EP1069235A1 - 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 transfer belt for a paper machine with a carrier and with a coating at least one flat side.

Modern paper machines reach ever higher speeds. In the next few years there will be speeds expected of 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. There is full support in the press section the paper web with the help of the Press felts are not given in most cases. To the Paper web also in areas where no support given by the press felt to guide - this applies in particular to the transition area to the dryer section -, so-called transfer belts used that the paper web by one or several presses of the press section together with the pass the associated press felt and after detachment of the press felt from the paper web to one point lead where the paper web mostly with the help of a Suction roller detached from the transfer belt and from one in the dryer section rotating dryer sieve taken over becomes. Examples of the management of transfer belts in the press section of a paper machine are shown in FIGS to 3 of EP-A 0 576 115.

In the other figures and the associated description This document describes a transfer belt that a carrier formed as a fabric, which ensures the structural strength of the transfer belt. On the flat side intended for the installation of the paper web is a coating made of a polymeric material, for example an acrylic or polyurethane resin, in which the carrier fabric is partially embedded. On the other flat side, a non-woven fabric can be placed on the carrier to be needled.

A transfer belt must have two contradicting requirements fulfill. On the one hand, the transfer belt must be sufficient Apply adhesive force to the paper web so that the Paper web in the area where the press felt lifts off does not detach from the transfer belt. On the other hand, the Holding force in the area where the paper web from the Transfer ribbon is lifted off, so low that the decrease is not hindered. With the transfer belt after EP 0 576 115 attempts to meet these requirements by means of a Roughening of the paper web Surface to comply. To explain the effect of Roughening indicates that the roughness of the surface decrease in the press nip of a press and consequently the Surface become smoother, so that there is a thin film of water between paper web and surface. Hereby there is a higher adhesive force between the two 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 of the press felt, even if this has a slight vacuum due to the expansion exercise after the press nip. In addition, the vacuum force generated by the transfer belt due to this Expansion lasts longer than that of press felt outgoing. This expansion also had the consequence that the roughness of the surface is restored, what a break in the water film and thus a decrease the adhesive force. It could also be possible be that air in the depressions of the surface of the Transfer belt included when entering the press nip and get compressed. After the press nip expand the compressed air, which helps the Break up the water film and thus reduce the adhesive force. This could be supported by areas high and low hydrophobicity or hydrophilicity.

With the well-known transfer belt none is made yet achieved satisfactory adhesion of the paper web so that it when lifting the press felt from the paper web to its Take-along comes, so the paper web comes off the transfer belt solves. Apparently, those described in EP-A 0 576 115 are Effects on the adhesion of the paper web guarantee the transfer belt, not sufficient. This may be due to the fact that the paper web - seen microscopically - only on the tips of the Roughness surveys are available.

The invention is therefore based on the object To design the transfer belt so that good adhesion of the Paper web is guaranteed so that the lifting of the Press felt does not cause the paper web to come off the Transfer ribbon leads.

This object is achieved in that the coating an inner layer and an adjacent one Has outer layer that has a porous structure has open cavities to the outside. Basic idea The invention is therefore an at least two-layer To provide structure of the coating, the Inner layer preferably elastic and impermeable to liquids be and the outer layer a porous structure should have. It has been shown that the Liability of the paper web after leaving the press nip is significantly improved and even where the press felt lifts off, not to detach the paper web comes from the transfer belt.

This appears to be based on two mechanisms of action. To the the paper web becomes a flat and smooth support offered only through the openings of the cavities is interrupted. This improves liability and promotes also the formation of a film of liquid that adheres supported. On the other hand, the cavities create additional a vacuum that tends to detach the paper web counteracts. This is because the cavities compressed when entering the press nip and this causes water and air to be present in the cavities is largely squeezed out 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 rewet help avoid the paper web.

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

As for the training of the carrier, it is for the Function of the transfer belt is advantageous if it is in the longitudinal direction has a certain elasticity so the elasticity the inner layer is also used in the longitudinal direction becomes. Preferably, the carrier's specific module should ≤ 70 N / tex. A material should be used be that at tensile stresses of 4 to 8 daN / cm of the carrier is elastic in the width direction. Come for this in particular materials with a corresponding elasticity like PBT, PES, PA6, PA6.6, PA6.10, PA6.12, PA11, PA12 and PTT in question, these materials also together can be combined.

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

Natural rubber is used as the material for the inner layer or an elastomer in question. Are particularly suitable Silicone elastomer, polyester elastomer and polyurethane. Prefers the hardness of the inner layer should be between 85 and 95 Shore A.

Organic filler particles, for example TiO ₂ or clay, can also be embedded in 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 µm. In order to achieve such a thickness tolerance, it can be turned and sanded accordingly before the outer layer is applied.

Polyurethane and / or silicone elastomer and / or polyester elastomer are preferred as the material for the outer layer. If such or other plastic materials are used, the cavities can be produced in a manner known per se by sprinkling and storing soluble particles on them, which can be dissolved out with a solvent to which the outer layer is resistant (cf. EP-A 0 786 551). Water-soluble particles in the form of salts such as NaCl, KCl and / or CaCO ₃ are particularly suitable for this. The particles should have a diameter of ≤ 2 µm in order to create 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, previously used in chemistry as pigments for color effects, cosmetics and data storage layers, whose particle sizes are in the nano range, effectively protect the outer layer against wear, especially if the nanoparticles consist of SiO ₂ or metals, for example. The nanoparticles can be applied in a suspension of a water-alcohol mixture, the mixture then being evaporated. In some areas, the nanoparticles can be provided with fluorocarbon chains in order to give surface areas of the outer layer a hydrophobic character and thereby facilitate the detachment 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. For this come in particular Silicones or polyurethanes in question in one Water-surfactant mixture are emulsified, which is used in electron beam curing is evaporated.

Finally, it is provided according to the invention that the Outer layer on the outside consists of materials that are areas different hydrophilicity or hydrophobicity form. Both are intended to detach the paper web from the Transfer ribbon facilitate, the areas and the differences with regard to hydrophilicity or hydrophobicity should be arranged and trained that still adequate adhesion of the paper web in the area of Lifting off 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.

The invention is illustrated in more detail in the drawing with the aid of schematically illustrated exemplary embodiments. Show it:

Figure 1

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

Figure 2

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

Figure 3

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

Figure 4

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

The transfer belt 1 seen in FIG. 1 has a carrier 2, which in this case is made from a fabric of polyamide threads. The carrier 2 has an inner layer 3 on the top and a base layer on the bottom 4, with the carrier 2 in both layers 3, 4 is embedded. Inner layer 3 and base layer 4 consist of a silicone elastomer.

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

In the embodiment shown in Figure 2, the outer layer 5 essentially from a cast polyurethane layer 7. To in this polyurethane layer 7 for Cavities open on the outside - designated by way of example with 8 - To be produced are in the polyurethane material before the application salt particles - designated 9 by way of example - evenly distributed and in an average Size <2 µm has been stored. After training the polyurethane layer 7 on the inner layer 3 those salt particles 9 are washed out with water that has not been completely removed from the polyurethane layer 7 were enclosed, i.e. connection to the outside had. In this way, cavities 8 were created the depth of the previous penetration depth of the salt particles 9 corresponds. Those salt particles 9 that with Distance to surface 6 were not stored has been removed and therefore still in the polyurethane layer 7 available.

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

In the embodiment shown in Figure 3 Outer layer 5 is also the starting material polyurethane. However, this material is in powder form applied and then sintered so that here also a polyurethane layer 10 with a smooth surface 11 has trained. In the polyurethane powder were Salt particles stored (cf. in this respect that in EP-A 0 786 551 described method), which then by a Washing process have been completely extracted so that a porous structure forming from the surface 11 open cavities - exemplified by 12 - came into being. The effect of the polyurethane layer 10 is the same as for the polyurethane layer 7 according to FIG Figure 2.

The embodiment shown in Figure 4 shows one Outer layer 5, which consists of an emulsion of prepolymers has been manufactured. This emulsion is on the inner layer 3 has been applied and then electron beam hardened been. As a result, individual, with each other in Related polymer particles - exemplary with 13 designated - emerged, between which there are cavities - designated 14 by way of example - have formed. All in all is also a porous structure with a comparatively smooth surface 15 arose.

Claims (19)

Transfer belt for a paper machine with a carrier (2) and with a coating (3, 5) on at least one flat side, characterized in that the coating has an inner layer (3) and an adjacent outer layer (5) which has a porous structure has cavities (8, 12, 14) open to the outside (6, 11, 15). Transfer belt according to claim 1, characterized in that the inner layer (3) is impermeable to liquids. Transfer belt according to claim 1 or 2, characterized in that the inner layer (3) is longitudinally and / or elastically elastic. Transfer belt according to one of claims 1 to 3, characterized in that the carrier (2) has a specific module of ≤ 70 N / tex in the longitudinal direction. Transfer belt according to claim 4, characterized in that material is used for the carrier which is elastic at tensile stresses of 4 to 8 daN per cm width of the carrier (2). Transfer belt according to one of claims 1 to 5, characterized in that the carrier (2) is a woven fabric, knitted fabric, scrim or a non-woven fabric or a combination thereof. Transfer belt according to one of claims 1 to 6, characterized in that the carrier (2) is at least partially embedded in the inner layer (3, 5). Transfer belt according to one of claims 1 to 7, characterized in that the inner layer (3) consists of natural rubber or an elastomer, in particular silicone elastomer, polyurethane and / or polyester elastomer. Transfer belt according to one of claims 1 to 8, characterized in that the inner layer (3) has a hardness between 85 and 95 Shore A. Transfer belt according to one of claims 1 to 9, characterized in that the inner layer has inorganic filler particles. Transfer belt according to one of claims 1 to 10, characterized in that the inner layer (3) has a thickness tolerance of at most 100 µm. Transfer belt according to one of claims 1 to 11, characterized in that the outer layer (5) consists of polyurethane and / or silicone elastomer and / or polyester elastomer. Transfer belt according to one of claims 1 to 12, characterized in that the cavities (8, 12, 14) in the outer layer (5) have an average diameter of ≤ 2 µm. Transfer belt according to one of claims 1 to 13, characterized in that the outer layer (5) is provided on its surface with nanoparticles. Transfer belt according to claim 14, characterized in that the nanoparticles at least partially consist of SiO ₂ . Transfer belt according to claim 14 or 15, characterized in that the nanoparticles have fluorocarbon chains. Transfer belt according to one of claims 1 to 11, characterized in that the outer layer (5) consists of an electron beam hardened prepolymer emulsion. Transfer belt according to one of claims 1 to 17, characterized in that the outer layer (5) consists on the outside of materials which form areas of different hydrophilicity or hydrophobicity. Transfer belt according to one of claims 1 to 18, characterized in that the outer layer has a thickness of ≤ 3 mm and the inner layer has a thickness of 1-3 mm.

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