Method for preparing an optical glass for edge grinding, resulting glass and method for edge grinding such a glass

ES 2 245 403 T3

DESCRIPTION

Procedure for preparing a glass suitable for edging, glass thus obtained and procedure for edging said glass.

The present invention relates to the field of glass beading, very particularly ophthalmic glasses.

An ophthalmic glass results from a succession of molding and / or surface treatment operations that determine the geometry of the two convex and concave surfaces of said glass, followed by appropriate surface treatments.

The last stage of finishing an ophthalmic glass is the edging operation that consists of machining the edge or the periphery of the glass so that it conforms to the dimensions required to adapt the glass to the spectacle frame in which it is intended to be placed.

The edging is generally carried out on a grinder comprising diamond grinding wheels that carry out the machining as defined above.

The glass is supported, during this operation, by means of locking members that intervene axially.

The relative movement of the glass with respect to the grinding wheel is controlled, generally numerically, in order to make the desired shape.

As can be appreciated, it is absolutely imperative that the glass remains firmly fixed during this movement .

To this end, before the edging operation, a glass fixing operation is performed, that is, a fixing or fixing means is placed on the convex surface of the glass.

A retention pad, such as a self-adhering pad, for example a double-sided adhesive, is placed between the fixative and the convex surface of the glass.

The glass equipped in this way is arranged on one of the aforementioned axial locking members, the second axial locking member then pressing the glass on its concave face by means of a stop, generally made of elastomer.

When machining takes place, a tangential torque is generated on the glass, which can cause the glass to rotate relative to the fixator if the glass support system is not efficient enough.

The good hold of the glass depends mainly on the good adhesion to the interface of the retaining pad / convex surface of the glass.

State-of-the-art ophthalmic glasses very often comprise anti-dirt hydrophobic and / or oleophobic surface coatings associated with anti-reflective coatings.

They are very often fluorosilane-type materials that reduce surface energy in order to avoid the adhesion of greasy dirt, which is thus easier to remove.

One of the problems generated by this type of surface coating is that it achieves such an efficiency that the adhesion at the skid / convex surface interface is altered, even compromised for the most efficient hydrophobic and / or oleophobic coatings.

It is therefore very difficult to perform satisfactory edging operations, in particular for polycarbonate glasses whose edging generates much greater stresses than with other materials.

The consequence of a badly carried out beading operation is purely and simply the loss of the crystal.

One of the objects of the invention is to provide a means that allows the edging of a glass that comprises on its surface a hydrophobic and / or oleophobic coating, means that can be integrated into the glass manufacturing process, and is easy to carry out by the operator who performs the hemming operation.

The technical problem is solved according to the invention by depositing on the glass comprising a hydrophobic and / or oleophobic surface coating, a temporary protective layer that confers on the glass a surface energy at least equal to 15 mJ / m².

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Thus, it is possible to obtain sufficient adhesion at the retaining skid / glass interface, for skids conventionally used in the technical field.

It has already been proposed previously to deposit temporary layers on ophthalmic glasses, but essentially with the aim of ensuring their protection against scratches and degradations that may appear during handling. This is the case, for example, in patent application WO00 / 68326 which refers to a method of manufacturing composite optical articles from glued optical films, films whose surface has previously been protected by a protective layer that can be dissolved. then.

It is also the case of US Patent No. 2,392,768 in which a temporary layer based on ureaformaldehyde resin is placed on the glass before proceeding to the different operations (edging, polishing) to be carried out. This layer is then removed with water.

In the present application, the term "glass" designates an organic or mineral glass substrate, treated or not, comprising one or more coatings of a diverse nature or which remains raw.

When the glass comprises one or more surface coating (s), the term "depositing a layer on the glass" means that a layer is deposited on the outer coating of the glass.

The surface energies are calculated according to the Owens-Wendt method described in the following reference: "Estimation of the surface force energy of polymers" Owens DK, Wendt RG (1969) J. APPL. POLYM. SCI, 13, 17411747.

The crystals treated by the process of the invention are crystals that comprise a hydrophobic and / or oleophobic surface coating and preferably crystals that comprise both a hydrophobic and / or oleophobic surface coating deposited on a mono or multilayer antireflective coating.

Indeed, hydrophobic and / or oleophobic coatings are generally applied to glasses comprising an anti-reflective coating, in particular of mineral material, in order to reduce their marked tendency to get dirty, for example against greasy deposits.

As indicated above, hydrophobic and / or oleophobic coatings are obtained by applying, on the surface of the anti-reflective coating, compounds that decrease the surface energy of the glass.

Such compounds have been widely described in the prior art, for example in US patents 4,410,563, EP-0 203 730, EP-749 021, EP-844 265, EP-933 377.

The most commonly used compounds are based on silanes bearing fluorinated groups, in particular a perfluorocarbon or perfluoropolyether group (s).

By way of example, mention may be made of silazane, polysilazane or silicone compounds comprising one or more fluorinated groups such as those mentioned above.

A known method consists in depositing on the antireflection coating compounds bearing fluorinated groups and Si-R groups, where R represents a -OH group or a precursor thereof, preferably an alkoxy group. Said compounds can carry out polymerization and / or crosslinking reactions on the surface of the antireflective coating, directly or after hydrolysis.

The application of the compounds that decrease the surface energy of the crystal is carried out in a classical way by immersion in a solution of said compound, by centrifugation or, in particular, by deposition in the vapor phase. Generally, the hydrophobic and / or oleophobic coating has a thickness less than 10 nm, and even better less than 5 nm.

The invention is preferably carried out on crystals comprising a hydrophobic and / or oleophobic surface coating that confers a surface energy of less than 14 mJoules / m² and even better even less than or equal to 12 mJ / m²

The temporary protective layer will raise the surface energy of the crystal to a value of at least 15 mJoules / m².

It can be applied on an area covering all of at least one of the two faces of the glass or only on the zone destined to receive the contact of the retaining skid of said glass.

More precisely, it is usual to deposit the retention pad, associated with the fixative, on the convex face of the glass. The entire convex face or, alternatively, only a central area of ​​the convex face can therefore be covered with the protective layer, using a mask or any other appropriate technique.

ES 2 245 403 T3

The reservoir can evenly cover the corresponding area, that is to say it has a continuous structure, but it can also have a discontinuous structure, for example take the form of a web.

In this case, an intermittent deposit is formed, the surface of which is sufficient to allow the required adhesion of the retaining pad.

Deposits with a discontinuous structure can be obtained by pad printing.

After depositing the temporary protective layer, a glass suitable for beading is obtained.

In other words, after beading according to the method of the invention, the glass will have the dimensions required to be conveniently inserted into the frame for which it is intended.

More precisely, this result is obtained when the glass, when the edging operation takes place, undergoes a maximum offset of 2 °.

An optimal ability for beading corresponds to a glass whose offset is less than equal to 1 °.

The protective layer is made up of any material that allows raising the surface energy of the glass with hydrophobic and / or oleophobic properties and that is capable of being removed in a subsequent operation subsequent to the edging step.

Obviously, the material must be such that it does not definitively alter the surface properties of the hydrophobic and / or oleophobic coating and that after its removal, the optical and surface properties of the glass are globally identical to those that the glass possessed before deposit of the protective layer.

Preferably, the temporary protective layer is a mineral layer, and particularly a fluoride or a mixture of metal fluorides, an oxide or a mixture of metal oxides.

As an example of fluorides, mention may be made of magnesium fluoride MgF₂, by lanthanum LaF₃, aluminum AlF₃ or cerium CeF₃.

Oxides that can be used are titanium, aluminum, zirconium, or praseodymium oxides.

Mixtures of alumina and praseodymium oxide are recommended.

A particularly recommended commercial material is STEP2 from the Leybold company.

The protective layer can be deposited by any convenient conventional procedure.

Generally, the anti-reflective, hydrophobic and / or oleophobic coatings have been deposited by evaporation, in vacuum hoods and it is desirable to deposit the temporary protective layer with the same technique, which allows all the operations to be carried out continuously, without excessive manipulations of the crystals between the stages.

When it is constituted by a mineral matter, the thickness of the protective layer is preferably less than or equal to 50 nm, and generally from 1 to 50 nm, and even better from 5 to 50 nm.

In general, if the thickness of the protective layer is too small, there is a risk of insufficiently modifying the surface energy.

If, on the other hand, the thickness of the protective layer is too great, in particular for essentially mineral layers, the inventors have found that there is a risk of mechanical stresses appearing within the layer, which could be harmful. for the expected properties.

Preferably, and very particularly when the temporary protective layer is deposited on the entirety of one of the faces of the glass, the material has a certain degree of transparency that allows classical power measurements to be carried out on the glass using a lensmeter.

Thus, the glass suitable for beading according to the invention preferably has a transmission of at least 18%, preferably at least 40% according to the ISO8980 / 3 standard.

As an alternative to the materials of a mineral nature mentioned above, conventional inks can be used for marking progressive ophthalmic crystals, and / or the resins that constitute the binder of these inks.

In this case, it is possible to deposit thicknesses much greater than in the case of purely mineral layers.

The required thicknesses can then vary between 5 and 150 microns.

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Resins of the alkyd type are particularly desirable.

The glass suitable for beading obtained according to the process of the invention can then be subjected to a completely conventional beading operation, except that, in a final stage, a temporary protective layer removal operation has to be carried out.

The invention therefore also relates to a process for obtaining a beaded glass with the property of a hydrophobic and / or oleophobic surface, characterized in that it comprises the following steps:

1) a glass suitable for beading is selected, according to the invention,

2) proceed to fix said glass,

3) said glass overflows,

4) proceed to the release of said crystal,

5) the beaded glass is recovered in this way, and

6) the temporary protective layer is removed to restore the glass to its hydrophobic and / or oleophobic surface properties.

As previously indicated, the edging stage 3) itself is a classical stage and known to those skilled in the art.

Therefore it will not be described in detail.

However, it can be specified that the retention pads used are preferably double-sided self-adhering tablets, for example 3M brand adhesives.

The step of removing the temporary protective layer can be carried out either in a liquid medium, or by dry cleaning, or even by a successive application of these two means.

The elimination step in a liquid medium is preferably carried out by an acid solution, in particular an orthophosphoric acid solution, with molarities between 0.01 and 1N.

The acidic solution can also comprise anionic, cationic, or amphoteric surfactants.

The temperature at which the elimination step is carried out is variable, but generally proceeds at room temperature.

The removal of the temporary protective layer can also be favored by a mechanical action, preferably by the use of ultrasound.

In general, after the treatment with the liquid medium such as the acid solution, the dry cleaning or the combination of the two, the elimination step comprises a cleaning step by means of an aqueous solution of a pH substantially equal to 7.

Thus, at the end of the temporary protective layer removal step, the glass has optical and surface characteristics of the same order, even almost identical to those of the initial glass, which comprises the hydrophobic and / or oleophobic coating.

The advantages related to the invention are numerous.

The method according to the invention is simple to use.

In particular, the person skilled in the art can use conventional grinding wheels and beading procedures, without having to modify them or to do so in an extremely limited way.

The stage of removing the temporary protective layer is quick.

The glasses suitable for beading according to the invention, in particular the glasses that carry a temporary protective layer of mineral matter, can be the object of marking with various inks, commonly used by those skilled in the art, for progressive glasses.

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Examples

The following examples illustrate the present invention.

Example 1

1.1 Preparation of crystals comprising a hydrophobic and oleophobic coating

Organic crystals are prepared bearing 3 coatings respectively anti-abrasion, anti-reflective, hydrophobic-oleophobic, deposited in this order on the substrate.

ORMA organic crystals^®, of power -2.00 diopters, obtained by polymerization of diethylene glycol diallylcarbonate (CR39® monomer) and comprising an anti-abrasion coating of the polysiloxane type corresponding to example 3 of patent application EP-614 957 in the name of the applicant, are heated in an oven for 3 hours at a temperature of 100 ° C.

The crystals are then placed in a LEYBOLD 1104 vacuum treatment machine equipped with an electron gun and a Joule-effect evaporation source.

A secondary vacuum is created by pumping the substrates, without heating them.

Evaporated successively with the electron gun, 4 high-index (HI) / low-index (BI) / HI / BI: ZrO anti-reflective optical layers₂, WIS₂, ZrO₂, WIS₂.

A hydrophobic and oleophobic coating is then deposited by evaporation of an OPTOOL dSx brand product (compound comprising perfluoropropylene motifs) marketed by DAIKIN.

The product, in liquid form, is poured into a copper capsule, then the liquid is allowed to dry at room temperature and atmospheric pressure.

The copper capsule is then placed in a joule effect crucible.

Evaporation of the product is carried out under a secondary vacuum.

The thickness of the deposited layer is less than 10 nm.

The control of the deposited thickness is carried out with a quartz scale.

1.2 Deposit of temporary protective layer

The temporary protective layer is then deposited by evaporation:

A material identified with the name of STEP 2, which is a mixture of alumina and praseodymium oxide, marketed by the Leybold company, is evaporated by means of an electron gun.

Evaporation is not reactive (without oxygen).

The physical thickness of the deposited protective layer is 25 nm.

The control of the deposited thickness is carried out with the quartz scale.

The glass is recovered after reheating the chamber, then placed back into the atmosphere of the treatment chamber.

1.3 Beaded

The crystal resulting from step 1.2 is subjected to a classical beading operation on a gamma grinder from Essilor.

A 3M self-adhesive pad with a diameter of 25 mm and a fixative from the Essilor company of the same diameter are used as the retention pad.

The plastic: polycarbonate grinding wheel has a diameter of 155 mm and rotates at 2850 rpm.

During the edging operation, the offset of the crystal axis is less than 1 °.

At this stage, the recovered beaded crystals can be placed directly on the frame that is attached to them.

ES 2 245 403 T3 intended, then treated according to the following step 1.4, or treated according to the step 1.4 before being inserted into the frame.

1.4 Removal of the protective layer

A small ultrasound cuvette is used for this stage, model: B2200 E2 BRANSON Ultrasound power: 60 watts Ultrasound frequency: 47 kHz / -6 kHz

The crystals obtained during stage 1.3 are immersed in a 0.1 N dilute orthophosphoric acid solution, at room temperature (with ultrasound and without heating) for a time of 2 minutes, then rinsed with water or isopropyl alcohol and dried.

The crystals obtained have excellent optical characteristics as well as excellent hydrophobic and oleophobic properties.

Example 2

Steps 1.1, 1.2 and 1.4 of Example 1 are reproduced identically except that they are carried out on flat sheets, of the same material as the ORMA® CR39® substrates.

Contact angles are measured at different stages of the procedure.

The use of flat sheets facilitates these measurements.

Contact angles are measured:

In an air-conditioned room: ambient temperature T '= 21 ° +/- 1 ° C, degree of relative humidity Rh = 55% + / 5%.

With a Digiprop model GBX goniometer with 3 liquids: deionized water, glycerol and diiodomethane

The surface energies are calculated according to the Owens-Wendt 2-component model by the DGD / fast 60 apparatus from GBX Scientific Instruments that uses a Windrop logic unit.

The results obtained appear in the following table:

TABLE I

<td></td><td>Flat substrate obtained after stage 1. (Initial substrate)</td><td>Flat substrate obtained after step 1.2 (with temporary protective layer from Step 2)</td><td>Flat substrate obtained after step 1.4 (after removal of the temporary protective layer from Step 2)</td>

<td>Water angle</td><td> 118°+/-0,75</td><td> 49° +/- 3,5</td><td> 112°+/-0,95</td>

<td>Glycerol angle</td><td> 105° +/- 0,97</td><td> 44° +/- 0,9</td><td> 103° +/- 0,65</td>

<td>Diiodomethane angle</td><td> 92° +/- 2</td><td> 30° +/- 3,8</td><td> 91°+/- 3,72</td>

<td></td><td></td><td></td><td></td>

<td>Polar component</td><td>0.93 mJ / m²</td><td>20.60 mJ / m²</td><td>2.29 mJ / m²</td>

<td>Dispersive component</td><td>10.34 mJ / m²</td><td>31.99 mJ / m²</td><td>9.78 mJ / m²</td>

<td>Total energy (Owens-Wendt)</td><td>11.4 mJ / m² +/-0,5</td><td>52.6 mJ / m² +/- 0,8</td><td>11.7 mJ / m² +/- 0,5</td>

It is found that with the temporary protective layer based on Step 2, the surface energies are high: Ophthalmic crystals made of said material are therefore suitable for edging and allow the use of a wide variety of self-adhesive tablets as well as a wide variety of inks for glass marking.

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The surface energies obtained after removing the protective layer in Step 2 are practically identical to those obtained for the initial glass, comprising the anti-reflective coating and the hydrophobic and oleophobic coating.

The surface characteristics of the hydrophobic and oleophobic coating are preserved.

Example 3

ORMA® crystals with optical power -2.00 diopters are treated according to the procedure of Example 1, step 1.1, in order to obtain crystals with anti-reflective, hydrophobic and oleophobic properties.

These crystals are then treated in halves: one half according to the protocol described in example 1 step 1.2 receives a protective layer, while the other half, masked by a metal cover, does not receive the protective layer.

The part of the glass covered by the protective layer is then treated according to the protocol of example 1, step 1.4, by immersing the sample in half in the acid bath.

On each of the two parts of the glass, the following are carried out:

• visual reflection Rv and mean reflection Rm measurements according to ISO / WD 8980-4, and • colorimetric measurements of the tint angle h and of Chroma C * with a ZEISS spectrophotometer (15 ° angle) and calculated on the CIE lab 1964 system (L *, a *, b *)

The results obtained appear in the following table II

TABLE II

<td></td><td>Half that has not received deposit of the protective layer</td><td>Half that has received the deposit of the protective layer and after its removal</td>

<td>h</td><td> 135°+/-2°</td><td> 135° +/-2°</td>

<td>C *</td><td> 7,2</td><td> 7,3</td>

<td>Rv</td><td> 0,72</td><td> 0,71</td>

<td>Rm</td><td> 0,74</td><td> 0,75</td>

The colorimetric values ​​obtained after the application of the layer from Step 2, and after its removal, are practically identical to those of the part of the glass that has not received the layer from Step 2: the protective layer from Step 2 and its removal. chemistry does not modify the colorimetric characteristics of the anti-reflective coating. Example 4

In this example, a temporary protective layer is deposited by pad printing. The deposits are made on negative power crystals -2.00 diopters in ORMA® identical to those obtained in step 1.1 of example 1.

An ink referenced with the number: 03XH622 2030 is used

Thinner 4909

Manufacturer: Tiflex address: BP3.01450.PONCIN.FRANCIA.

10% of the diluent is added in the initial ink formulation to adapt the viscosity of the solution.

The pad printing machine used is of the MTHV2 type (Manufacturer: Automation &amp; Robotics)

The tampon used is silicone

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Cliché engraved (depth 10 to 20 jum) and hatched (fill rate 20% to 40%)

The ink is applied by pad printing on the glass

Drying is carried out in ambient air or in an oven at 50 ° C for a time greater than or equal to 5 minutes.

The result is a discontinuous ink layer (screen), whose adhesion on the glass surface is sufficient not to be degraded during transport.

Edging of the glass coated in this way is then accomplished by placing a 3M double-sided self-adhesive chip over the ink layer.

The crystals obtained are suitable for beading and can be inserted into frames after beading.

A comparative example has been made on a glass that does not comprise a temporary protective layer.

The glass undergoes severe off-centering during the edging operation and cannot be inserted into the corresponding frame.

The results obtained appear in table III.

TABLE III

<td></td><td>ink</td><td>Cliche depth</td><td>plot</td><td>drying</td><td>Beading suitability</td>

<td>Ex1</td><td>Tiflex</td><td>10-12 pm</td><td> 20%</td><td>air</td><td>Yes</td>

<td>Ex2</td><td>Tiflex</td><td>10-12 pm</td><td> 25%</td><td>air</td><td>Yes</td>

<td>Ex3</td><td>Tiflex</td><td>10-12 pm</td><td> 30%</td><td>air</td><td>Yes</td>

<td>Ex4</td><td>Tiflex</td><td>10-12 pm</td><td> 40%</td><td>air</td><td>Yes</td>

<td>Example comparative</td><td> -</td><td> -</td><td> -</td><td> -</td><td>not</td>