Patent Application
20090186544
1. Field of the Invention
The present invention relates to a belt for a machine for the production of web material, especially paper or cardboard, as well as a method to produce the belt.
2. Description of the Related Art
Belts are utilized, for example, in dryer sections of paper machines which transport the web material to be produced through press nips created, for example, by two press rolls. Due to the physical load, the web material which is to be produced is compressed and liquid is squeezed from it. The liquid is to be absorbed by, and removed through, the belt which is in contact with the web material. A method is already known whereby the surface of a belt of this type is covered with thin material layers which, in order to permit liquid strike-through, are equipped with a plurality of openings. The production of such belt is very expensive and often results in insufficient water removal characteristic, as well as a tendency of marking.
What is needed in the art is a belt for a machine for the production of web material, especially paper or cardboard, as well as a method for the production of a belt of this type with which marking of the web material which is to be produced can be largely eliminated if the belt has good liquid removal characteristics.
The present invention provides a belt, especially a press felt, for a machine for the production of web material, for example, paper or cardboard including a carrying structure having a web material contact side. The carrying structure includes fibrous material with polymeric material contained therein which, together with the fibers of the fibrous material, create a fluid-permeable composite structure in that the polymeric material only partially fills and/or bridges the hollow spaces between fibers of the fibrous material and, whereby, a large part of the polymeric material is provided in a volumetric area of the fibrous material which is close to a web material contact surface. “Close,” as used in the specification and claims herein, is defined as a depth range of approximately 30% in the fibrous material viewed from the web material contact surface.
In other words, a permeable composite structure is created in the area of the web material contact surface by the fibers of the fibrous material and the polymeric material. The fibers are embedded, at least partially, into the polymeric material. The porosity of the composite structure is created in that the polymeric material only partially fills and/or bridges the hollow spaces between the fibers of the fibrous material. This means that the polymeric material itself is not porous or for example, foamed.
Since, in the belt of the present invention, the polymeric material contained in the fibrous material is provided in an area near the surface, or essentially also in an area of the fibrous material representing a web material contact surface, a predominantly mat-type configuration is formed by this polymeric material which nevertheless allows liquid to penetrate. Since this polymeric material is embedded into the structure of the fibrous material, the structure of the fibrous material will mark the web material contact surface in the style of a micro-structuring. On the one hand, this is not so strong as to mark the web material which is being manufactured but, on the other hand, permits better release of a belt of this type from the web material which is being manufactured due to the existing irregularity and in conjunction with the porosity.
Provision may be made, for example, that at least 80% of the polymeric material is provided at a depth range of approximately 20% in the fibrous material viewed from the web material contact surface. The belt of the present invention may include a plurality of layers of fibrous material, whereby, the bulk of the polymeric material is provided in the layer of fibrous material representing the web material contact surface.
In order to be able to even more efficiently provide the desired hollow space structure in conjunction with the polymeric material and, consequently, also the desired liquid absorption characteristic, the layer of fibrous material which represents the web material contact surface is finer than the layer of fibrous material beneath it. It may, for example, be provided that the layer of fibrous material representing the web material contact surface may be composed of fibers with a maximum of 17 dtex. In this context it is pointed out that, with regard to the present invention, “finer” is to be understood to mean that fewer hollow spaces are present in a layer of this type than in a coarser layer. This can be achieved, for example, by utilizing fibers of comparatively lower dtex value and, on the other hand, can also be influenced by the density of such a layer.
The polymeric material may form a single-component and permeable polymeric layer. In other words, a single-component and permeable polymeric layer is formed, which extends through the fibrous material in the area of the web material contact surface and, which is embedded, at least partially, in the fibers of the fibrous material. The polymeric layer is solidly bonded with the fibers.
A single-component polymeric layer is understood to be a polymeric layer which is formed by a single continuous piece. In order to provide permeability, the polymeric layer includes openings extending through the polymeric layer, and the openings in the polymeric layer are formed in that the polymeric material, which forms the polymeric layer, only partially fills and/or bridges the hollow spaces between the fibers of the fibrous layer. To verify that the permeable polymeric layer is a single component, the fibrous material—if it is, for example, polyamide—can be dissolved, for example, with formic acid.
With fibers of the fibrous material, the single component and permeably polymeric layer forms a permeable composite structure which provides a high water drainage capacity and does not compress much during operation. Due to the fact that the polymeric material forms a single component polymeric layer, the polymeric material separates from the fibrous material less easily when under the influence of shear forces or high pressure water jets than is the case with polymeric material which only forms a multitude of disconnected polymeric agglomerates in the fibrous material.
The present invention also provides a method for the manufacture a belt for a machine for the production of web material, including the following measures:
In order to simply achieve the desired layering, it is further suggested that measure b) include the provision of several layers of fibrous material on the carrying structure and that measure c) include the provision of the polymeric material essentially in only one layer of fibrous material providing a web material contact surface.
The layer of fibrous material providing the web material contact surface may be finer than a layer of fibrous material located beneath it. This results in the liquid, penetrating through the layer representing the web material contact surface and containing the polymeric material, can move very quickly through the coarser structure of the layer located beneath it, so that the risk of back-moistening can be clearly reduced.
Measure c) may include adding an aqueous dispersion with particle-like polymeric material from a web material contact side and melting the particle-like polymeric material. Prior to the melting process, liquid, which was added with the dispersion, can be removed from the fibrous material or carrying structure.
The carrying structure may, for example, be woven or randomly laid. The fibrous material may be non-woven or felt.
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 an embodiment 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 illustrates one embodiment of the invention, in one form, 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
It can be seen that especially in layer 20 of fibrous material, which represents web material contact surface 28, a multitude of particles 30 of polymeric material are provided. Also, particles 30 of this type may still be present in layer 22 of fibrous material located immediately beneath it, and in additional layers 24, 26 of fibrous material, whereby however a bulk, for example, at least half, of particles 30 are contained in uppermost layer 20 of fibrous material representing the web material contact surface. A “bulk” of the polymeric material as used in the specifications and claims herein is defined as at least half of the particles, for example, 80% of the polymeric material.
After adding particles 30, belt 10 is heated to a temperature above the melting temperature of the polymeric material of particles 30, for example, by means of running it through two heated rolls. Heating in an appropriate heating chamber is also feasible. For this purpose the belt can be heated, for example, for two minutes to a temperature of approximately 200° C. The melting point of thermoplastic polyurethane material which may, for example, be used for particles 30, is around approximately 187° C., while the melting point for polyamide 6 fibers used for the fibrous material is around 223° C. This means that particle material 28 will melt, however, the fibers of the fibrous material will retain their structure. The melting polymeric material will then distribute itself in the porous structure of the layer of fibrous material containing same, so that—as shown in FIG. 2—polymeric material 32 will form in this respective layer which, together with fibers of the layer, will form a permeable composite structure in that the polymeric material only partially fills and/or bridges (see
In an embodiment, the polymeric material forms a single component and permeable polymeric layer in the area of the web material contact surface. It is self evident that the principles of the invention may also be realized with other embodiments. For example, the number of layers of fibrous material may vary from the cited number of layers. Also, with only one, for example, thicker layer of fibrous material and, by adaptation of the particle size on the one hand and the fineness of the layer on the other hand, it can be provided that a bulk of the particles accumulates in the area near the surface so that the mat-type configuration with essentially high porosity is achieved during melting and subsequent curing.
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.
This is a non-provisional application based upon U.S. provisional patent application Ser. No. 61/015,863, entitled “DIFFERENTIAL PRESSING STRUCTURE”, filed Dec. 21, 2007, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61015863 | Dec 2007 | US |
