JP2015075542A - Method for manufacturing surface modified particle and method for manufacturing electrophoresis particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing surface modified particles, capable of more easily controlling a polymerization degree of a polymer formed on the surfaces of mother particles, and a method for manufacturing electrophoresis particles, capable of easily manufacturing the electrophoresis particles having desired mobility.SOLUTION: A method for manufacturing electrophoresis particles, capable of coupling a monomer 81 on the surfaces of core particles (mother particles) 71 by atom transfer radical polymerization to manufacture the electrophoresis particles (surface modified particles) 70 comprises: a dispersion preparation step of preparing a dispersion liquid 8 including core particles 71, a monomer 81 and a dispersion medium 82; and a salt addition step of adding a salt 83 obtained by ionically bonding at least one of an anion originated from an organic acid and a cation originated from an organic base to a dispersion 8.

Description

  The present invention relates to a method for producing surface-modified particles and a method for producing electrophoretic particles.

In general, it is known that when an electric field is applied to a dispersion system in which fine particles are dispersed in a liquid, the fine particles move (migrate) in the liquid by Coulomb force. This phenomenon is called electrophoresis. In recent years, an electrophoretic display device that displays desired information (image) using this electrophoresis has attracted attention as a new display device.
This electrophoretic display device has characteristics such as a display memory property and a wide viewing angle property in a state where voltage application is stopped, and a high-contrast display with low power consumption.
In addition, since the electrophoretic display device is a non-light emitting display device, it has a feature that it is easier on the eyes than a light emitting display device such as a cathode ray tube.

In such an electrophoretic display device, a dispersion system (electrophoretic dispersion) in which positively or negatively charged electrophoretic particles are dispersed in a dispersion medium is sealed between a pair of substrates having electrodes, and the pair of electrodes By applying a voltage between the electrophoretic particles, the electrophoretic particles migrate to one substrate side, and a desired image is displayed.
As the electrophoretic particles charged positively or negatively, generally, those having a coating layer formed by bonding a polymer to the surface of the mother particle are used, and a configuration including such a coating layer (polymer) is used. By doing so, the electrophoretic particles can be dispersed and charged in the electrophoretic dispersion.

The electrophoretic particles as described above are produced as follows using, for example, atom transfer radical polymerization (ATRP).
First, mother particles are prepared, and a silane coupling agent having a polymerization initiating group is bonded to the surface of the mother particles. Next, starting from this polymerization initiating group, a monomer is polymerized by atom transfer radical polymerization, thereby forming a polymer (polymer) on the surface of the mother particle. Thereby, properties such as dispersibility are imparted to the mother particles, and electrophoretic particles are produced (for example, see Patent Document 1).

JP 2007-225732 A

Atom transfer radical polymerization as described above has the advantage that the degree of polymerization can be controlled relatively accurately by the reaction time, and therefore it is easy to impart desired dispersibility to the mother particles.
On the other hand, not all of the monomers added to the reaction system are subjected to the polymerization reaction, and some remain unreacted. The method described in Patent Document 1 has a problem that it is difficult to control the degree of polymerization because the amount of the monomer remaining unreacted is relatively large.
One of the objects of the present invention is a method for producing surface-modified particles that make it easier to control the degree of polymerization of the polymer produced on the surface of the mother particles, and can easily produce electrophoretic particles having a desired mobility. The object is to provide a method for producing electrophoretic particles.

The above object is achieved by the present invention described below.
The method for producing surface-modified particles of the present invention is a method for producing surface-modified particles by bonding monomers to the surface of mother particles by atom transfer radical polymerization,
A dispersion preparation step of preparing a dispersion containing the mother particles, the monomer, and a dispersion medium;
A salt addition step of adding a salt formed by ion-bonding at least one of an anion derived from an organic acid and a cation derived from an organic base to the dispersion;
It is characterized by having.
As a result, the degree of polymerization of the polymer produced on the surface of the mother particles can be controlled more easily, and surface modified particles obtained by modifying the surface of the mother particles with a polymer having the desired degree of polymerization can be easily produced. it can.

In the method for producing surface-modified particles of the present invention, the amount of the salt added is preferably 0.1% by mass or more and 10% by mass or less of the dispersion medium.
Thereby, the salting-out effect can be sufficiently exhibited, and the reaction rate of atom transfer radical polymerization can be sufficiently increased.
In the method for producing surface-modified particles of the present invention, it is preferable to add the salt within 0.2 hours to 5 hours after the preparation of the dispersion.
This makes it easier for monomers to collect around the mother particles, and the reaction rate of polymerization transfer radical polymerization can be more reliably increased.

In the method for producing surface-modified particles of the present invention, the salt is preferably formed by ionic bonding of the anion derived from the organic acid and the cation derived from the organic base.
As a result, when the salt is dissolved in the dispersion medium, the anion derived from the organic acid and the cation derived from the organic base are combined (hydrated) with a relatively large number of water molecules, and the salting out ability (hydration power) is increased. It is thought to be higher. For this reason, by using a salt formed by ionic bonding of an anion derived from an organic acid and a cation derived from an organic base, the salting-out effect is particularly enhanced in the dispersion, and the reaction rate of atom transfer radical polymerization is particularly increased. be able to.

In the method for producing surface-modified particles of the present invention, the anion derived from the organic acid is preferably an acetate ion.
Thereby, even if the cation is not derived from an organic base, the salting-out effect can be particularly enhanced in the dispersion, and the reaction rate of atom transfer radical polymerization can be particularly increased.
In the method for producing surface-modified particles of the present invention, the cation derived from the organic base is preferably an ammonium ion.
Thereby, even if the anion is not derived from an organic acid, the salting-out effect can be particularly enhanced in the dispersion, and the reaction rate of atom transfer radical polymerization can be particularly increased.

The method for producing electrophoretic particles of the present invention is a method for producing electrophoretic particles obtained by bonding a monomer to the surface of a mother particle by atom transfer radical polymerization, and modifying the surface of the mother particle with the monomer,
A dispersion preparation step of preparing a dispersion containing the mother particles, the monomer, and a dispersion medium;
A salt addition step of adding a salt formed by ion-bonding at least one of an anion derived from an organic acid and a cation derived from an organic base to the dispersion;
It is characterized by having.
Thereby, electrophoretic particles having a desired mobility can be easily produced.

It is sectional drawing which shows the display apparatus containing the electrophoretic particle manufactured by the manufacturing method of the electrophoretic particle of this invention. It is a top view (top view) of the display apparatus shown in FIG. It is sectional drawing explaining the drive of the display apparatus shown in FIG. It is sectional drawing which shows typically the electrophoretic particle used for the display apparatus shown in FIG. It is the elements on larger scale of the electrophoretic particle shown in FIG. It is the schematic for demonstrating embodiment of the manufacturing method of the electrophoretic particle of this invention. It is a schematic diagram which shows the state by which the polymer was fixed to the surface of the mother particle through the silane coupling agent represented by General formula (5).

Hereinafter, the method for producing surface-modified particles and the method for producing electrophoretic particles of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
≪Display device≫
First, a display device including electrophoretic particles produced by the method for producing electrophoretic particles of the present invention will be described.

  1 is a cross-sectional view showing a display device including electrophoretic particles produced by the method for producing electrophoretic particles of the present invention, FIG. 2 is a plan view (top view) of the display device shown in FIG. 1, and FIG. FIG. 2 is a cross-sectional view illustrating driving of the display device illustrated in FIG. 1. In the following description, for convenience of explanation, the upper side in FIGS. 1 and 3 is described as “upper” and the lower side is described as “lower”. Further, as shown in FIG. 1, two directions orthogonal to each other in a plan view of the display device are referred to as “X direction” and “Y direction”.

A display device 20 shown in FIG. 1 is an electrophoretic display device that displays a desired image using particle migration. The display device 20 includes a display sheet (front plane) 21 and a circuit board (back plane) 22.
As shown in FIG. 1, the display sheet 21 is provided on a substrate (electrode substrate) 11 including a flat base 1 and a first electrode 3 provided on the lower surface of the base 1, and below the substrate 11. And a display layer 400 filled with the dispersion liquid 100 including the electrophoretic particles 70. In such a display sheet 21, the upper surface of the substrate 11 constitutes the display surface 111.

On the other hand, the circuit board 22 has a board 12 including a flat base 2 and a plurality of second electrodes 4 provided on the upper surface of the base 2, and an electric circuit (not shown) provided on the board 12. ing.
This electric circuit includes, for example, TFTs (switching elements) arranged in a matrix, gate lines and data lines formed corresponding to the TFTs, a gate driver that applies a desired voltage to the gate lines, and data lines A data driver for applying a desired voltage to the gate driver, and a gate driver and a controller for controlling the driving of the data driver.

Hereinafter, the structure of each part is demonstrated sequentially.
(substrate)
The base 1 and the base 2 are each composed of a sheet-like (flat plate) member, and have a function of supporting and protecting each member disposed therebetween. Each of the base portions 1 and 2 may be either flexible or hard, but is preferably flexible. By using the bases 1 and 2 having flexibility, it is possible to obtain a display device 20 having flexibility, that is, for example, a display device 20 useful in constructing electronic paper.

  A film-like first electrode 3 and second electrode 4 are provided on the surfaces of the bases 1 and 2 on the display layer 400 side, that is, on the lower surface of the base 1 and the upper surface of the base 2, respectively. In the present embodiment, the first electrode 3 is a common electrode, and the second electrode 4 is an individual electrode (pixel electrode connected to the TFT) divided so as to be aligned along the X direction and the Y direction. ing. In the display device 20, a region in which one second electrode 4 and the first electrode 3 overlap constitutes one pixel.

  Here, among the bases 1 and 2 and the electrodes 3 and 4, the base and the electrode arranged on the display surface 111 side are each transparent, that is, substantially transparent (colorless and transparent, colored and transparent). Or translucent). In the present embodiment, since the upper surface of the substrate 11 constitutes the display surface 111, at least the base 1 and the first electrode 3 are substantially transparent. Thereby, the image displayed on the display device 20 can be easily recognized visually from the display surface 111 side.

(Sealing part)
Between the board | substrate 11 and the board | substrate 12, the sealing part (sealing part) 5 is provided along those edge parts. The display layer 400 is hermetically sealed by the sealing portion 5. As a result, it is possible to prevent moisture from entering the display device 20 and more reliably prevent the display performance of the display device 20 from deteriorating.

(Wall)
As shown in FIG. 1, the display layer 400 includes a wall (partition) 91 provided so as to surround the outer edge thereof, and a space (dispersion liquid enclosed space) defined by the substrate 11, the substrate 12, and the wall 91. 101 and the dispersion liquid 100 filled in the space 101.
In the present embodiment, the cross-sectional shape of the wall portion 91 is a taper shape in which the width gradually decreases from the substrate 12 toward the substrate 11 side, but is not limited to such a shape, and is rectangular (rectangular), for example. There may be.
Moreover, the cross-sectional shape of the wall part 91 may not be constant over the whole, and a partially different shape may be sufficient as it.

(Dispersion)
The dispersion liquid 100 (electrophoretic dispersion liquid) includes the dispersion medium 7 and the electrophoretic particles 70 dispersed in the dispersion medium 7.
The electrophoretic particles 70 are positively or negatively charged and have a color different from the color exhibited by the dispersion medium 7.

  The color exhibited by the electrophoretic particles 70 is not particularly limited as long as the color is different from the color exhibited by the dispersion medium 7. For example, when the color exhibited by the dispersion medium 7 is light or white, the color is dark or black. On the other hand, when the color of the dispersion medium 7 is dark or black, it is preferably light or white. As a result, the difference in brightness between the electrophoretic particles 70 and the dispersion medium 7 increases. For example, when the electrophoretic particles 70 gather locally, the region and the adjacent region (the region occupied by the dispersion medium 7). ) And the brightness difference between the electrophoretic particles 70 is controlled, and display with high contrast becomes possible. The electrophoretic particles 70 will be described in detail later.

((Dispersion medium))
As the dispersion medium 7, a medium having a boiling point as high as 100 ° C. or higher and a relatively high insulating property is preferably used. Examples of the dispersion medium 7 include various water (eg, distilled water, pure water), alcohols such as butanol and glycerin, cellosolves such as butyl cellosolve, esters such as butyl acetate, ketones such as dibutyl ketone, Aliphatic hydrocarbons such as pentane (liquid paraffin), alicyclic hydrocarbons such as cyclohexane, aromatic hydrocarbons such as xylene, halogenated hydrocarbons such as methylene chloride, and aromatic heterocycles such as pyridine , Nitriles such as acetonitrile, amides such as N, N-dimethylformamide, carboxylate, silicone oil or other various oils, and the like can be used alone or as a mixture.

  Among these, as the dispersion medium 7, those mainly composed of aliphatic hydrocarbons (liquid paraffin) or silicone oil are preferable. Since the dispersion medium 7 containing liquid paraffin or silicone oil as a main component has a high aggregation suppressing effect on the electrophoretic particles 70, it is possible to suppress the display performance of the display device 20 from deteriorating with time. Further, liquid paraffin or silicone oil has an advantage that it has excellent weather resistance and high safety because it does not have an unsaturated bond.

  Moreover, as the dispersion medium 7, a material having a relative dielectric constant of 1.5 or more and 3 or less is preferably used, and a material having a dielectric constant of 1.7 or more and 2.8 or less is more preferably used. Such a dispersion medium 7 is excellent in the dispersibility of the electrophoretic particles 70 formed by bonding polymers having a relatively high degree of polymerization, and also has good electrical insulation. For this reason, it contributes to realization of the display device 20 with low power consumption and capable of high contrast display. The dielectric constant is a value measured at 50 Hz, and a value measured for the dispersion medium 7 having a water content of 50 ppm or less and a temperature of 25 ° C.

((Electrophoretic particles))
Hereinafter, the electrophoretic particles 70 included in the dispersion 100 will be described in detail.
FIG. 4 is a cross-sectional view schematically showing electrophoretic particles used in the display device shown in FIG. FIG. 5 is a partially enlarged view of the electrophoretic particles shown in FIG.
As shown in FIG. 4, the electrophoretic particle 70 includes a core particle 71 (mother particle) and a polymer 72 bonded to the surface of the core particle 71.

  Such electrophoretic particles 70 have high dispersibility with respect to the dispersion medium 7 by utilizing the polymer 72 having an affinity for the dispersion medium 7. Further, since the polymer 72 is provided, remarkable approaching between the electrophoretic particles 70 is suppressed, and thus aggregation of the electrophoretic particles 70 is suppressed. As a result, the electrophoretic resistance of the electrophoretic particles 70 is reduced, and sufficient electrophoretic electrophoresis is possible even under a weaker electric field. As a result, a display device that exhibits high responsiveness with low power consumption can be obtained. Further, high contrast and small display unevenness in display can be realized.

In addition, a dispersing agent may be added to the dispersion medium 7 as necessary, but even in that case, the polymer 72 is bonded to the surface of the core particle 71, so Since the addition amount of the dispersant added to the first electrode 3 can be reduced, it is possible to suppress a decrease in insulation between the first electrode 3 and the second electrode 4. Examples of the dispersant include polyamidoamine and salts thereof, basic functional group-modified polyurethane, basic functional group-modified polyester, basic functional group-modified poly (meth) acrylate, polyoxyethylene alkylamine, alkanolamine, and polyacrylamide. Etc., and a mixture of one or more of these is used.
The addition amount of the dispersant is preferably 0.3% by mass or less, and more preferably 0.1% by mass or less of the dispersion medium 7. By suppressing the addition amount of the dispersing agent within the above range, even if the dispersing agent is added, a decrease in insulation between the first electrode 3 and the second electrode 4 can be minimized.

Hereinafter, each part which comprises the electrophoretic particle 70 is demonstrated in detail sequentially.
First, the core particle 71 will be described.
The core particle 71 is not particularly limited. For example, oxide particles such as titanium oxide, zinc oxide, iron oxide, chromium oxide, and zirconium oxide, nitride particles such as silicon nitride and titanium nitride, zinc sulfide, and the like. Sulfide particles, boride particles such as titanium boride, inorganic pigment particles such as strontium chromate, cobalt aluminate, copper chromite, ultramarine, azo, quinacridone, anthraquinone, dioxazine, perylene Organic pigment particles such as can be used. Alternatively, composite particles obtained by applying a pigment to the surface of resin particles made of acrylic resin, urethane resin, urea resin, epoxy resin, polystyrene, polyester, or the like can be used.

The core particles 71 are preferably those having a hydroxyl group on the surface in consideration of the binding property to the polymer 72 described later. From this point, particles made of an inorganic material are preferably used.
The average particle size of the core particles 71 is not particularly limited, but is preferably 10 nm to 500 nm, more preferably 20 nm to 300 nm. By setting the average particle diameter of the core particles 71 within the above range, both sufficient chromaticity display by the electrophoretic particles 70 and rapid electrophoresis of the electrophoretic particles 70 can be achieved. As a result, both high contrast and high response speed in display can be achieved.

In addition, by setting the average particle diameter of the core particles 71 within the above range, it is possible to suppress sedimentation of the electrophoretic particles 70 and variations in electrophoretic speed, thereby suppressing display unevenness and display defects.
In addition, the average particle diameter of the core particle 71 means the volume average particle diameter measured with the dynamic light scattering type particle size distribution measuring apparatus (for example, product name: LB-500, manufactured by Horiba, Ltd.).

  In the present embodiment, the case where one type of core particle 71 is included in the dispersion 100 has been described, but a plurality of types of core particles 71 may be included. In this case, for example, by selecting a plurality of types of core particles 71 with a combination of greatly different brightness and chromaticity such as white and black, or light and dark, it is possible to display with better contrast. Moreover, when using multiple types of core particle 71, the kind, introduction amount, etc. of the polymer 72 may be the same or different between the core particles 71.

Next, the polymer 72 will be described.
The polymer 72 is obtained by polymerizing a monomer on the surface of the core particle 71 by atom transfer radical polymerization.
Such a polymer 72 may have a linear or branched molecular structure.
Among these, in the case of the polymer 72 having a linear molecular structure, the degree of difficulty in binding to the surface of the core particle 71 is slightly high, but a relatively high affinity for the dispersion medium 7 can be exhibited. For this reason, the electrophoretic particle 70 excellent in dispersibility can be obtained.

On the other hand, the polymer 72 having a branched molecular structure can exhibit a relatively high affinity for the dispersion medium 7 having a branched molecular structure. For this reason, the electrophoretic particle 70 which shows high dispersibility with respect to such a dispersion medium 7 is obtained.
Further, as the dispersion medium 7, a material having a relatively low polarity (nonpolar or low polarity) is often used. On the other hand, the polymer 72 may be slightly different depending on the structure of the side chain, but the polarity tends to be relatively low. Therefore, the electrophoretic particles 70 including such a polymer 72 exhibit good dispersibility with respect to the dispersion medium 7.

As shown in FIG. 5, the polymer 72 according to the present embodiment has a functional group-derived structure 721a derived from a reactive functional group capable of binding to the surface of the core particle 71 and a polymerization start derived from a compound having a polymerization initiating group. A first structure 721 including a group-derived structure 721b, a second structure 722 derived from a monomer polymerization portion obtained by polymerizing a monomer by atom transfer radical polymerization, and a halogen atom 723 deviated from the polymerization initiating group, It consists of
Among these, it is preferable that the first structure 721 is fixed to the surface of the core particle 71 by a covalent bond. Thereby, the polymer 72 can be more firmly bonded to the core particle 71.

  The functional group-derived structure 721 a is formed, for example, by bonding a compound having a hydrolyzable group that can react with the surface of the core particle 71 and a reactive functional group (such as various coupling agents) to the surface of the core particle 71. For example, the structure 721b derived from the polymerization initiating group is obtained by reacting a compound having a reactive functional group capable of reacting with the reactive functional group of the functional group derived structure 721a and the polymerization initiating group with the functional group derived structure 721a. The following structure is mentioned.

The polymerization initiating group generates a radical when the halogen atom 723 is removed. This radical reacts with the monomer, and the monomer is bonded to the polymerization initiating group-derived structure 721b. Thereafter, the halogen atom 723 is bonded to the tip of the bonded monomer and becomes a reaction point of another monomer. Accordingly, the halogen atom 723 is finally bonded to the tip of the second structure 722.
Moreover, the 1st structure 721 can be formed more easily by using the compound (various coupling agents etc.) which has both a hydrolysable group and a polymerization initiating group.

The polymer 72 is an organic group having a main skeleton and end groups and side chains bonded to the main skeleton.
Among these, examples of the main skeleton include a carbon-carbon bond, a carbon-oxygen bond, a siloxane bond, and other bonds, and one or more of these are mixed. Other bonds may include, for example, an unsaturated bond such as a double bond or a triple bond.

The total number of carbon atoms of the polymer 72 is not particularly limited, but is preferably about 45 or more and 5000 or less, and more preferably about 80 or more and 1200 or less.
Thereby, sufficient dispersibility can be imparted to the electrophoretic particles 70 while preventing the polymers 72 from being entangled with each other. If the total number of carbon atoms is less than the lower limit, depending on the amount of polymer 72 introduced, it may be difficult to impart sufficient dispersibility to the electrophoretic particles 70. On the other hand, when the total carbon number exceeds the upper limit, although depending on the introduction amount of the polymer 72, the polymers 72 may be entangled and the electrophoretic particles 70 may be aggregated. Further, it may be difficult to introduce the polymer 72 to the surface of the core particle 71.

  Moreover, the terminal and the side chain may be composed of a substituent having low polarity. As a result, the main skeleton is more compatible with the dispersion medium 7 and becomes easier to extend, so that the dispersibility of the electrophoretic particles 70 can be further improved. Specific examples of the substituent include a saturated hydrocarbon group such as an alkyl group. Such an effect is particularly effective for the nonpolar or low polarity dispersion medium 7.

The weight average molecular weight of the polymer 72 is preferably about 600 or more and 70000 or less, and more preferably about 1000 or more and 18000 or less.
By setting the weight average molecular weight within the above range, the length of the molecular structure of the polymer 72 is optimized, and both high dispersibility of the electrophoretic particles 70 with respect to the dispersion medium 7 and high mobility in electrophoresis are compatible. be able to.
In addition, the weight average molecular weight of the polymer 72 is a polystyrene conversion weight average molecular weight measured using gel permeation chromatography (GPC).

Further, the occupation ratio (coverage) of the region where the polymer 72 is bonded on the surface of the core particle 71 is preferably 0.05% or more and 20% or less, and is 0.1% or more and 10% or less. Is more preferably 0.2% or more and 5% or less. By setting the occupancy ratio of the region within the above range, the dispersibility mainly caused by the polymer 72 and the charging property mainly caused by the region where the polymer 72 is not bonded can be made more highly compatible. Can do. Thereby, for example, both dispersibility and charging characteristics can be achieved in an environment where the temperature at which the dispersion liquid 100 is placed changes greatly, or in an environment where the strength of the electric field is small. Good display is possible at. Also, by setting the occupation ratio within the above range, dispersion in the dispersibility and charging characteristics between the electrophoretic particles 70 can be suppressed. For this reason, the behavior of the electrophoretic particles 70 at the time of applying an electric field is easily aligned, and the occurrence of so-called display unevenness can be suppressed.
In addition, when the occupation rate of this area | region is less than the said lower limit, dispersibility falls and there exists a possibility that the electrophoretic particle 70 may aggregate depending on the environment where the dispersion liquid 100 is set | placed. On the other hand, when the occupation ratio of the region exceeds the upper limit, depending on the type of the core particle 71, the charging characteristics may be deteriorated.

Here, the occupation rate (coverage) [%] of the region where the polymer 72 is bonded to the surface of the core particle 71 is defined as “unit area” as the area occupied by one molecule of the polymer 72 on the surface of the core particle 71, When the number of molecules of the polymer 72 bonded to the surface of the core particle 71 is “number of molecules”, it can be obtained by the following formula.
Occupancy (coverage) = (unit area × number of molecules) / (surface area of core particle) × 100
Here, the “unit area” can be determined from the molecular structure of the polymer 72 by calculation.

The “number of molecules” is the mass [g] of the polymer 72 bonded per core particle, the molecular weight [g / mol] of the polymer 72, and the number of molecules per mole of 6.02 × 10 ²³ [pieces]. / Mol] and can be calculated.
When the abundance of the core particles 71 is 100 parts by mass, the abundance of the polymer 72 is preferably 0.1 parts by mass or more and 5 parts by mass or less, and 0.5 parts by mass or more and 4 parts by mass or less. Is more preferable. Thereby, since the occupation rate of the area | region which the polymer 72 has couple | bonded in the surface of the core particle 71 can be reliably stored in the range mentioned above, the above effects are exhibited reliably. Specifically, the dispersibility and the charging characteristics can be made more highly compatible, and the occurrence of display unevenness can be more reliably suppressed.
In addition, molecules other than the polymer 72 may be introduced on the surface of the core particle 71 as necessary. Examples of such molecules include a charged group that can be charged by dissociation or the like. By introducing the charging group, the charging characteristics of the core particles 71 can be freely controlled, and the mobility of the electrophoretic particles 70 in electrophoresis can be further increased.

The polymer 72 as described above is preferably introduced by covalent bonding to the surface of the core particle 71. Thereby, it is possible to more reliably prevent the polymer 72 from separating from the surface of the core particle 71. For this reason, the charged state of the electrophoretic particles 70 can be maintained over a long period of time.
In the above description, the example in which the surface-modified particles produced according to the present invention are applied to the electrophoretic particles has been described, but the present invention is also applicable to other than the electrophoretic particles. Surface modified particles other than electrophoretic particles include various fillers, various structural modifiers, various optical functional coating materials, various electromagnetic shielding materials, various secondary battery materials, various fluorescent materials, various electronic component materials, and various magnetic recordings. Examples include materials, various paints, various polishing materials, various pharmaceuticals, and various cosmetics.

While the configuration of the display device 20 has been described above, such a display device 20 is driven as follows, for example. In the following description, a case where a voltage is applied to one of the plurality of second electrodes 4 shown in FIG. 1 will be described. In the following description, it is assumed that the electrophoretic particles 70 are positively charged.
When a voltage at which the second electrode 4 has a negative potential is applied between the first electrode 3 and the second electrode 4, the electric field generated by the voltage application acts on the electrophoretic particles 70 in the display layer 400. To do. Then, the electrophoretic particles 70 migrate and gather on the second electrode 4 side. As a result, as shown in FIG. 3A, the display surface 111 displays mainly the color exhibited by the dispersion medium 7.
On the other hand, when a voltage at which the second electrode 4 has a positive potential is applied, the electric field generated by the voltage application acts on the electrophoretic particles 70 in the display layer 400. Then, the electrophoretic particles 70 migrate and gather on the first electrode 3 side. As a result, as shown in FIG. 3B, the color that the electrophoretic particles 70 mainly display is displayed on the display surface 111.

By driving the electrophoretic particles 70 as described above for each pixel (for each second electrode 4), a desired image can be displayed on the display surface 111.
As described above, in the display device 20, the electrophoretic particles 70 are migrated according to the direction of the electric field, and an image display is performed based on a difference in chromaticity and lightness caused thereby. At this time, in order to perform a good image display, it is necessary that the plurality of electrophoretic particles 70 exist stably in the dispersion medium 7 without aggregating with each other and quickly migrate when an electric field is generated. Become.

≪Method for producing electrophoretic particles≫
Next, an embodiment of a method for producing surface-modified particles of the present invention will be described. In the following description, an example in which electrophoretic particles are produced as an example of surface-modified particles (an embodiment of the method for producing electrophoretic particles of the present invention) will be described.
FIG. 6 is a schematic view for explaining an embodiment of the method for producing electrophoretic particles of the present invention. In FIG. 6, the illustration of halogen atoms that have deviated from the polymerization initiating group is omitted.

  The method for producing the electrophoretic particle 70 is a method in which the monomer 81 is bonded to the surface of the core particle 71 by atom transfer radical polymerization (ATRP), and the dispersion 8 containing the core particle 71, the monomer 81 and the dispersion medium 82 is prepared. A dispersion preparation step to be prepared; and a salt addition step of adding to the dispersion 8 a salt 83 formed by ionic bonding of at least one of an anion derived from an organic acid and a cation derived from an organic base. Hereinafter, each step will be described.

[1] Dispersion Preparation Step First, as shown in FIG. 6A, a dispersion 8 containing core particles 71, a monomer 81, a catalyst, and a dispersion medium 82 is prepared.
(Core particles)
Among these, as the core particle 71, the particles as described above can be used, but depending on the surface state of the core particle 71, a hydroxyl group and other functional groups may be exposed. A compound having a polymerization initiating group (coupling agent) is introduced into these hydroxyl groups and functional groups. Thereby, the starting point of atom transfer radical polymerization can be formed.
In addition, when hydroxyl groups and other functional groups are not exposed on the surface of the core particle 71, plasma treatment, corona treatment, surface treatment with a solvent, surface treatment with a surfactant, etc. are performed as necessary. A hydroxyl group or a functional group can be introduced.

The compound having a polymerization initiating group may be any compound as long as it has a polymerization initiating group and a hydrolyzable group or reactive functional group. A hydrolyzable group or a reactive functional group is bonded to a hydroxyl group or a functional group exposed on the surface of the core particle 71 to fix the polymerization initiating group 711 on the surface of the core particle 71 as shown in FIG. can do.
The polymerization initiating group 711 can be a starting point for polymerization in atom transfer radical polymerization, and by using the polymerization initiating group 711, the living radical polymerization can proceed more efficiently.

  Examples of the polymerization initiating group that is polymerized by atom transfer radical polymerization include those derived from organic halides and sulfonyl halide compounds, and those derived from organic halides are represented by the following general formula (1). Those having a benzyl derivative, those having an α-haloester group represented by the following general formula (2), and those having an α-haloamide group represented by the following general formula (3) can be mentioned. Furthermore, what is represented by the following general formula (4) is mentioned as what originates in a halogenated sulfonyl compound.

［式中、Ｒ^１およびＲ^２は、それぞれ独立して、水素、Ｘ、および炭素原子の数が１〜２０であり任意の−ＣＨ_２−が−Ｏ−またはシクロアルキレン基で置換されてもよいアルキル基から選択される基を表し、Ｘは、塩素、臭素またはヨウ素を表す。］

[Wherein, R ¹ and R ² each independently represent hydrogen, X, and the number of carbon atoms is 1 to 20, and any —CH ₂ — may be substituted with —O— or a cycloalkylene group. Represents a group selected from good alkyl groups, X represents chlorine, bromine or iodine. ]

［式中、Ｒ^３およびＲ^４は、それぞれ独立して、水素、炭素数１〜２０のアルキル基、炭素数６〜１２のアリール基または炭素数７〜２０のアリールアルキル基を表し、Ｒ^３およびＲ^４がともに水素であることが除かれる。また、Ｘ、は塩素、臭素またはヨウ素を表す。］

[Wherein, R ³ and R ⁴ each independently represent hydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an arylalkyl group having 7 to 20 carbon atoms, and R ³ And R ⁴ are both hydrogen. X represents chlorine, bromine or iodine. ]

［式中、Ｒ^３およびＲ^４は、それぞれ独立して、水素、炭素数１〜２０のアルキル基、炭素数６〜１２のアリール基または炭素数７〜２０のアリールアルキル基を表し、Ｒ^３およびＲ^４がともに水素であることが除かれる。また、Ｘ、は塩素、臭素またはヨウ素を表す。］

[Wherein, R ³ and R ⁴ each independently represent hydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an arylalkyl group having 7 to 20 carbon atoms, and R ³ And R ⁴ are both hydrogen. X represents chlorine, bromine or iodine. ]

［式中、Ｘ、は塩素、臭素またはヨウ素を表す。］
上述したような重合開始基を有する化合物が、例えばシラン系カップリング剤である場合、その化合物を下記一般式（５）で表すことができる。

[Wherein, X represents chlorine, bromine or iodine. ]
When the compound having a polymerization initiating group as described above is, for example, a silane coupling agent, the compound can be represented by the following general formula (5).

［式中、Ａは、重合開始基を表し、Ｚは、それぞれ独立して、水素原子、メチル基、塩素原子、メトキシ基またはエトキシ基を表すものの、３つのＺの全てが水素原子またはメチル基である場合は除かれる。また、ｎは、１〜２０の整数を表す。］

[Wherein, A represents a polymerization initiating group, and Z each independently represents a hydrogen atom, a methyl group, a chlorine atom, a methoxy group or an ethoxy group, but all three of Z are a hydrogen atom or a methyl group. Is excluded. Moreover, n represents the integer of 1-20. ]

Such a silane coupling agent having a polymerization initiating group A can be obtained by introducing a polymerization initiating group into a silane coupling agent having no polymerization initiating group.
Examples of silane coupling agents having no polymerization initiating group include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriphenoxysilane, p-styryltrimethoxysilane, p-styryltriethoxysilane, and p-styryltri. Phenoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-acryloxypropyltriphenoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3- Methacryloxypropyltriphenoxysilane, 3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-glycidoxypropyltrimeth Sisilane, allyltrimethoxysilane, allyltriethoxysilane, allyltriphenoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, n-propyltrimethoxysilane, n-butyltriethoxysilane, n-hexyltrimethoxysilane , N-hexyltriethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, etc., and one or more of these may be used in combination Can do.
The compound having a polymerization initiating group is not limited to a silane coupling agent, and may be a titanium coupling agent or a compound derived from silicone oil.

By using such a compound, a polymerization initiating group can be introduced on the surface of the core particle 71.
Specifically, the hydrolyzable group Z included in the silane coupling agent represented by the general formula (5) causes a hydrolysis reaction with a hydroxyl group on the surface of the core particle 71 and a dehydration condensation reaction. As shown in FIG. 7, a covalent bond of a bond of —Si—O— is generated. Thereby, the polymerization initiating group is reliably fixed to the surface of the core particle 71 by a covalent bond.

(monomer)
From the polymerization initiation group 711 thus introduced, the monomer 81 is polymerized by atom transfer radical polymerization.
The monomer 81 has a polymerizable group that can be polymerized by atom transfer radical polymerization, and is classified into a nonionic monomer, a cationic monomer, and an anionic monomer based on the properties imparted to the electrophoretic particles 70. . In addition, as a polymeric group which the monomer 81 has, what contains a carbon-carbon double bond like a vinyl group, a styryl group, and a (meth) acryloyl group is mentioned, for example.

When a monomer 81 containing a nonionic monomer is used, the monomer polymerization portion formed by atom transfer radical polymerization exhibits excellent affinity for the dispersion medium 7 contained in the dispersion 100. . Therefore, the electrophoretic particles 70 having excellent dispersibility in the dispersion 100 can be obtained.
Examples of such nonionic monomers include 1-hexene, 1-heptene, 1-octene, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, stearyl (meth) acrylate, lauryl ( Acrylic monomers such as meth) acrylate, decyl (meth) acrylate, isooctyl (meth) acrylate, isostearyl (meth) acrylate, isobonyl (meth) acrylate, cyclohexyl (meth) acrylate, pentafluoro (meth) acrylate, styrene, 2 -Methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 2-propylstyrene, 3-propylstyrene, 4-propylstyrene, 2-isopropyl Pirusuchiren, 3-isopropyl styrene, 4-isopropyl styrene, and styrene-based monomers such as 4-tert-butylstyrene.
In addition, according to atom transfer radical polymerization, the degree of polymerization of the monomer 81 can be controlled relatively easily and strictly. Therefore, a monomer polymerization portion whose length is controlled with high accuracy can be obtained. As a result, the dispersibility of the electrophoretic particles 70 can be controlled more finely. That is, the electrophoretic particles 70 having high dispersibility and hardly aggregated are obtained.

  The addition amount of the monomer 81 is appropriately set according to the length (degree of polymerization) of the polymer 72 to be formed, and is not limited, but is 0.01 mass of the addition amount of the core particle 71. % To about 20% by mass or less, more preferably about 0.05% to 15% by mass or less. By setting the addition amount of the monomer 81 within the above range, the reaction rate of atom transfer radical polymerization can be sufficiently increased. If the amount of monomer 81 is below the lower limit, depending on the composition of monomer 81 and the amount of core particle 71 added, the reaction rate of atom transfer radical polymerization may not be sufficiently increased. On the other hand, if the amount of the monomer 81 exceeds the upper limit, depending on the composition of the monomer 81 and the amount of the core particle 71 added, the fluidity of the dispersion is lowered, and thereby the ease of movement of the monomer 81 is also lowered. Again, there is a possibility that the reaction rate of atom transfer radical polymerization cannot be sufficiently increased.

(catalyst)
In the atom transfer radical polymerization, a catalyst is added to the dispersion 8 containing the core particle 71 and the monomer 81.
As the catalyst to be added, a catalyst capable of making the growth terminal a polymerizable group in the growth process of the monomer polymerization portion, or a catalyst having a relatively low Lewis acidity is used. Such catalysts include, for example, transition metal halides such as Cu, Fe, Au, Ag, Hg, Pd, Pt, Co, Mn, Ru, Mo and Nb, and organic groups such as copper phthalocyanine as ligands. Among them, transition metal complexes having a transition metal halide as a main component are preferably used.
Examples of the ligand include bipyridine.

(Dispersion medium)
Examples of the dispersion medium 82 for preparing the dispersion 8 include water, alcohols such as methanol, ethanol, and butanol, hydrocarbons such as hexane, octane, benzene, toluene, and xylene, diethyl ether, tetrahydrofuran, and the like. Examples include ethers, halogenated aromatic hydrocarbons such as chlorobenzene and o-dichlorobenzene, and these can be used alone or as a mixed solvent.

In the dispersion 8 containing the core particle 71, the monomer 81, the catalyst, and the dispersion medium 82 for dispersing them, the polymerization initiating group 711 introduced on the surface of the core particle 71 and the polymerizable group contained in the monomer 81 are used. A polymerization reaction occurs between the two. Thereby, a monomer polymerization part grows on the surface of the core particle 71.
For example, when the polymerization initiating group A is introduced onto the surface of the core particle 71 using the silane coupling agent represented by the general formula (5), the monomer polymerization portion formed by the above-described atom transfer radical polymerization is It is represented as a schematic diagram shown in FIG. FIG. 7 is a schematic diagram showing a state in which the polymer 72 is fixed to the surface of the core particle 71 through the silane coupling agent represented by the general formula (5). The functional group-derived structure 721a, the polymerization initiation group-derived structure 721b, the first structure 721, and the second structure 722 in FIG. 7 correspond to those shown in FIG.

  The polymerization initiating group A reacts with the monomer M by generating a radical when cleavage occurs in the dormant species. Thereafter, the halogen atom moves relative to the radical, and the radical is deactivated again to a dormant species (halogen atom X in FIG. 7). As a result, the methylene group in the silane coupling agent and the monomer M are linked through the structure A ′ derived from the polymerization initiating group A. The new species M reacts with the dormant species to cause a radical polymerization reaction again. As a result, as long as the monomer M is present, the radical polymerization of the monomer M can be continuously performed. Thereafter, if the monomer M is newly added, the polymerization can be continued again.

As described above, in the atom transfer radical polymerization, the degree of polymerization of the monomer polymerization part can be freely and accurately controlled by adjusting the amount of the monomer M supplied to the reaction system, the reaction time, and the amount of catalyst.
In addition, when the polymer polymerization parts are compared with each other, the degree of polymerization can be easily adjusted, so that the molecular weight distribution of the polymer 72 can be narrowed, and electrophoresis with little individual difference in characteristics such as dispersibility, mobility, and difficulty in aggregation. Particles 70 are obtained.
In addition, n in FIG. 7 represents the integer of 1-20. Further, m in FIG. 7 is appropriately set according to the number of monomers M to be polymerized, and is set to, for example, about 5 or more and 200 or less.

Moreover, it is preferable to perform a deoxygenation process with respect to the dispersion liquid before a polymerization reaction starts. Examples of the deoxidation treatment include substitution after vacuum degassing with an inert gas such as argon gas and nitrogen gas, purge treatment, and the like.
In the polymerization reaction, the polymerization reaction of the monomer 81 can be performed more quickly and reliably by heating the temperature of the dispersion 8 to a predetermined temperature (a temperature at which the monomer 81 and the catalyst are activated).
The heating temperature varies slightly depending on the type of the catalyst and is not particularly limited, but is preferably about room temperature to 100 ° C. The heating time is preferably about 10 hours or more and 20 hours or less when the heating temperature is within the above range.

[2] Salt addition step Next, the salt 83 is added to the dispersion 8 prepared in the dispersion preparation step (see FIG. 6B). This salt 83 is a salt formed by ionic bonding of at least one of an anion derived from an organic acid and a cation derived from an organic base. When such a salt 83 is added to the dispersion 8, the dispersion 8 has a salting-out effect. That is, it is considered that when the salt 83 is added to the dispersion 8 and the salt 83 is dissolved, the dispersibility (solubility) of the monomer 81 in the dispersion 8 is lowered. Thereby, the probability that the monomer 81 approaches the core particle 71 is increased, and the monomer concentration around the core particle 71 is increased. As a result, the reaction probability between the polymerization initiating group 711 introduced on the surface of the core particle 71 and the polymerizable group contained in the monomer 81 increases, and the reaction rate of atom transfer radical polymerization increases. For this reason, when adjusting a polymerization degree by reaction time, for example, the time concerning reaction can be shortened. In addition, a monomer polymerization portion having a higher degree of polymerization can be obtained even in a shorter time.
As described above, in the present invention, by providing the salt addition step, the reaction rate of atom transfer radical polymerization can be increased, and the degree of polymerization of the polymer 72 introduced into the core particle 71 can be more easily controlled. As a result, the electrophoretic particles 70 in which the length (polymerization degree) of the polymer 72 is strictly controlled can be obtained (see FIG. 6C).

More specifically, the salt 83 added in this step is a salt formed by ionic bonding of an anion derived from an organic acid and a cation derived from an organic base, or an anion derived from an organic acid or an organic base. Is a salt formed by ion bonding of other cations with other ions.
Among these, examples of the organic acid include acetic acid, formic acid, glycolic acid, citric acid, tartaric acid, mandelic acid, glutaric acid, oxalic acid, malic acid, malonic acid, benzoic acid, phthalic acid, and succinic acid. . When these become ions, for example, acetate ions and the like are obtained. Even if the cation is not derived from an organic base, the acetate ion can particularly enhance the salting-out effect in the dispersion 8 and can particularly increase the reaction rate of atom transfer radical polymerization.
On the other hand, examples of the organic base include quaternary ammonium. When these become ions, for example, ammonium ions and the like are obtained. Even if the anion is not derived from an organic acid, the ammonium ion can particularly enhance the salting-out effect in the dispersion 8 and can particularly increase the reaction rate of atom transfer radical polymerization.

  In addition, examples of other ions that ionically bond with anions derived from organic acids and cations derived from organic bases include phosphate ions, borate ions, carbonate ions, nitrate ions, nitrite ions, and sulfate ions. Various anions such as halide ions such as anion, fluoride ion, chloride ion, bromide ion and iodide ion derived from inorganic acid, sodium ion, magnesium ion, potassium ion, calcium ion, aluminum ion and barium ion And various cations such as metal ions.

  Of the salts 83 as described above, in particular, a salt formed by ionic bonding of an anion derived from an organic acid and a cation derived from an organic base is preferably used. Such a salt 83 is dissolved in the dispersion medium 82. At this time, an anion derived from an organic acid and a cation derived from an organic base are combined (hydrated) with a relatively large number of water molecules, and the salting-out ability (water Is considered to be high. For this reason, by using a salt formed by ionic bonding of an anion derived from an organic acid and a cation derived from an organic base, the salting-out effect becomes particularly high in the dispersion 8, and the reaction rate of atom transfer radical polymerization is particularly increased. Can be increased.

In addition, since the monomer 81 contained in the dispersion liquid 8 is generally hydrophobic, the dispersion medium may be nonpolar, but it is preferable to use a highly polar one (polar dispersion medium). . It is considered that the salting-out effect is further enhanced by using such a dispersion medium 82. For this reason, it is considered that the reaction rate of atom transfer radical polymerization can be further increased.
The presence or absence of the polarity of the dispersion medium 82 can be roughly divided according to, for example, the dielectric constant. Specifically, the dielectric constant of the dispersion medium 82 at 25 ° C. is preferably 8 or more and 120 or less, and more preferably 15 or more and 100 or less. It is considered that the dispersion medium 82 having such a dielectric constant contributes to the enhancement of the salting out effect.

  The amount of the salt 83 to be added is appropriately set according to the amount of the dispersion medium 82, but is preferably an amount that is 0.1% by mass or more and 10% by mass or less of the dispersion medium 82, and 0.5 It is more preferable that the amount is from 3% by mass to 3% by mass. By setting the amount of the salt 83 to be added within the above range, the salting-out effect can be sufficiently exhibited, and the reaction rate of atom transfer radical polymerization can be sufficiently increased. If the amount of the salt 83 is below the lower limit, depending on the amount of the monomer 81 added and the composition of the salt 83, the salting-out effect becomes insufficient and the reaction rate of atom transfer radical polymerization cannot be sufficiently increased. There is a fear. On the other hand, when the amount of the salt 83 exceeds the upper limit, depending on the amount of the monomer 81 added and the composition of the salt 83, the fluidity of the dispersion 8 is lowered, and thereby the ease of movement of the monomer 81 is also lowered. Again, there is a possibility that the reaction rate of atom transfer radical polymerization cannot be sufficiently increased.

  In addition, it is preferable to add the salt 83 after a predetermined time has elapsed after the preparation of the dispersion liquid 8. Thus, by setting time between the preparation of the dispersion 8 and the addition of the salt 83, the monomer 81 is easily collected around the core particle 71, and the reaction rate of the polymerization transfer radical polymerization can be more reliably increased. it can. In other words, the salt 83 is added to the dispersion 8 containing the core particles 71 before the monomer 81 is added, or the monomer 81 and the salt 83 are added to the dispersion 8 containing the core particles 71. If added at the same time (so that no time is taken between preparation of dispersion 8 and addition of salt 83), salt 83 gathers before monomer 81 around core particle 71, and core There is a possibility that the reaction probability between the polymerization initiating group 711 introduced on the surface of the particle 71 and the monomer 81 is lowered. The affinity of the monomer 81 for the core particle 71 is higher than the affinity of the monomer 81 for the dispersion medium 82 due to the introduction of the polymerization initiating group 711 and its accompanying structure on the surface of the core particle 71. It is considered that the monomer 81 is gathered around the core particle 71 based on the difference in affinity.

Specifically, the elapsed time from the addition of the core particle 71, the monomer 81, and the catalyst to the dispersion medium 82 to prepare the dispersion 8 and the addition of the salt 83 is 0.1 hours or more and 5 hours or less. It is preferable that it is 0.5 hours or more and 2 hours or less. By setting the time until the salt 83 is added within the above range, the reaction rate of atom transfer radical polymerization can be particularly increased. If the elapsed time is less than the lower limit, depending on the amount of monomer 81 or salt 83 added, sufficient time for the monomer 81 to collect around the core particle 71 cannot be secured, and the reaction of atom transfer radical polymerization The speed may not be increased sufficiently. On the other hand, if the elapsed time exceeds the upper limit, depending on the amount of the monomer 81 or salt 83 added, the effect cannot be further increased, and the time required for manufacturing the electrophoretic particles 70 may be increased.
Further, after the salt addition, stirring may be further continued. The stirring time at this time is preferably 30 minutes or more and 8 hours or less, and more preferably 2 hours or more and 5 hours or less.

As described above, the polymer 72 is introduced onto the surface of the core particle 71, and the electrophoretic particle 70 is obtained.
The electrophoretic particles 70 may be subjected to a solid / liquid separation process or a cleaning process as necessary. Examples of the solid-liquid separation process include decantation, filtration, and centrifugation. Further, the cleaning effect can be enhanced by repeating the process of immersing the electrophoretic particles 70 in the cleaning liquid and the process of performing the solid-liquid separation process. At this time, it has been found by the present inventor that the number of times of immersing in a cleaning liquid or performing a solid-liquid separation process can be reduced through the step [2]. The reason why such a secondary effect is brought about is not clear, but the polymer 72 introduced by the addition of the salt 83 is likely to be stretched, or the interval between the polymers 72 is likely to be widened. One reason is that the cleaning liquid penetrates into the gap between the polymers 72 and the remaining catalyst is washed away.

≪Electronic equipment≫
Each of the display devices 20 described above can be incorporated into various electronic devices. Specific electronic devices include, for example, electronic paper, electronic books, televisions, viewfinder types, monitor direct-view video tape recorders, car navigation devices, pagers, electronic notebooks, calculators, electronic newspapers, word processors, personal computers, work Examples include a station, a videophone, a POS terminal, and a device provided with a touch panel.
As mentioned above, although this invention was demonstrated based on embodiment of illustration, this invention is not limited to these. For example, an arbitrary target process may be added.

Next, specific examples of the present invention will be described.
1. Production of electrophoretic particles Electrophoretic particles were produced as follows. The production conditions in each example and each comparative example are shown in Table 1.

(Example 1)
[1] First, 20 mL of water was placed in an eggplant flask, and 2 g of bipyridine was further added, followed by stirring at room temperature (25 ° C.) for 3 hours.
Then 0.5 g of CuCl was added while bubbling with nitrogen. Thereby, a catalyst solution was obtained.
[2] On the other hand, isopropyl alcohol and isooctyl acrylate as a monomer were placed in another eggplant flask to prepare a monomer dispersion. Note that the dielectric constant of isopropyl alcohol is 19, and the dielectric constant of water is 80.

[3] Next, 200 mL of water was placed in another eggplant flask, and isopropyl alcohol and titanium oxide particles (“CR90” manufactured by Ishihara Sangyo Co., Ltd.) as core particles were added. The average particle diameter of the titanium oxide particles was 0.25 μm.
[4] Next, the monomer dispersion was placed in the eggplant flask prepared in [3]. And it stirred at room temperature for 20 minutes, bubbling with nitrogen. The amount of monomer in the monomer dispersion was set to an amount that would be 5% by mass of the titanium oxide particles.

[5] Subsequently, the catalyst solution prepared in [1] was added and stirred at room temperature for 40 minutes. As a result of adding the monomer dispersion, the ratio of water to isopropyl alcohol was 1: 1 by volume.
[6] Next, ammonium acetate as a salt was added, and the mixture was again stirred at room temperature for 4 hours. In addition, after adding a monomer dispersion liquid at process [4], it was 1 hour until ammonium acetate was added at this process. The amount of ammonium acetate added was 0.01% by mass of the dispersion medium.
Thereby, electrophoretic particles were obtained.

(Examples 2 to 7)
Electrophoretic particles were obtained in the same manner as in Example 1, except that the monomer composition, monomer addition amount, salt composition, salt addition amount, and salt addition timing were as shown in Table 1, respectively.
(Example 8)
Electrophoretic particles were obtained in the same manner as in Example 1 except that the monomer was changed to isostearyl acrylate and the addition amount of the salt was changed to 0.1% by mass.
(Examples 9 to 16)
Electrophoretic particles were obtained in the same manner as in Example 1, except that the monomer composition, monomer addition amount, salt composition, salt addition amount, and salt addition timing were as shown in Table 1, respectively.

(Comparative Example 1)
Electrophoretic particles were obtained in the same manner as in Example 1 except that the salt addition operation in Step [6] of Example 1 was omitted.
(Comparative Example 2)
Electrophoretic particles were obtained in the same manner as in Example 1 except that sodium chloride was used as the salt and the addition amount of the salt was 1% by mass of the dispersion medium.

(Comparative Example 3)
In step [4] of Example 1, electrophoretic particles were obtained in the same manner as in Example 3 except that the monomer dispersion was added and at the same time the salt (ammonium acetate) was added.
(Comparative Example 4)
Electrophoretic particles were obtained in the same manner as in Example 8, except that the salt addition operation in Step [6] of Example 8 was omitted.

(Comparative Example 5)
Electrophoretic particles were obtained in the same manner as in Example 8 except that sodium chloride was used as the salt and the addition amount of the salt was 1% by mass of the dispersion medium.
(Comparative Example 6)
In step [4] of Example 8, electrophoretic particles were obtained in the same manner as in Example 9 except that the monomer dispersion was added and at the same time the salt (ammonium acetate) was added.

2. 2. Evaluation of electrophoretic particles 2.1 Evaluation of easy cleaning The electrophoretic particles obtained in each of Examples and Comparative Examples are formed in a dispersion. For this reason, the dispersion obtained in the step [6] was subjected to solid-liquid separation by decantation, and the electrophoretic particles were washed using a mixed solvent of water and isopropyl alcohol.

In this washing treatment, the remaining part after removing the supernatant liquid by decantation is placed in a centrifuge tube, and IPA of 3 times mass and water of 5 times mass are added to the core particles and stirred. This is a process of repeating a process and a second process of centrifuging at 6000 rpm for 5 minutes by a centrifuge and eliminating the generated supernatant.
Then, the color of the supernatant liquid to be excluded in the second process is visually checked, the density of the color (blue due to the catalyst) is confirmed, and the washing process is repeated until the color disappears and the supernatant liquid becomes transparent. I counted the number of times.
Table 1 shows the number of cleaning treatments determined as described above.

2.2 Evaluation of Polymer Formation Amount The total amount of polymer introduced into the electrophoretic particles obtained in each Example and each Comparative Example was measured. Then, the ratio of the total amount of the introduced polymer to the mass of the core particle was calculated as “polymer formation amount”.
In addition, the ratio (percentage) of the polymer formation amount to the total amount of added monomers was calculated as “polymer yield”.
Table 1 shows the polymer formation amount and polymer yield calculated as described above.

2.3 Evaluation of dispersibility The electrophoretic particles obtained in each Example and each Comparative Example are dispersed in an electrophoretic dispersion medium (Isoper M, manufactured by ExxonMobil Corporation), and an ultrasonic wave is applied for 1 hour. An electrophoretic dispersion was prepared. The content of the electrophoretic particles in the electrophoretic dispersion was set to 10% by mass.

Next, an electrophoretic display device as shown in FIG. 1 was manufactured using this electrophoretic dispersion. The specifications of each part are as follows.
Base 1 and base 2
Size: 50 mm long x 50 mm wide x 100 μm thick
Constituent material: Polyethylene 1st electrode 3 and 2nd electrode 4 (In addition, the 2nd electrode is not divided | segmented.)
Size: 40mm long x 40mm wide x 4μm thick
Constituent material: ITO
・ Spacer size: Width 5mm x Height 50μm
Constituent material: Epoxy resin

A predetermined voltage (15 V, 400 msec) was applied to each electrophoretic display device so as to collect electrophoretic particles on the first electrode side.
As a result, white was displayed on the display surface. This white display is derived from titanium oxide, and the electrophoretic particles are dispersed as uniformly as possible without being aggregated as much as possible, so that a good white color with a high reflectance is displayed.
Therefore, the dispersibility of the electrophoretic particles was relatively evaluated by measuring the reflectance of white display. This evaluation was performed according to the following evaluation criteria.

<Evaluation criteria for dispersibility>
A: Dispersibility is particularly good (reflectance is particularly high and display unevenness is particularly small).
○: Dispersibility is good (high reflectance and little display unevenness)
Δ: Dispersibility is slightly good (reflectance is slightly high, display unevenness is slightly small)
X: Dispersibility is not good (low reflectance, many display unevenness)
Table 1 shows the evaluation results of the dispersibility obtained as described above.

  As is clear from Table 1, the electrophoretic particles obtained in each example were subjected to atom transfer radical polymerization for the most part of the added monomer. As a result, a relatively high proportion of the total amount of added monomer was obtained. It was confirmed that a polymer formed by polymerizing the monomers was formed. On the other hand, the amount of the polymer introduced into the electrophoretic particles obtained in each comparative example was relatively low with respect to the amount of added monomer. Thus, according to the present invention, since the polymer yield was high, it was recognized that the degree of polymerization of the polymer can be easily controlled, and a polymer having the desired degree of polymerization can be easily formed.

In addition, the number of cleaning processes required for cleaning the electrophoretic particles obtained in each example was compared with the number of cleaning processes required for cleaning the electrophoretic particles obtained in each comparative example. It was found that the former number was less than the latter number. From this, it was recognized that according to the present invention, a secondary effect that the catalyst and the like attached to the electrophoretic particles can be easily washed away is brought about. A single cleaning process may take up to about an hour, and such an effect is associated with increasing the production efficiency of electrophoretic particles (surface-modified particles) and reducing the amount of cleaning liquid used. This is very useful for reducing environmental impact.
Moreover, it was also recognized that the electrophoretic particles obtained in each example had higher dispersibility than the electrophoretic particles obtained in each comparative example. This is considered to be due to the fact that, according to the present invention, a polymer having a relatively uniform degree of polymerization can be formed, whereby the dispersibility of each electrophoretic particle can be easily aligned.

DESCRIPTION OF SYMBOLS 1 ... Base 2 ... Base 3 ... 1st electrode 4 ... 2nd electrode 5 ... Sealing part 7 ... Dispersion medium 70 ... Electrophoretic particle 71 ... Core particle 711 ... Polymerization initiating group 72 …… Polymer 721 …… First structure 721a …… Functional group-derived structure 721b …… Polymerization initiation group-derived structure 722 …… Second structure 723 …… Halogen atom 8 …… Dispersion 81… Monomer 82 …… Dispersion medium 83 ... salt 11 ... substrate 12 ... substrate 20 ... display device 21 ... display sheet 22 ... circuit board 91 ... wall portion 100 ... dispersion liquid 101 ... space 111 ... display surface 400 ... ... display layer

Claims (7)

A method for producing surface-modified particles by bonding monomers to the surface of mother particles by atom transfer radical polymerization,
A dispersion preparation step of preparing a dispersion containing the mother particles, the monomer, and a dispersion medium;
A salt addition step of adding a salt formed by ion-bonding at least one of an anion derived from an organic acid and a cation derived from an organic base to the dispersion;
A method for producing surface-modified particles, comprising:   The method for producing surface-modified particles according to claim 1, wherein the amount of the salt added is 0.1% by mass or more and 10% by mass or less of the dispersion medium.   The method for producing surface-modified particles according to claim 1 or 2, wherein the salt is added within 0.2 hours to 5 hours after preparation of the dispersion.   The method for producing surface-modified particles according to any one of claims 1 to 3, wherein the salt is formed by ionic bonding of an anion derived from the organic acid and a cation derived from the organic base.   The method for producing surface-modified particles according to claim 4, wherein the anion derived from the organic acid is an acetate ion.   The method for producing surface-modified particles according to claim 4, wherein the cation derived from the organic base is an ammonium ion. A method for producing electrophoretic particles obtained by bonding a monomer to the surface of a mother particle by atom transfer radical polymerization, and modifying the surface of the mother particle with the monomer,
A dispersion preparation step of preparing a dispersion containing the mother particles, the monomer, and a dispersion medium;
A salt addition step of adding a salt formed by ion-bonding at least one of an anion derived from an organic acid and a cation derived from an organic base to the dispersion;
A method for producing electrophoretic particles, comprising:

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