Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Of inorganic materials
Reexamination Certificate
1999-10-13
2001-11-27
Derrington, James (Department: 1731)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Of inorganic materials
C047S064000
Reexamination Certificate
active
06322734
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to stable growing media, such as plugs, for the germination of seeds and the growing or propagation of plants, and a method of manufacturing such growing media.
Plant seedlings or shoots can be planted in and grown in rooting media comprising soil mixture and a synthetic binder therefor, such as an organic resin polymer. Such rooting media or grow plugs eliminates the need to use pots, which add substantial weight and cost to transportation of plants. Such grow plugs are known, as is evident from U.S. Pat. No. 3,805,531, which discloses a rooting media formed by mixing a prepolymer with aggregate or soil mixture and adding water to the mixture. Upon curing of the prepolymer, a cohesive mass is formed. Similarly, U.S. Pat. No. 4,175,355 discloses soil plugs using a mixture of soil material comprising at least 15% polyurethane by weight on a dry basis of the soil material. A slurry is prepared by intensively mixing the prepolymer, soil material and water. The slurry is then cast into a die and after at least partial hardening of the polyurethane resin forming material, the resulting plug is removed from the die.
Because of the relatively high percentage of polyurethane in the plugs of the prior art, growing of the seedling is impeded. Indeed, it is generally believed that the less synthetic material in such plugs, the better the seedlings grow. Presumably the presence of the synthetic material impairs access of water and air to the plant roots. Ideally, therefore, grow plugs would contain no synthetic material. However, the synthetic material is a critical component of such plugs in order to provide a self-supporting, stable plug that does not disintegrate upon handling. Indeed, U.S. Pat. No. 4,175,355 discussed above expressly teaches that using less than about 15% polyurethane resin by weight on a dry basis results in the rooting media crumbling and falling apart. Moreover, plugs having a high concentration of polyurethane tend to be rubbery and insufficiently dense. As a result, the water retaining properties of such plugs are poor, and the penetration of air is impaired.
It would thus be highly desirable to produce a grow plug that mimics, as closely as possible, growing media that is free of synthetic material.
U.S. Pat. No. 5,209,014 discloses moulds for growing seedlings, the moulds being formed of turf, water, nutrients and a synthetic molding materials such as a polyurethane resin. The '014 patent states that the prepolymer is added in the amount of about 6 to 8% by weight to the turf mixture, the turf mixture first having been ground in a turf grinder. It is apparent from the disclosure that in referring to 6-8% prepolymer by weight of the dry mass, the term “dry mass” is being used to indicate turf mixture to which additional water has not yet been added.
That is, the turf mixture inherently contains moisture, and the “dry mass” referred to in the '014 patent includes that moisture, but does not include the water introduced to the turf mixture prior to the addition of the prepolymer. Were the amount of prepolymer in the '014 patent calculated on a true “bone dry” basis to be consistent with the other prior art, the percentage of prepolymer would be considerably more than the 6-8% disclosed.
It is therefore an object of the present invention to provide cohesive, stable, resilient, homogeneous, integral, self-supporting growing media with minimal amounts of synthetic material.
It is a further object of the present invention to provide growing media having improved water retaining properties and increased air space.
It is a still further object of the present invention to provide a process for preparing cohesive, stable, resilient, homogeneous, integral, self-supporting growing media with minimal amounts of synthetic binding material.
SUMMARY OF THE INVENTION
The problems of the prior art have been overcome by the present invention, which provides a process for producing hydrophilic growing media, preferably plugs, and provides growing media having improved properties and a minimal amount of binding agent. In general terms, a method is provided for forming a resilient, integral, dimensionally stable, cohesive, homogeneous mass by contacting an aggregate with a hydrophilic urethane prepolymer and water.
Upon curing, the prepolymer binds the aggregate material together.
The mixing of the aggregate, prepolymer and water is conducted under specific, carefully controlled conditions, which enables the use of less prepolymer to obtain a given strength and stable air space than would otherwise be necessary.
According to the invention a method is provided for preparing cohesive, stable, self-supporting, homogeneous, open celled growing media, said method comprising forming a slurry consisting essentially of aggregate, hydrophilic polyurethane prepolymer, and water; mixing said slurry at a temperature below about 20° C., said mixing being conducted for a time sufficient to create a homogeneous mix; pouring said mixture into at least one mould and allowing the mixture ultimately cure in said mould, wherein mixing is conducted longer than 30 sec. and shorter than 300 sec. under low sheer so as not to damage the aggregate particles.
According to a further aspect of the invention a method is provided for preparing cohesive, stable, self-supporting, homogeneous, open celled growing media, said method comprising forming a slurry consisting essentially of aggregate, hydrophilic polyurethane prepolymer, and water; mixing said slurry at a temperature below about 20° C., said mixing being conducted for a time sufficient to create a homogeneous mix; pouring said mixture into at least one mould and allowing the mixture ultimately cure in said mould, wherein during mixing about 90% of the volume increase in the transition from the slurry to cured growing media is effected. This will result in a negligible increase in volume after pouring said mixture into said mould. Because of that it is not necessary to take measures to maintain the volume of the material such as lids. It is possible to cast the mix in the moulds for the user and immediately after such casting shipment of the moulds is possible. According to a further aspect of the invention a stable self-supporting open celled growing media is provided comprising an aggregate being selected from the group comprising peat, soil, coir (coconut husk), perlite, vermiculite, pumice, baked clay, wood pulp, ground tree bark, sawdust, and mixtures thereof, said media having a dry density lower than 180 g/l. In particular the dry density is between 60 and 130 g/l.
REFERENCES:
patent: 3805532 (1974-04-01), Kistner
patent: 4114316 (1978-09-01), Cohen
patent: 4175355 (1979-11-01), Dedolph
patent: 5209014 (1993-05-01), Teichmann
patent: B1 3805532 (1985-07-01), Kistner
patent: 38 29 256 (1989-03-01), None
patent: 0 086 918 (1983-08-01), None
patent: 0 090 910 (1983-10-01), None
patent: 0 346 627 (1989-12-01), None
patent: 0 461 545 (1991-12-01), None
patent: 2.115.783 (1972-06-01), None
Leerdam Frans
Van Zanten Evert
Derrington James
Nields & Lemack
Preforma Westland B.V.
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