FR2545736A1 - APPARATUS FOR COATING A SHEET - Google Patents

Abstract

THE INVENTION RELATES TO AN APPARATUS FOR COATING ON ONE OR TWO SIDES OF A MOVING SHEET. THIS APPLIANCE IS CHARACTERIZED IN THAT THE APPLICATION DEVICE 8 INCLUDES A FLOW REGULATOR 26 PLACED SO AS TO DEFINE AN INTERVAL 18 BETWEEN ITSELF AND SHEET 1, THIS INTERVAL BEING CONVERGENT IN THE DIRECTION OF MOVEMENT OF THE SHEET, THE HEIGHT OF THE INTERVAL BEING LESS THAN A THICKNESS OF ANY LAYER OF COATING SUBSTANCE WHICH WOULD BOND TO THE SHEET IN THE ABSENCE OF COOPERATION OF THE REGULATOR AND THE SHEET. APPLICATION TO SHEET COATING DEVICES.

Description

The present invention relates to an apparatus for coating on

  one or both sides of a sheet in substantially vertical displacement, for example a sheet of paper, by unpressurized dispensing of a coating substance on the sheet and equalization of the coating substance adhering to the sheet by traction of the sheet through a pinch of overlay defined by a flexible coating blade and a support piece. In sheet-coating devices, in which the sheet is pulled vertically through a nip defined by a blade or the like and a support piece, the spreading of the coating substance

  on the sheet is usually done before the forceps

  by means of a spreading device In a

  As known, the spreading apparatus comprises two rolls forming a nip through which the sheet is drawn. The coating material is dispensed onto the

  least one of these cylinders, that is to say the cylinder of

  where it is transferred and spread on the sheet.

  At high leaf speeds, there is a difference in

  ficulty due to slippage of the sheet in the spreading nip, as the application roll moves more

  slowly that the sheet results in an irreversible

  Another known construction of a coating apparatus includes

  distribution nozzles instead of the applicator cylinders

  However, with this arrangement, it is difficult to uniformly spread the coating material on the sheet. A feature common to these two known constructions

  is that in the spreading phase, relative quantities

  large amounts of excess coating material are removed.

  of the leaf and the spreading apparatus

  excess water must be pumped back to the point of

  This also leads to an additional and uneconomic operation in the treatment. In addition, another recycling circuit must be provided to recycle the substance.

  coating scraped by the equalizer blade (s).

  complicates construction and increases manufacturing costs

  cation. In coating apparatus having a

  coating application device without pressure, that is

  ie a coating substance application device-

  At atmospheric pressure, the substance adhering to the moving sheet is equalized by means of a flexible blade. However, in such coating apparatus, there is encountered a phenomenon of forming bars which creates difficulties, in the form of variations. of the coating layer in the longitudinal direction of the sheet, especially at high coating speeds (over 500 m / min)> The exact cause has not been fully elucidated

  of this formation of bars A preferred mode of

  The invention is based on the assumption that a cause of the formation of bars lies in the non-uniform thickness of the coating layer on the sheet, prior to the smoothing nip. This causes movements of the smoothing blade and we get an uneven coating,

because of these movements.

  U.S. Patent No. 3,192,895 discloses a

  coating device in which a coating chamber

  is defined by a cross-dosing system which regulates the

  bit of coating substance between this crossbar and the sheet in horizontal displacement The disadvantage of this arrangement is that the gravity acts against the coating substance, between the crossbar and the flexible blade The crossbar allows only a setting of the exit slot but does not improve the quality of the equalization before

flexible blade.

  In an extrusion application device, in which the coating substance is applied under pressure on the sheet, the situation is different. In such application devices, a relatively long smoothing interval is used in association with the device. for application, for equalizing the pressure of the coating substance The invention does not relate to

such coating methods.

  The subject of the invention is a device for coating

  sheet in which the spreading of the coating substance is carried out safely and economically and with a homogeneous and even result, even at high sheet speeds. A device according to the invention is little

  expensive to manufacture and the amount of coating substance

  In addition, the coating material, scraped from the sheet by the clipping blades, is

  collected for reuse without any pumping action.

  According to the invention, the sheet is moved through a vertical coating application device,

  in which the sheet is in direct contact with the sub-

  coating pressure at atmospheric pressure.

  application has a small defined interval

  Be the sheet and a flow regulator, this interval being of constant height or inclined in the direction of movement of the sheet This height is set to a value less than a thickness of a possible layer

  of substance obtained without the regulator.

  the application device, there is provided a slot constituting a sheet entry, by which the sheet

  comes into contact with the coating substance The distribution

  The coating substance, the width of the bottom slit, the viscosity of the substance and the speed of the sheet are determined so as to effectively fix the gravitational flow of coating substance through the slit. Thus, only a small amount of the coating substance flows down, through

  the slot, during normal operation of the device.

  The application device also includes an overdrive

full gravity.

  The leaf is in direct contact with the substance

  this coating, in the application device The

  moving sheet entered then 5 then the coating substance

  This contributes to a strong adherence of the sub-

  coating stance on the entire surface of the sheet

  coating substance in excess, grate Me by the blade of re-

  garment, is collected even at high sheet speeds.

  the, for immediate reuse without any means of

  Since only a small amount of

  this of coating passes through the lower slot, down,

  a column of coating substance is formed in the chamber.

  This ensures wide and even contact

  between the sheet and the coating substance The construction

  It is economical since only a small amount of coating material escapes from the contact area. The viscosity of the substance is optimally matched to the speed of the sheet, no substance escapes.

  This means that no pumping means is

  necessary to recycle the substance.

  The level of the coating substance can

  it can be adjusted by means of a spillway or an overflow pipe, preferably adjustable, in a known manner.

  application device may comprise side walls

  the adjustable verticals whose upper edge constitutes the overflow weir It should be noted that the coating application device may have a length of 6 to 8 meters in the transverse direction of the sheet, in

  a device of normal size. It follows that

  even relatively large end margins however allow the application device to remain substantially

full of coating substance.

  The aim of the invention is to reduce the risk of forming bars. This is achieved by means of the flow regulator, arranged transversely to the sheet and to a certain extent

  distance from it The regulator defines, between itself

  same and the sheet, a game extending in the direction of movement of the sheet In a preferred embodiment of

  invention, this game has a configuration of conver-

  in the direction of movement of the feixflle

  the layout greatly reduces the thickness variations of the layer of coating substance that adheres to the

  sheet before the smoothing blade, as well as other ano-

  malities, and this results in a significant improvement in the quality and uniformity of the coating.

  can be located at the free level of the coating substance-

  However, this is not always absolutely necessary. The back edge of the application device must be sharp, in order to avoid

  harmful effects on the coating.

  A device resembling the embodiment

  preferred embodiment of the invention is described in several publications.

  earlier, for example in U.S. Patent Nos. 3,179,536, reference 28, No. 4,063,531, reference numerals 67 and

  a, and the FI 55,375 and SE 402,222 patents.

  Known embodiments differ from the present invention in that the flow control conduit is not convergent (US 3 179 536, Fi 55 375, SE 402 222 and US Pat. No. 4,063,531, reference a) and in that there is no contact between the element in question and the coating layer on the sheet (US

4,063,531, item 67).

  The height of the interval or conduit

  flow rate depends on the solids content

  and the viscosity of the substance If the coating substance contains a lot of liquid and has a

  low viscosity, the height of the gap should be

  In practice, the average height of the control duct

  The flow rate should be 0.5 to 5 mm.

  The length of the flow control duct in the direction of travel of the sheets can be chosen relatively freely.

  length is not a very important parameter O The length

  must be at least equal to the lowest height of the duct An advantageous length of the duct is 1

  at 200 mm, and preferably 10 to 100 mm.

  The flow control duct con Verge in

  the longitudinal direction of the sheet An angle of con-

  Suitable vergence is from 2 to 200 and preferably from 4 to 100. Hydrodynamic forces having a favorable effect on the uniformity of the coating layer occur due to the convergence of the conduit. A convergent conduit must have an appropriate length, preferably at least 4 mm. To ensure correct operation of the flow regulator, it is important that the level of the coating substance in the coating application device remains substantially constant. The free level control must be very accurate if the distance between the sheet and the regulator debit is small We usually get

  sufficiently precise regulation of the free level

  we equip the coating application device with an overflow which automatically maintains the free level

  at a desired height On the other hand, the economy of the

  overflow is reinforced by the

  vitaire. An appropriate support member for pinching

  coating, in the coating of a sheet on a

  this may be constituted by a plate extending vertically

  upwards a little above the pinch of

  and down to the bottom level of the collection tub or chute, or a little beyond the width of the plate should correspond to the width of the sheet, or

  In this way, the sheet is easily supported

  and firmly on one side and the support part of the nip and the slit limiting piece are constituted by a single member The setting of the game

  or slot relative to the support piece is easily

  To perform it, for these fixed elements Another support piece is constituted by a rotating cylinder. In a device according to the invention, the parts situated on the opposite faces of the sheet can

  be completely or partially identical For a coating

  on both sides, corresponding parts may be

  may be provided on each side of the sheet, preferably

  at the same vertical level These devices for

  can be fed with the same type or with

  different types of coating material In this last

  deny case, slot widths and level positions

  liquid can be very different on both sides.

  In order to obtain a uniform coating result, the device may comprise a load piece which exerts an adjustable pressure on the flexible coating blade,

known way.

  In addition to the foregoing, the invention also includes other arrangements which will emerge from

the following description.

  The invention will be better understood using the

  description below, which refers to the accompanying drawings in

  which: Figure 1 is a schematic sectional view of a first embodiment of the invention, illustrating the coating of a sheet on a single face; and

  FIG. 2 is a section of another embodiment of FIG.

  tion of an apparatus according to the invention.

  It must be understood, however, that these

  and the corresponding descriptive parts are given

  only as an illustration of the purpose of the invention.

  tion, of which they in no way constitute a limitation

tion.

  In the drawings, reference numeral 1 designates a sheet

  moving it which is pulled through a pinch of coating defined between a flexible blade 2 and a piece

  19 (Figures 1 and 2) The direction of movement

  The slot is indicated by an arrow. A narrow slot 5 is defined below this nip. The slot is formed between a slot-limiting piece, which is

  attached to the support piece 19, and an edge 11 of a regula-

  slot width width of slot width can vary from

  progressively to a maximum value which is preferably 5 cm. The support piece 19 and the associated limiting piece may be separated or combined into a single member which may be a cylinder, a flexible or rigid plate or a fixed piece of sheet guide A coating chamber is formed above the slot 5 This chamber is delimited by the sheet 1, the flexible blade 2, a rear wall 8 and side walls (not shown).

  extend beyond the side edges of the sheet,

  It is clear to those skilled in the art that in this case it may be advantageous to use in this part of the sheet a support piece (not shown) arranged in a suitable manner. In most cases, it is more practical to reduce slightly the distance between the side walls, so that their edges are applied sealingly against the sheet Thus, a narrow area is left uncoated on each edge of the sheet The upper part 8b of the chamber of coating is more or less filled with coating material, during the

  operation of the apparatus, because of the action of the

  me 2 which scrapes the excess coating material and let it back into the lower part of the coating chamber. Uhe support plate 9 carries the slot width regulator 10 which is movably suspended

  to allow adjustment of the slot width 5

  width width 10 may comprise threaded parts 27 arranged so that, by rotation of these parts,

  the width of the slot 5 is adjusted.

  slot-feeder can also be in the form of a

  rotating traverse, supported eccentrically, transverse

to the leaf.

  The coating substance 16 is sent into the chamber through a feed duct 13 A tray of

  12, opened near the sheet 1, is placed

  below the slot 5 Small amounts of substance

  coating, which flow through the slot 5 and are collected

  in the bin 12, are returned to the chamber by the

  intermediate of an outlet duct 14 connected to the supply duct 13 through pumping means (not shown) The chamber comprises means for adjusting the

  level of the coating substance contained in the chamber

  For example, the coating substance may flow over the upper edge of the sidewalls, towards the

  tray 12 These edges are preferably adjustable vertically

  is lying. The embodiment shown in FIG. 1 comprises a cylinder 19 which constitutes at the same time the

  support piece for the flexible blade 2 and the piece of

  The cylinder 19 rotates in the di-

  movement of the sheet 1 A wall of excess

  solid 23 is provided at the rear of the coating application device, so as to maintain the level 24 of the coating substance 16 at a constant height at this height, the coating application device comprises a flow regulator 26 , defining with the sheet a duct 18 slightly convergent The flow regulator

  26 decreases the amount of coating substance

  The layer 27 has a substantially uniform thickness, which has an undeniable influence on the operation of the coating blade 2 and thereby helps to prevent the formation of the layer 1, in the upper part 8b of the coating chamber 2. bar formation The distance between the flow regulator 26 and the sheet, and preferably also the angular position of the flow regulator

  Compared to the sheet, are adjustable.

  The coating substance is returned to the disc

  positive application 8 by pipes 13 and the coating stance which overflows over the overflow wall 23 is guided to a recycling circuit, by

  piping 33 The convergent duct 18, between the regulator

  flow limiter 26 and the sheet, is illustrated in a more

  Figure 2 represents another piece of

  support 19 The convergence angle d is of the order of 100.

  The duct has a height a on the entry side and a height b on the exit side The dimension a is in most

  cases of 1.5 to 7 mm and preferably 2 to 4 mm.

  the conduit must be greater than d and at least 4 mm, and preferably 10 to 100 mm

  Due to the convergence of the conduit 18, a

  this hydrodynamic P is generated in the Expressed duct

  in force per unit of width in the transverse direction

  Dirty to the flow regulator sheet, this force can be calculated by the known formula 6 n U 2 m-2 l P = 2 ln (m), where tan d L m + 1 n = viscosity of the coating substance U = speed of the sheet 1 d = convergence angle of the duct m = a / b (ratio of the height of the duct to the end

  entrance and exit end).

  Hydraulic force P has an equalizing effect

  layer 27 of coating material, which improves

  re the effect of the flow controller 26.

  The embodiments shown in Figures 1 and 2 are based on the coating of the sheet

  single-sided devices substantially symmetrical

  with respect to sheet 1 can be used for coating the sheet on both sides of such

  are described, for example, in the application for

  British vet 2,085,327 However, it is not indis-

  think of using a symmetrical coating

  For example, if we send to coating chambers,

  on both sides of the leaf, coating substances

  with different viscosities, the edges

  11 of slot adjustment can be at different distances

annuities of the sheet 1.

  The collecting tray 12 is suspended from the wall 8 of the coating chamber The tray 12 can also be integrally formed with the wall 8 and, in this case, the latter comprises a downward extension, which is folded at its lower edge towards the sheet 1, for

  constitute a chute The chute or tray 12 may extend

  outside the side edges of sheet 1.

  The support part of the coating pinch

  and the slot limiting part 5 can be

  bent into a single, substantially rigid guide plate

of leaf.

  Thus, as is apparent from the foregoing, the

  tion is not limited to those of its modes of

  implementation and application that have been described more explicitly; on the contrary, it embraces all the variants that may come to the mind of the technician in the field without departing from the scope or scope of the

present invention.

Claims (9)

claims   Apparatus for coating on one or both sides of a sheet in vertical displacement, which comprises a coating application device, in   the sheet (1) is brought into contact with a sub-   coating stance <16) in excess and maintained at atmospheric pressure, and a flexible blade (2) which cooperates with a support piece (19) to equalize a layer of coating substance adhering to the sheet,   characterized in that the application device (8) comprises   takes a flow regulator (26) placed so as to de-   ending an interval (18) between itself and the sheet (1),   this interval being convergent in the direction of de-   placement of the sheet, the height of the gap being   less than a thickness of a possible layer of sub-   stance of coating which adheres to the leaf in the ab-   of the regulator and of the sheet, the application device further comprising means for   overflow <23) and substance flow in the   this flow in the opposite direction being determined by the   of coating substance to the application device, the viscosity of the coating substance, the speed of movement of the sheet and a slot (5) of the application device, so that only a small amount of the substance of coating flows down through the slot during normal operation of the apparatus, this slot constituting a sheet entry to the part   lower the application device.   2 Apparatus according to claim 1, characterized in that the height of the gap decreases in the direction of travel of the sheet, so as to converge according to a angle (d).   Apparatus according to claim 1 or 2, characterized   in that the flow regulator (26) is placed vertically   the free level (24) of the coating substance   (16) in the application device.   Apparatus according to any one of the claims   1 to 3, characterized in that the average height of the gap (18) between the flow regulator (26) and the sheet (1) is 0.5 to 5 mm. Apparatus according to any of the claims   1 to 4, characterized in that the length c) of the in-   between the flow regulator (26) and the sheet (1), in the direction of travel of the sheet, is   from 1 to 200 mm and preferably from 10 to 100 mm.   Apparatus according to any one of the claims   1 to 5, characterized in that the flow regulator has a sharp edge defining the output end of   the interval between the flow controller and the sheet.   Apparatus according to claim 5 or 6, characterized   in that the length (c) of the interval between the   flow regulator and the sheet, in the direction of de-   placement of the sheet, is at least as large as the   smaller height (b) of the interval.   Apparatus according to any one of the claims   preceding, characterized in that the interval has a time   in the moving direction of the leaf, between the flow regulator and the leaf, which is at least 4 mm.   Apparatus according to any one of the claims   preceding, characterized in that the height of the inter-   valle between the flow regulator and the sheet decreases at a convergence angle (d) which is from 2 to 200 and preferably from 4 to 10.   Apparatus according to any of the claims   characterized in that the free level (24) of the coating substance (16) is regulated by a gravity-overflow device (23) which determines a   constant level of the coating substance in the positive application.