Ultra-high-index glass microspheres and products made therefrom
AssigneeMinnesota Mining and Manufacturing Company
InventorsChi F. Tung, James A. Laird
Life of this patent
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Abstract
Glass microspheres having an index of refraction of 2.7 or higher are prepared by (1) forming the microspheres from compositions based principally on 65-85 weight-percent Bi.sub.2 O.sub.3 and 5-35 weight-percent TiO.sub.2, and (2) rapidly heating the microspheres after they have been initially formed to cause an internal structural rearrangement that raises their index. Such microspheres are useful to form retroreflective products having superior properties and a more simplified construction.
Claims14
Transparent glass microspheres having an index of refraction of 2.7 or higher comprising 65-85 weight-percent Bi.sub.2 O.sub.3 and 5-35 weight-percent TiO.sub.2, with any added ingredients totaling up to about one-fourth of the composition by weight;
- said microspheres having been heat-treated, as indicated by the absence from their temperature profile during differential thermal analysis of an exothermic peak in the temperature interval of about 500.degree. to 650.degree. C.
Transparent glass microspheres having an index of refraction of 2.7 or higher consisting essentially of 65-85 weight-percent Bi.sub.2 O.sub.3, 5-35 weight-percent TiO.sub.2, 0 to 15 weight-percent WO.sub.3 and 0 to 15 weight-percent Nb.sub.2 O.sub.3 ;
- any ingredients besides Bi.sub.2 O.sub.3 and TiO.sub.2 totaling no more than about one-fourth of the composition by weight;
- and the microspheres having been heat-treated, as indicated by the absence from their temperature profile during differential thermal analysis of an exothermic peak in the temperature interval of about 550.degree. to 650.degree. C.
Dependencies are inferred from the claim text.