Printing on to a 3-dimensional article

Abstract

A process for printing on to a 3-dimensional article is described. An image is printed on to a first side of a stretchable carrier membrane having a first side and a second side. The membrane is mounted in a plane within a frame between a heating chamber defined on one side of the membrane, and an article receiving chamber defined on the other side of the membrane. A 3-dimensional article to be printed is placed on to a generally flat platen positioned generally parallel to the said plane, optionally with a nest for the article thereon, within the article receiving chamber. A thermo- and vacuum-forming step is performed in which there is relative movement of the platen with respect to the membrane in a direction perpendicularly to the said plane to bring the article into register with the image printed on the membrane and to carry the article into intimate contact with the membrane through the said plane into the heating chamber. A source of vacuum is applied to the membrane from the said other side, and heat is applied to the membrane from the said one side at a first temperature sufficient to soften the membrane, whereby the membrane is thermo- and vacuum-wrapped at least partially about the article with the membrane in intimate contact with surface details of the article. A dye-diffusion step is performed in which infra-red radiation is applied to the article with the membrane wrapped therearound using at least two infra-red sources to heat the membrane and underlying surface of the article over substantially a half-spherical solid angle uniformly to a temperature in excess of the first temperature and for a time sufficient to cause the printed image to diffuse into the surface of the article but insufficient to damage the article.

Claims

1. A process for printing on to a 3-dimensional article, the process comprising the steps of: (i) printing an image on to a first side of a stretchable carrier membrane having a first side and a second side; (ii) mounting the membrane in a plane within a frame between a heating chamber defined on one side of the membrane, being the said second side thereof, and an article receiving chamber defined on the other side of the membrane, being the said first side thereof; (iii) placing a 3-dimensional article to be printed on to a generally flat platen positioned generally parallel to the said plane within the article receiving chamber; (iv) performing a thermo- and vacuum-forming step comprising: (a) relatively moving the platen with respect to the membrane in a direction perpendicularly to the said plane to bring the article into register with the image printed on the membrane, and carrying the article into intimate contact with the membrane through the plane into the heating chamber, (b) applying a source of vacuum to the membrane from the other side, and (c) applying heat to the membrane from the said one side at a first temperature sufficient to soften the membrane, whereby the membrane is thermo- and vacuum-wrapped at least partially about the article with the membrane in intimate contact with surface details of the article; and (v) a dye-diffusion step in which infra-red radiation is applied to the article with the membrane wrapped therearound using at least two, and preferably a plurality in excess of two, of infra-red sources to heat the membrane and underlying surface of the article over substantially a half-spherical solid angle uniformly to a temperature in excess of the first temperature and for a time sufficient to cause the printed image to diffuse into the surface of the article but insufficient to damage the article; wherein the thermos- and vacuum-forming step (iv) further comprises: (aa) pausing or slowing the movement of the platen before the article has passed through the said plane when the article is around 0.2 mm to 1 cm from the membrane, (bb) drawing the membrane to register with the article by application of a partial vacuum on the first side of the membrane to draw the membrane, and (cc) then resuming the movement of the platen to pass the article through the said plane, while maintaining the partial vacuum.

2. A process according to claim 1, wherein the thermo- and vacuum-forming step (iv) further comprises: (dd) creating a stronger vacuum than said partial vacuum once the article is on the heating chamber side of the said plane.

3. A process according to claim 2, wherein the thermo- and vacuum-forming step further comprises: (ee) maintaining the stronger vacuum for a predetermined period of time while the article is on the heating chamber side of the said plane, and (ff) then reducing the vacuum to a lower predetermined strength.

4. A process according to claim 1, wherein the heat in the apparatus is controlled by altering the intensity and/or the position of the/each heat source, in response to information from a heat sensor.

5. A process according to claim 1, wherein the heat in the apparatus is controlled by the use of baffle(s), and/or reflector(s) and/or fan(s), in response to information from a heat sensor.

6. A process according to claim 1, wherein the membrane has a coating on said first side adhered to the remainder of the membrane, the coating being selected to receive said image in said printing step.

7. A process according to claim 1, wherein the surface proper of the 3-dimensional article to be printed is incapable of receiving the printed image, and wherein an additional preliminary step is performed to coat the article with a coating which adheres to said surface proper, the said coating of said preliminary step being capable of accepting the printed image by diffusion into the material of the said coating in said dye-diffusion step.

8. A process according to claim 7, wherein said coating exhibits grain boundaries, whereas the surface proper of the 3-dimensional article does not.

9. A process according to claim 7, wherein said coating is tailored to a wavelength or range of wavelengths of infra-red radiation used.

10. A process according to claim 1, wherein the generally flat platen has a nest for the article thereon.

11. A process according to claim 1, wherein a wavelength or range of wavelengths of the infra-red radiation is tailored to the membrane used.

12. An apparatus for printing on to a 3-dimensional article; the apparatus comprising: a heating chamber, an article receiving chamber, and a frame adapted to mount a stretchable carrier membrane having a first side and a second side in a plane separating the heating chamber from the article receiving chamber, the membrane having an image printed on to its first side; a generally flat platen positioned generally parallel to the said plane within the article receiving chamber; a mechanism for causing relative movement of the platen with respect to the membrane in a direction perpendicularly to the said plane to bring an article mounted on the platen into register with a said image printed on the first side of a said membrane held in the frame, and to carry the said article into intimate contact with the membrane through the said plane into the heating chamber; a source of vacuum associated with the article receiving chamber and adapted to apply a vacuum to the membrane held in the frame from the side of the article receiving chamber; a first source of heat in the heating chamber adapted to apply heat to the membrane held in the frame at a first temperature sufficient to soften the membrane, whereby, in concert with said vacuum source, to thermo- and vacuum-wrap the membrane at least partially about the said article with the membrane in intimate contact with surface details of the article; and a second source of heat in the form of infra-red radiation, which second source of heat may be the same as the first source of heat, the said second source of heat comprising at least two, and preferably a plurality in excess of two, of infra-red sources adapted to apply infra-red radiation to the said article with the membrane wrapped therearound, the second source of heat being adjustable both in position and in heating to allow it to heat the membrane and underlying surface of the article over substantially a half-spherical solid angle uniformly to a temperature in excess of the first temperature and for a time sufficient to cause the image to diffuse in liquid form into the surface of the article but insufficient to damage the article: wherein the mechanism is constructed and arranged to cause said relative movement in two stages, namely a first stage which ends before the article has passed through said plane when the article is around 0.2 mm to 1 cm from the membrane, and a second stage which commences when the membrane has been drawn into register with the article by a partial vacuum created by said source of vacuum on the first side of the membrane and ends when the article has passed through said plane.

13. An apparatus according to claim 12, wherein the apparatus further comprises baffle(s), and/or reflector(s) and/or fan(s) to direct heat within the apparatus.

14. An apparatus according to claim 13, wherein the apparatus further comprises at least one heat sensor, and the intensity of the fan(s) And/or the position of the baffle(s), and/or reflector(s) and/or fan(s) is(are) controllable in response to feedback from the or each heat sensor.

15. An apparatus according to claim 12, wherein the apparatus further comprises at least one heat sensor, and the intensity and/or the position of the or each source of heat is controllable in response to feedback from the or each heat sensor.

16. An apparatus according to claim 12, wherein the generally flat platen has a nest for the article thereon.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference may now be made to an embodiment of printing apparatus described hereinbelow by way of example only with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a sectional view of the printing apparatus with an article to be printed in the article receiving chamber;

(3) FIG. 2 shows a sectional view of the printing apparatus of FIG. 1 with the article in a raised position in contact with the carrier membrane;

(4) FIG. 3 shows a portion of the apparatus, in which the article has been brought close to the softened membrane;

(5) FIG. 4 shows a portion of the apparatus in which a partial vacuum has been created, drawing the softened membrane into contact with the article.

DESCRIPTION OF PREFERRED EMBODIMENTS

(6) Referring first to FIG. 1, there is a printing apparatus 1 including a heating chamber 2 and an article receiving chamber 3. Carrier membrane 4 is mounted in a frame 5, and initially lies in a plane separating heating chamber 2 and article receiving chamber 3. First side 6 of membrane 4 has an image digitally printed thereon, preferably as a pattern of pixel dots of dye using a digital micro-piezo head printer. Alternatively, the image may be produced by gravure printing, silkscreen printing or lithio-printing. The article 7 to be printed upon is positioned on a generally flat platen 8 mounted in a plane generally parallel to the plane of the membrane 4. In some embodiments the article 7 may be placed on a nest (not depicted) upon the platen 8, the nest providing support for the article during the printing process. Platen 8 is moveable, and may be moved by any suitable means, including, but not limited to, servo motors, spring based devices, hydraulic devices, pneumatic devices, or counter weights.

(7) The article 7, shown here for simplicity of illustration as a simple three-dimensional block without any surface relief, may take any form, including, but not limited to, a canvas sports shoe, a toy gun with intricate surface relief, or a motorcycle helmet.

(8) Heating chamber 2 contains a number of infra-red sources, in this case infra-red lamps 9. In this embodiment the lamps are arranged in groups 9a, 9b, 9c, etc, each group being independently controllable. Additionally, each individual lamp 9 of a group may be is independently controllable (both in position and in intensity). A heat sensor 10, here a PIR (passive Infra-Red) sensor, monitors the temperature of the heating chamber and feeds that information to a data processor (not shown). Lamps 9, motor driven fans 11 within chamber 2, reflectors (not visible in the drawings), and baffles (omitted from the drawings for clarity), are all controlled by the data processor to keep the temperature of the chamber 2 within pre-determined minimum and maximum temperatures that have been found to be optimal for each stage of the printing process, depending on the membrane used, the ink used, and the nature of the object to be printed. When heated, chamber 2 is sealed, in order that the air circulates but does not escape. Vents could optionally be inserted if desired. Multiple PIR sensors 10 may be used in different areas of the heating chamber 2 as required, in order to obtain a better overview of the temperature in different areas of the chamber. The temperature or temperature range required in the heating chamber will be determined by the nature of the article 7 to be printed, the nature of the carrier membrane 4 used, and the nature of the ink that is being transferred.

(9) The precise nature of the carrier membrane used and the ink used may be chosen to suit the nature of the article, the outcome quality desired, and the budget of the printer, but we have found that the use of so-called “3D Sublimation Film” from the Korean Company, Songjeong Co., Ltd., said to be for use with “sublimation ink”, and so-called “sublimation ink” obtained from the American Company, J-Teck USA, Inc., yield good results, although it should be noted that dye transfer is actually by diffusion rather than sublimation. Those involved in the art of transfer printing will readily be able to source alternative inks and membranes, and, where a membrane requires an additional coating to receive the ink, suitable coatings. Digital images may be printed on to the membrane using conventional micro piezo head printing.

(10) To print onto an article, the apparatus is set up generally as shown in FIG. 1. At this stage, the suitable carrier membrane 4 (in this embodiment, “3-D Sublimation Film” from Songjeong Co., Ltd) has already had the desired image printed thereon using an appropriate ink (in this embodiment, “sublimation ink” from J-Teck USA, Inc.) and membrane 4 has been suitably fixed in the apparatus using frame 5. The article 7 is positioned on the platen 8 in the article receiving chamber 3.

(11) Membrane 4 is heated using Infra-red lamps 9 to soften it. It is heated for around 5-10 seconds until it is between 50 and 87° C. If a different membrane were to be used, a there would be a different optimal temperature range, and a different heating time could be required. The temperature of membrane 4 is monitored by PIR sensor 10 during this stage and the information is fed to a data processor. If the membrane is found to be heating unevenly, or is being heated too quickly or too slowly, the data processor can arrange for the intensities or positions of individual lamps 9 or groups of lamps 9a, 9b etc. to be adjusted. When the membrane 4 has been suitably softened, platen 8 will raise article 7 from its position in the article receiving chamber 3, which is cooler than the heating chamber, towards the membrane 4 in a direction generally perpendicular to the plane of the membrane in its frame, as depicted in FIG. 2.

(12) The movement of platen 8 is paused before the article makes contact with the membrane 4, when the closest part of the article to the membrane is around 0.2 mm to 1 cm from the membrane, as depicted in FIG. 3.

(13) As shown in FIG. 4, article 7 is held between 0.2 mm and 1 cm below the softened membrane 4 while a slight vacuum is created in the article holding chamber 3, the vacuum drawing first side 6 of the softened membrane 4 downwards towards the article 7 and into contact with the upper part of the article, causing accurate registration of the image with the article 7. It should be noted that FIGS. 3 and 4 are not to scale, causing the bend in the membrane to appear severe in FIG. 4. The drawing is purely illustrative; when the membrane and the object are only 0.2 mm-1 cm from each other, the bend caused in the membrane by the vacuum will clearly be far more gentle. Upwards movement of platen 8 is then resumed while the slight vacuum is maintained, and platen 8 moves article 7 through the plane in which membrane 4 originally lay and into heating chamber 2, causing the remainder of the membrane 4 to wrap around article 7 in contact therewith. Now that article 7 is in the heating chamber, the surface of the article itself is heated through the membrane by the array of infra-red lamps 8 disposed substantially over a half-spherical solid angle. A stronger vacuum is caused, drawing membrane 4 into intimate contact with the article. The combination of thermo- and vacuum-wrapping allows good contact between the dye-carrier membrane and the surface details of the article, even where the article has significant surface relief. The combination of close contact between membrane 4 and article 7 and heating from lamps 9 to a higher temperature under control of the PIR sensors allows the dye to diffuse into the surface of the article 7.

(14) Applicant has found that although the above mentioned stronger vacuum is useful for drawing the carrier membrane into intimate contact with the surface of the article, it is preferable to only hold this stronger vacuum for around 15 seconds, before reducing the vacuum strength. Holding a weaker vacuum throughout the dye diffusion step keeps the membrane in contact with the article, but is less likely to cause tearing or perforation of the membrane than the strong initial vacuum employed during the vacuum- and thermo-forming step.

(15) As described, and depicted in FIG. 4, Applicant's adoption of an initial contact between membrane 4 and article 7 allows them accurately to control registration of the image on first side 6 of the membrane with the article 7 in a way that was simply not possible with the prior techniques of Neri, Howell and Hoggard discussed above.

(16) Membrane 4 and the surface of the article 7 are heated in the heating chamber 2 for a time and to a temperature that is sufficient to cause the pixel dots of dye to diffuse in liquid form into the surface of the article but insufficient to damage the article. When Songjeong's film is used in conjunction with J-Teck's ink, the surface temperature should be held between 120-170° C., more preferably between 143-155° C., for 1-4 minutes.

(17) The heating effect of infra-red radiation is focal length sensitive. Accordingly, Applicant arranges the lamps 9 or groups of lamps 9a, 9b to be moveable to ensure that the surface of article 7 is evenly heated. If an object with a complex shape is to be printed, the use of baffles and reflectors can ensure that an even surface temperature can still be obtained. Position adjustments of lamps, baffles, reflectors, and fans 11 may be made throughout the dye-diffusion step as required. As in the thermo- and vacuum-forming step, the temperature throughout this step is monitored by one (and preferably more than one) PIR sensor 9, and is fed to a data processor. The data processor is coupled to the infra-red lamps or groups of infra-red lamps to adjust their position and intensity, as necessary. As shown in FIGS. 1 and 2, infra-red lamps 9 are distributed around substantially a half-spherical solid angle around the article 7 in its position within the heating chamber 2, having passed through the initial plane of the membrane.

(18) It is desirable to achieve effective dye transfer without raising the average temperature of the article 6 too much, for a number of reasons. Firstly, once the dye-diffusion step is completed the article and membrane must be cooled, and the membrane 4 removed. The cooling step can take some time, and clearly the higher the average temperature of the object the longer the cooling step will take. If too high a temperature is required for too long, a process may be unsuitable for certain types of article, particularly, but not limited to, plastics that soften when heated and therefore may distort.

(19) Applicant's careful positioning of infra-red lamps 9, fans 10 (and baffles, reflectors etc. for more complex shaped articles) enables them to heat the membrane and the very outer surface of the article during the dye-diffusion step without heating up the entire body of the article as much. In addition, the initial heating of the membrane for thermo- and vacuum-forming is performed with the article on the other side of the membrane from the heating chamber and held some way away. Previous printing methods have needed to heat the entire article for longer periods of time.

(20) Improved results are achieved by tailoring the wavelength (or range of wavelengths) emitted by the infra-red heat lamps 9 to the carrier membrane 4 used. If membrane is more susceptible to the radiation used, then efficient dye-transfer may be achieved before the temperature of the entire object has had a chance to heat up as much.

(21) Where the article is coated to receive diffused dyes, the coating may be selected having regard to the wavelength of the infra-red radiation so that it heats without significantly heating the material of the underlying article.