MXPA99005510A

MXPA99005510A - Coating blade

Info

Publication number: MXPA99005510A
Application number: MXPA/A/1999/005510A
Authority: MX
Inventors: Eriksson Tore; Karlsson Hakan
Original assignee: Btg Kaelle Inventing Ab
Priority date: 1996-12-19
Filing date: 1999-06-14
Publication date: 2000-05-01

Abstract

Coating blade for applying coating material onto a travelling web (41), particularly coating liquid onto a travelling paper web, comprising a steel band (3), which, along the edge section (7) intended to engage the web (41), is provided with a wear-resistant coating (5). Said coating is constituted by a material which has a hardness according to Shore A of from about 10 to about 100.

Description

COVER BLADE OF SCRI PTION OF THE INVENTION The present invention relates to a coating blade for the application of a coating material on a mobile network, particularly a coating liquid or paste on a moving paper web, The traditional knife coating technology is based on the fact of that, the blade may deviate, for example that the blade in its transverse direction will be subject to deflection when the blade, by n longitudinal edge thereof, engages a moving network. Contrary to this, Swedish Patent 468,344 discloses a technology where the blade, instead of being deflected, has a movable coupling which makes it possible to move the blade towards and away from the mobile network. By using this technology it is possible to use coating blades which essentially do not have bending capacity. Since the main function of the coating blade is to uniformize and remove the excess of a coating liquid containing particles ref; 30549 hard, for example titanium dioxide, calcium carbonate and the like, the edge section of the blade that engages the mobile network will be subject to continuous wear. Such wear can also be caused by the particles found in the paper web itself. As soon as the roller has reached a certain degree of wear it has to be replaced. Such a replacement of the cucilla involves high costs, on the one hand caused by the cost of the blade per se, on the other hand also and essentially by the interruption of the production proyocada by the change of the blade. An important property of the coating blades is in this way that the resistance to wear or abrasion is as high as possible. Since the blades that are used in the traditional blade coating techniques will also have spring properties which in some degree result in a lower wear resistance, the quality of the blade becomes a problem between the spring properties and the wear resistance. • In addition to the fact that the wear resistance of the blades is dependent on the material of the blade, it is also known to coat the coupling surface of the blade with material that is resistant to wear, for example ceramic or chromium materials. In view of the fact that such wear resistant layers will be applied to lengthen and thin out materials, often steel surfaces, production limitations will arise, which result in high production costs, the main purpose of the present invention being provide a coating blade of improved resistance against wear. Still another object of the invention is to provide coating blades which can be manufactured at a low cost. Another additional object of the invention is to provide blades that give advantages in quality with respect to the coated layer. For these and other objects which will be clear from the following description, the present invention provides coating blades for the application of a coating material on a mobile network. Although the invention is not restricted thereto in the following it will be particularly described in connection with the application of a coating liquid on a mobile paper web. The covering blade according to the invention includes a band of steel or other material of stable shape which, along the edge section intended to be coupled to the net, is provided with a wear-resistant coating. In accordance with the present invention, it has surprisingly been found that if said coating is constituted by a material of a relatively low hardness, "namely a hardness of from about 10 to about 100 measured in accordance with Shore A, su.stancia.les advantages are obtained in relation to the use of the coating blade. The fact that the use of a coating blade having a coating of a relatively soft material results in a high wear resistance in combination with the important operational advantages, was completely surprising to the person skilled in the art. As is recognized in the conventional art, the coating has been sought with hard materials, for example ceramic7 metals or the like,. for purposes of obtaining a high resistance to wear, and the relatively complicated techniques that have to be used for the application of this type of hard coatings have involved high production costs, and with this a high unwanted price in the final product. In connection with the present invention it is preferred that the coating applied to the coating blade have a hardness according to Shore A of from about 30 to about 80, particularly about 40 to about VO. It is particularly preferred that the hardness according to Shore A falls within the range of about 50 to 60. The surprising observation on which the present invention is based, the possibility of using a relatively soft material as a coating, means that said material coating can be constituted by an organic polymer. Examples of useful polymers are polyurethanes, styrene-butadiene polymers, for example rubber-like polymers, and polyolefins. A particularly preferred type of polymer is the polyurethanes, the building stones, which in a conventional manner are constituted by polyols and diisocyanates. The usual diisocyanates for the polyurethane systems are toluene diisocyanate, diphenylmethane diisocyanate and naphthalene diisocyanate. Less common diisocyanates are also available, such as hexamethylene diisocyanate and isophorone diisocyanate. Polyurethanes are available, for example, as esteruretes, etherurethanes and urethanes based on hydroxyl-terminated polybutadienes. It is not critical which type of pure polyurethane is used in. the present invention for the practical result, as long as the hardness thereof falls within the ranges given above. The experiments carried out while using the techniques according to the present invention, have shown that the material results in high wear resistance or high abrasion resistance, but also other advantages, such as improved fiber coverage and Operating capacity, for example, low frequency of failure. The soft coating gives an improved compliance to the surface of the paper and with that results in a lower effect of caulking, compared to traditional hard blades or blade coatings. The improved operating capacity is probably due to the fact that the soft coating on the edge of the blade allows more easily the passage of the particles which are present in the paper web or in the coating paste in view of the fact that the Soft material will be elastically deformed by the particle. Immediately after the pasp of a particle, the coating material then resumes its initial position. In view of the elasticity of the coating on the edge of the blade in the coupling with the moving net, the edge of the blade, also, to a certain degree, conforms to the contour of the paper surface which results in the desired effect of the coating layer covering the fibers of the base paper in some way more uniform than the traditional coating using hard blades or knife coatings. This effect has been shown by extensive pilot experiments, where the result with respect to failure frequency and fiber coverage has been studied. In comparison with respect to the frequency of rupture, the number of ruptures of the network that r occur in the blade has been counted. Runs have been carried out at the same conditions with respect to the quality of the base paper, the running time, the variables of the coating machine, etc.

In the comparison with respect to the fiber coverage, the results have been studied by the so-called "burn tests" and the coloring with a "roda" color absorption type. The burn test is carried out by wetting the surface of coated paper, with approximately 10% ammonium chloride solution. This chemical results in the darkening of the cellulose fibers when the paper is heated to approximately 3Q0-400 ° C using a heat gun or in an oven. The white coating layer then appears in contrast against the dark surface. This test shows very clearly how the coating layer has been distributed on the surface of the paper. The result of this comparison clearly shows that a polymer-coated blade, according to the invention, results in a coating layer of a more uniform thickness compared to a steel blade of the conventional type, which results in an effect flaming and thus more coating in the "valleys" of the paper surface and less coating on the "tops" of the paper surface.

The coloring test also shows the same result, since the color is absorbed more on the sections where the coating layer is thinner. In view of the fact that the "valleys" of the paper surface are filled with the polymer coated blade, in comparison to the steel blade the surface irregularity will remain to a certain degree, while the positive effects of a reduced breaking frequency and improved fiber coverage is of greater importance for many grades of paper. The steel band used in the coating blade according to the present invention suitably has a thickness that falls within the range of from about 0.2 to about 2 mm. The applied coating has a thickness that falls adequately within the range of about 0.5 to about 5 mm. In a particular embodiment of the cover blade according to the invention, the cover covers the edge section and is provided with a chamfer for enlarging the coupling surface of the cover on the mobile network.

The width of the coating as observed in a plane of the blade and perpendicular to its longitudinal direction, is suitably from about 5 to 25 mm, but this dimension is not particularly critical. The invention also provides an apparatus for coating a mobile network comprising the means for carrying and transporting the network and two opposing coating blades extending through the network and coupling thereto with an edge section of the network. the same, and which on the opposite edge are accommodated in a blade holder for each blade, with a grip that allows mobility to and from the net of the edge section, without essential deviation of the blade. In this apparatus according to the invention, the pressure means are so arranged in the edge section that they can cause each blade to engage the web directed between the opposing coating blades. The characterizing feature of the apparatus is that both coating blades are provided with a coating according to the above description. The apparatus according to the invention is particularly useful for the coating of thin paper grades, which are difficult to produce at low breaking frequencies. In particular coating techniques where the network is fed between two opposing coating blades, it is particularly advantageous to use blades having smooth coatings. In the apparatus according to the present invention for coating on both sides of a mobile network, by using juxtaposed coating blades, Pilot experiments have shown a substantially reduced breaking frequency. The method of using juxtaposed coating blades has previously found limited use in view of the fact that it readily results in failure or breakage of the network when using traditional hard blades or blade coatings. The faults of the network arise in view of the fact that the lumps or particles in the pulp and / or in the network frequently can not pass the point of subjection between the blades without being stopped, with which I break) the network. As examples in the comparison tests between the traditional aqero blades and a steel blade which along the coupling edge section has been coated with a polymer consisting of a polyurethane based on diphenylmethane diisocyanate (MDI) with a hardness of approximately 60 ° Shore A and with. otherwise similar conditions have shown that traditional blades run for 2 hours result in 11 ruptures, while the blade coated with polyurethane did not result in any breakage at all. The techniques based on the use of soft coatings on hard carrier materials according to the present invention, are not restricted to the use only of the polyurethane of the types exemplified above, but may also be constituted by other materials having the properties of hardness that satisfy the requirements for operating capacity with the low frequency of concomitant rupture and the low quality related to a certain production. The characterizing feature of the coating blade according to the present invention is the fact that the coating is coupled by vulcanization, gluing or casting onto a carrier material in the form of a steel strip or other dimensionally stable material that complies with the required shape and position tolerances, such as stiffness, width, length and thickness. The techniques according to the present invention, based on the use of soft coating materials, also result in the advantage that the steel strip can be flexed and wound without the coating being damaged or detached. * The present invention will be exemplified in the following by the non-limiting examples, in relation to the attached drawings, wherein: Figures 1-3 diagrammatically show cross sections through the cover blades, according to the present invention, designed with varying cross sections; Figure 4 shows diagrammatically an apparatus according to the invention with two juxtaposed coating devices / and Figure 5 shows a detail of the area around the two juxtaposed coating blades, with associated coatings.

Figure 1 shows the edge section of a coating knife generally designated 1, comprising a steel strip 3, a coating 5 through the edge section 7 of the steel strip 3. The steel strip 3 is at its outer edge provided with a chamfer 9, and the covering 5 has a corresponding bevel 11, whereby the coupling surface against the mobile network will be enlarged. Figure 2 shows yet another embodiment of the cover 5, in this case provided with a part 15 covering the outer edge 17 of the. steel band 3. Also in this case the cover 5 has a chamfer 11. Finally, figure 3 shows a third embodiment of the coating blade according to the invention, where the free edge 17 of the steel strip 3 is straight and not coated. In this embodiment, the cover 19 is designed with a tetrahedral cross section, again with a chamfer 11 defining the coupling surface against the mobile network. In the modalities shown in Figures 1-3 certain dimensions and angles have been allowed designations. In the following Table the values and intervals are given with respect to these dimensions and angles. With respect to dimensions a, b, c and d the dimensions are in millimeters.

TABLE Figure 4 shows an apparatus according to the present invention, comprising two juxtaposed blade-covering devices, generally designated 25, 27. Each blade-coating device includes a coating blade 29, 31 and a fastener 33, 35 for the blade operating with movable engagement of the respective blade, so that they can move against and away from the mobile network. The blades 29, 31 are put into engagement against the mobile network 41, by means of pressure legs 37, 39 which actuate the blades near their free edges. The blade coating devices 25, 27 which are shown only diagrammatically in Figure 4, can be designed in accordance with the device described in Patent Application WO93 / 05887, and with reference to the construction details, reference is made to the description of the patent application. As is additionally clear from the Figure 4, a paper web 41 is fed in the downward direction at the clamping point between the two coating blades 29, 31. Before the clamping point of the network 41 is applied on both sides thereof with a coating paste by means of the applicators 43, 45 diagrammatically shown, which before the clamping point between the cover blades 29, 31 form ponds 47 of coating paste. Figure 5 shows a detail of the area around the free edges of the juxtaposed coating blades 29, 31 with the coatings 5 with the coupling surfaces 11, chamfered.

As previously indicated, the invention is not restricted to the modalities shown, since the changes and modifications are obvious to the person skilled in the art. Thus, the invention is not restricted other than that which is clear from the appended patent claims.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Claims

_ CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. A coating blade for the application of coating material on a mobile network, particularly coating liquid on a moving paper web, comprising a steel strip, which along the edge section designed to be coupled to the network , it is provided with a wear resistant coating, characterized in that the coating is constituted by a material having a hardness according to Shore A of from about 10 to about 100.

2. The coating blade according to claim 1, characterized in that the material has a hardness of about 30 to about 80, particularly about 40 to about 70.

3. The coating blade according to claim 1 or 2, characterized in that the material is constituted by an organic polymer.

4, The coating blade according to claim 3, characterized in that the organic polymer is selected from polyurethanes. styrene-butadiene polymers and polyolefins.

5. The coating blade according to claim 4, characterized in that the organic polymer is a polyurethane.

6. The coating blade according to any of the preceding claims, characterized in that the steel strip has a thickness in the range of about 0.2 to about 2 mm.

7. The coating blade according to any of the preceding claims, characterized in that the coating has a thickness in the range of 0.5 to about 5 mm.

8. The coating blade according to any of the preceding claims, characterized in that the coating covers the edge section and is provided with a level for the enlargement of the mating surface against the net.

9, The coating blade according to any of the preceding claims, characterized in that the coating observed in the plane of the blade and perpendicular to the longitudinal direction of the blade, has a width of about 5 to about 25-mm.

10. An apparatus for coating a mobile network, comprising the means for carrying and transporting the net and two opposite covering blades extending through the net, and which are coupled thereto with an edge section thereof , and which on the opposite edge are accommodated in a blade holder, for each blade with a grip that allows mobility to and from the net, of the edge section without essential deflection of the blade, further comprising the means of pressure arranged so that each blade, by the edge section, is brought into engagement with the network directed between the opposing coating blades, characterized in that both coating blades are designed in accordance with what is claimed in accordance with any of the Claims 1 to 9.