Title of Invention

"A PROCESS FOR THE PRODUCTION OF SUPER-WHITE VITRIFIED PORCELAIN TILES HAVING IMPROVED CHARACTERISTICS"

Abstract

In the present invention, a process has been developed for the production of super white vitrified porcelain tiles having improved characteristics using clay, beneficiated feldspar and quartz, without or with lower quantum of zircon opacifier, at lower temperature of firing. Iron oxide (Fe2O3) and TiO2 content, contaminants in the raw materials, are kept to a minimum level as they lead to a colouration in the fired body. Beneficiated feldspar used in the present invention as flux is purified material, virtually free from Fe2O3and TiO2 and does not contain mica as detected by XRD study. Since, the porcelain body produced in the present invention is free from mica inclusion, the flexural strength and surface finish is improved significantly. The porcelain tile produced by the present invention possess higher flexural strength of 55 to 65 kg/cm2. Due to super white appearance of the presently developed porcelain body without zircon opacifier, amount of stain required to obtain the intended colour becomes less. Hence, it is possible to achieve cost savings on three counts, namely, elimination or reduction of costly zircon opacifier, consumption of less stains for clouration and lower thermal energy for the production of super white vitrified porcelain tiles having improved characteristics.

Full Text

The present invention relates to a process for the production of super white vitrified porcelain tiles having improved characteristics. The present invention particularly relates to an economical process for the production of super white vitrified porcelain tiles having improved characteristics such as higher flexural strength and brightness at comparatively lower firing temperature. The process of the present invention reduces the overall product cost, thereby enabling enhanced commercial potential for use of high strength super white vitrified porcelain tiles in the floors and walls of residential and industrial buildings. Porcelain tiles are the fastest growing segment in the ceramic tile industry today in the entire world. This sector has emerged from a growing need to develop a type of tile that combines aesthetic appeal and inherent strength of marble with the advantage of modern day, eco friendly living. The main features of these tiles are very low level of open porosity, are often coloured throughout the bulk as per desired shade and finally polished rather than glazed. The overall effect is to produce a synthetic version of natural rocks such as granite and marble. The enhanced commercial potential for use of high strength super white vitrified porcelain tiles in the floors and walls of residential and industrial buildings has caused recent expansion announcement by the tile industries. This is a clear indication that the tile manufacturers are moving towards the vitrified porcelain tile sector to meet the present growing demand. The super white vitrified porcelain tiles having improved characteristics produced by the economical process of the present invention shall be useful to meet the growing demand of building industries. In the present day known prior art methods, the common raw materials used are clay, quartz and fluxing minerals such as feldspar, nepheline syenite to produce porcelain tiles. Reference may be drawn to the work of Y.Kobayashi and E. Kato, Journal American Ceramic Society, 106,9,1998 wherein a typical porcelain body is produced from a mixture of 50 wt % clay, 25 wt% potash feldspar, 25 wt% quartz. In another reference, Y.lqbal and W.E.Lee, Journal American Ceramic Society,83,12,2001 used 55wt% clay,15wt% nepheline syenite and 30 wt% quartz to produce porcelain body. The present day method of production of porcelain tile body generally follows route of wet milling/grinding of the batch, spray drying, pressing, firing and polishing. However the strength and whiteness of such type of porcelain tile (flexural strength 50-55 kg/cm2, brightness: 31-33) are not as per the requirement of today's new generation porcelain tile as observed by K.Dana and S.K.Das, in their research findings on "CGCRI-Johnson tiles scholarship programme" CGCRI,India,January 2002. The poor whiteness of these conventional porcelain bodies is due to presence of FezOa and TiO2 contaminated with the raw materials. The improvement of the poor whiteness of conventional porcelain bodies has been reported. Reference may be drawn to the paper of K.Hudson, H.Winbow and J.Cowley, Ceram.Eng.Sci.Proc. 17,1,1996 wherein it has been reported that Zirconium Silicate (Zircon, ZrSiO4) is a versatile material to add to porcelain body as opacifier to impart whiteness. High refractive index, chemical inertness, thermal stability of zircon are the key properties, which increases the whiteness. In practice most of the porcelain tile manufacturers use zirconium silicate powder to impart whiteness to porcelain bodies. In a paper in Asian Ceramics, Dec. 1999, I. Bozdogan reported that if the tile body contains zircon opacifier and it requires to be coloured, then consumption of stain will be higher. Hence, drawback encountered is that using zircon, which is the most costly component of such tile body, the cost increases further as use of zircon reduces the strength intensity of coloured stains and consumption of stain increases. As reported, in the hitherto known prior art, the temperature of firing to obtain porcelain tile product is in the range of 1180 to 1200°C. In all the above present day methods, the main drawbacks are: (a) requirement of more thermal energy due to higher vitrification temperature. (b) poor whiteness. (c) higher product cost due to addition of costly zircon opacifier (d) consumption of more coloured stains in the presence of zircon , if the body is required to be coloured. (e) Tailor made properties are not achievable. From the above reports of hitherto known prior art, it is clear that there is a definite need for reduction in the requirement of thermal energy by bringing about a reduction in the vitrification temperature. Further, as zircon is the most costly component of such tile body and it reduces the strength intensity of coloured stains, it is of utmost necessity to reduce or wholly eliminate the use of zircon, to bring about economy in the manufacturing process. The main object of the present invention is to provide a process for the production of super white vitrified porcelain tiles having improved characteristics, which obviates the drawbacks described above. Another object of the present invention is to provide a process for the production of super white vitrified porcelain tiles having improved characteristics at lower vitrification temperature to bring about economy in the manufacturing process. Yet another object of the present invention is to provide a process for the production of super white vitrified porcelain tiles having improved characteristics without using or reducing the quantum of zircon opacifier, thus requiring less amount of stain for making coloured tiles. Still another object of the present invention is to provide a process for the production of high strength super white vitrified porcelain tiles at lower cost. Still yet another object of the present invention is to provide a process for the production of super white vitrified porcelain tiles having tailor-made properties. In the present invention, a process has been developed for the production of super white vitrified porcelain tiles having improved characteristics using clay, beneficiated feldspar and quartz, without or with lower quantum of zircon opacifier, at lower temperature of firing. Iron oxide (Fe2O3) and TiO2 content, contaminants in the raw materials, are kept to a minimum level as they lead to a colouration in the fired body. Beneficiated feldspar used in the present invention as flux is purified material, virtually free from Fe2O3 and TiO2 and does not contain mica as detected by XRD study. Mica inclusion in the porcelain body reduces the fired strength. Mica being weaker than the body, they are fragmented and pulled out during polishing resulting in a collection of dents and potholes across the piece. Since, the porcelain body produced in the present invention is free from mica inclusion, the flexural strength and surface finish is improved significantly. Due to super white appearance of the presently developed porcelain body without zircon opacifier, amount of stain required to obtain the intended colour becomes less. Hence, it is possible to achieve cost savings on three counts, namely, elimination or reduction of costly zircon opacifier, consumption of less stains for colouration and lower thermal energy for the production of super white vitrified porcelain tiles having improved characteristics. Accordingly, the present invention provides a process for the production of super white vitrified porcelain tiles having improved characteristics, which comprises: characterized in that i) wet milling 52 to 60 wt% clay, 25 to 30 wt% beneficiated feldspar having composition as herein described , 10 to 18 wt% quartz and optionally adding zircon opacifier 0 to 8 wt% to obtain a slip, ii) sieving the slip through 200 mesh BS sieve and drying the resultant slip to reduce the moisture content below 0.5%, iii) powdering the dried slip and mixing the powder obtained with water to prepare a mouldable dough, iv) shaping the dough by hydraulic compaction at a pressure in the range of 350 to 400 kg/cm2, v) oven drying the shaped products so obtained at a temperature of the order of110 ° C for a period of 24 to 30 hours, vi) firing at a temperature in the range of 1160 to 1180°C for a period in the range of 60 to 70 minutes of the shaped and dried product to obtain vitrified porcelain tiles. In an embodiment of the present invention, the clay used is such as white burning kaolinite clay, ball clay. In another embodiment of the present invention, the chemical constituents of the beneficiated feldspar is in the range of SiO2:70 to 72 wt%, AI2O3:17 to18 wt%, Na2O : 9.5 to 10.0 wt%, K2O : 0.3 to 0.4 wt %, TiO2: max 0.06 wt%, Fe2O3: max 0.05 wt%. In yet another embodiment of the present invention, the chemical constituents of the quartz is in the range of SiO2 98.5 to 99 wt%, AI2O3 : 0.3 to 0.4 wt%, TiO2 0.01 to 0.02 wt%, Fe2O3 0.06 to 0.07 wt%, (Na2O+K2O): 0.2 to 0.3 wt%. In still another embodiment of the present invention, wet milling of clay, beneficiated feldspar, and quartz to obtain a slip is carried out for a time period in the range of 18 to 20 hours to obtain fineness retaining on 200 mesh BS sieve below 2.5 wt%. In still yet another embodiment of the present invention, the mouldable dough is prepared by mixing the dried and powdered slip with 5 to 6 wt% water to enable shaping of the product by hydraulic compaction. In a further embodiment of the present invention, the firing of the shaped and dried product to obtain vitrified porcelain is effected at a temperature in the range of 1160 to 1180°C, for a period in the range of 60 to 70 minutes. In a still further embodiment of the present invention, the flexural strength of the super white vitrified porcelain tiles is of the order of 55 to 65 kg/cm2 In yet another embodiment of the present invention, the brightness value of the super white vitrified porcelain tiles obtained without using zircon opacifier is of the order of 39 to 44. In still another embodiment of the present invention, to enable higher brightness value of the order of 44 to 48, zircon opacifier is optionally used in the range of 0 to 8 wt%. The novelty of the process of the present invention for the production of super white vitrified porcelain tiles having improved characteristics resides in achieving: (i) Lower vitrification temperature of the order of 1160 to 1180 ° C, as compared to 1180 to 1200 °C of presently available similar tiles produced, (ii) High flexural strength of the order of 55 to 65 kg/cm2 as compared to the flexural strength of 50 to 55 kg/cm2 of presently available similar tiles, (iii) Super white brightness value of the order of 39 to 44, without using costly zircon opacifier, as compared to the brightness value of the order of 31 to 33 of presently available similar tiles, (iv) Higher brightness value of the order of 44 to 48 may be obtained by optionally using zircon opacifier in the range of 0 to 8 wt%. The non-obvious inventive step which brings about the novel features in the process of the present invention for the production of super white vitrified porcelain tiles having improved characteristics lies in using beneficiated feldspar as a flux in the tile composition, which is virtually free from Fe2O3 ,TiO2 and mica and gives high strength, super white appearance even without using zircon opacifier and allows vitrification at lower temperature. The detailed process steps of the present invention are: i) Wet milling of 52 to 60 wt% clay, 25 to 30 wt% beneficiated feldspar and 10 to 18 wt% quartz for a period of 18 to 20 hours to obtain a slip, ii) Sieving the slip through 200 mesh BS sieve, iii) Drying of slip to reduce moisture content below 0.5%. iv) Powdering of dried batch, v) Mixing the dried batch with 5 to 6 wt% of water to prepare a mouldable dough, vi) Shaping the dough by hydraulic compaction at a pressure in the range of 350 to 400 kg/cm2. vii) Oven drying of the shaped products at around 110 °C for a period of 24 to 30 hours, viii) Firing the shaped and dried products at a temperature in the range of 1160 to 1180°C, for a period in the range of 60 to 70 minutes to obtain vitrified porcelain. The invention is described with the help of the following examples for understanding the process in actual practice. However, the examples, which are given here by way of illustration, should not be construed to limit the scope of the present invention. Example -1 600 gms clay,300 gms beneficiated feldspar, 100gms of quartz were to wet milled in a pot mill for a period of 18 hours. The slip thus produced passed through 200 mesh BS sieve and dried to reduce moisture content less than 0.5%. The dried batch was then powdered and uniformly mixed with 50 cc water. Samples of 50x50x8 mm size square tiles were prepared from the ready powder by hydraulic compaction at 350 kg/ cm2. The shaped products were oven dried at 110 °C for a period of 24 hours and finally fired at 1160 °C for a period of 60 mins. The fired tile samples had the following properties. Percent water absorption: 1.40; Flexural strength:55 kg/ cm2 Brightness: 40.2. Example -2 600 gms clay,300 gms beneficiated feldspar, 100gms of quartz are wet milled in a pot mill for a period of 18 hours. The slip thus produced passed through 200 mesh BS sieve and dried to reduce moisture content less than 0.5%. The dried batch was then powdered and uniformly mixed with 60 cc water. Samples of 50x50x8 mm size square tiles were prepared from the ready powder by hydraulic compaction at 380 kg/ cm2. The shaped products were oven dried at 110 °C for a period of 24 hours and finally fired at 1180 °C for a period of 70 mins. The fired tile samples had the following properties. Percent water absorption: 0.16; Flexural strength: 58 kg/ cm2 Brightness: 39.34. Example -3 580 gms clay,300 gms beneficiated feldspar, 120gms of quartz wet milled in a pot mill for a period of 20 hours. The slip thus produced passed through 200 mesh BS sieve and dried to reduce moisture content less than 0.5%. The dried batch was then powdered and uniformly mixed with 60 cc water. Samples of 50x50x8 mm size square tiles were prepared from the ready powder by hydraulic compaction at 400 kg/ cm2. The shaped products were oven dried at 110 °C for a period of 30 hours and finally fired at 1160 °C for a period of 60 mins. The fired tile samples had the following properties. Percent water absorption: 1.09; Flexural strength: 65kg/ cm2 Brightnesses.88. Example - 4 520 gms clay,250 gms beneficiated feldspar, 180gms of quartz and 50 gms zircon powder are wet milled in a pot mill for a period of 20 hours. The slip thus produced passed through 200 mesh BS sieve and dried to reduce moisture content less than 0.5%. The dried batch was then powdered and uniformly mixed with 55 cc water. Samples of 50x50x8 mm size square tiles were prepared from the ready powder by hydraulic compaction at 400 kg/ cm2. The shaped products were oven dried at 110 °C for a period of 30 hours and finally fired at 1180 °C for a period of 60 mins. The fired tile samples had the following properties. Percent water absorption: 0.57; Flexural strength: 57kg/ cm2 Brightness:44.12. Example -5 520 gms clay,300 gms beneficiated feldspar, 100gms of quartz and 80 gms zircon powder are wet milled in a pot mill for a period of 20 hours. The slip thus produced passed through 200 mesh BS sieve and dried to reduce moisture content less than 0.5%. The dried batch was then powdered and uniformly mixed with 60 cc water. Samples of 50x50x8 mm size square tiles were prepared from the ready powder by hydraulic compaction at 400 kg/ cm2. The shaped products were oven dried at 110 °C for a period of 30 hours and finally fired at 1180 °C for a period of 70 mins. The fired tile samples had the following properties. Percent water absorption: 0.11; Flexural strength: 61 kg/cm2 Brightness: 48.04. It may be observed from the properties obtained in the above examples that the process of the present invention without zircon opacifier, as in examples 1,2 &3, resulted in tiles with brightness level in the range of 39 to 43.88, which is superior to the brightness level of 31 to 33 of conventional porcelain tiles. From the examples 4 and 5, it may be further observed that the brightness of the tiles as obtained by the process of the present invention is further improved to the value 44 to 48 with the addition of 5 to 8 wt% zircon opacifier. The main advantages of the present invention are: 1) The present process requires lower firing temperature for vitrification, thereby saves energy. 2) The present process produces product of improved whiteness without zircon opacifier, thereby requires less stain for making coloured tiles. 3) The present process is economical as it reduces the overall product cost. 4) The present process achieves the production of super white vitrified porcelain tiles having tailor-made properties. We claim: 1. A process for the production of super white vitrified porcelain tiles having improved characteristics, which comprises: characterized in that i) wet milling 52 to 60 wt% clay, 25 to 30 wt% beneficiated feldspar having composition as herein described , 10 to 18 wt% quartz and optionally adding zircon opacifier 0 to 8 wt% to obtain a slip, ii) sieving the slip through 200 mesh BS sieve and drying the resultant slip to reduce the moisture content below 0.5%, iii) powdering the dried slip and mixing the powder obtained with water to prepare a mouldable dough, iv) shaping the dough by hydraulic compaction at a pressure in the range of 350 to 400 kg/cm2, v) oven drying the shaped products so obtained at a temperature of the order of 110 ° C for a period of 24 to 30 hours, vi) firing at a temperature in the range of 1160 to 1180°C for a period in the range of 60 to 70 minutes of the shaped and dried product to obtain vitrified porcelain tiles. 2. A process as claimed in claim 1, wherein the clay used is white burning kaolinite clay, ball clay. 3. A process as claimed in claims 1 - 2, wherein the chemical constituents of the beneficiated feldspar is in the range of SiO2:70 to 72 wt%, Al2O3:17 to18 wt%, Na20 : 9.5 to 10.0 wt%, K2O : 0.3 to 0.4 wt %, TiO2: max 0.06 wt%, Fe2O3 : max 0.05 wt%. 4. A process as claimed in claims 1 - 3, wherein the chemical constituents of the quartz is in the range of Si02 98.5 to 99 wt%, Al2O3: 0.3 to 0.4 wt%, Ti02 0.01 to 0.02 wt%, Fe2O3 0.06 to 0.07 wt%, (Na2O+K2O): 0.2 to 0.3 wt%. 5. A process as claimed in claims 1 - 4, wherein the wet milling of clay, beneficiated feldspar, and quartz to obtain a slip is carried out for a time period in the range of 18 to 20 hours to obtain fineness retaining on 200 mesh BS sieve below 2.5 wt%. 6. A process for the production of super white vitrified porcelain tiles having improved characteristics substantially as herein described with reference to the examples.

Documents:

67-DEL-2003-Abstract-(03-03-2009).pdf

67-del-2003-abstract.pdf

67-DEL-2003-Claims-(03-03-2009).pdf

67-DEL-2003-Claims-(21-04-2009).pdf

67-del-2003-claims.pdf

67-DEL-2003-Correspondence-Others-(03-03-2009).pdf

67-DEL-2003-Correspondence-Others-(21-04-2009).pdf

67-del-2003-correspondence-others.pdf

67-del-2003-correspondence-po.pdf

67-DEL-2003-Description (Complete)-(03-03-2009).pdf

67-DEL-2003-Description (Complete)-(21-04-2009).pdf

67-del-2003-description (complete).pdf

67-DEL-2003-Form-1-(03-03-2009).pdf

67-del-2003-form-1.pdf

67-del-2003-form-13-(06-05-2009).pdf

67-del-2003-form-18.pdf

67-del-2003-form-2.pdf

67-DEL-2003-Form-3-(03-03-2009).pdf