US20100170652A1

US20100170652A1 - Press felt

Info

Publication number: US20100170652A1
Application number: US12/699,561
Authority: US
Inventors: Hubert Walkenhaus; Robert Crook
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2007-08-03
Filing date: 2010-02-03
Publication date: 2010-07-08
Also published as: EP2185769A1; WO2009019060A1

Abstract

The present invention relates to a press felt having a first surface provided by a nonwoven structure and a second surface opposite the first surface, as well as a load absorbing base structure which is bonded with the nonwoven structure and is arranged between the first and the second surface. The press felt according to the present invention further includes particulate polymer material which is penetrated into the nonwoven structure from the first surface in sections in the direction of the second surface and which is adhered to the fibers of the nonwoven structure in a manner that the press felt has a permeability of at least 5 cfm, for example, at least 10 cfm. The present invention is characterized in that at least one filter layer is arranged in the nonwoven structure or at the barrier surface between the nonwoven structure and the base structure which is permeable for fluid and is substantially impermeable for polymer material from, for example, a predetermined particle size on.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of PCT application No. PCT/EP2008/057207, entitled “PRESS FELT”, filed Jun. 10, 2008, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a press felt for use in a machine for producing a fibrous web, especially in a paper, cardboard or tissue machine.
2. Description of the Related Art
Press felts are utilized predominantly in the press section of a paper, cardboard or tissue machine in order to transport the fibrous web through the press nip with the objective of absorbing the water which was pressed from the fibrous web in the press nip without again releasing it to the fibrous web. The quality and the dry content of the fibrous web after the press section depends greatly on the surface characteristic, the water absorption capacity and the rebound capacity of the press felts used at a respective position in the press section. The aforementioned properties can hereby be positively influenced through the introduction of polymer particles into the nonwoven structure of the press felt. It is, however, disadvantageous that the penetration depth of the polymer particles according to the related art cannot be purposefully targeted.
Since only the surface properties or only the rebound capacity of the felt is important for some applications, and the respective characteristics can be adjusted through the penetration depth of the polymer particles into the nonwoven structure, it is desirable to be able to purposefully target the penetration depth of the polymer particles into the nonwoven structure, especially depending upon their particle size.
What is needed in the art is a press felt whereby the penetration depth of the polymer particles into the nonwoven structure is purposefully targeted.

SUMMARY OF THE INVENTION

The present invention provides a press felt having a first surface provided by a nonwoven structure and a second surface opposite the first surface, as well as a load absorbing base structure which is bonded with the nonwoven structure and which is arranged between the first and the second surface. The present invention further provides a particulate polymer material which is penetrated into the nonwoven structure from the first surface in sections in the direction of the second surface and which is adhered to the fibers of the nonwoven structure in a manner that the press felt has a permeability of at least approximately 5 cfm, for example, at least 10 cfm.
The press felt according to the present invention is characterized in that at least one filter layer is arranged in the nonwoven structure or at the barrier surface between the nonwoven structure and the base structure. At least one filter layer is permeable for fluid and is essentially impermeable for polymer material, for example, from a certain particle size on. Thus, the filter layer forms a barrier layer between the nonwoven structure and the base structure.
In the present application, the term “substantially impermeable” is to be understood to mean that at least 98% of the polymer material of a predetermined particle size and larger reaching the filter layer adhere to the filter layer. The filter layer may also be completely impermeable for polymer particles having a predetermined particle size. Further, the second surface may be formed by an exposed surface of the nonwoven structure or by an exposed surface of the base structure. The filter layer, therefore, limits the penetration depth of the polymer material into the nonwoven structure from the first to the second surface, dependent upon the particle size of the polymer material.
The particulate polymer material may be provided by means of a fluid, for example, in the form of at least one dispersion, or with the assistance of air, from the first surface into the nonwoven structure. Since the filter layer is fluid permeable, for example, for liquid or gas or mixtures thereof, the polymer material can be transported by fluid into the nonwoven structure and can settle there in the area between the first surface and the filter layer, whereas the fluid after fulfilling its transport function passes the filter layer and can, therefore, be easily removed from the felt, for example, with the assistance of vacuum. Advantageously, the press felt according to the present invention, can be produced efficiently and thereby economically.
Bonding of the nonwoven structure with the base structure may occur, for example, through needle bonding, for example, prior to adding the particulate polymer material into the nonwoven structure.
The filter layer may have an original thickness of approximately 0.5 mm or less. Accordingly, the filter layer has insignificant or no influence on the structure of the press felt. The original thickness of the filter layer is understood to be that which it was prior to its installation into the press felt.
One embodiment of the present invention provides that at least one filter layer is a nonwoven layer which is formed particularly by fibers with approximately 3.3 dtex or less. Nonwoven layers of this type are used in press felts as membranes in order to prevent back-moistening of the paper web. They have the advantage that they can be produced simply and economically.
At the location of needling the filter layer, which prior to needle bonding was in the form of a nonwoven layer, the press felt has a reduced pore size. This means that in the area of this “needling point”, a zone with a locally increased fiber density extending in thickness direction of the press felt exists. In a thickness direction above and below this zone there is a lower fiber density and, therefore, an increased pore size. However, in the filter layer in the embodiment of a nonwoven layer, fibers with approximately 3.3 dtex or less are arranged inside the press felt, that is inside the nonwoven structure or at the boundary between the nonwoven structure and the base structure. Depending upon the size of the particles which are to be filtered through the filter layer, at least one filter layer may be formed by approximately 1.7 dtex fibers.
In order to be able to produce a filter layer formed by a nonwoven layer having good strength and/or very low thickness, a second embodiment of the present invention provides that fibers of at least one filter layer are fused together at common contact points. The fusing of the fibers occurs, for example, through heat effect. Such a fusion bonding process is referred to as “thermo-bonding”.
The filter effect of the filter layer can be influenced by the size of the openings in the filter layer. One possible influencing factor for the size of the openings in the filter layer in the form of a nonwoven layer exists in the basis weight of the nonwoven layer. In order to be able to filter polymer particles having a particle size of approximately 0.1 μm-600 μm, a third embodiment of the invention provides that at least one filter layer has a basis weight in the range of approximately 20 to 180 g/m².
The filter layer, in the form of a nonwoven layer, can include synthetic material fibers. For example, polyurethane (PU) fibers or polypropylene (PP) fibers or polyamide (PA) fibers or mixtures of two or more of the aforementioned fibers are conceivable. In addition it is conceivable that this nonwoven layer is formed from only polyurethane (PU) fibers or only polypropylene (PP) fibers or only polyamide (PA) fibers. Obviously fibers are also conceivable which consist of two materials, for example, a higher melting and a lower melting material. It is also conceivable that the fibers include natural materials.
An additional variation of the present invention provides that at least one filter layer is hydrophobic. Here, a slowing of the fluid flow occurs when applying the particles. A reduction in the fluid flow facilitates the filter process. The polymer particles can be positioned more easily across the filter layer.
Alternatively or in addition, it may be provided that at least one filter layer is formed by a sacrificial material, which can be, or which respectively was, dissolved from the press felt after fixing of the polymer particles in the nonwoven structure. Such a filter layer has the advantage that the characteristics of the completed press felt are not influenced by it.
Alternatively or in addition, at least one filter layer may be formed by a sacrificial material, especially thermoplastic polyurethane (PU) which was melted during fixing of the polymer particles in the nonwoven structure of the press felt. Since a filter layer of this type is melted during the fixing process, it is no longer recognizable as such in the completed felt, but instead only in the form of an increased quota of melted thermoplastic PU in the press felt.
Alternatively or in addition, at least one filter layer may be formed in that one layer in the nonwoven structure or the barrier surface between the nonwoven structure and the base structure is physically and/or chemically treated such that it is fluid permeable and substantially impermeable for polymer material having a predetermined particle size. In this context, a plasma treatment of, for example, one surface of one nonwoven layer of the nonwoven structure is, for example, conceivable before an additional nonwoven layer is applied to it so that the nonwoven structure in an intermediate layer embodies a filter layer.
Alternatively or in addition, it can be provided that at least one filter layer is a profiled foil with a thickness of approximately 0.5 mm or less. Foils can be produced especially simply and economically. The particle size which is to be filtered can be easily adjusted through the size of the perforations.
In order to influence the press felt characteristics as little as possible, a third embodiment of the present invention provides that at least one of the filter layers has a thickness of approximately 0.2 mm or less, for example, approximately 0.1 mm or less.
According to a fourth embodiment of the present invention, it is provided that the press felt includes two filter layers whereby one of the filter layers is impermeable to polymer material having a predetermined particle size, and the other filter layer is substantially impermeable for polymer material of another, smaller particle size.
In addition, a fifth embodiment of the present invention, provides that in a direction from the first to the second surface, first the one and then the other filter layer is arranged. One of the filter layers, therefore, limits the penetration depth of polymer material into the nonwoven structure having a first predetermined particle size, and the other of the two filter layers limits the penetration depth of polymer material into the nonwoven structure having another smaller particle size. In this context, the particulate polymer material may include particles of different particle sizes whereby during the production of the felt, initially smaller polymer particles and subsequently larger polymer particles are added into the nonwoven structure, emanating from the first surface. In addition, the particulate polymer material may include particles with different physical and/or chemical properties, for example, particles having different melting points.
Alternatively, the process may be structured so that the particles get into the structure from more than one side and alternating addition is feasible. This, in combination with the different filter media, permits great flexibility. In a press felt produced according to the above arrangement, larger and smaller polymer particles are located above the one filter layer, that is in the area of the first surface to the one filter layer, whereas between the one and the other filter layer only smaller polymer particles are located. This provides a press felt which has a higher polymer content in the area between the first surface and the one filter layer than in the area between the one and the other filter layer. The press felt consequently has a denser surface.
In order to be able to achieve a uniform distribution of the polymer particles in the range to their desired penetration depth, the present invention provides that during the production of the felt, the particulate polymer material is added into the nonwoven structure in the form of at least one dispersion. The dispersion can include water and polymer particles. In addition, the polymer particles may be thermoplastic or duroplastic polymer particles, or mixtures thereof. The particle size may be, for example, in the range of approximately 0.1-600 μm, for example, 20-150 μm. With regard to the concrete form of the dispersion we refer you to WO2004/085727.
In order to fix the particulate polymer material in the nonwoven structure, the polymer material, after being added into the nonwoven structure, may be fused together in sections with each other and in sections with fibers of the nonwoven structure by means of heat treatment, thereby creating a discontinuous and porous composite structure consisting of the polymer particles and the fibers of the nonwoven structure which are conjoined with the polymer particles. The polymer particles, therefore, partially impregnate fibers of the nonwoven structure and partially fill spaces between fibers of the nonwoven structure, thereby creating a porous composite structure. In addition, the heat treatment can cause a chemical reaction in the polymer particles, for example, cross-linking.
The nonwoven structure is, for example, formed of fibers of approximately 6.7 dtex or more. The nonwoven structure can include fibers in the range of approximately 17 to 600 dtex, for example, 22 to 67 dtex or 80 dtex. The nonwoven structure may further be formed by several nonwoven layers stacked one on top of another between the first and the second surface, whereby at least one of the nonwoven layers of the nonwoven structure may be formed by thicker fibers than one of the other nonwoven layers.
A sixth embodiment of the present invention provides that the first surface with polymer particles forms the paper-side surface of the press felt, in other words the surface which can be brought into contact with the fibrous web, and the second surface is the surface of the press felt which can be brought into contact with the machine. In this instance, the polymer particles are added into the nonwoven structure from the surface of the press felt which can be brought into contact with the fibrous web (paper side).
A seventh embodiment of the present invention provides that the second surface with polymer particles forms the surface of the press felt which can be brought into contact with the fibrous web and that the first surface is the machine-side surface of the press felt or the surface which can be brought into contact with the machine. In this instance, the polymer particles are added into the nonwoven structure from the surface of the press felt which can be brought into contact with the machine (machine side).
An eighth embodiment of the present invention provides that the polymer particles, together with fibers of the nonwoven structure, form a porous layer in the nonwoven structure located below the paper-side surface, which is applied to the filter layer and has a thickness of approximately 1.0 mm or less, for example, 0.7 mm or less. Here, the porous layer can assume the function of a layer minimizing or preventing back-moistening—a so-called “anti-rewet layer”. The thin layer can hereby be formed with the assistance of a vacuum during or after the addition of the polymer particles in that the particles are sucked by the vacuum onto the filter layer where they adhere as a thin layer so that a section of the nonwoven structure remains between the first surface of the nonwoven structure and porous layer in which no polymer particles are adhered to the fibers of the nonwoven structure.
Depending upon how the polymer particles are brought into the nonwoven structure, for example, with or without vacuum assistance, or depending upon the strength and direction of the vacuum assistance, in other words whether the vacuum assistance occurs from the direction of the first or second surface, it is possible that polymer particles of a predetermined particle size and larger are penetrated into the nonwoven structure from the first surface to the filter layer which filters this particle size, whereby the concentration of these polymer particles decreases over the penetration depth, or increases or remains constant.
The load-absorbing base structure may be formed by a flat textile structure, for example, a woven fabric, a group of threads or a foil arrangement with optional strengthening threads. The group of threads may include threads running in machine direction (MD) as well as in cross machine direction (CMD).

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross section of a first embodiment of a press felt according to the present invention;

FIG. 2 is a cross section of a second embodiment of a press felt according to the present invention;

FIG. 3 is a cross section of a third embodiment of a press felt according to the present invention;

FIG. 4 is a cross section of a fourth embodiment of a press felt according to the present invention; and

FIG. 5 is a cross section of a fifth embodiment of a press felt according to the present invention.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there is shown a cross section of press felt 1. Press felt 1 includes nonwoven structure 5 which is formed by nonwoven layers 2, 3 and 4, as well as base structure 6, which is needle bonded with nonwoven structure 5 and is embodied by woven fabric 6.
Nonwoven structure 5 includes first surface 7, which is provided by the exposed surface of top nonwoven layer 2 of nonwoven structure 5. Nonwoven layer 2 is formed from approximately 17 dtex fibers 11. Intermediate nonwoven layer 3 which is located between top nonwoven layer 2 and woven fabric 6, is formed from 67 dtex fibers 16. Second surface 8 of press felt 1 is provided predominantly by the exposed surface of lower nonwoven layer 4. Filter layer 9 is located between top nonwoven layer 2 and intermediate nonwoven layer 3, which is nonwoven layer 9 having a thickness of approximately 0.1 mm, and which consists of polyurethane fibers (PU fibers) of less than approximately 1.7 dtex. The PU fibers are hereby fused together at their common contact points. Filter layer 9 has a basis weight in the range of approximately 80 g/m².
According to the present invention, filter layer 9 is permeable for fluid, for example, water and air, and is substantially impermeable to polymer material of a predetermined particle size. In the current example, filter layer 9 is impermeable for particle sizes of approximately 30 μm and larger.
In FIG. 1, lower nonwoven layer 4 of nonwoven structure 5, which is formed from approximately 22 dtex fibers 15 is located below woven fabric 6. Woven fabric 6 is needle bonded with nonwoven structure 5 and filter layer 9. After the needle bonding, a dispersion of water and particulate polymer material 10 is brought into nonwoven structure 5 from first surface 7 during the production of press felt 1, whereby polymer particles 10 are penetrated in sections from first surface 7 in the direction of second surface 8 and have adhered to fibers 11 of nonwoven structure 5. Subsequently, felt 1 is heat treated so that polymer particles 10 in nonwoven structure 5 are fused to each other and with fibers 11 of nonwoven structure 5, thereby forming a composite structure. Polymer particles 10 hereby partially impregnate fibers 11 of nonwoven layer 2 and partially fill spaces between fibers 11 of nonwoven layer 2, causing the creation of the porous and permeable composite structure in the area of nonwoven layer 2.
Non-melted polymer particles 10 have a particle size in the range of approximately 30-50 μm.
Press felt 1 may have, for example, a permeability of approximately 50 cfm.
Because of filter layer 9, which is located between upper nonwoven layer 2 and intermediate nonwoven layer 3, and which is impermeable for added polymer particles 10 the penetration depth of polymer particles 10 into nonwoven structure is limited to upper nonwoven layer 2. Polymer particles 10 hereby penetrate into nonwoven structure 5 from first surface 7 to filter layer 9, which filters polymer particles 10, whereby the concentration of polymer particles 10 in upper nonwoven layer 2 remains constant over the penetration depth. This is achieved, for example, in that no vacuum assistance occurred during the addition and thereafter. Paper-side surface 12 of press felt 1 is formed by first surface 7 with polymer particles 10 which are adhered on fibers 11.
Now referring to FIG. 2, there is shown a cross section of a second embodiment of press felt 1. Below only the differences from the press felt in FIG. 1 are addressed.
Press felt 1 includes nonwoven structure 5, which is formed by two nonwoven layers 2 and 4, as well as base structure 6, embodied by woven fabric 6, which is needle bonded with nonwoven structure 5. In the current example, nonwoven structure 5 includes only one upper nonwoven layer 2 which, in FIG. 2 is located above woven fabric 6, as well as lower nonwoven layer 4 which, in FIG. 2, is located below woven fabric 6. Nonwoven layers 2 and 4 are identical in structure to the nonwoven layers with the same reference numbers shown in FIG. 1.
Here, filter layer 9′ is located at the barrier surface between upper nonwoven layer 2 and woven fabric 6 and embodies nonwoven layer 9′ with a thickness of approximately 0.1 mm, and which is formed by polyurethane fibers (PU fibers) with less than approximately 2.2 dtex. The PU fibers are hereby fused with each other at their common contact points. Filter layer 9′ has a basis weight in the range of approximately 40 g/m².
According to the present invention, filter layer 9′ is permeable for fluid, for example, water and air, and is essentially impermeable for polymer material of a predetermined particle size. Filter layer 9′ is, for example, impermeable for particle sizes of approximately 50 μm and larger.
Woven fabric 6 is needle bonded with nonwoven structure 5 and filter layer 9′. After the needle bonding a dispersion of water and particulate polymer material 10′ is brought into nonwoven structure 5 from first surface 7 during the production of press felt 1, whereby polymer particles 10 are penetrated in sections from first surface 7 in the direction of second surface 8 and have adhered to fibers 11 of nonwoven structure 5. Subsequently, felt 1 is heat treated so polymer particles 10′ in nonwoven structure 5 are fused to each other and with fibers 11 of nonwoven structure 5, thereby forming a composite structure. Polymer particles 10′ hereby partially impregnate fibers 11 of nonwoven layer 2 and partially fill spaces between fibers 11 of nonwoven layer 2, causing the creation of the porous and permeable composite structure in the area of nonwoven layer 2. Non-melted polymer particles 10′ have a particle size in the range of approximately 60-100 μm. Press felt 1 has a permeability of, for example, 20 cfm.
Because of filter layer 9′, which is located between upper nonwoven layer 2 and woven fabric layer 6 and which is impermeable for added polymer particles 10, the penetration depth of polymer particles 10′ into the nonwoven structure is limited to upper nonwoven layer 2. This means that no polymer particles have penetrated woven fabric 6. The polymer particles 10′ are hereby penetrated into nonwoven structure 5 from first surface 7 to filter layer 9′ which filters polymer particles 10′, whereby the concentration of polymer particles 10′ in upper nonwoven layer 2 increases over the penetration depth. This is achieved, for example, in that vacuum assistance occurs on the side of second surface 8 during/or after the addition. Paper-side surface 12 of press felt 1 is provided by first surface 7 with polymer particles 10′ which are adhered to fibers 11.
Referring now to FIG. 3, there is shown a cross section of a third embodiment of press felt 1. Components which are identical to those of the press felt in FIG. 1 have been allocated the same reference numbers. Below basically only the differences from the press felt in FIG. 1 are addressed. Press felt 1 consistent with the press felt in FIG. 1 includes nonwoven structure 5 which is formed by nonwoven layers 2, 3 and 4.
In the current example, filter layer 13 is located at the barrier surface between lower nonwoven layer 4 and woven fabric 6 and embodies penetrated PU foil 13 with a thickness of approximately 0.06 mm. As can be seen from the illustration in FIG. 3, first surface 7 is provided by the exposed surface of lower nonwoven layer 4. According to the present invention, filter layer 13 is permeable for fluid, for example, water and air and is essentially impermeable for polymer material of a predetermined particle size. In the current example, filter layer 13 is impermeable, for example, for particle sizes of approximately 150 μm and larger.
Woven fabric 6 is needle bonded with nonwoven structure 5 and filter layer 13. After the needle bonding a dispersion of water and particulate polymer material 10″ is brought into nonwoven structure 5 from first surface 7 during the production of press felt 1, whereby polymer particles 10″ are penetrated in sections from first surface 7 in the direction of second surface 8 and have adhered to fibers 15 of nonwoven structure 5. Subsequently, felt 1 is heat treated so that polymer particles 10″ in nonwoven structure 5 are fused to each other and with fibers 15 of nonwoven structure 5, thereby forming a composite structure. Polymer particles 10″ hereby partially impregnate fibers 15 of nonwoven layer 2 and partially fill spaces between fibers 15 of nonwoven layer 2, causing the creation of the porous and permeable composite structure in the area of nonwoven layer 2. Non-melted polymer particles 10″ have a particle size, for example, in the range of approximately 200-250 μm.
Press felt 1 has, for example, a permeability of approximately 40 cfm.
Because of filter layer 13, which is located between lower nonwoven layer 4 and woven fabric layer 6 and which is impermeable for added polymer particles 10″, the penetration depth of polymer particles 10 into nonwoven structure 5 is limited to lower nonwoven layer 4. In the current example, this means that no polymer particles have penetrated woven fabric 6 and upper nonwoven layers 2 and 3 above it. The polymer particles 10″ are hereby penetrated into nonwoven structure 5 from first surface 7 to filter layer 13 which filters polymer particles 10″, whereby the concentration of polymer particles 10″ in lower nonwoven layer 4 remains constant over the penetration depth. This was achieved, for example, in that no vacuum assistance occurs during the addition and thereafter. Machine-side surface 14 of press felt 1 is provided by first surface 7 with polymer particles 10″ which are adhered on fibers 15.
Referring now to FIG. 4, there is shown a cross section of a fourth embodiment of a press felt 1. Components which are identical to those of the press felts in FIGS. 1 and 2 have been allocated the same reference numbers. Below basically only the differences from the press felt in FIG. 1 are addressed. Press felt 1 includes nonwoven structure 5 which is formed by nonwoven layers 2 and 4—the same as the press felt in FIG. 1. In the current example, press felt 1 includes two filter layers, filter layer 9 and filter layer 9′. Here, upper filter layer 9′ is arranged between upper nonwoven layer 2 and intermediate nonwoven layer 3, whereas lower filter layer 9 is located at the barrier layer between intermediate nonwoven layer 3 and woven fabric 6.
According to the present invention, filter layers 9 and 9′ are permeable for fluid, for example, water and air, and are substantially impermeable for polymer material of a predetermined particle size. Upper filter layer 9′ is impermeable for polymer material of a particle size of approximately 50 μm or larger, whereas lower filter layer 9 is impermeable for a particle size of approximately 30 μm or larger. Filter layers 9 and 9′ are composed like the filter layers described in FIGS. 1 and 2. As can be seen in FIG. 4, viewed in the direction from first surface 7 to second surface 8, upper filter layer 9′ is located first and then lower filter layer 9.
The particulate polymer material includes particles 10 and 10′ of different particle sizes, whereby in the production of felt 1, first smaller polymer particles 10 and, subsequently larger polymer particles 10′, are added into nonwoven structure 5 from first surface 7.
Non-melted polymer particles 10 have a particle size, for example, in the range of approximately 30-50 μm. In addition, non-melted polymer particles 10′ have a particle size, for example, in the range of approximately 60-100 μm. As can be seen in FIG. 4, first surface 7 is provided by the exposed surface of upper nonwoven layer 2.
In press felt 1 that is produced in accordance with one of the above embodiments, larger polymer particles 10′ and smaller polymer particles 10 are located above upper filter layer 9′—that is in the area from first surface 7 to upper filter layer 9′, whereas only smaller polymer particles 10 are located between upper filter layer 9′ and lower filter layer 9. This provides a press felt which has a greater polymer content in the area between first surface 7 and upper filter layer 9′ than in the area between upper filter layer 9′ and lower filter layer 9.
Polymer particles 10 are hereby penetrated into the nonwoven structure, that is through nonwoven layers 2 and 3, from first surface 7 to filter layer 9 which filters polymer particles 10, whereby the concentration of polymer particles 10 in upper and intermediate nonwoven layer 2, 3 remains constant over the penetration depth. In addition, polymer particles 10′ are hereby penetrated into nonwoven structure through upper nonwoven structure 2, from first surface 7 to filter layer 9′ which filters polymer particles 10′, whereby the concentration of polymer particles 10′ in the upper and nonwoven layer 2 remains constant over the penetration depth. The press felt consequently has dense surface 12 which represents paper-side surface 12 of press felt 1.
Referring now to FIG. 5, there is shown an additional embodiment of press felt 1 whereby the nonwoven structure is created by upper nonwoven layer 2, intermediate nonwoven layer 2′ and lower nonwoven layer 4. The composition of nonwoven layers 2 and 2′ corresponds with composition of the nonwoven layer 2 in FIG. 1, as does the composition of nonwoven layer 4 with that of nonwoven layer 4 in FIG. 1. Filter layer 9, which corresponds in its composition to filter layer 9 in FIG. 1, is located between two nonwoven layers 2 and 2′. The first surface in the existing example represents paper-side 12 of the press felt.
As can be seen, polymer particles 10—which are consistent with those in FIG. 1—together with fibers 11 of nonwoven structure 5 form porous layer 17 in nonwoven structure 5, located below paper side surface 12, which is applied to filter layer 9. Porous layer 17 forms an anti-rewet layer and has a thickness, for example, of approximately 0.05 mm. This means that there is section A in upper nonwoven layer 2 where no polymer particles 10 are adhered on fibers 11 of nonwoven layer 2. Polymer particles 10 hereby partially impregnate fibers 11 of nonwoven layer 2 and partially fill spaces between fibers 11 of nonwoven layer 2, thereby creating porous and permeable layer 17. Polymer particles 11 are partially fused to each other and partially fused to fibers 11.
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Claims

1. A press felt, comprising:

a nonwoven structure having a first surface and a second surface opposite said first surface;

a load absorbing base structure bonded with said nonwoven structure, said base structure arranged between said first surface and said second surface;

particulate polymer material penetrated into said nonwoven structure from said first surface in sections of said nonwoven structure in a direction of said second surface, said particulate polymer material being adhered to fibers of said nonwoven structure in a manner such that the press felt has a permeability of at least approximately 5 cfm; and

at least one filter layer arranged in one of said nonwoven structure and at a barrier surface between said nonwoven structure and said base structure, said at least one filter layer being permeable for fluid and substantially impermeable for particulate polymer material of at least a predetermined particle size.

2. The press felt according to claim 1, wherein the press felt has a permeability of at least 10 cfm.

3. The press felt according to claim 2, wherein said at least one filter layer has a thickness of approximately 0.5 mm or less.

4. The press felt according to claim 3, wherein said at least one filter layer is a nonwoven layer formed by fibers with approximately 3.3 dtex or less.

5. The press felt according to claim 4, wherein said at least one filter layer is formed by fibers with approximately 1.7 dtex or less.

6. The press felt according to claim 5, wherein said fibers of said at least one filter layer are configured to be fused with each other at common contact points.

7. The press felt according to claim 6, wherein said fibers of said at least one filter layer are configured to be fused by heat effect.

8. The press felt according to claim 6, wherein said at least one filter layer has a basis weight in a range of between approximately 20 g/m²and 180 g/m².

9. The press felt according to claim 8, wherein said at least one filter layer includes at least one of polyurethane fibers, polypropylene fibers and polyamide fibers.

10. The press felt according to claim 9, wherein said at least one filter layer is one of hydrophobic and hydrophilic.

11. The press felt according to claim 10, wherein said at least one filter layer is formed by a sacrificial material configured to dissolve from the press felt at a time subsequent to fixation of said particles said nonwoven structure.

12. The press felt according to claim 11, wherein said sacrificial material is thermoplastic polyurethane configured to melt at the time of fixation of said polymer particles in said nonwoven structure.

13. The press felt according to claim 12, wherein said at least one filter layer is configured to be formed in one of a layer in said nonwoven structure and at said barrier surface between said nonwoven structure and said base structure, said at least one filter layer being at least one of physically and chemically treated and is fluid permeable and substantially impermeable to said particles of polymer material having a predetermined size.

14. The press felt according to claim 13, wherein said at least one filter layer is a perforated foil.

15. The press felt according to claim 14, wherein said at least one filter layer has a thickness of approximately 0.2 mm or less.

16. The press felt according to claim 15, wherein said at least one filter layer has a thickness of approximately 0.1 mm or less.

17. The press felt according to claim 16, wherein said at least one filter layer is two filter layers, said two filter layers including a first filter layer and a second filter layer, said first filter layer being impermeable to said particles of said polymer material having a predetermined size and a second of said two filter layers being substantially impermeable to said particles of said particulate polymer material having a smaller size.

18. The press felt according to claim 17, wherein in a direction from said first surface to said second surface, said first filter layer is arranged before said second filter layer.

19. The press felt according to claim 18, wherein said particulate polymer material includes particles of different sizes, a first portion of said particulate material having one of a predetermined size and a predetermined range of sizes in said nonwoven structure and a second portion of said particulate polymer material having one of a size and a range of sizes larger than said first portion, said larger particles emanating from said first surface.

20. The press felt according to claim 19, wherein said particulate polymer material is configured to be added into said nonwoven structure of the form of at least one suspension.

21. The press felt according to claim 20, wherein said particles of particulate polymer material are configured to be fused together and with fibers of said nonwoven structure subsequent to addition of said particulate polymer material.

22. The press felt according to claim 21, wherein said fibers of said nonwoven structure are at least approximately 6.7 dtex.

23. The press felt according to claim 22, wherein said nonwoven structure includes a plurality of nonwoven layers stacked one on top of another between said first and said second surface.

24. The press felt according to claim 23, wherein at least one of said nonwoven layers includes fibers having a greater thickness than fibers of another of said nonwoven layers.

25. The press felt according to claim 24, wherein said first surface including said polymer particles forms a paper-side surface of the press felt.

26. The press felt according to claim 25, wherein said first surface including said polymer particles forms a machine-side surface of the press felt.

27. The press felt according to claim 26, wherein said polymer particles and said fibers of said nonwoven structure are configured to form a porous layer in said nonwoven structure, said porous layer being located below said paper-side surface, said porous layer being applied to said filter layer.

28. The press felt according to claim 27, wherein said porous layer has a thickness of 1.0 mm or less.

29. The press felt according to claim 28, wherein said porous layer has a thickness of 0.7 mm or less.

30. The press felt according to claim 29, wherein said polymer particles include a plurality of particles having a predetermined size penetrated into said nonwoven structure from said first surface to said filter layer, a concentration of said polymer particles one of decreasing over a penetration depth, increasing over said penetration depth and remaining constant over said penetration depth.