US3664905A

US3664905A - Non-woven needled fibrous structure

Info

Publication number: US3664905A
Application number: US853362A
Authority: US
Inventors: Wilhelm August Schuster
Original assignee: FILZTUCHVERWALTUNGS GES MIT
Current assignee: FILZTUCHVERWALTUNGS GES MIT; FILZTUCHVERWALTUNGS-GESELLSCHAFT MIT
Priority date: 1965-02-17
Filing date: 1969-08-27
Publication date: 1972-05-23
Anticipated expiration: 1989-05-23
Also published as: NO135597B; BE676605A; DE1660768A1; FI45570B; FR1455454A; CH438756A; GB1069020A; AT267204B; NL6601602A; SE310981B; FI45570C; NO135597C

Abstract

A method of making a web suitable for use as papermakers'' felt including superposing a plurality of fibrous batts such that substantially parallel fibers in one batt extend in transverse direction to substantially parallel fibers in an adjacent batt, needling the superposed batts to form a laminated web, stretching the web to tension the fibers, applying a coating of adhesive to the surface of at least one side of the web, compressing the web, and subjecting the web to a jet of compressed air to break coherent films of the adhesive into globules leaving a portion of the adhesive adhered at points of contact and intersection of fibers on the surface of the web and driving the remaining globules into the web to adhere at points of contact of individual fibers near said surface.

Description

U Umted States Patent 1151 3,664,905

Schuster 14 1 May 23, 1972 [541 NON-WOVEN NEEDLED FIBROUS 1 Reiereneee cited STRUCTURE UNITED sTATEs PATENTS [721 lnvenm" Wilhelm A'lgusl sebum" Frankfurt/Maine 2,373,033 4/1945 Kopplin 161/154 x Germany 2,961,364 11/1960 Smith et al. ..l6l/l50 x 73 A Filzt h alt -Gesellschaft 't 1 ss'gnee z n a j' FOREIGN PATENTs OR APPLICATIONS 2 i Aug. 27 9 9 696,595 10/1964 Canada 161/155 PP 853,362 Primary ExaminerWilliam A. Powell Related U.S. Application Data Amway-Christen sabl [63] Continuation-impart of Ser. No. 512,407, Dec. 8, [57] ABSTRACT 1965, abandoned,

A method of making a web suItable for use as papermakers' Foreign Application P i it D felt including superposing a plurality of fibrous batts such that substantially parallel fibers in one batt extend In transverse Feb. 17, 1965 Germany ..F 45271 direction to Substantially parallel fibers in an adjacent ban, needling the superposed batts to form a laminated web, [52] U.S. Cl ..161/59, 1 17/62, 1 17/140, Stretching the web to tension the fibers, applying a coating of 156/148 156/291 0 adhesive to the surface of at least one side of the web, com- Int Cl B32) 5/06 1332b 5/12 B32b 3/1/22 pressing the web, and subjecting the web to a jet of com- Fieid 161/55 57 59 pressed air to break coherent films of the adhesive into l6l/146148, -158, 156/148, 291, 283; 28/722, 74; 117/16, 25, 26, 135.5, 140 R, 62

globules leaving a portion of the adhesive adhered at points of contact and intersection of fibers on the surface of the web and driving the remaining globules into the web to adhere at points of contact of individual fibers near said surface.

8 Claims, 8 Drawing Figures Patented May 23, 1972 3,564,905

2 Sheets-Sheet l Patented May 23, 1972 2 Sheets-Sheet 2 FIGB NON-WOVEN NEEDLED FIBROUS STRUCTURE This application is a continuation-in-part of application Ser. No. 512,407, filed Dec. 8, 1965, now abandoned.

This invention relates to needled non-woven fibrous structures suitable for industrial and papermakers felt, and to a method of making such structures.

It is known to make so-called synthetic felts by needling fibrous batts of different fibers and subjecting the needled structures to a shrinking treatment to increase the coherence and strength thereof. It is also known to bind the fibers of carded or aerodynamically produced webs together by various means such as impregnation with a latex, adhesive droplets, partial solution and resolidification of the surface layer, melting of the fibers or use of adhesive fibers.

Another needled fabric structure has been made by subjecting a needled web or batt first to a shrinking treatment, impregnating the web subsequently with a solution of a bonding agent, treating it, prior to the evaporation of the solvent, with water, and drying. Such non-Wovens have been used as such in the textile industry or have been further processed, for instance, to synthetic leather by coating with a plastic layer. Attempts to employ such non-wovens in the manufacture of felts for use in paper making machines have been without success because such non-woven fabrics have had low tensile strength and excessive elongation.

Conventional papermakers felt includes a woven base which has the purpose of supporting the surface fleece and imparting to the felt dimensional stability and resistance particularly to tension loads. In many respects, the woven base is inconvenient, for instance when the ends of a felt, which have been made as a finite piece, must be joined to an endless belt. In this operation, the drawing of each individual filament of the fabric base of one end of the felt into the opposite end is tedious and time consuming. The woven base fabric represents a compromise also in other respects. In order to withstand the tension loads generated in paper making operations, the warps must be strong and thick, and the nap must be sufficiently thick to prevent the base fabric from imprinting on the paper sheet being formed.

The art has long sought a base fabric which is free from the above-recited disadvantages. Recently a base fabric has been used which consists of a great number'of parallel fibers to which a fine surface layer is needled. However, such felts have not been fully satisfactory.

It is therefore a primary object of the present invention to providea process for making an improved web suitable particularly for paperrnakers and other industrial felts.

It is a further object of the present invention to provide a strong non-woven web which is suitable as a papermakers felt.

Other objects and advantages will become apparent from a consideration of the specification and claims.

For a more comprehensive disclosure of the nature, objects and advantages of the invention, reference is made to the following detailed description and to the accompanying drawing, in which:

FIG. 1 is a schematic side view showing a needling apparatus whereby an endless web or felt is needled;

FIG. 2 is an illustration of a felting needle for use in the apparatus of FIG. 1;

FIG. 3 is a fragmentary cross-sectional view showing a felt or web comprising several layers of fiber pile or batts which have been needled with the apparatus shown in FIG. 1;

FIG. 4 is a side view of an apparatus for stretching and heatsetting a felt or web produced by the apparatus of FIG. 3;

FIG. 5 is a fragmentary cross-sectional view of the felt of FIG. 3 after stretching and heat-setting by the apparatus of FIG. 4;

FIG. 6 is a side view of an apparatus for applying a coating to one side of a stretched felt;

FIG. 7 is an enlarged fragmentary cross-sectional view of a portion of the felt of FIG. 5 after being coated with adhesive and subjected to a compressed air jet by the apparatus of FIG. 6; and

FIG. 8 is a view of the felt taken along line 8-8 of FIG. 7.

The strong and dimensionally stable felt, shown in FIGS. 7 and 8 of the drawing, is obtained without a base fabric or reinforcing structure by first superposing several fibrous batts composed of substantially parallel oriented fibers in such way that the fibers of the successive superposed batts run substantially transverse to each other. Particularly suitable for this purpose are batts having a weight of 20 or 150 g. per sq. m. The web composed of such several superposed batts is then needled from one or both sides. The type of needles used, the advance motion of the fabric, the depth of penetration of the needles, and the number of needle penetrations per square centimeter will depend on the strength of the fibers, on the thickness of the web, and on the desired aspect of the needled structure.

Referring now more particularly to the drawing for a detailed description of the preferred mode of the invention there shown, two continuous fibrous batts l0 and 12 each containing substantially parallel oriented fibers are produced by two card apparatus, not shown. The batts are superposed such that one fibrous batt, for example lower batt 10 of FIG. 1, consists of fibers oriented substantially transversely of the running direction of the card apparatus and the batt, and the other batt, for example upper batt 12, consists of fibers oriented substantially longitudinally to the running direction of the card and the batt. Preferably, the longitudinally running fibers are stronger, e.g., l2 denier, than the transversely running fibers, e.g., 6 denier, since the felt structure will later preferably be stretched in the direction of the longitudinally running fibers.

In one preferred embodiment, the transversely running fibers are staple polyamide fibers (nylon 66) of 6 denier and a tensile strength of about 5 g./den. and about mm. in length. They are a substantially round cross section and are essentially crimped. The stronger longitudinally running fibers Y are preferably polyester fibers, have an essentially round cross section, are essentially smooth or stretched and have a tensile strength of about 10 g./den. These fibers also are staple fibers.

In another embodiment, the transversely running fibers may be natural fibers such as wool or cotton. Alternatively, up to 30 percent by weight of natural fibers may be admixed with the synthetic fibers in the individual fibrous batts as they are produced and superposed.

While polyamide fibers such as the nylons are preferred as thetransversely running fibers, other fibers may be used including polyester fibers, e.g., polyethylene terephthalate, polyacrylonitrile fibers and aromatic polyamide fibers. The thickness of these fibers may vary from 6 to 60 denier and the staple lengths may vary from 50 to I40 mm..Polyester fibers are preferably used for the longitudinally running fibers while other operable fibers include polyamide fibers such as nylon and aromatic polyamide fibers. The thickness of the longitudinally running fibers may range from 12 to 60 denier and their staple length from 80 to mm. Preferably the thickness is greater than that of the transversely running fibers.

Referring particularly to FIG. 1,

fibrous batts

10 and 12 are fed automatically by feeding table 14 into needling apparatus 16 between support 18 and needling loom 20 which contains 3 needles per square centimeter and are pieced by needles 22 provided with barbs 24 (see also FIG. 2) to at least partially intermingle the fibers of the two batts and form a laminated web 26. The web which emerges from needling apparatus 16 is thinner than the superposed batts l0 and 12 due to the needling operation. If a thicker web is desired, web 26 is guided around

rolls

28 and 30 in accordance with the directional arrow in FIG. 1 and is reintroduced into needling apparatus 16 beneath additional fibrous batts l0 and 12 and this is continued until the desired thickness is achieved. This procedure results in an endless web of felt. It is to be understood, however, that webs of any desired length may also be produced. In addition, needling of the web may be continued to further reduce the thickness and/or increase the density thereof after ceasing addition of

batts

10 and 12.

The web of felt is needled with needles 22 and it has been found that upon six passages of the web through apparatus 16, a total number of 360 penetrations per square centimeter will be achieved. If desired, the web may be inverted and needled on the reverse side. Two passages of the inverted web through apparatus 16 will result in 120 penetrations per square centimeter on the reverse side thereof.

The needled felt shown in FIG. 3 was produced in accordance with the above procedure with the modification that after two passages of web 26 through apparatus 16, introduction of batt was ceased while introduction of batt 12 was continued for one more passage so that the completed felt was provided with both outer layers containing substantially Iongitudinally running fibers. Thus, in FIG. 3, layers A, C and E contain substantially longitudinally running fibers and were formed from batt 12, while layers B and D contain substantially transversely running fibers and were formed from batt 10. The successive layers A E are therefore arranged in a manner that the fibers of each layer run substantially transversely to the fibers of the next successive layer.

After needling of endless web 26, it is strongly stretched in order to place a large portion of the interlooped fibers under tension and further orienting them in the direction of the applied stretch; the amount of said stretch will depend, to a certain extent, on the nature of the fibers.

Referring now to FIG. 4, there is shown schematically a stretching apparatus 32 for stretching and, if desired, heatsetting web 26 produced in accordance with the above teaching with regard to the apparatus shown in FIG. 1. Web 26 is arranged around calendar 34 and small roller 36. Calendar 34 may be heated by means not shown if it is desired to heat-set web 26 in the tensed state. The temperature of heating will vary depending on the fibers present in the web and will generally range between 120 and 190 C. In any event, the temperature should not exceed the melting point of the lowest melting fiber which is resent. The distance between calendar 34 and roller 36 and thus the tension on web 26, is variable by moving roller 36, for example, in guide rails, not shown, in which roller 36 may be mounted and fixed at any desired distance from calendar 34. Web 26 is fed around calendar 34 and roller 36 by rotation of calender 34 in accordance with the directional arrow thereon in FIG. 4. Ten sion placed on web 26 will vary according to the fibers used therein and will generally range between 50 and 1,000 kg. per meter width ofthe web.

FIG. 5 shows an enlarged partial section through web 26 after treatment on stretching apparatus 32. Layers A E correspond to the same layers in FIG. 3. It will be seen that the fibers and particularly those in layers A, C and E, are even more oriented in the longitudinal direction than are those in the felt of FIG. 3.

For further reinforcement, the web 26 is then bonded on one or both surfaces by means of a water-insoluble elastic adhesive, such as a solution of butadiene-acrylonitrile or 2- chlorobutadiene, in such a way that water can pass freely through the felt. Procedures used heretofore are not generally suitable for application of the adhesive according to the present invention. For example, when applied by spray nozzles, the adhesive does not penetrate the web or felt sufficiently; if applied by an immersion or impregnation procedure, the depth of the penetration of the adhesive cannot be controlled. Therefore, if the felt made according to the invention as set forth hereinabove is to be used as papermakers felt, it is coated on only one side with a water-insoluble elastic adhesive layer of even thickness; subsequently the coated felt is compressed and then treated on the coated surface with a strong jet of compressed air. Thereby, films or membranes which may have been formed by the adhesive which still contains the solvent, are broken up, and the adhesive is distributed on and near the surface of the felt in such a way that after releasing the compression pressure and after the treatment with the compressed air, adhesive remains only on the individual fibers and particularly at their points of contact.

Only as much adhesive must be applied that only the fibers of one or both surface layers are bonded while the fibers in the interior of the web remain essentially free of adhesive. The total pickup of adhesive will be in the range of l to 15 percent of weight of the finished felt.

While butadiene-acrylonitrile and 2-chlorobutadiene have been recited as preferred adhesives, other operable adhesives include polyurethane elastomers, modified polyester resins and polyacetals. Compatible mixtures of the above adhesives may also be used. The adhesive may contain a solvent for purposes of adjusting the viscosity to be suitable for application by applicator roll coating or other means. Such solvents include ethyl acetate, methyl ethyl ketone, isopropyl alcohol, xylol, ethylene glycol diacetate, and mixtures thereof.

The adhesive may be applied to the felt by any conventional method, e.g., by a doctor blade, or by running the felt over or between applicator rolls. The mechanical compression of the felt is then also carried out in any suitable manner, e.g., by means of two rollers rotating in opposite directions, thereby binding the adhesivelycoated fibers at additional points of contact.

In order to shorten the drying time of the felt to which the adhesive has been applied, compressed air of slightly elevated temperature may be employed. Instead of, or in addition to, the compression treatment after application of the adhesive, the felt may be subjected to such compression treatment after the compressed air treatment but before the adhesive is completely dried.

In a preferred embodiment of the invention, a needled felt of the character described hereinabove is compressed between two superposed metal rollers the lower one of which carries an adhesive layer kept at a constant thickness by means of a doctor; the adhesive penetrates the lower surface of the felt and envelops the fibers. When the felt has left the rollers, the fibers coil back into their original bulky position. The adhesive membranes left between many of the fibers are then torn by means of strong compressed air jets whereby a portion of the adhesive remains especially at the points of contact and intersection of the fibers at the surface of the felt and the adhesive is broken into globules which are driven by the air jets further into the web until they contact and are stopped by points of contact of other fibers near the surface.

FIG. 6 illustrates schematically an apparatus 38 for coating web 26 after it has been stretched. Web 26 is first fed between

rollers

40 and 42 which are arranged to compress the web, e.g., to about one-half its thickness in the relaxed state. Roller 42 is suspended in pan 44 which contains an elastomeric adhesive 46 and as roller 42 rotates therein, it picks up a layer 48 of adhesive 46, the thickness of which is controlled by doctor 50. When the surface of roller 42 reaches web 26, the layer 48 of adhesive 46 is transferred to surface 52 of web 26. The adhesive is then pressed by the compressive strength of

rollers

40 and 42 between the fibers on surface 52 of the web. Web 26 is then guided around roll 54 at which time surface 52 is subjected to the action of one or more compressed air jets 56 which flow under a pressure of from 2 to 8 atmospheres from nozzles 58. The strong jets 56 of compressed air will, first of all, rupture the thin film of adhesive between the individual fibers and, in addition, drive the resulting globules of adhesive into web 26 where they will contact and adhere to points of contact of individual fibers near the surface thereof. After the major proportion, e.g., from to 100 percent, of the solvent has evaporated or been driven from the adhesive, web 26 is fed between

compressive rollers

60 and 62 wherein it is strongly compressed at a pressure from 2.5 to 12 kg. per cm. width of the web.

The thickness of layer 48 of adhesive may range from 0.2 to 1.5 mm. With a preferred thickness of 0.4 mm., web 26 will take up about percent of the adhesive carried by roller 42. The depth of penetration of the adhesive into surface 52 of web 26 depends on the pressure extended between

rollers

40 and 42. For example, when a web having a thickness of 5 mm. in the relaxed state is compressed to 2.5 mm. by

rollers

40 and 42, web 26 upon emerging from the rollers and relaxing to its original thickness of 5 mm. will have adhesive penetrating to from 1 to 1.5 mm. into surface 52.

FIGS. 7 and 8 illustrate a portion of web 26 after the web has emerged from coating apparatus 38 shown in FIG. 6. It will be seen that discrete particles or globules 64 of adhesive are adhered to several of the fibers 66 and particularly at points of intersection of the fibers both at surface 52 and near the surface ofthe web.

The following is presented as a specific example of a preferred embodiment of the present invention.

Two continuous fibrous batts containing substantially parallel oriented fibers were superposed so that fibers of the lower batt were oriented substantially transversely of the running direction of the batt and the fibers of the upper batt were oriented substantially longitudinally or parallel to the running direction of the batt. The fibers of the lower batt were crimped staple fibers of 6 denier polyamide (nylon 66) having a tensile strength of about 5 g./den. and an average length of about 80 mm. The fibers of the upper batt were smooth uncrimped fibers of i2 denier polyester (polyethylene terephthalate) having a tensile strength of about 10 g./den. and an average length of about 80 mm. The superposed fibrous batts were fed into a needling machine and subjected to the action of a needling loom containing two barbed needles/sq. cm. The emerging laminated web was reintroduced into the needling apparatus beneath two additional fibrous batts to form a continuous, endless web. After two complete passages of the web through the needling apparatus, introduction of the lower batt was ceased while introduction of the upper batt was continued for one more passage so that the completed web of five layers contained two outer layers of substantially longitudinally running fibers. After a total of six passages through the needling apparatus, a total number of 360 penetrations/sq. cm. of web was achieved. The web was then turned and needled on the reverse side in two passages through the machine to achieve 120 penetrations/sq. cm. on the reverse side.

The web, having a thickness of about 5 mm., was then arranged around a large heated calender and a smaller roller, the latter being movably mounted to vary the distance between the calendar and the roller. A tension of 280 kg. per meter width was placed on the web and the calender was heated to a temperature of 150 C. to heat-set the tensed fibers.

The web was removed from the calendar and roller and then fed between two compression rollers, the lower of which was suspended in an elastomeric adhesive comprising 20 weight percent butadiene-acrylonitrile dissolved in 70 weight percent ethyl acetate and 10 weight percent methyl ethyl acetone. The thickness of adhesive picked up by the roller was controlled to be about 0.4 mm. As the surface of the roller carrying the adhesive contacted the web, about 95 percent of the adhesive was transferred to the web surface. As the coated web passed between the rollers, it was compressed to a thickness of about 2.5 mm. and the adhesive was pressed between the fibers on the surface of the web. After the web had again relaxed to a thickness of about 5 mm., it was found that the adhesive had penetrated to a depth between 1 and 1.5 mm. from the coated surface. The adhesive coated surface of the web was then subjected to the action of the air under a pressure of about 6 atmospheres to break the continuous film of adhesive into discrete particles or globules. A portion of the globules remained adhered to the fibers and to points of contact and intersection thereof on the surface of the web and the remaining globules of adhesive were driven into the web where they became adhered to fibers and points of contact thereof near the surface. After 90 percent of the solvent had evaporated from the adhesive, the web was passed between a second pair of compressive rollers and compressed at a pressure of 4 kg. per cm. width of the web.

Wet felts prepared in accordance with the present invention have a considerably higher breaking strength than conventional felts of the same wei ht per square foot. When used in papermaking machines, t ey lose substantially no fibers.

Marking does not occur due to the lack of a woven base fabric. The novel felts have a much longer life than conventional papermakers felts.

With a felt produced according to the present invention, running times up to days of 24 hours each can be achieved on a papermaking machine. On the other hand, felts produced in in the traditional manner achieve maximum running times. as a rule, of only about 30 days. The suction capacity of felt produced according to the present invention is in no way inferior to that of felt produced in the traditional manner. Its long, useful life can be explained by the fact that, through the coating with adhesive, the loss of fiber is reduced to a minimum. At the same time, the felt is given a decided stability of form by the present process.

The loss of fiber from felt produced according to the present invention is so small that paper for electronic condensers can be produced thereon. The requirements for purity of such a paper are so great that paper produced on customary felts could not previously be used for this purpose since the loss of fiber occurring with use of traditional felts influenced the dielectric constant in an unfavorable way.

In felts used in the papermaking process, it has been found of advantage to use blends of natural and synthetic fibers in order to combine the good properties of both. Accordingly, such blends can also be used for the making of the felts according to the invention, or batts of different fibers may be used. In the latter case, it is of advantage to place the batts composed of the stronger fibers in such a way that said fibers are in the longitudinal or stretching direction of the finished felt, so that the stretching step tends to maintain a larger portion of the fibers in tension and oriented in the stretching direction.

What is claimed is:

l. A method of making a laminated fibrous web which comprises: superposing a plurality of fibrous batts, each of said batts having fibers oriented substantially in parallel and the batts being superposed so that the fibers in one batt extend transverse to the fibers in an adjacent batt; needling the superposed batts to form a laminated web; stretching the web; applying a coating of adhesive to the surface of at least one side of said web; and subjecting the coated surface of the web to a jet of compressed air to break coherent films of said adhesive.

2. The method according to claim 1 wherein batts of different fiber composition are employed.

3. The method according to claim 2 wherein batts containing stronger fibers are arranged so that said fibers are oriented in the direction in which the web is stretched.

4. The method according to claim 1 wherein at least one batt contains a blend of material and synthetic fibers.

5. The method according to claim 1 wherein the web is compressed after the adhesive coating is applied thereto.

6. The method according to claim 1 wherein the web is compressed after subjection to compressed air and before the adhesive is completely dry.

7. The-method according to claim 1 wherein the adhesive is applied in a limited amount to form bonds between fibers on and near the coated surface only of the web.

8. A laminated fibrous web product according to the method of claim 1.

Claims

2. The method according to claim 1 wherein batts of different fiber composition are employed.
3. The method according to claim 2 wherein batts containing stronger fibers are arranged so that said fibers are oriented in the direction in which the web is stretched.
4. The method according to claim 1 wherein at least one batt contains a blend of material and synthetic fibers.
5. The method according to claim 1 wherein the web is compressed after the adhesive coating is applied thereto.
6. The method according to claim 1 wherein the web is compressed after subjection to compressed air and before the adhesive is completely dry.
7. The method according to claim 1 wherein the adhesive is applied in a limited amount to form bonds between fibers on and near the coated surface only of the web.
8. A laminated fibrous web product according to the method of claim 1.