GB2124136A

GB2124136A - Technique for double layer moulding of articles

Info

Publication number: GB2124136A
Application number: GB08318768A
Authority: GB
Inventors: David Lace
Original assignee: C R P Marine Ltd; CRP Marine Ltd
Current assignee: C R P Marine Ltd; CRP Subsea Ltd
Priority date: 1982-07-17
Filing date: 1983-07-12
Publication date: 1984-02-15
Also published as: GB8318768D0; GB2124136B

Abstract

A method of forming an article which is to have an inner layer or filling of a second material disposed on the inside surface of a hollow moulding made of a first material, in which there is introduced into the mould, in addition to the material which is to form the first outer layer when the mould is heated and rotated, a second material contained within an envelope of thermosoftening material capable of melting sufficiently to rupture as a result of the heat applied, whereby the second material is then released to form the second layer or filling on the inside surface of the first layer. In a preferred embodiment a toroidal lifebelt is made by locating polyethylene powder and at least one meltable envelope containing sand into a mould and rotating and heating the mould to cause the polyethylene powder to melt and form an outer layer and the envelope(s) to melt and allow the sand to form an inner layer.

Description

SPECIFICATION Technique for double layer moulding of articles The present invention is concerned with moulding and in particular with the moulding of articles which are to have an inner layer or filling of a second material disposed on the inside surface of a first material.

There is a requirement for putting a layer or filling of a second material on the inside surface of a hollow moulding made of a first material. The obvious way to do this would be to form a shell of the first material and to then break open the mould before inserting the ingredients necessary to form the second layer or filling in a separate moulding step. This would be a time and labour consuming process which would be correspondingly expensive to perform.

It would thus be highly advantageous if a means could be devised of forming the second, inner layer within the hollow moulding without having to to pen the mould again after the first layer or skin has been formed.

It is an object of the present invention to provide a technique for achieving the latter end.

In accordance with the present invention, this object is achieved by introducing into the mould, in addition to the material which is to form the first, outer layer when the mould is heated and rotated, a second material contained within an envelope of thermo-softening material capable of melting suffi cientlyto rupture as a result of the heat applied, whereby the second material is then released to form the second layer or filling on the inside surface of the first layer.

This technique is particularly useful for the formation of a toroidal lifebelt made of a relatively light material whose overall weight is to be increased by the incorporation therewithin of relatively heavy material particles which act as ballast.

In this case, polyethylene powder is introduced into the toroidal mould, along with one or more plastics envelopes containing a heavy ballast material such as sand. As the mould is rotated within an oven, the polyethylene powder melts and forms the outer skin of the lifebelt in conformity with the shape of the inner surface of the mould. During this process, the plastics envelope eventually breaks down, depositing the sand inside the already formed first layer in the mould. The sand particles are distributed evenly around the mould by the motion of the mould and adhere to the inner surface of the skin which has just been formed, thus becoming an integral part of the moulding.

The invention is not restricted to any particular moulding materials nor to any particular material for the envelope or envelopes providing that it is capable of melting or rupturing at the required time.

In the case of a toroidal lifebelt, the envelope could itself be toroidal or there could be any number of smaller envelopes of any desired shape.

There are many other instances, besides increasing the mass of the moulded article where this technique could be applied, for example to obtain a multiple skin sandwich construction orto obtain a decorative finish on the inside surface. In all cases the two layers are formed by what is in effect one process and not two.

In some cases, the plastics envelope could contain material necessary to fill or partially fill the outer shell with a foam constituting the second layer or filling. Thus, for example, the plastics envelope could contain polyethylene granules which when the envelope ruptures are released into the interior of the hollow outer layer to foam and fill the available space.

The term "envelope" is to be interpreted in its most general sense to include any closed bag, closed tube or other closed container.

In some embodiments, it can be advantageous to include one or more additional materials inside the envelope which, upon eventual rupturing of the envelope as described above, act as a bonding agent either to bond the ballast particles together so they are no longer loose inside the moulding or to bond them to the moulded outer layer itself. The bonding material can for example, be the same material as that used for the outer skin. Thus, where the mould contains polyethylene granules for forming the outer skin, the envelope might contain a mixture of sand or other heavy ballast material and more polyethylene granules.

In a further modification, it can be advantageous to place one envelope inside one or more further envelopes within the mould. Controlling the material and the gauge of the material, whether there is a single or a double envelope, enables control to be exercised over when the ballast material is released.

1. A method of forming an article which is to have an inner layer or filling of a second material disposed on the inside surface of a hollow moulding made of a first material, wherein there is introduced into the relevant mould, in addition to the material which is to form the first, outer layer when the mould is heated and rotated, a second material contained within an envelope of thermosoftening material capable of melting sufficiently to rupture as a result of the heat applied, whereby the second material is then released to form the second layer or filling on the inside surface of the first layer.

2. A method as claimed in claim 1 wherein the second material is denser than the first whereby to act as ballast for the finished article.

3. A method as claimed in claim 2 wherein the first material is a plastics powder and the second material is sand.

4. A method as claimed in claim 3 wherein the first material is polyethylene powder.

5. A method as claimed in claim 1 wherein the second material comprises polyethylene granules for forming a polyethylene foam filling with said first layer upon rupturing of the envelope.

6. A method as claimed in claim 2, 3 or 4, wherein the envelope contains, in addition to said second, denser material, an additional material which, upon rupturing of the envelope to release its

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Technique for double layer moulding of articles The present invention is concerned with moulding and in particular with the moulding of articles which are to have an inner layer or filling of a second material disposed on the inside surface of a first material. There is a requirement for putting a layer or filling of a second material on the inside surface of a hollow moulding made of a first material. The obvious way to do this would be to form a shell of the first material and to then break open the mould before inserting the ingredients necessary to form the second layer or filling in a separate moulding step. This would be a time and labour consuming process which would be correspondingly expensive to perform. It would thus be highly advantageous if a means could be devised of forming the second, inner layer within the hollow moulding without having to to pen the mould again after the first layer or skin has been formed. It is an object of the present invention to provide a technique for achieving the latter end. In accordance with the present invention, this object is achieved by introducing into the mould, in addition to the material which is to form the first, outer layer when the mould is heated and rotated, a second material contained within an envelope of thermo-softening material capable of melting suffi cientlyto rupture as a result of the heat applied, whereby the second material is then released to form the second layer or filling on the inside surface of the first layer. This technique is particularly useful for the formation of a toroidal lifebelt made of a relatively light material whose overall weight is to be increased by the incorporation therewithin of relatively heavy material particles which act as ballast. In this case, polyethylene powder is introduced into the toroidal mould, along with one or more plastics envelopes containing a heavy ballast material such as sand. As the mould is rotated within an oven, the polyethylene powder melts and forms the outer skin of the lifebelt in conformity with the shape of the inner surface of the mould. During this process, the plastics envelope eventually breaks down, depositing the sand inside the already formed first layer in the mould. The sand particles are distributed evenly around the mould by the motion of the mould and adhere to the inner surface of the skin which has just been formed, thus becoming an integral part of the moulding. The invention is not restricted to any particular moulding materials nor to any particular material for the envelope or envelopes providing that it is capable of melting or rupturing at the required time. In the case of a toroidal lifebelt, the envelope could itself be toroidal or there could be any number of smaller envelopes of any desired shape. There are many other instances, besides increasing the mass of the moulded article where this technique could be applied, for example to obtain a multiple skin sandwich construction orto obtain a decorative finish on the inside surface. In all cases the two layers are formed by what is in effect one process and not two. In some cases, the plastics envelope could contain material necessary to fill or partially fill the outer shell with a foam constituting the second layer or filling. Thus, for example, the plastics envelope could contain polyethylene granules which when the envelope ruptures are released into the interior of the hollow outer layer to foam and fill the available space. The term "envelope" is to be interpreted in its most general sense to include any closed bag, closed tube or other closed container. In some embodiments, it can be advantageous to include one or more additional materials inside the envelope which, upon eventual rupturing of the envelope as described above, act as a bonding agent either to bond the ballast particles together so they are no longer loose inside the moulding or to bond them to the moulded outer layer itself. The bonding material can for example, be the same material as that used for the outer skin. Thus, where the mould contains polyethylene granules for forming the outer skin, the envelope might contain a mixture of sand or other heavy ballast material and more polyethylene granules. In a further modification, it can be advantageous to place one envelope inside one or more further envelopes within the mould. Controlling the material and the gauge of the material, whether there is a single or a double envelope, enables control to be exercised over when the ballast material is released. CLAIMS

6. A method as claimed in claim 2, 3 or 4, wherein the envelope contains, in addition to said second, denser material, an additional material which, upon rupturing of the envelope to release its contents, acts as a bonding agent to bond the particles of said denser material together and/or to bond the particles of said denser material to the moulded first layer.

7. A method as claimed in any of claims 1 to 6 where said envelope is contained in the mould within the or more further envelopes similarly made of a thermosoftening material.

8. A moulded article made in accordance with the method of any of claims 1 to 8.

9. A method of forming an article which is to have an inner layer or filling of a second material disposed on the inside surface of a hollow moulding made of a first material, comprising introducing into a mould a first material for forming the outer skin or shell of the article, and at least one envelope which is made of a thermosoftening material and which contains a second material which is to form said inner layer or filling, and heating and rotating the mould whereby the first material forms a layer on the inside of the mould and the or each envelope eventually softens and ruptures to release said second material which then forms said inner layer or filling within said first layer.

10. Atoroidal lifebelt made by introducing polyethylene powder into a toroidal mould together with one or more plastics envelopes containing a heavy ballast material, rotating the mould in a heated environment so as to melt the polyethylene powder whereby to form an outer polyethylene skin which conforms to the shape of the inner surface of the mould and so as eventually to melt the or each plastic envelope so that it breaks down and deposits the heavy ballast material inside the already formed polyethylene skin in the mould.

11. Atoroidal lifebelt as claimed in claim 10 in which, in order to bond the ballast material to the outer skin, the or each said envelope contains a bonding agent in addition to the ballast material.

12. Atoroidal lifebelt as claimed in claim 10 in which, in order to bond the ballast material to the outer skin, one or more additional envelopes are included within the mould which contains a suitable bonding agent.