Injection valve, especially for a mould for an optical lens

An injection valve includes an injection channel (17) that opens outwards via an outlet (18) and has a specific inlet for the arrival of the molding material (19A) remote from the outlet (18), in addition to a slider unit (20) that is moveably mounted in the injection channel (17) and controls the outlet thereof (18). The injection channel (17) has a specific outlet (19B) for discharging the molding material. The invention can be used to mold an optical lens made from a polymerizable synthetic material.

The present invention relates generally to injection valves of the kind used to feed a mold of any kind with a molding material of any kind.

It is aimed more particularly at injection valves that have an injection channel, which opens to the outside via an outlet, and a slider unit which is mounted in the injection channel so as to be mobile in translation therein and which controls the outlet thereof. The injection channel has an inlet orifice to which the molding material is fed and which is located at a distance from the outlet.

DESCRIPTION OF THE RELATED ART

Injection valves of the above type are described in the following U.S. patents, for example: U.S. Pat. Nos. 5,221,509, 5,378,138, 5,470,219.

The present invention is more particularly aimed at the situation in which the nature of the molding material itself causes problems.

This is the case, for example, with polymerizable synthetic materials usually employed in molding optical lenses, and in particular ophthalmic lenses, that is to say spectacle lenses.

These polymerizable synthetic materials give rise to two kinds of problem during molding.

First of all, they frequently lead to unwanted deposition of a film of material on the inside of the injection valve through which they pass, even if the latter valve has been internally treated with a material supposedly opposing any such deposition, and this leads to unwanted fouling and even clogging of the injection valve.

Also, as soon as there is a certain level of discontinuity in their path, which obviously tends to be the case when they pass through an injection valve, these polymerizable synthetic materials are frequently subject to a phenomenon known as “bubbling”, i.e. bubbles tend to form spontaneously in them, which can lead to rejection of the products, for example optical lenses, molded under these conditions.

SUMMARY OF THE INVENTION

A general object of the present invention is an arrangement which is advantageous in that, somewhat unexpectedly, it minimizes or even cancels out the risk of fouling and “bubbling”.

It is based on the observation, not previously disclosed, that maintaining the molding material fed to the injection valve in circulation after the mold has been properly filled minimizes these risks of fouling and “bubbling”.

Thus the present invention provides an injection valve for feeding molding material to a mold, of the kind including an injection channel which opens to the outside via an outlet and which has, at a distance from said outlet, an inlet orifice to which the molding material is fed, and further including a slider unit that is mounted in the injection channel to be mobile in translation therein, and that controls the outlet thereof, characterized in that the injection channel has an outlet orifice for evacuating molding material.

Accordingly, once the mold has been filled, the molding material reaching the injection valve continues to circulate, being evacuated from the injection valve via the outlet orifice provided for this purpose.

This advantageously avoids stagnation of the molding material in the injection valve, as normally occurs when the molding material dead-ends at the closed end of the injection channel once the mold has been filled.

As a result of this, the risks of fouling of the injection valve are themselves advantageously minimized, which is what was wanted.

This advantageously further proves to apply to the risks of “bubbling” occurring in the molding material during molding thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The figures show, by way of example, the application of the invention to molding an optical lens, to be more precise an ophthalmic lens, not shown.

The mold10used for such molding is formed of two molding shells11A,11B at whose periphery is an annular closure member12defining with them the necessary molding cavity13. This is known in the art.

In the embodiment shown, the molding shells11A,11B are on edge and the closure member12is formed of two jaws12′,12″ which are carried by a common frame, not shown, and whose edges conjointly grip the molding shells11A,11B, having a semicircular inside contour for this purpose; at least one of the jaws, for example the top jaw12″, is mobile relative to the other jaw, here the bottom jaw12′, to enable the molding shells11A,11B to be inserted between them.

These arrangements are well known in the art, for example from French patent application No. 94/14926, filed Dec. 12, 1994, publication No. 2 727 894; being in themselves irrelevant to the present invention, they are not described in further detail here.

An injection valve15feeds the mold10, to be more precise its molding cavity13, with molding material. This is also known in the art.

As described in the previously cited French patent No. 94/14926, for example, the injection valve15is at the bottom of the molding cavity13, to be more precise at the lowest point thereof.

To this end, the bottom jaw12′ of the closure member12has a localized casting opening16to which the injection valve15is applied.

The injection valve15has an internal injection channel17which opens to the outside via an outlet18at one end, in corresponding relationship with the casting opening16of the mold10, and which has, as described in more detail later, an inlet orifice19A at a distance from the outlet18, and to which the molding material is fed, and a slider unit20that is mounted in the injection channel17so that it is mobile in translation therein, and which controls the outlet18thereof. This is also known in the art.

In accordance with the invention, the injection channel17has an outlet orifice19B for evacuating the molding material.

In the embodiments shown inFIGS. 3 to 13in particular, like its outlet18, the inlet orifice19A and the outlet orifice19B of the injection channel17are both controlled by the slider unit20.

As shown here, for example, the inlet orifice19A and the outlet orifice19B of the injection channel17are disposed laterally on a section T of the injection channel17, in contact with whose wall the slider unit20is slidably mounted.

In the embodiments shown inFIGS. 3 to 13in particular, the injection valve15is separate from the mold10and in practice includes a valve body23containing the injection channel17and adapted to be attached to the mold10, to be more precise to the bottom jaw12′ of the closure member12of the mold10, having a fixing flange24at the bottom for this purpose.

Conjointly, in these embodiments, the injection channel17has the same cross section throughout its length, passing completely through the valve body23from the fixing flange24to its outlet18. As described in more detail later, the slider unit20, which is shown separately inFIGS. 7 to 9, has a transverse opening25passing completely through it and by means of which the inlet orifice19A and the outlet orifice19B of the injection channel17can communicate with each other.

In practice, in the embodiments shown inFIGS. 3 to 13, the cross section of the injection channel17is rectangular, with a width L1very much less than its length L2(seeFIG. 5), and the overall shape of the slider unit20is that of a thin blade, whose rectangular cross section is complementary to that of the injection channel17, and whose contour, as seen in elevation, is also rectangular.

It results from the foregoing that, in the embodiments shown inFIGS. 3 to 13, the section T of the injection channel17including the inlet orifice19A and the outlet orifice19B is not materialized in concrete form, given the uniformity of the cross section of the injection channel17throughout its length.

In the embodiments shown inFIGS. 3 to 13, the valve body23is formed of two shells23A,23B that meet face-to-face on a joint plane P that intersects the injection channel17longitudinally.

As is the case in these embodiments, the joint plane P is preferably the plane of one of the larger faces of the injection channel17, and is therefore entirely part of one of the shells23A,23B, in this example the shell23B, as is clear fromFIGS. 5 and 6.

Thus only the shell23B has to be machined to form the injection channel17.

In contrast, the corresponding face of the shell23A is advantageously smooth.

The two shells23A,23B constituting the valve body23are suitably fastened together, of course, for example by screws, not shown, which pass transversely through the injection channel17.

To this end, and as can be seen in the case of the shell23B inFIG. 6, each of the shells23A,23B has appropriate bores26spaced along the injection channel17.

Similarly, the fixing flange24of the valve body23, which in practice is divided half-and-half between the two shells23A,23B, has spaced bores27through which screws, not shown, are passed to fix the valve body23to the mold10.

Also, in the embodiments shown inFIGS. 3 to 13, the valve body23has a nozzle-like external profile at the location of the outlet18of the injection channel17.

In other words, it forms a more or less tapered external nose28.

The free edge of the nose28is straight and substantially perpendicular to the axis A of the injection channel17, for example (seeFIG. 6).

As an alternative to this it can be concave, having the same profile as the contour of the molding cavity13(seeFIG. 13).

In the embodiments shown inFIGS. 3 to 13, the inlet orifice19A and the outlet orifice19B of the injection channel17are offset longitudinally from each other along the axis A of the injection channel17.

In practice, the inlet orifice19A of the injection channel17is then preferably nearer its outlet18than the outlet orifice19B.

However, when projected onto a common plane, and as is clear fromFIGS. 10A and 10B, the inlet orifice19A and the outlet orifice19B of the injection channel17partly overlap each other.

In practice, the inlet orifice19A and the outlet orifice19B of the injection channel17are on respective opposite sides of the injection channel17and therefore on respective opposite sides of its axis A, one being part of the shell23A of the valve body23and the other being part of the shell23B.

In the embodiments shown inFIGS. 3 to 13, the inlet orifice19A and the outlet orifice19B of the injection channel17are both at the ends of pipes30A,30B at least the end parts of which are substantially perpendicular to the axis of the injection channel17.

As shown in dashed outline inFIG. 3, the pipes30A,30B can themselves be connected, via chambers31A,31B, to tubes32A,32B in which the molding material circulates.

In practice, the pipes30A,30B have circular contours and likewise therefore the inlet orifice19A and the corresponding outlet orifice19B.

Likewise, in practice, the inlet orifice19A and the outlet orifice19B both have the same diameter D.

As a corollary of this, the opening25in the slider unit20is an elongate buttonhole whose length extends along the axis A of the injection channel17.

The width L3of the opening25is at least equal to the diameter D of the inlet orifice19A and the outlet orifice19B, so as to enclose them.

In practice, the width L3is substantially equal to the diameter D.

Conjointly, the length L4of the opening25is much greater than the overall contour of the combination of the inlet orifice19A and the outlet orifice19B.

In the embodiment shown inFIGS. 3 to 9in particular, the shells23A,23B constituting the valve body23are relatively massive, and are made of metal, for example.

Conjointly, the slider unit20is itself made of metal, preferably stainless steel.

Also, in this embodiment, the free end33of the slider unit20is straight, like the free edge of the nose28of the valve body23.

In service, the slider unit20is mobile between an advanced position, in which, as shown inFIG. 10A, its free end33is level with the outlet18of the injection channel17, and a retracted position, in which, as shown in continuous outline inFIG. 10B, it partly uncovers the inlet orifice19A but covers the outlet orifice19B.

In the advanced position, the opening25in the slider unit20establishes communication between the inlet orifice19A and the outlet orifice19B but completely blocks the injection channel17.

The molding material therefore circulates continuously through the injection valve15, without feeding the molding cavity13of the mold10.

In contrast, in the retracted position of the slider unit20the molding cavity13of the mold10is fed with the molding material, which is not diverted to the outlet orifice19B.

In all intermediate positions of the slider unit20, as long as its free end33has at least reached, and passed beyond, the inlet orifice19A, as shown in dashed outline inFIG. 10B, the molding cavity13of the mold10is advantageously fed, at a more or less variable flow rate.

Obviously, the fact that, when projected onto a plane, the inlet orifice19A and the outlet orifice19B of the injection channel17overlap has the advantage that this limits the stroke of the slider unit20.

To limit this stroke further, and optimally, the inlet orifice19A is preferably as close as possible to the outlet18of the injection channel17.

As will also be noted, the molding material is in contact with the walls of the injection channel17only when the slider unit20is in the retracted position, and its contact with those walls is then limited to just the end portion of the injection channel17.

This advantageously minimizes the risk of fouling of the injection channel17, especially as, on each outward and return movement, the slider unit20sweeps the walls of the injection channel17completely.

As a corollary of this, the risks of “bubbling” of the molding material are themselves minimized.

In the embodiment shown inFIGS. 11 to 13, the shells23A,23B constituting the valve body23are thinner than previously, ignoring the fixing clamp24.

They are made from a synthetic material, for example, preferably a fluoropolymer-based synthetic material such as PTFE, for example.

As shown in dashed outline inFIG. 11, the shells23A,23B can then each be reinforced laterally by a metal plate34A,34B, if required.

As a corollary of this, the slider unit20, not shown, is preferably still made of metal.

Also, in this embodiment, at least one of the pipes30A,30B with the inlet orifice19A and the outlet orifice19B at their ends is connected to the orifice by an enlargement36A,36B that is elongate in the direction of the outlet18of the injection channel17.

As shown here, for example, the enlargement36A,36B is produced by a bevel37A,37B which intersects the pipe30A,30B concerned obliquely.

In the embodiment shown, there is an enlargement36A,36B for each of the pipes30A,30B, and the enlargement36A,36B extends as far as the immediate vicinity of the outlet18of the injection channel17.

In practice, in the embodiment shown, the angle between the bevel37A,37B of the enlargement36A,36B of a pipe30A,30B and the axis A of the injection channel17is different for the two pipes30A,30B.

For example, it is greater for the pipe30A corresponding to the inlet orifice19A than for the pipe30B corresponding to the outlet orifice19B.

Otherwise, the features are of the same kind as previously.

In the embodiment shown inFIGS. 14 to 17, the injection valve15according to the invention is an integral part of the mold10.

In other words, it is incorporated into the mold10.

To be more precise, in the embodiment shown, it is incorporated into the bottom jaw12′ of the closure member12of the mold10, and is in one piece with the remainder of the bottom jaw12′.

Also, in this embodiment, the injection channel17has, successively, starting from its outlet18, which is coincident with the casting opening16of the mold10, at least two sections T′, T, namely a smaller first section T′, at the end of which is the outlet18, and a larger second section T, which incorporates the inlet orifice19A and the outlet orifice19B, and, conjointly, the slider unit20has two sections T′1, T1whose dimensions are complementary to those of the sections T′, T of the injection channel17.

As shown here, for example, the two sections T′, T of the injection channel17are both cylindrical and are connected by a frustoconical transition section T″.

In practice, the inlet orifice19A and the outlet orifice19B of the injection channel17are in diametrally opposed positions relative to each other, on respective opposite sides of the axis A of the injection channel17.

In the embodiment shown, the inlet orifice19A and the outlet orifice19B are at the ends of pipes30A,30B at least end parts of which are oblique to the axis A of the injection channel17, at an acute angle thereto.

As shown here, for example, this angle is the same for both pipes30A,30B.

In the embodiment shown, the profile of the free end33of the slider unit20is globally concave from its central part to its periphery.

In the advanced position of the slider unit20, its section T′1is interengaged with the section T′ of the injection channel17, which prevents feeding of the molding cavity13, and, conjointly, its section T1is interengaged with the section T of the injection channel17.

However, because of the length of the section T′1of the slider unit20, on the one hand, and because of the difference between the diameters of the section T′1and the section T1from which it follows on, on the other hand, the molding material still circulates continuously through the injection valve15, bypassing the section T′1.

This circulation of the molding material through the injection valve15continues in the retracted position of the slider unit20, but the molding cavity13is fed because of the proximity of the corresponding flow to the outlet18of the injection channel17, which is uncovered at this time, and because of the oblique nature of the passage30A through which the molding material is discharged into the injection channel17.

In the embodiment shown diagrammatically inFIGS. 18 and 19, instead of being cylindrical, the end section T′1of the slider unit20is in the form of a blade, as in the embodiments shown inFIGS. 3 to 13.

However, as shown here, its free end33can be profiled, as previously.

It is found that a profiled free end33on the slider unit20minimizes the risks of “bubbling” of the molding material in the molding cavity13at the location of the injection channel17.

Of course, the present invention is not limited to the embodiments described and shown, but encompasses any variant execution and/or combination of the components thereof.