Patent Description:
The invention more precisely relates to a method for supplying at least a molding device with a polymerizable mixture.

The invention also relates to a supply device for supplying at least a molding device with a polymerizable mixture.

The invention finds particularly advantageous, but not exclusive, application for the manufacturing of transparent optical articles such as ophthalmic lenses, and notably lenses for spectacles and sunglasses or vision correcting spectacles.

It is known to supply a molding device with polymerizable mixture by introducing nitrogen in a tank where is stored the polymerizable mixture. Such introduction of nitrogen increases the pressure inside said tank and therefore pushes the polymerizable mixture towards the molding device.

However, some gas can thus be dissolved in the polymerizable mixture and may result in bubbles trapped inside the final molded article, said molded article being then considered as defective. In general terms, any gas, either already present in the tank or newly generated (due for example to the presence of water), can be dissolved in the polymerizable mixture before the supply of the molding device and therefore induce a defective molded article.

Document <CIT> describes a method and apparatus for casting a resin around a metal body, within a mold.

One object of the invention is to provide a method for supplying a polymerizable mixture that allows reducing the quantity of defective molded articles exhibiting bubbles trapped therein.

A further object of the invention is to provide a method that allows continuously supplying of the molding device in degassed polymerizable mixture.

The above objects are achieved according to the invention by providing a method for supplying a polymerizable mixture to at least one molding device according to claim <NUM>.

Step c) of the method ensures that the polymerizable mixture contained in the tank is subjected to a pressure lower than ambient pressure, not only during the formation of said polymerizable mixture, but also while the molding device is being supplied. Therefore, the method of the invention not only ensures the degassing of the polymerizable mixture before it reaches the molding device, but also prevents any further regassing of the polymerizable mixture before it reaches the molding device, notably the regassing due to chemical reaction, the presence of water, gas trapped in the supply device, or due to any other factor.

By "continuous" or "continuously", it is meant "without stopping". The maintaining of the pressure in the tank at the set value of pressure, smaller than ambient pressure, occurs while the supply of the molding device takes place, without stopping, and such maintaining of low pressure in the tank occurs until the tank gets empty or needs to be refilled.

Other characteristics of the method of this invention, taken together or separately, are listed in claims <NUM> to <NUM>.

A further object of the invention is to provide a supply device that continuously supplies the molding device in degassed polymerizable mixture.

The above objects are achieved by the supply device for supplying at least one molding device with a polymerizable mixture according to claim <NUM>.

The vacuum regulator allows reaching a given pressure in the tank, smaller than ambient pressure, in order to remove the gas from the polymerizable mixture ahead of the supply of the molding device in polymerizable mixture, but also allows maintaining the pressure in the tank at the given value, even during the supplying of the molding device, in order to prevent any regassing of the polymerizable mixture.

The looping line connected by its two ends to the tank forms a closed loop with the tank in order to allow a continuous supply of the molding device simultaneously with the continuous degassing of the polymerizable mixture contained in the tank.

More precisely, the supply device can supply the molding device in polymerizable mixture without stopping as the polymerizable mixture circulates from the tank to the looping line and returns to the tank, as long as there is enough polymerizable mixture in the tank. While continuously circulating in the looping line and returning back to the tank where the polymerizable mixture is under continuously controlled pressure (at the set value of pressure lower than ambient pressure), the polymerizable mixture is prevented from regassing before it is supplied to the molding device.

Other characteristics of the supply device of this invention, taken together or separately, are listed in claims <NUM> to <NUM>.

The following description with reference to the accompanying drawings will make it clear what the invention consists of and how it can be achieved. The invention is not limited to the embodiments illustrated in the drawings. Accordingly, it should be understood that where features mentioned in the claims are followed by reference signs, such signs are included solely for the purpose of enhancing the intelligibility of the claims and are in no way limiting on the scope of the claims.

Other characteristics of the supply device of this invention, taken together or separately, are the following:.

In the rest of the description, the terms "upstream" and "downstream" will be used in the direction of fluid flow, in order to locate various elements with respect to one another in the supply device.

Similarly, the terms "inlet" and "outlet" will be used in the direction of fluid flow in order to describe the elements that can receive fluid from an inlet and discharge it through an outlet.

A polymerizable mixture is understood to be a mixture of reactants, notably monomers, pre-polymers and/or of polymers that are able to react with one another so as to form a final polymer material. These reactants are known as precursor reactants of the polymerizable mixture.

Here, the polymerizable mixture may for instance be a mixture of reactants that react at least partially with one another simply by being brought into contact, without necessarily requiring any external stimulation, such as a thermal, photonic, chemical or mechanical stimulation.

More particularly, the polymerizable mixture may comprise for instance, in weight relative to the total weight of the polymerizable mixture:.

The monomer A can be for example a diisocyanate. The monomer B can be for example a dithiol.

<FIG> shows a supply device <NUM> of the invention for supplying at least one molding device <NUM> with a polymerizable mixture. The at least one molding device <NUM> comprises at least one mold and a means of injection for injecting the polymerizable mixture inside said mold.

Here, the molding device <NUM> is a device for molding ophthalmic lenses. It thus comprises a plurality of molds, each mold being in the shape of a lens.

As shown on <FIG>, the supply device <NUM> here feeds three molding devices <NUM> with the same polymerizable mixture. Each molding device <NUM> is plugged on the supply device <NUM> by a valve <NUM>. Each valve <NUM> is here in the shape of a "T", as commonly used in the field. When the valve <NUM> is open, the corresponding molding device <NUM> is connected to the looping line <NUM>. When the valve <NUM> is closed, the corresponding molding device <NUM> is disconnected from the looping line <NUM>. By "connected", it is meant in the rest of the description that the elements are in fluidic communication, the fluid being either a liquid or a gas.

As shown on <FIG>, the supply device <NUM> comprises:.

More precisely, the polymerizable mixture stored in the tank <NUM> is preferably a degassed polymerizable mixture, that is to say a polymerizable mixture from which all gases have been removed. To transform the polymerizable mixture into a degassed polymerizable mixture, it is possible to place the polymerizable mixture under a very low pressure, for instance comprised between <NUM> bars or <NUM> bars. Such degassing can for instance occur while the polymerizable mixture is being formed, when mixing its reactants, or just after the polymerizable mixture was formed.

The looping line <NUM> is connected, on a first end, to an outlet <NUM> of the tank <NUM> for receiving the polymerizable mixture and, on a second end, to an inlet <NUM> of said tank <NUM> for returning to the tank <NUM> an excess in polymerizable mixture. In between its first and second ends, the looping line <NUM> is connected to (respectively disconnected from) an inlet of each of said molding devices <NUM>, by means of the valves <NUM> in open position (respectively in closed position). As represented in <FIG>, each of said molding devices <NUM> forms a dead end, that is to say that once the polymerizable mixture enters the molding device, said polymerizable mixture will not be able to return to the looping line <NUM>. The looping line <NUM> is here a pipe and its first end can be considered as an inlet of said looping line <NUM>, while its second end and the locations where said pipe is connected to the molding devices <NUM> can be considered as outlets of said looping line <NUM>.

Thus, when all the valves <NUM> are closed, the polymerizable mixture contained in the tank <NUM> flows in a closed loop from the tank <NUM>, through the outlet <NUM> of the tank <NUM> into the looping line <NUM> and back to the tank <NUM> through the inlet <NUM> of said tank <NUM>. In other words, when the valves are closed, the looping line <NUM> and the molding devices <NUM> are disconnected from one another, while the looping line <NUM> is still connected to the tank <NUM>. When at least one valve <NUM> is open, the polymerizable mixture flows from the tank <NUM>, through the outlet <NUM> of the tank <NUM> into the looping line <NUM>, and a part of the polymerizable mixture flows from the looping line <NUM> into the molding device <NUM> through the corresponding valve <NUM>, while the rest of the polymerizable mixture (commonly called "excess in polymerizable mixture") continues to flow in the looping line <NUM> beyond said valve <NUM> to go back to the tank <NUM>, through the inlet <NUM> of the tank <NUM>. The outlet <NUM> of the tank <NUM> can be provided with a valve (not represented) so that it is possible to close said valve in order to disconnect the looping line <NUM> from the tank <NUM> if necessary.

According to the invention, the supply device <NUM> also comprises a vacuum regulator <NUM>.

The vacuum regulator <NUM> aims at reaching a set value of pressure Ps in the tank <NUM> and at maintaining the pressure P in the tank <NUM> at said set value of pressure Ps, even when the molding devices <NUM> are being supplied in polymerizable mixture through the looping line <NUM>. Here, the vacuum regulator <NUM> is for instance a mechanical vacuum regulator. In the present example, the vacuum regulator <NUM> is connected to the tank <NUM>. Preferably, it is connected to the tank <NUM> in a part where the polymerizable mixture cannot get, preferably in the upper part of the tank <NUM>, so that only gases can flow between the vacuum regulator <NUM> and the tank <NUM>.

The set value of pressure Ps that is to be reached and maintained in the tank <NUM> is smaller than the ambient pressure Pam. Preferably, the set value of pressure Ps to be reached in the tank <NUM> is at least <NUM> bars under the ambient pressure Pam. More preferably, the set value of pressure Ps is between <NUM> to <NUM> bars under the ambient pressure Pam. In other words, the set value of pressure Ps is preferably comprised in the range [Pam - <NUM>; Pam - <NUM>], the ambient pressure Pam and the set value of pressure Ps being given in bars. The ambient pressure Pam is here defined as the pressure of the atmosphere outside the tank <NUM>. Such range of pressure for the set value of pressure Ps prevents the regassing of the polymerizable mixture in the tank <NUM>, while the molding devices <NUM> are being supplied in degassed polymerizable mixture. Such range of pressure for the set value of pressure Ps is a low pressure that is a good compromise, compatible with the higher pressure to which is exposed the degassed polymerizable mixture within the looping line <NUM> and feed the molding devices <NUM>.

Of course, it is also possible that the set value of pressure Ps is itself a range, instead of being a precise value. In such case when the set value of pressure Ps is an interval (or range), "the pressure P is higher than the set value of pressure Ps (P>Ps)" means that the pressure P is in fact higher than the upper limit of the range. Similarly, when the set value of pressure Ps is an interval (or range), "the pressure P is lower than, or smaller than, the set value of pressure Ps (P<Ps)" means that the pressure P is in fact lower than the lower limit of said range.

Here, the vacuum regulator <NUM> comprises a pressure sensor to measure the pressure P inside the tank <NUM>.

To be able to reach the set value of pressure Ps and maintain the pressure P in the tank <NUM> at said set value of pressure Ps, the vacuum regulator <NUM> is designed to control a vacuum pump <NUM> that is connected to the tank <NUM> for lowering the pressure P in the tank <NUM>.

The vacuum regulator <NUM> is able to measure the pressure P inside the tank <NUM> and to control the vacuum pump <NUM> in order to continuously adjust said pressure P inside the tank <NUM> to the set value of pressure Ps.

In the present example, as illustrated on <FIG>, the vacuum pump <NUM> is connected to the vacuum regulator <NUM>. In other words, the vacuum pump <NUM> is connected to the tank <NUM> through the vacuum regulator <NUM> that is itself connected to the tank <NUM>.

The vacuum regulator <NUM> is able to measure the pressure P inside the tank and to control the vacuum pump <NUM> in order for it to withdraw some of the gas(es) contained in the tank <NUM> whenever said pressure P is higher than the set value of pressure Ps.

The supply device <NUM> of the invention thus prevents regassing of the polymerizable mixture, that is to say prevents some gas to be dissolved in the polymerizable mixture once the supply of the molding devices <NUM> has started. The regassing is for instance caused by leaks of the looping line <NUM>, trapped gas in the looping line <NUM>, pump cavitation or even chemical reactions. Thanks to the supply device <NUM> of the invention, the polymerizable mixture is degassed before it starts to flow in the looping line <NUM>, but also each time it reaches the tank <NUM> after it flew in the looping line <NUM>. The potential regassing of the polymerizable mixture is prevented because the pressure in the tank <NUM> is continuously controlled.

Advantageously, as shown on <FIG>, the looping line <NUM> of the supply device <NUM> of the invention, also comprises, a pump <NUM>, with adjustable speed, for supplying at a set flow rate the inlet of said at least one molding device <NUM> with the polymerizable mixture from the tank <NUM>.

The pump <NUM> eases the flow of polymerizable mixture inside the looping line <NUM> towards the valves <NUM> and into the molding devices <NUM> so that less pressure needs to be applied in the tank <NUM> for pushing the polymerizable mixture through the outlet of said tank <NUM>. In other words, thanks to the pump <NUM>, the pressurization of the polymerizable mixture in the tank <NUM> can be lowered without affecting the flow of polymerization in the looping line <NUM>. Lowering the pressure P inside the tank <NUM> lowers the risk of regassing the polymerizable mixture.

Thanks to the pump <NUM>, the pressure in the looping line <NUM>, at the inlet of the molding device <NUM>, is maintained at a value higher than the set value of pressure Ps that is maintained in the tank <NUM>.

Advantageously, as shown on <FIG>, the looping line <NUM> of the supply device <NUM> of the invention comprises, in addition, a back pressure regulator <NUM> located downstream of the inlet of the molding device <NUM> and upstream of the inlet <NUM> of the tank <NUM>. Such back pressure regulator <NUM> regulates the pressure at the inlet of said at least one molding device <NUM>.

More precisely the back pressure regulator <NUM> aims at balancing the pressure in the looping line <NUM>, in order for the molding devices <NUM> to be fully filled. It therefore prevents the introduction of air inside the molds of the molding devices <NUM>.

To do so, the back pressure regulator <NUM> is designed to act on the flow rate of the polymerizable mixture that returns to the tank <NUM> through the looping line <NUM>, said flow rate being set based on the pressure in the looping line <NUM>, downstream of the inlet of the molding devices <NUM>. In fact, when at least one valve <NUM> leading to the molding device <NUM> is open, the pressure in the looping line <NUM>, upstream of said valve <NUM>, is naturally higher than the pressure in the looping line <NUM>, downstream of said valve <NUM>, because some polymerizable mixture flew into the corresponding molding device <NUM> and is therefore "missing" in the looping line <NUM>. The balance of pressure operated by the back pressure regulator <NUM> also forces the polymerizable mixture to flow beyond said valves <NUM>, back into the tank <NUM>.

In other words, the supply device <NUM> of the invention allows maintaining two different pressures in the closed loop: a first pressure in the tank <NUM>, fixed at the set value of pressure Ps, lower than ambient pressure Pam, that prevents regassing of the polymerizable mixture, and a second pressure in the looping line <NUM>, higher than the set value of pressure Ps, usually near ambient pressure Pam or higher than ambient pressure Pam, in order to properly fill the molding devices <NUM>.

Advantageously, the vacuum regulator <NUM> is here also designed to control an inert gas supplier <NUM> connected to the tank <NUM> for increasing the pressure P in the tank <NUM>.

In the present example, as illustrated on <FIG>, the inert gas supplier <NUM> is connected to the vacuum regulator <NUM>. In other words, the inert gas supplier <NUM> is connected to the tank <NUM> through the vacuum regulator <NUM> that is itself connected to the tank <NUM>.

The vacuum regulator <NUM> is thus able to control the inert gas supplier <NUM> in order for it to add some inert gas inside the tank <NUM> whenever the measured pressure P inside the tank <NUM> is lower than the set value of pressure Ps. The pressure P measured inside the tank <NUM> can for instance be lower than the set value of pressure Ps when the level L of polymerizable mixture is getting down in the tank <NUM> because of the molding devices <NUM> being supplied in degassed polymerizable mixture.

In the present example, the inert gas supplier <NUM> is designed to introduce nitrogen (N) in the tank <NUM> when the pressure P inside the tank is lower than the set value pressure Ps. In other words, the inert gas supplier <NUM> supplies nitrogen to compensate for the pressure variations. The use of nitrogen (N), which is a dry inert gas, prevents the introduction of humidity in the tank <NUM> and prevents that the atmosphere of the tank <NUM> reacts with the polymerizable mixture stored therein. We here call "atmosphere" of the tank <NUM> the material that is enclosed inside the tank <NUM> and that is not degassed polymerizable mixture nor any other liquid material. Of course, the inert gas supplier can introduce other inert gases into the tank <NUM>, such as argon or helium instead of nitrogen, or even a mix of inert gases.

Thus, during the whole process of supplying the molding devices <NUM> with polymerizable mixture, the supply device <NUM> of the invention allows, on one hand, the removal of the gas that is dissolved in the polymerizable mixture, such removal of dissolved gas occurring thanks to the vacuum pump <NUM>, and, on the other hand, preventing the pressure in the tank <NUM> to get to low, such prevention occurring thanks to the inert gas supplier <NUM>. In other words, thanks to the vacuum regulator <NUM> controlling the vacuum pump <NUM> and the inert gas supplier <NUM>, a partial vacuum is applied inside the tank <NUM> in order to remove the dissolved gas from the polymerizable mixture while the degassed polymerizable mixture is however still sufficiently pressurized, at the set value of pressure Ps, to be able to flow in the looping line <NUM> and to be supplied to the molding devices <NUM> at a high pressure. Thanks to the vacuum regulator <NUM>, the pressure in the tank <NUM> is maintained at the set value of pressure Ps, therefore allowing a balance of pressure with the looping line <NUM> in which higher pressures are met.

In an advantageous embodiment of the supply device <NUM> of the invention, such as the one shown on <FIG>, the supply device <NUM> comprises, in addition, a level sensor <NUM> for checking the level L of polymerizable mixture inside the tank <NUM>. This level sensor <NUM> prevents damaging the pump <NUM> and allows stopping the flow of polymerizable mixture into the looping line <NUM> and into the molding devices <NUM> when the level L of polymerizable mixture within the tank <NUM> is lower than a predetermined set value of level Ls. Such stopping notably occurs when the tank <NUM> is empty, or at least does not comprise enough polymerizable mixture to ensure the correct filling of the molds of the molding devices <NUM>. The set value of level Ls is predetermined based on the number of molding devices <NUM> and their characteristics, such as the number of molds they comprise and their injection rate. The set value of level Ls may also depend on the size of the tank <NUM> and on the flow rate set by the pump <NUM> in the looping line <NUM>.

In a further advantageous embodiment of the supply device <NUM> of the invention, such as the one shown on <FIG>, the inlet <NUM> of the tank <NUM> is provided with means <NUM> for orientating the excess in polymerizable mixture returning to the tank <NUM> against a wall <NUM> of the tank <NUM>. Such means is schematically represented by an arrow on <FIG>. The means <NUM> for orientating the polymerizable mixture is here designed to maximize the contact surface between the polymerizable mixture and the wall <NUM> of the tank <NUM>. In other words, the means <NUM> for orientating the polymerizable mixture forces the polymerizable mixture to touch the wall <NUM> of the tank <NUM> in order to form a thin sheet of polymerizable mixture sliding down said wall <NUM> of the tank <NUM>. The means <NUM> can in addition be designed to widen the surface of the flow of polymerizable mixture.

Such means <NUM> therefore lowers the risk that the polymerizable mixture regasses due to turbulences caused when the excess of polymerizable mixture drops violently on the surface of the polymerizable mixture lying in the tank <NUM>. In addition, the means <NUM> for orientating the polymerizable mixture increases the contact surface between the excess in polymerizable mixture returning to the tank <NUM> and the atmosphere of the tank <NUM>, thus enhancing the degassing of said excess in polymerizable mixture returning to the tank <NUM>.

In the present example, the means <NUM> for orientating the polymerizable mixture comprises a wall wiper distributor <NUM> as the one illustrated on <FIG>. As shown on <FIG>, the wall wiper distributor <NUM> comprises an inlet <NUM> designed to be connected to the inlet <NUM> on the tank <NUM>, and an outlet <NUM> located so as to face the wall of the tank <NUM>. The inlet <NUM> and the outlet <NUM> of the wall wiper distributor <NUM> are connected to one another through a pipe (here a cylinder pipe) that is curved in order to place the outlet <NUM> close to and facing the wall <NUM> of the tank <NUM>. The outlet <NUM> is delineated by a cylindrical wall (or cylinder) which free end is cut obliquely relatively to the axis of extension of the cylinder so as to form a sort of beak pointing towards the wall <NUM> of tank <NUM>. Here, the angle formed between the normal to the section of the free end of the cylinder and the axis of extension of said cylinder is about <NUM>°.

In an advantageous embodiment, not shown on <FIG>, the supply device comprises a filing line connected to an inlet of the tank. The inlet of the tank at which is connected the filling line can either be the same inlet <NUM> as the one at which the looping line <NUM> is connected or be a distinct inlet. The filling line is distinct and separate from the looping line <NUM>. Such filling line allows filling the tank <NUM> with fresh (or new) polymerizable mixture or with at least one of the reactants of said polymerizable mixture. In other words, thanks to the filling line, the tank <NUM> can at the same time be emptied by flowing the polymerizable mixture in the looping line <NUM> and into the molding devices <NUM>, and filled in by the introduction of new (or fresh) polymerizable mixture from the filling line. The introduction of fresh (new) polymerizable mixture in the tank <NUM> is for instance based on the measure of the level L of polymerizable mixture in the tank <NUM>, made by the level sensor <NUM> previously described. Such filling line allows continuous operation of the molding line, as the filling of the molds does not need to be stopped for refilling the tank <NUM>, said tank <NUM> being designed to be able to continuously receive fresh polymerizable mixture from the filling line. Of course, it is possible to provide the inlet of the tank <NUM> at which is connected the filling line with means for orientating the fresh polymerizable mixture arriving in the tank <NUM> against the wall <NUM> of the tank <NUM>, in a similar way as what was described above for the looping line <NUM>.

It is also possible that the supply device <NUM> of the invention comprises a control unit (not represented). The elements of the supply device <NUM> such as the valves <NUM>, the pump <NUM>, the vacuum regulator <NUM> and the back pressure regulator <NUM> are therefore designed to be controlled by said control unit. Such control unit is for instance designed to receive information from the vacuum regulator <NUM> and/or from the level sensor <NUM> and/or from the back pressure regulator <NUM> (when the supply device <NUM> is equipped with such). Of course, it is also possible to control the supply device <NUM> manually, by checking information given by the vacuum regulator <NUM>, the level sensor <NUM> and the back pressure regulator <NUM> (when the supply device <NUM> is equipped with such).

The invention also relates to a method for supplying the polymerizable mixture to the at least one molding device <NUM>. The method of the invention comprises the following steps:.

In practice, the method of the invention is for instance implemented with the supply device <NUM> of the invention.

Such method is more precisely illustrated on <FIG> and is for instance implemented by the control unit of the supply device <NUM>, using the supply device <NUM>.

Step a) of the method is illustrated by the box referenced E1 on <FIG>. At step a), the tank <NUM> is for instance filled with the polymerizable mixture that has been formed in a step prior to step a). Alternatively, it is possible to mix, at step a), the various reactants of the polymerizable mixture within the tank <NUM> in order to form the polymerizable mixture directly inside the tank <NUM>. It is also possible, in step a), that the tank <NUM> receives the polymerizable mixture, or at least one of the reactants of said polymerizable mixture, from a filing line connected to the tank <NUM>.

Advantageously, prior to step b), the polymerizable mixture contained in the tank <NUM> is subjected to a pressure smaller than ambient pressure Pam, preferably lower that the set value of pressure Ps, during a predetermined period of time, so as to form a degassed polymerizable mixture. The degassing of the polymerizable mixture by placing said polymerizable mixture under a low pressure can for instance occur inside the tank <NUM>, using the vacuum pump <NUM>. The low pressure applied to the tank <NUM> for degassing the polymerizable mixture can for instance be comprised between <NUM> and <NUM> bars. Alternatively, the degassing of the polymerizable mixture could occur at a pressure equal to the set value of pressure Ps, but the step of degassing would therefore last longer than when the degassing occurs at a pressure lower than said set value of pressure Ps. This degassing step occurs during a finite time, and stops once steps b) and c) are implemented.

Alternatively, it is also possible that the polymerizable mixture contained in the tank <NUM> at step a) is already a degassed polymerizable mixture, degassed in a step prior to step a).

Once step a) is achieved, step b) is implemented prior to step c).

At step b) (box referenced E2), the control unit of the supply device <NUM> controls the vacuum regulator <NUM> that itself controls the vacuum pump <NUM> in order to adjust the pressure P inside the tank <NUM> and reach the set value of pressure Ps. The set value of pressure Ps is the same as the one defined previously. Of course, if the pressure P inside the tank <NUM> is lower than the set value of pressure Ps, it is possible to increase said pressure by letting gas flow inside the tank <NUM>. For instance, it is possible to use the inert gas supplier <NUM> to increase the pressure inside the tank <NUM> to reach the set value of pressure Ps.

At step c), the polymerizable mixture is supplied to the molding device <NUM> while the pressure in the tank <NUM> is maintained at the set value of pressure Ps. Such supply here occurs through the looping line <NUM> which both ends are connected to the tank <NUM> and which is plugged to an inlet of said molding device, in between said ends, by means of a valve <NUM>.

Preferably, step c) comprises a first sub-step during which the filling of the looping line <NUM> occurs while the pressure in the tank <NUM> is maintained at the set value of pressure Ps (box referenced E3 on <FIG>), and a second sub-step during which the molding devices are supplied in degassed polymerizable mixture (boxes referenced E4, E41, E42, E5 and E51 on <FIG>).

The first sub-step of step c) (box referenced E3) occurs while the valves <NUM> connecting said looping line <NUM> to the molding devices <NUM> are closed so that the inlet of each molding device <NUM> is disconnected from the looping line <NUM>. To allow the polymerizable mixture to flow in the looping line <NUM>, the pressure P inside the tank <NUM> is controlled to be at the set value of pressure Ps, so that it is lower than ambient pressure Pam, but still sufficient for the polymerizable mixture to fill the portion of the looping line <NUM> that connects the outlet <NUM> of the tank <NUM> to the pump <NUM>. Once the pump <NUM> is submerged with polymerizable mixture, which implies that the pump <NUM> is purged from the gases it may contained, it is switched on to fill the whole looping line <NUM> and to return the polymerizable mixture to the tank <NUM> via the inlet <NUM> of the tank <NUM> and through the means <NUM> for orientating said polymerizable mixture against the wall <NUM>.

In step c), once the looping line <NUM> is filled with degassed polymerizable mixture, the pressure in said the looping line <NUM>, at the inlet of the molding device <NUM>, is set at a value higher than the set value of pressure Ps that is maintained in the tank <NUM>, and then maintained at said high value of pressure. Such difference of pressure between the tank <NUM> and the inlet of the molding device <NUM> is possible thanks to the pump <NUM> and the back pressure regulator <NUM> which can increase the pressure in the looping line <NUM>.

Once the tank <NUM> and the looping line <NUM> are both filled with degassed polymerizable mixture, and the pressure P inside the tank <NUM> is at the set value of pressure Ps, while the pressure at the inlet of the molding device is at a higher chosen value, the molding devices <NUM> are supplied with degassed polymerizable mixture at step c). Such supply of the molding devices <NUM> with the degassed polymerizable mixture is represented by the set of boxes referenced E4, E41, E42, E5 and E51 on <FIG>.

In order to guarantee that the pressure P inside the tank <NUM> is at the set value of pressure Ps while supplying the molding devices <NUM>, the vacuum regulator <NUM> regularly measures, preferably at very high frequency, the pressure P inside the tank <NUM> and the control unit then compares said pressure P with the set value of pressure Ps (box referenced E4).

If the pressure P inside the tank <NUM> is greater than the set value of pressure Ps (box referenced E41), the control unit controls the vacuum regulator <NUM> for it to control the vacuum pump <NUM> in order to lower said pressure P inside the tank <NUM>.

If the pressure inside the tank <NUM> is lower than the set value of pressure Ps (box referenced E42), the control unit controls the vacuum regulator <NUM> for allowing gas inside the tank <NUM>. Preferably, the vacuum regulator <NUM> here controls the inert gas supplier <NUM> in order to increase the pressure P inside the tank <NUM>.

If the pressure P inside the tank <NUM> is equal to the set value of pressure Ps (P = Ps), then the control unit checks the level L of polymerizable mixture enclosed within the tank <NUM>, said level L being for instance given by the level sensor <NUM> (box referenced E5).

If the level L is sufficient, that is to say is higher than or equal to the predetermined set value of level Ls (L ≥ Ls), then the control unit controls the supply of degassed polymerizable mixture to the molding devices <NUM> (box referenced E51 on <FIG>). To do so, the control unit for instance controls the flow rate of the pump <NUM>, the opening of at least one of the valves <NUM>, the injection means of the corresponding molding devices <NUM> and the back pressure regulator <NUM> in order to fill in the molds while keeping the pressure at the inlet of the molding devices at a high value. The control unit therefore guarantees that the supply is balanced in terms of pressure and quantity of polymerizable mixture flowing in the looping line <NUM> and returning back to the tank <NUM>. Indeed, as explained, while the molding devices <NUM> are supplied in degassed polymerizable mixture, a flow of degassed polymerizable mixture in excess continuously returns to the tank <NUM> via the looping line <NUM>. More precisely, the polymerizable mixture returns to the tank <NUM> at a flow rate that changes based on the pressure in the looping line <NUM>, downstream of the inlet of the molding device <NUM>. This flow rate for instance depends on the number of molding devices <NUM> being supplied in polymerizable mixture at the same time, that is to say on the number of valves <NUM> that are simultaneously open.

In step c), in order to compensate for the pressure P inside the tank <NUM> that is lower than the set pressure value Ps, due to filling of the molding devices <NUM>, it is possible to control an entry of gas, preferably an entry of inert gas, into the tank <NUM>. Here, the control of the entry of inert gas is based on the pressure P contained within the tank <NUM>. In practice, the entry of inert gas is here made through the vacuum regulator <NUM> and the inert gas supplier <NUM>.

If the level L of polymerizable mixture in the tank <NUM> is lower than the set value of level Ls (L < Ls), then the control unit stops the supply of the polymerizable mixture (box referenced E52 on <FIG>). It implies that the control units controls the closing of the valves <NUM>, the stopping of the pump <NUM> and the closing of the potential valve located at the outlet <NUM> of the tank <NUM>. The tank <NUM> is then refilled with fresh polymerizable mixture and the method starts again from step a) (box referenced E1).

On <FIG> is illustrated a graph showing the percentage of lenses that are rejected ("reject") after being molded and the percentage of lenses that are bubble free ("bubble free") after being molded, that is to say that do not include any bubbles. Such percentages are given for lenses obtained in a comparative test (Test C0 on <FIG>) implemented with a traditional device and/or method in which the pressure is not continuously controlled during the supply of the molds, and are also obtained in <NUM> other tests (Test <NUM>, Test <NUM> and Test <NUM> on <FIG>) implemented with the device and/or the method of the invention in which the pressure is continuously maintained at the set value of pressure Ps during the supply of the molds. From <FIG>, it can be concluded that the supply device <NUM> and the method of the invention allow obtaining more lenses that are bubble free, and less rejected lenses. In other words, it can be concluded from <FIG> that the supply device <NUM> and/or the method of the invention allow reducing the gas redissolved in the polymerizable mixture, even after the polymerizable has been initially degassed, and therefore increasing the lenses that are bubble free after they are molded. On the contrary, the traditional supply device and/ or method results in gas being dissolved in the polymerizable mixture after it has been initially degassed, and therefore in more lenses that include bubbles and that are rejected because they cannot be used or sold.

Claim 1:
Method for supplying a polymerizable mixture to at least one molding device (<NUM>), said method comprising the following steps:
a) providing a tank (<NUM>) containing the polymerizable mixture,
b) reaching a set value of pressure (Ps) in the tank (<NUM>), smaller than the ambient pressure (Pam),
c) continuously maintaining the pressure (P) in the tank (<NUM>) at the set value of pressure (Ps) while supplying the polymerizable mixture to the molding device (<NUM>) through a looping line (<NUM>) which both ends are connected to the tank (<NUM>) and which is connected to an inlet of said molding device in between said ends,
wherein in step c), an entry of inert gas into the tank (<NUM>) is controlled based on the pressure (P) contained within the tank (<NUM>).