KR100243849B1 - Thermostable paper machine clothing product - Google Patents

Abstract

The present invention relates to paper machine clothing and to paper machine clothing for use in press sections of paper machines, in particular suitable for use in hot presses or impact drying. A particular shape of the present invention is a sheet contact surface made of a polyfluorocarbon polymer which may be present in the form of a fibrous sheet.

Description

Heat resistant paper machine clothing product

1a, b and c are a series of graphs relating to Example 2. FIG.

2 is a photomicrograph of the sheet contact surface of the press fabric with PTFE surface of Example 3. FIG.

The following is by way of example only and with reference to the accompanying drawings, a method for effectively carrying out the invention.

FIELD OF THE INVENTION The present invention relates to paper machine clothing and, in particular, relates to paper machine clothing for use in the press and drying sections of the paper machine, although the invention described herein may be applied equally to other parts of the paper machine. .

Conventional paper machines form webs by immersing a slurry of pulp fibers to be formed into a sheet of paper, for example, over a running Foudrinier wire. After initial dewatering in the poe linear wire, the molded paper sheet or web is moved to a press section through which the web passes through one or more nips consisting of a roll or shoe combination. At this time, the sheet may be solidified and further characteristics of the sheet may be generated. The web is then passed over a series of heated dryer drums (and optionally through a calender) and then wound onto a roll. There are many variations on various parts of the paper machine, such as molding or pressing parts. In such an apparatus, the web typically reaches the press section with about 80% of the wet basic moisture (the ratio of water to fiber + water) and leaves the press section with a moisture ratio of about 60% (or 40% drying). Residual moisture must be removed by heat evaporation in the dryer section as the web passes over a series of heating drums. In the manufacture of typical paper machines, such as newspaper printing paper, a number of dryer drums will sometimes be used in orders of 50-70 drums per machine. Each dryer drum is expensive to manufacture and operate and requires the provision of steam accessories and supply of steam or other heating source to each drum.

British Patent No. 1455843 discloses that the felt has a hydrophobic surface layer in that it generates surface energy of 33 dynes / cm or less, and a backing layer having a thicker and greater water take-up capacity than the surface layer. A papermaking felt for use in a conventional papermaking method, consisting of a boy of a nonwoven fibrous material, is described and claimed. This specification addresses the drawbacks of PTFE fibers in this arrangement.

Recently, the principle of impulse drying has been introduced. Impact drying is a method of dewatering paper sheets by combining high temperature and pressure in the press section of the paper machine. During this process, the surface of the press roll is typically heated to a temperature of 150 ° C. or higher and in direct contact with the paper. In this way, the dryness of the paper sheet obtained is significantly increased to 60% or more. The effect of such a system is that it can generally reduce the number of dryer drums in the paper machine.

It is believed that the operating principle underlying the impact drying is that the heated rolls form a steam zone in the paper sheet during the press of the sheet, which drains liquid of water as steam passes through the sheet. The occurrence of this steam front and the high temperatures of the press rolls provide more stringent conditions for the press fabric.

To withstand these high temperatures, during breaks in the sheet of paper passing through the press fabric, the press fabric must have sufficient heat resistance to be continuously exposed to hot steam and sometimes to fine press rolls.

In addition, in order to provide acceptable sheet workability, such press fabrics must adequately release the paper sheet behind the nip. Also in order to produce sheets with maximum dryness, the press fabric should minimize rewetting of the sheet when the sheet is present in the nip. These properties must be combined with mechanical durability sufficient to withstand the harsh conditions of the impact drying process. According to conventional press theory, press fabrics must also provide and maintain adequate permeability to sheet breakout.

According to the present invention there is provided a product of paper machine clothing comprising a first woven base layer and a J sheet contact layer supported by the sheet, wherein the sheet contact surface of the J sheet contact layer is made of a polyfluorocarbon polymer.

The polyfluorocarbon polymer may be present in fibrous form. The second layer may have a fibrous structure of batt or staple fibers needled to the base layer. The second layer typically consists of a batt of 100% polyfluorocarbon polymer, or a high temperature resistant fiber such as polyamide, polyaramid, polyester, polyimide, polyetherketone, polybenzimidazole or polyether imide And a mixture of polyfluorocarbon fibers. The polyfluorocarbons may be polyterrafluoroethylene in a form that may be commercially available under the trade name "TEFLON" (PTFE).

In another embodiment of the present invention, the sheet contact surface may contain an effective amount of polyfluorocarbons in order to obtain desirable properties for the impact drying method. An effective amount of polyfluorocarbon is in the form of a separate surface layer, in the form of a coating on the surface of the fibers constituting the second layer, in the form of a preformed nonwoven layer of polyfluorocarbon, or of a finely woven polyfluorocarbon fabric. Each of which may be needled to the surface or otherwise coupled to the surface to integrate it as part of the surface layer.

In another embodiment of the present invention, the surface layer to which the polyfluorocarbon is bonded may be different from the textile form. The sheet contact surface of the second layer may be made of a film of polyfluorocarbon. For example, the layer can be formed by bonding, laminate or otherwise bonding the polyfluorocarbon polymer film to the rest of the second layer.

Monolithic, porous or microporous films can be used. The surface layer can also be formed by coating the fluorocarbon emulsion or suspension by spraying, dipping or other suitable method. It is also possible to form the surface layer by directly applying fluorocarbons in particulate form.

In the practice of the present invention, after being pressed several times in the press nip, the press fabric has significantly reduced air permeability and, more surprisingly, still exhibits high levels of sheet dryness; Even more so, conventional pressfabrics with such low air permeability typically cannot dewater the sheet effectively.

A series of test press fabrics were made by varying the percentage of Teflon fibers in the fabric contact layer of the fabric. The compounding ratio ranged from 0% Teflon-100% Teflon in 25% increments. The conditions of each fabric sample were 500 cycles at 1000 psi at 21 ° C. and then tested in a laboratory impact drying tester under the following conditions:

Pressure: 5500KPa

Nip Retention: 45 msec

Upper platen temperature: 190 ℃

The paper stock used in these tests was 100% Bleached Softwood Kraft as 500 CSF made from a 50 g / m 2 handsheet with 36% injection dryness. The injected moisture ratio of the felt to each fabric was 0.35. During the test, the final paper dryness and felt moisture increase were measured. In addition, after setting the conditions, the air permeability of each felt was also measured.

The results clearly show that as the percentage of Teflon fibers increases during paper contact, both the paper dryness and the felt moisture increase increase significantly, while the air permeability of the press fabric decreases. Typically, the lower the air permeability of the press fabric, the lower the dehydration capacity; In this case the trend is reversed. Under the test conditions discussed above, a sample with a 100% Teflon paper contact layer compared to a sample containing 0% Teflon achieves a paper dryness value higher than about 10%, while the air permeability is a 0% Teflon sample. Simultaneously reduced from 12.2cfm to 4.2cfm for 100% Teflon samples.

The results of this study are presented in Table 1 and shown in FIG. 1 of the accompanying drawings.

TABLE 1

Teflon Compound Press Fabric Structure Study

Example 2

Test press fabrics containing a 100% Teflon paper contact layer were tested in a pilot paper machine equipped with an impact drying roll and an inflated nip press shoe. The conditions used for this test were as follows:

Max Nip Pressure: 600pli

Device Speed: 820 m / min (2500 fpm)

Hot Roll Temperature: 177 ° C (350 ° F)

Paper basis weight: 45-50g / ㎡

Ingoing Paper Dryness: 25-36%

During this test, a final paper dryness of at least 60% was obtained. Following this test, a sample of the used press fabric was returned to the laboratory and tested. Appearance tests showed that the surface was strongly shielded and glossy. SEM photomicrographs of this surface (FIG. 2 of the accompanying drawings) confirmed this condition. Specimens were removed from the fabric at these sites and then tested in a laboratory impact drying tester for dehydration using a 50 g / m 2 handsheet at 36% initial dryness. Regardless of this shield surface, the results showed surprisingly high paper dryness as high as 65%. Experience shows that other press fabrics with similar gloss or shielded surface will exhibit very low levels of dehydration, and thus low paper dryness.

Claims (15)

A paper machine press roll comprising a first weave base layer, a heat resistant sheet contact surface containing a polyfluorocarbon polymer component, and a J sheet contact layer supported on the first weave layer with sheet release characteristics. Paper machine clothing for application. The papermaking clothing product according to claim 1, wherein the J sheet contact layer is a batt of staple fibers needled to the first loom layer. The papermaking clothing product according to claim 2, wherein the batt of staple fibers is a polyfluorocarbon polymer fiber. 3. The polyfluoro of claim 2, wherein the batt of staple fibers is at least one heat resistant fiber selected from the group consisting of polyamides, polyaramids, polyesters, polyimides, polyetherketones, polybenzimidazoles and polyetherimides. Paper machine clothing product, characterized in that a mixture of carbon polymer fibers. The paper machine clothing product according to claim 1, wherein the heat resistant sheet contact surface of the J sheet contact layer is a finely woven polyfluorocarbon fabric attached to the sheet contact layer. The paper machine clothing article according to claim 1, wherein the polyfluorocarbon polymer component is in fibrous form. The paper machine clothing product according to claim 1, wherein the polyfluorocarbon polymer component is polytetrafluoroethylene (PTFE). 3. The paper machine clothing article of claim 2 wherein the batt of staple fibers consists of fibers coated with a polyfluorocarbon polymer. The paper machine clothing product according to claim 1, wherein the heat resistant sheet contact surface of the J sheet contact layer is a non-woven layer of pre-formed polyfluorocarbon attached to the sheet contact layer. 2. The paper machine clothing product according to claim 1, wherein the sheet contact surface of the frying sheet contact layer is a polyfluorocarbon film attached to the sheet contact layer. 11. Paper machine clothing according to claim 10, wherein the film is monolithic. 11. The paper machine clothing product according to claim 10, wherein the film is perforated. The paper machine clothing product according to claim 10, wherein the film is a microporous layer. 2. The paper machine clothing product according to claim 1, wherein the heat resistant sheet contact surface of the J sheet contact layer is a coating of polyfluorocarbon polymer applied to the sheet contact layer. The paper machine clothing product according to claim 1, wherein the heat resistant sheet contact surface of the J sheet contact layer is a coating of polyfluorocarbon polymer in particulate form applied to the sheet contact layer.