CN100595662C - Microcapsules for electrophoretic display elements, preparation method and use thereof - Google Patents

Abstract

The object of the present invention is to provide microcapsules for electrophoretic display elements, which can suppress the subsequent decline in contrast, even when the electrophoretic display element is allowed to be exposed to high temperature and high humidity conditions, advantageously, for a long time under high temperature and high humidity conditions (such as The same is true when left still at 60° C. and 90% RH for 24 hours). As a means for achieving the object, the microcapsule for an electrophoretic display element of the present invention includes electrophoretic fine particles and a solvent, both of which are encapsulated in a shell, and is characterized in that the content of alkali metal ions in the entire microcapsule is 150 ppm or less .

Description

Microcapsules for electrophoretic display elements, preparation method and use thereof

technical field

The present invention relates to a microcapsule for an electrophoretic display element in which electrophoretic fine particles and a solvent are encapsulated in a shell; a production method thereof; and a sheet for an electrophoretic display element using the microcapsule.

Background technique

The electrophoretic display element is a non-emissive display element that utilizes the electrophoretic phenomenon of pigment particles in a dispersion liquid in which electrophoretic pigment particles are dispersed in a coloring solvent. More particularly, electrophoretic display elements have heretofore been referred to as elements having a structure in which a dispersion liquid is enclosed in a space provided between opposing electrode substrates (films), at least one of which is The electrode substrates are transparent, and in the structure, voltage is applied to a predetermined position between the two electrode substrates, the electrophoretic particles are electrophoresed, and the difference in optical density generated between other positions is used for display, and in the absence of power (Continuous supply) and low power consumption, it has many excellent properties, such as wide viewing angle performance and long-term memory performance.

In recent years, in order to replace the existing electrophoretic display element in which the aforementioned dispersion liquid is encapsulated when it enters the space between the counter electrode substrates (see, for example, Patent Document 1 below), development and research with the following An electrophoretic display element of a structure in which microcapsules in which the aforementioned dispersion liquid is encapsulated in a shell (capsule shell; also referred to as a wall membrane, the same below) as a wall material diffuse between counter electrode substrates (for example See Patent Documents 2 and 3 below), and various performances and functions such as long-term stability of display, response, contrast of display and number of rewritable times are greatly improved compared to the aforementioned existing electrophoretic display elements.

As a microcapsule technique that can be employed when producing microcapsules for electrophoretic display elements using the aforementioned dispersion liquid as a core substance, there is a so-called interface segmentation (segmentation) method such as an aggregation method (phase separation method) (see, for example, Patent Document 4 below) , melt softening (degradation) cooling method and powder bed method, and so-called interfacial reaction methods such as interfacial polymerization method, in-situ method, liquid internal solidification film (covering) method (pore method) and interfacial reaction method (inorganic chemical reaction method) . In particular, the agglomeration method is generally suitable because the method has the advantage that the strength and thickness of the shell are easily controlled, and a multilayer shell can be formed. For example, microcapsules having a shell obtained from gelatin and gum arabic as basic materials by an aggregation method are known as microcapsules for electrophoretic display elements (see, for example, Patent Document 2 below).

When electrophoretic display elements using microcapsules are tried to be applied to various display elements in various practical fields, further improvements in various properties such as contrast which mainly affects image clarity are eagerly desired.

[Patent Document 1] JP-B-015115/1975 (Kokoku)

[Patent Document 2] Japanese Patent No. 2551783

[Patent Document 3] JP-A-086116/1989 (Kokai)

[Patent Document 4] USP2800457

However, a problem with existing electrophoretic display elements using microcapsules is that when allowed to stand under high temperature and high humidity conditions, especially when allowed to stand under high temperature and high humidity conditions for a long time (for example, at 60° C., 90% RH for 24 hours), after which a significant drop in contrast was found.

Contents of the invention

A. The purpose of the invention

Therefore, the object of the present invention is to provide microcapsules for electrophoretic display elements, even when the electrophoretic display elements are allowed to be exposed to high temperature and high humidity conditions, advantageously, for a long time under high temperature and high humidity conditions (for example, at 60° C., 90% 24 hours under RH) which can suppress the subsequent decrease in contrast when it is left standing; its preparation method; and a sheet for electrophoretic display elements using it.

B. Invention Disclosure

In order to achieve the foregoing objects, the present inventors conducted intensive studies. During this process, the inventors noticed that various ionic substances that can be contained in microcapsules for electrophoretic display elements, especially alkali metals including Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ and Fr ⁺ The presence of ions, and found that if the ionic substances in the whole microcapsules are reduced, especially if the amount (concentration) of the above-mentioned ions in the whole microcapsules is not higher than a predetermined value, the aforementioned objects can be easily achieved. Specifically, in the process of producing microcapsules for electrophoretic display elements, a large number of compounds containing various ionic substances have heretofore been used as raw materials for shells or such as acids or neutralizing agents. Ionic substances containing the above-mentioned alkali metal ions can be contained not only in the core material (liquid containing electrophoretic particles and solvent) encapsulated in the shell, but also in the shell itself (especially containing a large amount of ions in the shell). In the case where the shell is in a hygroscopic state, such as the case where it is placed under high temperature and high humidity conditions once for a long time, when a constant voltage is applied between the two electrodes of the electrophoretic display element, it should generally act as a resistance The shell acting as a device becomes conductive, the alkali metal ions contained in the entire microcapsule flow into the shell member, and a leakage current is generated, and as a result, it is considered that it is difficult to apply a predetermined voltage, reducing the fluidity of the electrophoretic particles, and in addition this current The microcapsules also flowed at positions other than the predetermined positions, so that clear display was impossible, and sufficient contrast was not obtained. Therefore, the inventors of the present invention repeatedly experimented and studied methods for reducing ionic substances (especially the above-mentioned alkali metal ions) contained in the entire microcapsules for electrophoretic display elements. As a result, two new methods (processes) were discovered.

Specifically, regarding the first method (process), the present inventors found that, as a method for easily obtaining the microcapsules for electrophoretic display elements having the aforementioned amount (concentration) of alkali metal ions having a specific value or less, using a microcapsule containing Hydrophobic solvents and liquids of electrophoretic microparticles as core substances, and specific compounds in which polyamines and polycarboxylic acids are bonded to nonionic surfactants as water-soluble surfactants for dispersing core substances into aqueous media, and using simultaneously A water-soluble compound having an epoxy group or an episulfide group as a water-soluble compound to be added after dispersion, and further reacting them, that is, making a polyamine moiety or a polycarboxylic acid moiety and an epoxy group or an episulfide group reaction, a shell is formed on the surface of the core material (droplet surface). In the specification of the present invention, an episulfide group means a functional group in which an oxygen atom in an epoxy group is replaced with a sulfur atom, and is called a thioepoxy group or an epithio group in some cases.

In the first method (process), a specific compound as a water-soluble surfactant also acts as a raw material compound, which contributes to the formation of the shell, as described above with water-soluble surfactants having epoxy groups or episulfide groups. As with the water-soluble compounds reacting with the active compounds, and due to the fact that these are the raw material compounds for the shell, it is possible to obtain microcapsules in which the content of alkali metal ions, which were previously contained in large quantities in the shell, is significantly reduced.

In addition, in the first method (process), since the raw material compound having an epoxy group or an episulfide group in a free state is generally stable in an aqueous medium, the polyamine moiety and the polyamine moiety in a specific surfactant compound The carboxylic acid moiety exhibits high reactivity, the compound readily undergoes chemical bonding even at low temperatures, and has the nature of electrostatic attraction between the polyamine moiety or the polycarboxylic acid moiety and the epoxy group or episulfide group, therefore, it is A core material with a wide particle size can easily generate a response, in addition, a shell can be formed on the surface of the core material (droplet surface) in a highly selective, very efficient and well-controlled manner, and since there is no need to use various additives such as generating alkali metal The ionic pH adjuster or the amount thereof used can be greatly reduced, and thus, microcapsules in which the content of alkali metal ions in the shell is sufficiently reduced can also be obtained. In this case, at the same time, microcapsules in which the content of alkali metal ions in the core substance enclosed in the shell is sufficiently reduced are obtained.

In addition, in the first method (process) described above, a specific surfactant compound and a raw material compound having an epoxy group are added and reacted repeatedly, so that the surface of the core substance (droplet surface) can form A shell consisting of multiple layers. Therefore, by appropriately setting the conditions, a shell having very high strength and a shell having stickiness on the surface layer can be freely formed. In addition, since the microcapsules obtained by the aforementioned first method (process) have an appropriate degree of hydrophobicity due to the physical properties of the shell, their stability such as the degree of dispersion in an aqueous solvent is improved regardless of their particle size. Therefore, there is no aggregation of microcapsules in each production step, and microcapsules can be obtained very stably and in high yield.

On the other hand, with regard to the second method (process), the present inventors found that if a new method (process) is carried out, the method includes the steps of: causing microcapsules for electrophoretic display elements (wherein the microcapsules are obtained by the microencapsulation step ) coexists with the ion exchange resin in the aqueous medium, it is possible to effectively remove ionic substances (desalination) from the microcapsules (especially from the shell portion thereof), and as a result, the aforementioned objects can be achieved simultaneously.

The present invention has been accomplished based on the foregoing findings.

Therefore, the microcapsule for electrophoretic display element of the present invention includes electrophoretic fine particles and a solvent, both of which are enclosed in a shell, and is characterized in that the content of alkali metal ions in the entire microcapsule is 150 ppm or less.

The first method of the present invention for producing microcapsules for electrophoretic display elements comprises the steps of: dispersing a core substance in an aqueous medium containing a water-soluble surfactant, wherein the core substance is a liquid containing a hydrophobic solvent and electrophoretic particles; and thereafter A water-soluble compound is added to the aqueous medium; a shell is then formed on the surface of the core substance; and it is characterized in that a compound (A) represented by the following general formula (1) is used as the water-soluble surfactant:

R ¹ -(CH ₂ -CH ₂ -O-) _n -XR ² (1)

(wherein R ¹ represents an aliphatic or aromatic hydrophobic group with a carbon number of 5-25, R ² represents a polymer group with a polyamine structure or a polycarboxylic acid structure with a weight average molecular weight of 300-100000, and n represents an integer 3-85, and X represents a group derived from a group capable of reacting with at least one group selected from amino, imino and carboxyl, and is formed after the reaction, but has nothing to do with the presence or absence of X)

and a compound (B) having an epoxy group or an episulfide group as a water-soluble compound; and forming a shell by reacting a compound (A) with a compound (B).

The second method of the present invention for producing microcapsules for electrophoretic display elements includes the step of causing the microcapsules to coexist with ion exchange resins in an aqueous medium, wherein the microcapsules include electrophoretic particles and a solvent, both enclosed in a shell.

The sheet for electrophoretic display elements of the present invention includes: the microcapsules for electrophoretic display elements of the present invention described above; and a binder resin.

The electrophoretic display element of the present invention is provided with a sheet for an electrophoretic display element, wherein the sheet includes the above-mentioned microcapsules for an electrophoretic display element of the present invention; and a binder resin.

In detail, the microcapsules for electrophoretic display elements of the present invention can suppress the subsequent decline in contrast even when the electrophoretic display element is allowed to stand under high temperature and high humidity conditions, especially for a long time under high temperature and high humidity conditions (such as in The same is true at 60° C., 90% RH for 24 hours). The microcapsules for electrophoretic display elements obtained by the first method of preparing microcapsules for electrophoretic display elements of the present invention can suppress the subsequent decrease in contrast even when the electrophoretic display elements are allowed to stand for a long time under high temperature and high humidity conditions ( For example, at 60° C. and 90% RH for 24 hours), the same is true. On the other hand, the microcapsules for electrophoretic display elements obtained by the second method of preparing microcapsules for electrophoretic display elements of the present invention can suppress the subsequent loss of contrast. drop even when the electrophoretic display element was allowed to stand under high temperature and high humidity conditions.

C. Invention effect

The present invention can provide: a microcapsule for an electrophoretic display element that can suppress a subsequent decrease in contrast even when the electrophoretic display element is allowed to operate under high temperature and high humidity conditions, advantageously under high temperature and high humidity conditions When left standing for a long time (eg, 24 hours at 60° C., 90% RH); its production method; and a sheet for electrophoretic display elements using the same.

These and other objects and advantages of the present invention will be more apparent from the following detailed disclosure.

Detailed ways

The present invention will now be described in detail, but these descriptions do not limit the scope of the present invention, and with respect to embodiments other than those exemplified below, changes may be appropriately made without detracting from the gist of the present invention.

[Microcapsules for electrophoretic display components]:

The microcapsule for an electrophoretic display element of the present invention (hereinafter referred to as the microcapsule of the present invention), as described above, is a microcapsule comprising electrophoretic fine particles and a solvent, wherein the two are encapsulated in a shell (capsule shell, wall membrane) Inner, specifically, is a microcapsule in which a liquid in which electrophoretic particles are dispersed in a solvent (dispersion liquid) is encapsulated in a shell as a core substance, and importantly, Li ⁺ , Na ⁺ , The content (concentration) of alkali metal ions of K ⁺ , Rb ⁺ , Cs ⁺ and Fr ⁺ is 150 ppm or less. Thus, even when the electrophoretic display element using the above-mentioned microcapsules is allowed to stand for a long time under high temperature and high humidity conditions (for example, 24 hours at 60° C., 90% RH), subsequent decrease in contrast can be suppressed. The above content of alkali metal ions is preferably 120 ppm or less, more preferably 100 ppm or less. When the content of alkali metal ions exceeds 150 ppm, in the case where the electrophoretic display element using microcapsules is allowed to stand for a long time under high temperature and high humidity conditions (for example, 24 hours at 60° C., 90% RH), then The contrast ratio may drop significantly.

In particular, a decrease in the content of Na ⁺ (sodium ions) can further increase the effect of suppressing a decrease in contrast, and is therefore preferable. Specifically, the in-shell content is preferably 100 ppm or less, more preferably 80 ppm or less, further preferably 60 ppm or less, particularly preferably 50 ppm or less.

In addition, a problem with existing electrophoretic display elements in which TFT electrodes are used as display electrodes in contact with microcapsules is that ionic substances inhibit the action of TFTs, and thus the elements cannot be properly controlled. However, if the above-mentioned microcapsules of the present invention are used, specifically, microcapsules for electrophoretic display elements in which the content of alkali metal ions (especially sodium ions) in the entire microcapsules is reduced, there may be an effect that even the above-mentioned problems may be solved simultaneously. .

By the way, in the present invention, the ion content (the content of alkali metal ions (including the content of each of various alkali metal ions and the total content thereof)) in the whole microcapsule is determined by the following examples Values measured by methods described.

The shells in the microcapsules of the present invention are not limited, but preferred examples include shells formed from hitherto known shell materials that can be used to prepare microcapsules. But a shell formed by performing especially the below-mentioned "first method of the present invention for producing microcapsules for electrophoretic display elements" is particularly preferred because the aforementioned content range of alkali metal ions can be further easily satisfied. As hitherto known shell raw materials, for example, when using the coagulation method, it is preferable to combine cationic compounds such as compounds having an isoelectric point such as gelatin and polyethyleneimine and anionic substances such as gum arabic, carboxymethylcellulose, and styrene horsedot. Polyacrylic acid copolymer and polyacrylic acid. When an in situ polymerization method is used, melamine formaldehyde resins (melamine formaldehyde prepolymers) and free radical polymerizable monomers are preferred. When the interfacial polymerization method is used, it is preferable to combine hydrophilic monomers such as polyamines, diols, and polyvalent phenols with hydrophobic monomers such as polyacyl halides, bishalogenated formals, and polyvalent isocyanates, and form polyamide epoxy resins , polyurethane and polyurea shells.

A polyvalent amine can be further added to the shell raw material, and microcapsules excellent in the heat resistance retention of the shell can be obtained. The amount of polyvalent amine to be used may be such that the physical properties of the desired shell are not greatly impaired due to the shell raw material. Preferable examples of polyvalent amines include: aliphatic amines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1,3-propylenediamine, and hexamethylenediamine , epoxy compound adducts of aliphatic polyvalent amines such as poly(1-5) alkylene (C ₂ -C ₆ ) polyamine-oxyalkylene (C ₂ -C ₁₈ ) adducts, aromatic Polyvalent amines such as phenylenediamine, diaminonaphthalene and xylylenediamine, alicyclic polyvalent amines such as piperazine and heterocyclic diamines such as 3,9-bisaminopropyl-2,4,8,10-tetra Oxyspiro-[5.5]undecane. These may be used alone or in combination of two or more.

By telling specific examples, a dispersion liquid (a liquid in which electrophoretic particles are dispersed in a solvent; this liquid may be referred to as a dispersion liquid for an electrophoretic display element) encapsulated in a shell as a core substance will be explained below.

In general, as electrophoretic display, there is a method of displaying by the contrast between the color of the solvent in the dispersion liquid and the color of the electrophoretic particles, and by the contrast between the colors of at least two types of electrophoretic particles in the dispersion liquid. displayed method.

The solvent used in the dispersion liquid may be a solvent commonly used heretofore in dispersion liquids for electrophoretic display elements, but is not limited to these. More particularly, the solvent is substantially insoluble in water (hydrophobic), and may be a solvent that does not interact with the formed shell to such an extent that its function is impaired. For example, highly insulating organic solvents are preferred.

Preferable examples of highly insulating organic solvents include: aromatic hydrocarbons such as o-, m-, or p-xylene, toluene, benzene, dodecylbenzene, hexylbenzene, phenylxylylethane, and naphthyl hydrocarbons, and aliphatic hydrocarbons Hydrocarbons such as cyclohexane, n-hexane, kerosene and paraffinic hydrocarbons. In particular, long-chain alkylbenzenes such as dodecylbenzene and hexylbenzene and phenylxylylethane are more preferred because of their high boiling point and flash point and low toxicity. These solvents may be used alone or in combination of two or more.

When the solvent is colored, it is preferable to color the solvent to such an extent that sufficient contrast is obtained with respect to the electrophoretic fine particles (for example, white in the case of titanium oxide fine particles).

When the solvent is a coloring solvent, there are no particular limitations on the dye used in coloring, but oil-soluble dyes are preferred, and azo dyes and anthraquinone dyes are more preferred especially from the viewpoint of ease of use. Specifically, preferred examples of yellow dyes include azo compounds such as Oil Yellow 3G (manufactured by Orient Chemical Industries, Ltd.), preferred examples of orange dyes include azo compounds such as Fast Orange G (manufactured by BASF), blue Preferred examples of dyes include anthraquinones such as Macrolex blue RR (manufactured by Bayer A.G.), preferred examples of green dyes include anthraquinones such as Sumiplast Green G (manufactured by Sumitomo Chemical Co., Ltd.), preferred examples of brown dyes include azo Compounds such as Oil Brown GR (produced by Orient Chemical Industries, Ltd.), preferred examples of red dyes include azo compounds such as Oil Red 5303 (produced by Arimoto Chemical Co., Ltd.) and Oil Red 5B (produced by Orient Chemical Industries, Ltd. prepared), preferred examples of purple dyes include anthraquinones such as Oil Violet #730 (produced by Orient Chemical Industries, Ltd.), and preferred examples of black dyes include azo compounds such as Sudan Black X60 (produced by BASF), and anthraquinones A mixture of Macrolex Blue FR (manufactured by Bayer A.G.) and Azo Oil Red XO (manufactured by Kanto Chemical Co., Inc.). These dyes may be used alone or in combination of two or more.

The electrophoretic fine particles used in the dispersion liquid are not limited as long as it is an electrophoretic pigment particle, that is, colored particles showing positive or negative polarity, but not limited. Specifically, white particles such as titanium oxide, and black particles such as carbon black and titanium black are preferable, or other particles described later may be used. These may be used alone, or two or more kinds may be used in combination.

When titanium oxide fine particles are used, the kind of titanium oxide is not limited, but titanium oxide which is generally a white pigment can be used. Titanium oxide may be anatase or rutile. When considering the discoloration of the colorant due to the photoactive ability of titanium oxide, the anatase type having low photoactive ability is preferable, and in order to further reduce the photoactive ability, Si-treated, Al-treated, Si-Al-treated or Zn-Al treated titanium oxide.

As the electrophoretic fine particles, particles other than the aforementioned titanium oxide fine particles, carbon black, and titanium black may be used in combination, or other particles may be used instead of titanium oxide. Preferably the other particles are pigment particles like titanium oxide particles. In addition, other particles are not necessarily required to have the same electrophoretic properties as titanium oxide particles. If necessary, electrophoretic performance can be imparted by some hitherto known methods.

The above-mentioned other particles are not limited, but preferred examples of white particles include inorganic pigments such as barium sulfate, zinc oxide, and zinc white in addition to the aforementioned titanium oxide; preferred examples of yellow particles include inorganic pigments such as yellow iron oxide, cadmium yellow, Titanium yellow, chromium yellow and chrome yellow, insoluble azo compounds such as fast yellow, fused azo compounds such as chromophthal yellow, azo complex salts such as benzimidazolone azo Yellow, fused polycyclic such as fravans yellow, organic pigments such as Hansa yellow, naphthol yellow, nitro compounds, and pigment yellow; preferred examples of organic particles include inorganic pigments such as molybdate orange, and organic pigments such as azo complex salts Such as benzimidazolone azo orange and fused polycyclic rings such as perylene orange; preferred examples of red particles include inorganic pigments such as red iron oxide and cadmium red, and organic pigments such as dyed lakes such as mada lake, soluble diacetate Nitrogen compounds such as lake red, insoluble azo compounds such as naphthol red, fused azo compounds such as chromophthal scared, fused polycyclic compounds such as thioindigo Bordeaux, quinacridone pigments such as sinkasha red Y and hostapalm red, and azo Pigments such as permanent red and fast slow red; preferred examples of violet particles include inorganic pigments such as manganese magenta, and organic pigments such as dyeing lakes such as rhodamine lakes, and fused polycyclic rings such as dioxazine violet; blue particles Preferable examples include inorganic pigments such as Prussian blue, dark blue, cobalt blue, and cerulean blue, and organic pigments such as phthalocyanine such as phthalocyanine blue, indanthrene such as indanthrene blue, alkali blue; preferred examples of green particles are inorganic Pigments such as emerald green, chrome green, chromium oxide, and pyridian, and organic pigments such as azo complex salts such as nickel azo yellow, nitroso compounds such as pigment green and naphthol green, and phthalocyanines such as phthalocyanine green; black Preferable examples of the particles include inorganic pigments such as iron black, and organic pigments such as aniline black, in addition to the aforementioned carbon black and titanium black. These may be used alone, or two or more kinds may be used in combination.

The particle diameter of the electrophoretic fine particles is not limited, but is preferably 0.1-5 micrometers, more preferably 0.2-3 micrometers, expressed by volume average particle diameter. When the particle diameter (volume average particle diameter) is less than 0.1 micron, sufficient opacity properties cannot be obtained in the display part in the electrophoretic display element, and the degree of coloring is lowered, and an electrophoretic display element having high contrast performance may not be obtained. When the particle diameter exceeds 5 micrometers, it is necessary to increase the degree of coloring of the particles themselves to a higher degree than necessary (increasing the pigment concentration), and the smooth electrophoretic performance of the microparticles may be reduced.

The dispersion liquid may contain other components as needed in addition to the aforementioned solvent and electrophoretic particles, and the kinds thereof are not limited. Examples of other components include dispersants. The dispersant may be included before the electrophoretic fine particles are dispersed in the solvent, or the dispersant may be included after the particles are dispersed, without limitation.

The dispersant is generally not limited as long as it is a heretofore known dispersant that can assist the particles to disperse in the solvent. Preferable examples include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, fluorine-based surfactants, sorbitan fatty acid ester surfactants such as sorbitan sesquite Oleate, dispersants such as block type polymers and graft type polymers, and various coupling agents soluble in the dispersion liquid. These may be used alone or in combination of two or more. Among the aforementioned dispersants, a coupling agent is more preferable because the stability of the dispersion becomes better when an electric charge is applied. When the microparticles are treated with a coupling agent, a coating of the coupling agent is formed on the surface of the microparticles.

Preferable examples of coupling agents include: (i) silane coupling agents, (ii) titanate-based coupling agents, (iii) aluminum-based coupling agents, (iv) vinyl-based coupling agents, (v) A coupling agent having at least one group selected from an amino group, a quaternary ammonium salt, a carboxyl group, and a phosphate group, (vi) a coupling agent having an amino group or a glycidyl group at the terminal, and (vii) an organodisilazane. More preferably a titanate coupling agent and an aluminum-based coupling agent, and further preferably the aforementioned various coupling agents that also have a long-chain alkyl group, and especially preferably a titanate coupling agent that also has a long-chain alkyl group, and Aluminum-based coupling agents with long chain alkyl groups are also available. The aforementioned coupling agents may be used alone, or in combination of two or more.

The reason why a coupling agent having a long-chain alkyl group is preferable as described above is because long-chain alkylbenzene and the like, which are solvents with a high degree of safety, increase the affinity, and thus the effect of improving the dispersion stability of the electrophoretic fine particles is high .

When preparing the dispersion liquid, the method of dispersing the electrophoretic fine particles into the solvent may be a generally known dispersion method without limitation. Preferable examples include: a method comprising the steps of introducing, as raw material components, such as electrophoretic particles, a solvent, and a coupling agent into an ultrasonic bath, and then ultrasonically dispersing them under stirring; a method comprising the steps of using Capable instruments, such as paint shakers, ball mills and sand mills, to disperse particles; dry methods including the following steps: spraying coupling agent with dry air or nitrogen, while using forced agitation of solvent and particles such as a V blender; a wet method comprising the steps of appropriately dispersing the microparticles in a solvent to obtain a slurry, and then adding a coupling agent; and a spraying method comprising the steps of spraying the coupling agent while vigorously stirring the preheated solvent and microparticles .

The shape of the microcapsules of the present invention is not limited, but a granular shape such as a pearl shape is preferred.

The particle diameter (volume average particle diameter) of the microcapsules of the present invention is not limited, but is preferably 5-300 micrometers, more preferably 10-200 micrometers, further preferably 15-150 micrometers. When the microcapsules have a particle diameter of less than 5 microns, sufficient display concentration may not be obtained on a display member when the microcapsules are used in an electrophoretic display element. When the particle diameter exceeds 300 micrometers, there may be a problem in the mechanical strength of the microcapsule itself, and in addition, when the microcapsule is used in an electrophoretic display element, the fine particles of titanium oxide encapsulated in the dispersion liquid in the microcapsule will The electrophoretic performance may not be fully developed and the displayed onset voltage becomes high.

The coefficient of variation of the particle diameter (volume average particle diameter) of the microcapsules of the present invention is preferably 30% or less, more preferably 25% or less, further preferably 20% or less. When the coefficient of variation exceeds 30%, the presence ratio of those microcapsules having effective particle diameters as microcapsules for electrophoretic display elements may decrease, requiring the use of many microcapsules.

The particle size of the microcapsules of the present invention and its coefficient of variation (ie, the narrowness of the particle size distribution) are mainly determined by the particle size and particle size distribution of the dispersion liquid in which the particles are dispersed in the aqueous medium at the time of preparation. Therefore, by properly controlling the dispersion conditions for preparation, microcapsules with desired particle size and its coefficient of variation can be obtained.

The shell thickness in the microcapsules of the present invention is not limited, but in wet state, it is preferably 0.1-5 microns, more preferably 0.1-4 microns, further preferably 0.1-3 microns. When the thickness of the shell is less than 0.1 micrometer, sufficient strength as the shell may not be obtained. When the thickness exceeds 5 micrometers, the transparency decreases, which is the cause of the decrease in contrast. In addition, the flexibility of the microcapsule itself may decrease, and the adhesiveness to the electrode film becomes insufficient.

As the method for producing the microcapsules of the present invention, the "first method of the present invention for producing microcapsules for electrophoretic display elements" mentioned below is particularly preferable because the microcapsules for electrophoretic display elements having the aforementioned characteristics can be easily obtained. In addition, the method for preparing the microcapsules of the present invention is not limited to this one, and a hitherto known process including a microencapsulation step, for example using a so-called interfacial sedimentation method such as a coacervation method (phase separation method), can also be preferably used, In-liquid (in-liquid) drying method, melt softening cooling method, spray drying method, paint storage pan (pan) coating method, air suspension covering method and powder bed method, or the so-called interface reaction method, such as interface Polymerization method, in-situ polymerization method, liquid inner solidified film (covering) method (porosity method) and interfacial reaction method (inorganic chemical reaction method). In this case, for example, the "second method of the present invention for producing microcapsules for electrophoretic display elements" mentioned below is preferably employed. Specifically, a step (A) of causing microcapsules for electrophoretic display elements (in which microcapsules are obtained by means of a microencapsulation step and in which electrophoretic particles and a solvent are encapsulated in a shell) to coexist with an ion exchange resin in the In aqueous media, ionic species are thereby removed (desalination), ie the amount of ions is reduced (alkali metal ion content).

The microcapsule of the present invention is a microcapsule for an electrophoretic display element, and can be used in all various display elements utilizing and employing an electrophoretic display element therein. Examples include, in addition to normal electrophoretic display panels, flexible display elements that are as thin as paper and freely bend, which can be easily converted into large-area and cheap display elements, so-called digital paper (e-paper), such as paper-like displays and Rewritable paper, display components such as IC cards and IC tags, electronic whiteboards, guide panels, advertising boards, electronic paper, electronic books, and portable terminals such as PDAs.

[Method for producing microcapsules for electrophoretic display element]

(the first method for preparing microcapsules for electrophoretic display elements):

Regarding the first method of the present invention for producing microcapsules for electrophoretic display elements (hereinafter referred to as the first production method of the present invention), it is important that, as described above, when dispersing a core substance (which is a liquid containing a hydrophobic solvent and electrophoretic particles (specifically, a liquid in which the electrophoretic particles are dispersed in a hydrophobic solvent (hydrophobic dispersion liquid)), after which a water-soluble compound is added to the aqueous medium, Thus when a shell is formed on the surface of the core substance, the aforementioned compound (A) acts as a water-soluble surfactant, and the aforementioned compound (B) acts as a water-soluble compound, and the shell is formed by reacting these compounds (A) and (B). That is, in the first preparation method of the present invention, not only the compound (B) (which is a water-soluble compound), but also the compound (A) (which is a water-soluble surfactant) is used as a raw material for the shell compound.

It can be said that the first production method of the present invention is a method of producing microcapsules for electrophoretic display elements, which is classified as a so-called coagulation method (phase separation method).

A general method of producing microcapsules for electrophoretic display elements in order to carry out the first production method of the present invention will be explained, and features of the first production method of the present invention will be explained in detail below. In carrying out the present invention, as techniques and conditions other than those described below, techniques and conditions generally employed in the method of producing the microcapsules for electrophoretic display elements of the present invention can be suitably employed.

In the first production method of the present invention, first, a hydrophobic dispersion liquid as a core substance which will become a core substance is dispersed in an aqueous medium containing a specific water-soluble surfactant.

The aqueous medium usable in the first production method of the present invention is not limited, but for example, water or a mixture of a hydrophilic organic solvent and water can be used. When the hydrophilic organic solvent and water are used in combination, the blending ratio of water is preferably 95-70 wt%, more preferably 95-80 wt%.

Hydrophilic organic solvents are not limited, but preferred examples include alcohols such as methanol, ethanol, isopropanol, n-propanol, and allyl alcohol; glycols such as ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, pentylene glycol, Hexanediol, heptanediol, and dipropyleneglycol, ketones such as acetone, methyl ethyl ketone, and methyl propyl ketone; esters such as methyl formate, ethyl formate, methyl acetate, and methyl acetoacetate; ethers such as diethylene glycol mono Methyl ether, diethylene glycol monoethyl ether, diglyme, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and dipropylene glycol monomethyl ether. These may be used alone, or two or more kinds may be used in combination.

In the first production method of the present invention, an aqueous medium may be used together with other solvents besides the aforementioned water and hydrophilic organic solvents. Examples of other solvents include hexane, cyclopentane, pentane, isopentane, octane, benzene, toluene, xylene, ethylbenzene, aminyl squalane, petroleum ether, terpenes, castor oil, soybean oil, paraffins and keronine. When other solvents are used in combination, they are used in an amount of preferably 30 wt% or less, more preferably 25 wt% or less, further preferably 20 wt% or less, relative to the aforementioned aqueous medium including a hydrophilic organic solvent and water.

The hydrophobic dispersion liquid that can be used in the first production method of the present invention is not limited, but the explanation of "dispersion liquid" in the microcapsules of the present invention can be similarly applied.

In the first preparation method of the present invention, the amount of the hydrophobic dispersion liquid as the core substance to be dispersed in the aqueous medium is not limited, but it is preferably 5 to 70 parts by weight, more preferably 10 parts by weight, relative to 100 parts by weight of the aqueous medium. -65 parts by weight. When the amount is less than 5 parts by weight, since the concentration is low, the reaction of the compound (A) and the compound (B) takes a long time, and the target shell may not be formed, and microcapsules with a wide particle size distribution are obtained, resulting in a high yield. decline. On the other hand, when the amount exceeds 70 parts by weight, there may be cases where the hydrophobic dispersion liquid aggregates or condenses (forms into one body), and forms a reverse phase suspension, and it becomes impossible to prepare microcapsules.

In the first preparation method of the present invention, as mentioned above, the compound (A) represented by the following general formula (1) is used as the aforementioned specific water-soluble surfactant:

R ¹ -(CH ₂ -CH ₂ -O-) _n -XR ² (1)

(wherein R ¹ represents an aliphatic or aromatic hydrophobic group with a carbon number of 5-25, R ² represents a polymer group with a polyamine structure or a polycarboxylic acid structure with a weight average molecular weight of 300-100000, and n represents an integer 3-85, and X represents a group derived from a group capable of reacting with at least one group selected from amino, imino and carboxyl, and formed after the reaction, regardless of the presence or absence of X). By using the compound (A), the aforementioned objects of the present invention can be easily achieved.

In the general formula (1), R ¹ represents an aliphatic or aromatic hydrophobic group with a carbon number of 5-25, and examples include aliphatic hydrocarbon groups such as pentyl, hexyl, heptyl, octyl, decyl, dodecyl Alkyl, octadecyl and behenyl, and aromatic hydrocarbon groups such as phenyl, benzyl, tolyl, xylyl, biphenyl, p-terphenyl, indenyl, naphthyl and indenyl- Naphthyl, but not limited to these.

The carbon number of the hydrophobic group represented by R ¹ is 5-25, preferably 5-18. When the carbon number is less than 5, the compound (A) may not have sufficient surface active ability. When the carbon number exceeds 25, the hydrophobicity becomes too high, and the solubility of the compound (A) in water may be lowered.

In the general formula (1), "-(CH ₂ -CH ₂ -O-) _n -" is a polymer group having a polyether structure (polyethylene oxide structure), and importantly, the structural unit " The number of n of CH ₂ -CH ₂ -O-" is 3-85. Here, n is preferably 5-60, more preferably 5-50. When n is less than 3, the solubility in aqueous medium may not be sufficiently realized, resulting in water insolubility, and when n exceeds 85, the solubility in aqueous medium becomes too high even when reacting with compound (B) , it may be the case that the compound does not precipitate as an insoluble, and the shell is not sufficiently formed, depending on the balance between the hydrophobic groups.

In the general formula (1), X represents a group derived from a group capable of reacting (bonding reaction) with at least one group selected from amino, imino and carboxyl, and is formed after the reaction (bonding reaction), However, it does not matter whether X exists in the general formula (1). Here, the amino group, imino group, and carboxyl group refer more specifically to amino group and imino group that may exist in a polymer having a polyamine structure, and carboxyl groups that may exist in a polymer having a polycarboxylic acid structure. Examples of the group capable of reacting with at least one group selected from these groups include groups represented by X ² in the following general formula (3). As the group represented by X, specifically, "-CH ₂ -CH ₂ -S-" derived from a group represented by the following structural formula (b), "-NH-CO" derived from an isocyanate group, -, "-CO-NH-CH ₂ -CH ₂ -" derived from oxazoline group, "-CH(OH)-" derived from aldehyde group, "-CO-" derived from carboxyl group, "-CO- derived from amino group"-NH-", and "=N-" derived from an imino group.

In the general formula (1), R ² represents a polymer group having a polyamine structure or a polycarboxylic acid structure with a weight average molecular weight of 300-100,000, preferably a weight average molecular weight of 300-50,000. When the weight average molecular weight is less than 300, there may be cases in which insoluble matter slowly precipitates when reacting with compound (B), and it takes a long time to form a shell, and a shell with high strength cannot be obtained. When the molecular weight exceeds 100,000, there may be cases that the viscosity of the entire reaction system rapidly increases by reaction with the compound (B), and stirring becomes difficult. In addition, when stirring is forced, it is difficult to control the droplet particle size of the hydrophobic dispersion liquid, for example, the particle size may become too small.

Polymer groups having a polyamine structure are not limited, but examples include polymer groups having a polyamine structure containing primary and/or secondary amino groups, for example having at least one selected from the group consisting of polyethyleneimine, polyamine, poly Etheramine, polyvinylamine, modified polyvinylamine, polyalkylamine, polyamide, polyamine epichlorohydrin, poly(dialkylaminoalkyl vinyl ether), poly(dialkylaminoalkyl( meth)acrylate), polyallylamine, polyethyleneimine-grafted polyamidoamines and polymer groups in protonated polyamidoamines.

Examples of polymer groups having a polycarboxylic acid structure are not limited, but examples include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, α-hydroxyacrylic acid, crotonic acid, phthalic acid, A polymer group with a water-soluble polycarboxylic acid structure obtained from maleic acid, fumaric acid, itaconic acid, citraconic acid, aconitic acid and vinyl acetate.

The preparation method of the compound (A) represented by the general formula (1) is not limited, but preferably under stirring, by dropwise adding the compound represented by the following general formula (2) or the following general formula (3) to the polyamine or polycarboxylic acid A method of obtaining compound (A) by reacting them in an aqueous solution.

R ¹ -(CH ₂ -CH ₂ -O-) _n-1 -X ¹ (2)

(wherein ^X represents the group represented by the following structural formula (a):

R ¹ -(CH ₂ -CH ₂ -O-) _n -X ² (3)

(wherein ^X represents any group selected from the group represented by the following structural formula (b):

Cyanate group, oxazoline group, aldehyde group, carboxyl group, amine group and imino group, that is, ^X2 represents the reaction (bonding reaction) that can be selected from at least one group in amine group, imino group and carboxyl group. group)

When compound (A) is prepared using a compound represented by general formula (2), the group represented by X does not exist in general formula (1). On the other hand, when the compound represented by the general formula (3) is used, the group represented by X exists in the general formula (1).

The reaction temperature at the time of reaction is not limited, but when polyamine is used, it is preferably 10-90°C, more preferably 15-80°C, and when polycarboxylic acid is used, it is preferably 20-100°C, more preferably 20-90°C. The reaction time is not limited, but is preferably 0.5-5 hours, more preferably 1-5 hours.

In the first production method of the present invention, before the hydrophobic dispersion liquid is dispersed in the aqueous medium, the compound (A) as a water-soluble surfactant may be dissolved in the aqueous medium, or may be dissolved simultaneously with or after the dispersion Dissolved, but not restricted.

In the first preparation method of the present invention, relative to the hydrophobic dispersion liquid to be dispersed in the aqueous medium, the blending ratio of the compound (A) is preferably 1-30wt%, more preferably 3-25wt%, further preferably 5-25wt%. 25 wt%. When the blending ratio of the compound (A) is less than 1% by weight, the dispersed state of the hydrophobic dispersion liquid may not be maintained sufficiently stably, and droplets of the hydrophobic dispersion liquid aggregate or condense (form into one body). On the other hand, when the ratio exceeds 30 wt%, the viscosity of the entire reaction system may increase rapidly due to the reaction with the compound (B), thereby stirring becomes difficult, and when forced stirring, the droplet size of the hydrophobic dispersion liquid Control may become difficult, eg the diameter becomes too small.

In the first production method of the present invention, the method of dispersing the hydrophobic dispersion liquid into the aqueous medium is not limited, but generally known dispersion methods can be used. Preferable examples include stirring the mixture vigorously mechanically by using a disperser, a homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) or a homogenizer (manufactured by Nihonseiki Kaisha Ltd.), dispersion containing an aqueous medium, hydrophobic dispersion A method of a mixture of a liquid and a water-soluble surfactant; by making the aforementioned mixture flow through a static tubular (in-static-tube) mixer (Noritake Static Mixer (manufactured by Noritake Company Limited)), a throughzer mixer (manufactured by Sumitomo Heavy Machine Industries , Ltd.), a Sakea mixer (manufactured by Sakura Seisakusho Co., Ltd.) or a TK ROSS LPD mixer (manufactured by Tokushu Kika Kogyo Co., Ltd.); a method of dispersing by flowing through the pores Such as SPG membrane (silus porous glass) and microchannel emulsification equipment (manufactured by EP Teck), a method of dispersing a hydrophobic dispersion liquid in an aqueous medium containing a water-soluble surfactant.

In the first production method of the present invention, after dispersing the hydrophobic dispersion liquid, a shell is formed on the droplet surface of the hydrophobic dispersion liquid by adding a specific water-soluble compound to the aqueous medium.

As a specific water-soluble compound, a compound (B) having an epoxy group or an episulfide group is used. The aforementioned object of the present invention can be easily achieved by combining the aforementioned compound (A) and compound (B). Preferable examples of the epoxy group in the compound (B) include compounds represented by the structural formula (a) and groups represented by the following structural formula (c):

And preferred examples of the episulfide group in the compound (B) include a group represented by the structural formula (b) and a group represented by the following structural formula (d):

Compound (B) having an epoxy group is not limited, but water-soluble epoxy compounds having two or more epoxy groups in one molecule are preferred, and examples include sorbitol polyglycidyl ester, sorbitan Polyglycidyl esters, (poly)glycerol polyglycidyl esters, pentaerythritol polyglycidyl esters, triglycidyl (2-hydroxyethyl) isocyanurate, trimethylolpropane polyglycidyl esters, neopentyl di Alcohol diglycidyl ester, ethylene, polyethylene glycol diglycidyl ester, propylene, polypropylene glycol diglycidyl ester, and adipate diglycidyl ester. These may be used alone, or two or more kinds may be used in combination.

The compound (B) having an episulfide group is not limited, but water-soluble episulfide compounds having two or more episulfide groups in one molecule are preferred, and examples include sorbitol polythioglycidyl ester, (Poly)glycerol polythioglycidyl ester, trithioglycidyl tris(2-hydroxyethyl)isocyanurate, propylene glycol dithioglycidyl ester, polypropylene glycol dithioglycidyl ester, and hexadiene acid dithioglycidyl ester. These may be used alone, or two or more kinds may be used in combination.

The solubility of compound (B) in water is preferably 30 wt% or more, more preferably 40 wt% or more, further preferably 50 wt% or more. When the solubility of compound (B) in water satisfies the aforementioned range, the reaction with compound (A) proceeds uniformly and rapidly, forming a shell uniformly and rapidly, and obtaining the excellent effect of better control of the thickness and strength of the shell. On the other hand, when the solubility is less than 30% by weight, the reaction with the compound (A) becomes uneven, and the shell may be formed unevenly. In the present invention, the solubility of compound (B) in water is a value obtained by the method described in the following Examples.

The weight average molecular weight of the compound (B) is preferably 300-100,000, more preferably 300-75,000, further preferably 300-50,000. When the weight average molecular weight of the compound (B) satisfies the aforementioned range, excellent effects such as easy control of the thickness and strength of the shell are obtained. When the weight average molecular weight is less than 300, it is difficult to obtain a shell with sufficient strength, and it is difficult to control reactivity with compound (A), and it may be difficult to form a uniform shell. On the other hand, when the weight-average molecular weight exceeds 100000, the viscosity of the entire reaction system increases rapidly due to the reaction with the compound (A), and stirring may become difficult, and when forced stirring, it may be difficult to control the liquid droplet of the hydrophobic dispersion liquid. Particle size, eg particle size becomes too small.

The amount of compound (B) to be added is not limited, but is preferably 0.1-10 parts by weight, more preferably 0.5-5 parts by weight, further preferably 0.5-3 parts by weight relative to 1 part by weight of compound (A). The thickness of the formed shell can be easily controlled by adjusting the amount of the compound (B) to be added. When the amount of the compound (B) to be added is less than 0.1 parts by weight, a sufficient amount of the shell may not be formed, and when the amount exceeds 10 parts by weight, there may be a large deviation in the component composition of the shell, and the strength of the shell decline.

The method of adding the compound (B) to the aqueous medium is not limited; but it may be added at one time, or may be added sequentially (continuous addition and/or intermittent addition).

In the first production method of the present invention, a shell is formed on the droplet surface of the hydrophobic dispersion liquid by reacting the added compound (B) with the aforementioned compound (A). Specifically, the epoxy group of the compound (B) reacts with the polyamine moiety (amino group, imino group, etc.) or the polycarboxylic acid moiety (carboxyl group, etc.) of the compound (A) together, thereby causing the compound (A) and the compound ( B) The derivatized insoluble reaction product deposits on the surface of the droplets of the hydrophobically dispersed liquid, as a result of which a shell is obtained.

The temperature at ^which the compound (A) reacts with the compound (B) is not limited, but when a compound in which R in the general formula (1) is a polymer group having a polyamine structure is used as the compound (A), the temperature is preferably is 25-75° C., more preferably 30-75° C., and when using a compound in which R in the general formula ( ¹ ) is a polymer group having a polycarboxylic acid structure as the compound (A), the temperature is preferably 40-95°C, more preferably 45-90°C. In addition, the reaction time is not limited, but it is preferably 3-24 hours, more preferably 3-12 hours.

In the reaction between compound (A) and compound (B), a ripening stage may be further provided. The temperature at the time of aging is not limited, but preferably the same temperature as the aforementioned reaction temperature, and the aging time is not limited, but is preferably 1-5 hours, more preferably 1-3 hours.

In the first production method of the present invention, in addition to the compound (B), a crosslinking agent may be added to the aqueous medium after dispersing the hydrophobic dispersion liquid. By further adding and using a cross-linking agent, the strength of the formed shell can be further increased, and the decomposition and damage of the shell in the separation step and washing step after microencapsulation can be effectively suppressed. The time to add the crosslinking agent may be before the reaction between the compound (A) and the compound (B), such as adding together with the compound (B), or may be during or after the reaction between the compound (A) and the compound (B), but no limit.

The crosslinking agent is not limited, but examples include sodium diethyldithiocarbamate, diethylammonium diethyldithiocarbamate, dithiooxalic acid, and dithiocarbonic acid. These may be used alone, or two or more kinds may be used in combination. The amount of the crosslinking agent to be used is not limited, but is preferably 0.1-30 parts by weight, more preferably 0.3-20 parts by weight, further preferably 0.5-15 parts by weight relative to 100 parts by weight of compound (B). When the amount of the crosslinking agent to be used is less than 0.1 parts by weight, it takes a long time to form the shell, and it may be difficult to control the thickness and strength of the shell. When the amount exceeds 30 parts by weight, the reaction with the epoxy group or episulfide group in the compound (B) is excessive, and the reaction between the compound (A) and the compound (B) may be disturbed.

In the first production method of the present invention, as described above, by microencapsulation in which a shell is formed on the droplet surface of the hydrophobic dispersion liquid due to the reaction between the compound (A) and the compound (B), thereby A preparation solution containing microcapsules for electrophoretic display elements and an aqueous medium is obtained.

In the first preparation method of the present invention, if necessary, compound (A) is further added, and compound (B) is further added to the solution of the prepared microcapsules for electrophoretic display elements, and can be carried out similarly to the above Reaction. By performing this step, a shell can be further formed on the already formed shell, and as a result, a microcapsule for an electrophoretic display element in which a shell composed of multiple layers is formed is obtained. A microcapsule for an electrophoretic display element in which a shell composed of multiple layers is formed, for example, can further improve the physical properties obtained by a single-layer shell, and can also exhibit different physical properties on the inside and outside of the shell. Specifically, an effect is obtained in which physical properties such as stickiness, high hydrophobicity, and softness can be easily introduced while possessing the original properties of the shell.

In the first production method of the present invention, after the microcapsules for electrophoretic display elements are prepared by the microencapsulation step of the aforementioned reaction between the compound (A) and the compound (B), the microcapsules may be isolated as necessary. For example, after preparing the microcapsules for electrophoretic display elements, the microcapsules can be separated and separated from the aqueous medium by suction filtration or natural filtration.

After separation, the microcapsules may be sieved in order to obtain microcapsules for electrophoretic display elements having a narrow particle size distribution.

As for sieving, for example, a wet classification method (wet classification) is preferably employed. Wet classification is a method of performing classification of microcapsules for electrophoretic display elements on a preparation solution obtained by microencapsulation. Since the classification is performed on the prepared solution, the classification is wet classification. More specifically, the design mode is a mode of fractionally treating the prepared solution as it is or after diluting the solution with an arbitrary aqueous medium, so as to obtain the desired particle diameter and particle size distribution of the microcapsules for electrophoretic display elements in the prepared solution . Wet classification can be performed, for example, by using a method or apparatus such as a sieving method (filter method), a centrifugal sedimentation method, and a natural sedimentation method. The sieving method can be effectively used on microcapsules for electrophoretic display elements having relatively large particle diameters.

In addition, it is also preferable to carry out a washing process of the obtained microcapsules for electrophoretic display elements in order to remove impurities and improve product quality.

The microcapsules for electrophoretic display elements obtained by the first preparation method of the present invention can suppress the decline of the subsequent contrast ratio, even when the electrophoretic display elements that use this microcapsule are allowed to be used under high temperature and high humidity conditions for a long time (for example, at 60 The same is true when left still at 90% RH for 24 hours). With regard to its physical properties (e.g. content of alkali metal ions, particle diameter (volume average particle diameter), coefficient of variation of particle diameter (volume average particle diameter), thickness of the shell, use), the foregoing can be used in the same manner as for the present invention. Explanation of microcapsules.

(the second preparation method of microcapsules for electrophoretic display elements):

The second method of the present invention for preparing microcapsules for electrophoretic display elements (hereinafter referred to as the second preparation method of the present invention), as described above, comprises causing microcapsules for electrophoretic display elements and ion exchange resins to dissolve in an aqueous medium. Coexisting step (A) is a method as a basic step, wherein the microcapsule includes electrophoretic particles and a solvent, both of which are encapsulated in a shell. In detail, the above-mentioned step (A) is to cause microcapsules for electrophoretic display elements (wherein the microcapsules are obtained by the step of microencapsulating (to be the core substance) dispersion liquid for electrophoretic display elements) and ion exchange resin in an aqueous medium Coexistence steps.

The second production method of the present invention is not limited except that step (A) is included as a basic step, and all methods (such as various methods) for producing microcapsules for electrophoretic display elements (including a microencapsulation step) so far can be used. and various conditions). For example, all hitherto known production methods can be employed, for example: using so-called interfacial sedimentation methods such as coagulation methods (phase separation methods), in-liquid drying methods, melting softening cooling methods, spray drying methods, pan coating methods, The preparation method of the suspension covering method in the air and the powder bed method, and the method using the so-called interfacial reaction, such as the interfacial polymerization method, the in-situ polymerization method, the solidified film (covering) method in the liquid (porosity method) and the interfacial reaction method (inorganic chemistry Reaction method) preparation method. Certainly, in the second preparation method of the present invention, the above-mentioned mode applied in the first preparation method of the present invention can also be adopted. This mode is said to be probably the most advantageous mode for achieving the objects of the invention.

In the second preparation method of the present invention, there is no limitation on the shell raw materials usable in the microencapsulation step. Heretofore known shell materials that can be used for the production of microcapsules can be used, and the aforementioned explanations for the "shell materials" of the microcapsules of the present invention can be applied in the same manner.

In the second preparation method of the present invention, there is no limitation on the dispersion liquid (the liquid in which the electrophoretic particles are dispersed in the solvent, that is, the dispersion liquid for the electrophoretic display element), and in the microencapsulation step of the aforementioned various preparation methods, the The dispersion liquid is used as the core substance to be enclosed in the shell. Specifically, the aforementioned aforementioned explanation of the "dispersion liquid" of the microcapsules of the present invention can be applied in the same manner.

Hereinafter, as an example of a method of producing microcapsules for electrophoretic display elements, which includes a microencapsulation step, a brief description of the production method is given by an agglomeration method in which gelatin and gum arabic are used as shell raw materials.

In this preparation method, in general, shell materials containing gelatin and gum arabic are added to an aqueous medium, dissolved therein by raising the temperature, and then added (to be the core material) electrophoretic display The dispersion liquid is used for the element, and droplets of the dispersion liquid are formed. Next, the diluted aqueous acidic solution was added to the resulting dispersion liquid, the pH was lowered to 4, and the resulting dispersion liquid was cooled to deposit shells on the surface of the above-mentioned liquid droplets. The deposited shell was hardened with a crosslinking agent, and then an alkaline aqueous solution was added to the resulting dispersion liquid to increase the pH to 9, and then the temperature of the resulting dispersion liquid was returned to normal temperature, thereby obtaining microcapsules. Regarding other various specific conditions, known conditions, for example, can be suitably employed. However, the situations mentioned below, such as conditions, can also be advantageously applied.

The amount of the dispersion liquid for electrophoretic display elements added to the aqueous medium is not limited. However, this added amount is preferably 20-200 parts by weight, more preferably 130-150 parts by weight, relative to 100 parts by weight of the aqueous medium. If the above added amount is less than 20 parts by weight, the resulting microcapsules may have a wide particle size distribution, causing deterioration in production efficiency. If the above added amount is more than 200 parts by weight, a reverse phase suspension may be formed, resulting in failure to produce microcapsules.

In the second production method of the present invention, after the aforementioned microencapsulation step and before the aforementioned step (A), the microcapsules for electrophoretic display elements obtained by this step may be isolated or concentrated, if necessary. For example, where microencapsulation is carried out in an aqueous medium such as by coacervation, the microcapsules can be isolated or concentrated by separating them from the aqueous medium, for example by suction or natural filtration.

Before or after the separation described above, the microcapsules may be classified in order to obtain microcapsules for electrophoretic display elements in which the microcapsules have a narrow particle size distribution. For example, a wet classification system (wet classification) is preferably employed. Regarding the wet classification, the aforementioned explanation about "wet classification" in the first production method of the present invention can be applied in the same manner.

In addition, in order to remove impurities and improve product quality, if necessary, it is also advantageous to perform the following operation: after undergoing the above-mentioned separation, concentration and/or fractionation, washing the microcapsules for electrophoretic display elements obtained through the microencapsulation step.

The aqueous medium that can be used in step (A) is not limited. For example, water or a mixture of a hydrophilic organic solvent and water can be used. When the hydrophilic organic solvent and water are used in combination, the proportion of water to be blended is preferably 95-70 wt%, more preferably 95-80 wt%.

The above-mentioned hydrophilic organic solvents are not limited. However, examples thereof include the same as those exemplified for the "hydrophilic organic solvent" usable as the aqueous medium in the first production method of the present invention.

By the way, in the second production method of the present invention, there is a mode in which the microcapsules for electrophoretic display elements obtained by the aforementioned production method including the microencapsulation step, once separated, are blended with the above-mentioned aqueous medium to carry out Step (A). But there is no restriction on this mode. For example, in the case where, for example, a production method using an aqueous medium in the microencapsulation step is employed as in the aforementioned coacervation method, part or all of this aqueous medium may be replaced by part or all of the aqueous medium used in step (A).

In the step (A), there is no limitation on the blending ratio of the microcapsules for the electrophoretic display element that will cause coexistence in the aqueous medium. However, the proportion is preferably 5-50 wt%, more preferably 10-40 wt%, further preferably 15-30 wt%, in terms of solid components, relative to the total liquid after blending with the aqueous medium. Regarding the above-mentioned usage amount of microcapsules, if the above-mentioned blending ratio is less than 5% by weight, it may result in leaving a large amount of waste water and thus be uneconomical. If the above blending ratio is more than 50% by weight, it may result in high viscosity where uniform blending or stirring is impossible.

Ion exchange resins usable in step (A) are not limited. For example, as the cation exchange resin, known strongly acidic cation exchange resins such as DowX 50WX1 (manufactured by Dow Chemical Company), AMBERLITEI R118 (manufactured by Organo Co., Ltd.) and Duolite SC100 (manufactured by Sumitomo Chemical Co. ., Ltd. preparation). In addition, as the anion exchange resin, well-known strongly basic anion exchange resins such as OH-substituted products of DowX 1X1 (manufactured by Dow Chemical Company), OH-substituted products of AMBERLITEIRA400 (manufactured by Organo Co., Ltd. Manufactured) and Diaion TSA1200 (manufactured by Mitsubishi Chemical Corporation). In general, some microcapsules contain both cations and anions within the shell, and other microcapsules tend to aggregate by removing either cations or anions. It is therefore desirable to use cation exchange resins and anion exchange resins in combination.

There is no limit to the blending ratio of the ion exchange resins that will cause coexistence in the aqueous medium. However, the ratio is preferably 0.1-50 wt%, more preferably 0.5-20 wt%, further preferably 1-10 wt%, in terms of solid components, relative to the microcapsules for electrophoretic display elements (blended in an aqueous medium). If the above-mentioned blending ratio is less than 0.1% by weight, it may result in incomplete removal of ions. If the above-mentioned blending ratio is more than 50 wt%, the effect corresponding to the blending ratio may not be obtained, so it is not economical.

In the case where, as described above, a cation exchange resin and an anion exchange resin are combined as an ion exchange resin, there is no limitation on the blend ratio "anion exchange resin/cation exchange resin" (volume ratio) thereof. However, it is preferably not greater than 1, more preferably not greater than 0.9, even more preferably not greater than 0.8. If the above blending ratio is greater than 1, the amine-derived compound attached to the anion exchange resin may tend to remain within the shell of the microcapsule. In addition, the total blending ratio of the cation exchange resin and the anion exchange resin to all the ion exchange resins is not limited. However, based on the solid component content, it is preferably not less than 0.2 wt%, more preferably not less than 1 wt%, further preferably not less than 2 wt%. If the above-mentioned blending ratio is less than 0.2 wt%, it may result in insufficient removal of ions.

In step (A), the aforementioned microcapsules and ion exchange resin are caused to coexist in an aqueous medium.

The mode of causing the microcapsules to coexist with the ion exchange resin in the aqueous medium in the step (A) is not limited. But examples thereof include: a mode in which microcapsules are stirred in an aqueous medium in the presence of an ion exchange resin; and a mode in which a microcapsule-dispersed liquid flows through a filter filled with an ion exchange resin.

In the mode in which the microcapsules are stirred in the aqueous medium in the presence of the ion exchange resin, the stirring in the presence of the ion exchange resin in the step (A) can be performed by any of various well-known stirring means, and thus is not limited. The time required for the above stirring is not limited. However, for example, it is preferably 1-24 hours, more preferably 2-12 hours.

In the second preparation method of the present invention, advantageously, the microcapsules for electrophoretic display elements (which will cause coexistence in the aqueous medium in step (A)) include microcapsule shell surfaces and polyethylene glycol chains (hereinafter referred to as called PEG chains). In detail, it is advantageous to form the above-mentioned addition product of the PEG chains before or at the time of causing the microcapsules to coexist with the ion exchange resin in the aqueous medium. The inventors of the present invention have found that, as described above, when the ion exchange resin and microcapsules for electrophoretic display elements coexist in an aqueous medium, the degree of dispersion of the microcapsules deteriorates, resulting in secondary aggregation. When a varnish layer is prepared by adding such as a binder to microcapsules and then coating on the surface of the base material for electrodes, it is impossible to perform coating or the coating surface becomes uneven, resulting in failure to be used in electrodes. The microcapsules are evenly arranged on the surface of the base material, which is the secondary aggregation of the microcapsules. Therefore, the present inventors found that, as means for preventing and suppressing the above-mentioned secondary aggregation, it is effective to form an addition product of the shell surface of the microcapsules and the PEG chain before or during the above-mentioned stirring in the presence of an ion exchange resin.

The above-mentioned PEG chain is a polymer chain with repeating unit number "n" derived from ethylene glycol or ethylene oxide, and n is preferably 2-50, more preferably 3-40, and still more preferably 4-30. If the above repeating unit number "n" is less than 2, the effect of inhibiting secondary aggregation may not be sufficiently obtained. If the above repeating unit number "n" is greater than 50, it may be difficult for the addition product portion of the PEG chain to dissolve in an aqueous medium.

Advantageously, the addition product of the above-mentioned PEG chain is formed by using a compound having both a PEG chain and an epoxy group (in particular, a compound having an epoxy group at one or the opposite end of the PEG chain), and The compound is stirred in an aqueous medium together with the aforementioned microcapsules.

As the aqueous medium usable in the above stirring, the same aqueous medium usable in the aforementioned step (A) can be favorably employed. The above-mentioned stirring may be performed in another step before the step (A), or may be performed together with the step (A), but is not limited.

The amount of the above compound having a PEG chain and an epoxy group is suitably set in an amount of such a PEG chain that can inhibit secondary aggregation at a desired level. Therefore, there is no limit. However, relative to the microcapsules for electrophoretic display elements, in terms of solid content, for example, it is preferably 2-50 wt%, more preferably 5-40 wt%, even more preferably 10-30 wt%. If the above-mentioned amount is less than 2% by weight, the effect of inhibiting secondary aggregation of microcapsules may not be sufficiently obtained. If the above-mentioned usage-amount exceeds 50 wt%, the above-mentioned effect corresponding to the usage-amount may not be obtained, so it is not economical.

In the second production method of the present invention, the step of removing the ion exchange resin is carried out after the step (A). Specifically, after the step (A), it is sufficient to filter out the ion exchange resin with a filter having a mesh opening size smaller than that of the ion exchange resin (particle diameter).

In the second preparation method of the present invention, it is possible to concentrate the aqueous medium containing the microcapsules for electrophoretic display elements by performing an operation such as suction filtration or natural filtration after the microencapsulation step as necessary, as described above , or separate and isolate such microcapsules from the aqueous medium. In addition, it is also possible to perform a classification operation (such as wet classification) in order to obtain microcapsules for electrophoretic display elements in which the microcapsules have a narrow particle size distribution; or to perform an operation of washing the obtained microcapsules for electrophoretic display elements in order to Impurities are removed to improve product quality.

Hereinafter, the microcapsules for electrophoretic display elements obtained by the second production method of the present invention are explained.

The microcapsules for electrophoretic display elements obtained by the second preparation method of the present invention make it possible to reduce the content of ionic substances throughout the microcapsules, and to suppress the subsequent decrease in contrast, even when the electrophoretic display elements using the microcapsules are allowed to When left standing under high temperature and high humidity conditions. Specifically, the content (total content) of ions (such as sodium ions, potassium ions, magnesium ions, calcium ions, chloride ions, sulfate ions, carbonate ions and acetate ions) in the entire microcapsules is preferably not more than 200ppm , more preferably not greater than 150 ppm, further preferably not greater than 100 ppm. If the above ion content is more than 200 ppm, the contrast may decrease when the electrophoretic display element using the microcapsules is allowed to stand under high temperature and high humidity conditions.

In particular, it is preferable to reduce the content of sodium ions because the above-mentioned effect of suppressing a decrease in contrast can be further enhanced. Specifically, the content of sodium ions in the entire microcapsule is preferably not greater than 150 ppm, more preferably not greater than 100 ppm, further preferably not greater than 80 ppm, particularly preferably not greater than 50 ppm.

In addition, it is advantageous that the microcapsules for electrophoretic display elements obtained by the second preparation method of the present invention further meet the aforementioned requirements as the microcapsules of the present invention, that is, even if the entire microcapsules contain Li ⁺ , Na The content (concentration) of alkali metal ions of ⁺ , K ⁺ , Rb ⁺ , Cs ⁺ and Fr ⁺ is 150 ppm or less, preferably 120 ppm or less, more preferably 100 ppm or less. A microcapsule that further satisfies the aforementioned requirements as the microcapsule of the present invention can further obtain the effect of suppressing a subsequent decrease in contrast, even when the electrophoretic display element using this microcapsule is allowed to stand under high temperature and high humidity conditions for a long time (for example, at 60° C. , 24 hours under 90% RH) when standing still.

In addition, existing electrophoretic display elements in which TFT electrodes are used as display electrodes in contact with microcapsules have a problem in that ionic substances inhibit the action of TFTs, thereby failing to properly control the elements. However, if the microcapsules for electrophoretic display elements obtained by the second preparation method of the present invention are used, specifically, the microcapsules for electrophoretic display elements that reduce the ion content (especially the content of sodium ions) in the entire microcapsules, Then the effect of solving the above-mentioned problems at the same time can be achieved.

Regarding the particle diameter (volume average particle diameter), the particle diameter (volume average particle diameter) variation coefficient and the thickness of the shell of the microcapsules for electrophoretic display elements obtained by the second preparation method of the present invention, they can be respectively adopted in the same manner. The foregoing explanations about the "particle diameter (volume average particle diameter)", "coefficient of variation of particle diameter (volume average particle diameter)" and "thickness of the shell" of the microcapsules of the present invention.

The particle size of the microcapsules for electrophoretic display elements obtained by the second preparation method of the present invention and its coefficient of variation (i.e., the narrowness of the particle size distribution) mainly depend on the microcapsules used in the microencapsulation step, for example, the coagulation method used therein. In the case of the preparation method, the particle size and particle size distribution of the dispersion liquid dispersed in the aqueous medium. Therefore, similar to the aforementioned microcapsules of the present invention, microcapsules having a desired particle size and its coefficient of variation can be obtained by performing the microencapsulation step under suitably controlled conditions.

The microcapsules for electrophoretic display elements obtained by the second preparation method of the present invention, similar to the aforementioned microcapsules of the present invention, can be used for all various display elements on which the aforementioned electrophoretic display elements can be used (for example, the aforementioned related to the present invention) use of microcapsules).

[Sheets for electrophoretic display components]:

The sheet for electrophoretic display elements (display sheet) of the present invention is a sheet containing the above-mentioned microcapsules of the present invention and a binder resin. More particularly, for example, a sheet having a layer in which the microcapsules of the present invention are arranged so as to be flat as a whole fixed with a binder resin so as to easily maintain its layout is preferable. The aforementioned objects of the present invention can be easily achieved by using the microcapsules of the present invention as the microcapsules in the display sheet.

The binder resin is not limited, but preferable examples include various organic binder resins, and examples include synthetic resin-based binders such as acryl resin-based, polyester resin-based, fluororesin-based, alkyd-based, amino Resin base, vinyl resin base, epoxy resin base, polyamide resin base, polyurethane resin base, unsaturated polyester resin base, phenolic resin base, polyolefin resin base, silicone resin base, acryl silicone resin base, xylene resin base, ketone resin base, rosin-modified maleic acid resin base, liquid polybutadiene and benzofuran resins; natural or synthetic rubber-based adhesives such as ethylene propylene copolymer rubber, polybutadiene ethylene rubber, styrene-butadiene rubber, and acrylonitrile-butadiene copolymer rubber; natural resin-based adhesives such as shellac, rosin (pine resin), ester gum, hardened rosin, bleached shellac, and white shellac; thermoplastic or thermosetting polymers Physically based binders such as nitrocellulose, cellulose acetate butyrate, cellulose acetate, ethyl cellulose, hydroxypropyl methyl cellulose and hydroxyethyl cellulose. Synthetic resin based adhesives can be plastic (thermoplastic adhesives), or can be cured (heat cure, UV cure, electron beam cure or moisture cure) such as acryl, methacryl and epoxy based adhesives. These organic binders may be used alone, or two or more kinds may be used without limitation.

The form of the binder is not limited, but examples include solvent-soluble type, water-soluble type, emulsion type, and dispersion liquid type (arbitrary solvent such as water/organic solvent).

Examples of water-soluble type binders include water-soluble alkyd resins, water-soluble acryl-modified alkyd resins, water-soluble oil-free alkyd resins (water-soluble polyester resins), water-soluble acryl resins, water-soluble cyclic Oxygen ester resin and water soluble melamine resin.

Examples of emulsion-type binders include alkyl (meth)acrylate copolymer dispersions, vinyl acetate resin emulsions, vinyl acetate copolymer resin emulsions, ethylene vinyl acetate copolymer resin emulsions, acrylate (co)polymerized resin emulsions , styrene acrylate (co)polymerized resin emulsion, epoxy resin emulsion, urethane resin emulsion, acryloyl silicone emulsion and fluororesin emulsion.

The display sheet of the present invention may be a sheet composed of the microcapsules of the present invention and the binder resin, or may be provided with other components or constituents in addition to the microcapsules and the binder resin of the present invention, for which no limit. Preferable examples of the latter display sheet include those in which a layer containing the microcapsules of the present invention and a binder resin is formed on a film-like or sheet-like base, or after formation by means of this layer (the layer is laminated with the film-like base) ) A display sheet that further aligns a substrate such as another film and combines this layer with the substrate. The latter form is preferable because the preparation process is easy, and the properties of the microcapsules of the present invention can be easily maintained while being prepared.

Since the display sheet of the present invention is a display sheet for an electrophoretic display element, when it is also provided with a film-like substrate (in the case of the aforementioned latter display sheet) as a substrate, a conductive film is used as a substrate. Examples of the conductive film include an electrode film that can be used as an electrode for an electrophoretic display element. For example, the film may be an opaque electrode film, or a transparent electrode film such as a PET film with ITO, without limitation. Transparent electrode films are preferred and in particular, as described above, when a layer containing the microcapsules of the present invention and a binder resin is laminated together with two counter electrode films, at least one electrode film needs to be transparent.

There is no limitation on the method of preparing the display sheet of the present invention, but in general, as detailed below, the preferred method is to mix the microcapsules of the present invention and the binder resin to obtain a paint, which is applied to the film on the surface of a shape or sheet substrate and dry. When the display sheet of the layer and substrate combination containing the microcapsules and binder resin of the present invention is obtained, it may be treated as it is or after drying. But when a display sheet having only the aforementioned layer is obtained, then after drying, the layer is separated (peeled) from the substrate. In addition, when a display sheet in which the layer is laminated together with a base is obtained, the base may be further laminated on the coated surface after drying, and lamination may be performed.

The concentration of the microcapsules in the paint is not limited, but preferably 30-70 wt%, more preferably 30-60 wt%, further preferably 30-55 wt%. When the concentration of the microcapsules is within the aforementioned range, for example, a product in which a layer of microcapsules of the present invention is densely arranged on a substrate (electrode film, etc.), and when the display sheet of the present invention is used in an electrophoretic display element , excellent product quality (display quality) is obtained.

The viscosity of the paint is preferably 500-5000 mPa·s, more preferably 800-4000 mPa·s, further preferably 800-3000 mPa·s. When the viscosity of the paint is within the aforementioned range, a layer of the microcapsules of the present invention can be arranged on a substrate (electrode film, etc.) without gaps, and this can be processed in which the microcapsules of the present invention are densely packed into a coating film (coating layer).

In addition to the microcapsules and binder resins of the present invention, the paint may optionally contain other components. Examples of other components include viscosity modifiers, leveling agents and defoamers. The ratio of other components to be blended may be appropriately set within a range not hindering the effect of the present invention.

The method of coating the paint on the substrate is not limited, but for example, a method of coating one by one on the substrate using a coater or a knife coater, or continuous coating using a continuous coater such as a multicoater (multicoater) can be used. The method of coating, and these methods may be appropriately selected as needed.

The drying method after coating is not limited, but known drying techniques and drying conditions can be employed.

The thickness of the display sheet of the present invention is not limited due to the balance with the particle diameter of the microcapsules to be used. The thickness of the layer containing only the microcapsules and the binder resin in part is preferably 10-250 micrometers, more preferably 10-180 micrometers, further preferably 10-100 micrometers. When the thickness is less than 10 micrometers, in the case where the display sheet of the present invention is used in an electrophoretic display element, sufficient display density is not obtained at the display portion, and a clear distinction from other non-display portions may not be possible. When the thickness exceeds 250 micrometers, in the case where the display sheet of the present invention is used in an electrophoretic display element, it is necessary to increase the starting voltage in order to fully exert the electrophoresis of the electrophoretic particles in the dispersed liquid encapsulated in the microcapsules. performance, and this may be economically inferior. When a film-like or sheet-like base is used, the thickness of the base is not limited, but is preferably several tens of micrometers to several millimeters.

When the aforementioned laminated display sheet is obtained as the display sheet of the present invention, as a lamination method, known lamination techniques or lamination conditions can be employed.

When the display sheet of the present invention is the aforementioned laminated display sheet, in order to obtain an electrophoretic display element that can stably exert excellent display quality, it is preferable that the microcapsules of the present invention are sufficiently adhered to the two electrode films (contact large area). When the adhesiveness to both electrode films is low, a decrease in the response of the electrophoretic particles and a decrease in contrast may occur. In order to improve the adhesiveness, it is conceivable, for example, to increase the temperature and pressure during lamination. In addition, regarding the microcapsules to be used, by appropriately setting the ratio of the components constituting the shell to be contained, and improving flexibility and adhesiveness, the ease of adhesion to the electrode film can be further improved, and in this case, Sufficient adhesiveness can be obtained even in a state where various conditions such as temperature and pressure are mild to some extent at the time of lamination.

In the case of laminated display sheets as described above, the gap between the opposing electrode films is not limited, but is preferably 10-250 micrometers, more preferably 10-180 micrometers, further preferably 10-100 micrometers. When the gap is less than 10 micrometers, in the case where the display sheet of the present invention is used in an electrophoretic display element, sufficient display density may not be obtained in the display portion, and it may not be possible to distinguish clearly from other non-display portions. When the gap exceeds 250 micrometers, in the case where the display sheet of the present invention is used in an electrophoretic display element, in order to fully exert the electrophoretic performance of the electrophoretic particles in the dispersed liquid encapsulated in the microcapsules, it is necessary to increase the starting voltage, This may be economically inferior.

The display sheet of the present invention is a sheet for an electrophoretic display element, but the sheet can also be used for the same uses as known display sheets including the use of microcapsules, such as non-carbon paper and pressure measurement film.

[Electrophoretic display components]:

The electrophoretic display element of the present invention is equipped with a sheet for an electrophoretic display element, wherein the sheet includes: the above-mentioned microcapsules of the present invention; and a binder resin (in other words, the electrophoretic display element of the present invention is equipped with the aforementioned display sheet). An advantageous mode of the electrophoretic display element of the present invention is that the aforementioned sheet for an electrophoretic display element is a sheet in which a layer containing microcapsules and a binder resin is formed on a conductive film.

The electrophoretic display element of the present invention can be produced from the aforementioned display sheet of the present invention. Regarding the sheet for electrophoretic display element which is used for the electrophoretic display element of the present invention, the explanation in the section titled "Sheet for electrophoretic display element" can be adopted. For example, among the aforementioned display sheets of the present invention, an electrophoretic display element having a display in which a layer containing microcapsules and a binder resin is laminated together with two counter electrode films can be preferably exemplified. Sheets as constituent parts. The electrophoretic display element of the present invention includes the use of the display sheet of the present invention, and the aforementioned object of the present invention can be easily achieved.

In the electrophoretic display element of the present invention, for various components other than the display sheet (for example, a drive circuit and a power supply circuit), components used in hitherto known electrophoretic display elements can be used.

By applying a control voltage (for example, only applying a voltage to the part where the desired image is to be displayed) between the opposite electrode film, and changing the orientation position of the electrophoretic particles in the microcapsule, the required in the display element of the present invention can be performed. display function.

Detailed Description of the Preferred Embodiment

Hereinafter, the present invention is explained more specifically by way of examples and comparative examples, but the present invention is not limited thereto. Hereinafter, for convenience, "liter" is similarly referred to as "L" in some cases. In addition, "wt%" means "weight%" in some cases.

The ion content (the content of alkali metal ion or the content of sodium ion) in Examples and Comparative Examples was measured in the following manner.

<Content of various ions>:

1-3 below give an overview of the methods used to measure the various ion contents.

1. Place 1 g of microcapsules in 20 g of ultrapure water, and use an ultrasonic cleaner (180w, 42kHz) to irradiate with ultrasound for 45 minutes.

2. Filter the liquid after ultrasonic irradiation with a filter with a sieve opening size of 0.45 μm.

3. Use ICP atomic emission spectrometry to measure the content of various ions in the filtrate.

Specifically, 1 g of pre-dried microcapsules was accurately weighed, and it was placed in a 50 ml plastic container (product name: PP Vial PV-7, manufactured by Sogo Laboratory Glassworks Co., Ltd.) with 20 g of ultrapure water. Using an ultrasonic cleaner (product name: Bronson 5510, manufactured by Yamato Scientific Co., Ltd., output value: 180 W, frequency: 45 kHz), ultrasonic irradiation was performed for 45 minutes, and a process of extracting various ions was performed.

After ultrasonic irradiation, filter the liquid in the aforementioned container with a filter (product name: GL Chromatodisk 13I, manufactured by Kurabo Industries, Ltd., mesh opening size: 0.45 μm), and use an ICP atomic emission spectrometer (product name : InductivelyCoupled Plasma Atomic Emission Spectrometer (Inductively Coupled Plasma Atomic Emission Spectrophotometer), manufactured by Seiko Instruments Inc.), measures the content (ppm) of various ions in the filtrate flowing through the filter.

The numerical value obtained by multiplying the content (ppm) of various ions in the filtrate by the dilution ratio of the microcapsules is used as the content (ppm) of various ions in the entire microcapsule (20 times (ultrapure water 20g/microcapsule 1g) ).

(the embodiment of the first preparation method and its comparative example):

The measurement methods in the following Examples and Comparative Examples are given below.

<Average particle size of microcapsules>:

Using a laser diffraction/scattering type particle size distribution measuring device (product name: LA-910, manufactured by Horiba, Ltd.), the volume average particle diameter of the microcapsules was measured.

<Solubility in water>:

Accurately weigh 25.0 g of a sample compound (such as an epoxy compound such as compound (B)) in a 300 ml beaker, add 225 g of water, and vigorously stir with a magnetic stirrer for 1 hour to dissolve the sample compound. After that, allow it to stand still for 1 hour, extract the undissolved sample compound (oily matter) settled at the bottom of the beaker, place it in a 10ml (or 5ml) graduated cylinder, let it stand still for 30 minutes, and read the sample compound (oily matter) ) to the first decimal place, and substituting this value into the following equation, the solubility (%) of the sample compound in water was calculated.

Solubility in water (%)=100-(A/21)×100

(wherein A represents the reading (ml) of the liquid amount of the sample compound).

<contrast>:

When a series voltage of 15V was applied between the two electrodes of the electrophoretic display element for 0.4 seconds, using a Macbeth spectrodensitometer (product name: SpectroEye, manufactured by GretagMacbeth), the values of white display and blue display (or black display) were measured respectively. The reflectance, and the contrast (reflectance) were determined by the following equation. Incidentally, by switching the poles, the reflectance of white display and blue display (or black display) were measured independently, and each reflectance was defined as a value obtained by measuring the entire side of the electrophoretic display element.

Contrast = (reflectance of white display) / (reflectance of blue display (or black display))

[Synthesis Example 1-1]:

Into a 300 ml detachable flask, 14.5 g of polyethyleneimine (product name: Epomin SP006 (Mw=600), manufactured by Nippon Shokubai Co., Ltd.) and 43.5 g of water were initially introduced, after that, under stirring for 10 minutes 97.2 g of an aqueous solution of an epoxy compound (lauryl polyoxyethylene (n=22) glycidyl ester, solubility in water: 100%) prepared in advance 97.2 g was added dropwise.

While maintaining the temperature of the liquid in the flask at 25°C or lower, dropwise addition was performed, stirring was continued for 30 minutes after the addition was complete, and then the temperature was raised to 70°C and kept at this temperature for 2 hours, and it was Cooling to normal temperature afforded compound (A1) having a dispersity of 25% by weight of solid component content.

[Synthesis Example 1-2]:

According to the same method as Synthesis Example 1-1, the difference is that after the initial charge in Synthesis Example 1-1, 130.4g 25wt% of 130.4g prepared in advance was added dropwise within 10 minutes under stirring An aqueous solution of an epoxy compound (lauryl polyoxyethylene (n=44) glycidyl ester, solubility in water: 100%) obtained compound (A2) having a dispersity of 25 wt% solid component content.

[Synthesis Example 1-3]:

In the same flask as in Synthesis Example 1-1, 14.5 g of polyethyleneimine (product name: P-1000 (Mw=70000), manufactured by Nippon Shokubai Co., Ltd.) and 43.5 g of water were initially introduced, after which, 130.4 g of an aqueous solution of epoxy compound (lauryl polyoxyethylene (n=44) glycidyl ester, solubility in water: 100%) prepared in advance was added dropwise within 10 minutes under stirring.

Thereafter, as in Synthesis Example 1-1, Compound (A3) was obtained having a dispersion degree of 25% by weight of solid component content.

[Synthetic Examples 1-4]:

Into a 500 ml detachable flask, 93.7 g of an aqueous polyacrylic acid solution (product name: Aqualic HL-415 (Mw=10000, resin concentration: 45 wt%), manufactured by Nippon Shokubai Co., Ltd.) and 281.1 g of water were initially introduced, after which, Under stirring, 20 g of 25 wt % epoxy compound (phenol polyoxyethylene (n=5) glycidyl ester, solubility in water: 100%) aqueous solution was added dropwise within 10 minutes.

While maintaining the temperature of the liquid in the flask at 25°C or lower, dropwise addition was performed, stirring was continued for 30 minutes after the addition was complete, and then the temperature was raised to 70°C and kept at this temperature for 2 hours, and it was Cooling to room temperature afforded Compound (A4) having a dispersity of 25% by weight of solid component content.

[Synthesis Example 2-1]:

Into a 300 ml four-necked flask were introduced 100 g of titanium oxide (product name; Tipaque CR-97, manufactured by Ishihara Sangyo Kaishi, Ltd.), 100 g of n-hexane, and 4 g of octadecyltrichlorosilane (product name: LS6495, manufactured by Shin- etsu Chemical Co., Ltd.), the flask was placed in an ultrasonic bath at 55°C (in which an ultrasonic bath was generated by an ultrasonic homogenizer (product name: BRANSON5210, manufactured by Yamato)) while stirring and mixing, while ultrasonic Simultaneously with dispersion, coupler treatment was carried out for 2 hours.

This dispersed liquid is transferred in the centrifuge settling tube, adopts centrifuge (product name: high-speed cooling centrifuge GRX-220, is prepared by Tomi) to carry out settling process 15 minutes under 10000G, removes the supernatant liquid of settling tube afterwards, obtains Surface treated titanium oxide (p1).

11.5 g of titanium oxide (p1) and 1.5 g of anthraquinone-based blue dye were placed in 82 g of dodecylbenzene, and dispersed in the aforementioned ultrasonic bath for 2 hours to obtain a dispersion liquid (1) for electrophoretic display elements.

[Synthesis Example 2-2]:

Into a 200 ml beaker, 5 g of carbon black (product name: MA100, manufactured by Mitsuibishi Chemical Corporation) and 172.5 g of methyl methacrylate were introduced, dispersed using an ultrasonic homogenizer (product name: BRANSON5210, manufactured by Yamato), and 3.5 g of azobisisobutyronitrile and this material was dissolved to obtain a monomer composition.

An aqueous solution in which 2.5 g of anionic surfactant (product name: Hitenol NO8) was dissolved in 750 g of water was prepared in advance, all of the aforementioned monomer compositions were added thereto, and a high-speed stirring emulsifier (product name: Clear Mix CLM- 0.8S, prepared by M Technique) for dispersion treatment to obtain a suspension of the monomer composition.

The temperature of the suspension was raised to 75° C. and maintained for 5 hours to carry out a polymerization reaction, thereby obtaining a dispersion liquid of black fine particles. Using a laser diffraction/scattering type particle size distribution measuring device (product name: LA-910, manufactured by Horiba, Ltd.), the particle diameter (volume average particle diameter) of the black fine particles was measured and found to be 0.8 µm. The dispersion was filtered, washed and dried to obtain black microparticles (p2).

3.1 g of black fine particles (p2) and 11.5 g of titanium oxide (p1) obtained in Synthesis Example 2-1 were placed in 85.6 g of dodecylbenzene, and in the ultrasonic bath used in Synthesis Example 2-1 This was subjected to a dispersion treatment for 2 hours to obtain a dispersion liquid (2) for an electrophoretic display element.

[Example 1-1]:

40g of compound (A1) and 60g of water were placed in a 500ml flat-bottomed detachable flask, and under stirring, a disperser (product name: ROBOMICS, manufactured by Tokushu Kika Kogyo Co., Ltd.) was used to add 95g of electrophoretic display element for dispersion. Liquid (1), after that, the stirring speed was gradually increased, followed by stirring at 800 rpm for 5 minutes to obtain a suspension.

While keeping the suspension at 30° C., under stirring, add polyglycidyl ester of polyglycerol (product name: Denacol EX521, manufactured by Nagase Chemtex, solubility in water: 100%) the whole aqueous solution obtained as an epoxy compound (compound (B)), and the whole aqueous solution obtained by dissolving 2 g of sodium diethylthiocarbamate trihydrate in 100 g of water was added dropwise within 10 minutes. Thereafter, within 60 minutes, the temperature of the suspension was raised to 70° C. and kept at this temperature for 1 hour for aging.

After aging, it was cooled to normal temperature to obtain a dispersion liquid of microcapsules (m1) for electrophoretic display elements. The volume average particle diameter of the microcapsules (m1) for electrophoretic display elements was 65.0 microns.

Be 80 microns and 30 microns of sieves through the sieve opening aperture, classify this suspension, obtain the paste (solid component content: 63wt%) that particle diameter is 30-80 micron electrophoretic display element microcapsules (m1) ).

The paste was dried at 50° C. for 24 hours in a hot air drier to obtain only the microcapsules (m1) for electrophoretic display elements, and according to the aforementioned method, the alkali in the entire microcapsules (m1) for electrophoretic display elements was measured content of metal ions. The results are shown in Table 1.

Then, 2.1 g of an alkali-soluble type acrylic resin emulsion (product name: WR503A, manufactured by Nippon Shokubai Co., Ltd., resin content: 30 wt%) was diluted with water so that the solid component content became 5 wt%, and 0.2 g of 25 wt % ammonia water was added thereto to obtain an alkali-soluble type acryl resin. 12.8 g of this resin solution was added to 10 g of the paste, and mixed for 10 minutes using a mixer (product name: Awatori Neritarou AR-100, manufactured by Thinky) to obtain a coating solution.

Using an applicator, the coating solution was coated on a PET film with ITO, and dried at 90° C. for 10 minutes to obtain a sheet (1) for an electrophoretic display element.

Another PET film with ITO was layered on the coated side of the sheet for electrophoretic display element (s1), and laminated to prepare an electrophoretic display element (d1) with a counter electrode.

The electrophoretic display element (d1) was allowed to stand in a constant temperature and humidity chamber at 20°C and 50% RH for 1 day, and the contrast (A) was measured under the same temperature and same humidity environment.

Then, the electrophoretic display element (d1) was placed in a constant temperature and humidity device (product name: constant temperature and humidity device PL-ZF-P2, manufactured by Daiken Rikaaku Kiki) at 60°C and 90% RH for 24 hours (Humidity resistance test), allowed to stand for 1 hour in a constant temperature and constant humidity chamber at 20° C. and 50% RH, and measured the contrast (B) under the same temperature and same humidity environment.

Table 1 shows the measurement results of the contrast ratio (A) before the moisture resistance test and the contrast ratio (B) after the moisture resistance test.

[Example 1-2]:

According to the same manner as Example 1-1, the difference is that compound (A2) is used instead of compound (A1), and 100.2g electrophoretic display element is used to replace the 95g electrophoretic display in embodiment 1-1 with dispersion liquid (2) The dispersion liquid (1) for an element is a dispersion liquid of microcapsules (m2) for an electrophoretic display element. The volume average particle diameter of the microcapsules (m2) for electrophoretic display elements was 68.0 microns.

Be 80 microns and the 30 microns of sieves of sieve opening aperture, classify this dispersed liquid, obtain the paste (solid component content: 55wt%) of microcapsules (m2) for electrophoretic display element that particle diameter is 30-80 microns ).

According to the same manner as in Example 1-1, the content of alkali metal ions in the entire microcapsules (m2) for electrophoretic display elements was measured using this paste. The results are shown in Table 1.

Then, according to the same manner as in Example 1-1, except that the amount of paste added to the acrylic resin solution was 11.5 g, a coating solution was obtained.

After that, in the same manner as in Example 1-1, a sheet (s2) for an electrophoretic display element was obtained, and an electrophoretic display element (d2) was prepared.

The contrast (A) before the moisture resistance test and the contrast (B) after the moisture resistance test were measured for the electrophoretic display element (d2) in the same manner as in Example 1-1. The results are shown in Table 1.

[Example 1-3]:

In the same manner as in Example 1-1, except that Compound (A3) was used instead of Compound (A1) in Example 1-1, a dispersion liquid of microcapsules (m3) for electrophoretic display elements was obtained. The volume average particle diameter of the microcapsules (m3) for electrophoretic display elements was 71.0 microns.

Be 80 microns and 30 microns of sieves through the sieve opening aperture, classify this dispersed liquid, obtain the paste (solid component content: 66.5wt) of microcapsules (m3) for electrophoretic display elements with particle diameters of 30-80 microns %).

According to the same manner as in Example 1-1, the content of alkali metal ions in the entire microcapsules (m3) for electrophoretic display elements was measured using this paste. The results are shown in Table 1.

Then, according to the same manner as in Example 1-1, except that the amount of paste added to the acrylic resin solution was 9.5 g, a coating solution was obtained.

After that, in the same manner as in Example 1-1, a sheet (s3) for an electrophoretic display element was obtained, and an electrophoretic display element (d3) was prepared.

The contrast (A) before the moisture resistance test and the contrast (B) after the moisture resistance test were measured for the electrophoretic display element (d3) in the same manner as in Example 1-1. The results are shown in Table 1.

[Example 1-4]:

In the same manner as in Example 1-1, except that Compound (A4) was used instead of Compound (A1) in Example 1-1, a dispersion liquid of microcapsules (m4) for electrophoretic display elements was obtained. The volume average molecular weight of the microcapsules (m4) for electrophoretic display elements was 66.0 microns.

Be 80 microns and the 30 microns of sieves of sieve opening aperture, classify this dispersed liquid, obtain particle diameter and be the paste (solid component content: 57.8wt) of microcapsules (m4) for electrophoretic display elements of 30-80 microns %).

According to the same manner as in Example 1-1, the content of alkali metal ions in the entire microcapsules (m4) for electrophoretic display elements was measured using this paste. The results are shown in Table 1.

Then, according to the same manner as in Example 1-1, except that the amount of paste added to the acrylic resin solution was 10.9 g, a coating solution was obtained.

After that, in the same manner as in Example 1-1, a sheet (s4) for an electrophoretic display element was obtained, and an electrophoretic display element (d4) was prepared.

The contrast (A) before the moisture resistance test and the contrast (B) after the moisture resistance test were measured for the electrophoretic display element (d4) in the same manner as in Example 1-1. The results are shown in Table 1.

[Comparative example 1-1]:

Into a 500ml round bottom removable flask were introduced 60g of water, 6g of gum arabic and 6g of gelatin and allowed to dissolve.

While keeping at 43° C., under stirring, 95 g of a dispersion liquid for electrophoretic display elements warmed at 50° C. ( 1), after that, the stirring speed was gradually increased, and the material was stirred at 1200 rpm for 30 minutes to obtain a suspension. While adding 300 ml of hot water at 43°C to the suspension, gradually reduce the stirring speed.

Under stirring so that the entire suspension can be kept in a uniform state, about 11 m of 10 wt% aqueous acetic acid solution was quantitatively added within 22 minutes using a paddle-type stirring blade, the pH was adjusted to 4.0, and it was cooled to 10°C.

The suspension was kept in the cooled state for 2 hours, 3 ml of 37 wt % aqueous formalin was added, and 22 ml of 10 wt % aqueous sodium carbonate were dosed within 25 minutes.

Further, the temperature of the suspension was returned to normal temperature, and kept for 20 hours for aging to obtain a suspension of microcapsules (cm1) for electrophoretic display elements. The volume average particle diameter of the microcapsules (cm1) for electrophoretic display elements was 51.1 microns.

Be 80 microns and the 30 microns of sieves of sieve opening aperture, classify this dispersed liquid, obtain particle diameter and be the paste (solid component content: 57wt%) of microcapsules (cm1) for electrophoretic display element of 30-80 microns ).

According to the same manner as in Example 1-1, the content of alkali metal ions in the entire microcapsules (cm1) for electrophoretic display elements was measured using this paste. The results are shown in Table 1.

According to the same manner as in Example 1-1, except that the amount of paste added to the acrylic resin solution was 11.1 g, a coating solution was obtained.

After that, in the same manner as in Example 1-1, a sheet (cs1) for an electrophoretic display element was obtained, and an electrophoretic display element (cd1) was prepared.

The contrast (A) before the moisture resistance test and the contrast (B) after the moisture resistance test were measured for the electrophoretic display element (cd1) in the same manner as in Example 1-1. The results are shown in Table 1.

Table 1

(the embodiment of the second preparation method and its comparative example):

The measurement methods and evaluation methods in the following Examples and Comparative Examples are given below.

<Evaluation of Coatability>:

200 parts of ethyleneimine-modified acrylic emulsion (manufactured by Nippon Shokubai Co., Ltd., product name: Polyment SK-1000) and 30.4 parts of urethane emulsion (manufactured by Dai-ichi Kogyo Seiyaku Co. , Ltd., product name: Superflex 107M), and then add 4.6 parts of strongly basic anion exchange resin (manufactured by Mitsubishi Chemical Corporation, trade name: Diaion TSA1200) and 4.6 parts of strongly acidic cation exchange resin (manufactured by Sumitomo Chemical Co. , Ltd., product name: Duolite SC100), and then stirred the resulting mixture at room temperature for 12 hours. After this stirring, the mixture was filtered using a 100-mesh wire mesh to obtain a binder dispersion liquid (solid component content: 36% by weight).

Mix together 10 parts (in terms of solid content) of the concentrated liquid of the obtained microcapsules for electrophoretic display elements and 1.1 parts (in terms of solid content) of the above-mentioned binder dispersion liquid, and then appropriately add deionized water to prepare a paint composition with a solid component content of 40 wt%. Using an optical microscope, observe the degree of dispersion of the microcapsules in the paint composition (observe whether they are aggregated or not).

The above paint composition was applied onto an ITO/PET film (manufactured by Toray Industries, Inc., product name: HighBeam NT02) having a thickness of 125 μm by using a doctor blade with a gap of 100 μm. Regarding the paint composition that may be applied, it is dried at room temperature for 1 hour, and then dried in a hot air drier at 90° C. for 20 minutes. The appearance (uniform or uneven) of the paint film surface after drying was observed visually.

The coatability of the above-mentioned paint compositions was evaluated based on the following criteria.

◎: Microcapsules are not aggregated in the paint composition, and the surface of the paint film is uniform.

○: Microcapsules are not aggregated in the paint composition, but the surface of the paint film is somewhat uneven.

Δ: Microcapsules are somewhat aggregated within the paint composition, and the surface of the paint film is also somewhat uneven.

X: The microcapsules were aggregated too much in the paint composition, so that it could not be coated.

<Measurement of leakage current>:

In the same manner as described above regarding the evaluation of coatability, a paint composition containing microcapsules for electrophoretic display elements was obtained, which was then coated on an ITO-attached PET film and then dried to obtain a sheet for electrophoretic display elements .

A polyimide film with copper foil was stacked on the coated surface of the above-mentioned sheet, and vacuum-laminated at 60° C., thereby preparing an electrophoretic display element.

The above electrophoretic display element was allowed to stand for 1 hour in a constant temperature and humidity chamber at 23° C. and 65% RH. After that, under the same temperature and the same humidity environment, using a high-resistance meter, apply a voltage of 10V between the two electrodes of the element (between ITO and Cu) for 2 minutes, and measure the amount of current flowing (leakage current flow).

Next, the electrophoretic display element was placed in a constant-temperature and constant-humidity device at 60°C and 90%RH (humidity resistance test) for 2 hours, and then allowed to stand in a constant-temperature and constant-humidity chamber at 25°C and 40%RH Let stand for 1 hour. After that, under the same temperature and same humidity environment, the amount of current flowing between the two electrodes (leakage current amount) was measured in the same manner as before.

Among them, if the leakage current is not greater than 50nA/cm ² , the product quality is qualified.

<Evaluation of contrast>:

The electrophoretic display element prepared in the same manner as described above regarding the amount of leakage current was allowed to stand in a constant temperature and humidity chamber at 23° C. and 65% RH for 1 hour. After that, under the same temperature and same humidity environment, the contrast (A) was measured in the following manner. That is, when a series voltage of 15V is applied between the two electrodes of the electrophoretic display element for 0.4 seconds, a Macbeth spectrodensitometer (product name: SpectroEye, manufactured by GretagMacbeth) is used to measure white display and blue display (or black display) respectively. , and the contrast (reflectance) was determined by the following equation. Incidentally, by switching the poles, the reflectance of white display and blue display (or black display) were measured independently, and each reflectance was defined as a value obtained by measuring the entire side of the electrophoretic display element.

Contrast = (reflectance of white display) / (reflectance of blue display (or black display))

Next, the electrophoretic display element was placed in a constant-temperature and constant-humidity device at 60°C and 90%RH for 2 hours (humidity resistance test), and then allowed to stand in a constant-temperature and constant-humidity chamber at 25°C and 40%RH Let stand for 1 hour. After that, under the same temperature and same humidity environment, the contrast (B) was measured in the aforementioned manner.

[Example 2-1]:

Aminopropyltrimethoxysilane (manufactured by Shin-etsu Chemical Co., Ltd., product name: KBM-903) was mixed in an amount of 0.5 parts, and uniformly dissolved in 90 parts of methanol, and then 0.5 parts of 25 wt. % ammonia water. To the resulting solution was added 50 parts of titanium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd., product name: TipaqueCR-90), and then the temperature was adjusted to 50° C. under stirring, followed by ultrasonic dispersion treatment for 60 minutes. Thereafter, 1.5 parts of isopropyl triisostearyl titanate (manufactured by Ajinomoto Co., Ltd., product name: Purenakuto KR-TTS) was added, and then the same dispersion treatment was performed for another 60 minutes. The resulting dispersion liquid was subjected to centrifugation, the sediment was recovered, and the sediment was dried at 120° C., thereby obtaining surface-treated titanium oxide particles (p).

Separately, 19 parts of isopropyl triisostearyl titanate (manufactured by Ajinomoto Co., Ltd., product name: Purenakuto KR-TTS) was added to 546 parts of dodecylbenzene, and 10 ml of While bubbling was caused by air at 20 ml/min and nitrogen at 20 ml/min, the resulting mixture was heated at 200° C. for 4.5 hours, thereby obtaining a heat-treated dispersant solution (d).

43 parts of the above-mentioned titanium oxide particles (p) and 61 parts of the above-mentioned dispersant solution (d) were added to 207 parts of dodecylbenzene, and then the temperature was adjusted to 50° C., followed by ultrasonic dispersion treatment for 30 minutes. After that, 5 parts of blue dye (manufactured by Chuo Gosei Kagaku Co., Ltd., product name: Oil Blue F) were added and dissolved in the resulting dispersion to obtain a dispersion liquid (D) for electrophoretic display elements.

24 parts of gum arabic (manufactured by Wako Pure Chemical Industries, Ltd.) and 8 parts of gelatin (manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 180 parts of water in advance, and the resulting solution was adjusted to 43°C. Then, 316 parts of dispersion liquid (D) for electrophoretic display element (adjusted to the same temperature) was added to the solution using a disperser under stirring, thereby obtaining a suspension of the dispersion liquid (D).

To the resulting suspension were added 799 parts of hot water and 48 parts of urethane emulsion (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Superflex 700), then 20 parts of 10 wt% aqueous acetic acid, and then The resulting mixture was cooled to 10°C for coagulation. After cooling, 10 parts of 37 wt% formalin aqueous solution and 45 parts of 10 wt% sodium carbonate aqueous solution were added, then the temperature was raised to room temperature, and aged for 90 minutes. Afterwards, an aziridine compound (prepared by Nippon Shokubai Co., Ltd., product name: KemitaitoPZ-33) was added, then the temperature was raised to 50° C., and aging was carried out for another 60 minutes, thereby obtaining microcapsules for electrophoretic display elements (M ) of the dispersion liquid.

The dispersion liquid of the microcapsules (M) for electrophoretic display elements was cooled to room temperature, and then classified using a sieve with a sieve opening size of 106 μm. The dispersed liquid flowing through the sieve was transferred to a separatory funnel, and then 1000 parts of deionized water was added thereto to wash the microcapsules (M) for electrophoretic display elements, and then the substance was allowed to stand for 6 hours without being disturbed . Afterwards, extract the lower layer in the separatory funnel. Next, the remaining upper layer was subjected to the above-mentioned fractionation and washed 3 times in the same manner. Then, the last remaining upper layer was recovered from the separatory funnel, and then suction-filtered with filter paper to obtain a concentrated liquid of microcapsules (M) for electrophoretic display elements.

This concentrated liquid was dried with hot air at 110°C, and then the solid component content was measured. The result was 50 wt%. In addition, the particle diameter of the microcapsules (M) for electrophoretic display elements was measured using a laser diffraction/scattering type particle size distribution measuring device (manufactured by Horiba, Ltd., product name: LA-910). As a result, the volume average particle diameter was 70 µm.

Deionized water was appropriately added to the concentrated liquid of the microcapsules (M) for electrophoretic display elements to adjust the solid content to 25 wt%. To 200 parts of this adjusted liquid were added 2.5 parts of strongly basic anion exchange resin (manufactured by Mitsubishi Chemical Corporation, product name: Diaion TSA1200) and 2.5 parts of strongly acidic cation exchange resin (manufactured by Sumitomo Chemical Co., Ltd., Duolite SC100), and the resulting mixture was stirred at room temperature for 12 hours.

After this stirring, the mixture was filtered using a sieve with a mesh opening size of 300 microns. The resulting filtrate was subjected to filter paper suction filtration to obtain a concentrated liquid of microcapsules (M1) for electrophoretic display elements.

Using the obtained concentrated liquid, the ion content in the entire microcapsules (M1) for electrophoretic display elements (M1), evaluation of coatability, measurement of leakage current amount, and evaluation of contrast were measured in the aforementioned manner. The results are shown in Table 2.

[Example 2-2]:

Deionized water was appropriately added to the concentrated liquid of the microcapsules (M) for electrophoretic display elements obtained in Example 2-1 to adjust the solid content to 25 wt%. To 200 parts of this adjusted liquid was added 50 parts of an aqueous solution of 10 wt% polyethylene glycol diglycidyl ether (manufactured by Nagase Chemtex, product name: Denacol EX-841), and then the resulting mixture was adjusted to a temperature of 50° C., It was then stirred for 90 minutes and then cooled to room temperature. After cooling, 2.5 parts of strongly basic anion exchange resin (manufactured by Mitsubishi Chemical Corporation, product name: Diaion TSA1200) and 2.5 parts of strongly acidic cation exchange resin (manufactured by SumitomoChemical Co., Ltd., product name: Duolite SC100) were added , and the resulting mixture was stirred at room temperature for 12 hours.

After this stirring, the mixture was filtered using a sieve with a mesh opening size of 300 microns. The resulting filtrate was subjected to filter paper suction filtration to obtain a concentrated liquid of microcapsules (M2) for electrophoretic display elements.

Using the obtained concentrated liquid, the ion content in the entire microcapsule for electrophoretic display element (M2), evaluation of coatability, measurement of leakage current amount and evaluation of contrast were measured in the aforementioned manner. The results are shown in Table 2.

[Comparative example 2-1]:

Using the concentrated liquid of the microcapsules (M) for electrophoretic display elements obtained in Example 2-1, the ion content in the entire microcapsules (M) for electrophoretic display elements was measured in the aforementioned manner, the applicability was evaluated, the measurement Leakage current amount and evaluation contrast. The results are shown in Table 2.

Table 2

Industrial Applicability

In addition to commonly used electrophoretic display panels, the microcapsules and sheets for electrophoretic display elements of the present invention can also be suitably used in various electrophoretic display elements, such as so-called digital paper (electronic paper), such as paper-like displays and rewritable In paper, display components such as IC cards and IC tags, electronic whiteboards, guide panels, advertising boards, electronic newsprint, electronic books, and portable terminals such as PDAs.

The first and second production methods of the present invention are suitable as methods for easily obtaining microcapsules for electrophoretic display elements in which the ion content in the entire microcapsules is reduced. More importantly, the first production method of the present invention is a method for easily obtaining microcapsules for electrophoretic display elements in which the content of alkali metal ions in the entire microcapsules is reduced to a specific value or less, and this method is particularly suitable as The method for obtaining the above-mentioned microcapsules of the present invention is easy.

Many details of the invention may be changed without departing from its spirit and scope. Furthermore, the foregoing descriptions of the preferred embodiments of the present invention have been provided for the purpose of illustration only and not for the purpose of limiting the invention, the scope of which is defined by the appended claims and their equivalents.

Claims (10)

CLAIMS 1. A microcapsule for an electrophoretic display element, comprising electrophoretic fine particles and a solvent, both enclosed in a shell, wherein the content of alkali metal ions in the entire microcapsule is 150 ppm or less. 2. A method for preparing microcapsules for electrophoretic display elements defined in claim 1, the method comprising the steps of: dispersing the core material in an aqueous medium containing a water-soluble surfactant, wherein the core material is a hydrophobic solvent containing and the liquid of the electrophoretic particles; and then adding a water-soluble compound to the aqueous medium; thereby forming a shell on the surface of the core material; in: A compound (A) represented by the following general formula (1) is used as a water-soluble surfactant: R ¹ -(CH ₂ -CH ₂ -O-) _n -XR ² (1) Where ^R1 represents an aliphatic or aromatic hydrophobic group with a carbon number of 5-25, ^R2 represents a polymer group with a polyamine structure or a polycarboxylic acid structure with a weight average molecular weight of 300-100000, and n represents an integer of 3 -85, and X represents a group derived from a group capable of reacting with at least one group selected from amino, imino and carboxyl, and formed after the reaction, but has nothing to do with the presence or absence of X in the general formula (1), and Using a compound (B) having an epoxy group or an episulfide group as a water-soluble compound; and The shell is formed by reacting compound (A) with compound (B). 3. A method for preparing the microcapsules for electrophoretic display elements defined in claim 1, the method comprising the steps of: obtaining the microcapsules for electrophoretic display elements by microencapsulating a dispersing liquid for electrophoretic display elements to be a core substance, and allowing the microcapsules to coexist with the ion exchange resin in an aqueous medium, wherein the microcapsules include electrophoretic particles and a solvent, both encapsulated within a shell. 4. The method for producing microcapsules for electrophoretic display elements according to claim 3, wherein a strongly acidic cation exchange resin and a strongly basic anion exchange resin are combined as the ion exchange resin. 5. The method for producing microcapsules for electrophoretic display elements according to claim 3 or 4, wherein the microcapsules comprise an addition product of polyethylene glycol chains to the shell surface of the microcapsules. 6. The method for preparing microcapsules for electrophoretic display elements according to claim 5, wherein the addition product of the polyethylene glycol chain is formed by stirring together the compound having the polyethylene glycol chain and the epoxy group and the microcapsule in an aqueous medium . 7. A sheet for an electrophoretic display element comprising the microcapsules defined in claim 1 and a binder resin. 8. The sheet for electrophoretic display elements according to claim 7, wherein a layer containing microcapsules and a binder resin is formed on the conductive film. 9. An electrophoretic display element provided with a sheet for an electrophoretic display element, wherein the sheet comprises the microcapsules defined in claim 1 and a binder resin. 10. The electrophoretic display element according to claim 9, wherein the sheet for the electrophoretic display element is a sheet in which a layer containing microcapsules and a binder resin is formed on a conductive film.