Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/40—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used characterised by the base backcoat, intermediate, or covering layers, e.g. for thermal transfer dye-donor or dye-receiver sheets; Heat, radiation filtering or absorbing means or layers; combined with other image registration layers or compositions; Special originals for reproduction by thermography
  • B41M5/41—Base layers supports or substrates

Definitions

• This invention relates to dye-receiving elements used in thermal dye transfer, and more particularly to receiving elements having microvoided supports.
• thermal transfer systems have been developed to obtain prints from pictures which have been generated electronically from a color video camera.
• 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.
• 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.
• Dye-receiving elements used in thermal dye transfer generally comprise a polymeric dye image-receiving layer coated on a support.
• Supports are required to have, among other properties, adequate strength, dimensional stability, and heat resistance. For reflective viewing, supports are also desired to be as white as possible.
• Cellulose paper, synthetic paper, and plastic films have all been proposed for use as dye-receiving element supports in efforts to meet these requirements. Recently, microvoided films formed by stretching an orientable polymer containing an incompatible organic or inorganic material have been suggested for use in dye-receiving elements.
• Patent 4,778,782 of Ito et al. discloses supports comprising a microvoided film obtained by stretching a translucent plastic film containing fine fillers such as clay or talc. By this stretching, bonds between the polymers and fillers in the film are destroyed, whereby microvoids are considered to be formed in the film. The microvoids lower the density of the film and also make it appear white and opaque.
• European Patent Application 0 322 771 discloses dye-receiving element supports comprising a polyester film containing polypropylene and minute closed cells within the film formed upon stretching.
• EP 0 322 771 Comparative Example 4 shows that a high degree of microvoiding in polyester/polypropylene stretched films, as evidenced by a relatively low specific gravity, results in poor mechanical strength and frequent breakage of the film during stretching.
• the lowest apparent specific gravity for an operable film in EP 0 322 771 is 0.71 (Example 2).
• a dye-receiving element for thermal dye transfer comprising a support having thereon a polymeric dye image-receiving layer characterized in that the support comprises a continuous oriented polymer matrix having dispersed therein microbeads of a cross-linked polymer coated with a slip agent and which are at least partially bordered by void space.
• the combination of cross-linked microbeads and a slip agent coating allows supports with a relatively high degree of microvoiding to be manufactured.
• the cross-linking of the microbead polymer provides resiliency and elasticity while the slip agent permits easier sliding between the microbeads and the matrix polymer to result in more effective microvoiding.
• This allows films with a higher void percentage and thereby greater insulating effect to be manufactured. Such films have been found to be particularly advantageous for thermal dye transfer applications as the greater insulating effect results in greater dye transfer efficiency.
• the receiving elements of the invention use supports comprising a continuous thermoplastic polymer phase having dispersed therein microbeads of polymer which are at least partially bordered by voids.
• the microbeads of polymer have a size of 2 microns to 30 microns, preferably 5 to 20 microns, and are present in an amount of 5% to 50% by weight based on the weight of continuous phase polymer.
• the voids occupy up to 60% by volume of the support, preferably from 30% to 60% by volume. Larger beads generate a greater amount of void space upon stretching of the supports, but result in a rougher support surface. The use of smaller beads results in a smoother support surface, but they do not generate as much void volume.
• a dual layer support may be made.
• the bulk of such a support comprises a layer made with relatively large beads in order to generate a large void volume, and this layer is coated with a smoothing layer containing relatively small beads or no beads at all.
• the matrix polymer contains the generally spherical polymer microbeads which, according to one aspect of the invention, are cross-linked to the extent of having a resiliency or elasticity at orientation temperatures of the matrix polymer such that a generally spherical shape of the cross-linked polymer is maintained after orientation of the matrix polymer.
• the supports according to this invention in the absence of additives or colorants are very white, and are very resistant to wear, moisture, oil, tearing, etc.
• the supports are preferably in the form of a paper like sheet having a thickness of 50 to 300 microns.
• the supports are made by biaxial orientation using procedures well known in the art.
• the continuous phase polymer may be any article-forming polymer such as a polyester capable of being cast into a film or sheet.
• the polyesters should have a glass transition temperature between 50°C and 150°C, preferably 60-100°C, should be orientable, and have an intrinsic viscosity of at least 0.5, preferably 0.6 to 0.9.
• Suitable polyesters include those produced from aromatic, aliphatic or cyclo-aliphatic dicarboxylic acids of 4-20 carbon atoms and aliphatic or alicyclic glycols having from 2-24 carbon atoms.
• suitable dicarboxylic acids include terephthalic, isophthalic, phthalic, naphthalene dicarboxylic acid, succinic, glutaric, adipic, azelaic, sebacic, fumaric, maleic, itaconic, 1,4-cyclohexane-dicarboxylic, sodiosulfoisophthalic and mixtures thereof.
• suitable glycols include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, other polyethylene glycols and mixtures thereof.
• polyesters are well known in the art and may be produced by well-known techniques, e.g., those described in U.S. Patents 2,465,319 and 2,901,466.
• Preferred continuous matrix polymers are those having repeat units from terephthalic acid or naphthalene dicarboxylic acid and at least one glycol selected from ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol.
• Poly(ethylene terephthalate) which may be modified by small amounts of other monomers, is especially preferred.
• Polypropylene is also useful.
• Other suitable polyesters include liquid crystal copolyesters formed by the inclusion of a suitable amount of a co-acid component such as stilbene dicarboxylic acid. Examples of such liquid crystal copolyesters are those disclosed in U.S. Patent Nos. 4,420,607, 4,459,402 and 4,468,510.
• Suitable cross-linked polymers for the microbeads are polymerizable organic materials which are members selected from the group consisting of an alkenyl aromatic compound having the general formula wherein Ar represents an aromatic hydrocarbon radical, or an aromatic halohydrocarbon radical of the benzene series and R is hydrogen or the methyl radical; acrylate-type monomers including monomers of the formula wherein R is selected from the group consisting of hydrogen and an alkyl radical containing from 1 to 12 carbon atoms and R′ is selected from the group consisting of hydrogen and methyl; copolymers of vinyl chloride and vinylidene chloride, acrylonitrile and vinyl chloride, vinyl bromide, vinyl esters having the formula wherein R is an alkyl radical containing from 2 to 18 carbon atoms; acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, oleic acid, vinylbenzoic acid; the synthetic polyester resins which are prepared by reacting terephthalic acid and dialky
• Examples of typical monomers for making the cross-linked polymer include styrene, butyl acrylate, acrylamide, acrylonitrile, methyl methacrylate, ethylene glycol dimethacrylate, vinyl pyridine, vinyl acetate, methyl acrylate, vinylbenzyl chloride, vinylidene chloride, acrylic acid, divinylbenzene, arylamidomethylpropane sulfonic acid, vinyl toluene, etc.
• the cross-linked polymer is polystyrene or poly(methyl methacrylate). Most preferably, it is polystyrene and the cross-linking agent is divinylbenzene.
• Suitable slip agents or lubricants include colloidal silica, colloidal alumina, and metal oxides such as tin oxide and aluminum oxide.
• the preferred slip agents are colloidal silica and alumina, most preferably, silica.
• the cross-linked polymer having a coating of slip agent may be prepared by procedures well known in the art. For example, conventional suspension polymerization processes wherein the slip agent is added to the suspension is preferred. As the slip agent, colloidal silica is preferred.
• the following is an example illustrating a procedure for preparing the cross-linked polymeric microbeads coated with slip agent.
• the polymer is polystyrene cross-linked with divinylbenzene.
• the microbeads have a coating of silica.
• the microbeads are prepared by a procedure in which monomer droplets containing an initiator are sized and heated to give solid polymer spheres of the same size as the monomer droplets.
• a water phase is prepared by combining 7 liters of distilled water, 1.5 g potassium dichromate (polymerization inhibitor for the aqueous phase), 250 g polymethylaminoethanol adipate (promoter), and 350 g LUDOX® (a colloidal suspension containing 50% silica sold by DuPont).
• a monomer phase is prepared by combining 3317g styrene, 1421 g divinylbenzene (55% active crosslinking agent, the other 45% is ethyl vinyl benzene which forms part of the styrene polymer chain) and 45 g VAZO 52® (a monomer-soluble initiator sold by DuPont). The mixture is passed through a homogenizer to obtain 5 micron droplets.
• the suspension is heated overnight at 52°C to give 4.3 kg of generally spherical microbeads having an average diameter of approximately 5 microns with narrow size distribution (2-10 microns size distribution).
• the mol proportion of styrene and ethyl vinyl benzene to divinylbenzene is approximately 6.1%.
• the concentration of divinylbenzene can be adjusted up or down to result in 2.5-50% (preferably 10-40%) crosslinking by the active cross-linker.
• monomers other than styrene and divinylbenzene can be used in similar suspension polymerization processes known in the art.
• other initiators and promoters may be used as known in the art.
• slip agents other than silica may also be used.
• LEPANDIN® colloidal alumina is available from Degussa.
• NALCOAG® colloidal silicas are available from Nalco and tin oxide and titanium oxide are also available from Nalco.
• the polymer is crosslinked.
• the polymer is 2.5-50% cross-linked, preferably 20-40% cross-linked.
• percent crosslinked it is meant the mol % of crosslinking agent based on the amount of primary monomer.
• Beads of such crosslinking are also resilient, so that when they are deformed (flattened) during orientation by pressure from the matrix polymer on opposite sides of the microbeads, they subsequently resume their normal spherical shape to produce the largest possible voids around the microbeads to thereby produce articles with less density.
• the microbeads are referred to herein as having a coating of a "slip agent".
• a slip agent By this term it is meant that the friction at the surface of the microbeads is greatly reduced. Actually, it is believed this is caused by the silica acting as miniature ball bearings at the surface. Slip agent may be formed on the surface of the microbeads during their formation by including it in the suspension polymerization mix.
• Microbead size is regulated by the ratio of silica to monomer. For example, the following ratios produce the indicated size microbead:
• the supports according to this invention are prepared by:
• the mixture may be formed by forming a melt of the matrix polymer and mixing therein the cross-linked polymer.
• the cross-linked polymer may be in the form of solid or semi-solid microbeads. Due to the incompatibility between the matrix polymer and cross-linked polymer, there is no attraction or adhesion between them, and they become uniformly dispersed in the matrix polymer upon mixing.
• a shaped article is formed by processes such as extrusion, casting or molding.
• extrusion or casting would be extruding or casting a film or sheet, and an example of molding would be injection or reheat blow-molding a bottle.
• Such forming methods are well known in the art. If sheets or film material are cast or extruded, it is important that such article be oriented by stretching, at least in one direction. Methods of unilaterally or bilaterally orienting sheet or film material are well known in the art. Basically, such methods comprise stretching the sheet or film at least in the machine or longitudinal direction after it is cast or extruded an amount of 1.5-10 times its original dimension.
• Such sheet or film may also be stretched in the transverse or cross-machine direction by apparatus and methods well known in the art, in amounts of generally 1.5-10 (usually 3-4 for polyesters and 6-10 for polypropylene) times the original dimension.
• apparatus and methods are well known in the art and are described in such U.S. Patent No. 3,903,234.
• the voids, or void spaces, referred to herein surrounding the microbeads are formed as the continuous matrix polymer is stretched at a temperature above the Tg of the matrix polymer.
• the microbeads of crosslinked polymer are relatively hard compared to the continuous matrix polymer.
• the continuous matrix polymer slides over the microbeads as it is stretched, causing voids to be formed at the sides in the direction or directions of stretch, which voids elongate as the matrix polymer continues to be stretched.
• the final size and shape of the voids depends on the direction(s) and amount of stretching.
• stretching is only in one direction, microvoids will form at the sides of the microbeads in the direction of stretching. If stretching is in two directions (bidirectional stretching), in effect such stretching has vector components extending radially from any given position to result in a doughnut-shaped void surrounding each microbead.
• the dye image-receiving layer of the receiving elements 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.
• the dye image-receiving layer is a polycarbonate.
• polycarbonate as used herein means a polyester of carbonic acid and a glycol or a dihydric phenol.
• glycols or dihydric phenols examples include p-xylylene glycol, 2,2-bis(4-oxyphenyl)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.
• a bisphenol-A polycarbonate having a number average molecular weight of at least 25,000 is used.
• preferred polycarbonates include General Electric LEXAN® Polycarbonate Resin and Bayer AG MACROLON 5700®.
• a dye-donor element that is used with the dye-receiving element of the invention comprises a support having theron a dye containing layer.
• Any dye can be used in the dye-donor employed in the invention provided it is transferable to the dye-receiving layer by the action of heat.
• sublimable dyes such as or any other dye conventionally used for thermal dye transfer such as 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.
• the dye in the dye-donor element is dispersed in a polymeric binder such as a cellulose derivative, e.g., cellulose acetate hydrogenphthatate, 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.
• the reverse side of the dye-donor element can be coated with a slipping layer as is known in the art to prevent the printing head from sticking to the dye-donor element.
• 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 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 from 0.001 to 2 g/m2. If a polymeric binder is employed, the lubricating material is present in the range of 0.1 to 50 weight %, preferable 0.5 to 40, of the polymeric binder employed.
• the dye-donor elements and receiving 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 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.
• 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.
• a monochrome dye transfer image is obtained.
• Thermal printing heads which can be used to transfer dye from the dye-donor elements to the receiving elements 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.
• FTP-040 MCSOO1 Fujitsu Thermal Head
• TDK Thermal Head F415 HH7-1089 a Rohm Thermal Head KE 2008-F3.
• a thermal dye transfer assemblage of the invention comprises:
• 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.
• 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.
• a Welders Engineering Twin Screw Compounding Extruder heated to 282°C was used to mix polystyrene microbeads (sizes, crosslinking %, and slip agent coatings as indicated in the table below) and poly(ethylene terephthalate)("PET", commercially available as #7352 from Eastman Chemicals). Both components were metered into the compounder and one pass was sufficient for dispersion of the beads into the PET matrix.
• Cast sheets of the above bead/PET dispersion with a poly(ethylene terephthalate) smoothing layer were coextruded using a Killion Sample Coextruder System (a 1.5 inch Killion Extruder was used to produce the bead/PET melt stream, and a 1 inch Killion Extruder was used for the PET smoothing layer meltstream).
• the two meltstreams at 282°C were fed into a 7 inch "coat-hanger" type single manifold die also heated at 282°C.
• the final dimensions of the continuous cast sheet were 18 cm wide and 1270 microns thick.
• the bead/PET layer was 1016 microns thick and the PET smoothing layer was 254 microns thick.
• the cast sheet (18 x 18 cm) were then stretched at 110°C and 50 mm/sec using an Iwamoto Seisakusho Co. LTD Model BIX7025 Sample stretcher first 3.75 times in the X-direction and then 3.5 times in the Y-direction.
• the stretched sheets were annealed at 117-122°C for 90 sec and were allowed to cool at room temperature, and were then removed from the stretcher.
• microvoided supports each with the indicated composite densities were produced.
• Each support had the same PET smoothing layer of approximately 20 microns thickness after stretching.
• the void percentages were calculated using approximate densities of 1.4 g/cm3 for PET and 1 g/cm3 for polystyrene.
• the smooth side of the microvoided supports were first coated with a subbing layer of poly(acrylonitrile-co-vinylidene chloride-co-acrylic acid)(14:80:6 wt. ratio)(0.11 g/m2) from butanone.
• a dye receiving layer of Bayer AG MAKROLON 5700® (a bis-phenol A polycarbonate) (2.9 g/m2), 3M Corp. FLUORAD FC-431® (a fluorinated surfactant)(0.02 g/m2), and Dow Corning DC-510® Silicone Fluid (0.01 g/m2) was coated from dichloromethane.
• Each control support was coated with the same dye-receiving layer.
• Cyan dye-donor elements were prepared by coating the following layers in the order recited on a 6 ⁇ m poly(ethylene terephthalate) support:
• Magenta dye-donor elements were prepared by coating the following layers in the order recited on a 6 ⁇ m poly(ethylene terephthalate) support:
• the imaging electronics were activated causing the pulling device to draw the assemblage between the printing head and roller at 3.1 mm/sec.
• the resistive elements in the thermal print head were pulsed at a per pixel pulse width of 8 msec to generate a maximum density image.
• the voltage supplied to the print-head was approximately 25 V representing approximately 1.6 watts/dot (13. mjoules/dot).
• the receivers were separated from the donors.
• the Status A Green transmission density of the magenta donors and the Status A Red transmission density of the cyan donors were measured both before and after dye transfer. The greater the change in transmission density, the greater the amount of dye transferred to the receiver, demonstrating greater thermal efficiency.
• thermal dye transfer receiving elements of the invention results in improved transfer efficiency as a greater amount of dye is transferred from dye donor elements used with such receiving elements.

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Citations (5)

• 1991
  • 1991-03-14 CA CA 2038306 patent/CA2038306A1/en not_active Abandoned
  • 1991-04-26 JP JP3096809A patent/JPH06102390B2/ja not_active Expired - Lifetime
  • 1991-04-29 EP EP19910106909 patent/EP0455192B1/de not_active Expired - Lifetime
  • 1991-04-29 DE DE1991603666 patent/DE69103666T2/de not_active Expired - Fee Related

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