The present invention relates to a method for providing
prints with fluorescent effects on a document generated by color electrophotographic
print processes whereas four printing stations are equipped with black, yellow,
magenta and cyan toners.
In electrophototographic color printing usually subtractive
color mixing is used whereas the printing stations are equipped with cyan, magenta,
yellow and black toners. Using common pigments - like SWOP-colorants (Specifications
for Web Offset Publications), typically, only 50% of all Pantone colors can be reproduced
by SWOP colorants. Many popular colors fall out-side the color gamut. Specifically
the fluorescent colors cannot be reproduced using a CMYK-toner set. A fluorescent
tone is particularly difficult to reproduce by means of such a color mixture. It
has therefore already been proposed to incorporate fluorescent pigments or dyes
in the toner. For instance,
U.S. Patent No. 5,105,481
, issued on April 14, 1992, discloses providing a color toner composition,
which contains colored fluorescent dyes that glow in yellow fluorescence under UV
excitation. Examples describe liquid toners with particles size of 0.4µm -
1µm and dry toners of 15µm. These toners are colored and the application
of this technology is limited to available dyes. In addition for any fluorescent
shade a specific toner has to be designed and manufactured, which is extremely time
consuming and costly.
It is an object of this invention to provide a method to
print fluorescent toners together with and beside the process colors.
These objectives can be achieved according to the present
invention by using florescent toner in the fifth print module station of an electrophotographic
printer equipped with five print modules, where four printing stations are equipped
with black, yellow, magenta and cyan toners and a fifth station is equipped with
substantially clear fluorescent toners that are printed on top of the color toners.
The toners may contain various fluorescent dyes. The concentration of dyes varies
from 0.001 to 2% and more preferably from 0.01 to 0.5%.
This method allows having fluorescent marks on the paper
without significantly coloring these areas or without changing the colors of these
areas. On the other hand the method allows that any color appears fluorescent on
a print as well as any picture combined of different colors and uncolored areas.
The dyes maybe optionally melt-compounded or added to the
toner formulation consisting of polymer resin, optional charge control agent, via
a CPT (chemical prepared toner)- process. The binder can be compounded with a colorant,
i.e., a dye or pigment, either in the form of a pigment flush (a special mixture
of pigment press cake and resin well-known to the art) or pigment-resin masterbatch,
as well as any other desired addenda known to the art. If a developed image without
modification of the original color of the pigment is desired, no colorant need to
be added. Normally, however and this is the case for the first four colors, a colorant
can be included and it can, in principle, be any of the materials mentioned in
Colour Index, Vols. I and II, 2nd Edition (1987
) or listed in the
Pantone® Color Formula Guide, First Edition 2000-2001
. The choice of colorants is described as well in e.g., proceedings of
IS&T NIP 20: International Conference on Digital Printing Technologies, IS&T:
The Society for Imaging Science and Technology, 7003 Kilworth Lane, Springfield,
Virginia 22151 USA ISBN: 0-89208-253-4, p. 135
. Carbon black can especially be useful while other colorants can include
pigment blue, pigment red, and pigment yellow. Specific colorants can include copper
phthalocyanine, and pigment blue sold under the trade designation LUPRETON BLUE
SE1163. The amount of colorant, if used, can vary over a wide range, e.g., from
about 1 to about 25, and preferably from about 3 to about 20 weight percent of the
toner component. Combinations and blends of colorants may be used as well.
The colorant may have the function of a charge control
agent and vice versa.
Otherwise, the process of the present invention can conform
to any well-known process for preparing dry toners wherein pigments are conventionally
incorporated in a toner core, i.e., for example by compounding, classifying and/or
grinding. Instead of embedding pigments in a toner core it is also possible, for
example, to utilize a shell construction wherein a pigment is applied to the surface
of a toner body, especially as part of a coating, optionally alone or mixed with
other ingredients, for example with polymers, waxes, or charge control agents. Illustrative
U.S. Patent No. 5,298,356, issued on March 29, 1994
U.S. Patent No. 6,110,633, issued on August 29, 2000
, the disclosures of which are hereby incorporated by reference thereto.
Finally the inventive toner maybe coated with an additional
component on the surface consisting of hydrophobic fumed metal oxides like silica,
aluminia, or titania in concentrations of about 0.1 % to about 3%.
The toners may be alternatively produced by so-called chemical
toner processes, called as well "chemically prepared toners", "polymerized toners"
or "in situ toners". The toners may alternatively be produced using controlled growing
instead of grinding. Chemical process to be used are, among others, suspension polymerization
); emulsion aggregation (e.g.,
U.S. Patent No. 5,604,076
, issued on February 18, 1997); micro-encapsulation (e.g.,
); dispersion (e.g.,
U.S. Publication No. 2003/0087176 A1
, published on May 8, 2003); or chemical milling (e.g., proceedings of
IS&T NIP 17: International Conference on Digital Printing Technologies, IS&T:
The Society for Imaging Science and Technology, 7003 Kilworth Lane, Springfield,
Virginia 22151 USA ISBN: 0-89208-234-8, p. 345
). The disclosures of al the above references are hereby incorporated by
In further developments of the present invention, the clear
fluorescent toner absorbs light in the UV-A range and the mean particle size of
the toner is 4 - 20µm or preferably 4 - 8µm or even more restricted 5
- 7µm. The strict reduction of the particle size is found to be optimal for
this application. Coarser particles produce ragged lines and dots and thus degrade
copy quality. Smaller particle sizes require longer grinding times in manufacturing
and tend to produce more dirt at a given charge to mass relation.
The invention can be advantageously used in watermarking
and other security printing applications. Reference is made to the PCT-patent application
Another approach involves metallic pigments or metallic
effect pigments added to the clear fluorescent toner. The combination of fluorescent
and metallic effects on top of colored areas like parts of a photographic picture
is most attractive e.g. for advertisement purposes. In a further development of
the present invention, the pigment is made platelet shaped. This is particularly
advantageous for its adduction to a surface of a (larger) toner material particle.
Reference is made to
European patent application 05015165.3
, the disclosure is incorporated herein by reference.
It is another object of the invention to provide a print
item produced by use of color electrophotographic print processes that show fluorescent
effects and consist of a substantially clear fluorescent toner that is printed on
top of a printed image which is produced of black, yellow, magenta and cyan toners.
This print item may include fluorescent toner that absorbs light in the UV-A range.
Another approach provides a print item where the clear fluorescent toner has metallic
pigments or metallic effect pigments within. As mentioned above the combination
of fluorescent and metallic effects on top of colored areas like parts of a photographic
picture is most attractive e.g. for advertisement purposes and can be used for security
printing as well.
In the detailed description of the preferred embodiment
of the invention presented below, reference is made to the accompanying drawings,
- FIG. 1 shows a schematic representation of a printing machine that incorporates
five printing units,
- FIG. 2 shows the absorption spectra of a dye suitable to produce a substantially
clear fluorescent toner and
- FIG. 3 shows the emission spectra of a dye suitable to produce a substantially
clear fluorescent toner.
Referring now to the accompanying drawings, FIG. 1 shows
a schematic representation of a printing machine 1 that incorporates a printing
unit 2 for applying a colorless toner containing fluorescent dyes. The printing
machine incorporates four additional printing units 3 through 6. These printing
units 3 through 6 are shown collectively in FIG. 1, in a printing mechanism 7. In
this printing mechanism 7, toner images in the CMYK colors are applied to substrate
8 which consists for example of paper cardboard or other packaging materials like
In the printing machine 1, the substrate 8, as is shown
in FIG. 1, is conveyed along a travel path in the direction of the arrow 11. The
substrate 8 sequentially passes through the printing mechanism 7, the printing unit
2, and a fuser mechanism 13, by which the toner images in the CMYK colors and the
toner image formed by the colorless toner on top of the CMYK toner images or directly
on the substrate are fused onto the substrate 8.
The toner images can be fused by the application of heat
and pressure, but also by contact-free methods, for example, through continuous
or discontinuous irradiation fusing, such as IR fusing, flash fusing, or microwave
The dye that is to be added to the colorless toner is selected
on the basis of the composition of its wavelengths. Ideally its excitation wavelength
is in the UVA range, which is contained in natural light and many forms of artificial
Figure 2 shows the excitation spectrum of a fluorescence
dye that absorbs light in the UVA-range 325 - 380 nm und is added in a concentration
of 0.1 % receiving a clear fluorescent toner. Figure 3 shows the emission spectrum
of the same fluorescent dye, which shows that the toner emits blue fluorescent light.
Depending on the selection of the dye other fluorescent colors are achievable as