KINNUNEN, Petteri (Varesvuorenkatu 5, Salo, FI-24240, FI)
| CLAIMS 1. A method of treating optical lenses, the method comprising cleaning the lenses (2) by placing them in a receptacle (11) wherein the lenses (2) are subjected to ultrasound, and withdrawing the lenses (2) from the receptacle (11), placing the lenses (2) to be cleaned in the receptacle (11) such that they are arranged side by side in one row of lenses, arranging the row of lenses such that front and back surfaces (9, 10) of the lenses are unshadedly exposed towards side walls of the receptacle (11), and arranging an ultrasonic vibrator (23) on a side of the receptacle (11) such that an ultrasound beam emitted by the ultrasonic vibrator (23) is directed towards the front and back surfaces (9, 10) of the lens, characterized by maintaining a liquid (12) contained in the receptacle (11) in a laminar flow by feeding it to the receptacle (11) at a first end of the receptacle and by discharging it from the receptacle at a second end of the receptacle such that a direction of the laminar flow is at least substantially congruent with a longitudinal direction of the row of lenses. 2. A method as claimed in claim 1, characterized by arranging an ultrasonic vibrator (23) at each lens (2) such that the centre of the front or back surface (9, 10) of the lens resides substantially in the centre of a primary ultrasound beam (25) emitted by the ultrasonic vibrator (23). 3. A method as claimed in claim 1 or 2, characterized by arranging the lenses between two oppositely placed ultrasonic vibrators (23). 4. A method as claimed in any one of the preceding claims, characterized by taking the lenses (2) into the receptacle (11 ) in a jig (6) comprising a frame (72), and closing the receptacle by means of the frame (72). 5. A method as claimed in any one of the preceding claims, characterized by the liquid contained in the receptacle (11) having a temperature of at least 75°C. 6. An arrangement for treating optical lenses, the arrangement comprising at least one receptacle (11) provided with an ultrasonic vibrator (23), the lenses (2) being arranged to be placed in the receptacle (11) side by side in one row of lenses such that front and back surfaces (9, 10) of the lenses are unshadedly exposed towards side walls of the receptacle (11), and that an ultrasonic vibrator (23) is arranged on a side of the receptacle (11) such that an ultrasound beam emitted by the ultrasonic vibrator (23) is directed towards the front and back surfaces (9, 10) of the lens, characterized in that the arrangement comprises means for moving a liquid (12) contained in the receptacle (11) in a laminar flow whose direction is from a first end of the receptacle (11) to a second end of the receptacle, whereby the direction of the laminar flow is at least substantially congruent with a longitudinal direction of the row of lenses. 7. An arrangement as claimed in claim 6, characterized in that the receptacle (11) comprises an ultrasonic vibrator (23) for each lens (2) being simultaneously placed in the receptacle (11), the ultrasonic vibrator being placed such that the centre of the front or back surface (9, 10) of the lens resides substantially in the centre of a primary ultrasound beam (25) emitted by the ultrasonic vibrator (23). 8. An arrangement as claimed in claim 6 or 7, characterized in that ultrasonic vibrators (23) are provided on both sides of the receptacle (11) oppositely. 9. An arrangement as claimed in any one of claims 6 to 8, characterized in that it comprises a jig (6) provided with means for attaching at least one lens (2) by a spring force, and a frame (72) arranged to close the receptacle (11) when the lens (2) held by the jig (6) resides in the receptacle (11). 10. An arrangement as claimed in any one of claims 6 to 9, c h a r- acterized in that it further comprises a drying unit (37), a coating compartment (38), and a pre-hardening compartment (39) that are arranged inside a single housing (41). 11. An arrangement as claimed in claim 10, characterized in that inside the housing (41) is arranged a rinsing air flow (A) arranged to be directed from the coating compartment (38) towards the washing compartment (36) and, further, out of the arrangement. 12. An arrangement as claimed in any one of claims 6 to 11, characterized in that a measure of height (H) of the receptacle (11) is greater than its measure of width (W), and a measure of length (L) of the receptacle is greater than the measure of height (H) thereof. |
BACKGROUND OF THE INVENTION
[0001] The invention relates to a method of coating optical lenses, the method comprising cleaning the lenses by placing them in a receptacle wherein the lenses are subjected to ultrasound, and withdrawing the lenses from the receptacle.
[0002] The invention further relates to an arrangement for treating optical lenses, the arrangement comprising at least one receptacle provided with an ultrasonic vibrator.
[0003] Optical lenses made from an organic material, such as different plastics, have been hard-coated by chemical hard-coatings already since the early 1970's and generally since the 1980's, with varying success. Originally, only two (2) different kinds of plastic were used, a CR39 thermosetting plastic material and a polycarbonate plastic, which is an injection- mouldable thermoplast.
[0004] Both plastic types required completely different treatment processes and hard-coating chemicals, such as siloxane varnishes which, typically, are methanol-based even today. Owing to its toxicity, methanol in itself is already problematic as a solvent. Nowadays, coating processes are even more complex to manage since well over ten different raw materials are widely being used for lenses. A further challenge is to manage different refractive indices of materials in a hard-coating process. Typical refractive indices are 1.50, 1.56, 1.60, 1.67, 1.70, and 1.74. A general rule has been that the higher the refractive index of lenses, the more difficult the hard-coating becomes to carry out. In practice, activation of a surface in order to achieve a sufficient adhesion becomes more difficult as the refractive index increases. With CR39 plastic, the activation time is typically about 5 minutes, while with a refractive index of 1.74 it is more than 20 minutes.
[0005] Another general rule is that the varnishes used are the more short-lived the higher the refractive index of plastic lenses for which a varnish is intended. For instance, the life of a varnish having a low refractive index, such as a refractive index of 1.50, may be 90 days but, correspondingly, the life of a varnish having a refractive index of 1.74 is typically less than 12 days.
[0006] Today, a technique called dip coating is the most widely used hard-coating method for optical lenses, such as eyeglass lenses. The dip coating method may be divided into three main stages: A) washing and activating stage, B) drying stage, and C) dip coating stage including thermal hardening.
[0007] Figures 1 to 4 schematically show a prior art dip coating arrangement. This comprises seven washing and/or activating receptacles 1a to 1g, wherein the washing of lenses 2 is based on an ultrasound method. The liquid contained in the receptacle 1a to 1g is typically water, which may be admixed e.g. with a surfactant. The lenses 2 are attached to a jig 6.
[0008] Because the material of the lens 2 is typically porous, water is absorbed therein during the washing process. Water also remains on the surface of the lens. The lens 2 should be completely water-free before coating because water is extremely detrimental to solvent-based varnishes. Therefore, water is removed from the lens 2 by using an infrared heater 3 or a convection oven 4.
[0009] The arrangement shown in Figure 1 is provided with three different varnish receptacles 5a to 5c, which may contain varnishes having different refractive indices. The lens 2 is immersed or dipped in one or more varnish receptacles 5a to 5c one or more times. Next, the lens 2 is transferred to a precuring oven 7 whose temperature is typically 60 to 70°C. A plurality of pre- curing ovens may be provided in succession, e.g. in Figure 1 two such ovens are provided. A pre-drying time is about 10 to 15 minutes, whereafter the lenses 2 are dust-dry.
[0010] In the last work stage, the lens 2 is detached from the jig 6 and placed in an oven 8 whose temperature is about 100 to 120°C. The lens 2 is kept in the oven typically for 2 to 4 hours.
[0011] Figure 2 shows how the lenses 2 are placed in the washing and/or activating receptacles 1a to 1g and in the varnish receptacle 5a to 5c. The lenses 2a to 2n are placed in succession such that optical main surfaces, i.e. a front surface 9 and a back surface 10 of the lenses 2b to 2n-1 , which lenses reside between two other lenses, are situated opposite to the optical main surface of a lens preceding in the sequence and the optical main surface of a lens next in the sequence. In the case of the lenses 2a and 2n occupying the first and the last position in the sequence, only one of the optical main surfaces is situated opposite to the optical main surface of the next lens.
[0012] The bottom of the receptacle 5a made from stainless steel is provided with two ultrasonic vibrators 23 and 23 such that ultrasound waves 8 are directed upwards from the bottom of the receptacle towards the surface of the liquid contained in the receptacle, whereby they pass through the lenses 2a to 2n.
[0013] Figure 3 shows a problem concerning the prior art. The most essential point is that ultrasound waves 17 generated by the ultrasonic vibrator 23 do not meet different points of the surface of the lenses 2a and 2b with the same efficiency, if, in the first place, they meet all surfaces of the lenses at all.
[0014] The ultrasound waves 17 generated by the ultrasonic vibrator 23 serve as primary sound shock waves that spread mainly perpendicularly away from the vibrator 23 itself as a beam 25 with a spread of about 10°. In addition to said sound shock waves, secondary sound waves being reflected from different surfaces and having a substantially lower power also propagate in the liquid 12. The lenses 2a, 2b are left with points B that are not properly cleaned or activated because the ultrasound waves do not reach them in an optimal manner.
[0015] Figure 4 shows a third problem concerning the prior art in relation to washing and rinsing lenses 21. As already shown in Figure 2, the ultrasound waves do not reach all points of every lens in the same manner. This results in non-homogeneous cleaning and activation.
[0016] Figure 4 shows a typical receptacle 11 used as a wash basin. It is filled with liquid 12 which, most usually, is water or water-based mixture. The lenses 2a to 2f to be washed are arranged in the receptacle in a vertical position and in a succession as described in connection with Figure 2.
[0017] Clean liquid is fed to the receptacle 11 from a feed channel 13 provided at an end of the receptacle 11. A liquid discharge channel 14 is provided at an opposite end of the receptacle 11. The discharge channel 14 is formed as an overflow channel via which liquid is discharged from the receptacle 11 as new liquid is fed from the feed channel 13 to the receptacle 11. The discharge channel 14 may be connected to the feed channel 13 via a pump 15 and a filtering device 16.
[0018] Figure 3 shows no ultrasonic vibrators for the receptacle 11. Typically, the ultrasonic vibrators are located at the bottom of the receptacle, directed such that an ultrasound wavefront emitted by them is directed upwards towards the surface of the liquid.
[0019] The problem is that a liquid flow F is only directed at the first lens 2a at full capacity, but not at all at the surface of the next lens 2b or the surface of the next lenses 2c to 2f after that, since the liquid 12 does not circulate or is not directed with the same efficiency at these lenses 2b to 2f. Already loosened dirt becomes recycled back to the already rinsed lenses. The movement of the liquid is thus not homogeneous nor controlled nor directed with the same efficiency at every point of the surface of every lens. The end result is poor quality in terms of optical and physical properties.
[0020] The problem with the arrangement described above is thus that the washing of the lenses is not always sufficiently successful, in which case lenses that cannot be coated successfully are allowed to enter the coating stage. Poorly washed lenses may account for even 30% of the total amount of lenses washed. Such lenses cannot be used in an end product, such as eyeglasses, but they end up as waste.
BRIEF DESCRIPTION OF THE INVENTION
[0021] An object of the present invention is to provide a novel and improved method and arrangement for coating optical lenses.
[0022] A method according to the invention is characterized by placing the lenses to be cleaned in a receptacle, arranged side by side in one row of lenses, arranging the row of lenses such that front and back surfaces of the lenses are unshadedly exposed towards side walls of the receptacle, and arranging an ultrasonic vibrator on a side of the receptacle such that an ultrasound beam emitted by it is directed towards the front and back surfaces of the lens.
[0023] An arrangement according to the invention is characterized in that the lenses are arranged to be placed in a receptacle, side by side in one row of lenses such that front and back surfaces of the lenses are unshadedly exposed towards side walls of the receptacle, and an ultrasonic vibrator is arranged on a side of the receptacle such that an ultrasound beam emitted by it is directed towards the front and back surfaces of the lens.
BRIEF DESCRIPTION OF THE FIGURES
[0024] As already mentioned above, Figures 1 to 4 show prior art solutions. Some embodiments of the invention are described in closer detail in the accompanying drawings, in which
Figure 5 is a schematic, partially cross-sectional end view showing a receptacle for use in an arrangement and method according to the invention, Figure 6 is a schematic perspective view showing a receptacle for use in an arrangement and method according to the invention,
Figure 7 schematically shows a method according to the invention,
Figure 8 is a schematic side view showing an arrangement according to the invention, and
Figure 9 schematically shows a jig for use in a method and arrangement according to the invention.
[0025] For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. In the figures, like reference numerals identify like elements.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Figure 5 is a schematic, partially cross-sectional end view showing a receptacle for use in an arrangement and method according to the invention. The receptacle 11 is an ultrasound washing basin wherein one or more lenses 2a are arranged such that ultrasonic vibrators 23 are provided at least substantially perpendicularly to both surfaces of the lens 2a. The lenses are arranged in one row of lenses wherein the lenses are located side by side. Typically, such a row of lenses contains two lenses, but the number may differ between 1 and 100 or even more.
[0027] The ultrasonic vibrators 23 are thus located on both side walls of the receptacle. The ultrasonic vibrators 23 may be single- or multifre- quency vibrators. A single frequency vibrator may operate at a frequency of e.g. 40 kHz, and a multifrequency vibrator at a frequency of e.g. 28, 45, and 100 kHz. If a single receptacle 11 is provided with a plurality of ultrasonic vibrators 23, they may operate at different frequencies. For instance, a first ultrasonic vibrator 23 may operate at a low frequency, such as a frequency range of 15 to 30 kHz, a second one at a medium frequency, such as 30 to 70 kHz, and a third one at a high frequency, e.g. more than 70 kHz. All ultrasonic vibrators 23 of the receptacle 11 may also be multifrequency vibrators. As oscillation frequencies, frequencies of e.g. 40 kHz, 60 kHz, 90 kHz, 120 kHz, 200 kHz, 300 kHz, 900 kHz, 1 MHz may be used simultaneously or non- simultaneously. The higher the reproduction frequency, the more accurate the end result but, typically, correspondingly, the lower the power. Consequently, the multifrequency-ultrasound method has not been employed in the manufacture of optical products. [0028] The ultrasonic vibrators 23 are arranged preferably in pairs such that at each ultrasonic vibrator 23, but precisely on an opposite side of the receptacle 11 , resides another ultrasonic vibrator 23, and that the lens 2 is arranged between two oppositely placed ultrasonic vibrators 23, even more preferably such that the centre of the front and back surfaces 10, 11 of the lens 2 is located in the centre of the ultrasound beam 25 emitted by the ultrasonic vibrator 23. Consequently, the the ultrasound power produced by the ultrasonic vibrators 23 is distributed in a uniform manner and is homogeneous over the entire area of the lens 2. Since the distance between the ultrasonic vibrator 23 and the lens 2a is constant, the power distribution is identical across the entire lens area. This enables a multifrequency solution to be applied in an excellent manner. In order to be able to apply different frequencies either separately or simultaneously, the distance between the ultrasonic vibrator and the surface of the lens has to be constant, i.e. the volume of a water column between the ultrasonic vibrator and the lens is constant.
[0029] As shown in Figure 5, no shadow areas exist on the optical surface of the lens to be cleaned, i.e. the front or back surface 9, 10, where the power of the ultrasound would be substantially lower than in other parts of the surfaces to be cleaned.
[0030] It is most preferable that both sides of the receptacle are provided with at least one ultrasonic vibrator 23, even though in some embodiments of the invention, it will suffice that the receptacle 11 is provided with one or more ultrasonic vibrators 23 on one side of the receptacle only.
[0031] Figure 6 is a schematic perspective view showing a receptacle for use in an arrangement and method according to the invention. The shape of the receptacle 11 is substantially elongated, and its measure of height H is greater than its measure of width W, and a measure of length L of the receptacle is greater than the measure of height H thereof. The dimensions of the receptacle may be e.g. the following: width W 45 mm, height H 90 mm, and length L 120 mm. In a receptacle particularly advantageous as far as a laminar flow is concerned, the length L of the receptacle is at least four times the width L thereof. The volume of the receptacle is thus considerably smaller than that of the ultrasound washing basins known to be used for washing lenses.
[0032] The ultrasonic vibrators 23 are placed on the side walls of the receptacle in opposite positions such that the lenses remain therebetween substantially exactly in such a manner that the centre of the lens is placed at the centre of the ultrasonic vibrator 23.
[0033] Liquid flows into the receptacle 11 from a first end and is discharged from a second, opposite end of the receptacle. The ends are basically open. The flow direction of the cleaning liquid is shown by arrows F.
[0034] The elongated and narrow shape of the receptacle contributes to achieving a completely laminar flow of liquid. Preferably, a second end of the receptacle is provided with a restricting element which appropriately resists the liquid flow, e.g. a close-mesh wire net or perforated plate. In size, the restricting element is substantially similar to the entire second end so as to enable the laminar flow to be maintained for the liquid volume contained in the receptacle 11.
[0035] The lenses 2 are completely immersed in the laminarly flowing liquid. The flow of the liquid is directed at least substantially identically at all lenses, and each area of each lens becomes rinsed identically, and effectively.
[0036] The flow rate of the liquid flow determines how quickly the liquid in the receptacle is replaced. Owing to the shape of the receptacle 11 , it is possible to achieve a strong, one-directional homogeneous flow state therein, where the contact of the liquid with the lens and its surface is maximum but, however, substantially laminar. By means of the rapid and one-directional flow direction, together with the liquid having an optimal temperature, the dirt loosened by the ultrasound vibration is carried away from both the surface of the lens and even the entire receptacle 11.
[0037] Since a receptacle 34 has a small volume and is easy to close, extremely high process temperatures, such as 65°C to 90°C, e.g. 75°C, may be used.
[0038] Figure 7 schematically shows a method according to the invention.
[0039] First, the lenses are washed and/or activated in stages A to D. In the first work stage A, the surface of the lens is activated, i.e. etched, with an aqueous solution 24 containing 10% by weight of sodium hydroxide (NaOH), 2% by weight of a wettability-enhancing surfactant, such as sodium gluconate. If a washing function has been added to the work stage, e.g. 2% of butoxyethanol is added to the aqueous solution 24.
[0040] In the second work stage B, a surface activation process is carried out with a solution 25, which is weaker than the aqueous solution 24. The solution 25 removes the chemicals of the aqueous solution 24 used in the first work stage A, replacing them by chemicals of the second work stage B. These are otherwise the same as in the first work stage A but contain no washing chemical.
[0041] In the third work stage C, all the chemicals used above are removed preferably completely. Typically, the removal takes place by means of so-called hard water 26, i.e. an aqueous solution having a given electrical conductivity. The electrical conductivity is controlled typically by means of NaCI or another corresponding salt. At its most optimal, the electrical conductivity is set to be 330 to 500 pS/cm, and pH between 6 and 7.5.
[0042] The NaOH or the surfactant, such as sodium gluconate, used in the first and the second work stages A and B does not come off the pores or surface of the lens if the hard water 26 is not electrically conductive, the pH of the water is not under control or the flow of the water is not sufficient to carry away chemical residues.
[0043] In the fourth work stage D, all ions, which typically originate from the use of salt in the previous work process C and from ion residues of other work processes, are removed by Dl water 27 whose electric conductivity is typically less than 0.3 pS/cm, most preferably less than 0.1 pS/cm.
[0044] In order for each work stage A to D to succeed, an essential factor is that it is possible to dispose of used liquid efficiently and systematically and replace it by fresh liquid. This may be ensured by the receptacle arrangements shown in Figures 5 and 6.
[0045] The drier the lens when being taken to a next work stage 29, the better the end result since the removal of moisture/water from the lens has to take place completely prior to a coating process known per se, described by tanks 30 and 31. Even the slightest moisture remaining on the lens spoils the produced surface, creating pits and fogginess, and also ruins the varnish material used in the process.
[0046] Figure 8 is a schematic side view showing an arrangement according to the invention. The arrangement comprises, arranged in succession, an input buffer 35, a washing compartment 36, a drying unit 37, a coating compartment 38, a pre-hardening compartment 39, and a discharge buffer 40. Said parts of the arrangement are arranged as a processing unit having a uniform frame structure and enclosed by a housing 41. The housing 41 provides therein a preferably hermetically sealed clean room system wherein said parts, together with a lens transfer mechanism 62, are placed. The transfer mechanism 62 is arranged to transfer lenses in their jigs from one work stage to another along a line 61 , and to lower and lift the lenses into and from the receptacles. In the processing unit, the lenses are transferred and treated in the rows of lenses and the jigs set forth in this description.
[0047] The lenses to be cleaned and coated are taken to the input buffer 35 of the processing unit, and the coated and pre-hardened lenses are removed from the processing unit via the discharge buffer 41. The purpose of the input buffer 35 is to serve as a reception area for lenses to be treated and to control the amount of lenses heading for washing.
[0048] The washing compartment 36 includes one or more receptacles wherein the lenses are washed, rinsed, and activated when necessary. In the embodiment shown in the figure, the washing compartment 36 comprises four receptacles wherein work stages A to D are performed. The principle of the receptacles and work stages has already been described above in the description.
[0049] The drying unit 37 may comprise an air knife drying unit 45. Therein, after the last treatment stage carried out in the washing unit, water and moisture are removed from the lens 2 and the jig 6 so as to enable the lens 2 subsequently to be taken to the coating compartment 38. The air knife drying unit 45 comprises blow nozzles which blow air at a high pressure and which are arrangeable simultaneously on both sides of the lens 2. From above the lenses, the blow nozzles may be moved downwards, whereby all water and moisture is removed from the surface of both the lenses 2 and the jig 6. It is to be noted, however, that instead of blow nozzles, the lenses 2 and the jig 6 may be moved, and that in an embodiment of the invention, no movement is arranged between the blow nozzles and the lenses 2.
[0050] In place of the air knife drying unit, the drying unit 37 may have a vacuum drying unit. Therein, the lenses 2 and the jigs 6 are dried by means of underpressure.
[0051] In an embodiment of the invention, a plasma treatment unit 42 is arranged in connection with the drying unit, comprising means 47 for treating lenses with plasma. A plasma treatment may be used for cleaning lens surfaces or for activating or functionalizing lens surfaces for a coating process. The plasma may be e.g. O2 or H 2 0 plasma, these being particularly well suited for removing hydrocarbon-based dirt, such as grease. Of course, another plasma may also be used.
[0052] In activation and functionalization, the surface of the lens is provided with chemical groups, such as OH, CO, COC, CHO, and COOH groups, which improve the adhesion properties of the surface.
[0053] In known coating processes for optical lenses, a typical temperature of a washing liquid is 50°C, at most 60°C. The temperature of a rinsing liquid is no more than 50°C, but typically 20°C. In the known solutions, as far as the washing and rinsing result is concerned, the lenses are treated at low temperatures because the purpose is to avoid evaporation of the liquid, mainly water, from the receptacles. The higher the temperature of the liquid, the greater its rate of evaporation. A volatile liquid causes many problems: first, when the volatility of the liquid is high, its composition has to be controlled more accurately. In addition, ultrasound vibration enhances the evaporation of liquid substantially. When a typical washing or rinsing receptacle has a surface area of 300x400 mm and a machine contains 6 to 7 such receptacles, the volatility of the liquid would be immense. Second, steam hinders the coating process and increases the proportion of useless lenses produced in the coating process. Consequently, it has been necessary to keep both the temperature and evaporation of the liquid as low as possible.
[0054] In the coating arrangement and method shown in Figure 8, a rinsing air flow A is arranged inside a processing unit such that air flows substantially laminarly from a second end 43 of the processing unit to a first end 44 thereof and therefrom further out of the processing unit. The air to be blown into the processing unit is sufficiently filtered in order to remove impurities. Air pressure inside the processing unit is higher than that of the environment. The coating compartment 38 has a higher air pressure than the washing compartment 36, so the flow of air is directed from the coating compartment 38 towards the washing compartment 36 and, further, outside. The processing unit forms a sort of air channel wherein air flows substantially laminarly in one direction, i.e. from the coating compartment 38 towards the washing compartment 36. Owing to the difference in pressure, steam generated in the washing compartment 36 is not allowed to enter the coating compartment 38, thus preventing the steam from interfering with the coating process. Hence, the temperature of the liquids in the washing compartment 36 may be kept higher than before, e.g. at 75 to 90°C. [0055] The composition of the liquids used in the process is controlled by arrangements known per se.
[0056] The temperature of the lenses exiting the washing compartment 36 is at least about the same as the temperature of the liquids in the washing compartment, e.g. 80°C. The temperature of the lens is not increased from this in the drying unit 37 or the coating compartment 38 but, instead, the lens 2 cools down. The temperature of the lens is raised again in the pre- hardening compartment 39 so as to enable the coating varnish to be pre- hardened sufficiently.
[0057] In the coating compartment 38, the lenses are coated e.g. by dip coating. The coating compartment 38 typically comprises a plurality of receptacles containing coatings having different refractive indices 15, e.g. refractive indices 1.50, 1.60, and 1.67. The lenses are immersed in one or more coating receptacles in order to achieve the necessary varnish coating. The embodiment shown in the figure has three coating receptacles, and dip coating work stages E to G are carried out therein. Preferably, the coating receptacles are provided with covers 70 which reduce evaporation and deterioration of the varnish.
[0058] During the dip coating carried out in the coating compartment 38, the lenses are arranged in rows of lenses and jigs in a manner already described above. In other words, the lenses are treated in the same manner and with the same principles in both the washing process receptacles and the coating receptacles. Thus, the volume of the coating receptacle may be extremely small with respect to the space taken by the lenses. This is advantageous since a varnish has a certain pot life specific to each varnish. Typically, this is 30 to 180 days. Towards the end of the pot life of the varnish, the quality of the varnish surface is no longer optimal, and the reject percentage owing to various defects becomes higher. Therefore, at the end of the pot life, the entire varnish receptacle is replaced by a new one. The smaller the varnish receptacle, the greater its exchange percentage and the smaller the effect the age of the varnish has on the end result. If the varnish volume is sufficiently small with respect to the consumption of the varnish, a situation is achieved wherein, owing to the exchange of the varnish, it never has to be replaced, only added according to consumption. A typical calculated consumption of a varnish is 0.4 g/lens. [0059] The pre-hardening compartment 39 may comprise a procuring oven known per se, wherein a coating, e.g. a varnish coating, is hardened at least to an extent that it is dry to touch.
[0060] The coated and pre-hardened lenses are collected into the discharge buffer 40 and removed from the processing unit.
[0061] Figure 9 schematically shows a jig for use in an arrangement and method according to the invention. It is to be noted that typically, the lens 2 is round and its diameter is 45 to 80 mm. Treatment of lenses even this different in size may be implemented by using the jig 6 described herein.
[0062] Two lenses 2 are arranged in the jig 6. Each lens 2 becomes attached between two arms 85 and 87 made from a spring material such that no part of the jig, at least not substantially, covers the front or back surface of the lens. The attachment of the arms to the lens 2 is implemented by clamping claws 80 or the like known per se.
[0063] The arms 85 and 87 are bent and attached by their end to a frame 72 such that by their part attached to the lens they first rise above the plane of the frame 72 and then bend back downwards. Thus, the flexible section of the arms 85, 87 is long, enabling a spring force directed to the lens 2 to remain close to constant, irrespective of the size of the lens.
[0064] Preferably, the frame 72 forms a cover such that the washing and/or rinsing receptacle becomes a substantially closed space when the jig 6 is arranged in the receptacle in question. This enables evaporation of the liquid contained in the receptacle to be reduced.
[0065] The frame 72 is further provided with a grip element 81 for the transfer mechanism 62 to seize. The frame further includes supporting parts 84 on which the jig 6 may be left hanging by the edges of the receptacle.
[0066] In some cases, the features disclosed in the present application may be used as such, irrespective of other features. On the other hand, when necessary, the features set forth in the present application may be combined in order to provide different combinations.
[0067] The drawings and the related description are only intended to illustrate the idea of the invention. The details of the invention may vary within the scope of the claims.
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