EP1485183A2

EP1485183A2 - Industrial fabrics

Info

Publication number: EP1485183A2
Application number: EP03720324A
Authority: EP
Inventors: Robert L. Crook; William Daniel Aldrich; Sanjay Patel
Original assignee: Voith Fabrics Heidenheim GmbH and Co KG
Current assignee: Voith Fabrics Patent GmbH
Priority date: 2002-03-09
Filing date: 2003-03-07
Publication date: 2004-12-15
Also published as: AU2003223959A8; WO2003076046A3; CA2487651A1; WO2003076046A2; AU2003223959A1; GB0205574D0

Abstract

An industrial fabric including a base layer (2), a batt layer (8) and at least one low-melt polymeric film layer (6) which has been needled (12) into the batt layer (8) and subsequently thermoformed (20) to at least partially encapsulate fibres of that batt layer (8).

Description

1NDUSTRIAL FABRICS The present invention relates to industrial fabrics for use in phase separation applications such as media for filtration and like fabrics for papermaking. When in use, such industrial fabrics suffer from the problems of fibre shedding and wear. Also, rewetting of a paper sheet upon exit of the sheet from the press-nip of the papermaking machine is a recognized problem.

Various methods of alleviating the above drawbacks have been proposed.

In the papermaking felt described in US 5,372,876 (Appleton Mills), at least one hydrophobic layer of co-joined synthetic, e.g. nylon filaments is disposed between a base fabric and the batt material and/or between at least two batt layers. The various layers are joined by needling. In use, the batt layer receives water from the web, and such water is forced from the batt layer through the hydrophobic layer(s) under pressure in the press-nip. Upon exiting the press-nip, the pressure is relieved and the hydrophobic layer provides a barrier which reduces backflow of water to the batt, thereby alleviating rewetting.

In GB 2,285,935 (Scapa Group) the problem of fibre shedding and wear is addressed by providing polymer coated paper machine clothing which reduces fibre shedding and improves both abrasion resistance and surface smoothness.

The coating is applied by urging a polymer film coated release sheet on to the surface of the base cloth of the fabric, curing the polymer by passing such through heated roller and then removing the release sheet to leave a permeable coating.

In US 5, 1 18,557 (Albany) a thin layer of polymer foam is applied to the surface of the press fabric, which is allowed to dry, this procedure is repeated several times to form a coating. This fabric then has an increased resistance to rewet of the paper and produces a paper sheet with increased surface smoothness, due to increased surface contact area afforded by the foam coating together with its controlled porosity and void volume.

In EP 0239207 (Asten) a 0.4mm thick scrim of low melt synthetic material having a regular lattice configuration of 6mm squares is located between two upper batt layers of a papermaker's felt. The lattice structure is designed in order not to affect the moisture absorption of the felt and is provided to prevent excessive fibre migration as a result of the needling operation to join the various batt layers together. In a subsequent heat setting step the scrim, which has a lower melting point than that of the batt material, is softened to undergo deformation thereby adhering to the batt fibres and reducing the likelihood of fibre migration or layer separation of the batt during use of the papermaker's felt.

In US 4,199,401 (Asten) a coarse layer of batt is provided on the paper contacting side, and a finer denier batt sandwiched between this and a base layer of the papermaker's felt. This allows the water to migrate through the felt by capillary action thereby reducing rewet.

In US 5,232,768 (Nordiska filt) a batt layer is provided on the paper contacting side, and a barrier layer is sandwiched between this and the base layer of the press felt. The barrier layer may comprise filament threads as a perforated film or sintered polymeric particles as a foam layer. The barrier layer provides a high resistance to water flowing back through it to the paper contacting side.

In US 5,071 ,697 (Gulya) a permeable polymeric foam is secured to the surface of a base substrate, with a thin outer layer of polymeric film being bonded to the outer surface. This provides a flexible, tough skin to resist abrasion and tearing during operation. In US 4,830,905 (Gulya) a method to reduce web rewet is described in that a layer of closed cell polymeric foam is disposed on a face of the base fabric. A fibrous batt layer is needled thereon, this needling action penetrating the foam and intersecting the cells. Whilst compressed in the nip, the penetrated cell walls open up allowing water in, then on leaving the nip, the walls once again close, so trapping water in the cells.

US 3,214,326 (Lee) describes a press felt, the objective of which is to increase the quantity of water removed from the paper sheet, as well as to reduce rewet, whereby a barrier layer is attached to the upper, paper contacting surface of a woven base cloth. The barrier layer has been described as a fine, low permeability, woven fabric.

US 3,399,1 1 1 (Beaumont) describes a 'supplemental belt', for use in conjunction with a press felt, which runs on the machine-side. The construction includes at least one perforated film laminated to a foam or woven layer. One of the belt's purposes is to give good drainage and water removal characteristics. US 4,541 ,895 (Albert) describes a papermaker's fabric made up of a plurality of perforated plastic sheets, the size and distribution of the apertures being variable. US 4,550,588 (Lundstrom) describes an air impermeable felt/belt which has been manufactured by filling a felt, except for the upper surface, which retains a chamois-like surface. A barrier layer, for example a non-woven layer or additional batt layer may be inserted below the surface to prevent the filler material from penetrating to the surface.

US 4,565,735 (Murka) describes a felt which consists of at least two types of batt fibre, one being of lower melt material and being applied in a lower quantity than the other and then melted. The object is to give a felt with improved wear and compaction resistance.

It is an object of the present invention to provide an industrial fabric which has improved resistance to rewet, and improved smoothness and wear resistance.

It is a further object to provide an industrial fabric which has improved resistance to fibre shedding, superior macro and micro scale pressure uniformity, more economical to apply and process more consistently.

In accordance with a first aspect of the present invention there is provided a method of making an industrial fabric including the steps of providing a base

layer, at least one batt layer, and at least one polymeric film layer, the method further comprising the steps of needling the said layers and then thermoforming the at least one polymeric layer.

Needling results in perforation of the polymeric film layer enabling anchoring of the batt fibres therethrough. The subsequent thermoforming of that layer leads to at least partial encapsulation of the surrounding batt fibres and crossover points thereof. This gives improved locking of the fibres of the batt together, so reducing shedding. Furthermore, the combination of the batt fibres and polymeric film provide a resistance to re-wet and hence superior sheet dryness when the fabric is used for paper machine clothing. It also blocks the backflow of filtered substances in other applications. In comparison to the papermaking fabric described in US 5,372,876 the present fabric when used as a papermaking fabric has been found to provide a fabric with superior fibre bonding and wear resistance, with enhanced surface/pressure uniformity and contact area for sheet smoothness. It is intended that the term "thermoforming" not only covers the possibility of fully melting the plastics layer, but that it should cover the possibility of supplying enough thermal energy to soften, that is deform, that layer sufficiently to enable said at least partial encapsulation of the batt fibres. The polymeric film layer may be provided under at least one layer of batt and/or on at least one layer of batt.

In a preferred embodiment the polymeric film layer is beneath a fine, uniform, fibrous diffusion layer, which diffusion layer forms a surface layer. This has the advantage that once needled and thermoformed, the polymeric partially encapsulates and anchors the surface fibres, providing a reduction in shedding in this region and also an improved surface wear resistance.

For hot end use applications, polymeric film material with a higher melting point may be used, for example a material such as an ether based polyurethane. This has the advantage of minimal degradation thereby maintaining bonding and fibre adhesion in the structure. The permeability of the fabric can be controlled by varying the thickness and quantity of polymeric film layers used, as well as by adjusting the needling procedure, that is the number of punches per unit area, and the amount and coarseness of the batt driven through. The heat setting conditions which may include the use of compression from a calender can also be used to adjust the permeability of the fabric to the required level, by altering the degree of tension/compressive forces present during high temperature applications. In accordance with a second aspect of the present invention there is provided an industrial fabric including a base layer, a batt layer and at least one low-melt polymeric film layer which has been needled into the batt layer and subsequently thermoformed to at least partially encapsulate fibres of that batt layer.

The polymeric film layer may have a melting point of less than 215°C. Preferably the batt layer forms a surface layer of the fabric.

Preferably at least two batt layers are provided with the polymeric film layer being located under at least one of the said batt layers. The polymeric film layer may be provided as an elastomeric, thermoplastic polyurethane film. The film layer may have a thickness in the region of 0.05mm. Polyurethane has the advantage that it has a lower melting point than that of the nylon fibres usually used to form the various batt layers, whilst still having a melting point which is above 100°C thereby enabling continuous service of the fabric at relatively high temperatures without melting the polyurethane during use. Furthermore, being an elastomer, polyurethane maintains its original properties even after repeated melt/cool process cycles and it's high melt viscosity prevents it from "flowing" excessively at high temperatures. The polymeric film layer may be perforated and/or may include a filler.

The polymeric film layer may be of a multi-layer construction with at least two layers thereof having different characteristics.

The fabric may comprise a plurality of said polymeric film layers, and in a preferred embodiment at least two of said layers have different characteristics. By way of example only specific embodiments of the invention will now be described with reference to the accompanying drawings, in which:- Fig. 1 is a schematic view showing the production of an industrial fabric constructed in accordance with one aspect of the present invention; Fig. 2 is a scanning electron microscope photograph showing a detail of the constructed fabric of Fig. 1 illustrating the needled and subsequently molten plastics film;

Fig. 3 is a scanning electron microscope view of the paper contacting or the like surface of the fabric of Fig. 2; Fig. 4 is a comparative graphical representation illustrating density variations throughout the width of the constructed fabric; and Fig. 5 is a schematic view of the layers in an industrial fabric before they are needled and heat set constructed in accordance with a second aspect of the present invention.

With reference to Fig. 1 (a), an industrial fabric constructed in accordance with the invention comprises a base layer 2, a first upper batt layer 4, a fine 0.051 mm (0.002 inch) thick elastomeric, thermoplastic polyurethane film layer 6, an uppermost batt layer 8, and a lower batt layer 10. The polyurethane film layer 6 has a lower melting point than the other layers. These layers are joined, as best illustrated in Fig. 1 (b) by needling 12 the layers together. Needling causes the individual fibres of the batt layers to intermingle and to link through the base layer 2 to lock the layers together. Furthermore, the needling action perforates the polyurethane film 6 to give a more open structure, through which the batt fibre is driven. As best illustrated in Fig. 1 (c) the upper paper contacting surface of the fabric 18 is then heated at 200°C using a cylinder 20, this heat being sufficient to melt the lower melting point needled polyurethane film 6 only. This heat permeates through the fabric to melt the needled film 6 and causes it to flow upwards towards the upper surface 18 of the upper batt layer 8. As best illustrated in Figs. 2 and 3, once cooled the then needled and melted film 6 encapsulates the surrounding batt fibres and cross-over points thereof.

The fibres of the upper batt layer 8 thereby have a partial polyurethane coating which better interlocks the individual fibres thereof to provide a more cohesive structure less prone to fibre shedding. The gaps 22 within the coated fibres nevertheless present a porous layer.

As best illustrated in Fig. 4, in the region of the needled and thermoformed film layer 6 there is an increase in the density of the fabric, which means that it is more difficult for expressed water to pass through the fabric in this particular region.

However, when in use the fabric passes through the nip and is placed under very high pressure enabling expressed water, from the paper sheet carried on the fabric, to be more readily forced into and through the fabric. When the fabric emerges from the nip, the pressure of the nip is relieved, the fabric recovers, and the needled and thermoformed film layer 6 thereby once again presents a structure which is more difficult for the water to pass through. By this means, the water is not able to force its way back through the fabric, that is, through this denser region to the upper surface 18, so re- et of a paper sheet is minimised. The encapsulated and anchored batt fibres of the present invention give greater pressure uniformity due to the more homogenous surface thereof thus enabling more water to be squeezed out of a paper sheet transported thereon. In fact, experimental results have demonstrated that a fabric constructed in accordance with the present invention produced a paper sheet having an increase in sheet dryness of 1 .8%, when compared to a paper sheet produced by a fabric constructed in accordance with US 5,372,876.

US 5,571 ,590 and US 5,731 ,063 (Appleton Mills) describe the fusing/butt joining of plastics film supplied in narrow rolls to form full size endless loops. The film of the present invention can be joined in the manner described in these prior patents, but has the additional advantage that the actual join will not be evident after heat and pressure has been applied during the heat thermo-setting process.

A fabric constructed in accordance with the present invention (Sample A) was tested and compared to a control sample fabric (Sample B) which contained equivalent layers, however the film had not been thermoformed in this control sample, and a second control sample (Sample C) which contained equivalent layers with the exception that the film layer was omitted. The permeabilities of Samples A, B and C were measured on a Frazier permeameter with 12.7mm (0.5") water gauge pressure. The permeabilities of Sample B and Sample C were 2.8 litres/m²/sec and 8 litres/m²/sec respectively. This demonstrated that the initial addition of the thin film of polyurethane, which is needled but not thermoformed, results in a fabric which has a significant reduction in permeability thereby undesirably reducing the flow of expressed water therethrough. However, the permeability of Sample A, constructed in accordance with the present invention, is once again increased to 5.7 litres/m²/sec, giving a fabric with a permeability not significantly lower than control Sample C. Therefore, a fabric constructed in accordance with the invention has made only a slight compromise in permeability, whilst having the advantage of reduced fibre shedding, a more homogenous surface and a reduced incidence of re-wet. -l ilt was expected that thermoforming of the polyurethane film would severely reduce the permeability, however tests show that with a sufficiently thin film the fabric remained open due to the vertical and horizontal migration of the polyurethane melt and it's ability to actually wet the batt fibres. Although the film layer has been described as being provided between two upper batt layers, the film could be provided on the uppermost surface 18 before it is joined by needling and then subsequently thermoformed. Although two upper batt layers have been described, several such layers may be provided and also more than one film layer could be provided on, or between adjacent such batt layers. Additional film layers may be provided between or on adjacent batt layers. Although a lowermost batt layer has been illustrated, this could be omitted, or equally consist of several such layers. A film may also be provided between the lower batt layer(s), or immediately adjacent the base layer. Although in the described embodiment the base fabric has been illustrated as a woven layer, this could be a non-woven layer, for example a porous film could be employed.

In the embodiment of Fig. 5 the industrial fabric comprises a woven base cloth 22, batt layers 24, 26, 28 and a plastics layer 30. Batt layer 24 comprises a uniform, stiff, laminate non-woven batt structure which is substantially aligned in the machine direction (MD) of the fabric. The batt layer 24 is comprised of 0.1 mm (0.004") thick bi-axial non-woven fibres which both diffuses and masks the base cloth. Batt layer 26 comprises substantially cross-machine (CD) orientated fibres having a dtex of 17 and which via needling bonds the base cloth 22 and batt layer 24 together and also both diffuse and mask the coarser machine direction orientated fibres of the batt layer 24. Batt layer 28 essentially comprises a matrix of relatively fine batt fibres of 3.3 dtex. The batt layer 28 supports the sheet and facilitates ease of water movement from the sheet into the press fabric.

Although the film layer has been described as being an elastomeric, thermoplastic polyurethane film, the film layer could comprise other types of plastics, for example other types of thermoplastic polymers; thermoplastic resin and/or elastomer, or a cross linkable resin and/or elastomer. The film layer may also contain fillers such as release agents for example fluorinated polymers and polysiloxanes, or inorganic fillers, adhesion promoters, foamable fillers etc. The film layer could be of a multi-layer construction with each layer providing unique properties such as melting temperature, elasticity, hydrophilic and hydrophobic characteristics influencing water movement in and out of the composite structure, barrier properties etc. The film layer may also be of a multi-layer construction with varying hardness. The film may be pre-perf orated. The type of material and properties thereof can be selected depending on the required use of the fabric in terms of level of permeability required or the possible degree of hydrophobic properties required.

Although the specific example has been described in relation to a fabric suitable for use as a papermaker's belt, which could be seamed or endless, such fabrics could be used in other phase separation applications, such as filtration.

Although specific thickness of film has been described, it is to be understood that other thickness of film could be employed.

Claims

CLAIMS:

1 . A method of making an industrial fabric including the steps of providing a base layer, at least one batt layer, and at least one polymeric film layer, the method further comprising the steps of needling the said layers and then thermoforming the at least one polymeric layer.

2. A method as claimed in claim 1 , wherein the polymeric film layer is provided under at least one layer of batt and/or on at least one layer of batt.

3. A method as claimed in claim 1 or 2, wherein the polymeric film layer is beneath a fine, uniform, fibrous diffusion layer, which diffusion layer forms a surface layer.

4. A method as claimed in any one of claims 1 , 2 or 3, wherein the polymeric film material is an ether based polyurethane.

5. An industrial fabric including a base layer, a batt layer and at least one low- melt polymeric film layer which has been needled into the batt layer and subsequently thermoformed to at least partially encapsulate fibres of that batt layer.

6. An industrial fabric as claimed in claim 5, wherein the polymeric film layer has a melting point of less than 21 5°C.

7. An industrial fabric as claimed in claim 5 or 6, wherein the batt layer forms a surface layer of the fabric.

8. An industrial fabric as claimed in claim 5, 6 or 7, wherein at least two batt layers are provided with the polymeric film layer being located under at least one of the said batt layers.

9. An industrial fabric as claimed in any one of claims 5 to 8, wherein the polymeric film layer is an elastomeric, thermoplastic polyurethane film.

10. An industrial fabric as claimed in any one of claims 5 to 9, wherein the film layer has a thickness in the region of 0.05mm.

1 1 . An industrial fabric as claimed in any one of claims 5 to 10, wherein the polymeric film layer is perforated and/or includes a filler.

12. An industrial fabric as claimed in any one of claims 5 to 1 1 , wherein the polymeric film layer is of a multi-layer construction with at least two layers thereof having different characteristics.

13. An industrial fabric as claimed in any one of claims 5 to 12, wherein the fabric comprises a plurality of said polymeric film layers.

14. An industrial fabric as claimed in claim 13, wherein at least two of said plurality of polymeric film layers have different characteristics.

15. A method of making an industrial fabric substantially as described herein with reference to the accompanying drawings.

16. An industrial fabric constructed and adapted to operate substantially as described herein and as illustrated in the accompanying drawings.