Protective Coating For A Complex Watch Component
20210222297 · 2021-07-22
Inventors
- Cyriaque Boccard (Douvaine, FR)
- Xavier Multone (Lausanne, CH)
- Pierre Di Luna (Douvaine, FR)
- Alexandra Roulet (Petit-Lancy, CH)
Cpc classification
G04B37/22
PHYSICS
International classification
C23C16/455
CHEMISTRY; METALLURGY
Abstract
Provided is a method for protecting a complex watch component against gaseous environment, characterized in that the entire surface of the complex watch component or parts of said surface is/are coated with a protective coating, which is not visible by observation with the naked eye, by atomic layer deposition (ALD). Further provided are a method for obtaining a complex watch component, and a complex watch component comprising a protective ALD coating.
Claims
1. A method for protecting a complex watch component against gaseous environment, wherein an entire surface of the complex watch component or parts of the surface is/are coated by atomic layer deposition (ALD) with a protective coating, wherein the complex watch component comprises at least two parts made of different materials and comprises a watch dial.
2. A method for manufacturing a complex watch component, wherein the complex watch component comprises at least two parts made of different materials and comprises a watch dial, the method comprising conducting steps for manufacturing the complex watch component, wherein a protective coating is applied to an entire surface or parts of the surface of the thus-obtained complex watch component by atomic layer deposition (ALD).
3. The method according to claim 1, wherein the watch component comprises a finished watch dial.
4. The method according to claim 1, wherein the protective coating is not visible by observation with the naked eye.
5. The method according to claim 1, wherein a color change ΔELab between the complex watch component before ALD coating and the ALD-coated complex watch component is lower than 4.
6. The method according to claim 1, wherein the complex watch component is intended for after sales service and/or long-term storage.
7. The method of claim 1, wherein the ALD coating comprises one layer, or two or more layers which may be identical or different, selected from metal oxide, metal nitride, metal oxycarbonitride, metal carbonitride, and metal sulfide layers.
8. The method of claim 1, wherein the ALD coating comprises one metal oxide layer, or two or more identical or different metal oxide layers.
9. The method of claim 8 wherein the one metal oxide layer, or two or more identical or different metal oxide layers are selected from Al.sub.2O.sub.3, TiO.sub.2, Ta.sub.2O.sub.5 layers and/or a combination of layers of Al.sub.2O.sub.3 and TiO.sub.2.
10. The method according to claim 1, wherein the gaseous environment comprises at least one of water vapor, oxygen and sulfur-containing compounds.
11. The method according to claim 1, wherein thickness of the ALD coating is at least one atomic monolayer to 100 nm.
12. A complex watch component, wherein an entire surface of the complex watch component or parts of said surface is/are coated with a protective coating formed by atomic layer deposition (ALD), the complex watch component being obtainable by a process according to the method of claim 1, wherein the complex watch component comprises at least two parts made of different materials and comprises a watch dial.
13. The method according to claim 2, wherein the protective coating is applied either prior to or after applying a conventional coating.
14. The method according to claim 2, wherein the watch component is a finished watch dial.
15. The method according to claim 2, wherein the protective coating is not visible by observation with the naked eye.
16. The method according to claim 2, wherein a color change ΔELab between the complex watch component before ALD coating and the ALD-coated complex watch component is lower than 4.
17. The method of claim 2, wherein the ALD coating comprises one layer, or two or more layers which may be identical or different, selected from metal oxide, metal nitride, metal oxycarbonitride, metal carbonitride, and metal sulfide layers.
18. The method of claim 2, wherein the ALD coating comprises one metal oxide layer, or two or more identical or different metal oxide layers.
19. The method of claim 18 wherein the one metal oxide layer, or the two or more identical or different metal oxide layers are selected from Al.sub.2O.sub.3, TiO.sub.2, Ta.sub.2O.sub.5 layers and/or a combination of layers of Al.sub.2O.sub.3 and TiO.sub.2.
20. The method according to claim 2, wherein thickness of the ALD coating is at least one atomic monolayer to 100 nm.
21. The method of claim 1, wherein the at least two parts wherein the surface of the complex watch component or of parts of said surface comprises protruding and/or recessing parts.
22. The method of claim 3, wherein the watch component further comprises ink markings.
23. The method of claim 22, wherein the watch component further comprises metallic indexes.
24. The method of claim 1, wherein the watch dial comprises a visible side, back side and a dial feet and wherein the entire surface thereof is covered by the ALD coating.
25. The method of claim 1, wherein the ALD coating is made from TiO.sub.2, Ta.sub.2O.sub.5, or Al.sub.2O.sub.3/TiO.sub.2.
26. The method of claim 1, wherein the watch dial comprises the ALD coating and a varnish coating.
27. The method of claim 14, wherein the watch component further comprises ink markings.
28. The method of claim 27, wherein the watch component further comprises metallic indexes.
29. The method of claim 2, wherein the watch dial comprises a visible side, back side and a dial feet and wherein the entire surface thereof is covered by the ALD coating.
30. The method of claim 2, wherein the ALD coating is made from TiO.sub.2, Ta.sub.2O.sub.5, or Al.sub.2O.sub.3/TiO.sub.2.
31. The method of claim 2, wherein the watch dial comprises the ALD coating and a varnish coating.
Description
FIGURES
[0040]
[0041]
[0042]
[0043]
[0044]
DETAILED DESCRIPTION OF THE INVENTION
[0045] d
[0046] A complex watch component according to the invention can be any complex watch component which comprises at least two components or two parts made of different materials. That is, a complex watch component does not mean a monomaterial component. In particular it is a complex watch component which is intended for after sales service or long-term storage as a complete assembled part made of at least two components of different materials, as for example a finished watch dial with metallic indexes and ink markings or a finished watch dial with ink markings.
[0047] The ALD coatings of the invention have very low or no impact on the visible side' dial's aesthetic and will cover the complete dial, including the visible side with its decoration, drills, indexes, but also the back side and the dial feet.
[0048] Contrary to the conventional protection of watch components by bags or blisters, the gas barrier provided by the ALD coating of the invention allows a stable and sustainable protection against water vapor, oxygen and other gases.
[0049] “After sales service” of this kind of complex watch components means that a new complete complex component will be provided to repair service facilities or repair shops for repairing watches by replacing the deteriorated complete complex component. This is the case for dials, hands and winding crowns for example.
[0050] “Long-term” means up to 50 years, preferably at least 40 years, more preferably at least 30 years from the date of manufacturing the watch component.
[0051] In particular and preferably the watch component in this invention is a finished complete watch dial generally comprising a base plate of any geometric form suitable for a watch, i.e. circular, oval, rectangular, square, triangle, preferably circular, covered with any kind of decorative layer such as paint, lacquer, enamel, polymeric or metallic layer deposited by any known technique. It can also be covered with natural stone or other layers or coatings from a suitable material. It is optionally and preferably provided with numbers and/or indices/graduations marking the hours and/or minutes. It may comprise auxiliary dials for stopwatch, timer, second time zone, date etc. Further, the dial may comprise decorative elements such as, for example, inscriptions, engravings, precious stones such as diamonds, sapphires, emeralds, rubies and/or other precious stones. Numbers and/or indexes provided on the dial may be phosphorescent or fluorescent and/or photoluminescent by means of a corresponding layer provided on the surface of the number and or index.
[0052] The dial may be made of any material suitable for watch dials, such as technical fine ceramics, mother of pearl, stone, wood, carbon fibers, metal or metal alloys such as stainless steel, brass, nickel silver (German silver), bronze, precious metals such as silver, gold, platinum, any alloys thereof, silicon or high performance composite materials, for instance polymeric matrixes reinforced with any kind of fiber (glass, aramide, carbon).
[0053] The dial may be galvanized or covered with metal by electroplating for providing specific color impressions. For example, electroplated nickel, gold, silver, gold and copper layers can be provided on the dial, either alone or several different metal layers on top of each other. The dial may have two or areas of different colorings and/or may be formed of different materials.
[0054] The dial can be coated with a conventional coating such as Zapon, which is usually used in watch industry and which can give color depth to specific surfaces. The process of the invention can be applied to dials coated with such a conventional coating such as Zapon, or coated with any other conventional coating of that type known from the state of the art.
[0055] Zapon coating is a clear transparent coating (which may be colored, but mostly is colorless) commonly used for dials. Zapon coating is a liquid transparent acrylic varnish in volatile solvents. Zapon coating is commonly used for corrosion protection of metals such as brass or silver.
[0056] Moreover, a Zapon coating (or a comparable transparent coating) can be applied, as desired, after applying the ALD coating according to the invention in order to obtain a certain aesthetic effect such as deepening of the color.
[0057] A dial coated by conventional PVD, e.g. with an alumina coating, can also be additionally provided with a protective ALD coating of the invention, if desired.
[0058] Of course, the complex component, in particular the dial, can be made by any technique known from the state of the art.
[0059] Preferably all the surfaces of the complex component (such as the dial), i.e. the entire surface of the watch component, will be coated by the ALD coating according to the invention. In particular front side, back side, sides, holes, drills, as well as all protruding and/or recessing parts, including decorative elements, inscriptions, indices, numbers, marks, engravings, if present, are covered by the ALD coating according to the invention.
[0060] However, with common masking techniques the ALD coating can be limited to some areas only. This embodiment is also within the scope of the invention.
[0061] Other complex watch components of the invention are hands, movement blanks, crowns and the like.
[0062] According to the invention, a complete complex watch component to be protected by the ALD coating is first manufactured in a usual way well-known to the skilled person. Thereafter, the desired protective coating is applied on the complete complex finished watch component by means of ALD, or on parts thereof using conventional masking techniques. The ALD is carried out in a known manner by using process conditions well known by the skilled person. The process conditions and precursors are selected from conventionally known ones according to the layer to be provided.
[0063] Any commercially available ALD device can be used according to the invention. The processing temperature is usually from 30 to 500° C. The cycle time can be controlled according to need and is down to 1 second, which is the smallest time unit which can be controlled precisely in usual ALD apparatus. The precursors may be liquid, solid, or gaseous according to the ALD device manufacturer.
[0064] Layers of Al.sub.2O.sub.3 and/or SiO.sub.2 and/or Ta.sub.2O.sub.5 and/or HfO.sub.2 and/or ZnO and/or TiO.sub.2 and/or ZrO.sub.2 and/or AlN and/or TaN and/or TiN can be made according to the invention using this device. Preferably, layers of aluminum oxide (alumina, Al.sub.2O.sub.3), titanium oxide (TiO.sub.2), tantalum oxide (Ta.sub.2O.sub.5) and/or alternating nanolaminated layers of aluminum oxide and titanium oxide (Al.sub.2O.sub.3/TiO.sub.2) can be deposited onto the complete watch component according to the invention.
[0065] Indeed, it is possible to combine different layers to achieve the protective effect. By different layers, we mean layers of different chemical natures, different densities, and/or different reflection indices. By different stacking of these different layers, with different individual thicknesses, it results in a multitude of so-called nanolaminated coatings possibilities.
[0066] The following precursors and temperatures of the precursors are preferably employed according to the invention: [0067] TMA (trimethylaluminum) introduced at ambient temperature, [0068] TDMATi (tetradimethylaminotitanium) introduced at 73 to 80° C., [0069] TBTEMTa (tert-butylimido)tris(ethylmethylamido)tantalum) introduced at 90 to 100° C., [0070] TiCl.sub.4 (titaniumtetrachloride) introduced at ambient temperature.
[0071] Precursor's temperature is chosen between a minimal temperature that will ensure vaporization of the precursor and a maximal temperature above which the precursor is degraded.
[0072] The chamber's temperature, and consequently the substrate's temperature and the deposition's temperature, is preferably chosen between 120° C. and 200° C., preferably at 150° C., and maintained during all the process. If chamber's temperature is too low, the precursor gas will condense. If it is too high we quit the ALD regime for CVD, the reaction could occur in the chamber and not on the substrates' surface anymore, and there will be no more self-limitation of the reaction to one monolayer.
[0073] The technical lower limit for ALD layer thickness is one monolayer of the molecule AB. For the ALD coating of one embodiment of the invention, the coating has an OTR (oxygen transmission rate) smaller or equal to that of conventional Zapon coating, which is around 56 cm.sup.3/(m.sup.2 24 h).
[0074] The upper limit, to remain in the perimeter of the application, which requires the protective coating to be imperceptible to the eye, depends on the exact configuration of the coated component. It will also depend on the color, topography and roughness of the watch component to be coated, and on the chemical nature and stacking of the ALD individual layers constituting the coating.
[0075] Preferably, a coating thickness of 100 nm should not be exceeded in order to avoid a visible color change of the surface caused by the ALD coating. Preferably, the thickness of the ALD coating formed according to the invention is 95 nm or below, more preferably 60 nm or below, even more preferably 50 nm or below. It may even be 1 nm or monomolecular. However, generally 5 nm is appropriate as lower limit of the coating thickness, being sufficient to start to protect the substrate, and 100 nm is appropriate as higher limit as a thicker coating will not improve much the result. Thicker coatings could be designed, as long as they fulfill the criteria of not modifying the initial aspect of the substrate.
[0076] Coating thickness means overall thickness of the ALD coating deposited on the complex watch component. Layer thickness means thickness of a single compound layer; in case of a regular alternation of sub-layers having a different composition, layer thickness may also mean the thickness of the layer presenting this regular alternation. The coating's thickness is determined by ellipsometry as described below. The thicknesses of layers stacked to constitute a coating have to be determined by TEM observations.
[0077] In case of a coating made of multiple ALD layers, the thickness of each layer may be the same or different according to the invention.
[0078] In case of alternating ALD layers, such as e.g. alternating titanium oxide and alumina, the number of single alternating layers is basically not important. It is preferably 1 to 10, more preferably 5 to 8.
[0079] The coating time is usually 0.1 to 380 min, but it is selected according to the desired coating thickness.
Examples
[0080] All coatings of the examples have been deposited in a PICOSUN® P-300B ALD or in a R200 Advanced ALD device, at a temperature of 150° C., using TMA (introduced at ambient temperature), TDMATi (introduced at 80° C.), TBTEMTa (introduced at 90° C.) and TiCl.sub.4 (introduced at ambient temperature), as precursors at the respective precursor temperatures. The conditions of ALD deposition and description of the coatings are summarized in Table 1.
[0081] Each sample is related to a specific deposition run and identified with a sample number if substrate is a polyimide film. Due to the encapsulating nature of the ALD technique, polyimide films coated for OTR and WVTR measurements are coated on both sides. Some runs were conducted on folded polyimide film glued together with adhesive tape, so as to measure properties corresponding to the layer's thickness that would be deposited on a dial. OTR and WVTR were measured on the unfolded film, and these samples are identified with “−1”.
TABLE-US-00001 TABLE 1 run conditions and sample description Coating Time Pre- Pre- thick- (indic- Run Layer cursor cursor Nr ness Sample ative) Nr type 1 2 cycles [nm] Nr [min] 1 Al.sub.2O.sub.3 TMA H.sub.2O 200 23 1 60 2 Al.sub.2O.sub.3 TMA H.sub.2O 500 57 2 150 3 TiO.sub.2 TDMATi H.sub.2O 444 24 3 150 4 TiO.sub.2 TDMATi H.sub.2O 1111 54 D, 4 360 5 Ta.sub.2O.sub.5 TBTEMTa H.sub.2O 600 59 5 200 6 Ta.sub.2O.sub.5 TBTEMTa H.sub.2O 1 0 6-1 0.3 (1 ML) 7 Ta.sub.2O.sub.5 TBTEMTa H.sub.2O 11 1 7, 7-1 3.6 8 Ta.sub.2O.sub.5 TBTEMTa H.sub.2O 16 1.5 8-1 5.3 9 Ta.sub.2O.sub.5 TBTEMTa H.sub.2O 32 3 9 11 10 Ta.sub.2O.sub.5 TBTEMTa H.sub.2O 54 5 10 18 11 Ta.sub.2O.sub.5 TBTEMTa H.sub.2O 106 10 11 35 12 Ta.sub.2O.sub.5 TBTEMTa H.sub.2O 213 22 12 71 13 Ta.sub.2O.sub.5 TBTEMTa H.sub.2O 320 32 13 107 14 Ta.sub.2O.sub.5 TBTEMTa H.sub.2O 1052 97 14-1 350 15 Al.sub.2O.sub.3/ TMA/ H.sub.2O/ 2•(50 + 23 15 90 TiO.sub.2 TDMATi H.sub.2O 111) 16 Al.sub.2O.sub.3/ TMA/ H.sub.2O/ 5•(50 + 58 D1, 16 240 TiO.sub.2 TDMATi H.sub.2O 111) 17 Al.sub.2O.sub.3/ TMA/TiCl.sub.4 H.sub.2O/ 8•(50 + 95 D2, 380* TiO.sub.2 H.sub.2O 111) D2Z, 17 *= not measured; calculated based on previous data of other experiments ML = monolayer
[0082] Coating thickness has been measured by ellipsometry. The equipment is a Semilab® S-2000. The measurements are performed in ultra-violet, visible and near infra-red wavelengths. The integration time is 5 seconds and the incidence angle is 70°. The measurement type is PsiDelta.
[0083] Transmission Electron Microscopy (TEM) has been carried out in a Titan® 80-300, FEI, to perform bright field images at 300 kV, with a diaphragm objective of 40 μm. The samples have been prepared with a Focused Ion Beam (FIB) Strata® 400, FEI. Thicknesses of some coatings have also been measured on these images, as well as the control of their conformal characteristics.
[0084] When permeation measurements are performed, the ALD coatings are deposited on polyimide film. As coating can be present on one or both sides of the polyimide film, the tested thickness of the ALD coating is specifically mentioned in the results.
[0085] In the first embodiment, two materials are deposited alternatively in a nanolaminated structured layer. Brass dials, previously coated with metallic layers by electroplating in a conventional manner, and polyimide films have been coated with an ALD coating made of an alternation of Al.sub.2O.sub.3 and TiO.sub.2 layers, from precursors TMA/TiCl.sub.4+H.sub.2O/H.sub.2O at a deposition temperature of 150° C.
[0086] In the first variant, sample D1, a finished brass dial coated with metal layers and showing a pink color, has been coated with five alternations of Al.sub.2O.sub.3 and TiO.sub.2 layers (Run 16 of Table 1). Coating thickness is 58 nm. A TEM image of a FIB prepared cross-section of sample D1 is shown in
[0087] In a second variant, samples D2 and D2Z, two brass dials with a silver electroplated layer, have been coated by ALD, with a similar layer structure (defined by the nature of the layers in alternation, as well as their individual thicknesses) as in the first variant, but of a total thickness of 95 nm, with eight alternations of Al.sub.2O.sub.3 and TiO.sub.2 instead of five (Run 17 of Table 1).
[0088] The color change between such silver-plated brass dials with no coating, with only Zapon coating, with only ALD coating (sample D2) and with both ALD and Zapon coating (sample D2Z) has been measured by spectrocolorimetry (specular reflection included) and is expressed in the CIELab reference space. The equipment is a Minolta® CM-3610d, with lightening with standard day light D65, observation angle at 10°, and diaphragm diameter of 7 mm.
TABLE-US-00002 TABLE 2 color change on dials. Description Coating of the thickness Designation layers [nm] L* a* b* ΔELab Ag dial none 0 99.4 −0.3 2.7 Reference Z Zapon 8000 97.5 −0.8 10.0 7.6 D2 Al.sub.2O.sub.3/TiO.sub.2 95 97.7 −0.8 4.2 2.3 D2Z Al.sub.2O.sub.3/ 95 + 8000 96.2 −0.3 5.1 4.0 TiO.sub.2 + Zapon
[0089] Color changes are considered to be invisible to the human eye under a value ΔELab of 1. If both parts are directly compared, color changes ΔELab between 1 and 4 can be detected. For a ΔELab above 4, color change is perceptible even if parts are observed successively. In comparison to Zapon, the ALD coating only modifies little the perception of the base color. It even lowers the color change of a dial with Zapon if applied before the Zapon layer.
[0090] In order to verify the protective effect of this coating, an exposition to sulfur vapor has been conducted on dials, coated with only Zapon (traditional process, sample Z) or with an ALD nanolaminated layer Al.sub.2O.sub.3/TiO.sub.2 deposited according to run 17 previously to the Zapon layer (sample D2Z). The dials are exposed to 1 g of sulfur in an atmosphere with 95% of relative humidity, at 30° C. Exposition time can be from 1 day to 5 days. The results of the test are shown in
[0091] It can be observed that the back and side of the dial coated with Zapon (sample Z) only on the upper surface are degraded by the sulfur in the test. To the contrary, as the ALD coating covers all surfaces, the back and the sides of the ALD+Zapon dial of the invention (sample D2Z) are perfectly clean and preserved after the test.
[0092] The dial D2Z is perfectly protected from the sulfur vapor by the ALD coating, on all surfaces. The coating is overall and follows perfectly the surface of the substrate. It allows a complete encapsulation of the part.
[0093] Reading these results, the ALD coating could advantageously replace the Zapon in a protective point of view.
[0094] Nevertheless, as Zapon offers the aesthetic advantage to give depth to some decor of the dial, the ALD coating can be applied in addition to Zapon; in practice, it can be deposited before or after the Zapon. Process and nature of the ALD coating are compatible with such a polymeric layer.
[0095] This means that already stored dials coated by conventional Zapon can be treated by the ALD technique according to the invention, and no specific preparation is needed.
[0096] Complementary experiments have been performed to show the correlation between the results of resistance to sulfuration obtained on dials and permeability measurements performed on polyimide films coated with the same coating. These tests have allowed to define the thickness limits to be an efficient gas-barrier with no coloration induced.
[0097] Oxygen Transmission Rate (OTR) and Water Vapor Transmission Rate (WVTR) are the two values used for the evaluation of the results. They will allow easy and quantitative comparison of different chemical natures and different structures of coatings, as well as different thicknesses of the ALD coatings tested.
[0098] OTR has been measured with a Mocon Oxtran® model 2/61 equipment. The measurement area is 10 cm.sup.2, the temperature 23° C., the humidity 50%, the N.sub.2 flux 10 sccm (standard cubic centimeters per minute), the O.sub.2 flux 50 sccm, the oxygen partial pressure 10.sup.5 Pa. A measurement is performed during 30 minutes, every 5 hours, until stabilization.
[0099] WVTR has been measured in a Systech® 7001 equipment. The measurement area is 50 cm.sup.2, the temperature 23° C., the humidity 50%, the N.sub.2 flux 10 sccm, the N.sub.2 humid flux 20 sccm. A measurement is performed every 30 minutes.
[0100] A polyimide film of Kapton-HN® 75 micrometer thick (manufactured by DuPont®) has been used as a substrate for the measurements of permeation. This kind of film is permeable to water vapor and oxygen, as shown in the table below. The conventional Zapon coating is also permeable to oxygen, and to water vapor in a limited manner.
[0101] Polyimide films have been coated by ALD with same runs as dials (samples D1 and D2/D2Z), resulting in samples 15 and 16. As ALD is an encapsulation technique, these samples present a global thickness of the ALD deposited material that is twice the thickness of the coating on the dial's visible face, as the coating is present on both sides of the film. The test results are expressed in Transmission Rate in [cm.sup.3/(m.sup.2 24 h)] for OTR and in [g/(m.sup.2 24 h)] for WVTR and summarized in Table 3 and shown also in
TABLE-US-00003 TABLE 3 Transmission Rate results for alternate Al.sub.2O.sub.3/TiO.sub.2 type coatings. Coating structure and Coating OTR WVTR chemical thickness [cm.sup.3/ [g/ Designation nature [nm] (m.sup.2 24 h)] (m.sup.2 24 h)] Kapton-HN ® none 75'000 58 ± 2 4.3 Zapon Zapon 8000 57 ± 2 3.5 15 Al.sub.2O.sub.3/TiO.sub.2 46 (2 × 23) 0.73 0.054 16 Al.sub.2O.sub.3/TiO.sub.2 116 (2 × 58) <detection 0.042 limit
[0102] Other kinds of ALD coatings can fulfill the same function with the same or even better efficiency. It is possible to combine different layers to achieve the same protective effect. Different layers mean different chemical natures, different densities, different reflection indexes. Layers of different thicknesses can be included in the final coating. By a combination of these different layers, with different thicknesses and stackings, a multitude of nanolaminated coatings possibilities can be obtained.
[0103] As OTR and WVTR are measurable values, all tested coatings, including Al.sub.2O.sub.3/TiO.sub.2, have been applied on polyimide films in order to quantify the real permeability of the coating.
[0104] A polyimide sheet of Kapton-HN® 75 micrometer thick (manufactured by DuPont) has been used as a substrate for these measurements of permeation, as in the above-described samples. The measurements have been carried out as described above.
[0105] If not specified, runs have been performed on single Kapton-HN® sheets. In Runs 6, 7, 8 and 14, folded Kapton-HN® sheets have been coated in order to allow measurement of thinner ALD coatings by unfolding the polyimide film to have samples with only one coated side for the OTR/WVTR measurements.
[0106] A 160 nm thick PVD-MS (Physical Vapor Deposition Magnetron Sputtering) coating of Al.sub.2O.sub.3 and a 8 micrometer-thick Zapon coating have also been tested as comparison values.
Pure Al.sub.2O.sub.3 Coating
[0107] In a first variant of the second embodiment, pure Al.sub.2O.sub.3 coatings are deposited by ALD from TMA and H.sub.2O precursors, injected alternatively. 200 cycles (Run 1) allow a thickness of 23 nanometers to be built, 500 cycles (Run 2) lead to a 57 nanometers thick layer, perfectly compact and conform to the surface of the sample.
[0108] Permeation measurements carried out as described above confirm the tightness of the layer against oxygen and water vapor, with OTR and WVTR values detailed in Table 4 and shown also in
TABLE-US-00004 TABLE 4 Transmission Rate with an Al.sub.2O.sub.3 coating. OTR WVTR Chemical Thickness [cm.sup.3/ [g/ Designation nature [nm] (m.sup.2 24 h)] (m.sup.2 24 h)] Kapton-HN ® none 75000 58 ± 2 4.3 Zapon Zapon 8000 57 ± 2 3.5 Al.sub.2O.sub.3 PVD-MS Al.sub.2O.sub.3 160 8.7 0.3 1 Al.sub.2O.sub.3 46 (2 × 23) 1.03 0.039 2 Al.sub.2O.sub.3 114 (2 × 57) 0.79 0.047
[0109] It is apparent here that the ALD technique is more efficient than the PVD technique to deposit coatings with good tightness characteristics. The advantage of ALD over PVD is that the layer is conformal to the surface and no pin-holes are created. The ALD also allows to obtain conformal coating whereas special implementation and specific sample holders are needed to perform a 3D coating by PVD. With such a technical adaptation of the equipment and fitting of coating thickness, PVD could reach comparable results but with extra costs and a complicated process.
Pure TiO.SUB.2 .Coating
[0110] In a second variant of the second embodiment, pure TiO.sub.2 coatings are deposited by ALD from TDMATi and H.sub.2O precursors, injected alternatively. 444 cycles (Run 3) allow a thickness of 24 nanometers to be built, 1111 cycles (Run 4) lead to a 54 nanometers thick layer, perfectly compact and conform to the surface of the dial, as it can be observed on the TEM image shown in
[0111] Permeation measurements confirm the tightness level of the layer against oxygen and water vapor, with OTR and WVTR values (measured as described above) and detailed in Table 5 and shown also in
TABLE-US-00005 TABLE 5 Transmission Rate with a TiO.sub.2 coating. OTR WVTR Chemical Thickness [cm.sup.3/ [g/ Designation nature [nm] (m.sup.2 24 h)] (m.sup.2 24 h)] Kapton-HN ® none 75000 58 ± 2 4.3 Zapon Zapon 8000 57 ± 2 3.5 3 TiO.sub.2 48 (2 × 24) 1.05 0.058 4 TiO.sub.2 108 (2 × 54) 0.71 0.035
Pure Ta.sub.2O.sub.5 Coating
[0112] In a third variant of the second embodiment, pure Ta.sub.2O.sub.5 coatings are deposited by ALD from TBTEMTa and H.sub.2O precursors, injected alternatively (Runs Nr 5 to 13). The relation between cycle number, thickness and results is shown in Table 6, and variations of OTR/WVTR are detailed in
[0113] The tightness level of the Ta.sub.2O.sub.5 coating against oxygen and water vapor is confirmed even for very thin layers, starting at about 6 nm of Ta.sub.2O.sub.5.
TABLE-US-00006 TABLE 6 Transmission Rate with a Ta.sub.2O.sub.5 coating. OTR WVTR Chemical Thickness [cm.sup.3/ [g/(m.sup.2 Designation nature [nm] (m.sup.2 24 h)] 24 h)] Kapton-HN ® None 75'000 58 ± 2 4.3 Zapon Zapon 8'000 57 ± 2 3.5 6-1 Ta.sub.2O.sub.5 0 (1 ML) 59.7 * 7-1 Ta.sub.2O.sub.5 1 59.4 * 8-1 Ta.sub.2O.sub.5 1.5 ~60.6 * 9 Ta.sub.2O.sub.5 6 (2 × 3) 39.2 * 10 Ta.sub.2O.sub.5 10 (2 × 5) 3.9 * 11 Ta.sub.2O.sub.5 20 (2 × 10) 1.2 * 12 Ta.sub.2O.sub.5 44 (2 × 22) 0.7 0.08 13 Ta.sub.2O.sub.5 64 (2 × 32) 0.5 * 14-1 Ta.sub.2O.sub.5 97 0.4 * 5 Ta.sub.2O.sub.5 118 (2 × 59) <detection 0.04 limit * = not determined ML = Monolayer
[0114] Results on samples 6-1, 7-1, 8-1 and 14-1 have been obtained on single side coated polyimide sheets. The film is folded and the sides are assembled together with adhesive tape (Kapton® Polyimid-Film—Type 300 HN, 0.075 mm thick) before the ALD coating. The film is then unfolded and only one half, with a single side coated, is used for the OTR measurement. All other results have been obtained on double side coated polyimide sheets.
[0115] These more detailed values show that the minimal thickness to observe a protective effect is 5 nm, preferably 6 nm, preferably 10 nm, depending on the coating's nature. For any kind of the ALD coatings tested, the protective effect can be considered as complete from 50 nm and above. As color change will increase as the thickness of the coating increases, by interferential effect, usually such protective coatings don't go over 100 nm thick. The only upper limit here is the tolerance to color change, which will concretely be depending on the nature and color of the substrate. For our application and so as to keep as close as possible to the initial dial color, ALD coatings are limited to 100 nm to avoid average color change ΔELab going over a value of 4.