Plastic and nonmetallic article shaping or treating: processes – With printing or coating of workpiece – Coating or impregnating workpiece before molding or shaping...
Reexamination Certificate
2000-07-11
2003-09-30
Lee, Edmund H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With printing or coating of workpiece
Coating or impregnating workpiece before molding or shaping...
C264S510000, C264S553000, C264S322000
Reexamination Certificate
active
06627132
ABSTRACT:
FIELD OF INVENTION
This invention relates to the control of plant root growth and to an improved material from which a plant container can be made, and, more particularly, relates to an improved container for plant propagation or transplantation which includes a copper-containing compound to control plant root growth for ease of extraction of the plant from the plant container. The present invention also relates to a method of making a thermoformed plant container which includes a copper-containing compound to control plant root growth.
BACKGROUND OF THE INVENTION
Cultivated plants are often propagated by initially germinating seeds or rooting cuttings at one site and then transplanting the seedlings or transplants to another site. For example, plants can be initially grown at a nursery and then transplanted by the customer to a permanent site. However, transplanting can be harmful to a plant. One problem with transplanting is that the plant root system can be damaged when the plant is removed from the initial site. Plants with damaged root systems often undergo transplant shock which can slow plant growth, and, in some instances, kill the plant. To reduce transplant shock, plants are initially grown in containers and then transplanted. Removing a plant from its container is less likely to damage the plant's root system than digging the plant out of the ground. A variety of plants, trees, shrubs, and the like, are initially grown in containers and then transplanted. However, transplanting plants from containers still presents some problems. One problem occurs when plants such as vegetables are grown in containers placed close to one another. The root growth of each plant can extend beyond its container and become entangled with the roots of adjacent plants. When the containers are separated and the plants are removed from the containers for transplanting, the root systems are damaged and the plants can undergo transplant shock. Another problem with plants grown in containers is that the container prevents the root system of the plant from growing in a natural pattern. In a natural environment, plant root systems extend relatively far away from the plant in the lateral and vertical directions for plant stability and maximum nutritional intake. In a container, the area of growth of the root system is limited and the roots are forced to turn at the container walls and grow into a tangled root ball which takes the shape of the container.
To control root growth in a plant container, chemical root pruning has been used. Chemical root pruning involves the use of chemicals, such as copper compounds, to stop root growth. For example, a mixture of conventional latex house paint and copper carbonate or copper hydroxide effectively controls root growth when used to coat the interior of a plant container. The copper
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ions in the latex paint are adsorbed by the roots as the roots approach the sides of the container and stop the growth of the roots. The root systems then branch behind the point of root growth inhibition. The plant root systems so treated tend to maintain a more natural growth pattern although the growth of the root system is foreshortened. When the plants are transplanted, the root systems resume normal growth. Furthermore, woody plant cuttings rooted in coated containers will form significantly more roots from the stem of the cutting. This effect improves plant growth and stability when removed from the treated container and grown to larger size.
Containers for plants, such as plant propagation trays or flower pots, are typically formed by molding a sheet of thermoformable material, such as a thermoplastic, for example, polystyrene, polyethylene or polypropylene. In the molding process, a mold release compound is usually applied to the plastic sheet in order to allow the molded material to release from the mold die. Such mold release compositions are usually silicon or wax based. Although such mold release compositions aid in mold release, they make applying a copper-containing coating composition to a formed plant container difficult, if not impossible.
The previously known copper-containing coatings for plant containers have been applied to the interior of the container after the plant container has been formed. Application of these coatings to formed plant containers is difficult, expensive and labor intensive. Furthermore, adhesion of the coating to the formed plastic container is difficult and flaking or delamination of such coatings is a significant problem. Accordingly, an improved system for producing plant containers that will control root growth has long been sought.
SUMMARY OF THE INVENTION
The present invention satisfies the above-described needs by providing an improved material from which to make a plant container. The improved material of the present invention comprises a substantially flat sheet of thermoformable plastic having on at least one side thereof a coating composition comprising an acrylic latex emulsion, copper hydroxide, a filler, and a dispersant. The coating composition can be applied to all of a side of the plastic sheet or only to selected portions of the plastic sheet. Optionally, a second layer of the coating composition can be applied to all of a side of the plastic sheet or only to selected portions of the plastic sheet. The coated plastic sheet can then be used in a conventional forming process to form the sheet into a desired size and shape for a plant container.
The method of the present invention for making a plant container comprises the steps of applying to a substantially flat sheet of thermoformable plastic an aqueous coating composition comprising an acrylic latex emulsion, copper hydroxide, a filler, and an acrylate dispersant. The coating composition can be applied to all of a side of the plastic sheet or only to selected portions of the plastic sheet. Optionally, a second layer of the coating composition can be applied to all of a side of the plastic sheet or only to selected portions of the plastic sheet. The coating composition is dried. The coated plastic sheet is heated to a temperature sufficient to form the plastic. Then, the coated and heated plastic sheet is formed into a desired shape.
Accordingly, an object of the present invention is to provide for improved control of plant root growth in plant containers.
Another object of the present invention is to provide an improved composition from which plant containers can be made.
A further object of the present invention is to provide a method of producing plant containers by which a root growth controlling coating is applied to a plastic sheet prior to fabrication into a plant container.
Yet another object of the present invention is to provide a composition for coating thermoformable plastic sheet material which has improved properties of crack resistance and adherence during and after thermoforming of the plastic sheet.
Another object of the present invention is to provide an improved plant growing container, especially a plant propagation tray.
Still another object of the present invention is to provide an improved method of applying a root growth controlling coating to a plant container.
These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.
DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS
The present invention relates to containers for plants, such as plant propagation trays, flower pots and the like, made from molded sheets of plastic. The present invention provides a root growth inhibiting coating composition which can be applied to the plastic sheet before it is molded into a desired shape for a plant container.
The root growth inhibiting coating composition of the present invention comprises copper hydroxide, an acrylic latex, an acrylate dispersant and a filler. The coating composition is applied to at least one side of a sheet of plastic and then dried. Optionally, one or more additional layers of the
Crawford Mark Allen
Ullah Hamid
Griffin Corporation
Kilpatrick & Stockton LLP
Lee Edmund H.
LandOfFree
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