PROCEDURE FOR THE MANUFACTURING OF CORRUGATED BOARD

Abstract: The invention relates to a procedure for the manufacturing of corrugated board (6), in which procedure the middle layer (7) of the board is corrugated and then joined with the outside layers (1, 8) on both sides of it, at least one of the outside layers being provided with a lacquer coating. According to the invention, before the layers (1, 7, 8) forming the corrugated board (6) are joined, the lacquer (3) is spread on an outside layer (1), which is heated so as to harden the lacquer. After this, said outside layer is joined with the fluted middle layer (7) and the other outside layer (8) in such manner that the lacquer-coated surface constitutes an outside surface of the corrugated board (6) produced. Lacquers suited for use in the procedure of the invention are acrylic and silicone lacquers, which tolerate heating and are also usable on foodstuff packing materials, allowing the corrugated board produced to be used as material for the packing of foodstuffs.

Description: PROCEDURE FOR THE MANUFACTURING OF CORRUGATED BOARD The present invention relates to a procedure for the manu¬ facturing of corrugated board, in which procedure the middle layer of a board consisting of at least three material layers is corrugated and then joined with the outside layers, at least one of which is provided with a lacquer coating. Corrugated board is commonly used as a packing material and as a material to make boxes. Corrugated board typically consists of a fluted, rigidifying middle layer (fluting) and flat outside layers (liners) placed on each side of it. However, even five-layer corrugated board has been produced by joining two fluted layers alternately with three flat, unfluted layers, the latter forming the outside layers. Hydrophobic board can be produced by providing either one side or both sides of the board with a suitable polymer coating. This kind of board is needed especially to produce boxes used for the packing of foodstuffs. The requirement in this case is that the coating material must be of a kind suited for the packing of foodstuffs, i.e. it must not impart a smell or taste and it must not be toxic. An essential part of the process of production of corru¬ gated board is the heating of the material layers, provided with glue, to a temperature of approx. 180 °C. At this tem¬ perature the layers are glued together. The lacquer coat¬ ings currently used on corrugated board do not withstand such high temperatures. For this reason, the coating ma¬ terial has been spread on the surface of otherwise finished board only after the heating, as the last stage in the pro¬ duction process. However, such an arrangement is difficult as it retards further processing of the corrugated board, generally consisting of cutting the board into sheets of certain sizes. The object of the present invention is to achieve a solu¬ tion that makes it possible to eliminate the above-men¬ tioned drawback associated with the manufacture of corru¬ gated board. The invention is characterized in that the lacquer is spread on the material forming an outside layer of the board and this material layer is heated so as to harden the lacquer, whereupon said material layer is joined with the fluted middle layer and the other outside layer in such manner that the lacquer-coated surface constitutes an outside surface of the corrugated board. The present invention has become possible in consequence of the discovery of lacquers which, after hardening, are able to withstand heating to a temperature of approx. 180°C as required by the joining of the layers of corrugated board and are also usable on foodstuff packing materials. The invention provides the advantage that the lacquer, instead of being spread on finished corrugated board of at least three layers, is spread on the bare outside layer, which is easier to handle and can be heated separately to harden the lacquer, (eliminating the need to heat the whole board merely for this purpose) . The process of spreading the lacquer on the outside layer is also easier to control, and the result is a smooth and continuous lacquer coat which, when the board is subjected to humidity, prevents it from becoming wet. Moreover, the lacquer coating of the outside layer does not require any modification of the process equipment, and the lacquers used in the procedure of the invention have not shown any tendency to stick fast on the heating plates used for the joining of the material layers of corrugated I^oard. According to the invention, it is possible to produce corrugated board with a lacquer coating on one side only by treating one of the liners of the board in the manner described above, or alternatively it is possible to produce corrugated board with a lacquer coating on both sides by treating both liners of the board in this manner. The manufacturing of corrugated board is preferably imple¬ mented as a continuous process whereby the fluted middle layer and the flat unfluted liners are provided with glue and brought together against each other as continuous webs, which are then passed to a heater where the layers are glued together. Prior to this joining of the webs, at least one of the webs forming an outside layer has been coated with lacquer and passed through a heater to allow the lacquer to harden. After the lacquer coating operation, the web can be wound on a roll, from which it can then be unrolled and joined with the other material layers of the corrugated board as explained above. Examples of lacquers suited for use in the procedure of the invention are acrylic lacquers, siliconized acrylic lacquers and silicone lacquers. Different silicone based lacquers have the special advantage that, when used on frozen goods cardboard, they prevent the frozen goods from sticking to the corrugated board. Therefore, corrugated board coated with these lacquers is especially suitable for use in packing boxes intended for frozen food. In the following, the invention is described in detail by the aid of an example by referring to the drawing attached, in which fig. la illustrates the process by which the material web forming an outside layer of corrugated board is coated with lacquer, and fig. lb illustrates the process by which corrugated board is produced from a fluted middle layer and liners attached on each side of it. As shown in fig. 1a, a continuous web 1 of (liner) materi¬ al, which may be strong paper or thin cardboard, is passed between two rollers 2, of which the lower roller applies an even layer of lacguer 3, e.g. acrylic lacquer, to the underside of the web. After the application of the lacquer, the web 1 is passed to a heater 4 where the lacquer is hardened at a temperature of approx. 130 - 150 °C. From the heater 4, the lacquer-coated web is passed to a roll 5. Fig. 1b illustrates the process of producing corrugated board 6 from a web of material (fluting) 7 to be corrugated and webs (liners) 1,8 of material constituting the outside layers of the board. Of the latter, one is a lacquer-coated web of material 1 produced as illustrated by fig. 1a while the other web 8 forming an outside layer is without a lacquer coating. The web 7 forming the middle layer of the corrugated board, which may consist of reclaimed paper or cardboard, is passed from a roll 9 over a heating roller 10 to corru¬ gating rollers 11 , which are heated to a temperature of approx. 200 °C and press the web 7 between them so as to give it the desired flute profile. Arranged in conjunction with the corrugating rollers 11 is a glueing roller 12, which spreads a layer of starch size 13 on the web 7. Simultaneously, a web 8 of material forming one of the liners of the board is brought from another roll 14 over a heating roller 15 and applied against the sized surface of the corrugated web 7 so that the two webs 7,8 stick pre¬ liminarily together. As can be seen from the figure, the combined web 16 thus produced is as yet without rigidity. Next, starch size 13 is applied by another roller 17 to the other side of the fluted web 7 forming the middle layer of the board, whereafter the web of material 1 forming the other liner of the board, obtained from a roll 5 and passed over a heating roller 18, is brought onto the sized surface of web 7 so that the lacquer-coated side of web 1 will form an outside surface of the combined web 19 thus produced. Next, this web 19, consisting of three material layers brought together against each other, is passed through a heater 20, where it is heated between a movable pressing belt 21 and stationary heating plates 22 to a temperature of approx. 180 °C, at which the layers are definitely glued together to produce finished corrugated board 6. Finally, the web of corrugated board delivered from the heater 20 is cut by rollers 23 provided with cutoff tools into sheets 24, which can be used e.g. to make packing boxes. This final stage of the process may also include other opera¬ tions by which the sheets are treated so as to produce blanks (not shown) from which packages can be assembled directly. The process illustrated by fig. 1b produces sheets 24 of corrugated board with a water and grease repellent lacquer coating on one side. However, if the uncoated web 8 of ma¬ terial forming the other liner is replaced with a lacquer- coated web 1 produced as illustrated by fig. 1a, the pro¬ cess will produce corrugated board 6 with a protective lacquer coating on both sides. The invention has been tested by producing three-layer corrugated board with an acrylic lacquer coating on one side. The board had a mass of 175 g/m 2 and the amount of lacquer (dry matter) used was 6 g/m 2 . At 50 % relative humidity and 23 °C temperature, a measured water vapour permeability value below 30 g/m 2 /24 h and a measured water absorption (COBB 1 h) value of 15 g/m 2 were obtained. The grease permeability of the board was measured according to ISO standard 5634, and it was observed that the grease blotch began to be visible through the board within 24-48 h in 50 % of the cases and in the remaining 50 % of the cases only after 48 h. In all cases, grease penetration was only observed after 48 h. The acrylic lacquer used withstands heating to a tempera¬ ture of at least 190 °C. Thus it will not cause any pro¬ blems in the board production process. Furthermore, it will not prevent reclamation of the corrugated board for pulp production after it has been thrown away as waste. It is obvious to a person skilled in the art that different embodiments of the invention are not restricted to the ex¬ ample described above, but that they may instead be varied within the scope of the following claims. Thus it is pos¬ sible to produce five-layer corrugated board by the pro¬ cedure of the invention by joining alternately two fluted layers and three flat unfluted layers of material, at least one of the flat outside layers of the board being provided with a lacquer coating.

Claims: CLAIMS 1. Procedure for the manufacturing of corrugated board (6) , in which procedure the middle layer (7) of a board con¬ sisting of at least three material layers (1,7,8) is corru¬ gated and then joined with the outside layers (1,8), at least one of which is provided with a lacquer coating, c h a r a c t e r i z e d in that the lacquer (3) is spread on the material (1) forming an outside layer of the board and this material layer is heated so as to harden the lacquer, whereupon said material layer is joined with the fluted middle layer (7) and the other outside layer (8) in such manner that the lacquer-coated surface constitutes an outside surface of the corrugated board (6). 2. Procedure according to claim 1, c h a r a c t e r ¬ i z e d in that both of the outside layers (1,8) of the board are coated with lacquer (3), whereafter these layers are joined with the fluted middle layer (7) in such manner that the corrugated board (6) thus produced will have a lacquer coating on both outside surfaces. 3. Procedure according to claim 1 or 2, c h a r a c ¬ t e r i z e d in that the corrugated board (6) is produced by a continuous process from webs (1,7,8) of material which are provided with size (13) and brought together against each other, whereupon they are passed through a heater (20) where the materal layers are fastened together. 4. Procedure according to claim 3, c h a r a c t e r ¬ i z e d in that a web (1) of material forming an outside layer is coated with lacquer (3), which is hardened by heating, whereafter the web is wound on a roll (5), from which it is unwound at a later stage and joined in a continuous process with the other material layers (7,8) of the corrugated board (6) . 5. Procedure according to any one of the preceding claims, c h a r a c t e r i z e d in that the lacquer (3) is hard¬ ened by heating it to a temperature of approx. 130-150 °C. 6. Procedure according to any one of the preceding claims, c h a r a c t e r i z e d in that the lacquer (3) used is an acrylic lacquer. 7. Procedure according to any of claims 1-5, c h a r a c ¬ t e r i z e d in that the lacquer used is a siliconized acrylic lacquer. 8. Procedure according to any one of claims 1-5, c h a r ¬ a c t e r i z e d in that the lacquer used is a silicone lacquer.

Inventors: LAMPAINEN SEPPO, PENTTINEN TAPANI, LAMPAINEN, SEPPO, PENTTINEN, TAPANI
Applicants: ENSO GUTZEIT OY, ENSO-GUTZEIT OY
Application year: 1990
Main classification: B31F1
IPC codes: B31F1