High surface area carbon black and fumed silica are more effective as reinforcing agents than other equivalent weight rheology control additives. Carbon black can be used to increase viscosity, provide sag resistance, and increase the cohesive strength of automotive windshield adhesives. Similarly, coated precipitated calcium carbonate (PCCs) is also used for rheology control of STP and polyurethane adhesives and sealants. Those PCCs with hydrophobic coatings (eg, fatty acids, or stearic acid) provide shear thinning rheological properties and moderately increased bond strength in polyurethane systems.
Figure 3 shows a polyurethane prepolymer with a NCO content of <2% and a diisodecyl ester plasticizer, a heavy calcium carbonate filler and an organotin catalyst in a one-component moisture-curing polyurethane adhesive. Only one of hydrophobic fumed silica or coated PCC was used in the formulation for lap shear strength comparison.


As shown in Fig. 3, the hydrophobic fumed silica clearly exhibited higher bonding strength than the PCC on the basis of the same weight ratio. Not only can it reduce the amount of its input in the formulation; and the hydrophobic fumed silica has a lower specific gravity than calcium carbonate, which greatly reduces the weight of such fillers in the binder; thus contributing to some attention to the adhesive. Special application areas for weight ratio (for example, lightweight cars).
Pressure sensitive adhesive
Fumed silica aggregates can be used to improve film forming processes and properties such as natural rubber, polychloroprene, acrylates, and many other water-based latex emulsions. These submicron, high specific surface area particles reduce drying time and modulate capillary pressure by modulating capillary pressure to enhance the mechanical properties of the final product. Pre-dispersed gaseous metal oxide forms in water, such as CAB-O-SPERSE® dispersions, are an effective "invasive" means of allowing these particles to easily enter the adhesive film.
The Cabot application development team observed a significant improvement in bond shear strength and thermomechanical properties of the product due to the incorporation of well dispersed fumed silica in aqueous pressure sensitive adhesives. In the formulation of aqueous acrylic emulsions suitable for pressure sensitive adhesive applications, the content of fumed silica in the film formation of the adhesive ranges from 0 to 15% (dry weight), which can pour the latex on the Mara film and The wet film was dried in a 110 ° C oven for 20-40 minutes. The dry film was cooled at room temperature, coated with wax-coated release paper, and wound into a roll at a constant speed of 17 pounds, and allowed to stand at room temperature for 24 hours before the test. The dry film thickness is 1.0 to 1.3 μm, respectively.