WO2008074567A1 - Rubber mixture and tires - Google Patents

Abstract

The invention relates to a sulfur-crosslinkable rubber mixture, especially for the treads of bicycle tires, comprising, for low rolling resistance, low abrasion and good wet performance - 25 phr (parts by weight, based on 100 parts by weight of all of the rubbers in the mixture) of at least diene rubber with functionalizations which can interact chemically or electrostatically with polar fillers, - > 7.5 phr of at least one polar filler and - 4-12 phf (parts by weight based on 100 parts by weight of polar filler) of at least two organosilane mixtures as silane coupling agents, where the organosilanes, as a vulcanization-reactive, functional group, have a sulfur chain having 2 to 8 sulfur atoms and the first organosilane mixture has a content of S2 organosilanes of at least 80 mol% and the second organosilane mixture has a content of S2 organosilanes of less than 20 mol% and a content of S4 organosilanes of at least 50 mol%.

Description

 description

Rubber compound and tires

The invention relates to a sulfur-crosslinkable rubber compound, in particular for the tread of two-wheeled pneumatic tires, comprising at least one diene rubber, at least one polar filler and at least one silane coupling tang. The invention further relates to a pneumatic vehicle tire, in particular a two-wheeled tire, having a tread which consists at least in part of such a sulfur-vulcanized rubber mixture.

Since the driving characteristics of a tire, in particular pneumatic vehicle tires, depend to a great extent on the rubber composition of the tread, particularly high demands are placed on the composition of the tread compound. Thus, many attempts have been made to positively influence the properties of the tire by varying the polymer components, fillers and other additives in the tread compound. It should be remembered that an improvement in one tire property often results in a deterioration of another property. Thus, an improvement in the rolling resistance of the tire and a reduction in abrasion are usually associated with a decrease in the wetness properties of the tire.

In order to influence the rolling resistance, it is known to vary the degree of filling, the type of filler, the crosslinking system and / or the glass transition temperature of the rubber. To influence tire properties such as abrasion, wet skid and rolling resistance, it is z. For example, it is known to use various styrene-butadiene copolymers with different styrene and vinyl contents and with different modifications for the rubber blends. It is known from EP 1 270 657 A1 to improve the properties of a tire with regard to wet grip, winter properties, abrasion and rolling resistance by using 30 to 90 phr of a solution-polymerized styrene-butadiene copolymer for the rubber mixture which forms the tire tread strip. S-SBR) having a styrene content of 5 to 35% by weight and a vinyl content of 10 to 85% by weight. The S-SBR is coupled, for example with tin, and is chemically modified with an amino group. The rubber composition also contains 10 to 70 phr of at least one other diene rubber, 20 to 100 phr of silica, 1 to 15 phr of silane coupling agent and 5 to 60 phr of a specific plasticizer.

EP 1 457 501 A1 discloses styrene-butadiene copolymers having a high vinyl content modified with primary amino groups and alkoxysilyl groups, processes for preparing these styrene-butadiene copolymers, rubber mixtures with these styrene-butadiene copolymers and tires whose Treads consist of this rubber mixture. The tires should be characterized by a good balance between abrasion resistance, durability, hysteresis loss and wet grip behavior.

EP 1 153 972 A1 describes rubber compounds for tire treads which comprise styrene-butadiene copolymers having coupling centers with epoxide groups, optionally further diene rubbers, processing oil, silica and vulcanizing agent. The coupling centers are within the polymer backbone and not as end groups. The rubber compounds show good processability and should cause a low rolling resistance with good wet grip when tires.

Polar fillers such as silica, silicates or aluminosilicates have on their surface polar groups, eg. For example, OH groups, and have been used for many years in rubber blends to improve the properties of rubber blends.

In order to improve the processability and to bond the silica and other optional polar fillers to the diene rubber, silane Coupling agents used in rubber compounds. 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. In the latter group may be z. These may be, for example, the following chemical groups: -SCN, -SH, -NH ₂ or -S _x - (where x = 2-8). Thus, as silane coupling agents z. B. 3-mercaptopropyltriethoxysilane, 3-thiocyanato-propyltrimethoxysilane or 3,3'-bis (triethoxysilylpropyl) polysulfanes having 2 to 8 sulfur atoms, such as. B. 3,3'-bis (triethoxysilylpropyl) tetrasulfan (TESPT), the corresponding disulfane (TESPD) or mixtures of the AnIf anen having 1 to 8 sulfur atoms with different

Used in the various sulfanes, are used in the tire industry almost exclusively silane coupling agents with sulfur chains. As a dosage of the silane coupling agents, the manufacturers recommend amounts of 1 to a maximum of 10 phf (parts per hundred parts of filament by weight), since then an optimal binding of the filler to the rubber (s) can take place.

The invention is based on the object of providing rubber mixtures for the treads of pneumatic vehicle tires, in particular two-wheeled tires, which cause a reduced rolling resistance and a reduced abrasion while maintaining a good wet behavior during the tire.

This object is achieved according to the invention in that the rubber mixture

> 25 phr (parts by weight, based on 100 parts by weight of the total rubbers in the mixture) of at least diene rubber with functionalizations which can chemically or electrostatically interact with polar fillers,

-> 7.5 phr of at least one polar filler and - 4 - contains 12 phf (parts by weight based on 100 parts by weight of polar filler) of at least two organosilane mixtures as silane coupling agents, wherein the organosilanes as vulcanization reactive functional group having a sulfur chain with 2 to 8 sulfur atoms and the first organosilane a content of S ₂ - organosilanes of at least 80 mol% and the second organosilane mixture one

Content of S ₂ -organosilanes of less than 20 mol% and a content of S ₄ - organosilanes of at least 50 mol%.

The term phr (parts per hundred parts of rubber by weight) used in this document is the quantity used in the rubber industry for mixture formulations. The dosage of the parts by weight of the individual substances is always based on 100 parts by weight of the total mass of all the rubbers present in the mixture.

The term phf (parts per hundred parts of filament by weight) used in this document is the quantity used in the rubber industry for doses of silane coupling agents. The dosage of the parts by weight of the individual substances is based on 100 parts by weight of the mass of polar filler, in particular silica, with which the silane coupling agent interacts.

Surprisingly, it has been found that by the specific combination of a diene rubber with functionalizations that can chemically or electrostatically interact with polar fillers, with a polar filler and at least two different organosilane mixtures - one with a high content of S ₂ organosilane and one with a high content vulcanizates which, when used in tire treads, at the same time improve the abrasion and rolling resistance behavior without adversely affecting the wetness properties (wet brakes), can be obtained on S ₄ -organosilane.

As a diene rubber with functionalizations that can chemically or electrostatically interact with polar fillers, different rubbers with For example, be modified amino, alkoxysilyl and / or epoxy groups. As rubber types come z. As natural rubber, synthetic polyisoprene, polybutadiene and styrene-butadiene copolymers into consideration, which can also be coupled, for example with tin, can be used. Various functionalized diene rubbers can also be used in the blend.

It has been found to be particularly advantageous with regard to rolling resistance, abrasion and moisture properties when the diene rubber with the functionalizations is a solution-polymerized styrene-butadiene copolymer which is modified with primary amino groups, alkoxysilyl groups and / or epoxide groups. As solution-polymerized styrene-butadiene copolymers, for example, so-called HPR types from JSR Corporation, the preparation of which is disclosed, for example, in EP 1 457 501 A1, or NS 116 R from Nippon Zeon (see, for example, US Pat. No. 4,616,069) can be used ,

The solution-polymerized styrene-butadiene copolymer preferably has a vinyl content of 35-80% by weight and a styrene content of 10-35% by weight. For example, the amino groups and with alkoxysilyl groups functionalized solution polymerized styrene-butadiene copolymers HPR 355 _(Tg: -27 ⁰ C, 28 wt .-% styrene, 56 wt .-% vinyl) can and HPR (350 _Tg: -35 ⁰ C, 21% by weight of styrene, 55% by weight of vinyl) from JSR Corporation.

As a polar filler, the rubber mixture preferably contains silica in amounts of from 40 to 110 phr. 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. As silicas can thus z. B. those of the type VN3 (trade name) of the company Degussa as well as highly dispersed silicic acids, so-called HD silicas, (eg Ultrasil 7000 from Degussa) are used.

The rubber mixture according to the invention contains a total of 4-12 phf, preferably 6-10 phf, at least two organosilane mixtures as silane coupling agents, wherein the organosilanes as Vulcanisationsreaktive functional group having a sulfur chain with 2 to 8 sulfur atoms and the first organosilane a content of S ₂ - Organosilanes of at least 80 mol% and the second organosilane mixture has a content of S ₂ -organosilanes of less than 20 mol% and a content of S ₄ -organosilanes of at least 50 mol%.

According to an advantageous development of the invention, the first and second organosilane mixtures are used in a ratio of 0.25: 1 to 10: 1, preferably 1: 1 to 5: 1.

The S ₂ and S ₄ organosilanes may have different organic radicals, such as 3-trimethoxysilylpropyl or 3-trimethoxysilylhexyl radicals. However, it is preferred if the S ₂ organosilane is bis (3-triethoxysilylpropyl) disulfane and the S ₄ organosilane is bis (3-triethoxysilylpropyl) tetrasulfan. First organosilane mixture with a S ₂ -Organosilangehalt of more than 80 mol%, for example, Silquest ^® A-1589 from General Electric Specialty or Si-266 from Degussa can be used. As a second organosilane mixture having a content of S ₂ -organosilanes of less than 20 mol% and a content of S ₄ -organosilanes of at least 50 mol% z. B. Si-69 or X50S (silanes on carbon black N-330, 50:50) from Degussa be used.

In addition to the functionalized diene rubber (s), the rubber composition may also contain other non-functionalized or otherwise functionalized rubbers in amounts up to 75 phr. These rubbers may be selected from the group consisting of natural rubber (NR), synthetic polyisoprene (IR), polybutadiene (BR), styrene Butadiene copolymers (SBR), styrene-isoprene-butadiene terpolymer, butyl rubber, halobutyl rubber or ethylene-propylene-diene rubber (EPDM).

However, it is preferred if the rubber mixture as further rubbers at least one diene rubber selected from the group consisting of

Natural rubber, synthetic polyisoprene, polybutadiene and styrene-butadiene copolymers. These diene rubbers work well with the rubber compound and provide good tire properties in the cured tires.

The rubber mixture may contain polyisoprene (IR, NR) as the diene rubber. These may be both cis-1,4-polyisoprene and 3,4-polyisoprene. However, preference is given to the use of cis-1,4-polyisoprenes having a cis-1,4-content of> 90% by weight. First, such a polyisoprene can be obtained by stereospecific polymerization in solution with Ziegler-Natta catalysts or using finely divided lithium alkyls. On the other hand, natural rubber (NR) is one such 1,4-polyisoprene; the cis-1,4-content in natural rubber is greater than 99% by weight.

If the rubber mixture contains polybutadiene (BR) as the diene rubber, these may be both 1,4-vinyl and vinyl polybutadiene (40-90% by weight vinyl content). Preferably, the use of cis-l, 4-polybutadiene with a cis-l, 4-portion greater than 90 wt .-%, which z. By solution polymerization in the presence of rare earth type catalysts.

The other styrene-butadiene copolymers are those which do not fall under the specially modified solution-polymerized types of claim 1. It can be z. B. not or otherwise modified or coupled solution-polymerized styrene-butadiene copolymers act. However, it is also possible to use emulsion-polymerized styrene-butadiene copolymers (E-SBR) and also mixtures of E-SBR and S-SBR. The styrene content of the E-SBR is about 15 to 50 wt .-% and it can from The prior art types obtained by copolymerization of styrene and 1,3-butadiene in aqueous emulsion can be used.

In order to further improve the abrasion behavior and the rolling resistance of tires, it has proved to be advantageous if the rubber mixture contains, as plasticizer, 5 to 30 phr of at least one liquid polybutadiene having a molecular weight of 1500-10,000 g / mol and a vinyl content of 15-50 wt .-% contains.

In addition to the ingredients already mentioned, the rubber mixture can be further customary in the rubber industry additives such. As carbon blacks, short fibers, rubber gels, other plasticizers, aging inhibitors, activators, such as. As zinc oxide and fatty acids (eg., Stearic acid), waxes and Mastikationshilfsmittel in usual parts by weight.

The vulcanization is carried out in the presence of sulfur or sulfur donors, with some sulfur donors can also act as a vulcanization accelerator. Sulfur or sulfur donors are added in the last mixing step in the amounts customary by the person skilled in the art (0.4 to 4 phr, sulfur, preferably in amounts of 1.5 to 2.5 phr) of 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 groups of accelerators: thiazole accelerators such as. B. 2-mercaptobenzothiazole, sulfenamide accelerators such as. B. benzothiazyl-2-cyclohexylsulfenamid (CBS), guanidine accelerators such as. N, N'-diphenylguanidine (DPG), dithiocarbamate accelerators such as. 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 is carried out in a conventional manner, in which case a base mixture which contains all constituents except the vulcanization system (sulfur and vulcanization-influencing substances) is first prepared in one or more mixing stages and subsequently by addition of the vulcanization system Ready mix is produced. Subsequently, the mixture is further processed, for. B. brought by an extrusion process, and in the appropriate form. Preferably, the mixture is brought into the form of a tread. A tread blending blank produced in this way is laid down in the production of the vehicle pneumatic tire blank, in particular a two-wheeled tire blank, as is known. It is irrelevant in the tires whether the entire tread has been made from a single mixture or z. B. has a cap and base structure, because it is important that at least the coming into contact with the road surface of the rubber composition according to the invention has been prepared.

The invention will now be described by way of comparative and exemplary embodiments, which in the

Tables 1 and 2 are summarized.

The comparative mixtures are marked with V, the mixtures according to the invention are marked with E. The mixtures 1 to 6 differ only in the type and optionally amount of the following substances: solution-polymerized styrene-butadiene copolymer, plasticizer and silane coupling agents. For blends 4 and 6, the amounts of accelerator and sulfur were increased to keep the crosslink density in the polymer matrix constant.

Table 1

a High-cis Polybutadien b lösungspolymerisiertes Styrol-Butadien-Copolymer, VSL-5025, Lanxess, Deutschland c funktionalisiertes, lösungspolymerisiertes Styrol-Butadien-Copolymer, HPR 355, JSR

a high-cis polybutadiene b solution-polymerized styrene-butadiene copolymer, VSL-5025, Lanxess, Germany c functionalized, solution-polymerized styrene-butadiene copolymer, HPR 355, JSR

Coporation, Japan, vinyl content: 56 wt .-%, styrene content: 28 wt .-% of molecular weight: 2500 g / mol, vinyl content: 20-35%, Centricon ^® 130, Ricon Resins Inc,

USA

'Silica HD, RHODIA Zl 165 MP f Silquest ^® A-1589 from General Electric Specialty, USA, organosilane mixture with a mol S2-organosilane of more than 80% ^g X 50 S from Degussa, Germany, organosilane mixture (Si ^69® ) with an S ₄ -organosilane content of more than 50 mol% on carbon black N-330, weight ratio of carbon black / silane: 50/50

Mixture preparation was carried out under standard conditions in two stages in a laboratory tangential mixer. From all mixtures test specimens were prepared by vulcanization for 20 minutes under pressure at 160 ⁰ C and determined with these specimens for the rubber industry typical material properties listed in Table 2. The following test methods were used for the tests on test specimens: Tensile strength at room temperature in accordance with DIN 53 504

• Elongation at room temperature according to DIN 53 504

• Stress values at 50, 100 and 200% elongation at room temperature according to DIN 53 504

Shore A hardness at room temperature and 70 ^° C. in accordance with DIN 53 505. Rebound resilience at room temperature and 70 ^° C. in accordance with DIN 53 512

• Abrasion according to DIN 53516. The abrasion of the mixture 1 was set equal to 100, values greater than 100 mean an improvement of the abrasion, equivalent to a reduction of the DIN abrasion volume.

Table 2

From the data in Table 2 it can be seen that only when combining functionalized SSBR with the two organosilane mixtures (blends 5 (E) and 6 (E)) does the rebound resilience at 70 ^° C., which serves as a measure of rolling resistance in tires (higher Rebound resilience value at 70 ^° C. = lower rolling resistance), while the rebound resilience at room temperature serving as a measure of good wet braking of tires (lower rebound resilience value at room temperature = better wet braking) remains at the level of the starting mixture 1 (V) , At the same time, the abrasion behavior is surprisingly significantly improved. The sole use of the organosilane mixtures (mixture 2 (V)) or the use of only the special SSBR (mixtures 3 (V) and 4 (V)) do not show these effects.

In addition, Table 2 shows that abrasion performance and rolling resistance can be further improved by using a liquid polybutadiene as a plasticizer instead of an aromatic processing oil.

Claims

claims 1. Sulfur-crosslinkable rubber mixture, in particular for the tread of two-wheeled pneumatic tires, containing> 25 phr (parts by weight, based on 100 parts by weight of the total rubbers in the mixture) of at least diene rubber with functionalizations which can chemically or electrostatically interact with polar fillers,> 7.5 phr at least one polar filler and - 4 - 12 phf (parts by weight based on 100 parts by weight of polar filler) of at least two organosilane mixtures as silane coupling agents, wherein the Organosilanes as a vulcanization-reactive, functional group having a sulfur chain with 2 to 8 sulfur atoms and the first organosilane have a content of S ₂ organosilanes of at least 80 mol% and the second organosilane a content of S ₂ organosilanes of less than 20 mol% and a content at S ₄ -organosilanes of at least 50 mol%. 2. Rubber mixture according to claim 1, characterized in that the diene rubber with the functionalizations is a solution-polymerized styrene-butadiene copolymer which is modified with primary amino groups, alkoxysilyl groups and / or epoxy groups. 3. Rubber mixture according to claim 2, characterized in that the solution-polymerized styrene-butadiene copolymer has a vinyl content 35-80% by weight and a styrene content of 10-35% by weight. 4. rubber mixture according to at least one of the preceding claims, characterized in that the polar filler is silica and is used in amounts of 40 - 110 phr. 5. Rubber mixture according to at least one of the preceding claims, characterized in that it contains 6 to 10 phf of at least two organosilane mixtures as silane coupling agents. 6. rubber mixture according to at least one of the preceding claims, characterized in that the first and the second organosilane mixture in the ratio of 0.25: 1 to 10: 1, preferably 1: 1 to 5: 1, are used. A rubber composition according to at least one of the preceding claims, characterized in that the S ₂ organosilane is bis (3-triethoxysilylpropyl) disulfane. 8. Rubber mixture according to at least one of the preceding claims, characterized in that the S ₄ organosilane is bis (3-triethoxysilylpropyl) tetrasulfan. 9. Rubber mixture according to at least one of the preceding claims, characterized in that contains as further rubbers at least one diene rubber selected from the group consisting of natural rubber, synthetic polyisoprene, polybutadiene and styrene-butadiene copolymers. 10. Rubber mixture according to at least one of the preceding claims, characterized in that it contains as plasticizer 5 to 30 phr at least one liquid polybutadiene having a molecular weight of 1500 - 10000 g / mol and a vinyl content of 15 to 50 wt .-%. 11. Pneumatic vehicle tire, in particular two-wheeled tire, with a tread which consists at least in part of a sulfur-vulcanized rubber composition according to one of claims 1 to 10.