JP7650314B2 - Rice seed coating agent - Google Patents

Description

The present invention relates to a rice seed coating agent suitable for coating rice seeds, specifically, a rice seed coating agent that can be produced at low cost and solves the environmental problem of harvested bamboo by suppressing heat generation due to oxidation reactions even when using conventional iron powder-based coating agents.

With the aging of agricultural workers and the globalization of agricultural product distribution, labor saving in agricultural work and reduction of agricultural production costs have become issues that need to be resolved. To address these issues, for example, in rice cultivation, direct seeding methods in which rice seeds are sown directly in fields are becoming more widespread in order to save the labor of raising seedlings and transplanting. Among these methods, the method of using rice seeds coated with iron powder to increase the specific gravity of the rice seeds has attracted attention because it has the advantage of preventing rice seeds from floating or flowing out of paddy fields and preventing bird damage.
In order to coat rice seeds with iron powder, it is necessary to adhere and fix the iron powder to the surface of the rice seeds. Therefore, the technique described in Patent Document 1 has been proposed as a technique for adhering and solidifying the iron powder to the surface of the rice seeds.
Patent Document 1 discloses a technique of using a rice seed coating agent containing iron powder, a binder, and an additive.
Furthermore, Patent Documents 2 and 3 disclose a technique for suppressing the reaction rate of the exothermic oxidation reaction by using iron powder in which a white pig metal structure (pig iron in which carbon is in the form of plate-like cementite crystals and the fracture surface is white) is formed in part or in its entirety, instead of using reduced iron powder.

JP 2017-23082 A Patent No. 6588059 Patent No. 6734976

Conventional rice seed coating agents use finely ground reduced iron powder as the main raw material. The same is true for the rice seed coating agent described in Patent Document 1. However, with reduced iron powder, after coating, the temperature rises rapidly due to an exothermic oxidation reaction, and there is a risk that the coated rice seeds will die. Therefore, the rice seeds need to be cured by spreading them thinly in one or two layers to prevent heat buildup. In other words, when using conventional rice seed coating agents, a large curing area is required.
In addition, while the technologies described in Patent Documents 2 and 3 do indeed enable multi-layer curing by suppressing heat generation due to oxidation reactions and make it possible to provide a rice seed coating agent that is inexpensive to produce, these are different from commonly used rice seed coating agents, and therefore there is an urgent need to establish technology to suppress heat generation even with commonly used rice seed coating agents.

Incidentally, the heat generated by the rice seed coating agent is largely due to an exothermic oxidation reaction that occurs when the rice seed coating agent comes into contact with water. However, the gypsum was thought to be essential for the coating of rice seeds with the rice seed coating agent. For this reason, it was not possible to reduce the risk of the rice seeds dying due to the heat generated when the rice seeds were coated with the rice seed coating agent.

Therefore, after extensive research, the inventors investigated alternative materials to gypsum among the raw materials commonly used in rice seed coating agents, and discovered that the intricate intertwining of bamboo flour fibers allows iron powder to penetrate between the bamboo flour fibers, making it possible to coat the rice seeds and therefore making it possible to use this as an alternative material to gypsum, thus completing the present invention.
The present invention aims to provide a rice seed coating agent that can be produced inexpensively and that enables multi-layer curing by suppressing heat generation due to oxidation reactions even when conventional iron powder-based coating agents are used.

The invention described in claim 1 is a rice seed coating agent containing iron powder and an additive, in which part or all of the gypsum that promotes the oxidation of the iron powder is replaced with bamboo powder.
The invention described in claim 2 is the rice seed coating agent described in claim 1, in which the bamboo powder is added in an amount of 2 to 6 parts by weight per 100 parts by weight of the iron powder.
The invention described in claim 3 is the rice seed coating agent described in claim 1 or claim 2, wherein the calcined gypsum is contained in an amount of 10 parts by weight or less per 100 parts by weight of the iron powder.

The iron powder may be iron powder in which a white pig metal structure as found in the prior art is formed in part or in whole, or may be iron powder used in a conventional iron powder-based coating agent.
The bond (adhesion, fixation) between the rice seed and the rice seed coating agent occurs due to the progression of the oxidation reaction of the iron component contained in the rice seed coating agent, which generates heat. Powder with white pig iron metal structure has a slow reaction rate of oxidation reaction, so heat generation is also slow. Therefore, even with multi-layer curing, the death of rice seeds is suppressed, making it an excellent rice seed coating agent.
If the particle size of the rice seed coating agent is fine, the strength of the bond between the rice seeds and the rice seed coating agent will be increased. Therefore, the particle size of the rice seed coating agent is preferably 106 μm or less, and more preferably 63 μm or less.

Conventional rice seed coating agents contain gypsum, but in the present invention, part or all of the gypsum is replaced with bamboo powder.
When gypsum comes into contact with water, it promotes the oxidation of iron powder and coats the rice seeds, but according to the present invention, the bamboo powder fibers are intricately entangled, allowing the iron powder to penetrate between the bamboo powder fibers and coat the rice seeds. This makes it possible to use it as an alternative material to gypsum.
Even when a commercially available rice seed coating agent is used as the raw material for the rice seed coating agent, the bamboo powder suppresses heat generation due to oxidation reactions. Since the risk of rice seeds dying increases when the temperature exceeds 40°C, care must be taken not to exceed 40°C during curing. However, by including bamboo powder, the maximum heat generation temperature does not reach 40°C even when cured at room temperature (34.0°C) with 30 mm layers (about 15 layers). Therefore, the death of rice seeds is significantly suppressed even with multi-layer curing.

Bamboo powder is made by crushing (shredding) bamboo into a powder, but it does not have to be completely powdered and may contain fibrous material.
The bamboo powder is preferably added in an amount of 2 to 6 parts by weight per 100 parts by weight of iron powder. If the amount is less than 2 parts by weight, the bamboo powder fibers are not sufficiently entangled, and the rice seeds are not sufficiently coated. On the other hand, as long as the bamboo powder fibers are sufficiently entangled, there is no upper limit in the present invention, but for economic reasons, if the amount is 6 parts by weight or less, the effects of the present invention can be maximized.

When part of the calcined gypsum contained in the rice seed coating agent is replaced with bamboo powder, it is preferable that the amount of calcined gypsum contained in the rice seed coating agent is 10 parts by weight or less per 100 parts by weight of iron powder. If it is 10 parts by weight or more, the effect of the bamboo powder in suppressing heat generation is low, and the risk of the rice seeds dying increases.

The invention described in claims 4 and 5 is the rice seed coating agent described in any one of claims 1 to 3, in which the bamboo powder is pulverized into a fine powder and passes through a sieve with a standard mesh size of 355 μm.

The bamboo powder is crushed into a fine powder and is used only if it has passed through a sieve with a standard mesh size of 355 μm, which makes it possible to homogenize the coating and is advantageous in terms of appearance.

The invention described in claims 6 to 9 is the rice seed coating agent described in any one of claims 1 to 5, in which the bamboo powder is heat-treated with superheated steam.

Bamboo powder may be heat-treated (dried) with superheated steam before use, as described in claims 6 to 9. In this case, the bonds with the cellulose and lignin contained in the bamboo powder are broken, resulting in fine fibers, which are advantageous in terms of the quality of the coating of the rice seed coating agent.
In addition, the moisture contained in the bamboo powder can be removed, making it less likely to spoil and improving the shelf life of the rice seed coating agent.

According to the present invention, the bamboo powder fibers are intricately intertwined, allowing the iron powder to penetrate between the bamboo powder fibers and coat the rice seeds. This makes it possible to use it as an alternative to gypsum. Therefore, when there is no heat generation from gypsum or when it is partially replaced, the amount of heat generated is small, reducing the risk of the rice seeds dying.

In particular, according to the inventions described in claims 6 to 9, by heat treating (drying) the bamboo powder with superheated steam before use, the bonds between the cellulose and lignin contained in the bamboo powder are broken down, turning it into fine fibers, which is advantageous in terms of the quality of the coating film of the rice seed coating agent.
In addition, the moisture contained in the bamboo powder can be removed, making it less likely to spoil and improving the shelf life of the rice seed coating agent.

The rice seed coating agent of the present invention is used to coat the surface of rice seeds and contains iron powder.

(Iron powder A: iron powder used in conventional iron powder-based coating agents)
Iron powder for iron coating (S91) manufactured by JFE Steel Corporation was used.

(Iron powder B: Iron powder used in another type of iron powder coating agent)
Molten slag produced in a blast furnace is quenched with a large amount of water to produce sand-like granulated blast furnace slag, which is then magnetically separated, and the magnetic material obtained by magnetic separation is called granulated blast furnace metal, which is used as a raw material for rice seed coating agents. The non-magnetic material obtained by magnetic separation is used as a raw material for cement by cement companies, etc. In the blast furnace cement manufacturing process, the raw materials for cement are crushed and then magnetically separated, and the magnetic material components obtained at this time can also be used as granulated blast furnace metal (raw material).
The granulated blast furnace metal thus obtained was subjected to magnetic separation, and the magnetic material was further crushed and sieved to adjust the particle size, thereby obtaining a rice seed coating agent.
The pulverizer used was a ball mill (dimensions: φ1500×3000 mm) manufactured by Kahara Steel Works, Ltd. The sieving machine used was a Sato-type vibration sieve 500D-2S manufactured by Koei Sangyo Co., Ltd. For sieving, a sieve with a mesh size of 104 μm was used.

The moisture content, average particle size (median diameter), bulk density, and true density of iron powder A and iron powder B are shown in Table 1. The average particle size was measured using a laser diffraction/scattering type particle size distribution measuring device LA-350 (manufactured by Horiba, Ltd.). The true density was measured using a 100 ml Gay-Lussac type pycnometer.

The components of iron powder A and iron powder B were measured. The measurement results are shown in Table 2. The components of T, Fe, Si, Mn, P, and S were measured using an ICP emission spectrometer SPS3500DD (manufactured by SII NanoTechnology Co., Ltd.).
The amount of metallic iron was measured based on the metallic iron determination method specified in JIS M 8213 (method for determining acid-soluble ferrous iron), and the amount of carbon was measured based on the combustion-gas determination method specified in JIS G 1211 (method for determining total carbon).

(Preparation of rice seed coating agent)
The rice seed coating agent was prepared by mixing iron powder A or iron powder B with secondary materials such as calcined gypsum, silica gel, bentonite, ground granulated blast furnace slag, lignin sulfonate, starch, carboxymethyl cellulose (CMC), and polyvinyl alcohol (PVA). The proportions of the additives are described according to the type of test. All secondary materials used were commercially available. Three types of bamboo powder (bamboo powder A to bamboo powder C) were used as secondary materials. Bamboo powder A was made by crushing bamboo, bamboo powder B was made by crushing bamboo into a fine powder, and bamboo powder C was made by heat-treating bamboo with superheated steam at 200°C for 30 minutes and then crushing it into a fine powder.

(Covering a small amount of rice seeds)
The dried rice seeds were immersed in water for 3 days in a thermo-hygrostat (20°C, 60%), then removed from the water and air-dried. The dried seeds were then placed in a coating machine (pan pelletizer, manufactured by Japan Magnetic Dressing Co., Ltd., diameter 500 mm) and operated at a rotation speed of 25 rpm. The rice seed coating agent was then added in small amounts, and the rice seeds were coated while spraying water with a spray as necessary.
All the materials for coating the rice seeds were added, and the rice seeds were visually confirmed to be complete, and the coated rice seeds were removed from the coating machine.
After coating, the rice seeds were cured to dry out the moisture and oxidize the iron contained in the coating agent to form a strong layer of rust on the surface. The coated rice seeds were cured in a thermo-hygrostat (20°C, 60%) for six days. The coated rice seeds were sprayed with water once a day.

(Scaling up rice seed coating)
Water was poured into the germination machine, the water temperature was set to 35°C, the dried rice seeds were put into the germination machine, immersed in water for one day, then removed from the water and air-dried. The dried seeds were then put into a concrete mixer, the angle was adjusted, and the machine was operated at a rotation speed of 43 rpm. The rice seed coating agent was then put in three separate times, and the rice seeds were coated while spraying water with a spray as necessary.
All the materials for coating the rice seeds were added, and the rice seeds were visually confirmed to be completely coated.The coated rice seeds were then removed from the coating machine.
The coated rice seeds were stacked to a length of 265 mm, a width of 183 mm, and a thickness of 30 mm, and were cured for 6 days in an indoor laboratory without air conditioning. During the curing, the coated rice seeds were sprayed with water once a day.

(Peel test)
50 g of coated rice seeds were dropped five times onto an iron plate from a height of 1 m, and then sieved using a sieve with 2 mm openings. The remaining percentage (wt.%) on the sieve was evaluated as the coating strength (peel strength). If it was not possible to measure, it was indicated as (-).

(Appearance test)
The appearance of the coated rice seeds was visually checked, and those with little uneven adhesion of the material and a coating were rated as good (○). Seeds that formed clumps of rice seeds during coating, those that had a lot of adhesion to the equipment, or those that had a lot of material that could not be coated were rated as poor (×).

The results of the peel test and appearance test are shown in Tables 3 and 4. The units of the blend ratio are parts by weight, and the unit of the coating strength is wt. %.

From Tables 3 and 4, it was found that depending on the type of secondary material, the coating strength was higher than when no secondary material was added. In this case, it was revealed that by adding bamboo powder as an organic secondary material, the coating strength had the same performance as when an inorganic secondary material was added.
In addition, when comparing bamboo powder A and bamboo powder B, the appearance of bamboo powder A was poor. This is thought to be because bamboo powder A is made by crushing bamboo, while bamboo powder B is made by crushing bamboo into a fine powder, and bamboo powder A contains more long bamboo fibers than bamboo powder B.

Next, the amounts of bamboo powder A, bamboo powder B, and bamboo powder C were divided and subjected to coating strength tests and appearance tests. The results are shown in Table 5. The units of the blending ratio are parts by weight, and the units of coating strength are wt. %.

From Table 5, it was found that the coating strength increases as the amount of bamboo powder added increases, but once a certain amount is added, the coating strength decreases.

(Heat generation test)
In the heat generation test, the temperature (maximum heat generation temperature) during curing in the scale-up of the rice seed coating was measured using a T thermocouple with a diameter of 0.65 mm.

(Germination rate)
The germination rate was determined by placing 100 coated rice seeds after 7 days of curing in a petri dish, adding 40 ml of water, curing for 7 days in a thermo-hygrostat (30°C, 60%), and counting the number of germinated seeds immediately after curing. Two samples were prepared for the germination rate, and the average of the number of germinated seeds was calculated.
The germination rate of uncovered rice seeds was also measured under the same conditions.

The results of the heat generation test and germination rate are shown in Table 6. The units of the mixture ratio are parts by weight, the units of the maximum heat generation temperature are °C, and the units of the germination rate are %. The layering during curing was 30 mm, and the maximum room temperature was 33.8 °C.

Tables 7 and 8 show the changes in maximum heat generation temperature and germination rate when the curing conditions (length, width, height) are changed in the scale-up of rice seed covering. The germination rate is expressed in %.

Generally, in the curing conditions immediately after covering, the higher the curing height, the higher the heat storage capacity, and therefore the higher the maximum heat generation temperature. Rice seeds are at a higher risk of dying if the temperature exceeds 40°C, so care must be taken not to exceed 40°C during curing. When inorganic auxiliary materials are added, the higher the curing height, the higher the maximum heat generation temperature, and the lower the germination rate.
In contrast, when bamboo powder C was used, even if the height of the bed was increased, the maximum heat generation temperature sometimes exceeded 40°C, but no significant decrease in germination rate was observed. Therefore, the death of rice seeds was suppressed, and it can be said to be an excellent rice seed coating agent.

Next, the amount of bamboo powder C added was fixed at 4 parts by weight, the amount of calcined gypsum was distributed, and a coating strength test and an appearance test were performed. The results are shown in Table 9. The unit of the blending ratio is parts by weight, and the unit of the coating strength is wt. %.

The results of the heat generation test are shown in Table 10. The units of the blend ratio are parts by weight, and the units of the maximum heat generation temperature are °C.

According to Tables 9 and 10, in conventional rice seed coating agents, it is not necessary to replace all of the gypsum with bamboo powder; even if part of the gypsum is replaced with bamboo powder, it can contribute to suppressing heat generation and reduce the risk of rice seeds dying.

Claims (9)

A rice seed coating agent comprising iron powder and an additive,
A rice seed coating agent in which part or all of the gypsum that promotes the oxidation of the above iron powder is replaced with bamboo powder. The rice seed coating agent according to claim 1, in which the bamboo powder is added in an amount of 2 to 6 parts by weight per 100 parts by weight of the iron powder. The rice seed coating agent according to claim 1 or 2, wherein the calcined gypsum is 10 parts by weight or less per 100 parts by weight of the iron powder. The rice seed coating agent according to claim 1 or 2, wherein the bamboo powder is pulverized into a fine powder and passes through a sieve with a standard mesh size of 355 μm. The rice seed coating agent according to claim 3, wherein the bamboo powder is pulverized into a fine powder and passes through a sieve with a standard mesh size of 355 μm. The rice seed coating agent according to claim 1 or 2, wherein the bamboo powder has been heat-treated with superheated steam. The rice seed coating agent according to claim 3, wherein the bamboo powder has been heat-treated with superheated steam. The rice seed coating agent according to claim 4, wherein the bamboo powder has been heat-treated with superheated steam. The rice seed coating agent according to claim 5, wherein the bamboo powder has been heat-treated with superheated steam.