Transparent textured substrate and methods for obtaining same

The present invention relates to a transparent substrate for which the best optical properties required for glazing are sought at present, whether it is glazing for a transport vehicle or for a building. In addition to the optical properties presented to the highest degree, this substrate is designed to exhibit additional properties residing in the modification of the behavior of the wettability substrate into a behavior which can be qualified as superhydrophobic / oleophobic or super-hydrophilic / oleophilic, in anti-fouling, anti-reflection, electric conduction, anti-static properties.

The hydrophobicity / oleophobicity property of a substrate consists in that the contact angles between a liquid and this substrate are high, for example of the order of 120 ° 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. This phenomenon is the expression of an anti-rain effect. The drops are, on the other hand, capable of causing in their flow of dust, insects or more or less fatty stains of all kinds, the presence of which would result in an unsightly appearance or even, if necessary, a deterioration in vision. through the substrate. To this extent, the hydrophobic / oleophobic substrate also has an anti-fouling property.

Known hydrophobic / oleophobic agents are, for example, fluorinated chorosilanes, fluorinated alkylsilanes as described in the patent application <patcit id="pcit0001" dnum="EP0675087A1"><text>EP-A1-0 675 087</text></patcit>. They are applied in a known manner according to conventional deposition methods with or without heating.

The document <patcit id="pcit0002" dnum="WO0064829A"><text>WO 00/64829</text></patcit> describes substrates having a relief having growths spaced regularly from one to several micrometers.

The document <patcit id="pcit0003" dnum="US5242544A"><text>US 5,242,544</text></patcit> describes substrates whose surface has irregularities whose diameters are of the order of a few micrometers to a few tens of micrometers.

Patent applications <patcit id="pcit0004" dnum="JP7206475A"><text>JP 07 206475</text></patcit> describes outgrowths whose characteristic dimensions (heights, spacing of the apexes of the outgrowths) are of the order of a few tens to a few hundred micrometers.

On the contrary, the hydrophilicity / oleophilicity property of a substrate is manifested by small contact angles between a liquid and this substrate, for example between 0 and 5 ° and preferably much less than 5 ° for water on clean glass. This property promotes the formation of thin transparent liquid films, to the detriment of that of fogging, or of frost made up of tiny droplets which impair visibility through a transparent substrate. These anti-fog and anti-frost effects observed on a hydrophilic / oleophilic substrate are well known.

Many hydrophilic agents, in particular hydroxylated agents, such as hydroxyalkyl poly ((meth) acrylates) are used for this purpose, in known manner, for transparent substrates. Certain so-called photocatalytic compounds, such as TiO₂, are also used, in particular in combination with glass substrates, not only for their hydrophilic nature after exposure to light, but also for their ability to degrade, by a radical oxidation process, dirt of organic origin ; the hydrophilic / oleophilic and anti-fouling properties are then obtained simultaneously. It is known to deposit coatings with photocatalytic property comprising TiO₂ from at least one titanium precursor, if necessary in solution, by pyrolysis in the liquid phase, by a sol-gel technique or also by pyrolysis in the vapor phase.

In accordance with the above, the property of hydrophobicity / oleophobia is assessed quantitatively by measuring the contact angle formed, most often by a drop of water, on a given substrate. In the absence of additional information, this contact angle is measured for a horizontal substrate. In reality, as already mentioned above, it is the behavior of liquid droplets in dynamics which is targeted by the fact of imparting hydrophobicity to a substrate. This applies as well to substantially vertical static substrates such as exterior glazing for buildings, shower glazing as for glazing for transport vehicles. However, in the case of a drop of liquid on a substrate inclined relative to the horizontal, there are two different contact angles: the advancing angle and the retreating angle, determined at the front, respectively behind the drop, relative to the direction of its movement. These angles are values ​​reached at the limit of the drop of the drop. The difference between the angle of advance and the angle of retreat is called hysteresis. A drop of water with high hysteresis or a low back angle will have trouble flowing over a substrate. Thus, it is easily understood that an effective hydrophobicity is conditioned both by a high angle of advance and a low hysteresis. Finally, in a known manner, the size of the drop influences the angles of advance and retreat.

The invention now provides a transparent substrate capable of exacerbating the hydrophobic / oleophobic or hydrophilic / oleophilic intrinsic nature of the substrate material, capable of being obtained under excellent industrial conditions, in particular continuously, with all glazing dimensions. requested and used by the public, and having optical properties at the best level from those of current glazing. This substrate can be, as the case may be, superhydrophobic / oleophobic (characterized for information by a minimum forward angle of 160 ° and a minimum backward angle of 120 ° for a drop of water) or superhydrophilic / oleophilic (angle of contact less than 5 °, approaching 0 ° for water). It can also be made simply hydrophobic / oleophobic or hydrophilic / oleophilic in a perfectly controlled manner. As examples may be obtained according to the invention of hydrophobic / oleophobic substrates having for a drop of water forward / backward angles of 160 ° / 110 °, 140 ° / 130 ° ... (angles measured by drop growth and drop with pipette).

When the substrate is hydrophilic / oleophilic and photocatalytic, the exacerbation of the hydrophilic / oleophilic character goes hand in hand with that of the antifouling character.

To this end, the subject of the invention is a substrate of which at least part of the external surface has the geometry of a sheet comprising protuberances having, for at least 80% of them, heights between 40 and 250 nm, mean diameters between 1 and 500 nm, at least 80% of the distances between two neighboring outgrowths being between 1 and 500 nm. According to the invention, at least 80% of the protuberances constituting substantially cones or trunks of straight cones with axes perpendicular to the main plane of the substrate and half-angles at the apex between 0 and 60 °, this definition also designating, in the borderline case, cylinders.

Although the transparency of the substrate makes it possible to appreciate the specific advantages linked to its optical qualities, the substrate of the invention may also not be transparent.

The minimum of 80% set according to the invention is not absolutely imperative and in certain cases this minimum could be less than 80%, for example of the order of 70%. However, such a reduction is made to the detriment of the optical qualities so that in reality it will be almost all of the growths, in particular at least 90%, preferably at least 95% of the growths which will satisfy the required criteria.

The invention therefore makes it possible to obtain, by an industrially advantageous process in many respects as we will see below, a transparent superhydrophobic / oleophobic or superhydrophilic / oleophilic substrate for all shapes and sizes of glazing currently in demand, with the best optical qualities required glazing. Substrates produced according to the invention have moreover exhibited remarkable durability and resistance to abrasion and erosion.

In addition, thanks to the invention, additional functions such as anti-reflection, electricity conduction, anti-static can be imparted to the substrate according to an equally advantageous manufacturing process.

According to other characteristics of the invention:<ul id="ul0001" list-style="dash" compact="compact"><li>At least 80% of the protuberances have heights at least equal to 60 nm, in particular at least equal to 80 nm;</li><li>At least 80% of the protuberances have heights at most equal to 190 nm, in particular at most equal to 170 nm;</li><li>At least 80% of the outgrowths substantially constitute cones or trunks of straight cones with axes perpendicular to the main plane of the substrate and half-angles at the apex between 0 and 30 °, this definition also designating, in the limiting case, cylinders ;</li><li>at least 80% of the protuberances have average diameters of 40 to 380 nm, this average diameter can for example be considered as that of the truncated cone at mid-height.</li></ul>

Of course, numerous outgrowths according to the invention have geometries deviating more or less from those of a cone, truncated cone or cylinder which constitute only approximations of shapes frequently obtained. Mention should also be made of outgrowths in columns perpendicular to the main plane of the substrate, of regular or irregular sections, but defined by two orthogonal axes corresponding to a greater, respectively a smaller dimension, both of which lie in the range from 1 to 500 nm, that is to say the range of mean diameters defined in accordance with the invention. A ratio of said greater to said smaller dimension may advantageously be included between 1 and 4.

Also part of the invention are substrates whose protuberances, of sections generally different from each other, include section protuberances having a partially concave periphery.

According to preferred embodiments, the required geometry of at least part of the external surface of the substrate is given by a layer of a material containing one or more oxidation or nitriding products such as SiO₂, Yes₃NOT₄, AlN, Al₂O₃, SnO₂, ZnO_x with x&gt; 0, and / or formed by a vacuum technique, in particular by sputtering assisted by magnetic field, plasma magnetron, plasma CVD, atmospheric CVD, pyrolysis of powder and liquid, by a polymerization and / or crosslinking process, by a sol-gel type technique.

These compounds and methods are indeed well suited to the formation of the starting layer in which the growths defined above are formed, in order to obtain a product of high optical quality.

This layer giving the desired geometry to the external surface of the substrate may itself be external, or else covered with a coating which hardly modifies the surface geometry, such as a functional, hydrophobic or other, single-molecular coating of a few nanometers thick. The substrate of the invention can be exclusively composed of this layer provided, where appropriate, with its monomolecular coating, or of the latter laminated with an underlying sheet of glass or transparent plastic material, with possible interposition of an electrically conductive layer. . Can be used a soda-lime glass, in particular a float glass as used for transport vehicles, for the building or other application of flat glass, or a glass of the bottle or flask type, a borosilicate of the pyrex type, a phosphate glass usable as prosthesis or optical glass, lead glass (crystal), an aluminosilicate such as a glass ceramic, or an amorphous solid material free of silica. All transparent plastics are suitable, among which may be mentioned polyvinyl butyral, polyurethane, polycarbonate, polymethyl methacrylate, ionomer resin, etc. subject to their compatibility with the operating conditions (temperature, pressure, etc.) of the successive stages of substrate formation. On the other hand, several sheets of glass and / or plastic material can be laminated in the substrate of the invention: for example two sheets of glass connected to one another by an interlayer adhesive layer of polyvinyl butyral, a sheet of glass and a polyurethane sheet with energy absorption properties ...

The advantage of interposing an electrically conductive layer between the glass or plastic sheet and the protuberance layer is explained below in relation to one of the methods of manufacturing the substrate of the invention. As examples for this electroconductive layer, mention is made of substoichiometric and / or doped metal oxides known from the application.<patcit id="pcit0005" dnum="FR2695117"><text>FR-2 695 117</text></patcit>, in particular indium oxide doped with tin (ITO), zinc oxide doped with indium (ZnO: In), fluorine (ZnO: F), aluminum (ZnO: Al ) or tin (ZnO: Sn) and fluorine-doped tin oxide (SnO₂: F) or antimony (tetravalent or pentavalent) (SnO₂: Sb). In addition to their electrical conduction properties, these materials are described as having properties of reflection in the infrared, in particular of low-emissivity.

In this regard, any known association of functional layers of the low-emissive, anti-solar, anti-reflective, decorative type (acid mat, screen printed, lacquered, enameled, textured by rolling between rollers or by others equivalent methods) with the substrate in a monolithic or laminated glazing is included in the invention. We cite as an example:<ul id="ul0002" list-style="dash" compact="compact"><li>a reflective layer deposited on a PET sheet itself embedded in the PVB interlayer adhesive in a laminated windshield,</li><li>multiple or laminated glazing comprising a thin layer of solar control (for example of the type sold by the company SAINT-GOBAIN GLASS under one of the brands STARELIO, COOL-LITE) on face 2 and a substrate with growths of the invention in inner face of multiple glazing, in contact with the atmosphere of the protected enclosure,</li><li>or double glazing, the outer glass sheet of which is clear glass sold under the brand PLANILUX by the company SAINT-GOBAIN GLASS, which has an outer face with protuberances according to the invention and an inner face, facing the blade d air, provided with a thin layer of SnO₂: F deposited by CVD (product marketed under the brands EKO and EKO PLUS by the company SAINT-GOBAIN GLASS) or a silver layer deposited by sputtering under vacuum (product marketed by the company SAINT-GOBAIN GLASS under the PLANITHERM brand), each of these layers having a strong reflection in the field of infrared radiation of long wavelength (low emissivity) which greatly reduces the heat losses and gives the double glazing reinforced thermal insulation for high light transmission,</li><li>textured layer (side 1) / Planilux / sun protection layer: COOL-LITE, STARELIO (side 2),</li><li>textured layer (side l) / Planilux / rare gas air / low-emissivity layer SnO₂: F (EKO) or silver (PLANITHERM) (side 3) / Planilux / textured layer / Planilux / reflective layers (mirror: the substrate is always transparent, the layer is reflective),</li><li>texturing / glass / screen printing (SERALIT, trademark by SAINT-GOBAIN GLASS).</li></ul>

The substrate of the invention is capable of achieving remarkable optical quality. It thus advantageously has a light transmission at least equal to 80%, in particular at least equal to 85%, very particularly at least equal to 90% and a haze at most equal to 5%, in particular at most equal to 2% and especially at most equal to 1%.

According to one of the main variants of the invention, the substrate is hydrophobic / oleophobic. In known manner, the creation of irregularities on a surface increases its hydrophobic or hydrophilic character. As indicated above, an appropriate choice of geometry of the protrusions makes it possible to control this hydrophobic character. For example, a flat surface characterized by forward / backward angles of 100 ° / 80 ° is transformed into a surface with protuberances of angles 160 ° / 120 °.

In this case, the substrate consists, at its outer surface, at least in part:<ol id="ol0001" compact="compact" ol-style=""><li>a) of compounds obtained in particular by a vacuum technique, by evaporation, spraying, sol-gel, CVD or the like;</li><li>b) silicones; and or</li><li>c) of compounds corresponding to the formulas:<chemistry id="chem0001" num="0001"><img file="EP1296901B1_D0001.tif" /></chemistry>and         R_{p '}Six_{4-p '}     (II) in which :<ul id="ul0003" list-style="dash" compact="compact"><li>m = 0 to 15;</li><li>n = 1 to 5;</li><li>p = 0, 1 or 2;</li><li>R is a linear or branched alkyl group or a hydrogen atom;</li><li>X is a hydrolyzable group such as a halo, alkoxy, acetoxy, acyloxy, amino, NCO group;</li><li>p '= 0, 1, 2 or 3.</li></ul></li></ol>

The abovementioned production techniques are advantageous in that they make it possible to incorporate the hydrophobic compounds in a layer which would not be hydrophobic without this incorporation. To this end, it is therefore possible to use an additional precursor in order to obtain an organic / inorganic composite. It is however equally possible to use only one precursor capable of conferring the property of hydrophobicity.

An example is given of the implementation of a CVD plasma type process, using at least one of the precursors chosen from:<ul id="ul0004" list-style="dash" compact="compact"><li>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;</li><li>a fluorinated silane, in particular a perfluoroalkylalkyltrialkoxysilane or a perfluoroalkylalkyltrihalogénosilane;</li><li>a siloxane such as hexamethyldisiloxane;</li><li>a silazane such as hexamethyldisilazane.</li></ul>

By using, for example, hexamethyldisiloxane, a layer with a flat surface is obtained, that is to say before growth of the growths, with a static contact angle for a drop of water of 105 °.

This outer surface of the substrate, consisting at least in part of one or more of the aforementioned compounds, consists either of the layer giving the required geometry with protrusions described above, or of a coating applied to this layer, thin enough not to modify it. substantially the geometry. As mentioned above, it may be a grafted monomolecular film.

According to another variant, the substrate is hydrophilic / oleophilic in that it comprises an appropriate agent. As hydrophilic / oleophilic agent, mention may be made, as final product or precursor, of poly (meth) acrylic acid as it is or at least partially salified with sodium, potassium, cesium, nonionic surfactants, cellulose esters such as hydroxypropylcellulose, chitosan and chitin derivatives, polymethacrylates, poly (vinyl alcohols) and poly (vinyl acetate), polypyrrole, polyaniline, polyacrylamide, poly (N, N-dimethylacrylamide), poly (N-isopropylacrylamide), polyethylene glycol, polypropylene glycol, polyoxyethylene with terminal hydroxy or methoxy functions, polyallylamine hydrochloride, polysaccharide, dextrans (branched), pullulan (linear polysaccharide), poly (styrenecarboxylic acid and salt thereof, poly (styrenesulfonic acid, polystyrenesulfonate sodium, polyvinyl butyldiulfuride), -vinyl-N-methyl-pyridinium, 4-vinyl-N-methyl-pyridinium polyiodide, poly (2-vinyl-pyridine), 2-vinyl-pyridinium polybromide, polyvinylpyrrolidone, copolymers obtained from starting monomers of various aforementioned polymers, and in particular block copolymers, certain titanium compounds such as titanium tetraisopropyl or titanium tetraisobutyl, optionally stabilized, for example by acetylacetonate, titanium tetrachloride, etc.

Like the hydrophobic / oleophobic agents, the hydrophilic / oleophilic agents can in particular be incorporated into the layer constituting the growths itself, or be applied to this layer in a thin film.

The hydrophobic and hydrophilic properties contradict each other, the substrate of the invention generally comprises only one or more hydrophobic / oleophobic agents or one or more hydrophilic / oleophilic agents. However, the invention allows the coexistence of the two types of agents, in particular in a variant in which the external surface of the substrate comprises hydrophobic growths and a low level between the growths which is hydrophilic (it will be understood below how the manufacturing process of the substrate of the invention allows easy production of such a product). In this variant, the major part of a liquid coming into contact with the substrate flows on the hydrophobic growths, and only a tiny part of this liquid comes into contact with the low hydrophilic level and forms there a transparent uniform film.

Advantageously, the substrate of the invention has anti-fouling properties. These can partially result, as seen above, from (super) hydrophobic / oleophobic or (super) hydrophilic / oleophilic properties. These properties can also be directly linked to the nature of certain constituents of the substrate. As already mentioned, among the hydrophilic / oleophilic agents, certain titanium compounds, for example TiO₂, have the ability to decompose organic residues photocatalytically.

The invention provides substantial progress in controlling the evacuation of liquids on the substrate, the elimination of droplets, mist, frost formed from the residual liquid, that is to say not evacuated, the degradation of dirt in this residual liquid, so that the substrate can be kept clean in the absence of any cleaning.

According to a preferred embodiment, the substrate of the invention has anti-reflection properties. Conventionally, an anti-reflection substrate is obtained by combining a first outer thin layer, that is to say in contact with the atmosphere, of relatively low refractive index, with a second thin layer immediately below the first and with a higher refractive index then possibly with other layers of alternately weak and strong indices. In accordance with the present invention, the production of protrusions makes it possible to control the solid fraction relative to the air fraction. Thus in the corresponding thickness of the substrate, the refractive index is a function of the material index and the air index, equal to 1, that is to say minimum. This index is lower than that which a solid layer of the same material would have and can be lowered by tending towards 1, by the fact that the solid fraction is reduced, in a controlled manner.

An anti-reflection effect therefore results from the fact that the outer layer has an outer fraction corresponding to the growths and a full inner fraction. According to another variant, the outer layer does not have such a full interior fraction. Alternatively or in addition, the anti-reflection properties may result from a treatment in the form of a stack of thin interference layers, generally consisting of an alternation of layers based on dielectric material with high and low refractive indices or in the form of a layer having a refractive index gradient in its thickness, as described in the document <patcit id="pcit0006" dnum="EP1013622A"><text>EP-1 013 622</text></patcit>. The function of such a coating deposited on a transparent substrate is to reduce the light reflection, and therefore to increase the light transmission. It is emphasized that such stacks or layers are capable of being formed in particular by vacuum techniques of the plasma CVD type, CVD not assisted by a plasma, cathode sputtering in particular assisted by a magnetic field, reactive sputtering, that is to say -to say techniques which can easily be integrated in a continuous process with those of formation of the growths, developed in the continuation.

On the outside of an automobile windshield, the anti-reflection effect results in improved visual comfort for the driver and passengers.

According to an interesting embodiment, the substrate is electrically conductive. Such may be the case of a constituent layer of the substrate, whether or not in contact with the ambient atmosphere, or of the entire substrate. Examples of materials used are the sub-stoichiometric and / or doped metal oxides mentioned above. The ability of the substrate to conduct electricity is aimed here at the antistatic function, that is to say the ability to dissipate electrostatic charges and to avoid their accumulation locally, as well as the constitution of heating films, in particular for the demisting and defrosting of glazing. Other usable electrically conductive materials are a material comprising for example SiH₄ or CH₄ as a precursor in order to form metallic bonds of the Si-Si or CC type or metallic salts such as copper acetylacetonate. The advantage of avoiding local accumulations of electrostatic charges appears in applications such as aircraft windshields, in which, on the contrary, it is important to remove these charges by conduction. Charge accumulations would in fact constitute a source of cracking and destruction of any stacked functional layers, as well as of the very structure of the substrate, in particular when it is laminated.

Another object of the invention resides in a process for etching a layer, a glass, silica (quartz) or a polymer substrate, by a reactive plasma through a mask made of a material and of suitable dimensions. , so as to form there the growths as defined above.

We have indeed surprisingly noticed, and without the reasons being still well known, that the engraving hardly took place in the absence of a mask, in the case where it is a glass that the we hear burn.

In addition to the advantages provided by this process which reside in the qualities of the products obtained such as superhydrophobia, superhydrophilia, optical properties in the case of a transparent substrate, durability, over large surfaces, this process currently seems promising because it can be carried out. by techniques, in particular under vacuum, which make it possible to carry out treatments of the substrate with a view in particular to equipping it with ever more numerous functions required for glazing, continuously and using a single device. A suitable etching mode is reactive ion etching.

The layer to be etched (which, in the following, denotes both the layer, the glass, the silica or the polymeric substrate to be etched) may or may not be transparent; in the latter case it can in certain cases then be transformed into a transparent layer (for example oxidation of Ti or Al to TiO₂ or Al₂O₃ transparent).

According to advantageous characteristics of the process:<ul id="ul0005" list-style="dash" compact="compact"><li>the mask is made of an electrically conductive material, such as a metal, in particular a noble metal of the Au, Ag, Pt, Pd type, a metal alloy, a conductive oxide such as obtained by doping, in particular SnO₂: F, SnO₂: In and the like, a ceramic or a polymer;</li><li>the mask is used in contact with the layer to be etched; let us mention in this respect a mode of formation of the mask of the inkjet type, among other numerous possibilities;</li><li>on the contrary, the mask is used without contact with the layer to be etched; the mask may for example consist of a metal grid positioned parallel to and at a short distance from the latter;</li><li>said mask is used in the state supported by a sheet, in particular of plastic, which is particularly practical, the mask being obtained in particular from a product in rolls; in this embodiment, good results can be obtained, whether the mask is located on the face of said sheet oriented towards the layer to be etched, or on its other face.</li></ul>

To obtain the substrate of the invention by this method, the etching is anisotropic and oriented along the normal to the substrate. To do this, five variants are recommended.

According to the first, the layer to be etched is laminated to an underlying electrically conductive layer, which is polarized with a radio frequency generator during the etching. The nature of the electrically conductive layer has been specified above.

According to the second variant, the substrate is placed on an electrically conductive support connected to a radiofrequency generator during the etching.

In accordance with the three other variants:<ul id="ul0006" list-style="dash" compact="compact"><li>the layer to be etched is itself electrically conductive; for example, SnO₂: F or a metallic layer such as Ti or Al which will optionally, after etching, be oxidized to TiO₂ or Al₂O₃ transparent;</li><li>the layer to be etched is laminated to a sheet of electrically conductive glass;</li><li>the layer to be etched is laminated to a glass sheet provided on its opposite face with an electrically conductive layer such as SnO₂: F.</li></ul>

According to other characteristics of the process:<ul id="ul0007" list-style="dash" compact="compact"><li>one or more of the CF plasma gases are used₄, VS₃F₂, SF₆, VS₂F₄, CHF₃ to perform the engraving;</li><li>the mask consists of nodules comprising at least one of the elements Ag, Au, Pd, Pt, Cu, Al, Zn, Sn, Sb, Ti, Zr, W, Mb, Ta, Ir. A layer of one or more of these elements is easily subjected to dewetting to obtain the nodules under excellent reproducibility conditions, with the required dimensions comparable to less than the wavelengths of visible light in order to minimize blurring, over relatively large areas sizes (such as greater than 1 m²) and with a fast focusing speed;</li><li>the method comprises a step consisting in eliminating or transforming into transparent compounds the fraction of said mask consisting of nodules remaining after having carried out the etching. It is specified that the metal nodules can also be attacked during etching, it does not always remain at the end of it. A removal process may consist, in the case of Ag nodules for example, by immersing the etched substrates in an acidic aqueous solution, for example of HNO₃. One can also consider a mechanical removal, in particular using a brush. An example of transformation into transparent compounds is the oxidation of Al into Al₂O₃ by passing a flame over the etched substrate;</li><li>the method comprises a step consisting in forming a coating on the substrate after having carried out the etching then, if necessary, eliminating or transforming the fraction of said mask remaining after having carried out the etching. An example is the vacuum grafting of a monomolecular layer of a hydrophobic or hydrophilic agent.</li></ul>

According to a second method of manufacturing the transparent substrate described above, nodules are formed with the dimensions and geometry required for said growths, they are made transparent if necessary and a coating is formed such as the grafting under vacuum of a functional monomolecular layer.

The invention also relates to a glazing unit comprising the substrate described above, this glazing unit being intended for a land, sea or air transport vehicle, in particular for an automobile, for the building (window, door, sanitary furniture element or other such as a shower cubicle, table, tablet, etc.), to an interior decorative element such as an aquarium or exterior, to urban furniture (bus shelters, etc.), to household appliances (door to oven, fridge shelf ...). Apart from the frame or frame elements, such glazing may essentially consist of a substrate according to the invention, or comprise one or more such substrates associated with one or more sheets of glass or of plastic material or transparent laminated structures in a multiple glazing in which all the constituents are separated two by two by an air space or the like.

Other advantageous objects and applications of the invention are:<ul id="ul0008" list-style="dash" compact="compact"><li>a lenticular screen or a microprismatic substrate obtained according to one of the methods described above comprising surface irregularities of dimensions in the main plane in the range from 1 μm to 1 mm; let us quote regular and contiguous rows in projection, of 8 to 14 µm in height, of 300 to 400 µm of pitch (peak-to-peak distance between two adjacent rows), formed in order to obtain a three-dimensional display system;</li><li>an etched glass substrate for lamp or display obtained according to one of the methods described above comprising surface irregularities of dimensions in the main plane in the range from 0.1 to 10 μm;</li><li>the application of a substrate according to the invention having cavities with diameters between 0.1 and 500 nm as chemical or biochemical microreactors.</li></ul>

The invention is now described in the light of an exemplary embodiment.

EXAMPLE 1

A 0.7 mm thick sheet of clear float glass sold under the trade name "Planilux" by the company SAINT-GOBAIN GLASS France was provided with a coating of indium oxide doped with tin ( ITO) 110 nm thick using any known deposition technique for this purpose, followed by a layer of SiO₂ 100 nm thick by any suitable technique (magnetron plasma, pyrolysis, CVD plasma, sol-gel ...).

A 15 nm thick layer of Ag is deposited under vacuum by magnetron sputtering. This layer of Ag is then dewetted by heat treatment at 300 ° C. under a vacuum of 9 mTorr for 30 min. Ag nodules are thus formed on the SiO layer₂.

The substrate thus obtained is subjected to reactive ion etching under the following operating conditions. The cathode is supplied with direct current, the ITO conductive sublayer being polarized by being connected to a radiofrequency generator set to 13.56 MHz. We use SF₆ as plasma gas and a pressure of 75 mTorr. The power is 0.106 W / cm² and the duration of the treatment of 250 s.

Immersion overnight in a 1 molar aqueous solution of HNO₃ at room temperature has the effect of eliminating the fraction of Ag nodules which had not been attacked in the previous etching step.

The substrate obtained seen at an angle of 15 ° with a magnification of 50,000 using a scanning electron microscope is shown in the single figure in the appendix. A formation of growths is observed, at least 80% of which have heights between 70 and 200 nm, average diameters between 50 and 400 nm, at least 80% of the distances between two neighboring growths being between 1 and 500 nm . These outgrowths can be defined as straight truncated cones with axes perpendicular to the main plane of the substrate and weak half-angles at the top, less than 20 °.

A monolayer of perfluorooctylethyltrichlorosilane C is grafted under vacuum in the vapor phase₁₀F₁₇H₄SiCl₃.

The angles of advance and retreat measured by growth, respectively decay of a drop of water by means of a pipette are 165 °, respectively 122 °, corresponding to a superhydrophobic behavior.

In addition, a light transmission of 92.8% and a haze of less than 4% are measured using a Hazegard XL 211 device.

EXAMPLE 2

A glass sheet differing from that of the previous example in that it does not have an ITO coating or a layer of SiO₂, is subjected to the same dewetting of silver as previously, then to the subsequent operations described in the previous example, by simply being placed on an electrically conductive support connected to the same radio frequency generator, all other conditions being equal.

The cylindrical outgrowths (axes perpendicular to the plane of the sheet) formed are almost entirely characterized by a height of approximately 100 nm, a diameter of 80 to 100 nm, and a distance between the axes of two neighboring cylinders of between 130 and 150 nm.

The etching speed measured perpendicular to the surface of the substrate is 5 to 8 nm / min; in the absence of the mask formed by the silver nodules, this speed is zero.

Thus, the invention makes it possible to combine on a large substrate a surface tension functionality, remarkable optical quality and a possibility of providing additional functions, under excellent conditions of industrial implementation, in particular in many case by carrying out the various treatments continuously in a single apparatus.