JP2006259170A - Dispersion for electrophoresis display element, and electrophoresis display element using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrophoresis particles capable of developing dispersibility and charging properties without adding a charging adjustor in a dispersion medium and dispersion containing them, manufacturing methods for them, an electrophoresis display element which is free of aggregation of electrophoresis particles and deterioration in display even when driven for a long period and has high reliability, and a method of independently controlling particles having different charging characteristics and an electrophoresis display element having high display quality by the same. <P>SOLUTION: The dispersion for the electrophoresis display element contains a dispersion medium consisting of at least an organic solvent and pigment particles each having a polymer physically adsorbed to its surface, the polymer having a glass transition point (Tg) of -80 to 25°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pigment particle dispersion used for an electrophoretic display element, and an electrophoretic display element using the dispersion.

In recent years, with the development of the information society due to the development of the Internet, mobile phones, interactive TVs, etc., the need for high-quality thin display elements with low power consumption is increasing. Among them, the liquid crystal display element employs a display principle in which optical characteristics are changed by electrically controlling the arrangement of liquid crystal molecules. For this reason, active research and development has been carried out and commercialized as a display element that can meet the above needs.
However, most liquid crystal display elements display images by controlling the transmittance of light incident on the liquid crystal from a light source (backlight) provided on the back surface. Therefore, there is a drawback that it is difficult to see an image in a bright place. In addition, since it is necessary to always turn on the light source, it is not satisfactory in terms of power consumption.

Research on display elements that solve these problems has been actively studied. As one of them, an electrophoretic display element disclosed in Patent Documents 1 and 2 is known. These electrophoretic display elements are provided with a pair of substrates arranged with a gap therebetween, and each substrate is formed with electrodes each made of a transparent conductive layer, at least one of which is transparent. A space between the substrates is filled with a large number of charged and colored electrophoretic particles and a dispersion medium colored with a different color from the electrophoretic particles. In addition, there are some in which a plurality of types of electrophoretic particles having different charged polarities and colors are filled together with a colorless dispersion medium.
In such an electrophoretic display element, when a negative voltage is applied to one electrode and a positive voltage is applied to the other electrode, the positively charged electrophoretic particles gather to cover the negative electrode. When the display element is viewed from the negative electrode side, the color of the electrophoretic particles can be seen. Reversing the applied voltage will see the color of the colored medium or other electrophoretic particles. Arbitrary images and characters can be displayed by performing such voltage driving in units of a large number of arranged pixels.

  Several structural examples have been disclosed as electrophoretic display elements. For example, there is an electrophoretic display element in which a particle dispersion is encapsulated in a capsule and the capsule is sandwiched between a pair of electrode substrates transparent at least one (Patent Documents 3 to 10). Also disclosed is an electrophoretic display element in which a particle dispersion is emulsified and dispersed in water and sandwiched between a pair of electrode substrates, at least one of which is transparent (Patent Document 11). In addition, there is also an example in which the partition is arranged so that the gap of the substrate is divided into a large number of pixels along the surface direction of the substrate to prevent the uneven distribution of the electrophoretic particles and to define the gap of the substrate. It has been.

In such an electrophoretic display element, a charging agent (hereinafter also referred to as a charge adjusting agent) and a dispersing agent are added to an insulating dispersion medium so as to impart charging property and dispersibility. A dispersion is used. However, in this dispersion, when driven for a long time, the charging agent and the dispersing agent are desorbed from the electrophoretic particles. As a result, there is a problem that the electrophoretic particles are insufficiently charged or the display is deteriorated due to aggregation of the electrophoretic particles.
When a plurality of types of particles having different hues are used, the electrophoretic characteristics are uniquely determined (one polarity) by the charge adjusting agent added to the dispersion medium. Therefore, it is difficult to independently control the electrophoretic properties of different particles. For example, charging red and white particles to opposite polarities, charging only black particles of black and white particles positively, of red, black and white particles, red is positive, black is charged It is impossible to control the polarity of the particles such as negatively charging.

  In recent years, a method of treating electrophoretic particles with a titanate coupling agent and a sorbitan fatty acid ester as in Patent Document 12, or a method of grafting a polymer onto the surface of an electrophoretic particle as in Patent Document 3, 13, or 14 Has proposed to improve the dispersibility of electrophoretic particles. However, although effective in improving the dispersibility of the particles, sufficient chargeability cannot be obtained unless a charging agent is added. Therefore, the problem of display deterioration due to the desorption of the charging agent from the particle surface has not been fundamentally solved, and it is difficult to independently control the chargeability of the particles.

In addition, as disclosed in Patent Document 15, a proposal has been made to impart chargeability to the electrophoretic particles by coating the electrophoretic particles with a silicone resin. However, it is difficult to finely pulverize the electrophoretic particles to a predetermined size suitable for electrophoretic display elements after attaching and depositing a silicone resin on the surface of the electrophoretic particles, and it is difficult to independently control the chargeability of the particles. It is.
In addition, an electrophoretic particle in which at least an amphiphilic residue derived from a reactive surfactant is immobilized on the surface of the pigment particle has been proposed (Patent Document 16). However, the reactive surfactant is only adsorbed on the pigment particle surface. Therefore, even if a comonomer is added thereafter to form a polymerizable film together with the reactive surfactant, a strong bond cannot be formed between the film and the pigment particles. Conversely, the adsorption force may be reduced by polymerization, and it is still impossible to prevent the polymerizable film from desorbing. Therefore, the problem of display deterioration has not been solved, and it is difficult to independently control the chargeability of the particles.

Japanese Patent Publication No. 50-15115 Japanese Patent Publication No. 50-15119 US Patent Application Publication No. 2002/0185378 Japanese Patent No. 2551783 JP-T-2001-500172 US Patent Application Publication No. 2002/017910 US Patent Application Publication No. 2002/511607 US Patent Application Publication No. 2001/503873 US Patent Application Publication No. 2002/504696 US Patent Application Publication No. 2002/520665 US Patent Application Publication No. 2002/0131147 JP-A-2-284128 JP-A-5-173193 JP-T 8-510486 JP-A-2-189525 JP 2004-233630 A

The present invention relates to an electrophoretic particle capable of exhibiting dispersibility and chargeability without adding a charge adjusting agent to a dispersion medium, a dispersion for an electrophoretic display element containing the same, and production thereof To provide a method. Another object of the present invention is to provide a highly reliable electrophoretic display element that does not cause aggregation of electrophoretic particles or display deterioration even when driven for a long period of time.
Another object of the present invention is to provide a method for independently controlling particles having different charging characteristics, and an electrophoretic display element having high display quality.

The above problems have been achieved by the following means.
(1) A dispersion containing at least a dispersion medium composed of an organic solvent and pigment particles having a polymer physically adsorbed on the surface, wherein the polymer has a glass transition point (Tg) of −80 ° C. or more and 25 ° C. or less. Dispersion liquid for electrophoretic display elements characterized by the above.
(2) The dispersion for an electrophoretic display device according to (1), wherein the polymer is a polymer having an ionic functional group.
(3) The dispersion for an electrophoretic display device according to (2), wherein the ionic functional group is a carboxyl group or a quaternary amino group.
(4) The dispersion liquid for electrophoretic display elements according to any one of (1) to (3), wherein the polymer is insoluble in the dispersion medium.
(5) It further includes pigment particles that are non-ionic polymers insoluble in the dispersion medium and physically adsorbed with the non-ionic polymers having a glass transition point (Tg) of -80 ° C or higher and 25 ° C or lower. The dispersion liquid for electrophoretic display elements according to any one of (2) to (4), which is characterized.
(6) An electrophoretic display element, wherein the dispersion according to any one of (1) to (5) is sandwiched between a pair of substrates having a conductive layer.
(7) An electrophoretic display element characterized in that a microcapsule containing at least the dispersion liquid according to any one of (1) to (5) is sandwiched between a pair of substrates having a conductive layer. .

According to the dispersion for an electrophoretic display element of the present invention, the electrophoretic particles in the dispersion can exhibit dispersibility and chargeability without adding a charge adjusting agent or the like to the dispersion medium. Further, according to the dispersion liquid for electrophoretic display elements of the present invention, a highly reliable electrophoretic display element that does not cause problems of aggregation of electrophoretic particles and display deterioration even when driven for a long period of time can be obtained.
Furthermore, according to the dispersion liquid for electrophoretic display element of the present invention, since the pigment particles to which the polymer is physically adsorbed are used, an operation for fixing the polymer is unnecessary, and many combinations of the polymer and the pigment particles are realized. It is possible to coat the pigment surface evenly.
Further, the dispersion liquid for electrophoretic display element of the present invention and the electrophoretic display element using the same provide high white background reflectance, high contrast, and multicolor (white, black, red, etc.) display. Is possible.

  The dispersion for electrophoretic display elements of the present invention is a dispersion containing a dispersion medium containing an organic solvent and pigment particles having a polymer physically adsorbed on the surface, and the glass transition point (Tg) of the polymer is −80 ° C. The temperature is 25 ° C. or lower. The polymer is preferably insoluble in the dispersion medium. Hereinafter, the present invention will be described in detail.

The pigment particles used in the dispersion for electrophoretic display elements of the present invention are not particularly limited as long as the polymer can be physically adsorbed, but the hydrophilicity / hydrophobicity or wettability of the pigment particle surface is the same as the polymer to be physically adsorbed. Pigment particles having a functional group similar to a polymer at a level or physically adsorbed on the pigment particle surface (for example, a hydroxyl group, a carbonyl group, a long-chain alkyl group having 4 or more carbon atoms, or an aromatic ring) are preferable.
Examples of organic pigment particles include azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, isoindoline pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, anthraquinone pigments, nitro pigments, and nitroso pigments. Specifically, red pigments such as quinacridone red, lake red, brilliant carmine, perylene red, permanent red, toluidine red, and madder lake, green pigments such as diamond green lake, phthalocyanine green, and pigment green B, Blue pigments such as Victoria Blue Lake, Phthalocyanine Blue, Fast Sky Blue, Hansa Yellow, Fast Yellow, Disazo Yellow, Isoindolinone Yellow, Kinoff Yellow pigments such as Ron yellow, aniline black, diamond black, black pigments such as carbon black. Preferred are pigments used in color electrophotographic toners, and more preferred are phthalocyanine pigments, quinacridone pigments, azo pigments, and carbon black.

  Inorganic pigment particles include white pigments such as titanium oxide, aluminum oxide, zinc oxide, lead oxide, tin oxide, and zinc sulfide, black pigments such as manganese ferrite black, cobalt ferrite black, and titanium black, cadmium red, and red iron oxide. , Red pigments such as molybdenum red, green pigments such as chromium oxide, viridian, titanium cobalt green, cobalt green, Victoria green, blue pigments such as ultramarine blue, Prussian blue, cobalt blue, cadmium yellow, titanium yellow, yellow iron oxide Yellow pigments such as yellow lead, chrome yellow, and antimony yellow can be used. Titanium oxide, titanium black, or zinc oxide is preferable, and titanium oxide is more preferable.

  The particle shape of the pigment particles used in the dispersion for electrophoretic display elements of the present invention is not particularly limited, but the particle size is preferably 1 nm to 100 μm, more preferably 1 nm to 1,000 nm, and particularly preferably 10 nm to 700 nm ( In the present invention, unless otherwise specified, the particle diameter means a diameter in the case of a spherical shape, and an average value of a short axis and a long axis in the case of an irregular shape.)

  The polymer used in the dispersion for an electrophoretic display element of the present invention preferably has a glass transition point (Tg) of room temperature (about 25 ° C.) or less, more preferably −80 to 25 ° C., − 40-25 degreeC is especially preferable. A polymer having a glass transition point that is too high is in a rigid state near room temperature, and since the movement of the polymer terminal and the polymer side chain is small in the solvent, the influence of steric hindrance is great and dispersion stabilization cannot be expected. On the other hand, a polymer having a glass transition point that is too low has a strong movement of the polymer end and the polymer side chain in the solvent, and therefore the influence of steric hindrance is small and the effect of stabilizing the dispersion is large. However, there is a problem that it is sticky like an adhesive near room temperature and is difficult to handle.

Moreover, it is preferable that the polymer used for the dispersion liquid for electrophoretic display elements of the present invention is one that physically adsorbs to the pigment particles. In the present invention, physical adsorption refers to adsorption by weak intermolecular forces such as van der Waals force, and is distinguished from chemical bonds such as chemical adsorption, covalent bond, or ionic bond by electric attraction force. Is.
In the dispersion for electrophoretic display elements of the present invention, the polymer that is physically adsorbed on the pigment particles is preferably insoluble in the dispersion medium (in the present invention, insoluble means that it does not dissolve and solubility is 0.1). % By mass or less is preferred). This is because if the polymer is soluble in the dispersion medium, the polymer may be desorbed from the pigment and dissolved in the dispersion medium. The molecular weight of the polymer used in the dispersion liquid for electrophoretic display elements of the present invention is not particularly limited as long as preferable dispersibility and chargeability can be obtained in the dispersion liquid when adsorbed on the pigment particles. 1,000 to 1,000,000 are preferable, and 3,000 to 100,000 are more preferable (in the present invention, unless otherwise specified, the molecular weight refers to the weight average molecular weight).

The polymer used in the dispersion for an electrophoretic display element of the present invention may be an ionic polymer having an ionic functional group or a nonionic polymer having no ionic functional group. The ionic polymer may be a cationic polymer having a cationic functional group or an anionic polymer having an anionic functional group.
The ionic functional group is preferably an organic amine or an acid derivative.
Examples of the cationic functional group include a quaternary amino group, a primary amino group, a secondary amino group, a tertiary amino group, a guanidine derivative, and an amidine derivative, and a quaternary amino group is preferable. Examples of the anionic functional group include carboxylic acid, sulfonic acid, phosphoric acid, sulfinic acid, or a derivative thereof, and a carboxylic acid derivative is preferable.

Examples of the nonionic polymer used in the dispersion for an electrophoretic display device of the present invention include polystyrene, poly (meth) acrylate, cellulose derivatives, polyvinyl alcohol derivatives, proteins, or long-chain polymers having side chains thereof. Poly (meth) acrylate having an alkyl group having 4 to 22 carbon atoms as a side chain is preferable.
Examples of the cationic polymer include a nonionic polymer (specific examples and preferred ranges are the same as those of the nonionic polymer described above) and a cationic functional group (specific examples and preferred ranges are the same as the cationic functional groups described above). The same), and a poly (meth) acrylate having a quaternary amino group is preferred.
Examples of the anionic polymer include a nonionic polymer (specific examples and preferred ranges are the same as those of the above-mentioned nonionic polymer) and an anionic functional group (specific examples and preferred ranges are the above-mentioned anionic functional groups and The same), and a poly (meth) acrylate having a carboxylic acid derivative is preferred.
The method for synthesizing the polymer used in the dispersion for an electrophoretic display element of the present invention is not particularly limited, and for example, it can be synthesized by a method such as radical polymerization, anion polymerization, polycondensation, or addition polymerization.

  In the dispersion for electrophoretic display elements of the present invention, pigment particles obtained by physical adsorption of a polymer are used as the electrophoretic particles. The amount of the polymer adsorbed is preferably an amount in which the particles are stably dispersed in the dispersion. In the case of the particles adsorbed with the ionic polymer, an amount exhibiting electrophoretic properties is also preferable. When the amount of adsorbed polymer is expressed as a coverage with respect to pigment particles, it is preferably 3 to 50% by weight, and more preferably 5 to 20% by weight (in the present invention, unless otherwise specified, the coverage is “the weight of the coated polymer”). "Is divided by the sum of" mass of pigment "and" mass of coating polymer "(mass%), and can be determined by thermogravimetric analysis (TG).)

Any method can be used to adsorb the polymer to the pigment particles, but the pigment particles are dispersed in a polymer solution in which the polymer is dissolved in a good solvent, and the pigment particles adsorbed to the polymer are isolated by centrifugation or the like. It is preferable to do. In adsorbing the pigment particles, the polymer solution is preferably 5 to 65 ° C, more preferably 15 to 40 ° C. Further, it is preferable to promote dispersion by irradiating ultrasonic waves (for example, the irradiation time is preferably 2 to 60 minutes, and the frequency is preferably 10 to 50 kHz). In order to stabilize the adsorption state, the dispersed solution is preferably allowed to stand, and the standing time is preferably, for example, 2 to 48 hours. Centrifugation can be performed by a conventional method, the rotation time is preferably 1 to 120 minutes, and the rotation speed is preferably 1,000 to 100,000 rpm. After centrifugation, the supernatant can be removed by decantation, and the polymer adsorbed pigment particles that have settled and remain are preferably dried, for example, at 15 to 60 ° C. Also, drying is preferably performed under vacuum.
Examples of the good solvent for dissolving the polymer include ethyl acetate, toluene, THF, methylene chloride, n-hexane and the like, and ethyl acetate or toluene is preferable.
The amount for dissolving the polymer is not particularly limited as long as it can be uniformly dissolved in the solvent, but the concentration of the polymer is preferably 1 to 30% by mass, and more preferably 3 to 15% by mass. The amount of pigment particles dispersed in the polymer solution is not particularly limited as long as a preferable polymer adsorption amount (coverage) can be obtained, but the pigment particles should be 1 to 300 parts by mass with respect to 100 parts by mass of the polymer. Is preferable, and it is more preferable to set it as 10-100 mass parts.

  The dispersion medium used in the dispersion liquid for electrophoretic display elements of the present invention is preferably one that does not dissolve the polymer (insoluble). Further, a solvent in which pigment particles physically adsorbed with a polymer are dispersed is preferable. Among them, a dispersion medium composed of an organic solvent having a low dielectric constant, high resistance, and low viscosity is preferable. Examples of the organic solvent include n-hexane, n-octane, diisopropylnaphthalene, Isopar (trade name: manufactured by Exxon Mobil Corporation), Silicon oil etc. are mentioned, Diisopropyl naphthalene or Isopar is preferable. The dispersion medium may be a pure solvent, a mixed solvent of a plurality of solvents, or may contain other solvents (for example, a fluorine-based solvent).

  The method for dispersing the pigment particles adsorbed with the polymer in the dispersion medium is not particularly limited, but the particles are preferably added to the dispersion medium and maintained at 15 to 65 ° C, more preferably 15 to 40 ° C. At this time, it is also preferable to irradiate ultrasonic waves. For example, it is preferable to irradiate ultrasonic waves having a frequency of 10 to 50 kHz for 2 to 60 minutes. The dispersion liquid for electrophoretic display elements of the present invention does not hinder the addition of an additive, a dispersant or the like as long as the display operation is not hindered.

Furthermore, in the dispersion for electrophoretic display elements of the present invention, pigment particles physically adsorbed with a cationic polymer (hereinafter also referred to as “positively charged particles”), pigment particles physically adsorbed with an anionic polymer (hereinafter referred to as “ Any one of pigment particles (hereinafter also referred to as “non-charged particles”) physically adsorbed with a nonionic polymer may be used, and a plurality of them may be used in combination. Types of particles may be used.
However, when used in an electrophoretic display element, at least one particle needs to be electrophoresed, and therefore preferably contains at least one of positively charged particles and negatively charged particles. At this time, if positive and negative charged particles coexist, both particles may aggregate. When combining two types of particles, combine either positive or negative charged particles with uncharged particles. Is preferred.

  In the dispersion for electrophoretic display elements of the present invention, the surface of the pigment particles is modified by physical adsorption, so that there are less restrictions than chemical bonds, and many types of pigments and modified polymers can be used. In the method of fixing the polymer, the polymer is localized in the vicinity of the fixing position. However, the method by physical adsorption is excellent in that this problem is solved and there is no coating unevenness by the polymer. In addition, it is not necessary to use an azo coupling agent, a silane coupling agent or the like used in the preparation of particles for immobilizing the polymer, and it can be applied to a pigment having no functional group that reacts with the coupling agent. Are better.

The dispersion liquid for electrophoretic display elements of the present invention can be made into an electrophoretic display element by sandwiching it between a pair of substrates having a conductive layer. For example, substrates can be arranged to face each other at a predetermined interval, a partition wall can be provided between the substrates, and a plurality of spaces (hereinafter also referred to as “cells”) can be provided. Each cell is substantially in a sealed state, and is preferably in a state in which the dispersion liquid for electrophoretic display elements can be enclosed.
Here, the substrate having a conductive layer may have a structure in which an electrode layer, an insulating layer, a substrate layer, and the like are stacked. If a transparent material is used for the substrate having a conductive layer, the surface can be used as an image display surface. In the display element of the present invention, it may be displayed on one side or both sides.
When an arbitrary electric field is applied to the conductive layer, the electrophoretic particles can be moved toward the conductive layer depending on the relationship with the charge of the electrophoretic particles in the dispersion. Therefore, for example, if the charge applied to the conductive layer is positive, negative, and no charge, three types of display (for example, display of three colors of white, black, and red) can be performed.

The substrate material of the substrate having a conductive layer is not particularly limited, but a transparent material such as glass or plastic is used on the display side. The material of the non-display side substrate is not necessarily transparent, and examples thereof include metals and plastics. As the plastic, for example, acrylic resin, epoxy resin, fluororesin, silicone resin, polyimide resin, polystyrene resin, polyalkene resin, alkyd resin, polyester resin (for example, PET, PEN) and the like can be used. Further, for example, a metal vapor-deposited film such as ITO (Indium Tin Oxide), tin oxide, indium oxide, gold, or chromium can be used for the electrode. When the electrode is formed as a pattern, a photolithography method or the like is used. be able to.
The material of the partition wall is not particularly limited as long as each cell can be substantially sealed, but a polymer resin or the like can be used. As the partition wall formation, for example, a method by a photolithography method using a photosensitive resin, a method of bonding a partition wall prepared in advance to a substrate, a method of forming a partition wall by a mold, or the like can be used.
The method of filling the dispersion liquid for electrophoretic display elements in the cell is not particularly limited, but a method of using an ink jet type nozzle is generally applicable although a capillary phenomenon is usually used.

  In addition, the dispersion liquid for electrophoretic display elements of the present invention is encapsulated in microcapsules, and the microcapsules are sandwiched between a pair of substrates having a conductive layer, whereby an electrophoretic display element can be obtained. By using the microcapsules encapsulating the dispersion liquid, unlike the display element using the partition walls described above, the display element can be easily manufactured simply by filling the substrate with the microcapsules most closely. The relationship between the application of the electric field to the conductive layer and the control of the electrophoretic particles is the same as in the case of the display element using the partition walls.

Microcapsules enclosing the dispersion for electrophoretic display elements can be obtained by methods such as interfacial polymerization, in situ polymerization, and coacervation.
These methods are described in detail in the edition of the Japanese Standards Association, March 1991, edited by Yasu Kondo, “Microcapsules, Functions and Applications”.
The material forming the microcapsules is preferably a material that transmits light sufficiently, and examples thereof include urea-formaldehyde resin, melamine-formaldehyde resin, polyester, polyurethane, polyamide, polyethylene, polystyrene, polyvinyl alcohol, and gelatin, or These copolymers are mentioned. In addition, a method for arranging the microcapsules on the substrate is not particularly limited, but an ink jet type nozzle can be used.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.
(Synthesis Example 1) Synthesis of poly-lauryl methacrylate [P1] 51 g of lauryl methacrylate and 50 ml of toluene were added to a 100 ml three-necked flask equipped with a stirrer, a cooling tube, and a nitrogen gas inlet tube, and water was added while flowing nitrogen gas. The mixture was heated to 70 ° C. with a bath, 0.26 g of azobisisobutyronitrile was added, and the mixture was stirred and heated for 7 hours to obtain a viscous polymer solution. The polymer solution was cooled to room temperature and then added to 600 ml of methanol with slow stirring. The viscous polymer supernatant was removed by decantation, 100 ml of methanol was added again, the supernatant was removed by decantation, and the remaining polymer was dried at 40 ° C. under vacuum to obtain 46 g of polylauryl methacrylate [P1]. .

(Synthesis Example 2) Synthesis of poly-lauryl methacrylate-co-N, N, N-trimethyl-N-vinylbenzylammonium chloride [P2] In a 100 ml three-necked flask equipped with a stirrer, a condenser tube, and a nitrogen gas inlet tube , 51 g of lauryl methacrylate, 4.2 g of N, N, N-trimethyl-N-vinylbenzylammonium chloride (Qbm: manufactured by Seimi Chemical Co., Ltd.), 30 ml of toluene, and 20 ml of ethanol were added, and the mixture was heated in a water bath while flowing nitrogen gas. The mixture was heated to 0 ° C., 0.50 g of V-65 (manufactured by Wako Pure Chemical Industries, Ltd.) was added, the mixture was stirred and heated for 6 hours, and viscous poly-lauryl methacrylate-co-N, N, N-trimethyl-N -A 56 mass% solution of vinylbenzylammonium chloride [P2] was obtained.

Synthesis Example 3 Synthesis of poly-lauryl methacrylate-co-N, N-diethyl-N-benzyl-N-methacryloylethylammonium bromide [P3] 100 ml three-neck equipped with stirrer, condenser, and nitrogen gas inlet tube Add 45.8 g of lauryl methacrylate, 3.7 g of diethylaminoethyl methacrylate, and 50 ml of toluene to the flask, heat to 70 ° C. in a water bath while flowing nitrogen gas, add 0.26 g of azobisisobutyronitrile, and add 7 Stirring and heating were continued for a time to obtain a viscous polymer solution. The polymer solution was cooled to room temperature and then added to 300 ml of methanol with slow stirring. The viscous polymer supernatant was removed by decantation, 50 ml of methanol was again added, and the supernatant was removed by decantation to obtain 53 g of a poly-lauryl methacrylate-co-diethylaminoethyl methacrylate solution.
After 48.5 g of this polymer solution was diluted with 25 ml of toluene, 3.4 g of benzyl bromide was added and heated at 60 ° C. for 4 hours, and poly-lauryl methacrylate-co-N, N-diethyl-N-benzyl-N-methacryloyl. An ethylammonium bromide [P3] solution was obtained.

(Synthesis Example 4) Synthesis of poly-lauryl methacrylate-co-methacrylic acid / tridodecylamine salt [P4] In a 100 ml three-necked flask equipped with a stirrer, a condenser tube, and a nitrogen gas inlet tube, 45.9 g of lauryl methacrylate, Add 1.7 g of methacrylic acid and 50 ml of toluene, heat to 70 ° C. in a water bath while flowing nitrogen gas, add 0.26 g of azobisisobutyronitrile and continue stirring and heating for 7 hours. A polymer solution was obtained. The polymer solution was cooled to room temperature, 40 ml of THF (tetrahydrofuran) was added, and then added to 600 ml of methanol with slow stirring. The viscous polymer supernatant was removed by decantation to give 51 g of poly-lauryl methacrylate-co-methacrylic acid solution.
After diluting 1.5 g of this polymer solution with 55 ml of toluene, 0.8 g of tridodecylamine was added and stirred at room temperature for 2 hours to obtain a poly-lauryl methacrylate-co-methacrylic acid / tridodecylamine salt [P4] solution. Obtained.

(Synthesis Example 5) Synthesis of poly-2-ethylhexyl methacrylate [P5] To a 100 ml three-necked flask equipped with a stirrer, a condenser tube, and a nitrogen gas inlet tube, 39.6 g of 2-ethylhexyl methacrylate and 40 ml of toluene were added. The mixture was heated to 70 ° C. in a water bath while flowing nitrogen gas, 0.26 g of azobisisobutyronitrile was added, and the mixture was stirred and heated for 7 hours to obtain a viscous polymer solution. After the polymer solution was cooled to room temperature, 40 ml of THF was added, and the mixture was added into 600 ml of methanol with slow stirring. The viscous polymer supernatant was removed by decantation, 200 ml of methanol was again added, the supernatant was removed by decantation, the remaining polymer was dried at 40 ° C. under vacuum, and 35 g of poly-2-ethylhexyl methacrylate [P5] Got.

(Synthesis Example 6) Synthesis of poly-2-ethylhexyl methacrylate-co-N, N-diethyl-N-benzyl-N-methacryloylethylammonium bromide [P6] 100 ml equipped with a stirrer, a condenser tube, and a nitrogen gas inlet tube Into a three-necked flask, 35.7 g of 2-ethylhexyl methacrylate, 3.7 g of diethylaminoethyl methacrylate, and 40 ml of toluene were added, and heated to 70 ° C. in a water bath while flowing nitrogen gas, and 0.26 g of azobisisobutyronitrile was added. After the addition, the mixture was stirred and heated for 7 hours to obtain a viscous polymer solution. After cooling the polymer solution to room temperature, 40 ml of THF (tetrahydrofuran) was added, and the mixture was added to 600 ml of methanol with slow stirring. The viscous polymer supernatant was removed by decantation, 200 ml of methanol was added again, the supernatant was removed by decantation, and the remaining polymer was dried at 40 ° C. under vacuum to obtain 26 g of poly-2-ethylhexyl methacrylate-co-diethylamino. Ethyl methacrylate was obtained.
After diluting 19.7 g of this polymer with 40 ml of toluene, adding 3.4 g of benzyl bromide, heating at 60 ° C. for 4 hours, and poly-2-ethylhexyl methacrylate-co-N, N-diethyl-N-benzyl-N— A methacryloylethylammonium bromide [P6] solution was obtained.

(Preparation Example 1-1) Preparation of White Particles [W1] To a 100 ml flask, 9.7 g of P1 synthesized in Synthesis Example 1 was added and dissolved in 45 ml of toluene, and then titanium oxide (R960: manufactured by DuPont). ) After adding 30 g and irradiating ultrasonic waves for 20 minutes to disperse the titanium oxide, the polymer P1 was adsorbed on the titanium oxide by allowing it to stand overnight at room temperature. This dispersion is put into a centrifuge tube, centrifuged at 3000 rpm for 20 minutes, the supernatant is removed by decantation, and the remaining precipitate is dried at 40 ° C. under vacuum to obtain 19 g of white particles [W1] of the present invention. It was.

(Production Example 1-2) Production of white particles [W2] To a 100 ml flask, 25 g of the P3 solution synthesized in Synthesis Example 3 was added and dissolved in 23 g of toluene, and then titanium oxide (R960: manufactured by DuPont). After adding 30 g and irradiating ultrasonic waves for 20 minutes to disperse the titanium oxide, the polymer P3 was adsorbed on the titanium oxide by allowing it to stand overnight at room temperature. This dispersion is put into a centrifuge tube, centrifuged at 3000 rpm for 20 minutes, the supernatant is removed by decantation, and the remaining precipitate is dried at 40 ° C. under vacuum to obtain 24 g of white particles [W2] of the present invention. It was.

(Production Example 1-3) Production of white particles [W3] To a 100 ml flask, 8.9 g of P5 synthesized in Synthesis Example 5 was added and dissolved in 45 ml of toluene, and then titanium oxide (R960: manufactured by DuPont). ) After adding 30 g and irradiating ultrasonic waves for 20 minutes to disperse the titanium oxide, the polymer P5 was adsorbed onto the titanium oxide by allowing it to stand overnight at room temperature. This dispersion is put into a centrifuge tube, centrifuged at 3000 rpm for 20 minutes, the supernatant is removed by decantation, and the remaining precipitate is dried at 40 ° C. under vacuum to obtain 20 g of white particles [W3] of the present invention. It was.

Preparation Example 1-4 Preparation of Black Particles [K1] To a 100 ml flask, 5.5 g of the P2 solution synthesized in Synthesis Example 2 was added, diluted with 47 ml of toluene, and then carbon black (Printex A: Degussa Japan Co., Ltd.). 10 g) was added, and the carbon black was dispersed by irradiating with ultrasonic waves for 20 minutes, and then allowed to stand overnight at room temperature to adsorb the polymer P2 to the carbon black. The dispersion is placed in a centrifuge tube, centrifuged at 30000 rpm for 20 minutes, the supernatant is removed by decantation, and the remaining precipitate is dried at 40 ° C. under vacuum to obtain 10 g of black particles [K1] of the present invention. It was.

(Preparation Example 1-5) Preparation of Black Particles [K2] To a 100 ml flask, the total amount of the P4 solution synthesized in Synthesis Example 4 was added and diluted with 47 ml of toluene, and then carbon black (Printex A: manufactured by Degussa Japan Co., Ltd.) After adding 1.5 g and irradiating ultrasonic waves for 20 minutes to disperse the carbon black, the polymer P4 was adsorbed on the carbon black by allowing it to stand overnight at room temperature. This dispersion is placed in a centrifuge tube, centrifuged at 30000 rpm for 20 minutes, the supernatant is removed by decantation, and the remaining precipitate is dried at 40 ° C. under vacuum to obtain 1.6 g of black particles [K2] of the present invention. Got.

(Preparation Example 1-6) Preparation of Black Particles [K3] After adding 8.3 g of the P6 solution synthesized in Synthesis Example 6 to a 100 ml flask and diluting with 45 ml of toluene, carbon black (Printex A: Degussa Japan Co., Ltd.) (Manufactured) After adding 30 g and irradiating ultrasonic waves for 20 minutes to disperse the carbon black, the polymer P6 was adsorbed on the carbon black by allowing it to stand overnight at room temperature. This dispersion is placed in a centrifuge tube, centrifuged at 30000 rpm for 20 minutes, the supernatant is removed by decantation, and the remaining precipitate is dried at 40 ° C. under vacuum to obtain 10.7 g of the black particles [K3] of the present invention. Got.

(Preparation example 2-1) Preparation of comparative sample white particles [Wh1], [Wh2], [Wh3] To a 100 ml flask, 1.5 g of polycarbonate (manufactured by Aldrich) [Ph1] was added and dissolved in 47 g of methylene chloride. Then, after adding 1.5 g of titanium oxide (R960: manufactured by DuPont) and irradiating with ultrasonic waves for 20 minutes to disperse the titanium oxide, the mixture was allowed to stand overnight at room temperature to form a polymer [Ph1 ] Was adsorbed.
This dispersion was put into a centrifuge tube, centrifuged at 3000 rpm for 20 minutes, the supernatant was removed by decantation, and the remaining precipitate was dried at 40 ° C. under vacuum to obtain white particles [Wh1].
Instead of polycarbonate [Ph1], cellulose triacetate (manufactured by Aldrich) [Ph2], or polymethyl methacrylate (manufactured by Aldrich) [Ph3] was used in the same manner as in the above [Wh1] production method, White particles [Wh2] and [Wh3] were prepared, respectively.

(Preparation example 2-2) Preparation of comparative sample black particles [Kh1], [Kh2], [Kh3] To a 100 ml flask, 1.5 g of polycarbonate (manufactured by Aldrich) [Ph1] was added and dissolved in 53 g of methylene chloride. After adding 1.5 g of carbon black (Printex A: manufactured by DuPont Co., Ltd.) and irradiating with ultrasonic waves for 20 minutes to disperse the carbon black, it was allowed to stand at room temperature overnight. Polymer [Ph1] was adsorbed on carbon black.
This dispersion was placed in a centrifuge tube, centrifuged at 30000 rpm for 20 minutes, the supernatant was removed by decantation, and the remaining precipitate was dried at 40 ° C. under vacuum to obtain black particles [Kh1].
Instead of polycarbonate [Ph1], cellulose triacetate (manufactured by Aldrich) [Ph2], or polymethyl methacrylate (manufactured by Aldrich) [Ph3], respectively, was used in the same manner as in the above [Kh1] production method. Black particles [Kh2] and [Kh3] were prepared.

(Measurement Example 1) Measurement of polymer coverage Using TG / DTA6300 (manufactured by Seiko Instruments Inc.), heating from room temperature to 500 ° C. while feeding air into the particles, measuring the weight loss during The coverage (mass%) was determined. The results are summarized in Table 1.

(Measurement Example 2) Evaluation of dispersibility 2.89 g of a solvent mainly composed of hydrocarbons (trade name: Isopar G, manufactured by Exxon Mobil Corp.) and 0.01 g of sorbitan trioleate (trade name: Span 85, manufactured by Wako Pure Chemical Industries, Ltd.) And 2.0 g in the case of white particles and 0.1 g in the case of black particles were added to prepare a dispersibility measurement sample. Each measurement sample was irradiated with ultrasonic waves for 20 minutes while being heated to 40 ° C., and the sedimentation property of the particles after 1 hour was observed to evaluate the dispersibility of the particles. Those having poor dispersibility can be judged by the fact that the particles settle as coarse particles and are separated into a precipitate and a supernatant. The results are summarized in Table 1. In Table 1, those having good dispersibility were indicated by “◯”, and those having insufficient dispersibility were indicated by “x”.

(Measurement Example 3) Evaluation of electrophoretic properties Among the measurement samples prepared in Measurement Example 2, the samples containing particles W1 to W3 and K1 to K3 having good dispersibility were further diluted 10 times with IsoparG. An electrophoretic measurement sample was obtained. Each measurement sample was enclosed between two glass plates (spacer thickness 500 μm) with ITO deposited on the surface, and a cross-section was observed with an optical microscope while applying a DC voltage of 50 V between the electrodes. The electrophoretic properties of the particles were observed. The results are summarized in Table 1. In Table 1, “Yes” indicates electrophoretic properties, and “No” indicates no electrophoretic properties.

As can be seen from Table 1, in the dispersion containing particles (W1 to 3 and K1 to 3) using a polymer having a Tg (glass transition temperature) lower than room temperature (Example), both white and black particles are high polymers. It showed a coverage and good dispersibility for IsoparG. On the other hand, in a dispersion containing particles (Wh1 to 3 and Kh1 to 3) using a rigid polymer having a high Tg (Comparative Example), all the particles have a low coverage, aggregate in Isopar G, and have poor dispersibility. I understood that. In addition, Tg (glass transition temperature) of each polymer was measured by DSC.
Moreover, it turned out that the particle | grains (W2 and K1-3) coat | covered with the ionic polymer have high electrophoretic property among the particles (W1-3 and K1-3) with favorable dispersibility.

Example 1
0.01 g of Span 85 (manufactured by Wako Pure Chemical Industries, Ltd.) is dissolved in 2.89 g of Isopar G (manufactured by Exxon), and 2.0 g of white particles [W1] and 0.1 g of black particles [K1] are added thereto. Ultrasound was irradiated for 20 minutes while heating at 0 ° C. to prepare dispersion [B1].

(Example 2)
A 2 cm square glass plate with ITO deposited on the surface was opposed to each other so that the ITO surface came inside. An epoxy resin including spacer beads having a diameter of 100 μm around the periphery was applied with a cut to be a hole for injecting the dispersion. After the resin was cured by heating to 60 ° C., the dispersion [B1] prepared in Example 1 was injected to produce a display device [H1].
While applying a voltage of a peak value of 10 V with a 1 Hz rectangular wave between the opposing ITO surfaces, white light is irradiated from the direction of 45 ° to the glass surface, and the reflection density in the direction of 90 ° to the glass surface is obtained. , And measured at room temperature (about 25 ° C.).
The reflection density varies according to the applied rectangular wave, the reflectance when the applied voltage is minus 10V is 2% or less, the reflectance when the applied voltage is inverted to plus 10V is 56%, and the contrast ratio is excellent at 28. The display characteristics were shown.

(Example 3)
In a 100 ml container equipped with a stirrer, a dropping funnel and a pH meter, add 1.7 g of gelatin, add 31.7 g of deionized water to dissolve the gelatin, and slowly warm it up to 40 ° C. without entraining bubbles. The mixture was stirred, and 13.3 g of the dispersion [B1] was added dropwise from the dropping funnel over 15 minutes. After the completion, stirring was further continued for 30 minutes.
Thereafter, 1.7 g of gum arabic dissolved in 8.2 g of deionized water was added, the pH was adjusted to 4 with a 10% by mass aqueous acetic acid solution, cooled to 10 ° C., and 0.8 ml of a 25% by mass aqueous glutaraldehyde solution was added. The temperature was slowly returned to room temperature and stirring was continued for 3 hours.
Then, after standing overnight, the supernatant was removed by decantation, 30 g of deionized water was added, the mixture was slowly stirred and allowed to stand, and the supernatant was removed again by decantation. Polyvinyl alcohol (PVA217: Kuraray Co., Ltd.) (Manufactured) 10 g of a 5% by mass solution was added and the pH was adjusted to 7.5 with a 1% by mass aqueous ammonia solution to prepare a capsule solution [C1].

Example 4
The capsule liquid [C1] prepared in Example 3 was applied on a PET (polyethylene terephthalate) film having a thickness of 100 μm with ITO deposited on the surface using a doctor blade so as to have a thickness of 150 μm. After drying for 12 hours, an ITO-deposited PET film (thickness: 100 μm) coated with a 30 μm-thick adhesive was laminated thereon to produce a display device [H2].
While applying a voltage of 10V peak with a 1 Hz rectangular wave between the opposing ITO surfaces, white light is irradiated from the direction of 45 ° to the PET film surface, and the reflection density in the direction of 90 ° to the PET film surface. Was measured at room temperature (about 25 ° C.).
The reflection density changes according to the applied rectangular wave, the reflectance when the applied voltage is minus 10V is 2% or less, the reflectance when the applied voltage is inverted to plus 10V is 48%, and the contrast ratio is excellent at 24. The display characteristics were shown.

Claims (7)

  A dispersion comprising at least a dispersion medium composed of an organic solvent and pigment particles having a polymer physically adsorbed on the surface, wherein the polymer has a glass transition point (Tg) of −80 ° C. or more and 25 ° C. or less. A dispersion for an electrophoretic display element.   The dispersion for an electrophoretic display element according to claim 1, wherein the polymer is a polymer having an ionic functional group.   The dispersion liquid for electrophoretic display elements according to claim 2, wherein the ionic functional group is a carboxyl group or a quaternary amino group.   The dispersion liquid for electrophoretic display elements according to claim 1, wherein the polymer is insoluble in the dispersion medium.   It further comprises non-ionic polymer insoluble in the dispersion medium, and pigment particles obtained by physical adsorption of the nonionic polymer having a glass transition point (Tg) of −80 ° C. or more and 25 ° C. or less. The dispersion liquid for electrophoretic display elements according to any one of claims 2 to 4.   An electrophoretic display element, wherein the dispersion liquid according to claim 1 is sandwiched between a pair of substrates having a conductive layer. An electrophoretic display element, wherein a microcapsule containing at least the dispersion liquid according to claim 1 is sandwiched between a pair of substrates having a conductive layer.