Stock material or miscellaneous articles – Sheet including cover or casing
Patent
1985-01-23
1986-08-19
Van Balen, William J.
Stock material or miscellaneous articles
Sheet including cover or casing
428 76, 428166, 428178, 4283166, 428409, B32B 100, B32B 300
Patent
active
046069585
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a highly absorbent article that can be used to take up large volumes of aqueous liquids, including electrolytes. The article, which comprises a substrate carrying a highly absorbent polymeric material, is especially suitable for wiping surfaces, for example, in the home or in industry, to remove unwanted liquid.
EP 68 830 (Unilever) discloses inter alia an article for absorbing a liquid, in the form of a substrate carrying a pressure-sensitive porous polymeric material capable of retaining at least 5 times its own weight, defined in terms of water, of liquid. In a preferred embodiment of that invention, the porous polymer is the polymerisation product of a high internal phase emulsion, and is advantageously a styrene polymer. Polymers of this type have a high void volume and the void structure of the polymers may be used to hold liquids. They will spontaneously take up large volumes of hydrophobic liquids, for example, oils, and will retain them until external pressure is applied. They do not have a similar affinity for hydrophilic liquids, but can be filled under vacuum with such liquids, for example, water and some cleaning fluids, and will retain them within the void system of the polymer. On squeezing, liquid is expressed, but when the squeezing pressure is relaxed no significant immediate reabsorption of liquid takes place.
So-called "superabsorbent" materials that will spontaneously take up large volumes of water and some other hydrophilic liquids are also known. These are often modified polysaccharides, especially modified starches or celluloses. Examples of such materials include Spenco Absorption Flakes, ex Spenco Medical; SGP 147 ex Henkel; and Favor SAB Superabsorbent ex Stockhausen. Materials of this type are widely used in the medical art for the absorption of body fluids, for example, in sanitary towels, incontinence pads and wound dressings. In this context these materials may be carried in, on or between sheets or pads of nonwoven fabric or other suitable material. WO 80/01455 (Beghin-Say) and SE 81 05800 (Landstingens Inkopcentral LIC) are exemplary publications in this area.
In general superabsorbent materials of this type rely on chemisorption and thus suffer from the disadvantage that they are to some extent deactivated by the presence of electrolyte. While at low ionic strengths they will take up large volumes of liquid, the absorptive capacity falls deeply as the ionic strength rises. For example, GB 1 236 313 discloses a crosslinked cellulosic material, for absorbing body fluids, which can absorb up to 30 times its own weight of water but no more than 12 times its own weight of a 1% sodium chloride solution.
Furthermore, these materials retain absorbed liquids strongly and liquid cannot be released simply by applying hand pressure or the like. While this is obviously essential in the medical context, for household use such as the mopping up of spilt liquids it would be more useful to be able to squeeze out the absorbed liquid prior to a further wiping-up operation.
It has now been discovered that an article can be made that will rapidly and spontaneously take up large volumes of hydrophilic liquids even at high ionic strengths, will release liquid when hand pressure is applied, and will reabsorb liquid when pressure is released. The article of the invention may be used for repeatedly absorbing and expelling liquids, and can be used to dry a surface effectively. Furthermore, an article of the invention may be preloaded with a useful hydrophilic treatment liquid and used as a medium for delivering such a liquid in a controlled manner.
The present invention has been made possible by the discovery of a porous polymeric material that will rapidly, reversibly and spontaneously take up large volumes of hydrophilic liquid, even at high ionic strengths, and will retain the liquid against normal gravitational forces, yet will release liquid in a controlled manner when squeezed. This material, when supported and enclosed by a suitable substrate material, may for
REFERENCES:
patent: 4473611 (1984-09-01), Haq
patent: 4522953 (1985-06-01), Barby et al.
patent: 4536521 (1985-08-01), Haq
Haq Zia
Johnson Richard S.
Farrell James J.
Honig Milton L.
Lever Brothers Company
Van Balen William J.
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