GB2260906A - Process for the manufacture of disposable nappies - Google Patents

Abstract

Disposable nappies are made by forming a fibre mat from chopped wood pulp fibres incorporating a set amount of superabsorbent powder, wrapping the mat between layers of tissue, embossing the mat with desired shapes which are then separated, applying stretched elastic threads to each side of a liquid impermeable backing sheet, placing a shaped mat onto the backing and overlaying it with a permeable top sheet which is then adhered to the periphery of the backing sheet and applying adhesive fastening tabs/tape to the nappy. To form the fibre mat 19 sheets of wood pulp are sprayed with water prior to being chopped and the chopped fibres are deposited onto a rotating endless perforated bronze carpet 18 by means of a vacuum. The superabsorbent powder is sprayed onto the mat during formation thereof by a spray head 21 which can be adjusted relative to carpet 18 to control deposition of the powder. <IMAGE>

Description

"Disposable Nappy Manufacturing Process" This invention relates to a process for manufacturing disposable nappies.

It is known to provide disposable nappies comprising a wood fibre mat containing a superabsorbent powder, the mat sandwiched between an upper permeable sheet and a lower impermeable sheet. A number of difficulties arise in the manufacture of such disposable nappies. During the manufacturing process the fibre mat tends to dry out resulting in a more compact and less supple mat. The quality of the product therefore varies depending upon the amount of moisture lost from the mat.

When applying the superabsorbent powder to the mat it is important to have an even dispersion of the powder within the mat for optimum effectiveness of the superabsorbent powder in use.

The present invention is directed towards providing an improved process for manufacturing a disposable nappy.

According to the invention there is provided a process for manufacturing a disposable nappy, comprising the steps: (a) delivering a sheet of wood pulp from a supply roll to a milling machine, (b) chopping the sheet into pulp fibres in the milling machine, (c) forming a fibre mat from the pulp fibres incorporating a preset quantity of a superabsorbent powder, (d) wrapping the fibre mat between two layers of tissue, (e) embossing the fibre mat with desired nappy mat shapes and cutting the mat to separate the preformed shaped nappy mats, (f) applying a number of stretched elastic threads to each side of a liquid impermeable backing sheet, (g) mounting a nappy mat on the backing sheet and overlying the nappy mat with a permeable top sheet adhered to the backing sheet around a periphery of the sheet, thus forming a nappy, (h) applying adhesive fastening tabs to a rear end of the nappy and applying an adhesive tape to a front end of the nappy, and (i) folding and packing of the nappies.

In one embodiment of the invention the process includes the step of delivering the sheet of wood pulp through a humidifier prior to chopping the sheet, and spraying a controlled amount of water onto the sheet within the humidifier.

In one embodiment the water spray is regulated in response to ambient temperature and humidity conditions.

In another embodiment the water spray is controlled in response to the size of the nappy being manufactured.

In a further embodiment the water spray is controlled in response to the speed of the apparatus used for the nappy manufacture.

In another embodiment the fibre mat is formed by depositing the pulp fibres on a conveyer by means of a vacuum, and the superabsorbent powder is sprayed onto the mat during formation of the mat.

In a further embodiment the process includes the step of adjusting the position of spraying means for the superabsorbent powder spray relative to the conveyer to control the position of the superabsorbent powder deposited in the fibre mat.

In a particularly preferred embodiment the process includes the step of spraying a primary layer of superabsorbent powder onto the mat extending across the mat and a secondary layer of superabsorbent powder above the primary layer, the secondary layer only covering a preset portion of the mat.

In a further embodiment the process includes leading the adhesive tape from a supply reel around a peel-off roller which abuts the reel where the tape is parted away from the reel to a cutter and cutting the tape into bands of the required size for application to the nappy body.

Preferably the adhesive tape is a polypropylene tape and the process includes the step of regulating the temperature of the tape.

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic diagram of a nappy manufacturing process and apparatus according to the invention, Fig. 2 is a diagrammatic illustration of a humidifier forming portion of the apparatus, Fig. 3 is a side view of portion of the apparatus used to form a fibre mat, Fig. 4 is a perspective view of a fibre mat formed by the process, Fig. 5 is a detail cross-sectional view of the fibre mat, Fig. 6 is a diagrammatic illustration of another portion of the apparatus for carrying out the process, Fig. 7 is a detail side diagrammatic elevational view of another portion of the apparatus for applying fastening tabs to the nappies, Fig. 8 is a perspective view of a partially complete nappy formed by the process, Fig. 9 is a detail diagrammatic side view of another portion of the apparatus for applying an adhesive waistband tape to each nappy, and Fig. 10 is a perspective view of a completed nappy formed by the process.

Referring to the drawings the process of the invention will now be described. A pair of sheets of wood pulp 10 are delivered from supply rolls 11 through a humidifier 12 (Fig.

2). The humidifier 12 has a housing through which the sheets 10 are passed. A spray bar 13 is located within the housing, the sheets 10 being passed on either side of the spray bar 13 which sprays water onto the sheets 10. The quantity of water sprayed onto the sheets 10 is controlled according to the nappy size, the speed at which the nappy manufacturing apparatus is working and the ambient temperature and humidity of the workplace. Typically the pulp sheets 10 entering the humidifier 12 have a moisture content in the order of 6% by weight. During nappy manufacture this moisture content may be reduced to 2 - 4%. Sufficient water is added in the humidifier 12 to ensure that the moisture content of the pulp in finished nappies is in the order of 5 - 8%. However, it is important not to wet the sheets 10 too much, otherwise the pulp will not de-fiberise.

Downstream of the humidifier 12 the fibre sheets 10 are chopped in a mill 15 into pulp fibres. Pulp fibres are discharged from the milling machine 15 through a mesh to limit fibre size into a chamber 16 in which the fibres are deposited on a vertical rotating bronze carpet 18 to form a fibre mat 19. The bronze carpet 18 has a perforated surface and a vacuum is applied behind the bronze carpet 18 which attracts the fibres onto the carpet 18 to form the mat 19. A superabsorbent powder, typically a polyacrylic polymer, is incorporated in the mat 19 by means of a powder spraying apparatus 20 having an adjustable spray head 21. As shown in broken outline in Fig. 3 the spray head 21 can be moved towards or away from the mat 19 or up and down relative to the surface of the mat 19. In this way the area of the mat covered by powder can be controlled and the depth of the superabsorbent powder within the fibre mat 19 is also controlled. Fig. 5 shows the fibre mat 19 having a top surface 25 and a bottom surface 26. A layer 27 of the superabsorbent powder is formed by the spray apparatus 20 intermediate at the top surface 25 and bottom surface 26. By moving the spray head 21 vertically the position of this powder layer 27 within the mat 19 can be readily easily controlled.

In some cases a second layer of superabsorbent powder may be incorporated in the mat 19. In this case a second spray head (not shown) is mounted above the spray head 21 to apply a secondary layer of superabsorbent powder within the mat 19 above the layer 27. The secondary layer would only cover a preset desirable portion of the mat 19 for giving added absorbency in a particular area of the nappy. For example the secondary layer would be applied such that it would be located in a front portion of the nappies where the nappies are intended for boys and in a central portion of the nappy where the nappies are intended for girls.

Although not illustrated, as an alternative method for incorporating the superabsorbent powder within the mat, the superabsorbent powder and pulp may be thoroughly mixed and then be deposited in a mould shaped to a desired nappy size thus moulding the mat. This allows a good even distribution of the superabsorbent powder within the mat to be achieved.

The mat 19 formed is conveyed to a wrapping station 30 in which the mat 19 is wrapped between two layers of tissue.

Downstream of the wrapping station 30 embossing 32 is carried out by passing the mat between embossing rollers 33 which emboss the mat 19. The mat 19 then passes through a rotary die which cuts the mat 19 into the desired nappy shape as shown at 34 in Fig. 1. This embossed mat is then cut to form individual shaped nappy mats 36.

Each shaped nappy mat 36 is then laid on a waterproof plastics outer backing sheet 40 (see Fig. 6). A number of stretched lycra threads 41 are applied along each side of the backing sheet 40 prior to mounting the nappy mat 36 on the backing sheet 40. An inner liquid permeable sheet 43 is then applied over the nappy mat 36 and adhered around its periphery to the backing sheet 40 thus sandwiching the nappy mat 36 between the inner sheet 43 and outer sheet 40 thus forming a nappy body 44 with elasticated side leg portions.

The lycra threads 41 may in some cases be dyed prior to application to the backing sheet 40 for colour coding of the nappy. In this case the threads 41 are led from spools 46 through a dye bath 47 containing dye 48. Each thread 41 is passed around rollers 49 within the dye 48 and then passed around a number of rollers 50 above the dye bath 47 to remove excess dye which is collected by the dye bath 47. It will be noted that the rollers 50 are arranged such that each thread 41 is taken through a number of sharp turns which advantageously ensures that the thread 41 throws off any excess dye. Although not shown the dye bath 47 would normally have a spray cover to return spray thrown off by the rollers 50 to the dye bath 47.

Referring now in particular to Figs. 7 and 8. The nappy body 44 then has adhesive fastening tabs 52 attached to a rear end 53 of the nappy body 44. Adhesive tape 54 from a supply roll (not shown) is cut by a chilled cutting blade 56 on a rotatable support 57 which carries the tabs 52 upwardly and presses them against the rear end 53 of the nappy 44. The tabs 52 are then folded inwardly as indicated by the arrows in Fig. 8. Advantageously as the blade 56 is chilled the tabs 52 do not adhere to the support 57 and are easily transferred and stuck to the nappy body 44.

Referring now to Figs 9 and 10. An adhesive waistband 60 is applied to the outer sheet 40 at a front end 61 of the nappy body 44. The band 60 forms a landing area for the fastening tabs 52. This band 60 is cut from adhesive tape 62 led from a supply reel 63 to a cutter 64 having a blade 65 which cuts the tape into bands 60 of the required size for subsequent application to the nappy body 44. The tape is of polypropylene which is relatively brittle and in cold conditions difficulty can arise due to the tape braking as it is peeled off the supply roll 63. To overcome this problem an infra-red lamp 66 is advantageously provided which preheats the tape 62 to a suitable temperature for optimum handling prior to peeling the tape 62 off the roll 63.

As the tape adhesive is relatively strong it tends to peel away from the roll 63 with a jerky motion. This can result in the tape 62 snapping. This adversely affects production which has to be stopped until tape is again fed through the machine to the cutter 64. To overcome this problem a peel-off roller 67 is biased against the tape 62 on the roll 63 at the point where it is peeled off the roll 63. This advantageously ensures a smooth peel off of tape 62 from the roll 63.

The completed nappy is then folded and packed at folding stations 68 and packing stations 69.

It will be appreciated that the process according to the invention advantageously allows close control of nappy quality over a range of operating conditions. Further smooth and reliable operation of the apparatus for carrying out the process can be achieved.

The invention is not limited to the embodiment hereinbefore described which may be varied in both construction and detail.

Claims (12)

1. A process for manufacturing a disposable nappy, comprising the steps: (a) delivering a sheet of wood pulp from a supply roll to a milling machine, (b) chopping the sheet into pulp fibres in the milling machine, (c) forming a fibre mat from the pulp fibres incorporating a preset quantity of a superabsorbent powder, (d) wrapping the fibre mat between two layers of tissue, (e) embossing the fibre mat with desired nappy mat shapes, and cutting the mat to separate the pre formed shaped nappy mats, (f) applying a number of stretched elastic threads to each side of a liquid impermeable backing sheet, (g) mounting a nappy mat on the backing sheet and overlying the nappy mat with a permeable top sheet adhered to the backing sheet around a periphery of the sheet, thus forming a nappy body, (h) applying adhesive fastening tabs to a rear end of the nappy body and applying an adhesive tape to a front end of the nappy body to complete the nappy, and (i) folding and packing the nappy.

2. A process as claimed in claim 1 including the step of delivering the sheet of wood pulp through a humidifier prior to chopping the sheet, and spraying a controlled amount of water onto the sheet within the humidifier.

3. A process as claimed in claim 2 wherein the water spray is regulated in response to ambient temperature and humidity conditions.

4. A process as claimed in claim 2 or claim 3 wherein the water spray is controlled in response to the size of nappy being manufactured.

5. A process as claimed in any of claims 2 to 4 wherein the water spray is controlled in response to the speed of the apparatus used for the nappy manufacture.

6. A process as claimed in any preceding claim wherein the fibre mat is formed by depositing the pulp fibres on a conveyer by means of a vacuum, and the superabsorbent powder is sprayed onto the mat during formation of the mat.

7. A process as claimed in claim 6 including the step of adjusting the position of spraying means for the superabsorbent powder spray relative to the conveyor to control the position of the superabsorbent powder deposited within the fibre mat.

8. A process as claimed in claim 6 or 7 including the step of spraying a primary layer of superabsorbent powder onto the mat extending across the mat and a secondary layer of superabsorbent powder above the primary layer, the secondary layer only covering a preset portion of the mat.

9. A process as claimed in any preceding claim wherein the process includes leading the adhesive tape from a supply reel around a peel-off roller which abuts the reel where the tape is parted away from the reel, to a cutter and cutting the tape into bands of the required size for application to the nappy body.

10. A process as claimed in any preceding claim wherein the adhesive tape is a polypropylene tape and the process includes the step of regulating the temperature of the tape to within a preset temperature range.

11. A process substantially as hereinbefore described with reference to the accompanying drawings.

12. A disposable nappy whenever manufactured according to the process of any preceding claim.