Patent Application
20100252217
1. Field of the Invention
This invention relates to a clothing for a web-processing machine, in particular a paper machine, paperboard machine or tissue machine.
2. Description of the Related Art
To improve wear resistance and/or hydrolysis resistance, clothings for web-processing machines are often equipped in their edge region and/or seam region with a coating. These coatings frequently have the disadvantage of not adhering firmly enough to the threads of the, for example woven, structure of the clothing, and therefore, of flaking off the threads when exposed to the effects of tensile stress, abrasion forces, heat and moisture. In particular on dryer fabrics or through-air dryer (“TAD”) meshes, which are exposed to high temperature combined with a high level of moisture, and for this reason, are often equipped with or made from PET threads, it is a problem that the coatings known from the prior art flake off the PET threads after a short time already. These coatings frequently also improve the hydrolysis resistance of such meshes only to a limited extent or not at all.
What is needed in the art is a clothing of the type initially referred to on which the described flaking does not occur or occurs only to a much reduced extent and through which the hydrolysis resistance of the herewith equipped clothing is improved.
The present invention provides a clothing for a web-processing machine, in particular a paper machine, paperboard machine or tissue machine, including a flat basic structure with an upper side and a lower side, and with a coating which is applied to the upper side and/or lower side and includes at least one polymer material, whereby the at least one polymer material is a polyurea, for example, an elastomer polyurea.
By providing a coating containing a polyurea, a coating with a much improved adherence to the basic structure of the clothing, a far higher resistance to abrasion and a far higher resistance to chemicals is provided. The penetration of moisture into the material of the basic structure is prevented by the coating, leading to a clear improvement in the hydrolysis resistance of the clothing that is provided with said coating.
The inventive clothing is used in this case preferably but not exclusively, for applications in which the clothing is exposed to a high level of moisture combined with a high temperature. For example the inventive clothing is used as a dryer fabric or a TAD mesh. It is, however, also possible that the inventive clothing is a press felt or a forming screen.
One embodiment of the invention provides that the coating is applied only in some areas on the upper and/or underside of the basic structure. Alternatively it may be provided that the coating is applied to the entire upper- and/or underside of the basic structure. “In some areas” is to be understood specifically to mean that the coating is applied only to a section of the width of the clothing.
Preferably the flat basic structure is a fabric. The fabric is hereby formed, for example, by monofilament threads. In the section where the coating is applied the threads which form the fabric are advantageously covered at least partly, for example, completely, by the coating. The entire fabric may be covered by the coating in that area in which the coating is applied to the fabric. In this way the threads of the fabric are protected from harmful ambient influences.
In addition, in the area(s) which is (are) provided with the coating the threads of the fabric are, for example, connected with each other due to the coating at the thread crossing points and/or thread contact areas. Thread contact areas are created, for example, when the polyurea coating is applied to that area in which the threads run parallel to each other and touch each other. This improves the dimensional stability of the inventive clothing. In addition, the accumulation of dirt in the thread crossing points is hereby clearly reduced. Since the threads are connected with each other, the interior abrasion of the clothing is further obviated or at least minimized, determined by the relative movement of the threads between each other
In addition, trials conducted by the applicant have shown that the polyurea coating can accumulate also between the threads at the thread crossing points or contact areas and are separated from each other by this coating and are, so to speak, elastically stratified on the coating. In other words, the polyurea coating forms an elastic intermediate layer between threads at thread contact or thread crossing points.
In order to produce the inventive clothing it is possible to first produce the basic structure and to subsequently provide the completed basic structure with the coating. If the basic structure, for example, is in the embodiment of a woven fabric, then the fabric in this scenario is produced—in other words woven—first and is then provided with the coating.
Alternatively, it is possible to first provide a portion of the threads which make up the fabric with the coating, and to subsequently interweave the so coated threads during the production of the fabric.
Advantageously the basic structure is permeable for water and air. Depending on the requirements, the coating can be applied in this connection such that the permeability is not affected by the coating, meaning that the clothing in the coated area has the same or essentially the same permeability as in the uncoated area. Alternatively, the permeability of the clothing in the coated area can be lower than the permeability in the uncoated area. For example, the permeability of the clothing in the coated area can be a maximum of 20% less, for example a maximum of 15% less, for example a maximum of 10% less than in the uncoated area. With a fabric this is achieved, for example, by filling out the meshes of the fabric in at least some areas.
In addition, it is possible that the clothing in the coated area is impermeable for air and water and that the clothing in the uncoated area is permeable. This is achieved in particular by the upper side and the lower side of the basic structure in the coated area being covered completely by the coating.
The coating is applied to the basic structure such that the thickness of the clothing in the coated area is equal to or only non-essentially greater than that in the uncoated area. In this connection, essentially greater is understood to be a clothing thickness in the coated area which is a maximum 15%, in particular a maximum 10% greater than in the uncoated area. The thickness of the coating can be in the range of approximately 1 μm to approximately 6 μm, for example, in the range of approximately 3 μm to approximately 30 μm. Layer thicknesses in the range of 1-60 μm are advantageous if the clothing is permeable in the area of the coating.
The fabric is, for example, a three-dimensionally structured fabric, in particular a TAD mesh.
The inventive clothing can be used on a tissue machine on which the tissue web is formed on the clothing from the fibrous suspension and the formed tissue web is then conveyed on this clothing as far as the Yankee drying cylinder. The tissue web is charged in this case upstream from the drying cylinder with a hot air current and/or steam current.
For the previously mentioned application it makes sense in particular for the fabric to include polyethylene terephthalate (“PET”) and/or polyamide (“PA”) and/or polyphenylene sulfide (“PPS”) threads. It is therefore possible that the fabric representing the basic structure is formed entirely from threads of one of the PET, PA or PPS materials. It is, however, also possible that the fabric is formed partially from threads from one of the first of the aforementioned materials and partially from threads of one of the subsequently aforementioned materials.
It has been discovered that the inventive coating already possesses the advantageous properties when the polyurea is present in the coating with a weight fraction of 10% or more.
The polyurea can be a two-component polyurea, whereby the one component of the two is, for example, a diisocyanate and the other of the two components is, for example, a diamine. The use of a diamine is advantageous in particular due to its low viscosity, which permits auxiliary materials to be added without the viscosity and the mix behavior being affected thereby. Used in particular is a diisocyanate known under the trade-name Araltide AY 8683. Also preferably used is a diamine known under the trade-name Hardener HY 8683
It is also conceivable that the polyurea is a single-component polyurea. A single-component polyurea of this type may, for example, be moisture-hardening or moisture-crosslinking. A catalyst can be used to speed up the hardening or cross-linking reaction. Products to be considered as single-component polyurea are, for example, products produced by “Nitroil Performance Chemicals” under the label “PC MD 8.6” or “PC MD 11”.
Single or two-component polyurea may, for example, be applied onto the basic structure in diluted form or as a solution in an organic solvent. The solvent used in this application is in particular a non-protic solvent. For example, THF (Tetrahydrofurane) would be suitable as a non-protic solvent.
The coating including the polyurea possesses a temperature stability of 180° C. to 220° C. at a temperature reaction time of at least 2 minutes. In this context, temperature stability is to be understood to mean that the coating shows no degradation aspect, visible to the naked eye.
To improve further the adherence of the coating to the basic structure, an embodiment of the invention provides for the basic structure to be subjected, prior to the coating being applied, to a surface treatment at least at those points which are covered with the coating. The surface treatment can include, either alone or in combination, cleaning with a solvent or by way of corona discharge. The surface treatment can, for example, additionally include treatment of the basic structure with atmospheric pressure plasma. In this context, it is also possible that the atmospheric pressure plasma is an oxygen plasma.
A second embodiment of the present invention provides for the coating to contain an additive which increases the wear stability of the coating and/or reduces the coefficient of friction of the coating. In particular, colloidal silicone dioxide, ultra high molecular weight polyethylene (“UHMW PE”) or boronitride can be cited, by way of example, as additives for use alone or in combination in this connection.
In this connection, the additive may include particles, in particular nanoparticles, or for it to be formed by particles, in particular nanoparticles.
As it is in particular the longitudinal edges of the basic structure which are exposed to greater abrasion and/or an increased temperature stress, then it is an advantage in particular for the coating to be applied in the region of the two longitudinal edges of the basic structure. The increased temperature stress is caused especially in that the longitudinal edges along the edge areas of the clothing are not covered by a paper web and are therefore, for example, in a TAD machine, subjected directly to the full hot air flow.
Especially in order to increase the hydrolysis stability it is useful if the coating—when viewed in transverse machine direction—extends from each of the two longitudinal edges in direction toward the center of the clothing to a point where at least the two areas of the clothing are coated which are never in contact with the paper web during operation of the clothing. In order to further increase the hydrolysis stability of the inventive clothing the coating can extend from each of the two longitudinal edges in direction toward the center of the clothing to a point that the two areas of the clothing are coated which only come into contact with the paper web only temporarily while the paper web is in contact with the clothing, for example, edge strip areas.
In order to increase the abrasion resistance, coating can extend from the longitudinal edges over approximately ⅜ inch to 1 inch in the cross machine direction (“CMD direction”). In order to increase the hydrolysis stability the coating can extend from the longitudinal edges approximately 5 cm to 20 cm in CMD direction.
Also exposed to greater wear is the seam region. A third embodiment of the present invention thus provides for the basic structure to have transverse edges, which extend in the CMD direction and can be joined together in order to render the basic structure endless while constructing a seam region, and for the coating to be applied in the region of the transverse edges.
Possible application methods for applying the coating are, for example, dip-coating and subsequent wiping in order to equalize the coating, roll coating, knife-coating, spray coating or extrusion coating.
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:
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.
Referring now to the drawings, and more particularly to
The represented clothing 1 is a TAD mesh. Mesh 1 has a flat basic structure which is formed by permeable fabric 3 woven from PET threads 4 and 5.
In addition mesh 1 includes coating 6 which is applied respectively in the region of two longitudinal edges 7 and 8 extending in the machine direction (“MD direction”) and in edge areas 10, 11 on fabric 3 on upper side 2 and on lower side 9 (shown only in
According to the present invention, coating 6 includes a polymer material, which in the example in question is formed by a two-component elastomer polyurea and nanoparticles 12 of boronitride. The wear stability of coating 6 is increased by boronitride nanoparticles 12.
Coated edge areas 10, 11 extend in this case respectively by approximately 1 inch from longitudinal edges 7 and 8 in the CMD direction. The coating is applied in this case such that upper side 2 and lower side 9 of fabric 3 in coated edge areas 10, 11 are covered completely by the coating and edge areas 10, 11 are impermeable.
Illustrated clothing 1 represents a dryer fabric or TAD mesh. Mesh 101 has a flat basic structure which is formed by woven and permeable fabric 103 which consists of PET threads 104 and 105.
Mesh 101 further includes coating 106 which is applied respectively onto top side 102 of fabric 103 in edge regions 110, 111 which run along two longitudinal edges 107 and 108 progressing in MD direction, and onto underside 109 which is only depicted in
In accordance with the present invention coating 106 includes a polymer material which, in the current example, is composed by a single-component, or two-component elastomer polyurea.
The two broken lines in the illustration in
As can be seen in the illustration in
In this scenario, coating 106 is applied onto upper side 102 and underside 109 of fabric 103 in such a way that threads 104 and 105 are completely enveloped in coating 106. In addition, threads 104, 105 are connected with each other through coating 106 at thread crossing points 117. Coating 106 has a thickness which may be in the range of approximately 1 μm to approximately 60 μm. The permeability of clothing 101 is not substantially affected by coating 106, so that fabric 103 has a permeability in non-coated region 113 which is essentially the same as the permeability in two coated edge sections 110, 111.
“Essentially the same permeability” in this context is to be understood to mean that the permeability in coated edge sections 110, 111 is a maximum of 15%, for example, a maximum of 10% less than the permeability in non-coated section 113.
While this present 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 015 055.7 | Mar 2007 | DE | national |
This is a continuation of PCT application No. PCT/U.S.08/58135, entitled “PAPER MACHINE CLOTHING WITH EDGE REINFORCEMENT”, filed Mar. 25, 2008, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US08/58135 | Mar 2008 | US |
| Child | 12566979 | US |
