Printing – Processes – Specific ink
Reexamination Certificate
2003-04-29
2004-12-28
Nguyen, Anthony H. (Department: 2854)
Printing
Processes
Specific ink
C101S483000
Reexamination Certificate
active
06834589
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to certain colorants for utilization within water-based inks which exhibit improved chromatic properties. In particular, such colorants provide magenta or cyan colorations which exhibit increased color space characteristics, high water solubility, excellent compatibility with impurities, and correspondingly cost-effectiveness for flexographic printing procedures. The methods of utilizing such colorants within flexographic printing processes are also encompassed within the invention.
DISCUSSION OF THE PRIOR ART
Flexographic printing is widely accepted as a versatile overall method of large-scale printing on paper (such as, for example, on and for newspapers and paper advertisements), cardboard, and plastic film substrates. Such a procedure entails the utilization of relief-type printing, including raised rubber, and/or polymeric plates with images present thereon. Such a procedure requires specific inks exhibiting very specific physical characteristics, including, without limitation, aqueous-based and low viscosity, in order to ensure ease in application and omission of organic solvents. Of enormous importance within such a process, the inks utilized must not exhibit appreciable rub-off, and thus must possess a very low drying time after contact and application on the desired paper substrate surface. Such a requirement is rather difficult to accomplish with low viscosity, water-based inks. Examples of such traditional flexographic printing ink colorants may be found at Chapter 2, entitled “Printing Process”, and in particular Section 2.2, entitled The Flexographic Process, pages 33-42 and Chapter 9, entitled “Flexographic Inks”, pages 547-598 of
The Printing Ink Manual
(Fifth Edition, Edited by R. H. Leach, R. J. Pierce, Published by Blueprint of London, 1993), herein entirely incorporated by reference.
Such standard flexographic ink colors are black, yellow, cyan, and magenta. Although the desired physical properties have been obtained for such standard color inks in the past, there has been an unfortunate lack of corresponding coloring properties available to permit full benefit of such inks as coloring agents for and on the desired printing substrates. For example, the available color space for such traditionally utilized cyan and magenta flexographic inks has been rather limited. Colorability for sample inks and compounds and/or compositions are mathematically defined by measuring the individual components of the equation:
E
*=((
L
)
*2
+(
a
*
)
2
+(
b
*
)
2
)
1/2
wherein E* represents the total color measurement of the printed sample. L
*
, a
*
, and b
*
are the color coordinates; wherein L
*
is a measure of the lightness and darkness of the print sample; a
*
is a measure of the redness or greenness of the print sample; and b
*
is a measure of the yellowness or blueness of the print sample. For a further discussion and explanation of this testing procedure, see Billmeyer, F. W., et al.,
Principles of Color Technology
, 2nd Edition, pp. 62-64 and 101-04, herein entirely incorporated by reference. For process printing colors, such as magenta and cyan, the desired color characteristics minimize the inclusion of the other process shades. The best example of such a mixture of colorants would be where the individual process shades contained no trace of the other process shades; however, traditional practical colors usually exhibit absorbance characteristics outside of the pure shade range. Nevertheless, it is known within the colorant industry that colorants with specific pure absorbance measurements are necessary to provide better process shades. For instance, for magenta colors, higher redness and blueness is desired, with much lower yellowness and greenness; for cyan, higher blueness and greenness is desired with the others (redness and yellowness) much lower in content and degree. These measurements ultimately determine the effectiveness of a colorant, primarily for aesthetic purposes. Furthermore, it is of great importance, in relation to these measurements, that the target colorant exhibits a specific &lgr;
max
value in order to determine the proper color itself. For magenta, a range of such values is between 525 and 545 nm; however, the ultimate value for such a color is about 534 nm (of course, the measured a
*
and b
*
of such colors determine the absorbance characteristics as well; thus, attaining certain corresponding levels of such measurements is thus instrumental in obtaining such specific magenta or, as noted below, cyan colorants). To date, such a specific &lgr;
max
for a magenta colorant has not been attained, particularly for utilization within water-based flexographic inks. The best performing colorant is a rhodamine pigment exhibiting CIELAB values as follows at a density necessary for contact and retention on a printing substrate (cellulosic-based paper, for example) at about 0.96: L
*
=52.25, a
*
=51.60, and b
*
=−4.48. Although these measurements are acceptable for certain coloring processes, again, magenta colorants for water-based flexographic printing require even better absorbance characteristics to provide effective shades and hues (the hue error is relatively high for such a pigment, about 44.9, and the grayness is relatively high as well at about 16.8). Thus, improvements are still necessary to accord the desired magenta water-based flexographic colorants needed for effective and aestheticially pleasing print colorations. Again, the attainment of such a specific colorant would provide excellent bright colors and effective mixtures with other colorants for the purposes of providing different hues and shades on the target printing surface.
The same necessity holds true for the ultimate target for cyan color exhibiting a &lgr;
max
of about 629 nm (however, again, the a
*
and b
*
values for such a colorant actually determines the desired absorbance characteristics). In effect, such theoretical colorants as discussed above must also exhibit low hue errors and low grayness values as well. With such a colorant, the effective color space would expand to such a degree that the resultant colorant would prove to be extremely versatile, particularly as a color constituent in a combination of different colorants.
Furthermore, blends of colorants, either in terms of within actual compositions to be applied to printing surfaces or as overprints on such surfaces, also exhibit certain a* and b* values that are unique and determine the effectiveness of such blends in terms of colorations, brightness, and overall empirical appearance. As such, blends of colorants in terms of magenta and cyan constituents (and thus able to provide different hues shades such as violet, red, and blue, and other shades therefrom) should also exhibit sufficient and/or acceptable CIELAB values (again, a* and b* measurements) that provide the desired levels of aesthetic qualities. To date, the lack of effective magenta and cyan colorants exhibiting such necessary a* and b* values has in turn prevented such needed blends as well.
The diagrams of
FIG. 1
(individual color space measurements for certain traditional and inventive cyan and magenta colorants) show how traditional colorants are limited in their available coloring properties. The areas of color space presented with these diagrams indicate the limitations of such traditional colorants, particularly due to resultant high hue error and grayness characteristics. Such characteristics are problematic for flexographic printing in particular when mixing with other colors is necessary to provide a full complement of different hues and shades for and on the desired print substrate. A high hue error may present difficulty in producing desired colors requiring the cyan and/or magenta component (such as violet, red, blue, green, and the like). Grayness affects the shade and appearance, and if such a characteristic is too high, dullness, and the like, will be prevalent, particularly when such colorants are utilized in combination with others (
Harris Philip G.
Moore Patrick D.
Milliken & Company
Moyer Terry T.
Nguyen Anthony H.
Vick, Jr. John E.
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