WO1994018002A1 - Method for melt printing dyes on plastic or plastic coated substrates - Google Patents

Abstract

A method and apparatus (310) are disclosed for printing a meltable disperse dye image onto and into a workpiece (300) which comprises a metal substrate (204) coated on a surface to be printed with a disperse dye receptive plastic. An assembly is prepared of: 1) the workpiece (300), 2) a flexible sheet (108) bearing on one side one or more meltable disperse dyes in the mirror image of the image which will be melt printed, positioned with its dye image-bearing side adjacent ot the workpieces's printable plastic surface, and 3) a resiliently flexible membrane (16) overlaying the surface of the dye-bearing sheet (108) opposite its dye-bearing surface (206). The space between the dye-bearing sheet (108) and the membrane (16) is then evacuated to cause the membrane (16) to press the dye-bearing sheet (108) tightly against the printable plastic surface. A heat and pressure applying means (20), e.g., a heated plate (200) having a pressure-applying surface (206), is then pressed against the membrane (16) over the workpiece (300), while maintaining the vacuum, to cause the meltable disperse dye to melt onto and into the workpiece's printable plastic surface.

Description

METHOD FOR MELT PRINTING DYES ON PLASTIC OR PLASTIC COATED SUBSTRATES

BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to melt printing on plastic or plastic coated substrates.

More particularly, the present invention relates to melt printing techniques for printing dye images on plastic or plastic coated substrates, such as telephone, typewriter, or computer key arrays, and/or articles whose printable surfaces are appreciably greater in area than such key arrays, and to a system for cooling portions of the printing apparatus to prevent workpiece warpage and image mis-alignment. Melt printing is now well known in the art, and in one commercially important embodiment is typically done by heating meltable disperse dyes to temperatures above their melting points to liquify them and effect the transfer of the melted dye onto and into a plastic surface. The assignee of the present invention holds patents on highly improved techniques of melt printing, using heat and pressure, on plastic surfaces; see Durand U.S. Patent Nos. 4,670,084 ("the '084 patent") and 4,668,239 ("the '239 patent"), and Durand, et al. U.S. Patent No. 4,587,155 ("the '155 patent").

The '239 patent teaches preferred techniques of melt printing which involve imparting images formed by certain preferred meltable disperse dyes to a dye receptive plastic material.

Specifically, the '239 patent teaches that a dye forming the mirror image of the image to be printed on a plastic surface is first applied to a flexible paper sheet. Next, the image-bearing paper sheet is placed on the plastic surface, dye side down, then pressed (at 1-2 psi) and heated against the plastic surface. The heat melts the dye while the pressure forces the dye, once melted, to diffuse into the plastic surface. Heat and pressure also cause the image-bearing paper sheet to be permanently deformed to the configuration of the plastic surface on which it is printing, particularly when the sheet is one containing a thermosetting polymer intermixed with paper pulp. The preferred printable plastic materials used when practicing this technique are substantially or entirely crystalline polymers, but amorphous polymers and mixtures of crystalline and amorphous polymers can also be used.

The '084 patent teaches a further improved method of printing dye images on plastic surfaces. A flexible membrane is applied over the flexible paper sheet which bears the dye image. The image- bearing paper sheet is located on positioning pins to hold it accurately in registration with the plastic surface being printed ("the workpiece") , and once the sheet is accurately located, a vacuum is pulled underneath the flexible membrane to pull this membrane tightly against the paper sheet, the latter then being, in turn, pulled against the workpiece. This vacuum technique described in the '084 patent provides close contact between the image-bearing paper sheet and the plastic surface on which printing is to be conducted. Heating is accomplished when practicing the '084 patent's method using heaters which radiate heat while the paper sheet bearing a mirror image, in dye, of the image being printed is being pulled against the printable plastic surface. The combination of heat and vacuum also deforms the image-bearing paper sheet to the shape of the printable plastic surface. The invention disclosed in the '084 patent has proven to be enormously successful commercially. This invention depends in part for its proper operation, on a tight vacuum being achievable between the image-bearing paper sheet and the flexible membrane to force the sheet down against the surface of the workpiece. In a preferred embodiment, the '084 patent describes the use of a keyboard as the workpiece. Typically, telephone, typewriter and computer keys are relatively small, and the spaces between the rows of such keys readily permit a vacuum to be applied evenly over the entire flexible membrane. But as the surface of the workpiece increases in area, it becomes increasingly difficult to exert sufficient continuous pressure across the flexible membrane and the image-bearing paper sheet by vacuum alone to insure optimum print quality on the workpiece's printable surface.

The ^»084, '239 and '155 patents do not specifically address printing on large plastic or plastic coated substrates, e.g., plastic coated metal plates. And while it is believed that the teachings of the '084 patent could be used to print high quality images on such substrates, the present invention improves on the techniques taught in the •084 patent when large plastic or plastic coated objects are the intended printable substrates.

In light of the melt printing techniques known in the art prior to the present invention, applicants believe that if one skilled in this art were to attempt to melt print an image onto a large substrate, an appliance control display plate, for example, having a printable surface appreciably greater in area than those of workpieces, typically telephone, typewriter or computer keys, to which melt printing techniques have hitherto been applied — although applicants are unaware of any such attempt — the technique that would suggest itself would be a hot stamp method such as that discussed in the '239 patent. The problem with using hot melt stamp printing on large substrates, however, would be that the images produced would undoubtedly have an unacceptably high percentage of rejects due to ghosting: the formation of two dye printed images on the workpiece¹s printable surface, one slightly out of register with the other.

Ghosts in a melt printed image can result, first of all, from slight movements of the image- bearing paper sheet on the printable substrate, movements that can occur at several points in the melt printing process. For example, ghosts can occur at the moment the pressure-applying surface of a hot stamp is lifted from the workpiece, due to the image-bearing paper sheet's tendency to adhere momentarily to the hot stamp's surface and thus be lifted slightly from the workpiece's printed surface as well. When the paper sheet falls back onto the hot workpiece surface, it can do so in a slightly different orientation than it originally had, thus causing ghosting. To substantially or entirely avoid this would require an as yet undeveloped technique for tightly holding the paper sheet to the workpiece surface while the hot stamp was being removed. Ghosts can also result from variations in the flatness of the hot stamp's surface, or in the flatness of the printable surface, or both.

A hot stamp, if used by itself to melt print a large printable surface, would have to rely for its proper operation on the pressure applying surface of the stamping structure being precisely the same shape as the surface on which melt printing is to be accomplished. If the printable surface were flat, for example, the pressure applying surface would also have to be flat. More generally, the two surfaces would have to be in registry with one another, meaning that they would both have to be the same precise shape. Since it is of course impossible to obtain perfect registry between any two surfaces, no matter how flat, some kind of approximation would have to be made, and the more time and money one would spend on perfecting such a process, the better the approximation would be. However, applicants have found that as the printable surfaces of workpieces subjected to melt printing increase in area, it becomes even more difficult to bring such surfaces into perfect registry with the pressure-applying surface of a hot stamp.

Furthermore, the '239 patent teaches the use of pressures of 1 to 2 psi, and not higher, when using the hot stamping technique to melt print. Higher pressures, if used in operating the hot stamping apparatus disclosed in the '239 patent, although they undoubtedly would be conducive to obtaining better melt printed images, could cause increased movement of the image-bearing paper sheet in relation to the printable surface.

To the best of applicants' knowledge, melt printing has never been used successfully to transfer images to large plastic or plastic coated substrates, such as appliance control display plates of the type found in convection ovens, washing machines, automatic clothes dryers, microwave ovens, and like devices, or to chainsaw parts, Venetian blind slats, decorative containers and indeed any large surface on which one wishes to print a design for ornamental or utilitarian purposes. The advantages obtainable by now being able to use melt printing for such purposes are numerous. In the case of appliance control display plates, for example, the image-bearing sheet can be reverse printed in any language. Hence, the language in which instructions are given can be changed simply by changing the image-bearing sheet. Heretofore, such plates or panels have been made by first enamel-coating a metal substrate and then printing instructions, logos, etc. over the enamel coating. Aside from being a significantly more expensive method than that of the present invention, this prior art method also involves the use of large quantities of environmentally harmful solvents which must be disposed of in accordance with governmental regulations, if indeed they can still be used at all. The present invention provides means of avoiding the problems, summarized above, that would be expected to occur if the previously-known membrane plus vacuum method or hot stamping method were used to melt print images onto large printable plastic surfaces.

Thus, the melt printing method of the present invention, especially developed for accurate melt printing on large plastic surfaces, comprises: —providing a large workpiece having a melt printable plastic surface;

—positioning over the plastic surface of the workpiece a flexible sheet, dye side down, bearing one or more meltable disperse dyes in the mirror image of the image which will be melt printed onto and into the plastic surface; -overlaying the dye-bearing sheet with a flexible membrane having a first surface and a second surface, whose function it is to further hold the dye-bearing sheet in its proper position relative to the workpiece, so that the first surface of the flexible membrane overlies the dye-bearing sheet;

-pulling a vacuum (achieving a negative pressure differential) on the space between the uppermost (non-dye-bearing) surface of the dye- bearing sheet and the underside (first surface) of the flexible membrane sufficient to pull the first surface of the flexible membrane down tightly over the dye-bearing sheet, thus forcing or biasing this sheet against the workpiece and holding it in place for proper image transfer; and

—applying — by means of a heated, preferably relatively flat plate having a pressure- applying surface, or other relatively flat heat and pressure transfer surface — heat and pressure to the upper (second) surface of the flexible membrane sufficient to melt the dye and, preferably, somewhat soften the section of the workpiece's melt printable plastic surface which is to receive the dye, thus transferring the dye image onto and into the plastic surface.

Heat transfer from the frame assembly to the workpiece(s) can disadvantagesouly affect the workpiece's characteristics, particularly those of its printable plastic layer(s) . To aid in avoiding this problem, a heat transfer system (such as water chilling) can optionally be incorporated in the support plate to reduce the temperature of the frame assembly during continuous operations, or, a heat transfer system can be directly incorporated into the frame assembly to further provide heat removal. By using such features or combinations thereof, the primary source of heat to the workpiece can be made to be the heat and pressure applying plate, and thus the heat reaching the workpiece can be specifically controlled to maximize dye transfer and minimize undersired effects.

Furthermore, applicant has found that heat transferred to the plastic member(s) before during and/or after the dye transfer process can disadvantageously warp the product which may tear the image bearing paper and may make it difficult to align the parts and/or register the images. In addition, heat transferred to metal parts of the apparatus in the vicinity of the product may cause disproportionate expansion which can in turn generate registration problems and/or may tear the paper bearing the dye images. Thus, undesirable heat transfer may occur which may result in the production of a sub-standard or even unsalable product.

To avoid the above-identified potential problems, it is an object of this invention to incorporate a heat exchange system in an apparatus of the type summarized above, thereby to minimize heat transferred to and/or accumulated by the member(s) being processed and in close proximity thereto. Indeed, applicant has found that by suitably controlling the temperature of the apparatus in the vicinity of the image receiving members, the above noted warping problem can be effectively avoided even during continuous operations. Furthermore, in spite of the peripheral temperature control, applicant has found that the above-described advantageous image transfer can effectively take place. Thus, in accordance with the invention disclosed herein, the heat transferred to the dye images and the heat transferred to the workpiece assembly can be effectively controlled to maximize dye transfer and yet minimize undesired distortion of the workpiece.

Thus, the foregoing and other objects of the invention are realized by providing an apparatus including a bed assembly having a surface for receiving a member with a dye bearing sheet thereon, a flexible membrane which is positionable in overlying relation on the dye bearing sheet on the member and on the portion of the bed assembly surface adjacent thereto, vacuum means for drawing the membrane into pressurized communication with the sheet to effect the pressurized engagement thereof with the member, means for heating the membrane to thereby simultaneously heat the sheet, the dye, and the member in order to transfer the dye to the member to produce the desired image thereon, and a heat exchange system to control the temperature of the workpiece, to avoid warpage and/or mis-alignment of the dye images.

It is, therefore, an object of the present invention to provide a new melt printing process.

It is also an object of the present invention to provide a new process for melt printing dye images onto and into plastic surfaces.

A further object of the present invention is to provide a new process for melt printing dye images onto and into plastic or plastic coated substrates whose surfaces are appreciably greater in area than those to which melt printing methods have hitherto been applied. These and other objects, as well as the nature, scope and utilization of the present invention, will become readily apparent to those skilled in the art from the following description, the drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a printing apparatus which can be used to practice the present invention, with the heat plate raised and the membrane lowered;

FIG. 2 shows a closeup of the table area of the apparatus of FIG. 1 with the membrane raised;

FIG. 3 shows a sectional view taken along line 3-3 of FIG. 1; FIG. 4 shows a sectional view taken along line 4-4 of FIG. 1;

FIGS. 5 and 6 are sectional views showing a plate for applying heat and pressure in contact with the flexible membrane for pressing a dye- bearing sheet against a workpiece;

FIG. 7 is a perspective view of another melt print apparatus in accordance with the invention, with a heat exchange system incorporated therein; FIG. 8 is an enlarged perspective view of the front portion of the apparatus with the membrane in the raised inoperative position;

FIG. 9 is a perspective view of a keyboard assembly received in a frame assembly and a dye bearing sheet which is receivable in overlying relation on the keyboard assembly;

FIG. 10 is a sectional view taken along line 10-10 in FIG. 7; FIG. 11 is an enlarged perspective view of a single key of the keyboard assembly illustrated in FIG. 9;

FIG. 12 is a sectional view taken along line 12-12 in FIG. 11;

FIG. 13 is a schematic sectional view of a plurality of keys with a dye bearing sheet and the flexible membrane overlaid thereon and a plurality of radiation emitters; FIG. 14 is an enlarged perspective view of a key having first and second printing surfaces and a die-cut dye bearing sheet;

FIG. 15 is a schematic sectional view illustrating the application of heat to a plurality of keys of the type illustrated in FIG. 14 utilizing radiation emitters having parabolic reflectors;

FIG. 16 is a schematic sectional view showing the heat exchange system that is incorporated in the support plate of the bed assembly; and

FIG. 17 is a schematic plan view of the heat exchange system provided in the bed assembly, in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION Preferred substrates to which melt printed images can be applied in accordance with the present invention include, inter alia, planar metal base members, e.g., plates or sheets made of metals such as aluminum, aluminum alloys, steel, brass, bronze, copper, or the like, coated on at least one of their planar surfaces with a melt printable layer of a softenable, dye-permeable, thermoplastic or thermoset material ("plastic"), e.g., thermoplastics such as polyethylene terephthalate, polybutylene terephthal^'ate, or other linear thermoplastic polyesters, polycarbonates, and nylons, such as nylon 6, nylon 6/6, nylon 6/12, and thermosets such as cross-linked, e.g., epoxy cross-linked, urea- formaldehyde, melamine-formaldehyde and phenol- formaldehyde resins, epoxy resins, alkyd resins and other thermoset polyester resins, and the like, as well as resin blends, e.g., a blend of a polyester with a polycarbonate. Bilayer coatings of thermoplastic or thermoset materials can also be used, e.g., a base coat of a high molecular weight epoxy resin cross-linked with a urea-formaldehyde, melamine-formaldehyde or phenol-formaldehyde resin, top coated with a printable oilless alkyd (polyester) resin cross-linked with a melamine- formaldehyde resin. In such bilayer coatings, the base coat can optimally be provided with a pigment and the second layer can comprise a somewhat clear resin. Since neither the composition nor the thickness of either the substrate (except in the circumstance indicated immediately below) or the printable plastic layer(s) is critical to the practice of this invention, any non-metallic substrate capable per se, or capable above a given thickness, of withstanding, without substantial deformation or other damage, the degree of heat and pressure applied to the workpiece necessary to cause adequate melting and diffusion of the disperse dye onto and into its printable plastic surface, and capable as well of being coated with the plastic layer that will receive the dye image, can also be used. Such substrates include plastics the same as or different than the ones used to coat non-plastic substrates, e.g., an all-polyester substrate, as well as wood, leather, ceramics, and the like.

In those instances where the plastic layer that will receive the dye image adheres poorly, or not at all, to a particular substrate, adhesives can be used to provide, in effect, laminated structures whose plastic surfaces can be melt printed in accordance with the present invention.

Typically, substrates having surface areas of from about 3 to about 10 square feet can easily be melt printed by the method of the present invention. Another way to describe this advantage provided by the present invention is that plastic surfaces four times or more larger in surface area that those customarily printed by prior art techniques such as those described in the '084, '239 and '155 patents can now be successfully melt printed. Indeed, the only limitations at present on the area of the plastic surface that can be decorated in accordance with this invention are those imposed by the sizes of commercially available flexible membranes, by presently available melt printing machines and their heater controls, and by other such extrinsic limitations. In theory, any size plastic surface can be melt printed successfully by the process of this invention.

The sheet bearing the meltable disperse dye image will usually be a slightly flexible cellulosic paper sheet, preferably one as noted in, for example, the '155 patent at col. 4, lines 40- 56, which contains a thermosetting polymer intermixed with the paper pulp thereof to make the sheet heat deformable, and preferably one which, as also noted in the '155 patent at from col. 4, 1. 57 to col. 5, 1. 11, is also coated, on the surface to which the meltable disperse dye is applied, with a cross-linkable polymer to stabilize the sheet against adverse effects caused by humidity. However, "papers" or sheet materials made in part from materials other than cellulosic fibers, such as glass fibers, polymer fibers or fibrids, and the like, can also be used as the dye-bearing sheet.

The meltable disperse dyes used in practicing the present invention are those which, as taught in the '155 patent (col. 3, lines 45-54), have melting points below and vaporization points above the thermal deflection temperature of the printable plastic surface. An illustrative listing of such dyes and dye types is found in the '155 patent at from col. 6, 1. 22 to col. 7, 1. 5.

The preferred resilient flexible membranes used in practicing the present invention are made of silicone rubber of any suitable thickness, e.g., from about 1/32 to about 1/16 of an inch thick, and suitable degree of flexibility that will provide membranes of adequate durability for repeated industrial use. Particularly suitable silicone rubbers include COHRlastic® silicone rubbers, e.g., COHRlastic® 9235 silicone rubber and the like (Connecticut Hard Rubber Co., New Haven, Connecticut) .

The temperature at which the melt printing process of the present invention can be practiced is not critical, other than as indicated hereinabove and in the '084, '239 and '155 patents with regard to the melting points and vaporization points of the meltable disperse dyes used in relation to the thermal deflection temperature of the plastic surface being printed. The temperature of the surface being printed when printing in accordance with this invention on a polyethylene terephthalate surface typically will range from about 325°F to about 375°F. Increasing the printing temperature from room temperature (about 25°C) to about 325- 375°F customarily takes from about 45-90 seconds, with printing taking place during this time. Preferably, printing will take place at from about 350-360°F, a temperature range reached in about 50- 60 seconds, following which the heat and pressure applying means is removed and the workpiece allowed to cool.

Likewise, the pressures employed can vary from about 35 psi to about 50 psi, and preferably the pressure at which printing takes place will be about 40 psi. As also indicated hereinabove, one significant advantage of the present invention is that pressures significantly greater than those taught by the prior art can be applied to ensure the printing of clear, sharp images on the plastic surfaces being coated, with minimal rejects.

Once a vacuum has been pulled between the flexible membrane and the image-bearing sheet, e.g., a vacuum of about 1 atmosphere (at least about 28 inHg) , the assembly of printable substrate, image- bearing sheet and flexible membrane will be subjected to the necessary heat and pressure to accomplish satisfactory melt printing. A preferred method of practicing this step is by bringing a heat and pressure applying means, e.g., a hot plate which can comprise two substantially flat metal plates having an electric heating element sandwiched between them, into contact with the upper surface of the flexible membrane over the workpiece. Printing surfaces and pressure applying means which are somewhat less than substantially flat, e.g.. somewhat concave or convex complementary surfaces, can also be used.

The vacuum pulled between the flexible membrane and the image-bearing sheet serves primarily to secure this sheet in the proper position for printing. The heat and pressure applying means provides the bulk of the pressure actually used, with heat, to accomplish melt printing. Because of the flexible membrane being pulled down by vacuum onto the image-bearing sheet, resulting in the image-bearing sheet's being more tightly and precisely held on the plastic surface being printed, the assembly can be subjected to greater pressures than possible when using prior art melt-printing methods. This too leads to better melt-printed images being obtained than hitherto possible.

In a preferred embodiment, a heat plate, attached to an air cylinder arrangement to produce the necessary pressure to force the heat plate into tight registry against the flexible membrane, will be used. Any differences in registry between the heat plate and the assembly are absorbed by the flexible membrane's being depressed by the heat plate.

A preferred apparatus that can be used to practice the method of the present invention for melt printing large workpieces in accordance with the invention is shown in and described hereinbelow with reference to FIGS. 1-6. This apparatus is identified as the apparatus 10 in FIG. 1.

The apparatus 10 generally comprises a base 12, a bed assembly 14 , a flexible membrane assembly 16 positionable in overlying relationship to the bed assembly 14, a vacuum assembly 18, and a heat and pressure applying means 20. The vacuum assembly 18 serves to evacuate the area between the membrane assembly 16 and the bed assembly 14 when the membrane assembly 16 is positioned in overlying relationship to the bed assembly 14. The bed assembly 14 and the membrane assembly 16 are positionable beneath the heat and pressure applying means 20 so that the latter can be lowered into contact with the membrane 16. When a workpiece 300 is appropriately positioned on the bed assembly 14, and a sheet 108 bearing a meltable disperse dye in the mirror image of a preselected image (not shown in FIG. 1) is overlaid on the workpiece 300, the apparatus 10 is operable to transfer the dye image from the sheet

108 to the workpiece 300 to produce the preselected image thereon. Specifically, by evacuating the area between the membrane assembly 16 and the bed assembly 14 using the vacuum assembly 18, next positioning the assembly of the membrane 16, the dye image-bearing sheet 108 and the bed assembly 14 under the heat and pressure applying means 20, and then energizing and lowering the heat and pressure applying means 20, heat and pressure are simultaneously applied to the dye image-bearing sheet 108 (FIGS. 2, 5 & 6) and the surface of the workpiece to transfer the dye from the sheet 108 to the printable surface of the workpiece on the bed assembly 14. FIGS. 1 and 2 show that the base 12 comprises a table-like structure having a top 22 and legs 24 supporting the remainder of the apparatus 10. Of course, any other suitable supporting structures can be used as well. The bed assembly 14 is most clearly illustrated in FIGS. 1, 2 and 3 and comprises a rectangular frame 26 and a support plate portion 28 which defines a supporting surface for receiving a workpiece or a plurality of workpieces in the apparatus 10 for the application of dye images thereto. A mounting assembly 42 is included in the bed assembly 14 for the mounting thereof on the base 12. The mounting assembly 42 is most clearly illustrated in FIGS. 1 and 2, and comprises a pair of slide rods 44 which are mounted in upwardly spaced rearwardly extending relation on the table top 22 with front mounts 46 and rear mounts (not shown) . Received on the rods 44 are front and rear slide members 48 and 50, respectively; front and rear cross members 52 and 54, respectively, extend between the two front slide members 48 and between the two rear slide members 50, respectively. Front vertical members 56 and rear vertical members (not shown) extend upwardly from the cross members 52 and 54, respectively, and are secured to the frame 26, whereby the frame 26 is slidably mounted on the rods 44. The membrane assembly 16 is hingedly mounted on the bed assembly 14 along the rear edge thereof as at 57 and comprises an outer frame 58 and a resilient, flexible membrane 60 which is clamped to the frame 58 by inner frame 62 which, in turn, is secured by several pivot screw/wing nut assemblies 64 and frame support 63, as illustrated in FIGS. 2 and 3. FIG. 3 shows the frame 58 to be of L-shaped cross-sectional configuration, and an inner frame 62 is dimensioned to interfit in the frame 58 so that the membrane 60 is captured therebetween and thereby clamped to the frame 58. Bonded to the outer frame 58 is a silicone rubber "V" seal 34. As will be further seen, the frame 58 is dimensioned so that when the membrane assembly 16 is located in overlying relation on the bed assembly, the V seal 34 is pinched therebetween in order to seal the periphery of the flexible membrane 60. When the membrane assembly 16 is so positioned over the bed assembly and a vacuum is drawn between the membrane assembly and the bed assembly, the relatively greater (atmospheric) pressure on the exterior (open V) side of the seal 34 tends to force the lower arm of the V into a tight sealing relationship with the frame 26. Conventional telescoping arms 66 extend between the bed assembly 14 and the frame 58 for maintaining the membrane assembly 16 in the upwardly hinged or open disposition, when desired, as illustrated in FIG. 2. Handles 68 attached to the frame 58 are used to manually close the membrane assembly so that it overlies the bed assembly 14.

The vacuum assembly 18 comprises a vacuum pump 70 which is mounted on the base 12 and which is actuated by a manual switch 72 mounted on the top 22. The vacuum pump 70 is connected through vacuum lines 74 to the vacuum ports 36 on the bed assembly 14 for drawing a vacuum in the area between the membrane assembly 16 and the bed assembly 14 when the membrane assembly 16 is in its lowered or closed position. Vacuum ports 36 are included, but not shown, in the support plate 28 in positions so as to directly underlie the workpiece or workpieces when placed on support plate 28.

The heat and pressure applying means 20 is shown in FIG. 1 mounted to a housing 76 within which a support structure 84 is mounted. The support structure 84 is preferably rigidly mounted to the housing 76 by screws or welding or the like since it will be supporting the high pressure which will be exerted by the heat and pressure applying means.

Guide posts 196 and 198 are attached to the housing 76, and to pressure heat plate 200, and accurately guide the movement of pressure heat plate 200. A pneumatic pressure piston and cylinder assembly 80 which receives pressure via pressure line 81 is attached to support structure 84. The operation of the pressure piston moves extending piston rod 82 downward, thereby moving the heat and pressure applying plate 200 downward. In operation, pressure line 81 and electric line 81a carry pressure and electrical power to the heat and pressure applying plate 200. Specifically, electric line 81a carries electric current to the plate 200 to energize and heat the heaters on same. Pressure line 81 is configured such that pressure therein causes movement of piston 80 downwardly which in turn causes the piston rod 82 to extend downward and toward membrane assembly 16 and bed assembly 14. Removal of the pressure on line 81 causes the piston rod 82 to retract towards its uppermost position. This return movement may be accomplished by a suitable spring (not shown) within the piston and cylinder assembly 80, reversed pressures in the cylinder, or the like. FIGS. 4 and 5 show detailed drawings of the heat and pressure applying plate 200. FIG. 4 shows, by a sectional view, the plate 200 to consist of three sandwiched and connected layers. Layer 202 and 204 are upper and lower metal plates. Layer 204 includes a pressure applying surface 206 which is a substantially flat surface in this embodiment, and is adapted to apply pressure and heat to the membrane assembly 16. A piston rod 82 is suitably connected to the plate 202. Sandwiched between the two metal layers 202, 204 is a resistive heating network 210 which preferably has its electrical connection at the location shown as 212 in FIG. 4. The electrical connection to point 212 causes an electric current to be passed through the resistive heating network 210 thereby effecting a heating thereof. Heat is conducted by the metal layer 204 to the pressure applying surface 206 so that this surface applies pressure due to the downward extension of the piston rod 82 as well as applying the heat caused by the resistive heating in layer 210.

The operation of the apparatus described above will now be described in detail. The operation begins by positioning the workpiece on the support plate portion 28 and overlying a sheet 108 bearing a meltable disperse dye, in an image which is the mirror image of the preselected image to be printed on the workpiece, so that the mirror image is in the desired orientation thereon. The positioning is done while the apparatus is in the open position shown in FIG. 2. The membrane assembly 16 is then moved to its lowered or closed position illustrated in FIG. 1. The switch 72 is then manipulated to actuate the vacuum assembly 18, whereby the membrane 60 is drawn into pressurized communication with the sheet 108 overlying the workpiece to effect the pressurized engagement of the sheet with the workpiece. The bed assembly 14 and the membrane assembly 16 are then moved rearwardly in the apparatus 10, so that the membrane 60 is disposed beneath the hood 78 and below pressure/heat assembly 20. The control box 86 actuates the pressure system to increase pressure in line 81. This causes the piston rod 82 to be lowered to move the heated heat and pressure applying plate 200 down with considerable force against the membrane 60, thereby applying pressure and heat to the membrane 60 and accordingly to the image-bearing paper sheet 108 (positioned above the workpiece 300) and the workpiece itself.

Pneumatic pressure and electric power are maintained to energize heating elements 210 and to continue to press the heated pressure transmitting surface of the plate 200 against the workpiece 300. FIGS. 5 and 6 show alternate views of the heat and pressure applying plate 200 as it is pressed against the workpiece 300. FIG. 6 shows the plate 200 with its pressure transmitting surface 206 pressed against the flexible membrane 60, which in turn overlies the meltable disperse dye bearing sheet 108, which in turn overlies the workpiece 300. Workpiece 300 is shown with two layers, a metal substrate layer 302 and an overlying printable plastic layer 304. The connection of the heat and pressure applying plate 200 to the support guides

198, 196 is also shown, via the support connections 194,192 which attach to the support guides.

Various automated control mechanisms, not shown, can also be employed to monitor and regulate operating conditions such as temperature, pressure and vacuum in the system as well as to control the timing of the various operating steps.

FIG. 2 shows a frame assembly 86 operable for receiving four workpieces 300. Frame assemblies of this type can be constructed for receiving varying numbers of workpieces as desired. For example, it may be desired to transfer a number of similar or different images onto only one relatively large workpiece, then cut and form individual products from this larger workpiece. Alternatively, individual (relatively smaller) pieces can be first cut and formed and then have dye images transferred onto and into printable plastic surfaces of the individual smaller workpieces. Frame assembly 86 can also include workpiece receiving pad portions (not shown) corresponding approximately to the respective footprints of the workpieces to be processed. These pad portions can, for example, comprise approximately 1/4 inch thick pieces of silicone rubber or similar material bonded to the frame assembly 86. Alternatively, the workpiece receiving pad portion(s) can cover virtually the entire upper (workpiece receiving) surface of the plate portion 28, so long as sufficient vent holes are provided in such a unitary pad portion to allow the vacuum system to properly evacuate the area between the membrane assembly 16 and the bed assembly 14 when the membrane assembly 16 is positioned in overlying relationship to the bed assembly 14. Such pad portions serve not only to cushion and hold the workpiece(s) , but also insulate each workpiece from temperature increases within the frame assembly 86 which can occur during continuous operation of the apparatus. Heat transfer from the frame assembly to the workpiece(s) can disadvantageously affect the workpiece's characteristics, particularly those of its printable plastic layer(s) . To further aid in avoiding this problem, a heat transfer system (such as water chilling) can optionally be incorporated in the support plate 28 to reduce the temperature of the frame assembly 86 during continuous operations. Or, a heat transfer system can be directly incorporated into the frame assembly 86 to further provide heat removal. By using such features or combinations thereof, the primary source of heat to the workpiece can be made to be the heat and pressure applying plate 200, and thus the heat reaching the workpiece can be specifically controlled to maximize dye transfer and minimize undesired effects.

The frame assembly 86 typically is positioned over one or more vacuum ports 36 on the plate portion 28 and also includes holes or slots (not shown) extending through the assembly 86 to facilitate drawing a vacuum around or near the periphery of each workpiece on the frame assembly 86. A sheet 108 bearing dye images 100 and having positioning slots 112 therein is receivable on the frame 86 so that the positioning pins 106 are received in the slots 112. Rounded bars 114 are receivable on the portions of the pins 106 which protrude through the sheet 108 so that the pins 106 do not rupture the membrane 60 when it is drawn downwardly with the evacuating assembly 18. The frame assembly 86 typically remains on the plate portion 28 during continuous printing operations, with the individual workpieces being placed onto and removed from their respective positions on the assembly 86 with each printing cycle. However, the frame assembly 86 can also be removed from the plate portion 28 with each printing cycle if desired or necessary.

After sufficient heat and pressure have been applied to transfer the dye onto and into the plastic surface of the workpiece, the heat plate is lifted so that the workpiece 300 can be cooled. The vacuum is maintained for a certain amount of time in order to prevent the paper from moving before cooling, to prevent ghosting. The vacuum is subsequently released after the danger of ghosting is passed, the flexible membrane is lifted and the spent image-bearing sheet is removed.

The above discussion of this invention is directed primarily to preferred embodiments and practices thereof. It will be readily apparent to those skilled in the art that further changes and modifications in the actual implementation of the concepts described herein can easily be made without departing from the spirit and scope of the invention as defined by the following claims.

Referring now to FIGS. 7-17, another a melt printing apparatus is shown which incorporates a heat transfer system in accordance with the invention. The apparatus 310 is operable for applying dye images to members, particularly plastic members, in accordance with processes of the type wherein a sheet bearing dye in the mirror image of a desired image is overlaid on a member, and the image is transferred to the member through the application of heat to the dye while the sheet is maintained in pressurized engagement with the member. The apparatus 310 generally comprises a base 312, a frame or bed assembly 314, a flexible member 316 which is positionable in overlying relation on the bed assembly 314, a vacuum assembly 318, a radiant heating assembly 320, and a heat transfer assembly 321.

The vacuum assembly 318 is operable for evacuating the area between the membrane assembly 316 and the bed assembly 314 when the membrane 316 is positioned in overlying relation on the bed assembly 314. The bed assembly 314 and the membrane assembly 316 are positionable beneath the radiant heating assembly 320 to effect radiant heating of the membrane assembly 316. Accordingly, when a member is positioned on the bed assembly 314 and a sheet bearing dye in the mirror image of a preselected image is overlaid on the member, the apparatus 310 is operable for transferring the dye from the sheet to the member to produce the preselected image thereon. Specifically, by evacuating the area between the membrane assembly 316 and the bed assembly 314 with the vacuum assembly 318, and by thereafter positioning the membrane assembly 316 and the bed assembly 314 under the radiant heat assembly 320, heat and pressure are simultaneously applied to the dye bearing sheet to transfer the dye therefrom to the member on the bed assembly 314. The heat transfer assembly 321 reduces the temperature of the bed assembly 314 to control the heat transferred to, and the temperature of the workpiece.

Referring to FIGS. 7 and 8, it will be seen that the base 312 comprises a table-like structure having a table top 322 and legs 324. The base assembly 312 provides a supporting structure for the remainder of the apparatus 310.

The bed assembly 314 is most clearly illustrated in FIGS. 7, 8 and 10 and comprises a rectangular frame 326 and a support plate portion 328 which defines a supporting surface for receiving a member or a plurality of members in the apparatus 310 for the application of dye images thereto. As illustrated in FIG. 10, the plate portion 328 comprises a lower substrate 330 having a lamination 332 overlaid thereon, the lamination 332 defining the upper supporting surface of the plate portion 328. The lamination 332 is preferably of a substantially rigid construction and has a textured grid pattern on the upper surface thereof whereby an even vacuum can be applied over the entire area between the bed assembly 314 and the membrane assembly 316. Integrally molded in the lamination 332 is a raised ridge 334 which extends around the central portion thereof in slightly inwardly spaced relation to the periphery of the lamination 332. Provided in the plate portion 328 are vacuum caps 336 having peripheral openings therein (not shown) for evacuating the area between the bed assembly 314 and the membrane assembly 316 when the membrane assembly 316 is overlaid on the bed assembly 314, as will hereinafter be more fully brought out. Also included in the bed assembly 314 are latch members 338 and a handle 340. A mounting assembly 342 is included in the bed assembly 314 for the mounting thereof on the base 312.

The mounting assembly 342 is most clearly illustrated in FIGS. 7 and 8 and comprises a pair of slide rods 344 which are mounted in upwardly spaced rearwardly extending relation on the table top 322 with front mounts 346 and rear mounts (not shown) . Received on the rods 344 are front and rear slide members 348 and 350, respectively; and front and rear cross members 352 and 354 extend between the two front slide members 348 and the two rear slide members 350, respectively. Front vertical members 356 and rear vertical members (not shown) extend upwardly from the cross members 352 and 354, respectively, and are secured to the frame 326, whereby the frame 326 is slidably mounted on the rods 344. A front stop member 355 extends upwardly from the table top 322 to limit the extent of the forward movement of the bed assembly 314. The membrane assembly 316 is hingedly mounted on the bed assembly 314 along the rear edge thereof as at 57 and comprises an outer frame 358 and a resilient, flexible membrane 360 which is secured to the frame 358 with strips 362 and screws 364, as illustrated in FIGS. 2 and 10. As will be seen from FIG. 10, the frame 358 is of L-shaped sectional configuration, and the strips 362 are dimensioned to interfit in the frame 358 so that the membrane 360 is captured therebetween and thereby secured to the frame 358. As will be further seen, the frame 358 is dimensioned so that when the membrane assembly 316 is received in overlying relation on the bed assembly, the frame 358 overlies the ridge 334, whereby the membrane 360 is "pinched" therebetween in order to seal the periphery of the membrane 360. Conventional telescoping arms 366 extend between the bed assembly 314 and the frame 358 for maintaining the membrane assembly 316 in the upwardly hinged or open disposition illustrated in FIG. 8 when desired. Handles 368 are attached to the frame 358 and are interengageable with the latch members 338 to maintain the membrane assembly 316 in the closed position thereof illustrated in FIG. 7 wherein it overlies the bed assembly 314. The vacuum assembly 318 comprises a vacuum pump 370 which is mounted on the base 312 and which is actuated by a manual switch 372 mounted on the top 322. The vacuum pump 370 is connected through vacuum lines 374 to the vacuum caps 336 on the bed assembly 314 for drawing a vacuum in the area between the membrane assembly 316 and the bed assembly 314 when the membrane assembly 316 is in its lowered or closed position. Preferably the pump 370 is operable to produce a vacuum in the range of approximately twenty-eight inches of mercury as indicated by a gauge 75 in order to effect the desired pressurized communication between the membrane 360 and various members positioned on the bed assembly 314, although the operation of the apparatus 310 at other vacuum levels is possible.

The radiant heating assembly 320 is illustrated most clearly in FIG. 7 and comprises a housing 376 in which a hood 378 is mounted. A plurality of radiant heating elements 380 are mounted in the hood 378 in combination with parabolic reflectors 382 which reflect radiation from the elements 380 generally downwardly. Thus, in the preferred embodiment, the heating means comprises one or a plurality of radiant heating elements which emit radiant heat, primarily in the infrared wavelength range, to effect heating of the flexible membrane, the dye and the member to which the dye image is to be applied. The radiant heating means is also preferably constructed so that it emits radiation towards the bed assembly surface from various angles whereby a three-dimensional member on the bed assembly surface can be heated uniformly.

Also mounted in the hood 378 is a plurality of blowers 384 which exhaust downwardly past the elements 380 and the reflectors 382 for cooling the heating assembly 320 during periods when the emitters 380 are de-energized. Mounted on the front portion of the base 312 is a control box 386 which contains conventional control components and which is electrically connected to the heating elements 380 and the blowers 384 to control the energization thereof.

The heat exchange system 321 is illustrated in particular in FIGS. 7, 8, 16, and 17. The heat exchange system 321 comprises a cooling fluid inlet 440 and a cooling fluid outlet 142. The inlet 440 and outlet 442 are connected by tubing 444 within the bed assembly, (the support plate in the illustrated embodiment) to define a self-contained heat exchange unit for maintaining the temperature of the bed assembly. Indeed, in the illustrated embodiment, the circulating cooling fluid defines a sink that conducts away excess heat that can accumulate in the vicinity of the workpiece.

As an alternative to forming or providing the heat exchange unit within the bed, suitable coolant conducting conduits may be mounted to the undersurface of the bed, for example, although the heat transfer realized may not be as rapid. As will be appreciated, the heat exchange system itself may be of any known type or configuration. When a fluid coolant is provided, the system is preferably a system which re-circulates the cooling fluid with a suitable pump 446 and which includes a means for re- cooling the circulating fluid 448.

The control box 386 preferably includes control components of generally conventional design which are electrically and/or mechanically connected to the heat exchange system, and specifically the pump and cooling means, so as to control the temperature and rate of flow of fluid through the heat exchange system and hence the resultant cooling effected thereby. Generally, therefore, the operation of the apparatus 310 to effect the application of a preselected dye image to a member is accomplished by positioning the member of the lamination 332 and overlying a sheet bearing dye, preferably a disperse dye, in an image which is the mirror of the preselected image for the member so that the mirror image is in the desired orientation thereon. The member itself is preferably a plastic member having a melting point which is above the melting point of the dye, as described in applicants aforementioned Patent No. 4,587,155. The membrane assembly 316 is then moved to its lowered or closed position illustrated in FIG. 7, and the handles 368 are moved into interlocking engagement with the latch members 338. The switch 372 is then manipulated to actuate the vacuum assembly 318 whereby the membrane 360 is drawn into pressurized communication with the sheet overlying the member to effect the pressurized engagement of the sheet with the member. The bed assembly 314 and the membrane assembly 316 are then moved rearwardly in the apparatus 310 so that the membrane 360 is disposed beneath the hood 378. The heat exchange system 321 is then actuated to control the temperature of the bed assembly 314.

Thereafter, the control box 386 is manipulated to energize the radiant heating elements 380 to effect heating of the membrane 360 so that heating of the dye and the plastic member immediately beneath the membrane 360 is effected to transfer the dye to the member. After the desired image has been applied to the member in this manner, the heating elements 380 and the vacuum assembly 318 are de-energized. The blowers 384 are then energized to cool the hood 378 and the housing 376 to prevent damage thereto due to overheating, and the bed assembly 314 and the membrane assembly 316 are moved forwardly and out from beneath the hood 378. The membrane assembly 316 may then be raised to the open position thereof to remove the member with the preselected image(s) thereon.

In the preferred embodiment of the apparatus 310, the emitters 380 are constructed so that they emit radiation predominantly within the infrared range, and the membrane 360 comprises a silicone rubber membrane which is specifically receptive to radiation within the wavelength range emitted by the emitters 380 in order to achieve optimal heating conditions. Further, in the preferred embodiment, the apparatus 310 comprises conventional adjustable means for controlling the heating assembly 320 to effect the energization thereof for predetermined time intervals, and conventional adjustable feedback control means for controlling the heating elements 380 to effect heating of the membrane 360 to the desired temperature. Automatic control means for actuating the blowers 384 and the heat exchange system 321 may also be provided. It will be understood, however, that the operation of the apparatus 310 will be different for different types of members and for different dyes and that, therefore, adjustments in the heating cycles of the apparatus 310 may be necessary for different operations. Although it will be understood that the apparatus of the instant invention is operable for applying dye images to various types of members, it has proven to be particularly effective for simultaneously applying dye images to a plurality of keys on keyboards of the type used in computer input terminals, typewriters, and the like. To that end the apparatus of the instant invention further comprises a frame assembly 386 of the type illustrated in FIGS. 8 and 9 for receiving and positioning one or a plurality of keyboard assemblies 388 on the bed assembly 314. The frame assembly 386 as illustrated in FIG. 8 is operable for receiving four keyboard assemblies 388, although it will be understood that frame assemblies of this type can be constructed for receiving various numbers of keyboard assemblies 388 as desired. The frame assembly 386 includes a base frame portion 390 of generally rectangular configuration, end blocks 392 which are secured to the base frame portion 390, and positioning lugs 394 and 396. The keyboard assembly 388 is receivable in the frame assembly 386 so that it is located in desired registry therein by means of the lugs 394 and 396, and a skeleton plate 398 having a plurality of apertures 400 therein is receivable on the keyboard assembly 388.

Specifically, the skeleton plate 398 is receivable on the keyboard assembly 388, which includes a plurality of individual keys 402 having slightly concave printing surfaces 403, so that the keys 402 are received in the apertures 400 to maintain the keys 402 in fixed relation. End plates 404 having upwardly extending positioning pins 406 are also included in the frame assembly 386 and are receivable on the blocks 392 adjacent opposite ends of the skeleton plate 398. A sheet 408 bearing dye images 410 and having positioning slots 412 therein is receivable on the skeleton plate 398 and the end plates 404 so that the positioning pins 406 are received in the slots 412. Rounded bars 414 are receivable on the portions of the pins 406 which protrude through the sheet 408 so that the pins 406 do not rupture the membrane 360 when it is drawn downwardly with the evacuating assembly 318.

The sheet 408 preferably comprises a paper sheet having a layer of thermoset polymer applied to one surface thereof so that the polymer is intermixed with the paper fibers, as described in applicants aforementioned U.S. Patent No. 4,587,155. Accordingly, when heat and pressure are simultaneously applied to the sheet 408, it conforms to the configurations of the tops of the keys 402, whereby clear and undistorted images are applied to the keys 402. For purposes of illustration, the images 410 as shown in FIG. 9 are visible on the upper surface of the sheet 408. However, in actual application, the upper surface of the sheet 408 is preferably coated with the thermoset polymer as hereinabove mentioned, and the images 410 which comprise dye in the mirror images of the preselected images which are to be applied to the keys 402 are disposed on the underside of the sheet 408. The images 410 are positioned on the sheet 408 so that when the sheet 408 is overlaid on the skeleton plate 398 as hereinabove set forth, the images 410 are properly oriented on the tops of the appropriate keys 402. Accordingly, when heat and pressure are applied to the sheet 408, the dye comprising the images 410 is transferred to the keys 402 to produce the preselected images on the surfaces 403. In this regard, when the apparatus 310 is operated in accordance with applicants aforementioned U.S. Patent No. 4,587,155, so that the member 402 is a plastic member and the dye used comprises a disperse dye, the dye actually diffuses into the plastic as illustrated at 105 in FIG. 11. While the apparatus is operable for applying dye images to members having somewhat irregular surface characteristics, such as the keys 402 which have slightly concave upper surfaces 403, it is also operable for applying dye images to several different nonparallel surfaces of a member. In this regard, referring to FIGS. 14 and 15, it will be seen that a sheet 416 which is die-cut as at 418 to define first and second flaps 420 and 422 can be used to apply first and second images 424 and 426 to first and second nonparallel surfaces 428 and 430, respectively, of a member 432. As schematically illustrated in FIG. 15, when the sheet 416 is overlaid on the member 432 and the membrane 360 is urged into pressurized engagement with the sheet 416, the flaps 420 and 422 overlying the surfaces 428 and 430, respectively, in pressurized therewith. Accordingly, when the emitters 380 are energized to heat the membrane 360, the image 424 is applied to the surface 428, and the image 426 is applied to the surface 430. In this connection, since the emitters 380 include parabolic reflectors 382, the radiation emitted by the emitters 380 is directed toward the membrane 360 at various angles relative thereto so that the radiation is uniformly received thereon to effect heating of the surface 428, as well as the surface 430, which is at a substantial angle to the plane of the bed assembly 314. It is seen, therefore, that the instant invention provides an effective apparatus for applying images to members, particularly plastic members, utilizing dye bearing sheets. Because the apparatus of the instant invention uses the flexible membrane 360 for applying pressure to various members when the vacuum assembly 318 is activated, the apparatus of the instant invention is operable for applying images to irregular surfaces, such as the composite surface defined by the tops of the keys 402.

Furthermore, applicant's apparatus can be used for applying one or a plurality of images to a single member or for simultaneously applying a plurality of dye images to a plurality of members even though the various members have irregular printing surfaces and are three-dimensional in nature. In this regard, because the apparatus of the instant invention utilizes a flexible membrane and a means for applying a vacuum to the membrane to effect pressurized communication between a sheet and a member disposed on the bed assembly surface, a plurality of members can be positioned on the bed assembly surface, and dye images can be simultaneously applied to all of the members with one or a plurality of sheets. This is because the membrane will simultaneously conform to the configurations of all of the members and cause pressure to be applied to all of the various surfaces of the members notwithstanding some irregularities in the surface configurations thereof.

In addition, it is possible to simultaneously apply dye images to two or more different surfaces of a single member with the applicant's apparatus. Specifically, by utilizing a dye bearing sheet having a plurality of mirror images thereon wherein the sheet is die-cut so that it can conform to the various surfaces of a single member, when the membrane is moved into pressurized communication with the member the sheet will be positioned in pressurized engagement with the different surfaces thereof so that the different images are applied to the appropriate surfaces. It should be pointed out, however, that when applying images to surfaces which are in nonparallel relation to the bed assembly surface it is important that the radiant heating means be of the type hereinabove described herein radiation is directed at the bed assembly surface from various angles so that all of the surfaces of the member are heated uniformly.

Furthermore, because, in accordance with the invention, means are provided to control the temperature of the bed and/or the assembly to which the images are being applied, mis-alignment of the images and/or warpage of the product is avoided. In this manner a product which is consistently and predictably high quality can be produced.

Hence the apparatus of the instant invention is operable for applying one or a plurality of dye images to one or more plastic members having various surface configurations. Accordingly, it is seen that the apparatus of the instant invention represents a significant advancement in the art which has substantial commercial merit.

While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims. Thus, for example, while the invention has been described with reference to a heat exchange system which uses a cooling fluid, it is to be understood that other cooling means, such a thermoelectric unit and/or a suitably disposed air cooling system, may be employed.

Claims

WHAT IS CLAIMED IS:

1. An apparatus for simultaneously applying a plurality of dye images to an assembly having respective printing surfaces, from a flexible sheet bearing said dye in the mirror images of said preselected images, said dye being of the type requiring heat for the application thereof and having a melting point which is below the melting point of the material from which the assembly is constructed comprising: a) a base; b) a bed mounted on said base, said bed having a support surface for receiving said assembly with said flexible sheet overlying said printing surfaces of said assembly so that said dye mirror images face said printing surfaces in a predetermined orientation; c) a continuous resilient, flexible membrane attached to said apparatus and positionable in overlying relation to said flexible sheet on said assembly and on the portion of said bed surface adjacent thereto; d) means for establishing a pressure differential between opposite sides of said membrane to urge the membrane overlying said bed surface portion into engagement therewith and to urge said membrane overlying said flexible sheet and said assembly into pressurized communication with said flexible sheet to simultaneously register and conform the key images on said flexible sheet to said plurality of printing surfaces of said assembly to thereby effect the pressurized engagement of said dye images with said printing surfaces; and e) heating means for heating said membrane and thereby heating said sheet to apply said preselected images to said plurality of printing surfaces; characterized in that temperature control means are provided for controlling the temperature of at least one of said bed and said assembly thereby to minimize warpage of said assembly and mis-registry of said dye images on said printing surfaces.

2. An apparatus as in claim 1 further characterized in that means are provided for positioning individual keys of said assembly and said sheet so that said sheet overlies said keys with said mirror images facing said individual keys in a predetermined orientation.

3. An apparatus as in claim 2, characterized in that said plurality of keys are assembled as a keyboard assembly, said positioning means comprises a frame assembly received on said bed surface and including a skeleton plate having a plurality of apertures therein received on said keyboard assembly so that said keys are snugly received in said apertures and thereby securely positioned in said frame assembly, said skeleton plate also having a plurality of positioning pins thereon, said sheet having a plurality of spaced positioning apertures therein, said pins being receivable in said positioning apertures to position said sheet relative to said keys so that said dye mirror images face said keys in said preselected orientation.

4. An apparatus as in claim 1, characterized in that the printing surfaces are irregular printing surfaces which are disposed in nonparallel relation to said bed surface, the portion of said sheet adjacent said mirror images further characterized as being die-cut to define a flap therein and overlying said printing surfaces with said mirror images facing said printing surfaces.

5. An apparatus as in claim 4, characterized in that said assembly is a plurality of keys having irregular printing surfaces which include first and second nonparallel printing surfaces, said sheet having first and second dye mirror images thereon, the portions of said sheet adjacent both said first and second mirror images being die-cut to define first and second flaps in said sheet, respectively, and overlying said first and second printing surfaces, respectively, so that said first mirror image faces said first printing surface and said second mirror image faces said second printing surface.

6. An apparatus as in claim 1, characterized in that said heating means is radiant heating means which emits radiation directed to said printing surfaces.

7. An apparatus as in claim 1, characterized in that said temperature control means comprises means for cooling at least one of said assembly and said bed.

8. An apparatus as in claim 9 characterized in that said means for cooling comprises a heat exchange means for circulating a cooling fluid through said bed to control the temperature thereof.

9. An apparatus as in claim 8 characterized in that said fluid is water.

10. A method of printing a meltable disperse dye image onto and into a plastic surface on a workpiece, comprising: providing a workpiece which includes a plastic surface which can be disperse dye melt printed, the area of said surface being appreciably greater than that of a key in a telephone, typewriter or computer key array; positioning over the plastic surface a flexible sheet, dye side down, bearing one or more meltable disperse dyes in the mirror image of the image which will be melt printed onto and into the plastic surface; overlaying the dye-bearing sheet with a flexible membrane so that a first surface of the membrane overlies the sheet; pulling a vacuum on the space between the first surface of the flexible membrane and the non- dye-bearing side of the dye-bearing sheet to pull the flexible membrane into pressure contact with the dye-bearing sheet and bias the dye-bearing sheet into contact with the plastic surface of the workpiece and, while maintaining the vacuum; applying, by means of a heated plate having a pressure-applying surface, heat and pressure to the upper surface of the flexible membrane sufficient to melt the disperse dye and thereby transfer the dye image onto and into the plastic surface of the workpiece.

11. A method as recited in claim 10, wherein the workpiece comprises a planar base member coated on at least one of its planar surfaces with a coating comprising a melt printable layer of a softenable, dye-permeable thermoplastic or thermoset material.

12. A method as recited in claim 11, wherein the planar base member comprises a metal plate or sheet.

13. A method as recited in claim 12, wherein the metal is aluminum, an aluminum alloy, steel, brass, bronze or copper.

14. A method as recited in claim 11, wherein the planar base member comprises a non- metallic substrate.

15. A method as recited in claim 14, wherein the non-metallic substrate comprises a plastic, wood, leather or ceramic substrate.

16. A method as recited in claim 11, wherein the melt printable layer comprises a linear thermoplastic polyester.

17. A method as recited in claim 14, wherein the polyester is polyethylene terephthalate or polybutylene terephthalate.

18. A method as recited in claim 10, wherein the melt printable layer comprises a base coat of a high molecular weight epoxy resin cross- linked with a urea-formaldehyde, melamine- formaldehyde or phenol-formaldehyde resin and topcoated with a printable oilless alkyd resin cross-linked with a melamine-formaldehyde resin.

19. A method as recited in claim 10, wherein the plastic surface of the workpiece being melt printed has a printable surface area of from about 3 to about 10 square feet.

20. A method as recited in claim 10, wherein the meltable disperse dye has a melting point below and a vaporization point above the thermal deflection temperature of the printable plastic surface.

21. A method as recited in claim 10, wherein the method is practiced using a workpiece receiving pad positioned beneath the workpiece being printed.

22. A method as recited in claim 19, wherein the workpiece receiving pad comprises a silicone rubber pad.

23. A method as recited in claim 11, wherein the heat and pressure applied to the upper surface of the flexible membrane over the workpiece range from about 325°F to about 375°F and from about 35 psi to about 50 psi, respectively.

24. A method as recited in claim 10 further including the step of cooling the temperature of the workpiece to minimize warpage and misregistry of the dye images on the plastic surface of the workpiece.

25. A method as recited in claim 24, wherein the cooling comprises a heat exchanger for circulating a cooling fluid through a bed assembly to control the temperature thereof.

26. A method as recited in claim 25, wherein the cooling fluid is water.

27. A plastic surfaced workpiece printed with a disperse dye image by the method of any one of claims 10-26, inclusive.