JPH05212262A - Coating method of granular substance - Google Patents

Abstract

PURPOSE:To uniform thickness of a coating film, to prevent granulation of each particle and also to avoid breakage of the particle by adding the solvent solution of polymer substance to granular substance held at the temperature not higher than the temperature for dissolving the polymer substance. CONSTITUTION:The coating film of granular substance is formed by adding the solvent solution of polymer substance to granular substance held at the temperature not higher than the temperature for dissolving the polymer substance. Such a method that granular substance is agitated by movement of the movable part of an agitator is adopted as the method for agitating the granular substance. The temperature for dissolving the polymer substance in the solvent is the temperature for dissolving >=0.1wt.% polymer substance for the solvent. When the temperature of the granular substance is not higher than the temperature for dissolving the polymer substance and also granulation is caused, the temperature of the granular substance is preferably held at the lower temperature. However, when the temperature of the granular substance is excessively lowered, the removing speed of the solvent is lowered and an incompletely coated film may be obtained. Therefore, the temperature of the granular substance is ordinarily regulated to normal temperature or above preferably to >=30 deg.C.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for coating particulate matter. More specifically, the present invention relates to a method for coating a granular substance applied in the fields of medicines, foods, agricultural materials and the like.

[0002]

2. Description of the Related Art Conventionally, a technique for forming a film on the surface of a granular material has been used in various fields such as pharmaceuticals, foods, agricultural materials, etc., and contributes to improving the physical properties of the granular material and imparting functionality. ing. For example, by forming a film of a substance that is sparingly soluble or insoluble in water on the surface of a granular substance containing a water-soluble substance or a hydrolyzable substance, the hygroscopicity of the granular substance and the solidification property over time can be improved. It is possible to reduce the amount thereof and the elution property to water.

Generally, as the coating substance, a polymeric substance such as a thermosetting resin or a thermoplastic resin having a high film forming ability is often used. In order to efficiently exhibit the function of coating these substances with a small coating amount, it is important to form a film having a uniform thickness on the surface of the granular substance. When the coating substance is soluble in the solvent, if it is diluted with the solvent and added little by little to make it adhere, the dispersibility of the coating substance becomes high and a film having a uniform thickness can be obtained.

In the method using this solvent, it is necessary to remove the solvent in the coating substance solution adhered to the granular substance by heating or the like in order to form a coating film. Difficult to form Also,
When the coating substance solidifies in the state where the droplets of the coating substance solution adhere to two or more particles at the same time, a so-called agglomeration phenomenon occurs, and it becomes impossible to obtain the intended coated granular substance having a uniform particle diameter.

Therefore, various studies have been made for the purpose of increasing the removal rate of the solvent in the coating solution added to the surface of the granular material and avoiding the agglomeration of the particles. For example, the method disclosed in Japanese Examined Patent Publication No. 54-3104 is a method in which a large amount of high-speed hot air flow is used to instantaneously remove the solvent of the coating solution adhering to the particle surface in the state of individual jet flow of the particles. And is an effective method. In this method, the particle temperature rises due to a large amount of high-speed hot air flow, but even if the particle temperature exceeds the melting temperature of the coating substance in the solvent, the agglomeration phenomenon does not occur unless the temperature is raised to the melting temperature of the coating substance. It is speculated that this is because the solvent is instantaneously removed before the coating material on the particle surface is redissolved in the coating solution.

However, in the case of the above method, since the particles flow at high speed due to the high-speed hot air flow, the particles are likely to be damaged by a strong mechanical impact, and
It is difficult to scale up, and there are drawbacks such as low production efficiency due to batch operation.

[0007]

Conventionally, in a solvent-based coating method using a solvent solution of a polymer substance, in order to prevent the particles from agglomerating in order to have a uniform thickness, Although it has been impossible without using a jet fluidized bed, the present inventors have found that in the solvent-based coating method, in addition to preventing the particles from being agglomerated, the coating has a uniform thickness.
The present invention has been achieved as a result of extensive studies aimed at providing a coating method with high production efficiency without particle breakage.

[0008]

Means for Solving the Problems That is, the gist of the present invention is to stir a solvent solution of a polymeric substance by the motion of the stirrer itself, and keep it below the dissolution temperature of the polymeric substance in the solvent. A method for coating a particulate substance, which comprises adding a solvent to the particulate substance or after the addition to remove the solvent to form a film of the polymer substance on the surface of the particulate substance.

The present invention will be described in detail below. The polymer substance used in the present invention is not particularly limited, and is appropriately selected according to the type of the granular substance to be coated, the purpose of coating, and the like. For example, in order to reduce the hygroscopicity and the solidification property of a granular substance containing a water-soluble substance or a hydrolyzable substance such as fertilizer with time, or to reduce the elution property to water, the permeability of the formed film is reduced. Since it is preferable that the wettability is low, thermoplastic resins are preferably used. In particular, polyolefin resins such as polyethylene and polypropylene and polyvinylidene-series polyvinyl resins have a low moisture permeability, so that even a small amount has a high coating effect and is economically advantageous.

The solvent for the polymeric substance is not particularly limited, either,
It is appropriately selected in consideration of various conditions, for example, the type of the granular substance to be coated, the dissolving power and the dissolving temperature of the polymer substance, the handling property, the ease of collecting the solvent itself, the toxicity, the safety, the price, and the like. For example, when a polyolefin resin is used as the polymer substance, a hydrocarbon solvent such as hexane, octane, toluene, xylene and tetralin, and a chlorinated hydrocarbon solvent such as trichloroethylene and perchlorethylene are preferably used.

Although the concentration of the solvent solution is not particularly limited, it is appropriately selected depending on the kind of the polymer substance and the kind of the solvent. Generally, increasing the concentration reduces the amount of solvent used and shortens the treatment time.On the other hand, lowering the concentration reduces the viscosity and improves the handling properties, and also improves the dispersibility during addition. Tend to be advantageous, and it is necessary to select in consideration of these. Usually, it is about 1 to 15% by weight. For example, when a polyolefin resin, particularly low-density polyethylene, is used as the polymer substance and perchlorethylene is used as the solvent, the concentration of the solution is preferably 1 to 12% by weight, more preferably 3 to 10% by weight.

The granular substance is not particularly limited as long as it is a substance that needs to form a film of a polymeric substance on the surface, and its shape is usually in order to enhance the uniform dispersibility of the polymeric substance as a coating substance. It is preferable that the particle size distribution is sharp, the sphericity is high, and the surface is smooth. In the present invention, since it is possible to coat the granular material with a polymer substance which is hardly soluble or insoluble in water, the granular substance is granular when it is a granular substance containing a water-soluble substance or a hydrolyzable substance. It is possible to control the elution properties of the components in the substance. For example,
When fertilizer is used as granular material, its particle size is about 1
It is 10 mm, preferably 2 to 4 mm. Further, in the present invention, since the granular material is agitated by utilizing the motion of the agitation device itself (hereinafter, this agitation is also referred to as “mechanical agitation”), the hardness of the granular material is damaged by the mechanical agitation. It is preferable not to do so, and usually 1.0 kg / piece or more, preferably 1.5 kg / piece or more is sufficient. The method of the present invention is particularly effective when a fertilizer containing a water-soluble substance or a hydrolyzable substance is used as the granular substance. As such a fertilizer, for example, most fertilizers typified by organic nitrogen compounds such as crotylidene diurea (CDU), isobutylidene diurea (IBDU), oxamide and ureaform, and sparingly soluble salts such as magnesium ammonium phosphate can be applied.

In the method of the present invention, a film of a polymeric substance is formed on the surface of the granular substance, but if the purpose of coating the granular substance is not impaired, in addition to the polymeric substance, other inorganic substances and organic substances are added to the polymeric substance. Coating may be carried out by coexisting in a solvent solution (hereinafter referred to as "coating solution"). For example, when coating for the purpose of changing the water resistance as described above,
Coexistence of inorganic minerals such as talc, sparingly soluble inorganic salts such as magnesium carbonate and tricalcium phosphate, surfactants, and organic substances such as other thermoplastic resins for the purpose of adjusting the dissolution and increasing the amount of resin Is possible.

As a method of stirring the particulate matter, a method of stirring the particulate matter by the movement of the stirring device itself is adopted. In the present specification, the phrase "granular substance is stirred by the movement of the stirring device itself" means that the particulate substance is stirred by the movement of the movable portion of the stirring device, and is not particularly limited as long as such stirring is possible. However, an apparatus that can stir a large amount of particulate matter is preferable, and dispersibility of the coating solution to be added is enhanced if the particulate matter is vigorously stirred so as not to be damaged, which is preferable. Among such stirring methods, a method of stirring the particulate matter by moving the container itself in which the particulate matter is housed is particularly preferable. Specifically, for example, as disclosed in Japanese Patent Laid-Open No. 52-61216, a method of using a rotary drum to stir with the rotational force of the drum, and Japanese Patent Laid-Open No. 1-245847, are disclosed. A method of stirring with a vibrating force using a vibrating fluidizer is preferable since a large amount of granular material can be vigorously stirred. Especially when a rotary drum is used
If a louver or the like is installed on the wall surface of the rotating drum as disclosed in Japanese Patent No. 61216, the efficiency of converting the rotational force into the scraping force is increased, and the stirring efficiency is also increased. It is preferable because it can be produced and the production efficiency is high.

The method of adding the coating solution is not particularly limited, but it is preferable that the dispersibility of the solution becomes high at the time of addition, and it is usually added by spraying. Furthermore, it is preferable to add the granular substance to a portion where the granular substances are vigorously moving, because the dispersibility becomes high. For example, when a rotating drum type stirring device is used, it is preferably added to falling particle groups and to a vibrating stirring and fluidizing device to the most vibrating particle groups.

In the method of the present invention, it is necessary to maintain the temperature of the particulate matter below the melting temperature of the polymer substance in the solvent. Here, the dissolution temperature of the polymer substance in the solvent means the temperature at which the polymer substance dissolves in the solvent by 0.1% by weight or more. Even if the temperature of the granular material is below the dissolution temperature of the polymer substance in the solvent, if the temperature of the solvent solution of the polymer substance is higher than the melting temperature locally and the agglomeration phenomenon occurs, keep it at a lower temperature. It is preferable to do. However, if the temperature of the particulate matter is lowered too much,
The removal rate of the solvent may decrease, resulting in an incomplete film. Therefore, the temperature of the granular substance is usually room temperature or higher, preferably 30 ° C. or higher. In particular, for example, when a polyolefin resin, particularly low-density polyethylene is used as the polymer substance, perchlorethylene is used as the solvent, and the temperature of the solvent solution of the polymer substance is 80 to 100 ° C. The temperature is preferably 30 ℃ or more and 60 ℃
It is less than 35 ° C., more preferably 35 ° C. or more and 50 ° C. or less.

In the present specification, the temperature of the particulate matter means the surface temperature of the particulate matter, and the measurement thereof is performed, for example, by a secondary thermometer such as a thermocouple thermometer installed in a stirrer while stirring. It can be performed by contacting with a substance.
As a method of maintaining the temperature of the particulate matter at a constant temperature,
Usually, the factors that affect the temperature of the particulate matter, that is, the amount and temperature of the heated air, the temperature of the device itself, especially the part in contact with the particulate matter, the amount and surface area of the particulate matter, the specific heat, the concentration of the coating solution, and the addition rate -It is performed by controlling the temperature and the heat of evaporation of the solvent. Above all, it is preferable to adjust the amount and the temperature of the heated air or the addition rate of the solvent solution of the polymer substance, because the operation is simple and preferable.

The removal of the solvent is carried out while adding the coating solution or after the addition, and the method is not particularly limited as long as the temperature of the particulate matter can be maintained, but heated air is used to facilitate solvent recovery. It is preferable to increase the solvent removal rate while reducing the amount of the solvent-containing gas used as much as possible. For that purpose, it is necessary to increase the amount of the particulate matter that comes into contact with the unit heating air volume to improve the removal efficiency. For example, the above-mentioned Japanese Patent Laid-Open No. 52-6
In the air-permeable rotary drum type coating apparatus disclosed in Japanese Patent No. 1216, in addition to increasing the contact area with the particulate matter by installing the louver, heating the wall surface of the rotating drum with which the louver and the particulate matter contact each other. The provision of the air passage holes is preferable because the amount of the particulate matter in contact with the unit heating air volume is very large.

[0019]

In the conventional jet flow method, since the solvent is removed while the particles are jet-flowed individually and are substantially suspended without contact between particles, the coating material is coated even at a temperature higher than the melting temperature of the solvent. Aggregation is considered not to occur at the melting temperature of the substance or lower. Therefore, in the conventional method, it is preferable that the solvent is removed more quickly, so that it is advantageous that the temperature of the particulate material is high enough not to melt the coating material (Japanese Patent Publication No. 54-54).
-3104).

On the other hand, in the method of the present invention in which the coating is carried out by mechanical stirring, if the temperature of the heated air for removing the solvent is increased to increase the removal rate in the same manner as in the conventional method, unlike the conventional method, the granular substance is removed. Aggregation occurs at temperatures below the melting temperature of the coating material. The reason for this is that particles are in contact with each other when the solvent is removed in the mechanical stirring state as in the present invention. It is considered that aggregate formation occurs in the following process.

A new coating solution is added and adheres to the particle A. The particle A contacts the particle B. The coating solution adhered to the particle A redissolves the coating material on the surfaces of the particles A and B. The solvent is removed. When the coating substance solidifies, the particles A and B adhere and aggregate. In the method of the present invention, the temperature of the particulate substance is adjusted so that the newly added coating solution cannot substantially redissolve the coating substance on the surface of the particles. It is considered that since the solvent is removed while keeping the coating substance at a temperature not higher than the dissolution temperature in the solvent, it is possible to form a film having a uniform thickness without agglomeration.

[0022]

EXAMPLES Specific examples of the present invention will be described below with reference to examples, but the present invention is not limited to these examples. Example 1 A coating treatment of a granular material was performed under the following conditions. 8.0 kg of granular urea (particle size: 2.0 to 3.4 mm, hardness: 1.5 kg / piece) was charged as a granular material into a rotary ventilation coating apparatus (SRTA2-type manufactured by Okawara Seisakusho), and 19 r. p.
m. While rotating at a flow rate of 335 m ³ / h (110 ° C.) and 1
Air is blown at 10 ° C., and immediately, 16.0 kg of a low-density polyethylene (M420 manufactured by Mitsubishi Kasei Co., Ltd.) perchlorethylene solution (concentration: 5.0 wt%, liquid temperature: 85 ° C.) is sprayed at 400 g / min. Was added to coat the low density polyethylene solution and remove the solvent. A temperature sensor was inserted directly into the granular material during rolling and coating to measure the temperature of the granular material during coating, which was 40 ° C.
Also, perchlorethylene does not dissolve low-density polyethylene (M420 manufactured by Mitsubishi Kasei Co., Ltd.) at 50 ° C,
It was dissolved in. The particle size distribution and coating uniformity of the obtained coated granular material were measured and are shown in Table 1. The uniformity of the coating was judged by the presence or absence of color unevenness in the colored coating and the elution of the components of the coated particulate matter.

Example 2 Example 2 was repeated except that the air flow rate was 540 m ³ / h (80 ° C.), the air temperature was 80 ° C., and the spray rate was 370 g / min. The particle size distribution and coating uniformity of the obtained coated granular material were measured and are shown in Table 1. Example 3 The same procedure as in Example 1 was performed, except that the air flow rate was 270 m ³ / h (110 ° C.) and the blowing direction was the forward direction with respect to the spray direction of the coating solution. The particle size distribution and coating uniformity of the obtained coated granular material were measured and are shown in Table 1. Comparative Example 1 The procedure of Example 1 was repeated, except that the air flow rate was 378 m ³ / h (110 ° C.) and the temperature of the granular material during coating was 65 ° C. The particle size distribution and coating uniformity of the obtained coated granular material were measured and are shown in Table 1.

[0024]

[Table 1] Table-1 ──────────────────────────────────── Particle size distribution (mm) Uniform coating Characteristic 2.0-2.4-2.8-3.4- Color unevenness Dissolution rate 2.4 2.8 3.4 (%) (%) (%) (%) (%) ───── ─────────────────────────────── Untreated product 4 82 13 1-100 Example 1 1 78 20 1 No 4 Implementation Example 2 2 71 26 1 No 4 Example 3 1 75 23 1 No 3 Comparative Example 1 1 49 26 24 24 Yes 22 ───────────────────────── ──────────── In addition, the dissolution rate was calculated by adding 7 g of the coated particulate matter to 200 cc of water and allowing it to stand at 25 ° C for 1 week, and then quantifying the amount of urea in the water. It was calculated by the formula.

[0025]

## EQU1 ## Elution rate (%) = [amount of urea in water / amount of urea added] × 100 As is clear from the above results, the particle size distribution of the untreated product was compared with that of the coated granular substance obtained in the example. While there was almost no difference in the particle size distribution, aggregated particles were observed in the comparative example. Also in terms of coating uniformity, there is no color unevenness in the examples, and it can be judged that the uniformity of the coating is high because the elution rate is extremely low, but in the comparative example, there was color unevenness and the elution rate was high, and the uniformity was low. ..

[0026]

In a conventional solvent-based coating method in which a polymer substance is dissolved in a solvent to coat it on a granular substance, a large amount of high-speed hot air is used in order to prevent the particles from agglomerating. Since the solvent was instantly removed by using, there was a defect that the particulate matter was damaged. According to the present invention, a solvent solution of a polymeric substance is added to the surface of a granular substance that is mechanically stirred, and the solvent is removed by heating air or the like to form a film of the polymeric substance on the surface of the granular substance. In this case, by keeping the temperature of the particulate matter below the dissolution temperature of the polymer substance in the solvent, in addition to the fact that the coated film has a uniform thickness and there is no agglomeration of the particles, You can avoid damage.

Claims (2)

[Claims] 1. A solvent solution of a polymer substance is added to or while being added to a granular substance which is being stirred by the motion of a stirring device itself and which is maintained at a temperature below the dissolution temperature of the polymer substance in a solvent. After that, the solvent is removed to form a polymer film on the surface of the granular material, which is a method for coating the granular material. 2. The method for coating a granular substance according to claim 1, wherein the granular substance is a fertilizer.