Title of Invention

"A PROCESS OF MAKING A LEAD FREE FRIT USEFUL FOR APPLICATION ON POTTERY BODY"

Abstract

The invention provides a process of making a Lead free frit for application on pottery body, by mixing boron containing materials 35 to 60%, potash feldspar 0 to 12%, sodalime silica glass cullet 30 to 60%, zinc oxide 0 to 8%, potassium nitrate 2 to 8%. Steps of the present invention include incorporation of high purity KNO3, ZnO and B2O3 in the novel composition for making lead free frit and glaze which reduces blackening of the glaze and improves the gloss, durability and reduce maturing temperature of the glaze respectively. It also eliminates poisoning due to lead.

Full Text

The present invention relates to a process of making a Lead free frit for application on pottery body. Lead free frit and glaze are applied on blue pottery body for chemical durability, aesthetic beauty and. hygiene. The present day methods of producing low melting frits and glazes fits include various constituents and encompass various processes for which reference may be made to US Patents 2642633 assigned to R.H. Dalton "Soft glass and composite article" June 23, 1953; U.S., Patent 3258350 assigned to F. W. Martin, "Fusion seals and their production", June 28, 1966; and U.S. Patent 3404027 assigned to R. Kosiorek, "Satin finish vitrifiable enamels", Oct. 1, 1968. Wherein lead borosilicate frits have been used for the preparation of glazes and the draw backs are leaching of lead from the above glazes and hence can not be used for usage in contact with food Reference may also be made to US Patent 3873330 assigned to T. A. Sherk and R. R. Tummala, "Bi2O3 and AI2O3 containing PbO - B2O3 low temperature sealing glass", March 25, 1975 which deals with a lead zinc borate system containing bismuth oxide. This system also suffers from the draw back that both lead oxide and bismuth oxide are toxic and hence can not be used for glazing articles which come into contact with food. Reference may be made to "leadless glazes for dinnerware" J. E. Marquis and R. A. Eppler, A.m. Cer. Soc. Bull 53(5) 443-5, 449 (1974) and 53 (6) 472 (1974) which are lead, free alkali borosilicate glasses which are medium temperature melting, less durable in addition to exhibiting thermal expansion and as such not suitable to be applied on the blue pottery body. Reference may be to US Patent 3113878 assigned to F. W. Martin "Thermally devitrifiable sealing glasses and composite articles" which deals with zinc t i borosilicates which are lead free, with moderate durability, but these do not have the required low melting characteristics coupled with moderate expansion and high durability and thus can not be used as such. Reference may be made to the existing practice as adopted by the rural artisans of blue pottery in Jaipur utilizing lead borosilicate glazes which are brilliant but are easily blackened in reducing atmosphere and release toxic lead when in contact with food articles. Reference is made to French Patent 2732960 dated 18 Oct. 1996 assigned to Laborde Pascale, Dickenson James Edward (Eurokera, France) "Lead free enameling compositions and low expansion glass ceramic products decorated with the enamel/enamels obtained; German Patent No. DE 19,512,487 dated, 7 Nov., 1996 assigned to Siebers Friedrich et al. "Cadmium and lead free glass compositions for glazing, enameling and decorating glass products and their use"; Japanese patent No.08259258 (96259258) dated, 8 Oct., 1996 assigned to Sekine Hideyuki et al., "Lead free safely glass compositions useful for fluxes for decorating firing" the patents deals with system containing SiO2 ,B203, AI2O3, Li2O, Na2O, K2O, CaO, MgO, BaO, ZnO, SrO, TiO2) ZrO2, Fluoride etc. wherein a softening point of 750°C was reported which is although suitable for required for the blue pottery body but it contained toxic elements like BaO, SrO, fluoride. The drawbacks of the hitherto known process are : 1) Toxicity due to presence of lead bearing material. 2) High maturing temperature. 3) Non Flexibility in choicing of firing temperature. 4) Blackening of articles during firing & hence lowers the aesthetic value of the body. In the prior art processes lead free frit has been prepared which results in higher maturing temperature. Moreover, in order to maintain the glossyness and impart anti-blackening effect on the glaze, which normally comes from lead, use has been made of other oxides such' as Bi, Zn, Sr, Ba, Zr, Ca, Mg. The main object of the present invention is to provide a process of a lead free frit and glaze for application on pottery body having blue and other colour decorations which obviates the draw backs as detailed above. Another object of the present invention is to provide lead free glaze composition which matures at a relatively low temperature of 730°C and has a wide firing range of about 100°C compared to the conventional lead glaze, which eliminates blackening of articles during firing. Accordingly the present invention provides a process of making a lead free frit useful for application on pottery body which comprises mixing boron containing materials such as herein described 35 to 60%, potash feldspar 0 to 12%, sodalime silica glass cullet 30 to 60%, zinc oxide 0 to 8% and potassium nitrate 2 to 8%, getting a glass batch mix from obtained mixture, melting the glass batch mix at a temperature in the range of 1000 to 1100°C, for a period in the range of 60 to 90 minutes to obtain a molten glass, pouring the molten glass into water for cooling, crushing and grinding the cooled materials by conventional method to get the desired lead free frit. In an embodiment of the present invention boron containing materials such as borax and boric acid may be used. Yet in another embodiment of the present invention sodalime silica glass cullet of composition SiO2 65 to 75%, AI2O3 1.0 to 2.0%, MgO 1.5 to 2.0%, and Na2O + K2O 13 to 18% and CaO 5 to 12% may be used. In still another embodiment of the present invention zinc oxide of 99.5% purity may be used. The detail of the process is given below:- a) Boron containing materials 35 to 60%, potash 0 to 12%, sodalime silica glass cullet 30 to 60%, zinc oxide 0 to 8%, potassium nitrate 2 to 8% are mixed. b) The mixture prepared in step 'a' is melted at a temperature in the range of 1000°C to 1100°C for a period of 60 to 90 minutes. c). The molten glass prepared in step 'b' is poured in water trough. d). The material so produced in step 'c' is crushed and ground by conventional processes. Various ceramic products apart from' blue pottery require a low melting lead free glaze which can be applied to a conventional substrate and fused into a ceramic coating at temperatures from 550° to 800°C. Low melting, moderately durable glass frit formulations find use in such applications as vitrifiable glass decorating colours, glass to metal seals, and other vitreous coatings. The conventional frit and glaze formulations which are simultaneously low melting, moderately durable and moderate in coefficient of thermal expansion are the lead borosilicates and lead zinc borosilicates. In these systems, however,large quantities of highly toxic lead oxide should be added which must be carefully handled to avoid ingestion or inhalation. Hence, the invention avoids lead poisoning by eliminating lead and other toxic elements from the glaze. Secondly the usage of lead free glazes eliminates the blackening of glazed articles, improving thus, the quality and productivity. Further the developed leadless glazes possessed a wide firing range of 700° to 850°C, reasonably durable and moderate in the coefficient of thermal expansion (8.9 x 10-6 to 10.0 x 10-6/ °C) which enhanced the body-glaze adhesion. The novelty of the present invention, thus, is the dimination of lead which is a poisonous substance, from the composition of the prepared frit without sacrificing advantages of lead such as anti-blackening effect of glaze, imparting glossy ness to the glaze and lowering the maturing temperature of glaze. The inventive steps include incorporation of high purity KNO3 , ZnO and B2O3 in the novel composition used in the process of the present invention for making lead free frit and glaze which reduces blackening of the glaze and improves the gloss, durability and reduce maturing temperature of the glaze respectively. .It also eliminates poisoning due to lead. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. Example-1 Borox 40 gm, sodalime silica glass cullet 42 gm, boric acid 10 gm, potassium nitrate 3 gm, potash feldspar 5 gm are mixed in a pot mill. The mixed powder is melted at a temperature of 1050 °C for 90 minutes. The molten glass so produced is poured in water trough. The material so produced is crushed and ground by conventional process. Example- 2 Borax 35 gm, soda-lime-silica glass cullet 42 gm, boric acid 10 gm, zinc oxide 3 gms, potassium nitrate 3 gm, and potash feldspar 7 gm are mixed in a pot mill. The mixed powder is melted at a temperature of 1050°C for 90 minutes. The molten glass so produced is poured in water trough. The material so produced is crushed and ground by conventional process. Example - 3 Borax 48 gm, soda-lime-silica glass cullet 35 gm, boric acid 5 gm, boric acid 5 gm, zinc oxide 5 gm, potassium nitrate 2 gm, and potash feldspar 5 gm are mixed in a pot mill. The mixed powder is melted at a temperature of 1100°C for 90 minutes. The molten glass so produced is poured in water trough. The material so produced is crushed and ground by conventional process. The main advantages of the present invention are : 1) Free from lead bearing material and hence the toxicity is avoided. 2) A lower firing temperature. 3) Flexibility firing span of about 100oC. 4) Imparts antiblackening effect & hence improves the aesthetic value of glazing article. We Claim: 1. A process of making a lead free frit useful for application on pottery body which comprises mixing boron containing materials such as herein described 35 to 60%, potash feldspar 0 to 12%, sodalime silica glass cullet 30 to 60%, zinc oxide 0 to 8% and potassium nitrate 2 to 8% , getting a glass batch mix from obtained mixture, melting the glass batch mix at a temperature in the range of 1000 to 1100°C, for a period in the range of 60 to 90 minutes to obtain a molten glass, pouring the molten glass into water for cooling, crushing and grinding the cooled materials by conventional method to get the desired lead free frit. 2. A process as claimed in claim 1 wherein boron containing materials used is selected from borax, boric acid. 3. A process as claimed in claims 1 & 2 wherein sodalime silica glass cullet used is comprising SiO2 65 to 75% AI2O3 1.0 to 2.0%, MgO 1.5 to 2.0%, and Na2O + K2O 13 to 18% and CaO 5 to 12%. 4. A process as claimed in claims 1 - 3 wherein potassium nitrate used is of 99.5% purity. 5. A process as claimed in claims 1 - 4 wherein zinc oxide used is of 99.5% purity. 6. A process of making a lead free frit useful for application on pottery body substantially as herein described with reference to the examples.

Documents:

189-del-2000-abstract.pdf

189-del-2000-claims.pdf

189-del-2000-correspondence-others.pdf

189-del-2000-correspondence-po.pdf

189-del-2000-description (complete).pdf

189-del-2000-form-1.pdf

189-del-2000-form-19.pdf

189-del-2000-form-2.pdf

189-del-2000-form-3.pdf