JP2006247443A - Hollow liquid droplet forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hollow liquid droplet forming device for forming a liquid droplet containing a bubble therein and having a very small particle size. <P>SOLUTION: The hollow liquid droplet forming device is equipped with a gas producing means for producing gas from the liquid phase of a predetermined liquid and a liquid droplet forming means for forming the liquid droplet by applying dynamical energy to the predetermined liquid. The gas produced from the gas producing means is taken in the liquid droplet formed by the liquid droplet forming means to form the hollow liquid droplet. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus for generating droplets containing bubbles inside and having a very small particle diameter.

  Fine bubbles (for example, microbubbles having a diameter of the order of micrometers, nanobubbles having a diameter of the order of nanometers) are expected to be applied to various applications due to their unique characteristics.

  For example, microbubbles have been extensively studied. Microbubbles having a diameter of about 10 micrometers generated by cavitation can be used for environmental conservation by utilizing functions such as gas-liquid dissolution and floating separation or purifying contaminated water by oil. Expected. Alternatively, it is expected to be used for promoting the growth of aquatic animals and plants using the growth promoting effect in aquaculture and the like. In fact, in such applications, microbubbles are partially used.

  In addition, for example, nanobubbles are expected to be used as a further enhanced function of the microbubbles. More specifically, using the characteristics of nanobubbles such as reduced buoyancy, increased surface area, increased surface activity, generation of local high-pressure fields, surface active action by electrostatic polarization and bactericidal effect, Applications such as adsorption of objects and recovery of fatigue from living bodies are expected (see, for example, Patent Document 1).

  However, both the microbubbles and nanobubbles generate bubbles in the liquid phase. In other words, both the microbubbles and nanobubbles can exist only in the liquid. As a result, the range in which the excellent characteristics of microbubbles and nanobubbles can be used is extremely limited.

  As described above, a technique that can exhibit the characteristics of microbubbles and nanobubbles in the gas phase is strongly desired.

  On the other hand, as a technique for generating mist (fine droplets), a technique for generating droplets of several μm to several hundred μm by a cavitation effect using an ultrasonic oscillator is known. In recent years, small ultrasonic oscillators capable of generating droplets are generally marketed as products for healing. Recently, in the electrolyte solution in the form of droplets released into the gas phase, virus inactivation and infectivity titer reduction effects have been recognized (for example, see Non-Patent Document 1).

However, the droplets obtained as described above are solid. Therefore, it is expected that if the characteristics of microbubbles and nanobubbles can be imparted by adding bubbles to the droplets, an effect superior to that currently recognized for the droplets can be obtained.
JP 2004-121962 A http://www.sanyo.co.jp/koho/hypertext4/0501news-j/0121-1.html

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide an apparatus that can exhibit the characteristics of microbubbles and nanobubbles in a gas phase. It is also an object of the present invention to provide an apparatus for generating droplets having properties that are superior to those seen with solid droplets. That is, an object of the present invention is to provide an apparatus for generating droplets that contain bubbles and have a very small particle diameter.

  The hollow droplet generating apparatus of the present invention includes a gas generating unit that generates a gas from a liquid phase of a predetermined liquid, and a droplet generating unit that generates droplets by applying mechanical energy to the predetermined liquid. The gas generated from the gas generating means is taken into the droplet generated by the droplet generating means to generate a hollow droplet.

  In a preferred embodiment, the gas generating means generates gas by electrolysis.

  In a preferred embodiment, the droplet generating means generates ultrasonic droplets by applying ultrasonic vibration energy. In a more preferred embodiment, the ultrasonic vibration energy uses M-band ultrasonic vibration.

  In a preferred embodiment, the droplet generating means generates a droplet by applying pressure energy. In a further preferred embodiment, the pressure energy is applied by deformation of the piezoelectric element.

  According to the present invention, the generated gas (bubbles) is taken into the droplets, so that the gas generating means (for example, electrolysis means) and the droplet generating means (for example, ultrasonic nebulizer mechanism, ink jet mechanism) By combining them, it is possible to generate droplets containing bubbles inside and having a very small particle diameter. As a result, the characteristics of microbubbles and nanobubbles can be exhibited in the gas phase.

  Preferred embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

  The hollow droplet generating apparatus of the present invention includes a gas generating unit that generates a gas from a liquid phase of a predetermined liquid, and a droplet generating unit that generates droplets by applying mechanical energy to the predetermined liquid. The gas generated from the gas generating means is taken into the droplet generated by the droplet generating means to generate a hollow droplet. As used herein, “hollow droplet” refers to a droplet including at least one bubble therein. Such hollow liquid droplets, due to the gas-liquid equilibrium between the central gas part and the outer liquid part, increase the surface activity and generate a local high-pressure field, similar to nanobubbles and microbubbles in the liquid phase. In addition, the surface active action and the bactericidal effect by electrostatic polarization can be expressed. Therefore, if the hollow droplet is used, even if it is not in a liquid (for example, in a normal human living environment such as in the atmosphere), the same effect as that of a nanobubble or a microbubble can be expressed.

  FIG. 1 is a schematic diagram illustrating a hollow droplet generation mechanism of a hollow droplet generation apparatus according to a preferred embodiment of the present invention. The apparatus 100 includes an electrolysis unit 20 as a gas generation unit and an ultrasonic nebulizer mechanism 30 as a droplet generation unit in a predetermined liquid 10. As the liquid 10, any appropriate liquid that can generate gas by electrolysis by the electrolysis unit 20 and can be atomized by vibration of the nebulizer mechanism 30 (that is, can form fine droplets) is adopted. obtain. Specific examples of such liquids include physiological saline (0.9% solution of sodium chloride / pure water), tap water, electrolytic water, alkaline ionized water, acidic water, ultrapure water, deep ocean water, surface activity. Component-containing water is mentioned. Surface active component-containing water is preferred. This is because the bubbles can be taken into the droplets without collapsing.

  Any appropriate configuration may be employed as the electrolysis unit 20. For example, a platinum or carbon rod may be employed as the anode and a platinum or carbon rod may be employed as the cathode. Preferably, the electrode surface is hydrophilic. This is because bubbles generated by electrolysis can be quickly and satisfactorily detached from the electrode. Examples of a method for imparting hydrophilicity to the electrode surface include oxygen plasma treatment. The applied voltage in the electrolysis is typically a DC voltage, and its magnitude is 1.0 to 5.0V. By changing the applied voltage, the generation speed of bubbles and the size of bubbles to be generated can be changed. For example, if the applied voltage is lowered, the bubble generation rate is reduced. When the liquid is physiological saline, when a voltage is applied, oxygen bubbles and chlorine-based compounds are generated from the anode, and hydrogen bubbles and sodium-based compounds are generated from the cathode. The size of the obtained bubbles is typically several μm or less in diameter, preferably 1 nm to 10 μm, more preferably 100 nm to 10 μm. Realizing the generation of such fine bubbles is one of the major achievements of the present invention. Such fine bubbles are realized by controlling the applied voltage as described above, imparting hydrophilicity to the electrode surface as described above, applying ultrasonic vibration to the electrode surface, and combining them. Can be done. Without such treatment, the fine bubbles generated on the electrode surface are fine, so they have a small buoyancy and stay there, and because they are fine, they have a large specific surface area and easily adsorb other bubbles. Can do. As a result, the generated bubbles are combined with other bubbles on the surface of the electrode and become large and release from the electrode only after sufficient buoyancy is applied. In this case, the size of the bubbles can only be reduced to a diameter of about 20 to 30 μm at most. On the other hand, by performing the above treatment, the bubbles can be detached from the electrode before the bubbles become large.

Any appropriate configuration may be adopted as the ultrasonic nebulizer mechanism 30. Typically, in the ultrasonic nebulizer mechanism 30, the vibration energy of the ultrasonic vibrator 31 is concentrated on the surface of the liquid 10, and the liquid is atomized by the cavitation effect (that is, fine droplets are generated). . The diameter of the obtained droplet is preferably 1 to 20 μm. The ultrasonic vibrator 31 is typically a piezoelectric vibrator and has a diameter of about 20 mm. By changing the magnitude and frequency of ultrasonic vibration energy, the size of the generated droplets can be controlled. More specifically, as shown in the following formula (1), the obtained droplet diameter A becomes smaller in proportion to the square of the ultrasonic frequency. For example, in order to generate a droplet having a diameter of 10 μm or less, it is necessary to set the frequency to about 2 MHz. Therefore, the drive frequency of the ultrasonic transducer is typically in the M band (megahertz band), preferably 1 to 10 MHz, and more preferably 1 to 3 MHz.
A = (σ / (ρf ² )) ^1/3 (1)
A: droplet diameter, ρ: liquid density, σ: surface tension, f: oscillation frequency

Here, when f is the oscillation frequency, C is the propagation speed of the ultrasonic wave in the liquid, and λ is the wavelength, the relationship is λ = C / 2f. Therefore, in the case of the 2 MHz ultrasonic wave, the energy wave is λ = 0. Travels towards the gas-liquid interface at a very short wavelength of 36 mm. As described above, due to the extremely short wavelength, the reflection of the energy wave at the gas-liquid interface becomes irregular reflection, and the reflected energy does not return to the liquid. As a result, liquid resonance does not occur, so that droplets are formed relatively stably and efficiently. On the other hand, instead of generating liquid resonance, the molecular acceleration of the liquid is expressed by the following equation (2):
a = α * 2 * ω = α (2 * 3.14 * f) (2)
a: acceleration, α: vibrator amplitude, ω = π * f
When the oscillation frequency is 2 MHz, a = 1.58 * 10 ⁷ m / s ² , and an acceleration approximately 1.6 million times the gravitational acceleration is obtained. In other words, high-frequency ultrasonic waves such as 2 MHz are dominated by acceleration force and hardly damage fine bubbles generated in the electrolysis part. As a result, standing waves by ultrasonic waves can be taken into the droplets without destroying the bubbles, and hollow droplets can be generated.

The mechanism by which bubbles are taken into droplets will be described in more detail. The Laplace equation for the mechanical equilibrium at the gas-liquid interface is expressed as follows:
ΔP = Pg−Pl = 2 * σ / d
ΔP: Pressure difference between the central bubble and the outside liquid (Pa)
Pg: pressure in bubbles (Pa), Pl: pressure in liquid (Pa)
σ: surface tension of liquid (N / m), d: bubble diameter (m)
According to this equation, the relationship between the bubble size and the pressure difference is as shown in Table 1 below.

As is clear from Table 1, the pressure per unit area applied to the bubbles rapidly increases as the bubbles become smaller. Therefore, if the pressure in the bubble is not high enough to withstand it, the bubble will collapse. Therefore, as a method for reducing the pressure that the bubbles receive from the liquid, it is preferable to add a surfactant such as pentanol to the liquid forming the droplets. In this case, the pressure applied to the bubbles is relieved by the Marangoni effect caused by the adsorption of the surfactant molecules on the bubble surface (gas-liquid interface). As a result, not only the disappearance of the bubbles can be prevented, but also the rise due to the buoyancy of the bubbles and the coalescence of the bubbles can be prevented. In consideration of these, by using an appropriate surfactant and setting the size of the bubbles generated in the electrolysis unit 20 to preferably 100 nm to 10 μm, it is possible to incorporate the bubbles into the droplets without extinguishing the bubbles. It becomes. As for the Marangoni effect, for example, A. Frumkin and V. Levich, Zhur. Fiz. Khim,
21 (1947) 1183.

  Further, as a feature of the combination of the above electrolysis and an ultrasonic nebulizer mechanism (typically, M-band ultrasonic irradiation), when water is used as a liquid, a by-product of bubbles generated by electrolysis As a result, electrolytic ion water (that is, oxidizing water and reducing water) is obtained. Details thereof are described in “Ultra Clean Technology, New Wet Cleaning—Beyond RCA Cleaning—Pretech Technology Headquarters, Harada et al.”, The disclosure of which is incorporated herein by reference. Further, when M band ultrasonic waves are irradiated using water as a liquid, H radicals and OH radicals are generated in the water. Water containing such radicals can act as functional water having high-performance detergency.

  FIGS. 2A and 2B are schematic diagrams illustrating a hollow droplet generation mechanism of a hollow droplet generation apparatus according to another preferred embodiment of the present invention. The apparatus 200 includes an electrolysis unit 20 as a gas generation unit and a so-called inkjet mechanism 40 as a droplet generation unit. As the liquid 10, any appropriate liquid that can generate gas by electrolysis by the electrolysis unit 20 and can form fine droplets by the inkjet mechanism 40 can be adopted. A specific example of such a liquid is the same as in the description of FIG.

  As shown in FIGS. 2A and 2B, the electrode of the electrolysis unit 20 is preferably incorporated in the inkjet mechanism 40. By adopting such a configuration, bubbles generated in the electrolysis part can be favorably and efficiently taken into the droplets. The details of the electrolyzing unit 20 are the same as in the description of FIG.

  As shown in FIGS. 2A and 2B, the ink jet mechanism 40 includes a pressure generating member (actuator) 41, an elastic plate (diaphragm) 42, a liquid chamber (chamber) 43, and a nozzle 44. As shown in FIG. 4B, when a voltage is applied to deform the actuator 41, the liquid in the chamber 43 is pushed out by the pressure to form a droplet. Hereinafter, the detailed mechanism of droplet formation in the ink jet mechanism will be described with reference to FIGS.

  FIG. 3 is a schematic perspective view of the ink jet head, and a part thereof is cut and shown in cross section for explanation. Moreover, in FIG. 3 and FIG. 4, the electrode of the electrolysis part is abbreviate | omitting description. The nozzle 44 is disposed through the nozzle forming substrate 45 at a position communicating with the chamber 43. The actuator 41 contacts and presses one of the walls of the chamber 43 formed by the diaphragm 42. The actuator 41 is typically a piezoelectric element in which a piezoelectric material 46 such as lead zirconate titanate and internal electrodes 47a and 47b such as silver palladium are laminated. The diaphragm 42 is disposed so as to cover the entire surface of the liquid chamber, and is configured by a film having a uniform thickness. Typical examples of the material of the diaphragm 42 include metals such as Ni electroforming and stainless steel, or polymer films such as polyimide and polysulfone.

  FIG. 4 is a perspective view for explaining a contact state between the driving unit 48 and the liquid channel 49. A case 50 is joined to the actuator 41, and the end surface 51 that contacts the diaphragm 42 of the actuator 41 and the end surface 52 of the case 50 maintain a constant distance relationship g in the displacement direction. As shown in FIG. 3, the actuator 41 is uniformly pushed into the diaphragm 42 by contacting the end surface 52 of the case 50 and the surface 53 of the diaphragm 42 at the time of joining. FIG. 5 is a cross-sectional view illustrating a liquid discharge state. The liquid 54 reaches the nozzle 44 and forms a meniscus 55 by the pressure of the liquid 54. When the actuator 41 is uniformly pushed into the diaphragm 42, the diaphragm 42 is deformed, and the meniscus 55 projects by the pressure. As a result, the liquid 54 becomes a droplet 56 and flies outward from the nozzle 44. At the time of droplet formation, since bubbles (for example, oxygen and / or hydrogen) 57 generated from the electrode of the electrolysis unit 20 are present in the liquid 54 in the nozzle 44, the bubbles 57 are formed in the droplet 56. It is taken in well.

  The size of the generated bubbles can be controlled by changing the pressure from the diaphragm 42. For example, when the nozzle diameter is 10 μm and the nozzle length is 50 μm, the pressure required to form a droplet having a diameter of about 10 μm using water having a viscosity of 1 cps as the liquid is about 0.15 MPa. . The pressure from the diaphragm 42 can be controlled by changing the amount of deformation of the actuator 41 (and hence the drive voltage of the actuator). As a driving voltage of the actuator that can efficiently take in the bubbles, for example, a pulse voltage of about 10 KHz can be mentioned in consideration of the resonance frequency.

FIG. 6 is a graph for explaining the relationship between the size of the formed droplet and the pressure required for that purpose. The broken line in the graph shows the case where water having a viscosity of 1 cps is used, and the solid line shows the case where water having a viscosity of 1 cps is used. In addition, this graph was calculated | required by simulation by following formula (3)-(4) using a unimorph model as shown in FIG. As apparent from the graph of FIG. 6, when the viscosity of the liquid is 1 cps, it is difficult to control the droplet size because the droplet size changes drastically when the pressure is slightly changed. On the other hand, when the viscosity of the liquid is 10 cps, the pressure range capable of forming droplets of 10 μm to 15 μm is very wide, so that the droplet size can be easily controlled.
P = (9/2) * (t / L ² ) * (d ₃₁ * (Y / 8)) * V (3)
ΔV = (1/16) * (bL ³ / t ² ) * d ₃₁ * V (4)
t: Actuator thickness = diaphragm thickness Y: effective Young's modulus, V: applied voltage d ₃₁ : piezoelectric constant of actuator, ΔV: volume change For example, when the viscosity of the liquid is 10 cps, L = 0.4 mm, b = If 1 mm and t = 0.1 mm, P = 1.16 MPa and ΔV = 2.4 picoliters (pl) can be realized even with a driving voltage of about 20 V, and a droplet with a diameter of about 10 μm is realized. Is possible. It should be noted that bubbles can be a damper against pressure. That is, the pressure generated by the actuator may deform the bubbles, and as a result, large bubbles may be formed, making it difficult to eject the droplets. However, if the bubble is fine, the inside of the bubble is locally in a high pressure state. For example, if the bubble is 3 μm or less in diameter, the inside of the bubble is 1 atm or more. Therefore, the bubble damper effect is negligible. As a result, the ink jet mechanism can take in fine bubbles and form droplets.
ΔP = 2σ / d (5)
ΔP: bubble internal pressure in liquid, σ: bubble surface tension d: bubble diameter

  The hollow liquid droplets generated using the hollow liquid droplet generating apparatus of the present invention are locally formed with a high pressure field and become high temperature when the bubbles collapse / disappear. Therefore, the hollow droplet has an extremely excellent bactericidal action in addition to the thermal effect and the hydration effect. The apparatus of the present invention capable of generating such hollow liquid droplets can be suitably used for a hairdressing and cosmetic device such as a facial steamer. More specifically, the present invention can be applied to a device that can sterilize germs and acne bacteria on the skin surface and prevent and / or treat acne, pimples, rough skin, and the like.

It is a schematic diagram explaining the hollow droplet production | generation mechanism of the hollow droplet production | generation apparatus by preferable embodiment of this invention. It is a schematic diagram explaining the hollow droplet production | generation mechanism of the hollow droplet production | generation apparatus by another preferable embodiment of this invention. It is the schematic explaining the detailed mechanism of the droplet formation in the inkjet mechanism used for the hollow droplet production | generation apparatus of this invention. It is the schematic explaining the detailed mechanism of the droplet formation in the inkjet mechanism used for the hollow droplet production | generation apparatus of this invention. It is the schematic explaining the detailed mechanism of the droplet formation in the inkjet mechanism used for the hollow droplet production | generation apparatus of this invention. It is a graph explaining the relationship between the size of the droplet formed with an inkjet mechanism, and the pressure required for it. It is a schematic diagram for demonstrating the unimorph model used when simulating the size of the droplet formed with an inkjet mechanism.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Hollow droplet production | generation apparatus 200 Hollow droplet production | generation apparatus 10 Liquid 20 Electrolysis part 30 Ultrasonic nebulizer mechanism 40 Inkjet mechanism

Claims (7)

Gas generating means for generating gas from a liquid phase of a predetermined liquid;
Droplet generating means for generating droplets by applying mechanical energy to the predetermined liquid,
A hollow droplet generating device that generates a hollow droplet by taking the gas generated from the gas generating means into the droplet generated by the droplet generating means.   The hollow droplet generator according to claim 1, wherein the gas generating means generates gas by electrolysis.   The hollow droplet generator according to claim 1, wherein the droplet generation unit generates droplets by applying ultrasonic vibration energy.   The hollow droplet generator according to claim 3, wherein the ultrasonic vibration energy uses M-band ultrasonic vibration.   The hollow droplet generator according to claim 1, wherein the droplet generation unit generates a droplet by applying pressure energy.   The hollow droplet generating apparatus according to claim 5, wherein the pressure energy is applied by deformation of a piezoelectric element. The hollow droplet generation device according to any one of claims 1 to 6, wherein a diameter of the generated droplet is 1 to 20 µm, and a diameter of the bubble taken into the droplet is 100 nm to 10 µm.

Images