Surgery – Means and methods for collecting body fluids or waste material – Absorbent pad for external or internal application and...
Reexamination Certificate
1996-03-07
2001-02-27
Weiss, John G. (Department: 3761)
Surgery
Means and methods for collecting body fluids or waste material
Absorbent pad for external or internal application and...
C604S368000, C604S370000, C156S308200, C156S309900, C428S372000, C442S170000, C442S171000, C442S417000
Reexamination Certificate
active
06194630
ABSTRACT:
TECHNICAL FIELD
The present invention relates to superabsorbent fibres or non-woven materials in which particles of superabsorbent material have been bonded to individual fibres. The invention also relates to a method of producing the superabsorbent fibres or nonwoven material concerned, and to absorbent articles that contain the same.
BACKGROUND ART
It is known to admix particles of water-insoluble hydrogels, so-called superabsorbents, in fibre structures for absorption purposes, for instance absorbent bodies in diapers, sanitary napkins, incontinence guards, wound dressings etc. These superabsorbents are polymeric materials that are capable of absorbing large quantities of liquid. One problem encountered when mixing superabsorbents in fibre structures is to fix the superabsorbent particles in the structure so as to localize the superabsorbent in the correct position in the product, and so that the product can be handled in manufacture and during transportation without the superabsorbent being redistributed in the product or shaken from the fibre structure. Dusting caused by fine-grain superabsorbents can also lead to an environmental problem at the place of manufacture.
Several methods of adhering superabsorbent to fibres are known to the art. According to one method described in U.S. Pat. No. 4,354,487 and EP-A-0,402,650, a monomeric solution is allowed to infiltrate a fibre network or is mixed with free fibres. The monomers are then allowed to polymerize in place on the fibres. Prior publication U.S. Pat. No. 4,888,238 describes a method in which dissolved polyelectrolytes form complex bonds on the fibres. According to another method, described in U.S. Pat. No. 4,128,692, fibres are first suspended in water and the superabsorbent is then added and precipitates onto the fibres. In all of the aforesaid cases it is necessary to evaporate-off the solvent, i.e. the water, in one way or another, after having bound the superabsorbent to the fibres. This is difficult to achieve when the water is bonded firmly to the superabsorbent.
According to another method, described in U.S. Pat. No. 4,721,647, a water-soluble monomer having double bonds is allowed to form droplets around a hydrophobic fibre, these droplets being allowed to polymerize and form cross-links. The underlying concept is that the superabsorbent shall embrace the fibre so as not to be released when absorbing liquid. According to the measurements reported in said patent, less than 20% by weight of the superabsorbents are released in the process of absorption. It is also mentioned in the patent that the absorbent droplets should not be applied too densely, since this would stiffen the fibres.
Another method of adhering superabsorbents to fibres is described in WO 90/11181 and WO 91/10413, according to which fibres are coated with a binder which binds to superabsorbent particles. The binder may consist of an ethylene vinyl acetate copolymer, ethylene acrylic acid copolymer, polyvinyl chloride or some other thermosetting resin, for instance. The binder is sprayed onto the fibres a number of times, so as to effectively cover the fibre surfaces. Absorbent grains are then applied to the fibres before the binder has set. Between 15 and 50 % by weight of the absorbents, based on the dry fibre weight, are bonded when practicing this method, which is about equal to the amount of superabsorbents that is effectively bonded when practicing the other methods aforesaid.
U.S. Pat. No. 5,002,814 discloses another solution to the problem, in which a particle of a superabsorbent polymer has been bound to several short fibres.
SUMMARY OF THE INVENTION
The object of the present invention is to bind superabsorbent particles directly to essentially all surfaces of individual fibres so that distribution of the superabsorbents in a fibre structure can be better controlled. Adhesion between superabsorbent and fibre should preferably be relatively low or weak, so as not to limit to any great extent the swelling space that is available to the superabsorbents when absorbing liquid. Binding of the superabsorbent particles to the fibres shall also be effected without the aid of a solvent that must later be evaporated off, and also while avoiding the application of binder to the fibre.
This object has been achieved in accordance with the invention in that the individual fibre or at least a part of the individual fibres present in the nonwoven material is comprised of a thermoplastic polymer fibre to which solid particles of superabsorbent material have been directly thermobonded by heating said fibre to a temperature at which adhesion between fibre and particles is achieved.
Synthetic fibres may be fully crystalline, i.e. contain 100% crystalline material, although they may alternatively contain varying percentages of crystalline material. A high degree of stretching in connection with manufacturing the fibre will produce a high proportion of crystalline material. Partially crystalline fibres (0-40%) are preferably used in accordance with the invention, such fibres providing good adhesion at low temperatures. One speaks about the softening temperature or glass transition temperature (T
g
) in the case of amorphous fibres.
In the case of fibres that are part crystalline and part amorphous, the amorphous material will be soft at temperatures between the softening temperature and the crystalline melting point, whereas the crystalline material will still be hard. There is thus obtained a certain degree of adhesion, which improves, however, when the crystalline melting point is exceeded.
When the thermoplastic fibre consists of a crystalline or partly crystalline fibre, the crystalline melting point of the fibre will suitably not be higher than 300° C., and preferably not higher than 270° C. When the thermoplastic fibre is an amorphous fibre, its softening or glass transition temperature will preferably not be higher than 100° C.
The fibre may be comprised, for instance, of a polyolefin, such as polyethylene or polypropylene, polyester, polyamide, bicomponent fibre, or a copolymer of ethylene and acrylic/methacrylic acid or ethylene and vinyl acetate.
The superabsorbent particles will suitably have a mean particle size of up to 500 &mgr;m.
The invention also relates to a method of producing the superabsorbent fibre or nonwoven material concerned, this method being characterized by bringing solid particles of superabsorbent material directly into contact with essentially all surfaces of an individual thermoplastic polymeric fibre or a nonwoven material which includes thermoplastic polymeric fibres, said fibre being heated or having been heated to a temperature at which the superabsorbent particle adheres directly to the individual fibre, and thereafter allowing the mixture to cool.
The invention also relates to an absorbent article, such as a diaper, sanitary napkin, incontinence guard and the like, which is characterized in that the article has at least one absorbent layer which includes superabsorbent fibres or nonwoven material according to the invention, optionally in combination with other fibres, such as cellulose fibres.
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Canbäck Göran
Chihani Thami
Hjertberg Thomas
Wecke Urban
Burns Doane Swecker & Mathis L.L.P.
Reichle K. M.
SCA Hygiene Products Aktiebolag
Weiss John G.
LandOfFree
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