CA1072310A

CA1072310A - Nonwoven papermakers felt

Info

Publication number: CA1072310A
Application number: CA271,152A
Authority: CA
Inventors: Edward R. Hahn; Richard H. Root
Original assignee: Albany International Corp
Current assignee: Albany International Corp
Priority date: 1976-05-05
Filing date: 1977-02-07
Publication date: 1980-02-26
Also published as: SE7704505L; NL7704180A; AU2239377A; BR7702100A; AU511193B2; FI771351A; ZA77222B; MX145600A; NZ183405A; FR2350195A1; JPS52137010A; FR2350195B1; DE2718036A1; GB1536231A; FI60262B

Abstract

Abstract of the Disclosure A non-woven papermakers felt and methods of its fabrication are disclosed. The method of the invention comprises needling a fibrous bat to a woven base which includes soluble lengthwise yarns. The resulting felt is then treated to dissolve the lengthwise yarns, leaving a non-woven felt having cross-wise yarns. The felts of the invention have enhanced lateral stability, improved porosity and a more uniform cross-wise mass distribution.

Description

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The invention relates to press fabrics in belt form and more particularly relates to a non-woven paper-makers ~elt and methods of their manufacture.
Papermakers felts are available commercially in a wide variety of constructions. Woven felts are fabricated by weaving wool or wool-synthetic yarns and then shrinking or felting the fabric to obtain the desired finish charac-teristics and running size for a particular press position. Although such woven felts are still used extensively, needled felts are gaining in popularity. In the prior art needled felts are fabricated by needle punching a web of fibers into a previously woven base fabric. The base fabric is generally woven on a felt loom. The fibrous web is formed by cardin0 fibers and the com-pleted web is then laid on the woven base just prior to passage through a needling machine. Several successive layers of webs may be used, the felt passing through the needling machine after each web layer is added. Webs may be needled to one or both sides of the base fabric.
The surface quality of a papermakers felt has a direct bearing upon the quality and finish of paper formed thereon. One difficulty associated with the above described prior art felts is the surface irregularity produced by the structure of the weave or the woven fabric base in the case of a needled felt. For example, the cross-over points or knuckles of the weaves are prominent points which will emboss the paper being formed. Prior hereto, it has been suggested that elimination of the cross-wise yarns in the fabric base of needled felts would improve the surface quality of the felt;
see for e~ample U.S. Patent 3,~58,911. In the latter patent the patentee offered as a means for eliminatin~ the cross-wise yarns, providing them in the form of a soluble material. After the needling operation, the cross-wise yarns were eliminated by

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dissolution. The patentee did not suggest eliminating thelengthwise yarns, since those yarns are generally considered essential ~or tensioning of the f01t on the paper machine and for stability of the felt in the machine running direction. In addition, if one had a preference for eliminating one or the other of the directional yarns in the base fabric of a needled felt, he would be expected to select the cross-wise yarn for elimination because these are the yarns which normally increase hydraulic flow resistance and occlusion of the felt.
~nexpectedly, we have found that the leng-thwise yarns in a needled papermakers felt are not necessary when the cross-wise yarns are retained. In addition to retaining suf-ficient tensionability and directional stability in the machine running direction, the felts of the invention exhibit improved lateral strength and stability over felts without cross-wise yarns as well as excellent porosity or hydraulic profile, more uniform cross-wise mass distribution than a non-woven felt and reduce the accumulation of system impurities from the paper pulp.
The felts of the invention may also be fabricated by the method of the invention using monofilament yarns, advantage-ously enhancing the cross-wise strength of the felt. This is unexpected as web bonding does occur in monofilament yarns.
However it is our finding that by the method of our invention mechanical contraction of the felt during needling is better controlled, than with a non-woven felt.
The invention comprises'a papermakers felt, which comprises, a non-woven, porous, sheet of textile fibers, and a plurality of cross-wise yarns, .said ~heet being needled to said yarns. The invention also comprises intermediate fe~lts which may be converted to the final papermakers fel-ts of the invention.
The invention also comprises a method of fabricating 7;23~

a paperma~ers felt, which comprises, providing a base fabric which comprises lengthwise yarns which are soluble in a given solvent and cross-wise yarns which are substan~ially insoluble in said solvent, nee~ling into said base fabric a web of tex-tile fibers, and dissolving said lengthwise yarns in said solvent.
The term "length-wise yarn'' is used herein in its conventional sense to mean those yarns which run in the direction of the papermakers felt operation on the paper machine and the term "cross-wise yarn" is also used in its conventional sense to denote those yarns which run cross-wise to the direction of the felt operation on the paper machine.
Figure 1 is a view-in-perspective of a portion of an endless papermakers felt showing the needling of a non-woven web to a woven base fabric.
Figure 2 is a fragmentary view of the needled felt produced as shown in Figure 1.
Figure 3 is a view as in Figure 2 but after removal of the lengthwise yarns from the woven base fabric.
Figure 4 is a view as in Figure 3 but of another embodiment felt of the invention.
A complete understanding of the invention may be con-veniently obtained by a reading of the following description of the preferred embodiments in conjunction wi~h the drawings of Figures 1-4, inclusive.
Figure 3 is a view-in-perspective, partially bro~en away, of a papermakers felt which comprises cross-wise yarns 14 to which there has been needled an upper web 15 of -textile f.bers and a lower web 16 of textile fibers. The felt shown in Figure 3 is characterized further by the absence of and freedom from length-wise yarns interwoven with cross-wise yarns 14. Yarns 14 may be any yarn conventionally employed as a .

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component of a woven fabric base for needled felts and may be selected from known yarns to provide any desired properties of strength, rigidity, flexibility, weight and like properties.
Unconventional yarn materials may also be utiliæed as cross-wise yarns 14 and in a preferred embodiment yarns 14 are mono-filaments. Representative of monofilament yarns 14 are mono-~ilaments of synthetic polymer resins such as polyethylene, polypropylene and like polyoleflns, polyamides, polyimides, polyesters and the like. ~'iberglass and metallic monofilaments may also be employed.
The webs 15, 16 may be non-woven batts of wool, synthetic or blends of wool-synthetic textile fibers commonly and conventionally employed in the fabrication of needled papermakers felts. One embodiment, upper web 15 may be a batt of wool fibers while lower web 16 is a non-woven batt compxising synthetic textile fibers such as polypropylene fibers. The resulting felt is a sheet of a mixture o wool and synthetic polymer resin fibers having cross-wise yarns incorporated there-in.
The papermakers felt of Figure 3 may be fabricated by needling webs 15 and 16, in successive needling operations, to cross-wise yarns 14. A conventional needling loom may be employed and the cross-wise yarns held in spatial side-by-side relationship on a forming loom during the needling procedure.
By one method of the invention, webs 15, 16 are first needled into a woven base fabric which comprises length-wise yarns which are soluble in a given solvent and cross-wise yarns which are substantially insoluble in the same solvent.
Referring to E'igure 1, this fi.r~t step :is shown wherein a woven base fabric 10 in the form of an endle~s belt or tube is re-ceiving the application of a non-woven web 15 on a needling loom 17. Following the needling of web 15 to base ~abric 10, ~(~7Z39~(1 additional webs may be needled successively to the upper surface of base fabric 10. Lower web 16 is also needled to the base fabric 10 and optionally additional webs may be needled to the lower surface of base fabric 10. By needling, the webs are all intimately interlocked and mingled, one with the others and with the base fabric 10 to provide a tightly compacted sheet havin~ distributed therein the array of lengthwise yarns 12 ana cross-wise yarns 14 formin~ base fahric 10. ~his sheet is an inter-mediate felt which is treated in a second step of themethod of the invention to obtain the novel papermakers felt of the invention.
Figure 2 shows an intermediate felt in a fragmen-tary view of the needled felt produced as described above.
Upper and lower needled webs 15, 16 are compacted in a sheet intermingled with length-wise yarns 12 and previously - described cross-wise yarns 14. Length-wise yarns 12 may be mono or multifilament yarns of any conventional material soluble in a given solvent which will not, under the conditions of dissolving yarns 12, undesirably affect the properties of cross-yarns 14 or the webs needled thereto. For example, lengthwise yarns 12 may be formed from calcium alginate, sodium alginate, polystyrene, ethyl cellulose, polycarbonate and like materials. Such yarns are well known as are the solvents which may be employed in the method of the invention to dissolve them, see for example U.S. Patents 2,539,244,

3,311,928, and 3,458,911. Those skilled in the art will appreciate that by proper selection of yarns 12, 14 and solvent, the dissolution step of the method of the invention ~ay be readily carried out. In a preferred embodiment of ~7~23~6~

the invention, the lengthwise yarns 12 are polyvinylalcohol multifilaments which a~e readily soluhle in water at room temperature.
The second step of the method of the invention consists of dissolving the lengthwise yarns 12, thereby removing them from the intermediate felt without removing or substantially dissolving the webs or the cross-wise yarns 14. The terms llsubstantially insoluble~ and llwithout substantially dissolving" as used herein means that the solvent has insufficient solvating power to affect the desired characteristics of, for example, the cross-wise yarns 14 and the webs 15, 16. Dissolution of the lengthwise yarns 12 is readily carried out by washing the intermediate felt of Figure 2 in the appropriate solvent. Thereafter, the final papermakers felt may be rinsed, dried and finished according to conventional techniques.
Figure 4 is a fragmentary view-in-perspective of an alternate embodiment papermakers felt of the invention similar to the embodiment of E`igure 3 but differing in that a surface layer 18 of a homogeneous batt of wool fibers has been needled to web 15 and the underlying structure to provide a particular surface to the feltO
The following example describes the manner and process of making and using the invention and sets forth the best mode contemplated by the inventors of carrying out the invention, but is not to be construed as limiting.

An endless woven cloth base having a single layer, plain weave is provided. The cross-wise yarns are nylon monofilaments having a diameter of 0.008 in,hes and are woven 20 ends to the inch. The length-wise yarns are 3Lq;~7Z3~0 polyvinyl alcohol multi-filament yarn of 282 grains/100 yards weight and are woven 18 ends per inch. The woven base is heatset at 290F. at a length equal to felt length in the loom.
The woven heatset base is installed on a needle loom and length-wise and cross-wise oriented web la~ers of a mixture of polyamide, polyester and polypropylene skaple fibers are needled into the base in a conventional manner.
The needled felt is then washed in a soapy water solution at 180F., pulling the felt through the wash tank at 120 feet per minute for approximately 100 revolutions. The washed felt, free of length-wise yarns dissolved in the wash, is then dried on hot cylinders and stretched to proper length and tension for a papermakers felt free of length-wise yarns.
The product felt has the following properties.
Finished basis weight - 4.58 oz./sq. ft.

Air permeability - 42 cubic ft./min/ft. at 1/2 inch water pressure drop Density - 0.255 gms./cc measured at 5 oz/sq. in. load Void fraction - 0.653 at 350 psig.
Thickness - 0.139 inches at 350 psig.

LXZ Test * - Under 350 psig. and at an approach velocity of 28 meters/
second;
L - direction, 0.41 Newtons per cubic meter x 10, X - direction, 0.55 Newtons per cubic meter x 106, Z - direction, 0.59 Newtons per cubic meter x 106 (vertical direction ) :, .

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* The LXZ test simulates mid-nip conditions on a paperma]cers felt, measuring the pressure drop per unit length of a felt in the L, X and Z planes, see the Doctoral Thesis of To N. Kershaw, IIA Three Dimensional Study of The Factors Affecting the Water Permeability of Wet Felts", Rensselaer Polytechnic Institute, Troy, ~ew York, June 1972.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A papermakers felt, which comprises:
a non-woven, porous, sheet of textile fibers; and a plurality of cross-wise yarns;
said sheet being a fiber web needled to said yarns and said sheet being free of length-wise yarns.

2. A felt according to claim 1, wherein said cross-wise yarns are monofilaments.

3. A felt according to claim 1, wherein said textile fibers are a mixture of wool and synthetic polymer resin fibers, or comprised solely of synthetic polymer resin fibers.

4. A felt according to claim 3, which also comprises a homogeneous surface layer of wool fibers.

5. A felt according to claim 3, which also comprises a homogeneous surface layer of synthetic textile fibers.

6. A method of fabricating a papermakers felt, which comprises:
providing a base fabric which comprises length-wise yarns which are soluble in a given solvent and cross-wise yarns which are substantially insoluble in said solvent;
needling into said base fabric a web of textile fibers; and dissolving said length-wise yarns in said solvent.

7. The method of claim 6 wherein said cross-wise yarns are monofilaments.

8. The method of claim 6 wherein said length-wise yarns are polyvinyl alcohol.