CERAMIC INKS FOR INKJET PRINTERS
FIELD OF THE INVENTION
The present invention relates to ceramic inkjet inks and to a method for
decorating green or fired ceramic bodies by the use of inkjet printing.
The ceramic inkjet inks of the invention comprise ceramic inorganic pigments
having average particle size between 0.1 and 0.8 mih dispersed in an organic
medium, and a dispersant which is the reaction product of a
polyethyleneimine and a homo- or co-polyester based on lactic acid.
BACKGROUND OF THE ART
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 a 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 no 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.
Different techniques are used to transfer images to the ceramic substrate: i.e.
screen printing and photogravure (commonly referred to as rotocolor). These
technologies require flat substrate or with minimum roughness, they are
suitable for mass production, but have very limited flexibility of new design
set up and changeover between designs.
Another technique of printing decoration on ceramics is digital printing by
inkjet technique.
Digital printing and decoration by inkjet technique is widely used in multiple
sectors, such as graphic arts, textile industry, industrial marking and it is well
known, both referring to printing equipments and also to the inks used.
Peculiarly in ceramic applications, the thermal treatment, which is required
once the substrate has been printed, makes the conventional inks, that are used
in the other applications and are mainly based on organic pigments, unsuitable
for use.
Two kind of inks for inkjet printing of ceramics are known: inks constituted
by solutions of metallic cations and inks based on dispersions of inorganic
pigments.
Inorganic pigments used for traditional decoration in ceramic, such as screen
printing and photogravure, have average particle size above 1 m .
When inkjet inks based on dispersions of inorganic pigments are concerned, it
is mandatory that the inorganic pigments are well dispersed in the liquid
medium and possess nano-scale dimensions (i.e. below 1 mitc in diameter), for
the ceramic inkjet ink flows through small nozzles (30-100 m h in diameter) at
high speed.
Nano-scale dimensions of the inorganic pigments are usually obtained by
milling with microspheres the pigments, pre-dispersed in the medium, in the
presence of a milling aid.
Examples of ceramic inkjet inks based on dispersions of inorganic pigments
in polar organic mediums are described in EP 2159269, WO 2006/126189,
EP 1840178; the inks are genericaliy said to contain anti-settling and/or
dispersing agents.
Nonetheless, there is still the industrial need for improved ceramic inkjet inks
based on inorganic ceramic pigments having low viscosity, solid particle size
below 0.8 Dm, long shelf life and that can be printed on ceramic surfaces and
passed through a high temperature kiln to form a permanently glazed print.
The reaction products of polyamines and carboxyl terminated polyesters with
formation of amidic and/or salt linkages are known products that belongs to a
wide class of dispersants, which have been described in many patents; by way
of example we cite: US 4,224,212, US 4,861,380, US 5,700,395, US
6,197,877 and US 7,008,988. Such wide class of dispersants is generally
suitable for use as dispersing agents for various solids in organic liquids.
JP 2008184535 describes a reaction product of polyethylenimine with a copolyester
of caprolactone and lactic acid as dispersant mainly for the
preparation of light filters.
Nonetheless, none of the above cited documents suggests that the reaction
product of a polyethyleneimine and a homo- or co-polyester based on lactic
acid may be suitable as adjuvant for the preparation and stabilization of inkjet
inks for ceramic.
It has now been found that the reaction product of a polyethyleneimine and a
homo- or co-polyester based on lactic acid can conveniently be used in the
preparation of ceramic inkjet inks for inkjet printing machines.
Surprisingly, the reaction product of a polyethyleneimine and a co-polyester
based on lactic acid, is perfectly suitable, in the milling phase, to fluidize the
pre-dispersed inorganic pigments allowing their rapid milling and to
subsequently prevent agglomeration and sedimentation of the nano-scale
inorganic pigments in the final ink.
SUMMARY OF THE INVENTION
In one aspect, the invention is a ceramic inkjet ink comprising a ceramic
inorganic pigment, an organic medium and a dispersant which is the reaction
product of a polyethyleneimine and a homo- or co-polyester, based on lactic
acid, of formula (1)
R-[(-O-A-CO) -(-O-CH(CH 3)-CO)m-]-OH (1)
wherein:
R is hydrogen or a polymerization terminating group;
A is a linear or branched alkylene radical deriving from a hydroxycarboxylic
acid having between 2 and 20 carbon atoms or lactone thereof;
n and m are integers,
wherein said ceramic inorganic pigment has average particle size between 0.1
and 0.8 .
In another aspect, the invention is a method for decorating green or fired
ceramic bodies by inkjet printing that comprises the following steps:
i . a ceramic inkjet ink comprising a ceramic inorganic pigment having
average particle size between 0.1 and 0.8 pm is prepared by milling an
inorganic pigment having initial average particle size between 1.0 and
10.0 pm in an organic medium in the presence of a dispersant which is the
reaction product of a polyethyleneimine and a homo- or co-polyester, based
on lactic acid, of formula (1)
R-[(~O-A-CO) -(-O-CH(CH 3)-CO) -]-OH (1)
wherein:
R is hydrogen or a polymerization terminating group;
A is a linear or branched alkylene radical deriving from a hydroxycarboxylic
acid having between 2 and 20 carbon atoms or lactone thereof;
n and m are integers;
ii. a glaze is spread on the surface of the green or fired ceramic body;
iii. the decoration is made by means of inkjet printing, by using one or more
ceramic inkjet inks 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 OF THE INVENTION
As it is well known, ceramic inorganic pigments are inorganic pigments
dispersed in glass matrixes which are stable and elevated temperatures (up to
about 1300°C) and are used in ceramic processing.
The ceramic inorganic pigments useful for the ceramic inkjet inks of the
invention differ from conventional ceramic inorganic pigments because of
their particle size, which makes them suitable for inkjet applications.
The ceramic inorganic pigment of the ceramic inkjet ink of the present
invention shall exhibit an average particle size (d5 ) of less than 0.8 m h and
preferably from 0.1 to 0.5 miti, most preferably from 0.1 to 0.3 mih , as
measured by laser diffraction particle size analysis.
The average particle size, i.e. the average equivalent diameter, is the diameter
where 50 percent by weight of the particles have a larger equivalent diameter,
and the other 50 percent by weight have a smaller equivalent diameter.
Any of the recognized classes of pigments used in ceramic decoration
(ceramic pigments) may be used as the ceramic inorganic pigment, such as,
for example, zirconates and silicates of Cr, Sn, Ni, Pr, Fe, Co and oxides
thereof, and preferably those ceramic pigments selected from Zr-Pr, Zr-Pr-Si,
Zr-Fe-Si, Ti-Cr-Sb, Co-Al-Zn, Zr-Va-Si, Fe-Cr-Co-Ni, Cr-Ca-Sn-Si, Co-Si,
and Fe-Cr-Zn.
A list of utilizable ceramic pigments may be found in the CPMA
Classification and Chemical Descriptions of the Complex Inorganic Color
Pigments, Fourth Edition (2010), under the use category A.
The organic medium present in the ceramic inkjet ink is preferably a polar
organic medium or a substantially non-polar aliphatic or aromatic
hydrocarbon or halogenated hydrocarbon, including mixtures thereof.
For example, suitable polar media are selected from one of glycol ethers or
glycol ether esters exhibiting a flash point in excess of 75°C, such as
polypropylene glycol, tripropylene glycol monomethyl ether (TPM),
tripropylene glycol butyl ether (TPB), butyl glycol ether acetate.
Examples of suitable non-polar media are long chain aliphatic solvents such
as isoparaffins, commercially available as ISOPAR products from
ExxonMobil Chemical and the corresponding products from BP and Total,
dearomatised aliphatic hydrocarbons, commercially available as EXXSOL
from ExxonMobil Chemical and the corresponding products from Total,
2-isopropylnaphthalene and 2,6-diisopropylnaphthalene.
The preferred organic mediums are tripropylene glycol monomethyl ether and
tripropylene glycol butyl ether.
The dispersant of the disclosure, which is the reaction product of a
polyethyleneimine and a homo- or co-polyester of formula (1), is obtained
from the amidation and/or salification of a linear or branched
polyethyleneamine with the homo- or co-polyester of formula (1).
Branched polyethyleneimines of differing molecular weight are commercially
available, by way of example from BASF (under the trade name Lupasol ®)
and Nippon Shokubai (under the trade name Epomin ®).
Linear polyethyleneimines can be prepared by hydrolysis of poly (N-acyl)
alkyleneimines as described by Takeo Saegusa et al in Macromolecules, 1972,
Vol. 5, page 4470.
The polyethyleneimine is preferably branched and has a weight average
molecular weight from 100 to 600,000, more preferably from 1,000 to
200,000, even more preferably from 1,000 to 100,000 and especially from
1,000 to 70,000.
In formula (1) m is not greater than 100, preferably not greater than 50 and
more preferably not greater than 20, and m is not lower than 5; n is not greater
than 100, preferably not greater than 50 and more preferably not greater than
20 and n can be as low as 0.
When in formula (1) n is different from 0, the co-polyester of formula (1) can
be obtained by random or block polymerization of the hydroxycarboxylic
acids having between 2 and 20 carbon atoms or lactone thereof with lactic
acid.
The homo- or co-polyester based on lactic acid of formula (1) may be
prepared by polymerization of lactic acid and hydroxycarboxylic acids or
lactone thereof at temperature between 150 and 180°C, as described for
example in US 4,224,212; in the preparation of the polyester it is preferred to
include an esteriflcation catalyst such as a tin salt of an organic acid, for
example dibutyl tin dilaurate, a tetra-alkyl titanate, for example
tetrabutyltitanate, a zinc salt of an organic acid, for example zinc acetate, a
zirconium salt of an aliphatic alcohol, for example zirconium isopropoxide,
toluene sulphonic acid or a strong organic acid such as a halo acetic acid, for
example trifluoro acetic acid.
In formula (1), (-0-A-CO) is the residue of hydroxycarboxylic acids or
lactones, such as 12-hydroxydodecanoic acid, 5-hydroxydodecanoic acid, 5-
hydroxydecanoic acid, 4-hydroxydecanoic acid, e-caprolactone and 12-hydroxy
stearic acid.
In case that n is different from 0, the co-polyester may be random or block,
and the molar ratio of lactic acid and the other acid(s) m:n is from 10:1 to
1:10.
In the preferred embodiment the molar ratio of lactic and the other
hydroxycarboxylic acid m:n is from 2 :1 to :2.
The homo- or co-polyester based on lactic acid shall be carboxyl terminated,
and may be initiated with an organic carboxylic acid that can be aromatic,
heterocyclic, alicyclic or preferably aliphatic and is optionally substituted by
halogen, C - -alkoxy or hydroxy groups. Preferably, the organic carboxylic
acid is unsubstituted. When the organic carboxylic acid is aliphatic, it may be
linear or branched, saturated or unsaturated, but is preferably saturated. The
total number of carbon atoms in the initiating organic carboxylic acid can be
as high as 50, but it is preferred that it contains not less than 8 and more
preferably not less than 12 carbon atoms. It is also preferred that the organic
carboxylic acid contains not greater than 30, more preferably not greater than
25 and especially not greater than 20 carbon atoms.
Particularly useful effects have been obtained with homo- or co-polyesters
based on lactic acid having number-average molecular weight between 800
and 2,000 and polyethyleneimine having a number-average molecular weight
of from 1,000 to 70,000.
The dispersant of the invention is obtained by reacting the polyethyleneimine
and the above described homo- or co-polyester based on lactic acid at
temperature between 50 and 250°C and preferably in an inert atmosphere.
Preferably, the temperature is not less than 80°C and especially not less than
100°C and not greater than 150°C.
The weight ratio of homo- or co-polyester based on lactic acid to
polyethyleneimine is preferably from 1 to 100.
At least two moles of polyester shall be attached to each mole of
polyethy lenim ine.
The viscosity of the ceramic inkjet ink is between 5 and 50 mPa*s and
preferably between 8 and 30 mPa*s.
The ceramic inkjet ink typically contains from 5 to 60% by weight of the
pigment, the precise quantity depending on the nature of the pigment and on
the relative densities of the pigment and the organic medium. Preferably the
ceramic inkjet ink contains from 1 to 45% by weight of the pigment.
The content of organic medium is from 30 to 80% by weight based on the
total weight of the ink, preferably from 45 to 80% by weight.
The content of the dispersant in the ink is between 2 and 15% by weight
based on the total weight of the ink, preferably from 4 to 10% by weight.
The ceramic inkjet ink of the invention is prepared by milling a commercial
ceramic inorganic pigment having average particle size between 1.0 and 10.0
m i, in the presence of the organic medium and the reaction product of a
polyethyleneimine and the homo- or co-polyester based on lactic acid of
formula (1).
The pigment, the organic medium and the reaction product of a
polyethyleneimine and homo- or co-polyester based on lactic acid may be
mixed in any order, the mixture then being subjected to a mechanical
treatment to reduce the particles of the pigment to an appropriate size by
milling with milling beads having diameters from 0.1 to 0.5 mm.
When the pigment is milled, the temperature is preferably not greater than
45°C.
The invention is further illustrated by the following examples wherein all
references are to parts by weight unless expressed to the contrary.
EXAMPLES
Preparation of Dispersant A
A mixture of 230.4 parts of ricinoleic acid and 87 parts of a 80%
water solution of lactic acid was stirred, under nitrogen, and heated at 100°C;
vacuum was gradually applied to remove the lactic acid dilution water. The
temperature was decreased to 40°C and 0.6 parts of dibutyl tin dilaurate were
added; the mixture was heated at 170°C for 13 hours removing the
esterification water. The final product was an oil liquid with an acid value of
51.0 mg KOH/g
(Polyester 1).
A mixture of 250.0 parts of Polyester 1 and 19.7 parts of LUPASOL PR 85 15
(polyethylenimine from BASF having MW 2000) was stirred, under nitrogen,
and heated at 120°C for 2 hours. The dispersant was obtained as a viscous
liquid with an acid value of 45.0 mg KOH/g.
Preparation of Dispersant B
A mixture of 218.4 parts of ricinoleic acid and 164.5 parts of a 80% water
solution of lactic acid was stirred, under nitrogen, and heated at 100°C;
vacuum was gradually applied to remove the lactic acid dilution water. The
temperature was decreased to 40°C and 0.7 parts of dibutyl tin dilaurate were
added; the mixture was heated at 180°C for 16 hours removing the
esterification water. The final product was an oil liquid with an acid value of
51.5 mg KOH/g
(Polyester 2).
A mixture of 260.0 parts of Polyester 2 and 20.4 parts of LUPASOL PR
8 15 (polyethylenimine from BASF having MW 2000) was stirred, under
nitrogen, and heated at 120°C for 2 hours. The dispersant was obtained as a
high viscous liquid with an acid value of 48.6 mg KOH/g.
Preparation of Dispersant C
640 parts of a 80% water solution of lactic acid were stirred, under nitrogen,
and heated at 100°C; vacuum was gradually applied to remove the lactic acid
dilution water. The temperature was decreased to 40°C and 1.3 parts of
dibutyl tin dilaurate were added; the mixture was heated at 180°C for 6
hours removing the esterification water. The final product was an hard solid
with an acid value of 54.5 mg KOH/g (Polyester 3).
A mixture of 185.5 parts of Polyester 3 and 14.6 parts of LUPASOL PR
851 (polyethylenimine from BASF having MW 2000) was stirred, under
nitrogen, and heated at 120°C for 2 hours. The dispersant was obtained as an
hard solid with an acid value of 46.6 mg KOH/g.
Preparation of Dispersant D
A mixture of 77.7 parts of e-caprolactone and 76.7 parts of a 80% water
solution of lactic acid was stirred, under nitrogen, and heated at 100°C;
vacuum was gradually applied to remove the lactic acid dilution water. The
tempearture was decreased to 40°C and 0,3 parts of dibutyl tin dilaurate were
added; the mixture was heated at 170°C for 12 hours removing the
esterification water. The final product was an oil liquid with an acid value of
52.0 mg KOH/g (Polyester 4)
A mixture of 150.0 parts of Polyester 4 and ,7 parts of LUPASOL PR
85 15 (polyethylenimine from BASF having MW 2000) was stirred, under
nitrogen, and heated at 120°C for 2 hours. The dispersant was obtained as a
viscous with an acid value of 45.6 mg KOH/g.
Preparation of the Ceramic Inkjet Inks
Four ceramic Inkjet inks were prepared, by using in each a different
dispersant (Dispersant A, Dispersant B, Dispersant C and Dispersant D).
7.8 g of dispersant are stirred and dissolved it in 89.7 g of Dowanol TPM in 5
minutes.
52.5 g of blue pigment of cobalt silicoaluminate are added and mixed for 5
minutes.
The blue pigment has d5 = 2.0 m h, measured by particle size analysis
(Malvern Instruments Mastersizer 2000).
200 g of grinding media (yjz ® Grinding Media 0.3 mm, made of Yttrium
Stabilized Zirconia Grinding Beads, produced by Nikkato Corporation) and
60 g of the mixture prepared as described above are charged in a 125 ml
grinding jar and milled in a planetary ball mill (PM 200 produced by Retsch).
Al the inks prepared with the dispersants of the invention showed a viscosity
at 35°C lower than 30 mPa*s.
The dispersant prepared in the preceding Examples were evaluated by
measuring their solubility in Dowanol TPM, to the particle size of the
pigment measured as d after 3 hours milling and the stability of the
corresponding ceramic inkjet ink was checked after 30 days storage at room
temperature.
Solubility was determined at 20°C at 8% by weight in Dowanol TPM after
stirring with a magnetic stirrer for 5 minutes.
The results are reported in Table 1
Table 1- Solubility
* after heating
The particle sizes after milling (d 0) are reported in Table 2.
Particle size analysis has been performed by using a Malvern Instruments
Mastersizer 2000.
Table 2 - Particle size
Stability was determined by storing the ceramic inkjet inks at room
temperature. Ceramic inkjet inks are considered stable if they do not visually
show any solid sediment 30 days after their preparation.
The inks prepared form Dispersant A, Dispersant B, Dispersant C, Dispersant
D are stable. From the results reported in Tables 1 and 2 the dispersants of
the invention are soluble in the organic medium and their use in millbased ink
preparations give compositions that have particle size distributions suitable
for ink-jet decoration of ceramics. Moreover the dispersants of the invention
give millbased inks that have good stability.
CLAIMS
1. Ceramic inkjet ink comprising a ceramic inorganic pigment, an
organic medium and a dispersant which is the reaction product of a
polyethyleneimine and a homo- or co-polyester of formula (1)
R-[(-0-A-CO) -(-O-(CH)CH 3-CO)ffi-]-OH (1)
wherein:
R is hydrogen or a polymerization terminating group;
A is a linear or branched alkylene radical deriving from a
hydroxycarboxylic acid having between 2 and 20 carbon atoms or
lactone thereof;
n and m are integers,
wherein said ceramic inorganic pigment has average particle size from
0.1 to 0.8 m h.
2. Ceramic inkjet ink according to claim 1 wherein the ceramic inorganic
pigment has average particle size from 0.1 to 0.5 mhi.
3. Ceramic inkjet ink according to claim 1 in which the dispersant is
obtained from the amidation and/or salification of a linear or branched
polyethyleneamine with the homo- or co-polyester of formula (1).
4. Ceramic inkjet ink according to claim 3 in which the homo- or copolyester
of formula (1) is a co-polyester and m:n is from 10:1 to 1:10.
5. Ceramic inkjet ink according to claim 4 in which the homo- or copolyester
of formula (1) is a co-polyester and m:n is from 2:1 to 1:2.
6. Ceramic inkjet ink according to claim 3 in which the homo- or copolyester
of formula (1) has number average molecular weight
between 800 and 2,000 and the polyethyleneimine has a number
average molecular weight of from 1,000 to 70,000.
7. Ceramic inkjet ink according to claim 1 in which the weight ratio of
the homo- or co-polyester of formula (1) to polyethyleneimine is from
1 to 100.
8. Ceramic inkjet ink according to claim 1 containing from 5 to 60% by
weight of the pigment, from 30 to 80% by weight of the organic
medium and from 2 to % by weight of the dispersant.
9. Method for decorating green or fired ceramic bodies by inkjet printing,
comprising the following steps:
i . a ceramic inkjet ink according to any of claims from 1to 8 is
prepared by milling a ceramic inorganic pigment having average
particle size between 1.0 and 10 m h in an organic medium in the
presence of the dispersant which is the reaction product of a
polyethyleneimine and a homo- or co-polyester of formula (1), until
the average particle size of the pigment is between 0. and 0.8 m i;
ϋ . a glaze is spread on the surface of the green or fired ceramic body;
. iii. the decoration is made by means of inkjet printing, by using one or
more ceramic inkjet inks according to point i.;
iv. the obtained substrate is fired at a temperature comprised between
900 and 1250°C for 15-240 minutes.