Process for the preparation of a powder based on indium formiate for producing a thin layer on a substrate, especially on glass.

The present invention relates to the formation of thin layers of metal oxides on a substrate, in particular glass, by pyrolysis of powders of metallic compounds sprayed on said substrate, these thin layers, colored or not, having essentially low emissivity, electrical conduction properties. and transparency.

In order for a powdery metallic compound to form a good quality coating on a substrate, it must be able to be distributed regularly, to decompose with sufficient yield, at a temperature not exceeding 650 ° C or 700 ° C if the substrate to be coated is made of glass and that it contains a proportion of metal sufficient to lead to an oxide layer of appreciable thickness in a short instant (in particular if this substrate moves rapidly relative to the powder dispensing means, as is the case for a glass ribbon at the outlet of a so-called "float" bath.

It is already known to produce a coating of tin oxide on glass substrates which is formed by distributing on the substrate, powdered dibutyl tin oxide (DBTO) (see for example the French patent publications FR 2,380,997 and 2,391,966), or dibutyl tin difluoride powder (DBTF) (see for example European patent 0 039 256 and French patent publication No. 2 542 636).

These powders certainly lead to satisfactory layers; however, they are colored in reflection for the thicknesses necessary for obtaining advantageous electronic properties. However, the color may not please or may not be adapted to the style of the surrounding structure. In addition, slight variations in layer thickness lead to color irregularities.

In order to obtain perfect color uniformity, certain conditions must be scrupulously observed, in particular a constant and well-defined quality of the powder, and very precise adjustments to the installations used to distribute it.

The drawbacks of these tin oxide-based layers are the color itself and the aperitif conditions which must be observed in order for it to be perfectly uniform.

Indium compounds have also been used, not in powder, but in solution, in particular indium acetylacetonates, to make thin layers on glass. However, these compounds in powder form only pyrolyze at insufficient speeds. They are therefore not suitable for being applied to a ribbon of glass moving at high speed at the outlet of a "float bath".

The present invention aims to provide a powder based on at least one metallic compound which is capable of being distributed on a substrate at high temperature, such as a strip of glass moving past the outlet of a "float bath", in order to form after pyrolysis, a thin, transparent and electrically conductive coating layer. In addition, the pyrolysis of this metallic compound must be able to be carried out at a sufficiently high yield to be compatible with the rapid movement of the substrate. Furthermore, the layer must make it possible to obtain satisfactory electrical and optical performance for thicknesses corresponding to a neutral color in order to avoid the drawbacks of the colored layers of tin oxide of the prior art.

To this end, the powder according to the invention is characterized in that it contains indium formate.

The invention also relates to a method for manufacturing indium formate.

Indium formate can be the only metallic compound in the powder, but advantageously it can be combined with one or more other compounds having decomposition temperatures of the same order as that of indium formate.

Advantageously, after depositing and forming the metal oxide layer on the substrate, it undergoes a heat treatment intended to modify its electronic properties and in particular its emissivity and resistivity properties, in order to bring them to value. desired.

In a first embodiment, the substrate coated with its layer is made to stay in an enclosure heated to a temperature of at least 300 ° C. and compatible with the substrate, under a controlled atmosphere for a time which is a function of the temperature. and atmosphere, which can range from a few seconds to several hours.

In a second embodiment, the substrate coated with the layer to be treated is subjected to intense heating, but for a time less than the second, in a controlled atmosphere.

According to this second embodiment, intense heating can be obtained by means of a flame, in particular from a burner moved opposite and relative to the coated substrate.

The invention will now be described in more detail with reference to the examples and to the appended figure which represents a schematic view of a burner for carrying out the heat treatment according to the second embodiment.

The invention provides a method of manufacturing indium formate. This process consists in attacking the indium with an acid, then in precipitating the indium hydroxide by reacting on the indium salt thus obtained, ammonia at a temperature close to boiling, washing and drying the precipitate and reacting the latter with formic acid.

Thus by using HCl as acid, the manufacturing process can be summarized by the following equations:<chemistry id="chem0001" num="0001"><img file="EP0192009A2_D0001.tif" /></chemistry><chemistry id="chem0002" num="0002"><img file="EP0192009A2_D0002.tif" /></chemistry><chemistry id="chem0003" num="0003"><img file="EP0192009A2_D0003.tif" /></chemistry>

Instead of hydrochloric acid, it is also possible to use nitric acid or another acid.

Indium formate can be the only metallic compound in the powder, but advantageously it can be combined with one or more other compounds having decomposition temperatures of the same order as those of indium formate.

To obtain very conductive layers, it is possible to combine with indium formate tin compounds and in particular DBTO and / or DBTF which then occur in weight proportions of up to 30%. These compounds carry out a cationic doping of indium oxide. Indeed, the replacement of an indium atom by a tin atom introduced into the layer a free electron. By this doping, the density of the charge carriers and the conductivity of the layer are therefore increased.

The indium formate powder or the mixture of powders can be sprayed onto the substrate, in particular a glass ribbon using a nozzle, for example by one of the nozzles described in the French patent applications published under No. 2,542,636 and 2,542,637 preceded by the distribution device described in the French patent application published under No. 2,548,556.

Doping can also be carried out with gaseous compounds, such as SnCI₄ or gaseous organotins, such as BuSnCl₃. In this case, the dopant is mixed with the gas in which the powder is in suspension, and / or with the gases which serve to accelerate and / or homogenize the powder. The dopant can also be sucked by the nozzle into the control chamber described in the French patent application published under No. 2,542,636 and / or can also be brought to the exit of the projection nozzle by a special pipe.

Advantageously after deposition and formation of the metal oxide layer on the substrate, it undergoes a heat treatment.

This treatment generally seeks to increase the number of oxygen vacancies in the layer so as to lower the emissivity of said layer, therefore to improve its low emissivity properties. However, it is also possible, on the contrary, to decrease the number of oxygen vacancies in the layer so as to increase the emissivity of said layer and therefore to reduce its low emissivity properties which it previously possessed.

According to a first embodiment, this heat treatment consists of a stay of the coated substrate in a heated enclosure, under a controlled atmosphere, stay which is more or less long, which depends on the temperature, on the reducing nature of the atmosphere, and which can range from a few seconds to several hours.

Improving the low emissivity properties will require heat treatment in a reducing or possibly neutral atmosphere.

In the case of a reducing atmosphere, this can be constituted by an atmosphere of composition identical to that of the "float bath", namely 90% nitrogen and 10% hydrogen.

By this treatment in a reducing or neutral atmosphere, the concentration of oxygen vacancies in the layer is increased, which results in anionic doping favorable to the increase in the electrical conduction and the infrared reflection of the layer. Depending on the duration and temperature of the treatment, the density of the charge carriers can be varied considerably, for example from 1.1020 to 20.1020 carriers per cm³ and their mobility, for example from 10 to 50cm.Vl.sl.

This treatment can be carried out immediately after the formation of the oxide layer, directly on the glass production line, for example in an annealing drying rack, so as to take advantage of the heat of the glass.

It can also be practiced later on a separate installation from the glass production line (annex annealing arch, quenching, bending line).

In this case, the coated substrate is heated to a temperature of at least 300 ° C. compatible with the substrate, it is maintained in a reducing or neutral atmosphere at this elevated temperature for a time all the shorter as the temperature is higher and the atmosphere is more reducing (this holding time can range from a few seconds to several hours), then it is cooled under a reducing or neutral atmosphere at least to a temperature where contact with an oxidizing atmosphere no longer affects the performance of the layer.

Advantageously, the controlled cooling under a reducing or neutral atmosphere is carried out up to a temperature which is at most of the order of 300 ° C. In the case of simultaneous quenching treatment, the quenching gas blowing nozzles are supplied with the reducing or neutral gas necessary for the treatment.

In summary, the effectiveness of the layer treatment increases with:<ul id="ul0001" list-style="none"><li>. the reducing nature of the treatment atmosphere, for example with the percentage of hydrogen in a mixture N₂ + X% H₂ where X, is positive or zero, in particular X = 10 or X = 0,</li><li>. the temperature, this being between 300 and 650 ° C.,</li><li>. the time, which can vary from a few seconds to a few hours.</li></ul>

According to a second embodiment, this heat treatment is obtained by intense heating in a controlled, reducing or, on the contrary, oxidizing atmosphere depending on the desired purpose, for a time less than one second. Materially this is obtained by subjecting the substrate coated with the layer to be treated to the action of at least one flame, reducing or, on the contrary, oxidizing, depending on whether it is desired, to increase or, on the contrary, to decrease the low emissivity properties of the layer. thus treated, reduce the metal oxide or on the contrary oxidize the metal.

This treatment is then advantageously carried out by movement of the substrate coated in the flame of at least one burner supplied with gas whose reducing or oxidizing characteristics are controlled and adapted to the desired reducing or oxidizing nature of said treatment.

It is therefore an immediate treatment (treatment time less than a second), requiring only a reduced installation, simple, inexpensive and easy to drive.

The heating of the substrate to the flame may be low (less than 70 ° C.) insofar as the flame is placed relative to said substrate on the coating side, so that the level of quenching of a previously tempered glass substrate is preserved, or that substrates sensitive to heat, in material other than glass or comprising in combination with glass other materials such as polyvinylbutytal (PVB), are not altered.

The burner (s) necessary for the treatment of the layer are supplied with a mixture of oxidizing gas (oxygen or mixture of neutral gas and oxygen) and combustible gas containing hydrogen and / or carbon (hydrogen, carbon monoxide , alkane, alkene or alkyne gas).

The proportions of oxidizer and of fuels are such that the mixture is not stoichiometric but on the contrary contains either an excess of reducing gas, or an excess of oxidizing gas, depending on whether one wishes to carry out a reducing treatment or an oxidizing treatment.

The burners that can be used are, preferably for reasons of safety and ease of use, linear burners with external mixing.

These burners are of the type illustrated in the attached figure, that is to say that they have two chambers 1 and 2 for supplying combustible and oxidizing gases, themselves supplied by the pipes 3 and 4. Each of these chambers 1 and 2 open to the outside of the burner through holes 5 and 6, the holes 5 delivering the gas from the upper chamber 2 being connected to this chamber 2 by pipes 7 which pass through the lower chamber 1 in leaktight manner. For a good mixture of gases, the holes 5 and 6 are arranged in staggered rows. Insofar as long lengths of burners are necessary, deflectors not shown, or a bevelled shape of the chambers 1 and 2 can be provided to ensure equal distribution of the gases from one end to the other of the burner.

Burners of this type are distributed by the French company "AIR LIQUIDE" under the name "FMT burners".

The oxide layer obtained on a heated substrate, by spraying an indium formate powder, associated or not with tin compounds capable of acting as dopants with respect to indium, such as oxide dibutyl tin (DBTO), and / or dibutyl tin difluoride (DBTF), is by manufacturing too oxidized to have good characteristics of low emissivity and low resistivity. It can be subjected to the "burning" treatment according to the invention, so as to improve its characteristics. The adjustment of the flow rates and the proportions of oxidizing and reducing gas depends on the nature of the gases, the installation and the operating conditions, and is a function of the emissivity and the resistivity desired for the layer.

It is possible to determine experimentally for a given installation and for given operating conditions (running speed of the substrate, distance from the burners) the gas flow settings so as to establish the flow limits to reduce the layer completely in the metallic state, the appearance of this metallic state recognizing that the layer changes in appearance, acquires a certain reflectivity in the visible which can go as far as the reflectivity of a mirror and can in certain cases, in particular for transformed indium oxide, become not very adherent to the substrate.

For this, the respective proportions of oxidizing gas and reducing gas are adjusted so as to have a slightly more reducing mixture than the stoichiometric mixture, ie approximately 10% more reducing gas relative to the flow rate corresponding to the stoichiometric mixture. Then the flame treatment of the layer is practiced on various samples by gradually increasing the overall flow rate of the mixture until the reduction of the layer in the metallic state. This adjustment of limit flow rates having been obtained, it is known that the adjustments making it possible to achieve the desired levels of low emissivity and low resistivity will be obtained by reducing the flow rate of reducing gas relative to the limit flow rate determined previously.

Thanks to this rapid heating technique in a controlled atmosphere, it has been possible to obtain the optimum properties of low emissivity and low resistivity of a layer based on indium oxide, deposited by pyrolysis of powder as indicated above, by making run the substrate coated with its layer, at 1 cm under a linear burner with external mixture, having as length the width of the layer to be treated, at a speed of 3 cm / s, the oxygen flow rate being 1.9 l per minute and per centimeter of burner length, the hydrogen flow rate being 4 l / min.cm.

By varying the running speed of the same substrate and bringing it to 5 cm / s, an oxygen flow rate of 2.3 l / min.cm was required. and a hydrogen flow rate of 4.7 1 / min.cm.

By further increasing the running speed so that it reaches the running speed of the glass ribbon in "float" installations, for example 20 cm / s, it was necessary to obtain the maximum performance of the layer, around 6 1 / min.cm of oxygen and 13 1 / min.cm of hydrogen.

With either of these heat treatments, it was possible to treat layers obtained by pyrolysis of an indium formate powder and 4% by weight of DBTO and obtain the results listed in the examples which follow:

EXAMPLE I

<tables id="tabl0001" num="0001"><img file="EP0192009A2_D0004.tif" /></tables>

To obtain such a layer, an indium formate powder was used, mixed with 4% by weight of DBTO, which was distributed on a moving ribbon of glass at 18 m / min, the surface temperature of which was 600 ° C. After pyrolysis of the powder, the glass substrate thus coated was subjected to a heat treatment consisting of annealing in an enclosure at 600 ° C for 2 min under nitrogen atmosphere and then in gradual cooling to 300 ° C, always under a non-oxidizing atmosphere, nitrogen for 2 min.

EXAMPLE II

<tables id="tabl0002" num="0002"><img file="EP0192009A2_D0005.tif" /></tables>

EXAMPLE III

Under the same conditions as for Examples I and II, except for the flow rate of powder distributed on the glass substrate, a purple red layer was produced in reflection, slightly green in transmission, the characteristics of which before and after treatment thermal in an enclosure under a non-oxidizing atmosphere are as follows:<tables id="tabl0003" num="0003"><img file="EP0192009A2_D0006.tif" /></tables>

EXAMPLE IV

The same layer was subjected as that of Example II, then of Example III, before heat treatment, to the flame of a burner supplied with a mixture of oxygen and hydrogen as described above. Whatever the speed of travel under the flame of the coated substrate, with of course suitable gas flow rates, after treatment, layers having the same characteristics as those obtained after treatment were obtained in Examples II and III.

In the same way as the first type of heat treatment, this treatment by intense but short heating, for example in the flame of a burner, can be carried out immediately after the manufacture and coating of the glass, for example on the float line itself , but it can just as easily be done later. This is what is inevitable when the glass must be tempered or laminated. In this case, the coated glass is cut, tempered or laminated, then heat treated.

Thus, with one or other of the two heat treatments proposed, it was possible to obtain layers based on indium formate and an addition of DBTO or DBTF, having electrical resistivities of the order of 2 to 10-⁴ cm. It was also possible, by modulating the intensity of the heat treatment, to obtain layer performance, intermediate between the performance of the untreated layer and optimal performance measured on a layer having undergone the most intense treatment.

With such heat treatments, it is also possible, instead of lowering the resistivity and emissivity of a layer, on the contrary to increase it. Thus, from a coated substrate having a square resistance of 15 ohms, we could reach a resistance of 16 ohms, or 2000 ohms by running the substrate at 1 cm under the burner, respectively at 10 cm / s and at 6 cm / s, the oxygen flow in both cases being 2.4 1 / min.cm and that of hydrogen being 3 1 / min.cm. Such a treatment leading to the lowering of the resistivity and of the emissivity is of course also possible with the first mode of heat treatment, it suffices to provide a controlled atmosphere which is no longer reducing but oxidizing.

It is also possible with one or the other of the two modes of heat treatment proposed, to create on the same glazing coated zones of different electrical conduction by application of different heat treatments. This type of heat treatment differentiated according to the zones of the same glazing is particularly easy when the second type of heat treatment is implemented. For this, the conditions of exposure of the layer to the heating means are modified locally or momentarily.

In this order of idea, the running speed of the coated substrate to be treated is varied relative to the burner as a function of the desired result. With a burner arranged transversely to the running direction of the substrate, by modulating the running speed of said substrate, layers with transverse bands were obtained having differentiated properties.

It was also possible to obtain longitudinal strips in the direction of movement of the substrate, with different electrical and optical characteristics by adding additional burners to these areas or by carrying out the treatment over the entire width of the substrate using a plurality burners set differently from each other.

These heat treatments and in particular that by burners are therefore particularly suitable for the manufacture of layered glazing having zones with differentiated electrical, thermal, optical properties. Thus, for example, heated glazing with thin layers having more or less significant resistances depending on the zones can be manufactured.

The second mode of heat treatment proposed, authorizes, as already said, the manufacture of toughened or laminated glazing with thin layers.

Indeed, while the first mode of heat treatment proposed alters the quenching, prevents the treatment of laminates or substrates not resistant to temperature, the second mode of heat treatment proposed is so brief that the substrate does not have time to '' be heated, especially if the heating means is arranged on the side of the layer. Consequently the PVB spacers (polyvinyl butyral) or others, laminated glazing, non-heat resistant substrates, the stresses obtained by tempering, are preserved without alteration.

This second mode of heat treatment is therefore particularly suitable for the manufacture of toughened glazing with thin layers, the level of toughening being high and in particular allowing the use of such glazing as glazing for cars (that is to say with a fragmentation as defined in regulation 43 of the United Nations for the approval of automotive glazing) the level of emissivity and resistivity being also of good quality, that is to say an emissivity less than 0.15 and a resistivity less than 3. 10-⁴ ohm.cm.

It is therefore also particularly suitable for the manufacture of laminated glazing comprising at least one glass sheet coated with a thin layer requiring heat treatment to acquire its final characteristics.

This second mode of heat treatment has been described using one or more gas burners, remarkable for their simplicity, but other heating means capable of supplying high energy in less than a second can also be used; thus for example a microwave plasma torch supplied with reducing gas or on the contrary oxidizing depending on whether it is desired, as already said, either to reduce the oxide or to lower the emissivity and the resistivity of the layer, or on the contrary to oxidize the metal or increase the emissivity and resistivity of the layer.

The invention has been described by taking glazing, intended for example for buildings (low-emissivity glazing, heated glazing, and in general glazing using the optical and / or electrical properties of the layers), or for the automobile (heated glazing, security glazing using the conduction properties of the layer to detect a break-in, antenna glazing, etc.), but it can also find an interesting application in the coating of various substrates, insulators in particular, glass articles such as bottles, flasks, various glassware, optical elements, lighting lamps, fiberglass, or even silica articles, refractory materials, alumina.

The material used to spray the powder or the mixture of powders onto separate objects is therefore generally different from the nozzles referred to above. For example, conventional powder spray guns will be used.

The above description has exclusively concerned powdered canopies based on indium formate and their use in powder form.

However, these powders based on indium formate can also be processed and used in a phase other than solid and pulverulent.

In particular, the powder can be dissolved, in particular in methanol and the compound based on indium formate in solution, can be distributed on a substrate, be pyrolyzed therein and thus form a layer of metal oxide which may undergo a heat treatment capable of modifying the characteristics of the initial layer.

The heat treatments practiced after the deposition of the layer have been described as being applied to a layer of indium oxide doped or not with tin obtained by pyrolysis of a powder based on indium formate; but they can also be applied successfully to any layer based on indium oxide, doped or not, with tin or other, obtained by another route, for example liquid pyrolysis,_VSVD, or vacuum technique, whether the starting compound is formate or other.

These heat treatments can even be applied to any other metallic layer which, like the layer based on indium oxide, is non-stoichiometric, thus for example the layers based on vanadium oxide, Zn, Sn, etc.

These heat treatments can even make it possible to obtain, from layers of metal oxide, layers of metal. Obtaining a layer of metal from an oxide layer has been described as a phase of adjusting the burners used for heat treatments, but obtaining such a layer of metal may be the final goal.

Heat treatments can also be used to recrystallize a poorly crystallized or amorphous layer, in particular to modify its electronic properties.