Stock material or miscellaneous articles – Hollow or container type article
Reexamination Certificate
2000-12-20
2004-11-02
Pyon, Harold (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
C428S304400, C428S310500, C210S321600, C604S385101
Reexamination Certificate
active
06811842
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to liquid transport members useful for a wide range of applications requiring high flow and/or flux rate, wherein the liquid can be transported through such a member, and/or be transported into or out of such a member. Such members are suitable for many applications, as—without being limited to—disposable hygiene articles, water irrigation systems, spill absorbers, oil/water separators and the like. The invention further relates to liquid transport systems comprising said liquid transport members and articles utilizing these.
BACKGROUND
The need to transport liquids from one location to another is a well known problem.
Generally, the transport will happen from a liquid source through a liquid transport member to a liquid sink, for example from a reservoir through a pipe to another reservoir. There can be differences in potential energy between the reservoirs (such as hydrostatic height) and there can be frictional energy losses within the transport system, such as within the transport member, in particular if the transport member is of significant length relative to the diameter thereof.
For this general problem of liquid transport, there exist many approaches to create a pressure differential to overcome such energy differences or losses so as to cause the liquids to flow. A widely used principle is the use of mechanical energy such as pumps. Often however, it will be desirable to overcome such energy losses or differences without the use of pumps, such as by exploiting hydrostatic height differential (gravity driven flow), or via capillary effects (often referred to as wicking).
In many of such applications, it is desirable to transport the liquids at high rates, i.e. high flow rate (volume per time), or high flux rate (volume per time per unit area of cross-section).
Examples for applications of liquid transport elements or members can be found in fields like water irrigation such as described in EP-A-0.439.890, or in the hygiene field, such as for absorbent articles like baby diapers both of the pull-on type or with fastening elements like tapes, training pants, adult incontinence products, feminine protection devices.
A well known and widely used execution of such liquid transport members are capillary flow members, such as fibrous materials like blotting paper, wherein the liquid can wick against the gravity. Typically such materials are limited in their flow and/or flux rates, especially when wicking height is added as an additional requirement. An improvement particularly towards high flux rates at wicking heights particularly useful for example for application in absorbent articles has been described in EP-A-0.810.078.
Other capillary flow members can be non-fibrous, but yet porous structures, such as open celled foams. In particular for handling aqueous liquid, hydrophilic polymeric foams have been described, and especially hydrophilic open celled foams made by the so called High Internal Phase Emulsion (HIPE) polymerization process have been described in U.S. Pat. No. 5,563,179 and U.S. Pat. No. 5,387,207.
However, in spite of various improvements made on such executions, there is still a need to get significant increase in the liquid transport properties of liquid transport members.
In particular, it would be desired to obtain liquid transport members, that can transport liquid against gravity at very high flux rates.
In situations wherein the liquid is not homogeneous in composition (such as a solution of salt in water), or in its phases (such as a liquid/solid suspension), it can be desired to transport the liquid in its totality, or only parts thereof. Many approaches are well known for their selective transport mechanism, such as in the filter technology.
For example, filtration technology exploits the higher and lower permeability of a member for one material or phase compared to another material or phase. There is abundance of art in this field, in particular also relating to the so called micro-, ultra-, or nano-filtration. Some of the more recent publications are:
U.S. Pat. No. 5,733,581 relating to melt-blown fibrous filter;
U.S. Pat. No. 5,728,292 relates to non-woven fuel filter;
WO-A-97/47375 relating to membrane filter systems;
WO-A-97/35656 relating to membrane filter systems;
EP-A-0.780.148 relating to monolithic membrane structures;
EP-A-0.773.058 relating to oleophilic filter structures.
Such membranes are also disclosed to be used in absorbent systems.
In U.S. Pat. No. 4,820,293 (Kamme) absorbent bodies are disclosed, for being used in compresses, or bandages, having a fluid absorbent substance enclosed in a jacket made of one essentially homogeneous material. Fluid can enter the body through any part of the jacket, and no means is foreseen for liquid to leave the body.
Therein, fluid absorbent materials can have osmotic effects, or can be gel-forming absorbent substances enclosed in semipermeable membranes, such as cellulose, regenerated cellulose, cellulose nitrate, cellulose acetate, cellulose acetate butyrate, polycarbonate, polyamide, fiberglass, polysulfone, of polytetrafluoroethylene, having pore sizes of between 0.001 &mgr;m and 20 &mgr;m, preferably between 0.005 &mgr;m and 8 &mgr;m, especially about 0.01 &mgr;m.
In such a system, the permeability of the membrane is intended to be such that the absorbed liquid can penetrate, but such that the absorbent material is retained.
It is therefore desired to use membranes having a high permeability k and a low thickness d, so as to achieve a high liquid conductivity k/d of the layer, as being described herein after.
This can be achieved by incorporation of promoters with higher molecular weight (e.g. polyvinyl pyrrolidone with a molecular weight of 40,000), such that the membranes can have larger pores leading to larger membrane permeability k. The maximum pore size stated therein to be useful for this application is less than 0.5 &mgr;m, with pore sizes of about 0.01 &mgr;m or less being preferred. The exemplified materials allow the calculation of k/d values in the range of 3 to 7*10
−14
m.
As this system is quite slow, the absorbent body can further comprise for rapid discharge of fluids a liquid acquisition means, such as conventional acquisition means to provide interim storage of the fluids before these are slowly absorbed.
A further application of membranes in absorbent packets is disclosed in U.S. Pat. No. 5,082,723, EP-A-0.365.565, or U.S. Pat. No. 5,108,383 (White; Allied-Signal).
Therein, an osmotic promoter, namely a high-ionic strength material such as NaCl, or other high osmolality material like glucose or sucrose is placed inside a membrane such as made from cellulosic films. As with the above disclosure, fluid can enter the body through any part of the jacket, and no means is foreseen for liquid to leave the body. When these packets are contacted by aqueous liquids, such as urine, the promoter materials provide an osmotic driving force to pull the liquid through the membranes. The membranes are characterized by having a low permeability for the promoter, and the packets achieve typical rates of 0.001 ml/cm
2
/min. When calculating membrane conductivity k/d values for the membranes disclosed therein, values of about 1 to 2*10
−15
m result. An essential property of membranes useful for such applications is their “salt retention”, i.e. whilst the membranes should be readily penetrable by the liquid, they must retain a substantial amount of the promoter material within the packets. This salt retention requirements provides a limitation in pore size which will limit liquid flux.
U.S. Pat. No. 5,082,723 (Gross et al.) discloses an osmotic material like NaCl which is enclosed by superabsorbent material, such as a copolymer of acrylic acid and sodium acrylate, thereby aiming at improving absorbency, such as enhanced absorptive capacity on a “gram per gram” basis and absorption rate.
Overall, such fluid handling members are used for improved absorbency of liquids, but have only very limited fluid transport capability.
Thus
Desai Fred Naval
Ehrnsperger Bruno Johannes
Lavon Gary Dean
Roe Donald Carroll
Schmidt Mattias
Chevalier Alicia
Patel Ken K.
Pyon Harold
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