PRINTABLE LAMINATE

Abstract: The present invention relates to a printable laminate and method for transferring a printed image onto a substrate. The printable laminate includes a transparent or clear film carrier with an image recording layer of a mixture of a heat activated adhesive, such as a polyurethane, and ink absorbing material, such as an ink absorbent modified cellulose material. After transfer of the image to the substrate the carrier layer remains attached to the image recording layer aiding in the appearance and protection of the image.

Description: PRINTABLE LAMINATE The present invention relates to the transfer of a printed image onto a target substrate, especially foam board or rigid PVC . A wide variety of tecnmques have recently been developed for digitally capturing an image m the form of a computer-readable file, editing the image with the computer, printing the edited image onto a recording medium, and then transferring the image from the recording medium to a target substrate. Such target suostrate can be fabric, ceramic, or, in the case of greatest significance for the present invention, foam board or rigid PVC, as used for example, n the commercial graphics industry. The typical recording medium for receiving and transferring an mk-jet image, has a carrier and at least two of the following layers; a release layer, a protective barrier layer, an image transfer layer, and an adhesive layer. International Application PCT/GB/00481 filed February 16, 1998 for "Transfer Film" describes a carrier and a transfer film which has only one layer. This layer is a mixture of heat-activatable adhesive particles and a binder that also is mk- absorbmg, thereby defining a porous matrix. When used for commercial graphics, such transfer film can be adhered to the target substrate without removing the carrier, whereby the carrier remains affixed to and protective of the image. Through further investigation of the efficacy of the various reagents mentioned in said International Application, it has been discovered tnat the combination of polyurethane adhesive and a soluoie ink aosoroer n the wet formulation produces a noticeable cnange m the nature of the porosity of the dry, image-recording layer, and an exceptionally strong bonding not only between the recording layer and the target substrate, but also between the recording layer and the carrier. The carrier is preferably in the form of a substantially transparent or clear film, with the recording layer carried thereon presenting a relatively homogeneous, filmic surface for receiving and absorbing the ink. This combination of carrier and recording layer can be considered a printable laminate, i.e., it can record an image created through common printing techniques, most suitably, mκ-ιet printing techniques, and it can then be permanently laminated in its entirety to a target substrate, utilizing a conventional range of laminating temperatures and pressures . The carrier can be any transparent or clear material compatible with the materials of the recording layer and capable of withstanding the heat and pressure of the laminating process. The carrier must also adhere to the recording layer sufficiently well after lamination and provide adequate protection of the underlying image printed on the image recording layer. The materials suitable for use as the carrier include cast films such as those made from polyolefm, polyesters, nylon and polyvmyl chloride. Polyesters, polyolefms and polyvmyl chloride appear to have particular suitability as the carrier of the present invention . The polyurethane and the ink absorber together comprise at least 90%, and preferably at least 95% of the dry weight of the recording layer with optionally one or more defoamers and wetting agents comprising at least some of the balance of the dry weight of the recording layer. The polyurethane typically comprises at least 50% of the dry weight of the image recording layer, while the ink absorber comprises at least 30% of the dry weight of the recording layer. The polyurethane for use _.n the invention is preferably an aqueous dispersion of polyurethane which, if dried, forms a film of material. Upon application of heat and optionally pressure, the polyurethane is able to form an adhesive bond to other surfaces. In addition, it is preferable for the purposes of this invention that the polyurethane in combination with the ink absorptive material does not form a matrix of particles. To this end it is most preferable that the polyurethane have a small strand-like conformation so that m combination, the polyuretnane and ink absorber form a more homogenous mixture. A polyurethane strand size of around 0.2 microns appears to be highly suitable for making the film. The polyurethane dispersion sold under the trademark Luphen D DS 3507 and available from BASF Corp, Mount Olive, New Jersey is particularly suitable for use in this invention. The ink absorber is preferably a modified cellulose material and more preferably is a thermoplastic modified cellulose material. Suitable ink absorbers include hydroxypropyl cellulose and cellulose gum. Utilizing a thermoplastic ink absorber material permits plasticizmg (softening) of the absorber at the temperatures in the range in which the laminate is bonded to a substrate. It is believed that this assists the laminate in making better contact with and improves adhesion to the substrate. One particular thermoplastic modified cellulose of utility n the invention is Klucel E modified cellulose powder, commercially available from Hercules, Wilmington, Delaware. Other suitable materials include Blanose cellulose gum (sodium carboxymethylcellulose) and Glascol DP6 (cationically charged water-soluble polymer) . Typically, the ink absorber is a very fine particulate material which, when dissolved in water, is of a molecular size. The dry particle size for a material such as Klucel E is estimated to be in the range of 0.003-0.2 microns. It will be appreciated that these ink absorptive materials may work with a variety of inks, dyes and image forming (printing) processes. However, it has been found that these ink absorber materials work particularly well with the ink-jet printing process and ink-jet inks, especially those inks which are dye-based and which are m water-based or water and glycol-based systems. The defoammg and wetting agents for use in the invention are surfactants which may be anionic, cationic or nonionic m nature. The surfactants are intended to serve one or more functions in the invention, including: reducing bubble or foam formation in the image recording layer; promoting adequate wetting out and uniform formation of the recording layer on the carrier and promoting ink or dye absorption and diffusion m the carrier layer. Non-limiting examples of suitable surfactants for use in the invention include the nonionic surfactant sold under the trademark Pluronic PE6100, and the anionic surfactant sold under the trademark Lumiten I-AFK, both of which are commercially available from BASF Corp., Mount Olive, New Jersey. The recording layer is preferably formed by mixing m a water-based system: (a) an aqueous polyurethane dispersion; with (b) a water-soluble, powdered ink absorber; and (c) one or more defoamer/wettmg agents. This mixture is coated onto the carrier film, and dried below the minimum film forming temperature (MFFT) of the polyurethane dispersion. Accordingly, the invention m one aspect is a printable laminate comprising a substantially transparent film carrier having opposite first and second sides; a thermoplastic recording layer having an inner surface directly supported by one of said sides of the carrier and an exposed outer surface for receiving printing ink; wherein said recording layer comprises a heat activatable polyurethane adhesive and ink absorber which together constitute at least 90% of the total weight of the recording layer. In another aspect of the invention a printed laminate comprises a substantially transparent film carrier having opposite first and second sides; a substantially clear thermoplastic recording layer naving an inner surface directly supported by one of said sides of the carrier and an exposed outer surface, said recording layer comprising a heat activatable adhesive and an ink absorber which together constitute at least 90% of the total weight of the recording layer; and an ink pattern printed on said recording layer and extending from the outer surface to the inner surface of the recording layer. In another aspect of the invention a method of producing a substantially permanent image on a substantially flat target surface, comprises selecting a printable laminate consisting of a substantially transparent film carrier having opposite first and second sides, and a substantially homogeneous recording layer in which the two most significant constituents by weight per cent are heat-activatable adhesive and ink absorber, wherein said recording layer has an inner surface directly supported by the first side of the carrier, and an exposed outer surface; printing ink in a pattern onto the exposed surface of the recording layer, wherein said ink diffuses through the layer to the inner surface of the layer without substantial alteration of said pattern; placing tne outer surface or the printable laminate on saio target surface; and applying heat and pressure to the second surface of the carrier, thereby permanently adhering the outer surface of the recording layer to the target surface and the carrier to the inner surface of the recording layer. One embodiment of the invention will be described below with reference to the accompanying drawings, wherein FIG.l shows the printable laminate according to the invention, with an ink pattern printed thereon; and FIG.2 shows schematically how the printed laminate is used to decorate a target substrate. Figure 1 shows the printable laminate 10 according to the invention, consisting essentially of a substantially transparent carrier film 12 having first and second surfaces, and a recording layer 14 having an inner surface directly covering the first surface of the carrier film, and outer exposed surface. An image 16 has been printed on the exposed surface of layer 14, as by an mk-ηet printer (not shown), resulting m a pattern of distinct ink deposits such as 18, which have diffused through the thickness of the layer 14 without substantial degradation. As shown in Figure 2, the outer surface of the printed laminate 10 is placed on a target surface of, e.g., a foam board or rigid sheet of PVC 20, and permanently adhered thereto by the application of heat and pressure through the second surface of the carrier film 12. According to the invention, this heat and pressure also permanently adheres the first surface of the carrier film to the inner surface of the recording layer. This provides a protective covering for the printed image, without significantly affecting the observed quality of the image. It should be understood that the temperature and pressure conditions associated with the process shown m Figure 2, are within the range of convention, as is described in the material incorporated herein by reference. It should also be understood that the term "permanent" with reference to adhesion, means the useful life of the decorated board or sheet 20 under normal care and handling. The carrier is preferably a 50-mιcron clear polyester, polyvmyl chloride or polypropylene film, which requires no special surface treatment. In particular, no melt transfer or release layer is provided . The recording layer 12 is constituted on a weight basis, as follows: Material Function General Percent Preferred Percent Polyurethane Heat activated 50-70 60-65, esp 61 50 adhesive Hydroxypropyl Thermoplastic ink 30-50 30-35 esp 34 65 Cellulose absorber Ethylene Oxide- Nonionic surfactant 0-5 1 2, esp 1 73 Propylene Oxide Copolymer Sulfated Fatty Anionic surfactant 0-5 2-3, esp 2 1 2 Acid The recording layer is initially formulated as a coatable mixture, wherein the coating for the especially preferred layer is constituted on a weight basis as follows: Material Form or Function Percentage Luphen D DS 3507 Polyurethane dispersion in water 28 06 Klucel E Water soluble modified cellulose 7 1 1 powder Pluronic PE61 00 Defoamer/wetting agent 0 36 Lumiten I AFK Wetting agent 0 79 Water Diluent 63 68 The resins m the foregoing formulation are preferably of an extremely fine size (in the range of about 0.003 - 0.2 microns), i.e., generally finer than the particle size range of 0.08-3 micron described in said International Application. As a result, upon drying of the coating at a temperature below the MFFT of the adhesive dispersion a filmic yet microporous recording layer is formed. It is believed that the adhesive and absorber mix substantially randomly at the molecular level, providing substantial homogeneity of the recording layer, rather than a porous matrix of distinct adhesive particulates bound together by the absorber. The clarity of the coating upon drying, may also be attributable to this intimate homogeneity. Th s surprising result is believed to arise at least in part by the larger number of water molecules that form the polyurethane polymer, being replaced by molecules of the absorber material, as the coating is dried. The advantages of laminates according to the invention include (1) sharper printing resolution on the recording layer, (2) clarity of the recording layer, and (3) the high adhesive strength of polyurethane for holding the recording layer to the target surface and the carrier to the recording layer. The drying temperature is held below the MFFT of the adhesive dispersion. For example, the MFFT of the polyurethane dispersion Luphen D DS 3507 is about 60°C and the heat activation temperature of the entire laminate is typically in the range of 75° to 125°C.

Claims: C L A I M S : 1. A printable laminate comprises : a substantially transparent film carrier having opposite first and second sides; a thermoplastic recording layer having an inner surface directly supported by one of said sides of the carrier and an exposed outer surface for receiving printing ink; wherein the recording layer comprises a heat activatable polyurethane adhesive and an ink aosoroer which together constitute at least 90% of the total weignt of the recording layer. 2. A printable laminate according to claim 1, wherein the polyurethane weight is at least 50° o of the total weight of the recording layer. 3. A printable laminate according to claim 1 or 2, wherein the polyurethane weight is n the range of about 50-70 weight ° of the total weight of the recording layer. 4. A printable laminate according to any preceding claim wherein tne ink absorber is at least 30% of the total weight of the recording layer. 5. A printable laminate according to any preceding claim wherein the heat activatable polyurethane adhesive and ink absorber together constitute at least 95° 0 of the total weight of the recording layer. 6. A printable laminate according to any preceding claim wherein the ink absorber is a modified cellulose. 7. A printable laminate according to any preceding claim wherein the ink absorber is one or more members selected from the group consisting of hydroxypropyl cellulose or sodium carboxymethyl cellulose. 8. A printable laminate according to any preceding claim wherein the ink absorber is a cationicallv charged water- soluble polymer. 9. A printable laminate according to any preceding claim wherein the recording layer comprises: polyurethane in the range of about 60-65 weight ° 0 ; hydroxypropyl cellulose ιr the range of about 30-35 weignt °; and up to about 5o surfactants. 10. A printable laminate according to any preceding claim, wherein the carrier is one of clear polyester or clear polypropylene fa.lm. 11. A printable laminate according to any preceding claim, wherein the recording layer is substantially clear. 12. A printed laminate comprising : a substantially transparent film carrier having opposite first and second sides; a substantially clear thermoplastic recording layer having an inner surface directly supported by one of said sides of the carrier and an exposed outer surface, said recording layer comprising a heat activatable adhesive and an ink absorber which together constitute at least 90°o of the total weight of the recording layer; and an ink pattern printed on said recording layer and extending from the outer surface to the inner surface of the recording layer. 13. A printed laminate according to claim 12, wherein the heat activatable adhesive is polyurethane having a strand size of about 0.2 microns and constituting at least 50 o of the weight of the recording layer exclusive of ink. 14. A printed .animate according to claim 12 or 13 wherein the thermoplastic ±nk absorber is at least 30o of the total weiαht of the recording layer exclusive of ink. 15. A printed laminate comprising : a printable laminate according to any of claims 1 to 11; ana an ink pattern printed on the recording layer and extending from the outer surface to the inner surface of the recording layer. 16. A method of producing a substantially permanent image on a substantially flat target surface comprising the steps of : a] selecting a printable laminate consisting of a substantially transparent film carrier having opposite first and second sides, and a substantially homogeneous recording layer m which the two most significant constituents by weight ° are heat-activatable adhesive and ink absorber, wherein said recording layer has an inner surface directly supported by the first side of the carrier, and an exposed outer surface; b] printing ink in a pattern onto t e exposed surface of the recording layer, whereby said ink diffuses through the later to the inner surface of the layer without substantial alteration of said pattern; c] placing the outer surface of the printable laminate on said target surface; and d] applying heat and pressure to the second surface of the carrier, thereby permanently adhering the outer surface of the recording layer to the target surface and the carrier to the inner surface of the recording layer. 17. A method according to claim 16, wherein the heat- activatable adhesive is polyurethane. 18. A method according to claim 17 wherein oefore the step of printing, the recording layer is substantially clear. 19. A method according to claim 17 or 18, wherein the target surface is one of foam board or rigid PVC. 20. A printable laminate substantially as hereinbefore described.

Inventors: COOK COLIN JOHN, COOK, COLIN, JOHN
Applicants: COOK COLIN JOHN, HUNT GRAPHICS EUROP LTD, COOK, COLIN, JOHN, HUNT GRAPHICS EUROPE LTD.
Application year: 1998
Main classification: B32B27
IPC codes: B32B27, B41M5, B41M7, B44C1