Application of Garfinkel, Patent Appeal No. 8421.
| Decision Date | 18 February 1971 |
| Docket Number | Patent Appeal No. 8421. |
| Citation | 437 F.2d 1000,168 USPQ 659 |
| Parties | Application of Harmon M. GARFINKEL. |
| Court | U.S. Court of Customs and Patent Appeals (CCPA) |
Clinton S. Janes, Jr., Corning, N. Y., attorney of record, for appellant.
S. Wm. Cochran, Washington, D. C., for the Commissioner of Patents; Joseph F. Nakamura, Washington, D. C., of counsel.
Before RICH, ALMOND, BALDWIN and LANE, Associate Judges, and DAVIS, Judge, United States Court of Claims, sitting by designation.
This is an apeal from the decision of the Patent Office Board of Appeals affirming the rejection of claims 18-23 of appellant's application entitled "Glass Article and Method of Production."1 No claims have been allowed.
The invention relates to the strengthening of lithium aluminosilicate (Li2 O-Al2 O3-SiO2) and lithium zirconosilicate (Li2-ZrO2-SiO2) glasses by contacting the glass at an elevated temperature, but below the strain point of the glass, with a source of larger diameter, monovalent metal ions for a period of time sufficient to cause the replacement of the original lithium ions within the glass surface layer with the monovalent metal ions on an ion-for-ion basis. This treatment may be by immersion of the glass in a bath of a molten salt of a monovalent metal selected from the group consisting of sodium, potassium, rubidium, cesium, copper, silver, or thallium. The stuffing of the larger metal ions into the surface of the glass causes compressive stresses to be developed in situ, since the glass volume cannot increase inasmuch as the exchange temperature is too low to allow viscous flow and molecular rearrangement therein to release the stresses built up.
Acknowledging that this type of treatment has been known for alkali metal silicate glasses, and in particular sodalime-silica glass (Na2 O-CaO-SiO2), appellant states that the crux of his invention is the discovery that, contrary to prior experience with alkali silicate glasses, lithium silicate glasses having from 10-40% Al2 O3 or ZrO2 exhibit exceptionally large increases in mechanical strength which are retained reasonably intact even after substantial surface abrasion.
Illustrative are claims 18 and 21:
Claims 19 and 22 depend from claims 18 and 21, respectively, and limit the larger monovalent metal ions to sodium ions. Claims 20 and 23 also depend from claims 18 and 21, respectively, and limit the metal ions to potassium ions.
The references relied upon are:
Hood et al. (Hood) 2,779,136 January 29, 1957
Weber 3,218,220 November 16, 1965
Kurz (British) 855,820 May 25, 1960
Kistler, "Stresses in Glass Produced by Non-Uniform Exchange of
Monovalent Ions," Journal of the American Ceramic Society, Vol. 45
No. 2, February 1962, pages 59-68
Hood discloses a method of strengthening glass wherein lithium ions from an external source are exchanged with sodium and/or potassium ions present within the surface of the glass. Glasses containing 1-2% Li2 O, 7.5-25% Al2 O3, and SiO2 may be used. It is disclosed that high abraded tensile strength is obtained; however, this is due to a mechanism unrelated to the claimed subject matter.
Weber discloses the chemical strengthening of sodium silicate glass articles through the large-ion-for-small-ion type exchange at an elevated temperature below the strain point of the glass.
Kruz discloses a process different from that claimed here for improving the chemical durability of alkali silicate glasses which may contain the oxides of metals, including aluminum and zirconium.
Kistler discloses a chemical strengthening process similar to that of Weber in that compressive stresses are induced into the surface of the glass by exchanging larger ions for the smaller ions in the glass. Kistler states that it would be expected that "exposing a lithium glass to sodium ions, etc., would produce a compressive stress." The glasses used by Kistler are disclosed by him from 1-5.12% Al2 O3.
The examiner rejected claims 18-23 under 35 U.S.C. § 103 as being unpatentable over Kistler or Weber, each considered alone or with Hood and Kruz. The board considered Weber as generally reinforcing the disclosure of Kistler. Therefore, treating Kistler as the principal reference, the board affirmed the examiner's rejection, stating:
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