WO2006134063A2

WO2006134063A2 - Mediums for ceramic pigments

Info

Publication number: WO2006134063A2
Application number: PCT/EP2006/063008
Authority: WO
Inventors: Moreno Gatto; Eva Baldaro; Paolo Prampolini; Alan Nappa; Giuseppe Li Bassi
Original assignee: Lamberti Spa
Priority date: 2005-06-15
Filing date: 2006-06-08
Publication date: 2006-12-21
Also published as: BRPI0611568A2; EP1891172A2; WO2006134063A3; ITVA20050039A1; MX2007015903A

Abstract

The present invention relates to mediums for ceramic pigments comprising: a. from 0.1 to 6% by weight of hydroxypropyl guar having molar substitution (MS) comprised between 1.4 and 3 and Brookfield viscosity in water solution at 20°C and 20 rpm comprised between 50 mPa*s at 4% by weight and 2,200 mPa*s at 1% by weight; b. from 99.9 to 89% by weight of a glycol/water mixture, where the glycol is present in a percentage comprised between 10% and 90% by weight; to ceramic inks useful for the screen printing decoration of green or fired ceramic substrates; to a method for the decoration of green or fired ceramic substrates.

Description

MEDIUMS FOR CERAMIC PIGMENTS

Technical Field

[0001] The present invention relates to mediums for ceramic pigments, to the ceramic inks containing them and to a method for decorating green or fired ceramic substrates comprising the use of said inks.

[0002] Mediums for ceramic pigments are fluids thickened with rheology modifiers; they are used for in preparation of ceramic inks to regulate their viscosity, flowing properties, and binding-cohesive behaviour.

[0003] In particular, the mediums of the invention contain, as rheology modifier, hy- droxypropyl guar having high molar substitution.

[0004] Most traditional ceramic manufactured products, such as wall tiles and floor tiles, are made of a ceramic substrate conferring form and mechanical properties to the object; the ceramic substrate generally has some porosity and poor aesthetic qualities.

[0005] Said substrate, which is defined "green" or, alternatively, "fired", if previously fired, is then usually coated with another ceramic layer, called ceramic glaze; the ceramic glaze is completely sintered by firing, in such a way to gain suitable superficial 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.

[0006] The aesthetic finishing of the ceramic material can be completed by a decoration phase, that is by the application of sinterable and variably coloured ceramic materials deposed according to a precise drawing (decor) .

[0007] The decor can be applied either on the green or fired substrate, on which the glaze was previously set, or, in the decorations called third fire, after the firing on the glaze. The medium for ceramic pigments of the present invention is useful for the decoration of ceramic substrates, either green or fired, on which the glaze has already been set.

[0008] 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 (comprising the printing through laser engraved roller, or "rotogravure printing", and the printing through relief engraved roller, or "silicone stamp printing"); the decoration by silicon roller is also called rotogravure.

[0009] All these decoration techniques require a series of overlapping printings, as numerous as the number of colours composing the drawing.

[0010] The mediums for ceramic pigments of the present invention are useful for the decoration of either green or fired ceramic substrates by means of flat or rotary screen printing or rotogravure. Background Art

[0011] The rheology modifiers, which are employed in mediums for ceramic pigments useful in the preparation of ceramic inks for the decoration of green or fired ceramic substrate, are normally modified natural polymers or synthetic polymers which are soluble in water-glycols mixtures.

[0012] The selection of the rheology modifier is critical, because it affects the rheologic characteristics of the finished ink, influencing the definition of the printed dots, the definition and drying time of the decor, the colour homogeneity, the surface aspect and the decor adhesion.

[0013] Among modified natural polymers, hydroxyethyl cellulose is the most used rheology modifier in mediums for ceramic inks for the decoration of green or fired ceramic substrates.

[0014] According to what reported in US 5,326,390, hydroxyalkyl polysaccharides, and among them hydroxypropyl guar, can be used in solvent (glycol) based mediums for electronic pastes applicable on metal or ceramic substrates; nevertheless, US 5,326,390 does not describe the use of hydroxypropyl guar with molar substitution equal or higher than 1.4, but teaches the use of a particular combination of additives to obtain a paste with the desired rheological and flowing properties. Disclosure of Invention

[0015] It has now surprisingly been found that, by using hydroxypropyl guar having molar substitution between 1.4 and 3 as rheology modifier in the formulation of fluid mediums for ceramic pigments, stable inks are obtained that permit the realisation of decors having comparable or improved definition with respect to inks obtained using the commonly used rheology modifiers.

[0016] Moreover, the ceramic inks comprising the mediums of the present invention show good characteristics of printing quality and a drying time which is adequate to the above mentioned decoration techniques.

[0017] It is therefore a fundamental object of the present invention a medium for ceramic pigments comprising: a. from 0.1 to 6% by weight of hydroxypropyl guar having molar substitution (MS) comprised between 1.4 and 3 and Brookfield viscosity in water solution at 20°C and 20 rpm comprised between 50 mPa_*s at 4% by weight and 2,200 mPa_*s at 1% by weight;

[0018] b. from 99.9 to 89% by weight of a glycol/water mixture where the glycol is present in a percentage comprised between 10% and 90% by weight

[0019] and having an average viscosity measured by means of a Haake rheometer between 0.1 and 1,000 sec ¹ comprised between 30 and 500 mPa_*s.

[0020] It is further object of the present invention a ceramic ink useful for the screen printing decoration of green or fired ceramic substrates comprising from 3% to 60% by weight of ceramic pigments which are dispersed in a medium comprising:

[0021] a. from 0.1 to 6% by weight of hydroxypropyl guar having molar substitution (MS) comprised between 1.4 and 3 and Brookfield viscosity in water solution at 20°C and 20 rpm comprised between 50 mPa_*s at 4% by weight and 2,200 mPa_*s at 1% by weight;

[0022] b. from 99.9 to 89% by weight of a glycol/water mixture where the glycol is present in a percentage comprised between 10% and 90% by weight.

[0023] According to a further aspect, the invention is a method to decorate green or fired ceramic substrates, comprising the following steps:

[0024] (i) one or more ceramic inks are prepared dispersing from 3 to 60 parts by weight of ceramic pigments in a medium having an average viscosity measured by means of a Haake rheometer between 0.1 and 1,000 sec ¹ comprised between 30 and 500 mPa_*s and comprising:

[0025] a. from 0.1 to 6% by weight of hydroxypropyl guar having molar substitution (MS) comprised between 1.4 and 3 and Brookfield viscosity in water solution at 20°C and 20 rpm comprised between 50 mPa_*s at 4% by weight and 2,200 mPa_*s at 1% by weight;

[0026] b. from 99.9 to 89% by weight of a glycol/water mixture where the glycol is present in a percentage comprised between 10% and 90% by weight;

[0027] (ii) the glaze is spread on the green or fired substrate surface;

[0028] (iii) the decoration is made by means of flat screen printing, or rotary screen printing, or rotogravure, utilising one or more of the inks of point (i);

[0029] (iv) the obtained substrate is fired at a temperature comprised between 900 and 1250°C for 15-240 minutes.

[0030] Hydroxypropyl guar (HPG) is widely used in the most varied industrial applications, where its capacity to thicken and modify the rheology of water solution is exploited.

[0031] It is obtained by chemical reaction of propylene oxide, in presence of basic catalyst (sodium hydroxide, for example), on the hydroxyls of the galactomannan polysaccharide that constitutes what is commercially defined guar gum or simply guar.

[0032] The introduction of hydroxypropyl groups renders the guar more organophilic, increasing its solubility in organic solvents such as alcohols and glycols.

[0033] The most commonly commercialised hydroxypropyl guar has a molar substitution comprised between 0.3 and 1.2; hydroxypropyl guar with molar substitution higher than 1.2 is commercially available from Lamberti SpA, for example with the trade name Esacol Q.

[0034] In the present text, with the expression "molar substitution" (MS) it is intended the molar substitution of hydroxypropyl guar measured by means of ¹H-NMR.

[0035] As already stated, according to a fundamental aspect of the present invention, the medium for ceramic pigments contains hydroxypropyl guar having molar substitution comprised between 1.4 and 3.

[0036] More preferably, the molar substitution of the hydroxypropyl guar useful for the realisation of the present invention is comprised between 1.5 and 2, because this degree of molar substitution permits to quickly dissolve the hydroxypropyl guar in the water/ solvent mixtures commonly used as ceramic mediums.

[0037] Preferably, the hydroxypropyl guar used for the realisation of the present invention is cross-linked with a quantity of glyoxal comprised between 0.3 and 1.7 parts by weight, more preferably between 0.4 and 0.8 parts by weight, the total quantity of glyoxal present being determined by reaction with

2-hydrazon-2,3-dihydro-3-methylbenzothiazole hydrochloride, according to the method described in "Kunststoffe im Lebensmittelverkehr" Ed. Carl Heymanns Verlag KG, 1999, p 228-231.

[0038] The cross-linked hydroxypropyl guar is obtained through a treatment with from 0.3 to 1.7 parts by weight of glyoxal; or, advantageously, said hydroxypropyl guar is obtained through a treatment with from 2 to 3%, preferably from 2.2 to 2.8%, by weight of glyoxal in the form of water solution at pH <6 and at room temperature and subsequent washing for 30-90 minutes with water at pH<6, as described in the patent application WO 03/078473.

[0039] The glyoxal cross-linking is advantageous because it permits to easily dissolve the hydroxypropyl guar in water by shifting the pH at value higher than 7, with homogeneous development of the viscosity and without formation of lumps; to rise the pH, it is possible to use, for example, sodium hydroxide, triethanolamine, ammonium hydroxide, or aminomethyl propanol, in the form of water solution and in minimal percentage (about 0.05 - 0.5 parts by weight of base per part by weight of medium).

[0040] The glycol of the medium of the invention is a water-soluble glycol or a mixture of water-soluble glycols, preferably selected among mono-ethylene glycol (MEG), mono propylene glycol (MPG), diethylene glycol (DEG), dipropylene glycol (DPG), glycerine and polyethylene glycol (PEG).

[0041] The mediums of the present invention are fluids with a homogeneous aspect and a viscosity measured by means of a Haake rheometer between 0.1 and 1,000 sec ¹ comprised between 30 and 500 mPa_*s.

[0042] The viscosities reported in the present text were measured with a rheometer Haake Rotovisco RV 20 equipped with a measuring head M5 and measuring devices NV and MV; the viscosity measures were performed through flow curves at "controlled shear rate" between the said interval.

[0043] The viscosity of the medium is chosen according to the type of printing technique selected for the decoration. [0044] Mediums having low viscosity (30-100 mPa_*s) and newtonian or lightly pseu- doplastic behaviour are used when a rotogravure printing ceramic ink is to be prepared; mediums having higher viscosity (100 - 500 mPa_*s) and more pseudoplastic behaviour are used when a ceramic ink for flat or rotary screen printing is to be prepared.

[0045] Viscosity and pseudoplasticity can be regulated, according to what is well known to those skilled in the art, selecting the quantity and quality of the hydroxypropyl guar.

[0046] For the realisation of the present invention it is also possible to use mixtures of hydroxypropyl guars having different thickening properties and different rheological behaviour.

[0047] The preparation of the medium according the invention can be performed following the usual techniques, that is preparing the glycol/water mixture, adding gradually the hydroxypropyl guar under stirring, adding a base to develop the viscosity, if needed, and completing the preparation with the addition of the additives normally utilised for the preparation of mediums for ceramic pigments; the mediums of the present invention can actually contain up to 10% by weight of one or more additives among those commonly used, such as preservatives, biocides, antifoams, dispersants, binders, levelling agents, and so forth.

[0048] According to a particularly advantageous aspect, the preparation of the medium can be done at room temperature.

[0049] The hydroxypropyl guar having molar substitution higher or equal to 1.5 is actually completely cold-soluble in the glycol/water mixtures of the medium of the present invention and do not need warming to develop its thickening capacity.

[0050] 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 micron.

[0051] Typically, they include iron, titanium, chromium, zinc, magnesium, aluminium, cobalt, and cadmium oxides, and zirconium and praseodymium silicates.

[0052] Example 1.

[0053] Mediums Preparation.

[0054] 14 Mediums for ceramic pigments were prepared (Mediums A1-A4, Bl -B 3, C1-C5, D1-D2). The mediums Al, A4, Bl, Cl, Dl, B3, C4 are comparative mediums. Mediums A1-A4 and Bl -B 3 have a basic composition (quantity of water, type and quantity of glycols and additives) that render them fit for use in flat silk-screen printing; mediums C1-C5 are fit for rotogravure printing, mediums D1-D2 for Self-fix printing (rotary screen printing). The mediums preparation has been made preparing first the water/glycol mixture containing the other possible additives, dispersing the rheology modifier into it and, when indicated, viscosity is builded up through the addition of the base.

[0055] The basic compositions of the mediums are reported in Table 1, where the ingredients and their dosage are indicated (% by weight).

[0056]

Table 1

[0057] * 73% by weight maltodextnne based binder [0058] [0059] In Table 2 the rheology modifiers used in the mediums, their chemical nature (T), their molar substitution (MS), Brookfield viscosity (V), their quantity in the medium (%) and the average viscosity of the medium (v) are reported.

[0060] The viscosity (V) of the rheology modifier is the viscosity in mPa_*s measured using a Brookfield RVF viscosimeter at 20 rpm in a water solution containing the rheology modifier at the indicated concentration and at 20°C. The molar substitution (MS) is measured through ¹H-NMR.

[0061] The medium average viscosity (v) is expressed in mPa_*s and is measured using a Haake rheometer performing flow curves between 0.1 and 1,000 sec ¹ a 25°C. In Table 2, HEC means hydroxyethyl cellulose, HPG means hydroxypropyl guar. Moreover in Table 2 the appearance of the medium is indicated (Asp); the symbol + means good appearance (visibly homogeneous), the symbol - means visibly non-homogeneous aspect.

[0062]

Table 2

[0063]

[0064] Example 2. [0065] Preparation of ceramic inks and ceramic decoration. [0066] 14 Ceramic inks were prepared by mixing, using a mill, each of the 14 mediums prepared in Example 1 with a frit (Colorobbia TTB), in the proportion by weight indicated in Table 3 (the ink PAl is prepared starting from medium Al, ink PA2 starting from medium A2, and so on).

[0067]

Table 3

[0068]

[0069] The stability and viscosity of the thus prepared inks are reported in Table 4. [0070] The viscosity (Vp) is the average viscosity in mPa_*s measured using a Haake Rheometer through a flow curve between 0.1 and 200 sec ¹ at 25°C. It is considered stable an ink that stored at room temperature for 72 hour after its preparation does not present separation phenomena or lumps formation.

[0071] The stable inks are indicated in Table 4 using the symbol +, the non-stable inks with the symbol -. [0072] Inks PA1-A4 and PB1-PB3 were applied through flat silk-screen printing on the ceramic tile; inks PC1-PC5 were applied through rotogravure printing on the tile and the mediums PD1-PD2 through Self-fix printing. Afterwards, the drying time of the thus obtained decor (t) and, visually after drying, the definition quality of the decor itself (D) were determined.

[0073] The results are reported in Table 4. [0074]

Table 4

[0075] Comparative examples [0076] [0077] From the results of Table 4 it can be inferred how hydroxypropyl guars having a MS>1.4 have similar and sometimes better performance with respect to hydroxyethyl cellulose normally used in the preparation of such mediums.

Claims

[0001] Mediums for ceramic pigments having an average viscosity measured between

0.1 and 1,000 sec ¹ using a Haake rheometer comprised between 30 and 500 mPa _*s containing: a. from 0.1 to 6% by weight of hydroxypropyl guar having molar substitution (MS) comprised between 1.4 and 3 and Brookfield viscosity in water solution at 20°C and 20 rpm comprised between 50 mPa_*s at 4% by weight and 2,200 mPa_*s at 1% by weight; b. from 99.9 to 89% by weight of a glycol/water mixture, where the glycol is present in a percentage comprised between 10% and 90% by weight.

[0002] Mediums for ceramic pigments according to claim L, where the hydroxypropyl guar has molar substitution comprised between 1.5 and 2.

[0003] Mediums for ceramic pigments according to claim 1. or 2., where the glycol is selected among mono-ethylene glycol (MEG), mono-propylene glycol (MPG), diethylene glycol (DEG), dipropylene glycol (DPG), glycerine and polyethylene glycol (PEG).

[0004] Ceramic inks useful for the screen printing decoration of green or fired ceramic substrates comprising from 3% to 60% by weight of ceramic pigments dispersed in a medium containing: a. from 0.1 to 6% by weight of hydroxypropyl guar having molar substitution (MS) comprised between 1.4 and 3 and Brookfield viscosity in water solution at 20°C and 20 rpm comprised between 50 mPa_*s at 4% by weight and 2,200 mPa_*s at 1% by weight; b. from 99.9 to 89% by weight of a water/glycol mixture, where the glycol is present at a percentage comprised between 10% and 90% by weight.

[0005] Ceramic inks according to claim 4., where the medium comprises hydroxypropyl guar having molar substitution (MS) comprised between 1.5 and 2.

[0006] Ceramic inks according to claim 4. or 5., where the glycol is selected among mono-ethylene glycol (MEG), mono-propylene glycol (MPG), diethylene glycol (DEG), dipropylene glycol (DPG), glycerine and polyethylene glycol (PEG).

[0007] Method for the decoration of green or fired ceramic substrates, comprising the following steps: (i) one or more ceramic inks are prepared dispersing from 3 to 60 parts by weight of ceramic pigments in a medium having an average viscosity between 0.1 and 1,000 sec ¹ measured using a Haake rheometer comprised between 30 and 500 mPa_*s and containing: a. from 0.1% to 6% by weight of hydroxypropyl guar having molar substitution (MS) comprised between 1.4 and 3 and Brookfield viscosity in water solution at 20°C and 20 rpm comprised between 50 mPa_*s at 4% by weight and 2,200 mPa_*s at 1% by weight; b. from 99.9 to 89% by weight of a water/glycol mixture, where the glycol is present in a percentage comprised between 10% and 90% by weight; (ii) the glaze is spread on the green or fired substrate surface; (iii) the decoration is carried out through flat screen printing, or rotary screen printing, or rotogravure, using one or more of the inks of point (i); (iv) the substrate thus obtained is fired at a temperature comprised between 900 and 1250°C for 15-240 minutes.

[0008] Method for the decoration of green or fired ceramic substrates according to claim

7., where the medium comprises hydroxypropyl guar having molar substitution (MS) comprised between 1.5 and 2.

[0009] Method for the decoration of green or fired ceramic substrates according to claim

7. or 8. where the glycol is selected among mono-ethylene glycol (MEG), mono- propylene glycol (MPG), diethylene glycol (DEG), dipropylene glycol (DPG), glycerine and polyethylene glycol (PEG).