FIELD OF THE INVENTION

The present invention relates to a method for forming a coating on a surface of a substrate according to preamble of claim 1. The present invention further relates to an apparatus for forming a coating on a surface of a substrate according to preamble of claim 10.

BACKGROUND OF THE INVENTION

In liquid aerosol coating processes a liquid film is formed on a surface of a substrate. The liquid film is produced in a deposition step by first atomizing one or more liquid precursors into droplets or aerosol and then depositing the formed droplets or aerosol on the surface of the substrate such that a liquid film is formed on the surface of the aerosol. The atomization of the liquid precursors is advantageously carried out in inside a deposition chamber, but alternatively the formed droplets may be formed outside the deposition chamber and conducted into the deposition chamber as droplets or as aerosol. The droplets may be produced with pneumatic atomizers or by pneumatic atomization using atomizing gas or pressure. Alternatively, the atomization may also the carried out by ultrasonic atomizer or ultrasonic atomization. The formed droplets or the formed aerosol is then deposited on the surface of the substrate in the deposition chamber by supplying the droplets or the aerosol on the surface of the substrate, or by letting the droplets or the aerosol to settle on the surface of the substrate.

After the deposition step the formed liquid film is dried in a drying step in order to form a coating on the surface of the substrate. The formed coating is a solid coating. During the drying step liquid material is vaporized from the liquid film causing viscosity of the liquid film to increase and drying of the liquid film. In prior art solutions the drying step is carried out such that the liquid film has been let to dry freely on the surface of the substrate. The drying step has been conventionally carried out in chamber arranged downstream of the deposition chamber or in ambient atmosphere of the coating apparatus.

During free drying of the liquid film it is naturally formed locally different kinds of vaporization areas, in which the concentration of vaporized materials differ from the other or adjacent areas of the liquid film. The concentration differences cause weak gas flows which tend to intensify. In the areas where the vaporization is faster the liquid film will dry faster than in other areas. The liquid films tends maintain equilibrium and thus material is moved from the other areas to the areas having faster vaporization rate. This is shown also in figure 1. A vertical gas flow, shown with arrow B, may be generated in area of faster vaporization rate. Material and vaporized material from the neighbouring areas will flow to this area having faster vaporization rate, as shown with arrows C. When the liquid film dries thicker coating is formed to the areas having faster vaporization rate due to the fact the material has been moved from other areas. Therefore, the produced solid coating has unwanted thickness variations which are formed during the drying step.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide a method and an apparatus for forming a coating on a surface of a substrate so as to overcome or at least alleviate the prior art disadvantages. The objects of the invention are achieved by a method according to the characterizing portion of claim 1. The objects of the present invention are further achieved by an apparatus according to the characterizing portion of claim 10.

The preferred embodiments of the invention are disclosed in the dependent claims.

The invention is based on the idea of providing a method comprising: A) a deposition step in which a liquid film is formed on the surface of the substrate; and

B) a drying step in which the liquid film is dried for forming the coating on the surface of the substrate.

According to the present invention the drying step B) comprises drying the liquid film by forming two or more separate suction zones in which vaporized precursor or precursors are discharged from the surface of the substrate by vacuum for drying the liquid film. The two or more separate suction zones are formed successively and spaced apart for drying the liquid film in a staged manner. The substrate is transported successively through the two or more successive suction zones in a transport direction for drying the liquid film in a staged manner such that the liquid film on the surface of the substrate is subjected successively to vacuum of the two or more separate suction zones. According to the present invention, the drying step B) comprises increasing drying power in the transport direction of the substrate.

The drying step of the present invention may comprise forming a substitution gas zone between adjacent successive separate suction zones for providing substitution gas flow to the surface of the substrate. Alternatively, the drying step may comprise forming one or more separate substitution gas zones in which substitution gas flow is provided to the surface of the substrate, the one or more substitution gas zones being provided such that at least one substitution gas flow is between at least one pair of successive separate suction zones. Substitution gas zone may be formed by providing passive substitution gas flow from surrounding atmosphere to the surface of the substrate. The passive substitution gas flow may be generated by vacuum of the two or more suction zones. The substitution gas may also be provided by supplying substitution gas flow towards the surface of the substrate between adjacent separate suction zones. Alternatively, the substitution gas zone may be provided by supplying substitution gas flow to the surface of the substrate with one or more gas nozzles arranged between adjacent suction zones.

According to the present invention the drying step B) further comprises increasing drying power or drying efficiency in the transport direction of the substrate. This means that the drying power or drying efficiency increases along the transport direction as the substrate is transported through the drying step. Increasing the drying power in the drying step B) may comprise increasing suction power in successive separate suction zones in the transport direction of the substrate, and/or increasing the flow rate of the substitution gas in successive substitution gas zones in the transport direction of the substrate, and/or raising temperature of the substitution gas by heating in successive substitution gas zones in the transport direction of the substrate.

In one embodiment the drying step B) comprises forming the two or more separate suction zones as longitudinal suction zones extending transversely to the transport direction of the substrate, forming the two or more separate suction zones as longitudinal suction zones extending transversely to the transport direction of the substrate and the one or more substitution gas zones as longitudinal substitution gas zones extending transversely to the transport direction of the substrate.

The deposition step A) may comprise atomizing at least one liquid precursor into liquid droplets and depositing the liquid droplets on the surface of the substrate and forming the liquid film on the surface of the substrate. Alternative the deposition step A) may comprise depositing liquid precursor on the surface of the substrate using slot coating by moving a coating head having a liquid precursor slot over the surface of the, or depositing liquid precursor on the surface of the substrate using roll coating by spreading liquid precursor from a coating roll by moving the coating roll on the surface of the substrate, or depositing liquid precursor on the surface of the substrate by dipping the substrate into a bath of liquid precursor for forming the liquid film on the surface of the substrate.

The according to the present invention may also comprise a post- drying step C) which may comprise blowing a drying gas flow towards the surface of the substrate after the surface of the substrate is subjected to the suction zones; or blowing a heated drying gas flow towards the surface of the substrate after the surface of the substrate is subjected to the suction zones, or heating the surface of the substrate after the surface of the substrate is subjected to the suction zones.

The present invention and the above mentioned method may also be carried out with an apparatus for forming a coating on a surface of a substrate. The apparatus may comprise a deposition arrangement for forming a liquid film on the surface of the substrate and a drying arrangement arranged to dry the liquid film for forming the coating on the surface of the substrate. The deposition arrangement may comprise comprising one or more atomizers arranged to form liquid droplets from one or more liquid precursors, the deposition arrangement being arranged to deposit the liquid droplets on the surface of the substrate for forming the liquid film on the surface of the substrate and a drying arrangement arranged to dry the liquid film for forming the coating on the surface of the substrate. According to the present invention the drying arrangement may comprise two or more suction devices for discharging vaporized precursor or precursors from the surface of the substrate for drying the liquid film, the two or more suction devices being arranged successively and spaced apart from each other for drying the liquid film in a staged manner. The apparatus further comprises a transport arrangement for transporting the substrate through the drying arrangement in a transport direction. The drying arrangement is further arranged to increase the drying power in the transport direction of the substrate.

In one embodiment of the present invention the two or more suction devices may comprise a longitudinal suction nozzle for forming longitudinal suction zones.

The two or more suction devices may be arranged successively and spaced apart from each other such that gap is provided between successive suction devices for substitution gas flow to the surface of the substrate. Alternatively, one or more substitution gas devices may be provided between at least two successive suction devices for supplying substitution gas flow to the surface of the substrate. The one or more substitution gas devices may comprise longitudinal substitution gas nozzle extending parallel to the longitudinal suction nozzle for forming substitution gas zones.

In one embodiment the drying arrangement may comprise one or more substitution gas heaters or the one or more substitution gas devices may comprise one or more substitution gas heaters for heating the substitution gas.

The drying arrangement may comprise a drying chamber inside which two or more suction devices are arranged. The drying arrangement may further comprise a substitution gas source connected to the drying chamber for supplying substitution gas into the drying chamber and for forming a substitution gas atmosphere inside the drying chamber.

The apparatus according to the present invention may also comprise one or more gas distribution elements through which the substitution gas flow is flows to the surface of the substrate for forming a uniform substitution gas flow to the surface of the substrate. The one or more gas distribution elements may be provided to the gap between successive suction devices or in connection with the one or more substitution gas devices.

The drying arrangement may further comprise a post-drying device. The post-drying device may comprise a blower for blowing drying gas to the surface of the substrate or a heater for heating the surface of the substrate.

The substrate is transported through the deposition arrangement and drying arrangement with a transport arrangement in a transport direction such that the two or more suction devices are arranged successively and spaced apart from each other in the transport direction, or such that the two or more suction devices are arranged successively and spaced apart from each other in the transport direction and the post-drying device is arranged after the two or more suction devices in the transport direction.

An advantage of the present invention is that the drying of the liquid film and thus forming of the coating may be accelerated and also controlled. Accelerating the drying of the liquid film makes the coating process more efficient and increases the throughput of coated substrates. The present invention also enhances controlling the drying process of the liquid film such that the unwanted gas flows of the vaporized precursors on the surface of the liquid film during the free drying may be avoided by discharging vaporized precursors. The liquid film is sensitive to outer conditions such as gas streams due to low viscosity. However, carrying out the drying step by forming two or more separate suction zones in which vaporized precursor or precursors are discharged from the surface of the substrate by vacuum for drying the liquid film in a staged manner enables using low vacuum and weak gas streams as well as low heating temperatures which do not cause unwanted changes in the liquid film.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail by means of specific embodiments with reference to the enclosed drawings, in which

Figure 1 shows one example of prior art apparatus for coating a substrate;

Figure 2 shows one embodiment of a drying arrangement according to the present invention;

Figure 3 shows an upper view of a drying arrangement according to figure 2;

Figure 4 shows another embodiment of a drying arrangement according to the present invention;

Figure 5 shows yet another embodiment of a drying arrangement according to the present invention;

Figure 6 shows an upper view of a drying arrangement according to figure 5;

Figure 7 shows still another embodiment of a drying arrangement according to the present invention; and

Figure 8 an embodiment of a drying arrangement with a drying chamber according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a prior art apparatus for forming a coating 4 on a surface of a substrate 2. The apparatus comprises a deposition arrangement 3 for forming a liquid film on the surface of the substrate 2. The deposition arrangement 3 comprises a deposition chamber 6 which forms a deposition space 8 inside which the liquid film is formed on the surface of the substrate 2. The deposition chamber 6 comprises a first opening 14 via which the substrate 2 is transported into the deposition chamber 6, and a second opening 16 via which the substrate 2 is removed from the deposition chamber 6. The first and second openings 14, 16 may be provided with sealing gas nozzles (not shown) for forming a gas curtain and sealing the deposition space 8 of the deposition chamber such that gases and contaminations from outside the deposition chamber 6 may be prevented from entering the deposition chamber 6. The sealing gas nozzle of the second opening 16 may be omitted so that the produced liquid is not deteriorated by a sealing gas flow, or the sealing gas flow in the second opening 16 may be formed weak, weaker than in the first opening. Sealing gas may be some inert gas, such as N ₂ .

The deposition arrangement 3 may further comprise one or more atomizers 10 arranged to form liquid droplets 12 from one or more liquid precursors 15. The atomizers 10 may be two-fluid atomizers in which atomizing gas is used for atomizing the liquid precursors 15, pneumatic atomizers in which pressure is used for atomizing the liquid precursors 15 or ultrasound atomizers in which ultrasound is for atomizing the liquid precursors 15. The atomizers 10 may be arranged outside the deposition chamber 6 and thus the liquid droplets are transported into the deposition chamber 6, or as shown in figure 1, the atomizers may be arranged inside deposition space 8 of the deposition chamber 6. Alternative the atomizers 10 may be arranged in connection with the deposition chamber 6 such that the atomizers 10 atomize the liquid precursors 15 into the deposition space 8.

Figure 1 shows a deposition arrangement in which the atomizers 10 are two-fluid atomizers 10 in which the liquid precursor(s) from liquid precursor source 15 is atomized using atomizing gas from atomizing gas source 13. The liquid precursor(s) and the atomizing gas are supplied to the atomizer 10 via conduit 11. The atomizer 10 atomizes liquid precursor(s) into an aerosol or droplets 12.

The atomizers 10 may further be arranged in the deposition chamber 6 such that the droplets 12 are directed towards the surface of the substrate 2 for providing a direct deposition of the droplets 12 on the surface of the substrate 2. Alternatively, the atomizers 10 may be arranged directly towards each other in pairs such that the droplets 12 formed by the opposite atomizers collide to each other and then after the collision deposit of the surface of the substrate 2. The atomizers 10 may also be arranged otherwise provide indirect deposition of the droplets 12 on the surface of the substrate 2 by colliding the droplets 12 first a collision element and the guiding the droplets 12 on the surface of the substrate 2.

The deposition arrangement 3 is arranged to deposit the liquid droplets 12 on the surface of the substrate 2 in the deposition chamber 6 such that a liquid film of liquid precursors is formed on the surface of the substrate 2. Accordingly, the present invention is not restricted to any specific technical solution for producing the liquid droplets 12 and depositing the droplets 12 on the surface of the substrate 2.

The substrate 2 may be any substrate which needs to be coated with aerosol coating method and apparatus. In one embodiment the substrate 2 is a planar substrate. The planar substrate 2 may be for example sheet glass or some material web. In figures 1 to 7 the substrate 2 is sheet glass, but the present invention is not restricted to any specific planar substrate or substrate material.

It should be noted that the liquid film may be formed also in other alternative methods. In an alternative embodiment liquid precursor is deposited on the surface of the substrate 2 using slot coating by moving a coating head (not shown) having a liquid precursor slot in relation to the substrate 2 over the surface of the substrate 2 for forming the liquid film on the surface of the substrate 2. In another alternative embodiment liquid precursor is deposited on the surface of the substrate 2 using roll coating by spreading or rolling liquid precursor from a coating roll (not shown) by rotating the coating roll on the surface of the substrate 2 for forming the liquid film on the surface of the substrate 2. In a yet alternative embodiment liquid precursor is deposited on the surface of the substrate 2 by dipping the substrate 2 into a bath of liquid precursor for forming the liquid film on the surface of the substrate 2. Slot coating, roll coating and dip coating are generally known as such for skilled person and thus they are not described in detail.

The apparatus according to the present invention further comprises a drying arrangement 25 arranged to dry the mentioned liquid film for forming the coating 4 on the surface of the substrate 2. The drying arrangement 25 is provided after or downstream of the deposition arrangement 3, as shown in figure 1.

The apparatus further comprises a transport arrangement for transporting the substrate 2 to the deposition arrangement 3, through the deposition arrangement 3, to the drying arrangement 25 and through the drying arrangement 25, as shown in figure 1. The transport arrangement may be any conventional transport arrangement and comprise any known transports equipment. The transport arrangement is arranged to transport the substrate through the drying arrangement in the transport direction A. The apparatus may also comprise two or more similar or different transport arrangements, for example one for the deposition arrangement 3 and one for the drying arrangement 25. In the apparatus of figure 1 the transport arrangement comprises transport rolls 24 with which the substrate 2 is transported through the deposition arrangement 3 and through the drying arrangement 25 in a transport direction A.

Figure 1 shows a prior art drying arrangement 25 provided downstream of the deposition arrangement 3 in the transport direction A of the substrate 2. The drying arrangement 25 of figure 1 comprises drying chamber 18 having drying space 20. The drying chamber 18 comprises an inlet opening 16 through which the substrate 2 is transported into the drying chamber 18 and an outlet opening 22 through which the substrate 2 is transported out of the drying chamber 18. The inlet opening 16 of the drying chamber 18 is the second opening of the deposition chamber 6. The substrate 2 is dried in the drying chamber 18 between the inlet opening 16 and the outlet opening 22. In the drying chamber 18 the liquid film is let to dry freely on the surface of the substrate 2.

Figures 2 to 7 show embodiments according to the present invention. Its should be noted that the deposition arrangement 3 in figures 2 to 7 corresponds the deposition arrangement of figure 1, and thus the description of the deposition arrangement 3 in context of figures 2 to 7 is omitted.

Figure 2 shows one embodiment of the present invention, in which the drying arrangement 25 comprises suction devices 40, 50, 60, 70, 80 for discharging vaporized precursor or precursors from the surface of the substrate 2 for drying the liquid film. The two or more suction devices 40, 50, 60, 70, 80 are arranged successively and spaced apart from each other for drying the liquid film in a staged manner. This means that the separate suction devices 40, 50, 60, 70, 80 form successive and space apart suction zones in the drying arrangement 25 such that the substrate 2 moves successively through these suctions in the drying arrangement 25.

It should be noted, that exemplary embodiments shown in figures 2 to 8 comprise five successive separate suction devices40, 50, 60, 70, 80, but the drying arrangement 25 may comprise any number of successive separate suction devices 40, 50, 60, 70, 80 counting from two upwards.

As shown in figure 2, each suction device 40, 50, 60, 70, 80 may be connected to a vacuum source or vacuum equipment 44, 54, 64, 74, 84 for generating suction or vacuum and the suction zone. In figure 2 each suction device 40, 50, 60, 70, 80 is connected to a separate vacuum source 44, 54, 64, 74, 84 which enables controlling and adjusting suction power separately in each suction device 40, 50, 60, 70, 80 and in each suction zone. Alterative, two or more or all of the suction devices 40, 50, 60, 70, 80 may be connected to a common vacuum source such that the vacuum power provided from the common vacuum source is same for the suction devices 40, 50, 60, 70, 80 which are connected to the common vacuum source. However, the individual suctions devices 40, 50, 60, 70, 80 may also be provided with a controller (not shown) for controlling and adjusting the vacuum power of the individual suction device 40, 50, 60, 70, 80. This enables adjusting the suction power separately in the suction devices which re connected to a common vacuum source. The vacuum source 44, 54, 64, 74, 84 may be vacuum pump or the like.

The transport arrangement 24 for transporting the substrate 2 is arranged to transport the substrate 2 having the liquid film through the drying arrangement 25 in the transport direction A. The two or more suction devices 40, 50, 60, 70, 80 are arranged successively and spaced apart from each other in the transport direction A such that the surface of the substrate 2 and the liquid film are subjected successively to the suction devices 40, 50, 60, 70, 80.

The suction devices 40, 50, 60, 70, 80 are provided over the surface of the substrate 2, and more specifically over the liquid film provided on the surface of substrate 2 such that the formed suction zone acts on the liquid film or the precursors vaporized from the liquid film. The separate suction devices 40, 50, 60, 70, 80 may be all at the same height from the surface of the substrate 2, or alternatively they may be on different height from the surface of the substrate 2. Furthermore, drying arrangement 25 or the separate devices 40, 50, 60, 70, 80 may be provided with height adjuster(s) (not shown) for adjusting height of the suction devices 40, 50, 60, 70, 80 from the surface of the substrate 2. In one embodiment the height of all the suction devices 40, 50, 60, 70, 80 from the surface of the substrate 2 may be adjusted together with the height adjuster. In another embodiment height of each suction devices 40, 50, 60, 70, 80 from the surface of the substrate 2 may be adjusted separately. In one embodiment height of the suction devices 40, 50, 60, 70, 80 or the suction nozzles 42, 52, 62, 72, 82 from the surface of the substrate 2 may increase gradually in the transport direction A with each successive suction devices 40, 50, 60, 70, 80 or the suction nozzles 42, 52, 62, 72, 82 being higher from the surface of the substrate 2 than the previous one. Alternatively, each successive suction devices 40, 50, 60, 70, 80 or the suction nozzles 42, 52, 62, 72, 82 may be gradually lower from the surface of the substrate 2 than the previous one. The height of the suction devices 40, 50, 60, 70, 80 or the suction nozzles 42, 52, 62, 72, 82 from the surface of the substrate 2 may be used for controlling or adjusting the suction power of the suction devices 40, 50, 60, 70, 80.

As shown in figure 2 the separate successive suction devices 40, 50, 60, 70, 80 are arranged spaced apart from each other in the transport direction A of the substrate 2. The suction devices 40, 50, 60, 70, 80 may comprise longitudinal suction nozzle 42, 52, 62, 72, 82 for forming longitudinal suction zones. The suction nozzles 42, 52, 62, 72, 82 extend longitudinally and provide longitudinal suction zones. In a preferred embodiment the suction devices 40, 50, 60, 70, 80 and the suction nozzles 42, 52, 62, 72, 82 extend transversely, preferably perpendicularly, in relation to the transport direction A of the substrate 2 such that the suction zones are formed also transversely or perpendicularly to the transport direction of substrate.

Figure 3 shows a top view of the drying arrangement 25 and the suction devices 40, 50, 60, 70, 80. The suction devices 40, 50, 60, 70, 80 and/or suction nozzles 42, 52, 62, 72, 82 extend over the surface of the substrate transversely to the transport direction A of the substrate 2 and also across the surface of the substrate 2. Preferably the suction devices 40, 50, 60, 70, 80 and suction nozzles 42, 52, 62, 72, 82 extend over the side edges of the substrate 2 such that suction zones are homogenous across the whole surface of the substrate 2 and the ends of the suction nozzles 42, 52, 62, 72, 82 do not cause any unwanted effects to the liquid film and the coating 4.

There is provided a gap 45, 55, 65, 75 between each pair of successive suction devices 40, 50, 60, 70, 80 such that separate suction zones are formed. Width of each gap 45, 55, 65, 75 between successive suction devices 40, 50, 60, 70, 80 or suction zones in the transport direction A of the substrate 2 may be same or alternatively the width of the gaps 45, 55, 65, 75 may vary or be different. Furthermore, drying arrangement 25 or the separate devices 40, 50, 60, 70, 80 may be provided with horizontal adjuster(s) (not shown) for adjusting horizontal position of the suction devices 40, 50, 60, 70, 80 and the gaps 45, 55, 65, 75 between the suction devices 40, 50, 60, 70, 80. In one embodiment the horizontal position of all the suction devices 40, 50, 60, 70, 80 may be adjusted together with the height adjuster. In another embodiment horizontal position of each suction devices 40, 50, 60, 70, 80 may be adjusted separately such that the width of the gaps 45,55, 65, 75 between the successive suction devices 40, 50, 60, 70, 80 may be adjusted separately. In one embodiment width of the gaps 45, 55, 65, 75 may increase gradually in the transport direction A with each gap 45, 55, 65, 75 having larger width than the previous one. Alternatively, each successive gap 45, 55, 65, 75 may have gradually smaller width in the transport direction A than the previous one. The horizontal adjuster(s) and the height adjuster(s) may be separate pieces of equipment or they may be a single piece of equipment.

As shown in figure 2, the gaps 45, 55, 65, 75 between the suction devices 40, 50, 60, 70, 80 are open to atmosphere surrounding the drying arrangement 25 or the suction devices 40, 50, 60, 70, 80. Accordingly, the drying arrangement may be provided to open atmosphere, for example ambient atmosphere of the production facility. The atmosphere surrounding the drying arrangement 25 or the suction devices 40, 50, 60, 70, 80 may comprise gases. When the suction devices 40, 50, 60, 70, 80 produce suction zones the suction causes gases around the suction devices 40, 50, 60, 70, 80 to flow towards the suction devices 40, 50, 60, 70, 80 or the suction zones. Therefore, a substitution gas flows towards the suction devices 40, 50, 60, 70, 80 or the suction zones are generated. Thus the substitution gas may flow to the suction zones via the gaps 45, 55, 65, 75 between the successive suction devices 40, 50, 60, 70, 80. Accordingly, the two or more suction devices 40, 50, 60, 70, 80 are arranged successively and spaced apart from each other such that the gap 45, 55, 65, 75 is provided between the successive suction devices 40, 50, 60, 70, 80 for substitution gas flow to the surface of the substrate 2. The substitution gas flow enhances the dying of the liquid film. The apparatus may also be provided with one or more substitution gas heaters (not shown) for heating the substitution gas flowing towards the suction devices 40, 50, 60, 70, 80 for enhancing the drying of the liquid film.

Figure 4 shows an alternative embodiment of the apparatus. In this embodiment the drying arrangement 25 further comprises a post-drying device 90 the post-drying device comprising a blower 90 for blowing drying gas to the surface of the substrate 2. The post-drying device 90 is arranged downstream or after the suction devices 40, 50, 60, 70, 80 in the transport direction A of the substrate 2. The post-drying device 90 finishes the drying of the liquid film. The post-drying device 90 may extend longitudinally across the surface of the substrate 2 transversely or perpendicularly to the transport direction A of the substrate 2. Preferably the post-drying device 90 extends parallel to the suction devices 40, 50, 60, 70, 80 and suction zones. The blower 90 may comprise a supply nozzle 91 arranged towards the surface of the substrate 2 and extending across the substrate 2 transversely or perpendicularly to the transport direction A such that a drying gas blow zone is formed. The blower 90 may be used downstream of the suction devices 40, 50, 60, 70, 80 as the liquid film is in more solid state after the suction zones. The blower 90 may be arranged spaced apart from the last suction device 80 and over the surface of the substrate 2.

Figure 5 shows yet an alternative embodiment of the present invention. In this embodiment one or more substitution gas devices 46, 56, 66, 76 are provided to the gaps 45, 55, 65, 75 between successive suction devices 40, 50, 60, 70, 80 for supplying substitution gas flow to the surface of the substrate 2. The substitution gas may be for example N ₂ . The one or more substitution gas devices 46, 56, 66, 76 may comprise longitudinal substitution gas nozzles extending parallel to the longitudinal suction nozzles 42, 52, 62, 72, 82, or transversely or perpendicularly to the transport direction A for forming substitution gas zones between the suction zones.

The substitution gas devices 46, 56, 66, 76 may be all at the same height from the surface of the substrate 2, or alternatively they may be on different height from the surface of the substrate 2. Furthermore, drying arrangement 25 or the substitution gas devices 46, 56, 66, 76 may be provided with second height adjuster(s) (not shown) for adjusting height of the substitution gas devices 46, 56, 66, 76 from the surface of the substrate 2. In one embodiment the height of all the substitution gas devices 46, 56, 66, 76 from the surface of the substrate 2 may be adjusted together with the second height adjuster. In another embodiment height of substitution gas devices 46, 56, 66, 76 from the surface of the substrate 2 may be adjusted separately. In one embodiment height of the substitution gas devices 46, 56, 66, 76 from the surface of the substrate 2 may increase gradually in the transport direction A with each successive substitution gas devices 46, 56, 66, 76 or the substitution gas nozzles being higher from the surface of the substrate 2 than the previous one. Alternatively, each successive substitution gas devices 46, 56, 66, 76 or the substitution gas nozzles may be gradually lower from the surface of the substrate 2 than the previous one. The height of the substitution gas devices 46, 56, 66, 76 or the substitution gas nozzles from the surface of the substrate 2 may be used for controlling or adjusting the drying power. It should be noted that the substitution gas devices 46, 56, 66, 76 may also be connected to the suction devices 40, 50, 60, 70, 80 such that their height and position in relation to the substrate 2 may be adjusted together with the suction devices 40, 50, 60, 70, 80.

In figure 4 it is shown that each gap 45, 55, 65, 75 has one substitution gas device 46, 56, 66, 76. However it is also possible to provide gas device 46, 56, 66, 76 only to some of the gaps 45, 55, 65, 75. For example, the first gap 45 or the two first gaps 45, 55 in the transport direction A are without a substitution gas device. Similarly only the last gap 75 or two last gaps 65, 75 may be provided with a substitution gas device 66, 76. Therefore, the liquid film is subjected to gas flow only when it has already dried somewhat such that the substitution gas flow from the substitution gas device 46, 56, 66, 76 does not affect the uniformity of the liquid film.

In the embodiment of figure 4, the post-drying device is a heater 94 for heating the surface of the substrate 2 for finishing the drying of the liquid film. The heater 94 may be a radiant heater. The facts described in context with the post-drying device of figure 3 apply also to the embodiment of figure 4.

In one embodiment the one or more substitution gas devices 46, 56, 66, 76 may comprise one or more substitution gas heaters (not shown) for heating the substitution gas before supplying it towards the surface of the substrate 2. Heating the substitution gas enhances the drying of the liquid film.

Figure 5 shows a top view of the drying arrangement 25, the suction devices 40, 50, 60, 70, 80 and the substitution gas devices 46, 56, 66, 76. The suction devices 40, 50, 60, 70, 80 and substitution gas devices 46, 56, 66, 76 extend over the surface of the substrate 2 transversely to the transport direction A of the substrate 2 and also across the surface of the substrate 2. Preferably the suction devices 40, 50, 60, 70, 80 and substitution gas devices 46, 56, 66, 76 extend over the side edges of the substrate 2 such that suction zones and substitution gas zones are homogenous across the whole surface of the substrate 2. The substitution gas devices 46, 56, 66, 76 are provided to the gaps 45, 55, 65, 75 between the successive suction devices 40, 50, 60, 70, 80 and the post-drying device 94 is arranged downstream of the last suction device 80 such that the gap 85 is provided between them.

Figure 7 shows an embodiment of the drying arrangement 25 in which the drying arrangement comprises one or more gas distribution elements 98 through which the substitution gas flow flows to the surface of the substrate 2 for forming a uniform substitution gas flow to the surface of the substrate 2. The gas distribution elements 98 may be perforated plates, textile sheets or the like comprising small holes or openings via which the substitution gas flows. The one or more gas distribution elements 98 may be provided to the gaps 45, 55, 65, 75 between successive suction devices 40, 50, 60, 70, 80, as shown in figure 7. Alternatively, the one or more gas distribution elements 98 may be provided in connection with the one or more substitution gas devices 46, 56, 66, 76 or gas substitution gas nozzles for providing uniform substitution gas flow from the substitution gas devices 46, 56, 66, 76. It should be noted that the one or more gas distribution elements 98 may also be used in the embodiment of figure2 and 4 in which there is no substitution gas devices 46, 56, 66, 76.

Figure 8 shows an embodiment in which the drying arrangement 25 comprises a drying chamber 100 inside which two or more suction devices 40, 50, 60, 70, 80 are arranged. The drying arrangement 25 and the drying chamber 100 comprises a substitution gas source 104 connected to the drying chamber 100 with substitution gas conduit 106 for supplying substitution gas into the drying chamber and for forming a substitution gas atmosphere inside the drying chamber 100. The substitution gas then flows from above the suction devices 40, 50,60,70, 80 via the gaps 45, 55, 65, 75 to the surface of the substrate 2. The flow rate of the substitution gas to the surface of the substrate may be controlled by adjusting the supply of the substitution gas to the drying chamber 100. The one or more gas distribution elements 98 through which the substitution gas flow flows to the surface of the substrate 2 may be used for providing uniform substitution gas flow to the surface of the substrate 2 in all the gaps 45, 55, 65, 75, 85.

It should be noted that also the substitution gas devices 46, 56, 66, 76 may be used together with the drying chamber 100. In that case the substitution gas is supplied via the substitution gas devises 46, 56, 66, 76 and not to the atmosphere of the drying chamber 100.

The transport arrangement 24 is arranged to transport the substrate 2 through the drying arrangement 25 in a transport direction A such that the two or more suction devices 40, 50, 60, 70, 80 are arranged successively and spaced apart from each other in the transport direction A, and optionally the post-drying device 90, 94 is arranged after the two or more suction devices 40, 50, 60, 70, 80 in the transport direction A.

The present invention also provides a method for forming the coating

4 on the surface of a substrate The method comprises a deposition step in which at least one liquid precursor is atomized into liquid droplets 12 and the liquid droplets 12 are deposited on the surface of the substrate 2 and forming the liquid film on the surface of the substrate 2. The method further comprises a drying step in which the liquid film is dried for forming the coating 4 on the surface of the substrate. According to the present invention the drying step comprises drying the liquid film by forming two or more separate suction zones in which vaporized precursor or precursors are discharged from the surface of the substrate 2 by vacuum for drying the liquid film. The two or more separate suction zones are formed successively and spaced apart for drying the liquid film in a staged manner. In the method the substrate 2 is transported successively through the two or more successive suction zones in a transport direction A for drying the liquid film in a staged manner. The two or more separate suction zones are formed successively and spaced apart in the transport direction A. This enables drying the liquid film in staged manner such that the liquid film becomes more dry in every suction zone.

The drying step further comprises forming a substitution gas zone in between adjacent successive separate suction zones for providing substitution gas flow to the surface of the substrate 2. The substitution gas zone may be provided to the gap 45, 55, 65, 75 between the successive suction zones. This may be carried out by forming separate substitution gas zones in which substitution gas flow is provided to the surface of the substrate 2, the one or more substitution gas zones being provided such that at least one substitution gas flow is provided between at least one pair of adjacent successive separate suction zones.

The substitution gas zone may be formed by providing passive substitution gas flow from surrounding atmosphere to the surface of the substrate 2. Thus the passive substitution gas flow being generated by vacuum of the two or more suction zones. The passive substitution gas flow may flow to the surface of the substrate 2 via the gaps 45, 55, 65, 75 between the successive suction zones.

In an alternative embodiment the substitution gas zone may be formed by supplying substitution gas flow towards the surface of the substrate 2 between adjacent separate suction zones. This may be carried out for example by providing the drying chamber 100 and supplying substitution gas into the drying chamber 100 and further to the surface of the substrate 2 via the gaps 45, 55, 65, 75.

In a yet alternative embodiment the substitution gas zone may be formed by supplying substitution gas flow to the surface of the substrate (2) with one or more gas nozzles 46, 56, 66, 76 which may be arranged to the gaps 45, 55, 65, 75 between the successive suction zones.

In all embodiment the substitution gas flow may be provided to the surface of the substrate 2 through a gas distribution element 98 for forming a uniform substitution gas flow to the surface of the substrate 2. Therefore the substitution gas flow is provided or supplied in evenly distributed manner or uniformly towards the surface of the substrate 2.

The method may further comprise heating the substitution gas of the substitution gas flow before it flows to the surface of the substrate 2 for drying the liquid film. The substitution gas may be heated in the drying chamber 100, in the substitution gas device 46, 56, 66, 76 or in the gap 45, 55, 65, 75 between the successive suction zones. Accordingly, the drying chamber 100 may be heated or the gaps gap 45, 55, 65, 75 between the successive suction zones may be heated.

The method of the present invention comprises forming the two or more separate suction zones as longitudinal suction zones extending transversely or perpendicularly to the transport direction A of the substrate 2. Alternatively, the method comprise forming the two or more separate suction zones as longitudinal suction zones extending transversely to the transport direction A of the substrate 2 and the one or more substitution gas zones as longitudinal substitution gas zones extending transversely or perpendicularly to the transport direction A of the substrate 2. Thus the suction and/or substitution gas flow is provided transversely or perpendicularly to the transport direction A and across the surface of the substrate 2, as shown in figures 3 and 6.

The drying step may further comprise a port-drying step carried out after the drying step. The post-drying step may finish the drying of the liquid film such that the coating is formed. The post-drying step may comprise blowing a drying gas flow towards the surface of the substrate 2 with a blower 90 after the surface of the substrate 2 is subjected to the successive suction zones. Alternatively, the post-drying step may comprise blowing a heated drying gas flow towards the surface of the substrate 2 with a blower 90 after the surface of the substrate 2 is subjected to the suction zones. In a yet alternative embodiment the post-drying step may comprise heating the surface of the substrate 2 with a heater 94 after the surface of the substrate 2 is subjected to the suction zones. In one embodiment the post-drying step may comprise both heating and blowing the drying gas flow. The drying step may further comprise increasing drying power in the transport direction A of the substrate 2. This means that the drying power of the drying step increases as the substrate 2 travels through the drying arrangement in the transport direction A. This may be advantageous for enhancing the efficiency of the drying step. When the liquid film dries the viscosity of the liquid film increases and thus the liquid film may tolerate more efficient drying as the drying advances without causing unwanted alterations to the quality of the liquid film or the coating, such as thickness variations.

In one embodiment increasing the drying power in the drying step comprises increasing suction power in successive separate suction zones in the transport direction A of the substrate 2. Thus the suction power of the successive suction zones may be gradually higher in the transport direction A of the substrate 2.

In another embodiment increasing the drying power in the drying step comprises increasing the flow rate of the substitution gas in successive substitution gas zones in the transport direction A of the substrate 2. This means that substitution gas may be supplied with higher in the successive substitution gas zones or in the successive gaps 45, 55, 65, 75 in the transport direction A of substrate 2.

In yet another embodiment increasing the drying power in the drying step comprises raising temperature of the substitution gas by heating in successive substitution gas zones in the transport direction A of the substrate 2. Accordingly, the substitution gas may be heated to higher temperatures or supplied at higher temperatures in the successive substitution gas zones or in the successive gaps 45, 55, 65, 75 in the transport direction A of substrate 2.

The drying power may also be increased by arranging the substitution gas devices 46, 56, 66, 76 or the substitution gas nozzles 42, 52, 62, 72 gradually closer to the surface of the substrate 2 such that the substitution gas flow is more intense towards the liquid film. Alternatively, the width of the gaps 45, 55, 65, 75 may be shortened in the transport direction A of the substrate such that the liquid film is subjected more frequently to suction zones and substitution gas zones.

It is also obvious that the above mentioned methods for increasing the drying power may be combined in a way and in any combination.

The invention has been described above with reference to the examples shown in the figures. However, the invention is in no way restricted to the above examples but may vary within the scope of the claims.