Chemistry: fertilizers – Processes and products – Forms or conditioning
Reexamination Certificate
2001-03-06
2002-03-19
Sayala, Chhaya D. (Department: 1761)
Chemistry: fertilizers
Processes and products
Forms or conditioning
C071S064070, C071S064110
Reexamination Certificate
active
06358295
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing controlled-release granular fertilizer coated with urethane resin.
BACKGROUND ART
A controlled-release fertilizer, which is also referred to as slow-release fertilizer, is labor-saving and releases a fertilizer ingredient according to a growth of a plant in a designated time. At the present day, various controlled-release fertilizers are suggested and put to practical use, because of ripening of age employed in agriculture, decrease of the number of the employed and increase of side-job farmers.
Japanese Unexamined Patent Publication Nos. Hei-9-309785 and Hei-10-72272 describe a controlled-release granular fertilizer, which is coated with a thermosetting resin and a highly water-absorptive resin for accelerating a dissolution rate.
A fertilizer coated with urethane resin is described in Japanese Unexamined Patent Publication No. Hei-10-291881. In this reference, described is a fertilizer coated with a mixture of a highly water-absorptive resin and urethane resin, and another fertilizer coated with only uncured urethane resin, after coated a surface of the fertilizer with a mixture of a highly water-absorptive resin and urethane resin, for suppressing early dissolution and affording sigmoide type dissolution.
However, a method for coating a surface of fertilizer with a mixture of a highly water-absorptive resin and urethane resin, and a method of coating with only urethane resin, after coating a surface of fertilizer with a mixture of a highly water-absorptive resin and urethane resin, give a large amount of fine particles coated with only highly water-absorptive resin. The production of the fine particles causes a trouble floating of a large amount of fine particles absorbing water when applied in paddy field as well as decreasing an effect accelerating dissolution rate by loss of the highly water-absorptive resin.
Though a thickness of the coated resin layer should be lowered for increasing dissolution rate without the highly water-absorptive resin, too thick coated layer makes it difficult to form a completely uniform layer and causes often defects such as pinhole. Further, it also causes defects of the layer by an addition of physical force for transportation, storage and application.
It is difficult to control the dissolution precisely by using these coated fertilizers comprising the disproportional or defective layer. Further, there is a problem of low yield of the manufactured articles having good quality.
An object of the present invention is to provide a method for producing a controlled-release granular coated fertilizer, which can release fertilizer ingredient in a short time at room temperature or lower temperature constantly, especially at low temperature, using the highly water-absorptive resin without loss, and suppressing the by-production of fine particles coated only the highly water-absorptive resin. It is also the object that few floats are found when the obtained fertilizer is applied into water and that the obtained fertilizer has a uniform coat layer.
SUMMARY OF THE INVENTION
The present invention is provided to attain the object described above. It is a method for producing a granular fertilizer which comprises adding water-absorptive polymer to granular fertilizer and then coating it with at least one urethane resin layer. The obtained fertilizer comprises few fine particles coated only the water-absorptive polymer, gives few floats when applied in water, and releases fertilizer ingredient in a short time at room temperature or even at lower temperature.
Namely, the present invention provides a method for producing granular coated fertilizer, which comprises adding water-absorptive polymer to granular fertilizer and then coating it with urethane resin, typically a method given by the following steps:
(1) adding water-absorptive polymer to the granular fertilizer;
(2) placing the granular fertilizer in a tumbled state;
(3) adding liquid uncured urethane resin to the tumbled granular fertilizer in an amount enough to secure a layer thickness of 1 to 10 &mgr;m;
(4) coating the surface of each granular fertilizer with the uncured urethane resin while keeping the granular fertilizer in the tumbled state;
(5) curing thermally the urethane resin while keeping the granular fertilizer in the tumbled state; and
(6) repeating the above steps (2) to (5) one or more times, in this order.
DISCLOSURE OF THE INVENTION
The present invention is described in detail hereinafter.
When the water-absorptive polymer is added to the granular fertilizer in the present invention, the method for adding the water-absorptive polymer to the granular fertilizer and making it uniformly is, for example, given by heating the granular fertilizer to the temperature suitable for processing, adding the water-absorptive polymer and making it tumbled to be uniform, or given by adding the water-absorptive polymer to the tumbled granular fertilizer, while heating the granular fertilizer to the temperature suitable for processing, to be uniform.
In a method of placing the granular fertilizer into the tumbling state, an apparatus is not specifically limited and a known conventional apparatus can be used and examples thereof include rotary pan, rotary drum and the like. An apparatus with a heating equipment is suitable for realization of high accuracy of coating and adjustment of a processing time.
The granular fertilizer used in the present invention may be any conventional granular fertilizer. Specific examples thereof include nitrogen fertilizer such as urea, ammonium sulfate, ammonium chloride, ammonium phosphate, ammonium nitrate, ammonium nitrate lime, lime nitrogen, sodium nitrate and acetaldehyde condensed urea; phosphate fertilizer such as calcined phosphate, processed phosphate fertilizer, triple superphosphate and mixed phosphate fertilizer; potash fertilizer such as potassium chloride, potassium sulfate magnesia, potassium bicarbonate and potassium silicate fertilizer; complex fertilizer such as potassium phosphate fertilizer and potassium nitrate fertilizer; organic fertilizer; and granular fertilizer obtained by granulation of a mixture of these fertilizers using a per se known method.
A particle diameter of the granular fertilizer used in the present invention is not specifically limited, but is preferably within a range from 1 to 5 mm in view of manufacturing.
In the present invention, water-absorptive polymer means a polymer which is practically insoluble in water and can absorb and keep water in an amount of 2 to 2000 times by weight of the polymer. Water-absorptive resins can be used as the water-absorptive polymer.
Examples of the water-absorptive resin include acrylate polymers (typically, sodium polyacrylate) such as Sumikagel N-100, N-100P, N-100SH and NP-1010 manufactured by Sumitomo Chemical Co., Ltd., Aquakeep 10SH-P, 10SH, 10SH-NF, SA60S and SA60NTYPEII manufactured by Sumitomo Seika Chemicals Co., Ltd., and Aquaric CS-6 and CS-7 manufactured by Nippon Shokubai Co., Ltd.; acrylic acid-vinyl alcohol copolymers such as Sumikagel S-50, S-110, S-120, S-510 and S-520 manufactured by Sumitomo Chemical Co., Ltd.; isobutylene polymers such as KI gel-210K-F2 manufactured by Kuraray Co., Ltd.; ethylene oxide polymers; propylene oxide polymers; ethylene oxide-propylene oxide copolymers; and polyethylene oxide resins bonded with urethane resin at the hydroxy group terminal such as Aquacoak manufactured by Sumitomo Seika Chemical Co., Ltd. Further, examples of the water-absorptive polymer include starch, starch graft polymers, and carboxymethylcellulose salts such as sodium salt.
In the present invention, the urethane resin is a generic term of a resin, which is three-dimensionally cross-linked by reacting a polyisocyanate compound with a polyol compound. The uncured urethane resin in the present invention is a mixture of the polyisocyanate compound, the polyol compound and optionally a curing catalyst, and is obtained by mixing them without any reaction or by previously reacting a portion of them to such
Endo Kazuhisa
Saitou Noriaki
Tabei Nobuaki
Sayala Chhaya D.
Sughrue & Mion, PLLC
Sumitomo Chemical Company Limited
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