FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patents Rules  2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

1. "" CERAMIC MEDIUMS AND INKS IN POWDER FORM ""

2.

1. (A) LAMBERTI SPA
(B) Italy
(C) Ufficio Brevetti via Piave 18  I-21041 Albizzate (VA)  Italy

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present disclosure relates to printing mediums for ceramic pigments in powder form  to ceramic inks compositions in powder form and to methods for decorating green or fired ceramic bodies by the use of said printing mediums and compositions.
The ceramic inks compositions mainly consist of ceramic pigments  glazes and frits  dispersed in the printing mediums in powder form  which are based on glycols  urea and an inorganic absorbent.
BACKGROUND OF THE ART
Printing mediums for ceramic pigments (ceramic mediums) are generally fluids that are used in the preparation of ceramic inks to disperse ceramic pigments  to regulate their viscosity  flowing properties  and binding-cohesive behaviour.
Most traditional ceramic manufactured products  such as wall tiles and floor tiles  are made of a ceramic body that confers form and mechanical properties to the object; the ceramic body generally has some porosity and poor aesthetic qualities.
Said ceramic body  which is defined "green" or  alternatively  "fired"  if previously fired  is then usually coated with ceramic layer  called ceramic glaze; the ceramic glaze is completely sintered by firing  in such a way to gain suitable surface aesthetic qualities and  in the meantime  to become a fluid-proof barrier; as a matter of fact  after firing  the ceramic glaze has usually zero porosity and is generally resistant to abrasion and to the attack of chemical agents such as acids  bases  dyes.
The aesthetic finishing of the ceramic material can be completed by a decoration phase  that is by the application of sinterable and variously coloured ceramic materials (ceramic pigments) which are applied according to a precise drawing (decor).
The decor can be applied either on the green or fired ceramic body  on which the glaze was previously set  or  in the so called third firing decorations  after the firing on the glaze. The main printing techniques used in the decoration either of green or fired ceramic substrate are flat screen printing  rotary screen printing and the decoration by silicone roller (the latter comprising the printing through laser engraved roller  or "rotogravure printing"  and the printing through relief engraved roller  or "silicone stamp printing"); the decoration by silicone roller is also called rotogravure.
All these decoration techniques require a series of overlapping printings  one for each of the colours that compose the drawing.
Ceramic inks and printing mediums are formulated according to the kind of ceramic body to which they will be applied (green ceramic  fired ceramic  sintered glaze...) and according to the application technique (brush  spatula  screen printing  rotogravure printing...).
In the preparation of ceramic inks for the screen printing or rotogravure decorations of green or fired ceramic bodies  liquid printing mediums based on mixtures of water and glycols and normally containing additives  such as rheology modifiers  binders and plasticizers  are generally used.
Traditional liquid printing mediums contain large amounts of water  usually about 50 %wt of water; their transportation and storing costs are economically and energetically relevant.
Moreover  liquid printing mediums shall be stored in drums or tanks and  because of the variety of slightly different mediums that are normally used in an industrial plant  drums and tanks often need washing cycles with additional spoil of water and heavy duty detergents.
Therefore  it would be advantageous to provide concentrated ceramic mediums in powder form having good versatility.
In the prior art  BR PI0503487 describes a solid ceramic ink which is ready for use after dilution in water and contains frit  binder  thickening agent  antifoam and preserving agent; however BR PI0503487 does not disclose a solid powdery medium.
BR PI92202137 describes a silk print ceramic ink  in the form of paste  that contains a frit and a possibly waterless thixotropic medium  which comprises polyethylene glycol; however  also BR PI92202137 does not disclose a solid powdery medium.
I† has now been found that free-flowing mixtures of inorganic
absorbent  glycol  urea  and optionally conventional ingredients of ceramic mediums  can be prepared in the form of powder and used as concentrated ceramic mediums.
These concentrated ceramic mediums can be diluted in water and mixed with ceramic pigments to give ceramic inks with proper stability and rheology.
Alternatively  they can be mixed (or milled) with ceramic pigments to give ceramic inks compositions in powder form  which can be diluted in water before use to provide liquid ceramic ink; or  in another embodiment  the they can be milled together with the ceramic pigments and water to give in one step a liquid ceramic ink.
The powdery ceramic mediums of the present disclosure provide ceramic inks that allow the realisation of decors having comparable or improved definition with respect to inks obtained using traditional liquid mediums.
SUMMARY OF THE DISCLOSURE
In one aspect  the present disclosure relates to a mixture in powder form comprising:
a) from 5 to 50 %wt  preferably from 10 to 30 %wt  of an inorganic absorbent
b) from 10 to 50 %wt  preferably from 15 to 40 %wt  of a glycol c) from 20 to 70 %wt  preferably from 30 to 60 %wt  of urea
d) from 0.1%†o 10% of a rheology modifier
which can be used as concentrated ceramic medium.
In another aspect  the present disclosure relates to a ceramic ink composition in powder form which is useful for the flat screen printing  or rotary screen printing  or rotogravure decoration of green or fired ceramic bodies and consists of from 30 to 80 %wt by weight of ceramic pigments and from 20 to 70%wt of the above concentrated ceramic medium.
According to still another aspect  the disclosure is a method for decorating green or fired ceramic bodies comprising the following steps:
i. the above concentrated ceramic medium is prepared;
ii. the concentrated ceramic medium is dispersed in from 50 to 100 parts by weight of water to obtain a liquid ceramic medium; iii. a liquid ceramic ink composition is prepared by mixing from 30 to 70 parts by weight of ceramic pigments with from 30 to 70 parts by weight of the liquid ceramic medium; iv.a glaze is spread on the surface of the green or fired ceramic body;
v. the decoration is made by means of flat screen printing  or
rotary screen printing  or rotogravure  by using one or more liquid ceramic inks prepared according to the steps i. to iii.; vi.the obtained substrate is fired at a temperature comprised between 900 and 1250°C for 15-240 minutes.
According to a further aspect  the disclosure is a method for decorating green or fired ceramic bodies comprising the following steps:
i. a ceramic ink composition in powder form is prepared by mixing from 30 to 80 parts by weight of ceramic pigments with from 20 to 70 parts by weight of the above concentrated ceramic medium;
ii. the ceramic ink composition in powder form is dispersed with from 30 to 70 parts by weight of water  to obtain a liquid ceramic ink;
iii. a glaze is spread on the surface of the green or fired ceramic body;
iv.the decoration is made by means of flat screen printing  or rotary screen printing  or rotogravure  by using one or more liquid ceramic inks prepared according to steps i. and ii.; v. the obtained substrate is fired at a temperature comprised
between 900 and 1250°C for 15-240 minutes.
According to still a further aspect  the disclosure is a method for decorating green or fired ceramic bodies comprising the following steps:
i. a liquid ceramic ink composition is prepared by homogenising in a turbine mixer or by milling from 30 to 80 parts by weight of ceramic pigments and from 20 to 70 parts by weight of the above concentrated ceramic medium with water;
ii. a glaze is spread on the surface of the green or fired ceramic body;
iii. the decoration is made by means of flat screen printing  or rotary screen printing  or rotogravure  by using one or more liquid ceramic inks prepared according to step i.; iv. the obtained substrate is fired at a temperature comprised
between 900 and 1250°C for 15-240 minutes.
DETAILED DESCRIPTION
The powdery mixture comprising a) from 5 to 50 %wt of inorganic absorbent  b) from 10 to 50 %wt of glycol and c) from 20 to 70 %wt of urea advantageously additionally comprises up to 15 %wt of conventional organic ingredients of ceramic printing mediums  such as binders  plasticizers  preservative agents  anti-foam agents  dispersants and water retention agents.
The inorganic absorbents which may be employed to prepare the concentrated ceramic mediums of the disclosure are water-insoluble chemically non-reactive inorganic powders which are capable of absorbing liquids without losing their powdery form.
Examples of inorganic absorbents are precipitated silica  silica gel  calcium silicates and alumina.
Other microcrystalline materials which are suitable are aluminates  clays  including kaolin  bentonites  calcinated kaolin  molochite  zeolites  montmorillonites and the like.
The inorganic absorbent which is particularly preferred for the realization of the present invention is precipitated silica.
Precipitated silica is a highly absorbent material and consists of a three-dimensional network of coagulated primary silica particles; the latter grow to sizes higher than 4-100 nm before they coagulate to form the aggregated clusters  or agglomerate  having size from about 1 to 40 µ?t? and average pore size > 30 nm; the precipitated dried silica may be subjected to milling and classifying steps to obtain specific particle size distribution.
The use of precipitated silica as the inorganic absorbent is preferred because it confers excellent rheology stability to the final liquid ceramic inks.
The glycols of the concentrated ceramic mediums of the invention are water-soluble products.
Preferably they are selected among monopropylene glycol (MPG)  dipropylene glycol (DPG)  monoethylene glycol (MEG)  diethylene glycol (DEG)  glycerin and polyethylene glycol having average molecular weight below 5 000 (PEG)  and mixtures thereof.
More preferably the glycol is liquid a† standard conditions; most preferably the glycol is monoethylene glycol.
Urea is a low cost non noxious industrial product that is largely used in agriculture and even in personal care products  such as soaps  toothpaste  detergents.
Both purified and technical grade commercial urea can be used for the preparation of the powdery ceramic mediums of the invention. The preparation of the concentrated ceramic medium according to the invention can be performed by mixing to homogeneity the glycol and the inorganic absorbent  which is preferably precipitated silica  and adding urea and the additional conventional ingredients onto the resulting mixture  in the proper quantities  and further homogenising.
Preferably  urea is grinded with a hammer mill before being added to the glycol-absorbent mixture.
The resulting powdery  free-flowing mixture can be used as such to formulate ceramic ink composition in powder form or to provide liquid ceramic mediums upon dilution with water.
According to one embodiment of the disclosure a liquid ceramic ink is prepared by diluting the powdery free-flowing mixture in water and subsequently mixing the thus obtained liquid medium with the ceramic pigments and other possible solid components of the ink.
According†o another embodiment of the disclosure  a ceramic ink composition in powder form is prepared by mixing (or milling) the above powdery free-flowing mixture with ceramic pigments and other possible solid components of the ink.
The preparation of the ceramic ink can also be made by
homogeneising the concentrated ceramic medium in powder form with the rest of solid components (frits  glazes and pigments) and water to give in one step a liquid ceramic ink.
In order to help regulating the final viscosity of the liquid medium and ink  the concentrated ceramic medium of the disclosure comprises from 0.10 to 10% by weight of a rheology modifier.
Preferred rheology modifiers are modified natural polymers  such as hydroxyethyl cellulose  carboxymethyl cellulose  hydroxypropyl guar and hydroxypropyl starch and synthetic polymers  such as polyacrylic thickeners; it is also possible to use mixtures of rheology modifiers having different thickening properties and different rheological behaviour.
Viscosity and pseudoplasticity are regulated  according to what is well known to those skilled in the art  by the amount of water and by the amount and kind of rheology modifier.
After dilution with water  the ceramic mediums are fluids with
homogeneous aspect and viscosity comprised between 30 and 1000
mPa*s  measured by means of a Haake rheometer between 0.1 and 1  000 sec-1.
Mediums having low viscosity (30-100 mPa*s) and newtonian or lightly pseudoplastic behaviour are used when a rotogravure printing ceramic ink is to be prepared; mediums having higher viscosity (100 -1  000 mPa*s) and more pseudoplastic behaviour are used when a ceramic ink for flat or rotary screen printing is to be prepared.
The viscosity and pseudoplasticity of the liquid mediums and inks may be then further regulated by addition of more rheology modifiers  according to the type of printing technique selected for the
decoration  as it is well known in the art.
The ceramic pigments useful in the ceramic inks of the invention are solid sinterable materials  that means that they are transformed in ceramic during the firing process; these are oxides  pigments  frits  glasses and other ceramic materials; they are in the form of solid particles having dimensions varying from 0.5 to 100 microns.
Typically  they include iron  titanium  chromium  zinc  magnesium  aluminium  cobalt  and cadmium oxides  and zirconium and praseodymium silicates.
The viscosity of the liquid ceramic inks that can be obtained by diluting in water the powdery ceramic ink composition of the disclosure  measured with a Haake rheometer between 0.1 and 200 S-1   is between 50 and 2 000 mPa*s  as it is usual in the field.
EXAMPLES
All the viscosities reported in the present text were measured with a Haake rotational rheometer; the viscosity measures were performed through flow curves at "controlled shear rate" between 1 and 200 sec-1.
Example 1.
Mediums 1 - 7
Six concentrated mediums in powder form are prepared by firstly preparing the glycol/absorbent mixture  and then by adding urea and the other ingredients.
A comparative dry medium is prepared by homogenising a high molecular weight glycol (PEG 6 000) with urea and the other ingredients.
The composition of the mediums is reported in Table 1   where the ingredients and their dosage are indicated (% wt).
Table 1

EXAMPLE 2
Preparation of ceramic inks and ceramic decorations.
Seven powdery dry ceramic ink compositions were prepared by mixing in a mill each of the mediums prepared in Example 1 with a mixture of ceramic pigments in the proportion by weight indicated in Table 2 (the ink composition II is prepared from the medium 1   the ink composition 12 from medium 2  and so on).
Table 2

The ink compositions II   12  13 and 14 were then diluted with 50 parts by weight of water while the ink compositions 15  16 and 17 were diluted with 40 parts by weight of water  to give seven stable ready for use liquid ceramic inks (respectively Lll   LI2  LI3  LI4  LI5  LI6 and LI7).
The viscosity and stability of the liquid ceramic inks are reported in Table 3.
The viscosity (Vpo) is the average viscosity in mPa*s  measured within 1 hour from preparation of the ink.
The viscosity (Vpz2h) is the average viscosity in mPa*s  measured after
72 hours from preparation of the ink.
An ink is considered "insufficiently stable" (-) if it presents
sedimentation phenomena or lumps formation when stored at room temperature for 72 hour after its preparation.
An ink is considered "sufficiently stable" (+) if it does not presents sedimentation phenomena or lumps formation when stored at room temperature for 72 hour after its preparation.
An ink is considered "stable" (++) if it does not present separation phenomena or lumps formation after storing at room temperature for
72 hour after its preparation and additionally has Vp72h = ± 10%Vpo.
Inks Lll to LI4 were applied through rotogravure; inks LI5 to LI7 were applied by silk screen printing on the same support.
Afterwards  the drying time of the thus obtained decor (Drying†) and  visually after drying  the definition quality of the decor itself (D) were determined.
The results are reported in Table 3.
The results of Table 3 show that the inks  prepared with the powdery concentrated mediums of the disclosure have good rheological behaviour  sufficient stability and perform well  although the liquid inks obtained from the concentrated mediums that contain precipitated silica as the absorbent give a sensibly better performance  having excellent drying time and stability.


We Claim:-

1 ) Mixture in powder form comprising:
a) from 5†o 50 %wf of an inorganic absorbent 
b) from 10 to 50 %wt of a glycol
c) from 20 to 70 %wt of urea 
d) from 0.1% to 10% of a rheology modifier.
2) Mixture in powder form according to claim 1 comprising from 10 to 30 %wt of inorganic absorbent  from 15 to 40 %wt of glycol  from 30 to 60 %wt of urea and up to 15 %wt of conventional organic ingredients of ceramic printing mediums selected among binders  plasticizers  preservative agents  anti-foam agents  dispersants and water retention agents.
3) Mixture in powder form according to claim 1 or 2 wherein the inorganic absorbent is selected among precipitated silica  silica gel  calcium silicates  alumina  aluminates  clays.
4) Mixture in powder form according to claim 4 wherein the
inorganic absorbent is precipitated silica.
5) Mixture in powder form according to claim 4 wherein the glycol is selected among monopropylene glycol (MPG)  dipropylene glycol (DPG)  monoethylene glycol (MEG)  diethylene glycol (DEG)  glycerin and polyethylene glycol having average molecular weight below 5 000 (PEG)  and mixtures thereof.
6) Mixture in powder form according to claim 5 wherein the glycol is monoethylene glycol.
7) Ceramic ink composition in powder form consisting of from 30 to 80 %wt by weight of ceramic pigments and from 20 to 70%wt of a concentrated ceramic medium consisting of a mixture according to any of claims from 1 to 6.
8) Method for decorating green or fired ceramic bodies
comprising the following steps:
i. a concentrated ceramic medium consisting of a mixture according to any of claims from 1 to 6 is prepared;
ii. 100 parts by weight of the concentrated ceramic medium is dispersed in from 50 to 100 parts by weight of water to obtain a liquid ceramic medium;
iii. a liquid ceramic ink composition is prepared by mixing from 30 to 70 parts by weight of ceramic pigments with from 30 to 70 parts by weight of the liquid ceramic medium;
iv. a glaze is spread on the surface of the green or fired
ceramic body;
v. the decoration is made by means of flat screen printing  or rotary screen printing  or rotogravure  by using one or more liquid ceramic inks prepared according to the steps i. to iii.; vi. the obtained substrate is fired at a temperature comprised between 900 and 1250°C for 15-240 minutes.
9) Method for decorating green or fired ceramic bodies
comprising the following steps:
i. a ceramic ink composition in powder form according†o claim 7 is prepared;
ii. 100 parts by weight of the ceramic ink composition in
powder form is dispersed with from 30 to 70 parts by weight of water  to obtain a liquid ceramic ink;
iii. a glaze is spread on the surface of the green or fired
ceramic body;
iv. the decoration is made by means of flat screen printing  or rotary screen printing  or rotogravure  by using one or more liquid ceramic inks prepared according to steps i. and ii.; v. the obtained substrate is fired at a temperature comprised between 900 and 1250°C for 15-240 minutes.
10)Me†hod for decorating green or fired ceramic bodies
comprising the following steps:
i. a liquid ceramic ink composition is prepared by
homogenising in a turbine mixer or in a mill from 30 to 80 parts by weight of ceramic pigments and from 20 to 70 parts by weight of concentrated ceramic medium consisting of a mixture according to any of claims from 1 to 6  and water;
ii. a glaze is spread on the surface of the green or fired
ceramic body;
iii. the decoration is made by means of flat screen printing  or rotary screen printing  or rotogravure  by using one or more liquid ceramic inks prepared according to steps i.;
iv. the obtained substrate is fired at a temperature comprised between 900 and 1250°C for 15-240 minutes.

Dated this 17th day of July  2012.