KR19990076931A - Paper Machine Closure Woven with Expanded PTFE - Google Patents

Abstract

The present invention is a papermaking cladding suitable for use in the forming, pressing or drying parts of a papermaking machine, characterized in that it consists of a fiber structure made of expanded poly (tetrafluoroethylene) ("expanded PTFE"). It relates to paper machine clothing.

Description

Paper-making clothing with expanded PET

Technical Field of the Invention

FIELD OF THE INVENTION The present invention relates to paper machine clothing suitable for use in the molded, compressed, or dried portion of a paper machine. In particular, the present invention relates to a fabric woven from monofilament yarns of synthetic polymer resins, in particular expanded PTFE (poly (tetrafluoro ethylene)).

Current paper machines essentially include an apparatus for removing water from a paper furnish, which is a slurry of the components that make up the paper. Water is removed sequentially in three or three stages of the paper machine. In the first part, known as a molded part, the furnish is deposited on the transfer forming wire and the water is drained through the wire to form a paper sheet or web having a solids content of about 18 to 25% by weight. The web thus formed is transferred to the wet crimped felt portion and passed through one or more nip presses on a mobile crimped felt to sufficiently remove water to form a sheet having a solid content of about 36-50% by weight. The sheet is moved to a drying unit of the paper machine where the paper sheet is pressed against the steam heating cylinder by a dryer felt, so that a solid content of 92 to 96% by weight is obtained.

In paper machines, endless belts are used in various parts to move paper sheets or webs. There are many types of such endless belts, some of which are made of metallic materials, others of which are made from textile materials such as cotton, cotton and asbestos, asbestos and synthetic fibrous materials or filament materials. The choice of a given material is somewhat dependent on the case used for the fabric, such as forming fabric, dryer felt and the like.

One type of belt that is widely used as the forming wire of a forming part of a paper machine is a belt produced by open weave of a synthetic polymer resin monofilament. Such fabrics, although limited in general, generally work well in molded parts. For example, relatively open weaves have poor dimensional stability, especially when operated at high speeds. This shortens the overall life of the forming wire that wears when the position on the paper machine changes. Also relatively open weave is relatively less than the level of furnishing of the finished fiber deposited on the wire. Ideally the support properties of the fibers and sheets on the wire should be increased without significantly reducing the removal of water through the drain.

The press fabric is applied at the press of the paper machine. At the press, the paper sheet is transported by the press sheet and the sheet and the fabric are pressed between the sheet and the nip of the press roll exerting enormous pressure on the fabric so that liquid escapes and the water in the sheet is removed. Moreover, the temperature of the crimp part of the paper machine is relatively high. The crimp fabric generally consists of a base layer and a cotton layer laid down on the base layer. It is preferable to use polyamide which is a particularly favorable material as the synthetic material.

Fabrics in the drying section of the paper machine tend to become hot in harsh chemical environments with paper sheets. Dryer fabrics or "dry screens" used in the paper industry are typically formed from various materials such as poly (ethylene terephthalate), polyphenylene sulfide and polypropylene. Each material has different properties and prices. An important property of the material used as the dryer screen in paper machines is that the material should have good hydrolytic stability and good dimensional stability.

Polypropylene is the cheapest of the materials currently available. It has excellent hydrolytic stability in terms of properties, but poor dimensional stability at high temperatures. Therefore, it has a limitation in use.

Poly (ethylene terephthalate) (PET) is reasonably priced, has excellent dimensional stability and good hydrolytic stability. Poly (ethylene terephthalate) is the most widely used material on the market today, and in most cases the hydrolytic stability of poly (ethylene terephthalate) can be improved by the addition of carbodiimide stabilizers. Polyphenylene sulfides have excellent dimensional stability and hydrolytic stability, but are very expensive and difficult to work with, and tend to cause problems of breaking and breaking crystal states by the usual bending occurring on paper machines.

1 is a graph showing the results of wear tests performed in embodiments of the present invention.

2a to 2d are SEM images of the filaments used in the embodiment of the present invention.

3a to 3b are photographs showing the degree of wear in the prior art.

4a to 4b are photographs showing the degree of wear in the embodiment of the present invention.

5a to 5b are photographs showing the degree of wear in the prior art.

6a to 6b are photographs showing the degree of wear in the embodiment of the present invention.

The present invention is a paper machine clothing suitable for use in forming, pressing or drying parts of a paper machine, comprising a fiber structure woven from expanded poly (tetrafluoro ethylene) ("expanded PTFE") yarns. Relates to keeper clothing.

Expanded PTFE is available from USA, Newark DE, W.L. Gore and Associates, Inc. Commercially available material. As disclosed in US Pat. No. 3,953,566, expanded PTFE is a highly porous material characterized by the microstructure of nodes connected internally by fibrils. The '566 patent is incorporated herein by reference. This material is a highly porous material and exhibits high tensile strength.

The inventors have found that papermaking cladding woven from expanded PTFE filament yarn has excellent wear resistance, fouling resistance, and wrinkle resistance. Tensile properties of expanded PTFE woven products are equal to or greater than the currently available polyester or polyamide. Compared with other materials, it has improved tensile properties to improve the dimensional stability of the fabric. In addition, the use of expanded PTFE monofilament can increase the service temperature to 288 ° C, which is higher than that of conventional materials.

By using the fabric of the present invention, the above disadvantages caused by the use of conventional materials can be eliminated or significantly reduced. The forming wires produced according to the invention are made from all monofilament fabrics which provide a very smooth side to the side in contact with the paper sheet. Thus, maximum support is achieved. The result is a paper that is relatively free of marks, while effectively draining water while maintaining the desired benefits of all filament fabrics. In addition, the structure of the fabric and the wire of the present invention is a structure that exhibits excellent dimensional stability in both the instrument direction and cross instrument direction. This reduces the wear of the yarn and increases the working life. The overall working life of this molded fabric is significantly increased compared to conventional fabrics.

One of the more important features of the papermaking cladding according to the invention is that it can be used in the hot part of the papermaking machine, especially since it is not easily hydrolyzed in the case of drying fabric and drying screen fabric. That is, it is excellent in hydrolysis resistance. PTFE is a very inert and waterproof material.

Those skilled in the art using even higher temperatures in the shaping and pressing portions of the paper machine will be able to use paper making clothing made from expanded PTFE in all parts of the paper machine. In the forming section, it is possible to form an open weave by using a monofilament material in which a suitable support of the solid material in the furnish is made and then a cohesive sheet can be obtained by sufficient drainage. In the crimp, it is possible to obtain a crimp fabric that is much better able to withstand high temperature operation by providing at least one crimp fabric surface layer and support layer according to the present invention.

The present invention therefore provides another PMC structure as well as a Paper Machine Clothing (PMC) material having a woven or spiral or other suitable monofilament structure in which the monofilament can extend in the machine and cross machine directions. . Such materials can be used to use PMC fabrics composed of staples, multifilament and / or monofilament fibers.

Typical size ranges for monofilaments used in press fabrics and drying fabrics range from 0.20 mm to 1.27 mm in diameter and have corresponding mass in different cross-sectional shapes (eg square or oval).

In the case of molded fabrics, fine monofilaments (for example, about 0.05 mm) are used, and in special cases, monofilaments up to 3.8 mm are used.

The filaments of expanded PTFE can be formed by spirally winding the expanded PTFE sheet material. See US Patent 5 281 475.

The filaments are woven into paper machine belts according to conventional weaving techniques. The form and density of the weave depends on the type of paper and papermaking operations in which the belt is used. If single layer and multilayer configurations are suitable and formed into a woven fabric, the fabric may be endlessly circulated or flat. The following examples illustrate the advantages of the present invention.

(Example 1)

The single layer twill consists of expanded PTFE monofilament as a weft (commercially available from W.L. Gore & Associate) and a Hoescht 906Y polyethylene terephthalate material as warp. This twill is a 62 × 46 5 harness woven from 2 × 3 0.3mm monofilament weft. For comparison purposes, woven fabrics woven with 0.30 mm paste 906Y HMW PET monofilament yarn as weft and warp yarns were made to have the same shape as expanded PTFE containing fabrics. The coefficient of friction of the woven sample was calculated from the force required to pull the steel sheet over the sample as the test was performed in the instrument direction. The coefficient of friction thus obtained was 50% lower for both the short weft and the long weft knuckles for the expanded PTFE material. And it was observed that the expanded PTFE sample had a very smooth feel.

Coefficient of friction

Long Weft Knuckle Down Short Weft Knuckle Down

Expanded PTFE 0.10 0.12

Feest PET 0.20 0.21

(Example 2)

The fabric samples described above were tested for wear resistance. Long weft knuckle down was tested to maximize exposure of expanded PTFE to the wear cylinder. A force transducer was used to measure the force on the fabric during the test.

In the first task of the test, the sample failed. After 40 minutes, the PET sample lost all the weft-side exposed weft as shown in FIG. 3. All that is left is a short piece of weft on paper. Samples woven with expanded PTFE were run for 240 minutes without failure. By examining the expanded PTFE sample as can be seen from FIG. 4, it can be seen from the test that the expanded PTFE is completely filled by smearing with some calcium carbonate filler. The sample looks intact but the sample is easily pulled far away because there is no force to hold in the cross-machine direction.

A second operation was done when the sample was removed for caliper measurements after 20, 30 and 40 minutes. As shown in FIG. 1, the PET fabric loses calipers much faster than expanded PTFE samples.

Unlike the first test, the PET sample was intact after 40 minutes, but the weft was badly worn. Photos from the test results are shown in FIGS. 5 and 6. Expanded PTFE yarn was slightly worn at the edges. However, after 40 minutes the warp of the expanded PTFE sample was not worn at all.

Claims (8)

In the paper machine clothing used for the forming part, the pressing part, or the drying part of a paper machine, Said cladding is woven from filament yarn, wherein at least one of said filament yarns essentially contains expanded poly (tetrafluoroethylene). The method of claim 1, And the filament yarns extend in the machine direction and cross machine direction of the paper machine. The method of claim 1, Paper machine clothing, characterized in that the filament yarn is a woven fabric. The method of claim 1, Papermaking clothing, characterized in that the filament yarn is a non-woven fabric. The method of claim 1, And the filament yarns are made of expanded PTFE extending in the machine direction of the clothing. The method of claim 1, And said filament yarns comprise expanded PTFE extending in the cross machine direction of the clothing. The method of claim 1, Paper machine clothing, characterized in that it also contains a layer of fibrous material laid on the clothing. The method of claim 7, wherein Paper wool cladding, characterized in that the fiber wool material is made of expanded PTFE.