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Hollow Glass Microspheres Stronger Spheres Tackle Injection Molding

2019-03-15 16:17:41 1933

Looking for a way to make lighter parts without giving up properties? New hollow glass microspheres are stronger than ever—enough to withstand the rigors of injection molding.

Hollow glass microspheres have been used as low-density fillers for various kinds of polymeric compounds since the mid-1960s. For the first 20 years after their introduction, hollow glass microspheres weren’t strong enough to survive the high shear forces and high pressures involved in plastics compounding and injection molding.

In the late 1980s, introduced a glass microsphere with an isostatic crush strength of 10,000 psi, more than twice as strong as any previously available. Its enhanced survivability meant that hollow glass microspheres could be used as fillers in many high-shear processes.

Latest hollow glass microsphere, Performance Additives grade, has the highest compressive strength in the world for such a product. It also has the highest strength-to-density ratio of any glass or other microsphere in the marketplace. Made from soda/lime borosilicate, it can withstand injection molding pressures up to around 30,000 psi.

The new spheres, when compared with hollow glass microspheres grade, are about half the size—16 microns instead of 30 microns diam.—and exhibit a 50% greater isostatic crush strength—28,000 psi vs. 18,000 psi—at the same density of 0.6 g/cc. Although the microspheres have found some injection molding applications, the higher strength and smaller size of the newest grade provide polymer composites with much better physical and mechanical properties while at the same time offering better crush survivability when processed by extrusion or injection molding or other high-shear processes.

Relative to earlier hollow glass microspheres, the improved mechanical properties imparted include better impact strength and elongation, prevention of scratch or stress whitening, tighter tolerances for small parts, and improved surface finish on the end product due to better packing. Greater crush strength means there is much less breakage of the hollow glass microspheres during extrusion or injection molding.

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