JP2011105520A - Ceramic hollow particles and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture ceramic hollow particles at a lower cost than before in a method for manufacturing ceramic hollow particles using a pressure welding mixing apparatus, in which a process for mixing resin powder and ceramic powder is unnecessary and there is neither material loss. <P>SOLUTION: To a pressure welding mixing apparatus which mixes powders with each other in pressure welding by passing powders through a minute gap between the inner wall of a chamber which can rotate freely and presents the shape of a drum and a scraper, resin powder and ceramic powder of smaller size than the resin powder are individually supplied, and the resin powder and the ceramic powder are mixed by rotating the chamber at a lower speed than the rotation speed at the time of pressure welding mixture. Subsequently, pressure welding mixing is performed and a precursor which covers the surface of resin powder in a state that a part of the ceramic powder is embedded is formed. Subsequently, the ceramic powder is made to sinter while firing the precursor and making the resin powder burnt off. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to ceramic hollow particles that form a hollow shell layer formed by bonding ceramic powders to form a hollow structure, and a method for producing the same.

  For example, composite materials in which ceramic particles such as alumina particles are dispersed in a base material such as metal are widely used for the purpose of reducing the weight of the material and increasing the strength. In addition, today, ceramic hollow particles having a substantially spherical porous shell layer formed by bonding ceramic powders and having a hollow inside have been used for further weight reduction.

  This ceramic hollow particle forms a precursor in which the entire surface of a large-diameter resin powder as a core material is coated with a powder layer made of a ceramic powder having a smaller diameter than the resin powder, and removes the resin powder from the precursor. In general, it is produced by forming a porous shell layer in which ceramic powders are bonded together. For example, in Patent Document 1, a superabsorbent polymer powder swollen with water and an alumina powder are brought into contact with each other to form a powder layer of the alumina powder on the entire surface of the superabsorbent polymer powder. Describes a method for producing alumina hollow particles having a hollow structure by removing a superabsorbent polymer by drying or baking at a high temperature.

  However, in the manufacturing method described in Patent Document 1, as schematically shown in FIG. 4, since the precursor is only the ceramic powder 11 attached to the surface of the resin powder 10, high temperature drying or firing is performed. At this time, there is a problem that the ceramic powder 11 is easily peeled off from the resin powder 10 and it is difficult to hold the powder layer uniformly. Moreover, since the resin powder 10 is thermally expanded or vaporized by high-temperature drying or firing, the powder layer is likely to collapse due to the ceramic powder 11 receiving an outward pressure. As a result of the peeling of the ceramic powder 11 and the collapse of the powder layer, a homogeneous porous shell layer is not formed, which is a great obstacle to increasing the productivity of the ceramic hollow particles.

  In addition, today, in order to further reduce the weight, there is an increasing demand for fine ceramic hollow particles having a particle size of 20 μm or less. For this purpose, it is necessary to use submicron ceramic fine powder. . However, it becomes more difficult to maintain a uniform powder layer of such ceramic fine powder and to form a good porous shell layer.

  From such a background, the present applicant has proposed to manufacture ceramic hollow particles through a manufacturing process as shown in FIG. That is, as shown in FIGS. 4A and 4B, the resin powder 10 and the ceramic powder 11 are mixed, and the mixed powder 5 is put into the chamber 2 of the press-contact mixing apparatus 1 shown in FIG. The resin powder 10 and the ceramic powder 11 are pressed and mixed. This press-contact mixing apparatus 1 is schematically configured by disposing an inner 3 and a scraper 4 at a predetermined distance on a central axis of a chamber 2 that is rotatable and has a drum shape. The inner 3 has a substantially semicircular cross section on the side facing the inner wall of the chamber 2 so that the mixed powder 5 can be taken in and out smoothly, and slightly between the inner wall of the chamber 2 Gaps are formed. Then, the mixed powder 5 obtained by mixing the resin powder 10 and the ceramic powder 11 is put into the chamber 2 and the chamber 2 is rotated at high speed in the direction of the arrow, so that the mixed powder 5 is pressed against the inner wall of the chamber 2 by centrifugal force. Then, it passes through the gap between the inner 3 and the inner wall of the chamber 2. During this passage, the resin powder and the ceramic powder are pressed against each other by a shearing force, and a part of the ceramic powder is embedded in the surface of the resin powder. Then, the mixed powder 5 that has passed through the inner 3 is scraped off by the scraper 4, and the same process is repeated. Finally, as shown in FIG. 3, the ceramic powder 11 covers the entire surface of the resin powder 10. Part of it is embedded. Next, a precursor covering the surface of the resin powder 10 with the ceramic powder 11 embedded therein is fired, the resin powder 10 is burned off, and the ceramic powders 11 are sintered together to form a porous material. Form a shell layer.

  However, the manufacturing method described in Patent Document 2 requires a separate step of mixing the resin powder 10 and the ceramic powder 11 in advance, and the resin powder 10 and the ceramic powder 11 adhere to the mixing device used for mixing. It also causes material loss.

Japanese Patent Laid-Open No. 10-258223 Japanese Patent No. 3955477

  The present invention has been made in view of such a situation, and in the method for producing ceramic hollow particles using a pressure mixing device, a step of mixing resin powder and ceramic powder is unnecessary, and there is no material loss. The purpose is to manufacture at a lower cost than before.

  In order to achieve the above object, the present invention provides an inner wall of a chamber that is rotatable and has a drum shape in a method for producing a hollow ceramic hollow ceramic layer formed by bonding ceramic powders to form a hollow structure. In addition, resin powder and ceramic powder with a smaller diameter than the resin powder are separately put into a pressure mixing device that passes the powder through a minute gap with the scraper and mixes the powders together, and the chamber is pressed and mixed. The resin powder and the ceramic powder are mixed by rotating at a lower speed than the rotation speed, followed by pressure welding to form a precursor that covers the surface of the resin powder with the ceramic powder partially embedded. And then firing the precursor to burn out the resin powder and to sinter the ceramic powder together. To provide. The present invention also provides a ceramic hollow particle obtained by the above production method and comprising 65 to 100% of complete hollow particles and 0 to 35% of debris particles, solid particles and incomplete hollow particles. To do.

  According to the present invention, in the method for producing ceramic hollow particles using the pressure mixing device, the ceramic powder and the resin powder are directly put into the chamber without mixing, so that the mixing step is eliminated, and material loss due to mixing is also eliminated. Since it becomes nonexistent, ceramic hollow particles can be produced at a lower cost than before. Moreover, the obtained ceramic hollow particles contain 65 to 100% of complete hollow particles and have a high yield.

It is process drawing for demonstrating the manufacturing method of the ceramic hollow particle of this invention. FIG. 6 is a process diagram for explaining a method for producing ceramic hollow particles described in Patent Document 2. It is the figure which showed typically the precursor which consists of resin powder and ceramic powder in the manufacturing method of the ceramic hollow particle of this invention and patent document 2. FIG. It is the figure which showed typically the precursor which consists of resin powder and ceramic powder in the manufacturing method of the ceramic hollow particle of patent document 1. FIG. It is the electron micrograph (5000 times) which image | photographed the polymethylmethacrylate powder before mixing. It is the electron micrograph (3000 times) which image | photographed the powder after pressure welding mixing.

  Hereinafter, embodiments of the present invention will be described in detail.

  In the method for producing ceramic hollow particles according to the present invention, as shown in FIG. 1, the resin powder 10 and the ceramic powder 11 are not mixed and are directly put into the chamber 2 of the press-contact mixing apparatus 1. The pressure welding mixing apparatus 1 is as shown in FIG. As the pressure mixing device 1, for example, a mechano-fusion system (AMS-Lab manufactured by Hosokawa Micron Corporation) is known.

  In the press-contact mixing apparatus 1, after the mixed powder 5 is charged, the chamber 2 is rotated at a lower speed than during press-contact mixing. By this low speed rotation, the resin powder 10 and the ceramic powder 11 are appropriately mixed. In addition, since the rotation speed for this mixing requires a long time if mixing is too low, 65% to 95% of the rotation speed during pressure welding mixing is appropriate.

  Next, the chamber 2 is rotated at the same rotational speed as in the normal pressure-contact mixing to perform pressure-contact mixing. By this pressure mixing, a precursor coated with the resin powder 10 in a state where a part of the ceramic powder 11 is embedded as shown in FIG. 3 is obtained.

  The amount of the ceramic powder 11 embedded in the resin powder 10 at this time is preferably about 50 to 80% of the powder volume in order to more reliably prevent delamination during high temperature drying or firing. The gap between the inner wall and the inner 3 is appropriately adjusted.

  Further, the chamber 2 may be heated during the pressure mixing. The resin powder 10 is softened by heating, and the ceramic powder 11 is easily embedded. However, a slight amount of heat is generated by the pressing action of the inner 3, so that it is possible to carry out at room temperature when there is no need to shorten the time.

  The mixing ratio of the resin powder 10 and the ceramic powder 11 is not particularly limited and depends on the respective particle diameters. For example, the resin powder 10 and the ceramic powder 11 may be added in equal amounts by weight.

  Next, the obtained precursor is fired to gasify the resin powder 10 to disappear, and the ceramic powders 11 are bonded together. As the firing conditions, a temperature and a time sufficient for the resin powder 10 to completely disappear are appropriately set according to the type of the resin.

  In the precursor firing step, a temperature process in which the precursor is placed in an electric furnace or the like and gradually heated from room temperature to be gasified and fired may be employed, or the resin powder 10 is completely gasified. You may employ | adopt the temperature process heated up to the temperature which ceramic powder 11 couple | bonds, after putting a precursor in the electric furnace heated to temperature and processing. In particular, by adopting the latter temperature process, since the resin powder 10 is instantaneously gasified and disappears, ceramic hollow particles closer to a true sphere can be obtained. Moreover, although the processing temperature of the precursor in the latter temperature process is based on the kind of the resin powder 10, 700-800 degreeC is suitable.

  Although the ceramic hollow particles of the present invention are obtained by the firing, the ceramic powder 11 is not peeled off from the resin powder 10 during firing, so that a homogeneous and strong porous shell layer is formed.

  In the present invention, the type of the resin powder 10 is not limited, but is preferably a soft resin so that the ceramic powder 11 can be embedded. For example, a powder made of polystyrene, polymethyl methacrylate, polyethylene, polypropylene, or the like can be suitably used. Among them, polymethyl methacrylate (PMMA) is preferable because it decomposes more rapidly on the lower temperature side and almost completely has no residue at about 350 ° C. as compared with polystyrene (PS) or polyethylene (PE). By using this polymethyl methacrylate powder, ceramic hollow particles closer to a true sphere can be obtained.

  The particle size of the resin powder 10 is appropriately selected according to the particle size of the target ceramic hollow particles. In the present invention, one of the objects is to produce ceramic hollow particles having a particle size of 20 μm or less. At that time, the resin powder 10 classified to a particle size of 20 μm or less is used.

  On the other hand, there is no restriction | limiting also in the ceramic powder 11, According to the objective, it can select suitably. One kind of ceramic powder may be used, or two or more kinds may be used. In addition, when powders having different particle diameters are used, the small-diameter powder enters a gap formed by combining the large-diameter powder and the large-diameter powder, and finer ceramic hollow particles can be obtained. The mixing ratio of the large diameter powder and the small diameter powder is preferably less than 50% by mass of the small diameter powder, and more preferably 3 to 20% by mass from the viewpoint of the strength of the ceramic hollow particles.

  The ceramic hollow particles thus obtained have a ratio of complete hollow particles of 65 to 100%, a ratio of fragment particles, solid particles and incomplete hollow particles of 0 to 35%, and a high ratio of complete hollow particles. Become. Such ratio is obtained by collecting an appropriate amount of the obtained ceramic hollow particles, observing with an electron microscope, and counting the number of complete hollow particles, fragment particles, solid particles and incomplete hollow particles in the field of view. Desired.

  The present invention will be further described below with reference to examples, but the present invention is not limited thereto.

[Test 1: Verification of mixing method]
Example 1
A mechano-fusion system (AMS-Lab manufactured by Hosokawa Micron Co., Ltd .; see FIGS. 1 and 2) was prepared as a pressure mixing device, and the gap between the inner and the chamber was adjusted to 3 mm. And the polymethylmethacrylate powder classified to the average particle diameter of 15 μm, the alumina powder classified to the average particle diameter of 0.2 μm, and the silica powder classified to the average particle diameter of 0.01 μm are blended as shown in Table 1. The mixture was put into the chamber, mixed by rotating at a low speed of 1740 rpm, and then mixed by pressure by rotating at a high speed of 2600 rpm.

  After completion of the pressure mixing, a part of the powder was taken out of the chamber and observed with an electron microscope (3000 times), and particles in the field of view were observed. And when the ratio (coating rate) of the polymethylmethacrylate powder which was completely coat | covered with the alumina powder and the surface did not have an exposed part was calculated | required, the coating rate was 92.3%.

  FIG. 5 shows an electron micrograph (5000 times) of the polymethylmethacrylate powder before mixing, and FIG. 6 shows an electron micrograph (5000 times) of the powder after pressure mixing, after mixing at low speed. It can be seen that the surface of the polymethyl methacrylate powder is completely covered with the alumina powder by performing pressure welding mixing at high speed.

(Comparative Example 1)
The same operation as in Example 1 was performed except that the pressure contact mixing was performed at 1500 rpm. Similarly, the coating rate was determined to be 6.28%, and the coating with alumina powder was insufficient.

(Comparative Example 2)
After the polymethyl methacrylate powder and the alumina powder were individually put into a pressure mixing device, pressure mixing was performed at 2600 rpm without mixing at a low speed. The coating rate was determined in the same manner, but it was 43.9%, and the coating with alumina powder was insufficient.

[Test 2: Preparation of alumina hollow particles]
(Example 2)
The pressure-mixed powder obtained in Example 1 was put into an electric furnace heated to 800 ° C. to gasify polymethyl methacrylate, and then heated to 1600 ° C. at a heating rate of about 5 ° C./min. Baking was carried out at 1600 ° C. for 3 hours. Then, it was cooled to room temperature at a rate of 5 ° C./min.

  After cooling, the powder was taken out of the electric furnace and observed with an electron microscope. As a result, the ratio of complete hollow particles was 78%, and the ratio of debris particles, solid particles, and incomplete hollow particles was 22%.

  In addition, when the experiment of Example 2 was repeated 10 times and obtained in the same manner, the ratio of debris particles, solid particles, and incomplete hollow particles was 0 in the range of 65-100% of complete hollow particles. It was in the range of ˜35%.

(Comparative Example 3)
The same operation as in Example 2 was performed on the powder after pressure welding obtained in Comparative Example 1. When determined in the same manner, the ratio of complete hollow particles was 5%, and the ratio of fragment particles, solid particles, and incomplete hollow particles was 95%.

(Comparative Example 4)
The same operation as in Example 2 was performed on the powder after pressure mixing obtained in Comparative Example 2. When determined in the same manner, the ratio of complete hollow particles was 35%, and the ratio of fragment particles, solid particles, and incomplete hollow particles was 65%.

(Comparative Example 5)
The same polymethyl methacrylate powder, alumina powder, and silica powder were mixed with a mixing device to obtain a mixed powder, and this mixed powder was used for pressure contact mixing and firing in the same manner as in Example 1 and Example 2. When determined in the same manner, the ratio of complete hollow particles was 62%, and the ratio of fragment particles, solid particles, and incomplete hollow particles was 38%.

DESCRIPTION OF SYMBOLS 1 Pressure welding apparatus 2 Chamber 3 Inner 4 Scraper 5 Mixed powder 10 Resin powder 11 Ceramic powder

Claims (3)

In the method for producing ceramic hollow particles in which a porous shell layer formed by bonding ceramic powders to form a hollow structure is formed,
Resin powder and ceramic powder having a smaller diameter than the resin powder are mixed in a pressure mixing device that mixes powder while passing the powder through a minute gap between the inner wall of the chamber that is rotatable and has a drum shape, and a scraper. The resin powder and the ceramic powder are mixed by rotating individually and rotating the chamber at a speed lower than the rotational speed at the time of the pressure mixing, and then the pressure mixing is performed and the ceramic powder is partially embedded in the resin powder. A method for producing hollow ceramic particles, comprising: forming a precursor covering a surface; then firing the precursor to burn out the resin powder and sintering the ceramic powder together.   2. The method for producing ceramic hollow particles according to claim 1, wherein two or more kinds of ceramic powders having different particle sizes are used.   A ceramic hollow particle obtained by the production method according to claim 1 or 2 and comprising 65 to 100% of complete hollow particles and 0 to 35% of debris particles, solid particles and incomplete hollow particles.