Coating device for the coating of a size-press roll, paper, or board

Abstract: The invention concerns a coating device for the coating of a size-press roll, paper or board or of a corresponding moving base. The coating device comprises a revolving coating bar (11,21) which rests against the moving base (4,5), which extends across the machine width, and which is supported in a cradle (12,22) substantially over its entire length. The coating bar is fitted to spread and to smooth the coating agent onto the moving base (4,5), which coating agent has been introduced into the coating device (10,20) before the coating bar (11,21), in the direction of running of the moving base (4,5). The coating bar (11,21) in accordance with the invention is a large-diameter grooved bar fitted against the moving base (4,5).

Description: The invention concerns a coating device according to the preamble of claim 1. Further, the invention concerns a coating device according to the preamble of claim 2. At present, in the coating of paper or board, two alternative methods and devices are commonly used, i.e. a blade coater or a bar coater. The present invention is expressly related to the latter, bar coaters, which have proved excellent especially in the film size press technique. The material of the coating bars currently in use is usually steel, and, in view of increasing the service life of the bar, the bars are provided with chromium plating. In surface sizing of paper, the face of the bar has been provided with grooves, or steel wire may have been wound onto the bar to form a solution similar to grooves on the bar face. The use of a grooved bar for surface sizing of paper is based thereon that the thickness of the size film to be applied onto the base to be coated is determined by means of the depth of the grooves. It has been a highly significant drawback of grooved bars that they are worn rapidly. Pigmenting with a high dry solids content is also entirely impossible with grooved bars, because the wear of the bars is excessive in this connection. The diameters of the coating bars currently in use have been very little, the order of magnitude of the diameter being, as a rule, about 10 mm. Besides the wear, it is a further significant detrimental factor with the use of small-diameter bars that, especially in size-press operation, the roll faces are scratched excessively, because the nip between the bar and the roll coating is quite open (not sufficiently wedge-shaped). This is why the contaminations coming from the paper or size cannot pass through this open nip easily, but, when remaining in front of said nip, said contaminations wear grooves into the roll coating and, at the same time, they also wear the bar locally. When small-diameter bars are used, it is a further significant drawback that, when the bars are handled, they tend to undergo permanent distortions, after which they cannot be used any more. Likewise, web breaks frequently also bend and twist the bars permanently. With large-diameter bars, these problems have not occurred when said bars have been used as smooth-faced bars in pigment-coating operation. With respect to the prior art, reference is made further to the FI Patent No. 30,147. EP-A-454 643 discloses small diameter grooved coating bars and large diameter smooth faced coating bars. The object of the present invention is to provide a solution by whose means the drawbacks related to the prior art are avoided and by whose means a significant improvement is achieved in particular in surface-sizing and pigmenting of paper. In view of achieving this objective, the invention is characterized in that the coating bar is fitted against the moving base and in that its diameter is at least 18 mm. Further, in size-press operation, it is preferable to use roll coatings softer than usual, whose hardness is of an order of 35 P&J. In such a case, contaminations have better access through the nip between the coating bar and the roll coating without producing scratches into the roll coating. This comes from the fact that the contaminations are pressed into the soft coating. It is the most remarkable advantage of the invention over the prior art that, by means of a coating device in accordance with the invention and while using a large-diameter grooved coating bar, it has been possible to run coating pastes of high dry solids content even at high running speeds without excessive wear of the bars. In particular by using soft roll coatings, it has been possible to avoid scratching of the roll coatings substantially completely. With the device in accordance with the invention, the level of the coating quantity and the profile of the coating have been excellent. The further advantages and characteristic features of the invention come out from the following detailed description of the invention. In the following, the invention will be described in detail with reference to the figures in the accompanying drawing. Figure 1 is a fully schematic side view of a film size press in which a coating device in accordance with the invention is applied. Figure 2 is an enlarged and simplified illustration of an embodiment of the coating bar of the coating device in accordance with the invention. Figure 2A is a schematic sectional view of one alternative embodiment of the groove geometry of a coating bar in a coating device in accordance with the invention. Figure 3 is a schematic side view of an embodiment of the invention in which the invention is used in coating taking place directly onto a paper or board web. Fig. 1 is a schematic illustration of a film size press, which is denoted generally with the reference numeral 1. The film size press 1 comprises rolls 2 and 3 of the size press, so that the first roll 2 and the second roll 3 form a nip N with one another, through which nip the paper or board web W is passed. In the film size press 1, a first size film F 1 is metered onto the face of the first roll by means of the first coating device 10 and, in a corresponding way, a second size film F 2 is metered onto the face 5 of the second roll by means of the second coating device 20. In the roll nip N, the size films F 1 and F 2 are transferred to the paper or board web W running through the nip. In Fig. 1, the coated web is denoted with the reference W'. In the film size press 1 shown in Fig. 1, the coating devices 10 and 20, by whose means the size films F 1 and F 2 are spread onto the faces 4 and 5 of the size press rolls 2 and 3, are bar coaters, which are equal to one another, as is shown in Fig. 1. The coating devices 10 and 20 are coating devices of the so-called short-dwell type, in which the coating agent is introduced into a pressurized coating-agent chamber 16,26 placed before the coating bar 11,21, which chamber is, besides by said coating bar 11,21, also defined by the roll face 4,5, by the front wall 14,24 of the coating-agent chamber, as well as by possible lateral seals, if any (not shown). The coating bar 11,21 is fitted in a cradle 12,22 made of a suitable material, e.g. polyurethane, said cradle supporting the coating bar 11,21 over its entire length. The coating bar 11,21 is provided with a purposeful drive gear (not shown), by whose means the coating bar 11,21 is rotated in directions opposite to the directions of rotation of the rolls 2,3. Further, in Fig. 1, the holders of the cradles of the coating bars are denoted with the reference numerals 13 and 23, and the holders of the front wall with the reference numerals 15 and 25. Further, between the coating-bar 11,21 cradle 12,22 and the holder 13,23, an ordinary loading hose or equivalent (not shown) is fitted, by whose means the coating bar 11,21 can be loaded against the roll face 4,5 to produce the desired loading pressure. According to the invention, in the coating devices 10,20 shown in Fig. 1, a large-diameter grooved coating bar 11,21 is used. The coating bar 11,21 in accordance with the invention is grooved, and the diameter of the coating bar 11,21 is substantially larger than in the prior-art solutions. In a coating device in accordance with the invention, the diameter of the coating bar 11,21 is at least 18 mm, and very good results have been obtained in test runs with a coating device in which the diameter of the coating bar was 35 mm. Most advantageously, the diameter of the bar is 25...80 mm. A bar of a diameter larger than 25 mm is preferably made of a tube. Fig. 2 shows an alternative solution, by whose means the coating can be carried out by making use of a grooved large-diameter coating bar in accordance with the invention. In Fig. 2, the size-press roll is denoted with the reference numeral 6. The roll 6 is provided with a coating 7 in a conventional way, which coating is, e.g., of rubber or equivalent. For the purposes of the invention, the most appropriate hardness of the roll 6 face is about 15...100 P&J. In Fig. 2, the coating bar in accordance with the invention is denoted with the reference numeral 31, and, in the embodiment of Fig. 2, the coating bar 31 comprises a tube 32, whose diameter is, e.g., of an order of 35 mm. The tube 32 is provided with suitable grooves 33, by whose means the coating quantity is determined. In the embodiment of Fig. 2, the coating bar 31 is mounted revolvingly in a cradle 34, e.g., of polyurethane, which supports the coating bar over its entire length. The cradle 34 is attached to a holder 35, and, between the holder 35 and the cradle 34, a loading hose 36 or an equivalent loading member is fitted, by whose means the bar 31 can be loaded in the desired way against the roll 6 and, if necessary, be profiled by means of local differences in load. Fig. 2A illustrates one groove geometry of a coating bar 31 or of the tube 32 that forms the coating bar. The grooves are denoted with the reference numeral 33. The material of the tube 32 may be, e.g., chromium-plated copper or steel. The solution shown in Fig. 3 illustrates coating that takes place directly onto the paper or board web W. In Fig. 3, the roll is denoted with the reference numeral 110. The paper or board web W is passed over the roll face 111, and the coating is carried out by means of the coating device 100 directly onto the web W. The coating device 100 is a coating device of the so-called short-dwell type, which includes a large-diameter grooved coating bar 101 in accordance with the invention mounted revolvingly in a cradle 103. The cradle 103 is mounted on a holder 104 in the normal way. The coating bar 101 defines the pressurized coating-agent chamber 106 together with the front wall 102 of the coating device 100, into which chamber 106 the coating agent is introduced. The front wall 102 is mounted on a holder 105 in the normal way. In test runs that have been carried out, excellent results have been obtained with a coating device in accordance with the invention. The test runs were carried out with a solution in which a grooved coating bar of a diameter of 35 mm was mounted revolvingly in a coating-bar cradle of conventional construction. The coating device constructed in this way was fitted in a size press. By means of the device, test runs were carried out with pigmenting. In some test runs, when a highly abrading pigment, calcined kaolin, was used in the pigmenting size, a grooved bar of a diameter of 10 mm was worn during a wear test of 10 hours so that it became unusable because of excessive wear of the bar. With a bar of an equivalent construction but of a diameter of 35 mm, in a wear test carried out in the same way, no wear of the bar could be noticed. In several test runs, it has been noticed additionally that the larger the diameter of the bar is, the less does it scratch the roll in size press operation.

Claims: Coating device for the coating of a moving base consisting of size-press roll, paper or board, comprising a revolving grooved coating bar (11,21,31,101) which rests against the moving base (4,5,7,W), which extends across the machine width, which is supported in a cradle (12,22,34,103) substantially over its entire length, and which coating bar is fitted to spread and to smooth the coating agent onto the moving base (4,5,7,W), which coating agent has been introduced into the coating device (10,20,100) before the coating bar (11,21,31,101), in the direction of running of the moving base (4,5,7,W), characterized in that coating bar (11,21,31,101) is fitted against the moving base (4,5,7,W) and in that the diameter of the coating bar (11,21,31,101) is at least 18 mm. Coating device for the coating of a moving base consisting of, size-press roll, paper or board, which coating device (10,20,100) comprises a coating-agent chamber (16,26,106), which chamber is defined by a revolving grooved coating bar (11,21, 101), which is supported on the moving base (4,5,W), which acts as the coating member, and which extends across the width of the machine, by the front wall (14,24,102) of the coating-agent chamber, by the lateral seals of the coating device, and by the moving base (4,5,W), the coating agent being arranged to be fed into said coating-agent chamber (16,26,106) under pressure, characterized in that the coating bar (11,21,101) is fitted against the moving base (4,5,W) and in that the diameter of the coating bar (11,21,31,101) is at least 18 mm. Coating device as claimed in claim 1 or 2, characterized in that the coating bar (11,21,31,101) is loaded against the moving base (4,5,7,W) and can be profiled by means of local differences in loading. Coating device as claimed in any of the claims 1 to 3, characterized in that the diameter of the coating bar (11,21,31,101) is 25...80 mm. Coating device as claimed in any of the claims 1 to 4, characterized in that the coating bar (11,21,101) is made of a uniform solid material. Coating device as claimed in any of the claims 1 to 4, characterized in that the grooved coating bar (11,21,31,101) is made of a tube. Coating device as claimed in claim 6, characterized in that the material of the tubular coating bar (11,21,31,101) is chromium-plated copper or steel. Coating device as claimed in any of the preceding claims, which is fitted in connection with a roll (2,3,6) of a size press, which roll is provided with a coating (7), characterized in that the hardness of the coating (7) is 15...100 P&J.

Inventors: KORHONEN HANNU, LINTULA TIMO, LUMMILA MARKKU, RANTANEN RAUNO, KORHONEN, HANNU, LINTULA, TIMO, LUMMILA, MARKKU, RANTANEN, RAUNO
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1993
Main classification: D21H23
IPC codes: D21H23