SHORT DWELL APPLICATION WITH BIG EXCESS PASTE AMOUNT

Abstract: Arrangement for the coating of a running web (2), for instance a paper, a cardboard or a like web, by means of a so-called short dwell applicator (18), in which the paste supply, the paste doctoring and levelling of the supplied coating layer are carried out in the same arrangement and the amount of the excess supplied paste is collected for a recirculation. The arrangement comprises a rear edge seal (9, 12) and fore distributor (6, 15) so arranged that the coating paste is supplied on the web there, where the last quoted arrives in the arrangement, and that hereafter the paste flows mainly in the direction (22) ofthe material web (2) until it meets a doctor (3). The amount of supplied paste (1) is hereby big compared to the amount (5) of paste, which attached and levelled follows along with the running material web (2).

Description: SHORT DWELL APPLICATION WITH BIG EXCESS PASTE AMOUNT The invention relates to an arrangement for the coating of a running material web quoted in the preamble of claim 1. Paper, cardboard etc. are normally produced from natural cellulose fiber. The paper production is a complicated process, which is started by the defibration of natural logs or other plant parts, fibre preparation and finally sheet formation. In the sheet formation one strives to distribute the fibers so evenly as possible. Along with the dewatering, which is carried out by the sheet formation, the fibers are guided more near to each other and are linked, mainly through fluidum bonds. The paper comprises fibres located in several layers, arbitrarily distributed. If one examines the paper through a magnifying glass, cavities are found between the fibers and the surface is found uneven - everything depending on the micro structure quoted above. One might have different reasons for the desire to improve this uneven micro structure. One might have, for instance, the desire to reduce the porocity in the paper, in order to be able to apply it as packaging material. Or, it is also important to improve the paper surface itself, in order to be able to print on the paper with a good result. A common method for the surface levelling and the porocity reducing is the application of a layer on the top of the completed paper surface. A normal method is to mix finely divided pigment, for instance clay, with water along with some binding substance, for instance latex, and thereafter to supply this paste on the paper web. The surface smoothness is realized in that one doctors the paste by a trowel blade, a so called scraper knife. The doctored paper is hereafter dried, whereby the supplied paste is attached at the paper web through a certain penetration. A normal coating method is the guiding of the paper web through a nip located between two drums, in which the paste is supplied by the partial immersion of the other drum in a machine bin filled with paste. The paste excess is doctored off hereafter at a certain distance from the nip and the paste is levelled by a scraper knife. The drum nip can also be replaced by a fountain or a so-called applicator. Normal web speeds are 600-1000 m/min. but even higher speeds, up towards 2000 m/min are applied. The paste excess during the doctoring is hereby often 10-20 ggr. This excess amount is resupplied in to a trough for the return to the machine bin. A nip method has been developed during the past years, which combines the fountain application and the doctoring in to one member the so-called short " dwell technique. A benefit hereby is the short distance between the paste application and the doctoring. The so far constructed short dwell appliances comprise a defect, which is the minor paste excess amount realized. This is a result of the applied -technique, in which the eventual paste excess amount must be compressed out at the rear wall against the running direction of the paper web. This results even in a prolonged penetration extent than was intended for. The object of the invention is to realize a development of the familiar short dwell appliances so, that the amount of the paste excess, which is supplied on the web, can be increased. An object is also to realize an application with a favourably short penetration extent. A further object is to create an arrang¬ ement in which the application paste flow is smoothly arranged in the application arrangement and air bubbles in the paste can be separated before the paste reaches the running web. The characteristics of the invention are disclosed in claim 1. A big amount, in comparison to that paste amount attached at the web, of application paste is supplied on the web in the application chamber. The application chamber is divided by a distributor in an inlet and an exit channel. The paste is supplied on the web thereat, where the latter arrives in the application chamber, after which the paste follows along 'with the web to a doctor, which orms the front wail of the chamber, at which the excess paste is removed and guided in to the exit channel of the application chamber, for a resupply in the process. The appli¬ cation of the paste with a normal paste excess amount can be done in an arrangement according to the invention. By this means a so-called skip-coating, among other things, is avoided, that is, uncoated surfaces on the paper web. The doctor at the front edge of the application chamber is, according to a preferred embodiment, a so-called downstreams inclined scraper knife, which forms a sharp angle relative to the running web, in the web running direction. An alternative embodiment comprises an upstreams inclined scraper knife of that type which is described in the Swedish Patent Application Nr. 85033Ψ5- . A benefit within this embodiment lies in that one avoids those rheoiogy phenomena, which are generated with a "downstreams" scraper knife. Furthermore, a free exit is realized for the recycle paste. That gap which unavoidably must be found at the rear edge of the application chamber, can be made quite small, that is, a gap so big only is left which is necessary for a free passage of the paper. Furthermore, this gap can be provided with, for instance, a small roil, in order to prevent a reverse paste flow. Other appliances can even be imagined for the prevention of the paste reverse flow. By such means an increased pressure can be available in the space, in which the application of the paste is carried out. The invention is described more in detain with reference to the attached drawing in which Figure 1 illustrates an embodiment of the invention in a side view, Figure 2 illustrates another embodiment of the invention in a side view, Figure 3 illustrates a third embodiment of the invention in a side view; and Figure illustrates a fourth embodiment of the invention in a side view. The reference A in the drawing refers to a guide or support drum rotating in the rotation direction 22, which carries a running material web 2. Reference 1 refers to a πowing paste amount wnicn enters tne application arrangement through an inlet channel thereof. Reference 9 refers to a rear edge seal of the application chamber, which in the embodiment according to Figure 1 comprises a knife. Reference 6 refers to a distributor in the application chamber which divides the interior extent of the chamber in an inlet channel and an exit channel 7. Between the front edge of the distributor 6 and the running web is located a gap 13, through which the application paste flows. Reference 3 refers to a doctor, for instance a scraper knife, which by means of an appliance 17 is compressed - against material web 2. Application paste 1 is supplied on web 2, in the described arrangement, in the application chamber at that location, at which web 2 enters the application chamber at rear edge seal 9. A big amount of paste 16 is supplied hereat on web 2, and follows along with it ail the way to doctor 3, whereat the excess amount is removed and the sur ace is levelled for the realization of the desired coating layer 5 on the web. The removed excess amount streams hereafter through channel 7 in to a collector container 8 for a resuppiy in the • process. Thus, by means of the described arrangement one realizes a smooth and continuous flow of the coating paste in the arrangement, through that also the penetration extent is kept favourably short in the arrangement. In the embodiment according to Figure 2, distributor 6 is replaced by a distributor 15, which is movable in a direction 21 for the adjustment of gap 13 through an appliance 14. The minor amount of excess paste amount 10 in the reverse flow direction, which penetrates through rear edge seal 9, is collected in a container 11. The entire arrangment 18 is turnabie in a direction-of arrow 20, and hoistable and descendable in a direction of arrow 19, also. In the embodiment according to Figure 3, rear edge seal 9 is repiaced ' Tay a roil 12 arranged rotatably, for a further reduction of the paste amount 10 in the reverse flow direction. In the embodiment according to Figure , openings 23 are arranged in the inlet channel of the flowing paste for the separation of air bubbles from the paste. That amount of paste 2k, which hereby follows along with the air bubbles, is collected in the container 11. The invention is not limited to the embodiments shown, but several modification are feasible within the scope of the attached claims.

Claims: SHORT DWELL APPLICATION WITH BIG EXCESS PASTE AMOUNT CLAIMS 1. An arrangement for the coating of a running web (2), for instance a paper, a cardboard or a like web, by means of a so-called short dwell applicator (18), in which the paste " supply, the paste doctoring and levelling of the supplied coating layer being carried out in the same arrangement and the amount of the excess supplied paste being collected for a recirculation, characterized in that the arrangement comprises a rear edge seal (9,12) and- fore distributor (6,15) so arranged that the coating paste is supplied on the web there, where the last quoted arrives in the arrangement, and that hereafter the paste flows mainly in the direction of the material web (2) until it meets a doctor (3), and that the amount of the supplied paste (1) is big compared to the amount of paste, which attached and levelled follows along with the running material web (2). 2. Arrangement according to claim 1, characterized in that the fore, distributor (15) comprises an arrangement, by means of which a gap (13) between the fore distributor and the running material web can be adjusted. 3. Arrangement according to claim 1 or 2, characterized in that the rear edge 1 seal (9,12) in a biggest possible extension is arranged to prevent the paste to flow out of the arrangement in a direction against the web running direction, however so, that said seal is adjustable in order to allow the web to run freely in to the applicator, and that the minor amount of the paste ( 10), which hereby flows beyond the seal (9,12), is collected in a container (11) for a recirculation. . Ψ. Arrangement according to any of the preceding claims, characterized in that the rear edge seal is constructed to a roll (12), which either moves freely or alternatively is rotated by a speed of rotation which adapted to or deviates rom the speed and the running direction of the material web. 5. Arrangement according to any of the preceeding claims, characterized in that the amount of the excess paste (4) is doctored by a doctor (3) located at the fore edge of the arrangement, for instance by a scraper blade inclined downstreams or upstreams, after which the excess paste is allowed to flow via a channel (7) in to a collector container (8). 6. Arrangement according to any of the preceding claims, characterized in that the fore distributor (6,15) comprises a replaceable scraper blade (15) or the like. 7. Arrangement according to any of the preceeding claims, characterized in that eventually generated air bubbles' in the paste are allowed to flow " out through openings (23) in the applicator, before the paste is supplied on the material web (2), and that the paste amount (2Ψ) hereby eventually following along with the air bubbles is collected in a container (11) for the recirculation. 8. Arrangement according to any of the preceeding claims, characterized in that the entire applicator (18) carrying out the paste supply and the paste doctoring is hoistable, descendable ( 19 ) or turnable (20 ) .

Inventors: FUNDELL YNGVE, FUNDELL, YNGVE
Applicants: WAERTSILAE OY AB, OY WAERTSILAE AB
Application year: 1986
Main classification: B05C1
IPC codes: B05C1, B05C3, B05C11