Rubber tyre compound production method

Abstract

A method of producing rubber compounds, in which the polymer base is composed partly of a first polymer material having a glass transition temperature of over 50 C., and partly of a second polymer material having a glass transition temperature of below 50 C. and silica as a filler. The method includes a preliminary first polymer material treating step, in which the first polymer material, a silica having a surface area of 80 to 135 m.sup.2/g, a silane bonding agent, and at least one nucleophile agent are mixed together; a preliminary second polymer material treating step, in which the second polymer material, a silica having a surface area of 150 to 220 m.sup.2/g, a silane bonding agent, and at least one nucleophile agent are mixed together; a mixing step, in which the compounds resulting from the preliminary treating steps are mixed together; and a final step, in which stearic acid and a curing system are added and mixed with the compound being produced.

Claims

1. A method of producing a rubber compound, comprising: a preliminary first polymer material treating step in which a first polymer material having a glass transition temperature of over 50 C., a silica having a surface area of 80 to 135 m.sup.2/g, a silane bonding agent, and at least one nucleophile agent are mixed together; a preliminary second polymer material treating step in which a second polymer material having a glass transition temperature of below 50 C., a silica having a surface area of 150 to 220 m.sup.2/g, a silane bonding agent, and at least one nucleophile agent are mixed together; a mixing step, in which the mixtures resulting from the preliminary first and second polymer material treating steps are mixed into one compound; and a final step, in which stearic acid and a curing system are added to and mixed with the compound.

2. The method of producing a rubber compound as claimed in claim 1, characterized in that said nucleophile agents are curing accelerants.

3. The method of producing a rubber compound as claimed in claim 2, characterized in that the curing accelerants are selected from the group consisting of amines, disulphides, guanidines, and derivatives thereof, thiourea and derivatives thereof, thiazoles, thiurams, sulphenamides, and derivatives thereof, dithiocarbamates, dithiophosphates, and xanthates, and mixtures thereof; and preferably, the curing accelerants are selected from the group consisting of benzothiazyl-cyclohexyl sulphenamide (CBS), N-tert-butyl-2-benzothiazylsulphenamide (TBBS), 2-mercaptobenzothiazole (MBT), zinc salts of 2-mercaptobenzothiazole (ZMBT), benzothiazyl-2-dicyclohexyl sulphenamide (DCBS), diphenylguanidine (DPG), triphenylguanidine (TPG), di-ortho-tolyl-guanidine (DOTG), ortho-tolylbiguanidine (OTBG), diphenyl thiourea (DPTU), benzothiazole disulphide (MBTS), hexamethylenetetramine (HMT), tetrabenzyl thiuram disulphide (TBzTD), and mixtures thereof.

4. The method of producing a rubber compound as claimed in claim 1, characterized in that, in each of said preliminary polymer material treating steps, the amount of silica ranges from 10 to 80 phr with respect to the polymer material.

5. The method of producing a rubber compound as claimed in claim 1, characterized in that the rubber compound comprises 80 to 20 of said first polymer material and 20 to 80 phr of said second polymer material.

6. The method of producing a rubber compound as claimed in claim 1, characterized in that said first polymer material is a styrene-butadiene copolymer (SBR).

7. The method of producing a rubber compound as claimed in claim 1, characterized in that said second polymer material is polybutadiene (BR) or natural rubber (NR).

Description

BEST MODE FOR CARRYING OUT THE INVENTION

(1) The following are non-limiting examples for a clearer understanding of the present invention.

Examples

(2) Six control compounds (Ctrl 1-Ctrl 6) and one compound according to the present invention (Inv.) were produced.

(3) More specifically, compound Ctrl 1 relates to a known compound, in which all the polymer base, all the silica, all the silane bonding agent, and the stearic acid are added and mixed simultaneously at a first mixing step, whereas the nucleophile agents in the curing accelerant class are only mixed into the compound at the final mixing step, together with the curing system.

(4) Compound Ctrl 2 differs from Ctrl 1 by involving a preliminary over 50 C. Tg polymer treating step, which comprises only mixing the over 50 C. Tg polymer with the 80-135 m.sup.2/g surface area silica and part of the silane bonding agent.

(5) Compound Ctrl 3 differs from Ctrl 1 by involving a preliminary below 50 C. Tg polymer treating step, which comprises only mixing the below 50 C. Tg polymer with the 150-220 m.sup.2/g surface area silica and part of the silane bonding agent.

(6) Compound Ctrl 4 differs from Ctrl 1 by involving both a preliminary over 50 C. Tg polymer treating step, as in Ctrl 2, and a preliminary below 50 C. Tg polymer treating step, as in Ctrl 3.

(7) Compound Ctrl 5 differs from Ctrl 2 solely by the presence of the nucleophile agent at the preliminary over 50 C. Tg polymer treating step, and by only adding the stearic acid at the final mixing step.

(8) Compound Ctrl 6 differs from Ctrl 3 solely by the presence of the nucleophile agent at the preliminary below 50 C. Tg polymer treating step, and by only adding the stearic acid at the final mixing step.

(9) Compound Inv. according to the invention involves both preliminary treating steps, as in control compound Ctrl 4, plus the presence of the nucleophile agent at both preliminary treating steps, and only adding the stearic acid at the final mixing step.

(10) Compound Ctrl 1 was produced as follows:

(11) Compound Preparation

(12) (First Mixing Step)

(13) Prior to mixing, a 230-270-liter, tangential-rotor mixer was loaded with the ingredients shown in Table I to a fill factor of 66-72%.

(14) The mixer was operated at a speed of 40-60 rpm, and the resulting compound unloaded on reaching a temperature of 140-160 C.

(15) (Final Mixing Step)

(16) The ingredients in Table I were added to the compound from the preceding mixing step to a fill factor of 63-67%.

(17) The mixer was operated at a speed of 20-40 rpm, and the resulting compound unloaded on reaching a temperature of 100-110 C.

(18) Control compounds Ctrl 2-Ctrl 6 and compound Inv. according to the invention were produced as follows:

(19) Compound Preparation

(20) (Preliminary Treatment of the Over 50 C. Tg and Below 50 C. Tg Portions of the Polymer Base)

(21) Prior to mixing, a 230-270-liter, tangential-rotor mixer was loaded with the ingredients shown in Tables I-III to a fill factor of 66-72%.

(22) The mixer was operated at a speed of 40-60 rpm, and the resulting compound unloaded on reaching a temperature of 140-160 C.

(23) (Mixing Step)

(24) Prior to mixing, a 230-270-liter, tangential-rotor mixer was loaded with the ingredients shown in Tables I-III to a fill factor of 66-72%.

(25) The mixer was operated at a speed of 40-60 rpm, and the resulting compound unloaded on reaching a temperature of 140-160 C.

(26) (Final Mixing Step)

(27) The ingredients in Tables I-III were added to the compound from the preceding mixing step to a fill factor of 63-67%.

(28) The mixer was operated at a speed of 20-40 rpm, and the resulting compound unloaded on reaching a temperature of 100-110 C.

(29) Table I shows the compositions in phr of compounds Ctrl 1-Ctrl 3, and the steps in which the ingredients were added.

(30) TABLE-US-00001 TABLE I Ctrl. 2 Ctrl. 3 Preliminary Preliminary treatment treatment Ctrl. 1 (Tg > 50 C.) (Tg < 50 C.) E-SBR 50 BR 50 Silica* 40 Silica** 40 Silane bonding agent 4 4 Mixing step E-SBR 50 50 BR 50 50 Silica* 40 40 Silica** 40 40 Silane bonding agent 8 4 4 CB 10 10 10 Stearic acid 2 2 2 Final mixing step Sulphur 1.4 1.4 1.4 ZnO 2.0 2.0 2.0 DPG 1.5 1.5 1.5 MBTS 1.0 1.0 1.0 E-SBR is a polymer base obtained by a process of polymerization in emulsion, with a mean molecular weight of 800-1500 10.sup.3 and 500-900 10.sup.3 respectively, a 20 to 45% styrene content, and used with a 0 to 30% oil content; Silica* indicates silica with an 80 to 135 m.sup.2/g surface area and 40 to 70 nm particle diameter distribution; Silica** indicates silica with a 150 to 220 m.sup.2/g surface area and 40 to 70 nm particle diameter distribution;

(31) The silane bonding agent used is of formula (CH.sub.3CH.sub.2O).sub.3Si(CH.sub.2).sub.3SS(CH.sub.2).sub.3Si(OCH.sub.2CH.sub.3).sub.3 and is marketed by EVONIK under the trade name SI75;

(32) DPG stands for diphenyl-guanidine;

(33) MBTS stands for mercaptobenzothiazole disulphide.

(34) Tables II and III show the compositions in phr of compounds Ctrl 4-Ctrl 6 and Inv., and the steps in which the ingredients were added.

(35) The ingredients in Tables II and III are the same as in Table 1, and Mix 1 and Mix 2 stand for the compounds from the respective preliminary treatments.

(36) TABLE-US-00002 TABLE II Ctrl. 4 Ctrl. 5 Preliminary Preliminary Preliminary Treatment Treatment Treatment (Tg > 50 C.) (Tg < 50 C.) (Tg > 50 C.) E-SBR 50 50 BR 50 Silica* 40 40 Silica** 40 Silane bonding agent 4 4 4 DPG 0.5 Mixing Step E-SBR Mix 1 + Mix 2 BR 50 Silica* Silica** 40 Silane bonding agent 4 CB 10 10 Stearic acid 2 Final Mixing Step Stearic acid 2 Sulphur 1.4 1.4 ZnO 2.0 2.0 DPG 1.5 1.0 MBTS 1.0 1.0

(37) TABLE-US-00003 TABLE III Ctrl. 6 Inv. Preliminary Preliminary Preliminary treatment treatment treatment (Tg < 50 C.) (Tg > 50 C.) (Tg < 50 C.) E-SBR 50 BR 50 50 Silica* 40 Silica** 40 40 Silane bonding agent 4 4 4 DPG 0.5 0.5 0.5 Mixing step E-SBR 50 Mix 1 + Mix 2 BR Silica* 40 Silica** Silane bonding agent 4 CB 10 10 Final mixing step Stearic acid 2 2 Sulphur 1.4 1.4 ZnO 2.0 2.0 DPG 1.0 0.5 MBTS 1.0 1.0

(38) The compounds in Tables I-III were tested to determine their rolling resistance and abrasion resistance related properties.

(39) More specifically, dynamic properties were measured as per ISO Standard 4664 (as anyone skilled in the art knows, 60 C. tan values are closely related to, and indicative of, rolling resistance properties: the lower the 60 C. tan value, the better the rolling resistance); abrasion resistance was measured as per ISO Standard 4649.

(40) Table IV (in which RR stands for rolling resistance, and AR for abrasion resistance) shows the results from the above tests, the values of which are indexed on the basis of the standard method control compound Ctrl 1 results.

(41) TABLE-US-00004 TABLE IV Ctrl. 1 Ctrl. 2 Ctrl. 3 Ctrl. 4 Ctrl. 5 Ctrl. 6 Inv. RR 100 102 102 105 104 104 115 AR 100 103 103 107 108 108 125

(42) As shown clearly in Table IV, compared with the control compounds, the compound produced using the method according to the present invention shows a marked improvement in rolling resistance, and an even more marked improvement in abrasion resistance.

(43) The values in Table IV show the target advantages to be only achievable by combining all the characteristics indicated in Claim 1. Which characteristics can be summed up as the presence of both preliminary treating stepsin which the low Tg polymer is mixed with a high-surface-area silica and a nucleophile agent, and the high Tg polymer is mixed with a low-surface-area silica and a nucleophile agentand the addition of stearic axis at the final mixing step, together with the curing system.

(44) In fact, as shown by compounds Ctrl 2-Ctrl 6, even using only some of the above technical characteristics, the target advantages are achieved to a significant extent. More specifically, in the case of compounds Ctrl 2 and Ctrl 3, only one preliminary treating step is performed, with no nucleophile agent, and stearic acid is added prior to the final mixing step; in the case of compound Ctrl 4, both preliminary treating steps are performed, but with no nucleophile agent, and stearic acid is added prior to the final mixing step; and, in the case of compounds Ctrl 5 and Ctrl 6, stearic acid is only added at the final mixing step, but only one preliminary treating step is performed, albeit with the nucleophile agent.

(45) The compound relative to the invention, on the other hand, by combining all the characteristics of the invention, achieves much higher rolling and abrasion resistance values.