YELLOW DYE-DONOR ELEMENT USED IN THERMAL DYE TRANSFER

Abstract: A yellow dye-donor element for thermal dye transfer comprises a support having thereon a yellow dye dispersed in a polymeric binder, the yellow dye having the formula: wherein R is a substituted or unsubstituted alkyl group of from 1 to 10 carbon atoms; a cycloalkyl group of from 5 to 7 carbon atoms; or represents the atoms which when taken together with Z forms a 5- or 6-membered ring; R¹ is an alkylene or substituted alkylene group; X is -OJO-, -OJ-, -JO-, -OJNR³-, -NR³J-, -NR³JNR³, -JNR³- or -NR³JO-; J is CO or SO₂; R³ is hydrogen; a substituted or unsubstituted alkyl group of from 1 to 10 carbon atoms; a substituted or unsubstituted aryl group of from 6 to 10 carbon atoms; or represents the atoms which when taken together with R² forms a 5- or 6-membered ring; R² is a substituted or unsubstituted alkyl group of from 1 to 10 carbon atoms; a cycloalkyl group of from 5 to 7 carbon atoms; a substituted or unsubstituted aryl group of from 6 to 10 carbon atoms; or represents the atoms which when taken together with R³ forms a 5- or 6-membered ring; Z is hydrogen or represents the atoms which when taken together with R forms a 5- or 6-membered ring; Y is a substituted or unsubstituted alkyl or alkoxy group of from 1 to 6 carbon atoms or halogen; and n is a positive integer from 1 to 4.

Description: This invention relates to yellow dye-donor elements used in thermal dye transfer which have good dye stability and low retransfer properties. In recent years, thermal transfer systems have been developed to obtain prints from pictures which have been generated electronically from a color video camera. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to provide cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta and yellow signals. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Japanese Publications 60/031563, 60/028451, 60/028452 and 60/028453 relate to various di-and tri-cyanoaniline dyes. These dyes are structurally different from the compounds employed in the invention. There is a problem with many of these dyes proposed for use in thermal dye transfer printing in that they do not have adequate stability to light. As will be shown by comparative tests hereinafter, several di-cyanoaniline dyes which were tested for light stability were significantly poorer than the compounds employed in this invention. Other dyes proposed for use in thermal dye transfer printing exhibit a phenomenon called "retransfer". This occurs when the dye which has transferred from the donor element to a dye-receiving element, where it is supposed to remain, "retransfers" to another support, causing a loss in dye density in the dye-receiving element and an unwanted dye image in that other support. It is an object of this invention to provide dyes which have good stability to light and which do not retransfer to other unwanted supports. These and other objects are achieved in accordance with this invention which comprises a yellow dye-donor element for thermal dye transfer comprising a support having thereon a dye layer comprising a yellow dye dispersed in a polymeric binder, characterized in that the yellow dye has the formula: wherein R is a substituted or unsubstituted alkyl group of from 1 to 10 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl or such alkyl groups substituted with hydroxy, acyloxy, alkoxy, aryl, cyano, acylamido, halogen, etc.; a cycloalkyl group of from 5 to 7 carbon atoms such as cyclopentyl, cyclohexyl, p-methylcyclohexyl, etc.; or represents the atoms which when taken together with Z forms a 5- or 6-membered ring; R¹ is an alkylene or substituted alkylene group such as methylene, ethylene, hexylene, etc. or alkylene substituted with hydroxy, alkoxy, aryl, cyano, halogen, etc.; X is -OJO-, -OJ-, -JO-, -OJNR³-, -NR³J-, -NR³JNR³, -JNR³- or -NR³JO-; J is CO or SO₂; R³ is hydrogen; a substituted or unsubstituted alkyl group of from 1 to 10 carbon atoms such as those listed above for R; a substituted or unsubstituted aryl group of from 6 to 10 carbon atoms such as phenyl, p-tolyl, m-chlorophenyl, p-methoxyphenyl, m-bromophenyl, o-tolyl, etc.; or represents the atoms which when taken together with R² forms a 5- or 6-membered ring; R² is a substituted or unsubstituted alkyl group of from 1 to 10 carbon atoms, such as those listed above for R; a cycloalkyl group of from 5 to 7 carbon atoms, such as those listed above for R; a substituted or unsubstituted aryl group of from 6 to 10 carbon atoms, such as those listed above for R³; or represents the atoms which when taken together with R³ forms a 5- or 6-membered ring; Z is hydrogen or represents the atoms which when taken together with R forms a 5- or 6-membered ring; Y is a substituted or unsubstituted alkyl or alkoxy group of from 1 to 6 carbon atoms, such as those listed above for R, methoxy, ethoxy, etc., or halogen such as chloro, bromo or fluoro; and n is a positive integer from 1 to 4. In a preferred embodiment of the invention, R in the above structural formula represents the atoms which are taken together with Z to form a 6-membered ring. In another preferred embodiment of the invention, X is -OCONH- or -OCO-. In yet another preferred embodiment of the invention, R¹ is ethylene. In yet still another preferred embodiment of the invention, X is -NCH₃SO₂- or -NR³J-, wherein J is CO and R³ is combined with R² to form a 5- or 6-membered ring. In yet still another preferred embodiment of the invention, R² is a substituted aryl group of from 6 to 10 carbon atoms or C₆H₅. The compounds employed in the invention may be prepared by any of the processes disclosed in U.S. Patents 3,917,604, 4,180,663 and 3,247,211 referred to above. Compounds included within the scope of the invention include the following: A dye-barrier layer may be employed in the dye-donor elements of the invention to improve the density of the transferred dye. Such dye-barrier layer materials include hydrophilic materials. The dye in the dye-donor element of the invention is 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; a polycarbonate; poly(styrene-­ co-acrylonitrile), a poly(sulfone) or a poly(phenylene oxide). The binder may be used at a coverage of from 0.1 to 5 g/m². 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 thermal printing heads. Such materials include polyesters such as poly(ethylene terephthalate); polyamides; polycarbonates; glassine paper; condenser paper; cellulose esters; fluorine polymers; polyethers; polyacetals; polyolefins; and polyimides. The support generally has a thickness of from 2 to 30 µm. It may also be coated with a subbing layer, if desired. 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 a lubricating material such as a surface active agent, a liquid lubricant, a solid lubricant or mixtures thereof, with or without a polymeric binder. 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. For example, the support may by a transparent film such as poly(ethylene terephthalate) or may be reflective such as baryta-coated paper or white polyester (polyester with white pigment incorporated therein). The dye image-receiving layer may comprise, for example, a polycarbonate, a polyurethane, a polyester, polyvinyl chloride, poly(styrene- co -­ acrylonitrile), poly(caprolactone) or mixtures thereof. 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 yellow dye thereon as described above or may have alternating areas of other different dyes, such as sublimable cyan and/or magenta and/or black or other dyes. In a preferred embodiment of the invention, the dye-donor element comprises a poly(ethylene terephthalate) support coated with sequential repeating areas of cyan, magenta and the yellow dye as described above, and the above process steps are sequentially performed for each color to obtain a three-color dye transfer image. Of course, when the process is only performed for a single color, then a monochrome dye transfer image is obtained. Thermal printing heads which can be used to transfer dye from the dye-donor elements of the invention are available commercially. There can be employed, for example, a Fujitsu Thermal Head (FTP-040 MCS001), a TDK Thermal Head F415 HH7-1089 or a Rohm Thermal Head KE 2008-F3. A thermal dye transfer assemblage using 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 on three occasions during the time when heat is applied by the thermal printing head. 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. Example 1 A) A yellow dye-donor element was prepared by coating the following layers in the order recited on a 6 µm poly(ethylene terephthalate) support: 1) Dye-barrier layer of gelatin nitrate (gelatin, cellulose nitrate and salicylic acid in approximate 20:5:2 weight ratio in a solvent of acetone, methanol and water) (0.33 g/m²), and 2) Dye layer containing a yellow dye as identified in the following Table 1 (0.22 g/m²) in cellulose acetate (40% acetyl) (0.44 g/m²) coated from 2-butanone and acetone. If the dye had limited solubility, a small amount of tetrahydrofuran was also added. On the back side of the element, a slipping layer of Beeswax (0.55 g/m²) in cellulose acetate butyrate (0.55 g/m²) was coated from tetrahydrofuran solvent. A dye-receiving element was prepared by coating a solution of Makrolon 5705® (Bayer A.G.) polycarbonate resin (2.9 g/m²) in a solvent mixture of methylene chloride and trichloroethylene on an ICI Melinex 990® white polyester support. The dye side of the dye-donor element strip 0.75 inches (19 mm) wide was placed in contact with the dye image-receiving layer of the dye-receiver element of the same width. The assemblage was fastened in the jaws of a stepper motor driven pulling device. The assemblage was laid on top of a 0.55 (14 mm) diameter rubber roller and a Fujitsu Thermal Head (FTP-040MCS001) and was pressed with a spring at a force of 3.5 pounds (1.6 kg) against the dye-donor element side of the assemblage pushing it against the rubber roller. The imaging electronics were activated causing the pulling device to draw the assemblage between the printing head and roller at 0.123 inches/sec (3.1 mm/sec). Coincidentally, the resistive elements in the thermal print head were heated at 0.5 msec increments from 0 to 4.5 msec to generate a graduated density test pattern. The voltage supplied to the print head was approximately 19 v representing approximately 1.75 watts/dot. Estimated head temperature was 250-400°C. The dye-receiving element was separated from the dye-donor element and the Status A blue density of the step image was read. The image was then subjected to "HID-fading": 4 days, 50 kLux, 5400°K, 32°C, approximately 25% RH. The density loss at a density near 1.0 was calculated. The following dye stability data were obtained: Use of Compound 1 containing a carbamoyloxy group substituted in accordance with the invention showed superior light stability as compared to a control dye of similar structure without this substituent (Control 1) and other control dyes of related structures. Example 2 The extent of dye retransfer was estimated by taping with pressure the dye image-receiving element face-to-face with a waterproof polyethylene-­ titanium dioxide overcoated reflective paper support and incubating for 5 days at 49°C, approximately 50% RH. The extent of dye transferred to the reflective support was estimated visually as follows: No significant retransfer was visually observed for the dye employed in the invention. All control dyes, with the exception of Control dye 3, showed a greater degree of dye retransfer. Control dye 3, however, as shown in Example1, had the worst stability to light. Example 3 A) A yellow dye-donor element was prepared by coating the following layers in the order recited on a 6 µm poly(ethylene terephthalate) support: 1) Dye-barrier layer of poly(acrylic acid) (0.16 g/m²) coated from water, and 2) Dye layer containing a yellow dye as identified in the following Table 4 (0.62 mmoles/m²) and FC-431® surfactant (3M Corp.) (0.0022 g/m²) in cellulose acetate (40% acetyl) (at a weight equal to 1.2X that of the yellow dye) coated from a 2-butanone and cyclohexanone solvent mixture. On the back side of the element was coated a typical slipping layer. A dye-receiving element was prepared as in Example 1. The dye side of the dye-donor element strip 1 inch (25 mm) wide was placed in contact with the dye image-receiving layer of the dye-receiver element of the same width. The assemblage was fastened in the jaws of a stepper motor driven pulling device. The assemblage was laid on top of a 0.55 (14 mm) diameter rubber roller and a TDK Thermal Head (No. L-133) was pressed with a force of 8.0 pounds (3.6 kg) against the dye-donor element side of the assemblage pushing it against the rubber roller. The imaging electronics were activated causing the pulling device to draw the assemblage between the printing head and roller at 0.123 inches/sec (3.1 mm/sec). Coincidentally, the resistive elements in the thermal print head were pulse-heated at increments from 0 to 8.3 msec to generate a graduated density test pattern. The voltage supplied to the print head was approximately 22 v representing approximately 1.6 watts/dot (13 mjoules/dot) for maximum power to the 0.1 mm² area pixel. The dye-receiving element was separated from each dye-donor element and the Status A blue densities of the step image were read. The image was then subjected to "HID-fading": 7 days, 50 kLux, 5400°K, 32°C, approximately 25% RH. The density loss near mid scale was calculated. The following dye stability data were obtained: Use of the compounds substituted in accordance with the invention showed superior light stability as compared to control dyes of similar structure without this substituent.

Claims: 1. A yellow dye-donor element for thermal dye transfer comprising a support having thereon a dye layer comprising a yellow dye dispersed in a polymeric binder, characterized in that said yellow dye has the formula: wherein R is a substituted or unsubstituted alkyl group of from 1 to 10 carbon atoms; a cycloalkyl group of from 5 to 7 carbon atoms; or represents the atoms which when taken together with Z forms a 5- or 6-membered ring; R¹ is an alkylene or substituted alkylene group; X is -OJO-, -OJ-, -JO-, -OJNR³-, -NR³J-, -NR³JNR³, -JNR³- or -NR³JO-; J is CO or SO₂; R³ is hydrogen; a substituted or unsubstituted alkyl group of from 1 to 10 carbon atoms; a substituted or unsubstituted aryl group of from 6 to 10 carbon atoms; or represents the atoms which when taken together with R² forms a 5- or 6-membered ring; R² is a substituted or unsubstituted alkyl group of from 1 to 10 carbon atoms; a cycloalkyl group of from 5 to 7 carbon atoms; a substituted or unsubstituted aryl group of from 6 to 10 carbon atoms; or represents the atoms which when taken together with R³ forms a 5- or 6-membered ring; Z is hydrogen or represents the atoms which when taken together with R forms a 5- or 6-membered ring; Y is a substituted or substituted alkyl or alkoxy group of from 1 to 6 carbon atoms or halogen; and n is a positive integer from 1 to 4. 2. The element of Claim 1 characterized in that R represents the atoms which are taken together with Z to form a 6-membered ring. 3. The element of Claim 2 characterized in that R¹ is ethylene. 4. The element of Claim 2 characterized in that X is -OCONH- or -OCO-. 5. The element of Claim 2 characterized in that X is -NCH₃SO₂- or -NR³J-, wherein J is CO and R³ is combined with R² to form a 5- or 6-membered ring. 6. The element of Claim 2 characterized in that R² is a substituted aryl group of from 6 to 10 carbon atoms or C₆H₅. 7. The element of Claim 1 characterized in that a dye-barrier layer is located between said dye layer and said support. 8. The element of Claim 1 characterized in that the side of the support opposite the side having thereon said dye layer is coated with a slipping layer comprising a lubricating material. 9. The element of Claim 1 characterized in that said support comprises poly(ethylene terephthalate). 10. The element of Claim 1 characterized in that said dye layer comprises sequential repeating areas of cyan, magenta and said yellow dye.

Inventors: LUM, KIN KWONG, MOORE, WILLIAM HOWARD, WEAVER, MAX ALLEN
Applicants: EASTMAN KODAK COMPANY (A NEW JERSEY CORPORATION)
Application year: 1986
Main classification: B41M5
IPC codes: C09B23, B41M5