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Abstract

In a method of strengthening chemically a glass container comprising applying an aqueous solution of potassium salts to a soda-containing glass container to form a potassium salt adhered layer, holding at an ion exchange treatment temperature for a period of time sufficient, then cooling to room temperature and removing the residual potassium salts, the feature consists in using, as the aqueous solution of potassium salts, a concentrated aqueous solution containing a small amount of surfactant and a high concentration of mixed potassium salts consisting of potassium nitrate having a relatively low melting point and at least one potassium salt having a relatively high melting point selected from the group consisting of potassium chloride and potassium sulfate in such a proportion that 10 to 80% by weight of the potassium salts be present in solid phase, when heated at the ion exchange treatment temperature, to prevent the fused potassium salts from flowing off from the surfaces of the glass container, applying the concentrated aqueous solution to the outer surface and inner surface of the glass container at a temperature of lower than that of the concentrated aqueous solution, causing the potassium salts to deposit on the outer surface and inner surface of the glass container by virtue of the temperature difference, then drying and holding the glass container having the mixed potassium salt adhered layer at an elevated temperature below the strain point of the glass but as near the strain point as possible for a period of time sufficient to form a compressive stress layer on the outer surface and inner surface of the glass container.

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First Claim