JP5298920B2 - Display particles for image display device and image display device - Google Patents

Description

  The present invention relates to a display particle and an image display device used in an image display device capable of repeatedly displaying and erasing an image by moving charged display particles by applying an electric field.

  Conventionally, there has been a method in which charged display particles are enclosed in a cell between substrates and an image can be displayed by applying a voltage to move the display particles in the gas phase along the electric field direction. Are known. In this method, white particles and black particles are usually used as display particles, and a technique for improving the contrast between an image portion and a non-image portion has been demanded. As the display particles, white particles and black particles having different charging polarities have been used.

  In order to improve the contrast, when a relatively large amount of display particles were sealed in the cell, the particles were aggregated due to physical adhesion in the cell, and the movement was not performed smoothly. Therefore, sufficient contrast could not be obtained, and in particular, the whiteness decreased.

  An object of the present invention is to provide a display particle and an image display device capable of displaying an image having sufficiently high contrast between an image portion and a non-image portion.

The present invention encloses charged display particles between two substrates, at least one of which is transparent, and generates an electric field between the substrates, thereby moving the display particles in the gas phase to display an image. Display particles used in an image display device,
The display particles include two types of white particles A1 and A2 having the same charge amount peak value sign and different charge amount peak values, and black particles B1,
When the charge amount peak value of the white particle A1 is a1 (μC / g), the charge amount peak value of the white particle A2 is a2 (μC / g), and the charge amount peak value of the black particle B1 is b1 (μC / g). And the following formulas (1) to (3);
10 ≦ | a1 | ≦ 20 (1)
−1.2 ≦ a1 / b1 ≦ −0.8 (2)
0.35 ≦ a2 / a1 ≦ 0.65 (3)
It is related with the display particle characterized by satisfy | filling all of these, and the image display apparatus provided with this display particle.

The present invention is also the above image display device that generates an electric field between the substrates by applying a voltage between the upstream electrode and the downstream electrode in the viewing direction,
When a white image is displayed, a DC voltage having an absolute value of 40 to 75 V with a different sign from the charge amount peak value of the white particle A1 is applied to the upstream electrode, and then an absolute value of 150 to 400 V with a different sign. DC voltage is applied, and the downstream electrode is grounded,
When a black image is displayed, a DC voltage having an absolute value of 40 to 75 V with a different sign from the charge amount peak value of the black particles B1 is applied to the upstream electrode, and then an absolute value of 150 to 400 V with a different sign. The present invention relates to an image display device to which a direct current voltage is applied and a downstream electrode is grounded.

  According to the present invention, an image with improved whiteness can be displayed. As a result, an image having a sufficiently high contrast between the image portion and the non-image portion can be displayed.

(A) And (b) is a schematic schematic diagram which shows an example of the cross-sectional structure of an image display apparatus. (A)-(d) is a schematic schematic diagram for demonstrating the drive method of the image display apparatus of Fig.1 (a). (A)-(d) is a schematic schematic diagram for demonstrating the drive method of the image display apparatus of FIG.1 (b). (A)-(d) is a schematic schematic diagram for demonstrating an example of the manufacturing method of the image display apparatus of this invention. It is a schematic diagram which shows the example of a shape of an image display surface. (A) is a graph which shows a time-dependent change of the voltage when displaying a white image using a predetermined | prescribed image display apparatus in Experimental example C, (b) is when a voltage is applied as shown to (a). It is a graph which shows typically a density | concentration change. (A) is a graph which shows a time-dependent change of the voltage when displaying a black image using a predetermined image display apparatus in Experimental Example C, and (b) is when a voltage is applied as shown in (a). It is a graph which shows typically a density | concentration change.

[Display particles for image display devices]
The display particles for an image display device according to the present invention (hereinafter simply referred to as “display particles”) include positively or negatively charged white particles and black particles, the white particles have the same sign of the charge amount peak value, And it contains two types of white particles having different values.

  Specifically, the display particles include two types of white particles A1 and A2 having the same charge amount peak sign and different charge amount peak values, and black particles B1, and the charge amount peak value of the white particles A1 is represented by a1 ( μC / g), when the charge amount peak value of the white particle A2 is a2 (μC / g) and the charge amount peak value of the black particle B1 is b1 (μC / g), the following formulas (1) to (3) Satisfy all of

Formula (1);
10 ≦ | a1 | ≦ 20, preferably 12 ≦ | a1 | ≦ 18;
Formula (2);
−1.2 ≦ a1 / b1 ≦ −0.8, preferably −1.1 ≦ a1 / b1 ≦ −0.9;
Formula (3);
0.35 ≦ a2 / a1 ≦ 0.65, preferably 0.30 ≦ a2 / a1 ≦ 0.60.

  By using the white particles A1 and A2 and the black particles B1 that satisfy the relational expression of the charge amount peak value and controlling the driving voltage, a white image in which the white particles A2 are composed of the white particles A1 when the white image is displayed. Since it is reinforced, the whiteness is improved and as a result, the contrast is improved.

If the absolute value of a1 is too small, the white particles A1 have a small amount of charge, so that all particles are not driven, the whiteness is lowered, and the contrast is lowered. If the absolute value of a1 is too large, the white particles A1 have a strong electrostatic adhesion with the electrode, so that the whiteness decreases and the contrast decreases.
If a1 / b1 is too small, only the white particles A1 are driven first with respect to the driving voltage, and the black particles B1 are difficult to be driven by the white particles A1, and the contrast is lowered. If a1 / b1 is too large, only the black particles B1 are driven first with respect to the driving voltage, and the white particles A1 are difficult to be driven by the black particles B1, resulting in a decrease in contrast.
If a2 / a1 is too small or too large, the white particles A2 are difficult to drive before the white particles A1, so the whiteness is not improved and the contrast is lowered.

  In the present specification, the value measured by “E-Spart analyzer” (manufactured by Hosokawa Micron) is used as the peak value of the charge amount.

  In the present invention, the relationship between the charge amount peak values may be achieved by using two types of white particles and one type of black particles that satisfy the relationship at the time of manufacture. An image display device that satisfies the above relationship at the time of manufacture satisfies the relationship between the charge amount peak values even in white particles and black particles separated and collected from the device. That is, when white particles and black particles are separated and collected by the following method, the two charge amount peak values a1 and a2 (| a1 |> | a2 |) that the white particles have and one charge that the black particles have The quantity peak value b1 satisfies the relationship of the charge quantity peak value.

  Separation of white particles and black particles can be achieved by disassembling the image display device when the whitest image is displayed by a driving method described later, collecting white particles from the substrate side upstream in the viewing direction, This can be achieved by collecting black particles from the side of the substrate.

Specific examples of combinations of these codes (charging polarities) in the relationship between the charge amount peak values a1, a2 and b1 of the white particles A1 and A2 and the black particles B1 are shown below.
(A1, a2, b1)
= (+, +,-)
= (-,-, +)
That is, when the white particles A1 are positively charged, the white particles A2 are positively charged, the black particles B1 are negatively charged, and when the white particles A1 are negatively charged, the white particles A2 are Negative chargeability is exhibited, and the black particles B1 exhibit positive chargeability.

  The content ratio of the white particles A1 and A2 and the black particles B1 is not particularly limited as long as the object of the present invention is achieved. Usually, when the content of the white particles A1 is 100 parts by weight, the white particles A2 are 10 to 10 parts by weight. The proportion is 50 parts by weight, preferably 20 to 40 parts by weight, and the black particles B1 are 80 to 120 parts by weight, preferably 90 to 110 parts by weight.

[Production method of display particles]
The white particles A1, A2 and the black particles B1 are composed of base particles containing at least a binder resin and a colorant, and usually further include an external additive.

The binder resin that constitutes the base particles of the white particles A1, A2 and the black particles B1 is not particularly limited, and a polymer called a vinyl resin shown below is a typical one. In addition, there are condensation resins such as polyamide resin, polyester resin, polycarbonate resin, and epoxy resin. Specific examples of vinyl resins include polystyrene resins, polyacrylic resins, polymethacrylic resins, and polyolefin resins formed from ethylene monomers and propylene monomers. In addition to the above-described condensation resins, resins other than vinyl resins include polyether resins, polysulfone resins, polyurethane resins, fluorine resins, and silicone resins.
The polymer constituting the binder resin that can be used for the base particles is prepared by combining plural types of polymerizable monomers in addition to those obtained by using at least one type of polymerizable monomer that forms these resins. You can also. When a resin is prepared by combining a plurality of types of polymerizable monomers, for example, a method of forming a copolymer such as a block copolymer, a graft copolymer, or a random copolymer, or a mixture of a plurality of types of resins. There is also resin formation by a polymer blending method. As such a copolymer, for example, a styrene / acrylic resin is preferably used.

The colorant contained in the base particles of the white particles A1, A2 and the black particles B1 is not particularly limited, and a known pigment is used.
For example, specific examples of the white pigment constituting the white base particles of the white particles A1 and A2 include anatase type titanium oxide, rutile type titanium oxide, zinc oxide (zinc white), antimony white, zinc sulfide and the like. . Two or more white pigments can be contained in combination. The content of the colorant in the white base particles of the white particles A1 and A2 is 20 to 200 parts by weight, particularly 25 to 150 parts by weight with respect to 100 parts by weight of the binder resin, from the viewpoint of improving whiteness and improving contrast. Is preferred.

  For example, specific examples of the black pigment constituting the black base particle of the black particle B1 include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, and the like. Two or more black pigments can be contained in combination. The content of the colorant in the black base particles of the black particles B1 is preferably 5 to 20 parts by weight, particularly 8 to 15 parts by weight with respect to 100 parts by weight of the binder resin, from the viewpoint of improving the blackness and improving the contrast. .

  The average primary particle size of the colorant is not particularly limited as long as the coloring power can be exerted, and is usually 50 to 500 nm, particularly 100 to 300 nm in the case of a white pigment, and 10 to 50 nm, particularly 15 in the case of a black pigment. ˜35 nm is preferred.

In this specification, the average primary particle size is a value measured by the following method.
In a scanning electron microscope (commonly known as SEM), a photograph is taken at 10,000 times, and an average value of 100 particles of an actual image is used.

Other additives such as a charge control agent may be internally added to the base particles of the white particles A1 and A2 and the black particles B1.
In the case of white base particles, as the positively chargeable charge control agent, digrosine dye, triphenylmethane compound, quaternary ammonium salt compound, polyamine resin, imidazole derivative, etc., as the negatively chargeable charge control agent, metal salicylate Examples include complexes, metal-containing azo dyes, quaternary ammonium salt compounds, calixarene compounds, nitroimidazole derivatives, and the like.
In the case of black base particles, salicylic acid metal complexes, metal-containing azo dyes, quaternary ammonium salt compounds, calixarene compounds, nitroimidazole derivatives, etc. are used as negatively chargeable charge control agents. Examples include grosin dyes, triphenylmethane compounds, quaternary ammonium salt compounds, polyamine resins, and imidazole derivatives.

The white particles A1 and A2 and the black particles B1 can be produced by adding an external additive to the base particles and mixing them.
As the external additive, conventionally known external additives are used in the field of display particles of an image display device, and examples thereof include silica, titania, and alumina.

  The external additive is preferably used after being surface-treated with a hydrophobizing agent from the viewpoint of reducing physical adhesion between the particles and between the particles and the electrode. As the hydrophobizing agent, known hydrophobizing agents used for surface treatment of inorganic fine particles externally added in the field of display particles can be used, and examples thereof include aminosilane coupling agents, disilazane compounds, and silicone oils. .

  The average primary particle size of the external additive is 10 to 200 nm, preferably 20 to 150 nm.

  The addition amount of the external additive is not particularly limited, and is usually 0.1 to 20 parts by weight, particularly preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the base particles. As the external additive, two or more types of external additives having different average primary particle diameters and / or constituent materials may be used, and in this case, the total amount thereof may be within the above range.

The method for producing the base particles of the white particles A1, A2 and the black particles B1 is not particularly limited, and includes a resin and a colorant, such as a method for producing a toner used for electrophotographic image formation. This can be dealt with by applying a known method for producing particles. Specific examples of the method for producing the base particles include the following methods.
(1) A method of preparing base particles through kneading and classification steps after kneading a resin and a colorant;
(2) a so-called suspension polymerization method in which a polymerizable monomer and a colorant are mechanically stirred in an aqueous medium to form droplets and then polymerized to produce base particles; and (3) interface A polymerizable monomer is dropped into an aqueous medium containing an activator, a polymerization reaction is performed in micelles to produce polymer particles of 100 to 150 nm, and then colorant particles and an aggregating agent are added. So-called emulsification association method in which base particles are produced by associating particles.

  The volume average particle diameters D1 of the white particles A1 and A2 and the black particles B1 are each independently 0.1 to 50 μm, and preferably 1 to 20 μm from the viewpoint of ease of movement due to an electric field and reduction of concentration variation. .

The volume average particle diameter D1 of the particles is a volume-based median diameter (d50 diameter), and is measured and calculated using a device in which a computer system for data processing is connected to Multisizer 3 (manufactured by Beckman Coulter). Can do.
As a measurement procedure, 0.02 g of particles are mixed with 20 ml of a surfactant solution (for dispersing particles, a surfactant solution obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water). After that, ultrasonic dispersion is performed for 1 minute to prepare a particle dispersion. This particle dispersion is poured into a beaker containing ISOTON II (manufactured by Beckman Coulter, Inc.) in a sample stand with a pipette until the measurement concentration reaches 10%, and measurement is performed with a measuring machine count set to 2500 pieces. The aperture size of the multisizer 3 is 50 μm.

The charge polarity and charge amount peak value of the white particles A1, A2 and the black particles B1 are determined by mixing the white particles A1 or A2 or the black particles B1 and the carrier and bringing them into friction contact with each other. It can be controlled by adjusting.
For example, when a carrier coated with a fluorinated acrylate resin is used, particles mixed with the carrier are charged positively. For example, when a carrier coated with cyclohexyl methacrylate is used, the particles mixed with the carrier are charged negatively.
For example, when the carrier mixing ratio in the mixture of each particle and carrier is increased, the absolute value of the charge amount peak value is increased, and when the carrier mixing ratio is decreased, the absolute value of the charge amount peak value is decreased.
For example, when the mixing conditions such as the mixing time and the mixing speed are increased, the absolute value of the charge amount peak value is increased. When the mixing conditions are decreased, the absolute value of the charge amount peak value is decreased.

[Image display device]
An image display device according to the present invention is characterized by including the above-described display particles. Hereinafter, the image display apparatus of the present invention will be described in detail.

  The image display device according to the present invention encloses the display particles described above between two substrates, at least one of which is transparent, and generates an electric field between the substrates, thereby moving the display particles in the gas phase to generate an image. Is displayed.

  A typical cross section of an image display device according to the present invention is shown in FIG. In FIG. 1A, electrodes 15a and 15b having a layer structure are provided on substrates 11 and 12, and an insulating layer 16 is provided on the surfaces of the electrodes 15a and 15b. The image display device shown in FIG. 1B has a structure in which no electrode is provided in the device, and an electric field is applied through an electrode provided outside the device so that display particles can be moved. It is. The same reference numerals in FIGS. 1A and 1B denote the same members. FIG. 1 is meant to include FIGS. 1 (a) and 1 (b). As shown in the figure, the image display device 10 in FIG. 1 is configured to visually recognize an image from the substrate 11 side. However, in the present invention, the image display device 10 is not limited to an image viewed from the substrate 11 side. Further, the type shown in FIG. 1B has an advantage that the structure of the device can be simplified and the manufacturing process can be shortened because the electrodes 15a and 15b are not provided on the device itself. FIG. 3 shows a state in which voltage application is performed by setting the image display device 10 of the type shown in FIG. The cross-sectional configuration of the image display device according to the present invention is not limited to that shown in FIGS.

  At the outermost part of the image display device 10 in FIG. 1A, two substrates 11 and 12 that are casings constituting the image display device are arranged to face each other. The substrates 11 and 12 are provided with electrodes 15a and 15b for applying a voltage on the surface facing each other, and further, an insulating layer 16 is provided on the electrodes 15a and 15b. The substrates 11 and 12 are provided with electrodes 15a and 15b and an insulating layer 16, and display particles are present in a gap 18 formed by facing the surfaces having the electrodes 15a and 15b and the insulating layer 16 facing each other.

  The image display device 10 shown in FIG. 1 includes black display particles (referred to as black particles in this specification) B1 (21), white display particles (referred to as white particles in this specification) A1 (22a), and white as display particles. Three kinds of display particles of display particles (referred to as white particles in this specification) A2 (22b) are present in the gap 18. Strictly speaking, the surfaces of the black particles 21 and the white particles 22a and 22b are present with the above-mentioned external additives added, but are not illustrated. Further, in the image display device 10 of FIG. 1, the gap 18 is surrounded by the substrates 11 and 12 and the two partition walls 17, and the display particles are present in a state of being enclosed in the gap 18 in a powder form. doing.

  The thickness of the gap 18 is not particularly limited as long as the enclosed display particles can move and maintain the contrast of the image, and is usually 10 μm to 500 μm, preferably 10 μm to 100 μm. The volume occupation ratio of all display particles in the gap 18 is 5% to 70%, preferably 25% to 60%. By setting the volume occupancy of all the display particles within the above range, the display particles can move smoothly in the gap 18 and an image with better contrast can be obtained.

[Driving Method of Image Display Device]
Next, a driving method of the image display device 10 will be described.
In the image display device according to the present invention, since the white particles A1, A2 and the black particles B1 each have a predetermined charge amount peak value, when an electric field is formed by applying a voltage between the two substrates, It moves along the electric field direction based on the charge polarity and charge amount. In this way, when a voltage is applied between the substrates on which the display particles exist, the charged display particles move between the substrates to display an image.

Specifically, an electric field is generated between the substrates by applying a voltage between the upstream electrode 15a and the downstream electrode 15b in the viewing direction.
In the present invention, for example, when a white image is displayed, a DC voltage having an absolute value of 40 to 75 V, which is different from the charge amount peak value of the white particles A1, is applied to the upstream electrode 15a. A DC voltage having an absolute value of 150 to 400 V is applied, and at this time, the downstream electrode 15b is grounded.
Further, for example, when a black image is displayed, a DC voltage having an absolute value of 40 to 75 V with a different sign from the charge amount peak value of the black particle B1 is applied to the upstream electrode 15a, and then the absolute sign with the different sign. A DC voltage having a value of 150 to 400 V is applied, and at this time, the downstream electrode is grounded.

  Specifically, for example, in the present invention, the charge amount peak value a1 of the white particle A1 is a positive value, the charge amount peak value a2 of the white particle A2 is a positive value, and the charge amount peak value b1 of the black particle B1 is negative. In the case of a value, in order to display white, a DC voltage of −40 to −75 V is applied to the upstream electrode 15 a, and then a DC voltage of −150 to −400 V is applied. On the other hand, to display black, a DC voltage of +40 to + 75V is applied to the upstream electrode 15a, and then a DC voltage of +150 to + 400V is applied. The applied voltage range is a condition when the downstream electrode 15b is grounded. As long as a predetermined potential difference is set between the upstream electrode 15a and the downstream electrode 15b and the sign of the voltage applied to the upstream electrode 15a is the same as described above, the voltage is also applied to the downstream electrode 15b. May be applied.

  For example, in the present invention, when the charge amount peak value a1 of the white particle A1 is a negative value, the charge amount peak value a2 of the white particle A2 is a negative value, and the charge amount peak value b1 of the black particle B1 is a positive value. In order to display white, a DC voltage of +40 to +75 V is applied to the upstream electrode 15a, and then a DC voltage of +150 to +400 V is applied. On the other hand, to display black, a DC voltage of −40 to −75 V is applied to the upstream electrode 15a, and then a DC voltage of −150 to −400 V is applied. The applied voltage range is a condition when the downstream electrode 15b is grounded. As long as a predetermined potential difference is set between the upstream electrode 15a and the downstream electrode 15b and the sign of the voltage applied to the upstream electrode 15a is the same as described above, the voltage is also applied to the downstream electrode 15b. May be applied.

  Hereinafter, the case where the charge amount peak value a1 of the white particle A1 is a positive value, the charge amount peak value a2 of the white particle A2 is a positive value, and the charge amount peak value b1 of the black particle B1 is a negative value is shown in FIG. This will be described in detail with reference to FIG. Regarding the case where the charge amount peak value a1 of the white particle A1 is a negative value, the charge amount peak value a2 of the white particle A2 is a negative value, and the charge amount peak value b1 of the black particle B1 is a positive value, Since the description is the same as the following description except that the sign is reversed between positive and negative, the description of this case is omitted. 2 and 3, the white particles A1 are represented by 22a, the white particles A2 by 22b, and the black particles B1 by 21, as in FIG.

  In the image display device, when a DC voltage having a relatively small absolute value of −40 to −75 V, preferably −50 to −65 V is applied to the upstream electrode 15a in a black display state, FIG. As shown in FIG. 5, the white particles 22b move to the upstream side in the visual recognition direction in the gap 18 based on the charging polarity and adhere. At this time, the black particles 21 and the white particles 22a hardly move at the voltage because the absolute value of the charge amount peak value is significantly larger than that of the white particles 22b. In this state, the image display device 10 displays a black image as a whole, but does not display the blackest image. Thereafter, when a DC voltage having a relatively large absolute value of −150 to −400 V, preferably −200 to −300 V is applied to the upstream electrode 15a, as shown in FIG. The white particles 22a move at the same time based on the charged polarity and are replaced with each other. In this state, the image display device 10 displays the whitest image. At this time, if a relatively small DC voltage is not applied, the white particles having a large filling amount with respect to the cell are difficult to move, and the whiteness is not actually improved.

  Next, when a DC voltage having a relatively small absolute value of +40 to +75 V, preferably +50 to +65 V is applied to the upstream electrode 15a, the white particles 22b are based on the charged polarity as shown in FIG. Then, it moves to the downstream side in the visual recognition direction in the gap 18 and adheres. At this time, the black particles 21 and the white particles 22a hardly move at the voltage because the absolute value of the charge amount peak value is significantly larger than that of the white particles 22b. In this state, the image display device 10 displays a white image as a whole, but does not display the whitest image. Thereafter, when a DC voltage having a relatively large absolute value of +150 to +400 V, preferably +200 to +300 V is applied to the upstream electrode 15a, the black particles 21 and the white particles 22a are formed as shown in FIG. They move at the same time based on the charge polarity, and are replaced with each other. In this state, the image display device 10 displays the blackest image. At this time, unless a relatively small DC voltage is applied, the white particles having a large filling amount with respect to the cell are difficult to move, and the contrast is not actually improved.

  In FIG. 3, the image display device 10 of the type having no electrodes 15a and 15b shown in FIG. 1B is set in the voltage application device 30 having the external electrodes 25a and 25b, and voltage is applied in this state. The method of driving is shown. 3 (a) to 3 (d) can be applied to the description of FIGS. 2 (a) to 2 (d) by replacing the electrodes 15a and 15b with the external electrodes 25a and 25b, respectively. Description is omitted.

[Method for Manufacturing Image Display Device]
The image display device according to the present invention can be manufactured by the following electrophotographic development system.
Hereinafter, manufacture of an image display device in which the charge amount peak value a1 of the white particle A1 is a positive value, the charge amount peak value a2 of the white particle A2 is a positive value, and the charge amount peak value b1 of the black particle B1 is a negative value. The method will be described in detail with reference to FIG. For an image display device in which the charge amount peak value a1 of the white particle A1 is a negative value, the charge amount peak value a2 of the white particle A2 is a negative value, and the charge amount peak value b1 of the black particle B1 is a positive value. Since the voltage and the charging polarity are the same as those described below except that the sign is reversed between positive and negative, the description of the manufacturing method of the image display device is omitted. In FIG. 4, as in FIG. 1, the white particles A <b> 1 are represented by 22 a, the white particles A <b> 2 are represented by 22 b, and the black particles B <b> 1 are represented by 21.

  First, the charge polarity and the charge amount peak value of each of the white particles A1, A2 and the black particles B1 are controlled by adjusting the carrier material, the mixing ratio, the mixing conditions, and the like by the above-described method. On the other hand, electrodes 15a and 15b and optionally an insulating layer 16 are formed on the two substrates 11 and 12 to obtain a pair of substrates with electrodes.

  The mixture (21, 210) of the black particles 21 and the carriers 210 in which the charging polarity and the charge amount peak value of the black particles 21 are controlled is placed on a conductive stage 100 as shown in FIG. One electrode-attached substrate is placed at a predetermined interval from the stage 100. Thereafter, as shown in FIG. 4A, a positive DC voltage and an AC voltage are applied to the electrode 15 b to adhere the negatively charged black particles 21 on the insulating layer 16. The voltage application time may be adjusted so that the content ratio of the black particles 21 is within the above-described range.

  Next, the mixture (22b, 220) of the white particles 22b and the carrier 220 in which the charging polarity and the charge amount peak value of the white particles 22b are controlled is placed on the conductive stage 100 as shown in FIG. The substrate with electrodes to which the black particles 21 are attached is placed with a predetermined distance from the stage 100. Thereafter, as shown in FIG. 4B, a negative DC voltage and an AC voltage are applied to the electrode 15b to attach the positively charged white particles 22b on the insulating layer 16. The voltage application time may be adjusted so that the content ratio of the white particles 22b is within the above-described range.

  Further, the mixture (22a, 220) of the white particles 22a and the carrier 220 in which the charging polarity and the charge amount peak value of the white particles 22a are controlled is placed on the conductive stage 100 as shown in FIG. The substrate with electrodes to which the black particles 21 and the white particles 22b are attached is placed at a predetermined interval from the stage 100. Thereafter, as shown in FIG. 4C, a negative DC voltage and an AC voltage are applied to the electrode 15b to attach the positively charged white particles 22a onto the adhesion layer of the black particles 21 and the white particles 22b. The voltage application time may be adjusted so that the content ratio of the white particles 22a falls within the above-described range.

  As shown in FIG. 4 (d), the substrate with one electrode to which the black particles 21 and the white particles 22a and 22b are attached and the substrate with the other electrode are adjusted with a partition so as to have a predetermined interval. The image display device can be obtained by stacking and bonding the periphery of the substrate.

[Components of Image Display Device]
The substrates 11 and 12, the electrodes 15a and 15b, the insulating layer 16, and the partition wall 17 constituting the image display device 10 shown in FIG. 1 will be described.

  First, the substrates 11 and 12 constituting the image display device 10 will be described. In the image display device 10, the observer visually recognizes the image formed by the display particles from at least one side of the substrates 11 and 12, and therefore the substrate provided on the side viewed by the observer is required to be made of a transparent material. . Therefore, the substrate used on the side where the observer visually recognizes the image is preferably a light-transmitting material having a visible light transmittance of 80% or more, for example, and has a visible light transmittance of 80% or more. Sex is obtained. Of the substrates constituting the image display device 10, the material of the substrate provided on the opposite side of the image viewing side is not necessarily transparent.

  The thicknesses of the substrates 11 and 12 are each preferably 2 μm to 5 mm, and more preferably 5 μm to 2 mm. When the thicknesses of the substrates 11 and 12 are in the above range, sufficient strength can be given to the image display device 10 and the distance between the substrates can be kept uniform. In addition, since the image display device can be provided in a compact and lightweight manner by setting the thickness of the substrate within the above range, the use of the image display device in a wide field is promoted. Further, by setting the thickness of the substrate on the side where the image is viewed to be in the above range, the display image can be accurately viewed without impeding the display quality.

  Examples of the material having a visible light transmittance of 80% or more include an inorganic material having no flexibility such as glass and quartz, an organic material typified by a resin material described later, a metal sheet, and the like. Among these, organic materials and metal sheets can impart a certain degree of flexibility to the image display device. Examples of the resin material having a visible light transmittance of 80% or more include polyester resins typified by polyethylene terephthalate and polyethylene naphthalate, polycarbonate resins, polyethersulfone resins, and polyimide resins. . In addition, a transparent resin obtained by radical polymerization of a vinyl polymerizable monomer such as an acrylic resin or a polyethylene resin, which is a polymer of acrylic acid ester or methacrylic acid ester represented by polymethyl methacrylate (PMMA). It is done.

  The electrodes 15a and 15b are provided on the surfaces of the substrates 11 and 12, respectively, and form an electric field between the substrates, that is, in the gap 18 by applying a voltage. The electrodes 15a and 15b need to be transparent on the side where the observer visually recognizes the image, as in the above-described substrate.

  The thickness of the electrode provided on the side for visually recognizing the image is required to ensure conductivity and at a level that does not hinder the light transmittance. Specifically, the thickness is preferably 3 nm to 1 μm, and preferably 5 nm to 400 nm. More preferred. Note that the visible light transmittance of the electrode provided on the side where the image is viewed is preferably 80% or more, like the substrate. The thickness of the electrode provided on the side opposite to the side where the image is viewed is also preferably within the above range, but it is not necessary to be transparent.

  Examples of the constituent material of the electrodes 15a and 15b include metal materials, conductive metal oxides, and conductive polymer materials. Specific examples of the metal material include aluminum, silver, nickel, copper, and gold. Specific examples of the conductive metal oxide include indium tin oxide (ITO), indium oxide, and antimony tin. An oxide (ATO), a tin oxide, a zinc oxide, etc. are mentioned. Furthermore, examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, and the like.

  As a method of forming the electrodes 15a and 15b on the substrates 11 and 12, for example, when an electrode on a thin film is provided, a sputtering method, a vacuum evaporation method, a chemical vapor deposition method (CVD method; Chemical Vapor Deposition), a coating method is used. Etc. There is also a method of forming an electrode by mixing a conductive material with a solvent or a binder resin and applying the mixture to a substrate.

  The insulating layer 16 is provided on the surfaces of the electrodes 15a and 15b, and is in contact with the display particles 21, 22a and 22b on the surface of the insulating layer 16. The insulating layer 16 has a role of relaxing the change in the charge amount by the voltage applied when the display particles 21, 22 a, 22 b are moved. Further, by imparting a resin having a highly hydrophobic structure and unevenness, it is possible to reduce the physical adhesion with the display particles and to reduce the driving voltage. The material constituting the insulating layer 16 is an electrically insulating material that can be made into a thin film, and has transparency as desired. The insulating layer provided on the image viewing side preferably has a visible light transmittance of 80% or more, like the substrate. Specific examples include silicone resin, acrylic resin, and polycarbonate resin.

  The thickness of the insulating layer 16 is preferably 0.01 μm or more and 10.0 μm or less. That is, when the thickness of the insulating layer 16 is in the above range, the display particles 21, 22a, and 22b can move without applying a very large voltage between the electrodes 15a and 15b. It is preferable because an image can be displayed by applying a level voltage.

  The partition wall 17 secures the space 18 between the upper and lower substrates, and can be formed not only at the edges of the substrates 11 and 12 but also inside as needed, as shown in the right and left diagrams in the upper part of FIG. . The width of the partition wall 17, particularly the thickness of the partition wall on the image display surface 18 a side, is preferably as thin as possible from the viewpoint of ensuring the clarity of the display image, as shown in the right side of FIG.

The partition walls 17 formed inside the substrates 11 and 12 may be formed continuously or intermittently in the front and back directions in the right and left drawings in the upper part of FIG.
By controlling the shape and arrangement of the partition walls 17, the cells in the gap 18 partitioned by the partition walls 17 can be arranged in various shapes. An example of the shape and arrangement of the cells when the gap 18 is viewed from the viewing direction of the substrate 11 is shown in the lower diagram of FIG. As shown in the lower drawing of FIG. 5, a plurality of cells can be arranged in a rectangular shape, a triangular shape, a line shape, a circular shape, a hexagonal shape or the like in a honeycomb shape or a mesh shape.

  The partition wall 17 can be formed, for example, by processing the substrate on the side opposite to the side on which the image is viewed using the following method. Examples of the method for forming the partition wall 17 include embossing with a resin material or the like, uneven formation by hot press injection molding, photolithography, screen printing, and the like.

<Experimental example A (positively charged white particles A1—positively charged white particles A2—negatively charged black particles B1)>
<Example / comparative example>
[Production of white particles]
The resin and titanium oxide described below were put into a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.), the peripheral speed of the stirring blade was set to 25 m / second, and the mixture was mixed for 5 minutes to obtain a mixture.
Styrene acrylic resin (weight average molecular weight 20,000) 100 parts by weight Anatase type titanium oxide (average primary particle size 150 nm) 30 parts by weight The above mixture was kneaded with a twin-screw extrusion kneader and then coarsely pulverized with a hammer mill. Coarse powder was pulverized with a turbo mill pulverizer (manufactured by Turbo Kogyo Co., Ltd.), and further finely classified with an airflow classifier utilizing the Coanda effect to produce white base particles having a volume average particle size of 8.2 μm and CV30. . Next, to 100 parts by weight of the white base particles, 0.6 parts by weight of silica fine particles subjected to aminosilane coupling treatment (average primary particle size 50 nm) are added, and a hybridizer (manufactured by Nara Machinery Co., Ltd.) is used. The number of rotations was set to 15,000 rpm, and a mixing process for 10 minutes was performed. Subsequently, 1.0 part by weight of silica fine particles having an average primary particle size of 15 nm subjected to aminosilane coupling treatment was added, and white particles were produced by carrying out the same mixing treatment with a hybridizer.

[Production of black particles]
The resin and carbon black described below were put into a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.), the peripheral speed of the stirring blade was set to 25 m / sec, and the mixture was mixed for 5 minutes to obtain a mixture.
Styrene acrylic resin (weight average molecular weight 20,000) 100 parts by weight Carbon black (average primary particle size 25 nm) 10 parts by weight The above mixture is kneaded with a twin-screw extrusion kneader, then coarsely pulverized with a hammer mill, and then turbo milled. Coarse powder was pulverized with a machine (manufactured by Turbo Kogyo Co., Ltd.), and further finely classified with an airflow classifier utilizing the Coanda effect to produce black matrix particles having a volume average particle size of 8.0 μm and CV30. Next, 0.6 parts by weight of silica fine particles (average primary particle size 50 nm) subjected to aminosilane coupling treatment are added to 100 parts by weight of the black base particles, and a hybridizer (manufactured by Nara Machinery Co., Ltd.) is used. The number of revolutions was set to 15,000 rpm, and a mixing process for 10 minutes was performed. Subsequently, 1.0 part by weight of silica fine particles having an average primary particle size of 15 nm subjected to aminosilane coupling treatment was added, and black particles were produced by performing the same mixing treatment with a hybridizer.

[Carrier A for charging to positive polarity]
Two parts by weight of fluorinated acrylate resin particles are added to 100 parts by weight of the ferrite core having an average particle diameter of 80 μm, and these raw materials are put into a horizontal rotary blade type mixer so that the peripheral speed of the horizontal rotary blade is 8 m / sec. After mixing and stirring at 22 ° C. for 10 minutes under the conditions, the carrier A was manufactured by heating to 90 ° C. and stirring for 40 minutes.

[Carrier B for charging to negative polarity]
Conditions in which 2 parts by weight of cyclohexyl methacrylate resin particles are added to 100 parts by weight of ferrite core having an average particle diameter of 80 μm, and these raw materials are put into a horizontal rotary blade type mixer so that the peripheral speed of the horizontal rotary blade is 8 m / sec. Was mixed and stirred at 22 ° C. for 10 minutes, and then heated to 90 ° C. and stirred for 40 minutes to produce Carrier B.

[Manufacture of image display devices]
The image display apparatus was manufactured according to the following method so as to have the same structure as that shown in FIG. Two glass substrates 11 and 12 having a length of 80 mm, a width of 50 mm, and a thickness of 0.7 mm are prepared, and an indium tin oxide (ITO) film having a thickness of 300 nm (resistance of 30 Ω / □) is provided on each substrate surface. Electrodes 15a and 15b made of were formed by vapor deposition. On the electrode, a coating solution prepared by dissolving 12 g of polycarbonate resin in a mixed solvent of 80 ml of tetrahydrofuran and 20 ml of cyclohexanone is applied by spin coating to form an insulating layer 16 having a thickness of 3 μm. Got.

  Mixing black particles and carrier B with a shaker (manufactured by Yayoi YS-LD Co., Ltd.) to charge black particles, and a mixture containing black particles B1 having predetermined charge amount peak values shown in Table 1 Got. Since the charge amount peak value of the black particles changes depending on the material of the carrier and the black particles, the mixing ratio, and the mixing conditions, the charge amount peak value was adjusted by changing the mixing ratio of the carrier and the black particles. As shown in FIG. 4A, the obtained mixture (21, 210) was placed on a conductive stage 100, and one substrate with electrodes was placed at an interval of about 2 mm from the stage 100. A black bias 21 was adhered on the insulating layer 16 by applying a DC bias of +100 V, an AC bias of 2.0 kV, and a frequency of 2.0 kHz between the electrode 15 b and the stage 100. The voltage application time was adjusted so that the amount of black particles 21 adhered was 1.0 layer. One layer means the amount by which a particle layer whose thickness is the particle size of one particle is formed. The adhesion amount of the black particles 21 was 100 parts by weight with respect to 100 parts by weight of the white particles 22a attached later.

  Mixing white particles and carrier A with a shaker (manufactured by YS-LD Co., Ltd., Yayoi) to charge white particles, and a mixture containing white particles A2 having predetermined charge amount peak values shown in Table 1 Got. Since the charge amount peak value of the white particles changes depending on the material of the carrier and the white particles, the mixing ratio, and the mixing conditions, the charge amount peak value was adjusted by changing the mixing ratio of the carrier and the white particles. The obtained mixture (22b, 220) is placed on a conductive stage 100 as shown in FIG. 4 (b), and the substrate on which the black particles 21 are adhered is spaced from the stage 100 by about 2 mm. installed. A DC bias of −100 V, an AC bias of 2.0 kV, and a frequency of 2.0 kHz were applied between the electrode 15 b and the stage 100 to deposit white particles 22 b on the insulating layer 16. The voltage application time was adjusted so that the amount of white particles 22b deposited was 0.3 layers. The adhesion amount of the white particles 22b was 30 parts by weight with respect to 100 parts by weight of the white particles 22a adhered later.

  Mixing white particles and carrier A with a shaker (manufactured by YS-LD Co., Ltd., Yayoi) to charge white particles, and a mixture containing white particles A1 having a predetermined charge amount peak value shown in Table 1 Got. Since the charge amount peak value of the white particles changes depending on the material of the carrier and the white particles, the mixing ratio, and the mixing conditions, the charge amount peak value was adjusted by changing the mixing ratio of the carrier and the white particles. The obtained mixture (22a, 220) is placed on a conductive stage 100 as shown in FIG. 4 (c), and the substrate on which the black particles 21 and the white particles 22b are attached is placed on the stage 100 with about 2 mm. Installed at intervals. A DC bias of −100 V, an AC bias of 2.0 kV, and a frequency of 2.0 kHz were applied between the electrode 15 b and the stage 100 to deposit white particles 22 a on the insulating layer 16. The voltage application time was adjusted so that the amount of white particles 22a deposited was one layer.

  The substrate on which the white particles 22a, the white particles 22b, and the black particles 21 are adhered and the substrate on which the display particles are not adhered are adjusted with a partition so as to have an interval of 50 μm as shown in FIG. Then, the periphery of the substrate was adhered with an epoxy adhesive to obtain an image display device. The volume occupation ratio between all the display particles between the glass substrates was 25%.

[Evaluation]
Evaluation of drive characteristics Display characteristics were evaluated by applying a DC voltage to the image display apparatus according to the following procedure and measuring the reflection density of the display image obtained by the voltage application.
The electrode 15a was applied while changing the voltage (first voltage) at intervals of 5V from -40V to -75V. After applying each first voltage, it was applied while changing the voltage (second voltage) at intervals of 5V from -150V to -400V. As a result, a white image was obtained.
The voltage was applied to the electrode 15a while changing the voltage (first voltage) at intervals of 5V from + 40V to + 75V. After applying each first voltage, it was applied while changing the voltage (second voltage) from + 150V to + 400V at intervals of 5V. As a result, a black image was obtained.
The electrode 15b was electrically grounded.
Each predetermined voltage was applied for 5 seconds.
The density was measured using a reflection densitometer “RD-918 (manufactured by Macbeth)”.

(contrast)
The contrast was measured using a reflection densitometer “RD-918 (manufactured by Macbeth)”. Measure 10 points in the black image area, measure the average value of the five points with the highest density “black density”, measure 10 points in the white image part, and set the average value of the five points with the lowest density to “white density” The difference between “black density” and “white density” was evaluated as contrast.
Contrast was determined as pass (◯) when the density difference was 1.00 or more, and reject (x) when less than 1.00. In particular, the density difference is preferably 1.05 or more (◎).

<Experimental example B (negatively charged white particles A1-negatively charged white particles A2-positively charged black particles B1)>
<Example / comparative example>
[Production of white particles]
White particles were produced by the same method as the production method of the white particles of Experimental Example A.

[Production of black particles]
Black particles were produced by the same method as the production method of the black particles of Experimental Example A.

[Carrier A for charging to positive polarity]
Carrier A was produced by the same method as the carrier A production method of Experimental Example A.

[Carrier B for charging to negative polarity]
Carrier B was produced by the same method as the carrier B production method of Experimental Example A.

[Manufacture of image display devices]
The carrier B is used instead of the carrier A, the carrier A is used instead of the carrier B, and the black particles B1, the white particles A2, and the white particles A1 are charged so as to have predetermined charge amount peak values shown in Table 3, respectively. The voltage application conditions at the time of adhesion of the black particles B1 were DC bias −100 V, AC bias 2.0 kV, and frequency 2.0 kHz, and the voltage application conditions at the time of adhesion of the white particles A2 were DC bias +100 V, AC bias 2 0.0 kV, frequency 2.0 kHz, and the method for manufacturing the image display device of Experimental Example A, except that the voltage application condition at the time of adhesion of the white particles A1 is DC bias +100 V, AC bias 2.0 kV, frequency 2.0 kHz An image display device was manufactured by the same method as described above.

[Evaluation]
Evaluation was performed in the same manner as in Experimental Example A, except that a DC voltage was applied to the image display device according to the following procedure.
The voltage was applied to the electrode 15a while changing the voltage (first voltage) at intervals of 5V from + 40V to + 75V. After applying each first voltage, it was applied while changing the voltage (second voltage) from + 150V to + 400V at intervals of 5V. As a result, a white image was obtained.
The electrode 15a was applied while changing the voltage (first voltage) at intervals of 5V from -40V to -75V. After applying each first voltage, it was applied while changing the voltage (second voltage) at intervals of 5V from -150V to -400V. As a result, a black image was obtained.

<Experimental example C>
The image display apparatus of Example 2A (hereinafter referred to as apparatus X) was used.
Manufacture of image display particles (hereinafter referred to as “device Y”) in the same manner as the image display device of Example 2A, except that a large amount of white particles A1 were attached instead of the white particles A2 not being attached. did.

The change in density of the display image in the apparatuses X and Y was measured according to the following method.
First, a black image was displayed by applying 100 V to the electrode 15a in the device X for 5 seconds. Next, as shown in FIG. 6A, the density of the display image was measured from the substrate on the upstream side in the viewing direction while continuously decreasing the applied voltage from 0 V to −100 V at a speed of −10 V / second. The density change as shown by the solid line in FIG. Finally, a white image was displayed. The electrode 15b was grounded.
When the same voltage application was performed also in the apparatus Y, the density | concentration change as shown by the broken line of FIG.6 (b) was shown.

Next, as shown in FIG. 7A, in the apparatus X, the applied voltage is continuously increased from 0 V to +100 V at a speed of +10 V / second as shown in FIG. As a result, the change in concentration as shown by the solid line in FIG. 7B was measured. Finally, a black image was displayed. The electrode 15b was grounded.
When the same voltage application was performed also in the apparatus Y, the density | concentration change as shown by the broken line of FIG.7 (b) was shown.

  10: image display device, 11:12: substrate, 15a: 15b: electrode, 16: insulating layer, 17: partition, 18: gap, 18a: image display surface, 21: black particles, 22a: 22b: white particles.

Claims (1)

Encapsulating charged display particles between two substrates, at least one of which is transparent, and generating an electric field between the substrates, thereby moving the display particles in the gas phase to display an image;
And the upstream side of the electrode in the viewing direction, by applying a voltage between the downstream side of the electrodes, a field image display device Ru electric field is generated between the substrates,
The display particles include two types of white particles A1 and A2 having the same charge amount peak value sign and different charge amount peak values, and black particles B1.
When the charge amount peak value of the white particle A1 is a1 (μC / g), the charge amount peak value of the white particle A2 is a2 (μC / g), and the charge amount peak value of the black particle B1 is b1 (μC / g). And the following formulas (1) to (3);
10 ≦ | a1 | ≦ 20 (1)
−1.2 ≦ a1 / b1 ≦ −0.8 (2)
0.35 ≦ a2 / a1 ≦ 0.65 (3)
Meet all of the
When a white image is displayed, a DC voltage having an absolute value of 40 to 75 V with a different sign from the charge amount peak value of the white particle A1 is applied to the upstream electrode, and then an absolute value of 150 to 400 V with a different sign. DC voltage is applied, and the downstream electrode is grounded,
When a black image is displayed, a DC voltage having an absolute value of 40 to 75 V with a different sign from the charge amount peak value of the black particles B1 is applied to the upstream electrode, and then an absolute value of 150 to 400 V with a different sign. The direct current voltage is applied, and the downstream electrode is grounded.

Images