Coating knife for finishing surfaces of paper and paperboard

Abstract

The invention relates to a coating knife for directly or indirectly applying a liquid or pasty coating medium to a web. The bottom surface of the coating knife is provided with an inclined surface, so that the elasticity and the flexibility near the end surface (7) are improved. This greatly reduces the number of scratches at the surface of the coil to be finished.

Description

TECHNICAL FIELD

[0001] The present invention relates to a coating blade for directly or indirectly applying a liquid or paste-like coating medium to a moving web. The coating blade finishes the surface of the web and / or improves the performance characteristics of the web. Such coating blades are also referred to as "coating blades". They are mainly used to finish the surface of a moving paper web or a moving paperboard web. For this purpose, a mixture of calcium carbonate and water is usually applied to the web using a stationary coating blade. BACKGROUND

[0002] The coating blade is mounted in such a way that it is placed with a certain pre-tension or elastic force against the web or against a roller supporting the web or directly against the roller. The tip of the coating blade is placed against the web or against the underlying roller. This arrangement is well known. In the technical field, this arrangement is referred to as a "bent blade" arrangement.

[0003] A coating blade in a bent blade arrangement is known from DE 296 19 507 U1. For a description of the functioning of such a coating blade, reference is made to DE 296 19 507 U1.

[0004] A gap is formed between the roller and the front part of the coating blade, through which the liquid or paste-like coating medium passes during the coating process when the web is moved relative to the coating blade. This is due to the Newtonian adhesion force. A small portion of the coating medium in the gap is pressed into the surface of the web. The coating blade exerts a certain elastic force on the web using its own elasticity, which presses the coating medium into the surface of the web and at the same time smoothes the surface of the web or the coating medium. This results in a very smooth surface of the web after it has been coated with the coating medium and thus finished.

[0005] One problem is that in practice the coating medium usually consists of a mixture of calcium carbonate and water, wherein the solids content usually exceeds 60%. Fine scratches or micro traces occur on the surface of the finished web, which are ultimately caused by the agglomeration of the solids in the coating medium. These scratches or traces are undesirable because they reduce the quality of the surface of the finished web or limit the usability.

[0006] The finished web is usually wound onto a reel or spool and the surface of the finished web, which has been finished with a conventional coating blade, usually has more than 5000 scratches or micro traces per reel. SUMMARY

[0007] The present invention is based on the object of providing a coating blade which makes it possible to significantly reduce the number of traces and scratches in the finished surface of the web and thus significantly improve the quality of the finish or the surface quality of the finished web.

[0008] According to the invention, this object is achieved by a coating knife for an application device for directly or indirectly applying a liquid or pasty coating medium to a moving web, in particular a paper or cardboard roll, wherein the coating knife comprises a base body made of steel, wherein the base body has an end face, a bottom face and an upper side face, wherein during operation the upper side face faces the web, and wherein a bevel is formed at the bottom face of the base body.

[0009] The substrate is typically made of a ferrous material, particularly carbon steel (spring steel) or stainless steel. The substrate material must have a certain degree of elasticity, as the coating knife flexes during operation to provide the spring force that forces the paste coating medium into the surface of the web and smoothes it.

[0010] Furthermore, the thickness of the gap between the counter roller or web, the coating knife, and the paste coating medium between the web and the coating knife can be adjusted by the elastic tension of the coating knife. A static equilibrium is established between the counter roller or web, the coating knife, and the coating medium; similar to a hydrodynamic sliding bearing.

[0011] According to the present invention, a bevel is provided on the bottom surface of the substrate, i.e., on the side of the substrate facing away from the web. Alternatively or additionally, a counter-bevel may also be formed on the upper side of the substrate. In any case, the formation of the bevel has the effect of making the coating knife thinner and, therefore, more flexible towards the end face of the coating knife.

[0012] The profile / profile of the coating knife according to the invention surprisingly shows the effect of reducing the number of scratches or marks at the surface of the web from more than 5000 to less than 100.

[0013] This significant improvement in quality can be explained by the fact that the increased flexibility in the tip area allows agglomerates that form under the blade due to velocity gradients and prevailing pressure to pass more easily. Thus, the agglomerates that form can pass through the gap before reaching a critical size or (negatively) affecting the surface. Polishing the end face further complicates the formation of such deposits and agglomerates.

[0014] Due to the flexibility of the coating knife at its extreme end, where it is in closest contact with the web or the counter roller, the coating knife can be moved relatively easily if solid agglomerates are present in the pasty coating medium. Due to the flexibility of the coating knife in the rear region of the gap between the counter web and the coating knife, these agglomerates can be conveyed more easily through the gap, thus preventing them from getting stuck and causing scratches or marks.

[0015] It has proven to be advantageous if the angle α between the base surface and the inclined surface is in the range from 4° to 15°, preferably in the range from 5° to 12°.

[0016] Even these relatively small angles between the base of the bevel and the relatively short length of the bevel already result in a significant reduction of scratches or marks in the finished surface of the coil.The bevel may be formed, for example, by grinding.

[0017] It has also been shown that if the length of the inclined plane L F A thickness of at least 0.5 mm, preferably 0.7 mm or 0.9 mm, is sufficient.

[0018] A further reduction in the number of scratches and marks is achieved if the end face of the coating knife is polished. Due to the polished surface of the coating knife, the above-mentioned agglomerates adhere poorly to the coating knife. Simply by polishing the end face of the coating knife, the number of scratches and marks in the finished surface of the coil can be reduced by approximately 50%.

[0019] Certainly, the bottom surface of substrate or the bevel at upper side place are combined with the polishing of the end face of coating knife and effect is particularly remarkable.Yet these two inventions also can be used separately.

[0020] It has proven advantageous if the angle β between the bottom surface and the end surface of the coating knife is in the range of 85° to 95°. In certain applications, it is advantageous if the angle β is less than 90°, preferably less than 89°. In certain applications, it is advantageous if the angle β is greater than 90°, preferably greater than 91°.

[0021] Like other parameters, the choice of angle β must be determined by application tests. The choice of angle β depends on the web to be finished and, of course, on the consistency and characteristics of the coating medium.

[0022] A reverse bevel may be formed on the upper side of the coating knife in an area adjacent to the end face, wherein the reverse bevel forms an angle γ with the bottom face, and the angle γ is in the range of 2° to 12°, preferably about 4°.

[0023] This also improves the quality of the surface of the coil to be finished.

[0024] It has proven to be 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.

[0025] If a wear protection layer is present on the upper side of the coating knife according to the invention and this wear protection layer consists of a ceramic, a carbide material or a composite material of ceramic and metallic material (cermet), the service life of the coating knife is extended.

[0026] If the coating knife has a wear protection layer on its upper side, it is advantageous if the upper side of the substrate (and not the upper side of the coating knife) encloses an angle δ with the bottom side of the substrate, which angle δ is between 2° and 6°. An angle δ of 4° has proven to be particularly advantageous.

[0027] This also achieves a certain reduction in the bending stiffness of the coating knife towards the end face, and this can also reduce the number of scratches and fine marks on the surface of the web to be finished.

[0028] Advantageous thicknesses of the coating knife and the wear protection layer are specified in the dependent claims.

[0029] At this point, it should be noted again that it is also possible to polish a conventional scimitar coating knife only at the end face in order to achieve the desired reduction in the number of scratches and marks in the surface of the finished coil.

[0030] The applicant reserves the right to file a separate patent application for this invention.

[0031] Further advantages and advantageous embodiments of the invention can be found in the following figures, their description and the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In the attached figure:

[0033] Figure 1 A scimitar coating knife according to the prior art is shown;

[0034] Figure 2 An embodiment of a coating knife according to the present invention is shown; and

[0035] Figure 3 is a greatly enlarged view of a region of a coating knife according to the present invention. Specific embodiments

[0036] Figure 1 A coating knife known from DE 29619507 U1 is shown. The coating knife is designated overall by reference numeral 5. The coating knife known from the prior art comprises a first region 1, the material thickness of which is greater than the material thickness of a second region 2. An end face 7 forms the "front" end of the coating knife 5.

[0037] The coating knife 5 is straight in a relaxed state (not shown). Figure 1 In the illustrated state, the coating knife 5 is mounted in a curved manner (so-called “curved knife”). Therefore, a first region of the coating knife 5 exerts an elastic force on the application roller 3 in the direction of arrow 9.

[0038] The upper side of the coating knife 5 is indicated by reference numeral 17. Upper side 17 forms a gap 11 with the cylindrical surface of the coating roller 3. As the coating roller 3 moves in the direction of the arrow past the stationary coating knife 5, the generally cylindrical surface of the coating roller 3 draws the coating medium along and moves it through gap 11. The spring force of the coating knife 5 acting on the coating roller 3 in the direction of arrow 9 causes the coating medium to be bonded to the surface of the web to be finished in a direct coating manner. In both direct and indirect coating, the coating knife 5 smoothes the coating medium at the web or coating roller 3.

[0039] In direct coating, the web to be finished is stretched over a coating roller 3 (not shown). In indirect coating, a pasty or liquid coating medium is applied to the web (paper roll) and reduced to the desired thickness by a coating knife. This is well known to those skilled in the art.

[0040] In both cases, a pasty coating medium (not shown) is located in the gap 11 between the coating roller 3 and the coating knife 5. By rotating the coating roller 3, the coating roller 3, together with any web located at the coating roller 3, moves relative to the coating knife 5 and is thus evenly coated with the coating medium in a manner known per se. This finishes the surface of the web.

[0041] Figure 2 Now, a coating knife 5 according to the invention is shown. In this case, the first region 1 does not have an increased material thickness as is known from the prior art. Instead, in the first region 1, a bevel 13 is formed at the bottom surface 15 of the coating knife 5. This bevel 13 ends at the end surface of the coating knife 5 (see Figure 3 ). This results in a partial reduction in the thickness of the coating knife 5.

[0042] The upper side 17 together with the cylindrical surface of the coating roller 3 forms the aforementioned gap 11 , through which the coating medium is conveyed when the coating roller 3 moves past the stationary coating knife 5 in the direction of the arrow. Figure 2 The coating medium is also not shown.

[0043] The thickness of the gap 11 depends, among other things, on the viscosity of the coating medium, the peripheral speed of the coating roller 3 , the spring force of the coating knife 5 and the machine settings.

[0044] Figure 3 is an enlarged view of a region 1 of a coating knife 5 according to the invention. The geometrical features of the invention will now be explained by means of this enlarged view.

[0045] The end face of the coating knife 5 is designated by 7. The coating knife 5 comprises a base body 21 made of a ferrous material, preferably steel with elastic properties (spring steel). Stainless steel is also often chosen as the material for the base body 21 due to its corrosion resistance. The upper side of the base body (not the upper side of the coating knife 5) is designated by 23. A wear protection layer 25 is applied to this upper side 23, which in turn forms the upper side 17 of the coating knife 5.

[0046] According to the present invention, a bevel 27 is formed at the bottom surface 15 of the coating knife 5. The bevel 27 minimizes the thickness of the coating knife 5 near the end surface. The angle α between the bottom surface 15 and the bevel is in the range of 4° to 15°; in the embodiment shown, the angle α is about 9.5°.

[0047] In the embodiment shown, the length L of the inclined surface is F About 0.65mm.

[0048] The angle β between the bottom surface and the end surface 7 is in the range of 85° to 95°. In some applications, it is advantageous if the angle β is less than 90° and greater than 85°. In other applications, it is advantageous if the angle β is greater than 90° and less than 95°. The angle β may also be 90°.

[0049] Surprisingly, experiments and tests have shown that the bevel 27 according to the present invention leads to a significant improvement in the surface quality of the web. When coating a web, undesirable small scratches and marks may appear. These small scratches and marks may be caused by agglomerates of solids or particles present in the coating medium. If these agglomerates are pulled through a gap 11 that is too narrow, they can cause the undesirable scratches and marks.

[0050] According to the present invention, the bevel 27 on the coating knife 5 significantly reduces the number of scratches and marks per coil from over 5,000 to less than 100! This results in a significant improvement in the surface quality of the finished coil. In addition, the scrap rate and the number of operation interruptions are reduced.

[0051] There are several explanations for these beneficial effects. One view is that the coating knife 5 has greater flexibility due to the bevel near the end face, so that the agglomerates can pass through the gap 11 more easily.

[0052] In any case, the effect can be verified through various tests and their evaluation.

[0053] It may also be advantageous if a counter bevel 29 is formed on the upper side of the coating knife 5, which counter bevel forms an angle γ with the bottom surface 15 in the range of 2° to 12°, preferably 4°. The length L of the counter bevel GFTypically 0.4 mm or more. It is typically advantageous if the length of the counter bevel is 0.5 mm, 0.7 mm or 0.9 mm.

[0054] In most applications, a wear protection layer in the form of a coating is present at the upper side 17 of the doctor blade. This wear protection layer can consist of a ceramic, a carbide material or a composite of ceramic and metallic material.

[0055] For further optimization of the doctor blade 5, it is advantageous if the upper side 23 of the base body encloses an angle δ with the bottom side of the base body or of the doctor blade 5, which angle δ is between 2° and 6°, preferably 4°. The counter bevel moves the narrowest part of the gap 11 from the end face towards the gap, so that scratches and traces caused by the agglomerates can subsequently be smoothed out.

[0056] The object of the present application is also largely achieved by a surface finishing doctor blade, comprising a base body made of steel, wherein the base body has an end face, a bottom side and an upper side, wherein the upper side faces the paper or paperboard to be finished during operation, wherein the upper side has an optional wear protection layer at least in certain regions, and wherein the end face is polished.

[0057] Tests have shown that polishing the end face of the doctor blade 5 reduces the number of scratches and traces by about 50% even if there is no bevel at the bottom side of the doctor blade.

[0058] List of reference signs

[0059] 1 first region

[0060] 2 second region

[0061] 3 coating roll or counter roll

[0062] 5 doctor blade

[0063] 7 end face

[0064] 9 arrow

[0065] 11 gap

[0066] 13 bevel

[0067] 15 bottom side

[0068] 17 upper side

[0069] 19-21 base body

[0070] 23 upper side of the base body

[0071] 25 wear protection layer

[0072] 27 angle L between the bevels 13 and 15 FThe length of the inclined surface B is the angle between the bottom surface 15 and the end surface 7

[0073] 29 reverse slope γ Angle L between the bottom surface 15 and the reverse slope 29 GF The length δ of the counter-bevel is the angle between the upper side 23 of the substrate and the bottom side 15 of the substrate or the coating knife 5 .

Claims

1. A coating knife for an application device for directly or indirectly applying a liquid or pasty coating medium to a moving web, in particular a paper or cardboard roll, wherein: The coating knife (5) comprises a base body (21) made of steel, wherein the coating knife (5) has an end face (7), a bottom face (15) and an upper side face (17), wherein a bevel (13) is formed at the bottom face (15) of the coating knife (5).

2. The coating knife according to claim 1, characterized in that The angle (α) between the bottom surface (15) and the inclined surface (13) is in the range of 4° to 15°, preferably in the range of 5° to 12°.

3. The coating knife according to claim 1 or 2, characterized in that: The length (LF) of the inclined surface (13) is at least 0.5 mm, preferably 0.7 mm or 0.9 mm.

4. A coating knife according to any one of the preceding claims, characterised in that The end surface of the coating knife (5) is polished.

5. Coating knife according to any one of the preceding claims, characterized in that The angle (β) between the bottom surface (15) and the end surface is in the range of 85° to 95°.

6. The coating knife according to claim 4, characterized in that The angle (β) between the bottom surface (15) and the end surface (7) is smaller than 90°, preferably smaller than 89°.

7. The coating knife according to claim 4, characterized in that The angle (β) between the bottom surface (15) and the end surface (7) is greater than 90°, preferably greater than 91°.

8. Coating knife according to any one of the preceding claims, characterized in that A reverse bevel (29) is formed on the upper side surface (17) of the coating knife (5) in a region adjacent to the end surface (7).

9. The coating knife according to claim 8, characterized in that The reverse slope (29) forms an angle (γ) with the bottom surface (15) ranging from 2° to 12°.

10. The coating knife according to claim 8 or 9, characterized in that: The length of the reverse slope (L GF ) is 0.4 mm, preferably 0.5 mm, 0.7 mm or 0.9 mm.

11. A coating knife according to any one of the preceding claims, characterised in that The substrate (21) has an upper side (23), and a wear protection layer (25) is provided on the upper side (23) of the substrate (21), wherein the wear protection layer (25) forms the upper side (17) of the coating knife (5), and the wear protection layer (25) is composed of a ceramic material, a carbide material, or a composite material of ceramic and metal materials.

12. The coating knife according to claim 11, characterized in that The upper side surface (23) of the base (21) and the bottom surface (15) of the base (21) form an angle (δ), and the angle (δ) is between 2° and 6°, preferably 4°.

13. The coating knife according to claim 11 or 12, characterized in that: The thickness of the wear protection layer (25) near the end surface (7) is greater than 0.1 mm.

14. Coating knife according to any one of the preceding claims, characterized in that The thickness (D) of the coating knife (5) at the end surface (7) is greater than 0.2 mm.

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