This invention relates to a method and a device for printing objects, more particularly for printing the surface of three-dimensional objects.

A practical application intended by the invention is the application of a decorative coating on the casing of portable telephones, in particular on the front side of GSM devices. It is known that the front side of such devices comprises inwardly-directed parts, such as, for example, the seats of the push-buttons. Generally, these front sides are provided with a colour or ink coating by means of a paint spraying technique. A disadvantage of this technique consists in that it is difficult to provide the inward-bent parts with ink and/or colour.

This becomes even more difficult when the coating must not consist of only one and the same colour layer and, for example, it is desired to form images on the front side, as then it is necessary to work with masks. Another disadvantage consists in that this technique is little environment-friendly, as a large part of the colour or ink will get beside the object.

The present invention in the first place aims at a method and a device which are particularly suited for printing three-dimensional objects. More particularly, it aims at a technique whereby the aforementioned disadvantages when printing the front side of GSM devices and similar, are excluded.

To this aim, the invention concerns a method for printing objects, with as a characteristic that it at least consists in, on one hand, the application of printing ink on a carrier consisting of a flexible layer-shaped

material and, on the other hand, transferring the prin- ting ink to the object to be printed, by bringing said carrier and the object into mutual contact and by pressing-on said carrier, by means of supplementary pressing means, at least partially around the object to be printed.

By using a flexible carrier, it is obtained that the carrier easily can assume the shape of the surface to be printed and, by moreover applying supplementary pressing means therewith, a complete pressing-on can be guaran- teed.

Preferably, for the supplementary pressing means use is made of a fluid pressure, more particularly air pressure, with which a pressure is exerted on the side of the carrier which is opposite to the side which is brought into contact with the object to be printed.

According to another possibility, supplementary pressing means of mechanical nature are applied, such as a counterform of the object to be printed, with which the carrier can be pressed against the object.

In the most preferred form of embodiment, the aforemen- tioned two kinds of pressing means will be combined, which, in the first place, is useful when printing the front side of a portable telephone. By this combination, it is achieved that the carrier can be pressed into small, relatively deep indentations by means of the counterform, whereas by the pressing, realized by means of the compressed air, on one hand, always a perfect pressing over the entire surface to be printed is guaranteed, whereas, on the other hand, also the bent lateral edges of the object can be printed which are difficult to reach by means of a counterform.

In a preferred form of embodiment, the image to be printed is applied on the carrier in two-dimensional condition and then, by deformation of the carrier, printed on the object in three-dimensional condition.

This technique allows for that the application of the image which can consist of a figure as well as of an even coating of one and the same colour or similar, can easily be realized.

In a practical form of embodiment, the carrier will be stretched at least during the application of the printing ink, in such a manner that during the application a flat substructure is offered. According to a variant, however, it is not excluded to provide a support surface under this carrier during the application of the printing ink, whether or not combined with the stretching of the carrier.

Preferably, the carrier will also be stretched during the actual printing, for example, by pressing the object to be printed over a well-defined distance into the plane of the carrier.

More particularly, it is preferred that the carrier during the application of the printing ink and the actual printing is stretched in opposite direction, whereby it is displaced over approximately the same distance, and even better is displaced in such a manner that approximately the same extension at the location of the printed image takes place, with the advantage that there is almost no size difference between the image applied on the carrier and the printed image.

Practically, a carrier will be applied showing a contact surface consisting of a colour-or ink-repellent mate- rial. According to a particular characteristic of the

invention, to this aim use will be made of a silicone mat or a flexible layer of material based on silicones. Such material offers the advantage that it is very flexible and at the same time will easily release the printing ink during printing.

According to a particular aspect of the invention, the printing ink is provided on the support by means of a printer. As a result of this, forming different images and rapidly switching over from one image to the other is rendered very easy, simply by controlling the printer.

The invention also relates to a device for realizing the aforementioned method, with as a characteristic that it at least consists of a carrier of a flexible layer-shaped material; means for applying printing ink on the carrier; means for transferring the printing ink to the object to be printed, said means consisting of a displacement mechanism for bringing said carrier and the object into mutual contact; and supplementary pressing means which cooperate with the carrier and allow to press on the latter, at least partially around the object to be printed.

With the intention of better showing the characteristics according to the invention, hereafter, as an example without any limitative character, a preferred form of embodiment is described, with reference to the accompany- ing drawings, wherein: figure 1 schematically represents a device according to the invention; figure 2 represents a cross-section according to line II-II in figure 1; figures 3 and 4 represent the device of figure 1 in two other positions;

figure 5, at a larger scale, represents the part indicated by F5 in figure 4.

As represented in the figures, the device 1 of the invention substantially consists of a carrier 2 of a flexible layer-shaped material; means 3 for applying printing ink on the carrier 2; means 4 for transferring the printing ink to the object 5 to be printed, in this case the front part of a GSM device; and supplementary pressing means 6 which cooperate with the carrier 2 and allow to press on the latter, at least partially around the object 5 to be printed.

The carrier 2 consists of a colour-or ink-repellent material, more particularly a mat which is held at its circumference, in this case by being clamped at its circumference, by means of bolts 7, in a framing 8. In the example, the carrier 2 in the condition of figure 1 is not or almost not stretched.

According to the invention, this carrier 2 preferably consists of a silicone mat. Particularly good results can be obtained with a mat having, in un-stretched condition, a thickness of 1 to 3 mm, and preferably 2 mm.

The means 3 for applying the printing ink on the carrier 2 substantially consist of a printer 9 which can be controlled in a suitable manner, either by means of a suitable software package, or by means of a not represented computer unit.

This printer 9, in its turn, can show a classic construc- tion and substantially consists of a printing head 10, with which preferably several colours can be printed, and driving means for moving the printing head 10, on one hand, along one or more longitudinal guides 11 and, on

the other hand, one or more transversal guides 12.

Further, the device 1 comprises means 13 for presenting the object to be printed which, in the represented example, consist of a holder 14 with which the object 5 is held, and a driving cylinder 15 for moving the holder 14 up and down. According to a not represented variant, these means 13 may also consist of a robot arm which takes up the objects 5 to be printed one after the other and presents them to the device 1.

The means 4 for transferring the printing ink to the object to be printed, form a part of displacement means which allow to move the carrier 2 and/or the means 3 and/or the means 13 in respect to each other, in order to bring them, on one hand, into a first position, whereby the carrier 2 cooperates with the means 3 for applying the printing ink, and, on the other hand, into a second position whereby the carrier 2 cooperates with the object 5, in such a manner as will be further explained in the following.

Said supplementary pressing means 6 consist in the represented example of a pressure chamber 16, more particularly a compressed air chamber, which cooperates with the side 17 of the carrier 2 which is opposite to the side 18 which is brought into contact with the object 5 to be printed, as well as of a counterform 19 with which the carrier 2 can be pressed against the object 5 to be printed or at least is forced to take the the shape of the object 5 to be printed to a minor or major extent.

The pressure chamber 16 consists of a casing 20 which is closed off at the upper side by means of the carrier 2.

This casing 20, by means of a conduit 21, can be set under pressure, depressurized, respectively. In the

represented example, the counterform 19 is mounted fixedly in the pressure chamber 16.

In the represented example, said displacement means comprise, on one hand, the already mentioned driving cylinder 15 for displacing an object 5 carried thereby and, on the other hand, a driving cylinder 22 for displacing the pressure chamber 16 between a position under the printer 9, as represented in figures 1 to 3, and a position under the driving cylinder 15, as represented in figure 4.

The device is also provided with means 23 for stretching the carrier 2 during the application of the printing ink on this carrier 2, consisting of a frame 24 in the shape of a rectangular framing, which can cooperate with the underside of the carrier 2, more particularly can be moved up and down between a position whereby the frame 24, as represented in figure 1, is located freely under the carrier 2, and a position whereby the frame 24, as represented in figure 3, is moved upward, as a result of which the carrier 2 is stretched and tensioned. The movement of the frame 24 is performed by means of driving cylinders 25.

The whole is controlled by means of a control unit 26 which may consist of a computer or similar. The driving cylinders 15,22, and 25 are fed by means of a compressed air supply 27 and are controlled by means of valves 28 which, in a suitable manner, according to the working cycle explained in the following, are actuated by means of the control unit 26.

Figure 1 shows the non-operated condition. From this non- operated condition, the driving cylinders 25 are actuated, as a result of which the frame 24 is brought up

into the position of figure 3 which is such that the carrier 2 then is positioned precisely under the printing head 10, in stretched condition.

Subsequently, the printer 9 is controlled, in such a manner that printing ink 29 is deposited on the carrier 2, whereby the image to be printed is formed. Hereby, this may either relate to an image representing a picture, or to an image simply consisting of a quantity of printing ink of the same colour, preferably in the shape of the object 5 to be printed.

It is noted that the term printing ink has to be interpreted broadly and that, according to the invention, any material has to be subsumed thereunder with which a coating can be realized, thus, an actual ink as well as a paint, varnish or any other material.

After the image has been formed on the carrier 2, the frame 24 is lowered again and the pressure chamber 16 is moved up into a position whereby this latter is positioned with the counterform 19 under the object 5. By subsequently moving the object 5 downward, by means of the driving cylinder 15, and pressing it against the counterform 19 and also feeding compressed air into the pressure chamber 16, a condition is obtained as represented in figures 4 and 5. In this condition, the carrier 2, on one hand, due to the presence of the counterform 19, and, on the other hand, due to the pressure P in the pressure chamber 16, perfectly fits against the object 5 to be printed, as a result of which the printing ink 29 of the image is adequately transfer- red to the object 5. The protrusions 30 of the counter- form 19 hereby penetrate into the seats 31 for the telephone push-buttons.

For pressing-on the carrier 2, in the pressure chamber 16 preferably only a rather low pressure is applied, of less than 100 and even better of 50 to 60 gram/cm2.

Finally, the object 5 can be moved upward again and subsequently be transported off, after which the cycle can be repeated with a successive object 5.

It is noted that the distance A over which the carrier 2 is moved in figure 3 preferably almost coincides with the distance B over which this carrier 2 is moved in figure 4, in such a manner that an almost equal extension of the material of the carrier 2 at the location of the object 5 is obtained.

Possibly, the device 1 can be equipped with a cleaning mechanism, which may or may not work automatically, in order to remove inconvenient ink remainders from the carrier 2.

It is obvious that different variants are possible. So, for example, instead of attaching the framing 8 by means of bolts 7, this framing 8 can be equipped with an easy to handle stretching mechanism.

The movement cycle also does not necessarily have to be performed precisely such as represented in the figures.

So, for example, it is not excluded to mount the pressure chamber 16 in a fixed manner and to install the means 13 above the printer 9, whereby the printing head 10 is moved sidewards at the moment when the object 5 is brought into contact with the carrier 2.

According to a particular variant, the counterform 19 is positioned precisely under the carrier 2, whereby this is possible for the position of figure 1 as well as for the

one of figure 3.

It is noted that the invention also relates to methods and devices whereby for the supplementary pressing means, either use is made exclusively of fluid pressure, or use is made exclusively of mechanical pressing means. It is also not excluded to use a liquid for the fluid pressure instead of a gas.

The present invention is in no way limited to the form of embodiment described by way of example and represented in the figures, on the contrary may such method and device for printing objects be realized according to different variants, without leaving the scope of the invention.