FR2787354A1 - Continuously coating metal strip with thinner film of crosslinkable polymer comprises forming molten polymer on surface of applicator roll and lowering its viscosity before complete transfer to strip supported by cylinder - Google Patents

Abstract

Continuously coating a metal strip with a relatively thinner film of crosslinkable polymer comprises forming molten polymer with a viscosity at least 10 Pa.sec and cooler than its crosslinking temperature on the surface of an applicator roll whereby the film viscosity is lowered before complete transfer onto the strip supported by a cylinder. Continuously coating a metal strip with a relatively thinner film of crosslinkable polymer that is free of non-reactive diluent or solvent and has a softening temperature at least 50 degreesC comprises forming molten polymer with a viscosity at least 10 Pa.sec and cooler than its crosslinking temperature on the surface of an applicator roll. The molten polymer forms the film and its viscosity is lowered before complete transfer to the strip supported by a cylinder. The roll rotates in the opposite direction to the movement of the strip. An Independent claim is included for: (a) A device for performing as above. Preferred Features: The viscosity is at least halved. The roll has a deformable surface and the cylinder a hard surface or vice versa. The metal strip is pressed against the roll to transfer the film onto the strip. A heated transfer roll may be placed between the applicator roll and the cylinder.

Description

The subject of the present invention is a method and a device for

  continuous coating of at least one metal strip with a thin, thin film of crosslinkable polymer free of non-reactive solvent or diluent. Polymers are known which are crosslinkable

  thermally, such as thermopolymers

  curable, or physically, such as

photopolymerizable polymers.

  There are a wide variety of gold coatings

  thermosetting ganics which are applied continuously

on metallic substrates.

  In most cases, this is a formula-

  complex tions which combine in a solvent medium or

  aqueous a system of functional organic prepoly-

  mothers, a crosslinking system and additives such as

  pigments or fillers, various formulation adjuvants.

  Various methods of application are also known.

  tion of an organic thermoplastic or thermoset coating

  cissable on a bare or coated metal strip.

  The application of organic coatings such as for example paints or liquid varnishes is most often carried out by roller coating of these liquid coatings in the state of solution or dispersion in the medium

solvent or aqueous.

  For this, we deposit the li-coating

  on a metal strip by pre-dosing the solution or dispersion using a two or three roller system and transferring some or all of it

  of this liquid coating thus predosed on an applied roller

  cator in contact with the surface of the metal strip to be coated. The transfer is carried out either by friction of the applicator roller and the metal strip, the movement of the two surfaces in contact taking place in the opposite direction

  or either by contact in the same direction.

  An interesting evolution of technology

  continuous application of cross-linked polymer coatings

  lable, such as paints or thermo varnishes

  curable, on a metal strip consists of depositing this coating without using any solvent

or thinner.

  Several alternatives have been proposed for the development and application of organic coatings

  without the use of non-reactive solvent or diluent.

  But the implementation poses a double problem,

  that of achieving a homogeneous dispersion of the char-

  ages and pigments in the binder and app system

plication of the product thus obtained.

  One of the techniques used for the application of such coatings consists in carrying out the application of

  organic coating in the form of a powder.

  Another technique is also known.

  plication of a liquid coating on a metal strip

  which uses a heating tank commonly called a fun-

  doir, provided at its lower part with a flow orifice

  liquid polymer contained in the tank.

  Below this tank are arranged two parallel cylinders in contact with each other and the

  metal strip to be coated moves below these cy-

lindres.

  The liquid polymer is poured out at

  the air gap of the cylinders, then flows between said cylinders

  dres and is deposited on the metal strip.

  However, this technique has drawbacks

  nients which reside in the fact that the polymer can only be slightly reactive given its relatively long time of storage in the heating tank and in the fact that it does not allow the thickness of the film to be controlled.

  coating on the metal strip and therefore obtaining

  provide a homogeneous and thin coating.

  To make thin deposits of gold products

  viscous ganics, another technique is to use

  extrusion of the organic coating in the fluid state and using

  plying this coating on a substrate by coating or by lamination. Coating extrusion of a thin organic coating is commonly practiced, in particular with thermoplastic polymers on flexible surfaces, such as paper, plastic films, textiles, or even

  thin metal supports such as packaging materials

  age. The transfer of the molten coating is carried out by means of a rigid flat die or a nozzle positioned

in direct contact with the substrate.

  The pressure exerted by the sector on the sub-

  trat comes from the viscosity of the melt. Thus, the possibilities of correcting the flatness defects of the substrate by plating it on the support cylinder

are very limited.

  This coating extrusion technique requires perfect parallelism between the edges of the die and the substrate and this substrate must be either perfectly flat or deformable to allow the formation of a thin deposit.

of uniform thickness.

  Indeed, the thickness of material deposited is controlled by the play and the pressure between the die and the substrate, which imposes a perfect parallelism of these two elements when one wants to realize applications in very

thin thickness.

  This condition is not achievable in the case of steel strips of thickness between 0.3 and 2mm, which have too high rigidity and a flatness or regularity of thickness insufficient to allow a

  adjustment also close to the clearance between the die and the

  trat, especially in the case of large bands

  geur. The extrusion lamination technique of a uniform layer of fluid coating on a substrate uses the drawing under a die of a fluid sheet at the outlet of a flat die, this sheet then being pressed on the substrate using for example a cold roller, a rotary bar or an air knife or an electrostatic field. In this case, the thickness of the fluid layer is controlled by the flow of the material in the section of the

  die and by the speed of the substrate.

  To avoid sticking of the fluid layer on the plating roller, it must have a surface

perfectly smooth and cooled.

  The plating pressure must however be suf-

  fissant weak to avoid the formation of a bead of ca

  landrage and, therefore, this transfer mode does not compensate for any variations in thickness and

  flatness defects in the case of a rigid substrate.

  This technique of applying the coating with

  formation of a free strand at the outlet of the extrusion die

  Zion avoids coupling problems between the fi-

  rigid substrate, but it induces instability

  Application tees if the length of the free strand fluctuates and it is difficult to implement with thermosetting systems of viscosity less than 2000 Pa.s because of the difficulties in achieving regular drawing and

good tackle.

  In general, in the various known techniques listed above, the continuous application of a thin organic coating on substrates

  metal is carried out under low contact pressures

  bles, insufficient to allow a thin, uniform coating applied uniformly on

  rigid substrates which may have surface defects

  birth and heterogeneity of thickness.

  These different application techniques do not

  do not compensate for variations in thickness of the

  metallic trat, which induce unacceptable fluctuations in thickness of the coating, in particular in the case where the substrate is formed by a metallic strip which

  has rough surface roughness and / or undulations

  load-bearing structures of amplitude equal to or greater than the thickness of the

  coating to be produced on said metal strip.

  On the other hand, these different techniques of ap-

  bending do not accommodate variations in the width of the substrate, nor variations in the transverse positioning of this substrate, so that the coating does not

  cannot be applied uniformly over the entire width

substrate.

  Finally, during the application of the coating, micro-air bubbles can be inserted between the coating and the substrate, which affects the uniform application and

  the surface appearance of this coating.

  Furthermore, we know in EP-A-0 593 708

  a device for coating a defective metal strip

  in which this metal strip passes over a cy-

  support liner and is in contact with an applied cylinder

  on the surface of which is deposited a fluid coating agent. This applicator cylinder is rotated in a direction opposite to the direction of travel of the strip.

and this cylinder is made of metal.

  But, this tape coating device

  metallic scrolling has drawbacks.

  In fact, given the nature of the material constituting the applicator cylinder, this device does not make it possible to apply a uniform pressure at all of the points of application of the film on the metal strip between

  the two rollers, when the surface of this metal strip-

  lique has too much relief, i.e. roughness

  and / or corrugations equivalent to or greater than the thick-

  of the coating film to be deposited.

  In addition, the surface hardness of the roller

  applicator does not allow uniform application and distribution

  evenly and locally the pressure on the strip and there is even a risk of spreading of the coating film on

  expense of the homogeneity of its thickness.

  Consequently, the continuous application of a thin and uniform crosslinkable polymer coating on a metal strip poses problems because this metal strip has flatness and thickness defects as well as roughness and / or large undulations of amplitude equal to or greater than the thickness of the coating film to be deposited on said strip even when

  this strip is pressed under high tension on a cy-

uniform liner.

  In addition, the different techniques used so far do not allow to apply on a tape

  metallic a thin coating of re-polymer

  crosslinkable free of non-reactive solvent or diluent

  two contradictory requirements which are hardness

and deformability.

  Indeed, after crosslinking, the polymer coating must be sufficiently hard while being deformable to allow the shaping of the sheets thus coated

  without causing degradation or detachment of the coating

is lying.

  Now, we know that the rise in molecular mass

  the crosslinkable precursor polymer is very

  vorable in obtaining a final coating that is both hard and deformable. However, the increase in the molecular weight of the precursors has a very unfavorable effect on the viscosity of a polymer free of solvent or of non-reactive diluent, which does not promote the transfer and the application of the

tablecloth on the metal strip.

  The object of the invention is to avoid these inconveniences.

  by proposing a method and a device for coating

  ment of at least one metal strip continuously with a thin, thin film of crosslinkable polymer free of non-reactive solvent or diluent, making it possible to obtain a

  coating of uniform thickness of a few microns at whatever

  that tens of microns applied in a homogeneous manner 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 as well as allowing an application on a

  part or all of the coating, despite the fluc-

  width kills and transverse positioning of

this band.

  The subject of the invention is therefore a method of

  continuous clothing of at least one metal strip by a fluid film of crosslinkable polymer free of non-reactive solvent or diluent and of thickness less than that of the metal strip, characterized in that: - the strip is continuously scrolled metallic on at least one support cylinder, - a primary ply of said crosslinkable polymer having a viscosity greater than 10 Pa.s is formed by forced flow, on a hard surface take-up cylinder under the conditions of formation of said primary ply, - an intermediate ply is formed on the take-up cylinder, - said intermediate ply is transferred to an applicator element with a deformable surface by compressing this applicator element between the take-up cylinder and the support cylinder, - the film is formed on the applicator element crosslinkable polymer,

  - and we transfer the film from the applica-

  tor on the metal strip by the compression of said element

  applicator between the take-up cylinder and the metal strip

  metallic to obtain a coating of uniform thickness.

  According to another characteristic of the invention,

  between the formation by forced flow on the pre-cylinder

  neur of the primary water table and the transfer of the water table

  medium on the applicator cylinder and / or said transfer of this intermediate sheet and the transfer of the film onto the metal strip, the polymer is thermally conditioned

  crosslinkable to lower the viscosity of this crosslinked polymer

  culable at a value lower than said viscosity measured

  under the conditions of said flow formed.

  The invention also relates to a device for continuously coating at least one metal strip with a fluid film of crosslinkable polymer free of non-reactive solvent or diluent and of thickness less than that of the metal strip, characterized in that that it comprises: - means for continuously driving the metal strip, - at least one cylinder for supporting the metal strip,

  - training means, on a pre-

  hard surface neur, by forced flow of a primary

  mayor of said crosslinkable polymer having a high viscosity

  less than 10 Pa.s under the conditions of formation of the

  said primary ply, said take-up cylinder forming an intermediate ply of crosslinkable polymer, - a deformable surface applicator element, forming the film of crosslinkable polymer,

  - and means for compressing the element

  applicator between the take-up cylinder and the metal strip

  metal for transferring, on the one hand, the intermediate ply of the takeup cylinder onto the applicator element and, on the other hand, the film of this applicator element on said strip

metallic.

  According to another characteristic of the invention, the device comprises, between the formation by forced flow on the take-up cylinder of the primary ply and the transfer of the intermediate ply to the take-up cylinder and / or said transfer of this intermediate ply and the transfer film on the metal strip, mechanical conditioning means of the crosslinkable polymer for

  lower the viscosity of this crosslinkable polymer to a

  their lower than said viscosity measured under the conditions

tions of said forced flow.

  The characteristics and advantages of the invention

  will appear during the description which follows,

  born only by way of example and made with reference to the accompanying drawings, in which: - FIG. 1 is a schematic elevation view of an installation for coating a metal strip with a crosslinkable polymer film comprising a device for applying this coating, in accordance with the invention,

  - Fig. 2 is a schematic perspective view

  application device, according to the invention, - FIG. 3 is a schematic elevation view of the means for removing the excess of crosslinkable polymer deposited on the take-up cylinder of the application device, according to the invention,

  - Fig. 4 is a schematic elevational view

  tion of the means for removing excess crosslinked polymer

  lable deposited on the applicator element of the application device

plication according to the invention.

  In Fig. 1, there is shown schematically

  an installation for continuously coating a metal strip-

  1 by a fluid crosslinkable polymer film, free of non-reactive solvent or diluent and of thickness included

between 5 and 50 im.

  This metal strip 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 and can be

  coated or prepainted on one or both sides.

  The polymer used to coat the metal strip-

  lique 1 is a polymer free of solvent or diluent non-reactive and crosslinkable thermally such as for example a thermosetting polymer or physically such as

  example a photopolymerizable polymer.

  These polymers have softening temperatures.

  start of flow, start of crosslinking and

  of fast cross-linking which are different.

  In the exemplary embodiment shown in FIG. 1, the metal strip 1 is driven in scrolling according to the arrow F and this metal strip is supported on

at least one support cylinder 3.

  This support cylinder 3 can be constituted by a steel cylinder or by a cylinder comprising a core

  metallic power plant, such as steel, and a

  external cover in deformable material, such as elastomer.

  The installation includes means 2 for pre-

  heating of the metal strip 1 to a sensitive temperature

  definitely equal to or higher than the temperature of the fluid film

  of crosslinkable polymer to be deposited on said metal strip

  than 1 and at the softening temperature of this crosslinkable polymer.

  These means 2 for preheating the metal strip

  1 are constituted for example by at least one induction furnace.

  Thus, as shown in FIG. 1, the installation

  tion comprises from upstream to downstream: - a device designated as a whole by the reference 10 for coating the metal strip 1 with a film of fluid crosslinkable polymer, free of non-reactive solvent or diluent, - means 5 baking or crosslinking the crosslinkable polymer film,

  - And a block 7 for pulling the metal strip

that 1.

  In the case where the polymer is crosslinkable thermally, the cooking means 5 include

  example at least one induction furnace and means 6 for

  cooling and in the case where the polymer is crosslinkable by physical means, the cooking means 5 can be constituted by lamps with ultraviolet rays or by

electron beams.

  Referring now to FIG. 2, let's

  describe the device 10 for coating the metal strip

  than 1 by a film of fluid crosslinkable polymer.

  This crosslinkable polymer film to be deposited on the metal strip 1 must be of uniform thickness, although this metal strip 1 has thickness heterogeneities or flatness defects as well as a roughness and / or significant surface undulations d amplitude equal to or greater than the thickness of the film deposited on said

metal strip 1.

  According to an embodiment shown in FIG. 2, the coating device 10 comprises: - means 12, 13 and 15 for forming, on a gripping cylinder 16 of hard surface, by forced flow of a homogeneous primary sheet 30a and of uniform thickness of crosslinkable polymer having a viscosity greater than 10

  Pa.s under conditions of formation of said primary sheet

  mayor 30a, said taker cylinder 16 forming an insulating sheet

  intermediate 30b made of crosslinkable polymer with a uniform thickness

form,

  - an applicator element 17 of deformed surface

  ble, in contact with the take-up cylinder 16 and the metal strip

  size 1 and intended to transfer, on the one hand, the water table

  intermediate 30b of the take-up cylinder on the application element

  tor 17 to form the film 31 and, on the other hand, this film 31 of this applicator element 17 on the metal strip 1,

  - means of thermal conditioning of the po-

  crosslinkable lymer during the contact of the intermediate web

  diary 30b on the take-up cylinder 16 and / or the contact of the

  film 31 on the applicator element 17 to lower the visco-

  sity of this crosslinkable polymer to a value lower than the

  viscosity measured under the conditions of forced flow.

  - And means for compressing the applicator element 17 between the gripping cylinder 16 and the

metal strip 1.

  The means of formation by forced flow of the primary ply 30a of crosslinkable polymer comprise an extrusion machine, not shown, of the conventional type provided with a die 12 comprising an extrusion slot 13

  and a flow regulator, not shown, consisting of

  killed for example by a metering pump and disposed between the

  extrusion machine and die 12.

  The gripper cylinder 16 has a hard surface, machined or ground, and is positioned with a very

  high precision so as to present a geometry par-

  completely uniform and optimum parallelism with respect to the extrusion slot 13 of the die 12. This gripping cylinder 16 has a hard metallic surface such as for example based on coated or bare steel or based

of ceramic material.

  The take-up cylinder 16 is heated to a temperature

  erasure substantially equal to or greater, on the one hand, at the temperature of the primary sheet 30a and, on the other hand, at the softening temperature of the crosslinkable polymer and is

  driven in rotation, by suitable means not shown

  felt, in the same direction as the cylinder 3 for supporting the metal strip 1, as represented by the arrows fl on

Fig. 2.

  The formation of the primary ply 30a of said po-

  crosslinkable polymer is produced for example by extrusion

  coating or by lamination extrusion.

* In the case of coating extrusion, the means of formation by forced flow of the primary ply 30a are formed by the die 12 bearing against the surface of the takeup cylinder 16 and are provided with adjustment means, the

  classic type, from the position of the edges of the ex slot

  trusion 13 of said die 12 relative to said surface

of the take-up cylinder 16.

  The die 12 of the extrusion machine gives the

  uniform distribution of the primary sheet 30a which is obtained

  naked by playing on the flow rate of said die 12 and on the

  rotational speed of the take-up cylinder 16.

  Due to the perfect parallelism of the die 12 and the taker cylinder 16, there is formed on the latter

  primary ply 30a of uniform thickness.

  In the case of lamination extrusion, the

  means of formation by forced flow of the primary sheet

  mayor 30a are formed by the sector 12, means of

  rage of the primary ply 30 by adjusting the flow of the

  said die 12 and / or the speed of rotation of the taker cylinder 16, means of adjustment, of conventional type, of the

  position of the edges of the extrusion slot 13 of said fi-

  lière 12 relative to the surface of the take-up cylinder 16 and by means 15 for plating the primary ply 30a on

  said surface of the take-up cylinder 16.

  The means 15 for plating the primary ply a on the surface of the take-up cylinder 16 are formed by an air gap directed on the take-up cylinder 16 at the contact generator of said primary ply 30a on said take-up cylinder 16 or by electrostatic plating means. For electrostatic plating means, the

  take-up cylinder 16 must be made of metal.

  Upon contact with the take-up cylinder 16, the

  primary layer 30a of crosslinkable polymer is at a thick

uniform.

  The die 12 of the extrusion machine 11 gives

  the uniform distribution of the primary water table 30a and the thickness

  The thickness of the intermediate ply 30b and the thickness of the film 31 are obtained by varying the speed of rotation of the pick-up cylinder 16 and / or of the applicator element 17 and on

  the running speed of the metal strip 1.

  The applicator element 17 has a deformable surface and is compressed between the take-up cylinder 16 and

  the metal strip 1 resting on the support cylinder 3.

  In the embodiment shown in the figures, the applicator element 17 is formed by a cylinder comprising a metal core 17a coated with an envelope

  17b made of formable material, such as for example elastic

  mother. According to a variant, the applicator element is

  formed by an endless band which can be coated with a ma-

  deformable material, such as for example elastomer.

  In the following, the description will be made with

  an applicator element consisting of a cylinder.

  The applicator cylinder 17, heated to a temperature

  erasure substantially equal to or greater than the temperature of the gripping cylinder 16, is rotated in the same direction as the support cylinder 3 of the metal strip 1, as shown by the arrows f2 in FIG. 2.

  The thermal conditioning of the crosslinked polymer

  lable during the contact of the intermediate ply 30b on the take-up cylinder 16 and / or the contact of the film 31 on the applicator element 17 to lower the viscosity of this

  crosslinkable polymer, can be produced in different man-

  nières. According to a first embodiment, the means for thermal conditioning of the crosslinkable polymer are

  formed by an internal heating system of the pre-

  neur 16 and / or the applicator cylinder 17 and / or by at least

  a source 11 for applying a complementary thermal fluid

  shut up on the intermediate sheet 30b and / or on the film 31.

  According to a second embodiment, the means for thermal conditioning of the crosslinkable polymer are

  formed by an internal heating system of the pre-cylinder

  neur 16 and / or by an external heating system

  deformable face of the applicator cylinder 17 and / or by

  at least one source 11 for applying a combined thermal flux

  additional on the intermediate ply 30b and / or on the film 31.

  The internal heating system of the pressure cylinder 16 is constituted by electrical resistances embedded in the mass

  of this cylinder or through channels provided in said cylinder for the circulation of a heat transfer fluid,

such as oil.

  The internal heating system of the cylinder

  plicator 17 is constituted for example by electrical resistances embedded in the metal core 17a of this cylinder 17 or by channels formed in said core 17a for the circulation of a heat-transfer fluid, such as for example oil. The temperature of the applicator cylinder 17 must

  be adjusted, for example by means of a thermocouple not

  presented, so as not to exceed a limit value for

  avoid damaging the outer casing 17b of defective material

  formable by too high a temperature and deteriorate the

  bonding layer between the deformable material and the core

  size 17a of said applicator cylinder 17.

  In the case of an external heating system for the deformable surface of the applicator cylinder 17, this heating system, not shown, is arranged opposite this applicator cylinder 17 in the area not covered by the film 31 and is constituted for example by generators

  hot air or infrared lamps.

  The source or sources 11 of application of the heat flux

  additional mique on the intermediate sheet 30b and / or on the film 31 are constituted for example by infrared lamps of medium wavelength of absorption included

  between 1.5 and 4 pm or by hot air generators or

  core by microwave systems.

  The means of thermal conditioning of the poly-

  crosslinkable mother therefore make it possible to lower the viscosity of this polymer, that is to say the fluidity of said polymer in order to

  facilitate its transfer and application on the mete

metal 1.

  The viscosity of the crosslinkable polymer is thus

  lowered by at least a factor of 2.

  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 viscosity, this viscosity

  serve at least transiently, a very low level

  facilitating the transfer and application of the film 31 in poly-

  mother crosslinkable on the metal strip 1.

  The crosslinkable polymer leaves the means of

  forced flow at a viscosity of the order of

  400 Pa.s and during its transfer to the pre-cylinder

  neur 16 and on the applicator cylinder 17, this polymer is gradually heated by 130 C at the outlet of the means of

training up to around 150 C.

  Therefore, the viscosity of the crosslinkable polymer

  is lowered to a value of around 80 Pa.s faci-

  thus reading its transfer and its application on the tape

metallic 1.

  In addition, the coating device 10 comprises means, not shown, of the conventional type, for adjusting

  tangential speeds of the take-up cylinder 16 and the cy-

  applicator lint 17 in a ratio of between 0.5 and 2

  times the running speed of the metal strip 1.

  The speeds of the taker cylinder 16 and the cylinder

  dre applicator 17 can be adjusted independently one

the other.

  The coating device 10 also comprises

  means not shown for adjusting the pressure of the

  tact, on the one hand, between the take-up cylinder 16 and the cylinder-

  dre applicator 17 and on the other hand, between the cylinder

  cator 17 and the metal strip 1.

  These means consist for example of hydraulic cylinders or screw-nut systems which allow

  to adjust the contact pressures according to the visco-

  sity of the crosslinkable polymer so as to ensure a trans-

  total fertility of the material and to minimize the efforts of fric-

tion.

  As shown in FIG. 2, the ex-slot

  trusion 13 of the die 12 as well as the gripping cylinder 16 and the applicator cylinder 17 have a length greater than the width of the metal strip 1 so as to cover the entire surface of the face of this metal strip 1 in contact

with the applicator cylinder 17.

  According to a variant, the extrusion slot 13 of the die 12 and the taker 16 and applicator 17 cylinders may have a length less than the width of the

  metal strip 1 to cover only part of the surface

  face of the face of said metal strip 1 in contact with

the applicator cylinder 17.

  The application of the fluid and thin film 31 of polymer crosslinkable thermally or by

  physical route is carried out as follows.

  The metal strip 1 is maintained at a temperature

  erasure equal to or greater than the softening temperature of the crosslinkable polymer and the gripper 16 and applicator 17 cylinders are rotated in the same direction

  as the support cylinder 3 of the metal strip 1.

  For example, the metal strip 1 is preheated to a temperature of 140 ° C. immediately before it passes over the support cylinder 3 and it runs at

a speed of 30m / min.

  At the outlet of die 12 of the ex-

  trusion, the primary ply 30a formed by forced flow, is pressed against the takeup cylinder 16 so as to form the intermediate ply 30b of crosslinkable polymer of uniform thickness. Due to the pressure exerted by the cylinder

  taker 16 and the metal strip 1 on the cylinder applied

  tor 17 of deformable surface, the intermediate ply 30b

  is transferred from the take-up cylinder 16 to the applied cylinder

  cator 17 which forms the film 31 and this film 31 is transferred

  of the applicator cylinder 17 on the surface of the metal strip-

1 to be coated.

  Then, the metal strip 1 thus coated passes through the cooking means 5, then through the means 6

  for cooling the film 31 of crosslinkable polymer.

  This film 31 of crosslinkable polymer can be

  placed on a bare metal strip of steel or aluminum

  or made of aluminum alloy or on a metal strip pre-

coated or prepainted.

  The coating thus produced on the metal strip-

  lique 1 has for example a thickness between 5 and 50 microns with a thickness uniformity of a few microns

  and this in spite of the notable defects of flatness or hetero-

  thickness of the metal strip 1.

  Other means of flow training

  this primary web 30a can also be used.

  Thus, the means of formation by forced flow of the primary ply 30a can be formed by a rigid block of crosslinkable polymer applied under pressure.

  controlled to deposit crosslinked polymer particles

  ble on the take-up cylinder 16 and form said primary sheet

  mayor 30a or also by a transfer system under an electrostatic field of a crosslinkable polymer powder on this taker cylinder 16 to form this primary ply a.

  According to other variants, the training means

  tion by forced flow of the primary web 30a can

  be formed by a cross-linked polymer projection system

  fluid lable on the take-up cylinder 16 or by a system

  of application on this taker cylinder 16 of a contiguous strip

  bare cross-linkable polymer previously produced for

sea the primary water table 30a.

  According to yet another variant, the means of

  formation by forced flow of the primary water table 30a may

  wind be formed by a rotary bar disposed between the

  die 12 and this taker cylinder 16.

  The primary sheet 30a and the film 31 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 1 to coat all of it. of said

metal strip 1.

  In the case where the sheets 30a and 30b and the film 31 have a width greater than the metal strip 1, as shown in F.j. 2, there remains, on either side of the useful application area on said metal strip 1, a portion of crosslinkable polym-re which is not applied

on this metal strip 1.

  This excess of crosslinkable polymer must be

  lifted to prevent it from creating an excess thickness on the cylinder

  dre applicator 17 or on the take-up cylinder 16.

  Indeed, given the space that remains between the applicator cylinder 17 and the support cylinder 3 on either side of the metal strip 1 and because of the thickness of this metal strip 1, the excess of crosslinkable polymer remains on the applicator cylinder 17.

  To remove this excess material, two solutions

tions are possible.

  The first solution is to equip the cy-

  lindre taker 16 of means for removing excess poly-

crosslinkable mother.

  This excess material which has not been deposited on the metal strip 1 remains on the applicator cylinder 17 and is transferred to the gripping cylinder 16 due to the

  pressure exerted on the deformable face of the cylinder applied

17.

  In this case, the means for removing the excess of crosslinkable polymer deposited on the leading cylinder 16

  are formed by at least one doctor blade 20, for example metalli-

  that in contact with the take-up cylinder 16.

  According to an exemplary embodiment shown in

  Fig. 3, the means for removing excess polymer

  culable deposited on the taker cylinder 16 are formed by

  two doctor blades 20, for example metallic, in each contact

  can with a side edge of the take-up cylinder 16 upstream

  of the generator for applying the ply 30 to this cylinder

dre taker 16.

  Preferably, the transverse position of the ra-

  keys 20 on the take-up cylinder 16 is subject, by suitable means not shown, to the width of the metal strip 1 and / or to the transverse position of this strip

  metal 1 on the support cylinder 3.

  Indeed, the position of this metal strip

  1 on the support cylinder 3 may vary.

  The doctor blades 20 are therefore in contact with the cy-

  linder taker 16 and remove excess crosslinked polymer

  ble by friction on said cylinder 16.

  The second solution is to equip the cylinder

  dre applicator 17 of means for removing excess of po-

crosslinkable lymer.

  As shown in FIG. 4, these means of removing excess crosslinkable polymer on the cy-

  linder applicator 17 are formed by a recovery cylinder

  ration 21, preferably metallic in contact with cy-

  liner applicator 17, and by at least one doctor blade 22 in con-

  tact with said recovery cylinder 21.

  Thus, the excess of crosslinkable polymer deposited on the applicator cylinder 17 is transferred to the recovery cylinder 21 due to the pressure exerted by said

  recovery cylinder on the deformable surface of said cy-

  applicator liner 17 and this excess of crosslinkable polymer

  is removed from the recovery cylinder 21 by the doctor blade 22.

  According to another embodiment, the means

  removal of excess crosslinkable polymer on the cy-

  applicator liner 17 can be formed by a recovery cylinder 21 and by two doctor blades in contact each

  with a side edge of said recovery cylinder 21.

  The means for removing the excess crosslinkable polymer deposited on the applicator cylinder 17 or on the gripper cylinder 16 avoids having to add inserts at the level of the slot 13 of the extrusion die 12 so as to calibrate as soon as possible. leaving the sector 12 the primary water table

  has crosslinkable polymer and to accommodate varia-

  width and transverse positioning of the

  metal strip 1 within the predefined tolerance limits

  nies. According to a variant, the point of application of the film 31 of crosslinkable polymer can be located at another

  location opposite the support cylinder 3 of the metal strip

  size 1 and, for example, on a free strand stretched from this

  metal strip 1 downstream of said support cylinder 3.

  According to another variant, the two faces of the metal strip 1 can be coated with a film 31 in

crosslinkable polymer.

  In this case, a device 10 for applying the film 31 is arranged on one side of the metal strip 1 and another device 10 for applying the film 31 is arranged for

  the other side of said metal strip 1.

  The application of the film 31 on each face of the metal strip 1 can be offset or simultaneous. For a

  simultaneous application, the support cylinder 3 is removed

  mé and replaced by an applicator element of the second device

  application. The applicator element of each device

  tif forms the support cylinder for the metal strip.

  By way of example, the formulation of the mixture of crosslinkable polymer is carried out as follows: - 85% by weight of a polyester polyol called URALAC P1460 from the company DSM Resins (Netherlands) having the following characteristics: - Average number of - OH per molecule; Fo.mo, = 3 - Hydroxyl index of the polyol Io = 37 to 47 - Average molar mass (in mass) Mw = 20000g / mole - Average molar mass (in number of molecules) Mn = 4090 Polydispersity index Mw / M : Ip = 4.9 (The hydroxyl index of the polyol Ioh being defined as the necessary quantity of potassium hydroxide - in mg - to neutralize all the hydroxyl functions; we therefore have: FOH.moy = IOHX Mn / 56100) - as hardener, 15% by mass of blocked isocyanate called

  VESTAGON BF 1540 from the company H LS, consisting essentially of

IPDI uretidione ment.

  - Average number of -NCO per molecule: Fiso.moy = 2 - Melting temperature between 105 C and 115 C - Crosslinking release temperature = 160 C - Total amount of NCO radicals = 14.7 to 16% by mass

  - Proportion of free NCO radicals (not blocked) <1% by mass

than,

  - for a shear speed of 10s-1, there is a visco-

  sity C: 900 Pa.s at 130 C: 400 Pa.s at 140 C: 180 Pa.s at 150 C: 80 Pa.s This mixture is entirely in the fluid and / or viscous state from a temperature equal to 120 C and its rapid crosslinking temperature is between 170 and 250oC. Furthermore, the crosslinkable polymer can be pigmented and loaded for example at 40% and more by weight

titanium oxide.

  The coating device according to the invention allows, thanks to the use of an applicator element to

  deformable surface, to obtain a polymer coating

  spreadable of uniform thickness between for example 5

  and 50lm and applied homogeneously on a metallic strip

  metal with a significant roughness of amplitude

  comparable to the thickness of the film and this thanks to the contact

  made between the applicator element and the surface of the metal strip to be coated, despite the flatness defects and

  thickness heterogeneity of said metal strip.

  The speed of the applicator element can be adjusted to a level substantially higher than the speed of movement of the metal strip so as to obtain perfect continuity of the coating and an excellent surface condition of this coating of transferable crosslinkable polymer.

on this metal strip.

  The coating device according to the invention

  can also be used for a metal strip

ascent or horizontal.

  Furthermore, the coating device according to the invention makes it possible to be able to continuously coat strips

  of different widths or to coat simultaneously-

* several metal strips arranged in parallel

  to each other and to free themselves by simple means

  ples and effective fluctuations in width and position

  transverse operation of the metal strip (s).

  The coating device according to the invention makes it possible to facilitate the regular and uniform supply of the coating of crosslinkable polymer by selecting the mode.

  the most suitable feed according to the product to be

  to be implemented. The advantage of this wide choice is particularly

  important in the case of high thermosetting coatings

  reagents which cannot be fed

  at a high temperature close to the reactivity range.

  This device also makes it possible, in the case of a chemical crosslinking process, to raise the temperature of the coating of crosslinkable polymer so as to reduce its viscosity and to facilitate its transfer and its

  spreading on the metal strip.

  Indeed, the temperature of the material delivered by the supply system located upstream of the take-up cylinder is limited to a value lower than that at the start

  of crosslinking to avoid any risk of evolution of the pro-

  feeds into the fuel system.

  Due to this temperature limitation, it

  it is impossible to reduce the viscosity of the product to a level

  calf low enough to facilitate its transfer and its good spreading on the metal strip. During contact with the heated cylinders, the material to be transferred undergoes very significant heating, but for a very short period of time, which avoids any risk of crosslinking of the

produced at this level.

  Finally, the device according to the invention makes it possible to

  compensate for fluctuations in width or position

  versal of the retallic strip when applying and overcoming the uniformity damage of the metallic strip and achieving a coating of uniform thickness on the surface

  on a non-uniform metal substrate.

Claims (21)

  1. Process for continuously coating at least one metal strip (1) with a fluid film (31) of crosslinkable polymer free of non-reactive solvent or diluent and of thickness less than that of the metal strip (1), characterized in that: - the metal strip (1) is continuously scrolled on at least one support cylinder (3), - a primary ply is formed by forced flow, on a pickup cylinder (16) with a hard surface 30a) of said crosslinkable polymer having a viscosity greater than 10   Pa.s under the conditions of formation of said primary sheet   mayor (30a), - an intermediate ply (30b) is formed on the take-up cylinder (16), - said intermediate ply (30b) is transferred to an applicator element (17) with a deformable surface by compressing this applicator element (17) between the take-up cylinder (16) and the support cylinder (3), - the film of crosslinkable polymer is formed on the applicator element,   - And the film (31) is transferred from the app element   plicator (17) on the metal strip by the compression of said applicator element between the take-up cylinder (16) and   the metal strip (1) to obtain a thick coating homogeneous.   2. Coating method according to claim 1, characterized in that, between the formation by forced flow on the take-up cylinder (16) of the primary ply (30a) and the transfer of the intermediate ply (30b) on the applicator cylinder ( 17) and / or said transfer of this intermediate sheet (30b) and the transfer of the film (31) to   the metal strip (1), the po is thermally conditioned   crosslinkable polymer to lower the viscosity of this polymer   crosslinkable to a value lower than said viscosity measured   created under the conditions of said forced flow.   3. Coating method according to claim   2, characterized in that the viscosity of this crosslinked polymer   lable is lowered by at least a factor of 2.   4. Coating method according to any one   of the preceding claims, characterized in that   preheats the metal strip (1) to a temperature   at or above the film temperature (31)   crosslinkable polymer fluid at the softening temperature   smoothing of this crosslinkable polymer.   5. Coating method according to any one   of the preceding claims, characterized in that   heats the take-up cylinder (16) to a sensitive temperature   equal to or higher than the temperature of the main water table   mayor (30a) and at the softening temperature of this po-   crosslinkable polymer and said take-up cylinder is driven   (16) rotating in the same direction as the support cylinder   port (3) of the metal strip (1).   6. Coating method according to any one   of the preceding claims, characterized in that   heats the applicator element (17) to a temperature equal to or higher than the temperature of the gripping cylinder (16) and the said applicator element (17) is rotated in   the same direction as the support cylinder (13) of the metal strip metal (1).   7. Coating method according to any one   of claims 2 to 5, characterized in that one condi-   thermally crosslinkable polymer by heating   internal of the take-up cylinder (16) and / or of the applicator element   tor (17) and / or by application to the intermediate ply   (30b) and / or on the film (31) of a complementary thermal flux   to hush up. 8. Coating method according to any one   of claims 2 to 5, characterized in that one condi-   thermally crosslinkable polymer by internal heating of the gripping cylinder (16) and / or by external heating of the deformable surface of the applicator element (17) and / or by application to the intermediate ply (30b) and / or to   the film (31) of a complementary heat flow.   9. Device for continuously coating at least one metal strip (1) with a fluid film (31) of crosslinkable polymer free of solvent or non-diluent   reactive and of thickness less than that of the metal strip-   lique (1), characterized in that it comprises: - means for continuously driving the metal strip (1), - at least one cylinder (3) for supporting the metal strip, - means (12, 13, 15) of formation, on a gripping cylinder (16) of hard surface, by forced flow of a primary sheet (30a) of said crosslinkable polymer   having a viscosity greater than 10 Pa.s under the conditions   formation of said primary ply (30a), said cy-   grab liner (16) forming an intermediate sheet (30b) of crosslinkable polymer,   - an applicator element (17) of deformed surface   mable, forming the film (31) of crosslinkable polymer,   - and means for compressing the element   applicator ment (17) between the gripping cylinder (16) and the metal strip (1) for transferring, on the one hand, the intermediate ply (30b) from the gripping cylinder (16) to the element   applicator (17) and, on the other hand, the film (31) of this element   applicator ment (17) on said metal strip (1).   10. Coating device according to the claim   tion 9, characterized in that it comprises, between the formation by forced flow on the take-up cylinder (16) of the   primary water table (30a) and the transfer of the intermediate water table   diary (30b) on the applicator cylinder (17) and / or said transfer of this intermediate ply and the transfer of   film (31) on the metal strip (1), means for   thermal operation of the crosslinkable polymer to lower   the viscosity of this crosslinkable polymer at a lower value   lower than said viscosity measured under the conditions of said force flow.   11. Coating device according to the claim   tion 9 or 10, characterized in that it comprises means for preheating the metal strip (1) to a temperature equal to or higher than the temperature of the fluid film (31) of crosslinkable polymer and at the softening temperature of this crosslinkable polymer.   12. Coating device according to one which   conch of the preceding claims, characterized in   that it comprises means for heating the take-up cylinder (16) to a temperature substantially equal to or greater than the temperature of the primary sheet (30a) and the softening temperature of this crosslinkable polymer and means for driving in rotation this taker cylinder (16) in   the same direction as the cylinder (3) for supporting the metal strip metal (1).   13. Coating device according to any one   conch of the preceding claims, characterized in   that it includes means for heating the applica-   tor (17) at a temperature substantially equal to or higher than the temperature of the take-up cylinder (16) and of the means for driving this applicator element (17) in rotation in the same direction as the strip support cylinder (3) metallic (1).   14. Coating device according to one which   conch of claims 10 to 13, characterized in that the   means of thermal conditioning of the crosslinkable polymer are formed by an internal heating system of the take-up cylinder (16) and / or of the applicator element (17) and / or by at least one source (11) for applying a flux additional thermal on the intermediate ply (30b) and / or on the film (31).   15. Coating device according to one which   conch of claims 10 to 13, characterized in that the   means for thermal conditioning of the crosslinkable polymer are formed by an internal heating system of the take-up cylinder (16) and / or by an external heating system of the deformable surface of the applicator element (17) and / or by at least one source (11) applying an additional thermal flux on the intermediate ply (30b) and / or on the film (31).   16. Coating device according to any one   conch of claims 9 to 15, characterized in that   the applicator element is formed by a cylinder (17) comprising   both a metallic core (17a) coated with an envelope (17b)   in deformable material, such as for example elastomer.   17. Coating device according to any one   conch of claims 9 to 15, characterized in that the   internal heating system of the take-up cylinder (16) is   constituted by electrical resistances embedded in this cy-   liner for circulation of a heat transfer fluid.   18. Coating device according to any one   conch of claims 9 to 16, characterized in that the   internal heating system of the applicator cylinder (17) is constituted by electrical resistances embedded in the core (17a) of this cylinder (17) or by arranged channels   in said core for the circulation of a heat transfer fluid.   19. Coating device according to one which   conch of claims 9, 15 or 16, characterized in that   the external heating system of the deformable surface of the applicator cylinder (17) consists of generators   hot air or infrared lamps.   20. Coating device according to one which   conch of claims 9 to 16, characterized in that the-   said source (11) for applying the complementary heat flux   shutting down on the crosslinkable polymer is constituted by infrared lamps of medium wavelength of absorption   or by hot air generators or by mid-systems microwave.   21. Coating device according to one which   conch shell of claims 9, 14, 16 or 18, characterized in   that it includes means for adjusting the internal temperature   applicator cylinder (17) to avoid damage   the envelope of deformable material of this cylinder applied (17).