EP0016681B1 - Method of and apparatus for continuously coating sheet material, particularly a paper or cardboard web - Google Patents

Description

The present invention relates firstly to a new continuous surface coating process, using a coating composition, of a sheet element such as a sheet of paper, cardboard, or synthetic material. . It also relates to a device allowing the implementation of this method.

The surface coating of a sheet element is a common practice in order to improve the qualities of the element, in particular in the case of paper or cardboard. The coating is carried out in a known manner by depositing a coating composition on the sheet element driven in displacement, then by a spreading and smoothing action of the composition in order to obtain a layer thickness also constant as possible. The spreading and smoothing operation is particularly delicate and has been the subject of extensive technical studies with the aim of seeking the elimination of any malformation in the appearance of the layer produced.

More specifically, a process for the continuous coating of a sheet element corresponding to the preamble of claim 1 is already known from patent FR-A-2,359,650.

The known coating method consists in continuously scrolling the sheet element in a determined direction, in particular from bottom to top, between at least two members located on either side. One of these members, consisting of a spreading blade, is applied by one end against a face to be coated with the sheet element. The other end of the blade is moved away from the sheet element and directed relative to the first end in a direction opposite to that of the movement of the sheet element. The other member serves as a holding piece for the sheet member and as a reaction piece for the first. According to this known method, the coating composition is deposited in contact with the face to be coated upstream of the zone of application of said spreading blade against the sheet element. In addition, a pressing force is exerted on the spreading blade in the direction of the face to be coated so as to spread the coating composition on the face to be coated.

The present invention provides a new improvement in these coating methods. Indeed, the Applicant has detected that the coating techniques known up to now have a certain number of unfavorable consequences, on the one hand, at the level of the sheet element and, on the other hand, at the level of the layer of material with which the sheet element is coated.

• a) une possible modification (d'ailleurs variable en fonction de la texture de l'élément en feuille) de la structure mécanique et/ou chimique de l'élément en feuille avec les risques de détérioration de ce dernier (rupture, défaut de planéité, etc...);
• b) une modification corrélative de la composition d'enduction dont la viscosité dans la région où se produit l'étalement va être supérieure à la viscosité initiale de la composition, ce qui peut se traduire par des défauts de régularité de la couche et des difficultés de contrôle de l'opération d'étalement et de lissage.

Current techniques deposit the coating composition at a relatively large distance from the zone in which the spreading and smoothing takes place. As a result, said composition is kept in contact with the sheet element for a relatively long time before spreading occurs. Thus, it was found that the contact time of the composition with the sheet element varied from 0.01 second to 1 second depending on whether one operates with a fast or slow coater. Consequently, in the case where a coating composition comprising a liquid phase is used, there is a capillary migration of the liquid in the sheet element, the extent of this capillary migration during this contact time between the composition and the sheet element preceding the coating, being practically identical to that which is entrained by the actual spreading operation caused by the application of pressure on the coating composition. This migration of part of the liquid phase of the coating composition causes

• a) a possible modification (moreover variable depending on the texture of the sheet element) of the mechanical and / or chemical structure of the sheet element with the risks of deterioration of the latter (rupture, defect of flatness , etc ...);
• b) a correlative modification of the coating composition, the viscosity of which in the region where spreading occurs will be greater than the initial viscosity of the composition, which may result in irregularities in the layer and difficulties control of the spreading and smoothing operation.

The drawbacks noted above occur regardless of the coating techniques used (roller or blade applicator coating).

The object of the process according to the present invention is to eliminate the drawbacks mentioned above by reducing the contact time of the coating composition with the sheet element before the spreading and smoothing operation as much as possible.

It will immediately be noted that the method according to the invention can be used with coating compositions of any kind and, in a large number of industrial fields.

• - l'application de couches pigmentées, afin d'améliorer l'aspect et l'imprimabilité,
• - l'encollage en vue de renforcer les propriétés mécaniques ou d'autres propriétés particulières d'un support (propriétés diélectriques, conductrices, anti-adhésives, etc...); les compositions utilisées peuvent comporter par exemple de l'amidon, des dérivés cellulosiques, de l'alcool polyvinylique, des dispersions plastiques (acétate de polyvinyle, latex styrène-butadiène ou copolymères acryliques), résines diélectriques, polymères conducteurs, silicones, vernis et laques diverses.

Thus, it is particularly suitable for coating paper in an aqueous or solvent medium for:

• - the application of pigmented layers, in order to improve the appearance and the printability,
• - gluing in order to reinforce the mechanical properties or other specific properties of a support (dielectric, conductive, non-stick properties, etc.); the compositions used can comprise for example starch, cellulose derivatives, polyvinyl alcohol, plastic dispersions (polyvinyl acetate, styrene-butadiene latex or acrylic copolymers), dielec resins triques, conductive polymers, silicones, varnishes and various lacquers.

The process can also be used for coating paper in a molten medium, that is to say for the application of hot-melt polymers, paraffins, waxes, hot-melt. It also makes it possible to carry out coatings using pulverulent products subsequently fixed on the support by passage through an oven, for example if it is a hot-melt powder. Coating could also be carried out using foam products.

Furthermore, the method of the invention makes it possible to apply the coating composition either on one or on both sides of the sheet element.

The method according to the invention is preferably implemented using a known coating device, in particular as described in the aforementioned patent FR-A-2,359,650, in which the element is circulated in sheet between two members, at least one of which is constituted by a smoothing blade subjected to a force urging it towards the second member which can be constituted either by a fixed reaction part, or by a roller on which the element in sheet, either by a second blade arranged in opposition to the first blade.

It is, in fact, with this type of device that the method according to the invention provides the optimum results.

According to this document, it is recommended to use a flexible coating blade and to subject its end to a thrust acting perpendicularly so as to apply the blade against the sheet element.

According to an embodiment recommended by this document, the flexible blade is applied against the sheet element using a flexible tube filled with a pressurized fluid, so as to be bent with a concavity turned towards the outside and tangent to the sheet over a large area.

A first variant of use proposed consists of scrolling the sheet element vertically and from top to bottom. The flexible blade is then held at its upper part and applied at its lower part against the sheet element. The angle formed by the sheet element and the blade then forms a natural reservoir inside which a feed nozzle pours the coating composition so as to maintain an amount of excess composition that the sheet passes through.

A second variant of use proposed by this document consists in scrolling the sheet element in a direction different from the previous one and, more particularly, from bottom to top. The position of the spreading blade is then modified accordingly. The coating composition is brought and deposited on the sheet element using a nozzle system adjoining it. The sheet element then plays the role of conveyor for the composition which is conveyed to the necking zone where it is smoothed.

• - soit déversée par gravité et brassée de façon désordonnée, au voisinage de l'élément en feuille,
• - soit simplement déposée et transportée par l'élément en feuille avant couchage.

Thus, according to the teachings of this document, the composition is

• - either poured by gravity and stirred in a disorderly manner, in the vicinity of the sheet element,
• - either simply deposited and transported by the sheet element before coating.

In both cases and as in all known devices, the contact time between the sheet element and the composition previously smoothed is very long. In addition, the composition is either in a state of stagnation or in a state of vortex movement in the vicinity of the sheet element. This is the reason why, according to these methods, the capillary migration is very high and the viscosity of the composition tends to increase considerably before smoothing.

On the contrary, according to the most general form of the invention, the coating composition is channeled into a fluid vein, directed towards the end point of the insertion corner, by means of lateral routing walls. The composition comes from pressurized means which impart to it a total mechanical energy such that the vein which it constitutes is conveyed by pressure effect towards said point in a translational movement continuously oriented along a trajectory progressively approaching that of scrolling of the sheet element.

More specifically, the method according to the invention essentially consists in channeling the coating composition in the form of a fluid vein directed continuously towards the extreme corner of said introduction cone (mentioned above), this by means of two side routing walls located inside this introduction cone, and: following said means for making the composition available under pressure.

Another essential means of the process of the invention consists in imparting to the coating composition, by means of said means of provision under pressure, total mechanical energy such that the fluid vein which it constitutes is conveyed by effect pressure towards the extreme corner in a continuously oriented movement along a trajectory progressively approaching that of the scrolling of the sheet element.

It will be noted that the fact of injecting the composition in the immediate vicinity of the coating area has the additional advantage of maintaining, within the composition, a state of shear which keeps it fluid until it passes under the blade, thus ensuring a more efficient and homogeneous smoothing and consequently a significantly improved coating quality.

Note, moreover, that this arrangement limits the contact time between the composition and the sheet element previously to its smoothing. This reduces the migration of the liquid phase from the composition to the sheet element and the subsequent tearing of the latter.

An important aspect of the invention further lies in the fact that the sheet element is moved in displacement over at least part of its trajectory substantially vertically from bottom to top and that the coating composition is injected also in a direction oriented from bottom to top. This particular arrangement makes it possible to ensure good regularity of the deposition of the coating composition over the entire width of the sheet element while ensuring efficient evacuation of any excess of said composition, without risking the formation of a reserve. as would be the case if one proceeded to an injection from top to bottom with a scrolling of the sheet element in the same direction.

According to another aspect of the invention, the composition is applied, in a manner known per se, by an injector, the outlet orifice of the latter being placed, according to the invention, at or in the immediate vicinity of the area of contact (or smoothing) between the sheet element and the smoothing blade.

In the case where the coating composition cannot be applied exactly at the level of the smoothing zone, it is ensured that the outlet of the injector, arranged naturally upstream of this zone with respect to the direction of travel of the sheet element, or located at a distance from the outer edge of the blade, as short as possible according to the mechanical requirements imposed by the scrolling of the sheet element and the structure of the injector and oriented towards the top of the angle formed by the blade and the sheet.

However, the invention also relates to a coating device intended to implement the above method.

The closest prior art to the device of the invention is described in the aforementioned patent FR-A-2,359,650, the main known characteristics of which correspond to the preamble of claim 5 of the present application.

• - un système de guidage et de défilement en continu de l'élément en feuille,
• - un moyen pour déposer ladite composition d'enduction
• - et deux organes entre lesquels circule l'élément en feuille.

The device described in this document comprises:

• - a system for continuously guiding and scrolling the sheet element,
• a means for depositing said coating composition
• - And two organs between which the sheet element circulates.

At least one of the members is constituted by a spreading blade. This is applied by one end against a face to be coated with the sheet element. The other end of the blade is moved apart and directed with respect to the first in a direction opposite to that of travel of the sheet element. Finally, the spreading blade is provided with a possible pressure member, associated with the free end of the blade to exert on it a thrust substantially perpendicular to the sheet member, while the rest of the blade has a curvature with convexity turned towards the sheet element.

• - d'une part, l'orifice de sortie est situé entre les deux extrémités de la lame, au voisinage de l'extrémité de celle-ci en contact avec l'élément en feuille
• - et, d'autre part, l'injecteur est dirigé vers le sommet de l'angle entre l'élément en feuille et la lame.

Compared to this device known from patent FR-A-2,359,650, the coating device according to the invention is remarkable in that its means for depositing the coating composition has an outlet opening forming an injector. In addition, an essential feature is that

• - on the one hand, the outlet orifice is located between the two ends of the blade, in the vicinity of the end of the latter in contact with the sheet element
• - And, on the other hand, the injector is directed towards the top of the angle between the sheet element and the blade.

It will simply be specified that, preferably, the blade will be constituted by a flexible and thin blade which is elastically deformable and whose free end in contact with the sheet element will be associated with a pressure member ensuring the flatness of the end of the blade in contact with the sheet member and its parallelism with said sheet member.

The pressure member may consist of a tube containing a pressurized fluid. According to an advantageous embodiment of the invention, the pressure member consists of an elastic counter blade, which may be less flexible than the smoothing blade, located outside the smoothing blade, relative to the element in sheet form, the free end of which rests on the smoothing blade at the point of contact between said smoothing blade and the sheet element.

• - La figure 1 représente une première forme de réalisation d'un dispositif selon l'invention, constitué d'un rouleau coopérant avec une lame de lissage;
• - La figure 2 est une vue en perspective schématique d'une installation d'un système d'enduction utilisant une structure selon les figures 3 à 7;
• - La figure 3 est un exemple de réalisation d'un dispositif d'enduction à deux lames;
• - Les figures 4 et 5 représentent schématiquement deux variantes de réalisation du dispositif d'enduction;
• - La figure 6 représente une forme avantageuse de réalisation de l'invention;
• - La figure 7 est un schéma explicatif;
• - Les figures 8 et 9 montrent le montage du dispositif permettant une dissymétrie du couchage des faces de l'élément en feuille;
• - La figure 10 représente une vue en coupe schématique, perpendiculaire à l'arête des lames d'un dispositif d'enduction double face selon l'invention;
• - Les figures 11 et 12 sont des vues analogues à la figure 10 pour une variante; et
• - La figure 13 est une vue schématique en perspective du dispositif de la figure 12.

Several embodiments of the invention will now be described, by way of nonlimiting examples, with reference to the appended drawings in which:

• - Figure 1 shows a first embodiment of a device according to the invention, consisting of a roller cooperating with a smoothing blade;
• - Figure 2 is a schematic perspective view of an installation of a coating system using a structure according to Figures 3 to 7;
• - Figure 3 is an embodiment of a coating device with two blades;
• - Figures 4 and 5 schematically represent two alternative embodiments of the coating device;
• - Figure 6 shows an advantageous embodiment of the invention;
• - Figure 7 is an explanatory diagram;
• - Figures 8 and 9 show the mounting of the device allowing an asymmetry of the coating of the faces of the sheet element;
• - Figure 10 shows a schematic sectional view, perpendicular to the edge of the blades of a double-sided coating device according to the invention;
• - Figures 11 and 12 are views similar to Figure 10 for a variant; and
• - Figure 13 is a schematic perspective view of the device of Figure 12.

To facilitate the description of the embodiments below, it will be considered that one wishes to lay down a sheet of paper and, consequently, one will speak of a sheet of paper, of a coating composition and, in general, a sleeping system.

It is obvious, however, that this does not constitute a limitation of the invention and that, in the case where it is desired to treat something other than a sheet of paper, cardboard or nonwoven, and in particular a film of material plastic or strip fabric, it will suffice to carry out an adaptation of the means of the invention which is within the reach of the technician.

Figure 1 shows in perspective and in section a device for coating a sheet 1 intended for coating a single face of the sheet. Said sheet 1 is driven in displacement in the direction of the arrow by a conventional driving device which has not been shown. The sheet is partially wound on a rotating roller 2. The coating or coating device is generally indicated at 3 and comprises a fixed and hollow box 4, placed under the roller 2, being spaced from it from a distance "e" and the axis 4a of which extends substantially parallel to the axis of the roller and over the entire length of the latter. The internal chamber 5 of the box, closed at its ends, is supplied with a coating composition under pressure by a pumping group shown diagrammatically at 6 and connected to a reservoir containing the composition. A slot 7 is made along the length of the box in the vicinity of the roller 2. On one of the edges of the slot is fixed the stationary end of a flexible blade 8, the free end of which is elastically biased in abutment against the sheet 1, downstream of its fixed end in the direction of travel of the sheet, by virtue of the bending of said blade whose convexity is turned towards the roller 2. The arrangement is such that the free end 9 of the blade tangent the curvature of the roller. To ensure the flatness of the part 9 of the blade in contact with the sheet element, a pneumatic tube 10 mounted on the body 4 by means of a support 10a (holding the tube over its entire length) exerts pressure over the entire length of the end 9 of the blade. The tube is connected to a source of pressurized air for example, which makes it possible to regulate the pressure exerted on the blade.

As can be seen in Figure 1, the fixed end of the blade is spaced from the sheet member and the blade forms with the latter a corner 11. Furthermore, the edges of the slot 7 formed in the box are inclined, from the inside to the outside, in the direction of travel of the sheet element so that they guide, in the direction of the arrow 12, the composition leaving under pressure from the chamber 5 towards the corner 11 formed between the blade and the sheet element. It can be seen that the arrow 12 is oriented substantially 'along the bisector of the angle formed between the blade and the sheet element. It will be noted that the possible excess of coating composition may be evacuated from the corner 1 1 by trickling along arrow 3 on the part of the body located upstream of the slot 7, the fraction of composition thus eliminated being recovered for example in a bin 13 located under the body. The distance "e" between the top of the box and the sheet will be sufficient to allow passage of the excess part of the coating composition while avoiding contact between the latter and the sheet.

Naturally, it will be understood that the shape of the box as well as the system for supplying the composition could be different without departing from the scope of the invention. Similarly, one could provide another arrangement of the box relative to the roller, as soon as the box is located in the region of the lower half-circumference of the roller. Finally, instead of a continuous slot 7, one could provide in the box a series of separate passages from each other.

The embodiments which will now be described ensure the simultaneous coating of the two faces of the sheet element. FIG. 2 represents the general configuration of a coating installation according to the invention.

• - soit pour l'induction d'un élément en feuille préalablement fabriqué et, dans ce cas, il peut former une installation indépendante; cependant dans ce cas, il y aura bobinage et stockage intermédiaire de la feuille;
• - soit directement pour l'enduction d'un élément en feuille en un poste déterminé d'une machine de fabrication dudit élément en feuille.

We know that a coating device can be used:

• - either for the induction of a sheet element previously manufactured and, in this case, it can form an independent installation; however in this case, there will be winding and intermediate storage of the sheet;
• - Either directly for coating a sheet element at a specific station of a machine for manufacturing said sheet element.

It is this latter case which, by way of example, has been retained in the description which follows. Thus, Figure 2 shows the end of a paper making machine which is equipped with a device according to the invention.

Between two groups of drying cylinders 22, 23 and 32, 33, from the dryer of a conventional paper machine, the head and end of which have not been shown, the sheet 21 passes over a series of rollers 25 , 26, 27, 28 and 29 which ensure both its tension and its movement along a determined route.

Between the rollers 27 and 28, said sheet of paper circulates vertically and it is at this level that it passes through a coating device according to the invention, indicated generally at 130, and which will be described in more detail. thereafter.

In the particular case represented in FIG. 2, the two faces of the sheet are coated and, consequently, may have to undergo a pre-drying operation of the layer before the sheet comes into contact with the cylinders 32 and 33. , in order to prevent the still fresh layer from adhering to the cylinders and thereby being deteriorated.

There is shown in 340 a first pre-drying element for the face of the sheet intended to come into contact with the roller 28 and in 350 a second pre-drying element for the other face of the sheet.

Naturally, it will be understood that, as in the case of FIG. 1, the device according to the invention could only carry out the coating of one of the faces of the sheet and, in this case, we could only provide only one drying system.

The sheet element 21 circulates, in the case of Figure 2, vertically from bottom to top.

The coating device 130 could consist of one of the variant embodiments which will now be described.

In FIG. 3, the coating device has been produced using two crate assemblies 30 and 30a similar to the crate in FIG. 1 and arranged on either side of a sheet of paper 21 moving roughly vertically from bottom to top. In the example shown, the two body assemblies 30 and 30a are identical and symmetrical with respect to the plane of the sheet 21. It will therefore be sufficient to describe them alone. As in the case of FIG. 1, the box 34 has an internal chamber 35 in which the coating composition supplied under pressure circulates. An inclined slot 37 (serving as an injector) is made in the box and against the wall of the most distant slot of the sheet 21 is fixed one end of a flexible blade 38 elastically deformable. A support 40a fixed on the body 34 supports over its entire length a tube 40 filled with a pressurized fluid (the pressure being adjustable).

In the operating position shown in FIG. 3, the two blades 38 are applied on either side of the sheet 21, their free ends being exactly in opposition and forming a zone of contact with the sheet which is parallel to the latter. in order to achieve spreading and smoothing of the layer. The blades are kept under tension one against the other and they therefore have a curvature whose convexity is directed towards the sheet 21, the blades moving away from the sheet from their free end by providing therewith a corner 41. The axis of the slot, materialized by the arrow 42 (which also materializes the path of the vein of coating composition injected into the corner 41 is oriented substantially towards the smoothing zone provided by the free ends of the blades. vein of the composition therefore reaches the sheet immediately upstream of said smoothing zone. The possible excess of material M projected flows along the internal faces of the boxes 34 without being in contact with the sheet due to the spacing "g" between said sheet and the internal face of the box This excess M is recovered in a tank 13 and optionally returned to the internal chamber of the box, via the supply circuit, not shown, of the box.

In Figure 4, there is shown schematically another embodiment in which two blades 50 and 51 are used which are rigid and symmetrical of which only the blade 50 will therefore be described. This rigid blade has a general curvature turned towards the sheet 21 and is pierced with a median channel 52 for admitting the coating composition to the sheet. The channel 52 communicates on the one hand with a source of composition under pressure not shown and opens, on the other hand, at 53 on the free end of the blade, this free end having a flat area 54 and parallel to the sheet 21 which is responsible for spreading and smoothing the layer. The blades can be articulated at their lower ends mounted on a fixed support (not shown) to allow adjustment of the thickness of the layer to be deposited.

For their application against the sheet 21, provision may be made for any system for tensioning the blades and for example pneumatic tubes such as those which are shown in broken lines at 55, these tubes being of the same type as those of FIGS. 1 and 3 .

The example shown in FIG. 4 is the ideal case where the injection of the coating composition and the smoothing take place simultaneously and in the same place.

However, this solution can be difficult to carry out industrially.

In the alternative embodiment of FIG. 5, the coating and smoothing device consists of two pairs of blades 60 arranged symmetrically with respect to the vertical sheet 21 and therefore only one will be described. The two blades 61 and 62 of each pair of blades are flexible and elastically deformable. They are also fixed by their lower end in a blade support 63 by screws 64 allowing their removable. As seen in Figure 5, the supports 63 are spaced on either side of the sheet 21. Furthermore, in the support, the two blades are spaced from one another by a hollow box 65 which is used for the admission under pressure of the coating composition in the direction of the arrow; the box is connected to a composition source (not shown). Due to this arrangement, the two blades 61 and 62 are superimposed and sensitive parallel. In the operating position shown in FIG. 5, the two blades 61 are applied one against the other, under tension, on each side of the sheet 21 and the same is true of the two blades 62. The tension of the blades results of the position of the supports 63. Between the blades 61 and 62 is provided an injector passage 66 making it possible to inject the coating composition between the free ends 67 and 68 of the blades on the sheet 21. It will be noted that at least the free ends 67 of the downstream blades 61 (in the direction of travel of the sheet 21) are applied to the sheet so as to be plane and parallel to the sheet. The flatness of these ends is optionally maintained by a pneumatic tube 69 (shown in broken lines) identical to the tubes of FIGS. 1 to 4.

The embodiment of Figure 6 is that which appears to be particularly suitable for industrial use. A fixed structure (not shown) is equipped with two substantially horizontal bars 70, spaced apart and between which a sheet element 21 which is intended to receive a coating composition passes vertically. The coating device consists, as before, of two sets symmetrical with respect to the sheet and of which only one will therefore be described.

On the bar 70 is mounted a support structure 71 capable of tilting and being immobilized around the bar under the action of a position adjustment mechanism (not shown). The support structure 71 has a slide 72 in which a blade holder 73 is engaged which can be locked in the slide by any suitable means. The lower end 74 of a blade 75 is removably fixed in the support, for example by screws 76 in order to allow possible replacement of the blade.

The blade 75 is flexible and elastically deformable and when the two structures 71 are in the position shown in FIG. 6, the free ends 77 of the blades are applied to the sheet 21. The blades are kept in this position under tension and therefore have a curvature with convexity turned towards the sheet 21.

It will be noted that the blade holders 73 are spaced from the sheet 21 by a distance which can be adjusted by means of the structure 71, which makes it possible to modify the force applying the blade to the sheet and consequently, the thickness of the diaper.

Preferably, the free end 77 of each blade is associated with a pneumatic tube 78 containing a pressurized fluid (the pressure of which can be adjusted) and exerting on the end of the blade a pressure whose direction is substantially perpendicular to the sheet, this pressure ensuring the flatness of the end of the blade and its parallelism with the sheet. Each pneumatic tube can be carried over its entire length, for example by a support whose arms 79 (shown in broken lines) are fixed to the corresponding blade holder. An injector 80 of coating composition constituted by an elongated hollow box and open at 81 to constitute an injection nozzle is suspended from the structure 71, between the sheet 21 and each of the blades 75.

The suspension of the box is constituted by rods 88, one end 82 of which is adjustably engaged in the structure 71 while the other end 83 constitutes a bearing for an axis 84 integral with the box 80. The box is connected to its lower part , via a pipe 85, to a source of coating composition equipped with a pressurized supply system for the box (not shown).

Note that the position of the box is adjustable relative to the structure by pivoting around the suspension axes 84 and that once the box placed in a suitable position, it can be locked in this position by any locking system (not shown ) appropriate. As seen in Figure 6, the injection nozzle 81 of the box is located as close as possible to the smoothing area reserved between the ends 77 of the blades. During operation, the composition is injected directly into the corner formed between each of the blades and the sheet 21 and the injection nozzle is embedded in the product. The possible excess of product is evacuated from the injection zone by trickling onto the face 86 of the box opposite the sheet 21, this face progressively moving away from the sheet.

The excess is then collected in a tank 87.

The optimal position of the elements constituting the device will be specified with reference to the diagram in FIG. 7.

In fact, as we have seen previously, the distance between the nozzle of the injector and the smoothing zone must be as small as possible.

• - de l'épaisseur du bec de l'injecteur,
• - de la courbure des lames qui est fonction de la géométrie adoptée pour chaque application.

This distance depends on:

• - the thickness of the nozzle of the injector,
• - the curvature of the blades which is a function of the geometry adopted for each application.

• - en "e" l'épaisseur du bec de l'injecteur,
• - en "d" la distance optimale entre le bec de l'injecteur et l'arête du bord libre des lames,
• - en "a" l'angle apparent en bout de lame.

On the diagram of figure 7, one indicated:

• - in "e" the thickness of the nozzle of the injector,
• - in "d" the optimal distance between the nozzle of the injector and the edge of the free edge of the blades,
• - at "a" the apparent angle at the end of the blade.

Furthermore, it should be understood that the Greek letter ε represents the space necessary for the passage of the sheet without friction and for the return of the coating composition, as well as the possible interval between blade and injector.

soit

ε est compris en général entre 0 et 10 mm, espacement considéré comme normal pour le passage d'une feuille sur une machine à papier industrielle.Calculation and experimentation show that the optimal position of the injector is located at a distance "d" such that:

is

ε is generally between 0 and 10 mm, spacing considered normal for the passage of a sheet on an industrial paper machine.

In practice, a distance less than the length of the blade used will be chosen for "d".

• a/ avec un injecteur de 5 mm d'épaisseur au bec (ε=5 mm), placé à 2 mm du papier et à 1 mm de la lame (_E=3 mm) et une lame faisant un angle a de 12°8 (cotga=4,4), la distance optimale de l'injecteur sera:
  • d=[5+(2+1)]x4,4=35,2 mm
• b/ Si, dans la même configuration, on désire placer l'injecteur à 5 mm du papier, on aura:
  • d=[5+(5+1)[×4,4=48,4 mm
• c/ Si on dispose d'un injecteur de 10 mm d'épaisseur, situé à 10 mm du papier, on aura:
  • d=[10+(10+1)]×4,4=92,4 mm

Some concrete examples are given below:

• a / with an injector 5 mm thick at the nozzle (ε = 5 mm), placed 2 mm from the paper and 1 mm from the blade ( _E = 3 mm) and a blade making an angle a of 12 ° 8 (cotga = 4.4), the optimal distance from the injector will be:
  • d = [5+ (2 + 1)] x4.4 = 35.2 mm
• b / If, in the same configuration, we want to place the injector 5 mm from the paper, we will have:
  • d = [5+ (5 + 1) [× 4.4 = 48.4 mm
• c / If we have an injector 10 mm thick, located 10 mm from the paper, we will have:
  • d = [10+ (10 + 1)] × 4.4 = 92.4 mm

Furthermore, it should be noted that the device according to the invention makes it possible to produce both symmetrical coatings as in FIGS. 3 to 6 as well as asymmetrical coatings as in FIGS. 8 and 9.

• - soit pour obtenir volontairement un papier couché de caractéristiques différentes sur les deux faces;
• - soit, au contraire, pour corriger les caractéristiques existantes d'une des faces de façon à obtenir un papier identique sur les deux faces.

The asymmetry of the deposition of the layers on the two faces of the sheet element can be sought:

• - either to voluntarily obtain a coated paper with different characteristics on both sides;
• - Or, on the contrary, to correct the existing characteristics of one of the faces so as to obtain identical paper on the two sides.

• - soit par déplacement de l'axe des lames, c'est-à-dire en décalant simultanément dans un plan horizontal les deux chambres pneumatiques (figure 8);
• - soit par abaissement d'une des deux chambres pneumatiques (figure 9).

The practical experiments carried out to date show that, with the device according to the invention, the asymmetry can be obtained in at least two ways, as shown in FIGS. 8 and 9, namely:

• - Either by displacement of the axis of the blades, that is to say by simultaneously shifting in a horizontal plane the two pneumatic chambers (Figure 8);
• - either by lowering one of the two pneumatic chambers (Figure 9).

In Figure 8, there is shown in solid lines the device according to the invention in which, as in the previous figures, the blades I ₁ and I ₂ are symmetrical with respect to the sheet element S. By acting on the support of blades, one can move the axis of these and bring them into the asymmetrical position shown in broken lines in L ₁ and L _Z ; whereas in the case of symmetry, the blades make the same angle a with respect to the element S, in the case of asymmetry, the blade L ₁ forms an angle y and the blade L _z an angle β with the element S. β is smaller than y. The L _z blade is smoother.

In Figure 9, there is shown in solid lines the blades 1 ₄ and 1 ₃ in their symmetrical position (same angle a) relative to the element S. By lowering the pneumatic tube vertically by a distance "ab" from its initial position shown in broken lines at C ₄ in the solid line position C ' ₄ , the blade 1 _{4 is} moved consecutively to its broken line position L ₄ , the blade then making an angle β with the element S less than α.

These displacements of pneumatic chambers cause an increase in layer deposition on the side where the blade becomes smoother, that is to say on the side of the blade L _z in FIG. 8 and on the side of the blade L ₄ in FIG. 9.

These different positions of the pneumatic chambers made it possible to create relatively large asymmetries (for example, deposition of a layer of 8 g / m ² on one side, and of 14 g / m ² on the other).

In the case where the pressure member is not a pneumatic chamber, but, for example, a counter blade (FIGS. 10 to 13), the same asymmetries will obviously be obtained by moving the positions of the lines d under the same conditions. support of the counter blades on the smoothing blades.

These adjustments can be made continuously, during coating, without changing the composition of the layers and without other modifications to the device.

• - le choix d'une lame plus épaisse donc plus rigide sur une face (dans ce cas, le dépôt diminue par rapport à une lame souple);
• - la modification de la formule de couchage sur une des deux faces. Toutefois, il semble que ces deux derniers moyens soient difficilement applicables pour le couchage en continu.

There are obviously other ways to create such asymmetries, such as, for example

• - the choice of a thicker blade therefore more rigid on one side (in this case, the deposit decreases compared to a flexible blade);
• - the modification of the coating formula on one of the two faces. However, it seems that these last two means are difficult to apply for continuous coating.

Figures 10 to 13 show an advantageous means for exerting pressure on the smoothing blade, on the contact zone between this smoothing blade and the paper. In these embodiments, the pressing member is constituted by an elastic counterblade situated outside the smoothing blade, and the free end of which is kept applied elastically on the smoothing blade at the point of contact between said smoothing blade and the sheet element. The opposite end is anchored in a movable support so that, when it is tensioned, the counter blade has a curvature with convexity turned towards the sheet element. This counter blade can be made of any suitable flexible material: metal, plastic, etc.

The counter blade can be arranged either in the same direction as the corresponding smoothing blade, or in opposite direction, the respective anchoring points of the smoothing blade and the counter blade being, in the latter case, located on either side of the contact area between these two elements.

For the convenience of the description, we will limit ourselves to describing below embodiments in which the smoothing blade and counter blade are arranged in the same direction.

In FIG. 10, a strip of paper 1 runs from bottom to top, in the direction of the arrow, in a suitable machine. Two smoothing blades 75, 75 'held by supports 73, 73' exert on both sides of the paper strip, at a point 91, a pressure to smooth on each of the two faces a layer of a coating composition . The coating composition is brought between the paper strip and the blade 75, by means of a device not shown such as those described in the previous examples. The flatness of the free end of the blade 75, 75 ′ (smoothing area) is ensured by means of a counter blade 83, 83 ′. Preferably, the blades 83, 83 'are shorter than the blades 75, 75' which are advantageously very flexible, which also provides a more uniform smoothing effect over the width of the sheet.

Each counter blade 83 is anchored in a support 84. Thanks to simple conventional means not shown, the supports 84 can be turned on themselves, and moved vertically (y'y) and horizontally (x'x). It is thus possible to adjust the pressure force, by modifying the curvature of the counter blade, while placing the free edge of the counter blade in the vicinity of the free edge of the smoothing blade.

In FIG. 11, the device comprises the same elements as in FIG. 10 and in addition auxiliary means in the form of pneumatic tubes 78, 78 ′, which can be placed at any point of the counter blade, towards the middle, or towards the free edge. We can then adjust in addition the fluid pressure inside the pneumatic tube and the position of this tube on the counter blade.

The device of FIGS. 12 and 13 comprises all the elements of the device of FIG. 10, and in addition a pressure system constituted by a series of segments or fingers 85, arranged along the width of the sheet, and which can be placed so to act on the counter blade at any point situated between the free end of said counter blade and its anchor point. According to the invention, these fingers are adjustable. They can be adjusted one by one, or together, manually or automatically, for example controlled by a device connected to a sensor which detects irregularities in the layer across the width of the sheet, so as to modify the pressure exerted by one or more fingers, depending on the correction to be made to faults detected at their level.

It is thus possible to adjust the pressure exerted on the width of the smoothing blade from time to time as a function of the particular coating conditions (irregularity of the support or layer deposition on the width for example). It is also possible to compensate for a localized accidental deformation of the smoothing blade without having to immediately change said blade.

The fingers can be mounted in a support 86, which can include all the elements allowing automatic or manual control.

The embodiments of the pressure member described above (Figures 10 to 13) are particularly suitable for obtaining good straightness and high reliability of the support on the smoothing blades. They also allow, in industrial operation, an easy and precise adjustment of the support line, the latter being well defined and easy to visualize.

They can replace the pneumatic tubes in all the examples described above (FIGS. 1 to 9) in the case of a coating, both single-sided and double-sided.

Claims (16)

1. Process for continuously coating a web (1, 21) consisting in:

- continuously moving said web (1) from bottom to top in a substantially vertical direction, between at least two means (38) located on each side of the web,

. at least one of the said means being formed by an spreading blade (38)

+ applied by one end against one side of the web to be coated,

+ the other end being spaced apart from bhe web and directed in regards to the first in an opposite direction to the running direction of the web,

. the other means acting as reaction element for the first,

- placing the coating composition into contact with the said surface to be coated,

. upstream of the zone of contact of the said spreading blade against the web,

- and exerting pressure,

. on the said spreading blade,

. in direction of the side to be coated to ensure spreading of the said coating composition on the side to be coated,

the said process being characterized by the fact that

- on one hand, the coating composition is directed as a stream (42),

. continuously directed towards the top of the angle (a) formed by the web (21) and the blade (38, 61, 75), by the lateral walls,

. and fed from a delivery means under pressure (35) of this composition,

- and on the other hand, the coating composition received from the means under pressure (35)

. a total mechanical energy, as such as the stream (42) is directed by the effect of the pressure towards the apex of the angle (a), into a translation movement continuously oriented in a direction progressively closed to the direction of the web (21).

2. Process according to claim 1, characterized by the fact that the said spreading blade (38) is submitted to a force which is:

- different from its own flexion force,

- applied on the back of the contact point between the blade and the web,

- and directed towards the side of the web to be coated.

3. Process according to any of claims 1 and 2, characterized by the fact that the delivery of the coating composition is achieved by use of an injector (52, 66)

- made by the convergence of the said lateral conducting walls (61, 62) of the stream.

- the outlet orifice of which being located in the vicinity of the contact zone (54) between the web and the smoothing blade, upstream of this zone in regards to the running direction of the web (21).

4. Process according to any claims 1 and 2, characterized by the fact that the depositing of the composition in contact with the face of the web to be coated is provided by using an injector (80) the outlet of which being located to a distance (d) from the free end of the blade (75) in contact with the web which is equal:

- to the sum

. of the thickness (e) of the injector,

. and of the clearances (_E) between said injector (80) and the web (21) at one side, and the smoothing blade (75) at a second side,

- multiplied by the cotangent of the angle (a) formed by said smoothing blade and said web.

5. Device for continuously coating a web, namely a paper, cardboard, plastic sheet material or similar, with a coating composition, the said device comprising:

- a guiding and continuous running means from bottom to top of the web in a substantially vertical direction,

- a means for depositing said composition,

- and two means (8, 2, 38) between which runs the web (21),

. at least one being formed by a spreading blade,

+ applied by one end against one side of the web (21) to be coated,

+ the other end being spaced apart from the web and directed in regards to the first in an opposite direction of the running direction of the web,

+ and eventually provided with a pressure means (40, 40a) associated with the free end of the blade and applying on it a pressure in a direction substantially perpendicular to the web (21), in order that the said free end is substantially plane, as the other part of the blade has a curvature whose convexity is directed towards the web (21),

the said device being characterized by the fact that the means for depositing said composition comprises an outlet (81, 53) forming injector (80),

. located between the two ends of the blade (38) in the vicinity of this one which is in contact with the web (21),

. and directed towards the apex (a) formed by the web and the blade.

6. Device according to claim 5 for coating only one side of a web (1 ), characterized by the fact that the said spreading blade is fixed to a support (4) which further comprises:

- an internal closed space (5) for canalyzing the coating composition, whose convergency forms at least one orifice (7),

. adjacent to the end of the blade (8) fixed to the support,

. and communicating the said internal space with the area (11) located between the part of the blade external to the support and the part of the web (1) in front of the blade,

- means (6) provided in order to inject under pressure the coating composition in a stream movement out of the said internal space (5) of the support and into the said area (11).

7. Device according to claim 5. characterized by the fact that the spreading blade comprises at least one delivery channel (52) for the coating composition,

- bored into its 'thickness,

- and opened by a outlet (53) into the zone (54) of the blade in contact with the web (21), ), the said channel acting as injector, the said blade comprising, downstream of the outlet and in the running direction of the web, a plane portion (54) applied unto the web and smoothing the coating.

8. Device according to claim 5, characterized by the fact that the injector (66) is formed by a space between two flexible blades (61, 62) superposed, subjected to a tension and substantially parallel which are both. attached by one end to an holder (63) spaced apart from the web (21), whose free ends (67, 68) are applied against the web (21) by forming between them a space where the coating composition coming from the internal space between both blades is applied against the web (21), the blade located downstream in the running direction of the web, forming the smoothing blade of the device.

9. Device according to claim 5, characterized by the fact that the injector (80) of the coating composition is located in the angle (a) formed by the web and the smoothing blade, the outlet orifice of the said injector being posi- tionned at a distance (d) from the free edge of the spreading blade which is equal

- to the sum

. of the thickness (e) of the injector (80),

. and of the clearance (e) between the injector (80) and the web (21) at one hand, and the blade (75) at a second hand,

- multiplied by the cotangent of the apparent angle (a) formed by the blade and the web.

10. Device according to any claims 5 to 9, characterized by the fact that the pressure element on the spreading blade (38) comprises a flexible tube (40) filled in with a fluid under pressure.

11. Device according to any claims 5 to 9, characterized by the fact that the pressure element comprises a flexible counter-blade (83), different from the smoothing blade and located outside of the said smoothing blade (75) in regard to the web (1). the free end of which being exerting on the smoothing blade, near the contact zone between the blade and the web, a pressure consisting of the elastic flexion force of the counter-blade.

12. Device according to claim 1 1, characterized by the fact that the flexion of the counter-blade is provided by moving the fixing point of the said counter-blade (83) with respect to the web and/or by pivoting around the axis of the said fixing point.

13. Device according to claim 11, characterized by the fact that the flexion of the counter-blade is provided by a pneumatic tube (78) which exerts a pressure on the said counter-blade (83) in a point located between the fixing point and the free end of said counter blade (83).

14. Device according to claim 11, characterized by the fact that the flexion of the counter-blade is provided by a plurality of adjustable segments or fingers (85) posi- tionned in the width of the smoothing blade, the said fingers acting on the said counter-blade (83) following a line paralleJ to its free end and located between said free end and fixing point of said counter-blade.

15. Device according to claims 5 to 14, for simultaneous coating of both sides of a web, characterized by the fact that it comprises two identical assemblies (75, 75') positioned symetrically with respect to the web (1).

16. Device according to claims 5 to 14 for simultaneous coating of both sides of a web, characterized by the fact that it comprises two identical assemblies (L₃, L₄) located on each side of the web (S), the free ends of the smoothing blades being located at the same level with respect to the web, while the support lines of the pressure means being slightly displaced along the web and of one side with respect to the other, in order to achieve disymmetrical coating characteristics on respective sides of the web.

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