CA2273439A1 - Four color printing system - Google Patents

Abstract

A four color printing system having an expanded color gamut is disclosed that comprises four-inks, in which at least two of said inks are fluorescent inks. A
four color printing process is also disclosed which comprises printing a first ink having a first color, printing a second ink having a second color, printing a third ink having a third color, and printing a fourth ink having a fourth color, wherein the inks are printed in succession and at least two of the inks axe fluorescent inks and at least one of the fluorescent inks is UV
curable.

Description

FOUR COLOEt PRINTING SYSTEM
FIELD OF THE INVENTION ' i5 w i I - _ The invention relates generally to a four color printing system and more particularly to a tour color lithographic printing system wherein at least two of the ~.0 colors are created using fluorescent inks thereby providing an expanded color gamut. The invention also relates to a four color printing process and more particularly to a four color lithographi.c~printing . process wherein at least two of the four inks printed 15 during the process are fluorescent inks thereby providing for an expanded color gamut.
BACKGROUND OF THE INVENTION ' Today, most high quality color reproduction is done 20 by four color printing processes. Generally, in a four color printing process, the color original is separated into four separate images. Each image is printed from a separate printing plate or image carrier with a different ink to recreate a visual impression of the color 25 original.
Lithography (stone writing) is often used for such four Color printing processes. Lithography as invented in the late 1700s involved the direct transfer of an image from a stone or plate to paper. The lithographic 30 process requires that the ink adhere only to the image- -containing portions of the plate, and this adhesion selectivity is based on the principle that grease and water do not m~.x.
The offset principle was developed in the early 3,5 1900s and included an additional cylinder or the like covered with a rubber blanket or other material between i, the image plate and impression~cylinders. The ink is first transferred from the plate to the rubber blanket, and then from the blanket to the paper or other substrate. The offset press has important advantages aver other printing methods such as: (1) the abrasive ~;5 papex or substrate does not come into contact with the metal printing plate, resulting in less wear on the plate, (2) the speed of printing is increased, and (3) less ink is required for equal coverage, thereby reducing trapping problems and decreasing the tendency of the printed sheets to smudge and set off. Kirk-Othmer Encyclopedia of Chemical Technology (3d ed. 1985).
The first offset presses were single color.
However, two, three, four, five, six, seven and eight color presses have been developed and used. The °15 developments In lithographic printing equipment resulted mainly from improvements in the quality of printing plates and the efficiency of plate making methods.
Today, practically all printing plates are made photomechanically.
v20 Process color printing is based on the Young-Helmholt2 theory of three color vision. White light, i which is a combination of all the wavelengths of light, consists of three primary colors, blue, green and red.
These are broad bands of color in.which each wavelength .25 of light varies in color from every other wavelength.
i Color reproduction is based on the three color theory of vision in terms of duplicating the operations that the' j eye and brain perform when a color scene is viewed.
The four colors generally used in a four color '30 lithographic printing process are cyan (blue-green), -magenta (blue-red), yellow (green-red), and black, and -such combination is often referred to as the CMYK color space. The different colors in the reproduction are produced by combinations of the yellow, magenta, and cyan 35 inks. The black ink is used mainly for shadows. If the inks are transparent, they may be combined to produce many of the colors of the spectrum. If a color cannot be reproduced using some combination of these four inks, then it does not exist iri the CMYK color space.
CRT computer monitors use red, green, and. blue phosphors to reproduce colors (RGB color space). The RGB
phosphors color.space includes a greater variety of colors than the CMYK color space. This is why colors can be seen on a computer monitor which cannot be reproduced with CMYK. Also, While RGB monitor color space has a larger gamut than CMYK, it still does not include all 10 colors visible to the human eye. The color space differences between the computer monitor and the printer has lead to one common goal shared by printing developers and manufacturers - to achieve a printing system having an expanded color gamut which can print more of the 1S colors seen via the RGB color space on a computer CRT.
The gamut of a device is the subset of visible colors that device can display or reproduce.
Another problem shared by printing process developers and manufacturers is the a_uality of the ZO printing ink used in the processes. The colors of printing inks are not always ideal. As a result, a reproduction can lack crispness, cleanliness, color purity and saturation. Many of the colors can be dirty and muddied, and color correction may be necessary.
25 Various methods have heretofore been used to achieve a printing system having an expanded color gamut and cleaner, purer Colors. Often this is accomplished using five, six, or more colors. However, never before has a four color printing system been developed with an 30 expanded color gamut as in the system and process of the present invention.
CMYK four color printing is an important commodity item. The technical community is driven by the high end color market to develop new printing technologies to 35 produce images of superior color, tone, and detail than is obtainable with traditional printing processes, but is made possible using an expanded color gamin.

Augmenting a set of four CMYK inks with additional inks is one way to increase the gamut of printable colors. An example of this approach is shown in U.S.
Patent No. 5,563,724. In any printing process, colors 5 tend to become darker as more ink is laid down on the paper because of the subtractive interaction of the ink and the incident light. Some of the lighter hues of red, green, and blue are consequently difficult to achieve with the traditional set of CMYK primary inks since they 10 are produced from two ink combinations of the CMYK inks.
These lighter hues can be obtained by single zn.ks properly formulated to the desired hue. Additional inks tend to increase the color gamut in the darker tonal regions as well, thereby expanding the entire gamut up 15 and down the tonal range. The quarter tones and three quarter tones are especially augmented.
Commercial products are available which achieve an expanded color gamut. These include Hypercolox, by DuPont, which is CMYK plus any combination of cyan, 20 magenta and/or yellow again, and ResoLUT PS, by Scitex, which is a seven color gamut (CMYK plus red, green, and blue).
Pantone, Inc. also markets a multicolor printing system.. ?antone~s system is called Hexachrome and 25 requires six ink colors (CMYK plus vivid orange and intensified green). The increased number of inks increases color range and accuracy over four color process printing. The extra two colors increase the potential ink coverage from 400% to about 600%. However, 30 the~additional colors also increase the complexity of the color separations, the cost of the production process, and the amount of equipment needed to create a print.
Further, Hexachrome does not improve the printing of neutral colors and requires a method of proofing which is 35 not as accurate as four color process proofing.
Fluorescent inks reflect and emit light. Some commercial products have included fluorescent inks in 5:
addition to the traditional four CMYK inks. Pocket PaI, p. 151 (International Paper Company, 19?3). However, the combination of two or more fluorescent inks has not been used in a four color printing process to achieve an expanded color gamut. For example, Day-Glo Color Corporation and Color Systems Inc. have used fluorescent colors with process printing wherein the fluorescent color is a fifth color in addition to the basic four colors.
Importantly, Pantone, Inc., a developer and marketer of products for communication of color, declared that fluorescent colors cannot be used in four color process printing in the recent brochure, Pantone: Graphics Tips &
Techniques.
SUMMARY OF THE INVENTION
The present invention.overcomes the drawbacks of traditional four color printing processes by providing an expanded color gamut without the need to include. more than four inks i.n the printing process:
In general, the present invention comprises a four color printing system comprising four inks wherein at least two of said inks are fluorescent inks. Desirably, the process employed using the system of the present invention is a four color offset lithographic printing process. The inks employed are desirably cyan, black, fluorescent yellow, and fluorescent magenta. The inks can be formulated to be UV-curable if desired.
The present invention also comprises a four color .printing process which also is preferably a four color -offset lithographic printing process. Preferably, a black ink is printed first, a cyan ink is printed second, a fluorescent magenta ink is printed third, and a fluorescent yellow ink is printed last.

6.:
BRIEF DESCRIPxION OF TFLE DRAWINGS
The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawings) will be provided by the Patent snd Trademark Office upon request and payment of the necessary tee.
Figure 1 is a graphical representation of spectral data comparing the reflection of fluorescent magenta ink (ECG Magenta) to standard magenta printing ink.
ZO Figure 2 is a graphical representation of spectral data comparing the reflection of fluorescent yellow ink (ECG Yellow) to standard yellow printing ink.
Figure 3 is a three dimensional plot showing a comparison of the color gamut using conventional inks in a four color offset lithographic printing process against the expanded color gamut using two fluorescent inks, magenta and yellow, in a four color offset lithographic printing process.
Figure 4 is a slice of spectrophotometric data taken from the three dimensional plane of Figure 3 at approximately the luminance midpoint which shows the expanded color gamut achieved with two fluorescent inks in a four color printing process when compared to the color gamut achieved with conventional inks in the same, four solar printing pxocess.
DETAILED DESCRIPTION OF THE INVENTION
The present invention imparts the desirable ease and cost-effectiveness of four color process printing while achieving an expanded color gamut. Before now, such an -expanded gamut was only associated with more complicated and expensive process printing using five or more colors.
The four color printing system and printing process of the present invention therefore imparts an expanded color gamut efficiently and at a no greater cost than any previous four colox printing system o: printing process.

In general, the present invention is a four color printing system wherein at least two of the four colors are fluorescent. Use of only one fluorescent color does not increase the color gamut as significantly as the use of two or more fluorescent colors.
The printed colors may be selected from any colors which can be visualized with the human eye. Preferably.
the printed colors follow the CMYK color space and the colors of ink used are cyan, magenta, yellow, and black.
10 However, other ink colors which may be used include, but are not limited to, orange, green, pink, red, and. blue.
According to the present invention, at least two of the inks are fluorescent. Preferably, the yellow and the magenta colors are fluorescent. However, any combination of two or more colors may be fluorescent.
The inks used in the printing system of the present invention may be any conventional or waterless process printing inks. Preferably, the inks for use in the present invention are formulated to print in conventional 20 lithography, UV conventional lithography; or waterless lithography, including UV waterless lithography.
In conventional lithography using water or a fountain solution, the ink comes into intimate and .
continuous contact with water during printing. During 25 normal printing, the ink may take up about 20-40% of its weight in water as a water-in-~.nk emulsion. It is preferred that the ink be free from any tendency to bleed or to form an ink-in-water emulsion.
Conventional lithographic ink consists of a 30 concentrated dispersion of a colorant, such as a dye or -pigment, in a viscous oil vehicle containing various -additives, which give the ink suitable working properties. Preferably, the oil vehicle consists of a resin in a volatile solvent. Any suitable resin may be 35 used including, but not limited to, alkyd-phenolic-malic-soy oil, melamine linseed, and chinawood oil. Also, any suitable solvent may be used including, but not limited to, aliphatic hydrocarbons. These inks dry by evaporation of the solvent and the penetration of the solvent into the paper, as well as by oxidation.
Alternatively, tie vehicle may consist of reactive molecules, such. as monomers and oligomers of acrylates, instead of conventional oil/solvent vehicles. The reactive molecules polymerize when they are exposed to energy from, for example, a UV light or an electron beam, and the ink cures (dries) because of the hardening that occurs as the polymerization progresses. Inks which can be cured in this manner are used in processes such as UV
conventional lithography and UV waterless lithography;
Surprisingly, the fluorescent inks~used in the present invention, which absorb UV light, can also be formulated to cure upon exposure to UV light. The system and process of the present invention are therefore applicable to UV conventional lithography as well as UV waterless lithography, .
As mentioned above, dyes or pigments may be used as the colorants in the inks. Dyes tend to have better spectral characteristics than pigments. The minimum concentration of a dye which will produce a workable ink is governed by the desired color intensity and its workability with the printing press. As little as O.la by weight of the ink may be sufficient for certain applications. The maximum. concentration is governed largely by the depth of color desired and its workability in the printing system, but may be as high as 10% by weight of the ink. It is also dependent upon the characteristics of the desired end product. The -preferred concentration is from about 5% to about 7% by weight.
Any suitable dye which produces the desired color and is workable in the printing system of the present 3S invention may be used. Suitable dyes which may be used include, but axe not limited to, basic aniline dyes.

Examples of basic aniline dyes include Auramine and Rodamine (both manufactured by BASF).
Color pigments tend to have poorer spectral characteristics than dyes. To achieve coloring with pigments and to promote compatibility with other ink' components, the pigment is preferably utilized in the form of a dispersion, inasmuch as pigments axe by definition insoluble materials. Commercial pigment dispersions are available and typically contain from about 30 to 75% by weight of active pigment ingredients.
However, non-comme=cial pigment dispersions may also be prepared and used in the present invention.
In general, a workable pigment dispersion may have a wide or narrow particle size range depending upon the use to which the ink will be put. The lowex limit is determined by the ability to form a stable dispersion.
Pigments having a mean particle size of 0 to 2.0 microns may work in the inks of the present invention. Hdwever, it is preferable that the particle size be less than about 1 micron.
The minimum pigment concentration is governed by the desired color intensity. As little as 0.1% by weight of active pigment in the ink may be sufficient for cextain applications. The maximum pigment concentration varies widely depending upon the concentration of other components, but is usually no higher than about 30% by weight, since higher concentrations may cause ink instability and excessive ink viscosity. The preferred concentration range for most applications is from about 15% to about 30% by weight of active pigment in the ink.
Pigments are used in the preferred embodiment of the present invention. Although any suitable pigment may be used, examples include, but are not limited to, organic and inorganic pigments. Preferable organic pigments include Phalo Blue, Rubine beds, and Diarylyde (all manufactured by Ciba-Geigy). Preferable inorganic pigments include Carbon Black (manufactured by Cabot Company) and Titanium Dioxide (manufactured by DuPont).
Preferred process color inks consist of dispersions of organic yellow, rhodamine Y (magenta), and phthalocyanine blue (cyan) pigments in the proper vehicles. For greater 5 permanence or resistance to fading, rhodamine can be mixed or replaced with rubine. However, rubine does not reflect blue light as efficiently as rhodamine, and its use can therefore affect color balance.
Suitable commercial inks for.use in the practice of 10 the present invention include, but are not limited to, black ink; cyan ink, magenta ink, and yellow ink manufactured by Sun Chemical, INX International rnk Company or Kohl-Madden.
The fluorescent inks used in the present invention are bright inks capable of reflecting and emitting light.
Preferably, the inks should be transparent, so that an ink of one color can be printed over an ink of another color to provide clean, pure colors.
As with the conventional inks, the colorants for the 20 fluorescent inks employed in the present invention may be comprised of dyes or pigments.
. Dyes and pigments which fluoresce are generally within the color spectrum of yellows, oranges, reds, and greens. Typically, powders are created by pulverizing 25 solutions of the fluorescent dyes into resins. These powders can be unstable and are not very heat resistant, but do create bright colors that give a fluorescent effect in daylight, mainly in the yellow, orange, and red portions of the color spectrum. They are most brilliant 30 in~the dark when illuminated with a UV source of -radiation. Fluorescent dyes and daylight pigments are -capable of converting short wave visible and UV radiation into longer wavelengths, giving brilliant colors.
Although colors such as blue, indigo, and violet are 35 possible, they are less common as fluorescent colors.
Examples of suitable fluorescent dyes for use in the printing system of the present invention~xnclude, but are not limited to, basic dyes. Exemplary basic dyes include Rhodamine Y and Rhodamine B (both manufactured by BASF).
The minimum concentration o~ a fluorescent dye which will produce a workable ink is governed by the desired 5 fluorescence and color intensity, and its workability with the printing press. As little as 0.1% by weight in the ink may be sufficient for certain applications. The maximum concentration is governed largely by the level of fluorescence and depth of color desired, and its 10 workability in the printing system, and can be as high as 10% by weight iri the ink. It is also dependent upon the characteristics of the desired end product. The preferred concentration is from about 5% to about 7% by weight.
15 Like the conventional printing inks, the fluorescent pigments are also preferably used as dispersions.
Examples of suitable fluorescent pigments fox use in the printing system of the present invention include, but are not limited to, commercially available dispersions.
20 Exemplary commercially available dispersions include Yellow dispersion and Rhodamine dispersion (both manufactured by Radiant).
As with the fluorescent dyes, the minimum fluorescent pigment concentration in the ink is governed 25 by the desired fluorescence and color intensity, and as little as O.lo by weight of active pigment may be sufficient for certain applications. The maximum pigment concentration can vary widely depending upon the concentration of the other ink components, but is usually 30 no higher than about 30% by weight, since higher -concentrations may cause ink instability and excessive ink viscosity. The preferred concentration range for most applications is~from about 15% to about 30% active pigment by weight in the ink.
35 In general, a workable pigment dispersion may have a wide ox narrow particle size range depending upon the use to which the ink will be put. The lower limit is determined by the ability to form a stable dispersion.
Pigments having a mean particle size of 0 to 2.0 microns may work in tha inks of the present invention. However, it is preferable that the particle size be less than about 1 micron.
Preferably, the fluorescent ink colorants are fluorescent dyes dispersed into suitable flushing vehicles called flushes. Bxamples of flushing vehicles include vinyl toluenes and alkyds.
The fluorescent flushes may be combined with varnishes to produce the finished inks. Any varnish .
suitable for printing inks may be used. Preferable varnishes include alkyds and resins.
The fluorescent flushes may also be combined with 15 modifiers to produce finished process inks. Any modifier suitable for use in printing inks is acceptable.
Preferred modifiers include alkyds, resins, and aliphatic hydrocarbons. .
Suitable fluorescent inks for use in the present invention include ECG Magenta (fluorescent magenta) and ECG Yellow (fluorescent yellow) inks manufactured by INX
International Ink Company.
Both the fluorescent and non-fluorescent inks employed in the printing system of the present invention may contain additives such as humectants. drying agents, and preservatives such as biocides'and fungicides.
Addition of a humectant ensures that the ink does not prematurely dry in the plates during the printing process. Typical humectants which may be employed in the 30 inks may include glycols and hydroxylated starches.
The humectant is generally used in an amount of from about 0% 'to about 30% by weight, and preferably from about 15% to about 30% by weight in the ink.
To achieve a more rapid drying rate and accelerate hardening of the vehicle after printing, a drying agent may be added to increase the overall volatility and evaporation rate of water. Any compatible material which performs this function may be used. Suitable drying agents znclude, but are not limited to, manganese, cobalt, and other metallic drying agents.
A drying agent, when added, is preferably present in 5 an amount of from about 1% to about 2% by weight in the ink. Amounts in excess of about 10% by weight may adversely affect stability of the ink and may~cause flocculation of the pigment unless other stabilizing additives are employed.
10 In a preferred embodiment, the fluorescent inks for conventional lithography may be evaluated for use in a painting system by use of a Speedmaster 102 Heidelberg multi color offset press in 40" size. Preferably, the press is equipped with an Alcor dampening system to 15 accurately apply the correct amount of fountain solution to the printing plate, a Tower coater to accurately apply a transparent high gloss coating over the printed inks on coated stocks, and a Kodak Thermal plate imaged either analog or digitally (printing platey.
20 rn another preferred embodiment, the fluorescent inks formulated for UV conventional lithography may be evaluated in the same manner as described for the fluorescent inks formulated for conventional lithography, with an added step consisting of passing the printed 25 stocks under a UV curing system such as the Prime UV
model 120134.
In another preferred embodiment, for waterless lithography, the fluorescent inks may be evaluated for use in a printing system using a multi color GTO-DI
30 Heidelberg press having a Presstak Pearl waterless plate as the painting plate.
In another preferred embodiment, the fluorescent inks formulated for UV waterless lithography may be evaluated in the same manner as described for the 35 fluorescent inks formulated fox waterless lithography.
with an added step consisting of passing the printed stocks under a UV curing system such as the Prime Uv model 120134.
Spectral responses far INX ECG magenta and ECG
Yellow inks were determined. Although any conventional procedure known in the art may be used to determine spectral responses, the spectral responses are preferably measured with an X~Rite spectrophotometer model 938, from which the color space reproduction capabilities of the inks can be determined.
10 Figures 1 and 2 show the spectral responses of ECG
Magenta and ECG Yellow inks compared to standard magenta and yellow inks. Specifically, Figures I and 2 indicate that both ECG Magenta and ECG Yellow have greater reflection than standard magenta and yellow inks, respectively.
In the four colox printing system of the present invention, any four color lithographic printing process may be used. It is most preferable to use an offset lithographic printing process.
20 Although any suitable plates may be used, preferably lithographic printing is performed using aluminum plates.
Preferably, these plates are manufactured to a thickness of 0.15-0.51 mm, depending on the size and type of the press, with thickness tolerances of ~0.013 mm for the 25 smaller sizes and ~0.025 mm for the larger sizes.
Preferably the plates are flat with no buckles. Other metals, e.g., zinc, mild steel, stainless steel, and brass are used as bases for bimetal plates and they may be made in the sane tolerances as aluminum plates.
30 To improve the quality of the end product, the metal -plates are preferably grained or roughened priox to coating or processing. This can be done by any suitable means. For example, the plates can be placed within a flat, circularly oscillating tub containing steel balls, 35 marbles or abrasive grit an water, or can be dry grit blasted or brush grained with, for example, nylon or steel bxushes and abrasive. Grain depth is preferably 3-8 dun. Most modern lithographic plates are grained through electro chemical methods which provide greater consistency than the mechanical methods. The plate grain provides protrusions for anchorage of the coating and 5 ink, and recesses which help the surface carry moisture.
Paper, plastic, and foil-laminated plates can also be used.
For the press to work properly, the image areas on the lithographic plate are preferably ink-receptive and 10 water-repellant. The non-image areas are preferably water-receptive and ink repellent. The wider the difference in the ink and water receptivities of these two areas, the more efficient the plate is and the easier the printing.
15 The wettability of the plates may be improved by roughening the plate surface by ball or brush Braining or by sand or grit blasting. The surface may also be treated with hydrophilic materials, such as arabic gum or arabogalactan. They may be used alone or in combination 20 with phosphoric acid and salts, e.g.; ammonium bichromate, diammonium monohydrogen phosphate, and zinc or magnesium nitrate, to produce a hydrophilic layer on the lithographic plate. The acid and salts serve as buffers and conditioners to pacify the metal surface and 25 promote better adhesion of the hydrophilic gum.
The lithographic printing of the four color printing system of the present invention may occur on any suitable substrate. Generally, lithographic printing is performed on paper. The properties of the paper can affect the 30 color produced by the four color printing process. _-Although any suitable paper may be used, it is preferred that coated paper be used since it tends to produce a wider range of color than uncoated paper stock. This is because the rougher surface of uncoated stock scatters 35 the light as it is reflected back to the viewer. The four color printing system of the present invention lessens the disparity between coated and uncoated paper.

The~four color printing system of the present invention expands the color gamut when compared to traditional four color~printing processes. In particular, use of two or more fluorescent inks in a four color printing process increases the number of lighter and darker hues that may be printed. The comparison between traditional four color printing systems and the four color printing system of the present invention may be better understood by comparing the color gamut of a 10 traditional four color printing system with the color gamut of a four color printing system of the present invention wherein two of the four colors axe fluorescent.
This may be accomplished by looking at color space.
Color space describes and organizes the visible 15 colors on a set of axes so they can be communicated in a standard language. The Centre Internationale dEclairage (CIE) is an international organization that establishes methods for measuring~color. These standards for calorimetric measurements are internationally accepted 20 specifications that define color values mathematically.
CIE L* a* b* defines three axes and is used for color print production. CxE L* a* b* entails quantizing the available L* tonal range into 128 levels. For each L*
level, the hue angle is also quantized into 128 bins.
25 For a given quantized L* and hue value, the optimization routine finds the color of greatest chroma which represents the gamut boundary at that position. Both the CIE L* a* b* color and the inking which achieved that color are stored. The created color gamut represents 30 that volume of color space swept out when all combinations of its four input values (inks) are fed in.
As a data object, a gamut provides several important functions. It defines the position of the color boundary in CIE L* a* b* all along the tonal range, and it 35 determines whether a given color is in or out of the gamut. CIE colox models are device independent because the colors produced should not differ from one output device to another if properly calibrated.
Figure 3 is a three dimensional CIE ~* a* b* plot comparing the color gamut for conventional inks (cyan, 5 magenta, yellow, and black) with the expanded color gamut obtained using two conventional inks, cyan and black, and two fluorescent inks, yellow arid magenta. This plot shows an increase in the color gamut achieved by replacing two of the four conventional inks with two 10 fluorescent~inks in the same four color offset lithographic printing system. This result is confirmed by Figure 4, a slice of the spectxophotometric data from the three dimensional space of Figure 3 taken at approximately the luminance midpoint.
15 The present invention also encompasses a four color printing process. Preferably, the printing process is a -four color lithographic process, and more preferably a four color offset lithographic printing process. _~
The four color printing process comprises printing a 20 first ink, printing a second ink, printing a third ink, and printing a fourth ink, each in succession, wherein at least two of the four inks are fluorescent inks.
Preferably, each of the printed inks is a different color. Although inks of any color may be used, the most 25 preferable are yellow, magenta, cyan, and black, with at least the yellow and magenta inks being fluorescent.
Preferably, at least one of the fluorescent inks is UV curable. Even more preferably, both fluorescent inks are UV curable.
30 The inks used in the printing process of 'the present invention are preferably the same inks used in the four color printzng system of the present invention.
The inks may be printed in any sequence. For example, two common process color print sequences are (1) 35 first cyan, then magenta, then yellow, and finally black, and (2) first yellow, then magenta, then cyan, and finally black. However, the most preferred sequence is black down first, followed by cyan, and then magenta, and finally yellow down last.
All of the references cited herein are incorporated by reference.
While this invention has been described with an emphasis on preferred embodiments, it will be obvious to those of ordinary skill in the art that variations in the preferred four color printing system and process may be used and that it is intended that the invention be 7.0 practiced otherwise than as specifically described herein. Accordingly, this invention inc7.udes all modifications encompassed within the spirit and the scope of the invention as defined by the following claims.

Claims (11)

WHAT IS CLAIMED IS:

1. A four color printing system comprising four inks wherein at least two of said inks are fluorescent inks and where at least one of said two fluorescent inks is UV curable.

2. The printing system of claim l, wherein said printing system is a four color UV offset lithographic printing system.

3. The printing system of claim 1, where said printing system is a four color UV waterless offset lithographic printing system.

4. The printing system of claim 1, wherein said inks comprise colorants selected from yellow, magenta, cyan and black hues.

5. The printing system of claim 1, wherein the fluorescent inks comprise fluorescent colorants selected from yellow and magenta hues.

6. A four color printing process comprising:
(a) printing a first ink;
(b) printing a second ink:
(c) printing a third ink;
(d) printing a fourth ink, wherein said inks are printed in succession and wherein at least two of said inks are fluorescent inks and at least one of said two fluorescent inks is UV curable; and (e) curing said UV curable fluorescent ink.

7. The painting process of claim 6, wherein said printing process is accomplished using a UV offset lithographic printing process:

8. The printing process of claim 6, wherein said printing process is accomplished using a UV waterless offset lithographic printing process.

9. The printing process of claim 6, wherein said inks are selected from yellow, magenta, cyan, and black hues.

10. The printing process of claim 6, wherein said fluorescent inks are selected from yellow and magenta hues.

11. A four color printing process comprising:
(a) printing a black ink first:
(b) printing a cyan ink second:
(c) printing a UV curable fluorescent magenta ink third; and (d) printing a UV curable fluorescent yellow ink last.