Thermal dye sublimation transfer receiving element for obtaining a hard copy of a medical diagnostic image

Abstract: Dye-image receiving element printed according to thermal dye sublimation transfer comprising a transparant support having thereon a transparant dye image-receiving layer containing transferred dye image(s), characterized in that said dye-image receiving element is provided with black margins surrounding the image area(s).

Description: 1. Field of the invention. The present invention relates to dye-image receiving elements for use according to thermal dye sublimation transfer in particular to dye-image receiving elements for use according to a method for obtaining a hard copy of a medical diagnostic image by thermal dye sublimation transfer. 2. Background of the invention. Thermal dye sublimation transfer also called thermal dye diffusion transfer is a recording method in which a dye-donor element provided with a dye layer containing sublimable dyes having heat transferability is brought into contact with a receiver sheet and selectively, in accordance with a pattern information signal, heated with a thermal printing head provided with a plurality of juxtaposed heat-generating resistors, whereby dye from the selectively heated regions of the dye-donor element is transferred to the receiver sheet and forms a pattern thereon, the shape and density of which is in accordance with the pattern and intensity of heat applied to the dye-donor element. A dye-donor element for use according to thermal dye sublimation transfer usually comprises a very thin support e.g. a polyester support, one side of which is covered with a dye layer, which contains the printing dyes. Usually an adhesive or subbing layer is provided between the support and the dye layer. Normally the opposite side is covered with a slipping layer that provides a lubricated surface against which the thermal printing head can pass without suffering abrasion. An adhesive layer may be provided between the support and the slipping layer. A dye-image receiving element for use according to thermal dye sublimation transfer usually comprises a support, e.g. paper or a transparant film, coated with a dye-image receiving layer, into which the dye can diffuse more readily. An adhesive layer may be provided between the support and the receiving layer. On top of said receiving layer a separate release layer may be provided to improve the releasability of the receiving element from the donor element after transfer is effected. On the back side of the support. i.e. the side opposite to the receiving layer side, a back layer may be provided in order to improve, i.a. feeding of the separate sheets from a stack of sheets or to provide the sheet with antistatic treatment. The dye layer can be a monochrome dye layer or it may comprise sequential repeating areas of different colored dyes like e.g. of cyan, magenta, yellow and optionally black hue. When a dye-donor element containing three or more primary color dyes is used, a multicolor image can be obtained by sequentially performing the dye transfer process steps for each color. One of the possible applications of thermal dye sublimation transfer printing is the production of hard copies of medical diagnostic images. Although such a hard copy can be produced on a reflective support such as paper, in most applications hard copies are produced on transparancies. Depending on the particular application these hard copies can be monochrome, in particular monochrome black, or multicolored. Hard copies of medical diagnostic images produced on transparancies are read from the front of a light box through a light source. The practical circumstances wherein the images are actually viewed by the observer play an important role in the accurate assessment of the diagnostic information recorded in the hard copy. When images produced on known thermal dye sublimation transparancies are observed from the front of a light box, bright light escaping round the hard copy impairs the observer's visual perception and thus the interpretation by the observer. Further transparant film margins adjacent to the image produce dazzle which reduces the efficiency of the eye in evaluating the diagnostic information contained in the image. 3. Summary of the invention. Therefore it is an object of the present invention to provide a thermal dye transfer printing method for obtaining a hard copy of a medical diagnostic image on a transparancy and a transparant receiving element for use according to said method not having the disadvantages mentioned above. According to the present invention there is provided a dye-image receiving element printed according to thermal dye sublimation transfer, said dye-image receiving element comprising a transparant support having thereon a transparant dye image-receiving layer containing transferred dye image(s), characterized in that said dye-image receiving element is provided with black margins surrounding the image area(s). When medical diagnostic images printed on receiving elements of the present invention are viewed on a light box, reflection and dazzle are effectively eliminated and increased evaluation of detail in the denser areas is obtained by masking off of surrounding regions. 4. Detailed description of the drawings. FIG. 1 and FIG. 2 are each plan views of the receiving element which embodies the present invention. 5. Detailed description of the invention. In one embodiment of the present invention the black margins are provided solely along the borders and egdes of the receiving element thus surrounding the image area of only one image if only one image is reproduced on the receiving element as shown in figure 1. In another embodiment of the present invention black margins are provided not only along the borders and edges of the receiving element but also at several distances within the plane of the receiving element thus surrounding several image areas if a number of images is reproduced on the receiving element as shown in figure 2. The black margins surrounding the image area(s) of the receiving element according to the present invention preferably have a high transmission density of at least two. The density of said margins is measured in transmission with a densitometer type Macbeth TR 924 equipped with a visual filter. The black margins on the receiving element according to the present invention can be provided in a number of ways. During manufacture of the image receiving element of the present invention the margins can be realised by printing either on the backside or receptor side of the (uncoated) support of the receiving element. Printing can be effected by offset, gravure, screen, flexo, electrophotographic or ionographic printing using conventional black inks. Said printing can also be carried out after the support has been provided with one or more of the layers generally contained in thermal dye sublimation transfer receiving elements (for example, receiving layer, release layer on top of the receiving layer, back layer or adhesive layer provided between the support and any one of the aforementioned layers). Said margins can be provided before or after cutting the receiving material into sheets. The image receiving element of the present invention can also be provided with black margins during transfer printing of the receiving element. This can be accomplished by using a black dye donor element or a black dye donor area containing a mixture of sublimable dyes and having a printing area larger than the image area of the receiving element. In the case of black colored images this black dye donor element or dye donor area may be the same as the dye donor element or dye donor area used to print the image and the black margins can be provided simultaneously with the image by sublimation transfer printing. Alternatively a special dye donor element comprising a separate area containing black material (for example carbon black) in a wax layer can be used to provide said margins on the receiving element by thermal transfer wax printing. Providing the image receiving element with black margins during transfer printing can be accomplished by using separate thermal heads for the transfer printing of the black borders. The advantage of using separate thermal heads instead of one thermal head for printing the black borders and the image(s) is the fact that the size of the thermal head for printing the image(s) can be reduced: large size thermal heads show considerable voltage drop. After sublimation transfer the margins can be provided sheet by sheet on the image receiving element by any of the printing processes referred to above. In order to protect the obtained medical diagnostic image a transparant cover film may be laminated on the receiving element after transfer printing (such cover films are described for example in EP 178332, EP 305922, EP 273347, EP 394460 and JP 01/237193). Said cover film is used to improve the scratch resistance and the light stability of the obtained transferred dye image and further to prevent migration of the transferred dyes out of the receiving layer. Another way of providing black margins on the receiving element after transfer printing consists in providing black margins on said cover film to be laminated on the receiving element after transfer printing. The margins when provided before sublimation transfer can be used not only to avoid undesirable glare but also to accurately set the image receiving element at a desired position during transfer printing. They can contain detection marks for this purpose. The dye-image-receiving layer of the receiving element of the present invention may comprise as binder, which has to be transparant, for example, a polycarbonate, a polyurethane, a polyester, a polyamide, polyvinyl chloride, polystyrene-co-acrylonitrile, polycaprolactone or mixtures thereof. Suitable dye-receiving layers have been described in e.g. EP 133011, EP 133012, EP 144247, EP 227094, EP 228066. The dye-image-receiving layer may also comprise a cured binder such as the heat-cured product of poly(vinylchloride-co-vinylacetate-co-vinylalcohol) and polyisocyanate. The total amount of binder used in the dye receiving layer of the present invention is from 25 to 95 % by weight, preferably from 50 to 80 % by weight. The dye receiving element of the present invention can contain a release agent for improvement of the release property with respect to the donor element. As the release agent, solid waxes such as polyethylene wax, amide wax, and Teflon powder; fluorine based and phosphate ester based surfactants; and paraffin based, silicone based and fluorine based oils can be used. Silicone oils, preferably reactive silicone oils (such as hydroxy modified polydimethylsiloxane e.g. TEGOMER HSI 2111 supplied by Goldschmidt) and silicone containing copolymers such as polysiloxane-polyether copolymers and blockcopolymers, are preferred (e.g. TEGOGLIDE supplied by Goldschmidt and SILWET supplied by Union Carbide). High boiling organic solvents or thermal solvents or plasticizers can be included in the image-receiving layer, as substances which can accept or dissolve the dyes or as diffusion promotors for the dyes. Useful examples of such high boiling organic solvents and thermal solvents include the compounds disclosed in, for example, JP 62/174754, JP 62/245253, JP 61/209444, JP 61/200538, JP 62/8145, JP 62/9348, JP 62/30247, JP 62/136646. Also, for further enhancing the light resistance of the transferred image, one or two or more kinds of additives such as UV-ray absorbers, light stabilizers and antioxidants, can be added, if necessary. The amounts of these UV-ray absorbers and light stabilizers is preferably 0.05 to 10 parts by weight and 0.5 to 15 parts by weight, respectively, per 100 parts of the resin constituting the receiving layer. The dye-receiving layer of the present invention preferably has an overall thickness of from 0.5 to 50 µm, more preferably from 2.5 to 10 µm. In case a toplayer containing a release agent of the type described above is provided on top of the receiving layer the thickness of such a toplayer is preferably 0.01 to 5 µm. particularly 0.05 to 2 µm. As the support for the receiver sheet a transparant film or sheet of various plastics such as polyethylene terephthalate. polyolefin, polyvinyl chloride, polystyrene, polycarbonate, polyether sulfone, polyimide, cellulose ester or polyvinyl alcohol-co-acetal is used. Blue-colored polyethylene terephthalate film can also be used as long as it remains transparant: transparant being defined as having the property of transmitting light without appreciable scattering. In general the support has a thickness of at least 100 µm so that the hard copy can be easily put on a light box. The thickness of the support is preferably in the range of 120 to 200 µm, more preferably in the range of 160 to 190 µm, more preferably from 170 to 180 µm. The adhesion of a coating composition to the substrate may be improved by providing a subbing layer between the substrate and the coating layer (e.g. the receiving layer and/or the back layer). Particularly preferred subbing layers for polyethylene terephthalate supports are subbing layers based on copolymers of vinylidene chloride such as described in GB 1234755. The image receiving element of the present invention may also have one or more intermediate layers between the support and the image receiving layer. Depending on the material from which they are formed, the intermediate layers may function as cushioning layers, porous layers (as long as they remain transparant) or dye diffusion preventing layers, or may fulfill two or more of these functions, and they may also serve the purpose of an adhesive, depending on the particular application. The material constituting the intermediate layer may include, for example, an urethane resin, an acrylic resin, an ethylenic resin, a butadiene rubber, or an epoxy resin. The thickness of the intermediate layer is preferably from 1 to 20 µm. Dye diffusion preventing layers are layers which prevent the dye from diffusing into the support. The binders used to form these layers may be water soluble or organic solvent soluble, but the use of water soluble binders is preferred, and especially gelatin is most desirable. Porous layers are layers which prevent the heat which is applied at the time of thermal transfer from diffusing from the image receiving layer to the support to ensure that the heat which has been applied is used efficiently and possibly preventing deformation of the support. A transparant back layer may be provided on the side of the support opposite to the image receiving layer side. Said back layer may contain a matting agent as described in EP-A-0 543 441. Furthermore, the image receiving sheet can have a transparant lubricating layer provided on the back surface of the sheet support. The material for the lubricating layer may include methacrylate resins such as methyl methacrylate, etc. or corresponding acrylate resins, vinyl resins such as vinyl chloride-vinyl acetate copolymers. Also, the image receiving element of the present invention can have anti static treatment applied to the front or back surface thereof. Such anti static treatment may be carried out by incorporating an antistatic agent in, for example, the image receiving layer or in an antistatic layer applied upon or under the image receiving surface. A similar treatment can also be effected to the back surface. By such treatment, mutual sliding between the image receiving sheets can be smoothly performed, and there is also the effect of preventing the attachment of dust on the image receiving sheet. Further the receiving element can have a notch to discriminate the receiving layer side from the back layer side and may have rounded edges. A dye-donor element for use according to thermal dye sublimation transfer in combination with the present receiving element usually comprises a very thin support e.g. a polyester support, one side of which is covered with a dye layer, which contains the printing dyes. Usually an adhesive or subbing layer is provided between the support and the dye layer. Normally the opposite side is covered with a slipping layer that provides a lubricated surface against which the thermal printing head can pass without suffering abrasion. An adhesive layer may be provided between the support and the slipping layer. The dye layer can be a monochrome dye layer or it may comprise sequential repeating areas of different colored dyes like e.g. of cyan, magenta, yellow and optionally black hue. When a dye-donor element containing three or more primary color dyes is used, a multicolor image can be obtained by sequentially performing the dye transfer process steps for each color. The dye layer of such a thermal dye sublimation transfer donor element is formed preferably by adding the dyes, the polymeric binder medium, and other optional components to a suitable solvent or solvent mixture, dissolving or dispersing the ingredients to form a coating composition that is applied to a support, which may have been provided first with an adhesive or subbing layer, and dried. The dye layer thus formed has a thickness of about 0.2 to 5.0 µm, preferably 0.4 to 2.0 µm, and the ratio of dye to binder is between 9:1 and 1:3 by weight, preferably between 2:1 and 1:2 by weight. As polymeric binder the following can be used: cellulose derivatives, such as ethyl cellulose, hydroxyethyl cellulose, ethylhydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, nitrocellulose, cellulose acetate formate, cellulose acetate hydrogen phthalate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate pentanoate, cellulose acetate benzoate, cellulose triacetate; vinyl-type resins and derivatives, such as polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, copolyvinyl butyral -vinyl acetal -vinyl alcohol, polyvinyl pyrrolidone, polyvinyl acetoacetal, polyacrylamide; polymers and copolymers derived from acrylates and acrylate derivatives, such as polyacrylic acid, polymethyl methacrylate and styrene-acrylate copolymers; polyester resins; polycarbonates such as a polycarbonate derived from 2,2-bis-(4-hydroxyphenyl)-propane; copolystyrene-acrylonitrile; polysulfones; polyphenylene oxide; organosilicones, such as polysiloxanes; epoxy resins and natural resins, such as gum arabic. Preferably cellulose acetate butyrate or copolystyrene-acrylonitrile(-butadieen) is used as binder for the dye layer. Any dye can be used in such a dye layer provided it is easily transferable to the dye-image-receiving layer of the receiver sheet by the action of heat. Typical and specific examples of dyes for use in thermal dye sublimation transfer have been described in, e.g., European Patent Application no. 90203014.7, EP 209990, EP 209991, EP 216483, EP 218397, EP 227095, EP 227096, EP 229374, EP 235939, EP 247737, EP 257577, EP 257580, EP 258856, EP 279330, EP 279467, EP 285665, EP 400706, EP 432313, EP 432314, EP 432829, EP 453020, US 4743582, US 4753922, US 4753923, US 4757046, US 4769360, US 4771035, JP 84/78894, JP 84/78895, JP 84/78896, JP 84/227490, JP 84/227948, JP 85/27594, JP 85/30391 , JP 85/229787, JP 85/229789, JP 85/229790, JP 85/229791, JP 85/229792, JP 85/229793, JP 85/229795, JP 86/41596, JP 86/268493, JP 86/268494, JP 86/268495 and JP 86/284489. The coating layer may also contain other additives, such as curing agents, preservatives, organic or inorganic fine particles, dispersing agents, antistatic agents, defoaming agents, viscosity controlling agents, etc., these and other ingredients being described more fully in EP 133011, EP 133012, EP 111004 and EP 279467. Any material can be used as the support for the dye-donor element provided it is dimensionally stable and capable of withstanding the temperatures involved, up to 400°C over a period of up to 20 msec, and is yet thin enough to transmit heat applied on one side through to the dye on the other side to effect transfer to the receiver sheet within such short periods, typically from 1 to 10 msec. Such materials include polyesters such as polyethylene terephthalate, polyamides, polyacrylates, polycarbonates, cellulose esters, fluorinated polymers, polyethers, polyacetals, polyolefins. polyimides, glassine paper and condenser paper. Preference is given to a polyethylene terephthalate support. In general, the support has a thickness of 2 to 30 µm. The support may also be coated with an adhesive or subbing layer, if desired. 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. A dye-barrier layer comprising a hydrophilic polymer may also be employed in the dye-donor element between its support and the dye layer to improve the dye transfer densities by preventing wrong-way transfer of dye towards the support. The dye barrier layer may contain any hydrophilic material which is useful for the intended purpose. In general, good results have been obtained with gelatin, polyacryl amide, polyisopropyl acrylamide, butyl methacrylate grafted gelatin, ethyl methacrylate grafted gelatin, ethyl acrylate grafted gelatin, cellulose monoacetate, methyl cellulose, polyvinyl alcohol, polyethylene imine, polyacrylic acid, a mixture of polyvinyl alcohol and polyvinyl acetate, a mixture of polyvinyl alcohol and polyacrylic acid or a mixture of cellulose monoacetate and polyacrylic acid. Suitable dye barrier layers have been described in e.g. EP 227091 and EP 228065. Certain hydrophilic polymers, for example those described in EP 227091, also have an adequate adhesion to the support and the dye layer, thus eliminating the need for a separate adhesive or subbing layer. These particular hydrophilic polymers used in a single layer in the donor element thus perform a dual function, hence are referred to as dye-barrier/subbing layers. Preferably the reverse side of the dye-donor element can 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 surface active agents may be any agents known in the art such as carboxylates, sulfonates, phosphates, aliphatic amine salts, aliphatic quaternary ammonium salts, polyoxyethylene alkyl ethers, polyethylene glycol fatty acid esters, fluoroalkyl C₂-C₂₀ aliphatic acids. Examples of liquid lubricants include silicone oils, synthetic oils, saturated hydrocarbons and glycols. Examples of solid lubricants include various higher alcohols such as stearyl alcohol, fatty acids and fatty acid esters. Suitable slipping layers are described in e.g. EP 138483, EP 227090, US 4567113, US 4572860, US 4717711. Preferably the slipping layer comprises as binder a styrene-acrylonitrile copolymer or a styrene-acrylonitrile-butadiene copolymer or a cellulose ester or a polycarbonate derived from 2,2-bis-(4-hydroxyphenyl)-propane and as lubricant in an amount of 0.1 to 10 % by weight of the binder (mixture) a polysiloxane-polyether copolymer or polytetrafluoroethylene. The dye layer of the dye-donor element may also contain a releasing agent that aids in separating the dye-donor element from the dye-receiving element after transfer. The releasing agents can also be applied in a separate layer on at least part of the dye layer. For the releasing agent solid waxes, fluorine- or phosphate-containing surfactants and silicone oils are used. Suitable releasing agents are described in e.g. EP 133012, JP 85/19138, EP 227092. The dye-receiving elements according to the invention are used to form a dye transfer image. Such a process comprises placing the dye layer of the donor element in face-to-face relation with the dye-receiving layer of the receiver sheet and imagewise heating from the back of the donor element. The transfer of the dye is accomplished by heating for about several milliseconds at a temperature of 400°C. When the process is performed for but one single color, a monochrome dye transfer image is obtained. A multicolor image can be obtained by using a donor element containing three or more primary color dyes and sequentially performing the process steps described above for each color. The above sandwich of donor element and receiver sheet is formed on three occasions during the time when heat is applied by the thermal printing head. After the first dye has been 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 and optionally further colors are obtained in the same manner. In addition to thermal heads, laser light, infrared flash or heated pens can be used as the heat source for supplying heat energy. Thermal printing heads that can be used to transfer dye from the dye-donor element to the receiver sheet are commercially available. In case laser light is used, the dye layer or another layer of the dye element has to contain a compound that absorbs the light emitted by the laser and converts it into heat, e.g. carbon black. Alternatively, the support of the dye-donor element may be an electrically resistive ribbon consisting of, for example, a multi-layer structure of a carbon loaded polycarbonate coated with a thin aluminum film. Current is injected into the resistive ribbon by electrically adressing a print head electrode resulting in highly localized heating of the ribbon beneath the relevant electrode. The fact that in this case the heat is generated directly in the resistive ribbon and that it is thus the ribbon that gets hot leads to an inherent advantage in printing speed using the resistive ribbon/electrode head technology compared to the thermal head technology where the various elements of the thermal head get hot and must cool down before the head can move to the next printing position. The receiving element of the present invention is used to produce hard copies, in particular black-and-white hard copies of medical diagnostic images especially in ultrasound, C-arm surgery and nuclear medicine applications. The following examples are provided to illustrate the invention in more detail without limiting, however, the scope thereof. EXAMPLE 1 A transparant polyethylene terephthalate support of 175 µm thick was provided on one side with a conventional image receiving layer and on the other side with an antistatic layer. On top of this antistatic layer black margins were provided in a form as shown in figure 1. These black margins were printed using gravure printing. The printing solution comprised: 50 g of magenta dye I, 30 g of cyan dye II, 25 g of yellow dye III and 50 g of binder (Luran 388S supplied by BASF) in methylethylketone (total weight of the solution was 1000 g). The density of the obtained black margins measured with a Macbeth densitometer type TP924 behind visual filter was larger than 3. Small density variations were hardly observable, the black margins showed visually an even black impression and shielded off undesirable light. EXAMPLE 2 A transparant polyethylene terephthalate support of 175 µm thick was provided on one side with a conventional image receiving layer and on the other side with an antistatic layer. On top of this antistatic layer black margins were provided in a form as shown in figure 1. These black margins were offset printed using a printing plate type SUPERMASTER SPP supplied by Agfa-Gevaert and an offset printing machine type GT046 supplied by Heidelberg. The ink used was SONOPLAST VS494 supplied by Vanson and the fountain solution used was ROTAMATIC supplied by CP Bourg. The obtained black margins showed visual densities larger than 1.2 (measured with a Macbeth densitometer type TR924).

Claims: Dye-image receiving element printed according to thermal dye sublimation transfer comprising a transparent support having thereon a transparent dye image-receiving layer containing transferred dye image(s), characterized in that said dye-image receiving element is provided with black margins surrounding the image area(s). Dye-image receiving element according to claim 1, wherein said black margins are provided along the borders and edges of the receiving element. Dye-image receiving element according to claim 2, wherein further black margins are provided at several distances within the plane of the receiving element. Dye-image receiving element according to any one of the preceding claims, wherein said black margins have a transmission density of at least two. Dye-image receiving element according to any one of the claims 1 to 4, wherein said black margins are provided during manufacture of the receiving element by printing. Dye-image receiving element according to any one of the claims 1 to 4, wherein said black margins are provided during transfer printing of the receiving element. Dye-image receiving element according to any one of the claims 1 to 4, wherein said black margins are provided after transfer printing of the receiving element. Dye-image receiving element according to any one of the preceding claims, wherein a transparent cover film is provided on the receiving element after transfer printing. Dye-image receiving element according to claim 8, wherein said cover film is provided with black margins. Thermal dye transfer printing method for obtaining black-and-white hard copies of medical diagnostic images comprising the step of imagewise heating a black dye-donor element comprising a support having thereon a dye layer in face-to-face relation with the dye-receiving layer of a receiving element as defined in any one of the preceding claims.

Inventors: UYTTERHOEVEN HERMAN JOZEF, VERDONCK EMIEL AUGUST, UYTTERHOEVEN, HERMAN JOZEF, VERDONCK, EMIEL AUGUST
Applicants: AGFA GEVAERT NV, AGFA-GEVAERT NAAMLOZE VENNOOTSCHAP
Application year: 1992
Main classification: B41M5
IPC codes: B41M5