GB2056903A - Vacuum-moulded articles - Google Patents

Abstract

An article, especially for use in a bathroom, and a method of making the article, comprising a shell (15) permanently vacuum moulded onto a shaped supporting structure (7). In the illustrated embodiment an expanded polystyrene shell (10) having vacuum holes (13) is covered by a heat softened sheet (6) which is drawn onto it by vacuum applied through the holes. <IMAGE>

Description

SPECIFICATION Vacuum-moulded articles This invention relates to vacuum-moulded articles, especially articles for use in a bathroom.

In the manufacture of articles from synthetic plastics materials which have to be robust and, at the same time, have a quality exterior finish (which may have to be strong, hard-wearing, and/or waterproof), it has been found advantageous to make the article from a shell and an interior support structure. For example, a shower tray made in this way can comprise an upper section in the form of a shel which is vacuum-formed in high impact polystyrene, and a lower section, which fills the shell and supports it from below, in the form of injection-moulded expanded polystyrene or polyurethane (structural foam) which is so moulded that it makes a "fully-tailored" glove-tight fit in the underside of the shell.

Conventional vacuum forming techniques have hitherto been used in the manufacture of such shower trays. A sheet of synthetic plastics which can, for instance, be acrylic or high impact polystyrene is put into a vacuum forming machine and heated to approximately 1 35 C, at which it is in its plastic state. A tool made from aluminium or alluminious resin made exactly to the shape and size of the product to be produced and situated on a rising table in the machine is then brought upwards and into contact with the plasticised sheet and a vacuum is applied to remove air between the tool and the material. This vacuum having been created, external air pressure forces the material of the sheet into direct contact with the external surface of the tool so that the material conforms to the shape of the tool's external surface.For this to occur satisfactorily, it is necessary for the tool to have vacuum holes at the bases of all its recesses to enable air to be drawn from them and the sheet to hug their contours. The material is then cooled down by blowing air on to it so that it reverts to its rigid state. The sheet so formed is disengaged from the tool and the process is repeated.

The lower section of the shower tray is made separately by injection moulding expanded polystyrene or polyurethane (structural foam) into a mould which gives the expanded polystyrene or polyruethane the same shape and size externally as the internal shape and size of the shell. The lower section is then inserted into and bonded to the shell to complete the manufacture of the shower tray.

One disadvantage in the way the shower tray has been made hitherto is the additional manufacturing step involved in bringing the shell and lower section together, which increases the cost and time of production.

To overcome this disadvantage, we have devised a new method of making the shower tray, although it will be appreciated that the method has a wider application than this, and could be used in the manufacture of any shaped article, for example, a synthetic plastics bathroom cabinet or a sculptured door panel for a furniture unit.

Accordingly, from one aspect the present invention is directed to a shower tray, bathroom cabinet, sculptured door panel or other article comprising a shell-supporting structure having a given external shape or form with at least one depression, channel, indentation, groove or other recess, the structure also having at least one vacuum hole at the base of the or each recess, and a shell of material permanently vacuum moulded onto the structure so that the shell has the external shape or form of the structure, the shell covering the or each vacuum hole at the base of the recess.

From a second aspect, the invention is concerned with a method of manufacturing a shower tray, bathroom cabinet, sculptured door panel or other article which comprises making a shell-supporting structure having a given external shape or form with at least one depression, channel, indentation, groove or other recess, the structure also having at least one vacuum hole at the base of the or each recess for drawing air therefrom, and vacuum moulding a sheet of material permanently onto the structure, using the or each vacuum hole, so that the sheet takes up the external shape or form of the structure to become a shell thereon or therearound, the structure forming part of the article and the shell remaining permanently fixed on the structure.

It will be appreciated that one recess may need many vacuum holes for effective shaping of the shell into that recess during vacuum moulding.

It is to be understood that the word "recess" is used here in a broad sense to include, for example, the region at the base of a step.

This technique gives a further advantage, for example, in the manufacture of a shower tray, since the expanded polystyrene or polyurethane (structural foam) is both a forming tool and the means of supporting the shell of the tray. The sheet of material which forms the top surface of the tray is therefore not removed from what is used as the tool, and therefore the tray can be made with completely vertical sides or undercuts, that is to say, negative angles can be produced. In the manufacture of shower trays this is particularly helpful at the installation stage. With the previous method of manufacture, the sides of the shower tray had to be inclined inwardly from bottom to top, at least at 121 to the vertical, to enable the shell to be separated from the vacuum moulding tool.This made it necessary to channel out the bases of the shower walls to let the tray in when it was desired to fix tiles to the wall in contact with the top surface of the tray. With vertical sides on the shower tray, it is not necessary to channel out the shower walls.

In experiments we have found that the density of expanded polystyrene for an inside structure to which a relatively thin shell of high impact polystyrene is applied (of thickness of about 0.1" or 2.5 mm or less), is preferably in the region of 21b. to 31b. weight per cubic foot (32 to 48 kilograms per cubic metre). For thicker shells, from which a greater amount of heat has to be dissipated directly it is moulded onto the supporting structure, the latter has to have a higher density so that those parts of it which come into contact with the shell at the moulding stage are not deformed by the heat. Expanded polystyrene of a density in the region of 5 to 61bs. per cubic foot (80 to 96 kilograms per cubic metre) is then desirable.

For a shower tray, for example, it is desirable to have a shell thicknss in the region of 4111 to 2~ (6.0 mm to 12.0 mm). To avoid the heat deforming problems here, experiments have shown that polyurethane (or structural foam) of density 1 Olb/cubic foot (160 kilograms/cubic metre) is preferable for the shellsupporting structure. This thicker material is also less susceptible to inward curving of the underside edges between corners in the case of a shower tray, for example.

Additional experiments have indicated that, in certain instances, it may be advantageous to spray a surface treatment like a hard varnish coating for instance over the expanded polystyrene or polyruethane surface before moulding takes place. For example, if high impact polystyrene or acrylic is used as the shell material, it is preferable to provide for some additional protection against attack of the surface of the expanded polystyrene or polyurethane from the heat of the surface of the shell material at the time when the two surfaces are brought in contact with each other at the vacuum moulding stage.

If a large flat surface exists on the shellsupporting structure, as is often the case with a shower tray, it is also important to spray a glue or bonding agent on the supporting structure to prevent a slight separation that would tend to occur otherwise between the shell and support structure on cooling, due to differential thermal contraction. The glue or bonding agent must be capable of drying without exposure to air, of course.

Depressions, like cavities or apertures, in the expanded polystyrene or polyurethane, as would be the case with a conventional vacuum moulding tool, have to have vacuum holes to allow air sandwiched between the expanded polystyrene or polyurethane and the high impact polystyrene to be displaced.

Without such holes, it would not be possible to form 3-dimensional shapes with depressions or cavities inside the external periphery accurately.

Four materials which have been found useful for the shell are high impact polystyrene, ABS, acrylic capped ABS (which is co-extruded ABS and acrylic) and acrylic per se.

The latter two allow relatively easily removal of scratches on the finished article.

As already indicated, the invention is especially applicable to articles for use in a bathroom. It is, however, of wider application than that, and other articles for use in the home, offices, vehicles, aircraft or ships can equally well be made by the method of the invention.

Examples of an article, and a method and apparatus for manufacturing the article, in accordance with the present invention are illustrated in the accompanying drawings, in which Figure 1 shows a diagrammatic sectional elevational view of apparatus at a heating stage of the manufacture; Figure 2 is a perspective view, on a different scale, of a shell-support structure which is positioned on a table in the apparatus shown in Fig. 1; Figure 3 shows part of the apparatus shown in Fig. 1 during a stretching stage in the manufacture; Figure 4 shows a further diagrammatic sec tiona elevational view of the apparatus shown in Fig. 1, but in a vacuum moulding stage of the manufacture; Figure 5 shows a sectional elevational view of a second shell-support structure;; Figure 6 shows, on a different scale, an underneath view of the structure shown in Fig. 5; Figure 7 is a top perspective view of a third shell-support structure; Figure 8 is an underneath perspective view of the shell-support structure shown in Fig. 7; and Figure 9 is a perspective view of a finished shower tray made from the shell-support structure shown in Fig. 7.

The apparatus shown in Fig. 1 comprises a table 1 mounted on an hydraulic ram 2, a frame 3, and an upper and lower heater 4 and 5. A 4111 to 2111 (6.0 to 12.0 mm) thick sheet 6 of high impact polystyrene, acrylic, ABS, or acrylic capped ABS, is held around its periphery by the frame 3, and a shell-support structure 7 is positioned on the table 1 by means of spigots 8 in such a manner as to leave a bap 9 between the table 1 and the structure 7. The structure 7 is made of polyurethane (structural foam) of a density of about 10 Ibs. per cubic foot (260 kilograms per cubic metre), but it could be made of heavy expanded polystyrene of around 5 to 6 Ibs. per cubic foot (80 to 96 kilograms per cubic metre).

As can be seen more clearly from Fig. 2, the structure 7 has a depression 10 which is three to four inches deep. At the base of the depression 10, around its periphery, there is a channel 11, and at one side of the depression, adjacent to the channel 11, is a plughole 1 2. Vacuum holes 13 extend from the channel 11 to the underside of the structure 7. At the upper surface of the structure, the holes are between 1/32" and 1/1611(0.75 and 1.5 mm) in diameter.

During the stage of manufacture in Fig. 1, the heaters 4 and 5 raise the temperature of the plastics sheet 6 to about 1 35 C. At this temperature, the sheet is in a plasticised state.

It is then pre-stretched into a bubble by means of air-pressure from underneath, as shown in Fig. 3, after which the table 1 is lifted by the ram 2 until it is about level with the frame 3. Air is sucked out by means of a vacuum pump (not shown) and holes (also not shown) in the table 1, via the vacuum holes 1 3 and the gap 9 between the structure 7 and the table 1. The gap 9 allows air between vertical sides 14 of the structure 7 and the sheet 6 to be forced out. In this way the sheet 6 is sucked against the upper side of the structure 7 to conform to the external shape thereof, thereby to form a shell 15.

A bonding agent may be applied to the upper surface of the structure 7 or the lower surface of the sheet 6 before they are brought into contact with one another, so that the two stick more firmly together when they are brought into contact with one another. It is necessary, of course, that the bonding agent will be effective without exposure to air, since all air between the sheet 6 and structure 7 is withdrawn during the vacuum moulding stage.

Finally, cool air is blown onto the article to bring the material of the newly formed shell 1 5 back to its rigid state. The completed shower tray comprises the structure 7 together with the shell 15.

A second form for the shell-supporting structure is shown in Figs. 5 and 6. The structure 16 is made of polyurethane or structural foam. Since this is an expensive material, the body of the structure is made of crisscrossing vertical internal walls 17. The upper side of the structure is the same as that shown in Fig. 2, but the underside is as shown in Fig. 6. This alternative form can be made by injection moulding with two mould pieces, one having the shape defined by the desired upper side of the finished structure, and the other comprising upwardly extending square-sectioned blocks in matrix array with varying heights according to the shape of the upper side. The internal box-sections of the finished structure have a 3" to 4" (7.6 to 10.0cm) side.

A third support structure 24 for a shower tray is shown in Figs. 7 and 8. This structure is in the form of a square of injection-moulded expanded polystyrene or polyruethane (structural foam) which has a flat peripheral upper rim 26, a fluted depression 28, a peripheral channel 27 of the depression 28, and a plug hole 30. The depth of the structure 24 is 6" (1 8.2cm), its side walls are 30" (76.2cm) long, and its under-surface 32 (see Fig. 8) has four straight parallel depressions 34 to save material.

As already indicated, the density of the structure 24 needs to fall within a particular range for satisfactory results to be obtained.

This density is measured in the trade simply in pounds weight, and in this particular instance the density is substantially 61b. (96 kilograms per cubic metre) but it could be anywhere between 1.51b (24 kilograms per cubic metre) and 121b. (192 kilograms per cubic metre) or more.

Vacuum holes 31 extend right the way through the structure 24, opening out through its upper surface at the various recesses thereof including the base of the channel 27 and the bases of the flutes.

A shell 40 of high impact polystyrene is vacuum-formed over the support structure 24 to create the finished shower tray shown in Fig. 9. The same technique as illustrated and described with reference to Figs. 1 to 4 is used to do this. The resulting shower tray is shown in Fig. 9, and has a first peripheral rim 42 conforming to the upper rim 26 of the support structure 24, and a 3-4"-deep depression 44 the base of which has fan-shaped shallow flutes 46 as defined by the fluted depression 28 of the support structure 24. A plug hole 48 is also formed corresponding to the plug hole 30 of the support structure. In fact the hole is closed by the shell 40 in Fig.

9, but this is pierced when the shower tray is installed. The shower tray can be, say, 30" square (76.2cm square) and about 6" (1 5.2cm) in depth. The side walls 50 of the finished shower tray are spaced away from the peripheral walls 52 of the depression 44, the space between these walls and under the depression being filled by the support structure 24.

As in the foregoing examples, a bonding agent may be applied to the upper surface of the structure 24 and/or the lower surface of the sheet which forms the shell 40, before it is brought into contact with the sheet so that the two stick more firmly together when they are brought into contact with one another.

The bonding agent can set in the absence of air.

The foregoing vacuum-moulding technique ensures that no movement can take place between the shell and the support structure.

The vacuum holes in the shell-supporting structure of the finished article may be left open, or they may be plugged or otherwise sealed.

Claims (34)

1. A shower tray, bathroom cabinet, sculptured door panel or other article comprising a shell-supporting structure having a given external shape or form with at least one depression, channel, indentation, groove or other recess, the structure also having at least one vacuum hole at the base of the or each recess, and a shell of material permanently vacuum moulded onto the structure so that the shell has the external shape or form of the structure, the shell covering the or each vacuum hole at the base of the recess.

2. An article according to claim 1, in which the or each vacuum hole is plugged or otherwise sealed in addition to its being covered by the shell.

3. An article according to claim 1 or claim 2, in which the shell-supporting structure is an injection moulding.

4. An article according to any preceding claim, in which the shell-supporting structure comprises expanded polystyrene.

5. An article according to claim 4, in which the expanded polystyrene has a density of 1 .51b. to 31b. per cubic foot (24 to 48 kilograms per cubic metre).

6. An article according to claim 5, in which the density is 21b per cubic foot (32 kilograms per cubic metre).

7. An article according to claim 5, in which the density is substantially 5 to 6 lb.

per cubic foot (80 to 96 kilograms per cubic metre).

8. An article according to any one of claims 1 to 3, in which the shell-supporting structure comprises polyurethane (structural foam).

9. An article according to claim 8, in which the polyurethane (structural foam) has a density of substantially 10 lb. per cubic foot (1 60 kilograms per cubic metre).

10. An article according to any preceding claim in which the shell is substantially 0.1 to 1/8" thick (2.5 to 3.0 mm thick).

11. An article according to any one of claims 1 to 9, in which the shell is substantially 4111 to 21' thick (6.0 to 12.00 mm thick).

12. An article according to any preceding claim, in which the shell is made of high impact polystyrene, ABS, acrylic, or acrylic capped ABS.

13. An article accoding to any preceding claim, having sides which are substantially perpendicular to a main face of the structure, or sides having negative angles or undercuts.

14. An article according to any preceding claim, in which the shell and the shell-supporting structure are stuck together by means of a bonding agent between them.

15. An article according to any preceding claim having a shell-supporting structure with a multiplicity of criss-crossing internal walls.

16. An article according to any preceding claim, being a shower tray comprising an upper section in the form of a shell which is vacuum-formed in high impact polystyrene or other strong synthetic plastics material, and a lower section, which fills the shell and supports it from below, in the form of injectionmoulded expanded polystyrene, polyurethane or other synthetics material, there being a "fully-tailored" glove-tight fit between the upper and lower sections.

17. An article according to claim 16, having a fluted depression, a peripheral channel of the depression, and a plug hole.

18. A shower tray substantially as described herein with reference to Fig. 4 or without the modification shown in Figs. 5 and 6, or with reference to Fig. 9 of the accompanying drawings.

19. A method of manufacturing a shower tray, bathroom cabinet, sculptured door panel or other article which comprises making a shell-supporting structure having a given external shape or form with at least one depression, channel, indentation, groove or other recess, the structure also having at least one vacuum hole at the base of the or each recess for drawing air therefrom, and vacuum moulding a sheet of material permanently onto the structure, using the or each vacuum hole, so that the sheet takes up the external shape or form of the structure to become a shell thereon or therearound, the structure forming part of the article and the shell remaining permanently fixed on the structure.

20. A method according to claim 19, in which the shell-supporting structure is formed by injection moulding.

21. A method according to claim 19 or claim 20, in which, prior to the vacuum moulding, the shell-supporting structure is sprayed with a hard varnish coating.

22. A method according to any one of claims 19 to 21, in which the sheet is preheated by heaters arranged on both sides of the sheet.

23. A method according to any one of claims 19 to 22, in which the sheet is preheated to substantially 135 C.

24. A method according to any one of claims 19 to 23 in which, prior to the vacuum moulding, the sheet is pre-stretched.

25. A method according to claim 24, in which the prestretching is brought about by forming the sheet into a bubble.

26. A method according to claim 25, in which the bubble is formed by air-pressure applied on one side of the sheet.

27. A method according to any one of claims 19 to 26, in which spacing means are provided between the shell-supporting structure and means for supporting the latter during the vacuum moulding.

28. A method according to any one of claims 19 to 27, in which the shell-supporting structure is moved into adjacency with the sheet prior to the vacuum moulding.

29. A method according to claim 28, in which some movement of the shell-supporting structure is accomplished by means of an hydraulic ram.

30. A method according to any one of claims 19 to 29, in which a bonding agent is applied to the sheet and/or the shell-supporting structure prior to the vacuum moulding so that the sheet and the shell-supporting structure are more firmly stuck together after the vacuum moulding.

31. A method according to claim 30, in which the bonding agent is applied by spraying.

32. A method according to any one of claims 19 to 31, in which air is blown onto the vacuum moulded shell to cool it.

33. A method of manufacturing a shower tray substantially as described herein with reference to Figs. 1 to 4 with or without the modifications shown in (a) Figs. 5 and 6, or (b) Figs. 7 to 9 of the accompanying drawings.

34. An article according to any one of claims 1 to 18 made by a method as claimed in any one of claims 19 to 33.