JP2005284215A - Display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color display device which has superior visibility and light resistance and can be used outdoors for a long time. <P>SOLUTION: A display element is constituted by arranging a composite film including metal fine particles and a matrix structure surrounding the metal fine particles on at least one of substrates where a couple of electrodes are arranged. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to still image rewriting using nano-sized metal fine particles.

  In recent years, with the development of information devices such as personal computers and mobile devices and the enhancement of the network environment, display devices for information devices have been increasingly used not only in offices but also in homes and outdoors. Also, especially in offices, a huge amount of information obtained via information equipment is output once on paper, and then discarded after a while, and the consumption of paper continues to increase. Yes. At the same time, stress caused by being forced to look at a light-emitting display screen such as a liquid crystal display or CRT for a long time has been pointed out.

  In the modern society, the spread of low power consumption display rewriting devices that prevent environmental destruction due to an increase in paper consumption, have low visibility even when viewed for a long time, and have good visibility and excellent portability. Research and development of new display devices such as electronic paper, paper-like display, and rewritable paper are thriving. As the most typical display method, there is a method of performing monochrome rewriting by electrophoresis, and visual visibility such as paper by reflected light can be displayed. However, the electrophoretic method generally does not have a memory property, and a memory element and a battery that can be used for a long time are required to maintain display. In addition, when RGB color filters are stacked in order to perform a desired color display, there is a problem in that the use efficiency of reflected light is low and bright color display is difficult. In addition, there is a method of displaying using color particles, but generally dyes and pigments are not sufficiently light-resistant, and for example, they may fade when exposed to direct sunlight for a long time outdoors. In addition, there is a method of performing a desired color display by coloring the solvent liquid, but in this case also, the dye in the solvent may permeate into the resin particles and the contrast may be lowered.

  Reduces paper output from information equipment, has a reflective type that can be viewed for a long time without stress, realizes low power consumption that can be rewritten by low-voltage drive, and has memory characteristics. There is a need for a completely new color display system that will not fade even when used outdoors for hours.

  Generally, in addition to various color materials such as various dyes and pigments used in copying and printers, there are metal fine particles that are vividly colored by absorption.

  The metal usually shows metallic luster in the bulk, but when it becomes nano-sized fine particles, the phenomenon of absorbing and coloring electromagnetic waves of a specific wavelength (plasmon absorption) is well known (see Non-Patent Document 1, for example). . This phenomenon has been used for coloring stained glass etc. for a long time, shows a clear color without turbidity due to absorption and transmission of natural light, and hardly fades even if left exposed to direct sunlight for a long time. Have excellent coloring properties.

  The color of the nano-sized fine metal particles is greatly influenced mainly by the material, shape and size of the particles. For example, Au is famous for a red Au colloid having an absorption peak in the vicinity of 530 nm, and Ag is famous for a yellow Ag colloid having an absorption peak in the vicinity of 420 nm. Further, according to Non-Patent Document 2, even if the particles are the same Ag, even if they are spherical, for example, when the diameter increases, the color changes depending on the magnitude such that the absorption peak gradually shifts to the longer wavelength side. In addition, even when the TEM cross-sectional images have different shapes such as spheres, pentagons, and triangles, it has been observed that the absorption peak changes, and even with Ag alone, it is possible to change the absorption over almost the entire visible light. It is shown.

  On the other hand, it is known that the metal fine particles “blacken” regardless of the material in the state of ultrafine particles of 10 nm or less, particularly about 1 nm (for example, Non-Patent Document 3). It is well known that metal fine particles develop a specific color in the visible light range in the range of 1 nm to 200 nm.

Further, Non-Patent Document 4 reports that the color development state of these metal fine particles due to plasmon absorption changes due to aggregation of particles.
“What are ultrafine particles?” By Kiyoshi Kawamura (Maruzen) J. et al. J. et al. Mock et al. Chem. Phys. , Vol. 116, no. 15,15April 2002 “Introduction to Ultrafine Particle Technology” by Noboru Ichinose and others (Ohm) U. Kreibig and L. Genzel, Surface Science 156 (1985) 678-700.

  The present invention is a completely new display method that utilizes color development using metal fine particles, and can display colors with excellent visibility without stress due to absorption and transmission of natural light, and has excellent light resistance and can be used outdoors for a long time. An object is to provide a simple color display.

The present inventor has conducted extensive research to electrically rewrite the color development using metal fine particles, and as a result, the metal fine particles are surrounded by a matrix structure to form a composite film, and then an electric field is applied to perform color modulation. I found. That is,
<1> A display element in which a composite film including metal fine particles and a matrix structure surrounding the metal fine particles is disposed on at least one substrate between a pair of electrodes.
<2> A display element that performs color modulation by changing the chemical state of metal fine particles by applying a voltage.
<3> In the above display element, the metal fine particles have a particle size of 1 nm or more and 200 nm or less.
<4> In the display element, the metal fine particles are surrounded by the matrix structure made of fine particles.
<5> The composite film according to the above, wherein the composite film is impregnated with an electrolytic solution.
<6> The display element as described above, wherein the matrix structure contains at least semiconductor fine particles.
<7> The display element according to above, wherein the matrix structure includes at least titanium oxide.
<8> The display element according to the above, wherein the metal fine particle contains at least one of Ag, Au, and Cu.
<9> The display element as described above, wherein the metal fine particles are mainly composed of Ag.
<10> The method for producing a display element as described above, wherein the metal fine particles and the matrix structure are mixed in advance, and then a film is formed on the substrate.

  The present invention can provide a highly visible color display that is completely different from conventional displays such as a CRT, LCD, and EL. That is, according to the present invention, it is possible to provide a color display with good visibility due to absorption and transmission of natural light by the metal fine particles. In addition, the present invention can provide a color display that has display holding properties, excellent light resistance and durability, and good visibility.

  The composite film of the present invention is mainly composed of nano-sized metal fine particles and a matrix structure material densely surrounding the metal fine particles, and color modulation is performed by applying an electric field to the metal fine particles and the surroundings through the matrix structure. It is for display.

  In the present invention, any material may be used for the matrix structure as long as it is used to surround the metal fine particles and to disperse the individual metal fine particles independently. In order to prevent the movement of particles due to the application of an electric field and the accompanying aggregation, and realize good color reproduction, the metal fine particles are preferably fixed to the matrix structure. Further, as described above, since the color development is greatly influenced by the shape and size of the metal fine particles, it is preferably surrounded by a matrix structure material in order to prevent deformation of the particles in various environments.

  As a method for sufficiently surrounding and fixing the nano-sized metal fine particles, a method in which a material having a unit whose minimum unit volume is equal to or smaller than that of the metal fine particles is finally solidified with light or heat is preferable. . For example, when a metal oxide is used as the matrix structure, a method of sintering and using a material composed of particles having a primary particle size comparable to or smaller than the surrounding metal fine particles can be preferably used.

  The material is not particularly limited as long as an electric field can be applied to the fine metal particles and the periphery thereof through the matrix structure, but semiconductors such as TiO2, SiO2, and ZnO2, inorganic oxides such as metal oxides, and resins Alternatively, fine particle and fine particle-containing compositions such as a mixture of inorganic and organic fine particles are preferably used. In particular, as described later, those capable of easily creating a color tone such as white, milky white, and transparent as the background color are preferably used.

  Further, a method of adding an electrolyte to the composite membrane when the sintered membrane is porous or the composite membrane has insufficient contact with the pair of electrodes is also preferably used. The simplest is a liquid electrolyte. The liquid electrolyte is not particularly limited as long as it has a high withstand voltage and excellent reliability, but besides a general ionic aqueous solution, ethylene carbonate in which dilute sulfuric acid, perchloric acid or lithium perchlorate is dissolved, A propion carbonate solution or the like is also preferably used. In addition, solid electrolytes are also preferably used in order to improve the electrical connection between the electrode layer on which the composite film is not arranged and the composite film, although it is not suitable for filling in the nano-sized pores. Can do.

  The element structure in the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a state in which the composite film of the present invention is formed on a substrate.

  As the substrate 1, glass, stainless steel, polyimide film or the like is appropriately used, and is appropriately selected depending on the temperature required for the above-described composite film production step. When displaying a desired color on a white medium such as paper, in the configuration of FIG. 1A, the substrate 1 is white, or the electrode arrangement side of the substrate 1 is white, and in the configuration of FIG. The white layer 6 may be formed on the substrate 1, or the white layer 6 may be formed on the electrode 2 in the configuration of FIG. For the white layer 6, in addition to using inorganic oxides such as titanium oxide, zinc oxide, and alumina as they are, a method of mixing these with a binder as a white pigment is preferable.

  1A and 1B, when white is formed by the structural material behind the electrode 2, the electrode 2 must be a transparent electrode, and a transparent electrode such as ITO or tin oxide is preferable. Used. On the other hand, when the white layer 6 is separately disposed in front of the electrode 2 as shown in FIG. 1C, the electrode 2 may be made of a non-transparent material such as metal or carbon.

  The composite film 5 is mainly composed of the metal fine particles 3 and the matrix structure 4. In the composite film, the metal fine particles 5 are individually dispersed and arranged, and are finely surrounded by the matrix structure 4.

  As described above, the coloration by the metal fine particles 3 is greatly affected by the metal material, shape, size (size) and the arrangement state of the fine particles, so that the metal fine particles 3 in the composite film 5 are processed and stored in subsequent steps. In addition, it is desirable that the metal fine particles are confined in a closed area so that the fine metal particles cannot freely move because the fine particles are not deformed or aggregated by voltage application.

  For example, the metal fine particles 3 in the composite film 5 can be obtained by using a metal oxide fine particle having a primary particle diameter equal to or smaller than that of the metal fine particles 5 or further using a binder such as a monomer. It is possible to surround the entire area almost entirely.

  In addition, the appearance of the metal fine particles surrounded by the matrix structure material in the composite film 5 is obtained by scanning the fracture surface of the element with a scanning electron microscope (SEM), a field emission scanning electron microscope (FE-SEM), a transmission electron microscope ( (TEM) and the like can be observed and examined by structural analysis.

  Next, FIG. 2 shows an example of an element configuration for applying a voltage to the composite film 5 to perform color modulation. The electrodes 2 and 2 'are respectively disposed on the pair of substrates 1 and 1' to form a pair of electrodes, and the composite film 5 is disposed so as to be sandwiched between the electrode pairs. As described above, when making the display medium white, for example, when viewing the display element from the illustrated direction, a white layer is provided on the electrode 2 side of the substrate 1 or a white layer (not shown) is formed on the electrode 2. ) May be provided. Further, the composite film 5 may have a fine porous structure in which the metal particles 3 cannot move. When it has a porous structure, in order to apply a sufficient voltage in the vicinity of the metal fine particles, it is also preferably used to fill the porous structure with an electrolyte.

  Next, FIG. 3 shows another example of an element configuration for applying a voltage to the composite film 5 to perform color modulation. A pair of electrodes 2 and 2 'are arranged on the pair of bases 1 and 1' in the same manner as in the configuration of FIG. By forming the composite film 5 on one of the substrates and filling the electrolyte with the other electrode, a sufficient voltage can be applied to the vicinity of the metal fine particles through the composite film. As described above, when the display medium is whitened, a white layer (not shown) may be provided as appropriate according to the viewing direction.

  Next, FIG. 4 shows another example of an element configuration for applying a voltage to the composite film 5 to perform color modulation. A pair of electrodes 2 and 2 'are arranged on the pair of bases 1 and 1' in the same manner as in the configuration of FIG. The composite film 5 is formed on one of the substrates, and the facing layer 8 is disposed on the other electrode. When the electrodes 2 and 2 ′ are deteriorated by being exposed to the electrolyte solution, a method of providing the facing layer 8 is preferably used. Further, the facing layer 8 may also serve as the above-described white layer. FIG. 4A shows the electrolyte layer 7 so that when the voltage is applied between the electrode layers 2, 2 ′ via the opposing layer 8 and the composite film 5, the voltage is sufficiently applied in the vicinity of the metal fine particles 3. The element structure in the case of being applied via is shown. FIG. 4B shows the element configuration when the facing layer 8 is disposed between the composite film and the electrode 2 ′.

  The electrolyte layer 7 shown in FIGS. 3 and 4A is not limited to the liquid form, and a method of laminating a solid electrolyte in a vacuum process is also used.

  As described above, the metal fine particles used in the present invention are preferably used as long as they generate color corresponding to the wavelength in the visible range in the state of nano-sized particles. In addition to Au, Ag, and Cu that have significant absorption in the visible light region, K and Na are also preferably used because they have absorption on the longer wavelength side than yellow. Further, colloidal particles such as noble metals other than Au and Ag, Pt, Pd, Ir, Rh, Ru, Os, etc. are also preferably used.

  Although the mechanism of the color modulation of the present invention is not clarified, the influence of the matrix structure material can be obtained by applying a voltage through the matrix structure to the colored state by the plasmon vibration of the nano-sized metal fine particles. It is speculated that a chemical change occurs and the coloring effect due to plasmon vibration is lost as a result. Specifically, it is presumed that a chemical change occurs such that the metal fine particles locally lose electrons and form an ionic compound with the surrounding matrix structure material. In order to easily cause such a chemical change, a metal having a small redox potential and a metal that easily forms an oxide are particularly preferable, and among Au, Ag, and Cu, Ag and Cu are particularly preferable.

  In particular, it is easy to synthesize a colloidal solution in which nano-sized metal microparticles are monodispersed in a solution, and it is possible to develop colors in the entire visible light region depending on the size and shape of the microparticles, and relatively low Ag that can be easily electrically rewritten with voltage is particularly preferably used.

  Such chemical changes can be examined by an X-ray photoelectron spectroscopy (XPS) method, a Raman spectroscopy, a wide-area X-ray absorption fine structure (EXAFS) method, and the like. In addition, the bonding state can be identified by measuring the crystal lattice spacing of the metal fine particles with a transmission electron microscope (TEM).

  For example, when the XPS method is used to measure a colored film and a decolored film by applying a voltage to the composite film, an absorption peak derived from bulk metal (zero valence) is observed in the case of a colored composite film. However, in contrast, in the case of a composite film in a decolored state, the difference in chemical state can be identified by the difference that an absorption peak shift toward the high binding energy side is observed. This can be inferred from the fact that in the colored state, the metal fine particles were colored by surface plasmon, but the electronic state changed, and the color caused by surface plasmon absorbing electromagnetic waves of a specific wavelength no longer occurred.

  The method for forming the composite film of the present invention is not particularly limited as long as the above-described element configuration can be realized. However, as a particularly preferable method, desired metal fine particles are dispersed in a raw material solution for forming a matrix structure in advance. A method is preferably used in which a solution composition is prepared, a film is formed on a desired substrate by spin coating or dip coating, and then the entire film is solidified by light, heat, or the like.

  Since the shape and size of the metal fine particles greatly affect the color, display with high color purity is possible by separately producing metal fine particles having a desired size and shape and mixing them with the matrix structure material. Also, as a method of solidifying the solution composition mixed with metal fine particles, even when exposed to high temperatures by sintering or the like, there is almost no alteration of the metal fine particles themselves, so it is determined by the initial particle size and shape. A composite film can be produced without impairing color development.

[Example 1]
ITO is formed as a transparent electrode on a quartz substrate. On the other hand, 0.5 wt% of an aqueous solution in which silver nanoparticles having an average particle diameter of 10 nm are monodispersed in an aqueous ethanol solution is mixed with an aqueous solution of titanium oxide sol (Ishihara STS-21) and stirred well in an ultrasonic water bath. The stirred mixture is colored yellow by the addition of silver nanoparticles. This mixed solution is spin-coated on ITO to produce a composite film. After pre-baking in an oven at 90 ° C. for 30 minutes, the main baking is performed in a muffle furnace at 400 ° C. for 1 hour. After firing, the composite film was slightly milky white, but the yellow color had disappeared. Two substrates prepared in this way were bonded together and fixed, and impregnated with an electrolyte solution. When a voltage was applied between the electrodes of the bonded substrates, the element that was almost transparent with the electrolyte solution was colored yellow. The coloring became remarkable from about 5V, and when it was applied up to about 10V, it was the same as the color (yellow) of the film before the main baking. Thereafter, the voltage was removed, but the yellow coloration was retained.

  Further, after applying the voltage, the composite film colored yellow by peeling off again by applying voltage is quickly dried, and the composite film that has been erased by applying voltage to the composite film once peeled off and dried quickly are XPS (X The compositional analysis was performed using X-ray Photoelectron Spectroscopy (X-ray Photoelectron Spectroscopy). In the composite film colored yellow, an absorption peak derived from metallic silver was detected, whereas in the decolored composite film, it was derived from silver. It was observed that the absorption peak was shifted to the high bond side.

[Example 2]
Similar to Example 1, ITO is formed on the quartz substrate as a transparent electrode. On the other hand, 0.5 wt% of an aqueous solution in which silver nanoparticles having an average particle diameter of 10 nm are monodispersed in an aqueous ethanol solution is mixed with an aqueous solution of titanium oxide sol (Ishihara STS-21) and stirred well in an ultrasonic water bath. The stirred mixture is colored yellow by the addition of silver nanoparticles. This mixed solution is spin-coated on ITO to produce a composite film. After pre-baking in an oven at 90 ° C. for 30 minutes, the main baking is performed in a muffle furnace at 400 ° C. for 1 hour. After firing, the composite film was slightly milky white, but the yellow color had disappeared. The other substrate was spin-coated with only titanium oxide and pre-baked in the same manner, followed by main baking at 400 ° C.

  A composite film containing silver fine particles was opposed to one side and a substrate on which a film made only of titanium oxide was opposed to the other side, and the electrolyte solution was sandwiched therebetween. When a voltage was applied between the electrodes of the bonded substrates, the element that was almost transparent with the electrolyte solution was colored yellow. Then, when the voltage application direction was reversed, the color was erased. This color development / erasing due to the voltage application could be confirmed repeatedly.

Example 3
The element prepared in Example 2 was left in the vicinity of an indoor window and in a sunshine environment for about a month in a state colored yellow. At that time, the element was sufficiently sealed so that the electrolyte solution impregnated in the composite film was not damaged. When the voltage was applied between the counter electrodes in the same manner as shown in Example 2 after being allowed to stand, yellowing and decoloring could be repeated and displayed as before. Contrast reduction and color change were not observed.

Schematic cross-sectional view showing the composite film of the present invention formed on a substrate Schematic cross-sectional view showing an element structure for color modulation using the composite film of the present invention Schematic cross-sectional view showing an element configuration for color modulation using the composite film of the present invention Schematic cross-sectional view showing an element structure for color modulation using the composite film of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1 'base | substrate 2, 2' Electrode layer 3 Metal fine particle 4 Matrix structure 5 Composite film 6 White layer 7 Electrolyte layer 8 Opposite layer

Claims (10)

  A display element in which a composite film including metal fine particles and a matrix structure surrounding the metal fine particles is disposed on at least one substrate between a pair of electrodes.   The display element according to claim 1, wherein color modulation is performed by changing a chemical state of the metal fine particles by voltage.   The display element according to claim 1, wherein the metal fine particles have a particle size of 1 nm to 200 nm.   4. The display element according to claim 1, wherein the metal fine particles are surrounded by the matrix structure made of the fine particles.   The display element according to claim 1, wherein the composite film is impregnated with an electrolytic solution.   The display element according to claim 1, wherein the matrix structure contains at least semiconductor fine particles.   The display element according to claim 1, wherein the matrix structure includes at least titanium oxide.   The display element according to claim 1, wherein the metal fine particles contain at least one of Ag, Au, and Cu.   The display element according to claim 1, wherein the metal fine particles are mainly composed of Ag.   The method for manufacturing a display element according to claim 1, wherein a film is formed on the substrate after the metal fine particles and the matrix structure are mixed in advance.

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