Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-02-27
2004-04-27
Shosho, Callie (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C522S081000, C522S170000, C522S909000
Reexamination Certificate
active
06727295
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to low viscosity energy curable gravure and ink jet printing inks and methods for using same.
2. Description of Related Art
Low viscosity and good flow are the most important factors affecting liquid ink behavior and improved printability. These factors are particularly important for formulating inks for ink jet and gravure printing applications.
Schwartz et al. in U.S. Pat. No. 4,468,255, disclose rheology modifiers for arylide yellow pigment dispersions. The rheology modifiers which are derived from diarylide pigments improve the fluidity of non-aqueous arylide pigment dispersions prepared from either monoarylide or diarylide yellow pigments. Schwartz et al. in a series of patents (i.e., U.S. Pat. Nos. 4,946,508; 4,946,509; 5,024,698; and 5,062,894) have disclosed modified azo pigments for use in conventional, solvent and water based inks and coatings to function as rheology control agents. In each of these patents, Schwartz et al. modify an azo pigment (e.g., a diarylide pigment, a monoazo pigment, a disazo pyrazolone pigment and the like) by grafting a polyalkylene oxide to the pigment so that water based inks made from these pigment compositions exhibit high coloring strength, cleaner shades, lower rheology, and enhanced gloss compared with conventional water based inks.
To increase printing throughput, ultraviolet (UV) or electron beam (EB) curable inks have been developed that allow printers to reduce the solvent content of the ink. It is always a challenging task for a UV or EB curable liquid ink formulator to develop ink formulations with a viscosity low enough for improved flow, while at the same time maintaining other essential characteristics, such as to cure, adhesion, low odor, etc.
Traditional organic and inorganic pigments used in formulating energy curable liquid inks, are poorly dispersed in the vehicles used in the systems. As a result, poor pigment wetting leads to a thixotropic structure. If the inks are not subjected to high shear, the apparent viscosity will remain high and the ink will exhibit poor transfer resulting in poor printability. Flow additives have been tried, however, with limited success for different pigments. The situation becomes more critical in the case of cationic curable inks, where not all the pigments and additives can be used due to the presence of basic functionalities. In addition, some energy curable inks of the prior art contain fugitive solvent (such as water, alcohols and the like) as part of the vehicle to reduce viscosity, aid in pigment dispersion, and modify flow during printing. However, after printing but before curing, the fugitive solvent is typically removed to prevent interference with the curing process and to prevent it from having an adverse affect on the printed image. The curing delay required by solvent removal, as well as attendant unpleasant odors, are further undesirable limitations to printing. Furthermore, solvent removal is desirable for environmental reasons.
A UV-cured cationically polymerized printing ink is disclosed by Seng in Patent Application DE 195 00 968.1 for use in indirect letterpress printing or dry offset printing. Seng lists the differences between letterpress and flexographic printing and the list includes critical differences in ink viscosities. In particular, Seng discloses that printing inks used in flexographic printing have viscosities in the range of 0.01 to 2 cps and at 20° C. in the range of 3.0 to 100.0 cps, and more preferably in the range of 4.0 to 10 cps. Seng's inks are cationically polymerized and differ from the very high viscosity printing inks used in indirect letterpress printing in solvent content. While inks of this viscosity range are useful in high shear, indirect letterpress printing, such inks have high tack which causes them to be unsuitable for low shear applications such as flexography, which requires low tack inks.
U.S. Pat. No. 5,641,346, Mantell et al. teaches an ink jet ink that includes a colorant and a liquid component containing at least one of an epoxy and a vinyl ether. Water is dissolved in the liquid component. Preferably, the vinyl ether is ethylene glycol monovinyl ether. The ink jet recording process in Mantell et al. includes the steps of ejecting an ink jet ink from an orifice to form an image on a recording medium.
U.S. Pat. No. 5,275,646, Marshall et al. is directed to an energy curable conductive ink jet formulation patent disclosed a conductive ink and a method of ink jet printing with a conductive ink, containing a polar conductive material. The reference also teaches formulating non-conductive ink jet formulations, however, these formulations contain polymeric or further polymerizable material whose presence provides increased viscosity to the polymer blend. Though the patent states that the range of suitable polymers is vast, polyethylene oxide is not listed among the types of polymers that can be used (see col. 5, 11, 33-35). The '646 patent specification consistently states that in contrast to conductive ink, the viscosity of the patented non-conductive ink may be “somewhat higher, e.g. up to 40 or 50 cP at 25° C. (Col. 2, lines 25-26).
Although improvements have been made in energy curable cationic ink formulations, there continues to be a need for energy curable ink formulations (including free radical initiated curable formulations) which have a high color strength, cleaner shade and enhanced gloss but retain a very low viscosity as required by flexographic and ink jet printing.
SUMMARY OF THE INVENTION
In one aspect, the invention is an energy curable gravure ink comprising a pigment, a rheological additive having the structure:
P—(U—Y)
s
wherein P is the residue of an organic colorant, Y is a polyalkylene oxide moiety, U is a linking moiety covalently bonding Y to P and s is an integer from 1 to 3; and an energy curable liquid vehicle; wherein the ink is substantially free of fugitive solvent and has a viscosity ranging from about 3 cps to about 50 cps.
In another embodiment of this invention, this energy curable gravure ink further comprises a polymerization initiating system activatable by actinic radiation.
Another embodiment of this invention involves a method of gravure printing and curing the gravure ink composition comprising the steps of: preparing the energy curable gravure ink described supra; printing the ink onto a substrate surface to form an ink image; and subjecting the ink image to actinic radiation or thermal energy to form a cured ink image.
Another aspect of this invention involves an energy curable non-conductive ink jet ink comprising a pigment, a rheological additive having the structure:
P—(U—Y)
s
wherein P is the residue of an organic colorant, Y is a polyalkylene oxide moiety, U is a linking moiety covalently bonding Y to P and s is an integer from 1 to 3; and an energy curable liquid vehicle; wherein the ink is substantially free of fugitive solvent and has a viscosity ranging from about 3 cps to about 20 cps.
In another embodiment of this invention, this energy curable non-conductive ink jet ink further comprises a polymerization initiating system activatable by actinic radiation.
A further embodiment of this invention involves a method of ink jet printing and curing an ink jet ink composition comprising the steps of: preparing the energy curable non-conductive ink jet ink described supra; printing the ink onto a substrate surface to form an ink image; and subjecting the ink image to actinic radiation or thermal energy to form a cured ink image.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to a novel solvent-free, energy curable gravure and energy curable non-conductive ink jet printing inks having low to very low viscosities and their application. The term “energy curable or cured” as used herein, in reference to ink means an ink which can be cured, hardened, polymerized, or crosslinked by the action of actinic radiation such as UV or EB radiation and the like from a radiant energy source; o
Aurenty Patrice
Chatterjee Subhankar
Kotora Gordon
Laksin Mikhail
Merchak Paul A.
Persley Sidney
Shosho Callie
Sun Chemical Corporation
LandOfFree
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