Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-08-10
2001-12-11
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S035200, C428S035400, C428S483000, C428S516000, C428S518000, C428S520000, C428S036500, C428S035800
Reexamination Certificate
active
06329032
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a water absorptive thermoplastic polymer composition including a metal biocide, wherein the composition and plant containers made therefrom are capable of promoting plant root branching.
BACKGROUND
Plants with dense, branched root systems are generally stronger, healthier, and better able to survive transplantation than plants that do not have such dense, branched root systems. However, the roots of plants grown in containers tend to grow in a straight line, without branching, and the roots develop a characteristic container-circling structure as they fill the container.
Plants with container-circling root structures are not well suited to successfully survive transplantation because the roots generally continue to grow in a restricting line pattern once the circling growth pattern is established. As a result, the root system does not grow outward from the containerized root system to properly anchor the plant and the plant does not then seek nutrition and moisture from a large enough area to support itself as it grows. Furthermore, plants having this type of circling root structure are not readily transported because the portion of the root that is in contact with the container is exposed to the high temperatures that such containers, which are generally formed of a black plastic, will reach in the sun. These high temperatures are damaging to the roots, which have limited recuperative powers due to the lack of branching.
It is known that certain copper chemicals will terminate a root's growth on contact, thereby causing the root to branch in a manner similar to that in which the trimming of a tree causes a single branch to become many branches. This is desirable in the plant nursery trade as a plant grown in a container having these type of copper chemicals will have a dense, branched root ball or system. Such a dense, branched root ball will result in a stronger, healthier plant that is better able to survive transplantation.
It is conventional practice that to promote root branching, the interior surfaces of plant containers used at nurseries are coated with paints, thermoset coatings, or other fluid materials containing copper. The coating is often applied at the nursery. However, this practice is problematic because of the exposure of nursery workers to paint sprays and the like. Government regulations restrict such exposure and these restrictions, along with the time and resources required for application, represent an excessive burden to nurseries. Prior to this invention, however, no commercially viable alternative to container surface coating has been available to nurseries.
Copper is toxic to plants, so copper available to promote plant root branching should not dissolve and leach into plant soil. Copper in the form of a water-insoluble copper salt is suitable to reduce or essentially eliminate copper toxicity. In order to be available for root growth control, the water-insoluble copper salt may be fixed in the container such that it will not significantly slough from the container, yet be sufficiently exposed such that plants roots recognize the copper. Prior art methods to fix copper in a container utilize thermoset coatings containing insoluble copper salts. These thermoset coatings generally must have good water resistance to prevent cracking and sloughing of the coating.
Incorporation of copper or other metal biocides into a thermoplastic composition is known. Growth of marine flora and fauna on submarine structures such as boats hulls and piers is inhibited using copper metal at high concentrations, wherein the copper is the major component of a thermoset or thermoplastic composition. Inclusion of copper or other metal salts in relatively low or trace concentrations in a thermoplastic imparts improved weatherability and heat resistance, and promotes environmental degradation in some thermoplastics. However, the use of copper as a copper insoluble salt incorporated into a thermoplastic composition as an effective plant root branching promoter in plant containers has not been taught.
It is desirable then to provide a thermoplastic composition comprising copper such that plant containers made using the composition will be effective in promoting plant root branching.
SUMMARY
It is an object of the invention to provide a thermoplastic composition having incorporated copper or other biocides that is effective in promoting plant root branching.
It is a further object of the invention to provide a thermoplastic composition having incorporated copper or other biocides that is effective in promoting plant root branching that can be used to manufacture plant containers.
It is another object of the invention to provide a thermoplastic composition having incorporated copper or other biocides that is effective in promoting plant root branching that can be used to manufacture plant containers that can be used in a method to regulate the growth of plant roots.
It has heretofore been difficult to provide a thermoplastic composition having copper or other biocides available to control root growth in plant containers. Typical thermoplastic compositions encapsulate the copper so completely that the copper is not available to plant roots and, therefore, the roots do not branch. By incorporating the copper into a thermoplastic composition that can be subsequently used to fabricate a plant container, the present invention obviates the need for painting or otherwise coating of a plant container to promote root branching, and avoids the consequent problems with worker exposure.
In general, a thermoplastic composition having incorporated copper or other biocides is provided in accordance with the invention. The thermoplastic composition can be processed at low temperatures, readily absorbs water, and is readily formable into a film or other sheet suitable for producing plant containers. In particular, the thermoplastic composition includes at least one thermoplastic homopolymer or copolymer and the copper is present in the form of a water-insoluble copper salt. At least one water absorptive material is also included in the thermoplastic composition. In one embodiment, the water absorptive material is a lignosulphonate salt, such as calcium or ammonium lignosulphonate. The function of the lignosulphonate is to absorb water from the growth medium in the plant container, thereby effectively swelling the thermoplastic composition and making copper, present in the disclosed concentration range, available to be recognized by plant roots in the container.
Still other objects and advantages of the invention will be apparent to one of ordinary skill in the art upon reading the specification as follows.
DESCRIPTION
It has now been found that effective promotion of plant root branching is achieved using a thermoplastic composition comprising at least one thermoplastic polymer, at least one water insoluble copper salt or other biocide, and at least one water absorptive material.
In one embodiment, the thermoplastic composition contains copper in the form of a water-insoluble copper salt, which is known to cause polymer degradation at polymer processing temperatures in excess of about 350° F. Processing temperatures in excess of 350° F. can also cause the copper salts to change to a form that is less effective at promoting root branching. The thermoplastic polymer therefore should be processable at a temperature that is low enough to prevent heat degradation of the polymer due to the presence of copper in the thermoplastic composition and to prevent change of the copper to a less effective form. In particular, suitable thermoplastic polymers should be processable at temperatures less than about 320° F., and advantageously between about 270° and about 295° F. Suitable thermoplastic polymers include but are not limited to polyethylene homopolymers such as branched low density polyethylene, and polyethylene copolymers including ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer, ethylene ethyl acrylate copolymer, and eth
Crawford Mark
Lee Victor
Wykoff Ed
ICC Industries Inc.
John D. DeLong of Hahn, Loeser + Parks, LLP
Rajguru U. K.
Seidleck James J.
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