Patent Publication Number: US-6340504-B1

Title: Process for making a radiation-cured coated article

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of provisional application 60/101,807 filed Sep. 25, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a process of coating a plastic or high pressure laminated substrate with a radiation-cured sublimatable coating and more particularly relates to a process which provides a plastic or high pressure laminated substrate with a coating which is capable of accepting sublimatable inks by means of dye sublimation. 
     It is known in the art to create sublimated products with radiation-cured coatings by adhering them to wood, ceramic, or metal substrates. These coatings which are typically a polyester, polyurethane or an acrylic are then susceptible to receiving designs of selected indicia transferred into them wherein the use of a sublimatable ink transfer and a heat press is designed to provide sufficient heat and pressure to make the transfer possible. However, at the temperatures normally employed in preparing the coating or in transferring the sublimatable inks to plastic substrates, plastic substrates are normally affected adversely. For example, the plastic substrates can accept these images prepared by die sublimation but are not durable and require additional protective layers after the sublimatable ink has been transferred thereon. It is known that certain plastics in film form such as MYLAR and polyethylene terephthalate (PET) can accept sublimation images without a coating. However, these films are typically thin and laminated to a substrate after sublimation and are relatively expensive. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a plastic substrate coated on at least one side with a radiation-cured coating capable of accepting sublimatable inks which diffuse into the radiation-cured coated layer. 
     It is even another object of the present invention to provide a plastic substrate having at least one side coated with a radiation-cured layer capable of withstanding the temperatures required for transferring sublimatable inks into the radiation-cured coating. 
     It is also an object of the present invention to provide a process for making printed articles by means of die sublimation including one or more coatings prepared by radiation curing. 
     More particularly, the present invention is directed to a process for making a cured coated article which may be a plastic or high pressure laminate which may include a plastic, the process including coating a plastic or high pressure laminate substrate with a radiation curable top coat and then subjecting the top coat to a curing step which is either with an electron beam, ultraviolet radiation or a combination thereof. A sublimatable ink may then be transferred into the top coat. 
     Even more particularly, the present invention is directed to a cured coated plastic or high pressure laminate article which is comprised of a plastic or high pressure laminate substrate coated with a radiation cured coating wherein the radiation cured coating includes an outer surface susceptible to having with a sublimatable ink diffused therein. The radiation cured coating may include ultraviolet inhibitors therein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the invention will be had upon reference to the following description in conjunction with the accompanying drawings in which like numerals refer to like parts throughout the several views and wherein: 
     FIG. 1 is a cross-sectional view of the substrate coated according to a process of the invention showing the transfer of the sublimatable ink from a paper backing; and, 
     FIG. 2 is a cross-sectional view of the substrate of FIG. 1 after the sublimation ink has been transferred. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in the figures, a substrate material  12  with a thickness range generally of 0.005 to 0.250 inches is coated with a radiation-curable clear topcoat  16 . The substrate  12  is either plastic or a high pressure laminate which may include a plastic. For example, the high pressure laminate is generally a thermally fused paper or a phenolic fused into a paper under heat or the like. Top coat  16  may include ultraviolet inhibitors therein, such as, for example, benzothiazoles, hindered amine light stabilizer and the like. In the preferred state, this substrate is a fiberglass reinforced plastic (FRP) with a fiberglass content of 8-30% or a phenolic impregnated resin which is optionally coated or filled with a filling or sealing coating  14  of a polyester or epoxy acrylate to fill in irregularities of the substrate  12 . The optional fill layer  14  is generally ultraviolet (UV) radiation cured with 8 lamps at 300 watts intensity and a line speed of 65 feet per minute. The substrate  12  is then sanded both to increase smoothness and to provide a better physical bond for subsequent layers. 
     The filled substrate  12  may then be coated with a white layer  15 , typically a polyester or urethane acrylate electron beam (EB) or UV curable product of 0.5 to 4 mils, preferably about 1.5 mils in thickness and then overcoated with a clear top coat  16 . The top coat  16  may be one of a number of clear UV or EB/UV curable products including, but not limited to, polyesters, urethane acrylates, polyester acrylates, and epoxy acrylates as well as cationic cured systems which are known in the art. The preferred coating is a urethane acrylate/polyester acrylate blend. The top coat layer  16  will generally be about 0.2 to 6 mils but with a preferred thickness of about 2.8 mils of an acrylate. The coated substrate is then generally cured with an electron beam with preferred settings at 245 KV and 50 milliamps and a line speed of 90 feet a minute, preferably in an inert atmosphere, such as nitrogen. Alternatively, if a lower gloss is desired the product can be cured with a similar line speed and electron beam settings, but with a mixed nitrogen/oxygen atmosphere, preferably of about 94% nitrogen and 6% oxygen. This would then be followed by a UV cure in a fully inserted nitrogen atmosphere with 6 lamps at 200 watts and a line speed of 100 feet per minute to complete the curing process. 
     Another curing method is with ultraviolet radiation only. This cure can be carried out in an atmosphere ranging from 0 to 100% air with the balance typically made up of nitrogen. Lamp intensity will usually vary from 200 watts to 700 watts/inch cure systems with a typical setting of 300 watts/inch. If a white layer is utilized, one preferred curing method would be with a gallium doped mercury bulb UV system, typically at 300 watts/inch in air. It would typically be sanded after curing prior to the application of the clear topcoat or alternatively, the white coat may be slightly undercured to allow for a chemical bond between the two coating layers. 
     The electron beam or UV radiation coated substrate is now susceptible to the receipt of a sublimatable ink from a paper backed material and is identified in FIG. 1 by the numeral  20 . The paper backed material  20  includes the sublimatable ink  18  thereon which is to be transferred to the top coat  16 . The paper backing  20  with the ink  18  thereon is placed onto the top surface of the top coat  16  and under heat and sufficient pressure to hold the backing  20  firmly against the substrate  12 . The ink is transferred to the clear top coat  16  usually at from 350° to 400° F. 
     FIG. 2 shows the finished product after the sublimatable ink  18  has been transferred from the paper backing  20 . As shown, the sublimatable ink  18  penetrates into the clear top coat  16  generally to a sufficient depth so as to be protected against the elements. 
     Some of the different articles which may be printed with the sublimatable ink in accordance with the present invention includes flexible plastic materials or other high pressure laminates for license plates, luggage tags, identification badges, signage, and the like. 
     It is realized that in the explanation of the present invention first and second coatings are exemplified. However, when the article or substrate  12  is a non-porous type article, a first coating or fill may not be necessary and the top coat  16  may be applied directly to the substrate  12 . 
     The foregoing detailed description is given primarily for clearness of understanding and no unnecessary limitations are to be understood therefrom for modifications will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit of the invention and scope of the appended claims.