Method & Apparatus for Sublimation Printing

This invention relates to a method & apparatus for sublimation printing.

Ink sublimation printing has been known as a method of applying decorative transfers, print, photographs and other images to surfaces and articles.

Sublimation is when a substance, in this case an ink or dye, transitions between the solid and gas state without going through the liquid state. In ink sublimation printing process the ink is heated until it sublimes into a gas at which point it diffuses onto the printing media and solidifies.

The application of pressure to the printing media to assist in the ink transfer is often achieved by using heated rollers or a hot platen press. It is problematic to achieve good ink sublimation printing to 3 D articles as it is difficult for pressure and heat to be applied evenly to a 3D structure. It is necessary for each surface of the article to which print is to be applied, to have evenness of pressure and heat.

There is now a desire to produce uniformly printed articles by the ink sublimation technique with faster printing process and with the possibility of being able to print a number of articles during the same ink sublimation process.

We have now devised a sublimation printing process and associated apparatus which attempt to alleviate the above-mentioned problems.

In accordance with the present invention, there is provided sublimation printing apparatus comprising a chamber for housing a three dimensional component to be printed and a film carrying sublimable ink positioned adjacent the component and a heater for directing heat to said film such that upon the application of heat it thermoforms over the component, and enables sublimation of the ink to the component.

Preferably the sublimation printing apparatus is provided with a vacuum pump to the chamber.

Preferably the sublimation printing apparatus is provided with a second heater and said first heater and component are arranged to be moveable with respect to one

another such that the second heater is adjacent said component for providing the heat for the sublimation process and said first heater is arranged to provide heat only for the film thermoforming step.

Preferably the sublimation printing apparatus is provided with a fan is arranged adjacent the heater to direct the heat over the component.

Preferably the sublimation printing apparatus also comprises a second fan arranged adjacent the second heater to direct the heat over the component during the sublimation process.

Preferably the sublimation printing apparatus is also provided with a series of louvers between the heater and the component so as to direct the heated air to a desired location on the component said louvers being operable to open during the sublimation step and close when not required.

Preferably the heaters are positioned adjacent one another and said chamber is slidably moveable underneath said heaters so as to be able to be positioned underneath said first heater during the film thermoforming step and underneath the second heater during the sublimation step.

Preferably the fan is a centrifugal fan.

Preferably at least two centrifugal fans are arranged adjacent one another so as to provide turbulent air flow around the component during the sublimation process.

Preferably the first heater is slidably moveable with respect to the chamber housing the component.

Also according to the present invention there is provided a method of printing a three dimensional object by firstly heating a film carrying sublimable inks such that it deforms over an object and subsequently heating the object and film adhered thereto to a higher temperature such the ink sublimates onto the object.

Preferably turbulent airflow is provided around the object during the sublimation step.

Preferably said turbulent airflow is provided by at least two centrifugal fans positioned adjacent on another.

Embodiments of the present invention will now be described by way of an example only and with reference to the accompanying drawings, in which:

Figure 1 is a further diagrammatic sectional view through the ink sublimation printing apparatus in accordance with an embodiment of the present invention:

Figure 2 is a further diagrammatic sectional view through the ink sublimation printing apparatus in accordance with an embodiment of the present invention;

Figure 3 is a diagrammatic sectional view through the ink sublimation printing apparatus in accordance with a second embodiment of the present invention;

Figure 4 is a further diagrammatic side view through the ink sublimation printing apparatus of Fig 3 in accordance with a second embodiment of the present invention;

Figure 5 as a further diagrammatic sectional view through the ink sublimation printing apparatus in accordance with the second embodiment of the present invention;

Figure 6 is a further diagrammatic side view through the ink sublimation printing apparatus of Fig 5 in accordance with the second embodiment of the present invention.

Referring to Figures 1 to 3 of the drawings, there is shown ink sublimation printing apparatus 10. The apparatus 10 comprises a tray 12 suitable for supporting and containing an object to be printed. The tray 12 is itself mounted on a carriage 18 which is itself mounted on a roller mechanism 20 (not shown).

The base 20 of the tray 12 is connected via a pump line 22 to a vacuum pump 24. An on/off valve 26 and a bleed control valve 28 are provided to regulate and control the operation of the vacuum pump 24.

A film 26 containing the desired 'sublimation' inks is positioned over the open end 28 of the tray 12 and clamped in position at the edges 12a of the tray 12 via a clamp 30. The clamp 30 provides a seal between the film 26 and the tray 12. It is also

envisaged that the clamp 30 and the tray 12 may also include pins for locating the film correctly in position although these are not sown in the attached figures.

A first heater 32 is positioned above the tray 12 to provide heat to the film 26. A first fan 34 is positioned adjacent the first heater 32 so as to provide an even distribution of heat to the film 26.

An insulated chamber 36 comprises a suitable fabricated box structure (e.g. insulated steel box) is positioned above the carriage 16 such that the tray 12 can be slidably positioned thereunder during the printing process.

A second heater 38 is provided with an insulated chamber 31 and although only shown figuratively in the drawing is attached to the inner walls of the insulated chamber, a second fan 40 is positioned above the heater 38 and is operated by a motor 42. The heater 38 and the fan 40 are both located within a frustroconcial shaped chamber 42 which is itself positioned over a set of louver elements 44. Each louver 46 is moveable from a closed position as shown in figure 1 to an open position as shown in figure 2.

In use the object to be printed 13 is placed within the tray 12 and a print film 26 is placed over the open end 28 of the tray 12. The vacuum is introduced to the now sealed tray. Air is then removed from the tray by the vacuum pump so as to cause a vacuum to be formed within the tray. The air pressure within the tray is regulated by the valves.

The vacuum causes the film to thermoform around the object to be printed. Initially the level of vacuum is high (typically 16 - 24 in. Hg) to ensure that the object is fully coated where desired, with the film. When the film has formed around the object the vacuum is reduce by the operation of the control valves to typically between 5 and 1 1 in. Hg. The heater 32 is switched on and heat is applied to the film 26 and tray 12 assisted by the fan 34. This fan 34 and heater 32 function as a 'pre heating' fan. When the film 26 has been preheated to a suitable temperature, typically within the range of 80 - 130 ⁹ C and this temperature has been maintained for a suitable period of time to ensure even heating of the film 21.

Meanwhile the heater 38 is switched on and preheated to a high temperature. The tray 12 is then moved to be positioned under the insulation chamber 31 and louvered

elements 44. Once the vacuum is at its lower level the louvers are opened for a short period of time to allow the hot air to travel therethrough and heat the film covered object quickly thus causing the ink thereon to sublimate into the object. The time taken for this sublimation process step is variable dependent on the object to be coated but will typically be between 2 and 30 seconds. Smaller more lightweight components may need shorter times whilst larger heavier components may require longer.

The fan 40 creates a turbulent airflow and breaks down the boundary layer over the film surface and hence allow efficient hest transfer between the air and the film. As the airflow is highly turbulent the heat is evenly distributed over the whole surface of the film and target object such the sublimation process step is advantageously carried out in a relatively short time period so as to avoid any damage to the integrity of the object itself. Also advantageously the apparatus and method of the present invention pre heats the film separately to the sublimation process such that the higher heat application needed for sublimation is only needed for a short period of time. The hot air for the sublimation process is also applied turbulently to allow even heating of the object and film.

Figure 2 shows the apparatus of figure 1 with the louvers 46 in their open position.

Referring to figures 3 to 6 a further embodiment of the present invention is shown diagrammatically. Referring to Figures 1 to 3 of the drawings, there is shown ink sublimation printing apparatus 50. The apparatus 50 comprises a tray 52 suitable for supporting and containing an object to be printed.

The tray 52 is connected to a vacuum pump (not shown).

A film 56 containing the desired 'sublimation' inks is positioned over the open end 58 of the tray 52 and clamped in position.

A first heater 53 is provided in a slidably mounted 'preforming' unit 55 which is in essence a slidably mounted box housing both the first heater 52 and a first fan 54. The first fan 54 is positioned adjacent the first heater 52 so as to provide an even distribution of heat to the film 56 during use. A set of laterally positioned plates 57, 59 & 61 are positioned adjacent the first heater 52 and the fan 54 and direct air flow evenly over the film

An insulated chamber 57 comprises a suitable fabricated box structure (e.g. insulated steel box) is positioned above the slidably mounted performing unit 55.

A second heater 58 is provided with the insulated chamber 57 and although only shown figuratively in the drawing is attached to the inner walls of the insulated chamber. Two fans 60 and 62 are positioned within the insulated chamber and provide turbulence to the heated air therein. Barrier plates 64 and 66 are mounted on the inner ends 68 and 70 of the centrifugal fans 60 and 62. These plates assist in directing the heated air flow towards the component to be printed 72 underneath when required. The centrifugal fans 60 and 62 are also arranged to be backward running so as to assist with the turbulent air flow.

In use the component 72 is positioned in the base 74 of the tray 52 and a film containing the inks for the sublimation process is positioned over the open end of the tray 52. The first heater 52 and fan are operated so as to apply heat to the film 56 and cause it to wrap around the desired areas of the component. The temperature required for this step is approximately 120 ⁰ C. This stage is shown in figures 3 and 4.

Then the performing unit 55 is slidably removed and the fans 60 and 62 and heater 58 are operated so as to heat the air within the chamber 57. This air is circulated and directed via the barrier plates 64 and 66 such that the ink on the film sublimates and/or diffuses into the object 72 to be printed. The temperature required for this stage of the process is approximately 240 ⁰ C and takes approximately 3 to 4 minutes although the timing and heat required is dependent the size of the article.

It is also envisaged that a number of fans and heaters could be positioned adjacent on another so that concurrent printing processes could take place.

The centrifugal fans 60 and 62 are arranged to have their impellors 'backward running' such that a high degree of turbulent air flow is achieved. The hot air advantageously loses the minimum amount of heat by orientating the impellors so that the recirculation path of the heated air is kept within the chamber rather than requiring additional ductwork outside of the chamber.

The fans 60, 62 and 54 could be employed to assist in the cooling of the component after the ink sublimation process has been completed.