GB2442824A - Apparatus for diffusion dying a 3D surface and for vacuum forming - Google Patents

Abstract

The apparatus preferably comprises an infinitely variable speed fan 11 providing hot air flow at a low speed or Reynolds number to soften a film, and at a high speed or Reynolds number for dye diffusion. In the preferred embodiment, heaters (8, electric or 9, gas) are modulated to maintain air in an enclosure (acting as a hot air reservoir) between 160 and 260 degrees centigrade. Film 6, which may carry a dye, is mounted onto frame 5 on movable carriage 1a above workpiece (if dying) or former (if vacuum forming) 3. The carriage is then moved under chamber 12a, shutter 7 withdrawn and fan speed reduced to heat, soften and dry the film. The vacuum platen is then raised to seal around the film, and apply vacuum to form the film around the workpiece or former. The fan speed is then increased while dye is being transferred to the workpiece. The shutter then returns and the dyed or moulded component is removed when the carriage is returned to its starting point. The component may be removed following a cooling period. Compressed air may be used to remove the film.

Description

An apparatus for applying Dye Diffusion Techniques to imensional

Surfaces with additional Vacuum Forming capability 2 Dimensional Dye Diffusion has been well known for several years. In this technique special dyes are applied to a paper substrate The paper is then placed on or wrapped around an object to be coloured. With simultaneous application of pressure and heat the dye Diffuses and penetrates the object. Using paper as the carrier limits the objects that can be coated to 2 dimensions. In 3 dimensional dye diffusion a special film that can be printed on conventional printers but can be vacuum formed when heated is used 3 to Dimensional Diffusion techniques are fairly well developed for smaller applications but scaling up for industrial size equipment has been limited by the operational techniques used This application allows expansion of the process into industrial sized equipment without any process time penalties. The apparatus has the added benefit of being able to be used for pre-forming plastic components using the vacuum forming cycle. Vacuum forming technology is well known where plastic sheets are pre-heated and formed over a suitable former. Combining this with 3 Dimensional Dye Diffusion capabilities allows a large range of components to be formed and have applied patterns in one facility. The apparatus can be used exclusively for either function or as a combination machine for both.

Diffusion dyes are water based and any residual moisture on the film during diffusion can result in uneven transfer characteristics. This apparatus allows the control within the process to dry off excess moisture as part of the cycle.

Traditional 3 Dimensional Dye Diffusion equipment follow a cycle as below * Either:-The target objects are loaded The special pre-printed film is loaded The cycle starts.

Either: -the whole machine warms the special film slowly from a low reference point until it is soft enough to be vacuum formed around the target object. This is typically 110 to degrees C. The machine then is heated up to the Diffusion temperature for the required time period. This method results in a total cycle time of typically 5 minutes or more, as such it is typically ideally suited to an educational or occasional use.

* Or:-A dedicated film-preheater is used with separate fans and heaters, this is run until the special film softens enough to be vacuum formed around the target object. (Again, this is typically 110 to 120 degrees C). A hot chamber and fans above the preheater then exposes the film to Diffusion temperatures for the required time period. This method results in a total cycle time of typically 2 minutes or more, as such it is typically ideally suited to occasional use or very small scale production The improved apparatus allows simplification of the process along with reduction of the whole cycle time The apparatus uses air at the high Diffusion temperature to preheat the special film hence eliminating the need for a dedicated preheater Control of the preheat function being by utilising the variable speed of the main fan along with a time function For the vacuum forming cycle, the special film is replaced by the plastic sheet to be formed and the fan speed controlled to give the ideal heat transfer conditions to evenly heat the sheet. Varying the fan speeds allows variation of the heat transfer co-efficient which is normally assumed to be a function of Reynolds Number i.e. where p is the fluid density u is the fluid velocity d is a dimensional unit u is the fluid viscosity A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which Figure 1 shows the layout of the plastic sheet and/or special film pre-forming and final ink-sublimating area.

As shown in figure 1, the apparatus comprises a raise/lower table (1) mounted on a moving carriage (la) on which is mounted a vacuum platen (2) around the vacuum platen is a seal (2a). Workpieces or formers for vacuum forming of any shape (3) are loaded onto the table. Surrounding the vacuum platen is a carrier frame (4), this in turn is mounted on independent raise/lower devices shown here as pneumatic cylinders but may be any known method. The carrier frame supports the film frame (5) with the special film or plastic sheet (6) attached to its underside, the film may be positively located on the frame which in turn is located relative to the vacuum platen. A moving shutter (7) is mounted below the heated chamber to isolate the moving carriage and its associated components from the high temperature enclosure above it. The shutter is shown being actuated by pneumatic cylinders but may be any known method. The shutter is shown as a single component but may be made up of multiple parts which are moved independently.

The high temperature enclosure may be heated by either electric (8) or gas (9) heaters.

The air within the enclosure is recirculated by a variable speed controlled centrifugal fan (10); although mixed flow fans may be used (speed control is infinitely variable from 0 to 100%). The air is distributed across the full area of the vacuum platen by a combination of diffuser plates (11) and special nozzles (12) which results in a consistent vertical velocity of air at the outlet of each nozzle. Air after exiting the nozzles is recirculated via a duct (13) back to the heater/s and fan. The complete enclosure is insulated to prevent excessive heat loss and to protect operators from hot surfaces.

Connected to the vacuum platen is a vacuum pump (15) and a solenoid valve (16). A further valve (17) and fine adjustable flow controller are also fitted. A valve (18) is connected to a compressed air supply and to the vacuum platen.

Figure 2 shows the moving carriage and associated components in the load unload area.

In operation for Diffusion, the heated chamber is pie-heated to the required Diffusion temperature, typically between 160 and 260 deg C. The heaters are then modulated to maintain the temperature within a given range (typically +/-5degrees C). Workpiece/s are loaded onto the vacuum platen and the table is lowered The special film (6) is mounted onto the film frame (5) and then located in the carrier frame (4) The carriage (Ia) along with all the components mounted on it is moved into position under the heated chamber (1 2a). The special film (6) and its associated carrier frames (4 & 5) are at high level. The table (1) and vacuum platen (2) are at low level. The moving shutter (7) is withdrawn. The fan (11) speed is adjusted to the required (low speed) setting and the special film is gently heated for a set period of time (generally between 0 and 20 seconds) using hot air at low velocity. During this time, the special film softens and any excess moisture on the film is driven off. After the time period expires, the raise/lower table and vacuum platen is raised to a position where the special film is pressed onto the seal (2a) around the vacuum platen. The vacuum pump (15) and solenoid valve (16) are then operated to evacuate the air from around the workpiece (3). By operating the bleed valve (17) and flow controller (17a) the level of vacuum may be controlled to a set level. As the air is evacuated from the region between the vacuum platen and the special film, the special film is formed around the workpiece.

The speed of the main fan (11) is then increased to a high level for a pre-set time (typically between 10 and 360 seconds, this is dependant on the workpiece to be coated). This results in the dye being transferred into the surface of the workpiece.

Following the dye transfer, the main fan (11) speed is reduced to a lower speed to maintain an even temperature in the heated enclosure. The moving shutter (7) moves back into position to insulate the heated enclosure.

Dependent on the nature of the workpiece, 2 possible modes of operation are now followed.

1 The vacuum pump (15) and the solenoid valve (16) are switched off. The valve (18) is turned on allowing compressed air into the vacuum platen resulting in the film being lifted away from the workpiece 2. The vacuum pump (15) and the solenoid valve (16) continue operating for a preset time to allow the workpiece to cool to a lower temperature Extra cooling for the work piece may be added to speed up this process.

The carriage (la) and it s associated components are moved back to the load unload area (fig 2) and the film and the workpieces are removed ready for the next cycle.

In operation for vacuum forming, the heated chamber is pre-heated to the required forming temperature, typically between 150 and 200 deg C. The heaters are then modulated to maintain the temperature within a given range. The former is loaded onto the vacuum platen and the table is lowered The plastic sheet (6) is mounted onto the film frame (5) and then located in the carrier frame (4).The carriage (la) along with all the components mounted on it is moved into position under the heated chamber (12a). The plastic sheet (6) and its associated carrier frames (4 & 5) are at high level. The table (1) and vacuum platen (2) are at low level. The moving shutter (7) is withdrawn. The fan (11) speed is adjusted to the required (low speed) setting and the plastic sheet is gently heated for a set period of time (generally between 10 and 40 seconds) using hot air at low velocity. During this time, the plastic sheet softens. After the time period expires, the raise/lower table and vacuum platen is raised to a position where the plastic sheet is pressed onto the seal (2a) around the vacuum platen. The vacuum pump (15) and solenoid valve (16) are then operated to evacuate the air from around the former (3) By operating the bleed valve (17) and flow controller (17a) the level of vacuum may be controlled to a set level. As the air is evacuated from the region between the vacuum platen and the plastic sheet, the plastic sheet is formed around the former.

After the component has been formed, the table and film frames lower and the main fan speed returns to sower speed.

The moving shutter (7) moves back into position to insulate the heated enclosure.

Dependant on the nature of the workpiece, 2 possible modes of operation are now followed.

1. The vacuum pump (15) and the solenoid valve (16) are switched off. The valve (18) is turned on allowing compressed air into the vacuum platen resulting in the film being lifted away from the workpiece.

2. The vacuum pump (15) and the solenoid valve (16) continue operating for a preset time to allow the workpiece to cool to a lower temperature. Extra cooling for the workpiece may be added to speed up this process.

The carriage (la) and its associated components are moved back to the load unload area (fig 2) and the component is removed ready for the next cycle.

Alternately the component may be left in position on the table and a patterned special film loaded. The machine is then cycled in Diffusion mode to apply a pattern to the component.

Claims (9)

1. An apparatus for applying Dye diffusion to 3 dimensional objects.

2. An apparatus as in claim I where an infinitely variable speed fan is controlled to provide the required airflow conditions and consequently the heat transfer coefficients for the various stages of the process.

3. An apparatus as in claims 1 and 2 where a reservoir of hot air is maintained at temperatures typically between 160 and 260 degrees centigrade.

4. An apparatus as in claims 1, 2 and 3 where high temperature air from the hot reservoir at low Reynolds Numbers is utilised to pre soften the special film prior to vacuum forming.

5. An apparatus as in 1, 2, 3 and 4 where high temperature air at low Reynolds Numbers from the hot reservoir is used to drive off excess moisture from the Dye on the special film.

6. An apparatus as in 1, 2, 3, 4, and 5 where high temperature air at high Reynolds Numbers from the hot reservoir is used to perform the Dye diffusion operation.

7 An apparatus as in 1, 2, 3, 4, 5 and 6 which can also be used to vacuum form components.

8. An apparatus as in 1, 2, 3, 4, 5, 6 and 7 which uses high temperature air at low Reynolds Numbers to soften plastic sheet for vacuum forming

9. An apparatus substantially as herein described above and illustrated in the accompanying drawings.