EP0129023B1

EP0129023B1 - Apparatus for applying a dye image to a member

Info

Publication number: EP0129023B1
Application number: EP19840104630
Authority: EP
Inventors: David Durand
Original assignee: Key-Tech Inc
Current assignee: Key-Tech Inc
Priority date: 1983-06-20
Filing date: 1984-04-25
Publication date: 1989-11-29
Also published as: EP0129023A2; DE3480593D1; EP0129023A3

Description

The instant invention relates to the application of dye images to various types of members, and more particularly to an apparatus for applying dye images to members utilizing a sheet or sheets bearing dyes in the mirror images of the desired images, wherein the dyes are of the type which require heat for the application thereof.
Processes for applying dye images to various types of members, wherein dyes are transferred from sheets bearing the dyes in the mirror images of the desired images, are generally known in the printing art. In general, processes of this type are carried out by overlying a sheet bearing dye in the mirror image of the desired image on a member so that the image is in the desired orientation thereon and by thereafter simultaneously applying heat and pressure to the sheet to transfer the dye to the member so that the desired image is produced thereon.
DE-A-2,005,186 discloses a textile printing process in which a preselected dye image is applied to a textile by sublimation printing utilising a sheet bearing the dye in the mirror image of the pre-selected image. The textile material is substantially flat and the dye is sublimed onto the textile material by the application of heat and pressure.
EP-A-0,014,615 discloses a method of printing upon a substrate, in particular spectacle frames, by a sublimation printing process. The apparatus is not intended to print indicia upon a plurality of eye glass frames not to mention keycaps.
FR-A-2,368,364 discloses a method for marking the keys of a keyboard in which a thin honeycomb foil is formed into a plurality of cells marked with adistinctive marking and having a shape complementary to that of each key, the cells of the foil are separated and the marked and separated cells driven onto the corresponding keys in order to cap them.
The present invention provides an apparatus for simultaneously applying a plurality of pre- selected dye images to an assembly of a plurality of keycaps having respective irregular printing surfaces, by utilizing a flexible sheet bearing the dye in the mirror images of the preselected images, the 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 of which the assembly of keycaps is constructed, the apparatus comprising:

(a) a base;
(b) a bed mounted on the base, the bed having a support surface for receiving the assembly of keycaps and the flexible sheet thereon with the flexible sheet overlying the irregular printing surfaces of the assembly of keycaps so that the dye mirror images face the irregular printing surfaces in a predetermined orientation;
(c) a continuous resilient, flexible membrane -attached to the apparatus and positionable in overlying relation on the assembly of keycaps and on the portion of the bed surface adjacent thereto;
(d) means for positioning the assembly of keycaps and the flexible sheet so that the sheet overlies the assembly of keycaps with the mirror images facing the assembly of keycaps in a predetermined orientation;
(e) means for displacing the membrane into pressurized communication with the flexible sheet to thereby effect the pressurized engagement of the flexible sheet and the dye with the assembly of keycaps; and
(f) heating means for heating the membrane and thereby heating the sheet to apply the pre- selected image to the plurality of keycaps.

The means for displacing the membrane into pressurized communication with the flexible sheet may comprise vacuum means. In a preferred embodiment of the apparatus of the present invention, the heating means comprises one or a plurality of radiant heating elements which emit radiant heat, preferably primarily in the infrared wavelength range, to effect heating of the flexible sheet, the dye and the keycaps to which the dye images are to be applied. In addition, the radiant heating means is constructed so that it emits radiation towards the bed assembly surface from various angles, whereby three-dimensional keycaps on the bed assembly surface can be heated uniformly. In this regard,. preferably the radiant heating means comprises an infrared radiation emitter and a parabolic reflector which directs radiation from the emitter towards the bed assembly surface at various relative angles. Also in the preferred embodiment, the flexible membrane is preferably matched with the radiant heating means so that it is specifically absorptive to radiation within the wavelength range emitted therefrom to achieve optimum heating efficiency.
The apparatus of the present invention is particularly effective for applying disperse dye images to plastic keycaps. The apparatus of the present invention is used for simultaneously applying a plurality of dye images to a plurality of keycaps having irregular printing surfaces and which are three-dimensional in nature. In this regard, because the apparatus of the present invention utilizes a flexible membrane and a means for applying a vacuum to the membrane to effect pressurized communication between a flexible sheet and a plurality of keycaps disposed on the bed assembly surface, a plurality of keycaps can be positioned on the bed assembly surface, and dye images can be simultaneously applied to all of the keycaps with one or a plurality of sheets. This is because the membrane will simultaneously conform to the configuration of all of the keycaps and cause pressure to be applied to all of the various surfaces of the keycaps 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 plurality of keycaps with the apparatus of the present invention. 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 each keycap, when the membrane is moved into pressurized communication with the keycaps the sheet will be positioned in pressurized engagement with the different surfaces of the keycaps 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 hereinbefore described wherein radiation is directed at the bed assembly surface from various angles so that all of the surfaces of the member are heated uniformly.
The apparatus of the present invention is for the application of dye images to keys of the type utilized in keyboards for typewriters, computers and the like. Specifically, the apparatus of the present invention is adapted for simultaneously applying dye images to the keys of a fully assembled keyboard. In this regard, the apparatus may further comprise a frame on the bed assembly surface for receiving a fully assembled keyboard, and a skeleton plate which is receivable on the keyboard. The skeleton plate has a plurality of apertures therethrough wherein the keys are receivable to maintain the keys in substantially stationary relation while the desired images are applied thereto. A sheet having a plurality of dye images thereon, which are in the mirror images of the desired images is overlaid on the.keys·so that the images are in the desired orientation thereon. In the preferred embodiment, a plurality of registration pins are provided on the frame, and a plurality of apertures are provided in the sheet for receiving the registration pins to assure proper registration of the sheet relative to the keys on the keyboard. Accordingly, dye images can be simultaneously applied to all of the keys on a fully assembled keyboard by positioning a dye bearing sheet over the keys as hereinabove set forth by placing the membrane over the keyboard, evacuating the membrane so that it is drawn into pressurized communication with the keys, and thereafter applying heat to the membrane. Hence, a keyboard can be fully assembled with blank keys, and thereafter the keys on the fully assembled keyboard can be imprinted with the desired images utilizing the apparatus of the instant invention. As a result, keyboards which heretofore had to be manually assembled in order to assure that each different key was assembled in the proper location can now be-robotically assembled with blank keys, and thereafter the keys can be imprinted with the desired images. Therefore it is seen that substantial savings in labor costs can be realized with the apparatus of the instant invention, particularly when it is used for applying images to keys of a keyboard.
Accordingly, the instant invention provides for an apparatus for simultaneously applying a dye image to a plurality of keycaps utilizing a sheet bearing dye in the mirror of the image, the 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 comprising the keycaps.
The keycaps can be keys assembled on a keyboard.
The apparatus in accordance with the invention is particularly suitable for applying a dye image to plastic keycaps wherein a dye bearing sheet is first overlaid on the keycaps, a flexible membrane is overlaid on the sheet, and vacuum is applied to the membrane to effect the pressurized engagement of the dye bearing sheet with the keycaps and wherein thereafter radiation is directed toward the sheet to effect the heating of the dye and the keycaps so that the image is transferred to the member.
The present invention will be further described with reference to the accompanying illustrative drawings, in which:

FIG. 1 is a perspective view of the apparatus of the instant invention with the flexible membrane thereof in the closed operative position;
FIG. 2 is an enlarged perspective view of the front portion of the apparatus with the membrane in the raised inoperative position;
FIG. 3 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. 4 is a sectional view taken along line 4-4 in FIG. 1;
FIG. 5 is an enlarged perspective view of a single key of the keyboard assembly illustrated in FIG. 3;
FIG. 6 is a sectional view taken along line 6-6 in Fig. 5;
FIG. 7 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. 8 is an enlarged perspective view of a key having first and second printing surfaces and a die-cut dye bearing sheet; and
FIG. 9 is a schematic sectional view illustrating the application of heat to a plurality of keys of the type illustrated in FIG. 8 utilizing radiation emitters having parabolic reflectors.

Description of the Invention

Referring now to the drawings, the apparatus of the instant invention is illustrated and generally indicated at 10 in Fig. 1. The apparatus 10 is operable for applying dye images to keycaps particularly plastic keycaps, in accordance with processes of the type wherein a sheet bearing dye in the mirror of a desired image is overlaid on the keycaps and the image is transferred to the keycaps through the application of heat to the dye while the sheet is maintained in pressurized engagement with the keycaps. The apparatus 10 generally comprises a base 12, a bed assembly 14, a flexible membrane assembly 16 which is positionable in overlying relation on the bed assembly 14, a vacuum assembly 18, and a radiant heating assembly 20. The vacuum assembly 18 is operable for evacuating the area between the membrane assembly 16 and the bed assembly 14 when the membrane assembly 16 is positioned in overlying relation on the bed assembly 14. The bed assembly 14 and the membrane assembly 16 are positionable beneath the radiant heating assembly 20 to effect radiant heating of the membrane assembly 16. Accordingly, when keycaps are positioned on the bed assembly 14 and a sheet bearing dye in the mirror image of a preselected image is overlaid on the keycaps, the apparatus 10 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 16 and the bed assembly 14 with the vacuum assembly 18, and by thereafter positioning the membrane assembly 16 and the bed assembly 14 under the radiant heating assembly 20, heat and pressure are simultaneously applied to the dye bearing sheet to transfer the dye therefrom to the keycaps on the bed assembly 14.
Referring to Figs. 1 and 2, it will be seen that the base 12 comprises a table-like structure having a table top 22 and legs 24. The base assembly 12 provides a supporting structure for the remainder of the apparatus 10 as will be seen from the drawings.
The bed assembly 14 is most clearly illustrated in Figs. 1, 2 and 4 and comprises a rectangular frame 26 and a support plate portion 28 which defines a supporting surface for receiving a plurality of keycaps in the apparatus 10 for the application of dye images thereto. As illustrated in Fig. 4, the plate portion 28 comprises a lower substrate 30 having a lamination 32 overlaid thereon, the lamination 32 defining the upper supporting surface of the plate portion 28. The lamination 32 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 14 and the membrane assembly 16. Integrally molded in the lamination 32 is a raised ridge 34 which extends around the central portion thereof in slightly inwardly spaced relation to the periphery of the lamination 32. Provided in the plate portion 28 are vacuum caps 36 having peripheral openings therein (not shown) for evacuating the area between the bed assembly 14 and the membrane assembly 16 when the membrane assembly 16 is overlaid on the bed assembly 14, as will hereinafter be more fully brought out. Also included in the bed assembly 14 are latch members 38 and a handle 40. 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; and 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. A front stop member 55 extends upwardly from the table top 22 to limit the extent of the forward movement of the bed assembly 14.
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 secured to the frame 58 with strips 62 and screws 64, as illustrated in Figs. 2 and 4. As will be seen from Fig. 4, the frame 58 is of L-shaped sectional configuration, and the strips 62 are dimensioned to interfit in the frame 58 so that the membrane 60 is captured therebetween and thereby secured to the frame 58. As will be further seen, the frame 58 is dimensioned so that when the membrane assembly 16 is received in overlying relation on the bed assembly, the frame 58 overlies the ridge 34, whereby the membrane 60 is "pinched" therebetween in order to seal the periphery of the membrane 60. 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 illustrated in Fig. 2 when desired. Handles 68 are attached to the frame 58 and are interengageable with the latch members 38 to maintain the membrane assembly 16 in the closed position thereof illustrated in Fig. 1 wherein 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 caps 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. Preferably the pump 70 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 60 and various members positioned on the bed assembly 14, although the operation of the apparatus 10 at other vacuum levels is possible.
The radiant heating assembly 20 is illustrated most clearly in Fig. 1 and comprises a housing 76 in which a hood 78 is mounted. A plurality of radiant heating elements 80 are mounted in the hood 78 in combination with parabolic reflectors 82 which reflect radiation from the elements 80 generally downwardly. Also mounted in the hood 78 is a plurality of blowers 84 which exhaust downwardly past the elements 80 and the reflectors 82 for cooling the heating assembly 20 during periods when the emitters 80 are deenergized. Mounted on the front portion of the base 12 is a control box 86 which contains conventional control components and which is electrically connected to the heating elements 80 and the blowers 84 to control the energization thereof.
Generally, therefore, the operation of the apparatus 10 to effect the application of pre- selected dye images to a plurality of keycaps is accomplished by positioning the keycaps on the lamination 32 and overlying a sheet bearing dye, preferably a disperse dye, in images which are the mirrors of the preselected images on the keycaps, so that the mirror images are in the desired orientation thereon. The keycaps themselves are preferably plastic keycaps having a melting point which is above the melting point of the dye. The membrane assembly 16 is then moved to its lowered or closed position illustrated in Fig. 1, and the handles 68 are moved into interlocking engagement with the latch members 38. The switch 72 is then manipulated to actuate the vacuum assembly 28 whereby the membrane 60 is drawn into pressurized communication with the sheet overlying the keycaps to effect the pressurized engagement of the sheet with the keycaps. 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. Thereafter the control box 86 is manipulated to energize the radiant heating elements 80 to effect heating of the membrane 60 so that heating of the dye and the plastic membrane beneath the membrane 60 is effected to transfer the dye to the keycaps. After the desired images have been applied to the keycaps in this manner, the heating elements 80 and the vacuum assembly 18 are deenergized. The blowers 84 are then energized to cool the hood 78 and the housing 76 to prevent damage thereto due to overheating, and the bed assembly 14 and the membrane assembly 16 are moved forwardly and out from beneath the hood 78. The membrane assembly 16 may then be raised to the open position thereof to remove the keycaps with the preselected images thereon.
In the preferred embodiment of the apparatus 10, the emitters 80 are constructed so that they emit radiation predominantly within the infrared range, and the membrane 60 comprises a silicone rubber membrane which is specifically receptive to radiation within the wavelength range emitted by the emitters 80 in order to achieve optimal heating conditions. Further, in the preferred embodiment, the apparatus 10 comprises conventional adjustable means for controlling the heating assembly 20 to effect the energization thereof for predetermined time intervals, and conventional adjustable feedback control means for controlling the heating elements 80 to effect heating of the membrane 60 to the desired temperature. Automatic control means for actuating the blowers 84 may also be provided. It will be understood, however, that the operation of the apparatus 10 will be different for different types of keycaps and for different dyes and that therefore adjustments in the heating cycles of the apparatus 10 will be necessary for different operations.
One particularly useful and effective embodiment of the apparatus of the present invention further comprises a frame assembly 86 of the type illustrated in Figs. 2 and 3 for receiving and positioning one or a plurality of keyboard assemblies 88 on the bed assembly 14. The frame assembly 86 as illustrated in Fig. 4 is operable for receiving four keyboard assemblies 88, although it will be understood that frame assemblies of this type can be constructed for receiving various numbers of keyboard assemblies 88 as desired. The frame assembly 86 includes a base frame portion 90 of generally rectangular configuration, end blocks 92 which are secured to the base frame portion 90, and positioning lugs 94 and 96. The keyboard assembly 88 is receivable in the frame assembly 86 so that it is located in desired registry therein by means of the lugs 94 and 96, and a skeleton plate 98 having a plurality of apertures 100 therein is receivable on the keyboard assembly 88. Specifically, the skeleton plate 98 is receivable on the keyboard assembly 88, which includes a plurality of individual keys 102 having slightly concave printing surfaces 103, so that the keys 102 are received in the apertures 100 to maintain the keys 102 in stationary relation. End plates 104 having upwardly extending positioning pins 106 are also included in the frame assembly 86 and are receivable on the blocks 92 adjacent opposite ends of the skeleton plate 98. A sheet 108 bearing dye images 110 and having positioning slots 112 therein is receivable on the skeleton plate 98 and the end plates 104 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 sheet 108 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.
Accordingly, when heat and pressure are simultaneously applied to the sheet 108, it conforms to the configurations of the tops of the keys 102, whereby clear and undistorted images are applied to the keys 102. For purposes of illustration, the images 110 as shown in Fig. 3 are visible on the upper surface of the sheet 108. However, in actual application, the upper surface of the sheet 108 is preferably coated with the thermoset polymer as hereinabove mentioned, and the images 110 which comprise dye in the mirror images of the preselected images which are to be applied to the keys 102 are disposed on the underside of the sheet 108. The images 110 are positioned on the sheet 108 so that when the sheet 108 is overlaid on the skeleton plate 98 as hereinabove set forth, the images 110 are properly oriented on the tops of the appropriate keys 102. Accordingly, when heat and pressure are applied to the sheet 108, the dye comprising the images 110 is transferred to the keys 102 to produce the preselected images on the surfaces 103. When the dye used comprises a disperse dye, the dye actually diffuses into the plastic as illustrated at 105 in Fig. 6.
While the apparatus 10 is operable for applying dye images to keycaps having somewhat irregular surface characteristics, such as the keys 102 which have slightly concave upper surfaces 103, it is also operable for applying dye images to several different nonparallel surfaces of a plurality of keycaps In this regard, referring to Figs. 8 and 9, it will be seen that a sheet 116 which is die-cut as at 118 to define first and second flaps 120 and 122 can be used to apply first and second images 124 and 126 to first and second nonparallel surfaces 128 and 130, respectively, of a keycap 132. As schematically illustrated in Fig. 9, when the sheet 116 is overlaid on the keycap 132 and the membrane 60 is urged into pressurized engagement with the sheet 116, the flaps 120 and 122 overlay the surfaces 128 and 130, respectively, in pressurized engagement therewith. Accordingly, when the emitters 80 are energized to heat the membrane 60, the image 124 is applied to the surface 128, and the image 126 is applied to the surface 130. In this connection, since the emitters 80 include parabolic reflectors 82, the radiation emitted by the emitters 80 is directed toward the membrane 60 at various angles relative thereto so that the radiation is uniformly received thereon to effect heating of the surface 128, as well as the surface 130, which is at a substantial angle to the plane of the bed assembly 14.
It is seen, therefore, that the instant invention provides an effective apparatus for applying images to keycaps, particularly plastic keycaps, utilizing dye bearing sheets. Because the apparatus of the instant invention uses the flexible membrane 60 for simultaneously applying pressure to a plurality of keycaps when the vacuum assembly 18 is activated, the apparatus of the instant invention is most suitable for applying images to irregular surfaces, such as the composite surface defined by the tops of the keys 102. Hence the apparatus of the instant invention is operable for applying a plurality of dye images to keycaps 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.

Claims

1. An apparatus for simultaneously applying a plurality of preselected dye images to an assembly of a plurality of keycaps (102) having respective irregular printing surfaces, by utilizing a flexible sheet (108) bearing the dye in the mirror images (110) of the preselected images, the 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 of which the assembly of keycaps (102) is constructed, the apparatus comprising:

(a) a base (12);

(b) a bed (14) mounted on the base (12), the bed (14) having a support surface (32) for receiving the assembly of keycaps (102) and the flexible sheet (108) thereon with the flexible sheet (108) overlying the irregular printing surfaces of the assembly of keycaps (102) so that the dye mirror images (110) face the irregular printing surfaces (103) in a predetermined orientation;

(c) a continuous resilient, flexible membrane (60) attached to the apparatus and positionable in overlying relation on the assembly of keycaps (102) and on the portion of the bed surface (32) adjacent thereto;

(d) means for positioning the assembly of keycaps (102) and the flexible sheet (108) so that the sheet (108) overlies the assembly of keycaps (102) with the mirror images facing the assembly of keycaps (102) in a predetermined orientation;

(e) means (18) for displacing the membrane (60) into pressurized communication with the flexible sheet (108) to thereby effect the pressurized engagement of the flexible sheet (108) and the dye with the assembly of keycaps (102); and

(f) heating means (20) for heating the membrane (60) and thereby heating the sheet (108) to apply the preselected image (110) to the plurality of keycaps (102).

2. Apparatus as claimed in claim 1, wherein the keycaps (102) are formed from a plastics material.

3. Apparatus as claimed in claim 1 or claim 2 wherein the heating means is a radiant heating means.

4. Apparatus as claimed in any one of the preceding claims wherein the membrane (60) is a silicone rubber membrane.

5. Apparatus as claimed in claim 3 or claim 4 wherein the membrane (60) is specifically absorptive to radiation emitted by the heating means.

6. Apparatus as claimed in any one of the preceding claims wherein the keycaps (102) are assembled on a keyboard assembly (88), the positioning means comprising a frame assembly (86) received on the bed surface (32), the keyboard assembly (88) being received in the frame (86), the frame assembly (86) including a skeleton plate (98) having a plurality of apertures (100) therein received on the keyboard assembly (88) so that the keycaps (102) are snugly received in the apertures (100) and thereby securely positioned in the frame assembly (86), the skeleton plate (98) also having a plurality of positioning pins (106) thereon, the flexible sheet (108) having a plurality of spaced positioning apertures therein, the pins (106) being receivable in the positioning apertures to position the flexible sheet (108) relative to the keys (102) so that the dye mirror images (110) face the keys (102) in the preselected orientation.

7. Apparatus as claimed in any one of the preceding claims wherein the keycaps (102) have printing surfaces (128,130) which are disposed in nonparallel relation to the bed surface (32), the portions of the flexible sheet (108) adjacent the mirror images (110) being die-cut to define a plurality of flaps (120, 122) therein and overlying the printing surfaces (128, 130).

8. Apparatus as claimed in claim 7 wherein the keycaps (102) each have first and second nonparallel printing surfaces (128, 130) thereon, the flexible sheet (108) having a plurality of first and second dye mirror images (124,126) thereon, the portions of the sheet (108) adjacent to both the first and second mirror images (124,126) being die-cut to define a plurality of first and second flaps (120, 122) in the sheet (108), respectively, and overlying the first and second printing surfaces (128, 130), respectively, so that the first mirror images face the first printing surfaces and the second mirror images faces the second printing surfaces.

9. Apparatus as claimed in claim 8 wherein the heating means (20) is a radiant heating means which emits radiation directed at both of the first and second printing surfaces (128, 130).

10. Apparatus as claimed in claim 9 wherein the heating means comprises:

(a) a radiation emitter (80);

(b) a parabolic reflector (82) disposed adjacent the emitter (80) for directing radiation therefrom towards boththefirstand second printing surfaces (128, 130).

11. Apparatus as claimed in any one of the preceding claims wherein the means for displacing the membrane into pressurized communication with the sheet comprises vacuum means (18).