GB2177341A

GB2177341A - Method of bonding

Info

Publication number: GB2177341A
Application number: GB08614572A
Authority: GB
Inventors: Robert James Pritchatt; Peter Lindop Moulding
Original assignee: NAYLOR BROS
Current assignee: NAYLOR BROS
Priority date: 1985-07-01
Filing date: 1986-06-16
Publication date: 1987-01-21
Also published as: GB8516614D0; BE905021A; GB8614572D0; DE3621892A1

Abstract

A method of bonding a cross linked (vulvanised) elastomeric part within a thermoplastics part in a moulding process. So that a bond is formed between two materials, the materials employed are compatible with each other and the thermoplastics material is admitted to the mould cavity (16) in a manner which causes a surface area of the elastomeric part (18) to be cleansed and/or scoured by it. <IMAGE>

Description

SPECIFICATION Method of bonding The invention relates to the bonding of a cross linked (vulcanised) elastomeric part to or within a thermoplastics part.

There are many instances where it is required to secure a crosslinked elastomeric part to or within a thermoplastics part. For example, in the manufacture of many items which are required to be of a fairly rigid nature it is necessary to fit a flexible or compressible element to act as a resilient seal in a composite structure of which the manufactured item forms a part. Such an item may be an assembly of separately formed parts in which it is present practice for the flexible or compressible elements to be held in position by mechanical means or possibly the flexible or compressible element may be secured by use of an adhesive.

We have discovered that a satisfactory bond between a crosslinked elastomeric part and a thermoplastics part may be obtained in situ during the thermoplastics moulding process without using other means.

According to the invention, there is provided a method of making an article having first and second parts bonded together, the method comprising the placing of a pre-formed cross linked elastomeric first part in an injection mould in which the second part is formed and then injecting thermoplastics material into the mould to form the second part, the materials of the two parts and the positioning of the first part in the injection mould being such that, upon injection of the molten thermoplastics material of the second part, the flow of the molten material cleanses and/or scours a surface area of the first part, and a bond (either chemical of physical) is formed between the materials. The method may be such that the resulting bond is so high that failure is cohesive rather than adhesive, that is to say takes place only by the tearing apart of the material of the bond.The first part will preferably extend at least partially within the second part and remain partially exposed. The material of which the first part is made will preferably be a preformed cross linked elastomer, the second part being in this case a thermoplastics material. The preformed cross linked elastomer may be a co-polymer and the thermoplastic material may be a homopolymer or a co-polymer or a blend thereof. The thermoplastic material, which may be filled or unfilled, may become cross linked during or after the moulding operation. The materials of the first and second parts may have a monomer in common, or may have monomers which are chemical homologues, which will tend to produce compatibility of the materials, that is to say, will ensure that the materials of the first and second parts have a potential for bonding.

Throughout this specification the term "preformed elastomeric first part" is intended to mean a part which has been formed prior to the moulding of the thermoplastics part in apparatus other than that in which said thermoplastics part is formed. Consequently, the pre-formed elastomeric first part may well be (but need not necessarily be) a "bought out finished" component. The meaning of the phrase "placing a preformed cross linked elastomeric first part in an injection mould" is therefore to be construed accordingly.

In order that the invention may be fully understood and readily carried into effect, embodiments will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a sectional view of a mould, shown in open condition, in which an injection moulded thermoplastics item is to be produced, the mould being shown to contain a pre-formed cross linked elastomeric part which is to be bonded to the thermoplastics part during moulding, Figure 2 is a sectional view of the mould in closed condition, Figure 3 is a part of Figure 2 drawn to a somewhat larger scale and illustrating what is believed to occur when the thermoplastics material is injected into the mould, and Figure 4 is a sectional view of a mould for producing a different kind of product but embodying the same invention.

Referring now to Figures 1 and 2 of the drawings, the mould there illustrated includes a pair of mould halves 10 and 12 and a core portion 14, the mould in its closed condition, as shown in Figure 2, defining a generally cylindrical cavity 16 in which a generally cylindrical injection moulded part is to be formed in a thermoplastics material.

An elastomeric part 18 is a disc of ethylene propylene elastomer. This is manufactured separately beforehand employing normal commercial formulations and a conventional preparation and moulding technique. This part 18 is positioned in the mould so that when the mould closes the central area of the part 18 is sandwiched between the core portion 14 and the mould part 12. The disc of ethylene propylene elastomer is of such a diameter that its peripheral edge portion projects into the mould cavity as shown, the arrangement being such that when the generally cylindrical injection moulded part has been formed in the mould, the pre-formed part constitutes a flexible diaphragm at one end thereof.The means whereby the pre-formed elastomeric part has been retained in position in the mould until the mould halves have been brought together are best shown in Figure 1 where it can be seen that a series of elements 17 are located around a central spigot portion 18 which is formed on the mould half 12. (For sake of clarity the elements 17 are shown to be four in number in Figure 1 but it will be understood that in practice there will be a multiplicity of such elements spaced around the spigot portion 19). As shown, the elements 17 are provided with undercut recesses in which edge portions of the pre-formed part can be engaged. Molten thermoplastics material is injected into the mould to form the second part.

The projecting edge portion of the disc 18 is surrounded by this material. It has been found that in this way the two parts become bonded together securely while still in the mould. Referring to Figure 3, this illustrates diagrammatically what is believed to take place when the molten material of the second part enters the mould cavity. The arrows indicate how the molten material flows across and cleanses and/or scours the opposing surfaces of the peripheral edge portion of the pre-formed part.This creates the condition in which a chemical and/or physical bond between the materials is effected, the strength of the bond being such that failure is cohesive rather than adhesive. (It will be understood that for the sake of clarity the elements 17 which initially retained the pre-formed part in position in the mould, and which in fact support that portion of the pre-formed part first acted on by the inrush of molten polymeric material into the mould, have been omitted from this view).

The invention is able to be used in the production of any injection moulded part having a pre-formed part bonded to or within it provided the two parts are made of compatible materials. By way of further example there is illustrated in Figure 4 a pair of mould halves for producing a resilient mounting bracket for an engine or gear box or the like, the mould cavity 20 in the mould half 12 being bounded by a pre-formed elastomeric part 22 which has been located in a cavity in the mould half 10. An essential requirement, however, is that the injection mould must be designed in such a way that, at the time when the molten material is injected into the mould cavity, the material cleanses and/or scours at least part of the surface of that portion of the preformed elastomeric part which is to be bonded to or within the injection moulding. It has been found possible by careful design of the mould to bring about effective bonding of a particular portion of the preformed first part without the bonding of other portions thereof which may form, in effect, an edge portion of the mould cavity.

Compatible materials of which the first part and the second injection moulded part may be made may, for example, be as follows: a) Polypropylene and ethylene propylene rubber.

b) Polyethylene and ethylene propylene rubber c) Polystyrene and S.B.rubber.

d) ABS and nitrile rubber.

Examples of the products which might possibly be produced by the inventive method are as follows:Windscreen wiper blades.

Components generally which require resilient seals.

Vehicle transmission components.

Shaft bearings within a resilient housing.

Claims

1. A method of making an article having first and second parts bonded together, the method comprising the placing of a preformed cross linked elastomeric first part in an injection mould in which the second part is formed and then injecting thermoplastics material into the mould to form the second part, the materials of the two parts and the positioning of the first part in the injection mould being such that, upon injection of the molten thermoplastics material of the second part, the flow of the molten material cleanses and/or scours a surface area of the first part, and a bond (either chemical of physical) is formed between the materials.

2. The method according to claim 1, in which the resulting bond is so high that failure is cohesive rather than adhesive, that is to say takes place only by the tearing apart of the material of the bond.

3. The method according to either one of the preceding claims, in which the first part extends at least partially within the second part and remains partially exposed.

4. The method according to any one of the preceding claims, in which the material of which the first part is made is a preformed cross linked elastomer, and the second part is a thermoplastic material.

5. The method according to claim 4, in which the preformed cross linked elastomer is a co-polymer and the thermoplastic material is a homo-polymer or a co-polymer or a blend thereof.

6. The method according to claim 5, in which the thermoplastic material, which may be filled or unfilled, becomes cross linked during or after the moulding operation.

7. A method of making an article having first and second parts bonded together, substantially as hereinbefore described.

8. An article having first and second parts bonded together, the article having been made by the method claimed in any one of the preceding claims.