Painting method and apparatus of paint liquor to moving web

PATENT ATTORNEYS

A. GRÜNECKER

DLH-ING,

H. KlNKELDEY

DR INK *

W. STOCKMAIR

DR-ING - AeP (CALϊΈΟΗ »

K. SCHUMANN

DR BtaNAT. OPL FHYS

PH JACOB

DTPL-ING.

G.BEZOLD

Paper Converting Machine Company PO Box 889, Green Bay, Wisconsin 54305, United States

8th MUNICH 22

MAXIMIL LANDSCAPE - * 3

9th Kai 1978 P 12 615

Method and apparatus for applying a liquid coating to a moving web

The invention relates to a method and apparatus for applying a liquid coating to a moving web. It refers in particular to the so-called "source-free" coating. The invention therefore represents an improvement of the method according to US Pat. No. 3,695,221.

This document describes a device with which the foam formation in a swell-free coating system with an undercooked doctor blade is characterized

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is reduced by promoting the rapid flow of the coating liquid to minimize the shearing action developed by the inverted doctor - achieved by providing a guide or back wall at the liquid holding chamber very close to the coating roll , The back wall is provided with end walls which direct the outflow of excess liquid along the faces of the coating roll. In order to remove the Beschichtungsf liquid from the end faces and thus prevent fluid buildup and possible contamination of the bearings, wipers are arranged. Although the known device is effective in suppressing foaming in the coating liquid, which may result in spotted coating or printing, it has been found that the machine operators are unable to keep the wipers operational. For example, the wipers were not replaced when worn or did not adjust the wiper accurately, so that the flow fluid along the roll end surfaces on the journals and finally flowed into the camps.

To alleviate this problem, barrier-forming streaks were placed between the chamber end walls and the roll faces to prevent fluid flow to the roll faces. This resulted in reduced flow, so that in some cases the liquid had a tendency to trap air and eventually the liquid assumed a milk-shake-like consistency or foaming was present.

To avoid this drawback, a bore was introduced in the lower part of each end wall, which resulted in a higher flow rate of excess coating liquid and reduced the undesirable foaming. With the higher liquid access associated to achieve the greater flow rate, the liquid level height became so high that the liquid passed over the barrier strips

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spilled and in turn polluted the trunnions.

It was then decided to omit the end walls, so that the liquid can flow off quickly and thus contamination of the roll end faces and journals is avoided. This was less optimal because it did not give a uniform coating along the length of the coating roll. In particular, it was found that the rapid outflow of liquid from the liquid holding chamber (an open ended chamber) resulted in a level of liquid that was not uniform along the roll surface. So it lacked the end portions of the roller and thus the web edges of coating liquid.

Further attempts have been made to provide a partial end wall, ie an end wall, which does not completely close the gap. Although this could correct the level problem, there was still the problem that the roller end faces were soiled. This circumstance was further compounded by the fact that the liquid built up in the form of a bead or ring at the end of the roll and therefore left an unacceptable track on the web.

The problems associated with the foaming, non-uniform coating, unwanted beading and fouling of the roller end face are all solved according to the invention by arranging a device limiting the horizontal outflow of the excess coating liquid at a critical point within the source-free chamber. In particular, the restricting means is disposed slightly inward of the roll ends and provides a substantially uniform. Level height of standing in contact with the roller liquid along the length thereof, at the same time the foaming, beading and contamination of the roll end faces are avoided.

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The latter is particularly important, since this can be dispensed with the provision of wipers.

In summary, the invention provides a coating method and apparatus in which the horizontal flow of coating liquid near the ends of the coating roll is restricted or obstructed to avoid foaming due to the high liquid flow rates while preventing fouling of the roll bearings.

Embodiments of the invention are described below with reference to. Drawing explained in more detail. Show it:

1 is a fragmentary perspective view of a device constructed according to the invention,

FIG. 2 is an enlarged fragmentary perspective view (under a slightly different viewing angle) of the apparatus shown in FIG. 1; FIG.

FIG. 3 is a fragmentary end view of the chamber and roller portion of FIG. 1; FIG.

4 is a fragmentary plan view of the device of FIGS. 1 to 3,

Fig. 5 is a fragmentary rear view along the line 5-5 in Fig. 4, and

Fig. 6 is a substantially schematic end view of a modified embodiment of the invention.

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In the drawing, and in particular in Fig. 1, the frame of the machine for coating a web W (see Fig. 3) bears the general reference numeral 10. The means for applying the coating liquid to the web W comprises an applicator roll 11, which in frame 10 is rotatably supported in a suitable manner. The frame 10 also carries at 12 (see Fig. 1) pivotally a pressure roller 13 (which can also be seen in Fig. 3). A chamber 14 (see FIG. 3 and 4.) is provided for carrying the coating liquid to be applied to the web W. The chamber 14 is formed in part by a rear or rear vertical wall 15 which is shown in Figs. 1 and 2 in a maintenance or cleaning position, ie the wall 15 was from its position close to the roller 11 as shown in FIG pivoted.

In. 3, reference numeral 16 refers to a squeegee or scraper with reverse working angle provided on a part of the rear vertical wall 15. In particular, a holder 17 is suitably fixed to the lower portion of the wall 15 to hold the squeegee 16. A clamping plate connects the doctor blade 16 with the holder 17th The arrangement consisting of the elements 16 to 18 thus effectively closes off the lower end of the chamber 14 to such an extent that only a thin liquid film is metered onto the roller 11 by the doctor blade 16. Advantageously, the doctor blade 16 may be formed of a flexible plastic material so that it is readily interchangeable and can be clamped to the holder 17 in a substantially immovable position. It should be noted, however, that the ends of the chamber 14 are open so that the liquid introduced via the inlet 19 in the rear wall 15 (see Fig. 2) can exit at the end-side spaces 20 (see Fig. 4). The coating liquid emerging from the end-side openings 20 is collected in a basin 21 and returned to the inlet 19 via a pump (not shown) from the outlet 21a.

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The advantageous flow obstruction of the invention is formed in the illustrated embodiment by inserts 22 provided near the ends of the vertical wall 15 (see Figures 2 and 4). It has been found that the location of the inserts 22 is critical to achieving the beneficial effects. For example, For example, in a particular basting line having a roll length of about 1.5 m, the outboard end 22a of each particular insert 22 should be no less than about 8 to 10 mm from the end face 11a of the roll 11 (see Fig. 4). If the outside end of the insert 22 (which has a width of 20 mm and a thickness of 7 mm) is closer to the end face 11a, it has been found that the coating flow along the end faces 11a of the roller 11 and then on the bearing pins 11b and flows into the camps. A smaller distance does not eliminate the unwanted beading. A typical bead B is indicated in Fig. 4 at the upper right side.

Although the mechanisms by which the invention operates are not fully understood, it is believed, based on observations, that there is a unique fluid flow pattern described in connection with FIG. In this figure, an end portion of the roller 11 and the associated insert 22 can be seen. The profile P of the upper excess liquid is, as shown, within the peripheral region of the roller 11 and passes at the lower end, as indicated at R, in the main part of the outflowing excess liquid. As a result, the upper excess liquid is guided away from the end face 11a of the roller 11 and thus prevents contamination of the end face, while the flow velocity is maintained above the level leading to foaming.

The evolution of the beneficial liquid stream exiting over the lower portion of each open space 20 is further enhanced by the spacing of the pool end walls 24 from the

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Supported roller end faces 11a, which is of the order of about 60 to 75 mm in the illustrated embodiment and by which the occurrence of splashing is avoided. The basin end walls 24 are fastened to the frame 10 by screws 25.

Advantageously, the vertical end wall 15 extends beyond the end wall 11a of the roller 11 by a certain length. In a preferred embodiment, this overhang is about 5 to 10 ram. "

For optimum performance, it has been found that maintaining a minimum distance between the opposite face 22b of the insert 22 and the nearest point of the circumference of the roll 11 is important. For most coating liquids (with viscosities in the range of 10 to 100 centipoise - pressure and flexographic inks as well as acrylic lacquers), the distance S (see Fig. 3) should be about 2 to 3 mm. For coating liquids with higher viscosity, eg with viscosities greater than 100 centipoise, the distance S (eg, by partially pivoting away the rear wall 15) can be increased to about 5 to 8 mm. Thus, the flow obstruction can be rapidly changed to compensate for viscosity changes. However, other types of constraining inserts 22 that provide this adjustment feature may also be used. Advantageously, the inserts 22 are made of a resilient plastic material, so that in the event that the distance adjustment is not accurate and the insert is incident on the roller 11, no damage occurs.

For a given installation, the inserts 22 should have a width and thickness (in conjunction with the distance from the roll end) to obtain the profile P, rather than one that rolls around the roll 11 and onto the end face 11a.

The length of the inserts 22 is such that they extend sicfi above the liquid level and the opposite surface

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of each insert 22 may, if desired, be formed by thickening to conform to the circumference of the roll. As a result, however, no significant advantage is achieved, so that the simpler flat thin inserts are preferred for economic reasons and because of the easier adjustability. For example, it was determined that the inserts 22. are effective to maintain a uniform fill level of the order of 50 to 80 mm above the doctor blade 16 when the web running speed is about 350 m / min, above this speed slightly higher liquid levels above the doctor blade 16 are required to avoid liquid depletion at the edge portions to avoid the web W. A flow rate suitable for most conventional coating operations is in the range of 5 to 40 l / min, depending on the size of the machine, capacity of the paper, viscosity and the like.

In practice, in the invention, the rear vertical wall 15 is pivoted away from its close relationship to the roller 11, that is, in the position shown in Figs. 1 and 2. For this purpose, the wall 15 at 26 (see Fig. 2 to 4) is equipped with arms which are fixed to a rotary shaft 27. The rotary shaft 27 is in turn supported by blocks 28 which are supported by pivot arms 29. The inserts 22 can by means of countersunk screws 30 (see FIG. 2) are installed so that their distance position relative to the roller 11 is optimal. Thereafter, the wall 15 is pivoted to the position shown in Figs. 3 and 4 and entered into the chamber 14, the coating liquid. The web W passes through the nip between the rollers 11 and 13 and is coated in a controlled manner with the amount of coating liquid which adheres to the roller 11 after passing the squeegee 16. The excess coating liquid exits at the end chambers and is collected in the basin 21 to be recirculated (usually after filtration) via the outlet 21.

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As already mentioned, the inserts 22 perform several functions simultaneously due to their special arrangement. Once the inserts are responsible for maintaining a suitable level profile or level of coating liquid along the surface of the roller 11, so that a lack of liquid at the edges of the web W is avoided. The inserts are further responsible for ensuring that the upper excess liquid follows the profile P and exits at the lower portions of the open spaces 20 and does not flow around the edge of the roll 11 and onto the end faces 11a. At the same time, the spray or shear caused by the exiting coating liquid effectively prevents any tendency of the ink to form a bead, as indicated at 23 in FIG.

The invention is not limited to the use of reverse angle squeegees, but may also be advantageously used in conjunction with conventionally arranged squeegees according to FIG. In this figure, reference numeral 111 refers to the metering roller which cooperates with a conventional doctor blade 116. The inserts are numbered 122 and are again provided as part of the rear vertical wall 115. In the illustration of FIG. 6 it is an offset printing by a transfer roller 131 is disposed between the metering roller 111 and the pressure roller 113. In Fig. 6, the web W runs to the right so that its running direction is parallel to the running directions of the contacting portions of the rollers 113 and 131 to provide a direct spin coating. In the arrangement of FIG. 3 Although the web W in turn moves to the right, but it runs because of the different direction of rotation of the roller in the opposite direction to this; this is the application of the invention in a coating process with opposite direction of rotation. Therefore, the squeegee can either have an inverted angular position or be arranged in a conventional manner, and the relationship between applicator roll and web can be either direct or counter-rotating, retaining the advantages of the invention in all approaches.

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