Alpha-cyano arylidene pyrazolone magenta dye-donor element for thermal dye transfer
This invention relates to dye-donor elements used in thermal dye transfer which have good hue and dye stability. 
     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 produces 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. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271 by Brownstein entitled &#34;Apparatus and Method For Controlling A Thermal Printer Apparatus,&#34; issued Nov. 4, 1986, the disclosure of which is hereby incorporated by reference. 
     A problem has existed with the use of certain dyes in dye-donor elements for thermal dye transfer printing. Many of the dyes proposed for use do not have adequate stability to light. Others do not have good hue. It would be desirable to provide dyes which have good light stability and have improved hues. 
     JP No. 60/31,563 and JP No. 60/223,878 relate to arylidene magenta dyes used in a thermal transfer sheet. There is a problem with these dyes, however, with their stability to light. It would be desirable to provide arylidene dyes which have improved hue and stability to light and heat. 
     JP No. 61/268,760 relates to dyes similar to those used in the present invention. Those dyes, however, are used as disperse fabric dyes and are not disclosed for use in a thermal dye transfer system. 
     Substantial improvements in light stability and hues are achieved in accordance with this invention which comprises a dye-donor element for thermal dye transfer comprising a support having thereon a dye dispersed in a polymeric binder, the dye having the formula: ##STR2## wherein R 1  represents a substituted or unsubstituted alkyl group having from 1 to about 10 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, methoxyethyl, benzyl, 2-methanesulfonamidoethyl, 2-hydroxyethyl, 2-cyanoethyl, methoxycarbonylmethyl, etc.; a cycloalkyl group having from about 5 to about 7 carbon atoms, such as cyclohexyl, cyclopentyl, etc.; or an aryl group having from about 6 to about 10 carbon atoms, such as phenyl, pyridyl, naphthyl, p-tolyl, p-chlorophenyl, or m-(N-methyl sulfamoyl)phenyl; 
     R 2  represents a substituted or unsubstituted alkoxy group having from 1 to about 10 carbon atoms, such as methoxy, ethoxy, methoxyethoxy or 2-cyanoethoxy; a substituted or unsubstituted aryloxy group having from about 6 to about 10 carbon atoms, such as phenoxy; m-chlorophenoxy; or naphthoxy; NHR 5  ; or NR 5  R 6  ; 
     R 3  and R 4  each represents R 1  ; or either or both of R 3  and R 4  can be joined to the carbon atom of the aromatic ring at a position ortho to the position of attachment of the anilino nitrogen to form a 5- or 6-membered ring; or R 3  and R 4  can be joined together to form, along with the nitrogen to which they are attached, a 5- or 6-membered heterocyclic ring, such as a pyrrolidine or morpholine ring; 
     R 5  and R 6  each independently represents a substituted or unsubstituted alkyl group having from 1 to about 10 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, methoxyethyl, benzyl, 2-methanesulfonamidoethyl, 2-hydroxyethyl, 2-cyanoethyl, methoxycarbonylmethyl, etc.; a cycloalkyl group having from about 5 to about 7 carbon atoms, such as cyclohexyl, cyclopentyl, etc.; or an aryl group having from about 6 to about 10 carbon atoms, such as phenyl, pyridyl, naphthyl, p-tolyl, p-chlorophenyl, or m-(N-methyl sulfamoyl)phenyl; or R 5  and R 6  may be joined together to form, along with the nitrogen to which they are attached, a 5- or 6-membered heterocyclic ring, such as a pyrrolidine or morpholine ring; and 
     Z represents hydrogen or the atoms necessary to complete a 5- or 6-membered ring, thus forming a fused ring system such as napthalene, quinoline, isoquinoline or benzothiazole. 
     In a preferred embodiment of the invention, R 1  is phenyl or methyl. In another preferred embodiment, R 3  and R 4  are each methyl or ethyl. In another preferred embodiment, R 2  is NR 5  R 6 , wherein each R 5  and R 6  is methyl or ethyl. 
     In still another preferred embodiment, R 2  is NR 5  R 6 , wherein R 5  and R 6  are joined together to form, along with the nitrogen to which they are attached, a pyrrolidine or morpholine ring. In yet another preferred embodiment, R 2  is ethoxy or NHR 5 , wherein R 5  is methyl or phenyl. 
     In yet still another preferred embodiment, R 3  is joined together to form, along with the nitrogen to which it is attached, a 6-membered heterocyclic ring and R 4  is chloroethyl. 
     The aromatic ring in the formula above may be substituted with various substituents, such as C 1  to C 6  alkyl, C 1  to C 6  alkoxy, halogen, sulfanamido, aryloxy, acyloxy, acylamido, etc. 
     Compounds included within the scope of the invention include the following: 
     
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 ##STR3##                                                                 
Cmpd.                                                                     
    A      R.sup.3  R.sup.4                                               
                        R.sup.2      R.sup.1                              
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1   H      C.sub.2 H.sub.5                                                
                    C.sub.2 H.sub.5                                       
                        N(CH.sub.3).sub.2                                 
                                     C.sub.6 H.sub.5                      
2   H      CH.sub.3 CH.sub.3                                              
                        N(CH.sub.3).sub.2                                 
                                     C.sub.6 H.sub.5                      
3   H      CH.sub.3 CH.sub.3                                              
                        N(CH.sub.3).sub.2                                 
                                     CH.sub.3                             
4   3-OCH.sub.3                                                           
           C.sub.2 H.sub.5                                                
                    C.sub.2 H.sub.5                                       
                        N(CH.sub.3).sub.2                                 
                                     C.sub.6 H.sub.5                      
5   H      CH.sub.3 CH.sub.3                                              
                        NHCH.sub.3   C.sub.6 H.sub.5                      
6   H      CH.sub.3 CH.sub.3                                              
                         ##STR4##    C.sub.6 H.sub.5                      
7   H      C.sub.2 H.sub.5                                                
                    C.sub.2 H.sub.5                                       
                         ##STR5##    C.sub.6 H.sub.5                      
8   H      C.sub.2 H.sub.5                                                
                    C.sub.2 H.sub.5                                       
                        NHC.sub.6 H.sub.5                                 
                                     C.sub.6 H.sub.5                      
9   H      CH.sub.3 CH.sub.3                                              
                        OC.sub.2 H.sub.5                                  
                                     C.sub.6 H.sub.5                      
10  H      C.sub.2 H.sub.5                                                
                    C.sub.2 H.sub.5                                       
                        OC.sub.2 H.sub.5                                  
                                     C.sub.6 H.sub.5                      
11  2,5-(OCH.sub.3).sub.2                                                 
           n-C.sub.3 H.sub.7                                              
                    n-C.sub.3 H.sub.7                                     
                        NHC.sub.2 H.sub.4 OCH.sub.3                       
                                     C.sub.6 H.sub.4p-Cl                  
12  3-CH.sub.3                                                            
           C.sub.6 H.sub.5 CH.sub.2                                       
                    CH.sub.3                                              
                        OC.sub.6 H.sub.5                                  
                                     CH.sub.2 C.sub.6 H.sub.5             
13  H      CF.sub.3 CH.sub.2 O.sub.2 CCH.sub.2                            
                    C.sub.2 H.sub.5                                       
                         ##STR6##    C.sub.2 H.sub.5                      
14  3-F                                                                   
            ##STR7##    N(CH.sub.3).sub.2                                 
                                     C.sub.6 H.sub.5                      
15  2,5-(Cl).sub.2                                                        
           CH.sub.3 CH.sub.3                                              
                        NHC.sub.4 H.sub.9                                 
                                     2-C.sub.5 H.sub.4 N                  
16                                                                        
     ##STR8##                                                             
17                                                                        
     ##STR9##                                                             
18                                                                        
     ##STR10##                                                            
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     These dyes may be prepared using synthetic techniques similar to those diclosed in J. Signalaufzeichnungsmaterielen, 9, 31 (1981) the disclosure of which is hereby incorporated by reference. 
     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 such as those described and claimed in U.S. Pat. No. 4,716,144 by Vanier, Lum and Bowman. 
     The dye in the dye-donor element of the invention is dispersed in a polymeric binder such as a cellulose derivatives, 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. Pat. No. 4,700,207 of Vanier and Lum; a polycarbonate; poly(styrene-co-acrylonitrile), a poly(sulfone) or a poly(phenylene oxide). The binder may be used at a coverage of from about 0.1 to about 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 thermal printing heads. Such materials include polyesters such as poly(ethylene terephthalate); polyamides; polycarbonates; glassine paper; condenser paper; cellulose esters such as cellulose acetate; fluorine polymers such as polyvinylidene fluoride or poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as polyoxymethylene; polyacetals; polyolefins such as polystyrene, polyethylene, polypropylene or methylpentane polymers; and polymides such as polymide-amides and polyetherimides. The support generally has a thickness of from about 2 to about 30 μm. It may also be coated with a subbing layer, if desired, such as those materials described in U.S. Pat. No. 4,695,288 of Ducharme or U.S. Application Ser. No. 079,613 of Henzel, filed July 30, 1987. 
     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. Preferred lubricating materials include oils or semi-crystalline organic solids that melt below 100° C. such as poly(vinyl stearate), beeswax, perfluorinated alkyl ester polyethers, poly(caprolactone), silicone oil, poly(tetrafluoroethylene), carbowax, poly(ethylene glycols), or any of those materials disclosed in U.S. Pat. Nos. 4,717,711 of Vanier, Harrison and Kan and 4,717,712 of Harrison, Vanier and Kan; and U.S. Application Ser. Nos. 076,433 of Henzel, Lum and Vanier, filed July 21, 1987, 062,796 of Vanier and Evans, filed June 16, 1987, and 067,797 of Henzel and Vanier, filed June 16, 1987. Suitable polymeric binders for the slipping layer include poly(vinyl alcohol-co-butyral), poly(vinyl alcohol-co-acetal), poly(styrene), 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 about 0.001 to about 2 g/m 2 . If a polymeric binder is employed, the lubricating material is present in the range of 0.01 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 polymide, a cellulose ester such as cellulose acetate, a poly(vinyl alcohol-co-acetal) or a poly(ethylene terephthatlate). The support for the dye-receiving element may also be reflective such as baryta-coated paper, polyethylene-coated paper, white polyester (polyester with white pigment incorporated therein), an ivory paper, a condenser paper or a synthetic paper such as duPont Tyvek®. 
     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. 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 about 1 to about 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 dye thereon as described above or may have alternating areas of other different dyes, such as sublimable cyan and/or magenta and/or yellow and/or black or other dyes. Such dyes are disclosed in U.S. Pat. Nos. 4,541,830; 4,698,651 of Moore, Weaver and Lum; 4,695,287 of Evans and Lum; and 4,701,439 of Weaver, Moore and Lum; and U.S. Application Ser. Nos. 059,442 of Byers and Chapman, filed June 8, 1987; 059,443 of Evans and Weber, filed June 8, 1987; 095,796 of Evans and Weber, filed Sept. 14, 1987; and 123,441 of Byers, Chapman and McManus, filed Nov. 20, 1987, the disclosures of which are hereby incorporated by reference. Thus, one-, two-, three- or four-color elements (or higher numbers also) are included within the scope of the invention. 
     In a preferred embodiment of the invention, the dye-donor element comprises a poly(ethylene terephthalate) support coated with sequential repeating areas of yellow, cyan and a magenta 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 MCSOO1), a TDK Thermal Head F415 HH7-1089 or a Rohm Thermal Head KE 2008-F3. 
     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 wiht 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 example is provided to illustrate the invention. 
     EXAMPLE 
     A magenta dye-donor element was prepared by coating the following layers in the order recited on a 6 μm poly(ethylene terephthalate) support: 
     (1) Subbing layer of duPont Tyzor TBT® titanium tetra-n-butoxide (0.16 g/m 2 ) coated from a n-butyl alcohol and n-propylacetate solvent mixture, and 
     (2) Dye layer containing the magenta dye identified in the Table below (0.36 mmoles/m 2 ), FC-431® surfactant (3M Corp.) (0.002 g/m 2 ), in a cellulose acetate-propionate (2.5% acetyl, 48% propionyl) binder (weight equal to 2.6X that of the dye) coated from a cyclopentanone, toluene, and methanol solvent mixture. 
     A slipping layer was coated on the back side of the element similar to that disclosed in U.S. Application Ser. No. 062,797 of Henzel et al, filed June 16, 1987. 
     A dye-receiving element was prepared by coating a solution of Makrolon 5705®(Bayer AG Corporation) polycarbonate resin (2.9 g/m 2 ) in methylene chloride on a pigmented polyethylene-overcoated paper stock. 
     The dye side of the dye-donor element strip approximately 10 cm ×13 cm in area was placed in contact with the dye image-receiving layer of the dye-receiver element of the same area. The assemblage was clamped to a stepper-motor driven 60 mm diameter rubber roller and a TDK Thermal Head (No. L-231) (thermostatted at 26°C.) 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 donor/receiver assemblage to be drawn between the printing head and roller at 6.9 mm/sec. Coincidentally, the resistive elements in the thermal print head were pulsed at 29 μsec/pulse at 128 μsec intervals during the 33 msec/dot printing time. A stepped density image was generated by incrementally increasing the number of pulses/dot from 0 to 255 . The voltage supplied to the print head was approximately 23.5 volts, resulting in an instantaneous peak power of 1.3 watts/dot and a maximum total energy of 9.6 mjoules/dot. 
     The dye-receiving element was separated from the dye-donor element. The Status A green reflection densities of each stepped image consisting of a series of 11 graduated density steps 1 cm×1 cm were read. 
     The images were then subjected to High-Intensity Daylight fading (HID-fading) for 7 days, 50 kLux, 5400° K., 32° C., approximately 25% RH and the densities were reread. The percent density loss from D-max (highest density step) was calculated. The λ-max of each dye in an acetone solution was also determined. The following results were obtained: 
     
                       TABLE                                                       
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Dye-Donor            Status A Green Density                               
Element w/ .sup.λ max  % Loss                                      
Compound   (nm)      .sup.D Max                                           
                              After Fade                                  
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1          536       1.6      16                                          
2          522       1.3      16                                          
3          503       1.2      14                                          
4          536       1.0       8                                          
5          517       1.3       6                                          
6          519       1.2      26                                          
7          543       1.2      13                                          
8          549       1.1      11                                          
9          523       1.6      11                                          
10         532       1.6       9                                          
18         530       0.6      11                                          
Control 1  529       1.3      44                                          
Control 2  550       1.4      46                                          
Control 3  589       1.0      39                                          
Control 4  563       1.1      34                                          
Control 5  627       1.5      41                                          
Control 6  521       1.2      44                                          
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     The above results indicate that the dyes according to the invention have substantially improved light stability (lower % fade) in comparison ##STR11## Disclosed in JP No. 60/031,563 and JP No. 50/223,878. 
     The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.