The invention provides for this purpose a method for manufacturing a plastic object, for instance a table top, by injection moulding by means of an injection mould, which mould comprises : - two mould parts which can be displaced between a closed position, in which they bound a mould cavity with a form corresponding with that of the object for manufacture, and an open position in which a formed and cooled object can be removed ; - at least one first conduit debouching in the mould cavity and extending through mould parts for supplying heated, plasticized plastic to the mould cavity ; . - at least one second conduit debouching in the mould cavity and extending through said mould part for supplying gas, for instance air, under pressure to the mould cavity ; according to which method a plastic foil is placed between the mould parts, the mould is closed such that the foil is received in the mould cavity, gas is subsequently admitted under pressure into the mould cavity via the second supply such that the plastic foil is pressed against the opposite wall of the mould cavity while being stretched and/or displaced along the contact surfaces between the mould parts, heated plasticized plastic is then admitted under pressure into the mould cavity, which plastic adheres to the foil, the thus

formed product is then allowed to cool, the mould is opened and the formed product removed.

The invention also comprises an injection mould for performing this method. This mould comprises : - two mould parts which can be displaced between a closed position, in which they bound a mould cavity with a form corresponding with that of the object for manufacture, and an open position in which a formed and cooled object can be removed ; - at least one first conduit debouching in the mould cavity and extending through mould parts for supplying heated, plasticized plastic to the mould cavity ; - at least one second conduit debouching in the mould cavity and extending through said mould part for supplying gas, for instance air, under pressure to the mould cavity.

In order to ensure that the foil will come to lie as well as possible against the opposite wall, use can advantageously be made of pressure-equalizing means whereby air inclusions behind the foil are prevented.

The advantages of the technique according to the invention can be briefly summarized as follows.

The foil, also referred to as decorative material, completely covers the visual side of the product. The necessity for using qualitatively high-grade and relatively costly plastics can be hereby prevented and material of recycled quality can be used.

The invention can be applied very widely in combination with many injection moulding techniques in order to form both solid objects and objects of integral foam.

The method is not critical in respect of foil positioning and foil size.

Depending on the mechanical properties required by the configuration in question, the foil must have determined properties, for instance elasticity, breaking strain, thermal resistance and the like.

The placing of foil under gas pressure takes place at low temperature, for instance room temperature in the order of 20°C, without addition of heat.

The gate system of the injection mould can be of any suitable type, for instance a hot-runner, a sprue cone or a film.

Because in a determined embodiment the foil can still slip relative to the mould parts during closure and the addition of gas under pressure, little or even no stretching occurs, if desired, during the gas pressure phase. The thickness of the foil hereby remains practically uniform.

The invention provides the option of three- dimensional decoration of plastic products.

The accompanying five figures show five successive process steps. The figures are cross-sections through an injection mould according to the invention.

In the figures to be described hereinbelow all components are designated with the same reference numerals.-The following list is applicable.

1. mould 2. first mould part 3. second mould part 4. first ring 5. second ring 6. mould cavity 7. plastic injection conduit 8. compressed air line 9. compressed air line 10. pressure equalization conduit 11. pressure equalization conduit 12. pressure equalization conduit 13. pressure equalization conduit 14. foil 15. sealing ring 16. sealing ring

17. sealing ring 18. injection nozzle of plastic plasticizing and injection device 19. contact surface of ring 4 20. contact surface of ring 5 21. blind wall of mould cavity 6 opposite the outlets of plastic injection conduit 7 and compressed air lines 8 and 9.

22. gap between ring 5 and mould part 3 23. plastic object 24. plastic in injection conduit 7 The description following below omits mention of generally known mechanisms associated with the use and operation of a mould, such as provisions for opening and closing a mould, pressure means for holding a mould in closed position during injection of the plastic, tempering means for controlling the temperature in the relevant ranges, and the like.

It is further noted that the foil to be described hereinbelow must be suitable for adhering to the injected plastic at increased temperature and pressure.

Fig. 1 shows the situation in which mould 1 is closed and ready for use.

Fig. 2 shows the situation in which mould 1 is opened and foil 14 is positioned.

Fig. 3 shows the situation in which mould 1 is closed and foil 14 is lightly clamped between contact surfaces 19,20 with which the two mould parts 2,3 are directed toward each other. The clamping is light, whereby foil 14 can slip relative to these contact surfaces 19,20.

Fig. 4 shows the situation in which via two compressed air lines 8,9 adjacent to injection conduit 7 air under pressure is admitted into mould cavity 6, whereby foil 14 is pressed against the opposite wall 21

of mould cavity 6. Via a gap 22 which is present all around and to which pressure equalization conduits 11,13 connect, air enclosed behind foil 14 is discharged to the outside. In the situation shown in fig. 4 foil 14 now lies exactly against the"visual side"of the injection moulded article 23 (fig. 5) to be formed.

Plastic 24 is then injected (see fig. 5). After this injection the formed object 23, consisting of foil 14 and a plastic mass fused thereto, can be allowed to cool. Mould 1 is subsequently placed back in the opened position and the formed object 23 can be removed. After a final processing, in which for instance superfluous foil material is removed, the object is finished.

As is shown particularly clearly in fig. 4, the method according to the invention is highly suitable for providing a surface with an undercut form with a decorative or cover foil. This is particularly important in the case of objects such as table tops, wherein the edge, the bottom of which is also partly visible, must also satisfy high quality and aesthetic standards.