FI91298C - Method for coating a web of material - Google Patents

Description

91298

The present invention relates to a method according to the preamble of claim 1 for coating a web with a coating material and for adjusting the amount of coating.

The present invention relates to the production of an applicator and brush device in which the pulp is applied to the web at a small angle to the web through a blade formed by the web and the web and the applied coating is smoothed and the excess removed with a scraper blade.

10 GB patent application 8508431 describes such a method and apparatus for coating paper. In the solution according to the publication, the coating mass is pre-applied with a flexible blade and the final scraping is done with a drag scraper blade. The coating device is placed on the side of the counter roll and the coating mass is in contact with the web over a long distance. In the presented solution, the removal of air from the coating mass is cumbersome and the integration of the drag scraper blade 15 into the coating equipment complicates maintenance operations. In the solution shown, the coating mass in the pre-application zone of the leveling steel is sensitive to disturbances, such as the uneven distribution of the amount of material. This typically results in longitudinal streaks in the web coating.

In the coater developed from the above solution, the coating material is fed to the web in a laminar flow by means of a narrow gap and a blade placed at a small angle to the web. The coating is smoothed and the amount of coating is applied in the usual way with a scraper blade. Such a device is described in the applicant's previous application FI 890249. When the coating mass is fed to the web as a laminar flow. the streakiness of the coated paper 25 and the defects caused by air bubbles can be substantially reduced.

Adjusting the coating thickness on the scraper blade is quite difficult, especially with larger coating quantities, because a small change in the load on the blade causes a large change in the coating thickness. The structure of the blade must be carefully designed so that it does not show any hysteresis when the blade yield is changed.

The object of the present invention is to provide a novel method for coating a paper web with a device such as that described in application FI 890249.

30 2

The invention is based on the fact that the amount of coating applied to the web is irradiated by the application device by changing the amount of coating applied to the web.

More specifically, the method according to the invention is characterized by what is set forth in the characterizing part of claim 1.

The invention provides considerable advantages.

This method 10 makes it easier to control the exact amount of coating, especially with large amounts of coating, than with a conventional scraper blade. Changes in the load on the scraper blade are much more sensitive to changes in the amount of final coating than changes in the amount of coating applied. The change in the amount of coating applied affects the amount of coating at most by changing the impulse force that bends the scraper blade off the surface of the web. The change in the amount of application thus indirectly affects the shaping force of the actual scraper blade 15, which removes the excess coating from the surface of the paper. The accuracy requirements of a standard angle device used as a scraper are reduced because the load on the device does not have to be changed while driving. Thus, there is also no danger of peak angle hysteresis, which reduces the yield accuracy. The accuracy requirements of the blade bar of the actual scraper blade are substantially reduced, because the bar does not have to be carried while driving. For these 20 reasons, even machining errors in the beam are easier to compensate with fine feeders. Since the amount of coating is not irradiated with a scraper blade, the blade geometry can be designed in such a way that the blade profile is facilitated without having to worry about the hysteresis phenomenon. This makes the profile setting of the blade more stable. The service life of the scraper blade is extended because the driving conditions around the blade are stable. The maximum angle of the beam also does not limit 25 loads.

The invention will now be examined in more detail by means of an exemplary embodiment according to the accompanying drawing.

påållystin according January 30 Figure kåsittåå arrow H direction of the rotating backing roll 15, the surface of which myotåilee påållystettåvå paper web 1. The underside of the backing roll 15 is positioned 3 91 298 tu in the transverse direction of the web 1 extends over the applicator 2 on top of the cross-section of approximately triangular support beam 11. The support beam 11 is a remedy for -from the bearing point 10 to the frame structures of the coater. The coating mass is fed into the chamber-like space 16 along the transverse feed channel 3 of the web 1 located on the inlet side of the web 1 of the support beam 11, from where the pulp pushes into the narrow feed channel 4 under pressure under the mass flow. Feed channel 4 Auke-aa to the base of the pre-cut blade 5. The feed channel 4 is very narrow compared to conventional feed channels, in particular the height of the mouth of the feed channel 4 is typically 3-5 mm.

10 The pre-leveling blade 5 is supported at its base between the blade supports 6 and 18. The blade 5 rests resiliently on the web 1 at a small angle α. The angle α is typically less than 20 °. The blade supports 6 and 18 are designed in such a way that no significant threshold is formed between the mouth of the feed channel 4 and the base of the blade 5. In particular, the blade support 18 on the side of the feed channel 4 is wedge-shaped in cross section, tapering towards the tip of the blade 5. The load 15 of the pre-leveling blade 5 can be adjusted by means of a load control device 7. The control device 7 is divided in the transverse direction of the track 1 into independent control zones, whereby the load of the blade 5 can be varied in the transverse direction of the track 1. Since the coating is fed at a high speed, more than 1 m / s, the paste also spreads in the incoming direction of the web 1.

20 This pasta transfer is collected in the first pasta trough 9. The pasta transfer from the actual scraper blade is in turn collected in the second pasta trough 8.

The coating is leveled on the web by a leveling device 14 comprising an actual scraper blade 12 attached to the second frame beam 17. The load on the scraper blade 12 can be adjusted 25 by a load adjusting device 13. As shown in Fig. 1 large, typically 0.5 to 0.8 m. In practice, this distance corresponds to a time delay of about 30-40 pis at typical web speeds.

According to the method of the invention, a coating such as that mentioned above is used in the following manner.

4

At the start of the run, the blade load of the leveling device 14 is set roughly to the desired coating value. As a leveling device, the so-called vakioteråkulma-scraper. The blade load of the leveling device is usually kept at the same starting value throughout the run. The final coating thickness is adjusted by varying the amount of application.

In the applicator device 2, the amount of coating applied to the web can in principle be adjusted in three ways, by changing the amount of coating mass fed through the channel 3, the blade pressure or the size of the return gap between the web and the applicator device. The best yield is obtained by changing the blade pressure or return gap. The applicator blade 5 is attached to the support beam 11 forming the body of the device by means of a load-adjusting device 7. In use, the applicator blade 5 at a small angle to the web 1 floats on the hydrodynamic mattress formed by the coating. A part of the material to be fed as a laminar flow to the web 1 passes from the gap between the blade 5 and the web 1 and remains on the web. The rest of the coating pushes back against the direction of movement H of the web 1.

15 It is advantageous to control the total amount of coating remaining on the web by changing the return gap. In this case, when the gap is enlarged, the back pressure of the return flow decreases and the amount of coating remaining on the web decreases correspondingly. As the return gap is reduced, the back pressure rises and increases the pressure in the coating mattress between the applicator blade 5 and the web 1. As a result of the increase in pressure, the blade 5 rises slightly upwards from the web and more than 20 coatings can flow with the moving web 5.

The same yield can be achieved by changing the blade pressure of the applicator blade 5. However, the adjusting device 7 of the applicator blade 5 can be used in addition to the yield of the amount of coating to be applied to the yield of the transverse profile of the amount of coating. The profile adjustment can be implemented with all blade holders with the possibility of profile adjustment, and since the adjustment directly affects the amount of coating applied to the web, the profile adjustment is more accurate and stable than with the scraper blade 12.

Large changes in the amount of coating during driving are made roughly by changing the steel load of the leveling device 14 30. Thus, according to the invention, the actual gram weight of the coating on the web is adjusted by a leveling device and by means of changes in the application rate, it is ensured that the final amount of coating remains exactly within the desired limits.

The candle angle α of the blade 5 can possibly even be less than 15 °. With the optimum result of the blade angle and the amount of coating, the use of the actual scraper blade 5 12 can be avoided at best.

After the lubricating device 2, a normal short-stay coater can also be used, by means of which the coating thickness can be increased.

Claims (5)

6 The patent claims that the Court should: A method of applying and leveling a coating on a moving web of material (1) against a rotating counter-roll (15), comprising: - an applicator device (2) having a leveling member (5) arranged in close proximity to the surface of the material web (1) - for applying the material, which smoothing member is a flexible blade (5) with a coarse angle α of less than 20 ° and a small mouthpiece 10 (4) which opens without a substantial threshold to the base of the flexible blade to allow rapid laminar feed flow, - in the direction of web (1) a spaced-apart leveling device (14) for applying at least one blade (12) which can be pressed against the web (1), which method applies at least the following measures: 20. the web (1) is applied with a coating device (2), and - the coating material is leveled on the web (1) on the blade of the leveling device (12), see that 11 u of the fact that 25 - the blade of the leveling device (12) the load is set at the start of the run to approximately the desired coating thickness and kept substantially constant during the run, and 30. the amount of coating applied to the web is obtained during the run by changing the amount of coating applied to the web by the applicator (2). 91298 7 A method according to claim 1, characterized in that the amount of coating to be applied by the applicator is irradiated by changing the distance between the applicator and the web (1) on the inlet side of the blade web. Method according to one of the preceding claims, characterized in that the amount of coating to be applied is changed in the transverse direction of the web in order to adjust the coating profile. A method according to claim 3, characterized in that the amount of the coating 10 to be fed is irradiated in the transverse direction by changing the blade profile of the blade (5) of the applicator device. A method according to claim 3, characterized in that the amount of coating to be applied is irradiated in the transverse direction by changing the profile of the amount of coating to be applied via the feeding members. δ