WO1994004736A1

WO1994004736A1 - Process for the production of a fluff pulp

Info

Publication number: WO1994004736A1
Application number: PCT/US1993/007368
Authority: WO
Inventors: Bernhard Ernst Van Issum; Kurt Fuchs
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1992-08-13
Filing date: 1993-08-10
Publication date: 1994-03-03
Also published as: GB9217177D0; MX9304889A

Abstract

A process and apparatus are provided for adding fibrous additives such as polyester fibres to a fluff pulp which is useful as disposable diapers and incontinence pads. The apparatus comprises means for separating additive or enhancing fibres from a body of such fibres, such as a card sliver; means for adding the separated fibres to fluff pulp in a predetermined manner; and means for forming an absorbent product core or element from the fluff pulp.

Description

Title

PROCESS FOR THE PRODUCTION OF A FLUFF PULP

Field of the Invention

The present invention relates to a process or method for the production of a fluff pulp in which a fibrous additive has been incorporated, and to the fluff pulps so produced, and to absorbent products containing such fluff pulps.

Background to the Invention

With current non-woven or absorbent-"incontinence" product making systems, difficulty is experienced in dosing or applying small amounts of specialty fibrous materials. The use of synthetic fibres in pre-prepared fluff pulps and those used for absorbent products is not new, such pre-prepared fluff pulps including, for example, those marketed by Weyerhaeuser as "KITTYHAWK", registered trademark, ("RTM") (see US-A-4,900,377); or by Metsa-Serla as "SPHINX" Fluff D (RTM), the latter including small amounts of Dacron* AR (DuPont RTM) polyester fibre. The handicaps of using pre-prepared fluff pulps made in the paper industry are 1.) that product differentiation is difficult because blend ratios that can be used are limited by that of the original fluff pulp; 2.) that the use of Absorbent Gelling Material ("AGM") fibres in pulp making is not possible; 3.) that certain fibre-surface treatments such as making synthetic fibre surfaces hydrophilic, antisoiling, etc. can be damaged or washed off in pulp making; and 4.) that the synthetic fibre addition in the diaper or incontinence product is diluted over the whole pad area.

Various means have been described for continuously producing discrete shaped articles from fleece-like materials in which the fleece is introduced into the pad making operation after the hammermills have shredded or defibrised the fluff pulp or dry lap. Such methods are described by Procter & Gamble in the U.S. Patents US-A- 3,863,296, US-A-4,388,056 and US-A-4,592,708. Sakulich (USA- 3,519,211), Morgan (US-A-3,825,194) and others disclose apparatus to generally convert dry-lap, that is thick, fibrous webs or felt like materials, in a stream of air entrained fibres during the air-laying non-woven process.

Cook (US-A-4,551 ,143) discloses polyester fibre webs being air-laid onto a foraminous support followed by the addition of conventional binder, wood pulp, and cotton linters of less than 1/4 inch (6mm) and then curing of the binder to get pad integrity.

Koczab (US-A-4,826,498), Camor (US-A-4,650,481), Rockett (US-A- 4,609,580), Johnson & Johnson (US-A-4,551,143), and Freudenberg (US-A-4,413,032) also disclose the use of synthetic fibre fleeces or webs but do not disclose how intimate mixing with wood pulp is achieved.

Problems of uniformly opening and intimately distributing the synthetic fibres in the fluff occur with current bale-feed systems, screw feed volumetric dosing devices, and when dosing the fibre via dust-waste recycling lines at the diaper converting machine, because the crimped synthetic fibres remain in bundles of 5 or more unopened fibres. Additionally, the long air-fluff transport lines permit the fluff and synthetic fibres to separate owing to their respective fibre lengths and densities; usually fibres of 6mm length or less have been used. Non-uniform feeding to the forming zone of a diaper machine naturally results in poor product performance, and product variability. Webs of synthetic fibres which are opened and fed in along with wood pulp, because they are relatively long

(length/diameter (L/D) ratio is typically greater 1000:1, i.e. greater than 1/2 inch (12mm) for a 1.7 dtex fibre), can staple across screen holes in the shredding area causing plugging, extensive fibre fractionation defects and machine stops. The addition of synthetic fibres at or after pulp shredding and/or the forming zone during pad making has achieved neither the desired randomness of synthetic fibre lay-down nor an intimate mix. It is an object of the present invention to provide means and a process for incorporating a fibrous additive into fluff pulp whereby these difficulties are overcome and, preferably, whereby long fibres with L/D ratios >1000:1 can be added, even in very small addition/ dosing rates.

Summary of the Invention

The present invention provides a process for incorporating a fibrous additive in a fluff pulp which comprises feeding a body of fibres into means for separating the fibres, removing the separated fibers from the said separating means and mixing them with the fluff pulp.

The present invention also provides apparatus for incorporating a fibrous additive into a fluff pulp and further provides fluff pulp which comprises a fibrous additive and which has been prepared by the process according to this invention and/or in the apparatus according to this invention.

Furthermore, the present invention provides an absorbent product, e.g. a disposable personal-hygiene absorbent product, comprising an absorbent structure, for example a pad, formed of fluff pulp which contains a fibrous additive and which has been produced according to the present invention.

Brief Description of the Drawings

Figure 1 is a schematic section through a device for separating the fibres of a body of fibres, which can be used in the process of this invention.

Figure 2 is a schematic illustration, partly in section, of means for forming fluff pulp and converting same into an absorbent product.

Figure 3 is a schematic illustration of a drum forming means for fluff pulp conversion - showing more clearly how and where the "enhancing fibres" can be added to make products with different performance characteristics.

Description of Preferred Embodiments

Fluff pulp and dry shredding are defined in SIS Handbook 146 (Paper Vocabulary) issued by the Swedish Standards Institute. A clear description of the fibre lengths of the wood pulps that may be used is given by J.P. Casey in "Pulp and Paper", Volumes 1 and 2 published by Wiley Interscience, and this reference distinguishes pulp fibres from synthetic fibres.

The fibrous additive herein will generally comprise or consist of fibres which can be used to enhance product performance - hereinafter called "enhancing fibres" - and include natural, man- made, and synthetic fibres. Natural fibres include cotton, abaca, flax, sisal and other plant cellulosic fibres. Man-made fibres include the regenerated fibres, for example viscose rayon, and synthetic fibres, the latter including such organic fibres as polyamide (e.g. nylon), polyolefin (e.g. polyethylene or polypropylene), acrylic, cellulose acetate or polyimide fibres, aromatic polyamide (aramid) fibres, for example those marketed under DuPont's registered trademark "Kevlar" and polyester, e.g. poly(ethylene terephthalate), fibres for example those marketed under Du Pont's registered trademark "Dacron".

The enhancing fibres will generally have a fibre length of from 4 to 140 mm, usually from 4 to 120 mm, preferably from 6 to 100 mm and optimally from 10 to 40 mm.

The length-to-diameter (L/D) ratio of the enhancing fibres may be as low as 500:1 (6 mm for 1.7 dtex - 13 micron dia fibres). However, it is an advantage of the present invention that use may be made of fibres having an L/D ratio greater than 500:1 , and preferably greater than 800: 1 , these being fibres which cannot easily be added in pulp making. The "enhancing" fibres are preferably crimped to give good sliver cohesion but cotton and cotton linters and vegetable fibres, as described by K. Douglas in "Rotor Spinning - Technical Economic Aspects", Chapter 13, Textile Trade Press, are also suitable. It is, of course, possible to employ a blend of two or more different fibers. Typically, such a blend will comprise at least 50% by weight of crimped fibres, especially when the fibres are of similar length. If the uncrimped fibre is significantly longer than the crimped fibre, the proportion of crimped fibre may be reduced to, for example, 25 or even 20% by weight.

Fibre fineness or denier may typically vary from 0.4 to 20 denier or, more preferably, from 1.0 to 6.0 denier.

There is no restriction on fibre cross-section though a round or circular cross-section is usually preferred for economic reasons. Hollow fibres (e.g. as described in US-A-4,838,885 to Bernardin), which would tend to float in papermaking, are also suitable. Examples of various fibre cross-sections are described by G. Allen in "Cellulose Chemistry and Technology" (1968) p. 890, and (1970) p.

567; and by R.W. Moncrieff in "Man-Made Fibres", 6th ed. published by Newness & Butterworth.

The cross-sections may be selected according to the final absorbent product requirements: for example, "VIVAN" (RTM), a U-shaped cross-section described by Kanebo in "Textiles Japan" Jan. 1985, p.80, gives improved absorbent capacity. Arco in US-A-4,731,067 and Katz in US-A- 4,888,238 describe two types of superabsorbent fibres which also are used to enhance absorption capacity and to improve wicking rates. Textile fibres which have been surface coated or treated chemically could also be included; these include, for example, fibres treated with CMC-Aqualon C (from Hercules Inc. USA) wetting finish or with 0.2 % or more of Triton from Rohm & Haas.

Other examples of suitable "enhancing" fibres are given by Bagrodia in published European Patent Application EP-A-0,391,814 and Gorraffa in US -A-3, 914,488, viz typical fibre types that aid moisture transport through improved wicking. Fibres offering odor protection or control, washability, anti-microbial properties, as exemplified by Morrison US-A-3, 959,556 and Toray in Japanese Patents 90-258557/34 and 83-786569/41, and those which may be biodegradable/compostable, as described by e.g. Tietz in US Patent 5,053,482 granted October 1, 1991, are useful in "diaper" products. Fibres which were previously found unsuitable for textiles because of limited hydrolytic stability can now be used in disposable products. Several such families of products are described by J.M.

Preston, "Fibre Science", 1953 Chap. 6, etc. published by the Textile Institute Manchester, and byR. Hill "Fibres from Synthetic Polymers", 1953, Elsevier Polymer Series; these fibres are typically not suitable for incorporating into diapers by a "wet" or papermaking method.

It is also possible to use, as the enhancing fibre, a heat-shrinkable fibre, for example a partially drawn, partially quenched or latent crimped fibre, such as those fibres discussed in the present applicant's United Kingdom patent application 92 17 179.2, filed on

13 August, 1992, and entitled "Improvements in or relating to Fluff Pulps".

The amount of "enhancing" fibre, or other fibrous additive, that is incorporated in the fluff pulp can be varied within wide limits.

Typically, however, the amount of fibrous additive will be from 1 to 15% by weight of the mixture of fluff pulp and said additive. Such levels of addition will, in general, be suitable for the fluff pulp cores in personal hygiene absorbent products.

The present invention involves the feeding of a body of fibres into means for separating the fibres. In textile operations, fibres are forwarded from bales of fibrous material to a carding machine which opens the fibre bundles (which may contain as many as 500 fibres or more in one bundle). The resultant card sliver contains few if any unopened bundles and consists essentially of individual fibres which are still in a cohesive or coherent state. The body of fibres used herein is preferably a card sliver and the device for separating the fibres is employed to produce individual, discrete fibres (that is to say fibres that are essentially non-cohering). Obviously, in practice, a few fibre bundles, typically containing no more than 5 or so fibres, may remain but these can generally be tolerated. Also, it is in principle possible to feed unopened fibre material into the means for separating the fibres but this is not preferred since it could give rise to non-optimal/uniform dosing of the fibrous additive to the fluff pulp.

Figure 1 shows exemplary means for separating the fibres from the card sliver or other body of fibres, said means being in the form of a conventional textile open-end spinning or friction spinning opening and cleaning unit. Typically, such units will comprise a rotating roller having a peripheral surface provided with elements for combing fibres out of the card sliver or other body of fibres presented to it, such elements being typically needlepoints, wire clothing, teeth or the like. Fuller descriptions of such known opening - drafting zones and also fibre forwarding means are described by Rohlena in "Open- End Spinning" 1975, by Ripka in "Rotor Spinning Technical and Economic aspects" edited by Dry son and published by the Textile Trade Press, and in US-A-3,624,997 and US-A-3,750,380 respectively issued to Dideks and to Mladek. Rust and Lord in the "Textile Research Journal" 25 November 1991 describe means to improve and/or modify fibre alignment in yarn by configurational modifications of the feed tube in the rotor spinning device. The same means can be adapted to align fibres or control their orientation in the machine direction during diaper or other pad manufacturing according to this invention.

Ripka and others have demonstrated that uniform fibre drafting and forwarding fibres as individual and separate entities is not possible with traditional ring spinning; and that drafting waves occur. These, if not blended with other slivers, lead to irregular dosage, i.e. thick and thin places in a yarn. The present invention will now be described with reference to the exemplary embodiment illustrated in the accompanying drawings. Figure 1 shows a suitable means for separating fibres which is similar to a conventional fibre combing or opening device or unit of an open-end textile spinning unit. The card sliver(s) (not shown) comprising the chosen "enhancing" fibres (generally 4-8g/m in weight) are forwarded to inlet 2 of the combing-opening unit 1. The opening device comprises a grooved feed roll or "briseur" 3, which can be rotated by drive means (not shown) as this is well known in the art, and a cradle or condenser guide 4 to the combing or opening roll 5. The external curved surface of the said combing roll is clothed with pins or metallic wire 6.

The combing roll 5 is totally enclosed by the housing 7 of the unit 1 and runs therein in a circular hole, the diameter of which is larger than that of the said combing roll and its clothing 6. The annular gap 8 between the housing and the clothed combing roller 5 permits a negative or under-pressure to be developed due to centrifugal forces when the said roll 5 is rotated at high speed about its shaft 9 by drive means (not shown), thus liberating the individual combed fibres.

Drives for the combing roll 5 and for the feed roll 3 are equipped with clutch and brakes (not shown) for exact control of stop-start programs. The speed of the opening roll 5 may be from 2,-12,000 RPM, and that of the infeed may be increased beyond that known in textile technology as there are no constraints from the rotor-size and yarn counts to be spun. Additionally, the depth/width of the combing roller can be increased or two or more individual combing rolls/chambers may be mounted side by side to permit the "enhancing" fibres to spread over a larger width in the fluff pulp product, to blend different enhancing fibres, or to increase the number of enhancing fibres (total percentage) to be added into the fluff.

The fibre extension or draft between the feed roll 3 and the combing roll 5 can be varied from 25 to 300, the choice depending on sliver weights used, the amount of "enhancing" fibres in the fluff pulp, and fibre length. It is important, however, that the said fibres are substantially completely detached from one another and from the incoming sliver. The centrifugally ejected or liberated combed fibres pass into a tangentially disposed conduit 10 in a fibre-transport zone 11, which zone is provided with Venturi pipesl2 for the admission of air.

The annular gap 8 may be selectively opened, by means of the valve or closure 13 to an extraction chamber 14 for the removal of waste or "trash", if required.

The outlet 15 of the fibre transport zone is provided with a flange 16 or other means for mounting the fibre opening device 1 on or in the hammermill shredding area of Fig. 2 or in the forming zone of a diaper machine shown in Fig. 3. The term "diaper" machine as used herein relates to all machines making absorptive products such as baby diapers, feminine hygiene, adult incontinence, etc. using fluff pulps as part of the absorptive core and in which a hammermill or other pulp shredding device is used, and in which the resultant fluff is laid on a foraminous support comprising end product shaping devices as shown in Fig. 3. The air velocity in the annular gap should exceed the peripheral speed of the combing roller by a factor of approx. 1.5 to 2.

The shape of the fibre transport outlet 15 is generally converging to give a modicum of fibre control in conventional open end textile spinning and to present the opened fibres to the rotor. In contrast, this convergence is not required in the transport zone for "diaper" making as the intention is to spread the "enhancing" fibre over the operating width of the "diaper" pad where they will best fulfill their function. Generally this is in the central band, i.e. the crotch area of the body, or adult incontinence diapers. Thus, the outlet in the fibre transport zone may be flared, as illustrated, or of constant cross- sectional area. The cross-sectional shape of the said outlet is typically circular or oval. However, the constant or increasing dimension of the transport zone can lead to dead areas in which the fibres can collect; and, to overcome this, additional air can be applied from the Venturi jets 12 - so placed as to forward the fibres into the fluff pad forming zone. This extra injected air also prevents the shredded fluff pulp from blocking the transport outlet 15, as fibre fines and dust from the separately shredded wood pulp are all-pervasive.

Turning now to Figure 2, there is shown a traditional apparatus for forming an absorbent product from fluff pulp in which an enhancing fibre has been incorporated. The apparatus comprises, broadly, three sections, namely a pulp stand, a hammermill and a forming zone, as shown. The pulp stand includes a plurality of pulp rolls 21 supplying pulp to a feed roller 22, which forwards the pulp to a breaker bar 23 and hence to the hammermill 24. The latter is of conventional construction and comprises hammer elements 25 and a screen 26. In the hammermill 24, the pulp is shredded to form fluff pulp, which is then deposited onto a moving forming element 34.

The enhancing fibres may be introduced at one or more locations in the diaper machine. Thus, the reference numerals 28, 29 and 30 indicate opening units 1, such as described above with reference to Figure 1 , for producing separate enhancing fibres, these devices being at different locations, depending upon the desired end- product effect. Thus, the device 28 will tend to deposit enhancing fibres near the back of the diaper, i.e. that surface created adjacent the forming device 34. The device 29 will give a general application of enhancing fibres throughout the fluff pulp web, whereas the device 30 may be used to deposit fibres on the top surface of the diaper pad, namely the surface formed remote from the forming device and which in use, is intended to be situated closest to the wearer's body. The transport zone 15 of the fibre-separating device may advantageously be adjusted with regard to the distance between the outlet and the forming device. This is illustrated by the device 30: the closer the outlet 15 for the enhancing fibres is situated to the forming device 34, the narrower will be the band of enhancing fibres that is deposited on the fluff pulp web. Accordingly, it is possible to vary the band width across the absorbent product from broad to narrow, according to the desired characteristics of the end product. Continued under-pressure also comes from the vacuum applied in the diaper forming zone 27 in which both the fluff pulp and the "enhancing" fibres are sucked onto the forming device, typically a foraminous or woven wire gauze frame or drum support 26, to form the diaper. The vacuum is drawn through the vacuum chamber 31 by conventional means.

The forming device 34 moves on rollers 32, at least one of which is driven, whereby the web of fluff pulp and enhancing fibre is conveyed out of the forming zone 27 to a compression or embossing roller 33. It will be seen that the present invention, in one aspect, provides means to add "enhancing" fibres uniformly into a fluff or "diaper" pad, in which the means consist of small opening and combing units as exist in high speed open-end textile yarn spinning, and means to forward the opened individually separated fibres into the fluff pulp airstream or directly onto a foraminous support where the "diapers" are being formed.

Other feed or combing sections which separate the sliver into individual fibres for friction spinning of textile yarns as typified by the "Dref" RTM system and described in "Textile Technology

International" 1989 p. 118 may also be employed. Other means for feeding shorter fibres, e.g. with L/D ratio approx. 500:1 or less, or cotton linters or uncrimped fibre are possible, e.g. by means of pulp, dust recycling systems. The number of opening units can vary from 1 to 6 so that a blend of "enhancing" fibres can be added into the fluff pulp.

In the embodiment illustrated in Figure 3, each fibre-separating and forwarding device (28, 29, 30) is attached directly to the housing of a diaper machine 27 having a forming screen 26 to form a diaper with the assistance of a vacuum pulled through vacuum chamber 31, such an arrangement helping to maintain the enhancing fibres in an individualised or discrete state. The location of the enhancing fibres in the pad which were added at positions 28, 29, 30 are respectively 37c, 37b, & 37a that is clearly in different areas of the pad thereby fulfilling different product needs. However, where such an arrangement is not possible, it is possible to transport the fibres from the fibre-opening and separating device to the diaper machine using a suitable conduit 36, for example that also disclosed by Horii in US-A-4,969,481.

The diaper machine may also be varied. Other suitable machines are, for example, those disclosed by Lee et al in US-A-4,388,056 or by Feist et al in US-A-4,592,708.

The apparatus may additionally be provided with means or apparatus to apply absorbent gelling materials, especially powders, by injection into the fluff pulp-air stream.

The teaching in the patent and technical literature referred to above is incorporated herein by reference. It will, of course, be understood that the present invention has been described above purely by way of example and that modifications of detail can be made within the scope of the invention.

Claims

C l a i m s

1. A process for incorporating "enhancing" fibrous additive in a fluff pulp, which comprises feeding a body of "enhancing" fibres into means for separating the fibres, removing the separated individual fibres from the separating means and mixing them with fluff pulp.

2. A process according to claim 1, wherein the means for separating the fibres comprises a rotating roller having a peripheral surface provided with elements, for example needlepoints, wire clothing or teeth, for combing fibres out of the body of fibres.

3. A process according to claiml , wherein the said means for separating the fibres is a conventional fibre-combing or fibre- opening device as known in "open-end" or "friction" spinning.

4. A process according to claim 1, 2 or 3, wherein the said body of fibres is a card sliver.

5. A process according to any preceding claim wherein the separated fibres are fed directly into a shredding device in which pulp is being shredded to form fluff pulp, and/or directly to a mass of fluff pulp being conveyed to a web-forming zone, and/or directly into a web-forming zone.

6. A process according to any preceding claim wherein the said fibres are added in an amount of 1-10% by weight, relative to the mixture of said fibres and the fluff pulp.

7. A process of admixing "enhancing" fibres into a disintegrated - shredded fluff pulp sheet material to form absorbent or "diaper" products comprising the steps of

a) feeding a body of enhancing fibres into the feeding and combing section of a textile open-end or friction spinning system to separate the fibres; b) removing the said separated enhancing fibres through a tangentially located transport zone by means of under¬ pressure;

c) mixing the said separated enhancing fibres with the shredded fluff pulp to get an intimate mixture; and

d) impacting the said intimate mixture onto the forming zone of a "diaper" machine to form a fluff pulp absorbent element.

8. An absorbent product comprising an absorbent element, formed from a fluff pulp containing a fibrous additive, being fluff pulp produced according to any of the preceding claims; and a structural frame for holding the absorbent element for its intended use.

9. An apparatus for adding enhancing fibres to a fluff pulp comprising:

a) means for separating enhancing fibres from a body of such fibres;

b ) means for adding the separated enhancing fibres uniformly to a fluff pulp; and

c) means for forming an absorbent product element from said fluff pulp.