Field of the invention

This invention relates to a method for manu¬ facturing a planar product of corrugated fibreboard from single faced corrugated fibreboard consisting of a facing and a fluted paper glued on to its one side. The application also relates to a planar product of corru¬ gated fibreboard made from said single faced corrugated fibreboard.

Finnish Patent Application 870,822 and European Patent Application 323,761 disclose planar packaging materials comprising a honeycomb paper structure, positioned between two layers of paper, with the cell walls of the honeycomb structure perpendicular to the flat surfaces of the material. German Offenlegungs- schrift 4,140,053 discloses a similar product where the liners sandwich, however, loosely positioned discs cut out of a cylinder made by rolling up single faced corrugated fibreboard. Since the cylinder, out of which the discs are cut, is glued only at the beginning and the end, the layers of corrugated fibreboard can move inside the disc in relation to each other and the discs can thus be compressed to provide suitable filling material. Especially packaging material of the kind described in the first two references can be used for quite varying purposes which call for straight and firm packaging material with a good supporting capacity but also with the ability to adjust to, for example, different irregularities of the underlying surface. The material is typically used as end shields of paper reels. Paper reels are normally handled in a vertical

position, so it is extremely important to protect the ends of the paper reels well so that they would not be damaged during handling and transportation. Even the slightest damage to the end of a paper reel often makes the whole reel unusable, because a paper web which has been damaged at one edge easily breaks for instance in a printing machine, where the web moves at a high speed and under tension. The packaging materials with the honeycomb structure described above are well suited for use as the material for end shields of paper reels, for example, but the problem is how to provide the required honeycomb structure. In these prior-art solutions, the honeycomb structure is achieved by gluing strips of paper to each other at intervals and by spreading the resultant structure into a honeycomb construction. Alternatively, the paper strips may be preformed for instance with a profile similar to square waves already before gluing, so that they have straight counterpart surfaces which may be used to glue the strips together to provide a honeycomb structure. However, it is very difficult to automate such gluing methods and therefore such products have not been used more widely.

Summary of the invention

The present invention relates to a new type of method to provide a planar product of corrugated fibreboard without the aforementioned limitations or problems. This is achieved by means of a method according to the invention which is characterized in that it comprises the steps of spreading glue at least on one side of single faced corrugated fibreboard,

cutting a strip of even width out of the corrugated fibreboard, transverse to the longitudinal axis of the flute tubes of the fluted paper, and rolling the strip up into a disc-like roll to provide a planar product of corrugated fibreboard.

An alternative method is characterized in that it comprises the steps of cutting a strip of even width out of single faced corrugated fibreboard, transverse to the longitudinal axis of the flute tubes of the fluted paper, spreading glue at least on one side of the strip, and rolling the strip up into a disc-like roll to provide a planar product of corrugated fibreboard.

In the method according to the invention, the honeycomb structure is achieved by rolling a narrow strip of corrugated fibreboard into a disc-like whole. Thus both the diameter of the disc and the thickness of the resultant planar product of corrugated fibreboard can be controlled as desired. For example a disc intended as an end shield of a paper reel typically has a diameter of 800 to 1400 millimetres and a height, i.e. the width of the strip of corrugated fibreboard, of only a few millimetres.

The planar product of corrugated fibreboard according to the invention can be manufactured by spreading glue either on the flute tops of the fluted paper of the strip or on the free surface of the facing of the strip. In both cases, when the strip is being rolled up, its layers are glued together.

The strip may be rolled up with the facing either outwards or inwards. These alternative ways of implementation as well as the entire method according to the invention are, in fact, based on the

characteristic of single faced corrugated fibreboard that a strip cut out of it can be rolled into a circle where the diameter of the material layer in the inner circumference is smaller than the diameter of the material layer in the outer circumference, because the fluted paper of single faced corrugated fibreboard can both stretch and be compressed.

The product of corrugated fibreboard according to the invention can be used as such, i.e. comprising only the honeycomb material, but this honeycomb material can naturally be reinforced by gluing one layer of paper as a liner either on to one or both flat surfaces of the disc-like roll.

The invention also relates to a planar product of corrugated fibreboard, comprising a disc made by rolling up a strip cut out of single faced corrugated fibreboard consisting of a facing and a fluted paper glued on to its one side, the longitudinal axis of the flute tubes of the fluted paper being perpendicular to the flat surface of the disc. This planar product of corrugated fibreboard is characterized in that the flute tops of the fluted paper are glued at least substantially along the entire length of the strip on to the facing situated against the flute tops in the disc, to provide a planar product of corrugated fibreboard.

As noted above, the product of corrugated fibreboard according to the invention can be used as such as a honeycomb structure, but it can also be reinforced by means of a liner glued on to either one or both flat surfaces of the disc depending on its use.

Brief description of the drawings

In the following the product of corrugated fibreboard and the method for its manufacture according to the invention will be described in greater detail with reference to the accompanying drawing, in which

Figure 1 is a side view of single faced corrugated fibreboard,

Figure 2 is a top view of a product of corrugated fibreboard according to the invention, and

Figure 3 is a side view of one embodiment of the product of corrugated fibreboard according to the invention.

Description of the preferred embodiments

The starting material for the product of corrugated fibreboard according to the invention is single faced corrugated fibreboard 1 as presented in Figure 1, comprising a facing 2 and a fluted paper 3 glued on to its one side. The product of corrugated fibreboard according to the invention can be manu¬ factured by cutting a strip of even width out of the single faced corrugated fibreboard 1 by means of a normal slitter-winder, equipped with for example a scissor edge or a knife edge, transverse to the longitudinal axis of the flute tubes of the fluted paper 3, and by then spreading glue at least on one side of the strip. Alternatively, the glue may be spread before the cutting. The cutting may naturally also be completed in more than one stage, which may be necessary if the initial paper web is relatively wide. If the cutting is performed only after the glue has been spread, the glue may be applied by means of a roll, a spray gun or in some other usual manner by which the glue can be spread

advantageously in narrow stripes. If the glue is applied only after the web of corrugated fibreboard has already been cut into strips, it is not possible to use the roll, but rather a glue pistol, for example. The glue can be applied either on to the free surface of the paper layer 2 or the flute tops of the fluted paper 3. After this, the strip is rolled up into a disc-like roll to provide the planar product of corrugated fibreboard. It is essential to spread the glue at least substantially along the entire length of the strip to be rolled, so that the layers of the resultant disc cannot move in relation to each other, but are glued tightly to each other to provide the desired stiffness.

Figure 2 shows such a disc-like roll 5. In Figure 2 the roll 5 is not represented with the spiral structure it has, but for the sake of clarity the Figure shows the different layers simply in the form of circles. Figure 2 and Figure 3, which is a side view of the roll shown in Figure 2 equipped with a liner 4, show the resultant planar product of corrugated fibreboard where both the facing 2 and the fluted paper 3 of the strips cut out of the single faced corrugated fibreboard

1 are perpendicular to the flat surfaces of the final product. In this way the compression resistance of the product is decidedly better than that of conventional corrugated fibreboard.

In the embodiment shown in Figure 2, the strip of corrugated fibreboard is rolled up with the facing

2 outwards, and thus the outer circumference of the round disc 5 is even, since it is formed by the facing

2 of the outermost layer of the corrugated fibreboard. Alternatively, the rolling could be reversed and then the facing 2 would be inwards and the fluted paper 3 outwards. Thus the outer circumference of the resultant disc-like roll would be formed by the fluted paper 3.

The round product of corrugated fibreboard shown in Figure 2 can be used as such as an end shield of a paper reel. In the most common applications, this so-called inner end shield is placed directly at the end of a paper reel before the reel is wrapped in protective packaging paper. The ends of this packaging paper are then turned on top of the end shield and equipped with a so-called outer end shield, with one paper layer, which protects the reel from dampness. Thus an end shield of the type shown in Figure 2 can be satisfactorily used as such.

Either one or both flat surfaces of the disc¬ like roll 5 shown in Figure 2 may be reinforced with a liner, if desired. Such a liner 4 is shown in Figure 3 placed on one flat surface of the disc 5. As already noted, the liner can also be placed on both flat surfaces of the product. Even though the product of corrugated fibreboard according to the invention is originally round, rectangular pieces or pieces with some other form can naturally also be cut out of such a round preform. In view of the described application, i.e. the use of the product as an end shield of a paper reel, the round form is very useful, however, since the shield may be manufactured directly in the required size, whereas conventionally the shield must be cut out of a web-like product, whereupon a large part of the material has to be cut away and recycled.

The method and the resultant product of corru¬ gated fibreboard according to the invention are described above by means of only one illustrative embo¬ diment, and it is natural that it may be modified in various ways without imparting, however, from the scope of the claims. Thus, for instance the type of the flute tube of the single faced corrugated fibreboard used as starting material may vary and so can also the diameter

and thickness of the final product and the diameter of the central opening in the final product. The thickness can be controlled simply by changing the width of the strip which is the starting material for the product.