NZ199540A - Paper machine dryer fabric:proportion of wefts heat set - Google Patents

Description

Priority Ds:te{s): .. p.} '- i -Sz Complete Specification Filed: Class >lete bpecmcauon hiled: : J?.?.! F .7//-?. j pl|. . ^ IS3 SEP 1985 Publication Dc.ts: ... .*»............. 3 r\ .tr-ifna' ? ry NEW ZEALAND Patents Act 1953 N.Z. No. 199540 21 January 1982 7 V '27JUNl98$5j) & COMPLETE SPECIFICATION DRYER FELT FABRIC We, ALBANY INTERNATIONAL CORP., an American Corporation of 1 Sage Road, Menands, New York 12204, United States of America, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- 199540 The invention relates to paper machine clothing and more particularly relates to fabrics useful as dryer felts, and their use and to method of stabilizing them.

The art is replete with descriptions of dryer felts and dryer felt fabrics used to fabricate dryer belts for use in the dryer section of a papermaking machine. In spite of the wide variety of fabric materials available, the ideal dryer fabric is yet to be found, many of them suffering from dimensional instability.

One form of dryer belt commonly employed in the dryer section of a papermaking machine is referred to as a "screen" and is fabricated by weaving synthetic monofilaments or twisted multifilaments together in an open weave. Although not subjected to any form of milling, and therefore not "felts" in the original sense of the term, these screen fabrics have also become known as "dryer felts". The endless belts made therefrom are generally woven flat and the ends thereafter joined to form an endless belt. The weave selected may be for example, a two or three layer weave of synthetic yarns such as multifilament, spun or monofilament yarns.

It will be appreciated that the screen type of "dryer felt" fabric is relatively open in design, resulting in a relatively high fabric permeability, i.e., air permeability of the order of from about 70 to 700 CFM/sq. ft. at 1/2" water (21.35 to 213.5 m3 /min/m2 at 1.27 cm water). Such fabrics permit free vapour passage through the fabric during operation of the papermaking machine. This high degree of openness has some disadvantages. For example, the fabrics lack a high degree of dimensional stability in use, particularly in the cross-machine direction (the machine direction being supported by tension on the dryer belt). 2 199540 The invention provides a paper machine dryer fabric comprising woven textile yarns and including first yarns of a synthetic polymeric resin having a given melting point and, in the cross-machine direction of the weaving second yarns which are heat-softened and of a synthetic, thermoplastic polymeric resin having a softening point lower than the melting point of the first yarns.

The invention further provides a dryer felt fabric which comprises: a plurality of yarns extending crosswise to the machine direction of the fabric and disposed in a plurality of separate layers, each layer being on a plane parallel to the crosswise plane of the fabric; a plurality of yarns extending lengthwise of the machine direction, interwoven with the crosswise yarns and binding the layers of crosswise yarns together to form a multilayer textile fabric; the crosswise and lengthwise yarns being synthetic monofilaments and the crosswise yarns in a given layer being separated from adjacent crosswise yarns in the adjacent layer at points along their length by void spaces within the body of the woven fabric; a plurality of stuffer yarns running substantially parallel to the crosswise yarns, between layers of crosswise yarns and partially filling a portion of the void spaces between the layers of crosswise yarns; said stuffer yarns being softened by heat and resolidified and having a softeneing point lower than the melting point of the crosswise and lengthwise yarns. 199540 The invention also provides a method of stabilizing a dryer felt fabric, said fabric comprising interwoven first yarns of a synthetic, polymeric resin having a given melting point, which method comprises; weaving, into the fabric, synthetic thermoplastic, polymeric resin second yarns which have a softening point lower than said melting point; and heat-setting the fabric under conditions wherein the thermoplastic yarns soften while the first yarns remain unmelted.

A dryer felt fabric embodying the present invention obviates a number of problems associated with the prior art dryer fabrics, particularly of the screen type. The fabric is characterized by a wide range of permeabilities of the order of from 30 to 700 CFM/sq. ft. at 1/2" water (9.15 to 213.5 m^/min/m^ at 1.27 cm water). However, even at high permeability it also exhibits a high degree of dimensional stability in use. The fabric is advantageously used to fabricate "dryer felts" for papermaking machines.

Fabrics embodying the invention also resist absorption of water, permitting excellent passage of moisture vapour from the paper sheet being dried, enhancing the drying rate. The openness of the fabric also resists filling of the fabric voids with contaminant particles from the paper sheet.

By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, of which:- Figure 1 is a cross-section side elevation along the machine direction of a precursor fabric embodying the invention.

Figure 2 is a view as in Figure 1 but of a fabric embodying the invention, 199540 Figure 3 is a view along lines 3-3 of Figure 2, Figure 4 is an enlarged view of a portion of the fabric shown in Figure 3, and ( Figure 5 is a view-in-perspective of a dryer belt made from a fabric embodying the invention.

The present invention relates to dryer felt fabrics. In general, such fabrics comprise a woven structure of weft and warp yarns. The yarns may be monofilaments, multifilaments or spun from staple fibres. The fabrics may be made in simple, monolayer weaves or they may be complex, multilayer weaves depending on the particular properties required.

Figure 1 shows a portion of precursor dryer fabric embodying the invention in a cross-sectional side elevation. The fabric 10 comprises a plurality of crosswise yarns 12 disposed in an upper layer A and in a lower layer B. The layers A, B are parallel to the crosswise plane of the fabric 10 (crosswise to the machine direction of felt travel during use, the machine direction M.D. being shown by the arrow in Figure 1). The crosswise yarns 12 and the layers A and B are bound together by the interwoven lengthwise yarns 14. The yarns 12, 14 may be monofilament, multifilament or spun yarns of any conventional denier.

Preferably for a dryer felt, low absorption monofilament yarns are employed. Representative of preferred monofilament yarns 12, 14 are monofilament yarns of polyesters, polyamides, polyaramids, and polyolefins which do not absorb high proportions of moisture. Preferably the monofilaments will have a diameter of from about 0.008 to 0.04 inches (0.02 to 0.1 cm) to enhance stability and structural integrity in the fabric.

It will be observed from Figure 1 that there are a plurality of interstices or voids 16 among the layers A, B separating 199540 adjacent crosswise yarns 12 at select points along the length of the crosswise yarns 12. These voids 16 are open areas within the body of fabric 10 which permit unimpeded flow of air through the fabric 10, accounting in part for the high permeability associated with these "screen" types of fabric. In the fabric 10, the voids 16 are partially filled with stuffer pick yarns 18 which act as fillers and are disposed in the crosswise plane of the fabric 10, substantially parallel to the crosswise yarns 12. The nature of the stuffer pick yarns 18 is critical and a dimension is selected suitable for partially filling the voids 16 without expending the thickness of the fabric 10 or closing all void space 16. Representative of yarns which may be employed as the yarns 18 are monofilament, spun and multifilament yarns of synthetic thermoplastic polyers. Representative of such yarns are mono and multifilaments of polyolefins such as polypropylene and polyethylene. A feature of the fabric is the selection of the yarns 18 from a thermoplastic polyermic resin material having a softening (and, possibly, melting) point substantially lower than the melting point of yarns 12 and 14. The reason for this will be apparent from the following discussion. Preferably the yarns 18 are spun yarns of polypropylene textile fibres.

The fabric 10 may be woven by conventional weaving techniques, well known to those skilled in the art.

Following the weaving of fabrics embodying the invention, as exemplified by fabric 10, they are heat-set to stabilize the fabric and to draw the yarns into their desired relative positions. The lengthwise yarns 14 are drawn inwardly of the outer surfaces of the fabric 10 and this pressure "crimps" the yarns 12 and 18 to some extent. The degree of heat-setting required to achieve the desired structure of the fabric 10 will 6 199540 of course vary depending on the nature of the yarns 12, 14 and 18. The temperature employed must be within a range lower than the melting point of the yarns 12, 14 but higher than the softening (and, possibly, melting) point of the yarns 18. During the heat-setting step, the yarns 12, 14 do not appreciably soften or melt, while the yarns 18 do. In softening, the polymer chains relax and the yarns mould in the particular configuration of their weave. Upon cooling of the heat-set fabric 10 below the softening point of the yarns 18 they resolidify in the weave configuration and stabilize in those positions. When the preferred spun polypropylenen forms the polymeric substance of the preferred yarns 18, the fibres melt during heat-setting and upon resolidification the yarns 18 take on the appearance of woven monofilaments. The resolidified yarns 18 also pick up and retain less moisture than the precursor spun yarn 18. Figure 2 is a view as in Figure 1 but after heat-setting of the fabric 10. As shown, the yarns 18 have been transformed so as to take on the appearance of monofilaments? see also Figure 3, a view along lines 3-3 of Figure 2.

Figure 4 is a view of an enlarged portion of yarns 18 following heat treatment and shows the yarn 18 now locked in place, due to its melting and resolidication, in the weave with lengthwise yarns 14. This "locking" stabilizes the fabric 10 in the cross-machine (C.D.) direction (see arrow in Figure 3). The tendency of the fabric to exhibit dimensional instability in the C.D. direction is obviated. Optimum times, temperatures and tensions placed on the fabric during heat-setting can be determined by those skilled in the art, employing trial and error technique for the different yarn materials. In general, heat-setting may be carried out at temperatures of from about W9540 200°F to 380°C (93.3°C to 19.3°C) for from 15 to 60 minutes. The fabrics may be woven flat and the end joined by conventional seaming methods, known to those skilled in the art to form dryer belts 5 as shown in Figure 5. The seamed belts so made are readily employed as dryer felts in the dryer section of a papermaking machine.

The following example sets forth a particular mode of making and using the invention but is not to be considered as limiting.

Permeability was determined with a Frazier type air permeability tester manufactured by the United States Testing Company. The measurements of this instrument are given in units which refer to the number of cubic feet of air which pass per minutes through one square foot of fabric at a pressure corresponding to 1/2 inch of water (abbreviated, cu. ft./min./sq. ft. (or CFM/sq.ft.) at 1/2" H20).

Example 1 There is provided a quantity of 0.020 inch (0.051 cm) diameter polyester monofilament (melting point 482°F or 250°C) and a quantity of 0.021 inch (0.053 cm) diameter polyamide (nylon) monofilament yarn (melting point 420° to 430CF or 215.6° to 221.1°C). There is also provided a quantity of 500 grain per 100 yard (29.63 gms per 100 metre) size spun yarns composed of polypropylene fibres (melting point 320° to 350°F or 160° to 176.7°C; softens at 285° to 320°F or 140.6° to 160°C).

The density of the polyester monofilament warp in the product is 80 ends to the inch (31.5 ends per cm). The number of polyester weft yarns per inch in the product is 18 monofilaments and 8.3 polyproylene spun yarns (stuffer yarns) for a total of 26.3 wefts per inch (a total of 10.4 wefts per cm). 199540 The fabric of the Example is finished in a conventional manner, i.e. by heat-setting under tension at a temperature of 380°F (193.3"C) for 15 minutes to offer specific properties of runnability and dimensional stability.

Upon completion of making the fabric, it is subjected to physical testing and found to have the following physical properties, in comparison to the same fabric before heat-setting: Permeability Before Heat-Set 75 CFM/sq.ft. (22.88 m^/min/ m2) After Heat-Set 210 CFM/sq.ft. (64.05 m3/nun/ m2) Dimensional Stability 3.0% elongation with 5 lb (2.27 Kg) tension on diagonal 0.2% elongation with 5 lb (2.27 Kg) tension on diagonal An endless dryer felt is made from the fabric. When installed on a paper machine as a dryer felt, the fabric performs well in the manufacture of papers. The belt tracks well, is easily guided and exhibits a long life even after exposure to temperatures of circa 250°F (121°C).

The felts of the invention may be finished in any conventional manner, i.e.; by chemical treatments to offer specific properties of runnability and resistance to chemical and abrasive degradation.

-I! .f' 199540

Claims (11)

WHAT WE CLAIM IS:-

1. A paper machine dryer fabric comprising woven textile yarns and including first yarns of a synthetic polymeric resin having given melting point and, in the cross-machine direction of the weaving, second yarns which are heat-softened and of a synthetic thermoplastic polymeric resin having a softening point lower the the melting point of the first yarns.

2. A fabric as claimed in claim 1 in which the heat-softened yarns are stuffer yarns.

3. A fabric as claimed in claim 1 or claim 2, in which the second yarns have a melting point which is also lower than the melting point of the first yarns.

4. A dimensionally stable dryer felt fabric, which comprises: a plurality of yarns extending crosswise to the machine direction of the fabric and disposed in a plurality of separate layers, each layer being on a plane parallel to the crosswise plane of the fabric; a plurality of yarns extending lengthwise of the machine direction, interwoven with the crosswise yarns and binding the layers of crosswise yarns together to form a multilayer textile fabric; the crosswise and lengthwise yarns being synthetic monofilaments and the crosswise yarns in a given layer being separated from adjacent crosswise yarns in the adjacent layer at points along their length by void spaces within the body of the woven fabric; 199540 a plurality of stuffer yarns running substantially parallel to the crosswise yarns, between layers of crosswise yarns and partially filling a portion of the void spaces between the layers of crosswise yarns; said stuffer yarns being softened by heat and resolidified and having a softening point lower than the melting point of the crosswise and lengthwise yarns.

5. A dimensionally stable dryer felt fabric substantially as herein described with reference to and illustrated by Figures 1 to 4 of the accompanying drawings.

6. An endless dryer belt made from a fabric according to any preceding claim.

7. A method of stabilizing a dryer felt fabric, said fabric comprising interwoven first yarns of a synthetic, polymeric resin having a given melting point, which method comprises: weaving, into the fabric, synthetic thermoplastic, polymeric resin second yarns which have a softening point lower than said melting point; and heat-setting the fabric under conditions wherein the thermoplastic yarns soften while the first yarns remain unmelted.

8. A method as claimed in claim 7, in which the second yarns have a melting point which is also lower than the melting point of the first yarns and in which the heat-setting is carried out under conditions wherein the thermoplastic yarns also melt while the first yarns remain unmelted. 199540

9. A method as claimed in claim 7 or claim 8, in which the heat-setting is carried out as a finishing step following the weaving.

10. A method as claimed in any one of claims 7 to 9, in which the second yarns are stuffer yarns.

11. A method of stabilizing a dryer felt fabric, said fabric comprising interwoven first yarns of a synthetic, polymeric resin having a given melting point, the method being substantially as herein described with reference to and as illustrated by Figures 1 to 4 of the accompanying drawings. ALBANY INTERNATIONAL CORP By Their Attorneys 12