GB2315242A - A Printing Process - Google Patents

Abstract

In a printing process a bezel (10) is mounted in a fixture (4) which has a recess seat (16) to hold the bezel in position. A fixed insert (20) within the seat (16) provides upper surface continuity after the bezel (10) has been mounted in place within the seat (16). The bezel passes through a decontamination station at which negative ions are generated to neutralise positively-charged particles adhering to the printing surfaces of the bezel. Immediately after passing under the deioniser, the neutralised particles are blown away in a swirling motion by a nozzle (37). In the downward stroke of a flexible printing pad (40), air is pre-dried by a warm air blower (45). After application of ink a flexible printing pad is used in application of an adhesive gasket in a uniform manner for efficient and reliable application.

Description

"A Printing Process" The invention relates to a printing process, and more particularly to a process for printing moulded plastics casings of the type having printing surfaces which are both uneven and are also separated by apertures. An example of such a casing is a bezel for a mobile telephone, which has the additional aspects of being thin and therefore easily distorted in handling, and the fact that the printed ink will need to withstand repeated rubbing of the surfaces during use such as by the user's finger when using keys.

Printing of indicia on uneven surfaces is well known generally in the art and is often referred to as "tampo" or "tampon" printing. In this type of printing, a printing pad of flexible material such as silicone is moved between a position at which it receives ink from a reservoir shaped according to the printing indicia, to an application position at which it moves downwardly and presses against the printing surface. Such apparatus are described, for example, in EP337169B2 (Tampoflex), EP474262B1 (Tampoprint), EP537649 (Madag), Wot3/04862 (Tampoprint), US4723485 (Tampoflex) and DE4105535 (Tampoprint). While such apparatus are generally effective for most applications, it has been found that conventional tampo printing is not effective at providing a high quality print on casings of the type described above in a repeatable manner in a high-volume production environment. This is because the printing surfaces are both uneven and separated by apertures, the casing distorts easily, and because the printing surfaces are easily contaminated by airborne particles attracted by static charge and which prevent thorough application of ink. To address the problem of static generally, the provision of vanadium oxide anti-static coatings on the printing pads is described in EP573365A2 (Minnesota Mining and Manufacturing Company).

It is therefore an object of the invention to provide a printing process for printing casings of the type described above in a high volume situation and with low defect rate providing quality of print sufficient to withstand the wear and tear of subsequent use.

According to the invention, there is provided a process for printing a moulded plastics casing of the type having printing surfaces and apertures adjacent the printing surfaces, the process comprising the steps of: mounting the casing in a movable fixture, the fixture having a recessed seat and a fixed insert projecting upwardly within the seat, the casing being received within the seat so that it is immobilised and an aperture is in registry with the fixed insert to provide upper surface continuity between the insert and adjacent printing surfaces; conveying the fixture through a charged atmosphere which neutralises static attraction of particles to the casing; blowing air over the printing surfaces to remove the particles from the casing after the static charge attraction has been neutralised; applying ink to a printing surface using a flexible pad; and removing the casing from the fixture and inspecting for print quality.

Preferably, the fixed insert is of flexible material.

Preferably, the charged atmosphere is generated by a deioniser producing positive and negative ions in a downwardly-directed stream towards the bezel. Ideally, air is blown over the printing surfaces within four seconds of being conveyed through the charged atmosphere.

Ideally, the air is blown over the printing surfaces in a swirling flow.

In one embodiment the air is blown by a rotatable air nozzle, the air pressure causing rotation for blowing over a large surface area.

Preferably the air pressure is in the range of 2 to 4 bar.

In another embodiment, warm air is blown at the printing pads as they lower to apply ink to pre-dry the ink on the pad.

In a further embodiment, warm air is blown by a nozzle having an adjustable position.

In a still further embodiment, the process comprises the further steps of applying a gasket having a body with double sided adhesive and peel-off films to an inside surface of the casing by: peeling a lower film to expose the gasket body and locating the body on the inside surface of the bezel; and a piston pressing a flexible printing pad down against the gasket top film in a manner whereby the pad spreads out on impact to comprehensively press all parts of the gasket body against the casing and cause it to adhere in position.

Preferably, the casing is located by edge registry against a stop, position being sensed by a proximity sensor which activates the piston.

In another embodiment, the process is carried out in a controlled environment having an ambient temperature in the range of 14"C to 180C.

The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which: Fig. 1 is a perspective view from the front of a printing apparatus used in a process of the invention; Fig. 2 is a perspective view from the rear of the apparatus; Fig. 3 is a perspective view of a bezel to be printed by a process of the invention; Fig. 4 is a perspective view of a fixture in which the bezel is mounted; Fig. 5 is a perspective view showing the fixture with the bezel mounted within it; Fig. 6 is a perspective view showing a decontamination station with a bezel beginning to pass through the station; Fig. 7 is a diagrammatic cross-sectional side view showing the bezel passing through the decontamination station; Fig. 8 is a perspective view showing the bezel exiting the station; Fig. 9 is a diagrammatic rear view showing the manner in which air is blown over the bezel; Figs. 10 and 11 are diagrammatic side views showing application of print in the process of the invention; Fig. 12 is a perspective view showing a post-printing assembly station; Figs. 13 and 14 are diagrammatic side views showing the station in operations; and Fig. 1S(a) shows a gasket in perspective and side views, Fig. 15(b) is a perspective view from underneath showing a bezel within which the gasket is to be mounted, Fig. 15(c) is a perspective view showing the gasket being located within the bezel, and Fig. 15(d) is a perspective view showing the bezel with the gasket both located and pressed in position.

Referring to the drawings, and initially to Figs. 1 and 2 there is shown a printing apparatus 1 for use in carrying out a printing process of the invention. The apparatus 1 comprises a tampo printing head 2 beneath which casings to be printed are fed by a rotating carousel 3 having fixtures 4. The fixtures 4 are conveyed on the carousel 3 through a decontamination station 5 immediately before application of ink at the printing station 2.

The process of the invention is for printing of moulded plastics casings of the type which have printing surfaces which are both uneven and are separated by apertures. A major example of such a type of casing is a bezel for a mobile telephone such as the bezel 10 shown in Fig. 3.

The bezel 10 comprises a moulded plastics body having a thickness of less than two millimetres and which has a relatively large aperture 12 for reception of an LCD display and a set of relatively small apertures 13 for keys.

The process is carried out under ambient conditions with constant air extraction and a temperature of 14"C to 180C, preferably 16"C. In the printing process the bezel 10 is mounted in a fixture 4, illustrated most clearly in Fig.

4. The fixture 4 comprises a body 15 of machined aluminium construction having a recessed seat 16 which receives the bezel 10. On each side of the seat 16 there is a gripping recess 17 to allow insertion and removal of the bezel. A peripheral track 18 runs around within the seat 16 for accommodation of the side walls of the bezel.

The fixture body 15 forms a platform 19 within the seat 16 and supports a fixed insert 20 which is secured to it.

The insert 20 is of rectangular shape and of rubber material and is positioned so that it is in registry with the large aperture 12 when the bezel 10 is placed within the seat 16. This is shown in Fig. 5 in which the bezel 10 is located in position within the seat 16 so that it is immobile and the upper surface of the fixed insert 20 provides continuity with the adjacent printing surfaces on the bezel 10.

After mounting in the fixture, the bezel is conveyed on the carousel 3 through the decontamination station 5.

This is illustrated most clearly in Figs. 6 to 9 inclusive. The decontamination station 5 comprises a support plate 30 mounted over the carousel 3 at one end and which supports a bracket 31. This in turn supports a deioniser 32 which is directed downwardly towards the carousel 3 and which is supplied with power from cables 33. The deioniser 32 is of the type which generates a charged environment around its tip, the resulting positive and negative ions acting on the bezel and the particles adhered to the bezel to neutralize them. Thus, as the bezel 10 passes underneath the deioniser 32, any particles which had adhered by static electricity to the printing surfaces are no longer attracted to the bezel. The ions which are generated, neutralise the static charge of the bezel which is generated during moulding.

The plate 30 also supports an air duct 35 supplied by a pneumatic supply 36, and which directs air into a rotatable nozzle 37. The nozzle 37 is coil-shaped so that, as shown in Fig. 9, it rotates under the air pressure (4 bar) to blow air in a swirling motion across the printing surfaces of the bezel 10. It will be appreciated that this is a very effective way of blowing air in a comprehensive manner across the printing surfaces. Because the nozzle 37 is mounted only less than ten centimetres from the deioniser 32, the particles which have been neutralised by the deioniser 32 are very quickly blown away from the bezel 10, in this embodiment within four seconds.

Immediately after passing through the decontamination station 5 the bezel is conveyed by the fixture on the carousel 3 to a position at the printing station 2. This conveying action is carried out at a speed whereby application of ink takes place within ten seconds, and preferably within six seconds of decontamination of the bezel. At the printing station 2 a printing pad 40 is supported by a vertically reciprocating head 41 to move down and press against the bezel 10 at the appropriate location for printing. Ink which is on the printing pad 40 is dried by the action of a warm air stream from an adjustable air nozzle 45 mounted on a manifold 46, as shown in Fig. 10. The ink is of the acrylic-based type, mixed with hardener in a ratio of 10:1 by weight for high mechanical resistance. In more detail, the ink is of the type marketed under the code TP 300 and the hardener under the code TP219, both by Wiederhold.

As shown in Fig. 11, irregular deformation of the printing pad 40 is avoided by the fact that the fixed insert 20 provides a continuity in the surface which comes into contact with the printing pad. It has been found that this simple arrangement considerably reduces wear on the printing pad, thus reducing production costs. Another important advantage is the fact that quality of the print, particularly next to the aperture is very high because there is little or no distortion of the pad. It is found that where the apertures are relatively small such as the apertures 13, there is no need for a fixed insert, however, if ink is to be applied very close to such apertures and the surface is quite uneven, a fixed insert may easily be provided as required. For the application of ink, it has been found that by pre-drying the ink as it is on the printing pad and moving in the downward stroke towards the bezel, an optimum situation has been found whereby the ink is sufficiently liquid for comprehensive and effective application, but also dries quickly after application, again reducing the defect rate.

After printing, the bezel may be further processed by application of a gasket of the type having adhesive on both sides. This is achieved by use of a post-printing assembly station 50 having a controller 51 mounted on an inverted U-shaped bracket 52 supporting a pneumatic ram 53 driving a flexible printing pad 54 in a vertical stroke.

The station 50 also comprises a infra-red sensor, not shown, for detection of insertion of a bezel 10 underneath the pad 54. A gasket of the type which is applied is shown in Fig. 15(a). The gasket 60 initially comprises a lower peel-off layer, a gasket body 61 having adhesive on both sides, and an upper peel-off layer 62. The gasket 60 is shown in Fig. 15(a) after the lower layer has been peeled off. The underneath of the bezel 10 is shown in Fig. 15(b) in which it is clear that the gasket 60 must be applied to an underneath surface adjacent a protruding pad 65 and around the aperture 12. This is achieved by, as shown in Fig. 15(c), initially locating the gasket 60 after the lower layer has been peeled off at the correct position by placing in position without pressing it down.

As shown in Figs. 13 and 14 the bezel is then pushed into position underneath the pad 54, this position being sensed by an infra-red sensor which causes the ram 53 to move the pad 54 downwardly so that it presses against the gasket 60 as shown in Fig. 14. It is clear from this drawing that the pad 52 spreads out so that it comprehensively presses the gasket 63 downwardly at all of the awkward locations around the pad 65 and the aperture 12. The resulting bezel 10 is shown in Fig. 15(b) in which the upper peeloff layer 62 is still in place with a tab 66 protruding from it to allow subsequent removal when the bezel 10 is being used to assemble a complete mobile telephone. It will be appreciated that application of the gasket in this manner is very comprehensive and effective and achieves uniform adhesion throughout the gasket 60. It will also be appreciated that very simple parts have been used, such as standard flexible printing pads 54 which are required for application of ink. Indeed, it has been found that pads which would otherwise be disposed of are often suitable for this application and the cost is minimal.

The invention is not limited to the embodiments hereinbefore described but may be varied in construction and detail.

Claims (14)

1. A process for printing a moulded plastics casing of the type having printing surfaces and apertures adjacent the printing surfaces, the process comprising the steps of: mounting the casing in a movable fixture, the fixture having a recessed seat and a fixed insert projecting upwardly within the seat, the casing being received within the seat so that it is immobilised and an aperture is in registry with the fixed insert to provide upper surface continuity between the insert and adjacent printing surfaces; conveying the fixture through a charged atmosphere which neutralises static attraction of particles to the casing; blowing air over the printing surfaces to remove the particles from the casing after the static charge attraction has been neutralised; applying ink to a printing surface using a flexible pad; and removing the casing from the fixture and inspecting for print quality.

2. A process as claimed in claim 1, wherein the fixed insert is of flexible material.

3. A process as claimed in claims 1 or 2, wherein the charged atmosphere is generated by a deioniser producing positive and negative ions in a downwardly directed stream towards the bezel.

4. A process as claimed in any preceding claim, wherein air is blown over the printing surfaces within four seconds of being conveyed through the charged atmosphere.

5. A process as claimed in any preceding claim, wherein the air is blown over the printing surfaces in a swirling flow.

6. A process as claimed in claim 5, wherein the air is blown by a rotatable air nozzle, the air pressure causing rotation for blowing over a large surface area.

7. A process as claimed in claim 6, wherein the air pressure is in the range of 2 to 4 bar.

8. A process as claimed in any preceding claim, wherein warm air is blown at the printing pads as they lower to apply ink to pre-dry the ink on the pad.

9. A process as claimed in claim 8, wherein the warm air is blown by a nozzle having an adjustable position.

10. A process as claimed in any preceding claim, comprising the further steps of applying a gasket having a body with double sided adhesive and peel-off films to an inside surface of the casing by: peeling a lower film to expose the gasket body and locating the body on the inside surface of the bezel; and a piston pressing a flexible printing pad down against the gasket top film in a manner whereby the pad spreads out on impact to comprehensively press all parts of the gasket body against the casing and cause it to adhere in position.

11. A process as claimed in claim 10, wherein the casing is located by edge registry against a stop, position being sensed by a proximity sensor which activates the piston.

12. A process as claimed in any preceding claim, wherein the process is carried out in a controlled environment having an ambient temperature in the range of 14"C to 180C.

13. A process substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

14. A printed casing whenever produced by a process as claimed in any preceding claim.