JP2002236299A - Image display medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the density contrast, the angle of field, etc., of a display image in an image display medium which can repeatedly be used, and images displayed by which can be outputted on a paper sheet by using a copying machine or a printer. SOLUTION: The image display medium consists of at least a display substrate, a counter substrate arranged oppositely to the display substrate, an enclosed material to be enclosed in the gap between the display substrate and the counter substrate. The enclosed material consists of at least two kinds of concealale particles different in color and volume resistivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

2. Description of the Related Art Conventionally, as a so-called electronic paper technique,
Many display techniques such as rotation of colored particles, electrophoresis, thermal rewritable, liquid crystal, and electrochromy are known. Among them, as a display technology using toner, a conductive colored toner and white particles are sealed between opposing substrates, and charges are injected into the conductive colored toner via a charge transport layer provided on the inner surface of a non-display substrate. Then, the charged electrically conductive toner moves toward the display substrate, which is located opposite to the non-display substrate, by an electric field between the substrates, and the electrically conductive colored toner adheres to the display substrate, and the electrically conductive colored toner and the white color become white. It is known that an image is displayed by contrast with particles. In the above prior art, there is room for improvement in low contrast, narrow viewing angle, and the like.

[0002]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an image display which can be used repeatedly and which can be output to paper using a copying machine or a printer. An object of the present invention is to improve the density contrast and the viewing angle of a display image in a medium.

[0003]

The above object of the present invention is attained by providing the following image display medium. That is, the present invention provides: <1> an image comprising at least a display substrate, a counter substrate disposed to face the display substrate, and an enclosure sealed in a gap between the display substrate and the counter substrate. An image display medium, wherein the encapsulant comprises at least two types of concealing particles having different concealing properties having different colors and different volume resistivity.

<2> Among the at least two types of opaque particles having different color and volume resistivity, the volume resistivity of at least one type of opaque particle is 10%.
The image display medium according to <1>, wherein the image display medium has a resistivity of not more than ⁷ Ω · cm and at least 10 ² Ω · cm or more than the volume resistivity of at least one other opaque particle.

<3> Among the at least two types of concealable particles, one type of opaque particles having the largest average particle size and one type of concealable particles having the smallest average particle size have the above-mentioned average particle size. The ratio is 1/30 to 30/1.
An image display medium according to <1> or <2>.

<4> Of the at least two types of hiding particles, the total number of one type of hiding particles is N × 1/900 ≦ N ≦ N
<900><1> to <3>
The image display medium according to any one of the above.

<5> Of the at least two types of concealable particles, the total surface area of one type of opaque particles having the largest volume resistivity is greater than the total surface area of the other type of concealable particles. The image display medium according to any one of <1> to <4>, wherein S × 1/25 ≦ S ≦ S × 100.

<6> At least one of the at least two types of opaque particles contains 1 to 70% by mass of a pigment.
The image display medium according to any one of <1> to <3>.

<7> At least one of the at least two types of opaque particles has a glass transition point of 55 ° C. or more, <1> to <6>.
The image display medium according to any one of the above.

<8> The adhesive force formed between the display substrate and at least one of the at least two types of opaque particles is 1 pN to 0.1 N. The image display medium according to claim 1.

<9> At least one of the at least two concealing particles has an adhesion of 1 pN to 0.1 N formed between the concealing particles. An image display medium according to any one of claims 1 to 8.

<10> A sliding friction coefficient between the display substrate and at least one of the at least two opaque particles is 0.8 or less. An image display medium according to any one of <1> to <9>.

<11> The sliding friction coefficient of at least one of the at least two types of opaque particles is 0.8 or less.
0 is an image display medium.

<12> A rolling friction coefficient between the display substrate and at least one of the at least two types of opaque particles is 0.3 or less. An image display medium according to any one of <11>.

<13> At least one of the at least two concealing particles has a rolling friction coefficient of 0.3 or less. <1> to <12>
The image display medium according to any one of <1> to <3>.

<14> The image display medium according to any one of <1> to <13>, wherein the relative humidity of the gap between the display substrate and the counter substrate is 5 to 90%.

<15> The volume filling ratio of the at least two or more opaque particles (total volume of the opaque particles / the volume of the gap between the display substrate and the counter substrate) is 0.001 to 0.001.
The image display medium according to any one of <1> to <14>, wherein the value is 0.5.

<16> At least one of the at least two types of hiding particles has a bulk density of:
<1> to 0.2 g / cm ³ or more
An image display medium according to any one of <15>.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION An image display medium according to the present invention comprises at least a display substrate and a counter substrate disposed opposite to the display substrate (hereinafter, the display substrate and the counter substrate are referred to as “a pair of substrates”). In some cases) and an enclosure sealed in the gap between the display substrate and the counter substrate. The image display medium forms an image by applying an electric field to the display substrate and the counter substrate, and moving at least one of the at least two types of concealing particles having different volume resistivity, which are inclusions, to the display substrate side. I do. Hereinafter, these will be described.

<Display substrate and counter substrate>
Various concealing particles as an encapsulation described later are appropriately moved to the display substrate side to perform image display. The display substrate is
If it is substantially transparent, a known substrate material can be used, and a pixel electrode layer, a pixel electrode layer, a glass or plastic (for example, polycarbonate, acrylic, polyester, polypropylene, polyethylene, etc.) surface can be used.
An insulating layer and the like are appropriately formed. In addition, “substantially transparent” means that light transmittance is 50% or more (preferably 70%
Above).

The opposing substrate moves opaque particles, which will be described later, which do not contribute to image display, to the opposing substrate side. As the counter substrate, a known substrate material can be used, and a transparent support such as described above, or an opaque support such as a printed board (since the counter substrate does not need to be particularly transparent). A body can be used, and a uniform electrode layer, an insulating layer, and the like are appropriately formed on the surface thereof.

Each of the display substrate and the counter substrate is a light-transmitting electrode layer or a laminate in which a light-transmitting insulating layer is sequentially laminated on the light-transmitting electrode layer on at least the surface of the support. Preferably, the non-conductive electrode layer is a pixel electrode, or the light-transmitting electrode layer of the display substrate and / or the counter substrate is a matrix electrode layer. Further, it is preferable that the distance between the display substrate and the counter substrate is appropriately set according to the use of the image display medium.

<Enclosure> The enclosure comprises at least two kinds of concealing particles having different concealing properties, which are different from each other in color and volume resistivity.

At least two different colors and different volume resistivity
By using species of opaque particles, it is possible to selectively dispose different types of opaque particles in an image region and a non-image region by an electric field or the like, thereby improving the density contrast and the viewing angle of the obtained image. be able to.
Further, by using the opaque particles that appropriately satisfy various conditions as shown below as an enclosure, the performance of the image display medium, for example, density contrast, density uniformity,
Sharpness, viewing angle, display responsiveness, repetitive displayability, image retention, lifespan, and the like can be improved.

The volume resistivity of at least one kind of concealing particles is 10 ⁷ Ω · cm or less, and the volume resistivity of at least one other kind of concealing particles is 10 ² Ω more than the volume resistivity of the concealing particles.・ It is preferable to increase the size by 1 cm or more.
It is more preferable to increase 0 ⁵ Ω · cm or more. By setting the volume resistivity of at least two types of opaque particles in this manner, sufficient charge is injected from the substrate into the low volume resistivity opaque particles, and the particles become high-charged particles easily along the electric field. On the other hand, the opaque particles having a high volume resistivity have a small amount of movement due to an electric field since no charge is injected. As a result, if an electric field is formed in the image area, the opaque particles having high conductivity can be selectively moved to the image area, and an image can be displayed with a high contrast and a wide viewing angle.

As the opaque particles having different volume resistivity, for example, a combination of conductive particles and insulating particles can be used. Here, the conductivity refers to a material having a volume low efficiency of 10 ⁷ Ω · cm or less, and the insulation refers to a material having a volume low efficiency of 10 ⁹ Ω · cm or more. As the conductive particles, metal particles such as carbon black, nickel, silver, gold, tin and the like, or particles in which these are coated or contained on the particle surface are preferable. For example,
Spherical conductive particles (Micropearl NI manufactured by Sekisui Chemical Co., Ltd.) obtained by performing electroless nickel plating on the surface of fine particles made of a crosslinked copolymer containing divinylbenzene as a main component, for ferrite carriers for electrophotographic developers, And then
Spherical conductive particles (Micropearl AU manufactured by Sekisui Chemical Co., Ltd.) plated with gold are available. In addition, spherical conductive particles of amorphous carbon obtained by carbonizing and calcining a thermosetting phenol resin (Univex GCP, H-Type: volume specific resistance ≦ 10 ⁻² Ω manufactured by Unitika Ltd.)
Cm), and spherical conductive particles (Univex GCP conductive particles manufactured by Unitika Ltd .: volume resistivity ≤ 10 ^-4 Ωcm) coated with a metal such as gold or silver, and spherical particles of silica and alumina. Spherical conductive particles obtained by coating Ag and tin oxide on the surface of oxide fine particles (Admafine Co., Ltd.) can also be used.

As the insulating particles, commercially available glass beads, white fused alumina particles, true spherical particles composed of a crosslinked copolymer containing divinylbenzene as a main component (Micropearl SP, Micropearl manufactured by Sekisui Chemical Co., Ltd.) B
B), fine particles of cross-linked polymethyl methacrylate (MBX-20 black, white, manufactured by Sekisui Chemical Co., Ltd.),
Fine particles of polytetrafluoroethylene (Lubron L, manufactured by Daikin Industries, Ltd., Shamrock Techno)
logs Inc. SST-2), silicone resin fine particles (Tospearl manufactured by Toshiba Silicone Co., Ltd.), MB-C, MBE, EMA, SBX, B manufactured by Sekisui Plastics Co., Ltd.
MX, ARX-15, UB, and Toray Torayceram,
And the like. Usable are ordinary electrophotographic toners and transparent toners in which pigments are not dispersed.

As the two kinds of particles having different colors and volume resistivity in the present invention, the conductive particles and the insulating particles as described above include various colors (including chromatic, achromatic, and transparent). Are given. For example, in addition to black conductive particles (carbon black, metal color, etc. in the above conductive particles) and white insulating particles (white fused alumina particles, etc. in the above insulating particles, glass beads, transparent toner, etc. Insulating colored particles obtained by adding pigments such as yellow, magenta and cyan pigments and pigments such as red, green and blue pigments to resin binders, and ITO, indium.
A hexagonal layered compound composed of a zinc oxide and a transparent conductive material such as indium oxide (In ₂ O ₃ (ZnO) _n , n is an integer of 3 or more, IDIXO manufactured by Idemitsu Kosan Co., Ltd.), antimony oxide-doped tin oxide, etc. The added or coated colored conductive particles may be combined, or these colored conductive or colored insulating particles may be combined with the white conductive or insulating particles as described above. Further, full-color image display is possible by using colored particles and enclosing them in an image display medium as described below.

The average particle size of at least two types of concealing particles is determined by using one type of opaque particles having the largest average particle size (hereinafter, referred to as “the type of opaque particles”)
The ratio of the average particle size of the “large-diameter particles”) to one kind of opaque particles having the smallest average particle size (hereinafter sometimes referred to as “small-diameter particles”) is 1/30 to 30/1
It is preferable that By setting such a range, display driving can be improved.

However, large-diameter particles move at low voltage due to low adhesion to the substrate and between particles, whereas small-diameter particles cannot move at low voltage due to high adhesion, and are resistant to large-diameter particles. Display is possible, but it is difficult to obtain high display contrast. Therefore, in order to separate each opaque particle by an electric field and move it in another direction to obtain a larger contrast, it is preferable that the average particle diameter of each opaque particle is close. Specifically, from the viewpoint of performing good display with high display contrast, the average particle diameter R ′ of the opaque particles having the smallest volume resistivity relative to the average particle diameter R of the opaque particles having the largest volume resistivity is R /
It is preferable that 5 ≦ R ′ ≦ 10R, and R / 3 ≦ R ′
More preferably, ≦ 5R.

A method of driving a display medium using three or more kinds of opaque particles changes the adhesion of at least two kinds of conductive particles, which are opaque particles, to a substrate and the adhesion between concealment particles, Thus, by changing the display characteristics of each opaque particle with respect to the applied voltage, these opaque particles can be driven independently. For example, by changing the average particle size of each concealing particle, a difference can be provided in the adhesive force.

FIG. 1 shows an example of display characteristics with respect to applied voltage when an image is displayed using three kinds of concealing particles. In this example, negatively charged white particles having an average particle size of 5 μm are used as insulating particles, and gray particles having an average particle size of 20 μm and black particles having an average particle size of 5 μm are used as conductive particles. .

As shown in the display characteristics of each opaque particle in FIG. 1, the gray particles having an average particle diameter of 20 μm have a weak adhesive force and move to the display substrate side when a voltage of −200 V is applied to the display substrate. Black particles having a small average particle diameter and a large adhesive force cannot move at this voltage, and as a result, gray display is possible. Next, when a voltage of -350 V is applied to the display substrate, black particles having a large adhesive force can also move, and black display can be performed. Then, +
When a voltage of 350 V is applied, both the gray particles and the black particles move to the rear substrate side and are hidden by the white particles.
White display becomes possible.

As a method of changing the adhesive force to the substrate, in addition to the method of changing the average particle diameter, the material of the opaque particles themselves is changed to a material capable of obtaining a desired adhesive force, or the shape or surface roughness is changed. A method of controlling the height can be applied.
It is also possible to control the adhesive force by externally adding fine particles to the opaque particles.

Also, by controlling the charge amount of each conductive particle, each opaque particle can be driven independently. Since the movement of the opaque particles between the substrates is performed by the Coulomb force received from the electric field formed between the substrates, the Coulomb force received from the same electric field can be made different by changing the charge amount of each conductive particle. . Therefore, by controlling the charge amount of each conductive particle, it is possible to change the display characteristics with respect to the applied voltage of each conductive particle. The control of the charge amount of each conductive particle can be realized by providing a difference in the conductivity of each conductive particle, thereby providing a difference in a charge injection rate per unit time to each conductive particle. is there.

The amount of the insulating particles and the conductive particles used in this example is 50% by mass for white particles, 25% by mass for black particles, and 25% by mass for gray particles. The number of particles is adjusted to be sufficient. The display substrate and the counter substrate are made of glass (thickness: 1.1 mm)
An ITO film (thickness: 0.1 μm (1000 °)) is formed on the substrate, and PC-Z (polycarbonate, thickness: 2 μm)
m) is used. The distance between the display substrate and the counter substrate is set to 0.25 mm.

Normally, the amount of each insulating particle to be enclosed is set to be at least the number of insulating particles sufficient to cover at least the display surface of the display substrate (saturate the display density). The amount of the insulating particles encapsulated is sufficient to cover the color of the conductive particles moved from the display surface to the rear substrate (counter substrate) when the conductive particles are moved to the rear substrate. It is set to be more than the proper number of particles. However, if the concealing particles are excessively encapsulated, the porosity between the substrates decreases, and the movement of the insulating particles cannot be performed smoothly.
Excessive insulating particles form aggregates to form display defects. Therefore, it is preferable to set the encapsulation amount to an extent necessary and sufficient for each opaque particle to cover the display surface.

When the insulating particles are charged to have the opposite polarity to the conductive particles due to collision with the conductive particles, the two move in the same electric field in the opposite direction and adhere to different substrates. . In this case, it is preferable that the number of the insulating particles is set to a number of particles sufficient to cover at least the display surface (hide the conductive particles), similarly to the conductive particles. Therefore, the ratio of the number of particles of each particle is 1 / (the square of the particle size)
It is preferable to encapsulate at a ratio such that the ratio of

When the average particle diameters of the opaque particles are not substantially equal, the total number of the opaque particles of the other type is N × 1 / N
It is preferable to seal in the range of 900 ≦ N ≦ N × 900. By doing so, the total surface area of each opaque particle can be made equal. Here, "total surface area"
It refers to the sum of the respective surface areas of the same kind of opaque particles. The surface area can be calculated by measuring the particle size distribution of the particles with a particle size distribution meter.

At least one of the at least two concealing particles preferably contains a pigment, and the pigment concentration (the weight of the pigment / the weight of the concealing particle) is preferably used.
Although it depends on the type of material to be selected, it is preferably 1% by mass or more in consideration of concealment. In particular, when opaque particles having a particle size of several μm are used, higher opacity is required, and 3% by mass or more is more preferable. If the pigment concentration is too high, the resin component that binds the pigment becomes insufficient,
Since the mechanical strength of the opaque particles is significantly reduced, the content is preferably set to 70% by mass or less.

As a combination of at least two types of opaque particles, for example, as a combination of two types of opaque particles having different colors, a combination of white and black may be used from the viewpoint of providing the same visibility as an image printed on paper. Can be mentioned. Especially when the display is emphasized, a combination of complementary colors (for example, blue and yellow)
Can be used. From the viewpoint of cell juxtaposition color display, combinations of white and Y (yellow), M (magenta) and C (cyan), black and R (red), G
(Green) and B (blue). The opaque particles having different colors refer to particles having different spectral characteristics such as particles having different colors (hues), different densities (brightness), and different chromas.

The combination of the three kinds of opaque particles having different colors includes white, black, and chromatic colors; white, black, and Y, M, and C, respectively, from the viewpoint of producing a special color expression or the viewpoint of a cell juxtaposed color display. Combinations of white, black and R, G, B
Each combination; and the like. further,
Monotone gradation can be obtained by combining white, black, and gray particles, and cell juxtaposition color display can be performed while providing gradation by combining white and two or more types of Y, M, and C having different densities. It can be carried out. Similarly, by combining black and two or more types of R, G, and B having different densities, it is possible to perform the cell side-by-side color display while providing gradation.

In addition to the above, combinations of opaque particles having different spectral characteristics besides the visible region can be used for the color combination. According to this, rewritable invisible information can be provided.

Further, by making at least one kind of opaque particles exhibit a metallic color, an image area or a non-image area becomes a metallic color, and an impressive image can be displayed.

The glass transition point of the opaque particles affects the heat resistance of electronic paper. Accordingly, the glass transition point of the opaque particles is 55 ° C. or higher (office environment), preferably 8 in consideration of the usage environment, transportation environment, and storage environment of the electronic paper.
It is preferable that the temperature is 5 ° C. or more (the environment in the car). Since the opaque particles used in the image display medium of the present invention do not need to have the heat melting property of the toner used in the heat fixing method of electrophotography, a thermosetting resin can be used. Therefore, it is also possible to use a resin whose glass transition point is not clear and which thermally decomposes at 200 ° C. or higher.

The bulk density of a hiding particle is a characteristic value representing its fluidity, and is the weight of the particle per unit volume (g / c).
m ³ ). Generally, for particles of the same composition, the larger the value of the bulk density, the higher the fluidity. The bulk density can be measured using a powder tester manufactured by Hosokawa Micron Corporation. It is preferable that the fluidity of the opaque particles is high because the movement of the particle group is smooth. Therefore, the bulk density of the concealing particles may have higher, 0.2 g / cm ³ or more preferably, 0.3 to 3.0 g / cm ³ is more preferable. However, this does not apply when using foamed particles. Here, the expanded particles refer to particles having air bubbles in particles such as styrene foam, or particles having a network structure such as sponge.

The volume filling ratio of the concealing particles as the enclosure may be such that (total volume of the concealing particles / volume of the gap between the display substrate and the counter substrate) is 0.001 to 0.5. preferable. If it is 0.5 or less, the concealing particles can move between the substrates, and if the concealing particles exceed 0.5, they may be clogged between the substrates and cannot move. Further, by setting the filling rate to 0.4 or less, it is possible to move the opaque particles to an extent that display is possible, and when the filling rate is set to 0.25 or less, the opaque particles are more easily moved. Can be
Good display can be performed. Although the lower limit of the volume filling rate varies depending on the projected area ratio of the opaque particles adhering to the display surface, the pigment concentration, and the like, it cannot be determined unconditionally.
001 is preferable.

The adhesive force formed between the display substrate and at least one kind of opaque particles (hereinafter, sometimes referred to as “adhesive force between substrates”) is preferably 1 pN to 0.1 N, More preferably, it is 1 nN to 1 mN.
By setting the adhesive force to such a numerical value, sufficient image contrast, display responsiveness, and image retention can be obtained.

The adhesive force formed between the display substrate and the opaque particles can be determined as follows. First, one kind of cloud-shaped opaque particles is deposited on a substrate in a thin layer, and then a counter electrode is provided to form an electric field. The electric field is gradually increased, and the electric field intensity and the amount of the separated opaque particles (or the amount of the remaining particles) are measured. The electric field strength when half of the concealing particles are peeled off is defined as the peeling electric field strength. Separate force is calculated from the amount of charge of the opaque particles separately from the amount of charge multiplied by the peel electric field strength, and finally the gravity is subtracted to obtain the adhesive force (electric field method).
Alternatively, the measurement may be performed by a centrifugal method, an impact method, a method using an atomic force microscope, a tensile method, or the like.

Adhesive force of at least one kind of opaque particles among the at least two kinds of concealable particles formed between the concealable particles (hereinafter, also referred to as "adhesive force between particles").
Is preferably 1 pN to 0.1 N, and 0.1 n
More preferably, it is N to 1 mN. By setting the adhesive force to such a value, as in the above case,
Sufficient image contrast, display responsiveness, and image retention can be obtained. The adhesion between particles may be measured in the same manner as described above, after uniformly applying the particles on the substrate.

The adhesion between the substrates is van der Waals force,
It is the total sum of the liquid bridging force and the like, and is an index indicating the strength of bonding between contacting objects. The inter-substrate adhesion indicates the difficulty of peeling the opaque particles from the substrate, and affects image contrast and display responsiveness. That is, when the opaque particles adhered to the display surface are difficult to peel off, display switching may not be performed normally, leading to a decrease in image contrast or a problem that switching takes time. At the same time, it may affect the image retention when an image is formed. That is, if the opaque particles adhered to the display substrate surface can be easily peeled off, the particles may be peeled off by the action of an external impact, gravity, or the like after the display, and a problem such as damage to the displayed image may occur. There is.

Further, the adhesion between particles indicates good fluidity of particles, and may greatly affect image contrast, display responsiveness, and repetitive display. That is, when the opaque particles are strongly adhered to each other and are difficult to separate, a problem may occur that the particles are aggregated and the movement at the time of display switching becomes difficult. Further, when the opaque particles of different colors are aggregated in this way to form an image, problems such as a decrease in the image density or an increase in the background density may occur.

The adhesion between the substrates and the adhesion between the particles can be controlled by the kind of the concealing particles, the material and the shape of the surface of the substrate, and the contact angle, the surface energy, the surface roughness, the particle size, and the particle size. It is preferable to optimally design or select characteristics such as shape, hardness, and Young's modulus.

The coefficient of sliding friction between the display substrate and at least one kind of concealing particles (hereinafter sometimes referred to as the “sliding friction coefficient between particle substrates”) is preferably 0.8 or less. Further, it is preferable that the sliding friction coefficient of at least one kind of the concealing particles (hereinafter, also referred to as “particle sliding friction coefficient”) is 0.8 or less.

The coefficient of sliding friction between the display substrate and the opaque particles can be determined by measuring the force when the substrate is placed, a flat plate on which the opaque particles are uniformly coated and fixed is placed, and a horizontal load is applied under a predetermined load. And the coefficient of sliding friction can be calculated from the ratio of the horizontal force to the load. The coefficient of sliding friction between particles can be determined by uniformly applying and fixing particles on a substrate and then performing the same measurement as described above.

The above-mentioned coefficient of sliding friction indicates good fluidity of particles and greatly affects image contrast, display responsiveness and repetitive display. That is, if the sliding friction coefficient is too large, the movement of the particles is hindered by the frictional force,
There is a problem that the movement at the time of switching the display becomes difficult. In consideration of these characteristics, it is appropriate to set the value to 0.8 or less, and more preferably to 0.5 or less. By setting the sliding friction coefficient to such a value, sufficient image contrast and display responsivity can be obtained.

The rolling friction coefficient between the display substrate and the opaque particles (hereinafter, sometimes referred to as the “rolling friction coefficient between particle substrates”) is preferably 0.3 or less. Further, the rolling friction coefficient (hereinafter, referred to as at least one kind of concealing particles)
"Coefficient of rolling friction between particles") is 0.3
The following is preferred.

The rolling coefficient of friction between the display substrate and the opaque particles can be determined by setting the substrate, placing the same substrate on which the opaque particles are applied almost uniformly in a single layer, and pulling in the horizontal direction with a predetermined load applied. The rolling force can be calculated from the ratio of the horizontal force to the load by measuring the force at that time. The rolling friction coefficient between particles can be determined by performing the same measurement as described above after applying particles in multiple layers on a substrate.

The rolling coefficient of friction indicates the good flowability of particles and greatly affects image contrast, display responsiveness, and repetitive display. That is, when the rolling friction coefficient is too large similarly to the sliding friction coefficient, the movement of the particles is hindered by the frictional force, which causes a problem that the movement at the time of display switching becomes difficult. Taking these characteristics into account, 0.
It is appropriate to set it to 3 or less, and more preferably,
0.1 or less is more preferable. By setting the rolling friction coefficient to such a value, sufficient image contrast and display responsivity can be obtained.

The relative humidity of the gap between the display substrate and the counter substrate is preferably 5 to 90%. To achieve such a range, the image display medium of the present invention may be manufactured by filling particles in a room or a chamber adjusted to a uniform predetermined atmosphere (such as a nitrogen atmosphere) and shutting off particles from outside air.

The relative humidity in the display medium affects the electrical properties and adhesion properties of the concealed opaque particles, and further affects the image contrast, display responsiveness, and repetitive display. That is, if the humidity is too high, first, the adhesive force such as the liquid crosslinking force becomes high, and the opaque particles may adhere to each other firmly and become difficult to peel. In this case, there may be a problem that the opaque particles are aggregated and the movement at the time of display switching becomes difficult. Further, in the case where the opaque particles of different colors aggregate to form an image in this manner, problems such as a decrease in the density of the image or an increase in the density of the background may occur. If the humidity is too high, the resistance value of the opaque particles and the surface of the substrate decreases, and the charge on the surface of the opaque particles is easily attenuated, so that a sufficient electrostatic force as a driving force cannot be provided. On the other hand, if the humidity is too low, the resistance values of the opaque particles and the surface of the substrate increase, and problems such as easy discharge due to accumulation of excessively charged charges on the surface of the opaque particles occur. In consideration of these characteristics, it is preferable to set the range of 5 to 90%.
~ 70% is more preferred. By setting the relative humidity in the display medium to such a value, sufficient image contrast, display responsiveness, and repetitive displayability can be obtained.

Of at least two kinds of concealable particles, at least one kind of concealable particles has a particle diameter in the range of average particle diameter ± 50% of the average particle diameter, and the weight ratio of the concealable particles is 30%. % Is preferable. By doing so, the movability of the opaque particles is improved, image display can be performed stably and at high speed, and the uniformity and definition of image density are improved. Furthermore, the weight ratio of the concealing particles having a particle size within 50% of the average particle size ± the average particle size is set to 50.
% Or more, and by uniformly dispersing the particles over the entire surface of the substrate, the distance between the substrates can be maintained with high accuracy. As a result, the ease of movement of the particles is improved, image display can be performed stably and at high speed, and the aggregation and the like of the particles can be prevented for a long time, so that the reliability and life of the medium are improved.

It is preferable that the sphericity of at least one of the at least two types of hiding particles be 0.1 to 1. By doing so, the movability of the opaque particles is improved, and image display can be performed stably and at high speed, and aggregation and the like of the opaque particles can be prevented for a long time. improves.

It is preferable that at least one of the at least two concealing particles has a specific surface area shape factor of 15 or less. By doing so, the ease of movement of the opaque particles is improved, and image display can be performed stably and at high speed, and the aggregation and the like of the particles can be prevented for a long time, so that the reliability and life of the image display medium are improved. I do.

The surface energy of at least one of the at least ^two opaque particles is ² J / m ^2.
It is preferable to set the following. By doing so, the movability of the opaque particles is improved, and image display can be performed stably and at high speed, and aggregation and the like of the particles can be prevented for a long period of time, so that the reliability and life of the image display medium can be improved.

It is preferable that at least one of the at least two concealing particles has an angle of repose of 80 ° or less. By doing so, the movability of the opaque particles is improved, image display can be performed stably and at high speed, and the aggregation and the like of the opaque particles can be prevented for a long time, so that the reliability and life of the medium are improved. .

It is preferable that the longitudinal elastic modulus of at least one of the at least two types of opaque particles be 1 MPa or more and 300 GPa or less. By doing so, the movability of the opaque particles is improved, image display can be performed stably and at high speed, aggregation of the opaque particles can be prevented for a long time, and deterioration of particles due to repeated display is small, so that the medium The reliability and service life are improved.

[0068] Among at least two concealing particles, it is preferable to 21500kg / m ³ or less at a volume density of at least one concealment particles 10 kg / m ³ or more.
By doing so, the ease of movement of the particles is improved, and image display can be performed stably and at high speed.

The melting point of at least one of the at least two types of opaque particles is preferably 70 ° C. or higher. By doing so, aggregation of the opaque particles can be prevented for a long time even under a high temperature environment, and
Since the deterioration of particles due to repeated display is small, the reliability and life of the medium are improved.

It is preferred that the spectral reflection characteristics of at least two kinds of opaque particles are different from each other. By doing so, a high-contrast image can be displayed.

By making at least one kind of opaque particles colorless and transparent or white and making at least one other kind of opaque particles black, a natural and high-contrast image display like a normal black-and-white print image is obtained. Becomes possible.

The colorless and transparent particles have a refractive index of 1.2 to 1.
It is preferably 85. In this way, the whiteness in the non-image area can be improved, and a natural and high-contrast image can be displayed as in a normal black-and-white print image.

It is preferable that the reflection density of the white particles is 0.2 or less. In this way, the whiteness in the non-image area can be improved, and a natural and high-contrast image can be displayed as in a normal black-and-white print image.

The reflection density of the black particles is preferably 0.3 or more. By doing so, the density of the image area can be improved, and a natural and high-contrast image can be displayed like a normal black-and-white print image.

It is preferable to provide a conductive coating layer on the surface of at least one kind of opaque particles. By doing so, the selection range of the opaque particle material is expanded, and the medium can be manufactured at low cost. Examples of the conductive coating layer include metal materials such as nickel, gold, silver, and tin, ITO, and antimony oxide-doped tin oxide. Further, the thickness of the layer is preferably 0.1 to 2 μm.

The volume resistivity of the conductive coating layer is 10 ⁷ Ω
・ It is preferable that the diameter be not more than cm. This makes it possible to inject sufficient charges from the substrate, and facilitate the movement of particles by an electric field or the like. In addition, stable movement can be ensured for a long time, and the reliability and life of the medium are improved.

It is preferable to provide a charge transporting coating layer on the surface of at least one kind of opaque particles. This makes it possible to inject sufficient charges from the substrate, and facilitate the movement of particles by an electric field or the like. In addition, stable movement can be ensured for a long time, and the reliability and life of the medium are improved. Examples of the charge transporting coating layer include hole transporting substances such as hydrazone compounds, stilbene compounds, pyrazoline compounds, and arylamine compounds. Examples of the electron transporting substance include a fluorenone compound, a diphenoquinone derivative, a pyran compound, and zinc oxide. The thickness of the layer is 1 to
Preferably it is 5 μm.

Since the charge transporting coating layer has an electron transporting property, a sufficient charge can be injected from the substrate.
The movement of particles by an electric field or the like becomes easy. In addition, stable movement can be ensured for a long time, and the reliability and life of the medium are improved. Furthermore, since the polarity of the injected charge can be selected, the charge state after the injection of the charge is stabilized, and the performance of holding and adhering to the substrate is improved, so that a stable image display can be performed for a long time.

Further, since the charge transporting coating layer has a hole transporting property, a sufficient charge can be injected from the substrate, and particles can be easily moved by an electric field or the like. In addition, stable movement can be ensured for a long time, and the reliability and life of the medium are improved. Furthermore, since the polarity of the injected charge can be selected, the charge state after the injection of the charge is stabilized, and the performance of holding and adhering to the substrate is improved, so that a stable image display can be performed for a long time. By combining the above charge transporting and hole transporting configurations,
Particles having different charged electrode properties are obtained. As a result, the selective movement of the particles is facilitated, the speed of image display is increased, the contrast is improved, and the aggregation and the like of the opaque particles can be prevented for a long period of time, so that the reliability and life of the image display medium are improved.

For at least one kind of opaque particles, the covering ratio of the opaque particles to the display area is preferably 40% or more, more preferably 70 to 100%. By doing so, the movability of the opaque particles is improved, image display can be performed stably and at high speed, and the aggregation of the particles can be prevented for a long period of time.
The life is improved.

At least two different colors and different volume resistivity
The mixing ratio of the concealing particles of one kind is preferably in the range of 1/9 to 9/1 with respect to one kind of concealing particles. By doing so, the mixing of foreign particles in both the image area and the non-image area can be reduced, and the contrast is improved.

Next, an image display medium using the particles will be described with reference to the drawings. FIG. 2 shows an example of the image display medium of the present invention. As shown in FIG.
0a and an opposing substrate (non-display substrate) 100b are arranged to face each other in parallel via spacer particles (not shown). The distance between the two substrates is 6 to 15000 μm, preferably 20 to 750 μm.
μm is suitable, for example about 100 μm apart. The display substrate 100a and the counter substrate 100b are respectively provided on the support members 101a and 101b.
2. A structure in which a uniform electrode layer 104 is provided, and further, the charge transport layers 103a and 103b are provided thereon. 2, reference numeral 108 denotes an electrode driving device. The supports 101a and 101b are preferably plastic films excellent in strength, flexibility and light transmittance, and the film thickness of the films is suitably about 10 to 1000 μm.
For example, a polyethylene terephthalate film having a thickness of about 100 μm is used. The pixel electrode layer 102 and the uniform electrode layer 104 are preferably formed of a light-transmitting conductive film, and the thickness is suitably about 0.05 to 1 μm. For example, an ITO film having a thickness of about 0.1 μm manufactured by vapor deposition is used.

As the components constituting the charge transport layer, the components used for the charge transport layer constituting the electrostatic latent image carrier of the electrophotographic apparatus can be applied without any particular limitation. Alternatively, a self-supporting resin or the like having charge transport ability is used. The film thickness is suitably about 1 to 50 μm. Among the charge transport materials added to the binder resin, hydrazone compounds, stilbene compounds, pyrazoline compounds, arylamine compounds and the like are used as hole transport materials, and fluorenone compounds are used as electron transport materials.
Diphenoquinone derivatives, pyran compounds, zinc oxide and the like. The layer containing the hole transport material transports holes,
The layer containing the electron transporting substance enables transport of negative charges. As the binder resin, a polycarbonate resin or the like is preferably used. As the charge transport layer, for example, Ae (triphenylamine) is dispersed as a charge transport material in a binder containing a polycarbonate resin as a main component.
A charge transport layer having a thickness of about 5 μm is used.

The self-supporting resin having charge transporting ability will be described later. Charge transport layers 103a and 103b in which the above-mentioned triphenylamine (hole transport material) is dispersed.
In, only holes are transported. An electrode driving device 108 for supplying a voltage at a predetermined timing is connected to the pixel electrode layer 102 and the uniform electrode layer 104. Pixel electrode layer 1
In 02, a voltage is selectively supplied to individual microelectrodes corresponding to pixels in accordance with an image signal. Between the display substrate and the counter substrate, in addition to the spacer particles, two types of particles having different colors and volume resistivity, for example, black conductive particles (average particle diameter of 7.0 μm and volume density of 1370 Kg / m ³ ). Carbon particles) 105 and white insulating particles (crosslinked polyacrylic acid ester having an average particle diameter of 15 μm and a volume density of 1090 Kg / m ³ ) 106 are almost equivalent, and the volume filling ratio in the voids is 50%.
It is enclosed so that it becomes a degree.

FIG. 3 shows the principle of displaying an image on the display substrate side using the image display medium shown in FIG. FIG. 3A shows an initial state of the image display medium, in which black conductive particles 105 and white insulating particles 106 are mixed and sealed. Between each pixel electrode 102 and the uniform electrode 104,
It is connected via a switching 110. In the initial state, the switching is off. In the display stage, as shown in FIG. 3B, a low voltage is applied to the image area pixel electrode 102b, a high voltage is applied to the non-image area pixel electrode 102a, and an intermediate voltage is applied to the uniform electrode 104 on the counter substrate side. Is supplied, a positive charge is induced in a portion of the uniform electrode 104 facing the pixel electrode 102b. The induced positive charges are injected into the black conductive particles 105 via the charge transport layer 103b, and the conductive particles 105 are positively charged and move in the direction of the opposing low-potential pixel electrode 102b. The moved black conductive particles 105 reach the pixel electrode 102b and are held in a state of being attached to the charge transport layer 103a by an adhesive force such as a mirror image force or a Van der Waals force. In this way, the black conductive particles 105 are attached only to the image portion,
The non-image portion is displayed as an image by keeping the white insulating particles 106 dense. When erasing an image, if the pixel electrodes 102a and 102b are set to a high potential and the uniform electrode 104 is set to a low potential, the black conductive particles 105 move downward over the entire surface, and the image is erased. As described above, black conductive particles are densely attached to the portion corresponding to the image on the display substrate side, while white insulating particles are densely attached to the non-image portion, and a high-contrast image is obtained. Been formed.
It was much better than conventional display media.

Next, another example of the image display medium of the present invention will be described with reference to FIGS. The image display medium of this example has a basic configuration similar to that of FIG. 2, but as shown in FIG. 4, a display substrate 100a and a counter substrate (non-display substrate) 1
00b is a charge transporting layer 103a, 10
3B is different from that of FIG. The thickness of the charge transport layer is suitably from 10 to 1000 μm, preferably from 50 to 500 μm. Since the pair of substrates is composed of only the charge transport layer, a resin having the same self-supporting property as that of the above-mentioned support is used for this layer, and a structure which is strong against an external force applied to the image display medium such as bending and elongation. Is preferred.
The self-supporting resin having the charge transporting ability will be described later. By using such a resin layer, a visible light transmitting layer having a charge transporting ability can be obtained. Between the substrates, in addition to spacer particles (not shown), two types of particles similar to those used in the image display medium of FIG. 2, a black conductive particle 105 and a white insulating particle 106 were added at the same filling rate. Encapsulate. The image display medium in this example performs image display using an apparatus having a configuration as shown in FIG. That is, the image display medium 401 is passed between the electrostatic latent image carrier 402 and the conductive roller 403, and a display operation is performed at this time. The electrostatic latent image carrier 402 holds an electrostatic latent image produced by performing negative charging and image portion exposure in exactly the same manner as in a normal electrophotographic image forming process.

Before the display operation, the image display medium is initialized. That is, a DC voltage is supplied to the conductive roller 402 so that the opposite substrate has a low potential and the display substrate has a high potential,
The black conductive particles 105 are uniformly moved downward similarly to the principle described in the description of FIGS. After initialization,
At the same time, the electrostatic latent image on the surface of the electrostatic latent image carrier 402 is brought into contact with the image display medium, and at the same time, the conductive roller is pressed from below the counter substrate. The electrostatic latent image has a low potential (negative polarity and a large absolute value) in the image portion and a high potential in the non-image portion. If the potential of the conductive roller is set in the middle, the image in FIG. According to the same principle as the display medium, black conductive particles 10
5. An image in which the white insulating particles 106 adhere to the non-image area can be formed. A high quality display image can be obtained. The image display medium of this example has a simple configuration of a pair of substrates and can be manufactured at a low cost, and can display images with a high contrast and a wide viewing angle as in FIG. Further, even when repeatedly used, stable image display without aggregation of particles or the like is possible. The image display operation can be performed by using a normal electrophotographic apparatus, and has an advantage that no special device is required.

The self-supporting resin having the charge transporting ability includes a charge transporting polymer. For example, polyvinyl carbazole, US Pat. No. 4,806,443
Polycarbonate by polymerization of a specific dihydroxyarylamine and bischloroformate described in the specification
U.S. Pat. No. 4,806,444 describes a polycarbonate obtained by polymerization of a specific dihydroxyarylamine and phosgene; U.S. Pat. No. 4,801,517 describes a bishydroxyalkylarylamine and bischloroformate; Polycarbonate by polymerization with phosgene, described in U.S. Pat. Nos. 4,937,165 and 4,959,288, with certain dihydroxyarylamines or bishydroxyalkylarylamines and bischloroformates. Polycarbonate by polymerization or polyester by polymerization with bisacyl halide, US Pat. No. 5,034,296
Or polyester of an arylamine having a specific fluorene skeleton described in the specification of JP-A No. 4983,482, a polyurethane described in U.S. Pat. No. 4,983,482, and a specific bisstyrylbisarylamine described in JP-B-59-28903. Polyester with the main chain as
JP-A-61-20953, JP-A-1-13445
6, JP-A-1-134457, JP-A-1-134457
134462, JP-A-4-1330065,
Japanese Patent Application Laid-Open No. 4-133066 discloses a polymer having a pendant charge-transporting substituent such as hydrazone or triarylamine, “The Sixth Int.
electronic Congress on Ad
vances in Non-impact Prin
ting Technologies, 306,
(1990). And the like, polymers having a tetraarylbenzidine skeleton.

Further, for example, a charge transporting polymer represented by the following formula (I-1) or (I-2) described in JP-A-8-253568 can be used. In the general formula (I-1) or (I-2), Y represents a divalent hydrocarbon group, Z represents a divalent hydrocarbon group, and A is represented by the following formula (I-3). . In Formula (I-3), R ₁ and R ₂ each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a substituted amino group, or a halogen atom, and X represents a substituted or unsubstituted divalent aromatic group. And n represents an integer of 1 to 5, and k
Represents 0 or 1. Formula (I-1) or (I-
In 2), B and B ′ each independently represent a group —O— (Y
-O) m-H or a group -O- (YO) m-CO-Z-
CO-OR '(where R' is a hydrogen atom, an alkyl group,
Represents a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, Y represents a divalent hydrocarbon group,
Z represents a divalent hydrocarbon group, and m represents an integer of 1 to 5. ), M represents an integer of 1 to 5, and p represents an integer of 5 to 5000. Further, the compound represented by the general formula (I-1) or (I-
X in 2) represents the following structural formula (II) or (III)
)) Can be used.
By using a self-supporting resin having a charge transporting ability, a structure that is strong against external force applied to the image display medium such as bending and elongation can be obtained.

[0090]

Embedded image

Next, still another example of the image display medium of the present invention will be described. FIG. 6 shows the configuration of the image display medium.
In FIG. 6, the image display medium is arranged such that a display substrate 500a and a counter substrate 500b face each other in parallel with spacers (not shown) at the same interval as the image display medium of FIG.
The display substrate 500a includes an electrode layer 5 on a support 501a.
02a, the charge generation layer 503, and the charge transport layer 504a
Is a laminated body provided in order. The counter substrate 500b is
An electrode layer 502b and a charge transport layer 504b are sequentially provided over a similar support 501b. As the supports 501a and 501b, those similar to the supports of the image display medium in FIG. 2 can be used. For example, a polyethylene terephthalate film having a thickness of about 100 μm is used. Electrode layer 502a
And 502b are the same as those in the image display medium of FIG.
A μm ITO film is used. The charge transport layer may be the same as the charge transport layer of the image display medium in FIG. 2. For example, Ae (triphenylamine) is used as a charge transport material in a binder containing a polycarbonate resin as a main component.
And a charge transport layer having a thickness of about 5 μm is used. In this charge transport layer, only holes are transported. As the components constituting the charge generation layer, the components used for the charge generation layer constituting the electrostatic latent image carrier of the electrophotographic apparatus can be applied without any particular limitation. The thickness is 0.05 to 30 μm, preferably 1
Suitably, it is in the range from 10 to 10 μm. For example, a layer containing a phthalocyanine compound is used. Between the two substrates, spacer particles (not shown) and two types of particles similar to those used in the image display medium of FIG.
5 and the white insulating particles 106 are sealed at the same filling rate.

The image display medium shown in FIG. 6 displays an image based on the principle shown in FIG. By default,
The black conductive particles and the white insulating particles are sealed in a mixed state (see FIG. 6). First, as shown in FIG. 7A, in the initialization process, the display substrate side electrode 502a is set to a low potential, the counter substrate side electrode 502b is set to a high potential, and the black conductive particles 105a are set as described above. By injecting positive charges only from the counter substrate-side electrode 502b and positively charging the black conductive particles 105, the black conductive particles 105 are uniformly moved in the direction of the display substrate-side electrode 502a. After initialization, the display substrate side electrode 502a is set to a high potential, the counter substrate side electrode 502b is set to a low potential, and light irradiation is performed on the non-image portion as shown in FIG. A hole-electron pair is generated in the layer, and the hole moves downward according to the electric field, and positive charges are injected into the black conductive particles 105. The positively charged black conductive particles 105 move toward the opposing substrate side electrode 502b according to the electric field. On the other hand, in the non-light-irradiated portion, the charge is not injected into the black conductive particles 105 due to the presence of the charge generation layer, so that no movement is performed. In this manner, the black conductive particles 105 are adhered only to the image portion, and the non-image portion is densely filled with the white insulating particles 106, whereby an image is displayed.

Since the image display medium of this example displays an image by light irradiation, it can display a high-definition image, and can also display an image with a high contrast and a wide viewing angle. Further, even when repeatedly used, stable image display is possible without aggregation of particles.

Next, FIG. 8 shows an example of an image display medium capable of performing full-color display using the two types of particles having different volume resistivity. The image display medium of this example has the same basic configuration and operation as the image display medium shown in FIG. That is, the display substrate 100a has a structure in which the pixel electrode layer 102 and the charge transport layer 103a are stacked on the support 101a, and the counter substrate has a uniform electrode layer 104 on the support 101b.
And the charge transport layer 103b. A plurality of partitions 905 corresponding to pixels are provided between the display substrate 100a and the counter substrate 100b to partition the display substrate 100a.
In the gap between the counter substrate 100a and the counter substrate 100b, micro cells corresponding to pixels are formed at regular intervals. Each microcell has white insulating particles 106 and yellow particles 90
2. Magenta particles 903 and cyan particles 904 are sealed in separate cells.

The same white insulating particles as those used in the image display medium of FIG. 2 are used. The colored particles are obtained by dispersing a predetermined amount of each pigment and a transparent conductive material in a resin. In each of the micro cells, the white insulating particles and the colored conductive particles are almost equal in volume, and the volume filling in the voids is performed. It is sealed so that the ratio becomes about 50%. In each of the microcells, the conductive colored particles are charged and moved by the same operation as that of the image display medium of FIG. 2 and adhered to the display substrate. By performing the attaching operation in accordance with the image signal corresponding to each cell, a color image can be displayed. Regarding the color of the colored particles, besides yellow, magenta and cyan, red,
The color gamut can be adjusted by appropriately adding green, blue, black, and the like. The image display medium of this example can display a full-color image using conductive colored particles of three colors.
Also, as in the case of FIG. 2, it is possible to display an image with a high contrast and a wide viewing angle. Further, even when repeatedly used, stable image display is possible without aggregation of particles.

In the present invention, the characteristics of the particles are defined as follows. (1) Volume resistivity JIS C-231 using bulk material constituting particles
Measure according to 8. (2) Average particle size (d) It is defined by the formula of d = Σmdp / M. Here, d is the average particle size, m is the weight of the particle group in the predetermined particle size category,
dp means the central value of the particle size classification, and M means the total weight. (3) Sphericity The sphericity is defined by sphericity = (dpv / dps) ² . Here, dpv is an equivalent volume sphere equivalent diameter (diameter of a sphere having the same volume as the volume of the corresponding particle), and dps is an equivalent area sphere equivalent diameter (diameter of a circle having the same area as the projection area of the corresponding particle). Meaning respectively. (4) Specific surface area shape coefficient Defined by specific surface area shape coefficient = dp × s / v. Here, dp is a representative diameter (short axis diameter, long axis diameter, thickness, biaxial arithmetic average diameter, triaxial arithmetic average diameter, triaxial geometric average diameter, projected area circle equivalent diameter, equivalent surface area sphere equivalent diameter, equivalent volume sphere S indicates the actual surface area, and v indicates the volume. (5) is defined by the surface energy _{(σ) σ = σ 1 (} 1 + cosθ) 2/4. Here, σ is the surface energy, σ ₁ is the surface tension of the liquid, and θ is the contact angle of the liquid with the particles alone or the bulk material constituting the particles. (6) Angle of repose The angle of repose means an angle formed by a slope of a mountain formed by a group of particles and a deposition surface when particles are deposited in a mountain shape on a surface. (7) Young's modulus E defined by E = F × L / (A × ΔL)
Means The bulk material constituting the particles is formed into a rectangular parallelepiped test piece having a predetermined size (cross-sectional area A, length L), a predetermined load F is applied in the length direction, a deformation amount ΔL is measured, and inserted and calculated. Find the Young's modulus. (8) Refractive index Using a bulk material constituting particles, ASTM D54
Measure according to 2-70. (9) Reflection Density The bulk material constituting the particles is used to form a sheet, and then measured using a commercially available reflection densitometer (such as a Macbeth densitometer).

[0097]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited to these Examples.

(Examples 1 to 10, Comparative Examples 1 and 2) Images were displayed using the image display medium having the structure shown in FIG. 2, and the density contrast, the viewing angle, and the like were evaluated. The particles used were as shown in Table 1 and were combined as shown in Table 2. A polyethylene terephthalate film of about 100 μm was used as a support, and a pixel electrode composed of an ITO film having a thickness of about 0.1 μm, and triphenylamine as a charge transport material dispersed in a binder containing polycarbonate resin as a main component were dispersed therein. A display substrate in which a charge transport layer having a thickness of about 5 μm was sequentially laminated was manufactured. A counter substrate was manufactured in the same manner except that a uniform electrode was used instead of the matrix electrode as the electrode layer. Place both substrates at an interval of about 100 μm,
Two types of particles having different colors and different volume resistivity were encapsulated in the gaps by a combination of the particles shown in Tables 1 and 2. The image display medium thus manufactured is wired as shown in FIG. 3, a low voltage is applied to the image area pixel electrode 102b, a high voltage is applied to the non-image area pixel electrode 102a, and a uniform electrode on the counter substrate side. When an intermediate voltage is supplied to 104, an image is displayed in the image area based on the above-described principle. Table 3 shows the results.

The particles A in Table 1 are spherical conductive particles of amorphous carbon obtained by carbonizing and sintering a thermosetting phenol resin (Univex GC, manufactured by Unitika).
P, H-type) are standard black conductive particles, and particles B are standard white insulating particles made of cross-linked polyacrylate. Further, the black insulating particles of the particles C are formed by dispersing carbon black in a resin containing a crosslinked polymethyl methacrylate resin as a main component,
The white conductive particles of the particles D are obtained by coating particles of a crosslinked polyacrylate with ITO. Particle E
And H and the black conductive particles and the white insulating particles of the particles N are particles having the same components as the particles A or the particles B, respectively, and are obtained by classifying them into predetermined average particle diameters and particle diameter distributions. is there.

The black conductive particles of the particles I are particles A
Particles having the same components as described above, and formed by laminating the particles after carbonization and firing and deforming them under pressure. The black conductive particles of the particles J are produced by using particles having the same components as the particles A and coating the surface with a metal layer. The black conductive particles of the particles K are obtained by dispersing carbon black in a low-hardness silicone rubber material and adjusting the color and volume resistivity. The black conductive particles L are obtained by dispersing carbon black in a wax-based low-melting resin material and adjusting the color and volume resistivity. The black conductive particles of the particles M are foamed particles produced by the same process as commercially available foamed particles using a base material in which carbon black is dispersed in a resin material and the color and the volume resistivity are adjusted. The evaluation indexes for Table 3 are as follows (the same applies to Tables 4, 6, and 9). ◎: Practically sufficient performance ：: Practically acceptable level ×: Practical level

[0101]

[Table 1]

[0102]

[Table 2]

[0103]

[Table 3]

As shown in Table 3, Examples 1 to 10 which are image display media of the present invention are all excellent in density contrast and viewing angle, and can be sufficiently used as image display media. In contrast, Comparative Example 1
Comparative Example 2 is inferior in both the density contrast and the viewing angle, and cannot be used as an image display medium. Table 3 shows the average particle size of the particles, the weight ratio of particles having a particle size within ± 50% of the average particle size, sphericity, specific surface area shape factor, surface energy, angle of repose, refractive index, and reflection density. It has been shown that the above-described performance can be obtained by variously changing the elastic modulus, the melting point, and the volume density.

Example 11 In this example, an image was displayed using the image display medium shown in FIG. As a display substrate, an about 0.1 μm thick ITO film formed by vapor deposition, a about 0.1 μm thick charge generation layer made of a phthalocyanine-based compound, and a polycarbonate resin were formed on a about 100 μm thick polyethylene terephthalate film. A substrate was used in which a charge transport layer having a thickness of about 5 μm, in which triphenylamine was dispersed as a charge transport material in a binder as a main component, was laminated in this order. In the charge transport layer, only holes are transported. As the counter substrate, a laminated body including a support, an electrode layer, and a charge transport layer having a structure excluding the charge generation layer among the four layers of the display substrate was used.

Between the two substrates with a space of 100 μm, in addition to the spacer particles, the standard black conductive particles 105 and the standard white insulating particles 106 used in the above-mentioned Example 1 were almost equal in volume. Was sealed so as to have a volume filling ratio of about 50% to obtain an image display medium. As described in the description of FIG. 6,
When no voltage is applied, black conductive particles and white insulating particles are mixed. Next, the display substrate side electrode is set to a low potential, the opposing substrate side electrode is set to a high potential, and the black conductive particles are uniformly moved in the direction of the display substrate side electrode to perform initialization. When the non-image area was irradiated with light after setting the potential of the opposite substrate electrode side to a low potential, the black conductive particles in the irradiated part moved toward the counter substrate side electrode, and the irradiated part became white insulating. The non-image portion was formed in a state where the particles became dense, while the black conductive particles adhered only to the non-irradiated portion to form an image portion. The evaluation of the displayed image is shown in Table 4 below.

[0107]

[Table 4]

Further, an image display medium having the same configuration as described above was prepared by changing the particles used and the combination thereof as shown in Table 5, and the characteristics of the displayed image were examined. In Table 5, the black conductive particles used were particles A, which are the standard black conductive particles of Table 1, and the white insulating particles used were the particles B, which were the standard white insulating particles. Further, as the black insulating particles, particles C (the volume resistivity is equivalent to the standard white insulating particles and the spectral characteristics are equivalent to the standard black conductive particles), which are the black insulating particles in Table 1, are used; As the white conductive particles, particles D (the volume resistivity is equivalent to the black conductive particles and the spectral characteristics are equivalent to the white insulating particles), which are the white conductive particles in Table 1 above, were used. Table 6 shows the evaluation of the display image characteristics.

[0109]

[Table 5]

[0110]

[Table 6]

(Examples 12 to 15) With respect to the particles B and N produced in the above examples, the adhesive force formed between the display substrate and the opaque particles, and the adhesion formed between the concealable particles. The adhesive force, the coefficient of sliding friction between the display substrate and the opaque particles, the coefficient of sliding friction of the opaque particles, the rolling friction coefficient between the display substrate and the concealing particles, and the rolling friction coefficient of the concealing particles were measured. In addition, the particles B produced in the above-described example were used.
A particle P having an average particle diameter of 45 μm was used, and silicone rubber was added to the surface of the particle to increase the adhesion. The same measurement was performed for these particles. Table 7 shows the results. In addition, each said measurement was performed as follows.

Adhesion Force Formed Between Display Substrate and Hiding Particles and Adhesion Force Forming Hiding Particles: The adhesion force was measured by the electric field method described above. First, after the particles were sufficiently positively charged by a corona charger, the particles were deposited on a display substrate in the form of a cloud in a thin layer, and the particle coverage area on the surface was confirmed. The particle coverage area ratio was calculated by enlarging and photographing the substrate surface with a digital camera and performing image processing on the photographed data.

A part of the particles was sampled, and the amount of charge was confirmed by using a charge spectrograph (a device for measuring the amount of charge from the amount of movement of the particles under an electric field). Next, a sample substrate was prepared in which a counter electrode (a glass plate on which IOT was vapor-deposited) was installed on this substrate via a spacer having a thickness of 100 to 500 μm. To avoid Paschen discharge, the sample substrate was placed in a chamber in a low pressure environment, the display substrate side electrode was grounded, and a negative voltage was applied to the counter electrode. By gradually lowering the applied voltage (so that the absolute value increases with the negative polarity), the relationship between the electric field strength and the amount of particles separated and adhered to the counter electrode side was measured. The measurement of the amount of particles attached to the counter electrode side was performed in the same manner as the measurement of the particle coverage area ratio. From the relationship between the electric field strength and the amount of particles adhered to the counter electrode side after peeling, the electric field strength when half of the particles are peeled is determined as the peeling electric field strength, and the product of the initially measured average charge amount of the particles at the time of peeling Acting force (adhesive force). Finally, the weight per particle was determined from the average particle diameter and the average volume density of the particles to calculate the gravity, and the value subtracted from the acting force was defined as the adhesive force. The adhesion between particles was determined by performing the same measurement as described above after uniformly applying and adhering particles on a substrate as described above.

Sliding coefficient of friction between the display substrate and the opaque particles and the sliding friction coefficient of the concealable particles: First, a flat plate on which particles were uniformly coated and fixed was prepared as a sample. At this time, an adhesive was applied to the surface of the flat plate, and the particles were deposited in a thin layer in the form of a cloud. After bonding, unnecessary particles were removed by vibration to form a substantially single-layer particle layer. Next, the display substrate was fixed, a flat plate was stacked so that the particle fixing surface was in contact with the display substrate, and a weight was placed on the flat plate and lightly pressed against the flat plate. In this state, the flat plate was pulled in the horizontal direction at a speed of about several mm / s, and the force generated in the horizontal direction at that time was detected by the load cell. The sliding friction coefficient was determined from the ratio of the normal force (the total load between the weight and the flat plate) acting on the contact surface between the particles and the display substrate and the sliding friction force in the horizontal direction. The coefficient of sliding friction between particles was measured and applied in the same manner as described above, with the particles coated and fixed on the display substrate surface in the same manner as the flat plate, and placed so that the particles were in contact with each other.

The rolling friction coefficient between the display substrate and the opaque particles and the rolling friction coefficient of the opaque particles: The rolling friction coefficient was measured in exactly the same procedure as the sliding friction coefficient. It is possible to rotate without fixing. The rolling friction coefficient between particles was measured by increasing the number of particles serving as a sample and generating rolling motion between particles. In this case, the frictional force at the time of measuring the rolling friction coefficient between the display substrate and the opaque particles was subtracted from the measured frictional force (detected load in the horizontal direction) to obtain the inter-particle rolling frictional force.

[0116]

[Table 7]

The particles B, N and P were blended at a mixing ratio as shown in Table 8, and image display media were produced in the same manner as in Examples 1 to 10 (Examples 12 to 15). Also,
The relative humidity in the image display medium and the volume filling ratio of the particles were determined as follows. Table 8 also shows these results.

Measurement of Volume Filling Rate: The volume filling rate was calculated by the following method. First, the volume of the inter-substrate space was calculated from the distance between the substrates and the substrate size. On the other hand, the volume ratio occupied by the particles was calculated and defined as the volume filling ratio. The volume occupied by the particles was determined by conversion from the weight of the filled particles and the average volume density of the particles.

Measurement of Relative Humidity: A display medium sample was prepared in a chamber shielded from the outside air, and the relative humidity in the chamber was measured using a commercially available hygrometer to obtain the relative humidity in the display medium.

[0120]

[Table 8]

Example 1 of the manufactured image display medium
The same evaluation as that of No. 10 to No. 10 was performed. Table 9 shows the results.

[0122]

[Table 9]

From the results shown in Table 9, good characteristics were obtained in all the examples. In particular, in Example 12, excellent results were obtained in all evaluations.

[0124]

As described above, in the present invention, a plurality of types of particles having different concealing properties and different colors are used as particles to be sealed in the gap between the display substrate and the counter substrate, and have different colors and different volume resistivity. By using at least two types of particles,
The density contrast, the wide viewing angle, and the like, which cannot be obtained by the conventional technology, are greatly improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of display characteristics with respect to applied voltage when an image is displayed using three types of opaque particles.

FIG. 2 is a diagram schematically showing a cross-sectional view of an example of the image display medium of the present invention.

3A and 3B are conceptual diagrams showing the principle of image display of the image display medium of FIG. 2, wherein FIG. 3A shows an initial state and FIG. 3B shows an image display state.

FIG. 4 is a diagram schematically showing a cross-sectional view of another example of the image display medium of the present invention.

FIG. 5 is a conceptual diagram showing a principle of displaying an image on the image display medium of FIG. 4 using an electrostatic latent image carrier.

FIG. 6 is a diagram schematically showing a cross-sectional view of another example of the image display medium of the present invention.

7A and 7B are conceptual diagrams illustrating a principle of performing image display by irradiating the image display medium of FIG. 6 with light, and FIG. 7A is a diagram illustrating an initialization process of arranging conductive particles on a display substrate side. 7 (B)
Indicates a process of irradiating light thereafter to display an image.

FIG. 8 is a diagram schematically illustrating a cross-sectional view of an example of an image display medium capable of performing color display.

[Explanation of symbols]

100a, 500a: display substrate, 100b, 500b:
Counter substrate (non-display substrate), 105; black conductive particles, 1
06: white insulating particles, 402: electrostatic latent image carrier, 90
5: Partition wall

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoshi Shigehiro 430 Green Tech Nakai, Nakai-cho, Ashigara-kami, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. Inside (72) Inventor Ken Matsunaga 430 Green Tech Nakai, Nakai-machi, Ashigara-Kan, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. (72) Inventor Yasufumi Suwabe 430 Green Tech Nakai, Nakai-cho, Ashigara-Kan, Kanagawa Prefecture Inside Fuji Xerox ( 72) Inventor Yoshiro Yamaguchi 430 Green Tech Nakai, Nakai-cho, Ashigara-gun, Kanagawa Fuji Xerox Co., Ltd. (72) Inventor Takeo Kakinuma 430 Green Tech Nakai, Nakai-cho, Nakai-cho, Ashigara-gun, Kanagawa Fuji Xerox Co., Ltd. (72) Minoru Koshimizu 430 Green Tech Nakai, Nakai-cho, Ashigagami-gun, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. (72) Inventor Shota Oba 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (16)

[Claims] 1. An image display medium comprising at least a display substrate, a counter substrate disposed to face the display substrate, and an enclosure sealed in a gap between the display substrate and the counter substrate. An image display medium, wherein the enclosure comprises at least two kinds of concealing particles having different concealing properties having different colors and volume resistivity. 2. The opaque particles having at least two opaque particles having different color and volume resistivity from each other have a volume resistivity of 10 ⁷ Ω · c.
^2. The image display medium according to claim 1, wherein the volume resistivity is not more than m and at least 10 ² Ω · cm larger than the volume resistivity of at least one other concealing particle. 3. A ratio of the average particle size of one of the at least two types of opaque particles having the largest average particle size to the one of the at least two types of concealable particles having the smallest average particle size. The image display medium according to claim 1 or 2, wherein the ratio is 1/30 to 30/1. 4. The total number N of one kind of concealable particles is N × 1/900 ≦ N ≦ N with respect to the total number N of one kind of concealable particles among the at least two kinds of concealable particles. × 9
The image display medium according to claim 1, wherein the image display medium is in the range of 00. 5. The total surface area of one kind of opaque particles having the largest volume resistivity among the at least two kinds of insulating particles, and the total surface area of each of the other kinds of opaque particles is S. The image display medium according to claim 1, wherein x 1/25 ≦ S ≦ S × 100. 6. The opaque particle of at least one of the at least two opaque particles contains 1 to 70% by mass of a pigment. 2. The image display medium according to 1. 7. The glass transition point of at least one of the at least two types of opaque particles is 5 or more.
The image display medium according to claim 1, wherein the temperature is 5 ° C. or higher. 8. An adhesive force formed between the display substrate and at least one of the at least two opaque particles is 1 pN to 0.1 N. The image display medium according to claim 1. 9. The method according to claim 1, wherein at least one of the at least two opaque particles has an adhesive force formed between the opaque particles of 1 pN to 0.1 N. Item 10. The image display medium according to any one of Items 1 to 8. 10. The sliding friction coefficient between the display substrate and at least one of the at least two concealing particles is 0.8 or less. 10. The image display medium according to any one of 9. 11. The sliding friction coefficient of at least one of the at least two types of opaque particles is as follows:
The image display medium according to claim 1, wherein the value is 0.8 or less. 12. The rolling friction coefficient between the display substrate and at least one of the at least two types of opaque particles is 0.3 or less. The image display medium according to any one of the above. 13. The method according to claim 1, wherein at least one of the at least two opaque particles has a rolling friction coefficient of 0.3 or less. Image display medium. 14. The image display medium according to claim 1, wherein a relative humidity of a gap between said display substrate and said counter substrate is 5 to 90%. 15. A volume filling ratio of the at least two or more opaque particles (total volume of the opaque particles / volume of a gap between the display substrate and the counter substrate) is 0.001 to 0.5.
The image display medium according to claim 1, wherein: 16. The bulk density of at least one of the at least two opaque particles is 0.2 g.
The image display medium according to any one of claims 1 to 15, characterized in that at / cm ³ or more.