EP1818448B1 - Use of a forming screen - Google Patents

Abstract

Sheet former wire for a paper machine comprises a permeable support and a pattern of discrete islands of UV-curable resin that are less permeable than the surrounding network structure and do not project above the sheet-forming side of the wire.

Description

The invention relates to the use of a forming wire as a wire for the forming section of a paper machine having a permeable carrier having a forming side and a machine side and having a pattern of discrete surface islands of cover material whose permeability is less than that of the surface islands surrounding a web structure forming surface areas, wherein the cover material does not project beyond the sheet forming side of the carrier.

Wrapping paper is understood to mean wrapping papers which are subdivided into different groups according to the requirements imposed on them, depending on the strength, density, describability and / or printability as well as the material composition. Such packaging papers have a basis weight of at least 25 g / m ² . If packaging papers are used for pack sacks used in the industrial sector, for example for the transport of bulk goods (industrial bags), the basis weight is at least 30 g / m ² and reaches up to 200 g / m ² .

Packing papers, like other types of paper, are made in papermaking machines by feeding fiber pulp comprising paper fibers onto a forming wire which is uniformly permeable over the surface and which is formed as a wire and circulates in the forming section of the paper machine. On the sheet forming side of the sheet forming screen, this causes a paper web formation while dewatering the paper web through the sheet forming screen. In the subsequent press section of the paper machine, the paper web is further dehydrated mechanically by pressing. Thereafter, a thermal dewatering takes place in the dryer section of the paper machine.

The known packaging papers have a density and thickness substantially equal over the surface. They must have a tensile strength and tensile elongation at break and tensile breaking load capacity to ensure that they do not break or break during transport. If such packaging papers or paper bags made from them are used for the transport of bulk material, the packaging paper must be permeable to air so that the air in the paper bag can also escape through the packaging paper when filling the bulk material. This property determines the speed of the filling process. High strength on the one hand and good air permeability On the other hand, however, requirements are contradictory because a wrapping paper with good air permeability has a low strength, while a wrapping paper with high strength has a low air permeability. It must therefore be sought in each case for a suitable compromise, but in the first place, the required strength for transport is determining. If high strength is required, a low air permeability and thus a correspondingly low filling speed must be accepted.

For the production of other types of paper, namely paper cleaning wipes, sanitary towels, etc. sheet forming fabrics are used, which have a permeable carrier, in particular in the form of a fabric having a covering pattern produced by a regular pattern, which forms a network structure with remaining free islands or inversely discrete surface islands as required which are surrounded by a remaining network structure. In the area of the covering material, the permeability of the carrier is greatly reduced or equal to zero. Examples of such sheet forming screens are the US 5,245,025 . US 5,514,523 . US 2001/0035598 A1 . US 2001/0051224 A1 and the US 2004/0126601 A1 refer to. These sheet forming fabrics can be used to make sanitary papers having low bulk density high bulk (bulky) areas which provide high absorbency and softness of the tissue paper. To promote this Properties, the cover material is applied to the forming wire so that it stands up from the sheet forming side and thus forms raised surface areas.

The invention has for its object to provide a sheet forming screen, which can be used to produce packaging papers that have a higher porosity or air permeability for a given strength than the known packaging papers of the same strength.

This object is achieved by a sheet forming screen with the features of the preamble of claim 1. It has been found that this sheet forming screen is particularly suitable for the production of kraft paper, in particular with an average basis weight of at least 30 g / m ² . When using this sheet forming screen arise in the dewatering of the fiber pulp or the then forming paper web flow conditions, which leads to a densification of the paper fibers in the network structure forming surface areas and an alignment of the paper fibers tangentially around the surface islands. A wrapping paper produced from such a paper web thus obtains a network structure with paper fibers concentrated therein, which give the wrapping paper a high strength. Included in the network structure are discrete islands of land in favor of the Net structure are depleted of paper fibers and thus have a low density and thus a high air permeability. The resulting kraft paper is thus characterized by a significantly better air permeability for a given strength. A paper bag made from it, which is intended for the transport of bulk material, can thus be filled considerably faster, whereby the process costs are reduced accordingly. It is of particular advantage that a paper web and thus a wrapping paper is obtained, which - unlike the sanitary papers - has a relatively uniform thickness, which is of considerable importance for their processability and printability.

In an embodiment of the invention, it is provided that the covering material is completely embedded in the carrier, that is, it does not protrude beyond the carrier on the machine side either. In addition, the surface islands should have no permeability, so be tight.

As a carrier for the sheet forming of the invention, any type of fabric comes into question, for example, single or multi-layer fabric, knitted fabrics, scrims, nets, felts or a combination thereof. As materials for the textile such plastics can be used, as they are commonly used in paper machine belts.

In principle, all plasticizable materials which are suitable for use in a paper machine and as known in the prior art in the production of sheet forming screens, in particular of the generic type, can be used as covering material, as far as the starting components are concerned. You should either harden or harden after the order. In particular, suitable as covering material is a crosslinkable by means of exposure to plastic, which can be cured after the application of the cover material by means of UV irradiation. In question, however, are plastics that crosslink under the influence of heat. Alternatively, two components can be used for the curable plastic, which react with each other in mutual contact.

Another possibility is to use as a masking material a fusible plastic, which cures after application by cooling by itself- These may be, for example, hot melt adhesives.

Suitable curable plastics are epoxides, silicones, polyacrylates, polyurethanes, polystyrenes, polyolefins, polyesters, polysulfides, polyamides, butadienes, copolymers or combinations thereof.

For most applications, it is expedient if the network structure extends over the entire surface of the sheet forming screen. However, this does not rule out that only a portion of the sheet forming screen has a network structure. The network structure can also be distributed over a plurality of discrete subregions, wherein the subregions are preferably arranged in a regular, recurring pattern. By expanding and distributing these subregions, the air permeability of the packaging paper produced with the sheet forming screen can be adjusted as desired in accordance with the respective requirements.

For the strength of the packing paper, it is essential that the individual webs, which make up the network structure of the packing paper, have a certain minimum cross-section. Therefore, the smallest free space between two surface islands of the forming wire should not be less than 0.7 mm.

The network structure itself should form a regularly recurring pattern, preferably even be completely regular. Again, it is not excluded that an irregular network structure is useful in certain applications. It is part of the basic idea of the invention that the formation of the network structure and the surface islands can be adapted as desired to the requirements of the packaging paper to be produced with the sheet forming screen. Conveniently, however, the surface islands are the same size and have the same shape. They may be circular, oval, rectangular or polygonal, for example.

An expedient variant of the network structure results when the network structure forms two families of parallel network lines, with one group of parallel network lines running at an angle, expediently perpendicular to the other family of parallel network lines. This results in a grid-like network structure with, for example, rectangular, in particular square surface islands, which are enclosed by the network lines. In this case, the network lines may have at least one share, better of both at an angle to each other flocks of network lines the same distance from each other to obtain a regular network structure. Preferably, the network lines of a crowd should run in the direction of the sheet forming screen. At the same time, the netlines should have the same distance to each other, at least for one group, or better for both groups.

As an alternative to the lattice-like network structure, it is possible to form the network structure such that the surface islands each form parallel lines running parallel to one another and columns of surface islands running parallel to the lines, wherein the surface islands of adjacent lines or columns each extend by half the center distance two adjacent surface islands are offset. It is advantageous if the surface islands are arranged so that lie on mutually parallel diagonals. The diagonals can make an angle with the rows of surface islands 15 ° to 75 °, suitably from 45 ° to 70 °, including an angle of 60 ° is particularly advantageous because it allows a dense packing of the surface islands. Preferably, the rows and / or columns have the same distance from one another.

It is particularly advantageous if the size of the surface islands is adapted to the fiber lengths of the paper fibers. Preferably, the diameter of circularly shaped surface islands and / or of the surface islands each enclosing the smallest possible enveloping circles should be at most 2.5 times the average length-weighted fiber length of the paper fibers from which the packaging paper is produced by means of the sheet forming screen according to the invention. Preferably, the diameter to fiber length ratio as defined above should be less than 1.0, but at least 0.1.

• Figur 1 einen Längsschnitt durch ein Blattbildungssieb;
• Figur 2 eine Schrägansicht einer Vorrichtung zur Herstellung des Blattbildungssiebes gemäß Figur 1 in schematischer Darstellung;
• Figur 3 eine Draufsicht auf einen Ausschnitt eines Packpapiers, hergestellt mit dem Blattbildungssieb gemäß den Figuren 1 und 2 und;
• Figur 4 eine Draufsicht auf einen Ausschnitt eines anderen Packpapiers.

In the drawing, the invention is illustrated by means of embodiments in more detail. Show it:

• FIG. 1 a longitudinal section through a sheet forming screen;
• FIG. 2 an oblique view of an apparatus for producing the sheet forming according to FIG. 1 in a schematic representation;
• FIG. 3 a plan view of a section of a packaging paper, made with the forming wire according to the Figures 1 and 2 and;
• FIG. 4 a plan view of a section of another packaging paper.

This in FIG. 1 Partial forming sheet 1 has a carrier 2 in the form of a fabric with longitudinal threads 3, 4 and an upper layer of transverse threads - by way of example denoted by 5 - and a lower layer of transverse threads - exemplified by 6. The longitudinal threads 3, 4 bind in each case in the lower layer only a transverse thread 6, then float between the two layers over three transverse threads 6 and then tie in the upper layer five transverse threads 5 alternately top and bottom, before they again between the layers float over three transverse threads 5, 6.

In the carrier 2 are stored - each spaced - in plan view circular Abdeckinseln - exemplified denoted by 7. They close the top side, ie flush with the sheet forming side, so there are not on the sheet forming side before. On the lower side, ie on the machine side, they go to about the lower position of the Cross threads 6. The cover islands 7 are made of a plastic material as described above and are impermeable. Around the cover islands 7 are free surface areas - designated by way of example with 8 - over which takes place when using the sheet forming wire 1 in the paper machine dewatering of the paper web.

FIG. 2 shows a device 11 with which the Abdeckinseln 7 can be introduced into the carrier 2. It merely represents an example. The introduction of the cover islands 7 can also be done in other ways.

How out FIG. 2 can be seen, the carrier 2 is made endless by a seam known per se. It is mounted on two spaced-apart rollers 12, 13, wherein one of the rollers 12, 13 is designed as a tension roller, so that the carrier 2 receives a certain longitudinal tension. At least one of the rollers 12, 13 is driven by a motor. Upon activation of the drive, the carrier 2 is moved at a predetermined speed in the direction of the arrow A, wherein the rollers 12, 13 perform a rotational movement in the direction of the arrows B, C. In addition, it is possible, the carrier 2 - possibly several times - move back and forth to make multiple jobs- It is understood that the rollers 12, 13 are mounted in a device frame not shown here, in which the drive is housed.

Above the plane of the rollers 12, 13 an applicator 14 is arranged. It serves to the Abdeckinseln 7 on the top of the carrier 2 up and bring in this. The application device 14 has two longitudinal rails 15, 16, which are shown here only in abbreviated form, and extend parallel to the plane of the rollers 12, 13 and above them parallel to one another and are firmly connected to the device frame. The longitudinal rails 15, 16 have a distance which is greater than the width of the carrier 2, which are to be processed in the device 11.

On the longitudinal rails 15, 16, a transverse rail 17 is slidably mounted in the directions of the double arrow D. It extends perpendicular to the longitudinal rails 15, 16 and thus parallel to the axes of the rollers 12, 13. On the cross rail 17 is mounted an applicator head 18. It can be reciprocated on the cross rail 17 in the directions of the double arrow E. In addition, it can be pivoted about the longitudinal axis of the cross rail 17 in the directions of the double arrow F. The movement of the cross rail 17 relative to the longitudinal rails 15, 16 and the movement of the applicator head 18 relative to the cross rail 17 is effected by means of motors not shown here.

The application head 18 has an injection device 19, which has an outlet opening 20 in the form of one or more spray nozzles at the bottom. About the outlet 20 and provided in the injection device 19 Durchflußsteuerelement covering material for forming the Abdeckinseln 7 can be sprayed in liquid form from the outlet opening 20 down on the support 2.

The device 11 has a control device also not shown here, for example, a CNC control, with which the individual motors and the spray device 19 are controlled in mutual coordination. In the present example, the circular cover islands 7 - they are in FIG. 2 shown only in part - in transverse rows - exemplified with 21 - applied. For this purpose, the rollers 12, 13 are moved by applying a first transverse row 21 by a certain amount in the direction of the arrow A. Then, the subsequent transverse row 21 of cover islands 7 is made by moving the applicator head 18 from an initial position near the longitudinal rail 15 toward the opposite longitudinal rail 16, alternately activating the spray device 19 to create the cover islands 7 and deactivating it is to interrupt the application of masking material and thereby to form the free surface areas 8. In this case, two adjacent transverse rows 21 are offset by half the center distance of two adjacent cover islands 7, so that the cover islands 7 are adjacent to each other two transverse rows 21 on the gap.

FIG. 3 shows a section of a packaging paper 31 produced with the sheet forming screen 1. The wrapping paper 31 has a network structure 32 which substantially corresponds to the free surface areas 8 of the forming wire 1. Because of the cover islands 7 of the sheet forming screen 1, in the production of the wrapping paper 1 around the surface areas 8, dewatering flows result, which lead to a concentration of paper fibers in this area and thus to the formation of a fiber-rich network structure 32 in the wrapping paper 31. The network structure 31 encloses surface islands-designated by way of example by 33-whose arrangement, shape and size of the arrangement, shape and size of the cover islands 7 of the sheet-forming screen 1 correspond.

The surface islands 33 form in one direction adjacent rows of islands - exemplified by 34 - and in the direction perpendicular island columns - exemplified by 35 -, with two adjacent island rows 34 - like the Abdeckinseln 7 two adjacent rows of rows 21 - each by half Center offset are offset. The same applies to the island columns 35. The distance between two adjacent island rows 34 and two adjacent island columns 35 is identical. Also, the distances of the surface islands 33 with each other are the same, so that a regular pattern on the surface of the packaging paper 31 results.

Due to the above distribution, the surface islands 33 are each adjacent or on diagonal - by way of example denoted by 36 - which includes an angle α with a straight line - exemplified by 37 - include Shen, which runs parallel to the island rows 34, in the present case is the Angle α approx. 45 °. In a preferred embodiment, the angle α has a value of 60 °, which can be effected by increasing the distances of the island lines 34.

Due to the above-described flow conditions, the surface islands 33 are depleted of paper fibers, i. There, the density of the packaging paper 31 is reduced compared to the density in the region of the network structure 32. When filling a paper sack made of this wrapping paper 31, therefore, the displaced air can escape over the surface islands 33 in an efficient manner, so that the paper sack can be filled quickly. The strength of the wrapping paper 31 is substantially ensured by the net structure 32 in which the paper fibers are concentrated.

The size ratios between surface islands 33 and network structure 32 can of course be adapted according to the respective requirements. A larger area fraction of the network structure 32 provides higher strength, but with loss of permeability. The same applies vice versa when increasing the proportion of the surface islands 33. Moreover, it is also not mandatory that the surface islands 33 have round shape. Other shapes, such as polygonal, honeycomb or rectangular shapes are possible.

FIG. 4 shows a variant of the packing paper 31 according to FIG. 3 , The wrapping paper 41 has a grid-like network structure 42 with parallel network lines - for example denoted by 43 - in one direction and also parallel network lines - for example denoted by 44 - perpendicular to the network lines 43. The network lines 43, 44 have identical distances to each other, so that the network structure 42 square islands - exemplarily with 45 - include. The surface islands 45 are also depleted of paper fibers in favor of the network structure 42, ie in the network structure 42, the paper fibers are concentrated at the expense of the surface islands 45. The strength of the packaging paper 41 is therefore ensured essentially by the network structure 42, while the surface islands 45 provide good air permeability and thus favor the filling of a paper bag produced from the packaging paper 41.

The production of the packaging paper 41 is carried out with a correspondingly adapted sheet forming screen. This sheet forming screen then has in deviation from the forming wire 1 according to the Figures 1 and 2 lattice-like free surface areas, which are produced by the fact that each spaced square cover islands in the arrangement, as they are as surface islands 45 in the kraft paper 41 have deposited, applied and stored.

It is understood that the network structure according to the wrapping paper 41 can also be designed differently. For example, the distances of the network lines extending in one direction can be selected to be greater than the distances between the network lines extending perpendicularly therefrom, so that rectangular islands of surface of high permeability arise. Of course, the width of the network lines in relation to the extension of the surface islands can be changed in the same direction, so that smaller surface islands arise. Such a wrapping paper would then have greater strength, with the permeability being controlled by the size and number of surface islands. In addition, the surface islands may also have other shapes, such as a round shape. It would then be a wrapping paper, which differs from the wrapping paper 31 according to FIG. 3 differs in that the individual surface islands adjacent island rows or island columns would not be offset from each other.

Claims (23)

1. Use of a forming screen (1) as a Fourdrinier wire for the forming zone of a paper machine with a permeable carrier (2) that has a forming side and a machine side and also has a pattern of discrete surface islands (7) made from cover material, which have lower permeability than that of the surface zones surrounding the surface islands (7) and forming a mesh structure (8), wherein the cover material projects over the forming side of the carrier (2), characterised in that the forming screen is used for the production of wrapping paper (31, 41).
2. Use according to claim 1, characterised in that the cover material is fully embedded in the carrier (2).
3. Use according to claim 1 or 2, characterised in that the surface islands (7) have no permeability.
4. Use according to either of claims 1 and 3, characterised in that the carrier (2) is in the form of a textile product.
5. Use according to claim 4, characterised in that the textile product is a single or multi layer woven, knitted or threaded fabric, mesh, felt or a comb i-nation of these.
6. Use according to any of claims 1 to 5, characterised in that the cover material consists of a meltable plastic, which cures or is curable after application.
7. Use according to claim 6, characterised in that the cover material is a light curing plastic.
8. Use according to claim 7, characterised in that the cover material is a UV-reactive plastic, which can cure by UV light exposure.
9. Use according to claim 6, characterised in that the cover material is a heat curable plastic.
10. Use according to claim 6, characterised in that the curable plastic is an epoxy, silicone, polyacrylate, polyurethane, polystyrene, polyester, polyolefin, polysulphide, polyamide, butadiene, copolymers or a combination of these.
11. Use according to claim 6, characterised in that the curable plastic consists of two resin components, which react on mutual contact.
12. Use according to claim 6, characterised in that the cover material is a meltable plastic that cures after application by cooling.
13. Use according to one of claims 1 to 12, characterised in that the mesh structure (8) extends over the whole area of the forming screen (1).
14. Use according to one of claims 1 to 12, characterised in that only a part or parts of the forming screen (1) have the mesh structure (8).
15. Use according to claim 14, characterised in that said parts are arranged in a regular pattern.
16. Use according to one of claims 1 to 15, characterised in that the smallest clear distance between two surface islands (7) is not less than 0.7 mm.
17. Use according to any of claims 1 to 16, characterised in that the mesh structure (8) forms a regularly repeating pattern.
18. Use according to any of claims 1 to 17, characterised in that the surface islands (7) are equal in size and have the same shape.
19. Use according to any of claims 1 to 18, characterised in that the surface islands (7) are circular, oval, rectangular or polygonal in form.
20. Use according to any of claims 1 to 19, characterised in that the mesh structure (8) is regular in form.
21. Use according to any of claims 1 to 20, characterised in that the mesh structure forms two sets of parallel grid lines, one set of parallel grid lines running at an angle to the other set of parallel grid lines.
22. Use according to claim 21, characterised in that the angle is 90°.
23. Use according to claim 21 or 22, characterised in that the grid lines in a set run in the direction of travel of the forming screen.

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