Methods for processing printed substrates

Abstract: Methods for processing substrates (12) printed with an ink layer (14) having a non-planar surface topography, eg curved ink droplets, to produce a composite laminate (10) and the composite laminates produced thereby are disclosed. A printed substrate (12) is laminated to a transparent film (18) using an intermediate adhesive layer (16). During lamination processing, the adhesive layer (16) conforms to the surface topography of the printed ink layer (14), while the conformation of the printed ink layer remains substantially unchanged. The lamination processing methods are especially suitable for processing light transmissive substrates (12), such as transparencies, printed with phase change color inks (14) to produce composite laminates that project clear, color saturated images upon overhead projection.

Description: The present invention relates generally to methods for processing substrates printed with an ink layer having a non-planar surface topography and composite laminates produced thereby. Preferred embodiments of the invention relate more specifically to methods for processing light transmissive substrates printed with a phase change ink layer to produce a composite laminate that provides improved color images by overhead projection. Ink jet printers operate by ejecting ink onto a print substrate, such as paper, in controlled patterns of dots. By selectively regulating the pattern of ink droplets, such ink jet printers can be used to produce a wide variety of printed images, including text, graphics, and the like. Moreover, ink jet printers are capable of recording permanent images on a wide variety of substrates, including both light reflective and light transmissive substrates. Ink jet printers utilize a variety of inks, including phase change inks, which are often referred to as hot melt inks. In general, phase change inks are solid at ambient temperatures and liquid at the elevated operating temperatures of an ink jet printing device. Liquid phase ink droplets are ejected from the printing device at an elevated operating temperature and, when the ink droplets contact the surface of a substrate, they quickly solidify. Early references to phase change inks for ink jet printing involved monochrome inks jetted by electrostatic printing devices. Thus, for example, U.S. Patent No. 3,653,932 discloses a low melting point (30°C to 50°C) ink having a base comprising diesters of sebacic acid. In a similar process, U.S. Patent No. 3,715,219 describes low melting point (30°C to 60°C) inks including a paraffin alcohol-based ink. One disadvantage of printing with low melting point phase change inks is that they frequently exhibit offset problems. Specifically, when substrates printed with these inks are stacked and stored for subsequent use, the ink adheres to adjacent surfaces, particularly if the printed substrates are exposed to high ambient temperatures. Phase change inks are well known in the art. U.S. Patent Nos. 4,390,369 and 4,484,948 describe methods for producing monochrome phase change inks that employ a natural wax ink base, such as Japan wax, candelilla wax, and carnauba wax, which are subsequently printed from a drop-on-demand ink jet device at a temperature ranging between 65°C and 75°C. U.S. Patent No. 4,659,383 discloses a monochrome ink composition having an ink base including a C20-24 acid or alcohol, a ketone, and an acrylic resin plasticizer. These monochrome ink compositions are not durable and, when printed, may become smudged upon routine handling and folding. Japanese Patent Application No. 1,280,578 discloses the use of aliphatic and aromatic amides that are solid at room temperature, such as acetamide, as printing inks. U.S. Patent No. 4,684,956 is directed to monochrome phase change inks utilizing synthetic microcrystalline wax (hydrocarbon wax) and Microcrystalline polyethylene wax. This molten composition can be applied to a variety of porous and non-porous substrates using drop-on-demand ink jet application techniques. European Patent Application Nos. 0 287 352 and 0 206 286 disclose phase change ink jet printing in color. The ink bases for these systems include fatty acids, a thermoplastic polyethylene and a phase change material in the first application; and the alcohol portion of a thermosetting resin pair, a mixture of organic solvents (o- and p-toluene sulfonamide) and a dye in the second application. A system for applying phase change inks, described in U.S. Patent No. 4,751,528, relates to an ink jet apparatus for controlled solidification of phase change inks to assist in controlled penetration of the substrate. This apparatus includes a substrate-supporting, thermally conductive platen as well as a heater and a thermoelectric cooling arrangement, both disposed in heat communication with the platen. Several prior art references disclose manipulation of printed images formed from phase change inks, either during or following the printing process. In U.S. Patent No. 4,745,420, droplets of a phase change ink are ejected onto a target and subsequently spread by the application of pressure to increase the ink surface area coverage and minimize the volume of ink required. In other words, droplets of phase change ink that may not initially cover the entire target are spread over the entire target surface by application of pressure. In xerographic image fusing, the area of contact between the toner and the substrate may be substantially increased by causing the toner to spread and penetrate somewhat into the underlying substrate. See Williams, "The Physics and Technology of Xerographic Processes," J. Wiley & Sons (1984). The mechanical properties of the toner are such that plastic deformation and flow occur during fusing. In both of the aforementioned references, the ink or toner spreads across the paper, forming characters or patterns thereon. Although several references describe fusing of images between a pair of mechanically loaded rollers at ambient temperatures, hot roll fusing has seen widespread use in toner applications. In hot roll fusing, two rolls (typically one is heated) are mechanically loaded together and rotated to provide transient application of heat and pressure to the substrate. The toner is typically heated to above its glass transition temperature (T g ), which enables it to coalesce, flow, and penetrate the substrate. Rolling pressure and capillary action facilitate coverage. See Dr. John W. Trainer, "Trends and Advances in Dry Toner Fusing," Institute for Graphic Communication (June 1985). Ink jet printing of colored inks onto light transmissive media for displaying color images by overhead projection has historically been a problem. When aqueous inks are employed, for example, special coatings must be provided on the light-transmissive medium to absorb the solvent so that images of high quality are formed. See U.S. Patent Nos. 4,503,111, 4,547,405 and 4,555,437. The development of phase change inks that are substantially transparent provides improved capability to print images on many types of substrates. Phase change ink compositions disclosed in U.S. Patent No. 4,889,761 are exemplary. Special coatings are not required for phase change ink jet printing on transparencies. Images produced by prior art color phase change inks printed on light transmissive substrates, however, are not generally acceptable for use in overhead projection systems as a consequence of color ink jet printing techniques. U.S. Patent Nos. 4,889,761, 4,801,473 and 4,853,706 describe problems associated with projection of images from light transmissive substrates ( e.g. , transparencies) printed with phase change inks. Projection problems result because ink deposited on substrates by an ink jet printer solidifies as curved droplets that refract and scatter impinging light, notwithstanding the substantial transparency of the phase change ink material. Impinging light is transmitted through printed ink droplets in a non-rectilinear path, and the refracted light is directed away from the collection lens of a projection system. Consequently, the projected image is visible primarily in contrast, and the colors of the projected image have a dull grayish cast. This problem is exacerbated by printing techniques wherein multiple layers of ink droplets are applied to produce secondary colors. U.S. Patent No. 4,801,473 is directed to a method of processing transparencies printed with curved, light scattering ink droplets. Printed ink droplets are overlaid with a transparent layer having an index of refraction substantially the same as the index of refraction of the ink droplets. Preferred coating materials include transparent polyurethane and acrylic. The ′473 publication teaches that the exterior surface of the coating layer need not be parallel to the substrate surface to achieve an improvement in projection. Application of a liquid coating to a printed substrate is impractical in several respects. Liquid coating application techniques are generally difficult to control. Moreover, drying periods are frequently required to permit evaporation of solvents. This technique moreover only provides some improvement because, although processing reduces the radius of curvature of individual ink spots, the coating itself is curved and refraction of transmitted light, although less severe, remains problematic. U.S. Patent No. 4,853,706 discloses methods for processing transparencies having curved, light scatting ink droplets thereon. The printed substrate is exposed to heat and/or pressure to flatten the curved ink droplets. This processing requires a time interval of about 30 seconds to 5 minutes, and may be achieved by bringing the transparency into close thermocoupling or contact with a heater to remelt the ink. Coating the printed substrate with a transparent coating to minimize the amount of light reflected and refracted by the curved ink droplets scattered from the air/ink interface is also disclosed. Additionally, the ′706 patent teaches that ink droplets may be spread and flattened by application of a second substantially transparent resinous support utilizing a hot melt adhesive in a lamination process. After the adhesive-covered support sheet is applied to cover the printed transparency, both the adhesive and the printed image pattern are heated to melting temperatures, and the ink droplets are thereby flattened. U.S. Patent No. 4,889,761 discloses substrates having a light-transmissive phase change ink printed thereon that are processed to improve the quality of images projected by overhead projection techniques. Printed substrates are processed to reorient the surface configuration of solidified phase change ink droplets to provide a printed ink layer having a generally uniform thickness that is capable of transmitting light in a substantially rectilinear path. Reorientation is achieved by the application of pressure or a combination of heat and pressure to the printed substrate by means of a dual roller assembly. Rollers having various constructions are disclosed, including a TEFLON® coated heated roller and silicone rubber covered pressure roller. Reorientation of printed phase change ink layers has many practical limitations. It typically requires application of relatively high pressures and/or the use of elevated temperatures. Moreover, even under optimal conditions, it is difficult to achieve sufficient reorientation of ink droplets in areas of transition from one ink layer thickness to another. Prior art techniques for processing and/or reorienting phase change ink droplets printed on light transmissive substrates such as transparencies generally have not provided optimal results. Offset problems and problems resulting from the non-uniform distribution of ink droplets persist, especially where multiple ink droplet layers are utilized in color printing techniques. Moreover, most existing processing cycles require complex, bulky equipment and/or unacceptable time periods for completion and thus are not commercially viable alternatives. The present invention provides methods for processing substrates printed with an ink layer having a non-planar surface topography, e.g. , curved ink droplets, to produce a composite laminate. The composite laminate comprises a printed substrate laminated to a substantially optically transparent film with an adhesive layer interposed between the printed substrate and the film. The methods of the present invention are especially suitable for processing light transmissive substrates, such as transparencies, having phase change inks printed thereon to produce a composite laminate that projects a clear, color saturated image upon projection by overhead projection techniques. The adhesive layer interposed between the printed substrate and the transparent film is substantially optically clear and has an index of refraction substantially matching that of the printed ink. The thickness of the intermediate adhesive layer is preferably at least about as great as the maximum thickness of the printed image. Suitable adhesive materials include hot-melt adhesives, pressure sensitive adhesives, and the like. When hot-melt adhesives are employed, the softening point of the material is preferably lower than the melting point of the printed ink. Application of the substantially transparent film and intermediate adhesive layer to the printed substrate may involve application of a combination of heat and pressure using planar surfaces, rollers, or a combination thereof, to produce a composite laminate. The processing apparatus, or a portion of the processing apparatus that contacts the transparent film, is preferably heatable to a temperature at which the adhesive softens and flows. During processing, the intermediate adhesive layer is heated to a temperature at which it flows to intimately contact and conform to the topography of the printed ink layer. The adhesive layer bonds to the ink layer, the substrate in regions that are unprinted, and to the transparent film, to provide a durable composite laminate. Additionally during processing, air trapped between the layers is expelled to produce a composite laminate that is substantially free from visible bubbles. According to preferred embodiments, the surface contacting the printed substrate during lamination is at a lower temperature than the heated surface contacting the transparent film. It is unnecessary and, for many applications, undesirable to heat the printed ink layer to melting temperatures during the lamination process. Methods of the present invention contemplate manipulation and reorientation of the adhesive layer, rather than the printed ink layer, to provide a composite printed ink/adhesive layer of uniform thickness bonded between the substrate and the transparent film. The composite laminate produced according to methods of the present invention demonstrates substantially improved projection by overhead projection techniques. As a result of the lamination process, the composite laminate is generally planar. This feature facilitates transmission of impinging light through the composite laminate in a substantially rectilinear fashion and results in improved image clarity and color saturation during overhead projection. As used herein with reference to composite laminates, the term "planar" means that the surfaces of the substrate and the transparent film are substantially parallel to one another in areas having similar image densities. Because the image density, i.e. , the volume of printed ink per unit surface area may vary over the surface of the printed substrate, there may be transitional regions where the substrate and the transparent film are not perfectly parallel. Such transitional regions do not deviate substantially from a parallel orientation and generally do not affect the quality of the composite laminate. The composite laminate of the present invention provides numerous practical advantages. Composite laminates comprising a light transmissive substrate exhibit a high degree of lightness and chroma and transmit light in a substantially rectilinear path. Offset and abrasion problems are eliminated because the printed ink layer is protected from exposure. Moreover, the laminated composite transparencies exhibit improved durability for extended storage periods. Additionally, the composite laminate can be temporarily or permanently marked with inks or the like. Frames, borders, logos, and the like may be provided on the transparent film and incorporated in the composite laminate product. The lamination methods of the present invention are preferably incorporated in a post-printing processing step utilized in conjunction with an ink jet printing device, such as a drop-on-demand ink jet printer. Lamination processing may be utilized as a stand alone process, or it may be utilized in conjunction with other post-processing techniques, such as reorientation of the printed image. According to preferred embodiments, printed substrates may undergo a pressure reorientation step prior to lamination processing. The foregoing and other objects, features and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments which proceeds with reference to the drawings. Fig. 1 is a schematic representation illustrating the laminated composite product of the present invention. Fig. 2 is an exploded side view schematic representation of a dual roller processing apparatus according to the present invention. Fig. 3 is a side view schematic representation of a lamination processing kit according to the present invention. Fig. 4 is a side view schematic representation of another arrangement employing a platen and a roller for laminating printed substrates. Fig. 5 is an exploded side view schematic representation of a dual platen lamination apparatus according to the present invention with a printed substrate and transparent film/adhesive sheet positioned therein for lamination. Phase change inks useful in accordance with the present invention are solid at ambient temperatures and liquid at printing temperatures. Phase change inks preferably exhibit low viscosity in the liquid phase and transparency and durability in the solid phase. Phase change inks disclosed, for example, in U.S. Patent No. 4,889,761, which is incorporated herein by reference in its entirety, are suitable. Suitable printing substrates may be permeable, such as paper and the like, or substantially impermeable, such as light reflective films, or light transmissive films, such as transparencies and the like. Lamination processing according to the present invention may advantageously be utilized with permeable, generally light reflective substrates to improve the durability of the printed substrate. Lamination processing according to the present invention, however, is especially suitable for utilization in connection with light transmissive substrates, such as transparencies. The term "lamination processing," as used herein, refers to the application and bonding of a substantially optically clear protective film on a printed ink layer to provide a composite laminate. More specifically, lamination processing according to the present invention involves application of an intermediate adhesive layer and a protective film layer on a printed ink layer whereby the printed ink layer and the adhesive layer form a composite intermediate layer that has substantially parallel planar faces. The surfaces of the substrate and the protective film consequently are substantially planar and parallel. Prior art transparency lamination techniques, as exemplified by the disclosure of U.S. Patent No. 4,853,706, have utilized application of heat during or after lamination to spread and flatten the curved ink droplets. Heat is applied, for example, by bringing the transparency into close thermocoupling or contact with a heater to remelt the ink. Remelting of the printed ink layer generally results in a lower definition image and may result in smears or runs in the printed image. It is not necessary to remelt the printed ink droplets or layer utilizing the lamination techniques of the present invention. In fact, preferred lamination processing techniques of the present invention are designed to prevent remelting of the printed ink layer. A highly schematic diagram illustrating a composite laminate in accordance with the present invention is illustrated in Fig. 1. Composite laminate 10 comprises a print substrate 12, a printed ink layer comprising a plurality of generally curved ink droplets 14 deposited on substrate 12, an adhesive layer 16, and a protective film 18, which forms a second exterior face of the composite laminate. During lamination processing, adhesive layer 16 conforms to the surface topography of ink droplets 14 and intimately contacts and bonds to substrate 12, ink droplets 14 and protective film 18. The thickness of composite layer (A) formed by ink droplets 14 and adhesive layer 16 is preferably substantially uniform, as shown, and the composite laminate is substantially free of trapped air bubbles. As a consequence, the outer faces 20 and 22 of substrate 12 and protective film 18, respectively, are planar and are oriented substantially parallel to one another. When substrate 12 comprises a light transmissive material, such as a transparency, and the composite laminate is intended for use in applications such as overhead projection, substrate 12, ink droplets 14, and adhesive layer 16 comprise materials that are substantially optically transparent and have substantially similar indices of refraction. The term "substantially optically transparent," as used herein, means a material having a transmittance of about 80% or greater in the visible light range. The term "substantially similar," as used herein with reference to indices of refraction (n), means that the difference between the index of refraction of the adhesive material and that of the substrate and the printed ink, respectively, is not more than about 10% to 12%. Composite laminate 10 has a generally uniform thickness, and the outer faces 20 and 22 formed by substrate 12 and protective film 18, respectively, are planar. Incident light, such as from a projection source located beneath substrate 12, is therefore transmitted in a substantially rectilinear path through composite laminate 10. Substrate 12 may comprise a light reflective, somewhat permeable material such as paper. Lamination processing according to the present invention is especially beneficial, however, when substrate 12 comprises a light transmissive material, such as a transparency. Many light transmissive substrates are known in the art and would be suitable. Substrates comprising materials such as polyester ( e.g. MYLAR), cellulose triacetate, polystyrene, polycarbonate, and the like are suitable. Hot melt adhesives, waxy materials, pressure sensitive adhesives, and the like that are substantially optically clear are generally suitable adhesive materials for use in composite laminates of the present invention. Hot melt adhesives are generally preferred. Hot melt adhesives include materials that are generally solid and do not exhibit adhesive properties at ambient temperatures but, at elevated temperatures, become viscous fluids and conform and bond, upon cooling, to contact surfaces. Numerous hot melt adhesive materials are known in the art for adhering fabrics, paper, cardboard, and the like, but most would not be suitable for use in the present invention. Hot melt adhesives that soften and flow at temperatures below the melting point of printed inks are required, so that the heated adhesive softens, flows, and becomes a viscous liquid at temperatures where the printed ink remains solid. Hot melt adhesives having a softening point about 10° to 20°C below the melting point of the printed ink are especially preferred. Adhesive materials having a viscosity of about 10 to 30,000 centipoise (cp) at 140°C are preferred, and adhesive materials having a viscosity of about 5,000 to 10,000 cp at 140°C are especially preferred. As the adhesive material is heated during lamination processing, it conforms to the non-planar surface topography of the printed ink layer. The printed ink layer preferably does not undergo melting or reorientation to a substantial degree during lamination processing. Preferred hot melt adhesive substances according to the present invention comprise substantially optically clear polymeric hot melt adhesives that exhibit relatively low melt viscosity. Adhesive formulations comprising from about 25% to about 80% of a substantially optically clear base polymer and from about 20% to 75% of various additives, such as tackifiers, waxes, and antioxidants are suitable. Copolymers marketed by Dupont as "ELVAX" resins are particularly suitable base polymers for this application, particularly those having a relatively low molecular weight (or high melt index). A hot melt adhesive formulation consisting of 60% ELVAX 205W, 30% of an Arakawa Chemical Co. KE-311 resin as a tackifier, and 10% Witco M-445 microcrystalline wax is especially preferred for use in the methods and composite laminates of the present invention. The formulation may also contain small amounts of an antioxidant such as Irganox 1010 (Ciba-Geigy), or the like, to facilitate stability during the coating process. This formulation is designed to exhibit substantially lower melt viscosity compared to typical hot melt adhesive formulations, while still providing good adhesive strength and flexibility in the composite lamination, and retaining optical clarity. Alternatively, the adhesive layer may comprise a wary material or a pressure sensitive adhesive material. Materials having substantial optical clarity and compositions similar to that of phase change inks are suitable, although waxy materials that soften and flow at a temperature below the melting point of the printed ink layer are preferred. Materials such as Witco Kenamide EX-774 are suitable. Pressure sensitive adhesive materials typically exhibit bonding properties at ambient temperatures and do not require application of elevated temperatures during processing according to the present invention. Numerous pressure sensitive adhesive substances that exhibit substantial optical clarity and conform and bond to materials having a non-planar surface topography are known in the art and would be suitable. Adhesive-backed transparent films available, for example, from Adhesive Research, Inc., Glen Rock, PA, and marketed as ARCLAD, are suitable. Substantially transparent films suitable for use as the protective layer are also well known in the art. Flexible, polymeric sheet materials such as polyester, e.g. MYLAR, and the like are well known in the art and would be suitable. The protective film may comprise the same material as a light transmissive substrate. According to preferred embodiments, protective film 18 has a thickness (B) less than thickness (C) of substrate 12, suitably from about 10% to about 80% the thickness of the substrate, and most preferably from about 30% to about 70% the thickness of the substrate. According to especially preferred embodiments, substrate 12 has a thickness of about 100 microns and protective film 18 has a thickness of 50 microns. The adhesive layer may be applied independently from the protective film, but the protective film and adhesive layer are preferably provided as a unitary sheet for lamination to the printed substrate. This may be accomplished, for example, by heating a hot melt adhesive substance to flow temperatures and applying a uniform thickness hot melt adhesive coating on one surface of the protective film. Additionally, a release layer may be provided between the hot melt adhesive and the protective film so that the protective film is removable after application of the adhesive layer to the printed substrate. According to preferred embodiments, the thickness of the adhesive coating corresponds generally to at least about 50% of the maximum thickness of the printed ink layer. Thus, for example, as illustrated in Fig. 1, the maximum thickness of the printed ink layer is (D), and the adhesive layer coating on transparency film 18 preferably has a thickness of at least about 50% (D). Adhesive coating layers having a thickness of at least about 100% (D) are especially preferred. An adhesive layer having a thickness of about 25 to 100 microns and most preferably about 70 microns is preferred, for example, for use with printed ink layers having a thickness of about 66 microns. Lamination processing of the printed substrate is accomplished by application of heat and/or pressure sufficient to provide intimate contact and bonding of the intermediate adhesive layer to printed ink droplets and the substrate. Suitable contact pressures and/or temperatures vary depending upon the properties of the adhesive material and the configuration of the lamination apparatus. When hot melt adhesives are employed, lamination processing preferably involves application of both heat and pressure. Exemplary lamination processing apparatus are shown schematically in Figs. 2-4. Fig. 2 illustrates a dual roller processing apparatus including a first roller 26 and a second roller 28 aligned on substantially parallel longitudinal axes. Roller diameters of about 1.25 to 5 cm are preferred, and rollers having a diameter of about 2.5 cm are especially preferred. Rollers 26 and 28 are preferably constructed from a rigid material and one or both rollers may be provided with a resilient support means 30 in the form of an outer resilient layer. Resilient support means 30 preferably comprises an elastomeric material such as silicone rubber having a Durometer of about 40 Shore A and a thickness of at least about 2 mm. Rollers 26 and 28 are positioned to apply pressure to the printed substrate, the intermediate adhesive layer and the protective film at the roller interface upon rotation of the rollers in opposite directions. Processing pressures of about 70 to about 700 kpascals, and most preferably about 140 to about 420 kpascals, are generally utilized when conventional hot melt polymeric adhesives and waxes are employed as the adhesive layer. Processing pressures of about 250 to about 700 kpascals are generally suitable for pressure sensitive adhesive materials. Processing rates (the rate at which the printed substrate is passed between the rollers) of about .25 to about 2.5 cm/sec are generally suitable, and processing rates of about 0.6 to about 1.25 cm/sec are preferred. Processing of laminated composite products incorporating hot melt adhesive materials involves application of heat in addition to pressure. Roller apparatus for lamination processing are preferably heatable to temperatures at which the adhesive substance flows and bonds. In the embodiment shown in Fig. 2, roller 26 contacting protective film 18 having adhesive layer 16 bonded thereto is preferably heatable. Temperatures of about 100° to about 145°C are preferred for use with preferred adhesive and ink compositions disclosed herein. Roller 28 contacting the printed substrate is preferably not actively heated and, according to preferred embodiments, is therefore maintained at a temperature not greater than that of heatable roller 26. A thermal insulating layer may also be provided to thermally isolate the printed substrate from roller 28. This thermal insulating layer facilitates lamination processing by effectively ensuring that the majority of the thermal energy from roller 26 is transferred to the adhesive layer and other composite laminate constituents. Suitable thermal insulating layers include sheet materials having dimensions corresponding generally to or slightly larger than the dimensions of the printed substrate. The thermal insulating layer comprises a flexible sheet material having a relatively low thermal conductivity. Preferred materials include heavy papers such as tag board, or the like, having a thickness of about 200 to about 300 microns. The thermal insulating layer is fed into the lamination apparatus between non-heated roller 28 and the printed substrate and serves to isolate the printed substrate from thermal energy stored in non-heated roller 28. Utilization of a thermal insulating layer during lamination processing also renders the lamination process less sensitive to temperature variations of roller 28. It may therefore be unnecessary to monitor or control the temperature of roller 28 during lamination processing using a thermal insulating layer. A lamination processing kit including a thermal insulating layer 30 and an adhesive layer 16 may also be provided, as shown in Fig. 3. The printed substrate is positioned between the thermal insulating layer and the adhesive layer, with the printed ink layer positioned adjacent the adhesive layer. The lamination processing kit, with the printed substrate positioned therein, may then be processed by application of heat and pressure. In lamination processing assemblies of this type, the adhesive layer is preferably provided as a coating on transparent film 18 and the adhesive layer and transparent film are simultaneously applied to the printed substrate. Additionally, the lamination processing assembly may include a cover sheet 32 comprising a flexible sheet material having a relatively low thermal resistance positioned adjacent the transparent film. Preferred cover sheet materials include Vellum, or the like, that readily conduct heat from heated roller 26 to the transparent film and adhesive layer. The cover sheet preferably has a thickness less than that of the thermal insulating layer. Thicknesses of about 10 to about 100 microns are suitable, and thicknesses of about 50 to 75 microns are preferred. Multiple sheets comprising the lamination processing kit may be joined along one edge, such as at edge 31, to facilitate accurate alignment of the various sheets and the printed substrate. Lamination processing kits of this type may be provided as single use assemblies that facilitate convenient handling and improve thermal energy management during lamination processing. Fig. 4 illustrates another processing apparatus according to the present invention comprising a pressure application roller assembly 34 and a stationary platen 36. A resilient support means 38 may be mounted on a substrate contact face of platen 36 and/or provided as an outer surface layer on roller assembly 34. Roller 34 is preferably constructed from a rigid material such as stainless steel, or the like. Rollers having a diameter of about 2.5 cm are preferred. Platen 36 preferably has dimensions that are slightly larger than those of printed substrates to be processed. Platen 36 and/or roller 34 may be heated during processing to a temperature that melts the adhesive layer. A printed substrate and an adhesive coated protective film are positioned between platen 62 and roller 34 for processing. The adhesive layer is preferably positioned adjacent the heated surface during lamination processing. The surface adjacent to the printed substrate may be thermally isolated from the heated surface to prevent melting of the printed ink layer. During processing, roller 34 traverses the upper surface of platen 36 along a path substantially parallel to the contact surface of resilient support means 38 and preferably exerts a pressure of about 70 to about 700 kpascals on the composite laminate components. A dual platen processing apparatus having composite laminate components positioned therein for processing is illustrated in Fig. 5. The processing apparatus comprises a first platen 42 and a second platen 44 mounted for movement relative to one another between a substrate insertion position, wherein the first and second platens are in a spaced apart relationship, and a pressure application position, wherein the platens apply a substantially uniform pressure over the surface area of a printed substrate 12. A dual platen processing apparatus of this type may be utilized in a variety of orientations, provided that the first and second platens are positioned so that their contact surfaces 43 and 45, respectively, are substantially parallel to one another in the pressure application position. Resilient support means having dimensions at least co-extensive with those of substrate 12 is preferably positioned on one or both of the platen contact surfaces. Where the adhesive layer comprises a hot melt adhesive, one or both of platens 42 and 44 are heated to preferred processing temperatures that cause the hot melt adhesive to flow and bond. Preferred processing temperatures are preferably below the melting point of the printed ink layer. It is preferred that the platen contacting protective film 18, shown as platen 42 and Fig. 4, is heated to suitable processing temperatures, while platen 44 contacting printed substrate 12 is not actively heated. In the embodiment shown, platen 44 contacting printed substrate 12 preferably is not substantially passively heated as a result of its proximity to heated platen 42. Pressure may be applied to platens 42 and/or 44 in any convenient manner. For example, platens 42 and 44 may be incorporated in a conventional platen press design, wherein a manual or automatic actuator applies force to at least one of the platens to exert pressure in a direction substantially perpendicular to the contact surface during lamination processing. Substantially uniform pressure is applied simultaneously to the entire surface area of the composite laminate components by means of the dual platen apparatus. Processing times using a dual platen apparatus are reasonably short as a result of the large contact area. The composite laminate produced according to methods of the present invention exhibits numerous practical advantages. It is not subject to offset or abrasion problems because the printed ink layer is protected. Laminated composite transparencies are more durable over extended storage periods. Additionally, the laminated composite product can be temporarily or permanently marked with inks or the like, and borders, logos, and the like may be provided on the transparent film and incorporated in the laminated composite product. While in the foregoing specifications, this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purposes of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein may be varied considerably without departing from the basic principles of the invention.

Claims: A method for processing substrates (12) printed with an ink layer (14) having a non-planar surface topography, the method comprising applying an adhesive layer (16) on the surface of the printed substrate (12), the adhesive layer (16) having a first surface that conforms and bonds to the non-planar surface topography of the ink layer (14) and an opposite, substantially planar surface arranged substantially parallel to the plane of the substrate (12); and applying a substantially planar transparent film (18) to the planar surface of the adhesive layer (16). A method as claimed in Claim 1 and including the step of heating the adhesive layer (16) during its application to the printed substrate (12) to a lamination temperature at which the adhesive layer (16) conforms and bonds to the non-planar surface topography of the ink layer (14), the printed ink layer (14) being maintained in a substantially solid condition during application of the adhesive layer (16). A method as claimed in Claim 1 or Claim 2 and comprising applying pressure to the printed substrate (12) during application of the adhesive layer (16) thereto. A method as claimed in Claim 2 or Claim 3 wherein the transparent film (18) in the form of a composite with adhesive layer (16) is contacted with a heatable contact surface (26) whereby the adhesive layer (16) is heated to lamination temperature during application of the adhesive layer (16) to the printed substrate (12) and wherein the printed substrate (12) is contacted with a second surface (28) having a temperature not greater than the lamination temperature during application of the adhesive layer (16) to said printed substrate (12). A method as claimed in Claim 4 wherein both the second surface (28) and the heatable contact surface (26) are in the form of rollers. A method as claimed in Claim 4 or Claim 5 and comprising positioning a thermal insulating layer between the printed substrate (12) and the second surface (28). A method as claimed in any preceding claim and comprising applying to the printed substrate (12) about 140 to about 420 kpascals pressure during application of the adhesive layer (16) thereto. A method as claimed in any preceding claim wherein the adhesive layer (16) and the transparent film (18) are applied simultaneously to the printed substrate (12). A printed substrate comprising a print substrate (12) printed with an ink layer (14) having a non-planar surface topography, an adhesive layer (16) provided upon the printed substrate (12) and having a first surface conforming and bonded to the non-planar surface topography of the ink layer and preferably also to the underlying print substrate (12) and a second and opposed substantially planar surface disposed substantially parallel to the plane of the print substrate (12), and a substantially planar transparent film (18) disposed over and secured to the substantially planar second surface of the adhesive layer (16).

Inventors: HIRSCHY LINDA M, MARTENSON DAVID D, REEVES BARRY D, RISE JAMES D, TITTERINGTON DONALD R, HIRSCHY, LINDA M., MARTENSON, DAVID D., REEVES, BARRY D., RISE, JAMES D., TITTERINGTON, DONALD R.
Applicants: TEKTRONIX INC, TEKTRONIX INC.
Application year: 1992
Main classification: B41J2
IPC codes: B41M5, B41M7, B41J29, B41J2