JP4947470B2 - Method for controlling dispersion / aggregation of nanoparticle slurry - Google Patents

Description

  The present invention relates to a nanoparticle slurry dispersion / aggregation control method that can be applied at an actual production level so that nanometer-size solid particles mixed in a liquid can be dispersed close to primary particles.

Submicron-sized particles could be dispersed in a liquid to a high degree by adding a suitable dispersant in a ball mill or bead mill using millimeter-order balls. However, even if a suitable dispersing agent is added to nano-sized particles, it cannot be highly dispersed by the mechanical / physical dispersion method. Recently, it has been proposed that the following two types are effective as methods for controlling aggregation / dispersion of nanoparticles in a liquid (for example, Non-Patent Documents 1 and 2).
a Add a nanoparticle to a mixed solution of a suitable dispersant and solvent, and adjust the peripheral speed of the rotor for stirring the beads to 10 m / s in a bead mill using beads of several tens of μm. Dispersion processing is performed under conditions such as% (bulk capacity).
b Nanoparticles are added to a mixed solution of an appropriate dispersant and solvent, and subjected to dispersion treatment by irradiating with ultrasonic waves having a frequency of 20 kHz and an amplitude of 35 μm for a long time.

Among the above-mentioned treatment methods, in the method shown in a, the aggregate is broken by the shearing force, and at the same time, an appropriate dispersant is adsorbed on the nanoparticles and the dispersion state is stabilized. By setting the bead diameter to several tens of μm, a uniform shearing force can be imparted to the aggregate. However, in addition to the shearing force, the beads collide with the nanoparticles, and the long-time treatment destroys the nanoparticle surface state, the dispersant is detached, the dispersion stabilization is destroyed, and the aggregation progresses as a result. Therefore, it is a necessary condition for this technique to make the bead diameter as small as possible, to increase the peripheral speed and to obtain the desired dispersion state in a short time. This method still has the following problems.
1. By combining the centrifugal separation and the micro size filter, the nanoparticles and beads of several tens of μm are separated, but the separation is not reliable.
Slurries with a high particle concentration exceeding 2, 2 to 3% by volume cannot be treated because they clog the filter and it is difficult to separate by centrifugal force.
3. When deformed particles such as needles are processed, shape deformation occurs.

On the other hand, the technique shown in b above generates a shock wave due to the collapse of cavitation by ultrasonic irradiation, whereby the nanoparticles collide with each other, the aggregated state is destroyed, and an appropriate dispersant added simultaneously is present. The dispersion / aggregation state is controlled by adsorbing to the nanoparticles. It takes a considerable amount of time to disperse a practical level amount to a high degree by this method, and there is a problem that it is not suitable for practical use in industry. In addition, it seems that the processing time can be shortened by attaching an extremely large number of ultrasonic irradiators, but this is not practical because the price of the device that is dispersed by a mechanical and physical method is extremely expensive.
M. Inkyo, T. Tahara, T. Iwaki, F. Iskandar, C.-J. Hogan, K. Okuyama, “Experimental Investment of Nanoparticle Dispersion by Beads Milling with Centrifugal Beads Separation "(Experimental Investigation of Nanoparticle Dispersion by Beads Milling with Centrifugal Bead Separation), Journal of Colloid and Interface Sci. (USA), 2006, No. 304, P535-540 K. Sato, J. G. Li, T. Ishigaki, H. Kamiya, "Effect of Ultrasonic on Dispersion" Size of TI2 Nanoparticles in Concentrated Aqueous Suspension, Ceramic Transaction (America), 2007 198, P361-367

  The problem to be solved by the present invention is to make it possible to disperse the nanoparticle slurry to a high degree by using beads of a size that can be reliably separated by a screen widely used as a filter for separating beads. However, it does not cause clogging of the filter, does not cause a change in shape even with irregularly shaped particles, and can be highly dispersed in a short time compared to the case of ultrasonic irradiation alone. It is to provide a dispersion / aggregation control method.

  According to the present invention, beads having a volume in the range of 0.3 to 1.0 mm that can be separated by a screen (gap) method, which has been known as a reliable method, are used in a vessel with a bulk capacity of 50 to 90. Nanoparticles processed by combining or combining a bead mill that stirs and disperses slurry and beads supplied in the vessel with a rotor and a method of irradiating ultrasonic waves with a frequency of 15 to 30 kHz and an amplitude of 5 to 50 μm. A method for controlling dispersion / aggregation of a slurry, which is a method of controlling the dispersion / aggregation in two stages by using these bead mills and ultrasonic irradiation, is provided. Specifically, as a first step, the rotor peripheral speed is set to 1 to 4 m / s, and the bead mill under the condition of 5 to 20 passes (the number of passes through the bead mill) is used alone, and the rotor peripheral speed is set to 4 to 8 m / s. s, 2 to 10 passes (number of passes through the bead mill), the rotor peripheral speed is set to 8 to 12 m / s, and the beads mill under the conditions of 1 to 5 passes (number of passes through the bead mill) alone or the ultrasonic wave Use with radiation. As a second step, there is provided a dispersion / aggregation control method of the nanoparticle slurry using the above-mentioned bead mill alone or in combination with the above-mentioned bead mill in which the rotor peripheral speed is 0.5 m / s or less. Prior to the first step, stirring and dispersion treatment may be performed as pretreatment by rotation of a mechanical stirring splash.

  According to the present invention, dispersion / aggregation control of nanoparticles in a liquid can be processed without problems at a level that can be put into practical use in industry. Furthermore, it is possible to control dispersion / aggregation in a relatively short time while maintaining high purity, with the amount of slurry at a practical level of high particle concentration up to 30% by volume, which could not be achieved by conventional methods. it can. In addition, because beads with a size of the order of mm are used, beads and slurry can be separated using a normal screen without using a special separation method such as a centrifugal separation method. Reliable separation without contamination is possible.

  In the present invention, as described above, a bead mill filled with beads having a volume of 0.3 to 1.0 mm, preferably 0.3 to 0.5 mm in a vessel with a bulk capacity of 50 to 90%, preferably 70 to 80%, and a frequency of 15 to 30 kHz, The treatment is preferably performed in combination with or in combination with a method of irradiating ultrasonic waves of 20 to 30 kHz and amplitude of 5 to 50 μm, preferably 20 to 50 μm. The reason for limiting the bead diameter of the bead mill in this way is the bead diameter that can be separated by a screen that has been known as a reliable method rather than using a special separation method such as centrifugation. 0.3 mm or more is used, and since it is desirable that the bead diameter is smaller so that the shearing force can be uniformly applied to the nanoparticles, it is defined as 1.0 mm or less. If it is larger than 1.0 mm, the shearing force cannot be uniformly applied, so that the aggregate cannot be broken smaller. Preferably it is 0.5 mm or less.

  In addition, the reason for limiting the ultrasonic wave to be irradiated to a frequency of 15 to 30 kHz and an amplitude of 5 to 50 μm is that a large amount of cavitation was generated and the conditions for increasing the collision energy between the nanoparticles due to the shock wave caused by the collapse were selected. It is. Preferably, a frequency range of 20 to 30 kHz and an amplitude of 20 to 50 μm are desirable.

  Furthermore, the dispersion process is divided into two stages. As a first step, the bead mill having a condition of 5 to 20 passes (the number of passes through the bead mill) is used alone, with the rotor peripheral speed of the bead mill being 1 to 4 m / s, or The above-mentioned bead mill with a rotor peripheral speed of 4 to 8 m / s and 2 to 10 passes (number of passes through the bead mill), or a rotor peripheral speed of 8 to 12 m / s and 1 to 5 passes (number of passes through the bead mill) Use alone or in combination with the aforementioned ultrasonic irradiation. As the second step, the ultrasonic irradiation is performed alone or the bead mill with a rotor peripheral speed of 0.5 m / s or less is used in combination. Thus, it divided into the 1st step and the 2nd step, and the rotor peripheral speed of the 2nd step was made slower than the 1st step. The reason for limiting the rotor peripheral speed of the bead mill and the number of treatments of the nanoparticle slurry is that the bead mill applies a shearing force to the agglomerated particles to break the agglomerates. On the other hand, in addition to the shearing force, the beads collide with the nanoparticles at a high speed and an impact force is applied to the particles. For this reason, if the treatment is performed for a long time, it should be possible to apply a shearing force until the agglomerates are destroyed, but in reality, a phenomenon in which reaggregation occurs is observed. When the bead diameter is increased, the rotor peripheral speed is increased, and the number of times the nanoparticle slurry passes through the bead mill is increased, the impact force applied to the nanoparticles by the beads destroys the surface state of the nanoparticles, and the addition This is because the dispersed dispersant is detached and the steric hindrance repulsive force or electrostatic repulsive force does not act.

  The present invention can be applied to various bead mills (wet medium dispersers, media mills, bead dispersers, etc.), and FIG. 1 shows an embodiment thereof. In the figure, a bead mill 1 has a vessel 2 and a rotor 4 rotated by a drive shaft 3 in the vessel 2, and a predetermined amount of grinding media (beads) supplied from a bead supply port 5 in the vessel 2. The processing material (mill base, slurry) that is a mixture of solid particles and liquid is supplied into the vessel 2 from the mill base supply port 6.

  The rotor 4 is formed in a cylindrical shape and the surface is formed in a substantially smooth surface. However, as shown in Japanese Patent Publication No. 4-70050, for example, a suitably shaped protrusion is provided so as to give motion to the grinding medium. A guide member may be provided so that the processing material can be moved forward or backward in a vessel and allowed to flow substantially in the form of plug flow (plug flow). The rotor is provided with a rotor opening 7 at a suitable position so that the grinding medium circulates from the inner surface to the outer surface.

  A stator 8 is formed on the inner surface of the rotor 4, and a stator opening 10 having a medium separating device such as a screen 9 is formed at an appropriate position of the stator 8 so as to separate the pulverized medium and allow only the processing material to flow out. The stator opening 10 communicates with the mill base discharge port 11.

  The bead mill shown in FIG. 1 has a horn type ultrasonic oscillator 13 in a space 12 formed inside the stator 8. With this configuration, first, particles are crushed by the shearing force by the beads that are subjected to high-speed rotation in the rotor rotating part in the vessel before passing through the screen, and immediately after that, before the slurry passes through the screen and exits to the discharge port. Since the horn type ultrasonic oscillator 13 is mounted in the storage space 12, the collision between the nanoparticles occurs here, and as a result, the aggregated nanoparticles are pulverized to the vicinity of the primary particles by receiving both actions almost simultaneously. Can be distributed.

  In addition to the apparatus shown in FIG. 1, a pocket is formed in a part of the vessel through which the slurry flows, and an ultrasonic oscillator is provided in the pocket, or the pocket is not formed to be exposed on the inner surface of the vessel. An ultrasonic oscillator can be provided, or an ultrasonic oscillator can be provided at other appropriate positions (not shown). Furthermore, the present invention can be applied to a system combining a bead mill and an ultrasonic oscillator in which a slurry collection tank is installed outside the bead mill body and an ultrasonic oscillator is installed in the slurry collection tank. However, a system in which an ultrasonic oscillator is incorporated in the bead mill body as shown in FIG. 1 is more preferable.

  As the material of the grinding medium, an optimum material is selected depending on the application, and any material such as engineering plastic, glass, ceramics, and steel may be used. Zirconia material is preferred for applications where wear and defects are likely to occur. In addition to the water, the solvent for treating the nanoparticles may be an organic solvent such as various alcohols, cyclohexane, methyl ethyl ketone, methyl acetate, toluene, and hexane.

EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to the form in these Examples.
The apparatus shown in FIG. 1 was used for all of the apparatuses used in this example and the comparative example.

(Examples 1 to 3)
15% by volume of Nippon Aerosil Co., Ltd. P25 powder having a primary particle diameter of 35 nm composed of titanium oxide nanoparticles, and 0.5 mg / m ² of polyacrylic acid ammonium salt having a molecular weight of 8000 as a polymer dispersing agent per surface area of the P25 powder. The added water slurry was mixed for 20 minutes using a rotating blade of 500 rpm. Using 4000 ml of the slurry, the dispersion effect was examined by using both the bead mill and the ultrasonic irradiation. As a first step, a bead mill filled with 80% bulk capacity of 0.5 mm zirconia beads in a vessel and ultrasonic irradiation with an amplitude of 40 μm and a vibration frequency of 20 kHz are used for 90 minutes (the number of passes through the bead mill is 13.5 passes). Equivalent) distributed processing. The slurry feed rate was 10 ml / s, and the bead mill was performed under two conditions of a rotor peripheral speed of 1 m / s and 4 m / s. As a second step, for the bead mill peripheral speed of 1 m / s, the bead mill process was stopped, and the dispersion process (Example 1) was performed for up to 40 hours only by ultrasonic irradiation, and the bead mill rotor peripheral speed was 0.5 m. Two types of conditions for dispersion treatment (Example 2) using ultrasonic irradiation for a total of 40 hours were used. Furthermore, the bead mill was stopped for the bead mill rotor peripheral speed of 4 m / s, and dispersion treatment was performed for up to a total of 40 hours only by ultrasonic irradiation (Example 3). Using an X-ray sedimentation particle size analyzer, the particle concentration was diluted to 1% by volume, the agglomeration size in water was measured, and the dispersion state was evaluated. The results are summarized in Table 1.

Example 4
A slurry was prepared using rotating blades in the same manner as in Examples 1 to 3. Using 4000 ml of this slurry, the dispersion effect was examined using both a bead mill and ultrasonic irradiation. As a first step, a bead mill filled with 80% bulk volume of 0.5 mm zirconia beads in a vessel and ultrasonic irradiation with an amplitude of 40 μm and a vibration frequency of 20 kHz are used for 35 minutes (number of passes through the bead mill: 5.2 passes) Equivalent) distributed processing. The slurry feed rate was 10 ml / s, and the bead mill was run at a rotor circumferential speed of 8 m / s. As a second step, the bead mill treatment was stopped, and dispersion treatment was performed for up to 40 hours only by ultrasonic irradiation. The dispersion state was evaluated in the same manner as in Examples 1 to 3, and the results are shown in Table 1.

(Comparative Example 1)
A slurry was prepared using rotating blades in the same manner as in Examples 1 to 3. The slurry was irradiated with ultrasonic waves having an amplitude of 40 μm and a vibration frequency of 20 kHz, and the operation was performed for up to 40 hours. Evaluation of the dispersion state was performed in the same manner as in Examples 1 to 3. The results are summarized in Table 1.

(Comparative Examples 2 to 4)
A slurry was prepared using rotating blades in the same manner as in Examples 1 to 3. As a first step, 90 minutes (corresponding to 13.5 passes) or 300 using a bead mill filled with 80% by volume of 0.5 mm zirconia beads in a vessel and ultrasonic irradiation with an amplitude of 40 μm and a frequency of 20 kHz. Dispersed for 1 minute (equivalent to 45 passes). For rotor circumferential speed 4 m / s (Comparative Example 2), 300 minutes (corresponding to 45 passes), for rotor circumferential speed 6 m / s (Comparative Example 3), 90 minutes (corresponding to 13.5 passes), rotor circumference The speed of 10 m / s (Comparative Example 4) was 55 minutes (corresponding to 8.2 passes). As a second step, the bead mill treatment was stopped, and dispersion treatment was performed for up to 40 hours only by ultrasonic irradiation. Evaluation of the dispersion state was performed in the same manner as in Examples 1 to 3. The results are summarized in Table 1.

(Discussion)
In the treatment with only ultrasonic irradiation (Comparative Example 1), the particle size in water gradually decreased, but it took 40 hours to reach 50 nm, and it was difficult to put it to practical use industrially. On the other hand, as the first step, the bead mill is used in combination with the ultrasonic irradiation (corresponding to 13.5 passes) at a rotor circumferential speed of 1 or 4 m / S for 90 minutes (Examples 1 to 3). By using only the ultrasonic irradiation or the bead mill treatment with a rotor peripheral speed of 0.5 m / s in combination with the ultrasonic irradiation, the time reached 50 nm in about 20 hours, and the time to reach 50 nm was halved. In the second step, the bead mill may be stopped (Examples 1 and 3) or stirred at a low peripheral speed of the rotor peripheral speed of 0.5 m / s (Example 2). When the bead mill treatment and the ultrasonic irradiation are used in combination for 35 minutes at a rotor peripheral speed of 8 m / s (corresponding to 5.2 passes), when the ultrasonic irradiation is irradiated alone for 40 hours, 50 nm is obtained in about 30 hours. (Embodiment 4), 90 minutes (corresponding to 13.5 passes) at a rotor peripheral speed of 6 m / s, and after using both the bead mill treatment and the ultrasonic irradiation, the ultrasonic irradiation is performed alone. Even after irradiation up to the time, only a size of 79 nm was obtained after 40 hours, and a highly dispersed state could not be obtained (Comparative Example 3). In a bead mill using milli-order beads, a shear force is applied to the aggregated particles to destroy the aggregates, but they collide with the nanoparticles at high speed and damage the surface. By operating the bead mill under conditions where damage to the nanoparticle surface does not occur and using or combining with ultrasonic irradiation, the nanoparticle slurry can be dispersed to near the primary particles in a short time due to its synergistic effect. As described above, as the first step, the peripheral speed of the rotor is set to 1 to 4 m / s, and the bead mill under the condition of 5 to 20 passes (the number of passes through the bead mill) is used alone or in combination with the ultrasonic irradiation. Alternatively, the peripheral speed of the rotor is 4 to 8 m / s, and the bead mill under the condition of 3 to 10 passes (number of passes through the bead mill) is used alone or in combination with the ultrasonic irradiation. Alternatively, the peripheral speed of the rotor is 8 to 12 m / s, and the bead mill under the condition of 1 to 5 passes (the number of times the bead mill has passed) is used alone or in combination with the ultrasonic irradiation. As a second step, the above ultrasonic irradiation can be used alone or in combination with the above bead mill with a rotor peripheral speed of 0.5 m / s or less. Aggregation control can be enabled.

Sectional drawing which shows one Example of the bead mill used for this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Bead mill 2 Vessel 3 Drive shaft 4 Rotor 5 Bead supply port 6 Mill base supply port 7 Rotor opening 8 Stator 9 Screen 10 Stator opening 12 Space 13 Ultrasonic oscillator

Claims (1)

  A bead mill treatment step in which 50 to 90% by volume of beads in the range of 0.3 to 1.0 mm are filled in a vessel and supplied into the vessel and the beads are stirred and dispersed by a rotor, and the slurry and the slurry A separation step of separating the beads into only the slurry by a medium separation device, and an ultrasonic treatment step of irradiating only the slurry with ultrasonic waves having a frequency of 15 to 30 kHz and an amplitude of 5 to 50 μm immediately after the separation step. A method for controlling dispersion / aggregation of nanoparticle slurry.

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