JP2011175167A - Electrophoretic dispersion liquid, image display medium having the electrophoretic dispersion liquid, and image display device using the image display medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: an electrophoretic dispersion liquid having a memory property; an image display medium having the electrophoretic dispersion liquid; and an image display device using the image display medium. <P>SOLUTION: The electrophoretic dispersion liquid at least contains, in a dispersion medium: anionic charged graft carbon black particles comprising carbon black particles with an organic group having a nitro group or a sulfone group and an organic group having a polymerizable group imparted to surfaces thereof, and a graft polymer chain bonded thereto; and cationic charged graft titanium oxide particles comprising titanium oxide particles with an organic group imparted directly or via a cover layer to surfaces thereof, wherein the organic group is an amino group via a silyl group or a polymerizable functional group via a silyl group, and a graft polymer chain bonded thereto. The image display medium is formed by using the dispersion liquid, and the image display device (10) is constructed by using the image display medium. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrophoretic dispersion having memory properties, an image display medium having the electrophoretic dispersion, and an image display device using the image display medium.

  Conventionally, cathode ray tubes (CRT), liquid crystal displays, and the like are 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, although hard copies are discarded or recycled after use, they require a lot of labor and cost, which is problematic 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, and the colored dispersion medium has different colors and is charged on the surface. Are 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 is displayed on an image display medium using an electrophoretic element 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, the 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. On the other hand, regarding the steric effect, Non-Patent Document 1 describes a method for producing a stable non-aqueous solvent-based dispersion, and the component has compatibility with particles dispersed in the solvent and is dissolved in the solvent. A block copolymer or graft copolymer containing a component having a property is produced in a solvent and used.

A number of patents have been filed so far for methods for producing electrophoretic particles. These patents mainly describe the dispersion stability as electrophoretic particles.
Patent Document 1 proposes an electrophoretic medium in which pigment particles to which a polymer is bound are suspended in a suspending fluid, and a diazonium group is preferable for reacting carbon black with a compound. “Cabot Corporation, Boston, Massachusetts series of patents describe the use of diazonium chemistry to attach a wide range of functional groups to carbon black. " However, a series of patents do not cover electrophoretic dispersions, but describe the diazonium reaction of carbon black as a dispersion for use in inkjet inks.
Patent Document 2 proposes an electrophoretic medium containing charged particles having a polymer shell suspended in a suspending fluid. In order to control the optical stability of the electrophoretic particles, charged particles are used. Are described for compatibility and incompatibility in suspension fluids.
However, none of the above prior arts has sufficient memory properties for image display based on electrophoresis of electrophoretic particles, and further improvements are desired.

  Display characteristics as well as dispersion stability are important for the preparation of electrophoretic particles. Display characteristics mainly include high contrast and memory. In patents filed so far, emphasis has been placed on improving black and white reflectance. For this reason, there are many applications concerning improvement of the surface treatment method of particles. However, the biggest selling point when using electrophoretic particles as a display medium is the memory property, and it is apparent that it is difficult to use the image display medium without the memory property.

Regarding the memory property, for example, Patent Document 3 discloses an electrophoretic display containing an alkyl polyetheramine having a specific structural unit, resin particles colored with a dye and / or pigment, white titanium oxide particles, and a dispersion medium. A solution has been proposed. It is described that by adding alkyl polyetheramine as an additive to graft-polymerized titania particles and carbon black particles, the visual state can be changed reversibly by the action of an electric field (providing memory). Has been.
In Patent Document 4, organic or inorganic particles are added as electrophoretic particles of an electrophoretic display solution capable of reversibly changing the visual state by the action of an electric field or the like, or a charge control agent is added thereto. The use of the prepared particles is described.
However, with these electrophoretic particles, it is difficult to obtain particles having a sufficiently large charge amount, and it cannot be said that the sensitivity to an electric field is sufficiently high.

In Patent Document 5, in order to prevent aggregation and sedimentation of electrophoretic particles, an electrophoretic dispersion liquid (including a liquid phase dispersion medium and electrophoretic particles) and a partition wall for dividing the electrophoretic dispersion liquid are provided. Has been proposed.
Patent Document 6 proposes blending polyisobutylene in order to improve the memory performance of the image display medium.
Further, Patent Document 7 proposes a method for producing charged particles capable of controlling the charging of particles, and describes that a polymer having an ionic group in a regular chain is bonded to the surface of titania particles by living polymerization. ing.
Patent Document 8 proposes a display method capable of full-color display having memory properties by using metal colloidal particles having a plasmon coloring function.
Patent Document 9 proposes organic white particles (fine particles) having a specific structural formula, and fine particle dispersions (dispersions having a memory property) using the same.
Further, in Patent Document 10, in order to provide an electrophoretic display element and an electrophoretic display device, dispersible particles having no charge, dispersible particles having a positive charge, and dispersible particles having a negative charge are placed in a solvent. It is proposed to use an electrophoretic display medium dispersed in the above, and a three-particle display element having a memory property that enables three-color display is described.
Moreover, in patent document 11, while giving the polymeric group to the surface of carbon black using the silane coupling agent which has a polymeric group, and providing the cationic group using the silane coupling agent which has a cationic group A method for producing electrophoretic particles in which the surface of carbon black is graft-polymerized from a polymerizable group has been proposed.

According to the above-mentioned patent document, it is said that it is natural that the electrophoretic particles are used. However, it cannot be said that the memory property is manifested. There is no specific description about the conditions and methods.
However, when the patent document is reexamined as in the embodiment, even if the particles are synthesized as in Patent Document 1, for example, the memory property is not seen at all. For other patents, it is the actual situation that sufficient memory properties do not appear even if we try to make particles and add a charge control agent or polymer.
Therefore, it is considered that the electrophoretic particles are not originally provided with a memory property simply by preparing particles, and further processing of particles or setting of conditions for expression are necessary to obtain the memory property. This study on memory performance is an important issue and seems to have been done for a long time, but there are few display media that have sufficient memory performance to date. In addition, it can be said that there are almost no satisfactory results regarding the memory property.

The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide an electrophoretic dispersion having memory properties, an image display medium having an electrophoretic dispersion, and an image display device using the image display medium. .
In particular, negatively charged black electrophoretic particles (anion-charged graft carbon black) and positively charged white electrophoretic particles (cationic charge) with good dispersion stability and display characteristics (maintaining excellent memory properties and high contrast). It is an object of the present invention to provide an electrophoretic dispersion liquid containing a conductive graft titanium oxide), an image display medium having the electrophoretic dispersion liquid, and an image display device using the image display medium.

  As a result of intensive studies, the present inventors have found that the above problems can be solved by the inventions described in the following [1] to [10], and have reached the present invention. The present invention will be specifically described below.

[1]: The above problem is solved in the dispersion medium.
An anionically charged graft carbon black particle to which an organic group having a nitro group or a sulfone group and an organic group having a polymerizable functional group are imparted to the surface of the carbon black particle and a graft polymer chain is bonded;
An organic group is imparted to the surface of the titanium oxide particle directly or through a coating layer, and the organic group is an amino group via a silyl group or a polymerizable functional group via a silyl group and has a cationic chargeability with a graft polymer chain bound thereto. Grafted titanium oxide particles;
It is solved by an electrophoretic dispersion characterized by containing at least.

  [2]: In the electrophoretic dispersion liquid according to [1], the polymerizable functional group is at least one selected from a vinyl group, a methacryloxy group, an acryloxy group, and a styryl group. .

  [3]: In the electrophoretic dispersion liquid described in [1] or [2] above, the organic group having the nitro group or the sulfone group and the organic group having a polymerizable functional group are carbon atoms using an arylamine compound. It is characterized by being applied to the surface of black particles.

  [4]: In the electrophoretic dispersion liquid according to any one of [1] to [3] above, the organic group imparted to the surface of the titanium oxide particles directly or via a coating layer uses a silane coupling agent. It is characterized by being applied to the surface of the titanium oxide particles.

  [5]: In the electrophoretic dispersion liquid according to any one of [1] to [4], the coating layer is made of aluminum oxide and / or silicon oxide.

  [6]: In the electrophoretic dispersion liquid according to any one of [1] to [5], the graft polymer chain is formed on the surface of the carbon black particles to which the organic group has been added by a polymerization reaction using a reactive monomer. Is grafted.

  [7]: In the electrophoretic dispersion liquid according to any one of [1] to [6], the graft polymer chain is formed on the surface of the titanium oxide particles to which the organic group has been added by a polymerization reaction using a reactive monomer. Is grafted.

  [8]: In the electrophoretic dispersion liquid according to the above item [6] or [7], the reactive monomer is a methacrylic acid derivative or an acrylic acid derivative.

  [9]: The above problem is solved by an image display medium comprising the electrophoretic dispersion according to any one of claims [1] to [8].

  [10] The above problem is solved by an image display device using the image display medium described in [9].

  According to the present invention, anion-charged graft carbon black particles (negatively charged black electrophoretic particles) having excellent dispersion stability and display characteristics (maintaining excellent memory properties and high contrast) and cation-chargeable particles can be obtained. An electrophoretic dispersion liquid containing grafted titanium oxide particles (positively charged white electrophoretic particles), an image display medium having the electrophoretic dispersion liquid, and an image display device using the image display medium can be provided.

It is a schematic diagram for demonstrating the reaction mechanism of a silane coupling agent and an inorganic surface. It is sectional drawing which shows the 1st structural example of the image display medium which concerns on this invention. It is sectional drawing which shows the 2nd structural example of the image display medium which concerns on this invention. It is an expanded sectional view which shows the microcapsule of FIG. It is sectional drawing which shows the 3rd structural example of the image display medium which concerns on this invention. It is a perspective view which shows the 4th structural example of the image display medium which concerns on this invention. It is a perspective view which shows an example of the image display apparatus which concerns on this invention. It is the graph showing the state which has memory property in the image display cell which enclosed the electrophoresis dispersion liquid of the Example. It is the graph showing the state without memory property in the image display cell which enclosed the electrophoresis dispersion liquid of the comparative example.

As described above, the electrophoretic dispersion in the present invention is contained in the dispersion medium.
An anionically charged graft carbon black particle to which an organic group having a nitro group or a sulfone group and an organic group having a polymerizable functional group are imparted to the surface of the carbon black particle and a graft polymer chain is bonded;
An organic group is imparted to the surface of the titanium oxide particle directly or through a coating layer, and the organic group is an amino group via a silyl group or a polymerizable functional group via a silyl group and has a cationic chargeability with a graft polymer chain bound thereto. Grafted titanium oxide particles;
It is characterized by containing at least.

[1] Dispersion Liquid with Memory Property By adopting the configuration of the present invention, an electrophoretic dispersion liquid having a memory property (hereinafter sometimes abbreviated as “dispersion liquid”) can be obtained.
In the case of a dispersion having a memory property, the carbon black is divided into two types of positively charged particles and negatively charged particles, but the dispersion of the present invention has anion-charged graft carbon black particles and cationically charged particles. -Containing grafted titanium oxide particles. Thereby, it can be set as the dispersion liquid with favorable dispersion stability and a display characteristic. That is, it is possible to obtain a dispersion that can maintain excellent memory properties and obtain high contrast.
Hereinafter, “anion-charged graft carbon black particles” may be referred to as “negatively charged carbon black particles” or “negatively charged black electrophoretic particles”. In addition, “cationically charged grafted titanium oxide particles” may be referred to as “positively charged titanium oxide particles” or “positively charged white electrophoretic particles”. Further, the “polymerizable functional group” may be referred to as “polymerizable group”.

Next, the best mode for carrying out the electrophoretic dispersion having the memory property of the present invention will be described with reference to the drawings as necessary.
A combination of negatively charged black electrophoretic particles (black particles) and positively charged white electrophoretic particles (white particles) can be used as a two-color display medium. In principle, this display method is the same except that positively charged carbon black particles are used as black particles and combined with white particles to form a display medium, except that the chargeability of the particles is reversed. As a result of extensive studies by the inventor, it was possible to develop a dispersion having a memory property by using negatively charged carbon black (negatively charged carbon black particles).
That is, negatively charged carbon black particles to which an organic group having a nitro group or a sulfone group and an organic group having a polymerizable functional group are provided on the particle surface and to which a graft polymer chain is bonded, and the titanium oxide particle surface directly or a coating layer An organic group is provided via the cation group, and the organic group contains at least a cation-charged grafted titanium oxide particle that is an amino group via a silyl group or a polymerizable group via a silyl group and has a graft polymer chain bonded thereto. In the electrophoretic dispersion liquid, it has been found that the reflectance and memory properties, which are display characteristics, vary greatly depending on the charging characteristics of each particle. In other words, as a result of intensive studies on the mechanism of memory characteristics, it was found that the aforementioned interaction of migrating particles is greatly involved.
The cationically charged grafted titanium oxide particles are, for example, provided with an organic group having an amino group and a silyl group and an organic group having a polymerizable functional group and a silyl group on the surface of the titanium oxide particle, or polymerized with an amino group. It can also be referred to as positively charged titanium oxide particles to which an organic group having a functional functional group and a silyl group is added and a graft polymer chain is bonded.
Hereinafter, the memory property of the migrating particles will be described.

[2] Evaluation of memory properties of migrating particles due to changes in reflectivity In order to investigate how the memory properties of the dispersion appear, the following two types of dispersion (I) and (II) are combined. Liquids (using a hydrocarbon solvent as a dispersion medium) were prepared and sealed in an image display cell, respectively, and the reflectance and memory properties were evaluated.
(I) Negatively charged grafted carbon black particles and grafted titanium oxide particles (nearly uncharged)
(II) Negatively charged graft carbon black particles and positively charged titanium oxide particles (dispersion liquid of the present invention)
As a result of the evaluation, the following was found.
In the case of (I): When plus 15V is applied to one of the electrodes and minus 15V is applied to the other, negatively charged carbon black particles are attached to the plus electrode, and titanium oxide particles are attached to the electrode to which minus 15V is applied. . However, when the voltage application was stopped thereafter, the negatively charged carbon black particles diffused into the cell within a few seconds, and both sides of the cell became gray in which carbon black and titanium oxide were mixed.
In the case of (II): When voltage is applied to the electrode in the same manner as (I), negatively charged carbon black particles adhere to the electrode applied with plus 15V, and positively charged titanium oxide particles adhere to the electrode applied with minus 15V. did. Thereafter, even after 2 hours, the two types of particles did not diffuse into the cell.
From the results of these observations, it was found that when negatively charged carbon black (II) and positively charged titanium oxide particles (II) were used, memory properties appeared due to the interaction between the two types of particles. In particular, it was found that the memory property does not appear only by using the negatively charged carbon black particles, and can be obtained by the combination with the white particles described above. The reason why the memory property appears in the dispersion of the present invention is considered to be the interaction between the two kinds of particles. Hereinafter, the expression of memory property will be described.

[3] Reason why memory property is exhibited in the dispersion of the present invention Memory property means that when a voltage is applied to an electrode, when the electrophoretic particles migrate according to the polarity of the electrode, the voltage application is stopped or both This is a phenomenon in which an image is maintained without disappearing even when the electrodes are short-circuited.
Regarding the memory property, it has been confirmed that there is no memory property when a charged group is not imparted to the surface of the electrophoretic particle and a graft polymer chain is simply bonded to the particle surface by graft polymerization.
The mechanism by which a memory function appears when an electrophoretic particle (substantially, “particle”) is charged with a charged functional group (addition of a charged group) is not clear, but the particle has a positive or negative voltage. When migrating toward an applied electrode, particles with a charged group are more likely to adsorb to the electrode than particles without a charged group, or are more likely to deposit or aggregate near the electrode. I guess that. Actually, when the particles migrated in the vicinity of the electrode are observed with a microscope, it is observed that particles having a chargeable group are deposited or aggregated in the vicinity of the electrode, and it can be confirmed that they do not change over time. On the other hand, it is observed that particles having no chargeable group are diffused over time without depositing or aggregating. From this, it is clear that the memory property appears by having a charged group on the particle surface.
In the present invention, the expressions “attach a functional group having a charge” and “have a chargeable group” are abbreviations for “providing an organic group having a chargeable group”.

In the present invention, the reason why the memory property is developed will be described first.
<Anion-charged graft carbon black particles (negatively charged carbon black particles)>
The negatively charged carbon black particles in the present invention are an organic group having a nitro group or a sulfone group on the particle surface (hereinafter sometimes referred to as “compound”) and an organic group having a polymerizable functional group (“compound”). And a graft polymer chain bonded to each other. That is, anion-charged graft carbon black particles to which a compound having a nitro group or a sulfone group is added are optimal. For this reason, it can be said that carbon black having a nitro group or a sulfone group is electron-donating and highly anionic as described below.

  The property of a substituent having the effect of decreasing the electron density at a specific position of the molecule is called electron withdrawing property, and the property having the effect of increasing the electron density is called electron donating property. A substituent having such an effect is referred to as an electron withdrawing group or an electron donating group. The electron withdrawing property or electron donating property cannot be explained only by the difference in electronegativity. That is, the induction effect, the mesomery effect, etc. act in a complex manner, and the appearance changes depending on the presence of aromaticity, conjugated system, and topological positional relationship.

  The numerical value of the effect of the substituent on the acid dissociation equilibrium constant of the substituted benzoic acid is called Hammett's substituent constant, which is a parameter indicating the strength of the electron withdrawing property and electron donating property of the substituent. This is because the stability of the state in which protons are eliminated from benzoic acid to form carboxylate ions depends on how much the negative charge on the carboxyl group can be delocalized.

  As shown in the following Tables 1 (A) and 1 (B), it can be seen that the Hammett substituent constant of the nitro group is considerably high among various functional groups, and is electron donating and anionic. Therefore, it is considered that the graft carbon black particles to which the compound (organogroup) having a nitro group is added have a considerably higher anionic property of the electrophoretic particles than the simple graft carbon black particles to which nothing is added to the particle surface.

  For the sulfone group, ions are dissociated and the Hammett's substituent constant such as a nitro group is not determined. However, in the dispersion medium [for example, isoparaffinic hydrocarbon solvent: Isopar (manufactured by Exxon Chemical Co., Ltd.)], it is presumed that the anionicity is high similarly to the nitro group. The graft carbon black to which a compound having a sulfone group (organic group) is added is also considered to have a considerably higher anionic property of the migrating particles compared to a mere graft carbon black to which nothing is added to the particle surface.

<Cationically charged grafted titanium oxide particles (positively charged titanium oxide particles)>
The positively charged titanium oxide particles contained in the dispersion of the present invention are provided with organic groups (molecules) on the surface of the titanium oxide particles directly or via a coating layer (for example, an oxide such as alumina or silica described later), The organic group (molecule) is an amino group via a silyl group or a polymerizable group via a silyl group and has a graft polymer chain bonded thereto.
Hereinafter, “an organic group is imparted (bonded) to the titanium oxide particle surface directly or via a coating layer” is abbreviated as “an organic group is imparted (bonded) to the titanium oxide particle surface”. Sometimes.
That is, the organic group (molecule) having a silyl group imparted to the surface of the titanium oxide particle is bonded to the surface of the titanium oxide particle using a silylating agent [a silyl compound having a substituent (for example, an alkoxy group)]. be able to. This bond can be generally expected to be due to a substitution reaction between the functional group of the silylating agent and the functional group on the particle surface as shown in the schematic diagram of FIG. A silane coupling agent is preferably used as the silylating agent. Even when the titanium oxide particles are treated with a silane coupling agent, it is considered that a similar reaction occurs on the surface of the titanium oxide particles to give an organic group (molecule) having a silyl group.
The symbol “X” in FIG. 1 represents a group defined in the same manner as “X” in the general formula (1) described later.

In the present invention, among silane coupling agents, in particular, a compound having a structure having both a functional group of a cationic group and a polymerizable functional group (polymerizable group) (a molecule having an amino group, a polymerizable functional group, and a silyl group). It is preferable to use it. The polymerizable group is preferably at least one selected from a vinyl group, a methacryloxy group, an acryloxy group, and a styryl group.
The reason why it is preferable to use a compound having a structure having both a cationic functional group and a polymerizable functional group (polymerizable group) (a molecule having an amino group, a polymerizable functional group, and a silyl group) is silane. Silanes that have both a cationic functional group and a polymerizable group, considering the molecular structure and molecular morphology of the charged group on the surface of the particle formed when coupled to the titanium oxide particle surface by a coupling agent The specificity of the reaction with titanium oxide particles (hereinafter sometimes referred to as “pigment particles” or “particles”) by the coupling agent was considered.
As a result, when the reaction is performed on the surface of the titanium oxide particles using a silane coupling agent having a structure having both a functional group of a cationic group and a polymerizable group (in this case, a vinyl group) in the compound, and a cationic functional group When a reaction is performed on the surface of titanium oxide particles using a silane coupling agent having a group and a silane coupling agent having a polymerizable group (here, a vinyl group) separately, the reaction selectivity between the two is compared. It became clear that there was a big difference in height and position selectivity.

First, reaction selectivity is a reaction when a silane coupling agent (a silyl compound having a reactive substituent such as an alkoxy group) having a charged group (cationic functional group) is chemically bonded to the pigment particle surface. It means the amount of reaction between the speed and the functional group. Next, regioselectivity refers to the reaction of a specific functional group (for example, an alkoxy group) of the silane coupling agent with a specific functional group (for example, a hydroxyl group) on the particle surface in the reaction between the silane coupling agent and the pigment particle surface. ) Means the affinity (compatibility) of each other. Although it is preferable to react uniformly on the surface of the pigment particle, an unfavorable situation may occur if the reaction is biased to a part of the pigment particle.
The above both selectivity is more suitable for the reaction with a silane coupling agent having both an amino group and a vinyl group in the same structure as compared with the reaction with a silane coupling agent having an amino group and a vinyl group separately. it is conceivable that.
The reason is that in the case of a silane coupling agent having both a silyl group having a reactive substituent such as an alkoxy group and other functional groups (for example, an amino group and a vinyl group) in the same compound, the reactive substitution of the silyl group This is because when a group (alkoxy group or the like) reacts with the particle surface, other functional groups are simultaneously immobilized on the particle surface along with the reaction. Therefore, if one functional group is uniformly added to the particle surface, the other functional groups are considered to be uniformly present on the particle surface as well.

On the other hand, when the silane coupling agent having a different amino group and vinyl group is reacted separately, the silane coupling agent having one functional group is imparted to the particle surface in the first reaction. In the second reaction, the silane coupling agent having the other functional group may be inhibited from being imparted to the particle surface, thereby adversely affecting the reactivity. Furthermore, in the case of reacting separately, the reaction occurs with uneven distribution on the surface of the particle, and the effects of the respective functional groups may appear separately.
Therefore, as a result of considering the reaction selectivity and regioselectivity of the compound, a molecule having an amino group, a silyl group and a polymerizable functional group in the same structure (a silane coupling agent having both an amino group and a vinyl group) is used. It is presumed that the molecular structure of the charged group on the particle surface formed when bound to the particle surface is arranged neatly without gaps. This structure is considered to provide a high charge amount and good display characteristics (memory properties, contrast).
These facts also indicate that when an organic group (molecule) having a chargeable group is added to the particle surface by a reaction using the above-mentioned separate silane coupling agents, the high memory performance cannot be obtained. It is clear that the position and amount of bonding of the chargeable group are related. The above is considered to be related to the excellent effect of memory property.

  Using the silane coupling agent having the structure described above, positively charged titanium oxide particles (cation-charged grafted titanium oxide particles) were synthesized, and the above-mentioned negatively charged carbon black particles (anion-charged grafted carbon black particles) were synthesized. It was found that the effect of developing the memory property was particularly excellent when combined with.

  Next, an anion-charged graft carbon in which an organic group having a nitro group or a sulfone group and an organic group having a polymerizable functional group are imparted to the surface of the carbon black particles and a graft polymer chain is bonded to the dispersion medium. Black particles (negatively charged carbon black particles) and an organic group are imparted directly or via a coating layer to the titanium oxide particle surface, and the organic group is an amino group via a silyl group or a polymerizable group via a silyl group The reason why the memory property can be obtained by the electrophoretic dispersion liquid in which the cationically charged grafted titanium oxide particles (positively charged titanium oxide particles) combined with the graft polymer chain are dispersed will be described.

For example, the negatively charged carbon black particles and the positively charged titanium oxide particles are dispersed in a dispersion medium (for example, a nonpolar solvent such as isoparaffinic hydrocarbon or silicone oil) between a pair of opposed conductive layers (electrodes). When the dispersed electrophoretic dispersion liquid is sealed and a positive and negative voltage is applied to each electrode, both particles dispersed in the dispersion medium migrate to each electrode depending on the polarity. After that, when the voltage application is stopped, it is presumed that each migrating particle is attached or deposited on each electrode. At this time, the negatively charged carbon black particles (anionic carbon black particles) and the positively charged titanium oxide particles (cationic titanium oxide particles) are not present separately on both electrodes. It is considered that the cationic titanium oxide particles surround the carbon black particles, and both form an associated state.
That is, in an electrode on which negatively charged carbon black particles are attached or deposited, a negatively charged carbon black particle having a high anionic property and a positively charged titanium oxide particle having a high cationic property, both particles are well balanced by Coulomb force. As a result, it is speculated that an ideal state of association has occurred for the development of memory. When this aggregate is generated, the diffusion observed in the negatively charged carbon black particles alone is suppressed, and the aggregate of the negatively charged carbon black particles is considered to remain in the vicinity of the electrode.
As described above, in the electrophoretic dispersion of the present invention, it is considered that the interaction between the negatively charged carbon black particles and the positively charged titanium oxide particles works as a mechanism that exhibits an excellent effect of memory performance. .
In fact, as described in the above-described experiment, the combination of anionic carbon black particles and grafted titanium oxide (nearly uncharged) cannot provide memory properties. It is clear that a memory effect is exhibited in the combination of the positively charged titanium oxide particles.

  As described above, it has been found that the memory property is expressed by the interaction between the two particles of the negatively charged carbon black particle and the positively charged titanium oxide particle. However, as a result of the present invention, not only the memory property but also the contrast is exhibited. It was also revealed that there are excellent characteristics in height. The high contrast cannot be strictly divided in the above-mentioned reaction selectivity and regioselectivity, but it is related to the bonding position (regioselectivity) of the charged group bonded to the pigment particles to some extent. It is thought that. On the other hand, it is considered that the high memory effect is related to the amount (reaction selectivity) of the charged group bonded to the pigment particles.

[4] Preparation Method of Electrophoretic Particles Anion-charged graft carbon black particles (negatively charged carbon black particles) and cation-charged grafted titanium oxide particles (positively charged titanium oxide particles) of the present invention are provided by an organic group. At the same time, the graft polymer chain is bonded, and each particle (fine particle) is produced by chemical surface treatment.
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. Examples of the organic pigment include, for example, carbon black, diazonium reaction, Friedel-Crafts alkylation reaction, Friedel-Crafts acylation reaction, and the like. Inorganic pigments include silane coupling reactions and are often used for surface treatment of titanium oxide.
The surface treatment method for the negatively charged carbon black particles and the positively charged titanium oxide particles of the present invention will be described below, although not limited thereto.
The surface functional groups of the carbon black particles and titanium oxide particles will be described later.

(4-1) Surface treatment of negatively charged carbon black particles An organic group having a nitro group or a sulfone group is imparted to the surface of the carbon black particles by a diazo coupling reaction via a diazonium compound. The same applies to the case of providing an organic group having a polymerizable functional group.
(A) Diazonium Compound The diazonium compound is an organic nitrogen compound obtained by diazotization and containing a [—N ⁺ ≡N] substituent in the molecule. Diazotization is a reaction in which a primary amine compound is reacted with nitrous acid (HNO ₂ ) or nitrite ester (RONO) to obtain a corresponding diazonium compound.
Examples of the primary amine compound include the following arylamine compounds.
<1> 4-vinylaniline <2> p-aminobenzoic acid <3> sulfanilic acid <4> 4-nitroaniline <5> 4-amino-3-nitrobenzoic acid <6> 4-nitroaniline-2-sulfone Sodium acid (b) Diazo coupling reaction Aromatic diazonium salts perform an electrophilic attack on the para-position of an aminoaryl compound or phenol compound having an electron-donating group, and an aromatic electrophilic substitution reaction via a sigma complex Gives an azo compound (azobenzene derivative) in which the N terminal of [—N ⁺ ≡N] and aryl are coupled. This reaction is also called diazo coupling.

(4-2) Surface Treatment of Positively Charged Titanium Oxide Particles The cationically charged grafted titanium oxide particles (positively charged titanium oxide particles) of the present invention are composed of an organic group having an amino group and a silyl group on the surface of the titanium oxide particles and polymerizable. Each particle (fine particle) is provided with an organic group having a functional group and a silyl group, or an organic group having an amino group, a silyl group, and a polymerizable functional group and a graft polymer chain bonded thereto. Is produced by chemical surface treatment.
As the organic group to be imparted, a silane coupling agent having one of functional groups selected from a vinyl group, a methacryloxy group, an acryloxy group, and a styryl group as a polymerizable functional group (polymerizable group) is preferably used. . That is, the positively charged titanium oxide particles generally have a polymerizable group using a silane coupling agent having one of functional groups selected from a vinyl group, a styryl group, a methacryloxy group, and an acryloxy group on the surface of the particle. In addition, a cationic functional group is added using a silane coupling agent having an amino group, a reactive monomer is used for the polymerizable group, grafting is performed by a polymerization reaction, and a graft polymer chain is bonded. To do.

That is, the organic group (molecule) having a silyl group imparted to the particle surface is directly or on the surface of the titanium oxide particle using a silylating agent [a silyl compound having a substituent (for example, an alkoxy group)]. (For example, a coating layer made of aluminum oxide or silicon oxide) can be bonded. This bond can be generally expected to be due to a substitution reaction between the functional group of the silylating agent and the functional group on the particle surface as shown in the schematic diagram of FIG.
The silane coupling agent used as the silylating agent has at least two different functional groups in one molecule as shown by the following general formula (1), for example.

  [In formula (1), X represents a polymerizable functional group such as a vinyl group, a styryl group, a methacryloxy group, an acryloxy group, or an amino group that is chemically bonded to the graft polymer chain. OR is a reactive group chemically bonded to the surface of the titanium oxide particle directly or via a coating layer, and represents an alkoxy substitution such as a methoxy group or an ethoxy group. ]

The silane coupling agent having an alkoxy-substituted silyl group is hydrolyzed with water to form silanol and partially condensed into an oligomer state. Silanol is adsorbed to inorganic surfaces [surfaces of titanium oxide particles and coating layers (aluminum oxide, silicon oxide, etc.)] by hydrogen bonding, and the inorganic group is dried to treat active groups on the surface of titanium oxide particles or the surface of the coating layer. And a dehydration condensation reaction to form a strong chemical bond.
Specific examples of the silane coupling agent include, for example, N- [3- (trimethoxysilyl) propyl] -N ′-(4-vinylbenzyl) ethylenediamine, N- (vinylbenzyl) -3-aminopropyltrimethoxysilane. N-allyl-3-aminopropyltrimethoxysilane, N- (N-allyl-2-aminoethyl) -3-aminopropyltrimethoxysilane, and the like. These coupling agents may be used alone or in combination of two or more.

  In the present invention, among silane coupling agents, a silyl compound having a cationic functional group (amino group) and a polymerizable functional group (for example, vinyl group) in the molecule is preferably used. If a silane coupling agent having such a structure is used, it can be chemically bonded to the surface of the titanium oxide particles or the coating layer to exhibit cationic properties and simultaneously impart a polymerizable functional group. If the graft polymer chain is bonded by using the graft polymerization reaction, the surface treatment of the titanium oxide particles can be performed at once.

[5] Carbon Black Particles Next, the surface functional groups of carbon black particles (substantially, carbon black) and the formation process thereof will be described.
Carbon black is defined as an aggregate of fine spherical particles obtained by incomplete combustion of various hydrocarbons or carbon-containing compounds, and is a generic name for carbon materials that are nearly pure and have a chemical composition of 98% or more. It is. The types are generally classified according to the production method, and as shown in Table 2 below, they are roughly classified into either pyrolysis of raw material hydrocarbons or incomplete combustion, and further subdivided according to the type of raw material. .
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 raw material hydrocarbons 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. Yes.

The chemical composition of the carbon black produced as described above varies depending on the production method, process conditions, raw materials, water quality, varieties, etc., but is approximately 95 to 99% carbon, oxygen to 1.0%, hydrogen 0. It is known to comprise 3 to 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 3 below shows the surface functional group amount and content of typical carbon black.
Surface functional groups are measured by neutralization titration using inorganic and organic bases, organic chemical analysis methods using various organic reagents, instrumental analysis such as X-ray photoelectron spectroscopy, infrared spectroscopy, and heating of carbon black. In addition to identification by cracked gas analysis, extensive attempts have been made.

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

  The particle diameter and the specific surface area are opposite to each other, and the specific surface area of the 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 preferably has a primary particle size of 20 nm or more. The development of the structure can be estimated from the amount of DBP refueling, and an appropriate structure development is optimal. If the structure is developed too much, it will have a negative effect on migration and response speed.

  The volatile matter and pH defined by the chemical properties of the surface can be considered to indirectly represent the abundance of functional groups on the surface of the carbon black particles, and the dispersion medium [e.g., isoparaffin hydrocarbon solvent (isopar: It is thought that there is some influence on the dispersibility in Exxon Chemical Co.).

  The pH of carbon black is obtained by the following measurement method. 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 (a few drops of ethanol may be added to make the sample easy to wet). 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 JISZ8802 (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 with the same shape and capacity as a drop lid by shaking to a level not exceeding 2 mm, and the mass is measured. Cover it, 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, and calculate the volatile content by the following formula To do.
V = [(WD−WR) / WD] × 100
[Wherein, V: volatile content (%), WD: mass (g) of dry sample, WR: mass (g) of sample after heating. ]

  As carbon black (carbon black particles) used in the present invention, one kind or a plurality of kinds of carbon blacks may be used in combination. Such carbon blacks include 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, Mitsubishi Chemical Corporation MA7, MA77 , MA8, MA11, MA100, MA100R, MA230, MA220, # 2200B, MONARCH700 manufactured by Cabot Corporation MONARCH800, MONARCH880, MONARCH900, MONARCH1000, MONARCH1300, MONARCH1400, MOGUL-L, REGAL400R, VULCAN XC-72R, Colombia's Raven1255, Color's REGAL400R, MOGUUL1F, Black Commercially available products such as Black S170, Color Black S150, and Printex U can be used, and even those newly manufactured for this purpose can be used.

[6] Titanium oxide particles Currently, the most suitable material for forming white electrophoretic particles is metal oxide (and / or hydroxide), particularly titania (titanium oxide) particles.
The titanium oxide particles can be coated with an oxide such as alumina or silica. In the presence of such a coating, electrophoresis is inhibited by suppressing reactions such as photochemical reactions (which can occur at the interface between the uncoated bare titania surface and the suspending fluid). It appears that the stability of titania in the medium is improved. These titania particles can have one to two or more layers of metal oxide coating.
For example, as the titanium oxide particles (titania particles) used in the present invention, those having one layer of alumina coating and one layer of silica coating are preferably used. That is, in the titania particles having a coating layer, the titania is completely covered by the coating, so that any reagent used in the bonding of the organic groups and graft polymer chains imparted to the surface of the particles is mainly used. It will react with the coating of the coating layer.
Examples of the titanium oxide particles (titania particles) include trade names, R960, E.I. I. Du Pont de Nemours and Company (Wilmington, Delaware), trade name, Type CR-90, average particle size: 0.25 μm, manufactured by Ishihara Sangyo Co., Ltd. are preferable.

[7] Electrophoretic dispersion liquid In the electrophoretic dispersion liquid of the present invention, electrophoretic particles composed of anion-charged graft carbon black particles and cation-charged graft titanium oxide particles are dispersed in a dispersion medium. Although it does not specifically limit as a dispersion medium used here, Nonpolar solvents, such as an isoparaffin type hydrocarbon (Isson by Exxon Chemical Co., Ltd.) and modified silicone oil (made by Shin-Etsu Chemical Co., Ltd.), can be used.

  The electrophoretic dispersion of the present invention may further contain a dispersing agent 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, but 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), polyoxyethylene sorbitan fatty acid esters (for example, polyoxyethylene sorbitan monostearate, Polyoxyethylene sorbitan monooleate, etc.), polyethylene glycol fatty acid esters (eg, polyoxyethylene monostearate, polyethylene glycol diisostearate, etc.), polyoxyethylene alkyl phenyl ethers (eg, polyoxyethylene nonylphenyl ether, poly Nonionic surfactants such as oxyethylene octyl phenyl ether and 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 (Zeneca), and the like. In addition, it is mentioned that the polymer dispersant preferably has a number average molecular weight of 1000 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.
Among them, a graft copolymer disclosed in JP-A-3-188469 is preferable.

The amount of the dispersant further added to the electrophoretic particle-containing dispersion medium is preferably 0.05 to 5% in terms of the weight ratio to the electrophoretic particles (dispersant / electrophoretic particles). For example, the electrophoretic particles can be stably dispersed in the dispersion medium.
In addition to the electrophoretic particles, the electrophoretic dispersion liquid of the present invention may contain a dye for improving color display and responsiveness. Although it does not specifically limit as dye, Macrolex blue RR (made by Bayer) etc. are mentioned.

[8] Image display medium An image display medium can be obtained by using the electrophoretic dispersion of the present invention. For example, the electrophoretic dispersion liquid of the present invention is sealed between a pair of opposingly disposed conductive layers (hereinafter sometimes referred to as “electrodes”), at least one of which is light transmissive, to form an image display medium. be able to. A configuration example of the image display medium of the present invention will be described with reference to the drawings.
The first configuration example of the image display medium according to the present invention is shown in the sectional view of FIG.
In FIG. 2, in the image display medium 10, an electrophoretic dispersion liquid 11 is sandwiched between conductive layers 12 and 13. The electrophoretic dispersion liquid 11 is obtained by dispersing anion-charged grafted carbon black particles (black particles) 11a and cation-charged grafted titanium oxide particles (white particles) 11b in a nonpolar solvent 11c. It has both electrophoresis effect and memory effect. Furthermore, the conductive layer 12 has a light transmitting property, and the conductive layer 13 may or may not have a light transmitting property. Although not shown, the conductive layers 12 and 13 are divided so as to be divided into a right half and a left half in FIG. 2 so that a voltage can be applied, so that the functions as an image display medium can be exhibited. . The electrophoresis dispersion liquid 11 is the electrophoresis dispersion liquid of the present invention.

FIG. 3 is a sectional view showing a second configuration example of the image display medium according to the present invention. In FIG. 3, the same components as those in FIG. 2 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 the enlarged sectional view of FIG. 4, the microcapsule 21 contains the electrophoretic dispersion 11 by 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 formed by, for example, 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 a microcapsule film 21a. It is produced by doing.

The sectional view of FIG. 5 shows a third configuration example of the image display medium according to the present invention.
In FIG. 5, an image display medium 30 has transparent electrodes 32A and 32B patterned on transparent substrates 31A and 31B, respectively, and a spacer 33 is interposed between the transparent electrodes 32A and 32B arranged to face each other. An electrophoresis dispersion liquid 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 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 32A due to electrostatic attraction, and white particles adhere to the transparent electrode 32B due to electrostatic attraction. When the image display medium 30 is viewed from above, black is observed. On the other hand, when negative and positive voltages are applied to the transparent electrodes 32A and 32B, respectively, white particles adhere to the transparent electrode 32A due to electrostatic attraction, and black particles adhere to the transparent electrode 32B due to electrostatic attraction. When the image display medium 30 is viewed from above, white 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.

The perspective view of FIG. 6 shows a fourth configuration example of the image display medium according to the present invention.
In FIG. 6, the image display medium 40 can be folded in a sheet shape, and thus can be carried in a folded state.

An image display device can be configured by using the image display medium of the present invention.
An example of an image display device according to the present invention is shown in the perspective view of FIG.
In FIG. 7, the image display device 50 uses the image display medium 10 on a flat screen, and can display an image by inputting image information from the input unit 51.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by a following example. In addition, a part means a weight part.

The graft amount shown in the following synthesis examples was measured by the following thermogravimetric analysis.
[Thermogravimetric analysis]
Thermogravimetric analysis was started using TGA-50H (manufactured by Shimadzu Corporation) by putting about 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 was held at 600 ° C. for 10 minutes, and after 3 minutes reaching 600 ° C., the atmosphere was switched to air and cooled. At this time, the polymer thermally decomposed in a nitrogen atmosphere.

The following electrophoretic particles used in Examples and Comparative Examples were synthesized.
[AGT]: Cationic chargeable grafted titanium oxide particles to which an organic group having an amino group, a silyl group, and a polymerizable functional group (vinyl group) is added and graft polymer chains are bonded [abbreviation: amino group-added grafted titanium oxide] [AGT]]
[GT]: Cation-charged grafted titanium oxide particles that do not have a cationically charged group (amino group), are provided with an organic group having a silyl group and a polymerizable functional group (vinyl group), and have graft polymer chains bonded [Abbreviation: Synthesis of grafted titanium oxide [GT]]
[NGC]: Anion-charged graft carbon black particles to which an organic group having a nitro group and an organic group having a polymerizable functional group (vinyl group) are added and a graft polymer chain is bonded [abbreviation: nitro group-added graft carbon] Black [NGC]
[SGC]: Anion-charged graft carbon black particles to which an organic group having a sulfone group and an organic group having a polymerizable functional group (vinyl group) are added and a graft polymer chain is bonded [abbreviation: sulfone group-added graft carbon] Black [SGC]

[Synthesis of amino group-added grafted titanium oxide [AGT]]
(A) Synthesis of titanium oxide provided with an organic group having an amino group and a vinyl group 600 g of ethanol, titanium oxide R-960 (manufactured by Dupont) and 50 g were charged into a 1 L glass reaction vessel and stirred at 150 rpm. However, a solution prepared by dissolving 10.0 g of N- [3- (trimethoxysilyl) propyl] -N ′-(4-vinylbenzyl) ethylenediamine in 100 g of methanol was added dropwise in about 60 minutes, and then 4 ° C. at 60 ° C. Stir for 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 400 mL of ethanol, stirred and redispersed, and then centrifuged at 10000 rpm for 30 minutes and decanted. The obtained white powder was allowed to stand overnight and dried, followed by vacuum drying at 70 ° C. for 4 hours to obtain surface-treated titanium oxide.
By the above method, an organic group having a vinyl group and an amino group was introduced onto the surface of titanium oxide via a silyl group.

(B) Introduction of graft polymer chain onto titanium oxide particle surface (synthesis of amino group-added grafted titanium oxide)
Next, a cationic reaction vessel in which 25.0 g of lauryl methacrylate, 160.0 g of paraffin hydrocarbon neothiozole (manufactured by Chuo Kasei Co., Ltd.) and a previously pulverized organic group having a vinyl group and an amino group were introduced into a 1 L pressurized reaction vessel. Nitrogen substitution was performed by adding 25.0 g of titanium oxide and 0.250 g of AIBN. After pressurizing with 0.1 Mpa with nitrogen, dispersion was performed 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 300 mL of isooctane, stirred and redispersed, and then centrifuged at 10000 rpm for 30 minutes and decanted twice. Furthermore, after standing overnight and drying, it was vacuum dried at 70 ° C. for 4 hours to obtain amino group-added grafted titanium oxide [AGT]. The thermogravimetric analysis of amino group-added grafted titanium oxide [AGT] showed a weight loss of 9.4%.

[Synthesis of grafted titanium oxide [GT]]
(A) Synthesis of titanium oxide having no chargeable group and having an organic group having a vinyl group Into a 1 L glass reaction vessel, 300.0 g of ethanol and 20.0 g of deionized water were added and stirred at 150 rpm. Then, 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 in which 20 g of 3- (trimethoxysilyl) propyl methacrylate was dissolved in 80 g of ethanol was added in about 1 hour. After dropping, the mixture was stirred at 60 ° C. for 4 hours. Next, the dispersion obtained by returning to room temperature and stirring was centrifuged at 5000 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 5000 rpm for 30 minutes and decanted. The obtained white powder was left to stand overnight, dried, and then vacuum-dried at 70 ° C. for 4 hours to obtain a surface-treated titanium oxide having no chargeable group (amino group) and having an organic group having a vinyl group added thereto. Obtained.

(B) Introduction of graft polymer chain onto titanium oxide particle surface (synthesis of grafted titanium oxide)
Next, 100.0 g of lauryl methacrylate, 300.0 g of paraffin hydrocarbon neothiozole (manufactured by Chuo Kasei Co., Ltd.), 96.0 g of the above-mentioned surface-treated titanium oxide, and 0.600 g of AIBN were put into a 1 L pressurized reaction vessel. After nitrogen substitution and pressurization with nitrogen to 0.1 MPa, 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 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 standing overnight and drying, it is vacuum dried at 70 ° C. for 4 hours, and grafted titanium oxide [GT] having no chargeable group.
was gotten. When the grafted titanium oxide was subjected to thermogravimetric analysis, the weight loss was 9.3%.

[Synthesis of nitro group-added graft carbon black [NGC]]
(A) Synthesis of carbon black provided with an organic group having a nitro group and a vinyl group Carbon black Printex A (Degussa, Inc.) was charged into a 4 L glass reaction vessel with 3.0 L of deionized water and stirred at 250 rpm. Manufactured): specific surface area 45 m 2 / g, DBP oil supply amount 118 ml / 100 g, A (manufactured by Degussa), specific surface area 45 m 2 / g, DBP oil supply amount 118 ml / 100 g, 115 g were charged. 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 30000 rpm for 20 minutes and decanted. The resulting black powder was charged with 500 mL of deionized water, stirred and redispersed, then centrifuged at 30000 rpm for 20 minutes and decanted. The resulting black powder was allowed to stand overnight, dried, and then vacuum dried at 40 ° C. for 4 hours to obtain carbon black provided with an organic group having a vinyl group.
Next, using 100 g of carbon black to which an organic group having a vinyl group was added, using 4-nitroaniline instead of 4-vinylaniline, the same operation as described above was performed, and a nitro group was further added. A surface-treated carbon black provided with an organic group having a nitro group and an organic group having a vinyl group was obtained.

(B) Introduction of graft polymer chain into surface-treated carbon black (nitro group-added graft carbon black)
Next, 50 g of the surface-treated carbon black, 100 mL of toluene, 100 mL of 2-ethylhexyl methacrylate, and 0.65 g of 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 THF was added and stirred, and then reprecipitated in 3 L of methanol, and suction filtered. The obtained residue was stirred and redispersed in 1.5 L of THF, 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 nitro group-added graft carbon black [NGC]. The obtained nitro group-added graft carbon black [NGC] was subjected to thermogravimetric analysis. As a result, the weight loss was 8.3%.

[Synthesis of sulfone group-added graft carbon black [SGC]]
(A) Synthesis of carbon black provided with an organic group having a sulfone group and a vinyl group Using the same method as described above, a grafted carbon black having a sulfone group added thereto using sulfanilic acid instead of 4-nitroaniline. Synthesized.
That is, while adding 3.0 L of deionized water into a 4 L glass reaction vessel and stirring at 250 rpm, carbon black Printex A (manufactured by Degussa): specific surface area 45 m 2 / g, DBP oil supply 118 ml / 100 g, A (Manufactured by Degussa), specific surface area 45 m @ 2 / g, DBP oil supply 118 ml / 100 g, 115 g were charged. 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 30000 rpm for 20 minutes and decanted. The resulting black powder was charged with 500 mL of deionized water, stirred and redispersed, then centrifuged at 30000 rpm for 20 minutes and decanted. The resulting black powder was allowed to stand overnight, dried, and then vacuum dried at 40 ° C. for 4 hours to obtain carbon black provided with an organic group having a vinyl group.
Next, using 100 g of the carbon black to which the vinyl group has been added, using sulfanilic acid in place of 4-vinylaniline, the same operation as described above is performed, and a sulfone group is further added to form an organic group having a sulfone group. And the surface treatment carbon black which provided the organic group which has a vinyl group was obtained.

(B) Introduction of graft polymer chain into surface-treated carbon black (nitro group-added graft carbon black)
Next, 50 g of surface-treated carbon black provided with the organic group having a sulfone group and an organic group having a vinyl group, 100 mL of toluene, 100 mL of 2-ethylhexyl methacrylate, and 0.65 g of 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 THF was added and stirred, and then reprecipitated in 3 L of methanol, and suction filtered. The obtained residue was stirred and redispersed in 1.5 L of THF, 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 sulfone group-added graft carbon black [SGC]. When the obtained sulfone group-added graft carbon black [SGC] was subjected to thermogravimetric analysis, the weight loss was 8.0%.

[Example 1]
Each composition was mixed according to the following formulation, and dispersed for 1 hour with an ultrasonic wave to obtain an electrophoretic dispersion of Example 1.
<Formulation of electrophoretic dispersion>
Nitro group-added graft carbon black [NGC]: 1.7 parts Amino group-added graft titanium oxide [AGT]: 40 parts Dispersant [Solsperse 17000 (manufactured by Avicia)]: 0.47 parts Nonionic surfactant [Sorbitan trio Rate (manufactured by Wako Pure Chemical Industries, Ltd.)]: 0.53 parts Isopar G (manufactured by ExxonMobil): 57.3 parts

[Example 2]
The electrophoretic dispersion liquid of Example 2 was obtained in the same manner as in Example 1 except that the nitro group-added graft carbon black [NGC] was replaced with the sulfone group-added graft carbon black [SGC].

[Comparative Example 1]
The electrophoretic dispersion liquid of Comparative Example 1 was obtained in the same manner as in Example 1 except that amino group-added grafted titanium oxide [AGT] was replaced with grafted titanium oxide [GT] having no chargeable group. .

[Comparative Example 2]
In Example 1, the nitro group-added graft carbon black [NGC] is replaced with the sulfone group-added graft carbon black [SGC], and the amino group-added graft titanium oxide [AGT] is replaced with the grafted titanium oxide [GT] having no chargeable group. An electrophoretic dispersion of Comparative Example 2 was obtained in the same manner as in Example 1 except that

  The combinations of the electrophoretic particles (carbon black, titanium oxide) in the electrophoretic dispersions of Examples 1 and 2 and Comparative Examples 1 and 2 are shown together in Table 4 below.

  Each of the electrophoretic dispersions of Examples 1 and 2 and Comparative Examples 1 and 2 obtained above was sealed in an image display cell equipped with a pair of opposed electrodes (ITO electrodes). The method was evaluated.

[Evaluation method and evaluation result of image display cell]
<In the case of Example 1 and Example 2>
When 15V was applied to the upper ITO electrode of the image display cell and -15V was applied to the lower ITO electrode, the black carbon black particles of Examples 1 and 2 were negatively charged and thus moved rapidly to the upper ITO electrode. . On the contrary, since the white titanium oxide particles are positively charged, they moved to the lower ITO electrode. When this cell is observed from the upper ITO electrode, black is observed. Next, when −15 V was applied to the upper ITO electrode, the black carbon black particles quickly moved to the lower ITO electrode, and the white titanium oxide particles quickly moved to the upper ITO electrode. Similarly, white is observed when observed from above.
<In the case of Comparative Example 1 and Comparative Example 2>
Carbon black is negatively charged, and the grafted titanium oxide without a charging group is also slightly negatively charged, so the response speed is slow and there is no memory property, but electrophoresis occurs according to the polarity of the ITO electrode. Is possible.
Therefore, in Comparative Example 1 and Comparative Example 2, when 15 V was applied to the upper ITO electrode and −15 V was applied to the lower ITO electrode, the black carbon black particles moved upward. On the contrary, when -15V was applied to the upper ITO electrode, the black electrophoretic particles moved to the lower part.
[Evaluation results]
The application switching of the voltage was performed about 100 times at a frequency of 0.1 Hz. However, in Example 1 and Example 2, it could be stably repeated. Moreover, even if voltage was removed, in Example 1 and Example 2, the electrodeposited state (memory property) was maintained (see FIG. 8). FIG. 8 shows temporal changes in white reflectance and black reflectance in the example.
In contrast, Comparative Example 1 and Comparative Example 2 did not show memory properties (see FIG. 9).
LCD EVALUATION SYSTEM LCD- The reflectance, contrast, response speed, and memory performance of 1.5 hr (90 minutes) of the image display cells in which the electrophoretic dispersions of Examples 1 and 2 and Comparative Examples 1 and 2 are sealed are shown. Measurement was performed using 5000 (manufactured by Otsuka Electronics Co., Ltd.). The evaluation results are shown in Table 5 below.

  As described above, an anion chargeable graft carbon in which an organic group having a nitro group or a sulfone group and an organic group having a polymerizable functional group are imparted to the surface of the carbon black particle and the graft polymer chain is bonded to the dispersion medium. An organic group is imparted to the black particles and the titanium oxide particle surface directly or through a coating layer, and the organic group is an amino group via a silyl group or a polymerizable functional group via a silyl group and a graft polymer chain is bonded. By containing at least cationically charged grafted titanium oxide particles, an electrophoretic dispersion having excellent memory properties was obtained.

  That is, the electrophoretic dispersion liquid of the present invention can be applied as a rewritable paper-like image display medium because it has good dispersion stability, can maintain excellent memory properties, and provides high contrast. An image display device that is excellent in terms of quality, power consumption during display operation, and the like can be provided.

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

JP 2004-526210 Announcement (Japanese Patent No. 4188091) Special table 2007-508588 published JP 2006-235137 A JP 2006-215181 A JP 2003-66494 A Special table 2004-526199 published JP 2007-225732 A JP 2007-79532 A JP 2007-231208 A JP 2009-9092 A JP 2010-20220 A

F. A. Waite, J .; Oil Col. Chem. Assoc. , 54, 342 (1971)

Claims (10)

In the dispersion medium,
An anionically charged graft carbon black particle to which an organic group having a nitro group or a sulfone group and an organic group having a polymerizable functional group are imparted to the surface of the carbon black particle and a graft polymer chain is bonded;
An organic group is imparted to the surface of the titanium oxide particle directly or through a coating layer, and the organic group is an amino group via a silyl group or a polymerizable functional group via a silyl group and has a cationic chargeability with a graft polymer chain bound thereto. Grafted titanium oxide particles;
An electrophoretic dispersion characterized by containing at least.   2. The electrophoretic dispersion according to claim 1, wherein the polymerizable functional group is at least one selected from a vinyl group, a methacryloxy group, an acryloxy group, and a styryl group.   The electricity group according to claim 1 or 2, wherein the organic group having the nitro group or the sulfone group and the organic group having a polymerizable functional group are imparted to the surface of the carbon black particles using an arylamine compound. Electrophoretic dispersion.   The organic group imparted to the surface of the titanium oxide particles directly or via a coating layer is imparted to the surface of the titanium oxide particles using a silane coupling agent. Electrophoretic dispersion liquid.   The electrophoretic dispersion according to claim 1, wherein the coating layer is made of aluminum oxide and / or silicon oxide.   6. The electrophoretic dispersion according to claim 1, wherein the graft polymer chain is grafted by a polymerization reaction using a reactive monomer on the surface of the carbon black particles provided with the organic group. liquid.   The electrophoretic dispersion according to any one of claims 1 to 6, wherein the graft polymer chain is grafted by a polymerization reaction using a reactive monomer on the surface of the titanium oxide particles provided with the organic group. liquid.   The electrophoretic dispersion according to claim 6, wherein the reactive monomer is a methacrylic acid derivative or an acrylic acid derivative.   An image display medium comprising the electrophoretic dispersion according to claim 1.   An image display device using the image display medium according to claim 9.