EP1874703A1

EP1874703A1 - Low-emissivity glazing

Info

Publication number: EP1874703A1
Application number: EP06725109A
Authority: EP
Inventors: Daniel Decroupet; Jean-Michel Depauw
Original assignee: AGC Glass Europe SA
Current assignee: AGC Glass Europe SA
Priority date: 2005-03-17
Filing date: 2006-03-16
Publication date: 2008-01-09
Also published as: EA012597B1; WO2006097513A1; EA200701994A1; BE1016553A3; US7745009B2; US20090004412A1; CN101171206B; CN101171206A; JP2008532914A

Abstract

The invention concerns a low-emissivity glazing. The inventive glazings comprise an assembly of thin layers including at least one metal layer reflecting infrared rays between one or more dielectric layers located between the metal layer and the glass sheet and on the metal layer, the light transmission for one clear float glass sheet 4 mm thick coated with said layers being not less than 83 %, the metal layer being selected such that the emissivity is not higher than 0.042.

Description

Low emissivity glazing

The present invention relates to low emissivity glazings, ie glazings which have the property of reflecting the infrared radiation emitted for example from the inside of dwellings, and therefore limiting the heat losses.

The demand for such glazing is often linked to that of having as high a light transmission as possible. The two requirements of low emissivity and high transmission normally lead to opposite solutions in terms of structure. Difficult compromises need to be made.

The most common practice is to have thin film systems with one or more layers capable of reflecting infrared radiation. Systems of this type generally consist of metal layers, in particular of a few nanometers thick silver layer. The layers must be thin enough not to reduce the visible light transmission too much. The thickness must also be sufficient to hinder the transmission of infrared rays, the thickness directly determining the fraction of these which are actually reflected.

The systems applied to the glazing must simultaneously fulfill other conditions. First, it is necessary to protect the reflective metal layers against chemical or mechanical aggression to which they may be exposed. The Metal layers are usually deposited on the glass substrate by vacuum deposition techniques of the magnetic field assisted sputtering type, more commonly known as magnetron sputtering. The layers obtained by these techniques offer the advantage of a great regularity of composition, thickness and surface condition. However, they are very fragile and must be protected by additional layers. Transparent dielectric layers, metal oxides and / or nitrides, or mixtures thereof, which offer the required strength, are used in a perfectly conventional manner.

At the same time, the metal layers must also be protected from possible diffusion from the substrate, which diffusion would disadvantageously modify the properties of the reflective metal layer. The nature of the dielectric layers between the substrate and the metal layer is often similar to that of the layers above the same metal layer. These are oxides and / or metal nitrides.

Traditionally, the sequence of layers consists of the following:

glass / dielectric I / metal / dielectric II

Among the most widely used dielectrics are ZnO, TiO ₂ , SnO ₂ and Si ₃ N ₄ ... These dielectrics offer various optical properties and are also distinguished by industrial production conditions.

The most common structures still incorporate a particular layer between the metal and the outer dielectric, a layer whose function is to protect the metal especially during the deposition of the layer of this dielectric. Indeed most often the formation of this dielectric is so called "reactive". In these techniques the dielectric (oxide or nitride) is formed at the very moment of the deposition by reaction of metallic vapor emitted by bombardment of a metal cathode, with the atmosphere at very reduced pressure in which this deposition takes place, for an oxide an oxygen atmosphere or a gaseous mixture containing oxygen. Under these conditions, the deposited metal layer is in contact with this atmosphere and can be impaired in particular because of the high reactivity of the plasma.

For protection against this alteration, it is still customary to have a layer called "barrier" or "sacrificial" layer directly on the metal or oxidized or nitrided reflecting infrared layer. It is a metal layer or partially oxidized very thin whose function is to react with the constituents of the atmosphere that could alter the metal layer reflecting infrared rays. The barrier layer is carefully selected for both its nature and its thickness. It is not itself intended to intervene in the infrared reflection, but to react with the atmosphere in which the dielectric deposits of the layers deposited after that of the infrared reflective metal layer are performed. To avoid that it substantially reduces the light transmission, it is important to ensure that the barrier layer is as thin as possible, but even more so, that it is practically completely transformed into dielectric transparent during its filing or deposit operations succeeding its own filing.

The traditional systems consequently have the following succession of layers:

glass / dielectric I / metal / barrier / dielectric II If necessary, the use of ceramic targets instead of metal targets, avoids reactive deposition. In other words, the oxide deposit can be conducted in a substantially inert atmosphere (generally less than 10% oxygen), thus avoiding the risk of oxidation of the previously deposited silver layer. In this event, it is possible to build a stack of layer without a barrier layer on top of the silver.

The formation of these sets of layers must also lead to satisfactory colors in both reflection and transmission. The demand is in the direction of the most perfect neutrality possible. In the CIELab colorimetric coordinates this corresponds to the values a * and b * close to zero. Negative values, especially for b *, are also acceptable. They give the glazing either a blue shade for the negative values of b *, or a green shade for the negative values of a *. Conversely, we try to avoid positive values of a *, which would lead to purple and brownish shades.

The neutrality of glazing depends on the choice of layer combinations. The layers constituting the sets in question intervene to constitute an interference system which makes it possible to eliminate most of the undesired wavelengths. The elimination of these colors follows a mechanism well known in this field. The difficulty is to combine both the colorimetric requirements with those related to "basic" conditions: high light transmission and very low emissivity.

Moreover, if the principles governing the optical properties of the materials constituting the layers are well known, an additional difficulty comes from the production techniques of these glazings. The deposit conditions, and in particular the deposit speed, are dependent on the nature of the materials considered. For an economically acceptable industrial production, the speed must be sufficient. It depends on multiple factors that ensure the stability of operation over time and over the entire surface of the sheet, and the absence of defects in the layer.

If many sets of layers have been proposed to meet these various requirements, other combinations must be sought to access changes in new applications. In this sense, the regulatory provisions that closely follow the progress of technology call for ever-improving performances.

Recent regulatory changes include double glazing, which is the usual method for building insulation. The performance of these glazings are defined for a composition comprising the use of insulating gas between the two glass sheets insulating glass. The degree of insulation achieved depends on the nature of the gas. Previously measurements were made in a regulatory way based on pure argon.

It has become apparent in practice that it is not possible to guarantee that the glazings thus formed retain a gas consisting of 100% argon. As a result, the performance of glazing approved for pure argon was not assured.

In order to restore a good consistency between the approval criteria and the expected results for the products marketed, the certifying bodies have defined new conditions of approval in which the performances must be established for an insulating gas consisting of 90% of argon, the remaining 10% being air. The decrease in the argon content is accompanied by a poorer insulation, due to a increased thermal loss by conduction. Consequently, to restore the performance of the glazings, the layers used must be even more efficient, especially as regards their emissivity.

As an indication, the current demand is to obtain a coefficient U at most equal to 1.1 W / m ² .K under the non-ideal filling conditions indicated above.

The metal layers, as indicated above, are those which determine the emissivity of the whole. While different metals are named in the literature, virtually all existing products use silver-based layers as the reflective metal. It represents the best compromise in terms of infrared reflection and transparency to visible wavelength radiation and color neutrality in transmission and reflection.

Various means have been proposed to ensure that these silver layers achieve the best performance. Particularly noteworthy is the teaching of US Pat. No. 5,110,662, which belongs to the applicant, which shows the decisive influence of a ZnOx layer disposed immediately below the silver layer and of a well-defined thickness. It should be emphasized that this idea is alternatively adopted in a number of patents or subsequent patent applications, such as WO 99/00528.

Various hypotheses have been formulated to explain the mechanism by which this ZnOx layer improves, under certain conditions, the emissivity and conductivity properties. Among these hypotheses some concern for example the "hanging" of silver on the dielectric layer, others the fact that the presence of ZnOx promotes the crystallization of silver in systems leading to less grain boundaries etc.

The conductivity, and consequently the emissivity, of silver layers deposited under industrial conditions have been appreciably improved over time, without reaching the ideal values of metallic silver. The choice is of course to use the layers having the best conductivity and therefore the best possible emissivity. On the basis of the best characteristics of the silver, a further improvement of the emissivity passes by the increase of the thickness of the silver layer, all the other characteristics of this layer being preserved.

It is well known that emissivity decreases when the thickness of money increases. Nevertheless, the consequences of this increase in the thickness of silver are not all favorable. If the light transmission, within the limits of the usual thickness variations of the silver layer, is relatively unaffected, the main difficulty lies in the significant alteration of the induced colorings especially in reflection. The windows in question tend to lose in neutrality.

The inventors have therefore endeavored to develop glazing whose emissivity is further reduced, while retaining as much light transmission and acceptable color neutrality as possible.

The glazings according to the invention are constituted for this purpose by a succession of layers comprising at least one layer of silver of thickness such as the emissivity of the assembly, for a traditional clear float glass whose transmission for the glass alone

TL4 is 90%, not more than 0.042, and preferably not greater than 0.038 and most preferably not greater than 0.035.

For glazing according to the invention, obtaining these emissivities can be achieved by using a thicker silver layer. The silver thickness according to the invention is advantageously at least 12 nm. It does not exceed 18 nm so that the light transmission is maintained at least 83% always under the same conditions of a clear glass of 4mm thick. Preferably, the thickness of the silver layer is 12.5 to 16 nm, and more particularly 12.5 to 14 nm.

The thicknesses indicated relate to the silver layer supposed to be unique. It is possible to replace this layer by two distinct layers separated by one or more dielectric layers. In practice, the division of the silver layer, by multiplying the interfaces, is not the most efficient solution for obtaining the best emissivity. It may be necessary, for the same emissivity, to slightly increase the total thickness. The solution consisting of using two silver layers instead of one opens up different possibilities as regards the adjustment of the interference systems with the dielectric layers, in order to improve the color neutrality, especially in reflection. Since the control of color neutrality can be obtained without dividing the silver layer, this solution is preferred because it makes it possible to ensure a higher light transmission.

The layer systems associated with the silver layer of the glazings according to the invention advantageously comprise a barrier layer situated immediately above the silver. This barrier layer consists of an oxide or suboxide or nitride of a metal easily oxidizable or nitrurable. The barrier layer, after deposition of the higher dielectric, should be as transparent as possible in the visible range, and should not induce undesirable coloring.

The choice of the metal and the thickness of the layer are such that, in the fully oxidized or nitrided state, the reduction in the transmission caused by this barrier remains less than 3%, and preferably less than 1.5%. Traditionally, the metals used to form these barriers are: Ti, Zr, Al, Ni, Fe, Cr, Zn, Nb, Ta,

Sn, In and their combinations. Preferably the barrier is made of at least partially oxidized titanium. Titanium oxide has the advantage of having high transparency.

The thicknesses of the barrier layers do not generally exceed 5 nm, and preferably lie from 1 to 4 nm and particularly from 1 to 3 nm.

The sets of layers according to the invention preferably comprise a layer of zinc oxide or suboxide, ZnOx, on which the silver layer is directly applied. As indicated above, the presence of this layer of oxide, or of zinc oxide, contributes to improving the performance of the silver layer. This improvement is reflected in particular by a lower emissivity with equal thickness of silver.

The oxide or zinc sub-oxide layer is preferably at least 3 nm thick, which corresponds in industrial plants to the use of a single cathode. This thickness is also limited to what appears useful to promote the performance of the silver layer. The thickness of this layer advantageously does not exceed 15 nm. It is advantageously at most 10 nm, and preferably from 3 to 8 nm. The interferential systems that make it possible to "neutralize" the color in reflection lead to having at least one layer of relatively high refractive index beneath the silver layer, outside the zinc oxide layer mentioned below. above, and lower refractive index layers above this same layer of silver or, above the barrier layer above the silver layer.

According to the invention for obtaining the highest possible light transmission, the interferential system of the dielectric layers comprises between the glass sheet and the metal layer a set of at least three dielectric layers, including a zinc oxide layer, optionally substoichiometric, layer immediately below the metal layer, and at least two layers of metal oxides, nitrides or oxynitrides whose refractive indices are greater than that of the glass sheet.

The choice of the dielectric layers, not only must correspond to the conditions of index allowing to reduce as much as possible the reflection in the visible, without altering the neutrality, either in reflection or in transmission, but still this choice of the layers must lead to absorption as low as possible. These layers must still be perfectly compatible with the layers with which they are in contact, and above all be relatively easy and economical to produce industrially in traditional installations.

Among the candidates for the dielectric layers located under silver, it has been proposed previously in particular the oxides of titanium, bismuth or niobium. Of these TiO ₂ titanium oxide is particularly interesting in that it offers a high refractive index with a very low visible absorption for as long as it is deposited under strictly controlled conditions. A difficulty related to the use of this oxide, however, remains its deposition rate.

It is the insufficient deposition rate that has long led in practice to use titanium oxide only in thin layers, even though the interest of thicker layers was obvious.

The formation of a set of layers is carried out industrially in a succession of enclosures that communicate with each other, each chamber being the seat of one or more deposits corresponding to one or more cathodes. The glass to be coated passes continuously in all the speakers. The speed of scrolling under each cathode is therefore necessarily the same for all the deposits made. Consequently, the thickness of the deposit depends directly on the deposition rate specific to each constituent, which itself depends on the voltage applied, the nature of the cathode, the possible reaction with the atmosphere and, consequently, the nature of the the latter etc. These parameters are not all modifiable at will. In particular reactions on the surface of the cathodes often lead to having to limit the formation rate to avoid for example the appearance of arcs between the cathode and the substrate.

A few years ago, the development of new magnetron sputtering techniques significantly increased the deposition rate of certain compounds such as titanium oxide or silicon nitride. Such a development is reported for example in the publication "Glas Ingénieur" 7 (1997). Nevertheless, some compounds, including titanium oxide, remain difficult to produce with all the necessary homogeneity and reproducibility when the deposition rate is too dramatically increased. If one must avoid the multiplication of cathodes and targets in the installation, and also avoid the multiplication of depositing enclosures, it is preferable to keep the thickness of the layers, such as those of titanium oxide, within certain limits.

As an indication when to obtain large thicknesses of titanium oxide without increasing the number of cathodes, while maintaining the same rate of production, the deposition conditions are forced, significant variations in thickness can occur reaching relative values of 8% or more. Variations of this magnitude are incompatible for example with the qualities required in terms of color uniformity. In practice the thickness variations must be kept as low as possible, and not exceed 3% and preferably remain less than 2%. For these reasons, it is preferable as indicated below to limit the thickness of the titanium oxide layers used.

The optical filter constituted by the silver layer and the set of dielectric layers requires a certain optical path, in other words a certain value of the geometrical thickness of each layer multiplied by the index of this layer (exn). For the silver thicknesses considered according to the invention, the optical paths of the set of layers located respectively under and above the silver are 50 to 90 nm below, and 70 to 110 nm below the silver. -above. Preferably these optical paths that achieve neutrality in both reflection and transmission, are 55 to 80 nm under the silver, and 75 to 100 nm above the silver.

To obtain a suitable optical path under the silver layer it is necessary to ensure that the titanium oxide layer has a thickness of not less than 6 nm and preferably not less than 10 nm. Conversely the thickness of this layer is advantageously less than 16 nm. The preferred thickness is 12 to 15 nm.

The titanium oxide obtained by reactive deposition has a refractive index for a wavelength of 550 nm, which is not usually greater than 2.6, and is most often between 2.35 and

2.5 according to the deposition conditions, the highest indices being obtained for the highest deposition rates.

The layer of oxide or sub-oxide of zinc located under the silver, as indicated above, is advantageously limited to the thickness which makes it possible to improve at best the properties of the layer of silver which is superimposed on it. The total optical path can be advantageously adjusted by introducing an additional layer whose deposit conditions are less restrictive than those for titanium oxide. According to the invention, the optical path under the silver is advantageously adjusted by introducing at least one layer of an oxide or nitride, or a metal oxy-nitride MO (N) of refractive index intermediate between that of the glass and that of titanium oxide.

The introduction of an additional layer also has the advantage of influencing the behavior of the silver layer. It can be seen that the multiplicity of interfaces between the layers located between the glass substrate and the silver layer tends to minimize the sensitivity of silver to the age of the glass or to the preparation of the surface of the latter. . These factors, which are difficult to analyze, nevertheless have a significant impact on the properties obtained. Any element that reduces their negative influence is therefore significant. In this sense, the presence of additional interfaces has advantageous aspects. Preferably, the additional layer is a layer of oxide or nitride or of oxy-nitride of a metal of the group comprising zirconium, zinc possibly containing aluminum, or a mixture based on titanium. and one of the metals of the group comprising aluminum, tin, zinc, indium, hafnium, antimony and zirconium.

The choice of the nature of the additional layer depends on various factors. In particular it is important in practice that the facilities used are easily implemented to obtain these successions of layers. In this regard, it is necessary to underline the particular difficulty which exists for certain installations to manage to juxtapose extremely different deposit conditions taking into account the specificities of the cathodes used.

It is customary for example to deposit the titanium oxide in an atmosphere containing very little oxygen. This procedure is necessary to prevent the formation of an oxidized layer on the metal cathode, which contamination significantly reduces the rate of deposition. Titanium oxide can advantageously for this reason be deposited from ceramic target (based on titanium oxide). Conversely, for example, the deposition of oxide or zinc sub-oxide is carried out with a richer oxygen atmosphere if one wishes to avoid a significant light absorption. Given these constraints, the transition from a zinc oxide deposition station, to a titanium oxide deposition station requires a partitioning that not all facilities can provide perfectly. For this reason in those installations for which the partitioning stations is likely to raise difficulties, it is preferable according to the invention to choose layers whose deposits are performed under conditions, including atmosphere, compatible with each other. others. One advantage of zirconium-based layers, or those formed from an alloy of titanium and aluminum or other metals of the group indicated above, is that they are deposited under the conditions of which do not differ fundamentally from those used for the deposition of the titanium oxide layer.

All the layers indicated above have a refractive index which is between that of the substrate and that of the titanium oxide. For example, zinc oxide, even containing a small proportion of aluminum, is of the order of 1.9 to 2. That of zirconium oxide is close to 2.1 to 2.2. For mixed oxides based on titanium and another metal, the index depends on the proportion of the latter content in the alloy. Preferred alloys have an index of between 2.1 and 2.3 corresponding, for a titanium-aluminum-based alloy, for example, to percentages of aluminum which can be up to 50% of aluminum, and which are preferably between 10 and 30% by weight in the target, which proportion remains about the same in the deposited layer.

The succession of layers comprising a growing index is particularly preferred. It corresponds to the most advantageous results in neutrality and visible light transmission. For this reason an advantageous sequence is as follows:

glass / MO (N) / titanium oxide / zinc oxide / silver / ...

Nevertheless, the sequence that swaps the oxide layers may be preferred in some cases for reasons of convenience of implementation in the installation, resulting in the sequence:

glass / titanium oxide / MO (N) / zinc oxide / silver / ... In such a sequence according to the invention MO (N) is not zinc oxide, which is said above that its thickness under the silver does not exceed 15 nm.

The thicknesses of the MO (N) layer are adjusted according to the optical path required. In view of the other layers present under the silver, the thickness of the layer is advantageously from 3 to 14 nm, and preferably from 4 to 10 nm, for the layers whose index is greater than 1.9, preferably greater than 1.9. at 2.1, and particularly preferably greater than 2.2.

In order to constitute a satisfactory interference filter, the dielectrics situated above the barrier layer form, in a traditional way, an assembly which, in addition to the properties leading to the establishment of the satisfactory interference filter, offers a suitable protection of the silver layer both from the chemical point of view that mechanical.

For their deposition convenience associated with a good light transmission, preferred dielectric layers located above the silver are based on oxides of zinc, tin, indium, mixtures of these oxides or nitrides such as than those of silicon or aluminum and their mixtures.

It is usual to combine if necessary several layers of different natures to take into account the specificities of each. Thus zinc oxide widely used because of its relatively easy formation, has the disadvantage of offering a low chemical resistance due to the "columnar" structure that tends to develop when its thickness is sufficient. This columnar growth facilitates the penetration of moisture and chemicals into the layer towards the silver layer. For this reason, if the use of a zinc layer is usual, it is generally associated with a substantially more "compact" layer preventing chemical agents. An optionally doped layer of tin oxide or indium oxide or a layer of silicon nitride is advantageously introduced into the layer system located above the silver.

A particularly advantageous combination is the following set above the money:

... / money / barrier / ZnO / SnO ₂ ...

Given the respective indices (preferably less than or equal to 2) of the layers located above the silver, the total of the physical thicknesses is between 35 and 60 nm, and preferably between 40 and 50 nm to lead to the path. adequate optics.

The layer system glazing according to the invention can still receive a surface layer chosen to particularly provide a high mechanical strength. Titanium oxide layers have been proposed previously for this purpose. They can be used in the context of glazing according to the invention. However, the high index of the titanium oxide layers makes it preferable to substitute other layers, in particular silicon oxide layers, which in addition to their hardness, have a very low index which contributes the fitting of the appropriate interferential system.

The hard surface layer having essentially a role of mechanical protection, its thickness is limited to what is effective in this area. The thickness will not generally be greater than 15 nm. If silicon oxide is chosen, the difficulty of production of this type of layer preferably leads to not exceed a thickness of 12 nm.

To meet the requirements of users, it is not only necessary to improve the emissivity by maintaining the light transmission, it is still necessary that the glazing according to the invention remain neutral especially in reflection.

A glass sheet according to the invention comprises a set of layers as indicated above, and whose respective thicknesses of silver and dielectrics are chosen so that the values of colorimetric coordinates CIELab under illuminant D65 are established in reflection at :

- 4 <a * <0.5 and - 14 <b * <l

and preferably to:

- 3 <a * <0 and - 12 <b * <0.

In transmission the good performance of the colors is capital.

For this reason a stricter neutrality is necessary. Preferably, the same silver thicknesses and dielectrics are chosen so that the colorimetric coordinates in the CIELab system are as follows:

- 4 <a * <0 and b * <4

and preferably:

- 3 <a * <0 and b * <3.

The important point for the transmitted light is not to have a pronounced yellow color, that is, b * is not too positive. The invention also relates to double glazing consisting of two sheets of glass, one of which carries all the layers indicated above. In these double glazing units the layers are advantageously arranged in a position facing the space between the two sheets, and more particularly in position 3 according to the traditional designation, ie on the glass sheet in contact with the interior atmosphere and on the face of it inside the double glazing. The double glazings according to the invention advantageously meet the neutrality conditions obtained as above by adjusting the thicknesses of the layers within the limits indicated with respect to the emissivity and light transmission characteristics, such that the colorimetric coordinates in external reflection in the CIELab system are established at:

- 3 <a * <0 and - 8 <b * <0

and preferably:

- 2 <a * <0 and - 6 <b * <- 2

By choosing the nature and the thickness of the dielectric layers under and above the silver, the double glazing according to the invention also advantageously have two sheets of clear float glass, the transmission without layers at 82%, a light transmission of not less than 73%, and preferably not less than 75%. The transmission for these double glazing may advantageously be greater than 76%.

Other features and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings among which: - Figure 1 shows schematically an insulating double glazing in section;

FIG. 2 schematically represents a vacuum deposition installation for the constitution of layer systems according to the invention;

- Figure 3 schematically shows a section of a sheet coated with a layer system according to the invention;

- Figure 4 shows a section of a glass sheet coated with another layer system according to the invention.

The insulating glass shown schematically in Figure 1 is formed in the traditional manner of two sheets of glass 1 and 2, respectively in contact with the outside atmosphere, and with the interior of the house. The two glass sheets delimit, in cooperation with a gas-impermeable seal 3 located on the periphery of the bend between the two sheets, a space 4. The space 4 is advantageously filled with an insulating gas such as argon.

The gas trapped in the glazing contributes significantly to the performance of the glazing. For this reason it is important on the one hand, to ensure a good "filling" at the time of manufacture, in other words to ensure that all the ambient air is well evacuated and replaced by the insulating gas, but also, on the other hand, to ensure that the seal is sufficient and prevents the entrapped gas from escaping or diffusing over time.

The low-emissive layer system is normally disposed on the face 3 of the double glazing. (The numbering of the faces starts with the face turned towards the outside). In this arrangement, the layers are protected against mechanical alterations. They are also safe from chemical attack. The position in face 3 is preferred to that in face 2, for the opto-energetic characteristics obtained. This position is more favorable to the penetration of solar energy.

The glass sheets constituting these glazings may be identical or different, both in composition and thickness. The sheets may also consist of a single sheet of glass, or a laminated assembly, that is to say uniting several sheets assembled by means of plastic interlayer sheets such as PVB (polyvinyl butyral). The characteristics of the glazing according to the invention are given in the present application for substrates of clear float glass of 4 mm thickness. These conditions are chosen as particularly representative of the largest proportion of commercial insulated glass units. The latter also correspond to the best performances with regard to the overall light transmission.

The assemblies whose characteristics are given in the examples are two sheets of glass separated by a spacing of 15 mm filled with argon. In practice, the proportion of argon in the double glazing is not less than 85%, and preferably is greater than 90%.

If the transmission of the lenses alone is not negligible, a sheet of clear glass of 4 mm thick transmitting about 90% of the incident visible radiation, and double glazing alone a little more than 80%, the presence of a system Low-emissive layers of suitable layers, as provided by the invention, limit the transmission reduction by only a few percent. Of course, if the glazing simultaneously has to fulfill additional functions, for example soundproofing or burglar resistance, the presence of thicker glass and / or synthetic interlayer sheets leads to a decrease in light transmission. In these cases, however, the choice of a layer system according to the invention makes it possible to limit the transmission loss associated with the low-emissivity nature of these glazings.

The production facilities of the layers composing these systems may differ from one to the other, in particular according to the manufacturer considered. Their operating principle remains the same. This is deposition performed under vacuum, by "sputtering".

A schematic representation of this type of installation is given in FIG. 2. In these installations, the glass sheets 5 carried by conveyors progress in a succession of enclosures 6, 7, 8, 9, in which the partial vacuum is maintained. Airlocks 10, 11 allow the introduction and the exit of the sheets without breaking the void existing in the deposit chambers.

The targets 12, usually metal (for a sufficient deposition rate), attached to cathodes are bombarded by the ions of the inert gas, under the effect of an intense electric field. Metal atoms torn from a target condense on the glass sheet. The addition of oxygen or nitrogen to the atmosphere of the chamber allows a "reactive" deposition of oxide or nitride or oxynitride.

The mechanisms developed in particular at the cathode, and the differences in reactivity of the materials lead to extremely variable deposition rates depending on the metals considered. The speed can be modulated according to certain parameters such as the applied voltage or the precise composition of the atmosphere in each enclosure or the flow rate of the gases admitted into them. In all cases, overall, the nature of the metal remains a determining factor in the deposition rate that can be achieved. As an indication if layers of zinc oxides or tin are relatively easy to deposit, in comparison titanium oxide is much less. The ratio of the deposition rates can reach 10/1. The most recent techniques have reduced this ratio, but it remains significant.

To constitute the layers of the complete system, the enclosures contain in their succession the various metals necessary. The atmospheres of each chamber can also be chosen separately, the deposition of a metal can thus for example be followed by that of an oxide or vice versa with the limits imposed by the contiguity of different atmospheres for metals also different when perfect partitioning can not be assured.

The saving of this type of deposit requires that all the layers be made during a single passage of the sheets in the installation. Given the differences in deposition rates and different thicknesses of each layer, it is necessary for some to multiply the targets to achieve the required thicknesses. This requirement is particularly evident in the deposition of certain constituents such as titanium oxide.

It is understood that the cost of production is a function of the investment required for this type of installation, and the multiplication of targets and enclosures for the most difficult metals, leads to an increase in the cost of this investment but also the cost operation of these facilities. Any measure to operate more quickly is therefore advantageous. It is an object of the invention to allow this improvement without the properties of the glazings being compromised.

FIG. 3 schematically shows a glass sheet 12 coated with a layer system according to the invention. Successively starting from the substrate, the following sequence of layers is deposited:

- MO (N) / titanium oxide / zinc oxide / silver / titanium oxide / zinc oxide (zinc oxide equivalent).

Figure 4 is similar to the previous one. Layers

MO (N) and titanium oxide are inverted.

The properties of the assemblies according to the invention appear in the following table. The values of the transmission TL and the colorimetric coordinates reflection a * and b *, are given first for the single sheet carrying all the layers, and then for a double glazing comprising this simple sheet. The clear glass sheets are each 4 mm thick. In double glazing, the space between the two 15 mm sheets is filled with argon. The layers are in position 3.

In a first series the thickness of money is adjusted to

130A so as to achieve the U coefficient of 1.1 W / m2.K. The silver is deposited on a 40Å ZnOx zinc oxide layer. The silver is covered with a 25Å titanium oxide barrier layer.

Under the ZnOx layer, and directly in contact therewith, is a layer of TiO ₂ , whose refractive index at 550 nm wavelength, under the deposition conditions, is 2.37.

The dielectrics located above the silver are represented by their equivalent thickness in ZnO. The dielectrics in question as indicated above, in practice are usually made of several layers, the outermost of which is chosen to provide good mechanical and chemical resistance. Reflective staining results are given for different MO (N) layers on the glass.

All layer thicknesses are expressed in

Angstroms.

The double glazings obtained (second row in the table for each set of layers), corresponding to the characteristics of the invention, offer a coefficient U of 1.1 W / m ² .K, corresponding to an emissivity of 0.038, with light transmissions. in the field of high visible, and neutral to bluish colorations.

Another series of tests is done this time with a layer of silver a little thicker with the assemblies indicated in the table next. The indices of the TiSnOx and TiInOx layers are respectively 2.22 and 2.24 for the materials thus deposited.

The emissivity of the two following assemblies is respectively 0.033 and 0.034.

Similar tests to the previous ones are carried out by changing the respective positions of the layers TiO ₂ and MO (N) in the stack, all the other conditions remaining the same. The results in this case are slightly modified as regards the optical aspects. The results are shown in the following table:

Claims

A low-emissivity glazing comprising a set of thin layers including at least one metal layer reflecting infra-red rays between one or more dielectric layers located between the metal layer and the glass sheet on the one hand and on the metal layer on the other. on the other hand, the light transmission for a 4 mm thick clear float glass sheet coated with these layers is at least 83%, in which the thickness of the metal layer is chosen so that the emissivity not be greater than 0.042.

2. Glazing according to claim 1 wherein the thickness of the metal layer is chosen so that the emissivity is not greater than 0.038.

3. Glazing according to claim 1 wherein the thickness of the metal layer is chosen so that the emissivity is not greater than 0.035.

4.Vitrage according to one of the preceding claims wherein the metal layer is a silver layer whose thickness is at least equal to 12 nm.

5. Glazing according to claim 4 wherein the thickness of the silver layer is not greater than 18 nm.

6. Glazing according to claim 5 wherein the silver layer is 12.5 to 16 nm.

7. Glazing according to one of claims 4 to 6 wherein the nature and the thicknesses of the layers of the dielectrics are chosen so that the optical path of all layers under the silver is 50 to 90 nm, and that of the layers above the silver is 70 to 110 nm.

8. Glazing according to claim 7 wherein the optical path of the set of layers under the silver is 55 to 80 nm, and that of the layers located above the silver of 75 to 100 nm.

9. Glazing according to one of claims 4 to 8 wherein the nature and the thicknesses of the dielectric layers are chosen so that the reflection color expressed in the CIELab coordinates are such that: - 4 <a * ≤ 0, 5 and - 14 <b * ≤ 1.

10. Glazing according to claim 9 wherein the color in reflection is such that: - 3 <a * ≤ 0 and - 12 <b * ≤ 0.

11. Glazing according to one of the preceding claims wherein the dielectric assembly between the substrate and the silver layer comprises directly in contact with the silver layer a zinc oxide layer optionally sub-stoichiometric form.

12. Glazing according to claim 11 wherein the zinc oxide layer has a thickness of not greater than 15 nm.

13. Glazing according to claim 12 wherein the thickness of the zinc oxide layer is between 3 and 8 nm.

14. Glazing according to one of the preceding claims wherein a barrier layer is superimposed directly on the silver layer, which layer is formed of a metal oxide or nitride, the metal being of the group comprising: Ti, Zr, Al, Ni, Fe, Cr, Zn, Nb, Ta, In and mixtures thereof.

15. Glazing according to claim 14 wherein the thickness of the barrier layer is at most equal to 5 nm.

16. Glazing according to claim 15 wherein the thickness of the barrier layer is at most equal to 4 nm.

17. Glazing according to one of the preceding claims wherein, to obtain the highest possible light transmission, the interferential system of the dielectric layers comprises between the glass sheet and the metal layer a set of at least three dielectric layers, of which a layer of zinc oxide, optionally sub-stoichiometric layer located immediately below the metal layer, and at least two layers of metal oxides, nitrides or oxynitrides whose refractive index is greater than that of the glass sheet and go by growing away from this leaf.

18. Glazing according to claim 17, wherein in addition to the zinc oxide layer in contact with the silver layer, two metal oxide layers are located under this layer of silver, including a refractive index layer. between 1.9 and 2.3 and preferably between 2.1 and 2.3, and a titanium oxide layer deposited on the previous layer.

19. Glazing according to claim 18 wherein the layer of oxides of nitrides or metal oxynitrides of index between 1.9 and 2.3 is zirconium, zinc optionally alloy with aluminum, or an alloy based on titanium and a metal of the group comprising aluminum, tin, zinc, indium, hafnium, antimony and zirconium, which layer is deposited on the glass.

20. Glazing according to one of claims 1 to 16 wherein, to obtain the highest possible light transmission, the interferential system of the dielectric layers comprises between the glass sheet and the metal layer a set of at least three dielectric layers , including a layer of zinc oxide, optionally substoichiometric, layer immediately below the metal layer, and at least two layers of metal oxides, nitrides or oxynitrides whose refractive indices are greater than that of the glass sheet , the layer beneath the zinc oxide layer in contact with the silver layer being a layer of zirconium oxide, nitride or oxynitride or of a titanium-based alloy and a metal of group comprising aluminum, tin, zinc, indium, hafnium, antimony and zirconium.

21. Glazing according to claim 20 wherein the layer in contact with the glass is a titanium oxide layer.

22. Glazing according to one of claims 19 to 21 wherein the oxide layer of zirconium or oxide of a titanium-based alloy has a thickness of 3 to 10 nm.

23. Glazing according to the preceding claim wherein the zirconium oxide or oxide layer of a titanium-based alloy is 4 to 8 nm.

24. Glazing according to one of claims 18 19 and 21 to 23 wherein the titanium oxide layer has a thickness greater than 12 nm and less than 16 nm.

25. Glazing according to claim 24 wherein the titanium oxide layer has a thickness of 10 to 15 nm.

26. Glazing comprising two sheets of glass, one of them being constituted according to one of the preceding claims, the space between the two glass sheets trapping an atmosphere consisting of at least 85% argon.

27. Glazing according to claim 26 wherein for two sheets of clear float glass 4mm thick, the light transmission is not less than 73%, and preferably not less than 75%.

28. Glazing according to claim 26 or claim 27 wherein in reflection the colorimetric coordinates in the CIELab system are established at:

- 3 <a * <0 and - 8 <b * <0