GB2235407A

GB2235407A - Contact lens mould

Info

Publication number: GB2235407A
Application number: GB9017839A
Authority: GB
Inventors: Michael James Sealey; Michael James Kelly
Original assignee: MJS Scientific Ltd
Current assignee: MJS Scientific Ltd
Priority date: 1989-08-29
Filing date: 1990-08-14
Publication date: 1991-03-06
Anticipated expiration: 2010-08-14
Also published as: GB8919532D0; GB9017839D0; GB2235407B

Abstract

A pair of cast plastics mould parts, for moulding an ophthalmic contact lens, comprising a female, mould part with upwardly facing concave surface and with a tubular portion extending upwardly from its periphery; and a male, mould part which has a downwardly facing convex surface at its lower end and is received within the tubular portion of the female mould, so that the convex and concave moulding surfaces are juxtaposed to define therebetween a moulding cavity and, around and above the moulding cavity, an annular reservoir for liquid moulding material; wherein the radially inner surface of the tubular portion of the female mould has three angularly spaced radially inwardly extending projections for abutment with the outer surface of the male mould; or the outer surface of the male mould has three angularly spaced radially outwardly extending projections for abutment with the inner surface of the tubular portion of the female mould; in either case for maintaining axial alignment between the two parts. <IMAGE>

Description

CONTACT LENS MOULD A technique, which has recently become popular for the manufacture of ophthalmic correction contact lenses from plastics material, is known as cast moulding. In this technique, two plastics male and female mould parts with respective convex and concave moulding surfaces are injection moulded from master dies and are subsequently juxtaposed to provide a moulding cavity between the convex and concave moulding surfaces. A polymerisable liquid moulding material is cast and polymerised within the moulding cavity to form a contact lens, whereafter the mould parts are separated to release the lens and are disposed of.

Conventionally each female mould part is positioned with its concave surface facing upwardly and a predetermined dose of polymerisable material is fed into the female mould part, after which the male mould part is caused to move downwardly so that an annular portion engages and seals against the female mould part to define the periphery of the moulding cavity with a predetermined volume of the polymerisable material trapped within the cavity. The two mould parts are then held together over a period of some hours, while the liquid moulding material polymerises. The integrity and shape of the moulding cavity, and hence of the moulded lens are critically dependent upon exact axial alignment between the two mould parts.If there is any tilting of one relatively to the other, one side of the lens will be too thick and the other side too thin, resulting in unacceptable, so called, lens prism.

In accordance with the present invention, a pair of cast plastics mould parts, for use in the moulding of an ophthalmic contact lens, comprises a first, female, mould part with a nominally upwardly facing concave moulding surface and with a tubular portion extending upwardly from a peripheral portion of the concave moulding surface; and a second, male, mould part which has a nominally downwardly facing convex moulding surface at its lower end and which is arranged to be received within the tubular portion of the first mould part, so that the convex and concave moulding surfaces are juxtaposed to define therebetween a moulding cavity and, around and above the moulding cavity, an annular reservoir for liquid moulding material; wherein the radially inner surface of the tubular portion of the first mould part has three angularly spaced radially inwardly extending projections for substantial abutment with the radially outer surface of the second mould part; or the radially outer surface of the second mould part has three angularly spaced radially outwardly extending projections for substantial abutment with the radially inner surface of the tubular portion of the first mould part; in either case for maintaining substantial axial alignment between the two mould parts.

By substantial abutment is meant touching or a clearance of up to 0.015mm, and preferably no more than O.Olmm.

With this arrangement, the essential annular reservoir between the two mould parts is maintained, for accommodating excess liquid moulding material when the two mould parts are juxtaposed, and for providing any liquid moulding material which needs to be drawn into the moulding cavity during polymerisation, to accommodate shrinkage, whilst the three projections provide automatic self alignment between the two mould parts, to avoid tilting and the production of undesirable lens prism.

The invention is illustrated diagrammatically in the accompanying drawings, in which: Figure 1 is an axial section; and, Figure 2 is a section taken on the line II-II in Figure 1.

The illustrated mould has female and male parts 3 and 4 which provide respective part spherical concave and convex moulding surfaces 5 and 6 defining therebetween a moulding cavity 7, when the parts are brought into abutment in coaxial alignment. The abutment occurs where an annular rib 9 on the part 4 engages and seals against the surface 5. The seal separates the moulding cavity 7 from an annular reservoir 8. It would be equally possible for the rib 9 to be formed at an edge of the concave surface 5.

Axial alignment between the mould parts 3 and 4 is assured either by three equiangularly spaced projections 10 on a cylindrical tubular portion 11 of the mould part 3, substantially engaging a cylindrical tubular portion 12 of the mould part 4; or by three equiangularly spaced projections 13 on the cylindrical portion 12 of the mould part 4 substantially engaging the cylindrical part 11 of the mould part 3.

Claims

1. A pair of cast plastics mould parts, for use in the moulding of an ophthalmic contact lens, the pair comprising a first, female, mould part with a nominally upwardly facing concave moulding surface and with a tubular portion extending upwardly from a peripheral portion of the concave moulding surface; and a second, male, mould part which has a nominally downwardly facing convex moulding surface at its lower end and which is arranged to be received within the tubular portion of the first mould part, so that the convex and concave moulding surfaces are juxtaposed to define therebetween a moulding cavity and, around and above the moulding cavity, an annular reservoir for liquid moulding material; wherein the radially inner surface of the tubular portion of the first mould part has three angularly spaced radially inwardly extending projections for substantial abutment with the radially outer surface of the second mould part; or the radially outer surface of the second mould part has three angularly spaced radially outwardly extending projections for substantial abutment with the radially inner surface of the tubular portion of the first mould part; in either case for maintaining substantial axial alignment between the two mould parts.

2. A pair of cast plastics mould parts, for use in the moulding of an ophthalmic contact lens, substantially as described with reference to the accompanying drawings.