Coating blade for finishing the surface of paper and cardboard

Abstract

A coating blade for directly or indirectly applying a liquid or pasty coating medium to a web of material is proposed, the blade having a bevel on its underside to improve the elasticity and flexibility in the region of an end face (7). This drastically reduces the number of scratches on the surface of a web of material to be finished.

Description

[0001]Applicant: Clouth Sprenger GmbH Johann-Clouth-Straße 1-5 42499 Hückeswagen 10730002WO 06.10.2023 THE / BRK Title: Coating blade for the surface finishing of paper and cardboard Description The invention relates to a coating blade for the direct or indirect application of a liquid or pasty coating medium to a moving web of material. This refines the surface of the web of material and / or improves its usage properties. Such coating blades are also referred to as "coating blades". They are primarily used for the surface finishing of moving webs of paper or cardboard. For this purpose, a calcium carbonate water mixture is usually applied to the web of material by a stationary coating blade. ^ The coating blade is mounted in such a way that it rests with a certain pre-tension or spring force on the web of material or a roller which supports the web of material, or directly on the roller. The tip of the coating blade rests on the web of material orthe roller underneath. This arrangement is known per se. It is referred to in expert circles as a "bent blade" arrangement. A coating blade in a bent blade arrangement is known from DE 29619 507 U1. For an explanation of the functioning of such a coating blade, reference is made to DE 29619 507 U1. A gap forms between the roller and the front part of the coating blade, through which the liquid or pasty coating medium passes during the coating curtain when the web moves relative to the coating blade. This occurs due to the Newton's adhesion condition. A small portion of the coating medium located in the gap is pressed into the surface of the web. The coating blade, which exerts a certain spring force on the web due to its elasticity, presses the coating medium into the surface of the web and simultaneously smoothes the surface of the web or the coating medium.This results in a very smooth surface on the web after it has been coated with the coating medium and the surface of the web has been finished in this way. One problem is that in practice the coating medium often consists of a calcium carbonate water mixture with a solids content of often more than 60%. This results in small scratches or tiny marks on the surface of the finished web, which are ultimately due to agglomeration of the solids in the coating medium. These scratches or marks are undesirable because they reduce the quality of the surface of the finished web or limit its use. The surface of finished webs, which are usually wound onto a drum or roll and whose surface has been finished with a conventional coating blade, often has more than 5,000 scratches or tiny marks per roll.The invention is based on the object of providing a coating blade which makes it possible to significantly reduce the number of markings and scratches in finished surfaces of webs of material and thereby significantly improve the quality of the finishing or the surface finish of the finished webs of material. This object is achieved according to the invention by a coating blade for an application device for the direct or indirect application of a liquid or pasty coating medium to a moving web of material, in particular a paper web or a cardboard web, wherein the coating blade comprises a base body made of steel, wherein the base body has an end face, a bottom side and an upper side, wherein the top side faces the web of material during operation, and wherein a bevel is formed on the underside of the base body. The base body is usually made of an iron material, in particular a carbon-containing steel (spring steel) or stainless steel.The material of the base body must have a certain degree of elasticity, as the coating blade is bent during operation to provide a spring force. This spring force serves to work the pasty coating medium into the surface of the web and smooth the surface. In addition, the spring tension of the coating blade can be used to adjust the thickness of the gap between the counter roller or web, the coating blade, and the pasty coating medium present between the web and the coating blade. A stationary equilibrium is established between the counter roller or web, the coating blade, and the coating medium; similar to a hydrodynamic plain bearing. According to the invention, a chamfer is formed on the underside of the base body, i.e. on the side of the base body facing away from the web. Alternatively or additionally, it is also possible to form a counter chamfer on the top side of the base body.In any case, the formation of the bevel has the effect that the coating blade becomes thinner and thus more elastic towards its end. The contour / profile of the coating blade according to the invention has surprisingly shown the effect of reducing the number of scratches or marks in the surface of a web of material from more than 5,000 to fewer than 100. This drastic improvement in quality can be explained by the fact that the greater flexibility in the area of ​​the tip allows agglomerates that form under the blade due to the speed difference and prevailing pressure to pass through more easily. As a result, any agglomerates that form can pass through the gap before reaching a critical size or before (negatively) affecting the surface. The formation of such adhesions and agglomerates is further complicated by the polished end face.Due to the flexibility of the coating blade at its very last end, where the coating blade has the most intensive contact with the web or the counter roller, the former can move away relatively easily if there is an agglomeration of solids in the pasty coating medium. Due to the flexibility of the coating blade in the rear area of ​​the gap between the counter web and the coating blade, these agglomerates can be transported more easily through the gap so that they do not get stuck there and cause scratches or marks. It has proven advantageous if the angle α between the underside and the bevel is in a range between 4° and 15°, preferably between 5° and 12°. Even this comparatively small angle between the underside of the bevel and the comparatively short length of the bevel has already brought about a significant reduction in scratches or marks in the finished surface of the web.The chamfer can be created, for example, by grinding. It has also proven sufficient to use a length L. Fthe bevel is at least 0.5 mm, preferably 0.7 mm, or 0.9 mm. A further reduction in the number of scratches and marks results if the front side of the coating blade is polished. Due to the polished surface of the coating blade, the agglomerates mentioned above adhere less well to the coating blade. Simply by polishing the front side of the coating blade, the number of scratches and marks in the finished surface of a web of material could be reduced by around 50%! Naturally, the combination of a bevel on the underside or top side of the base body and the polishing of the front side of the coating blade is particularly effective. However, both inventions can also be used individually. It has also proven advantageous if an angle β between the underside and the front side of the coating blade lies in a range between 85° and 95°.In some applications, it is advantageous if the angle β is less than 90°, preferably less than 89°. In some applications, it has proven advantageous if the angle β is greater than 90°, preferably greater than 91°. The selection of the angle β - like the other parameters - must be determined through application tests. It depends on the web to be finished, but also, of course, on the consistency and properties of the coating medium. It is also possible to form a counter bevel on the upper side of the coating blade in an area adjacent to the front side, whereby the counter bevel and the underside enclose an angle γ that lies in a range between 2° and 12°, preferably around 4°. This has also been shown to improve the quality of the surface of the finished web. It has proven advantageous if the length of the counter bevel is at least 0.4 mm, but preferably 0.5 mm, 0.7 mm or even 0.9 mm.The service life of the coating blade according to the invention is extended if a wear-resistant layer is present on its upper side, and this wear-resistant layer consists of a ceramic, a carbide material, or a composite material made of ceramic and metallic materials (cermet). If the coating blade has a wear-resistant layer on its upper side, it is advantageous if the upper side of the base body (not the upper side of the coating blade) and the underside of the base body form an angle δ of between 2° and 6°. An angle δ of 4° has proven particularly advantageous. This also achieves a certain decrease in the flexural rigidity of the coating blade towards the end face, and this also allows the number of scratches and small marks in the surface of the finished web to be reduced. Advantageous thicknesses of the coating blade and the wear-resistant layer are specified in the subclaims.At this point, it should be pointed out again that it is also possible to polish a conventional bent-blade coating blade only on the end face in order to achieve the desired reduction in the number of scratches and marks in the surface of the finished web. The applicant reserves the right to file a separate patent application for this invention. Further advantages and advantageous embodiments of the invention can be found in the following drawing, its description, and the patent claims. Drawing Shown are: Figure 1: a bent-blade coating blade according to the prior art; Figure 2: an embodiment of a coating blade according to the invention; and Figure 3: a greatly enlarged view of the area of ​​a coating blade according to the invention. Description of the Embodiments Figure 1 shows a coating blade known from DE 29619 507 U1. The coating blade has the reference numeral 5 as a whole.The coating blade known from the prior art comprises a first region 1, the material thickness of which is greater than that of a second region 2. An end face 7 forms the "front" end of the coating blade 5. The coating blade 5 is straight in its relaxed state (not shown). In the state shown in Figure 1, it is mounted in such a way that it is bent (so-called "bent blade"). This results in the first region of the coating blade 5 exerting a spring force in the direction of arrow 9 on an applicator roller 3. The upper side of the coating blade 5 has the reference numeral 17. The upper side 17 forms a gap 11 with the cylindrical surface of the applicator roller 3. When the applicator roller 3 moves past the stationary coating blade 5 in the direction of the arrow, the generally cylindrical surface of the applicator roller 3 entrains the coating medium and moves it through the gap 11.During direct coating, the spring force acting from the coating blade 5 on the application roller 3 in the direction of arrow 9 causes the coating medium to be worked into the surface of the web to be finished. In both direct and indirect coating, the coating blade 5 smooths the coating medium onto the web or the application roller 3. During direct coating, the web to be finished (not shown) runs over the application roller 3. During indirect coating, a pasty or liquid coating medium is applied to the web (paper web) and reduced to the desired thickness by the coating blade. This is well known to those skilled in the art. In both cases, the pasty coating medium (not shown) is located in the gap 11 between the application roller 3 and the coating blade 5.By rotating the application roller 3, it moves, along with any web material located thereon, relative to the coating blade 5 and is thereby evenly coated with the coating medium in a conventional manner. This refines the surface of the web material. Figure 2 shows a coating blade 5 according to the invention. Here, the first region 1 does not have an increased material thickness or thickness, as is known from the prior art. Rather, a chamfer 13 is formed on the underside 15 of the coating blade 5 in the first region 1. The chamfer 13 ends at an end face (see Figure 3) of the coating blade 5. This leads to a reduction in the thickness of the coating blade 5 in certain areas.The upper side 17, together with the cylindrical surface of the application roller 3, forms the aforementioned gap 11 through which the coating medium is conveyed when the application roller 3 moves past the stationary coating blade 5 in the direction of the arrow. The coating medium is also not shown in Figure 2. The thickness of the gap 11 depends, among other things, on the viscosity of the coating medium, the peripheral speed of the application roller 3 and the spring force of the coating blade 5 as well as on the machine settings. Figure 3 is an enlarged view of area 1 of the coating blade 5 according to the invention. The special geometric features of the invention will now be explained with reference to this enlarged view. The end face of the coating blade 5 is designated 7. The coating blade 5 comprises a base body 21 made of a proprietary material, preferably a steel with elastic properties (spring steel).Very frequently, stainless steels are also chosen as the material for the base body 21 due to their corrosion resistance. An upper side of the base body (not of the coating blade 5) is designated 23. A wear-resistant layer 25 is applied to this upper side 23, which in turn forms the upper side 17 of the coating blade 5. According to the invention, a chamfer 27 is formed on the underside 15 of the coating blade 5. The chamfer 27 results in the thickness of the coating blade 5 being at a minimum in the area of ​​the end face. The angle α between the underside 15 and the chamfer lies in a range between 4° and 15°; in the illustrated embodiment, it is approximately 9.5°. A length L. FIn the illustrated embodiment, the bevel is approximately 0.65 mm. An angle β between the underside and the end face 7 lies in a range between 85° and 95°. In some applications, it is advantageous if the angle β is less than 90° and greater than 85°. In other applications, an angle β greater than 90° and less than 95° is advantageous. The angle β can also be 90°. Surprisingly, experiments and tests have shown that the bevel 27 according to the invention leads to a significant improvement in the quality of the surface of a web of material. When a web of material is coated, small, undesirable scratches and marks occur. They are presumably due to agglomerates of the solids or particles present in the coating medium. If these agglomerates are pulled through a gap 11 that is too narrow, they cause the undesirable scratches and marks.The inventive bevel 27 on the coating blade 5 drastically reduces the number of scratches and marks. From more than 5,000 per web to fewer than 100! This results in a significant improvement in the surface quality of the finished web. In addition, the reject rate and the number of operational disruptions are reduced. There are various explanations for these advantageous effects. One approach assumes that the coating blade 5 is more flexible in the area of ​​the end face due to the bevel, so that agglomerates can pass through the gap 11 more easily. Independently of this, the effectiveness has been proven through various tests and their evaluation. It can also be advantageous if a counter-bevel 29 is formed on the upper side of the coating blade 5, which forms an angle γ with the underside 15 in the range between 2° and 12°, preferably 4°. The length of the counter-bevel L. GFis usually 0.4 mm or more. It is often advantageous if it is 0.5 mm, 0.7 mm or 0.9 mm. In most applications, a wear protection layer in the form of a coating is present on the upper side 17 of the coating blade. This wear protection layer can consist of a ceramic, a carbide material or a composite material made up of ceramic and metallic materials. In order to further optimize the coating blade 5, it can be advantageous if the upper side 23 of the base body and the underside of the base body or the coating blade 5 enclose an angle δ which is between 2° and 6°, but preferably 4°. The counter bevel moves the narrowest point of the gap 11 from the front side into the gap so that the scratches and markings caused by the agglomerates can subsequently be smoothed out.The object underlying the invention is also achieved to a substantial extent by a surface finishing coating blade comprising a base body made of steel, wherein the base body has an end face, a bottom face and an top face, wherein during operation the top face faces the paper or cardboard to be finished, wherein the top face has an optional wear-resistant coating at least in some areas, and wherein the end face is polished. Tests have shown that by polishing the end face of a coating blade 5, the number of scratches and marks is reduced by approximately 50%, even if the coating blade does not have a bevel on the bottom face. List of reference numerals 1 first region 2 second region 3 application or counter roller 5 coating blade 7 end face 9 arrow 11 gap 13 bevel 15 bottom face 17 top face 19 - 21 base body 23 top face of the base body 25 wear-resistant coating 27 bevel α angle between the 15 and bevel 13 L. FLength of the chamfer β Angle between bottom side 15 and d face 7 29 Counter chamfer γ Angle between bottom side 15 and counter chamfer 29 L GF The length of the counter bevel δ angle between the top side 23 of the base body and the bottom side 15 of the base body or the coating blade 5

Claims

Patent claims 1. Coating blade for an application device for the direct or indirect application of a liquid or pasty coating medium to a moving web of material, in particular a paper web or a cardboard web, wherein the coating blade (5) comprises a base body (21) made of steel, wherein the coating blade (5) has an end face (7), an underside (15) and an upper side (17), wherein a bevel (13) is formed on the underside (15) of the coating blade (5).

2. Coating blade according to claim 1, characterized in that an angle (α) between the underside (15) and the bevel (13) lies in a range between 4° and 15°, preferably between 5° and 12°.

3. Coating blade according to claim 1 or 2, characterized in that a length (LF) of the bevel (13) is at least 0.5 mm, preferably 0.7 mm or 0.9 mm.

4. Coating blade according to one of the preceding claims, characterized in that the end face of the coating blade (5) is polished.Spreading blade according to one of the preceding claims, characterized in that an angle (β) between the underside (15) and the front side lies in a range between 85° and 95°.

6. Spreading blade according to claim 4, characterized in that the angle (β) between the underside (15) and the front side (7) is less than 90°, preferably less than 89°.

7. Coating blade according to claim 4, characterized in that the angle (β) between the underside (15) and the end face (7) is greater than 90°, preferably greater than 91°.

8. Coating blade according to one of the preceding claims, characterized in that a counter-bevel (29) is formed on the upper side (17) of the coating blade (5) in a region adjoining the end face (7).

9. Coating blade according to claim 8, characterized in that the counter-bevel (29) and the underside (15) enclose an angle (γ) between 2° and 12°.

10. Coating blade according to claim 8 or 9, characterized in that a length (L GF) of the counter bevel is 0.4 mm, preferably 0.5 mm, 0.7 mm or 0.9 mm.

11. Coating blade according to one of the preceding claims, characterized in that the base body (21) has an upper side (23), and that on the upper side (23) of the base body (21) there is a wear protection layer (25) which forms the upper side (17) of the coating blade (5), and that the wear protection layer (25) consists of a ceramic, a carbide material or a composite material made of ceramic and metallic materials.

12. Coating blade according to claim 11, characterized in that the upper side (23) of the base body (21) and its underside (15) enclose an angle (δ) between 2° and 6°, preferably 4°.

13. Coating blade according to claim 11 or 12, characterized in that a thickness of the wear protection layer (25) in the region of the end face (7) is greater than 0.1 mm.

14. Spreading blade according to one of the preceding claims, characterized in that the spreading blade (5) has a thickness (D) of more than 0.2 mm on the end face (7).

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