JP7660084B2 - Granular fertilizer containing guanylurea using biodegradable resin emulsion - Google Patents

Description

The present invention relates to a granular fertilizer containing guanylurea as its main ingredient, which utilizes an emulsion of a biodegradable resin.

Since their development in the 1970s, coated fertilizers have been used to reduce the labor required for fertilization, particularly in paddy fields where fertilization is heavy labor, and have been positioned as environmentally friendly agricultural materials because they reduce fertilizer resources by limiting the amount of fertilizer used, as well as prevent water pollution caused by runoff of fertilizer components and reduce the generation of nitrous oxide gas, a greenhouse gas. However, since 2000, environmental pollution caused by microplastics has come to light, and coated fertilizer husks remain and run off as microplastics, creating a demand for controlled-release fertilizers to replace the conventional non-degradable coated fertilizers.

As for controlled-effect fertilizers that can replace non-degradable coated fertilizers, patent documents 1 to 3 disclose technologies for coating granulated fertilizers with biodegradable resins, while patent document 4 discloses a technology for coating grains containing liquid fertilizer components with polylactic acid and using the resulting fertilizer for granulation. There have been many technical proposals and publications about fertilizer coatings that use biodegradable resins.

In addition, as controlled release fertilizers, many slow-release nitrogen fertilizers are known from Non-Patent Document 1, and among these, isobutyraldehyde condensed urea, acetaldehyde condensed urea, methylol urea polymer fertilizer, guanylurea sulfate, and oxamide are particularly widely used.

In particular, Patent Documents 5 and 6 show that the fertilizer effect of guanylurea can be adjusted according to the situation of use by adding a decomposition inhibitor, making it a slow-release nitrogen fertilizer that is highly effective as an alternative to non-decomposable coated fertilizers.

Special table 2019-534837 publication JP 2003-55079 A Patent No. 4050052 Patent No. 6491380 Patent No. 6125446 Patent No. 6364394

Pocket Fertilizer Handbook 2019/2020, by Agriculture and Forestry Statistics Association, p.88 Pocket Fertilizer Handbook 2019/2020, by Agriculture and Forestry Statistics Association, p.377-379

Among the widely used slow-release nitrogen fertilizers, guanylurea sulfate and guanylurea phosphate are highly soluble in water, and when these are granulated by the commonly used wet tumbling granulation method, the guanylurea dissolves in the granulation water, resulting in a significant drop in yield. For this reason, no fertilizer containing a large amount of guanylurea and granulated by tumbling granulation has been produced. As a similar fertilizer, Patent Documents 5 and 6 show guanylurea granules granulated by compression molding, but the guanylurea content of the examples granulated by tumbling granulation is 20% by weight or less, and no examples of granular fertilizers containing more than 80% by weight of guanylurea according to the present invention have been produced by tumbling granulation.

In granulating fertilizers, additives described in Non-Patent Document 2 are used as granulation promoters to improve granulation and quality, but in order to improve the yield reduction associated with guanylurea granulation, the raw material ratio of guanylurea must be significantly reduced, resulting in a reduction in the amount of nitrogen components and making it impossible to obtain the effectiveness of a slow-release nitrogenous granular fertilizer.

After investigating methods for granulating guanylurea, the inventors discovered that a high product yield could be achieved by using an emulsion of a biodegradable resin as the granulation water and granulation promoter, which led to the completion of the present invention.

That is, the gist of the present invention is as follows.
(1) A granular fertilizer containing 80% by weight or more of guanylurea sulfate or guanylurea phosphate, and having a biodegradable resin formed from an aqueous emulsion of a biodegradable resin having a minimum film-forming temperature of 80°C or less dispersed within the granular fertilizer.
(2) A granular fertilizer according to (1) above, wherein the biodegradable resin contains polylactic acid.
(3) A granular fertilizer according to (1) or (2) above, which does not contain 1-amidino-2-thiourea and sulfathiazole.
(4) A method for producing a granular fertilizer according to any one of (1) to (3) above, comprising granulating a raw material containing guanylurea sulfate or guanylurea phosphate with an aqueous emulsion of a biodegradable resin having a minimum film-forming temperature of 80° C. or less.
(5) The method according to (4) above, wherein the aqueous emulsion contains 1 to 50% by weight of a biodegradable resin.
(6) The method according to (4) or (5) above, wherein the aqueous emulsion is sprayed or dropped and granulated by rolling.
(7) The method according to any one of (4) to (6), wherein the granulation is carried out using a pan granulator, a drum granulator or an agitator granulator.

According to the present invention, it is possible to suppress the dissolution of guanylurea during granulation and bond the raw material powders together, thereby achieving a high product yield with just two steps: granulation and drying.

The granulation method for guanylurea sulfate or guanylurea phosphate according to the present invention is not particularly limited as long as it is a granulation method classified as tumbling granulation, but examples include the following methods.

That is, powdered fertilizer raw materials with a particle size of less than 1.00 mm are thoroughly mixed. The mixing method can be a known method, for example, a powder mixer, a crusher, a V-type mixer, or a sugar coating machine.

The granulator used for granulation can be any known granulator classified as a rolling granulator, but it is particularly preferable to use a pan granulator, drum granulator, or agitator granulator.

If the viscosity of the biodegradable resin emulsion is high, the viscosity can be reduced by mixing the biodegradable resin emulsion with water. Mixing can be performed using a known liquid mixing method and liquid mixing device. The viscosity of the biodegradable resin emulsion can be adjusted by appropriately changing it within the range in which the biodegradable resin emulsion can be added, depending on the performance of the sprayer and discharge nozzle attached to the tumbling granulator.

The viscosity of the biodegradable resin emulsion is not limited as it depends on the performance of the granulator, but it can usually be used within the range of 1 to 1100 mPa·s, and it is preferable to use a range of 1 to 50 mPa·s, especially when spraying.

The fertilizer raw powder prepared by the above method is placed in a tumbling granulator, and tumbling granulation is carried out while the viscosity-adjusted biodegradable resin emulsion is sprayed or dropped from a spray nozzle. At this time, the biodegradable resin emulsion is added to the position where the fertilizer raw powder, which has been stirred up by the tumbling, falls and flows most rapidly inside the granulator, thereby allowing the biodegradable resin emulsion and the fertilizer raw powder to be mixed uniformly. The biodegradable resin emulsion also serves as granulation water, which binds the particles of the fertilizer raw powder, and it is possible to granulate by adding only the biodegradable resin emulsion, but if the formation of particles is insufficient with the addition of only the biodegradable resin emulsion, additional granulation water can be added.

The composition ratio of guanylurea sulfate or guanylurea phosphate must be 80% by weight or more in order to maximize the nitrogen content, preferably 85% by weight or more, and more preferably 85 to 95% by weight.

The biodegradable resin in the biodegradable resin emulsion can be selected from polyvinyl alcohol, polybutylene adipate terephthalate, polybutylene succinate, polybutylene succinate adipate, polyethylene terephthalate succinate, polyethylene terephthalate copolymer, polytetramethylene adipate-co-terephthalate, aliphatic aromatic polyester, polybutylene adipate/terephthalate, butanediol/long-chain dicarboxylic acid copolymer, polylactic acid, polylactic acid/polyether copolymer, polylactic acid/polycaprolactone copolymer, polyglycolic acid, cellulose acetate, and starch polyester, but it is preferable to use polylactic acid, which can form a film at a relatively low temperature. In addition, multiple biodegradable resins can be mixed in any ratio to adjust the minimum film-forming temperature. The minimum film-forming temperature can also be lowered by using polylactic acid in this case.

In the present invention, a biodegradable resin emulsion is used whose minimum film-forming temperature has been adjusted to 80°C or less, preferably 60°C or less. If the minimum film-forming temperature of the biodegradable resin emulsion exceeds 80°C, the biodegradable resin will not function as a granulation promoter that binds guanylurea in the rolling granulation process, and instead the fertilizer raw material will adhere to the inside of the granulator due to the viscosity derived from the biodegradable resin emulsion, resulting in the generation of large particles or lumps that exceed the product size, or an increase in the amount of powdered material recovered, significantly reducing the product yield. This occurs in the same way whether the guanylurea to be granulated is guanylurea sulfate or guanylurea phosphate. In order to avoid the effects of raw material dissolution that occurs during granulation, it is necessary that the minimum film-forming temperature of the biodegradable resin emulsion be 80°C or less.

In the present invention, the minimum film-forming temperature refers to the minimum temperature at which a coating film made of an aqueous emulsion of a biodegradable resin changes from white to transparent.

The minimum film-forming temperature can be measured, for example, by coating a sample on black paper with a doctor blade (coating thickness: 50 μm) to create a test piece, then heating and drying the test piece in a hot air dryer at a specified temperature for 5 minutes, and determining the minimum temperature at which the coating changes from white to transparent.

As an example of an aqueous emulsion of a biodegradable resin with a minimum film-forming temperature of 80°C or less, polylactic acid emulsion is commercially available, and such a commercially available product can be used.

The content of the biodegradable resin in the granular fertilizer of the present invention is usually 0.5 to 10.0% by weight, preferably 1.0 to 5.0% by weight.

If necessary, the granular fertilizer of the present invention may contain granulation promoters (e.g., attapulgite, CMC (carboxymethylcellulose), lignin sulfonic acid, sodium polyphosphate, polyethylene glycol, polyvinyl alcohol, attapulgite, starch, gum arabic, molasses), peat moss, humic acid materials, bentonite, zeolite, vermiculite, perlite, pulverized coal incineration ash, gypsum, etc.

The proportions of these fertilizer components can be varied as appropriate as long as they do not impair the effects of the present invention.

Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these. All parts below refer to parts by weight.

Below, the minimum film-forming temperature of the biodegradable resin emulsion was measured as follows.

(Method for measuring the minimum film-forming temperature of biodegradable resin emulsion)
A test piece (15 cm x 7.5 cm) made of black paper was fixed to a smooth plastic board, and 0.5 g of biodegradable resin emulsion was dropped onto the center of the test piece and coated onto the test piece using a doctor blade film applicator (Allgood Co., Ltd., coating width 5 cm, coating thickness 50 μm). The test piece coated with the biodegradable resin emulsion in a uniform thickness was heated and dried for 5 minutes in a ventilated dryer set to a predetermined temperature, and the transparency of the coating was visually confirmed. The lowest temperature at which the coating became transparent enough to confirm the black color of the test piece was recorded as the minimum film-forming temperature.

(Example 1) 95.0 parts of guanylurea sulfate, spraying of 20°C film-forming resin emulsion 95.0 parts of guanylurea sulfate, the particle size of which was adjusted to less than 1.00 mm by sieving, was put into a pan granulator (pan diameter 80 cm, rotation speed 22 rpm, inclination angle 52.5°; the same applies below). A 10.0% by weight polylactic acid emulsion (commercial product A, minimum film-forming temperature 20°C) was sprayed until the amount of polylactic acid added reached 5.0 parts, and tumbling granulation was performed to obtain a granular fertilizer. The prepared granular fertilizer was dried for 5 hours in a ventilated dryer set at 80°C.

(Example 2) 87.0 parts of guanylurea sulfate, dropwise addition of 20°C film-forming resin emulsion 87.0 parts of guanylurea sulfate, the particle size of which was adjusted to less than 1.00 mm by sieving, 3.0 parts of attapulgite, a known granulation promoter, and 5.0 parts of gypsum dihydrate were charged into a stirring granulator (Nihon Eirich Co., Ltd., Intensive Mixer R02 type), and a 40.0% by weight polylactic acid emulsion (commercial product A, minimum film-forming temperature 20°C) was added dropwise until the amount of polylactic acid added reached 5.0 parts, and tumbling granulation was performed to obtain a granular fertilizer. The prepared granular fertilizer was dried for 5 hours in a ventilated dryer set at 80°C.

(Example 3) 87.0 parts of guanylurea sulfate, spraying of 80°C film-forming resin emulsion 87.0 parts of guanylurea sulfate, the particle size of which was adjusted to less than 1.00 mm by sieving, 3.0 parts of attapulgite, a known granulation promoter, and 5.0 parts of gypsum dihydrate were mixed by rolling in a sugar coating machine and then put into a pan granulator. A 10.0% by weight polylactic acid emulsion (commercial product B, minimum film-forming temperature 80°C) was sprayed until the amount of polylactic acid added reached 5.0 parts, and granular fertilizer was obtained. The prepared granular fertilizer was dried for 5 hours in a ventilated dryer set at 80°C.

Comparative Example 1: 87.0 parts of guanylurea sulfate, dripping of 180°C film-forming resin emulsion 87.0 parts of guanylurea sulfate, the particle size of which was adjusted to less than 1.00 mm by sieving, 3.0 parts of attapulgite, a known granulation promoter, and 5.0 parts of gypsum dihydrate were charged into a stirring granulator (Nihon Eirich Co., Ltd., Intensive Mixer R02 type), and a polylactic acid emulsion adjusted to 40.0% by weight (commercial product C, minimum film-forming temperature 180°C) was dripped in until the amount of polylactic acid added reached 5.0 parts, and tumbling granulation was performed to obtain a granular fertilizer. The prepared granular fertilizer was dried for 5 hours in a ventilated dryer set at 80°C.

Comparative Example 2: 100.0 parts of guanylurea sulfate, no granulation promoter used 100.0 parts of guanylurea sulfate, the particle size of which was adjusted to less than 1.00 mm by sieving, was put into a pan granulator. A granular fertilizer was obtained by rolling granulation while spraying tap water. The granular fertilizer was dried for 5 hours in a ventilated dryer set at 80°C.

(Comparative Example 3) 90.0 parts of guanylurea sulfate, 10.0 parts of a known granulation promoter 90.0 parts of guanylurea sulfate, the particle size of which was adjusted to less than 1.00 mm by sieving, and 5.0 parts of attapulgite and 5.0 parts of bentonite, which are known granulation promoters, were mixed by rolling in a sugar coating machine and then put into a pan granulator. The mixture was granulated by rolling while spraying tap water, to obtain a granular fertilizer. The granular fertilizer was dried for 5 hours in a ventilated dryer set at 80°C.

(Comparative Example 4) 75.0 parts of guanylurea sulfate, 25.0 parts of a known granulation promoter 75.0 parts of guanylurea sulfate, the particle size of which was adjusted to less than 1.00 mm by sieving, 18.7 parts of superphosphate, and 6.3 parts of attapulgite, a known granulation promoter, were mixed by rolling in a sugar coating machine and then put into a pan granulator. While spraying tap water, rolling granulation was performed to obtain a granular fertilizer. The prepared granular fertilizer was dried for 5 hours in a ventilated dryer set at 80°C.

(Comparative Example 5) 71.2 parts of guanylurea sulfate, 5.8 parts of a known granulation promoter 71.2 parts of guanylurea sulfate, the particle size of which was adjusted to less than 1.00 mm by sieving, 23.0 parts of superphosphate, 1.1 parts of attapulgite, a known granulation promoter, and 4.7 parts of diatomaceous earth were mixed by rolling in a sugar coating machine and then put into a pan granulator. Granulated by rolling while spraying tap water, a granular fertilizer was obtained. The granular fertilizer was dried for 5 hours in a ventilated dryer set at 80°C.

(Test Example 1) Product Yield and Particle Size Distribution Evaluation The total amount of the fertilizer raw materials in the Examples and Comparative Examples shown in Table 1 was taken as 100, and the yield was calculated from the weight of the granular fertilizer obtained after the drying step. Furthermore, the granular fertilizer was sieved through 4.00 mm and 2.00 mm sieves, which are general particle size standards for commercially available chemical fertilizers, and the product yield was calculated from the weight of the granular fertilizer with particle sizes less than 4.00 mm and not less than 2.00 mm, and evaluated as shown in Table 2. In addition, the weight lost from the tumbling granulation to the drying step and the weight of the granular fertilizer with particle sizes of not less than 4.00 mm or not less than 2.00 mm due to sieving were totaled to calculate the loss rate in the production step of the granular fertilizer and evaluate it together with the product yield. In addition, the product standards with particle sizes between 4.00 mm and 2.00 mm were further sieved, and the weights of the granular fertilizers sieved into large particle sizes of 4.00 mm to 3.35 mm, medium particle sizes of 3.35 mm to 2.83 mm, and small particle sizes of 2.83 mm to 2.00 mm were measured to calculate the particle size distribution, which was evaluated as shown in Table 3.

In Examples 1 to 3, where the minimum film-forming temperature of the biodegradable resin emulsion is 80°C or less, the added biodegradable resin prevents excessive particle enlargement due to dissolution of guanylurea sulfate, and the product yield is mainly obtained in the small particle size range of 2.83 mm to 2.00 mm, while preventing an increase in the loss rate due to particle sizes exceeding 4.00 mm.

In Comparative Example 2, which did not use either a biodegradable resin or a granulation promoter, the loss due to the particle size being 4.00 mm or more exceeded 60% by weight. Even when the particle size was less than 4.00 mm, the yield was high despite the larger particle size, and the dissolution of guanylurea sulfate could not be prevented, making it prone to enlargement.

Comparative Example 1, in which the minimum film-forming temperature of the biodegradable resin was 180°C, and Comparative Examples 3 to 5, in which granulation was performed using only a known granulation promoter without using a biodegradable resin, had a loss rate of around 50% by weight due to particle sizes of 4.00 mm or more. Even within the product specifications, many of the particles had larger particle sizes, and the fertilizer granules were prone to enlarging.

Claims (7)

A granular fertilizer containing 80% by weight or more of guanylurea sulfate or guanylurea phosphate, and having a biodegradable resin formed from an aqueous emulsion of a biodegradable resin having a minimum film-forming temperature of 80°C or less dispersed within the granular fertilizer. The granular fertilizer according to claim 1, wherein the biodegradable resin contains polylactic acid. The granular fertilizer according to claim 1 does not contain 1-amidino-2-thiourea or sulfathiazole. A method for producing the granular fertilizer according to any one of claims 1 to 3, comprising granulating a raw material containing guanylurea sulfate or guanylurea phosphate using an aqueous emulsion of a biodegradable resin having a minimum film-forming temperature of 80°C or less. The method according to claim 4, wherein the aqueous emulsion contains 1 to 50% by weight of a biodegradable resin. The method according to claim 4, in which the aqueous emulsion is sprayed or dropped and granulated by rolling. The method according to claim 4, in which granulation is carried out using a pan granulator, drum granulator or agitator granulator.