FI93886C - Cardboard and process for making them - Google Patents

Description

93886

CARTON AND METHOD FOR ITS MANUFACTURE

The invention relates to a paperboard structure comprising two surface layers made of lignocellulosic fibers or similar web material and an intermediate layer interposed therebetween. The invention further relates to a method for manufacturing said cardboard structure.

Folding boxboard is mainly used as a packaging material. Due to its intended use, an important property of folding car-10 tong is its rigidity. In order to obtain good stiffness properties, folding boxboard is traditionally three-layered, comprising two surface layers and a middle or intermediate layer placed between them. The intermediate layer is generally prepared by an inexpensive 15-we-mechanical pulp or recycled pulp, an intermediate layer on each side is usually made of chemical pulp of high strength (high modulus of elasticity having) the surface layers. The intermediate layer connects the surface layers to each other, and the function of the intermediate layer is to keep the surface layers 20 as far apart as possible, thus making the structure as rigid as possible. Due to their structure, folding boxboard is usually made on multi-ply board machines, nowadays most commonly on multi-wire machines.

There are some 25 problems associated with the manufacture of folding boxboard. The web control of the multilayer board machine used in the manufacture is quite complex, and the manufacture thus causes some practical problems. In addition, the order sizes are small on average, which means that the board machine has to make type changes very often.

Furthermore, the proportion of the intermediate layer in the weight of the board is considerable. For strength reasons, the basis weight of the surface layers is at least 25 to 40 g / m 2, e.g. 225 g / m 2, and in folding boxboard the intermediate layer accounts for about 65 to 35% of the basis weight. If the interlayer could be replaced by a light, rigid material, the basis weight of the board could probably be reduced without compromising the thickness and stiffness of the board.

Developments in the Central European market and legislation are likely to require a reduction in the amount of packaging materials in the future. With current raw materials, this seems quite difficult to achieve if the current board quality requirements are to be maintained.

In order to solve the problems, e.g. replacement of the intermediate layer with a foamed plastic that adheres firmly to the surface layers. Cardboards prepared in this way are used in the graphic industry, e.g. as priming and bonding materials. However, the use of plastics as an intermediate layer for packaging boards may not be possible due to the poor recyclability of plastics.

It is an object of the present invention to obviate the above drawbacks. In particular, the object of the invention is to provide a new type of cardboard structure, mainly intended for packaging material, which is more advantageous in terms of manufacturing method and price than before, and which is completely recyclable.

It is a further object of the invention to provide a method for manufacturing said paperboard structure.

The features of the invention are set out in the claims.

The invention is based on the basic idea that the middle or intermediate layer of the board is replaced by starch. The starch is foamed and / or expanded and hardened between the surface layers. Appropriately foamed starch is rigid, slightly elastic and 30 quite strong. The board according to the invention is then very rigid and meets the criteria set for good folding boxboard.

According to the invention, the intermediate layer contains starch as an essential building component, the intermediate layer may then contain more than 20% by weight, preferably more than 50% by weight of starch, i. preferably the intermediate layer consists mainly of starch.

»93886 3

An intermediate layer made of starch alone, e.g. foamed and / or expanded starch, is quite transparent. To improve the opacity of the foam, additives such as lig-5 nosellulose fibers or mineral pigment may be added. Thus, the intermediate layer may contain less than 50% by weight, preferably less than 30% by weight and most preferably less than 10% by weight of lignocellulosic fibers. The lignocellulosic fibers can be, for example, groundwood, cellulose, recycled pulp, etc. The fibers increase the strength (internal bonding) and processing resistance of the intermediate layer.

The paperboard according to the invention can be produced e.g. by producing surface layers and an intermediate layer in separate process steps; an intermediate layer by frothing or swelling the starch into a web-like product which can also be pre-cured. The intermediate layer may also be cured after being placed between the surface layers, e.g., between smooth-surfaced rolls, heated planes, or combinations thereof; the swellable intermediate layer of täl-20 swells the surface papers against the heated rolls or the like and the surface of the web becomes smooth, even if the basis weight of the surface papers is not completely uniform.

In general, surface papers can be made into Erik-25 with efficient paper and / or coating machines.

"I The change of grade from one board to another is very simple; the change in basis weight level only requires a change in the amount or density of the middle layer of foam.

By mixing a small amount of carbonate or other gas-disintegrating or otherwise gaseous material with the starch to be foamed or expanded, foaming can be maintained and controlled during drying, whereby the resulting foam better fills the space between the surface layers of the product.

The expansion of the foam can also be carried out by mixing the pretreated, e.g. cooked binder and the gas-forming substance at a suitable temperature into a foam and by extruding the mixture between the surface layers. During drying, the foam swells under the influence of gas.

10 The lamination of the intermediate layer and the surface layer can be combined with sheet cutting. In this case, the hardening can be carried out immediately without rolling the product. In this case, the problems of curvature or the like caused by rolling the board are reduced.

It is already known from US 5,061,345 to add starch to plywood in order to increase the strength of the recycled paper used. It is further known from US 5,106,880 to use a foamed plastic material containing starch with corrugated board materials. It is further known from US 4,369,080 to add starch to the interlayer of corrugated board. In addition, it is known from Wochenblatt 6, 1993, pp. 213-217 (presented in Munich 1992) to add starch between two sheets; The li-25 coating is carried out by spraying between the layers, possibly also with corrugated board. However, in said publications, the addition of starch takes place as such, i.e. without foaming and / or swelling.

In the method according to the invention, the starch to be added is instead foamed and / or expanded, which improves the strength properties of the plywood in question without increasing the basis weight of the board and / or the amounts of material used. The product according to the invention differs substantially from that disclosed in the referenced publications in terms of its specific performance characteristics and rigidity.

The product according to the invention is suitable for use as a recyclable material. The use of starch as a raw material for paperboard may further solve the problems of agricultural overproduction, i.e. starch can be made, for example, from cereals, potatoes, etc. from a carbohydrate-5-containing agricultural product. Appropriately foamed / expanded starch does not lose its strength very easily, e.g. a product foamed or expanded from corn is reasonably water resistant.

The product according to the invention is competitive in its properties and cheaper in manufacturing costs than similar products. Furthermore, the equipment required to manufacture it is simple and the investment involved is relatively small. Furthermore, starch is currently a cheaper raw material than lignocellulosic acid.

The invention will now be described in detail with reference to the accompanying drawing, in which Figure 1 shows a section of a board made according to the invention, and Figures 2 to 4 show schematically some embodiments of the method according to the invention.

Figure 1 shows an enlarged view of a paperboard structure comprising two surface layers 1 and 2 made of a web-like material and a middle or intermediate layer 3 interposed therebetween. The surface layers are made of a lignocellulosic fibrous material, e.g.

paper, etc. The intermediate layer consists mainly of starch which has been foamed and / or expanded.

Instead of the intermediate layer 3, which consists mainly of starch only in Fig. 1, an intermediate layer made of several different materials can also be used, as long as it contains starch as an essential component. Thus, the intermediate layer may further comprise lignocellulosic fibers, e.g. ground fibers, to improve the light scattering properties and / or to improve the strength properties. Furthermore, the intermediate layer may also contain some other light scattering additive 93886 6.

Figure 2 shows an embodiment of the implementation of the method according to the invention, in which the surface layers 1, 2 prepared in a conventional process in separate process steps are guided between two rolls 4 arranged at a certain distance from each other. At the same time, foamed or expanded starch 3 is passed between the surface layers. Between the rolls 4, the raw materials form a finished board 5, which can be passed 10 further between other rolls and / or planes, e.g. for curing.

The embodiment shown in Figure 3 corresponds in principle to the embodiment shown in Figure 1, i. the surface layers 1 and 2 formed in the separate processes are passed between the heated planes 6 and the pairs of rollers 4, while foamed starch is passed between the surface layers, which forms an intermediate layer of the formed cardboard web.

In Fig. 3, the surface layers 1 and 2 are formed between the roll 4 20 and the wire 7 and the counter-rolls 8 supporting them. The wire 7 then rotates the roll 4 and compresses the surface layers 1 and 2 and the foamed starch 3 to be passed between them into cardboard 5.

In Figures 2-4, the starch is passed as a foam 25 or expanded between the surface layers. However, if desired, the starch can also be formed into a solid web-like product to which the surface layers are attached. The paperboard formed in this way can be further heated to expand the interlayer into the surface layers.

The embodiments are intended to illustrate the invention, and embodiments of the invention may vary within the scope of the appended claims.

Claims (17)

A cardboard structure to which two layers of lignocellulosic fibers or similar web material (1, 2) and an intermediate layer (3) placed between them belong, characterized in that the intermediate layer contains as a major component starch, and that the starch is made of foam and / or thick. Cardboard structure according to claim 1, characterized in that the intermediate layer (3) contains more than 20% by weight, preferably over 50% by weight of starch. Cardboard structure according to claim 1 or 2, characterized in that the intermediate layer (3) contains less than 50% by weight, advantageously below 30% by weight and most preferably less than 10% by weight lignocellulosic fibers. Cardboard structure according to any one of claims 1 to 3, characterized in that the intermediate layer (3) consists mainly of starch and that the intermediate layer contains light-spreading supplementary material. Cardboard structure according to any of claims 1 to 4, characterized in that the intermediate layer (3) containing starch is glued to the surface layers (1, 2). Cardboard structure according to any one of claims 1 to 5, characterized in that the intermediate layer (3) containing starch is formed in a separate production stage and the surface layers (1, 2): have subsequently been connected to each side of the intermediate layer. . Cardboard structure according to any of claims 1-5, characterized in that the surface layers (1, 2) are made in a separate process stage and the intermediate layer (3) containing starch has been placed between the surface layers here. and the starch has been made into foam and / or made thick. Cardboard structure according to any of claims 1 to 7, characterized in that the cardboard structure is non-rollable and that it is cut into sheets after the cardboard structure is formed. A process for producing a cardboard structure / tile which comprises two surface layers (1, 10 2) made of lignocellulosic fibers or similar web material and an intermediate layer (3) located therebetween, which are joined together into a uniform cardboard structure, characterized in thereof, that the intermediate layer (3) is reinstalled by using as a substantial component starch, and that the starch is foamed and / or thickened and that the intermediate layer (3) is formed therefrom. 10. A process according to claim 9, characterized in that the surface layers (1, 2) and the intermediate layer (3) containing more than 20% by weight, preferably more than 50% by weight of starch, are combined into a uniform carton structure. . 11. A process according to claim 9 or 10, characterized in that in the starch material, less than 50 wt.%, Preferably below 30 wt.% And most preferably less than 10 wt.% Lignocellulosic fibers are mixed. ': Laminate layer (3) and surface layer (1, 2) are connected between layers. 12. A method according to claims 9 - 11, characterized in that, to the starch material, light spreading additive material is added, the intermediate layer is made of the obtained material, and: the surface layers (1, 2) are connected to the intermediate layer. 13. A method according to claim 12, characterized in that the foaming and / or thickening is done after the starch and possible additives have been mixed together, and that the intermediate layer is formed from foam made from starch material. • · 93886 Method according to any of claims 9-13, characterized in that the surface layers (1, 2) are formed in separate process stages and the intermediate layer (3) is made into a foam in a separate process stage, and that the surface layers are connected to the foam. interlayer. Method according to any of claims 9 to 13, characterized in that the surface layers (1, 2) are formed in a separate process stage and the intermediate layer (3) is foamed between the surface layers. Method according to any of claims 13 to 15, characterized in that the intermediate layer (3) containing starch is made into foam and / or thickened after the surface layers (1, 2) have been connected to each side of the intermediate layer. and that the foam making and / or thickening is realized between rollers (4, 5) or the like. 17. A method according to any of claims 9-16, characterized in that the cardboard structure is not rolled and cut into sheets. «I • I • I