DE102005029522A1 - Sulfur-crosslinkable rubber mixture, useful in the production of pneumatic tire, comprises diene rubber, silicic acid and a silane-coupling agent - Google Patents

Abstract

Sulfur-crosslinkable rubber mixture comprises at least a diene rubber, 20-150 phr of at least a silicic acid and a silane coupling agent that exhibits sulfur chain containing 2-8 sulfur atoms as the vulcanization reactive functional group, where the silane coupling agent is bis(3-triethoxysilylpropyl)tetrasulfane or an organosilane mixture with a bis(3-triethoxysilylpropyl)tetra-sulfane or bis(3-triethoxysilylpropyl) disulfane or an organosilane mixture with a bis(3-triethoxysilylpropyl)disulfane. Sulfur-crosslinkable rubber mixture comprises at least a diene rubber, 20-150 phr (parts per hundred parts of rubber by weight) of at least a silicic acid and a silane coupling agent (bifunctional organosilane) that exhibits sulfur chain containing 2-8 sulfur atoms as the vulcanization reactive functional group, where the silane coupling agent is bis(3-triethoxysilylpropyl)tetrasulfane or an organosilane mixture with a bis(3-triethoxysilylpropyl)tetra-sulfane portion of at least 60 mol%, having a quantity of more than 10 phf (parts per hundred parts of silicic acid by weight) or bis(3-triethoxysilylpropyl) disulfane or an organosilane mixture with a bis(3-triethoxysilylpropyl)disulfane portion of at least 80 mol%, having a quantity of more than 11.5 phf. An independent claim is included for a tire, preferably vehicle pneumatic tire, in which tread is based on at least partially sulfur vulcanized rubber mixture.

Description

The The invention relates to a sulfur crosslinkable rubber mixture containing at least one diene rubber, 20 to 150 phr of at least one silica and a silane coupling agent (bifunctional organosilane) which acts as a vulcanization-reactive, functional Group has a sulfur chain with 2 to 8 sulfur atoms. Further the invention relates to tires, in particular pneumatic vehicle tires, their treads at least partially vulcanised on the sulfur Rubber mixture based.

since Long is used in rubber compounds for tire tread as filler silica used, since the tires with these blends various advantages compared to tires with pure carbon black mixtures. For example the tires have a low rolling resistance, which reduced one Fuel consumption brings with it. Also the wet sliding behavior and the winter properties are improved.

In order to improve the processability and to attach the silica and other optional polar fillers to the diene rubber silane coupling agents are usually used in rubber mixtures. The silane coupling agents react with the superficial silanol groups of the silica or other polar groups during the mixing of the rubber or the rubber mixture (in situ) or even before the addition of the filler to the rubber in the sense of a pretreatment (pre-modification). The silane coupling agents used are bifunctional organosilanes which have at least one alkoxy, cycloalkoxy or phenoxy group as leaving group on the silicon atom and which have a vulcanization-reactive group as other functionality which, if appropriate, can undergo a chemical reaction with the double bonds of the polymer after cleavage. The latter group may be, for example, the following chemical groups: -SCN, -SH, -NH ₂ or -S _x - (where x = 2-8). Thus, as silane coupling agents, for example, 3-mercaptopropyltriethoxysilane, 3-thiocyanato-propyltrimethoxysilane or 3,3-bis (triethoxysilylpropyl) polysulfanes having 2 to 8 sulfur atoms, such as 3,3-bis (triethoxysilylpropyl) tetrasulfane (TESPT), the corresponding disulfane (TESPD) or mixtures of the sulfanes having 1 to 8 sulfur atoms with different contents of the various sulfanes, are used in the tire industry almost exclusively silane coupling agents with sulfur chains.

The expensive silane coupling agents are commonly used in the also of recommended quantities from 1 to a maximum of 10 phf (parts per hundred parts of filler by weight), since then an optimal Connection of the filler to the one or more rubbers) can take place. In the KGK rubber Rubber plastics, no. 5/2002, pp. 236-243 are for example examinations for optimum dosage of silane coupling agent and free sulfur in Silica mixtures described the TESPD in amounts of 0 to 11.25 phf and TESPT in Use amounts of 5.5 to 9.25 phf. As optimal amounts of TESPT 8 phf are recommended. An increasing amount of silane coupling agent leads to this to higher Voltage values and lower elongation at break. The specialist In the field of tread development, it is known that an increase in the Voltage value usually a deterioration of both winter and wet grip properties pulls. For a significant increase the voltage value would the professional as well the increase the amount of silane over the recommended level not considered Since the silane coupling agents are expensive and the Professional therefore other common and much cheaper Methods to increase the voltage value, e.g. a fill level increase, would choose.

to Influencing the mixing and vulcanizate properties the mixtures mixed with a variety of aggregates and / or special polymers are used. As additives are for example at this point fillers (e.g., silica and soot), Plasticizers, crosslinking systems and anti-aging agents called. If a property is improved by varying the mixture, it works but often accompanied by a deterioration of another property, so that certain conflicting goals exist.

It For example, it is known to increase the stiffness of the vulcanizates of a given mixing system, measured across the stress value at elongation, the degree of filling (Proportion of filler in the mix), a filler with active surface or to increase the crosslink density. The above measures to lead but inevitably to a worsening of the frequently desired Low temperature flexibility (Cold flexibility) of vulcanizates. It is also known to increase the loss factor tan δ 0 ° C, the in the tire industry as a measure of the wet grip a mixture is considered to increase the degree of filling, a Polymer with higher Glass transition temperature to choose or to use high hysteresis additives. These measures too Deterioration entails low temperature flexibility.

Become the rubber mixtures for the tread of vehicle tires, in particular pneumatic vehicle tires, used, a high low-temperature flexibility characterizes one Tires with good winter properties, especially ice brakes, and good wet braking. The use of a mixture with high rigidity for the Tire tread ensures good handling, high durability and low abrasion.

Of the The present invention is therefore based on the object, rubber mixtures, especially for to provide the treads of vehicle tires, their vulcanizates through improved rigidity and increased loss factor tan δ at Mark 0 ° C, while at the same time increasing the low-temperature flexibility. For vehicle tires, whose treads are based on such a mixture so an improved handling and an improved wet grip with simultaneously improved winter properties.

• a) Bis(3-triethoxysilylpropyl)tetrasulfan oder ein Organosilangemisch mit einem Bis(3-triethoxysilylpropyl)tetrasulfan-Anteil von mindestens 60 mol% jeweils in einer Menge von mehr als 10 phf (Gewichtsteile bezogen auf 100 Gewichtsteile Kieselsäure) oder
• b) Bis(3-triethoxysilylpropyl)disulfan oder ein Organosilangemisch mit einem Bis(3-triethoxysilylpropyl)disulfan-Anteil von mindestens 80 mol% jeweils in einer Menge von mehr als 11,5 phf

eingesetzt wird.This object is achieved according to the invention that in a rubber mixture of the type mentioned as a silane coupling agent

• a) bis (3-triethoxysilylpropyl) tetrasulfan or an organosilane mixture having a bis (3-triethoxysilylpropyl) tetrasulfan portion of at least 60 mol% each in an amount of more than 10 phf (parts by weight based on 100 parts by weight of silica) or
• b) bis (3-triethoxysilylpropyl) disulfane or an organosilane mixture having a bis (3-triethoxysilylpropyl) disulfane content of at least 80 mol% each in an amount of more than 11.5 ph

is used.

The used in this specification phr (parts per hundred parts of rubber by weight) is the usual quantity in the rubber industry for mix recipes. The dosage of the parts by weight of the individual substances is thereby always to 100 parts by weight of the total mass of all present in the mixture Rubbers purchased.

The used in this specification phf (parts per hundred parts of filler by weight) is the usual quantity in the rubber industry for dosages of silane coupling agents. The dosage of the parts by weight of the individual substances is thereby based on 100 parts by weight of the mass of filler, in particular silica, interacts with the silane coupling agent.

Surprisingly was found by the high excess of the special Silane coupling agents in diene rubber mixtures containing silica the conflict between themselves opposite behaving properties stiffness and low temperature flexibility or loss factor tan δ at 0 ° C and Low temperature flexibility solved can be. The specialist would have by no means expects that when using a surplus on expensive silane coupling agent, which is known to increase the Stiffness, while improving low-temperature flexibility because these properties are contrary to his knowledge. The properties of rigidity and low-temperature flexibility or loss factor tan δ at 0 ° C and Low temperature flexibility could in terms of their usual behavior be decoupled.

The Sulfur crosslinkable rubber mixture contains at least one diene rubber. To include diene rubbers all rubbers with one unsaturated Carbon chain that is at least partially conjugated To derive service. Particularly preferred is when the diene rubber or the diene rubbers selected is or are from the group consisting of natural rubber (NR), synthetic polyisoprene (IR), polybutadiene (BR), isoprene-butadiene rubber (IBR) and styrene-butadiene copolymer (SBR). These diene elastomers can be easily processed to the rubber composition according to the invention and give good tire properties in the vulcanized tires.

The Rubber mixture may contain as diene rubber polyisoprene (IR, NR). These may be both cis-1,4-polyisoprene and 3,4-polyisoprene act. However, the use of cis-1,4-polyisoprenes is preferred with a cis-1,4 share> 90 Wt .-%. On the one hand, such a polyisoprene can be produced by stereospecific Polymerization in solution with Ziegler-Natta catalysts or using finely divided Lithium alkylene can be obtained. On the other hand it concerns with Natural rubber (NR) to such a cis-1,4 polyisoprene, the cis-1,4-portion in natural rubber is greater than 99 wt .-%.

If the rubber mixture contains polybutadiene (BR) as the diene rubber, these may be both cis-1,4- and vinyl-polybutadiene (40-90% by weight vinyl content). The use is preferred of cis-1,4-polybutadiene having a cis-1,4 content greater than 90% by weight, which can be prepared, for example, by solution polymerization in the presence of rare earth type catalysts.

at the styrene-butadiene copolymer may be solution-polymerized styrene-butadiene copolymer (S-SBR) having a styrene content, based on the polymer, of approx. 10 to 45 wt .-% and a vinyl content (content of 1,2-bound Butadiene, based on the total polymer) of 10 to 70% by weight which, for example, using lithium alkyls in organic solvent can be produced. The S-SBR can also be coupled and end-group modified be. It can but also emulsion-polymerized styrene-butadiene copolymer (E-SBR) and blends of E-SBR and S-SBR. The styrene content of the E-SBR about 15 to 40 wt .-% and it can the types known from the prior art, by copolymerization of styrene and 1,3-butadiene in aqueous Emulsion were used.

In addition to The said diene rubbers, the mixture but also other Types of rubber, such as Styrene-isoprene-butadiene terpolymer, butyl rubber, Halobutyl rubber or ethylene-propylene-diene rubber (EPDM), contain.

The rubber mixture according to the invention contains from 20 to 150 phr, preferably from 50 to 110 phr, of at least one silica. As far as the silica content is concerned, in the context of the present invention it is possible in principle to use any finely divided precipitated silica which is conventionally used for the preparation of rubber mixtures. In particular, such silicas are used as a filler having a BET surface area (according to ASTM D 5604) of 35 to 350 m ² / g, preferably from 145 to 270 m ² / g, a CTAB surface (according to ASTM D 3765) of 30 to 350 m ² / g, preferably from 120 to 285 m ² / g, a pore volume (according to DIN 66133) of 0.2 to 3.4 mL / g, preferably from 0.7 to 1.7 mL / g and a DBP number (according to ASTM D 2414) of 50 to 300 mL / 100 g, preferably from 150 to 250 mL / 100 g. Thus, for example, those of the type VN3 (commercial name) from Degussa and also highly dispersed silicas, so-called HD silicas (eg Ultrasil 7000 from Degussa) can be used as silicas.

When fillers In addition to silica, the rubber mixture may also contain carbon blacks, aluminum hydroxide, phyllosilicates, Chalk, starch, Magnesium oxide, titanium dioxide, rubber gels, etc. in any combination.

When Silane coupling agents can according to the invention Bis (3-triethoxysilylpropyl) tetrasulfane (TESPT) or commercial Organosilane mixtures having a bis (3-triethoxysilylpropyl) tetrasulfan moiety of at least 60 mol%, such as Si-69 or X50S (silanes on carbon black N-330, 50:50) from Degussa, or bis (3-triethoxysilylpropyl) disulfane (TESPD) or commercial Organosilane mixture with a bis (3-triethoxysilylpropyl) disulfane content of at least 80 mol%, such as Si-266 from Degussa become.

It has proved to be advantageous when the rubber mixture according to the invention up to 15 phf of the usually very expensive silane coupling agent contains because with these quantities a good compromise between the price of Mixture and the desired Properties can be achieved.

Next the already mentioned ingredients can the rubber mixture other additives customary in the rubber industry, such as e.g. Plasticizers, anti-aging agents, activators, e.g. zinc oxide and fatty acids (e.g., stearic acid), Waxes, resins and Mastikationshilfsmittel in usual parts by weight.

The Vulcanization is in the presence of sulfur or sulfur donors carried out, some sulfur donors at the same time as a vulcanization accelerator can act. Sulfur or sulfur donors are in the final mixing step in the usual by the expert Quantities (0.4 to 4 phr, sulfur preferred in amounts of 1.5 to 2.5 phr) was added to the rubber mixture.

Furthermore, the rubber composition may contain vulcanization-affecting substances such as vulcanization accelerators, vulcanization retarders and vulcanization activators in conventional amounts in order to control the time and / or the required temperature of the 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), guanidine accelerators such as N, N'-diphenylguanidine (DPG), dithiocarbamate accelerators such as zinc dibenzyldithiocarbamate, disulfides , The accelerators can also be used in combination with each other, which can result in synergistic effects.

The Preparation of the rubber mixture according to the invention done on conventional Way, being first usually a basic mix containing all ingredients except of the vulcanization system (sulfur and vulcanization-influencing Substances), is produced in one or more mixing stages and subsequently by adding the vulcanization system produces the finished mixture becomes. Subsequently the mixture is further processed, e.g. by an extrusion process, and in the appropriate form, e.g. the shape of a tread blank, brought. A thus produced tread blending blank is added the production of the pneumatic vehicle tire blank as known. The tread may also be in the form of a narrow rubber strip to be wound up.

To vulcanization, the vulcanizates have a good stiffness and an elevated one Loss factor tan δ at 0 ° C at improved low temperature flexibility. Car pneumatic tires with a tread of such a mixture have good handling properties and improved wet braking with ABS while improving Winter properties, i. good traction on icy and snowy Underground, on.

The Invention will now be described with reference to comparative and exemplary embodiments, which are summarized in Tables 1, are explained in more detail.

at all in the Table 1 mixture examples are the indicated Quantities Parts by weight based on 100 parts by weight of total rubber are related (phr). The comparative mixtures are marked V, the mixtures according to the invention are marked with E. The mixtures in Table 1 differ only in the quantities of silane coupling agent and aromatic used Mineral oil plasticizers. The amounts of plasticizer were varied to adjust the Shore A hardness of the vulcanizates.

• • Zugfestigkeit bei Raumtemperatur gemäß DIN 53 504
• • Spannungswerte bei 100, 200 und 300 % Dehnung bei Raumtemperatur gemäß DIN 53 504
• • Shore-A-Härte bei Raumtemperatur gemäß DIN 53 505
• • Rückprallelastizität bei Raumtemperatur gemäß DIN 53 512
• • Bruchenergiedichte bestimmt im Zugversuch nach DIN 53 504, wobei die Bruchenergiedichte die bis zum Bruch erforderliche Arbeit, bezogen auf das Volumen der Probe, ist
• • Verlustfaktor tan δ bei 0 gemäß DIN 53 513 aus Messung konstanter Spannungsamplitude von 50 ± 30 N bei einer Frequenz von 10 Hz
• • dynamischer Speichermodul E' bei –15 °C gemäß DIN 53 513 aus Messung mit konstanter Spannungsamplitude von 50 ± 30 N bei einer Frequenz von 10 Hz

Mixture preparation was carried out under standard conditions in two stages in a laboratory tangential mixer. Test specimens were prepared from all mixtures by vulcanization under pressure at 160 ° C. for 20 minutes, and the material properties typical of these rubber specimens, which are listed in Table 1, were determined. The following test methods were used for the tests on specimens:

• Tensile strength at room temperature in accordance with DIN 53 504
• • Tension values at 100, 200 and 300% elongation at room temperature according to DIN 53 504
• • Shore A hardness at room temperature according to DIN 53 505
• • Rebound resilience at room temperature according to DIN 53 512
• • Breaking energy density determined in the tensile test according to DIN 53 504, wherein the fracture energy density is the work required up to the break, based on the volume of the sample
• • Dissipation factor tan δ at 0 according to DIN 53 513 from measurement of constant voltage amplitude of 50 ± 30 N at a frequency of 10 Hz
• • dynamic storage modulus E 'at -15 ° C according to DIN 53 513 from measurement with a constant voltage amplitude of 50 ± 30 N at a frequency of 10 Hz

Table 1

• ^a High-cis polybutadiene type Nd-BR
• ^b 40 each of Traxsyn 5050 and 40 phr of Traxsyn 3070 from Goodyear
• ^c Ultrasil ^® VN3 from Degussa
• ^d X 50 S Degussa, organosilane mixture (Si 69 ^®) with a TESPT content of more than 80 mol% on carbon black N-330, a weight ratio of carbon black / silane: 50/50

The stress values at 100, 200 and 300 are a measure of the stiffness of the vulcanizates and high stress values are an indication of a good handling potential of the mixture and a good dry braking behavior when used in tires. The smaller the dynamic modulus E 'at -15 ° C, the higher the low temperature flexibility of the vulcanizates. In tires, a small dynamic modulus E 'at -15 ° C is associated with good winter properties. An increase in the loss factor tan δ at 0 ° C is in the tire industry as Measured for the wet grip of a mixture.

The Mixture 1 (V) contains 13.3 phr of X50S, corresponding to 7.65 phr of organosilane mixture, corresponding to 8 phf organosilane mixture. Mixtures 2 (E) and 3 (E) contain 21.0 phr X50S, corresponding to 10.5 phr organosilane mixture, respectively 11.05 phf organosilane mixture.

Out Table 1 shows that an increase in the proportion of silane coupling agent according to mixture 2 (E) a significant increase stiffness while increasing the loss factor tan δ at 0 ° C and improvement the low-temperature flexibility brings with it. If the mixtures according to mixture 3 (E) to almost same hardness as mixture 1 (V), so receives one with improved rigidity, a significant increase in the Loss factor tan δ at 0 ° C and a significant improvement in the low-temperature flexibility. For tires with a tread of the mixtures 2 (E) and 3 (E) leads this compared to a tire with the mixture 1 (V) as a tread to an improvement of the winter properties by 5 or 13% and in the wet grip when ABS brakes by 2 or 6%.

Claims (4)

Sulfur-crosslinkable rubber mixture, containing at least one diene rubber, 20 to 150 phr (parts by weight based on 100 parts by weight of the total rubber mass) of at least one of silica and a silane coupling agent (bifunctional organosilane) having as vulkanisationsreaktive, functional group, a sulfur chain having from 2 to 8 sulfur atoms, characterized characterized in that as silane coupling agent a) bis (3-triethoxysilylpropyl) tetrasulfan or an organosilane mixture having a bis (3-triethoxysilylpropyl) tetrasulfan portion of at least 60 mol% each in an amount of more than 10 phf (parts by weight based on 100 parts by weight Silicic acid) or b) bis (3-triethoxysilylpropyl) disulfane or an organosilane mixture having a bis (3-triethoxysilylpropyl) disulfane content of at least 80 mol% in each case in an amount of more than 11.5 phf. Rubber mixture according to claim 1, characterized in that that it contains 50 to 110 phr of silica. Rubber mixture according to claim 1 or 2, characterized characterized in that it contains up to 15 phf silane coupling agent. Tires, in particular pneumatic vehicle tires, whose treads at least in part on a sulfur vulcanized rubber compound according to one of the claims 1 to 3 based.