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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

                                                        2
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,

                                                          3
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.


                                                        4
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.




                                                             5
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


                                                          6
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.




                                                             7
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.
                                                                                                       8

				
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