WO2002026399A1

WO2002026399A1 - Method and device for continuously coating a metal strip with a multilayer crosslinkable polymer fluid film

Info

Publication number: WO2002026399A1
Application number: PCT/FR2001/002971
Authority: WO
Inventors: Claude Bonnebat; Frédéric JENNY; Thierry Soas; Richard Verhalle
Original assignee: Usinor
Priority date: 2000-09-29
Filing date: 2001-09-25
Publication date: 2002-04-04
Also published as: AU2001291992A1; FR2814689A1

Abstract

The invention concerns a method for continuously coating at least a surface of a metal strip with a multilayer crosslinkable polymer fluid film (20) obtained from solid precursors at room temperature, free of non-reactive solvent or diluent and whereof the softening temperature is higher than 50 °C. The method consists in continuously unwinding the preheated metal strip (1), in forming by forced flow on the applicator roll (12) with deformable surface a multilayer coat (13) of said crosslinkable polymer and in transferring said coat onto the metal strip for forming a multilayer film (20) on the corresponding surface of the metal strip (1). The invention also concerns a coating device for implementing the method.

Description

Method and device for continuously coating at least one face of a metal strip with a multilayer fluid film of crosslinkable polymer.

The present invention relates to a process for continuously coating at least one face of a metal strip with a thin multilayer fluid film of crosslinkable polymer produced from solid precursors at room temperature and free of solvent or diluent not reactive.

In the processes for continuously coating metal strips, it is common to apply a film formed from several successive layers of paint or varnish, which have strong affinities with one another in terms of their adhesion, but different functionalities for the decoration or the anti-corrosion protection of this metal strip.

The first layer is generally called the primer layer and the second layer or appearance layer is called the top coat.

The primary layer generally has the specific role of obtaining excellent adhesion with the metal strip and inhibiting the corrosion of this strip which can be obtained by incorporation of an organic or inorganic pigment or by the addition of particles of a more oxidizable metal than the substrate.

An opacifying pigment can also be incorporated into this primer.

Regarding the top coat, it allows the addition of pigments or dyes to obtain a uniform shade as well as the use of binders with very good photochemical resistance or the incorporation of ultraviolet absorbers or radical inhibitors free. This finishing layer also allows the creation of a homogeneous structured surface to obtain the "orange peel" effect. Finally, it also allows the addition, for example, of lubricants, anti-marking additives or anti-scratch treatment. The coating film may also comprise one or more intermediate layers which, from a _. in general, add thickness to this film with economical formulations and said intermediate layer can can also be used as a light barrier to protect the primary layer from photodegradation under a finish layer partially transparent to ultraviolet.

For the application of this kind of multi-layer organic coatings, it is common to use low viscosity paint or varnish formulations based on solutions or dispersions of binders and dispersions of mineral fillers in solvents, in water or in mixed systems.

These dispersions or solutions then have a low level of viscosity under the intense shearing conditions of the paint or varnish application system, for example of the order of 0.5 Pa.s and are easily applicable to the roller which is a commonly used technique.

However, application by roller does not make it possible to superpose several so-called "wet" layers, that is to say before polymerization, or their simultaneous baking, which makes the continuous coating process of the metal strips more complex. two essential reasons.

Indeed, the roller application process requires a thickness adjustment step which is most often carried out by crushing ^~ dvjilLiide between a metering roller and an applicator roller which therefore does not allow the application of a so-called layer "wet" on another layer called "wet".

In addition, it is difficult to dry very thick layers without showing bubbling defects which are manifested in particular because volatile departures continue to occur at the primary layer while the finishing layer is already closed. The development of techniques for applying a film to a moving metal strip makes it possible to use crosslinkable polymers which do not contain non-reactive solvents or diluents.

Polymers are known which are crosslinkable thermally, such as for example thermosetting polymers, or physically, such as for example photopolymerizable polymers or crosslinkable under an electron beam. There is a wide variety of organic thermosetting coatings which are applied continuously to metallic substrates.

Among the techniques used to coat a metal strip with a crosslinkable polymer film produced from precursors which are solid at room temperature and free of non-reactive solvent or diluent, the technique of strip dusting or application with a block of solid paint.

In the case of a powder-based system, it is difficult to produce deposits of thin thicknesses and the superposition of several crosslinked layers in a single melting and baking operation.

Regarding the application of paint in the form of a solid block, this is a technique which is not suitable for the application of several superimposed layers due to the use of a smoothing roller. which acts as a homogenizing system. The coextrusion technique is commonly used in the field of transformation of thermoplastic materials in the molten state in order to produce multilayer deposits. This technique is used in particular to manufacture multilayer films by coating ^~ metallic surτtes-rσuïeaux or to coat substrates, such as paper or cardboard or plastic films.

Metal / polymer associations can be made by forming a film or a sheet of molten polymer which is first stretched in air, then pressed between a cooled cylinder and the moving metal strip.

The technique of coextrusion of multilayer organic thermoplastic coatings is described in particular in patent EP-A-067 060 for the application of polyolefins, the adhesion of which to the thick metallic substrate is achieved by coextrusion of an appropriate adhesive.

Another possible mode of application of a thermoplastic coating film melted on a preheated and moving metal strip consists of forming a sheet in a nozzle or a die positioned close to the metal strip and applying it directly to the strip. , without air travel nothing self-supporting, the molten material ensuring contact between the lips of the nozzle or of the die and the surface of the metal strip.

However, the application by this technique of a fluid multilayer film of crosslinkable polymer free of solvent or non-reactive diluent cannot be satisfactorily achieved by direct deposition on the strip in the case where the metal support is relatively thick. .

Indeed, the irregularity of a metal surface due to flatness defects and its variations in thickness become too great so that the sheet formed, calibrated by the distance between the surface of the nozzle and that of the metal strip, presents significant variations in thickness compared to its average thickness, in particular if it is sought to make deposits of thickness less than 50 μm.

In general, the various known application techniques do not make it possible to compensate for the variations in thickness of the metal substrate, which thereby induce unacceptable fluctuations in thickness of the coating, in particular in the case where the substrate is formed by a metal strip which has a large surface roughness and / or undulations of amplitude equal to or greater than the thickness of the coating to be produced on said metal strip. Furthermore, these different application techniques do not allow variations in the width of the substrate, nor variations in the transverse positioning of this substrate, so that the coating cannot be deposited uniformly over the entire width. of the substrate.

Finally, during the application of the coating, micro-air bubbles can be interposed between the coating and the substrate, which affects the uniform application and the surface appearance of this coating. .

Thus, the continuous application of a multilayer coating of crosslinkable polymer of small and uniform thickness on a moving metal strip poses problems because this metal strip has flatness and thickness defects as well as roughness and / or significant undulations, even when this strip is plated under high tension on a uniform cylinder. The object of the invention is therefore to avoid these drawbacks by proposing a method and a device for continuously coating at least one face of a metal strip with a multilayer fluid film of small thickness of crosslinkable polymer made from precursors. solids at room temperature, free of non-reactive solvent or diluent and whose softening temperature is above 50 ° C, making it possible to obtain in a single step a multilayer coating of uniform thickness from a few microns to a few tens of microns applied homogeneously on this strip, while preventing micro-bubbles of air from being inserted between the film and the metal strip and by eliminating the flatness and roughness defects of this strip.

The subject of the invention is a process for continuously coating at least one face of a metal strip with a multilayer fluid film of crosslinkable polymer produced from precursors which are solid at room temperature, free of non-reactive solvent or diluent. and the softening temperature of which is greater than 50 ° C., said film being formed from at least one primer layer and one finishing layer and having a thickness less than that of the metal strip, characterized in that:

the metal strip is continuously scrolled, the metal strip is preheated to a temperature equal to or higher than the softening temperature of this crosslinkable polymer,

- A sheet of deformable surface and by forced flow at a temperature above the softening temperature of the crosslinkable polymer is formed, a sheet of said crosslinkable polymer in the molten state having a viscosity greater than 10 Pa under the conditions of formation of this sheet, said sheet comprising at least. a primary layer and a finishing layer in contact with the applicator cylinder and having a formation temperature below the start of crosslinking temperature of the crosslinkable polymer, - the applicator cylinder is rotated in opposite direction to the direction of travel of the strip metallic, - The crosslinkable polymer is thermally conditioned, during the transfer of the ply to the applicator cylinder, according to methods adapted to lower the viscosity of this crosslinkable polymer to a value lower than said viscosity measured under the conditions of said forced flow, and - performs a total transfer in thickness of the layer of the applicator cylinder on one face of the metal strip by compressing this metal strip against said applicator cylinder to coat said face of said crosslinkable polymer film by applying the primer on this face and obtaining a multilayer coating of uniform thickness and smooth surface. A subject of the invention is also a device for continuously coating at least one face of a metal strip with a multilayer fluid film of crosslinkable polymer produced from precursors which are solid at room temperature, free of non-reactive solvent or diluent. and whose softening temperature is greater than 50 ° C, said film being formed from at least one primer layer and one finishing layer and having a thickness less than that of the metal strip, characterized in that it comprises:

- means for continuously driving the metal strip,

means for preheating the metal strip at B temperature equal to or greater than the softening temperature of this crosslinkable polymer,

- Means for forming, on an applicator cylinder with a deformable surface and by forced flow at a temperature above the softening temperature of the crosslinkable polymer, a sheet of said crosslinkable polymer in the molten state having a viscosity greater than 10 Pa. s under the conditions of formation of this ply, said ply comprising at least one finishing layer and one primer layer in contact with the applicator cylinder and having a formation temperature lower than the start of crosslinking temperature of the crosslinkable polymer,

means for driving the applicator cylinder in rotation in the opposite direction to the direction of travel of the metal strip,

- thermal conditioning means, during the transfer of the sheet onto the applicator cylinder, of the crosslinkable polymer according to methods adapted to lower the viscosity of this crosslinkable polymer to a value lower than said viscosity measured under the conditions of said forced flow, and

means for compressing the metal strip against the applicator cylinder to effect a total transfer in thickness of the ply of this applicator cylinder on one face of the metal strip in order to coat said face of said film of crosslinkable polymer by applying the layer primer on this face and obtain a multilayer coating of homogeneous thickness and smooth surface. The characteristics and advantages of the invention will become apparent during the description which follows, given solely by way of example and made with reference to the appended drawings, in which:

- Fig. 1 is a schematic sectional view of an installation for coating one face of a metal strip with a multilayer film of crosslinkable polymer comprising a device for applying this coating according to the invention,

- Fig. 2 is a schematic perspective view of the application device according to the invention,

- Fig. 3 is a schematic sectional view of a first variant of the application device according to the invention,

- Fig. 4 is a schematic sectional view of a second variant of the application device according to the invention.

In Fig. 1, there is shown schematically an installation for continuously coating a metal strip 1 with a .20 multilayer film of fluid crosslinkable polymer produced from precursors which are solid at room temperature, free of non-reactive solvent or diluent and thickness between 5 and 50μm. In this figure, the thickness of the strip 1 has been exaggerated in order to differentiate it from the film.

This metal strip 1 has a thickness of, for example, between 0.10 and 4mm and is for example made of steel or aluminum or also of an aluminum alloy. The polymer of each layer may be different and the polymer used to coat the metal strip 1 is a polymer produced from precursors which are solid at room temperature, free from solvent or diluent which is not reactive and which can be crosslinked thermally, such as for example a thermosetting polymer, or by physical means, such as for example a photopolymerizable polymer. This polymer has, in the non-crosslinked state, a softening temperature greater than 50 ° C.

This polymer also has different softening, start of flow, start of crosslinking and rapid crosslinking temperatures.

In general, the temperature at the start of crosslinking of a thermosetting polymer is the temperature from which an increase in viscosity greater than 10% is observed in less than 15 minutes. In the case of a polymer crosslinkable under radiation, there is no temperature limit to reduce its viscosity in the absence of radiation. It is therefore easier to heat the polymer at the level of the application system in order to reduce its viscosity without the risk of causing the onset of crosslinking.

The metal strip 1 is driven in scrolling according to the arrow

F and the installation comprises means 2 for preheating the metal strip 1 to a temperature equal to or higher than the temperature of the fluid film 20 of crosslinkable polymer to be deposited on said metal strip 1 and at the softening temperature of this crosslinkable polymer.

The means 2 for preheating the metal strip 1 are constituted for example by at least one induction furnace. As shown in FIG. 1 the installation comprises, from upstream to downstream:

- a device designated as a whole by the reference 10 for coating the metal strip 1 with the multilayer film 20 of crosslinkable polymer produced from precursors which are solid at room temperature, free of solvent or non-reactive diluent and whose temperature is softening is greater than 50 ° C, means 3 for baking or crosslinking the film of crosslinkable polymer, and

- a block 6 for pulling the metal strip 1.

In the case where the polymer is crosslinkable thermally, the cooking means 3 comprise for example at least one induction furnace and cooling means 4 and in the case where the polymer is crosslinkable by physical means, the cooking means 3 can consist of lamps or electron beams.

In the embodiment shown in Figs. 1 and 2, the metal strip 1 is supported on at least one support cylinder 5 comprising a central metal core 5a, such as steel, and an outer casing 5b made of deformable material, such as elastomer.

Other embodiments of the support cylinder 5 can be envisaged, such as for example the use of a metal-coated cylinder. The multilayer film 20 of crosslinkable polymer to be deposited on the metal strip 1 must be of uniform thickness although this metal strip 1 exhibits thickness heterogeneities or flatness defects as well as roughness or significant surface undulations of amplitude equal to or greater than the thickness of the film 20 deposited on said metal strip 1. As shown in particular in FIG. 1, the multilayer film 20 comprises at least two layers, a so-called primary layer 21 and a so-called finishing layer 22.

The primary layer is for example an anti-corrosion layer and the finishing layer makes it possible to obtain a uniform shade by the addition of pigments or dyes and / or the incorporation of anti-ultraviolet absorbers and / or d free radical inhibitors.

In addition to these two layers, the film 20 can also include one or more intermediate layers used for example as a light barrier to protect the primary layer from photodegradation in a finish partially transparent to ultraviolet light and, in general, this or these intermediate layers can add thickness to the film 20. The device for coating a face of the metal strip 1 comprises:

- Means 11 for forming, on an applicator cylinder 12 with a deformable surface and by forced flow at a temperature above the softening temperature of the crosslinkable polymer, of a homogeneous sheet 13 of uniform thickness of crosslinkable polymer in the state melt with a viscosity greater than 10 Pa.s under the conditions of formation of this sheet,

means for driving the applicator cylinder 12 in rotation in a direction opposite to that of movement of the metal strip 1,

means 25 for thermal conditioning, during the transfer of the sheet 13 to the applicator cylinder 12, of the crosslinkable polymer according to methods adapted to lower the viscosity of this crosslinkable polymer to a value lower than said viscosity measured under the conditions of said flow strength,

- And means for compressing the metal strip 1 against the applicator cylinder 12 to effect a total transfer in thickness of the ply 13 of this applicator cylinder 12 on one face of the metal strip 1 and to obtain a coating formed by the film multi-layered 20 with an odd thickness and a smooth surface.

The ply 13 also includes at least one primary layer 13a and a finishing layer 13b. Depending on the nature of the film 20 to be obtained on the metal strip 1, the sheet 13 may include one or more intermediate layers. The applicator cylinder 12 comprises a central metal core 12a, such as for example of steel, and an external envelope 12b of deformable material, such as for example of elastomer.

The means of formation by forced flow of the ply 13 comprise at least one extrusion nozzle 11 connected to means of aiimenta- o. tion in molten crosslinkable polymer, not shown.

A special feature of the extrusion nozzles is that it allows a wide variety of adjustment modes for applying the ply 13 to the cylinder. applicator 12 by adjusting the position or the pressure of the nozzle 11 relative to said cylinder 12 or by modifying the inclination of the front face of said nozzle 11 relative to normal at the point of contact with the cylinder 12 or by choosing the geometry lips of said extrusion nozzle 11. The applicator cylinder 12 is heated to a temperature equal to or higher, on the one hand, at the temperature of formation of the ply 13 and, on the other hand, at the softening temperature of the crosslinkable polymer and is rotated by suitable means, not shown, in a direction opposite to the direction of travel of the metal strip 1. To perform the prior formation of the multilayer ply 13 in the molten state on the applicator cylinder 12 to deformable surface, several possibilities exist.

The first consists in carrying out successive applications of the different layers 13a and 13b making up the sheet 13 in several stages with. separate extrusion nozzles.

In addition, avoid creating turbulence when applying the second layer and possibly subsequent ones on the first layer.

A second possibility consists in successively applying the two layers 13a and 13b of the sheet 13 with a single extrusion nozzle 11 with two separate supply slots.

A third possibility consists in applying simultaneously the two layers 13a and 13b, already superimposed in the extrusion nozzle 11.

At the outlet of the extrusion nozzle 11, the sheet 13 of crosslinkable polymer in the molten state is deposited on the applicator cylinder 12 so that the primary layer 13a is in direct contact with the external surface of the applicator cylinder 12 and that the finishing layer 13b is located above said primary layer 13a, as shown in FIG. 1.

During its transfer to the applicator cylinder 12, the polymer of the ply 13 is thermally conditioned in order to lower its viscosity of this polymer to facilitate its transfer and its application to the metal strip 1. The thermal conditioning methods are adapted to lower the viscosity of the crosslinkable polymer, for example by a factor of 2; the temperature of said crosslinkable polymer possibly possibly exceeding the temperature at the start of crosslinking of this polymer. Thus, despite the increase in the temperature of the crosslinkable polymer to a level usually considered to be capable of causing the onset of crosslinking and therefore an increase in the viscosity, this viscosity retains at least temporarily a very low level facilitating the transfer and the application of the ply 13 of crosslinkable polymer on the metal strip l.

The means for thermal conditioning of the crosslinkable polymer are formed, for example, by an internal heating system of the applicator cylinder 12 and / or by at least one source 25 for applying a complementary thermal flux to the ply 13. The internal heating system of the applicator cylinder 12 is constituted for example by electrical resistances embedded in the mass of this cylinder or by channels provided in said cylinder for the circulation of a heat transfer fluid, such as for example oil.

The internal temperature of the applicator cylinder 12 must be adjusted, for example by means of a thermocouple, not shown, so as not to exceed a limit value to avoid damaging the external envelope 12b made of deformable material at too high a temperature and deteriorate the bonding layer between the deformable material and the metallic core of said applicator cylinder 12. Immediately before it passes against the applicator cylinder

12, the metal strip 1 is maintained at a temperature equal to or higher than the softening temperature of the crosslinkable polymer and, for example, this metal strip 1 is preheated to a temperature of 140 ° C.

According to the first embodiment shown in FIG. 1, the transfer of the ply 13 to the corresponding face of the metal strip 1 is obtained by the compression of this metal strip 1 against the applicator cylinder 12 by means of the support cylinder 5. Due to this pressure, the ply 13 is completely transferred to the corresponding face of the metal strip 1 so as to form the film 20 with the primary layer 21 directly applied to the corresponding face of the metal strip 1 and the finishing layer 22 above said primer 21.

A transfer is considered to be total or almost total in thickness when more than 90% of the material has been transferred.

The other face of the metal strip 1 can be bare or pre-coated with a coating suitable for the use of the metal strip 1. Next, the metal strip 1 thus coated passes through the cooking means 3, then through the means 4 for cooling the film 20 of crosslinkable polymer.

The coating thus produced on the metal strip 1 has for example a thickness of between 5 and 50 μm with a uniformity of thickness of a few microns and this despite the notable flatness or heterogeneity defects in thickness of the metal strip 1 .

The ply 13 and the film 20 of crosslinkable polymer may have a width less than the width of the metal strip 1 to coat only part of this metal strip 1 or a width greater than the width of this metal strip to coat all of said metal strip 1.

In the case where the ply 13 and the film 20 have a width greater than the metal strip 1, as shown in particular in FIG. 2, there remains on either side of the useful application area on said metal strip 1, a portion of crosslinkable polymer which is not applied to this metal strip 1.

This excess of crosslinkable polymer must be removed in order to prevent it from creating an additional thickness on the applicator cylinder 12.

Indeed, since the space which remains between the applicator cylinder 12 and the support cylinder 5, on either side of the metal strip 1 and because of the thickness of this metal strip 1, l excess crosslinkable polymer remains on the applicator cylinder 12. To remove this excess material, the coating device 10 is equipped for example with two doctor blades, respectively 14a and 14b, for example metallic, in contact with the applicator cylinder 12 in each zone situated outside the zone in contact with said cylinder 12 with the metal strip 1. The doctor blades 14a and 14b in contact with the applicator cylinder 12 are arranged upstream of the generator for applying the ply 13 to this cylinder 12 relative to the direction of rotation of said cylinder 12.

The transverse position of these doctor blades 14a and 14b on the applicator cylinder 12 can be subjected, by suitable means not shown, to the width of the metal strip 1 and / or to the transverse position of this metal strip 1 on the support cylinder 5.

In fact, the position of this metal strip 1 on the support cylinder 5 can vary and the doctor blades 14a and 14b are therefore in contact with the applicator cylinder 12 and remove the excess of crosslinkable polymer by friction on said cylinder 12.

Furthermore, the transverse position of the extrusion nozzle 11 can be permanently centered relative to the metal strip 1 as a function of variations in the transverse position of this metal strip ir for example by placing this extrusion nozzle 11 on a support transversely movable.

In Figs. 3 and 4, two variants have been shown which comprise means for simultaneously coating the two faces of the metal strip 1 with a fluid film of crosslinkable polymer produced from solid precursors at room temperature, free of solvent or non-reactive diluent and whose softening temperature is greater than 50 ° C.

In these two embodiments, the first face of the metal strip 1 is coated with a multilayer film 20 by means of a device 10 identical to the previous embodiment and which comprises an extrusion nozzle 11, an applicator cylinder 12 and means 25 for thermal conditioning of the multilayer sheet 13 of crosslinkable polymer formed on the applicator cylinder 12. According to the embodiment shown in FIG. 3, the means for compressing the metal strip 1 against the applicator cylinder 12 are formed by a second applicator cylinder 30 with a deformable surface and driven in rotation in the opposite direction to the direction of travel of the metallic strip 1. The second applicator cylinder 30 comprises for example a metal core 30a coated with an envelope 30b of deformable material, as for example an elastomer.

The second applicator cylinder 30 is associated with means 31 for forming by forced flow at a temperature above the softening temperature of the crosslinkable polymer, of a sheet 32 of said crosslinkable polymer in the molten state and having a viscosity greater than 10 Pa.s in the conditions of formation of this sheet.

The means for forming the sheet 32 are constituted by an extrusion nozzle 31 connected to means for supplying crosslinkable polymer, not shown.

The ply 32 is formed either by a monolayer ply, or by a multilayer ply comprising at least one primary layer and a finishing layer and optionally or several intermediate layers between said primary layer and said finishing layer. During its transfer to the second applicator cylinder 30, the viscosity of the crosslinkable polymer of this sheet 32 is lowered in order to facilitate its transfer and its application to the metal strip 1.

For this, the second applicator cylinder 30 is associated with means 33 for thermal conditioning of the crosslinkable polymer and which are formed for example by an internal heating system of the second applicator cylinder 30 and / or by an external heating system of this second cylinder. applicator 30 and / or by at least one source 33 for applying a heat flux, complementary to the ply 32.

The total thickness transfer of the sheet 32 of crosslinkable polymer to the other face of the metal strip is carried out by the second applicator cylinder 30 which allows this face to be coated with a monolayer film 24 or multilayer of crosslinkable polymer and to obtain a coating of uniform thickness with a smooth surface.

According to the embodiment shown in FIG. 4, the means for compressing the metal strip 1 against the applicator cylinder 12 are formed by a second applicator cylinder 40 with a deformable surface and driven in rotation in the same direction as the direction of travel of the metal strip 1.

The second applicator cylinder 40 comprises a metal core 40a coated with an envelope 40b of deformable material, such as for example an elastomer.

The second applicator cylinder 40 is associated with means 41 for forming by forced flow at a temperature above the softening temperature of the crosslinkable polymer, of a sheet 42 of said crosslinkable polymer in the molten state and having a viscosity greater than 10 Pa.s under conditions of formation of this sheet.

The means for forming the sheet 42 are constituted by an extrusion nozzle 41 connected to means for supplying crosslinkable polymer, not shown.

The ply 42 is formed either by a monolayer ply, or by a multilayer ply comprising at least one primary layer and a finishing layer and optionally one or more intermediate layers between said primary layer and said finishing layer.

During its transfer to the second applicator cylinder 40, the viscosity of the ply 42 is lowered in order to facilitate its transfer and its application to the corresponding face of the metal strip 1.

For this, the second applicator cylinder 40 is associated with means for thermal conditioning of the crosslinkable polymer and which are formed for example by an internal heating system of the second applicator cylinder 40 and / or by an external heating system of this second applicator cylinder. 40 and / or by at least one source 43 for applying a complementary thermal flux on the web 42. In this case, the sheet 42 is partially transferred to the corresponding face of the metal strip 1 by the second applicator cylinder 40 so as to coat this face with a film 44 of crosslinkable polymer and obtain a coating with a homogeneous structured surface, it ie with an "orange peel" surface appearance. This film 44 can be a monolayer film or a multilayer film.

The applicator cylinders 30 and 40 can also be equipped, like the applicator cylinder 12, with means for removing excess crosslinkable polymer deposited on these cylinders and constituted for example by at least one doctor blade 14a.

These applicator cylinders 30 and 40 comprise means for adjusting their tangential speed in a ratio of between 0.5 and 2 times the running speed of the metal strip 1.

The coating device also comprises means, not shown, for adjusting the contact pressure between the metal strip 1 and the applicator cylinders 12, 30 and 40 and the support cylinder 5. These means consist, for example, of hydraulic cylinders or screw / nut systems which make it possible to adjust the contact pressures as a function of the viscosity of the crosslinkable polymer so as to ensure transfer of the material under the best conditions and to minimize friction forces.

By way of example, the formulation of the mixture of crosslinkable polymer of the different layers can be carried out as follows:

- Polyester resin (hydroxylated): 55%

- Uretdione hardener (blocked isocyanate): 10% - Pigment Ti 02 (for white formulation): 30%

- Additives: spreading agent, catalysis, crosslinking, color adjustment, etc.: 5%

The characteristics of this thermosetting organic coating are:

Tg: 25 ° C (before crosslinking); 40 ° C (after crosslinking) Average molar mass: Mn: 4000 g / mol For example, the sheet of crosslinkable polymer melted at the outlet of the extrusion nozzle has a temperature of 125 ° C and the thermal conditioning carries the temperature of the crosslinkable polymer, for example at 155 ° C by means of thermal conditioning and the metal strip 1 is preheated to a temperature of for example 140 ^C C.

The coating device according to the invention makes it possible to obtain, on a metal strip, a coating of crosslinkable polymer of small thickness and with excellent precision, and this on a metal strip which exhibits significant roughness and defects in flatness and heterogeneity. thick.

The coating device according to the invention offers the possibility of being able to carry out in a single operation the application and cooking of the various organic coatings, which makes it possible to considerably reduce the investment costs as well as the production costs.

Thus, this device considerably increases the flexibility of the production lines which are not limited either by the number of layers or by their thickness.

Furthermore, the fact that the temperature of formation of the sheet is lower than the crosslinking temperature of the polymer is an important characteristic in the case of thermosetting polymers otherwise the forced flow through the extrusion nozzle can cause significant stagnation. of the polymer which can deteriorate the good distribution of this polymer over the entire width of this nozzle. Finally, the device according to the invention makes it possible to compensate for fluctuations in width or in transverse position of the metal strip during application and to overcome the uniformity defects of the metal strip and thus to produce a coating of uniform thickness on a non-uniform metal substrate. It also makes it possible to continuously coat metal strips of different widths or to simultaneously coat several metal strips arranged parallel next to each other and to overcome by simple and effective means of width and positioning fluctuations of the metal strip (s).

Claims

CLAIMS 1. Process for continuously coating at least one face of a metal strip (1) with a multilayer fluid film (20) of crosslinkable polymer produced from solid precursors at room temperature, free of solvent or diluent non-reactive and whose softening temperature is greater than 50 ° C, said film (20) being formed of at least one primer layer and a finishing layer having a thickness less than that of the metal strip (1), characterized in what:

- the metal strip (1) is continuously scrolled, - the metal strip (1) is preheated to a temperature equal to or higher than the softening temperature of this crosslinkable polymer,

- On a applicator cylinder (12) with a deformable surface and by forced flow at a temperature above the softening temperature of the crosslinkable polymer, a sheet (13) of said crosslinkable polymer in the molten state having a higher viscosity is formed. at 10 Pa under the conditions of formation of this ply, said ply (13) comprising at least one primer layer and a finishing layer in contact with the applicator cylinder (12) and having a formation temperature lower than the start temperature crosslinking the crosslinkable polymer, - the applicator cylinder (12) is rotated in the opposite direction to the direction of travel of the metal strip (1),

thermally conditioning, during the transfer of the ply (1) to the applicator cylinder (12), the crosslinkable polymer according to methods adapted to lower the viscosity of this crosslinkable polymer to a value lower than said viscosity measured in the conditions of said forced disposal, and

- a total transfer in thickness of the ply (13) of the applicator cylinder (12) is carried out on one face of the metal strip (1) by compressing this metal strip (1) against said applicator cylinder (12) to coat said face of said film (20) of crosslinkable polymer by applying the primer on this face and obtaining a multilayer coating of uniform thickness and smooth surface.

2. Coating method according to claim 1, characterized in that the metal strip (1) is compressed between said applicator cylinder (12) and a support cylinder (5) with deformable or non-deformable surface.

3. Coating method according to claim 1, characterized in that:

the metal strip (1) is compressed between said applicator cylinder (12) and a second applicator cylinder (30) with a deformable surface rotated in opposite direction to the direction of travel of the metal strip (1),

- A sheet (32) of said crosslinkable polymer in the molten state having a viscosity greater than 10 Pa is formed on the second applicator cylinder (30) and by forced flow at a temperature above the softening temperature of the crosslinkable polymer. s under the conditions of formation of this ply (32),

- Thermally conditioning, during the transfer of the web (32) to the second applicator cylinder (30), the crosslinkable polymer according to methods adapted to lower the viscosity of this crosslinkable polymer to a value lower than said viscosity measured under the conditions said forced flow, and

- a total transfer in thickness of the ply (32) of the second applicator cylinder (30) is carried out on the other face of the metal strip (1) to coat this face with a film (24) of crosslinkable polymer and obtain a homogeneous structured surface coating.

4. Coating method according to claim 1, characterized in that: - the metal strip (1) is compressed between said applicator cylinder (12) and a second applicator cylinder (40) with deformable surface rotated in the same direction as the direction of travel of the metal strip d).

- A sheet (42) of said crosslinkable polymer in the molten state is formed on the second applicator cylinder (40) and by forced flow at a temperature higher than the softening temperature of the crosslinkable polymer having a viscosity greater than 10 Pa.s under conditions of formation of this ply (42),

- Thermally conditioning, during the transfer of the web (42) on the second applicator cylinder (40), the crosslinkable polymer according to

5 methods adapted to lower the viscosity of this crosslinkable polymer to a value lower than said viscosity measured under the conditions of said forced flow, and

a partial transfer in thickness of the sheet (42) of the second applicator cylinder (40) is carried out on the other face the metal strip (1) to coat this face with a film (44) of crosslinkable polymer and obtain a homogeneous structured surface coating.

5. Coating method according to claim 3 or 4, characterized in that the film (24; 44) of crosslinkable polymer deposited on the face of the metal strip (1) via the second applicator cylinder (30; 40) 5 is formed from a monolayer ply.

6. Coating method according to claim 3 or 4, characterized in that the film (24; 44) of crosslinkable polymer deposited on the face of the metal strip (1) via the second applicator cylinder (30; 40) is formed from a multilayer ply comprising at least one primary o layer and one finishing layer.

7. Coating method according to any one of the preceding claims, characterized in that the methods are adapted to lower the viscosity of the crosslinkable polymer by at least a factor of 2.

8. Coating method according to any one of the preceding claims, characterized in that the crosslinkable polymer is thermally conditioned by heating the or each applicator cylinder (12; 30; 40) and / or by application to the or each ply (13; 32; 42) of a complementary thermal flux.

9. Coating method according to any one of claims 3 or 4, characterized in that the or each sheet (20; 24; 44) is formed by extrusion.

10. A coating method according to any one of the preceding claims, characterized in that the tangential speed of the or each applicator cylinder (12; 30; 40) is adjusted in a ratio of between 0.5 and 2 times the running speed of the metal strip (1).

11. Coating method according to any one of the preceding claims, characterized in that the or each sheet (13; 32; 42) of fluid crosslinkable polymer is formed at a width less than the width of the metal strip (1 ) to coat only part of the corresponding face with this metal strip (1).

12. Coating method according to any one of claims 1 to 10, characterized in that the or each sheet (13; 32; 42) of fluid crosslinkable polymer is formed at a width greater than the width of the metal strip. (1) to coat the entire corresponding face with this metal strip (1).

13. Coating method according to claim 12, characterized in that the crosslinkable polymer deposited in excess on the or each applicator cylinder (12; 30; 40) is removed.

14. Device for continuously coating at least one face of a metal strip (1) with a multilayer fluid film (20) of crosslinkable polymer produced from solid precursors at room temperature, free of solvent or non-reactive diluent and whose softening temperature is above 50 ° C, said film being formed from at least one primer and one finishing layer and having a thickness less than that of the metal strip (1), characterized in that that it includes: - means for continuously driving the metal strip

- (1),

- means for preheating the metal strip (1) to a temperature equal to or greater than the softening temperature of this crosslinkable polymer, - means (11) for forming, on an applicator cylinder (12) with deformable surface and by flow forced to a temperature higher than the softening temperature of the crosslinkable polymer, of a sheet (13) of said crosslinkable polymer in the molten state having a viscosity greater than 10 Pa.s under the conditions of formation of this ply (13), said ply (13) comprising at least one finishing layer and one primer layer in contact with the cylinder applicator (12) and having a formation temperature below the crosslinking start temperature of the crosslinkable polymer,

means for driving the applicator cylinder (12) in rotation in the opposite direction to the direction of travel of the metal strip (1),

- Means (25) for thermal conditioning, during the transfer of the ply (13) to the applicator cylinder (12), of the crosslinkable polymer 0 according to methods adapted to lower the viscosity of this crosslinkable polymer to a value below said viscosity under the conditions of said forced flow, and

- Means (5; 30; 40) for compressing the metal strip (1) against the applicator cylinder (12) to effect a total transfer in thickness of the ply (13) of this applicator cylinder (12) on a face of the metal strip (1) in order to coat said face of said film (20) of crosslinkable polymer by applying the primer on this face and obtain a multilayer coating of homogeneous thickness and with smooth surface.

15. Coating device according to claim 14, characterized in that the means for compressing the metal strip (1) against the applicator cylinder (12) are formed by a support cylinder (5) with deformable surface. or non-deformable.

16. Coating device according to claim 14, characterized in that the means for compressing the metal strip (1) against the applicator cylinder (12) are formed by a second applicator cylinder (30) of deformable surface driven by rotation in opposite direction to the direction of travel of the strip (1) and in that it comprises means (31) for forming on the second applicator cylinder (30) and by forced flow and at a temperature higher than the softening temperature crosslinkable polymer, a web (32) of said crosslinkable polymer in the molten state having a viscosity greater than 10 Pa.s under the conditions of formation of this web (32) and means (33) for thermal conditioning, during the transfer of the tablecloth (32) on the second applicator cylinder (30), crosslinkable polymer according to methods adapted to lower the viscosity of this crosslinkable polymer to a value lower than said viscosity measured under the conditions of said forced flow, the total transfer in thickness of this sheet (32) on the other face of the metal strip (1) being effected by said second applicator cylinder (30) to coat this face with a film (24) of crosslinkable polymer and obtain a coating of uniform thickness with a smooth surface .

17. Coating device according to claim 14, characterized in that the means for compressing the metal strip (1) against the applicator cylinder (12) are formed by a second applicator cylinder (40) of deformable surface driven in rotation in the same direction as the direction of travel of the strip (1) and in that it comprises means (41) for forming on the second applicator cylinder (40) and by forced flow at a temperature higher than the softening temperature of the crosslinkable polymer of a sheet (42) of said crosslinkable polymer in the molten state having a viscosity greater than 10 Pa.s under the conditions of formation of this sheet and of means (43) of thermal conditioning during the transfer of the ply (42) on the second applicator cylinder (40), of the crosslinkable polymer according to methods adapted to lower the viscosity of this crosslinkable polymer to a value lower than said viscosity é measured under the conditions of said forced flow, the partial transfer in thickness of this ply (42) on the other face of the metal strip (1) being effected by said second applicator cylinder (40) to coat this face with a film (44) of crosslinkable polymer and obtain a homogeneous structured surface coating.

18. Coating device according to claim 16 or 17, characterized in that the film (24; 44) of crosslinkable polymer deposited on the face of the metal strip (1) via the second applicator cylinder (30; 40) is formed from a monolayer web (32; 42).

19. Coating device according to claim 16 or 17, characterized in that the film (24; 44) of crosslinkable polymer deposited on the face of the metal strip (1) via the second applicator cylinder (30; 40) is formed from a multilayer ply comprising at least one primer layer and one finishing layer.

20. Coating device according to claim 14 or 19, characterized in that the finishing layer is thicker than the primary layer.

21. Coating device according to any one of claims 14 to 17, characterized in that the means of formation by forced flow of the or each ply (13; 32; 42) comprise at least one extrusion nozzle (11 ; 31; 41).

22. Coating device according to any one of claims 14 to 21, characterized in that it comprises means for adjusting the tangential speed of the or each applicator cylinder (12; 30; 40) in a ratio between 0.5 and 2 times the running speed of the metal strip

(1).

23. Device according to any one of claims 14 to 22, 5 characterized in that the or each sheet (13; 32; 42) of fluid crosslinkable polymer has a width less than the width of the metal strip (1) for coating only part of this metal strip (1).

24. Coating device according to any one of claims 14 to 22, characterized in that the or each sheet (13; 32; 42) of fluid crosslinkable polymer has a width greater than the width of the metal strip ( 1) to coat all of this metal strip (1).

25. Coating device according to any one of claims 14 to 23, characterized in that it comprises means (14a, 14b) for removing the excess of crosslinkable polymer deposited on the or each applicator cylinder. (12; 30; 40).

26. Coating device according to claim 25, characterized in that the removal means are formed by at least one doctor blade (14a, 14b) in contact with the or each applicator cylinder (12; 30; 40) corresponding in each zone located outside the area in contact with or from each applicator cylinder with the metal strip (1).

27. Coating device according to any one of claims 14 to 26, characterized in that the thermal conditioning means crosslinkable polymer are formed by a heating system of the or each applicator cylinder (12; 30; 40) and / or by at least one source (25; 33; 43) for applying a complementary thermal flux on the or each tablecloth (13; 32; 42).

28. Coating device according to claim 27, characterized in that the source (25; 33; 43) of application of the additional thermal flux consists of hot air generators or infrared lamps or micro systems. waves.