EP0731214A2

EP0731214A2 - Paper pulp mouldings

Info

Publication number: EP0731214A2
Application number: EP96301570A
Authority: EP
Inventors: Ivor Philpott; Chris Kirk
Original assignee: Rexam Corrugated South West Ltd
Current assignee: Rexam Corrugated South West Ltd
Priority date: 1995-03-07
Filing date: 1996-03-07
Publication date: 1996-09-11
Also published as: GB9504808D0; EP0731214A3

Abstract

A mould (8) comprises an integral body (11) having a surface (7) of the desired shape for the pulp moulding. The body (11) is porous so that water can be drawn therethrough under a vacuum. The mould (8) is suitable for pulp moulding, and can be formed by flowing a particulate material over and appropriately shaped template, then setting the particulate material. A transfer tool for use in pulp moulding is also described.

Description

This invention relates to pulp mouldings and their manufacture.
In the conventional manufacture of pulp mouldings, an aqueous pulp slurry is applied to a shaped mould and the water in the slurry is drawn through the mould, leaving a shaped mat of pulp fibres on the mould. The moulding is then removed from the mould, usually by use of a correspondingly shaped transfer tool, and the moulding is dried.
The shaped mould conventionally comprises wire mesh in a support, the water being drawn under vacuum through the mesh. Such wire mesh moulds work well in practice, but they have a number of disadvantages. One of these is that, especially for complex shapes, they can be very difficult to make and hence expensive. The wire mesh has to be bent to the exact shape required, and then supported on an underlying member, with water flow channels to conduct away the water strained out of the deposited pulp. Currently, there is a requirement in the industry to produce quickly and easily a variety of samples of pulp mouldings for customers to review and test prior to bulk production. To produce a representative sample, a wire mesh mould is needed and this is time-consuming and often expensive to make.
We have now found a way in which this problem can be reduced or overcome. According to a first feature of the invention, instead of having wire mesh on a support, a mould is made as an integral body of porous material. Thus, the body includes one or more faces of the desired shape for the pulp moulding, and the body is porous so that water can be drawn therethrough under vacuum. It will be apparent that the continuous body of the mould according to the invention is distinct from a wire mesh comprising a plurality of individual wires or filaments.
There are various ways in which a porous mould of the invention can be made. For example, porous steel and porous plastics materials can be used.
In accordance with a preferred feature of the present invention, we prefer to form the mould body from a particulate material which is or becomes bound in an integral form. Thus, the particulate material may be capable of binding itself into the body, or a binder may be provided in order to bind the particulate material into the body. One example is a particulate solid such as sand (or any generally similar inert hard material) bound by a binder, such as an adhesive or resin, the binding being such that an open pore structure is formed. Instead of using sand and a resin, it is possible to use sintered metal powder shapes, for example. It is preferred that the particulate material has a particle size in the range 0.1 to 2mm, more preferably 0.5 to 1mm.
In the use of a particulate material such as sand, it is possible for example to coat the sand particles with a resin and to dry the particles so that they remain single and free-flowing. They can then be poured on to a shape to take up the devised configuration, and heat can then be applied to solidify the sand in that configuration. There is thus formed an integral porous body of the desired shape, which is suitable for use as a suction tool mould in a pulp moulding manufacturing process.
It will be appreciated that other curing means can be provided to solidify the particulate material. For example, a hardener can be added.
It is a highly preferred feature of the invention to make the porous mould from a flowable particulate material, and then to be able easily to solidify the material in the desired shape. Resin-coated sand (or the like) is one way of achieving this, but there are other ways as will be clear to those skilled in the art, and the invention includes these other ways.
The particulate material itself is inherently porous. It is within the normal abilities of the skilled person to control the solidification of the particulate material in order to maintain a sufficient number of pores therein.
As will be understood, in making a mould for use in pulp moulding manufacture, the appropriate shape has first to be provided. For some purposes, especially where the shape is relatively simple or commonplace, this is not a problem. However, especially where pulp moulding samples of new shapes are required, the provision of the shape can be difficult.
We have now found a way in which this problem can be reduced or overcome whereby moulds for pulp moulding production can be made relatively simply and economically, even in novel complex shapes.
According to the invention, the shape is constructed out of sheet material, such as paper, card or the like. The sheet material preferably has a certain amount of rigidity in order to hold it in shape. In this way, and using relatively simple folding (eg. Origami-like) techniques and cutting and adhesion, complex shapes can be constructed at low cost. These shapes can then be used to make moulds. The method is especially useful in the manufacture of the porous moulds of the invention, but it is of much broader applicability to the manufacture of shaped moulds not only for pulp moulding production but for other purposes too.
According to another feature of the invention, the shapes are made using a computer-based design system which, after the design of the three-dimensional shape, can "flatten out" the design. Each section of the design can then be plotted on to thick paper or card (or the like) and the whole shape subsequently assembled from these sections. Thus, the invention includes a process in which a three-dimensional shape is constructed by assembly of sections, and the shape is then used to make a suction tool mould for a pulp moulding process. Whilst reference has been made to the use of paper or card, it is to be understood that other sheet or sheet-like materials can be used such as wood, metal, plastics or otherwise.
When a computer-generated design is used, this can take into account possible dimensional variations in the formation of the eventual suction mould tool. Thus, the technique enables the production of pulp moulds of very closely controlled dimensions.
As is well known, pulp mouldings as formed wet on the mould are fragile and need to be carefully handled before they are dried. A transfer tool is generally used to lift the wet moulding from the mould and transfer it to a drying oven.
According to a further feature of the present invention, there is provided a way of making a transfer tool for use in removing a pulp moulding from a mould having a surface of the desired shape of the pulp moulding, said method comprising applying a pulp layer to said surface of the mould, applying a flowable material over said pulp layer, setting the flowable material to form a transfer tool body having a surface of the shape of the desired pulp moulding, and removing the pulp layer, wherein either: (a) the transfer tool body is formed of a porous material, whereby air can be drawn therethrough; or (b) the transfer tool body is formed of a non-porous material, and apertures (30) are subsequently formed in the body, whereby air can be drawn therethrough.
In one embodiment, a moulding material such as a plastics material, preferably an expanding foam material, is applied to a wet pulp moulding on a mould, so that the foam takes up and conforms to the shape of the reverse (exposed) face of the moulding. The expanded foam is then removed (usually taking with it the wet pulp) and a series of air passage holes are formed therein. The foam shape is attached to a machine carriage and to a vacuum source, and can then be used on a transfer tool for subsequent mouldings.
The invention thus includes the use of a moulding material for manufacture of a transfer tool. The moulding material can vary widely. For example, it can be an expanding foam as described, or it can be another plastics material such as a polyurethane, or it can be a particulate material as previously described.
The invention further includes a process for making a pulp moulding wherein there is used any feature of the invention herein described.
In order that the invention may be more fully understood, reference is made to the accompanying drawings which illustrate, as a step-wise process, various preferred aspects of the invention. The Figures are all schematic vertical sections, and in the Figures, like numerals indicate like parts.
Referring to the drawings, Fig. 1 shows the profile of origami of a complex shape 1 made of paper and/or card. The shape is a three-dimensional shape, the lower surface 2 being of the configuration required in the eventual pulp moulding. The upper surface 3 is shown of the same shape as lower surface 2 but this is not essential.
In Fig. 2, the shape 1 is located in a container 4 with lower surface 2 exposed within the container.
Fig. 3 shows the container 4 filled with a particulate material 5 which, after being placed in container 4, then sets to an integral mass 6 (Fig. 4) which is porous. (Container 4 would normally be inverted with shape 1 forming the bottom of the container, for this step.) The mass 6 is rigid, and is formed of a continuous porous solid material, rather than of a plurality of individual wires or filaments.
The shape 1 is removed and the mass 6 (with or without the container 4) forms a suction tool mould 8. The upper surface 7 conforms to the shape of lower surface 2 of the shape 1.
Fig. 5 illustrates the use of the tool mould 8. A vacuum is applied to lower surface 9 and an aqueous pulp is fed to upper surface 7. The water from the pulp is drawn into and through the mould (8), leaving a layer 10 of wet pulp on the upper surface 7. The layer 10 is then removed to dry and so forms the desired pulp moulding.
Figs. 6 to 9 illustrate the manufacture of a transfer tool. Starting with the arrangement of Fig. 5, a container 20 is provided above the pulp layer 10, and into this is placed an expanding foam 21. This fills container 20 and takes up, at its lower surface 22, the shape of the upper surface of pulp layer 10.
In Fig. 7, the set foam 21 is lifted (in container 20) from the suction tool 8, and any parts of pulp layer 10 thereon are washed away.
Then (Fig. 8), holes 30 are drilled through the foam 21 and a lid 31 is provided to container 20, the upper part of the foam 21 being removed if necessary to provide a vacuum chamber 32 communicating with holes 30. The resulting transfer tool, which is designated 33, can then be mounted on a machine so that it operates in conventional manner to lift wet pulp mouldings from the suction tool mould 8, transfer them to a drying station (not shown) and release them there.
Fig. 9 shows the suction tool mould 8 previously described.
In order that the invention may be more fully understood the following example is given, by way of illustration only.

Example

A sand mould for making a pulp moulding in the shape of a Hewlett Packard Dat Drive was made by the following method.
The shape of the Hewlett Packard Dat Drive was plotted out on thick paper, cut out and glued together to form a paper origami. The rear of the paper origami was reinforced with support medium and the origami fitted into a surround box.
The correct weight of sand for the mould was measured out and mixed with sufficient resin and hardener. The ratio of sand:resin:hardener mixed together to thoroughly coat the sand. The mix was then packed into the mould side of the origami. This was left to set for 24hrs.
After the mix had set the origami and surround box were then stripped off to form a porous sand mould. The sand mould can be used to form a pulp moulding. A transfer tool was made by the following method. The sand mould was fitted onto a suction plate which was connected to a vacuum source.
A layer of pulp was then drawn onto the sand tool, and a wood surround was then fitted around the top side of the sand mould, with the pulp covering remaining in place.
Casting plaster was then poured into the wooden box over the pulp, and was left to set for 24 hrs. The sand and plaster casts were then separated and the pulp was removed. Holes were then drilled in the plaster transfer tool to act as suction/blow off holes. A top cover was fitted to the transfer tool. The sand mould and transfer tools were fitted to a pulp moulding machine having a vacuum source, and pulp samples were made.

Claims

A mould (8) suitable for pulp moulding, comprising an integral mould body (11) having a surface (7) of the desired shape for the pulp moulding, wherein the mould body (11) is porous so that water can be drawn therethrough under a vacuum.
A mould (8) according to claim 1, wherein the mould body (11) is formed of a particulate material (5), preferably having a particle size of in the range 0.1 to 2mm.
A mould (8) according to claim 2, wherein the particulate material (5) is bound together with a binder.
A mould (8) according to any preceding claim, wherein the body (5) is formed from a material that is flowable and that is settable to form a solid integral mass.
A mould (8) according to any preceding claim, wherein the body (5) is formed of sand coated with a resin.
A method of making a mould (8) suitable for pulp moulding, comprising covering a surface (2) of a template (1) with a flowable, particulate mould-forming material (5), setting the particulate mould-forming material (5) to form a porous mould body (11) having a surface (7) of the same shape as said surface (2) of the template, and removing the template.
A method according to claim 6, further comprising placing the particulate mould-forming material (5) into a container (4), placing the template (1) over an open upper face of the container (4), and inverting the container (4) so that said particulate mould-forming material flows over said surface (2) of the template (1).
A method according to claim 6 or 7, further comprising forming a plurality of template sections from sheet material, and assembling said sections to form said template (1).
A method according to claim 8, further comprising using a computer aided design program to design the template sections, and printing each template section onto the sheet material using a printer in communication with said computer aided design program.
A method of making a transfer tool (33) for use in removing a pulp moulding from a mould (8) having a surface (7) of the desired shape of the pulp moulding, said method comprising applying a pulp layer (10) to said surface (7) of the mould (8), applying a flowable material (21) over said pulp layer (10), setting the flowable material (21) to form a transfer tool body having a surface (22) of the shape of the desired pulp moulding, and removing the pulp layer (10), wherein either: (a) the transfer tool body is formed of a porous material, whereby air can be drawn therethrough; or (b) the transfer tool body is formed of a non-porous material, and apertures (30) are subsequently formed in the body, whereby air can be drawn therethrough.
A method of pulp moulding using a mould according to any one of claims 1 to 5, or using a mould formed by a method according to any one of claims 6 to 9.