EP1169384A1

EP1169384A1 - Rubber compositions containing hydroxyl groups

Info

Publication number: EP1169384A1
Application number: EP00920517A
Authority: EP
Inventors: Thomas Scholl; Jürgen Trimbach
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1999-04-01
Filing date: 2000-03-20
Publication date: 2002-01-09
Also published as: AU4106600A; WO2000059994A1; US6699937B1; JP2002541289A; CA2364587A1; DE19914848A1

Abstract

The invention relates to rubber compounds that contain rubbers polymerized in solution with a secondary hydroxyl group content of 0.1 to 5 wt.- % that are not more than 4 carbon atoms away from the respective side chain end. The invention also relates to mixtures thereof with fillers, optionally additional rubbers and rubber auxiliary agents and the vulcanized rubbers produced thereof. The inventive rubber compounds are useful for producing highly reinforced, abrasion-resistant molded bodies, especially for producing tires that are characterized by excellent non-skid properties on wet surfaces.

Description

Solution rubbers containing hydroxyl groups

The present invention relates to rubber mixtures containing rubbers polymerized in solution with a secondary hydroxyl group content of 0.1 to

5 wt .-%, which are not more than 4 carbon atoms from the respective side chain end, as well as their mixtures with fillers, optionally further rubbers and rubber auxiliaries and vulcanizates produced therefrom. The rubber mixtures according to the invention are suitable for the production of highly reinforced, abrasion-resistant moldings, in particular for the production of tires which have a particularly high wet slip resistance and low rolling resistance.

Double bond-containing anionically polymerized solution rubbers, such as solution polybutadiene and solution styrene / butadiene rubbers, have advantages over the corresponding emulsion rubbers in the production of low rolling resistance tire treads. The advantages include in the controllability of the vinyl content and the associated glass transition temperature and the molecular branching. In practical use, this results in particular advantages in relation to the wet skid resistance and rolling resistance of the tire. For example, U.S. Patent No. 5,227,425 describes the

Manufacture of tire treads from a solution SBR rubber and silica. To further improve the properties, numerous methods for end group modification have been developed, for example as described in EP-A 334 042, with dimethylarninopropyl acrylamide or, as described in EP-A 447 066, with silyl ethers. Due to the high molecular weight of the rubbers, however, the weight fraction of the end group is low and can therefore have little influence on the interaction between the filler and the rubber molecule. It was an object of the present invention to produce solution SBR rubbers with a significantly higher content of effective groups for the interaction of fillers. Another object of the present invention was to produce rubber vulcanizates with a more favorable wet slip resistance / rolling resistance ratio.

Solution-polybutadiene rubbers containing hydroxyl groups are also described in DE-OS

2,653,144. However, these rubbers are not suitable as the main component in tire treads because of their insufficient strength.

A process for the hydroxylation of rubbers is described in EP-A 464 478, in which the hydroxylated rubbers differ structurally from those of the present invention. In particular, the secondary hydroxyl groups of EP-A 464 478 are in a more unfavorable position in the polymer and are therefore far less effective than the hydroxyl groups of the present invention, which are not further than 4 carbon atoms from the respective side chain end.

EP-806 452 A1 also describes hydroxyl group-containing emulsion and solution rubbers, the hydroxyl contents described here for solution rubbers being in a significantly lower range (0.009 to 0.061%) due to the process. The present patent application shows that these contents have no significant influence on the wet slip resistance and that the position of the hydroxyl groups is particularly important.

The earlier applications DE-198 32 459.6 and DE-198 32 458.8 describe solution rubbers containing hydroxyl groups. However, they do not describe secondary ones

Hydroxyl groups and also not that the hydroxyl groups are not more than 4 carbon atoms away from the respective side chain end.

It has now been found that hydroxyl-containing solution vinyl aromatic / diolefin rubbers with a content of 0.1 to 5 bound secondary hydroxyl groups, which are not more than 4 carbon atoms from each Side chain end removed and produce a 1.2-vinyl content of 5 to 60 wt .-% rubber mixtures and rubber vulcanizates with surprisingly improved dynamic damping properties in the temperature range relevant to wet skid resistance (0 to 20 ° C) and in the temperature range relevant to rolling resistance (60 to 80 ° C) as well as improved abrasion behavior to let. Further surprising advantages were obtained when the rubber mixture was not produced in the kneader as usual, but by mixing a solution of rubber containing hydroxyl groups and oxidic or silicate filler in organic solvent and then removing the solvent with steam, since then the filler was removed is completely precipitated with the rubber and does not remain in the wastewater, as when using unmodified rubber.

The present invention therefore relates to rubber mixtures comprising one or more rubbers containing hydroxyl groups and polymerized in solution, composed of diolefins and vinylaromatic monomers, containing secondary hydroxyl groups bonded in the range from 0.1 to 5% by weight, characterized in that the secondary hydroxyl groups are not are located more than 4 carbon atoms from the respective side chain end. Another object of the invention is the use of said rubber mixtures for the production of rubber vulcanizates, in particular silica-filled tire treads with particularly high abrasion resistance, particularly high wet skid resistance and low rolling resistance.

The vinyl aromatic / diolefin rubbers polymerized in solution advantageously have average molecular weights (number average) of 50,000 to 2,000,000 and glass transition temperatures of -50 ° to + 20 ° C.

Preferred Vinvlaromat contents are between 0.01 and 50 particularly preferably between 5 to 40% by weight. Suitable vinyl aromatic monomers are styrene, o-, m- and p-methylstyrene, p-tert-butylstyrene, α-methylstyrene, vinylnaphthalene, divinylbenzene, trivinylbenzene and divinylnaphthalene. Styrene is particularly preferred.

Suitable diolefins are all diolefins known to the person skilled in the art, in particular 1,3-butadiene, isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene, 1-pheny 1-1,3 -butadiene and 1,3-hexadiene. 1,3-Butadiene and isoprene are particularly preferred.

The rubbers according to the invention for the rubber mixtures according to the invention are preferably produced by anionic solution polymerization, i.e. by means of an alkali metal based catalyst, e.g. n-butyllithium, in a hydrocarbon as a solvent. In addition, the known randomizers and control agents can be used for the microstructure of the polymer. Such anionic solution polymerizations are known and e.g. in I. Franta Elastomers and Rubber Compounding Materials; Elsevier 1989, pages 73-74, 92-94 and in

Houben-Weyl, Methods of Organic Chemistry, Thieme Verlag, Stuttgart, 1987, Volume E 20, pages 114 to 134. The hydroxyl groups are introduced in a subsequent reaction on the finished polymer. A preferred method for introducing hydroxyl groups is e.g. the addition of hydroxyl-containing mercaptans.

Examples of suitable alkali metal polymerization catalysts for the purposes of the present invention are lithium, sodium, potassium, rubidium, cesium metal and their hydrocarbon compounds and complex compounds with polar organic compounds.

Lithium and sodium hydrocarbon compounds with 2 to 20 carbon atoms, for example ethyl lithium, are particularly preferred. n-propyllithium. i-propyllithium. n-butyllithium. sec-butyllithium. tert-octyllithium. n-decyllithium, phenyllithium. 2-naphthyllithium. 2-butylphenyllithium. Cyclohexyllithium. 4-

Cyclopentyllithium. 1.4-Dilithiobutene-2, sodium naphthalene. Sodium biphenyl. Potassium tetrahydrofuran complex, potassium diethoxiethan complex, sodium tetramethylethylenediamine complex. The catalysts can be used alone and in a mixture.

Preferred amounts of catalyst are between 0.2 and 15 mmol / 100 g of polymer.

The anionic solution polymerization is carried out in a hydrocarbon or in another solvent which does not adversely affect the catalyst, for example tetrahydrofuran, tetrahydropyran or 1,4-dioxane. Suitable hydrocarbons as solvents are, for example, aliphatic, cycloaliphatic or aromatic hydrocarbons having 2 to 12 carbon atoms. Preferred solvents are propane, butane, pentane, hexane, cyclohexane, propene, butene, 1-pentene, 2-pentene, 1-hexene, 2-hexene, benzene, toluene, xylene. The solvents can be used alone or as a mixture.

The hydroxyl groups are preferably introduced by the addition of hydroxyl mercaptans of the general formula (1), hydroxyl group-containing mercapto carboxylic esters of the general formula (2) and / or hydroxyl mercaptans (3). The reaction is preferably carried out in solution, if appropriate in the presence of free radical initiators.

HS - (CH ₂ ) _n -CHOH -R ¹ (1)

HS- (CHR ² ) _m - (CO ₂ -R ³ - CHOH -R ¹ ) (2)

HS-CH CH-OH (3) CHN

wherein R ¹ for one stands, which can optionally carry further hydroxyl groups

R ^{2 represents} hydrogen, a Cj-Cg-alkyl group or a group -CO ₂ -R ³ -CHOH-R ¹ and

R ^{3 represents} a linear, branched or cyclic C2-C36 alkyl group which can optionally be substituted by up to 6 further hydroxyl groups or can be interrupted by nitrogen, oxygen or sulfur atoms,

OH stands for a secondary hydroxyl group.

n, m independently of one another represents an integer from 1 to 7,

q represents an integer in the range from 3 to 4.

Preferred hydroxyl mercaptans are 1-mercapto-2-propanol and 1-mercapto-2-butanol. l-mercapto-3-butanol, l-mercapto-2-pentanol, l-mercapto-2-hydroxycyclohexane and 1-mercaptopropanediol. 1-Mercapto-2-propanol are particularly preferred. 1-mercapto-2-butanol, 1-mercapto-2-hydroxy-cyclohexane and 1-mercapto-propanediol (thioglycerol).

Preferred mercaptocarboxylic acid esters containing hydroxyl groups are monoesters of mercaptoacetic acid, mercaptopropionic acid. Mercapto butyric acid and mercapto succinic acid with 1,2-propylene glycol, 1,2- and 1,3-butylene glycol. Dipropylene glycol. Tripropylene glycol, tetrapropylene glycol. Glycerin. Sorbitol. The corresponding esters of 3-mercaptopropionic acid are particularly preferred. Hydroxyl mercaptans and hydroxyl group-containing mercaptocarboxylic acid esters, which in addition to the special secondary hydroxyl group carry a further hydroxyl group in the 2- or 3-position, such as thioglycerol, are very particularly preferred.

Suitable radical initiators for the attachment of the hydroxyl mercaptans to the solution rubbers are e.g. Azo initiators such as azobisisobutyronitrile, azobiscyclohexanenitrile and peroxides such as dilauroyl peroxide, benzpinacols and benzpinacolsilyl ether or photoinitiators in the presence of visible or UV light. Diacyl peroxides, in particular di- (3,3,5-trimethylhexanoyl) peroxide, didecanoyl peroxide and dilauroyl peroxide, are particularly preferred.

Preferred amounts of radical initiators are in the range from 0.5 to 20% by weight, based on hydroxyl mercaptan.

The Mooney viscosity ML 1 + 4 of the copolymers is in the range from 10 to 200, preferably 30 to 150, measured at 100 ° C.

The content of polymerized 1,2-butadiene units (“vinyl content”) is in the range from 5 and 60% by weight, preferably 10 to 50% by weight.

The copolymerized vinyl aromatic content is in the range of 0.0 40% by weight, preferably 5 to 40% by weight, particularly preferably 10 to 30% by weight.

The content of secondary hydroxyl groups is in the range from 0.1 to 5% by weight. preferably in the range from 0.1 to 3% by weight. particularly preferably in the range from 0.1 to 2% by weight, very particularly preferably in the range from 0.1 to 1% by weight. based on rubber.

The method according to the invention thus allows a targeted introduction of hydroxyl groups depending on the desired distance from the side chain end. The content of hydroxyl groups can be determined by known methods, for example by spectroscopy, tritrimetry, elemental analysis or by determining the so-called hydroxyl number (OH number), that is to say by conversion with reagents which release acids which can be titrated in contact with OH groups. See also DLN 53 240.

Of course, in addition to the specific secondary hydroxyl groups that are not more than 4 carbon atoms from the respective side chain end, the rubbers can also contain further functional groups, such as, for example, Carboxylic acid and carboxylic ester groups.

The hydroxyl-containing rubbers polymerized in solution can be used alone, in admixture with aromatic or aliphatic oils or in a mixture with other rubbers. In addition to natural rubber, synthetic rubbers are also suitable as additional rubbers for the production of vulcanized rubber. Preferred synthetic rubbers are described, for example, by W. Hofmann, Kautschuktechnologie, Gentner Verlag, Stuttgart 1980 and I. Franta, Elastomers and Rubber Compounding Materials, Elsevier, Amsterdam 1989. They include

BR - polybutadiene

ABR - butadiene / acrylic acid-Ci-C ^ alkyl ester copolymers

CR polychloroprene

IR - polyisoprene SBR - styrene / butadiene copolymers with styrene contents of 1 to 60%, preferably 20 to 50% by weight IIR - isobutylene / isoprene copolymers

NBR - butadiene / acrylonitrile copolymers with acrylonitrile contents of 5 to 60. preferably 10 to 40 wt .-% HNBR - partially hydrogenated or fully hydrogenated NBR rubber

EPDM - ethylene / propylene / diene copolymers as well as mixtures of these rubbers. Natural rubber, emulsion SBR and solution SBR rubbers with a glass transition temperature above -50 ° C., which can optionally be modified with silyl ethers or other functional groups, such as, for example, in EP-A, are particularly suitable for the production of motor vehicle tires - 447 066, polybutadiene rubber with a high 1.4-cis content (> 90%), which is produced with catalysts based on Ni, Co, Ti or Nd, and polybutadiene rubber with a vinyl content of 0 to 75% and mixtures thereof of interest .

The rubber mixtures according to the invention contain 5 to 500 parts by weight of an active or inactive filler, such as e.g.

finely divided silicas, e.g. by precipitation of solutions of silicates or flame hydrolysis of silicon halides with specific

Surfaces of 5 to 1000, preferably 20 to 400 m / g (BET surface area) and with primary particle sizes of 10 to 400 nm. The silicas can optionally also be mixed oxides with other metal oxides, such as Al, Mg, Ca, Ba, , Zn, Zr, and Ti oxides are present,

synthetic silicates, such as aluminum silicate, alkaline earth metal silicate, such as magnesium silicate or calcium silicate, with BET surface areas from 20 to 400 m ² / g and primary particle diameters from 10 to 400 nm,

- natural silicates, such as kaolin and other naturally occurring silica.

Glass fibers and glass fiber products (mats, strands) or micro glass balls.

- metal oxides, such as zinc oxide, calcium oxide. Magnesium oxide. Alumina. Metal carbonates, such as magnesium carbonate, calcium carbonate, zinc carbonate,

Metal hydroxides, e.g. Aluminum hydroxide, magnesium hydroxide,

- soot. The carbon blacks to be used here are produced by the flan black, furnace or gas black process and have BET surfaces of 20 to 200 m ² / g, such as SAF, ISAF, HAF, FEF or GPF carbon blacks.

Rubber gels, especially those based on polybutadiene, butadiene / styrene copolymers, butadiene / acrylonitrile copolymers and polychloroprene.

Highly disperse silicas and carbon blacks are particularly preferred. The oxidic and silicate fillers can be activated and / or hydrophobicized with the known filler activators, in particular sulfur-containing silyl ethers and / or known hydrophobizing agents.

The fillers mentioned can be used alone or in a mixture. In a particularly preferred embodiment, the rubber mixtures contain, as fillers, a mixture of light fillers, such as highly disperse silicas, and carbon blacks, the mixing ratio of light fillers to carbon blacks being from 0.05 to

20, preferably 0.1 to 10.

The fillers are preferably added as solids or as a slurry in water or a solvent to the solution of the hydroxyl-containing rubbers polymerized in solution. The rubber solution can be prepared beforehand, but the solution originating from the polymerization is preferably used directly. The solvent is then removed thermally or preferably with the aid of steam. The conditions of this stripping process can easily be determined by preliminary tests. The fillers are furthermore preferably added to the solid hydroxyl-containing rubber or a mixture of rubbers and mixed in in a known manner, for example using a kneader.

The rubber mixtures according to the invention may also contain

Crosslinker. Sulfur or peroxides can be used as crosslinking agents, with sulfur being particularly preferred. The rubber mixtures according to the invention can contain further rubber auxiliary products, such as reaction accelerators, anti-aging agents, heat stabilizers, light stabilizers, ozone protection agents. Processing aids, plasticizers, tackifiers, blowing agents, dyes, pigments,

Waxes, extenders, organic acids, retarders, metal oxides and activators such as triethanolamine, polyethylene glycol, trimethylolpropane etc. which are known to the rubber industry.

The use of additional filler activators is particularly advantageous in the preferred rubber mixtures with highly active precipitated silicas. Preferred filler activators are sulfur-containing silyl ethers, in particular bis- (trialkoxysilyl-alkyl) polysulfides, as described in DE 2 141 159 and DE-AS 2 255 577, oligomeric and / or polymeric sulfur-containing silyl ethers of DE-OS 4,435,311 and EP -A 670 347, mercapatoalkyltrialkoxisilane. in particular

Mercaptopropyltriethoxysilane and thiocyanatoalkylsilyl ether, e.g. described in DE-OS 19 544 469.

The rubber auxiliaries (see also J. Franta in Elastomers and Rubber Compounding Materials, Elsevier. 1989) are used in customary amounts, which depend, among other things, on the intended use. Common amounts are e.g. Quantities from 0.1 to 50% by weight, based on rubber.

The rubber mixtures according to the invention are outstandingly suitable for the production of moldings of all kinds. Non-limiting examples of these shaped bodies are O-rings, profiles, seals, membranes, tires, tire treads, damping elements and tubes.

Tires and tire treads are particularly preferred.

example 1

A solution of 500 g of solution SBR rubber Buna ^® VSL 5025-0 (Bayer AG, content of bound styrene 25% by weight, content of 1,2-linked butadiene 50% by weight) in 4 l of cyclohexane is added 70 ° C with 25 g l-mercapto-2-propanol and 2 g

Azobiscyclohexanenitrile added. The mixture was then stirred at 80 ° C for 16 hours. Then 2.5 g Antioxidant Vulkanox.RTM ^® BKF (Bayer AG) added and the solvent was distilled off with steam. After drying at 70 ° C. in vacuo, a colorless rubber with a glass transition temperature (DSC) -6 ° C. and an OH content of 0.9% by weight was obtained.

Example 2

The procedure was as in Example 1, the following amounts were used: 500 g Buna ^® VSL 5025-0 (Bayer AG)

41 cyclohexane 12.5 g l-mercapto-2-propanol

1 g dilauroyl peroxide (as a replacement for azobiscyclohexanenitrile) (Interox LP, Peroxid Chemie, D) Reaction temperature: 3 hours at 80 ° C. Then 2.5 g of anti-aging agent Vulkanox ^® 4020 (Bayer AG) were added. A colorless rubber with a glass transition temperature of -13 ° C. and an OH content of 0.45% by weight was obtained.

Comparative Examples

The procedure was as in Example 1, the following amounts being used:

Comparison solution hydroxyl radical starter glass OH content example SBR mercaptan and reaction time temperaim End¬

B. VSL tur product

5025-0

1 500 g 1.6 g 0.2 g -18 ° C 0.07% by weight

1 -Mercapto-2-azobiscyclohexane ethanol nitrile

16 hours / 80 ° C

2 500 g 73.5 g 1 g dilauroyl peroxide -27 ° C 1.0 wt%

(according to 1 -Mercapto-2-3 hours / 80 ° C

EP 464.478) hydroxydodecane

Example 3

The following rubber mixtures were produced (apart from sulfur and accelerator) at 140 ° -150 ° C in a 1.5 l kneader. Mixing time in the kneader: 5 minutes. Sulfur and accelerator were then mixed in at about 50 ° -70 ° C on a roller.

Components of comparison comparison comparison invention example example example

3.A 3.B 3.C 3.1

Solution SBR- 70 0 0 0

Buna® rubber

VSL 5025-0

(Bayer AG)

Rubber acc. 0 0 0 70

Ex. 1

Rubber according to 0 0 70 0

Comparative example

1 (EP 806 452)

Rubber according to 0 70 0 0

Comparative example

2 (EP 464 478)

BR rubber 30 30 30 30

Buna® CB 25

(Bayer AG)

Silica 70 70 70 70

Vulkasil® S

(Bayer AG) aromat. Mineral oil 37.5 37.5 37.5 37.5

Enerthene 1849-1

(BP)

Silane Si 69 6 6 6 6

(Degussa)

Carbon black N 121 10 10 10 10

(Degussa)

Zinc oxide RS® 2.5 2.5 2.5 2-5

(Bayer)

Stearic acid 1 1 1 1

Vulkanox® 4020 1 1 1 1

(Bayer)

Sulfur 1.5 1.5 1.5 1.5

(Kali Chemie, D)

Vulkacit® CZ 1.8 1.8 1.8 1.8

Vulkacit® D 2 2 2 1

The rubber mixtures were then vulcanized at 170 ° C for 20 minutes. The vulcanizates had the following properties: Vulcanizate comparison comparison comparison invention

Property example 3.A example 3.B example 3.C example 3.1

Tensile strength (Mpa) ⁽¹⁾ 14.6 16.3 14.6 12.6

Elongation at break (%) ^(,) 390 380 380 275

Voltage value at 100

% Elongation (Mpa) ^(,) *> 3 2.9 3.7

Shore A hardness (23 ° C) ⁽²⁾ 73 69 72 73

Shore A hardness (70 ° C) ⁽²⁾ 69 65 69 69

Rebound resilience at

23 ° C (%) ⁽³⁾ 28 28 28 22

Rebound resilience at 47 49 49 49

70 ° C (%) ⁽³⁾

Difference between the

Rebound elasticities 19 21 21 27 at 23 ° and 70 ° C

Abrasion DIN 53.516 104 83 98 75

(ccm)

(1) determined by tensile test according to DIN 52 504 with standard rod 2

(2) determined according to DIN 53 505

(3) determined according to DIN 53 512 The test results show that the properties of the rubber according to the invention with a specific content and arrangement of the hydroxyl groups compared to the unmodified rubber (comparison 3.A), the rubbers with the same hydroxyl group content (1% by weight, comparison 3. B) and with too little Hydroxyl group content (0.07% by weight, comparison 3.C) were improved; a significantly lower rebound resilience was measured at room temperature, which experience has shown to be accompanied by a significant improvement in wet slip resistance. The difference between the rebound elasticities at room temperature and 70 ° C. is considerably greater in the rubber mixtures according to the invention, so that the relationship between wet skid resistance and rolling resistance in the tire is also significantly more favorable.

Example 4

A solution of 500 g of solution rubber Buna VSL 5025-0 (Bayer AG) in 4 l

4.15 g of thioglycerol (3-mercapto-1,2-propanediol) and 0.5 g of dilauroyl peroxide were added to cyclohexane at 80 ° C. and the mixture was stirred at 80 ° C. for 2 hours. Then 2.5 g of Vulkanox 4020 (antioxidant from Bayer AG) were added and the solvent was distilled off with steam. After drying at 70 ° C. in vacuo, 504.1 g of rubber with the viscosity ML 1 + 4 (100 ° C.) 70 and an OH content of 0.26% by weight were obtained.

Example 5

The following rubber mixtures were produced (apart from sulfur and accelerator) at 140 ° C. in a 1.5 l kneader. Mixing time in the kneader: 5 minutes. Sulfur and accelerator were then mixed in at about 50 ° C to 70 ° C on a roller. Components of comparative invention example example

5.A 5.1

Solution SBR rubber Buna® VSL 70 0

5025-0

(Bayer AG)

Rubber acc. Ex. 4 0 70

BR rubber Buna® CB 25 (Bayer AG) 30 30

Silica Vulkasil® S 70 70

(Bayer AG) aromat. Mineral oil 37.5 37.5

Enerthene 1849-1 (BP)

Silane Si 69 (Degussa) 5.6 5.6

Soot N 121 (Degussa) 10 10

Zinc oxide RS® (Bayer) 3 y

Stearic acid 1 1

Vulkanox® HS (Bayer) 1 1

Vulkanox® 4020 (Bayer) 1 1

Sulfur 1.5 1.5

Vulkacit® CZ 1.8 1.8

Vulkacit® D 2 2

The rubber compounds were then vulcanized at 170 ° C for 20 minutes. The vulcanizates had the following properties: Vulcanizate property comparative invention. example 5.A Example 5.1

Tensile strength (Mpa) ⁽¹⁾ 15.6 19.6

Elongation at break (%) ⁽¹⁾ 380 400

Tension value at 100% elongation (Mpa) ⁽¹⁾ 1.8 1.4

Shore A hardness (23 ° C) ⁽²⁾ 72 65

Shore A hardness (70 ° C) ⁽²⁾ 69 65

Rebound resilience at 23 ° C (%) ⁽³⁾ 28 25

Rebound resilience at 70 ° C (%) ⁽³⁾ 46 50

Difference between the rebound elasticities at 23 ° and 70 ° C 22 25 tan delta 0 ° C 0.387 0.562 tan delta 60 ° C 0.153 0.11

(1) determined by tensile test according to DIN 52 504 with standard rod 2

(2) determined according to DIN 53 505

(3) determined according to DIN 53 512

The test results show that the damping properties of the rubber according to the invention with a special content and arrangement of the hydroxyl groups are significantly improved compared to the unmodified rubber (comparison 5.A); a significantly lower rebound resilience was measured at room temperature and a higher tan delta at 0 ° C, both of which experience has shown to result in a significant improvement in wet skid resistance. The higher rebound elasticities at 70 ° C and the lower tan delta at 60 ° C of the rubber mixture according to the invention both show a lower rolling resistance compared to the reference rubber mixture without the hydroxyl group content according to the invention. The difference between the rebound elasticities at room temperature and 70 ° C and between the tan delta values at 0 and 60 ° C is The rubber compound is considerably larger, so that the relationship between wet skid resistance and rolling resistance in the tire is also significantly more favorable.

Claims

claims

1. Rubber mixtures containing one or more hydroxyl-containing, solution-polymerized rubbers composed of diolefins and vinylaromatic monomers containing in the range from 0.1 to 5% by weight bound secondary hydroxyl groups, characterized in that the secondary hydroxyl groups do not differ from the carbon atoms by more than 4 the respective side chain ends are removed.

2. Rubber mixtures according to claim 1, characterized in that the or the hydroxyl-containing rubbers polymerized in solution have a copolymerized vinyl aromatic content in the range from 5 to 40% by weight and a 1,2-vinyl content in the range from 5 to 60% by weight. % to have.

3. Rubber mixtures according to claim 1, characterized in that styrene is used as the vinyl aromatic monomer.

4. Rubber mixtures according to claim 1, characterized in that 1,3-butadiene and / or isoprene are used as diolefins.

Use of the rubber mixtures according to claim 1 for the production of moldings of all kinds, in particular for the production of tire treads.