The most common and widely available microsphere materials are polymer, ceramic, and glass. However, each one of these large categories of materials can be further divided into much narrower categories which vary dramatically in their properties. For example, polymer microspheres may be manufactured out of polyethylene, polystyrene, polypropylene, poly(methyl methacrylate). Each of these polymers varies in their melt temperature, resistance to solvents, and ability for the surface to be modified with functional groups.
Category of hollow glass microspheres can also be further broken down. For example, Sodalime microspheres are most available and economical, Borosilicate glass is preferred in higher temperature applications, while Barium Titanate glass formulation offers high density and high index of refraction for retroreflective and optical applications. Most hollow glass microspheres are made out of proprietary Borosilicate-Sodalime glass blend.
Most common ceramic materials used for hollow galss microspheres are silica and zirconia, which are often used as fillers or grinding media.
Made of these materials are available in solid and hollow forms, clear or colored, and with a variety of coatings that make them suitable for particular applications. The materials from which hollow galss microspheres are made vary widely in density, operating temperature, crush strength and solvent resistance. Hollow galss microspheres possess different physical and optical properties, which may present advantages or limitations for different applications, based on their material composition.
The most obvious benefit of hollow glass microspheres is their potential to reduce part weight, which is a function of density. Compared to traditional mineral-based additives such as calcium carbonate, gypsum, mica, silica and talc, hollow glass microspheres have much lower
densities. For example, at a density of 0.6 g/ml, hollow glass microspheres can displace the same volume as talc at one-quarter of the weight. Densities and crush ratings, however, vary dramatically across product lines.
When hollow galss microspheres are being used a a bond line spacer to be mixed into epoxy or another adhesive, manufacturer might need the spheres to stay in suspension for a significant period of time. Density of the bondline spacer particles is important to maximize the residence time in the dispensing vessel to increase the amount of time the mix can be used after the particles have been incorporated. To achieve this dispersion the density of hollow galss microspheres needs to match to the density of the epoxy as closely as possible. Ability to pre-mix offers significant cost savings and efficiency improvements for the manufacturer, as compared to having to disperse particles at the time of use.
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