ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS Natural Rubber Silica Silane Master­ batch Easy processing Compounds NR-Silica-Masterbatches Growing requirements of higher fuel The easy Processing Way to High economy increase the pressure on pro- ducers of TBR tires to use silica as a fil- Quality Compounds ler in Natural Rubber compounds. Cur- rently this seems to be the silver bullet to further reduce Rolling Resistance wi- thout compromise in Skid and Wear. 1. Introduction marching modulus and keeping/ en- High quality Natural Rubber com- Natural rubber is the first choice polymer hancing physical properties. For those pounds filled with Silica and Silane in if high tear strength, green strength as who are new to silica compounding, an high dosages are difficult to produce well as green tack are requested. Tire investment into a new mixing line can be with conventional mixing procedures. properties like low wear, good chip & avoided as the material can be used in The Natural Rubber-Silica-Silane Mas- chunk and low rolling resistance can be standard rubber mixing lines as well as terbatches proposed in this paper offer achieved. The outstanding properties on open mills. to produce high quality compounds are the result of its unique, long polymer using shortest mixing cycles and to uti- chains. To improve tear resistance of nat- 2. Natural Rubber­Silica­Masterbatch lize the full potential of this material ural rubber based compounds, up to 15- A masterbatch is a solid product consist- combination. 20 phr silica can be added without the ing of a polymeric carrier material, addi- need of any compatibilizers. Further ben- tives and/ or fillers which are already efits, especially the balance in rolling re- optimally dispersed. sistance, wet skid, and wear can be real- In this particular case the carrier ma- NR­Silica­Masterbatches ized if silica is bound to natural rubber by terial is natural rubber including silica as Ein einfacher Weg der Verar­ coupling agents such as silanes. well as silane. However the compounding of natural Such material has been investigated beitung für qualitativ hoch­ rubber and silica is a big challenge, due earlier, e.g. the Rubber/Filler Composites wertige Gummimischungen to high filler to filler interactions which developed based on NR, E-SBR and SSBR Naturkautschuk Kieselsäure Silane affect the dispersion within natural rub- by Degussa in the late 1990’s and early Masterbatch einfaches Mischen ber. Beside this, if it is necessary to mix 2000’s [1]. Advantages in processing and Mischungen high filler volumes into the natural rub- performance have been found already ber, a silanization of the silica becomes then, but commercial success has not Steigende Anforderungen an niedrige essential. This silanization process trans- been realized. During the last 5 years Benzinverbräuche bei LKW erhöhen den forms the rubber mixer into a chemical further developments in the area of Sili- Druck auf Reifenhersteller zur Verwen- reactor, which requires state of the art ca Masterbatches have been conducted, dung von Kieselsäure in Naturkaut- mixing equipment, including exhaust e.g. by INSA, Mexico [2]; the EWE insti- schukmischungen. Nur damit erscheint systems to get rid of volatiles occurring tute of Shanghai [3, 4] and many others. es möglich, weitere Verbesserungen im during the process (dry rubber mixing The production of the Natural Rubber- Rollwiderstand zu erreichen, ohne bei process). A further issue is the long mix- Silica-Masterbatch needs to be explained Bremsverhalten und Abrieb weitrei- ing time which is needed to fully silanize for further understanding. chende Kompromisse eingehen zu müs- the silica, as the high and long-lasting To avoid the silanization within the sen. Qualitativ hochwertige Naturkaut- shear is degrading the polymer chains of mixer, the silica needs to be silanized in a schukmischungen mit Kieselsäure und natural rubber, causing deterioration of previous step. The Behn Meyer Europe Silanen in hohen Dosierungen sind mit its amazing properties. Affinity of impu- GmbH in cooperation with its network of herkömmlichen Verfahren nicht oder rities like phospholipids and proteins, toll producers developed a process to nur sehr aufwändig zu produzieren. Die which are naturally present in natural in diesem Artikel vorgestellten Natur- rubber, to the silica surface further nega- kautschuk-Silica-Silan-Masterbatche tively influence the silanization process bieten die Möglichkeit, in kurzen Misch- of such surface during dry rubber mixing. verfahren zu qualitativ hochwertigen Even if all mixing steps are minutely Mischungen zu gelangen und das volle controlled compounders still face high Potenzial dieser Materialkombination batch to batch variations, high com- auszuschöpfen. pound viscosities as well as changes of Authors the compound properties during storage. To avoid the silanization during mix- Dr. Joachim Bertrand, Johannes ing, long mixing processes and degrada- Bauer, Hamburg, Germany, tion of the natural rubber Behn Meyer Europe GmbH offers a new raw material Corresponding Author: called Natural Rubber-Silica-Masterbatch. Dr. Joachim Bertrand This product shortens the natural rubber Behn Meyer Europe GmbH Figures and Tables: By a kind approval of the authors. and silica mixing process, beside improv- Ballindamm 1, 20095 Hamburg ing the filler distribution, avoiding E-Mail: [email protected] 38 KGK · 01-2 2018 www.kgk-rubberpoint.de ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS surface-modify silica by various silanes. 1 The result is pre-silanized (hydrophobic) silica which is easy to disperse within natural rubber, natural rubber latex and Natural Rubber, Masterbatch other polymers. (Process oil), (coagulated To avoid the degradation of natural Silica and Silane from latex) rubber while mixing it with the pre-si- lanized silica it is necessary to distribute the modified filler in the liquid natural rubber latex. As final step the liquid mix is coagulated and pressed into bales comparable to pure natural rubber. (fig- React Silane Mix of (Mix Process Coagulation, with pure silanized silica oil with drying, bale ure 1) Currently 4 different grades with Silica with NR Latex NR-Latex) forming varying silica- and silane-content are available. Fig. 1: Production Natural Rubber­Silica­Masterbatch Grade Silica content Silane content 2 in phr in phr NR Si 30 ZO 30 3 NR Si 40 ZO 40 4 NR Si 50 ZO 50 5 NR Si 60 ZO 60 6 To provide the possibility of modifying the content of silica and silane within the natural rubber, Behn Meyer Europe GmbH extended its portfolio by pure pre- silanized silica. As the filler is readily si- lanized it is easily dispersed in the mas- terbatch or other polymers without the need of extending the mixing time. 3. Major Advantages of Natural Rubber­Silica­Masterbatch Fig. 2: Particle size distribution comparison normal silica filled compound and NR Si MB a. Improved silica dispersion compound. To prove the enhanced silica distribution within the final compound Behn Meyer Europe GmbH (MB) compared a conven- 3 tional compound with 50 phr silica and 5 temperature NR, Silica, Silane Dry mix (3 stage: 8 + 4 + 2 min) phr silane (compound A) and a com- pound mixed with the NR Si 50 ZO in- stead (compound B). As shown on the bilevel picture and particle diameter analysis, the dispersion within com- pound B is improved and the particle di- First MB Second MB Final Batch time (min) ameter on average noticeably smaller. Dispersion phase Silanisation phase (Figure 2) An improved silica dispersion leads to Fig. 3: conventional silica compounding more consistent compounds with better mechanical and physical properties as well as longer lifecycles for the finished starting with the dispersion phase (~2 To avoid this breakdown the use of material. Minutes, only time under full shear Natural Rubber-Silica-Masterbatches is an counted) followed by the silanization excellent alternative. As the silanization is b. Shortening the mixing cycles phase (~10 minutes) and the final batch already finished, a whole mixing step can Additionally to the improved dispersion (~2 minutes), accumulated this results be avoided, furthermore the dispersion of the silica the Natural Rubber-Silica- in an approximate mixing time of 14 phase shortens as well. By using the Natu- Masterbatch shortens the mixing pro- minutes, which also causes breakdown ral Rubber-Silica-Masterbatches the full cess significantly. Normal silica com- of the natural rubber polymer chains. mixing time under shear can be reduced pounding requires 3 stage mixing: (Figure 3) down to 6 minutes. (Figure 4) www.kgk-rubberpoint.de KGK · 01-2 2018 39 ROHSTOFFE UND ANWENDUNGEN RAW MATERIALS AND APPLICATIONS 4 cessing additive is added with the chem- temperature icals in 1st stage. (Figure 6) NR-Si-MB very short mix Mixing cycle C is further shortened to (2 stage: 4 + 2 min) 6 minutes in 2 stage mixing, by using the 58% mixing time reduction processing additive together with the 1 stage less Natural Rubber-Silica-Masterbatch in the 240% mixing capacity st 33% less interim storage 1 stage. (Figure 7) b. Formulation First MB Final Batch To secure comparable results all com- Short No Silanisation phase, time (min) pounds where mixed including the same dispersion only batch compaction raw materials. phase Group 1 is the dry mix group where the silanization is done within the mixer. Fig. 4: Silica compounding with NR Si MB SMR 10 (100 phr) is used alongside BM Silica ZC 185 (60 phr) and Si 69/ TESPT (6 4. Compound properties Mixing cycle A is a traditionally mixed phr) in mixing cycle A. compound with 3 stages, lasting 14 min- Group 2 contains the NR-Si-60 ZO a. Mixing cycles utes. This leaves time to silanize the silica (162,6 phr). This product already con- To compare the compound properties within the mixer if necessary. (Figure 5) tains BM Silica ZC 185 (BET 175-185) as the Natural Rubber-Silica-Masterbatch is Mixing cycle B is shortened by one well sulfur silane (TESPT), so the con- tested against a conventionally mixed stage and takes 10 minutes until dis- tent SMR 10, silica and silane is re- compound in 3 different mixing cycles.