EP0866681A1

EP0866681A1 - Apparatus for air-laying fibre bodies on a moving air-permeable conveyor path

Info

Publication number: EP0866681A1
Application number: EP96941257A
Authority: EP
Inventors: Gunnar Edwardsson
Original assignee: SCA Molnlycke AB; Molnlycke Vafveri AB
Current assignee: Essity Hygiene and Health AB
Priority date: 1995-11-27
Filing date: 1996-11-25
Publication date: 1998-09-30
Also published as: SE9504215L; WO1997019659A1; SE505835C2; JP2000501145A; SE9504215D0

Abstract

The present invention relates to an arrangement for air-laying on a moving air-permeable conveyor path (2; 7; 12) fibre bodies that have a profiled cross section transverse to the movement direction (A) of the conveyor path, wherein the arrangement includes at least one air-laying unit having means for delivering a stream of air-carried fibres to a region above the moving conveyor path; means (3; 8; 13, 14) for subjecting the stream of air-carried fibres in the delivery region to a subpressure beneath the whole of that part of the conveyor path located in the delivery region; and means (4; 5; 9, 10) for delimiting the stream of air-carried fibres from ambient air. According to the invention, the means for delimiting the stream of air-carried fibres includes at least one part (b; 9) which coacts with the air-permeable conveyor path and which has smaller dimensions transverse to the direction of movement than the air-permeable conveyor path.

Description

APPARATUS FOR AIR-LAYING FIBRE BODIES ON A MOVING AIR-PERMEABLE CONVEYOR PATH

The present invention relates to apparatus for air-laying on a moving air-permeable conveyor path fibre bodies which have a profiled cross-section transversely to the direction of path movement, wherein the apparatus includes at least one air-laying unit which includes meanε for delivering a stream of air-carried fibres to a region above the moving conveyor path, means for generating a subpressure in the region in which the stream of air-carried fibres is delivered beneath the whole of that part of the air-permeable conveyor path located in said delivery region, and means for delimiting the stream of air-carried fibres from ambient air.

Apparatus which function to air-lay fibre bodies on a moving air-permeable conveyor path are often used to shape the absorbent bodies of disposable diapers, sanitary napkins, incontinence guards and like products. In many cases, these absorbent bodies are given suitable properties by profiling the bodies during manufacture, i.e. by producing fibre bodies which, in cross-section, have parts of mutually different thicknesses. This iε achieved, for instance, by laying a layer of one dimension on top of an earlier layer of a different dimension. One problem with this procedure is that the earlier laid layer is prone to be disturbed or damaged when air-laying the subsequent layer. It is also desirable to be able to readily produce absorbent bodies that contain different types of fibre in different parts of the absorbent body.

The primary object of the present invention is to solve this problem.

This object is achieved by the present invention with an apparatus of the kind defined in the introduction which is characterized in that the means for delimiting the stream of air-carried fibres includes at least one part which coacts with the aid-permeable conveyor path and which when seen transversely to the direction of path movement has smaller dimensions than the air-permeable conveyor path. Because the air-permeable conveyor path and the subpressure-generating devices coacting therewith extend beyond the means that delimit the stream of air-carried fibres, ambient air iε able to flow through the air-permeable conveyor path in directions parallel with the fibre-carrying air εtream. Thiε counteracts the occurrence of cross air flows that are able to disturb layers of fibres earlier laid on the air-permeable conveyor path, while, at the same time, providing an air seal at the edges of the means which delimit the stream of air-carried fibres, this air seal preventing fibres, or possible super- absorbents, from spreading outside the delivery region. Earlier laid fibre layers will also be influenced by a retaining suction force which strives to maintain the shape of theεe earlier laid fibre layerε.

In one preferred embodiment, the continuouε conveyor path is comprised of a succession of moulds having air-permeable bottoms and extending sequentially in the direction of conveyor path movement, and the means for delimiting the stream of air-carried fibres is comprised of at least one first mat-forming hood which coacts with a vacuum box that extends transversely across the entire mould, wherein at least a part of the first mat-forming hood extends across a part of the bottoms of respective by-passing moulds trans¬ versely to the direction of conveyor path movement, and wherein ambient air has free access to those regions of the mould bottoms which extend transversely beyond the mat- forming hood. The moulds are also disposed sequentially around the periphery of a mat-forming cylinder.

In a first variant of this embodiment, a second mat-forming hood is mounted upstream of the first mat-forming hood as seen in the direction of conveyor path movement and extends transversely across essentially the whole of the bottom of respective by-passing moulds.

In a second variant of this embodiment, the firεt mat-forming hood includes a part having side walls which diverge in the direction of conveyor path movement.

In a third variant of this embodiment, the first mat-forming head includes a part which has side walls that converge in the direction of conveyor path movement.

The invention will now be described in more detail with reference to the accompanying drawings, in which

Fig. 1 is a schematic, perspective view of a mat-forming hood and a mat-forming cylinder or wheel according to a firεt embodiment of the invention;

Fig. 2 is a section view taken on the line II-II in Fig. 1;

Fig. 3 is a section view taken on the line III-III in Fig.1;

Fig. 4 is a schematic perspective view of a mat-forming hood and a mat-forming cylinder according to a second embodiment of the invention;

Fig. 5 is a sectional view taken on the line V-V in Fig. 4;

Fig. 6 is a section view taken on the line VI-VI in Fig. 4;

Fig. 7 illustrates two mat-forming hoods and a mat-forming cylinder according to a third embodiment of the invention;

Fig. 8 is a sectional view taken on the line VIII-VIII in Fig. 7;

Fig. 9 illustrates three mat-forming hoods and a mat-forming cylinder according to a fourth embodiment of the invention; and

Fig. 10 is a sectional view taken on the line X-X in Fig. 9.

Figs. 1-3 illustrate schematically a firεt embodiment of the inventive arrangement comprising a mat-forming cylinder or wheel 1 which rotates in the direction of the arrow A. Moulds 2 having air-permeable bottoms are dispoεed εequentially around the cylinder periphery. A vacuum box 3 is mounted in the interior of the cylinder 1, radially inwards of the mould-containing peripheral surface of the cylinder, and remains stationary aε the cylinder rotates. The vacuum cylinder 3 extends over the full extension of the mould bottoms transversely to the direction of cylinder rotation. A mat-forming hood iε mounted radially outside the cylinder periphery and within the region of the peripheral extension of the vacuum box 3. The mat-forming hood 4 is connected to means (not shown) for delivering air-carried fibres or like material, e.g. air-carried cellulose fibres. When the arrangement is operating, a stream of air-carried fibres is drawn into respective moulds 2 as they pass beneath the mat- forming hood 4, the air passing through the air-permeable mould bottoms and into the vacuum box, while the fibres remain in the moulds.

After having passed the mat-forming hood, the moulds are emptied of their fibre bodies onto a conveyor (not shown) in a conventional manner, for further processing of said bodies in a procesε line.

The width of the hood 4 varies in the direction of its periphery. A first part a of the hood 4 located upstream in the direction of cylinder rotation has a width which corre- sponds to the width of the vacuum box 3, whereby a fibre layer will be air-laid in a mould 2 across the whole length of the mould bottom when the mould arrives in thiε region of the hood. A sectional view of this part of the hood 4 is shown schematically in Fig. 2. The sectioned arrows in this Figure, and also in Figs. 3, 5, 6 and 8, indicate streams of air-carried fibres or the like, while hollow arrows indicate streams of air alone. As illustrated in Fig. 2, air-carried fibres flow from this firεt part of the hood 4 and into the mould 2, over its full length, i.e. its extension perpendicu¬ lar to the direction in which the cylinder rotates, wherewith the fibres are deposited on the mould bottom as the air passes through said bottom and also through a fibre layer or layers earlier deposited thereon. A fibre layer of uniform thickness will thus be laid on the mould bottom as the mould 2 passes thiε first part of the mat-forming hood.

Downstream of the aforesaid first part of the hood 4, the hood has a εecond part b having walls which converge in the direction of movement of the moulds, thiε second hood part being terminated with a section c having walls which are mutually parallel in said movement direction, wherein the section c extends transversely over only a central part of the cylinder and its moulds. The arrangement is so configured that ambient air has free accesε to the region outside the mat-forming hood 4. Fig. 3 is a cross-sectional view which illustrates the fibre layer laid in a mould 2 immediately prior to the mould having passed the hood 4. As shown in this Figure, a stream of air-carried fibres passes through the mould bottom while leaving its fibre content solely in a central part of the mould, while ambient air flows through the mould bottom on both sides of the hood. The streamε of ambient air and air-carried fibres are parallel with one another, and the εtreams of ambient air will therefore function as air seals and ensure that fibres are unable to flow laterally from the hood. Because the ambient air has free access to the mould bottom in the region outside the hood 4, the occurrence of transverse air streams that would be liable to impair the fibre layer earlier laid on the mould bottom is prevented. Thus, as the mould 2 passes the section c of the hood 4, a fibre layer will be laid on the earlier laid layer solely in the central part of the mould.

The part b of the hood 4 narrowε successively, which means that as the mould 2 passes this part of the hood, that portion of the layer earlier laid on the mould bottom and located outside the side edges of the hood 4 will succesεive- ly increaεe. Consequently, there will be laid on the mould bottom as the mould paεεes the hood 4 a fibre layer whose thickness increases successively from the end edges of the mould 2 on both sides of the central region of the mould 2 defined by the side edges of the hood 4 in the section a.

Figs. 4-6 illustrates a second embodiment of an inventive arrangement in views similar to Figs. 1-3. The mat-forming hood 5 of the second embodiment has a different form to the mat-forming hood 4 of the first embodiment illustrated in

Figs. 1-3. The mat-forming hood 5 has a first part a which is located upstream in the direction of rotation of the mat- forming cylinder 6 and which has side edges that are parallel with the direction of cylinder rotation, and a second part b that has side edges which diverge in said direction.

Disposed around the cylinder periphery is a succession of moulds 7 that have air-permeable bottoms and which coact with a vacuum box 8 mounted in the cylinder interior during part of their rotational movement.

As the moulds rotate, each mould 7 will first pass beneath the first part a of the hood 5, wherewith a well-delimited fibre layer is deposited centrally on the bottom of the mould 7, as illustrated in Fig. 5. The mould then passes beneath the second part b of the hood 5 , wherewith a successively greater part of the mould bottom is contacted by the stream of air-carried fibres from the mat-forming hood, such that the layer of fibres which becomes successively wider trans¬ versely to the direction of cylinder rotation, this succes¬ sively wider layer being laid on top of a fibre layer earlier laid on the mould bottom. Fig. 6 is a cross-sectional view which shows the fibre layer that has been laid in the mould 7 immediately before the mould has completely passed the downstream end of the hood 5. As will be seen from Fig. 6, the laid fibre layer exiting from the hood 5 will qualita¬ tively have the same form as the fibre layer exiting from the hood 4 in the Fig. 3 embodiment.

It will be understood that the inclination of the curve of the upper sideε of the bodieε whoεe thickneεε increaεeε successively from the end edges of the mould bottom towards the central parts of the fibre bodies shown in Figs. 3 and 6 will naturally depend on the slope and shape of the convergent or divergent εides of the respective mat-forming hoods. If these sides are straight, then the upper sides of corresponding parts of the fibre bodies will also be straight. Conversely, curved sideε of these parts of the hoods will result in curved upper sides. The slope of these upper sideε is also influenced by the slope of the converging or diverging sides of the hood, wherein the slope of the upper sides becomes greater the more the sides of the hoods are inclined to the rotational direction of the cylinder. Thus, the shape and the angle of inclination of these parts of the upper sides of the fibre bodies can be varied in many different ways within the scope of the invention, by varying the shape and the slope of the convergent and divergent sides of the hoods; for instance, said sides may include both straight and curved sections.

Figs. 7 and 8 illustrate a third embodiment of the invention. In this embodiment, two mat-forming hoods 9, 10 are placed sequentially in the direction of movement of a succession of moulds 12 disposed in the peripheral εurface of a mat-forming cylinder 11. Mounted stationarily in the cylinder interior and radially inwards of the cylinder periphery are two vacuum boxes 13, 14 which, by virtue of their respective positions, coact with respective hoods 10 and 9. Both hoods 9, 10 have sides which extend parallel with the direction of mould movement, although the hood 9 has a significantly smaller transverεe extension than the hood 10, this latter hood extending transversely over essentially the full length of the moulds 12. As the moulds 12 pass the upstream hood 10, a first, broad fibre layer is deposited in the moulds, this broad layer being overlaid with a central narrower fibre layer as the mould passes the downstream hood 9, as shown schematically in Fig. 8. The air-borne fibres contained in the hoods 9, 10 may be of one and the same kind or of different kinds, with or without an admixture of particulate superabsorbent material. When the same fibre mixture is used in both hoods 9, 10, the hoods may be integrated to form one single hood, although the illustrated arrangement of two hoods 9, 10 is suitable when the various layers are to include precise quantities of fibre.

Figs. 9 and 10 illustrate a fourth embodiment of an inventive arrangement which includes three mat-forming hoods 15, 16, 17 which coact with a suction box 19 mounted in the interior of a mat-forming wheel or cylinder 18. The hoods 15-17 are placed in side-by-side relationship and together cover essentially the full length of the moulds 20, each of the hoods having a much smaller width than the length of the mould.

When in operation, the arrangement illustrated in Fig. 9 will thus lay three profiled part-bodies 21-23 in each mould 20, these bodies being juxtaposed and therewith forming together a complete absorbent body. In this case, harmful cross-flowε in the fibre layer laid beneath the hood 15 are prevented by virtue of the surrounding air, which in this case is com¬ prised of a stream of air-carried fibres, having free access to those regions of the mould bottom that extend transversely outwardly of the mould bottom.

The central part-body 22, which is located in the wet region of the combined absorbent body thus formed, is conveniently comprised of a type of fibre which will provide good liquid abεorbency, e.g. CTMP or croεε-linked cellulose fibres, whereas the outer part-bodies 21 and 23 will conveniently be comprised of a type of fibre which provides good liquid dispersion properties, for instance chemical pulp. Thus, the embodiment illustrated in Figs. 9 and 10 enables absorbent bodies having desired properties with regard to liquid absorbency, liquid dispersion and liquid storage in a simple and effective manner. It is also possible to admix different quantities of superabsorbents in different partε of the absorbent body in a simple manner.

It will be understood that the described and illustrated embodiments can be modified in many ways within the scope of the invention. For instance, additional mat-forming hoods can be arranged adjacent the hoods illustrated in Figs. 1, 4, 7 and 9. Furthermore, the hoods whose widths are smaller than the lengths of the moulds need not be placed centrally, but may be displaced transversely in one direction or the other and several such hoods may be placed adjacent one another. The embodiment illustrated in Figs. 7 and 8 can be combined with one of the remaining two embodiments, for instance by providing the hood 10 with a part having converging or diverging side walls. This also applies to the embodiment illustrated in Figs. 9 and 10. For instance the hoodε 16 and 17 may have converging outer walls. It will also be under¬ stood that the invention can also be applied to continuously moving parts other than mat-forming cylinders, for instance a moving linear air-permeable conveyor path. The moulds may alternatively be disposed with their longitudinal axes in the movement direction, therewith producing transversely profiled fibre bodies. The invention iε therefore only restricted by the content of the following Claims.

Claims

1. An arrangement for air-laying on a moving air-permeable conveyor path (2; 7; 12; 20) fibre bodies that have a profiled cross-section transversely to the movement direction (A) of said conveyor path, wherein the arrangement includes at least one air-laying unit having means for delivering a stream of air-carried fibres to a region above the moving conveyor path; means (3; 8; 13, 14; 19) for subjecting the stream of air-carried fibres in said delivery region to a subpressure beneath the whole of that part of the conveyor path located in said delivery region; and means (4; 5; 9, 10; 15, 16, 17) for delimiting the stream of air-carried fibres from ambient air, characterized in that the means for delimiting the stream of air-carried fibres includes at least one part (b; 9; 15, 16, 17) which coacts with the air- permeable conveyor path and which has smaller dimensions transversely to the direction of movement than the air- permeable conveyor path.

2. An arrangement according to Claim 1, in which the moving conveyor path comprises a succession of moulds (2; 7; 12; 20) having air-permeable bottoms and disposed sequentially in said movement direction, and in which the means for deli it- ing the stream of air-carried fibres comprises at leaεt one first mat-forming hood (4; 5; 9; 15) which coacts with a vacuum box that extends transversely over the entire mould, characterized in that at least one part of the first mat- forming hood extends transversely relative to said movement direction across a part of the bottom of the by-passing moulds; and in that the ambient air has free access to those regions of the mould bottomε that extend transversely beyond the mat-forming hood.

3. An arrangement according to Claim 2, characterized by a second mat-forming hood (10) which is mounted upstream of the first hood (9) as seen in said movement direction and which extendε tranεverεely across essentially the entire bottom of the by-passing moulds (12).

4. An arrangement according to Claim 2, characterized in that the first mat-forming hood (5) includes a part (b) that has side walls which diverge in said movement direction.

5. An arrangement according to Claim 2, characterized in that the first mat-forming hood (4) includes a part (b) that haε εide walls which converge in said movement direction.

6. An arrangement according to Claim 2, characterized in that several mat-forming hoods (15, 16, 17) having trans¬ versely a smaller extension than the bottom of the mould (20) are disposed in side-by-εide relationship.

7. An arrangement according to any one of Claims 2-6, characterized in that the succession of moulds (2; 7; 12) is disposed around the periphery of a mat-forming cylinder (1; 6; 11).