WO2015003736A1

WO2015003736A1 - Ceramic inkjet ink

Info

Publication number: WO2015003736A1
Application number: PCT/EP2013/064387
Authority: WO
Inventors: Tri Ratna TULADHAR; Domenico DI LONARDO; Fabio Enzo FENZI
Original assignee: Fenzi Spa
Priority date: 2013-07-08
Filing date: 2013-07-08
Publication date: 2015-01-15

Abstract

The present invention relates to a ceramic inkjet ink suitable for printing on ceramic substrates such as glass comprising: a) 20-70 wt. % of a glass frit composition which is a zinc oxide and/or bismuth oxide based glass frit composition comprising 20-60 wt. % SiO₂, 3-30 wt % B₂O₃, 10- 40 wt. % ZnO and/or 10-70 wt. % Bi₂O₃ of the total weight of the zinc oxide and/or bismuth oxide based glass frit composition wherein the glass frit has the form of particles having an average size distribution in the range from 1.2 μm to 3 μm;b) 0-30 wt % of pigment; c) 20-70 wt % of a carrier, and the manufacturing method thereof. Further, the present invention relates to a glass frit composition and the manufacturing method thereof. Furthermore, the present invention relates to an inkjet process.

Description

CERAMIC INKJET INK

The present invention relates to a ceramic inkjet ink and the manufacturing method thereof for printing on ceramic substrate such as glass. Further, the present invention relates to a glass frit composition and the manufacturing method thereof. Furthermore, the present invention relates to an inkjet process.

Traditionally, inorganic ceramic paints (containing glass frit and inorganic pigments) are printed on ceramic surfaces by silk-screen, roller coating, curtain coating and spray. Typical paint viscosities for such applications are in

100-lOOOs mPa.s (system dependent). These ceramic paints have high solid contents (> 50%) and particle size up to 10-20 μπι.

Digital printing ceramic paints are being explored with limited success. Standard commercial inkjet systems have tighter ink guidelines in terms of both physical and

chemical properties to meet printhead and jetting criteria. Most industrial inkjet printheads require low fluid

viscosity (less than 50 mPa.s) in order to eject drop. The high solid concentration and particle size in the ink is also an issue in terms of nozzle blockage and reliable jetting. For reliable jetting, typical drop on demand inkjet printhead require ink bulk viscosity of 6-20 mPa.s, a surface tension of 20-40 mN/m, a highly stable

particle/pigment size which is commonly less than 1 μηι and a solid content below 20 wt . %.

Accordingly, it is a goal of the present invention to provide a ceramic inkjet ink with the requested bulk

viscosity and surface tension which comprises particles with an average size distribution of more than 1 μηι and with a solid content higher than 20 wt. % which does not incur the drawback of nozzle blockage and therefore provides a

reliable jetting.

This goal, amongst other goals, is achieved by the ceramic inkjet ink composition according to the present invention. In particular, the ceramic inkjet ink composition according to the present invention comprises:

a) 20-70 wt . % of a glass frit composition (which is a

zinc oxide and/or bismuth oxide based glass frit composition) comprising 20-60 wt . % S1O₂, 3-30 wt % B₂0₃, 10-40 wt. % ZnO and/or 10-70 wt . % Bi₂0₃ of the total weight of the (zinc oxide and/or bismuth oxide based) glass frit composition wherein the glass frit has the form of particles having an average size distribution in the range from 1.2 μιη to 3 μιη;

b) 0-30 wt % of pigment; and/or

c) 20-70 wt % of a carrier.

The ceramic inkjet ink composition according to the present invention has suitable properties for inkjet printing. The ceramic inkjet ink composition according to the present invention can be used for printing on any substrate, in any printing conditions. The substrate can be for example glass, ceramic tiles. The ceramic inkjet ink composition according to the present invention can be used in commercial drop on demand inkjet devices.

In the context of the present invention, the ceramic inkjet ink composition comprises ' a glass frit composition'. The ceramic inkjet ink comprises advantageously one glass frit composition, or the ceramic inkjet ink can comprise more than one glass frit composition, such as two, three, or four different glass frit compositions. Accordingly, the ceramic inkjet ink composition can comprise 'one or more glass frit composition'. The glass frit composition is based on zinc oxide, or on bismuth oxide, or on zinc oxide and bismuth oxide. In other words, the glass frit composition respectively comprises an amount of zinc oxide in weight percent of the total weight of the glass frit composition, or an amount of bismuth oxide in weight percent of the total weight of the glass frit composition, or an amount of zinc oxide and an amount of bismuth oxide in weight percent of the total weight of the glass frit composition.

In the context of the present invention, the glass frit composition has the form of particles. The shape of the particles can be any shape. The size of the particle is defined by their "average particle size distribution".

In the context of the present invention, the term "average particle size distribution" is to be understood as defining the relative amount, typically by mass, of particles present according to size. In the context of the present invention, the average particle size distribution is also designated as D₉₀ (defining the distribution of the size (or diameter) of 90 percent of the particles) .

Advantageously, in the present invention, the glass frit composition is a glass frit which has the form of particles having an average size distribution in the range from 1.2 μιη to 3 μιτι, more advantageously from 1.2 μιη to 2.5 μιτι, even more advantageously from from 1.2 μιη to 2.0 μιτι, yet more advantageously from 1.5 μιη to 2.0 μιτι, most advantageously at about 1.7 μιη (e.g. 1.7 μιη +/- 0.25 μιη) . In other words, in the context of the present invention, most of the particle size, or dimensions, are within the above-mentioned range. In the context of the present invention, the term "about" is to be understood as within the boundaries of experimental error, i.e. +/- a certain value, such as 1% to 15% of the given parameter.

In the context of the present invention, the glass frit composition comprises 20-70 wt . % of one glass frit composition, advantageously 20-60 wt . %, more advantageously 30-60 wt . %, most advantageously 45-60 wt . % . The glass frit composition of the present invention is a zinc oxide and/or bismuth oxide based glass frit composition. The glass frit composition according to the present invention comprises 20- 60 wt. % Si0₂, 3-30 wt % B₂0₃ and 10-40 wt . % ZnO, or 10-70 wt. % Bi₂0₃, or 10-40 wt . % ZnO and 10-70 wt . % Bi₂0₃, of the total weight of the zinc oxide and/or bismuth oxide based glass frit composition.

Specifically, the glass frit composition can have the following formulations:

Formulation 1: bismuth based

- 20-60 wt. % Si0₂,

- 30-70 wt. % Bi₂0₃,

- 3-10 wt. % B₂0₃,

- 3-10 wt. % Ti0₂,

- 2-8 wt. % Na₂0,

- 0-4 wt . % Li0₂, advantageously 0.1-4 wt . % Li0₂.

Optionally, other oxides such as K₂0, CaO, ZnO, MgO, BaO, P₂05, ZrO, A1₂0₃ can be present in an amount of less than 10 wt . % .

Formulation 2: zinc based

- 20-60 wt. % Si0₂,

- 10-40 wt. % ZnO,

- 10-30 wt. % B₂0₃,

- 3-8 wt. % Ti0₂,

- 10-15 wt. % Na₂0,

- 3-6% wt. % K₂0,

- 0-4 wt . % Li0₂, advantageously 0.1-4 wt . % Li0₂

- 2-5% wt. % CaO.

Optionally, other oxides such as MgO, BaO, A1₂0₃, P₂0₅, ZrO can be present in an amount of less than 10 wt. %. Formulation 3

- 20-60 wt. % Si0₂

- 10-30 wt. % Bi₂0₃,

- 5-30 wt. % ZnO,

- 10-30 wt. % B₂0₃,

- 3-8 wt. % Ti0₂,

- 10-15 wt. % Na₂0,

- 3-6 wt. % K₂0,

- 0-4 wt . % Li0₂, advantageously 0.1-4 wt . % Li0₂

- 2-5 wt. % CaO.

Optionally, other oxides such as MgO, BaO, A1₂0₃, P₂0₅,

ZrO.can be present in an amount of less than 10 wt. %.

Advantageously, the glass frit composition used in the ceramic inkjet ink composition is the glass frit composition described hereafter.

In the context of the present invention, the pigment can be any inorganic colour pigment. The inorganic pigments powder is produced by high temperature calcination. The pigments can be oxides of metals such as cobalt, iron, nickel, copper, titanium dioxide for different colours.

Examples of inorganic pigments used in the formulations can be Cobalt chromite Blue green Spinel (Shepherd Blue 211, Shepherd Blue 30C527), Cobalt Aluminate Blue Spinel

(Rockwood Cobalt Blue 28, Rockwood Cobalt blue 419, Shepherd Blue 214, Shepherd Blue 299, Shepherd Blue 385, Shepherd Blue 424), Iron oxide (SiOF 1020, SiOF 3029M, SiOF 2019M, SiOF 3021M, Bayferrox 120, Bayferrox 180, Rockwood Ferroxide 206M) , Maganese Ferrite (Rockwood FM2400), Nickel Antimony Titanium Yellow Rutile (Shepherd Yellow 25, Shepherd Yellow 195), Copper Chromite Black Spinel (Shepherd Black 1 GM, Shepherd Black 430), manganese ferrite (Rockwood FM2400), White: Huntsman Ti0₂ A-HR; DuPont Ti-Pure® R-101, DuPont Ti- Pure® R-102, Green: Cobalt Titanate Green Spinel (Shepherd Green 223), Cobalt Chromite Blue Green Spinel (Shepherd Green 187 B) .

These pigments are heat resistant inorganic pigments, chemically inert and stable to ultraviolet light. They have high durability and hiding power.

The pigment type, size and its particle interaction can be adjusted during formulation to meet the final tempered colour of the ink as well as fulfil the requirement of hiding power (optical property used to describe the light- scattering efficiency of a white pigment) and opacity

(degree to which light is not allowed to travel through) . In the context of the present invention, the term "carrier" is to be understood as a liquid or organic solvent, such as at least one organic solvent, such as at least two organic solvents. Advantageously, the carrier is a mixture of two or more different organic solvents which are low volatility solvents to prevent ink drying in the nozzle and prevent nozzle blockage. They can also be high volatile solvent to enhance drying post landing and prevent ink bleed/spread . Examples of solvents can be alcohols, such as Methyl alcohol, Ethyl alcohol, propyl alcohols, butyl alcohols. Glycol: Methyl glycol (MG) , Ethyl glycol, propyl glycol, Butyl glycol (BG) , and/or glycol ether, such as Methoxy propanol (PM) , Ethoxy propanol (EP) , Diacetone propanol (DAA) , Methoxy butanol, Dipropylene glycol monomethyl ether (DPM) , Tripropylene glycol methyl ether (TPM) , propylene glycol mono methyl ether (PM) , di or tri Propylene glycol mono propyl ether (DPnP, TPnP) , Butyl diglycol (BDG) and/or esters such as Methyl acetate, Ethyl acetate (ETAC) , Propyl acetate ( IPAC) , Butyl acetate (BUAC) , Methoxy propyl acetate (PMA) , Ethyl-3-ethoxy-propanol (EEP) and/or ketones such as Acetone, Methyl ethyl ketone (MEK) , Methyl butyl ketone, cyclohexanone, and/or aromatics such as Toluene, Xylene, solvent Naptha, and/or aliphatics, such as Cyclohexane, petroleum ether, White spirit, turpentine.

The carrier can also be mixtures of short chain alkane waxes with a low melting point of 40-100°C. It is solid at room temperature. Example of such carrier could be low melting paraffin wax. According to the present invention, if the carrier is a mixture of short chain alkane waxes with a low melting point of 40-100°C, the inkjet ink composition according to the present invention is a wax based inkjet ink.

According to an embodiment of the present invention, the carrier is a mixture of alkanes with short chains, i.e.

short chain alkanes, such as n-alkanes (linear alkanes) with a chain having 25 carbon atoms (C25) or less, preferably 22 carbon atoms (C₂₂) or less, more preferably 21 carbon atoms (C₂₁) or less, more preferably 18 carbon atoms (Cis) or less. Preferably, the n-alkanes have at least 10 carbon atoms, preferably 12 carbon atoms, more preferably 14 carbon atoms. Advantageously, the carrier is a mixture of alkanes with short chains, such as a C₁₀-C25 chain, more advantageously a C10-C22 chain, even more advantageously a Cio-Cis chain, most advantageously a C₁₂-C18 chain. The mixture of alkanes can comprise at least two, at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, or at least ten (or more) different n-alkanes. Additionally, the ceramic ink composition of the present invention can comprise additives in an amount up to

10 wt. %. Accordingly, the ceramic ink composition of the present invention can comprise 0-10 wt . % of one or more additives to meet jetting and substrate requirements. The additives can be chosen from the group consisting of

rheology additives, surfactants, ant i-sett ling/stat ic agents, dispersant, flow and levelling agent,

defoaming/deaeration agents, resins for grip.

According to the present invention, the glass frit

composition and the pigment form a solid content in the range 20-70 wt%, such as 30 to 60 wt%, preferably 40 to 60 wt%, more preferably 40 to 50 wt% of the total weight of the composition. The remaining portion (in wt . %) of the total weight of the composition is the carrier and additives.

According to the present invention, the glass frit

composition and the pigment form a solid content having an average particle size distribution in the range of 1.2 μιη to 3 μιτι, advantageously 1.2 μιη to 2.5 μιτι, more advantageously 1.5 μιη to 2.0 μιη.

The ceramic inkjet ink composition according to the present invention has accordingly an average particle size

distribution in the range of 1.2 μιη to 3 μιη and a solid content up to 70 wt . %. According to the present invention, the ink properties are tightly controlled and optimised to meet printhead and in-flight conditions in order to generate reliable drops, namely:

- a viscosity of 6-20 mPa.s at the jetting temperature and jetting conditions,

- the apparent zero shear viscosity of the ink can be significantly higher than 20 mPa.s at room temperature, - a surface tension of 20-40 mN/m (process and substrate dependent ) ,

- high particle stability for reliable jetting.

Further, the ink properties of the ceramic inkjet ink composition according to the present invention are such, that at jetting, the following is prevented: drop

splattering, bleed and spread after landing on hard surfaces such as glass. Additionally, the edge definition of the printed image during drying and tempering is retained. Furthermore, the ceramic inkjet ink composition according to the present invention is tuned with appropriate

resins/additives to give good grip after drying the ink on the substrate at temperature equal to or above 150°C, for manual handling.

Additionally, the ceramic inkjet ink composition according to the present invention has a high chemical resistance, e.g. resistance to acid, base, UV resistance, a high

mechanical resistance, e.g. scratch, abrasion, durability. Another aspect of the present invention is the glass frit composition comprising:

- 20-60 wt. % Si0₂,

- 3-30 wt % B₂0₃,

- 10-40 wt. % ZnO and/or 10-70 wt . % Bi₂0₃,

- 3-10 wt. % Ti0₂

- 2-15 wt. % Na₂0

- 0-4 wt . % Li0₂, advantageously 0.1-4 wt . % Li0₂.

According to an embodiment of the present invention, the glass frit composition comprises 20-60 wt . % Si0₂ and/or - 30-70 wt. % Bi₂0₃,

- 3-10 wt. % B₂0₃,

- 3-10 wt. % Ti0₂,

- 2-8 wt. % Na₂0,

- 0-4 wt . % Li0₂, advantageously 0.1-4 wt . % Li0₂

According to an embodiment of the present invention, the glass frit composition comprises 20-60 wt . % Si0₂ and

- 10-40 wt. % ZnO,

- 10-30 wt. % B₂0₃,

- 3-8 wt. % Ti0₂,

- 10-15 wt. % Na₂0,

- 3-6% wt. % K₂0,

- 0-4% wt . % Li0₂, advantageously 0.1-4 wt . % Li0₂ and/or - 2-5% wt. % CaO.

According to an embodiment of the present invention, the glass frit comprises 20-60 wt . % S1O₂ and

- 10-30 wt. % Bi₂0₃,

- 5-30 wt. % ZnO,

- 10-30 wt. % B₂0₃,

- 3-8 wt. % Ti0₂,

- 10-15 wt. % Na₂0,

- 3-6 wt. % K₂0,

- 0-4 wt . % Li0₂, advantageously 0.1-4 wt . % L1O₂

- 2-5 wt. % CaO.

According to the present invention, the glass frit

composition has the form of particles having an average size distribution equal to or below 3 μιτι, advantageously equal to or below 2 μιη. The particles have preferably an average size distribution in the range from 1.2 μιη to 3 μιτι, more

preferably in the range from 1.5 μιη to 3 μιη. It may as well be advantageous for the glass frit particles to have an average size distribution of at least 1.2 μιη, more

advantageously at least 1.5 μιτι, most advantageously at least 2.0 μιη.

In any aspect of the present invention, the particle of the glass frit can have any value with the above range, such as about 1.2 μιη, about 1.3 μιτι, about 1.4 μιη, about 1.5 μιτι, about 1.6 μιτι, about 1.7 μιη, about 1.8 μιτι, about 1.9 μιτι, about 2.0 μιτι, about 2.1 μιη, about 2.2 μιη, about 2.3 μιτι, about 2.4 μιη, about 2.5 μιτι, about 2.6 μιτι, about 2.7 μιη, about 2.8 μιη, about 2.9 μιη, about 3.0 μιη.

According to the present invention, the composition of the frit can be fine-tuned during frit preparation to meet the final substrate requirements after tempering (thermal treatment) : frit glass transition temperature is reached to melt the composition material and fuse on to the ceramic surfaces. The glass frit according to the present invention has a high chemical resistance, e.g. resistance to acid, base, UV resistance, a high mechanical resistance, e.g.

scratch, abrasion, durability.

In the context of the present invention, the ceramic inkjet ink composition consists of components a) , b) and c) . In the context of the present invention, the glass frit composition consists of the above mentioned components.

Yet another aspect of the present invention is a method for the manufacture of a glass frit having a composition

according to the present invention, comprising:

1) mixing the components of the glass frit composition;

2) melting the mixed ingredients to obtain a melted mixture;

3) cooling (also designated as quenching) the obtained melted mixture;

4) milling the cooled (quenched) melted mixture by dry- milling to obtain a milled frit having an average particle size distribution of 5-12 μιη, preferably 5-8 μιτι, such as 7-8 μιη;

5) reducing the size of the milled frit obtained in step 4) by wet milling to obtain a frit wherein the particles have an average particle size distribution equal to or below 3 μιη.

In the context of the present invention, melting the

different components of the glass frit composition (step 2) of the method according to the present invention) occurs at the glass transition temperature of the glass frit

composition .

The frit stability and particle size is maintained through multiple grinding steps (steps 4) and 5)) to reduce the particle size below 3 micron: Milling is carried out in two stages: first, dry Milling followed by wet milling: The dried quenched frit is initially milled dry. An example of such unit used in our application is fluidised jet mill. Commercial fluidised jet mill and ultra fine grinding system is used where milling is achieved by particle to particle impact along the gas stream and at the centre of the chamber. The frit is milled to achieve the final size around 7|im.

Further size reduction of jet mill frit is carried out in high speed wet mill with carriers such as glycol ethers or aliphatic hydrocarbons. Dispersants or grinding aids are added to prevent the fine frit particles from re-aggregating during the grinding stage.

In the context of the present invention, milling is to be understood as a process of grinding materials. Dry milling is a milling process occurring without solvent. Wet milling occurs with additives. In the context of the present invention, jet milling is to be understood as a process of using highly compressed air or other gasses, usually in a vortex motion, to impact fine particles against each other in a chamber.

The concentrated premixed jet milled frit is milled in commercial high speed mill with special grinding chamber components such as zirconia, silicon nitrite and/or silicon carbide .

In the context of the present invention, the milling can be carried in batch in multipass operation until the desired particle size is obtained. The final composition is well dispersed frit paste with final particle size equal to, or below 3 μηι.

The definitions and preferences described for the ceramic inkjet ink composition according to the present invention are applicable to the glass frit composition and the method for the manufacture of the glass frit composition according to the present invention.

Still another aspect of the present invention relates to a method for the manufacture of an inkjet ink comprising the steps of :

i) preparing a pigment paste having an average particle size distribution equal to, or below 1 μηι;

ii) preparing a glass frit having an average particle size distribution equal to, or below 3 im;

iii) mixing the pigment paste and the glass frit;

iv) adding a carrier to the mixture obtained after step

iii) in order to obtain a mixture having 30 to 60 wt. % of solid content of the total weight of the mixture; v) filtering the mixture obtained in step iv) and thereby providing an inkjet ink having a viscosity of 6-20 mPa.s at the jetting temperature and jetting

conditions .

In the context of the method for manufacturing the ceramic inkjet ink according to the present invention, additives can be added in steps iii) and/or iv) , such as 0-2 wt . % of surfactant, and/or 0-10 wt . % of dispersants, and/or

0-5 wt . % of one or more additives chosen from the group consisting of deaerating agents, defoaming agents, flow and leveling agents, rheology modifiers. The wt . % given for the additives is to be referred to the total weight of the ceramic inkjet ink mixture frit/pigment/carrier/eventual additives. The additives are commercially available product or specifically tailored to the formulations.

Examples of such additives include one or more compound of the following list:

- surfactant: solution of polyether-modified

polydimethylsiloxane (BYK-301, BYK-302, BYK 306, BYK 337, BYK 341), polyether modified polydimethylsiloxane (BYK-307, BYK 333), solution of a polyester-modified polydimethylsiloxane (BYK-310, BYK-313) solution of polyester-modified

polymethylalkylsiloxane (BYK-315) polyether modified

dimethylpolysiloxane (BYK378);

- dispersant: copolymer with acidic group (Disperbyk 110, Disperbyk 111), Alkylol ammonium salt of Copolymer with acidic groups (Disperbyk-180 ) , solution of high molecular weight block copolymers with pigment affinic groups

(Disperbyk 182, Disperbyk 184, Disperbyk 190), copolymer with pigment affinic groups (Disperbyk 191, Disperbyk 192,

Disperbyk 194, Tego Dispers 7502, Tego Dispers 752W) , block- copolymer with pigment affinic groups (Disperbyk 2155), solution of alkylol ammonium salt of a higher molecular weight acidic polymer (Anti-terra-250 ) , structured acrylate copolymer with pigment affinic groups (Disperbyk 2010

Disperbyk 2015), polyvinylpyrrolidone (PVP K-15, PVP K-30, PVP K-60), polymeric hyperdispersant (Solsperse J930,

Solsperse J945, Solsperse J955, Solsperse J980Solsperse J981, Solsperse J944, Solsperse J950, Solsperse J955 ) ;

- flow and leveling agents: Polymeric, non silicone (Dynoadd F-l, Dynoadd-FlOO, Dyonadd F-101, Dynoadd -F102), solution of polyester modified acrylic polymer (Dynoadd F201), special dimethyl polysiloxanes (Tego Flow ATF 2), polyether siloxane copolymer (Tego Glide 100, Tego Wet 240);

- deaerating/defoaming agents: Silicone free (BYK 051, BYK 052, BYK 053, BYK 054, BYK 055, BYK 057, BYK 1752, BYK-A 535), emulsion of hydrophobic solids, emulsifiers and foam destroying polysiloxanes (BYK-610), Fluoro modified silicone defoamer (Dynoadd F-470), non-silicone anionic (Dynoadd F- 603), organo-modified polysiloxane (Tego Airex 900,

Deaerating organic polymers with tip of silicone (Tego Airex 990, Tego Airex 991), silicone free deaerator (Tego Airex 920), solution of polyacrylate (Tego Flow ZFS 460); - rheology and anti-settling additives: solution of modified urea (BYK 410, BYK 420), solution of urea modified

polyurethane (BYK-425), solution of polyurethane with a highly branched structure (BYK-428), solution of high molecular urea modified polar polyamide (BYK-430, BYK-431), hybridised amide (Disparlon AQH 800), non-ionic polyurethane based thickner (Tego ViscoPlus 3000, Tego ViscoPlus 3030, Tego Viscoplus 3060), fumed silica (Aerosil);

- resins: Hydroxypropyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, nitrocellulose, methacrylic copolymer .

Advantageously, when carrying out the method according to the present invention, the amount of glass frit is 20-70 wt %, preferably 20-60wt. % of the total weight of the mixture frit/pigment/carrier/eventual additives, the amount of inorganic pigment is 0-30 wt % of the total weight of the mixture frit/pigment/carrier/eventual additives, the carrier is 20-60 wt . % of the total weight of the mixture

frit /pigment/carrier/eventual additives .

According to the present invention, the pigment paste in step i) is prepared by reducing the size of pigment

particles to an average size distribution equal to or below 1 μιη, preferably equal to or below 0.5 μηι, by milling and grinding in the presence of a dispersant and a carrier.

Commercially available inorganic pigments powders have size up to 5 μηι and are unsuitable inkjet applications. For optimal colour brilliance and failure free printing, pigmented particle should be ideally below 1 μηι, preferably below 0.5 μιη.

According to the method of the present invention, the pigment size is reduced to an average size distribution equal to or below 1 μηι by milling and grinding in the presence of dispersant and carrier. The pigment inter- medium paste must have defined particle size with a narrow particle size distribution and should be very stable.

The concentrated pigment paste (50-80 wt . % of the pigment paste) is then prepared using bead/ball mill resulting in a well dispersed pigment with a size less than 1 μηι. The mechanical grinding in agitator bead mills produce particles in sub-micron range with a narrow particle size

distribution .

Improper choice of the additive and milling process results in unstable pigments resulting in hard sedimentation in a matter of days .

The most suitable additives for each pigment are determined through a series of dosage ladder tests. The selection of effective additives, optimum dosage and the milling process conditions are based on meeting criteria such as good affinity to pigments, excellent wetting and stabilising of particle during milling, reduction of inter particle

attraction, particle size reduction and good stabilisation of particle, viscosity reduction, compatibility with the medium and sedimentation stability of the final product. The compatibility of the additive with the medium is also evaluated throughout the final drying and tempering stages to prevent any aggregation or flocculation .

Pigment paste is prepared in two stages: (A) the primary mixing is done with a standard mixer to achieve homogenous mixture of the pigment, solvent, dispersant and other additives. The resultant pre-mix is then subjected to (B) secondary grinding in a ball/bead mill or a roller mill. Dispersants prevent the fine pigment particles from re- aggregating during the grinding stage.

According to the present invention, the pigment paste comprises 50-80 wt . % pigment, 3-10 or 3-20 wt . % dispersant and 10-50 wt . % carrier. According to the present invention, the glass frit in step ii) is the glass frit manufactured in the method according to the present invention.

According to the present invention, additives can be added with the carrier in step iv) .

The definitions and preferences described any aspect of the present invention are applicable to the method for the manufacture of the ceramic inkjet ink composition according to the present invention.

Another aspect of the present invention is a jetting process comprising :

I) jetting the inkjet ink composition according to the

present invention or the inkjet ink obtainable by the method according to the present invention, onto a substrate such as a ceramic, preferably glass;

II) increasing the viscosity of the jetted ink on the

substrate such as ceramic, preferably glass.

Accordingly, the present invention relates to the use of the inkjet ink composition according to the present invention or the inkjet ink obtainable by the method according to the present invention for inkjet printing onto a substrate such as a ceramic, preferably glass.

The definitions and preferences described for any aspect of the present invention are applicable to the jetting process according to the present invention.

The properties of the ceramic inkjet inks according to the present invention are the following. The viscosity is 6-20 mPa.s at the jetting temperature and conditions (printhead channel flow rate, print frequency and drop speed) . The jetting temperature is 5-60°C.

Ideally a Newtonian fluid (no change in viscosity over the range of shear rates) is preferable for most applications. The ink rheology is deliberately tailored to achieve

controlled shear thinning behaviour to reduce particle sedimentation during storage and drop spread/bleeding on glass substrate.

Static surface tension is 20-40 mN/m to meet the printhead and substrate requirements.

The specific additives are incorporated to adjust the dynamic properties of the ink to give uniform distribution of the particles during drying, thus preventing particle migration towards the edges or to the centre.

Another aspect of the present invention relates to a method for the manufacture of hot melt inkjet printing comprising of paraffin wax as the main carrier. The frit and pigments are milled and stabilised in the molten paraffin with a combination of dispersants. The carrier could also be a mixture of paraffin wax and aliphatic and /or aromatic solvents at different proportions. An example of such mixture could be paraffin wax and kerosene.

The ink is solid at room temperature and is heated to change its phase to liquid prior to entering the printhead. The printhead ejects hot melt above the ink melting temperature. One of the advantage of such ink is instantaneous

solidification upon contact with the substrate thus avoiding drop spread.

The jetting temperature of the wax based ink can be above the wax melting temperature of 40-100°C depending on the type of wax.

The present invention is illustrated, without being limited, by the following figures and Examples. Reduction in glass frit particle size. Jet milled : Frit size dropped from lump particle to around 7 μιη Dg o . Wet milled of jet milled frit to reduce particle size from 7 μιη to 3 μιη. The particle size analysis has been performed using a Malvern Instruments

Mastersizer 2000.

Ceramic inkjet inks according to the present invention .

Inkjet printing of the ink composition according to the present invention after tempering .

Influence of mixing steps on the final stability : pictures taken after one month. Both formulation have the same composition

(a) high shear mixing; (b) bead mixing.

Influence of additives on the final

stability: pictures taken after one week. Both compositions have the same mixing protocol: (a) with non optimized additives;

(b) with optimized additives.

Viscosity profile of ceramic inkjet black 1 and black 2 (higher thixotropic behavior) at the jetting condition.

Effective control of ink properties and composition to eliminate ink bleeding, fingering instability formation on glass surfaces (a) colour bleeding/spread and fingering instability formation; (b) optimal effect .

Effective control of ink properties to prevent particle migration during drying (a) particle migration towards edges; (b) pigment distribution during drying.

Examples

Example 1 : pigment compositions for wet milling Recipe 1 : Black pigment paste 1

Pigment: Black = 80%

Dispersant Disperbyk 180: 4%

Carrier: dipropylene glycol methyl ether = 16%

Recipe 2 : Black pigment paste 2

Pigment: Black = 52%

Dispersant Disperbyk 180: 8%

Carrier: Butyl diglycol = 40%

Recipe 3 : Black pigment paste 3

Pigment: Black = 52%

Dispersant Disperbyk 180 : 8%

Carrier: Butyl diglycol = 37%

Resin: Hydroxypropyl cellulose = 3%

Recipe 4 : Blue pigment paste

Pigment: Blue = 60%

Dispersant: Solsperse J955: 10%

Carrier: dipropylene glycol methyl ether = 30%

Recipe 5 : Red pigment paste

Pigment: Red = 60%

Dispersant: Tego Dispers 752W: 7%

Carrier: Butyl diglycol = 33%

Recipe 6 : White pigment paste

Pigment: Titatnium dioxide A-HR = 70% Dispersant: Disperbyk 190: 5%

Carrier: Butyl diglycol = 25%

For small batch, inkjet medium components (as specified in the above example) are milled in a bead/ball mill mixer.

The components are vigorously shaken in an enclosed ceramic container containing ziroconia grinding beads resulting in well dispersed pigment paste and with a final particle size below 1 μιη.

For larger quantities, high speed agitator beads mill is utilised. In our case, the premixed pigment paste is grinded in a horizontal high speed mill with Zirconia grinding chamber in multi-pass operations for a fixed time. This resulted in a highly stable concentrated pigment paste with no or minimal sedimentation with particle size below 1

Example 2 :

The specific composition and formulation procedure for wet milling of the frit used here is described below.

Sample 1 : Wet milled frit Fl .0

Components

• Jet Mill frit: Frit 1 =65%

· Polyvinylpyrrolidone =2%

Butyl diglycol = 33%

Sample 2 : Wet milled frit F2.0

Components

• Jet Mill frit: Frit 2 = 70%

· Disperbyk 180 = 3%

• Butyl diglycol = 27%

The three components are initially mixed in a high shear mixer and then milled in horizontal high speed mill with Zirconia grinding chamber in multi-pass operations for fixed time. This resulted in a highly stable frit with no or minimal sedimentation with particle size up to 3 lm.

The figure 1 shows the frit size profile as a result of jet milling and wet milling.

Example 3 : Ceramic inkjet ink composition according to the present invention and method for the manufacture thereof. The composition of the ceramic inkjet inks according to the present invention is the following:

1) Frit (Bismuth /Zn or hybrid based) : 20-60 wt . %

2) Inorganic pigment: 0-30 wt . %

3) Carrier (two or more) : 20-60 wt . %

4) Additives: Surfactants 0-2 wt . %, dispersants 0-5 wt . %, other additives 0-5 wt . %, such as

Deaerat ing/Defoaming agent

Flow and levelling agents

Rheology modifiers

The physical properties of such a composition are:

η =6-20 mPa.s at 5-60°C

a₂₅°c = 20-40 mN/m

Dgo < 3 μπι

The manufacture process of such ink is the following:

1. Prepare frit paste

a. Mix additives and carrier and add Jet milled frit. b. Pre-mix for 30 minutes.

c. Further carry out high speed wet mill for set time until the desired final particle size is obtained. 2. Separately prepare pigment paste as described in section 4. For example,

a. Premix pigment, dispersant and carrier.

b. Add pre-mixed pigment in a bead mixer and mix until the desired particle size is obtained.

3. Mix wet milled frit and pigment paste at right proportion in bead mixer resulting in the concentrated mixture of frit and pigment solution.

a. Improper mixing leads to flocculation of white frit on the top, which should be avoided.

4. Add top up carrier (which could be one or combination of other organic solvents) with additives such as surfactant, thixotropic additives, flow and levelling additives) and further mix for a fixed time.

5. The final ink is filtered without clogging the filter and without significantly changes in the solid content.

Example 4 : Black ceramic inkjet inks according to the present invention.

The exact composition and properties of black ceramic inkjet inks are presented in the table below.

Inkjet Black 1:

ID F1038-4 Compositions Wt Solid Properties

(gm) %

Fl .0 Wet mill Frit 1.0 57.2 50% ΐ|25°0 = 22 mPa . s ,

P32- Black pigment paste 2 24.3 <725°C = 28 4 mN/m

Surfactant BYK 378 0.3 Dg o = 1.8

Butyl glycol, 18.2

Butyl acetate Inkjet Black 2 (with thixotropic additives)

Formulation steps:

1. Mix wet mill frit and pigment paste in bead mill mixer for 20 min.

a. This results in homogeneous mixing of frit and pigment .

2. Add carrier and other additives and bead mill for 10 min .

3. Filter inks using micrometer filter. The figure 2 shows the photographs of the sets of final ink et inks .

Example 5 : Jetting samples

The jetting of these inks at the jetting temperature of 30-

45°C with standard commercial inkjet printing system showed reliable jetting. The figure 3 shows the photograph of the image of final tempered samples.

Overall performance of the inks were very good satisfying low mistings and satellites and good jetting reliability.

No nozzle blockage, print failures was observed.

Printing on the glass was performed in single pass and multipass (several layers) in order to achieve sufficient thickness to meet the final requirements such as optical density after high temperature heat treatment or tempering at temperature above 500°C.

Final printed pattern on the glass showed good colour, hiding power and good mechanical and chemical resistance.

Example 6 : Influence of choice of additive and mixing step on ink properties.

Non-optimised mixing steps results in non-homogeneous mixing between frits and pigments and hence sedimentations of pigments (figure 4) .

Additives are tailored to specific pigments. Non- optimisation of additives results in non-homogeneous mixing between frits and pigments and hence sedimentation and flocculation (figure 5).

The properties of the ceramic inkjet inks according to the present invention are the following. The viscosity is 6-20 mPa.s at the jetting temperature and conditions (printhead channel flow rate, print frequency and drop speed) . The jetting temperature is 5-60°C. The jetting temperature of wax based ink is above the wax melting temperature in the range of 40-100°C.

A Newtonian fluid (no change in viscosity over the range of shear rates) is preferable for most applications

• For low solid loadings and where particle

stability/sedimentation is not an issue, or

· For drops printed on soft or porous surfaces such as ceramic tiles.

The ink rheology is deliberately tailored to achieve

• Low shear viscosity (at shear rates < 50 1/s) is

deliberately maintained at least several times greater than that of the high shear steady viscosity of 6-20 mPa.s (at shear rate > 1000 1/s) at the jetting temperature (figure 6) .

o This delays/prevent ink sedimentation during storage .

o The viscosity of the ink in the printhead channel prior to jetting drops to 6-20 mPa.s meeting printhead bulk viscosity requirements creating optimum condition for drop ejection and generate reliable drop in-flight,

o After the drop lands on the substrate, the viscosity is quickly increased thus

^■ minimising drop spread upon impact

^■ maintaining drop edge definition Prevent ink fingering/dendrite instability formation which sometime forms as a result of air-stream caused by fast linear carriage movement of printhead during printing or marangoni stress, or contaminated glass substrate (Figure 7) .

• The static surface tension satisfies the drop contact angle on substrate.

· The choice of the surfactant is carefully controlled to achieve final static value.

Uniform distribution of the particles during drying is obtained, thus preventing particle migration towards the edges or to the centre (Figure 8) .

Claims

1. Ceramic ink et ink suitable for printing on ceramic substrates such as glass comprising:

a) 20-70 wt . % of a glass frit composition comprising

20-60 wt. % Si0₂, 3-30 wt % B₂0₃, 10-40 wt . % ZnO and/or 10-70 wt . % B1₂O₃ of the total weight of the glass frit composition wherein the glass frit has the form of particles having an average size distribution in the range from 1.2 μιη to 3 μιη;

b) 0-30 wt % of pigment;

c) 20-70 wt % of a carrier.

2. Ceramic inkjet ink composition according to claim 1, wherein the glass frit composition and the pigment form a solid content in the range 30-60 wt% of the total weight of the composition.

3. Ceramic inkjet ink composition according to claim 1 or 2, wherein the glass frit composition and the pigment form a solid content having an average particle size distribution in the range of 1.2 μιη to 3 μιη.

4. Ceramic inkjet ink composition according to claim any one of claims 1 to 3, wherein the carrier is a mixture of alkanes with a Cio-Cis chain.

5. Glass frit composition comprising:

- 20-60 wt. % Si0₂,

- 3-30 wt % B₂0₃,

- 10-40 wt. % ZnO and/or 10-70 wt . % Bi₂0₃,

- 3-10 wt. % Ti0₂

- 2-15 wt. % Na₂0 - 0-4 wt. % Li0₂.

6. Glass frit composition according to claim 5, wherein the composition comprises 20-60 wt . % Si0₂ and

- 30-70 wt. % Bi₂0₃,

- 3-10 wt. % B₂0₃,

- 3-10 wt. % Ti0₂,

- 2-8 wt. % Na₂0,

- 0-4 wt. % Li0₂;

7. Glass frit composition according to claim 5, wherein the composition comprises 20-60 wt . % Si0₂ and

- 10-40 wt. % nO,

- 10-30 wt. % B₂0₃,

- 3-8 wt. % Ti0₂,

- 10-15 wt. % Na₂0,

- 3-6% wt. % K₂0,

- 0-4% wt. % Li0₂,

- 2-5% wt. % CaO.

8. Glass frit composition according to claim 5, wherein the composition comprises 20-60 wt . % Si0₂ and

- 10-30 wt. % Bi₂0₃,

- 5-30 wt. % ZnO,

- 10-30 wt. % B₂0₃,

- 3-8 wt. % Ti0₂,

- 10-15 wt. % Na₂0,

- 3-6 wt. % K₂0,

- 0-4 wt. % Li0₂,

- 2-5 wt. % CaO.

9. Glass frit composition according to any one of claims 5 to 8, wherein the glass frit composition has the form of particles having an average size distribution equal to or below 3 μιη.

10. Method for the manufacture of a glass frit having a composition according to claims 5 to 9, comprising:

1) mixing the components of the glass frit composition;

2) melting the mixed components to obtain a melted mixture;

3) cooling the obtained melted mixture;

4) milling the cooled melted mixture by dry-milling to obtain a milled frit having an average particle size

distribution of below 8 μιτι, preferably from 5 to 8 μιη;

11. Method for the manufacture of an ink et ink comprising the steps of :

iii) mixing the pigment paste and the glass frit;

iv) adding a carrier to the mixture obtained after step

iii) in order to obtain a mixture having 30-60 wt . % of solid content of the total weight of the mixture;

v) filtering the mixture obtained in step iv) and thereby providing an inkjet ink having a viscosity of 6-20 mPa.sat the jetting temperature and jetting conditions.

12. Method according to claim 11, wherein the pigment paste is prepared by reducing the size of pigment particles to an average size distribution equal to or below 1 μιη by milling and grinding in the presence of a dispersant and a carrier.

13. Method according to claim 11 or 12, wherein the pigment paste comprises 50-80 wt . % pigment, 3-20 wt . % dispersant and 10-50 wt . % carrier.

14. Method according to any one of claim 11 to 13, wherein the glass frit in step ii) is the glass frit manufactured in the method according to claim 10.

15. Method according to any one of claims 11 to 14, wherein additives are added with the carrier in step iv) .