SUBBING LAYER FOR DYE IMAGE-RECEIVING LAYER USED IN THERMAL DYE TRANSFER

Abstract: A dye-receiving element for thermal dye transfer comprises a support, such as polyethylene-coated paper or poly(ethylene terephthalate), having thereon a subbing layer of a vinylidene chloride copolymer and a polymeric dye image-receiving layer, such as a polycarbonate. Use of the subbing layer of the invention improves the adhesion of the dye image-receiving layer to the support.

Description: This invention relates to dye-receiving elements used in thermal dye transfer, and more particularly to the use of a subbing layer between the support and a polymeric dye image-receiving layer to improve the adhesion of the dye image-receiving layer to the support. 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. Patent No. 4,621,271 by Brownstein entitled "Apparatus and Method For Controlling A Thermal Printer Apparatus," issued November 4, 1986. In Japanese laid open publication number 19, 138/85, an image-receiving element for thermal dye transfer printing is disclosed. The dye image-receiving layer disclosed comprises a polycarbonate containing a plasticizer. From EP-A- 0,227,094 a dye-receiving element for thermal dye transfer is known, said element comprising a support having thereon a dye-image receiving layer comprising a polycarbonate, such as a bisphenol A polycarbonate, having a number average molecular weight of at least 25,000. While polycarbonate is a desirable material for a dye image-receiving layer because of its effective dye compatibility and receptivity, there is a problem in getting proper adhesion of the layer to the support. It is an object of this invention to provide a dye-receiving element which would have good adhesion between a polymeric dye image-receiving layer and the support. These and other objects are achieved in accordance with this invention which comprises a dye-receiving element for thermal dye transfer comprising a support having thereon a subbing layer comprising a vinylidene chloride copolymer and a polymeric dye image-receiving layer. From EP-A- 0,228,065 a dye-donor element for thermal dye transfer is known, said element comprising a support having on one side thereof a dye layer, wherein a hydrophilic dye-barrier layer is located between the dye layer and the support, and a subbing layer is located between the dye-barrier layer and the support. In a preferred embodiment the subbing layer comprises poly(acrylonitrile-co-vinylidene chloride-co-acrylic acid) (14 : 80 : 6 wt.ratio). In a preferred embodiment of the invention, the vinylidene chloride copolymer comprises from 5 to 35 percent by weight of recurring units of an ethylenically unsaturated monomer, from 0 to 20 percent by weight of recurring units of an ethylenically unsaturated carboxylic acid, and from 55 to 85 percent by weight of recurring units of vinylidene chloride. Any ethylenically unsaturated monomer which is different from the other monomers in the polymer can be used to prepare the polymer described above including alkyl acrylates and methacrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, or butyl methacrylate; vinyl esters, amides, nitriles, ketones, halides, ethers, olefins, or diolefins as exemplified by acrylonitrile, methacrylonitrile, styrene, α-methyl styrene, acrylamide, methacrylamide, vinyl chloride, methyl vinyl ketone, fumaric, maleic and itaconic esters, 2-chloroethylvinyl ether, dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate, N-vinylsuccinamide, N-vinylphthalamide, N-vinylpyrrolidone, butadiene, or ethylene. A preferred monomer is acrylonitrile. Examples of ethylenically unsaturated carboxylic acids which can be included in the polymer described above include acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, or their anhydrides. The preferred carboxylic acids are acrylic acid and itaconic acid. In a preferred embodiment of the invention, the subbing layer comprises from 5 to 35 percent by weight of acrylonitrile from 2 to 10 percent by weight of acrylic acid, and from 55 to 85 percent by weight of recurring units of vinylidene chloride. The subbing layer of the invention may be employed at any concentration which is effective for the intended purpose. In general, good results have been obtained at from 0.03 to 1.0 g/m² of coated element. The polymeric dye image-receiving layer of the dye-receiver of the invention 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 1 to 5 g/m². In a preferred embodiment of the invention, the dye image-receiving layer is a polycarbonate. The term "polycarbonate" as used herein means a polyester of carbonic acid and a glycol or a dihydric phenol. Examples of such glycols or dihydric phenols are p-xylylene glycol, 2,2-bis(4-oxy-phenyl)propane, bis(4-oxyphenyl)methane, 1,1-bis(4-oxyphenyl)ethane, 1,1-bis(oxyphenyl)butane, 1,1-bis(oxyphenyl)cyclohexane, 2,2-bis(oxyphenyl)butane, etc. In another preferred embodiment of the invention, the polycarbonate dye image-receiving layer is a bisphenol-A polycarbonate having a number average molecular weight of at least 25,000. In still another preferred embodiment of the invention, the bisphenol-A polycarbonate comprises recurring units having the formula wherein n is from 100 to 500. Examples of such polycarbonates include General Electric Lexan® Polycarbonate Resin #ML-4735 (Number average molecular weight app. 36,000), and Bayer AG Makrolon #5705® (Number average molecular weight app. 58,000). The later material has a T g of 150°C. The support for the dye-receiving element of the invention 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 polyethylene-coated paper which has been subjected to a corona discharge treatment. In a preferred embodiment, polyethylene-coated paper or poly(ethylene terephthalate) is employed. It may be employed at any thickness desired, usually from 50 µm to 1000 µm. The corona discharge treatment that is used for the polyethylene-coated paper support can be carried out in an apparatus such as described in U.S. Patents 2,864,755, 2,864,756, 2,910,723 and 3,018,189. Advantageously, the polyethylene-coated paper support is subjected to a corona discharge of from .1 to 3.5 rfa. For further details, reference is made to U.S. Patent 3,412,908. A dye-donor element that is used with the dye-receiving element of the invention comprises a support having thereon a dye layer. Any dye can be used in such a layer provided it is transferable to the dye image-receiving layer of the dye-receiving element of the invention by the action of heat. Especially good results have been obtained with sublimable dyes such as those 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. As noted above, dye-donor elements are used to form a dye transfer image. Such a process comprises imagewise-heating a dye-donor element and transferring a dye image to a dye-receiving element as described above to form the dye transfer image. 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 example is provided to illustrate the invention. Example 1 A) A dye-receiver in accordance with the invention was prepared by coating the following layers on a 175 µm (7 mil) thick poly(ethylene terephthalate) (PET) support containing 8% by weight titanium dioxide: (a) Subbing layer of poly(acrylonitrile- co -vinylidene chloride- co -acrylic acid (ANVcA) (14:79:7 wt. ratio) (0.13 g/m²) coated from a butanone and cyclopentanone solvent mixture; and (c) Dye-receiving layer of Makrolon 5705® polycarbonate (Bayer AG) (2.9 g/m²), 1,4-didecoxy-2,5-dimethoxybenzene (0.38 g/m²), and FC-431® surfactant (3M Co.) (0.016 g/m²) coated from methylene chloride. B) A control receiver was prepared similar to A) except that it did not have any subbing layer. C) Other dye-receivers were prepared by coating the following layers on a 175 µm (7 mil) thick commercial paper stock consisting of 180 g/m² mixture of hard wood-craft and soft wood-sulfite bleach pulp: (a) Pigmented polyethylene (PE) layer of total laydown 30 g/m² with approximately 12% by weight anatase titanium dioxide and 3% zinc oxide; (b) Subbing layer of ANVcA in the amount stated in the table coated from a butanone and cyclopentanone solvent mixture; and (c) Dye-receiving layer of Makrolon 5705® polycarbonate (Bayer AG) (2.9 g/m²), 1,4-didecoxy-2,5-dimethoxybenzene (0.38 g/m²), and FC-431® surfactant (3M Co.) (0.016 g/m²) coated from methylene chloride. The PE-coated support was subjected to a corona discharge treatment (CDT) at approximately 450 joules/m² before applying the subbing layer. D) Control receivers were prepared similar to C) except that they either did not have the corona discharge treatment, did not have any subbing layer, or had a known subbing layer of duPont Tyzor TBT® titanium tetra-n-butoxide coated from 1-butanol as a solvent (0.16 g/m²). Each receiver element was subjected to a tape adhesion test. The receiver surface was first carefully scored in an "X" pattern. A small area (approximately 3/4 inch x 2 inches) of Scotch® Magic Transparent Tape (3M Corp.) was firmly pressed by hand over the scored area of the receiver surface leaving enough area free to serve as a handle for pulling the tape. Upon manually pulling the tape, ideally none of the receiving layer would be removed. Receiving layer removal indicated a weak bond between the support and the receiving layer. The following categories were established: E - excellent (no layer removal after two attempted tries with tape) G - good (a small amount of layer removal after two tries) F - fair (partial layer removal after two tries) P - unacceptable (substantial or total layer removal upon one try) The following results were obtained: Subbing Layer (g/m²) Support CDT Tape Test None (control) PET no P ANVcA (0.13) PET no E None (control) PE-coated paper yes P Tyzor (0.016 cont.) PE-coated paper yes P ANVcA (0.05 cont.) PE-coated paper no P ANVcA (0.05) PE-coated paper yes E ANVcA (0.11 cont.) PE-coated paper no F ANVcA (0.11) PE-coated paper yes E ANVcA (0.22 cont.) PE-coated paper no F ANVcA (0.22) PE-coated paper yes E ANVcA (0.34) PE-coated paper yes E The above results indicate that the subbing layer according to the invention was effective in bonding the dye image-receiving layer to the PET or PE-coated paper support which was subjected to a CDT, in comparison to the control elements which had no subbing layer, had a different subbing layer, or, in the case of PE-coated paper, did not have a CDT.

Claims: A dye-receiving element for thermal dye transfer comprising a support having thereon a subbing layer comprising a vinylidene chloride copolymer and a polymeric dye image-receiving layer. The element of Claim 1 characterized in that said vinylidene chloride copolymer comprises from 5 to 35 percent by weight of recurring units of an ethylenically unsaturated monomer, from 0 to 20 percent by weight of recurring units of an ethylenically unsaturated carboxylic acid, and from 55 to 85 percent by weight of recurring units of vinylidene chloride. The element of Claim 2 characterized in that said ethylenically unsaturated monomer comprises acrylonitrile and said ethylenically unsaturated carboxylic acid comprises either acrylic acid or itaconic acid. The element of Claim 3 characterized in that said subbing layer comprises from 5 to 35 percent by weight of acrylonitrile, from 2 to 10 percent by weight of acrylic acid, and from 55 to 85 percent by weight of recurring units of vinylidene chloride The element of Claim 1 characterized in that said support is polyethylene-coated paper which has been subjected to a corona discharge treatment. The element of Claim 1 characterized in that said support is poly(ethylene terephthalate). The element of Claim 1 characterized in that said dye image-receiving layer is a bisphenol-A polycarbonate having a number average molecular weight of at least 25,000. The element of Claim 7 characterized in that said bisphenol-A polycarbonate comprises recurring units having the formula wherein n is from 100 to 500.

Inventors: LUM, KIN KWONG, VANIER, NOEL RAWLE
Applicants: EASTMAN KODAK COMPANY (A NEW JERSEY CORPORATION)
Application year: 1988
Main classification: B41M5
IPC codes: B41M5