JPS61167442A - Manufacturing method of micro hollow spheres - 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 Field of Industrial Application The present invention relates to an extremely excellent method for manufacturing microscopic hollow spheres used in lightweight aggregates used as building materials.

Conventional technology In recent years, microscopic hollow spheres have been manufactured using materials such as glass, shirasu, alumina, slag, and polymers, and are used as building materials by taking advantage of their light weight, heat insulation, and heat resistance, and by utilizing their electrical properties. Attempts are being made to use it for electrical applications such as high-frequency insulating materials and dielectric materials, and to use it as a catalyst for catalytic reactions and to prevent the evaporation of volatile liquids by utilizing its adsorption and catalytic properties.

The manufacturing method of micro hollow spheres can be classified as follows depending on the means for forming a single spherical shell structure (Industrial Materials, Vol. 21,
No. 8, pp. 10-13).

(1) A spherical shell is formed by melting the raw material for hollow microspheres and using its viscosity and surface tension to encapsulate air bubbles with an air jet, such as alumina bubbles, zirconia bubbles, magnesia bubbles, etc. bubble etc.

(2) Materials that gasify the volatile components structurally contained in the raw material by heating to form microscopic hollows in the melted or softened material, such as whitebait, calcined pearlite, and fly ash.

(3) Inorganic and organic compounds that are decomposed and vaporized by heating are added as a foaming agent to the raw materials and melted.

Things that cause hollow microspheres to form, such as glasses, natural and synthetic polymers.

(Around a spherical liquid or solid core material with a micro diameter of 0,
Materials for hollow microspheres are formed into a wall film and the core material is removed by melting or thermal decomposition to form hollow microspheres, such as saran, tungsten, and for those with a sphere diameter of 111 or more, activated carbon, graphite, coke. , kaolin, quartz, black mineral rhinoceros, orthoclase, etc.

(5) Hollow microspheres of organic material containing carbon are prepared in advance and heated and decomposed in an inert gas to form hollow microspheres of carbon.

However, since the method (1) utilizes viscosity and surface tension, there are restrictions on the raw material composition, and if the composition is outside the allowable range, hollow spheres will not be formed, but fibrous or real spheres will be formed. Furthermore, since the manufacturing method involves high-pressure gas spraying, there is a drawback that the particle size of the hollow spheres is limited to a narrow range.

Furthermore, method (2) structurally contains volatile components, and the types of raw materials are limited.

Furthermore, since method (3) requires high viscosity and surface tension during foaming, there are limitations on the raw material composition that can be used. Furthermore, if the particle size of the fired raw material is coarse, it will not form a single hollow sphere but will become a multi-foamed body with internal partition walls, and if the particle size is too fine, it will be difficult to foam and cause fusion in the furnace. is limited to a narrow range.

Furthermore, method (4) has the advantage that the size of the pores inside the sphere and the thickness of the outer shell can be freely controlled by changing the size of the core material and the coating thickness of the raw material powder.

In the firing process of the spheres, it is necessary to prevent the spheres from adhering to each other, so the process cannot be performed at temperatures above the melting point of the raw materials, leaving raw materials in the middle of reaction in the outer shell. Reduces strength and heat resistance.

Further, in the method (5), the outer shell is limited to carbon.

Problems to be Solved by the Invention The present invention aims to provide a simple and novel method for manufacturing microscopic hollow spheres that is applicable to a wide range of raw materials, without relying on the above-mentioned method.

The present inventor has developed a mold additive used in the continuous casting of steel, that is, a CaO-S i02-M 203-based slag slag agent for the purpose of lubrication between the molten steel and the mold, and prevention of oxidation and heat retention of the molten steel surface during the melting process. We conducted a detailed study on the influence of carbon powder and found that when carbon powder is coated on the surface of slag slag granules, even if the inside of the granules melts due to heating and becomes molten droplets, the molten droplets do not interact with each other. There is no fusion, and especially when this heating is carried out rapidly, fusion of fine powders, confinement of internal pores, aggregation of pores, formation of hollow molten droplets, formation of spherical molten droplets, and melting occur. It was discovered that the melting process was followed by the formation of a slag layer. If this melting process is stopped at the stage of forming hollow molten droplets, it is possible to manufacture hollow spheres. The present invention was completed by discovering that the method can be applied to a wide range of materials such as ceramics.

Means for solving the problems, namely 1 The present invention consists of (1) granulating a fine powder of an inorganic substance with an average particle size of 200 μm or less to obtain a granulated product with an average particle size of several tens of μm to several layers; The surface of the granules is coated with carbon powder having an average particle diameter of 10% or less to a thickness of 300 to 12,000 cm, and then the granules coated with carbon powder are heated to a temperature 100°C or more higher than the melting point of the inorganic substance. temperature and rapidly heating for 5 minutes or less at a high temperature of 3500 ° C. or less to form hollow molten droplets of the inorganic material with a hollow interior and a carbon powder layer on the exterior,
A method for producing lightweight and strong micro hollow spheres, characterized by rapidly cooling the hollow molten droplets and solidifying the outer shell of the hollow molten droplets before they become real spherical molten droplets, and (2) an average particle size. Diameter 2
A foaming agent that decomposes and vaporizes or expands when heated is added to a fine powder of an inorganic substance having a particle size of 0.00 or less, and is granulated to form a granulated product with an average particle size of several tens of particles to a few tens of particles, and the surface of the granulated material is 10μ
The following carbon powder is coated to a thickness of 300 to 12,000i+x, and then the granules coated with carbon powder are heated for 5 minutes at a temperature 100°C or more higher than the melting point of the inorganic substance and at a high temperature of 3500°C or less. Thereafter, the hollow molten droplet is heated rapidly to form a hollow inside and a carbon powder layer on the outside to form a hollow molten droplet of the inorganic material, and before the hollow molten droplet becomes a real spherical molten droplet, the hollow molten droplet is rapidly cooled. This is a method for manufacturing lightweight and strong microscopic hollow spheres, which is characterized by solidifying the outer shell of.

action The present invention will be explained in detail below along with its operation.

First, the micro hollow spheres in the present invention are hollow spheres with diameters ranging from several tens of micrometers to several centimeters, and the fine inorganic powder that is the material of the outer shell of the micro hollow spheres with a heated melting diameter is at a carbon volatilization temperature. Minerals, glass, slag, etc. that have a melting point below 3,500°C at normal pressure (glass and slag have a softening point at which they deform under their own weight, as they do not have a clear melting point); It is preferable that the average particle size of the fine powder is 200 mm or less.The material of the outer shell is selected depending on the final use, but the melting point of the above-mentioned inorganic material depends on its composition. It depends on the glass, but to give one example, the glass is about 3
70-1510℃, wollastonite as a mineral 1540℃, steelmaking slag about 700-1500℃, ceramics about 184
The temperature is 0 to 4000°C.

The reason why the average particle size of the fine powder is set to 200 particles or less is because if the particle size is too large, granulation becomes difficult.

Since the present invention performs high-temperature heating, organic matter is not applicable as a material for the outer shell.

Granulation is usually carried out by adding a binder solution to fine powder of an inorganic substance.The binder used can be either inorganic or organic. Typical inorganic binders include sodium silicate, Sodium aluminate,
Includes tar, pitch, silica sol, alumina cement, portland cement, bentonite, phosphate, etc.
Examples of the organic binder include starch, dextrin, carboxymethyl cellulose, thermosetting resin, thermoplastic resin, and the like. It is usually sufficient to use water as the solvent, but organic solvents can also be used without limitation.

The amount of binder used is such that granulation can be easily performed.
Although it may be determined as appropriate depending on the type of the granulated material, it is generally used in an amount of several weight percent to several tens of weight percent based on the granulated material (the inorganic substance constituting the outer shell).

As the granulation method, existing extrusion granulation method, transfer granulation method, stirring granulation method, spray granulation method, fluidized bed granulation method, etc. can be used.

When forming hollow molten droplets in the subsequent heating step, the particle shape of the granulated product is spherical regardless of the initial shape due to the surface tension of the molten droplets.

After drying, the surface of the granulated material is coated with carbon powder. Drying may be carried out under normal conditions to evaporate the solvent, but it is preferable to carry out drying because if drying is not carried out, the surface of the granules will turn into powder in the next drying step and it will be difficult to obtain good hollow spheres.

Covering the surface of the granules with the carbon powder can be achieved simply by mixing the granules and the carbon powder, and a mixer such as a drum mixer, (1) mixer, or Nauta mixer may be used.

Carbon powders include tar, pitch, carbon black,
Adjusted from coke, graphite, etc. It is desirable that these carbon powders have an average particle diameter of 10 W or less from the viewpoint of good mixing and coating properties on the surface of the granules.

The coating of carbon powder is 300 to 12,000 u on the surface of the granules.
Cover to a thickness of . Therefore, in the mixing, at least 0.5% by weight or more, preferably 5% by weight or more of carbon powder is added to the weight of the granules. However, if the mixing amount exceeds 10%, the amount of coating increases, which is disadvantageous in terms of rapid heating described later.

After the granules are coated with carbon powder, they are heated in an atmosphere at a temperature above the melting point of the constituent inorganic substances and below the carbon volatilization temperature, that is, below about 3500°C.During this heating process, the external and internal shapes of the granules change. It changes every moment. This process of change is explained first.
In the figure, (a) shows the shape of the granulated product before heating, and the granulated constituent material fine powder 2 is coated with the carbon powder 1. Immediately when the granules are placed in the heating furnace, the constituent fine powder inside the granules begins to melt and adhere, resulting in the state shown in (b). Since the fine powder melts quickly, the pores 3 between the fine powders do not come out of the granule, and the pores continue to aggregate, resulting in the state (C) having several independent pores. As the melting progresses further, the pores become one, and hollow molten droplets (d) whose outer shells are molten due to the surface tension of the molten material are produced.

As time passes further, the hollow molten droplet releases gas and becomes a solid spherical molten droplet with a clogged interior. When it comes to real molten droplets, they do not become hollow even when cooled, so the micro hollow spheres of the present invention cannot be obtained.The transition from hollow molten droplets to real spherical molten droplets takes about 5 minutes; It is extremely important that the rapid heating of the particles be carried out at a high temperature and in a short time; for example, it is preferable to heat the particles at a temperature as high as possible above the melting point of the inorganic substance and at a temperature of 3500° C. or less at which carbon does not volatilize, within about 5 minutes. If the temperature exceeds .degree. C., carbon will volatilize and there is a risk that the hollow spheres will fuse together.

Furthermore, according to the research conducted by the present inventors, it has been found that the pressure resistance of the outer shell of the obtained micro hollow spheres is increased by setting the heating temperature to a temperature higher than the melting point of the inorganic substance by at least 100°C.

Note that fluidizing or vibrating the granules in the heating furnace has the effect of equalizing the degree of carbon consumption among the granules and preventing fusion of the granules. Furthermore, the carbon powder coated on the surface of the granules is subject to oxidative consumption to a greater degree at high temperatures. It is essential that the carbon powder remains on the surface of the molten droplet until the stage of hollow molten droplet formation is reached. Therefore, it is preferable to replace the atmosphere with nitrogen gas or argon gas to reduce the degree of oxidative consumption of the carbon powder and stabilize the operation.

In the production of hollow spheres, in step (d), the hollow molten droplet is taken out from the heating furnace and rapidly cooled to a temperature below the melting point of the constituent materials to solidify the outer shell of the molten droplet. The approximate time to take out the granules from the heating furnace and start cooling is immediately after the granules have become spherical in shape. If it is necessary to remove the residual carbon powder on the surface of the hollow sphere depending on the intended use, after solidifying the outer shell, the hollow sphere should be placed in an oxidizing atmosphere at a temperature of 300°C or higher and below the softening temperature of the hollow sphere. The micro hollow spheres of the present invention can be obtained through zero or more operations in which the remaining carbon powder can be oxidized and completely removed by charging the carbon powder for several minutes to several tens of minutes.

Furthermore, during granulation, foaming agents that decompose and vaporize or expand upon heating, such as carbon powder, calcium carbonate, magnesium carbonate, hematite, pyrite, barium sulfate, strontium sulfate, sodium silicate, and acid treatment are added to the inorganic powder during granulation. It is also possible to produce minute hollow spheres by adding graphite, mica, vermiculite, shirasu, foamed clay, shale, obsidian, nacre, pine charcoal, etc., and then performing the same operations. The foaming agent that can be added to increase the volume of the hollow portion is determined by considering the melting point of the inorganic substance.

The particle diameter r of the micro hollow spheres is such that when the constituent inorganic materials do not contain gas generating substances, the volume of the hollow spheres is almost the same as the volume V of the granules, and the outer shell thickness of the hollow spheres is t, If the porosity of the granules is ε, then (is (1-t/r)3
It is expressed as From this equation, in order to reduce the outer shell thickness, it is sufficient to increase the porosity of the granules.

Example 1 Examples of the present invention are shown in Tables 1, 2, and 3.
The table shows the conditions for producing granules. Three types of slag with significantly different melting temperatures and viscosities and wollastonite, a natural mineral, were used as constituent inorganic materials.

All of the produced granules had an average particle size of 750 and a particle specific gravity of about 1.20. After granulation, the surface of the granulated product was coated with 5% by weight of carbon black, and then heat-treated under the conditions shown in Table 2. After a predetermined period of time, it was taken out of the furnace, cooled in the atmosphere, and then put back into the furnace at 450° C. for 30 minutes to remove residual carbon powder. As a result of these operations, hollow spheres were obtained for each material. The properties of the obtained hollow spheres were as shown in Table 3.

Example 2 Differential formation of hollow and real molten droplets when rapid heating conditions are changed, and Example 1, which is a hollow sphere manufactured according to the present invention.
Table 4 shows a strength comparison between Samples C and D, and a hollow sphere made by a conventional method, such as a shirasu balloon and a borosilicate soda glass microballoon.

The fracture rate of the hollow sphere under hydrostatic pressure was used as the strength index of the hollow sphere. In other words, a sample placed under a pressure condition of 100 kg/c layer 2 in a closed container with water as the pressurizing medium is released to atmospheric pressure again, and the percentage of the sample weight that exceeds the specific gravity of the hollow sphere before pressurization is determined as the failure rate. In order to eliminate the influence of the hollow sphere particle size, we used particles with a particle size of 14131L to 198μ when measuring the zero intensity.

As shown in Table 4, in the present invention, formation of hollow molten droplets was observed when heating was performed for 2 to 3 minutes at a temperature 100° C. or more higher than the melting point.

It was also found that the produced hollow spheres had a lower fracture rate under constant pressure and were superior in strength compared to the shirasu balloons and borosilicate soda glass microballoons produced by conventional methods.

Example 3 In order to reduce the weight of uninvented small hollow spheres, we investigated the characteristics of hollow sphere particles produced when a blowing agent that decomposes and vaporizes or expands upon heating is added during granulation of an inorganic substance with an average particle diameter of 200 μm or less. It is shown in Table 5.

C of Example 1 was used as a sample, and the manufacturing conditions were the same as those of C of Example 1 except for the addition of zero blowing agent in which fine whitebait powder was used as a blowing agent.

The particle shapes obtained by adding fine whitebait powder were all hollow spheres, and as the amount of fine whitebait powder added increased, the specific gravity of the hollow spherical particles decreased.

Table 5 Addition of blowing agent and characteristics of hollow spherical particles Effects of the invention As detailed above, the surface of the inorganic granules is coated with carbon powder, and the surface of the inorganic granules is rapidly heated to a temperature higher than the melting point of the inorganic substance to generate hollow molten droplets. After the hollow molten droplets become spherical, but before they become real spherical molten droplets, they are rapidly cooled to below the melting point, whereby uniform microscopic hollow spheres can be easily obtained. In particular, by rapidly heating at a temperature higher than the melting point of inorganic substances, homogeneous and strong microscopic hollow spheres can be obtained, which can be used in various material fields such as building materials, electrical, chemical, etc., and is suitable for industrial use. This is an extremely useful invention.

[Brief explanation of the drawing]

FIGS. 1(a), (b), (c), and (d) are explanatory diagrams of the process of forming hollow molten droplets. 1-... coated carbon powder, 2... inorganic substance, 3... pores.

Claims (1)

[Claims] 1. A fine powder of an inorganic substance with an average particle size of 200 μm or less is granulated to form a granule with an average particle size of several tens of μm to several mm, and the surface of the granule is coated with an average particle size of 10 μm or less. 300~12000 for carbon powder
The granules coated with carbon powder are then rapidly heated at a temperature of 100°C or more higher than the melting point of the inorganic substance and at a high temperature of 3,500°C or less for 5 minutes or less to remove the internal Form a hollow molten droplet of the inorganic material, which is hollow and has a carbon powder layer formed on the outside, and rapidly cools the hollow molten droplet before it becomes a real spherical molten droplet to solidify the outer shell of the hollow molten droplet. A method for producing lightweight and strong microscopic hollow spheres characterized by: 2. Add a foaming agent that decomposes and vaporizes or expands when heated to a fine powder of an inorganic substance with an average particle size of 200 μ or less, and granulate it to make a granule with an average particle size of several tens of μ to several mm. 300 to 12,000 m with carbon powder with an average particle size of 10 μ or less
The granules coated with carbon powder are then rapidly heated at a temperature of 100°C or more higher than the melting point of the inorganic substance and at a high temperature of 3,500°C or less for 5 minutes or less to form an internal forming a hollow molten droplet of the inorganic material, which is hollow and has a carbon powder layer formed on the outside, and rapidly cooling the hollow molten droplet before it becomes a solid line molten droplet to solidify the outer shell of the hollow molten droplet. A method for producing lightweight and strong microscopic hollow spheres, characterized by: