FR2585591A1 - METHOD AND APPARATUS FOR THE CONTINUOUS APPLICATION OF A REGULAR COATING ON A MATERIAL BASKET ON A COUNTER-PART CYLINDER, PARTICULARLY A PAPER OR CARDBOARD - Google Patents

Abstract

THE COATING MATERIAL IS DELIVERED OVER THE MATERIAL BABY 5 UNDER LOW PRESSURE USING A COATING CYLINDER 2 AND IS GUIDED BY A GUIDANCE SHEET 8 TO THE COATING SLOT 7 FORMED BY THE COUNTERPART CYLINDER AND THE COATING CYLINDER, AFTER WHICH THE MATERIAL IS DOSED BY A MEASURING ELEMENT 15 AND PARTIALLY DEHYDRATED IN THE AREA OF A LAYER CLOSE TO THE TABLECLOTH IN ORDER TO FORM A BARRIER LAYER; THE FINAL DOSAGE SHALL BE CARRIED OUT WITH A DEFINITIVE DOSING ELEMENT 24 UNDER LOW APPLICATION PRESSURE. THIS ALLOWS TO OBTAIN, EVEN AT HIGH TABLE SPEEDS, CONSISTENT GOOD PROPERTIES OF THE COATING, EVEN WHEN THE QUANTITIES OF APPLIED PRODUCTS ARE EXTREMELY LOW. APPLICATION: FOR EXAMPLE ON COATING OF PAPER AND CARDBOARD.

Description

METHOD AND DEVICE FOR THE CONTINUOUS APPLICATION OF A

  REGULAR COATING ON A MATERIAL BASE ON

  A COUNTER-COUNTER CYLINDER, IN PARTICULAR A FLOOR

PAPER OR CARDBOARD

  The invention relates to a method and a device for the continuous application of a regular coating on a sheet of material passing a counterpart cylinder, in particular a sheet of paper or cardboard, on which the coating material is applied by means of a coating roll, first in quantity

  excess and then equalized by scraping.

  During the coating of webs of moving material, in particular paper or paperboard webs, it is increasingly desirable to advance the webs at higher speeds, to use coatings with a high concentration of solids, in order to save the energy required for drying, and possibly obtain at the same time lower weights of applied products. Usually, the speeds of the water table are currently around 1200 to 1400 m / min. At such speeds, the coating of common printing papers, such as paper called LWC (dry weight of

applied product 4 to 8 g / m2).

  Due to the dosing and coating methods currently in use, it is not possible to substantially exceed the speed mentioned above without significantly lowering the solids content of the coating in order to maintain the desired weight of the product. Sleeping. Among the known dosing and application methods, mention may be made of single-drum coating mechanisms (Flooded-Nip-Coater) and secondly those

called Short-Dwell-Coater.

  A single cylinder coating mechanism is known in particular from patent application DE 2931800. In this process, the coating is applied in excess quantity by means of a coating roll on the paper web and then equalized and dosed. by a metering element which, most often, is made in the form of a rigid blade

  when the weights of applied materials are low.

  The excess can then be adjusted through the width of the slot between the coating roll and the counterpart roll, and passing through the rotational speed of the coating roll. The liquid pressure that occurs in the slit dewaters a layer of the coating facing the paper web, forming a barrier layer or filter layer that prevents the the coating is driven too strongly inside the paper web. With relatively low web speeds, the liquid pressure inside the slot can be adjusted through the width of this slot and the rotational speed. At high web velocities, the slit should be set very narrow because otherwise turbulence in the slit would cause some points of the web to not be covered. A narrow adjustment of the slot, however, increases the hydrodynamic pressure in an over-proportioned manner and the positive effect in the first stage of the partial dehydration is transformed into its opposite with the result that the coating is pressed into and through the

tablecloth of matter.

  In addition, the "filmsplitting effect" is reinforced in the diverging portion of the coating slot, which leads to

  excessively uneven film.

  The method known also known as "Short-Dwell" is apparent from the European patent application 51 698. The coating is, in this case, conducted under pressure in a chamber which is delimited on the outlet side of the sheet by the metering element, on the inlet side of the sheet by an overflow plate disposed at a limited distance from the

  web and the front side by sealing elements.

  Depending on the operating conditions, from five to thirty times the quantity of coating to be applied passes over the overflow head. Since the coating roll has been eliminated, it is a compact mechanism with which it is possible, by correctly matching the sheet and the coating, at machine speeds of about 600 to 700 m / min., with the same marginal conditions, to apply in certain circumstances lower coating weights than those applied with a single cylinder mechanism, since with lower speeds the hydrodynamic pressure on the metering element is it is also relatively weak and it is not necessary in all cases to have a barrier layer in front of the metering element. At the speeds mentioned above, the excess of the coating is carried out relatively regularly, so that as a rule

  general a total coating of the tablecloth is ensured.

  However, at the high speeds of the web, the liquid pressure on the metering element disproportionately increases and due to the absence of the barrier layer, the coating is embedded in

and through the tablecloth.

  In addition, the impulse of the liquid boundary layer formed on the web increases in such properties that the metering element which, most often, is made in the form of a rigid blade, can not resist any longer. this pressure, especially when the coating has a high content of solid particles. The weight of applied materials thus increases strongly. Thus, under equal secondary conditions, the weight of applied material of a "Flooded-Nip-Coater" is, as a rule, lower than that of a "Short-Dwell-Coater" for speeds greater than 700 m / min. In addition, the sheet metal

  overflow has a disadvantage, with the "Short-Dwell-

  Coater "fast, in that the coating is thrown uncontrollably outside at the location of the overflow slot, because the boundary layer of air penetrating with the web into the coating zone can partially advance to the metering element, which also results in the presence of uncovered points in the coating.The invention aims to provide a method by means of which it is possible to obtain, relatively high speeds of the web of material, good constant properties, where appropriate even with extremely low coating weights, and the object of the invention is to provide a device with which the good quality of the coating is obtained, even at high speeds of the machine, by mechanical means cooperating with each other and advantageously selected, and this

in a surprisingly simple way.

  This problem is solved thanks to the process according to the invention, in that the coating material is transported in pre-measured proportions, with the aid of the coating roll, over a certain distance into the coating slot. between the coating cylinder and the counterpart cylinder and applied under a slight pressure on the web of material, the coating material being partially dewatered in a thin boundary layer close to the web of material. The low pressure is achieved by means of a reciprocal arrangement without known contact between the coating roll and the counterpart cylinder or the sheet of material, a subsequent guide without pressure

  coating material and subsequent scraping.

  The device for the continuous application of a regular coating on a sheet of material passing on a counterpart cylinder, in particular a sheet of paper or cardboard, by means of a coating roll which takes the material for coating in a liquid chamber and a metering device and a subsequent scraping device, is characterized in that the coating cylinder has a guide plate on the sampling side which extends into the slot coating between the coating cylinder

and the counterpart cylinder.

  Preferably, the guide plate is made with a curved shape corresponding to the periphery of the coating roll, at least in the region facing the slot between the coating roll and the

counterpart cylinder.

  The guide plate can be made in an adjustable manner in whole and / or in part, which concerns its

  distance to the periphery of the coating roll.

  The guide plate may constitute an extension of the edge of the liquid chamber containing the coating material so that between said chamber and the lower portion of the guide plate is created a passage for the excess coating material

  having the shape of a slot or a similar shape.

  The line of separation between the guide plate and the edge of the chamber can constitute a plane substantially

  horizontal with the axis of the coating cylinder.

  In the sampling direction behind the coating slot may be provided a guide body provided with a metering element and overflow orifices, said body being fitted at its lower or upper side substantially to the periphery of the cylinder. of coating and counter-part cylinder at a distance from them or

in contact with them.

  The metering element operates at an energetic level with respect to the surface specific force in the zone of contact with the web and has, at its front surface facing the web, a geometry such that a geometry occurs. partial dewatering of the coating material in a thin boundary layer

close to the sheet of material.

  The metering element is preferably in the form of a scraper rod and has on its front surface facing the web a convergent, preferably convex, convex convergence, in the direction of

  the metering element, with respect to the web of material.

  The process for applying the coating material to a web of moving material provides considerable advantages. Thanks to the pre-dosing transfer of the coating material into the coating gap between the coating cylinder and the counterpart cylinder, it is possible to vary within wide limits by adjusting the slot , the hydrodynamic pressure that is established, this pressure can preferably be reduced by enlarging the slot. The coating material is transported more evenly, i.e. without inclusions of air and in greater amounts, into the coating slot, so that it can be adjusted in dimensions larger than the usual "Flooded-Nip-Coaters", and with lower hydrodynamic pressure, less turbulence occurs and, therefore,

  risk of uncoated points decreases.

  By "lower application pressure of the pre-dosing device" is meant a value between 0 and 20% of the application force (linear pressure) in the area of the finishing dosage, where 0% means that a metering element used for the metering is set on a fixed slot of 0.01 to 0.1 mm, and this as a function of the speed, the coating material, etc. By the dosing of the coating material, it is ensured that for the finishing dosage, an excess quantity exactly equal to that required for an abundant rinsing at this point is entrained, being important that during the dosing operation a partial dewatering of a thin boundary layer of the coating material, close to the web, boundary layer in which the solid constituents (pigments and binders) of the coating material are largely immobilized. The layer which is formed in this way then acts, during the finishing dosage, as a barrier and prevents the penetration of solid constituents of the

  coating material in the paper web.

  Thanks to the proposed device for the implementation of the method which provides that only a pre-measured quantity of coating material is transported in the coating slot, it is ensured even at high speeds of the machine, that is produced a defined boundary layer in the metered coating material applied to the web of material, this layer preventing the pressure of the liquid on the final metering element causes too much coating material inside the web. In addition, thanks to the guide plate, the coating material can be distributed absolutely uniformly, both in the direction of advancement of the web and transversely to this direction and is introduced into the coating slot without presence of air bubbles. For this purpose, in an advantageous embodiment of the invention, the guide plate is curved according to the periphery of the coating roll at least in the region facing the coating slot located between the cylinder of the invention. coating and the counterpart cylinder. This has the effect of precisely guiding the coating material, in particular when the distance between the sheet and the periphery of the application roll is adjustable. Thus, it is possible to adjust accurately, and even reproducible, the hydrodynamic pressure that is established inside the slot. In particular, the inclusion of air bubbles in the slot is avoided, which allows to obtain a particularly regular coating, without defective points. In order to compensate for pressure oscillations which may arise, for example, from the coating material feed line, there is provided, between the guide plate and the liquid chamber, a slit-like passageway through which dispose of excess coating material that has not been transported

  the coating slot by means of the coating roll.

  To guide the coating material, there is provided between the slot and the metering element, a guide body provided with overflow orifices, which is fitted on its lower side and its upper side to the peripheral zone of the coating cylinder and counter-part cylinder, to

  a certain distance or in contact with these cylinders.

  To achieve partial dewatering, i.e. a barrier layer in the coating material, the geometric conformation of the metering element is important. Advantageously, the metering element is in the form of a squeegee and has on its front surface facing the web a convergent profile preferably with convex convergence, in the direction of the metering element finisher and by

compared to the tablecloth.

  The finishing metering element is made of

  preferably in the form of a rigid blade.

  So that the device is easily accessible on all of its three separate parts, the finishing metering element, the support elements of the latter, o10 a collector disposed below and the metering element and its support elements are arranged with an associated collection chamber, on a frame pivotable about a substantially horizontal axis. By pivoting the entire device downwards, easy access is thus provided for the cleaning, repair and replacement of certain parts. In addition, the guide plate can be folded separately to release the

coating cylinder.

  Two preferred embodiments of the invention are shown in the drawings and are explained in more detail below. In these schematic drawings: Figure 1 shows a side view of a coating and dosing device with a coating mechanism, a metering device and a finishing metering device; FIG. 2 represents the coating of a sheet of material on a device according to FIG. 1; Figure 3 shows another embodiment of the pre-dosing device of Figure 1, also in side view; and FIG. 4 is a front view of the

  pre-dosing device of FIG.

  The pre-dosing and coating device shown in FIG. 1 has a coating mechanism 1 comprising a rotary coating roll 2 which, in known manner, transports, from a liquid chamber 3, connected to a feed 4, coating material in a coating slot 7 located between the coating roll 2 and a counter-roll 6 serving to support a web of material 5. The coating material is fed in a pre-metered manner between the peripheral surface of the coating roll 2 and a guide plate 8, and this until it reaches the region of the coating slot 7. The guide plate 8 can be adjusted with respect to its distance 44 relative to the peripheral surface of the coating roll 2, by means of an adjusting device 9, so that the hydrodynamic pressure of the coating material which is established inside the

  At slot 7, be adjustable and reproducible.

  On its upper side opposite the coating roll 2, the guide plate 8 has a flow surface 11 on which the coating material can flow, in the direction of the arrow 10, from the slot 7 to a return line 12 and thence in a collecting duct 13. Next, the material returns to a collecting tank (not shown) from which

  again the supply of the arrival 4.

  In this case, the coating roll 2 and the

  counterpart cylinder 6 rotate in opposite directions.

  Behind the coating slot 7 seen in the direction of the movement of the sheet 5, is mounted a metering device 14. This metering device 14 has a metering member 15 in the form of a squeegee which is guided to the outside. the interior of a carrier body 16 serving as a support member and which is supported by a pressurized hose 17. By correspondingly adjusting the pressure inside the pipe 17, the dosing element

  is adjustable with respect to the sheet 5.

  Between the metering device 14 and the slot 7 there is provided a wedge-shaped guide body 18 which also serves to guide the coating material and which is provided with overflow orifices 19 through which the material scraped by the metering element 15 returns to a collection chamber 21 and thence, through a return pipe 22, into the collector pipe 13. The upper side and the lower side of the guide body 18 are arranged at a distance from the around the coating cylinder 2 and the counterpart cylinder 6, or in contact with the coating roll 2, so that the material

  coating is fed in and guided in the desired manner.

  Seen in the direction of advancement of the web, behind the metering device 14, is mounted a finishing metering device 23. The finishing metering device has a rigid blade 24 whose support elements are> made in the form of support rods 25, clamping bars 26 and a tensioning element 27. To this finishing metering device 23 is associated a receiving pan 28 which is connected to the collecting chamber 21 via an orifice 29. sealed with respect to the liquid chamber 3 by a seal 31. The finishing metering device 23 with the receiving tray 28 associated therewith is, like the metering device 14 with the collecting chamber 21 which associated with it, mounted on a frame 32 which is mounted so as to be pivotable about a substantially horizontal axis 33, so that the metering device 14 and the finishing metering device 23 can be tilted and thus release the mech coating 1 for repair and cleaning

or the like.

  The operating mode of the coating and dosing device is explained in more detail with reference to FIG. 2, in the case of high speeds of advancement.

of the tablecloth.

  By means of the coating roll 2, and by means of the guide plate 8, the coating material is conveyed into the slot 7, so that the web of material 5 made of paper or cardboard is covered with material coated on its side facing the coating roll 2. The coating is carried out under a very low liquid pressure so that the penetration of the aqueous constituents of the material

  coating is reduced, as indicated in reference 34.

  Since the coating material is applied in excess amount, the excess portion returns to the manifold in the direction of the arrow 10 passing over the

  upper side of the guide plate 8.

  The metering element 15 has a convex front surface convergent with respect to the web 5. The adjustable metering element 15 operates, with respect to the specific surface force in the contact zone, with a reduced force, so that a regular distribution of the coating material is obtained both in the advancement direction of the ply 5 and transversely in this direction, with a low penetration 34. Thanks to the geometrical conformation of the metering element 15, we obtain a partial dewatering of a thin boundary layer 35 on the web 5, boundary layer in which the solid constituents such as pigments and binders of the coating material

are largely immobilized.

  This boundary layer 35 has the consequence, in the area of the finishing metering element 24, that the coating material does not penetrate too strongly inside the ply 5. The excess of equalized material, and the As the amount is reduced to a minimum, reaching the finishing dispenser 24 with low penetration 34, the application forces required for the finishing dosage can be reduced to a minimum. This results in reduced wear of the finishing metering element 24 and / or low application weight with higher web speeds or higher

  solid constituents of the coating material.

  In Figures 3 and 4 is shown another embodiment of the guide plate 8 shown in Figure 1 and here designated by the numeral 8 '. The other numerical references corresponding to those of FIG. 1 have the same meaning here as in the

  corresponding description. In addition, the sheet metal

  8 'is arranged separately from the liquid chamber 3, the separation line 37 forming a substantially horizontal plane with the axis 38 of the cylinder

coating 2.

  Between the guide plate 8 'and the liquid chamber 3 there is provided a slot 30 which serves as overflow for the excess coating material so as to obtain a

high accuracy of pre-dosing.

  To maintain the guide plate 8 ', the latter is provided on its two ends, inside the flow line 12 of legs 40 which are connected to

a bearing shaft 41.

  This bearing shaft 41 is rotatably mounted in the wall in the flow line 12 and passed therethrough outwardly supporting at each of its ends a rotary lever 42 which is integral therewith. These levers in their turn have at their free ends cylinders 43 with which the guide plate 8 is tilted about the axis of the shaft 41. To adjust the slot 44, it is provided externally to the pipe. 12, on both sides of this pipe, respectively an adjustable stop 45 against which the levers 42 abut when the guide plate 8 'is in the operating position. So that the tip 50 of the sheet 8 'which penetrates into the coating slot 7 can be adjusted even finer, there is provided an elastic plate 46 fixed by screws 47 and an elastic spacer element in the manner of a lever cantilever recessed from the tip 50 of the sheet 8 '. The free end 49 of the plate 46 exceeds the tip 50 of the sheet 8 'and the plate 46 bears on the tip 50 between its two ends. By turning the screws 47, the free end 49 of the elastic sheet 46 which penetrates into the coating slot 7, can be moved up and down around the point 5 of the sheet 8 'which serves as a point of rotation, which has the effect of further varying the distance 44 inside the coating slot 7. This complementary elastic plate 46 is also provided for

  the guide plate 8 shown in FIG.

  The mode and operation of the arrangement described above is as follows: The coating material is pumped excessively into the liquid chamber 3 while a regular level is always established thanks to the presence of the slot 39 of such that the coating material which has not been removed by the coating roll 2 flows through the slot 39 in the flow line 12. To do this, the slot 39 must be dimensioned in such a way that that the material transported by the coating roll 2 can be transported substantially without pressure through the transport slot 44 so that only inside the coating slot 7 can be established

  a controlled hydrodynamic pressure.

  It goes without saying that the invention is not limited to the embodiments shown and that many modifications are conceivable within the scope of the invention. Thus, the metering element 25 is not necessarily made in the form of a doctor blade, it can also be made in the form of a blade called "Bent-Blade" and where appropriate also in the form of a rolling squeegee. Similarly, in certain circumstances and under the conditions of service, the finishing metering element 24 may be in the form of a doctor blade and, where appropriate, also in the form of a doctor blade.

  so-called "Bent-Blade" blade or a rolling squeegee.

Claims (10)

  A process for the continuous application of a regular coating on a web of material passing over a counterpart cylinder, in particular a paper or paperboard web, on which the coating material is applied by means of a coating cylinder first in excess quantity and then scraped off, characterized in that the coating material is transported in pre-measured proportions, with the aid of the coating roll, over a distance even into the coating gap between the coating cylinder and the counterpart cylinder and applied under a slight pressure on the web of material, the coating material being partially dewatered on a boundary layer   thin close to the web of material.   2. Method according to claim 1, characterized in that the low pressure is achieved by means of a reciprocal arrangement without known contact between the coating roll and the counterpart cylinder or the sheet of material, a subsequent guidance without pressure   coating material and subsequent scraping.   3. Device for the continuous application of a regular coating on a sheet of material passing on a counterpart cylinder, in particular a sheet of paper or cardboard, by means of a coating roll which takes the coating material in a liquid chamber and a metering device and a subsequent scraping device, characterized in that the coating roll (2) has a guide plate (8, 8 ') on the drawing side. ) extending into the coating slot (7) between the coating roll   (2) and the counterpart cylinder (6).   4. Device according to claim 3, characterized in that the guide plate (8, 8 ') is formed with a curved shape corresponding to the periphery of the coating roll (2), at least in the region facing the slot (7) between the coating roll (2) and the counterpart cylinder (6).   5. Device according to claim 3 or 4, characterized in that the guide plate (8, 8 ') is adjustable in all and / or in part with respect to its distance (44) towards the periphery. of coating cylinder (2).   6. Device according to any one of   Claims 3 & 5, characterized in that the sheet   for guiding (8, 8 ') is an extension of the upper edge of the liquid chamber (3) containing the coating material so that between said chamber (3) and the lower part of the guide plate (8) , 8 ') is created a passage for excess coating material   having the shape of a slot (39) or a similar shape.   7. Device according to any one of   claims 3 to 6, characterized in that the line   separation between the guide plate (8, 8 ') and the edge of the chamber constitutes a substantially horizontal plane   with the axis (38) of the coating roll (2).   8. Device according to any one of   Claims 3 to 7, characterized in that in the   sampling direction behind the coating slot (7) is provided a guide body (18) provided with a metering element (15) and overflow orifices, said body (18) being fitted at its lower side or substantially greater than the circumferential area of the coating roll (2) and the counter-roll (6), at a distance of these or in contact with them.   9. Device according to any one of   Claims 3 to 8, characterized in that   the metering element (15) operates at a low energy level with respect to the surface specific force in the area of contact with the web (5) and has, at its front surface facing the web (5), a geometry such that partial dewatering of the coating material occurs in a thin boundary layer (35) close to the sheet of material.   10. Device according to any one of   claims 3 & 9, characterized in that   the metering element (15) is in the form of a scraper rod and has on its front surface facing the web (5) a convergent, preferably convex, convergence towards the element metering device (24), with respect to the tablecloth material (5).