Spray-coating method and spray coater

Spray coating method and spray coating

The invention relates to a spray coating method according to claim 1.

The invention also relates to a spray coater.

According to the prior art, the paste is coated with so-called spray coaters, in which a coating jet is sprayed at a distance from the paper or board web. The quality of the coating is controlled by the distance between the nozzle and the web, the spray rate and the mass flow. The quality of the coating is also controlled by the structure and material ratios of the coating paste. Nozzles that use compressed air for dispersing also have a control variable for the dispersing air pressure. The spray equipment is protected by a trough surrounding the nozzle, extending over the entire width of the web, with a nozzle at the bottom to remove excess paste. The spray paste is spread as a coating mist over the entire pool area. The mist also forms large droplets which, when in contact with the web, impair the coating result. Because it is difficult to seal the gap between the coating and the web, the coating material mist also spreads outside the coating trough, contributing to a weakening of the coating result and soiling of the equipment outside the coating. The removal of mist under reduced pressure is difficult because separating the paste from the flow back into circulation requires expensive and complex separators.

U.S. Patent 4,944,960 describes a spray coater that uses the aforementioned vacuum technique to reduce the spread of coating mist.

The object of the present invention is to obviate the drawbacks of the technique described above and to provide a completely new type of spray coating method as well as a spray coating.

The invention is based on the formation of a coating mass flow on the walls of the basin surrounding the nozzles, which binds the generated pasta vapor to itself.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1. The spray coater according to the invention, in turn, is characterized by what is stated in the characterizing part of claim 5.

The invention provides considerable advantages.

With the arrangement according to the invention, the resulting coating mist can be substantially reduced, since the mist adheres efficiently to the flowing coating material. Separators are not required and the mist does not have time to form large droplets that interfere with the coating. The invention increases the efficiency of the spray coating apparatus by collecting the mist generated therein back into the machine circuit, from where it returns to the nozzle. The equipment can also improve the coating imprint of the spray coating, as it reduces the air mass accompanying the web, which interferes with the coating process, as the flowing coating material provides a good air barrier in the vicinity of the web.

The invention will now be examined in more detail by means of exemplary embodiments according to the accompanying figures.

Figure 1 shows a schematic side view of one spray coating apparatus according to the invention.

Figure 2 shows a side view of another spray coater according to the invention.

Fig. 3 schematically shows the coater according to Fig. 2 connected to the coating agent supply means.

Figure 4 shows a side view of an alternative spray coating apparatus according to the invention.

Figure 5 shows a side view of another alternative spray coating apparatus according to the invention.

According to Figure 1, the web 1 is fed by guide rollers 8 supported on the surface of the counter roll 2. Below the counter roll is a spray coater 3, the nozzles 4 of which supply the coating material mass to the surface of the paper web 1. The nozzles 4 are located along the entire width of the paper web. The nozzles 4 are surrounded by a basin 19, on the outer edges of which are overflow basins 5, which are fed so full of coating material that it flows as a flow 18 along the side surfaces 6 of the basin 19 and further as an outlet flow 7 through the outlet connection 20 back to the coating material circuit. The distance of the spray coater 3 from the web 1 is adjustable. By moving the coater 3 as close as possible to the web, the air mass carried by the moving web 1 can be reduced. overflow pools

5 the coating material flow over the edges then acts as an effective air barrier. The distance of the nozzles 4 from the web 1 is also separately adjustable, as is the mass flow to the nozzles 4. The angle of attack between the spray jet and the paper or board web 1 can also be adjusted within the limits allowed by the dimensions of the basin 19. This arrangement affects the quality of the resulting coating and also the formation of mist in the pool 19.

Figure 2 shows an embodiment in which the coater 3 is divided into two blocks 10 and 11, which can be opened around the joints 9 for cleaning the equipment according to the arrows. This procedure makes the equipment easy to clean.

According to Figure 3, the material flow system comprises a first supply connection 15 for supplying coating material to the nozzle 4 and second supply connections 12 and 13 for supplying coating material to the overflow basins 5. Excess coating material is discharged via an outlet connection 14 to a paste container 16. This arrangement is capable of re-coating.

According to Fig. 4, the coater can be provided with air supply / suction pipes 17 located in the vicinity of the nozzle 4, which can be rotated about its longitudinal axis according to the figure, if necessary. With these air currents, the paste can be made to adhere in a more controlled manner to the flows 18 shown in Fig. 1. By means of the air supply pipes, the pressure inside the basin 19 can also be adjusted whenever necessary. From the air tubes 17, air is discharged in a controlled manner through small holes over the entire width of the web 1. The direction of air discharge can be changed by rotating the air tubes 17. If the supplied compressed air causes the paste mist to pass outside the system, the equipment must be equipped with a pressure relief valve.

According to Figure 5, the spray coating unit can also be placed below the endless belt or wire 21.