JP2006018026A - Electrophoretic coloring particle and display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrophoretic coloring particles which are properly dispersed in an insulating liquid with a low drive voltage, and further which exhibit an image-retaining memory properties due to excellent coagulation of the particles with each other, when the voltage is turned off. <P>SOLUTION: The electrophoretic coloring particles are to be subjected to electrophoresis in the insulating liquid, and are characterized by comprising base material particles coated with a copolymer of a monomer, having a fluoro group on the terminal and a monomer having a ≥8C alkyl group on the terminal and having ≤-50 mV ζ potential value for the electrophoretic coloring particles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to electrophoretic colored particles and particles for display elements utilizing electrophoresis.

  So-called electronic paper is an electronic display that can be easily handled like paper. Electronic paper is required to be easy to see like paper, to be easily erased and written, and to have low energy required for display maintenance. Electronic paper is roughly divided into an approach from an electronic display and an approach from paper. As an approach as an electronic display, a liquid crystal system and an organic electroluminescence system are known. As an approach from paper, an electrophoresis method or a twist ball method is known.

Patent Document 1 discloses crosslinked polymer particles based on styrene-co-divinylbenzene, and Patent Document 2 discloses titanium oxide and carbon as particles used for display of a display device using electrophoresis. Particles in which black is dispersed in wax are disclosed.
Japanese National Patent Publication No. 8-510790 Japanese Patent Laid-Open No. 11-202372

Display devices are disclosed in, for example, Patent Document 2 and Patent Document 3. As the particles used for these displays, inorganic particles, polymer resins, composite particles thereof, and the like as described above are used.
JP 2002-55366 JP

  In electronic paper using the electrophoretic phenomenon, display particles are dispersed in an insulating dispersion fluid, and the cells having electrodes are filled with particles, or the particles are filled in the form of microcapsules. When a voltage is applied to the cell, particles having a charge opposite to the polarity of the electrode are attracted and fixed to the insulating layer on the electrode. Moreover, particles are released from the electrode by reversing the polarity of the electrode.

  In recent years, with the development of information equipment, the need for low power consumption is increasing. An advantage of the electrophoretic display device is display image holding performance (memory property), but it is difficult to hold a display image semipermanently with zero power. As a display image holding method, there is a method of increasing the viscosity of the insulating liquid and preventing the migration of the electrophoretic particles. However, this method requires a large voltage to cause the particles to undergo electrophoresis.

  For example, after a particle is attracted to a wall surface and a display image is displayed, the image must be kept in contact with the wall surface when the voltage is turned off so that the image is retained when the voltage is turned off. There is. However, this alone is insufficient from the viewpoint of image memory. This is because when only one layer of particles is formed on the wall surface, the contrast of the image is low and it is difficult to improve the image quality. For this reason, it is necessary to introduce a sufficiently large amount of particles into the cell so that the particles are aligned on the wall surface in a plurality of layers. However, even when the particles are adsorbed to the wall surface when the voltage is turned off, if the adsorbing force between the particles is weak, the particles that are not in direct contact with the wall surface move away, and the image contrast Decreases. Therefore, in order to express the memory property of the image, it is necessary that the particles are adsorbed to each other after the voltage is turned off.

However, for the purpose of maintaining the contrast of the image, especially the contrast after turning off the voltage, if the cohesive force between the particles is increased, the aggregated particles are difficult to separate when a voltage is applied and dispersed in the insulating liquid. It becomes difficult to do. In order to disperse such particles, it is necessary to apply a high voltage, but the drive voltage is required to be as low as possible.
Accordingly, it is desired that the particles easily disperse well in the insulating liquid at a low driving voltage, and exhibit a memory property in which particles are well aggregated and hold an image when the voltage is turned off.

  It is an object of the present invention to provide an electrophoretic property that easily disperses well in an insulating liquid at a low driving voltage, and exhibits a memory property in which particles are well aggregated and retain an image when the voltage is turned off. It is to provide colored particles.

  The present invention relates to an electrophoretic colored particle for electrophoresis in an insulating liquid, wherein the substrate particle comprises a monomer having a fluoro group at the terminal and a monomer having an alkyl group having 8 or more carbon atoms at the terminal. It is covered with a copolymer, and the ζ potential value of the electrophoretic colored particles is -50 mV or less.

According to the present invention, the substrate particles are coated with a copolymer of a monomer having a fluoro group at the terminal and a monomer having an alkyl group having 8 or more carbon atoms at the terminal.
A memory that stores images by aggregation of particles when the voltage is turned off by appropriately copolymerizing a monomer having an alkyl group having 8 or more carbon atoms at the end with a monomer having a fluoro group at the end. Sex is expressed. At the same time, the dispersibility of the particles in the insulating liquid can be obtained, and the aggregation of the particles can be easily solved when a voltage is applied, so that the display device can be operated with a low driving voltage.

  When the base particle is coated with a homopolymer of a monomer having a fluoro group at the terminal, the dispersibility of the particle is lowered. When a monomer having an alkyl group having 8 or more carbon atoms at the terminal is used in combination, particles are easily dispersed in the insulating liquid when a voltage is applied. However, when the number of monomers having an alkyl group having 8 or more carbon atoms at the terminal increases, the charging direction of the polymer is positive, and thus the ζ potential value approaches zero. That is, the repulsion between particles due to charging during voltage application is reduced, and the aggregation of particles increases. Further, when the number of monomers having an alkyl group having 8 or more carbon atoms increases, the dispersibility in the insulating liquid becomes too good, and the cohesive force between the particles becomes weak and scattered. It can no longer be obtained.

  Here, in the present invention, the combined amount of the monomer having an alkyl group having 8 or more carbon atoms at the terminal is used with respect to the monomer having a fluoro group at the terminal so that the ζ potential value of the electrophoretic colored particles is −50 mV or less. By controlling it appropriately, we succeeded in simultaneously solving the above-mentioned image memory property and particle dispersibility.

Hereinafter, the present invention will be described in more detail.
(Insulating dispersion fluid)
In the present invention, the insulating dispersion fluid is not particularly limited. The insulating dispersion fluid is preferably an insulating organic compound, and is an aliphatic hydrocarbon, aromatic hydrocarbon, alicyclic hydrocarbon, halogenated hydrocarbon, aliphatic ester, aromatic ester, aliphatic alcohol, Aromatic alcohols and oils can be exemplified. In particular, an aliphatic hydrocarbon is preferable, and paraffin (for example, n-paraffin, isoparaffin) is preferable.

(Coating method with polymer)
The method for forming the coating on the substrate particles is not particularly limited. Preferably, the following method described in JP-A-5-232480 can be used.
(1) Vinyl group introduction method A functional group such as a hydroxyl group, a carboxyl group, an epoxy group, a silyl group, a silanol group or an isocyanate group is present on the surface of the base particle, and reacts with this functional group to form a covalent bond. The substrate particles are surface-treated with the obtained monomer to introduce vinyl groups on the surface. Next, the substrate particles are surface-treated with a monomer having an alkyl group having 8 or more carbon atoms at the terminal and a monomer having a fluoro group at the terminal, and graft polymerization is performed. Suitable examples of such substrate particles will be described later.

(2) Initiator introduction method A functional group such as a hydroxyl group, a carboxyl group, an epoxy group, a silyl group, a silanol group or an isocyanate group is present on the surface of the substrate particle, and a peroxide, a peroxide which can be covalently bonded to this functional group. By reacting an initiator such as a hydroxide or an azo compound, the initiator is introduced onto the surface of the substrate particles. Next, the substrate particles are surface-treated with a monomer having an alkyl group having 8 or more carbon atoms at the terminal and a monomer having a fluoro group at the terminal, and graft polymerization is performed.

  Preferably, the base particles having a reducing group on the surface can be reacted with an oxidizing agent to generate radicals on the surface of the base particles, and a polymer film can be formed on the surface of the base particles using the radical as a starting point. . This method is described in JP-A-11-223821. As the oxidizing agent, a cerium salt is preferable, and examples thereof include cerium sulfate, cerium nitrate, cerium ammonium sulfate, cerium ammonium pyrophosphate, and cerium iodide.

(Base particle)
The substrate particles used in the present invention may be inorganic particles such as carbon black and silica, polymer resins such as polystyrene, or composite particles thereof, and are not particularly limited. The particle size of the substrate particles is preferably 0.5 μm to 8 μm. Particles of less than 0.5 μm are not easy to produce, and if the particle size is too large, it is difficult to obtain the resolution required when electronic paper is used.

It is preferable that the shape of the substrate particles is a perfect sphere and the surface is uniform. This is because the particle surface charge needs to be constant in order to cause all particles to migrate uniformly. From this viewpoint, it is preferable that the coefficient of variation Cv of the particle diameter of the present invention is 20% or less. The coefficient of variation is calculated according to the following formula from the measured value of the particle size by a Coulter measuring machine (“Multisizer 2” manufactured by Beckman Coulter, Inc.).
Cv value = (standard deviation of particle size / average particle size) × 100

  The polymerization method of the base particles is not particularly limited, and examples thereof include dispersion polymerization, suspension polymerization, seed polymerization, and emulsion polymerization. In order to use the present particles in a display medium utilizing electrophoresis, it is preferable that the particle diameter is uniform. For this reason, classification may be performed, but in this case, particles outside the desired particle size are lost, and the production yield is reduced. As disclosed in JP-A-2-97504, a crosslinked polymer obtained by subjecting a vinyl monomer having a hydrolyzable silyl group to dispersion polymerization, followed by hydrolysis and crosslinking is particularly preferable. By using this method, Particles with a uniform particle size can be obtained.

Examples of the polymerizable monomer having a hydrolyzable silyl group include the following.
γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-acryloxypropylmethyldimethoxysilane, γ-methacryloxy Propylbis (trimethoxy) methylsilane, 11-methacryloxyundecamethylenetrimethoxysilane, vinyltriethoxysilane, 4-vinyltetramethylenetrimethoxysilane, 8-vinyloctamethylenetrimethoxysilane, 3-trimethoxysilylpropyl vinyl ether, vinyl Triacetoxysilane, p-trimethoxysilylstyrene, p-triethoxysilylstyrene, p-trimethoxysilyl-α-methylstyrene, p-triethoxysilane Le -α- methyl styrene, .gamma.-acryloxypropyltrimethoxysilane, vinyltrimethoxysilane, N-beta (N-vinylbenzylaminoethyl -γ- aminopropyl) trimethoxysilane hydrochloride

Furthermore, the following monomers can also be used.
Epoxy group-containing (meth) acrylates such as glycidyl (meth) acrylate, β- (3,4, epoxycyclohexyl) ethyl (meth) acrylate, and carboxyl group-containing (meth) acrylates such as (meth) acrylic acid. Moreover, after polymerization, it can be converted to (meth) acrylic acid by hydrolysis with acid or alkali. Methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) esterified from (meth) acrylic acid Acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, tetrafurfuryl (meth) Acrylate, isobornyl (meth) acrylate, β- (parafluorooctyl) ethyl (meth) acrylate, 2,2,2-trifluoroethyl (meth) acrylate, 2,2,3,3-trifluoropropyl (meth) acrylate 2,2,3,4,4,4-hexafluorobutyl (meth) acrylate, Butoxy polyethylene glycol monomethacrylate methyl ether, ethyl vinyl ether, n- propyl vinyl ether, n- butyl vinyl ether, isobutyl vinyl ether, styrene, alpha-methyl styrene, (meth) acrylonitrile

(Coloring agent)
The colorant for the substrate particles is not particularly limited. Specific examples of the colorant include pigments such as carbon black and titanium oxide, and dyes. The kind and color of the dye compound are not limited, and two or more kinds may be used. Since the dye compound is impregnated into the polymer particles, it is preferable that the dye compound is dissolved in an aqueous solvent for handling. The kind of dye can illustrate the following.
Azo dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoneimine dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, naphthalimide Specific examples of dyes, azine dyes, phthalocyanine dyes, triphenylmethane dyes include “Valifast Red” and “Valifast Black” (manufactured by Orient Chemical Co., Ltd.).

  As the most preferable coloring method, as disclosed in JP-A-10-319412, a crosslinkable polymer particle having a hydrolyzable silyl group is used as a base particle, and the hydrolyzable silyl group has at the time of crosslinking. The dye compound is incorporated by chemical bonding.

(Monomer having a fluoro group at the terminal)
Trifluoroethyl methacrylate, 2,2,3,3,3-pentafluoropropyl methacrylate, 2- (perfluorofluorobutyl) ethyl methacrylate, 2- (perfluorohexyl) ethyl methacrylate, 2- (perfluorooctyl) ethyl methacrylate, 2- (perfluorodecyl) ethyl methacrylate, 2- (perfluoro-3-methylbutyl) ethyl methacrylate, 3- (perfluoro-3-methylbutyl) ethyl methacrylate, 2- (perfluoro-5-methylhexyl) ethyl methacrylate, 2- (Perfluoro-7-methyloctyl) ethyl methacrylate, 2- (perfluoro-9-methyldecyl) ethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 1H, 1H, 5H-octafluoropentyl methacrylate 1H, 1H, 7H-dodecafluoroheptyl methacrylate 1H, 1H, 9H-hexadecafluorononyl methacrylate, 1H, 1H, 11H-eicosafluoroundecyl methacrylate, 2,2,2-trifluoro-1-trifluoromethylethyl methacrylate, 2,2,3,4 4,4-hexafluorobutyl methacrylate, and the like.

(Monomer having an alkyl group having 8 or more carbon atoms at the terminal)
By making the carbon number of the alkyl group present in the side chain of the polymer 8 or more on average, the memory property of the display image particles is improved.

This includes the following two cases.
(1) When there is one kind of alkyl group present in the side chain of the polymer, the alkyl group has 8 or more carbon atoms.
(2) When there are two or more types of alkyl present in the side chain of the polymer, it is a weighted average of the number of carbon atoms of each alkyl group. In this case, the polymer is composed of different monomers having different alkyl groups. Therefore, the average carbon number of the alkyl group is calculated according to the following formula.
(Average number of carbon atoms in the alkyl group) =
Σ [(each carbon number of each alkyl group) × (mol% of each monomer for introducing each alkyl group)] / 100

Examples of the alkyl group having 8 or more carbon atoms include the following.
2-ethylhexyl, octyl, isooctyl, nonyl, decyl, isodecyl, undecyl, dodecyl, isododecyl, tridecyl, tetradecyl, hexadecyl, octadecyl, behenyl

  Examples of the monomer having an alkyl group having 8 or more carbon atoms at the terminal include 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, lauryl ( Examples include meth) acrylate, stearyl (meth) acrylate, and behenyl methacrylate.

  When a base material having no polymerization starting point such as active hydrogen is used on the surface of the base material particle, these polymers may be physically adsorbed by mechanochemical treatment.

  Further, the coating film thickness (one side) of the polymer is preferably in the range of 1 nm to 300 nm. By setting the coating film thickness to 1 nm (particularly preferably 5 nm) or more, the particle dispersion effect and the image memory property become remarkable. Further, even if the coating film thickness exceeds 300 nm, there is no problem from the viewpoint of the present invention, but there is little advantage because the particle size is increased as a result. From this viewpoint, the coating film thickness is particularly preferably 100 nm or less.

  In the present invention, the ζ potential value of the electrophoretic colored particles is −50 mV or less. Thereby, the dispersibility of particles and the image memory property can be remarkably improved. From this viewpoint, it is more preferable that the ζ potential value of the particles is −60 mV or less. Further, there is no particular lower limit of the ζ potential value of the particles, but it is often −90 mV or more.

  In a preferred embodiment, the ratio of the monomer having a fluoro group at the terminal and the monomer having an alkyl group having 8 or more carbon atoms at the terminal is (monomer having a fluoro group at the terminal) / (monomer having 8 or more carbon atoms at the terminal). Monomer having alkyl group) = 76 to 99 (% by weight) / 24 to 1 (% by weight).

  By making the addition amount of the monomer having an alkyl group having 8 or more carbon atoms at the terminal 1% by weight or more of the total addition amount of the monomer, the dispersibility due to the long-chain alkyl group in the insulating liquid is easily exhibited effectively, Aggregation can be prevented. Further, by setting the addition amount of the monomer having an alkyl group having 8 or more carbon atoms at the terminal to be 24% by weight or less of the total addition amount of the monomer, the ζ potential of the particles can be made −50 mV or less, Aggregation of particles can be prevented by increasing repulsion between particles due to charging. When the addition amount of the monomer having an alkyl group having 8 or more carbon atoms at the terminal exceeds 24% by weight, there is a tendency that aggregation at the time of voltage application increases.

  Particularly preferably, (monomer having a fluoro group at the terminal) / (monomer having an alkyl group having 8 or more carbon atoms at the terminal) = 80 to 90 (wt%) / 20 to 10 (wt%).

  Particularly preferably, the monomer having an alkyl group having 8 or more carbon atoms at the terminal is trifluoroethyl methacrylate, and the monomer having an alkyl group having 8 or more carbon atoms at the terminal is alkyl methacrylate.

  Various auxiliaries can be added to the fluid. Examples of such auxiliary agents include charge control agents and dispersants. Charge control agents include cobalt naphthenate, zirconium naphthenate, copper naphthenate, iron naphthenate, lead naphthenate, manganese naphthenate, zinc naphthenate, cobalt octenoate, zirconium octenoate, iron octenoate, lead octenoate , Nickel octenoate, manganese octenoate, zinc octenoate and the like.

The zeta potential value of electrophoretic colored particles is determined by Brookheaven instruments
Measured using a “ZetaPALS” zeta electrometer manufactured by corporation. A specific measurement method will be described.
(principle)
The phase difference of scattered light due to particles in a sinusoidal electric field is detected, and the zeta potential is measured. The zeta potential is obtained by the mobility and electric field when the particles move between the two electrodes.

The zeta potential generally varies depending on the type of dispersion solvent and auxiliary agent. Therefore, “Isopar H” is used as a dispersion solvent, “OLOA-1200” is used as an auxiliary agent, and the zeta potential value in this system is set as a standard value.
“Isoper H”: manufactured by Exxon Corporation: composition: mixture of 100% by weight of aliphatic hydrocarbon and 0.01% by weight of aromatic hydrocarbon: average molecular weight = 160
"OLOA-1200" Polybutenyl succinimide manufactured by Chevron Chemical Company

(Measurement procedure)
“Isopar H” / “OLOA-1200” /particles=100/0.1/1.0 are mixed at a weight ratio, and the particles are dispersed to prepare a sample. This sample is placed in a measurement plastic cell and measured.
Note that “OLOA-1200”, which provides a stable zeta potential value at the time of zeta potential measurement, is used as an auxiliary agent, but the type of auxiliary agent is not limited at the time of migration in an actual cell.

  Although the use of the particle | grains of this invention is not limited, The image display use is especially preferable. FIG. 1 is a diagram schematically illustrating an example of a display element. In FIG. 1, cells are formed between the substrate 2 and the counter substrate 1. A planar common electrode 6 is formed on the substrate 2, a white scattering insulating layer 5 is formed on the common electrode 6, and a driving electrode 3 and a transparent insulating layer 4 are formed thereon. An insulating dispersion fluid 8 is filled on the transparent insulating layer 4, and the electrophoretic particles 7 are dispersed in the fluid 8. When the particles 7 are negatively charged, when the common electrode 6 is grounded and a positive bias voltage is applied to the drive electrode 3, the particles 7 are concentrated on the drive electrode 3 and the white scattering layer 5 is exposed. The display surface turns white. When a negative bias voltage is applied to the drive electrode 3, the particles are dispersed in the fluid 8, the white scattering layer 5 is shielded, and the display surface is blackened.

  In the above, the method of the image display element is not particularly limited, and other methods may be used. For example, the fluid 8 can be interposed between the common electrode and the drive electrode. Alternatively, the display can be performed by enclosing the dispersion in a microcapsule and causing the particles to undergo electrophoresis in the microcapsule. These display elements themselves include, for example, “Semiconductor FPD World 200.12”, pages 116-118: “Semiconductor FPD World 2001.5”, pages 116-118: “NIKKEI MICRODEVICES”, February 2001, Japanese Patent Laid-Open No. -119704, Unexamined-Japanese-Patent No. 2000-89261, and Unexamined-Japanese-Patent No. 2000-258805 can illustrate.

(Preparation of substrate-colored crosslinked polymer particles)
(Production of dye compound solution A to which a hydrolyzable silyl group was added)
Dye having amino group in molecule ("VALIFAST" manufactured by Orient Kogyo Co., Ltd.
BLAK 3810 ") 10 g, 4 g of 3-isocyanatopropyltriethoxysilane and 100 g of methyl ethyl ketone were charged into a 200 ml-dissolved flask, heated to 50 ° C and held for 1 hour, and then cooled. Next, 4 g of methanol was added and evaporated to obtain a reaction solution A containing a dye compound having a hydrolyzable silyl group.

Comparative Example 1 (Production of colored crosslinked polymer particles D having silanol groups on the particle surface)
In a 2000 ml separable flask equipped with a stirrer, condenser, thermometer and gas inlet tube, 157 g of styrene, 157 g of γ-methacryloxypropyltrimethoxysilane, 79 g of polyvinylpyrrolidone, 1190 g of methanol and 21 g of water Was heated to 62 ° C. under a nitrogen stream. Thereafter, 12 g of 4,4′-azobis (2-methylbutyronitrile) was added and subjected to precipitation polymerization for 6 hours to obtain slurry B containing crosslinkable polymer particles having hydrolyzable silyl groups. .

  50 g of the reaction solution A was added to 100 g of the methanol dispersion from which the unreacted polymerizable vinyl monomer present in the slurry was removed, and the mixture was heated to 60 ° C. Subsequently, 11.5 g of p-toluenesulfonic acid dissolved in 50 g of methanol was added as a crosslinking catalyst, reacted for 3 hours, cooled and neutralized. Thereafter, the slurry was filtered and washed. Furthermore, the dyeing crosslinking step was performed again to obtain colored crosslinked polymer fine particles C. The colored crosslinked polymer particles C were heat-treated at 180 ° C. for 16 hours in order to cause dehydration condensation of hydrolyzable silyl group-derived silanol groups present inside the particles. As a result, colored crosslinked polymer particles D having silanol groups derived from hydrolyzable silyl groups on the particle surface (those that did not bond because they were in contact with the dispersion medium) were obtained. The obtained colored crosslinked polymer particles D had an average particle size of 5.1 μm. Further, the ζ potential value of the colored crosslinked polymer particles D was 5 mV.

(Introducing a polymerizable vinyl group into the colored polymer particle D)
The colored crosslinked polymer particles D10 g obtained in Comparative Example 1 were dispersed in 20 g of methyl ethyl ketone, charged with 3 g of methacryloyl isocyanate, reacted at room temperature for 30 minutes and then washed, and then washed on the surface of the colored crosslinked polymer particles D. Colored crosslinked polymer particles E having a polymerizable vinyl group were obtained.

[Comparative Example 2] (Production of colored crosslinked polymer particles F having a graft polymer layer having trifluoroethyl methacrylate)
To the colored crosslinked polymer particles E1 g having a polymerizable vinyl group on the surface, 20 g of methyl ethyl ketone, 20 g of trifluoroethyl methacrylate, and 0.4 g of benzoyl peroxide are charged into a reactor, and the temperature is raised to 80 ° C. in a nitrogen stream. And then react for 60 minutes. Thereafter, by washing with methyl ethyl ketone, colored crosslinked polymer particles F having a graft polymer layer made of a trifluoroethyl methacrylate polymer on the surface were obtained. The ζ potential value of the colored crosslinked polymer particles F was −76 mV.

[Example 1] (Production of colored crosslinked polymer particles G having a graft polymer layer having trifluoroethyl methacrylate and lauryl methacrylate)
With respect to the colored crosslinked polymer particles E1 g having a polymerizable vinyl group on the surface, 20 g of methyl ethyl ketone, 19 g of trifluoroethyl methacrylate, 1 g of lauryl methacrylate, and 0.4 g of benzoyl peroxide were charged into a reactor, and the nitrogen gas flow was 80%. After raising the temperature to 0 ° C., the reaction is carried out for 60 minutes. Thereafter, by washing with methyl ethyl ketone, colored crosslinked polymer particles G having a graft copolymer layer of trifluoroethyl methacrylate and lauryl methacrylate on the surface were obtained. The ζ potential value of the colored crosslinked polymer particles G was −75 mV.

[Example 2] (Production of colored crosslinked polymer particles H having a graft polymer layer having trifluoroethyl methacrylate and lauryl methacrylate)
With respect to the colored crosslinked polymer particles E1 g having a polymerizable vinyl group on the surface, 20 g of methyl ethyl ketone, 18 g of trifluoroethyl methacrylate, 2 g of lauryl methacrylate, and 0.4 g of benzoyl peroxide were charged into a reactor, and the nitrogen gas flow was 80%. After raising the temperature to 0 ° C., the reaction is carried out for 60 minutes. Thereafter, by washing with methyl ethyl ketone, colored crosslinked polymer particles H having a graft copolymer layer of trifluoroethyl methacrylate and lauryl methacrylate on the surface were obtained. The ζ potential value of the colored crosslinked polymer particles H was −73 mV.

[Example 3] (Production of colored crosslinked polymer particles I having a graft polymer layer having trifluoroethyl methacrylate and 2-ethylhexyl methacrylate)
To the colored crosslinked polymer particles E1 g having a polymerizable vinyl group on the surface, 20 g of methyl ethyl ketone, 16 g of trifluoroethyl methacrylate, 4 g of 2-ethylhexyl methacrylate and 0.4 g of benzoyl peroxide were charged into a reactor, and a nitrogen stream After raising the temperature to 80 ° C., the reaction is carried out for 60 minutes. Thereafter, by washing with methyl ethyl ketone, colored crosslinked polymer particles I having a graft copolymer layer of trifluoroethyl methacrylate and 2-ethylhexyl methacrylate on the surface were obtained. The ζ potential value of the colored crosslinked polymer particles I was −60 mV.

[Example 4] (Production of colored crosslinked polymer particles J having a graft polymer layer having trifluoroethyl methacrylate and stearyl methacrylate)
With respect to the colored crosslinked polymer particles E1 g having a polymerizable vinyl group on the surface, 20 g of methyl ethyl ketone, 16 g of trifluoroethyl methacrylate, 4 g of stearyl methacrylate, and 0.4 g of benzoyl peroxide were charged into a reactor, and the mixture was charged under a nitrogen stream. After raising the temperature to 0 ° C., the reaction is carried out for 60 minutes. Thereafter, by washing with methyl ethyl ketone, colored crosslinked polymer particles J having a graft copolymer layer of trifluoroethyl methacrylate and lauryl methacrylate on the surface were obtained. The ζ potential value of the colored crosslinked polymer particles J was −58 mV.

[Example 5] (Production of colored crosslinked polymer particles K having a graft polymer layer containing 1H, 1H, 5H-octafluoropentyl methacrylate and lauryl methacrylate)
To the colored crosslinked polymer particles E1 g having a polymerizable vinyl group on the surface, 20 g of methyl ethyl ketone, 16 g of 1H, 1H, 5H-octafluoropentyl methacrylate, 4 g of lauryl methacrylate, and 0.4 g of benzoyl peroxide were used in a reactor. Charge and heat up to 80 ° C under a nitrogen stream, then react for 60 minutes. Thereafter, by washing with methyl ethyl ketone, colored crosslinked polymer particles K having a graft copolymer layer of trifluoroethyl methacrylate and lauryl methacrylate on the surface were obtained. The ζ potential value of the colored crosslinked polymer particles K was −59 mV.

[Comparative Example 3] (Production of colored crosslinked polymer particles L having a graft polymer layer containing trifluoroethyl methacrylate and lauryl methacrylate: charging on the positive side of -50 mV)
To the colored cross-linked polymer particles E1 g having a polymerizable vinyl group on the surface, 20 g of methyl ethyl ketone, 15 g of trifluoroethyl methacrylate, 5 g of lauryl methacrylate, and 0.4 g of benzoyl peroxide were charged into a reactor, and the nitrogen gas flow was 80 After raising the temperature to 0 ° C., the reaction is carried out for 60 minutes. Thereafter, by washing with methyl ethyl ketone, colored crosslinked polymer particles L having a graft copolymer layer of trifluoroethyl methacrylate and lauryl methacrylate on the surface were obtained. The ζ potential value of the colored crosslinked polymer particles L was −49 mV.

[Comparative Example 4] (Production of colored crosslinked polymer particles M having a graft polymer layer containing trifluoroethyl methacrylate and lauryl methacrylate, positive charge)
With respect to the colored crosslinked polymer particles E1 g having a polymerizable vinyl group on the surface, 20 g of methyl ethyl ketone, 2 g of trifluoroethyl methacrylate, 18 g of lauryl methacrylate, and 0.4 g of benzoyl peroxide were charged into a reactor, and the nitrogen gas flow was 80 After raising the temperature to 0 ° C., the reaction is carried out for 60 minutes. Thereafter, by washing with methyl ethyl ketone, colored crosslinked polymer particles M having a graft copolymer layer of trifluoroethyl methacrylate and lauryl methacrylate on the surface were obtained. The ζ potential value of the colored crosslinked polymer particles M was +25 mV.

(Memory evaluation)
(Evaluation cell production)
A glass substrate provided with a transparent insulating layer and ITO electrode was superposed to produce a cell having a cell gap of 100 μm as shown in FIG. That is, in this cell, the cell is formed between the upper transparent glass substrate 1 and the lower transparent glass substrate 2. A planar first transparent drive electrode 11 is formed on the substrate 2, and a transparent insulating layer 10 is formed on the drive electrode 11. An insulating dispersion liquid 8 is filled on the transparent insulating layer 10, and the electrophoresis particles 7 are dispersed in the liquid 8. A second transparent drive electrode 9 is formed on the inner side of the upper glass substrate 1, and a transparent insulating layer 8 is formed on the inner side thereof.

  Next, 1 g of each of the colored crosslinked polymer particles D, F, G, H, I, J, K, L, and M prepared is dispersed in 20 g of an insulating transparent liquid (Isopar H manufactured by Exxon Chemical Co., Ltd.). Then, 10 mg of zirconium octenoate was added as a charge control agent to prepare a dispersion and filled in the cell.

  A voltage of 100 Vrms was applied to the cell at a frequency of 1 Hz and the particles were electrophoresed. After electrophoresis for about 10 minutes, the voltage was turned off while the particles were stuck on the upper wall surface, and it was confirmed whether or not the particles had fallen to the lower substrate. In this example, since the specific gravity of the particles is higher than that of Isopar H, the particles were stuck on the upper substrate.

  From the above results, as in Examples 1, 2, 3, 4, 5, a copolymer of a monomer having a fluoro group at the terminal and a monomer having a long-chain alkyl group (carbon number of 8 or more) at the terminal It was confirmed that particles that were coated and had a negative ζ potential value of −50 mV had an appropriate affinity for each other and were excellent in dispersibility and memory properties.

It is a figure which shows an example of electronic paper typically. It is a schematic diagram of the electrophoresis cell used in the Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Counter substrate 2 Substrate 3 Drive electrode 4 Transparent insulating layer 5 White scattering insulating layer 6 Common electrode 7 Electrophoresis particles 8 Insulating dispersion fluid

Claims (7)

Electrophoretic colored particles for electrophoresis in an insulating liquid,
The substrate particles are coated with a copolymer of a monomer having a fluoro group at the terminal and a monomer having an alkyl group having 8 or more carbon atoms at the terminal, and the ζ potential value of the electrophoretic colored particles is −50 mV or less Electrophoretic colored particles, characterized in that The electrophoresis according to claim 1, wherein the monomer having a fluoro group at the terminal is trifluoroethyl methacrylate, and the monomer having an alkyl group having 8 or more carbon atoms at the terminal is an alkyl (meth) acrylate. Colored particles. The electrophoretic colored particles according to claim 1 or 2, wherein the base particles have active hydrogen on the surface, and the base particles are coated with the copolymer. The electrophoretic colored particle according to any one of claims 1 to 3, wherein the base particle having a hydrolyzable silyl group is coated with the copolymer. The electrophoretic colored particles according to claim 1, wherein the base particles and the copolymer are chemically bonded. The electrophoretic colored particles according to claim 1, wherein the copolymer has a coating thickness of 1 nm to 300 nm. A display element comprising the electrophoretic colored particles according to any one of claims 1 to 6.

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