Title of Invention

"A PROCESS FOR THE MANUFACTURE OF COLOURED ENGOBE COATING"

Abstract This invention describes a novel engobe coating composition and a process for the manufacture of coloured engobes as coatings and coated terracotta articles and ceramic tiles. The present day engobes made from platelet shaped transparent substrates like mica, talc or glass coated with metal oxides or metal hydroxides along with/without alkaline earth metal compound and some with aluminium oxide for use as pigments in cosmetics for use at ambient temperature or as pigmenting glazes and enamels for very low to medium temperature applications are not suitable for terracotta articles, ceramic tiles and noveltywares for medium and high temperature applications. The compositions are also based on some specific raw materials available in a specific region or a country and thus, suffers from limited use. The compositions of engobes of the present invention possesses yellow and other colour decorations and consists of naturally occurring common clays as the major ingredient and talc powder, titanium dioxide and deflocculants as minor ones with the optional presence of dolomite and additional transitional metal compounds as colourants for universal applications on terracotta articles and ceramic tiles. These engobes form an impervious vitreous coating on to terracotta wares and ceramic tiles fulfilling the requirements such as surface smoothness, good adherence to the body, good frost resistance, colour stability with a matt finish, chemical durability, resistance to weathering, abrasion. These engobes also avoid the use of glaze as second coat over the engobe coat and thus, make the production process more economical.
Full Text The present invention relates to a synergistic engobe coating composition and a process for the manufacture of coloured engobe coatings .
The main use of coloured engobes is as coatings applied over unfired or biscuited clay products such as terracotta articles, ceramic tiles, novelty wares in order to change the surface colour, smoothness as well as improvement in the appearance. It also serves as a protective layer to the products for water absorption and offers resistance to scratch, acids and alkalies.
The word engobe has a wide meaning and is often used as a synonym for a slip or coloured slurry of mineral powders. In its earliest form an engobe was a coating of a plastic red firing clay whose preparation by repeated dispersions in a dilute alkaline suspension and decantation yielded a thin slip separated from all coarse particles. This suspension is applied to green or biscuit fired ceramic ware and fired normally to hide the colour of underlying body. Engobe in white colour is also applied between the ceramic biscuit and the glaze. Its role is to mask on one hand the undesired biscuit colouration and on the other hand reduce glaze defects such stains, spots and pitting, make the tile water proof, thus preventing water from rising to the surface after laying, as well as limit the quantity of glaze necessary to cover the surface. The engobe of this type must have maximum whiteness and high opacity, but of controlled fusibility and thus, not suitable for making a fully vitreous coating on the wares in order to make them free from stains and hygienic during use. As glaze is applied over the engobe layer, such properties are not needed to be developed on the intermediate engobe layer. The engobe of former type which is developed conventionally from particular plastic red firing clay although develops and impervious coating but these compositions are specific to a particular region or a country.

The present day methods for the preparation of engobes are from coloured pigments as glass enamel coatings and also based on some specific common clays and minerals available at certain places and applied over certain specific products like bricks and roofing tiles. Reference for which may be made to US Patent 5106419 assigned to Hechler ; Wolfgang ; Osterried Karl; Weigand and Manfred for "Glass-Stable Colored Pigments", April 21,1992 wherein inventors claimed for colored pigments having an improved stability in decorative colours, engobes, glazes and enamels based on platelet-type substrates coated with metal oxides, in which the coating is free from alkaline earth metal oxides and contains a colored metal oxide or metal hydroxide and at least 10 wt.% of aluminium oxide, are outstandingly suitable for pigmenting glazes and enamels.
Reference may also be made to US Patent 4435220 assigned to Watanabe ; Takaji; Naguchi and Tamio for "Transparent Colored Pigments", March 6,1984; based on platelet-shaped, transparent substrates, such as mica, talc or glass, are coated with colored metal oxides or metal hydroxides, where in the metal oxide or hydroxide layer contains 0.1 - 5% by weight of an alkaline earth metal compound. The pigments have improved dispersibility, gloss, color power and stability to heat and weathering and also filling and adhesion properties. The pigments can be used for all the customary purposes, especially in cosmetics.
Reference may also be made to US Patent 4867793 assigned to Franz Klaus D.; Ambrosius ; Kalus ; Kanpp ; Angust ; Brucker and Hands D. for "Nacreous Pigments", September 19, 1989 in which a platelet-shaped substrate is provided with a compact coating containing iron (II) oxide, which coating has a high gloss and, depending on the layer thickness, shows the interference color of thin platelets, are described.

Reference may also be made to US Patent 4959090 assigned to Reinherz ; Barry P. for "Glass Enamel Coating Compositions", September 25, 1990 wherein the investigators have claimed for glass enamel coating compositions containing a glass frit system, optionally a metal oxide pigment and a vehicle there for, the improvement comprising the presence therein of a series of metal powders to provide anti-stick, color maintenance and adhesion properties ; the resulting coatings being particularly effective for application to glass sheets which are subsequently subjected to high temperature forming procedures.
The drawbacks of all the above noted processes are that these coatings are developed based on platelet shaped transparent substrates, such as mica, talc or glass coated with metal oxides or metal hydroxides along with / without alkaline earth metal compound and some with aluminium oxide for use as pigments in cosmetics or as pigmenting glazes and enamels for very low to medium temperature applications.
Hence these coatings are not suitable for terracotta articles, ceramic tiles and noveltywares for medium and high temperature applications. Further, such prior art materials are costly and are not suitable for use as an impervious permanent coating over ceramics.
The permanent coating can only be developed after prolonged heat treatment at high temperature and the coating formed due to pyrochemical reactions as well as sintering. Reference may be made to "Terra Sigillata : A sintered slip in use since Antiquity", S.Cizer, F.Uludinc, H.G. Ozcalik, S. Ozkan, H.Yoleri, S.Dogan, N.Canbolat, N.Balac ; Tile & Brick Int. 15(4), 253-255 (1999), wherein the authors described about antique slip which was prepared from naturally occurring clays after separating the coarse particles from the clays by adding water. It has been stated that the brightness and the smoothness of the pieces after application of engobes / coatings depend on the fineness of the particles as

well as the reducing atmosphere maintained in the kiln and develop black and red painted figurines. The drawback of the system is that the success of this technique depends on the plasticity of the clay, the brightness and the smoothness of the pieces depend on the fineness of the particles and the duration they are kept in the container for ageing as well as the reduction firing. Other drawback of the system is that it depends on some specific clays that sinters at low temperature and that it contains a high amount of iron. Further this material has limited scope for applications as well as lacked in variety for colour development.
Reference may be made to "Engobe Clay from Underground", U.Ladnorg, K.Schroder, "Tile & Brick Int. 11(5), 360-367, (1995), wherein the authors have used an underground clay collected from 60 m depth from a clay mine at Eisenberg in Southwest Germany. The tertiary age clay extracted from the Abendtal mine is a special raw material, which has a high content of glauconite (75%) responsible for its low sintering temperature. The drawback of this technique is that the preparation of engobe is dependent on a specific raw material containing glauconite ~ 75%, Kaolinite ~ 15% and quartz ~ 10% in the composition and thus cannot be used elsewhere.
Reference may be made to the existing practice as adopted by the rural artisans in Nizamabad district in Uttar Pradesh in India, utilizing engobe popularly known as "Kabiz" prepared from a locally available red burning clay mixed with water and different types of additives like bamboo leaves, ardosi leaves and bark of mango tree and aged for months, the clay slurry sieved through a fine cloth, used as a coating /engobe on unfired terracotta articles, polished and then fired in a specially constructed kiln under reducing condition and additions of goat bits several times during firing to obtain black pottery / black terracotta. The drawback of the above process is that it depends on a specific raw material

available in a particular region in India and the success of the process also depends on the additions of some leaves as well as ageing for a longer duration.
The drawbacks of the hitherto known engobe coatings and processes are
summarised below :
(i) the composition for coating have limited use as enamel coating on glass
for low temperature application as well as in cosmetics for use at ambient
temperature, (ii) the compositions of engobe are based on some specific raw materials
available in a specific region or a country and thus, suffers from limited
use.
The main object of the present invention is to provide a synergistic engobe coating composition.
Another object of the present invention is to provide a process for the manufacture of coloured engobe coatings and coated terracotta articles and ceramic tiles, which obviates the drawbacks as detailed above.
Still another object of the present invention is to provide engobe coatings which fulfill the requirements of surface smoothness, good adherence to the body, good frost resistance, colour stability with a matt finish, chemical durability, weathering resistance against atmospheric conditions, resistance to abrasion and permeability with different colour shades using different colour stains or colouring oxides which can be matured at a temperature range of 1100° to 1200°C and has a wide firing range of 50 to 100°C.
Yet another object of the present invention is to avoid the use of a region specific raw material.
A further object of the present invention is to provide a composition consisting of naturally occurring red burning clays from different origin/ having specified range of physical properties and are available in plenty in India and outside.
A still yet another object of the present invention is to provide a formulation of engobes which will form an impervious vitreous coating, thus avoiding the use of a second glaze coat and therefore, making the production process more economical.
Another object of the present invention is to provide a composition wherein talc in combination with titanium dioxide in the engobe compositions facilitates the dispersion of fine TiQz particles in the matrix and increases the performances w.r.t. whiteness, opacity and colour intensity.
This invention describes a synergistic engobe coating composition and a process for the manufacture of coloured engobes as coatings and coated terracotta articles and ceramic tiles. The present day engobes made from platelet shaped transparent substrates like mica, talc or glass coated with metal oxides or metal hydroxides along with/without alkaline earth metal compound and some with aluminium oxide for use as pigments in cosmetics for use at ambient temperature or as pigmenting glazes and enamels for very low to medium temperature applications are not suitable for terracotta articles, ceramic tiles and noveltywares for medium and high temperature applications. The compositions are also based on some specific raw materials available in a specific region or a country and thus, suffers from limited use. The compositions of engobes of the present invention possesses yellow and other colour decorations and consists of naturally occurring common clays as the major ingredient and talc powder, titanium dioxide and deflocculants as minor ones with the optional presence of dolomite and additional transitional metal compounds as colourants for
universal applications on terracotta articles and ceramic tiles. These engobes form an impervious vitreous coating on to terracotta wares and ceramic tiles fulfilling the requirements such as surface smoothness, good adherence to the body, good frost resistance, colour stability with a matt finish, chemical durability, resistance to weathering, abrasion. These engobes also avoid the use of glaze as second coat over the engobe coat and thus, make the production process more economical.
The novelty of the present invention, thus lies in developing synergistic compositions for engobes having yellow and other colour decorations for universal applications through the use of common clays of different origin and places after simple beneficiation to remove extraneous grit materials as well as a process for making coated article there of. The novel composition for the manufacture of engobe coatings of the present invention for making coated terracotta articles and ceramic tiles to make them impervious, matt textured, durable, scratch and chemical resistant as well as possessing the property of wide colour compatibility, the use of different colouring oxides and finally possessing a wide firing range of 50° to 100°C along with versatility of use over various types of terracotta articles and ceramic tiles.
The inventive steps to achieve the above stated novelty resides in the composition containing, as the primary ingredients / substrates, naturally occurring common terracotta clay as the major ingredient and talc powder, titanium dioxide and deflocculants as minor ones with the optional presence of dolomite and additional transitional metal compounds as colourants. Talc has in the present compositions, the function of "titanium extender" and this property has been applied to yellow and other coloured engobes including sodium tetra poly phosphate (STPP) or other sodium poly phosphates and dolomite as flux with TiOa content in the range of 5 to 15%. The inventive steps
also include incorporation of talc and titanium dioxide in combination and in varied percentages along with sodium poly phosphates and dolomite as flux. In particular, the applicable transitional metal compounds include ferric oxide (Fe2Os), cuprous oxide (Cu2O), nickel oxide (NiO), manganese dioxide (MnO2), chromium oxide (CteOs), cobalt oxide (CoO), cadmium sulfide (Cds) and Vanadium penta oxide (¥205) of purity of about 98% used alone and also in combination of two, three and four colourants in equal parts in the range of 5 to 15 wt% in partial and / or full replacements of TiC>2 in the compositions had shown particular advantage in developing various colour shades and tones and had constituted the essential inventive step. It is preferred that the metal oxide power exhibit an average particle size of smaller than 325 mesh (0.03mm), the performance of the metal powder being improved by the finer particle sizes.
The novelty of the process allows the use of single coating of engobe over the articles to be coated and employs once firing process and also avoids the use of the second glaze coat as conventionally used for industrial products and thus, making the production process more economical.
Accordingly the present invention provides a synergistic engobe coating
composition, which comprises:
beneficiated red burning common clay 40 to 60 wt % ;
talc powder 5 to 25 wt% ;
titanium dioxide 5 to 15 wt % ;
dolomite powder 0 to 20 wt % ;
deflocculant 10 to 20 wt % .
In an embodiment of the present invention the red burning common clay is such as having composition : SiO2 55.0 to 66.0 wt %, A12O315 to 22 wt %, TiO2 0.50 to 2.0 wt %, Fe2O3 5.5 to 9.5 wt %, CaO 0.1 to 2.0 wt %, MgO 0.0 to 0.5 wt %, K2O
1.8 to 2.5 wt %, Na2O 0.6 to 1.0 wt %, P2Os 0.2 to 1.2 wt % , and moisture plus impurities 7.0 to 11.0 wt % (LOI: loss on ignition).
In another embodiment of the present invention, the beneficiated red burning common clay is such as having grit content of 38 micron (400 mesh) less then 30.0 wt % and particle size distribution as follows: partcles coarser than 30 microns not over 40 wt % ; particles finer than 10 microns not less than 55 wt % ; particles finer than 5 microns not less than 50 wt % ; particles finer than 2 microns not less than 40 wt % ; and particles finer than 1 micron not less than 35 wt % .
In still another embodiment of the present invention, the talc is such as having composition : MgO 30.0 to 32.0 wt %, SiO2 59.0 to 60.0 wt %, CaO 2.0 to 3.0 wt %, A12O3 0.4 to 0.6 wt %, Fe2O3 0.3 to 0.5 wt %, Na2O 0.01 to 0.03 wt %, K2O 0.1 to 0.3 wt % and moisture plus impurities 5.0 to 7.0 wt % (LOI: loss on ignition).
In yet another embodiment of the present invention, the titanium dioxide is of 99.5% purity.
In still yet another embodiment of the present invention, the dolomite is such as having composition : MgO 19.0 to 21.0 wt %, CaO 29.0 to 30.0 wt %, SiO2 8.0 to 10.0 wt %, A12O3 1.0 to 1.5 wt % , Fe2O3 0.1 to 0.3 wt %, Na2O 0.04 to 0.06 wt %, K2O 0.04 to 0.06 wt % moisture plus impurities 38.0 to 43.0 wt % (LOI : loss on ignition).
In yet still another embodiment of the present invention, the deflocculant is such as sodium tri-poly phosphate (STPP), sodium-poly phosphates, alone or in combination.
In another embodiment of the present invention, the titanium dioxide in the composition is replaced in part or full by colourants such as transition metal compounds selected from Fe2O3, Cu2O, NiO, MnOa, CteOs, CoO, Cds, V2Os and SnC>2 of purity 98 to 99%, used alone or in combination in the range of 5 to 15
wt% .
In a further embodiment of the present invention the novel engobe coating
composition comprises:
beneficiated red burning common clay 40 to 60 wt % ;
talc powder 5 to 25 wt% ;
titanium dioxide 5 to 15 wt % ;
dolomite powder 0 to 20 wt % ;
sodium tetra poly phosphate (STPP) 10 to 20 wt % .
The novel engobe coating composition of the present invention is not a mere admixture but a synergistic mixture having properties which are distinct from the mere aggregated properties of the individual ingredients. Further, there is no chemical reaction.
Accordingly the present invention provides a process for the manufacture of coloured engobe coatings and coated terracotta articles and ceramic tiles, which comprises mixing and wet grinding the synergistic engobe coating composition of the present invention as detailed above, with water to make a slurry having density in the range of 1.10 to 1.20 g.cnr3 by conventional process, applying the said slurry on terracotta articles and ceramic tiles by conventional methods such as dipping, spraying, brushing and pouring to obtain coated articles, followed by drying the coated articles at a temperature in the range of 80° to 120°C to obtain dried coated articles, firing the dried coated articles so obtained at a temperature
in the range of 1100° to 1200°C with dwelling time in the range of 90 to 120 minutes.
In an embodiment of the present invention, the red burning common clay is disintegrated and beneficiated by sieving through 250 micron IS sieve.
In another embodiment of the present invention, the mixing and wet grinding is effected in a pot mill using 100% water and steatite grinding media, wherein the ratio of material and grinding media is maintained at 1: 2.
In yet another embodiment of the present invention, the composition is ground to a fineness of the order of 45 micron to obtain a slurry which is passed through 75 micron sieve to obtain an engobe coating.
In still another embodiment of the present invention, the engobe coating is passed through a magnetic channel to obtain engobe coating free of iron particles.
The details of the process of the present invention are given below :
a) Initially red burning common clay is disintegrated and beneficiated by
sieving through 250 micron IS sieve.
b) Constituents of the composition are weighed and loaded in a
pot mill for grinding and mixing using 100% water and steatite grinding media.
The ratio of material and grinding media is maintained at 1: 2. The grinding and
mixing is carried out for about 20 hours to obtain fineness of the order of 45
micron.
c) The mixture in the form of slurry / slip prepared in step "b" is passed
through 75 micron sieve after addition of some water and density of slurry / slip
is maintained in the range of 1.10 to 1.20 gm.cnr3.
d) The prepared engobe coating slurry / slip in "b & c" is used for coating
application on various types of unfired terracotta tiles and terracotta cast articles
by known processes such as dipping, spraying, brushing and pouring.
e) The coated articles in 'd' are dried at a temperature in the range of 80° to
120°C to obtain dried coated articles.
f) The dried coated articles in "e" are fired in a kiln at a temperature in the
range of 1100° to 1200°C with dwelling time in the range of 90 to 120 minutes.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. In the examples the red burning common clays used are sher black plastic clay (SBPC), vadali black plastic clay (VBPC) and dhamoliya black plastic clay (DBPC). The composition of the various red burning common clays, dolomite and talc used are given below:
Example -1
Beneficiated common clay {Sherblack Plastic Clay, Kheda district, Gujarat (SBPC)}- 40%, Talc-25%, STPP-20%, Titania -15% are mixed together in pot mill by wet process using conventional method for 20 h up to the fineness of 45 micron, sieved through 75 micron sieve, passed through a magnetic channel and then the prepared engobe is applied on decorative facing tiles by spraying process after adjustment of density to 1.10 gm.cnr3. The coated decorative facing tiles are then fired at the temperature of 1150°C. The yellow coloured matt textured smooth surface is obtained.
Example - 2
Beneficiated common clay {Vadali black Plastic Clay, Sabarkantha district, Gujarat (VBPC)} - 40%, Talc-25%, STPP-20%, Titania-15% are mixed together in pot mill by wet process using conventional method for 20 h up to the fineness of 45 micron, sieved through 75 micron sieve, passed through a magnetic channel and then the prepared engobe is applied on decorative facing tiles by spraying process after adjustment of density to 1.15 gm.cnr3. The coated decorative facing tiles are then fired at the temperature of 1160°C The yellow coloured matt textured smooth surface is obtained.
Example -3
Beneficiated common clay {Dhamoliya Black Plastic Clay, Sabarkantha district, Gujarat (DBPC)}-40%, Talc-25%, STPP-20%, Titania-15% are mixed together in pot mill by wet process using conventional method for 20 h up to the fineness of 45 micron, sieved through 75 micron sieve, passed through a magnetic channel and then the prepared engobe is applied on decorative facing
tiles by spraying process after adjustment of density to 1.20 gm.cm-3. The coated decorative facing tiles are then fired at the temperature of 1200°C. The yellow coloured matt textured smooth surface is obtained.
Example - 4
Beneficiated common clay (SBPQ-50%, Dolomite-10%, Talc-15%, STPP-15%r TiO2-10% are mixed together in pot mill by wet process using conventional method for 20 h up to the fineness of 45 micron, sieved through 75 micron sieve, passed through a magnetic channel and then the prepared engobe is applied on terracotta articles by spraying process after adjustment of density to 1.15 gm.cm-3. The coated terracotta articles are fired at the temperature of 1100°C. The articles developed yellow colour, matt texture and smooth surface.
Example - 5
Beneficiated common clay (SBPC)-60%, STPP-10%, Talc-5%, Dolomite-20% & TiO2-5% are mixed together in pot mill by wet process using conventional method for 20 h up to the fineness of 45 micron, sieved through 75 micron sieve, passed through a magnetic channel and then the prepared engobe is applied on terracotta novelty wares by spraying process after adjustment of density to 1.20 gm.cm-3. The coated articles are then fired at the temperature of 1150°C. The articles developed light yellow colour, matt texture and smooth surface.
Example - 6
Beneficiated common clay (SBPC)-45%, Talc-25%, STPP-15%, and Fe2O3-15% are mixed together in pot mill by wet process using conventional method for 20 h up to the fineness of 45 micron, sieved through 75 micron sieve, passed through a magnetic channel and then prepared engobe is applied on decorative ceramic tiles by spraying process after adjustment of density to 1.1 gm.cm-3. The
coated decorative tiles are then fired at the temperature of 1150°C. The maroon coloured matt textured smooth surface is obtained.
Example - 7
Beneficiated common clay (SBPC) -45%, Talc-25%, STPP-15%, Cobalt oxide-5% and TiOa-10% are mixed together in pot mill by wet process using conventional method for 20 h up to the fineness of 45 micron, sieved through 75 micron sieve, passed through a magnetic channel and then the prepared engobe is applied on decorative ceramic tiles by spraying process after adjustment of density to 1.2 gm.cnv3. The coated tiles are then fired at the temperature of 1100°C. The mud green coloured matt textured smooth surface is obtained.
The examples 1 to 3 incorporated beneficiated common clays from different sources of Gujarat State in the compositions keeping other constituents constant but the clays having chemical compositions, grit contents etc. developed the same yellow coloured matt textured coatings on the tile surface. This has justified the novelty of using common clays from different origins without restricting the invention dependent on a clay from a specified source. Similarly the examples 1,4 and 5 showed that the end result is obtainable in the specified range of clay contents as well as the contents of other raw materials and this once again showed the novelty of the invention. The examples 6 & 7 highlighted the incorporations of other colouring oxides like FezOs in complete replacement of TiOa as well as CoO in partial replacement of TiO2 in the compositions for the development of other colour decorations. These examples showed and justified that through the partial or complete replacement of TiO2, by colouring oxides
like Fe2O3, CoO, Cr2CO3, MnO2, Cu2O, Ni2O, V2O5/ As2O3, SnO2 on individual basis or in combinations of two, three and four oxides, a wide range of other colour decorations can be developed. This once again showed the novelty and the versatility of the invention for obtaining a wide range of colours according to the requirements of the connoisseurs. The above examples also showed the use of engobes as the only coatings on various types of articles without the use of glaze coat and thus, justifies the economy of the production process.
The main advantages of the present invention are :
(i) Engobe coatings can be made from any common clays falling in the range
of chemical analyses, grit content and particle size distribution as specified.
(ii) Economic production process.
(iii) Engobe coatings can be made on commercial basis and used for
commercial production.
(iv) Allows wide firing range.
(v) Can be used on various types of terracotta and other decorative tiles.
(vi) Can be made in a wide colour range using conventional colouring oxides.
(vii) Durable and chemically resistant.
(viii) Crazing and scratch resistant.
(ix) Provides matt and semi-glossy surfaces which provide aesthetic appeal
and easily cleanable.
(x) The articles after engobing / coating provide an elegant, defect free
and aesthetic appeal to the connoisseurs and enhance the marketability
of the product, (xi) Removes the need for a glaze coat, thus saving cost.


We Claim:
1. A synergistic engobe coating composition which consists of
beneficiated red burning common clay 40 to 60 wt%;
talc powder 5 to 25 wt%
Titanium dioxide 5 to 15 wt%
Dolomite powder 0 to 20 wt%
deflocculant 10 to 20 wt% and
a process for the manufacture of coloured engobe coatings tiles, which comprises mixing and wet grinding the synergistic composition , with water to make a slurry having density in the range of 1.10 to 1.20 g/cm"3 by conventional process, applying the said slurry on terracotta articles and ceramic tiles by conventional methods such as dipping, spraying, brushing and pouring to obtain coated articles, followed by drying the coated articles at a temperature in the range of 80°C to 120°C to obtain dried coated articles, firing the dried coated articles so obtained at a temperature in the range of 1100°C to 1200°C with dwelling time in the range of 90 to 120 minutes.
2. A synergistic composition as claimed in claim 1, wherein the red burning common clay as having composition : Si02 55.0 to 66.0 wt%, Al203 15 to 22 wt%, Ti02 0.50 to 2.0 wt%, Fe203 5.5 to 9.5 wt%, CaO 0.1 to 2.0 wt% , MgO 0.0 to 0.5 wt% , K20 1.8 to 2.5 wt%, Na20 0.6 to 1.0 wt%, P205 0.2 to 1.2 wt%, and moisture plus impurities 7.0 to 11.0 wt%.
3. A synergistic composition as claimed in claim 1 , wherein the beneficiated red burning common clay is such as having grit content of

38 micron (400 mesh) less than 30.0 wt% and particle size distribution
as follows:
Particles coarser than 30 microns not over 40 wt%;
Particles finer tan 10 microns not less than 55 wt%;
Particles finer than 5 microns not less than 50 wt%;
Particles finer than 2 microns not less than 40 wt%; and
Particles finer than 1 micron not less than 35 wt%.
4. A synergistic composition as claimed in claim 1 , wherein the talc is having composition : MgO 30.0 to 32.0 wt%, Si02 59.0 to 60.0 wt%, CaO 2.0 to 3.0 wt%, Al203 0.4 to 0.6 wt%, Fe203 0.3 to 0.5 wt%, Na20 0.01 to 0.03 wt%, K20 0.1 to 0.3 wt% and moisture plus impurities 5.0 to 7.0 wt% (LOI: loss on ignition).
5. A synergistic composition as claimed in claim 1 , wherein the dolomite is having composition : MgO 19.0 to 21.0 wt%, CaO 29.0 to 30.0 wt%, Si02 8.0 to 10.0 wt%, AI203 1.0 to 1.5 wt%, Fe203 0.1 to 0.3 wt%, Na20 0.04 to 0.06 wt%, K20 0.04 to 0.06 wt% moisture plus impurities 38.0 to 43.0 wt%.
6. A synergistic composition as claimed in claim 1, wherein the de flocculant used is sodium tri-poly photophate (STPP), sodium-poly phosphates, alone or in combination.
7. A process as claimed in claims 1 , wherein the red burning common clay is disintegrated and beneficiated by sieving through 250 micron IS sieve.

8. A process as claimed in claims 1 wherein the mixing and grinding is effected in a pot mill using 100% water and steatite grinding media, wherein the ratio of material and grinding media is maintained at 1 : 2.
9. A process as claimed in claims 1 , wherein the composition is ground to a fineness of the order of 45 micron to obtain a slurry which is passed through 75 micron sieve to obtain an engobe coating.
10. A process as claimed in claims 1 wherein, the engobe coating is passed through a magnetic channel to obtain engobe coating free of iron particles.
11. A synergistic engobe coating composition a process for the preparation of coatings substantially as herein described with reference to the examples.

Documents:

700-del-2002-abstract.pdf

700-DEL-2002-Claims-(31-07-2008).pdf

700-del-2002-claims.pdf

700-DEL-2002-Correspondence-Others-(31-07-2008).pdf

700-del-2002-correspondence-others.pdf

700-del-2002-correspondence-po.pdf

700-del-2002-description (complete)-31-07-2008.pdf

700-del-2002-description (complete).pdf

700-del-2002-form-1.pdf

700-del-2002-form-18.pdf

700-DEL-2002-Form-2-(31-07-2008).pdf

700-del-2002-form-2.pdf

700-del-2002-form-3.pdf


Patent Number 249476
Indian Patent Application Number 700/DEL/2002
PG Journal Number 43/2011
Publication Date 28-Oct-2011
Grant Date 21-Oct-2011
Date of Filing 28-Jun-2002
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110 001,INDIA
Inventors:
# Inventor's Name Inventor's Address
1 KEDAR NATH MAITI CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, NARODA CENTRE,AHMEDABAD 382 330,INDIA
2 RUGNATH MULJIBHAI SAVSANI CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, NARODA CENTRE,AHMEDABAD 382 330,INDIA
PCT International Classification Number C04B 41/86
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA