GB2435629A

GB2435629A - Moulding of polymers

Info

Publication number: GB2435629A
Application number: GB0503428A
Authority: GB
Inventors: Keith Fawdington; Paul Tranter
Original assignee: UVASOL Ltd
Current assignee: UVASOL Ltd
Priority date: 2005-02-18
Filing date: 2005-02-18
Publication date: 2007-09-05
Also published as: GB0503428D0

Abstract

A method of moulding articles made at least in part from a polymer 5 comprises placing a polymer which is in a formable state in a mould 1, 2; exposing the polymer to radiation thereby causing the polymer to become solid, wherein the radiation is transmitted to the polymer through the mould by a radiation guide or guides 3. The guides may be optical guides that terminate at an inner surface of the mould or sufficiently close to it to enable radiation such as ultra violet to issue from the end of the fibers into the mould cavity. The polymer may be mixed with a photo-initiator and injected into the mould. Later embodiments relate to a moulded article made by said method and a mould comprising two separable parts for use with said method.

Description

1 2435629

MOULDING OF POLYMERS

This invention relates to the moulding of articles made, at least in part, from a polymer which is set or "cured" by exposure to radiation. During manufacture of such articles, the polymer, in liquid form, is mixed with a photo-initiator before being introduced into a mould. When exposed to radiation, usually ultraviolet radiation, the photoconductor causes the polymer to cure. This technique is sometimes used to produce a finished product and sometimes to produce a "preform" i.e. a shaped mat for use as a reinforcing layer within a finished moulded product.

This technique is satisfactory for making articles which can be moulded in an open mould so that one side is exposed and can be illuminated with the radiation. However, it cannot be so easily employed in situations where the article is formed in an enclosed mould cavity because the radiation cannot reach the polymer to cure it. This problem is addressed in US patent Specification 5338169 which describes the use of a transparent mould. However, there may be conflict between the need for transparency and the structural requirements of the mould IS and, in the arrangement described in the aforementioned specification, only a small proportion of the radiation may usefully employed in the curing process.

According to a first aspect of this invention there is provided a method of moulding articles, made at least in part from a polymer, in which the polymer, in a formable state, is placed in a mould and then exposed to radiation, causing the polymer to become solid; characterised in that of the radiation is transmitted to the polymer through the mould by a radiation guide or guides.

Expressed another way, the invention provides a mould for making articles of a polymer material which hardens when exposed to radiation, characterised by at least one guide for conducting radiation into an interior cavity of the mould.

It is believed that, by employing the invention, the required structural requirements for a mould can be met whilst allowing all the radiation to be directed exactly where it is needed.

The invention is of course particularly relevant to a moulding process where the mould would, but for the use of the invention, prevent radiation from illuminating the material being moulded. Examples are injection moulding and in dough moulding.

It is possible to use a number of guides, each of which extends from a position outside the mould to a point at or very close to an interior surface defming of the mould cavity. Another possibility is to arrange for the guide to extend along the interior surface. In this latter case, the guide is designed so that radiation will leak from its lateral surface into the polymer.

In a preferred embodiment of the invention, at least one part of the mould is defined by a bundle of optical fibres embedded in a body of synthetic plastics material such as an epoxy resin. In this arrangement, those ends of the optical fibres which lie outside the mould are preferably collected together to receive radiation from a suitable radiation source such as an ultraviolet lamp. When the mould is made from a material (eg steel, aluminium, kirksite or wood) which does not permit this mode of manufacture, holes could be drilled through the mould to receive the optical fibres.

Examples of how the invention may be carried out will now be described by way of example with reference to the accompanying drawings in which:-Fig I illustrates a first mould, constructed in accordance with the invention; Fig 2 shows a second mould, also constructed in accordance with the invention; Fig. 3 shows, very schematically, a mat of fibres employed in the construction of Fig 2 with optical connections thereto; and Fig 4 shows a detailed view of an optical fibre employed in the mat of Fig 3.

Referring first to Fig 1, the illustrated mould is formed from a first mould part I and a second mould part 2 defining a cavity between them. The mould part 2 is formed from a large number of optical fibres 3 embedded in an epoxy resin.

The free ends of the optical fibres 3 are gathered together at a position close to the output of a source 4 of ultraviolet radiation.

In operation, liquid polyester 5 that has been mixed with a photo-initiator is injected into the mould cavity through an injection duct 6. Ultraviolet radiation, from the lamp 4, then irradiates the polymer mixture, causing the photo-initiator to cure of the polymer. Finally, the two mould parts I and 2 are separated and the, now solid, fmished article removed.

Fig 2 shows a different construction employing top and bottom mould parts 7 and 8.

The mould part 8 is formed, like that shown in Fig I, from epoxy resin but has a mat 9 of woven optical fibres embedded just below its inner surface, i.e. the surface facing the mould cavity. Fig 3 shows how the ends of these fibres are bundled together at 10, where UV radiation is fed into them causing rapid curing of the polyester. A detail of a length of fibre is shown in Fig 4 which shows an inner glass core 11 and an outer coating 12 designed to cause total internal reflection of ultra violet radiation 13. The coating is deliberately damaged by forming grooves 14 on its top side, this allowing radiation to escape as shown by the arrows 15. The spacing of the grooves 14 is regulated so as to be closer at points further from the sources of radiation.

It will be appreciated that the illustrated arrangement has been described only by way of example and that many other ways of employing the invention are possible. One alternative possibility would be to use, instead of polyester in liquid form, a polyester "dough" which is pressed into the mould before the two mould parts are brought together.

Claims

CLAIMS

1. A method of moulding articles, made at least in part from a polymer, in which the polymer, in a formable state is placed in a mould and then exposed to radiation, causing the polymer to become solid; characterised in that the radiation is transmitted to the polymer through the mould by a radiation guide or guides.

2. A method according to Claim I characterised in that the mould has at least two separable parts preventing access of radiation to the polymer in the mould except via a path or paths through the mould.

3. A method according to Claim 1 or 2 characterised in that the radiation passes through optical guides in the mould.

4. A method according to Claim 3 characterised in that the or each optical guide terminates at an inner surface of the mould or sufficiently close to it to enable radiation to issue from the end of the fibre into a mould cavity.

5. A method according to Claim 3 or 4 characterised in that the radiation leaks from a lateral surface of the or each fibre into an internal cavity of the mould.

6. A method according to any preceding Claim characterised in that the radiation is ultra violet radiation.

7. A method according to any preceding claim characterised in that the polymer is mixed with a photo-initiator.

8. A method according to any preceding claim characterised in that the formable polymer is injected into a cavity in the mould.

9. A method according to any of claimsi to 7 in which the formable material is of malleable or dough-like consistency.

10. A moulded article made by the method of any preceding Claim.

11. A mould for making articles from a polymer material which hardens when exposed to radiation characterised by at least one guide for conducting the radiation into an interior cavity of the mould.

12. A mould according to Claim 11 characterised in that the mould has at least two separable parts and prevents access of radiation to the polymer except via a path through one of the mould parts.

13. A mould according to Clam 11 or 12 characterised in that the or each optical guide terminates at an inner surface of the mould.

14. A mould according to Claim 11 or 12 characterised in that the guide is designed so that radiation leaks from a lateral surface thereof.

15. A mould according to any of Claims 11 to 14 characterised by a source of radiation connected thereto.

16. A mould according to Claim 15 characterised in that the source of radiation is an ultra violet lamp.