FI121189B - Edge Guide and Method for Extending the Life of Curtain Edge Edge Guide - Google Patents

Description

Edge Controller and Method for Extending the Operating Time of an Edge Controller for Curtain Coating

The present invention relates to an edge guide for guiding a curtain coating web 5 to a point of impact of a web to be coated, which edge guide includes a suction slot arranged in the region of its trailing edge, the lower edge of which forms the lower lip.

As coated paper types and coatings become more common, increasing demands are placed on the coating processes and equipment. In coating, more specifically in pigment coating, a coating / coating composition layer is formed on the surface of the paper, followed by drying of excess water. The formation of the coating composition layer can be divided into the export of the coating composition to the surface of the paper, i.e. application, and the adjustment of the final amount of coating composition. The most important pigment coating method is the so-called blade coating, in which the amount of coating is adjusted by means of a so-called doctor blade. The most common types of blade coating stations are a blade roller with a brush roller and a blade coating with a nozzle application. In addition, the coating utilizes the so-called "infiltration head" which has become more common in the last 20 years. Similarly, curtain coats are becoming a new technology.

Curtain coaters can be divided into slot-fed or slide-fed coatings. In a flat-feed curtain coater, the coating is fed by means of a nozzle assembly to an inclined plane along which the overlay extends toward the edge of the plane forming the feed lip, whereby the curtain is formed as the coating drips from the feed lip. In slit-fed appliqué beams, the coating is pumped through a distribution chamber into a narrow vertical slot, with a lip forming a curtain and dripping onto the web. The coating may be applied in one or more layers.

The resulting curtain is held at its full width up to the point of impact by an edge guide located, as its name suggests, on the edge of the feed slot / feed lip.

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There are a number of different types of paper and board, and they can be divided into two classes by basis weight: single-ply paper with a basis weight of 25-300 g / m 2 and paperboard made with a multilayer technology and 100-600 g / m 2. As noted, the boundary between paper 5 and board is sliding, since the lightest board is lighter than the heaviest paper. Usually paper is used for printing and cardboard for packaging. The paper and board may be coated or uncoated.

10 The following descriptions are examples of currently used values for coated fiber webs and may exhibit considerable variations in the values given. The descriptions are mainly based on Papermaking Science and Technology, part Papermaking Part 3, Finishing, ed. Jokio, M., published by Fapet Oy, Jyväskylä 1999, 361 pages.

LWC (Light Weight Coated) Paper contains 40-60% mechanical pulp, 25-40% bleached softwood pulp and 20-35% fillers and fillers. Common values for LWC paper include: basis weight 40-70 g / m2, Hunter gloss 50-65%, PPS S10 roughness 0.8-1.5 pm 20 (offset) and 0.6-1.0 pm (rot), density 1100-1250 kg / m3, brightness 70-75% and opacity 89-94%.

Generic values for machine finished coated MFC paper are: 50-70 g / m2 basis weight, Hunter gloss 25-70%, PPS S10 roughness 25 2.2-2.8 pm, density 900-950 kg / m3, lightness 70 -75% and opacity 91-95%.

Common values for FCO (film coated offset) paper are: 40-70 g / m2 basis weight, Hunter gloss 45-55%, PPS S10 roughness 1.5-2.0 pm, density 1000-1050 kg / m3, brightness 70-70 75% and opacity 91-95%.

Common values for MWC (medium weight coated) paper are: 70-90 g / m2, Hunter gloss 65-75%, PPS S10 roughness 30 3 0.6-1.0 μηι, density 1150-1250 kg / m3, lightness 70-75% and opacity 89-94%.

The HWC (heavy weight coated) has a basis weight of 100-135 g / m2 and can be coated even more than twice.

In coated pulp-free wood-free printing papers, i.e. fine paper (WFC), the amount of coating varies greatly according to requirements and application. The following are typical values for once and twice 10 coated pulp-based printing papers: 90 g / m2 coated once weight, Hunter gloss 65-80%, PPS S10 roughness 0.75-2.2 pm, brightness 80-88% and opacity 91-94% and double coated, 130 g / m 2, Hunter gloss 70-80%, PPS S10 roughness 0.65-0.95 µm, brightness 83-90% and opacity 95-97%.

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Cartons form a highly heterogeneous group, including high-weight species up to 500 g / m2 and low weight species up to about 120 g / m2, ranging from primary to up to 100% recycled fiber-based and coated . Coated board is: - Primary fiber based (FBB = folding boxboard), SBS (solid bleached board), Liquid packaging board (LPB), coated white top liner, carrier board 25 (WLC = White Lined Chipboard, Recycled Cardboard).

In principle, curtain coating is suitable for the production of all of the above types of coatings. The curtain coating does not achieve the same smoothness as the blade coating, but the coverage achieved by it is better than the blade coating.

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When using curtain coating, one of the problems is the limitation by the edge guides to the duration of the coating process. The shapes and surface materials of the edge guides vary considerably, as do the shapes of the lower or trailing edge of the edge guide and the possible suction arrangements. A commonly used solution 5 is to provide suction at the trailing edge to squeeze out a larger amount of coating material flowing along the edge guide and to remove the edge liquid used to improve curtain adherence. One such prior art solution is schematically illustrated in Fig. 1, in which the edge guide of the coating material web 11 is designated by reference numeral 4. A suction slot 5 for suction chamber 6 is provided at the lower end or at the trailing edge of the edge guide forms a lower lip 7. Reference numeral 1 denotes a coated portion of a web and reference numeral 3 a support surface, e.g. a roll. Known solutions generally perform well on test machines and by far on production machines, with continuous run cycles of up to a few hours. The problem with long-term continuous coating is the drying agent on the lower lip of the suction nozzle. This dried coating material interferes with the removal of the curtain from the edge guide, causing problems with the operation of any edge bar removal means. When the amount of coating material to dry becomes sufficiently large, it blocks the suction slot, whereby a greater amount of coating material and edge lubricant flowing along the edge guide are directed directly to the web, causing a multiple coating amount to be applied to the edge of the coating. This overcoat coating does not dry during the drying of the coating machine but adheres to the surface of the rolls in contact with the wet coated web. With known solutions, the running times vary, e.g., from about a couple of hours to about 8 hours, depending on the composition of the coating agent, viscosity.

It is an object of the present invention to provide an edge guide solution that can significantly extend the duration of the coating process, up to more than 30 times, whereby the difficult coating agents can increase from about a few hours to about 20 hours and light coatings from about eight to about 80 hours.

To achieve this goal, the edge guide of the invention is characterized in that the lubricating fluid is provided with lubricating fluid supply means which guide the lubricating fluid to the lower lip area of the aspirator, preventing the coating material from drying to the lower edge of the aspirator.

In the following, the invention will be described in more detail with reference to the accompanying drawings, in which: Figure 1 shows a prior art edge guide, and Figure 2 shows a schematic view of an edge guide according to the invention, Figure 3 shows a partial magnification of Figure 2.

According to Figure 2, the edge guide 4 of the coating material web 11 according to the invention includes a lubricating fluid supply slot 9, which is tracked on the lower lip 7 of the suction slot 5 to which the lubricating fluid is directed from the lubricating fluid space 8. The lubricant is directed to the suction slot 5 by means of a feed slot 9 located at the tip of the lower lip 7 so that it lubricates the suction opening at the lower lip, preventing the coating agent from drying there. The lubricant is supplied over the entire width of the feed slot 9 at a flow rate such that it flows substantially without jetting out of the feed slot, leading mainly to suction slot 5. This is achieved by dimensioning the slot width of at a calm flow that does not cause the flow rate to rise so high that the liquid would spray out of the feed slot. Preferably, the fluid space 8 has a gap width of about 1 mm for the mouth 30, and a feed slot outlet opening preferably for the order of about 0.1 to 0.5 mm. These dimensions are only indicative and depend, e.g. the amount of lubricant feed required. The apex portion of the lower lip is shaped such that the coating of the coating material is cut off from the tip and does not turn beneath it. The lower lip of the suction nozzle is preferably coated on its outer and / or inner surface with a coating agent repellent. The upper edge of the suction gap may also be coated with such a coating agent repellent 5 which may be based, for example, on polytetrafluoroethylene.

Preferably, the lubricant is supplied cooler than ambient temperature, thereby causing swelling of the lower lip 7, which contributes to preventing the coating agent from adhering to the lower lip surfaces. The peripheral fluid 12, 10 flowing along the edge guide 4, which is sucked into the suction slot, extends substantially along the upper edge of the suction slot 5, thereby maintaining the upper edge substantially free of coating material without the need for additional lubricant.

The solution of the invention provides an improved solution in terms of usability and reliability, which allows the duration of the continuous coating process to be multiplied by several times compared to current solutions. The solution according to the invention is particularly suitable for dry-edge coating, but it can also be used for over-edge coating.

Claims (6)

1. Edge guide for guiding a coating medium curtain (11) formed during ridging coating to the impact point on the web (W) to be coated, to which edge guide (4) belongs a suction gap (5) arranged below its rear edge, The rear edge forms a lower lip (7), characterized in that, in connection with the suction gap, lubricant feeding means (8, 9) are provided which guide lubricant to the area of the lower lip (7) of the lubricant fluid preventing the coating from drying suction gap lower lip. 10 2. Edge guide according to claim 1, characterized in that the lubricant supply means comprises a lubricant liquid space (8) formed below the suction slot which opens into a lubricant gap (9) arranged in the tip portion of the lower lip (7). extends substantially along the entire width of the lower lip. 3. Edge guide according to claim 2, characterized in that the feed slot (9) is arranged to direct lubricating fluid so that it is directed substantially to the suction slot (5). 20 Edge guide according to any of the preceding claims, characterized in that the lower lip (7) of the suction gap is coated on its outer and / or inner surface with a repellent repellent. 25 5. A method for extending the operation time of an edge guide for a coating agent (11) formed during ridging coating, to which edge guide (4) includes a suction gap (5) arranged below its rear edge, which rear edge forms a lower lip (7), characterized in that used in the process in connection with the suction slot for lubricant supply means (8, 9) which control lubricant in the area of the lower lip (7) of the lubricant fluid preventing the coating agent from drying on the lower lip of the suction slot. The method according to claim 5, characterized in that the lubricant supply means used in the process belongs to a lubricant space (8) formed below the suction slot (8), which opens into an apex portion of the lower lip (7). lubricant supply gap (9) extending substantially along the entire width of the lower lip, and lubrication fluid being measured over the entire width of the supply gap (9) at such a flow rate that it flows substantially without ejecting from the supply gap and controlled suction slot (5).