PROCESS OF PREPARING LENSES

Abstract: A process of preparing a lens (1) using a de-blocking step to remove the lens from a wax mount (7) is described. For the de-blocking step the wax is only partially dissolved so that the lens remains associated with the wax but can be easily removed therefrom. Preferably, for the de-blocking step, the wax is treated with a terpene under conditions of agitation.

Description: PROCESS OF PREPARING LENSES The present invention relates to a process of preparing lenses. In particular the present invention relates to a process of preparing lenses, such as contact lenses, by a new de-blocking process. In the following description, the term "lens" or "lenses" shall include contact lens(es) and intra-ocular lens(es) (IOL's). Typically, a lens is prepared by taking a blank, usually a button of for example a polymer of polymerised ethylenically unsaturated monomers - such as methacrylic acid and 2-ethylhexylacrylic acid - and then cutting by suitable means (collectively hereinafter referred to as "lathing") one side of the blank to form a desired concave surface. The concave surface is then mounted on a supporting stud (sometimes referred to as an "arbor") via an intermediate layer of wax - commonly known as a "blocking wax". The other side of the blank is then lathed to form, for example, a desired convex surface. In order to prepare d e lenses for packaging and subsequent use they must removed from the wax mounts. This removal step is called "de-blocking". Various ways have been tried to remove the lenses from their wax mounts. For example, freeze-drying techniques and the use of a razor blade to cut the lens from the wax have been tried - but each of methods is undesirable as the lathed lenses are often damaged. Accordingly, most (if not all) manufacturers of lenses use chlorinated/fluorinated hydrocarbons (CHC's and CFC's) or petroleum solvents (such as Pet-ether) to clean and to remove the lathed lens from the stud. The most widely used solvent for the de¬ blocking step is 1,1,2 trichloro, 2,2,1 trifluoro ethane - which is commonly known as " Arklone P" . In these prior art de-blocking processes, which include the use of both heat and ultrasound, the solvent completely dissolves the blocking wax. thus completely freeing the lens from its mount. There are, however, a number of problems associated with the prior art de-blocking process. In this regard, the prior art process uses solvents that are environmentally hazardous - such as the CHC's and CFC's (see the Montreal Protocol). These solvents are also hazardous to safety as they are inflammable and to health as they display a greater likelihood for causing skin relating ailments (e.g the petroleum based solvents). In addition, the prior art solvents are expensive to use. Furthermore, the prior art solvents are very volatile and are therefore not easily re¬ cyclable. Also the process reduces the wax to a sludge which forms at the bottom of the tank holding the solvent. The amount of sludge formation depends on the solvent, the type of wax used to mount the lens on the stud, the type of wax modifiers (e.g. polish) and the amount of polish remaining on the lens. This sludge formation leads to extra costs as the tanks have to be cleaned on a regular basis. In addition to these problems, the prior art de-blocking step also takes a long time, usually in the order of from four to ten minutes. This long time frame and the above- mentioned problems restrict the automation of the prior art process. Two further problems with the prior art process are associated with the fact that the de¬ blocked lenses float on the surface of the solvent. Firstly, the de-blocked lenses can be damaged by contacting, for example, the sides of the tank. They can even be damaged when they are collected by use of scoops or sieves. Secondly, it is usual in preparing a large numbers of lenses to mount the studs on a holder. Accordingly, if at least one of the mounted lenses were different from the others (e.g. a different refractive index), there would be no way of telling, apart from a time consuming inspection process, which of the freely floating lenses is which once the de¬ blocking step had occurred - unless the lenses were coloured according to type which is a rare event. The present invention seeks to overcome the many problems associated with the prior art process of preparing a lens. According to the present invention there is provided a process of preparing a lens comprising a de-blocking step to remove the lens from a wax mount characterised in mat the de-blocking step comprises a) partially dissolving the wax mount so that the lens remains associated with the wax mount but can be removed therefrom; and then b) physically removing the lens from the partially dissolved wax mount. According to a highly preferred embodiment of the present invention there is provided a process of preparing a lens comprising a de-blocking step to remove the lens from a wax mount wherein the wax is treated with a low volatile hydrocarbon under conditions of agitation to dissolve partially the wax mount so that the lens remains associated with the wax mount but can be removed therefrom, and then physically removing the lens from the partially dissolved wax mount. According to the present invention there is also provided the use of a low volatile hydrocarbon in conjunction with a dearomatised hydrocarbon as a de-blocking agent. According to the present invention there is also provided d e use of terpene as a deblocking agent. According to the present invention there is further provided a lens obtained by a process according to the present invention. The term "partially dissolved" means that not all of the wax is dissolved or degraded. Instead, only some of the wax is dissolved or degraded and to such an extent that the lens is still associated with the wax on the smd but wherein the lens can be easily removed therefrom such as, by way of example, picking off the lens by hand or by suction. It is believed that the partial dissolving of the wax lowers or relieves the surface adhesion or tension between the lens and the wax by breaking down the surface layer of the wax exposed to the lens on a macromolecular level but to such an extent that the lens is still associated with the wax on the smd but wherein the lens can be easily removed therefrom. The partial dissolving aspect of me de-blocking step of the present invention is in contrast to the afore-mentioned prior art de-blocking process wherein the wax is totally dissolved or degraded so d at the lens dissociates completely from its wax mount on the smd. The term "treated" includes contacting the wax mount wim a low volatile hydrocarbon (e.g. terpene) such as dipping d e wax mount(s) into a bath of the low volatile hydrocarbon held for example in an ultrasonic tank. The term "low volatile hydrocarbon" preferably covers any suitable hydrocarbon having an evaporation rate of less man 1 (when ether = 1), more preferably an evaporation rate of less than 0.1 (when ether = 1); and/or a boiling point of at least 100 degrees C (at standard pressure), more preferably a boiling point of at least 130 degrees C (at standard pressure). These characteristics are in contrast to those for the prior art de-blocking solvents such as Arklone P and Pet ether which both have an evaporation rate of about 1.9 (when ether = 1) and which have boiling points of 48 degrees C (at standard pressure) and 60-83 degrees C (at standard pressure) respectively. Examples of suitable low volatile hydrocarbons for the present invention include kerosene and terpene. The low volatile hydrocarbon can be a mixture/blend of low volatile hydrocarbons. Preferably, the low volatile hydrocarbon is or contains terpene. Preferably the low volatile hydrocarbon is terpene, more preferably (+) limonene. Examples of suitable commercially available low volatile hydrocarbons for use in the present invention include CITROCLEAR™ (which is mainly pure (+) limonene - sold by HD Supplies), DE.SOLV.IT.™ 1000 (B,C) (a blend of (+) limonene and technical white oil - sold by J. Manger & Son), ODOURLESS KEROSINE (sold by Carless Refining & Marketing Limited), ODOURLESS KEROSENE (sold by Samuel Banner & Co. Limited), SOLBAN 40 (which is kerosene based - sold by Samuel Banner & Co. Limited) and SOLBAN 45 (which is kerosene based - sold by Samuel Banner & Co. Limited). Preferably the low volatile hydrocarbon is used in conjunction with a dearomatised hydrocarbon - such as a blend of (+) limonene and technical white oil. The term "dearomatised hydrocarbon" covers any suitable hydrocarbon that does not ; contain any aromatic groups. The dearomatised hydrocarbon improves the properties of the de-blocking agent such as increasing the flash point of the low volatile hydrocarbon. Likewise, the dearomatised hydrocarbon should have low volatility (as hereinbefore defined). A suitable example of a dearomatised hydrocarbon is Shellsol™ D70 (Shellsol, which has an evaporation rate of 0.01, is sold by Shell Industrial Chemicals). The de-blocking agent of the present invention can be made up entirely of the low volatile hydrocarbon, such as (+) limonene. However, the de-blocking agent may contain from 20 to less than 100% of me low volatile hydrocarbon and from more than 0 to 80% of the dearomatised hydrocarbon. Preferably, the de-blocking agent contains from 20 to 60% of the low volatile hydrocarbon and from more 40 to 80% of me dearomatised hydrocarbon. A highly preferred de-blocking agent is a blend of (+) limonene and technical white oil, such as DE.SOLV.IT.™ 1000 (B,C) (J. Manger & Son). The conditions of agitation can be achieved by the use of any suitable agitating means such as, by way of example, a high pressure jet or an ultrasonic tank. Preferably the wax mount is agitated by means of an ultrasonic tank. Preferably the 5 operating frequency of the ultrasonic tank is between about 15 and 80 KHz, preferably from 25 to 60 KHz. In a preferred embodiment, during the agitation there is a frequency sweep from 15 to 80 KHz, preferably from 25 to 60 KHz. The ultrasonic generator may be modulated at full wave length or half wavelength. o Preferably the wax is treated for a time period of less than a minute - such as less than 30 seconds, preferably less then 15 seconds. Preferably a plurality of lenses, preferably at least six, are exposed simultaneously to the de-blocking step. Preferably the de-blocking step is automated. Preferably the lens is a contact lens. The wax may be a beeswax or paraffin wax or a mixture thereof. If the low volatile hydrocarbon comprises a terpene, preferably the terpene is a natural terpene. Preferably the terpene is isolatable from the fruit of the orange tree. Preferably the terpene is a monoterpene. Preferably the terpene is limonene. Preferably the limonene is (+) limonene. In accordance with standard chemical knowledge, such as d e teachings of Introduction To Organic Chemistry by Streitwieser and Heati cock (published by Collier MacMillan Publishers), terpenes are a class of organic compounds that are the most abundant components of me essential oils of many plants and flowers. Terpenes can be isolated from plants and the like. They may even be prepared in the laboratory. Generally, terpenes are biosynthesized from acetic acid by way of isopentenyl pyrophosphate and may be dissected into "isoprene units". Compounds constructed from two isoprene units are monoterpenes, C, 0 compounds. Compounds built up from three isoprene units are sesquiterpenes, C I5 compounds. Diterpenes, C 20 compounds, consist of four isoprene units. Examples of polyterpenes are natural rubber and gutta percha. A number of terpenes are open chain systems - such as geraniol, citonellal. Terpenes can even be cyclic such as the monocyclic menthol or zingiberene, or the bicyclic beta-santalol or beta-cadinene, or the tricyclic matricarin, or the polycyclic copaene. In the present invention a highly preferred terpene is a monoterpene. more preferably limonene, most preferably (+)-limonene. There are a number of advantages associated with die present invention. One main advantage is d at in the de-blocking step of present invention, each lens remains associated widi the smd and so d e possibility of damage to me lens is greatly reduced. Also, as me lens remains associated with me treated wax, so more man one type of lens may be de-blocked at me same time. In this regard, each mount can be coded and so an operator can tell automatically which lens is which. These aspects of the present invention make the present de-blocking step more amenable to automation. Other advantages, and witii particular reference to the highly preferred embodiment, are that me process uses a natural solvent that is not hazardous to the environment, health and safety. Furthermore, the solvent is not volatile and is relatively inflammable. Another advantage is diat the solvent is much cheaper to use. The solvent may even be re-cycled as me dissolved wax can be easily separated from the terpene by, for example, fractional distillation. The solvent may also be used as a common de-blocking agent for a large number of wax types. In addition, die time scale of the de-blocking step of the present invention is relatively much shorter than die prior art de-blocking process. In this regard, it is usually less than 1 minute and is typically in die order of ten seconds. However, die time scale is largely dependent on the degree of agitation. This shorter time scale means mat the process of the present invention is even more amenable to automation. Anodier key advantage is that the present process can be conducted at room-temperature. Hence there is no requirement for a heat supply - thus reducing even further the costs of preparing a lens. Also use of me terpene does not damage me lens or even the smd. The use of terpene is especially suited for die pharmaceutical industry because of its natural occurrence. Some of the main advantages associated widi die use of (- -)-limonene as the highly preferred solvent are that it is non-toxic, environmentally safe, and cheap. (+)-Limonene is also a naturally occurring solvent which occurs in various ediereal oils, particularly in oils of citric fruits, caraway, dill and bergamot and is merefore readily available. Its other advantages are that it is not a CHC solvent, it is not a CFC solvent and it is not petroleum based. It is also biodegradable and therefore easily disposed. It has a low volatility, vapour pressure and evaporation rate and as a result of these factors its usage is very low. Typically its usage is in die order of approximately 10% of that of conventional CFC usage. In our studies we noted diat limonene could not be used as an effective substitute for Arklone P in the de-blocking process of the prior art. In this regard, after the wax mounted lenses had been exposed to limonene and heat for up to 10 minutes the wax often formed a sticky mass on me smd and in some cases even lead to a greater adhesion of the lenses to their mounts. Also, when die lenses did fully dissociate from their mounts, they did not float on die limonene. Instead, mey sank to the bottom of the tank holding me limonene. Hence, the tank holding d e studs had to be tipped up to remove the limonene in order to allow an operator to retrieve the prepared lenses. Clearly, if diis were the only way to prepare lenses using limonene it would be commercially unacceptable. However, and as it is made clear above, the process of the present invention even overcomes these problems. In general merefore the preferred embodiment of me present invention relates to the use of a low volatile hydrocarbon, preferably a terpene, as a de-blocking agent. In this process the mounted lenses are treated (e.g. contacted) widi d e hydrocarbon (e.g. terpene) under conditions of agitation for a very short period of time - for example 10 seconds mough this is dependent on die extent of agitation and d e size (e.g. diameter) of the smd. The de-blocking step of d e present process can be carried out at room temperature. In the process according to die present invention die terpene only partially dissolves die wax so that die lenses remain associated widi the smd. After the contacting step die lenses can be easily removed from their mounts - such as by hand. If any of the lenses should become dissociated during d e de-blocking step then they can be easily retrieved - such as by a simple filtration process. The essential characteristic of this aspect of die present invention is d e partial dissolution of me wax. This is achieved by exposing the wax on the smd to short periods of agitation. We have even found diat the lenses when mounted on the studs via d e wax can remain in a bam of terpene in die absence of agitation for even up to twelve hours and d e lenses will not dissociate completely from their mounts. This is advantageous as die mounted lenses can be exposed to die terpene and die agitating means, such as an ultrasonic bam, for me requisite time and men die mounted lenses can be removed from the ultrasonic bath or the ultrasonic generating means can be turned off and die mounted lenses can be left to stand in me terpene for a certain period of time to allow the terpene to act then as a cleaning solvent to clean the lenses. Storage in the low volatile hydrocarbon (e.g. terpene) will also prevent the lenses from hydrating. Odier advantages of diis preferred embodiment are that it uses a relatively non- volatile solvent diat can be recycled - d us leading to substantial cost reductions; as d e lenses remain mounted on die studs an operator knows which lens is which and also die chances of damaging the lenses are minimalised; and d e process lends itself well to automation. The terpene is a good solvent because it dissolves die wax and because it is easily filtered to remove debris such as die polishing agents mat may be present in the wax. Even when it contains a substantial level of dissolved wax, die limonene still acts as a good de-blocking agent. O ier embodiments and advantages will become apparent in me light of the following description. The present invention will now be described only by way of example in which reference shall be made to d e following Figures: Figure 1 is a cross-sectional view of a lens mounted on a smd via an intermediate wax layer (which has been enlarged); Figure 2 is a pictorial representation (not to scale) of a series of studs shown in Figure 1 mounted in a holder; Figure 3 is a cross-sectional view of an ultrasonic tank containing an ultrasonic fluid; Figure 4 is a cross-sectional view of die ultrasonic tank of Figure 3 with a further tank; and Figure 5 is a cross-sectional view of the tank of Figure 4 with a sieve. Figure 1 shows a lens 1 having a concave surface 3 and a convex surface 5 mounted on a wax layer 7. The wax layer 7 in turn is mounted on a smd 9, such as a magnetic metal smd. For contact lens preparation die s ds generally have an outside diameter of less man about 15 mm, such as from about 5 mm to about 14 mm, typically 9.5 mm or 11 mm. For IOL preparation the smds generally have an outside diameter of less than about 8 mm, typically about 4 mm. However, any suitably sized smd may be chosen. The lens 1 is prepared by first lathing a polymer blank (not shown) to form the concave surface 3. The concave surface 3 is tiien mounted on die wax layer 7 which in turn is mounted on die smd 9. The surface of die blank distanced away from the wax layer 7 is then ladled to form convex surface 5. In the preferred embodiment shown in Figure 2 a plurality of smds, in diis case six smds 9a-9f, are mounted on to me underneath surface of a disk 23 of a holder 21. The smds 9a-9f are releasably connected to die disk 23 such as, by way of example, magnets (not shown). In mis preferred embodiment many (e.g. six) lenses can be prepared at die same time. One way to remove me lens 1 from its wax layer 7 uses me apparatus shown in Figure 3 which comprises an ultrasonic tank 11 containing an ultrasonic fluid 13. A typical example of an ultrasonic tank is sold by Crest Ultrasonics (e.g. tank model number XHT 1014-6 and ultrasonic generator model number XG 500-6). In die highly preferred embodiment of me present invention the ultrasonic fluid 13 contains a terpene 15, preferably (+) limonene, more preferably DE.SOLV.IT.™ 1000 (B,C) (a blend of (+) limonene and technical white oil - sold by J. Manger & Son). In the deblocking step according to d e present invention the mounted lens 1 of Figure 1 is lowered into the ultrasonic tank 11 until die lens 1 and at least part of die wax layer 7 are submerged under the terpene 15. Preferably all of the wax layer 7 is submerged. Preferably the lens 1 is placed close to die bottom of the ultrasonic tank 11 diereby ensuring mat die wax layer 7 will experience die maximum degree of agitation. The lens 1 and die wax layer 7 are dien subjected to a short period of agitation between the frequencies of 25 to 60 KHz (preferably in a sweep format) - such as for example about 10 seconds - during which time some but not all of die wax layer 7 dissolves - diereby allowing the lens 1 to be removed easily from me wax layer 7 at an appropriate moment. After this short period of agitation the agitation is switched off and die mounted lens 1 can men be men taken out of d e terpene 15 at a suitable moment. Alternatively the mounted lens 1 need only be taken out of die terpene 15 after the short period of time. The mounted lens 1 can dien be easily prised away from the wax layer 7 such as for example by hand or suction (not shown). It is observed diat die surface of die wax left on die smd is pitted - indicating partial dissolution of die wax layer. The removed lens can dien be cleaned to remove any residual wax. Anod er way to remove the lens 1 from its wax layer 7 uses die apparatus shown in Figure 4 which comprises an ultrasonic tank 11 containing an ultrasonic fluid 13 and a tank 17. The tank 17 can sit on die bottom of the ultrasonic tank 11 or it can be mounted providing at least a portion of the tank 17 is submerged in the ultrasonic fluid 13 (as shown in Figure 4). The tank 17 contains terpene 15, preferably (+) limonene. As wi i the apparatus of Figure 3, in the deblocking step according to die present invention the mounted lens 1 of Figure 1 is lowered into d e tank 17 until the lens 1 and at least part of the wax layer 7 are submerged under die terpene 15. Preferably all of the wax layer 7 is submerged. The lens 1 and d e wax layer 7 are then subjected to a short period of agitation - such as for example about 10 seconds - during which time some but not all of me wax layer 7 dissolves -diereby allowing the lens 1 to be removed easily from the wax layer 7 at an appropriate moment. After this short period of agitation die agitation is switched off and die mounted lens 1 can dien be taken out of die terpene 15 at a suitable moment. Alternatively die mounted lens 1 need only be taken out of die terpene 15 after die short period of time. The mounted lens 1 can men be easily prised away from die wax layer 7 such as for example by hand or suction (not shown). In d e event d at a lens 1 should become completely dissociated from the wax layer 7 during die deblocking step using me apparatus of Figure 4 then that lens can be retrieved simply by holding a sieve 19 containing holes 20 over the top of die tank 17 (as shown in Figure 5) and dien upturning die tank 17 to drain out the terpene 15. The lens 1 can tiien be retrieved. Odier modifications widiin the scope of die present invention will be apparent to mose skilled in me art.

Claims: CLAIMS 1. Use of terpene as a deblocking agent. 2. A process of preparing a lens comprising a de-blocking step to remove die lens from a wax mount characterised in mat die de-blocking step comprises a) partially dissolving die wax mount so mat the lens remains associated widi die wax mount but can be removed dierefrom; and tiien b) physically removing die lens from the partially dissolved wax mount. 3. A process of preparing a lens comprising a de-blocking step to remove the lens from a wax mount wherein the wax mount is treated widi a low volatile hydrocarbon under conditions of agitation to dissolve partially die wax mount so mat the lens remains associated widi die wax mount but can be removed dierefrom, and dien physically removing the lens from the partially dissolved wax mount. 4. A process according to claim 3 wherein the low volatile hydrocarbon comprises a terpene. 5. A process according to claim 4 wherein the terpene is a natural terpene. 6. A process according to claim 5 wherein the terpene is isolatable from the fruit of the orange tree. 7. A process according to any one of claims 4 to 6 wherein the terpene is a monoterpene. 8. A process according to claim 7 wherein the terpene is limonene. 9. A process according to claim 8 wherein the limonene is (+) limonene. 10. A process according to any one of claims 2 to 8 wherein the low volatile hydrocarbon is used in conjunction with a dearomatised hydrocarbon. 11. A process according to any one of claims 3 to 10 wherein the wax mount is agitated by means of an ultrasonic tank. 12. A process according to any one of claims 3 to 11 wherein the wax is treated for a time period of less than a minute. 13. A process according to any one of claims 2 to 12 wherein a plurality of lenses, preferably at least six, are exposed simultaneously to the de-blocking step. 14. A process according to any one of claims 2 to 13 wherein the de-blocking step is automated. 15. A process according to any one of claims 2 to 14 wherein the lens is a contact lens. 16. Use of a low volatile hydrocarbon in conjunction with a dearomatised hydrocarbon as a de-blocking agent. 17. Use according to claim 1 or claim 16 wherein the terpene or the low volatile hydrocarbon is a terpene as defined in any one of claims 4 to 9. 18. A lens obtained by a process according to any one of claims 2 to 15. 19. A process substantially as described herein and with reference to the accompanying drawings.

Inventors: SIDHU JOTINDERPAL SINGH, TOMNEY JOHN, SIDHU, JOTINDERPAL, SINGH, TOMNEY, JOHN
Applicants: HYDRON LTD, SIDHU JOTINDERPAL SINGH, TOMNEY JOHN, HYDRON LIMITED, SIDHU, JOTINDERPAL, SINGH, TOMNEY, JOHN
Application year: 1995
Main classification: B29D11
IPC codes: B24B13, B29D11