DEGRADABLE GLASS SUITABLE FOR CONTAINERS

摘要

1420678 Coated glass CORNING GLASS WORKS 18 April 1973 [1 May 1972] 18740/73 Heading B2E [Also in Division C1] An article comprising a glass, which glass is self-degrading under predetermined conditions, is made by: shaping an article from a glass consisting essentially of, by weight, 10-30% Na 2 O and/or K 2 O, 65-90% SiO 2 , and 0-20% of one or more of: CaO ZnO, MgO, B 2 O 3 , ZrO 2 , Al 2 O 3 , SrO, PbO, BaO, Fe 2 O 3 , NiO, TiO 2 , MnO, CuO, CoO and FeO; subjecting the article to an environment containing at least 50% by weight H 2 O at at least 50‹C to hydrate the glass on at least a portion of the surface, the hydrated surface glass having 5-35% by weight H 2 O within its volume; and simultaneously or subsequently providing a weathering-resistant skin coating layer to protect the hydrated surface, the hydrated portion being subject to self-degradation upon exposure to the ambient atmosphere by penetration or removal of at least a portion of the skin coating layer. The skin layer may be a coating of silicon polymer, or of vinylidene chloride polymer or copolymer (applied as a 20% by weight solution in butyl acetate). The surface hydration may be carried out using a liquid or gas (e.g. steam), and preferably at at least one atmosphere for “-24 hours at 50-300‹C. The liquid, if used, may be a dilute aqueous solution either of neutral salts of Li, Na, or K; or of acid salts of Al, B, Ca, Mg or P; or of an acid. If the article is a container, the outside alone may be contacted with the hydration medium, or the inside may be protected against hydration. This protection may be by an initial treatment, at above the annealing temperature of the glass, with SO 3 , CuCl_ or fluorine vapour or with a molten salt of Li+ and/or Cu+, or by filling the container with a hydration-preventing liquid which is a concentrated aqueous solution of a Li+ or Cr+++ salt, an acid salt, or an acid.