SLIPPING LAYER FOR DYE-DONOR ELEMENT USED IN THERMAL DYE TRANSFER

Abstract: A dye-donor element for thermal dye transfer comprising a support having on one side thereof a dye layer and on the other side a slipping layer comprising a lubricating material dispersed in a polymeric binder, the lubricating material being poly(vinyl stearate), poly(caprolactone) or a straight chain alkyl or polyethylene oxide perfluoroalkylated ester or perfluoroalkylated ether.

Description: This invention relates to dye-donor elements used in thermal dye transfer, and more particularly to the use of a certain slipping layer on the back side thereof to prevent chatter marks and tearing of the donor element during the printing operation. 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. There is a problem with the use of dye-donor elements for thermal dye-transfer printing because a thin support is required in order to provide effective heat transfer. For example, when a thin polyester film is employed, it softens when heated during the printing operation and then sticks to the thermal printing head. This causes intermittent rather than continuous transport across the thermal head. The dye transferred thus does not appear as a uniform area, but rather as a series of alternating light and dark bands (chatter marks). Sufficient friction is often created to tear the dye-donor element during printing. It would be desirable to eliminate such problems in order to have a commercially acceptable system. European Patent Application 169,705 relates to dye-donor elements having a slipping layer on the back side thereof comprising compounds having a perfluoroalkyl group or ultraviolet ray-curing type resins. U.S. Patent 4,572,860 relates to slipping layers comprising urethane or vinyl chloride resins or higher fatty acids. There is a problem with many of the materials proposed for use in thermal dye transfer printing in that they do not always provide adequate performance. It is an object of this invention to provide slipping layer materials for dye-donor elements which do not stick or tear upon passage through the thermal head. These and other objects are achieved by this invention which comprises a dye-donor element for thermal dye transfer comprising a support having on one side thereof a dye layer and on the other side a slipping layer comprising a lubricating material dispersed in a polymeric binder, characterized in that the lubricating material is poly(vinyl stearate), poly(caprolactone) or a straight chain alkyl or polyethylene oxide perfluoroalkylated ester or perfluoroalkylated ether. The poly(vinyl stearate) which can be employed in the invention is available as a commercial material from Polysciences Corp. (No. 3169). The poly(caprolactone) which can be used in the invention can have, for example, recurring units of the following formula: wherein n is from about 100 to about 600. This material is available commercially from Union Carbide as Tone PCL-700®. The straight chain alkyl or polyethylene oxide perfluoroalkylated ester or perfluoroalkylated ether used in the invention in a preferred embodiment thereof has the following formula: wherein R¹ is an alkyl or substituted alkyl group having from 1 to 6 carbon atoms such as methyl, ethyl, butyl, isopropyl, 2-hydroxyethyl, or 2-ethoxy­ ethyl; or an aryl or substituted aryl group having from 6 to 10 carbon atoms such as phenyl, p -tolyl or p -methoxyphenyl; R³ is H or R¹; n is an integer of from 4 to 20; and x, y and z each independently represents an integer of from 2 to 50. In a preferred embodiment, R¹ is ethyl, R² is n is 8 and x′ is 25 to 50. In another preferred embodi­ ment, R¹ is ethyl, H, n is 8 and y′ is 25 to 50. In yet another preferred embodiment, R¹ is ethyl, R² is -CH₂-OCH₂-CH₂-OH, n is 8 and z′ is 2 to 30. Specific compounds within the scope of the above formula include the following: This material is supplied commercially as Fluorad® FC-431 (3M Company). This material is supplied commercially as Fluorad® FC-432 (3M Company). This material is supplied commercially as Fluorad® FC-170 (3M Company). Any polymeric binder can be used in the slipping layer of the invention provided it has the desired effect. There can be employed, for example, poly(vinyl alcohol- co -butyral) (available commercially as Butvar 76® by Dow Chemical Co.; polystyrene; poly(vinyl acetate); cellulose acetate butyrate; cellulose acetate; ethyl cellulose; bisphenol-A polycarbonate resins; poly(vinyl acetal); poly(vinylbenzal); cellulose triacetate; poly(methylmethacrylate); poly(styrene- co -­ acrylonitrile; poly(styrene- co -butadiene); etc. The lubricant employed in the slipping layer of the invention can be employed in any amount which is effective for the intended purpose. In general, good results have been obtained at a coating coverage ranging from 1 to 2,000 mg/m². The amount of polymeric binder used in the slipping layer of the invention is not critical. In general the polymeric binder may represent from 1 to 80% of the total layer coverage. In a preferred embodiment of the invention, the polymeric binder in the slipping layer is poly(styrene- co -acrylonitrile). In another preferred embodiment of the invention, the lubricant in the slipping layer comprises poly(vinyl stearate). 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 such as or any of the dyes disclosed in U.S. Patent 4,541,830. The above dyes may be employed singly or in combination to obtain a monochrome. The dyes may be used at a coverage of from 0.05 to 1 g/m² and are preferably hydrophobic. A dye-barrier layer may be employed in the dye-donor elements of the invention to improve the density of the transferred dye. 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-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 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 be 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 one dye thereon or may have alternating areas of different dyes, such as sublimable cyan, magenta, yellow, black, etc., as described 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. 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. 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 magenta 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 (gela­ tin, cellulose nitrate and salicylic acid in approximately 20:5:2 weight ratio in a solvent of acetone, methanol and water) (0.17 g/m²), and 2) Dye layer containing the following magenta dye (0.22 g/m²), and cellulose acetate hydrogen phthalate (18-21 % acetyl, 32-36% phthalyl) (0.39 g/m²) coated from 8% cyclohexanone in 2-butanone: A slipping layer was coated on the back of the dye-donor element having the lubricant indicated in Table 1 (0.43 g/m²) in a poly(vinyl alcohol- co -­ butyral) Butvar 76®) binder (0.43 g/m²) coated from tetrahydrofuran solvent. A dye-receiving element was prepared by coating 2.9 g/m² of Makrolon 5705® polycarbonate resin (Bayer A. G.) using a solvent mixture of dichloromethane and trichloroethylene or chlorobenzene on an ICI Melinex 990® white polyester support. The dye side of each 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. Passage of the assemblage through the thermal head was evaluated. If no tearing was observed, the assemblage was separated, the dye-donor was discarded, and the dye transferred to the dye-receiver was evaluated visually. The following data were obtained: The above data show the unique ability of the materials employed in the slipping layer of the invention to promote smooth passage through the thermal head. The control materials either tore or gave only fair or poor performance. Example 2 - Use of different binders Example 1 was repeated except that poly(vinyl stearate) was employed as the lubricant (0.43 g/m²) in the polymeric binders (0.43 g/m²) listed in Table 2. The following results were obtained. The above data show the use of a variety of polymeric binders with a poly(vinyl stearate) lubricant to give excellent or good performance.

Claims: 1. A dye-donor element for thermal dye transfer comprising a support having on one side thereof a dye layer and on the other side a slipping layer comprising a lubricating material dispersed in a polymeric binder, characterized in that said lubricating material is poly(vinyl stearate), poly(caprolactone) or a straight chain alkyl or polyethylene oxide perfluoroalkylated ester or perfluoroalkylated ether. 2. The element of Claim 1 characterized in that said lubricating material is present in an amount of from 1 to 2000 mg/m² and said polymeric binder represents 1 to 80% of the total layer coverage. 3. The element of Claim 1 characterized in that said polymeric binder is poly(styrene-co-acrylonitrile). 4. The element of Claim 1 characterized in that said lubricant is poly(vinyl stearate). 5. The element of Claim 1 characterized in that said straight chain alkyl or polyethylene oxide perfluoroalkylated ester or perfluoroalkylated ether has the following formula: wherein R¹ is an alkyl or substituted alkyl group having from 1 to 6 carbon atoms or an aryl or substituted aryl group having from 6 to 10 carbon atoms; R³ is H or R¹; n is an integer of from 4 to 20; and x, y and z each independently represents an integer of from 2 to 50. 6. The element of Claim 5 characterized in that said lubricant is 7. The element of Claim 1 characterized in that said support comprises poly(ethylene terephthalate). 8. The element of Claim 7 characterized in that said dye layer comprises sequential repeating areas of cyan, magenta and yellow dye.

Inventors: HARRISON, DANIEL JUDE, KAN, HSIN-CHIA, VANIER, NOEL RAWLE
Applicants: EASTMAN KODAK COMPANY (A NEW JERSEY CORPORATION)
Application year: 1986
Main classification: B41M5
IPC codes: B41M5