The choice of fumed silica in epoxy-based system

Epoxy adhesives are a class of engineering adhesives with very strong versatility. Because of its good bonding performance, good functionality, relatively low price, easy bonding process and other advantages, for decades in home appliances, automobiles, water conservancy transportation, electrical and electronic appliances and aerospace industry has been widely used. In recent years, with the continuous development of high-tech and nanotechnology, the modified epoxy resin continues to deepen, by epoxy resin made of a variety of high-performance adhesive varieties are also more and more, epoxy-based system has become excellent performance, variety, adaptability of a wide range of important adhesives .
gas phase silicon dioxide (gas silicone) is a highly dispersed, synthetic white powder, can meet the special requirements of different adhesives and sealants in rheumation, enhancement, thickening and so on, widely used in silicone gel, chemical anchoring, tile seams, electric wind trucks and automotive, electronics, aviation industry adhesives and sealants. So how do you choose the right gas silicon product in the epoxy-based system to meet the needs of different applications? Today, we have brought in Ms. Fan Qin, Senior Technical Manager of Gas Phase Silica in WACKER Asia Pacific, a technical expert at WACKER Chemical, the world's leading producer of gas silicon, to introduce her to the options of gas silicon in the epoxy-based system.
: We all know that WACKER's HDK® gas phase silicon dioxide is a very efficient rheological control agent, chemical inert in a variety of reactive systems, but also has anti-flow performance control, mechanical performance adjustment, maintaining the viscosity stability during storage and other functions, then what is its working mechanism?
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yes, by adding the right amount of HDK® series of products can enable adhesives and sealants to achieve excellent rheodranic performance. HDK ® well-moisturized and dispersed in the formulation, and its aggregate particles interact to form a shear-sensitive 3D mesh structure. The formation of this mesh structure enhances the viscosity of the adhesive during storage and prevents the precipitation of the parts. When the adhesive is subjected to shear force during processing, the branched mesh structure is destroyed, resulting in a decrease in viscosity (shearing becomes thinner), making the adhesive easier to process. When the adhesive is applied to the substrate, HDK® will re-form the mesh structure (touch-change performance), the viscosity will quickly rebound, effectively avoid the phenomenon of hanging, and ensure that the adhesive can be cured in the desired part.
: What type of gas silicon should be used in epoxy-based systems? Why?
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in the epoxy-based system we recommend the use of hydrophobic HDK ®. Epoxy adhesive systems usually contain epoxy resins and curing agents, where epoxy resins are mainly configured with BPA, and curing agents are usually free or closed amine-like parts. Although hydro-hydro-type HDK® can be used in epoxy system, but also give the epoxy system better thickening, but it is not suitable for all epoxy-based system product performance requirements, because the use of hydro-hydro-type HDK® in epoxy may lead to instability of some systems, no obvious denaturation. For example, silane alcohol in HDK® and adsorbed water molecules act as polar groups, which may cause high reaction activity of epoxy erythropoietin groups, leading to instability of the system® Variable properties have a positive impact, but if the concentration of this hydrogen bond-forming substance is too large, it is easy to close the hydro-hydro-HDK® silica base group without sufficient tentacles, so the use of hydro-hydro-type HDK® may limit the choice of formulation raw materials.
Hydrophobic HDK® series ensures that epoxy adhesives have low viscosity when coated, high viscosity and excellent flow resistance during sit-in, and prevent parts precipitation during storage.
asked: WACKER HDK ® hydrophobic gas silicon has several brands, what are their characteristics? How exactly should I choose?
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VAC offers a range of hydrophobic and hydrophobic gas silicon products, and adhesive and sealant customers can choose according to the different requirements of the product in terms of thickening, anti-flow hanging, storage stability and processing performance.
example:
. HdK® H18 is highly surface hydrophobic and gives epoxy-based formulations excellent thickening, anti®-hanging performance and storage stability compared to the less hydrophobic HDK® product line.
HDK® H21 not only offers excellent processing efficiency and performance characteristics, but is also easy to disperse, while also achieving superior rheodration control.
HDK® H20RH is alkyl silane-modified and requires only a small amount of addition to improve the tentacle performance of amine-like parts. HDK-H20RH maintains stability in amine ® high pH compared to silicon dioxide treated with silica.
Finally, hydrophobic gas silicon provides efficient fluid control for epoxy-based systems, as well as the equivalent of anti-flow-hanging performance control, mechanical performance adjustment, and maintaining viscosity stability during storage, a series of excellent performance depends on the degree of dispersion of gas-silicon in the system. For different system viscosity, different dispersion devices should also be considered in order to achieve the best performance of the product.
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