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, 30 to 300 phr of at least one silica and 1 to 20 phf of at least one substance of formula I) as silane coupling agent
(R.sup.1R.sup.2R.sup.3)Si—S.sub.4—Si(R.sup.3R.sup.2R.sup.1)  II)
where R.sup.1, R.sup.2, R.sup.3 in the structure may be the same or different and may be selected from linear or branched alkoxy, cycloalkoxy, alkyl, cycloalkyl or aryl groups having 1 to 20 carbon atoms.

Claims

1. A rubber blend comprising: at least one solution-polymerized diene polymer A of high molecular weight, formed from at least one conjugated diene and one or more vinylaromatic compound(s), wherein the one or more 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<−61° C., a molecular weight Mw according to GPC of more than 350000 g/mol and a polydispersity PD of 1.1<PD<3; at least one solution-polymerized polymer B of low molecular weight, formed from 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 −32° 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; 30 to 300 phr of at least one silica; and, 1 to 20 phf of at least one substance of formula I) as a silane coupling agent:
(R.sup.1R.sup.2R.sup.3)Si—S.sub.4—Si(R.sup.3R.sup.2R.sup.1)  I) wherein R.sup.1, R.sup.2, R.sup.3 in the structure may be the same or different and may be selected from linear or branched alkoxy, cycloalkoxy, alkyl, cycloalkyl or aryl groups having 1 to 20 carbon atoms; 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, and wherein the polymers A and B are combined and processed together to give a rubber blend without solvent to obtain a transportable and processible blend.

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, wherein the amino groups are bonded to the chain end of the polymer chain with or without spacers.

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. The rubber blend as claimed in claim 1, wherein the at least one substance of formula I) is bis(3-triethoxysilylpropyl) tetrasulfide (TESPT).

12. The rubber blend as claimed in claim 1, comprising 0.1 to 20 phr of carbon black.

13. A vehicle tire in which at least one component includes the with sulfur-crosslinked rubber mixture as claimed in claim 12.

14. The vehicle tire as claimed in claim 13, wherein at least the part of a tread that comes into contact with a driving surface comprises the sulfur-crosslinked rubber mixture.

Description

PRODUCTION OF THE RUBBER BLEND

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

(2) 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 (18560 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.

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

(4) 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.

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

(8) 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 (18560 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.

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

(10) 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.

(11) 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.

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

(13) 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.

(14) 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.

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

(16) TABLE-US-00001 TABLE 1 Vinyl Styrene M.sub.w M.sub.n Mooney content content T.sub.g [g/mol] [g/mol] viscosity [% by wt.] [% by wt.] [° C.] Diene polymer A 436080 396421 92.5 29.3 15.0 −60.5 (functionalized) Diene polymer A-1 438020 393900 95.3 29.2 15.1 −60.6 (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)

(17) 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.

(18) 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.

(19) 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.

(20) TABLE-US-00002 TABLE 2a Content Content Content of Content of Mooney of polymer of polymer viscosity polymer A-1 polymer B-1 (ML 1 + 4) A (phr) (phr) B (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

(21) 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. 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.

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

(23) The rubber blends in table 2a were used to create the rubber mixtures in table 3 with the 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 TESPD as silane coupling agent as comparative mixtures V1 to V5. In addition, the inventive rubber mixtures E1 to E3 have been produced with the specific rubber blends E-1 to E-3 in combination with a substance of formula I) as silane coupling agent.

(24) TABLE-US-00004 TABLE 3 Constituents 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 carbon black phr 9 9 9 9 9 9 9 9 Silica.sup.e phr 90 90 90 90 90 90 90 90 Silane coupling agent .sup.f phr 6.5 6.5 6.5 6.5 — — — — Silane coupling agent .sup.g phr — — — — 7.2 7.2 7.2 7.2 ZnO phr 2 2 2 2 2 2 2 2 Aging stabilizer/ phr 5 5 5 5 5 5 5 5 antiozonant/stearic acid Processing auxiliary.sup.j phr 3 3 3 3 3 3 3 3 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 1.4 1.4 1.4 1.4 .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.gTESPT Si69, from Evonik; .sup.jAktiplast TS, from Rheinchemie

(25) 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.

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

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

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

(29) The abrasion values are the weight loss of the tire after driving for 10000 kilometers.

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

(31) TABLE-US-00005 TABLE 4 Tire property V1 V2 V3 V4 V5 E1 E2 E3 ABS dry 100 100 101 103 101 102 102 103 braking ABS wet 100 100 102 101 100 100 101 102 braking Rolling 100 104 104 108 102 106 106 110 resistance Winter 100 100 101 101 102 104 104 106 properties Abrasion 100 106 106 106 104 116 116 116 Processing o o o − o o + o

(32) Table 4 shows that the use of the specific rubber blend in combination with a substance of formula I) as silane coupling agent offers a distinct improvement with regard to rolling resistance, winter properties and abrasion resistance, without any deterioration in wet grip properties; see E1 to E3. As a result, dry braking performance remains practically unaffected or is likewise slightly improved. 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.

(33) 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, V7, V13 and V14. In V7 and V13, a liquid SBR is added in the mixture production. Mixtures V6 to V11 contain TESPD as silane coupling agent, while mixtures V12, V13 and E4 to E7 contain a substance of formula I) (TESPT) as silane coupling agent. 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 53512 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 53516 or the new DIN/ISO 4649

(34) TABLE-US-00006 TABLE 5 Unit V6 V7 V8 V9 V10 V11 V12 V13 E4 E5 E6 E7 Constituents NR phr 10 10 10 10 10 10 10 10 10 10 10 10 SBR.sup.b phr 90 90 — — — — 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 35 17 17 17 17 17 35 17 17 17 17 17 Silica.sup.h phr 95 95 95 95 95 95 95 95 95 95 95 95 Silane c. agent.sup.f phr 6.8 6.8 6.8 6.8 6.8 6.8 — — — — — — Silane c. agent.sup.g phr — — — — — — 7.6 7.6 7.6 7.6 7.6 7.6 ZnO phr 2.5 2.5 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 6.5 6.5 antiozonant/ stearic acid DPG phr 2 2 2 2 2 2 2 2 2 2 2 2 CBS phr 2 2 2 2 2 2 2 2 2 2 2 2 Sulfur phr 2 2 2 2 2 2 2 2 2 2 2 2 Properties Shore hardness ShA 71.2 69.2 70.0 65.3 71.4 66.3 72.5 69.9 69.5 64.7 69.7 65.4 RT Shore hardness ShA 66.8 64.8 66.5 62.1 67.2 63.2 67.0 65.2 66.4 60.4 66.8 62.7 70° C. Resil. RT % 17.6 15.2 19.0 24.4 15.4 16.2 18.2 16.2 18.6 23.8 15.4 15.2 Resil. 70° C. % 51.4 47.7 46.6 57.6 47.4 53.2 52.8 49.1 47.2 58.8 49.2 54.6 tan δ 0° C. — 0.627 0.686 0.529 0.539 0.643 0.691 0.589 0.638 0.500 0.551 0.649 0.683 tan δ 70° C. — 0.113 0.139 0.135 0.091 0.14 0.111 0.114 0.134 0.129 0.076 0.135 00 Abrasion mm.sup.3 136 147 125 131 143 147 131 140 101 110 126 121 .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.dTDAE oil; .sup.hUltrasil ® VN3, from Evonik (BET 180 m.sup.2/g) .sup.fTESPD Si261, from Evonik; .sup.gTESPT Si69, from Evonik.

(35) The results listed in table 5 show that there is a distinct improvement in the abrasion characteristics on exchange of a TESPD as silane coupling agent for a substance of formula I) in combination with the specific rubber blends. At same time, wet grip properties (indicator: resilience at room temperature) remain at the same level or are slightly improved. Rolling resistance (indicators: resilience to 70° C. or loss factor tan 8 at 70° C.) also remains at the same level. 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.