GB2319982A

GB2319982A - Forming ornamented plastics articles

Info

Publication number: GB2319982A
Application number: GB9723009A
Authority: GB
Inventors: Robert Detenon
Original assignee: Robobond Ltd
Current assignee: Robobond Ltd
Priority date: 1996-12-04
Filing date: 1997-11-03
Publication date: 1998-06-10
Also published as: WO1998024614A1; AU4790397A; GB9723009D0; GB9708151D0; CA2207313A1

Abstract

The present invention relates to a method of forming ornamented plastics articles, especially but not exclusively items of furniture, building components and picture frame members which comprises firstly extruding a plastics article then re-moulding it in a hot stamp press. This enables highly complex forms of article to be manufactured with large dimensions and at much lower cost than is currently possible.

Description

METHOD OF FORIVIING ORNAMENTED PLASTICS ARTICLES Field of the Invention The present invention relates to a method of forming ornamented plastics articles and to articles formed by the method and relates especially but not exclusively to manufacture of items of furniture, building components and picture frame members Background to the Invention Plastics materials have been used widely throughout the furniture and building industries for many years whether it be in the form of, for example, the flexible plastics sheet upholstery covers or stuffed flexible plastic foam upholstery filling of sofa suites, the substantially rigid mouldings of diner or patio plastics chairs or the completely rigid hard plastics tops of patio tables One area, however of the furniture and building industries that has not previously significantly benefited from the range of plastics materials currently available is the manufacture of heavily ornamented or embossed designer furniture and building products.

Existing materials and techniques of forming substantially rigid plastics articles do not allow for efficient economical manufacture of products that have a heavy ornate embossed appearance and the furniture and building industries have, therefore, largely ignored use of plastics materials for this purpose. injection moulding, the commonest method for forming thermoplastic articles. does not allow for low cost large scale (high production rate) manufacture of sizeable ornamented plastics articles.

It is, therefore, a general objective of the present invention to provide a method of forming plastics materials to provide them with a heavy ornate, embossed appearance and in an efficient, cost effective manner.

Summary of the Invention According to a first aspect of the present invention there is provided a method of forming ornamented plastics articles which comprises firstly extruding plastics material and then re-moulding it in a hot stamp press.

A hydraulic press of a metre or longer in length and suitably of the order of four metres in length is ideally provided for the second stage of the forming process to enable sizeable furniture or building components to be formed by the technique A particular problem that occurs when seeking to form components of this size is the problem of bowing. It has been found, however, that by controlling the temperature of the press not only at the die above but also at the platen below the extrusion any tendency to bow upwardly may be counteracted Embodiments of the invention may comprise use of a hydraulic press of even four metres in length. This may be particularly useful for such items as cornices. dado rails and coving. Indeed, it is with the longest extrusions that the greatest cost advantage is achieved over injection moulding.

The preferred plastics materials for use in the invention include polyvinylchloride and polystyrene. Preferably the plastics material is extruded as a foam and suitably comprises foamed polystyrene or foamed PVC.

The pressing of the plastics extrusion may be carried out on or off line, ie with the press physically positioned immediately after the extruder to press the plastics extrusion before it is cut and transported elsewhere or first cut and then transported to a nearby hydraulic press.

In order to form the plastics extrusions in an on-line configuration while enabling substantially continuous extrusion the hydraulic press is suitably mounted on wheels or other transport means and powered to move with the advancing extrusion until the pressing step is complete.

In a preferred form, the hot stamp press is provided with a removable cutting tool which enables the extrusion to be cut during pressing by the hot stamp press.

Advantageously, the plastics material is cut at substantially the same time as the re-moulding in the hot stamp press.

The effect achievable from the invention is similar to the ornate appearance achievable from an injection moulding but at a fraction of the cost.

Brief Description of the Drawings A preferred embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings.

wherein: Figure 1 is a longitudinal elevation view of an on-line assembly of extruder and heated press, Figure 2 is a transverse sectional view of the heated press taken along the line Ii II in Figure 1, Figure 3 is a top view of an edge-cut extrusion, showing the material to be removed; and Figure 4 is a schematic diagram indicating how two finished products can be pressed and cut from a single extrusion.

Description of the Preferred Embodiment As illustrated in Figures 1 and 2, the production line assembly comprises firstly an extruder 1 from which foamed polystyrene or other plastics material is continuously extruded. In the examples shown, the extrusion 2 is destined to become a series of picture frame members and has a generally rectangular crosssection with a depth of between 1 and 3 centimetres and a width of 4 to 8 centimetres and with a rebate 3 along one edge intended to accommodate a picture and glazing panel The outer, in use, (upper, as shown) face 4 of the extrusion 2 is to be ornamented.

As the extrusion 2 progresses from the extruder 1 it enters a four metre long hot stamp press 5 being a hydraulic press having an underlying support platen 6 and an overhanging die 7 configured to stamp the desired detail of ornamentation into the upper face 4 of the extrusion 2.

Both the platen 6 and die 7 are heated, suitably electrically under thermo-static control.

Careful control of the temperature gradient across the extrusion 2 enables an inherent tendency of the extrusion 2 to bow upwardly to be counteracted. More particularly, heating of the platen 6 preferably by use of heated oil circulating through it or by electric heating, counteracts the upward bowing tendency of the extrusion 2 under pressure. Generally, the greater the depth of impression to be made onto the extrusion 2 the greater the tendency to bow and the greater the temperature of the platen 6 needs to be to counteract this.

The precise temperatures and pressures and compression times within the hot stamp press 5 are selected to suit the nature of the extrusion to be ornamented and the depth of ornamentation. The required temperature, pressure and time are generally substantially lower than for corresponding injection moulding technique and, therefore, the energy input required is relatively low. Temperatures of between 100 and 180go are not untypical and compression times are generally between 10 and 40 seconds with pressures of the order of, for example, 5 to 10 bars per square centimetre Temperatures below 140"C are preferable when compression times of greater than 60 seconds are used, to avoid risk of edge damage to the moulding and to avoid reblowing of the original blowing agent.

The preferred size of the press 5 is of the order of 3m in length and 70cm width.

This enables, for example, three or four picture frame members to be pressed simultaneously alongside each other. A press of 70cm width is also well-suited to moulding of, for example, a cabinet door which is commonly 60cm in width.

To accommodate for the continuous progression of the extrusion 2 in the illustrated assembly the hot stamp die 5 is adapted to advance with the extrusion 2 at the same rate as the extrusion 2 by means of motorised transport carriage 8 with wheels 9 that roll along a track 10 co-extensive with the production line.

Once the ornament or moulding has been pressed on to the upper face 4 of the extrusion 2 the sectioning machine 11 cuts the extrusion into the desired lengths.

Although illustrated with respect to a picture frame member extrusion 2, the method has found applicability to a range of different items of furniture or building members. Ornamented chair legs and backs may be formed by this process as may cabinet doors and other more sizeable members.

Although the invention has been described with respect to a continuous extrusion process, the method in the invention may be carried out in discrete extrusion and hot stamp pressing stages with the extruder 1 and press 5 off-line relative to each other.

A positive benefit can be obtained by pressing the extrusion 2 shortly after it is extruded most especially when it is of a foamed nature since this assists in the ease of pressing and reduction of need for energy inputs at the pressing stage.

In further refined aspects of the invention it has been found that hot stamp pressing of extrusions provides a distinctive somewhat distressed surface characteristic. This is most notable with "gold" or othenvise wood-coloured plastics which upon heating in the hot stamp press 5 are slightly facially burnt.

The result of this effect is generally aesthetically desirable rendering the plastics material with an appearance similar to wood and, therefore, better disguising the artificiality ofthe material.

If desired, hot stamp foil as is commonly used in the picture frame manufacturing industry for adorning plastics extrusions with transfer patterns, can be conveniently applied to the moulding actually within the hot stamp press 5 avoiding the need for a separate application process. Suitably the hot stamp foil is reeled through the hot stamp press 5 with rollers being positioned at the entrance and exit to the press 5 so that the transfer foil passes over their rounded surfaces and is not accidentally pierced. The rollers or additional rollers may act as spindles to remove the used foil tape and to pick up the slack. The foil is suitably laid against the plastics extrusion prior to the press 5 being operated to press down upon it.

Alternative effects can be achieved by adding streaking dyes of different melt temperatures to give a "wood grain" effect.

In a preferred embodiment, the hot stamp press 5 is provided with a removable cutting edge which enables excess material to be cut from the extrusions so as to form an ornamented edge as shown in Figure 3.

The hot stamp pressing and cutting to remove excess material occur in one single stage, thus providing an ornamented extrusion having both a pressed, ornamented surface pattern and an ornamented cut edge.

Excess material 15 is removed after the pressing and cutting operation and can be reclaimed and reused.

Depending upon the intended design of the ornamented edge 16, it may be possible to press and cut a single extrusion into two pieces as indicated in Figure 4, obviously so long as the ornamented edges 16 are intended to be symmetrical.

Claims

1. A method of forming ornamented plastics articles which comprises firstly extruding plastics material and then re-moulding it in a hot stamp press.

2. A system for forming ornamented plastics articles which comprises a plastics extruder in combination with a hot stamp press with a platen and a heated mould-forming press for re-moulding the upper face of the extrusion from the plastics extruder.

3. A system as claimed in Claim 2, wherein the hot stamp press is a hydraulic press of a metre or longer, and preferably of the order of four metres in length.

4. A system as claimed in Claim 2, wherein the platen of the hot stamp press is also heated.

5. A system as claimed in Claim 4, wherein control means are provided to control the temperature of the heated platen of the press allowing adjustment to a temperature that prevents bowing of the plastics extrusion due to the heating of the upper face of the extrusion by the press of the hot stamp press.

6. A system as claimed in Claim 2, wherein the hot stamp press has associated therewith a dispenser for hot stamp foil to dispense hot stamp foil within the hot stamp press to enable transfer patterns on the hot stamp foil to be transferred to the plastics extrusion upon pressing by the hot stamp press.

7. A system is claimed in any of Claims 2-6 wherein the hot stamp press is provided with a removable cutting tool which enables the extrusion to be cut during pressing by the hot stamp press.

8. A method as claimed in Claim 1 wherein the plastics material is cut at substantially the same time as said re-moulding.

9. A system for forming ornamented plastics articles substantially as described herein with reference to and as illustrated by any appropriate combination of the accompanying drawings.

10. A method of forming ornamented plastics articles substantially as described herein with reference to and as illustrated by any appropriate combination of the accompanying drawings.