Thermally transferable image-protecting layer

Abstract: A transfer laminating element for laminating ink jet prints comprising a flexible, polymeric support having thereon a porous, fusible, transferable protection layer comprising fusible, thermoplastic polymeric particles in a polymeric binder, the protection layer having a thickness of between 2 and 100 µm and a particle-to-binder ratio of between 95:5 and 70:30, the thermoplastic polymeric particles having a particle size of less than 10 µm and a Tm or softening point of greater than 50°C. and the polymeric binder having a Tg of less than 20 ° C.

Description: This invention relates to an element for laminating ink jet prints, more particularly to a polymeric support having thereon a porous, fusible, transferable protection layer. In a typical ink jet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol or mixtures thereof. An ink jet recording element typically comprises a support having on at least one surface thereof a base layer for absorbing fluid and an ink-receiving or image-forming layer, and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support. Ink jet prints prepared by printing onto ink jet recording elements are subject to environmental degradation such as water smearing and light fade. For example, since ink jet dyes are water-soluble, they can migrate from their location in the ink-receiving layer when water comes in contact with the recording element after imaging. To reduce the vulnerability of prints to degradation and to enhance gloss, ink jet prints are often laminated. Typically, such conventional lamination is a process whereby a continuous polymeric film bearing an adhesive is brought into contact with the surface of the print. Heat and/or pressure is then used to affix the continuous polymeric film to the print surface. The continuous polymeric film then serves as a barrier layer that is impermeable to water and further acts to diminish the fading of the print image caused by light. However, there is a problem with prior art laminating films since they are typically supplied in roll format and must be cut, or less desirably torn, to separate the laminated print from the continuous roll of laminating film. A requirement to cut adds expense to a laminator design that is required to run in a continuous mode. US-A-5,662,976 discloses an assembly for creating laminated cards which comprises a sheet of card stock with a release coating and a sheet of laminating film adhering to the release coating. A card form is cut into the sheet of card stock, and a lamination strip, which is sufficiently large to fold over so as to laminate both surfaces of the card, is cut into the lamination sheet. After printing, the card and the lamination strip are removed, and the lamination strip folded over to laminate the card. However, there is a problem with this laminating film in that expensive cutting and perforating steps are required to prepare the laminated card. US-A-5,387,573 discloses a dye-donor element for thermal dye transfer comprising a support and a transferable protection layer wherein the transferable protection layer is less than 1µm thick and contains particles in an amount of up to 75% of the transferable protection layer. However, there is no disclosure in this patent that the protection layer can be used with ink jet prints. EP-A-0 943 453 relates to a thermal transfer sheet having a releasable protective laminate prepared by laminating a protective layer composed mainly of solvent-insoluble organic fine particles and a binder resin. However, these organic fine particles are not capable of being fused to form a substantially continuous film which is optically clear upon the application of heat and pressure. EP-A-0 487 727 relates to a thermal transfer cover sheet containing uan ionizing radiation-curing resin, silicone-modified resin and wax-containing resin. However, there is no disclosure of particles which are capable of being fused to form a substantially continuous film which is optically clear upon the application of heat and pressure. Research Disclosure (1996) March, No. 383, Emsworth, Great Britain, pp. 169-172, "Protective layers for imaged transparent thermal dye transfer receivers" relates to a protective layer for imaged transparent thermal dye transfer receivers comprising porous beads. However, there is no disclosure of particles which are capable of being fused to form a substantially continuous film which is optically clear upon the application of heat and pressure. It is an object of the invention to provide a transfer laminating element for laminating ink jet prints wherein the protection layer is sufficiently thick to protect ink jet images from degradation by water, and yet can be employed without resort to expensive cutting steps. It is another object to provide a transfer laminating element for laminating an ink jet print of arbitrary geometric shape. It is still another object to provide a transfer laminating element that allows for the direct visual distinction between laminated and unlaminated regions of the print. These and other objects are provided by the present invention which comprises a transfer laminating element for laminating inkjet prints comprising a flexible, polymeric support having thereon a porous, fusible, transferable protection layer comprising fusible, thermoplastic polymeric particles in a polymeric binder, the protection layer having a thickness of between 2 and 100 µm and a particle-to-binder ratio of between 95:5 and 70:30, the thermoplastic polymeric particles having a particle size of less than 10 µm and a Tm or softening point of greater than 50°C. and the polymeric binder having a Tg of less than 20 ° C, said porous, fusible, transferable protection layer being capable of forming a continuous film which is optically clear upon the application of heat and pressure. In using the invention, the transfer laminating element is contacted with an ink jet image using heat and pressure to form a fused composite. Within the composite, the porous, fusible, transferable protection layer fuses to become a continuous film which is optically clear. After cooling below the Tg of the polymer used to make the particles, the support is peeled from the composite. The continuous film easily separates, without cutting, from the unfused porous region, thereby forming a protection layer on the surface of the ink jet image. As noted above, the particle-to-binder ratio in the protection layer is between 95:5 and 70:30. If the particle-to-binder ratio is above the range stated, the layer will not have any cohesive strength. If the particle-to-binder ratio is below the range stated, the layer will not be porous, and on peeling the support away from the cooled composite after laminating, a continuous film is present which must be cut. It is believed that when a fusible, transferable protection layer is used which is porous, cutting is obviated by the weak cohesive strength at the interface between the area of the continuous film formed on fusing and the unfused, porous area. Thus, the interface acts as a micro-perforated edge of the film that facilitates a clean rupture. Further, during the fusing step, otherwise entrained air escapes via the interface between the continuous film and the unfused, porous area. The polymer used to make the fusible, thermoplastic polymeric particles employed in the invention may be an amorphous polymer which has softening point greater than 50°C., such as an amorphous polyester, e.g., Kao C ® (Kao Corp.) or an acrylic polymer such as Carboset 526 ® (BF Goodrich Specialy Chemicals); or a partially crystalline polymer having a Tm greater than 50°C., such as a partially crystalline polyester, e.g., Griltex Polyester® (EMS American Grilon Corp) or an ethylene-vinyl acetate copolymer such as Elvax ® (DuPont Corp.); or a thermoplastic, modified cellulose such as Ethocel ® (Dow Chemical Co.), etc. In a preferred embodiment, the fusible, thermoplastic polymeric particles are made from an amorphous polyester having a silica shell. In another preferred embodiment, the fusible, thermoplastic polymeric particles contain a UV-absorber. The fusible, thermoplastic polymeric particles used in the invention may be made using various techniques, such as, for example, evaporative limited coalescence as described in US-A-4,833,060, limited coalescence as described in US-A-5,354,799, grinding as described in US-A-4,304,360, or cryogenic grinding as described in US-A-4,273,294. As noted above, the polymer used to make the fusible, thermoplastic particles will have a Tm or softening point greater than 50°C, preferably between 60°C and 150°C. The Tm is measured using a differential scanning calorimeter (DSC). In a preferred embodiment, the Tm is between 60°C and 120 ° C. A softening point of a polymer can be measured by the Ring and Ball method as described in ASTM E28. In addition, the polymer used to make the fusible, thermoplastic particles usually will have a Tg of less than 100°C, preferably between 0°C and 90°C. As noted above, the polymeric binder used in the invention has a Tg of less than 20° C., preferably between -60°C and 20°C. The polymeric binder used in the invention may be, for example, a polyurethane such as a Witcobond ® Aqueous Urethane Dispersion (Witco Corp.), a vinyl acetate-ethylene copolymer emulsion, an ethylene-vinyl chloride copolymer emulsion, a vinyl acetate-vinyl chloride-ethylene terpolymer emulsion such as Airflex ® (Air Products Corp.), or an acrylic emulsion such as Flexbond® (Air Products Corp). In a preferred embodiment, the binder comprises a polyurethane. A subbing/release layer may also be used to provide adhesion between the porous, fusible, transferable protection layer and the support. The subbing/release layer must be capable of initially adhering the protection layer to the support and must be capable of subsequently releasing the protection layer from the support upon application of heat and pressure followed by cooling. Any material that performs this adhesion/release function can be used. In general, a coated subbing/release layer has a final coating weight of 90 mg/m 2 . Suitable materials include, for example, lattices such as a terpolymer latex of acrylonitrile, vinylidene chloride and acrylic acid, or partially hydrolyzed vinyl chloride-vinyl acetate copolymers. Alternatively, a subbing/release layer can be generated directly on the support surface by corona-discharge-treatment of the support prior to applying the porous, fusible, transferable protection layer. As the flexible, polymeric support for the invention, there may be used, for example, various plastics including a polyester-type resin such as poly(ethylene terephthalate), poly(ethylene naphthalate), polycarbonate resins, polystyrene resins, polysulfone resins, methacrylic resins, cellophane, acetate plastics, cellulose diacetate, cellulose triacetate, vinyl chloride resins and polyester diacetate. The thickness of the support may be, for example, from 12 to 500 µm, preferably from 75 to 300 µm. In a preferred embodiment, the support is a transparent poly(ethylene terephthalate) film. Since the transfer lamination element may come in contact with other image recording articles or the drive or transport mechanisms of laminating devices, additives such as surfactants, lubricants, matte particles and the like may be added to the element to the extent that they do not degrade the properties of interest. The protection layer described above may be coated by conventional coating means onto the support such as wound wire rod coating, slot coating, slide hopper coating, gravure, curtain coating and the like. Ink jet inks used to prepare the images to be laminated by the transfer lamination element of the invention are well-known in the art. The ink compositions used in ink jet printing typically are liquid compositions comprising a solvent or carrier liquid, dyes or pigments, humectants, organic solvents, detergents, thickeners, preservatives, and the like. The solvent or carrier liquid can be solely water or can be water mixed with other water-miscible solvents such as polyhydric alcohols. Inks in which organic materials such as polyhydric alcohols are the predominant carrier or solvent liquid may also be used. Particularly useful are mixed solvents of water and polyhydric alcohols. The dyes used in such compositions are typically water-soluble direct or acid type dyes. Such liquid compositions have been described extensively in the prior art including, for example, US-A-4,381,946; US-A-4,239,543 and US-A-4,781,758. Although the elements disclosed herein have been referred to primarily as being useful for laminating ink jet prints, they also can be used to protect images created employing other technologies such as photographic prints, laser printer prints, prints made via offset lithography and the like. The following examples further illustrates the invention. Example 1 -Lamination Test Preparation of Thermoplastic Polymeric Particles To 225 g ethyl acetate was added 22.5 g of Kao C® polyester resin and 2.5 g UV absorber Escalol® 597 (ISP Corp.) and stirred to solution. Separately, an aqueous solution was prepared of 375 g pH 4 buffer, 21 g Ludox TM® colloidal silica (DuPont Corp.), and 4.5g of 10% poly(adipic acid-comethylaminoethanol). The aqueous phase was placed in a Silverson mixer, the organic phase was added and emulsified at 3,000 s -1 (rev/min) for one minute. The emulsion was then passed through a Microfluidizer (Microfluidics Manufacturing model 110T) to further reduce the emulsion droplet size. After evaporating the ethyl acetate, there was obtained a narrowly distributed population of silica coated polyester beads, µm= 3.0 +/- .36 µm, with incorporated UV absorber. Sufficient water was decanted to give a dispersion with 30% solids. Coating Solutions A series of coating solutions at 24% solids were prepared, at the particle-to-binder ratios shown in Table 1, by mixing the above polyester particles and a polyurethane binder, Witcobond® 215, a 35% aqueous polyurethane dispersion. Solution 1 of the Invention (Particle:Binder 90:10) 14.4 g of thermoplastic polymeric particles, 1.37 g of binder and 4.23 g of deionized water were mixed together to form a coating solution with a particle-to-binder ratio of 90:10. Solution 2 of the Invention (Particle:Binder 75:25) 12.0 g of thermoplastic polymeric particles, 3.43 g of binder and 4.57 g of deionized water were mixed together to form a coating solution with a particle-to-binder ratio of 75:25. Control Solution 1 (Particle:Binder 50:50) 8.0 g of thermoplastic polymeric particles, 6.86 g of binder and 5.14 g of deionized water were mixed together to form a coating solution with a particle-to-binder ratio of 50:50. Control Solution 2 (Particle:Binder 25:75) 4.0 g of thermoplastic polymeric particles, 10.28 g of binder and 5.72 g of deionized water were mixed together to form a coating solution with a particle-to-binder ratio of 25:75. Control Solution 3 (Particle:Binder 5:95) 0.8 g of thermoplastic polymeric particles, 13.03 g of binder and 6.17 g of deionized water were mixed together to form a coating solution with a particle-to-binder ratio of 5:95. Coating Each of the above solutions were coated on 100µm thick, poly(ethylene terephthalate) support using a wire wound rod, calibrated to give a wet laydown of 120µm. The support had been previously subbed with a terpolymer latex of acrylonitrile, vinylidene chloride and acrylic acid. The coatings were air dried forming Elements 1 and 2 of the invention with an unfused porous layer thickness of 57µm, and non-porous Control Elements 1-3 with a layer thickness of 30µm. All the elements were then cut to give 9.5 cm wide by 28 cm long segments. Lamination Test Ink jet images for lamination testing were printed on an ink jet receiver consisting of a resin-coated paper receiver with an 102 mg/m 2 ink receiving layer, comprised of 75% gelatin, 15% polyvinylpyrrolidone and 10% of a cationic latex mordant. After imaging, a 9.5 cm wide by 28 cm long segment was cut from the receiver. The protection layer of each of the above elements was then contacted with the ink jet image and laminated by passing through the nip of a pair of heated rollers. Laminating speed was 46 cm/minute, with the upper roller at 150°C and at nip pressure of 0.41 MPa. Only 10 cm of the 28 cm long segments, corresponding to the length of the image, were passed into the nip. The fused composites were allowed to cool to room temperature, and the support was then peeled away from the fused composite. After fusing, the transferred protection layers from porous Elements 1 and 2 of the invention, having been compressed under heat and pressure, formed a 34µm thick non-porous continuous layer. The same size image was also laminated with a 75µm thick commercial laminating film, Seal ThermaShield R ®(Hunt Graphics Americas Co.) to provide an additional Element, Control 4. The elements were then evaluated for peel. Peel ratings from 1 to 5 are listed below. A peel rating of 1 corresponds to a continuous film that extends beyond the edge of the fused area and must be cut to separate it from the image, i.e., failure. A rating of 5 corresponds to a clean break at the interface. The following results were obtained: Element Particle/Binder Ratio Peel Rating Comment 1 90/10 5 Clean break at interface 2 75/25 4 Breaks at interface Control 1 50/50 1 Continuous film that requires cutting Control 2 25/75 1 Continuous film that requires cutting Control 3 5/95 1 Continuous film that requires cutting Control 4 0/100 1 Continuous film that requires cutting The above results show that costly cutting steps can be eliminated using the transfer laminating element employed in the process of the invention. Example 2 (Arbitrary Shaped Lamination Without Cutting) Circular images having a 4.4 cm diameter were printed on commercial Kodak® photographic ink jet media using a Hewlett Packard® 895 printer. The transfer laminating Element 1 prepared above was placed on top of the circular image. A 5.1 cm diameter circular steel disk heated to 150°C was placed on the laminating element, centered over the image, and pressed at 0.70 MPa for ten seconds. After cooling, the laminating element was peeled from the composite, leaving a fused circular film layer over the circular ink jet image. The above process was repeated using Control Elements 1-4 described above. However, they could not be separated from the circular image without cutting. This example shows that the laminating element employed in the process of the invention can be used to deposit protective layers in varying geometries without requiring a cutting step. Example 3 (Waterfastness of the Transferred Protection Layer) A pair of ink jet images was printed using each of five commercially available ink jet printers on commercially available Kodak® photographic quality ink jet paper. One member of the pair was then contacted with Element 1 of the invention and passed through the nip of a pair of rollers. The other image was not laminated. Laminating speed was 46 cm minute, with the upper roller at 150°C and at nip pressure of 0.41 MPa. The composite was allowed to cool. Peeling easily separated the support layer of the transfer laminate from the composite to afford a laminated image. Waterfastness and Smudge Tests With the prints laying image side up and on a flat surface, one drop of water was placed near the left edge of the print and 2.54 cm from the top edge. Likewise, a drop was place near the right edge of the print and 2.54 cm from the top. After a minute exposure to the water drops, the right drop is wiped with a Kim Wipe ® using light pressure (smudge test) and immediately afterward the print is turned upright allowing the water drop on the left side to run to the bottom of the print (drip test). The tested prints are hung and allowed to dry. They are then rated on a subjective scale ranging from 1-No visible smearing or running to 5- Catastrophic running and/or smearing (image ruined) and reported below. Laminated Printer Smudge Drip Yes HP 895 1 1 No HP 895 5 5 Yes Epson 900 1 1 No Epson 900 5 5 Yes Lexmark 5700 1 1 No Lexmark 5700 5 5 Yes Canon 4400 1 1 No Canon 4400 5 5 The above results show that the polymeric particles fuse and transfer to form a continuous protective layer which functions as a barrier to effectively resist water penetration into the ink jet prints.

Claims: A transfer laminating element for laminating ink jet prints comprising a flexible, polymeric support having thereon a porous, fusible, transferable protection layer comprising fusible, thermoplastic polymeric particles in a polymeric binder, said protection layer having a thickness of between 2 and 100 µm and a particle-to-binder ratio of between 95:5 and 70:30, said thermoplastic polymeric particles having a particle size of less than 10 µm and a Tm or softening point of greater than 50 ° C. and said polymeric binder having a Tg of less than 20°C, said porous, fusible, transferable protection layer being capable of forming a continuous film which is optically clear upon the application of heat and pressure. The element of Claim 1 wherein a subbing/release layer is present between said support and said protection layer, said subbing/release layer being capable of initially adhering said protection layer to said support and being capable of subsequently releasing said protection layer from said support upon application of heat and pressure followed by cooling. The element of Claim 1 wherein said support is poly(ethylene terephthalate). The element of Claim 1 wherein said fusible, thermoplastic polymeric particles comprise an amorphous polyester, a partially crystalline polyester, an acrylic polymer, an ethylene-vinyl acetate copolymer or a thermoplastic, modified cellulose. The element of Claim 1 wherein said fusible, thermoplastic polymeric particles comprise an amorphous polyester having a silica shell. The element of Claim 1 wherein said fusible, thermoplastic polymeric particles contain a UV-absorber. The element of Claim 1 wherein said polymeric binder is a polyurethane, a vinyl acetate-ethylene copolymer, an ethylene-vinyl chloride copolymer, a vinyl acetate-vinyl chloride-ethylene terpolymer or an acrylic polymer. The element of Claim 1 wherein said polymeric binder is a polyurethane.

Inventors: WEXLER ALLAN, WEXLER, ALLAN, Wexler, Allan, Eastman Kodak Company
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 2001
Main classification: B41M7
IPC codes: G03C11, B41M7, B41M5, G03G8, B32B27, B41J2