IL45507A - Apparatus for compacting an adhesively bonded nonwoven fabric - Google Patents

Abstract

A moistened fibre fleece (11), which contains a thermoplastic binder and which is already preconsolidated, is guided over a rotating drum (12), the outer surface of which is covered with a layer (31) of low-friction material, for example Teflon. This outer surface is heated to a temperature which is higher than the softening temperature of the binder in the fibre fleece. A further adhesive binding of the fibres in the fibre-fleece region guided so as to rest on this outer surface thereby takes place. The drum outer surface is part of a device for compressive shrinkage. This includes an elastic band (16) which partially loops round the drum and against which the running fleece bears. As a result of the contraction of this band, the fleece is also moved by adhesion and at the same time shrunk by longitudinal compression. The fleece thereby slips along the low-friction layer (31) covering the drum outer surface. Simultaneously with the further adhesive binding of the fibres of the fleece, an improved shrinkage takes place, since the drum outer surface opposes only slight resistance to the longitudinal compression of the fleece. <IMAGE> [GB1449417A]

Description

APPARATUS FOR COMPACTING A NONWOVEN FABRIC TO IMPROVE HAND AND DRAPE Ernest J„ Groome and Henry L. Hamrick Abstract of Invention This disclosure teaches an apparatus for compacting a non-woven fabric to improve its hand and drape „ A bar compresses a relatively thick endless elastomeric belt againsi: a steam heated drum so that a nip is formed therebetween. The nonwoven fabric is passed through the nip between the belt and the drum and thence onto the drum. The nonwoven fabric adheres fractionally to a stretched surface of the belt as it goes through the nip and is thereafter compacted by the belt as the belt unstretches onto the drum. Fibers of the fabric are crowded together, rearranged and crimped locally (all between the faces of the fabric) and more of the fibers of the fabric are caused to be oriented crosswise,, To allow compacting at sufficiently high temperatures (160-280* F.) without sticking of the fabric to the drum, as well as to obviate need for addition of release agents to the drum surface, the drum is lined with tetrafluoroethylene resin (available commercially as TEFLON, a trademark of Du Pont de Nemours & Go.) .

Background of Invention This invention relates to nonwoven fabrics that are formed of fibers bonded randomly to one another by small discrete particles of an added polymeric material or at contacts between thermoplastic fibers by heat. These nonwoven fabrics have improved kinesiological properties over prior nonwoven fabrics made of the same materials.

Nonwoven fabrics have been limited in their, applications^ by stiffness in simple bending and resistance to deformation under complex stresses such as those encountered in bodily movements.

Consequently handle or feel of nonwoven fabrics is liable to be harsh and such fabrics generally do not drape well, Achievements of softness and draping properties (without substantial loss of strength) have been major obstacles to more extensive applications of nonwoven fabrics Nonwoven fabrics usually are formed by laying loose fibers on a moving support, hence the fibers are guided in a direction of their lay to some extent by initial contact of ends of the fibers with the moving support and this initial contact generally causes them to lie largely in the direction of movement of the support, which would be the length of the fabric. Such fabrics when supported solely by a central area thereof tend to flex along an axis that is substantially parallel to the length of the fabric, the direction in which most of the fibers are oriented..

Considerable developmental work has been performed to improve nonwoven fabrics so as to make them soft to the feel and to impart to them greater kinesiological properties. With particular respect to kinesiological properties, emphasis has been placed on making the crosswise strengths more compatible with lengthwise strengths (while not subs antially weakening the fabrics lengthwise) . Nonwoven fabrics have been produced commercially which have hand and-drape properties quite imilar- o. woven fabrics, are relatively inexpensive to make, can be terilized, and.axe relatively quiet-when flexed whereby said nonwoven fabrics are suitable for use in-expendable garments, diaper skins , skins for sanitary napkins and the like. These results have been achieved in the prior art by subjecting such non oven fabrics to compacting- forces between faces "^ of the fabrics, which forces crowd, flex and rearrange the fihers together lengthwise with stretches of fibers between their point of bonding to other fibers . Also these forces locally flex, crimp and bend the fibers crosswise,, During such compacting, pressure also is applied to opposite faces of the fabrics adequate to prevent creping of the fabrics „ In essential features known apparatus suitable for achieving the desired compacting forces include a heated cylinderical drum mounted for rotation on its axis,, A relatively thick endless belt of an elastomeric material passes between one peripheral sector of the drum and a compactor bar and thence onto the drum, The compactor bar engages the belt approximately radially of the drum until a suitr able nip between the belt and the drum is. estabilished. The belt on or near its surface that engages the bar has a cord reinforcement that restricts lengthwise stretching of the belt along the reinforced face, but permits local stretching of the other face that abuts the_ drum. The nonwoven fabric is fed through the nip between the belt and the drum thence onto the drum for some distance around its periphery and then the nonwoven fabric is removed from contact with both the drum and the belt.

In passing through the nip between the belt and the drum, the nonwoven fabric adheres frictionally to the stretched surface of the belt passing the nip} and as the elastic belt surface un-stretches in passing onto the drum, the fabric is compacted lengths wise Because pressure on the fabric (which is substantially normal to its faces) restricts the fabric from becoming materially thicker due to its lengthwise compaction, the f ihers are crowded together crosswise, rearranged and crimped locally all within the space between the faces of the fabric „ This compaction causes more of the fibers to be oriented crosswise and increases crosswise tens ile strength of the fabric , In implementing- such compacting..on a commercial, scale, it has been found that for some nonwoven fabrics hand., and drape imp rove.?, ments require relatively high, temperatures of- operati on of- the drum in the order of ■ 160e.F„ t-o . ?80°F . When the drum, temperatures are not sufL- -ficiently high, same nonwoven fabrics are found— ot . to compact ..satis--factorily „ However . with. high., tpmperafurps ,. the- fabrics can stick -to— the drum resulting- in damage, to the fabrics and /or poor or. no jcompae-tion. This sticking is especially troublesome in nonwoven fabrics which contain heat scalable thermoplastic hinders such as are used, generally in diaper skins , skins for sanitary napkins And .the . like-,, Steam sprays have been used to provide lubr ica t ion on the drum surface , but such s team sprays have not proven to be completely satisfactory „ . Des irable high operating temperatures have been achieved hy use of release agents such as s ilicone oils and . the like, but these release agents are expens ive , they inhibit heat sealing properties of polymeric materials and they may be quite unacceptable in the resulting nonwoven fabric „ Brief Statement of Invention.

The present invention overcomes difficulties of - dpJera. i.ng--at sufficientl high temperatures to compact nonwoven fabrifcs satisfactorily without need for any release agents „ The crux of the present invention is to line the heated drum with polytetrafluoro-ethylene resin (available commercially as TEFLON, a trademark of Du Pont de Nemours & Co,) - Accordingly one object of this invention is to achieve superior compacting of nonwoven fabrics whereby their hand is improved.

Another object of this invention is to achieve more isotropic properties of nonwoven fabrics whereby their drapes and crosswise strengths are improved, Still another object of this invention is to permit opera-of compacting apparatus at higher temperatures than had been feasible according to the prior art.

Still another dbject of this invention is to avoid sticking of nonwoven fabrics to drums of compacting apparatus.

Still another object of this invention is to obviate need for release agents in compacting nonwoven fabrics.

Still another object of this invention is to improve heat sealability of nonwoven fabrics „ Still another object of this invention is to promote efficienc of compacting nonwoven fabrics „ Still another object of this invention is to produce non-woven fabrics having superior absorbency and which are suitable otherwise for further processing and/or conversion.

Brief Description of Drawings Other objects and advantages, will appear from the following description of a preferred embodiment of apparatus for compacting non-woven fabrics viewed in conjunction with an accompanying drawing and novel features will be pointed out particulary in claims appended hereto. In the accompanying drawing? Fig. 1 is an illustration of a fiber arrangement in a lo Fig, 2 is a similar illustration to Fig. 1 of the fiber arrangement of a local area of such nonwoven fabric after it has been treated in accordance with this invention.

Figo 3 is a schematic illustration on a much larger scale than that of Figs, 1 and 2 to demonstrate some changes in the fiber relationships of nonwoven fabric before and after treatment in accordance with this inventionc Fig. is a schematic view partly in section showing a compacting apparatus capable of carrying out this invention.

Detailed Description of Preferred Embodiment In accordance with this invention, a nonwoven fabric formed of layed fibers that are bonded randomly to one another at intervals by fusion or by discrete added particles of polymeric material, is subjected to compacting forces entirely between its faces in a direction parallel to a lengthwise dimension of the fabric that compact, crowd, flex and rearrange the fibers together in such direction of compaction with stretches of fibers between their points of bonding to other fibers, also locally flexed, crimped or bent laterally of. their lengths. During such subjection to compaction forces, pressure is applied also to the opposite faces of the fabric normal to such faces-, adequate to inhibit or prevent creping of the fabric.

Fig. 1 illustrates a small portion of a nonwoven fabric before compaction in accordance with this invention. It will be noted that the fibers of this fabric lie predominantly in one direction which likely would be the direction in which the support as the fibers were deposited theron, Fig, 2 is a small portion of such a fabric after it has passed through apparatus such as that shown in Fig„ 4 during which the fibers were compacted and crowded together in a direction lengthwise of the fabric and also flexed and rearranged locally. It should be noted that the treatment in an apparatus such as shown in Fig, 4 has increased the number of crosswise disposed fibers in this areas so that the fibers now offer about as much resistance to tensile stresses in the crosswise direction as the lengthwise direction, and more fiber stretches now are disposed cross wise of the length of the fabric. It will be noted also that the fibers, particularly those disposed to extend gererally lengthwise of the fabric, have also between points of bonding to one another been bent locally, flexed or crimped in their crosswise direction. This concept is demonstrated more clearly schematically in Fig. 3 where full lines represent a few fibers A} B and C bonded together by discrete particles of resin where they cross on another at D, E and F. Dash lines a,b, and c represent positions and shapes of the fibers A,B, and C respectively after the fabric has been compacted and its fibers After compaction rearranged in accordance with this invention,, AssumingiJrtajfc.-hcmd has moved to location d point D remains. i , l,-s¾a£-i-Qfta¾t-r-it-will- e-jgat^ad,-th t bond point E has moved to position e and bond point F has moved to position f„ This movement shortens the distance between the bond point D and the new position e and f of the bond points E and F and hence the fibers A and B are bent, flexed or collapsed randomly laterally upon themselves as shown by the dash lines a and b. The bond points E and F also are moved closer together to the positions e and f, hence fiber C is also flexed or bent sideways upon itself locally as shown by the dash line Co The nonwoven fabric web 11 is shown in Fig. 4 to be supplied from some preceding operation. As in the disclosure of Cluett patent 2,624,245 according to which this apparatus is designed, the7* compacting apparatus includes a steam heated drum 12 of substantial diameter,. The drum 12 is of sturdy construction and is mounted on a shaft 13 which is driven rotatively by a suitable means (shown as arrow 14) „ A thick blanket 16 made of resilient elastomeric material (such as rubber) is mounted on three rolls 17, 18 and 19 which are arranged to tension the blanket 16, The blanket 16 has a run which travels on a segment 21 of the drum 120 The blanket 16 may have a Shore Durometer hardness of between 40 and 80 depending upon its application and is provided with a nonstretchable backing of cord 22. The blanket 16 is driven by the drum 12. The rotary parts thus far described all are mounted in rigid side frame members (not shown), which are disposed outside the lateral bounds of the nonwoven web 11 and the blanket 16 „ Typically a bar 23 extends across the machine through substantially the full length of the drum 12 being supported at its ends. The bar 23 comprises a thick walled but hollow metal cylinder 24 and a rigid beam 26, The cylinder 24 and the beam 26 are desirably of steel or steel alloy and are of substantial strength and rigidity.

The cylinder 24 is of small diameter, but the total depth of the bar 23 as constituted by the cylinder 24 and the beam 26, is considerably greater than the diameter of the cylinder 24 „ The cylinder 24 is disposed to engage the back of the blanket 16 and to press the blanket 16 radially agijanst the drum 12 to form a uniform nip for the non-woven web 11. This is the nip in which the compacting of the web 11 of nonwoven fabric takes place„ Means are provided for applying an evenly distributed pressure across the width of the bar 23 and for causing thereby a pressure which is distributed evenly across the blanket 16 from edge to edge thereof. It is important that evenly distributed pressure be applied to the bar 23. It is important also, however, to be able to maintain the pressure at any predetermined level throughout a wide pressure range„ Therefore, a dependable hydraulic or pneumatic pressure source (not shown) is provided, capable of maintaining any desired pressure throughout a wide range. Because devices of this character are well known, no detailed showing and description are thought necessary.

Feed roller 28 and exit roller 29 are also provided.

As has been pointed out sticking of fibers of the nonwoven fabric web 11 to the drum 12 is avoided by polytetrafluoroethylene resin layer 31 (TEFLON is the trademark of Du Pont de Nemours & Co.) for polytetrafluoroethylene resin). It is desirable to operate the drum 12 at from 160PF„ to 280^F„ so that adequate compacting of the non-woven fabric web 11 is assured. The polytetrafluoroethylene resin coating 31 eliminates need for Release agents (such as silicone oils) being applied to the drum 12, A trial has been run on 13" laboratory compacting apparatus such as that here disclosed to determine benefits derived from a polytetrafluoroethylene resin covering on the drum 12 when processing the nonwoven web 11 which in this instance contains a thermoplastic binder„ The sheet composition and compactor conditions are given in the following table* With Teflon 31 covered drum 12, the nonwoven fabric web 11 was processed at 250°F. without dif- ^ ficulty. After removing the TEFLON 31 it was necessary to reduce the drum 12 temperature to 150°F, before the nonwoven fabric web 11 could be compacted, This temperature reduction was necessitated because binders in the nonwoven fabric web 11 stuck to the drum 12.

Even at this reduced temperature, the nonwoven fabric web 11 could not be compacted when it was rewetted to a 107o water content by means of a steam shower. In order to process a moistened sheet, it was necessary to reduce the temperature of the drum 12 to 120°F.

Tensile strength, elongation, tensile energy absorption and stiffness were all improved by operating the apparatus at the higher temperature (250®F,) made possible by the TEFLON covering 31 on the drum 12.

TABLE DRUM COMPACTOR S SHHEEEETT E ELLOONN-- 1 T TEEAA**** STIFFNESS TEMPo Driven MMooiissttuurree T TEENNSSIILLEE ggaattiioonn T TEEAARR ((FFtt## vv (Drape Fle F. Surface ( (¾%)) ((W#/iinn . (a%)) '. (gm) (ΨΈ22¾) ' .. inches) 250°F, Teflon 6 6 9 9..22 . 2 255..88 .8 82277 1 122..11 1.7 10 9.5 32.5 810 13.7 1.9 CHROME 66** ** ** * ** * 10* * * * * CHROME 8,8 19.2 819 * . .* CHROME 6 8,4 14.7 821 10 8,5 18,1 840 NO COMPACTION -- 9,4 9,1 587 Compactors 12% nip, 60 pound per lineal inch blanket tension, 50 Shore A durometer blanket hardness.

Sheet? 34#/3000 ft , 50% Hardwood Sulfite, 20% Nylon 66, 30% Polyvinyl alcohol, ^ ■ Sheet stuck to compactor drum - no compaction ** 'EA means tensile energy absorption.

It will be understood by those familiar with compacting nonwoven fabric webs that various departures may be made from the foregoing detailed description without departing from the main theme of invention set forth in the following claims. It will be understood further that the example set forth above is merely illustrative and in no way limiting^

Claims (5)

45507/2 WHAT IS CLAIMED IS: ;

1. An apparatus for treating a web of adhesively bonded nonwoven fabric to improve its hand and drat^e, the apparatus comprising in combination: a heated cylindrical drum mounted for rotatio about its axis, a bar, a relatively thick endless belt of an elaetomeric material and organized to pass between one peripheral sector of the drum and the bar, the bar organized to engage the belt approximately radially of the drum so that a nip between the belt and the drum is established, the belt at its face which engages the bar having a reinforcement that restricts lengthwise stretching of the belt along the reinforced face but permits stretching of the face that abuts the drum, means for feeding a web of the fabric through the nip between the belt and the drum whereby ϊ the web adheres irictionally to the stretche d surface of the belt passing through the nip and as the elastic belt surface unstr etches in passing onto the drum the fabric is compacted, the drum being heated to a temperature higher than the softening temperature of the fabric to be treated and its periphery being Coated with a stick resistant material.

2. The apparatus of Claim 1 with the stick resistant material a ' - , " ; V ' , . V 1 \ polytetrafluoroethylene resin* .45507/2 A

3. The apparatus of Claim 2 with the polytetrafluoroethyle xe resin " clad to the drum*

4. The appratus of Claim 2 and means for maintaining the drum at a temperature in a range from 160°F to 280°F.

5. * An apparatus for treating a web of adhesively bonded nonwoven fabric, substantially as hereinbefore described and referring to the accompanying drawings.