RU2308469C1 - Curable rubber compound for low-hysteresis tire treads with improved catenation properties and wear resistance - Google Patents

Abstract

FIELD: rubber industry.

SUBSTANCE: invention relates to rubber compounds used in tire manufacture, in particular to rubber compounds for manufacturing low-hysteresis treads of fuel-sparing tires showing improved bite properties. Reduced-density curable polydiene-based rubber compound comprises precipitated silica extender, silane binders, and target additives, said silane binders rubber compound containing triethoxysilyl-propyl-mercaptobenzothiazole sulfide combined with bis[3-triethoxysilyl-propyl] tetrasulfide at ratio between 0.3 and 3.3 and in summary proportion to percentage of precipitated silica extender between 0.097 and 0.133.

EFFECT: reduced hysteresis in tread rubber at 60°C, enhanced hysteresis and bite properties at 0°C and simultaneously reduced residual compaction after repetitive deformations and increased wear resistance of rubber.

2 tbl, 2 ex

Description

The invention relates to rubber mixtures used in the manufacture of tires, specifically to rubber mixtures for the manufacture of treads of low hysteresis fuel-efficient tires with improved grip. In rubber mixtures of the indicated type, emulsion (BSK) or solution (DSS) styrene-butadiene rubbers or their mixtures with other polydienes are used as the main polymer, modern brands of precipitated silicic acid fillers (OKN) with small additives of carbon black are used as reinforcing fillers, silane coupling agents, mainly bis- [3- (triethoxy) silylpropyl, are used as additives to ensure hydrophobization of hydrophilic particles of OKN in the hydrophobic matrix of rubber and its dispersion ] -tetrasulfide (TESPT).

The first stage of the manufacture of low-hysteresis rubber compounds is carried out in closed-type mixers in a mode that ensures silanization of OKN particles by TEPST molecules at temperatures in the range of 145-155 ° C. When the mixing temperature is increased above 155 ° C, in addition to silanization of the OKN particles and improvement of its dispersion in the rubber matrix, an undesirable decomposition of TEPST sulfide bridges occurs and TEPST joins not only to the surface of the OKN particles, but also to the rubber, which causes an increase in the viscosity of rubber compounds and a decrease safety of their further processing.

To overcome this disadvantage, TEPST is known to use blocked mercaptosilane binding agents (BMSSA) as CCAs, in which there are no di- and polysulfide groups capable of thermal dissociation, and instead a substituent is introduced - a thioacid residue (US Patent: 6,528,673 (prototype); 6,414,061) or the radical mercaptobenzthiazolyl (RF patent No. 2267493 with priority dated January 15, 2004).

Blocked BMSSA proposed in rubber mixtures according to the prototype and in RF patent No. 2267493 allow avoiding viscosity increase at the first stage of preparation of rubber compounds, however, hysteresis in the resulting rubbers obtained at 60 ° C achieved using known BMSSA correlates with rolling losses in the tire tread, and an increase in hysteresis at 0 ° C, which correlates with an increase in the adhesion properties of wet and icy rubbers, is insufficiently provided. This is manifested in an insufficiently high ratio of hysteresis indices, measured by the tangent of the angle of mechanical loss (tanδ), at 0 ° C and at 60 ° C in the rubber according to the prototype, that is, in an insufficiently high value of tanδ (0 ° C) / tanδ (60 ° C ) In addition, in rubbers with BMSSA according to the prototype, advantages are not achieved over reference rubbers with TEPST in terms of wear resistance, and in most cases, in terms of the residual compressive strain associated with the ability of rubbers to accumulate residual strain during repeated compression, which increases heat generation and reduces the durability of rubber products.

The objective of the invention is to create vulcanizable rubber compounds with low viscosity for treads of low hysteresis tires, which provide higher ratios tgδ (0 ° C) / tgδ (60 ° C) than prototype rubbers, the growth of which reflects an increase in the adhesion properties of rubbers with wet and icy coating, as well as having increased wear resistance and low residual deformation of compression in comparison with the prototype rubbers. The solution of this problem is achieved by the fact that in rubber mixtures with low viscosity, providing low hysteresis at 60 ° C rubbers with high adhesion properties, the known (patent of the Russian Federation No. 2267493) blocked mercaptosilane - triethoxysilylpropyl mercaptobenzthiazole sulfide - TESPMSS in combination with the widely used TEPS are used as CCAs moreover, these ingredients are taken in ratios of from 0.3 to 3.3 with the ratio of their total content in the mixture (in parts by weight per 100 parts by weight of rubber) to the filler dosage from 0.097 to 0.133.

The difference between the rubber compounds with low viscosity to obtain low hysteresis at 60 ° C tire tread with increased adhesive properties according to the invention from similar rubber compounds according to the prototype is that not only one blocked mercaptosilane binding agent is used as CCA, but its combination with the known bifunctional CCA bis- [3- (triethoxy) silylpropyl] -tetrasulfide (TEPST), triethoxysilylpropyl mercaptobenzothiazole sulfon is used as a blocked mercaptosilane coupling agent (BMCCA) d described in Russian patent №2267493, wherein the thiol group (-SH) of the corresponding 3-mercaptopropyl-triethoxysilane substituted 2-merkaptobenztiazilnym radical instead tioatsilnogo radical in merkaptoakilsilanovyh blocked binding agents according to the prototype.

The specified difference between vulcanized rubber compounds with reduced viscosity for the tread of low hysteresis tires with improved grip according to the invention from similar rubber compounds according to the prototype creates their advantages compared to the prototype, which consists in increasing the ratio tgδ (0 ° C) / tanδ (60 ° C), which correlates with an increase in grip, compared to this ratio for standard rubbers with TESPT, as well as in a decrease in residual compression during repeated deformations and in an increase in wear resistance and rubbers.

The possibility of carrying out the invention is illustrated by the following examples, in which Ultrasil 7000, Ultrasil 7005, Zeokol 8745, Hisil 255 can also be used as OKN.

Example 1

The effect of the combination of a blocked mercaptosilane coupling agent triethoxysilyl-propylmercaptobenzothiazole sulfide (TESPMSB) and the known bis- [3- (triethoxysilylpropyl) -tetrasulfide (TESPT), taken in various ratios, in the formula of the standard rubber compound based on the formula -30ARK obtained using OKN, in comparison with the action of the widely used TESPT, produced, for example, by OSI Specialties under the trade name Silquest A-1289.

Rubber compounds are made based on 100 wt. parts (parts) of emulsion butadiene-styrene rubber SKS-30ARK, 40 parts by weight OKN of Zeosil 1165 MP brand (manufactured by Rhodia), process oil PN-6 w (8.0 parts by weight), zinc oxide (2.5 parts by weight), stearic acid (2.0 parts by weight) , a vulcanization accelerator of sulfenamide C (1.0 parts by weight), a secondary vulcanization accelerator, which is at the same time a release agent for the blocked mercaptosilane according to the proposed invention, DFG (1.2 parts by weight) and sulfur (1.6 parts by weight) in the standard, in the mixtures according to the invention, is variable and calculated taking into account the deficiency of sulfur atoms in the TESPMSS molecule in comparison with the TEPST molecules).

The reference mixture (I) contains 4 parts by weight of silane coupling agent. per 100 parts by weight bifunctional rubber TESPT.

In the mixture II-IV according to the invention, together with TESPT in a reduced dosage compared to its dosage in the reference mixture, blocked mercaptosilane (TESPMS) is introduced in an amount of 0.3-3.3 respectively from the dosage of TESPT in the reference mixture, while the dosage of sulfur in the mixtures according to the invention is increased so that the number of gram atoms of free and sulfide (in silanes) sulfur in the mixtures is the same. The number of sulfur atoms in TESPT was taken equal to 4.

The secondary DFG vulcanization accelerator, which is also a release agent in the mixtures of the invention, is introduced into all mixtures in the first stage of the production of mixtures.

The manufacture of mixtures is carried out in a closed laboratory mixer according to the following mode:

I stage

The temperature of the rubber mixer chamber is 70 ° C, the load factor is 0.65-0.67

- rubber, 3/4 OKN of the Zeosil 1165 MP brand, stearic acid, silane coupling agent (or blocked mercaptosilane), DFG - for 0 s;

- 1/4 OKN of the Zeosil 1165 MP brand, PN-6 sh oil, ZnO - for 120 s;

- unloading the mixture at a temperature of 155 ± 5 ° C;

- total mixing time - 270-300 s.

II stage

The temperature of the rubber mixer chamber is 40 ° С

- masterbatch - for 0 s;

- sulfur and accelerators - for 30 s;

- unloading at a temperature of 100-110 ° C;

- total mixing time is 150-180 s.

The vulcanization of the mixtures is carried out at 155 ° C for 1500 s.

The properties of the reference and experimental rubber compounds and vulcanizates are shown in table 1.

As can be seen in table 1, the reference mixture I, where TESPT was used, has a high Mooney viscosity at 100 ° C.

The viscosities of all the mixtures according to the invention (60-66 Mooney units) are noticeably lower than that of the reference mixture, due to the better dispersing effect of TESPMSBS, the monofunctional blocked mercaptosilane, on the WIND in the first stage of manufacturing the rubber mixture and its inability to chemically bind KN particles with rubber macromolecules at this stage due to the absence of a polysulfide group in the TESPMSS molecule. The reduced viscosity reduces the risk of vulcanization of the mixtures according to the invention during further processing.

The best dispersion of OKN in mixtures II-IV with TESPMS according to the invention is also manifested in higher than in the reference rubber, the values of the stress ratios at 300 and 100% elongations (M300 / M100). Such an action of silane coupling agents (both conventional, such as TESPT, and blocked) is called “promoting” with respect to OKN.

Providing the best “promotion” of OKN and the best technological properties of rubber compounds, the proposed joint use of TESPT and TESPMSS allows to obtain hysteresis indices (tgδ) at 60 ° C for rubbers III and IV according to the invention, which are 20% lower than that of the reference rubber associated with the level of mechanical losses in the tire tread during rolling, and higher tanδ values at 0 ° C, which indirectly characterize the adhesion properties of the tread rubber. Table 1 also provides direct confirmation of the growth of dry and wet adhesion coefficients for all rubbers of the invention compared to a reference rubber.

For rubbers II and V according to the invention with a lower stress than 300% elongation, values of tgδ at approximately 60 ° C are approximately equal to the reference rubber, while maintaining advantages over the reference rubber, that is, with a higher tgδ value of these rubbers at 0 ° C. These data are consistent with a higher rebound elasticity (59-62) for the rubbers of the invention than the reference (57) at 100 ° C, and with higher dry and wet adhesion ratios of these rubbers compared to the reference.

In comparison with the best rubber of the prototype (rubber E in example 15 of US patent No. 6,528,673), for which the ratio tgδ (0 ° C) / tgδ (60 ° C) is higher than that of the reference rubber by 25%, but the abrasion resistance is lower than the standard, in the best rubber according to the invention - IV, the growth of the ratio tgδ at 0 ° and 60 ° C compared to the standard rubber reaches 29%, and it exceeds the standard with one TESPT in a number of other indicators (abrasion resistance, residual deformation and heat generation with multiple compression), which provides its advantage over rubbers with locked measurements ptosilanami prototype.

Example 2

The effect of the combination according to the invention of the blocked mercaptosilane binding agent TESPMSS and the known TESPT taken in different respects is illustrated in comparison with the action of one TESPT in the formulation of a typical tread rubber composition for passenger tires based on oil-filled (oil content 37.5%) Buna grade DSSK VSL 5025-1, 25 parts by weight, as well as butadiene rubber SKD and OKN.

The formulation of mixtures per 103 wt. including Buna VSL 5025-1 includes: SKD rubber - 25 parts by weight, Zeosil 1165 MP OKN - 60 parts by weight, process oil PN-6 w - 10 parts by weight, carbon black N-234 -6 parts by weight, zinc oxide - 2 parts by weight, stearic acid - 2 parts by weight, salicylic acid - 1 parts by weight, vulcanization accelerator sulfenamide C-1.5 parts by weight, secondary DFG accelerator, which is at the same time as a deblocking agent in mixtures with TESPMSS - 1.5 parts by weight, microcrystalline wax - 1.5 parts by weight, antiazonant and anti-tear agent Diafen FP - 2 parts by weight, sulfur - in the standard 1.6 parts by weight ., in the mixtures according to the invention is variable and calculated taking into account defi cytosis of sulfur atoms in the TESPMSS molecule as compared to the TEPST molecules.

The reference mixtures (VI and VII) contain 5 wt.h. per 100 parts by weight TESPT rubber and differ among themselves in the preparation mode in the first stage. The sulfur content in them is the same and is 1.6 parts by weight per 100 parts by weight rubber.

In a mixture of VIII (reference 3) 5 parts by weight bifunctional TESPT completely replaced by 7.2 wt.h. blocked mercaptosilane TESPMSS, and the indicated dosage of TESPMSS is taken based on the equality in it of the molar content of ethoxy groups reactive with respect to OKN to the amount of these groups in 5 parts by weight TESPT. In the same mixture, the sulfur dosage is increased from 1.6 parts by weight. up to 2.1 parts by weight taking into account the missing 7.2 wt.h. TESPMSS of the number of gram-sulfur atoms in comparison with their number in replaceable 5 parts by weight reference TESPT.

In IX-X mixtures, equilibrated (1: 1) dosages of TESPT on TESPMSS (2.5 and 2.9 parts by weight) are used, while in mixture IX the dosage of sulfur is taken as in a reference mixture (1.6 wt. hours), and in a mixture of X it increases to 2 parts by weight taking into account its deficit in the used amount of TESPMS in comparison with its quantity in the replaced amount of TESPT.

Finally, in the mixture XI according to the invention, the total content of CCA is taken to be equal to the mixture X, however, the dosage ratio of TESPMS and TESPT increases to 1.5, taking into account the possible reduction in the price of the mixture.

A secondary vulcanization accelerator, DFG, which is also a release agent in the mixtures of the invention, is introduced into all mixtures in the first mixing stage.

The manufacturing mode of the VI-XI rubber compounds according to example 2 in the first and second stages does not differ from the mode according to example 1, except that before the first stage of manufacturing the mixture VI (reference 1), the temperature of the rubber mixer chamber is 60 ° C, and for the rest of the mixtures - 100 ° C. The discharge temperature of mixture VI is 155 ° C, and of mixtures VII and VIII (standards 2 and 3) is 165 ° C, as for the other mixtures IX-XI. By increasing the discharge temperature, better dispersion and “promotion” of the OKN is achieved, which, based on the results given in Example 1, can be easily implemented in the mixtures according to the invention, where there is no danger of viscosity increase in the first stage of the production of mixtures, in contrast to the mixture of reference VII.

The properties of the reference and experimental rubber compounds and vulcanizates are shown in table 2.

As can be seen from table 2, the reference mixture VII with TEPST discharged in the first stage at 165 ° C, there is an undesirable increase in viscosity, which in the future may adversely affect the technological properties. Lowering the discharge temperature for the reference mixture VI, although it leads to a slight decrease in viscosity, does not allow the full use of the enhancing effect of OKH due to the reduction of silanization of the surface of OKH particles and the deterioration of its dispersion conditions.

In rubber from mixture VIII (reference 3), in which the entire TESPT is replaced by TESPMS, judging by the stress index at 300% elongation (M300 = 5.1 MPa), the degree of crosslinking equivalent to the reference rubbers is not achieved (M300 = 7.6-7 , 9 MPa), and the required level of other strength properties. Only the combined use of TESPT and TESPMSS with a ratio of their total content in the mixture to a dosage of OKN of at least 0.097, as in the X-XI mixtures according to the invention, allows them to obtain values of elastic strength properties equivalent to reference rubbers 1 and 2.

The better promoting effect of the blocked mercaptosilane TESPMSBS compared to the bifunctional TESPT when dispersing the OKN in the first stage of the manufacture of rubber compounds X, XI according to the invention made it possible to significantly reduce by 14 Mooney units their viscosity compared to the viscosity of the standard mixtures, while simultaneously increasing the temperature of the first stage of the manufacture of mixtures, which provides the best promotion of OKN, and greater safety during further processing. In rubbers from mixtures X, XI according to the invention, higher values are achieved than for standard rubbers, stress at 300% elongation, hardness at lower hysteresis (tanδ) at 60 ° C.

In addition, for rubbers from mixtures X, XI according to the invention, as can be seen in Table 2, lower elasticities at 20 ° C are achieved than for reference rubbers and, accordingly, higher than the prototype rubbers, the ratios tgδ ( 0 ° C) / tanδ (60 ° C), which is consistent with the increase in wet grip coefficients in these rubbers.

Table 2 also shows the superiority of rubbers from mixtures X, XI according to the invention over reference rubbers and, accordingly, over rubbers of the prototype in terms of abrasion resistance.

Claims (1)

Low viscosity vulcanizable rubber compound for low hysteresis rubbers of tire treads based on polydienes, precipitated silicic acid filler, silane coupling agents and target additives, characterized in that the mixture contains blocked mercaptosilane triethoxysilylpropyl mercaptoxybisthiazole as silane coupling agents ) -silylpropyl] -tetrasulfide, and the dosages of these components are taken in the ratio of from 0.3 to 3.3, with respect to their total content in the mixture (wt. .h) to a dosage of precipitated silica filler from 0.097 to 0.133.