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New Raw Materials
for High Temperature UV Inkjet
By James Goodrich
Sartomer Company, Inc.
Exton, Pennsylvania
USA
Sartomer Company, Inc. • Oaklands Corporate Center • 502 Thomas Jones Way • Exton, PA 19341
Tel:610-363-4100 • 800-SARTOMER (800-727-8663) • Fax: 610-363-4140 • Web: www.sartomer.com
5059 06/08
ABSTRACT Diacrylate (DPGDA) (SR508), as the main
Conventional inkjet has been an enabling diluents. Higher functionality materials such as
technology for marking and variable data for thirty Trimetholpropane Triacrylate (TMPTA) (SR351),
years. In the past few years the advantages of energy Di- Trimetholpropane Tetraacrylate (Di-TMPTA)
curable technology have been applied to inkjet inks (SR295), and Di-Pentaerythritol Pentaacrylate (Di-
to improve upon the performance and reliability PEPA) (SR399) were used at low levels to further
of the current conventional systems. The 100% UV increase the hardness of the formulation and
inkjet formulations that are now in use have some provide better wear properties. Traditional UV
excellent characteristics, but also some drawbacks oligomers, such as epoxy acrylates, urethane
due to constraints in viscosity and functionality of acrylates, and polyester acrylates, which improve
the raw materials. The ability of today’s Drop-on- the physical properties of cured films, could only
Demand (DOD) print heads to heat the UV ink be used at additive levels due to viscosity
allows the end-user and the formulator another constraints. At such low levels of use in the
method by which to lower the viscosity of their formulation, questions were brought up whether
inks. New UV raw materials designed for use in or not oligomers were offering improvements to
high temperature UV inkjet applications will be the cured film.
introduced and application data presented to
support their use. As UV inkjet formulations are utilized in more
demanding applications, better physical properties
INTRODUCTION of the cured films are becoming necessary. This
The introduction of UV technology into the realm means the ink formulations need more high
of inkjet printing has followed the same path seen functionality monomers and more oligomer
in other industries now penetrated by UV. Inkjet content. As discussed earlier, the incorporation of
printing has been in use for thirty years in the high functionality monomers and oligomers also
marking and variable data markets. These inks leads to higher viscosity formulations that cannot
usually contain a binder resin, pigment, additives, be jetted at room temperature. But what if you
and have been traditionally based on water, solvent, increased the temperature of the ink to lower the
or oils. As expected, the dried inks did not have viscosity? UV monomers and oligomers decrease
great physical properties, which limited their use dramatically in viscosity when heated. Urethane
in applications where resistance to physical wear and epoxy acrylates, especially, see a drop in
and solvents was deemed necessary. UV technology viscosity because the hydrogen bonds that make
was looked at as a way to improve the properties them high viscosity at room temperature are broken
of the cured or dried ink film. The issue with UV, at elevated temperatures.
of course, was the inherent higher viscosity of the
raw materials being used in the ink. Current printhead technology available from
suppliers such as Spectra and Xaar enables heating
In general, the lower viscosity a UV material is, of the printhead up to 70°C. And with printheads
the lower its functionality. First generation UV on the drawing boards capable of heating the UV
inkjet inks contained large percentages of mono- inks to 80°C and beyond, the hardware exists to
functional materials, such as Isodecyl Acrylate, heat the UV inkjet inks to elevated temperatures
(SR440) to achieve the desired low viscosities. The for jetting. Surprisingly, it is the ink formulations
inks based on low functionality materials were very that have issues at the elevated temperatures.
slow curing and yielded soft, scratchable films
whose physical properties were not improvements The gelation stability of UV systems at 80°C and
on the current solvent and waterbased technologies. above tends to be poor. Monomers and oligomers
Second generation inks started using difunctional contain peroxides, hydroperoxides and other
monomers, such as Propoxylated Neopentyl Glycol contaminants that will cause gelation of the UV
Diacrylate (2PO NPGDA) and Dipropylene Glycol materials once an elevated temperature is obtained
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and held for a period of time. Alkoxylated materials SR9003IJ is 2-mole propoxylated neopentyl glycol
tend to contain higher levels of peroxides and diacrylate. The neopentyl glycol structure is used
hydroperoxides, which make their gelation issues extensively in solvent-based and UV liquid inks
even worse. The gelation issues in UV inkjet because of its excellent performance in pigmented
formulations are exasperated by the presence of systems. The propoxylation lowers the health and
high amounts of alkoxylated materials, pigments, safety rating and the Draize value versus that of
and fast-reacting photoinitiators. The average UV neopentyl glycol diacrylate (SR247). The SR9003IJ
inkjet ink is currently jetted at 50 - 55°C, but in also has a low surface tension of 32 D/cm so it will
order to increase that even 15°C, it requires new aid in adhesion by wetting out the surface of poorly
technology in the UV materials used in the treated or untreated substrates.
formulation.
Diagram 1. Structure of 2 PO Neopentyl Glycol
EXPERIMENTAL Diacrylate (SR9003IJ).
Sartomer has striven to develop a line of UV
O O
materials that possess excellent high temperature
O O
stability for use in UV inkjet formulations. O O
SR9003IJ and SR508IJ are the first two products
introduced in Sartomer’s line of Inkjet Grade
materials. These two products were chosen since SR508IJ is a diacrylate of dipropylene glycol.
they are currently represented in the majority of Dipropylene glycol diacrylate has a lower
UV inkjet formulations. The standard SR9003 and molecular weight than the propoxylated neopentyl
SR508 monomers traditionally have poor high glycol diacrylate. SR508IJ imparts hardness and
temperature gelation stability that will translate into scratch resistance to UV ink systems due to its high
poor ink gelation stability. Sartomer uses a Tg and cross-link density. The polypropylene oxide
proprietary manufacturing process to improve the structure is commonly used in UV ink systems as
purity and reduce the contaminants such as a general purpose diluent.
peroxides, free acrylic acid, water, and solvent in
the final monomer. The results are purer materials Diagram 2. Structure of Dipropylene Glycol
with improved high temperature stabilities that are Diacrylate (SR508IJ).
well suited for UV inkjet applications.
O O
O
O O
Table 1: Physical properties for SR9003IJ and SR508 IJ.
SR9003IJ SR508IJ
Viscosity – cps, 25° C 15 10
Specific Gravity – g/cm3, 25° C 1.005 1.052
Static Surface Tension – D/cm, 25° C 32.0 32.8
Refractive Index - 25° C 1.4464 1.4502
Color - APHA 35 40
Haze Clear Clear
Tg – Homopolymer by DSC, ° C 32 104
To verify the improvements made in the inkjet printhead technology can reach 100°C, but this
grade monomers, first the 100°C stability of the testing temperature gives an idea of what is possible
materials was examined. Currently no inkjet with UV chemistry. If a material is stable at 100°C,
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then its stability at 80° C will be even better. The simply judged as the time, in hours, necessary for
samples were placed into dark brown bottles that the visible gel to appear in the container. In all of
were sealed, but contained 20% of air headspace the failure cases, gelation of the sample was
so oxygen was available for aiding in stability. The complete. The stability testing was stopped after
samples were not stirred nor were they uncapped 672 hours (4 weeks).
during the testing period. Gelation stability was
Figure 1: Gelation stability of SR508, SR508IJ, SR9003, and SR9003IJ at 100° C.
168
672
SR508
1
SR508IJ
24
SR9003
SR9003IJ
672
0 168 336 504 672
Hours
When simply the monomers are tested the Inkjet after 672 hours. The next step was to look at the
Grade materials show drastic improvements in the materials in simple formulations to see if the trend
their gelation stability at 100°C. Gelation of the holds true.
standard monomers occurred within a week in both
instances and both samples were entirely gelled. The same testing procedure was used for the simple
The SR508IJ and the SR9003IJ did not gel during formulations containing both the standard
the testing period and still appeared clear and fluid monomers and the Inkjet Grade monomers.
Table 2: Unpigmented formulations for evaluating the SR9003IJ and SR508IJ. The SR399LV is Di-
Pentaerythritol Pentaacrylate and the SR1135 is a blend of phosphine oxide, alpha-hydroxy ketone and a
benzophenone derivative.
SR9003 Evaluation SR508 Evaluation
Standard Standard
Inkjet Grade Inkjet Grade
Monomer Monomer
Formula Formula
Formula Formula
% SR9003 57.0 32.0
% SR9003IJ 25.0
% SR508 57.0 32.0
% SR508IJ 25.0
% SR399LV (DiPEPA) 35.0 35.0 35.0 35.0
% Esacure® KTO46 (Photoinitiator) 8.0 8.0 8.0 8.0
PI is Esacure® KTO46 from Lamberti USA, Inc.
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Figure 2: Gelation stability at 100°C of the formulations from Table 2.
192
672
SR508
1
SR508IJ
144
SR9003
SR9003IJ
672
0 168 336 504 672
Hours
An improvement in the 100°C stability of the Inkjet temperature for testing was brought down from
Grade formulations is seen, however the 100°C to 80°C so as not to bring the stability of
formulations based on the standard monomers did the pigment dispersion into the equation. The
perform better due to less of the standard monomers dispersion was based on CN2279 and SR9003. The
being used. The stability of these formulations is CN2279 is a low viscosity polyester acrylate
surprising, since eight percent of photoinitiator is designed for UV inkjet systems. In the evaluation
present to aid in any gelation while the overall a blue dispersion using Ciba Blue GLVO and a
acrylate functionality of the formulation is black dispersion using Cabot Mogul E were used.
increased by 45%. Each UV inkjet ink formulation contained 5%
pigment solids. Cyan tends to cause gelation
The most caustic test for high temperature gelation stability issues at room temperature that are only
stability is in a pigmented system. For this test the exasperated at the elevated temperatures.
Table 3: Pigmented formulations evaluated for 80°C gelation stability.
SR9003 Evaluation SR508 Evaluation
Standard Standard
Inkjet Grade Inkjet Grade
Monomer Monomer
Formula Formula
Formula Formula
% SR9003 37.0
% SR9003IJ 37.0
% SR508 37.0
% SR508IJ 37.0
% SR399LV (DiPEPA) 35.0 35.0 35.0 35.0
% Pigment Dispersion 20.0 20.0 20.0 20.0
% Esacure ® KTO46 (Photoinitiator) 8.0 8.0 8.0 8.0
PI is Esacure® KTO46 from Lamberti USA, Inc.
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Figure 3: Gelation stability at 80°C of black ink formulations found in Table 3.
384
672
SR508
1
SR508IJ
288
SR9003
SR9003IJ
672
0 168 336 504 672
Hours
Figure 4: Gelation stability at 80°C of cyan ink formulations found in Table 3.
288
600
SR508
1
SR508IJ
240
SR9003
SR9003IJ
672
0 168 336 504 672
Hours
All of the pigmented formulations based on the clear evaluations. Also as expected, the cyan inks
Inkjet Grade materials showed considerable had worse gelation stability than the black inks.
increases in the gelation stability over the standard Both of the standard monomers saw a decrease in
monomers. The black inks in Figure 3 all showed gel times, as did the SR508IJ that failed 72 hours
good stability, and, as expected, the Inkjet Grade before cessation of the testing. The cyan ink based
materials did not gel before the completion of the on SR9003IJ still looked good after the 4-week
testing. The standard monomer inks became testing period.
thixotropic, as opposed to a solid gel seen in the
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Finally, formulations containing urethane acrylate acrylate oligomers into UV inkjet formulations
oligomers were examined to see how much could drastically increase the formulation latitude
urethane could be incorporated, what kind of and allow for inks that are weatherable, more
physical properties could be obtained, and the 80°C scratch and abrasion resistant, and have better
stability of the ink. The incorporation of urethane adhesion.
Table 5: Formulations used to evaluate the use of aliphatic urethane in 80°C UV inkjet formulations. N
represents the % of urethane acrylate used in the formulation.
SR9003 Evaluation
CN991 Based CN968 Based
% Aliphatic Urethane Acrylate N N
% SR9003IJ 25.0 25.0
% SR9003 47.0 – N 47.0 – N
% Black Pigment Dispersion 20.0 20.0
% Esacure® KTO465 (Photoinitiator) 8.0 8.0
PI is Esacure® KTO46 from Lamberti USA, Inc.
Figure 5: 80°C viscosity of UV inkjet formulations from Table 5 containing CN991 and CN968
aliphatic urethane acrylate oligomers.
CN991 Formulations
CN968 Formulations
20
Viscosi ty (80C)
15
10
5
0
20 23 26 29 32
% Urethane Acrylate in Formulation
As seen in Figure 5, increasing the temperature to Evaluations of the physical properties were
80°C allowed for the incorporation of at least 32% performed on unpigmented systems so as to ensure
of the aliphatic urethane oligomers while still complete cure of the film and to obtain the most
falling in the viscosity range for jetting. This is representative data. As in Figure 5, the SR9003IJ
enough oligomer in the formulation to positively was used in the evaluation of the physical properties
affect the physical properties of the cured ink. of the urethane acrylate UV inkjet inks.
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Figure 6: 1% modulus, in pounds / in2 (psi), of the formulations found in Table 5.
CN991 Formulations
CN968 Formulations
35000
30000
1% Modulus (psi)
25000
20000
15000
10000
5000
0
0 8 16 24 32
% Urethane Acrylate in Formulation
Figure 7: Maximum elongation, in %, of the formulations found in Table 5.
CN991 Formulations
CN968 Formulations
25
Maximum Elongation (%)
20
15
10
5
0
0 8 16 24 32
% Urethane Acrylate in Formulation
As expected, the addition of the urethane acrylates at 30% would greatly increase the weatherability
to the formulation improved the physical properties. of the UV inkjet formula.
The modulus, which relates to the toughness of the
film, is increased as more of each oligomer is CONCLUSION
added. More of an effect is seen with the CN968, As UV inkjet penetrates into new markets where
which is hexafunctional and is increasing the cross- better-cured ink films are a requirement, more
link density. The CN968 also decreases the robust formulations will need to be developed.
elongation, making the film more hard and brittle, Jetting at higher temperatures allows for the
but also more scratch resistant. The addition of the incorporation of the raw materials necessary to
CN991, which is difunctional, increases the improve the physical properties of the cured films.
elongation and flexibility of the cured film and Sartomer’s Inkjet Grade materials greatly increase
would increase the adhesion characteristics of the the gelation stability of UV inkjet formulations at
formulation. The films made with the CN991 and higher temperatures, allowing ink makers more
the CN968 exhibit better scratch resistance than formulation latitude to achieve their customer’s
the film made with just monomer. Both materials requirements. SR9003IJ and SR508IJ are the first
are aliphatic urethane acrylates and their addition two Inkjet Grade materials available, but look for
additional monomers in the future.
The information in this bulletin is believed to be accurate but all recommendations are made without warranty, since the conditions of use are beyond SARTOMER Company’s control. The listed properties are
illustrative only, and not product specifications. SARTOMER Company disclaims any liability in connection with the use of the information, and does not warrant against infringement by reason of the use of its
products in combination with other material or in any process.
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