Plant protecting and regulating compositions – Plant growth regulating compositions
Reexamination Certificate
2000-11-03
2002-06-18
Pryor, Alton (Department: 1616)
Plant protecting and regulating compositions
Plant growth regulating compositions
C504S117000
Reexamination Certificate
active
06407039
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a biodegradable, weed-preventing sheet having naturally mild and slow biodegradability. It has extremely high weatherability, durability and light-shielding properties. It also has suitable water permeability, high mechanical strength and is resistant to breakage by dogs, cats, digging by mice and invasion by weed seeds.
The conventional weed-preventing sheet has been used for preventing growth of weeds by directly laying the sheet in the culture ground such as orchards and kitchen gardens, or used for preventing growth of weeds in order to keep the beauties of parks, gardens, residential lands and roadsides trees, or used for surface treatment of an embankment normal in development of roads and shore protection works.
Generally, as a means of preventing growth of weeds, there is a means of laying a colored synthetic resin film in the ground to stop sunlight completely and water necessary for growth of plants. However, such a film for completely stopping water, when used against roots of plants, does not permit passage of rainwater thus causing drying of the soil, which may result in withering of cultivated plants as well, while the film does not permit evaporation and discharge of rainwater so that puddles occur between the film and the ground surface, and roots seeking the water in these puddles float just below the ground surface, resulting in spoiling roots and preventing growth of cultivated plants.
Further, there arises the problem that if such a synthetic resin film is used for surface treatment of an embankment normal in development of roads and shore protection works, water retained between the film and the ground surface may cause flowing of underground earth and sand to generate a cave-in, or an outflow of topsoil from the site of shore protection works.
Further, there is the problem that the synthetic resin film is generally inferior in mechanical strength such as tear strength, tensile strength and piercing strength so that the film may be broken by mechanical strength upon surface treatment of an embankment normal or upon stretch for construction, or cleaved by the growing force of vigorously growing plants of Gramineae family represented by Japanese pampas grass.
In addition, a frequently used synthetic resin film such as colored polyolefin film, colored polyvinyl chloride film etc. hardly undergoes biodegradation, thus causing a deterioration in the environment, necessitating enormous costs for post-treatment of the film after use, and upon combustion, causing secondary disasters, such as breakage of an incinerator and generation of dioxin.
In place of the synthetic resin film, a water-permeable weed-preventing sheet using non-woven fabric, woven fabric or knit article made of polyolefin-based fibers or polyvinyl chloride-based fibers has also been proposed, but both the polyolefin-based fibers and polyvinyl chloride-based fibers are hydrophobic, and when voids in this water-permeable weed-preventing sheet are small, water cannot pass through the sheet because of surface tension, and water thus retained may cause the same problems as in the synthetic resin film described above, while when the voids are made larger, the light-shielding properties are lowered, and because of penetrating light, the sheet fails to achieve a sufficient effect of preventing growth and overgrowth of weeds.
Under these circumstances, there has been proposed a biodegradable, weed-preventing sheet formed from non-woven fabric consisting of biodegradable and thermoplastic aliphatic polyester fibers, wherein the fineness of single yarn in the polyester fibers is 1 to 15 denier, and the weed-preventing sheet has a weight ranging 50 to 300 g/m
2
, has a light shielding degree of 95% or more, and has a water permeation coefficient of 0.02 to 0.8 cm/sec. (JP-A 11-229260).
As the thermoplastic aliphatic polyester in this case, a polymer selected from poly(D-lactic acid), poly(L-lactic acid), a D-lactic acid-L-lactic acid copolymer, a D-lactic acid-hydroxycarboxyhc acid copolymer, and a blend thereof, is mentioned.
However, this biodegradable, weed-preventing sheet is formed from a polymer selected from poly(D-lactic acid), poly(L-lactic acid), a D-lactic acid-L-lactic acid copolymer, a D-lactic acid-hydroxycarboxylic acid copolymer, and a blend thereof. Hence, the biodegradability of this sheet is varied depending on the degree of polymerization or raised by hydrolysis of ester linkages by bacteria, causing poor durability and permitting growth and overgrowth of weeds at its biodegraded site. By the growing force of these weeds, the biodegradable weed-preventing sheet is further cleaved, and more weeds grow and overgrow at that site, so the role of the biodegradable weed-preventing sheet is rapidly lost.
Accordingly, the biodegradable weed-preventing sheet must be exchanged frequently with new one, and this is a very troublesome and costly operation. There are further troublesome tasks for estimating the timing of exchange and for grasping the state of the laid biodegradable weed-preventing sheet.
Further, this biodegradable weed-preventing sheet is formed from D-lactic acid and L-lactic acid, and these are expensive and also problematic from the viewpoint of durability.
The present invention was made to solve the problems described above. The present inventors paid attention to the fact that biodegradable fibers containing coconut fibers have mild and slow biodegradability in the environment as well as excellent durability, and they found that a sheet formed from such biodegradable fibers containing coconut fibers can work as a biodegradable weed-preventing sheet exhibiting sufficient lightshielding properties, mechanical strength, and suitable water permeability for a prolonged period of time, and on the basis of this finding, the present invention was completed.
SUMMARY OF THE INVENTION
That is, a sheet which has been formed from biodegradable fibers containing g coconut fibers as essential constituent fibers according to the present invention can exhibit naturally mild and slow biodegradability, and do not adversely affect the environment during use and when left after use. Further, when the effect of preventing generation and growth of weeds becomes insufficient because of the progress of biodegradation during use, a new biodegradable weed-preventing sheet can be laid thereon and used successively without adversely affecting the environment. Further, this sheet has significantly improved weatherability, durability and mechanical strength and can thus endure mechanical stress upon surface treatment of an embankment normal and upon a stretch of construction. As a result, the film is not broken by such mechanical stress, has excellent lightshielding properties and suitable water permeability, is not cleaved by the growing force of vigorously growing plants of Gramineae family represented by Japanese pampas grass, is resistant to breakage by dogs, cats, digging by mice, and invasion by weed seeds. The object of the present invention is to provide such a biodegradable weed-preventing sheet capable of preventing generation and growth of weeds as well as a method of preventing generation and growth of weeds by use of said sheet.
To achieve the object, the biodegradable weed-preventing sheet of the present invention comprises biodegradable fibers containing coconut fibers as essential constituent fibers formed in the form of sheet (hereinafter, this sheet is referred to as the first weed-preventing sheet of the present invention).
In the first weed-preventing sheet of the present invention, the biodegradable fibers are formed preferably from a fiber blend consisting of coconut fibers whose content is 30% by weight or more and other biodegradable fibers, and in this case, the content of the coconut fibers in the biodegradable fibers is preferably 50% by weight or more, more preferably 75% by weight or more.
The reason that the content of the coconut fibers in the biodegradable fibers is 30% by weight or more in the first weed-preventing
Nishimura Motoyoshi
Ueda Toshiya
Jordan and Hamburg LLP
K.K. Ueda Shikimono Kojyo
Pryor Alton
LandOfFree
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