Abstract:
A system and method for achieving process spot color consistency using white and CMYK toners is disclosed. The present application employs traditional CMYK using the automated spot color editing approach and enhances this approach by applying a white toner to the printing substrate prior to applying the color. This new and novel method will improve the color printing technology for printing or alternately, applying the application of the white as a distinct separation layer for the color toner separations, on plastics, ceramics, woods, and other such non-paper materials.

Description:
This application claims the benefit of U.S. Provisional Application No. 61/056,731, filed May 28, 2008, the disclosure of which is incorporated herein in its entirety by reference. 
    
    
     BACKGROUND 
     The current art of printing technology is deficient in presenting an effective way to print a wide variety of colors on a plastic, synthetic, or other non-paper surface. Reproduction of a wider variety of colors can be achieved by improving inks to incorporate a white opaque ink layer which serves to achieve a high L* gamut in comparison with a plastic substrate that does not have a sufficiently white layer. 
     BRIEF DESCRIPTION 
     The present application extends the process spot color and process color simulation/emulation of spot color gamut. The present application produces color consistency in images containing process spot colors by using white toner as an additional separation and employing color control algorithms. White toner has the ability to make the colors light and to extend the upper part of the spot color gamut in the high L* range. One present embodiment uses white toner in the appropriate xerographic station/housing to apply white first onto the substrate, followed by MYCK. In another embodiment, the process spot color control system will use WMY, WCY, WCMY, WCM gamuts to extend the spot colors in the lighter region of the gamut. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a flowchart of the method of creating process spot colors; 
         FIG. 2  illustrates a gamut with K values of 0 and 255, with no intervening values; 
         FIG. 3  illustrates a gamut with K values of 0 and 255 with one intervening value of 153; and 
         FIG. 4  illustrates a gamut with K values of 0 and 255 with four intervening value of 51, 102, 153, and 204. 
         FIG. 5  illustrates a flowchart of the method of creating process spot colors which also incorporates sub-gamuts to enhance spot color. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1 , presents a new means for creating process spot colors using a white and using a plurality of toners  100 , where the plurality of toners could be, but is not limited to, MYCK, WMYC, WMYCK, or CMKYF. The process begins by preparing at least one color separation layer  110  comprised of the plurality of toners. Then the white toner is applied to a substrate as a separation layer  120 . The white layer may be the first layer, but the scope of the present application is not limited to the white layer being the first layer. Finally, the previously prepared color separation layers comprised of a plurality of toners are applied to the substrate  130 . An addition step may be undertaken to apply color separation layers of WMY, WCY, WCMY and WCM associated with sub-gamuts onto the substrate  140  in order to bring out the spot colors. 
     In an alternative embodiment, the separation layers may also be prepared using color processing algorithms. In such an embodiment, a user would prompt a computer operable system by inputting a request for the preparation of the color separation layer and the software would break out the color separation layers in conformity with the user input specifications. A user request and user specifications may be input into the computer operable by use of a user interface such as, but not limited to, a keyboard, touch screen, mouse click, and the like. 
     The problem is to expand the range of process spot colors, process color simulation/emulation of spot color, printable on plastic, paper, synthetic or other media and achieve color consistency. In current document printing, the spot color gamut for high L* region is limited by the white measurement of the paper or other media. Color consistency is achieved in document printing using process controls and color controls technology. The current art of printing on packaging entails printing on flexible packaging, labels/tags, folding or corrugated cartons, plastics, ceramics, woods, and other such non-paper materials. To enable such printing, a white opaque ink layer is frequently used to achieve the proper color. Color consistency in packaging printing is currently achieved by an operator-controlled mechanical setups, ink control such as concentration, viscosity, mixing, ink key control, and the like. 
     This embodiment is particularly useful in printing on plastics because the white layer can change the achievable high L* region of the spot color gamut significantly compared with selected plastic substrates without the white layer. For document printing, this invention offers a smaller, incremental spot color gamut increase because the L* region of paper is approximately 95 and will change by only a few units with a white layer. 
     Two applications for this embodiment are xerographic printing systems for flexible packaging, where 85% of the substrates are plastic, and xerographic systems for printing labels. White toner may be fabricated by conventional means or by an emulsion aggregation process, where the Emulsion Aggregation (EA) is a process of growing 1-15 micron size particles from smaller, nanometer size constituents. The process is environmentally advantaged in that it is water based and does not use organic solvents commonly required to make particles in this size range. The process begins with the preparation of polymer particles in the nanometer size range emulsified in water. These particles and other desired components are then brought together in an aqueous based environment. Through control of the required chemical and physical conditions, the constituent particles are aggregated together to form larger particles. Once the particles reach their target size, the growth mechanism is halted and the particles are heated to achieve the desired shape. Particles can be completely spherical or somewhat irregular in shape. Since the mechanism of particle formation is one of controlled growth, rather than mechanical breakage, there is effective control of the particle size distribution and excellent geometric standard deviations are achieved. 
       FIG. 2  demonstrates how a change in the value of black level, represented by K, is inversely related to the volume of the total spot color gamut  200 . The CMY gamut  210  is a three-dimensional graphical representation of spot color. A CMY or a CMYK gamut is a representation of the colors that can be printed by a printing technology. The CMYK gamut represents color printing and differs from the RGB gamut that represents colors displayed by a computer terminal. The CMYK gamut comprises a smaller area than the RGB gamut indicating that not all colors displayable on a computer terminal can be displayed by printing means. 
     The size or volume of the CMYK (i.e., spot color) gamut may be increased by adjusting the black level, also known as K. An increase in K results in a decrease in total spot color gamut volume, while a decrease in the value of K represents an increase in spot color gamut volume  200 . The black levels, represented by the value K, changes in variation between a minimum value of K=0 to a maximum value of K=255. The top portion of the gamut  210  volume shown in  FIG. 2  has a large volume as signified by the large size of the shape. The bottom portion of the gamut  220  volume shown in  FIG. 2  has a much smaller volume as illustrated by an almost flat and colorless gamut. This change in black level is comparable to adding white toner. Generally, colors represented close to the origin  230  of the gamut volume are dark or grayish and weak, while colors represented further away from the origin appear more vivid and strong. 
     Within the L*a*b* response, the origin  230  represents the intersection of three axis, known as a*, b*, and L*. The a* axis  240  runs horizontally from left  250  to right  255  and represents the green to red values. Here the positive values running from the origin  230  to the right  255  cause a color to become more red in appearance as the value increases. The negative values running from the origin  230  to the left  250  cause a color to become more green in appearance as the negative number decreases moving further away from the origin. Another axis, the b* axis  260  runs back into the page and from left forward  270  to right rearward  275  and represents the blue and yellow values. Here the positive values running from the origin  230  back and right  275  cause a color to become more yellow in appearance as the value increases, while the negative values running from the origin to the front and left  250  cause a color to become more blue in appearance as the negative number decreases in value. The axis values typically run from zero at the origin to  150 . Taken together, these two axes represent color saturation and hue. The axis running from top to bottom  280  of the page represents L* which is a measure of the lightness of the color, with the value at the origin  230  zero representing black. As the values increase from zero at the bottom or origin of the graph, the color becomes less black and more white with a numerical value of one hundred representing diffuse white  290  and a value exceeding one hundred representing specular white. This is the upper part of the gamut volume in the high L* range which is extended by the addition of white toner as a separation layer. 
       FIG. 3  also illustrates use of an intermediate gamut  300  in the gamut volume. The large gamut  310  and a small gamut  320  are located on a set of axis that intersects at an origin  330 , where the axis are an a* axis  340  running left to right, a b* axis  360 , and an L* axis  380 . The gamut also increases in volume as k decreases, but also uses an intermediate gamut  350  where k=153 and is located between the large gamut  310  that occurs when k=0 and the bottom gamut  330  that occurs when K=255. Here the intermediate gamut  350  is smaller in size to the large gamut  310 , but is larger than the small gamut  320  located toward the bottom of the graph where k=0. The area closest to representing diffuse white is where k=0 at the top of the large gamut  370 . These are the upper part of the gamut in the high L* range which are extended by the addition of white toner as a separation layer. 
       FIG. 4  shows more than one gamut located on the same set of axis  400 . The size of the gamuts decrease as the value k increases and also when the value of L* decreases. The top gamut  410  that occur when K=0; to the bottom gamut  420  that occurs when k=255 both bracket a series of intermediate gamuts. The common set of axis share a common origin  430 . The three axis are the a* axis  440 , the b* axis  460  and the L* axis  480 . The intermediate gamuts occur when k=51 gamut  470 , at K=102 gamut  490 ; at K=153 gamut  450 , and at K=204 gamut  499 . This illustrates that the size and volume of a gamut progressively increases as the value of K progressively decreases and as L progressively increases. 
     Using flood coating of white limits colors presented to a 100% area coverage white under layer. Using white toner in the xerographic station/housing allows for the incorporation of colors represented by additional gamuts in the lighter part of the chromatic colors, using any digitally addressable percent area coverage of white. 
       FIG. 5  illustrates an embodiment method  500  which entails preparing a series of color separation layers  510 . The prepared separation layers are then applied to the substrate  520 , with the white toner being applied to specific areas and spots on the substrate where the white toner is needed to bring out the spot colors. The colors WMY, WCY, WCMY and WCM represented by sub-gamuts could also be added in a similar manner. The color separation layers and the white toner may be applied in any order such as, but not limited to, color separation layers first, followed by white toner, or the white toner being applied first followed by the color separation layers, or the color separation layers and the white toner may be applied at the same time, at a substantially similar time, or at close to the same time. The color separation layers and the white toner could be applied intermittently, in an order such as but not limited to, applying a portion of the color separation layer, followed by applying a portion of white toner, followed by more color separation layer, followed by more toner, repeating as necessary. 
     In one embodiment of the current application uses white toner in the appropriate xerographic station/housing such that white toner is applied first onto the substrate. For the purpose of the color controls algorithms, the imaging system will comprise of the use of four stations/housings; WMYC, when white toner is used for process spot colors. When black toner is used normal MYCK approach will be considered. 
     The differences and advantages between these embodiments and existing technology are:
         The addition of a digitally addressable white toner image.   The process spot color control system will use additional sub-gamuts representing colors WMY, WCY, WCMY and WCM to extend the spot colors in the lighter region of the spot color gamut.   Alternatively, depending on the requirement for toner usage, the same basic technology is used for producing spot colors with the full WMYC four color gamut.   Generally, white paper has absolute L* of around 95. White toner will make the absolute L* higher than 95.       

     Hence, all spot color controls using an automated spot color editor approach will be done with respect to absolute L*a*b* targets. Current algorithms use L*a*b* relative to paper. 
     The present application is not limited to colors using the CMK gamut or the CMKY gamut, and may also incorporate additional colors such as but not limited to the CMYKF gamut used in Hi-Fi color printing devices which may use extra colorants such as red, green, blue, orange, or purple colors. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.