PROCEDURE FOR THE MANUFACTURING OF CORRUGATED BOARD OR THE LIKE

Abstract: The invention relates to a procedure for the manufacturing of corrugated board (12) or the like from webs of material (1, 13, 14) brought together against each other, in which procedure at least one (1) web is corrugated and then joined with at least one essentially flat, unfluted web (13, 14). The basic application of the invention is a three-layer corrugated board consisting of a fluted middle layer and flat outside layers on each side of it. The essential feature of the invention is that the web (1) of material to be corrugated is produced by laminating together two layers (2, 3) of paper or cardboard by applying between them an adhesive (4) which is a hot-melt type polymer or wax and which is allowed to solidify before the web is corrugated. The adhesive layer (4) forms a moisture proofing in the corrugated board. Moreover, this solution is intended to improve the flat crush resistance of corrugated board.

Description: PROCEDURE FOR THE MANUFACTURING OF CORRUGATED BOARD OR THE LIKE The present invention relates to a procedure for the manu¬ facturing of corrugated board or the like from webs of material brought together against each other, in which procedure at least one web is corrugated and then joined with at least one essentially flat, unfluted web. 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. In addition, two-layer board consisting of one fluted layer and one unfluted layer has also been produced for use as a packing filler and e.g. as a parquet base material. The corrugated material layer usually consists of card¬ board, which is easy to corrugate if it is not too thick. However, problems are encountered when the mass of the layer increases, because the corrugation tends to break the structure of the material. The critical limit for the mass of the layer is 175 g/m 2 . The need to increase the mass of the fluted layer arises from the fact that doing so improves the flat crush resist¬ ance of the board. As it has not been possible, due to the rupturing problem, to increase the mass of individual layers, the solution has been the five-layer corrugated board mentioned above, which has two fluted material layers. However, such board is considerably more massive, and this again involves certain drawbacks. The object of the present invention is to achieve a solu¬ tion enabling the flat crush resistance of corrugated board to be improved without the above-mentioned drawbacks of the previously known solutions. The procedure of the invention for the manufacturing of corrugated board or equivalent is characterized in that the web of material to be corrugated is produced by laminating together two layers of paper or cardboard by applying between them an adhesive which is a hot-melt type polymer or wax and which is allowed to solidify before the web is corrugated. By making the corrugated layer from a laminate produced as provided by the invention, the flat crush resistance of corrugated board can be increased without notably increas¬ ing the thickness of the board. Moreover, the increase in the weight of the board is considerably less than in the case of five-layer board. The laminate can be corrugated using conventional existing corrugating equipment without any need for modifications and without problems in its use. Another essentiual advantage provided by the invention is that the polymer or wax layer in the fluted laminate forms an effective moisture proofing in the corrugated board. This prevents the board from getting wet and helps the board retain its strength in wet circumstances. According to the invention, the web of material to be corrugated can be produced separately and wound on a roll which can be stored or moved from one place to another and from which it can be unwound at a later stage when the web is to be corrugated and joined with the other material layers of corrugated board. Hot-melt polymers suitable for lamination as provided by the invention are those which have a melting point of at least 100 °C. An example is atactic polypropylene, but any other equivalent polymer can be used just as well. 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 the corrugated middle layer of the board is produced, and fig. 1b illustrates the process by which corrugated board is produced from this fluted web and the webs attached on each side of it, forming the outside layers of the board. As illustrated by fig. la, the web of material to be fluted is produced as a laminate consisting of two cardboard layers 2,3 and a layer of adhesive 4 between them. The cardboard layers have a mass of e.g. 115 g/m 2 , while the adhesive layer 4, consisting of a suitable hot-melt polymer such as atactic polypropylene, has a mass preferably in the range 20-30 g/m 2 . In the process illustrated by fig. 1a, molten polymer 5 is supplied via a pipe 6 into a feed funnel 7, from where it is forced by toothed bars 8 into a nozzle head 10. The nozzle head 10 comprises a rotating bar which applies an even layer of molten polymer on a cardboard web 2 moving past the nozzle head, the width of the web being essentially equal to that of the feed slot 9. After the nozzle head 10, another cardboard web 3 is applied against the web 2 with a polymer layer 4 so as to produce a laminated three-layer material web 1 as mentioned above. The laminate is wound on a roll 11. Fig. 1b illustrates the process by which corrugated board 12 is produced from a corrugated web of material 1 forming the middle layer (fluting) of the board and webs of materi¬ al 13,14 forming the outside layers (liners). The fluting consists of a laminated web 1 of material produced as illustrated by fig. la. The web 1 forming the middle layer of the board is passed from a roll 11 over a heating roller 15 to two corrugating rollers 16, which are heated to a temperature of approx. 200 °C and press the web 1 between them so as to give it the desired flute profile. Arranged in conjunction with the corrugating rollers 16 is a glueing roller 17, which spreads a layer of starch size 18 on the web 1. A web 13 of material forming one of the liners of the board is then brought from another roll 19 over a heating roller and applied against the sized surface of the corrugated web 1 so that the two webs 1,13 stick preliminarily together. As can be seen from the figure, the combined web 20 thus produced is as yet without rigidity. Next, starch size 18 is applied by another roller 21 to the other side of the fluted web 1 forming the middle layer of the board, whereafter the web of material 14 forming the other liner of the board, obtained from a roll 22 and passed over a heating roller, is brought onto the sized surface of web 1. Next, this web of three material layers brought together against each other is passed through a heater 23, where it is heated between a movable pressing belt 24 and stationary heating plates 25 to a temperature of approx. 180 °C, at which the layers are definitely glued together to produce finished corrugated board 12. Finally, the web of corrugated board delivered from the heater 23 is cut by rollers 26 provided with cutoff tools into sheets 27, 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. In the following table, three-layer corrugated board manufactured as provided by the invention is compared with conventional three-layer corrugated board and corresponding fivel-layer board comprising two fluted material layers. 3-layer 5-layer 3-layer corr. corrugated corrugated board of the board board invention Weight of board g/m : 550 867 717 Weight of fluted layer g/m : 127 3 x 127 277 Edgewise crush resist¬ ance (ECT) kN/m 6.27 10.28 8.04 Flat crush resistance (FCT) kPa 283 514 Thickness mm 4.3 6.8 4.4 Water vapour permeability of fluted layer at 50% g/mVd 300 300 relative humidity at 23°C The table indicates that, compared to normal three-layer corrugated board, the corrugated board of the invention shows a considerable increase in strength without a sub¬ stantial increase in thickness. As regards the water vapour permeability, the improvement achieved is dramatic both as comapared to normal three-layer board and five-layer board. It is obvious to the person skilled in the art that dif¬ ferent embodiments of the invention are not restricted to the example described above, but that they may instead be varied within the scope of the following claims. For instance, it is possible to use the procedure of the invention to produce two-layer board consisting of one fluted layer and one flat, unfluted layer by directing the combined web 20 appearing as an intermediate product in fig. 1b past the next stages directly to the heater 23. The product can be used e.g. as a packing filler.

Claims: CLAIMS 1. Procedure for the manufacturing of corrugated board (12) or the like from webs of material (1,13,14) brought to¬ gether against each other, in which procedure at least one (1) web is corrugated and then joined with at least one essentially flat, unfluted web (13,14), c h a r a c ¬ t e r i z e d in that the web (1 ) of material to be cor¬ rugated is produced by laminating together two layers (2,3) of paper or cardboard by applying between them an adhesive (4) which is a hot-melt type polymer or wax and which is allowed to solidify before the web is corrugated. 2. Procedure according to claim 1 , c h a r a c t e r ¬ i z e d in that the laminated web of material (1 ) is wound on a roll (11), from which it is unwound at a later stage, to be corrugated and joined with at least one unfluted web (13,14). 3. Procedure according to claim 1 or 2, c h a r a c ¬ t e r i z e d in that corrugated board (12) consisting of three material layers (1,13,14) is produced by the pro¬ cedure by corrugating the web of material (1 ) forming the middle layer of the board and joining this web with two fla , unfluted webs (13,1 ). 4. 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 lamination of the web (1 ) to be corrugated is implemented using a polymer (4,5) with a melting point of at least 100 °C. 5. Procedure according to claim 4, c h a r a c t e r ¬ i z e d in that the lamination is implemented using atactic polypropylene.

Inventors: LEHTINEN MIRJA, NOUSIAINEN HANNU, PENTTINEN TAPANI, LEHTINEN, MIRJA, NOUSIAINEN, HANNU, PENTTINEN, TAPANI
Applicants: ENSO GUTZEIT OY, ENSO-GUTZEIT OY
Application year: 1990
Main classification: B31F1
IPC codes: B31F1