JP5530883B2 - Crosslinked (meth) acrylic acid ester colored resin particles and silicone oil dispersions thereof - Google Patents

Description

  The present invention relates to a crosslinked (meth) acrylate-based colored resin particle suitably used for an image display element, electrostatic latent image toner particles, electrorheological fluid particles, and the like, and a silicone oil dispersion thereof.

  Colored resin particles are used in various fields such as paint, toner, and fluid visualization. Among them, colored resin particles having the property of moving between opposite electrodes by electrophoresis by applying a voltage in a non-polar solvent are image display elements such as electronic paper, electrostatic latent image particles, It is attracting attention as an indispensable raw material in various fields for uses such as viscous fluids.

  Here, an example in which the colored resin particles are used as an image display element of an image display device will be introduced. A display panel is formed in which a display liquid in which colored resin particles as an image display element are dispersed in a dispersion medium is sealed between two electrode substrates that are arranged to face each other with a spacer interposed therebetween. . By applying an electric field between the two electrode substrates of the display panel, the colored resin particles are moved by electrophoresis, whereby a display can be obtained. An image display device based on such a principle has been attracting attention as an inexpensive display device because it has advantages such as a wide viewing angle, a low power consumption, and a memory property.

  In such an image display device using electrophoresis of colored resin particles, a nonpolar material is generally used as a dispersion medium in the display liquid. Examples of the nonpolar dispersion medium include aliphatic hydrocarbons such as silicone oil and paraffinic hydrocarbons. However, since the specific gravity difference between the colored resin particles and the dispersion medium is very large, the colored resin particles settle and agglomerate in the display liquid, and there is a problem that display unevenness and malfunction occur in the image display device.

  As a conventional technique for solving such a problem, the particle diameter of the titanium dioxide particles is made very fine (0.001 to 0.1 μm), so that the particles undergo a Brownian motion and are due to a difference in specific gravity from the display liquid. There is known one that improves the dispersibility of particles by obtaining a stable dispersion state against gravity (see Patent Document 1). Further, it is known that the colored resin particles are hollow or porous to reduce the specific gravity difference between the dispersed particles and the dispersion medium, thereby ensuring long-term dispersibility of the particles (Patent Documents 2 and 3). reference).

JP-A-1-105990 Patent 3949308 JP 2003-280045 A

  However, in the method of Patent Document 1, the particles to be electrophoresed are very fine, 0.1 μm or less, and therefore it is necessary to increase the concentration of the particles in order to ensure the color density necessary for display. It was found that the viscosity of the particles became very high, and it was difficult to move the particles by electrophoresis. Further, in the methods of Patent Documents 2 and 3, it is very difficult to accurately adjust the number and amount of voids existing in the hollow particles and porous particles. It was found that a specific gravity distribution occurs, and display unevenness and malfunction of the image display device occur due to variations in the movement of the colored resin particles due to electrophoresis.

  The present invention solves the above-mentioned problems, and the object of the present invention is to reduce sedimentation in a nonpolar dispersion medium, to have excellent dispersion stability, and to disperse the pigment uniformly in the particles. Therefore, it is to obtain colored resin particles having excellent color developability.

Thus, according to the present invention, the polymerizable vinyl monomer having a partial岐鎖chain alkyl group having 8 to 20 carbon atoms with (meth) acrylic acid ester monomer containing at least one or more, crosslinking agents, It is obtained by polymerizing a polymerizable monomer composition in which a pigment and a pigment dispersant having an acid value of 1 to 80 mg KOH / g are mixed, and has a true density of 0.9 to 1.04 g / cm ^3. Crosslinked (meth) acrylic acid ester-based colored resin particles are provided.

  Further, according to the present invention, there is provided a silicone oil dispersion of crosslinked (meth) acrylate colored resin particles exhibiting positive charging property obtained by dispersing the crosslinked (meth) acrylate colored resin particles in silicone oil. Provided.

  Cross-linked (meth) acrylic acid ester colored resin particles according to the present invention have little sedimentation in a nonpolar dispersion medium, excellent dispersion stability, and pigments are uniformly dispersed in the particles. It is suitable for use as an image display element, electrostatic latent image toner particles, electrorheological fluid particles, and the like.

Further, when the pigment and the pigment dispersant are contained in an amount of 1 to 30% by weight and 0.05 to 15% by weight, respectively, with respect to 100% by weight of the polymerizable monomer composition, they are further precipitated in a nonpolar dispersion medium. Cross-linked (meth) acrylic acid ester-based colored resin particles having a low content and excellent dispersion stability can be obtained.

  Further, when the polymerizable monomer composition further contains a compound having an electron donating group, the crosslinked (meth) acrylic acid ester-based colored resin particles have positive chargeability.

  Further, when the pigment dispersant has a weight average molecular weight of 1500 to 100,000, crosslinked (meth) acrylic acid ester colored resin particles with less sedimentation in a nonpolar dispersion medium and excellent dispersion stability are obtained. It is done.

Furthermore, a silicone oil dispersion obtained by dispersing the above-mentioned crosslinked (meth) acrylic acid ester-based colored resin particles in silicone oil exhibits positive chargeability and is suitable as a display liquid for an image display device free from display unevenness and malfunction. Used for.
Further, when the silicone oil has a dynamic viscosity of 2 to 20 centistokes and the crosslinked (meth) acrylic acid ester-based colored resin particles are contained in an amount of 1 to 50% by weight with respect to 100% by weight of the dispersion, the image A silicone oil dispersion more suitable as a display liquid for the display device can be obtained.

It is a TEM image of the bridge | crosslinking (meth) acrylic acid ester system coloring resin particle by Example 2 of this invention. It is a photograph which shows the evaluation result of the dispersion stability by Example 1 of this invention (it is a photograph immediately after dispersion | distribution). It is a photograph which shows the evaluation result of the dispersion stability by Example 1 of this invention (it is a photograph after 48-hour progress after dispersion).

The crosslinked (meth) acrylic acid ester colored resin particles according to the present invention (hereinafter also simply referred to as “colored resin particles”) are (meth) acrylic acid having a linear or branched alkyl group having 8 to 20 carbon atoms. A polymerizable monomer composition comprising a vinyl polymerizable monomer containing at least one ester monomer mixed with a crosslinking agent, a pigment, and a pigment dispersant having an acid value of 1 to 80 mg KOH / g. Obtained by polymerization. The colored resin particles have a true density of 0.9 to 1.04 g / cm ³ .

(Crosslinked (meth) acrylic ester colored resin particles)
(1) True density The general density of general crosslinked (meth) acrylic acid ester-based colored resin particles (for example, methyl methacrylate particles) is about 1.2 g / cm ³ , even if a colorant is contained. This true density will not change significantly. Such true density particles agglomerate in the dispersion medium. The inventors of the present invention have surprisingly found that sedimentation and aggregation in the dispersion medium can be suppressed by adjusting the true density to a range of 0.90 to 1.04 g / cm ³ .
The true density means a density in which only the volume occupied by the substance itself is a volume for density calculation. The true density measurement method will be described in the Examples section.

When the true density is less than 0.90 g / cm ³ , depending on the type of the dispersion medium, most of the colored resin particles are suspended in the dispersion medium due to the difference in specific gravity between the colored resin particles and the dispersion medium. Stability may deteriorate. On the other hand, when the true density exceeds 1.04 g / cm ³ , the sedimentation rate of the colored resin particles in the dispersion medium increases, and sedimentation aggregation occurs, which may deteriorate the dispersion stability.
The colored resin particles may be solid particles, hollow particles, or porous particles. From the viewpoint of preventing unevenness of display and malfunction of the image display device as a result of the dispersion of the colored resin particles by electrophoresis due to a large specific gravity distribution between the colored resin particles, the colored resin particles are Solid particles are preferred. Here, the solid means that there is substantially no space, and may include an unintentionally formed space.

(2) Average particle diameter The average particle diameter of the crosslinked (meth) acrylic ester-based colored resin particles is preferably 0.2 to 50 µm. More preferably, it is 1-30 micrometers. When the average particle diameter is less than 0.2 μm, it is difficult to ensure the color density necessary for display, and it is necessary to increase the density of the colored resin particles in the dispersion medium. If it does so, the viscosity of a dispersion | distribution will become very high, and the movement by electrophoresis of a colored resin particle may become difficult. On the other hand, if it exceeds 50 μm, even if the specific gravity difference with the dispersion medium is small, the particle size is large, so that the sedimentation speed increases and the sedimentation may occur immediately in the dispersion medium.

(3) Dispersibility The cross-linked (meth) acrylic acid ester-based colored resin particles are preferably excellent in monodispersibility. The term “monodispersity” as used herein refers to a state in which the particles have a substantially uniform size and are likely to be scattered without agglomeration. In the particle size distribution, which is one index of monodispersity, the coefficient of variation (CV value) is preferably 40% or less. More preferably, it is 30% or less. If the CV value exceeds 40%, the electrophoretic properties of the colored resin particles vary greatly, and display unevenness and further malfunction may occur. In addition, the measuring method of CV value is demonstrated in the column of an Example.

(Polymerizable monomer composition)
(1) (Meth) acrylic acid ester-based monomer Crosslinked (meth) acrylic acid ester-based colored resin particles are vinyl polymerizable monomers containing at least one (meth) acrylic acid ester-based monomer. It is obtained by polymerizing a polymerizable monomer composition in which a crosslinking agent, a pigment and a pigment dispersant are mixed.
As the (meth) acrylic acid ester monomer, one having a linear or branched alkyl group having 8 to 20 carbon atoms is used. Examples of such monomers include n-octyl (meth) acrylate, i-octyl (meth) acrylate, i-nonyl (meth) acrylate, lauryl (meth) acrylate, and dodecyl (meth) acrylate. , Stearyl (meth) acrylate, and isostearyl (meth) acrylate. Only one of these monomers may be used, or two or more may be used in combination.

  The addition amount of the (meth) acrylic acid ester monomer is preferably 50 to 98% by weight in 100% by weight of the polymerizable monomer composition in which the vinyl polymerizable monomer, the pigment and the pigment dispersant are mixed. . More preferably, it is 60 to 97% by weight. If it is less than 50% by weight, the true density of the colored resin particles produced by polymerization increases, so that the sedimentation rate of the resin particles in the dispersion medium increases, and sedimentation aggregation or the like may occur. On the other hand, if it exceeds 98% by weight, the glass transition temperature of the resulting resin will be low, and the solvent resistance will be low, which may make it difficult to produce and use under general use conditions.

(2) Vinyl polymerizable monomers other than (meth) acrylate monomers (vinyl) polymerizable monomers other than (meth) acrylate monomers (hereinafter "other vinyl polymers") As the “monomeric monomer”), various kinds of vinyls that are widely used as long as they do not prevent the obtained colored resin particles from having a predetermined true density (0.90 to 1.04 g / cm ³ ). System monomers can be used. For example, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-tert-butylstyrene, p-phenylstyrene, o-chlorostyrene, m-chlorostyrene , Styrene monomers such as p-chlorostyrene, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, (Meth) acrylic acid 2-ethylhexyl, (meth) acrylic acid ester-based monomers such as tetrahydrofurfuryl (meth) acrylate, acrylic acid, methacrylic acid, vinyl chloride, vinyl acetate, etc. are used alone or 2 A combination of more than one species can be used.

  The addition amount of the other vinyl polymerizable monomer is preferably 40% by weight or less in 100% by weight of the polymerizable monomer composition in which the vinyl polymerizable monomer, the pigment and the pigment dispersant are mixed. More preferably, it is 30% by weight or less. When the added amount exceeds 40% by weight, the true density of the resulting (meth) acrylate colored resin particles increases, so that the sedimentation rate of the resin particles in the dispersion medium increases, and sedimentation aggregation occurs. There is a case.

(3) Crosslinking agent Examples of the crosslinking agent used when producing crosslinked (meth) acrylate colored resin particles include aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, and derivatives thereof, and ethylene glycol dimethacrylate. , Diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, trimethylolpropane triacrylate, allyl methacrylate, t-butylaminoethyl methacrylate, tetraethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, etc. , N, N-divinylaniline, divinyl ether, divinyl sulfide, all divinyl compounds of divinyl sulfonic acid and compounds having three or more vinyl groups. It is done.

  The addition amount of the crosslinking agent is preferably 1 to 30% by weight in 100% by weight of the polymerizable monomer composition in which the vinyl polymerizable monomer, the pigment and the pigment dispersant are mixed. More preferably, it is 5 to 20% by weight. If the added amount of the crosslinking agent is less than 1% by weight, the degree of crosslinking of the resin is low and the solvent resistance is low, so that the resulting colored resin particles may swell or partially dissolve, and the colored resin Particles may coalesce. On the other hand, if it exceeds 30% by weight, the resin density is increased by the crosslinking agent, and the true density of the obtained colored resin particles is increased, so that the settling speed of the colored resin particles in the dispersion medium is increased, and the sedimentation aggregation is performed May occur.

(4) Pigment A known inorganic pigment or organic pigment may be used as the pigment mixed as a colorant in the polymerizable monomer composition. Examples of inorganic pigments include alumina, titanium dioxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, chromium oxide, cerium oxide, bengara, antimony trioxide, magnesium oxide, zirconium oxide, and sulfuric acid. Examples thereof include powder or particles of barium, barium carbonate, calcium carbonate, silica fine powder, silicon carbide, silicon nitride, boron carbide, tungsten carbide, titanium carbide and the like. Examples of organic pigments include C.I. I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104 , 108, 109, 110, 117, 120, 138, 153, C.I. I. Pigment Red 1, 2, 3, 5, 17, 22, 23, 31, 38, 48: 2, 48: 2, 48: 3, 48: 4, 49: 1, 52: 2, 53: 1, 57: 1, 60: 1, 63: 1, 63: 2, 64: 1, 81, 83, 88, 101 (Bengara), 104, 105, 106, 108, 112, 114, 122 (Quinacridone magenta), 123, 146 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209, 219, C.I. I. Pigment Blue 1, 2, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17: 1, 56, 60, 63, C.I. I. Pigment green 1, 4, 7, 8, 10, 17, 18, 36, and the like.
The pigment may be surface-treated by acid / base treatment, coupling agent treatment, polymer graft treatment, plasma treatment, oxidation / reduction treatment, or the like.

  The mixing ratio of the pigment in the polymerizable monomer composition is slightly different depending on the kind of the pigment, but is preferably 1 to 30% by weight in 100% by weight of the polymerizable monomer composition. More preferably, it is 1.5 to 15% by weight. When the mixing ratio of the pigment is less than 1% by weight, the coloring degree in the colored resin particles obtained may not be sufficient. On the other hand, if it exceeds 30% by weight, the viscosity of the polymerizable monomer composition becomes very high, and it may be difficult to obtain colored resin particles. In addition, since the specific gravity of the particles increases, sedimentation and aggregation may occur in the dispersion medium.

(5) Pigment dispersant As the pigment dispersant, amine salts, ammonium salts or alkylamine salts of unsaturated carboxylic acid copolymers such as polyacrylic acid, polyurethanes, unsaturated polyamides, polysiloxanes, long chains Examples thereof include polyaminoamide phosphates, amides obtained by reaction of poly (lower alkyleneimine) and free carboxyl group-containing polyesters, and salts thereof.

  In the present invention, a pigment dispersant having an acid value of 1 to 80 mgKOH / g is used. Preferably, it is 1-50 mgKOH / g. The acid value here is the mg number (unit: mgKOH / g) of potassium hydroxide in the alcoholic potassium hydroxide solution required to neutralize the acid group in 1 g of the pigment dispersant. Examples of such acid groups include carboxylic acid groups, sulfonic acid groups, phosphoric acid groups, and phenolic hydroxyl groups.

  When the acid value is larger than 80 mgKOH / g, polymerization may become unstable and spherical particles may not be obtained. On the other hand, if it is less than 1 mg KOH / g, the affinity with the pigment tends to be low, and the pigment dispersion may be insufficient.

  Specific examples of the pigment dispersant used in the present invention include, for example, polymer pigment dispersants commercially available as “Solsperse” series from Lubrizol Corporation. Specific examples include product numbers 13240, 13650, 13940, 16000, 17000, 18000, 24000SC, 24000GR, 26000, 28000, and the like. In addition, a polymer pigment dispersant commercially available as “Ajisper” series from Ajinomoto Fine Techno Co., Ltd. may be used. Specifically, product numbers PB-821, PB-822, PB-827, PB-881 and the like can be mentioned.

As the pigment dispersant, those having a weight average molecular weight of 1500 to 100,000 can be used. A more preferred weight average molecular weight is 2000-30000.
The weight average molecular weight here is measured using gel permeation chromatography (GPC). In addition, a weight average molecular weight means a polystyrene (PS) conversion weight average molecular weight, The measuring method is as follows.
[Analysis equipment]
Tosoh HLC-8120GPC
[column]
Tosoh TSKgel SuperHZM-H / HZ4000 / HZ3000 / HZ2000
[Column size]
6.0 mmI. D. × 150mm
[Measurement condition]
Column temperature (40 ° C.), mobile phase (tetrahydrofuran), mobile phase flow rate (0.6 mL / min), pump temperature (room temperature), measurement time (25 min), detection (RI), injection volume (20 μL)
[Measurement solution preparation method]
A 10 mg ± 5 mg sample is weighed and dissolved in 3 mL of tetrahydrofuran to obtain a measurement solution.
[PS reference material for calibration curve]
From TSK standard polystyrene (manufactured by Tosoh Corporation), a total of 19 (weight average molecular weights 4480000, 3840000, 210000, 1110000, 707000, 397000, 189000, 98900, 37200, 17100, 9490, 4920, 2500, 1010, 578, 474, 370 266, 162) are selected and used to create a calibration curve.

  Further, the pigment dispersant may have a functional group composed of a base, and a plurality of bases may exist. Specifically, the base may be present so as to give a base number of 100 to 2000.

The mixing ratio of the pigment dispersant in the polymerizable monomer composition is somewhat different depending on the type of the pigment dispersant, but is preferably 0.05 to 15% by weight in 100% by weight of the polymerizable monomer composition. If the mixing ratio of the pigment dispersant is less than 0.05% by weight, the dispersion of the pigment in the colored resin particles is poor and causes aggregation, so that it may be difficult to obtain colored resin particles exhibiting uniform coloring. On the other hand, if it exceeds 15% by weight, the dispersibility of the pigment may not be able to obtain an effect commensurate with the amount added.
In order to disperse the pigment in the polymerizable monomer composition, it is preferable to use a dispersing machine such as a paint shaker, a ball mill, an attritor, a sand mill, or a jet mill.

(6) Compound having an electron donating group A compound having an electron donating group may be mixed in the polymerizable monomer composition that is polymerized in order to obtain crosslinked (meth) acrylic ester colored resin particles.
The compound having an electron donating group is not particularly limited. For example, N-methylaminoethyl (meth) acrylate, N-ethylaminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate N, N-diethylaminoethyl (meth) acrylate, N, N-dibutylaminoethyl acrylate, N, N-di-tert-butylaminoethyl acrylate, N-phenylaminoethyl methacrylate, N, N-diphenylaminoethyl methacrylate and (Meth) acrylates such as 2-N-piperidylethyl (meth) acrylate, aminostyrene, dimethylaminostyrene, N-methylaminoethylstyrene, dimethylaminoethoxystyrene, diphenylaminoethylstyrene, N-phenylamino Styrenes such as ethylstyrene, heterocycles such as 2-vinylpyridine, 4-vinylpyridine, 2-vinyl-6-methylpyridine, N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, N-vinylpyrrolidone And the like, as well as polymers composed of one or more of these, and electron donating compounds such as quaternary ammonium salts.

(Example of polymerization method of polymerizable monomer composition)
As a method for polymerizing a polymerizable monomer composition for obtaining crosslinked (meth) acrylic acid ester-based colored resin particles, a known polymerization method such as a suspension polymerization method, an emulsion polymerization method, a dispersion polymerization method, or the like is used. be able to. Hereinafter, although an example of the manufacturing method of the (meth) acrylic acid ester system colored resin particle by a suspension polymerization method is demonstrated, this invention is not limited only to this manufacturing method.

  A polymerizable monomer composition is obtained by adding and mixing a pigment as a colorant and other additives (polymerization initiator, crosslinking agent, surfactant, pigment dispersant, etc.) to the polymerizable monomer. . The obtained polymerizable monomer composition is suspended in an aqueous dispersion medium. Here, in order to stabilize the suspended particles, it is preferable to use 100 to 1000 parts by weight of the aqueous dispersion medium with respect to 100 parts by weight of the polymerizable monomer composition. In addition, as an aqueous dispersion medium, the mixture of water or water and a water-soluble solvent (for example, lower alcohol) is mentioned.

  The suspension stabilizer is preferably added to the aqueous dispersion medium before the addition of the polymerizable monomer composition. The suspension polymerization can be performed by heating the aqueous dispersion medium to a temperature of, for example, 40 to 120 ° C, preferably 45 to 110 ° C. After the suspension polymerization is completed, the obtained colored resin particles are separated from the aqueous dispersion medium, washed and dried, and then subjected to a classification step as necessary to obtain colored resin particles having a desired particle diameter.

  The suspension stabilizer is not limited as long as the desired colored resin particles can be obtained. For example, phosphates such as calcium phosphate, magnesium phosphate, aluminum phosphate, zinc phosphate, Pyrophosphates such as calcium pyrophosphate, magnesium pyrophosphate, aluminum pyrophosphate, zinc pyrophosphate, calcium carbonate, magnesium carbonate, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, calcium metasilicate, calcium sulfate, barium sulfate, colloidal silica Examples thereof include dispersion stabilizers of hardly water-soluble inorganic compounds. Among them, it is preferable to use an inorganic compound that can be easily dissolved and removed by adjusting the pH of the system after the completion of polymerization. For example, it is preferable to use tribasic calcium phosphate, magnesium pyrophosphate, calcium pyrophosphate, or colloidal silica produced by the metathesis method because the desired colored resin particles can be obtained more stably.

  The suspension stabilizer is used by appropriately adjusting the composition and amount of use so that the particle diameter of the colored resin particles to be obtained becomes a predetermined size. The addition amount of the suspension stabilizer is preferably 0.1 to 30 parts by weight with respect to 100 parts by weight of the polymerizable monomer composition. More preferably, it is 0.5 to 20 parts by weight.

  When an aqueous dispersion medium is used as the dispersion medium, a surfactant such as an anionic surfactant, a cationic surfactant, a zwitterionic surfactant, or a nonionic surfactant may be added. The addition amount of the surfactant is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the polymerizable monomer composition. More preferably, it is 0.02 to 3 parts by weight.

  Examples of anionic surfactants include fatty acid oils such as sodium oleate and castor oil potassium, alkyl sulfate salts such as sodium lauryl sulfate and ammonium lauryl sulfate, alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, and alkylnaphthalene sulfonates. , Alkane sulfonate, dialkyl sulfosuccinate, naphthalene sulfonic acid formalin condensate, polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene alkyl sulfate, and the like.

Examples of the cationic surfactant include alkylamine salts such as laurylamine acetate and stearylamine acetate, and quaternary ammonium salts such as lauryltrimethylammonium chloride.
Examples of the zwitterionic surfactant include lauryl dimethylamine oxide and phosphate ester or phosphite ester surfactants.
Nonionic surfactants include, for example, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxysorbitan fatty acid ester, polyoxyethylene alkylamine, glycerin fatty acid ester, oxy Examples include ethylene-oxypropylene block polymers.

  As the polymerization initiator used for the polymerization, an oil-soluble peroxide-based or azo-based initiator usually used for suspension polymerization is used. For example, for example, benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxydicarbonate, cumene hydroperoxide, cyclohexanone peroxide, t -Peroxide-based initiators such as butyl hydroperoxide and diisopropylbenzene hydroperoxide, 2,2-azobisisobutyronitrile, 2,2-azobis (2,4-dimethylvaleronitrile), 2,2- Azobis (2,3-dimethylbutyronitrile), 2,2-azobis (2-methylbutyronitrile), 2,2-azobis (2,3,3-triazobis (2-methylbutyronitrile), 2, 2-azobis (2,3,3 Trimethylbutyronitrile), 2,2-azobis (2-isopropylbutyronitrile), 1,1-azobis (cyclohexane-1-carbonitrile), 2,2-azobis (4-methoxy-2,4-dimethylvalero) Nitrile), 2- (carbamoylazo) isobutyronitrile, 4,4-azobis (4-cyanovaleric acid), dimethyl-2,2-azobisisobutyrate, etc. The amount of polymerization initiator added is determined by polymerization. 0.05 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the polymerizable monomer composition.

  After completion of the polymerization, the colored resin particles are centrifuged as necessary to remove the aqueous medium, washed with water and a solvent, and then dried and isolated. A method for isolating the colored resin particles obtained from the aqueous dispersion medium by suspension polymerization performed in the present invention is not particularly limited, but a known method is, for example, a spray drying method represented by a spray dryer. Examples thereof include a method of adhering to a heated rotating drum typified by a drum dryer and drying or a freeze-drying method.

In order to suppress the generation of emulsified particles in the aqueous system in the polymerization step, water-soluble polymerization inhibitors such as nitrites, sulfites, hydroquinones, ascorbic acids, water-soluble vitamin Bs, citric acid, polyphenols, etc. May be used.
The resulting crosslinked (meth) acrylic acid ester-based colored resin particles can be used for applications that utilize electrophoresis of particles such as image display elements and particles for electrorheological fluid, and for electrostatic latent image toner particles. it can. Among these, it is preferable to use for the use using electrophoresis.

(Dispersion of colored resin particles)
The dispersion medium used for electrophoresis of the crosslinked (meth) acrylic acid ester-based colored resin particles is not particularly limited as long as it is nonpolar. Nonpolar dispersion media include, for example, paraffinic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane and dodecane, isoparaffinic hydrocarbons such as isohexane, isooctane and isododecane, and alkylnaphthene hydrocarbons such as liquid paraffin. , Silicone oils such as dimethyl silicone oil, phenylmethyl silicone oil, dialkyl silicone oil, alkylphenyl silicone oil, cyclic polydialkylsiloxane or cyclic polyalkylphenylsiloxane.

Among these non-polar dispersion media, considering the environmental impact, ease of electrophoresis of colored resin particles, etc., dimethyl silicone oil, phenylmethyl silicone oil, dialkyl silicone having a dynamic viscosity of 2 to 20 centistokes It is preferable to use silicone oil such as oil, alkylphenyl silicone oil, cyclic polydialkylsiloxane, or cyclic polyalkylphenylsiloxane. The liquid specific gravity at 25 ° C. of these silicone oils is generally in the range of 0.79 to 1.00 g / cm ³ .

  In a dispersion obtained by dispersing colored resin particles in silicone oil, the proportion of the colored resin particles is preferably 1 to 50% by weight with respect to 100% by weight of the dispersion. More preferably, it is 10 to 40% by weight. If it is less than 1% by weight, the color density necessary for display may not be ensured. On the other hand, when it exceeds 50% by weight, the viscosity of the dispersion increases, and the colored resin particles may not move by electrophoresis.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto. First, measurement methods, calculation methods, and evaluation methods in Examples and Comparative Examples will be described.

(Measuring method of average particle diameter and CV value)
The measurement method of the average particle diameter of the colored resin particles is a method in which calibration is performed using an aperture having a pore size suitable for the particle size according to Reference MANUAL FOR THE COULTER MULTISIZER (1987) issued by Coulter Electronics Limited. The aperture diameter used is 50 μm for colored resin particles having an average particle diameter of less than 1 to 10 μm and 100 μm for colored resin particles having an average particle diameter of less than 10 to 30 μm.
For the measurement, a precision particle size distribution measuring device (Beckman Coulter, Inc .: Coulter Multisizer III) is used. Specifically, 0.1 g of colored resin particles are predispersed in 10 ml of a 0.3% nonionic surfactant solution using a touch mixer and ultrasonic waves, and this is provided with ISOTON II (measured by Beckman Coulter, Inc.) provided on the main body. In a beaker filled with (electrolyte), drop with a dropper while stirring gently, and adjust the reading of the densitometer on the main body screen to about 10%. Next, an aperture is set in the Multisizer III body, and measurement is performed under predetermined conditions in which Current, Gain, and Polarity are matched to the aperture size. During the measurement, the inside of the beaker is gently stirred to the extent that bubbles do not enter, and the measurement is terminated when 100,000 colored resin particles are measured.

The volume-weighted average diameter (arithmetic average diameter in volume% mode: volume median diameter) is calculated as the average particle diameter (Y) of the colored resin particles.
The coefficient of variation (CV value) is a value calculated from the standard deviation (σ) and the average particle diameter (Y) by the following equation.
CV value (%) = (σ / Y) × 100

(Measurement method of acid value)
The acid value is measured according to JIS K0070.

(Measurement method of true density)
Using a dry density meter Accupic 1330 (gas displacement method) manufactured by Shimadzu Corporation-Micromeritics, take 4 g of the colored resin particles in a 10 cc cell, repeatedly measure 5 times or more, and determine the average value.

(Confirmation of colorant dispersion in colored resin particles)
Colored resin particles are embedded in an epoxy resin, an ultrathin section is prepared, and a cross section is observed with a transmission electron micrograph. Note that H-7600 manufactured by Hitachi, Ltd. is used as the transmission electron microscope apparatus.

(Evaluation of coloring)
The coloring degree of the colored resin particles is measured by the following method.
A silicone oil dispersion of 10% by weight colored resin particles (kinematic viscosity: 10 centistokes, KF-96L) between two glass plates coated with indium tin oxide (ITO) on one side of a parallel flat plate with a gap of 50 μm. −10CS (manufactured by Shin-Etsu Chemical Co., Ltd.) was prepared, the cell was placed on a white plate, and the L ^* a ^* b ^* value (from the top using a spectrocolorimeter (504 manufactured by Konica Minolta)) F10) is measured. Moreover, about the colored resin particle using a yellow pigment, YI value (D1925) is also measured.

(Evaluation of polarity)
The polarity of the colored resin particles in the silicone oil is measured by the following method.
Weigh the colored resin particles into a 20 ml glass bottle and add silicone oil (kinematic viscosity: 2 centistokes, KF-96L-2CS, manufactured by Shin-Etsu Chemical Co., Ltd.) so that the solid content of the colored resin particles is 5% by weight. 10 g, and this is used as a measurement sample.
Next, two flat glass plates coated with indium tin oxide (ITO) on one side, with the coated surface on the inside, a spacer with a copper tape attached between the glass plates, and a parallel plate with an interval of 1 mm between the glass plates Prepare a jig. The jig is immersed in the measurement sample, a voltage of +100 V is applied to the left side of the jig, and the sample is allowed to stand for 10 seconds. After 10 seconds, the jig is lifted from the measurement sample. If particles are attached to the left glass plate, the particle polarity is negative. If particles are attached to the right glass plate, the particle polarity is positive. .

(Evaluation of dispersion stability)
The dispersion stability of the colored resin particles in the silicone oil is evaluated by the following method.
The colored resin particles described in Examples and Comparative Examples are weighed, and silicone oil (kinematic viscosity: 10 centistokes, KF-96L-10CS, manufactured by Shin-Etsu Chemical Co., Ltd.) is added so that the solid content of the colored resin particles is 10% by weight. ) Is added to disperse the colored resin particles, and this is used as a measurement sample. Transfer 50 ml of the sample for measurement to a 50 ml graduated cylinder, observe the dispersion state of the colored resin particles after standing for 48 hours, and evaluate based on the following three evaluation criteria.
(Evaluation criteria)
A: There is almost no precipitation of colored resin particles, and the colorless and transparent supernatant portion is less than 10%. O: Colored resin particles are slightly precipitated, but the colorless and transparent supernatant portion is less than 40%. X: The colored resin particles are precipitated. The colorless and transparent supernatant portion is 40% or more. Examples and Comparative Examples will be described below. Unless otherwise specified, “parts” means parts by weight, and “%” means% by weight.

Example 1
180 parts by weight of isostearyl acrylate (hereinafter ISTA), 20 parts by weight of pigment (manufactured by Sanyo Dye: Fast Yellow 7416, CI Pigment Yellow 74), Solsperse 18000 (manufactured by Lubrizol, polyamide, acid) as a pigment dispersant (Value: 1 mg KOH / g, weight average molecular weight: 2600) 2.5 parts by weight were placed in a bead pod containing 5 mm diameter zirconia beads and stirred for 6 hours to disperse the pigment. Next, a part of the above mixture was weighed, the remaining ISTA, ethylene glycol dimethacrylate (hereinafter EGDMA) and diethylaminoethyl methacrylate (hereinafter DEAEMA) were added, and ISTA / EGDMA / DEAEMA / pigment / pigment dispersant = 88. A polymerizable monomer composition having a weight ratio of 6.0 / 2.0 / 3.0 / 1.0 (% by weight) was prepared.

To 100 parts by weight of this polymerizable monomer composition, 0.8 part of 2,2-azo-bis- (2,4-dimethylvaleronitrile) (manufactured by Nippon Hydrazine Kogyo Co., Ltd., hereinafter ABNV) as a polymerization initiator. Added and dissolved. Next, it is charged into 500 parts by weight of water in which 0.020% by weight of sodium laurylbenzenesulfonate and 1.0% by weight of magnesium pyrophosphate dispersed in advance are dispersed, and a homomixer (manufactured by Koki Kogyo Co., Ltd.) is used. The mixture was stirred at 5000 rpm for 5 minutes to obtain a primary suspension. Next, a nanomizer LA-33 (manufactured by Nanomizer) was connected to a nanomizer processor LD-500 (manufactured by Nanomizer), and the primary suspension was treated at a primary pressure of 5 kg / cm ² to obtain a secondary suspension. Got.

  This suspension was heated in a nitrogen atmosphere while uniformly stirring the whole, and polymerized at 60 ° C. for 5 hours. Furthermore, the temperature was raised to 105 ° C., and polymerization was continued for 1 hour to complete the polymerization. Next, the mixture was cooled to room temperature, and hydrochloric acid was added to dissolve magnesium pyrophosphate as a suspension stabilizer. Subsequently, solid-liquid separation and water washing were repeated, followed by drying with a hot air dryer at 70 ° C. for 24 hours to obtain crosslinked (meth) acrylic acid ester-based colored resin particles.

The obtained colored resin particles had a true density of 0.97 (g / cm ³ ), an average particle diameter of 13.0 μm, and a CV value of 20.5%. Further, the polarity in silicone oil was positive, the dispersion stability was excellent, there was almost no precipitation of particles, and the colorless and transparent supernatant portion was less than 10% (（).

(Example 2)
180 parts by weight of ISTA, 20 parts by weight of pigment (manufactured by Sanyo Dye: Fast Yellow 7416, CI Pigment Yellow 74), Solsperse 18000 as a pigment dispersant (manufactured by Lubrizol, polyamide system, acid value: 1 mg KOH / g, weight average) (Molecular weight: 4100) 3 parts by weight were placed in a bead pod containing 5 mm diameter zirconia beads and stirred for 6 hours to disperse the pigment. Next, a part of the mixed solution is weighed, the remaining ISTA, ethylene glycol dimethacrylate (hereinafter EGDMA) and diethylaminoethyl methacrylate (hereinafter DEAEMA) are added, and ISTA / EGDMA / DEAEMA / pigment / pigment dispersant = 86. A polymerizable monomer composition having 9 / 7.0 / 0.5 / 5.0 / 0.6 (% by weight) was prepared.

To 100 parts by weight of this polymerizable monomer composition, 0.8 part of ABNV was added and dissolved. Next, it is charged into 500 parts by weight of water in which 0.040% by weight of sodium laurylbenzenesulfonate and 1.0% by weight of magnesium pyrophosphate dispersed in advance are dispersed, and a homomixer (manufactured by Koki Kogyo Co., Ltd.) is used. The mixture was stirred at 5000 rpm for 5 minutes to obtain a primary suspension. Next, a nanomizer LA-33 (manufactured by Nanomizer) was connected to a nanomizer processor LD-500 (manufactured by Nanomizer), and the primary suspension was treated at a primary pressure of 5 kg / cm ² to obtain a secondary suspension. Got.

  This suspension was heated in a nitrogen atmosphere while uniformly stirring the whole, and polymerized at 60 ° C. for 5 hours. Further, the temperature was raised to 105 ° C. and polymerization was continued for 1 hour, and then the polymerization was terminated. Next, the mixture was cooled to room temperature, and hydrochloric acid was added to dissolve magnesium pyrophosphate as a suspension stabilizer. Subsequently, solid-liquid separation and water washing were repeated, followed by drying with a hot air dryer at 70 ° C. for 24 hours to obtain crosslinked (meth) acrylic acid ester-based colored resin particles.

The obtained colored resin particles had a true density of 0.99 (g / cm ³ ), an average particle size of 4.4 μm, and a CV value of 23.5%. FIG. 1 shows a TEM image of the obtained crosslinked (meth) acrylic ester-based colored resin particles. In FIG. 1, black portions are portions where pigments are mainly present. Further, the polarity in silicone oil was positive, the dispersion stability was excellent, and some precipitation of particles was observed, but the colorless and transparent supernatant portion was less than 40% (◯).

(Examples 3-7 and Comparative Examples 1-4)
Examples 3 to 7 and Comparative Examples 1 to 4 were obtained under the same conditions as in Example 1 except that the blending composition of monomer / crosslinking agent / electron donating group-containing compound / pigment / pigment dispersant was changed. Measurement and evaluation of colored resin particles were performed. These results are shown together in Table 1 together with Examples 1 and 2 described above.
Furthermore, the photograph which shows the evaluation result of the dispersion stability in Example 1 is shown in FIG.2 and FIG.3. FIG. 2 is a photograph immediately after dispersion, and FIG. 3 is a photograph after 48 hours have passed since dispersion. The dispersion is filled up to a 50 ml scale in a 50 ml graduated cylinder. In FIG. 3, it can be seen that the colored resin particles are precipitated and the supernatant portion occupies a scale portion of 46.5 to 50 ml.

ISTA: Isostearyl acrylate IOCA: Isooctyl acrylate MMA: Methyl methacrylate St: Styrene EGDMA: Ethylene glycol dimethacrylate DVB: Divinylbenzene DEAEMA: Diethylaminoethyl methacrylate quaternary ammonium salt: Trade name BONTRON P-51 (Orient Chemical Industries) (Made by company)
Solsperse 18000: Pigment dispersant (manufactured by Lubrizol: Solsperse 18000, polyamide series, acid value: 1 mg KOH / g, weight average molecular weight: 2600)
Solsperse 28000: Pigment dispersant (manufactured by Lubrizol: Solsperse 28000, polyamide series, acid value: 30 mgKOH / g, weight average molecular weight: 4100)
Pigment Y: trade name Fast Yellow 7416 (manufactured by Sanyo Dye)
Pigment R: trade name Chromo Fine Red 6605T (manufactured by Dainichi Seika Kogyo Co., Ltd.)
Pigment B: trade name Cyanine Blue KRO (manufactured by Sanyo Dye)

The evaluation of Comparative Examples 1 to 3 is considered to be caused by the fact that the true density of the colored resin particles exceeded 1.04 g / cm ³ . Moreover, since the comparative example 4 does not use the pigment dispersant, the color development of the particles is poor.

Claims (6)

Having a partial岐鎖chain alkyl group having 8 to 20 carbon atoms in the polymerizable vinyl monomer (meth) acrylic acid ester monomer and comprising at least one or more, crosslinking agents, pigments and 1~80mgKOH / g Obtained by polymerizing a polymerizable monomer composition mixed with a pigment dispersant having an acid value of 0.9 to 1.04 g / cm ³ and having a true density of 0.9 to 1.04 g / cm ^3. ) Acrylic ester-based colored resin particles. The cross-linking (meth) according to claim 1, wherein the pigment and the pigment dispersant are contained in an amount of 1 to 30 wt% and 0.05 to 15 wt%, respectively, with respect to 100 wt% of the polymerizable monomer composition. Acrylic ester colored resin particles.   The crosslinked (meth) acrylic acid ester-based colored resin particles according to claim 1 or 2, wherein the polymerizable monomer composition further contains a compound having an electron donating group.   The crosslinked (meth) acrylic acid ester-based colored resin particles according to any one of claims 1 to 3, wherein the pigment dispersant has a weight average molecular weight of 1500 to 100,000.   A silicone oil dispersion of cross-linked (meth) acrylic ester-based colored resin particles exhibiting positive chargeability obtained by dispersing the cross-linked (meth) acrylic ester-based colored resin particles according to claim 3 or 4 in silicone oil.   The silicone oil has a dynamic viscosity of 2 to 20 centistokes, and the crosslinked (meth) acrylic ester-based colored resin particles are contained in an amount of 1 to 50% by weight with respect to 100% by weight of the dispersion. A silicone oil dispersion of cross-linked (meth) acrylic acid ester-based colored resin particles as described in 1.