Sulfur-crosslinked rubber mixture containing carbon nanotubes (cnt), vehicle tire of sulfur-crosslinked rubber mixture, and method for producing sulfur-crosslinked rubber mixture containing carbon nanotubes

Abstract

The present invention relates to a sulfur-crosslinked rubber mixture comprising carbon nanotubes (CNTs) for vehicle tyres, to a vehicle tyre comprising the sulfur-crosslinked rubber mixture, and to a method for producing the sulfur-crosslinked rubber mixture comprising CNT. The sulfur-crosslinked rubber mixture according to the invention is characterized in that the CNTs are pre-dispersed in at least one polyisoprene. The vehicle tyre according to the invention preferably comprises the sulfur-crosslinked rubber mixture in the tread and / or the sidewall and / or the conductive track.

Description

Technical Field

[0001] The present invention relates to a sulfur-crosslinked rubber mixture containing carbon nanotubes (CNTs) for vehicle tires, a vehicle tire comprising the sulfur-crosslinked rubber mixture, and a method for producing the sulfur-crosslinked rubber mixture containing CNTs. Background Art

[0002] The rubber composition of the various components of a vehicle tire, particularly the composition of the tread, determines its running characteristics to a large extent.

[0003] The properties of the mixture and the vulcanizate can be influenced by adding a wide variety of different admixtures to the mixture and / or by using specific polymers. Examples of admixtures that may be mentioned herein are fillers (e.g., carbon black), plasticizers, aging stabilizers, and different crosslinking systems consisting of sulfur, accelerators, and activators.

[0004] WO 2012 / 080160 A1 discloses a rubber mixture for vehicle tire treads containing a masterbatch of carbon nanotubes (CNTs) in ESBR (emulsion-polymerized styrene-butadiene rubber). Compared to a mixture without CNTs, this mixture shows improved indicators for traction, dry handling behavior, and rolling resistance under winter conditions. Summary of the Invention

[0005] In view of the prior art, the object of the present invention is to provide a sulfur-crosslinked rubber mixture containing carbon nanotubes (CNTs) which features optimized conductivity properties, wherein the other properties, in particular the wear behavior, remain at the same level or are even likewise improved.

[0006] This object is achieved when, in a sulfur-crosslinked rubber mixture, the CNTs are predispersed in at least one polyisoprene.

[0007] It has been surprisingly found that this provides unexpectedly good electrical conductivity for sulfur-crosslinked rubber mixtures. This effect is particularly pronounced when compared with rubber mixtures containing polymer blends of styrene-butadiene rubber and polyisoprene; unexpectedly high electrical conductivities were observed in the case of CNTs predispersed in at least one polyisoprene (polyisoprene-CNT masterbatch).

[0008] At the same time, the other tire properties remain at approximately the same high level or are even improved, in particular the wear properties of the rubber mixture remain at approximately the same high level or are even improved.

[0009] A further object of the invention is to provide a vehicle tyre which exhibits an improvement over the prior art in terms of conductivity.

[0010] This object is achieved when the vehicle tire comprises, in at least one component, at least one sulfur-crosslinked rubber mixture having the characteristics listed above or explained in more detail below.

[0011] Vehicle tires containing the rubber mixture according to the invention have improved conductivity in at least one component, preferably at least in the tread and / or at least one sidewall and / or at least one conductivity track.

[0012] If vehicle tires contain the sulfur-crosslinked rubber mixture according to the invention at least in the tread, the wear behavior remains at least at the same level or is likewise improved.

[0013] In the case of a two-part tread (upper part: cap and lower part: base), the rubber mixture according to the invention can be used for both the cap and the base. It is preferred that at least the cap comprises at least one sulfur-crosslinked rubber mixture according to the invention.

[0014] "Sulfur-crosslinked rubber mixture" is understood to mean a rubber mixture produced from a ready-to-use rubber mixture (or raw rubber mixture) by sulfur vulcanization. A sulfur-crosslinked rubber mixture is therefore a vulcanizate.

[0015] In the context of the present invention, a conductive track is any embodiment of a rubber compound known to those skilled in the art that is suitable for ensuring conductivity between at least two tire components and / or between at least one inner tire component and the road surface or other external surface with which the tire contacts. The conductive track can be a so-called "carbon center beam" or a belt arranged in the shoulder region of a vehicle tire. Furthermore, the conductive track can also be arranged between an electrically conductive tire component and a tire sensor, thereby transmitting information about the tire's electrical conductivity to the sensor.

[0016] In the context of the present invention, "vehicle tyres" are understood to mean vehicle pneumatic tyres and solid rubber tyres, including tyres for industrial and construction site vehicles, trucks, cars and bicycles, and motorcycle tyres.

[0017] The rubber mixture according to the invention is furthermore suitable for other components of vehicle tires, such as, in particular, flange profiles, and also for internal tire components. The rubber mixture according to the invention is furthermore suitable for other industrial rubber products, such as bellows, conveyor belts, air springs, belts, transmission belts or hoses, and also shoe soles.

[0018] The components of the sulfur-crosslinkable rubber mixture according to the invention are described in more detail below. All statements also apply to vehicle tires according to the invention, which contain at least one rubber mixture according to the invention in at least one component. The description of the individual components relates to the rubber mixture before vulcanization, i.e., the sulfur-crosslinkable rubber mixture, unless otherwise stated.

[0019] The unit "phr" (parts per hundred parts of rubber by weight) used in this document is a standard unit of quantity for mixture formulations in the rubber industry. In this document, the parts by weight of the individual substances measured are based on 100 parts by weight of the total composition of all rubbers present in the mixture, i.e., at least one polyisoprene plus the optionally further sulfur-crosslinkable rubber added to the rubber mixture according to the invention.

[0020] The present invention provides a sulfur-crosslinked rubber mixture containing carbon nanotubes (CNTs).

[0021] In principle, all types of CNTs known to those skilled in the art are included in the subject matter of the present invention. Discrete carbon nanotubes have an elongated shape and therefore have a high aspect ratio. The aspect ratio corresponds to the quotient of the average length of the CNTs divided by the average diameter of the CNTs.

[0022] In a preferred embodiment of the invention, the CNTs have an aspect ratio of 10 to 200, particularly preferably 30 to 150, very particularly preferably 50 to 120.

[0023] As known to those skilled in the art, the size of CNTs is determined by scanning electron microscopy (SEM).

[0024] In a preferred embodiment of the present invention, the CNTs have a length of 0.2 μm to 1.4 μm, preferably 0.5 μm to 1 μm, ie 200 nm to 1400 nm, preferably 500 nm to 1000 nm.

[0025] Essential to the present invention is that the CNTs are pre-dispersed in at least one polyisoprene. Surprisingly, only pre-dispersing the CNTs in at least one polyisoprene results in unexpectedly high electrical conductivities.

[0026] This is to be understood as meaning that CNT is preferably only pre-dispersed in at least one polyisoprene, and there is no additional following masterbatch in the rubber mixture: wherein CNT is pre-dispersed in the rubber matrix except polyisoprene. Especially, the rubber mixture according to the present invention preferably does not contain any following masterbatch: wherein CNT is pre-dispersed in ESBR. The presence of plasticizer or other substances in the masterbatch is unaffected, i.e. the polyisoprene-CNT masterbatch can include other substances, such as plasticizer, vide infra.

[0027] The at least one polyisoprene may be natural polyisoprene (NR, natural rubber) and / or synthetic polyisoprene (IR).

[0028] In all embodiments, both cis-1,4-polyisoprene and 3,4-polyisoprene are contemplated. However, preference is given to using cis-1,4-polyisoprene with a cis-1,4 ratio greater than 90% by weight. Such polyisoprenes are primarily obtainable by stereospecific polymerization in solution with Ziegler-Natta catalysts or using finely dispersed alkyl lithium. Natural rubber (NR) is one such cis-1,4-polyisoprene; the cis-1,4 content in natural rubber is greater than 99% by weight.

[0029] Mixtures of one or more natural polyisoprenes with one or more synthetic polyisoprenes are furthermore conceivable.

[0030] In a preferred embodiment of the invention, the at least one polyisoprene is at least one natural polyisoprene. This results in particularly good properties with respect to the requirements for the rubber mixture used in at least one tire component, while achieving exceptional electrical conductivity.

[0031] It is essential for the present invention that the CNTs in at least one polyisoprene are pre-dispersed, that is, pre-distributed and preferably untied from each other. Therefore, CNTs are preferably present in at least one polyisoprene in the form of single, separate CNTs. However, residual agglomerates are not inconceivable. Therefore, in the rubber mixture according to the present invention, CNTs can be in the form of single CNTs and optionally also in the form of agglomerates. Both the length and diameter of the CNTs and agglomerates separated can be determined using SEM, and for details, reference is made to the description in WO 2012 / 080160A1. Agglomerates are in the form of CNT bundles. In this case, the effective aspect ratio is determined as the quotient of the average length (arithmetic mean) and the diameter of the bundle.

[0032] The dispersion of the CNTs in the at least one polyisoprene is carried out by methods known to those skilled in the art, such as, for example, by the method described below.

[0033] As described in US 7785701, dispersion of CNTs can be performed by shear forces, for example by one of the following methods:

[0034] - kneading on a roller mill with a nip width of 0.5 mm or less ("open roller method");

[0035] - kneading in a closed mixer with a rotor spacing of 1 mm or less ("closed kneading method");

[0036] - Kneading in a multi-screw extruder having a screw pitch of 0.3 mm or less ("multi-screw extrusion kneading method").

[0037] The incorporation of CNTs into a rubber matrix in an internal mixer at 110° C. for 30 minutes is described in S. Sagar et al.: “MWCNTS Incorporated Natural Rubber Composites: Thermal Insulation, Phase Transition and Mechanical Properties,” IACSIT International Journal of Engineering and Technology (June 2014), Vol. 6, No. 3, p. 168.

[0038] CNTs can also be integrated into a rubber matrix by initial wetting with ethanol and subsequent evaporation of the ethanol, as described, for example, in HHLe et al.: “Effect of rubber polarity on selective wetting of carbon nanotubes in ternary blends,” eXPRESS Polymer Letters (2015), Vol. 9, No. 11, pp. 960-971.

[0039] The CNTs and the at least one polyisoprene in which they are predispersed form a masterbatch which may contain further ingredients.

[0040] The viscosity of the masterbatch (Mooney ML 1+4 at 100° C.) is preferably from 80 to 120 MU.

[0041] The weight fraction of CNTs in the masterbatch is preferably 0.1 to 20% by weight based on the total weight of the masterbatch.

[0042] In a particularly advantageous embodiment of the invention, the proportion of CNTs in the masterbatch is 13% to 20% by weight, particularly preferably 14% to 18% by weight, and in particular, for example, 15% to 17% by weight. Such a CNT concentration in the masterbatch of at least one polyisoprene achieves good distribution of the CNTs in the polyisoprene and particularly good electrical conductivity, along with other good tire properties in the sulfur-crosslinked rubber mixture.

[0043] As a further component, the masterbatch can contain, in particular, at least one plasticizer.

[0044] The weight fraction of the plasticizer, based on the total amount of the masterbatch, is preferably 0.1 to 20% by weight. In an advantageous embodiment of the invention, the fraction is 6 to 16% by weight, particularly preferably 8 to 14% by weight, in particular and for example 9 to 10% by weight.

[0045] Here too, the weight fraction of CNTs in the masterbatch is preferably 0.1 to 20% by weight, based on the total weight of the masterbatch, and in particularly advantageous embodiments of the invention is 13 to 20% by weight, particularly preferably 14 to 18% by weight, in particular and for example 15 to 17% by weight.

[0046] In sulfur-crosslinked rubber mixtures, the amount of CNTs is preferably 0.1 to 25 phr (MB=rubber+CNTs), preferably 0.1 to 15 phr. Such amounts achieve an improvement in the electrical conductivity together with good rolling resistance behavior.

[0047] In a preferred embodiment, the rubber mixture according to the invention contains 0.1 to 2 phr of CNTs. This amount particularly advantageously resolves the conflicting objectives of high electrical conductivity combined with the lowest possible rolling resistance.

[0048] In an advantageous embodiment of the invention, the sulfur-crosslinked rubber mixture contains, in addition to the polyisoprene in which the CNTs are predispersed, at least one further rubber which is sulfur-crosslinkable before vulcanization and is therefore at least one further diene rubber.

[0049] The term diene rubber is understood to mean rubbers which are formed by polymerization or copolymerization of dienes and / or cycloolefins and therefore contain C═C double bonds in the main chain or in side groups.

[0050] The at least one further diene rubber is preferably selected from the group consisting of natural polyisoprene and / or synthetic polyisoprene and / or epoxidized polyisoprene and / or butadiene rubber and / or butadiene-isoprene rubber and / or solution-polymerized styrene-butadiene rubber and / or emulsion-polymerized styrene-butadiene rubber and / or styrene-isoprene rubber and / or liquid rubber (having a molecular weight Mw of more than 20 000 g / mol) and / or halogenated butyl 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 hydrogenated styrene-butadiene rubber.

[0051] 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 industrial rubber articles such as belts, transmission belts and hoses, and / or shoe soles.

[0052] The rubber mixture is particularly suitable for vehicle tires and can in principle be used in any components, such as, in particular, treads, sidewalls, flange profiles, and also in other so-called body components.

[0053] For this purpose, the diene rubber is preferably selected from the group consisting of synthetic polyisoprene (IR) and natural polyisoprene (NR) and styrene-butadiene rubber (SBR) and polybutadiene (BR) and butyl rubber (IIR) and halogenated butyl rubber.

[0054] The diene rubber is particularly preferably selected from the group consisting of synthetic polyisoprene (IR) and natural polyisoprene (NR) and styrene-butadiene rubber (SBR) and polybutadiene (BR),

[0055] This results in particularly good properties with regard to the requirements in vehicle tires.

[0056] The above remarks concerning the microstructure, etc., apply to the synthetic or natural polyisoprene which may be added as at least one further sulfur-crosslinkable rubber.

[0057] If the rubber mixture according to the invention contains butadiene rubber (i.e., BR, polybutadiene), any type known to those skilled in the art can be considered. These include, in particular, so-called high-cis and low-cis types, polybutadiene having a cis content of not less than 90% by weight being referred to as high-cis types, and polybutadiene having a cis content of less than 90% by weight being referred to as low-cis types. Low-cis polybutadiene is, for example, Li-BR (lithium-catalyzed butadiene rubber) having a cis content of 20% to 50% by weight. High-cis BR achieves particularly good wear properties and low hysteresis in the rubber mixture.

[0058] The one or more polybutadienes employed can be end-group modified and / or functionalized along the polymer chain by modification and functionalization. The modification can be selected from modifications with hydroxyl groups and / or ethoxy groups and / or epoxy groups and / or siloxane groups and / or amino groups and / or aminosiloxanes and / or carboxyl groups and / or phthalocyanine groups and / or silane-sulfide groups. However, other modifications known to those skilled in the art, also referred to as functionalized, are also suitable. Metal atoms can be components of such functionalized modifications.

[0059] In the case where at least one styrene-butadiene rubber (styrene-butadiene copolymer) is present in the rubber mixture, the styrene-butadiene rubber(s) may be selected from solution-polymerized styrene-butadiene rubber (SSBR) and emulsion-polymerized styrene-butadiene rubber (ESBR), mixtures of at least one SSBR and at least one ESBR also being employable. The terms "styrene-butadiene rubber" and "styrene-butadiene copolymer" are used synonymously in the context of the present invention.

[0060] The styrene-butadiene copolymers used can be end-group modified and / or functionalized along the polymer chain by the modifications and functionalizations listed above for polybutadiene.

[0061] In an advantageous embodiment of the invention, the rubber mixture contains at least one further reinforcing filler, wherein the ratio of the amount of further reinforcing filler to the CNTs is from 1000:1 to 2:1.

[0062] The ratio is particularly preferably from 200:1 to 2:1, very particularly preferably from 80:1 to 2:1.

[0063] In the context of the present invention, “additional reinforcing fillers” are understood to include in principle all fillers which provide a reinforcing effect to the rubber mixture, ie in particular modify the viscoelastic properties by interaction with the rubber matrix.

[0064] The amount of the at least one further reinforcing filler is preferably from 0.1 to 250 phr, particularly preferably from 20 to 250 phr, very particularly preferably from 20 to 150 phr.

[0065] The further reinforcing filler is preferably at least one carbon black and / or at least one silica.

[0066] In a preferred embodiment of the invention, the rubber mixture contains 0.1 to 250 phr, preferably 2 to 200 phr, particularly preferably 10 to 100 phr, and even more preferably 20 to 80 phr of at least one carbon black.

[0067] In the context of the present invention, all carbon black types known to those skilled in the art are conceivable. However, preference is given to using carbon blacks having an iodine adsorption value according to ASTM D 1510 of 20 to 180 g / kg, particularly preferably 30 to 140 g / kg, and a DBP value according to ASTM D 2414 of 30 to 200 ml / 100 g, preferably 90 to 180 ml / 100 g, particularly preferably 110 to 180 ml / 100 g. Particularly suitable carbon blacks for the purposes of the present invention are, for example, ASTM type N339 with an iodine adsorption value of 90 g / kg and a DBP value of 120 ml / 100 g. This allows for use in vehicle tires, particularly in treads.

[0068] Silica is known to those skilled in the art as a reinforcing filler. In a preferred embodiment of the present invention, the rubber mixture contains 0.1 to 30 phr of at least one silica, preferably 5 to 30 phr of at least one silica. Therefore, so-called partial silica mixtures are also conceivable.

[0069] In a further preferred embodiment of the invention, the rubber mixture contains 5 to 250 phr, particularly preferably 20 to 200 phr, and even more preferably 20 to 100 phr of at least one silica.

[0070] The silica may be any silica known to those skilled in the art as a filler for tire rubber mixtures. However, particular preference is given to using silica having a diameter of 35 to 350 m 2 / g, preferably 35 to 260m 2 / g, particularly preferably 70 to 235m 2 / g and very particularly preferably from 70 to 205 m 2 / g nitrogen surface area (BET surface area) (according to DIN ISO 9277 and DIN 66132), and 30 to 400m 2 / g, preferably 30 to 255m 2 / g, particularly preferably 65 to 230m 2 / g and very particularly preferably from 65 to 200 m 2 / g of finely divided precipitated silica with a CTAB surface area (according to ASTM D 3765).

[0071] Such silicas produce, for example, rubber mixtures for internal tire components, resulting in particularly good physical properties of the vulcanized product. Advantages in the processing of the mixture can also be achieved by reducing the mixing time while retaining the same product characteristics, thus leading to improved productivity. Thus, the silicas that can be used include, for example, not only the types from Evonik VN3 (trade name), but also silicas with relatively low BET surface areas (such as for example Silica from Solvay 1115 or 1085) and highly dispersible silicas such as so-called HD silicas (e.g. from Solvay 1165MP).

[0072] Further optional reinforcing fillers are, for example, graphite and graphene, and also so-called “carbon-silica dual-phase fillers”.

[0073] The rubber mixture according to the invention may contain additional non-reinforcing fillers, preferably in very small amounts, i.e. preferably 0 to 3 phr. In the context of the present invention, additional non-reinforcing fillers include aluminosilicates, kaolin, chalk, starch, magnesium oxide, titanium dioxide or rubber gel and also fibers (e.g. aramid fibers, glass fibers, carbon fibers, cellulose fibers).

[0074] In the context of the present invention, zinc oxide does not belong to the group of fillers.

[0075] The silica optionally present can be present in the form of bound or unbound silica.

[0076] In the case where the silica is present in the form of bonded silica, the rubber mixture preferably contains at least one silane coupling agent.

[0077] In the context of the present invention, silane coupling agents are also referred to as "silanes".

[0078] One or more different silane coupling agents can be used in combination with one another. The rubber mixture can therefore contain a mixture of different silanes.

[0079] During the mixing (in situ) of the rubber / rubber mixture or in the context of pretreatment (pre-modification) before even adding the filler to the rubber, the silane coupling agent reacts with the surface silanol groups or other polar groups of the silica. The silane coupling agent that can be used includes any silane coupling agent known to those skilled in the art for use in rubber mixtures. Such coupling agents known from the prior art are difunctional organosilanes having at least one alkoxy, cycloalkoxy or phenoxy group as a leaving group on the silicon atom and a group as another functional group that can optionally undergo a chemical reaction with the double bond of the polymer after dissociation. The latter group can include, for example, the following chemical groups:

[0080] -SCN, -SH, -NH2 or -S x -(wherein x=2 to 8).

[0081] Thus, silane coupling agents that can be used include, for example, 3-mercaptopropyltriethoxysilane, 3-thiocyanatopropyltrimethoxysilane or 3,3'-bis(triethoxysilylpropyl)polysulfides having 2 to 8 sulfur atoms, such as 3,3'-bis(triethoxysilylpropyl)tetrasulfide (TESPT), the corresponding disulfides (TESPD) or mixtures of sulfides having 1 to 8 sulfur atoms with various contents of various sulfides. TESPT can also be used as a coupling agent with industrial carbon black (e.g. (trade name from Evonik: )) of the mixture was added.

[0082] Preference is given to using silane mixtures containing 40 to 100% by weight of disulfide, particularly preferably 55 to 85% by weight of disulfide and very particularly preferably 60 to 80% by weight of disulfide. Such mixtures are available, for example, from Evonik under the trade name Si Such mixtures are available, for example, as described in DE 102006004062 A1.

[0083] End-capped mercaptosilanes, such as those known from WO 99 / 09036, can also be used as silane coupling agents. It is also possible to use silanes such as those described in WO 2008 / 083241 A1, WO 2008 / 083242 A1, WO 2008 / 083243 A1, and WO 2008 / 083244 A1. Silanes that can be employed include those sold, for example, under the name NXT (e.g., 3-(octanoylthio)-1-propyltriethoxysilane) from Momentive, USA, or under the name VP Si Those that are sold.

[0084] It is also conceivable to use one of the abovementioned mercaptosilanes, in particular 3-mercaptopropyltriethoxysilane, in combination with a processing aid (listed below), in particular a PEG carboxylate.

[0085] In a preferred embodiment of the invention, the rubber mixture contains a combination of 3-mercaptopropyltriethoxysilane and PEG carboxylate, which results in particularly good properties, especially with regard to the technical objectives to be achieved, and a good overall level with regard to other properties.

[0086] Rubber stock can also contain other activator and / or the reagent that is used for combining weighting agent (particularly carbon black).These can for example comprise compound S-(3-aminopropyl) thiosulfate and / or its metal salt that for example discloses in EP 2589619 A1, it has realized the very good physical property of rubber stock, especially with at least a carbon black combination as weighting agent.

[0087] In a preferred embodiment, rubber mixture according to the present invention contains at least one plasticizer that is no more than 35phr, if wherein there is at least one plasticizer, then the total amount of one or more plasticizers is preferably 0.1 to 35phr.Especially with above-mentioned composition combination, this produces rubber mixture, particularly the especially good processability of the extrudate before crosslinking, together with the good characteristic about purpose to be achieved.Under the amount of one or more plasticizers more than 35phr, heat-generating property (hysteresis) is impaired.In addition, the contradiction of the target between strengthening characteristic (rigidity / hardness) and hysteresis is impaired.

[0088] The plasticizer can also be introduced in corresponding amounts into the rubber base mixture in whole or in part via the above-described masterbatch comprising CNTs and polyisoprene.

[0089] Plasticizers used in the context of the present invention include all plasticizers known to those skilled in the art, such as aromatic, naphthenic or paraffinic mineral oil plasticizers, for example MES (mild extraction solvate) or RAE (residual aromatic extract) or TDAE (treated distillate aromatic extract), or rubber-to-liquid oil (RTL) or biomass-to-liquid oil (BTL) or rapeseed oil, preferably with a polycyclic aromatic hydrocarbon content of less than 3% by weight according to method IP 346, or in particular resin acids or oil pastes, or liquid polymers with an average molecular weight of between 500 and 20,000 g / mol (determined by GPC = gel permeation chromatography according to BS ISO 11344:2004). If additional liquid polymers are used as plasticizers in the rubber mixtures according to the invention, these are not included as rubber in the calculation of the composition of the polymer matrix.

[0090] The plasticizer is preferably selected from the group consisting of the above-mentioned plasticizers.

[0091] In a particularly preferred embodiment of the invention, the masterbatch already contains at least one plasticizer (see above), preferably at least one resin acid, in particular a disproportionated resin soap (e.g. SYLVAROS from Kraton). TM DRS215 or SYLVAROS from Kraton TM DRS 40) or at least one mineral oil plasticizer.

[0092] In a further preferred embodiment of the invention, the rubber mixture is mixed with at least one plasticizer in addition to any plasticizer present in the masterbatch.Mineral oil is particularly preferred as plasticizer.

[0093] When mineral oil is used, the oil is preferably selected from the group consisting of DAE (Distilled Aromatic Extract) and / or RAE (Residual Aromatic Extract) and / or TDAE (Treatened Distilled Aromatic Extract) and / or MES (Mild Extracted Solvent) and / or naphthenic oil.

[0094] In a preferred embodiment of the present invention, the rubber mixture contains at least one mineral oil plasticizer, preferably at least TDAE and / or RAE as plasticizer. This results in particularly good processability characteristics of the rubber mixture, in particular good miscibility.

[0095] In the production of the rubber mixture according to the invention, one or more plasticizers not already present in the masterbatch are preferably added in at least one basic mixing stage.

[0096] Furthermore, the rubber mixture may contain customary additives in customary parts by weight, which are preferably added in at least one basic mixing stage during the production of the mixture. These additives include

[0097] a) Aging stabilizers, 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),

[0098] b) activators, such as zinc oxide and fatty acids (such as stearic acid) and / or other activators, such as zinc complexes, for example zinc ethylhexanoate,

[0099] c) wax,

[0100] d) hydrocarbon resins which have not been included as plasticizers,

[0101] e) plasticizing aids, such as 2,2'-dibenzamidodiphenyl disulfide (DBD), and

[0102] f) Processing aids, such as, in particular, fatty acid esters and metal soaps, for example zinc soaps and / or calcium soaps.

[0103] The quantitative fraction of the total amount of further additives is 3 to 150 phr, preferably 3 to 100 phr and particularly preferably 5 to 80 phr.

[0104] The total amount fraction of the additional additives may contain zinc oxide (ZnO) in the above-mentioned amount.

[0105] This can be any type of zinc oxide known to those skilled in the art, such as ZnO granules or powder. Conventionally used zinc oxide usually has a particle size of less than 10 m 2 / g. However, it is also possible to use a BET surface area of ​​10 m 2 / g to 100m 2 / g of zinc oxide with a BET surface area of ​​​​1000 μg, such as the so-called "nano zinc oxide".

[0106] Rubber mixture according to the present invention is sulfur cross-linked, i.e. uses a vulcanization accelerator to carry out the vulcanization of this raw mixture based on the raw mixture in the presence of sulphur and / or a sulphur donor. Some vulcanization accelerators can serve as sulphur donors simultaneously. Accelerator is preferably selected from the group consisting of the following: thiazole accelerator and / or accelerator containing sulfhydryl and / or sulfenamide accelerator and / or thiocarbamate accelerator and / or thiuram accelerator and / or thiophosphate accelerator and / or thiourea accelerator and / or xanthate accelerator and / or guanidine accelerator.

[0107] It is preferred to use a sulfenamide accelerator selected from the group consisting of N-cyclohexyl-2-benzothiazolylsulfenamide (CBS) and / or N,N-dicyclohexylbenzothiazolyl-2-sulfenamide (DCBS) and / or benzothiazolyl-2-sulfenomorpholide (MBS) and / or N-tert-butyl-2-benzothiazolylsulfenamide (TBBS).

[0108] The sulfur-donating substance used may be any sulfur-donating substance known to the person skilled in the art. 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) and / or tetramethylthiuram disulfide (TMTD) and / or tetraethylthiuram disulfide (TETD), and / or thiuram tetrasulfides, such as dipentamethylenethiuram tetrasulfide (DPTT) and / or dithiophosphates, such as

[0109] DipDis (bis(diisopropyl)thiophosphoryl disulfide) and / or bis(O,O-2-ethylhexylthiophosphoryl) polysulfide (e.g. Rhenocure SDT Rheinchemie GmbH) and / or zinc dichlorooxydithiophosphate (e.g. Rhenocure Rhein Chemie AG) and / or zinc alkyldithiophosphate, and / or 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane and / or diaryl polysulfide and / or dialkyl polysulfide.

[0110] Further network-forming systems, such as those sold under the trade name or Obtainable, or as described in WO 2010 / 049216 A2 network forming system also can be used in this rubber mixture.This system contains with the crosslinked vulcanizing agent greater than four functionality and at least one vulcanization accelerator.With the crosslinked vulcanizing agent greater than four functionality have for example general formula D):

[0111] D)G[C a H 2a -CH2-S b Y] c

[0112] wherein G is a polyvalent cycloalkyl and / or polyvalent heteroalkyl and / or polyvalent siloxane radical containing from 1 to 100 atoms; wherein each Y is independently selected from rubber reactive groups comprising sulfur-containing functionality; and wherein a, b, and c are integers, wherein independently a=0 to 6; b=0 to 8; and c=3 to 5.

[0113] The rubber-reactive groups are preferably selected from thiosulfonate groups, dithiocarbamate groups, thiocarbonyl groups, mercapto groups, hydrocarbon groups and sodium thiosulfate groups (Bent salt groups).

[0114] In this way, very good wear and tensile properties of the rubber mixture according to the invention are achieved.

[0115] Particular preference is given to using the accelerators TBBS and / or CBS and / or diphenylguanidine (DPG).

[0116] The rubber mixture may also contain vulcanization retarders.

[0117] The terms "vulcanized" and "cross-linked" are used synonymously in the context of the present invention.

[0118] The invention further provides a vehicle tire comprising at least one sulfur-crosslinked rubber mixture according to the invention in at least one component.The vehicle tire according to the invention can contain different embodiments of the rubber mixture according to the invention in different components.

[0119] It is particularly preferred that the at least one component is at least the tread and / or the sidewall and / or the conductive track.

[0120] The present invention further provides a method for producing a sulfur-crosslinked rubber mixture containing CNTs, comprising at least the following method steps:

[0121] a) producing a masterbatch from at least one polyisoprene and CNTs, wherein the CNTs are intensively mixed into the polyisoprene; and

[0122] b) optionally providing further ingredients, these further ingredients comprising at least one reinforcing filler and / or at least one sulfur-crosslinkable rubber and / or an aging stabilizer and / or at least one silane coupling agent; and

[0123] c) optionally mixing the additional ingredients from step b) with the polyisoprene-CNT masterbatch; and

[0124] d) providing at least one sulfur vulcanization system;

[0125] e) mixing the mixture from step a) or c) with the sulfur vulcanization system from step d); and

[0126] f) vulcanizing the mixture from step e) to provide a sulfur-crosslinked rubber mixture.

[0127] All statements given above with regard to the rubber mixture according to the invention apply to these components.

[0128] It is therefore essential to the present invention that, according to step a), a masterbatch containing at least one polyisoprene and CNTs is produced and then optionally mixed with further ingredients to provide a rubber base mixture. In the absence of steps b) and c), the masterbatch itself is a rubber base mixture which, according to step e), can likewise be mixed with a sulfur vulcanization system to provide a ready-to-use rubber mixture.

[0129] The production of the polyisoprene-NR masterbatch according to step a) is carried out using methods known to those skilled in the art as described above.

[0130] The ready-to-use mixture is subjected to further processing, for example by extrusion operations or calendering, and introduced into suitable moulds.

[0131] This is followed by further processing by vulcanization according to step f), wherein the vulcanization system added in the context of the present invention enables sulfur crosslinking to take place.

[0132] For use in vehicle tires, the mixture is preferably molded into a tread and / or sidewall and / or conductive track as a ready-to-use mixture before vulcanization and applied in a known manner in the production of green vehicle tires. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The specific volume resistance according to DIN IEC 60093 is shown; the diagram plots ohm mm (y-axis) against vol% CNTs based on the corresponding rubber mixture (x-axis). DETAILED DESCRIPTION

[0133] Reference is now made to Table 1 and Figure 1The present invention is described in more detail with reference to the comparative examples and working examples summarized in . The mixtures marked with "E" are mixtures of the present invention, while the mixtures marked with "V" are comparative mixtures.

[0134] The mixtures were produced in three stages under customary conditions in a laboratory tangential mixer.

[0135] All mixtures were used to produce test specimens by vulcanization, and these test specimens were used to determine the material properties typical for the rubber industry. The following test methods were used for the above-mentioned tests on the test specimens:

[0136] Table 1:

[0137] Mooney viscosity according to ASTM D1646; for example ML1+4 at 100°C (Mooney units MU

[0138] Shore A hardness at room temperature according to DIN ISO 7619-1 by durometer

[0139] Resilience at 70°C according to DIN 53 512 or ISO 4662 or ASTM D 1054

[0140] Tensile strength at room temperature, elongation at break and stress values ​​at 50% and 300% elongation (M50 and M300) according to DIN 53 504

[0141] Wear at room temperature according to DIN / ISO 4649

[0142] Dispersion using a DisperGRADER microscope (100x magnification)

[0143] Figure 1 :

[0144] Specific volume resistivity according to DIN IEC 60093; the diagram plots ohm mm (y-axis) against vol% CNT based on the corresponding rubber compound (x-axis)

[0145] Table 1

[0146]

[0147]

[0148] The substances used are listed in Table 1:

[0149] a) NR-CNT masterbatch: CNT pre-dispersed in NR: 67.3% by weight NR, 18.7% by weight CNT, 14% by weight resin acid; density 1.03 g / cm 3

[0150] b) Silane: TESPD + 3-mercaptopropyltriethoxysilane

[0151] c) Additional additives: Processing aids: PEG carboxylates; hydrocarbon resins; aging stabilizers; antiozonant waxes, zinc oxide; stearic acid

[0152] d) Accelerator: DPG+CBS

[0153] As shown in Table 1, the inventive rubber mixtures E1 and E2 exhibit improved wear behavior. The other properties are improved at a comparable level or even identically.

[0154] The conductivity / resistance of various comparative mixtures and mixtures according to the invention were also investigated. The results are summarized in Figure 1 middle.

[0155] The mixture series has the following composition (involving Figure 1 (Explanation of ):

[0156] Comparative Example V2

[0157] ESBR1500_CNT_1: ESBR is the only rubber matrix, partly from ESBR-CNT masterbatch and partly added separately:

[0158] For a data point of 5 vol% CNTs in the rubber compound, 67.8 phr of a masterbatch containing 16.1% by weight CNTs and 82.9% by weight ESBR, with the balance being plasticizer, was mixed with 43.8 phr of ESBR. The other ingredients were 3 phr of zinc oxide, 2 phr of stearic acid, 1.5 phr of sulfur, and 1.3 phr of the accelerator TBBS.

[0159] Examples E3, E4, and E5 of the present invention

[0160] NR_CNT_1: NR is the only rubber matrix, partly from NR-CNT masterbatch and partly added separately:

[0161] For the 3 data points of 4.5 and 6.5 and 7.6 vol% CNTs in the rubber compound:

[0162] E3: 4.5 vol% CNT: 60 phr of NR-CNT masterbatch - containing 82.8% by weight NR and 17% by weight CNT with the balance being plasticizer - and 50.32 phr of NR.

[0163] E4: 6.5 vol% CNT: 90 phr NR-CNT masterbatch (as described under 4.5 vol% CNT) and 25.48 phr NR.

[0164] E5: 7.6 vol% CNT: 120.77 phr of the same NR-CNT masterbatch and no additional NR, i.e., 0 phr of separated NR.

[0165] The mixture also contained the same additional ingredients as listed under ESBR1500_CNT_1.

[0166] Examples E6, E7, E8, E9, and E10 of the present invention

[0167] 50NR / 50ESBR (NR_CNT_MB): The rubber matrix consists of 50% by weight of ESBR and 50% by weight of NR; CNTs are pre-dispersed only in NR (NR-CNT masterbatch):

[0168] For the 5 data points of 1.5 and 2 and 3 and 4 and 4.7 vol% CNTs in the rubber compound:

[0169] E6: 1.5 vol% CNT: 18.59 phr NR-CNT masterbatch (as described under 4.5 vol% CNT) and 34.61 phr NR and 50 phr ESBR;

[0170] E7: 2 vol% CNT: 24.91 phr of the same NR-CNT masterbatch, 29.37 phr of NR, and 50 phr of ESBR;

[0171] E8: 3 vol% CNT: 37.75 phr of the same NR-CNT masterbatch with 18.74 phr of NR and 50 phr of ESBR;

[0172] E9: 4 vol% CNT: 50.86 phr of the same NR-CNT masterbatch with 7.89 phr of NR and 50 phr of ESBR;

[0173] E10: 4.7 vol% CNT: 60.39 phr of the same NR-CNT masterbatch without additional NR (i.e., 0 phr of NR), and 50 phr of ESBR;

[0174] The mixture also contained the same additional ingredients as listed under ESBR1500_CNT_1.

[0175] Comparative Examples V3, V4, V5 and V6

[0176] 50NR / 50ESBR (ESBR_CNT_MB): The rubber matrix consists of 50% by weight of ESBR and 50% by weight of NR; CNTs are pre-dispersed only in ESBR (ESBR-CNT masterbatch):

[0177] For the 4 data points of 2 and 3 and 4 and 4.5 vol% CNTs:

[0178] V3: 2 vol% CNT: 26.55 phr ESBR-CNT masterbatch (as described under ESBR1500_CNT_1) and 27.99 phr ESBR and 50 phr NR;

[0179] V4: 3 vol% CNT: 40.26 phr ESBR-CNT masterbatch (as described under ESBR1500_CNT_1) and 16.63 phr ESBR and 50 phr NR;

[0180] V5: 4 vol% CNT: 54.22 phr ESBR-CNT masterbatch (as described under ESBR1500_CNT_1) and 5.05 phr ESBR and 50 phr NR;

[0181] V6: 4.5 vol% CNT: 60.31 phr ESBR-CNT masterbatch (as described under ESBR1500_CNT_1) with no additional ESBR (i.e., 0 phr ESBR), and 50 phr NR;

[0182] The mixture also contained the same additional ingredients as listed under ESBR1500_CNT_1.

[0183] Comparative Examples V7, V8, V9 and V10

[0184] 50NR / 50ESBR (1 / 2NR_CNT_MB, 1 / 2ESBR_CNT_MB): The rubber matrix consists of 50% by weight of ESBR and 50% by weight of NR; CNTs are pre-dispersed in both ESBR (ESBR-CNT MB) and NR (NR-CNT masterbatch):

[0185] V7: 1.5 vol% CNT: 9.29 phr NR-CNT masterbatch (as described under 4.5 vol% CNT) and 42.3 phr NR and 9.91 phr ESBR-CNT masterbatch (as described under ESBR1500_CNT_1) and 41.79 phr ESBR;

[0186] V8: 2 vol% CNT: 12.46 phr NR-CNT masterbatch (as described under 4.5 vol% CNT) and 39.69 phr NR and 13.27 phr ESBR-CNT masterbatch (as described under ESBR1500_CNT_1) and 39 phr ESBR;

[0187] V9: 5 vol% CNT: 32.12 phr NR-CNT masterbatch (as described under 4.5 vol% CNT) and 23.4 phr NR and 34.24 phr ESBR-CNT masterbatch (as described under ESBR1500_CNT_1) and 21.61 phr ESBR;

[0188] V10: 8.7 vol% CNT: 60.39 phr of NR-CNT masterbatch (as described under 4.5 vol% CNT), and no additional, i.e., 0 phr, NR, and 60.31 phr of ESBR-CNT masterbatch (as described under ESBR1500_CNT_1), and no additional, i.e., 0 phr, ESBR;

[0189] The mixture also contained the same additional ingredients as listed under ESBR1500_CNT_1.

[0190] As in Figure 1 As is evident from the above explanations, the rubber mixtures according to the invention (E3, E4, E5 and also E6, E7, E8, E9, E10), in which the CNTs are pre-dispersed only in at least one polyisoprene (here NR), surprisingly achieve significantly lower electrical resistance and thus significantly improved electrical conductivity.

Claims

1. A sulphur-crosslinked rubber mixture for vehicle tyres, The rubber mixture contains carbon nanotubes (CNTs) and is characterized in that The CNTs are pre-dispersed in at least one polyisoprene, and the pre-dispersed CNTs form a masterbatch, wherein the masterbatch has a Mooney viscosity of 80 to 120 Mooney units at 100° C. according to ASTM D1646.

2. The rubber mixture according to claim 1, characterized in that The at least one polyisoprene is at least one natural polyisoprene.

3. The rubber mixture according to any one of the preceding claims, characterized in that The rubber mixture contains said CNTs in an amount ranging from 0.1 to 25 phr.

4. The rubber mixture according to any one of the preceding claims, characterized in that Besides the polyisoprene in which the CNTs are predispersed, the rubber mixture also contains at least one further sulfur-crosslinkable rubber.

5. The rubber mixture according to any one of the preceding claims, characterized in that The rubber mixture contains at least one additional reinforcing filler, and the ratio of the amount of additional reinforcing filler to the CNTs is from 100:1 to 2:

1.

6. The rubber mixture according to any one of the preceding claims, characterized in that The rubber mixture contains not more than 35 phr of plasticizer.

7. A vehicle tire, characterized in that: The vehicle tire comprises, in at least one component, at least one sulfur-crosslinked rubber mixture as claimed in any one of claims 1 to 6 .

8. The vehicle tire according to claim 7, wherein The component is the tread and / or the sidewall and / or the conductive track.

9. A method for producing a sulfur-crosslinked rubber mixture containing CNTs for vehicle tires, comprising at least the following method steps: a) producing a masterbatch from at least one polyisoprene and CNTs, wherein the CNTs are intensively mixed into the polyisoprene and the masterbatch has a Mooney viscosity of 80 to 120 Mooney units at 100° C. according to ASTM D1646; and b) optionally providing further ingredients, these further ingredients comprising at least one reinforcing filler and / or at least one sulfur-crosslinkable rubber and / or an aging stabilizer and / or at least one silane coupling agent; and c) optionally mixing the additional ingredients from step b) with the polyisoprene-CNT masterbatch; and d) providing at least one sulfur vulcanization system; e) mixing the mixture from step a) or c) with the sulfur vulcanization system from step d); and f) vulcanizing the mixture from step e) to provide a sulfur-crosslinked rubber mixture.

10. The method according to claim 9, wherein In the masterbatch produced in step a), the CNTs are present in an amount ranging from 0.1% to 20% by weight, based on the total amount of the masterbatch.

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