GB2187999A

GB2187999A - Contact lens mould

Info

Publication number: GB2187999A
Application number: GB08705862A
Authority: GB
Inventors: Michael James Sealey
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-03-17
Filing date: 1987-03-12
Publication date: 1987-09-23
Also published as: GB2187999B; GB8606505D0; GB8705862D0

Abstract

A mould for plastics contact lenses comprises cast plastics mould parts (4, 5), respectively defining convex and concave moulding surfaces (6, 7), which are sealed together in use by an annular projection (9), which extends from the convex part (4) into abutment with the concave part (5) at a radially inwardly extending lip (10) which is of vanishing thickness, the radially inner surface, of the projection being of a concave arcuate curvature which is substantially tangential at its ends with the concave and convex surfaces (6, 7). The lip is preferably splayed away from the convex surface when out of sealing contact with the concave surface, to ensure sealing engagement at the free edge of the lip (10). The apparatus provide a smooth curved peripheral lens edge. The concave mould surface (5) is at least part spherical in the region abutting the seal, to avoid lens errors arising from mould part misalignment, and is preferably entirely part spherical so that the lens characteristics are entirely determined by the shape of the convex mould part (4). <IMAGE>

Description

SPECIFICATION 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 mould parts with convex and concave moulding surfaces are cast from master dies and are subsequently juxtaposed to provide a moulding cavity between the convex and concave moulding surfaces. A polymerizable liquid is polymerized within the moulding cavity to form a contact lens, whereafter the mould parts are separated to release the lens, and are disposed of.

The edge profile of the moulding cavity, and hence the edge profile of the moulded lens, is of critical importance in avoiding irritation to the user's eye. Some profiles require post moulding polishing.

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 part with a convex moulding surface and a second part with a concave moulding surface, the mould parts being arranged to be juxtaposed so that the two moulding surfaces define therebetween a moulding cavity for moulding a plastics contact lens, the edge profile of the cavity being defined by an annular projection on the first mould part which, when the mould parts are juxtaposed, abuts firmly against the concave moulding surface to define the separation of the two moulding surfaces, the projection terminating in a radially inwardly extending annular lip of vanishing thickness which bears against the concave moulding surface, and the radially inner surface of the projection providing, in axial section, a concave arcuate curvature which is substantially tangential at its ends with the convex and concave moulding surfaces.

This arrangement provides an extremely smooth curved peripheral edge to the lens.

The only place, where any irregularity, in the smoothness of the moulded lens, can occur, is at the annular line contact between the free edge of the lip and the concave moulding surface. This is on the outer convex side of the lens, where it is always out of contact with the user's eyeball, and sufficiently close to the edge of the lens so as not to interfere with the central optically correcting portion of the lens. It follows that, if there is any irregularity around this line, it may be satisfactorily smoothed by buffing, and no polishing, or other surface finishing of the lens is necessary.

The face of the annular projection, including the lip, which abuts against the concave moulding surface of the second mould part may be shaped permanently to conform to the shape of the part of the opposing surface of the concave moulding surface, against which it will abut. However, there is then the danger that any slight distortion of the very thin free edge of the lip, may space this free edge from the concave moulding surface, and produce a significant irregularity in the convex surface of the moulded lens.Preferably therefore the annular lip is, prior to being brought into abutment with the concave moulding surface, splayed slightly away from the convex moulding surface in the sense that when the two moulding surfaces are brought into mutual abutment, the lip is flexed back towards the convex moulding surface, and thus then remains in firm engagement with the concave moulding surface.

If at least the annular portion of the concave moulding surface, in the region in which it will be abutted by the annular projection from the convex moulding surface is part spherical, exact radial alignment between the two mould parts is unnecessary, without affecting the prism of the moulding cavity and resulting lens. For example, the concave moulding surface may be, in its entirety, part spherical, whereby the strength and optical characteristics of a lens produced from the mould parts are determined by the shape of the convex moulding surface.This simplifies and cheapens the overall working procedure, as, although it will still be necessary to provide a range of master dies for casting a range of mould parts with different convex moulding surface corresponding to the different characteristics required in different lenses, all the second mould parts formed with the concave moulding surfaces may be identical, so that only a single master die is required for these mould parts.

A mould constructed in accordance with the invention is illustrated diagrammatically in the accompanying drawing, in which: Figure 1 is an axial section; Figure 2 is an enlargement of the part ringed in Figure 1; and, Figure 3 corresponds to but showing the approach of the mould parts.

The mould has parts 4 and 5, of which a first part 4 provides a convex moulding surface 6 and a second part 5 provides a concave moulding surface 7. The moulding surfaces define between them a moulding cavity 8 when the parts 4 and 5 are brought into mutual abutment. The abutment occurs around an annular zone, part of which is ringed in Figure 1, and which is shown in more detail in Figure 2. Thus the mould part 4 has an annular projection 9 terminating in a radially inwardly extending annular lip 10 of vanishing thickness. The inner face 11 of the projection 9 is arcuately concavely shaped and merges at its ends tangentially into the surfaces 6 and 7.

Figure 3 shows how, prior to mutual abutment of the parts 4 and 5, the lip 10 is splayed slightly towards the concave moulding surface 7 so that, during the latter part of the movement of the two mould parts together, to close the mould cavity 8, the lip 10 is flexed until a rigid portion 12 of the projection bottoms on the concave moulding surface 7.

This defines precisely the spacing of the surfaces 6 and 7 whilst ensuring that the extreme edge of the lip 10 bears firmly against the surface 7.

Claims

1. A pair of cast plastics mould parts for use in the moulding of an ophthalmic contact lens comprises a first part with a convex moulding surface and a second part with a concave moulding surface, the mould parts being arranged to be juxtaposed so that the two moulding surfaces define therebetween a moulding cavity for moulding a plastics contact lens, the edge profile of the cavity being defined by an annular projection on the first mould part which, when the mould parts are juxtaposed, abuts firmly against the concave moulding surface to define the separation of the two moulding surfaces, the projection terminating in a radially inwardly extending annular lip of vanishing thickness which bears against the concave moulding surface, and the radially inner surface of the projection providing, in axial section, a concave arcuate curvature which is substantially tangential at its ends with the convex and concave moulding surfaces.

2. Mould parts according to claim 1, in which the annular lip is, prior to being brought into abutment with the concave moulding surface, splayed slightly away from the convex moulding surface in the sense that when the two moulding surfaces are brought into mutual abutment, the lip is flexed back towards the convex moulding surface.

3. Mould parts according to claim 1 or claim 2, in which the annular portion of the concave moulding surface, in the region in which it will be abutted by the annular projection from the convex moulding surface is part spherical.

4. Mould parts according to claim 3, in which the concave moulding surface is in its entirety, part spherical, whereby the strength and optical characteristics of the a lens produced from the mould parts are determined by the shape of the convex moulding surface.

5. 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.