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(19) United States
(12) Patent Application Publication (io) Pub. No.: US 2004/0250726 Al
Mott et al. (43) Pub. Date: Dec. 16,2004
INKJET INKS HAVING CYAN, YELLOW, MAGENTA, AND/OR BLACK COLORANTS AND METHODS OF USING THE SAME TO PRODUCE BLACK AND WHITE IMAGES
FIELD OF THE INVENTION
 The present invention relates to ink-jet inks having cyan, magenta, yellow, or black colorants in an ink vehicle. The inkjet inks can be used to produce neutral, cool, warm, and sepia tones of gray.
BACKGROUND OF THE INVENTION
 Black and white images having a high resolution, such as black and white photographs, are growing in popularity. Despite accounting for only a small percentage of the total images produced each year, photographers continue to produce black and white photographs using conventional silver halide techniques. The photographers are also adapting inkjet printing techniques to produce high resolution, black and white images. For instance, black and white images are printed using a color inkjet printer by applying ink-jet inks of composite colors on the print medium. The color inkjet printer mixes cyan, magenta, yellow, and black inkjet inks on the print medium to achieve a composite black. To create gray tones, the cyan, magenta, yellow, and black inkjet inks are mixed in varying ratios on the print medium. One disadvantage of using color inkjet inks to print a black and white image is that the black and white image retains a non-neutral hue due to the intense colors of the color inkjet inks. Oftentimes, this hue deviates as a function of ink density. For example, as the ink density increases, the hue deviation from neutral can drift from a bluish hue to a rosy hue. In addition, the resolution of the black and white image is not as high as a black and white photograph because individual dots of the color inkjet ink are sometimes visible, especially in light areas of the image.
 High resolution black and white images are printed by applying dots of inkjet ink adjacent to one another to create the desired shades of black and gray. Dithering is a process that simulates shades of gray by printing various sizes and shapes of dots adjacent to one another. Dithering reduces the contrast between dots of different shades and creates a more natural look between adjacent dots. Halftoning is a process of printing black and white images by printing dots of various sizes in an ordered array, such as on a fixed grid.
 While artists typically desire the black and white image to have a neutral tone, artists sometimes want the black and white image to have a warm, cool, or sepia tone. As used herein a "neutral tone" is a tone that lacks chroma. A "warm tone" has a red or pink color, a "cool tone" has a blue, purple, or green color, and a "sepia tone" has a brown or yellow color. These tones are used to create a different mood in black and white images. Some photographers enhance their silver halide images using darkroom processes, such as platinum development baths, to create black and white image tones that deviate from neutral.
 It would be desirable to produce high quality black and white images having a desired neutral, warm, or cool tone without using expensive, time consuming, and environmentally unfriendly photographic techniques. In addition, it would be desirable to improve the graininess and
pixilation in black and white images. It would also be desirable to provide gray inkjet inks that are consistent at any dilution. Furthermore, it would be desirable to provide black and white images that are not negatively affected by particular lighting conditions.
BRIEF SUMMARY OF THE INVENTION
 A gray inkjet ink comprising a black pigment and at least one cyan, magenta, or yellow pigment is disclosed. The total amount of pigment present in the gray inkjet ink is approximately 0.1 wt % to approximately 3.0 wt % of the total inkjet ink. The at least one cyan, magenta, or yellow pigment are present at less than approximately 1.5% by weight.
 A black ink set comprising at least one gray inkjet ink is also disclosed. The at least one gray inkjet ink comprises a black colorant and at least one cyan, magenta, or yellow colorant.
 An eight-color ink set for printing color and black and white images is disclosed. The eight-color ink set comprises a cyan, yellow, magenta, black, gray, light gray, light cyan, and light magenta inkjet ink. The gray and light gray inkjet inks comprise a black colorant and at least one cyan, magenta, or yellow colorant in an aqueous ink vehicle. The at least one cyan, magenta, or yellow colorant is present at less than approximately 1.5% by weight.
 A method of producing a black and white image having a desired gray tone is also disclosed. The method comprises providing a multiple color ink set comprising at least one cyan, yellow, magenta, black, light cyan, light magenta, and gray inkjet ink. The at least one gray inkjet ink comprises a black colorant and at least one cyan, magenta, or yellow colorant in an aqueous ink vehicle. The at least one gray inkjet ink of the black ink set is applied to a print medium to produce the black and white image having a neutral, warm, cool, or sepia gray tone.
 An additional method of producing a black and white image having a desired gray tone is disclosed. The method comprises providing an ink set having at least one color inkjet ink, a black inkjet ink, and at least one gray inkjet ink. The inkjet inks of the ink set are applied to a print medium to produce the black and white image having a neutral, warm, cool, or sepia gray tone.
BRIEF DESCRIPTION OF THE DRAWING
 The accompanying drawing illustrates an embodiment of the present invention and is a part of the specification. The illustrated embodiment does not limit the scope of the invention.
 In one embodiment of the present invention, the color space is depicted in FIG. 1 as a triangle and includes a neutral gray tone in the center and a sepia tone, a warm tone, and a cool tone in each corner of the triangle.
DETAILED DESCRIPTION OF THE
 A gray inkjet ink having at least one colorant in an ink vehicle is disclosed. The inkjet ink includes a combination of cyan, magenta, yellow, or black colorants to produce a desired gray tone. By adjusting the amount of cyan,
magenta, yellow, or black colorant in the ink vehicle, the inkjet ink has a neutral, warm, cool, or sepia tone when printed. The inkjet ink does not produce hue deviations or color casts when diluted to a low concentration.
 The amounts of the components in the inkjet ink are expressed in weight percent ("wt %") of the total weight of the ink composition. The purity of all components is that used in normal commercial practice for inkjet inks.
 The colorants in the inkjet ink may be dyes or pigments. If the colorant is a dye, the dye may be nonionic, cationic, anionic, or a mixture of nonionic, cationic, and/or anionic dyes. Dyes for use in inkjet inks are well known in the art and are commercially available from sources such as BASF, CIBA, and Sensient. The dye may be water-soluble or water-insoluble and may include an Acid, Direct, Food, Mordant, or Reactive dye. Specific examples of dyes that may be used include, but are not limited to, Sulforhodamine B, Acid Blue 113, Acid Blue 29, Acid Red 4, Rose Bengal, Acid Yellow 17, Acid Yellow 29, Acid Yellow 42, Acridine Yellow G, Acid Yellow 23, Acid Blue 9, Nitro Blue Tetrazolium Chloride Monohydrate or Nitro BT, Rhodamine 6G, Rhodamine 123, Rhodamine B, Rhodamine B Isocyanate, Safranine O, Azure B, and Azure B Eosinate, all of which are available from Sigma-Aldrich Chemical Company (St. Louis, Mo.). Examples of anionic, water-soluble dyes include, but are not limited to, Direct Yellow 132, Direct Blue 199, Magenta 377 (available from Ilford AG, Switzerland), alone or together with Acid Red 52. Examples of water-insoluble dyes include azo, xanthene, methine, polymethine, and anthraquinone dyes. Specific examples of water-insoluble dyes include Ciba-Geigy Orasol Blue GN, Ciba-Geigy Orasol Pink, and Ciba-Geigy Orasol Yellow. Black dyes may include, but are not limited to, Direct Black 154, Direct Black 168, Fast Black 2, Direct Black 171, Direct Black 19, Acid Black 1, Acid Black 191, Mobay Black SP, and Acid Black 2. The dyes may be present in the inkjet ink from approximately 0 wt % to approximately 10 wt %.
 Pigments for use in inkjet inks are also well known in the art and are commercially available from sources, such as BASF, Cabot Corp., CIBA, Clariant, Degussa, DuPont, Heubach, and Mobay Chemical Corp. If the colorant in the inkjet ink is a pigment, the pigment may include, but is not limited to, the following pigments available from BASF: Paliogen®) Orange, Heliogen® Blue L 6901F, Heliogen®) Blue NBD 7010, Heliogen® Blue K 7090, Heliogen® Blue L 7101F, Paliogen®) Blue L 6470, Heliogen®) Green K 8683, and Heliogen® Green L 9140. The following black pigments are available from Cabot: Monarch® 1400, Monarch® 1300, Monarch®) 1100, Monarch® 1000, Monarch®) 900, Monarch® 880, Monarch® 800, and Monarch®) 700. The following pigments are available from CIBA: Chromophtal®) Yellow 3G, Chromophtal®) Yellow GR, Chromophtal®) Yellow 8G, Igrazin® Yellow 5GT, Igralite® Rubine 4BL, Monastral® Magenta, Monastral® Scarlet, Monastral® Violet R, Monastral® Red B, and Monastral® Violet Maroon B. The following pigments are available from Degussa: Printex U, Printex V, Printex 140U, Printex 140V, Color Black FW 200, Color Black FW 2, Color Black FW 2V, Color Black FW 1, Color Black FW 18, Color Black S 160, Color Black S 170, Special Black 6, Special Black 5, Special Black 4A, and Special Black 4. The following pigment is available from DuPont: Tipure®)
R-101. The following pigments are available from Heubach: Dalamar® Yellow YT-858-D and Heucophthal) Blue G XBT-583D. The following pigments are available from Clariant: Permanent Yellow GR, Permanent Yellow G, Permanent Yellow DHG, Permanent Yellow NCG-71, Permanent Yellow GG, Hansa Yellow RA, Hansa Brilliant Yellow 5GX-02, Hansa Yellow-X, Novoperm®) Yellow HR, Novoperm®) Yellow FGL, Hansa Brilliant Yellow 10GX, Permanent Yellow G3R-01, Hostaperm® Yellow H4G, Hostaperm® Yellow H3G, Hostaperm® Orange GR, Hostaperm®) Scarlet GO, and Permanent Rubine F6B. The following pigments are available from Mobay: Quindo® Magenta, Indofast® Brilliant Scarlet, Quindo® Red R6700, Quindo® Red R6713, and Indofast® Violet. The following pigments are available from Sun Chemical: L74-1357 Yellow, L75-1331 Yellow, and L75-2577 Yellow. The following pigments are available from Columbian: Raven 7000, Raven 5750, Raven 5250, Raven 5000, and Raven 3500. The following pigment is available from Sun Chemical: LHD9303 Black.
 In one embodiment, the cyan, yellow, magenta, or black pigments may be present from approximately 0.1 wt % to approximately 3.0 wt % of the total weight of the inkjet ink. However, it is also contemplated that dyes may be used. The colorants may be present in the ink vehicle in precise amounts because slight deviations in the amount of the colorants may change the tone of the inkjet ink from its neutral or other desired gray tone. However, as discussed in detail herein, the desired gray tone may also be achieved on the print medium by a color correction algorithm using additional color inkjet inks in the printer. If a black pigment is used in the inkjet ink, the pigment may be present from approximately 0.1 wt % to approximately 3.0 wt % of the total ink-jet ink. If a cyan pigment is used in the inkjet ink, the pigment may be present from approximately 0.01 wt % to approximately 1.0 wt % of the total inkjet ink. If a magenta pigment is used in the inkjet ink, the pigment may be present from approximately 0.005 wt % to approximately 1.0 wt % of the total inkjet ink. If a yellow pigment is used in the inkjet ink, the pigment may be present from approximately 0.01 wt % to approximately 1.0 wt % of the total inkjet ink.
 The colorant used in the inkjet ink is not critical to the operability of the present invention. Therefore, the selection of dye or pigment is not discussed in detail herein. Rather, it is understood that one of ordinary skill in the art could select any suitable dye or pigment for use in the present invention.
 The inkjet ink may include an aqueous-based ink vehicle and at least one cyan, magenta, yellow, or black colorant in the ink vehicle to produce a neutral, warm, cool, or sepia gray tone. In a dye-based inkjet ink, the dyes are soluble in the ink vehicle, while in a pigment-based inkjet ink, the pigments are dispersed in the ink vehicle. In one embodiment, a dark gray ink is produced using a black pigment while lighter gray inks are produced by using at least one cyan, magenta, yellow, or black pigment in the ink vehicle. For sake of example only, the inkjet ink may include predetermined amounts of the black pigment, the cyan pigment, and the magenta pigment to achieve the lighter gray tones. Since the inkjet ink may include varying