JP2005345512A - Electrophoretic particles and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: A conventional production method in which polymer chains are grafted onto the surface of pigment particles by using atom transfer radical polymerization has a problem that in the case of white electrophoretic particles, the color changes due to the remaining catalyst used in the polymerization. It was.
The electrophoretic particles of the present invention precisely form a polymer chain imparting dispersibility and chargeability to the surface of pigment particles by renitroxide-mediated polymerization, and do not use a catalyst that causes discoloration. As a result, it is possible to provide an electrophoretic particle having superior dispersibility, chargeability, and sharpness compared to conventional electrophoretic particles, and a method for producing the same.
[Selection figure] None

Description

  The present invention relates to an electrophoretic particle grafted with a polymer chain and a method for producing the same.

  In recent years, with the development of information equipment, the need for low power consumption and thin display elements has increased, and research and development of display elements that meet these needs has been actively conducted.

  One such display element is an electrophoretic display element.

  The electrophoretic display element includes a pair of substrates arranged with a predetermined gap therebetween, and electrodes are formed on each substrate. The gap between the substrates is filled with a large number of electrophoretic particles that are positively charged and colored, and a dispersion medium that is colored with a color different from the electrophoretic particles. Further, the partition is arranged so as to divide the gap into a large number of pixels along the surface direction of the substrate, and is configured to prevent the uneven distribution of the electrophoretic particles and to define the substrate gap.

  In such an electrophoretic display element, when a positive voltage is applied to the electrode on the viewer side and a negative voltage is applied to the opposite electrode, the positively charged electrophoretic particles are applied to the opposite electrode. When the display element is viewed from the observer, the same color as the dispersion medium is displayed. On the other hand, when a negative voltage is applied to the electrode on the viewer side and a positive voltage is applied to the electrode on the opposite side, the electrophoretic particles gather to cover the electrode on the viewer side, and the display element is moved from the viewer. When viewed, the same color as the electrophoretic particles is displayed. By performing such driving in units of pixels, an arbitrary image or character is displayed by a large number of pixels.

  Electrophoretic particles used in electrophoretic display elements have a uniform particle size, are colored, need to be stably charged and dispersed in a dispersion medium, and various types have been proposed.

  A suspension polymerization method is known as a method for obtaining particles having a relatively uniform particle size. Patent Document 1 describes a method for producing electrophoretic particles in which a composition in which a colorant is dispersed in a polymerizable monomer is suspended in an aqueous medium to perform polymerization, and the colorant is uniformly formed into a polymerizable monomer. In order to make it disperse | distribute to, the method of adding a coloring agent dispersion medium and a coloring agent water phase transfer inhibitor is proposed.

  In addition, so-called core-shell type electrophoretic particles in which the core particles are coated with another material in order to adjust the physical properties such as the specific particle size and the specific gravity and mechanical strength have been proposed. Patent Document 2 discloses a method of forming a core-shell structure by two-stage emulsion suspension polymerization, and reacting a metal oxide with a double bond remaining in the core to dye it black.

  Patent Document 3 discloses a method of obtaining electrophoretic particles having a structure in which pigment particles are covered with a polymer layer by introducing a polymerizable group on the surface of the pigment particles and bonding a polymer chain thereto. ing.

  In recent years, it has become known to form a polymer chain having a uniform chain length on the surface of a mother particle by living radical polymerization and coat the mother particle with a polymer.

Patent Document 4 proposes a method in which a molecule having an atom transfer radical polymerization initiating group is bonded to the surface of pigment particles, and a polymer chain is grown from the initiating group by atom transfer radical polymerization. Patent Document 5 discloses a method of obtaining a mother particle by polymerization or copolymerization from a monomer containing an atom transfer radical polymerization initiation group, and by using this as a core by atom transfer radical polymerization from the initiation group in a polymerizable monomer solution. A method has been proposed in which polymer chains are grafted to obtain composite particles in which polymers having a uniform chain length are grafted together.
JP 2003-212913 A JP 9-508216 gazette US Pat. No. 6,194,488 WO2002093246A1 specification JP 2004-18556 A

  In many conventional electrophoretic display elements, in order to prevent the electrophoretic particles from aggregating in the electrophoretic dispersion medium, a dispersion stabilizer is added to the electrophoretic dispersion medium to make the electrophoretic particles dispersible. It was granted. Further, if the zeta potential of the electrophoretic particles is low, the particles are not sufficiently charged, and the particles cannot be stably electrophoresed. Therefore, a charging agent is added to the electrophoretic dispersion medium to improve the chargeability. However, there has been a problem that the dispersibility and chargeability of the electrophoretic particles applied by such a method often deteriorate with time.

  On the other hand, core-shell type electrophoretic particles in which the surface of the electrophoretic particles is coated with a polymer in order to increase dispersibility and chargeability have also been proposed. The thickness of the shell is likely to vary due to the manufacturing method. As a result, the dispersibility and chargeability of the electrophoretic particles become unstable, and a stable electrophoretic display cannot be provided.

  The manufacturing method of polymer particles using living radical polymerization solves the problem of making the particle size and shell thickness uniform, but for use as electrophoretic particles, it is colored with the desired color and concentration. There is a need. In addition, the polymer chain grafted on the surface of the fine particles must be designed so as to exhibit a dispersion function and a charging function in the electrophoretic dispersion medium.

  In particular, in the case of white electrophoretic particles, it is necessary to prevent discoloration due to the remaining catalyst used in the polymerization.

  As a result of various studies to solve such problems, the present inventor has found electrophoretic particles superior in dispersibility, chargeability, and sharpness than conventional electrophoretic particles, and has led to the present invention. It is a thing.

  That is, the present invention is an electrophoretic particle in which a polymer chain is grafted on the surface of a pigment particle, and the polymer chain is grafted by nitroxide-mediated polymerization from a nitroxide-mediated polymerization initiation group on the particle surface. It is characterized by that.

  The present invention also relates to a method for producing electrophoretic particles, wherein pigment particles having a functional group that reacts with a precursor of a nitroxide-mediated polymerization initiating group are reacted with a precursor of a nitroxide-mediated polymerization initiating group. The method comprises the steps of introducing a nitroxide-mediated polymerization initiation group onto the surface of the polymer, and then grafting a polymer chain from the living radical polymerization initiation group by nitroxide-mediated polymerization.

  Since the electrophoretic particles of the present invention precisely form a polymer chain imparting dispersibility and chargeability to the surface of pigment particles by renitroxide-mediated polymerization and do not use a catalyst that causes discoloration. Electrophoretic particles having superior dispersibility, chargeability, and sharpness compared to the electrophoretic particles, and a method for producing the same can be provided.

1. Electrophoretic Particles The electrophoretic particles of the present invention can be obtained by introducing a nitroxide-mediated polymerization initiator group on the surface of pigment particles, and then grafting a polymer chain from the nitroxide-mediated polymerization initiator group by nitroxide-mediated polymerization.

(Introduction of nitroxide-mediated polymerization initiation group)
Hereinafter, a process of introducing a nitroxide-mediated polymerization initiating group on the surface of the pigment particle will be described.

  According to the following reaction formula (I), a nitroxide-mediated polymerization initiating group can be introduced on the surface of the pigment particle. That is, the nitroxide-mediated polymerization initiating group can be introduced to the surface of the pigment particle by adding the pigment particle and the precursor 1 of the nitroxide-mediated polymerization initiating group 1 to the reaction solvent for reaction. The triethoxysilyl group of the precursor of the nitroxide-mediated polymerization initiating group may be a trimethoxysilyl group or a trichlorosilyl group.

  The pigment particles preferably have a functional group that reacts with the precursor of the nitroxide-mediated polymerization initiating group. The pigment particles that do not have a functional group are appropriately treated to introduce a functional group. It is preferable to keep it. Examples of the functional group include a hydroxyl group.

  The reaction solvent is not particularly limited, and for example, dimethyl sulfoxide, dimethylformamide, benzene, toluene, xylene and the like can be used.

  In addition to the precursor 1 of the nitroxide-mediated polymerization initiating group of reaction formula (I), the following precursors of nitroxide-mediated polymerization initiating groups may be used. In any case, n is an integer of 1 to 10. Further, the triethoxysilyl group of the precursor of the nitroxide-mediated polymerization initiating group may be a trimethoxysilyl group or a trichlorosilyl group.

(Nitroxide-mediated polymerization)
Next, the process of forming a polymer chain using the pigment particles into which the nitroxide-mediated polymerization initiating group of reaction formula (I) has been introduced as core particles will be described.

  After the above core particles are dispersed in a reaction solvent, a polymerizable monomer that becomes a polymer chain is added, and the reaction system is replaced with an inert gas to perform nitroxide-mediated polymerization.

  The reaction solvent is not particularly limited as long as the pigment particles are dispersed. For example, dimethyl sulfoxide, dimethylformamide, benzene, toluene, xylene, diphenyl ether and the like can be used. Alternatively, the polymerization may be performed without using a reaction solvent.

Nitrogen gas or argon gas can be used as the inert gas.
The polymerization temperature is in the range of 40 to 150 ° C, preferably in the range of 60 to 120 ° C. When the polymerization temperature is less than 40 ° C., the formed polymer chain has a low molecular weight, or polymerization is difficult to proceed, which is not preferable.

  Moreover, when performing superposition | polymerization, it is preferable to add the free superposition | polymerization seed | species which is not fix | immobilized by particle | grains. The free polymer produced from the free polymerization initiating species can be used as an indicator of the molecular weight and molecular weight distribution of the polymer chain grafted to the particles.

  As the free polymerization initiating species, it is preferable to select the same species as the nitroxide-mediated polymerization group immobilized on the particles. That is, for the particles of the reaction formula (I), the same nitroxide as the precursor 1 of the nitroxide-mediated polymerization initiating group is preferable.

  After completion of the reaction, the generated particles are separated and purified by a suitable method such as washing, filtration, decantation, precipitation fractionation, and centrifugation to obtain electrophoretic particles.

  The concentration of the electrophoretic particles is preferably 0.5 to 50% by weight, more preferably 1 to 30% by weight with respect to the electrophoretic dispersion medium.

(Polymerizable monomers and polymer chains that become polymer chains)
The polymer chains of the above electrophoretic particles can have a charging function and a dispersion function.

  First, a polymer chain having a dispersion function will be described. The polymer chain having a dispersion function is a polymer having a high affinity for the electrophoretic dispersion medium. High affinity here means that the polymer chain and the electrophoretic dispersion medium are excellent in compatibility without phase separation, and the polymer chain has a spread in the electrophoretic dispersion medium. Thus, a steric exclusion effect that prevents aggregation between particles is exhibited.

  As described above, the polymerizable monomer to be a polymer chain having a dispersion function is required to be a polymer having a high affinity with the electrophoretic dispersion medium. For example, 1-hexene, 1-heptene. , 1-octene, 1-decene, butadiene, isoprene, isobutylene and the like, and these may be used alone or in admixture of two or more.

  Next, a polymer chain having a charging function will be described. As the polymerizable monomer that becomes a polymer chain having a charging function, a basic polymerizable monomer, an acidic polymerizable monomer, or a fluorine-based polymerizable monomer can be used.

  Examples of basic polymerizable monomers include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, and (meth) acrylic. 2-ethylhexyl acid, heptyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, tetradecyl (meth) acrylate, (meth) Hexadecyl acrylate, octadecyl (meth) acrylate, aminomethyl (meth) acrylate, aminoethyl (meth) acrylate, N, N-dimethylaminomethyl (meth) acrylate, N, N-dimethyl (meth) acrylate Aminoethyl, (meth) acrylamide, N, N-dimethyl (meth) acrylami , May be mentioned N, N-diethyl (meth) acrylamide, 4-vinylpyridine.

  When an acidic additive is added to a polymer chain composed of a basic polymerizable monomer, an acid-base interaction works between these substances, and a positive charge can be imparted to the particles. In addition, by selecting the type of the basic polymerizable monomer and the acidic additive, and further adjusting the addition amount of the acidic additive, the polymer chain having a charging function can also have a dispersion function. In such a case, the polymer chain having a dispersing function may not be grafted to the particles.

  As the acidic additive, an acidic substance that dissolves in the electrophoretic dispersion medium is preferable. For example, rosin acid, rosin acid ester, rosin acid derivative, poly (meth) acrylic acid, polyisobutylene succinic anhydride, etc. may be used. it can.

  The addition amount of the acidic additive is appropriately determined depending on the kind thereof, but is preferably 0.001 to 10% by weight, and more preferably 0.01 to 5% by weight with respect to the electrophoretic dispersion medium.

  On the other hand, as an acidic polymerizable monomer, (meth) acrylic acid, 2-butenoic acid (crotonic acid), 3-butenoic acid (vinyl acetic acid), 3-methyl-3-butenoic acid, 3-pentenoic acid, 4- Pentenoic acid, 4-methyl-4-pentenoic acid, 4-hexenoic acid, 5-hexenoic acid, 5-methyl-5-hexenoic acid, 5-heptenoic acid, 6-heptenoic acid, 6-methyl-6-heptenoic acid, 6-octenoic acid, 7-octenoic acid, 7-methyl-7-octenoic acid, 7-nonenoic acid, 8-nonenoic acid, 8-methyl-8-nonenoic acid, 8-decenoic acid, 9-decenoic acid, 3- Phenyl-2-propenoic acid (cinnamic acid), carboxymethyl (meth) acrylate, carboxyethyl (meth) acrylate, vinyl benzoic acid, vinylphenylacetic acid, vinylphenylpropionic acid, maleic acid, fumaric acid, Len succinic acid (itaconic acid), hydroxystyrene, styrene sulfonic acid, vinyl toluene sulfonic acid, vinyl sulfonic acid, sulfomethyl (meth) acrylate, 2-sulfoethyl (meth) acrylate, 2-propene-1-sulfonic acid, 2-methyl- Examples thereof include 2-propene-1-sulfonic acid and 3-butene-1-sulfonic acid.

  When a basic additive is added to a polymer chain composed of an acidic polymerizable monomer, an acid-base interaction works between these substances, and a negative charge can be imparted to the particles. In addition, by selecting the type of acidic polymerizable monomer and basic additive, and further adjusting the addition amount of the basic additive, the polymer chain having a charging function can also have a dispersing function. In such a case, the polymer chain having a dispersing function may not be grafted to the particles.

  The basic additive is preferably a basic substance that dissolves in the electrophoretic dispersion medium, such as polyisobutylene succinimide, polyvinyl pyridine, pyridine, lecithin, polyvinyl acetate, polyethylene oxide, polymethyl methacrylate, polydecyl methacrylate, Polydodecyl methacrylate, polyoctadecyl methacrylate, polyacrylamide, polyester, polyether, and the like can be used.

  The addition amount of the basic additive is appropriately determined depending on the kind thereof, but is preferably 0.001 to 10% by weight, and more preferably 0.01 to 5% by weight with respect to the electrophoretic dispersion medium.

  Fluoropolymerizable monomers include trifluoromethyl (meth) acrylate, 2,2,2-trifluoroethyl (meth) acrylate, pentafluoroethyl (meth) acrylate, heptafluoropropyl (meth) acrylate, 3,3 , 3-trifluoropropyl (meth) acrylate, nonafluorobutyl (meth) acrylate, 3,3,4,4,4-pentafluorobutyl (meth) acrylate, undecafluoropentyl (meth) acrylate, 4,4 Examples include 5,5,5-pentafluoropentyl (meth) acrylate, tridecafluorohexyl (meth) acrylate, pentadecafluoroheptyl (meth) acrylate, and the like.

  A polymer chain made of a fluorine-based polymerizable monomer can impart a negative charge to particles by having a fluorine atom having a large electronegativity.

  A polymer chain composed of a fluorine-based polymerizable monomer does not have a high affinity for an electrophoretic dispersion medium, so that a polymer chain having a dispersion function may be block-copolymerized with a fluorine-based polymer chain. preferable.

  The polymer chain to be grafted is a polymer chain whose molecular weight distribution index (weight average molecular weight / number average molecular weight) is controlled to 1.8 or less, and the molecular weight distribution index is preferably 1.5 or less Furthermore, 1.3 or less is preferable. That is, when the molecular weight distribution index of the polymer chain to be grafted exceeds 1.8, it is difficult to say that the chain length is uniform, and dispersion and chargeability of the electrophoretic particles are likely to vary. It is not preferable.

  Further, the number average molecular weight of the polymer chain may be appropriately determined depending on the dispersion function type or the charging function type, but when the polymer chain is the dispersion function type, a range of 500 to 1000000 is preferable, and 1000 to 500000 is more preferable. When the number average molecular weight of the polymer chain is less than 500, it is difficult to develop a dispersion function, and when the number average molecular weight of the polymer chain exceeds 1,000,000, the solubility in the electrophoretic dispersion medium decreases, which is not preferable.

  The graft density of the polymer chain can be controlled by the introduction rate of the nitroxide-mediated polymerization initiating group. Further, the chain length of the polymer chain can be controlled by the addition amount of the polymerizable monomer, the polymerization time, and the like.

(Pigment)
Organic pigment particles, inorganic pigment particles, and the like can be used as pigment particles that serve as core particles of the electrophoretic particles. Examples of organic pigment particles include azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, isoindoline pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, anthraquinone pigments, nitro pigments, and nitroso pigments. Specifically, red pigments such as quinacridone red, lake red, brilliant carmine, perylene red, permanent red, toluidine red, madder lake, green pigments such as diamond green lake, phthalocyanine green, pigment green B, Blue pigments such as Victoria Blue Lake, Phthalocyanine Blue, Fast Sky Blue, Hansa Yellow, Fast Yellow, Disazo Yellow, Isoindolinone Yellow, Kinoff Yellow pigments such as Ron yellow, aniline black, black pigments such as diamond black.

  Examples of inorganic pigment particles include white pigments such as titanium oxide, aluminum oxide, zinc oxide, lead oxide, tin oxide, and zinc sulfide, and black pigments such as carbon black, magnetite, manganese ferrite black, cobalt ferrite black, and titanium black. Red pigments such as cadmium red, red iron oxide and molybdenum red, green pigments such as chromium oxide, viridian, titanium cobalt green, cobalt green and victoria green, blue pigments such as ultramarine blue, Prussian blue and cobalt blue, cadmium yellow Yellow pigments such as titanium yellow, yellow iron oxide, chrome lead, chrome yellow, and antimony yellow can be used.

  The average particle diameter of the pigment particles is preferably 10 nm to 2 μm, more preferably 20 nm to 1 μm. If the average particle diameter of the pigment particles is less than 10 nm, handling is extremely lowered, which is not preferable. Further, if the average particle diameter of the pigment particles exceeds 2 μm, the coloring degree (sharpness) of the pigment particles is lowered, which is not preferable.

2. Application to an Electrophoretic Display Element An embodiment of an electrophoretic display element using electrophoretic particles of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing one embodiment of an electrophoretic display element using electrophoretic particles of the present invention.

  In the electrophoretic display element of FIG. 1A, the first substrate 1a provided with the first electrode 1c and the second substrate 1b provided with the second electrode 1d are opposed to each other at a predetermined interval through the partition wall 1g. Is arranged. An electrophoretic dispersion liquid including at least electrophoretic particles 1e and an electrophoretic dispersion medium 1f is sealed in a cell (space) including the first substrate 1a, the second substrate 1b, and the partition walls 1g. An insulating layer 1h is formed on each electrode. In the electrophoretic display element, the side on which the second substrate 1b is provided is a display surface.

  FIG. 1B shows an electrophoretic display element using microcapsules. A microcapsule 1i containing the electrophoretic dispersion is disposed on the first substrate 1a and covered with the second substrate 1b. When the microcapsule 1i is used, the insulating layer 1h may not be provided.

  In FIG. 1, the first electrode 1c is a pixel electrode that can independently apply a desired electric field to the electrophoretic dispersion liquid in each cell (or microcapsule), and the second electrode 1d has the same potential on the entire surface. This is a common electrode to be applied. This pixel electrode is provided with a switch element, a selection signal is applied to each row from a matrix drive circuit (not shown), and a control signal and an output from the drive transistor are applied to each column. A desired electric field can be applied to the electrophoretic dispersion in the cell (or microcapsule). The electrophoretic particle 1e in each cell (or microcapsule) is controlled by the electric field applied by the first electrode 1c, and each pixel has a color of the electrophoretic particle (for example, white) and a color of the dispersion medium 1f (for example, blue). ) Is displayed. By performing such driving in units of pixels, an arbitrary image or character can be displayed by a large number of pixels.

(Configuration of electrophoretic display element)
The first substrate 1a is an arbitrary insulating member that supports the electrophoretic display element, and glass, plastic, or the like can be used.

  For the first electrode 1c, a metal vapor-deposited film such as ITO (Indium Tin Oxide), tin oxide, indium oxide, gold, or chromium can be used, and a photolithography method is used for pattern formation of the first electrode 1c. be able to.

  As the second substrate 1b, an insulating member such as a transparent glass substrate or a plastic substrate can be used.

  A transparent electrode such as ITO or an organic conductive film can be used for the second electrode 1d.

  As the insulating layer 1h, a colorless and transparent insulating resin can be used. For example, acrylic resin, epoxy resin, fluorine resin, silicone resin, polyimide resin, polystyrene resin, polyalkene resin, or the like can be used.

  A polymer resin can be used as the material of the partition wall 1g. Any method may be used for forming the partition wall. For example, a method of forming a partition wall by a photolithography method using a photosensitive resin, a method of bonding a partition wall prepared in advance to a substrate, or a partition wall by a mold. A forming method or the like can be used.

  A method for filling the electrophoretic dispersion liquid in the cell is not particularly limited, but an ink jet type nozzle can be used.

(Application to microcapsule type electrophoretic display elements)
The microcapsule 1i enclosing the electrophoretic dispersion liquid can be obtained by a known method such as an interfacial polymerization method, an in situ polymerization method, or a coacervation method.

  The material forming the microcapsule 1i is preferably a material that transmits light sufficiently. Specifically, urea-formaldehyde resin, melamine-formaldehyde resin, polyester, polyurethane, polyamide, polyethylene, polystyrene, polyvinyl alcohol, gelatin, or These copolymers can be mentioned.

  Further, the method for disposing the microcapsule 1i on the first substrate 1a is not particularly limited, but an ink jet type nozzle can be used.

  For the purpose of preventing the displacement of the microcapsule 1i disposed on the substrate, the gap between the microcapsules 1i may be impregnated with a light-transmitting resin binder and fixed on the substrate. Examples of the light-transmitting resin binder include water-soluble polymers, such as polyvinyl alcohol, polyurethane, polyester, acrylic resin, and silicone resin.

  When sealing the first substrate 1a and the second substrate 1b, the microcapsule 1i is pressed down so that the length in the horizontal direction is longer than the length in the vertical direction with respect to the first substrate 1a. It is preferable to seal between the substrates (see FIG. 1B).

(Electrophoretic dispersion medium)
An example of the electrophoretic dispersion medium 1f is a highly insulating and colorless and transparent liquid. For example, aliphatic hydrocarbons such as hexane, cyclohexane, kerosene, normal paraffin, and isoparaffin can be used, and these may be used alone or in admixture of two or more.

  In order to color the electrophoretic dispersion medium 1f, an oil-soluble dye having colors such as R (red), G (green), B (blue), C (cyan), M (magenta), and Y (yellow) is used. Can do. These oil-soluble dyes include azo dyes, anthraquinone dyes, quinoline dyes, nitro dyes, nitroso dyes, penoline dyes, phthalocyanine dyes, metal complex dyes, nafur dyes, benzoquinone dyes, cyanine dyes, indigo dyes, and quinoimine dyes. Dyes are preferred, and these may be used in combination.

  For example, the following oil-soluble dyes can be mentioned. Bali First Yellow (1101, 1105, 3108, 4120), Oil Yellow (105, 107, 129, 3G, GGS), Bali First Red (1306, 1355, 2303, 3304, 3306, 3320), Oil Pink 312, Oil Scarlet 308, Oil Violet 730, Bali First Blue (1501, 1603, 1605, 1607, 2606, 2610, 3405), Oil Blue (2N, BOS, 613), Macrolex Blue RR, Sumiplast Green G, Oil Green (502 BG) and the like, and the concentration of the oil-soluble dye is preferably 0.1 to 3.5% by weight with respect to the electrophoretic dispersion medium.

(Electrophoretic dispersion)
The electrophoretic dispersion liquid contains at least electrophoretic particles 1e and an electrophoretic dispersion medium 1f. In order to charge the electrophoretic particles 1e, it is preferable to add the above-mentioned acidic additive or basic additive.

(Display example 1)
A display example of another electrophoretic display element using the electrophoretic particles 1e of the present invention is shown in FIG. FIG. 2 is a display example when the cell is filled with an electrophoretic dispersion liquid comprising white electrophoretic particles 1e and an electrophoretic dispersion medium 1f colored with a blue dye. The electrophoretic particle 1e is assumed to be negatively charged.

  When the second electrode 1d is set to 0 V and a negative voltage is applied to the first electrode 1c, the electrophoretic particles 1e gather at the second electrode 1d, and when the cell is observed from above, the distribution of the white electrophoretic particles 1e causes white (Fig. 2 (a)).

  On the other hand, when the second electrode 1d is set to 0 V and a positive voltage is applied to the first electrode 1c, the electrophoretic particles 1e gather on the first electrode 1c, and when the cell is observed from above, it looks blue (FIG. 2 ( b)).

(Another display example 2)
A display example of another electrophoretic display element using the electrophoretic particles of the present invention is shown in FIG. FIG. 3 shows a display example when a cell is filled with an electrophoretic dispersion liquid composed of positively charged white electrophoretic particles 1ew, negatively charged black electrophoretic particles 1eb, and a colorless and transparent electrophoretic dispersion medium 1f. It is.

  When the second electrode 1d is set to 0V and a negative voltage is applied to the first electrode 1c, the black electrophoretic particles gather at the second electrode 1d and the white electrophoretic particles gather at the first electrode 1c. When the cell is observed from above, it appears black due to the distribution of the black electrophoretic particles (FIG. 3A).

  On the other hand, when the second electrode 1d is set to 0 V and a positive voltage is applied to the first electrode 1c, the white electrophoretic particles 1ew collect on the second electrode 1d, and the black electrophoretic particles 1eb collect on the first electrode 1c. Therefore, when the cell is observed from above, it looks white due to the distribution of the white electrophoretic particles 1ew (FIG. 3B).

  The applied voltage varies depending on the amount of charge of the electrophoretic particles, the distance between the electrodes, and the like, but usually, several volts to several tens of volts are necessary, and gradation display can be controlled by the applied voltage and time. By performing such driving in units of pixels, an arbitrary image or character can be displayed by a large number of pixels.

3. Horizontally Moving Electrophoretic Display Element Another embodiment of the electrophoretic display element using the electrophoretic particles of the present invention will be described with reference to the drawings. FIG. 4 is a sectional view showing an embodiment of a horizontal movement type electrophoretic display element using the electrophoretic particles of the present invention.

  In the electrophoretic display element of FIG. 4A, a first electrode 4c and a second electrode 4d are provided on a first substrate 4a, and insulating layers 4h and 4i are formed between the electrodes and on the second electrode 4d, respectively. ing. The insulating layer 4h may be colored or colorless and transparent, but the insulating layer 4i is colorless and transparent. The 1st board | substrate 4a and the 2nd board | substrate 4b are arrange | positioned so that it may oppose with the predetermined space | interval through the partition 4g. An electrophoretic dispersion liquid including at least electrophoretic particles 4e and an electrophoretic dispersion medium 4f is enclosed in a cell (space) including the first substrate 4a, the second substrate 4b, and the partition walls 4g. In the electrophoretic display element, the side on which the second substrate 4b is provided is a display surface.

  FIG. 4B shows an electrophoretic display element using microcapsules. A microcapsule 4j containing the electrophoretic dispersion is disposed on the first substrate 4a and covered with the second substrate 4b. Note that when the microcapsule 4j is used, the insulating layer 4i may not be provided.

  In FIG. 4, the second electrode 4 d is a pixel electrode that can independently apply a desired electric field to the electrophoretic dispersion liquid in each cell (or microcapsule), and the first electrode 4 c is the same potential on the entire surface. This is a common electrode to be applied. This pixel electrode is provided with a switch element. A selection signal is applied to each row from a matrix drive circuit (not shown), and a control signal and an output from the drive transistor are applied to each column. A desired electric field can be applied to the electrophoretic dispersion in the cell (or microcapsule). The electrophoretic particles 4e in each cell (or microcapsule) are controlled by the electric field applied by the second electrode 4d, and each pixel has a color of the electrophoretic particles (for example, black) and a color of the insulating layer 4h (for example, white). ) Is displayed. By performing such driving in units of pixels, an arbitrary image or character can be displayed by a large number of pixels.

(Configuration of electrophoretic display element)
The first substrate 4a is an arbitrary insulating member that supports the electrophoretic display element, and glass, plastic, or the like can be used. An insulating member such as a transparent glass substrate or plastic substrate can be used for the second substrate 4b.

  As a material of the first electrode 4c, a light reflective metal electrode such as Al is used. As the insulating layer 4h formed on the first electrode 4c, a mixture of fine particles for scattering light, such as aluminum oxide and titanium oxide, in a colorless and transparent insulating resin can be used. Examples of the colorless and transparent insulating resin include the insulating resin described above. Or you may use the method of scattering light using the unevenness | corrugation of the metal electrode surface, without using microparticles | fine-particles.

  For the second electrode 4d, a conductive material that appears dark black when viewed from the viewer side of the display element, for example, titanium carbide, blackened Cr, Al, Ti, or the like having a black layer formed on the surface can be used. Further, a photolithography method can be used for pattern formation of the second electrode 4d.

  Subsequently, an insulating layer 4i is formed on the second electrode 4d. For the insulating layer 4i, the above-described colorless and transparent insulating resin can be used.

  Since the display contrast of this embodiment greatly depends on the area ratio between the second electrode 4d and the pixel, it is necessary to reduce the exposed area of the second electrode 4d with respect to that of the pixel in order to increase the contrast. It is preferably about 1: 2 to 1: 5.

  For the partition 4g, the same partition formation method and material as described above can be used. A method for filling the electrophoretic dispersion liquid in the cell is not particularly limited, but the above-described inkjet nozzle can be used.

(Application to microcapsule type electrophoretic display elements)
As described above, the microcapsule 4j enclosing the electrophoretic dispersion can be obtained by a known method such as an interfacial polymerization method, an in situ polymerization method, a coacervation method, or the like. The same polymer materials as described above can be used.

  Further, the method for disposing the microcapsules 4j on the first substrate 4a is not particularly limited, but the above-described inkjet type nozzle can be used.

  For the purpose of preventing displacement of the microcapsules 4j arranged on the substrate, the gap between the microcapsules 4j may be impregnated with a light-transmitting resin binder and fixed on the substrate as described above. As the light transmissive resin binder, the above-described resins can be used.

  When sealing the first substrate 4a and the second substrate 4b, the microcapsule 4j is pressed down so that the length in the horizontal direction is longer than the length in the vertical direction with respect to the first substrate 4a. It is preferable to seal between the substrates (see FIG. 4B).

(Electrophoretic dispersion medium)
For the electrophoretic dispersion medium 4f, the same liquid as described above can be used.

(Electrophoretic particles)
As the electrophoretic particles 4e, black particles obtained by the same method as described above can be used. The concentration of the electrophoretic particles 4e in the present embodiment varies depending on the particle diameter, but is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight with respect to the electrophoretic dispersion medium 4f. If the concentration of the electrophoretic particles 4e is less than 0.5% by weight, it is not preferable because the first electrode 4c cannot be completely hidden and the display contrast becomes light. In addition, if the concentration of the electrophoretic particles 4e exceeds 10% by weight, it overflows from the colored second electrode 4d and the display contrast deteriorates.

(Display example)
A display example of a horizontal movement type electrophoretic display element using the electrophoretic particles of the present invention is shown in FIG. FIG. 5 is a display example when the cell is filled with an electrophoretic dispersion liquid composed of black electrophoretic particles 4e and a colorless and transparent electrophoretic dispersion medium 4f. The electrophoretic particles 4e are assumed to be negatively charged. In addition, the insulating layer 4h is white and the second electrode 4d is black.

  When the first electrode 4c is set to 0 V and a positive voltage is applied to the second electrode 4d, the electrophoretic particles 4e gather on the second electrode 4d, and when the cell is observed from above, it looks white (FIG. 5A). ).

  On the other hand, when the first electrode 4c is set to 0V and a negative voltage is applied to the second electrode 4d, the electrophoretic particles 4e gather on the first electrode 4c, and when the cell is observed from above, it looks black (FIG. 5 ( b)).

  The applied voltage varies depending on the amount of charge of the electrophoretic particles, the distance between the electrodes, and the like, but usually, several volts to several tens of volts are necessary, and gradation display can be controlled by the applied voltage and time. By performing such driving in units of pixels, an arbitrary image or character can be displayed by a large number of pixels.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
Titanium oxide particles (average particle size 200 nm, containing hydroxyl groups on the particle surface) and nitroxide-mediated polymerization initiator precursor 1 (n = 10) are reacted in toluene to form nitroxide-mediated polymerization initiator groups on the surface of titanium oxide particles. Is introduced.

  Next, after dispersing titanium oxide particles into which nitroxide-mediated polymerization initiating groups are introduced in toluene, dodecyl acrylate is added, the reaction system is replaced with nitrogen gas, and nitroxide-mediated polymerization is performed at 90 ° C. for a predetermined time. In addition, as a free polymerization initiating species, a nitroxide similar to the precursor 1 of the nitroxide-mediated polymerization initiating group is previously introduced into the reaction system as an index of the molecular weight and molecular weight distribution of the polymer chain grafted onto the titanium oxide particles. Add it. After completion of the polymerization, the target electrophoretic particles are obtained through washing, purification, and drying steps.

  Since the electrophoretic particles are well dispersed in chloroform, it can be confirmed that polydecyl acrylate is grafted on the surface of the titanium oxide particles. In addition, when the molecular weight and molecular weight distribution of the polymer produced from the nitroxide added as a free polymerization starting species were measured, the number average molecular weight was about 50,000 and the molecular weight distribution index was 1.20. It can be confirmed that the polymer chains grafted to the particles are polymer chains having a uniform chain length.

  5% by weight of electrophoretic particles (white particles), 0.1% by weight of oil blue N (Aldrich), 2.5% by weight of rosin acid (acidic additive), and 92.4% by weight of ISOPAR H as an electrophoretic dispersion medium, An electrophoretic dispersion was obtained. The grafted polydecyl acrylate imparts a positive charge to the electrophoretic particles by acid-base interaction with rosin acid. Further, the grafted polydecyl acrylate exhibits a dispersion function by spreading in the electrophoretic dispersion medium.

  The electrophoretic dispersion liquid described above is injected into the cell using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG.

  When contrast display is performed for a long time at a driving voltage of ± 10 V, the electrophoretic particles are excellent in dispersibility, chargeability, and sharpness, and can display vivid blue and white.

(Example 2)
Using the electrophoretic dispersion liquid obtained in the same manner as in Example 1, microcapsules 1i enclosing the dispersion liquid are prepared by an in situ polymerization method. The membrane material of the microcapsule is urea-formaldehyde resin. The microcapsule 1i is arranged on the first substrate 1a using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG.

  When contrast display is performed for a long time at a driving voltage of ± 10 V, the electrophoretic particles are excellent in dispersibility, chargeability, and sharpness, and can display vivid blue and white.

(Example 3)
A nitroxide-mediated polymerization initiating group is introduced onto the surface of magnetite particles by reacting magnetite particles (average particle size 100 nm, containing hydroxyl groups on the particle surface) with nitroxide-mediated polymerization initiating group precursor 1 (n = 10) in toluene. To do.

  Next, after dispersing the magnetite particles introduced with the nitroxide-mediated polymerization initiating group in toluene, octadecyl acrylate is added, the reaction system is replaced with nitrogen gas, and nitroxide-mediated polymerization is performed at 90 ° C. for a predetermined time. Also, as a free polymerization initiating species, the same nitroxide as the precursor 1 of the nitroxide-mediated polymerization initiating group is added to the reaction system in advance so as to be an indicator of the molecular weight and molecular weight distribution of the polymer chain grafted onto the magnetite particles. Keep it. After completion of the polymerization, the target electrophoretic particles 4e are obtained through washing, purification, and drying steps.

  Since the electrophoretic particles 4e are well dispersed in chloroform, it can be confirmed that polyoctadecyl acrylate is grafted on the surface of the magnetite particles. The molecular weight and molecular weight distribution of the polymer produced from the nitroxide added as a free polymerization starting species were measured, and the number average molecular weight was about 80,000 and the molecular weight distribution index was 1.26. It can be confirmed that the polymer chains grafted to the particles are polymer chains having a uniform chain length.

  Electrophoretic particles 4e (black particles) 1% by weight, rosin acid (acidic additive) 0.5% by weight, and electrophoretic dispersion medium 4f using Isopar H 98.5% by weight was used as an electrophoretic dispersion. The grafted polyoctadecyl methacrylate imparts a positive charge to the electrophoretic particles 4e by an acid-base interaction with rosin acid. Further, the grafted polyoctadecyl acrylate exhibits a dispersion function by spreading in the electrophoretic dispersion medium 4f.

  The electrophoretic dispersion liquid described above is injected into the cell using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG.

  When contrast display is performed for a long time at a drive voltage of ± 10 V, the electrophoretic particles 4e are excellent in dispersibility, chargeability, and sharpness, and can perform vivid black and white display.

Example 4
Using an electrophoretic dispersion obtained in the same manner as in Example 3, microcapsules 4j enclosing the dispersion are produced by an interfacial polymerization method. The membrane material of the microcapsule is a polyamide resin. The microcapsule 4j is arranged on the first substrate 4a using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG. 4B.

  When contrast display is performed for a long time at a drive voltage of ± 10 V, the electrophoretic particles 4e are excellent in dispersibility and chargeability and can perform vivid black and white display.

(Example 5)
A nitroxide-mediated polymerization initiating group is introduced onto the surface of magnetite particles by reacting magnetite particles (average particle size 100 nm, containing hydroxyl groups on the particle surface) with nitroxide-mediated polymerization initiating group precursor 5 (n = 10) in toluene. To do.

  Next, after dispersing the magnetite particles into which nitroxide-mediated polymerization initiating groups are introduced in dimethylformamide, acrylic acid is added, the reaction system is replaced with nitrogen gas, and nitroxide-mediated polymerization is performed at 100 ° C. for a predetermined time. After the acrylic acid is consumed, isoprene is added to the reaction system to form a graft polymer chain of the block copolymer. Add so that the molar ratio of acrylic acid to isoprene is 1: 9. Further, as a free polymerization initiating species, the same nitroxide as the precursor 5 of the nitroxide-mediated polymerization initiating group is added to the reaction system in advance so as to be an indicator of the molecular weight and molecular weight distribution of the polymer chain grafted onto the magnetite particles. Keep it. After completion of the polymerization, the target electrophoretic particles 4e are obtained through washing, purification, and drying steps.

  Since the electrophoretic particles 4e are well dispersed in chloroform, it can be confirmed that the block copolymer of polymethacrylic acid and polyisoprene is grafted on the surface of the magnetite particles. Further, the molecular weight and molecular weight distribution of the polymer produced from the nitroxide added as a free polymerization starting species were measured. As a result, the number average molecular weight was about 70,000 and the molecular weight distribution index was 1.28. It can be confirmed that the polymer chain grafted to the particles is a block copolymer having a uniform chain length.

  1% by weight of electrophoretic particles 4e (black particles), 0.5% by weight of polyisobutylene succinimide (basic additive), and 98.5% by weight of Isopar H as an electrophoretic dispersion medium 4f were used as an electrophoretic dispersion. . The polyacrylic acid portion of the grafted block copolymer imparts a negative charge to the electrophoretic particles 4e due to acid-base interaction with polyisobutylene succinimide. Further, the polyisoprene portion of the grafted block copolymer has a spreading function in the electrophoretic dispersion medium 4f, thereby expressing a dispersion function.

  The electrophoretic dispersion liquid described above is injected into the cell using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG.

  When contrast display is performed for a long time at a drive voltage of ± 10 V, the electrophoretic particles 4e are excellent in dispersibility, chargeability, and sharpness, and can perform vivid black and white display.

(Example 6)
Using an electrophoretic dispersion obtained in the same manner as in Example 5, microcapsules 4j enclosing the dispersion are produced by an interfacial polymerization method. The membrane material of the microcapsule is a polyamide resin. The microcapsule 4j is arranged on the first substrate 4a using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG. 4B.

  When contrast display is performed for a long time at a drive voltage of ± 10 V, the electrophoretic particles 4e are excellent in dispersibility, chargeability, and sharpness, and can perform vivid black and white display.

(Example 7)
In the same manner as in Example 5, a nitroxide-mediated polymerization initiating group is introduced on the surface of the magnetite particles.

  Next, after dispersing the magnetite particles into which nitroxide-mediated polymerization initiating groups are introduced in dimethylformamide, aminoethyl acrylate is added, the reaction system is replaced with nitrogen gas, and nitroxide-mediated polymerization is performed at 100 ° C. for a predetermined time. . After the aminoethyl acrylate is consumed, isoprene is added to the reaction system to form a graft polymer chain of the block copolymer. Add so that the molar ratio of aminoethyl acrylate to isoprene is 1: 9. Further, as a free polymerization initiating species, the same nitroxide as the precursor 5 of the nitroxide-mediated polymerization initiating group is added to the reaction system in advance so as to be an indicator of the molecular weight and molecular weight distribution of the polymer chain grafted onto the magnetite particles. Keep it. After completion of the polymerization, the target electrophoretic particles 4e are obtained through washing, purification, and drying steps.

  Since the electrophoretic particles 4e are well dispersed in chloroform, it can be confirmed that a block copolymer of aminoethyl acrylate and polyisoprene is grafted on the surface of the magnetite particles. The molecular weight and molecular weight distribution of the polymer produced from the nitroxide added as a free polymerization starting species were measured. The number average molecular weight was about 60,000 and the molecular weight distribution index was 1.29. It can be confirmed that the polymer chain grafted to the particles is a block copolymer having a uniform chain length.

  Electrophoretic particles 4e (black particles) 1% by weight, rosin acid (acidic additive) 0.5% by weight, and electrophoretic dispersion medium 4f using Isopar H 98.5% by weight was used as an electrophoretic dispersion. The aminoethyl polyacrylate portion of the grafted block copolymer imparts a positive charge to the electrophoretic particles 4e by an acid-base interaction with rosin acid. Further, the polyisoprene portion of the grafted block copolymer has a spreading function in the electrophoretic dispersion medium 4f, thereby expressing a dispersion function.

  The electrophoretic dispersion liquid described above is injected into the cell using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG.

  When contrast display is performed for a long time at a drive voltage of ± 10 V, the electrophoretic particles 4e are excellent in dispersibility, chargeability, and sharpness, and can perform vivid black and white display.

(Example 8)
Using the electrophoretic dispersion obtained in the same manner as in Example 7, microcapsules 4j enclosing the dispersion are produced by an in situ polymerization method. The membrane material of the microcapsule is melamine-formaldehyde resin. The microcapsule 4j is arranged on the first substrate 4a using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG. 4B.

  When contrast display is performed for a long time at a drive voltage of ± 10 V, the electrophoretic particles 4e are excellent in dispersibility, chargeability, and sharpness, and can perform vivid black and white display.

Example 9
5% by weight of electrophoretic particles (white particles) obtained in the same manner as in Example 1, 2.5% by weight of rosin acid (acidic additive), and 3 electrophoretic particles (black particles) obtained in the same manner as in Example 5. % By weight, 1.5% by weight of polyisobutylene succinimide (basic additive), 88% by weight of Isopar H as an electrophoretic dispersion medium were used as an electrophoretic dispersion. In the electrophoretic dispersion medium, white electrophoretic particles are positively charged, while black electrophoretic particles are negatively charged.

  The electrophoretic dispersion liquid described above is injected into the cell using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG.

  When contrast display (FIG. 3) is performed for a long time at a drive voltage of ± 10 V, the electrophoretic particles are excellent in dispersibility, chargeability, and sharpness, and can perform vivid black and white display.

(Example 10)
Using the electrophoretic dispersion liquid obtained in the same manner as in Example 9, microcapsules 1i enclosing the dispersion liquid are prepared by an in situ polymerization method. The membrane material of the microcapsule is melamine-formaldehyde resin. The microcapsule 1i is arranged on the first substrate 1a using an inkjet nozzle, and a voltage application circuit is connected to produce the electrophoretic display element shown in FIG.

  When contrast display (FIG. 3) is performed for a long time at a drive voltage of ± 10 V, the electrophoretic particles are excellent in dispersibility, chargeability, and sharpness, and can perform vivid black and white display.

It is sectional drawing which shows the example of 1 embodiment of the electrophoretic display element using the electrophoretic particle of this invention. It is the schematic which shows the example of a display of the electrophoretic display element using the electrophoretic particle of this invention. It is the schematic which shows the example of a display of the electrophoretic display element using the electrophoretic particle of this invention. It is sectional drawing which shows the other embodiment example of the electrophoretic display element using the electrophoretic particle of this invention. It is the schematic which shows the example of a display of the electrophoretic display element using the electrophoretic particle of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a 1st board | substrate 1b 2nd board | substrate 1c 1st electrode 1d 2nd electrode 1e Electrophoretic particle 1f Electrophoretic dispersion medium 1g Partition 1h Insulating layer 1i Microcapsule 4a 1st board | substrate 4b 2nd board | substrate 4c 1st electrode 4d 2nd electrode 4e Electrophoretic particles 4f Electrophoretic dispersion medium 4g Partition walls 4h Insulating layer 4i Insulating layer 4j Microcapsules

Claims (11)

  Electrophoretic particles having polymer chains grafted on the surface of pigment particles, characterized in that the polymer chains are grafted by nitroxide-mediated polymerization from a nitroxide-mediated polymerization initiation group on the pigment particle surface. Electrophoretic particles.   2. The electrophoretic particle according to claim 1, wherein the molecular weight distribution index (weight average molecular weight / number average molecular weight) of the polymer chain is 1.8 or less.   The electrophoretic particle according to claim 1, wherein the polymer chain is a polymer having high affinity with the electrophoretic dispersion medium.   2. The electrophoretic particle according to claim 1, wherein the polymer chain is a polymer chain having a dispersion function.   The electrophoretic particle according to claim 1, wherein the polymer chain is a polymer chain having a charging function.   2. The electrophoretic particle according to claim 1, wherein the polymer chain comprises a copolymer of a polymer chain having a charging function and a polymer chain having a dispersion function.   The electrophoretic particle according to claim 6, wherein the copolymer is a block copolymer.   Filled with electrophoretic particles in which polymer chains are grafted by nitroxide-mediated polymerization from the nitroxide-mediated polymerization initiation group on the surface of the pigment particle, a dispersion medium for dispersing the electrophoretic particles, and the electrophoretic particles and the dispersion medium An electrophoretic display element having a cell formed thereon.   A method for producing electrophoretic particles, in which pigment particles having a functional group that reacts with a precursor of a nitroxide-mediated polymerization initiator group are reacted with a precursor of a nitroxide-mediated polymerization initiator group, and nitroxide-mediated polymerization is performed on the surface of the pigment particle A method for producing electrophoretic particles, comprising the steps of introducing an initiating group and then grafting a polymer chain from the living radical polymerization initiating group by nitroxide-mediated polymerization.   The method for producing electrophoretic particles according to claim 9, wherein the precursor of the nitroxide-mediated polymerization initiating group is a triethoxysilyl group, a trimethoxysilyl group, or a trichlorosilyl group. The method for producing electrophoretic particles according to claim 9, wherein the functional group that reacts with the precursor of the nitroxide-mediated polymerization initiating group is a hydroxyl group.

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