Methods For Manufacturing Corrugated Board

Abstract

A method and an apparatus for manufacturing corrugated board in which layers of material for the corrugated board are coated with a mixture of a thermoplastic and a wax which can be brought into liquid form and which after melting and setting on the layers keeps said layers together.

Description

This invention relates to a method and an apparatus for manufacturing corrugated board having at least one layer with alternating ridges and grooves and at least one smooth layer interconnecting the ridge crests of said ridged and grooved layer with the aid of a binder, and for carrying the method into effect the apparatus includes supply rolls of starting materials for the layers of corrugated board, cylinders for producing the ridged and grooved layer, and cylinders for compressing all layers, webs of the starting materials being caused to run together at an angle between the cylinders.

Prior art methods and apparatus of these types suffer from serious deficiencies. The apparatus employed take up a very large space mainly because the binders hitherto utilized, which are deposited on one or more of the different layers of the corrugated board, must be hard and dry before the board can be allowed to leave the apparatus. The binder being enclosed in the interior of the corrugated board, it is very difficult to influence and accelerate the setting and drying of the binder and therefore the setting and drying can take place only extremely slowly, thus necessitating the provision of an apparatus that takes up a great deal of room. Moreover, prior art methods and apparatus do not give the possibility of individually shaping the corrugated board for various purposes and various uses. Decorative or informative print can be applied to the corrugated board only in a very primitive form without any sales-promoting properties. Therefore, advanced one-color print and multicolor print cannot be used in connection with corrugated board.

The present invention has for its object to eliminate the above and further deficiencies of the prior art methods and apparatus. To this end, the method according to the invention is characterized by using as starting material for one or more of the corrugated board layers paper having applied to it a coating which can be melted into liquid form by application of heat, and directly subjecting said coating to streams of hot air from a source of hot air through nozzles, whereby the coating is brought into liquid form in connection with the ridged and grooved layer being produced and/or the smooth layers being united with the ridge crests of the ridged and grooved layer produced.

The apparatus for carrying the method of the invention into effect is characterized in that the nozzles connected to a suitable source of hot air are located between the cylinders for producing the ridged and grooved layer and the cylinders for compressing the layers, and more precisely in the angle between two of the webs of material supplied from the supply rolls and caused to run together at the compression cylinders, said nozzles being directed toward the apex of said angle.

The above features of the invention and the advantages gained thereby will appear from the following description in which reference is made to the accompanying drawings illustrating in FIGS. 1 and 2 two embodiments of apparatus for carrying the method of the invention into effect.

The apparatus in the two embodiments thereof illustrated in FIGS. 1 and 2 comprises supply rolls 1, 2, 3 of starting materials for the different layers 4, 5, 6 of the corrugated board produced by the apparatus illustrated. The apparatus also has toothed cylinders 7 between which the web of material 8 taken from the supply roll 1 is passed for providing, in the known manner, the alternating ridges and grooves in said web which is to form the ridged and grooved layer 4. The apparatus further has nozzles 9 which are connected to a suitable source of hot air having a temperature of 400.degree. to 600.degree. C. and which are disposed in the angle formed between two of the webs of material 8, 11 and 12 supplied from the supply rolls 1, 2, 3 and caused to run together at compression cylinders 10. More precisely, the nozzles 9 are located between the toothed cylinders 7 and the compression cylinders 10. As will appear from the drawing figures, the nozzles 9 have their mouths directed toward the apex of said angle and thus toward the nip of the pair of cylinders 10 closest to the nozzles. The toothed cylinders 7 are adapted to be heated by means (not shown) for a purpose that will appear from the following.

The embodiment of the apparatus illustrated in FIG. 2 differs from that in FIG. 1 by an electronic oven 13 being arranged between the nozzles 9 and the cylinders 10 for a purpose that will also appear from the following. The compression cylinders preferably are cooling cylinders that are cooled by any suitable coolants.

In the manufacture of the corrugated board by the method of the invention at least one layer 4 with alternating ridges and grooves is produced and at least one smooth layer 5 or 6 is united with the ridge crests of said ridged and grooved layer 4 with the aid of a binder. As starting material in the method of the invention use is made of such a paper for one or more of the layers 4, 5, 6 as has a coating which can be melted into liquid form by application of heat and which is directly subjected to the action of streams of hot air whereby said coating is brought into liquid form in connection with the ridged and grooved layer 4 being produced and/or the smooth layers 5, 6 being united with the ridge crests of the ridged and grooved layer 4. Such paper can have the desired advanced print applied to it in connection with the manufacture. Use is made, for the meltable coating on such paper, of mixtures of thermoplastics and waxes, having a melting point of about 65.degree. to 85.degree. C. The heated toothed cylinders 7 preheat the web 8 at the formation of the alternating ridges and grooves therein, and one or both faces of the resulting ridged and grooved layer 4 as well as the face or faces of the smooth layers 5, 6 turned toward the layer 4 are subjected to a final heating by the hot air projected through the nozzles immediately before the smooth layers 5, 6 are united with the ridge crests of the layer 4. As a result of the preheating performed by the cylinders 7 the thermoplastic coatings on the web of material 8 will be flexible and will retain their original continuous character without any breaks at the bending points, the ridge crests. The web of material 8 can therefore be subjected without disadvantage to very sharp bendings, and the bends formed by the cylinders 7 are fixed in shape because the coats are given a certain time in which to set before the further steps of the manufacturing method are performed, as will become apparent from the following. For the final heating and for the melting of the thermoplastic coating into liquid form the hot air is projected through the nozzles 9 into the angles of the webs of material 8, 11, 12 caused to run together in the junction area at the cylinders 10 in FIG. 1. The compression cylinders 10, which preferably are cooling cylinders, determine the thickness of the forming corrugated board and provide a reliable connection between the webs of material 8, 11, 12 because the melted coating or coatings set.

As it is expedient in certain cases, after the layers 4, 5, 6 have been united with each other, to provide a still more reliable connection between the different layers and simultaneously a more exact calibration of the thickness of the corrugated board, the electronic oven 13 is suitably arranged after the nozzles 9 and between the latter and the compression cylinders 10, as will appear from FIG. 2. Further compression cylinders 14 are provided in the electronic oven 13, the purpose of these cylinders being on the one hand to keep the layers 4, 5, 6 together during the heating thereof in the electronic oven to cause the thermoplastic layers to melt again, and on the other hand in certain cases to exert such a pressure on the corrugated board in a direction at right angles to the main plane thereof that the ridge crests are compressed to a certain extent, whereby a larger contact surface is obtained between the ridged and grooved layer 4 and the smooth layers 5, 6. As a consequence, the ridges and grooves of the layer 4 will have an approximately rectangular shape in cross section, resulting in an extremely resistant corrugated board with excellent shock-absorbing properties for heavy articles.

It will readily be seen that all webs of material 8, 11 and 12 need not be provided with coatings which can be melted by application of heat, and that such a coating can be applied only to one surface of one of the webs of material. In the latter case but one smooth layer is combined with the ridged and grooved layer. However, by providing all layers of the corrugated board with coatings meltable by application of heat and thus being weldable, the corrugated board will be extremely resistant to liquids and quite naturally be of increased usefulness. The smooth layers or any other layers whatever can readily be provided with the most advanced print whereby the corrugated board will have the same effective sales-promoting properties as other packaging materials. Further, it will be readily understood that the number of ridged and grooved layers and smooth layers can be varied and that the method of the invention and the apparatus for carrying it into effect can thus yield corrugated boards having an optional number of ridged and grooved layers 4 as well as smooth layers 5, 6.

The cylinders 10 may be adjustable toward and away from the main plane of the formed corrugated board to allow regulation of the thickness of the board.

Coatings formed by mixtures of thermoplastics and waxes and having been brought into liquid form imply the advantage that the materials having such coatings practically need only be brought together without essential pressure and but momentarily to ensure a reliable interconnection of these materials after the mixtures have set. As distinguished from the previously known methods it is not necessary, when making use of the present invention, to exert a prolonged and relatively high pressure on the corrugated board.

Further modifications are conceivable within the scope of the invention defined in the appended claims.

Claims

I claim:

1. A method of manufacturing corrugated paper board having at least a first even layer of paper and a second, corrugated layer of paper attached to said first layer by means of an adhesive binder; the method comprising the steps of supplying said first and second layers with one layer having on one of its surfaces an adhesive coating comprised of a mixture of thermoplastic and wax having a melting point of about 65.degree. to 85.degree. C. which coating may be melted into a liquid by application of heat, moving said first and second layers towards each other at an acute angle into initial overlying contact at a certain station with the apex of the acute angle coinciding with said certain station and with the coating on said one layer facing the other layer, and applying a stream of hot air to said coating precisely at said station through a nozzle located between said layers adjacent and in alignment with said apex to melt said coating into a liquid immediately prior to bringing the layers into initial overlying contact with each other at said station, the said one layer including the coating thereon being supplied from a supply source, the claimed method excluding application of the coating to said one layer.

2. The method defined in claim 1 further including the step of preheating said coating at a second station prior to bringing said layers into contact with each other at said first defined station.

3. The method defined in claim 2 wherein said one layer having the coating is said second layer, the method further including the step of corrugating said second layer at said second station by heated cylinders prior to bringing the layers into said overlying contact to thus effect said preheating step defined in claim 2 while said second layer is being corrugated.

4. The method defined in claim 1 further including the step of passing the formed corrugated board through a heated area at a third station to be heated further after the layers are moved into overlying contact.

5. The method defined in claim 4 further including the step of subjecting the formed corrugated board to inward pressure exerted on the opposite sides thereof on said layers generally at right angles to the main plane of the formed corrugated board during passage of the corrugated board through said heated area at said third station.

6. The method defined in claim 5 further including the step of cooling the formed corrugated board at a fourth station after it leaves said heated area at said third station and while cooling, exerting inward pressure on the opposite sides of the corrugated board in a direction generally at right angles to the main plane.

7. The method defined in claim 1 further including the step of cooling the formed corrugated board after it leaves said station and simultaneously applying inward pressure to opposite sides of the formed corrugated board in directions extending generally at right angles to the main plane of the corrugated board.