Cyan dye mixtures for thermal color proofing

Abstract: A cyan dye-donor element for thermal dye transfer comprising a support having thereon a dye layer comprising a mixture of cyan dyes dispersed in a polymeric binder, at least one of the cyan dyes having the formula: and at least one of the other of the dyes having the formula:

Description: This invention relates to use of a mixture of dyes in a cyan dye-donor element for thermal dye transfer imaging which is used to obtain a color proof that accurately represents the hue of a printed color image obtained from a printing press. In order to approximate the appearance of continuous-tone (photographic) images via ink-on-paper printing, the commercial printing industry relies on a process known as halftone printing. In halftone printing, color density gradations are produced by printing patterns of dots or areas of varying sizes, but of the same color density, instead of varying the color density continuously as is done in photographic printing. There is an important commercial need to obtain a color proof image before a printing press run is made. It is desired that the color proof will accurately represent at least the details and color tone scale of the prints obtained on the printing press. In many cases, it is also desirable that the color proof accurately represent the image quality and halftone pattern of the prints obtained on the printing press. In the sequence of operations necessary to produce an ink-printed, full-color picture, a proof is also required to check the accuracy of the color separation data from which the final three or more printing plates or cylinders are made. Traditionally, such color separation proofs have involved silver halide photographic, high-contrast lithographic systems or non-silver halide light-sensitive systems which require many exposure and processing steps before a final, full-color picture is assembled. Colorants that are used in the printing industry are insoluble pigments. By virtue of their pigment character, the spectrophotometric curves of the printing inks are often unusually sharp on either the bathochromic or hypsochromic side. This can cause problems in color proofing systems in which dyes, as opposed to pigments, are being used. It is very difficult to match the hue of a given ink using a single dye. In U.S. Patent 5,126,760, a process is described for producing a direct digital, halftone color proof of an original image on a dye-receiving element. The proof can then be used to represent a printed color image obtained from a printing press. The process described therein comprises: a) generating a set of electrical signals which is representative of the shape and color scale of an original image; b) contacting a dye-donor element comprising a support having thereon a dye layer and an infrared-absorbing material with a first dye-receiving element comprising a support having thereon a polymeric, dye image-receiving layer; c) using the signals to imagewise-heat by means of a diode laser the dye-donor element, thereby transferring a dye image to the first dye-receiving element; and d) retransferring the dye image to a second dye image-receiving element which has the same substrate as the printed color image. In the above process, multiple dye-donors are used to obtain a complete range of colors in the proof. For example, for a full-color proof, four colors: cyan, magenta, yellow and black are normally used. By using the above process, the image dye is transferred by heating the dye-donor containing the infrared-absorbing material with the diode laser to volatilize the dye, the diode laser beam being modulated by the set of signals which is representative of the shape and color of the original image, so that the dye is heated to cause volatilization only in those areas in which its presence is required on the dye-receiving layer to reconstruct the original image. Similarly, a thermal transfer proof can be generated by using a thermal head in place of a diode laser as described in U.S. Patent 4,923,846. Commonly available thermal heads are not capable of generating halftone images of adequate resolution but can produce high quality continuous tone proof images which are satisfactory in many instances. U.S. Patent 4,923,846 also discloses the choice of mixtures of dyes for use in thermal imaging proofing systems. The dyes are selected on the basis of values for hue error and turbidity. The Graphic Arts Technical Foundation Research Report No. 38, "Color Material" (58-(5) 293-301, 1985) gives an account of this method. An alternative and more precise method for color measurement and analysis uses the concept of uniform color space known as CIELAB in which a sample is analyzed mathematically in terms of its spectrophotometric curve, the nature of the illuminant under which it is viewed and the color vision of a standard observer. For a discussion of CIELAB and color measurement, see Principles of Color Technology , 2nd Edition, F. W. Billmeyer, p. 25-110, Wiley-Interscience and Optical Radiation Measurements, Volume 2, F. Grum, p. 33-145, Academic Press. In using CIELAB, colors can be expressed in terms of three parameters: L*, a* and b*, where L* is a lightness function, and a* and b* define a point in color space. Thus, a plot of a* vs b* values for a color sample can be used to accurately show where that sample lies in color space, i.e., what its hue is. This allows different samples to be compared for hue if they have similar density and L* values. In color proofing in the printing industry, it is important to be able to match the proofing ink references provided by the International Prepress Proofing Association. These ink references are density patches made with standard 4-color process inks and are known as SWOP® (Specifications Web Offset Publications) color aims. For additional information on color measurement of inks for web offset proofing, see "Advances in Printing Science and Technology", Proceedings of the 19th International Conference of Printing Research Institutes, Eisenstadt, Austria, June 1987, J. T. Ling and R. Warner, p.55. In U.S. Patent 5,024,990, the use of a mixture of dyes to give a good match to the CIELAB parameters of the cyan SWOP color aim is disclosed. There is a problem with these dye mixtures, however, in that they do not give an acceptable gray balance when printed sequentially with yellow and magenta thermal transfer dyes. In U.S. Patent 5,177,052, use of a yellow dye in admixture with cyan dyes to improve the overprint gray dye balance is described. While this mixture of dyes provides a hue angle match to the cyan SWOP color aim, there is a problem with this mixture in that the resulting color is somewhat darker and less saturated than that of the cyan SWOP color aim, as shown by lower L* and C* values (defined hereafter). It is an object of this invention to provide a mixture of cyan dyes for color proofing to approximate a hue match of the cyan SWOP color aim. It is another object of this invention to provide a mixture of cyan dyes for color proofing wherein an acceptable gray balance is obtained when printed sequentially with yellow and magenta thermal transfer dyes. These and other objects are obtained by this invention which relates to a cyan dye-donor element for thermal dye transfer comprising a support having thereon a dye layer comprising a mixture of cyan dyes dispersed in a polymeric binder, at least one of the cyan dyes having the formula: wherein: R 1 and R 2 each independently represents hydrogen; an alkyl group having from 1 to 6 carbon atoms; a cycloalkyl group having from 5 to 7 carbon atoms; allyl; or such alkyl, cycloalkyl or allyl groups substituted with one or more groups such as alkyl, aryl, alkoxy, aryloxy, amino, halogen, nitro, cyano, thiocyano, hydroxy, acyloxy, acyl, alkoxycarbonyl, aminocarbonyl, alkoxycarbonyloxy, carbamoyloxy, acylamido, ureido, imido, alkylsulfonyl, arylsulfonyl, alkylsulfonamido, arylsulfonamido, alkylthio, arylthio, trifluoromethyl, etc., e.g., methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, methoxyethyl, benzyl, 2-methanesulfonamidoethyl, 2-hydroxyethyl, 2-cyanoethyl, methoxycarbonylmethyl, cyclohexyl, cyclopentyl, phenyl, pyridyl, naphthyl, thienyl, pyrazolyl, p-tolyl, p-chlorophenyl, m-(N-methylsulfamoyl)phenyl-methyl, methylthio, butylthio, benzylthio, methanesulfonyl, pentanesulfonyl, methoxy, ethoxy, 2-methanesulfonamidoethyl, 2-hydroxyethyl, 2-cyanoethyl, methoxycarbonyl-methyl, imidazolyl, naphthyloxy, furyl, p-tolylsulfonyl, p-chlorophenylthio, m-(N-methylsulfamoyl)phenoxy, ethoxy-carbonyl, methoxyethoxycarbonyl, phenoxycarbonyl, acetyl, benzoyl, N,N-dimethyl-carbamoyl, dimethylamino, morpholino, anilino, pyrrolidino etc.; or R 1 and R 2 can be joined together to form, along with the nitrogen to which they are attached, a 5- to 7-membered heterocyclic ring such as morpholine or pyrrolidine; or either or both of R 1 and R 2 can be combined with R to form a 5- to 7-membered heterocyclic ring; and R represents hydrogen or a substituted or unsubstituted alkyl group having from 1 to 6 carbon atoms; and at least one of the other of the dyes having the formula: wherein: R 8 and R 9 each independently represents hydrogen; an alkyl group having from 1 to 8 carbon atoms such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, methoxyethyl, benzyl, 2-methanesulfonylamidoethyl, 2-hydroxyethyl, 2-cyanoethyl, methoxycarbonylmethyl, etc.; a cycloalkyl group having from 5 to 8 carbon atoms, such as cyclohexyl, cyclopentyl, etc,; or an alkenyl group having from 2 to 8 carbon atoms, such as CH 2 CH=CH 2 , CH 2 CH=CHCH=CH 2 , CH 2 CH=CHCH 2 OCH 3 , or CH 2 CH=CHC 5 H 11 ; R 8 and R 9 may represent the elements which may be taken together to form a 5- or 6-membered heterocyclic ring, such as pyrazole, pyrrolidone or piperazine; each Y independently represents hydrogen; an alkyl group having from 1 to 8 carbon atoms such as those listed above for R 8 ; an alkoxy group such as OR 8 ; halogen such as fluorine, chlorine or bromine; or two adjacent Y's may represent the atoms which may be taken together to form a fused carbocyclic aromatic ring such as naphthalene; n is 0 to 4; the position of Y ortho to the nitrogen may also be combined with R 8 to form a 5- or 6-membered non-aromatic, single or double nitrogen-containing, heterocyclic ring, thus forming a fused ring system such as tetrahydroquinoline, dihydroquinoline, indoline, etc, and R 10 is a substituted or unsubstituted alkyl group having from 1 to 8 carbon atoms such as those listed above for R 8 , a substituted or unsubstituted allyl group having from 3 to 6 carbon atoms, such as CH 2 CH=CH 2 or CH 2 CH=CHCH 3 ; a substituted or unsubstituted acyl group having from 2 to 9 carbon atoms such as a substituted or unsubstituted aroyl group having from 7 to 18 carbon atoms, such as or a substituted or unsubstituted heteroaroyl group having from 2 to 10 carbon atoms, such as Cyan dyes included within the scope of the above formula I include the following: Compound R R 1 R 2 A H C 4 H 9 C 4 H 9 B CH 3 C 2 H 5 C 2 H 5 C CH 3 CH 3 OCH 2 CH 2 - C 2 H 5 D CH 3 CH 3 (C 2 H 5 )CH- C 2 H 5 E CH 3 C 4 H 9 C 2 H 5 In a preferred embodiment of the invention, R in formula I is hydrogen or methyl and R 1 and R 2 are each C 4 H 9 or C 2 H 5 . Cyan dyes included within the scope of the above formula II include the following: The use of dye mixtures in the dye-donor of the invention permits a wide selection of hue and color that enables a closer hue match to a variety of printing inks to be achieved and also permits easy transfer of images to a receiver one or more times if desired. The use of dyes also allows easy modification of image density to any desired level. The dyes of the dye-donor element of the invention may be used at a coverage of from 0.02 to 1 g/m 2 . The dyes in the dye-donor of the invention are dispersed in a polymeric binder such as a cellulose derivative, e.g., cellulose acetate hydrogen phthalate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose triacetate or any of the materials described in U. S. Patent 4,700,207; a polycarbonate; poly(vinyl acetate); polystyrene-co-acrylonitrile); a polysulfone or a poly(phenylene oxide). The binder may be used at a coverage of from 0.1 to 5 g/m 2 . The dye layer of the dye-donor element may be coated on the support or printed thereon by a printing technique such as a gravure process. Any material can be used as the support for the dye-donor element of the invention provided it is dimensionally stable and can withstand the heat of the laser or thermal head. Such materials include polyesters such as poly(ethylene terephthalate); polyamides; polycarbonates; cellulose esters; fluorine polymers; polyethers; polyacetals; polyolefins; and polyimides. The support generally has a thickness of from 5 to 200 µm. It may also be coated with a subbing layer, if desired, such as those materials described in U. S. Patents 4,695,288 or 4,737,486. The reverse side of the dye-donor element may be coated with a slipping layer to prevent the printing head from sticking to the dye-donor element. Such a slipping layer would comprise either a solid or liquid lubricating material or mixtures thereof, with or without a polymeric binder or a surface-active agent. Preferred lubricating materials include oils or semicrystalline organic solids that melt below 100°C such as poly(vinyl stearate), beeswax, perfluorinated alkyl ester polyethers, polycaprolactone, silicone oil, polytetrafluoroethylene, carbowax, poly(ethylene glycols), or any of those materials disclosed in U. S. Patents 4,717,711; 4,717,712; 4,737,485; and 4,738,950. Suitable polymeric binders for the slipping layer include poly(vinyl alcohol-co-butyral), poly(vinyl alcohol-co-acetal), polystyrene, poly(vinyl acetate), cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate or ethyl cellulose. The amount of the lubricating material to be used in the slipping layer depends largely on the type of lubricating material, but is generally in the range of 0.001 to 2 g/m 2 . If a polymeric binder is employed, the lubricating material is present in the range of 0.1 to 50 weight %, preferably 0.5 to 40 %, of the polymeric binder employed. The dye-receiving element that is used with the dye-donor element of the invention usually comprises a support having thereon a dye image-receiving layer. The support may be a transparent film such as a poly(ether sulfone), a polyimide, a cellulose ester such as cellulose acetate, a poly(vinyl alcohol-co-acetal) or a poly(ethylene terephthalate). The support for the dye-receiving element may also be reflective such as baryta-coated paper, polyethylene-coated paper, an ivory paper, a condenser paper or a synthetic paper such as DuPont Tyvek®. Pigmented supports such as white polyester (transparent polyester with white pigment incorporated therein) may also be used. The dye image-receiving layer may comprise, for example, a polycarbonate, a polyurethane, a polyester, poly(vinyl chloride), poly(styrene-co-acrylonitrile), polycaprolactone, a poly(vinyl acetal) such as poly(vinyl alcohol-co-butyral), poly(vinyl alcohol-co-benzal), poly(vinyl alcohol-co-acétal) or mixtures thereof. The dye image-receiving layer may be present in any amount which is effective for the intended purpose. In general, good results have been obtained at a concentration of from 1 to 5 g/m 2 . As noted above, the dye-donor elements of the invention are used to form a dye transfer image. Such a process comprises imagewise-heating a dye-donor element as described above and transferring a dye image to a dye-receiving element to form the dye transfer image. The dye-donor element of the invention may be used in sheet form or in a continuous roll or ribbon. If a continuous roll or ribbon is employed, it may have only the dyes thereon as described above or may have alternating areas of other different dyes or combinations, such as sublimable cyan and/or yellow and/or black or other dyes. Such dyes are disclosed in U. S. Patent 4,541,830. Thus, one-, two-, three- or four-color elements (or higher numbers also) are included within the scope of the invention. Thermal printing heads which can be used to transfer dye from the dye-donor elements of the invention are available commercially. A laser may also be used to transfer dye from the dye-donor elements of the invention. When a laser is used, it is preferred to use a diode laser since it offers substantial advantages in terms of its small size, low cost, stability, reliability, ruggedness, and ease of modulation. In practice, before any laser can be used to heat a dye-donor element, the element must contain an absorbing material which absorbs at the emitting wavelength of the laser. When an infrared laser is employed, then an infrared-absorbing material may be used, such as carbon black, cyanine infrared-absorbing dyes as described in U.S. Patent 4,973,572, or other materials as described in the following U.S. Patents: 4,948,777; 4,950,640; 4,950,639; 4,948,776; 4,948,778; 4,942,141; 4,952,552; 5,036,040; and 4,912,083. The laser radiation is then absorbed into the dye layer and converted to heat by a molecular process known as internal conversion. Thus, the construction of a useful dye layer will depend not only on the hue, transferability and intensity of the image dyes, but also on the ability of the dye layer to absorb the radiation and convert it to heat. Lasers which can be used to transfer dye from dye-donors employed in the invention are available commercially. A thermal printer which uses the laser described above to form an image on a thermal print medium is described and claimed in U.S. Patent 5,268,708. Spacer beads may be employed in a separate layer over the dye layer of the dye-donor in the above-described laser process in order to separate the dye-donor from the dye-receiver during dye transfer, thereby increasing the uniformity and density of the transferred image. That invention is more fully described in U.S. Patent 4,772,582. Alternatively, the spacer beads may be employed in the receiving layer of the dye-receiver as described in U.S. Patent 4,876,235. The spacer beads may be coated with a polymeric binder if desired. The use of an intermediate receiver with subsequent retransfer to a second receiving element may also be employed in the invention. A multitude of different substrates can be used to prepare the color proof (the second receiver) which is preferably the same substrate as that used for the printing press run. Thus, this one intermediate receiver can be optimized for efficient dye uptake without dye-smearing or crystallization. Examples of substrates which may be used for the second receiving element (color proof) include the following: Flo Kote Cover® (S. D. Warren Co.), Champion Textweb® (Champion Paper Co.), Quintessence Gloss® (Potlatch Inc.), Vintage Gloss® (Potlatch Inc.), Khrome Kote® (Champion Paper Co.), Consolith Gloss® (Consolidated Papers Co.), Ad-Proof Paper® (Appleton Papers, Inc.) and Mountie Matte® (Potlatch Inc.). As noted above, after the dye image is obtained on a first dye-receiving element, it may be retransferred to a second dye image-receiving element. This can be accomplished, for example, by passing the two receivers between a pair of heated rollers. Other methods of retransferring the dye image could also be used such as using a heated platen, use of pressure and heat, external heating, etc. Also as noted above, in making a color proof, a set of electrical signals is generated which is representative of the shape and color of an original image. This can be done, for example, by scanning an original image, filtering the image to separate it into the desired additive primary colors, i.e., red, blue and green, and then converting the light energy into electrical energy. The electrical signals are then modified by computer to form the color separation data which are used to form a halftone color proof. Instead of scanning an original object to obtain the electrical signals, the signals may also be generated by computer. This process is described more fully in Graphic Arts Manual, Janet Field ed., Arno Press, New York 1980 (p. 358ff). A thermal dye transfer assemblage of the invention comprises a) a dye-donor element as described above, and b) a dye-receiving element as described above, the dye-receiving element being in a superposed relationship with the dye-donor element so that the dye layer of the donor element is in contact with the dye image-receiving layer of the receiving element. The above assemblage comprising these two elements may be preassembled as an integral unit when a monochrome image is to be obtained. This may be done by temporarily adhering the two elements together at their margins. After transfer, the dye-receiving element is then peeled apart to reveal the dye transfer image. When a three-color image is to be obtained, the above assemblage is formed three times using different dye-donor elements. After the first dye is transferred, the elements are peeled apart. A second dye-donor element (or another area of the donor element with a different dye area) is then brought in register with the dye-receiving element and the process repeated. The third color is obtained in the same manner. The following examples are provided to illustrate the invention. EXAMPLES Example 1 Cyan individual dye-donor elements were prepared by coating on a 100 µm poly(ethylene terephthalate) support a dye layer containing a mixture of the cyan dyes identified above, the cyanine infrared absorbing dye disclosed in U.S. Patent 5,024,990 (column 13 lines 1-15) at 0.054 g/m 2 in a cellulose acetate propionate binder (CAP 482-20 from Eastman Chemical Company) at 0.54 g/m 2 . The following experimental ratios shown in Table 1 were used in laydowns as listed: Cyan Dye-Donor Cyan Dye (wt. %) Cyan Dye (wt. %) Cyan Dye (wt. %) Dry Coverage g/m 2 1 B (33.3) A (17.9) 2 (48.7) 0.420 2 B (37.1) A (20.0) 2 (42.8) 0.380 3 B (45.4) A (15.2) 2 (39.4) 0.360 4 B (40.5) A (13.5) 2 (45.9) 0.380 Control-1 for comparative purposes was Kodak APPROVAL® Cyan Digital Color Proofing Film, CAT # 805 2300. An intermediate dye-receiving element, Kodak APPROVAL® Intermediate Color Proofing Film, CAT # 831 5582, was used with the above dye-donor elements to print an image. For the monochrome cyan images, the power to the laser array was modulated to produce a continuous tone image consisting of uniform "steps" of varying density as described in U.S. Patent 4,876,235. After the laser array had finished scanning the image area, the laser exposure device was stopped and the intermediate receiver containing the transferred image was laminated to Textweb® (Champion Papers, Inc.) 60# paper stock which had been previously laminated with Kodak APPROVAL® Prelaminate, CAT # 173 9671. All measurements were made using a Gretag SPM100 portable spectrophotometer set for D 50 illuminant and 2° observer angle. Readings were made with black backing behind the samples. The CIELAB L* a* b* coordinates reported are interpolated to a Status T density of 1.30. The color differences between the samples can be expressed as ΔE where ΔE is the vector difference in CIELAB color space between the laser thermal generated image and the SWOP aim. ΔE = square root ((L* e -L* s ) 2 + (a* e - a* s ) 2 + (b* e - b* s ) 2 ) Hue angle = arctan b*/a* +180 C* = square root (a* 2 + b* 2 ) wherein subscript e represents the measurements from the experimental material and subscript s represents the measurements from the SWOP standard color aim. Table 2 summarizes the results obtained. The SWOP standard was taken from the Committee for Graphic Arts Technology Standards publication ANSI CGATS.6-1995. Cyan Dye-Donor L* a* b* Δ E Hue Angle Δ Hue Angle C* Δ C* SWOP 54.7 -36.9 -40.0 --- 227.3 --- 54.4 --- Control-1 51.3 -34.3 -35.2 6.4 225.7 -1.6 49.1 -5.3 1 55.2 -37.6 -40.4 0.9 227.1 -0.2 55.2 0.8 2 55.7 -36.8 -40.4 1.1 227.7 0.4 54.6 0.2 3 54.6 -36.9 -40.7 0.7 227.8 0.5 54.9 0.5 4 55.2 -38.5 -39.6 1.7 225.8 -1.5 55.2 0.8 The above results show that the cyan combinations of the invention are closer to the SWOP color aim than is Control-1, particularly in L* and C*, which are measures of lightness and saturation. Example 2 It is desirable to provide proofs which can be used in parts of the world which do not use the SWOP aims. For example, in Japan, a different standard is used and it would be desirable to provide a closer match to Japan Color. Cyan dye-donors 1-4 and Control-1 described above were printed as above and then laminated to Mitsubishi Tokyo Art paper. The Japan Color/Color Sample colorimetry values published by the Japan National Committee for ISO/TC130 were used as the color reference. The CIELAB L* a* b* coordinates reported are interpolated to a Status T density of 1.55. The data are summarized in the following Table 3: Cyan Dye-Donor L* a* b* ΔE Hue Angle Δ Hue Angle C* Δ C* Japan Color 53.8 -37.9 -49.4 --- 232.5 --- 62.3 --- Control-1 46.7 -33.7 -42.0 11.1 231.3 -1.2 53.8 -8.5 1 51.5 -37.9 -46.2 3.9 230.6 -1.9 59.8 -2.5 2 50.8 -35.9 -48.4 3.7 233.4 0.9 60.3 -2.0 3 51.0 -36.6 -47.7 3.5 232.5 0.0 60.1 -2.2 4 51.2 -37.5 -47.2 3.4 231.5 1.0 60.3 -2.0 The above data show that the cyan combination of the invention provides a much closer match to Japan Color than does Control-1, particularly in L* and C*. The cyan dye-donors of the invention provide improved lightness and saturation. Example 3 In Europe, ISO 12647-2:1996(E) specifies standards for proofing and production printing on various paper substrates. Paper Type 3 from Table 1 of ISO 12647-2:1996(E) closely matches Champion Textweb®. Table 3 from ISO 12647-2:1996(E) specifies CIELAB coordinates for the color primaries. Cyan dye-donors 1-4 and Control-1 described above were printed as above and then laminated to Champion Textweb® paper. The CIELAB L* a* b* coordinates reported are interpolated to a Status T density of 1.35. The data are summarized in the following Table 4: Cyan Dye Donor L* a* b* ΔE Hue Angle Δ Hue Angle C* ΔC* ISO 12647-2 54 -37 -42 --- 228.6 --- 56 --- Control-1 49.7 -32.6 -37.2 7.8 228.8 0.2 49.5 -6.5 1 54.3 -38.7 -40.2 2.5 226.1 -2.5 55.8 -0.2 2 53.3 -36.1 -42.2 1.2 229.5 0.9 55.5 -0.5 3 53.3 -36.4 -41.9 0.9 229.0 0.4 55.5 -0.5 4 54.1 -38.2 -40.7 2.2 226.8 -1.8 55.8 -0.2 The above data show that the cyan dye-donor of the invention printed on Champion Textweb® provides a good match to the color coordinate specifications for the ISO 12647-2, particularly in L* and C*. The cyan dye-donors of the invention provide improved lightness and saturation. Example 4 -Gray Scale Overprint This example uses the cyan dye combination of the invention along with a magenta dye combination described in U.S. patent No. 5 866 509, not prepublished, to provide a gray scale overprint. The magenta dye-donor Control-2 was Kodak APPROVAL® Magenta Color Proofing Film CAT # 803 0314. The magenta dye-donors in OP-3, OP-4 and OP-5 used a combination of dyes listed in Table 5 as Em-6 and Em-7 and identified in U.S. patent No. 5 866 509. The yellow donor used for the three-color overprint is Kodak APPROVAL® Yellow Digital Color Proofing Film, CAT # 194 9668. Three-color overprint images were then prepared by sequentially imaging various combinations of the cyan, magenta and yellow dye-donors described above in register onto the same intermediate receiver layer. In this case, the laser array was modulated to produce stepped half-tone images of varying density, by printing dot patterns of varying dot size (area coverage). The cyan donors were printed so that the stepped image varied from 10-100% dot area, while the yellow and magenta donors were printed at a dot area reduction relative to the cyan donor, which is a typical graphic arts industry practice. For example, when the cyan donor was printed at 50% dot area, the magenta and yellow donors were each printed at 41% dot area. The intermediate dye-receiving element used was Kodak APPROVAL® Intermediate Color Proofing Film. Three-color overprint images were printed as described in U.S. Patent 4,876,235. After the laser array had finished scanning the image area, the laser exposure device was stopped and the intermediate receiver containing the transferred image was laminated to Textweb® which had been previously laminated with Kodak APPROVAL® Prelaminate. Proofs were generated using the set-up conditions described in the SWOP Off-Press Proof Application Data Sheet for the KODAK APPROVAL® Digital Color Proofing System (Kodak Publication # PG-830). This data sheet provides guidance on how users are to set up their APPROVAL® systems to emulate press proofing and production printing done to SWOP specifications. Except for the darker, less saturated cyan, the results of this set-up, when proofed with existing product, are accepted by the industry as a faithful representation of such proofing and printing. Any newly introduced cyan donor should not greatly change the overall color results, particularly gray balance, of this set-up. Colorimetric data were measured on the 3-color overprints for the 100%, 75%, 50% and 25% dot patches and the results are shown in Table 5: Overprint Element Cyan Dye-Donor Magenta Dye-Donor 100 % Dot 75 % Dot 50 % Dot 25 % Dot a* b* a* b* a* b* a* b* OP-1 Control-1 Control-2 -4.7 -3.1 -1.3 -0.1 -0.6 -0.4 0.6 1.5 OP-2 1 Control-2 -8.4 -2.6 -4.7 -0.2 -4.1 -0.6 -1.7 1.1 OP-3 1 Em-6 -4.5 -2.5 -2.5 -0.4 -2.3 -0.9 -0.7 0.8 OP-4 2 Em-7 -2.2 -2.2 -0.9 -0.4 -1.2 -0.9 -0.1 0.7 OP-5 3 Em-7 -3.5 -2.1 -1.9 -0.4 -2.1 -0.9 -0.6 0.7 In order to have a satisfactory overprint, the patches should be as neutral across the dot scale as the current product and more neutral at the 100% Dot where even the current product has a greenish hue, as shown by a* being more negative (OP-4 has -2.2 at 100 % Dot compared to OP-1 having -4.7 at 100 % Dot). As can be seen from the above data, the cyan dye combination of the invention when overprinted with the magenta dye combinations of U.S. Application Serial No. 08/920,921 provide a neutral color very similar to the current product controls in addition to showing an improved 100% Dot neutral.

Claims: A cyan dye-donor element for thermal dye transfer comprising a support having thereon a dye layer comprising a mixture of cyan dyes dispersed in a polymeric binder, at least one of the cyan dyes having the formula: wherein: R 1 and R 2 each independently represents hydrogen; a substituted or unsubstituted alkyl group having from 1 to 6 carbon atoms; a substituted or unsubstituted cycloalkyl group having from 5 to 7 carbon atoms; or a substituted or unsubstituted allyl group; or R 1 and R 2 can be joined together to form, along with the nitrogen to which they are attached, a 5- to 7-membered heterocyclic ring; or either or both of R 1 and R 2 can be combined with R to form a 5- to 7-membered heterocyclic ring; and R represents hydrogen or a substituted or unsubstituted alkyl group having from 1 to 6 carbon atoms; and at least one of the other of the dyes having the formula: wherein: R 8 and R 9 each independently represents hydrogen; an alkyl group having from 1 to 8 carbon atoms; a cycloalkyl group having from 5 to 8 carbon atoms; or an alkenyl group having from 2 to 8 carbon atoms; R 8 and R 9 may represent the elements which may be taken together to form a 5- or 6-membered heterocyclic ring; each Y independently represents hydrogen; an alkyl group having from 1 to 8 carbon atoms; an alkoxy group OR 8 ; halogen; or two adjacent Y's may represent the atoms which may be taken together to form a fused carbocyclic aromatic ring; n is 0 to 4; the position of Y ortho to the nitrogen may also be combined with R 8 to form a 5- or 6-membered non-aromatic, single or double nitrogen-containing, heterocyclic ring, thus forming a fused ring system, and R 10 is a substituted or unsubstituted alkyl group having from 1 to 6 carbon atoms; a substituted or unsubstituted allyl group having from 3 to 6 carbon atoms; a substituted or unsubstituted acyl group having from 2 to 9 carbon atoms; a substituted or unsubstituted aroyl group having from 7 to 18 carbon atoms; or a substituted or unsubstituted heteroaroyl group having from 2 to 10 carbon atoms; or a dye having the formula: or The element of Claim 1 wherein R in formula I is hydrogen or methyl. The element of Claim 1 wherein R 1 and R 2 in formula I are each C 4 H 9 or C 2 H 5 . The element of Claim 1 wherein said dye-donor element contains an infrared-absorbing dye in said dye layer. The element of Claim 1 wherein in formula II, the position of Y ortho to the nitrogen is combined with R 8 to form a tetrahydroquinoline ring system. The element of Claim 1 wherein R 10 in formula II is an allyl group. A process of forming a dye transfer image comprising imagewise-heating a cyan dye-donor element as described in claim 1 and transferring a dye image to a dye-receiving element to form said dye transfer image. The process of Claim 7 wherein R in formula I is hydrogen or methyl and R 1 and R 2 are each C 4 H 9 or C 2 H 5 . A thermal dye transfer assemblage comprising: a) a cyan dye-donor element as described in claim 1, and b) a dye-receiving element comprising a support having thereon a dye image-receiving layer, said dye-receiving element being in a superposed relationship with said cyan dye-donor element so that said dye layer is in contact with said dye image-receiving layer. The assemblage of Claim 9 wherein R in formula I is hydrogen or methyl and R 1 and R 2 are each C 4 H 9 or C 2 H 5 .

Inventors: AMBRO JOSEPH HAYES, CHAPMAN DEREK DAVID, KASZCZUK LINDA ANN, AMBRO, JOSEPH HAYES, CHAPMAN, DEREK DAVID, KASZCZUK, LINDA ANN, Ambro, Joseph Hayes, Eastman Kodak Company, Chapman, Derek David, Eastman Kodak Company, Kaszczuk, Linda Ann, Eastman Kodak Company
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1998
Main classification: B41M5
IPC codes: C09B67, G03F7, B41M5, G03F3