JPH03232525A - Formation of uniform liquid drop - Google Patents

Abstract

PURPOSE:To form uniform liquid drops of a low conductivity liquid in synchronization with a specified period by impressing an AC electrostatic field of this period to multiple liquid columns covering the outer side of the low-conductivity liquid with a high-conductivity liquid which is incompatible with this liquid. CONSTITUTION:The multiple liquid columns formed by covering the low- conductivity liquid 5 (e.g. high molecular material soln.) ejected from the inner nozzle 11 of a nozzle 1 with the high-conductivity liquid 7 (e.g. water) which is ejected from the outer nozzle 12 and is incompatible with the liquid 5 pass between parallel flat plate shaped electrodes 3. The AC electrostatic field applied between the nozzle 1 and the electrodes 3 by an AC high-voltage power source 2 of the specified period is impressed to the above mentioned multiple liquid columns during this time. Consequently, the uniform liquid drops having the low conductivity of about 5 to 1000mu diameter are formed in synchronization with this period. The particles effective for various purposes, such as chromatography, adsorbent, carrier and spacer, are produced by utilizing this method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for obtaining uniform droplets of a low-conductivity liquid, and in particular uses a liquid containing a particle-forming material as the low-conductivity liquid. This can be applied to the production of uniform particles useful for various purposes such as chromatographic spacers for medical diagnostics.

[Prior Art] When a fixed period of mechanical vibration is applied to a liquid ejected from a nozzle at a constant flow rate, a number of droplets synchronized with this period, that is, uniform droplets are formed. is well known. Furthermore, it is already known to apply this technique to liquids containing particle-forming materials to produce uniform particles. For example, Japanese Patent Application Laid-Open No. 52-129686 discloses that uniform droplets of six liquids containing a particle-forming material and a coating liquid are formed by applying mechanical vibrations at a constant period to a jet consisting of six liquids containing a particle-forming material and a coating liquid. A method for obtaining uniform particles by forming and then forming particles drop by drop is described.

Niss B Sample et al.
Interface Science Volume 41, No. 2 (197
2nd year) (S, B, Sample R, B
ollllnl, journal of' Co
11o1d andInterface 5cien
ce, Vol. 41. No. 2.1972))
When an alternating current electrostatic field with a constant period is applied to a jet of distilled water instead of mechanical vibration between a nozzle and an electrode placed near the nozzle, a uniform number of droplets are formed in synchronization with the period. I am finding that it will be done.

[Problems to be Solved by the Invention] When mechanical vibration is used, problems such as noise and instability of vibration characteristics such as amplitude and frequency arise. especially,
If the particle size of the droplet is approximately 1000 ρ or less, the synchronized vibration frequency will be in the audible frequency range of approximately 1000 Hz or less, causing physiological and psychological discomfort. These problems become major obstacles when actually applying this technology to industrial production.

A method that applies an alternating current electrostatic field instead of mechanical vibration would solve this problem, but Sample et al.'s method does not produce uniform droplets unless the liquid is highly conductive.

The present invention has been accomplished with the object of forming uniform droplets of a low-conductivity liquid using an alternating current electrostatic field.

[Means for Solving the Problems] The present invention applies a constant synchronized alternating current electrostatic field to multiple liquid columns in which the outside of a low conductivity liquid is covered with a high conductivity liquid that is incompatible with the low conductivity liquid. The present invention relates to a method for forming uniform droplets, which is characterized by forming droplets in synchronization with a period.

[Example] The present inventors used multiple nozzles to create multiple liquid columns in which the outside of a low-conductivity liquid was covered with a high-conductivity liquid that was incompatible with this liquid, and It has been found that by applying an alternating current electrostatic field of , a droplet synchronized with the period, that is, a droplet of low conductivity surrounded by a highly conductive liquid is formed.

As the nozzle, multiple nozzles of double or more are used as appropriate. However, the outermost liquid must be highly conductive. The structure of the opening of the nozzle may be such that when particularly minute droplets of a low conductive liquid are to be obtained, the low conductive liquid forms a contracted flow as disclosed in Japanese Patent Application Laid-Open No. 129886/1986.

There is no particular limit to the electrical conductivity of low conductive liquids, but
If the liquid has a value equal to or higher than that of water, droplets synchronized with an alternating current electrostatic field can be formed by itself, so it is not necessary to use the present invention. Of course, the present invention can also be practiced with such liquids. However, the electrical conductivity of the outermost conductive liquid is approximately the conductivity of water, 0.06μS/
c■ or more is required. In the present invention, an alternating electrostatic field provides a controlled initial disturbance to a liquid column ejected from a nozzle by inducing a periodically varying charge on its surface. Therefore, the rate of charge induction must be significantly greater than the alternating current period. In other words, since the relaxation time of ionic species in water or an aqueous solution is on the order of 10'sec, the lower limit of the AC cycle is on the order of 10'sec.
That is, the upper limit of the frequency is several tens of kHz.

The density of the induced charges must also be sufficiently large. According to the present inventors, this standard is the aforementioned water conductivity.

The magnitude of the applied voltage and the range of synchronized frequencies must be large enough to produce the controlled initial disturbance described above. This range depends on the type of liquid, the thickness of the liquid column, the ejection speed of the liquid, the position of the electrode, etc., and can be determined by trial and error depending on these factors.

The movement of the uniform droplets formed as described above is disturbed by air resistance as they move away from the nozzle, and some of them collide and coalesce. This phenomenon becomes noticeable when the droplet size becomes approximately 1 square inch or less. Such coalescence can be prevented by superimposing a DC electric field larger than the voltage on the AC electrostatic field so that the droplets are charged with the same sign.

When producing uniform particles using the present invention, a liquid containing a particle forming material as a low conductive liquid, for example,
Solutions of polymeric substances, solutions containing vinyl polymerizable monomers and their reaction initiators that are polymerized into uniform polymer particles by known polymerization methods, etc. can be used, and highly conductive liquids that coat low conductive liquids can be used. As a solvent, water, an aqueous solution of a surfactant, etc. can be used. Droplets containing such a particle-forming material can be further subjected to various known treatments to transform them into uniform particles.

Next, the present invention will be specifically explained using the drawings.

FIG. 1 shows a model experimental apparatus of the present invention. FIG. 2 is an enlarged view of the tip of the double nozzle used. The structure of the nozzle is not limited to this example;
Of course, it is also possible to use a structure in which the liquid inside is condensed, as in Japanese Patent No. 129888, and a structure with different dimensions.

The low conductivity liquid 5 is sent by the pump 4 to the inner nozzle 11 of the nozzle 1 at a constant flow rate. Various organic liquids whose electrical conductivity is not particularly limited can be used as the low-conductivity liquid. As mentioned above, among these, those containing particle-forming materials are particularly useful.

Suitable hydrophobic monomers include monovinyl monomers such as styrene, ethylstyrene, chloromethylated styrene, methyl acrylate, methyl methacrylate, acrylonitrile, vinyl acetate, maleic anhydride, divinylbenzene, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, phthalic acid. Examples include polyfunctional monomers such as diallyl. A polymerization initiator such as benzoyl peroxide or azobisisobutyronitrile is added to these hydrophobic monomers. Combinations such as styrene-divinylbenzene, chloromethylated styrene-divinylbenzene, styrene-maleic anhydride-divinylbenzene, methyl methacrylate-divinylbenzene, and methyl methacrylate-ethylene glycol dimethacrylate are packing materials and adsorbents for chromatography. Alternatively, it is preferable for obtaining an ion exchange resin. Furthermore, in order to adjust the structure of the obtained particles,
Benzene, diethylbenzene, xylene, toluene, an aliphatic saturated hydrocarbon having 5 to 12 carbon atoms, an aliphatic lower alcohol having 5 to 12 carbon atoms, and the like can also be added to these monomer solutions.

The viscosity of the low conductivity liquid containing the vinyl polymerizable monomer is 200 cps or less, preferably 50 cps or less.

Examples of liquids containing other particle-forming materials include solutions of polymeric substances. The solution must not solidify rapidly when it comes into contact with the highly conductive liquid coating it. In such a case, the liquid column does not break up into droplets. As will be described later, since water or an aqueous solution is often used as a highly conductive liquid, it is preferable that the solvent is hydrophobic. The polymeric substance forming the particles may be a natural polymer or a synthetic polymer. As natural polymeric substances, for example, cellulose derivatives can be used. In addition, synthetic polymer substances such as poly-7-methyl-L
- polyamino acids such as glutamate, methyl methacrylate/hydroxyethyl methacrylate copolymers, etc., which provide particles suitable for functional adsorbents and carriers. Polymers into which a crosslinked structure and ion exchange groups can be introduced, such as styrene/butadiene copolymers and styrene/chloromethylated styrene copolymers, are useful for ion exchange resins. The solvents for these polymer substances are described in "Natural Polymers J (1
984), Kyoritsu Shuppan and JΦBrandlap, "Polymer Handbook", 2nd edition, 1975, John Wiley & Sons Incorporate Sodo (J,
Brandrup, polymer hand bo
OK', 2nd edition, (1975
), John Wily and 5ons Inc.
), etc., to make a selection. As specific examples of the solvent, chlorinated hydrocarbons such as methylene chloride, chloroform, dichloroethane, and trichloroethane are commonly used alone or in combination of two or more.

In some cases, it is effective to add a small amount of lower alcohol to these solvents as a coagulation accelerator. Furthermore, if it is desired to make the polymer particles porous, an aliphatic alcohol having 4 to 12 carbon atoms may be added.

The viscosity of the solution containing the particle-forming polymer substance is 200
cps or less, preferably 50 cps or less.

The lower the viscosity of the highly conductive liquid, the lower the viscosity is, 5ocps.
It is preferably 20 cps or less.

A high conductivity liquid 7 covering a low conductivity liquid is delivered at a constant rate by a pump 6 to the outer nozzle 12 of the nozzle 1 . Water or an aqueous solution is preferably used as the highly conductive liquid. Aqueous solutions of surfactants are particularly effective for stably holding droplets of low conductivity liquids.

The multiple liquid columns, in which a low-conductivity liquid is coated with a high-conductivity liquid, ejected from the nozzle 1 are connected between the nozzle 1 and the electrode 3 by an AC high-voltage power source 2 while passing between the parallel plate-shaped electrodes 3 An applied alternating current electrostatic field is applied. In order to charge the droplets with the same sign as described above, it is sufficient to superimpose a DC voltage larger than the AC voltage between the nozzle 1 and the electrode. The frequency and voltage range of the AC that provides the state in which multiple liquid columns split in synchronization with the cycle of the AC and form uniform droplets, that is, the synchronized state, depends on the ejection speed and thickness of the liquid column, and mainly on the outer side. It has a specific region determined by the surface tension, density, viscosity, etc. of the highly conductive liquid. Therefore, this region is determined by trial and error, but especially in the frequency region, highly conductive liquid is ejected using only the outer nozzle of multiple nozzles, and mechanical vibration is applied to create uniform droplets. The present inventors have found that the tuning frequency region is approximately equal to the tuning frequency region when the frequency is divided into
T., Sagaben et al., Abstracts of the 4th International Conference on Liquid Atomization and Spray Systems (T.

5aka1 et al, Proceedings
of 4thInternational Confe
rence on LiquidAtoa+1zati
on and 5play Systems), A
It can be roughly estimated from the formula 2A2-4 (see 198). Practically useful frequencies are from several hundred Hz to several tens of kHz, and this frequency corresponds to droplets with a diameter of 11 to several tens of microns. On the other hand, the minimum value of the tuned AC voltage is clearly recognized, but the upper limit is unclear. In reality, several hundred volts or more are used.

As mentioned above, this voltage is necessary to induce a charge that provides a periodically varying, controlled initial disturbance to the liquid column ejected from the nozzle. Therefore, it is considered that the lower limit is clear but the upper limit is unclear.

In this device, parallel plate-shaped electrodes are used, but the electrode 3
There is no reason to limit the shape, and it may be cylindrical or the like. Although there is no particular strict limit to the distance between the electrode and the nozzle, a distance of several Im to several tens of square meters is appropriate. However, the location of the other end of the electrode should approximately coincide with the location where the liquid column splits. In this way, especially when a DC electric field is superimposed on an AC electrostatic field, not only can the maximum amount of charge be applied to the surface of the liquid column, but also the movement of the generated droplets will not be affected by the electrode charge. So it becomes stable.

If the droplet generation is in a synchronous state, when the flashing cycle of the stroboscope 9 matches an integer multiple or an integer fraction of the AC cycle, the droplet will be seen stationary, and it will be photographed by the camera 8. I can do it.

By the method described above, it is possible to form uniform droplets with a diameter of 5 to 1000 mm and a low conductivity.

If the droplets contain particle-forming material, they are further processed to form particles. The processing method differs depending on which of the above particles is used as the material for forming the particles, but usually the droplets are first collected in the same liquid as the outer liquid of the droplets, that is, the highly conductive liquid, and a homogeneous solution containing the particle forming material is collected. Obtain a dispersion of droplets. Thereafter, if the monomer is the above-mentioned monomer, it can be made into uniform particles by generating radicals in the polymerization initiator and polymerizing it by a known method. If the droplets containing the particle-forming material are a solution of a polymeric substance, known techniques may be used, for example, to evaporate the solvent while the particles are in a dispersed state, or to add a coagulant to the dispersion. In addition, the droplets can be solidified into uniform particles of the polymeric material.

EXAMPLES The method of the present invention will be explained in more detail with reference to examples below, but the present invention is not limited to the following examples.

Example 1 A model experiment of the present invention was conducted using the apparatus shown in FIG.

FIG. 2 is an enlarged cross-sectional view of the tip of the double nozzle used in this experiment.

The inner diameter of the outer nozzle 12 constituting the nozzle 1 is 400ρ,
The inner and outer diameters of the inner nozzle were 150 f and 250 f, respectively.

Kerosene was used as the model liquid 5 with low conductivity, and was sent to the nozzle 1 with the pump 4 so that the jet flow rate from the inner nozzle 11 was 300 cm/see.

As a highly conductive model liquid, the electrical conductivity is 0.3μS/
cm of ion-exchanged water was used and sent to the nozzle 1 with a pump 6 so that the jet flow rate from the outer nozzle was 300 cm/sec.

The parallel plate-shaped electrode 3 has a length of 25 m in the liquid ejection direction.
5. A stainless steel plate with a width of 30 mm was used. The electrode should be 10mm away from the nozzle, and the other end of the electrode should be 3mm away from the nozzle.
I made it to be in the position of 5-year-old.

In this experiment, no DC voltage was superimposed between the electrode and the nozzle.
Only an alternating voltage of V was used.

The splitting state of a double liquid column in which kerosene was coated with ion-exchanged water was observed by changing the cycle of the alternating current voltage from 1 to 3 kHz in 0.5 kHz increments. At 1.0, 1.5 and 3.0kHz, the droplets were irregularly split, but at 2.0 and 2.5kHz, the liquid column split in synchronization with the cycle of the applied AC voltage, and uniform droplets were observed. Ta. In more detail, the result of observing the tuning period region by changing the ejection speed of the liquid column is shown in FIG. 3 using the upper and lower limit frequencies of the uniform region. The straight line in Figure 3 is the calculated value of the tuning period region obtained by the above-mentioned formula of Sagaben et al. when the inner nozzle is removed and the same ion-exchanged water is ejected at the corresponding flow rate using only the outer nozzle. It shows. As shown in FIG. 3, the tuning frequency region can be predicted using this method.

The lower limit AC voltage required to obtain a tuned state was 1 kV.

Strobe photography of the synchronous droplets clearly showed that one kerosene droplet was uniformly formed into double droplets surrounded by water. The average diameter of the droplets was 530 mm, all of the droplets were in the range of 500 to 600 mm, and had an extremely sharp distribution.

In the present invention, kerosene was used as the low conductivity liquid and ion exchange water was used as the high conductivity liquid, but instead of these, the liquid containing the particle forming material was used as the low conductivity liquid, and a surfactant was used as the low conductivity liquid. Even if an aqueous solution containing .

[Effects of the Invention] According to the method of the present invention, a uniform double layer is formed by wrapping a low conductive liquid, such as a solution of a polymeric substance or a liquid containing a polymerizable monomer, with a highly conductive liquid, such as an aqueous solution of a surfactant. Since droplets can be produced stably without making noise, this method can be used to produce uniform particles that are extremely effective for various purposes such as chromatography, adsorbents, carriers, and spacers. can.

[Brief Description of the Drawings] Figure 1 is a model experimental device used to specifically explain the present invention, Figure 2 is an enlarged cross-sectional view of the nozzle in Figure 1, and Figure 3 is an enlarged cross-sectional view of the nozzle in Figure 1. The frequency range of the AC voltage (2 kV) in which the splitting of the double liquid column is synchronized is shown using the upper and lower limit frequencies; the straight line shows the value based on the prediction formula of Sagaben et al., and the plot shows the actually measured value. (Main symbols in the drawing) (1): Nozzle (2) Two AC voltage power supply (3): Electrode (5): Low conductivity liquid (7), High conductivity liquid 01): Inner nozzle 02): Outer nozzle Figure 1 Figure 2 Liquid jet flow velocity (cm/s)

Claims (1)

[Claims] 1. Droplets synchronized with a constant period by applying an alternating current electrostatic field with a constant period to multiple liquid columns in which the outside of a low conductive liquid is covered with a highly conductive liquid that is incompatible with the low conductive liquid. A method for forming uniform droplets, characterized by forming a uniform droplet. 2. The method for forming uniform droplets according to claim 1, wherein the low conductivity liquid is a liquid containing a particle forming material, and the high conductivity liquid is water or an aqueous solution.