FR2792003A1 - Durable hydrophobic and oleophobic coating, for glass, ceramic, glass-ceramic, metal and plastic substrates, is formed by plasma CVD while reducing the substrate temperature - Google Patents

Abstract

Hydrophobic/oleophobic coating formation, by ionizing a precursor while reducing the substrate temperature, is new. A hydrophobic/oleophobic coating is formed on a substrate by ionization of one or more precursors while reducing the substrate temperature from above 80 deg C to below 80 deg C. Independent claims are also included for the following: (i) a substrate with a 10-100 (preferably 20-80) nm thick external hydrophobic/oleophobic coating formed by the above process; and (ii) a monolithic, laminated or multiple glazing for buildings or transport vehicles, in which the or each surface in contact with the ambient atmosphere has a hydrophobic/oleophobic coating formed by the above process.

Description

TRANSPARENT SUBSTRATE HAVING A COATING

  HYDROPHOBE / OLEOPHOBE FORMED BY CVD PLASMA

  The present invention belongs to the field of substrates, in particular transparent substrates, endowed with the property of hydrophobicity / oleophobia with a view to obtaining certain anti-rain / anti-fouling effects. To this end, such a substrate is, for example, provided with a coating in the context of various applications, such as glazing for aeronautical, maritime, land (rail, road) transport vehicles, for building (windows), urban furniture (display panel, Bus shelter ...) or interior design (decorative panel, furniture), household appliances (refrigerator door, oven, display case, ceramic hob), kitchen utensils, sanitary furniture (sink, bathtub ...), building materials, etc. The substrate is therefore transparent or not and generally consists of glass, ceramic, glass ceramic, metal, plastic (poly (methyl methacrylate) (PMMA), polyvinyl butyral (PVB), polycarbonate (PC) or polyurethane (PU), ethylene copolymer / thermoplastic vinyl acetate (EVA), poly (ethylene terephthalate) (PET), poly (butylene terephthalate) (PBT), polycarbonate / polyester copolymers, cycloolefinic copolymer of the ethylene / norbornene or ethylene / cyclopentadiene type, ionomer resins , for example an ethylene / (meth) acrylic acid copolymer neutralized by a polyamine, thermosetting or thermosetting agents such as polyurethane, unsaturated polyester (UPE), ethylene / vinyl acetate copolymer ... or a combination of several of these materials The property of hydrophobicity / oleophobia to which reference is made relates to the fact that polar or non-polar liquids do not adhere to the substrate in form. ant a troublesome film. A substrate with this property will have a weak or almost zero tendency to retain dust or dirt of all kinds, fingerprints, insects, etc. The presence of water and / or soiling causes an unsightly appearance and, if necessary, a reduction in the transparency of the substrate as well as a deterioration of vision through it. These are particularly troublesome when the substrate is a glazing

  used in the transport sector.

  The hydrophobicity / oleophobicity - or non-wettability - property of a substrate consists in that the contact angles between a liquid and this substrate are high, for example at least 90 for water. The liquid then tends to flow easily, in the form of drops, on the substrate, by simple gravity if the substrate is inclined or under the effect of aerodynamic forces in the case of a moving vehicle. Agents known to impart this hydrophobicity / oleophobicity property are, for example, fluorinated alkylsilanes as described in

  Patent applications EP 0 492 417, EP O 492 545 and EP 0 672 779.

  Common hydrophobic / oleophobic agents are in particular alkyltrihalogeno- or -trialkoxy-silanes in which the alkyl group comprises at least one perfluorinated end, that is to say consisting of a group F3C- (CF2) n- in which n is a positive or zero integer,

  as described in patent application EP 0 719 743.

  The hydrophobic / oleophobic agents are applied in a known manner in solution according to conventional deposition methods with or without heating. One of the most acute problems in the field of the invention is that of the durability of the hydrophobic / oleophobic coating. The latter is in fact affected by erosion which does not fail to occur more or less, for example during the cleaning operations of the substrate which are periodically essential when the latter is transparent, when it is a question of restoring a satisfactory vision through the substrate. It is thus constantly sought to slow down the progressive elimination of the hydrophobic / oleophobic coatings of the aforementioned types which occurs in particular under the action of wipers, all the more so since such elimination can,

  moreover, result from degradation by ultraviolet radiation.

  Two main routes have so far been explored for

  increase the durability of coatings by limiting the effects of erosion.

  These two ways consist in increasing the adhesion of coatings to

substrates.

  According to a first approach, application EP 0 484 746 recommends the preparation of the substrate by a preliminary treatment using a

  primer of the tetrahalogeno- or tetraalkoxy-silane type.

  Application EP 0 497 189 A2 proposes, in accordance with a second approach, to create beforehand on the surface of the substrate irregularities of dimensions ranging for example between 1 and micrometers, either by addition of particles, or by various attacks.

such as chemical or sandblasting.

  On the other hand, a progressive disappearance of the hydrophobic / oleophobic property is commonly observed under the effect of prolonged exposure to ultraviolet radiation which more or less destroys the

  hydrophobic / oleophobic coatings.

  It is specified, on the other hand, that in all cases the reformation of a new hydrophobic / oleophobic coating to remedy the erosion of the previous coating does not pose any particular difficulty; it can be carried out on the old coating, once it has been succinctly cleaned. The advantage of delaying this

  operation remains obvious.

  The inventors have now implemented a different technique making it possible to obtain hydrophobic / oleophobic coatings with improved durability, in particular under demanding conditions of solid friction and exposure to ultraviolet light. To this end, the subject of the invention is a process for forming a hydrophobic / oleophobic coating on a substrate by ionization of at least one precursor. This process has the particularity that during this formation, the temperature of the substrate decreases from more than 80 C to less than 80 C. To do this, the substrate rests conveniently on

  thermostated support with variable temperature.

  This technique makes it possible to form coatings in thin and homogeneous layers, having a high adhesion with respect to the substrate, and an adjustable refractive index - by a judicious choice of the

  precursors - especially at a value almost identical to that of glass.

  Thus, according to an advantageous embodiment of the process of the invention, the final product is transparent and has the optical qualities of a glazing, the substrate is made of glass or plastic such as poly (methyl methacrylate) (PMMA) or polycarbonate (PC) optionally coated with a primer in particular based on silica to promote the adhesion of the overlying coating, and said precursor is a silicon compound. An organometallic precursor, alone or in combination with one or more other precursors, in particular silicon precursors as mentioned above, may also be suitable: proves to be particularly suitable, for example, a compound comprising

  tin oxide groups distributed in a carbon chain.

  As silicon precursors, the following give full satisfaction: - a silane such as tetramethylsilane, hexamethyldisilane, an alkoxysilane, for example an alkoxytrialkylsilane in which the alkyl group is a methyl, ethyl, propyl, isopropyl group, the methyl group being preferred - a fluorinated silane, in particular a perfluoroalkylalkl-ltrialkoxysilane or a perfluoroalkylalkyltrihalogénosilane; - a siloxane such as hexamethyldisiloxane; - a silazane such as hexamethyldisilazane; - and their derivatives. Preferably, the precursor is introduced into an enclosure in which pulses of frequency between 10 kHz and 10 GHz and of power between 100 and 2000 W for a surface of substrate to be coated of 0.4 m2 are created by a generator, power being good

  heard proportional to the surface to be coated.

  According to a particularly advantageous embodiment, the precursor is hexamethyldisiloxane, introduced into the enclosure at a flow rate of between 50 and 500 cm3 / min, so as to establish and maintain there

a pressure of 0.1 to 70 Pa.

  Furthermore, the method of the invention has three main variants. According to the first, the vaporized precursor is introduced into the enclosure which is connected to ground through a porous cathode or

  pierced with holes, connected to a pulse generator.

  According to the second, the vaporized precursor is introduced into the enclosure which is connected to ground through bored gas ramps, and waves are emitted into the enclosure by a waveguide connected to a pulse generator. The waveguide is for example metallic with a rectangular section, and located above the enclosure of which it follows the shape; the waves are transmitted through a quartz window provided

in the wall of the enclosure.

  According to the third main variant, the vaporized precursor is introduced into an enclosure connected to ground, and the substrate is coated with a conductive layer connected to an alternating current generator. A perfectly suitable conductive layer is based on substoichiometric and / or doped metal oxides such as indium oxide doped with tin ITO, zinc oxide doped with indium ZnO: In, with fluorine ZnO: F, with aluminum ZnO: Al or with tin ZnO: Sn, tin oxide doped with fluorine

  SnO2: F or antimony (tetravalent or pentavalent) SnO2: Sb.

  The substrate is therefore used here as an electrode to create the discharge. This embodiment is particularly indicated for a deposit on a large substrate. The homogeneity of the coating produced is better; the activated chemical species do not have time to diffuse inhomogeneously between the cathode and the substrate but are directly created on the surface of the latter. Compared to the first variant using a porous cathode or one pierced with holes, it is specified that the deposits must be carried out here with a low power so that the conductive layer is not destroyed during the electric discharge: the optimal power for a deposit area of cm x 20 cm then goes from 100 W to 25 W. Simultaneously, the speed of

  deposit is greatly increased, for example from 0.5-0.6 A / s to 17-

38 A / s.

  The invention also relates to a substrate provided with an external hydrophobic / oleophobic coating, that is to say intended for direct exposure to the ambient atmosphere, and formed by implementing a process such as described above, the thickness of this hydrophobic / oleophobic coating being between 10 and 100 nm, preferably

between 20 and 80 nm.

  On the other hand, it is desirable to avoid local accumulations of electrostatic charges which appear in applications such as aircraft windshields, that is to say on the contrary to provide for the evacuation of these charges by conduction. . These accumulations indeed constitute a source of cracking and destruction of any stacked layers and in particular of the hydrophobic / oleophobic coating. The inventors propose two distinct ways to solve this problem: - either the hydrophobic / oleophobic coating itself is antistatic, - or its thickness does not exceed 50 nm, the substrate on which it is

formed being antistatic.

  Can be used as antistatic materials, those mentioned above for the conductive layer used in accordance with the third variant of the process of the invention. and / or materials formed by methods similar to those used for the formation of the hydrophobic / oleophobic coating. In addition, the hydrophobic / oleophobic coating can be made antistatic, for example by adding to the hexamethyldisiloxane used as precursor, a certain proportion of SiH4, so as to create in the coating produces Si-Si bonds; CH4 is in this respect capable of assuming a function analogous to that of

  SiH4, as well as metal salts of the copper acetylacetonate type.

  The invention also makes available, in a particularly advantageous manner, a substrate comprising an anti-reflective coating covered by said hydrophobic / oleophobic coating or whose

  the latter constitutes the outer part.

  An anti-reflective coating usually consists of a stack of thin interference layers, generally an alternation of layers

  based on dielectric material with high and low refractive indices.

  Deposited on a transparent substrate, such a coating has the function of reducing the light reflection, therefore increasing the

light transmission.

  On the outside of an automobile windshield, for which high levels of light transmission, generally greater than 75%, and very low residual blurring (less than 1% of the transmitted light) are imposed, the anti-reflection effect results in improved comfort

  visual of the driver and passengers.

  The inventors make possible the subsequent formation of an anti-reflective coating and a hydrophobic / oleophobic coating using a single installation and similar or even identical processes, with excellent adhesion between the two coatings being obtained, or alternatively the formation of '' an anti-reflective and hydrophobic / oleophobic coating. Indeed, such coatings can in particular be obtained by applying to compositions of variable precursors

  over time a plasma CVD technique at radio frequency or micro-

  waves. The precursor compositions vary discontinuously (separate layers) or continuously (single layer with composition gradient). The different precursors used are chosen with a view to obtaining materials with different refractive indices. Such materials are for example based on SiOxN, with x and v varying

  between 0 and 2 respectively and between 0 and 1.33.

  Another object of the invention is a monolithic, laminated or multiple glazing for the building or for transport vehicle, at least one face intended to be in contact with the ambient atmosphere and constituted by a hydrophobic / oleophobic coating formed on a

  substrate by implementing a method as described above.

  Other characteristics and advantages of the invention will appear

  in the description of the following example:

EXAMPLE

  A hydrophobic / oleophobic coating is applied to three samples of soda-lime-silica float glass of 20 cm x cm.

the following procedure.

  The samples are placed consecutively on a support

  thermostatically controlled at variable temperature, in a grounded enclosure.

  Hexamethyldisiloxane (HMDSO) vaporized is sent into the enclosure through a cathode pierced with holes of 2 mm in diameter, which was preferred to a porous cathode, because in the present case it seems to provide better stability of the plasma. The HMDSO flow rate is 300 cm3 / min and makes it possible to establish and maintain a pressure in the enclosure.

of HMDSO of 6.67 Pa.

  The plasma is created by transmission of waves in the enclosure at a frequency and a power of 100 kHz, respectively 100 W. The deposition rate of the hydrophobic / oleophobic coating thus obtained is 0.5 A / s. For the three samples, the duration of deposit is

  800 s, corresponding to a coating thickness of 40 nm.

  The first two samples are kept at constant temperature throughout the duration of the deposition, that is to say at 200 ° C., respectively at room temperature. The third sample is at C during the first half of the treatment, then at temperature

ambient for the second.

  The resistance to erosion of the three coatings is first evaluated by measuring the persistence of the hydrophobic / oleophobic property during a Taber test carried out with a load of 500 g and CS 10 F grinding wheels. the contact angle of the water at equilibrium in the absence of abrasion on the one hand and after

100 wheel turns on the other hand.

  Secondly, the resistance to ultraviolet radiation is evaluated by measuring the contact angle of water at equilibrium after 1000 h of weather-ometer (WOM) test combining an ultraviolet stress and a

temperature of 90 C.

  The results are recorded in the following table: Deposited layer Deposited layer Two-layer 200 C / at 200 C at room temperature ambient temperature Initial water 100 + 5 100 + 5 100 + 5 Water after 90 <50 '80 turns Taber Water after 70 84- 84 1000 h WOM It appears that the layer deposited at 200 C resists abrasion but much less well to UV radiation, unlike the layer deposited at room temperature. Only the third coating, conforming to

  the invention resists satisfactorily both stresses.

  This remains valid under real conditions of use where the two causes of wear coexist, in particular in the form of a combination of the wiper action and solar radiation. Increased durability is observed, with respect to abrasion, of the layer deposited at room temperature on the layer deposited at 200 ° C. compared with the 1o layer deposited at room temperature directly on the glass. It is assumed that the adhesion and cohesion in the thickness of this layer

  are higher in the first case.

  Another remarkable advantage of the coating formed according to the process of the invention is its resistance to the thermal bending cycle (8 minutes at 620 ° C. then cooling to ambient temperature) during

  which the contact angle of water at equilibrium goes from 100 to 96.

  Thus, the invention provides a hydrophobic / oleophobic coating which is excellent for a transparent substrate such as 1o glass; the refractive index of the HMDSO coating of the example

  n _ 1.47 is very close to that of glass.

  The durability of the coating is also excellent, even under severe conditions of abrasion and exposure to ultraviolet radiation.

Claims (14)

  1. Method for forming a hydrophobic / oleophobic coating on a substrate by ionization of at least one precursor, characterized in that during this formation the temperature of the substrate decreases from a temperature above 80 C to a temperature less than 80 C. 2. Method according to claim 1, characterized in that the final product is transparent and has the optical qualities of a glazing, in that the substrate is glass or plastic such as poly (methyl methacrylate) (PMMA) or polycarbonate (PC) o0 optionally coated with a primer, in particular based on silica, to promote the adhesion of the overlying coating, and in that said   precursor is a compound of silicon.   3. Method according to claim 2, characterized in that said silicon compound is chosen from: - a silane such as tetramethylsilane, hexamethyldisilane, an alkoxysilane, for example an alkoxytrialkylsilane, in which the alkyl group is a methyl, ethyl, propyl group , isopropyl, the methyl group being preferred; - a fluorinated silane, in particular a perfluoroalkylalkyltrialkoxysilane or a perfluoroalkylalkyltrihalosilane; - a siloxane such as hexamethyldisiloxane; - a silazane such as hexamethytdisilazane; - and their derivatives.   4. Method according to one of the preceding claims, characterized   in that the precursor is introduced into an enclosure in which pulses of frequency between 10 kHz and 10 GHz and of power between 100 and 2000 W for a surface of substrate to be coated with   0.4 m2 are created by a generator.   5. Method according to claim 4, characterized in that the precursor is hexamethyldisiloxane, introduced into the enclosure at a flow rate between 50 and 500 cm3 / min, so as to establish and maintain there a pressure of 0.1 to 70 Pa.   6. Method according to one of the preceding claims, characterized   in that the vaporized precursor is introduced into an enclosure connected to ground through a porous cathode or pierced with holes connected to a pulse generator.   7. Method according to one of claims 1 to 5, characterized in that   that the vaporized precursor is introduced into the enclosure which is connected to ground through pierced gas ramps, and waves are emitted in   the enclosure by a waveguide connected to a pulse generator.   8. Method according to one of claims i to 5, characterized in that   that the vaporized precursor is introduced into an enclosure connected to ground, and that the substrate is coated with a conductive layer connected   to an alternating current generator.   9. Method according to claim 8, characterized in that the conductive layer is based on sub-stoichiometric and / or doped metal oxides such as indium oxide doped with tin ITO, zinc oxide doped indium ZnO: In, fluorine ZnO: F, aluminum ZnO: Al, or tin ZnO: Sn, tin oxide doped with fluorine SnO2: F or antimony (tetravalent or pentavalent) SnO2: Sb.   10. Substrate provided with an exterior hydrophobic / oleophobic coating   formed by a method according to one of claims 1 to 9, the thickness of   this coating being between 10 and 100 nm, preferably between 20 and 80 nm.   11. Substrate according to claim 10, characterized in that said   hydrophobic / oleophobic coating is antistatic.   12. Substrate according to claim 10, characterized in that said hydrophobic / oleophobic coating has a thickness at most equal to 50 nm and said substrate is antistatic.   13. Substrate according to one of claims 10 to 12, comprising a   anti-reflective coating, including said hydrophobic / oleophobic coating   possibly constitutes the external part.   14. Monolithic, laminated or multiple glazing for the building or for transport vehicle, at least one face of which is intended to be in contact with the ambient atmosphere is constituted by a hydrophobic / oleophobic coating formed on a substrate by employing a   method according to one of claims 1 to 9.