Rubber blend, sulfur-crosslinkable rubber mixture, and vehicle tire

Abstract

The invention relates to a sulfur-crosslinkable rubber mixture comprising a rubber blend composed of at least one solution-polymerized diene polymer A of high molecular weight and at least one solution-polymerized polymer B of low molecular weight, wherein at least one of polymers A and B has been functionalized at the chain end and/or along the polymer chain and/or at a coupling site with at least one group selected from epoxy groups, hydroxyl groups, carboxyl groups, silane sulfide groups, amino groups, siloxane groups, organosilicon groups, phthalocyanine groups and amino group-containing alkoxysilyl groups, and as filler at least one silica and/or at least one carbon black in an amount of 25 to 300 phr,
wherein the ratio of carbon black to silica in the mixture is 100:0 to 3:97.

Claims

1. A rubber blend comprising: a solution-polymerized diene polymer A of high molecular weight, formed from at least one conjugated diene and one or more optional vinylaromatic compound(s), wherein the one or more optional vinylaromatic compound(s) have a content of vinylaromatic compound of 0% to 50% by weight, a vinyl content of 8% to 80% by weight based on any diene content present, and wherein the one or more optional vinylaromatic compound(s), has a glass transition temperature Tg according to DSC of −100° C.<Tg<+20° C., a molecular weight Mw according to GPC of at least 438020 g/mol and a polydispersity PD of 1.1<PD<3; a solution-polymerized polymer B of low molecular weight, formed from at least one conjugated diene, at least one conjugated diene and one or more vinylaromatic compound(s), or at least one or more vinylaromatic compound(s), wherein the one or more vinylaromatic compound(s) has a content of vinylaromatic compound of 0% to 50% by weight, a vinyl content of 8% to 80% by weight based on any diene content present, and wherein the one or more vinylaromatic compound(s) has a glass transition temperature Tg according to DSC of −100° C.<Tg<+80° C., a molecular weight Mw according to GPC of 1300 g/mol<Mw<10000 g/mol and a polydispersity PD of 1<PD<1.5; and, and as filler, at least one optional silica and at least one carbon black in an amount of 25 to 300 phr, wherein the ratio of carbon black to silica in the mixture is 100:0 to 3:97; wherein at least one of polymers A and B has been functionalized at the chain end and/or along the polymer chain and/or at a coupling site with at least one group selected from epoxy groups, hydroxyl groups, carboxyl groups, silane sulfide groups, amino groups, siloxane groups, organosilicon groups, phthalocyanine groups and amino group-containing alkoxysilyl groups; and, wherein polymers comprised in the rubber blend consist of the solution-polymerized diene polymer A, the solution-polymerized diene polymer B, and a diene rubber selected from the group consisting of synthetic polyisoprene (IR), natural polyisoprene (NR), polybutadiene (BR), and mixtures thereof.

2. The rubber blend as claimed in claim 1, wherein at least the solution-polymerized polymer B of low molecular weight has been functionalized.

3. The rubber blend as claimed in claim 2, wherein the solution-polymerized diene polymer A of high molecular weight has been functionalized.

4. The rubber blend as claimed in claim 1, wherein at least one of polymer A and polymer B has been functionalized at the chain end with an amino group-containing alkoxysilyl group and at least one further amino group and/or at least one further alkoxysilyl group and/or at least one further amino group-containing alkoxysilyl group.

5. The rubber blend as claimed in claim 1, wherein at least one of the polymers A and B has been functionalized at the chain end and/or along the polymer chain and/or at a coupling site with a silane sulfide group.

6. The rubber blend as claimed in claim 1, wherein at least one of the polymers A and B has been functionalized at the chain end and/or along the polymer chain and/or at a coupling site with a siloxane group.

7. The rubber blend as claimed in claim 1, wherein at least one of the polymers A and B has coupling sites.

8. The rubber blend as claimed in claim 1 comprising 5 to 100 phr of the at least one solution-polymerized polymer B of low molecular weight, based on the at least one solution-polymerized diene polymer A of high molecular weight.

9. The rubber blend as claimed in claim 1 having a Mooney viscosity (ML1+4, 100° C. according to ASTM-D 1646) of 40 to 100 Mooney units.

10. The rubber blend as claimed in claim 1, wherein the proportion of the diene polymer A of the rubber blend in the rubber mixture is at least 50 phr based on the total amount of solid rubbers present in the rubber mixture.

11. A vehicle tire in which at least one component includes the with sulfur-crosslinkable rubber mixture as claimed in claim 1.

12. The vehicle tire as claimed in claim 11, wherein at least a part of a tread that comes into contact with a driving surface comprises the sulfur-crosslinked rubber mixture.

Description

(1) The invention will now be illustrated in detail by comparative examples and working examples.

(2) Production of the Rubber Blend:

Copolymerization of 1,3-butadiene with Styrene (Diene Polymer A)

(3) The copolymerization was conducted in a jacketed 40 L steel reactor that was purged with nitrogen prior to the addition of the organic solvent, the monomers, the polar coordinator compound, the initiator compound and other components. The following components were added in the sequence specified: cyclohexane solvent (18 560 g), butadiene monomer (1777 g), styrene monomer (448 g) and tetramethylethylenediamine (TMEDA, 1.0 g), and the mixture was heated to 40° C., followed by titration with n-butyllithium to remove traces of moisture or other impurities. n-BuLi (14.08 mmol) was added to the polymerization reactor to initiate the polymerization reaction. The polymerization was conducted for 20 min, in the course of which the polymerization temperature was not allowed to rise to more than 70° C. Then butadiene (1202 g) and styrene (91 g) as monomers were added over the course of 55 min. The polymerization was conducted for a further 20 min, followed by the addition of 63 g of butadiene monomer. After 20 min, the polymerization was stopped by adding hexamethylcyclotrisiloxane (D3) for functionalization (0.5 equivalent based on the initiator). The resultant polymer has been siloxane group-functionalized. 0.25% by weight of IRGANOX® 1520, BASF, based on the total monomer weight, was added to the polymer solution as stabilizer. This mixture was stirred for 10 min.

(4) For preparation of the unfunctionalized polymer A-1, rather than hexamethylcyclotrisiloxane (D3), the polymerization was ended by addition of methanol.

Copolymerization of 1,3-butadiene with Styrene (Polymer B of Low Molecular Weight)

(5) The copolymerization was conducted in a jacketed 5 L steel reactor that was purged with nitrogen prior to the addition of the organic solvent, the monomers, the polar coordinator compound, the initiator compound and other components. The following components were added in the sequence specified: cyclohexane solvent (3000 g), tetrahydrofuran (45 g), butadiene monomer (375 g), styrene monomer (125 g), and the mixture was heated to 25° C., followed by titration with n-butyllithium to remove traces of moisture or other impurities. n-BuLi (5.6 g) was added to the polymerization reactor to initiate the polymerization reaction. The polymerization was conducted for 15 min, in the course of which the polymerization temperature was not allowed to rise to more than 70° C. After 15 min, the polymerization was stopped by adding hexamethylcyclotrisiloxane (D3) for functionalization (0.5 equivalent based on the initiator). The resultant polymer has been siloxane group-functionalized. 0.25% by weight of IRGANOX® 1520, BASF, based on the total monomer weight, was added to the polymer solution as stabilizer. This mixture was stirred for 10 min.

(6) For preparation of the unfunctionalized comparative polymer B-1, rather than hexamethylcyclotrisiloxane (D3), the polymerization is ended by addition of methanol.

Copolymerization of 1,3-butadiene with Styrene (Diene Polymer C)

(7) The copolymerization was conducted in a jacketed 40 L steel reactor that was purged with nitrogen prior to the addition of the organic solvent, the monomers, the polar coordinator compound, the initiator compound and other components. The following components were added in the sequence specified: cyclohexane solvent (18 560 g), butadiene monomer (1412 g), styrene monomer (507 g) and tetramethylethylenediamine (TMEDA, 7.8 g), and the mixture was heated to 40° C., followed by titration with n-butyllithium to remove traces of moisture or other impurities. n-BuLi (8.32 mmol) was added to the polymerization reactor to initiate the polymerization reaction. The polymerization was conducted for 20 min, in the course of which the polymerization temperature was not allowed to rise to more than 70° C. Then butadiene (955 g) and styrene (103 g) as monomers were added over the course of 55 min. The polymerization was conducted for a further 20 min, followed by the addition of 50 g of butadiene monomer. After 20 min, the polymer was functionalized by addition of 3-tert-butyldimethylsilylthiopropyldimethoxymethylsilane [(MeO).sub.2(Me) Si—(CH.sub.2).sub.3—S—SiMe.sub.2C(Me).sub.3] (0.97 equivalent based on the initiator). After a further 20 min, the polymerization was ended by adding methanol. The resultant polymer has been silane sulfide group-functionalized. 0.25% by weight of IRGANOX® 1520, BASF, based on the total monomer weight, was added to the polymer solution as stabilizer. This mixture was stirred for 10 min.

Polymerization of 1,3-butadiene (Polymers D-1 and D-2 of Low Molecular Weight)

(8) The polymerization was conducted in a jacketed 5 L steel reactor that was purged with nitrogen prior to the addition of the organic solvent, the monomer, the polar coordinator compound, the initiator compound and other components. The following components were added in the sequence specified: cyclohexane solvent (3000 g), 2,2-ditetrahydrofurylpropane (1.05 g), butadiene monomer (409 g), and the mixture was heated to 40° C., followed by titration with n-butyllithium to remove traces of moisture or other impurities. n-BuLi (5.2 g) was added to the polymerization reactor to initiate the polymerization reaction. The polymerization was conducted for 15 min, in the course of which the polymerization temperature was not allowed to rise to more than 70° C. After 15 min, the polymer was stopped by adding 3-tert-butyldimethylsilylthiopropylmethoxydimethylsilane for functionalization (0.97 equivalent based on the initiator). After 60 min, the remaining living polymer chains were terminated by addition of methanol. The resultant polymer has been silane sulfide group-functionalized. 0.25% by weight of IRGANOX® 1520, BASF, based on the total monomer weight, was added to the polymer solution as stabilizer. This mixture was stirred for 10 min.

(9) For preparation of the unfunctionalized polymer D-1, rather than 3-tert-butyldimethylsilylthiopropylmethoxydimethylsilane [(MeO)(Me).sub.2Si—(CH.sub.2) .sub.3—S—SiMe.sub.2C(Me).sub.3], the polymerization was ended by addition of methanol.

Copolymerization of 1,3-butadiene with Styrene (Polymers D-3 and D-4 of Low Molecular Weight)

(10) The copolymerization was conducted in a jacketed 5 L steel reactor that was purged with nitrogen prior to the addition of the organic solvent, the monomers, the polar coordinator compound, the initiator compound and other components. The following components were added in the sequence specified: cyclohexane solvent (3000 g), tetrahydrofuran (45 g), butadiene monomer (400 g), styrene monomer (100 g), and the mixture was heated to 25° C., followed by titration with n-butyllithium to remove traces of moisture or other impurities. n-BuLi (5.7 g) was added to the polymerization reactor to initiate the polymerization reaction. The polymerization was conducted for 15 min, in the course of which the polymerization temperature was not allowed to rise to more than 70° C. After 15 min, the polymer was stopped by adding 3-tert-butyldimethylsilylthiopropylmethoxydimethylsilane for functionalization (0.97 equivalent based on the initiator). After 60 min, the remaining living polymer chains were terminated by addition of methanol. The resultant polymer has been silane sulfide group-functionalized. 0.25% by weight of IRGANOX® 1520, BASF, based on the total monomer weight, was added to the polymer solution as stabilizer. This mixture was stirred for 10 min.

(11) For preparation of the unfunctionalized polymer D-3, rather than 3-tert-butyldimethylsilylthiopropylmethoxydimethylsilane [(MeO)(Me).sub.2Si—(CH.sub.2).sub.3—S—SiMe.sub.2C(Me).sub.3], the polymerization was ended by addition of methanol.

(12) Table 1 lists the analytical data for polymers A to D.

(13) TABLE-US-00001 TABLE 1 Moo- Vinyl Styrene ney content content M.sub.w M.sub.n vis- [% [% T.sub.g [g/mol] [g/mol] cosity by wt.] by wt.] [° C.] Diene polymer A 436080 396421 92.5 29.3 15.0 −60.5 (functionalized) Diene polymer 438020 393900 95.3 29.2 15.1 −60.6 A-1 (unfunctionalized) Polymer B-1 9450 7800 n. d. 66.0 25.0 −32 (unfunctionalized) Polymer B 9450 7800 n. d. 66.0 25.0 −32 Diene polymer C 568000 418000 91.7 59.1 19.1 −22.5 (functionalized) Polymer D-1 8280 7990 n. d. 20 0 −83 (unfunctionalized) Polymer D-2 9260 8860 n. d. 21 0 −83 (functionalized) Polymer D-3 8340 7840 n. d. 67 20 −19.1 (unfunctionalized) Polymer D-4 9230 8500 n. d. 63 22 −21 (functionalized)

(14) The polymer solutions of diene polymer A or A-1 and 2.149 mixtures of polymer B or B-1 were combined in various combinations. This was followed by stripping with steam in order to remove solvents and other volatile substances, and drying in an oven at 70° C. for 30 min and then additionally at room temperature for three days. The rubber blends obtained in this way contained, based on 100 parts of the diene polymer A or A-1 and 30 parts (phr) of polymer B or B-1.

(15) For preparation of the pure polymers A/B or A-1/B-1, the polymer solutions were worked up directly from the mixtures for preparation of these components, i.e. without combination with any other polymer solution.

(16) Table 2a lists the designations for the various blends produced. E identifies blends of the invention, V the corresponding comparative blends. In addition, table 2a lists the Mooney viscosities of the respective blends in MU (Mooney units) as analytical index.

(17) TABLE-US-00002 TABLE 2a Content Content Content Content of of of of Mooney polymer polymer polymer polymer viscosity A A-1 B B-1 (ML 1 + 4) (phr) (phr) (phr) (phr) (MU) Rubber blend V 0 100 0 30 61 Rubber blend E-1 100 0 0 30 62 Rubber blend E-2 0 100 30 0 62 Rubber blend E-3 100 0 30 0 65

(18) Proportions of the polymer solutions of diene polymer C and proportions of the polymer solutions of the mixtures of polymer D-1/D-2/D-3/D-4 were likewise combined such that the weight ratio based on the polymer C present to the polymer D-1/D-2/D-3/D-4 present is 100:20. This was followed by stripping with steam in order to remove solvents and other volatile substances, and drying in an oven at 70° C. for 30 min and then additionally at room temperature for three days. The rubber blends obtained in this way contained, based on 100 parts of the diene polymer C, 20 parts (phr) in each case of polymer D-1/D-2/D-3/D-4.

(19) Table 2b lists the designations for these various blends produced. Here too, E identifies blends of the invention. In addition, table 2b lists the Mooney viscosities of the respective blends in MU (Mooney units) as analytical index.

(20) TABLE-US-00003 TABLE 2b Content Content Content Content Content Mooney of of of of of viscosity poly- polymer polymer polymer polymer (ML mer D-1 D-2 D-3 D-4 1 + 4) C (phr) (phr) (phr) (phr) (phr) (MU) Rubber 100 20 0 0 0 64.9 blend E-4 Rubber 100 0 20 0 0 66.1 blend E-5 Rubber 100 0 0 20 0 76.6 blend E-6 Rubber 100 0 0 0 20 75.7 blend E-7

(21) The rubber blends in table 2a were used to create the rubber mixtures with high filler level in table 3 with the rubber blend V composed of the unfunctionalized polymers A-1 and B-1 and the inventive rubber blends E-1 to E-3 with and without the use of carbon black as filler as comparative mixtures V1 to V5. In addition, the inventive rubber mixtures E1 to E3 have been produced with the inventive rubber blends E-1 to E-3 in combination with the use of carbon black as filler. In this case, the total content of fillers was kept constant and the amount of silanizing reagent was matched to the silica content.

(22) TABLE-US-00004 TABLE 3 Con- stituents Unit V1 V2 V3 V4 V5 E1 E2 E3 BR.sup.a phr 20 20 20 20 20 20 20 20 Blend V phr 104 — — — 104 — — — Blend E-1 phr — 104 — — — 104 — — Blend E-2 phr — — 104 — — — 104 — Blend E-3 phr — — — 104 — — — 104 N339 phr — — — — 15 15 15 15 carbon black Silica.sup.e phr 110 110 110 110 95 95 95 95 Plasticizer phr 20 20 20 20 20 20 20 20 oil.sup.g Silane.sup.f phr 8.0 8.0 8.0 8.0 6.86 6.86 6.86 6.86 ZnO phr 2 2 2 2 2 2 2 2 Aging phr 5 5 5 5 5 5 5 5 stabilizer/ anti- ozonant/ stearic acid Processing phr 3 3 3 3 3 3 3 3 auxiliary.sup.j DPG phr 2 2 2 2 2 2 2 2 CBS phr 2.6 2.6 2.6 2.6 2.6 2.6 2.6 2.6 Sulfur phr 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 .sup.aBR with cis content greater than 80% by weight; .sup.eZeosil 1165MP, from Rhodia (BET 149 m.sup.2/g, CTAB 154 m.sup.2/g); .sup.fTESPD Si261, from Evonik; .sup.gTDAE plasticizer oil; .sup.jAktiplast TS, from Rheinchemie

(23) The test results summarized in table 4 were ascertained on 195/65 R15 size tires with the ContiWinterContact TS830 profile. For this purpose, the rubber mixture for the tread of the tire in each case was produced analogously to the compositions shown in table 3. All results are reported as a relative assessment based on 100% for tire V1. Values exceeding 100% are superior to comparative tire V1 and represent an improvement.

(24) The ABS wet braking characteristics were determined by the braking distance from 80 km/h on a wet driving surface.

(25) The ABS dry braking characteristics were determined by the braking distance from 100 km/h on a dry driving surface.

(26) Rolling resistance corresponds to the rolling resistance force measured on the corresponding machine at 90 km/h.

(27) The abrasion values are the weight loss of the tire after driving for 10 000 kilometers.

(28) To assess the winter properties, snow traction, i.e. traction force in an acceleration run on a snow-covered driving surface, is ascertained.

(29) TABLE-US-00005 TABLE 4 Tire property V1 V2 V3 V4 V5 E1 E2 E3 ABS dry braking 100 100 101 103 98 99 100 103 ABS wet braking 100 100 102 101 95 98 100 100 Rolling resistance 100 104 104 108 97 106 106 110 Winter properties 100 100 101 101 97 99 99 100 Abrasion 100 106 106 106 105 115 115 120 Processing o o o − o + + o

(30) Table 4 shows that the use of the specific rubber blend in combination with carbon black as filler achieves a distinct improvement with regard to abrasion resistance, rolling resistance and processing properties without any deterioration in wet grip and winter properties; see E1 to E3. As can also be seen, however, these advantages arise only when one constituent of the rubber blend E has been functionalized. The mixtures containing the specific rubber blends also have advantages in processing characteristics (+=very good, o=good, −=with difficulties) over the remaining mixtures.

(31) In addition, the rubber blends in table 2b were used to create the rubber mixtures in table 5. Mixtures with a functionalized SBR have also been introduced as comparative mixtures in the form of mixtures V6 and V11. Mixtures V6 to V10 contain silica as filler, while mixtures V11 and E4 to E7 contain carbon black and silica as filler. The mixtures were produced under standard conditions with production of a base mixture and subsequently of the finished mixture in a tangential laboratory mixer. All mixtures were used to produce test specimens by optimal vulcanization under pressure at 160° C., and these test specimens were used to determine the material properties typical for the rubber industry by the test methods that follow. Shore A hardness at room temperature and 70° C. by durometer to DIN ISO 7619-1 Resilience (Resil.) at room temperature and 70° C. to DIN 53 512 Loss factor tan δ at 0° C. and 70° C. from dynamic-mechanical measurement to DIN 53 513 at a preliminary compression of 10% with an expansion amplitude ±0.2% and a frequency of 10 Hz (temperature sweep) Abrasion at room temperature to DIN 53 516 or the new DIN/ISO 4649

(32) TABLE-US-00006 TABLE 5 Constituents Unit V6 V7 V8 V9 V10 V11 E4 E5 E6 E7 NR phr 10 10 10 10 10 10 10 10 10 10 SBR.sup.b phr 90 — — — — 90 — — — — Blend E-4 phr — 108 — — — — 108 — — — Blend E-5 phr — — 108 — — — — 108 — — Blend E-6 phr — — — 108 — — — — 108 — Blend E-7 phr — — — — 108 — — — — 108 Liquid SBR.sup.c phr 18 — — — — 18 — — — — Plasticizer oil.sup.g phr 17 17 17 17 17 17 17 17 17 17 N339 carbon phr — — — — — 45 45 45 45 45 black Silica.sup.d phr 95 95 95 95 95 50 50 50 50 50 Silane c. agent.sup.f phr 6.8 6.8 6.8 6.8 6.8 6.8 6.8 6.8 6.8 6.8 ZnO phr 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Aging stabilizer/ phr 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 antiozonant/ stearic acid DPG phr 2 2 2 2 2 2 2 2 2 2 CBS phr 2 2 2 2 2 2 2 2 2 2 Sulfur phr 2 2 2 2 2 2 2 2 2 2 Properties Shore hardness ShA 68.2 69.1 65.3 70.4 67.3 72.4 72.3 70.2 73.8 71.3 RT Shore hardness shA 62.8 64.5 63.7 67.2 64.2 66.9 68.3 67.4 69.4 67.3 70° C. Resil. RT % 15.2 19.0 23.4 15.4 16.2 13.6 17.4 21.6 14.0 14.8 Resil. 70° C. % 47.4 45.6 51.6 46.1 49.2 41.6 41.9 49.2 41.7 45.7 tan δ 0° C. — 0.684 0.527 0.519 0.645 0.691 0.689 0.531 0.529 0.659 0.699 tan δ 70° C. — 0.135 0.134 0.089 0.139 0.111 0.175 0.155 0.112 0.165 0.137 Abrasion mm.sup.3 147 125 121 142 135 145 116 101 132 121 .sup.bSBR, Sprintan ® SLR-4602, from Trinseo, vinyl content: 63% by wt., styrene content: 21% by wt., functionalized .sup.cLiquid SBR, Ricon ® 100, from Cray Valley .sup.gTDAE plasticizer oil; dUltrasil ® VN3, from Evonik (BET 180 m.sup.2/g) .sup.fTESPD Si261, from Evonik;

(33) The results listed in table 5 show that there is a distinct improvement in the abrasion characteristics on exchange of silica for carbon black in combination with the specific rubber blends. At same time, wet grip properties (indicator: resilience at room temperature) remain at the same level. There is also minimization of the typically adverse effect of carbon black on rolling resistance (indicators: resilience to 70° C. or loss factor tan δ at 70° C.). It is possible to achieve an improvement in the trade-off between abrasion, rolling resistance and wet grip. The data in table 5 also reflect the advantages shown in table 4.