DE102009044393A1 - Sulfur crosslinkable rubber mixture, useful for producing tires, preferably commercial vehicle tires, comprises polyisoprene, a highly crosslinked microgel whose surface is modified with polar groups and carbon black - Google Patents

Abstract

Sulfur crosslinkable rubber mixture comprises greater than 75 parts per hundred parts of rubber by weight (phr) of polyisoprene, up to 10 phr of at least one highly crosslinked microgel whose surface is modified with polar groups, on the basis of a butadiene rubber and carbon black, where the rubber mixture is free of silane coupling agents. An independent claim is included for tires, preferably commercial vehicle tires, where at least to some extent, the tire tread is based on the sulfur-vulcanized rubber mixture.

Description

The invention relates to a sulfur-crosslinkable rubber mixture which is free of silane coupling agents and contains polyisoprene, at least one microgel and carbon black. Furthermore, the invention relates to a tire, in particular a commercial vehicle tire whose tread consists at least partly of the 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 and fillers in the tread compound. It should be remembered that an improvement in one tire property often results in a deterioration of another property.

In pneumatic vehicle tires, especially in commercial vehicle tires, great attention is paid to the durability of the tires. The durability of pneumatic vehicle tires is z. B. impaired by a poor tear and tear propagation behavior and poor Dauerermüdungseigenschaften the tread compound.

In order to obtain rubber compounds with high tear propagation resistance, it is customary to use a large proportion of polyisoprene, in particular natural rubber, for the mixture. However, the use of natural rubber causes a higher tendency of the vulcanizates to reversion, which is accompanied by a deterioration of the fatigue properties. Although the reversion of natural rubber can be counteracted by the addition of anti-reversion agents, such as 1,3-bis (citracoimidomethyl) benzene, the additional crosslinking results in negative changes in the ultimate tear properties of tensile strength and elongation at break.

In order to improve the tear propagation of a rubber article, in particular a tread of a pneumatic vehicle tire, after damage, it is also known to use non-silanized silica (non-activated silicic acid) in the rubber mixture. For this purpose, usually 6 to 10 phr of silica are used. However, this shows that the tear propagation behavior at room temperature and other physical properties does not always reach the desired level.

For some time so-called "microgels" have been used as fillers for rubber compounds to improve their properties. Microgels are polymeric fillers based on rubber gels, which generally consist of particles of peroxide-crosslinked diene rubbers (BR, SBR, IR, etc.). The microgel particles are often prepared by emulsion polymerization or suspension polymerization, which can be adjusted particle sizes between about 5 and 1000 nm.

The microgels are used as a substitute for silica or carbon black, with full or partial replacement being contemplated.

To improve the physical / mechanical properties of rubber mixtures, chemically modified microgels have also been used. For example, microgels are from the WO 02/12389 and those cited herein US 5,124,408 . US 5,395,891 . DE 197 67 29 and DE 197 01 487 known. WO 02/12389 also mentions chemically modified microgels, in particular hydroxyl-modified microgels, the acrylates and methacrylates of hydroxyethanol, hydroxypropanol and hydroxybutanol being used for the modification.

It is an object of the present invention to provide a sulfur crosslinkable rubber composition which, when used as a tread compound of pneumatic vehicle tires, improves the durability of the tires.

• – mehr als 75 phr Polyisopren,
• – bis 10 phr zumindest eines hochvernetzten, mit polaren Gruppen oberflächenmodifizierten Mikrogels auf der Basis eines Butadien-Kautschuks und
• – Ruß enthält.

This object is achieved according to the invention in that the rubber mixture is free of silane coupling agents and

• More than 75 phr of polyisoprene,
• At least one highly cross-linked, polar group surface-modified microgel based on a butadiene rubber, and
• - contains carbon black.

The term phr used in this document (parts per hundred parts of rubber by weight) is the usual quantity 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.

Silane coupling agents are understood as meaning those substances which serve to improve the processability and simultaneous attachment of polar fillers, in particular silica, to the diene rubber and to the superficial polar groups or silanol groups of the silica during the mixing of the rubber or the rubber mixture (in situ). or react before the addition of the filler to the rubber in the sense of a pretreatment (pre-modification). Bifunctional organosilanes which have at least one alkoxy, cycloalkoxy or phenoxy group as leaving group on the silicon atom and which as other functionality have a group which, if appropriate, can undergo a chemical reaction with the double bonds of the polymer after cleavage, are known from the prior art as coupling agents , 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). Examples of silane coupling agents are: 3-mercaptopropyltriethoxysilane, 3-thiocyanato-propyltrimethoxysilane or 3,3'-bis (triethoxysilylpropyl) polysulfides having 2 to 8 sulfur atoms, such as. 3,3'-bis (triethoxysilylpropyl) tetrasulfide (TESPT). Such substances are not included in the mixture.

By using up to 10 phr of at least one highly crosslinked, polar group surface modified, butadiene rubber-based microgel in a substantially polyisoprene-based, rubbery rubber composition, it is possible to improve the cracking and fatigue properties of the vulcanizates from such a blend become. This results in an improvement in durability when using the mixture as a tread of pneumatic vehicle tires. The mixture is free of silane coupling agents that would allow attachment of the polar groups of the microgel to the rubber. It is therefore believed that the microgel is present as an inactive filler in the rubber composition.

The sulfur crosslinkable rubber compound contains more than 75 phr of polyisoprene (IR, NR). 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, preference being given to using natural rubber whose cis-1,4 content is greater than 99% by weight ,

The remaining rubber content is usually formed from further diene rubbers. The diene rubbers include, in addition to polyisoprene, all rubbers having an unsaturated carbon chain derived at least in part from conjugated dienes, such as polybutadiene (BR) and styrene-butadiene copolymer (SBR). The diene elastomers work well with the rubber composition according to the invention and give good tire properties in the vulcanized tires.

If the rubber mixture contains polybutadiene (BR) as the diene rubber, these may be both cis-1,4- and 1,2-polybutadiene (both in syndiotactic and atactic form). Preference is given to the use of cis-1,4-polybutadiene with a cis-1,4 content greater than 90 wt .-%, which z. By solution polymerization in the presence of rare earth type catalysts.

The styrene-butadiene copolymer can be a solution-polymerized styrene-butadiene copolymer (S-SBR) having a styrene content, based on the polymer, of about 10 to 45% by weight and a vinyl content (content of 1.2 bound butadiene, based on the total polymer) of from 10 to 70% by weight, which can be prepared, for example, using lithium alkyls in organic solvent. The S-SBR can also be coupled and end-group modified. However, it is also possible to use emulsion-polymerized styrene-butadiene copolymer (E-SBR) and mixtures of E-SBR and S-SBR. The styrene content of E-SBR is about 15 to 50% by weight and the types known in the art obtained by copolymerization of styrene and 1,3-butadiene in aqueous emulsion can be used.

In addition to the diene rubbers mentioned, however, the mixture may also contain other types of rubber, such as. Styrene-isoprene-butadiene terpolymer, isoprene-butadiene rubber, butyl rubber, halobutyl rubber or ethylene-propylene-diene rubber (EPDM). The rubber composition may also contain modified diene rubbers. These may be based on solution or emulsion polymerized styrene-butadiene rubber. The modification may be those with hydroxyl groups and / or Epoxy groups and / or siloxane groups and / or amino groups and / or aminosiloxane and / or carboxyl groups and / or phthalocyanine groups act.

As microgels whose surfaces are modified with polar groups, it is possible in principle to use all microgels which are known in the prior art and are currently already being used as fillers or proposed. In particular, microgels based on butadiene rubbers, preferably based on a styrene-butadiene rubber, are used. These microgels work well into the rubber compounds.

For the surface modification come as polar groups z. As OH groups, COOH groups, NH groups or siloxyl groups in question. With regard to the resulting vulcanizate properties, however, the surface modification with OH groups has proven to be particularly useful.

The glass transition temperatures of the microgels used can be varied over a range from T _g = -75 ° C to T _g = + 90 ° C. However, it has proved particularly advantageous if the microgel has a glass transition temperature T _g of -20 to + 70 ° C. In this way, mixtures with particularly good damping behavior are provided.

The microgel particles may have particle diameters of about 5 to 1000 nm. However, the microgels can be incorporated particularly well with particle diameters of 30 to 80 nm in a rubber mixture.

The surface-modified microgel with polar groups is preferably used in amounts of 2 to 8 phr. This improves durability without affecting other properties of the tire.

The rubber mixture contains carbon black as filler. The carbon blacks used preferably have the following characteristics: DBP number (according to ASTM D2414 ) 90 to 200 mL / 100 g, CTAB count (according to ASTM D 3765 ) 80 to 170 m ² / g and Iodadsorptionszahl (according to ASTM D 1510 ) 10 to 250 g / kg. For example, carbon blacks of the N220 or N339 type can be used. The carbon black (s) are used in conventional amounts, preferably from 30 to 100 phr.

The improvement in tear propagation properties can be achieved with complete absence of silica in the blend. This embodiment of the invention additionally offers the advantage that the reversion resistance and thus the tensile strength and elongation at break are improved.

In addition to carbon black, the rubber mixture may contain further fillers such as chalk, fibers or non-surface-modified microgels.

In view of improving the low-temperature cracking properties and the high-speed breaking elongation, it has proved advantageous if the rubber mixture contains, in addition to the microgel, 2 to 10 phr of unactivated silicic acid (not linked via silane coupling agent).

The silicas may be the silicas known to those skilled in the art which are suitable as a filler for tire rubber mixtures. However, it is particularly preferred if a finely divided silica is used, which has a nitrogen surface (BET surface area) (according to DIN 66131 and DIN 66132 ) from 35 to 350 m ² / g, preferably from 145 to 270 m ² / g and a CTAB surface (according to ASTM D 3765 ) of 30 to 350 m ² / g, preferably from 120 to 285 m ² / g. Such silicas may, for. Example, be prepared by precipitation from the liquid phase or a pyrogenic process, which can be produced using pyrogenic method silicas with a higher surface area.

According to a preferred embodiment of the invention, the silica is a so-called precipitated silica, which is produced by precipitation from the liquid phase. By using this silica, the high-speed breaking elongation is improved without deteriorating the cracking properties.

Alternatively, it is also possible to use a pyrogenically produced silica. This has the advantage that the tear propagation properties are greatly improved.

The rubber mixture according to the invention may contain other conventional additives in conventional amounts.

Other additives include plasticizers, anti-aging agents, such. N-phenyl-N '- (1,3-dimethylbutyl) -p-phenylenediamine (6PPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), 2,2,4-trimethyl-1, 2-dihydroquinoline (TMQ) and other substances, such as those from J. Schnetger, Encyclopedia of Rubber Technology, 2nd edition, Hüthig Book Verlag, Heidelberg, 1991, pp. 42-48 are known activators, such. As zinc oxide and fatty acids (eg., Stearic acid), waxes, resins and Mastikationshilfsmittel such. B. 2,2'-Dibenzamidodiphenyldisulfid (DBD).

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 of the rubber mixture customary in the art.

Further, the rubber composition may contain vulcanization-affecting substances such as vulcanization accelerators, vulcanization retarders and vulcanization activators in conventional amounts to control the time and / or temperature required 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, thiophosphates or Thiurambeschleunigern. 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, wherein initially a base mixture which contains all components except the vulcanization system (sulfur and vulcanization-influencing substances) is prepared in one or more mixing stages and then by adding the vulcanization 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 in the production of the green tire, in particular the pneumatic vehicle tire blank, as known. However, the tread may also be wound onto a green tire, which already contains all the tire parts except the tread, in the form of a narrow rubber compound strip. The tires produced in this way with the mixture according to the invention have a high durability.

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

For all mixing examples contained in the tables, the amounts given are parts by weight based on 100 parts by weight of total rubber (phr). The mixtures 1 to 4 are comparative mixtures without microgel. The mixtures 5 to 8 are mixtures according to the invention, wherein the mixtures 5 and 6 are free of silicic acid, the mixture contains 7 precipitated silica and the mixture contains 8 fumed silica.

• • Shore-A-Härte bei 70°C gemäß DIN 53 505
• • Zugfestigkeit bei Raumtemperatur gemäß DIN 53 504
• • Reißdehnung bei Raumtemperatur gemäß DIN 53 504
• • Spannungswert (Modul) bei 300% Dehnung bei Raumtemperatur gemäß DIN 53 504
• • Hochgeschwindigkeitsbruchdehnung als Reißenergie pro verformtem Volumen bei Raumtemperatur gemäß High Speed Tear Energy Test nach DIN EN 10 045 (HSTE)
• • Weiterreißwiderstand bei Raumtemperatur und 100°C nach Graves gemäß DIN 53515

Tabelle 1 Bestandteile Einheit 1 2 3 4 5 6 7 8 Naturkautschuk phr 85 85 85 85 85 85 85 85 BR^a phr 15 15 15 15 15 15 15 15 Ruß N220 phr 47 47 47 47 47 47 47 47 Kieselsäure A^b phr - - 6 12 - - 6 - Kieselsäure B^c phr - 6,6 - - - - - 6,6 Alterungsschutzmittel phr 3,5 3,5 3,5 3,5 3,5 3,5 3,5 3,5 Ozonschutzwachs phr 2,5 2,5 2,5 2,5 2,5 2,5 2,5 2,5 Zinkoxid phr 3 3 3 3 3 3 3 3 Stearinsäure phr 2 2 2 2 2 2 2 2 Mikrogel^d phr - - - - 3,2 6,3 3,2 3,2 Beschleuniger phr 1,1 1,1 1,1 1,1 1,1 1,1 1,1 1,1 Schwefel phr 1,1 1,1 1,1 1,1 1,1 1,1 1,1 1,1 Eigenschaften t₁₀ min 3,2 2,9 2,9 2,8 3,2 3,4 2,9 3,0 t₁₀₀ min 12,4 10,9 10,6 9,9 12,6 13,2 11, 11,1 t₉₈(Reversion) min 17,4 15,0 14,7 13,2 17,8 18,5 15,5 15,4 t₉₅(Reversion) min 21,8 18,5 18,4 15,9 22,4 23,6 19,2 19,2 Shore-A-Härte 70°C Shore A 53,3 54,0 51,7 52,6 54,0 54,55 54,1 53,6 Zugfestigkeit bei RT N/mm² 24,9 23,0 23,9 21,4 24,5 24,6 24,1 24,0 Reißdehnung bei RT % 579 557 585 551 575 597 575 585 Spannungswert 300% N/mm² 10,2 10,2 9,8 9,5 10,3 10,3 10,6 9,8 HSTE MJ/m³ 8,32 10,03 9,11 12,9 8,27 8,6 9,5 9,54 Weiterreißwiderstand bei RT N/mm 108,2 99,0 99,1 99,9 124,1 120,7 115 141,6 Weiterreißwiderstand bei 100°C N/mm 54,2 61,9 62,2 60,0 53,3 53,0 61,1 67,5 ^a High-cis Polybutadien
^b Fällungskieselsäure, Typ VN3, Evonic Degussa, Deutschland
^c pyrogene Kieselsäure, Aerosil 150 GR, Evonic Degussa, Deutschland
^d Mikrogel auf der Basis von S-SBR mit OH-Gruppenmodifizierung, Glasübergangstemperatur T_g = +60°C, Nanoprene P60OH, Lanxess, DeutschlandMixture preparation was carried out under customary conditions in several stages in a laboratory tangential mixer. The conversion times were up to reaching the relative crosslinking levels of 10 and 100% (t ₁₀ , t ₁₀₀ ) and the reversion times to 98 and 95%, respectively, via a rotorless vulcameter (MDR = Moving Disc Rheometer) according to DIN 53 529 determined. 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 were determined by the test methods indicated below.

• • Shore A hardness at 70 ° C according to DIN 53 505
• • tensile strength at room temperature according to DIN 53 504
• • Elongation at room temperature according to DIN 53 504
• • Voltage value (modulus) at 300% elongation at room temperature according to DIN 53 504
• • High-speed breaking elongation as tensile energy per deformed volume at room temperature according to High Speed Tear Energy Test after DIN EN 10 045 (HSTE)
• • Tear resistance at room temperature and 100 ° C according to Graves according to DIN 53515

Table 1 ingredients unit 1 2 3 4 5 6 7 8th natural rubber phr 85 85 85 85 85 85 85 85 BR ^a phr 15 15 15 15 15 15 15 15 Carbon black N220 phr 47 47 47 47 47 47 47 47 Silica A ^b phr - - 6 12 - - 6 - Silica B ^c phr - 6.6 - - - - - 6.6 Anti-aging agents phr 3.5 3.5 3.5 3.5 3.5 3.5 3.5 3.5 Ozone protection wax phr 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 zinc oxide phr 3 3 3 3 3 3 3 3 stearic acid phr 2 2 2 2 2 2 2 2 Microgel ^d phr - - - - 3.2 6.3 3.2 3.2 accelerator phr 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 sulfur phr 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 properties t ₁₀ min 3.2 2.9 2.9 2.8 3.2 3.4 2.9 3.0 t ₁₀₀ min 12.4 10.9 10.6 9.9 12.6 13.2 11 11.1 t ₉₈ (reversion) min 17.4 15.0 14.7 13.2 17.8 18.5 15.5 15.4 t ₉₅ (reversion) min 21.8 18.5 18.4 15.9 22.4 23.6 19.2 19.2 Shore A hardness 70 ° C Shore A 53.3 54.0 51.7 52.6 54.0 54.55 54.1 53.6 Tensile strength at RT N / mm ² 24.9 23.0 23.9 21.4 24.5 24.6 24.1 24.0 Elongation at RT % 579 557 585 551 575 597 575 585 Voltage value 300% N / mm ² 10.2 10.2 9.8 9.5 10.3 10.3 10.6 9.8 HSTE MJ / m ³ 8.32 10.03 9.11 12.9 8.27 8.6 9.5 9.54 Tear resistance at RT N / mm 108.2 99.0 99.1 99.9 124.1 120.7 115 141.6 Tear propagation resistance at 100 ° C N / mm 54.2 61.9 62.2 60.0 53.3 53.0 61.1 67.5 ^a high-cis polybutadiene
^b precipitated silica, type VN3, Evonic Degussa, Germany
^c fumed silica, Aerosil 150 GR, Evonic Degussa, Germany
^d Microgel based on S-SBR with OH group modification, glass transition temperature T _g = + 60 ° C, Nanoprene P60OH, Lanxess, Germany

It can be seen from Table 1 that by adding a microgel based on S-SBR with OH group modification in a natural rubber mixture with carbon black, the tear propagation resistance at room temperature can be greatly increased (blends 5 and 6). Therefore, cracks formed in a tire tread do not propagate so quickly and tire durability is increased. Durability is additionally improved by reducing the tendency of the mixtures 5 and 6 to be reversible in comparison with mixture 1 and leaving the other tire properties at the same level.

If the mixture additionally contains a precipitated silica, as mixture 7 shows, in particular the tear propagation resistance increases at room temperature and the high-speed breaking elongation is likewise increased in comparison to mixture 3. The effect of high-speed breaking strain goes far beyond the purely additive effect of the addition of precipitated silica (Mixture 3) and microgel (Mixture 5) and was not expected.

Mixture 8 shows the effect of combining special microgel with fumed silica. Compared to the mixture 2, which contains only the silica, but no microgel, the tear strength at both room temperature and at 70 ° C is significantly increased, the increase at room temperature compared to the individual effects of fumed silica (mixture 2) and Microgel (mixture 5) precipitates particularly high, which suggests an unexpected synergistic interaction of the two substances.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 02/12389 [0008]
• US 5124408 [0008]
• US 5395891 [0008]
• DE 1976729 [0008]
• DE 19701487 [0008]

Cited non-patent literature

• ASTM D2414 [0024]
• ASTM D 3765 [0024]
• ASTM D 1510 [0024]
• DIN 66131 [0028]
• DIN 66132 [0028]
• ASTM D 3765 [0028]
• J. Schnetger, Encyclopedia of Rubber Technology , 2nd edition, Hüthig Buch Verlag, Heidelberg, 1991, pp. 42-48 [0032]
• DIN 53 529 [0038]
• DIN 53 505 [0038]
• DIN 53 504 [0038]
• DIN EN 10 045 [0038]
• DIN 53515 [0038]

Claims (10)

Sulfur crosslinkable rubber mixture which is free of silane coupling agents containing More than 75 phr of polyisoprene, At least one highly cross-linked, polar group surface-modified microgel based on a butadiene rubber, and - soot. Sulfur-crosslinkable rubber mixture according to claim 1, characterized in that the polar groups of the surface-modified microgel are OH groups. Sulfur-crosslinkable rubber mixture according to claim 1 or 2, characterized in that the microgel has a glass transition temperature T _g of -20 to + 70 ° C. Sulfur-crosslinkable rubber mixture according to at least one of claims 1 to 3, characterized in that the microgel particles have a diameter of 30 to 80 nm. Sulfur-crosslinkable rubber mixture according to at least one of claims 1 to 4, characterized in that the microgel is used in amounts of 2 to 8 phr. Sulfur-crosslinkable rubber mixture according to at least one of claims 1 to 5, characterized in that it is free of silica. Sulfur-crosslinkable rubber mixture according to at least one of claims 1 to 5, characterized in that it contains 2 to 10 phr of non-activated silicic acid. Sulfur-crosslinkable rubber mixture according to claim 7, characterized in that the silica is a precipitated silica. Sulfur-crosslinkable rubber mixture according to claim 7, characterized in that the silica is a pyrogenic silica. Tires, in particular commercial vehicle tires, whose tread consists at least in part of a sulfur-vulcanized rubber composition according to claim 1.