ITEM COMPRISING AN ORGANIC-INORGANIC LAYER WITH A LOW REFRACTIVE INDEX

Abstract

The invention relates to an article comprising a substrate having at least one main surface coated with a layer L of a material M obtained by vacuum deposition, by co-evaporation, of at least one metallic compound A chosen from alkaline-earth metal fluorides and of at least one organic compound B, the material M having a refractive index at the wavelength of 632.8 nm ranging from 1.38 to 1.47. According to the invention: the organic compound B comprises an organosilicon compound or a mixture of organosilicon compounds; and the deposition of the compound B, in gaseous form, is carried out in the presence of an ion bombardment.

Claims

1. An article comprising a substrate having at least one main surface coated with at least one layer L of at least one material M obtained by vacuum deposition, by co-evaporation, of at least one metallic compound A chosen from alkaline-earth metal fluorides and of at least one organic compound B, the material M having a refractive index at the wavelength of 632.8 nm ranging from 1.38 to 1.47, wherein: the organic compound B comprises an organosilicon compound or a mixture of organosilicon compounds; and the deposition of the compound B, in gaseous form, is carried out in the presence of an ion bombardment.

2. The article as claimed in claim 1, wherein that the organic compound B does not comprise any fluorocarbon.

3. The article as claimed in claim 1, wherein the ion bombardment is carried out using an ion gun.

4. The article as claimed in claim 1, wherein the deposition of the organosilicon compound B under ion bombardment is carried out in the presence of a gas chosen from oxygen, noble gases, nitrogen and a mixture of two or more of these gases.

5. The article as claimed in claim 1, wherein the evaporation of the metallic compound A is carried out using an electron gun.

6. The article as claimed in claim 1, wherein the metallic compound A is MgF.sub.2.

7. The article as claimed in claim 1, wherein the organosilicon compound B comprises at least one SiC bond.

8. The article as claimed in claim 1, wherein the organosilicon compound B comprises at least one divalent group of formula: ##STR00006## where R.sup.1 to R.sup.4 independently denote alkyl, vinyl, aryl or hydroxyl groups or hydrolysable groups, or in that the compound B corresponds to the formula: ##STR00007## in which R.sup.5, R.sup.6, R.sup.7 and R.sup.8 independently denote hydroxyl groups or hydrolysable groups, such as OR groups, in which R is an alkyl group.

9. The article as claimed in claim 1, wherein the compound B is chosen from octamethylcyclotetrasiloxane, 2,4,6,8-tetramethylcyclotetrasiloxane, decamethyltetrasiloxane, decamethylcyclopentasiloxane, dodecamethylpentasiloxane or hexamethyldisiloxane.

10. The article as claimed in claim 1, wherein the silicon atom or atoms of the organosilicon compound B do not comprise any hydrolysable group or hydroxyl group.

11. The article as claimed in claim 1, wherein the layer L constitutes at least one layer of a multilayer interference coating.

12. The article as claimed in claim 11, wherein the layer L constitutes the layer of the interference coating furthest from the substrate and wherein a thin organic-inorganic layer is deposited on said layer L, said organic-inorganic layer with a thickness of 1 to 20 nm having been obtained by deposition of an organosilicon compound or a mixture of organosilicon compounds in gaseous form, in the presence of an ion bombardment and in the absence of a mineral precursor.

13. The article as claimed in claim 11, wherein the interference coating is an antireflective coating.

14. The article as claimed in claim 1, further defined as an optical lens.

15. The article as claimed in claim 1, wherein it possesses a critical temperature greater than or equal to 70 C.

16. A process for the manufacture of an article as claimed in claim 1, comprising at least the following steps: supplying an article comprising a substrate having at least one main surface, depositing, on said main surface of the substrate, a layer L of a material M having a refractive index ranging from 1.38 to 1.47 at the wavelength of 632.8 nm, and recovering an article comprising a substrate having a main surface coated with a layer L, said layer L having been obtained by deposition, by co-evaporation, of at least one metallic compound A chosen from alkaline-earth metal fluorides and of at least one organosilicon compound B, the deposition of the organosilicon compound B, in gaseous form, being carried out in the presence of an ion bombardment.

17. The article as claimed in claim 14, wherein the optical lens is an ophthalmic lens.

Description

EXAMPLES

s1. General Procedures

[0124] The articles employed in the examples comprise an Orma Essilor lens substrate with a diameter of 65 mm, with a power of 2.00 dioptres and with a thickness of 1.2 mm, coated on its concave face with the impact-resistant primer coating and with the abrasion-resistant and scratch-resistant coating (hard coat), which are disclosed in the experimental section of the application WO-2010/109154, and a layer L according to the invention.

[0125] In example 4 and comparative example no. 2, the above articles are additionally coated with an antireflective coating comprising, in order, starting from the abrasion-resistant and scratch-resistant coating, a ZrO.sub.2 layer (30 nm), an SiO.sub.2 layer (30 nm), a ZrO.sub.2 layer (70 nm) and an ITO layer (5 nm), the layer L or an MgF.sub.2 layer being deposited directly on the ITO layer, a thin organic-inorganic layer optionally being deposited on the layer L.

[0126] The vacuum deposition reactor is a Leybold LH1100+ machine equipped with an electron gun for the evaporation of the precursor materials, with a thermal evaporator, with a KRI EH 1000 F ion gun (from Kaufman & Robinson Inc.), for the preliminary phase of optional preparation of the surface of the substrate by argon ions (IPC) and also for the deposition of the layer L under ion bombardment (IAD), and with a system for the introduction of vapor, which system is used when the precursor compound of the layer L is a liquid under standard temperature and pressure conditions (case of DMTS). This system comprises a tank containing the liquid precursor compound of the layer L, resistive heaters for heating the reservoir, and tubes connecting the reservoir of liquid precursor to the vacuum deposition machine, and a vapor flowmeter from MKS (MKS1150C).

[0127] The DMTS vapor exits from a copper pipe inside the machine, at a distance of about 30 cm from the ion gun. Flows of oxygen and/or argon and/or nitrogen are introduced into the ion gun.

[0128] The layers L according to the invention are formed by ion-beam-assisted vacuum evaporation during the deposition (evaporation source: electron gun) of decamethyltetrasiloxane, supplied by Sigma-Aldrich and of a magnesium fluoride.

[0129] The optional thin organic-inorganic layer is also formed by ion-beam-assisted vacuum evaporation during the deposition of decamethyltetrasiloxane.

[0130] Unless otherwise indicated, the thicknesses mentioned are physical thicknesses. Several samples of each lens were prepared.

2. Procedures

[0131] The process for the preparation of the optical articles coated with a layer L according to the invention comprises the introduction of the substrate, coated with the primer coating and with the abrasion-resistant coating (substrate no. 1) and optionally with the antireflective coating (substrate no. 2) which are defined above, into the vacuum deposition chamber; the preheating of the tank, the pipes and the vapor flowmeter to the chosen temperature (15 min), a primary pumping stage, then a secondary pumping stage for 400 seconds making it possible to obtain a high vacuum (210.sup.5 mbar, pressure read from a Bayard-Alpert gauge), an optional stage of activation of the surface of the substrate by a beam of argon ions (IPC: 1 minute, 100 V, 1 A, the ion gun remaining in operation at the end of this stage) and then the deposition by evaporation of the layer L, carried out in the following way.

[0132] Since the ion gun was started with argon, oxygen and/or nitrogen are/is added to the ion gun with a programmed flow rate, the desired anode current (2-3 A) is programmed and the argon flow is optionally halted, depending on the deposition conditions desired.

[0133] The magnesium fluoride is preheated so as to be in a molten state and then evaporated using an electron gun, the shutter of the ion gun and that of the electron gun being opened simultaneously. At the same time, the DMTS compound is introduced into the chamber in gaseous form, at a controlled flow rate or partial pressure.

[0134] A thin organic-inorganic layer is deposited under similar conditions, but without co-evaporation of MgF.sub.2.

[0135] The thickness of the layers deposited was controlled in real time by means of a quartz microbalance, the rate of deposition being modified, if need be, by adjusting the current of the electron gun. Once the desired thickness has been obtained, the two shutters are closed, the ion and electron guns are switched off and the gas flows (oxygen, nitrogen, optionally argon and DMTS vapors) are halted.

[0136] Finally, a venting stage is carried out.

[0137] The precise parameters of the process for forming the layer L and the thin organic-inorganic layer (examples according to the invention) and the sole MgF.sub.2 layer (comparative examples) are given in table I below.

TABLE-US-00001 TABLE I Layer deposited Ion assistance DMTS * Nature Deposition Current Gas flow flow of the Thickness rate intensity rate (sccm) rate Example Substrate layer (nm) (nm/s) (A) O.sub.2 Ar N.sub.2 (sccm) 1 no. 1 L 300 2 3 20 0 0 20 2 no. 1 L 300 2 2 0 0 20 20 3 no. 1 L 300 2 3 0 20 20 20 4 no. 2 L 80 2 3 20 0 0 20 organic- 5 2 3 20 0 0 20 inorganic layer C1 no. 1 MgF.sub.2 300 2 3 20 10 0 C2 no. 2 MgF.sub.2 80 2 3 20 0 0 * decamethyltetrasiloxane

3. Characterizations

[0138] Critical Temperature

[0139] The critical temperature of the article is measured 24 hours or one week after its preparation, in the following way:

The coated ophthalmic organic lens is placed in an oven thermostatically maintained at a temperature T of 50 C. for 1 hour, removed from the oven and then the visual appearance of the article is evaluated in reflection under a desk lamp. If the coating appears intact, the ophthalmic organic lens is placed back in the oven for 1 hour at the temperature T+10 C. As soon as the coating appears cracked, the test is stopped. The critical temperature corresponds to the crack appearance temperature.

[0140] Refractive Index

[0141] The refractive index measurements were carried out at the wavelength of 632.8 nm, unless otherwise indicated, by ellipsometry. More specifically, the refractive index is obtained by an ellipsometric measurement using an ellipsometer (RC2, J. A. Woollam) equipped with a dual rotating compensator. The refractive index is deduced from the dispersion relationship which models the optical response provided by the ellipsometric angles and . For dielectric materials, such as MgF.sub.2, the Tauc-Lorentz equation, known to a person skilled in the art, models well the optical properties of the layers deposited. All the measurements were carried out at angles of incidence of 45, 55, 65 and 75 in a range of wavelengths of 190-1700 nm.

[0142] The adhesion properties of the whole of the interference coating adhering to the substrate were verified on the convex face of the lens by means of the n10 rubs test, following the procedure described in international patent applications WO 2010/109154 and WO 99/49097. The test consists in noting the number of cycles that a lens was able to be subjected to before the appearance of a defect. Therefore, the higher the value obtained in the n10 rubs test, the better the adhesion of the interference coating to the substrate.

[0143] The abrasion resistance of the article was evaluated by determining Bayer ASTM (Bayer sand) values for the substrates coated with the antireflective coating, using the methods described in application WO 2008/001011 (standard ASTM F 735.81). The higher the value obtained in the Bayer test, the higher the abrasion resistance. Thus, the Bayer ASTM (Bayer sand) value is deemed to be good when it is greater than or equal to 3.4 and less than 4.5 and excellent for values of 4.5 or more.

4. Results

[0144] The optical and mechanical performance of various articles, according to the invention or comparative, and also the conditions for the deposition of the various layers are presented in table II below.

TABLE-US-00002 TABLE II Critical temperature ( C.) Refractive index T + T + Bayer n 10 rubs Examples at 632.8 nm 24 h 1 week sand test Cc/Cx 1 1.41-1.42 120 2 1.39-1.41 110-120 3 1.37-1.40 120 4 70 5.5-6.7 13/13 C1 1.37-1.38 50 C2 50 7.0 13/13

[0145] The articles according to invention have a markedly improved critical temperature relative to a layer exclusively composed of MgF.sub.2. Moreover, they have an abrasion resistance (example 4) and also mechanical strength properties (Bayer) similar to an MgF.sub.2 layer.

[0146] The refractive index of the hybrid layers according to the invention has a value very close to that of a low-index layer composed solely of MgF.sub.2.