the vehicle tire containing the rubber mixture according to the invention as described above in at least one component. All of the above-mentioned statements regarding the components and their features apply.

[0054] The component is preferably a tread. As is known to those skilled in the art, the abrasion resistance and wet grip properties of vehicle tires depend significantly on the abrasion behavior of the tread's rubber compound. The vehicle tire is preferably a pneumatic vehicle tire, particularly preferably for passenger cars.

[0055] A further object of the present invention is to improve the abrasion behavior and wet grip properties of vehicle tires. This object is achieved according to the invention by the use of the above-described rubber mixture with all embodiments and features in vehicle tires.

[0056] The invention will now be explained in more detail using comparative and exemplary embodiments, which are summarized in Table 1.

[0057] The comparison mixtures are marked with V, the mixtures according to the invention are marked with E.

[0058] The compounds were manufactured under standard conditions in two stages in a tangential internal mixer. Test specimens were prepared from all compounds by optimal vulcanization under pressure at 160 °C. These specimens were used to determine material properties typical for the rubber industry using the test methods described below. • Shore A hardness at room temperature (RT) according to DIN ISO 7619-1 • Rebound resilience at room temperature (RT) according to DIN 53 512

[0059] Furthermore, the comparison mixtures and the rubber mixtures according to the invention were installed in the tread of vehicle tires according to a procedure known in the prior art by extrusion, application to a respective green tire and subsequent vulcanization of the green tire.

[0060] The vehicle tires were then tested for the following properties: Furthermore, pneumatic vehicle tires measuring 205 / 55 R16 with a tread made of the respective compounds were manufactured, and tests were conducted on the tires for wet braking on asphalt (low µ) and asphalt (high µ), as well as for braking on dry asphalt (dry braking), and for rolling resistance. Furthermore, wear was measured via the weight loss of the respective tires.

[0061] The determined values ​​were converted into performance, with the reference mixture V1 being standardized to 100% performance for each tested property. All other mixture performances refer to this reference mixture V1. Values ​​< 100% indicate a deterioration in properties, while values ​​> 100% represent an improvement. Table 1 Components Unit V1 E1 V2 E2 V3 E3 SBR a) phr 26 26 26 26 26 26 SBR b) phr 96 96 96 96 96 96 NR: TSR phr 4 4 4 4 4 4 Soot N339 phr 85 85 85 85 85 85 RAE phr 22,5 22,5 13,5 13,5 22,5 22,5 Anti-aging agents phr 5 5 5 5 5 5 Stearic acid phr 1 1 1 1 1 1 ZnO phr 2 2 2 2 2 2 Accelerator CBS phr 1,4 - 1,12 - 1,12 - Accelerator TBBS phr - 2,1 - 1,58 - 1,58 Accelerator DPG phr 0,5 0,5 0,5 0,5 0,5 0,5 Accelerator MBT phr 0,1 0,1 0,1 0,1 0,1 0,1 TBzTD phr - 2,32 - 1,75 - 1,75 sulfur phr 2,1 0,56 1,68 0,42 1,68 0,42 Physics. Properties Shore hardness RT Shore A 58 55 59 59 55 54 Rebound load at RT % 25 24,6 25,2 25,1 24,4 24,6 Tire results Wet braking low µ % 100 105 99 104 101 107 Wet braking high µ % 100 111 103 108 104 108 Dry braking % 100 100 100 101 103 104 Rolling resistance % 100 100 100 98 100 99 Abrasion % 100 110 111 118 113 132 Substances used from Table 1: a) SBR: Styrene-butadiene rubber: SBR 1500, ESBR INTOL 1500, Polimeri Europa, non-oil extended. b) SBR: Styrene-butadiene rubber: SBR 1723, ESBR INTOL 1723, Polimeri Europa, oil-extended

[0062] As shown in Table 1, the inventive rubber compounds E1, E2, and E3 exhibit significantly improved wet braking properties and significantly higher abrasion resistance in tire tests compared to their respective reference compounds V1, V2, and V3. At the same time, rolling resistance and dry braking are not significantly adversely affected.

[0063] Thus, with the rubber mixtures according to the invention it is possible to produce vehicle tires, in particular pneumatic vehicle tires, which have improved abrasion behavior and improved wet braking properties without showing disadvantages with regard to other requirements, such as rolling resistance and dry braking.

Claims

[1] Rubber mixture for the manufacture of vehicle tires containing at least the following components: - 50 to 100 phr of at least one styrene-butadiene rubber and - 0 to 50 phr of at least one other diene rubber and - 40 to 130 phr of at least one carbon black and - 0.25 to 0.95 phr sulfur and - 1 to 3 phr N-tert.butyl-2-benzothiazylsulfenamide (TBBS) and - 1 to 4 phr tetrabenzylthiuram disulfide (TBzTD), characterized by that the rubber compound contains 0.01 to 0.15 phr of the accelerator 2-mercaptobenzothiazole. [2] Rubber mixture according to claim 1, characterized by that the carbon black has a DBP number according to ASTM D 2414 of 115 to 200 ml / 100 g. [3] Rubber mixture according to one of claims 1 or 2, characterized by that the rubber compound is free of silica. [4] Rubber mixture according to one of claims 1 to 3, characterized bythat it contains 80 to 100 phr of at least one styrene-butadiene rubber. [5] Vulcanized product, in particular vehicle tires, producible by vulcanization of a rubber mixture according to one of the preceding claims. [6] Use of a rubber mixture according to one of claims 1 to 4 in the production of vehicle tires for improving the abrasion behavior and the wet grip properties of vehicle tires.