EP1069235B1 - Transfer belt for a paper machine - Google Patents

Abstract

The transfer belt, for a papermaking machine, has a carrier (2) with a coating (3,5) on at least one of its flat surfaces. The coating has an inner layer (3) and an adjacent outer layer (5) with a porous structure comprising hollow zones open to the outer surface. The inner coating layer (3) is impermeable to fluids, and has longitudinal and/or pressure elasticity. The carrier (2) has a specific longitudinal module of ≤ 70 N/tex. The carrier material has an elasticity on draw tensions of 4-8 daN per cm of carrier (2) width. The carrier (2) material is woven, knitted, yarn layers or a fiber nonwoven, or combinations of material structures. The carrier (2) is at least partially embedded with the inner layer of the coating (3,5). The inner coating layer (3) has a hardness of 85-95 Shore A, and contains inorganic filling particles. The inner coating layer (3) has a thickness tolerance of max. 100 microns. The hollow zones in the outer coating layer (5) have an average dia. of ≤ 200 microns. The outer surface of the outer coating layer (5) contains nano particles, at least partially of SiO2, or fluorocarbon chains. The outer surface of the outer coating layer (5) has a prepolymer emulsion, hardened by electron beam treatment. The outer surface of the outer coating layer (5) is of materials which form local and different hydrophilic or hydrophobic zones. The outer coating layer has a thickness of ≤ 3 mm and the inner coating layer thickness is 1-3 mm.

Description

The invention relates to a liquid-impermeable Transfer belt for a paper machine with a carrier and with a coating on at least one flat side.

Modern paper machines are reaching ever higher speeds. In the next few years will be speeds expected from more than 2000 m / min. Such high speeds make it necessary that the paper web when passing through the press and dryer section the paper machine at no point without support is. In the press section is a complete support the paper web with the help of the circulating there Press felts in most cases not given. To the Paper web also in areas where no support given by the press felt, to lead - this especially applies to the transition area to the dryer section -, so-called transfer ribbons (transfer work) used the paper web through one or several presses of the press section together with each Pass the corresponding press felt and after detachment the press felt from the paper web to a place lead, where the paper web mostly with the help of a Suction roller detached from the transfer belt and from a taken over in the drying section circulating dryer becomes. Examples of the guidance of transfer tapes in The press section of a paper machine is US-A-4,483,745 and FIGS. 1 to 3 of EP-A-0 576 115.

In the other figures and the associated description This document describes a transfer belt which having a carrier formed as a tissue, which ensures the structural strength of the transfer belt. On the flat side intended for the installation of the paper web is a liquid-impermeable coating of a polymeric material, for example an acrylic radiator Polyurethane resin, provided, in which the carrier fabric partially embedded. On the other flat side can be pinned on the carrier a nonwoven fabric.

A transfer band must have two conflicting demands fulfill. On the one hand, the transfer ribbon must have sufficient Apply adhesive force to the paper web, so that the Paper web in the area where the press felt lifts off not detached from the transfer belt. On the other hand, the Adhesive force in the area where the paper web of the Transfer ribbon is lifted, so low that the decrease not hindered. With the transfer band after EP 0 576 115 attempts to meet these requirements by a Roughening provided for the plant of the paper web Surface to comply. To explain the effect of Roughening is indicated that the roughness of the surface in the press nip of a press and consequently the Surface becomes smoother, so that a thin film of water form between paper web and surface. hereby create between both a higher adhesion than between Paper web and press felt with the result that the paper web the transfer belt after leaving the press nip episode. The adhesive force is greater than that for the press felt, even if this is a low vacuum due to the expansion exercise after the press nip. Add to that the fact that the vacuum force generated by the transfer belt due to this Expansion stop longer than that of the press felt outgoing. This expansion also has the consequence that the roughness of the surface is restored, what a breaking up of the water film and thus a decrease the adhesion force. In addition, it could be possible be that air into the recesses of the surface of the Transfer belt included on entry into the press nip and compressed. After the press nip expand the compressed air, which contributes to the Break up water film and thus reduce the adhesive force. This could still be supported by areas high and low hydrophobicity or hydrophilicity.

Nevertheless, with the known transfer belt is still no achieved satisfactory adhesion of the paper web, so that it when lifting the press felt from the paper web to the Take along comes, so the paper web from the transfer belt solves. Apparently, those described in EP-A 0 576 115 Effects that affect the adhesion of the paper web to ensure the transfer belt, not sufficient. This may be related to the fact that the paper web - seen microscopically - only on the tips of the Roughness surveys.

In addition, drainage tapes for paper machines are known, which are liquid permeable. In the drainage tape according to EP-A-0 786 551 are passageways present over which the squeezed from the paper web Water can be diverted. The passageways become by communicating cavities formed in the manufacture of the web through Removal of soluble particles from the plastic layer arise. In EP-A-0 547 816 is a liquid-permeable Press felt disclosed in particular Way is constructed, with it the so-called impulse drying to carry out. It will be special Care is taken that the press felt is well off the paper web solve.

The invention is based on the object, a transfer belt to make that a good adhesion of the paper web is guaranteed, so that the lifting of the press felt not to release the paper web from the transfer belt leads.

This object is achieved in that the coating an inner layer and an adjacent thereto Outer layer, wherein the outer layer has a porous structure with open to the outside cavities having. The basic idea of the invention is therefore a provide at least two-layer structure of the coating, wherein the inner layer is preferably elastic and liquid impermeable and the outer layer a should have porous structure. It has been shown that thereby the adhesion of the paper web after leaving the press nip is significantly improved and it even where the press felt lifts, not to a detachment the paper web comes from the transfer belt.

This seems to be based on two mechanisms of action. To the one of the paper web is a flat and smooth edition offered only through the openings of the cavities is interrupted. This improves the adhesion and promotes also the formation of a liquid film, the adhesion supported. On the other hand, the cavities additionally generate a vacuum that tends to peel off the paper web counteracts. This arises because the cavities compressed upon entering the press nip and thereby water and air present in the cavities is, is largely pressed and that the cavities expand again after leaving the press nip and thereby generate suction forces that adhere favor the paper web on the transfer belt. in addition comes that these suction forces also a Wiederbefeuchtung help avoid the paper web.

It has been found that the improved adhesion of the Paper web on the transfer belt does not cause problems in the Decrease in the paper web leads, as in the paper machines existing suction rolls develop sufficient suction power, to lift the paper web and another tape, for example, a drying wire to feed. Corresponding does not come to breaking the liquid film the importance attached to him in the construction of the transfer ribbon according to EP-A-0 576 115 and that has led to a surface design that due to their roughness, the breaking up of the liquid film promotes.

As for the training of the wearer, it is for the Function of the transfer belt beneficial if it is in the longitudinal direction has a certain elasticity, hence the elasticity the inner layer also utilized in the longitudinal direction becomes. Preferably, the specific modulus of the carrier should be ≤ 70 N / tex. A material should be used at tensile stresses of 4 to 8 daN / cm of the carrier is elastic in the width direction. Come for this in particular according to elastically adjusted materials such as PBT, PES, PA6, PA6.6, PA6.10, PA6.12, PA11, PA12 and PTT in question, these materials also with each other can be combined.

The carrier secures - as with all tapes for a paper machine - The structural strength of the transfer belt. For this purpose, the carrier may be constructed of threads, for example in the form of a woven, knitted or laid fabric. But there are also appropriately trained Nonwoven fabrics, for example in impregnated or compressed Form, in question, where possible a should have uniform thickness. On the side, up The coating should be applied to the surface smooth, e.g. ground, be trained. To one establish firm connection between carrier and coating, It is beneficial if the carrier is in the coating at least partially embedded. Also one full embedding is possible.

The material used for the inner layer is natural rubber or an elastomer in question. Particularly suitable Silicone elastomer, polyester elastomer and polyurethane. Prefers The hardness of the inner layer should be between 85 and 95 Shore A have.

In addition, inorganic filler particles, for example TiO ₂ or clay, can be incorporated into the inner layer in order to influence their hardness. For the function of the inner layer, it is advantageous if it has a thickness tolerance of a maximum of 100 microns. To achieve such a thickness tolerance, it can be appropriately turned off and ground before applying the outer layer.

As the material for the outer layer is preferably polyurethane and / or silicone elastomer and / or polyester elastomer in question. When using such or other plastic materials, the cavities in a conventional manner can be prepared by sprinkling on them and stored in them soluble particles which can be dissolved out with a solvent against which the outer layer is resistant (see EP-A 0 786 551). For this purpose, in particular water-soluble particles in the form of salts such as NaCl, KCl and / or CaCO _{3 are} suitable. The particles should have a diameter of ≤ 2 μm in order to produce correspondingly large cavities.

To improve the wear resistance of the outer layer, it is proposed to provide it with a layer of nanoparticles on its surface. These particles used hitherto in chemistry as pigments for color effects, cosmetics and data storage layers whose particle sizes are in the nano range, protect the outer layer effectively against wear, especially if the nanoparticles consist for example of SiO ₂ or metals. The nanoparticles may be applied in a suspension of a water-alcohol mixture, the mixture then being evaporated. In some areas, the nanoparticles may be provided with fluorocarbon chains to impart a hydrophobic character to surface areas of the outer layer, thereby facilitating separation of the paper web from the transfer belt.

Another alternative for the production of the outer layer is an electron beam hardened To use prepolymer emulsion. This is especially true Silicones or polyurethanes in question in one Water-surfactant mixture are emulsified, the electron beam curing is evaporated.

Finally, it is provided according to the invention that the Outer layer on the outside is made of materials, the areas different hydrophilicity or hydrophobicity form. Both should be the detachment of the paper web from the Facilitate transfer ribbon, the areas and the differences in terms of hydrophilicity or hydrophobicity so should be arranged and designed that still sufficient adhesion of the paper web in the area of Lifting the press felt is secured.

Figur 1

einen teilweisen Längsschnitt durch ein Transferband für eine Papiermaschine;

Figur 2

einen Längsschnitt durch eine erste Ausbildung der Außenschicht des Transferbandes gemäß Figur 1;

Figur 3

einen Längsschnitt durch eine zweite Ausbildung einer Außenschicht des Transferbandes gemäß Figur 1 und

Figur 4

einen Längsschnitt durch eine dritte Ausführungsform einer Außenschicht des Transferbandes gemäß Figur 1.

In the drawing, the invention is illustrated by means of schematically illustrated embodiments. Show it:

FIG. 1

a partial longitudinal section through a transfer belt for a paper machine;

FIG. 2

a longitudinal section through a first embodiment of the outer layer of the transfer belt according to Figure 1;

FIG. 3

a longitudinal section through a second embodiment of an outer layer of the transfer belt according to Figure 1 and

FIG. 4

a longitudinal section through a third embodiment of an outer layer of the transfer belt according to Figure 1.

The transfer belt 1 to be seen in FIG. 1 has a carrier 2, which in this case from a tissue using consists of polyamide threads. The carrier 2 has an inner layer 3 at the top and a base layer at the bottom 4, wherein the carrier 2 in both layers 3, 4 is embedded. Inner layer 3 and base layer 4 consist of a silicone elastomer.

On the upper side of the inner layer 3 is an outer layer 5 applied, which has a porous structure and a smooth surface 6 has. The surface 6 is for the plant a paper web provided while the bottom the base layer 4 over the rolls of a paper machine running.

In the embodiment of Figure 2, the outer layer 5 essentially of a cast polyurethane layer 7. In order in this polyurethane layer 7 for Outside open cavities - exemplified with 8 - to produce are in the polyurethane material salt particles prior to application - exemplified by 9 - evenly distributed and in an average Size <2 microns has been stored. After training the polyurethane layer 7 on the inner layer 3rd those salt particles 9 are washed out by means of water that has not been completely removed from the polyurethane layer 7 were so enclosed, so connection to the outside had. In this way cavities 8 have been created, their depth of the previous penetration depth of the salt particles 9 corresponds. Those salt particles 9, which with Distance to the surface 6 were stored are not removed and therefore still in the polyurethane layer 7 available.

Although the cavities 8 interrupt the surface 6. Nevertheless, remain between the openings of the cavities Areas of the surface 6, which lie in a plane as well interconnected and smooth. The paper web Thus, a large contact surface is offered, which a correspondingly high adhesive force is created. The Cavities 8 generate due to their expansion after passing through the press nip a negative pressure, the liability supports the paper web on the surface 6.

In the embodiment shown in Figure 3 a Outer layer 5, the starting material is also polyurethane. However, this material is in powder form applied and then sintered so that Again, a polyurethane layer 10 with a smooth surface 11 has formed. Into the polyurethane powder were Embedded salt particles (see insofar as in EP-A 0 786 551 described method), which then by a Washing process have been completely dissolved out, so that a porous structure under formation to the surface 11 open cavities - exemplified with 12 - originated. The effect of the polyurethane layer 10 is the same as for the polyurethane layer 7 according to FIG FIG. 2.

The embodiment shown in Figure 4 shows a Outer layer 5, which consists of an emulsion of prepolymers has been produced. This emulsion is on the inner layer 3 and then electron beam cured Service. As a result, individual, each other in Compound polymer particles - exemplified by 13 designated - emerged, between which cavities-exemplary denoted by 14 - have formed. All in all is also a porous structure with a comparatively smooth surface 15 emerged.

Claims (19)

1. Liquid-impermeable transfer belt for a paper machine, having a substrate (2) and having a coating (3, 5) on at least one flat side, characterized in that the coating has an inner layer (3) and an outer layer (5), adjacent thereto, wherein the outer layer (5) has a porous structure having cavities (8, 12, 14) open toward the outer side (6, 11, 15).
2. Transfer belt as defined in Claim 1, characterized in that the inner layer (3) is impermeable to liquid.
3. Transfer belt as defined in Claim 1 or 2, characterized in that the inner layer (3) is configured in longitudinally and/or compressively elastic fashion.
4. Transfer belt as defined in one of Claims 1 through 3, characterized in that the substrate (2) has a specific modulus = 70 N/tex in the longitudinal direction.
5. Transfer belt as defined in Claim 4, characterized in that a material that is elastic in the presence of tensile stresses of 4 to 8 daN per cm of width of the substrate (2) is used for the substrate.
6. Transfer belt as defined in one of Claims 1 through 5, characterized in that the substrate is a woven fabric, knitted fabric, thread layer, or a fiber batt, or a combination thereof.
7. Transfer belt as defined in one of Claims 1 through 6, characterized in that the substrate (2) is at least partially embedded into the inner layer (3, 5).
8. Transfer belt as defined in one of Claims 1 through 7, characterized in that the inner layer is made of natural rubber or an elastomer, in particular silicone elastomer, polyurethane, and/or polyester elastomer.
9. Transfer belt as defined in one of Claims 1 through 8, characterized in that the inner layer (3) has a hardness between 85 and 95 Shore A.
10. Transfer belt as defined in one of Claims 1 through 9, characterized in that the inner layer has inorganic filler particles.
11. Transfer belt as defined in one of Claims 1 through 10, characterized in that the inner layer (3) has a thickness tolerance of max. 100 µm.
12. Transfer belt as defined in one of Claims 1 through 11, characterized in that the outer layer (5) is made of polyurethane and/or silicone elastomer and/or polyester elastomer.
13. Transfer belt as defined in one of Claims 1 through 12, characterized in that the cavities (8, 12, 14) in the outer layer (5) have an average diameter = 200 µm.
14. Transfer belt as defined in one of Claims 1 through 13, characterized in that the outer layer (5) is equipped on its surface with nanoparticles.
15. Transfer belt as defined in Claim 14, characterized in that the nanoparticles are made at least partially of SiO₂.
16. Transfer belt as defined in Claim 14 or 15, characterized in that the nanoparticles have fluorocarbon chains.
17. Transfer belt as defined in one of Claims 1 through 11, characterized in that the outer layer (5) is made of an electron beam-cured prepolymer emulsion.
18. Transfer belt as defined in one of Claims 1 through 17, characterized in that the outer layer (5) is made externally of materials that form regions of different hydrophilicity and hydrophobicity.
19. Transfer belt as defined in one of Claims 1 through 18, characterized in that the outer layer has a thickness = 3 mm and the inner layer a thickness of 1-3 mm.

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