Plant husbandry – Plant irrigators and/or fertilizers – apparatus or method
Reexamination Certificate
1999-08-06
2002-11-26
Jordan, Charles T. (Department: 3644)
Plant husbandry
Plant irrigators and/or fertilizers, apparatus or method
C047S065500
Reexamination Certificate
active
06484439
ABSTRACT:
This invention relates generally to irrigation devices and specifically to irrigation devices comprising a hydrophilic membrane.
BACKGROUND OF THE INVENTION
In most cases the cultivation of plants requires the provision at intervals of water; however, the frequency of these intervals and the amount of water provided varies widely, from the occasional watering of a pot plant or garden plants, to the almost continuous provision of water during commercial agriculture in particularly dry regions of the world. The various methods of irrigation adopted reflect these different requirements; however, most still suffer from serious disadvantages in that they may be labor intensive (e.g. watering of garden plants by hand or the monitoring of agricultural crops), wasteful of water (e.g. automated non-regulated agricultural or large scale domestic watering systems) or particularly complex and expensive (e.g. computer regulated, automated agricultural systems). Furthermore, many large-scale agricultural systems are buried in the ground requiring major preparation before installation and causing difficulties in maintenance and detecting, isolating and repairing leaks.
There is therefore a need for simple, easy to install and maintain irrigation devices that release water only when required.
Numerous materials that allow the passage of water whilst restricting the passage of suspended or even dissolved materials are known. One recently identified group of materials are hydrophilic polymers. Membranes of these materials are known to be impervious to liquid water but to allow the passage of water vapor (a process known as pervaporation). If there is a vapor pressure gradient across a hydrophilic membrane, water will be absorbed from the side with the higher vapor pressure, and transported across the membrane and released as water vapor on the side with the lower vapor pressure; the released water vapor may be used directly or condensed back to liquid water. However, in either case, it may be pure (both chemically and microbiologically) as any contaminants will be retained either on the other side of the membrane or (in some cases) in the membrane itself.
SUMMARY OF THE INVENTION
It has now been found that a container of water having at least one surface constructed from a hydrophilic membrane, when placed with that surface in contact with an area of growing medium, will release water at variable rates to maintain a particular moisture level in that area of growing medium and a surrounding area. Furthermore, this rate of water release may be controlled by the choice of materials used to construct the said one or more hydrophilic membrane surfaces.
There is therefore provided an irrigation device comprising a container for water consisting of a plurality of surfaces, each surface substantially being either a hydrophilic membrane or impervious to water in all forms, and wherein at least one of the surfaces is substantially a hydrophilic membrane and at least one of the surfaces is substantially impervious to water in all forms.
Preferably in the devices of the present invention, each surface is either a hydrophilic membrane or is impervious to water in all forms.
DETAILED DESCRIPTION OF THE INVENTION
By irrigation is meant the provision of sufficient water to an area of growing medium having plants therein to allow the plants to grow. Preferably a sufficient amount of water is delivered to the growing medium to optimize the growth of the plants therein.
Devices of the present invention may be used for all forms of irrigation; for example, for individual pot plants; in domestic gardens; in commercial plant nurseries or in all scales of agriculture.
Devices of the present invention regulate the amount of water released into an area of growth medium because the hydrophilic membrane will only allow the passage of water vapor across a vapor pressure gradient, i.e. if the growth medium below the device is waterlogged, no transport at all will occur, and the drier the growth medium becomes the faster will the rate of water transport out of the device into the growth medium become. As the water diffuses away from the point of contact with the device, a larger area of growing medium will become irrigated, and more water will be released from the device unless an equilibrium is reached.
In the context of the present invention, growth medium means any solid medium in which plants are planted and includes naturally occurring or artificially amended soils, and other materials for growing plants, such as vermiculite, perlite, peat moss, shredded tree fern trunks, chipped or shredded tree bark and shredded coconut husks.
In the context of the present invention hydrophilic membranes mean membranes that are impervious to liquid water but that allow the passage of water vapor, i.e. by pervaporation. Hydrophilic membranes or coatings, hereinafter collectively referred to as membranes in this disclosure, feature sufficiently high water vapor transmission rates, as defined below, so that water that has passed through the membranes can be used directly in applications including irrigating plants. Such membranes can comprise one or more layers made from materials including but not limited to the same or different hydrophilic polymers. As long as the water vapor permeation rate of the membrane in total is sufficiently high, this water can be provided at a rate consistent with its use in a given practical application as described. The non-porous nature of the membranes disclosed here serves to exclude any particulate impurities from passing through such a membrane, including microbes such as bacteria and viruses. In addition, it has been discovered that membranes made from the hydrophilic polymers described in the present invention significantly reduce or prevent the passage of dissolved salts. Therefore, the ability to use not only fresh water, but also water that may contain suspended or dissolved impurities, to produce desired amounts of purified water by ervaporation allows saline water, including but not limited to sea water or brackish water, after processing through the devices of the present invention, to be used to irrigate land and sustain plant growth.
The rate at which water pervaporates through the hydrophilic membrane depends to a large extent upon the nature of the material from which it is made, and upon the thickness of the one or more separate or combined layers of polymer from which the hydrophilic membrane is constructed. With the appropriate choice of material, thickness and membrane construction, the rate at which water pervaporates through the said hydrophilic membrane may be adjusted to suit the particular water requirements of the plants to be irrigated.
The rate at which water pervaporates through the membrane made from the hydrophilic polymer also depends, among other factors, upon the moisture content on the non-water side. Therefore, irrigation systems based on the membranes of the present invention are self-regulating and may be “passive” in nature, providing more water to plants under dry conditions and less under humid conditions.
The standard test for measuring the rate at which a given membrane transmits water is ASTM E-96-95—Procedure BW, previously known and named as ASTM E-96-66—Procedure BW, which is used to determine the Waver Vapor Transmission Rate (WVTR) of a membrane.
The hydrophilic membrane for use with devices of the present invention are made from hydrophilic polymers. “Hydrophilic polymers” means polymers which absorb water when in contact with liquid water at room temperature according to the International Standards Organization ISO 62 (Equivalent to the American Society for Testing and Materials specification ASTM D 570).
The hydrophilic polymer can be one or a blend of several polymers, for example, the hydrophilic polymer can be a copolyetherester elastomer or a mixture of two or more copolyetherester elastomers as described below, such as polymers available from E.I. du Pont de Nemours and Company under the trade name Hytrel®; or a polyether-block-polyamide or a mixtu
Cahill Charles William
Kirchner Olaf Norbert
Tonkin Mark Christopher
Young Mark Andrew
E.I. du Pont de Nemours and Company
Nelson Judith A.
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