JP2010020220A - Electrophoresis particle, method for producing it, image display medium, and image display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrophoresis particles excellent in memory properties, a method for efficiently generating the electrophoresis particles, an image display medium containing the electrophoresis particles, and an image display having the image display medium. <P>SOLUTION: The method for generating the electrophoresis particles includes a polymerizing group addition process for adding a polymerizing group to the surface of carbon black by using a silane coupling agent having the polymerizing group, a cationic group addition process for adding a cationic group to the surface of the carbon black by using a silane coupling agent having a cationic group, and a graft polymerization process for performing graft polymerization on the surface of the carbon black by using the polymerizing group. Preferably, the polymerizing group addition process and the cationic group addition process are carried out by using a silane coupling agent having both the polymerizing group and the cationic group. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophoretic particle having excellent memory properties, a method for producing the electrophoretic particle, an image display medium, and an image display device.

  Conventionally, cathode ray tubes (CRT), liquid crystal displays, and the like have been used as image display devices that display images such as characters, still images, and moving images. These image display devices can display images instantly and can be rewritten, but they are difficult to carry around, eyes are easily fatigued, and images cannot be displayed when the power is turned off. There are problems such as.

On the other hand, images such as characters and still images are distributed or stored after being recorded on a paper medium using a printer. A paper medium on which such an image is recorded is widely used as a hard copy. The hard copy has features such as easy-to-read characters, less fatigue of eyes, reading in a free posture, lightweight and free to carry than a display. However, the hard copy is discarded or recycled after use, but requires a lot of labor and cost, and there is a problem in terms of resource saving.
For this reason, there is an increasing need for a rewritable paper-like image display medium that has the advantages of both display and hard copy. For example, polymer dispersed liquid crystal elements, bistable cholesteric liquid crystal elements, electrochromic elements Electrophoretic elements and the like are known. Since these image display media are of a reflective type, they can display bright images and have a memory property, and thus are attracting attention. Among these, an image display medium using an electrophoretic element is excellent in terms of display quality, power consumption during display operation, and the like.

  In such an image display medium, for example, a colored dispersion medium is sealed between a pair of transparent electrodes. In the colored dispersion medium, electrophoretic particles having different colors and charged surfaces are provided. Is distributed. For this reason, when a voltage opposite to the charged charge of the electrophoretic particles is applied to one of the transparent electrodes, the electrophoretic particles are deposited and the color of the electrophoretic particles is observed. In addition, when the same voltage as the charged charge of the electrophoretic particles is applied to one of the transparent electrodes, the electrophoretic particles move to the other side of the transparent electrode, and the color of the dispersion medium is observed. An image display medium using an electrophoretic element displays an image based on such a principle.

The stability of the electrophoretic particles in the dispersion medium is generally obtained by an electrostatic effect or a steric effect (also called an adsorption layer effect).
Regarding the electrostatic effect, DLVO theory is known, and the spread of the electric double layer and the interface potential (so-called ζ potential) are important factors. In order to form these, the presence of ions is required.
Regarding the steric effect, for example, Non-Patent Document 1 discloses a method for producing a stable non-aqueous solvent dispersion. In Non-Patent Document 1, a block copolymer or graft copolymer containing a component having compatibility with particles dispersed in a solvent and a component having solubility in the solvent is produced in the solvent. Has been.
As described above, a number of proposals have been made regarding the method for producing electrophoretic particles, and these mainly describe the dispersion stability as electrophoretic particles.

Further, in Patent Document 1, a diazonium group is preferable for reacting carbon black with a compound. “In order to bond a wide range of functional groups to carbon black in a series of patents of Cabot Corporation, Boston, Massachusetts” Are described using the chemistry of " This Patent Document 1 discloses a diazonium reaction of carbon black as a dispersion used for inkjet, not an electrophoretic dispersion.
Patent Document 2 discloses compatibility and incompatibility of charged particles in a suspension fluid in order to control optical stability of electrophoretic particles. Display characteristics as well as dispersion stability are important for the preparation of electrophoretic particles. Display characteristics mainly include high contrast and memory. In previous proposals, emphasis has been placed on improving black and white reflectance. For this reason, many proposals regarding improvement of the surface treatment method of particles are seen. However, the biggest selling point when using electrophoretic particles as a display medium is the memory property, and it is clear that the use as an image display medium is difficult without the memory property.

Regarding the memory property, for example, Patent Document 3 proposes that the memory property is imparted by adding alkyl polyetheramine as an additive to the graft-polymerized titania particles and carbon black particles.
Patent Document 4 proposes an example in which organic particles, inorganic particles, or particles obtained by adding a charge control agent to these particles are used as the electrophoretic particles.
However, it is difficult to obtain such electrophoretic particles having a sufficiently large charge amount, and it cannot be said that the sensitivity to an electric field is sufficiently high.

Patent Document 5 proposes blending polyisobutylene in order to improve the memory performance of the image display medium.
Patent Document 6 proposes the content of binding a polymer having an ionic group in the regular chain by surface living polymerization of titania particles.
Patent Document 7 proposes a display method capable of full-color display having memory properties by using metal colloid particles having a plasmon coloring function.
In these proposals, it is natural that when electrophoretic particles are used, there is naturally a memory property, but there is no description regarding a method that expresses a special memory property. And even if we try the examples of these proposals, the memory performance is not seen at all, and even if the electrophoretic particles are prepared and the charge control agent or polymer is added, sufficient memory performance is achieved. The fact is that does not appear.

  Thus, the electrophoretic particles are not originally provided with a memory property simply by making them, and further processing of the particles is necessary to obtain the memory property. Although various studies have been made on memory performance for a long time, there have been few image display media that have sufficient memory performance so far, and almost all have achieved satisfactory results regarding memory performance. There is no current situation.

Special table 2004-526210 gazette Special table 2007-508588 JP 2006-235137 A JP 2006-235137 A JP 2003-66494 A JP-T-2004-526199 JP 2007-225732 A JP 2007-79532 A F. A. Waite, J .; Oil Col. Chem. Assoc. , 54, 342 (1971)

  This invention is made | formed in view of this present condition, and makes it a subject to solve the said various problems in the past and to achieve the following objectives. That is, the present invention relates to an electrophoretic particle capable of maintaining excellent memory properties and obtaining a high contrast, a method for producing an electrophoretic particle capable of efficiently producing the electrophoretic particle, and an image having the electrophoretic particle. It is an object of the present invention to provide a display medium and an image display apparatus having the image display medium.

Means for solving the above problems are as follows. That is,
<1> A polymerizable group imparting step for imparting a polymerizable group to the surface of carbon black using a silane coupling agent having a polymerizable group;
A cationic group imparting step of imparting a cationic group to the surface of carbon black using a silane coupling agent having a cationic group;
And a graft polymerization step of graft-polymerizing the surface of carbon black from the polymerizable group.
<2> The method for producing an electrophoretic particle according to <1>, wherein the polymerizable group is at least one selected from a vinyl group, a styryl group, a methacryloxy group, and an acryloxy group.
<3> The method for producing electrophoretic particles according to any one of <1> to <2>, wherein the cationic group is an amino group.
<4> The electricity according to any one of <1> to <3>, wherein the polymerizable group imparting step and the cationic group imparting step are performed using a silane coupling agent having both a polymerizable group and a cationic group. This is a method for producing migrating particles.
<5> Electrophoretic particles produced by the method for producing electrophoretic particles according to any one of <1> to <4>.
<6> An image display medium comprising a pair of electrode substrates and the electrophoretic particles according to <5> between the pair of electrode substrates.
<7> An image display device using the image display medium according to <6> as a display unit.

  According to the present invention, electrophoretic particles that can solve various problems in the past, can maintain excellent memory properties, and can obtain high contrast, and the electrophoretic particles that can efficiently produce the electrophoretic particles can be produced. A method, an image display medium having the electrophoretic particles, and an image display apparatus having the image display medium can be provided.

(Electrophoretic particles and method for producing electrophoretic particles)
The method for producing electrophoretic particles of the present invention includes a polymerizable group imparting step, a cationic group imparting step, and a graft polymerization step, and further includes other steps as necessary.
The electrophoretic particles of the present invention are produced by the method for producing electrophoretic particles of the present invention.
Hereinafter, the details of the electrophoretic particles of the present invention will be clarified through the description of the method for producing electrophoretic particles of the present invention.

<Polymerizable group imparting step and cationic group imparting step>
The polymerizable group imparting step is a step of imparting a polymerizable group to the surface of carbon black using a silane coupling agent having a polymerizable group.
The cationic group imparting step is a step of imparting a cationic group to the surface of carbon black using a silane coupling agent having a cationic group.
In this case, the polymerizable group imparting step and the cationic group imparting step may be performed separately or simultaneously.
It is particularly preferable that the polymerizable group imparting step and the cationic group imparting step are performed using a silane coupling agent having both a polymerizable group and a cationic group.

Here, in general, there are various methods for the surface treatment of fine particles, and there are various reactions in the case of chemical surface treatment. In the case of an organic pigment (such as carbon black), there are a diazonium reaction, a Friedel-Crafts alkylation reaction, a Friedel-Crafts acylation reaction, and the like. In the case of an inorganic pigment (such as titanium oxide), there is a silane coupling reaction.
Thus, it has been generally considered that the silane coupling reaction is a reaction used for bonding an inorganic pigment and an organic compound.

-Surface treatment of carbon black with silane coupling agent-
In the present invention, when the silane coupling agent that has been used for the reaction with the inorganic pigment is used for the reaction with the carbon black, how it reacts with the functional group on the surface of the carbon black is obtained. The display characteristics of electrophoretic particles were investigated. As a result, it was thought that in addition to the normally considered reaction between the silane coupling agent and the hydroxyl group on the surface of carbon black (first reaction), another reaction may have occurred. Also, excellent display characteristics such as memory properties were observed for the electrophoretic particles.

  Although the reaction between the silylating agent and carbon black can be expected to be a substitution reaction between the functional group of the silylating agent and the functional group on the surface of the carbon black, the reaction between the silane coupling agent and carbon black is also one of the reactions. As for the mechanism of this part, it can be expected that a reaction (second reaction) similar to the substitution reaction occurring between the silylating agent and the organic compound occurs. And it was thought that a functional group was formed on the carbon black surface by the first reaction and the second reaction. For this reason, a positively charged group is bonded to the surface of carbon black by using a reaction of a silane coupling agent, so that the effect of developing the memory property is excellent, and electrophoretic particles having a high memory property can be obtained. I found it possible.

Here, the memory property is a phenomenon in which, when a voltage is applied to an electrode, electrophoretic particles migrate according to the polarity of the electrode, but the image is maintained without disappearing even if the voltage application is stopped and both electrodes are short-circuited. Means.
Regarding the memory property, it has been confirmed that there is no memory property when a cationic group is not imparted to the surface of the electrophoretic particles and only graft polymerization is performed on the surface of the carbon black particles. The mechanism by which cationic properties appear on the particle surface is not clear, but when particles migrate toward an electrode to which a positive or negative voltage is applied, particles with cationic groups Is likely to be adsorbed to the electrode more easily than particles having no cationic group, or is likely to be deposited or aggregated in the vicinity of the electrode. In fact, when the particles that migrated near the electrode were observed with a microscope, it was observed that particles with cationic groups were deposited or aggregated near the electrode, and it was confirmed that they did not change over time. Yes. On the other hand, it has been observed that particles that do not have a cationic group are diffused over time without any deposition or aggregation. From this, it is considered that the memory property appears by having a cationic group on the particle surface.

  It has been clarified that by reacting the silane coupling agent with carbon black in this way, the carbon black exhibits a memory property. However, not only the memory property is manifested, but also a high contrast and a sustained memory property. It was also observed that there are excellent properties in the effect of sex. The high contrast is presumed to be related to the bonding position of the cationic group bonded to the carbon black. It is presumed that the effect of maintaining the memory property is related to the amount of the cationic group bonded to the carbon black.

As a mechanism for realizing these excellent memory effects, the specificity of the reaction with carbon black by the silane coupling agent was examined. Specifically, the specificity of the molecular structure and molecular form of the cationic group on the particle surface formed when bound to the carbon black particles by a silane coupling agent was investigated.
In the reaction with the silane coupling agent, another nucleophilic substitution reaction (second reaction) occurs in addition to the conventionally considered reaction (first reaction). When the reaction by the silane coupling agent is compared with other reactions such as a diazonium reaction, there is a difference in high reactivity and reaction selectivity.

First, the reactivity means the reaction rate when the charged group is chemically bonded to the particle surface and the reaction amount of the functional group. This reactivity is considered to be higher in the reaction with the silane coupling agent than in other reactions such as diazonium.
Next, the reaction selectivity is such that the functional groups that are reacted by the silane coupling agent are compatible with each other when they react with certain functional groups on the particle surface. It is preferable that the functional groups to be reacted react with each other, but it is difficult to react with the functional groups that are not desired to react. This reaction selectivity is considered to be superior to other reactions such as diazonium reaction in the reaction with the silane coupling agent from the viewpoint of the reaction yield of the preferred functional group.

  As a result of considering the reactivity and selectivity of the compound, it is estimated that in the reaction with the silane coupling agent, the molecular structure of the cationic group on the particle surface formed when bound to the particle surface is arranged precisely and without gaps. Is done. Then, it is considered that the charge amount and display characteristics expressed in the state of being bonded to the particle surface are higher than the charge amounts and display characteristics of the functional groups bonded by other reactions. This is because this reactivity and reaction selectivity are obtained from the reaction with the silane coupling agent, and it is considered that the effect on the memory property due to the bond between Si and the carbon black surface is high. The reason is that display characteristics such as memory properties are higher when the functional group containing Si atoms is present on the surface of the carbon black than when there is no functional group. This is because when the cationic group is attached by other synthesis methods, the memory property is not so high, so the position and amount of the cationic group on the particle surface may be related. It is done. This effect is supported by the experimental reaction yield and the display characteristics of the obtained electrophoretic particles. Therefore, these are considered to be related to the effect of excellent memory property.

-Silane coupling agent-
Next, the case where the surface of an inorganic pigment is modified using a silane coupling agent will be described. FIG. 1 is a diagram showing a reaction mechanism between a silane coupling agent and an inorganic surface.
The silane coupling agent has two types of functional groups having different reactivity in one molecule, as represented by the following general formula (1).
<General formula (1)>
In the general formula (1), X is a reactive group chemically bonded to an organic material such as various synthetic resins, and represents a vinyl group, a styryl group, a methacryloxy group, an acryloxy group, an amino group, or the like.
OR is a reactive group that chemically bonds to an inorganic material such as glass, metal, or silica, and represents, for example, a methoxy group or an ethoxy group.

  The silane coupling agent is hydrolyzed with water to become silanol and partially condensed into an oligomer state. Subsequently, it adsorbs to the inorganic surface in a hydrogen bonding manner. Thereafter, the inorganic material is subjected to a dehydration condensation reaction to form a strong chemical bond (first reaction).

Next, an example of the reaction between the silylating agent and the organic compound, which is important in considering the reaction mechanism between the silane coupling agent and carbon black, is shown.
As an example of the use of a silylating agent, silylation is often used for derivatization in which a hardly volatile compound is changed to a volatile compound. The silylation in a broad sense is a substitution reaction represented by the following reaction formula.

<Substitution reaction between silylating agent and organic compound>
In the above reaction formula, HY is a functional group having active hydrogen in the organic compound (H represents active hydrogen, and Y represents a functional group). Y represents, for example, a hydroxyl group, an amino group, a carboxyl group, an amide group, a mercapto group, or the like.
Z is a functional group such as a chloro group, a methoxy group, and an ethoxy group, and is a leaving group.
R represents an alkyl group or a halocarbon, such as a methyl group, an ethyl group, a butyl group, an isopropyl group, or a chlorofluorocarbon group.

  In the polymerizable group imparting step and the cationic group imparting step of the present invention, (1) When chemically bonding to the carbon black surface using a silane coupling agent having both a cationic group and a polymerizable group in the compound (2) The compound may be chemically bonded in two steps using a silane coupling agent having only one of a cationic group and a polymerizable group in the compound.

In said (1), the silane coupling agent which has both a cationic group and a polymeric group in a compound is used, and it chemically binds to the carbon black surface and gives a polymeric group while providing a cationic property. Using such a silane coupling agent, the surface treatment of the carbon black can be performed at once by sequentially performing a cationic group binding reaction and a polymerization reaction on the surface of the carbon black.
Examples of the silane coupling agent having both a cationic group and a polymerizable group in the compound (1) include N- [3- (trimethoxysilyl) propyl] -N ′-(4-vinylbenzyl) ethylenediamine, N- [3- (trimethoxysilyl) propyl] -N ′-(4-vinylbenzyl) amine, N- [3- (trimethoxysilyl) propyl] -N ′-(4-vinylbenzyl) diethylenetriamine, N— And [3- (trimethoxysilyl) propyl] -N ′-(4-vinylbenzyl) urea.

A functional group is imparted in two steps using a silane coupling agent having only one of a cationic group and a polymerizable group in the compound (2).
Examples of the polymerizable group include at least one selected from a vinyl group, a styryl group, a methacryloxy group, and an acryloxy group.
Examples of the cationic group include amino groups.
Examples of the silane coupling agent having a polymerizable group for graft polymerization include the following compounds.
[Vinyl group]
(1) Vinyltrimethoxysilane (2) Vinyltriethoxysilane [styryl group]
p-styryltrimethoxysilane [methacryloxy group]
(1) 3-methacryloxypropylmethyldimethoxysilane (2) 3-methacryloxypropyltrimethoxysilane (3) 3-methacryloxypropylmethyldiethoxysilane (4) 3-methacryloxypropyltriethoxysilane [acryloxy group]
3-acryloxypropyltrimethoxysilane

Examples of the silane coupling agent having a cationic group include the following compounds. Used for imparting a cationic group to the surface of carbon black particles.
[Amino group]
(1) N-2- (aminoethyl) -3-aminopropylmethyldimethoxysilane (2) N-2- (aminoethyl) -3-aminopropyltrimethoxysilane (3) N-2- (aminoethyl)- 3-aminopropyltriethoxysilane (4) 3-aminopropyltrimethoxysilane (5) 3-aminopropyltriethoxysilane (6) 3-triethoxysilyl-N- (1,3-dimethyl-butylidene) propylamine ( 7) N-phenyl-3-aminopropyltrimethoxysilane

In said (2), a functional group is provided in two steps using a silane coupling agent having only one of a cationic group and a polymerizable group in the compound.
First, a cationic group is bonded to the surface of carbon black using a silane coupling agent having a cationic group (amino group).
Next, in order to use as electrophoretic particles, it is necessary to graft polymerize the particle surface and make it easy to disperse in a non-polar solvent, so a polymerizable group (such as vinyl group) for graft polymerization is bound to the carbon black surface. To do. In these reactions, the polymerizable group bonding reaction may be performed first, and the cationic group bonding reaction may be performed later. Moreover, these reactions may be performed simultaneously or separately. In either case, a graft polymerization reaction may be performed thereafter.

-Carbon black-
The carbon black is an aggregate of fine spherical particles obtained by incomplete combustion of various hydrocarbons or compounds containing carbon, and is a generic name for carbon materials whose chemical composition is nearly 98% or more and is almost pure. is there.
The type of the carbon black is generally classified by a manufacturing method, and as shown in Table A, it is roughly divided into either pyrolysis of raw material hydrocarbons or incomplete combustion, and further, depending on the type of raw material. Subdivided.

The contact method is a manufacturing method in which a flame is brought into contact with iron or stone, and includes a channel method and a gas black method (roller method) which is an improved method thereof. Channel black is a representative product of the contact method, and is collected by bringing a flame into contact with the bottom surface of channel steel.
The furnace method is a method of generating carbon black by continuously pyrolyzing hydrocarbons as raw materials by combustion heat of fuel air, and is classified into a gas furnace method and an oil furnace method.
The thermal method is a special production method in which natural gas is used as a raw material carbon source, and combustion and thermal decomposition are repeated periodically. The feature is that carbon black having a large particle size can be obtained. Acetylene black is a kind of thermal process that uses acetylene as a raw material. However, the thermal decomposition of acetylene is an exothermic reaction while other raw materials are endothermic, so it is possible to omit the combustion cycle in the thermal process. Continuous operation is possible. The characteristics of acetylene black are that it develops crystallinity compared to ordinary carbon black and has a high structure, so it has excellent conductivity and is used as a conductivity-imparting agent for dry batteries and various rubbers and plastics. .

The chemical composition of the carbon black thus produced varies depending on the production method, process conditions, raw materials, water quality, varieties, etc., but carbon 95 to 99%, oxygen to 1.0%, hydrogen 0.3 to It consists of 0.7%, sulfur to 0.7%, and ash (iron, aluminum, silicon, etc.) to 1.0%. Of these, the oxygen content is exceptionally around 3% for channel black, and extremely low for acetylene black and thermal black.
PH and volatile matter are used as a simple evaluation method for the oxygen content of carbon black. Hydrocarbon remains inside the carbon black particles, and various functional groups containing oxygen exist on the particle surface. Various functional groups on the surface of carbon black are formed at the edge of the plane of the polycyclic aromatic layer exposed on the particle surface, and are mainly phenol, quinone, carboxyl, lactone and the like. Table B shows the surface functional group content and content of typical carbon black. The surface functional group amount is measured by neutralization titration using inorganic base or organic base, organic chemical analysis method using various organic reagents, instrumental analysis such as X-ray photoelectron spectroscopy, infrared spectroscopy, carbon It can be performed by identification by pyrolysis gas analysis of black.

Chemical and thermal analysis of functional groups on carbon black surface.
[Type]
Ca, C: Channel black
F, Fb: Furnace black
Tc: Thermal black

-Three major basic characteristics of carbon black-
The important factors when using carbon black in electrophoretic dispersion are (I) particle size, (II) structure, and (III) physicochemical properties of the particle surface, which are usually the three basics of carbon black. It is called a characteristic.
(I) Particle size: Particle size and specific surface area (II) Structure: DBP oil supply (ml / 100 g) and structure index (III) Physicochemical properties of the surface: Volatile content (%), pH

The particle diameter and the specific surface area are opposite to each other, and the specific surface area of particles having a large particle diameter is small. The electrophoretic dispersion requires a certain particle size from the viewpoint of obtaining blackness and memory properties, and the primary average particle size is preferably 10 nm or more, more preferably 10 nm to 100 nm. The specific surface area of the carbon black is preferably 20 to ²⁰⁰ m ² / g.
The development of the carbon black structure can be estimated from the DBP oil supply amount, and an appropriate structure development is preferable. If the structure is developed too much, it will have a negative effect on migration and response speed. The DBP oil supply amount of the carbon black is preferably 50 to 150 ml / 100 g.
Regarding the volatile content and pH specified by the physicochemical properties of the surface, it can be considered to indirectly represent the amount of functional groups present on the surface of the carbon black particle, and some dispersibility in isopar is somehow. It seems that there is an influence. Since the silane coupling reaction in the present invention is a substitution reaction between a silylating agent and a carbon black surface functional group, it is not particularly specified, but it is considered to be related to reactivity.
The pH of the carbon black is preferably 3-10.

Here, the pH of the carbon black can be measured by the following method.
First, weigh 1 to 10 g of carbon black sample in a beaker, add water at a rate of 10 ml per 1 g of sample, cover with a watch glass, and boil for 15 minutes. (To make the sample easy to wet, several drops of ethanol may be added. ). After boiling, the mixture is cooled to room temperature, and the supernatant is removed by a gradient method or a centrifugal separation method to leave a mud. An electrode of a glass electrode pH meter is placed in this mud and the pH is measured by JIS Z8802 (pH measurement method). In this case, the measured value may change depending on the electrode insertion position. Therefore, move the beaker to change the electrode position, carefully measure the electrode surface so that the muddy surface is in full contact, and maintain a constant pH value. Read the value when. Moreover, the volatile matter of carbon black is obtained by the following measuring method. A dry sample of carbon black is packed into a platinum crucible or a porcelain crucible of the same shape and capacity with a drop lid by shaking it so that it does not exceed 2 mm below the lid, and its mass is measured. Cover this, put it in an electric furnace, heat it at 950 ± 25 ° C for exactly 7 minutes, take it out, let it cool to room temperature in a desiccator, weigh the mass after heating, calculate.
<Formula 2>
V = (WD−WR) / WD × 100
In the formula, V represents volatile matter (%), WD represents the mass (g) of the dried sample, and WR represents the mass (g) of the sample after heating.

  As said carbon black, what was synthesize | combined suitably may be used and a commercial item may be used. The commercially available product is not particularly limited and may be appropriately selected depending on the intended purpose. For example, Degussa Color Black FW200, Color Black FW2, Color Black FW2V, Color Black FW1, Color Black FW18, Special Black 6 , Color Black S170, Color Black S160, Special Black 5, Special Black 4, Special Black 4A, Printex 150T, Printex U, Printex V, Printex 140U, Printex 140V, Special Black 550, Special Black 350, Special Black 250, Special Black 100; MA7, MA77, MA8, MA11, MA100, MA100R, MA230, MA220, # 2 manufactured by Mitsubishi Chemical Corporation 00B; manufactured by Cabot Corporation of MONARCH700, MONARCH800, MONARCH880, MONARCH900, MONARCH1000, MONARCH1300, MONARCH1400, MOGUL-L, REGAL400R, VULCAN XC-72R; Columbia Co. Raven 1255, and the like.

<Graft polymerization process>
The graft polymerization step is a step of graft polymerization of the surface of carbon black from a polymerizable group.
The method for graft polymerization of the surface of the carbon black from the polymerizable group is not particularly limited and may be appropriately selected depending on the intended purpose. For example, 2-ethylhexyl methacrylate using a radical initiator in a solvent such as toluene. There are a method of radical polymerization by heating a monomer having a double bond such as lauryl methacrylate to 70 ° C. to 80 ° C., ionic polymerization using an anion or cation initiator, and living polymerization.

  The electrophoretic particles produced by the method for producing electrophoretic particles of the present invention are graft carbon black having a cationic group. The surface treatment of the carbon black surface with a graft having a cationic group can be detected by, for example, generated gas analysis or instantaneous thermal analysis. Examples of equipment used include a gas chromatograph mass spectrometer (GCMS) and a double shot pyrolyzer.

  The electrophoretic particles produced by the method for producing electrophoretic particles of the present invention are composed of graft carbon black having a cationic group, can maintain excellent memory properties, and provide high contrast. It is widely used for a medium and an image display device having the image display medium.

<Electrophoretic dispersion>
The electrophoretic dispersion used in the present invention contains the electrophoretic particles of the present invention, and contains titanium oxide particles as white electrophoretic particles, a dispersion medium, a dye, and other components as necessary. .

-Titanium oxide particles-
A preferable material for forming the white electrophoretic particles includes at least one of a metal oxide and a hydroxide. Among these, titanium oxide (titania) particles are particularly preferable.
The titanium oxide particles can be coated with an oxide (for example, alumina or silica), for example. The presence of such a coating in the electrophoretic medium by suppressing reactions such as photochemical reactions (which can occur at the interface between the bare titania surface and the suspending fluid). It seems that the stability of the titania of this is improved. These titania particles have one, two or more layers of metal oxide coating. For example, the titania particles used in the present invention have one layer of alumina coating and one layer of silica coating.
In such coated particles, the titania is completely covered by the coating, so any reagent used to attach initiators or polymerizable groups to the surface of the particle will react with the coating. There must be no reaction with titania.
Examples of the titania particles include trade names R960, E.I. I. Du Pont de Nemours and Company (Wilmington, Delaware), trade name, Taipei CR-90, average particle size: 0.25 μm, and Ishihara Sangyo Co., Ltd. are preferable.

The dispersion medium differs depending on the electrophoretic particles used and cannot be defined unconditionally. However, the dispersion medium may be colorless and transparent, or may be colored by dissolving a dye having a color different from that of the electrophoretic particles.
The dye is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include azo dyes, anthraquinone dyes, phthalocyanine dyes, triallylmethane dyes, and the like. Examples of the dye include spirit black (SB, SSBB, AB), nigrosine base (SA, SAP, SAPL, EE, EEL, EX, EXBP, EB), and oil yellow (105, 107, 129, 3G, GGS). , Oil Orange (201, PS, PR), Fast Orange, Oil Red (5B, RR, OG), Oil Scarlet, Oil Pink 312, Oil Violet # 730, Macrolex Blue RR, Sumiplast Green G, Oil Brown (GR 416), Sudan Black X60, Oil Green (502, BG), Oil Blue (613, 2N, BOS), Oil Black (HBB, 860, BS), Bali First Yellow (1101, 1105, 3108, 4120), Bali First Oren (3209, 3210), Bali First Red (1306, 1355, 2303, 3304, 3306, 3320), Bali First Pink 2310N, Bali First Brown (2402, 3405), Bali First Blue (3405, 1501, 1603, 1605, 1607) , 2606, 2610), Bali First Violet (1701, 1702), Bali First Black (1802, 1807, 3804, 3810, 3820, 3830), Macrolex Blue RR (manufactured by Bayer), and the like.

  The dispersion medium is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include paraffinic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, and dodecane, isohexane, isooctane, and isododecane. Iso-paraffin hydrocarbons, alkyl naphthenic hydrocarbons such as liquid paraffin, aromatic hydrocarbons such as benzene, toluene, xylene, alkyl benzene, solvent naphtha, dimethyl silicone oil, phenyl methyl silicone oil, dialkyl silicone oil, alkyl phenyl silicone oil And silicone oil such as cyclic polydialkylsiloxane or cyclic polyalkylphenylsiloxane. Among these, isoparaffin hydrocarbons and silicone oils are particularly preferable. As the isoparaffinic hydrocarbon, Isoper manufactured by Exxon Chemical Co., Ltd., modified silicone oil (manufactured by Toray Dow Chisso Corporation) and the like can be used.

The electrophoretic dispersion may further contain a dispersant in order to further improve the storage stability of the electrophoretic particles. The dispersant is not particularly limited as long as it is compatible with the dispersion medium and can stably disperse the electrophoretic particles, and a conventionally known pigment dispersant can be used.
Examples of the dispersant include sorbitan fatty acid esters (for example, sorbitan monooleate, sorbitan monolaurate, sorbitan sesquioleate, sorbitan trioleate, etc.); polyoxyethylene sorbitan fatty acid esters (for example, polyoxyethylene sorbitan monostearate). Polyethylene glycol fatty acid esters (eg, polyoxyethylene monostearate, polyethylene glycol diisostearate, etc.); polyoxyethylene alkylphenyl ethers (eg, polyoxyethylene nonylphenyl ether, Polyoxyethylene octyl phenyl ether, etc.); nonionic surfactants such as aliphatic diethanolamides can be used.
Examples of the polymer dispersant include, for example, styrene-maleic acid resin, styrene-acrylic resin, rosin, urethane polymer compound BYK-160, 162, 164, 182 (manufactured by Big Chemie), urethane dispersant EFKA. -47, LP-4050 (manufactured by EFKA), polyester polymer compound Solsperse 24000 (manufactured by Zeneca), aliphatic diethanolamide polymer compound Solsperse 17000 (manufactured by Geneca), and the like.
The polymer dispersant preferably has a number average molecular weight of 1,000 or more.

Other polymeric dispersants include monomers such as lauryl methacrylate, stearyl methacrylate, 2-ethylhexyl methacrylate, and cetyl methacrylate that can form a solvated part in the dispersion medium, and a part that is difficult to solvate in the dispersion medium. Random copolymers of monomers such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, styrene, vinyltoluene and monomers having polar functional groups that can be formed, and graft copolymers disclosed in JP-A-3-188469. A polymer etc. are mentioned. Monomers having a polar functional group include monomers having an acidic functional group such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, styrene sulfonic acid; dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, vinylpyridine, Monomers having basic functional groups such as vinylpyrrolidine, vinylpiperidine, vinyllactam; salts thereof; styrene-butadiene copolymers, styrene and long-chain alkyl methacrylates disclosed in JP-A-60-10263 Examples thereof include block copolymers. Of these, the graft copolymers disclosed in JP-A-3-188469 are preferred.
The mass ratio of the dispersant to the electrophoretic particles when the electrophoretic particles are dispersed in the dispersion medium is preferably 0.05% by mass to 5% by mass. Thereby, electrophoretic particles can be stably dispersed.

(Image display medium)
The image display medium of the present invention has a pair of electrode substrates and at least the electrophoretic particles of the present invention between the pair of electrode substrates, and applies a voltage between the pair of electrode substrates. An image is displayed by electrophoresis of fine particles.
In this case, it is preferable that at least one of the pair of electrode substrates is light transmissive.
In the image display medium of the present invention, the dispersion medium may be separated into a minute space between a pair of substrates by partition walls or microcapsules in order to suppress aggregation and bias of particles in the dispersion medium. In any case, it is preferable to divide the two electrodes by a large number of fine cells because it can prevent the deviation of particles and the aggregation of particles due to gravity.
There is no restriction | limiting in particular as a preparation method of the said microcapsule, Although it can select suitably according to the objective, For example, well-known methods, such as a coacervation method and a phase-separation method, can be used.

-Electrode substrate-
There is no restriction | limiting in particular as said electrode substrate, Although it can select suitably according to the objective, Usually, the electrode substrate etc. which formed the conductive layer on the board | substrate which consists of glass, plastics, etc. are mentioned.
Examples of the material of the plastic substrate include acrylic resin, polycarbonate resin, and epoxy resin.
The conductive layer is not particularly limited and may be appropriately selected according to the purpose. However, a transparent conductive layer is preferable, and metals such as Al, Ag, Ni, and Cu, ITO, SnO ₂ , ZnO: Al, and the like are preferable. A transparent conductor formed into a thin film by a sputtering method, a vacuum deposition method, a CVD method, a coating method, or the like, or a coating obtained by mixing a conductive agent with a solvent or a synthetic resin is used.
Examples of the conductive agent include cationic polymer electrolytes such as polymethylbenzyltrimethyl chloride and polyallylpolymethylammonium chloride, anionic polymer electrolytes such as polystyrene sulfonate and polyacrylate, and electron conductive oxidation. Zinc, tin oxide, indium oxide fine powder or the like is used.
The conductive layer may be thick enough to have a self-holding function, or the conductive layer may be provided on a substrate having a self-holding function.
The conductive layer may be a layer exhibiting anisotropic conductivity, or may be a layer having a patterned or multi-dot segment in which a conductive portion penetrates in the thickness direction. In any case, if the power supply electrode is brought into contact with a part of the conductive layer, an electric field can be generated between the conductive layers, so that white or colored particles can move reliably. In order to perform the display, voltage applying means between the conductive layers may be prepared, which is convenient.

-Other components-
Examples of the other members include a metal reflection plate, a light diffusion plate, and an antireflection layer. These may be used alone or in combination of two or more.
A TFT or the like may be further attached to the electrode substrate (lower substrate).

  Here, FIG. 2 shows a first embodiment of the image display medium of the present invention. In the image display medium 10, an electrophoretic dispersion liquid 11 is sandwiched between conductive layers 12 and 13. The electrophoretic dispersion liquid 11 has black particles 11a and white particles 11b dispersed in a nonpolar solvent 11c, and has both an electrophoretic effect and a memory effect. The black particles 11a are positively charged. Furthermore, the conductive layer 12 has a light transmitting property, and the conductive layer 13 may or may not have a light transmitting property. The conductive layers 12 and 13 are divided into a right half and a left half. The electrophoresis dispersion liquid 11 is an electrophoresis dispersion liquid used in the present invention.

  Next, an operation for displaying an image on the image display medium 10 will be described with reference to FIGS. 3A to 3D. First, negative and positive voltages are respectively applied to the right halves of the conductive layers 12 and 13 using an external voltage applying means (not shown) (see FIG. 3A). Thereby, the black particles 11a move upward by electrostatic attraction (see FIG. 3B), but gradually reach the conductive layer 12 (see FIG. 3C) and adhere to the conductive layer 12 (see FIG. 3D). At this time, when the image display medium 10 is viewed from above, the color of the white particles 11b can be seen in the left half, and the color of the black particles 11b can be seen in the right half. In addition, since an image can be displayed reversibly on the image display medium 10, the image display medium 10 can be used repeatedly.

FIG. 4 shows a second embodiment of the image display medium of the present invention. In FIG. 4, the same components as those in FIG. 3 are denoted by the same reference numerals and description thereof is omitted. In the image display medium 20, the microcapsule 21 is sandwiched between the conductive layers 12 and 13.
Further, as shown in FIG. 5, the microcapsule 21 includes the electrophoretic dispersion 11 in a microcapsule film 21a. The image display medium 20 is produced by arranging the microcapsules 21 on the conductive layer 12 or 13 so as to form a single layer by electrodeposition coating or the like. The microcapsule 21 is obtained by dispersing the electrophoretic dispersion 11 in water in which gelatin is dissolved, encapsulating with gelatin and gum arabic coacervate, and then crosslinking with glutaraldehyde to form the microcapsule film 21a. It is produced by.

  FIG. 6 shows a third embodiment of the image display medium of the present invention. The image display medium 30 includes transparent electrodes 32A and 32B that are patterned on transparent substrates 31A and 31B, respectively, and an electrophoretic dispersion liquid via a spacer 33 between the transparent electrodes 32A and 32B that are arranged to face each other. 34 is enclosed. Thereby, generation | occurrence | production of the display nonuniformity by aggregation of electrophoretic particle and adhesion | attachment can be suppressed. Although it does not specifically limit as transparent substrate 31A and 31B, A film etc. can be used. Further, in the electrophoretic dispersion liquid 34, white and black particles are dispersed in a nonpolar solvent. In addition, the spacer 33 is not particularly limited, but a mesh or porous perforated spacer can be used.

  Next, an operation for displaying an image on the image display medium 30 in FIG. 6 will be described. First, when positive and negative voltages are applied to the transparent electrodes 32A and 32B, black particles adhere to the transparent electrode 32B due to electrostatic attraction, and white particles adhere to the transparent electrode 32A due to electrostatic attraction, When the image display medium 30 is viewed from above, white is observed. On the other hand, when negative and positive voltages are applied to the transparent electrodes 32A and 32B, white particles adhere to the transparent electrode 32B due to electrostatic attraction, and black particles adhere to the transparent electrode 32A due to electrostatic attraction. When the image display medium 30 is viewed from above, black is observed. As described above, since the image can be displayed reversibly on the image display medium 30, the image display medium 30 can be used repeatedly.

  FIG. 7 shows a fourth embodiment of the image display medium of the present invention. The image display medium 40 in FIG. 7 can be folded in a sheet form, and can be carried in a folded state.

(Image display device)
The image display device of the present invention uses the image display medium of the present invention as a display means, and includes a drive circuit, an arithmetic circuit, an internal memory, a power source, and other means as required.

  Here, FIG. 8 is a schematic view showing an example of the image display apparatus of the present invention. The image display device 50 of FIG. 8 includes an image display medium 10, a housing 52, an information input unit 51, a drive circuit, an arithmetic circuit, an internal memory, a power source, and the like which are not shown. The electrodes in the image display medium 10 in FIG. 8 form a dot matrix, and can display an image as a whole by displaying ON a designated dot.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by a following example.
The measurement of the graft amount on the particle surface in the following examples was performed by the following thermal mass spectrometry.

<Thermal mass spectrometry>
Thermal mass spectrometry was started by using TGA-50H (manufactured by Shimadzu Corporation) and putting 20 mg of the dried sample into a platinum cell. Next, after raising the temperature from room temperature to 600 ° C. at 20 ° C./min in a nitrogen atmosphere, the temperature is held at 600 ° C. for 10 minutes, and after 3 minutes reaching 600 ° C., the atmosphere is switched to air. The temperature was raised to 600 ° C to 1000 ° C at a rate of 1 minute. At this time, the polymer thermally decomposed in a nitrogen atmosphere, and carbon black or titanium oxide burned in an air atmosphere.

(Production Example 1)
-Synthesis of titanium oxide having a polymerizable group-
Into a 1 L glass reaction vessel, 300.0 g of ethanol and 20.0 g of deionized water were added, and while stirring at 150 rpm, acetic acid was added dropwise to adjust the pH to 4.5. Next, after adding 200 g of titanium oxide (R-960, manufactured by Dupont) and stirring at 150 rpm for 30 minutes, a solution obtained by dissolving 20 g of 3- (trimethoxysilyl) propyl methacrylate in 80 g of ethanol is about 1 hour. Then, the mixture was stirred at 60 ° C. for 4 hours. Next, the dispersion obtained by returning to room temperature and stirring was centrifuged at 5,000 rpm for 30 minutes and decanted. The obtained white powder was charged with 400 mL of ethanol, stirred and redispersed, and then the obtained dispersion was centrifuged at 5,000 rpm for 30 minutes and decanted. The obtained white powder was allowed to stand overnight, dried, and then vacuum dried at 70 ° C. for 4 hours to obtain titanium oxide having a polymerizable group.

-Graft polymerization-
Next, 100.0 g of lauryl methacrylate, 300.0 g of paraffin hydrocarbon (neothiozole, manufactured by Chuo Kasei Co., Ltd.), 96.0 g of titanium oxide having a previously pulverized polymerizable group, azobisisobutyrate in a 1 L pressurized reaction vessel After adding 0.600 g of nitrile (AIBN) and performing nitrogen substitution, pressurizing with 0.1 MPa with nitrogen, and then dispersing for 30 minutes while stirring at 300 rpm. Then, it heated to 75 degreeC in about 1 hour, and stirred at 75 degreeC for 7 hours. Next, the dispersion obtained by returning to room temperature and stirring was centrifuged at 10,000 rpm for 30 minutes and decanted. The obtained white powder was charged with 600 mL of isooctane, stirred and redispersed, and then centrifuged at 10,000 rpm for 30 minutes and decanted twice. Furthermore, after leaving it to stand overnight, it was dried in vacuo at 70 ° C. for 4 hours, and grafted titanium oxide T was obtained.
When the obtained grafted titanium oxide T was subjected to thermal mass spectrometry, the mass reduction was 9.3%.

Example 1
<Preparation of electrophoretic particles>
-Synthesis of carbon black having a polymerizable group and a cationic group-
A 1 L glass reaction vessel was charged with 600 g of ethanol and 50 g of carbon black (Printex A, manufactured by Degussa, specific surface area 45 m ² / g, DBP oil absorption 118 ml / 100 g, average primary particle size 41 nm, pH 9) at 150 rpm. While stirring, a solution prepared by dissolving 10.0 g of N- [3- (trimethoxysilyl) propyl] -N ′-(4-vinylbenzyl) ethylenediamine in 100 g of methanol was dropped in about 60 minutes, and then at 60 ° C. For 4 hours. Next, the dispersion obtained by returning to room temperature and stirring was centrifuged at 10,000 rpm for 30 minutes and decanted. The resulting black powder was charged with 400 mL of ethanol, stirred and redispersed, and then centrifuged at 10,000 rpm for 30 minutes and decanted. The obtained black powder was left to stand overnight, dried, and then vacuum dried at 70 ° C. for 4 hours to obtain surface-treated carbon black. By the above method, a polymerizable group and a cationic group were introduced on the surface of carbon black.

-Graft polymerization-
Next, 25.0 g of lauryl methacrylate, 160.0 g of paraffin hydrocarbon (neothiozole, manufactured by Chuo Kasei Co., Ltd.), 25.0 g of carbon black having a preliminarily pulverized polymerizable group and a cationic group in a 1 L pressurized reaction vessel, Nitrogen substitution was performed by adding 0.250 g of azobisisobutyronitrile (AIBN), and after pressurizing with 0.1 MPa with nitrogen, dispersion was performed for 30 minutes while stirring at 300 rpm. Thereafter, the mixture was heated to 75 ° C. in about 1 hour and stirred at 75 ° C. for 7 hours. Next, the dispersion obtained by returning to room temperature and stirring was centrifuged at 10,000 rpm for 30 minutes and decanted. The resulting black powder was charged with 300 mL of isooctane, stirred and redispersed, and then centrifuged at 10,000 rpm for 30 minutes and decanted twice. Furthermore, after leaving it to stand overnight, it was dried in vacuum at 70 ° C. for 4 hours to obtain Graft Carbon Black G1.
When the obtained graft carbon black G1 was subjected to thermal mass spectrometry, the mass loss was 9.4%.

(Comparative Example 1)
-Synthesis of carbon black having a polymerizable group-
Carbon black (Printex A, manufactured by Degussa, specific surface area 45 m ² / g, DBP oil supply 118 ml / 100 g, average primary, while adding 3.0 L of deionized water to a 4 L glass reaction vessel and stirring at 250 rpm 115 g of particle size 41 nm, pH 9) was added. Next, after adding 3.0 mL of 37% hydrochloric acid, 2.5 g of 4-vinylaniline was added and stirred at 65 ° C. for 30 minutes or more. Further, a solution obtained by dissolving 1.43 g of sodium nitrite in 10 mL of deionized water was dropped in about 1 hour and stirred at 65 ° C. for 3 hours. Next, the dispersion obtained by returning to room temperature and stirring overnight was centrifuged at 30,000 rpm for 20 minutes and decanted. The resulting black powder was charged with 500 mL of deionized water, stirred and redispersed, then centrifuged at 30,000 rpm for 20 minutes and decanted. The obtained black powder was allowed to stand overnight and dried, followed by vacuum drying at 40 ° C. for 4 hours to obtain a carbon black having a polymerizable group.

-Graft polymerization-
Next, 50 g of carbon black having a polymerizable group, 100 mL of toluene, 100 mL of 2-ethylhexyl methacrylate, and 0.65 g of azobisisobutyronitrile (AIBN) were charged into a 1 L glass reaction vessel. Next, while stirring at 250 rpm, the atmosphere was replaced with nitrogen for 20 minutes, heated to 70 ° C. for about 1 hour, stirred for 7 hours, and cooled to room temperature. Further, 500 mL of tetrahydrofuran (THF) was added and stirred, and then reprecipitated in 3 L of methanol and suction filtered. To the resulting residue, 1.5 L of tetrahydrofuran (THF) was added, stirred and redispersed, then cooled to 10 ° C., centrifuged at 30000 rpm for 20 minutes, and decanted three times in total. Furthermore, it was left to stand overnight and vacuum dried at 70 ° C. for 4 hours to obtain graft carbon black G0.
When the obtained graft carbon black G0 was subjected to thermal mass spectrometry, the mass reduction was 10.3%.

(Example 2)
-Preparation of electrophoretic dispersion-
1.7 parts by weight of grafted carbon black G1, 40 parts by weight of grafted titanium oxide T, dispersant (Solsperse 17000, manufactured by Avicia) 0.47 parts by weight, nonionic surfactant (sorbitan triolate, Wako Pure Chemical Industries) 0.53 parts by mass of the company) and 57.26 parts by mass of Isopar G (manufactured by ExxonMobil) were mixed and dispersed with an ultrasonic wave for 1 hour to prepare an electrophoretic dispersion liquid.

-Fabrication of image display cell-
Fabrication by capillary action using a microsyringe in a space provided by sandwiching a 50 μm thick polyester film with an opening of 1 cm ² between ^two glass substrates with ITO electrodes (Geomatec). The electrophoretic dispersion liquid was sealed.
The glass substrate with an ITO electrode is made of soda glass, the dimensions are 29.8 ± 0.1 mm × 39.8 ± 0.1 mm, the outer periphery is chamfered, and the surface of the ITO electrode The resistance was 50 ± 10Ω / □.

(Comparative Example 2)
In Example 2, an electrophoretic dispersion was prepared in the same manner as in Example 2 except that graft carbon black G0 was used instead of graft carbon black G1.
An image display cell of Comparative Example 2 was produced in the same manner as in Example 2 except that the obtained electrophoretic dispersion was used.

<Evaluation method of image display cell>
When 15 V was applied to the upper ITO electrode of the image display cell, the black carbon black particles of Example 2 were positively charged and thus moved quickly to the lower ITO electrode. Since the white electrophoretic particles are slightly negatively charged with titanium oxide itself, they can move according to the polarity of the ITO electrode, so that white is observed when observed from the upper ITO electrode. Next, when −15 V was applied to the upper ITO electrode, the black carbon black particles of the example quickly moved to the upper ITO electrode. Similarly, when observed from the lower part, white was observed.
In contrast, in Comparative Example 2, the carbon black and titanium oxide pigments are slightly charged positively and negatively, respectively, so that the response speed is slow and there is no memory property, but it is possible to perform electrophoresis according to the polarity of the ITO electrode. Met. Therefore, in Comparative Example 2, when 15 V was applied to the upper ITO electrode, the black electrophoretic particles moved to the lower part, and the white electrophoretic particles moved to the upper part. On the contrary, when -15 V was applied to the upper ITO electrode, the black electrophoretic particles moved to the upper part, and the white electrophoretic particles moved to the lower part.
The voltage application was switched about 100 times at a frequency of 0.1 Hz, but could be repeated stably. Further, even when the voltage was removed, in Example 2, the electrodeposited state (memory property) was maintained (see FIG. 9). On the other hand, the memory property was not seen in the comparative example 2 (refer FIG. 10).

  Next, the LCD EVALUATION SYSTEM LCD-5000 (manufactured by Otsuka Electronics Co., Ltd.) is used for the reflectance, contrast, response speed, and memory performance of 1.5 hours (90 minutes) of the image display cells of Example 2 and Comparative Example 2. It measured using. Note that the presence / absence of the memory property was determined by the rate of change in black and white reflectance during 90 minutes. The results are shown in Table 1.

From the results shown in Table 1, in Example 2, the white reflectance was 40% or more and the black reflectance was 5% or less, both of which were not significantly changed for 90 minutes. In this case, it was judged that there was a memory property.
On the other hand, in Comparative Example 2, both the black and white reflectance for 90 minutes are greatly changed. In this case, it was judged that there was no memory property.
As a criterion for determining whether or not there is a memory property, in principle, the white reflectance is 40% or more and the black reflectance is 5% or less during a holding time of 90 minutes. It is judged. When it is determined that there is no memory property, both black and white change greatly.

  As described above, carbon with excellent memory properties is obtained by chemically bonding a cationic group and a polymerizable group to the surface of the carbon black particles using a silane coupling agent and graft polymerization from the polymerizable group on the surface of the carbon black. It was found that black particles were obtained.

  Since the electrophoretic particles produced by the method for producing electrophoretic particles of the present invention can maintain excellent memory properties and obtain high contrast, they are suitably used for various paper-like image display media.

FIG. 1 is a diagram showing a reaction mechanism between a silane coupling agent and an inorganic surface. FIG. 2 is a cross-sectional view showing a first embodiment of the image display medium of the present invention. 3A is a cross-sectional view illustrating an operation for displaying an image on the image display medium in FIG. 2, and is a diagram illustrating a state in which negative and positive voltages are applied. FIG. 3B is a cross-sectional view illustrating an operation for displaying an image on the image display medium in FIG. 2, and is a diagram illustrating a state in which black particles move upward due to electrostatic attraction. FIG. 3C is a cross-sectional view illustrating an operation for displaying an image on the image display medium in FIG. 2, and is a diagram illustrating a state in which black particles gradually reach the conductive layer. FIG. 3D is a cross-sectional view illustrating an operation for displaying an image on the image display medium in FIG. 2, and is a diagram illustrating a state where black particles are attached to the conductive layer. FIG. 4 is a cross-sectional view showing a second embodiment of the image display medium of the present invention. FIG. 5 is a cross-sectional view showing the microcapsule of FIG. FIG. 6 is a cross-sectional view showing a third embodiment of the image display medium of the present invention. FIG. 7 is a perspective view showing a fourth embodiment of the image display medium of the present invention. FIG. 8 is a perspective view showing an example of the image display device of the present invention. FIG. 9 is a graph showing a state of the memory property of Example 2. FIG. 10 is a graph showing a state without memory property of Comparative Example 2.

Explanation of symbols

10, 20, 30, 40 Image display medium 11, 34 Electrophoretic dispersion liquid 11a Black particles 11b White particles 11c Nonpolar solvent 12, 13 Conductive layer 21 Microcapsule 21a Microcapsule film 31A, 31B Transparent substrate 32A, 32B Transparent Electrode 33 Spacer 50 Image display device 51 Input section

Claims (7)

A polymerizable group imparting step for imparting a polymerizable group to the surface of carbon black using a silane coupling agent having a polymerizable group;
A cationic group imparting step of imparting a cationic group to the surface of carbon black using a silane coupling agent having a cationic group;
And a graft polymerization step of graft-polymerizing the surface of carbon black from the polymerizable group.   The method for producing electrophoretic particles according to claim 1, wherein the polymerizable group is at least one selected from a vinyl group, a styryl group, a methacryloxy group, and an acryloxy group.   The method for producing electrophoretic particles according to claim 1, wherein the cationic group is an amino group.   The method for producing electrophoretic particles according to any one of claims 1 to 3, wherein the polymerizable group imparting step and the cationic group imparting step are performed using a silane coupling agent having both a polymerizable group and a cationic group.   Electrophoretic particles produced by the method for producing electrophoretic particles according to claim 1.   An image display medium comprising: a pair of electrode substrates; and the electrophoretic particles according to claim 5 between the pair of electrode substrates.   An image display device using the image display medium according to claim 6 as display means.