Fabrics Having Hydrophilic and Hydrophobic Coatings

Europa,schesP_ Nil II II II Nil M II UN Mill Ml J European Patent Office _ _ _ © Publication number: 0 367 738 B1 Office europeen* des.. brevets ,

EUROPEAN PATENT SPECIFICATION

@ Date of filing: 24.10.89

@ Priority: 31.10.88 US 265257 © Proprietor: ALBANY INTERNATIONAL CORP. 1373 Broadway @ Date of publication of application: Albany, New York 12204(US) 09.05.90 Bulletin 90/19 @ Inventor: Barnewall, James M. © Publication of the grant of the patent: 8 Pine Stump 27.07.94 Bulletin 94/30 Albany New York 12205(US)

© Designated Contracting States: AT DE FR GB IT NL SE © Representative: Hermansson, Birgitta et al AB Dahls Patentbyra © References cited: P.O. Box 606 DE-A- 1 619 108 S-182 16 Danderyd (SE) FR-A- 2 434 235 GB-A- 1 050 545 GB-A- 1 455 843

00 00 00 IV

CO oo Note: Within nine months from the publication of the mention of the grant of the European patent, any person ® may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition CL shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee LU has been paid (Art. 99(1) European patent convention). Rank Xerox (UK) Business Services (3. 10/3.09/3.3.3) EP 0 367 738 B1

Description

This invention is directed to press fabrics having improved water removal capability. More specifically, this invention is directed to the improvement of the water removal characteristics of press fabrics by 5 applying hydrophobic and hydrophilic coatings.

BACKGROUND OF THE INVENTION

Papermakers' press fabrics are endless belts used for conveying a wet paper web from a forming zone, io through a pressing zone, to a drying zone. In the pressing zone there is usually provided rotating cylindrical squeeze rolls between which the freshly formed paper web is passed. As the web enters the nip of the rolls, water is squeezed from the paper and is accepted by the press fabric upon which the paper is conveyed through the nip. Papermakers' press fabrics are well known. Such fabrics are typically formed from materials such as 75 wool, nylon, and/or other synthetic polymeric materials and the like. With such fabrics, the paper web, after passing through the nip of the pressing rolls, usually still contains an appreciable amount of water (50 to 64% water), which adds substantially to manufacturing costs due to the high energy required to evaporate the water during the subsequent drying stage. Improving the sheet water removal characteristics of the fabrics would thus be highly advantageous in that manufacturing costs would be reduced. 20 In GB, A, 1 455 843 one way of making paper-maker's wet felts showing different characteristics as to water-repellency is described. These felts, which are endless belts or bands of water absorbent material, have a woven backing, a wad of fibers needled to the backing layer to provide a hydrophilic (or less hydrophobic) intermediate layer and a surface layer of hydrophobic fibres, i.e. the different layers having different capacities as to being hydrophobic or hydrophilic are made up from different materials. 25 OBJECTS OF THE INVENTION

It is an object of the invention to provide an improved press fabric. It is also an object of the invention to provide a press fabric having enhanced water removal capability. 30 It is a further object of the invention to improve the water removal capability of the press fabric by applying hydrophobic and hydrophilic coatings thereto. These and other objects of the invention will be more apparent in the discussion below.

DETAILED DESCRIPTION OF THE INVENTION 35 According to the present invention, there is provided a method of modifying a press fabric for a papermaking machine to impart a combination of hydrophilic and hydrophobic characteristics, said method characterised by comprising the steps of: (a) applying a hydrophilic or hydrophobic polymeric coating as a liquid, foam or froth composition to the 40 surface of a fabric to form a layer thereon; (b) drying said coating to form a layer; (c) applying to said dried layer a hydrophobic coating if a hydrophilic coating was used in step (a) or a hydrophilic coating if a hydrophobic coating was used in step (a); (d) drying said coating applied in step (c) to form a second layer; 45 (e) repeating steps (a) to (d) as necessary; and (f) curing the thus modified fabric. Moreover, there is also provided a press fabric for papermaking machines comprising a felt having a combination of hydrophobic and hydrophilic characteristics characterised in that the surface of said felt is coated with at least two successive Resin layers, one being hydrophobic and the other hydrophilic. 50 It has been found that when a fabric according to the invention is used to convey a freshly formed paper web through the nip formed by pressing rolls, the amount of water remaining in the paper upon emergence from the nip can be much reduced. It is believed that this situation is due to the combination of hydrophilic and hydrophobic properties reducing the tendency for water to return to the paper web, a phenomen termed "rewet". Thus, since less water is left on the surface layers of the press fabric, less 55 water is available to be returned to the paper web. More specifically, according to the invention a press fabric is alternately coated with layers of hydrophilic and hydrophobic coating. The order of application, whether a hydrophobic coating or a hydrophilic coating is applied first, is not as important as the presence of layers of both the hydrophobic

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and hydrophilic resins. Further, more than one layer of one type can be applied before or after application of one or more layers of the other type. The fabrics to be treated include those known in the art. Typical such fabrics are described in, for example, U.S. Patents Nos. 2,354,435, 2,567,097, 3,059,312, 3,158,984, 3,617,442, 3,657,068, and 5 4,382,987, and British Patent No. 980,288, all of which are incorporated herein by reference. Useful resin compositions include polyurethanes, polyether, polyester, polyisocyanate, polyolefins, polyacrylonitrile rubbers, polyacrylates, polyvinyl chlorides, epoxies, and the like, or a combination of two or more such polymeric resins. Typical of useful resin compositions are Emulsion 26172 (an acrylic emulsion representative of a large series of emulsions available from B.F. Goodrich) and Permuthane HD2004 (a io water-based polyurethane emulsion available from C.L. Hauthaway). Polyurethane coatings tend to be hydrophobic, and polyacrylic coatings tend to be hydrophilic. However, polyurethane foams can be made hydrophilic by addition of surfactant and/or detergent, or the like. The resin coating composition can be prepared by admixing the various components and can then be is applied as a liquid coating, foam, or froth. According to the invention a coating is applied to a surface, or surfaces, of a press fabric and then allowed to dry and cure. The coating can be applied in one or more layers in conventional fashion. Each layer is dried. After the topmost layer is dried, the coated fabric is cured by a suitable means. The temperature and time for drying or curing will be dependent upon the coating employed, manufacturing 20 conditions, and the like. The following examples are intended to illustrate the invention and should not be construed as limiting the invention thereto.

EXAMPLES 25 Example 1

Samples of DURAVENT™ press fabric (available from Albany International Corp., Felt Div.) were coated with alternating layers of a foam from polyurethane (available as Permuthane UE41-035 water based 30 emulsion from C.L. Hauthaway) and polyacrylic (available as HYCAR 26138 from B.F. Goodrich). The foams were high blow ratio (low density) to keep from reducing air permeability excessively during application of several layers. Each successive coat was dried and cured before the next coat was added. Even after several coats, air permeability was reduced only slightly. Although a significant amount of resin was added, air permeability and felt stiffness were relatively unchanged. 35 Data for these samples is set forth in the following table:

TABLE I

Sample Coating ** % Add-On During Pass Total Accumulated Air Permeability Add-On m3/min/m2(cfm/ft.2) A* Uncoated -- -- 4.88(16) B ACR Coating 3.73 3.73 4.88(16) C ACR/PUR Coatings 0.46 4.19 4.88(16) D ACR/PUR/ACR Coatings 1.10 5.29 4.57 (15) E* Uncoated ~ ~ 6.71 (22) F PUR Coating 3.09 3.09 4.88 (16) G PUR/ACR Coatings 3.53 6.62 4.88 (16) H PUR/ACR/PUR Coatings 1.70 8.32 4.88(16) * Control ** "ACR" = polyacrylic foam coating; "PUR" = polyurethane foam coating

55 Example 2

A polyurethane foam, which tends to be hydrophobic, was made hydrophilic by adding 20% detergent to the emulsion and then foaming the mixture.

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Layers of foam were applied to fabric samples. The first layer was hydrophobic polyurethane foam, the second layer was detergent loaded hydrophilic foam, and the final coating was the hydrophobic polyurethane foam. Each layer was dried prior to the addition of the next layer. After all layers were applied, the samples were cured at 148.9 ° C (300 ° F). 5 The resultant sandwich structures were washed and dried for several cycles. The samples wet up much more rapidly than untreated fabric samples. After three layers were coated onto the fabrics the total add-on was nearly 15% solids. However, the results of air permeability tests set forth in the table below indicate that the fabrics were not appreciably closed up, i.e., the voids were not filled: 10 TABLE II

Sample Fabric Air Permeability m3/min/m2(cfm/sq.ft.) A* Uncoated 6.10(20) B Coated 6.10(20) C* Uncoated 20.42 (67) D Coated 20.12 (66) * Control 20

It follows that by coating a fabric with alternating layers of hydrophilic/hydrophobic foams, the hydrophilic/hydrophobic nature of the fabric structure and underlayer can be modified. Thus, the location and movement of water in the fabric structure could be controlled. In addition, sheet pickup and dewatering 25 ability of the fabric should be improved, and there should be a reduced tendency to re-wet the sheet as the fabric and sheet emerge from the press nip. The preceding specific embodiments are illustrative of the practice of the invention and should not be construed to be limiting of the scope of the claims in any way.

30 Claims

1. A method of modifying a press fabric for a papermaking machine to impart a combination of hydrophilic and hydrophobic characteristics, said method characterised by comprising the steps of: (a) applying a hydrophilic or hydrophobic polymeric coating as a liquid, foam or froth composition to 35 the surface of a fabric to form a layer thereon; (b) drying said coating to form a layer; (c) applying to said dried layer a hydrophobic coating if a hydrophilic coating was used in step (a) or a hydrophilic coating if a hydrophobic coating was used in step (a); (d) drying said coating applied in step (c) to form a second layer; 40 (e) repeating steps (a) to (d) as necessary; and (f) curing the thus modified fabric.

2. The method according to claim 1 wherein the hydrophobic coating is a polyurethane coating.

45 3. The method according to claim 1 wherein the hydrophilic coating is a polyacrylic coating or a polyurethane coating containing one or more additives selected from the group consisting of surfac- tants, detergents, stabilizers, and emulsifiers.

4. The method according to claim 1 , wherein 2 or more layers are applied to the fabric. 50 5. The method according to claim 1 , wherein each layer is air dried at room temperature.

6. The method according to claim 1 , wherein the modified fabric is air dried at room temperature to cure it. 55 7. The method according to claim 1, wherein the modified fabric is heated at elevated temperature for from about 1 minute to 5 hours.

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8. A press fabric for papermaking machines comprising a felt having a combination of hydrophobic and hydrophilic characteristics characterised in that the surface of said felt is coated with at least two successive Resin layers, one being hydrophobic and the other hydrophilic.

5 9. The fabric of claim 8, which has from two or more resin layer, at which one or more layers of the hydrophilic type have been applied before or after the application of one or more layers of the hydrophobic type.

10. The fabric of any of the claims 8 or 9, wherein the first layer is a hydrophobic layer. 10 11. The fabric of any of the claims 8 or 9, wherein the first layer is a hydrophilic layer.

Patentanspruche

is 1. Verfahren zum Modifizieren eines Pressengewebes fur eine Papierherstellungsmaschine zur Verleihung einer Kombination aus hydrophilen und hydrophoben Eigenschaften, wobei das Verfahren dadurch gekennzeichnet ist, dal3 es folgende Schritte aufweist: (a) Aufbringen einer hydrophilen oder hydrophoben polymeren Beschichtung als flussige Zusam- 20 mensetzung, Schaumzusammensetzung oder Aufschaumzusammensetzung auf die Oberflache eines Gewebes zur Bildung einer Schicht auf dieser; (b) Trocknen der Beschichtung zur Bildung einer Schicht; (c) auf die getrocknete Schicht erfolgende Aufbringung einer hydrophoben Beschichtung bei Ver- wendung einer hydrophilen Beschichtung in Schritt (a) oder einer hydrophilen Beschichtung bei 25 Verwendung einer hydrophoben Beschichtung in Schritt (a); (d) Trocknen der in Schritt (c) aufgebrachten Beschichtung zur Bildung einer zweiten Schicht; (e) Wiederholen der Schritte (a) bis (d) je nach Erfordernis; und (f) Ausharten des auf diese Weise modifizierten Gewebes.

30 2. Verfahren nach Anspruch 1 , wobei es sich bei der hydrophoben Beschichtung urn eine Polyurethanbe- schichtung handelt.

3. Verfahren nach Anspruch 1, wobei es sich bei der hydrophilen Beschichtung urn eine Polyacrylbe- schichtung oder eine Polyurethanbeschichtung mit einem oder mehreren Zusatzstoffen handelt, die 35 ausgewahlt sind aus der Gruppe bestehend aus oberflachenaktiven Mitteln, Detergentien, Stabilisatoren und Emulgatoren.

4. Verfahren nach Anspruch 1, wobei zwei oder mehr Schichten auf das Gewebe aufgebracht werden.

40 5. Verfahren nach Anspruch 1, wobei jede Schicht bei Raumtemperatur an der Luft getrocknet wird.

6. Verfahren nach Anspruch 1 , wobei das modifizierte Gewebe zur Aushartung desselben bei Raumtem- peratur an der Luft getrocknet wird.

45 7. Verfahren nach Anspruch 1, wobei das modifizierte Gewebe fur eine Zeitdauer von ca. 1 Minute bis 5 Stunden auf eine erhohte Temperatur erwarmt wird.

8. Pressengewebe fur Papierherstellungsmaschinen, mit einem Filz mit einer Kombination aus hydrophoben und hydrophilen Eigenschaften, so dadurch gekennzeichnet, dal3 die Oberflache des Filzes mit wenigstens zwei aufeinanderfolgenden Harzschichten beschichtet ist, von denen die eine hydrophob und die andere hydrophil ist.

9. Gewebe nach Anspruch 8, das zwei oder mehr Harzschichten aufweist, wobei eine oder mehrere 55 Schichten des hydrophilen Typs vor oder nach der Aufbringung einer oder mehrerer Schichten des hydrophoben Typs aufgebracht worden sind.

10. Gewebe nach einem der Anspruche 8 oder 9, wobei die erste Schicht eine hydrophobe Schicht ist.

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11. Gewebe nach einem der Anspruche 8 oder 9, wobei die erste Schicht eine hydrophile Schicht ist.

Revendicatlons

5 1. Procede de modification d'un tissu de presse pour machine de fabrication de papier, afin de conferer une combinaison de caracteristiques hydrophiles et hydrophobes, ce procede etant caracterise en ce qu'il comprend les etapes consistant : (a) a appliquer un revetement a base de polymere hydrophile ou hydrophobe sous la forme d'une composition liquide, formant mousse ou ecume, sur la surface d'un tissu afin d'y former une couche io ; (b) a secher ce revetement pour former une couche ; (c) a appliquer sur cette couche sechee, un revetement hydrophobe si Ton a employe un revetement hydrophile dans I'etape (a), ou un revetement hydrophile si Ton a employe un revetement hydrophobe dans I'etape (a) ; is (d) a secher ce revetement applique dans I'etape (c) pour former une deuxieme couche ; (e) a repeter les etapes (a) a (d) ainsi que cela est necessaire ; et (f) a durcir le tissu ainsi modifie.

2. Procede selon la revendication 1 , dans lequel le revetement hydrophobe est un revetement a base de 20 polyurethanne.

3. Procede selon la revendication 1 , dans lequel le revetement hydrophile est un revetement polyacrylique ou un revetement a base de polyurethanne contenant un ou plusieurs additifs choisis parmi les tensioactifs, les detergents, les stabilisants et les emulsifiants. 25 4. Procede selon la revendication 1, dans lequel on applique au moins deux couches sur le tissu.

5. Procede selon la revendication 1, dans lequel chaque couche est sechee a I'air a la temperature ambiante. 30 6. Procede selon la revendication 1, dans lequel le tissu modifie est seche a I'air a la temperature ambiante afin de le durcir.

7. Procede selon la revendication 1 , dans lequel le tissu modifie est chauffe a temperature elevee pendant 35 environ 1 minute a 5 heures.

8. Tissu de presse pour machines de fabrication de papier, comprenant un feutre ayant une combinaison de caracteristiques hydrophobes et hydrophiles, caracterise en ce que la surface de ce feutre est revetue avec au moins deux couches successives a base de resine, I'une etant hydrophobe et I'autre 40 hydrophile.

9. Tissu selon la revendication 8, comportant au moins deux couches de resine, au moins une couche du type hydrophile ayant ete appliquee avant ou apres I'application d'au moins une couche du type hydrophobe. 45 10. Tissu selon I'une quelconque des revendications 8 et 9, dans lequel la premiere couche est une couche hydrophobe.

11. Tissu selon I'une quelconque des revendications 8 et 9, dans lequel la premiere couche est une 50 couche hydrophile.