MULTI-LAYER PAPER AND METHOD OF MAKING THE SAME

Abstract: At the making of multi-layer paper it has been a problem to bringabout sufficient adhesion between the layers in an efficient and economic way. According to the invention this problem is solved, in that a cellulose pulp with a beating degree exceeding 40<o>SR in an amount of at maximum 10 g/m<2> is inserted between the layers.

Description: Multi-layer paper and method of making the same This invention relates to a mult-layer paper, which for increasing the adhesion between the layers has been supplied with a binder, and to a method of making such paper. At the making of cardboard and other multi-layer paper, the paper is manufactured by the couching of separately formed paper webs. When the paper is used, problems can arise if the adhesion forces between .the layers are not sufficiently great. To-day the problems are coped with primarily either by increased beating of the pulps for each layer or by supplying starch in each layer or between the layers prior to couching. Increased beating primarily involves--the disadvantages of higher energy consumption, loss of bending stiffness of the cardboard due to decrease in thickness, and reduced machine capacity. The addition of starch causes disadvantages such as high material, equipment and handling costs and clogging of the nozzles in spray installations. The object of the present invention is to overcome the said disadvantages. . The principle of the invention is in a separate head box, spray nozzle or other application device to add a cellulose-based thin layer' between two layers already formed. The material in this thin layer can consist of intensely beaten papermaking pulp, fine material made separately, sedimented fine material or fibres and fine material from white water or other waters containing cellulose and fibres, it is essential that the material has a beating degree of at least 4θ°SR. The amount of added material must not exceed 10 g/m . The thin cellulose-based layer has the capacity of acting as a size layer increasing the adhesion capacity between the two layers formed. As the layer adhesion between two formed layers has a strength equal to the inner " strength in each layer, the layer adhesion does not limit the general strength level. The beating degree in each layer, thus, can be chosen so that optimum bending stiffness is obtained. The invention is described in greater detail in the follow- ing by way of an embodiment and with reference to the accompanying drawings, in which Fig. 1 shows a machine design for making the paper according to the invention, and Fig. 2 shows the Scott-bond value for different test " conditions. Fig. 1 shows a twin wire machine with the wires 1 and, respectively, 2. A first pulp suspension is supplied through a head box 3 and results in a web 5- In a corresponding way, a web 6 web 6 is formed by supplying a second pulp suspension through the head box 4. The binder according to the invention consisted of an intensely beaten paper- making pulp with a beating degree of about 6θ°SR and was sprayed between the two already formed layers through the nozzle 7. The amount of material applied was 5 g/m . The material was applied in a concentration of about 1% . Each layer consisted of 75 g/m unbleached sulphate pulp beaten to 18 or 27°SR. After the layers had been combined in usual manner, a web 8 was obtained which subsequent to its pressing in a number of rolls 8,9 yielded the two-layer paper 11. Sheets of the paper were dried off-machine partially , freely and partially clamped in frames. The results were compared to application of starch in the same amount and only water. The diagram in Fig. 2 show-s the Scott-bond value (a measure of layer adhesion) for different test conditions. The figure shows the Scott-bond values MD (machine direction) at constant press conditions (50 + 60 + 70 KN/m pressure applied). Besides, two drying methods have been used. As can be seen, the Scott-bond increases substantially with said additions and shows an effect equal to or better than with starch addition. The invention is not restricted to the embodiment shown, but can be varied within the scope of the invention idea.

Claims: Claims 1. A multi-layer paper containing between at least two of the layers a material acting as a binder for improving the adhesion therebetween, c h a r a c t e r ¬ i z e d i n that the material consists of a cellulose pulp with a beating degree exceeding 40 SR, preferably exceeding 60°SR, in an amount of at maximum 10 g/m , 2 preferably at maximum 3 g/m • 2. A multi-layer paper as defined in claim 1, c h a r a c t e r i z e d i n that the material con- sists of intensely beaten paper aking pulp, fine material separated from intensely beaten papermaking pulp and/or fine material, possibly containing fibres, from white water. 3. A method of making multi-layer paper according to the claims 1 - 2, by addition of a material acting as a binder, c h a r a c t e r i z e d -- i n that the material consists of a cellulose pulp with a beating degree exceeding 40 SR, preferably exceeding 60 SR, which after the wet forming of the layers is inserted between at least two of the layers in an amount of at maximum 10 g m 2, preferably at maximum 3 g/m2, whereafter the layers are combined in a way known per se. 4. A method as defined in claim 3, c h a r a c t e r ¬ i z e d i n that the material consists of intensely beaten papermaking pulp, fine material separated from intensely beaten papermaking pulp and/or fine material, possibly containing fibres, from wite water.

Inventors: FELLERS NILS CHRISTER, HTUN MYAT THOUNG, LILJA JONAS EVERT, FELLERS, NILS, CHRISTER, HTUN, MYAT, THOUNG, LILJA, JONAS, EVERT
Applicants: SVENSKA TRAEFORSKNINGSINST, SVENSKA TRAEFORSKNINGSINSTITUTET
Application year: 1984
Main classification: D21H3
IPC codes: D21F11, D21H27