Dispersion composition for electronic paper

Abstract

To provide a dispersion composition for electronic paper having excellent electrophoretic properties and re-electrophoretic properties, and electronic paper display element and electronic paper containing the dispersion composition for electronic paper.SOLUTION: A dispersion composition for electronic paper comprises pigment dispersion particles for electronic paper containing a pigment and a pigment dispersant, and an insulating liquid, where the pigment dispersant includes a copolymer (D) containing a constitutional unit derived from an ethylenically unsaturated monomer (d-1) having a tertiary amino group, a constitutional unit derived from a (meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group having 6 or more and 24 or less carbon atoms, and a constitutional unit derived from a vinyl-based monomer (d-3) having an epoxy group, and where the content of the constitutional unit derived from the ethylenically unsaturated monomer (d-1) in the copolymer (D), is 50 mol% or more and 85 mol% or less, and the content of the constitutional unit derived from the (meth)acrylic acid alkyl ester monomer (d-2) is 10 mol% or more and 30 mol% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dispersion composition for electronic paper, and an electronic paper display element and electronic paper containing the dispersion composition for electronic paper. [Background technology]

[0002] With the spread of e-books and the increased demand for teleworking since the COVID-19 pandemic, the e-paper market has expanded rapidly, with approximately 400 million e-shelf tags and 130 million e-book devices already in use. E-paper is also being adopted as a replacement for paper, and is attracting attention from the perspectives of SDGs and ESG, as it contributes to reducing carbon dioxide emissions. Electronic paper generally displays desired information by applying an electric field to colored particles dispersed in oil, causing the particles to move (electrophoresis), and since electronic paper must be able to instantly switch between all types of information, including text and images, the colored particles used in electronic paper must have uniform and high electrophoretic properties.With the rapid expansion of the electronic paper-related market, there is a demand for better electrophoretic particles for electronic paper.

[0003] Furthermore, in recent years, the applications of electronic paper have evolved beyond static image-based applications such as electronic shelf labels and electronic books to tablets that instantly switch between displays of fluid information. In response to this trend, electrophoretic particles for electronic paper are required to have not only excellent electrophoretic properties, but also excellent electrophoretic properties after repeated electrophoresis (hereinafter also referred to as "re-migration properties"). Patent Document 1 discloses a dispersion liquid for electrophoretic display elements, which contains a dispersion liquid in which pigment particles having a graft copolymer adsorbed on their surfaces are dispersed in a non-polar solvent, and is characterized in that the graft copolymer is a graft copolymer having either a nitrogen-atom-containing polymer (A) or an acrylic polymer (B) containing, as a constituent monomer, a (meth)acrylic acid alkyl ester having an alkyl group of 8 or more carbon atoms as a main chain and the other as a side chain. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-173539 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the dispersion for an electrophoretic display element as described in Patent Document 1 still has the problem that re-migration is not stable.

[0006] The present invention relates to a dispersion composition for electronic paper having excellent electrophoretic properties and remigration properties, and to an electronic paper display element and electronic paper containing the dispersion composition for electronic paper. [Means for solving the problem]

[0007] The present invention encompasses the following aspects [1] to [4]. [1] A dispersion composition for electronic paper, comprising: pigment dispersion particles for electronic paper containing a pigment and a pigment dispersant; and an insulating liquid, the pigment dispersant comprises a copolymer (D) containing a structural unit derived from an ethylenically unsaturated monomer (d-1) having a tertiary amino group, a structural unit derived from a (meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group having from 6 to 24 carbon atoms, and a structural unit derived from a vinyl-based monomer (d-3) having an epoxy group, In the copolymer (D), the content of the structural units derived from the ethylenically unsaturated monomer (d-1) is 50 mol% or more and 85 mol% or less, and the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer (d-2) is 10 mol% or more and 30 mol% or less. Pigment dispersion particles for electronic paper. [2] An electronic paper display element comprising the dispersion composition for electronic paper according to [1]. [3] An electronic paper comprising the electronic paper display element according to [2]. [4] Pigment dispersion particles for electronic paper containing a pigment and a pigment dispersant, the pigment dispersant comprises a copolymer (D) containing a structural unit derived from an ethylenically unsaturated monomer (d-1) having a tertiary amino group, a structural unit derived from a (meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group having from 6 to 24 carbon atoms, and a structural unit derived from a vinyl-based monomer (d-3) having an epoxy group, In the copolymer (D), the content of the structural units derived from the ethylenically unsaturated monomer (d-1) is 50 mol% or more and 85 mol% or less, and the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer (d-2) is 10 mol% or more and 30 mol% or less. Pigment dispersion particles for electronic paper. [Effects of the Invention]

[0008] The present invention provides a dispersion composition for electronic paper having excellent electrophoretic properties and re-migration properties, as well as an electronic paper display element and electronic paper containing the dispersion composition for electronic paper. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Dispersion composition for electronic paper] A dispersion composition for electronic paper according to one embodiment of the present invention (hereinafter also simply referred to as "dispersion composition") contains pigment dispersion particles for electronic paper and an insulating liquid.

[0010] <Pigment dispersion particles for electronic paper> The pigment dispersion particles for electronic paper contained in the dispersion composition for electronic paper of the present invention (hereinafter simply referred to as "pigment dispersion particles") are pigment dispersion particles containing a pigment and a pigment dispersant. The pigment dispersion particles include a copolymer (D) containing structural units derived from an ethylenically unsaturated monomer (d-1) having a tertiary amino group, structural units derived from a (meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group with 6 to 24 carbon atoms, and structural units derived from a vinyl-based monomer (d-3) having an epoxy group, wherein the content of the structural units derived from the ethylenically unsaturated monomer (d-1) in the copolymer (D) is 50 to 85 mol %, and the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer (d-2) is 10 to 30 mol %. According to the above configuration, it is possible to provide a dispersion composition for electronic paper having excellent electrophoretic properties and re-migration properties.

[0011] The reason why the present invention is effective is not clear, but is thought to be as follows. The pigment dispersion particles for electronic paper contained in the dispersion composition for electronic paper of the present invention contain a pigment and a pigment dispersant, and the pigment dispersant includes a copolymer (D) containing structural units derived from an ethylenically unsaturated monomer (d-1) having a tertiary amino group, structural units derived from a (meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group with 6 to 24 carbon atoms, and structural units derived from a vinyl-based monomer (d-3) having an epoxy group. Because copolymer (D) contains a large amount of structures derived from the ethylenically unsaturated monomer (d-1), the pigment dispersant interacts strongly with the pigment and has high responsiveness to an electric field, resulting in excellent electrophoretic properties of the pigment dispersion particles. Furthermore, the structure derived from the (meth)acrylic acid alkyl ester monomer (d-2) functions to disperse the pigment dispersion particles in an insulating liquid, and the structure derived from the vinyl-based monomer (d-3) functions to firmly adsorb the pigment dispersant to the pigment. Therefore, it is believed that the amount of unadsorbed pigment dispersant in the dispersion composition for electronic paper is reduced, and the pigment dispersion particles also have excellent re-migration properties.

[0012] The definitions of various terms used in this specification are shown below. The electrophoretic property is evaluated by determining the amount of particles dispersed in oil that migrate toward the electrodes when the particles are caused to migrate between a positive electrode and a negative electrode to which a voltage is applied, and specifically, the evaluation is performed by the method described in the examples. Volume median particle size (D 50 )" means the particle size at which the cumulative volume frequency calculated by volume fraction is 50% calculated from the smallest particle size. "(Meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid.

[0013] [Pigment dispersant] The pigment dispersant contained in the pigment dispersion particles includes a copolymer (D) containing a structural unit derived from an ethylenically unsaturated monomer (d-1) (hereinafter simply referred to as "d-1") having a tertiary amino group, a structural unit derived from a (meth)acrylic acid alkyl ester monomer (d-2) (hereinafter simply referred to as "d-2") having a hydrocarbon group having 6 to 24 carbon atoms, and a structural unit derived from a vinyl monomer (d-3) (hereinafter simply referred to as "d-3") having an epoxy group.

[0014] (Ethylenically unsaturated monomer (d-1) having a tertiary amino group) d-1 has a polymerizable unsaturated functional group and a tertiary amino group, and preferably includes at least one ethylenically unsaturated monomer having a tertiary amino group represented by the following general formula (1):

[0015] [ka]

[0016] In general formula (1), R 1 represents a hydrogen atom or a methyl group, and R 2 and R 3 each independently represents a linear or branched alkyl group having 1 to 4 carbon atoms; A 1 represents a linear or branched alkylene group having 2 to 4 carbon atoms, and X represents an oxygen atom or NH.

[0017] In general formula (1), R 2 and R 3 Examples of the linear or branched alkyl group having 1 to 4 carbon atoms as R include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an s-butyl group, a t-butyl group, and an isobutyl group. 2 and R 3 may be bonded to each other to form a ring structure. In general formula (1), R 2 and R 3 is preferably a methyl group or an ethyl group, and R 2 and R 3 and R are more preferably simultaneously a methyl group or an ethyl group, 2 and R 3 More preferably, is an ethyl group.

[0018] In general formula (1), A 1 Examples of the linear or branched alkylene group having 2 to 4 carbon atoms as A include an ethylene group, a trimethylene group, a tetramethylene group, a propylene group, and a butylene group. 1 is more preferably a linear alkylene group, and A 1 is more preferably an ethylene group.

[0019] In general formula (1), X is preferably an oxygen atom.

[0020] From the viewpoint of providing the pigment-dispersed particles with excellent electrophoretic properties and re-migration properties, the copolymer (D) preferably contains, as a structural unit derived from the ethylenically unsaturated monomer (d-1) having a tertiary amino group, at least one selected from a structural unit derived from dimethylaminoethyl (meth)acrylate and a structural unit derived from diethylaminoethyl (meth)acrylate, and more preferably contains a structural unit derived from diethylaminoethyl (meth)acrylate.

[0021] In copolymer (D), the content of structural units derived from d-1 is 50 mol% or more, preferably 53 mol% or more, more preferably 55 mol% or more, from the viewpoint of excellent electrophoretic properties of the pigment dispersion particles, and is 85 mol% or less, preferably 80 mol% or less, more preferably 75 mol% or less, from the viewpoint of re-migration properties.

[0022] ((Meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group having 6 to 24 carbon atoms)

[0023] In order to provide pigment-dispersed particles with excellent electrophoretic properties and re-migration properties, copolymer (D) contains, as a structural unit derived from a (meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group having from 6 to 24 carbon atoms, at least one structural unit selected from the group consisting of a structural unit derived from 2-ethylhexyl (meth)acrylate, a structural unit derived from dodecyl (meth)acrylate, a structural unit derived from tetradecyl (meth)acrylate, a structural unit derived from hexadecyl (meth)acrylate, and a structural unit derived from octadecyl (meth)acrylate. is preferred, and it is more preferred that the copolymer contains at least one selected from structural units derived from dodecyl (meth)acrylate, structural units derived from tetradecyl (meth)acrylate, structural units derived from hexadecyl (meth)acrylate, and structural units derived from octadecyl (meth)acrylate, and it is even more preferred that the copolymer contains at least one selected from structural units derived from dodecyl methacrylate, structural units derived from tetradecyl methacrylate, structural units derived from hexadecyl methacrylate, and structural units derived from octadecyl methacrylate.

[0024] In copolymer (D), the content of the structural unit derived from d-2 is 10 mol% or more, preferably 11 mol% or more, more preferably 12 mol% or more, and 30 mol% or less, preferably 29 mol% or less, more preferably 28 mol% or less, from the viewpoint of imparting excellent electrophoretic properties and re-migration properties to the pigment dispersion particles.

[0025] In copolymer (D), the molar ratio of the structural units derived from d-1 to the structural units derived from d-2 (d-1 / d-2) is preferably 55 / 45 or more, more preferably 60 / 40 or more, even more preferably 65 / 35 or more, from the viewpoint of imparting excellent electrophoretic properties and re-migration properties to the pigment dispersion particles, and is preferably 90 / 10 or less, more preferably 88 / 12 or less, even more preferably 87 / 13 or less, even more preferably 86 / 14 or less.

[0026] (Vinyl monomer having an epoxy group (d-3)) The structural unit derived from d-3 has a polymerizable vinyl group and an epoxy group. The structural unit derived from d-3 includes at least one selected from a structural unit derived from a vinyl-based monomer having an epoxy group represented by the following general formula (2) and a structural unit derived from a vinyl-based monomer having an epoxy group represented by the following general formula (3).

[0027] [ka]

[0028] In general formula (2), R 4 represents a hydrogen atom or a methyl group, and A 2 represents a linear or branched alkylene group having 1 to 6 carbon atoms. In addition, in the general formula (3), R 5 represents a hydrogen atom or a methyl group, and A 3 represents a linear or branched alkylene group having 1 to 6 carbon atoms, and Y represents an oxygen atom or NH.

[0029] In general formula (2), A 2 Examples of the linear or branched alkylene group having 1 to 4 carbon atoms as A include a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, a propylene group, a butylene group, a pentylene group, and a hexylene group. 2 When A is a branched alkylene group, 2 may form a cyclic structure together with the epoxy group. In addition, one methylene group in the alkylene group may be substituted with an oxygen atom.

[0030] In general formula (3), A 3 The straight or branched alkylene group having 1 to 4 carbon atoms as A 2 Examples include the same straight or branched alkylene groups having 1 to 4 carbon atoms as in the above, provided that the methylene group bonding to Y in the alkylene group is not an oxygen atom.

[0031] From the viewpoint of providing excellent electrophoretic properties and re-migration properties to the pigment-dispersed particles, the copolymer (D) preferably contains, as a structural unit derived from the vinyl monomer (d-3) having an epoxy group, at least one selected from the group consisting of a structural unit derived from 1,2-epoxy-3-butene, a structural unit derived from 1,2-epoxy-5-hexene, a structural unit derived from 1,2-epoxy-9-decene, a structural unit derived from 1,2-epoxy-4-vinylcyclohexane, a structural unit derived from allyl glycidyl ether, a structural unit derived from glycidyl (meth)acrylate, and a structural unit derived from (3,4-epoxycyclohexyl)methyl (meth)acrylate, more preferably a structural unit derived from glycidyl (meth)acrylate, and even more preferably a structural unit derived from glycidyl methacrylate.

[0032] In copolymer (D), the content of the structural unit derived from d-3 is preferably 5 mol % or more, more preferably 8 mol % or more, and even more preferably 10 mol % or more, from the viewpoint of providing excellent re-migration properties of the pigment-dispersed particles, and is preferably 20 mol % or less, more preferably 18 mol % or less, and even more preferably 16 mol % or less, from the viewpoint of providing excellent electrophoresis properties and re-migration properties of the pigment-dispersed particles.

[0033] In copolymer (D), the content of the d-1-derived structural units, the d-2-derived structural units, and the d-3-derived structural units is preferably 95 mol% or more, more preferably 98 mol% or more, from the viewpoint of providing the pigment dispersion particles with excellent electrophoretic properties and re-migration properties, and is preferably 100 mol% or less, more preferably 100 mol%.

[0034] (Method for producing copolymer (D)) The copolymer (D) is produced, for example, by a method including a step of copolymerizing an ethylenically unsaturated monomer (d-1) having a tertiary amino group, a (meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group with a carbon number of 6 to 24, and a vinyl-based monomer (d-3) having an epoxy group, which are contained in a raw material mixture. The copolymerization step may be carried out by radical polymerization, solution polymerization, bulk polymerization, or the like. From the viewpoint of providing the pigment-dispersed particles with excellent electrophoretic and re-migration properties, the copolymer (D) is preferably a random copolymer obtained by randomly polymerizing the raw material mixture.

[0035] In the copolymerization step, a radical polymerization initiator may be used, for example, a peroxide such as di-tert-butyl peroxide, or an azo compound such as 2,2'-azobis(2,4-dimethylvaleronitrile). The amount of the radical polymerization initiator used is preferably 1 part by mass or more and 10 parts by mass or less relative to 100 parts by mass in total of d-1, d-2, and d-3. The temperature in the copolymerization step is preferably 60°C or higher, more preferably 70°C or higher, from the viewpoint of reaction efficiency, and is preferably 100°C or lower, more preferably 90°C or lower, from the viewpoint of preventing a ring-opening reaction of the epoxy group contained in d-3.

[0036] In the production of copolymer (D) of the present invention, since the conversion rate of the raw material mixture is nearly 100%, the contents of d-1, d-2, and d-3 in the raw material mixture are nearly equal to the contents of the d-1-derived structural units, the d-2-derived structural units, and the d-3-derived structural units in copolymer (D), respectively.

[0037] (Physical properties of copolymer (D)) The amine value of the copolymer (D) is preferably 120 mgKOH / g or more, more preferably 130 mgKOH / g or more, even more preferably 140 mgKOH / g or more, and preferably 280 mgKOH / g or less, more preferably 250 mgKOH / g or less, even more preferably 240 mgKOH / g or less. The number average molecular weight (Mn) of the copolymer (D) is preferably 5,000 or more, more preferably 6,000 or more, even more preferably 6,500 or more, and preferably 10,000 or less, more preferably 9,000 or less, even more preferably 8,000 or less. The amine value and number average molecular weight (Mn) of copolymer (D) can be appropriately adjusted by the types and amounts of d-1, d-2, and d-3 used, as well as production conditions such as reaction temperature, reaction time, and cooling rate, and these values ​​can be determined by the methods described in the examples. When two or more types of copolymers (D) are used in combination, it is preferable that the amine value and number average molecular weight (Mn) of each of them are within the above-mentioned ranges.

[0038] [Pigments] Known pigments can be used. Examples include carbon black, phthalocyanine blue, permanent brown FG, brilliant fast scarlet, pigment green B, rhodamine-B base, solvent red 49, solvent red 146, solvent blue 35, quinacridone, carmine 6B, isoindoline, and disazo yellow. The pigment is preferably carbon black.

[0039] The volume median particle size of the pigment (D 50 ) is preferably 100 nm or more, more preferably 140 nm or more, and even more preferably 180 nm or more, from the viewpoint of dispersibility of the pigment-dispersed particles in the insulating liquid described below, and is preferably 400 nm or less, more preferably 380 nm or less, and even more preferably 360 nm or less, from the viewpoint of electrophoretic property.

[0040] The mass ratio of the pigment dispersant to the pigment in the pigment-dispersed particles (pigment dispersant / pigment) is preferably 5 / 95 or more, more preferably 10 / 90 or more, and even more preferably 15 / 85 or more, from the viewpoint of imparting excellent electrophoretic properties and re-migration properties to the pigment-dispersed particles, and is preferably 60 / 40 or less, more preferably 55 / 45 or less, and even more preferably 50 / 50 or less, from the viewpoint of improving the image density displayed on electronic paper.

[0041] (Method of manufacturing pigment dispersion particles for electronic paper) The method for producing pigment-dispersed particles for electronic paper includes a step of dispersing a mixture of the pigment and the pigment dispersant, and allowing the pigment dispersant to adsorb to the pigment. From the viewpoint of allowing the pigment dispersant to be firmly adsorbed to the pigment, the method preferably includes a step of heating.

[0042] In the step of adsorbing the pigment dispersant to the pigment, there are no particular limitations on the dispersion method. The average particle size of the pigment particles with the pigment dispersant adsorbed thereto and the pigment dispersion particles is approximately the same before and after the step of crosslinking the pigment dispersants together, so in this step, the average particle size of the pigment dispersion particles can be atomized to a desired particle size. Although the average particle size of the pigment dispersion particles can be atomized to a desired particle size only by the main dispersion, it is preferable to perform the main dispersion after preliminary dispersion and then further apply shear stress to control the average particle size of the pigment particles to a desired particle size.

[0043] When the mixture is pre-dispersed, a commonly used mixing and stirring device such as an anchor blade or a disper blade, among which a high-speed stirring and mixing device is preferred. The temperature in the pre-dispersion is preferably -10°C or higher, and preferably 10°C or lower. The time for pre-dispersion is preferably 10 minutes or more, and preferably 1 hour or less.

[0044] Examples of means for applying shear stress for this dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as Microfluidizer (trade name, Microfluidics), and media-type dispersers such as paint shakers and bead mills. Commercially available media-type dispersers include Ultra Apex Mill (trade name, manufactured by Kotobuki Industries Co., Ltd.) and Picomill (trade name, manufactured by Asada Iron Works Co., Ltd.). Multiple devices can also be combined. The temperature in this dispersion is preferably 10°C or higher and preferably 30°C or lower. The time for carrying out this dispersion is preferably 10 minutes or more and preferably 1 hour or less.

[0045] From the viewpoint of production efficiency, when an insulating liquid described below is used for dispersion, the subsequent step of crosslinking pigment dispersants can be carried out in the same manner, thereby producing pigment dispersion particles and a dispersion composition for electronic paper at the same time, which is preferable from the viewpoint of production efficiency.

[0046] In the heating step, the temperature at which the structure derived from d-1 and the structure derived from d-3 are reacted is preferably 60°C or higher, more preferably 70°C or higher, from the viewpoint of production efficiency, and is preferably 100°C or lower, more preferably 90°C or lower, from the viewpoint of preventing gelation of the pigment dispersant.

[0047] The time for reacting the structure derived from d-1 with the structure derived from d-3 is preferably 30 minutes or more, more preferably 45 minutes or more, from the viewpoint of production efficiency, and is preferably 2 hours or less, more preferably 1.5 hours or less, from the viewpoint of preventing gelation of the pigment dispersant.

[0048] The reaction medium may be any dispersion medium in which the reaction between the structure derived from d-1 and the structure derived from d-3 in the copolymer (D) proceeds. As described above, when an insulating liquid is used as the reaction medium, the dispersion composition for electronic paper can be produced simultaneously with the production of pigment dispersion particles, which is preferable from the viewpoint of production efficiency.

[0049] The volume median particle size of pigment dispersion particles (D 50 ) is preferably 100 nm or more, more preferably 140 nm or more, and even more preferably 180 nm or more from the viewpoint of dispersibility in the insulating liquid described below, and is preferably 400 nm or less, more preferably 380 nm or less, and even more preferably 360 nm or less from the viewpoint of electrophoresis. The volume median particle size of pigment dispersion particles (D 50 ) can be determined by the method described in the Examples.

[0050] [Insulating liquid] The insulating liquid means a liquid through which electricity does not easily flow. In the present invention, the conductivity of the insulating liquid is preferably 1×10 -11 S / m or less, preferably 5×10 -12 S / m or less, and preferably 1×10 -14 S / m or more.

[0051] Examples of insulating liquids include hydrocarbon insulating liquids such as aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons, such as liquid paraffin, isoparaffin, and polyisobutene. From the viewpoint of the migration of pigment dispersed particles, the insulating liquid in the present invention is preferably isoparaffin. The insulating liquid may be one type or a combination of two or more types. Commercially available aliphatic hydrocarbon insulating liquids include Isopar G, Isopar H, Isopar L, and Isopar K (all manufactured by ExxonMobil Corporation), Shellsol 71 (Oxalis Chemicals Co., Ltd.), IP Solvent 1620 and IP Solvent 2080 (all manufactured by Idemitsu Kosan Co., Ltd.), and "NAS-3," "NAS-4," and "NAS-5H" (all manufactured by NOF Corporation).

[0052] The content of the pigment dispersion particles in the dispersion composition is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of improving the image density displayed on the electronic paper, and is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of dispersion stability of the pigment dispersion particles. The content of the dispersion medium in the dispersion composition is preferably 85% by mass or more, more preferably 88% by mass or more, and even more preferably 90% by mass or more, from the viewpoint of particle dispersion stability, and is preferably 97% by mass or less, more preferably 96% by mass or less, and even more preferably 95% by mass or less, from the viewpoint of improving the image density displayed on electronic paper.

[0053] The dispersion composition may contain, in addition to the pigment dispersed particles and the insulating liquid, other additives that are generally used in electronic paper.

[0054] (Method for producing dispersion composition for electronic paper) As described above (Method for producing pigment-dispersed particles for electronic paper), the method for producing the dispersion composition for electronic paper of the present invention includes fixing the pigment dispersant to the surface of the pigment in the insulating liquid. Alternatively, the dispersion composition can be produced by fixing the pigment dispersant to the surface of the pigment and then dispersing the isolated pigment-dispersed particles in the insulating liquid.

[0055] [Electronic paper display element] The electronic paper display element of the present invention includes, for example, a rear electrode substrate having a rear substrate and a rear electrode, a transparent electrode substrate having a transparent substrate and a transparent electrode, and a display medium layer disposed between the rear electrode substrate and the transparent electrode substrate, and the above-mentioned dispersion composition for electronic paper is enclosed in the display medium layer. As the back electrode substrate, transparent electrode substrate, and display medium layer, general-purpose back electrode substrate, transparent electrode substrate, and display medium layer can be used.

[0056] [Electronic Paper] The electronic paper of the present invention includes, for example, the electronic paper display element, a battery, a control unit, and a housing that houses them. In the electronic paper, a protective film or the like may be provided on the surface of the electronic paper display element. As the battery, the control unit, and the housing, general-purpose batteries, control units, and housings can be used.

[0057] The electronic paper of the present invention can be used in devices such as electronic book devices and electronic POP displays.

[0058] [Pigment dispersion particles for electronic paper] The pigment dispersion particles for electronic paper according to one embodiment of the present invention are pigment dispersion particles contained in a dispersion composition for electronic paper. That is, the pigment dispersion particles for electronic paper according to one embodiment of the present invention contain a pigment and a pigment dispersant, and the pigment dispersant includes a copolymer (D) containing structural units derived from an ethylenically unsaturated monomer (d-1) having a tertiary amino group, structural units derived from a (meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group having from 6 to 24 carbon atoms, and structural units derived from a vinyl-based monomer (d-3) having an epoxy group, wherein the content of the structural units derived from the ethylenically unsaturated monomer (d-1) in the copolymer (D) is from 50 mol % to 80 mol %, and the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer (d-2) in the copolymer (D) is from 10 mol % to 30 mol %. The pigment and pigment dispersant contained in the pigment dispersion particles for electronic paper according to one embodiment of the present invention may be the same as the pigment and pigment dispersant contained in the pigment dispersion particles contained in the dispersion composition for electronic paper, and the preferred ranges are also the same. [Example]

[0059] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Physical properties of resins and the like were measured by the following methods.

[0060] [Measurement of Amine Value of Copolymer (D)] 1.0 to 1.5 g of sample was accurately weighed into a 150 mL beaker and dissolved in approximately 70 mL of ethyl alcohol to prepare a sample solution. Using a potentiometric titrator, the sample was titrated with a 0.2 mol / L alcoholic hydrochloric acid standard solution until the equivalence point was reached. The amine value was then calculated using the following formula. Amine value (mgKOH / g) = (A × f × 56.11 × 0.2) / S In the formula, A, S, and f are as follows: A: Amount (mL) of 0.2 mol / L alcoholic hydrochloric acid standard solution required for titration up to the equivalence point S: Amount of sample collected (g) f: Factor of 0.2 mol / L alcoholic hydrochloric acid standard solution

[0061] [Measurement of number average molecular weight (Mn) of copolymer (D)] The number average molecular weight (Mn) of the copolymer (D) was determined by gel permeation chromatography (GPC). (1) Preparation of sample solution The sample was dissolved in tetrahydrofuran to a concentration of 0.5 g / 100 mL, and then filtered through a 2 μm fluororesin filter "FP-200" (manufactured by Sumitomo Electric Industries, Ltd.) to remove insoluble components, yielding a sample solution. (2)Molecular weight distribution measurement The following measuring equipment and analytical column were used, and tetrahydrofuran was used as the eluent at a flow rate of 1 mL per minute. The column was stabilized in a thermostatic bath at 40°C. 100 μL of sample solution was injected into the column and the measurement was carried out. The molecular weight of the sample was calculated based on a calibration curve prepared in advance. The calibration curve used here included several types of monodisperse polystyrene "A-500" (5.0 × 10 2 ), "A-1000" (1.01 x 10 3 ), "A-2500" (2.63 x 10 3 ), "A-5000" (5.97 x 10 3 ), "F-1" (1.02 x 10 3 ), "F-2" (1.81 x 10 4 ), "F-4" (3.97 x 10 4), "F-10" (9.64 x 10 4 ), "F-20" (1.90 x 10 5 ), "F-40" (4.27 x 10 5 ), "F-80" (7.06 x 10 5 ), "F-128" (1.09 x 10 6 ) (all manufactured by Tosoh Corporation) were used as standard samples. The numbers in parentheses indicate molecular weights. Measuring device: "HLC-8220CPC" (Tosoh Corporation) Analytical column: "GMHXL" + "G3000HXL" (manufactured by Tosoh Corporation)

[0062] [Volume median particle size (D 50 ) Measurement The volume median particle diameter (D 50 A dispersion composition for electronic paper, Isopar L (manufactured by Exxon Mobil, isoparaffin, viscosity at 25°C: 1 mPa·s), was added to the measurement cell and diluted to a concentration at which the scattering intensity was 5 to 15%, and the volume median particle diameter (D 50 ) was measured.

[0063] Production Examples 1 to 5 and Comparative Production Examples 1 to 3 (Copolymers D-1 to D-5 and D'-1 to D'-3) 100 g of methyl ethyl ketone was placed in a 1 L four-neck flask equipped with a condenser, nitrogen inlet tube, stirrer, and thermocouple, and the flask was purged with nitrogen gas. The flask was heated to 80°C, and a mixture of raw material monomers and polymerization initiators shown in Table 1 was added dropwise over 2 hours. After the dropwise addition was completed, the reaction was continued for an additional 3 hours at 80°C. The solvent was distilled off at 80°C to obtain copolymers D-1 to D-5 and D'-1 to D'-3. The physical properties of each copolymer are shown in Table 1.

[0064] [Table 1]

[0065] Example 1 The copolymer, pigment, and insulating liquid shown in Table 2 were placed in a 500 mL polyethylene container. The mixture of copolymer, pigment, and insulating liquid was stirred under ice cooling at 7000 r / min for 30 minutes using a homomixer "TK Robomix" (manufactured by Primix Corporation) to obtain a preliminary dispersion with a solids concentration of 6% by mass. The resulting preliminary dispersion was then wet-ground using 0.8 mm diameter zirconia beads at a volumetric filling rate of 60% by volume in a six-cylinder bead mill "TSG-6" (manufactured by Imex Co., Ltd.) at 1300 r / min (circumferential speed of 4.8 m / sec) at 25°C for 30 minutes. The beads were then removed by filtration to obtain a wet-ground solution. The resulting wet-ground solution was then placed in a 0.5 L four-neck flask, and the reaction vessel was heated to 80°C for 1 hour. Thereafter, the reacted wet-pulverized liquid was filtered to obtain a dispersion composition for electronic paper (solid content concentration: 6% by mass) containing dispersed particles of electrophoretic pigment for electronic paper.

[0066] Examples 2 to 7 and Comparative Examples 1 to 3 A dispersion composition for electronic paper containing electrophoretic pigment dispersion particles for electronic paper was obtained in the same manner as in Example 1, except that the type and amount of copolymer as the pigment dispersion and the amount of the insulating liquid were changed as shown in Table 2.

[0067] (1) Evaluation of electrode migration 3 g of the dispersion composition for electronic paper obtained above was poured into a plastic container equipped with two copper plate electrodes spaced 3 mm apart, and a voltage of 500 V was applied for 3 seconds with one copper plate electrode as the positive electrode and the other as the negative electrode. The copper plate electrodes were then removed, and the insulating liquid was completely evaporated in a vacuum dryer (21.3 kPa) set at 200°C. The ratio (mass%) of pigment dispersion particles attached to the copper plate electrode connected to the negative electrode to the mass of pigment dispersion particles in the dispersion composition for electronic paper was calculated, and this was used as an index of migration (negative electrode %), which was taken as electrode migration. The evaluation results are shown in Table 2.

[0068] (2) Evaluation of re-migration In the above "(1) Evaluation of electrode migration property," a voltage of 500 V was applied for 3 seconds, and this was repeated 10 times. After each voltage application, the interval before the next voltage application was 10 seconds. Thereafter, the copper plate electrode was removed, and the insulating liquid was completely evaporated in a vacuum dryer (21.3 kPa) set at 200°C. The proportion (mass%) of the electrophoretic pigment dispersion particles for electronic paper attached to the copper plate electrode connected to the negative electrode relative to the mass of the electrophoretic pigment dispersion particles for electronic paper in the dispersion composition for electronic paper was calculated, and this was taken as re-migration property. The evaluation results are shown in Table 2.

[0069] [Table 2]

[0070] From the above results, the pigment-dispersed particles for electronic paper of Examples 1 to 7 were excellent in electrophoretic mobility, and even after repeated electrophoresis, they retained high electrophoretic mobility and were excellent in re-migration. On the other hand, Comparative Examples 1 and 2, which used pigment-dispersed particles for electronic paper containing a pigment dispersant containing a copolymer that does not contain structural units derived from the vinyl monomer (d-3) having an epoxy group, had excellent electrophoretic properties but poor re-migration. Comparative Example 3, which used pigment-dispersed particles containing a copolymer with a low content of structural units derived from the ethylenically unsaturated monomer (d-1) having a tertiary amino group, had poor electrophoretic properties and poor re-migration.

Claims

1. A dispersion composition for electronic paper, comprising: pigment dispersion particles for electronic paper containing a pigment and a pigment dispersant; and an insulating liquid, the pigment dispersant comprises a copolymer (D) containing a structural unit derived from an ethylenically unsaturated monomer (d-1) having a tertiary amino group, a structural unit derived from a (meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group having from 6 to 24 carbon atoms, and a structural unit derived from a vinyl-based monomer (d-3) having an epoxy group, In the copolymer (D), the content of the structural units derived from the ethylenically unsaturated monomer (d-1) is 50 mol% or more and 85 mol% or less, and the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer (d-2) is 10 mol% or more and 30 mol% or less. Dispersion composition for electronic paper.

2. 2. The dispersion composition for electronic paper according to claim 1, wherein the content of the structural unit derived from the vinyl monomer (d-3) in the copolymer (D) is 5 mol% or more and 20 mol% or less.

3. 2. The dispersion composition for electronic paper according to claim 1, wherein in the copolymer (D), the molar ratio (d-1 / d-2) of the structural units derived from the ethylenically unsaturated monomer (d-1) to the structural units derived from the (meth)acrylic acid alkyl ester monomer (d-2) is 55 / 45 or more and 90 / 10 or less.

4. The dispersion composition for electronic paper according to claim 1 , wherein the amine value of the copolymer (D) is 120 mg KOH / g or more and 280 mg KOH / g or less.

5. The dispersion composition for electronic paper according to claim 1 , wherein the mass ratio of the pigment dispersant to the pigment (pigment dispersant / pigment) is 5 / 95 or more and 60 / 40 or less.

6. 2. The dispersion composition for electronic paper according to claim 1, wherein the ethylenically unsaturated monomer (d-1) comprises at least one selected from ethylenically unsaturated monomers having a tertiary amino group represented by the following general formula (1): 【Chemistry 1】 (In general formula (1), R １ represents a hydrogen atom or a methyl group, and R ２ and R ３ each independently represents a linear or branched alkyl group having 1 to 4 carbon atoms; A １ represents a linear or branched alkylene group having 2 to 4 carbon atoms, and X represents an oxygen atom or NH.

7. 2. The dispersion composition for electronic paper according to claim 1, wherein the vinyl monomer (d-3) comprises at least one selected from a vinyl monomer having an epoxy group represented by the following general formula (2) and a vinyl monomer having an epoxy group represented by the following general formula (3): 【Chemistry 2】 (In general formula (2), R ４ represents a hydrogen atom or a methyl group, and A ２ represents a linear or branched alkylene group having 1 to 6 carbon atoms. In general formula (3), R ５ represents a hydrogen atom or a methyl group, and A ３ represents a linear or branched alkylene group having 1 to 6 carbon atoms, and Y represents an oxygen atom or NH.

8. An electronic paper display element comprising the dispersion composition for electronic paper according to any one of claims 1 to 7.

9. An electronic paper comprising the electronic paper display element according to claim 8 .

10. A pigment dispersion particle for electronic paper containing a pigment and a pigment dispersant, the pigment dispersant comprises a copolymer (D) containing a structural unit derived from an ethylenically unsaturated monomer (d-1) having a tertiary amino group, a structural unit derived from a (meth)acrylic acid alkyl ester monomer (d-2) having a hydrocarbon group having from 6 to 24 carbon atoms, and a structural unit derived from a vinyl-based monomer (d-3) having an epoxy group, In the copolymer (D), the content of the structural units derived from the ethylenically unsaturated monomer (d-1) is 50 mol% or more and 85 mol% or less, and the content of the structural units derived from the (meth)acrylic acid alkyl ester monomer (d-2) is 10 mol% or more and 30 mol% or less. Pigment dispersion particles for electronic paper.

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