Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Bulk deposition of particles by differential fluid pressure
Patent
1997-05-27
1999-03-23
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Bulk deposition of particles by differential fluid pressure
264510, 264113, 425 811, 425 831, B27N 304, D21H 2742
Patent
active
058855165
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the production of air-laid paper webs containing a liquid super absorbing powder. The basic material in such webs is cellulose fibres, though normally with a certain content of heat activated synthetic fibres for bonding of the laid out web, and it is well known that such a fibrous material may also contain super absorbing fibres evenly distributed in the web.
However, in particular for economical reasons it is desirable to use the said powder, also known as SAP, instead of the absorbing fibres, but it is much more difficult to achieve a reasonably homogenous admixture of the SAP in the web material.
It is well known that with different prior art laying techniques it is possible to produce an absorbing web material on a moved wire passing a first distributor head for laying out a bottom web layer on the wire, then passing a powder dispenser laying out a SAP layer on the bottom web layer, and then passing another distributor head operating to lay out an upper top web layer. However, the SAP particles are not really bonded in the web material, which dusts heavily during the further processing, whilst also the final absorbing products exhibit strong tendencies to delamination.
On this background it is also known that instead it should be endeavoured to mix the SAP material into the fibre material, and to this end it has been a natural measure to add the powder to the flow of the air fluidised fibre material supplied to the distributor head, normally from a hammer mill in which a dry pulp material is desintegrated. This may result in an efficient admixing due to high turbulence in the air, but it has nevertheless been necessary to accept a noticeable inhomogeneity in the final product, all according to the applied airlaying technique. Thus, by a concentrated supply of the fibre/SAP/air flow down into a distributor head having means for agitating and distributing of the material over a classification screen above the forming wire, there may be found a higher SAP concentration underneath the flow supply area than at the periphery; in the web product, this gives rise to a formation of stripes with mutually different SAP concentrations, and if the SAP is dosed at such high rate that a desired concentration is obtained in the peripheral areas, then dusting may occur from the more concentrated zone or zones, which is inconvenient and loss giving, and also for other reasons a higher concentration can be directly undesired.
At its outset, the invention is based on another airlaying technique than indicated above, viz. of the type disclosed in EP-B-0,032,772. This is a technique which, among experts, is recognised as highly characteristic for the present applicant. It is advantageous by a high production capacity and evenness of the formed web, but it has been noted that there are problems with respect to achieving a homogenous admixture of the absorbing powder in the fibre material as laid out on the production wire.
The technique in question is particularly relevant for the production of relatively large web widths, e.g. in the range of 50-300 cm, so for the production of narrower, absorbing pad products it is actual to cut the web into stripes, rendering such a production more economical than the forming of single webs with the required width or widths.
However, it is then critical to obtain a high degree of evenness of the SAP distribution across the width of the web, as the web stripes will otherwise be non-uniform.
The discussed technique is based on the air fluidized fibres being moved in an air flow across the forming wire inside a perforated, rotating drum pipe and back again through another, corresponding drum pipe, whereby this set of drum pipes constitutes a forming head, from which the fibres are brought out into a space, in or through which, as conventionally, an air flow is drawn downwardly by the action of a suction fan connected to a suction box beneath the foraminous wire. The flow of fibres thus leaving the drum pipes will have a certain movement component transversel
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patent: 5429788 (1995-07-01), Ribble et al.
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patent: 5558832 (1996-09-01), Noel et al.
Scan-Web I/S
Theisen Mary Lynn
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