JP2014080356A - Inorganic hollow particle and method of producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide inorganic hollow particles obtained by simple means and having high strength, and a method of producing the inorganic hollow particles.SOLUTION: A inorganic hollow particle has multi-layer shells or composite shells including inorganic acid alkaline earth metal salt and alkali silicate metal salt.

Description

  TECHNICAL FIELD The present invention relates to inorganic hollow particles useful for resin-molded parts, members such as portable electronic devices and automobiles, fillers such as various building materials, wire coating materials, semiconductor encapsulants, and the like, and a method for producing the same.

  Inorganic hollow particles are used as fillers for various resin molded parts. Examples of such hollow particles include silica, alumina, zirconia, titania and other metal oxide particles (Patent Documents 1 and 2), calcium carbonate particles. (Patent Document 3), calcium phosphate particles (Patent Document 4) and the like have been reported. However, these hollow particle production methods have problems such as using a device having a special structure, incineration of organic substances as a core at a high temperature, and requiring a sintering process at a high temperature of 1000 ° C. or higher. .

  On the other hand, the present inventor has reported that hollow particles such as calcium carbonate and magnesium carbonate can be easily obtained by spray drying (Non-patent Documents 1 and 2).

International Publication No. 2009/110514 Pamphlet Japanese Patent Laid-Open No. 48-15798 JP-A-6-127938 JP 2007-70211 A

Abstracts of the 113th Academic Lecture Meeting of the Society of Inorganic Materials, p. 40-41 (2006) Abstracts of the 123rd Academic Lecture Meeting of the Inorganic Materials Society of Japan p96-97 (2011)

However, the conventional inorganic hollow particles cannot be industrially mass-produced in terms of high-temperature treatment and special equipment. On the other hand, although the spray drying method is suitable for mass production, the conventional method can obtain hollow particles formed of calcium carbonate or magnesium carbonate, but its strength is not sufficient.
Therefore, the subject of this invention is providing the inorganic hollow particle with high intensity | strength obtained by a simple means, and its manufacturing method.

  Therefore, the present inventor studied to obtain inorganic hollow particles having high strength by spray drying, and as a result, inorganic acid alkaline earth metal salt having low solubility in water and alkali metal silicate having relatively high solubility in water. It was found that inorganic hollow particles having excellent strength can be obtained by dissolving both of the salts in water and spray-drying the resulting aqueous solution, thereby completing the present invention.

That is, the present invention provides the following [1] to [12].
[1] An inorganic hollow particle having a multilayer shell or composite shell containing an inorganic acid alkaline earth metal salt and an alkali metal silicate salt.
[2] The inorganic hollow particles according to [1], wherein the outer layer contains an inorganic acid alkaline earth metal salt and the inner layer has a multilayer shell containing an alkali metal silicate salt.
[3] The inorganic hollow particles according to [1] or [2], which are obtained by spray drying an aqueous solution containing an alkaline earth metal salt of an inorganic acid and an alkali metal silicate.
[4] Any of [1] to [3] having an average particle diameter of 0.1 to 100 μm, a bulk density of 0.02 to 0.5 g / cm ³ , and a sphericity of 0.85 or more. The inorganic hollow particle according to 1. [5] The outer layer side of the multilayer shell or composite shell is a layer mainly composed of an inorganic acid alkaline earth metal salt, and the inner layer side is a layer mainly composed of an alkali metal silicate metal salt. The inorganic hollow particle in any one.
[6] The inorganic acid alkaline earth metal salt is a calcium salt, barium salt or magnesium salt of an acid selected from carbonic acid, phosphoric acid and sulfuric acid, and the alkali metal silicate is a sodium salt, potassium salt of silicic acid or The inorganic hollow particle according to any one of [1] to [5], which is a lithium salt.
[7] A multilayer shell or composite shell containing an inorganic acid alkaline earth metal salt and an alkali metal silicate characterized by spray-drying an aqueous solution containing the inorganic acid alkaline earth metal salt and the alkali metal silicate salt The manufacturing method of the inorganic hollow particle which has this.
[8] The method according to [7], wherein the obtained inorganic hollow particles are inorganic hollow particles having a multilayer shell or a composite shell containing an inorganic acid alkaline earth metal salt in the outer layer and an alkali metal silicate salt in the inner layer. .
[9] The production method according to [7] or [8], wherein the spray drying temperature is 80 to 200 ° C.
[10] The average particle diameter of the inorganic hollow particles is 0.1 to 100 μm, the bulk density is 0.02 to 0.5 g / cm ³ , and the sphericity is 0.85 or more [7] to [9 ] The manufacturing method in any one of.
[11] The outer layer side of the multilayer shell or composite shell is a layer mainly composed of an inorganic acid alkaline earth metal salt, and the inner layer side is a layer mainly composed of an alkali metal silicate metal salt. The manufacturing method in any one.
[12] The inorganic acid alkaline earth metal salt is a calcium salt, barium salt or magnesium salt of an acid selected from carbonic acid, phosphoric acid and sulfuric acid, and the alkali metal silicate is a sodium salt, potassium salt of silicic acid or The production method according to any one of [7] to [11], which is a lithium salt.

  According to the present invention, high-strength inorganic hollow particles can be obtained by a simple method called spray drying, and the obtained inorganic hollow particles are spherical and have improved strength. It is useful as a filler for various materials such as a low dielectric constant material, a light powder, and a cosmetic powder.

It is a figure which shows the relationship between potassium silicate solution addition amount and an average film thickness. The SEM image (a) and EPMA mapping (b) of the cross section of this invention inorganic hollow particle are shown. Red: Si. Green: Ca. The compressive strength of this invention inorganic hollow particle is shown. The stability of the inorganic hollow particles of the present invention to water is shown. The change of the compressive strength of this invention inorganic hollow particle before and behind immersion in water is shown. The relationship of the average particle diameter of this invention inorganic hollow particle by calcium carbonate and potassium silicate, the addition amount of potassium silicate, and a film thickness is shown.

  The inorganic hollow particle of the present invention has a multilayer shell having an outer layer and an inner layer formed by two kinds of components, or a composite shell composed of two kinds of components, and these two kinds of components are inorganic acid alkaline earths. Includes metal salts and alkali metal silicates. Among these, a form having a multilayer shell is preferable, and a form having a multilayer shell containing an inorganic acid alkaline earth metal salt in the outer layer and an alkali metal silicate salt in the inner layer is preferable.

  In the multilayer shell structure, the outer layer may contain an inorganic acid alkaline earth metal salt, but is preferably a layer mainly composed of an inorganic acid alkaline earth metal salt. Here, the main component means that 60 to 100% by mass of the inorganic acid alkaline earth metal salt is contained.

  Examples of the inorganic acid of the inorganic acid alkaline earth metal salt include carbonic acid, phosphoric acid, and sulfuric acid. Among these, carbonic acid and phosphoric acid are particularly preferable. Examples of the alkaline earth metal salt include calcium, barium, magnesium, and strontium, but calcium, barium, and magnesium are more preferable, and calcium is particularly preferable. Specific examples include calcium carbonate, calcium phosphate, calcium hydrogen phosphate, calcium sulfate, basic magnesium carbonate, magnesium phosphate, barium carbonate, barium phosphate, and barium sulfate, with calcium carbonate and calcium phosphate being particularly preferable.

  In the multilayer shell structure, the inner layer may contain an alkali metal silicate, but is preferably a layer mainly composed of an alkali metal silicate. Here, the main component means containing 60 to 100% by mass of an alkali metal silicate salt.

  Examples of the alkali metal silicate include sodium silicate, potassium silicate, and lithium silicate.

The composite shell structure has a structure in which an inorganic acid alkaline earth metal salt and an alkali metal silicate are combined. On the other hand, in a multi-layer shell structure, an inorganic acid alkaline earth metal salt layer and an alkali metal silicate salt layer form an outer layer and an inner layer. It is preferred that an acid alkali metal salt is present. The interface between the outer layer and the inner layer does not require the inorganic acid alkaline earth metal salt layer and the alkali metal silicate salt layer to be clearly separated. It may be.
The inorganic hollow particles of the present invention are hollow and have a composite shell or a multilayer shell. That is, the scanning electron microscope (SEM) and electron beam microanalysis (EPMA) of the cross section at the center. Can be confirmed. For example, if SEM and EPMA are performed and the SEM image is EPMA mapped, the hollow portion, the outer layer (Ca is green), and the inner layer (Si is red) can be confirmed.

  The mass ratio (A: B) of the inorganic acid alkaline earth metal salt (A) and the alkali metal silicate (B) can be appropriately adjusted depending on the intended strength, solubility, and the like. 10 is preferable, 50: 1 to 1: 1 is more preferable, and 10: 1 to 1: 1 is more preferable. Such a mass ratio can be adjusted by adjusting the concentration of an aqueous solution of an inorganic acid alkaline earth metal salt and an alkali metal silicate used as a raw material.

  The average particle diameter of the inorganic hollow particles of the present invention can be adjusted by the nozzle diameter of the spray dryer, the drying temperature, and the spray pressure. From the viewpoint of handling as a powder and the smoothness of the product surface mixed as a filler. 0.1-100 μm is preferable, 0.1-50 μm is more preferable, and 0.3-50 μm is more preferable.

The bulk density of the inorganic hollow particles of the present invention, strength, heat insulation, light weight, in terms of a dielectric such as, preferably 0.02 to 0.5 g / cm ^3, is 0.03~0.20g / cm ³ More preferred is 0.05 to 0.15 g / cm ³ . This bulk density is inversely correlated with the hollowness of the hollow particles. The bulk density can be measured by a tap method.

  The film thickness of the multilayer shell or composite shell of the present invention can be measured from a cross-sectional SEM image, can be in the range of 100 to 400 nm, and is preferably 200 to 300 nm, particularly 250 nm.

The shape of the inorganic hollow particles of the present invention is spherical as long as it is produced by a spray drying method, and the average sphericity is 0 from the viewpoint of dispersibility, mixing properties and fluidity when mixed with a substrate such as a resin. .85 or more is preferable.
Here, the average sphericity is determined by measuring the projected area (A) and the perimeter (PM) of a particle from a scanning electron micrograph, and assuming that the area of a perfect circle with respect to the perimeter (PM) is (B). Is expressed as A / B. Therefore, assuming a perfect circle having the same circumference as that of the sample particle (PM), PM = 2πr and B = πr ² , so that B = π × (PM / 2π) ² , The sphericity is calculated as sphericity = A / B = A / 4π / (PM) ² . The sphericity is measured for 100 particles, and the average value is taken as the average sphericity. As long as the inorganic hollow particles of the present invention are produced by the spray drying method, the average sphericity is 0.85 or more, preferably 0.90 or more, without needing to measure again.

  The compressive strength of the inorganic hollow particles of the present invention is improved by several tens of times compared to the single-layer hollow particles formed of an inorganic acid alkaline earth metal salt. The compressive strength can be adjusted by the amount of alkali metal silicate added.

  The inorganic hollow particles of the present invention can be produced by spray drying an aqueous solution containing an inorganic acid alkaline earth metal salt and an alkali metal silicate salt. In the present invention, spray drying of an aqueous solution containing these components is important for obtaining hollow particles having a multilayer shell or a composite shell. When a slurry containing these two components is spray-dried, solid particles become nuclei and particles grow, so that hollow particles cannot be obtained. The inorganic acid alkaline earth metal salt used in the present invention generally has low solubility in water, so that it precipitates outside the first sprayed droplet, and the alkali metal silicate confined in the inside later precipitates. It is presumed that hollow particles having a multilayer shell are formed. When the solubility of the two components approximates, hollow particles having a composite shell are formed.

  More specifically, an aqueous solution containing an inorganic alkaline earth metal and a silicate metal salt is made into fine droplets, sprayed into a dryer, and dried in contact with hot air in the dryer to produce hollow particles. To do. As a method to make the aqueous solution into fine droplets, a sprayer using a two-fluid nozzle, a pressure nozzle, a rotating disk nozzle, etc. can be used. At this time, the particle diameter can be controlled by the two-fluid nozzle, the pressure nozzle, etc. preferable.

  The particle size can be controlled by adjusting the diameter of the sprayer or spray nozzle used for spray drying. Moreover, the mass ratio of these components can be controlled by adjusting the inorganic acid alkaline earth metal salt concentration and the alkali metal silicate concentration. The preferred inorganic acid alkaline earth metal salt concentration is 0.1 to 10.0 g / L, and the alkali metal silicate concentration is preferably 0.05 to 3.00 g / L. Although it is difficult to prepare a high-concentration solution because the solubility of the inorganic acid alkaline earth metal salt is low, the solubility can be increased by blowing carbon dioxide into a bicarbonate. On the other hand, since the solubility of alkali metal silicate is high, it can be selected from a wide range.

  The temperature for spray drying is preferably 80 to 200 ° C., more preferably 90 to 120 ° C., from the viewpoints of drying property, yield, strength, spherical shell formation, and yield of spherical particles. The pressure for spray drying is preferably 50 to 500 kPa.

  Since the hollow particles obtained by spray drying are very light, they cannot be recovered in their entirety with a cyclone. Therefore, a bag filter is preferably used as the collection method in the present invention. In addition, by using a cyclone and a bag filter in series, coarse particles can be collected by the cyclone and fine particles can be collected by the bag filter. Therefore, the particle size can be adjusted and the application can be easily developed.

  Since the obtained inorganic hollow particles of the present invention employ a spray drying method, particles having a small particle size distribution and a controlled particle size can be obtained efficiently. In addition, because of its high strength, it can be widely used in the field of fillers for various materials such as functional fillers for plastic filling, lightweight powder, powder insulation for cosmetics, heat insulation, or low dielectric constant materials. it can.

  EXAMPLES Next, an Example is given and this invention is demonstrated still in detail.

Example 1
0 to 5.0 g of potassium silicate aqueous solution (SiO ₂ / K ₂ O molar ratio = 4.0, concentration 35 wt%) is added to 1 liter of pure water, and the Ca / P atomic ratio is 1.67. Thus, calcium carbonate and phosphoric acid-calcium hydrogen phosphate dihydrate (DCPD) were added to prepare a suspension having a suspension concentration of 0.1 mass%. Carbon dioxide was dissolved in this suspension while blowing at a flow rate of 1 dm ³ · min ⁻¹ for 1 hour and filtered to obtain an aqueous calcium phosphate solution having a concentration of about 0.5 g / L. Further, this aqueous solution is made into a spray solution with a two-fluid nozzle (nozzle diameter 0.71 mm) and sprayed under the conditions of a drying temperature of 100 ° C., a spraying pressure of 200 kPa, a liquid feed flow rate of 500 cm ³ / h, and a dry air amount of 0.75 m ³ / min. A powder sample was obtained by drying.

  The obtained sample was characterized using X-ray diffraction, scanning electron microscope (SEM) observation, and electron beam microanalyzer (EPMA). The particle size was measured by SEM observation and was measured by measuring 100 or more particles by photographic method. The thickness of the hollow particles was measured by impregnating the particles with an epoxy resin, cutting with a microtome, and SEM observation. The bulk density was measured by the tap method. Further, the compressive strength of the obtained product was determined by measuring the compressive strength of one particle with a dynamic ultra-micro hardness meter.

(1) Products obtained by spray-drying aqueous solutions with different amounts of potassium silicate aqueous solution are all spherical hollow particles, and the particle size is about 4 μm if the spray-drying conditions are the same. The degree was 0.90 or more, and there was almost no difference in the appearance of the spherical particles. However, the film thickness of the spherical hollow particles was about 200 nm when no potassium silicate aqueous solution was added (0 g), but the film thickness tended to increase as the amount added increased, and the amount added was 5.0 g / L. Then, it increased to 300 nm (FIG. 1). The bulk density was 0.11 g / cm ³ .

(2) Next, an SEM photograph and EPMA mapping of the product when the potassium silicate aqueous solution addition amount is 3.0 g / L are shown in FIG. When mapping was performed on Si and Ca of particles having an average particle diameter of about 4 μm and an average film thickness of about 500 nm (FIG. 2A), it was found that Ca and Si were contained in the hollow walls of the spherical hollow particles. Okay (Figure 2 (b)). Furthermore, since the outer side of the hollow wall contains a large amount of Ca and the inner side contains a large amount of Si, it was confirmed that the particles were composition gradient particles.

(3) When the compressive strength of the obtained composition-graded spherical particles was measured, the compressive strength, which was about 0.6 MPa without addition, increased with the addition of potassium silicate to 3.0 g. It was confirmed that the addition was about 16.9 MPa, an increase of about 26 times that in the case of no addition, and the strength was almost the same as that of the HAp solid substance although it was a hollow particle (FIG. 3). The HAp solid substance used was prepared by spray-drying a calcium phosphate suspension prepared by adding an aqueous phosphoric acid solution to the calcium hydroxide suspension so that the Ca / P atomic ratio was 1.67.

(4) The resulting hollow particles were immersed in water for 1 week to examine the stability to water. That is, the hollow particles of the calcium phosphate monolayer (without potassium silicate added) collapse in a short time when immersed in water (FIG. 4 (a)), but the hollow particles of the present invention can be immersed in water for one week. The shape was maintained (FIG. 4B). Moreover, the compression strength hardly changed even when immersed in water for one week (FIG. 5).

Example 2
Calcium carbonate is suspended by suspending reagent calcium carbonate in pure water to a suspension concentration of 0.15 mass% and blowing CO ₂ gas at a flow rate of 1 dm ³ · min ⁻¹ for 1 hour in a constant temperature water bath at 3 ° C. Dissolved. Thereafter, this suspension was filtered to obtain a calcium hydrogen carbonate supersaturated solution having a Ca ²⁺ ion concentration of about 400 ppm (0.01 mol · dm ⁻³ ). Furthermore, what added potassium silicate so that it might become 0-0.40 mass% to this solution was used as the spray solution. This spray solution is spray-dried under the conditions of a drying temperature of 100 to 200 ° C., a spraying pressure of 50 to 200 kPa, a liquid flow rate of 0.5 dm ³ · h ⁻¹ , and a dry air amount of 0.75 m ³ · min ^−1. Tilted spherical hollow particles were produced.

In the same manner as in Example 1, the characteristics of the obtained hollow particles were evaluated.
(1) When the amount of potassium silicate added increases, the shape of the particles becomes distorted and the surface becomes porous, so the maximum amount added that can maintain a spherical shape was 0.25% by mass. FIG. 6 shows the influence of the amount of added potassium silicate on the average particle diameter and film thickness of the spherical hollow particles and the internal structure. The film thickness of the spherical hollow particles increased from about 0.17 μm to 0.31 μm as the addition amount increased, but the average particle size did not change and was about 2.0 μm. On the other hand, from the EPMA mapping, it was confirmed from the EPMA mapping that a large amount of Ca was present on the outer side of the hollow wall, and that Si was deposited while being compositionally inclined toward the inside. Next, the drying temperature was examined. As the temperature was increased, the average particle size increased and the particle size distribution tended to widen. In addition, clean spherical hollow particles were obtained at 100 ° C., but the shape tended to be distorted and porous as the drying temperature increased. On the other hand, the higher the spraying pressure, the smaller the average particle size and the film thickness.

(2) From the X-ray diffraction results, the spherical hollow particles to which potassium silicate is not added are a single phase of calcite-type calcium carbonate, but when potassium silicate is added, the formation of a vaterite type is recognized, The crystallinity decreased with the increase, and became amorphous at 0.35% by mass or more. Further, the formation of a vaterite type was confirmed at drying temperatures of 100 and 125 ° C., but it became amorphous at 150 ° C. or higher. Furthermore, when the compressive strength of the produced composition-graded spherical hollow particles was measured, the compressive strength was 13.7 MPa, and the strength was improved by about 50% compared to the one without added potassium silicate.

Claims (12)

  An inorganic hollow particle having a multilayer shell or a composite shell containing an inorganic alkaline earth metal salt and an alkaline metal silicate.   2. The inorganic hollow particle according to claim 1, wherein the outer layer contains an inorganic acid alkaline earth metal salt and the inner layer has a multilayer shell containing an alkali metal silicate salt.   The inorganic hollow particle according to claim 1 or 2, obtained by spray drying an aqueous solution containing an alkaline earth metal salt of an inorganic acid and an alkali metal silicate. The inorganic material according to any one of claims 1 to ³ , wherein the average particle size is 0.1 to 100 µm, the bulk density is 0.02 to 0.5 g / cm ³ , and the sphericity is 0.85 or more. Hollow particles.   The outer layer side of the multilayer shell or the composite shell is a layer mainly composed of an inorganic acid alkaline earth metal salt, and the inner layer side is a layer mainly composed of an alkali metal silicate metal salt. Inorganic hollow particles.   The inorganic acid alkaline earth metal salt is a calcium salt, barium salt or magnesium salt of an acid selected from carbonic acid, phosphoric acid and sulfuric acid, and the alkali metal silicate salt is a sodium salt, potassium salt or lithium salt of silicic acid. The inorganic hollow particle according to any one of claims 1 to 5.   An inorganic material having a multilayer shell or a composite shell containing an inorganic acid alkaline earth metal salt and an alkali metal silicate characterized by spray-drying an aqueous solution containing the inorganic acid alkaline earth metal salt and the alkali metal silicate salt A method for producing hollow particles.   The method according to claim 7, wherein the obtained inorganic hollow particles are inorganic hollow particles having a multilayer shell containing an inorganic acid alkaline earth metal salt in the outer layer and an alkali metal silicate in the inner layer.   The method according to claim 7 or 8, wherein the spray drying temperature is 80 to 200 ° C. The average particle diameter of the inorganic hollow particles is 0.1 to 100 µm, the bulk density is 0.02 to 0.5 g / cm ³ , and the sphericity is 0.85 or more. The manufacturing method of description.   The outer layer side of the multilayer shell or the composite shell is a layer containing an inorganic acid alkaline earth metal salt as a main component, and the inner layer side is a layer containing an alkali metal silicate as a main component. Manufacturing method.   The inorganic acid alkaline earth metal salt is a calcium salt, barium salt or magnesium salt of an acid selected from carbonic acid, phosphoric acid and sulfuric acid, and the alkali metal silicate salt is a sodium salt, potassium salt or lithium salt of silicic acid. The manufacturing method of any one of Claims 7-11.