Absorbent nonwoven fabric and its production

Paper making and fiber liberation – Processes and products – Utilizing non-aqueous suspending medium

Patent

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Details

162146, 1621574, D21H 1312

Patent

active

056075502

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a wet-laid nonwoven fabric useful in absorbent products such as diapers, incontinence pads, sanitary napkins and tampons and in wiping materials for mopping up spills of aqueous fluids. A wet-laid nonwoven fabric is a fabric comprising fibres which have been deposited from an aqueous suspension of fibres.


BACKGROUND ART

EP-A-437816 discloses a nonwoven wet-laid superabsorbent material produced by the process of blending superabsorbent polymer particles with a liquid to form a slurry, mixing fibres with that slurry, filtering that slurry/fibre mixture to remove a portion of the liquid and drying the superabsorbent slurry/fibre mixture to form a nonwoven wet-laid superabsorbent material.
EP-A-359615 discloses a method for the manufacture of a superabsorbent fibrous structure in which a dry solid absorbent is applied directly to a wet-laid web of cellulosic fibres prior to drying the wet web.
EP-A-273075 discloses a high water-absorbency paper made by sheeting a mixture of wood pulp fibre, water-soluble resin and high water-absorbency resin.
Absorbent products such as diapers which include particles of a superabsorbent polymer such as crosslinked sodium polyacrylate disposed between layers of wood pulp are known for example from EP-A-257951.


DISCLOSURE OF INVENTION

A wet-laid nonwoven fabric according to the invention comprises a blend of 1 to 50% by weight of fibres of a water-swellable water-insoluble superabsorbent polymer and 99 to 50% by weight of less absorbent fibres, for example fibres having an absorbency of less than 10 g/g measured by retention to centrifuging of a 0.9% by weight saline solution.
In a process according to the invention for the production of a wet-laid nonwoven fabric, fibres of a water-swellable water-insoluble superabsorbent polymer and less absorbent fibres, for example fibres having an absorbency of less than 10 g/g as measured above, are slurried together in water, the slurry is deposited as a layer on a foraminous support so that part of the water drains from the layer of slurry on the support, and the resulting fibrous layer is dried to form the nonwoven fabric.
The use of fibres of the water-swellable water-insoluble superabsorbent polymer, rather than the same polymer in particulate form, has significant advantages in many respects. The superabsorbent polymer fibres are more securely retained both during formation of the wet-laid nonwoven fabric and when the fabric is in use as an absorbent product. Uniform dispersion of the superabsorbent polymer is facilitated. The superabsorbent polymer fibres become part of the fibrous structure of the nonwoven fabric and contribute towards its cohesive strength, whereas the presence of superabsorbent polymer particles reduces the strength of the nonwoven fabric.
The absorbency of fibres can be measured by the free swell test, in which 0.5 g fibre is dispersed in 30 ml aqueous liquid and left for 5 minutes. The aqueous liquid used is generally 0.9% by weight saline solution, which is generally absorbed to a extent similar to body fluids such as urine. The test can alternatively be carried out with either tap water or demineralised water. For all absorbency measurements, the fibre is conditioned at 65% relative humidity and 20.degree. C. before being tested. The dispersion is then filtered through a sintered Mark 1 funnel of pore size 100-160 microns and is left for 5 minutes or until it stops dripping, whichever is the longer. The amount of aqueous liquid filtered through the funnel is weighed and the weight of aqueous liquid absorbed by the fibres is calculated by subtraction. A superabsorbent polymer is one having an absorbency of at least 20 g/g in the free swell absorbency test using 0.9% by weight saline solution. Usually, superabsorbent polymers have an absorbency in the range 30-60 g/g in this test.
In addition to the above test, the retention by the fibre or filament of the aqueous liquid (such as saline solution) after application of pressure can be measured in a retention test b

REFERENCES:
patent: 3826711 (1974-07-01), Scitoggen et al.
patent: 4552618 (1985-11-01), Kopolow
patent: 4654039 (1987-03-01), Brandt et al.
patent: 4655877 (1987-04-01), Horimoto et al.
patent: 4808266 (1989-02-01), Faurie
patent: 4986882 (1991-01-01), Mackey et al.
patent: 5147343 (1992-09-01), Kellenberger

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