Method for obtaining a mark on a low surface energy ophthalmic lens

The present invention relates to the marking of ophthalmic lenses including eyeglass lenses, to identify the origin, manufacturer and / or its technical features and distinctive signs such as a logo. Such markings are known under the name of "monogram". There are many methods of marking ophthalmic lenses, some of which involves the removal of the material of the ophthalmic lens and / or its coatings, in particular by etching or by means of lasers, in particular excimer lasers.

The last generation ophthalmic lenses most often comprise a hydrophobic surface coating and / or oleophobic anti-smudge conjunction with an anti-reflection coating. The antireflection coating, which may be mono or multi layers, consists of a high surface energy material. On this anti-reflective coating is deposited a thin protective layer consisting of a low surface energy organic material. This thin layer reduces fat deposits and dirt and in practice constitutes a hydrophobic surface coating and / or oleophobic.

Such markings are preferably normally invisible in order not to hinder the wearer. They are made visible by fogging, the thin film of condensation that forms on the surface producing microdroplets on the low surface energy portions, while on the high surface energy portion, the condensation film is spread over the entire surface to form larger droplets. Under ambient lighting, diffusion microdroplets produces a tone much lighter than the larger droplets.

Publication WO 01/68384, on behalf of the applicant, describes a method and apparatus for marking ophthalmic lenses at low surface energy which implements an energizing discharge selectively increasing surface energy corresponding to cuts of a mask placed between the latter and the ophthalmic lens to be marked. Such a mask comprises a flexible foil applied under tension against the surface to be marked or an ink layer applied to said surface and subsequently removed with an appropriate solvent. According to a preferred embodiment, the energization discharge is a discharge die corona source.

According to the method described in PCT application WO 01/68384, the discharge energization produces a chemical reaction with the only anti-fouling coating breaking the molecular bonds thus destroying the integrity of the antifouling coating thus revealing the surface energy most high underlying anti-reflective coating. The resulting marking is clearly visible by fogging.

This method is effective and gives good results.

After the surface treatment, the ophthalmic lens undergoes a trimming or edging operation which consists in machining the edge or periphery of the lens to conform to the the frame rim of the dimensions to which it is intended.

Edging is performed normally on a grinder. During this operation, the glass is maintained by locking members acting axially. The relative movement of the glass relative to the grinding wheel is numerically controlled to obtain the desired peripheral contour. These locking members must ensure ie maintaining the glass during edging.

For the holding device, positioning a holding device, or tassel, on the convex face of the lens, a holding pad, such as a double-sided adhesive pad being disposed between the holding means, or tassel, and the convex face glass. A second axial clamping member clamps the concave face of the lens by means of an abutment normally elastomer.

During edging, the tangential section can generate a rotation of the lens relative to the locking members and hence rejection of the glass and overflowed, if they are not sufficiently effective. The good retention of glass mainly depends on the good adhesion of interface holding pad / convex surface of the lens.

However, the hydrophobic surface coatings and / or oleophobic anti-fouling, more usually fluorosilane type reached such efficiency that the adhesion at the interface pad / convex surface of the lens is altered or compromised. This is particularly the case with polycarbonate lenses including edging generates much greater efforts than those required for other materials. This results in a high percentage of rejection of lenses for which the edging operation could not be performed correctly.

To overcome this problem, it has been proposed to lay upon the antifouling coating an adhesion promoting layer to the glass a surface energy greater than that of the outer layer, namely the antifouling coating. This temporary protection layer may be applied to the entire convex face of the lens or only the central region for receiving the holding pad. Through the temporary protection layer, the maximum misalignment time is between 2 °, or even less than or equal to 1 °.

This protective layer consists of all materials to increase a surface energy and capable of being removed after trimming without altering the optical properties of the glass and its features of the face concerned. Preferably, the temporary protective layer is a mineral layer and more particularly fluoride or a mixture of a metal fluoride, an oxide or a mixture of metal oxides, such as for example magnesium fluoride (MgF₂), Lanthanum (LaF₃), Aluminum (AlF₃) Or cerium (CeF₃). Mixtures of alumina and praseodymium oxide are recommended. Such a protective layer may be deposited by any conventional method but is preferably deposited by evaporation in vacuum chambers, as is generally the case for anti-reflective coating, as well as for the hydrophobic antifouling coating and / or oleophobic.

The thickness of the temporary protective layer is preferably between 5 and 50 nm. If the thickness of the protective layer is too low, the modification of the surface energy which results may be insufficient, whereas if this thickness is too high, there is a risk of revealing mechanical stresses within the layer, possibly detrimental to the expected properties.

Finally, the temporary protective layer has preferably a minimum degree of transparency, for example at least 18% or even at least 40%, according to ISO 8980/3, for performing on the glass on its protective layer of the conventional steps power by frontofocometer.

Alternatively, conventional inks for marking ophthalmic lenses may be used and / or resins constituting the binder of such inks. With organic protective layers, much greater thicknesses can be obtained, ranging from 5 to 150 .mu.m. alkyd resins satisfactory.

Furthermore, antireflection coatings, as well as the hydrophobic / oleophobic coatings are generally deposited by evaporation in vacuum bells. Glasses, on which the antireflection coatings and antifouling must be deposited, are placed above the openings of a carousel in the vacuum enclosure and rely on the periphery on a fixed annular ring of the carousel by means blocking. The processing device is located in the lower part of the enclosure and includes a crucible in which is placed the material to be evaporated which is generally heated by means of an electron beam or a single source to the Joule effect, depending on the nature of the material to evaporate.

The material to be evaporated to form a coating layer is deposited on the face of the glass to be treated until the desired thickness, and thereafter evaporating the first material is stopped. This is followed by evaporation of the following material. Generally is deposited all coatings on one side of the glass. Then, after turning over the glass, is deposited on the other face of the lens all the coatings which is normally identical to that deposited on the first face of the glass.

It goes without saying that during the processing of the second face, it is necessary to preserve the integrity of the layers deposited on the first face and more particularly the outer layer thereof. Indeed, the hydrophobic antifouling coating layer and / or oleophobic coating has very low thickness, 2 to 10 nm, or even 2 to 5 nm. However, it is sometimes necessary to subject the front glass to treatments using high-energy species, that is to say, species with energies above 0.1 eV or reactive species is -to say the species could chemically react with the glass surface. In particular, before the deposition of anti-reflective multi-layer coatings, the ophthalmic lens is subject to a surface preparation, such as ion bombardment (for example with rare gas, oxygen, mixtures thereof , nitrogen or air), a plasma treatment or a corona treatment (typically oxygen plasma treatment at a pressure of 10-2 mbar). It may also be necessary to perform an activation treatment to prepare a surface prior to deposition of a coating layer, for example to increase adhesion of the layer. Similarly, one can apply an ion bombardment on evaporation of materials (called deposition or ion assistance IAD) to improve its mechanical properties and particularly to densify the layer.

Cash generated are highly energetic and / or reactive and may alter the deposit made on the first face of the glass, including those located on the peripheral part of the carousel. The same problem is also found when the lenses to be treated have a generally similar form of glass ready for installation according to the frame, the energetic and / or reactive species may then pass between the circular orifice of the carousel and the glass peripheral edge to reach the deposit made on the first face.

To overcome this problem, it has also been envisaged to deposit the thin outer antifouling layer, ie the outer layer of glass, a temporary protective coating to protect the outer layer of the first face of the glass during the deposition of coating layers on the second side in a vacuum chamber.

This temporary protective layer must be of sufficient thickness to prevent the alteration of the properties of the outer thin layer and be selected depending on the energy of the species which may vary from 40 to 150 eV with a current density at the surface glass of 30-700 uA / cm2. The thickness of the protective layer for this application is preferably between 5 nm and 10 microns. When the protective layer is an inorganic layer deposited by evaporation, its thickness is preferably between 5 and 200 nm. In any case, the thickness of the protective layer should not be too low, the risk of not sufficiently protecting the thin outer layer hydrophobic and / or oleophobic or too high, particularly for essentially mineral protective layers at risk show mechanical stress within the layer, damaging these properties.

The layer used for this purpose can have the same composition as the adhesion layer mentioned above. Mixtures of alumina and praseodymium oxide are also recommended for this purpose.

As for the temporary protective layers of organic material include those based on polytetrafluoroethylene (PTFE), for example that sold under the Teflon® brand.

One may also consider a temporary protective coating multi-layer and in particular bi-layers, the first layer being of inorganic nature, of small thickness (5 to 200 nm) while the second layer of organic nature can be obtained by deposition and curing of a latex. This layer has a greater thickness, from 0.2 to 10 .mu.m.

The organic layer provides a good mechanical protection and can be easily removed by peeling. The organic nature of layer is selected so that the adhesion with the first inorganic layer is higher than that with the interface between the first layer of inorganic nature and the hydrophobic layer and / or oleophobic. Thus during peeling, the inorganic layer is also removed.

However, depositing a temporary protective layer to ensure good adhesion between a pad and the convex face of the lens and / or to protect the first face of the glass when treated with high energy or reactive species, is a screen or mask, sources of corona discharges which prevents them from reaching the thin layer of low surface energy through the temporary protection layer for either of the above applications.

It was therefore necessary to carry out the corona treatment before depositing the temporary protective layer, which involved the transfer of the glass of the vacuum chamber to the processing device by corona and then return to the vacuum chamber to deposit the temporary protective layer.

However, it was found unexpectedly that the corona treatment can be performed on the thin layer hydrophobic and / or oleophobic through the temporary protection layer provided that its thickness is less than 5nm approximately, that is to say a thickness which was hitherto considered insufficient for one or other of the aforementioned applications. It turns out that despite this very reduced thickness of the temporary protective layer, it provides an adequate function for one and other of the aforementioned applications.

One aspect of the present invention therefore is a method for marking on a surface of a ophthalmic lens of the type comprising a hydrophobic outer layer and / or oleophobic low surface energy on a substrate or a high surface energy coating, a mask whose the configuration is complementary to the desired marking is positioned between a side of the glass on which the marking will be performed and a discharge source energizing able to oxidize the outer layer to reveal the substrate or high energy underlying coating, characterized in that is deposited on said outer layer a temporary protection layer having a surface energy higher than that of the outer layer and a thickness less than about 5 nm to enable the discharge to act on the outermost layer through the temporary protection layer .

Preferably, the protective layer is made of inorganic material deposited by evaporation and includes, for example, a fluoride or a mixture of metal fluorides such as MgF₂, LaF₂, AlF₃Or CeF₃ or an oxide or mixture of metal oxides, such as TiO₂, AL₂O₃, ZrO₂ and praseodymium oxide and the mixture of metal oxides is a mixture of alumina and praseodymium oxide.

The temporary protective layer may have a structure substantially continuous or discontinuous, particularly in the form of a frame.

According to another embodiment, the temporary protective layer is an organic material, preferably based on polytetrafluoroethylene.

Alternatively, the protective layer comprises a marking ink for ophthalmic glass and / or a polymer constituting a marking ink binder.

The temporary protective layer is removed preferably after edging of the glass, especially with an acid solution, wiped dry or application of ultrasound.

In practice, the deposition of the hydrophobic outer layer and / or oleophobic coating on a first face of the lens is preceded by the deposition of one or more mineral or organic layers, and performing at least one step of treatment by energetic and / or reactive able to attack and / or chemically modify the surface of the first face of the glass before the filing of the (or) layer (s) mineral (s) or organic (s). The glass can then be returned to its location in the carousel to perform a treatment by energetic species and / or reactive on the second face thereof prior to the deposition of one or more mineral or organic layers and then a layer hydrophobic and / or oleophobic outer. then it may make a temporary protective layer on the hydrophobic outer layer and / or oleophobic coating on the glass secondeface to improve its adhesion with the blocking member which cooperates with said second surface during edging.

The marking itself is performed according to the method described in PCT application WO 01/68384. Although the corona discharge source is preferred as energizing source to selectively oxidize the hydrophobic outer layer and / or oleophobic, other sources may be adopted, such as a cold plasma source or ultraviolet radiation for the photo-oxidation molecules of the hydrophobic outer layer and / or oleophobic.

The invention will be described with reference to the accompanying drawings, in which:<ul><li>Figure 1 is a schematic view of a processing apparatus at low frequency corona for marking a glass; and</li><li>Figure 2 is a schematic partial view of a glass according to the invention after corona treatment through a temporary protective layer.</li></ul>

The treated glass of the present invention comprises a substrate of inorganic or organic glass. Both sides of the lens have different layers some of which are deposited one on the other, by evaporation of materials contained in a crucible with an electron gun or Joule in a vacuum chamber. These include Balzers BAK 760 machine equipped with an electron gun, an ion gun of the end-Hall type Mark 2 Commonwealth and an evaporation source to the Joule effect, or the processing machine Leybold vacuum 1104, equipped with an electron gun and an evaporation source to the Joule effect. Before depositing a first layer on a first face, which is preferably the convex surface, it is treated with the energetic and / or reactive particular by ion bombardment, for example with an argon ion beam and oxygen using the ion gun, or plasma treatment to obtain a chemical modification of the surface to improve adhesion of deposits.

Usually the first coating comprises an anti-abrasion layer, in particular the polysiloxane type corresponding to example 3 of European patent application No. 0614957, which protects the substrate from scratches, particularly in the case of substrate organic polycarbonate and has a high surface energy.

On this first coating is then deposited an antireflective monolayer or multi-layer coating having a high surface energy. Such a coating is to e preferably multi-layers, the layers are successively high or low refractive index and may, for example, include a first layer of ZrO₂, A second layer of SiO₂, A third layer of ZrO₂And finally a fourth layer of SiO₂. Such a coating is relatively insensitive to energy discharges, such as corona discharge, cold plasma or UV irradiation. Thereby marking implementing such energy discharge will leave substantially intact the antireflective coating layers and in particular the outer layer. It goes without saying that other anti-reflection coatings may be adopted, in particular those consisting of a plurality of inorganic layers. Similarly, other anti-reflection layers of the coating deposition processes may be implemented in particular sputtering or chemical reaction of vapor phase processes assisted by plasma.

On the anti-reflection coating is then deposited to the outer hydrophobic layer and / or oleophobic by evaporation in a Joule effect crucible of a compound comprising perfluoropropylene units marketed by Daikin under the trademark Optool DSX. The thickness of such a hydrophobic and oleophobic coating is less than 10 nm or 5 nm, and preferably is about 2 nm. Its surface energy is less than 14 millijoules / m² and preferably equal to or less than 12 millijoules / m².

According to the invention, a temporary protective layer of less than about 5 nm thickness is deposited, also by evaporation, preferably in the same vacuum chamber, on the hydrophobic and / or oleophobic coating on the whole of the treated side to protect it during the processing of the other face of the lens or possibly on an area intended to come into contact with the holding pad, particularly in the case where the convex face is treated in the vacuum chamber after the concave face and where, consequently, the vis-a-vis protection of energetic and / or reactive is not essential.

The temporary protective layer is for example an inorganic layer made of a fluoride or a mixture of a metal fluoride, an oxide or a mixture of metal oxides. Preferably, use is MgF₂ whose average particle size is 2.5 mm, available from Merck, which is loaded into the crucible and then evaporated by the electron gun. The deposition rate was about 0.50 nm / second and the duration of 4 to 8 seconds, so that the thickness of the temporary protection layer is from about 2 to 4 nm. The coating thickness is monitored by a quartz microbalance.

After filing the temporary protective layer, the procedure for heating the chamber and returned to the atmosphere of the treatment chamber before returning the glasses. All the processing steps already described is then extended on the second face of the glass. The temporary protective layer, preferably of MgF₂Deposited on the convex side would aim to increase the surface energy thereof to improve adhesion during edging.

After the deposition of the coating layers on both sides of the glass, the glass is removed from the enclosure to its marking in a processing unit low frequency corona. This apparatus 10, schematically illustrated in Figure 1, comprises a screen or mask 12 tensioned by a Mylar® Mylar® tensioning mechanism. This screen comprises a complementary cutout 13 of the pattern to be marked on the glass 20. The glass 20 is held by a pivot arm 15 (shown in a position 90 ° from its normal position to simplify the view) and biased toward a position making its flange 16 with the center of the concave face 21 of the glass, so that the corresponding area of ​​the convex surface 22 is in intimate and continuous contact with the portion of the screen having the marking cutting.

The corona discharge means 30 sold by the Softal-3DT company under the brand MultiDyne is mounted under the screen within a housing of which only the top plate 11 is shown. It comprises two electrodes 31 in thread hook-shaped or D-shaped, with a straight portion followed by a semicircular portion. The semi-circular portions are disposed vis-a-vis. The distance between the electrodes and the glass to be treated is about 5 mm. This arrangement permits treating an oval whose major axis area can be up to 65 mm. These electrodes are connected to the secondary windings 33 of a transformer 32 to high voltage of 12 kV. For safety reasons, the secondary windings have a grounded center which reduces the voltage by 50% from the high voltage conductor and earth. A source of air pressure 35, preferably a fan, constant flow is directed between the electrodes. This air flow has the effect of deflecting the arc 40 and to spread it along a curvature determined by the electrode configuration. The higher the voltage and speed of the air, the higher the arc can be spread. Bows are produced at a constant rate of 50 to 60 cycles / second for a period of 5 seconds. The continuous arc produces a corona discharge highly charged ions. This field of energy is capable of disintegrating the fine thickness of the hydrophobic and / or oleophobic opposite cutouts 13 in the screen 12 through the protective layer whose thickness is less than about 5 nm and preferably between about 2 and 4 nm, and more preferably about 2 nm deposited on ie coating. The device comprises means (not shown) for regulating the air flow at the desired rate. It may further include a filtration system and ozone extraction produced in the corona treatment which converts ozone into oxygen and the thus filtered gas escapes in the housing.

2 shows a partial schematic view on a larger scale of part of the temporary protective layer 23 of the convex face 22, the hydrophobic layer and / or oleophobic coating 24 on which the temporary protection layer is deposited and having disintegrated areas 25 by energizing the source of discharge, is exposed so that the surface of the outer layer of the antireflection coating having a high surface energy. The glass is then overflowed to fit the rim of the frame. This edging, for example that of a glass can be produced on a Gamma grinder Essilor, the glass being held between a holding pad in this case a self-adhesive patch of the 3M Company of 25 mm diameter cooperates with the convex face and an acorn Essilor of the same diameter. Misalignment observed during trimming is less than 1 °, and therefore is perfectly satisfactory.

The temporary protective layer can be subsequently removed by wiping dry with a cotton cloth or liquid medium. Preferably, it is eliminated in a liquid medium with an acidic solution, in particular an orthophosphoric acid solution at molarity between 0.01 and 1 N. This solution may also comprise anionic surfactants, cationic or amphoteric. The glass is immersed in the ultrasonic bath in the orthophosphoric acid solution at room temperature for a period of 2 minutes and then rinsed with water or isopropyl alcohol and then wiped. The temperature of this solution can vary, with room temperature being satisfactory. One can even combine the two wiper means, followed by a cleaning step with an aqueous solution with a pH substantially equal to 7. This layer may also be removed by ultrasound in an ultrasonic tank B2200 E2 of the company having a power Branson 60W

example 1

Depositing a first coating comprising an anti-abrasion layer polysiloxane corresponding to the European example 3 of the patent application No. 0,614,957 and then an anti-reflective coating comprising a succession of four layers of ZrO₂, SiO₂, ZrO₂, SiO₂ and then a coating layer of a fluorosilazane KP801M reference marketed by Shinetsu company. This glass is then processed to monogramming with the corona discharge means, as described above, for a period of 5 seconds.

example 2

Depositing a first coating comprising an anti-abrasion layer polysiloxane corresponding to the European example 3 of the patent application No. 0,614,957 and then an anti-reflective coating comprising a succession of four layers of ZrO₂, SiO₂, ZrO₂, SiO₂ and then a coating layer of a compound comprising perfluoropropylene patterns of the mark Optool DSX commercialized by Daikin. It is then processed for monogramming as in Example 1.

example 3

Is deposited on another glass prepared according to Example 1 a temporary protective layer of MgF₂ of a thickness of 20 nm. It is then treated to monogramming as in Example 1, but during a period of 10 seconds. The temporary protective layer is then removed by wiping with a Selvyt® polishing cloth.

example 4

The procedure of Example 3 with the treatment for monogramming for five periods lasting 10 seconds, that is to say a total of 50 seconds.

example 5

Is deposited on another glass prepared according to Example 2 a temporary protective layer of MgF₂ of a thickness of 20 nm. It is then treated to monogramming as in Example 1, but during a period of 10 seconds, then the temporary protection layer is eliminated by wiping with a Selvyt® polishing cloth.

example 6

The procedure of Example 5 with the treatment for monogramming for five periods lasting 10 seconds, that is to say a total of 50 seconds.

example 7

Is deposited on a further glass prepared according to Example 1 a temporary protective layer of MgF₂ with a thickness of 2 nm. It is then treated to monogramming as in Example 1, and then the temporary protection layer is eliminated by wiping with a Selvyt® polishing cloth.

example 8

Is deposited on a further glass prepared according to Example 2 a temporary protective layer of MgF₂ with a thickness of 2 nm. It is then treated to monogramming as in Example 1, and then the temporary protection layer is eliminated by wiping with a Selvyt® polishing cloth.

Then, all the glasses are treated in misty cold to bring out the monogrammed pattern. The monogramming on glasses in Examples 1 and 2 is good. The high-energy areas of complementary surface corresponding to the screen blanks are covered with a film of condensation comprising large droplets and your dark under ambient lighting, while on the areas protected by the screen, low surface energy, the condensate film is made of micro-droplets of a tone much clearer.

With fogging of the glasses according to Examples 7 and 8, there is obtained the same good quality condensation units with lenses according to Examples 1 and 2. In addition, the optical and physical qualities of the outer coating, -to say the hydrophobic antifouling coating and / or oleophobic glass, after removing the temporary protective layer according to examples 7 and 8 are almost identical to those of glass before depositing the temporary protective layer of glass according examples 1 and 2.

However, fogging glasses of examples 3 and 5 does not bring out additional condensation patterns cutouts of the screen. Similarly, with the examples 4 and 6, fogging in areas complementary cutouts of the screen, there are micro-droplets taile superior to those present in the areas protected by the screen but the contrast between these zones is very low and therefore the monogramming is of mediocre quality.

According to the described embodiment, the energizing discharge source is a corona discharge. Other energy discharge sources can be used such as, for example, a cold plasma source or a source of ultraviolet radiation.

A cold plasma source may comprise an electrical discharge or microwave or a source of glow discharge. An electrical source or microwave can produce a discharge in a gas such as oxygen, argon, nitrogen, carbon tetrafluoride, helium, ammonium at reduced pressures of the order of one millibar. The discharge duration can vary from several seconds to several tens of seconds and preferably will be of the order of several seconds. A cold plasma discharge source is manufactured by Atea and sold under the brand Matis. It is also possible to use a cold plasma discharge source at atmospheric pressure Lectro Treat which produces a hybrid corona discharge.

A source of ultraviolet radiation will produce a photo-oxidation of molecules in the irradiated surface. The molecular dissociation is obtained with wavelengths of the order of 2357A ° and 1849A °. A decontamination unit Uvocs surfaces can be used as UV radiation source for this invention.

Similarly, instead of the screen described in the preferred embodiment, it is possible to implement another form of mask, for example an ink layer applied directly to the surface to be marked, as described in publication WO 01/68384 supra.

Such other energy discharges are also likely to selectively disintegrating the hydrophobic layer and / or oleophobic coating, in particular by oxidation or destruction of covalent bonds.

Of course, many modifications may be made to the embodiments described above without departing from the scope of the invention.