MXPA96001132A - Method to transfer thermally printing on a metal substrate and article manufactured through the mi - Google Patents

Abstract

A method for thermally transferring printing onto a metal substrate surface, and an article such as a cigarette lighter containing that impression. A white coating followed by a clear coating is applied to the surface of the substrate, and the print is thermally transferred from a transfer medium onto the surface of the substrate. The coatings are preferably applied electrostatically

Description

METHOD FOR THERMAL TRANSFER PRINTING ON A METAL SUBSTRATE AND ARTICLE MANUFACTURED THROUGH THE SAME The present invention relates generally to thermal transfer printing, sometimes referred to as sublimation, thermostatic, or dye diffusion printing. More particularly, the present invention relates to thermally transferring printing onto a metal substrate such as, for example, thermally transferring a color image onto a cigarette lighter. In the process of printing by dye diffusion, the color images are pre-printed on a reverse transfer medium using thermal transfer inks. The conventional process is illustrated in Figure 1. The substrate 12 to be printed is placed on a block 16 of heat resistant resilient material. The printed medium 10, commonly referred to as a transfer, is placed on the substrate 12, and is subjected to heat and pressure, as illustrated in item 14, by means of a rigid heated platen 18. In this manner the transfer 10 is sandwich between the platen 18 and the substrate 12 for the thermal transfer of the print from the transfer 10 on the substrate 12. When the transition temperature of the printed dyes is reached, the dyes are gasified or liquefied and migrate from the transfer 10. to the substrate 12 being printed, and are absorbed into the surface of the substrate. The dye diffusion printing process is commonly used in the printing of clothing and accessories, by clothing manufacturers and specialty stores. Unlike other surface printing methods, the property of the substrates for dye diffusion printing is limited by their absorption and receptivity characteristics for the dyes that are being used. As a result, the process has historically been limited to the transfer of print onto fabric. When the transfer between the platen 18 and the substrate 12 for dye diffusion printing is walled, as illustrated in Figure 1, the transfer paper 10 undesirably acts as an insulating thermal barrier between the heat source (platen) and the part (substrate) that is being printed. See U.S. Patent Nos. 5,260,127 to Umise et al., And 5,322,751 to Chou et al., Which are incorporated herein by reference in connection with this thermal barrier effect. U.S. Patent No. 5,336,658 to Edwards, which is incorporated herein by reference, discloses a thermal transfer printing receptor comprising a substrate containing metal salts in metal particles or oxides, a polymeric interlayer protecting an acidic polymer composition, and a dye receptor polymer receiving layer containing a cross-linked silicone release system, and having a softening temperature lower than the temperature used during printing. It is reported that the purpose of the interlayer is to alleviate the problems with the effectiveness of the release system when the substrate contains metal oxides or particulate metal salts. None of the substrates described are metallic. In one example, a substrate has a white coating of rutile-titanium dioxide dispersed in a polyester urethane binder. Since Edwards process dyes penetrate the pigment-containing coating, any amount of pigment in it would be in competition with the dyes. As a result, the color density can be sacrificed and the results washed. Edwards' polyester urethane binder would require a solvent system, so that it could be applied in a liquid form. Solvents compatible with polyester urethane resins are generally considered very aggressive and dangerous. Another technique that may be of interest is the Patents of the United States of North America Numbers 5,096,877; 5,262,231; and 5,314,862. The latter patent describes a transparent layer and a white opacifying layer laminated on a thermal transfer sheet. The absorption characteristics and the receptivity for metal dyes are such that they must first be coated with typically a clear coating before they can be printed by diffusion. The impressions on these coated metals have undesirably been of a metallic appearance and with a limited density and color definition, and the entire color scale has been limited. In accordance with the foregoing, it is an object of the present invention to provide a high-quality thermal transfer of printing onto a metallic object without resulting in the metallic appearance of the printing. It is another object of the present invention to produce full color prints high resolution and high density on metal objects. It is a further object of the present invention to eliminate or reduce the use of hazardous solvents during this process. It is still another object of the present invention to provide this printing in an economical manner. In order to provide a high quality printed metal object without the metallic appearance of the printing, in accordance with the present invention, a white coating is then applied and then a transparent coating to the metal object, after which the printing It is thermally transferred on the object. The white coating, as well as the transparent coating, are preferably applied electrostatically, whereby a hazardous solvent is not required. Heat is transferred from the heat source through the metal object to the transfer medium, whereby the metal object can reach a suitable temperature before heat is supplied to the transfer sheet to obtain effective and consistent results. The foregoing and other objects, features, and advantages of the present invention can be found in the following detailed description of the preferred embodiments thereof, when read in conjunction with the accompanying drawings, wherein the same reference numerals denote the same parts or similar parts through all the different views.

In the Drawings: Figure 1 is a schematic sectional view illustrating a thermal transfer printing process in accordance with the prior art. Figure 2 is a schematic sectional view illustrating a thermal transfer printing process in accordance with the present invention. Figure 3 is an enlarged partial schematic sectional view of the metal substrate to be printed and the transfer medium.

Detailed Description of the Preferred Modalities. Referring to Figures 2 and 3, a metal substrate that is being printed by dye diffusion according to the present invention is illustrated in item 20. The printed image, illustrated schematically at point 22, is contained in reverse on a surface 24 of a transfer medium 26, whose surface 24 is brought into contact with the surface of the rigid substrate 28 to receive the print 22. "Printing" means that not only includes letters and numbers and other symbols, but also some images, such as those provided by photographs. The substrate 20 and transfer 26 are placed between a rigid heated platen 30 and a heat resistant resilient block 32, and heat and pressure, as illustrated in item 34, are suitably applied to transfer the print 22 onto the substrate 20. When the transition temperature of the printed dyes is reached, the dyes are gasified (or can be such that they liquefy) and migrate from the transfer 26 to the surface of the substrate 28 to be printed and absorbed on the surface of the substrate 28. The possibility The printing of the substrates by using dye diffusion printing is limited by its absorption and receptivity characteristics for the dyes that are being used. This has historically resulted in the colorant diffusion printing process being limited in general to the printing of cloth substrates. The application of transparent coatings to metals to allow the absorption and receptivity of the dyes has still undesirably resulted in prints on metals being of a metallic appearance with a limited density and color definition, and with a limited full-color scale . Referring to Figure 3, in order to provide a higher quality print on the metal substrate 20 without the metallic appearance, in accordance with the present invention, first a white opaque base coat, illustrated at 40, is applied to the surface of the substrate 28, to provide maximum adhesion and coverage on the metal, the white coating providing opacity to eliminate metallic appearance, and allowing a full color scale to be printed on it, the coating serving as the white color. The pigment for white base coat 40 can be titanium dioxide or another suitable pigment. Then a clear topcoat, illustrated at point 42, is applied on the white layer 40, to provide maximum receptivity to the heat transfer dyes with minimal loss and color bleeding. The transition temperature of the finishing layer 42 is preferably close to the gasification temperature of the dyes in the transfer 26, such that the coatings can be re-milled during the transfer printing process to promote transfer and improve the color density. For example, the finish layer 42 can be a polyester resin having a transition temperature of about 201.6 ° C, which is close to the typical gasification temperature of about 204.4 ° C of the dyes. A polyester urethane binder for the finish coating would require a solvent system, so that it could be applied in a liquid form. Solvents typically compatible with polyester urethane resins are considered very aggressive and dangerous. In order to eliminate the safety and environmental problems inherent in the application of conventional solvent-based polyester urethane coatings, as well as other solvent-based coatings, in accordance with the present invention, coating 42, as well as coating 40, are electrostatically applied in a suitable manner in accordance with principles commonly known to those of ordinary skill in the art to which The present invention pertains, the metal substrate being electrically conductive to allow this electrostatic application. The transparent coating 42 is preferably a clear polyester resin that has been milled to a powder. The electrostatic application of the white basecoat 40 has the additional advantage of providing a uniform application on the surface of the substrate 28, so that a printed image of higher quality can be achieved. The white basecoat 40, alternatively, however, can be applied as a water based pigment. It should be noted, from Figure 1, that the conventional dye diffusion printing process shown therein requires that the thermal conductive path of the heat in the heated heated stage be through the transfer medium, and then towards inside the substrate that is being printed. This heating of the transfer sheet from the back side results in the paper of the transfer sheet acting in an inconvenient manner as an insulating thermal barrier between the heat source and the part being printed. In addition, the rigid stage will not conform to an irregular substrate surface, thus inhibiting heat transfer and transfer of the print. Referring to Figure 2, in order that the metal substrate 20 can conveniently reach a suitable temperature before heat is supplied to the transfer sheet 26, in accordance with a preferred embodiment of the present invention, the source of Heat 30 is applied directly to the metal substrate 20, i.e., the substrate 20 is placed between the heat source 30 and the transfer sheet 26, such that heat is transferred from the heat source 30 through the substrate 20. and up to the transfer means 26. This also conveniently places the resilient heat resisting block 32 following the transfer 26, such that it conforms to an irregular substrate surface 28 for better heat transfer and transfer of the print . The use of the conventional silk mesh process to provide printing directly on the substrate using wet inks (without involving the transfer sheet) requires a mesh for each color, requiring the meshes a record that is difficult and results in rejections if the meshes are not recorded properly. This process also does not allow shadows or halftones, and does not provide images that look like photographs. In order to achieve better color densities and mesh line definitions, while eliminating these registration problems, in accordance with a preferred embodiment of the present invention, the transfer 26 is printed using four-color lithographic offset printing, which is a process commonly known to those of ordinary skill in the art to which the present invention pertains. In this process, the image that is going to be applied is explored and then decomposed into colored points through computerization. Then a printing plate is generated for each of the three primary colors and the color black. Then each color is printed in turn in the respective stations. The printing plates are kept captive, in such a way that there are no problems of registration. The printing inks used may be the same inks that are commercially available and are conventionally used for printing by diffusing dye onto fabric. For example, these inks can be commercially available sublimation inks in Superior Printing Inks, Inc. of Cheektowaga, New York. The carrier medium 26 is suitably a conventional paper material that maximizes performance and eliminates adhesion to the surface of the coated substrate 28. The high receptivity resulting from the coating and the maximum performance characteristics of the carrier medium are desired to allow transfers to be carried out. print in better color densities and definitions of the mesh line.

In order to provide a finer grain, so that a clearer and sharper image can be printed, according to an alternative embodiment of the present invention, the transfer sheet 26 is printed by using a process commonly known as a "continuous tone" process that prints stripes rather than dots. This process is commonly known to those of ordinary skill in the art to which the present invention pertains. There is a full-color continuous tone printer commercially available from Eastman Kodak Company of Rochester, New York, and identified as a 1525+ copier / printer. This printer preferably includes digital imagery, in such a way that the cost of printing can be reduced. It should be understood that, although the invention has been described in detail herein, the invention may be incorporated in another manner without departing from its principles, and these other embodiments actually fall within the scope of the present invention, as defined in attached claims.

Claims (18)

1. A method for applying printing onto a metal substrate surface, which comprises the steps of: (a) applying a white coating to the surface of the substrate, (b) applying a transparent coating on the white coating, and (c) transferring thermally printing from a transfer medium on the surface of the coated substrate.

2. A method according to claim 1, which further comprises selecting a pigment for the white coating which will be titanium dioxide.

3. A method according to claim 1, which comprises electrostatically applying the white coating.

4. A method according to claim 1, which comprises electrostatically applying the transparent coating.

5. A method according to claim 1, which comprises electrostatically applying the white and transparent coatings.

6. A method according to claim 1, which further comprises selecting the transparent coating to be composed of a polyester resin.

7. A method according to claim 1, which further comprises selecting the transparent coating to have a transition temperature that is substantially equal to the gasification temperature of the dyes in the transfer medium. A method according to claim 1, which comprises thermally transferring the colored print from the transfer medium onto the surface of the coated substrate. A method according to claim 1, wherein the step of thermally transferring the print comprises transferring heat from a heat source through the substrate and into the transfer medium. A method according to claim 1, wherein the step of thermally transferring the print comprises placing the transfer medium between the surface of the substrate and a resilient member to form the resilient member to an irregular substrate surface. A method according to claim 1, wherein the step of thermally transferring the printing comprises applying the transfer medium to the surface of the substrate, applying a resilient member to the transfer medium to form the resilient member to the surface of the substrate , and applying a heat source to an opposite surface of the substrate to transfer heat through the substrate and to the transfer medium. 12. A method according to claim 1, which further comprises forming the print on the transfer medium by lithographic offset printing. 13. A method according to claim 1, which further comprises forming the print on the transfer medium by continuous tone printing. A method according to claim 1, which further comprises forming the impression on the transfer medium by printing continuous-tone digital imagery. 15. A manufacturing article comprising a metal substrate having a surface, a white coating on the surface of the substrate, a transparent coating on the white coating, and elements defining the printing on the surface of the coated substrate that has been transferred thermally on it. 16. An article according to claim 15, wherein the white coating is composed of titanium dioxide. 17. An article according to claim 15, wherein the printing is color printing. 1

8. An article according to claim 15, wherein the transparent coating is composed of polyester resin.