WO2008123643A1

WO2008123643A1 - Electronic display paper made with cellulose

Info

Publication number: WO2008123643A1
Application number: PCT/KR2007/004763
Authority: WO
Inventors: Jae Hwan Kim
Original assignee: Inha-Industry Partnership Institute
Priority date: 2007-04-06
Filing date: 2007-09-28
Publication date: 2008-10-16
Also published as: KR20080090781A

Abstract

Disclosed is an electronic paper made of cellulose which is flexible, light and inexpensive. In order to solve drawbacks of a conventional electronic paper made of a glass substrate having insufficient flexibility or a plastic substrate raising environmental pollution, a cell structure is made of biodegradable cellulose, an illuminant or electrophoresis solution is introduced in the cell structure, a color of the illuminant being varied when an electric field is applied thereto. After the resultant cell structure is encapsulated with cellulose, transparent electrodes are installed on at least one of upper and lower surfaces of the cell structure to display an image in both directions or one direction.

Description

[DESCRIPTION]

[Invention Title]

ELECTRONIC DISPLAY PAPER MADE WITH CELLULOSE

[Technical Field]

The present invention relates to a light flexible display panel made of cellulose, and more particularly, to an electronic paper capable of decreasing a manufacturing cost thereof.

[Background Art]

Among display media, an electronic paper is a digital paper having the best visible characteristic. The portable electronic paper which is rolled like a general paper is regarded as a next generation of a flat display such as PDP or LCD. The electronic paper refers to platform technology required for the ubiquitous computer age in which information can be accessed anywhere and any time. The electronic paper can serve as a substitute for general paper prints and conventional display devices, and thus, before long, it can be conveniently carried like paper. The electronic paper has high resolution, wide viewing angle, and bright background. Also, since the electronic paper does not require a backlight like an LCD, a lifespan of a battery is prolonged, a manufacturing cost thereof is reduced, and its weight is reduced.

The conventional electronic paper utilizes various principles of a flexible LCD, an OLED (Organic Light Emitting Diode), electrophoresis and so forth. Since the OLED has advantages of wide viewing angle, ultra-fast response rate, and self-emitting, the OLED from a small size to a full size is by no means inferior to any moving picture displaying media. Also, since the OLED does not require a backlight, power consumption is small, and it can be manufactured to have a thin and light structure. Also, since the manufacturing process thereof is simple, the manufacturing cost thereof can be reduced. According to the trend of developing the electronic paper, IBM, Sarnoff, UDC, E-ink Bell Lab., Palo Alto Research Center and so forth in U.S.A. have studied on the electronic paper using a flexible LCD, OLED and micro-capsule. Hitachi, Sony, AIST, Seiko-Epson and so forth in Japan have studying on the electronic paper using an OTFT, a polycrystalline silicon TFT, and an OLED. Also, there are a Gyricon display using a twist ball that is developed by Gyricon LLC, a cholesterol liquid crystal display using electrophoresis that is developed by Neolux Co., Ltd and Kent, an electrowetting display developed by Phillips, an electronic paper using MEMS technology that is developed by Iridigm Display Corp., and an LPD developed by Bridgestone. Samsung Electronics, Samsung SDI, LG Electronics, Softpixel Inc., I-Components, ETRI, KETI and several universities in Korea have studied on the electronic paper using a flexible LCD, OLED, and electrophoresis. After an initial electronic paper implemented by Xerox in 1975 and a product Immedia (trademark) released by E-ink in 1999, many prototypes have been released, but most of the newly developed electronic papers utilize glass in the cell structure or a substrate, which leads to lower the flexibility of the electronic paper.

[Disclosure]

[Technical Problem]

Therefore, there is a need for a plastic substrate. To this end, a problem of forming a transparent electrode on a plastic substrate and blocking a gas of the substrate should be solved. Sony and Seiko-Epson have developed a display having a polycrystalline silicon TFT on a polymer substrate based on the technology of producing and transferring polycrystalline silicon. This plastic substrate has the good flexibility in comparison with the glass substrate, but raises environmental pollution since the plastic substrate is not decomposed. University of Texas at Austin attempted an electronic paper including cellulose coated with dye to change color. This electronic paper does not raise environmental pollution, but has drawbacks of slow response rate and complicated manufacturing process.

[Technical Solution]

Therefore, the present invention has been made in view of the above- mentioned problems. An object of the present invention is to manufacture an electronic paper including a cell structure or substrate of biodegradable cellulose, without using glass with insufficient flexibility or a plastic raising environmental pollution. The substrate of the electronic paper is a base to support the electronic paper. Preferably, the substrate exerts an enormous effect on the flexibility, but does not raise the environmental pollution when it is wasted. A plastic film is an environmental waste since it is not biodegraded, and it is difficult to print a transparent electrode. By contrast, the cellulose is a major component of paper, which is flexible, tough and inexpensive, and can be easily formed in a thin film. In particular, since the biodegradable cellulose is decomposed when it comes into disuse, it does not raise the environmental pollution.

In a case where the electronic paper is made by using the cellulose, it is possible to make a display cell structure of a micro unit that is a basic element of the electronic paper. Therefore, the present invention teaches a concept of the electronic paper made of the cellulose and a manufacturing method thereof.

[Advantageous Effects]

As can be seen from the foregoing, the present invention can manufacture an environment-friendly electronic paper, like flexible paper, by making a cell structure using cellulose and then forming an illuminant layer or electrophoresis ink layer on the cell structure, encapsulating the resultant with cellulose, and installing transparent upper electrodes on upper and lower surfaces of the transparent electrode. It does not raise the environmental pollution when it comes into disuse, because of its biodegradability. Also, a cost required to manufacture the electronic paper is inexpensive. [Description of Drawings]

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view showing the construction of a unit portion of an electronic display paper according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of another embodiment of the present invention;

FIG. 3 is a cross-sectional view of other embodiment of the present invention; and

FIG. 4 is a flowchart describing a process of manufacturing a cell structure according to an embodiment of the present invention. [Best Mode]

Reference will now be made in detail to the preferred embodiments of the present invention. It is to be understood that the following examples are illustrative only and the present invention is not limited thereto.

FIG. 1 shows an electronic display paper made of cellulose according to an embodiment of the present invention. A cell structure 1 of micro unit is provided on a flexible cellulose material formed in a plate shape, and after transparent electrodes 3 and 4 are mounted on upper and lower portions of the cell structure 1, organic illurainants or electrophoresis dispersions 2-1, 2-2 and 2-3 are introduced between two electrodes 3 and 4. Before the organic il luminants 2-1, 2-2 and 2-3 are introduced, the transparent lower electrode 4 is formed on the bottom surface of the cellulose cell structure 1 having barrier ribs, and then the organic illuminants are introduced in the cell. The introduced organic il luminants are encapsulated by an upper encapsulation layer 5 of cellulose, and then the transparent upper electrode 3 is formed thereon. The upper and lower electrodes 3 and 4 are covered by cover layers 6 and 7 of cellulose, thereby manufacturing a transparent display device with a cellulose paper.

An electron transport layer, a hole transport layer and a hole injection layer are deposited on each surface of the upper and lower portions of the organic il luminants 2-1. 2-2 and 2-3. When a voltage is applied to the organic il luminants, electrons and holes are injected into the organic illuminants from cathode and anode to generate light by recombination of the electrons and the holes in the illuminator. The OLED may be have a single layer structure of which one organic layer is deposited between two electrodes, and an electron transport layer, a hole transport layer and a hole injection layer may be deposited on each surface of the upper and lower portions of the organic il luminants in order to further activate the injection of charge. The organic layer of the OLED may be made of a low molecular compound or polymer compound, and may utilize both fluorescence and phosphorescence. Also, the OLED may be driven by a passive matrix and an active matrix. In case of the passive matrix, an organic layer is inserted between an anode interconnection and a cathode interconnection, which causes the simple structure. Consumption power is relatively high, but its manufacturiαg cost is low. By contrast, in case of the active matrix, since each pixel is provided with a TFT, it has advantages of low consumption power and high resolution, but its manufacturing cost is low.

If the cellulose cell structure 1 is packaged with micro encapsulation of electrophoresis type, it can manufacture a reflective electronic paper of which reflection of light is varied in accordance with an electric signal. Such a reflective electronic paper can be in a black and white type or color type in accordance with a kind of ink, of which a color is varied depending upon electrophoresis.

Since the cellulose cell structure 1 has a size of several or hundreds microns, it is not easy to make the same cell structure on the cellulose paper or film of large area. In particular, in a case where cellulose is melted by a solution and then is made in a paper or film shape, expansion and contraction of the cellulose is increased in volume. Consequently, the present invention discloses a method of manufacturing a cell structure on a cellulose paper using micro-molding. In this instance, the cellulose may use a compound solution made by melting cellulose fiber with DMAc (N,N- dimethylacetamide) solvent or cellulose acetate. FIG. 4 shows an example of the micro-molding, which explains the process of manufacturing the cell structure using the solution made by melting the cellulose fiber with the DMAc solvent. The cellulose solution is applied on a silicon wafer 12 having a mold of cell structure. The coated cellulose film 11 and the silicon wafer 12 are heated in an oven at constant temperature during a certain time, and then are subjected to cleaning and drying process to manufacture the cellulose paper having the cell structure.

The dried cellulose film has a micro-cell structure, in which the bottom surface with no cell is coated with indium tin oxide and then is subjected to micro-patterning to form a transparent lower electrode. In the method of forming the OLED layer on the cell structure, thermal vacuum deposition, organic vapor phase deposition, laser-induced thermal imaging or the like is used for the low molecular material, while wet process, ink jet, spin coating, LITI or the like is used for the polymer material. In recent, the ink jet is mainly used to form a light emitting layer of large area. Only selected areas of the cellulose cell structure with barrier ribs placed at regular intervals is printed with the organic polymer melted in a solution. This method can form the light emitting layer on the selected area, irrespective of the area, and does not damage the material, which is advantageous in view of productivity. As shown in FIGs. 1 to 3, a color OLED includes three illuminants such as a red illuminant 2-1, a green illuminant 2-2 and a blue illuminant 2-3. Three illuminants are successively filled in the cell structure, an electrode 4 is formed thereon, and then the resultant structure is encapsulated. The cell structure 1 may be formed in various shapes such as a square, a rectangular, a circle, a hexagon or like. The cell has a depth sufficient to bury the illuminant.

After forming the illuminant layer, a conductive layer is coated on the illuminant, and then is subjected to a micro-patterning process to form the upper electrode 3. Surfaces of the upper and lower layers are coated and encapsulated with a cellulose solution. In this instance, if the illuminant layer is opaquely coated with the conductive layer such as gold, aluminum, platinum or the like, the light emitted from the light emitting layer progresses towards the lower layer, thereby making an electronic paper that can allow the light to be seen only at one side thereof. By contrast, the upper electrode is made of a transparent electrode such as ITO, thereby making a transmission OLED electronic paper that can be seen at both sides thereof. Since transmittance of the cellulose is the highest in the range of a visible ray, it is possible to make the transmission electronic paper. In order to improve color mixture of the surface emitting the light and sharpness of the light, as shown in FIGs. 2 and 3, micro-lens arrays 8-1 and 8-2 may be installed. For example, FIG. 2 shows the state where the micro- lens 8-1 is installed on only the lower portion, and FIG. 3 shows the state where the micro-lens arrays 8-1 and 8-2 are installed on both upper and lower portions.

While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment and the drawings. On the contrary, it is intended to cover various modifications and variations within the spirit and scope of the appended claims.

Claims

[CLAIMS]

[Claim 1]

An electronic display paper including a cell structure 1, an illuminant or electrophoresis dispersion 2, a transparent upper electrode 3, a transparent lower electrode 4, an upper encapsulation layer 5 and cover layers 6 and 7, wherein at least one of the cell structure 1, the encapsulation layer 5 and the cover layers 6 and 7 is made of cellulose.

[Claim 2]

The electronic display paper as claimed in claim 1, wherein the illuminant 2 is introduced in the cellulose cell structure 1, the cell structure 1 is encapsulated by a transparent material of cellulose, and the transparent electrodes 3 and 4 are installed on upper and lower surfaces of the cell structure to display an image in both directions.

[Claim 3]

The electronic display paper as claimed in claim 1, wherein the illuminant 2 is introduced in the cellulose cell structure 1, the cell structure 1 is encapsulated by a transparent material of cellulose, and the transparent electrode 3 is installed on only one surface of the cell structure to display an image in one direction.

[Claim 4]

The electronic display paper as claimed in claim 1, wherein the illuminant 2 is replaced with ink that selectively reflects light if an electric field is applied to the cell structure 1.

[Claim 5]

The electronic display paper as claimed in claim 1, wherein black and white or color illuminant or ink is introduced in the cell structure 1 so as to selectively display a black and white image or color image.

[Claim 6]

The electronic display paper as claimed in claim 1, wherein a pixel corresponding to a cell is driven in a passive matrix or active matrix.

[Claim 7] The electronic display paper as claimed in claim 1, wherein a micro- lens array 8 is installed on a surface of the cell structure that displays an image, so as to improve mixture of colors and sharpness of light.