U.S. patent application number 11/259792 was filed with the patent office on 2006-05-25 for radiofrequency activated inkjet inks and apparatus for inkjet printing.
Invention is credited to David E. Brotton, J. David Campbell, Richard W. JR. Chylla, Michael A. Dalton, Jon A. Debling, Arthur S. Diamond, Jonathan M. Gorbold, Timothy D. Gorbold, Brian L. Teachout.
Application Number | 20060109327 11/259792 |
Document ID | / |
Family ID | 35999467 |
Filed Date | 2006-05-25 |
United States Patent
Application |
20060109327 |
Kind Code |
A1 |
Diamond; Arthur S. ; et
al. |
May 25, 2006 |
Radiofrequency activated inkjet inks and apparatus for inkjet
printing
Abstract
This invention relates to fast-drying RF inkjet composition and
apparatus for inkjet printing RF inkjet compositions. The
compositions and apparatus are useful for inkjet printing onto a
variety of media including both porous and non-porous substrates.
The RF inkjet composition desirably includes RF susceptors combined
with polar carriers which may be activated by RF energy to generate
heat within the RF inkjet composition, resulting in enhanced
evaporative drying.
Inventors: |
Diamond; Arthur S.; (Ojai,
CA) ; Gorbold; Jonathan M.; (Pittsford, NY) ;
Gorbold; Timothy D.; (Scottsville, NY) ; Teachout;
Brian L.; (Dansville, NY) ; Brotton; David E.;
(Racine, WI) ; Campbell; J. David; (Racine,
WI) ; Chylla; Richard W. JR.; (Racine, WI) ;
Dalton; Michael A.; (Racine, WI) ; Debling; Jon
A.; (Oak Creek, WI) |
Correspondence
Address: |
JOHNSON POLYMER, INC.
8310 16TH STREET- M/S 510
P.O. BOX 902
STURTEVANT
WI
53177-0902
US
|
Family ID: |
35999467 |
Appl. No.: |
11/259792 |
Filed: |
October 27, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60522721 |
Nov 1, 2004 |
|
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|
60680256 |
May 12, 2005 |
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Current U.S.
Class: |
347/102 ;
347/93 |
Current CPC
Class: |
B41J 2/17593 20130101;
D06P 1/5221 20130101; D06P 5/2066 20130101; D06P 5/30 20130101;
B41J 11/00216 20210101; C09D 11/34 20130101; D06P 1/5257 20130101;
D06P 5/2083 20130101; B41J 11/002 20130101; D06P 5/2011 20130101;
C09D 11/30 20130101; C09D 11/40 20130101 |
Class at
Publication: |
347/102 ;
347/093 |
International
Class: |
B41J 2/01 20060101
B41J002/01 |
Claims
1. An apparatus for printing and drying an RF inkjet composition,
the apparatus comprising a print cartridge adapted to travel in a
line above a medium, the print cartridge comprising at least one
ink nozzle, and at least one RF emitter adapted to travel along
with the cartridge.
2. The apparatus of claim 1, wherein the at least one RF emitter is
positioned to activate an RF inkjet composition as it passes from
the at least one print nozzle to the medium.
3. The apparatus of claim 1, wherein the at least one RF emitter
comprises an interdigitated RF probe assembly.
4. The apparatus of claim 3, wherein the interdigitated probe
assembly is incorporated into a flex circuit on the cartridge.
5. The apparatus of claim 1 comprising a first RF emitter
associated with the leading edge of the cartridge and a second RF
emitter associated with the trailing edge of the cartridge.
6. The apparatus of claim 5, wherein the first and the second RF
emitters comprise interdigitated RF probe assemblies.
7. A method of printing and drying an RF inkjet composition using
the apparatus of claim 1, the method comprising ejecting an RF
inkjet composition from the at least one print nozzle onto the
medium and activating the RF inkjet composition using the at least
one RF emitter.
8. The method of claim 7, wherein the medium incorporates, or is
coated with, an RF susceptor, the method further comprising
activating the RF susceptor using the at least one RF emitter.
9. An apparatus for printing and drying an RF inkjet composition,
the apparatus comprising a print cartridge comprising at least one
ink nozzle and a roller drive comprising a roller for guiding a
medium under the print cartridge, the roller comprising an outer
rotating cylinder and a nested inner cylinder having an RF emitter
incorporated into its outer surface.
10. The apparatus of claim 9, wherein the RF emitter comprises an
interdigitated RF probe assembly.
11. A method for printing and drying an RF inkjet composition using
the apparatus of claim 9, the method comprising printing an RF
inkjet composition onto a medium using the at least one ink nozzle
and activating the printed ink using the RF emitter.
12. An apparatus for printing and drying an RF inkjet composition,
the apparatus comprising a print cartridge comprising at least one
ink nozzle, a roller drive comprising a roller for guiding a medium
under the print cartridge, a first RF emitter incorporated into the
roller for directing RF energy onto the lower surface of the medium
and a second RF emitter spaced apart from the roller for directing
RF energy onto the upper surface of the medium.
13. The apparatus of claim 12, wherein the second RF emitter is
disposed on a plate shaped to conform to the curvature of the
roller.
14. The apparatus of claim 12, wherein one or both of the first and
second RF emitters comprises an interdigitated RF probe
assembly.
15. A method for printing and drying an RF inkjet composition using
the apparatus of claim 12, the method comprising printing an RF
inkjet composition onto a medium using the at least one ink nozzle
and activating the printed ink using the first and second RF
emitters.
16. An apparatus for printing and drying an RF inkjet composition,
the apparatus comprising a print cartridge comprising at least one
ink nozzle, a plate positioned to support a medium that been
printed using the print cartridge and an RF emitter incorporated
into the plate.
17. The apparatus of claim 16, wherein the RF emitter comprises an
interdigitated RF probe assembly.
18. An RF-activatable sublimation ink comprising, an RF-activatable
binder, a sublimation colorant and a polar carrier.
19. The ink of claim 18, wherein the RF-activatable binder is an
ionomer and the sublimation colorant is a sublimation dye.
20. A method of sublimation printing comprising applying the ink of
claim 18 to a transfer substrate and exposing the transfer
substrate to RF radiation sufficient to heat the ink and cause the
sublimation colorant to sublimate and deposit onto a medium.
21. The method of claim 20, wherein the medium is selected from the
group consisting of paper, textiles and non-woven materials.
22. The method of claim 20, wherein the ink is heated to a
temperature of at least about 300.degree. C.
23. An RF-activated impulse inkjet printer comprising at least one
nozzle containing an RF inkjet composition and a RF emitter coupled
to the at least one nozzle.
24. A method of impulse printing comprising activating the RF
inkjet composition of claim 23 using the RF emitter such that a
bubble of vapor is created in the ink, wherein the bubble forces a
drop of the ink out of the nozzle.
25. A method for printing and drying an RF inkjet composition, the
method comprising printing an RF inkjet composition onto a medium
using the at least one ink nozzle and activating the printed ink
using the RF emitter.
26. An RF-activatable hot melt ink comprising, about 20 to 80
weight percent RF susceptor and about 20 to 80 weight percent
colorant; wherein the ink is free of or substantially free of
solvents.
27. A method of hot melt printing comprising activating the RF
susceptor to melt the ink and printing the molten ink onto a
medium.
28. An RF inkjet composition comprising an RF susceptor, a polar
carrier, a crosslinking agent, and a binder selected from the group
consisting of polymers polymerized from keto- or
aldehyde-containing amide-functional monomers or from monomers
bearing acetoacetoxy functional groups.
29. The composition of claim 28, wherein the monomers comprise
diacetone acrylamide monomers and the crosslinking agent is a di-
or polyamine or a dihydrazide.
30. The composition of claim 28, wherein the monomers comprise
acetoacetoxymethacrylate or actoacetoxy ethyl acrylate monomers and
the crosslinking agent is a di- or polyamine.
31. An RF inkjet composition comprising an RF susceptor comprising
carboxylic acid functional groups, a multivalent metal crosslinking
agent and a solvent.
32. The composition of claim 31, wherein the multivalent metal
crosslinking agent is a zinc ammonium carbonate or zirconium
ammonium carbonate.
33. A method of inkjet printing comprising printing the ink of
claim 28 onto a medium and activating the RF susceptor or
RF-activatable ionomer to generate heat in the ink.
34. A method of printing an RF inkjet composition comprising an RF
susceptor, a colorant, a polar carrier and optionally a binder, the
method comprising printing the ink onto a medium and activating the
RF susceptor to induce a reaction between the RF susceptor, the
colorant or the binder and the medium.
35. The method of claim 34, wherein the RF susceptor is an ionomer
and the reaction is a crosslinking reaction between the ionomer and
the medium.
36. The method of claim 34, wherein the ink comprises a carboxylic
acid functional binder and a multivalent metal crosslinking agent
and the medium is a corona treated plastic film, and further
wherein the reaction occurs between the binder and the plastic
film.
37. The method of claim 34, wherein the ink comprises a cationic or
amine-functional binder and the medium is a paper comprising alkyl
diketene, and further wherein the reaction occurs between the
binder and the alkyl diketene.
38. The method of claim 34, wherein the ink comprises a reactive
colorant and the reaction occurs between the reactive colorant and
the medium.
39. A method of printing an ink comprising a binder, a colorant,
and a solvent, the method comprising either printing the ink onto a
medium having an RF-activatable coating or printing the ink onto a
medium and coating the printed ink with an RF-activatable coating,
and activating the RF-activatable coating to induce a reaction
between the colorant or the binder in the ink and the coatings.
40. The method of claim 39, wherein the ink comprises an RF
susceptor.
41. The method of claim 39, wherein the RF susceptor comprises an
RF-activatable binder.
42. A method of inkjet printing comprising printing the ink of
claim 31 onto a medium and activating the RF susceptor or
RF-activatable ionomer to generate heat in the ink.
Description
FIELD OF THE INVENTION
[0001] The present invention provides radiofrequency (RF)
activatable inkjet inks, methods for printing the inks and
apparatus for inkjet printing using RF inkjet compositions.
BACKGROUND OF THE INVENTION
[0002] Most inkjet inks currently available are low viscosity
liquids which contain large amounts of water, often 90 weight
percent or greater. The use of water as a solvent in these inks is
advantageous because it is inexpensive, environmentally friendly
and non-toxic. Unfortunately, water also has a relatively high
boiling point and a high latent heat of evaporation. For this
reason, inkjet inks which contain large amounts of water tend to be
slow-drying. Slow-drying inks are disfavored for many printing
applications because they lead to slow printing rates.
[0003] To speed up the printing rate of water-based inkjet inks,
printing equipment may employ external heating devices to speed up
the evaporation of water from the inks. Inkjet drying techniques
include passing media with wet ink images against or near heated
rollers or platens. Another approach to increasing the drying rate
of water-based inkjet inks is to generate heat internally within
the inks by coupling energy into the water or incorporating
radiation susceptors into the ink formulations. The heating of
water or susceptors is achieved by exposing the ink to radiation of
a suitable frequency, causing heat to be generated within the ink
and speeding up the evaporation of water and other volatile
solvents. Most of these susceptors are microwave activated
inorganic salts and the use of microwaves to heat and dry the water
is slow and relatively inefficient. The use of external heating
devices entails several complications. For example, contact of
heating devices with wet ink image can produce smudging or
smearing. Also, application of heat and subsequent drying of media
while in contact with rollers can produce undesirable buckling or
curvature of the output. This may require additional steps to
flatten the media after printing and drying.
[0004] Therefore, a need exists for an improved, fast drying inkjet
compositions and apparatus for inkjet printing using these
compositions.
SUMMARY OF THE INVENTION
[0005] One aspect of the present invention provides fast-drying RF
inkjet compositions. The RF inkjet compositions include at least
one RF susceptor, a colorant and at least one polar carrier. It is
believed that the RF inkjet composition generates heat when exposed
to radiofrequency energies from ionic conduction caused by the
movement of dissociated ions. This internally-generated heat
enhances evaporation of volatile liquids from the ink compositions
and results in shorter drying times. In some instances, the inkjet
compositions provided herein, may be dried at a rate fast enough to
allow for a printing speed of one page per second, or even faster,
without any smearing of the inks.
[0006] In one embodiment of the RF inkjet composition, RF energy is
used to cause a chemical reaction in the ink during drying. This
produces images with improved resistance properties due to
crosslinking. However the wet inks retain resolubility during
printing as drying and crosslinking occur upon RF activation.
Accordingly these inks cause reduced clogging of the inkjet
heads.
[0007] Another embodiment of the inkjet inks provides RF inkjet
compositions wherein chemical reactions are used for binding of
inks to media. In one aspect of this invention, media containing
reactive groups for reaction with the RF activated inkjet inks are
used. Reaction between inks and media occur upon exposure to RF
energy. This allows printing on non-porous media such as plastic
films or modified paper substrates with improved resistance
properties of images produced.
[0008] In still another embodiment of the inkjet inks, exposure of
the inks to RF energy causes reaction of a polar carrier in the ink
with ionomers or other components present in the inks. This
produces images with improved resistance properties due to
consumption or reduction in the amount of polar carrier. Another
advantage of these inks is their reduced sensitivity to RF energy
as the heating progresses so that these inks are self limiting and
show controlled increase in temperature.
[0009] In some embodiments, the RF inkjet compositions are
sublimation inks. These inks include RF susceptors and sublimation
colorants in inkjet ink. In a preferred variation of this
embodiment, the RF susceptor provides a polymeric binder for the
sublimation colorants. The binders are used to support the
colorants prior to sublimation in a transfer sublimation printing
process. In one exemplary embodiment, the RF-activatable binder is
an RF-activatable ionomer and the sublimation colorant is a
sublimation dye. The sublimation inks may initially be provided in
the form of a dispersion that is applied to a transfer substrate.
Application of RF energy to the transfer substrate results in
sublimation of the sublimation colorants and subsequent deposition
of the colorants onto a suitable media to produce an inkjet image.
The use of RF-activatable binders provides improved rate of ink
transfer to the media.
[0010] In another embodiment of the invention, RF-activitable
sublimation inks including RF susceptors and sublimation colorants
are used for direct printing to a media such as textile or paper.
RF activation is used for sublimation of dyes onto the media. This
RF activation also results in heating of the media, making the
media receptive to dye. The use of RF inkjet compositions results
in printing with little or no distortion of the media in comparison
with a thermal process that does not use RF activatable inks.
[0011] The present invention also provides RF-activatable solid hot
melt inkjet inks for printing. These inks allow rapid heating of
the hot melt and ejection on to the media used for printing.
Examples of RF-activatable hot melts include those based on
ionomers such as those from acrylic copolymers with polar carriers
such as glycerol. These hot melt inks contain no or reduced amount
of solvents.
[0012] In addition to inkjet inks, the present invention provides
compositions for RF-activatable protective water-borne coatings,
such as an overprint varnishes for application over previously
applied inkjet images. The protective water-borne coatings contain
ionomers and a polar carrier so that the composition can be
activated by RF energy. The heating and drying of the protective
coating provides a high gloss, protective barrier for the inkjet
images. Similarly, the RF-activatable coatings may be applied to
media prior to inkjet printing. The media so coated may then be
heated using RF energy, such that the rate of drying for an ink
subsequently printed onto the media is increased. This aspect
allows high gloss printing applications which require coatings of
higher thickness. RF-activitable inks and overprint varnishes can
dry faster than those by IR or forced drying means.
[0013] A second aspect of the invention provides an inkjet printer
and a method for impulse or drop on demand inkjet printing using RF
energy to superheat a droplet of ink for deposition on a media.
Although the RF inkjet compositions described herein are
well-suited for use with the printers, other RF inkjet compositions
may also be employed. The printers use an RF emitter coupled to a
printing nozzle to rapidly heat an RF inkjet composition in the
nozzle which generates a pressure pulse. The pressure pulse results
in the ejection of an ink drop from the nozzle. The use of RF
heating to create a pressure pulse has advantages over
piezoelectric and thermal resistive heating-based impulse printing
methods because RF heating does not require contact with the ink
droplet. Therefore the RF emitter does not require changing upon
changing the ink such as an ink of different color. Moreover RF
heating provides a more uniform heating of the ink droplets in
comparison with thermal resistive heating, resulting in less
clogging of the inkjet heads. Examples of RF inkjet composition
useful for this purpose include inks containing at least one RF
susceptor, a colorant and a polar carrier described above.
[0014] A third aspect of the invention provides apparatus for the
delivery of RF energy in inkjet printers for the purposes of drying
and/or crosslinking RF inkjet inks and coatings. Although the
present RF inkjet compositions and coatings are well-suited for use
with these apparatus, other RF inkjet compositions and coatings may
also be employed. One apparatus in accordance with the present
invention provides an inkjet printer for drop on demand and
continuous inkjet systems wherein one or more transistor RF modules
are used to drive a low-power applicator system for inks. In some
embodiments, the applicator system couples RF energy into the ink
stream before its contact with the media onto which it is
ultimately printed. A part of the volatile components such as water
and/or other solvents are removed as a result of RF activation. The
resulting inks therefore dry faster, produce less ink bleeding and
higher gloss. In one embodiment of this invention the inks dry in
less than one second after application on the media. Another aspect
of this invention provides an inkjet printer for color printing
wherein each colored cartridge is provided with separate RF modules
to drive the applicator system for inks. In one embodiment of this
invention, the RF module is incorporated into the ink cartridge. In
another embodiment of this invention, the RF module is mounted
separately on a carriage for the ink cartridge.
[0015] Another exemplary apparatus provides an RF module to couple
RF energy into an image or a portion of the image immediately after
printing on media. This results in volatilization of water and/or
other solvents and faster drying of the RF inkjet compositions. In
one embodiment of this invention the inks dry in less than one
second after application on the media. In one embodiment of this
invention, one or more transistor RF modules drive a low-power
applicator system to couple the RF energy into the image or a
portion of the image immediately after printing. In one aspect of
this invention, the applicator is incorporated into the ink
cartridge by utilizing the traces on the flexible printed circuit
of the cartridge. Another embodiment of this invention mounts the
RF applicator on the print carrier separately from the ink
cartridge. Two RF applicators are desirable to provide heating of
the RF activitable ink when used with multidirectional
printing.
[0016] Another apparatus provides a RF power source to drive an
applicator system incorporated into the roller drive used to move
media through a printing zone in an inkjet printer. This apparatus
couples RF energy generated in the roller of the roller drive into
the image printed on the media. This produces faster drying inks
due to application of RF energy shortly after printing of the media
and volatilization of water and/or other solvents. In one
embodiment of this invention the inks dry in less than one second
after application on the media. One example of this invention
includes a RF power source mounted inside the roller used for
moving media. In another embodiment, the RF power source is mounted
separately on the printer chassis. An interdigitated probe (IDP)
system utilizing a series of alternating electrodes may be used as
the RF emitter to achieve uniform drying of inks using stray field
energy. In another embodiment the media passes between two
electrodes after printing and drying is achieved in the through
field.
[0017] Yet another apparatus provided by this invention includes a
RF power source which drives an interdigitated radiofrequency
applicator system. After printing with the RF inkjet composition,
the media is passed over the applicator so as to couple the RF
energy with the image present on the media. This causes faster
drying of the image.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows a block diagram of a suitable heating system
that is capable of generating an electromagnetic field for
activating the inks of the present invention.
[0019] FIG. 2 shows an interdigitated probe system for generating
RF energy.
[0020] FIG. 3 shows an RF applicator that includes interdigitated
probes embedded into the substrate roller of an inkjet printer.
[0021] FIG. 4 shows a through field RF applicator applied to a
roller for activating RF ink on the printed medium.
[0022] FIG. 5 shows the printed medium passing over an RF
applicator having a page wide interdigitated probe assembly mounted
after the drive roller.
[0023] FIG. 5a shows a block diagram of the RF field generating
system that can be assembled to demonstrate and test the
invention.
[0024] FIG. 5b shows an example of the ink application equipment
and the interdigitated probe assembly mounted in a paper transport
mechanism.
[0025] FIG. 6 shows an inkjet cartridge that includes an
interdigitated RF applicator integrated into the flex circuit of an
inkjet cartridge.
[0026] FIG. 7 shows an inkjet cartridge with two RF applicators,
mounted on the print head carrier on each side of the
cartridge.
DETAILED DESCRIPTION
Definition of Terms
[0027] "RF Susceptors" mean either ionic or polar compounds
introduced as a component into a composition such that RF heating
of the resulting RF inkjet composition occurs.
[0028] "Polar Carrier" provides a mobile medium in which RF
susceptors are dissolved, distributed, or dispersed. Polar carriers
can be liquids such as solvents, plasticizers, and humectants.
These can be organic or aqueous type
[0029] "RF Inkjet Composition" comprises at least one RF susceptor
and at least one polar carrier interfaced with one and other and/or
mixed or blended together. The RF Inkjet Composition will also
include colorants, binders, surfactants, wetting agents,
de-foamers, humectants, buffers, chelating agents, solubilizers and
biocides sufficient for the performance of the inkjet ink.
[0030] "RF-activatable coating" comprises at least one RF susceptor
and at least one polar carrier interfaced with one and other and/or
mixed or blended together. The RF-activatable coating will also
include colorants, binders, surfactants, wetting agents,
de-foamers, humectants, buffers, chelating agents, solubilizers and
biocides sufficient for the performance of the coating
[0031] This invention relates to fast-drying RF inkjet compositions
and apparatus for inkjet printing RF inkjet compositions. The
compositions and apparatus are useful for inkjet printing onto a
variety of media including both porous and non-porous substrates.
Specific examples of suitable media include, but are not limited
to, papers, including paperboard, plastic and rubber substrates,
textiles, and woven and non-woven materials. The RF inkjet
composition may be activated by RF energy to generate heat within
the RF inkjet composition, resulting in enhanced evaporative
drying. The RF inkjet compositions include at least three
components: (1) a RF susceptor; (2) a polar carrier; and (3) a
colorant. The RF susceptor is an ionic or polar compound and acts
as either a charge-carrying or an oscillating/vibrating component
of the RF inkjet composition. The RF inkjet composition generates
thermal energy in the presence of an RF field. According to the
present invention, the RF susceptor can be an inorganic salt (or
its respective hydrate), such as stannous chloride, zinc chloride
or other zinc salt, or lithium perchlorate, or an organic salt,
such as lithium acetate. The RF susceptor can be a
non-ferromagnetic ionic salt. In some embodiments, the RF susceptor
is an ionomer. As used herein, an ionomer is a macromolecule in
which a small but significant proportion of the constitutional
units have ionizable or ionic groups, or both. The ionomers in the
RF inkjet compositions generate heat when exposed to radiofrequency
energies from ionic conduction caused by the movement of
dissociated ions in the polar liquid media. The polar media in
inkjet inks comprises the water and or other additives such as
solvents and humectants that have high dielectric constants
suitable for dissociation of the ions.
[0032] In certain embodiments, RF susceptor can be carbon black or
metallic particles. RF activation of these susceptors is via
conductive heating.
[0033] The RF susceptors are present in the RF inkjet composition
in amounts sufficient to provide a desired printing speed. The
maximum printing speed achievable by a given inkjet ink composition
will depend on the amount of RF energy converted to heat. This is a
function of both the radiofrequency susceptibility of the inkjet
ink as well as how balanced the RF field generating circuitry is.
However too much heating may lead to arcing. The amount of RF
susceptor in the RF inkjet composition may also affect viscosity of
the compositions. Balancing these considerations of maximizing
printing speed, avoiding arcing and optimizing viscosity, the
inventors have discovered certain formulations of fast-drying, RF
inkjet compositions that are well-suited for inkjet printing
applications.
[0034] In some embodiments, the RF inkjet compositions contain
substantial amounts of RF susceptors. For example, the RF inkjet
composition may include about 0.1 to 35 wt. % of a susceptor such
as an ionomer, based on the total weight of the inkjet ink
composition. This includes embodiments where the inks contain about
0.5 to 10 wt. % ionomer and further includes embodiments where the
inks contain about 1 to 3 wt. % ionomer, based on the total weight
of the inkjet ink composition. A variety of RF-activatable ionomers
may be used in the RF inkjet composition. Examples of such ionomers
are described in detail in U.S. Pat. No. 6,348,679. One specific
class of ionomers that may be used in the RF inkjet composition is
based on acrylic acid polymers and copolymers. The copolymers are
polymerized from at least one of an acrylic acid or methacrylic
acid monomer and at least one additional monomer such as a vinyl
aromatic monomer (e.g., styrene) or ethylene. Specific examples of
such copolymers include, but are not limited to, styrene-acrylic
copolymers and salts thereof, ethylene-acrylic copolymers and salts
thereof and vinyl acetate-acrylic copolymers and salts thereof. The
acrylic acid copolymers may be made using well-known polymerization
techniques, including batch, continuous and semi-continuous
polymerizations. Suitable polymers may also be made by
living/controlled polymerization methods that produce narrow
molecular weight distributions or alternative structures such as
block copolymers. Exemplary methods include but are not limited to
anionic polymerization, reversible addition fragmentation transfer
or atom transfer methods. In addition, commercially available
suitable acrylic polymers may be used. One example of a
commercially available styrene-acrylic copolymer is JONCRYL.TM.
682, available from Johnson Polymer LLC, Sturtevant, Wis. From
these polymers and copolymers, ionomers may be obtained by
neutralization with a suitable base. In some embodiments acrylic
acid polymers or copolymers have acid numbers in the range 35 to
350 mg of KOH/g and weight-average molecular weight in the range
1500 to 50,000. Suitable bases include, but are not limited to,
KOH, LiOH, NaOH, Mg(OH).sub.2, Ca(OH).sub.2 and amines, including
ammonia.
[0035] Other suitable acrylic acid polymers and copolymers and
salts thereof are described in U.S. Pat. Nos. 5,821,294; 5,717,015;
5,719,244; 5,670,566; 5,618,876; 5,532,300; 5,530,056; 5,519,072;
5,371,133; 5,319,020; 5,037,700; 4,713,263; 4,696,951; 4,692,366;
4,617,343; 4,948,822; and 4,278,578; the entire disclosures of
which are incorporated herein by reference. Examples of
commercially available acrylic acid copolymers include ethylene
acrylic acid copolymer and the ammonium (MICHEM.TM. 4983P) and
sodium (MICHEM.TM. 48525R) salts thereof available from Michelman
Incorporated, Cincinnati, Ohio. Additional examples are vinyl
acetate-acrylic copolymers (e.g. ROVACE.TM. HP3442) available from
Rohm and Hass, Philadelphia, Pa.
[0036] Maleic anhydride polymers, copolymers and salts thereof are
another class of ionomer that may be used in the RF inkjet
composition. Specific examples of suitable maleic anhydride-based
copolymers include, but are not limited to, styrene-maleic
anhydride, ethylene-maleic anhydride and propylene-maleic anhydride
copolymers. Examples of this type of polymer include copolymers of
styrene and maleic anhydride available under the trade name SMA.TM.
resins from Sartomer Company, Exton, Pa.
[0037] Sulfonated polymers are another class of ionomers that may
be used in the RF inkjet composition. This class includes
sulfonated polyesters, copolymers and salts thereof. Also included
in this group are sulfonated polystyrenes, acrylamidopropane
sulfonate based polymers and urethane ionomers polymerized from a
diisocyanate diol with a sulfonate functionality. More information,
including specific examples of each of the above-referenced types
of ionomers, may be found in U.S. Pat. No. 6,348,679, the entire
disclosure of which is incorporated herein by reference. Suitable
sulfonated polyesters and copolymers thereof are also described in
U.S. Pat. Nos. 5,750,605; 5,552,495; 5,543,488; 5,527,655;
5,523,344; 5,281,630; 4,598,142; 4,037,777; 3,033,827; 3,033,826;
3,033,822; 3,075,952; 2,901,466; 2,465,319; 5,098,962; 4,990,593;
4,973,656; 4,910,292; 4,525,524; 4,408,532; 4,304,901; 4,257,928;
4,233,196; 4,110,284; 4,052,368; 3,879,450; and 3,018,272; the
entire disclosures of which are incorporated herein by reference.
Some sulfonated polyesters may be purchased commercially.
Commercially available sulfonated polyesters are sold by Eastman
Chemical Company, Kingsport, Tenn., under nos. AQ1045, AQ1350,
AQ1950, AQ14000, AQ35S, AQ38S, AQ55S and EASTEK.TM. 1300.
[0038] Cationic polymers, such as those made from monomers
comprising N,N-dimethylaminoethyl (meth)acrylate and the hydrogen
chloride and methyl chloride salts thereof may also be used as
ionomers in the present RF inkjet composition for some inks with
cationic compatible formulations.
[0039] In addition to, or instead of, the ionomers, other
RF-activatable compounds, such as inorganic salts, may be included
in the compositions. Examples of inorganic salts useful in this
invention include salts of multivalent metals such as Ca.sup.+2,
Cu.sup.+2, Co.sup.+2, Ni.sup.+2, Fe.sup.+2, La.sup.+3, Nd.sup.+3,
y.sup.+3, or Al.sup.+3. Salts of these metals with anions such as
nitrate, halide, acetate or sulfate can be used. However, for some
applications it may be desirable to provide RF inkjet composition
that are free of or substantially free of (e.g., contain no more
than about 0.05, or even no more than about 0.01 wt. %) inorganic
salts. The absence of inorganic salts is advantageous because salts
may negatively impact the latency of the inks. Suitable inorganic
salt RF susceptors and inks made from such susceptors are described
in U.S. Pat. No. 5,220,346, the entire disclosure of which is
incorporated herein by reference.
[0040] RF susceptors in the ink may be surfactants bound to or
polymerized into polymeric binders, dispersants or ionomers present
in the ink. In some cases, the RF susceptors may be the pigments or
dyes used as colorants in the ink. In other embodiments, the RF
susceptors are present in the media and become RF susceptible when
ink contacts the substrate. One example of this is paper that
contains ion containing materials. By itself, paper is only
slightly RF active, however, when ink contacts the paper, the ions
from the paper additives dissociate in the ink water so as to make
the ink more susceptible to RF energy.
[0041] In addition to increasing the rate of evaporative drying,
the RF heating of the inks may be used to initiate or increase the
rate of crosslinking reaction in the inks. For example, many inks
include crosslinkable binders which undergo more rapid crosslinking
at elevated temperatures. By using RF susceptors in such inks, the
rate of crosslinking may be increased by RF heating of the binders.
In some instances, the binder itself may be an RF susceptor (e.g.,
an RF-activatable acrylic acid polymer or copolymer), while in
other instances a polymeric binder is present in addition to an RF
susceptor. A variety of crosslinkable binders are useful for RF
inkjet inks wherein chemical reaction or crosslinking occurs after
exposure of the ink to RF energy. Examples of suitable
crosslinkable binders include those based on crosslinking reactions
of epoxy groups with phenolic, hydroxyl, amine, carboxylic acid,
acid anhydrides, etc. Other types of crosslinkable binders are
those based on crosslinking reactions of isocyanate groups,
including those of blocked isocyanate groups or those encapsulated
or protected to reduce or eliminate the reaction with water. Still
other types of crosslinkable binders are those based on
thermosetting acrylics and appropriate crosslinking agents.
Examples include acrylic copolymers containing hydroxyl groups with
amino resins as crosslinking agents. Other suitable crosslinkable
binders include those based on reactions of carbon-carbon double
bonds. Still other crosslinkable binders also include those based
on crosslinking reactions of hydroxyl group containing polymers
such as polyester polyols with blocked isocyanates, amino resins,
and the like.
[0042] In some instances, the crosslinkable binders are
self-crosslinkable polymers, where a self-crosslinkable polymer is
a polymer having a reactive functionality that is able to provide
crosslinks between polymer chains via a suitable crosslinking agent
that reacts with the reactive functionalities. For example,
self-crosslinking binders may be polymerized from keto- or
aldehyde-containing amide-functional monomers such as diacetone
acrylamide (DAAM) that react with di- or polyamine or dihydrazide
crosslinking agents. Other examples of self-crosslinkable monomers
from which binders may be polymerized include monomers having
acetoacetoxy functional groups (e.g., acetoacetoxymethacrylate
(AAEM) or acetoacetoxy ethyl acrylate (AAEA) which crosslink with
di- or poly-amine crosslinking agents.
[0043] In some instances the crosslinkable binders may be
polymerized from carboxylic acid functional monomers, such as
acrylic or methacrylic acid monomers, that crosslink with
multivalent metal crosslinking agents, such as zinc or zirconium
ammonium carbonate.
[0044] The polar carrier present in the RF inkjet composition may
be used to dissolve or disperse binders, such as RF susceptors, and
colorants and desirably also serves to enhance the RF activation of
the composition. Thus, preferred embodiments of the RF inkjet
composition will include a polar carrier composed of water and
optionally, at least one water-miscible organic polar carrier
capable of reducing the RF drying time of the compositions. The
amount of polar organic carrier and water present in the
compositions will depend, at least in part, on the desired RF
susceptibility and viscosity of the ink formulations. As discussed
above, the RF susceptibility of the formulation should be
sufficient to allow for fast RF activation without arcing, while
the viscosity of the formulation should be low enough to provide an
ink formulation that is compatible with inkjet printing
applications. In some embodiments, the RF inkjet composition will
contain about 0.1 to 40 wt. % organic polar carrier. This includes
embodiments where the RF inkjet composition include about 1 to 30
wt. % organic polar carrier and further includes embodiments where
the RF inkjet composition include about 5 to 20 wt. % organic polar
carrier. In some embodiments, the RF inkjet composition may contain
about 40 to 95 wt. % water. This includes embodiments where the RF
inkjet composition include about 60 to 90 wt. % water and further
includes embodiments where the RF inkjet composition include about
65 to 80 wt. % water.
[0045] Solvents (including some which are polar organic carriers)
that may be present in the polar carrier include, but are not
limited to, ethylene glycol, propylene glycol, butylene glycol,
diethylene glycol, polyalkylene glycols, glycerol, polyvinyl
alcohol, amides, ethers, carboxylic acids, esters, alcohols,
organosulfides, organosulfoxides, sulfones, alcohol derivatives,
ether derivatives, amino alcohols, ketones, water soluble acrylic
copolymers containing hydroxyl groups and mixtures thereof. In some
cases, the solvents act as humectants for the ink.
[0046] The organic polar carriers used in the RF inkjet composition
are desirably high boiling point solvents with high dielectric
constants. For example, the organic polar carriers may have a
dielectric constant of at least about 10 or even at least about 20
at 20.degree. C. Because they have high boiling points, the organic
polar carriers do not evaporate to a significant extent during ink
jetting or drying. This allows for continuous RF susceptibility as
the water in the ink is heated and evaporated. Specific examples of
suitable polar organic carriers are listed in U.S. Pat. No.
6,348,679, the entire disclosure of which is incorporated herein by
reference. Glycerol and polyethylene glycol are two examples of
preferred organic polar carrier. When glycerol is present as a
polar organic carrier, it may be present in an amount of about 1 to
20 wt. %, based on the total weight of the inkjet ink composition.
This includes embodiments where glycerol is present in an amount of
about 1 to 10 wt. % and further includes embodiments where the
glycerol is present in an amount of about 1 to 5 wt. %, based on
the total weight of the inkjet ink composition. In some embodiments
organic polar carrier comprises formamide or
N,N-dimethylformamide.
[0047] The colorants used in the RF inkjet composition may be
pigments, dyes or mixtures thereof. Suitable colorants include, but
are not limited to, cyan, yellow, magenta and black colorants.
Examples of dyes that may be used in the RF inkjet composition
include, but are not limited to, acid dyes, basic dyes, direct
dyes, reactive dyes and anionic and cationic dyes. Examples of
pigments that may be used in the RF inkjet composition include, but
are not limited to, titanium dioxide pigments, iron oxide pigments,
carbon black and organic pigments. The pigments desirably have
particle sizes that are sufficiently small to avoid clogging of
inkjet printer nozzles. Clogging of the nozzles may generally be
avoided by employing pigments having an average particle diameter
of no more than about 5 microns, and, preferably, no more than
about 1 micron. The amount of colorant present in the RF inkjet
composition will depend on the desired color and intensity of the
final ink product. However, in some illustrative embodiments,
colorants may be present in an amount of about 1 to 10 wt. % based
on the total weight of the inkjet ink composition. This includes
embodiments where the inkjet inks include about 1 to 8 wt. % and
further include embodiments where the inkjet inks include about 2
to 6 wt. % colorant based on the total weight of the inkjet ink
composition. Examples of suitable pigments and dyes for use in the
present ink formulations may be found in U.S. Patent Application
Publication No. US 2004/0080593 and in U.S. Pat. No. 5,814,138, the
entire disclosures of which are incorporated herein by reference.
Some non-limiting examples of dyes that may be used in the present
RF inkjet composition include anthraquinones, monoazo dyes, disazo
dyes, phthalocyanines, aza[18]annulenes, formazan copper complexes,
triphenodioxazines, Bemacid Red 2BMN; Pontamine Brilliant Bond Blue
A; Pontamine; Food Black 2; Direct Blue 199; Direct Blue 86;
Reactive Red 4; Acid Red 92; Cartasol Yellow GTF Presscake,
available from Sandoz, Inc.; Acid Yellow 23; Basacid Black X34,
available from BASF, Carta Black 2GT, available from Sandoz, Inc.;
Direct Brilliant Pink B (Crompton-Knolls); Levaderm Lemon Yellow
(Mobay Chemical Company); Spirit Fast Yellow 3G; -Sirius Supra
Yellow GD 167; Pyrazol Black BG (ICI); Morfast Black Conc A
(Morton-Thiokol); Diazol Black RN Quad (ICI); Direct Yellow 86;
Acid Red 249); Direct Black 168; Direct Yellow 132; Aminyl
Brilliant Red F-B, available from Sumitomo Chemical Co. (Japan) and
mixtures thereof. Some non-limiting examples of pigments that may
be used in the compositions include titanium dioxide, iron oxide,
carbon black, copper tetra-4-(octadecyl sulfonamido)
phthalocyanine, X-copper phthalocyanine pigment, CI Pigment Blue,
Anthradanthrene Blue, Special Blue X-2137, diarylide yellow
3,3-dichlorobenzidene acetoacetanilides, CI Solvent Yellow 16, CI
Dispersed Yellow 33, 2,5-dimethoxy-4-sulfonanilide
phenylazo-4'-chloro-2,5-dimethoxy aceto-acetanilide, and Permanent
Yellow FGL. In some cases the colorants themselves may provide
sufficient ions to promote adequate ionic conduction in the
presence of the RF energy.
[0048] Optionally, a polymeric binder may be added to the RF inkjet
composition. These polymeric binders act as viscosity control
agents and help to affix colorant to a substrate after the ink has
been printed and dried. However, it should be recognized that when
RF-activatable ionomers are present, the RF-activatable ionomers
themselves may provide an adequate binder, eliminating the need for
additional polymeric binder. Where a polymeric binder is present,
the amount of polymeric binder added should be sufficient to
provide an inkjet ink composition having a viscosity suitable for
inkjet printing applications. For example, some RF inkjet
composition in accordance with the present invention will contain
about 0.1 to 20 wt. % polymeric binder. This includes embodiments
where the RF inkjet compositions contain about 1 to 10 wt. %
polymeric binder. Suitable polymeric binders are listed in U.S.
Patent application publication No. 2004/0080593. These polymeric
binders include water soluble polymers such as gum Arabic,
polyacrylate salts, polymethacrylate salts, polyvinyl alcohols,
hydroxypropylcellulose, hydroxyethylcellulose,
polyvinylpyrrolidinone, polyvinylether, starch, polysaccharides and
polyethyleneimines derivatized with polyethylene oxide and
polypropylene oxide, water-soluble acrylic resins and emulsion
polymers.
[0049] Other additives that may be found in RF inkjet composition
include, but are not limited to, surfactants, wetting agents,
defoamers, humectants, buffers, chelating agents, solubilizers and
biocides. These additives may be present in amounts of about 0.1 to
15 wt. % (e.g., about 0.5 to 10 wt. %), based on the total weight
of the ink composition. More specifically, a typical ink
composition might contain about 0.1 to 10 wt. % surfactant, about
0.05 to 1 wt. % biocide, about 0.1 to 0.5 wt. % buffer and/or about
0.01 to 1 wt. % other additives, such as chelating agents,
defoamers and solubilizers.
[0050] The inkjet inks are characterized by high ionic
conductivities and RF energy susceptibilities. Ionic conductivity
is not the same as electric conductivity as highly ionic conductive
materials may be substantially electrical insulators. One measure
of radiofrequency susceptibility is the dielectric loss factor
otherwise known in the art as the imaginary portion of the relative
permittivity. In contrast, the real portion of the relative
permittivity of a material is known as the dielectric constant. For
some of the inkjet inks provided herein the dielectric loss factor
is at least about 15. This includes embodiments where the
dielectric loss factor at a frequency of 30 MHz is at least about
15, further includes embodiments where the dielectric loss factor
at a frequency of 30 MHz is at least about 100, still further
includes embodiments where the dielectric loss factor at a
frequency of 30 MHz is at least about 1000, even further includes
embodiments where the dielectric loss factor at a frequency of 30
MHz is at least about 10,000.
[0051] In other embodiments, ions required for promoting ionic
conduction in the radio frequency field are additionally provided
by the substrate itself. The act of printing the ink onto the
substrate causes these ions to dissociate in the water and polar
solvent, thus providing sufficient ionic character for ionic
conduction. In some embodiments, the colorant itself may be active
in the RF field. For example, some carbon black pigments are
electrically active as a result of their structure. Inks containing
these materials can be a problem unless the RF susceptibility is
controlled so as to prevent arcing in the field.
[0052] The inkjet inks may be formulated such that they have
viscosities and surface tensions that are appropriate for inkjet
printing applications. Viscosities of about 1 to 25 cp at
25.degree. C. and surface tensions of about 30 to 60 dynes/cm at
25.degree. C. are typically suitable for inkjet printing. However,
the present compositions are not limited to those having
viscosities and surface tensions that fall within these ranges.
[0053] In one embodiment of the invention, the RF inkjet
compositions are sublimation inks. These inks include a RF
susceptor and a heat activated sublimation colorant. The RF
susceptor may be a RF-activatable ionomer, as described herein.
However other RF susceptors, including metal salts, may also be
used. The sublimation colorant may be any dye, pigment or coloring
agent that is caused to sublimate at an elevated temperature. As
used herein, an elevated temperature is any temperature above the
printing temperature at which the inks are printed onto a transfer
substrate. For typical inkjet printers, the elevated temperatures
will generally be at least about 300.degree. C. (e.g., about 300 to
500.degree. C.). Sublimation colorants are known and commercially
available. The sublimation colorants may have a sublimation
temperature or activation temperature of 120.degree. to 300.degree.
C. Examples of such colorants are the following dyes: C.I. Disperse
3 (cyan), C.I. Disperse 14 (cyan), C.I. Disperse Yellow 54
(Yellow), C.I. Disperse Red 60 (Red), Solvent Red 155 (Diaresin Red
K, red), etc. Commercial sources of such dyes include Keystone
Aniline's Sublaprint.RTM. series, BASF Corporation's Bafixan.RTM.
Transfer Printing dyes series, Eastman Chemical's Eastman.RTM.
disperse series and Crompton & Knowles Corporation's
Intratherm.RTM. disperse dyes series.
[0054] The sublimation inkjet inks may further contain a solvent,
which may be water, an organic solvent or a mixture of water and at
least one other organic co-solvent. Suitable solvents include the
polar carriers and solvents described previously. In formulating
the inkjet inks, it may be desirable to first prepare a dispersion
of the sublimation colorant in the solvent, with or without the
help of a dispersion aid. Sublimation colorant dispersion are
commercially available in the form of ink formulations. These ink
formulations may be combined with the RF susceptor and any optional
binders and additives to provide an RF-activatable sublimation ink.
Examples of sublimation ink formulations that may be used to make
the present RF-activatable sublimation inks include those described
in U.S. Pat. Nos. 5,487,614; 5,488,907; 5,601,023; 5,640,180;
5,642,141; 5,734,396; and 5,830,263; the entire disclosures of
which are incorporated herein by reference.
[0055] In addition to the RF susceptors, the sublimation colorant,
solvents and dispersants, the sublimation inkjet inks may include
various additives commonly found in inkjet inks. These include,
humectants, biocides, surfactants, complexing agents, and other
similar components. The RF inkjet inks of the present invention can
be provided in water soluble, water dispersible, water reducible or
emulsion forms.
[0056] Methods of printing with the RF-activatable sublimation
inkjet inks include the steps of applying the inks to a transfer
substrate and activating the inks by exposing them to RF radiation
to generate heat in the inks, causing the sublimation colorants to
sublime (vaporize) and deposit onto the media to be printed where
they transform back into solids. Media that may be advantageously
printed using a sublimation printed process include, but are not
limited to, papers, textiles and non-woven materials. The
sublimation inks may be printed onto the transfer substrate by a
printer, but the sublimation colorants are not sublimated during
this initial printing process. However, in some embodiments the
sublimation inks may undergo RF heating during the initial printing
step in order to speed up the drying of the sublimation ink
composition on the transfer substrate. Using RF energy to sublime
the sublimation colorants provides faster heating than conventional
heat presses and, therefore, greatly increases the rate of ink
transfer.
[0057] In another embodiment of the invention, the RF inkjet
composition react with media used for printing. In one aspect of
this invention, media containing reactive groups for reaction with
the RF inkjet composition are used. The reactive component in the
ink may be the RF susceptor itself, or another reactive component,
such as a binder, that is heated by an RF susceptor. In some
embodiments, the reactions occur between binders and/or polymeric
RF susceptors in the inks and the media upon exposure to RF energy.
This allows printing on non-porous media, such as plastic films,
with improved resistance properties of images produced. For
example, plastic films that are corona treated can be used with
inks based on multivalent metal crosslinkers (e.g., zinc or
zirconium ammonium carbonate) and carboxylic acid functional
binders. Similarly, paper containing alkyl diketene can be used for
inks containing binders with cationic or amine functionalities. In
other embodiments, the colorant used in the RF inkjet composition
has a reactive group that reacts with a medium, such as a textile,
to fix the colorant to the medium. These "reactive colorants" are
well-known. In many instances, the reactivity of the colorant
depends on the temperature. Therefore, the use of RF heating, as
provided by the RF susceptors described herein, may be useful in
promoting reactions between reactive colorants and media.
[0058] RF-activatable hot melt inks are also provided. In their
basic form these inks include an RF susceptor (e.g., a metal salt)
and a colorant, such as a dye or pigment. The hot melt inks are
printed in a molten state at an elevated temperature and then
allowed to yield a printed image. The hot melt inks may be heated
to a molten state by activating the RF susceptors contained within
the hot melt inks.
[0059] In other embodiments of the invention, a coating is provided
on the media to be printed. The coating may be applied to the media
prior to printing or it may be applied over the ink after printing,
as in the case of an overprint varnish. The RF susceptor may be
present in the ink, the coating or both. In some embodiments, the
coating includes an RF susceptor. In these embodiments RF heating
of the coating may be used to increase the evaporative drying of
the coating and/or an ink printed over or under the coating. In
some embodiments, the coating includes functional groups that are
capable of reacting with (e.g., crosslinking with) at least one
component in the inks and the reaction is initiated by, or the rate
of the reaction is increased by, RF heating resulting from the
activation of the RF susceptor in the ink and/or the coating. For
example, the RF heating initiated or facilitated reactions may
occur between reactive functionalities in the coating and reactive
functionalities on polymeric binders or reactive colorants in the
inks. Media coatings for inkjet printing are known and commercially
available. RF susceptors, including those described herein, may be
added to such coatings to provide RF-activatable media coatings.
Examples of media coatings (or "fixers") to which the RF susceptors
may be added to provide RF-activatable over- and under-print
varnishes are described in U.S. Pat. No. 6,443,568, the entire
disclosure of which is incorporated herein by reference. By
activating the RF susceptors, the coatings are heated, which may
increase the rate of ink drying on the coated media and/or initiate
or increase the rate of reactions between the coatings and the inks
and/or cause the coating to flow and provide high gloss and
optionally barrier properties. Suitable RF-activitable media
coatings are described in U.S. Pat. No. 5,500,668, the entire
disclosure of which is incorporated herein by reference.
[0060] The present RF inkjet inks can also be formulated with
polymers made by controlled polymerization processes such as
reversible addition fragmentation transfer (RAFT) polymerization.
These polymers can be presence as or in addition to the components
of RF inkjet inks discussed above.
[0061] In one other embodiment of the invention, a surfactant or
polar carrier present in the RF activitable inkjet ink undergoes a
chemical or physical change upon RF activation of the ink. This
provides printed media with increased resistance properties.
[0062] RF drying of the RF inkjet compositions provided herein may
be accomplished by printing the inks onto a substrate and exposing
the printed inks to RF energies suitable for activating the
RF-activable materials. As used herein, the term "RF" may include
any frequencies that fall within the RF range of the
electromagnetic spectrum. In some embodiments the RF susceptors are
activatable at radiofrequencies of about 100 kHz to 5.0 GHz. In
some embodiments it is advantageous to use RF susceptors that are
activatable at frequencies of less than about 3 GHz or even less
than about 1 GHz, that is, at frequencies lower than microwave
frequencies (i.e., about 1 GHz to 300 GHz). One standard preferred
frequency is 27.12 MHz which is an international industrial,
scientific and medical band. Other standard frequencies exist as
well and may be preferred but not required for this invention.
Without wishing or intending to be bound to any particular theory
of the invention, the inventors believe RF wavelengths below the
microwave frequency range may be superior because at these
frequencies, the heat generated due to ionic conductivity is much
more significant than at the higher microwave frequencies where
dielectric type dipole rotation dominates as a source of heat.
Otherwise stated, at radiofrequencies below microwave frequencies
ionic conductivity dominate the loss mechanism whereas at microwave
frequencies the relaxation process (i.e., the reorientation of
permanent dipoles) is more important. Equipment that may be used to
expose the printed inks to the appropriate RF energies is known and
commercially available.
[0063] The power of the radio frequency field to which the inks are
exposed generally ranges from about 1 to 1000 W for home and office
printers. However, a higher power may be desirable for industrial
printing devices. Thus, in some embodiments the ink compositions
are exposed to radiofrequency fields with a power of about 50 to
5000 W. This includes embodiments where the ink compositions are
exposed to radiofrequency fields with a power of about 200 to 4000
W.
[0064] Since ink tends to spread, wet and penetrate porous
substrates, the print characteristics can be manipulated by
adjusting the time between jetting of ink on the substrate surface
and heating by radio frequency energy by locating the RF field
source at a selected distance from the jetted ink to obtain desired
properties. For example one can put the field closer to the ink to
increase drying on the surface of the substrate or to increase time
by increasing the distance to the field so as to allow further
penetration and spreading of the ink into and on the substrate.
Additionally, this can be accomplished by providing a plurality of
RF heating elements in series/parallel combination, each of which
can be independently controlled in terms of RF power and frequency.
In such a case, by selectively turning off or on certain elements,
the distance between the ink contact point with the substrate and
the first powered RF element can be manipulated. In these cases,
the time the ink has to spread or penetrate the substrate can be
adjusted and the ink bound to the substrate or dried at various
locations in the substrate as desired to obtain the required print
quality such as color intensity and/or strikethrough.
[0065] In some cases the RF field can be used to preheat the
substrate prior to contact with the ink to improve printing
characteristics and optionally post heating the substrate and the
ink print in a radio frequency field. In some preferred cases, the
preheating of the substrate such as porous paper material pre-dries
and heats the sheet so that the subsequent ink print dries
faster.
[0066] Generally, the inkjet inks of the present invention may be
heated (i.e., activated) by any system capable of generating an
electromagnetic field of sufficient strength and frequency.
Examples of suitable systems are described in U.S. Pat. No.
6,348,679, the entire disclosure of which is incorporated herein by
reference. FIG. 1 illustrates a high level block diagram of a
suitable heating system 100 that is capable of generating an
electromagnetic field for activating the inks of the present
invention. Heating system 100 includes an alternating voltage
generator 102 and a probe 104, which is connected to an output
terminal 101 of voltage generator 102. Voltage generator 102
alternately positively charges and negatively charges probe 104,
thereby creating an electromagnetic field 106 centered at probe
104. Heating can occur when an RF inkjet composition 110 is placed
in proximity to probe 104. How quickly and how much heating occurs
depends on the ink itself, the strength of the electromagnetic
field at the ink, and the frequency of the alternating voltage 109
produced by voltage generator 102.
[0067] Generally, probe 104 is a conductive material, such as, but
not limited to, copper, brass, aluminum, or stainless steel.
Generally, probe 104 can have a variety of shapes, including
cylindrical, square, rectangular, triangular, etc. Generally, probe
104 can be straight or non-straight, such as curved. The preferred
characteristics of probe 104 ultimately depends on the application
that it is being used for.
[0068] FIG. 2 illustrates one specific embodiment of a suitable
system for generating RF energy. This system is termed an
"interdigitated probe system." The interdigitated probe system 201
is advantageous because it provides an extended activation zone, as
shown by the dotted rectangle 250. Interdigitated probe system 201
includes a first element 202 and a second element 204. The first
element 202 includes a first conductor 210 and one or more second
conductors 222 connected to the first conductor 210. Preferably,
conductors 222 are coplanar and uniformly spaced apart, but this is
not a requirement. Additionally, in one configuration of element
202, each conductor 222 forms a right angle with conductor 210, but
this is also not a requirement. Similarly, the second element 204
includes a first conductor 212 and one or more second conductors
220 connected to the first conductor 212. Preferably, conductors
220 are coplanar and uniformly spaced apart, but this is not a
requirement. Additionally, in one configuration of element 204,
each conductor 220 forms a right angle with conductor 212, but this
is also not a requirement. In one embodiment, first element 202 and
second element 204 are orientated such that conductors 220 are
coplanar with conductors 222 and each conductor 220 is adjacent to
at least one conductor 222.
[0069] RF applicator systems that use RF emitters, such as the
probes and interdigitated probes of the type described above, may
be incorporated into inkjet printing systems in order to facilitate
printing with RF inkjet compositions. Such systems have the
advantage of providing high power RF drying systems with short
drying cycles. FIG. 3 shows an embodiment of a RF applicator 300
that includes interdigitated probes 302 embedded into a substrate
roller 304. Many inkjet printers already have roller drives that
include one or more rollers used to guide a medium, such as paper,
through the printing zone. In the embodiment shown in FIG. 3, the
roller includes two nested cylinders. The outer cylinder 304 is a
rotating drive cylinder that propels the medium 308 (here, a roll
of paper) through the printing zone and the inner cylinder 306 is a
stationary cylinder having a plurality of interdigitated probes
running longitudinally along its outer surface. Although the length
of the probes may vary, they are desirably long enough to expose
the entire width of the medium to RF radiation. The RF power source
for the probes could be mounted inside the inner cylinder.
Alternatively, the power source could be mounted external to the
roller.
[0070] In one variation of the above-described RF applicator
system, both the upper and lower surfaces of the printed medium may
be exposed to RF radiation simultaneously. In this embodiment one
surface (e.g., the lower surface) of the medium is exposed to RF
radiation from an interdigitated probe system embedded in a roller,
as described above. In addition, a second RF source is located
above the medium. This second RF emitter may be spaced apart from,
and shaped to conform to, the curvature of, the roller. The second
RF emitter and may also be an interdigitated probe system wherein
the probes are aligned in a substantially parallel arrangement
above the upper surface of the medium, provided that the polarity
of the probes is such that the electromagnetic fields above and
below the medium do not cancel each other out.
[0071] Another example of an RF applicator incorporating one of the
printer rollers is shown in FIG. 4. In this design, a parallel
plate electrode system is created by the conductive plates 402 and
404 disposed on opposite sides of a printed medium 406. The first
conductive plate 402 is a curved plate electrode disposed over the
printed medium. The second conductive plate 406 is a roller
electrode under the printed medium. Capacitor plates 408 may be
used to couple RF energy into the roller electrode. Plates 402 and
404 are preferably constructed of copper, but may be constructed of
any suitable conductive material. The printed medium 406 may be
stationary or moving when exposed to the activation region between
plates 402 and 404.
[0072] Instead of being embedded in a roller, the RF emitters may
be incorporated into a plate positioned past the printing zone.
FIG. 5 shows one such embodiment where the RF emitter is an
interdigitated probe assembly 502 built into the upper surface of a
horizontal plate 504 which supports the printed medium. Although
the length of the probes may vary, they are desirably long enough
to expose the width of the printed medium to RF radiation. In some
embodiments the horizontal plate is the printer platen. In other
embodiments the horizontal plate may be purchased separately from
the printer and designed to mount to the printer. In still other
embodiments, the plate is a stand-alone plate. These RF applicators
provide physical separation between the print zone and the RF
activation zone and are easily adapted to for use with existing
inkjet printers.
[0073] FIG. 5a shows a block diagram of the RF field generating
system that can be assembled to demonstrate and test the invention.
The RF generator 510 is an Ameritherm 27.12 MHz variable frequency
1 KW output part number 312-0028 (Ameritherm, Rochester, N.Y.)
connected to the impedance matching circuit 512 using a 50 ohm
cable. The interdigitated probe assembly 514 is constructed in
accordance with the principles described in U.S. Pat. No.
6,812,445, with 3 mm spacing between the electrodes. In the
interdigitated probe assembly shown in cross-section in FIG. 5a,
the conductors 516 of the first element 518 are oriented parallel
to the conductors 520 of the second element (not shown). The
interdigitated probe assembly used in this example has an RF field
activation zone that is 50 mm wide and 75 mm long, and a
capacitance of 23.7 picofarad. The impedance matching circuit
consists of variable parallel plate capacitors of 15.2 picofarad
with a parallel resonating copper tube coil of 1.4 micro henries.
All connections within the impedance matching circuit and to the
interdigitated probe assembly are kept short to minimize stray
capacitance and inductance. During the initial start up of the
system it is necessary to match the impedance of the interdigitated
probe assembly loaded with the wet ink to the 50 ohm source
impedance of the RF Generator. An Agilent model E4991A impedance
analyzer (Agilent Technologies, US) is temporarily connected to the
50 ohm connector on the impedance matching network 512 and the
adjustable capacitors are adjusted to achieve an impedance match of
50 ohms, zero phase at 27.12 MHz.
[0074] FIG. 5b shows an example of the ink application equipment
and the interdigitated probe assembly 522 mounted in a paper
transport mechanism. Other methods of applying the ink may be used
including the correct placing of ink jet cartridges or ink jet
heads. In this example parts available from the Lee Company (USA)
were assembled to provide a rate controllable ink application
method. A 2 oz polypropylene Nalgene (Nalgene, USA) screw top jar
522 is pressurized with a clean dry supply of air at a pressure
between 0.5 psi and Spsi. The air may be supplied through an air
inlet line 524 attached to a bulk head fitting 526 extending
through a cap 528 on the jar 522. Ink 530 from the jar is supplied
to a solenoid valve 532 (e.g., through soft walled tubing 533)
which provides the ink to an atomizing nozzle 534. Ink from the
nozzle 534 may be sprayed onto a paper substrate 538 traveling
under the nozzle in a given direction of travel 540. The applied
ink 542 may be activated from below by the RF field 544 of the
interdigitated probe assembly 514. The pressure of the atomizing
air supply 536 and the ink application air supply are regulated and
adjusted to provide the desired coating weight. The solenoid valve
is used to turn on and off the supply of ink to the nozzle and the
valve may be controlled by a paper present sensor.
[0075] In one embodiment, a Cyan inkjet ink with an e'' (dielectric
loss factor) equal to 12,000, applied to a thin substrate material
at an equivalent coverage volume of 0.6 milliliters per
8.5.times.11 in. of substrate, will change the capacitance of the
interdigitated probe assembly 514 from 23.7 picofarads to 24.4
picofarads. The impedance matching circuit 512 is adjusted to
maximize the energy transfer efficiency to the ink. For example, if
the desired resonant frequency is 27.12 MHz and the impedance needs
to be 50 ohms at 0.degree. phase angle, the inductor located within
the impedance matching network 512 will have a value of
approximately 1.3 microhenrys and the capacitors within the
impedance matching network 512 will have a value of approximately
18 picofarrads. This example of optimizing the energy transfer
efficiency to the ink by adjusting the RF impedance matching
network 512 to the capacitance of the interdigitated probe assembly
514 has been successfully tested with applied RF power ranging from
20 W up to 400 W at a frequency of 27.12 MHz and achieving an
energy transfer efficiency of 85% as measured by the -3 db Q value
efficiency method disclosed in US patent application number (JD
586).
[0076] To implement this invention into an inkjet printer, it is
necessary to balance the susceptablity of the RF active inks to the
applicator RF circuit characteristics. The RF circuit
characteristics are constrained by the physical constraints of the
systems described in FIG. 3 through FIG. 7. Specifically the
capacitance of the probe system is restricted by the physical
constraints of the RF electrode applicator system location within
the inkjet printing system. Adjusting the RF susceptibility of the
RF active inks to maximize the delivery of energy from the RF field
to the inks is achieved through the formulation of the RF active
inks composition by adjusting the ionomer or other susceptor
component levels within the formulation.
[0077] Examples of apparatus suitable for fast-drying RF inkjet
compositions of this invention include an RF module to drive an
applicator system that couples energy into the ink stream before
contact of ink with the media. In one embodiment of this invention,
the probe could be incorporated into the ink cartridge. In another
embodiment of this invention, the probe could be mounted separately
on a carriage for the ink cartridge.
[0078] In one exemplary embodiment of an applicator system in
accordance with the present invention, an inkjet printing assembly
includes an inkjet cartridge and an RF applicator for heating
localized areas of media along print lines so that RF inkjet
compositions, upon ejection from the inkjet cartridge and after
contact with the media, are exposed to RF heating substantially
immediately, increasing the rate of evaporative drying of the inks.
The RF applicator may include an RF emitter incorporated into the
ink cartridge itself or it may include at least one RF emitter that
travels with the cartridge. In a preferred embodiment, at least one
RF emitter is attached to the trailing edge of the cartridge such
that it activates the RF inkjet composition substantially
immediately after the ink is deposited onto the medium. In a still
more preferred embodiment, the ink cartridge includes a first RF
emitter mounted to the cartridges leading edge and a second RF
emitter mounted to the trailing edge of the cartridge. This latter
construction allows for post-application RF heating of a RF inkjet
composition in a bi-directional type inkjet print head. In
addition, the print substrate may itself include, or be coated
with, an RF susceptor. In this latter embodiment, an RF emitter
associated with the leading edge of the print cartridge may be used
to preheat the substrate in order to speed up the evaporative
drying of the ink that is subsequently applied thereto. In an
alternative embodiment, the RF emitters may travel along with the
print cartridge without being attached directly to that cartridge.
For example, the RF emitters may be slidably mounted to the same
guide shaft to which the cartridge is slidably mounted. If more
than one cartridge is present in the print head, each cartridge may
be supplied with its own RF emitter or emitters or a single RF
emitter, or pair, or set of emitters may be provided for the entire
print head.
[0079] FIG. 6 generally shows an inkjet cartridge that includes an
RF applicator in accordance with the present invention. The
cartridge 600 may be slidably mounted on a guide shaft (not shown)
on which it traverses back and forth across over a medium, such as
a sheet of paper. The cartridge has a bottom surface 602 that
remains substantially parallel to the medium surface 604 during
printing. A motor-driven device such as a band or belt is
mechanically coupled to cartridge to drive it back and forth on the
guide shaft. In the embodiment shown in FIG. 6, the RF applicator
comprises an RF probe that is built into the flexible circuit 606
on the ink cartridge. These flexible circuits (or "flex circuits")
are standard components of most inkjet ink cartridges. In this
embodiment the RF applicator comprises of an RF module, impedence
matching network and an RF probe mounted on the ink jet cartridge
with a source of DC power from the printer chasis.
[0080] FIG. 7 shows an alternative embodiment where the ink
cartridge 700 has two RF applicators 702, 704, one attached to each
side of the cartridge. As shown in the embodiment of FIG. 7 each RF
applicator 702, 704 includes an RF probe 706, 708 facing the
surface of print substrate 710 while being proximately spaced there
from. Normally, the RF emitters are mounted on planar surfaces of
the applicators and oriented substantially parallel to the surface
of the medium to be printed, generally, but not necessarily, at an
elevation of about 2 millimeters or less above the print lines. In
this embodiment the RF applicator comprises of an RF module,
impedence matching network and an RF probe with a source of DC
power from the printer chassis.
[0081] The RF emitters are desirably low power emitters that are
incorporated directly onto the ink cartridge by utilizing available
traces on the flexible circuit of the ink cartridge, as shown in
FIG. 6. In one embodiment of the invention, the traces on the
flexible circuit are used to provide an interdigitated probe
radiofrequency emitter, of the type described above. The circuit
traces used to convey the printing signals to the ink jet head are
configured on the printed circuit or flex circuit in the form of an
interdigitated probe of the correct dimension to sufficiently
couple energy into the RF ink on the print medium. The RF power and
the print signals are multiplexed into the circuit traces allowing
both the correct operation of the printing and the heating of the
RF ink.
[0082] Operation of the systems of FIGS. 6 and 7 will now be
generally described. The ink cartridge prints swaths of ink drops
across the surface of a medium as it moves both back and forth
along its guide shaft. In each swath, ink dots are printed in a
print line. The RF applicator or applicators pass directly over
each print line on the surface of the medium as the cartridge
deposits an RF inkjet composition onto the surface of the
substrate. As the applicators pass over each print line, the RF
emitters activate the inks, causing internal RF heating, which
hastens evaporative drying and or crosslinking reactions within the
inks. In the embodiment shown in FIG. 7, the leading RF applicator
may be used to activate the surface of the medium in localized
areas ahead of each print line, provided the substrate incorporates
or is coated with an activatable coating or varnish. The trailing
RF applicator begins drying each print line substantially
immediately after ink is applied. Accordingly, the systems of FIGS.
6 and 7 function to dry printed lines before ink droplets forming
the lines can bleed substantially into the substrate, or merge with
adjacent ink droplets, or cause cockling.
[0083] Due to the proximity of the RF emitters to the printed
medium, the RF inkjet compositions may be activated after they
leave the printing nozzles and prior to contact with the medium,
causing some of the volatile solvents (e.g., water) in the inks to
be removed prior to impact on the medium. As a result, reduced ink
bleed and higher gloss can be achieved because the ink has less
time to migrate into porous substrates.
[0084] The inkjet printers used to apply the RF inkjet compositions
of the present invention include drop on demand or impulse printers
and continuous printers. One aspect of the invention provides an
impulse inkjet printer where RF heating, instead of conventional
resistive heating, is used to eject the inks from the nozzles in a
print head. These RF activated impulse printers are modeled after
conventional impulse printers where each printing nozzle in the
printer is equipped with a resistive heating element or a
piezoelectric element. In conventional impulse inkjet printing, a
rapid pressure impulse is created in the print nozzle by either
rapid heating (in the case of a thermal impulse) or rapid
deformation of the piezo element (in the case of piezo impulse). As
a result, a bubble of vapor is created by the excess pressure and
this bubble catapults an ink drop out of the nozzle and onto the
media. In the RF activated impulse inkjet printers of the present
invention, the resistive heating element on the nozzles of an
inkjet printer are replaced by RF emitters. These emitters are used
to cause rapid superheating of a RF inkjet composition inside the
nozzle. This rapid heating creates a pressure pulse and a vapor
bubble which catapults an ink drop out of the nozzle.
[0085] Suitable RF emitters that may be mounted to the inkjet
nozzles of an inkjet printer include RF probes, such as those
described in U.S. Pat. No. 6,348,679, the entire disclosure of
which is incorporated herein by reference. For example, the RF
applicator may be either a miniaturized shaped interdigitated
electrode system or a miniaturized shaped parallel plate electrode
system as determined by the optimum energy transfer required for
the ink jet system.
[0086] The use of an RF heater, rather than resistive heating, is
advantageous because RF heating is a non-contact method of heating
that provides uniform heating of the ink and lower cogation of the
ink heads.
[0087] The RF activitable inkjet inks and apparatus described above
can be used in a wide variety of printing locations, devices and
applications, including, but not limited to, homes, offices, narrow
and wide format commercial printing, for printing labels, barcodes,
in photo kiosks, and the like.
[0088] The following illustrative embodiments are intended to
further exemplify the RF inkjet compositions. These embodiments
should be not interpreted as limiting the scope of the inkjet inks
disclosed herein.
EXAMPLES
Example 1
Preparation of a Radiofrequency-Activatable Styrene-Acrylic
Ionomer
[0089] This example describes the production of a styrene-acrylic
resin ionomer for use in radiofrequency-activatable RF inkjet
composition. The solution was prepared from a commercially
available styrene-acrylic resin, JONCRYL.TM. 682. JONCRYL.TM. 682
is a low molecular weight styrene-acrylic resin available from
Johnson Polymer, Sturtevant, Wis. JONCRYL.TM. 682 has an acid
number of 238 mg KOH/g, glass transition temperature of 56.degree.
C. and a weight average molecular weight of approximately 1700. An
amount of 25.424 parts by weight of JONCRYL.TM. 682.TM. was
neutralized with 7.926 parts of a 85 wt. % active potassium
hydroxide pellets and 66.649 parts water. The resulting neutralized
batch was then heated to 80.degree. C. under nitrogen and agitated
for 3 hours until a clear mixture was obtained. The resulting
solids of the mixture was 30% and pH of 13.3.
Example 2
Preparation of RF Inkjet Composition from a Styrene-Acrylic
Ionomer
[0090] This example describes the production of
radiofrequency-activatable black inks from the ionomer of Example
1. Six inkjet inks are made from a commercially available ink to
which the ionomer of Example 1 is added. Three inks also include
glycerol as an organic polar carrier. The ink formulations (I1-I6)
for each of the six inkjet inks are provided in Table 1. The amount
of each component in Table 1 is given in wt. %, based on the total
weight of the ink formulation. TABLE-US-00001 TABLE 1 INK
FORMULATIONS I1 I2 I3 I4 I5 I6 Water 50-90 43-77 38-68 50-90 43-77
38-68 Isopropanol 0-15 0-13 0-11 0-15 0-13 0-11 Butylene Glycol
0.1-15 0.75-13 0.75-12 0.1-15 0.75-13 0.75-12 Glycerol 0 0 0 1.3
3.8 6.3 Ionomer 5 15 25 3.75 11.25 18.75 Carbon Black 1-15 0.5-13
0.75-7.5 1-15 0.5-13 0.75-7.5
Example 3
Preparation of RF Inkjet Composition from a Styrene-Acrylic
Ionomer
[0091] This example describes the production of
radiofrequency-activatable inks from the ionomer of Example 1. Six
inkjet inks are made from a commercially available ink to which the
ionomer of Example 1 is added. Each of the inks include glycerol as
an organic polar carrier. The ink formulations (I7-I12) for each of
the six inkjet inks are provided in Table 2. The amount of each
component in Table 2 is given in wt. %, based on the total weight
of the ink formulation. TABLE-US-00002 TABLE 2 INK FORMULATIONS I7
I8 I9 I10 I11 I12 Water 70-90 60-77 53-68 70-90 60-77 53-68
Isopropanol 0-5 0-4 0-4 0-5 0-4 0-4 Ethylene Glycol 0-10 0-9 0-8
0-10 0-9 0-8 Glycerol 5-10 5-10 5-10 6.5-11.5 8-12.5 10-14 Ionomer
5 15 25 3.75 11.25 18.75 Water Soluble Dye 5-10 4-8.5 4-7.5 5-10
4-8.5 4-7.5
Example 4
Preparation of RF Inkjet Composition from a Styrene-Acrylic
Ionomer
[0092] This example describes the production of crosslinking
radiofrequency-activatable inks from the ionomer of Example 1. Four
inkjet inks are made from a commercially available binder with
which the ionomer of Example 1 crosslinks upon exposure to RF
energy. Each of the inks include glycerol as an organic polar
carrier. The ink formulations (1-4) for each of the six inkjet inks
are provided in Table 3. The amount of each component in Table 3 is
given in wt. %, based on the total weight of the ink formulation.
TABLE-US-00003 TABLE 3 WATERBORNE CROSSLINKING INK FORMULATIONS #1
#2 #3 #4 DI Water 60-90 60-90 60-90 60-90 Isopropanol 0-5 0-5 0-5
0-5 Surfactant 0.1-10 0.1-10 0.1-10 0.1-10 Glycerol 1-5 1-5 1-5 1-5
Ionomer 5 5 5 5 JONCRYL .TM. 1980.sup.1 0.1-5 0 0 0 JONCRYL .TM.
89.sup.2 0 0.1-5 0 0 JONCRYL .TM. 60.sup.3 0 0 0 0.1-5 EPI-REZ
3515.sup.4 0 0.1-5 0 0.1-5 JONCRYL .TM. 540.sup.5 0 0 0.1-5 0 CYMEL
.TM. 1172.sup.6 0 0 0.1-5 0 Water Soluble Dye 5-10 5-10 5-10 0
Carbon Black 0 0 0 1-15 .sup.1A self-crosslinkable emulsion,
Johnson Polymer LLC, Sturtevant, WI. .sup.2A styrene acrylic
emulsion polymer, Johnson Polymer LLC, Sturtevant, WI.
.sup.3Solution of a styrene acrylic resin, Johnson Polymer LLC,
Sturtevant, WI. .sup.4An epoxy resin, Resolution Performance.
.sup.5A thermosetting acrylic emulsion, Johnson Polymer LLC,
Sturtevant, WI. .sup.6An amino resin crosslinker, Cytec Industries,
West Patterson, NJ.
Example 5
Preparation of RF-Activatable Hotmelt Ink from a Styrene-Acrylic
Ionomer
[0093] This example describes the production of a
radiofrequency-activatable hot melt ink. A hot melt ionomer that is
RF active is made by dissolving 6.61 parts by weight of potassium
hydroxide pellets (85% active) in 23.4 parts of glycerol. After
dissolving under heating, 23.4 parts by weight of JONCRYL.TM. 690
is added and reacted over 2 hours at 130.degree. C. to form a
viscous molten material. A soluble dye is then added to mixture
which is allowed to cool to form a solid hot melt that is active to
RF energy. The amount of each component in Table 4 is given in wt.
%, based on the total weight of the ink formulation. This ink is
particularly useful for printing labels and barcodes.
TABLE-US-00004 TABLE 4 Amount Ionomer in a polar carrier 80-99 Dye
1-20
[0094] The invention has been described with reference to various
specific and illustrative embodiments. However, it should be
understood that many variations and modifications may be made while
remaining within the spirit and scope of the invention.
* * * * *