EP2678120A1

EP2678120A1 - Equipment and method for depositing a film of ordered particles on a moving substrate

Info

Publication number: EP2678120A1
Application number: EP12704426.1A
Authority: EP
Inventors: Olivier Dellea; Pascal Fugier; Philippe Coronel
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2011-02-24
Filing date: 2012-02-20
Publication date: 2014-01-01
Anticipated expiration: 2032-02-20
Also published as: US9505021B2; EP2678120B1; FR2971956A1; WO2012113745A1; US20130330471A1; FR2971956B1; ES2545224T3

Abstract

The invention relates to equipment for depositing a film of ordered particles (4) on a moving substrate (38), the equipment including: a transfer area (14) including a particle inlet (22) and a particle outlet (26) spaced apart from each other by two opposite side rims (28), and retaining a carrier liquid (16) on which the particles are floating; and a capillary bridge (42) providing the connection between the carrier liquid (16) contained in the transfer area (14) and the substrate (38). According to the invention, the equipment comprises a plurality of suction nozzles (32a, 32b) capable of drawing the particles (4) toward the two side rims (28).

Description

INSTALLATION AND METHOD FOR DEPOSITING PARTICLE FILM ORDERED ON A SCROLLING SUBSTRATE

DESCRIPTION

TECHNICAL AREA

The invention relates to the field of installations and methods for depositing a film of ordered particles on a moving substrate.

More specifically, it relates to the deposition of a film of ordered particles, preferably of the monolayer type, the particle size may be between a few nanometers and several hundred micrometers. The particles, preferably of spherical shape, may for example be silica particles.

The invention has many applications, particularly in the field of fuel cells, optics, photonics, polymer coating, chips, MEMs, surface structuring for organic electronics and photovoltaic, etc. STATE OF THE PRIOR ART

From the prior art, there are known such methods and installations for depositing a film of ordered particles on a moving substrate, the latter being flexible or rigid. In general, there is provided a transfer zone fed with particles, which float in a carrier liquid contained in the same transfer zone. The ordered particles in the transfer zone, forming a monolayer of particles called thin film, are pushed by the arrival of other particles to an output of this zone, by which they reach the moving substrate on which they are deposited. . To do this, a capillary bridge usually ensures the connection between the substrate and the carrier liquid contained in the transfer zone.

Under normal operating conditions of the installation, in the transfer zone, the particles are maintained ordered by the pressure exerted upstream by the moving particles intended to later reach this transfer zone. By way of indicative example, when the particle transfer zone is connected upstream to an inclined ramp on which the particles coming from a dispensing device run past, it is these same particles present on the inclined ramp which exert an pressure on the particles contained in the transfer zone, and which therefore make it possible to maintain the order of the particles in this zone, until the deposition on the substrate, by capillarity.

Still in this same configuration example incorporating an inclined ramp, it is the kinetic energy associated with moving particles on the ramp which allows them to be automatically arranged on the same ramp, when they impact the particle front, also on the inclined ramp. The scheduling is thus established on the ramp, then preserved when the ordered particles enter the transfer zone, thanks to the continuous supply of the particles coming to impact the front.

The kinetic energy required for the ordering of the particles is here brought by the inclined ramp carrying the carrier liquid and the particles. Other solutions are nevertheless possible, such as the setting in motion, with the aid of a pump, of the carrier liquid on a horizontal plane, the downstream part of which constitutes the zone of transfer of the particles. Another solution is to replace said pump by a blower for applying a flow of air to the surface of the carrier liquid, on which the particles float.

In all these embodiments of the prior art, and in particular in that implementing the inclined ramp, there is a problem occurring at the time of putting into operation of the installation. Indeed, during this priming phase, during which the substrate is not yet set in motion, the transfer zone is gradually filled with particles. However, these particles do not have the possibility of ordering before entering the transfer zone, since the particle front does not rise sufficiently upstream yet. Instead, the particles first disperse in a disordered manner in the transfer, then form clumps due to capillary forces between the particles.

If these clusters of particles eventually meet each other during the initial filling of the transfer zone, when the filling rate thereof becomes high, gaps are formed between these clusters, which makes the film non homogeneous, and therefore unsatisfactory. In other words, if the ordering of the particles within each cluster may be suitable, the clusters together form a set of particles in which there are voids, which does not make it possible to obtain a film having, in every point, a structure called "compact hexagonal" in which each particle is surrounded and contacted by six other particles in contact with each other.

Still during the priming phase, when the particle front rises beyond the transfer zone, upstream, the particles impacting the front then make it possible to exert pressure on the clusters united in the transfer zone. . Moreover, it is noted that these particles are able to arrange themselves automatically on the inclined ramp, as described above. Nevertheless, the pressure forces exerted by these particles are very often insufficient to fill the gaps between the aggregates, because of the strong internal stresses within these clusters that prevent the re-ordering of the particles.

To increase the pressure applied to the clusters gathered in the transfer zone, it is possible to raise the particles on the ramp. However, this usually results in overlapping logs, which eventually overlap rather than arrange in a single layer. In such a case, the quality of the film is of course judged equally unsatisfactory.

As a result, the particle film located in the transfer zone before the plant is put into operation has quality defects that require it to be removed by deposition on a dedicated substrate. This first results in unnecessary consumption of particles and substrates, impacting production costs. These same costs are also increased because of the complexity of the process, which therefore requires a purge phase to deposit the part of the non-conforming film, then to evacuate. In addition, the risks of dissemination of the particles are amplified, especially when they are small, for example less than 400 nm. STATEMENT OF THE INVENTION

The object of the invention is therefore to remedy at least partially the disadvantages mentioned above, relating to the embodiments of the prior art.

To do this, the invention firstly relates to an installation for depositing a film of ordered particles on a moving substrate, the installation comprising:

a transfer zone comprising a particle inlet and a particle outlet spaced from one another by two opposite lateral flanges, retaining a carrier liquid on which the particles float,

said installation being designed to allow the deposition, on the substrate, of the film of ordered particles escaping from said particle outlet, preferably by means of a capillary bridge which thus ensures the connection between the carrier liquid contained in the transfer zone and said substrate on which the ordered particle film is intended to be deposited.

According to the invention, the installation further comprises a plurality of suction nozzles capable of attracting the particles present in the transfer zone towards its two lateral flanges.

The invention therefore provides suction nozzles for stretching the film of particles over the entire width of the transfer zone, in order to avoid the formation of a set of particles in which there are voids, like this. was the case in the prior art. Thus, these nozzles allow a satisfactory ordering of the particles in the transfer zone, during the priming phase consisting of its initial filling. Then, in normal mode, these nozzles can be inactivated, the particle ordering then being performed automatically.

By obtaining a satisfactory scheduling, since the priming phase, no part of the particles or the substrate must be evacuated, implying that it is not necessary to isolate the portion of the finished product from the boot phase. Production costs are significantly reduced. They are also reduced by the simplification of the process, which no longer requires a purge phase to deposit a portion of the non-conforming film, then to evacuate. In addition, the risk of particle spread is also reduced.

Thus, the invention is remarkable in that it makes it possible, in a simple and effective manner, to avoid the formation of clusters first isolated and then grouped together in an unsatisfactory way, as was the case in the prior art. The suction nozzles are indeed a simple way to stretch the film laterally, towards each of the two flanges, and ensure that the film produced has, in every point, a so-called "compact hexagonal" structure, in which each particle is surrounded and contacted by six other particles in contact with each other.

Preferably, the installation comprises only two suction nozzles, respectively capable of attracting the particles present in the transfer zone towards one and the other of the two lateral flanges. Nevertheless, each flange could be associated with several nozzles, without departing from the scope of the invention.

Preferably, the installation comprises an inclined ramp of particle circulation, attached to said inlet of the transfer zone, and on which said carrier liquid is also intended to circulate. The kinetic energy necessary for the ordering of the particles in the normal regime is here brought by the inclined ramp carrying the carrier liquid and particles. Other solutions are nevertheless possible, such as the setting in motion, with the aid of a pump, of the carrier liquid on a horizontal plane, the downstream part of which constitutes the zone of transfer of the particles. Another solution is to replace the pump by a blower for applying a flow of air to the surface of the carrier liquid, on which the particles float.

Preferably, the installation comprises means for temporary retention of the particles in the transfer zone at a distance from said substrate, these retention means being able to be displaced towards this substrate while retaining said particles. This displacement can be envisaged manually or automatically.

Overall, these retention means make it possible to reduce the size of the transfer zone during its initial filling, during the priming phase. There are several advantages.

First, it reduces the area on which the nozzles assist the particles to ensure their scheduling. The piloting of these nozzles is thus simpler to achieve. In addition, this facilitates scheduling, in that the pressure exerted on the particles of the transfer zone by the particles situated upstream of this zone is more effective in constraining the particles to be ordered when those they extend over a shorter length. It has been found that the beneficial effects mentioned above are even more important when an upstream end of these means of Temporary detention is less than 20 mm from the entrance to the transfer area.

Then, these temporary retention means are provided to be moved towards the exit of the transfer zone and the substrate, to allow the deposition of the particle film on the latter. Moreover, according to a preferred embodiment of the invention, the retention means are also provided for depositing on the substrate upstream of the particle film. Nevertheless, solutions without deposit on the substrate can be envisaged, without departing from the scope of the invention.

Preferably, said means for temporary retention of the particles takes the form of a layer of hydrophobic material, floating on the surface of the carrier liquid. This solution proves to be simple and effective for blocking particles that can not pass over the layer because of the hydrophobic nature which prevents wetting of the upper surface of the layer, or to pass between the layer and the carrier liquid. thanks to the small thickness of the dam which allows to deform easily to adapt to variations in shape of the surface of the carrier liquid. Moreover, this layer has a thickness preferably between a few microns and several tens of microns for example between 50 and 100 μπι.

It is preferably a layer of polytetrafluoroethylene (PTFE).

Preferably, said temporary retention means take the form of a layer of which one downstream end is also remote from the substrate. Alternatively, said temporary retention means take the form of a layer of which a downstream end is located on said substrate. In the latter case, it is not necessary to provide specific means to maintain and set in motion the retention means, since it is the substrate that blocks them in the transfer zone and causes their movement to the desired moment, by training. In both cases, the layer can then have, on the carrier liquid, a behavior substantially identical to that of the ordered particle film formed in the transfer zone. This makes it possible to deposit this layer of particle retention on the substrate, also preferably via the capillary bridge, as was mentioned above.

The invention also relates to a method for depositing a film of ordered particles on a moving substrate, using an installation as described above, according to which during at least part of the step initial filling of the particle transfer zone, said suction nozzles are actuated to attract the particles present in the transfer zone to its two lateral flanges.

Preferably, said nozzles are actuated alternately so as to attract the particles present in the transfer zone towards one and the other of the two lateral flanges, alternately. Simultaneous operation is nevertheless possible without departing from the invention. However, the alternating actuation, which may incorporate pause periods between nozzle changes, is preferred for its greater simplicity of focus. In addition, the pause periods allow the particles to continue to accumulate, thus allowing the particles already present to be pressurized.

Preferably, after setting up the temporary retention means for the particles in the transfer zone at a distance from said substrate, and after the initial filling by particles of the part of the transfer zone situated upstream of said temporary retention means, these are moved in said transfer zone to the substrate, while retaining said particles. Of course, during this displacement of the retention means which aims to bring the downstream front of particles of the substrate, the transfer zone which extends progressively continues to be fed continuously by other particles, so that the downstream front is maintained. preferentially at the same location on the installation.

Finally, as mentioned above, it is preferentially made so that said temporary retention means take the form of a layer which is deposited progressively on the moving substrate, while the downstream front of the ordered particle film that it holds moves to the output of said transfer area. Thus, on the finished product obtained, the retention layer is deposited on the substrate in the continuity of the deposition of the film of particles, in the same way as this layer of retention was in the continuity of the particle film in the transfer zone, before their deposition.

Other advantages and features of the invention will become apparent in the detailed non-limiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be made with reference to the appended drawings among which;

Figure 1 shows a deposition installation according to a preferred embodiment of the present invention, in schematic section taken along the line I-I of Figure 2;

FIG. 2 represents a schematic view from above of the depot installation shown in FIG. 1;

Figures 3 to 9 show different stages of a deposition process implemented using the installation shown in the previous figures; and

FIG. 10 represents an alternative for the implementation of the method schematized in FIGS. 3 to 9.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring firstly to Figures 1 and 2, we can see a facility 1 for the deposition of a film of ordered particles on a moving substrate.

The installation comprises a device 2 for dispensing particles 4, whose size may be between a few nanometers and several hundreds of micrometers. The particles, preferably of spherical shape, may for example be silica particles.

More specifically, in the preferred embodiment, the particles are silica spheres of about 1 μπι in diameter, stored in solution in the dispensing device 2. The proportion of the medium is about 7 g of particles per 200 ml of solution, here butanol. Naturally, for the sake of clarity, the particles shown in the figures adopt a diameter greater than their actual diameter.

The dispensing device 2 has a controllable injection nozzle 6, about 500 μπι in diameter.

The installation also comprises a liquid conveyor 10, incorporating an inclined ramp 12 for circulating the particles, and a substantially horizontal transfer zone 14. The upper end of the inclined ramp is designed to receive the particles injected from the dispensing device 2. This ramp is straight, inclined at an angle of between 5 and 60 °, preferably between 20 and 60 °, allowing the particles to be conveyed to the transfer zone 14. In addition, a carrier liquid 16 flows on this ramp 12, into the transfer zone. This liquid 16 can also be re-circulated using one or two pumps 18, between the transfer zone 14 and the upper end of the ramp. This is preferably a deionized water, on which the particles 4 can float. The lower end of this same ramp is connected to an inlet of the particle transfer zone 14. This inlet 22 is located at an inflection line 24 showing the junction between the surface of the carrier liquid present on the plane inclined of the ramp 12, and the surface of the carrier liquid present on the horizontal part of the transfer zone 14.

The particle inlet 22 is spaced apart from a particle outlet 26 by means of two lateral flanges 28 holding the carrier liquid 16 in the zone 14. These flanges 28, opposite and at a distance from one another , extend parallel to a main flow direction of the carrier liquid and particles in the installation, this direction being shown schematically by the arrow 30 in Figures 1 and 2. The zone 14 therefore takes the form of a corridor or an open path to its entrance and exit.

The transfer zone 14 is equipped with two suction nozzles 32a, 32b, capable of sucking the particles towards the two flanges 28, as will be described hereinafter. More precisely, at each rim 28 is associated a suction nozzle whose axes 34a, 34b are oriented orthogonally to the direction 30.

The nozzles 32a, 32b can be fixed directly on the flanges 28, or on another part of the installation 1. The suction axes 34a, 34b are parallel to the inflection line 24, and at a short distance from that in a top view such as that shown in FIG. 2, this distance being for example between 0 mm (on the inflection line). 24) and 10 mm. The suction axes are preferably positioned at the air / liquid carrier interface. Each nozzle has an inner diameter of the order of 3 to 5 mm.

The installation 1 is also provided with a substrate conveyor 36, for putting the substrate 38 in motion. This substrate can be rigid or flexible. In the latter case, it can be set in motion on a roll 40 whose axis is parallel to the outlet 26 of the zone 14, near which it is located. Indeed, the substrate 38 is intended to scroll very closely to the outlet 26, so that the particles escaping from this outlet can be easily deposited on the substrate, via a capillary bridge 42 connecting it to the carrier liquid 16. Alternatively the substrate may be in direct contact with the transfer zone without departing from the scope of the invention. The capillary bridge mentioned above is then no longer required.

In the example shown in the figures, the width of the substrate corresponds to the width of the zone 14 and its outlet 26. The capillary bridge 42 is provided between the carrier liquid 16 which is located at the outlet 26, and a part of the substrate 38 conforming to the guide / driving roller 40. The axis of rotation of the latter roller may lie in the plane of the upper surface of the carrier liquid retained in the zone 14.

Alternatively, particularly when the substrate 38 is solid, it may be in scrolling in the vertical direction, orthogonal to direction 30.

A method of depositing an ordered particle film will now be described with reference to FIGS. 3-9.

Firstly, there is an effective and temporary reduction in the length of the transfer zone 14. This reduction, although optional, makes it possible to obtain a finished product with an even more satisfactory quality, in particular when the length zone 14 is considered high. In this regard, it is ensured that the new length "1" of the zone 14, referenced in FIGS. 3 and 4, is less than 20 mm.

To do this, it is set up means for temporary retention of the particles in the transfer zone, these means being intended to move the downstream front of particles from the outlet 26 and the substrate 38, which is not yet in operation. scrolling.

These means preferably take the form of a layer 50 of polytetrafluoroethylene (PTFE), with a thickness of between 50 and 100 μπι, floating on the surface of the carrier liquid 16. This technical solution proves to be simple and effective for later dam to the particles that can not pass over the layer because of the hydrophobic nature that prohibits the wetting of the upper surface of the layer, or pass between the layer 50 and the carrier liquid 16 thanks to the small thickness of the dam, which allows to easily deform for adapt to the variations of shapes of the surface of the carrier liquid.

The layer 50 extends between the two flanges 28, so that no particle can pass to the interfaces. Its downstream end is located at a distance from the substrate 38 and the outlet 26, upstream. Likewise, as mentioned above, its upstream end is at a distance "1" from the inlet 22 and the inflection line 24.

Once the Teflon layer 50 is in place, the injection nozzle 6 is activated to begin dispensing the particles 4 on the ramp 12. This involves implementing an initial step of filling the transfer zone 14, by the particles 4, upstream of the layer 50.

During this priming phase, the particles dispensed by the device 5 circulate on the ramp 12, then enter the zone 14 in which they disperse, until being retained by the layer 50, as shown schematically in FIGS. 5 and 5a.

In order to limit random scattering and to obtain satisfactory scheduling of the particles upstream and against the layer 50, the nozzles 32a and 32b are activated so as to stretch the particle film orthogonally to the direction in which they flow.

More specifically, at first, it is the nozzle 32b which is activated, the other remaining inactive. Figure 6a shows that at the beginning of suction, convection currents are established towards the associated rim 28. Next, FIG. 6a 'shows that the film is pulled towards the suction nozzle 32b, and stretches laterally, with the particles moving along the layer 50. Therefore, they organize themselves by causing the decrease of the gaps, and causing the beginning of the ordering in the vicinity of the layer 50, as shown in Figure 6a ''. A flow rate of the order of 65 ml / min can be applied.

The nozzle 32b is then deactivated, during a stopping time during which the particles 4 can reorder, as shown in Figure 6b, thanks in particular to the pressure exerted by the particles arriving in the transfer zone.

Then it is the turn of the nozzle 32a to be activated, the other now remaining inactive.

FIG. 6c shows that at the beginning of the suction, convection currents are established in the direction of the other flange 28. Then, FIG. 6c 'shows that the film is pulled towards the suction nozzle 32a, and stretches laterally, with the particles moving along the layer 50. As a result, the particles continue to organize themselves further leading to the decrease of the gaps, and causing further sequencing of the film. A flow rate of the order of 65 ml / min can also be applied.

The nozzle 32a is then deactivated, during a stopping time during which the particles 4 can reorder again, as shown in FIG. 6d, thanks in particular to the pressure exerted by the particles arriving in the transfer zone.

The suction alternation described above can be repeated as many times as necessary, each suction time and each stopping time for example about 15 to 30 s. The activation of the nozzles is normally stopped after the complete filling of the part of the transfer zone 14 situated upstream of the layer 50.

As the particles 4 are injected onto the ramp 12 and enter the transfer zone 14, the upstream front of particles tends to shift upstream towards the inflection line 24. L particle injection is continued even after this upstream front has passed line 24, so that it rises on the inclined ramp 12.

It is arranged that the upstream particle front 54 rises on the ramp 12 so that it is situated at a given horizontal distance "d" from the inflection line 24, as shown in FIG. distance "d" may be of the order of 30 mm.

At this moment, the particles 4 are perfectly ordered in the transfer zone and on the ramp 12, on which they are automatically ordered, without assistance, thanks to their kinetic energy put to use at the moment of the impact on the front 54. The scheduling is of the type shown in FIG. 6d near the layer 50a, namely that the film obtained has, at all points, a so-called "compact hexagonal" structure, in which each particle 4 is surrounded and contacted by six other particles 4 in contact with each other.

It is only from this moment that the layer 50 is moved downstream, toward the outlet 26 and the substrate 38, while continuing to retain the particles with its upstream end. The speed of displacement of the layer 50 on the surface of the carrier liquid 16 is adapted so that the position of the upstream front 54 of particles remains substantially unchanged. The means for ensuring this displacement are conventional, even if a manual movement could be envisaged, without departing from the scope of the invention. The displacement speed of the layer 50 may be of the order of 1.3 mm / s.

When the downstream end of the layer 50 arrives at the outlet 26, the substrate 38 is set in motion, then the layer 50 is deposited on the same substrate 38 in the manner of the particle film that follows it, by borrowing the capillary bridge 42. This stage of the process has been shown diagrammatically in FIG.

Then it is the turn of the ordered particle film to be deposited on the substrate 38, in the continuity of the layer 50, as has been schematized in FIG. 9, in the manner of that described in the document CA 2 695 449. .

In an alternative embodiment shown in Figure 10, the layer 50 initially extends to the substrate 38, so as to overcome the presence of additional means for its movement to the substrate. Indeed, the layer 50 can be driven directly by the substrate in scroll, on which it is initially deposited, preferably manually.

Of course, various modifications may be made by those skilled in the art to the invention which has just been described, solely by way of non-limiting examples.

Claims

1. Installation (1) for depositing a film of ordered particles (4) on a moving substrate (38), the installation comprising:

a transfer zone (14) comprising a particle inlet (22) and an outlet of particles (26) spaced from each other by two opposite lateral edges (28), retaining a carrier liquid (16) on which float the particles,

said apparatus being adapted to deposit on the substrate (38) the ordered particle film escaping from said particle outlet (26),

characterized in that it further comprises a plurality of suction nozzles (32a, 32b) capable of attracting the particles (4) present in the transfer zone (14) towards its two lateral flanges (28).

2. Installation according to claim 1, characterized in that it comprises only two suction nozzles (32a, 32b), respectively capable of attracting the particles (4) present in the transfer zone to the one and the other of the two side edges (28).

3. Installation according to claim 1 or claim 2, characterized in that it comprises an inclined ramp (12) for circulating particles, attached to said input of the transfer zone, and on which said carrier liquid (16) is also intended to circulate.

4. Installation according to any one of the preceding claims, characterized in that it comprises means (50) for temporary retention of the particles (4) in the transfer zone (14) away from said substrate (38), these means with retention being able to be moved to this substrate while retaining said particles.

5. Installation according to claim 4, characterized in that said means (50) for temporary retention of the particles take the form of a layer of hydrophobic material, floating on the surface of the carrier liquid (16).

6. Installation according to claim 5, characterized in that said means (50) for temporary retention of the particles take the form of a layer with a thickness between a few microns and several tens of microns.

7. Installation according to any one of claims 5 and 6, characterized in that said means (50) for temporary retention of the particles take the form of a layer of polytetrafluoroethylene (PTFE).

8. Installation according to any one of claims 5 to 7, characterized in that said means (50) for provisional retention take the form of a layer whose downstream end is also at a distance from the substrate.

9. Installation according to any one of claims 5 to 7, characterized in that said means (50) for temporary retention take the form of a layer, a downstream end is located on said substrate.

10. Installation according to any one of claims 5 to 9, characterized in that said means (50) for temporary retention take the form of a layer capable of being deposited on said substrate (38).

11. Installation according to any one of claims 4 to 10, characterized in that said means (50) of provisional retention comprise an upstream end located at a distance "1" of less than 20 mm from the entrance of the zone. transfer.

12. A method of depositing a film of ordered particles (4) on a moving substrate (38), using an installation (1) according to any one of the preceding claims, characterized in that during least part of the initial step of filling the particle transfer zone, said suction nozzles (32a, 32b) are actuated to attract the particles present in the the transfer zone to its two lateral flanges (28).

13. The method of claim 12, characterized in that said nozzles (32a, 32b) are actuated alternately so as to attract the particles present in the transfer zone towards one and the other of the two lateral flanges (28). , alternatively.

14. The method of claim 12 or claim 13, characterized in that after the establishment of the means (50) of temporary retention of the particles in the remote transfer zone of said substrate (38), and after the initial filling by particles of the portion of the transfer zone (14) located upstream of said temporary retention means (50), these are moved in said transfer zone to the substrate, while retaining said particles (4).

15. The method of claim 14, characterized in that said means (50) of temporary retention take the form of a layer which is deposited progressively on the moving substrate, while the downstream front of the ordered particle film (4). it retains moves to the outlet (26) of said transfer zone (14).