JP2011158783A - Display particle, method for producing display particle, and image display medium and image display device using display particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce degradation in image display characteristics and maintain high contrast in an image display medium even when repeatedly displaying at least three colors. <P>SOLUTION: Display particles are provided, to be used for an image display medium 1, which includes a pair of substrates 11 and 21 disposed opposing to each other, at least one of which has light transmitting property, and a display particle group 5 sealed between the substrates and having a prescribed charging polarity, and which displays an image by applying an electric field between the substrates to move the display particle group. The display particles include first display particles HB and second display particles HR having different colors from each other and having the same charging polarity, and third display particles HW having a different color and different charging polarity from the first display particles and the second display particles. Inorganic fine particles having an average particle diameter of 6 nm to 50 nm are adhered to the surfaces of the first display particles. Organic fine particles having an average particle diameter of 0.1 μm to 5 μm are adhered on the surfaces of the second display particles. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to display particles used for image display, a method for manufacturing display particles, an image display medium using the display particles, and an image display device.

  Conventionally, regarding image display media applied to electronic paper or the like, a plurality of types of display particles having different colors and charging polarities are encapsulated between a pair of substrates to which an electric field is applied, and between the substrates according to the electric field. A configuration for displaying an image by moving is known (see Patent Document 1). In this type of image display medium, as a writing method using electricity / magnetism, a wet display method (electrophoresis method or the like) in which display particles are dispersed in a solvent filled between substrates, or a gap between substrates. Dry display systems (charged toner type display system, electronic powder fluid system, etc.) in which display particles are dispersed (in air, nitrogen, argon, etc.) have been developed.

  When displaying not only a monochrome image but also a plurality of color images on the image display medium as described above, a method of selectively moving display particles of three or more colors according to the electric field applied between the substrates is considered. It is done. However, it is difficult to accurately control the movement of each display particle only by using a plurality of types of display particles having different colors that are positively or negatively charged. Therefore, for example, a plurality of types of particle groups having different colors with different adhesion forces to the substrate are enclosed in a space between a pair of translucent substrates, and selected for the plurality of types of particle groups. An image display device having an electric field generating means for applying an electric field having an intensity corresponding to a particle group to be moved is known (see Patent Document 2).

JP 2001-31225 A JP 2001-290178 A

  By the way, the display particles of the image display medium as described above are, for example, first and second display particles having at least different colors and the same charging polarity, and different colors from these first and second display particles. And a case where it is composed of third display particles having different charging polarities. In such a configuration, when a predetermined electric field is applied between the substrates with the first and second display particles adhering to the third display particles, the first and second display particles are third. Since the first display particles and the second display particles are mixed in the vicinity of the substrate surface (inner surface) when they are separated from the display particles substantially simultaneously and moved to one substrate (that is, Since the other display particles are not stacked in an orderly manner on one display particle attached to the substrate surface), it is difficult to display an appropriate color.

  In order to solve such a problem, it is not sufficient to consider the adhesion force (charge amount etc.) of the particle group to the substrate as in the conventional image display medium described in Patent Document 2 described above. It is necessary to promote separation between attached display particles.

  The present invention has been devised in view of such problems of the prior art, and facilitates separation between colored particles attached to each other, so that even when at least three or more colors are repeatedly displayed. The main object of the present invention is to provide display particles, a method for producing display particles, an image display medium using the display particles, and an image display device that are capable of maintaining a high contrast with little deterioration in image display characteristics. .

  The display particles of the present invention include a pair of substrates that are arranged so that at least one of them is translucent and a group of display particles having a predetermined charging polarity enclosed between the substrates, and an electric field is generated between the substrates. Applied to an image display medium that displays an image by moving the display particle group by applying the first display particle and the second display particle having different colors and the same charge polarity, and the first display particle The first display particles and the second display particles include third display particles having different colors and charging polarities, and inorganic fine particles having an average particle diameter of 6 nm to 50 nm are attached to the surface of the first display particles. Organic fine particles having an average particle size of 0.1 μm to 5 μm are attached to the surface of the second display particles.

  As described above, according to the present invention, when displaying an image on an image display medium, separation between colored particles attached to each other is facilitated, and even when at least three colors are repeatedly displayed, image display characteristics are deteriorated. There is an excellent effect that a high contrast can be maintained.

Schematic sectional view of an image display device according to an embodiment Schematic plan view of an image display device according to an embodiment Schematic sectional view showing one process of the display operation of the image display device Schematic sectional view showing one process of the display operation of the image display device Schematic sectional view showing one process of the display operation of the image display device Schematic sectional view showing one process of the display operation of the image display device Schematic sectional view showing one process of the display operation of the image display device Schematic sectional view showing one process (dry film laminating process) in partition formation Schematic sectional view showing one process (exposure process) in partition formation Schematic sectional view showing one process (development process) in partition formation Schematic perspective view showing the main part of a roll melt kneader Schematic plan view showing the main parts of a roll melt kneader Configuration diagram of micronization processing equipment Configuration diagram of surface modification processing equipment

  A first invention made to solve the above problems includes a pair of substrates, at least one of which is disposed facing each other, having translucency, and a display particle group having a predetermined charging polarity enclosed between the substrates. Display particles used in an image display medium for displaying an image by applying an electric field between the substrates and moving the display particle group, wherein the display particles have different colors and the same charging polarity. And second display particles, and third display particles having colors and charging polarities different from those of the first display particles and the second display particles, and an average particle size of 6 nm to 50 nm on the surface of the first display particles. The inorganic fine particles adhere to the surface of the second display particles, and organic fine particles having an average particle diameter of 0.1 μm to 5 μm adhere to the surface of the second display particles.

  According to this, when displaying an image on the image display medium, separation between the colored particles attached to each other is easy, and even when at least three or more colors are repeatedly displayed, there is little deterioration in image display characteristics and high. The contrast can be maintained.

  Further, according to a second aspect of the present invention, the first display particles are at least 200 ° C. to 300 ° C. above the softening point of the binder resin on the surface of the first colored resin particles formed from at least the binder resin and the colorant. The inorganic fine particles are fixed by treatment with hot air at a high temperature, and the second display particles are softened on the surface of the second colored resin particles formed from at least the binder resin and the colorant. It can be set as the structure by which the said organic fine particles are adhere | attached by the process using the hot air of temperature 200 to 300 degreeC higher than a point.

  According to this, the colored resin particles can be bonded to the fine particles, and fluctuations in fluidity and chargeability due to the separation of the fine particles can be suppressed, the image display operation can be stabilized and high contrast can be maintained. Is possible.

  According to a third aspect of the invention, the inorganic fine particles are made of silica or titanium oxide, and the organic fine particles are made of at least one selected from the group of styrene acrylic resin, acrylic resin, polymethyl methacrylate, and silicone resin. It can be.

  According to this, it is possible to form display particles in which fine particles are stably bonded to the colored resin particles.

  According to a fourth aspect of the present invention, the binder resin has a softening point of 90 ° C to 150 ° C, and the organic fine particles are made of a thermoplastic resin having a softening point of 150 ° C to 250 ° C, which is higher than the softening point. It can be set as the structure adhere | attached on the surface of the said colored resin particle by the process using a 130 degreeC-200 degreeC high temperature hot air.

  According to this, the melting of the organic fine particles can be appropriately progressed to more firmly fix the colored resin particles, and the occurrence of secondary aggregation between the organic fine particles and the colored resin particles can be suppressed.

  In addition, according to a fifth aspect, the colored resin particles may have a shape factor of 125 or less and a variation coefficient of the shape factor of 15 or less.

  According to this, it becomes possible to stabilize the repeated image display operation by bringing the shape of the colored resin particles closer to a true sphere.

  According to a sixth aspect of the present invention, there is provided a pair of substrates, at least one of which is disposed facing each other, having translucency, and a display particle group having a predetermined charging polarity enclosed between the substrates, and an electric field between the substrates. The display particles are used in an image display medium that displays an image by moving the display particle group by applying the first display particles, wherein the display particles have at least different colors and the same charge polarity. Display particles and second display particles, and third display particles having colors and charging polarities different from those of the first display particles and the second display particles, and the first display particles are at least bound. A step of adhering inorganic fine particles having an average particle diameter of 6 nm to 50 nm to first colored resin particles having an average particle diameter of 3 to 15 μm containing a resin and a colorant; and 200 to 300 than the softening point of the binder resin. It has a step of fixing the inorganic fine particles to the surface of the first colored resin particles by hot air at a high temperature, and the second display particles have an average particle size of 3 to 15 μm including at least a binder resin and a colorant. The step of attaching organic fine particles having an average particle size of 0.08 μm to 5 μm to the second colored resin particles and hot air at a temperature 200 to 300 ° C. higher than the softening point of the binder resin And a step of fixing the organic fine particles to the surface of the resin particles.

  A seventh invention is an image display medium having display particles according to any one of the first to fifth inventions.

  The eighth invention is an image display device comprising the image display medium according to the seventh invention and an electric field applying means for applying an electric field between substrates of the image display medium, wherein the first display The particles have a higher charge amount than the second display particles, and the electric field applying means applies an electric field having a polarity opposite to the charged polarity of the third display particles to one substrate having translucency. By displaying the color of the third display particles from the one substrate side and applying an electric field having the same polarity as the charge polarity of the third display particles to the one substrate, the charge amount is high. When the color of the first display particles is displayed from the one substrate side and an electric field having the same polarity as the charge polarity of the third display particles is applied to the one substrate, the first display particles move. A second voltage value that is smaller in absolute value than the first voltage value that can be By executing the first step to be applied and the second step to apply the first voltage value after the first step, the color of the second display particles having a low charge amount is changed from the one substrate side. The configuration is to be displayed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Configuration of image display medium>
FIG. 1 is a schematic cross-sectional view of the image display apparatus according to the present embodiment. As shown in FIG. 1, the image display device 1 includes two types of display particle groups having different colors and charging polarities in a gap 4 between a top sheet 2 and a back sheet 3 that are opposed to each other at a predetermined interval. A power supply unit (electric field application) that applies an electric field between the image display medium 10 in which 5A, 5B, and 5C (hereinafter collectively referred to as the display particle group 5) are sealed, and the top sheet 2 and the back sheet 3 are encapsulated. Means) 6 is mainly configured. The image display medium 10 is used as electronic paper or the like, and an electric field is applied between the top sheet 2 and the back sheet 3 by the power supply unit 6 having a known configuration to dispose the display particle group 5 on both sheets 2. , 3 can be displayed in a direction substantially perpendicular to the plurality of colors to display images of a plurality of colors made up of characters, figures, etc., and the image display can be held without power.

  FIG. 2 is a schematic plan view of the image display medium according to the present embodiment. As shown also in FIG. 2, between the top sheet 2 and the back sheet 3, a grid-like partition wall 7 is disposed so as to be orthogonal to each other as a member for maintaining a gap. Thus, the size of the gap 4 between the sheets 2 and 3 is kept constant. A plurality of cells 8 are defined in the gap 4 in plan view by the partition walls 7, and three types of display particle groups 5A and 5B are provided in each cell filled with gas (air, nitrogen, argon, etc.). , 5C is enclosed.

  Here, the display particle group 5A is composed of negatively charged black first display particles (hereinafter referred to as black particles) HB, and the display particle group 5B is negatively charged red second display particles (hereinafter referred to as black particle). The display particle group 5C is composed of positively charged white third display particles (hereinafter referred to as white particles) HW. The red particles have a higher charge amount (absolute value) than the black particles. That is, the image display medium 10 uses display particles composed of black particles HB, red particles HR, and white particles HW. The charge polarity (positive charge polarity or negative charge polarity) and charge amount of these display particles can be adjusted by selecting the type of charge control agent and the amount of addition thereof, as will be described later. The charge polarity and charge amount can also be adjusted by surface treatment using fine particles described later.

(Surface sheet)
As shown in FIG. 1, the surface sheet 2 is formed of a transparent substrate (polyethylene terephthalate) and a transparent substrate (indium tin oxide) formed on one side (inside) of the surface substrate 11. A plurality of strip-shaped column electrodes 12 and a dielectric film 13 formed of polycarbonate that covers and protects the column electrodes 12 and stabilizes the charging polarity of the display particle group 5. ing.

  As the surface substrate 11, for example, in addition to the above PET, a flexible sheet such as a transparent resin film or a transparent resin sheet made of polyethersulfone, polyethylene, polycarbonate, polyimide, polyethylene naphthalate, acrylic, or the like is used. It can be used suitably. Further, as the surface substrate 11, a non-flexible sheet made of an inorganic material such as glass or quartz may be used.

  The thickness of the surface substrate 11 is 1 to 10000 μm, preferably 5 to 5000 μm. When the thickness of the surface substrate 11 is less than 1 μm, it is difficult to maintain the strength of the surface sheet 2 and the uniformity of the gap 4 between the surface sheet 2 and the surface substrate 11 when the thickness exceeds 10,000 μm. In addition to the decrease, the weight increases and the size of the partition wall 7 needs to be increased, or the strength of the partition wall 7 is insufficient.

  Each column electrode 12 extends in a predetermined direction and is made of a conductive material that is transparent and can be patterned. As the conductive material, in addition to the above ITO, metals such as aluminum, gold, silver and copper, metal oxide materials such as ITO, indium oxide, zinc oxide and tin oxide, polyaniline, polypyrrole, polythiophene, etc. These conductive polymers can be used.

  Each column electrode 12 can be formed as a conductive film by vapor deposition, sputtering, coating, or the like. For example, a coated metal oxide conductive film can be patterned by screen printing with an acid etching material on an electrode substrate on which an electrode material (for example, ITO) is applied or deposited on the entire surface.

  The pattern formation of each column electrode 12 can be performed by a laser etching method, a screen printing method, a patterning method by vapor deposition using a mask, an ink jet method, or the like. The laser etching method is a method of patterning a transparent conductive film by laser processing. In the screen printing method, a screen (for example, 200 to 500 mesh) on which an opening pattern is formed is placed on a substrate to be printed, and the conductive polymer is applied only to the opening pattern portion using the opening pattern. And a paste material (electrode material) in which inorganic transparent conductive particles are dispersed is attached and printed to perform patterning. A known technique can be used as such a screen printing method. If a more detailed explanation is necessary, refer to, for example, Japanese Patent Application Laid-Open No. 2004-287011.

  The width of each column electrode 12 is preferably 30 to 5000 μm, more preferably 100 to 2000 μm. If the width of each column electrode 12 is less than 30 μm, the possibility of disconnection or the like increases, while if it exceeds 5000 μm, the size of one pixel increases and the display becomes rough. The space between adjacent column electrodes is preferably 20 to 500 μm, more preferably 40 to 300 μm. If the space between the electrodes is less than 20 μm, there is a possibility of short-circuiting with the adjacent column electrode due to variations in manufacturing accuracy. On the other hand, if it exceeds 500 μm, the area where no image is displayed becomes large and the display quality deteriorates.

  The surface resistance of the column electrode 12 is preferably 1000Ω / □ or less, and more preferably 500Ω / □ or less. If the surface resistance of the column electrode 12 exceeds 1000 Ω / □, waveform rounding occurs during rewriting of the image display, and the rewriting speed becomes slow. In addition, there is a problem that display quality is deteriorated due to a decrease in the voltage at the end of the image display unit.

  In addition to the polycarbonate, polyester, polyimide, epoxy, polyisocyanate, polyamide, polyvinyl alcohol, polybutadiene, polymethyl methacrylate, copolymerized nylon, ultraviolet curable acrylic resin, or the like can be used for the dielectric film 13.

(Back sheet)
As shown in FIG. 1, the back sheet 3 is configured in substantially the same manner as the top sheet 2. The back sheet 3 is formed on the back substrate 21 made of transparent PET, a plurality of strip-like row electrodes 22 made of transparent ITO, formed on the inside of the back substrate 21, and covers and protects the row electrodes 22. A dielectric film 23 made of polycarbonate that stabilizes the charging polarity of the particle group 5 is laminated. Each row electrode 22 extends in a direction perpendicular to the column electrode 12 and is arranged at a predetermined interval from each other.

  For the back substrate 21 and the dielectric film 23, the same materials as those for the surface substrate 11 and the dielectric film 13 of the above-described top sheet 2 can be used. Further, as the conductive material of the row electrode 22, it is not always necessary to display an image from the back substrate 21 side, and therefore, copper, aluminum, silver paste, or a material obtained by adding carbon to silver paste may be used. it can.

(Partition wall)
The partition wall 7 is provided as necessary, and is made of an insulating material such as a thermosetting resin. The shape of the partition wall 7 can be appropriately set depending on the characteristics of the display particle group 5 used. The width | variety of the partition 7 is 10-100 micrometers, Preferably it is 20-60 micrometers. Moreover, the height of the partition 7 is 20-100 micrometers, Preferably it is 30-70 micrometers.

  The partition walls 7 can be formed by using a method in which ribs are formed on each of the facing top sheet 2 and the back sheet 3 and then bonded to each other, a method in which ribs are formed only on one substrate, or the like. In the present embodiment, one cell includes a plurality of pixels, but one cell may constitute one pixel. Here, each pixel is formed in a region where each column electrode 12 and row electrode 22 intersect.

  The shape of each cell can be, for example, a square shape, a line shape, a circular shape or a hexagonal shape, depending on the shape of the partition walls 7 that define them. It can arrange | position at mesh shape. The area of the cell frame corresponding to the cross-sectional portion of the partition wall 7 as viewed from the display surface side (here, the surface sheet 2 side) should be as small as possible in order to improve the sharpness of the display image. good.

  For the formation of the partition walls 7, for example, a photoresist method, a screen printing method, a sand blast method, an additive method, or a mold transfer method can be used. Among these, a photoresist method using a resist film and a screen printing method are preferably used.

  In the photoresist method, the partition wall can be formed by the steps of attaching a dry film on one of the transparent substrate and the counter substrate, exposing to a predetermined pattern, developing, and washing. A known technique can be used as such a photoresist method. If a more detailed explanation is necessary, refer to, for example, JP-A-2005-003892. In the screen printing method, a paste serving as a partition wall material is applied and transferred onto a substrate on which the above electrode pattern is formed via a plate making made of stainless mesh or the like. This is cured by heating, ultraviolet rays or the like. Such a process is repeated until a partition wall having a desired height is formed. A known technique can be used as such a screen printing method. If a more detailed explanation is necessary, refer to, for example, JP-A-2004-341018.

  Each cell is filled with display particles such as a white display particle group 5C, a black display particle group 5A, and a red display particle group 5B, for example, in a weight ratio of 2: 1: 1 to 1: 1: 1. And mixing the particles in a desired amount through the screen and into the cell. At this time, the display particles placed on the tops of the partition walls 7 are dropped into each cell so as to be scraped off by a rubber blade. Thereafter, the front substrate 11 and the rear substrate 21 are brought into intimate contact with each other through the partition wall 7, and the two substrates are pressed and held to bond the partition wall 7 and both the substrates 11 and 21, respectively. The filling rate of the display particle group 5 with respect to each cell is preferably 20 to 70%, more preferably 30 to 70%, and still more preferably 40 to 60%.

<Configuration of display particles>
The black particles are composed of at least first colored resin particles and inorganic fine particles added to the first colored resin particles. The red particles are composed of at least second colored resin particles and organic fine particles added to the second colored resin particles. The white particles are composed of the third colored resin particles, but inorganic fine particles or organic fine particles may be externally added in the same manner as the black particles and the red particles.

The red particles can use inorganic fine particles together with organic fine particles. In that case, the fine metal oxide powder of hydrophobic silica, titanium oxide or alumina is preferable as the inorganic fine particles. In addition, the particle size of the inorganic fine particles is preferably smaller than that of the organic fine particles. The average particle size of the organic fine particles is preferably half or less than the average particle size of the colored resin particles.
(Colored resin particles)
The first colored resin particles are formed so as to include at least a binder resin as a binder and a colorant, and optionally include additives such as a charge control agent. Similarly, the second colored resin particles and the third colored resin particles are each formed at least from a binder resin as a binder and a colorant, and optionally contain an additive such as a charge control agent.

(Binder resin)
As the binder resin, for example, urethane resin, urea resin, acrylic resin, polyester resin, acrylic urethane resin, acrylic urethane silicone resin, acrylic urethane fluororesin, acrylic fluororesin, silicone resin, acrylic silicone resin, epoxy resin, polystyrene resin Styrene / acrylic resin, polyolefin resin, butyral resin, vinylidene chloride resin, melamine resin, phenol resin, fluororesin, polycarbonate resin, polysulfone resin, polyether resin, polyamide resin, etc. can be used. It can also be used as a mixture.

  In this embodiment, a polyester resin obtained by polycondensation of an alcohol component and a carboxylic acid component such as a carboxylic acid, a carboxylic acid ester, or a carboxylic acid anhydride is used as a material suitable for the binder resin.

  Here, examples of the divalent carboxylic acid or lower alkyl ester include aliphatic dibasic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, hexahydrophthalic anhydride, maleic acid, maleic anhydride, and fumaric acid. It is possible to use aliphatic unsaturated dibasic acids such as itaconic acid and citraconic acid, aromatic dibasic acids such as phthalic anhydride, phthalic acid, terephthalic acid and isophthalic acid, and methyl esters and ethyl esters thereof. it can. Of these, aromatic dibasic acids such as succinic acid, phthalic acid, terephthalic acid, and isophthalic acid, and lower alkyl esters thereof are more preferable. Further, it is more preferable to use a combination of succinic acid and terephthalic acid or phthalic acid and terephthalic acid.

  Examples of the trivalent or higher carboxylic acid component include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 2,5,7-naphthalenetricarboxylic acid. Acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexatricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarbopropane, tetra (Methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, emporic trimer acid and acid anhydrides thereof, alkyl (C1-12) ester, and the like can be used. .

  Examples of the dihydric alcohol include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, neopentyl glycol, Diols such as diethylene glycol, dipropylene glycol, bisphenol A ethylene oxide adduct, and bisphenol A propylene oxide adduct, triols such as glycerin, trimethylolpropane, and trimethylolethane, and mixtures thereof can be used.

  Examples of the trivalent or higher alcohol component include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol. 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene, etc. Can be used. For the polymerization, known polycondensation, solution polycondensation or the like can be used. Thereby, the color of favorable black-and-white and color coloring material can be expressed.

  In addition, about the usage rate of polyhydric carboxylic acid and polyhydric alcohol, it is common to make the ratio (OH / COOH) of the number of hydroxyl groups with respect to the number of carboxyl groups 0.8-1.4.

  Further, as thermoplastic binder resins, styrenes such as styrene, parachlorostyrene, α-methylstyrene, methyl acrylate, ethyl acrylate, n-propyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, etc. Acrylic monomers, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, methacrylic monomers such as 2-ethylhexyl methacrylate, acrylic acid, methacrylic acid, maleic acid, fumaric acid, etc. A homopolymer such as an unsaturated polyvalent carboxylic acid monomer having a carboxyl group as a dissociating group, a copolymer obtained by combining two or more of these monomers, or a mixture thereof can be used.

  Here, a styrene / acrylic copolymer is preferably used as the copolymer. In particular, a styrene / butyl acrylate copolymer is preferable, and those containing 75 to 90% by weight of styrene and 10 to 25% by weight of butyl acrylate are preferably used. Styrene monomers include styrene, O-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, pnbutylstyrene, p-tert-butylstyrene, p Styrene and its derivatives such as -n-hexyl styrene, pn-octyl styrene, pn-hexyl styrene and P-chlorostyrene can be used, and styrene is particularly preferable.

  Examples of the acrylic monomer include acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, acrylate-2-ethylhexyl, cyclohexyl acrylate, phenyl acrylate, methyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, ethyl β-hydroxyacrylate, propyl γ-hydroxyacrylate, butyl α-hydroxyacrylate, ethyl β-hydroxymethacrylate, propyl γ-aminoacrylate, γ-N, N-diethylaminoacrylic Acid propyl, ethylene glycol dimethacrylic acid ester, tetraethylene glycol dimethacrylic acid ester and the like can be used.

  The binder resin has a weight average molecular weight of 10,000 to 300,000 and a ratio of the weight average molecular weight to the number average molecular weight (weight average molecular weight / number average molecular weight) of 3 to 100 in terms of molecular weight by GPC (Gel permeation Chromatography). is there. The binder resin has a melting temperature (hereinafter referred to as a softening point) of 90 to 150 ° C. by a 1/2 method using a constant load extrusion capillary rheometer flow tester, an outflow start temperature of 80 to 135 ° C., and a resin glass. The transition point is in the range of 60 to 85 ° C.

  Preferably, the binder resin has a weight average molecular weight of 20,000 to 250,000, a weight average molecular weight / number average molecular weight of 3 to 50, a softening point of 95 to 140 ° C., an outflow start temperature of 85 to 125 ° C., and a glass transition point. Is in the range of 65 to 85 ° C. More preferably, the binder resin has a weight average molecular weight of 50,000 to 200,000, a weight average molecular weight / number average molecular weight of 3 to 15, a softening point of 105 to 140 ° C., an outflow start temperature of 90 to 125 ° C., and a glass transition. The point is in the range of 68-85 ° C.

  When the weight average molecular weight of the binder resin is less than 10,000, the weight average molecular weight / number average molecular weight is less than 3, the softening point is less than 90 ° C., and the outflow start temperature is less than 80 ° C., the dispersibility during kneading decreases. However, the vivid color expression is reduced. This leads to a decrease in durability of the display particles.

  When the weight average molecular weight of the binder resin is greater than 300,000, the weight average molecular weight / number average molecular weight is greater than 100, the softening point is greater than 150 ° C., or the outflow start temperature is greater than 120 ° C., the colored resin particles in the heat treatment Sphericalization becomes difficult and, for example, the interchangeability of white particles and black particles during the image display operation or the interchangeability of white particles and red particles deteriorates, leading to a decrease in contrast.

  In forming the binder resin, it is also preferable to mix two or more resins having different thermal properties (low softening or low molecular weight resin particles, high softening or high molecular weight resin particles) as follows.

  In the case of low softening or low molecular weight resin particles, the weight average molecular weight is 10,000 to 60,000, the ratio of the weight average molecular weight to the number average molecular weight (weight average molecular weight / number average molecular weight) is 1.5 to 6, and the softening point is 90. -140 degreeC, outflow start temperature shall be 80-120 degreeC, and glass transition point shall be the range of 65-90 degreeC. Preferably, the weight average molecular weight is 20,000 to 50,000, the weight average molecular weight / number average molecular weight is 1.5 to 3.9, the softening point is 95 to 135 ° C., the outflow start temperature is 85 to 115 ° C., and the glass transition point is The range is 68 to 88 ° C. More preferably, the weight average molecular weight is 20,000 to 45,000, the weight average molecular weight / number average molecular weight is 1.5 to 3, the softening point is 100 to 130 ° C., the outflow start temperature is 90 to 110 ° C., and the glass transition point. Is in the range of 70 to 88 ° C.

  The purpose of blending the low softening or low molecular weight resin particles is to ensure the sphericity of the colored resin particles and to promote the melting and fixing of the organic fine particles. The weight average molecular weight is less than 10,000, the weight average molecular weight / number average molecular weight is less than 1.5, the softening point is less than 90 ° C., the outflow start temperature is less than 80 ° C., and the glass transition point is 65 ° C. If it is smaller than that, secondary agglomeration tends to occur in the heat treatment for spheroidization, and the particle size tends to increase. On the other hand, the weight average molecular weight is greater than 60,000, the weight average molecular weight / number average molecular weight is greater than 6, the softening point is greater than 140 ° C., the outflow start temperature is greater than 120 ° C., and the glass transition point is 90 ° C. If it is larger than the range, the spheroidization tends to hardly progress in the heat treatment for spheroidization.

  Further, relatively high softening or high molecular weight resin particles have a weight average molecular weight of 50,000 to 500,000, a ratio of weight average molecular weight to number average molecular weight (weight average molecular weight / number average molecular weight) of 2 to 10, softening The point is 140 to 180 ° C, the outflow start temperature is 110 to 160 ° C, and the glass transition point is 55 to 85 ° C. Preferably, the weight average molecular weight is 80,000 to 480,000, the weight average molecular weight / number average molecular weight is 2 to 7, the softening point is 145 to 180 ° C, the outflow start temperature is 115 to 155 ° C, and the glass transition point is 55 to 80 ° C. The range. More preferably, the weight average molecular weight is 100,000 to 450,000, the weight average molecular weight / number average molecular weight is 2 to 5, the softening point is 150 to 180 ° C, the outflow start temperature is 120 to 150 ° C, and the glass transition point is 55 to 70. The range is ° C.

  The purpose of blending the high softening or high molecular weight resin particles is to maintain durability for maintaining stable and repeatable display characteristics of the display particles. That is, it is for improving the durability with respect to collision between particles, a board | substrate, and a partition. It is also for making the dispersibility of the additive uniform in the melt-kneading process and stabilizing high chargeability.

  The weight average molecular weight is less than 50,000, the weight average molecular weight / number average molecular weight is less than 2, the softening point is less than 140 ° C., the outflow start temperature is less than 110 ° C., or the glass transition point is from 55 ° C. If it is too small, the durability for maintaining the repeated display characteristics tends to decrease.

  The weight average molecular weight is greater than 500,000, the weight average molecular weight / number average molecular weight is greater than 10, the softening point is greater than 180 ° C, the outflow start temperature is greater than 160 ° C, or the glass transition point is greater than 85 ° C. Is too large, the spheroidization tends to hardly progress in the heat treatment for spheroidization. Moreover, the smoothness of the colored resin particle surface is inferior, and unevenness tends to remain on the surface.

  The blending ratio of the low softening or low molecular weight resin particles to the high softening or high molecular weight resin particles is in the range of 5: 5 to 9: 1. This is to ensure a good balance between the durability and the progress of spheroidization. Preferably, the range is 6: 4 to 9: 1. More preferably, the range is 7: 3 to 9: 1.

(Coloring agent)
As the colorant, various organic or inorganic pigments and dyes as shown below can be used.

  As the black colorant, particles containing organic or inorganic dye / pigment black pigments such as carbon black, aniline black, manganese ferrite black, titanium black, magnetic powder, oil black and the like can be used.

  Here, the DBP oil absorption (ml / 100 g) of carbon black is preferably 45 to 70. Specifically, for example, # 52 (particle size 27 nm, DBP oil absorption 63 ml / 100 g), # 50 (28 nm, 65 ml / 100 g), # 47 (23 nm, 64 ml / 100 g) manufactured by Mitsubishi Chemical Co., Ltd. , # 45 (24 nm, 53 ml / 100 g), # 45 L (24 nm, 45 ml / 100 g), REGAL250R (35 nm, 46 ml / 100 g), REGAL330R (25 nm, 65 ml / 100 g) manufactured by Cabot. ), MOGULL (24 nm, 60 ml / 100 g). More preferably, # 45, # 45L, and REGAL250R are used. By using carbon black having a relatively low DBP oil absorption, there is an effect of obtaining high contrast. This is considered to be an effect due to dispersibility and colorability in the resin.

  The DBP oil absorption is a quantitative representation of the chain assembly state (structure) of the particles, and is expressed by a primary structure by chemical bonding and a secondary structure by physical bonding by van der Waals force.

DBP oil absorption (JISK6217) was measured by putting 20 g (Ag) of sample dried at 150 ° C. ± 1 ° C. for 1 hour into a mixing chamber of an absorber meter (manufactured by Brabender, spring tension 2.68 kg / cm), After setting the limit switch to about 70% of the maximum torque in advance, the mixer is rotated. At the same time, DBP (specific gravity 1.045 to 1.050 g / cm ³ ) is added from the automatic burette at a rate of 4 ml / min. As the end point is approached, the torque increases rapidly and the limit switch is turned off. The DBP oil absorption (= Bx100 / A) (ml / 100 g) per 100 g of the sample is determined from the DBP amount (Bml) added so far and the sample weight.

  In addition, the arithmetic mean diameter by a SEM electron microscope is used for a particle size. The particle size of carbon black is preferably 20 to 40 nm, more preferably 20 to 35 nm. If the particle size is larger than the preferred range, the coloring power tends to decrease. Moreover, when the particle diameter is smaller than the preferred range, dispersion in the resin tends to be difficult.

  Examples of blue colorants include C.I. I. Pigment blue 15: 3, C.I. I. Pigment Blue 15, Bituminous Blue, Phthalocyanine Blue, Metal-free Phthalocyanine Blue, First Sky Blue, Indanthrene Blue BC and the like can be used. The addition amount is preferably 3 to 12 parts by weight with respect to 100 parts by weight of the binder resin.

  Red colorants include brilliant carmine 6B, eosin lake, rhodamine lake B, brilliant carmine 3B, C.I. I. Red pigments such as CI Pigment Red 48, 49: 1, 53: 1, 57, 57: 1, 81, 122, 5; I. Red dyes such as Solvent Red 49, 52, 58, 8 can be used.

  Examples of yellow colorants include naphthol yellow S, benzidine yellow G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, C.I. I. Acetoacetic acid arylamide monoazo yellow pigments such as C.I. Pigment Yellow 1, 3, 74, 97 or 98; I. Acetoacetic acid arylamide disazo yellow pigments such as C.I. Pigment Yellow 12, 13, 14, and 17; I. Solven Yellow 19, 77, 79 or C.I. I. Disperse Yellow 164 is blended, and C.I. I. Benzimidazolone pigments of CI Pigment Yellow 93, 180 and 185 are preferred.

  As the white colorant, particles containing white pigments such as zinc oxide, tin oxide, rutile type titanium oxide, anatase type titanium oxide, lead white, zinc sulfide, aluminum oxide, silicon oxide and zirconium oxide can be used.

  The above pigments and inorganic additives can be used alone or in combination. Carbon black is particularly preferable as the black pigment, and titanium oxide is particularly preferable as the white pigment.

(Charge control agent)
Examples of the negative charge control agent include salicylic acid metal complexes, metal-containing azo dyes, metal-containing oil-soluble dyes (including metal ions and metal atoms), calixarene compounds, boron-containing compounds (for example, benzyl acid boron complexes), Nitroimidazole derivatives, acrylic sulfonic acid polymers (vinyl copolymers of styrene monomers and acrylic acid monomers having a sulfonic acid group as a polar group, particularly preferably a copolymer of acrylamido-2-methylpropane sulfonic acid) Polymer) and the like.

  In the salicylic acid metal complex, the functional group bonded to the benzene ring is preferably independently a hydrogen atom, a linear or molecular chain alkyl group having 1 to 10 carbon atoms, or an aryl group, a methyl group, an ethyl group, n- A propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, or the like can be used. Moreover, as a metal, zinc, nickel, cobalt, copper, and chromium can be used, and zinc and chromium are particularly preferable.

  As the metal salt of the benzylic acid derivative, lithium, sodium, potassium, or the like can be used as the alkali metal, and potassium is particularly preferable.

  On the other hand, as the positive charge control agent, for example, a nigrosine dye, a triphenylmethane compound, a quaternary ammonium salt compound, a polyamine resin, an imidazole derivative, or the like can be used.

  The addition amount of the charge control agent is 0.5 to 8 parts by weight, preferably 1 to 6 parts by weight, and more preferably 2 to 5 parts by weight with respect to 100 parts by weight of the binder resin. When the addition amount of the charge control agent is less than 0.5 parts by weight, the charging effect is lost. On the other hand, when the addition amount exceeds 8 parts by weight, the charge amount becomes excessively high and tends to be overcharged.

(Inorganic fine particles)
Examples of inorganic fine particles used for display particles include fine metal oxide powders such as silica, alumina, titanium oxide, zirconia, magnesia, ferrite, and magnetite, and titanates such as barium titanate, calcium titanate, and strontium titanate. Alternatively, a zirconate salt such as barium zirconate, calcium zirconate or strontium zirconate, or a mixture thereof can be used.

  The inorganic fine particles are hydrophobized as necessary. Examples of silicone oil-based materials include dimethyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, epoxy-modified silicone oil, carboxyl-modified silicone oil, methacryl-modified silicone oil, alkyl-modified silicone oil, fluorine-modified silicone oil, amino An external additive that is treated with at least one of silicone oil-based materials consisting of modified silicone oil and chlorophenyl-modified silicone oil is preferably used. For example, SH200, SH510, SF230, SH203, BY16-823 or BY16-855B manufactured by Toray Dow Corning Silicone can be used.

  For the hydrophobization treatment, inorganic fine particles and silicone oil-based materials are mixed with a mixer such as a Henschel mixer (FM20B manufactured by Mitsui Mining Co., Ltd.), silicone oil-based materials are sprayed onto the inorganic fine particles, For example, a method in which a silicone oil-based material is dissolved or dispersed and then mixed with inorganic fine particles, and then the solvent is removed to prepare the material can be used. The silicone oil-based material is preferably blended in an amount of 1 to 20 parts by weight with respect to 100 parts by weight of the inorganic fine particles.

  The inorganic fine particles are preferably treated with a silicone oil-based material after silane coupling treatment. As silane coupling agents, dimethyldichlorosilane, trimethylchlorosilane, allyldimethylchlorosilane, hexamethyldisilazane, allylphenyldichlorosilane, benzylmethylchlorosilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, Vinyltriacetoxysilane, divinylchlorosilane, dimethylvinylchlorosilane, or the like can be suitably used. The silane coupling treatment is a dry process in which a vaporized silane coupling agent is reacted with a cloud of inorganic fine particles by stirring or the like, or a wet method in which a silane coupling agent in which inorganic fine particles are dispersed in a solvent is dropped. Etc. can be performed.

  The inorganic fine particles having positive chargeability are treated with aminosilane, amino-modified silicone oil or epoxy-modified silicone oil. Moreover, in order to improve hydrophobic treatment, the combined use of treatment with hexamethyldisilazane, dimethyldichlorosilane, or other silicone oil is also preferable. For example, it is preferable to treat with at least one of dimethyl silicone oil, methylphenyl silicone oil, and alkyl-modified silicone oil.

  It is also preferable to treat the surface of the external additive with one or more selected from the group of fatty acid esters, fatty acid amides, fatty acids and fatty acid metal salts (hereinafter referred to as fatty acids and the like). In this case, surface-treated silica or titanium oxide fine powder is more preferable.

  Examples of fatty acid esters include esters comprising higher alcohols having 16 to 24 carbon atoms and higher fatty acids having 16 to 24 carbon atoms such as stearyl stearate, palmityl palmitate, behenyl behenate or stearyl montanate, and butyl stearate. , Esters of higher fatty acids having 16 to 24 carbon atoms and lower monoalcohols such as isobutyl behenate, propyl montanate or 2-ethylhexyl oleate, or fatty acid pentaerythritol monoester, fatty acid pentaerythritol triester, or fatty acid triester Methylolpropane ester and the like are preferable.

  Examples of the fatty acid amide include 16 to 24 carbon atoms such as palmitic acid amide, palmitoleic acid amide, stearic acid amide, oleic acid amide, arachidic acid amide, eicosenoic acid amide, behenic acid amide, erucic acid amide, or ligrinoselic acid amide. Saturated or monovalent unsaturated aliphatic amides are preferred.

  Examples of the fatty acid or fatty acid metal salt include caprylic acid, capric acid, undecylic acid, lauric acid, myristylic acid, parimitic acid, stearic acid, behenic acid, montanic acid, laccellic acid, oleic acid, erucic acid, sorbic acid or linoleic acid. An acid or the like can be used. Of these, fatty acids having 12 to 22 carbon atoms are preferred.

Moreover, as a metal which comprises a fatty-acid metal salt, aluminum, zinc, calcium, magnesium, lithium, sodium, lead, or barium is mentioned, for example, Among these, aluminum, zinc, or sodium is preferable. More preferably, aluminum distearate (Al (OH) (C ₁₇ H ₃₅ COO) ₂ ) or aluminum monostearate (Al (OH) ₂ (C ₁₇ H ₃₅ COO)), etc. Aluminum is mentioned. By having an OH group, overcharging can be prevented and transfer defects can be suppressed. Moreover, the processability with inorganic fine particles is also improved.

  Furthermore, materials such as polyhydroxy alcohol fatty acid esters such as hydroxystearic acid derivatives, glycerin fatty acid esters, glycol fatty acid esters or sorbitan fatty acid esters are preferable for the surface treatment, and these may be used alone or in combination of two or more. Is possible.

  As a preferred form of the surface treatment, the surface of the inorganic fine particles to be treated may be treated with a coupling agent and / or a polysiloxane such as silicone oil and then treated with a fatty acid or the like. As a result, it is possible to perform a more uniform treatment than when the fatty acid of the hydrophilic silica is simply treated, the display particles can be highly charged, and the fluidity is improved. In addition, the same effect can be obtained with a configuration in which a fatty acid or the like is treated together with a coupling agent and / or silicone oil.

  In the surface treatment, a fatty acid or the like is dissolved in a hydrocarbon-based organic solvent such as toluene, xylene or hexane, and it is mixed with inorganic fine particles such as silica, titanium oxide, alumina, etc. by wet mixing, and the treatment agent is added to the surface of the inorganic fine particles. It is carried out by adhering to. Thereafter, the solvent is distilled off and a drying treatment is performed to produce surface-treated inorganic fine particles.

  In this case, the mixing ratio of polysiloxane and fatty acid is preferably 1: 2 to 20: 1. Moreover, the ignition loss of the inorganic fine particles whose surface is treated with a fatty acid or the like is preferably 1.5 to 25% by weight, more preferably 5 to 25% by weight, and further preferably 8 to 20% by weight.

  The inorganic fine particles are preferably metal oxide fine powders such as hydrophobic silica, titanium oxide or alumina. The inorganic fine particles have an average particle size of 6 to 50 nm, and 0.5 to 6 parts by weight are added to 100 parts by weight of the colored resin particles. The average particle diameter of the inorganic fine particles is preferably 6 to 40 nm, more preferably 6 to 20 nm. When the average particle diameter of the inorganic fine particles is less than 6 nm, the crushing becomes difficult and the separation between the black particles and the red particles adhering to each other deteriorates. On the other hand, if the average particle diameter exceeds 50 nm, it is difficult to improve the powder fluidity of the display particles and the contrast of three-color display is not improved. Moreover, if the addition amount of the inorganic fine particles is less than 0.5 parts by weight, it is difficult to improve the fluidity. On the other hand, when the addition amount exceeds 6 parts by weight, floating particles of inorganic fine particles are likely to be generated.

  The average particle diameter is a value obtained by taking an enlarged photograph with an SEM (scanning electron microscope) and obtaining an average value of major and minor axes of about 100 particles.

For ignition loss, about 1 g of a sample is placed in a magnetic crucible that has been dried, allowed to cool, and precisely weighed in advance, and weighed accurately. Ignite for 2 hours in an electric furnace set to 500 ° C. After standing to cool in a desiccator for 1 hour, its weight is precisely weighed and calculated from the following formula.
Loss on ignition (% by weight) = [Loss on ignition (g) / Sample amount (g)] × 100

  Further, the moisture absorption amount of the treated external additive is preferably 1% by weight or less. Preferably it is 0.5 weight% or less, More preferably, it is 0.1 weight% or less, More preferably, it is 0.05 weight% or less. When the moisture adsorption amount is more than 1% by weight, the chargeability and filming resistance are lowered. The moisture adsorption amount was measured with a continuous vapor adsorption apparatus (BELSORP18: Nippon Bell Co., Ltd.).

The degree of hydrophobicity is determined by methanol titration, weighing 0.2 g of the product to be tested in 50 ml of distilled water charged in a 250 ml beaker. At the tip, methanol is dropped from a burette immersed in the liquid until the total amount of the external additive is wet. In that case, it stirs slowly slowly with an electromagnetic stirrer. The degree of hydrophobicity is calculated by the following equation from the amount of methanol a (ml) essential for complete wetting.
Hydrophobic degree = (a / (50 + a)) × 100 (%)

(Organic fine particles)
As the organic fine particles used for the display particles, polyolefin fine particles such as polyethylene and polypropylene, styrene acrylic resin fine particles, acrylic resin fine particles, polymethyl methacrylate fine particles, or silicone resin fine particles can be suitably used. Further, as the organic fine particles, fine particles having a low dynamic friction coefficient such as fluorinated or trifluorinated resin fine particles, melamine fine particles, polymethyl methacrylate fine particles, polystyrene fine particles, polyacetal fine particles, and the like are preferable. The organic fine particles are fine particles having a dynamic friction coefficient of 0.3 or less, and the dynamic friction coefficient can be measured according to JIS K 7125.

  The organic fine particles are preferably a thermoplastic resin having a softening point of 150 to 250 ° C. Moreover, it is preferable that a glass transition point is 85-120 degreeC. More preferably, the organic fine particles have a softening point of 170 to 220 ° C and a glass transition point of 90 to 115 ° C, more preferably a softening point of 185 to 200 ° C and a glass transition point of 95 to 110 ° C.

  The organic fine particles have an average particle size of 0.1 to 5 μm, and 0.5 to 6 parts by weight are added to 100 parts by weight of the colored resin particles. The average particle size is preferably 0.2 to 1 μm. When the average particle size is less than 0.1 μm, the separation between the black particles and the red particles adhering to each other does not proceed smoothly, and it becomes difficult to obtain the effect of improving the contrast. On the other hand, when the average particle diameter exceeds 5 μm, it is difficult to improve the powder fluidity of the display particles. On the other hand, when the addition amount of the organic fine particles is less than 0.5 parts by weight, the separation between the black particles and the red particles adhering to each other does not proceed smoothly and it becomes difficult to obtain the effect of improving the contrast. On the other hand, when the addition amount of the organic fine particles exceeds 6 parts by weight, floating particles of the organic fine particles are easily generated.

(Physical properties of display particles)
Each display particle preferably has a volume average particle diameter of 3 to 15 μm and a volume-based variation coefficient of 10 to 20%. More preferably, the display particles have a volume average particle size of 5 to 10 μm and a volume-based variation coefficient of 10 to 18%, and more preferably a volume average particle size of 6 to 9 μm and a volume-based variation coefficient of 10. ~ 16%.

  Here, the variation coefficient is obtained by dividing the standard deviation in the particle size distribution of the display particles by the average particle size, and represents the extent of the particle size distribution. The particle size was measured using a Coulter counter (Coulter). If the variation coefficient of the volume particle size distribution is less than 10%, production becomes difficult, which causes a cost increase. On the other hand, if the coefficient of variation of the volume particle size distribution exceeds 20%, the particle size distribution becomes broad and the contrast tends not to be improved.

  Further, the shape factor (SF) of the colored resin particles is preferably 125 or less, and the variation coefficient of the shape factor is preferably 15% or less.

  This is because the colored resin particles are processed into a spherical shape or a more spherical shape to stabilize repeated display characteristics, and organic fine particles with a small radius of curvature are attached to the surface of the colored resin particles. The purpose is to reduce the presence of particles that increase the BET specific surface area of the particles and stick to the partition walls and become inoperable.

  In this case, by setting the shape factor to 125 or less, the shape of the colored resin particles becomes closer to a sphere, and it is possible to stabilize the repeated display characteristics. For the shape factor, a real surface view microscope (VE7800) manufactured by Keyence Corporation was used, about 100 toner base particles magnified 1000 times were taken, the maximum length and the projected area were measured, and the following (formula 1) Determined (d: maximum long axis length of colored resin particles, A: projected area of colored resin particles).

Shape factor (SF) = π × d ² / (4 × A) × 100 (Equation 1)

  Further, when the measured BET specific surface area of the display particles is BTr and the specific surface area value calculated from the particle size distribution of the display particles is BSr, BTr / BSr is preferably 2.5 to 10.

  By specifying the specific surface area ratio (BTr / BSr), the state of adhesion of the organic fine particles to the surface of the colored resin particles can be quantified. When the specific surface area ratio is less than 2.5, the contact between the display particles and the partition walls is so dominated by so-called point contact to surface contact, and it is easy to stick to the partition walls. In addition, the charge retention is also reduced. On the other hand, when the specific surface area ratio exceeds 10, it is assumed that the fine particles are not adhered to the surface of the colored resin particles, or the surface of the display particles is too rough, and the contrast in display characteristics tends to be lowered.

  The specific surface area measured value (BTr) was measured using Flowsorb II2300 manufactured by Shimadzu Corporation. The calculated specific surface area (BSr) was calculated from BSr = 6 / (ρ · r). Here, ρ is the true specific gravity of the display particles, and r is the volume particle diameter of the display particles.

  That is, by satisfying the relationship of the following (Expression 2) and (Expression 3), more preferably, by satisfying the relationship of (Expression 4) and (Expression 5), more preferably, (Expression 6) and (Expression 7). ), The above-described characteristics can be achieved with good reproducibility.

100 ≦ SF ≦ 125 (Equation 2)
2.5 ≦ BTr / BSr ≦ 10 (Expression 3)

100 ≦ SF ≦ 122 (Equation 4)
3 ≦ BTr / BSr ≦ 8 (Formula 5)

100 ≦ SF ≦ 118 (6)
5 ≦ BTr / BSr ≦ 8 (Expression 7)

  The particle size distribution of the colored resin particles is measured by using a Coulter Counter TA-II type (Coulter Counter Co., Ltd.) and connecting an interface (manufactured by Nikkiki) that outputs the number distribution and volume distribution and a personal computer. A known method can be used for the measurement of the particle size distribution. If a more detailed explanation is necessary, refer to JP-A-2005-284269.

  By narrowing the particle size distribution of the display particles and making the shape more spherical, the powder fluidity increases. In addition, making the particle size and amount of the external additive appropriate also determines the fluidity. For example, when the particle size of the external additive is small, the degree of compression is small and the powder fluidity is high. The degree of compression is preferably 5 to 40%. More preferably, it is 10 to 30%. It is well known to use a powder tester manufactured by Hosokawa Micron Corporation for the measurement of static bulk density and dynamic bulk density. Here, the degree of compression is one of the indicators of the fluidity of the display particles, and is calculated from the static bulk density and the dynamic bulk density.

  The molecular weight of the resin is a value measured by gel permeation chromatography (GPC) using several types of monodisperse polystyrene as a standard sample. The measuring device is HLC8120GPC series manufactured by Tosoh Corporation, the column is TSKgel superHM-H H4000 / H3000 / H2000 (6.0 mm ID-150 mm × 3), eluent THF (tetrahydrofuran), flow rate 0.6 mL / min, sample concentration 0.1%, injection amount 20 μL, detector RI, measurement temperature 40 ° C. As a pretreatment for measurement, the sample is dissolved in THF and allowed to stand overnight, and then filtered through a 0.45 μm membrane filter to measure a resin component from which an additive such as silica has been removed. The measurement conditions are conditions in which the molecular weight distribution of the target sample is included in a range in which the logarithm of the molecular weight and the count number are linear in a calibration curve obtained with several types of monodisperse polystyrene standard samples.

  The softening points of the binder resin and the organic fine particles are measured by a constant load extrusion type capillary rheometer flow tester (CFT500) manufactured by Shimadzu Corporation. A known method can be used to measure the softening point. If a more detailed explanation is necessary, refer to JP 2009-077554. From the flow curve in this known method, the outflow start temperature (Tfb) described later and the melting temperature (softening point Tm ° C.) in the 1/2 method are defined.

  The glass transition point of the binder resin and organic fine particles is measured with a differential scanning calorimeter (TA Instruments, Q100 type (a genuine electric refrigerator is used for cooling)). A known method can be used for measuring the glass transition point. If a more detailed explanation is necessary, refer to JP 2009-077554.

<Method for producing display particles>
In producing the colored resin particles, the binder resin and the colorant and, if necessary, an additive such as a charge control agent are uniformly mixed and dispersed by a mixer equipped with a stirring blade. As the mixer, a known mixer such as a super mixer (manufactured by Kawada Manufacturing Co., Ltd.), a Henschel mixer (manufactured by Mitsui Miike Kogyo Co., Ltd.), a PS mixer (manufactured by Shinko Pantech Co., Ltd.) or a Ladige mixer can be used.

(Melt kneading process)
Next, in the melt-kneading process, the binder resin in the mixture is melted by a heating action or a shearing action, and the additive is dispersed in the binder resin. For the melt-kneading treatment, a split segment type twin-screw kneading extruder in which a cylinder and a kneading shaft are divided into a plurality of segments can be suitably used. An example is a kneading extruder (trade name PCM30) manufactured by Ikegai.

  For the melt-kneading treatment, a two-roll kneader that melts and kneads the material between two rotating rolls can also be suitably used. For example, a two-roll kneader (trade name KNEADEX140-800) manufactured by Mitsui Mining Co., Ltd. may be mentioned. The melt-kneading process using the two-roll kneader can be performed in the same manner as the known toner melt-kneading process. If a more detailed explanation is necessary, refer to Japanese Patent Application Laid-Open No. 2004-013049.

  In the melt-kneading process using a two-roll kneader, the surface temperature of the roll to be heated is set lower than the softening point of the binder resin. More specifically, it is necessary to lower the surface temperature of the roll by 10 ° C. or more than the softening point of the binder resin. When the temperature is increased in order to quickly melt the resin and wrap it around the roll when the material is charged (that is, the difference between the resin softening point and the roll surface temperature is less than 10 ° C.), shear force is applied during kneading. This is because non-uniform dispersion occurs. On the other hand, if the temperature difference exceeds 70 ° C., the resin is transported without being completely melted, which also causes a decrease in dispersibility. Further, by setting the temperature difference between the two rolls to be equal to or higher than half the glass transition point of the resin, ultrahigh molecular weight molecular cutting during kneading can be kneaded and dispersed in an appropriate state, and contrast can be increased. It is possible to achieve both improvement of the above and improvement of repeatability. Furthermore, by providing a temperature gradient between the first half and the second half of one roll and setting the temperature difference to be 40 ° C. lower than the glass transition point of the resin, an effect of improving display characteristics can be obtained.

(Crushing process)
The kneaded mass obtained by cooling by melt kneading is coarsely pulverized with a cutter mill or the like, and then jet mill pulverized (for example, trade name IDS pulverizer, Nippon Pneumatic Industry) or rotated with respect to a fixed stator. Finely pulverized by rotating rotor type pulverization (for example, trade name kryptron pulverizer, Kawasaki Heavy Industries) that pulverizes by putting the material to be pulverized into a minute gap with the roller to be used, and further, if necessary, an airflow classifier Colored resin particles having a desired particle size distribution can be obtained by (for example, trade name Elbow Jet Classifier, manufactured by Nippon Steel Mining Co., Ltd.).
(Emulsion aggregation method)

  In producing colored resin particles, an emulsion aggregation method can be used as a suitable alternative method. In the emulsion aggregation method, first, a dispersion obtained by dispersing resin particles of a vinyl monomer homopolymer or copolymer (vinyl resin) in an ionic surfactant is prepared, and then a polymerization initiator or Using a chain transfer agent, emulsion polymerization is performed to prepare a resin particle dispersion having a fine particle size. Further, a colorant particle dispersion is prepared by adding colorant particles in water to which a polar surfactant is added and dispersing the particles using a known dispersing means. .

  Then, in the aqueous medium, at least the resin particle dispersion in which the resin particles are dispersed and the colorant particle dispersion in which the colorant particles are dispersed are mixed, and the pH of the aqueous medium is set to a certain value (for example, pH 8 to 13), and in the presence of an inorganic salt, colored resin particles can be generated by heating the temperature of the aqueous medium to a temperature equal to or higher than the glass transition point of the resin particles for a certain time (1 to 5 hours). it can.

  Also, a resin particle dispersion containing an ionic surfactant and a colorant particle dispersion are prepared, mixed, and agglomerated by an ionic surfactant having a polarity opposite to that of the ionic surfactant. Then, the aggregated particles can be formed by forming the resin particles, and then heated to a temperature equal to or higher than the glass transition point of the resin particles to fuse the aggregated particles, and the colored resin particles can be produced by washing and drying.

(Suspension polymerization method)
Furthermore, in the production of colored resin particles, a suspension polymerization method can be used as a suitable alternative method. This suspension polymerization method can be carried out in the same manner as a known method for producing a small particle toner. If a more detailed explanation is necessary, refer to Japanese Patent Application Laid-Open No. 2004-191598.

(Fixed fine particles)
Colored resin particles formed in a desired particle size distribution and at least inorganic fine particles having an average particle diameter of 6 to 50 nm or organic fine particles having an average particle diameter of 0.1 to 5 μm are mixed to form fine particles (inorganic fine particles or organic fine particles). Is attached to the surface of the colored resin particles. Thereafter, the colored resin particles to which the fine particles are adhered are put into hot air, thereby fixing the fine particles to the colored resin particles whose surface is melted by heat. The average particle diameter of the colored resin particles is preferably 3 to 15 μm. The average particle size of the organic fine particles is preferably half or less than the average particle size of the colored resin particles.

  For mixing the colored resin particles and the fine particles, a known mixer such as the Henschel mixer or the supermixer described above is used. When mixing the colored resin particles and the fine particles, it is preferable to add and mix the fine particles and the colored resin particles into a mixer at the same time, and then add the colored resin particles to which the fine particles are adhered to hot air.

  The surface treatment using hot air is preferably performed with hot air having a temperature 200 to 300 ° C. higher than the softening point (° C.) of the binder resin (that is, a range of 290 to 450 ° C.). More preferably, the temperature is 220 to 300 ° C. higher than the softening point of the binder resin, and more preferably 250 to 300 ° C. higher than the softening point of the binder resin. The colored resin particles to which the fine particles are attached are in contact with hot air for several milliseconds, and the colored resin particles and the fine particles are melt-fixed by processing at a temperature 200 ° C. or higher than the softening point of the binder resin. Can be sufficiently performed, and spheroidization can proceed. On the other hand, when the treatment is performed at a high temperature exceeding the range of 300 ° C. from the softening point of the binder resin, the secondary aggregation of the colored resin particles occurs frequently, the particles become coarse and the particle size distribution tends to be widened.

  Further, the surface treatment using hot air of the red particles to which the organic fine particles are attached is preferably performed by hot air having a temperature 130 to 200 ° C. higher than the softening point (° C.) of the organic fine particles. More preferably, the temperature is 150 to 200 ° C. higher than the softening point of the organic fine particles, and more preferably 180 to 200 ° C. higher than the softening point of the organic fine particles. Thereby, the surfaces of both the organic fine particles and the colored resin particles can be melted, and the organic fine particles can be more firmly attached to the colored resin particles and fixed. By processing at a temperature of 130 ° C. or higher than the softening point of the organic fine particles, the organic fine particles can be melted and fixed to the colored resin particles more firmly. On the other hand, when the treatment is carried out at a high temperature exceeding the range of 200 ° C. from the softening point of the organic fine particles, secondary aggregation of the organic fine particles and the colored resin particles tends to occur, and the particles tend to be enlarged. .

  The binder resin preferably has a melting temperature (defined as a softening point) of 90 to 150 ° C. by a 1/2 method using a constant load extrusion capillary rheometer flow tester. Moreover, it is preferable that the glass transition point of resin is the range of 60-85 degreeC. Thereby, by rapidly melting the surface of the colored resin particles, spheroidization can be promoted by surface tension, and adhesion (fixation) of fine particles to the surface of the molten colored resin particles can be promoted. Further, the colored resin particles and the organic fine particles can be sufficiently fixed, and the occurrence of secondary aggregation between the organic fine particles can be suppressed.

  The softening point of the organic fine particles is preferably 60 to 150 ° C. higher than the softening point of the binder resin. Since the organic fine particles have a smaller particle size than the colored resin particles, if the softening point of the organic fine particles is lower than the softening point of the binder resin, the melting of the organic fine particles proceeds rapidly, and the black particles and the red particles adhering to each other are separated. Does not proceed smoothly, making it difficult to obtain the effect of improving contrast. By preventing the softening point of the organic fine particles from exceeding the range of 150 ° C. on the high temperature side from the softening point of the binder resin, the melting and fixing of the colored resin particles and the organic fine particles can be sufficiently advanced, The separation and release of organic fine particles from the colored resin particles can be suppressed.

(Function of display particles)
In the display particles produced as described above, fine particles having a smaller radius of curvature than the colored resin particles adhere to the surface of the colored resin particles, and the radius of curvature of the fine particles adhered to the surfaces of the black particles and the red particles, respectively. Has a different configuration. As a result, the effect of promoting the separation between the black particles and the red particles adhering to each other is exhibited, and between the white particles and the black particles adhering to each other, or between the white particles and the red particles adhering to each other. The effect of promoting separation is also exhibited. As a result, in an image display medium using a mixture of display particles of at least three colors, deterioration of characteristics can be reduced and high contrast can be maintained even when three or more colors are repeatedly displayed.
<Operation of image display medium>

  The image display medium 10 having the above configuration displays an image by being driven by the image display device 1. The image display device 1 displays on the image display medium 10 a control unit that controls the operation of the power supply unit 6 in addition to the power supply unit 6 that applies a voltage to the column electrode 12 and the row electrode 22 shown in FIG. And an image storage unit (not shown) for storing images.

 In the image display medium 10, as shown in FIG. 1, at least black particles and red particles having different colors and the same charge polarity, and white particles having different colors and charge polarities from the black particles and the red particles are at least. In each sealed cell, a voltage is applied between the column electrode 12 provided on the top sheet 2 and the row electrode 22 provided on the back sheet 3. Accordingly, the display particle groups 5A, 5B, and 5C can be moved between the top sheet 2 and the back sheet 3 in accordance with the electric field generated to display an image.

3 to 7 are schematic cross-sectional views illustrating one process of the display operation of the image display apparatus. For example, as shown in FIG. 3, a voltage is applied between the substrates in the image display medium 10 in which the display particle groups 5A, 5B, and 5C are mixed in each cell 8. The white particles HW and the black particles HB, and the white particles HW and the red particles HR having different charging polarities are in a state of being easily attached to each other due to the Coulomb force between the particles. At this time, a predetermined reference voltage (for example, the absolute value is 150 V) is applied between both electrodes so that the front substrate side is a negative electrode and the back substrate side is a positive electrode.
By applying this voltage, the positively charged white particles HW constituting the display particle group 5C move to the display substrate side and adhere to the inner surface of the display particle group 5C, as shown in FIG. The negatively charged black particles HB and red particles HR that are configured move to the back substrate side and adhere to the inner surface side thereof. As a result, the image display medium 1 can visually recognize a white display from the display substrate side.

  At this time, the positively charged white particles HW and the negatively charged red particles HR are relatively higher in the charge amount level of the red particles HR than that of the black particles HB. It tends to become stronger. On the other hand, the positively charged white particles HW and the negatively charged black particles HB have a relatively lower level of charge of the black particles HB than the red particles HR, so that the Coulomb force between the particles is relatively weak. There is a tendency. Therefore, when an electric field is applied, first, the white particles HW and the black particles HB, which are relatively weak in Coulomb force between the particles, are separated from each other, and the separated white particles HW move to the display substrate side. While adhering to the inner surface, the separated black particles HB move to the back substrate side and adhere to the inner surface.

  Thereafter, the white particles HW and the red particles HR, which have a relatively strong Coulomb force between the particles, are separated from each other, and the separated white particles HW move to the display substrate side and adhere to the inner surface of the display substrate. The particles HR are moved to the back substrate side to which the black particles HB are already attached, and are almost stacked on the black particles HB (display particle group 5A).

  Next, when a reference voltage is applied between both electrodes so that the front substrate side is a positive electrode and the back substrate side is a negative electrode, positively charged white particles HW attached to the front substrate are, as shown in FIG. It moves to the back substrate side and adheres to the inner surface. On the surface substrate side, black particles HB having a negative charge polarity and a low charge level move in advance and adhere to the inner surface, and thereafter red particles HR having a negative charge polarity and a high charge level move. It adheres to the inner surface of the lever. As a result, a black display can be visually recognized from the display substrate of the image display medium 1.

  Next, the direction of the electric field is reversed again from the state shown in FIG. At this time, a voltage lower than the reference voltage may be applied stepwise. More specifically, first, a first voltage (for example, an absolute value of 95 V) lower than a reference voltage (for example, an absolute value of 150 V) is applied between both electrodes so that the front substrate side is a negative electrode and the back substrate side is a positive electrode. Apply to. Thereby, first, the black particles HB having a low charge amount level overcome the mirror image force with the front substrate and start moving toward the back substrate. Since the charging of the display particles has a distribution, the second voltage (for example, the absolute value is 120 V) that is lower than the reference voltage and higher than the first voltage is applied to the display particle, thereby remaining on the surface substrate. The black particles HB that have been started to move further. Thereby, the movement of all the black particles HB is completed.

  Thereafter, a reference voltage is applied between both electrodes. By applying this voltage value, the red particles HR attached to the surface substrate with a stronger mirror image force start to move, move to the back substrate side where the black particles HB are already attached, and are stacked on the black particles HB. It adheres in such a way. As a result, as shown in FIG. 6, the image display medium 1 can visually recognize a white display from the front substrate side. Here, the step of applying the voltage has two steps (first voltage and second voltage). However, the movement efficiency of the black particles HB and the red particles HR is increased by further increasing the steps of applying the voltage. Therefore, it becomes possible to make the laminated state of the display particles shown in FIG. 6 more uniform.

  Next, in the state shown in FIG. 6, a reference voltage is applied between both electrodes so that the front substrate side is a positive electrode and the back substrate side is a negative electrode. Thereby, the white particles HW, the black particles HB, and the red particles HR move to the opposite substrates as they are, and adhere to the inner surfaces thereof. As a result, as shown in FIG. 7, the image display medium 10 can visually recognize a red display from the surface substrate.

  Once the image is displayed, the electrostatic adhesion between the display particles and the dielectric films 13 and 23 is maintained even when the application of voltage between the electrodes is stopped. The state where the image is displayed while being attached can be maintained for a long time.

  Note that an alternating voltage is preferably applied in advance between the electrodes of the top sheet 2 and the back sheet 3 when displaying an image. The alternating voltage is applied for a predetermined time (for example, about 0.1 to 1 s) with a frequency of 100 to 400 Hz and a voltage between the peak and peak of the waveform of ± 150 to 300 V. As the waveform of the alternating voltage, a sine wave is preferable, but a rectangular wave or a triangular wave may be applied depending on the characteristics of the display particles.

  In this way, by applying an alternating voltage to rapidly move the display particles between the top sheet 2 and the back sheet 3, the charging is stabilized and the particles are aggregated between the display particle groups 5A, 5B, and 5C. Can be relaxed.

  When displaying an image after applying the alternating voltage, a DC voltage is applied according to the image display pattern stored in the image storage unit. In the case of a simple matrix configuration of the row electrodes 22 and the column electrodes 12, first, a negative potential (for example, -75V) is applied to all the row electrodes 22, and a positive potential (for example, -75V) is applied to all the column electrodes 12, so Is preferably displayed once in white.

  Hereinafter, the image display medium and display particles according to the present invention will be described with reference to more specific examples.

<Configuration of image display medium>
The configuration of the image display medium 10 is the same as that shown in FIG. Here, both the front substrate 11 and the rear substrate 21 are made of transparent PET having a thickness of 175 μm. The height H of the partition wall 7 corresponding to the size of the gap 4 was 50 μm, and the width W of the partition wall 7 was about 50 μm. The distance D between adjacent partition walls 7 was 1000 μm. Each cell 8 was filled with white particles HW having a positively charged polarity, and black particles HB and red particles HR having both negatively charged polarities.
<Method for producing image display medium>

  In the production of the surface sheet 2, first, an A4-sized transparent PET film (that is, the surface substrate 11) having a thickness of 175 μm obtained by depositing ITO having a thickness of 50 nm on the entire surface is prepared. Next, a column electrode 12 having a width of each electrode of 900 μm and a space between the electrodes of 100 μm was formed on the surface substrate 11 by laser etching. The resistance of the column electrode 12 was 150Ω / □. Next, a coating film having a thickness of 12 μm is formed on the column electrode 12 by a pulling dipping method in a solution in which polycarbonate is dissolved in a THF solution at a weight ratio of 10%. The dielectric film 13 having a thickness of 3 μm was laminated by drying at 80 ° C. for 5 minutes.

  FIG. 8 is a schematic cross-sectional view showing one step (dry film laminating step) in the partition wall formation. Subsequent to the formation of the laminated dielectric film 13, as shown in FIG. 8, with a dry film laminator, the surface sheet 2 in which the column electrodes 12 and the dielectric film 13 are formed on the surface substrate 11, the epoxy resin, and the acrylic resin A UV curable resin dry film 31 having a thickness of 55 μm made of a mixed system is adhered and bonded together. At this time, the roll temperature was 60 ° C. and the feed rate was 0.4 m / min.

FIG. 9 is a schematic cross-sectional view showing one process (exposure process) in the partition formation. In the subsequent exposure step, as shown in FIG. 9, an exposure mask 32 was placed on the surface sheet 2 and the resin dry film 31 bonded together, and exposure was performed at an exposure amount of 100 mJ / cm ² . The exposure mask 32 defines an ultraviolet irradiation portion for forming a partition wall having a vertical line width and a horizontal line width of 50 μm and a pitch of 500 μm.

  FIG. 10 is a schematic cross-sectional view showing one process (development process) in the partition formation. In the subsequent development step, the ultraviolet curable resin dry film 31 that has been exposed is fed by an alkali developing machine using a 1% sodium carbonate developer at a feed rate of 0.6 m / min, a liquid temperature of 35 ° C., a shower pressure of 0. Development was performed under the condition of 15 MPa. As a result, as shown in FIG. 10, the ultraviolet curable resin dry film 31 was removed with the developer except for the ultraviolet irradiation portion in the exposure process, and only the cured portion 7 'that later became a partition remained.

Then, after sufficiently washing with ion-exchanged water, draining and drying at room temperature were performed for 1 hour. Further, after curing at 1000 mJ / cm ² with an ultraviolet curing device, after baking was performed in a drying furnace at 130 ° C. for 30 minutes.

  The partition walls formed had a height of 48 μm, a partition wall width of 45 μm, and a pitch of 500 μm as measured by a step difference measuring instrument using a microscope.

  The back sheet 3 was prepared by using a film with a copper foil in which a 18 μm thick copper foil was pasted on a 175 μm thick A4 size PET film (that is, the back substrate 21).

  In the laminating process, an acrylic UV-curable resin dry film having a thickness of 20 μm was closely adhered to and bonded to a PET film with a copper foil using a dry film laminator. At this time, the roll temperature was 110 ° C. and the feed rate was 0.4 m / min.

Next, an exposure mask was prepared in which the width of each electrode was 900 μm and the space was 1 mm. In the subsequent exposure process, an exposure mask was placed on a PET film with copper foil laminated with an ultraviolet curable resin dry film, and exposure was performed at an exposure amount of 100 mJ / cm ² .

  Further, in the subsequent development process, the ultraviolet curable resin dry film that has been exposed is fed by an alkali developing machine using a 1% sodium carbonate developer at a feed rate of 0.6 m / min, a liquid temperature of 35 ° C., and a shower pressure of 0. Development was performed under the condition of 15 MPa. The pattern of the electrode part was formed by the ultraviolet curable resin dry film remaining without being removed by this development. Thereafter, using an etching apparatus using a ferric chloride solution, copper was etched and developed under the conditions of a feed rate of 0.5 m / min, a liquid temperature of 45 ° C., and a shower pressure of 0.13 MPa. Thus, unnecessary portions of the copper foil corresponding to the spaces between the electrodes were removed.

  Subsequently, the ultraviolet curable resin dry film remaining on the electrode part was subjected to an alkali developing machine using a 3% aqueous solution of sodium hydroxide under the conditions of a feed rate of 0.6 m / min, a liquid temperature of 45 ° C., and a shower pressure of 0.12 MPa. Peeling was performed. This confirmed that unnecessary portions could be removed. Finally, it was thoroughly washed with ion-exchanged water, and then immediately drained by air blow.

  Through the above steps, it was confirmed that the row electrodes 22 having the width of each electrode of 895 μm, the space of 105 μm, and the pitch of 1 mm were formed. Each row electrode 22 is formed with the same width and space as the column electrode 12, and is arranged so as to be orthogonal to each column electrode 12 at a predetermined interval, and has a so-called passive matrix configuration.

  On the row electrode 22, a coating film having a thickness of 12 μm was formed by a pulling dipping method in a solution in which polycarbonate was dissolved at a weight ratio of 10% in a THF solution, and then at 80 ° C. in a drying furnace. A dielectric film 23 having a thickness of 3 μm was laminated by drying for 5 minutes.

  Next, the display particle filling step will be described. The ratio of the packing arrangement amount of three kinds of display particle groups (white particles HW20g, black particles HB20g, and red particles HR20g) having different colors and charged polarities is 1: 1: 1, and the mixed particles are in powder spray. Filled. Then, after fixing the surface substrate in which the partition was formed on the ITO electrode with the tape on the glass plate, the powder was sprayed using the powder spray. The injection into the cell was adjusted and sealed so that the volume occupation ratio was about 50%. Thereafter, the particles on the top of the partition walls were removed using a silicone rubber squeegee having a width of 5 mm, a length of 30 mm, and a width of 300 mm.

  Thereafter, the rear substrate was superposed on the surface substrate filled with the particles via the partition walls, and adhered and sealed with an acrylic rubber adhesive to produce the image display medium 10.

<Configuration of display particles>
(Binder resin)
Table 1 shows the characteristics of the binder resin used in the examples. The binder resin is a polyester resin composed mainly of alcohol of bisphenol A propyl oxide adduct and divalent carboxylic acid of terephthalic acid, succinic acid or fumaric acid, or trivalent carboxylic acid of trimellitic acid. Then, a resin whose thermal characteristics were changed depending on the blending ratio and polymerization conditions was used.

  In Table 1, Mnf is the number average molecular weight of the binder resin, Mwf is the weight average molecular weight of the binder resin, Mzf is the Z average molecular weight of the binder resin, Wmf is the ratio Mwf of the weight average molecular weight Mwf to the number average molecular weight Mnf / Mnf and Wzf are the ratio Mzf / Mnf of the Z-average molecular weight Mzf and the number-average molecular weight Mnf of the binder resin, Tmr (° C.) is the softening point, Tfb (° C.) is the outflow start temperature, and Tgr (° C.) is the glass transition point. .

(Pigment)
Table 2 shows the composition of the pigments used in the examples.

  In Table 2, titanium oxide (SJR-405S) is rutile titanium oxide having an average particle size of 0.21 nm, which is obtained by treating the surface with silicone oil. Carbon black is a pigment having a particle diameter of 24 nm, a DBP oil absorption of 53 ml / 100 g, and a low DBP oil absorption. Rdp is a red pigment. The particle diameter is about 100 arithmetic average diameters measured with an SEM electron microscope.

(Charge control agent)
Table 3 shows the structure of the charge control agent used in the examples.

(Colored resin particles)
Table 4 shows the composition of the colored resin particles used in the examples. In the parentheses, the blending parts by weight with respect to 100 parts by weight of the binder resin are shown.

(Organic fine particles)
Table 5 shows the constitution and characteristics of the organic fine particles used in the examples. In addition, some PMMA softening points were 400 degreeC or more, and the softening point of the silicone resin particle was 800 degreeC or more.

(Inorganic fine particles)
Table 6 shows the composition and characteristics of the inorganic fine particles used in the examples.

<Method for producing display particles>
(Preparation of colored resin particles)
In producing the colored resin particles, first, the binder resin, the colorant, and the charge control agent are about 4 kg using a Henschel mixer FM20B (manufactured by Mitsui Miike Kogyo Co., Ltd.) equipped with a stirring blade, the rotation speed is 800 min ⁻¹ , and the time is 5 min. The mixing was performed with the blade Z0S0 under the conditions of:

  FIG. 11 is a schematic perspective view showing the main part of the roll melt kneader, and FIG. 12 is a schematic plan view showing the main part of the roll melt kneader. Following the mixing of the binder resin, the colorant and the charge control agent, a kneading process was performed in a two-roll melt kneader. In the kneading process, as shown in FIG. 11, the colored resin particle raw material charged from the metering feeder 50 toward the end of the first roll 51 is wound around the first roll 51 to form the colored resin particles. A molten film 53 is formed. Here, as shown in FIG. 12, the first roll 51 and the second roll 52 are configured by front half parts 51A and 52A and latter half parts 51B and 52B, respectively, with a broken line part as a boundary. More specifically, the raw material is wound around the first half 51 </ b> A of the first roll 51 when the resin is melted by the heat of the first roll 51 and the compressive shearing force of the second roll 52. Thereafter, the melted raw material spreads to the end of the second half 51B of the first roll 51, and from the second half 52B of the second roll 52 heated at a lower temperature than the first half 51A of the first roll 51. It is peeled off.

Here, both the diameter of the 1st roll 51 and the 2nd roll 52 is 140 mm, and length is 800 mm. The rotation speed of the first roll 51 is 75 min ⁻¹ , and the rotation speed of the second roll 52 is 55 min ⁻¹ . The temperature of the heat medium that heats the first half 51A of the first roll 51 is 140 ° C., and the temperature of the heat medium that heats the second half 51B of the first roll 51 is 70 ° C. Moreover, the 2nd roll 52 is 15 degreeC. Further, the clearance between the first roll 51 and the second roll 52 is 0.1 mm, and the raw material supply amount is 5 kg / h.

  The kneaded mass obtained by cooling after the kneading treatment was coarsely pulverized by a cutter mill.

  FIG. 13 is a configuration diagram of the pulverization processing apparatus. Then, it refined | miniaturized to the average particle diameter of about 8 micrometers by the refinement | pulverization grinding | pulverization apparatus 60 shown in FIG. The fine pulverizing apparatus 60 is fitted with a cylindrical rotating body 61 having irregularities on the surface and rotating at a high speed, and a gap of 0.5 mm to 40 mm on the outside of the rotating body 61. A crushing processing unit 63 including a cylindrical fixed body 62 having irregularities on the surface sharing the same is provided.

  In the refinement process by the refinement and pulverization apparatus 60, the pulverized product 71 that has passed the mesh diameter of about 5 mm by coarse pulverization is input from the quantitative supply device 72, and then the cooling air 74 that is supplied from the cooler 73. Is sent to the supply port 75 of the pulverization processing unit 63. The object to be crushed 71 is conveyed to the gap between the rotator 61 and the fixed body 62 in the pulverization processing unit 63, and is exchanged with the flow of the high-speed air current generated between the rotator 61 and the fixed body 62 that rotates at high speed. It is crushed by repeating strong collisions. The obtained pulverized product 80 is discharged from the discharge port 76 of the pulverization processing unit 63, sent to the cyclone 82 through the coarse powder classifier 81, and finally collected in the collection container 83. In the coarse powder classifier 81, coarse particles are sent again to the supply port 75 of the pulverization processing unit 63 by the cooling air 74 via the reprocessing path 84.

  In the pulverization process, the peripheral speed of the rotating body 61 is 130 m / s, the gap between the rotating body 61 and the fixed body 62 is 1.5 mm, the raw material supply rate is 3 kg / h, the temperature of the cooling air 74 is 0.5 ° C., and the discharge is performed. The part temperature was 40 ° C.

(Mixing method of colored resin particles and fine particles)
The external addition treatment for mixing the colored resin particles and the fine particles was performed using a Henschel mixer (FM20B manufactured by Mitsui Mining Co., Ltd.) under the conditions of a stirring blade Z0S0 type, a rotation speed of 2200 min ⁻¹ , a treatment time of 4 min, and an input amount of 1 kg.

(Surface modification treatment)
FIG. 14 is a configuration diagram of the surface modification treatment apparatus. A surface modification treatment with hot air was performed on the colored resin particles to which fine particles adhered by the external addition treatment using a surface modification treatment apparatus 90 shown in FIG. In the surface modification treatment, the colored resin particles 91 to which the fine particles are attached are introduced from a fixed amount feeder 92 and sent by a compressed air 93 to a dispersion nozzle 94 which is a particle dispersion means. Four dispersion nozzles 94 are arranged at symmetrical positions. The colored resin particles 91 are jetted downward at an angle of about 45 degrees with respect to the horizontal plane from the plurality of dispersion nozzles 94 toward the hot air 96 discharged from the hot air generator 95. The colored resin particles 91 pass through the hot air 96 while being dispersed, whereby the surface modification treatment is performed, and the adhered fine particles are firmly fixed. Thereby, the surface-modified display particles are taken into the hood 97, sent to the cyclone 98, and then collected and collected in the collection box 99.

In the surface modification treatment, multistage treatment was performed. That is, the hot air flow rate is 1.0 Nm ³ / min (wind pressure 5 × 10 ⁴ Pa), the raw material supply dispersion flow rate of the dispersion nozzle 94 is 0.5 Nm ³ / min (wind pressure 3 × 10 ⁴ Pa), and the supply rate is 1 kg / h. The first stage heat treatment was performed under the following conditions, followed by increasing the hot air temperature, the hot air flow rate was 1.0 Nm ³ / min (wind pressure 5 × 10 ⁴ Pa), and the raw material supply dispersion flow rate was 0.5 Nm ³ / min. The second stage heat treatment was performed under the conditions of (wind pressure 3 × 10 ⁴ Pa) and supply rate of 1 kg / h. The first stage heat treatment is aimed at fixing a part of the external additive and spheroidizing the colored resin particles, and the second stage heat treatment further promoting the spheroidization of the colored resin particles. For the purpose. In the first stage, hot air having a temperature 140 to 270 ° C. higher than the softening point was used, and in the second stage, hot air having a temperature 200 to 300 ° C. higher than the softening point of the binder resin was used.

Hot air volume, 0.35~1.0Nm ³ / min in air pressure 3 to 5 × ¹⁰ 4 Pa is the preferred range, also the raw material supply dispersed air volume, wind pressure 1~3 × ¹⁰ 4 Pa, 0. A suitable range is from 05 to 0.5 Nm ³ / min. Further, the ratio of the hot air flow rate to the raw material supply dispersion air flow rate is preferably in the range of 10: 1 to 4: 1. If the air volume of the hot air 96 relative to the raw material supply dispersion air volume is too large, the particles to be treated are repelled and uniform processing becomes difficult. Moreover, when the raw material supply dispersion | distribution air volume with respect to a hot air volume is too large, it will become difficult for the to-be-processed particle to cross | intersect a hot air and to perform a uniform process.

  In the surface modification process, it is preferable that the surface-modified display particles taken into the hood 97 are cooled by the cooling air 102 generated from the cooler 101. The rapid cooling by the cooling air 102 can stabilize the processing state. The air volume of the cooling air 102 can be appropriately set according to the processing volume. The distance from the position where the display particles are treated with hot air to the point where the cooling air is applied is determined by the amount of treatment, but is generally 10 cm to 100 cm, preferably 20 cm to 80 cm. The temperature of the cooling air 102 is not particularly limited, but is preferably 10 ° C. or lower. As another method, a method using water cooling, a method of arranging a solid object (dry ice or the like) cooled around the pipe, and the like can also be used.

  In the surface modification process, the colored resin particles 91 are ejected from a plurality of dispersion nozzles 94 disposed at symmetrical positions, and thus are uniformly processed. Although the heater heated by propane gas etc. was used as the hot air generator 95, it is not restricted to this, What is necessary is just what can generate | occur | produce a hot air.

<Evaluation of image display media>
(Initial characteristics)

  Evaluation of drive voltage (voltage applied between electrodes when image display is performed by switching white particles, black particles, and red particles) for the image display medium having the above configuration (evaluation of relationship between drive voltage and contrast) Went.

  Prior to the evaluation, an alternating voltage was applied in advance between the electrodes of the front substrate and the rear substrate to initialize the image display medium. The alternating voltage has a rectangular waveform, a frequency of 100 Hz, a voltage between the peak and peak of the waveform of 200 V, and an application time of 500 ms. After that, a constant DC voltage is applied between the electrodes of the front substrate and the rear substrate, and the drive voltage characteristics are measured by measuring the reflected image density during black / red / white display when the polarity is reversed at the voltage value. Was evaluated.

  Specifically, the potential of the column electrode on the front substrate side is set to 0 V and the potential of the row electrode on the rear substrate side is set to +150 V to display white (the state of FIG. 4), and the reflected image density is measured using a Macbeth densitometer. Measure. Next, the column electrode potential is kept at 0V, the row electrode potential is set at -150V, black is displayed, and the reflection image density is measured using a Macbeth densitometer.

  Next, by applying a positive voltage to the column electrode on the surface substrate side, the positively charged white particles HW move to the back substrate 21 side and adhere to the inner surface, and the surface substrate has a negatively charged polarity. Then, the black particles HB having a relatively low charge amount level are attached in advance, and thereafter, the red particles HR having a negative charge polarity and a relatively high charge amount level are moved and attached to the rear substrate 21 side (FIG. 5). State). As a result, the image display medium can visually recognize a black display from the display substrate side.

  From the state of FIG. 5, the potential of the column electrode on the front substrate side is set to 0 V, and a potential of +90 V is applied to the row electrode on the rear substrate side. Then, the black particles HB having a low charge amount level overcome the mirror image force with the front substrate and start moving toward the back substrate. Furthermore, by applying a slightly higher voltage of +120 V to the row electrode on the back substrate side, the black particles HB remaining on the front substrate further start to move.

  After that, by applying a voltage of +150 V to the row electrode on the back substrate side, the red particles HR attached to the front substrate with a stronger mirror image force start to move, and the black particles HB already attached to the back substrate. It adheres in the form of being laminated on top (state of FIG. 6). As a result, the image display medium can visually recognize a white display from the display substrate side.

  Further, from the state of FIG. 6, the potential of the column electrode on the front substrate side is set to 0 V, and a potential of −150 V is instantaneously applied to the row electrode on the rear substrate side. As a result, the white particles HW, the black particles HB, and the red particles HR move to the opposite substrates as they are (the state of FIG. 7). As a result, the image display medium can visually recognize a red display from the display substrate side.

<Evaluation of display particles>
Tables 7 to 9 show characteristics of display particle samples subjected to the above-described surface modification treatment. Here, the value in parentheses indicates the blended part by weight of inorganic fine particles or organic fine particles with respect to 100 parts by weight of the colored resin particles. Tmr is the softening point (° C.) of the binder resin, Tmp is the softening point (° C.) of the binder resin, and Tsmr is the hot air temperature (° C.) of the second stage and the softening point Tmr (° C.) of the binder resin. The temperature difference, Tsmp, is the temperature difference between the hot air temperature (° C.) in the second stage and the softening point Tmp (° C.) of the organic fine particles, and SF is the shape factor of the colored resin particles.

The charge amount was measured by a known blow-off method used for toner. Specifically, in an environment of 25 ° C. and 45 RH%, a ferrite carrier (sample number: PC-43, manufactured by Powder Tech Co., Ltd.) having a toner concentration of 3% and a silicone resin-coated average particle size of 35 μm in a 100 ml polyethylene container After mixing with display particles and adding 100 g, stirring for 10 minutes at a speed of 100 min ⁻¹ , 0.3 g was collected and measured by blowing with nitrogen gas 1.96 × 10 ⁴ (Pa) for 1 minute.

  The positively charged white particles HW progressed to spheroidization, and the shape factor and its variation coefficient also showed small values. The red particles HR were subjected to surface modification treatment with hot air after adding and mixing organic fine particles. Some of them contain silica and titanium oxide. As the organic fine particles, styrene acrylic resin fine particles, silicone resin particles, and PMMA (polymethyl methacrylate) fine particles were used. Further, the black particles HB were subjected to surface modification treatment with hot air after adding and mixing inorganic fine particles. Silica and titanium oxide fine particles were used as the inorganic fine particles.

  The surface modification treatment with hot air was performed in two stages. It entered at 320-350 ° C. in the first step and 360-420 ° C. in the second step.

  The adhesion of fine particles to the surface of the colored resin particles and the spheroidization of the colored resin particles are in progress. It is considered that the state close to the so-called point contact is dominant among the display particles because the fine particles adhere to the surface of the display particles. However, in the display particles HR7, HR8, and HR9, when the softening point of the organic fine particles is high, the fixing force with the colored resin particles tends to be slightly weakened.

  Table 10 shows the results of evaluating the image display characteristics by enclosing the sample in an image display medium and using the method described above. The evaluation results are as follows: white image density (2-B) in the state of FIG. 4, black image density (2-C) in the state of FIG. 5, white image density (2-D) in the state of FIG. 6, and state of FIG. The red image density (2-E).

  The white image density (2-B) is 0.30 between the display particles obtained by mixing the white particles HW1, the red particles HR5 and the black particles HB12 and the display particles obtained by mixing the white particles HW2, the red particles HR6 and the black particles HB13. The black image density (2-C) was 1.4 or more and the white image density (2-D) was 0.3 or less, which was a very good result. Further, the red image density (2-E) in the state of FIG. 7 is 1.4 or more, and there is little mixing of black particles and white particles, and a clear red is displayed, which is a very good result.

  Further, display particles obtained by mixing white particles HW3, red particles HR7, and black display particles HB14, display particles obtained by mixing white particles HW1, red particles HR8, and black particles HB15, white particles HW2, red particles HR9, and black particles HB14. And white particles HW3, red particles HR10, and black particles HB15 are mixed, and the white image density (2-B) is 0.35 or less and the black image density (2-C). Was 1.35 or more and the white image density (2-D) was 0.35 or less, which was a good result. Further, the red image density (2-E) in the state shown in FIG. 7 was 1.35 or more, which was a good result with little mixing of black particles and white particles.

  As comparative examples, display particles in which white particles HW1, red particles HR9 and black particles hb16 are mixed, display particles in which white particles HW1, red particles hr4 and black particles HB14 are mixed, white particles HW1, red particles hr11 and black particles In the display particles mixed with HB14, the white image density (2-B) is 0.40 or more, the black image density (2-C) is 1.30 or less, and the white image density (2-D) is 0.40. As a result, the contrast was low. In addition, the red image in the state of FIG. 7 also has a mixture of black particles and white particles, and it is difficult to obtain a clean red image display.

  Although this invention was demonstrated based on specific embodiment containing an Example, these embodiment is an illustration to the last and this invention is not limited by these embodiment. The display particles according to the present invention shown in the above embodiment, the manufacturing method thereof, and the constituent elements of the image display medium using the display particles are not necessarily all essential, and at least as long as they do not depart from the scope of the present invention. Can be used.

  The display particles, the display particle manufacturing method, the image display medium using the display particles, and the image display device according to the present invention provide at least three or more colors by facilitating separation between the colored particles attached to each other. Even in the case of repeated display, it is possible to maintain high contrast with little deterioration in image display characteristics, display particles used for image display, display particle manufacturing method, and image display medium using display particles, and It is useful as an image display device.

DESCRIPTION OF SYMBOLS 1 Image display apparatus 2 Top sheet 3 Back sheet 4 Gap 5 Display particle group 7 Partition 8 Cell 10 Image display medium 11 Surface substrate 12 Column electrode 13 Dielectric film 21 Back substrate 22 Row electrode 23 Dielectric film 31 Resin dry film 32 Exposure Mask 50 Quantitative supply device 51 First roll 52 Second roll 60 Fine pulverizing device 63 Grinding processing unit 81 Coarse powder classifier 90 Surface modification processing device HB Black particles HR Red particles HW White particles

Claims (8)

A display particle group having a predetermined charging polarity enclosed between the pair of substrates, at least one of which is disposed so as to be transparent, and applying an electric field between the substrates to display the display particle group Display particles used in an image display medium that displays an image by moving
First display particles and second display particles having different colors and the same charge polarity, and third display particles having different colors and charge polarities from the first display particles and the second display particles,
Inorganic fine particles having an average particle diameter of 6 nm to 50 nm adhere to the surface of the first display particles, and organic fine particles having an average particle diameter of 0.1 μm to 5 μm adhere to the surface of the second display particles. Display particles characterized by The first display particles are treated using hot air having a temperature higher by 200 ° C. to 300 ° C. than the softening point of the binder resin on the surface of the first colored resin particles formed from at least the binder resin and the colorant. The inorganic fine particles are fixed by
The second display particles are treated by using hot air having a temperature 200 ° C. to 300 ° C. higher than the softening point of the binder resin on the surface of the second colored resin particles formed from at least the binder resin and the colorant. The display particles according to claim 1, wherein the organic fine particles are fixed by. The inorganic fine particles are made of silica or titanium oxide,
The display particles according to claim 1, wherein the organic fine particles are made of at least one selected from the group consisting of styrene acrylic resin, acrylic resin, polymethyl methacrylate, and silicone resin. The binder resin has a softening point of 90 ° C to 150 ° C,
The organic fine particles are made of a thermoplastic resin having a softening point of 150 ° C. to 250 ° C., and are fixed to the surface of the colored resin particles by treatment with hot air having a temperature 130 ° C. to 200 ° C. higher than the softening point. The display particle according to any one of claims 1 to 3, wherein   The display particles according to any one of claims 1 to 4, wherein the colored resin particles have a shape factor of 125 or less and a variation coefficient of the shape factor of 15 or less. A display particle group having a predetermined charging polarity enclosed between the pair of substrates, at least one of which is disposed so as to be transparent, and applying an electric field between the substrates to display the display particle group A method for producing display particles used in an image display medium that displays an image by moving
The display particles are different in color and charge polarity from the first display particles and the second display particles having at least different colors and the same charge polarity, and the first display particles and the second display particles. Including third display particles,
The first display particles are:
Attaching inorganic fine particles having an average particle size of 6 nm to 50 nm to first colored resin particles having an average particle size of 3 to 15 μm including at least a binder resin and a colorant;
A step of fixing the inorganic fine particles on the surface of the first colored resin particles by hot air having a temperature 200 to 300 ° C. higher than the softening point of the binder resin;
The second display particles are:
Attaching organic fine particles having an average particle size of 0.08 μm to 5 μm to second colored resin particles having an average particle size of 3 to 15 μm including at least a binder resin and a colorant;
And a step of fixing the organic fine particles to the surface of the second colored resin particles with hot air having a temperature 200 to 300 ° C. higher than the softening point of the binder resin.   The image display medium which has a display particle in any one of Claims 1-5. An image display device comprising: the image display medium according to claim 7; and an electric field applying unit that applies an electric field between substrates of the image display medium,
The first display particles have a higher charge amount than the second display particles,
The electric field applying means includes
By applying an electric field having a polarity opposite to the charged polarity of the third display particles to one substrate having translucency, the color of the third display particles is displayed from the one substrate side,
By applying an electric field having the same polarity as the charge polarity of the third display particles to the one substrate, the color of the first display particles having a high charge amount is displayed from the one substrate side,
When an electric field having the same polarity as the charged polarity of the third display particles is applied to the one substrate, the second voltage having a smaller absolute value than the first voltage value at which the first display particles can move. By executing a first step of applying a voltage value and a second step of applying the first voltage value after the first step, the color of the second display particles having a low charge amount is changed to the one of the ones. An image display device displaying from a substrate side.

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