WO2014015978A1 - Drainage screen - Google Patents

Description

 dewatering

The invention relates to a dewatering screen for the production of paper with at least one hole, as well as a method for papermaking with such a dewatering screen.

In papermaking on rotary screening machines or screening machines, pulp accumulates continuously on a moving dewatering sieve and is solidified to such an extent that it can be removed as a moist paper web for further processing by the dewatering sieve. Above all, security papers for banknotes, identity documents and the like are often provided with continuous holes (holes in the paper) for securing a few years ago, which allow verification of the authenticity of the security paper and at the same time serve as protection against unauthorized reproduction.

If the holes are already produced during papermaking, they may have characteristic irregularities in the edge region, which are produced by the irregular deposition of fibers in the edge region and by individual fibers protruding into the hole, as described for example in document WO 03/054297.

Conventionally, holes in the paper are often produced by flakes welded onto a round screen. However, the thick plates lead to heavy strains of the screen, which reduce the mileage. In some cases, an inaccurate edge area or even no hole in the paper can occur during papermaking.

Based on this, the invention has for its object to provide a dewatering screen of the type mentioned, which has the disadvantages of State of the art avoids. In particular, the dewatering screen should enable a gentle and reliable production of paper with a hole. This object is solved by the features of the independent claims. Further developments of the invention are the subject of the dependent claims.

According to the invention, a dewatering screen of the type mentioned at the beginning contains a carrier screen which has a cut-out in a partial area

Includes screen fabric, as well as arranged in the cut-out portion of the mesh fabric insertion plate for generating the at least one hole in the paper. The insert tile contains a perforated, peripheral edge surface with a first level height and a cup enclosed by the edge surface, which has smooth, non-perforated cup walls and a cup base lowered relative to the first level height.

Due to the lowered bottom of the well and the smooth, non-perforated well walls can be achieved that either no paper mass accumulates in the cup in the paper, or that in the wells attached paper mass is not related to the accumulated outside of the cup paper pulp. In both cases, the paper web removed from the wire has a hole in the shape of the pot outline, which shows the irregularities of the margins which are characteristic for the production of holes during paper formation.

In an advantageous embodiment, the well bottom is lowered to a second level height, which is between 1.5 mm and 2.5 mm below the first level. level height. The term "below" designates the direction toward the expansion cylinder or the like in which a negative pressure prevails in papermaking and in the direction of which the paper pulp is pulled during papermaking. Accordingly, the first level height is 1.5 mm to 2.5 mm above the second level height, so is further in the direction of the impacted with pulp surface of the dewatering screen.

In a preferred variant of the invention, the bottom of the well, as well as the wells, is not perforated. This completely prevents sheet formation in the region of the bottom of the pot.

In other, likewise advantageous variants of the invention, the bottom of the well is perforated. In this case, the perforations of the base of the bowl and the edge surface can have the same shape and size, but the perforations of the base of the bowl can advantageously also be provided with large perforations whose area is more than twice the area of the perforations of the rim. Preferably, the smooth, non-perforated well wall are almost perpendicular to the bottom of the well and have, based on the bottom of the well, in particular a pitch angle between 90 ° and 115 °, preferably between 90 ° and 100 °. The defined by the peripheral edge surface first level level is advantageously on the screen level of the top wire layer of the support wire, so that the insert plate fits smoothly into the surface of the support wire. In advantageous embodiments, it can be provided that the cell walls pass over into a wall which runs around the base of the cell and projects beyond the edge surface. The peripheral wall preferably projects beyond the edge surface by 0.3 mm to 1.5 mm, in particular by 0.5 mm to 1.2 mm, and preferably has a wall width of 0.1 mm to 2.5 mm, in particular 0, 5 mm to 2.0 mm.

The shape of the cup is largely freely selectable within the scope of the invention. In particular, as cup shapes and thus as hole shapes in paper, star-shaped, rectangular, polygonal or other geometric shapes may be used in addition to rounds. Even wells that create a hole in the form of a picture motif are conceivable. It can also be provided several holes in a security paper, which preferably have complementary or related forms.

The insert plate itself is preferably made of plastic, in particular of injection-molded plastic. The perforations are advantageously introduced by laser loading in the insert platelets. The described drainage screens may in particular be round screens.

The invention also includes a method for producing paper having at least one hole, wherein the paper deposition takes place on a dewatering screen of the type described above. In particular, the method produces a hole with characteristic edge irregularities. The paper is in particular security paper for the production of security and value documents, such as banknotes, checks, identity cards, certificates or the like. The inventive design of a dewatering screen holes can be generated in the paper with a clean deckle edge. The hole formation is very reliable and without load for the round screen, the dandy and the pick-up screen. Position and position of the holes can be specified within the carrier screen with high accuracy. The shape of the hole to be produced is almost arbitrary, since it is generated by the outline shape of the injection-molded lowered cup or the course of the cup walls. The injection molding allows a great flexibility in the production of such wells and thus a high degree of design freedom in the design of the hole shapes.

Further exemplary embodiments and advantages of the invention will be explained below with reference to the figures, in the representation of which a representation true to scale and proportion has been dispensed with in order to increase the clarity.

Show it:

1 is a schematic representation of a banknote with an irregularly bounded hole, which is closed on one side by a film strip,

2 shows schematically in cross section a dewatering screen after a

 Embodiment of the invention, shown along the line II-II of Fig. 3,

3 shows the insert plate of the dewatering screen of FIG. 2 in a perspective view, FIG. FIG. 4 schematically shows the addition of paper pulp to the dewatering screen of FIG. 2 during sheet formation; FIG.

Fig. 5 shows another embodiment of an inventive

 Drainage sieve with not-perf ored well bottom, and

Fig. 6 shows another embodiment of an inventive

 Entwässerungssiebs.

The invention will now be explained using the example of the production of security paper for banknotes. 1 shows a schematic representation of a banknote 10 with a hole 12 which is closed on one side by a foil strip 16. The film strip 16 has a security feature in the region of the hole 12, which is visible from both sides of the banknote 10 in the upward direction and optionally also in transmitted light.

The hole 12 was thereby produced during the production of the security paper used for the banknote 10 and has a fibrous, irregular edge 14. Such an irregular rim 14 is characteristic of apertures already made in sheet formation and can not be subsequently produced by punching or cutting the paper.

In order to produce a security paper having a hole 12 with an irregular edge 14, a dewatering screen of the kind shown schematically in cross section in FIG. 2 is used according to the invention. The Entwässerungssieb 20 includes a support 22, the mesh 24 in the embodiment of four Sieblagen 24- A, 24-B, 24-C and 24-D consists. Three of the four Siebelages 24-A, 24-B and 24-C are cut out in one section around a injection molded insert 30 record. Insertion plate 30 is shown in more detail in perspective view in FIG. 3, the cross-sectional view of FIG. 2 being along line II-II of FIG. The injection-molded inserting plate 30 contains a peripheral edge surface 32 whose plane surface defines a first level height hi. The level height h in this case corresponds to the screen level h _{s of} the uppermost screen layer 24-A of the carrier screen 12, so that the insert plate 30 fits continuously into the screen surface. The outer contour of the edge surface 32 is arbitrary but, for practical considerations, is generally rounded and more typically circular or oval.

The circumferential edge surface 32 encloses a cup 34 whose shape and size corresponds to the shape and size of the desired hole 12 in the security paper. The well 34 contains a well bottom 36 at a lowered second level height h ₂ , wherein the second level height h ₂ with respect to the first level height hi and the sieve level h _s usually by 1.5 mm to 2.5 mm and in the embodiment by 2, 0 mm is lowered. If an even deeper cup is desired, the fourth sieve 24-D of the carrier can also be cut out.

The edge surface 32 and the well bottom 36 are each provided with perforations 38, 38 ', which ensure the drainage of the deposited paper. The dimensions of the perforations 38, 38 'are chosen so small that they do not adhere to fibers in papermaking. Typically, the diameter of the perforations 38, 38 'is between 10 μη to 750 μιη, preferably between 50 μιη and 250 μιη. In the embodiment of Figures 2 and 3, the perforations 38 'of the well base 36 and the perforations 38 of the edge surface 32 have the same shape and size. In other However, the perforations 38, 38 'may also differ, as illustrated, for example, in FIG. 6.

The bottom of the well 36 is surrounded by approximately vertical well walls 40 which are smooth and unperforated. The cup walls 40 have, based on the bottom of the cup 36, generally a pitch angle α between 90 ° and 115 °, in the illustrated embodiment of α = 100 °. Advantageously go the cell walls 40, as in the embodiment of Figures 2 and 3, in a bottom of the well 36 wall 42 which projects beyond the edge surface 32 by a few tenths of a millimeter, for example by 0.6 mm.

FIG. 4 schematically illustrates the attachment of pulp to the dewatering screen 20 of FIG. 2 during sheet formation. In this case, due to the pressure prevailing in the interior of the expansion cylinder 50 under pressure over the perforated surface regions 32, 36 and the screen fabric 24 paper pulp 52, 54 deposits. As shown in FIG. 4, the paper mass 54 deposited on the base 36 of the cup does not hang together with the paper mass 52 deposited on the edge surface 32 and the screen fabric 24 because of the smooth, non-perforated cup walls 40 separating the paper masses.

In the subsequent tumbling process, the paper mass 54 then remains on the bottom of the well 36, so that the paper web removed by the dewatering sieve 20 has a hole 12 in the shape of the cell contour and with characteristic irregularities in the edges (FIG. 1).

5 shows a further embodiment of a dewatering screen 60 according to the invention, in which the bottom of the pot 62 of the cup 34 is non-porous. perforated. As a result, sheet formation in the area of the bottom of the pot 62 is completely prevented in papermaking.

In the dewatering screen 70 of the embodiment shown in Fig. 6, the well bottom 72 of the well 34 is provided with perforations 74 twice as large as the area of the perforations 38 of the peripheral surface 32. Again, the well walls 76 are smooth and imperforate , However, in the exemplary embodiment of FIG. 6, no wall projecting beyond the edge surface 32 is provided, but rather, the cell walls 76 move continuously into the edge surface 32 at the first level height hi.

Although the invention has been illustrated above with reference to a substantially circular hole 12, the shape of the wells 34, and thus the shape of the holes that can be created, are largely freely selectable. In particular, hole shapes other than rounds may also include star-shaped, rectangular, polygonal or other geometric shapes, or hole shapes that represent a motif. It can also be provided several holes in a security paper, which preferably have complementary or related forms.

Not only single-ply paper with one or more holes can be produced with the aid of the dewatering screen according to the invention, but also, for example, two-ply paper which has a hole in a paper ply or two-ply paper with holes in both paper plys. Of course, these designs can be generalized to papers with more than two layers. LIST OF REFERENCE NUMBERS

10 banknote

 12 holes

14 edge

 16 film strips

 20 drainage screen

22 strainer

 24 screen cloth

 24-A to 24-D Sieblagen

 30 insert tiles

 32 border area

 34 wells

 36 well bottom

 38, 38 'perforations

 40 cell walls

 42 Wall

 50 expansion cylinders

52, 54 pulp

 60 drainage screen

62 well bottom

 70 drainage screen

72 well bottom

 74 perforations

 76 cell walls

Claims

Patent claims 1. A dewatering screen for the production of paper with at least one hole, with a carrier wire containing a screen fabric cut out in a partial area, and an insert plate arranged in the cut-out section of the screen fabric for producing the at least one hole in the paper Insertion plate has a perforated circumferential edge surface with a first level height and a cell enclosed by the edge surface, which has smooth, non-perforated Well walls and a lowered compared to the first level height Well bottom. 2. Entwässerungssieb according to claim 1, characterized in that the bottom of the well is lowered to a second level level, the between 1.5 mm and 2.5 mm below the first level height. 3. Drainage screen according to claim 1 or 2, characterized in that the bottom of the well is not perforated. 4. Entwässerungssieb according to claim 1 or 2, characterized in that the bottom of the well is perforated, the perforations of the bottom of the well preferably provided with large perforations whose area is more than twice as large as the area of the perforations of the edge surface. 5. Entwässerungsieb according to at least one of claims 1 to 4, characterized in that the smooth, non-perforated Näpfchenwan- de, based on the bottom of the well, have a pitch angle between 90 ° and 115 °, preferably between 90 ° and 100 °. 6. Entwässerungssieb according to at least one of claims 1 to 5, characterized in that the first level height is on the sieve level of the uppermost Sieblage of the support wire. 7. Entwässerungssieb according to at least one of claims 1 to 6, characterized in that the cup walls pass into a bottom of the pot wall circulating over the edge surface. 8. Entwässerungssieb according to at least one of claims 1 to 7, characterized in that the insert plate made of plastic, in particular of injection-molded plastic. 9. dewatering screen according to at least one of claims 1 to 8, characterized in that it is the dewatering screen is a round screen. 10. A process for the production of paper with at least one hole, wherein the paper attachment takes place on a dewatering screen according to one of claims 1 to 9. A method according to claim 10, wherein a hole having characteristic edge irregularities is produced.