Sulfur-linkable rubber compound

Description

[0001] The invention relates to a vehicle pneumatic tire comprising a sulfur-crosslinked rubber compound for textile reinforcement, which contains at least one polyisoprene, at least one further diene elastomer made of at least one conjugated diene and optionally one or more vinylaromatic compounds with a vinylaromatic compound content of 0 to 50 wt.%, at least one silica, at least one silane coupling agent and an adhesion system.

[0002] Sulfur-curable rubber compounds for textile reinforcements are often based on a polymer blend of natural rubber and polybutadiene. In sulfur-curable rubber compounds used as rubber compounds for textile reinforcements such as rayon, polyamide, and polyester, adhesion systems such as so-called methylene acceptor-methylene donor pairs are typically employed to achieve, in addition to bonding via the sulfur network, a bond for adhesive impregnation of the textile reinforcement, usually an RFL dip. The RFL dip contains resorcinol and formaldehyde or their precondensates.

[0003] In tires, compounds for the rubber coating of textile reinforcement elements typically contain carbon black as an inexpensive filler. These rubber compounds must ensure sufficient and durable adhesion to the textile reinforcement elements, and this adhesion must withstand high dynamic and thermal loads.

[0004] In recent years, reducing tire rolling resistance has become increasingly important. One well-known approach is to use low-hysteresis, and therefore low-rolling-resistance, rubber compounds in the tread. Measures used to reduce the rolling resistance of a rubber compound include, for example, the use of silica instead of carbon black as a filler.

[0005] Thus, EP 2159074 A1, DE 10 2018 209559 A1, EP 2 738 014 A2, US 2016 / 052340 A1, DE 10 2015 210424 A1, EP 3 156 443 A1, DE 10 2015 210422 A1 and DE 10 2016 201053 disclose rubber compounds for treads of vehicle tires that are intended to have special properties such as low rolling resistance and / or low abrasion and / or good wet grip.

[0006] In DE 696 02 212 T2, it was proposed to reduce the rolling resistance of vehicle tires by using a mixture for the rubber lining of the metallic reinforcing elements of the belt. This mixture contains natural rubber and a silica with a specific CTAB surface area of ​​less than 125 m² / g. In addition to reducing rolling resistance, this mixture also exhibits a lower Mooney viscosity compared to mixtures containing a silica with a larger specific surface area.

[0007] German patent application DE 10 2011 053 450 A1 proposes a rubber compound for the rubber coating of reinforcing elements in tires, in particular metallic reinforcing elements, which contains natural rubber, polybutadiene and 55 phr of the silica Zeosil® < 1115 MP with a CTAB surface area of ​​105 m² / g. The compound exhibits improved resistance to cracking.

[0008] US patent 20100032071 A1 discloses a rubber compound for the rubber lining of a tire carcass, containing natural rubber, up to 30 phr of a styrene-butadiene copolymer, up to 40 phr of silica, and a silane coupling agent. In combination with other compounds in the tire, the compound is said to exhibit low rolling resistance and high tire strength.

[0009] US patent 2008009570 A1 describes rubber compounds containing natural rubber, up to 40 phr of a modified styrene-butadiene copolymer, up to 46 phr of silica, and an adhesion system. Tires made with these compounds are said to exhibit improved properties, such as fuel consumption and durability.

[0010] Further rubberizing compounds are described in DE 10 2011 055966 A1 and in EP 2 628 767 A1.

[0011] The invention is based on the objective of providing a rubber compound for the rubber coating of textile reinforcement carriers in vehicle pneumatic tires, which is characterized by improved fatigue resistance with simultaneously low rolling resistance when used in the tire.

[0012] The problem is solved according to the invention by the fact that the rubberizing mixture 25 to 55 phr (parts by weight, based on 100 parts by weight of the total rubbers in the mixture) of at least one polyisoprene, 45 to 75 phr of at least one further diene elastomer consisting of at least one conjugated diene and optionally one or more vinylaromatic compounds with a vinylaromatic compound content of 0 to 50 wt.%, 30 to 90 phr of at least one silica, at least one silane coupling agent and an adhesion system for rubber-textile bonding, the other diene elastomer is a styrene-butadiene copolymer.

[0013] The unit phr (parts per hundred parts of rubber by weight) used in this document is the standard unit of measurement for compound formulations in the rubber industry. The dosage of the individual substances by weight is always based on 100 parts by weight of the total mass of all rubbers present in the mixture. The mass of all rubbers present in the mixture adds up to 100.

[0014] The specific combination of components in the specified quantities surprisingly results in a significant improvement in fatigue resistance. Rolling resistance remains low when using this rubber compound to coat textile reinforcement elements in the tire, such as the carcass. At the same time, good adhesion between the rubber and the textile reinforcement element is ensured, which also contributes to good product durability.

[0015] The rubber compound contains 25 to 55 phr of at least one polyisoprene. This can be either cis-1,4-polyisoprene or 3,4-polyisoprene. However, the use of cis-1,4-polyisoprenes with a cis-1,4 content > 90 wt.% is preferred. Such polyisoprene can be obtained by stereospecific polymerization in solution (synthetic polyisoprene, IR). Natural rubber (NR) is also such a cis-1,4-polyisoprene, with a cis-1,4 content greater than 99 wt.%. Natural rubber 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 koksaghyz)).

[0016] Different types of polyisoprene can be used in the blend. Natural rubber is preferably used as the polyisoprene, as it yields the best results in terms of adhesion.

[0017] The rubber compound contains 45 to 75 phr of at least one additional diene elastomer consisting of at least one conjugated diene and optionally one or more vinylaromatic compounds with a vinylaromatic compound content of 0 to 50 wt.%. Diene elastomers include all rubbers with an unsaturated carbon chain that are at least partially derived from conjugated dienes. Several other diene elastomers of this type may also be used.

[0018] The rubber compound also contains a styrene-butadiene copolymer as a further diene elastomer. This can be either solution-polymerized styrene-butadiene rubber (SSBR) or emulsion-polymerized styrene-butadiene rubber (ESBR) with varying vinyl and styrene contents, and a mixture of at least one SSBR and at least one ESBR can also be used.

[0019] The other dienelastomers can be end-modified and / or functionalized along the polymer chains. The modifications can involve hydroxy groups, ethoxy groups, epoxy groups, siloxane groups, amino groups, aminosiloxane, carboxy groups, phthalocyanine groups, and / or silane sulfide groups. Other modifications and functionalizations known to a competent person are also possible. Metal atoms can be part of such functionalizations. Preferably, the other dienelastomer is functionalized at one chain end with an organosilyl group containing an amino group and / or an ammonium group, and at the other chain end with an amino group.

[0020] To further improve rolling resistance, it has proven advantageous to use a styrene-butadiene copolymer with a glass transition temperature (Tg) of less than -40 °C and a styrene content of at least 20 wt.%. The glass transition temperature (Tg) of the polymers is determined using Dynamic Scanning Calorimetry (DSC) according to DIN 53765: 1994-03 or ISO 11357-2: 1999-03 (calibrated DSC with low-temperature equipment, calibration according to instrument type and manufacturer's instructions, sample in an aluminum crucible with aluminum lid, cooling to temperatures below -120 °C at 10 °C / min). The styrene content is determined by 13< C-NMR (solvent: deuterochloroform CDCl 3 ; NMR: engl. "nuclear magnetic resonance") and comparison with data from infrared spectrometry (IR; FT-IR spectrometer of the company Nicolet, KBr window 25 mm diameter x 5 mm, 80 mg sample in 5 mL 1,2-dichlorobenzene).

[0021] In addition to the aforementioned rubbers, the rubberizing mixture may also contain other rubbers commonly used in the rubber industry, such as styrene-isoprene-butadiene terpolymer, butyl rubber, halobutyl rubber or ethylene propylene diene rubber (EPDM), which may also be modified.

[0022] The rubber compound contains 30 to 90 phr, preferably 50 to 70 phr, of at least one silica. Various silicas, including mixtures, can be used. It is preferred to use a finely dispersed, precipitated silica with a CTAB number (according to ASTM D 3765) of 30 to 350 m² / g. Both conventional silicas, such as Evonik's VN3 (trade name), and highly dispersible silicas, so-called HD silicas (e.g., Evonik's Ultrasil® < 7000), can be used.

[0023] To further improve the properties with regard to rolling resistance when used in tires, it has proven advantageous to use at least one silica whose CTAB number (according to ASTM D 3765) is less than 120 m² / g, preferably less than 100 m² / g.

[0024] In addition to silica, the rubber compound may also contain other fillers such as carbon black, aluminosilicates, kaolin, chalk, starch, magnesium oxide, titanium dioxide, rubber gels, fibers, carbon nanotubes, graphite, graphene and so-called "carbon-silica dual-phase fillers".

[0025] According to an advantageous embodiment of the invention, the rubberizing compound contains 5 to 50 phr of carbon black, wherein the ratio of silica to carbon black is 1:5 to 5:1. Conventional carbon blacks with an iodine adsorption number according to ASTM D 1510 of 30 to 250 g / kg can be used. The simultaneous use of silica and carbon black in the rubberizing compound results in improved adhesion to the textile reinforcement and further enhanced fatigue resistance.

[0026] The rubber compound contains an adhesive system for rubber-textile bonding in typical quantities of 1 to 10 phr. The adhesive system is preferably a methylene acceptor-methylene donor pair. The methylene donor can be, for example, hexamethoxymethylmelamine (HMMM) or hexamethylenetetramine (HMT). The methylene acceptor can be, for example, resorcinol, phenol, a resorcinol, phenol, or acetone derivative, or a novolac resin. During the vulcanization process, a resin is formed from the methylene donor and the methylene acceptor. In addition to the sulfur network, a second network based on methylene donor and methylene acceptor forms, which interacts adhesively with the RFL dip of the textile reinforcement.

[0027] To improve processability and bond the silica to the rubber, silane coupling agents can be added to the rubber compound. These silane coupling agents react with the surface silanol groups of the silica or other polar groups during the mixing of the rubber or rubber compound (in situ) or even before the addition of the filler to the rubber as a pretreatment (pre-modification). Any silane coupling agents known to those skilled in the art for use in rubber compounds can be used. Such coupling agents known from the prior art are bifunctional organosilanes that have at least one alkoxy, cycloalkoxy, or phenoxy group as a leaving group on the silicon atom and possess, as a further functionality, a group that, if necessary after cleavage, can undergo a chemical reaction with the double bonds of the polymer.The latter group can include, for example, the following chemical groups: -SCN, -SH, -NH₂, or -S⁻ (where x = 2-8). Silane coupling agents can thus include, 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 the sulfides with 1 to 8 sulfur atoms and varying concentrations of the different sulfides. The silane coupling agents can also be added as a mixture with carbon black, such as TESPT on carbon black (trade name X50S from Evonik). Blocked mercaptosilanes, such as those found in... Silanes known from WO 99 / 09036, for example, can 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.Suitable materials include silanes marketed under the name NXT in various formulations by Momentive, USA, or those marketed under the name VP Si 363 by Evonik Industries. Also suitable are so-called "silated core polysulfides" (SCPs), which are described, for example, in US 20080161477 A1 and EP 2 114 961 B1.

[0028] Furthermore, the rubber compound according to the invention can contain conventional additives in conventional proportions by weight. These additives include plasticizers, such as glycerides, Faktisse, hydrocarbon resins, aromatic, naphthenic or paraffinic mineral oil plasticizers (e.g., MES (mild extraction solvate) or TDAE (treated distillate aromatic extract)), oils based on renewable raw materials (such as rapeseed oil, terpene oils (e.g., orange oils) or Faktisse), so-called BTL oils (as disclosed in DE 10 2008 037714 A1) or liquid polymers (such as liquid polybutadiene)); antioxidants, such as... B. N-Phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), N-Isopropyl-N'-phenyl-p-phenylenediamine (IPPD), 2,2,4-Trimethyl-1,2-dihydroquinoline (TMQ) and other substances, as known, for example, from J. Schnetger, Lexikon der Kautschuktechnik, 2nd edition, Hüthig Buch Verlag, Heidelberg, 1991, pp. 42-48, activators such as zinc oxide and fatty acids (e.g.B. stearic acid), waxes, adhesive resins, such as hydrocarbon resins and rosin, and masticating aids, such as 2,2'-dibenzamidodiphenyl disulfide (DBD).

[0029] Vulcanization is carried out in the presence of sulfur and / or sulfur donors, some of which can also act as vulcanization accelerators. Sulfur or sulfur donors are added to the rubber compound in the final mixing step in quantities customary by those skilled in the art (0.4 to 8 phr). To improve adhesion, particularly to textile reinforcements, the rubber compound preferably contains less than 5 phr of sulfur.

[0030] Furthermore, the rubber compound may contain vulcanization-modifying substances such as vulcanization accelerators, vulcanization retarders, and vulcanization activators in typical quantities to control the required time and / or temperature of vulcanization and to improve the vulcanizate properties. The vulcanization accelerators may be selected, for example, from the following accelerator groups: thiazole accelerators such as 2-mercaptobenzothiazole, sulfenamide accelerators such as benzothiazyl-2-cyclohexylsulfenamide (CBS), benzothiazyl-2-tert-butylsulfenamide (TBBS), and benzothiazyl-2-dicyclohexylsulfenamide (DCBS), guanidine accelerators such as N,N'-diphenylguanidine (DPG), dithiocarbamate accelerators such as zinc dibenzyldithiocarbamate, disulfides, and thiophosphates. The accelerators can also be used in combination with each other, which can result in synergistic effects.

[0031] Other network-forming systems, such as Vulcuren®, Duralink®, Perkalink® or systems as described in WO 2010 / 049261 A2, can also be used in the rubber compound.

[0032] The vulcanization accelerators can be used in typical quantities. According to an advantageous embodiment of the invention, the rubber compound contains 0.8 to 1.5 phr of benzothiazolyl-2-dicyclohexylsulfenamide (DCBS) as a vulcanization accelerator and less than 0.5 phr of other vulcanization accelerators. Using DCBS as a vulcanization accelerator results in a further improvement in adhesion.

[0033] The rubber compound according to the invention is produced in a conventional manner, whereby a base mixture containing all components except the vulcanization system (sulfur and vulcanization-influencing substances) is first produced in one or more mixing stages, and the finished mixture is then produced by adding the vulcanization system. The mixture is then further processed.

[0034] The rubber compound is used in vehicle tires. The textile reinforcements can consist of, for example, aramid, polyester, polyamide, rayon, or hybrid cords made from these materials.

[0035] The rubber compound can be used for rubberizing a wide variety of tire components, such as the bead core, bead covers, bead reinforcements, belt, carcass, or belt bands. It can also be used for other compounds closely related to structural components, such as bead liners, squeegees, belt edge pads, shoulder pads, tread base plates, or other body compounds. Furthermore, several components within a single tire can be provided with the compound according to the invention. The production of the pneumatic tires according to the invention is carried out using a method known to those skilled in the art.

[0036] Preferably, the rubber compound is used as carcass rubber, where the good fatigue resistance leads to a long service life of a vehicle pneumatic tire with low rolling resistance.

[0037] Alternatively or additionally, the rubber compound can also be used as a bandage rubber compound, which in turn positively influences the service life of the vehicle pneumatic tire.

[0038] The invention will now be explained in more detail with reference to the table below.

[0039] Table 1 shows mixtures for the rubber coating of textile reinforcement carriers in vehicle pneumatic tires.

[0040] In the mixtures listed in Table 1, the polymers and fillers were varied in terms of quantity and type. The comparison mixtures are marked with V, and the mixtures according to the invention are marked with E.

[0041] The mixture was prepared under normal conditions by producing a base mixture and then the finished mixture in a laboratory tangential mixer.

[0042] Test specimens were produced from the mixtures by vulcanization for 20 minutes under pressure at 160 °C, and material properties typical for the rubber industry were determined using these test specimens with the test procedures specified below. Shore A hardness at room temperature according to DIN ISO 7619-1; rebound elasticity at 70 °C according to DIN 53 512; maximum loss factor tan δ max from dynamic-mechanical measurement at 55 °C according to DIN 53 513, strain sweep.

[0043] Furthermore, adhesion tests, so-called peel tests, were performed with the mixtures from Table 1 according to ISO 36:2011 (E) and DIN 53 530, with evaluation according to DIN ISO 6133, on unaged polyester textile reinforcement cords. For this purpose, polyester reinforcement cords (1440 x 2 dtex) treated with RFL-Dip were coated with the unvulcanized rubber mixtures and then vulcanized for 10 minutes at 170 °C. Subsequently, the force required to peel the mixture from the cords was determined, and the coverage of the cords with the mixture after peeling was visually assessed (5: complete coverage, 0: no coverage). For the peeling force, the value of mixture 1(V) was set to 100%; the values ​​of the other mixtures were referenced to mixture 1(V).

[0044] Fatigue crack resistance was also assessed using the mixtures listed in Table 1. Monsanto performed fatigue-to-failure tests based on ASTM D4482 at 101% strain and room temperature. The results are reported in kilocycles (kC). Table 1 Components Unit 1(V) 2(V) 3(V) 4(E) 5(E) natural rubber phr 50 100 50 50 50 Polybutadiene a)< phr - - 50 - - Styrene-butadiene copolymer b)< phr 50 - - 50 50 Carbon black N660 phr 65 - 65 - 32,5 Silica c)< phr - 65 - 65 32,5 Plasticizers, anti-aging agents. phr 17 17 17 17 17 Vulcanization activators phr 4 4 4 4 4 Silane coupling agent phr - 2,5 2,5 2,5 1,3 methylene acceptor d)< phr 1,6 1,6 1,6 1,6 1,6 Methylene donor e)< phr 2 2 2 2 2 accelerator phr 1 1,9 1,9 1,9 1,4 sulfur phr 2,5 2,5 2,5 2,5 2,5 Characteristics Hardness at RT Shore A 59 58 61 63 59 Rebound strength at 70 °C % 57 59 55 56 58 tan δ max at 55 °C - 0,169 0,119 0,141 0,148 0,149 Adhesive strength (unaged) % 100 115 102 106 106 Coverage (unaged) - 4,3 1,7 1,3 2,5 4,2 Fatigue test kC 185 126 336 219 380 a) < BR, Tg = -75 °C b) < ESBR, Tg = -51 °C, styrene content 23.5 wt% c) < Zeosil® < 1085 MP, CTAB number = 80 m² / g, BET 90 m² / g, Solvay d) < butylcarbamate-functionalized phenol-formaldehyde resin e) < hexamethoxymethylmelamine 65% on silica

[0045] The rubber compounds according to the invention, listed in Table 1, exhibit a significant improvement in fatigue resistance. The loss factor tan δ max at 55 °C is low, indicating low rolling resistance when used in vehicle tires. If silica and carbon black are incorporated into the compound (see Compound 5(E)), the fatigue resistance can be further improved, and the coverage, as a measure of the adhesive bond between the textile reinforcement and the rubber compound, reaches the level of a carbon black-based rubber compound.

Claims

1. Pneumatic vehicle tyre which comprises a sulfur-crosslinked rubberization mixture for textile strength members, containing - 25 to 55 phr (parts by weight, based on 100 parts by weight of all rubbers in the mixture) of at least one polyisoprene, - 45 to 75 phr of at least one further diene elastomer comprising at least one conjugated diene and optionally one or more vinyl-aromatic compounds, with a content of vinyl-aromatic compound of 0% to 50% by weight, - 30 to 90 phr of at least one silica, - at least one silane coupling agent and - an adhesion system for rubber-textile adhesion, wherein the further diene elastomer is a styrene-butadiene copolymer.

2. Pneumatic vehicle tyre according to Claim 1, characterized in that the polyisoprene used comprises natural rubber.

3. Pneumatic vehicle tyre according to Claim 1 or 2, characterized in that a styrene-butadiene copolymer having a glass transition temperature Tg of less than -40°C and a styrene content of at least 20% by weight is used.

4. Pneumatic vehicle tyre according to at least one of the preceding claims, characterized in that the rubberization mixture contains 50 to 70 phr of at least one silica.

5. Pneumatic vehicle tyre according to at least one of the preceding claims, characterized in that at least one silica has a CTAB number according to ASTM D 3765 of less than 120 m2 / g, preferably less than 100 m2 / g.

6. Pneumatic vehicle tyre according to at least one of the preceding claims, characterized in that the rubberization mixture contains 5 to 50 phr of carbon black, wherein the ratio of silica to carbon black is 1:5 to 5:1.

7. Pneumatic vehicle tyre according to at least one of the preceding claims, characterized in that the adhesion system for rubber-textile adhesion is a methylene acceptor-methylene donor pair.

8. Pneumatic vehicle tyre according to at least one of the preceding claims, characterized in that it comprises a carcass rubberization composed of the rubberization mixture.

9. Pneumatic vehicle tyre according to at least one of the preceding claims, characterized in that it comprises a bandage rubberization composed of the rubberization mixture.