Infrared Absorbing Nickel-Dithiolene Dye Complexes for Dye-Donor Element Used in Laser-Induced Thermal Dye Transfer

This invention relates to dye-donor elements used in laser-induced thermal dye transfer, and more particularly to the use of certain infrared absorbing nickel-dithiolene dye complexes which are located in the dye layer.

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 produce 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 "Apparatus and Method For Controlling A Thermal Printer Apparatus," issued Nov. 4, 1986.

Another way to thermally obtain a print using the electronic signals described above is to use a laser instead of a thermal printing head. In such a system, the donor sheet includes a material which strongly absorbs at the wavelength of the laser. When the donor is irradiated, this absorbing material converts light energy to thermal energy and transfers the heat to the dye in the immediate vicinity, thereby heating the dye to its vaporization temperature for transfer to the receiver. The absorbing material may be present in a layer beneath the dye and/or it may be admixed with the dye. The laser beam is modulated by electronic signals which are representative of the shape and color of the original image, so that each dye is heated to cause volatilization only in those areas in which its presence is required on the receiver to reconstruct the color of the original object. Further details of this process are found in GB 2,083,726A, the disclosure of which is hereby incorporated by reference.

In U.S. Pat. No. 4,753,923, dithiolene-nickel(II) complexes are described for use in a dye-donor element for transfer to a receiving layer. The dye-donor element described therein also has a slipping layer on the back thereof. The nickel complexes described herein are located in the dye layer itself or in an adjacent coextensive layer and are used in a laser-induced thermal dye transfer process which does not employ a dye-donor which has a slipping layer on the back thereof.

In GB 2,083,726A, the absorbing material which is disclosed for use in their laser system is carbon. There is a problem with using carbon as the absorbing material in that it is particulate and has a tendency to clump when coated which may degrade the transferred dye image. Also, carbon may transfer to the receiver by sticking or ablation causing a mottled or desaturated color image. It would be desirable to find an absorbing material which did not have these disadvantages.

Japanese Kokai 63/319,191 relates to a transfer material for heat-sensitive recording comprising a layer containing a substance which generates heat upon irradiation by a laser beam and another layer containing a subliming dye on a support. Compounds 17-20 of that reference which generate heat upon irradiation are similar to the dyes described herein. However, the materials in the reference are specifically described as being located in a separate layer from the dye layer, rather than being in the dye layer itself. There is a problem with having the infrared-absorbing materials located in a separate layer in that the transfer efficiency, i.e., the density per unit of laser input energy, is not as great as it would be if the infrared-absorbing material were located in the dye layer.

JP 51/088,016 discloses a recording material which contains an absorbing agent. Compounds 2-4 and 12 of that reference relate to nickel-dye complexes similar to those described herein. However, the definition of the complexes described herein do not include those compounds.

Accordingly, this invention relates to a dye-donor element for laser-induced thermal dye transfer comprising a support having thereon a dye layer comprising a polymeric binder, an image dye and an infrared-absorbing material which is different from the image dye in the dye layer, and wherein the infrared-absorbing material is a nickel-dithiolene dye complex which is located coextensively with the image dye in the dye layer, the dye complex having the following formula: ##STR2## wherein: each R.sup.1 and R.sup.2 independently represents a substituted or unsubstituted alkyl group having from 1 to about 10 carbon atoms or one of R.sup.1 and R.sup.2, but not both simultaneously, represents a substituted or unsubstituted aryl or hetaryl group having from about 5 to about 10 atoms such as t-butyl, 2-ethoxyethyl, n-hexyl, benzyl, 3-chlorophenyl, 2-imidazolyl, 2-naphthyl, 4-pyridyl, methyl, ethyl, phenyl or m-tolyl; or R.sup.1 and R.sup.2 may be combined together with the carbon atoms to which they are attached to form a 5- to 7-membered substituted or unsubstituted carbocyclic ring, such as cyclopentane, cyclohexane, cyclopentenyl, cyclohexenyl, phenyl, chlorophenyl and naphthyl; each Z independently represents the atoms necessary to complete a 6-membered substituted or unsubstituted benzene ring; and X.sup..sym. is a monovalent cation such as

(n--C.sub.4 H.sub.9).sub.4 N.sup..sym., C.sub.5 H.sub.5 (CH.sub.3)N.sup..sym.,

(C.sub.2 H.sub.5).sub.4 N.sup..sym. or (C.sub.6 H.sub.5 CH.sub.2) (CH.sub.3).sub.3 N.sup..sym..

In a preferred embodiment of the invention, R.sup.1 is C.sub.6 H.sub.4 (p--OCH.sub.3) and R.sup.2 is n--C.sub.3 H.sub.7. In another preferred embodiment, each Z represents the atoms necessary to complete a benzene ring. In another preferred embodiment, each Z represents the atoms necessary to complete a methyl-substituted benzene ring.

The above infrared absorbing dye complexes may employed in any concentration which is effective for the intended purpose. In general, good results have been obtained at a concentration from about 0.05 to about 0.5 g/m.sup.2 within the dye layer itself or in an adjacent coextensive layer.

The above infrared absorbing dye complexes may be synthesized by procedures similar those described in G. N. Schranzer and V. P. Mayweg, J. Am. Chem. Soc., 84, 3221 (1962) or M. J. Baker-Hawkes, E. Billig, and H. B. Gray, J. Am. Chem. Soc., 88, 4870 (1966).

Spacer beads may be employed in a separate layer over the dye layer in order to separate the dye-donor from the dye-receiver thereby increasing the uniformity and density of dye transfer. That invention is more fully described in U.S. Pat. No. 4,772,582. The spacer beads may be coated with a polymeric binder if desired.

Dye complexes included within the scope of the invention include the following:

Any dye can be used in the dye layer of the dye-donor element of the invention provided it is transferable to the dye-receiving layer by the action of heat. Especially good results have been obtained with sublimable dyes. Examples of sublimable dyes include anthraquinone dyes, e.g., Sumikalon Violet RS.RTM. (Sumitomo Chemical Co., Ltd.), Dianix Fast Violet 3R-FS.RTM. (Mitsubishi Chemical Industries, Ltd.), and Kayalon Polyol Brilliant Blue N-BGM.RTM. and KST Black 146.RTM. (Nippon Kayaku Co., Ltd.); azo dyes such as Kayalon Polyol Brilliant Blue BM.RTM., Kayalon Polyol Dark Blue 2BM.RTM., and KST Black KR.RTM. (Nippon Kayaku Co., Ltd.), Sumickaron Diazo Black 5G.RTM. (Sumitomo Chemical Co., Ltd.), and Miktazol Black 5GH.RTM. (Mitsui Toatsu Chemicals, Inc.); direct dyes such as Direct Dark Green B.RTM. (Mitsubishi Chemical Industries, Ltd.) and Direct Brown M.RTM. and Direct Fast Black D.RTM. (Nippon Kayaku Co. Ltd.); acid dyes such as Kayanol Milling Cyanine 5R.RTM. (Nippon Kayaku Co. Ltd.); basic dyes such as Sumicacryl Blue 6G.RTM. (Sumitomo Chemical Co., Ltd.), and Aizen Malachite Green.RTM. (Hodogaya Chemical Co., Ltd.); ##STR22## or any of the dyes disclosed in U.S. Pat. No. 4,541,830, the disclosure of which is hereby incorporated by reference. The above dyes may be employed singly or in combination to obtain a monochrome. The dyes may be used at a coverage of from about 0.05 to about 1 g/m.sup.2 and are preferably hydrophobic.

The dye in the dye-donor element 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-coacrylonitrile), 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.sup.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 generated by the laser beam. 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. The support generally has a thickness of from about 2 to about 250 .mu.m. It may also be coated with a subbing layer, if desired.

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, white polyester (polyester with white pigment incorporated therein), an ivory paper, a condenser paper or a synthetic paper such as duPont Tyvek.RTM..

The dye image-receiving layer may comprise, for example, a polycarbonate, a polyurethane, a polyester, polyvinyl chloride, poly(styrene-coacrylonitrile), 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.sup.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 using a laser, 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 one dye 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; 4,695,287; 4,701,439; 4,757,046; 4,743,582; 4,769,360; and 4,753,922, 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 cyan, magenta and yellow dye, 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.

Several different kinds of lasers could conceivably be used to effect the thermal transfer of dye from a donor sheet to a receiver, such as ion gas lasers like argon and krypton; metal vapor lasers such as copper, gold, and cadmium; solid state lasers such as ruby or YAG; or diode lasers such as gallium arsenide emitting in the infrared region from 750 to 870 nm. However, in practice, the diode lasers offer substantial advantages in terms of their 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 laser radiation must be 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, sublimability and intensity of the image dye, 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 the dye-donor elements of the invention are available commercially. There can be employed, for example, Laser Model SDL-2420-H2.RTM. from Spectrodiode Labs, or Laser Model SLD 304 V/W.RTM. from Sony Corp.

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 adjacent to and overlying the 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 using the laser beam. 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.

A dye-donor element according to the invention was prepared by coating a 100 .mu.m thick poly(ethylene terephthalate) support with a layer of the magenta dye illustrated above (0.16 g/m.sup.2), the cyan dye illustrated above (0.48 g/m.sup.2), the nickel-dithiolene complex indicated in Table 1 below (0.16 g/m.sup.2) in a cellulose acetate propionate binder (2.5% acetyl, 45% propionyl) (0.12 g/m.sup.2) coated from a butanone and cyclohexanone solvent mixture.

A control dye-donor element was made as above containing only the magenta and cyan imaging dyes.

A dye-receiver was prepared by coating a layer of Makrolon 5705.RTM. polycarbonate resin (Bayer AG) (4.0 g/m.sup.2) on a 150 .mu.m thick titanium dioxide pigmented poly(ethylene terephthalate) support from a dichloromethane and chlorobenzene solvent mixture.

The dye-receiver was overlaid with the dye-donor placed on a drum with a circumference of 295 mm and taped with just sufficient tension to be able to see the deformation of the surface of the dye-donor by reflected light. The assembly was then exposed with the drum rotating at 180 rpm to a focused 830 nm laser beam from a Spectra Diode Labs laser model SDL-2430-H2 using a 33 micrometer spot diameter and an exposure time of 37 microseconds. The spacing between lines was 20 micrometers, giving an overlap from line to line of 39%. The total area of dye transfer to the receiver was 6.times.6 mm. The power level of the laser was approximately 180 milliwatts and the exposure energy, including overlap, was 0.1 ergs per square micron.

Each image was examined visually. The following results were obtained:

The above results indicate that the coatings containing an infrared absorbing dye complex according to the invention gave more density than the control.

A dye-donor element according to the invention was prepared by coating a 175 .mu.m thick poly(ethylene terephthalate) support with a layer of the yellow dye illustrated above (0.22 g/m.sup.2) and the nickel-dithiolene complex indicated in Table 2 below (0.33 g/m.sup.2) in a cellulose acetate propionate binder (2.5% acetyl, 45% propionyl) (0.22 g/m.sup.2) coated from a dichloromethane solvent.

A control dye-donor element was made as above containing only the yellow imaging dye.

A dye-receiver was prepared by coating on an unsubbed 100 .mu.m poly(ethylene terephthalate) support a layer of polystyrene beads (12 .mu.m average diameter) cross-linked with m- and p-divinylbenzene and containing m- and p-ethyl benzene (0.086 g/m.sup.2) in a poly(vinylbutyral) binder, Butvar.RTM. 76, (Monsanto Corp.) (3.4 g/m.sup.2) from butanone.

The dye-receiver was overlaid with the dye-donor placed on a drum of a laser exposing device with a circumference of 312 mm and taped with just sufficient tension to be able to see the deformation of the surface beads. The assembly was then exposed with the drum rotating at 100 rpm to a focused 816 nm laser beam from a Spectra Diode Labs laser model SDL-2430-H2. The nominal spot diameter was 33 .mu.m. The power level was 115 milliwatts and the exposure energy was 1.55 joules/cm.sup.2.

After laser transfer, the receiver was treated with saturated methylene chloride vapor for five minutes to fuse the dyes. The reflection density of each transferred receiver was then measured at 455 nm. The following results were obtained:

The above results indicate that the coatings containing an infrared absorbing dye complex according to the invention produced a high density of transferred yellow image dye, whereas no yellow dye was transferred from the control coating containing no infrared-absorbing dye.

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.