JPS58190889A - Manufacture of ferrite magnetic composition for mixing in explosive - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of a ferrite magnetic material to be mixed into an explosive, and more specifically, a ferrite magnetic composition that can maintain stability for a long period of time when mixed into an explosive. It is about the method.

When blasting with explosives such as dynamite, the placed explosives may remain unexploded. Normally, such unexploded explosives are found and removed with the naked eye, but this work is labor-intensive and dangerous, and it is difficult to completely remove them, as remaining explosives may come into contact with the drill during the next excavation. They often explode, causing serious human damage.

As one measure to prevent such disasters, a method has been proposed in which explosives are mixed with magnetic powder and then magnetized to become magnetic explosives, and after blasting is complete, unexploded explosives are detected with a magnetic sensor.

However, if ordinary ferrite powder is mixed into explosives, the explosives will deteriorate during long-term storage and their effects will be impaired, so the development of magnetic materials that do not impair the stability of the explosives. has become an important issue.

The inventors found that when ferrite powder was added to explosives,
After examining various causes of impairing its stability, we learned that the main cause was alkaline substances mixed in as impurities in ferrite powder, and coated ferrite powder particles containing alkaline substances to be mixed with explosives with polymer. As a result, he discovered and proposed an effective method to cut off direct contact between alkaline substances and explosives.

However, in this method, even if the surface of the ferrite powder particles is coated with a polymer and then dried at a high temperature of 130°C or higher for a short time, deterioration of the coated polymer is unavoidable. had to be dried at relatively low temperatures. Since this low-temperature drying takes a long time, it is necessary to perform low-temperature drying under reduced pressure in order to prevent polymer deterioration as much as possible and to speed up the drying rate.

Although this method does provide a satisfactory ferritic magnetic material that does not mix with explosives and reduce its thermal stability, this method requires (1) polymer coating of ferrite powder, (2) filtration, ( 3) Processing steps such as heating and drying under reduced pressure, (4) crushing, and (5) classification are required, and there are drawbacks such as the large number of processing steps and the complexity of each step, and the production cost is also low. This is not an advantageous method as it will increase your chances.

The present inventors have devised a desirable ferrite-based magnetic material for mixing explosives that effectively overcomes these drawbacks, is easy to operate, and does not reduce its thermal stability when mixed with, for example, dynamite. As a result of extensive research to find an industrially advantageous manufacturing method, a highly practical and highly effective manufacturing method was discovered, leading to the present invention.

The present invention provides a method for producing a ferrite-based magnetic composition for mixing with explosives, which comprises polymerizing the monomer and spray-drying the obtained polymer-coated powder slurry.

The ferrite magnetic materials used in the method of the present invention include Mn-Zn-based materials having a spinel crystal structure, Ni-Zn
Soft magnetic ferrite such as ferrite, lithium-based, Mn-based, etc.
- Semi-hard magnetic ferrite such as Mg type, or general formula MO・6Fe203 (where M is Oa″ square, Ba++, S
divalent metal ions such as r+1 and pb)
Examples include hard magnetic ferrite having a magnetobrambite crystal structure represented by the following, but hard magnetic ferrite having a strong coercive force is preferable from the viewpoint of detecting residual magnetism. These can be used alone or in combination of two or more.

The particle size of the ferrite magnetic material is preferably 10μ or less due to the problem of residual magnetism after explosion and the problem of wear of the kneader when kneading with explosives, but the effect of the present invention depends on the particle size. Since it is not affected, there are essentially no restrictions.

Furthermore, the polymerizable monomers used in the method of the present invention include monomers capable of radical polymerization or radical copolymerization,
Such monomers include, for example, acrylic acid, methacrylic acid and methyl acrylate, butyl acrylate, ethylene glycol diacrylate, methyl methacrylate,
Acrylic esters and methacrylic esters such as ethyl methacrylate, ethylene glycol dimethacrylate, and 2-hydroxyethyl methacrylate, aliphatic vinyl esters such as vinyl propionate, styrene, α-methylstyrene, etc. Examples include aromatic vinyl compounds, dienes such as butadiene, isoprene, and chlorobrene, and acrylonitrile.These may be used alone or in combination of two or more.The monomer is usually used in proportion to the weight of the magnetic powder. Based on this, for example, a weight ratio of about 3 to 30 is used, but it can be changed as appropriate depending on the powder particle size and the like.

In the method of the present invention, the ferrite magnetic powder material and the polymerizable monomer are thoroughly stirred in an aqueous medium to form a slurry in the form of suspension and dispersion, and monomer microdroplets with powder particles as cores are formed. The monomers are then polymerized in the presence of a polymerization catalyst while keeping the two in close contact.

In this way, a magnetic powder composition whose surface is densely coated with the polymerized polymer can be easily formed.

For the polymerization of the polymerizable monomers, all known radical polymerization initiators can be used, for example polymerization catalysts such as potassium persulfate, benzoyl peroxide, azobisisobutyronitrile, hydrogen peroxide, etc., but the present invention The polymerization catalysts proposed by the inventors, such as substances that donate acidic sulfite ions and azobisisobutyramidine (see Japanese Patent Publication No. 55-25482 and Japanese Patent Publication No. 56-015422), have advantages in ease of reaction and improvement in coating yield. It can be used more advantageously. Examples of the acidic sulfite ion donating substance include sulfite water, sulfite gas, sulfite aqueous solution, and acidic sulfite aqueous solution. Of course, in the present invention, one type or a combination of two or more types of catalysts may be used. The polymerization catalyst is used in a normally used amount, for example, 0.1 to 10% of the weight of the monomers.
used within the range.

In the polymerization system in the method of the present invention, in order to stably disperse the fine magnetic powder particles in the medium, it is preferable to add a suspending agent or an emulsifier as a dispersing agent. Any known dispersant that does not adversely affect the effectiveness of the invention can be used. In addition, the polymerization reaction medium and 1
When water is used in ~, water is the most preferred medium since the polymerization reaction effectively suppresses the formation of oligomers and the formation of free polymers that do not participate in the coating.

In the polymerization system of the present invention, for example, pretreated ferrite magnetic powder is dispersed and suspended in 1 to 10 parts by weight of water per 1 part by weight of ferrite magnetic powder, and the above-mentioned monomer and polymerized Add initiator and disperse well, then heat to 10℃
The monomers are polymerized at a temperature in the range from ~100<0>C, preferably from 20<0>C to 70<0>C. During this polymerization treatment, the monomer is polymerized under the action of the surface of the magnetic powder particles to form a polymer, and the particles are substantially completely coated to form a dense polymer layer. This polymerization treatment time is usually 1
In about 4 hours, almost 100% of the monomer is converted to the polymer, and a slurry of the composition in which all the magnetic powder particles are coated with the polymer is obtained.

When an acidic or alkaline polymerization catalyst is used, the slurry or suspension coated by polymerization is usually neutralized because the liquid is acidic or alkaline.
It is desirable to adjust the pH of the liquid to 7.0, and this adjustment process can effectively render harmless substances that may interfere with the stability of the explosive.

The neutral slurry of the polymer-coated ferritic magnetic powder composition thus obtained is directly spray-dried. Various conditions for the spray drying process can be selected depending on the processing capacity and capacity of the spray dryer, the solid content concentration of the slurry, the slurry supply rate, etc., but preferably the slurry supply inlet temperature is 150 to 300 °C, and the dry material is Outlet temperature is 8
Operating conditions are selected to result in a temperature range of 0 to 130°C.

Although the heating drying time is extremely short, if the inlet temperature is, for example, 310° C. or higher, particularly 330° C. or higher, the deterioration of the coating polymer becomes noticeable, and if it is too low, drying becomes insufficient, which is not preferable. In order to efficiently dry the slurry under such operating temperature conditions of the dryer, it is preferable that the solid content concentration of the slurry is, for example, 30 to 600 to 60 parts by weight. If the concentration is too high, it will be difficult to feed the dryer, and if the concentration is too low, a large amount of water will evaporate, reducing the drying speed and increasing energy loss, which is not preferable. This solid content concentration may be adjusted after the above-mentioned polymerization coating treatment, but it can also be adjusted in advance during the preparation stage before polymerization.

When a slurry of ferritic magnetic powder coated with a polymer is spray-dried in this manner, the suspended particles can be substantially completely dried in a very short time, and the fine particle size of the polymer is sospherical. A coated magnetic composition can be easily obtained.

Furthermore, the coating composition obtained by the method of the present invention is highly desirable because it does not mix with the explosive and reduce its stability even though it is treated at a relatively high temperature in a dryer. It is.

The spray drying process in the present invention is an entirely inconceivable method considering that conventional high-temperature drying of 130°C or higher was a processing condition that should be avoided in the production of polymer-coated materials for ferrite-based magnetic materials for mixing with explosives. It is a single operation that is extremely easy compared to conventional processes such as filtration of polymer slurry, low-temperature vacuum drying, crushing, and classification, and the resulting composition material can be processed using conventional methods. It was completely unexpected that the particle size distribution was narrower and finer, and the explosive stability was much better than that obtained in the previous step.

Explosive stability tests for ferrite-based materials used to mix explosives use the Abel heat test method, which is one of the stability tests stipulated in the Enforcement Regulations of the Explosives Control Law. A test was conducted on the added and mixed mixture at 72°C.

In the test, it is determined that the product passes the test if the time required for the decomposition of the nitrogen compound to be detected is 30 minutes or more, and the product of the present invention was tested in accordance with this standard.

The above-mentioned Abel heat resistance test is a very sensitive test method, and even the presence of even a trace amount of explosive stability inhibitors decomposes the nitro group or nitrate ester group in the explosive, and the resulting nitrogen oxides are extremely reduced. Detects even the smallest amount. Therefore, passing this test means that impurities that pose a risk of decomposing and deteriorating the coating polymer itself have been sufficiently removed or stabilized, or that the ferritic magnetic composition has been used in a non-explosive manner. Even when mixed, impurities that may deteriorate or inhibit the mixing must be sufficiently removed or stabilized.

According to this stability test, the ferritic magnetic composition produced by the method of the present invention can be mixed into explosives and does not impede the stability of explosives for a long period of time, and can be used for mixing explosives (or for magnetic explosives). It was confirmed that the material had excellent performance as a material and had higher practical value than those produced by conventional methods.

Furthermore, the method of the present invention is not limited to use only for mixing explosives, but can also be fully applied as a method for producing ferrite-based magnetic compositions with high stability resistance.

Next, the present invention will be explained in more detail with reference to Examples, but it goes without saying that the present invention is not limited to the scope described in the Examples.

Example 1 Internal capacity 50 with stirrer, thermometer and reflux condenser
Barium ferrite powder (average particle size 1
μ) 51 (Add 9 and 20 tons of water, heat to 80℃,
After stirring vigorously for 0 minutes, IN hydrochloric acid was added to adjust the pH to 7.
Adjusted to 0. Next, this neutralized suspension was kept at a temperature of 50°C, and methyl methacrylate monomer 250y and 6
Add 1 kg of sulfurous acid water and bring to temperature 5 while stirring.
The polymerization reaction was carried out at 0°C for 2 hours. After the reaction was completed, the reaction solution was neutralized with IN caustic soda water to have a PHi of 7.0.

The amount of polymerized methyl methacrylate polymer applied to coat the ferrite particles in this operation was 2,102. The neutralized reaction solution was divided into two parts, and one part was washed with water for 15 minutes.
It was dried under normal pressure at a temperature of 0° C. and ground into fine particles of 10 to 200 μm in a mortar. The moisture content of this pulverized product was 0.2% by weight. The other reaction liquid is a slurry of 40% by weight,
It was dried in a spray dryer under temperature conditions of an inlet temperature of 200°C and an outlet temperature of 100°C.

All of the obtained dry particles were substantially spherical, with a particle size of 5 to 60 microns, which was finer than the ground particles and had a narrower particle size distribution. Further, its water content was 0.2% by weight.

Each sample 102 of the dry fine powder thus obtained was mixed with Dynamite No. 2 Enoki 1002, thoroughly kneaded, and then subjected to an explosive stability test at a temperature of 72° C. using an Abel heat resistance test. As a result, in the spray-dried samples,
The time it takes for nitrogen oxides produced by thermal decomposition to be detected is 3.
It took more than 0 minutes, which was the same as the standard dynamite No. 2 Enoki itself, whereas it was only 20 minutes for the normal pressure dried sample.

Examples 2 to 6 Using the equipment used in Example 1, put strontium ferrite powder (particle size 1 μ) and 20 tons of water into the equipment, and stir vigorously for 30 minutes while heating at 80°C. After preparing a suspension, IN hydrochloric acid was added to neutralize the suspension to pH 7.0. Next, the suspension was maintained at a temperature of 40°C, and methyl acrylate monomer 6002 and sodium bisulfite 407 were added thereto, and a polymerization reaction was carried out at a temperature of 40°C for 2 hours while stirring. After the reaction was completed, the pH of the suspension was adjusted to 7.0 by neutralizing with IN caustic soda water. The amount of methyl acrylate provided to coat the ferrite particles by this polymerization reaction was 533 il.

This reaction solution was prepared into a slurry having a concentration of 45% by weight, and was spray-dried using a spray dryer under various temperature conditions shown in Table 1 to obtain various samples. All of the dried powders obtained were substantially spherical, with particle sizes ranging from 5 to 60 microns.

Each of the obtained samples was thoroughly kneaded with dynamite No. 2 in the same manner as in Example 1, and then an explosive stability test was conducted under the same conditions. The results are summarized in Table 1 below.

Table 1 Comparative Examples 1 to 3 In Examples 2 to 6, the reaction liquid obtained by neutralization after the polymerization reaction was filtered, and each powder sample was dried under normal pressure under the temperature conditions shown in Table 2, and thoroughly dried in a mortar. The particles were ground to a particle size of 10 to 200μ. Each of these prepared samples was subjected to an explosive stability test in the same manner as in Example 1, and the results are shown in Table 2.

15-Table 2 From these results, it is clear that the production method of the present invention is not foolproof and is extremely simple to operate compared to the conventional method, but also produces a fine powder of ferrite magnetic material for mixing with explosives that has far superior explosive stability. It can be seen that the compositions are provided. It is also observed that when the inlet temperature of the spray dryer is 310°C, the obtained material slightly reduces the heat resistance of the explosive.

Patent applicant: Tohoku Metal Industry Co., Ltd. Agent Akira Agata -17-509- 16 one

Claims (1)

[Scope of Claims] A method for producing a ferrite-based magnetic composition for mixing with explosives, which comprises polymerizing and spray-drying the obtained polymer-coated powder slurry. 2 Spray drying is carried out when the inlet temperature of the spray dryer is 150 to 30
The method according to claim 1, wherein the method is carried out under temperature conditions such that the temperature is 0°C and the outlet temperature is 80 to 130°C. 3. The method according to claim 1 or 2, wherein the slurry is a slurry using water as a medium.