Substrate comprising a stack having thermal properties

CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -1SUBSTRATE EQUIPPED WITH A STACK WITH THERMAL PROPERTIES The invention relates to transparent substrates, in particular made of rigid mineral material such as glass, said substrates being coated with a stack of thin layers comprising at least two functional layers of metallic type capable of acting on solar radiation and / or infrared radiation of long wavelength.

The invention relates more particularly to the use of such substrates for manufacturing thermal insulation and / or solar protection glazing.

These glazing can be intended both to equip buildings and vehicles, in particular with a view to reducing the air conditioning effort and / or preventing excessive overheating (so-called solar control glazing) and / or reducing the quantity of energy. dissipated to the outside (so-called low-emissive glazing) caused by the ever increasing importance of glazed surfaces in buildings and vehicle interiors.

These glazings can moreover be integrated into glazings having particular functionalities, such as for example heated glazing or electrochromic glazing.

A type of stack of layers known to give substrates such properties consists of at least two functional metal layers with reflection properties in the infrared and / or in solar radiation, in particular functional metal layers based on silver or metal alloy containing silver.

Each metallic functional layer is deposited in a crystallized form on a wetting layer also crystallized favoring the adequate crystalline orientation of the metallic layer deposited thereon.

Each functional layer is located between two coatings of dielectric material of the metal oxide or nitride type.

This stacking is generally obtained by a succession of deposits carried out CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -2 by a technique using vacuum such as cathodic sputtering possibly assisted by magnetic field.

There may also be provided one, or even two, very fine coating (s) called blocking coating (s), arranged directly under, on or on each side of each functional metal layer based on silver, the underlying coating as an attachment coating, nucleation and / or protection during a possible heat treatment after deposition, and the overlying coating as a protective or sacrificial coating in order to avoid the deterioration of the silver if a layer on top of it is deposited by sputtering in the presence of oxygen or nitrogen and / or if the The stack undergoes a heat treatment after the deposition.

It is thus known from European patent application EP-0 638 528 of stacks of this type, with two silver-based layers.

It is also known from European patent application N EP 803 481, the use under a wetting layer based on zinc oxide of an amorphous layer based on mixed oxide of zinc and tin directly in contact with the substrate.

It turns out that such an amorphous layer when it is not deposited directly on the substrate but that it is interposed between an underlying dielectric layer and a wetting layer makes it possible to modify the interface between the dielectric layer. and the wetting layer located above and thereby substantially improving the crystallization of the wetting layer as well as the crystallization of the functional metal layer.

However, the integration of such an amorphous layer in each coating underlying a functional layer and provided with at least one dielectric layer under this amorphous layer in a stack with several functional layers does not make it possible to achieve in all cases. the desired improvement in the crystallization of the functional layers and thus the desired improvement in the resistivity of the complete stack.

CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -3 The aim of the invention is to overcome the drawbacks of the prior art, by developing a new type of stack with functional layers of type of those described above, a stack which has improved resistivity, which is lower than in a similar stack with a thickness of functional layers and equivalent coatings, whether the stack is subjected or not, one (or more) heat treatment (s) at high temperature of the bending, tempering or annealing type and in the case where it undergoes one (or more) such treatment (s), while preserving its optical quality and its mechanical strength.

The subject of the invention is thus, in its broadest sense, a substrate, in particular transparent glass substrate, provided with a stack of thin layers comprising an alternation of n functional layers with reflection properties in the infrared and / or in the infrared. solar radiation, in particular metallic functional layers based on silver or a metallic alloy containing silver, and (n + 1) coatings, with n integers> 2, said coatings being composed of a plurality of dielectric layers, so that each functional layer is disposed between two coatings, at least two functional layers each being deposited on a wetting layer itself deposited respectively directly on a sub-coating. underlying, characterized in that two underlying coatings each comprise at least one dielectric layer and at least one non-crystallized smoothing layer of a material different from the material of said dielectric layer inside each coating, said smoothing layer being in contact with said overlying wetting layer and in that these two underlying coatings being of different thickness, the thickness of the smoothing layer of the underlying coating having a total thickness less than that of the other underlying coating is less than or equal to the thickness of the smoothing layer of this other underlying coating.

CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -4 The invention thus consists in providing an uncrystallized smoothing layer under the wetting layer which is crystallized to allow adequate growth of the functional layer located at the bottom. above this wetting layer, directly in contact with the wetting layer or via an underblocking coating.

The crystallographic appearance of the smoothing layer is necessarily different from that of the wetting layer since the smoothing layer is non-crystallized while the wetting layer is essentially crystallized; they cannot therefore be confused from this point of view.

However, it appeared that in stacks with several functional layers, it was important to take into account the thickness of the underlying coatings to calculate the thickness of the smoothing layers present in these underlying coatings.

The invention thus consists in providing that the thickness of the smoothing layer of a thinner underlying coating cannot be greater than the thickness of the smoothing layer of a thicker underlying coating.

The invention applies to coatings which are underlying a functional layer, regardless of the location of the functional layers in the stack; however, it is preferable that, in the same stack of thin layers, all the underlying coatings comprising a smoothing layer meet the definition of the invention.

For the purposes of the present invention, when it is specified that a deposit of a layer or coating (comprising one or more layers) is carried out directly under or directly on another deposit, it means that there can be no interposition of 'no layer between these two deposits.

The smoothing layers are preferably based on an oxide; they are therefore not metallic.

The smoothing layers are said to be non-crystallized in the sense that they can be completely amorphous or partially amorphous and CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -5 thus partially crystallized, but they cannot be completely crystallized, over their entire thickness.

The advantage of such a smoothing layer is that it makes it possible to obtain an interface with the directly overlying wetting layer which is not very rough.

This low roughness can also be observed under a transmission electron microscope.

Furthermore, the wetting layer is textured better and also has a more marked preferential crystallographic orientation.

Each smoothing layer is thus made of a different material, both crystallographically and stoichiometrically, from that of the wetting layer under which it is directly placed.

The invention does not apply only to stacks comprising only two functional layers, arranged between three coatings, two of which are underlying coatings.

It also applies to stacks comprising three functional layers alternating with four coatings, three of which are underlying coatings, or four functional layers alternating with five coatings, four of which are underlying coatings.

For these multilayer functional stacks, at least one, and preferably each, functional layer is disposed directly on at least one underlying blocking coating and / or directly under at least one overlying blocking coating.

In the case of functional bilayer stacks, or even also in the other cases, the thinner coating of said two underlying coatings comprising a smoothing layer is preferably the closest to the substrate, or even in contact with the substrate, directly or indirectly via a contact layer, for example based on titanium oxide (TiO 2).

In the case of stacks with more than two functional layers, the underlying coating farthest from the substrate is the thinner of two adjacent underlying coatings.

CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -6 Preferably, at least one smoothing layer, or even all the smoothing layers, is (or are) an oxide layer, and in particular an oxide layer mixed, based on an oxide of one or more of the following metals: Sn, Si, Ti, Zr, Hf, Zn, Ga, In and more precisely a layer of mixed oxide based on zinc and tin or of mixed oxide of zinc and indium (ITO) cold deposited.

The index of the smoothing layer is preferably less than 2.2.

Preferably also, at least one smoothing layer, or even all of the smoothing layers, is (or are) a layer of non-stoichiometric oxygen oxide and more particularly still a layer of mixed oxide based on zinc and substoichiometric tin, doped with antimony (SnZnOX: Sb, x being a number).

Furthermore, the (or each) smoothing layer preferably has a geometric thickness between 0.1 and 30 nm and more preferably between 0.2 and 10 nm, in particular for the thinner of the two concerned.

In a preferred variant, at least one blocking coating is based on Ni or Ti or is based on an Ni-based alloy, in particular is based on an NiCr alloy.

In addition, at least one, and preferably each, wetting layer underlying a functional layer is preferably zinc oxide based; these wetting layers may in particular be based on zinc oxide doped with aluminum.

The geometric thickness of each wetting layer is preferably between 2 and 30 nm and more preferably between 3 and 20 nm.

Further, at least one, and preferably each, dielectric layer adjacent to a smoothing layer within said underlying coatings and in particular the dielectric layer directly underlying the smoothing layer, is preferably based of nitride, in particular of silicon nitride and / or of aluminum nitride.

CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -7 The index of this nitride-based dielectric layer is preferably less than 2.2.

The glazing according to the invention incorporates at least the substrate carrying the stack according to the invention, optionally associated with at least one other substrate.

Each substrate can be clear or colored.

At least one of the substrates, in particular, can be made of glass colored in the mass.

The choice of the type of coloring will depend on the level of light transmission and / or the colorimetric appearance desired for the glazing once its manufacture has been completed.

Thus for glazing intended to equip vehicles, certain standards require that the windshield has a light transmission TL of approximately 75% and other standards require a light transmission TL of approximately 65%; such a level of transmission is not required for the side windows or the car roof, for example.

The tinted glasses that can be used are for example those which, for a thickness of 4 mm, have a TL of 65% to 95%, an energy transmission TE of 40% to 80%, a dominant wavelength in transmission from 470 nm to 525 nm associated with a transmission purity of 0.4% to 6% according to Illuminant D65, which can be translated in the colorimetry system (L, a *, b *) by values ​​of a * and b * in transmission respectively between -9 and 0 and between -8 and +2.

For glazing intended to equip buildings, the glazing preferably has a light transmission TL of at least 75% or more for low-emissive applications, and a light transmission TL of at least 40% or more for solar control applications.

The glazing according to the invention may have a laminated structure, combining in particular at least two rigid substrates of the glass type with at least one sheet of thermoplastic polymer, in order to present a structure of the glass / stack of thin layers / sheet (s) / type. glass.

CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -8polymer may in particular be based on polyvinylbutyral PVB, ethylene vinyl acetate EVA, polyethylene terephthalate PET, polyvinyl chloride PVC.

The glazing can also have a so-called asymmetric laminated glazing structure, associating a rigid substrate of the glass type with at least one sheet of polyurethane-type polymer with energy-absorbing properties, optionally combined with another layer of polymers with self-absorbing properties. -healing.

For more details on this type of glazing, it is possible to refer in particular to patents EP-0 132 198, EP-0 131 523, EP-0 389 354.

The glazing can then have a structure of the type of glass / stack of thin layers / sheet (s) of polymer.

The glazing according to the invention is suitable for undergoing a heat treatment without damage to the stack of thin layers.

They are therefore possibly convex and / or hardened.

The glazing can be curved and / or toughened by being made up of a single substrate, that provided with the stack.

It is then a so-called monolithic glazing.

In the case where they are curved, in particular with a view to constituting glazing for vehicles, the stack of thin layers is preferably located on an at least partially non-planar face.

The glazing can also be a multiple glazing, in particular a double glazing, at least the substrate carrying the stack being able to be curved and / or toughened.

It is preferable in a multiple glazing configuration that the stack is arranged so as to be turned towards the side of the interlayer gas knife.

In a laminated structure, the substrate carrying the stack is preferably in contact with the polymer sheet.

When the glazing is monolithic or multiple of the double glazing or laminated glazing type, at least the substrate carrying the stack may be of curved or tempered glass, this substrate possibly being curved or tempered before or after the deposition of the stack.

In a variant, the glazing is provided with means making it possible to supply said stack with electrical energy.

CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -9 The invention also relates to the process for manufacturing the substrates according to the invention, which consists in depositing the stack of thin layers on its substrate by a technique under vacuum of the cathodic sputtering type optionally assisted by a magnetic field, then in carrying out on the coated substrate a bending / tempering or annealing heat treatment without degradation of its optical and / or mechanical quality.

However, it is not excluded that the first or the first layers of the stack may (s) be deposited by another technique, for example by a thermal decomposition technique of pyrolysis type.

The details and advantageous characteristics of the invention emerge from the following non-limiting examples, illustrated with the aid of the attached figures:

- Figure 1 illustrates the evolution, before heat treatment, of the resistance per square of a functional monolayer stack provided with a monolayer over-blocking coating, without and with a smoothing layer, as a function of the thickness of the dielectric layer placed below;

FIG. 2 illustrates the change, after heat treatment, of the resistance per square of the same functional monolayer stack as in FIG. 1, without and with a smoothing layer, as a function of the thickness of the dielectric layer placed below;

FIG. 3 illustrates the evolution, before heat treatment, of the resistance per square of a functional single-layer stack provided with a single-layer over-blocking coating as a function of the thickness of the smoothing layer;

FIG. 4 illustrates the change, after heat treatment, of the resistance per square of the same functional monolayer stack as in FIG. 3 as a function of the thickness of the smoothing layer;

- Figure 5 illustrates a functional bilayer stack according to the invention, each functional layer being provided with a CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -10 over-blocking coating but not a coating underblocking;

FIG. 6 illustrates a functional bilayer stack according to the invention, each functional layer being provided with an underlocking coating but not with an overlocking coating;

FIG. 7 illustrates a functional bilayer stack according to the invention, each functional layer being provided with an under-blocking coating and an over-blocking coating;

FIG. 8 illustrates a functional three-layer stack according to the invention, each functional layer being provided with an underlocking coating but not with an overlocking coating; and FIG. 9 illustrates a functional four-layer stack according to the invention, each functional layer being provided with an underlocking coating but not with an overlocking coating.

In the figures illustrating stacks of layers, the proportions between the thicknesses of the different materials are not strictly observed in order to facilitate their reading.

Moreover, in all the examples below, the stack of thin layers is deposited on a substrate 10 made of soda-lime glass with a thickness of 2 mm, unless explicitly mentioned otherwise.

In all cases where heat treatment was applied to the substrate, it was annealing for about 5 minutes at a temperature of about 660 C followed by cooling in ambient air (about 20 C).

Figures 1 to 4 are intended to illustrate the importance of the presence of a smoothing layer in a stack.

CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -11 However, the stack which was used to produce these figures is not a stack according to the invention because it is a stack functional monolayer of the type:

Substrate / Si3N4 / SnZnO,: Sb / ZnO / Ag / Ti / ZnO / Si3N4 Variable / Variable / 8nm / lOnm / 2nm / 8nm / 20 nm In figures 1 and 2, curves Cl and C11 illustrate the variation in resistance per square (in ohms) of the stack as a function of the thickness of the dielectric layer based on silicon nitride (e Si3N4) in contact with the substrate, respectively before (BHT) and after (AHT) heat treatment, when the stack is not provided with a smoothing layer.

Curves C2 and C12 illustrate the variation in resistance per square (in ohms) of the stack as a function of the thickness of the dielectric layer based on silicon nitride (e Si3N4) in contact with the substrate, respectively before and after heat treatment, when the stack is provided with a smoothing layer of SnZnOX: Sb with a thickness of 6 nm (x denotes a non-zero number).

Curves C3 and C13 illustrate the variation of the resistance per square (in ohms) of the stack as a function of the thickness of the dielectric layer based on silicon nitride (e Si3N4) in contact with the substrate, respectively before and after heat treatment, when the stack is provided with a smoothing layer based on SnZnOX: Sb with a thickness of 20 nm.

As can be seen in these FIGS. 1 and 2, for the same thickness of dielectric in contact with the substrate (for example 20 nm), the resistance per square of the stack is always lower - therefore better - for the curves C2, C3, C12 and C13 when the stack comprises a smoothing layer based on SnZnOX: Sb between the dielectric layer based on silicon nitride in contact with the substrate and the underlying wetting layer based on zinc oxide ZnO to the functional layer based on silver CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 - 12 Ag; moreover, the resistance per square of the stack is always lower for a smoothing layer thickness of 20 nm (curves C3 and C13).

It has been verified that the mixed oxide smoothing layer is amorphous over its entire thickness, while the wetting layer and the metallic functional layer are both crystallized over their entire thickness.

Consequently, the presence of a smoothing layer significantly improves the resistance per square of the stack with comparable underlying dielectric thickness and this improvement is all the greater as the thickness of the layer of dielectric. smoothing is important.

In Figures 3 and 4, the curves illustrate the variation of the resistance per square (in ohms) of the stack as a function of the thickness of the smoothing layer based on zinc oxide and tin doped with l 'antimony (e SnZnOX: Sb), respectively before (BHT) and after (AHT) heat treatment, when the stack is provided with a layer based on silicon nitride Si3N4 of nm between the substrate and the layer based on SnZnOX: Sb.

It has also been verified that the mixed oxide smoothing layer is amorphous throughout its thickness, while the wetting layer and the metallic functional layer are both crystallized throughout their thickness.

As can also be seen in these FIGS. 3 and 4, the presence of a smoothing layer significantly improves the resistance per square of the stack for a smoothing layer between> 0 and 4 nm thick and this improvement is all the stronger as the thickness of the smoothing layer is important.

Similar findings can be made with a functional single layer stack provided with an underlocking coating and without an overlocking coating or provided with an underlocking coating and an overlocking coating.

CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 - 13 Tests were also carried out to make it possible to measure the roughness of the layers.

Table 1 below illustrates the roughness measured by X reflectometry and expressed in nm (the roughness of the substrate being approximately 0.4) Layer (s) Thickness (nm) Roughness o (nm) Si3N4 28.5 1.1 Glass Substrate Sn02 29.5 0.8 Glass Substrate SnZnOX: Sb 32.0 0.7 Glass Substrate SnZnOX: Sb 11.2 0.8 Si3N4 19.7 0.5 Glass Substrate Sn02 10.4 0.8 Si3N4 19, 3 0.5 Glass Substrate Table 1 As visible in this table, the roughness of the layer based on silicon nitride Si3N4 deposited alone on the glass is high, but the final roughness of a stack comprising a mixed oxide layer based on tin oxide and indium SnInOX (ITO) or a layer based on mixed oxide of zinc and tin SnZnOX: Sb deposited on the layer based on silicon nitride is lower.

The wetting layer based on mixed oxide thus makes it possible to improve the roughness of the interface with the wetting layer, by reducing this roughness.

Based on these observations, it is thus possible to deposit on a substrate 10 a stack of thin layers comprising an alternation of n functional layers 40, 80, 120, 160 with reflection properties in the infrared and / or in solar radiation, in particular metallic functional layers based on silver or a metallic alloy containing silver, and (n + 1) coatings 20, 60, 100, 140, 180, with n integer greater than or equal to 2, said coatings being composed CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -14 of a plurality of dielectric layers 24, 26; 62, 64, 66; 102, 104, 106, 142, 144, 146, 182, 184, so that each functional layer 40, 80, 120, 140 is disposed between two coatings 20, 60, 100, 140, 180, at least two layers functional, and preferably each functional layer, being deposited on a wetting layer 30, 70, 110, 150 itself deposited respectively directly on an underlying coating 20, 60, 100, 140.

Thus, on the basis of the above functional monolayer tests, several functional bilayer tests were carried out but not all of them give satisfaction.

Two examples, numbered 1 and 2, were carried out on the basis of the functional bilayer stacking structure illustrated in FIG. 5 in which each functional layer 40, 80 is provided with an over-blocking coating 45, 85, but with a coating. of under-blocking.

Table 2 below illustrates the thicknesses in nanometers of each of the layers Material Layer Ex. 1 Ex. 2 104 Si3N4 20 20 102 ZnO 8 8 85 Ti 2 2 80 Ag2 10 10 70 ZnO 8 8 66 SnZnOX: Sb 20 6 64 Si3N4 40 52 62 ZnO 8 8 45 Ti 2 2 40 Ag, 10 10 30 ZnO 8 8 26 SnZnOX: Sb 6 20 24 Si3N4 20 6 Table 2 CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 -15 Thus, in Example 1 according to the invention, the thickness of the smoothing layer 26 based on zinc oxide and tin doped with antimony SnZnOX: Sb of the thinner underlying coating 20 is less than the thickness of the smoothing layer 66 based on of zinc and tin oxide doped with antimony SnZnOX: Sb of the thicker underlying coating 60, while in counterexample 2, the thickness of the smoothing layer 26 of the thinner underlying coating 20 is greater than the thickness of the smoothing layer 66 of the thicker underlying coating 60.

The resistivities obtained are presented in Table 3 below Ex. 1 Ex. 2 Before R = Ag2 4.80 5.4 thermal treatment R = Ag, 4.75 4.5 thermal R = Total 2.39 2.45 After R = Ag2 3.73 4.35 thermal treatment R = Ag, 3.65 3.45 R = Total 1.84 1.92 Table 3 Thus, the resistivity of Example 1 according to the invention is better than that of Example 2 both before heat treatment and after heat treatment.

In the case of Example 2, the integration of the smoothing layer in a stack with several functional layers does not make it possible to achieve the desired improvement obtained in the case of Example 1 of the crystallization of the layers. functional, even though (and this has been verified) the smoothing layer is amorphous and the wetting layer is crystallized.

Another series of examples, numbered 3, was carried out on the basis of the functional bilayer stacking structure illustrated in figure 6, in which each functional layer 40, 80 is provided with a coating of CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 - 16 subblocking 35, 75, however without a mechanical protective layer 200 visible in FIG. 6.

Table 4 below illustrates the thicknesses in nanometers of each of the layers Layer Material Ex. 3 104 Si3N4 27 102 ZnO 8 80 Ag2 10 75 Ti 2 70 ZnO 10 66 SnZnOX: Sb Y 64 Si3N4 65-Y 62 ZnO 8 40 Ag , 10 35 Ti 2 30 ZnO 7 26 SnZnOX: Sb X 24 Si3N4 23-X Table 4 On this basis six examples, numbered 3a to 3f, were produced.

Table 5 below illustrates the values ​​of X and Y in nanometers for each example:

Ex. type XY 3a X <Y 2 6 3b X> Y 6 2 3c X <Y 2 10 3d X> Y 10 2 3e X <Y 2 4 3f X> Y 4 2 Table 5 CA 02644862 2008-09-04 WO 2007 / 101963 PCT / FR2007 / 050881 - 17 Thus, in Examples 3a, 3c and 3e according to the invention, the thickness of the smoothing layer 26 of the thinner underlying coating 20 is less than the thickness of the layer of smoothing 66 of the thicker underlying coating 60, while in counter-examples 3b, 3d and 3f, the thickness of the smoothing layer 26 of the thinner underlying coating 20 is greater than the thickness of the smoothing layer 66 of the thicker underlying coating 60.

The resistivity, optical and energy characteristics of these examples are reported in Table 6 below (the optical and energy characteristics were measured after annealing and insertion into a laminated glazing having the structure: exterior / 2.1 glass substrate mm / 0.25 mm PVB / 2.1 mm glass substrate carrying the stack; the layer stack is thus on face 3, numbered in relation to the direction of the incident sunlight):

Ex. R- TE TL (A) a * (D65) b * (D65) RE RL (D65) (ohms) 3a 2.7 45.02 77.25 -2.36 -5.75 33.40 11.29 3b 2.9 44.58 75.30 -4.88 -4.64 32.70 13.08 3c 2.6 45.46 78.31 -1.98 -4.78 33.36 10.96 3d 2, 8 45.21 77.33 -2.81 -4.38 33.08 11.79 3rd 2.8 44.96 77.49 -3.02 -4.51 33.43 11.42 3f 2.9 45 , 12 77.81 -1.79 -4.72 33.64 11.19 Table 6 Thus, the resistivity of the stack (measured here after heat treatment) of Examples 3a, 3c, 3e according to the invention is always lower respectively to counter-examples 3b, 3d, 3f corresponding.

In addition, the energy transmission TE, the light transmission TL measured according to the illuminant A, the energy reflection RE, the light reflection RL (D65) measured according to the illuminant D65 and the colors in reflection a * and b * in the system. LAB measured according to the illuminant D65 on the layer side does not CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 - 18 not really vary significantly between the examples according to the invention and the counter-examples 3b, 3d, 3f correspondents.

By comparing the optical and energy characteristics measured here before heat treatment with these same characteristics after heat treatment, no degradation was observed.

Further tests were carried out based on the functional bilayer stack structure illustrated in Figure 7 in which each functional layer 40, 80 is provided with an underlock coating 35, 75 and an overcoat. blocking 45, 85.

These tests made it possible to arrive at similar findings.

For functional bilayer structures, it has been found to be preferable that the smoothing layer of the thinner underlying coating is closest to the substrate and therefore the smoothing layer of the thicker underlying coating is the closest to the substrate. farther from the substrate.

It is also possible to apply the invention to a stack with three functional layers, such as for example the stack illustrated in FIG. 8.

In the illustrated configuration, each functional layer 40, 80, 120 is provided with an underlock coating 35, 75, 115; however, it is also possible to provide, in addition to or without this underlocking coating 35, 75, 115, an overlocking coating.

In addition, in the illustrated configuration, each underlying coating 20, 60, 100 has a smoothing layer 26, 66, 106 in accordance with the invention.

For functional tri-layer structures, it has been found that it is preferable that the smoothing layer of the thinner underlying coating is closest to the substrate and the smoothing layer of the thicker underlying coating is the layer of central smoothing 66 and that the most layer CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 - 19 far from the substrate 106, either thicker than the smoothing layer 26 closest to the substrate and thinner than the central smoothing layer 66.

In this structure, it is possible to provide only two smoothing layers, that is to say to provide that only two underlying coatings correspond to the invention.

In this case, the thinner coating of said two underlying coatings is the furthest from the substrate.

It is also possible to apply the invention to a stack with four functional layers, such as for example the stack illustrated in FIG. 9.

In the illustrated configuration, each functional layer 40, 80, 120, 160 is provided with an underlock coating 35, 75, 115, 155; however, it is also possible to provide, in addition to or without this underlocking coating 35, 75, 115, 155, an overlocking coating.

In addition, in the illustrated configuration, each underlying coating 20, 60, 100, 140 has a smoothing layer 26, 66, 106, 146 in accordance with the invention.

This stack can be obtained, for example, by passing the substrate 10 twice through a device for depositing a functional bilayer stack, as is known from international patent application N W02005 / 051858, in order to deposit:

- during a first pass the layers 24 to 102, then - during a second pass the layers 104 to 182, then - in a deposit finishing device, the layers 184 and 200.

In this structure, it is possible to provide only two smoothing layers, that is to say to provide that only two underlying coatings correspond to the invention.

In this case, the thinner coating of said two underlying coatings is the furthest from the substrate.

CA 02644862 2008-09-04 WO 2007/101963 PCT / FR2007 / 050881 - 20 The present invention is described in the above by way of example.

It is understood that a person skilled in the art is able to produce different variants of the invention without, however, departing from the scope of the patent as defined by the claims.