MULTILAYER PAPER CONTAINING WASTEPAPER AND GRASS FIBERS

Abstract

A paper (10) is disclosed, especially for use in the production of corrugated cardboard. The paper (10) is formed from at least two layers couched together and having different composition and it contains wastepaper fibers and grass fibers. The special feature of the paper is that a first layer of the paper (10) is formed as a support layer (11) and contains a maximum fraction of 30 wt. % of grass fibers, a second layer of the paper (10) forms a top layer (12) with a minimum fraction of 20 wt. % of grass fibers and a maximum fraction of 80 wt. % of wastepaper fibers, and the fraction of grass fibers in the top layer (12) is higher than the fraction of grass fibers in the support layer (11).

Claims

1. A paper, especially for use in the production of corrugated cardboard, wherein the paper comprises at least two layers couched together and having different composition and wherein the paper contains wastepaper fibers and grass fibers, wherein a first layer of the at least two layers of the paper is formed as a support layer and contains a maximum fraction of 30 wt. % of grass fibers, a second layer of the at least two layers of the paper forms a top layer with a minimum fraction of 20 wt. % of grass fibers and a maximum fraction of 80 wt. % of wastepaper fibers, and the fraction of grass fibers in the top layer is higher than the fraction of grass fibers in the support layer.

2. The paper according to claim 1, wherein the fraction of grass fibers in the top layer is at least 5 wt. % higher than the fraction of grass fibers in the support layer.

3. The paper according to claim 1, wherein the fraction of grass fibers in the support layer is at most 25 wt. %.

4. The paper according to claim 1, wherein the fraction of grass fibers in the top layer is from about 20 wt. % up to about 70 wt. %.

5. The paper according to claim 1, wherein the minimum fraction of grass fibers in the top layer is 25 wt. %.

6. The paper according to claim 1, wherein the support layer has a minimum fraction of wastepaper fibers of 70 wt. %.

7. The paper according to claim 1, wherein the paper contains no virgin fibers.

8. The paper according to claim 1, wherein the at least two layers contain different kinds of wastepaper fibers.

9. The paper according to claim 8, wherein the top layer contains wastepaper fibers obtained from white wastepaper and the support layer contains brown wastepaper fibers.

10. The paper according to claim 8, wherein the support layer contains wastepaper fibers of kraft paper or kraft cardboard.

11. The paper according to claim 1, wherein the paper has a weight per unit area of from about 80 g/m2 up to about 200 g/m2.

12. The paper according to claim 1, wherein the support layer has a weight per unit area of from about 60 g/m2 up to about 170 g/m2.

13. The paper according to claim 1, wherein the top layer has a weight per unit area of 30 g/m2 to 50 g/m2.

14. The paper according to claim 1, wherein the paper has a cleavage strength determined by the International Scott bond test per DIN ISO 16260 of from about 180 J/m2 up to about 300 J/m2.

15. The paper according to claim 1, wherein the paper has a Cobb60 value of the top layer per DIN EN ISO 535 of at most 40 g/m2.

16. A method for production of a paper with the following steps carried out in a paper making machine: placement of a first fiber composition containing water, grass fibers in a maximum fraction of 30 wt. % or less, in terms of the dry weight, as well as wastepaper fibers, in the form of a web on a first screen; placement of a second fiber composition containing water, grass fibers in a minimum fraction of 20 wt. % or less, in terms of the dry weight, as well as wastepaper fibers in a maximum fraction of 80 wt. %, in terms of the dry weight, in the form of a web on a second screen, wherein the second fiber composition has a higher fraction of grass fibers than the first fiber composition; couching of the webs formed on the first and second screens to produce an at least two-layer paper web; and drying of the paper web.

17. The paper according to claim 2, wherein the fraction of grass fibers in the top layer is at least 10 wt. % higher than the fraction of grass fibers in the support layer.

18. The paper according to claim 2, wherein the fraction of grass fibers in the top layer is at least 15 wt. % higher than the fraction of grass fibers in the support layer.

19. The paper according to claim 3, wherein the fraction of grass fibers in the support layer is at most 20 wt. %.

20. The paper according to claim 5, wherein the minimum fraction of grass fibers in the top layer is 30 wt. %.

21. The paper according to claim 5, wherein the minimum fraction of grass fibers in the top layer is 35 wt. %.

22. The paper according to claim 5, wherein the minimum fraction of grass fibers in the top layer is 40 wt. %.

23. The paper according to claim 11, wherein the paper has a weight per unit area of from about 125 g/m2 up to about 175 g/m2.

24. The paper according to claim 14, wherein the paper has a cleavage strength determined by the International Scott bond test per DIN ISO 16260 of from about 220 J/m2 up to about 300 J/m2.

25. The paper according to claim 15, wherein the paper has a Cobb60 value of the top layer per DIN EN ISO 535 of less than 35 g/m2.

26. The paper according to claim 15, wherein the paper has a Cobb60 value of the top layer per DIN EN ISO 535 of less than 30 g/m2.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0034] Further advantages and features of the invention will emerge from the following specification and from the referenced figures. There are shown:

[0035] FIG. 1 a schematic representation of the production of a paper web containing grass fibers as a single web according to the prior art, and

[0036] FIG. 2 a schematic representation of the production of a two-layer paper web according to the invention, composed of a support layer and a top layer containing grass fibers.

DETAILED DESCRIPTION

[0037] FIG. 1 first of all shows a traditional method for the production of a single-layer paper in highly schematic representation. A paper web 1 is produced in familiar manner in a paper making machine by placing pulp based on wastepaper onto a screen and by a first dewatering, as well as subsequent drying, and it is then wound up onto a paper roll. It is known here that a fraction of grass fibers is added to the paper so produced as a paper web 1, more precisely, to the fiber composition. However, the possible fraction of added grass fibers is limited, since grass fibers are even shorter than the already not particularly long fibers of the wastepaper, so that they may cause less strength in the fiber bonds of the paper. In order to achieve the required tear strength and other technological properties of the paper, the admixture of grass fibers in with a pulp mixture otherwise based on wastepaper for the paper making is limited, typically to a maximum of 20 to 30 wt. %.

[0038] In order to meet the requirements of the consumers and users of such paper, who desire in particular on account of ecological considerations on the one hand a higher overall fraction of grass fibers in the paper and on the other hand also demand an appearance of the paper, or at least a visible or top surface, which clearly reveals the grass fibers contained in the paper, i.e., its grass paper nature, the inventors have now created a different method for the production of such paper, which is shown schematically in FIG. 2.

[0039] Here, a paper web 10 is produced in multiple layers, in the present case two layers. For this, a first paper layer, or support layer 11, is formed by placing a first fiber composition on a first screen of a paper making machine, e.g., on a bottom wire. In parallel, a second paper layer, or top layer 12, is formed by placing a second fiber composition on a second screen of a paper making machine, e.g., on a top wire. The support layer 11 contains a high fraction of wastepaper fibers, e.g., wastepaper fibers in a fraction of at least 70 wt. %, in terms of the dry weight. The top layer 12 on the other hand is characterized by a high fraction of grass fibers, namely, at least 20 wt. % by dry weight. The fraction of grass fibers in the top layer 12 may in particular be between 30 and 70 wt. %. The support layer 11 may also contain grass fibers, the fraction of grass fibers being limited there to a maximum of 30 wt. %, preferably to a maximum of 25 wt. %, especially a maximum of 20 wt. %, and the fraction of grass fibers in the top layer 12 being in any case higher, especially significantly higher, than a fraction of grass fibers in the support layer 11. Preferably, the remainder of the dry weight in the support layer 11 is formed entirely by wastepaper fibers. However, it may also contain virgin fibersbut preferably only in a small fraction. Thus, the support layer 11 has a sufficiently stable formation, in order to guarantee the tear strength and also other qualities demanded of the paper of the paper web 10.

[0040] In the top layer 12, the fraction of fibers not formed by grass fibers is likewise realized entirely by wastepaper fibers, and here as well it may also contain apreferably smallfraction of virgin fibers. The top layer 12 on account of the high fraction of grass fibers is not in itself sufficiently stable and as such it does not fulfill the technological properties demanded of the paper in the paper web 10.

[0041] By the merging of the two webs of support layer 11 and top layer 12 at position 13 and by the couching of the two webs here, the two-layer paper 10 is then obtained, having the demanded technological propertiesprimarily due to the properties of the support layer 11. This paper web 10, after further dewatering and drying, is typically wound up onto a paper roll 14.

[0042] The paper web 10 in particular may have a weight per unit area of 80 to 200 g/m2. The paper may be such, for example, as is used in a later use in the production of corrugated cardboard.

[0043] The support layer 11 in particular may have a weight per unit area of 60 to 170 g/m2, The top layer 12 in particular may have a weight per unit area of 30 to 50 g/m2. By an adjusting of the ratio of thicknesses, i.e., weights per unit area, of the support layer 11 and the top layer 12, an adjusting of the required technological properties and moreover also an adjusting of the fraction of grass fibers in the two-layer paper web 10 can be done (for preadjusted fractions of grass fibers in the top layer 12 and optionally also the support layer 11).

[0044] The two-layer paper web 10 preferably has a cleavage strength, determined by the international Scott bond test per DIN ISO 16260, of 180 to 300 J/m2, especially 220 to 300 J/m2.

[0045] For the top layer 12, a Cobb60 Wert per DIN EN ISO 535 of at most 40 g/m2, especially less than 35 g/m2, preferably less than 30 g/m2, is preferably adjusted. This is then maintained by a familiar adding of glue and/or starch.

[0046] In order to obtain a particular appearance of the top layer 12, it may be provided e.g. that the wastepaper fibers used there are obtained from white wastepaper. Especially in a white-base top layer the greenish grass fibers are especially evident and thus easily perceived by the observer of an end product made from the paper according to the invention, having the top layer 12 as a visible surface.

[0047] It has once again been made evident from the preceding specification what benefits are provided by the paper according to the invention and the method for its production. In particular, it is made clear that, on the one hand, the total fraction of grass paper fibers can be increased in a paper produced on the basis of wastepaper fibers and adjusted in a very broad manner, and that at the same time a top layer can be obtained, which may afterwards serve in particular as a visible surface, in which an especially high fraction of grass fibers is incorporated, having an appearance which accordingly reveals very well the grass paper nature of the paper.

LIST OF REFERENCE NUMBERS

[0048] 1 Paper web

[0049] 2 Paper roll

[0050] 10 Paper web

[0051] 11 Support layer

[0052] 12 Top layer

[0053] 13 Position

[0054] 14 Paper roll