U.S. patent application number 17/125585 was filed with the patent office on 2021-05-13 for inkjet ink set for preparing conductive layers or patterns.
The applicant listed for this patent is Agfa-Gevaert NV. Invention is credited to Fernando Cortes Salazar.
Application Number | 20210139732 17/125585 |
Document ID | / |
Family ID | 1000005348500 |
Filed Date | 2021-05-13 |
![](/patent/app/20210139732/US20210139732A1-20210513\US20210139732A1-2021051)
United States Patent
Application |
20210139732 |
Kind Code |
A1 |
Cortes Salazar; Fernando |
May 13, 2021 |
INKJET INK SET FOR PREPARING CONDUCTIVE LAYERS OR PATTERNS
Abstract
An inkjet ink set including a silver inkjet ink and a flushing
liquid, characterized in that the flushing liquid comprises at
least 25 wt % of 2-phenoxy ethanol based on the total weight of the
flushing liquid.
Inventors: |
Cortes Salazar; Fernando;
(Mortsel, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Agfa-Gevaert NV |
Mortsel |
|
BE |
|
|
Family ID: |
1000005348500 |
Appl. No.: |
17/125585 |
Filed: |
December 17, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16306975 |
Dec 4, 2018 |
10870773 |
|
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PCT/EP2017/063756 |
Jun 7, 2017 |
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17125585 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D 11/037 20130101;
C09D 11/322 20130101; C09D 11/033 20130101; C09D 11/36 20130101;
B41J 2/1652 20130101; C09D 11/40 20130101; B41M 5/0023 20130101;
C09D 11/52 20130101; B41J 11/002 20130101; C09D 11/326
20130101 |
International
Class: |
C09D 11/52 20060101
C09D011/52; C09D 11/322 20060101 C09D011/322; C09D 11/326 20060101
C09D011/326; B41J 2/165 20060101 B41J002/165; B41J 11/00 20060101
B41J011/00; B41M 5/00 20060101 B41M005/00; C09D 11/033 20060101
C09D011/033; C09D 11/037 20060101 C09D011/037; C09D 11/36 20060101
C09D011/36; C09D 11/40 20060101 C09D011/40 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2016 |
EP |
16173509.7 |
Claims
1-15. (canceled)
16. An inkjet ink set comprising: a silver inkjet ink; and a
flushing liquid; wherein the flushing liquid includes at least 25
wt % of 2-phenoxy ethanol based on a total weight of the flushing
liquid.
17. The inkjet ink set according to claim 16, wherein the flushing
liquid further includes a solvent selected from the group
consisting of propylene carbonate, n-butanol, and
2-pyrrolidone.
18. The inkjet ink set according to claim 16, wherein the flushing
liquid further includes between 5 and 20 wt % of n-butanol based on
the total weight of the flushing liquid.
19. The inkjet ink set according to claim 16, wherein a viscosity
of the flushing liquid is lower than 15 mPas, measured at
25.degree. C. at a shear rate of 1000 s.sup.-1.
20. The inkjet ink set according to claim 16, wherein the silver
inkjet ink includes silver nanoparticles
21. The inkjet ink set according to claim 16, wherein the silver
inkjet ink includes a liquid carrier
22. The inkjet ink set according to claim 21, wherein the liquid
carrier is a high boiling solvent selected from the group
consisting of 2-phenoxy ethanol, 4-methyl-1,3-dioxolan-2-one,
n-butanol, 1,2 propanediol, 4-hydroxy-4-methyl pentan-2-one,
pentan-3-one, 2-butoxy-ethanol, 1-methoxy-2-propanol and mixtures
thereof.
23. The inkjet ink set according to claim 21, wherein the liquid
carrier includes at least 25 wt % of 2-phenoxyethanol and between 5
and 20 wt % of n-butanol.
24. An inkjet printing method of preparing a conductive layer or
pattern comprising the steps of: providing an inkjet ink set
including the silver inkjet ink and the flushing liquid as defined
in claim 16; cleaning a printhead with the flushing liquid; jetting
the silver inkjet ink on a support to form a silver layer or a
pattern on the support; and curing the silver layer or the pattern
to form the conductive layer or the pattern.
25. The inkjet printing method according to claim 24, wherein the
step of curing is performed at a temperature below 150.degree.
C.
26. The inkjet printing method according to claim 24, wherein the
step of curing has a curing time of less than 30 minutes.
27. The inkjet printing method according to claim 24, wherein the
step of curing is performed with near infrared radiation.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an inkjet ink set for
preparing conductive layers or patterns, in particular conductive
silver layers or patterns.
[0002] The invention also relates to a method of preparing the
conductive layers or patterns at moderate curing conditions.
BACKGROUND OF THE INVENTION
[0003] The interest in metallic printing or coating fluids
comprising metallic nanoparticles has increased during the last
decades due to their unique properties when compared to the bulk
properties of a given metal. For example, the melting point of
metallic nanoparticles decreases with decreasing particle size
making them of interest for printed electronics, electrochemical,
optical, magnetic and biological applications.
[0004] The production of stable and concentrated metallic printing
or coating fluids which can be printed, for example by inkjet
printing, or coated at high speed is of great interest as it
enables the preparation of electronic devices at low costs.
[0005] Metallic printing or coating fluids are typically a metallic
nanoparticle dispersion comprising metallic nanoparticles and a
dispersion medium. Such metallic nanoparticle dispersions can be
directly used as a printing or coating fluid. However, additional
ingredients are often added to the metallic nanoparticle dispersion
to optimize the properties of the resulting metallic printing or
coating fluids.
[0006] Typically, after applying the metallic printing or coating
fluids on a substrate, a sintering step, also referred to as curing
step, at elevated temperatures is carried out to induce/enhance the
conductivity of the applied patterns of layers. The organic
components of the metallic printing or coating fluids, for example
the polymeric dispersants, may reduce the sintering efficiency and
thus the conductivity of the applied patterns of layers. For this
reason, higher sintering temperatures and longer sintering times
are often required to decompose the organic components.
[0007] EP-A 2671927 discloses a metallic nanoparticle dispersion,
for example a silver inkjet ink, comprising a specific dispersion
medium, for example 2-pyrrolidone, resulting in a more stable
dispersion without using a polymeric dispersant.
[0008] Unpublished EP-A 14199745.2 (filed 22 Dec. 2014) discloses a
metallic nanoparticle dispersion comprising silver nanoparticles, a
liquid carrier and specific dispersion stabilizing compounds.
[0009] A problem often encountered when using a silver inkjet ink
is so-called clogging of the inkjet printheads. Such clogging of
the inkjet printheads may result in printing defects and may
shorten the lifetime of the printhead.
[0010] It is known to use so-called "flushing" or "washing" liquids
for unclogging inkjet nozzles and cleaning the nozzle plate of the
print head, as well as all the tubing and connections between the
ink tank to the printhead. Such flushing liquids typically comprise
of a solvent or a solvent mixture able to remove efficiently all
inkjet ink residues without affecting the stability of the
printhead. Additionally, the flushing solution must be also
compatible in all its proportions with the employed inkjet ink.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide an
inkjet ink set for preparing conductive layers or patterns, in
particular conductive silver layers or patterns, whereby no or a
minimal amount of printing defects are observed and whereby the
lifetime of the inkjet printheads is improved.
[0012] This object is realized by an inkjet ink set including a
silver inkjet ink and a flushing liquid as defined in claim 1.
[0013] The invention also relates to a method of preparing the
conductive layers or patterns at moderate curing conditions using
the inkjet ink set.
[0014] Further advantages and embodiments of the present invention
will become apparent from the following description and the
dependent claims.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
[0015] The terms polymeric support and foil, as used herein, mean a
self-supporting polymer-based sheet, which may be associated with
one or more adhesion layers, e.g. subbing layers. Supports and
foils are usually manufactured through extrusion.
[0016] The term layer as used herein, is considered not to be
self-supporting and is manufactured by coating or spraying it on a
(polymeric) support or foil.
[0017] PET is an abbreviation for polyethylene terephthalate.
[0018] The term alkyl means all variants possible for each number
of carbon atoms in the alkyl group i.e. methyl, ethyl, for three
carbon atoms: n-propyl and isopropyl; for four carbon atoms:
n-butyl, isobutyl and tertiary-butyl; for five carbon atoms:
n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl and
2-methyl-butyl etc.
[0019] Unless otherwise specified a substituted or unsubstituted
alkyl group is preferably a C.sub.1 to C.sub.6-alkyl group.
[0020] Unless otherwise specified a substituted or unsubstituted
alkenyl group is preferably a C.sub.2 to C.sub.6-alkenyl group.
[0021] Unless otherwise specified a substituted or unsubstituted
alkynyl group is preferably a C.sub.2 to C.sub.6-alkynyl group.
[0022] Unless otherwise specified a substituted or unsubstituted
aralkyl group is preferably a phenyl group or a naphthyl group
including one, two, three or more C.sub.1 to C.sub.6-alkyl
groups.
[0023] Unless otherwise specified a substituted or unsubstituted
alkaryl group is preferably a C.sub.1 to C.sub.6-alkyl group
including an aryl group, preferably a phenyl group or naphthyl
group.
[0024] Unless otherwise specified a substituted or unsubstituted
aryl group is preferably a substituted or unsubstituted phenyl
group or naphthyl group.
[0025] A cyclic group includes at least one ring structure and may
be a monocyclic- or polycyclic group, meaning one or more rings
fused together.
[0026] A heterocyclic group is a cyclic group that has atoms of at
least two different elements as members of its ring(s). The
counterparts of heterocyclic groups are homocyclic groups, the ring
structures of which are made of carbon only. Unless otherwise
specified a substituted or unsubstituted heterocyclic group is
preferably a five- or six-membered ring substituted by one, two,
three or four heteroatoms, preferably selected from oxygen atoms,
nitrogen atoms, sulphur atoms, selenium atoms or combinations
thereof.
[0027] An alicyclic group is a non-aromatic homocyclic group
wherein the ring atoms consist of carbon atoms.
[0028] The term heteroaryl group means a monocyclic- or polycyclic
aromatic ring comprising carbon atoms and one or more heteroatoms
in the ring structure, preferably, 1 to 4 heteroatoms,
independently selected from nitrogen, oxygen, selenium and sulphur.
Preferred examples of heteroaryl groups include, but are not
limited to, pyridinyl, pyridazinyl, pyrimidyl, pyrazyl, triazinyl,
pyrrolyl, pyrazolyl, imidazolyl, (1,2,3)- and (1,2,4)-triazolyl,
pyrazinyl, pyrimidinyl, tetrazolyl, furyl, thienyl, isoxazolyl,
thiazolyl, isoxazolyl, and oxazolyl. A heteroaryl group can be
unsubstituted or substituted with one, two or more suitable
substituents. Preferably, a heteroaryl group is a monocyclic ring,
wherein the ring comprises 1 to 5 carbon atoms and 1 to 4
heteroatoms.
[0029] The term substituted, in e.g. substituted alkyl group means
that the alkyl group may be substituted by other atoms than the
atoms normally present in such a group, i.e. carbon and hydrogen.
For example, a substituted alkyl group may include a halogen atom
or a thiol group. An unsubstituted alkyl group contains only carbon
and hydrogen atoms.
[0030] Unless otherwise specified a substituted alkyl group, a
substituted alkenyl group, a substituted alkynyl group, a
substituted aralkyl group, a substituted alkaryl group, a
substituted aryl, a substituted heteroaryl and a substituted
heterocyclic group are preferably substituted by one or more
substituents selected from the group consisting of methyl, ethyl,
n-propyl, isopropyl, n-butyl, 1-isobutyl, 2-isobutyl and
tertiary-butyl, ester, amide, ether, thioether, ketone, aldehyde,
sulfoxide, sulfone, sulfonate ester, sulphonamide, --Cl, --Br, --I,
--OH, --SH, --CN and --NO.sub.2.
[0031] Inkjet Ink Set.
[0032] The inkjet ink set includes a silver inkjet ink and a
flushing liquid, wherein the flushing liquid comprises at least 25
wt % of 2-phenoxy ethanol based on the total weight of the flushing
liquid.
[0033] Flushing Liquid
[0034] The flushing liquid comprises at least 25 wt %, preferably
at least 40 wt %, more preferably at least 50 wt % of 2-phenoxy
ethanol based on the total weight of the flushing liquid.
[0035] The flusing liquid may comprise another solvent, preferably
a high boiling solvent.
[0036] High boiling organic solvents referred to herein are
solvents which have a boiling point that is higher than the boiling
point of water (>100.degree. C.).
[0037] Preferred high boiling solvents are shown in Table 1.
TABLE-US-00001 TABLE 1 Chemical formula Chemical name Bp (.degree.
C.) ##STR00001## 4-methyl-1,3-dioxolan-2-one (propylene carbonate)
242 ##STR00002## n-butanol 117 ##STR00003## 1,2-propanediol 211-217
##STR00004## 4-hydroxy-4-methylpentan-2-one (diaceton alcohol) 168
##STR00005## Pentan-3-one (diethyl ketone) 102 ##STR00006##
2-Butoxyethanol Ethylene glycol monobutyl ether 171 ##STR00007##
Dihydrofuran-2(3H)-one (Gamma-butyrolacton) 204 ##STR00008##
2-pyrrolidon 245 ##STR00009## 1-methoxy-2-propanol
(propyleneglycolmonomethylether 120
[0038] The flushing liquid preferably comprises at least 25 wt % of
2-phenoxyethanol and a further solvent selected from the group
consisting of propylene carbonate, n-butanol and 2-pyrrolidone.
[0039] A particularly preferred flushing liquid comprised at least
25 wt % of 2-phenoxy ethanol and from 5 wt % to 20 wt % of
n-butanol, all based on the total weight of the Flushing
liquid.
[0040] The viscosity at 25.degree. C. of the flushing liquid
preferably is preferably lower than 20 mPas, more preferably less
than 15, most preferably less than 10 mPas.
[0041] Silver Inkjet Ink
[0042] The silver inkjet ink preferably comprises silver
nanoparticles, a liquid carrier and a dispersion-stabilizing
compound (DSC).
[0043] The silver inkjet ink may further comprise a polymeric
dispersant and additives to further optimize its properties.
[0044] Dispersion-Stabilizing Compound (DSC)
[0045] The silver inkjet ink preferably comprises silver
nanoparticles, a liquid carrier and a dispersion-stabilizing
compound (DSC) according to Formulae I, II, III or IV,
##STR00010##
wherein Q represents the necessary atoms to form a substituted or
unsubstituted five or six membered heteroaromatic ring; M is
selected from the group consisting of a hydrogen, a monovalent
cationic group and an acyl group; R1 and R2 are independently
selected from the group consisting of a hydrogen, a substituted or
unsubstituted alkyl group, a substituted or unsubstituted alkenyl
group, a substituted or unsubstituted alkynyl group, a substituted
or unsubstituted alkaryl group, a substituted or unsubstituted
aralkyl group, a substituted or unsubstituted aryl or heteroaryl
group, a hydroxyl group, a thioether, an ether, an ester, an amide,
an amine, a halogen, a ketone and an aldehyde; R1 and R2 may
represent the necessary atoms to form a five to seven membered
ring; R3 to R5 are independently selected from the group consisting
of a hydrogen, a substituted or unsubstituted alkyl group, a
substituted or unsubstituted alkenyl group, a substituted or
unsubstituted alkynyl group, a substituted or unsubstituted alkaryl
group, a substituted or unsubstituted aralkyl group, a substituted
or unsubstituted aryl or heteroaryl group, a hydroxyl group, a
thiol, a thioether, a sulfone, a sulfoxide, an ether, an ester, an
amide, an amine, a halogen, a ketone, an aldehyde, a nitrile and a
nitro group; R4 and R5 may represent the necessary atoms to form a
five to seven membered ring.
[0046] The dispersion-stabilizing compound is preferably a compound
according to Formula I.
[0047] The dispersion-stabilizing compound is more preferably a
compound according to Formula I, wherein Q represents the necessary
atoms to form a five membered heteroaromatic ring.
[0048] A particular preferred dispersion-stabilizing compound is a
compound according Formula I, wherein Q is a five membered
heteroaromatic ring selected from the group consisting of an
imidazole, a benzimidazole, a thiazole, a benzothiazole, an
oxazole, a benzoxazole, a 1,2,3-triazole, a 1,2,4-triazole, an
oxadiazole, a thiadiazole and a tetrazole.
[0049] Some examples of dispersion-stabilizing compounds according
to the present invention are shown in the following table.
TABLE-US-00002 DSC Chemical Formula DCS-01 ##STR00011## DCS-02
##STR00012## DCS-03 ##STR00013## DCS-04 ##STR00014## DCS-05
##STR00015## DCS-06 ##STR00016## DCS-07 ##STR00017## DCS-08
##STR00018## DCS-09 ##STR00019## DCS-10 ##STR00020## DCS-11
##STR00021## DCS-12 ##STR00022## DCS-13 ##STR00023## DCS-14
##STR00024## DCS-15 ##STR00025## DCS-16 ##STR00026##
[0050] The dispersion-stabilizing compound is preferably selected
from the group consisting of
N,N-dibutyl-(2,5-dihydro-5-thioxo-1H-tetrazol-1-yl-acetamide,
5-heptyl-2-mercapto-1,3,4-oxadiazole, 1-phenyl-5-mercaptotetrazol,
5-methyl-1,2,4-triazolo-(1,5-a) primidine-7-ol, and
S[5-[(ethoxycarbonyl)amino]-1,3,4-thiadiazol-2-yl] O-ethyl
thiocarbonate.
[0051] The dispersion-stabilizing compounds according to Formula I
to IV are preferably non-polymeric compounds. Non-polymeric
compounds as used herein means compounds having a Molecular Weight
which is less preferably than 1000, more preferably less than 500,
most preferably less than 350.
[0052] The amount of the dispersion-stabilizing compounds (DSC)
expressed as wt % relative to the total weight of silver (Ag) in
the silver inkjet ink is preferably between 0.005 and 10.0, more
preferably between 0.0075 and 5.0, most preferably between 0.01 and
2.5. When the amount of the dispersion-stabilizing compound
relative to the total weight of silver is too low, the stabilizing
effect may be too low, while a too high amount of the
dispersion-stabilizing compound may adversely affect the
conductivity of the coating or patterns obtained with the silver
inkjet ink.
[0053] Silver Nanoparticles
[0054] The dispersed silver nanoparticles have an average particle
size or average particle diameter, measured with Transmission
Electron Microscopy, of less than 150 nm, preferably less than 100
nm, more preferably less than 50 nm, most preferably less than 30
nm.
[0055] The amount of silver nanoparticles in the inkjet is
preferably at least 5 wt %, more preferably at least 10 wt %, most
preferably at least 15 wt %, particularly preferred at least 20 wt
%, relative to the total weight of the silver inkjet ink.
[0056] The silver nanoparticles are preferably prepared by the
method disclosed in EP-A 2671927, paragraphs [0044] to [0053] and
the examples.
[0057] Polymeric Dispersant
[0058] The silver inkjet ink may contain a polymeric
dispersant.
[0059] Polymeric dispersants typically contain in one part of the
molecule so-called anchor groups, which adsorb onto the silver
particles to be dispersed. In another part of the molecule,
polymeric dispersants have polymer chains compatible with the
dispersion medium, also referred to as liquid vehicle, and all the
ingredients present in the final printing or coating fluids.
[0060] Polymeric dispersants are typically homo- or copolymers
prepared from acrylic acid, methacrylic acid, vinyl pyrrolidinone,
vinyl butyral, vinyl acetate or vinyl alcohol monomers.
[0061] The polymeric dispersants disclosed in EP-A 2468827, having
a 95 wt % decomposition at a temperature below 300.degree. C. as
measured by Thermal Gravimetric Analysis may also be used.
[0062] However, in a preferred embodiment the silver inkjet ink
comprises less than 5 wt % of a polymeric dispersant relative to
the total weight of the dispersion, more preferably less than 1 wt
%, most preferably less than 0.1 wt %. In a particularly preferred
embodiment the dispersion comprises no polymeric dispersant at
all.
[0063] Liquid Carrier
[0064] The silver inkjet ink comprises a liquid carrier.
[0065] The liquid carrier is preferably an organic solvent. The
organic solvent may be selected from alcohols, aromatic
hydrocarbons, ketones, esters, aliphatic hydrocarbons, higher fatty
acids, carbitols, cellosolves, and higher fatty acid esters.
[0066] Suitable alcohols include methanol, ethanol, propanol,
1-butanol, 1-pentanol, 2-butanol, t-butanol.
[0067] Suitable aromatic hydrocarbons include toluene and
xylene.
[0068] Suitable ketones include methyl ethyl ketone, methyl
isobutyl ketone, 2,4-pentanedione and hexa-fluoroacetone.
[0069] Also glycol, glycolethers, N,N-dimethyl-acetamide,
N,N-dimethylformamide may be used.
[0070] A mixture of organic solvents may be used to optimize the
properties of the metallic nanoparticle dispersion.
[0071] Preferred organic solvents are high boiling solvents. High
boiling organic solvents referred to herein are solvents which have
a boiling point that is higher than the boiling point of water
(>100.degree. C.).
[0072] Preferred high boiling solvents are shown in Table 2.
TABLE-US-00003 TABLE 2 Chemical formula Chemical name Bp (.degree.
C.) ##STR00027## 2-phenoxy ethanol (ethylene glycol
monophenylether) 247 ##STR00028## 4-methyl-1,3-dioxolan-2-one
(propylene carbonate) 242 ##STR00029## n-butanol 117 ##STR00030##
1,2-propanediol 211-217 ##STR00031## 4-hydroxy-4-
methylpentan-2-one (diaceton alcohol) 168 ##STR00032## Pentan-3-one
(diethyl ketone) 102 ##STR00033## 2-Butoxyethanol Ethylene glycol
monobutyl ether 171 ##STR00034## Dihydrofuran-2(3H)-one
(Gamma-butyrolacton) 204 ##STR00035## 2-pyrrolidin 245 ##STR00036##
1-methoxy-2-propanol (propyleneglycol- monomethylether 120
[0073] Particularly preferred high boiling solvents are 2-phenoxy
ethanol, propylene carbonate, propylene glycol, n-butanol,
2-pyrrolidone and mixtures thereof.
[0074] The silver ink preferably comprises at least 25 wt % of
2-phenoxyethanol, more preferably at least 40 wt %, based on the
total weight of the silver ink.
[0075] Additives
[0076] To optimize the printing properties, and also depending on
the application for which it is used, additives such as reducing
agents, wetting/levelling agents, dewettting agents, rheology
modifiers, adhesion agents, tackifiers, humectants, jetting agents,
curing agents, biocides or antioxidants may be added to the silver
inkjet ink described above.
[0077] The silver inkjet ink may comprise a surfactant. Preferred
surfactants are Byk.RTM. 410 and 411, both solutions of a modified
urea, and Byk.RTM. 430, a solution of a high molecular urea
modified medium polar polyamide.
[0078] The amount of the surfactants is preferably between 0.01 and
10 wt %, more preferably between 0.05 and 5 wt %, most preferably
between 0.1 and 0.5 wt %, relative to the total amount of the
metallic nanoparticle dispersion.
[0079] It may be advantageous to add a small amount of a metal of
an inorganic acid or a compound capable of generating such an acid
during curing of a metallic layer or pattern formed from the silver
inkjet ink such as disclosed in EP-A 2821164. Higher conductivities
and/or lower curing temperatures were observed of layers or
patterns formed from such silver inkjet ink.
[0080] Higher conductivities and/or lower curing temperatures may
also be obtained when using silver inkjet ink containing a compound
according to Formula X, as disclosed in EP-A 3016763.
##STR00037## [0081] wherein [0082] X represents the necessary atoms
to form a substituted or unsubstituted ring.
[0083] A particularly preferred compound according to Formula X is
an ascorbic or erythorbic acid derivative compound.
[0084] Preparation of the Silver Inkjet Ink
[0085] The preparation of the silver inkjet ink according to the
present invention typically comprises the addition of the liquid
carrier, the dispersion-stabilizing compound and optional additives
to the silver nanoparticles by using a homogenization technique
such as stirring, high shear mixing, ultra-sonication, or a
combination thereof.
[0086] The silver nanoparticles from which the silver inkjet ink is
made is typically a paste or a highly concentrated dispersion of
silver nanoparticles. A preferred preparation method of the
metallic nanoparticles is disclosed in EP-A 2671927.
[0087] It has been observed that better results are obtained when
all, or a portion, of the dispersion-stabilizing compound are added
during the preparation method of the silver nanoparticles. Due to
their adsorption to the silver nanoparticles, the
dispersion-stabilizing compounds added during the preparation of
the silver nanoparticles will be retained, at least partially, in
the final silver nanoparticle disperision, even if one or more
washing steps have been carried out in the preparation method.
[0088] The homogenization step can be carried out at elevated
temperature up to 100.degree. C. In a preferred embodiment, the
homogenization step is carried out at temperature equal or below
60.degree. C.
[0089] Silver Layers or Patterns
[0090] Silver layers or patterns may be printed with the silver
inkjet ink.
[0091] Conductive silver layers or patterns are prepared by an
inkjet printing method comprising the steps of jetting the silver
inkjet ink on a support followed by a curing step. Such a curing
step is also referred to as a sintering step.
[0092] The support may be a glass, a paper or a polymeric
support.
[0093] Preferred polymeric supports are polycarbonate, polyethylene
terephthalate (PET) or polyvinylchloride (PVC) based supports.
[0094] The above mentioned supports may be provided with one or
more layers to improve the adhesion, absorption or spreading of the
applied conductive inkjet inks.
[0095] Polymeric supports are preferably provided with so-called
subbing layers to improve the adhesion of the applied conductive
inkjet or flexo inks. Such subbing layers are typically based on
vinylidene copolymers, polyesters, or (meth)acrylates.
[0096] Useful subbing layers for this purpose are well known in the
art and include, for example, polymers of vinylidene chloride such
as vinylidene chloride/acrylonitrile/acrylic acid terpolymers or
vinylidene chloride/methyl acrylate/itaconic acid terpolymers.
[0097] Suitable vinylidene chloride copolymers include: the
copolymer of vinylidene chloride, N-tert.-butylacrylamide, n-butyl
acrylate, and N-vinyl pyrrolidone (e.g. 70:23:3:4), the copolymer
of vinylidene chloride, N-tert.-butylacrylamide, n-butyl acrylate,
and itaconic acid (e.g. 70:21:5:2), the copolymer of vinylidene
chloride, N-tert.-butylacrylamide, and itaconic acid (e.g.
88:10:2), the copolymer of vinylidene chloride, n-butylmaleimide,
and itaconic acid (e.g. 90:8:2), the copolymer of vinyl chloride,
vinylidene chloride, and methacrylic acid (e.g. 65:30:5), the
copolymer of vinylidene chloride, vinyl chloride, and itaconic acid
(e.g. 70:26:4), the copolymer of vinyl chloride, n-butyl acrylate,
and itaconic acid (e.g. 66:30:4), the copolymer of vinylidene
chloride, n-butyl acrylate, and itaconic acid (e.g. 80:18:2), the
copolymer of vinylidene chloride, methyl acrylate, and itaconic
acid (e.g. 90:8:2), the copolymer of vinyl chloride, vinylidene
chloride, N-tert.-butylacrylamide, and itaconic acid (e.g.
50:30:18:2). All the ratios given between brackets in the
above-mentioned copolymers are ratios by weight.
[0098] Other preferred subbing layers include a binder based on a
polyester-urethane copolymer. In a more preferred embodiment, the
polyester-urethane copolymer is an ionomer type polyester urethane,
preferably using polyester segments based on terephthalic acid and
ethylene glycol and hexamethylene diisocyanate. A suitable
polyester-urethane copolymer is Hydran.TM. APX101 H from DIC Europe
GmbH.
[0099] The application of subbing layers is well-known in the art
of manufacturing polyester supports for silver halide photographic
films. For example, the preparation of such subbing layers is
disclosed in U.S. Pat. No. 3,649,336 and GB 1441591.
[0100] In a preferred embodiment, the subbing layer has a dry
thickness of no more than 0.2 .mu.m or preferably no more than 200
mg/m.sup.2.
[0101] Another preferred support is an ITO based support. Such a
support is typically a glass or polymer support whereupon an ITO
layer or pattern is provided.
[0102] A preferred paper based support is the Powercoat.RTM. paper
substrate, a substrate designed for printed electronics by
Arjowiggins Creative Papers.
[0103] Multiple silver layers or patterns, i.e. a stack of
patterned or unpatterned layers, may be applied on a substrate. The
support referred to in the method of preparing the silver layers or
patterns thus also encompass a previously applied silver layer or
pattern.
[0104] An inkjet printing method of preparing a conductive layer or
pattern comprising the steps of: [0105] cleaning the print head
with a flushing liquid as described above prior to load the Ag
inkjet ink, [0106] jetting a silver inkjet ink with an inkjet
printer comprising a print head on a support thereby forming a
silver layer or pattern on the support; [0107] curing the silver
layer or pattern thereby forming a conductive layer or pattern; and
[0108] cleaning the print head with a flushing liquid as described
above.
[0109] The silver inkjet ink is preferably as described above.
[0110] In a preferred inkjet printing method the curing temperature
is below 150.degree. C. and the curing time is less than 30
minutes.
[0111] Inkjet Printing Devices
[0112] Various embodiments of an apparatus for creating silver
layers or pattern from the silver inkjet inks according to the
present invention by inkjet printing may be used.
[0113] In a flat bed printing device a support is provided on a
flat bed. Droplets of a silver inkjet fluid are jetted from a print
head on the support.
[0114] The print heads typically scan back and forth in a
transversal direction (x-direction) across a moving support
(y-direction). Such bi-directional printing is referred to as
multi-pass printing.
[0115] Another preferred printing method is the so-called
single-pass printing method wherein the print heads, or multiple
staggered print heads, cover the entire width of the support. In
such a single-pass printing method, the print heads usually remain
stationary while the support is transported under the print heads
(y-direction).
[0116] To obtain maximal dot placement accuracy, the print heads
are positioned as close as possible to the surface of the support.
The distance between the print heads and the surface of the support
is preferably less than 3 mm, more preferably less than 2 mm, most
preferably less than 1 mm.
[0117] As the distance between the printhead and the surface of the
support may influence the dot placement accuracy, it may be
advantageous to measure the thickness of a support and adapting the
distance between the printhead and the surface of the support based
on the measurement of the thickness of the support.
[0118] The distance between a stationary printhead and the surface
of a support mounted on the printing device may also vary over the
whole support, due to for example waviness of the support, or other
irregularities in the surface of the support. Therefore it may also
be advantageous to measure the surface topography of the support
and to compensate the differences in the measured surface
topography by controlling the so-called firing time of the droplets
of curable fluids on the support, or by adjusting the distance
between the printhead and the surface of the support. Examples of
measurement devices to measure the surface topography of a
lithographic supports is disclosed in ISO 12635:2008(E).
[0119] In a preferred embodiment the inkjet printing device has
holding down means, such as a vacuum chamber under the support, to
hold down the support in a so-called hold-down zone, for example by
vacuum. In a more preferred embodiment the support is hold down
against the support by independent working holding down means such
as a plurality of vacuum chambers under the support which are
independently controlled to enhance the vacuum pressure on the
support so that more than one hold down zones are generated on the
support. The holding down of the support enhances the drop
placement of the jetted droplets and position accuracy.
[0120] Print Head
[0121] A preferred print head for the inkjet printing system is a
piezoelectric head.
[0122] Piezoelectric inkjet printing is based on the movement of a
piezoelectric ceramic transducer when a voltage is applied thereto.
The application of a voltage changes the shape of the piezoelectric
ceramic transducer in the print head creating a void, which is then
filled with ink. When the voltage is again removed, the ceramic
expands to its original shape, ejecting a drop of ink from the
print head. However the inkjet printing method according to the
present invention is not restricted to piezoelectric inkjet
printing. Other inkjet print heads can be used and include various
types, such as the continuous printing type.
[0123] Preferred print heads eject droplets having a volume
.ltoreq.50 pL, more preferably .ltoreq.35 pL, most preferably
.ltoreq.25 pL, particularly preferred .ltoreq.15 pL.
[0124] Another preferred print head is a throughflow piezoelectric
inkjet print head. A throughflow piezoelectric inkjet print head is
a print head wherein a continuous flow of liquid is circulating
through the liquid channels of the print head to avoid
agglomerations in the liquid which may cause disturbing effects in
the flow and bad drop placements. Avoiding bad drop placements by
using throughflow piezoelectric inkjet print heads may improve the
quality of the conductive patterns on the support. Another
advantage of using such throughflow print heads is a higher
viscosity limit of the curable fluids to be jetted, widening the
scope of compositional variations of the fluids.
[0125] Curing Step
[0126] After the layers or patterns are applied on the support, a
sintering step, also referred to as curing step, is carried out.
During this sintering step, solvents evaporate and the silver
particles sinter together. Once a continuous percolating network is
formed between the metallic particles, the layers or patterns
become conductive. Conventional curing is typically carried out by
applying heat. The curing temperature and time are dependent on the
support used and on the composition of the metallic layer or
pattern. The curing step for curing the silver layers may be
performed at a temperature below 200.degree. C., preferably below
180.degree. C., more preferably below 150.degree. C., most
preferably below 130.degree. C.
[0127] The curing time may be less than 60 minutes, preferably
between 2 and 30 minutes and more preferably between 3 and 20
minutes, depending on the selected temperature, support and
composition of the metallic layers.
[0128] However, instead of or in addition to the conventional
sintering by applying heat, alternative sintering methods such as
exposure to an Argon laser, to microwave radiation, to UV radiation
or to low pressure Argon plasma, photonic curing, plasma or plasma
enhanced, electron beam, laser beam or pulse electric current
sintering may be used.
[0129] Another curing method uses the so-called Near infrared (NIR)
curing technology. The metal of the coating or the pattern, for
example silver, may act as absorber for the NIR radiation.
[0130] The silver layers of the present invention allow to use
lower curing temperatures than the prior art processes. In
consequence it is possible to use polymeric substrates that can not
withstand thermal treatment at high temperature, such as for
example PET. The curing time may also be substantially reduced
leading to the possibility of having higher production per hour
than the prior art processes. The conductivity of the silver layers
are maintained or even improved in certain cases.
[0131] To further increase the conductivity or to lower the curing
temperature it may be advantageous to contact the silver layer or
pattern with a solution containing an acid or an acid precursor
capable or releasing the acid during curing of the metallic layer
or pattern, as disclosed in EP-A 13175030.9 (filed on Apr. 7,
2013).
[0132] The silver layers or patterns may be used in various
electronic devices or parts of such electronic devices as for
example organic photo-voltaics (OPV's), inorganic photo-voltaics
(c-Si, a-Si, CdTe, CIGS), OLED displays, OLED lighting, inorganic
lighting, RFID's, organic transistors, thin film batteries,
touch-screens, e-paper, LCD's, plasma, sensors, membrane switches
or electromagnetic shielding.
[0133] Additionally, the silver layers or patterns may be used in
various security or decorative devices or parts of such security or
decorative devices, for example when an image with special features
that will impede its complete or partial reproduction or a light
reflective layer with metal appearance is required.
EXAMPLES
[0134] Materials
[0135] All materials used in the following examples were readily
available from standard sources such as ALDRICH CHEMICAL Co.
(Belgium) and ACROS (Belgium) unless otherwise specified. The water
used was deionized water.
[0136] DSC-01 is the dispersion-stabilizing compound
N-dibutyl-(2,5-dihydro-5-thioxo-1H-tetrazol-1-yl)acetamide
(CASRN168612-06-4) commercially available from Chemosyntha.
##STR00038##
[0137] Silver oxide, Ag.sub.2O commercially available from
UMICORE.
[0138] 2-phenoxy-ethanol (CASRN122-99-6) commercially available
from BASF.
[0139] Gamma-butyro-lactone (CASRN96-48-0) commercially available
from BASF.
[0140] Propylenecarbonate (CASRN108-32-7) commercially available
from Sigma Aldrich.
[0141] Diaceton alcohol (CASRN123-42-2) commercially available from
ACROS CHIMICA.
[0142] n-butanol (CASRN71-36-3) commercially available from ACROS
CHIMICA.
[0143] 1,2 propanediol (CASRN57-55-6) commercially available from
ACROS CHIMICA.
[0144] 1-methoxy-2-propanol (CASRN107-98-2) commercially available
from DOW CHEMICALS.
[0145] 2-butoxyethanol (CASRN111-76-2) commercially available from
DOW CHEMICALS. Copol (ViCl.sub.2-MA-IA), a copolymer of
vinylidenechloride-methacrylic acid and itaconic acid from Agfa
Gevaert.
[0146] Mersolat H40, a surfactant from Lanxess.
[0147] Kieselsol 100F, a silica from Bayer.
[0148] Measurements Methods
[0149] Conductivity of the Silver Coatings
[0150] The surface resistance (SER) of the silver coatings was
measured using a four-point collinear probe. The surface or sheet
resistance was calculated by the following formula:
SER=(.pi./ln 2)*(V/I)
wherein SER is the surface resistance of the layer expressed in
.OMEGA./square; .pi. is a mathematical constant, approximately
equal to 3.14; ln 2 is a mathematical constant equal to the natural
logarithmic of value 2, approximately equal to 0.693; V is voltage
measured by voltmeter of the four-point probe measurement device; I
is the source current measured by the four-point probe measurement
device.
[0151] For each sample, six measurements were performed at
different positions of the coating and the average value was
calculated.
[0152] The silver content M.sub.Ag (g/m.sup.2) of the coatings was
determined by WD-XRF.
[0153] The conductivity of the coated layers was then determined by
calculating the conductivity as a percentage of the bulk
conductivity of silver using the following formula:
% .times. Ag ( b .times. u .times. l .times. k ) = .sigma. C
.times. o .times. a .times. t .sigma. Ag .times. 1 .times. 0
.times. 0 ##EQU00001## % .times. Ag ( b .times. u .times. l .times.
k ) = .rho. Ag .sigma. Ag .times. S .times. E .times. R .times. M
Ag .times. 1 .times. 0 .times. 0 ##EQU00001.2##
wherein a .sigma..sub.Ag the specific conductivity of silver (equal
to 6.3.times.10.sup.7S/m), .sigma..sub.Coat is the specific
conductivity of the Ag coating and .rho..sub.Ag is the density of
silver (1.049.times.10.sup.7 g/m.sup.3).
[0154] Measuring the Instability Index
[0155] The stability of a silver ink/flushing liquid mixture was
measured using multiple light scattering coupled with a vertical
scanning to monitor the dispersion state of the mixture.
Acceleration of the sedimentation phenomena can be induced for
example by fast centrifugation of the sample during the
measurement.
[0156] A commercial available apparatus is for example a
Lumisizer.RTM. from LUM GmbH. The samples were measured during 4
hours at 3000 rpm with 880 nm radiation. An instability index
provided by the Lumisizer.RTM. ranges between 0 and 1, wherein the
instability increases from 0 to 1.
[0157] Viscosity Measurements
[0158] Unless otherwise provided, viscosities were measured at
25.degree. C. at a shear rate of 1000 s.sup.-1 using a commercially
available viscometer for example as a DHFR-2 Rheometer (double wall
ring) from TA Instruments.
Example 1
[0159] Preparation of the Silver Ink AgInk-01
[0160] 450 g of silver oxide (commercially available from Umicore)
was added to a mixture of 875 g of ethanol and 517 g of
2-pyrrolidone while stirring. The obtained predispersion was then
further stirred at 23.degree. C. for 15 hours.
[0161] Then, 2.8 g of DSC-01 was added to the mixture followed by
the addition of 73 g of formic acid (10.0 mL/min) while stirring
and keeping the temperature at 23.degree. C. After the addition of
the formic acid, the mixture was further stirred for another 15
hours at 23.degree. C.
[0162] The dispersion was then concentrated by evaporation of the
organic solvent to obtain a concentrated silver nanoparticle
dispersion with a silver content of approximately 45 wt %.
[0163] The silver ink AgInk-01 were then prepared by mixing 44 wt %
of the concentrated silver nanoparticle dispersion with 50 wt % of
2-phenoxyethanol, 6 wt % propylenecarbonate and 10 wt % n-butanol,
all wt % based on the total weight of the silver ink.
[0164] Preparation of the Flushing Liquids Flush-01 to Flush-12
[0165] The flushing liquids Flush-01 to Flush-12 having a
composition as shown in Table 3 have been prepared by mixing the
different solvents at room temperature.
TABLE-US-00004 TABLE 3 Ingredients Flush- (wt %) Flush-01 Flush-02
Flush-03 Flush-04 Flush-05 06 2-phenoxyethanol 69 64 59 54 50 50
Propylene 21 16 11 6 50 -- carbonate n-butanol 10 20 30 40 0 --
2-pyrrolidone -- -- -- -- -- 50 ethanol -- -- -- -- -- -- Flush-
Flush-07 Flush-08 Flush-09 Flush-10 Flush-11 12 2-phenoxyethanol 50
100 -- -- -- -- Propylene 25 -- 100 -- -- -- carbonate n-butanol --
-- -- 100 -- -- 2-pyrrolidone 25 -- -- -- 100 -- ethanol -- -- --
-- -- 100
[0166] The viscosity of each prepared flushing (determined as
described above and measured at 25.degree. C. at a shear rate of
1000 s.sup.-1) is presented in Table 4, as well as, the instability
index (determined as described above) for a full series of Ag
ink:flushing liquid mixtures. The instability index has been
measured for several mixtures of the silver ink AgInk-01 and the
flushing liquids Flush-01 to Flush-06 having a wt/wt ratio as shown
in Table 4. In Table 4 the mixture 1:99 stands for a mixture
comprising 1 wt % silver ink and 99 wt % flushing liquid, etc.
TABLE-US-00005 TABLE 4 Flushing viscosity instability index liquid
(mPa s) 1:99 10:90 30:70 50:50 Flush-01 7.3 0.09 0.13 0.08 0.09
Flush-02 6.2 -- 0.15 0.10 0.09 Flush-03 5.4 -- 0.22 0.17 0.12
Flush-04 4.9 0.33 0.36 0.23 0.17 Flush-05 5.0 0.92 0.18 0.25 0.30
Flush-06 17.0 0.01 0.03 0.04 0.06 Flush-07 9.4 0.03 0.13 0.17 0.24
Flush-08 20.4 0.00 0.02 0.03 0.03 Flush-09 2.6 1.00 1.00 0.64 0.61
Flush-10 2.7 1.00 1.00 0.93 0.64 Flush-11 13.3 1.00 0.08 0.08 0.015
Flush-12 0.9 1.00 1.00 1.00 1.00
[0167] From the results of Table 4 it is clear that mixtures of the
silver inkjet ink AgInk-01 and the flushing solutions, which do not
contain at least 25 wt % of 2-phenoxy ethanol (Flush-09 to
Flush-12), are not stable.
[0168] The Flushing solution, which contains 100 wt % 2-phenoxy
ethanol, has a viscosity higher than 20 mPass (25.degree. C. at a
shear rate of 1000 s.sup.-1). Such a high viscosity may, depending
on the printheads and printer systems, result in difficulties when
introducing and flowing such high viscous liquid through the
printer tubings and printhead, for instance before loading the Ag
inkjet ink into the system or during a cleaning process.
[0169] The best results, combining a low viscosity and a high
stability are obtained with Flush-01, comprising at least 25 wt %
of 2-phenoxy ethanol and from 5 wt % to 20 wt % of butanol, all
based on the total weight of the Flushing liquid. Thus, when
loading the Ag inkjet ink into the printing system or during a
cleaning process, no sedimentation of Ag nanoparticles will occur
inside the printhead or printing system which will increase the
lifetime of the printhead and also allows for a better jetting
performance of the Ag inkjet ink.
* * * * *