Method for permanent visible marking of an optical article and marked optical article

Abstract

Disclosed is a method for marking an optical article coated with an interference coating including at least two layers, an inner layer and an outer layer, and having reflection coefficient Re; by exposure of the inner layer, at a marking point, by way of a laser beam at a marking wavelength, in such a way as to ablate the inner layer and any layer further away from the substrate; the ablated area having a reflection coefficient Rm different from Re by at least 1%; the inner layer absorbing the marking wavelength to a greater degree than any layer further away from the substrate. Also disclosed is an optical article coated with an interference coating having at least two layers, an inner layer and an outer layer, the article including a marking pattern formed by local absence of layers.

Claims

1. A method for marking an optical article, said method comprising: at least one step of using a marking machine on the optical article, the marking machine including an electromagnetic source configured to emit an electromagnetic beam having a set radiation wavelength called the marking wavelength, and the optical article including a substrate having a main face coated with an interference coating, said interference coating comprising at least two superposed layers including an interior layer and an exterior layer, the interior layer being located between the substrate and the exterior layer, the interference coating having a reflection coefficient Re in a visible domain of 380-780 nm, the at least one step of using the marking machine comprising: irradiating at least the interior layer in a marking spot, by means of the electromagnetic beam at the marking wavelength, so as to ablate, in the marking spot, the interior layer, over at least one portion of a thickness of the interior layer, and any layer located between the electromagnetic source and the interior layer, an ablated zone thus ablated having a reflection coefficient Rm in the visible domain, Rm being different from Re by at least 1%, the interior layer absorbing the marking wavelength more greatly than any layer that is located, prior to carrying out the at least one step of using the marking machine, between the electromagnetic source and the interior layer.

2. The marking method as claimed in claim 1, wherein the difference between Rm and Re is, in absolute value, larger than 3%.

3. The marking method as claimed in claim 2, wherein the difference between Rm and Re is, in absolute value, larger than 5%.

4. The marking method as claimed in claim 1, wherein the irradiating is carried out by emitting a focused beam of pulsed ultraviolet laser radiation having at least the following parameters: a radiation wavelength comprised in an interval of 200 to 400 nm, and a pulse duration comprised in an interval of 0.1 to 5 ns, and an energy per pulse comprised in an interval of 0.1 to 10 ρJ, and, in the marking spot, a beam diameter comprised in an interval of 5 to 50 μm.

5. The marking method as claimed in claim 4, wherein the radiation wavelength of the beam of pulsed ultraviolet laser radiation performing the irradiating is comprised in an interval of 200 to 300 nm, and the interior layer comprises tin.

6. The marking method as claimed in claim 5, wherein the interior layer consists essentially of tin dioxide SnO.sub.2.

7. The marking method as claimed in claim 4, wherein the radiation wavelength is within a range of 200 to 300 nm, and the energy per pulse is within a range of 0.5 to 3 μJ.

8. The marking method as claimed in claim 1, wherein the interior layer has a thickness comprised in an interval of 1 to 100 nm, and the sum of ire thicknesses of the interior layer and of the exterior layer is comprised between 5 and 300 nm.

9. The marking method as claimed in claim 8, wherein the interior layer has a thickness within a range of 4 to 15 nm, and wherein the sum of the thicknesses of the interior layer and of the exterior layer is in a range of 45 to 175 nm.

10. The marking method as claimed in claim 1, wherein the interference coating includes at least one absorbent layer.

11. The marking method as claimed in claim 10, wherein all the layers counted from the interior layer to the exterior layer together absorb at least 0.5% of the transmitted visible light.

12. The marking method as claimed in claim 1, wherein a difference between the amount of light transmitted by the ablated zone and by the unablated zone is comprised between −0.5×(Rm-Re) and 0.5×(Rm-Re), (Rm-Re) being understood to represent the absolute value of the difference between Re and Rm.

13. The marking method as claimed in claim 1, wherein the interference coating is an antireflection coating and comprises, from the surface of the substrate or of a varnish present on the substrate, to the exterior, a layer of ZrO.sub.2, of 5 to 40 nm thickness, a layer of SiO.sub.2, of 10 to 55 nm thickness, a layer of ZrO.sub.2, of 20 to 150 nm thickness, an interior layer of SnO.sub.2, of 4 to 15 nm thickness, and an exterior layer of SiO.sub.2, of 50 to 120 nm thickness.

14. The marking method as claimed in claim 1, wherein the interference coating is itself coated with a surface coating.

15. The marking method as claimed in claim 1, wherein the irradiating is carried out repeatedly so as to locally mark a region of a main surface of the substrate of the optical article by means of multiple marking spots, said region forming a predefined pattern called the marking pattern.

16. The marking method as claimed in claim 15, wherein there is a continuity between the marking spots that define the region forming the marking pattern, said region including less than 1% per unit area of residues from the ablated layers.

17. The marking method as claimed in claim 15, wherein the irradiating is carried out with a pitch of dimension smaller than or equal to the dimensions of the marking spot.

18. The marking method as claimed in claim 1, wherein the reflection at the marking spot has a colour, in saturation and/or in hue, different from that of the reflection of an unablated zone.

19. The marking method as claimed in claim 1, wherein the electromagnetic beam is a laser beam, and the electromagnetic source is a laser source.

20. An optical article, comprising: a substrate having a main face coated with an interference coating, said interference coating comprising at least two superposed layers of materials including an interior layer and an exterior layer, the interior layer being located between the substrate and the exterior layer, the interference coating having a reflection coefficient Re in a visible domain of 380-780 nm; said optical article comprising a marking pattern on a surface of the interference coating, the marking pattern being formed by a plurality of substantially identical marking spots, each marking spot corresponding to a localized absence of at least one portion of a thickness of the interior layer and of any layer located between said surface and the interior layer, an ablated zone having a reflection coefficient Rm in the visible domain such that Re is different from Rm by at least 1%, wherein the interior layer absorbs a marking wavelength more greatly than any layer located between an electromagnetic source and the interior layer.

Description

(1) The invention will be better understood in light of the appended drawings, in which:

(2) FIGS. 1 to 3 schematically show a first embodiment of the marking method according to the invention, FIG. 1 schematically showing, in cross section, the principle of the marking method before its performance, FIG. 2 schematically showing, in cross section, the marking method in the process of being performed, and FIG. 3 schematically showing, in cross section, the marking method at the end of its performance; and

(3) FIGS. 4 and 5 illustrate the results obtained in reflection (R) and in transmission (T) for the ophthalmic lens (1) obtained according to the first embodiment of FIGS. 1 to 3 in the zone of the marking spot (25) and in other zones of the surface of the ophthalmic lens; and

(4) FIGS. 6 to 9 schematically show a second embodiment of the marking method according to the invention, FIGS. 6 and 7 showing the ophthalmic lens before the marking method is performed and FIGS. 8 and 9 showing the ophthalmic lens after the marking method has been performed; more precisely, FIG. 6 shows an overview of the ophthalmic lens before the marking method is performed, FIG. 7 shows, in perspective, a section of the layers present on the ophthalmic lens before the marking method is performed, FIG. 8 shows an overview of the ophthalmic lens after the marking method has been performed, and FIG. 9 shows, in perspective, a section of the layers present on the ophthalmic lens after the marking method has been performed.

(5) The invention will be better understood in light of the following example embodiments, if reference is made to the appended drawings as indicated above. FIGS. 1 to 9 are described in more detail in the following examples.

EXAMPLES

(6) The following examples illustrate the invention without however limiting its scope.

(7) In the two following example embodiments, the interior layer is made from tin dioxide SnO.sub.2; the exterior layer is made from silicon oxide, namely either silicon monoxide SiO, or silicon dioxide SiO.sub.2; and the electromagnetic beam is a 266 nm (UV) laser beam. The marking wavelength is therefore 266 nm.

Example 1: Marking of an Ophthalmic Lens Consisting of a Substrate, of a First Layer of Chromium (“Cr1”), of an SnO.SUB.2 .Interior Layer, of an Absorbent Second Layer of Chromium (“Cr2”), and of an SiO.SUB.2 .Exterior Layer

(8) The ophthalmic lens (1) consists of a substrate (6) on which are superposed, in succession, a first metal layer (5) (of chromium, “Cr1”), an interior layer (4) of tin dioxide SnO.sub.2, a second metal layer (3) (of chromium, “Cr2”) or absorbing layer, and an exterior layer (2) of silicon monoxide SiO. The substrate (6) is here a polarized or tinted substrate including an anti-scratch coating of trademark Mithril®.

(9) Such a substrate-metal-dielectric-metal-dielectric structure is to similar to that of the lens marked in the prior art US 2004/0095645, with the exception that, according to the invention, an SnO.sub.2 layer has been added between the layer Cr1 and the layer Cr2.

(10) Layers (2) SiO, (3) Cr2, (4) SnO.sub.2 and (5) Cr1 are of nature and have a thickness such that the coating that they form creates an interference effect that increases reflexes so as to create a mirror with reflection. This coating has an average reflection coefficient of about 12 to 15%, the reflection being greatest in the violet.

(11) The layer (5) of chromium Cr2, which is very slightly absorbent in the visible, substantially decreases the overall transmittance of the system, this posing no problem in the case of the used ophthalmic lens (1), which is here a sunglass lens.

(12) The nature and physical and optical characteristics of the layers are indicated in the following table:

(13) TABLE-US-00001 Number of the layer counted starting from the substrate/ Material Thickness of the Layer reference (illustration) of the layer layer (±2 nm) 1/(5) Cr 15 nm 2/(4) SnO.sub.2  6 nm 3/(3) Cr  5 nm 4/(2) SiO 65 nm

(14) The marking process according to the invention has been carried out by means of a pulsed laser emitting a beam at a wavelength of 266 nm with pulses of 1 ns duration, an energy per pulse of 3 μJ and a marking-spot area of about 10 μm diameter.

(15) FIGS. 1 to 3 schematically illustrate this first example embodiment of the marking method according to the invention. The laser beam 23 is shown very symbolically by a lightning bolt that is focused on the interior layer 4.

(16) FIG. 1 schematically shows, in cross section, the principle of the marking method before it is performed on the ophthalmic lens 1. In this figure the following may be seen: the substrate (6), on which the first layer (5) of chromium Cr1 has been deposited, and the interior layer (4) of tin oxide SnO.sub.2, then the layer (3) of chromium Cr2, and lastly the exterior layer (2) of silicon monoxide SiO, the latter three being superposed on said first layer.

(17) FIG. 2 schematically shows, in cross section, the marking method in the process of being performed by local removal of the layers (4), (3) and (2) with the electromagnetic beam (23), which irradiates the interior layer (4) made of SnO.sub.2 and destroys it, the layers (3) and (2) indirectly being removed during the destruction of the layer (4). The portion (24) of the layers (4), (3) and (2) in the process of removal, which portion will become the marking spot (25) of FIG. 3, may be seen. In this cross section, the layer (4) is divided into two portions (4′) and (4″), the layer (3) is divided into two portions (3′) and (3″) and the layer (2) is divided into two portions (2′) and (2″). The ophthalmic lens (1′) on which the marking is begun also comprises the layer (5) on the substrate (6).

(18) FIG. 3 schematically shows, in cross section, the marking method at the end of performance thereof. In this cross section, layers (4), (3) and (2) have been ablated following irradiation with the electromagnetic beam (23), dividing them into two portions (4′) and (4″), into two portions (3′) and (3″) and into two portions (2′) and (2″), respectively. An engraved ophthalmic lens (10) is thus obtained.

(19) The embodiment performed as illustrated has allowed a marking spot (25) to be produced. Repetition of the irradiating step of the method of the invention allows a plurality of marking spots forming a marking pattern, such as a logo, to be produced.

(20) Advantageously, the layer (5) of chromium Cr1, which layer is comprised between the interior layer (4) and the substrate, absorbs only little or even very little of the light emitted at the wavelength of the laser (260 nm), this making it practically insensitive to the marking electromagnetic beam. It is therefore not destroyed by irradiation by the marking electromagnetic beam. It is therefore possible to superpose the marking spots without running the risk of over-engraving in the overlap between two marking spots. Therefore, the method according to the invention advantageously allows a continuous marking to be produced on the surface of the ophthalmic lens (1), i.e. a marking such as a logo of large area, that is uniform i.e. not “dotted”.

(21) In contrast, prior-art technologies that aimed to create residue-free markings by laser ablation needed to produce marking spots that were partially superposed, this implying, with respect to the rest of the pattern, deeper over-engraving locally in two contiguous marking spots, this for example causing local ablation of at least one additional layer, i.e. the layer (5) Cr1.

(22) FIG. 4 illustrates the results obtained in reflection (R) for the ophthalmic lens (1) obtained according to the first embodiment of FIGS. 1 to 3 in the ablated zone of the marking spot (25): R.sub.m and in the unablated zone of the surface of the ophthalmic lens (1): R.sub.e.

(23) It may be seen that the interference coating (2, 3, 4, 5) is characterized by a specific reflectance spectrum R.sub.e, illustrated in FIG. 4, and that, in the unablated zone, the average reflectance spectrum Ref2, which is of about 12 to 15%, reflects slightly more in the violet. It may also be seen that the layer (5) Cr1, alone, present on the anti-scratch material, causes the lens to have locally a reflection coefficient Ref1 that is about 33% (this being higher than Ref2), and that is relatively uniform in wavelengths in the visible.

(24) Thus, when the ophthalmic lens (1) is observed, the observer perceives an additional reflection in the zone of the marking, that contrasts with the reflection of surrounding points.

(25) The difference in reflection coefficient between the marking spot (25) and the other (unablated) zones of the surface of the ophthalmic lens (1) is therefore about 18% on average, thereby allowing patterns to be formed via a difference in intensity in reflection but also in hue and in chroma in reflection from the surface of the ophthalmic lens. Specifically, there is a factor of as much as about two and a half, at the central wavelengths of the spectrum of the visible, between the reflection coefficient R.sub.m of the pattern formed by the ablated zone of the marking spot (25) and the reflection coefficient of the unablated zone of the surface of the ophthalmic lens (1).

(26) This variation in hue and in chroma may also be achieved by means of the invention with interference coatings other than that of example 1.

(27) Moreover, as will be clear from the above data, the hue of the reflex and the intensity of this hue varies between the ablated zone of the marking spot (25) and the unablated zone of the surface of the ophthalmic lens (1). The marking spot (25) has a substantially uniform reflectance over the spectrum of visible light, this giving a substantially white reflex, or in any case a reflex with a low hue intensity. In contrast, the unablated zone of the surface of the ophthalmic lens (1) more particularly reflects the violet, giving the ophthalmic lens (1) a hue that is rather violet on the whole.

(28) Preferably, the absorbance A2 of the layer (3) Cr2 in the visible is such that the following equation is respected or approached: Ref2+A2=Ref1. In this case, the transmittance of the light passing through the ophthalmic lens (1) in the ablated zone of the marking spot (25) is substantially identical to the transmittance outside of the marking, in the unablated zone of the surface of the ophthalmic lens (1). This makes it possible for the ophthalmic-lens wearer to practically not perceive the difference, or even to perceive no difference, in transmittance level with the marking spot (25). The latter is therefore visible to an exterior observer and not visible to the wearer of the ophthalmic lens (1).

(29) Thus, according to this example embodiment, the absorbance, in the visible (380-780 nm) of the layer (3) Cr2 is such that it is equivalent to the decrease in the effectiveness of the interference coating devoid of the layers (2) SiO.sub.2, (3) Cr2, and (4) SnO.sub.2.

(30) FIG. 5 illustrates the transmittance (T) measured as a function of wavelength through the ophthalmic lens (1) obtained according to the first example embodiment of FIGS. 1 to 3 in the zone of the marking spot (25): T.sub.m and in the unablated zone of the surface of the ophthalmic lens (1): T.sub.e.

(31) It may be seen that, during the ablation of at least one portion of the thickness of the interior layer (4), the layer (3) Cr2 is also removed and no longer participates, in the ablated zone of the marking spot (25), in the absorption of light. Therefore, as may be deduced from the curve of FIG. 5, the transmittance is substantially identical in the ablated zone of the marking spot (25) (curve T.sub.m) and in the unablated zone of the surface of the ophthalmic lens (1) (curve T.sub.e).

(32) Thus, the decrease in the amount of light passing through the ophthalmic lens (1) caused by the absorption of the chromium layer (3) Cr2 in the unablated zone of the surface of the ophthalmic lens (1) is approximately equivalent to the decrease in the amount of light passing through the ophthalmic lens (1) caused by the presence of a higher reflection coefficient in the ablated zone of the marking spot (25).

(33) Various variants of this first example embodiment may be envisioned, all of which are within the ability of a person skilled in the art to implement. Certain of these variants are described below.

(34) Thus, the layer (5) Cr1 may be replaced by a coating of layers each having the property of not absorbing the marking wavelength too greatly.

(35) Likewise, the layer (2) of SiO and the layer (3) of Cr2 may be replaced by another coating of similar layers.

(36) Lastly, it is possible for the layer (3) Cr2 not to be absorbent, even slightly, in the visible (380-700 nm), or to not be present at all. This is particularly the case when the interior layer (4) is itself chosen to be made of a material that is absorbent in the wavelength range of the visible.

Example 2: Marking of an Opthalmic Lens Consisting of a Substrate, of a Layer of ZrO.SUB.2., of a Layer of SiO.SUB.2., of a Layer of ZrO.SUB.2., of an Interior Layer of SnO.SUB.2., of an Exterior Layer of SiO.SUB.2., of a Layer of an Antifouling Agent and of a Double Temporary Layer

(37) The ophthalmic lens (20) consists of a substrate (21) that is a lens of 1.5 index from Essilor International® including an anti-scratch coating of trademark Mithril®, on which is superposed an interference coating consisting of a coating including, successively, starting from the varnish present on the substrate, a first layer (18) of zirconium oxide ZrO.sub.2, a first layer (17) of silicon dioxide SiO.sub.2, a second layer (16) of zirconium dioxide ZrO.sub.2, a layer (15) of tin dioxide SnO.sub.2 or interior layer, a second layer (14) of silicon dioxide SiO.sub.2 or exterior layer, a (hydrophobic and/or oleophobic) anti-fouling layer (13), a layer (12) of magnesium difluoride MgF.sub.2 of 37 nm thickness and a layer (11) of magnesium oxide MgO of a few nanometres thickness.

(38) Layers (14, 15, 16, 17 and 18) together, ignoring the respective layers 12 and 11 of MgF.sub.2 and MgO, which are temporary layers, form an interference coating that is here an antireflection coating, the thicknesses of the layers being calculated by means of a software package known to those skilled in the art (which takes into consideration the nature of these layers) in order to achieve a total reflection coefficient (Re) lower than 1%, for example 0.7 or 0.8% depending on the samples measured.

(39) The nature and physical and optical characteristics of the layers of the interference coating are indicated in the following table:

(40) TABLE-US-00002 Number of the layer counted Refractive Thickness starting from the substrate/ Material index of the of the layer Layer reference (illustration) of the layer layer (±3 nm) 1/(18) ZrO.sub.2 2.0038 30 nm 2/(17) SiO.sub.2 1.4741 40 nm 3/(16) ZrO.sub.2 2.0038 60 nm 4/(15) SnO.sub.2 1.8432  6 nm 5/(14) SiO.sub.2 1.4741 110 nm 

(41) Performing the method according to the invention causes a local ablation of the exterior SiO.sub.2 layer 14, of the layers 13, 12 and 11, which are outside the exterior layer SiO.sub.2, and an at least partial ablation of the interior layer 15, which is made of SnO.sub.2. In this marking spot (P), the value of the reflectance (Rm) measured in the ablated zone is about 8.5%, or about 10 times more than Re.

(42) FIGS. 6 to 9 schematically illustrate this second example embodiment of the marking method according to the invention.

(43) FIGS. 6 and 7 show the ophthalmic lens before the marking method is performed and FIGS. 8 and 9 show the ophthalmic lens after the marking method has been performed.

(44) FIG. 6 schematically shows an overview of the ophthalmic lens (20) before the marking method is performed.

(45) FIG. 8 schematically shows an overview of the ophthalmic lens (30) after the marking method has been performed. The marking-pattern engraving or marking (22) forming the word “Essilor” may be seen therein.

(46) FIG. 7 schematically shows in perspective a section of the layers present on the ophthalmic lens (20), before the marking method is performed.

(47) In this figure the substrate (21) may be seen, on which has been deposited in succession a “UL” UV filtering layer (19), a first layer (18) of ZrO.sub.2, a first layer (17) of SiO.sub.2, a second layer (16) of ZrO.sub.2, an interior layer (15) of SnO.sub.2, an exterior second layer (14) of SiO.sub.2, an antifouling coating layer (13), a layer (12) of MgF.sub.2 and a layer (11) of MgO.

(48) FIG. 9 schematically shows in perspective a section of the layers present on the ophthalmic lens (20) after the marking method has been performed.

(49) The layers (11), (12), (13), (14) and (15) have been ablated in a marking spot (P) (here schematically shown in two dimensions whereas, in fact, as explained above, it is substantially a cylinder that, by repetition of the irradiating step of the method of the invention, forms part of the marking (22), this having led to the layers (11′), (12′), (13), (14) and (15) being obtained. An engraved ophthalmic lens (30) is thus obtained.

(50) In practice, at the bottom of the marking spot (P), a slight marking (25) (here shown schematically in two dimensions whereas in fact it is substantially a cylinder) is observed to exist in the layers (16) and (17) present immediately under the layer (15). The zirconium dioxide ZrO.sub.2 of the layer (16) and the silicon dioxide SiO.sub.2 of the layer (17) therefore absorb the marking wavelength slightly. The absorption being relatively weak, as may well be deduced from the resulting marking, this is compatible with the performance of the marking method according to the invention, because the visibility of the marking is not affected.

Example 3: Marking of an Ophthalmic Lens Consisting of a Substrate, an SiO.SUB.2 .Sub-Layer, a Layer of ZrO.SUB.2., of a Layer of SiO.SUB.2., of a Layer of ZrO.SUB.2., of an Interior Layer of SnO.SUB.2., of an Exterior Layer of SiO.SUB.2., of an Antifouling Layer and of a Double Temporary Layer

(51) FIGS. 6 to 9 schematically illustrate this third example embodiment of the marking method according to the invention, only the nature of the layer (19) being modified with respect to the second example embodiment.

(52) The ophthalmic lens (20) consists of a substrate (21) that is a lens of 1.5 index from Essilor Internationale including an anti-scratch coating of trademark Mithril®, and that includes, thereabove, an interference coating including, successively, starting from the varnish present on the substrate, a thick layer (19) made of SiO.sub.2, a first layer (18) of zirconium oxide ZrO.sub.2, a first layer (17) of silicon dioxide SiO.sub.2, a second layer (16) of zirconium dioxide ZrO.sub.2, a layer (15) of tin dioxide SnO.sub.2 or interior layer, a second layer (14) of silicon dioxide SiO.sub.2 or exterior layer, a (hydrophobic and/or oleophobic) anti-fouling coating layer (13), a layer (12) of magnesium difluoride MgF.sub.2 of 37 nm thickness and a layer (11) of magnesium oxide MgO of a few nanometres thickness.

(53) Layers (14, 15, 16, 17 and 18) together, ignoring the respective layers 12 and 11 of MgF.sub.2 and MgO, which are temporary layers, form an interference coating that is here an antireflection coating, the thicknesses of the layers being calculated by means of a software package known to those skilled in the art (which takes into consideration the nature of these layers) in order to achieve a total reflection coefficient lower than 1%, for example 0.7% or 0.8% depending on the samples measured.

(54) The nature and physical and optical characteristics of the layers are indicated in the following table:

(55) TABLE-US-00003 Number of the layer counted Refractive Thickness starting from the substrate/ Material index of the of the layer Layer reference (illustration) of the layer layer (±3 nm) 1/(19) SiO.sub.2 1.4658 150 nm 2/(18) ZrO.sub.2 2.0038 20 nm 3/(17) SiO.sub.2 1.4741 20 nm 4/(16) ZrO.sub.2 2.0038 100 nm 5/(15) SnO.sub.2 1.8432 6 nm 6/(14) SiO.sub.2 1.4741 75 nm

(56) This embodiment of the method according to the invention, under the operating conditions of example 1 and in the same way as example 2, creates a pattern on the surface of the ophthalmic lens by local ablation of the exterior SiO.sub.2 layer 14, of the layers 13, 12 and 11, which are outside the exterior SiO.sub.2 layer 14, and an at least partial ablation of the interior layer 15, which is made of SnO.sub.2, which is the interior layer ablated by the electromagnetic beam. In this marking spot (P), the value of the reflectance (Rm) measured in the ablated zone is about 10%, or more precisely between 9.5% and 10.5% depending on the samples, i.e. about 12 times more than Re.