GB2235406A

GB2235406A - Casting contact lenses

Info

Publication number: GB2235406A
Application number: GB9017838A
Authority: GB
Inventors: Michael James Sealey
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: GB9017838D0; GB2235406B; GB8919530D0

Abstract

A machine for moulding contact lenses, comprises a nest for locating an array of interconnected female moulds, each with an upwardly facing concave surface, said moulds initially containing male moulds with downwardly facing convex surfaces; a vacuum head reciprocatable vertically above the nest has vacuum ports aligned, with pairs of female and male moulds, such that when is lowered, the male moulds are captured thereby and lifted out of the female moulds upon raising of the vacuum head; at least two sets of nozzles, movable from retracted to extended positions where they can direct polymer into respective female mould parts; at least one pump for dosing a predetermined amount of polymer from a reservoir to said nozzles; and means for controlling the vacuum head, nozzles, and pump, such that, in sequence, the male moulds are lifted out of the female moulds, the nozzles are moved to their extended position, the polymer is dosed into the female moulds, the nozzles are retracted and the head is lowered to lower the male moulds back into the respective female moulds prior to curing of the polymer. <IMAGE>

Description

MACHINE FOR MAKING CONTACT LENSES 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 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.

In accordance with the present invention, a machine for use in cast moulding contact lenses comprises a nest for locating an array of interconnected female mould parts, each formed with an upwardly facing concave moulding surface, the female mould parts initially locating therein a corresponding plurality of respective male mould parts each formed with a downwardly facing convex moulding surface; a vacuum head which is reciprocatable upwardly and downwardly above the nest and has a plurality of vacuum ports aligned, in use, with respective pairs of female and male mould parts, such that when the vacuum head is lowered, the male mould parts may be captured by the vacuum ports and lifted out of the female mould parts upon raising of the vacuum head; at least two sets of nozzles, which are movable from retracted positions to extended positions in which the nozzles are positioned to direct polymerisable material into respective ones of the female mould parts; at least one pump for dosing a predetermined amount of polymerisable material from a reservoir of the polymerisable material to respective ones of the nozzles; and means for controlling the vacuum head, the sets of nozzles, and the pump, such that, in sequence, the male mould parts are lifted out of the female mould parts, the nozzles are moved to their extended position, the polymerisable material is dosed through the nozzles into the female mould parts, the nozzles are retracted, and the head is lowered to lower the male mould parts back into the respective female mould parts prior to curing of the polymerisable material.

With this arrangement, problems of axial misalignment of the male and female mould parts when they are separated and brought together again, which could lead to distortion of the mould cavity and consequently of the moulded lens, are minimised. This is because the female mould parts can be accurately located in the nest, which may be an array of recesses in a base plate in a pattern corresponding to the relative positions of the interconnected female mould parts. Initially the male mould parts will be naturally aligned within the female mould parts and the vacuum ports will be aligned with the respective pairs of male and female mould parts, because it will have been preset relatively to the nest.Since the vacuum head only needs to reciprocate upwardly and downwardly above the nest, with one degree of freedom, literal misalignment owing to inaccuracies in the movement of the vacuum head in a lateral direction is avoided.

In one configuration, the female mould parts are, as cast, in a symmetrical circular array, each integrally joined by a respective spoke to a central hub.

Each set of nozzles may be mounted on a carrier which is supported by a pivotal linkage such that, in the extended position, the nozzles are directed downwardly into respective female mould parts, but are raised and withdrawn laterally so as not to obstruct the vacuum head, when moved to the retracted position. The pivotal linkage may incorporate a pair of parallel pivotal links which support the carrier by a parallel motion linkage from below, and which move over a top dead centre position as the carrier moves between the extended and retracted positions. The carrier is then raised, moved laterally towards or away from the mould parts, and lowered, when extended or retracted. If there are, say, a ring of eight of the interconnected female mould parts, there may be two sets of four nozzles, working on opposite sides of the circular array.

The vacuum head may be raised and lowered, and the nozzle sets may be extended and retracted, by respective hydraulic, or preferably pneumatic, cylinders.

Most simply there is a single pump which pumps the polymerisable material from a common reservoir container to all of the nozzles. The container may need to be refrigerated, or at least thermally insulated, to prevent premature polymerisation.

An example of a machine constructed in accordance with the invention is illustrated diagrammatically in the accompanying drawings, in which: Figure 1 is a partial plan omitting the vacuum head; Figure 2 is an elevation showing part of the vacuum head; and, Figure 3 is an elevation of one set of nozzles.

The illustrated machine has a base plate 3 which is formed with a ring of eight recesses 4. These recesses provide a nest for a circular array of eight integrally cast female mould parts 5, which rest in the recesses and are thereby located in position. The female mould parts are interconnected via spokes 6 with a central hub. A vacuum head reciprocates vertically above the nest and has an array of eight tubes 7, of which one is shown in Figure 2, each aligned with a respective one of the recesses. The upper end of each tube 7 is connected to a controlled source of vacuum and the lower end terminates in a vacuum port which, when the vacuum head is lowered, can engage a male mould part 6 within the respective female mould part 5.In this way, by lowering and raising the vacuum head twice, and controlling the vacuum, the male mould parts can be lifted out, for filling of the female mould parts with liquid polymerisable material, and then pushed back into the female mould parts to seal the moulding cavities, between the pairs of mould parts, and then released.

The filling of the female mould parts is carried out by the two sets of four nozzles 8, each of which extends generally horizontally and downwardly, as shown in Figure 3. Each set of four nozzles are carried by a manifold 9 which is mounted on a block 10, in turn supported by two pairs of similar parallel pivotal links 11 which form a parallel motion linkage. The block 10 is operated by a pneumatic cylinder 12 and when the cylinder is extended, the block 10 and nozzles are moved on the pivotal linkage upwardly, forwardly and downwardly so that the tips of the nozzles are located just within the top of respective ones of the female mould parts. Similarly, when the cylinder 12 is retracted, the block and nozzles are lifted upwardly, rearwardly and downwardly so that they do not obstruct movement of the vacuum head.Each manifold 9 is connected by piping to a thermally insulated reservoir 13 of liquid polymerisable material, via a pump 14.

In operation, a set of eight female mould parts, with corresponding male parts loosely located therein, is placed manually on the nest. The vacuum head is lowered, so that the vacuum ports enter the male mould parts, the vacuum is started so that the male parts are captured, and the vacuum head is then lifted. The cylinders 12 are then operated so that the nozzles move into their extended positions above the female mould parts, whereupon the pump 14 is operated to dose a predetermined quantity of the liquid polymerisable material into each of the female mould parts.

The cylinders 12 are then retracted and the vacuum head lowered to push the male mould parts back into the respective female mould parts, prior to shutting off the vacuum and upward withdrawal of the vacuum head. The array of moulds are then ready to be placed in an oven for curing of the polymerisable material.

Claims

1. A machine for use in cast moulding contact lenses, the machine comprising a nest for locating an array of interconnected female mould parts, each formed with an upwardly facing concave moulding surface, the female mould parts initially locating therein a corresponding plurality of respective male mould parts each formed with a downwardly facing convex moulding surface; a vacuum head which is reciprocatable upwardly and downwardly above the nest and has a plurality of vacuum ports aligned, in use, with respective pairs of female and male mould parts, such that when the vacuum head is lowered, the male mould parts may be captured by the vacuum ports and lifted out of the female mould parts upon raising of the vacuum head; at least two sets of nozzles, which are movable from retracted positions to extended positions in which the nozzles are positioned to direct polymerisable material into respective ones of the female mould parts; at least one pump for dosing a predetermined amount of polymerisable material from a reservoir of the polymerisable material to respective ones of the nozzles; and means for controlling the vacuum head, the sets of nozzles, and the pump, such that, in sequence, the male mould parts are lifted out of the female mould parts, the nozzles are moved to their extended position, the polymerisable material is dosed through the nozzles into the female mould parts, the nozzles are retracted, and the head is lowered to lower the male mould parts back into the respective female mould parts prior to curing of the polymerisable material.

2. A machine according to claim 1, in which the nest is formed by an array of recesses in a base plate.

3. A machine according to claim 1 or claim 2, in which the nest is configured to accommodate a symmetrical circular array of female mould parts.

4. A machine according to any other of the preceding claims, in which each set of nozzles is mounted on a carrier which is supported by a pivotal linkage such that, in the extended position, the nozzles are directed downwardly into respective female mould parts, but are raised and withdrawn laterally so as not to obstruct the vacuum head, when moved to the retracted position.

5. A machine according to claim 4, in which the pivotal linkage incorporates a pair of parallel pivotal links which support the carrier by a parallel motion linkage from below, and which move over a top dead centre position as the carrier moves between the extended and retracted positions.

6. A machine for use in cast moulding contact lenses, substantially as described with reference to the accompanying drawings.