Silica compounds mixing process

COMPARATIVE STUDIES ON EFFECTS OF TESPT AND TESPD TREATED SILICA COMPOUNDS ON PROCESSING AND SILICA DISPERSION DURING MIXING IN NATURAL RUBBER... 

Silica compounds are generally processed in conventional internal mixers, preferably with intermeshing rotors. These mixers are designed and optimized for carbon black-fiUed compounds in which mixing is based only on physical processes. When a silica-silane reinforcing system is used, additionally a chemical reaction, the sUanization, occurs. One of the main influencing factors of the silanization reaction is the concentration of ethanol in the compound as well as in the mixer [25,26]. As the silanization finally reaches an equilibrium, low concentrations of ethanol in the compound are expected to enhance the reaction rate. 

Mixing Silica-Filled Compound Rubber Process Analyzer-Fourier Transform (RPA-FT) Results at 100°C Complex Modulus Dependence on Strain Fit Parameters of Equation 30.3... 

FIGURE 35.13 Typical fingerprint of a masterbatch mixing process of a solution-based styrene-butadiene rubber (S-SBR)/Silica/TESPT tread compound on a GK 320E (Harburg Freudenberger) with PES5 rotors. 

Filler dispersion is a property that determines how well the filler partciles in a given rubber compound are dispersed as a result of the mixing process. This relates to carbon black dispersion as well as the dispersion of nonblack fillers such as silica, clay, calcium carbonate, titanium dioxide, etc. Also rubber curatives such as sulfur and accelerators can be poorly dispersed (commonly these ingredients are added late in the mixing cycle). Poor dispersion makes a mixed stock less uniform, and commonly the cured ultimate tensile strength will have more variability. Poor dispersion can affect other important cured physical properties such as abrasion, tear, and fatigue resistance, flexometer heat buildup, and other dynamic properties. 

Silica-filled systems will produce higher viscosity compounds when compared to the use of carbon black although this effect can be moderated through the use of silane coupling agents. The mixing process with silanes must be very well controlled to avoid wide fluctuations in processing and end component properties. 

The potential for the formation of ionic crosslinks with Vamac terpolymers precludes the use of fillers that may contain soluble divalent metal ions. Metal stearates, metal stearate-coated fillers, clays, and precipitated silicas are not recommended for use in Vamac terpolymers. Precipitated fillers can contain impurities, which can lead to ionic bonding. Another potential source of soluble divalent metal ions is the pigment used to color mineral-filled compounds. Ionic bonds can significantly increase the viscosity of the uncured stock and increase the compression set of vulcanizates. The effect of metal ions and ionic bonds on stock and vulcanizate properties can vary considerably from batch to batch and is dependent on the impurity concentration in the lot of filler as well as the mixing/processing procedures. 

No.6, March 2004, p.33/40 IMPROVING SILICA COMPOUND PROCESSING OPTIMIZATION OF THE MIXING EQUIPMENT... 

OPTIMISATION OF THE MIXING PROCESS AND EQUIPMENT FOR SILICA COMPOUNDS... 

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