JP2012173539A - Dispersion liquid for electrophoretic display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersion liquid for an electrophoretic display element which is inexpensive, excellent in dispersion stability and response speed and capable of forming a high quality image and an image display device using the same.SOLUTION: A dispersion liquid for an electrophoretic display element is obtained by dispersing pigment particles, which are physically adsorbed on the surface of a graft copolymer having either a nitrogen atom-containing polymer (A) or an acrylic polymer containing (meth)acrylate having an alkyl group having carbon atoms of 8 or more as a constituting monomer unit in the main and side chains, in a nonpolar solvent. The nitrogen atom-containing polymer (A) preferably has a tertiary amino group and/or a quaternary ammonium group and the acrylic polymer (B) preferably has a carboxyl group.

Description

  The present invention relates to a dispersion for an electrophoretic display element including a non-aqueous dispersion pigment slurry used for electronic paper and the like, and an electrophoretic display element using the same.

In recent years, a display medium having both display and hard copy functions called by names such as electronic paper and electronic book has the same portability as a conventional paper medium, and has the advantages of space saving and power saving. Because of this, it has been actively researched.
As a display medium used for electronic paper, various types of electronic paper such as an electronic powder fluid type, a twist ball type, a liquid crystal type, and an electrophoretic type have been developed. Among these, display media using an electrophoretic method are excellent in terms of display quality and power consumption at the time of display operation, and are actually in practical use.

  In an electrophoretic display medium, a large number of capsules or cells exist between a pair of transparent electrodes, and a dispersion liquid in which a plurality of electrophoretic particles having different colors and charges are dispersed (electrophoretic slurry). (Also called). The electrophoretic particles have a charge on the surface, and when a voltage is applied to one or both electrodes, the electrophoretic particles having a charge different from the charge accumulate, and the color of the particles is observed. When the voltage is switched to the opposite voltage after the voltage application, the migrating particles are separated from the accumulated electrode side and accumulated on the opposite electrode side. In the electrophoresis method, an image can be displayed by utilizing this change.

In general, electrophoretic particles used in image display media are required to have dispersion stability in a dispersion medium in addition to electrophoretic properties. As methods for satisfying such requirements, for example, Patent Documents 1 and 2 propose electrophoretic particles in which a polymer is grafted on the surface of pigment particles in order to impart electrophoretic particles with affinity for a dispersion medium. Patent Documents 3 and 4 disclose a method in which a polymer prepared in advance is adsorbed on the surface of pigment particles as a dispersion stabilizer.
On the other hand, Patent Document 5 describes a method of stabilizing dispersion by adsorbing a graft polymer having a polydimethylsiloxane segment in the side chain to pigment particles in silicone oil.

Special table 2004-526210 gazette JP 2005-352053 A JP 2006-259170 A JP 2004-67999 A JP 2002-338642 A

  However, the methods disclosed in Patent Documents 1 and 2 require a specific surface treatment on the pigment particle surface, and it is necessary to remove the residual monomer and the ungrafted polymer after the polymer is grafted onto the pigment surface. There is a problem that the operation is complicated. Further, according to the methods described in Patent Documents 3 and 4, it is easy to remove the residual monomer and purify the polymer, and easily obtain a pigment dispersion simply by grinding the pigment in the presence of the polymer. it can. However, the dispersion based on the random linear polymer described in Patent Document 3 has insufficient dispersion stability. In Patent Document 4, the block polymer used as the dispersion stabilizer is expensive, so that industrial use is limited. There is a problem.

On the other hand, according to the method disclosed in Patent Document 5, it is possible to stably disperse the pigment in the silicone oil. However, the dispersion can be used in an inexpensive dispersion medium such as an aliphatic or aromatic hydrocarbon solvent. There is a problem that the medium is limited. Moreover, since the reactive silicone oil used as a raw material is expensive, it is difficult to obtain a dispersant at low cost.
The present invention has been made in view of the above circumstances, and an object thereof is to provide an image display medium that has an inexpensive and high-quality image and has an excellent response speed. That is, an object of the present invention is to provide a dispersion for an electrophoretic display element that can be easily synthesized with a general-purpose reagent or the like and has excellent dispersion stability and response speed, and an image display device using the same.

  As a result of intensive studies on the above problems, the present inventors have found that it is effective to use a dispersion in which pigment particles having a specific graft copolymer adsorbed on the surface thereof are dispersed in a nonpolar solvent. Completed the invention.

The present invention is as follows.
1. A dispersion for an electrophoretic display device comprising a dispersion in which pigment particles having a graft copolymer adsorbed on a surface are dispersed in a nonpolar solvent, wherein the graft copolymer is a nitrogen atom-containing polymer (A), Graft copolymer with one of the acrylic polymers (B) containing a (meth) acrylic acid alkyl ester having an alkyl group having 8 or more carbon atoms as a constituent monomer as the main chain and the other as the side chain A dispersion for electrophoretic display elements, characterized by being a coalescence.
2. 2. The dispersion for an electrophoretic display element according to the above 1, wherein the nitrogen atom-containing polymer (A) has a tertiary amino group and / or a quaternary ammonium group.
3. 3. The dispersion for an electrophoretic display element according to the above 2, wherein the nitrogen atom-containing polymer (A) has an amine value of 40 to 300 mgKOH / g.
4). 4. The dispersion liquid for electrophoretic display elements according to any one of 1 to 3, wherein the acrylic polymer (B) has a carboxyl group.
5. 5. The dispersion for an electrophoretic display element as described in 4 above, wherein the acrylic polymer (B) has an acid value of 1 to 80 mgKOH / g.
6). The dispersion liquid for electrophoretic display elements according to any one of 1 to 5 above, wherein the acrylic polymer (B) has a weight average molecular weight of 1000 to 40000.
7). 7. The dispersion for electrophoretic display elements according to 1 to 6, wherein the graft copolymer has a weight average molecular weight of 2000 to 80000.
8). 8. The dispersion for an electrophoretic display element according to any one of 1 to 7 above, wherein the ratio of the nitrogen-containing polymer (A) in the graft copolymer is 10 to 50% by mass.
9. An acrylic polymer in which the graft copolymer includes, as a constituent monomer, a (meth) acrylic acid alkyl ester having a main chain of the nitrogen atom-containing polymer (A) and the alkyl group having 8 or more carbon atoms. 9. The dispersion liquid for electrophoretic display elements according to any one of 1 to 8 above, wherein B) is a side chain.
10. 10. The dispersion for electrophoretic display device as described in 9 above, wherein the side chain is derived from a macromonomer having a polymerizable unsaturated double bond at the terminal.
11. 11. The dispersion for an electrophoretic display element according to any one of 1 to 10 above, wherein the graft copolymer is present in a ratio of 1 to 100 parts by mass with respect to 100 parts by mass of the pigment.
12 The dispersion for electrophoretic display elements according to any one of 1 to 11 above, wherein the volume average particle diameter of the pigment particles dispersed in the nonpolar solvent is in the range of 0.1 to 1.0 μm. liquid.
13. The dispersion liquid for electrophoretic display elements according to any one of 1 to 12 above, wherein the pigment particles are carbon black.
14 14. The dispersion for electrophoretic display element according to any one of 1 to 13, wherein the nonpolar solvent contains an aliphatic hydrocarbon and / or a fatty acid alkyl ester.
15. 15. The dispersion for electrophoretic display device as described in 14 above, wherein the nonpolar solvent is a fatty acid alkyl ester having 10 or more carbon atoms and a viscosity at 25 ° C. of 15 mPa · s or less.
16. 16. An image display element comprising the dispersion liquid for electrophoretic display elements according to any one of 1 to 15 above.
17. 17. An image display device using the image display element described in 16 above.

In the graft copolymer used in the present invention, a segment containing a nitrogen atom and a segment containing a (meth) acrylic acid alkyl ester having an alkyl group having 8 or more carbon atoms as a constituent monomer are clearly divided. Therefore, the adsorptivity to the pigment by the former and the affinity to the medium by the latter can be highly balanced.
Therefore, according to the dispersion liquid for electrophoretic display elements of the present invention containing pigment particles adsorbed with the graft copolymer, a display medium and a display device capable of displaying a high-quality image can be obtained. Specifically, it is possible to provide an image display device that is excellent in re-migration and response speed when the voltage applied to the electrode is switched.

It is sectional drawing which shows typically an example of the image display element by this invention. It is a schematic diagram of the apparatus for evaluation used in the Example of this application.

The present invention relates to a dispersion for an electrophoretic display element and an image display device using the same, and uses a dispersion in which pigment particles physically adsorbed with a specific graft copolymer are dispersed in a nonpolar solvent. It is characterized by.
The present invention will be described in detail below. In the present specification, acrylic acid or methacrylic acid is represented as (meth) acrylic acid.

The graft copolymer in the present invention is composed of a nitrogen atom-containing polymer (A) and an acrylic polymer (B) containing (meth) acrylic acid alkyl ester having an alkyl group having 8 or more carbon atoms as constituent monomers. It is a graft copolymer having one of the main chains as the main chain and the other as the side chain.
Here, the nitrogen atom-containing polymer (A) can be obtained by using a nitrogen atom-containing vinyl monomer as a constituent monomer.

  As said nitrogen atom containing vinyl monomer, the monomer which has nitrogen atom containing functional groups, such as an amide group, an amino group, a quaternary ammonium group, can be used suitably, and 3 from a point with favorable adsorbability. Monomers having a quaternary amino group and a quaternary ammonium group are particularly preferred.

  Specific monomers having a tertiary amino group include, for example, dialkylaminoethyl (meth) acrylates such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dibutylaminoethyl (meth) acrylate, Examples include dialkylaminopropyl (meth) acrylate, dimethylaminopropylacrylamide, vinylbenzyldimethylamine and the like. Among these, dialkylaminoethyl (meth) acrylate, dialkylaminopropyl (meth) acrylate and dimethylaminopropylacrylamide are preferable because of their good adsorptivity to the pigment.

Examples of the monomer having a quaternary ammonium group include a quaternized product of the monomer having a tertiary amino group such as dimethylaminoethyl methacrylate quaternary ammonium salt.
Moreover, it is good also as a polymer which has a quaternary ammonium salt by copolymerizing the monomer which has the said tertiary amino group, and quaternizing in accordance with a well-known method.

The nitrogen atom-containing polymer (A) is preferably in the range of 40 to 300 mgKOH / g, more preferably 50 to 200 mgKOH / g, as the amine value. When the amine value is less than 40 mgKOH / g, the adsorptive power of the graft copolymer to the pigment may be insufficient, which may cause aggregation or the like. On the other hand, when the amine value exceeds 300 mgKOH / g, aggregation and the like occur, and remigration properties tend to deteriorate.
In the present invention, the amine value is a value calculated from the amount of raw material used.

The nitrogen atom-containing polymer (A) can copolymerize other vinyl monomers in addition to the nitrogen atom-containing vinyl monomer. There is no limitation on the type and amount of the other vinyl monomer as long as it does not impair the properties such as adsorptivity, but the obtained polymer is insoluble in the medium, and is not soluble in pigments such as carbon black. Those having high affinity are preferred. From this viewpoint, a monomer having a solubility parameter (SP) value in the range of 17 to 20 [MPa ^1/2 ] is preferable, and specifically, an aromatic vinyl unit such as styrene, α-methylstyrene, benzyl methacrylate and the like. (Meth) acrylic acid alkyl esters such as methyl acrylate, methyl methacrylate, butyl acrylate, and isobutyl acrylate; and ω-carboxy-polycaprolactone monoacrylate (for example, trade name “Aronix, manufactured by Toagosei Co., Ltd.) M-5300 ") and the like. Among these, benzyl methacrylate and Aronix M-5300 are preferable from the viewpoint of excellent adsorptivity to pigments.

  As the SP value, a value described in “POLYMER HANDBOOK 4th edition” (published by John Wiley & Sons, Inc.) can be adopted. Collman, John F. Graf, Paul C.M. Described in "Specific Interactions and the Miscibility of Polymer Blends" (Methods published by Technological Publishing Co. Inc.) by Painter (Pensylvania State Univ.). However, for -COOH group and -OH group, R.I. F. Values described in “Polymer Engineering and Science” 14 (2), 147 (1974) written by Fedors are used.

The acrylic copolymer (B) in the present invention contains a (meth) acrylic acid alkyl ester having an alkyl group having 8 or more carbon atoms as a constituent monomer. Specific examples of the (meth) acrylic acid alkyl ester having an alkyl group having 8 or more carbon atoms include 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, ( N-nonyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, myristyl (meth) acrylate, cetyl (meth) acrylate, stearyl (meth) acrylate and (Meth) acrylic acid behenyl and the like can be mentioned, and one or more of these can be used.
Of these, (meth) acrylic acid alkyl esters having an alkyl group having 10 to 16 carbon atoms are preferred, and more preferred are (meth) acrylic acid alkyl esters having an alkyl group having 12 to 13 carbon atoms. Examples include Blemmer SLA, Blemmer SLMA (both manufactured by NOF Corporation, synthetic lauryl (meth) acrylate), lauryl (meth) acrylate, and the like.
When the alkyl group has less than 8 carbon atoms, the compatibility with the nonpolar solvent is low, and a sufficient dispersion stabilizing effect cannot be imparted. On the other hand, even when the alkyl group has more than 16 carbon atoms, the reason is unclear, but the dispersion stability may decrease.

  The (meth) acrylic acid alkyl ester having 8 or more carbon atoms is preferably used in an amount of 50 to 100 mol%, more preferably 80 to 100 mol%, based on all monomers constituting the acrylic copolymer (B). When the amount is less than 50 mol%, the dispersion stability may be insufficient due to insufficient affinity for a nonpolar solvent.

  The acrylic copolymer (B) may have a carboxyl group. The carboxyl group is easily introduced by copolymerizing a carboxyl group-containing monomer such as (meth) acrylic acid, crotonic acid, maleic acid, maleic anhydride and itaconic acid. Alternatively, after copolymerizing a hydroxyl group-containing unsaturated monomer, a carboxyl group is also introduced by addition reaction of a dibasic acid anhydride such as succinic anhydride, maleic anhydride or phthalic anhydride. be able to.

The introduction amount of the carboxyl group in the acrylic copolymer (B) is preferably in the range of 1 to 80 mgKOH / g as the acid value. When the acid value is less than 1 mgKOH / g, the dispersion stability is not sufficient, and aggregation of dispersed particles tends to occur, which is not preferable. Further, when the acid value exceeds 80 mgKOH / g, aggregation of the dispersed particles occurs and the re-migration property is lowered.
In the present invention, the acid value is a value calculated from the charged raw materials.

  Moreover, it is preferable that the weight average molecular weights (henceforth "Mw") of an acrylic copolymer (B) are 1000-40000, and it is further more preferable that it is 2000-20000. When Mw is less than 1000, the steric repulsion effect is insufficient, so that the stability of the electrophoretic particles is not ensured, and aggregation is caused. On the other hand, when Mw exceeds 40000, the re-migration property may be poor when the voltage applied to the electrode is switched. This is presumed to be due to the entanglement of the medium affinity parts.

Examples of other monomers constituting the acrylic copolymer (B) include carbon such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth) acrylate. (Meth) acrylic acid alkyl ester having an alkyl group of less than 8;
(Meth) acrylic acid cycloalkyl ester having a cycloalkyl group having less than 8 carbon atoms such as (meth) acrylic acid cyclohexyl; styrene derivatives such as styrene, α-methylstyrene and p-methylstyrene; (meth) acrylonitrile; ) Acrylamide and the like, and one or more of them can be used.

As described above, the graft copolymer in the present invention is an acrylic polymer (A) containing a nitrogen atom-containing polymer (A) and a (meth) acrylic acid alkyl ester having an alkyl group having 8 or more carbon atoms as constituent monomers ( B) is a graft polymer having one of the main chains as the main chain and the other as the side chain. Among these, a dispersion obtained from a graft copolymer having a nitrogen atom-containing polymer (A) as a main chain and an acrylic polymer (B) as a side chain is preferred because the dispersion stability tends to be high.
Here, the component (A) serves as a segment responsible for the adsorptivity to the pigment particle surface, and the component (B) serves as a segment for imparting medium affinity.

The ratio of the nitrogen atom-containing polymer (A) and the acrylic polymer (B) is preferably such that the (A) component is 10 to 50% by mass and the (B) component is 50 to 90% by mass. Preferably, (A) component is 20-40 mass%, and (B) component is 60-80 mass%.
When the component (A) is less than 10% by mass (when the component (B) exceeds 90% by mass), the adsorptivity to the pigment becomes insufficient and aggregation or the like tends to occur, which is not preferable. Further, when the component (A) exceeds 50% by mass (when the component (B) is less than 50% by mass), the dispersion stability is lowered, so that the re-migration property when the voltage at the electrode is switched is deteriorated. To do.

  Mw of the graft copolymer is preferably 2,000 to 80,000, more preferably 4,000 to 40,000. When the Mw is less than 2,000, the adsorptive power of the graft copolymer to the pigment particles is reduced, so that aggregation or the like is likely to occur. When the Mw exceeds 80,000, the viscosity of the dispersion increases and the migration speed increases. Is not preferable because of lowering.

  There is no restriction | limiting in particular about the manufacturing method of a graft copolymer, The acrylic polymer (A) which contains a nitrogen atom containing polymer (A), and the (meth) acrylic-acid alkylester which has a C8 or more alkyl group in a constituent monomer ( Any method may be used as long as it is a method capable of producing a graft copolymer having either one of B) as a main chain and the other as a side chain.

As a manufacturing method of the above-mentioned graft copolymer, for example,
(I) a nitrogen atom in the presence of a macromonomer comprising, as a constituent monomer, a (meth) acrylic acid alkyl ester having a polymerizable unsaturated double bond at the terminal and an alkyl group having 8 or more carbon atoms In the presence of a macromonomer having a polymerizable unsaturated double bond at the terminal and a nitrogen atom, a copolymer containing the monomer and other monomers is obtained to obtain a graft copolymer. A method (macromonomer method) in which a graft copolymer is obtained by copolymerizing (meth) acrylic acid alkyl ester having 8 or more alkyl groups and other monomers;
(Ii) a (meth) acrylic acid alkyl ester having a polymerization initiation group such as an azo group or a peroxide group in the polymer segment and an alkyl group having 8 or more carbon atoms in the presence of a polymer having a nitrogen atom; Another monomer is copolymerized to obtain a graft copolymer, or the polymer segment has a polymerization initiating group such as an azo group or a peroxide group and an alkyl group having 8 or more carbon atoms (meta ) A method for obtaining a graft copolymer by copolymerizing a nitrogen atom-containing monomer and another monomer in the presence of a polymer comprising an alkyl acrylate ester as a constituent monomer;
(Iii) Graft polymerization of (meth) acrylic acid alkyl ester having an alkyl group having 8 or more carbon atoms and other monomers on a polymer having a group having a large chain transfer ability in the side chain and a nitrogen atom. A copolymer is obtained, or a nitrogen atom is added to a polymer comprising (meth) acrylic acid alkyl ester having a group having a large chain transfer ability in the side chain and an alkyl group having 8 or more carbon atoms as a constituent monomer. A method of obtaining a graft copolymer by graft polymerization of the containing monomer and other monomers.

Among the above-described production methods, the macromonomer method (i) is preferable from the viewpoint that the graft copolymer can be produced efficiently.
Further, the terminal polymerizable unsaturated double bond in the macromonomer is preferably a (meth) acryloyl group or a styryl group from the viewpoint of copolymerizability, and among them, a (meth) acryloyl group is particularly preferable.

It is preferable that 1-100 mass parts is used for the graft copolymer in this invention with respect to 100 mass parts of pigment particles, 10-60 mass parts is more preferable, and 20-40 mass parts is further more preferable.
When the amount of the graft copolymer used is less than 1 part by mass, the pigment cannot be stably dispersed, which causes an increase in particle size or aggregation, which is not preferable. In addition, re-migration properties tend to deteriorate. On the other hand, aggregation also tends to occur when the amount of the graft copolymer exceeds 100 parts by mass. This is presumably because the amount of graft copolymer present in the continuous phase increases and the dispersion stabilizing effect of the dispersant adsorbed on the pigment particles (graft copolymer) decreases.

The nonpolar solvent, which is a dispersion medium in the dispersion for an electrophoretic display device of the present invention, can be used without particular limitation as long as it is a solvent immiscible with water, and various aliphatic hydrocarbon compounds having a linear, branched or cyclic structure. Alternatively, solvents such as fatty acid alkyl esters, aromatic hydrocarbon compounds, heteroaromatic hydrocarbon compounds, halogen-containing solvents and silicone oils are included. Here, “a solvent immiscible with water” means a solvent having a water solubility of 1% by mass or less at 25 ° C.
As the nonpolar solvent, those having low volatility are preferable from the viewpoint of ease of handling and safety, and various aliphatic hydrocarbon compounds or fatty acid alkyls having a linear, branched or cyclic structure having 10 or more carbon atoms. Esters are preferred.

  Moreover, since the electrophoresis speed decreases in inverse proportion to the viscosity of the solvent, the viscosity of the solvent is preferably 20 mPa · s or less at 25 ° C. Particularly preferred are fatty acid alkyl esters having 10 or more carbon atoms and a viscosity at 25 ° C. of 15 mPa · s or less. Specific examples include “Isosol” series (manufactured by JX Nippon Oil & Energy Corporation), “Isopar” series (manufactured by ExxonMobil Corporation), “IP Solvent” series (manufactured by Idemitsu Petrochemical Co., Ltd.), “Exepal” series. (Manufactured by Kao Corporation), 2-ethylhexyl caprylate, 2-ethylhexyl palmitate and the like. Among these, from the viewpoint of dispersion stability and migration speed, “Isopar” series, 2-ethylhexyl caprylate and 2-ethylhexyl palmitate are preferable, and 2-ethylhexyl caprylate is particularly preferable.

The dispersed particle diameter of the pigment particles in the dispersion liquid for electrophoretic display elements of the present invention is preferably in the range of 0.1 to 1.0 μm, and in the range of 0.2 to 0.6 μm as the volume average particle diameter. It is more preferable.
When the particle diameter exceeds 1.0 μm, sedimentation tends to occur in the dispersion. In addition, when the voltage is turned off, the pigment particles fall off from the electrode portion due to gravity and the image is not maintained (so-called memory property is deteriorated), which is not preferable. On the other hand, when the particle diameter is smaller than 0.1 μm, the migration speed is slow, which is not preferable.

  In the dispersion for electrophoretic display elements of the present invention, known organic pigment particles and inorganic pigment particles can be used as pigment particles. As organic pigment particles, for example, azo pigments, phthalocyanine pigments, anthraquinone pigments, dioxazine pigments, quinacridone pigments, perylene pigments, indigoid pigments, diketopyrrolopyrrole pigments, perinone pigments, isoindolinone pigments, isocindrone pigments and quinophthalone pigments are used. can do.

  Examples of inorganic pigment particles include white pigments such as zinc oxide, titanium oxide, aluminum oxide, and calcium carbonate; red pigments such as iron oxide; yellow pigments such as yellow lead, cadmium yellow, and strontium yellow; ultramarine blue, Prussian blue, and the like Blue pigments; black pigments such as carbon black and titanium black can be used. Among these, carbon black is widely used from the viewpoint of image visibility and versatility.

  In the present invention, when carbon black is used as the pigment particle, the type of carbon black is not specified as long as the dispersed particle size of the pigment particle is within a range preferable in the present invention, but the primary particle size is 20 When carbon black of ˜200 nm is used, the dispersed particle diameter tends to be in a preferred range. Specific examples include Lamp Black 101, Printex A, Special Black 100 (manufactured by Evonik Degussa Co., Ltd.) and the like under the trade names.

  The dispersion for electrophoretic display elements of the present invention can be easily obtained by mixing and stirring the above-mentioned graft copolymer, pigment, dispersion medium and the like. For the stirring, a known stirring device generally used in pigment dispersion can be used, and specific examples include a ball mill, a bead mill, a sand mill, a paint shaker, and a disper.

  In the dispersion for electrophoretic display elements of the present invention, a charge adjusting agent such as metal soap for dispersing the pigment particles, a dispersing agent and a dispersion aid for improving the dispersibility of the electrophoretic particles are added. Also good.

  FIG. 1 schematically shows an example of an image display device using the electrophoretic element dispersion of the present invention. The image display device can be used without limitation as long as it is a known one, but at least one has a pair of light-transmitting electrode substrates, and electrophoretic pigment particles are dispersed in a white medium between the substrates. The electrophoretic display element is filled with the electrophoretic dispersion liquid. An image is displayed by applying a voltage to these electrodes and moving the electrophoretic pigment particles.

Hereinafter, the present invention will be specifically described based on examples. In the following description, “part” means part by mass, and “%” means mass%.
The macromonomer, graft copolymer and pigment dispersion obtained in each example were evaluated by measuring the following physical properties and properties.
(1) Characteristics of Macromonomer and Graft Copolymer a) About 1 g of a solid content measurement sample is weighed (a), then the residue after drying for 60 minutes at an air dryer 200 ° C. is measured (b). It was calculated from the following formula. A weighing bottle was used for the measurement. Other operations were in accordance with JIS K 0067-1992 (chemical product weight loss and residue test method).
Solid content (%) = (b / a) × 100

b) Molecular weight When a monomer having a nitrogen atom was not included as a monomer constituting the copolymer and the macromonomer, the molecular weight and molecular weight distribution were measured by the following operation.
A sample was dissolved in tetrahydrofuran (hereinafter referred to as “THF”) to prepare a solution having a concentration of 0.2%, and then 100 μL of the solution was added to a column (“TSK-GEL MULTIPIORE HXL-M” (four) manufactured by Tosoh Corporation. The sample was measured by gel permeation chromatography (GPC method) in which THF was passed through the column at a flow rate of 1.0 mL / min at a column temperature of 40 ° C. to elute the components adsorbed on the column. The number average molecular weight (Mn) and the weight average molecular weight (Mw) were calculated from a calibration curve prepared in advance using polystyrene having a known molecular weight as a standard substance.
When the monomer constituting the copolymer and / or the macromonomer includes a monomer having a nitrogen atom, THF containing 0.5% triethylamine dissolved therein is used for eluent and sample preparation. GPC measurement was performed by operation.

(2) Characteristics of Electrophoretic Display Device Dispersion a) Volume average particle diameter Sample prepared by adjusting a dispersion obtained by diluting a slurry in which electrophoretic particles are dispersed in an insulating liquid to 0.3% with the nonpolar solvent It was. 30 mL of the sample was measured by a dynamic light scattering method (manufactured by Nikkiso Co., Ltd., UPA-250) to obtain a volume average particle size.

b) Viscosity Using an E-type viscometer, the viscosity at 25 ° C. was measured.

<Manufacture of macromonomer>
Synthesis Example 1: Production of Macromonomer 1 2-hydroxyethyl methacrylate (hereinafter referred to as “HEMA”) as a monomer in a glass flask equipped with a stirrer, a dropping funnel, a reflux condenser, a nitrogen gas inlet tube, and a thermometer 1.2 parts and 98.8 parts of Bremer SLMA (manufactured by NOF Corporation, synthetic lauryl methacrylate, hereinafter referred to as “SLMA”), 1.5 parts of 3-mercaptopropionic acid (hereinafter referred to as “MPA”) as a chain transfer agent, and 50 parts of 2-ethylhexyl palmitate was charged as a polymerization solvent, and the mixture was heated and stirred at 90 ° C. under a nitrogen stream. In a separate container, 2.4 parts of methyl ethyl ketone (hereinafter referred to as “MEK”) and 45 parts of 2-ethylhexyl palmitate with 2,2′-azobis (2-methylbutyronitrile) (manufactured by Nippon Finechem Co., Ltd., trade name “ABN”) -E ") 0.9 part was added and dissolved to prepare a polymerization initiator solution, and this polymerization initiator solution was dropped into the flask over 5 hours while keeping the solution in the flask at 90 ° C. Furthermore, the polymerization was completed by continuing the heating and stirring for 2 hours to obtain a polymer solution having a carboxyl group at one end.
1. Switch nitrogen flow to air bubbling, and then continue 0.02 part hydroquinone monomethyl ether (hereinafter referred to as “MQ”) 0.6 part tetrabutylammonium bromide, glycidyl methacrylate (hereinafter referred to as “GMA”) in the same flask. 1 part was added, and it heated and stirred at 110 degreeC for 4 hours.
Next, 0.9 part of succinic anhydride was added to the same flask, reacted at 110 ° C. for 4 hours, cooled to room temperature, and adjusted to a solid content of 52% with 2-ethylhexyl palmitate. A 2-ethylhexyl palmitate solution of macromonomer 1 having a polymerizable unsaturated double bond and a carboxyl group was obtained.
The number average molecular weight (Mn) of the obtained macromonomer 1 was 7,900, and the weight average molecular weight (Mw) was 12,100. Moreover, it has a carboxyl group equivalent to 4.9 mgKOH / g as an acid value.

Synthesis Examples 2, 3, 5, 6, 8: Production of Macromonomer 2, 3, 5, 6, 8 The same as Synthesis Example 1 except that the monomer, chain transfer agent and GMA were used as shown in Table 1. Operation was performed to obtain a 2-ethylhexyl palmitate solution of macromonomers 2, 3, 5, 6, and 8.
It shows in Table 1 about the physical-property value of each obtained macromonomer.

Synthesis Example 4: Production of Macromonomer 4 Macromonomer was prepared in the same manner as in Synthesis Example 1 except that the monomer, chain transfer agent and GMA were used as shown in Table 1 and carboxylic acid modification with succinic anhydride was not performed. 4 solution of 2-ethylhexyl palmitate was obtained.
The physical property values of the obtained macromonomer 4 are shown in Table 1.

Synthesis Example 7 Production of Macromonomer 7 In a glass flask equipped with a stirrer, a dropping funnel, a reflux condenser, a nitrogen gas introduction tube, and a thermometer, benzyl methacrylate (hereinafter referred to as “BzMA”) as a monomer was obtained. 7 parts, 33.3 parts of N, N-dimethylaminoethyl methacrylate (hereinafter referred to as “DMA”), 2.5 parts of 2-mercaptoethanol (hereinafter referred to as “MTG”) as a chain transfer agent, and palmitic acid as a polymerization solvent 50 parts of 2-ethylhexyl acid was charged and stirred at 90 ° C. under a nitrogen stream. In a separate container, add ABN-E 0.9 part to 2.7 parts of MEK and 45 parts of 2-ethylhexyl palmitate to prepare a polymerization initiator solution, and start this polymerization while keeping the solution in the flask at 90 ° C. The agent solution was dropped into the flask over 5 hours. Furthermore, by continuing the heating and stirring for 2 hours, the polymerization was completed to obtain a polymer solution having a hydroxyl group at one end.
The nitrogen stream was switched to air bubbling, and subsequently 0.02 part of 4-methoxyphenol, 0.01 part of dioctyltin dilaurate (manufactured by Nitto Kasei Co., Ltd., trade name “Neostan U-810”), 2-isocyanate in the same flask. 5.0 parts of ethyl methacrylate (trade name “Karenz MOI”, manufactured by Showa Denko KK) was added, heated at 80 ° C. for 3 hours, cooled to room temperature, and macromonomer 7 having a methacryloyl group at one end 2- An ethylhexyl solution was obtained.
The physical property values of the obtained macromonomer 7 are shown in Table 1.

Details of the compounds used in Table 1 are shown below.
SLMA: Synthetic lauryl methacrylate (manufactured by NOF Corporation, trade name “Blemmer SLMA”)
LA: lauryl acrylate BMA: butyl methacrylate BzMA: benzyl methacrylate HEMA: 2-hydroxyethyl methacrylate HEA: 2-hydroxyethyl acrylate DMA: dimethylaminoethyl methacrylate MPA: 3-mercaptopropionic acid MTG: 2-mercaptoethanol GMA: glycidyl methacrylate Karenz MOI: 2-isocyanate ethyl methacrylate (made by Showa Denko)

<Production of graft copolymer>
Production Example 1: Production of Graft Copolymer 1 75 parts of MEK was charged into a glass flask equipped with a stirrer, a dropping funnel, a reflux condenser, a nitrogen gas inlet tube and a thermometer, and heated to 78 ° C. under a nitrogen stream. In a separate container, 134.6 parts of a 2-ethylhexyl palmitate solution of macromonomer 1 obtained above (70 parts as the solid content of the macromonomer), 20 parts of BzMA, 10 parts of DMA, 18 parts of MEK, and 0.3 part of MTG are included. A monomer mixed solution and an initiator solution in which 1 part of 2,2′-azobis (2,4′-dimethylvaleronitrile) (trade name “V-65”, manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 30 parts of MEK. It was adjusted. Next, the monomer mixed solution and the initiator solution were dropped into the flask to initiate polymerization. The monomer mixed solution was added dropwise over 3 hours, and the initiator solution was added dropwise over 5 hours. After completion of the addition of the initiator solution, the mixture was further heated and stirred at 78 ° C. for 1.5 hours to complete the polymerization. 1 MEK solution (solid content 35%) was obtained.
The number average molecular weight (Mn) of the obtained graft copolymer 1 was 13,500, and the weight average molecular weight (Mw) was 31,700. Further, this graft copolymer 1 contains an amine group corresponding to 119.0 mgKOH / g as the amine value in the main chain, and has an acid value corresponding to 4.9 mgKOH / g in the side chain polymer.

Production Examples 2-9, 11-18: Production of Graft Copolymers 2-9, 11-18 As shown in Tables 2-1 to 2-3, monomers constituting the main chain and macromonomers serving as side chains are shown. Except having used, operation similar to manufacture example 1 was performed and the graft copolymers 2-9 and 11-18 were obtained.
The physical properties of the obtained graft copolymers 2 to 9 and 11 to 18 are shown in Tables 2-1 to 2-3.

Production Example 10 Production of Graft Copolymer 10 A glass flask equipped with a stirrer, a dropping funnel, a reflux condenser, a nitrogen gas inlet tube and a thermometer was charged with 10 parts DMA, 0.5 part MQ, 250 parts propylene glycol monomethyl ether acetate. The mixture was heated and stirred at 60 ° C. under a nitrogen stream. 33 parts of methyl chloride was blown in over 6 hours, and stirring was further continued at 60 degreeC for 2 hours, and reaction was complete | finished. After the reaction product was cooled to room temperature, the precipitated crystals were collected by filtration. The recovered crystals were dried at 50 ° C. under reduced pressure, and volatile components including the residual solvent were removed to obtain DMA quaternary ammonium salt (hereinafter referred to as “DMA-Q”).
Using the monomers and macromonomers shown in Table 2-2 including DMA-Q, and using the polymerization solvent as propylene glycol monomethyl ether acetate, the same operation as in Production Example 1 was carried out to obtain graft copolymer 10. It was.
The physical property values of the obtained graft copolymer 10 are shown in Table 2-2.

Details of the compounds used in Tables 2-1 to 2-3 are shown below.
DMA: N, N-dimethylaminoethyl methacrylate DMAAm: N, N-dimethylacrylamide DMA-Q: N, N-dimethylaminoethyl methacrylate quaternary ammonium salt BzMA: benzyl methacrylate M5300: ω-carboxy-caprolactone monoacrylate
(Product name "Aronix M-5300", manufactured by Toagosei Co., Ltd.)
IBMA: Isobutyl methacrylate SLMA: Synthetic lauryl methacrylate (manufactured by NOF Corporation, trade name “Blemmer SLMA”)
NK ester SA: 2-methacryloyloxyethyl succinate
(Manufactured by Shin-Nakamura Chemical Co., Ltd.)

Comparative Production Examples 1 to 5: Production of Linear Copolymers 1 to 2 and Graft Copolymers 19 to 21 The same operation as in Production Example 1 was performed except that the monomers and macromonomers were used as shown in Table 3. Linear copolymers 1-2 and graft copolymers 19-21 were obtained.
The physical property values of the obtained linear copolymers 1 and 2 and graft copolymers 19 to 21 are shown in Table 3.

Example 1
After adding 40 parts of Isopar L (ExxonMobil Corporation, isoparaffinic hydrocarbon solvent) to 60 parts of the MEK solution of graft copolymer 1 obtained in Production Example 1, MEK under reduced pressure of 80 ° C. and 15 mmHg, Unreacted monomer and low molecular weight oligomer were distilled off to obtain an Isopar L solution (solid content 28%) of graft copolymer 1.
2.14 g of Isopar L solution of Graft Copolymer 1 above, 11.5 g of Isopar L and carbon black (trade name “Lamp Black 101” manufactured by Evonik Degussa) 1.5 g are put in a pressure-resistant glass container, and zirconia beads (bead diameter) : 0.3 mm) After mixing 30 g, the mixture was stirred with a paint shaker for 2 hours. In this case, the amount of the graft copolymer 1 used for carbon black is 40%. Thereafter, the beads were removed to obtain a dispersion for an electrophoretic display element.
The obtained dispersion had a volume average particle diameter of 270 nm and a viscosity of 2.2 mPa · s.

  Next, the prepared dispersion was sealed using a microsyringe in a space in which a copper electrode having a width of 100 μm was arranged between glass substrates as shown in FIG. A voltage of 15 V and −15 V is applied alternately for 30 minutes at intervals of 30 seconds (a period until migration of the slurry is not observed when migration is observed even after exceeding 30 seconds) to move the electrophoretic particles to the glass substrate. It observed with the optical microscope from the upper part, and evaluated the dispersion stability, the migration speed, and the re-migration property with the following parameters | indexes. The evaluation results are shown in Table 5.

<Dispersion stability>
○: Aggregates are not observed Δ: Aggregates of about 10 to 10 μm are observed ×: Aggregates exceeding 10 μm are observed <Migration speed>
After applying a voltage between the copper electrodes, the time until no slurry movement was observed was measured. Each sample was measured five times, and the average value (seconds) was taken as the migration speed.
<Remigration properties>
◎: Almost all particles migrate from the electrode after voltage switching ○: Particles migrate from the electrode after voltage switching, but a small amount of particles remain attached to the electrode (all particles attached to the electrode Less than 30% of particles)
Δ: After voltage switching, particles migrate from the electrode, but a large amount of particles remain attached to the electrode (particles attached to the electrode are 30% or more of all particles)
X: Almost no migration of particles is observed even when the voltage is switched.

Examples 2 to 23, Comparative Examples 1 to 5
A dispersion for an electrophoretic display device was obtained by the same operation as in Example 1 except that the copolymer (dispersant), pigment, dispersant concentration and solvent were used as shown in Table 4.
The evaluation results of each dispersion are shown in Table 5.

Details of the compounds used in Table 4 are shown below.
Lamp Black101: Carbon Black (Evonik Degussa)
Printex A: Carbon black (Evonik Degussa)
MA11: Carbon black (Mitsubishi Chemical Corporation)
Isopar L: Isoparaffinic hydrocarbon solvent (ExxonMobil Corp.)
Isopar V: Isoparaffinic hydrocarbon solvent (manufactured by ExxonMobil)
Caprylic acid 2EH: 2-ethylhexyl caprylate Palmitic acid 2EH: 2-ethylhexyl palmitate

  In Examples 1 to 23 using the dispersion liquid for electrophoretic elements according to the present invention, it was confirmed that the electrophoretic element dispersion had good migration speed and re-migrating property, and its dispersion stability was also excellent. In particular, in Example 2 using 2-ethylhexyl caprylate as the nonpolar solvent, results showing excellent migration speed in addition to dispersion stability and re-migration properties were obtained.

In comparison between Examples 1, 14, and 15, Example 1 in which the nitrogen atom-containing polymer (A) has a tertiary amino group and Example 15 having a quaternary ammonium salt are more effective than Example 14 having an amide group. It was confirmed that better dispersion stability and re-migration properties can be obtained.
As for the particle size of the dispersion, Example 7 with a slightly smaller particle size resulted in a slightly slower migration speed than Example 6 using the same dispersant.
Furthermore, in the comparison of Examples 6, 18 and 19, Example 6 which is a preferred range in the present invention with respect to Example 19 in which the ratio of nitrogen atom content (A) in the graft copolymer is as high as 70% by mass. No. 18 and No. 18 gave the results that the dispersion stability and re-migration properties were good.

  On the other hand, in Comparative Examples 1 and 2 using a linear copolymer as a dispersant, it was confirmed that the dispersion stability was insufficient. Moreover, even if it is a graft copolymer, the comparative monomer 3 and 4 which do not contain a nitrogen atom in a principal chain or a side chain, and the (meth) acrylic acid alkyl which has a C8 or more alkyl group are included in a constituent monomer In Comparative Example 5 where there was no, poor results were obtained with respect to dispersion stability and electrophoretic properties.

  According to the dispersant of the graft copolymer of the present invention, a dispersion for an electrophoretic display element having an inexpensive and high-quality image and an excellent response speed can be obtained. It can be effectively used for a display medium.

Claims (17)

  A dispersion for an electrophoretic display device comprising a dispersion in which pigment particles having a graft copolymer adsorbed on a surface are dispersed in a nonpolar solvent, wherein the graft copolymer is a nitrogen atom-containing polymer (A), Graft copolymer with one of the acrylic polymers (B) containing a (meth) acrylic acid alkyl ester having an alkyl group having 8 or more carbon atoms as a constituent monomer as the main chain and the other as the side chain A dispersion for electrophoretic display elements, characterized by being a coalescence.   The dispersion for electrophoretic display elements according to claim 1, wherein the nitrogen atom-containing polymer (A) has a tertiary amino group and / or a quaternary ammonium group.   The dispersion for an electrophoretic display element according to claim 2, wherein the nitrogen atom-containing polymer (A) has an amine value of 40 to 300 mgKOH / g.   The dispersion liquid for electrophoretic display elements according to claim 1, wherein the acrylic polymer (B) has a carboxyl group.   The dispersion liquid for electrophoretic display elements according to claim 4, wherein the acrylic polymer (B) has an acid value of 1 to 80 mgKOH / g.   The dispersion liquid for electrophoretic display elements according to claim 1, wherein the acrylic polymer (B) has a weight average molecular weight of 1000 to 40000.   The dispersion liquid for electrophoretic display elements according to claim 1, wherein the graft copolymer has a weight average molecular weight of 2000 to 80000.   The dispersion for an electrophoretic display element according to claim 1, wherein a ratio of the nitrogen-containing polymer (A) in the graft copolymer is 10 to 50% by mass.   An acrylic polymer in which the graft copolymer includes, as a constituent monomer, a (meth) acrylic acid alkyl ester having a main chain of the nitrogen atom-containing polymer (A) and the alkyl group having 8 or more carbon atoms. The dispersion for an electrophoretic display element according to claim 1, wherein B) is a side chain.   The dispersion for an electrophoretic display element according to claim 9, wherein the side chain is derived from a macromonomer having a polymerizable unsaturated double bond at the terminal.   The dispersion for an electrophoretic display element according to any one of claims 1 to 10, wherein the graft copolymer is present in a ratio of 1 to 100 parts by mass with respect to 100 parts by mass of the pigment.   The volume average particle diameter of the pigment particles dispersed in the nonpolar solvent is in the range of 0.1 to 1.0 µm, for an electrophoretic display element according to any one of claims 1 to 11. Dispersion.   The dispersion liquid for electrophoretic display elements according to claim 1, wherein the pigment particles are carbon black.   The dispersion liquid for electrophoretic display elements according to claim 1, wherein the nonpolar solvent contains an aliphatic hydrocarbon and / or a fatty acid alkyl ester.   The dispersion for an electrophoretic display element according to claim 14, wherein the nonpolar solvent is a fatty acid alkyl ester having 10 or more carbon atoms and a viscosity at 25 ° C of 15 mPa · s or less.   An image display element comprising the dispersion liquid for electrophoretic display elements according to any one of claims 1 to 15.   An image display device using the image display element according to claim 16.

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