SK1122000A3 - Multi-layer screen for the wet area of a paper machine and product manufactured using the same - Google Patents

Abstract

The invention relates to a multi-layer screen (10, 11) for the wet area of a paper machine and to a tissue paper produced using the same. The inventive screen consists of threads, preferably woven threads, forming at least two layers. These layers are joined to each other by additional threads (14) which are interlaced with the layers. Together with the threads which make up the layers, the additional threads (14) form constricted points (16), said constricted points being spread across the length and breadth of the screen. A significantly less quantity of water can pass through these points than through the areas adjacent thereto. Arranged in special sequences, the additional threads are a means of influencing the drainage of water through the screen at the constricted points for producing tissue paper with alternating areas of high and low GSM substance. The invention therefore provides a simple means of producing a tissue paper with a flexible, thin, non-homogeneous, net-like structure.

Description

Technical field

The invention relates to a multilayer screen for the wet part of a paper machine, in particular for the production of tissue paper, with at least two layers made of fibers, preferably woven fibers which are interconnected by means of other interwoven fibers, and an article made using this screen.

BACKGROUND OF THE INVENTION

Such a multilayer screen is known from US 5,219,004.

In the manufacture of paper, in particular tissue paper, it is known to produce alternately high and low basis weight in the wet region by targeted selective dewatering through a screen with regions of differently laid fibers. In places where the screen is more permeable for draining water, ie. in so-called open zones, more fibers are deposited than in so-called closed zones. Typically, the closed and open zones are formed such that the weft and / or warp threads of the fabric forming the screen are arranged at different distances relative to each other in the machine direction of operation and transverse to it.

Thus it is possible to produce paper, e.g. tissue or tissue paper, with a web-like structure in which a generally flat, homogeneous, external force, usually inflexible structure of dried tissue or tissue is replaced by the basis weight differences created by the macroscopic region in sheet production by a flat, inhomogeneous web a similar structure that responds flexibly to external loads. Here, the paper, like conventional tissue or thin paper, has a planar structure in which the individual fibers are firmly anchored. Due to the binding of the fibers to the structure, a non-flexible rigid structure is formed at macroscopic homogeneous basis weight. In the non-crepe state, the tissue or tissue paper has very low elongation values, in the range <6%. By creping, typically used in the production of tissue paper, the tissue paper becomes more flexible to the external forces, but mainly in the machine direction. Higher flexibility in machine direction, with a homogeneous paper structure achievable by creping, results in increased effect due to greater elongation in machine direction.

By converting a flat, homogeneous structure on a web-like, flat, non-homogeneous structure, the flexibility of the paper and hence of the tissue or tissue paper can be further improved, this improvement being not limited to the machine direction, but can also be achieved in the transverse direction machine operation.

As already mentioned, the web-like structure is obtained by varying the basis weight, wherein the regions of high basis weight and the regions of low basis weight alternate in the macroscopic area. Changes in basis weight are achieved by varying the drainage capacity of the screen. The locations where many fibers are deposited according to the above embodiments are high basis weight zones. Places where few fibers are deposited are low basis weight zones.

Furthermore, due to the locally different dewatering power of the screen, partial flows parallel to the screen surface arise, whereby the fibers more or less strongly equalize, similar to the formation of true watermarks.

It is known to obtain zones of different drainage performance by sieving the sieve by closing the zones in the sieve with plastic adhesive or paint, etc. (e.g. WO 93/00474).

The openness variations of the screen can also be realized by a combination of different fabric patterns. In this case, the base fabric of the sieve forming the structure may be single or multilayer, but preferably bilayer. As already mentioned in connection with U.S. Pat. No. 5,219,004, it is already known to bond the layers to one another by means of further fibers.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multilayer structure forming a mesh of the type mentioned above which makes it possible in a simple manner to adjust said modified drainage characteristics for the manufacture of an improved product.

This object is achieved according to the invention in that the other fibers form, together with the layer-forming fibers, ticked spots, distributed over the width and length of the sieve, through which significantly less water can flow than through adjacent areas.

This solution is characterized in that the other fibers serving to join the layers of the screen are used to form closed or substantially closed screen zones, the substantially open zones being formed in areas of the screen where the other fibers do not close the meshes in the base fabric. Thus, the other fibers perform a double function. With such a screen it is possible to produce a substantially improved paper product, in particular tissue or tissue paper.

In a preferred further embodiment of the present invention, the other fibers that form the checkpoints may be e.g. in the direction of machine operation and to appear at predetermined locations on the top of the screen or on the layer located therein, thereby forming, through checkpoints located in a grouping or in different directions, checkboxes which form a pattern on the screen surface . These spots form macroscopic regions of low basis weight on the tissue or tissue paper, i.e., on the tissue. with lower fiber deposition than in adjacent regions, thereby affecting the elongation behavior in the longitudinal and transverse directions, but particularly preferably in the transverse direction. This is due to the fact that, in a particular arrangement, portions of the low basis weight area result in a weakening compared to the homogeneous structure, thereby achieving the desired increased flexibility of the non-homogeneous structure over the homogeneous structure. The above-mentioned basis weight differences, which can be produced by a predetermined structure in the fibrous structure of the paper, in particular tissue or tissue paper, result in an increase in effect in the longitudinal and transverse directions, which is particularly desirable for tissue paper.

For example, when the checkpoints for forming the elongated sections are aligned obliquely to the direction of operation of the machine comprising the screen, greater flexibility is achieved transversely to the direction of operation of the machine, in addition to the flexibility in the machine direction.

In the same sense, the check points for forming the elongated sections may be aligned partly perpendicular to the machine operating direction and partly in the machine operating direction.

Due to the possibility of further construction, the elongated sections can also be arranged alternately in opposite directions. However, the elongated sections may also be arranged in parallel in groups with the same orientation.

According to another embodiment, the ticked locations may be aligned to form zigzag waveforms or waveforms.

The checkpoints may be arranged such that they are formed closed or at least partially open but also continuous. The arrangement of the checked locations may also be such that there is only a discontinuous waveform or a discontinuous waveform and a continuous waveform.

A paper product made with such a screen, in particular tissue or tissue paper, has greatly improved properties, in particular with respect to feel or softness. There is a positive effect on dry and wet strength as well as a positive effect on the creping, drying, pressing and dewatering process.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in more detail by way of examples, purely schematically shown in the drawings. In the drawings:

Fig. 1 is a plan view of a multilayer screen according to the invention;

Fig. 1a shows a section through the screen of FIG. 1 along line a-a;

Fig. 1b shows a section through the screen of FIG. 1 along line b-b;

Fig. 2-5 is a plan view of various tissue structure patterns made using multi-layered sieves similar to that shown in FIGS. 1;

Fig. 6-12 is a schematic representation of other multilayer screens with a different arrangement of additional fibers as bonding fibers;

Fig. 13a the usual homogenous tissue paper before and after the application of a tensile force in the direction of the arrow; and FIG. 13b is a flat, non-homogeneous tissue-like tissue paper according to the invention, both before and after the application of a tensile force in the direction of the arrow.

DETAILED DESCRIPTION OF THE INVENTION

The double-layer screen is formed as a fabric, with the top fabric 10 and the bottom fabric 11. The direction of operation of the machine with the screen is shown by the arrow A. The fibers 12a of the top fabric (paper contact side) may be designed as warp fibers, or also as weft fibers, but preferably as warp fibers. The same applies, but vice versa, to the fibers 12b of the top fabric. The same applies to the fibers 13a and 13a, respectively. 13b of the bottom fabric.

In this embodiment, the other filaments 14 run in the same direction and parallel to the filaments 12a so that in the representation of FIG. 1b, further fibers 14 extend between the fibers 13b and the fibers 13c of the backsheet 11 and close the mesh meshes 15 at the points shown in FIG. 1 by appearing on the upper side of the top fabric 10 and extending over the fibers 12c of the top fabric. There, the other fibers 14 form a check mark 16 in the machine direction. These check points 16 aligned obliquely to the machine direction A form check areas 17 formed as elongate sections. For example, two parallel check regions 17 and 18 may be arranged in one direction in each direction. These check areas can be e.g. arranged alternately in mutually perpendicular directions, so that the check areas form a pattern. These check areas form the aforementioned low basis weight zones of tissue or tissue formed on this web, thereby giving it the desired non-homogeneous web-like non-homogeneous structure, which has a high flexibility in stress. Various embodiments of such a structure are apparent from FIG. 2 to 5. FIG. 2 shows the product produced by the screen structure of FIG. 1. In this case, the dark areas of the surface form the aforementioned network-like structure. This creates a continuous high basis weight zone. The same applies to the product of FIG. 3, 4 and 5. 2, 3, 4 and 5, dark areas of high basis weight may also represent low basis weight zones, and light areas of low basis weight may represent respective high basis weight zones (see, e.g., FIG. 2a, 3a). Then, the aforementioned network-like structure forms part of the surface, represented by light.

Further variations of the screen structure are shown schematically in FIG. 6 to 8. In the case of the product produced by the screen structure of FIG. 7 or 8, portions of the low basis weight surface form the aforementioned network-like structure.

As shown in FIG. 13a, in the case of ordinary tissue paper, virtually no elongation of the tissue paper is detectable under the action of a pulling force, but is significant with the tissue paper of FIG. 13b.

Claims (14)

PATENT CLAIMS Multilayer screen for a wet part of a paper machine, made of fibers, preferably woven fibers, having at least two layers (10, 11) which are joined by means of further fibers (14) intertwined by layers (10, 11), characterized in that: that the other fibers (14) form, together with the fibers (12a, 12b, 12c; 13a, 13b, 13c) forming the layers (10, 11), ticked spots (16) divided by the width and length of the screen through which it can flow significantly less water than through neighboring areas. The multilayer screen according to claim 1, characterized in that the other fibers (14) forming the check points (16) extend in the machine operating direction (A) and appear at predetermined points on the top side (10) of the screen or on the screen. The layer (17, 18) forms a pattern on the screen surface by means of check points located in a mutual grouping or in rows of different directions. Multilayer screen according to claim 1 or 2, characterized in that the check points (16) are aligned obliquely to the machine operating direction (A) to form the elongated sections (17, 18). Multilayer screen according to claim 1 or 2, characterized in that the check points (16) are aligned partly perpendicular to the machine operating direction (A) and partly in the machine operating direction to form the elongate sections (17, 18). Multilayer screen according to claim 3 or 4, characterized in that the elongated sections (17, 18) are arranged alternately in opposite directions. Multilayer screen according to claim 3 or 4, characterized in that the elongated sections (17, 18) are arranged in parallel in groups with the same orientation. Multilayer screen according to at least one of Claims 1 to 3, characterized in that the check points (16) are aligned to form a zigzag pattern or a wave pattern. Multilayer screen according to claim 1 or 2, characterized in that the check points (16) are arranged to form closed courses. The multilayer screen according to claim 1 or 2, characterized in that the check points are arranged so as to form at least partially open waveforms. Multilayer sieve according to claim 1 or 2, characterized in that the check points are arranged to form continuous courses. Multilayer sieve according to claim 1 or 2, characterized in that the check points are arranged to form discontinuous waveforms. The multilayer screen according to claim 1 or 2, characterized in that the check points are arranged to form continuous and discontinuous waveforms. A product made on a paper machine by means of a multilayer screen according to at least one of claims 1 to 12. Product according to claim 13, characterized in that it is tissue paper.