JP7691104B2 - Method for producing coated photochromic particles and apparatus for producing coated photochromic particles using the same - Google Patents

Description

The present invention relates to a method for producing coated photochromic microparticles and an apparatus for producing coated photochromic microparticles using the same.

Photochromic compounds (also called photochromic dyes) have the property that their color or tone changes when exposed to light, and then return to their original state when exposed to heat or light of a different wavelength. They are widely used, for example, in photochromic lenses.

On the other hand, it has been proposed to use such photochromic compounds in light-sensitive nanodevices, but this has proved difficult to realize. This is because, while it is possible to use photochromic compounds to manufacture capsules with a diameter of, for example, a few millimeters, it is difficult to create microcapsules or composite materials with a diameter of several hundred nanometers.

Technologies for atomizing photochromic compounds are known, for example, from Patent Documents 1 to 4.

Patent Document 1 discloses a method of forming an O/W emulsion containing a photochromic dye, and then polymerizing the photochromic dye in the emulsion to form fine particles. However, the fine particles obtained by the method of Patent Document 1 have a drawback in that the stability is lost depending on the type of photochromic dye, since the surface of the fine particles is not coated with a polymer.
Patent Document 2 discloses a method for producing a photochromic composite material through a sol-gel method. However, the method of Patent Document 2 lacks industrial productivity in that it takes a long time to obtain the desired fine particles because it involves multiple steps of hydrolysis, condensation, and drying. Patent Document 3 discloses a method for forming a photochromic nanocomposite material by inserting one or more organic photochromic colorant molecules into a transparent polymeric plastic material having nano-sized pores. However, the method of Patent Document 3 has the disadvantage that the types of photochromic colorant molecules that can be used are limited to organic photochromic compounds, and the selectivity is poor. Patent Document 4 describes a method in which a nanoemulsion containing a photochromic dye is produced, and then the surface is coated with a polymer such as a silicate by a chemical reaction. However, the method of Patent Document 4 lacks industrial productivity in that it takes about two days to dry the organic solvent used.

JP 2016-150961 A Special Publication No. 2012-515356 Special Publication No. 2009-518696 JP 2007-154198 A

The present invention aims to solve the above problems, and its purpose is to provide a method for producing coated photochromic microparticles that can efficiently produce desired photochromic microparticles regardless of the type of photochromic compound used, and a manufacturing device for coated photochromic microparticles using the same.

The present invention relates to a method for producing coated photochromic fine particles,
A step of directly irradiating a premix of photochromic core particles, a polymer, a polar solvent, and a low-polarity organic solvent with ultrasound to prepare an O/W emulsion;
mixing the O/W emulsion with a supercritical fluid in a closed container; and opening the closed container.
The method includes:

In one embodiment, the supercritical fluid is supercritical carbon dioxide.

In one embodiment, the low polarity organic solvent is at least one solvent selected from the group consisting of toluene and hexane.

In one embodiment, the polymer is a thermoplastic resin.

In a further embodiment, the thermoplastic resin is polystyrene.

In one embodiment, the mixing step is carried out at a temperature of 35°C to 55°C.

In one embodiment, the ultrasound is irradiated by a horn-type ultrasonic transducer.

In a further embodiment, the ultrasonic waves are applied uniaxially to the premix.

The present invention also provides an apparatus for producing coated photochromic fine particles, comprising:
an ultrasonic irradiation means for directly irradiating a premix of photochromic core particles, a polymer, a polar solvent, and a low-polarity organic solvent with ultrasonic waves to prepare an O/W emulsion; and a closable container in which the O/W emulsion and a supercritical fluid are mixed;
The device comprises:

According to the present invention, nano-order particles can be efficiently processed from photochromic compounds. This makes it possible to increase the industrial productivity of photochromic particles.

1 is a schematic diagram showing an example of an apparatus for producing coated photochromic fine particles using the method for producing coated photochromic fine particles of the present invention. 1 is a photograph of the liquid photochromic material used in Reference Example 1. 1 is a photograph showing the state of the photochromic core material particles (R1) obtained in Reference Example 1 when placed under artificial light (indoor fluorescent light). 1 is a photograph showing the state of the photochromic core material particles (R1) obtained in Reference Example 1 when irradiated with UV light (wavelength 302 nm) under an indoor fluorescent lamp. 1 is an electron microscope photograph of the photochromic core material particles (R1) obtained in Reference Example 1. 1 is an electron microscope photograph of the coated photochromic fine particles (E1) obtained in Example 1. Graphs for comparing the particle size distribution of the photochromic core particles (R1) obtained in Reference Example 1 and the coated photochromic microparticles (E1) obtained in Example 1, where (a) is a graph showing the particle size distribution of the photochromic core particles (R1) obtained in Reference Example 1, and (b) is a graph showing the particle size distribution of the coated photochromic microparticles (E1) obtained in Example 1. These are photographs taken by opening the top lid of Example 1 to confirm the presence or absence of photochromism in the reaction liquid (containing the coated photochromic microparticles (E1) of Example 1) present in container 110, where (a) is a photograph of a sample bottle containing the reaction liquid without exposure to UV light, and (b) is a photograph of a sample bottle containing the reaction liquid with exposure to UV light.

(Method for producing coated photochromic fine particles)
In the method for producing coated photochromic fine particles of the present invention, an O/W emulsion is first prepared from the preliminary mixture.

The preliminary mixture contains photochromic core particles, a polymer, a polar solvent, and a low-polarity organic solvent.

The photochromic core particles of the present invention are a material (core material or core substance) that can form the core of the coated photochromic microparticles, and are solids that contain a photochromic compound.

Photochromic compounds are broadly classified into P-type compounds, whose molecular structure changes when irradiated with light and then returns to its original structure when irradiated with light of a different wavelength, and T-type compounds, whose molecular structure returns to its original structure when irradiated with light of a different wavelength by a thermal reaction. The photochromic core particles of the present invention may contain either a P-type or a T-type photochromic compound. Photochromic compounds are not necessarily limited, but examples thereof include azobenzene-based compounds, spiropyran-based compounds (e.g., naphthopyran), fulgide-based compounds, fulgimide-based compounds, and diarylethene-based compounds. Such photochromic core particles can be obtained, for example, by pulverizing the cured product of commercially available photochromic materials (monomers) containing various photochromic compounds.

The size (average particle diameter) of the photochromic core particles is not necessarily limited, but may be larger than the size (average particle diameter) of the coated photochromic microparticles that can be finally produced. For example, the average particle diameter is 1 μm to 500 μm, preferably 10 μm to 100 μm. Photochromic core particles with an average particle diameter of less than 1 μm are difficult to produce because they themselves become nano-order microparticles. If the average particle diameter of the photochromic core particles exceeds 500 μm, the photochromic core particles may not be sufficiently dissolved in the oil phase, and the average particle diameter of the obtained coated photochromic microparticles may vary. The shape of the photochromic core particles is also not necessarily limited. For example, they may be spherical, elliptical, discoid, scale-like, columnar, polyhedral, irregular three-dimensional, or any other three-dimensional shape.

The amount (concentration) of photochromic core particles contained in the closed container described below varies depending on the type of photochromic core particles, and is not necessarily limited, but is, for example, 0.01 (w/v)% to 1 (w/v)%. By containing photochromic core particles in such a range in the closed container, coated photochromic microparticles can be efficiently produced in the closed container.

The polymer contained in the premix is a resin that has affinity for the supercritical fluid described below and can form an interface with the supercritical fluid. Such a polymer is a material that can coat part or all of the surface of the photochromic core particles, and is preferably a thermoplastic resin. Examples of thermoplastic resins that can be used include polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyvinyl acetate, polyurethane, ABS (acrylonitrile-brassine-styrene) resin, and combinations thereof. Polystyrene is preferred because it has a high affinity with supercritical carbon dioxide that can be used as the supercritical fluid described below, and the average particle size of the resulting coated photochromic microparticles is stable.

The content of the polymer contained in the premix is not necessarily limited, but is preferably 10 to 100 parts by mass, more preferably 40 to 60 parts by mass, relative to 100 parts by mass of the photochromic core particles. If the content of the polymer contained in the premix is less than 10 parts by mass, a sufficient coating cannot be formed on the photochromic core particles, and the components constituting the core particles may leak through the coating, resulting in a loss of stability depending on the type of photochromic dye used. If the content of the polymer contained in the premix exceeds 100 parts by mass, the polymer becomes excessive relative to the photochromic core particles, which may reduce industrial productivity.

The polar solvent is water, which can function as the aqueous phase for preparing the O/W emulsion. Specific examples of water include ultrapure water, pure water, ion-exchanged water, and distilled water. Considering that emulsion extraction with a supercritical fluid using the SFEE (Supercritical Fluid Extractions of Emulsion) method is performed, it is preferable to use ultrapure water.

The content of the polar solvent contained in the premix is not necessarily limited, but is preferably 5,000 to 30,000 parts by mass, more preferably 15,000 to 20,000 parts by mass, relative to 100 parts by mass of the photochromic core particles. If the content of the polar solvent contained in the premix is less than 5,000 parts by mass, it may be difficult to form an O/W emulsion across all of the added materials, which may reduce industrial productivity. If the content of the polar solvent contained in the premix is more than 30,000 parts by mass, the concentration of the prepared O/W emulsion may be low, and it may not be possible to expect a sufficient yield of coated photochromic microparticles.

Low-polarity organic solvents, also called non-polar organic solvents, include organic solvents that are less polar than water, which is a polar solvent. Low-polarity organic solvents can function as an oil phase for preparing O/W emulsions, and specific examples include toluene, hexane, dioxane, tetrahydrofuran, and combinations thereof. Toluene and hexane, as well as combinations thereof, are preferred because they have a high affinity with supercritical fluids and provide a high extraction yield of low-polarity organic solvents in the SFEE (Supercritical Fluid Extractions of Emulsion) method.

The content of the low-polarity organic solvent contained in the pre-mixture is not necessarily limited, but is preferably (500 to 3000 parts by mass, more preferably 1500 to 2000 parts by mass) relative to 100 parts by mass of the photochromic core particles. If the content of the low-polarity organic solvent contained in the pre-mixture is less than 500 parts by mass, an O/W emulsion may not be formed, making it difficult to obtain the desired coated photochromic fine particles. If the content of the low-polarity organic solvent contained in the pre-mixture exceeds 3000 parts by mass, the amount of low-polarity organic solvent contained in the obtained O/W emulsion may be excessive, which may lengthen the extraction time of the low-polarity organic solvent in the SFEE method and reduce industrial production efficiency.

It is preferable that the premix contains a small amount of surfactant. The amount of surfactant contained in the premix is not particularly limited, and an appropriate amount can be selected by a person skilled in the art.

The photochromic core particles, polymer, polar solvent, and low-polarity organic solvent, as well as the surfactant added as needed, are mixed in any order, and may or may not be stirred as needed.

The O/W emulsion is prepared by directly irradiating the above premix with ultrasound.

In the present invention, an O/W emulsion can be prepared, for example, by adding a premix to a specified container and directly irradiating it with ultrasonic waves to promote stirring of the premix, thereby promoting the formation of micelles at the interface between the oil phase and the water phase, and encapsulating the oil phase with the micelles. In other words, an oil-in-water emulsion is prepared.

Ultrasonic waves are directly irradiated to the premix through the vibrating portion of an ultrasonic transducer introduced so as to come into contact with the premix. Here, the term "direct irradiation (of ultrasonic waves)" used in this specification refers to irradiating the target (premix) with ultrasonic waves emitted from an ultrasonic transducer without going through other members. In the present invention, by directly irradiating ultrasonic waves to the premix, the particle size of the particles constituting the obtained O/W emulsion can be reduced to, for example, one percent of the size obtained when ultrasonic waves are irradiated through other members.

In the present invention, it is preferable that ultrasonic waves are irradiated in one axial direction to the premix. By irradiating ultrasonic waves in one axial direction, convection (vortex flow) is promoted in the premix due to the irradiation, and as a result, the entire premix can be efficiently stirred. Because such convection can be easily formed in the premix, it is preferable to use a horn-type ultrasonic vibrator as the ultrasonic vibrator.

In a horn-type ultrasonic transducer, electrical energy amplified to, for example, 20 kHz by a solid-state power supply can be converted into mechanical vibration in one axis direction (vertical direction) by a converter, and this converted mechanical vibration can be transmitted to the horn as ultrasonic vibration. The ultrasonic vibration becomes a pressure wave, and the continuous formation and attenuation (cavitation) of countless extremely small bubbles due to local pressure drop in the solution (fluid) can be performed in one axis direction. Such a horn-type ultrasonic transducer is preferably arranged vertically in a closed container in order to more easily generate convection of the premixture (i.e., vortex flow of the premixture based on the direction of gravity).

The ultrasonic frequency is preferably 15 kHz to 25 kHz, more preferably 19 kHz to 21 kHz. By keeping the frequency within the above range, the efficiency of forming an O/W emulsion can be further improved. Ultrasonic irradiation may be performed once, or may be performed multiple times with appropriate intervals between each.

In this way, an O/W emulsion is prepared from the above premix.

Next, in the present invention, the O/W emulsion and the supercritical fluid are mixed in a closed container.

The closed container in the present invention is a container that can hold an O/W emulsion and a supercritical fluid in a closed state and can be repeatedly closed and opened (i.e., an openable container), and examples of such containers include high-pressure cells, pressure-resistant cells, and autoclaves in supercritical devices. There are no particular limitations on the capacity that the closed container can hold, and a container having an appropriate capacity can be selected by a person skilled in the art.

A supercritical fluid is a fluid in which a substance is in a supercritical state and has the diffusivity of a gas and the solubility of a liquid.

The term "supercritical state" as used herein refers to a state in which a substance is placed in a temperature/pressure region above the critical point. In contrast, a subcritical state refers to a state in which a substance is placed in a region near but slightly below the critical point. A liquid state refers to a state in which a substance is placed at a temperature lower than the supercritical or subcritical temperatures. These states can be changed by controlling the pressure or temperature. High pressure refers to a pressure higher than atmospheric pressure (i.e., greater than 0.1 MPa) at which a substance can be placed in a supercritical state, subcritical state, or liquid state. High pressure can vary depending on the type of substance used as the fluid.

A supercritical fluid is a dense fluid above its critical point and pressure, preferably having a density between 200 kg/m ³ and 900 kg/m ³ , a viscosity between 10 ⁻⁵ Pa·s and 10 ⁻⁴ Pa·s, a diffusion coefficient between 10 ⁻⁸ m ² /s and 10 ⁻⁷ m ² /s, and/or a thermal conductivity between 10 ⁻³ W/m ² ·K and 10 ⁻¹ W/m ² ·K.

A subcritical fluid is a fluid that is in a liquid state at a temperature range below its critical temperature and at a pressure above its vapor pressure curve, and preferably has a density of 500 kg/m ³ to 1100 kg/m ³ , a viscosity of preferably 10 ⁻⁴ Pa·s to 10 ⁻³ Pa·s, a diffusion coefficient of preferably 10 ⁻¹⁰ m ² /s to 10 ⁻⁹ m ² /s, and/or a thermal conductivity of preferably 0.08 W/m·K to 0.10 W/m·K.

The supercritical, subcritical, or liquid state can be altered by controlling temperature and pressure. Thus, during the manufacturing method of the present invention, the fluid in the closed container can be in a supercritical, subcritical, or liquid state. Thus, for example, even when "supercritical carbon dioxide is used" in this specification, this does not necessarily exclude the use of carbon dioxide in a subcritical state or in a liquid state (especially under high pressure).

The supercritical fluid may be a single substance or a mixture of two or more substances. Examples of substances constituting the supercritical fluid include carbon dioxide, water, methane, propane, nitrogen, and ammonia, as well as combinations thereof. In the present invention, the supercritical fluid is preferably supercritical carbon dioxide, because it is chemically inert and non-toxic, the density is easy to control, and it is released as a gas at room temperature and pressure, making it easy to remove and perform other post-processing. Supercritical carbon dioxide refers to carbon dioxide at a critical temperature (Tc: 31.1°C) or higher and a critical pressure (Pc: 7.38 MPa) or higher. Supercritical carbon dioxide can be handled at a relatively low temperature. For this reason, supercritical carbon dioxide has the advantage of being effective for heat-unstable raw materials such as the above-mentioned heat-labile core material particles.

Because the temperature of a supercritical fluid exceeds the critical temperature, the thermal motion of the molecules is intense, and the density can be continuously changed from a dilute state close to that of an ideal gas to a high-density state equivalent to that of a liquid. Therefore, the physical properties of a supercritical fluid that depend on its density (solubility, diffusion coefficient, thermal conductivity, dielectric constant, ionic product, etc.) can be controlled by small changes in temperature and pressure. The density of a supercritical fluid is close to that of a liquid, and its viscosity and diffusion coefficient are close to that of a gas. Since the greater the density of a solvent, the greater its ability to dissolve the target substance, it is thought that a supercritical fluid has a dissolving power comparable to that of a liquid. On the other hand, its viscosity and diffusion coefficient have a high fluidity comparable to that of a gas. From these physical properties, it can be said that a supercritical fluid is a functional solvent that combines the characteristics of both a liquid and a gas.

The above-mentioned O/W emulsion can be mixed with a supercritical fluid, for example, by adding the supercritical fluid to the O/W emulsion that has been previously contained in a closed container. When mixed with the supercritical fluid, the photochromic core particles and polymer contained in the O/W emulsion may be, for example, in a molten state (molten liquid) or in a state dissolved in a solvent (solution).

The mixing of the O/W emulsion and the supercritical fluid in the closed container is preferably carried out at a temperature of 35°C to 55°C, preferably 38°C to 42°C. If the temperature set during the mixing is below 35°C, the O/W emulsion and the supercritical fluid may not dissolve uniformly, and the production efficiency of the resulting coated photochromic microparticles may decrease. If the temperature set during the mixing is above 55°C, the inherent properties of the encapsulated photochromic core particles and the type of polymer used for coating may change depending on the temperature.

In the present invention, it is preferable to carry out the mixing in the closed container for a predetermined time. The mixing time is not necessarily limited because it varies depending on the volume of the closed container and the type and amount of the photochromic core particles and/or polymer contained in the O/W emulsion, but is, for example, 0.5 to 5 hours.

In the present invention, the closed container is then opened.

By opening the container, the pressure inside is reduced and the supercritical fluid is released outside the container, for example through a nozzle. At that time, the mixture of photochromic core particles and polymer inside the container expands rapidly to nearly atmospheric pressure, promoting the precipitation of the molten or dissolved photochromic core particles and polymer. Then, as the photochromic core particles and polymer precipitate, the average particle size of the photochromic core particles is reduced and the polymer coats the surfaces of the photochromic core particles as a coating.

In this way, the desired coated photochromic microparticles can be obtained.

(Apparatus for manufacturing coated photochromic fine particles)
An example of an apparatus that can be used in the method for producing coated photochromic fine particles of the present invention will be described.

Figure 1 shows a manufacturing apparatus 100 for coated photochromic microparticles when supercritical carbon dioxide is used as the supercritical fluid. This apparatus 100 is composed of a pressure increasing section A1 for providing supercritical carbon dioxide obtained by pressurizing carbon dioxide, a preparation section A2 for preparing an O/W emulsion from a preliminary mixture, and a mixing section A3 for mixing the O/W emulsion and supercritical carbon dioxide with a closable container closed. The pressure increasing section A1 and the mixing section A2 are separated by a stop valve 202. The preparation section A2 and the mixing section A3 are separated by a stop valve 206.

In the pressurization section A1, the carbon dioxide can be pressurized by a liquid carbon dioxide pressurization pump 105. A cylinder 101 is provided to supply carbon dioxide to the pressurization pump 105. A cylinder with a siphon filled with liquid carbon dioxide can be used as a supply source of liquid carbon dioxide.

Between the cylinder 101 and the boost pump 105, a drying tube 102 filled with a desiccant is provided. As the liquid carbon dioxide from the cylinder 101 passes through this drying tube 102, the moisture in the liquid carbon dioxide is removed.

A cooling unit 103 is provided downstream of the drying tube 102. The cooling unit 103 is filled with, for example, ethylene glycol, which is cooled to approximately 260 K. The liquid carbon dioxide, from which moisture has been removed by the desiccant while passing through the drying tube 102, is cooled by the ethylene glycol in the cooling unit 103 and supplied to the boost pump 105.

A filter 104 is provided between the cooling unit 103 and the boost pump 105. The filter 104 removes impurities such as dust and prevents impurities from entering the boost pump 105.

The carbon dioxide that has passed through the filter 104 is supplied to the boost pump 105. A cooler may be attached to the head of the boost pump 105 to prevent the liquid carbon dioxide from evaporating (not shown).

The boosting section A1 is provided with a pressure adjustment valve 201. The pressure adjustment valve 201 can be used to set the pressure inside the boosting section A1 system to any desired pressure. The boosting section A1 may also be provided with a pressure gauge 106. The pressure gauge 106 can be used to measure the pressure inside the boosting section A1 system. The pressure gauge 106 is equipped with an upper limit contact output terminal, and can be set to turn off the power to the boosting pump 105 at a specified pressure.

The supply of carbon dioxide from the pressure increasing section A1 to the mixing section A3 can be adjusted by a stop valve 202 disposed between the pressure increasing section A1 and the mixing section A3. Furthermore, a safety valve 107 may be provided between the pressure increasing section A1 and the mixing section A3 to ensure safety.

The preparation section A2 is composed of a preliminary container 182 that contains the preliminary mixture 180, an ultrasonic vibrator 190 arranged in the preliminary container 182, and a pipe 206 that delivers the O/W emulsion obtained from the preliminary mixture 180 to the mixing section A3.

The reserve container 182 contains the photochromic core particles, polymer, polar solvent, low-polarity organic solvent, and surfactant as necessary, supplied from each storage tank (not shown) as the reserve mixture 180. In FIG. 1, the reserve container 182 is open at the top, but the present invention is not particularly limited to this. The reserve container 182 may be a closed container.

The ultrasonic transducer 190 is electrically connected to a predetermined power source 184 such as a solid-state power supply, and is arranged in the preliminary container 182 so that the vibration part 192 is in contact with the preliminary mixture 180. In FIG. 1, the vibration part 192 of the ultrasonic transducer 190 is arranged so that the vibration part 192 faces downward relative to the preliminary mixture 180. In such an arrangement, ultrasonic waves emitted from the vibration part 192 of the ultrasonic transducer 190 can be irradiated in a downward uniaxial direction to the preliminary mixture 180. By irradiating ultrasonic waves in a uniaxial direction, convection occurs in the preliminary mixture 180 in the preliminary container 182 in the vertical direction as shown in FIG. 1, and an O/W emulsion having a smaller micelle diameter can be prepared, for example, compared to the case of stirring in the horizontal direction.

The prepared O/W emulsion is supplied from the spare container 180 to the mixing section A3 by opening the stop valve 208 and using a liquid supply pump (not shown) through the pipe 206.

The mixing section A3 is installed in a constant temperature water bath 112. The water temperature in the constant temperature water bath 112 can be controlled to within ±0.1°C by a temperature controller (not shown), and the temperature inside the closable container 110 can be set to any desired temperature, preferably between 35°C and 55°C. The constant temperature water bath 112 is provided with a temperature measuring section 116 as necessary.

The closable container 110 is, for example, a high-pressure cell that is heat-resistant and pressure-resistant. The O/W emulsion obtained from the preparation section A2 and the supercritical carbon dioxide (supercritical fluid) obtained from the pressure-increasing section A1 are contained in the closable container 110, and are mixed with the container 110 closed. The closable container 110 may be provided with a stirrer 111 to promote mixing.

The supply of supercritical carbon dioxide to the closable container 110 shown in FIG. 1 is performed, for example, as follows. Liquid carbon dioxide supplied from the stop valve 202 is prepared as a supercritical fluid (supercritical carbon dioxide) in the constant temperature water bath 112 before being supplied to the container 110. Specifically, the liquid carbon dioxide supplied from the stop valve 202 is prepared as supercritical carbon dioxide via the auxiliary piping (preheater) 108, check valve 109, and stop valve 203 installed in the constant temperature water bath 112, and introduced into the closable container 110. The pressure inside the closable container 110 is appropriately monitored by a pressure gauge 113.

In the mixing section A3, the closable container 110 containing the O/W emulsion and supercritical carbon dioxide (supercritical fluid) is closed, and then mixing is carried out for a predetermined time, after which the container 110 is opened again by the stop valve 204. This allows the carbon dioxide fluid to be discharged from the tube 205, and the internal pressure of the container 110 can be reduced to atmospheric pressure. To prevent condensation of the liquid in the container 110 and the generation of dry ice by the carbon dioxide fluid due to this reduction in pressure, the stop valve 204 may be provided with a heater (not shown).

By opening the stop valve 204, the carbon dioxide fluid contained in the closable container 110 is discharged from the tube 205 to the outside in a state where it has returned from a supercritical state to normal pressure. At that time, the polymer surrounds the photochromic core particles in the closable container 110 in a state where the average particle diameter of the photochromic core particles is reduced, forming a coating, and coated photochromic microparticles are produced. The coated photochromic microparticles obtained by the present invention have an average particle diameter (e.g., 0.05 μm to 0.5 μm) smaller than that of the photochromic core particles used in preparing the O/W emulsion. This makes it possible to obtain so-called nano-order photochromic microparticles.

The coated photochromic microparticles obtained by the present invention are useful, for example, as a constituent material for photosensitive nanodevices (specific examples include nanoquantum dots, nanosensors, nanotubes, biosensors, etc.).

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Reference Example 1: Preparation of photochromic core particles)
10 g of liquid photochromic material (commercially available photochromic lens material containing naphthopyran) was placed in a beaker, 0.1 g each of polymerization initiators Irgacure 184 (98.0%, manufactured by Tokyo Chemical Industry Co., Ltd.) and Irgacure 819 (96.0%, manufactured by Tokyo Chemical Industry Co., Ltd.) were added thereto, and the mixture was cured by UV irradiation (wavelength 302 nm) at room temperature for 24 hours. The obtained cured product of the photochromic material was subjected to a freeze grinder to obtain photochromic core particles (R1) in the form of solid powder.

(Example 1: Preparation of coated photochromic fine particles)
As the aqueous phase, 9.5 g of ultrapure water and 0.08 g of a surfactant (Tween 80 manufactured by SIGMA-ALDRICH) were charged into a beaker. As the oil phase, 1.5 g of toluene (99.5%, manufactured by FUJIFILM Wako Pure Chemical Co., Ltd.), 0.025 g of polystyrene (manufactured by Aldrich Chemical Company, Inc. / weight average molecular weight (Mw) 200,000), and 0.05 g of the photochromic core material particles (R1) obtained in Reference Example 1 were charged into another beaker. Next, the oil phase was added to the aqueous phase, and then ultrasonic irradiation was performed for 5 minutes to prepare an O/W emulsion.

Then, using the manufacturing apparatus 100 shown in Figure 1, coated photochromic microparticles were produced as follows.

A stainless steel closureable container 110 (50 cc) was placed in the container 110 with the stop valve 208 open, and the container 110 was closed and placed in a thermostatic chamber 112 previously controlled to a reaction temperature (40°C). The container 110 was left to stand until the temperature inside the closed container 110 reached the reaction temperature (40°C). Next, the stop valves 201, 202, and 203 were opened, and supercritical carbon dioxide was pumped into the container 110, creating a high pressure state (10 MPa) inside the container 110. In this state, the container 110 was stirred for one hour by the magnetic stirrer 111. After that, the stop valve 204 was opened, the container 110 was depressurized, and carbon dioxide gas was discharged from the container 110 through the stop valve 204 and the tube 205. Then, the top lid of the container 110 was opened, and the product in the container 100 was collected together with the reaction liquid of the reaction residue, and centrifuged and freeze-dried to obtain coated photochromic fine particles (E1) in the form of a solid powder.

(Photochromism of photochromic core particles (R1))
An appropriate amount of the liquid photochromic material used in Reference Example 1 was placed on a petri dish. The state of the petri dish at that time is shown in FIG. 2. In addition, an appropriate amount of the photochromic core material particles (R1) obtained in Reference Example 1 was placed on another petri dish under artificial light (indoor fluorescent light). The state of the petri dish at that time is shown in FIG. 3. Furthermore, the photochromic core material particles (R1) placed on this petri dish were irradiated with UV light (wavelength 302 nm) under indoor fluorescent light. The state of the petri dish at that time is shown in FIG. 4.

As shown in Figures 2 to 4, the liquid photochromic material (Figure 2) was clearly transformed into a solid powder through the above-mentioned operations (Figures 3 and 4). Furthermore, the photochromic core particles (R1) obtained in Reference Example 1 exhibited different colors under natural light (Figure 3) and UV light (Figure 4), demonstrating that the photochromic properties were properly maintained even in the form of a solid powder.

(Electron microscope photographs of photochromic core particles (R1) and coated photochromic fine particles (E1))
The surface conditions of the photochromic core particles (R1) obtained in Reference Example 1 and the coated photochromic fine particles (E1) obtained in Example 1 were observed and measured using a scanning electron microscope (JSM6060 manufactured by JEOL Ltd.) The results are shown in Figures 5 and 6.

As shown in Figure 5, the photochromic core particles (R1) obtained in Reference Example 1 had the form of solid particles with large surface irregularities. In contrast, the photochromic core particles (E1) obtained in Example 1 had the form of particles with a smooth surface.

(Particle size distribution of photochromic core particles (R1) and coated photochromic fine particles (E1))
The particle size distribution of each of the photochromic core particles (R1) obtained in Reference Example 1 and the coated photochromic fine particles (E1) obtained in Example 1 was measured by a dynamic light scattering (DLS) method using a laser diffraction particle size distribution measuring device (SALD-7500 manufactured by Shimadzu Corporation). The obtained results are shown in FIG.

As shown in FIG. 7(a), the photochromic core particles (R1) obtained in Reference Example 1 had a particle size distribution generally ranging from 10 μm to 1000 μm, whereas the coated photochromic fine particles (E1) obtained in Example 1 had a particle size centered around 0.1 μm, and almost no particles reaching 1 μm were observed. The average particle size of the photochromic core particles (R1) obtained in Reference Example 1 from these measurements was 71.295 μm, whereas the average particle size of the coated photochromic fine particles (E1) in Example 1 was 0.1532 μm. Thus, it can be seen that the average particle size of the coated photochromic fine particles obtained by mixing the O/W emulsion with the supercritical fluid was clearly refined to the nano order compared to that before mixing.

(Photochromism of Coated Photochromic Fine Particles (E1))
The top lid of Example 1 was opened, and the reaction liquid (containing the coated photochromic fine particles (E1) of Example 1) present in the container 110 was separated into a sample bottle, and UV light (wavelength: 302 nm) was irradiated from the side of the sample bottle. A photograph of the sample bottle containing the reaction liquid before irradiation is shown in (a) of Figure 8, and a photograph of the sample bottle after irradiation with UV light is shown in (b) of Figure 8.

As is clear from a comparison of Figures 8(a) and (b), when UV light was irradiated from a non-UV light-irradiated state (Figure 8(a)), the reaction liquid in the sample bottle darkened and was observed to change color (Figure 8(b)). After that, when the UV light irradiation was stopped, it was confirmed that the dark reaction liquid had returned to its normal state (Figure 8(a)). This shows that the coated photochromic fine particles (E1) contained in the reaction liquid obtained in Example 1 had photochromic properties.

The present invention is useful in various technical fields, such as electronics, electricity, the automotive industry, textiles, cosmetics, and printing.

REFERENCE SIGNS LIST 100: Apparatus for producing coated photochromic fine particles 101: Cylinder 102: Drying tube 103: Cooling unit 104: Filter 105: Pressure boosting pump 106: Pressure gauge 107: Safety valve 108: Spare piping (preheater)
109 Check valve 110 Closable container 111 Stirrer 112 Thermostatic water bath 113 Pressure gauge 116 Temperature measuring unit 180 Premixture 182 Preliminary container 184 Power source 190 Ultrasonic vibrator 192 Vibration part 201 Pressure control valve 202, 203, 204, 208 Stop valve 205, 206 Tube

Claims (9)

A method for producing coated photochromic microparticles, comprising the steps of:
A step of directly irradiating a premix of photochromic core particles, a polymer, a polar solvent, and a low-polarity organic solvent with ultrasound to prepare an O/W emulsion;
mixing the O/W emulsion with a supercritical fluid in a closed container; and opening the closed container.
The method includes: The method of claim 1, wherein the supercritical fluid is supercritical carbon dioxide. The method according to claim 1 or 2, wherein the low polarity organic solvent is at least one solvent selected from the group consisting of toluene and hexane. The method according to any one of claims 1 to 3, wherein the polymer is a thermoplastic resin. The method of claim 4, wherein the thermoplastic resin is polystyrene. The method of any one of claims 1 to 5, wherein the mixing step is carried out at a temperature of 35°C to 55°C. A method according to any one of claims 1 to 6, wherein the ultrasonic irradiation is performed by a horn-type ultrasonic transducer. The method of claim 7, wherein the ultrasonic waves are irradiated uniaxially to the premix. An apparatus for producing coated photochromic fine particles, comprising:
an ultrasonic irradiation means for directly irradiating a premix of photochromic core particles, a polymer, a polar solvent, and a low-polarity organic solvent with ultrasonic waves to prepare an O/W emulsion; and a closable container in which the O/W emulsion and a supercritical fluid are mixed;
An apparatus comprising:

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