Surgery – Means and methods for collecting body fluids or waste material – Absorbent pad for external or internal application and...
Reexamination Certificate
1998-08-11
2002-06-18
Weiss, John G. (Department: 3761)
Surgery
Means and methods for collecting body fluids or waste material
Absorbent pad for external or internal application and...
C604S366000, C604S378000, C442S409000, C442S411000, C442S413000, C442S416000, C428S298100, C428S299700, C428S300400, C428S311710
Reexamination Certificate
active
06407309
ABSTRACT:
The present invention relates to a method of producing an absorbent sheet or web material by the dry forming of a layer of short cellulose fibres in admixture with relatively long, thermoplastic binding fibres which are actuated by heating. Products of this type are typically used as absorbent inserts in sanitary articles, e,g. in sanitary napkins for women, With respect to both production price and absorption capacity it is desirable to use a relatively low degree of admixture of the binding fibres, normally some 15%, but in return the problem arises that the products “dust” with the short fibres, which may amount to a serious problem, in particular in relevant further processing operations. In principle, it is possible to avoid the dusting by applying a bonding substance onto the product surfaces, but this will complicate the manufacturing and make the products more expensive.
With the invention it has surprisingly been found that it is possible to achieve an inexpensably obtained surface sealing which will effectively prevent any noticeable dusting from the products. To this end, the production is arranged such that a laminated product is built up, comprising a first, very thin layer of pure binding fibres, e.g. with an amount of only some 3 g/m
2
and thus with a rather open structure conditioning a good penetration of liquid, a following layer of a fibre mixture of short cellulose fibres and longer binding fibres, though preferably with a reduced content of binding fibres, e.g. with a ratio of 93:7 or 95:5 of cellulose and binding fibres, respectively, and a final top layer corresponding to the thin layer of binding fibres as first laid out. The product thus shaped is passed through a heating zone for actuation of the binding fibres generally in the entire laminated product.
The low content of binding fibres in the middle layer may result in a delamination in small areas of the product in response to folding. This can be avoided by calandering the product in a heated calander such that top and bottom layers of the product are welded together, though only over 5-20% of the surface, preferably about 10%.
With an amount of binding fibres of only 1-5 g/m
2
in the outer layers, preferably 2-4 g/m
2
, it is easily understood that these layers will be readily liquid permeable, as the open surface area will amount to 80-90%. On the other hand, it is partly inexplainable how the same limited fibre coating can effect a marked reduction or almost total elimination of the dusting of short fibres from the products. However, both laboratory tests and test productions have verified that this effect with respect to dust binding is indeed achieved.
In connection with the invention it has been found, surprisingly, that the very thin surface layers' provide for a marked increase of the tensile strength of the products, by as much as 3-4 times, and that the surface wear strength of the material is also considerably increased. From a quality point of view the material is hereby upgraded from an absorbent insert material, which requires a surface protecting layer, to a self contained product that is usable e.g. for cleaning purposes domestically and in the industry, while still having a low content of binding fibres of only some 15% or less.
From U.S. Pat. No. 4,054,141 it is known to produce relatively thick pad members with a core layer of absorption fibres and with surface layers consisting of a mixture of these fibres and binding fibres. The surface layers are in no way “thin” layers with binding fibres oriented mainly in the plane of the surface, as to the contrary it is emphasized that a large part of the fibres project inwardly in or from the surface so as to enable an easier penetration of liquid and a certain cohesion in the outer layer. Thus, the the relatively thick core layer is not internally bonded, whereby it will easily delaminate, and for the formation of the surface layers it will be necessary to use a considerable amount of binding fibres, which will only partially be active as a coherent, liquid permeable surface, It is well thinkable that in some way, not further specified, it is possible to achieve a certain surface barrier effect against extrusion of the non-bonded, short fibres in the core layer, but then only with a rather large concentration of binding fibres in a surface layer of noticeable thickness.
Moreover, the relatively large amount of binding fibres with this known method will, not result in the said surprising increase of product strength, inasfar as this increase has to be connected with the fact that the binding fibres are present in a thin layer with the fibres oriented in the surface plane itself; fibres projecting inwardly from the surface cannot contribute to a strength increase and not either to a e barring against extruding short fibre dust, which is an established problem in connection with aftertreatment of the is products.
The method known from the said U.S. Pat. No. 4,054,141 is based on a cell filling of special moulds for forming shaped, limited pad mambers, while the present invention is based on a production of a relatively thin web material which can be manufactured with much higher capacity and can be folded or pleaded. into a plural layer shape and then be cut to form pad members consisting of tore layers. The web or sheet material, of course, also finds many other possibilities of application.
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Bogart Michael
Browdy and Neimark , P.L.L.C.
Scan-Web I/S
Weiss John G.
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