JP7104656B2 - How to make halloysite powder and halloysite powder - Google Patents

Description

The present invention relates to halloysite powder and a method for producing halloysite powder.

Halloysite nanotubes, which are tubular halloysites, are used for various purposes by taking advantage of their shapes (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2009-91236

In recent years, the development of materials having a new fine structure has been required in anticipation of various applications. The present inventor has focused on a new microstructure using halloysite powder (haloysite powder), especially halloysite nanotubes.

Such halloysite powder is expected to be used in water depending on the application. As a result of examination by the present inventor, it has been found that some halloysite powders have insufficient stability (water resistance) to water and gelle, which may not be suitable for use in water.

The present invention has been made in view of the above points, and an object of the present invention is to provide a halloysite powder having excellent water resistance and a method for producing the same.

The present inventor has diligently studied to achieve the above object. As a result, when the fracture strength measured under specific conditions of the granules obtained by spray-drying the slurry containing the halloysite nanotubes is a certain value or more, the water resistance of the halloysite powder containing the granules is excellent. I found. Through such a process, the present invention was completed.

That is, the present invention provides the following [1] to [10].
[1] A halloysite powder containing granules formed by aggregating halloysites containing halloysite nanotubes, wherein the breaking strength of the granules soaked in pure water for 24 hours and impregnated with water is 7.60 MPa or more.
[2] The halloysite powder according to the above [1], wherein the granules have a first pore derived from a tube hole of the halloysite nanotube and a second pore different from the first pore. ..
[3] The halloysite powder according to the above [2], wherein the differential pore distribution obtained from the nitrogen adsorption isotherm by the BJH method shows two or more pore diameter peaks in the range of 10 to 100 nm.
[4] The halloysite powder according to any one of the above [1] to [3], which has an average particle size of 0.5 to 200 μm.
[5] The halloysite powder according to any one of the above [1] to [4], which has a BET specific surface area of 30 to 200 m ² / g.
[6] The halloysite powder according to any one of [1] to [5] above, wherein the average pore diameter is 11.0 nm or more.
[7] The halloysite powder according to any one of [1] to [6] above, wherein the total pore area is 59.0 m ² / g or more.
[8] The halloysite powder according to any one of [1] to [7] above, wherein the total pore volume is 0.20 cm ³ / g or more.
[9] The method for producing a halosite powder according to any one of the above [1] to [8], wherein a step of preparing a halosite slurry containing a halosite nanotube, a step of preparing a powder from the above slurry, and a step of preparing a powder. A method for producing halloysite powder, comprising a step of calcining the prepared powder at a firing temperature of more than 420 ° C. and lower than 500 ° C.
[10] The method for producing halloysite powder according to [9] above, wherein the step of preparing the powder from the slurry is the step of spray-drying the slurry.

According to the present invention, it is possible to provide a halloysite powder having excellent water resistance and a method for producing the same.

It is a TEM photograph of the dispersed phase recovered after centrifugation. It is a TEM photograph of the dispersed phase recovered after centrifugation, and is a TEM photograph of a field of view different from FIG. It is an SEM photograph which shows the halloysite powder of Example 2. It is an SEM photograph which shows the halloysite powder of Example 2, and is the enlarged photograph of FIG. It is an SEM photograph which shows the halloysite powder of Example 2, and is the enlarged photograph of FIG. 6 is an SEM photograph showing the halloysite powder of Comparative Example 3. It is a graph which shows the differential pore distribution of the halloysite powder of Example 1. It is a graph which shows the differential pore distribution of the halloysite powder of Example 2. It is a graph which shows the differential pore distribution of the halloysite powder of Example 3. It is a graph which shows the differential pore distribution of the halloysite powder of the comparative example 3. It is a graph which shows the XRD pattern of the halloysite powder of Example 1 and Comparative Examples 1 and 2.

Hereinafter, the halloysite powder of the present invention and the method for producing the halloysite powder of the present invention will be described.
The numerical range represented by using "-" means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.

[Overview of Halloysite]
Halloysite is a clay mineral represented by Al ₂ Si ₂ O ₅ (OH) _{4.2H 2} O or Al ₂ Si ₂ O ₅ (OH) ₄ .
Halloysites exhibit various shapes such as tubular (hollow tubular), spherical, angular nodule, plate, and sheet.
The inner diameter (diameter of the tube hole) of the halloysite nanotube, which is a tubular (hollow tubular) halloysite, is, for example, about 10 to 20 nm. The outer surface of the halloysite nanotube is mainly composed of silicate SiO ₂ , and the inner surface is mainly composed of alumina Al ₂ O ₃ .

[Manufacturing method of halloysite powder]
Before explaining the halloysite powder of the present invention, first, a method for producing the halloysite powder of the present invention (hereinafter, also referred to as "a method for producing a halloysite powder of the present invention" or simply "a method for producing the halloysite powder of the present invention") will be described. ..
The production method of the present invention is a method for producing the halloysite powder of the present invention described later, and at least a step of preparing a halloysite slurry containing halloysite nanotubes (slurry preparation step) and a step of preparing powder from the above slurry. (Powder preparation step), and a step of firing the prepared powder at a firing temperature of more than 420 ° C and less than 500 ° C.
Hereinafter, preferred embodiments of the production method of the present invention will be described.

<Slurry preparation process>
The slurry preparation step is not particularly limited as long as it is a step in which halloysite containing halloysite nanotubes can prepare a slurry dispersed in a dispersion medium such as water, but a preferred embodiment of the slurry preparation step will be described below. In the embodiments described below, the dispersed phase recovered after centrifugation corresponds to the slurry prepared in the slurry preparation step.

<< Raw material (Iitoyo clay) >>
At the Osodani Plant of JFE Mineral Co., Ltd.'s Iide Mining Works (Osodani, Iide-cho, Nishioki-gun, Yamagata Prefecture), clay sand is produced from clay sand and clay deposits. , Called "Iide clay" for convenience) can be used as a raw material.
Iitoyo clay is a clay having a water content of about 40% by mass and having plasticity, and contains halloysite and fine sand (quartz) represented by SiO ₂ as main components. Iitoyo clay may also contain a small amount of cationic polymer flocculant.
As the Iitoyo clay, the one containing water may be used as it is (while containing about 40% by mass of water), or the clay naturally dried (including semi-dried) by the sun may be used. .. Moisture-containing or semi-dry Iitoyo clay may be dried using equipment.
The dried Iitoyo clay may be crushed and, if necessary, subjected to dry purification, classification, magnetic separation, color selection and the like before use.
Needless to say, in addition to using Iitoyo clay, which has a large amount of halloysite, the raw material can be used.

《Pre-slurry》
Next, a slurry (pre-slurry) in which Iitoyo clay is dispersed in water is obtained. The method for dispersing Iitoyo clay in water is not particularly limited, and conventionally known devices such as a high-speed mixer, a dispenser, a bead mill, and a homomixer can be used.
The solid content concentration of the pre-slurry is not particularly limited, and is, for example, 5 to 20% by mass.

《Coarse grain removal》
The pre-slurry is then sieved, for example, to remove coarse particles. Examples of the mesh size of the sieve used include 25 to 100 μm. As the sieve, for example, a JIS test sieve can be used, but at the time of mass production, a general large-sized wet sieving device can be used. In addition to using a sieve, coarse particles may be removed by sedimentation separation or by using a wet cyclone.

《Filtration》
Next, the pre-slurry from which the coarse particles have been removed is suction-filtered using a filter and recovered as a dehydrated cake. At the time of mass production, for example, a dehydrator such as a filter press or an Oliver filter can be used.
It is also possible to omit this filtration and use the slurry from which the coarse particles have been removed as it is as a slurry which will be described later. At this time, a dispersant may be added if necessary.

<< Post-slurry >>
By adding water to the dehydrated cake and stirring at high speed, a slurry (post-slurry) in which Iitoyo clay from which coarse particles have been removed is dispersed in water is obtained. As the disperser, as in the case of pre-slurrying, conventionally known devices such as a high-speed mixer, a dispenser, a bead mill and a homomixer can be used.
The solid content concentration of the post-slurry is not particularly limited, and is, for example, 5 to 30% by mass.

Since the dispersed state of the particles (Iitoyo clay) in the slurry greatly affects the accuracy of the subsequent centrifugation, it is preferable to add a surfactant as a dispersant in the post-slurry formation.
As the surfactant, when Iitoyo Clay contains a cationic polymer flocculant, it is preferable to use an anionic surfactant, and in particular, a polymer can be obtained with a small amount of use. It is more preferable to use a type of anionic surfactant (anionic polymer surfactant).

Even when Iitoyo clay does not contain a cationic polymer flocculant, it is anionic from the viewpoint that the obtained slurry maintains a high dispersion state and that fine sand is stably removed by centrifugation, which will be described later. It is preferable to add a polymer surfactant.
By adding an anionic polymer surfactant, a higher-concentration post-slurry can be obtained, which also has the effect of improving productivity in drying using a spray dryer or the like, which will be described later.

Specific examples of the anionic polymer surfactant include special polycarboxylic acid type poisons 520, 521, 530 or 532A (all manufactured by Kao Corporation) from the viewpoint of obtaining a stable post-slurry that does not settle even when left to stand. Can be mentioned.
Depending on the intended use, Caosera 2000, 2020 or 2110 (same as above), which does not contain metal ions such as sodium and potassium, can also be used.

The content of the surfactant in the post-slurry is not particularly limited, but for example, 0.5 to 3.0% by mass is preferably mentioned with respect to the total solid content of the post-slurry.
If the content of the surfactant is too low, the dispersion of halloysite and fine sand particles in the post-slurry may be insufficient. On the other hand, if the amount of the surfactant is too large, a cohesive state may occur and the cost may increase. Further, defects in the post-process (decrease in recovery rate of dispersed phase by centrifugation, insufficient drying by spray drying, consolidation or insufficient burning in firing, etc.) may easily occur.

《Centrifugation》
After the obtained slurry is centrifuged, it is separated into a sedimentary phase in the lower layer and a dispersed phase in the upper phase. The sedimentary phase contains a large amount of fine sand, and the dispersed phase contains a large amount of halloysite. The solid content concentration of the dispersed phase (slurry) is, for example, 2 to 10% by mass.
Centrifugal force and processing time for centrifugation are, for example, 2000 to 3000 G and 3 to 30 minutes, respectively, but are not limited to these, and are appropriately set in consideration of the dispersion state, application, cost, and the like. ..
A large centrifuge can be used for mass production.
After centrifugation, the dispersed phase can be recovered by suction using a pump or the like. A skimming nozzle may be used to recover the dispersed phase. In this way, halloysite can be purified and separated from Iitoyo clay containing halloysite and fine sand. It can be confirmed by, for example, a transmission electron microscope (TEM) photograph that the recovered dispersed phase contains halloysite nanotubes (see FIGS. 1 and 2).

<< Other aspects >>
The slurry preparation step is not limited to the above embodiment. For example, when a raw material other than Iitoyo clay is used, the solid content concentration of the post-slurry, the content of the surfactant in the post-slurry, the conditions for centrifugation, and the like are appropriately changed.
Step shortening (eg, pre-slurrying, sieving, and / or omission of filtration) or additions are also modified as appropriate.
For example, as a commercially available product, a halloysite (haloysite nanotube) manufactured by SIGMA-ALDRICH, which is dispersed in water using a conventionally known device, may be used as a slurry prepared in this step. Commercially available halloysite nanotubes may be used after being subjected to dry purification, classification, magnetic separation, color selection and the like, if necessary.

If necessary, the slurry prepared in the slurry preparation step may be used after being subjected to wet purification, classification, magnetic separation, or the like.

<Powder preparation process>
The powder preparation step is a step of preparing a powder from the slurry prepared in the slurry preparation step.
The powder obtained in the powder preparation step may be further granulated by subjecting it to treatments such as rolling, stirring, and extrusion. As a result, the size of the granules constituting the powder can be increased.

《Spray dry》
Examples of the powder preparation step include a step of obtaining a powder by spray-drying the slurry prepared in the slurry preparation step (for example, the dispersed phase obtained by the above-mentioned centrifugation).

In order to spray dry the prepared slurry, a spray dryer is used, which is a device that instantly obtains powder by spraying (micronizing) a liquid raw material into fine droplets and exposing it to hot air to dry it. Will be done. The spray dryer is a conventionally known device, and examples thereof include a spray dryer manufactured by Okawara Kakoki Co., Ltd., Fujisaki Electric Co., Ltd., Nippon Kagaku Kikai Seisakusho Co., Ltd., or Yamato Scientific Co., Ltd.
In the spray dryer, the particle size of the powder particles (granule) obtained by drying is also controlled by changing the size of the droplets obtained by spraying (micronizing) the liquid raw material.
The method for atomizing the liquid raw material using a spray dryer is not particularly limited, and depending on the desired droplet size, for example, a two-fluid nozzle method, a pressure nozzle (pressurized nozzle) method, or a four-fluid nozzle method. (Twin jet nozzle method) or a conventionally known method such as a rotating disk method can be appropriately selected. The particle size of the powder particles (granule) obtained by drying also changes depending on the concentration and / or the amount of treatment of the slurry. Therefore, in order to obtain the desired particle size, in addition to the atomization method, the state of the slurry is adjusted. It will be selected as appropriate.
Regarding the contact method between the hot air and the spray droplets, for example, a general parallel flow type in which both the hot air and the spray droplets go downward; the spray droplets flow downward and the hot air flows upward. A countercurrent type; a parallel current type in which the spray droplets are directed upward and hot air is directed downward; and the like are appropriately selected.

Since spray drying applies heat instantaneously, the powder itself does not get hot. In spray drying, since the slurry is dried to directly obtain powder, treatments such as filtration, drying and pulverization are unnecessary, and contamination that may occur during these series of operations can be suppressed.

《Media flow drying》
The means for preparing the powder from the slurry is not limited to the spray drying described above as long as the halloysite powder of the present invention described later can be obtained, and may be, for example, medium fluidized drying (fluidized bed drying with balls). ..
That is, the powder preparation step may be a step of obtaining a powder by fluid-drying the slurry prepared in the slurry preparation step.
In the medium flow drying, for example, first, a slurry to be dried is first continuously supplied to a flowing ceramic ball layer having a diameter of 1 to 3 mm, so that the slurry is adhered to the ball surface. The object to be dried is instantly dried by heat conduction from the heated balls and convection heat transfer from the fluidized hot air, and is separated from the ball surface by collision between the balls. In this way the powder is obtained.

<Baking process>
The production method of the present invention includes a step (baking step) of firing the powder obtained in the powder preparation step at a firing temperature of more than 420 ° C and less than 500 ° C. By undergoing such a firing step, the breaking strength of the granules becomes equal to or higher than a predetermined value, and the water resistance is excellent. It is presumed that this is because the primary particles of halloysites constituting the granules are firmly bonded to each other through the firing step. However, this mechanism is an estimation, and it is assumed that other than this mechanism is within the scope of the present invention.

When a surfactant is used in the post-slurry described above, the surfactant may remain in the powder obtained by spray drying or the like, but the surfactant can be removed by firing. Will be removed.

The calcination temperature is a temperature at which the crystal structure of halloysite can be maintained in the XRD measurement after calcination. The firing temperature is preferably 430 ° C. or higher and 480 ° C. or lower, and more preferably 440 ° C. or higher and 470 ° C. or lower.
The firing time is not particularly limited, and is, for example, 0.5 to 2 hours, preferably 0.75 to 1.5 hours.

[Haloysite powder]
Next, the halloysite powder of the present invention obtained by the above-mentioned production method of the present invention will be described.
The halloysite powder of the present invention (hereinafter, also simply referred to as "powder of the present invention") is a powder containing granules formed by aggregating halloysites containing halloysite nanotubes, and is immersed in pure water for 24 hours to contain water. A halloysite powder having a breaking strength of 7.60 MPa or more.
In the present specification, an aggregate of a plurality of "granule" is referred to as "powder".
The powders of the present invention have better fluidity than powders without such particles (eg, mere halloysite powders), which facilitates automation and quantification of transportation, supply, packaging, etc .; bulk density. Because of its high value, it can be made compact in terms of transportation, storage, packaging, etc .; dust generation that scatters fine powder and pollutes the surrounding environment is suppressed, and in particular, concerns about the safety of nano-sized particles to the human body are reduced. Yes; bias in the container due to differences in particle shape and size, that is, segregation is less likely to occur, and adhesion to containers, machine walls, packaging materials, etc. is reduced; gas or liquid as a catalyst or adsorbent When used in contact with, the fluid resistance can be reduced, and it has the effects of easy separation / recovery, drying / regeneration; and the like.
The granules in the powder of the present invention have the above-mentioned effects without impairing the function of halloysite nanotubes, which are also the primary particles constituting the granules.

Further, in the powder of the present invention, it is preferable that the granules have first pores derived from the tube pores of the halloysite nanotubes and second pores different from the first pores.

<XRD>
From the results of X-ray diffraction (XRD) measurement, for example, it can be confirmed that the powder of the present invention has a halloysite crystal structure (see FIG. 11).
FIG. 11 is a graph showing an XRD pattern of the halloysite powder of the present invention (the halloysite powder of Example 1 described later). FIG. 11 also shows the XRD of the halloysite powders of Comparative Examples 1 and 2 described later.
As shown in FIG. 11, in the powder of the present invention, the XRD pattern of halloysite represented by Al ₂ Si ₂ O ₅ (OH) ₄ is maintained.

The specific conditions in the XRD measurement are as follows.
-Device used: X-ray diffraction analyzer D8ADVANCE (manufactured by BRUKER)
・ X-ray tube: CuKα
・ Optical system: Centralized method ・ Tube voltage: 35kV
・ Tube current: 40mA
・ Detector: One-dimensional semiconductor detector ・ Scan range: 2 to 70 deg
-Scan step: 0.021 deg
・ Scan speed: 4deg / min

<destruction strength>
The powder of the present invention has a breaking strength of 7.60 MPa or more of granules soaked in pure water for 24 hours to contain water. As a result, the powder of the present invention has excellent water resistance.
The breaking strength is preferably 8.00 MPa or more, more preferably 8.30 MPa or more, because the water resistance is more excellent.
On the other hand, the upper limit of the breaking strength is not particularly limited, and is, for example, 20.00 MPa or less, preferably 17.00 MPa or less, and more preferably 15.00 MPa or less.

The breaking strength of the granules is measured by a compression test using a microcompression tester and is an average value of the results of five tests.
More specifically, first, a sample obtained by immersing the powder (granule) in pure water (deionized water) for 24 hours to contain water is used as a sample. This sample is sprayed on a sample table (lower pressure plate) of the micro-compression tester MCT-510 (manufactured by Shimadzu Corporation) in a very small amount, and a compression test is performed for each sample to determine the fracture strength. The average value of the results of five tests (breaking strength) is taken as the breaking strength of the powder.
In the compression test, the diameters of each sample in the X and Y directions are measured on a sample table, and the average value thereof is taken as the particle size of each sample.

<SEM>
The granules contained in the powder of the present invention (hereinafter, also referred to as "granule of the present invention" for convenience) are granules formed by aggregating halloysites containing halloysite nanotubes, and holes derived from the tube holes of the halloysite nanotubes. Having (first pores) can be confirmed, for example, by scanning electron microscope (SEM) photographs (see FIGS. 3 to 5).

3 to 5 are SEM photographs showing the halloysite powder of the present invention (the halloysite powder of Example 2 described later, which was prepared by spray drying and fired at 450 ° C.). The enlarged photograph of FIG. 3 is FIG. 4, and the enlarged photograph of FIG. 4 is FIG.

In FIGS. 3 and 4, spherical granules are confirmed. From FIGS. 4 and 5, it can be confirmed that the granules are aggregated with halloysites containing halloysite nanotubes. Further, in FIGS. 4 and 5 (particularly, FIG. 5), the presence of tube pores (derived from the first pores) of halloysite nanotubes can be confirmed on the surface of the granules.
It is considered that the reason why the granule structure having the first pores is obtained is that the halloysite nanotubes aggregate while maintaining the tube shape by spray-drying the slurry containing the halloysite nanotubes.

Further, in FIGS. 4 and 5, it is possible to confirm the presence of pores (second pores) having a diameter larger than that of the halloysite nanotube tube pores (usually, the inner diameter is about 10 to 20 nm) on the surface of the granules. can.
It can be confirmed by, for example, an SEM photograph (not shown) of the cross section of the granule that the granule of the present invention has a second pore different from the first pore. The cross section of the granules is exposed, for example, by processing the granules with a focused ion beam (FIB).
It is considered that the reason why such a second pore is obtained is that when the slurry becomes granules by spray drying or the like, the dispersion medium of the slurry evaporates from (inside) the granules and escapes.

Note that FIG. 6 is an SEM photograph showing a halloysite powder (haloysite powder of Comparative Example 3 described later) that was not fired after spray drying.
In FIG. 6, as in FIG. 5, first pores derived from the tube pores of the halloysite nanotubes and second pores larger than the tube pores can be confirmed on the surface of the granules.
Therefore, from the comparison between FIGS. 5 and 6, it can be seen that the granule structure before firing (FIG. 6) is not lost and is maintained even after firing at 450 ° C. (FIG. 5).

<Measurement of pore distribution>
It can be confirmed from the results of pore distribution measurement of the powder of the present invention (see FIGS. 7 to 9) that the granules contained in the powder of the present invention have the above-mentioned peculiar structure.
The powder of the present invention is based on the fact that the differential pore distribution (Log differential pore volume distribution) obtained from the nitrogen adsorption isotherm by the BJH method shows two or more pore diameter peaks within the range of 10 to 100 nm. It is preferable to show two or more pore size peaks in the range of 10 to 70 nm, and it is particularly preferable to show two or more pore size peaks in the range of 10 to 50 nm. Hereinafter, a more detailed description will be given.

7 to 9 show the differential pore distribution (Log differential pore volume distribution) obtained by the BJH method from the nitrogen adsorption isotherm of the halloysite powder of the present invention (the halloysite powder of Examples 1 to 3 described later). In the graph, the horizontal axis represents the pore diameter [nm], and the vertical axis represents the differential pore volume (dVp / dlogDp) [cm ³ / g] (hereinafter, the same applies).

In the graph of FIG. 7 (Example 1), two pore diameter peaks clearly appear in the range of 10 to 100 nm. The two pore size peaks are in the range of 10 to 70 nm, in the range of 10 to 50 nm, and in the range of 10 to 40 nm.
The peak with the smaller pore diameter (the peak with the pore diameter of 10 nm or more and 20 nm or less) represents the first pore derived from the tube hole (inner diameter: about 10 to 20 nm) of the halloysite nanotube, and the one with the larger pore diameter. It can be said that the peak (pore diameter peak over 20 nm) represents a second pore different from the tube hole.

In the graph of FIG. 8 (Example 2), two peaks appear in the range of the pore diameter of 10 to 40 nm, and one peak also appears at the position where the pore diameter is approximately 50 nm.
It is understood that the pore diameter peak of 10 nm or more and 20 nm or less represents the first pore, and the two pore diameter peaks of more than 20 nm represent the second pore.

FIG. 10 is a graph showing the differential pore distribution of the halloysite powder (Comparative Example 3 described later) which was prepared in the same manner as the halloysite powder of FIG. 8 but was not calcined after spray drying. Is. FIG. 10 shows a pore diameter peak similar to that in FIG. Therefore, it can be seen that the granule structure before firing (FIG. 10) is not lost and is maintained even after firing at 450 ° C. (FIG. 8).

In the graph of FIG. 9 (Example 3), three peaks appear in the pore diameter range of 10 to 40 nm.
It is understood that the pore diameter peak of 10 nm or more and 20 nm or less represents the first pore, and the two pore diameter peaks of more than 20 nm represent the second pore.

In the halloysite powders of Examples 2 and 3, second pores are formed in the granules, but it is understood that the pore diameters are largely divided into two types. It is presumed that the viscosity of the slurry used when preparing the halloysite powder, the dispersibility of the particles, and the like affect the second pores.

It is more preferable to show two or more pore diameter peaks in the range of 10 to 40 nm, and it is particularly preferable to show two pore diameter peaks in the range of 10 to 40 nm.
At this time, the pore diameter peak corresponding to the first pore preferably appears in the range of 10 nm or more and 20 nm or less, and the pore diameter peak corresponding to the second pore is in the range of more than 20 nm and 40 nm or less. It is preferable that it appears.

When the powder of the present invention has a second pore, the total pore area and the total pore volume described later are large.

Specifically, the total pore area of the powder of the present invention is preferably 59.0 m ² / g or more, more preferably 65.0 m ² / g or more, and even more preferably 75.0 m ² / g or more. The upper limit is not particularly limited, but is, for example, 200.0 m ² / g or less, preferably 150.0 m ² / g or less.

The total pore volume of the powder of the present invention is preferably 0.20 cm ³ / g or more, more preferably 0.23 cm ³ / g or more. The upper limit is not particularly limited, but is, for example, 0.80 cm ³ / g or less, preferably 0.60 cm ³ / g or less.

In addition, the average pore diameter of the powder of the present invention is, for example, 5.0 nm or more, preferably 11.0 nm or more. The upper limit is not particularly limited, but is, for example, 30.0 nm or less, preferably 20.0 nm or less.

The BET specific surface area (specific surface area determined by the BET method) of the powder of the present invention is, for example, 30 to 200 m ² / g, preferably 50 to 150 m ² / g.

Next, a measurement method such as pore distribution will be described.
First, the powder is pretreated (vacuum deaeration at 120 ° C. for 8 hours), and then the adsorption isotherm with nitrogen is measured under the following conditions using a constant volume method. The equilibrium waiting time is the waiting time after reaching the adsorption equilibrium state.
The BET specific surface area [m ² / g] is determined by applying the BET method from the nitrogen adsorption isotherm.
The average pore diameter [nm] is calculated from the values of the BET specific surface area and the total pore volume [cm ³ / g]. The total pore volume used to calculate the average pore diameter (also referred to as "total pore volume for calculation" for convenience) is that capillary condensation is established in the pores existing up to the relative pressure of 0.99 of the adsorption isotherm. It is calculated from the adsorption amount of the relative pressure of 0.99 of the adsorption isotherm.
Furthermore, by applying the BJH method from the nitrogen adsorption isotherm using the FHH reference curve, the Log differential pore volume distribution, total pore volume [cm ³ / g] and total pore area [m ² / g] can be obtained. Ask. Plot spacing of pores from about 2.6 nm to about 200 nm uses standard conditions of analysis software. The total pore volume and the total pore area obtained by the BJH method are also referred to as "BJH total pore volume" and "BJH total pore area", respectively.
In the present invention, the terms "total pore volume" and "total pore area" mean "BJH total pore volume" and "BJH total pore area", respectively, unless otherwise specified. do.
・ Adsorption temperature: 77K
・ Cross-sectional area of nitrogen: 0.162 nm ²
・ Saturated vapor pressure: measured ・ Equilibrium waiting time: 500 sec
・ Pretreatment device: BELPREP-vacII (manufactured by Microtrack Bell)
-Measuring device: BELSORP-mini (manufactured by Microtrack Bell)
-Analysis software: BELMaster Version 6.4.0.0 (manufactured by Microtrack Bell)

<Average particle size>
The average particle size of the powder of the present invention is not particularly limited and is appropriately selected depending on the intended use, but is, for example, 0.5 to 200 μm. When the powder of the present invention is prepared by spray drying, the average particle size is preferably 1 to 100 μm.
Granules having such a particle size may be granulated as described above to increase the size. However, in that case, the average particle size is preferably 5 mm or less.
Considering the size of the granules invading the respiratory tract due to concerns about harmfulness, the minimum size of the granules is preferably 1 μm or more.

The average particle size is measured by a dry method using a laser diffraction / scattering type particle size distribution measuring device (Microtrac MT3300EXII) manufactured by Microtrac Bell.

<Use of halloysite powder>
The halloysite powder of the present invention can be applied to a wide variety of applications.
Examples of applications are cosmetics, coloring materials, precision polishing nanoparticles, nanomagnetic materials, catalysts, catalyst carriers, humidity control materials, deodorants, deodorants, adsorbents, sustained release agents, antibacterial agents, pharmaceuticals, and artificial Examples include enzymes. It is not limited to these uses.
For example, the halloysite powder of the present invention has characteristics such as humidity control characteristics as compared with the powder having no first pores derived from the tube pores by having the first pores derived from the tube pores. Excellent for.
The halloysite powder of the present invention is also suitable as a filler, a coating material, or the like that imparts properties such as light weight, heat insulation, sound absorption, and environmental purification.
In addition to being used alone for these purposes, the halloysite powder of the present invention contains one or more of ions, molecules, polymers, nanoparticles and the like having a size of 100 nm or less for the purpose of improving functionality. It can also be applied as a hybrid body. For example, when it is used as a hybrid containing an active ingredient such as a drug, the active ingredient acts uniformly, and the effect of maintaining the efficacy for a long time can be expected.

The halloysite powder of the present invention has a second pore, and when the pore diameter of the second pore is close to the size of the bacterium or virus, the bacterium or virus (hereinafter referred to as “)”. It can also be applied to trap (called "viruses, etc.").
Specifically, for example, the halloysite powder of the present invention has excellent water resistance and is therefore suitable as a water purification filter for trapping viruses and the like in water.
The halloysite powder of the present invention after trapping a virus or the like can be reused after removing the trapped virus or the like by performing a heat treatment.
In addition to such applications, the halloysite powder of the present invention maintains a granular structure and exhibits its function due to its excellent water resistance, even if it may come into contact with water in the process of being processed into a final product. ..

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited thereto.

<Preparation of halloysite powder>
Halloysite powders of Examples 1 to 3 and Comparative Examples 1 to 4 were produced as follows.

<< Raw material (Iitoyo clay) >>
The above-mentioned Iitoyo clay was used as a raw material. When XRD measurement of Iitoyo clay was performed, peaks (not shown) representing halloysite and fine sand (quartz) were confirmed.

《Pre-slurry》
Iitoyo clay and water were put into a high-speed mixer (Ultra Homo Mixer UHM-20 (20 liters) manufactured by Nissei Tokyo Office Co., Ltd.) and treated at 8,000 rpm for 10 minutes to disperse Iitoyo clay in water. A pre-slurry (solid content concentration: 10% by mass) was obtained.

《Coarse grain removal》
By passing the pre-slurry through a JIS test sieve having a mesh size of 45 μm, coarse particles (about 30%) of +45 μm on the net were removed. At this time, in order to prevent clogging and enhance the recovery of −45 μm under the net, water was appropriately added to the sieve and the sieve was dropped with a brush. The final quality was similar when using a sieve with a mesh size of 25 μm or 100 μm.

《Filtration》
The pre-slurry of −45 μm under the net was suction-filtered using a filter and recovered as a dehydrated cake.

<< Post-slurry >>
Dehydrated cake and water are added to a high-speed mixer (Ultra Homo Mixer UHM-20 manufactured by Nissei Tokyo Office), an anionic polymer surfactant (Poise 520 manufactured by Kao Co., Ltd.) is added, and 10,000 rpm for 10 minutes. After the Iitoyo clay was dispersed in water, a slurry (solid content concentration: 20% by mass) was obtained. The content of the anionic polymer surfactant with respect to the total solid content of the post-slurry was 1.5% by mass.

《Centrifugation》
The post-slurry is agitated, and 80 mL per tube is collected from the post-slurry in a stirred state, and a centrifuge (manufactured by Kokusan Co., Ltd., small desktop centrifuge H-19α, rotor: RF-109L, bucket: MF-109L, tube: 100 mL x 4 pieces, made of PP, outer diameter 45 mm, inner diameter 40 mm, height: 100 mm) were set.
Centrifugal force of 2470G was carried out for 10 minutes to separate the sedimentary phase and the dispersed phase.
The dispersed phase was recovered by sucking a portion having a height of +5 mm or more from the sedimented phase with a pump. The solid content concentration of the recovered dispersed phase (slurry) is shown in Table 1 below.
1 and 2 are TEM photographs of the dispersed phase recovered after centrifugation in Example 1. The fields of view of FIGS. 1 and 2 are different from each other. As shown in FIGS. 1 and 2, the presence of halloysite nanotubes could be confirmed in the recovered dispersed phase. More specifically, FIG. 1 shows a long halloysite nanotube, and FIG. 2 shows a side surface (cross section) of the halloysite nanotube. Although not shown in the TEM photograph, halloysites having shapes other than tubular (for example, sheet-like) were also confirmed.

《Spray dry》
The recovered dispersed phase (slurry) was spray-dried using a spray dryer to obtain a powder (haloysite powder).
As the spray dryer, a spray dryer L-8i manufactured by Okawara Kakohki Co., Ltd. was used, and the slurry was quantitatively supplied by a pump to atomize (spray) the slurry. The contact method between the hot air and the spray droplets was a parallel flow type in which both the hot air and the spray droplets went downward.
At this time, as shown in Table 1 below, for each example, spray-drying conditions (slurry solid content concentration, atomization method, water evaporation amount [kg / h], inlet temperature [° C.], and outlet temperature [° C.] ) Was changed to adjust the average particle size of the obtained powder.
When the rotating disk method was adopted as the atomization method, the rotation speed [rpm] of the rotating disk was also changed for each example as shown in Table 1 below. When the two-fluid nozzle method or the four-fluid nozzle method (twin jet nozzle method) was adopted as the atomization method, the spray air pressure [MPa] was also changed for each example as shown in Table 1 below.

《Burning》
Except for some examples, the powder after spray drying was calcined.
Specifically, the powder after spray-drying is heated from room temperature at a heating rate of 5 ° C./min using an electric furnace of a siliconit heating element, and held at the firing temperature shown in Table 1 above for 1 hour. After that, it was cooled in a furnace. In order to promote the burning of the surfactant during the temperature rise and the holding at the firing temperature, exhaust was performed while supplying a certain amount of air into the furnace.
It was confirmed by TG-DTA (thermogravimetric analysis-differential thermal analysis) that the surfactant was removed from the powder after firing.
In the case of not firing, "-" is described in the column of firing temperature in Table 1 above.

<Evaluation of halloysite powder>
The halloysite powders of Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated as follows.

<< XRD >>
The halloysite powders of Examples 1 to 3 and Comparative Examples 1 to 4 were XRD-measured. The measurement conditions are as described above.
FIG. 11 is a graph showing the XRD patterns of the powders of Example 1 and Comparative Examples 1 and 2. As shown in FIG. 11, the XRD pattern of halloysite represented by Al ₂ Si ₂ O ₅ (OH) ₄ was confirmed in all the powders. This was the same in the XRD patterns (not shown) of the powders of Examples 2 to 3 and Comparative Examples 3 to 4.
The peak near 2θ = 26 ° is a peak representing quartz, indicating that a small amount of quartz contained in the raw material is present.

《Compression test (after water content)》
The halloysite powders of Examples 1 to 3 and Comparative Examples 1 to 4 were immersed in pure water for 24 hours and impregnated with water as a sample. This sample was subjected to a compression test while measuring the particle size to determine the breaking strength. The details of the compression test are as described above. The average value of the results of the five tests is shown in Table 2 below.

<< SEM >>
SEM photographs of halloysite powders of Examples 1 to 3 and Comparative Examples 1 to 4 were taken.
3 to 5 are SEM photographs showing the halloysite powder of Example 2, FIG. 4 is an enlarged photograph of FIG. 3, and FIG. 5 is an enlarged photograph of FIG. FIG. 6 is an SEM photograph showing the halloysite powder of Comparative Example 3, and is an SEM photograph having the same magnification as that of FIG.
From the SEM photographs of FIGS. 3 to 5, the halloysite powder of Example 2 contains granules formed by aggregating halloysites containing halloysite nanotubes, and holes derived from the tube holes of the halloysite nanotubes on the surface of the granules (first). It was confirmed that there are pores (second pores) in the granule cross section of the halloysite nanotubes, which are larger in diameter than the tube holes of the halloysite nanotubes.
This was also the case in the SEM photographs of the halloysite powders of Examples 1 and 3 and Comparative Examples 1 to 4 (other than Comparative Example 3 are not shown).
Further, from the comparison between FIGS. 5 and 6, it was confirmed that the granule structure before firing (FIG. 6) was not lost and maintained even after firing at 450 ° C. (FIG. 5).

<< Measurement of pore distribution >>
Nitrogen adsorption isotherms were measured for the halloysite powders of Examples 1 to 3 and Comparative Examples 1 to 4. The measurement conditions are as described above.
7 to 9 are graphs showing the differential pore distribution of the halloysite powders of Examples 1 to 3 obtained by the BJH method from the nitrogen adsorption isotherm, respectively. In each graph, the horizontal axis represents the pore diameter [nm], and the vertical axis represents the differential pore volume (dVp / dlogDp) [cm ³ / g].
In the graphs of FIGS. 7 to 9 (Examples 1 to 3), two or more pore diameter peaks were confirmed in the range of 10 to 100 nm.
FIG. 10 is a graph showing the differential pore distribution of Comparative Example 3. FIG. 10 (Comparative Example 3) shows a pore diameter peak similar to that of FIG. 8 (Example 2). From this, it was confirmed that the granule structure before firing (FIG. 10) was not lost and maintained even after firing at 450 ° C. (FIG. 8).

With the measurement of pore distribution, for the halloysite powders of Examples 1 to 3 and Comparative Examples 1 to 4, the total pore area of BJH, the total pore volume of BJH, the BET specific surface area, the total pore volume for calculation, and the average pore diameter were measured. I asked. The results are shown in Table 2 below.

《Average particle size》
The average particle size of the halloysite powders of Examples 1 to 3 and Comparative Examples 1 to 4 was measured. The results are shown in Table 2 below.

"water resistant"
The water resistance of the halloysite powders of Examples 1 to 3 and Comparative Examples 1 to 4 was evaluated.
Specifically, 2 g of halloysite powder (sample) and 8 g of pure water are placed in a screw tube bottle (glass container with a lid), shaken 5 times, and then the container is subjected to an ultrasonic cleaner. The contents of the above were dispersed for 30 minutes, and further dispersed by ultrasonic waves for 110 minutes.
After standing, observe the inside of the container, and if the sample and pure water are separated, "A" is displayed. If the sample and pure water are not separated and gelled uniformly, "B" is displayed. Are listed in Table 2 below. If it is "A", the halloysite powder can be evaluated as having excellent water resistance. That is, if it is "A", it can be evaluated that the primary particles are hard to peel off from the surface of the granules in water.

As shown in Table 2 above, it was found that the halloysite powders of Examples 1 to 3 were superior in water resistance to the halloysite powders of Comparative Examples 1 to 4.

When comparing Comparative Example 1 (without firing) and Example 1 (fired at 450 ° C.) with respect to the total pore volume of BJH, the difference is not large, and the granule structure before firing is large even after firing. It turned out to be maintained. This was the same in the comparison between Comparative Example 3 and Example 2 and the comparison between Comparative Example 4 and Example 3.

Claims (10)

A halloysite powder containing granules formed by aggregating halloysites containing halloysite nanotubes, wherein the breaking strength of the granules soaked in pure water for 24 hours and impregnated with water is 7.60 MPa or more. The halloysite powder according to claim 1, wherein the granules have first pores derived from the tube pores of the halloysite nanotubes and second pores different from the first pores. The halloysite powder according to claim 2, wherein the differential pore distribution obtained from the nitrogen adsorption isotherm by the BJH method shows two or more pore diameter peaks in the range of 10 to 100 nm. The halloysite powder according to any one of claims 1 to 3, which has an average particle size of 0.5 to 200 μm. The halloysite powder according to any one of claims 1 to 4, which has a BET specific surface area of 30 to 200 m ² / g. The halloysite powder according to any one of claims 1 to 5, which has an average pore diameter of 11.0 nm or more. The halloysite powder according to any one of claims 1 to 6, wherein the total pore area is 59.0 m ² / g or more. The halloysite powder according to any one of claims 1 to 7, wherein the total pore volume is 0.20 cm ³ / g or more. The method for producing a halloysite powder according to any one of claims 1 to 8.
The process of preparing a halloysite slurry containing halloysite nanotubes,
The step of preparing powder from the slurry and
A method for producing a halloysite powder, comprising a step of calcining the prepared powder at a firing temperature of more than 420 ° C. and less than 500 ° C. The method for producing halloysite powder according to claim 9, wherein the step of preparing the powder from the slurry is the step of spray-drying the slurry.

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