Optimized rolling resistant tire treads with Aflux 37 and Aflux 72

Transcription

1 Technical Report 76 ptimized rolling resistant tire treads with and Aflux 7 Dietmar Hoff, Applications Technology, Rubber Division Rhein Chemie Rheinau GmbH, Mannheim [ Contact: dietmar.hoff@rheinchemie.com] Key words: tread, SBR, BR, silica, silane, 69, VP 6, rolling resistance,, Aflux 7, Aktiplast PP, dithiophosphates Summary The further reduction of C emissions set in the Kyoto Protocol and the planned Euro 5 Standard is currently one of the most important topics in international environmental policy. The decrease in gasoline consumption for motor vehicles will have to make a significant contribution to this objective. ne of the ways in which this can be achieved is by reducing the rolling resistance of tires, especially regarding the tire treads. With the newly developed processing promoters (GE 87) and Aflux 7 (GE 87) specially designed for silica mixtures, we have seen considerable improvement in the processing behavior of rubber compounds with polar fillers []. New functional polymers as well as new types of silane offer new opportunities in this regard. For example, the mercaptosilane VP 6* is improving properties compared to the standard 69 []. The efficient shielding of the silica surface with VP 6 leads to reduced filler to filler interactions, which in turn reduces the rolling resistance. However, silica tread mixtures that contain VP 6 as a coupling reagent show a changed processing behavior. This is exhibited by high Mooney viscosities after the first mixing stage up to significant hardening of the compounds after storage depending on the applied conditions. *) VP 6 is a product of Evonik x Degussa GmbH, Frankfurt.

2 Technical report 76 page The polar ingredients of these new types of processing promoters are compatible with the silica filler and can coat the surfaces (fig. ). These new materials are characterized by the fact that the physical properties of the vulcanizates remain nearly unchanged. The use of zinc soaps and fatty acid derivatives as processing materials usually has a significant influence on the cross-link density of the vulcanizate. In addition, the new Aflux types are also completely zinc free. The reduction of zinc oxide and other zinc containing compounds is becoming more and more important in the tire industry. The use of zinc-free processing agents such as and Aflux 7 can make an additional contribution in this case.. Experimental The different processing promoters were each dosed with phr to a model formulation based on VP 6 and then compared with the formulation without a processing promoter and a 69 standard formulation (s. tab. ). The VP 6-based formulations were then mixed in the different series (s. tab.). Series reproduces typical mixing conditions that can also be used for systems containing other silanes such as 69. It has been shown in preliminary testing that the mixing quality, simulated in series and, can vary depending on the addition of shearing forces as well as the sequence of adding the different ingredients. The flow temperature for cooling the mixer was increased to C for both series. Fig. : lica interactions without (left) and with processing agent (right) Agglomeration No silica agglomeration H H H H H H lica H H lica H H H H H H H H H Repulsion Interaction H A H H H H lica lica H A H H H H Process. Prom. H

3 Technical report 76 page Tab. : Formulations Buna VSL 505-HM Buna CB 4 Ultrasil 7000 GR TDAE oil Antilux 654L 6PPD Zinc oxide WS Stearic acid 69 VP 6 Aflux 7 Sulfur CBS DPG TBzTD 69 VP 6 Aflux ) As an alternative to TBzTD Rhenocure SDT/S (.0 phr) can also be used. Tab. : Mixing series Series Series Series st stage Rotation 70 rpm Mixer flow temperature 70 C C C Polymers lica, oil, wax, antioxidant, Zn, stearic acid lane,5 Ventilate, 5 4 Emission 6 5 5,5 Emission temperature approx.50 C approx.50 C approx.50 C nd stage Rotation 70 rpm Mixer flow temperature C C C Mixing time Emission temperature approx.50 C approx.50 C approx.50 C rd stage Rotation Mixer flow temperature 60 C 60 C 60 C Accelerator, sulfur Emission temperature < 0 C < 0 C < 0 C

4 Technical report 76 page 4. Results and discussions Fig. shows the Mooney viscosities for the series mixtures after the first mixing stage. The VP 6 mixture compared to the 69 compound shows a significantly higher Mooney viscosity (ML(+4)) of approx. 40 units after the first mixing stage for the same mixing conditions. The viscosity can be reduced significantly by using processing promoters such as zinc soap, or Aflux 7. sheets show improved shape and green strength with and zinc soap after series. The corresponding mixture without a processing promoter could certainly not be processed easily under production conditions. The delayed addition of the silane for the simultaneous use of a processing promoter in series leads to improvements of the appearance and haptic of the sheet. Using increased mixing temperatures and lower shearing forces in series, we also found significantly higher values for the Mooney viscosities (fig. ) after the first mixing stage. nly The silanization reaction of the silicica with VP 6 differs from the one with 69. The 69 has several opportunities for condensation (in general two) because of the Fig. : Mooney viscosities at 0 C after st mixing stage series 00 Mooney SI 69 VP 6 Aflux time [min] the Mooney viscosities of compounds with and zinc soap could be measured. The experiments without a processing agent or with Aflux 7 could not be carried out due to extremely high viscosities. The initial value of the Mooney viscosity was over 00 units and the device shut down. The delayed addition of the VP 6 silane after series at comparable temperatures lead by using of a processing agent to lower the Mooney viscosities compared to series (fig. 4). existence of three ethoxy groups. VP 6, on the other hand, has only one ethoxy group, which only allows for one condensation step. It is possible that this is linked to a significant increase in the silanization reaction speed when using higher temperatures with a simultaneous decrease of shearing forces. For VP 6-based compounds, this could lead increasingly to the silanization of incompletely homogenized silica, which in turn leads to higher viscosities. Along with the decreased Mooney viscosity, a reduction of the filler to filler interactions was also observed in RPA measurements when using processing promoters. In addition, the

5 Technical report 76 page 5 Fig. : Mooney viscosities at 0 C after st mixing stage series Mooney VP 6 Aflux time [min] The viscosity of compounds in systems with regular silanes such as 69 is also dependent on the addition of shearing forces. For VP 6 systems, this dependency seems to be much stronger. The significantly increased viscosities when using reduced shearing forces in mixing series are not because of insufficient dispersion and/or deagglomeration of the silica. This is partially confirmed by the results in mixing series : when using a processing agent and a delayed addition of the silane, lower viscosities are measured. The silica-specific processing promoter can partially take over the dispersion effect of the silane. The Mooney viscosity values of all mixtures can be reduced further in all three series by using the remill in the second mixing stage as well as adding the accelerator in the third mixing stage. In series, there are Mooney ML(+4) values under 65 for all VP 6 compounds with or without a processing agent after the third mixing stage. These values are lower than the 69 control. In mixing series and, Mooney ML(+4) values under units are obtained only when using or zinc soap while the values for the corresponding compounds without a processing agent are approx. 0. Fig. 4: Mooney viscosities at 0 C after st mixing stage of mixtures series VP 6 Aflux 7 Mooney time [min]

6 Technical report 76 page 6 The different cross-linking characteristics are documented in the rheometer curves in fig. 5. The rheometer curve for the mixture with Aflux 7 shows hardly any deviation from the VP 6 control. As expected, the zinc soap has the most obvious influence on the crosslinking behavior. Zinc soaps can affect the polymer matrix as a plasticizer. The first indication for this phenomenon is the decreased torque of the rheometer curve. As has already been determined from the measurements of the Mooney viscosity, the use of and/or zinc soap in particular show the most significant improvement of the flow behavior of the compounds. The results of the physical testing of the vulcanizates show the enormous advantages of the new processing agents and Aflux 7 compared to regular zinc soaps (fig. 6 & tab. ). The physical values such as hardness, static and dynamic coefficients as well as the loss angle are unchanged when using the new Aflux types. Using Aflux 7 even leads to slightly increased values for modules and hardness. The negative influence of the zinc soap on the physical properties has been shown by modulus 0 reduced by approximately 0%. The vulcanizates of compounds containing show very constant values for Shore A hardness in different conditions. Fig. 5: Rheometer curves at 60 C series elasticity [Nm],5 SI 69 VP 6 Aflux 7 0, time [min] The cross-linking system of VP 6 mixtures differ, above all, in the partial use of TBzTD instead of DPG. In rubber compounds that contain mercaptosilane VP 6, larger amounts of DPG result in an extreme scorch behavior []. In this case, a non-aminic secondary accelerator has to be used. Dithiophosphates are the accelerator class of choice [4]. The latest studies have shown that approx..0- phr of After days of hot air aging at 0 C, only a loss of one Shore A unit was determined for hardness. The measurement of Shore A hardness at higher temperatures results in only a one point decrease in hardness. the dithiophosphate accelerator Rhenocure SDT/S can be used instead of 0.5 phr TBzTD & 0.5 phr DPG. Rhenocure SDT/S is a technically adequate and cost-effective alternative to the special accelerator TBzTD.

7 Technical report 76 page 7 Fig. 6: Stress strain curves (series ) stress [MPa] 0 5 SI 69 VP 6 Aflux strain [%] The comparison of the physical properties of the VP 6 vulcanizate with those of the 69 vulcanizate show the superiority of the VP 6 system regarding the optimization of rolling resistance. Through the reduced filler to filler interactions, significantly higher values were consistently found for elasticity. The dynamic/mechanical analysis shows the decrease of the loss angle at 60 C by approx. 5 %. However, the corresponding tan delta at 0 C is nearly constant, indicating an unchanged wet skid resistance. The reduced hardness of the vulcanizate can be seen as a disadvantage compared to 69. In order to avoid additional reductions in hardness from processing promoters such as the zinc soap, Rhein Chemie has developed and Aflux 7 as two technical alternatives. In addition, Aflux 7 can be combined with zinc soap such as Aktiplast PP to achieve excellent processability with good physical values. Application ratios for Aflux 7 and Aktiplast PP in the range of : up to : have been shown as especially suitable. The processing agent is available in pastille form (melting point: approx. 60 C). Aflux 7 is a waxy substance melting between 0-40 C. This product is also available as a silica-bound dry liquid. The recommended quantity of or Aflux 7 respectively depends on the amount of silica in the formulation ( phr processing agent at phr filler).

8 Technical report 76 page 8 Tab. : Selected physical data for the vulcanizate series 69 VP 6 Aflux 7 Hardness [Shore A] C d/0 C h/0 C Elasticity C d/0 C h/0 C MTS. 6 Hz. 50 N preload E* 0 C [Mpa] E 0 C [Mpa] tan delta 0 C E* 60 C [Mpa] E 60 C [Mpa] tan delta 60 C Summary The use of functional polymers and new silanes in silica-filled tread mixtures is an option to reduce rolling resistance for tires. The use of these new materials as well as increased use of silica with over 0 phr poses new challenges to the processing behaviors of these kinds of compounds. The processing behavior of compounds of this type can be improved by using the new silica-specific processing promoters and Aflux 7. In addition, the user also does not have to make any compromises when it comes to the physical properties of the corresponding vulcanizate. While the use of zinc soaps have a negative influence on properties such as modules and hardness, nearly unchanged levels are reached using und Aflux Literature [] Klockmann, A. Hasse, KGK 60 (007), 8 [] D. Hoff, H.-M. Issel, M. Saewe, Newly designed high-performance processing promoters for silica tire treads, SRC Púchov 006 [] A. Hasse,. Klockmann, GAK 60 (007), 554 [4] D. Hoff, H.-M. Issel, M. Saewe, Tire Technology International, 006, 6

9 ur technical advice - whether verbal, in writing or by way of trials - is given in good faith but without warranty, and this also applies where proprietary rights of third parties are involved. It does not release you from the obligation to test the products supplied by us as to their suitability for the intended processes and uses. The application, use and processing of the products are beyond our control and, therefore, entirely your own responsibility. Should, in spite of this, liability be established for any damage, it will be limited to the value of the goods delivered by us and used by you. We will, of course, provide products of consistent quality within the scope of our General Conditions of Sale and Delivery. Aflux, Aktiplast, Antilux and Rhenocure are registered trademarks of Rhein Chemie Rheinau GmbH, Mannheim. Buna is a registered trademark of Lanxess Deutschland AG, Leverkusen. Ultrasil and 69 are registered trademarks of Evonik Degussa GmbH, Frankfurt. Image by courtesy of Continental AG, Germany. Rhein Chemie Rheinau GmbH Duesseldorfer Strasse Mannheim, Germany Phone: +49 (0) Fax: +49 (0) rubber.rcr@rheinchemie.com Rhein Chemie Corporation 45 Parker Court Chardon, H 4404, USA Phone: Fax: rubber.rcc@rheinchemie.com Rhein Chemie Japan Ltd. Marunouchi Kitaguchi, Bldg. F -6-5 Marunouchi, Chiyoda-ku Tokyo , Japan Phone: Fax: Rubber.rcj@rheinchemie.com Rhein Chemie (Qingdao) Ltd. 4 liubei Road Li Cang District Qingdao 6604, PR China Phone: Fax: rc.asia@rheinchemie.com G9/pdf/KR/0608