RUBBER MIXTURES WITH IMPROVED PROPERTIES

Abstract

The invention relates to a rubber mixture comprising rubber and a liquid polybutadiene, liquid at a temperature of 20° C. and a pressure of 98.0665 kPa, wherein the liquid polybutadiene only consists of C— and H-atoms, and has an average molecular weight (Mw), determined by gel permeation chromatography as described in the description, of from 1500 to 5000 g/mol, to a process for preparing rubber articles by vulcanization using the inventive rubber mixtures as raw material, and to rubber articles obtained by this process.

Claims

1. A rubber mixture comprising rubber and a liquid polybutadiene, liquid at a temperature of 20° C. and a pressure of 98.0665 kPa, wherein the liquid polybutadiene comprises the 1,3-butadiene-derived monomer units ##STR00006## ##STR00007## and ##STR00008## and wherein the proportion of A in the entirety of the 1,3-butadiene-derived monomer units present in the liquid polybutadiene is from 55 to 70 mol % and wherein the sum of the proportions of B and C in the entirety of the 1,3-butadiene-derived monomer units present in the liquid polybutadiene is from 30 to 45 mol %, and that the liquid polybutadiene only consists of C-and H-atoms, and has an average molecular weight (Mw), determined by gel permeation chromatography as described in the description, of from 1500 to 5000 g/mol.

2. The rubber mixtures according to claim 1, wherein said mixtures comprise 0 to 150 parts by wt of precipitated silica, 0 to 100 parts by wt of carbon black and 1 to 50 parts by wt of the liquid polybutadiene, in each case based on 100 parts by weight of rubber.

3. The rubber mixtures according to claim 1, wherein said mixtures comprise an organosilane.

4. The rubber mixtures according to claim 3, wherein said mixtures comprise 0.5 to 20 parts by wt of organosilane based on 100 parts by wt of rubber.

5. The rubber mixtures according to claim 14, wherein said rubber is one kind of rubber or a mixture of different kinds of rubbers.

6. The rubber mixtures according to claim 15, wherein said rubber is selected from natural rubber and/or synthetic rubber.

7. The rubber mixtures according to claim 5, wherein said rubber is a mixture of Nd-BR and S-SBR.

8. The rubber mixtures according to claim 1, wherein said liquid polybutadiene has an average molecular weight (Mw), determined by gel permeation chromatography, of from 1750 to 3500 g/mol.

9. A process for preparing rubber articles by vulcanization of rubber mixtures, wherein a rubber mixture as claimed in claim 1 is used as raw material.

10. The rubber articles obtained by a process as claimed in claim 9.

11. The rubber articles according to claim 10, wherein it is a tire or a part of a tire.

12. The rubber articles according to claim 11, wherein it is a tire tread.

13. The rubber articles according to claim 11, wherein the tire is an all-season tire or a snow (winter) tire.

Description

EXAMPLES

Raw Materials Employed

[0068] The raw materials employed are given in table 1 below.

TABLE-US-00001 Raw materials used Name Material Abbreviation Producer Europrene® SOL R 72613 Solution polymerized, dry styrene-butadiene random copolymer that contains a non-staining antioxidant S-SBR Versalis S.p.A. Buna® CB 24 Neodymium Butadiene Rubber, not oil extended; cis 1,4 content: min. 96%. Nd-BR ARLANXEO Deutschland GmbH LBR 307 Liquid polybutadiene with a ratio of 1,2-vinyl groups of about 16 % LBR 16% Kuraray Ricon® 131 Liquid polybutadiene with a ratio of 1,2-vinyl groups of about 21 % LBR 21% Cray Valley Inventive product Liquid polybutadiene with a ratio of 1,2-vinyl groups of about 60 % LBR 60% Evonik Resource Efficiency GmbH VIVATEC® 500 plasticizer oil (Treated Distillated Aromatic Extract) TDAE H&R GmbH Co, KGaA ULTRASIL® 7000 GR precipitated silica U7000GR Evonik Resource Efficiency GmbH Si 266™ bifunctional silane Si 266 Evonik Resource Efficiency GmbH CORAX® N330 Carbon black CB Orion Engineered Carbons GmbH ZnO RS RAL 844 C zinc oxide ZnO Carl Arnsperger Chemikalien GmbH & Co Edenor® ST1 GS stearic acid ST1 Caldic Deutschland GmbH Rhenogran® DPG-80 dipropylene glycol 80 % Wirkstoff DPG Rhein Chemie additives GmbH Rubber Accelerator TBZTD-OP tetrabenzylthiuram disulfide TBzTD WEBER & SCHAER GmbH & Co, KG (produced by Dalian Richon) Vulkacit® CZ/EG-C N-cyclohexyl-2-benzothiazolesulfenamide CBS LANXESS Deutschland GmbH Sulfur pulverized sulfur HENSELER GmbH The amount of vinyl monomer units was determined by IR spectroscopy as described below. LBR 60% obtainable as described in Example 3 of WO 2018130703 A1.

Methods

Determination of the Micro-Structure

[0069] IR spectroscopy using polybutadiene standards were used for determination of the molar ratio of the monomer units according to formula (A), (B), and (C). 80 to 250 mg samples of the polybutadiene to be examined were dissolved in 10 mL of carbon disulfide (CS.sub.2). If high amounts of monomer units of formula (A) are expected, low concentration (e.g. 80 mg samples) of the polybutadiene is used, if high amounts of monomer units of formula (C) are expected, a higher concentration (e.g. 250 mg samples) of the polybutadiene is used. The termination is done using IR cuvettes (KBr) with a thickness of 0.5 mm. The solvent is subtracted and the spectrum is shown in the evaluation range of extinction from 1100 bis 600 cm.sup.-1. If the resultant extinction exceeds 1, the measurement is repeated using a lower concentration of polybutadiene. The extinctions above base line of the following signals were determined: [0070] trans-1,4-Polybutadiene: 968 cm.sup.-1 [0071] 1,2-Polybutadiene: 911 cm.sup.-1 [0072] cis-1,4-Polybutadiene: 730 cm.sup.-1 [0073] The molar ratio of the monomer units is calculated according to the following formula: [0074] %Comp(i) = Ext(i) * 100% / ( E(i) * c * d *) [0075] with [0076] Ext(i) = Extinction above base line [0077] E(i) = Extinction coefficient (substance-specific, determined by calibration measurements) [E] = [0078] L/(g*cm) [0079] d = thickness of the cuvette in cm [0080] c = concentration of the sample in g/L.

Mooney-Viscosity

[0081] Mooney viscosity of the raw rubber mixture was determined at 100° C. The value Ms (1+4) / MU was determined according to DIN 53523/3, ISO 289-1, and the value M.sub.L (1+4) / MU was determined according to DIN 53523/3, ISO 289-2.

Tensile Strength

[0082] The maximum tensile strength, given in MPa, and the elongation at break, given in %, of the vulcanizate were determined according to DIN 53504 / ISO 37. The measurements were done at a temperature of 23° C. using a standard dumb-bell S1 type specimen. The pull-off speed was set to 500 mm/min.

Shore-A-Hardness

[0083] The Shore-A-Hardness of the vulcanizates given in SH was determined according to ISO 7619-1 using a test temperature of 23° C.

Ball Rebound

[0084] The rebound resilience of the vulcanizates given in % was determined according to ASTM D 2632 using a steel ball with a weight of 28 g and a diameter of 19 mm and a drop height of 500 mm.

Viscoelastic Properties

[0085] Viscoelastic properties of the vulcanizates were determined according to ASTM D 6601-02, DIN 53513 / ISO 4664-1, and ISO 1827.

[0086] The maximum loss factor (tan δ max) was determined according to ASTM D 6601-02 using a RPA 2000 from Alpha Technologies as described in the operators manual dated February 1997 at 60° C. and 1.6 Hz within a range of from 0.28 % to 42.0 % elongation.

[0087] The complex modulus E* given in MPa of the vulcanizate was determined according to DIN 53513 / ISO 4664-1 using a Zwick Rel 2100, servo-hydraulic testing machine from ZwickRoell GmbH & Co. KG at 16 Hz, with an initial force of 50 N, an amplitude force of 25 N, a temperature adjustment time of 5 min. and a value recording after a testing time of 30 sec.

[0088] The complex shear modulus G* in MPa and dissipation factor tan δ were determined according to ISO 1827 using a EPLEXOR® 4000N (Serial No. 1101, NETZSCH GABO Instruments GmbH) in temperature sweep mode with 1.6 Hz, a dynamic deformation of 0.2 %, a static deformation of 0.0%, and a temperature range of from -80° C. to 80° C.

[0089] The molecular weight of the polybutadienes was determined using gel permeation chromatography. Measurements were carried out at 40° C. in tetrahydrofuran (THF) at a concentration of 1 g/L and a flow rate of 0.3 ml/min. Chromatographic separation was achieved using a PSS SDV Micro 5 .Math. / 4.6 × 30 mm precolumn and a PSS SDV Micro linear S 5.Math. / 4.6 × 250 mm (2x) separation column. Detection was by means of an RI detector. Calibration was carried out by means of a polybutadiene standard (PSS-Kit polybutadiene-1,4, Mp 831-106000, Part No.: PSS-bdfkit, Mn: 1830/4330/9300/18000/33500).

Viscosity

[0090] The viscosities (cone-plate) of the polybutadienes were determined to DIN 53018 with a Rheometer Physica MCR 301 from ANTON PAAR Germany GmbH.

Example 1

[0091] The formulation used for the rubber mixtures is specified in table 2 below for stage 1, 2, and 3. In this table, the unit phr means parts by weight based on 100 parts of rubber (S-SBR and Nd-BR) employed. The liquid polybutadiene (LBR) is employed as substitute for plasticizer oil “TDAE” in the inventive rubber mixtures in varying amounts.

TABLE-US-00002 Composition of the rubber mixtures used Raw material (abbreviation) Reference rubber mixture I Reference rubber mixture II Reference rubber mixture III Inventive rubber mixture IV 1.sup.st stage phr phr phr Phr S-SBR 70.00 70.00 70.00 70.00 Nd-BR 30.00 30.00 30.00 30.00 U7000GR 80.00 80.00 80.00 80.00 Si 266 5.80 5.80 5.80 5.80 TDAE 25.00 LBR 16% -- 25.00 -- -- LBR 21% -- -- 25.00 -- LBR 60% -- -- -- 25.00 CB 5.00 5.00 5.00 5.00 ZnO 2.00 2.00 2.00 2.00 ST1 2.00 2.00 2.00 2.00 2.sup.nd stage Batch 1.sup.st stage DPG 2.5 2.5 2.5 2.5 3.sup.rd stage Batch 2.sup.nd stage TBzTD 0.20 0.20 0.20 0.20 CBS 1.60 1.60 1.60 1.60 Sulfur 2.00 2.00 2.00 2.00

[0092] The amount of plastizicer oil, e.g. the LBR XX% and the TDAE, were given to the mixture using processible LDPE bags (Polybeutel 150 × 200 mm, IGEFA Handelsgesellschaft) having a low melting point, filled with 5.0 phr each.

[0093] The general process for producing rubber mixtures and vulcanizates thereof is described in “Rubber Technology Handbook”, W. Hofmann, Hanser Verlag 1994.

[0094] The equipment and the parameters used for processing each rubber mixture are given for stage 1 in table 3a, for stage 2 in table 3b, and for stage 3 in table 3c below.

TABLE-US-00003 equipment and parameters used for processing of each rubber mixture in stage 1 stage 1 settings mixing unit HF mixing group GmbH; type GK 1.5 E (Harburg-Freudenberger Maschinenbau GmbH) Fill factor 0.66 speed 65 rpm ram pressure 5.5 bar Mixing chamber temperature 70° C. Friction ratio 1:1 mixing operation 0.0 min to 0.5 min addition of S-SBR, Nd-BR, and 1.sup.st bag of plasticizer oil 0.5 min to 1.0 min addition of 2.sup.nd bag of plasticizer oil 1.0 min to 2.0 min addition of ½ amount of U7000GR and full amount of Si 266, CB, ZnO, ST1 and 3.sup.rd bag of plasticizer oil 2.0 min to 2.0 min aerate and purge (lifting the piston) 2.0 min to 3.0 min addition of 2.sup.nd ½ of U7000GR and 4.sup.th bag of plasticizer oil 3.0 min to 3.0 min aerate and purge (lifting the piston) 3.0 min to 7.0 min addition of 5.sup.th bag of plasticizer oil and mixing at 140 to 155° C. (temperature adjusted within this range by varying the speed) 7.0 min discharge and weigh the batch. Finally form a milled sheet on laboratory two roll mill for 45 s (laboratory roll mill: diameter 250 mm, length 190 mm, roll gap 4 mm, flow temperature 60° C., speed front roll 25 rpm, speed back roll 18 rpm) 24 h storage at a temperature of 23° C.

TABLE-US-00004 equipment and parameters used for processing of each rubber mixture in stage 2 stage 2 settings mixing unit as in stage 1 Fill factor 0.63 speed 70 rpm ram pressure 5.5 bar Mixing chamber temperature 75° C. mixing operation 0.0 min to 1.0 min addition and plasticize of stage 1 batch 1.0 min to 3.0 min addition of DPG and mixing at 140 to 155° C. (temperature adjusted within this range by varying the speed) 3.0 min discharge and weigh the batch. Finally form a milled sheet on laboratory two roll mill for 45 s, (laboratory roll mill: diameter 250 mm, length 190 mm, roll gap 4 mm, flow temperature 60° C., speed front roll 25 rpm, speed back roll 18 rpm) storage at 23° C. for up to 24 hours

TABLE-US-00005 equipment and parameters used for processing of each rubber mixture in stage 3 stage 3 settings mixing unit as in stage 1 fill level 0.60 speed 55 rpm Mixing chamber temperature. 50° C. mixing operation 0.0 min to 2.0 min Plasticize stage 2 batch, adding CBS, TBZTD and sulfur. Mixing at 90 to 110° C. (temperature adjusted within this range by varying the speed) 2.0 min discharge and weigh the batch. Finally form a milled sheet on laboratory two roll mill for 20 s (laboratory roll mill: diameter 250 mm, length 190 mm, roll gap 4 mm, flow temperature 80° C., speed front roll 16 rpm, speed back roll 11.5 rpm) then, cut and fold over 3* to the right, 3* to the left, and roll 3* with a narrow roll gap (3 mm) and then draw off a milled sheet via roll mill gab with 4 mm.

[0095] The Mooney viscosity of the rubber mixtures (sheets) obtained after 1.sup.st and 3.sup.rd stage was determined as described above. The results are given in table 4.

[0096] The rubber mixtures obtained after stage 3 were vulcanized to obtain the test plates and test specimens. Vulcanization was carried out at a temperature of 165° C. in a typical vulcanizing press for 17 minutes with a compression pressure of 130 bar as per the optimum cure time of t.sub.95. The t.sub.95 time was determined by moving die rheometer (rotorless vulcameter) according to DIN 53529/3 procedure at 165° C.

[0097] The rubber testing was executed in accordance with the test methods specified above. The results of the rubber testing are also given in table 4.

TABLE-US-00006 results of the rubber testing Reference rubber mixture I Reference rubber mixture II Reference rubber mixture III Inventive rubber mixture IV M.sub.s (1+4); (1. stage) / MU 145 145 132 128 M.sub.L (1+4); (3. stage) / MU 87 85 83 82 Tensile strength at break / MPa 13.5 10.7 10.5 13.6 Elongation at break / % 240 250 230 270 Shore-A-Hardness / SH 69 66 67 68 Ball Rebound at 60° C. / % 60 55 55 57 Loss factor maximum at 60° C.; tan δ max/- 0.188 0.199 0.217 0.187 complex modulus E* at 60° C. / MPa 10.2 10.1 9.7 10.5 complex shear modulus G* at 60° C. / MPa 3.6 2.9 2.7 3.3 loss factor tan δ at -10° C. / - 0.276 0.240 0.243 0.251

[0098] The inventive rubber mixture IV has an improved processability compared to the rubber mixtures I to III, indicated by the lower Mooney viscosity values for the inventive rubber mixture IV after 1.sup.st and 3.sup.rd stage.

[0099] Surprisingly, the rubber mixture IV used in the invention achieves an enhanced reinforcing effect to all other mixtures, as it not only has the highest tensile strength but also the highest elongation at break. With approximately the same hardness, the dynamic data can be compared well. Rubber mixture IV according to the invention, has a lower hysteresis in the dynamic tests at 60° C., which are important for predicting rolling resistance, compared to the reference rubber mixtures I, II, and III.

[0100] This can be seen in the increased Ball Rebound values, i.e. improved values compared to the other compounds containing liquid polybutadienes and is confirmed in the lowest tan δ max value measured at 60° C. Thus, the rubber mixture according to the invention should lead to improved rolling resistance and lower fuel consumption if a tire is equipped with a tread based on the rubber mixture according to the invention.

[0101] At the same time, the rubber mixture IV according to the invention can achieve high dynamic complex moduli measured at elevated temperatures of 60° C. (E* and G* at 60° C.), which is an indicator to predict the dry traction of passenger car tire as per the literature. Especially compared to the reference rubber mixtures II and III, an improved dry handling of a passenger car tire equipped with a tread compound according to the rubber mixture IV according to the invention can be expected. In addition, the rubber mixture IV according to the invention shows a higher loss factor value than the reference rubber mixtures II and III at -10° C. According to the relevant literature, this should lead to improved winter properties and/or have a positive influence on wet grip if this mixture is used to be the basis for a winter tire tread mixture.