JP2020023631A - Production method of polymethyl methacrylate particle, production method or colloidal crystal, and aqueous suspension liquid - Google Patents

Abstract

To provide a technique that produces a clean particle the particle surface of which is not modified and produces a colloidal crystal of a polymethyl methacrylate particle capable of exhibiting a desired structural color by a simple method.SOLUTION: The production method of a polymethyl methacrylate particle has a step of subjecting an aqueous medium and a (meth)acrylic monomer to dispersion treatment by agitating the same to produce an aqueous dispersion and a step of adding a polymerization initiator to the aqueous dispersion and polymerizing the (meth)acrylic monomer to produce an aqueous suspension liquid including a polymethyl methacrylate particle.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing polymethyl methacrylate particles, a method for producing colloidal crystals, and an aqueous suspension.

  Conventionally, it is known that a colloidal crystal in which particles having a particle size from nano size to micron size are regularly arranged exhibits a structural color of an arbitrary color resulting from Bragg reflection corresponding to the particle size. Therefore, in order to obtain a structural color of any color, it is necessary to control the particle size of the particles in the colloidal crystal. Therefore, in the synthesis of polymer particles, surfactants, heterogeneous monomers, ionic copolymers, etc. A third component was used. At this time, the surface of the synthesized particles is modified.

  In recent years, a method has been reported in which the size of PMMA particles having a clean surface is controlled only by ultrasonic treatment, even in multiple stages, without adding the third component. For example, Non-Patent Documents 1 to 3 disclose techniques relating to a nanoemulsion solution and a polymer fine particle thereof using a tandem ultrasonic emulsification method without using a surfactant.

Koji Nakabayashi, Maya Kojima, Shinsuke Inagi, Yuki Hirai and Mahito Atobe, "Size-Controlled Synthesis of Polymer Nanoparticles with Tandem Acoustic Emulsification Followed by Soap-Free Emulsion Polymerization", ACS Macro Letters, 2013, 2 (6), pp.482 ? 484 Yuki Hirai, Koji Nakabayashi, Maya Kojima and Mahito Atobe, "Size-controlled spherical polymer nanoparticles: Synthesis with tandem acoustic emulsification followed by soap-free emulsion polymerization and one-step fabrication of colloidal crystal films of various colors", Ultrasonics Sonochemistry, 2014 , 21, pp.1921-1927 Yuki Hirai, Miharu Koshino and Yoshimasa Matsumura, "Synthesis of Spherical Polymer Nanoparticles Reflecting Size of Monomer Droplets Formed by Tandem Acoustic Emulsification", Mahito Atobe Chemistry Letters, 2015, 44, pp.1584-1585

However, even in the techniques disclosed in Non-Patent Documents 1 to 3, the fact is that colloidal crystals that reflect light of all three colors of RGB, which are the three primary colors of light, have not yet been prepared. That is, a method for preparing a colloidal crystal having a clean particle surface and exhibiting a desired structural color has not yet been established.
In the prior art, most reports have shown that colloidal crystals of PMMA particles that reflect light of an arbitrary wavelength form a face-centered cubic lattice using a special device such as dip coating or a flow cell.

  The present invention has been made in view of the above-described problems, and in a simple method, clean particles having unmodified particle surfaces are obtained, and polymethyl methacrylate particles capable of expressing a desired structural color. The present invention relates to a technique for obtaining colloidal crystals.

The present invention
An aqueous medium, and a process of stirring and dispersing the (meth) acrylic monomer to obtain an aqueous dispersion;
A step of further adding a polymerization initiator to the aqueous dispersion, and polymerizing the (meth) acrylic monomer to obtain an aqueous suspension containing polymethyl methacrylate particles;
A method for producing poly (methyl methacrylate) particles, comprising:

  Further, the present invention provides a method for producing colloidal crystals, comprising a step of colloidally crystallizing the surface of polymethyl methacrylate particles obtained by the above-mentioned method for producing polymethyl methacrylate particles in a clean state.

Also, the present invention
Provided is an aqueous suspension containing polymethyl methacrylate particles, wherein the aqueous suspension is configured to satisfy the following conditions.
Conditions: One drop of the aqueous suspension was dropped on a polyethylene terephthalate film, and left standing at 20 ° C. and 50% RH for 24 hours. The surface of the colloidal crystals obtained was clean polymethyl methacrylate. When the average particle size of the particles is Rs, Rs is 100 nm or more and 400 nm or less.

  According to the present invention, there is provided a technique for obtaining colloidal crystals of poly (methyl methacrylate) particles, which can obtain clean particles having an unmodified particle surface and exhibit a desired structural color by a simple method. it can.

FIG. 2 is a photograph showing a colloidal crystal of PMMA particles obtained in Example 1. FIG. 4 is a photograph showing a colloidal crystal of PMMA particles obtained in Example 2. FIG. 5 is a photograph showing a colloidal crystal of PMMA particles obtained in Example 3. FIG. 4 is a photograph showing colloidal crystals of PMMA particles obtained in Example 4. FIG. 9 is a photograph showing a colloidal crystal of PMMA particles obtained in Example 5. FIG. 9 is a photograph showing a colloidal crystal of PMMA particles obtained in Example 6.

  Hereinafter, embodiments of the present invention will be described. Hereinafter, methyl methacrylate monomer is also referred to as “MMA”, and polymethyl methacrylate particles are also referred to as “PMMA particles”.

<Method for producing PMMA particles>
The method for producing PMMA particles in the present embodiment includes:
An aqueous medium, and a process of stirring and dispersing the (meth) acrylic monomer to obtain an aqueous dispersion;
A step of further adding a polymerization initiator to the aqueous dispersion and polymerizing the (meth) acrylic monomer to obtain an aqueous suspension containing PMMA particles;
Having.
As a result, clean PMMA particles having an arbitrary diameter and an unmodified surface can be easily obtained. As a result, the interaction between the PMMA particles can be reduced, and the colloidal crystallization of the particles can be stably obtained. Further, since the PMMA particles can be adjusted to an arbitrary diameter, the structural color of the colloidal crystal can be controlled to a desired color while the particle surface is clean.

[Water dispersion]
The aqueous dispersion in the present embodiment is obtained by stirring and dispersing an aqueous medium described below and a (meth) acrylic monomer.
The dispersion treatment is for uniformly dispersing the (meth) acrylic monomer in the aqueous medium, and does not chemically react the (meth) acrylic monomer.
From the viewpoint of obtaining PMMA particles having a clean surface by a simple method, it is preferable to perform ultrasonic treatment. The ultrasonic treatment is preferably performed at 10 Hz to 200 kHz, more preferably at 1 kHz to 100 kHz, and still more preferably at 5 kHz to 20 kHz.

The aqueous dispersion preferably contains 1 to 1000 parts by weight of the aqueous medium, more preferably 8 to 100 parts by weight, based on 1 part by weight of the (meth) acrylic monomer. This makes it possible to prepare PMMA particles having an arbitrary diameter, and it is possible to obtain a colloidal crystal having a desired structural color with a clean particle surface.
For example, to obtain a blue structural color, the weight ratio between MMA and the aqueous medium (MMA / aqueous medium) is 0.1 (parts by weight) /99.9 (parts by weight) to 3 (parts by weight) / 97 (parts by weight) is preferable, and 0.5 (parts by weight) /99.5 (parts by weight) to 2 (parts by weight) / 98 (parts by weight) is more preferable.
To obtain a green structural color, the weight ratio of MMA to the aqueous medium (MMA / aqueous medium) is 2 (parts by weight) / 98 (parts by weight) to 6 (parts by weight) / 94 (parts by weight). It is more preferably 4 (parts by weight) / 96 (parts by weight) to 6 (parts by weight) / 94 (parts by weight).
When it is desired to obtain a yellow-green structural color, the weight ratio between MMA and the aqueous medium (MMA / aqueous medium) is 6 (parts by weight) / 94 (parts by weight) to 8 (parts by weight) / 92 (parts by weight). And more preferably 7 (parts by weight) / 93 (parts by weight) to 8 (parts by weight) / 92 (parts by weight).
When it is desired to obtain a red structural color, the weight ratio of MMA to the aqueous medium (MMA / aqueous medium) is 8 (parts by weight) / 92 (parts by weight) to 17 (parts by weight) / 83 (parts by weight). More preferably, 12 (parts by weight) / 88 (parts by weight) to 14 (parts by weight) / 86 (parts by weight) are more preferable.
To obtain a white structural color, the weight ratio of MMA to the aqueous medium (MMA / aqueous medium) is 14 (parts by weight) / 86 (parts by weight) to 30 (parts by weight) / 70 (parts by weight). More preferably, the ratio is 22 (parts by weight) / 78 (parts by weight) to 26 (parts by weight) / 74 (parts by weight).

The (meth) acrylic monomer has one or more kinds of “(meth) acrylic groups” and is used for polymerization.
(Meth) acrylic monomers include monofunctional and polyfunctional (meth) acrylic monomers.

  Examples of the monofunctional (meth) acrylic monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, cumyl (meth) acrylate, cyclohexyl (meth) acrylate, and myristyl. Alkyl (meth) acrylates such as (meth) acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate, isobornyl (meth) acrylate, (meth) acrylonitrile, (meth) acrylamide, (meth) acrylic acid, glycidyl (meth) Monofunctional monomers such as acrylate, 2-hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate are exemplified.

Examples of the polyfunctional (meth) acrylic monomer include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, 1.6-hexanediol di (meth) acrylate, Di (meth) acrylates such as methylolpropane di (meth) acrylate; tri (meth) acrylates such as trimethylolpropane tri (meth) acrylate, ethylene oxide-modified trimethylolpropane tri (meth) acrylate, and pentaerythritol tri (meth) acrylate Is mentioned.
Among them, preferred are methyl methacrylate, ethyl methacrylate, butyl methacrylate and (meth) acrylic acid.
These may be used alone or in combination of two or more.

  Specific examples of the polymer formed from these monomers include a methacrylate polymer or a copolymer of a methacrylate and an acrylate.

  Examples of the aqueous medium include water such as tap water, ion-exchanged water, distilled water, and ultrapure water, or a mixed medium of water and a hydrophilic organic solvent.

Examples of the hydrophilic organic solvent include ketones such as acetone and ethyl methyl ketone; pyrrolidones such as N-methylpyrrolidone and N-ethylpyrrolidone; ethers such as diethyl ether and dipropylene glycol dimethyl ether; methanol, ethanol, n Alcohols such as propanol, isopropanol, ethylene glycol and diethylene glycol; and amides such as β-alkoxypropionamide. These may be used alone or in combination of two or more.
The amount of the hydrophilic organic solvent is preferably 0 to 20% by mass relative to the total amount of the aqueous medium, and from the viewpoint of obtaining clear PMMA particles, it is more preferable that the hydrophilic organic solvent does not contain the hydrophilic organic solvent.

[Water suspension]
The water suspension in the present embodiment contains PMMA particles.
The aqueous suspension is obtained by adding a polymerization initiator described below to the aqueous dispersion and polymerizing the (meth) acrylic monomer to generate PMMA particles.
The polymerization conditions are preferably a temperature of 30 to 100 ° C., a rotation speed of 50 to 1000 rpm, and a polymerization time of 0.5 to 24 hours. Further, the polymerization temperature is more preferably from 40 to 100C, and still more preferably from 60 to 80C. Further, a more preferable rotation speed is 50 to 1000 rpm, and 100 to 500 rpm is still more preferable. Further, the polymerization time is more preferably 0.5 to 12 hours, and still more preferably 1 to 3 hours. Due to the formation of PMMA particles, the aqueous suspension becomes cloudy.

  Examples of the polymerization initiator include azo compounds such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile); ammonium persulfate, potassium persulfate, and Persulfates such as sodium sulfate; and peroxides such as hydrogen peroxide, t-butyl hydroperoxide, benzoyl peroxide, and lauoil peroxide. These polymerization initiators may be used alone or in combination of two or more.

  The amount of the polymerization initiator to be used may be appropriately adjusted according to the reaction conditions, and the polymerization initiator or a decomposition product thereof is contained in the aqueous suspension within a range that does not impair the function or characteristics of the aqueous suspension. May be. The amount of the polymerization initiator to be used is preferably 0.1% by mass or more and 20% by mass or less, more preferably 5% by mass or more and 15% by mass or less based on the total amount of the (meth) acrylic monomer.

  Further, it is preferable to remove the remaining (meth) acrylic monomer, which has not been reacted, from the aqueous suspension in the present embodiment. For the removal, for example, it is preferable to perform centrifugal dehydration by supplying the water suspension after polymerization to a centrifuge (centrifugal dehydrator).

  The aqueous suspension is substantially free of surfactant. Thereby, the surface of the PMMA particles becomes clear, and the surface treatment for dispersing the PMMA particles in the aqueous suspension can be omitted. In addition, substantially means that an additive is added in order to obtain dispersibility of PMMA particles.

  The aqueous suspension of the present embodiment may be a crosslinking agent, a thickener, a photosensitizer, a curing catalyst, an ultraviolet absorber, a light stabilizer, or an antifoaming agent, depending on the purpose, within a range not to impair the effects of the invention. , A plasticizer, a surface conditioner, an anti-settling agent, a heat stabilizer, a lubricant, a coloring agent, a silicone oil, a foaming agent, and an additive such as a flame retardant, but from the viewpoint of obtaining clear PMMA particles. And no additives.

The above crosslinking agents are used to crosslink the monomers. Thereby, the glass transition temperature of the PMMA particles can be increased, and the heat resistance can be improved. According to the findings of the present inventors, it is estimated that the glass transition temperature can be increased by 5 ° C. or more.
Examples of the crosslinking agent include vinyl compounds such as vinyl methacrylate; (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, (poly) tetramethylene glycol di (meth) acrylate, and the like. (Poly) alkylene glycol di (meth) acrylate; 1,6-hexanediol di (meth) acrylate, 1,8-octanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, 1, 10-decanediol di (meth) acrylate, 1,12-dodecanediol di (meth) acrylate, 3-methyl-1,5-pentanediol di (meth) acrylate, 2,4-diethyl-1,5-pentanediol Di (meth) acrylate, butylethylpropanediol Alkanediol-based di (meth) acrylates such as di (meth) acrylate, 3-methyl-1,7-octanediol di (meth) acrylate and 2-methyl-1,8-octanediol di (meth) acrylate; multifunctional Compounds such as (meth) acrylate are exemplified. These can be used alone or in combination of two or more.

In the present embodiment, the aqueous suspension is an aqueous suspension containing polymethyl methacrylate particles, and is configured to satisfy the following conditions.
Conditions: One drop of the aqueous suspension was dropped on a polyethylene terephthalate film, and left standing at 20 ° C. and 50% RH for 24 hours. The surface of the colloidal crystals obtained was clean polymethyl methacrylate. When the average particle size of the particles is Rs, Rs is 100 nm or more and 400 nm or less.

  By satisfying the above conditions, the aqueous suspension of the present embodiment can obtain a colloidal crystal of polymethyl methacrylate particles having a clean surface capable of expressing a desired structural color by a simple method. An aqueous suspension satisfying such conditions can be obtained by the method described in the method for producing PMMA particles described above.

Further, the water suspension preferably has a CV value represented by the following formulas (1) and (2) of 20% or less.
CV value (%) = {standard deviation S / Rs (nm)} × 100 (1)

  In the aqueous suspension of the present embodiment, by setting the above-mentioned CV value to 20% or less, the particle diameter of the colloidal crystal becomes more uniform, and a desired structural color is easily developed.

  Further, the aqueous suspension of the present embodiment can be applied to various uses such as a paint composition and a coating composition.

<Method for producing colloidal crystals>
The method for producing a colloidal crystal of the present embodiment includes a step of causing the surface of the polymethyl methacrylate particles obtained by the method for producing polymethyl methacrylate particles to undergo colloidal crystallization in a clean state. In particular, when colloidal crystallization is performed, it is preferable that the aqueous suspension is dropped on the substrate, the aqueous medium is volatilized and dried, whereby the polymethyl methacrylate particles are colloidally crystallized.
Conventionally, when preparing colloidal crystals from an aqueous suspension, a special method using a dipping method or a fluid cell has been used. On the other hand, according to the method for producing a colloidal crystal of the present embodiment, a colloidal crystal can be obtained by a simple method and a desired structural color can be exhibited. Although the details of such a reason are not clear, since the surface of the polymethyl methacrylate particles obtained by the method for producing polymethyl methacrylate particles in the present embodiment is clean, a colloid crystal is obtained by a simple method. It is speculated that this can be done.

<PMMA particles>
In the present embodiment, the PMMA particles include the following.
(I) Those contained in an aqueous suspension.
(Ii) An aqueous dispersion of an aqueous suspension is removed by natural drying to form a regular array and form colloidal crystals.

  In the case of (i), the average particle size Rc of the PMMA particles in the aqueous suspension is preferably 100 nm or more and 400 nm or less, more preferably 110 nm or more and 370 nm or less, and 115 nm or more and 330 nm or less. It is more preferred that there be. By setting Rc to be equal to or more than the lower limit value, in a colloidal crystal to be formed later, transmission of visible light can be suppressed and a structural color due to light reflection can be obtained. On the other hand, by controlling Rc to be equal to or less than the upper limit value, in a colloidal crystal to be formed later, light of all wavelengths in a visible light region is prevented from being reflected by irregular reflection on the crystal surface to appear white, and structural colors other than white are suppressed. Easier to obtain.

  The average particle size Rc of the PMMA particles (i) can be measured, for example, by a dynamic light scattering method (DLS) using “ELSZ-2” manufactured by Otsuka Electronics Co., Ltd.

In the case of (ii), natural drying means dropping an aqueous suspension onto a polyethylene terephthalate (PET) film and volatilizing the aqueous medium at room temperature (20 ° C.) and 50% RH. Thereby, a colloidal crystal in which PMMA particles are regularly arranged can be obtained. In addition, colloidal crystals can be grown by increasing the regularly arranged portions with the evaporation of water.
In the present invention, by evaporating the aqueous medium in the aqueous suspension containing PMMA particles, the PMMA particles can be easily arranged regularly and form a face-centered cubic lattice. Thereby, a desired structural color corresponding to the PMMA particle diameter is obtained.

  In the present embodiment, when the average particle diameter of the PMMA particles in the colloidal crystal of (ii) is Rs (nm), Rs is preferably 100 nm or more and 400 nm or less, and 110 nm or more and 370 nm or less. Is more preferable, and it is still more preferable that it is 115 nm or more and 330 nm or less. By setting Rs to the lower limit or more, it is possible to suppress the transmission of visible light and obtain a structural color by light reflection in the colloidal crystal. On the other hand, by controlling Rs to be equal to or less than the upper limit, in the colloidal crystal, light of all wavelengths in the visible light region is prevented from being reflected white due to irregular reflection of the crystal surface, and a structural color other than white is easily obtained. Become.

  In the measurement of the average particle size Rs of the PMMA particles in the colloidal crystal of (ii), the sample is coated with amorphous (amorphous) osmium by osmium vapor deposition, and a scanning electron microscope (SEM: “SU8020” manufactured by Hitachi, Ltd.) is used. Then, the particle size of 50 PMMA particles in the sample is measured, and the average value is determined.

  Since the PMMA particles in the present embodiment are obtained by the above-described specific manufacturing method, the surfaces are clean and do not contain impurities, so that good redispersibility can be obtained.

  PMMA particles can be applied to various uses such as coating compositions, ink compositions, electric / electric materials, and adhesives. Among them, from the viewpoint of obtaining the design effect of the PMMA particles, it is suitable for a light diffusion sheet, a colloidal photonic crystal, a mold for an inverted opal structure, and the like.

  Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than the above can be adopted.

  Next, the present invention will be described in detail with reference to examples, but the contents of the present invention are not limited to the examples.

[Preparation of water suspension]
<Example 1>
0.1335 g (1.34 mmol) of methyl methacrylate monomer (MMA) and 11.22 g of ion-exchanged water were added to a 15 ml pressure-resistant tube. Next, a horn-type vibrator (3 mmΦ) was inserted to perform ultrasonic irradiation at 20 kHz. Thereafter, 0.03 g (0.11 mmol) of potassium peroxodisulfate (K ₂ S ₂ O ₈ ) was added as a polymerization initiator, the pressure-resistant tube was sealed, and the tube was heated in an oil bath. The mixture was stirred at 250 rpm and the polymerization was allowed to proceed for 2 hours. Thereafter, the polymerization liquid was cooled with ice water to stop the polymerization, and a milky white aqueous suspension was obtained.

<Example 2>
A milky-white aqueous suspension was obtained in the same manner as in Example 1 except that the amount of MMA was changed to 0.534 g (5.34 mmol).

<Example 3>
A milky-white aqueous suspension was obtained in the same manner as in Example 1, except that the amount of MMA was changed to 0.801 g (8.01 mmol).

<Example 4>
A milky-white aqueous suspension was obtained in the same manner as in Example 1, except that the amount of MMA was changed to 1.068 g (1.065 mmol).

<Example 5>
A milky-white aqueous suspension was obtained in the same manner as in Example 1, except that the amount of MMA was changed to 1.335 g (11.34 mmol).

<Example 6>
A milky-white aqueous suspension was obtained in the same manner as in Example 5, except that 0.0145 g (0.013 mmol) of vinyl methacrylate was added as a crosslinking agent.

  The following evaluation and measurement were performed on the aqueous suspension obtained in the above example. Table 1 shows the results.

[Measurement of particle size-1]
The average particle size Rc of the PMMA particles in the aqueous suspension obtained in the example was measured by a dynamic light scattering method (DLS) using “ELSZ-2” manufactured by Otsuka Electronics Co., Ltd.

[Measurement of particle size-2]
The aqueous suspension obtained in the example was dropped on a PET film, dried at room temperature (20 ° C.) and 50% RH to grow colloidal crystals. With respect to the obtained colloidal crystal, the sample is coated with osmium amorphous (amorphous) by osmium vapor deposition, and subjected to a scanning electron microscope (SEM: “SU8020” manufactured by Hitachi, Ltd.) to obtain particles of 50 PMMA particles in the colloidal crystal. The diameter was measured, and the average value was set to Rs.

[Calculation of CV value]
CV value (%) = {standard deviation S / Rs (nm)} × 100 (1)

[Redispersibility / Chemical resistance]
The aqueous suspension obtained in the example was subjected to a centrifugal separation (13.5 rpm, 10 min) using a centrifuge (MCF-1350) manufactured by MS Co., Ltd. Next, the clear supernatant liquid was removed to obtain a wet precipitate (PMMA particles). Thereafter, the precipitate was allowed to stand at 20 ° C. and 50% RH for 76 hours to obtain dry powdery PMMA particles.
The obtained PMMA particles were added to acetone, THF, and chloroform, respectively.
The presence or absence of PMMA particles was confirmed by a dynamic light scattering method (DLS) using "ELSZ-2" manufactured by Otsuka Electronics Co., Ltd., and evaluated according to the following criteria. When added to THF and chloroform, they were visually observed and evaluated according to the following criteria.
：: PMMA particles were observed or clouded.
×: No PMMA particles were observed or no cloudiness was observed.

[Heat-resistant]
The aqueous suspension obtained in the example was centrifuged, and the precipitate was collected and dried at room temperature to obtain PMMA particles. The glass transition temperature (° C.) of the obtained PMMA particles was measured using a differential scanning calorimeter (“DSC8500” manufactured by Perkinelmer).

[Observation of structural color]
The aqueous suspension obtained in the example was dropped on a PET film, dried at room temperature (20 ° C.) and 50% RH to grow colloidal crystals. With respect to the obtained colloidal crystal, the sample was coated with osmium amorphous (amorphous) by osmium vapor deposition, and the colloidal crystal was observed with a scanning electron microscope (SEM: “SU8020” manufactured by Hitachi, Ltd.). 1 to 6, SEM photographs are shown in the order of Examples 1 to 6.
In addition, the obtained colloidal crystals were visually observed by a plurality of specialist evaluators to evaluate the hue of the structural color. Table 1 shows the results.

  From FIGS. 1 to 6, it is understood that PMMA particles are regularly arranged and colloidal crystals are obtained. It was also confirmed that the particle diameter of the PMMA particles increased in the order of Examples 1 to 6. It is understood from Table 1 that when the particle size of the PMMA particles changes, the hue of the observed structural color also changes.

Claims (9)

An aqueous medium, and a process of stirring and dispersing the (meth) acrylic monomer to obtain an aqueous dispersion;
A step of further adding a polymerization initiator to the aqueous dispersion, and polymerizing the (meth) acrylic monomer to obtain an aqueous suspension containing polymethyl methacrylate particles;
A method for producing poly (methyl methacrylate) particles, comprising:   The method for producing poly (methyl methacrylate) particles according to claim 1, wherein the aqueous dispersion contains 10 to 1000 parts by weight of the aqueous medium based on 1 part by weight of the (meth) acrylic monomer.   The method for producing poly (methyl methacrylate) particles according to claim 1 or 2, wherein ultrasonic treatment is performed in the step of obtaining the aqueous dispersion.   The method for producing poly (methyl methacrylate) particles according to any one of claims 1 to 3, wherein substantially no surfactant is used.   The method for producing poly (methyl methacrylate) particles according to any one of claims 1 to 4, further comprising a step of removing remaining (meth) acrylic monomer in the step of polymerizing.   A method for producing colloidal crystals, comprising a step of colloidally crystallizing the surface of the poly (methyl methacrylate) particles obtained by the method for producing poly (methyl methacrylate) particles according to claim 1 in a clean state.   The step of colloidal crystallization, the aqueous suspension is dropped on a substrate, the aqueous medium is volatilized and dried to colloidally crystallize polymethyl methacrylate particles having a clean surface, Item 7. A method for producing a colloidal crystal according to Item 6. An aqueous suspension containing poly (methyl methacrylate) particles, wherein the aqueous suspension is configured to satisfy the following conditions.
Conditions: One drop of the aqueous suspension was dropped on a polyethylene terephthalate film, and left standing at 20 ° C. and 50% RH for 24 hours. The surface of the colloidal crystals obtained was clean polymethyl methacrylate. When the average particle size of the particles is Rs, Rs is 100 nm or more and 400 nm or less. The aqueous suspension according to claim 8, wherein the CV value represented by the following formulas (1) and (2) is 20% or less.
CV value (%) = {standard deviation S / Rs (nm)} × 100 (1)