WO2015172813A1 - Electrophoretic display panel structure and its manufacturing process - Google Patents

Abstract

This Invention provides specific panel structure and its manufacturing process means specifically for electrophoretic displays. With specific physical barrier-rib wall structure dividing each display pixel element area, this divided area enables sustaining fluid passing through freely, and preventing from electrophoretic particles travel beyond each display element area. This specific barrier-rib wall structure also enables high manufacturing efficiency based on self-adjustment ability of sustaining fluid amount at each display element area divided by barrier-rib wall structure.

Description

Electrophoretic display panel structure and its manufacturing process Technical Field

This invention is about flat panel display manufacturing technology, specifically for dispersion based display medium type of flat panel display devices manufacturing technology.

Background Art

Flat panel displays have been widely used in many varieties of uses from a personal hand held type to the large TV applications. In particular last two decades, rapid spread of high capacity of information transmission technologies has been promoting interactively connected flat panel display systems. Among those systems, a public announcement domain application of flat panel display system is highly expected of its rapid growing market. Unlike personal uses, nor well-known use modes, such an expected rapid growing public announcement board display system is somehow recognized between personal uses and large public domain announcement board system. Most of personal uses are like cell phone displays, lap-top computer screens, and they are specifically personal uses and not required very large screen such as over 25-inch diagonal. Moreover, such uses are mostly for single viewer’s purpose under relatively comfortable environment such as a normal office and usual street environment. On the other hand, large venue public announcement board requires huge screen size such as over 300-inche and most of those huge screens are installed out-door environment. This invention is for specific public domain uses between those personal uses and huge public announcement board. The most expected screen size is between 25-inch up to 150-inch, and typical expected viewers are transportation passengers, street pedestrians, retail shop customers, and so on. As those viewers’ nature, this specific category of public announcement board is not for specific personal use purpose, but at the same time, it is not for non-specific purpose of viewers’ purpose. For instance, airport passengers need their flight information. Such flight information is obviously for public domain information, but not for personal information. On the other hand, such public domain information is only necessary for specific purpose of people like the passengers intending to use a specific flight. Retail shoppers are similar situation in terms of necessity of information on the public announcement board screen. Among many shoppers, only certain shoppers those who are interested in specific goods such as flowers, the public announcement board provide necessary information.

In short, this invention is focusing on the specific purpose of viewers’ public announcement board screen technology, specifically of its effective manufacturing process technology.

Present technologies for the specific field of public announcement board system

Currently, LED (Light Emission Diode) displays are widely used in public transportation system. In some applications, TFT-LCD units similar to the home TV set are also used. These uses have the following specific requirements as a public announcement board system.

1. Typical viewing distance is between 0.5 meters up to 3 meters
2. Picture element pitch is between 0.3 mm up to 20 mm
3. Installed ambient light condition is usually very bright
4. Installed ambient condition is semi-out-door environment
5. Information content is somehow limited like letters display base with some limited graphics
6. Good enough legibility in a bright ambient condition keeping wide enough viewing angles are required
7. Its own information content source (no general information source, but customized information source
8. Number of colours are somehow limited such as 8 up to 64 colours
9. Motion video image is not required. Some specific uses need limited moving image such as moving letters, blinking and so on.

Technical issues current technology is required to solve as total display announcement board

For the specific public domain information display board system, current main in use technologies are using LED array panel and TFT-LCD module units. Both are, however, being used in slightly different uses. LED array panel has relatively large picture element pitch such as over 10 mm. Due to required heat dissipation of each LED element, such picture element pitch is designed. Therefore, LED array panels are mainly used relatively long distance view application among the specific purpose of public announcement board such as train departure/arrival information, gas station’s pricing information, and so on. On the contrary, TFT-LCD unit based public announcement board is mainly used for displaying relatively complicated information and/or relatively small sized letter information such as airport flight information, train departure/arrival time tables. Since TFT-LCD unit has smaller picture element pitch such as 0.3 mm, showing high letter (large letter) makes significant limitation of display content. Moreover, it requires significant drive scheme consideration, TFT-LCD unit based public announcement board is used for a smaller letters information board. TFT-LCD unit, however, has great display image capability compatible TV image quality. Therefore such TFT-LCD unit based public announcement board is used for natural color picture image such as sample food at grocery, restaurant menu samples.

As described above, current emerging needs for a specific public domain announcement board is specifically required to show some specialized information. Most of such information needs some limited area of information. Some cases, it is only character information with several colours, some cases, mixture of multi-color graphics image and character images, and some case is large character image with several colours. Because of the nature of announcement information, this type of emerging uses needs very customized information content. For instance, airport flight information board needs to show very limited information such as departure/arrival times and their status such as on time, delay and so on. At fast food restaurant counter, announcement board display needs to show menu, price and sometimes photo image of the food. For flight information announcement board case, typical viewing distance is 0.5 meters up to 3 meters, however, fast food restaurant menu board has typical viewing distance of up to 1 meter. Moreover, fast food restaurant menu board needs to show much more information content than flight information board. As discussed above, most of these uses are under bright ambient light environment. Therefore, announcement board screen luminance is required relatively high. In particular under the condition of sun light environment, as most of cell phones are difficult to read out the screen image, same so called wash-out phenomenon happens. Therefore, these specific uses are also strongly required sun light readability, or another word, non-wash-out screen readability is highly required. Both of current major uses those are both LED panel arrays and TFT-LCD units are substantially light emissive displays, and those light emissive displays are well known to be not good in terms of was-out problem under very bright ambient light conditions.

Current LED array panels and TFT-LCD based public announcement board systems do not have flexibility to meet with such specialized or customized information content display requirement, therefore, users of such public announcement board systems need to compromise their desired information fitting for given pixel layout format of LCD array panels and TFT-LCD units. This makes limitation of effectiveness of specific information content uses. Without pixel layout flexibility, picture element size and shape flexibility, users of such specific public announcement board systems could not show their most effective information.

With such non-effective display information content problems, both LED array panels and TFT-LCD based display systems are not effective. From specific category of public announcement board uses, depending on the required information content, it is highly required to have flexible enough pixel layout, pixel size and shape to meet with specialized and customized information content as well as wash-out phenomenon free screen images under bright ambient light environment.

Disclosure of Invention

Given current demand for specific category of public announcement information board, and current technology’s limitation, this Invention provides flexible enough public announcement board technology and its effective manufacturing process technology for the display panel.

In order to realize the purpose of this Invention, this Invention has following premise.

This Invention’s inventors have invented new type of display mode based on electrophoretic system

US 8383010 B VISITRET DISPLAYS OÜ 20130226 , WO WO 2010/089386 WO WO 2010/089386 A VISITRET DISPLAYS OÜ 20100812 . These inventions have potential to meet with above specific emerging demand of specific public announcement board uses. Therefore, this Invention is based on above cited specific electrophoretic display premise.

For some limited number of pixels and limited number of colours display technologies fitting for the bright ambient light condition, electrophoretic displays are known to be potential match. Current known electrophoretic display technologies are such as US patent # US 6120839 B E INK CORPORATION 20000919 , US 6262833 B E INK CORPORATION 20010717 , US 8018640 B E INK CORPORATION 20110913 . These electrophoretic display technologies are using so-called encapsulation of nano-sized particles in order to avoid aggregation of each particle in a display panel. Usually, such encapsulated dispersion system is prepared as some sort of “film” or another word as a self-sustained display medium. On the other hand, the other type of known electrophoretic display technologies such as US patent # US 8300300 B FUJI XEROX CO.,LTD. 20121030 , US 8331015 B FUJI XEROX CO.,LTD. 20121211 , US 8319916 B FUJIFILM CORPORATION 20121127 is using non-self-sustaining display medium, and this type of display medium requires some “pixilation” means such as physically isolated pixel structure, or sub-isolated pixel structure described in those US patents.

A self-sustained display medium has an advantage enabling a pixel boundary free lamination as long as required pixel pitch is large enough compared to the unit element size of the electrophoretic displays as described in above US patent # US 6120839 B E INK CORPORATION 20000919 . This is a great advantage both to provide high resolution display image without any product level of complexity for lamination. However, for color image reproduction using whatever, color filters, and/or multi-colored different dispersed particles, this type of display medium makes color-sub-pixel registration between two substrates extremely difficult. Due to the light scattering nature of the display medium, usual two substrates lamination process using visible light and/or near infra-red light CCD camera registration system does not work for the light scattering display medium. This type of display medium has self-sustaining property, and this self-sustaining property does not allow display medium filling process after lamination. Because of elastic single layer property, before the panel lamination, this type of self-sustaining display medium is required to be placed on one of the two substrates. Therefore, for color display medium case, it is extremely limited in its color sub-pixel registration. On the other hand, non-self-sustaining type of dispersed fluid is treated similar to liquid crystal materials in terms of display panel manufacturing process. When only monochrome or black/white display is produced, non-self-sustained electrophoretic fluid may not show any superiority at panel lamination process. On the other hand, for multi-color display case, non-self-sustaining fluid does not require any specific registration process other than very popular registration and lamination process already well-established at most of other types of flat panel display manufacturing process. On the other hand, non-self-sustaining display medium still needs specific sub-pixel positioning process. When different colored particles are used for multi-color reproduction purpose, each primary colored particle should be placed at specific sub-pixel portion only, otherwise, color mixing happens, resulting in color contamination and significant degradation of color image. In order to avoid such color mixing problem, US patent # US 6639580 B CANON KABUSHIKI KAISHA 20031028 , US 6750844 B CANON KABUSHIKI KAISHA 20040615 , US 7679813 B SIPIX IMAGING, INC. 20100316 are providing specific means. They are using so-called barrier-rib structures. The barrier-rib structure, here, means a wall structure to divide each sub-color pixel from other sub-color pixel as shown in Figure 1. This wall structure effectively prevent from different colored particles mixing, resulting in keeping good color purity. Actually, such wall structure has been widely in use for plasma display panels or PDP to divide red, green and blue phosphor placing at each sub-color pixel area as described in US patent # US 5791960 B FUJITSU LTD. 19980811 , US 5825128 B FUJITSU LIMITED 19981020 , US 6482575 B FUJITSU LIMITED 20021119 . Therefore, wall structure, or barrier-rib sub-pixel structure itself is well known technology.

At electrophoretic display system which uses incident light scattering and reflection method for its display image, however, such barrier-rib structure is one of the image quality degradation factors. Due to barrier-rib structure, effective aperture ration has some limitation and this limitation decreases light reflectivity of the screen. Moreover, when the barrier-rib height is relatively higher compared to sub-pixel size, due to wall structure, the display has viewing angle restriction. Since, shallow incident light could not reach at light scattering particles in effectively, such shallow incident light is not scattered effectively as illustrated in Figure 2. Therefore, a barrier-rib structure should be considered its structure and aspect ratio between height and size of the sub-color pixel. Moreover, unlike liquid crystal materials, electrophoretic display medium contains both continuous fluid and dispersed solid particles, such display medium’s rheological flow characteristic properties are very different from that of liquid crystal materials. In this different point of view, even wall structure is very good to avoid any color-sub-pixel lamination complexity at volume manufacturing of such a panel, in order to have well enough multi-color image equality panel avoiding wash-out phenomenon, still some specific wall structure is considered.

Above cited electrophoretic display technology as well as barrier-rib structure formation for PDPs is potentially good fit for the above described uses. One of the most important factors to meet with above demand is its non-self-sustaining display medium with incident light scattering/absorption capability. LED array panel system has light emission capability. This is very good to show very good legible image as long as ambient light condition is somehow dim, or no particular light ray exposure condition causing wash-out problem. Self-light emission type of display has significant influence of ambient light color temperature of its color purity, and its legibility by human eyes. Although TFT-LCD based public announcement board is basically non-emissive display, its back lighting display nature makes TFT-LCD unit substantially self-emissive display. Therefore, regardless basic display configuration, both LED array panels and TFT-LCD units are very much influenced with ambient light condition, specifically with wash-out problem. On the contrary, light scattering/absorption basis public announcement board display system is just like paper poster announcement board display. It is of course, also dependent on ambient light condition of its look. However, unlike substantial self-light emissive display system, most of human eyes are very much familiar with paper based announcement board image quality. Using subtract primary color system, instead of additive primary color reproduction, light scattering/absorption type of announcement board enables intrinsically same type of image with paper based announcement board. Therefore, light scattering/absorption based display system is the key requirement for this specific emerging demand of public announcement board users.

Moreover, light scattering/absorption basis display technology, specifically non-self-sustaining display medium technology is very good match for flexible pixel element size/shape and layout. Unlike self-sustaining display medium such as above LED array panel, non-self-sustaining display medium can change its shape fitting for any shape, size along with given pixel layout and/or cell design. Moreover, as long as unit pixels pitch size is large enough compared to visible light wavelength (~ 0.6 micron), light scattering/absorption capability is basically independent from pixel size and shape unlike self-sustained display system. LCDs are also categorized as non-self-sustained display medium displays, however, most of LCDs control birefringence. Governing birefringence requires specific size of pixel to provide uniform enough viewing angle. This viewing angle limitation makes TFT-LCD unit non-flexible in terms of meeting with above emerging demand. Some of LCDs are using light scattering such as Cholesteric LCDs. However, those Choresteric LCDs use only light scattering function, and do not have capability to absorb light by liquid crystal display medium itself as described in A. MOCHIZUKI, K. SAITO, K. IKEGAMI, T. NARUSAWA AND H. OKUYAMA, Study on Liquid Crystal Materials for Storage-type LCDs Driven by C-MOS LSIs, I& EC Product Research and Development, 1984, 23, 609-612 Therefore, it is extremely limited in its contrast ratio.

With above current available technologies’ limitation, only non-self-sustaining, light scattering/absorption type of display system enables good enough solution to meet with above emerging demand. As described above, non-self-sustaining display medium is required to enable flexible enough pixel layout. However, non-self-sustaining display medium requires “block” to decide non-self-sustaining display medium a certain shape of unit structure. In short, such display medium needs boundary structure to keep its single unit structure three dimensionally. As described above, LCDs have also using non-self-sustaining display medium. However, liquid crystal does not have light absorption capability by liquid crystal molecule itself. Light absorption capability of birefringence based LCD unit is given by a pair of linear polarizers. Use of a pair of linear polarizers creates viewing angle limitation, moreover, use of light efficiency is less than 50%. In order to keep high enough ambient light efficiency both in terms of display image natural view and low enough power consumption, non-self-sustaining light scattering/absorption type of display medium is critical necessity.

Non-self-sustaining display medium is one of the critical necessities to meet with above emerging demand of public announcement board display, its effective and practical method to give a certain boundary area as unit pixel structure is the most required practical needs. In addition to necessity of an effective isolated sub-pixel structure for multi-color electrophoretic displays, volume manufacturing throughput is also of one of the most important factors as a product. This Invention is to provide one of the most effective means to give practical manufacturing solution for the boundary structure to the electrophoretic display system.

Four step wise manufacturing method is engaged in this Invention. The first step is forming specific boundary structure on the display substrate. The second step is to inject dried particles into the formed each boundary area. The third step is to laminate the panel. The final step is to fill sustaining fluid medium in the laminated panel.

This Invention also consists of specific boundary structure. In order to have effective display panel manufacturing methods as well as well enough display performance, the specific boundary structure is also the critical requirement.

Brief Description of Drawings

In order to specify this Invention, following four steps process are explained sequentially with references to the following drawings. Of course, this Invention is not limited in following sequence, but includes any other sequence as long as each sequence is long with the concept of this Invention.

Figure 1 A standard barrier-rib structure

[Rectified under Rule 91, 24.09.2014]
Figure 2(a) A standard barrier-rib structure on a substrate

Figure 2(b) Cross sectional view of the partial low wall height barrier-rib structure with a slit

Figure 3(a) A partial low wall height barrier-rib structure with a slit

Figure 3(b) Cross sectional view of the partial low wall height barrier-rib structure with a slit

Figure 4(a) A partial low wall height barrier-rib structure with a slit

Figure 4(b) Cross sectional view of the partial low wall height barrier-rib structure with a slit

Figure 5(a) A partial low wall height barrier-rib structure with a slit

Figure 5(b) Cross sectional view of the partial low wall height barrier-rib structure with a slit

Figure 6(a) Relative size of the slit

Figure 6(b) Relative size of the bump

Figure 6(c) Relative size of the spacer bunk

Figure 7 A partial low wall height barrier-rib structure with a slit

Figure 8 A wet particles injection process into pre-fabricated barrier-rib structure

Figure 9 A dry particles injection process into pre-fabricated barrier-rib structure

Figure 10 Lamination process

Figure 11 An outer wall barrier-rib structure for after lamination process

Figure 12 Slit structure with polyethylene film

Figure 13 Open slit barrier-rib structure

Figure 14 Lamination method

Figure 15 The electro-optic measurement set-up

Figure 16 Particle switching behavior with application of electric field

Figure 17 Particle switching behavior with application of electric field

Figure 18 Wet spacer particle dispersion method

Figure 19 Particle switching behavior with application of electric field

Figure 20 Non-open area perimeter seal pattern with barrier-rib wall having open slit and/or dent structure

Figure 21 Particle switching behavior with application of electric field

Figure 22 Non-open area perimeter seal pattern without barrier-rib wall having open slit and/or dent structure

Best Mode for Carrying Out the Invention

First step

This step is formation of boundary structure, or specific shape of barrier-rib structure at each sub-pixel. Unlike known relevant barrier-rib structures, this Invention’s first step is directly related to the following steps such as the second and third steps. The specific structured barrier-rib shape is designed both for display performance need as the emerging announcement board displays and volume manufacturing high throughput in terms of manufacturing high yield. Figures 2(a) and 2(b) illustrate a standard barrier-rib structure for this Invention. These figures show a specific barrier-rib structure for the Invention. Figures 2(a) and 2(b) illustrate barrier-rib structures with a certain size of slits. This Invention requires specific size of slit and other values. As Figures 2(a) and 2(b) show, the height of the barrier rib is h, the slit width is d. The averaged particle size is a. Figures 2(a) and 2(b) specifies these relationships among the values. In Figure 2 case, the specific relationship using values in Figure 6(a) is:

h > a > d Equation (1)

Here, a is an average size of electrophoretic particles, d is slit open area size, and h is height of barrier-rib wall.

This Invention also includes same concept with different shape of barrier-rib structures. Figures 3(a) and 3(b) illustrate with slits and shallow open area barrier-rib structure. In this shape, the relative relationships among values using in Figure 6(b) are:

h > c, a > d, a > c Equation (2)

Here, c is height of lower area of the barrier-rib wall.

This structure has both complete open slit and partial height of open area in barrier-rib wall.

Figures 4(a) and 4(b) illustrate other shape of barrier-rib structure with this Invention. This structure does not have complete open slit structure, but has partial height of open area in barrier-rib wall. This case needs following relationships using in Figure 6(b):

a > d, a > c Equation (3)

Figures 5(a) and 5(b) also show other shape of this Invention’s barrier-rib structure. This shape does not have open slit structure, but has spacer structure on the wall of barrier-ribs. As Figure 5(a) shows, the spacer is placed on the wall of barrier-rib structure. Depending on sub-pixel size and using dispersed particles’ average size, number of spacers and their size and located place on the wall of barrier-rib is varied. However, intrinsic requirement of this specific structure is described in Equation (4) using Figure 6(c) values:

n + m > a, p > a, a > l Equation (4)

Here, n is base height of barrier-rib wall, m is height of spacer portion of barrier-rib wall, p is distance between the spacer portion of barrier-rib wall, and l is width of spacer portion of barrier-rib wall.

Above specific structure barrier-ribs are prepared using several processes. The preparation process itself is available using known process such as photo-lithography process using photo-reactive low melting glass particles slurry as described in US Patent # 5,791,960, or such as using sand-blasting graving method widely used in PDP manufacturing. A selection criterion of above barrier-rib structure preparation is mainly decided by size of sub-pixel, specifically height of the barrier-ribs. When the sub-pixel size is relatively large such as over 10 mm, and barrier-rib wall height is relatively high such as over 0.2 mm, pre-fabricated punched-out barrier-rib mesh is laminated on the substrate as illustrated in Figure 7. Figure 7 shows pre-fabricated barrier rib structure specifically Figure 2 shape. The pre-fabricated Figure 7 shape of barrier-rib structure is prepared using metal relief original injection plate. The material forming barrier-rib is selected with consideration of sub-pixel size, single display screen size and so on. When the screen size is relatively large such as over 600 mm X 500 mm, and sub-pixel size is relatively large such as over 10 mm X 10 mm, high density poly-urethane forms would be used as a base material. Using poly-urethane form sheet, its surface is formed barrier-rib shape using above described relief metal plate. The surface shaped poly-urethane form is laminated on the electrode formed substrate directly, or the form is laminated on thin plastic film and the laminated film is placed on the electrode formed substrate. Preparation of above barrier-rib structure itself is not limited in above described method. This Invention provides specific shape and form of barrier-rib structure in related to used dispersed particle size and open area size of the barrier-rib structure. Therefore, regardless methodology of barrier-rib structure, this Invention restricts the specific structure of the barrier-rib as well as following consecutive process.

Above open slit and/or dent structure at barrier-rib walls are not limited in above shape, but the intrinsic requirement to satisfy this Invention’s effect is self-adjustment capability of sustaining fluid after and/or middle of panel lamination process. In order to have uniform enough panel gap which is one of the critical requirements to provide uniform screen luminance, contrast ratio and optical response time as well as uniform gray shade image reproduction, self-adjustment ability of sustaining fluid without changing pre-set-particle number at each separated barrier-rib wall area is the most intrinsic effect of this Invention. Therefore, the barrier-rib physical structure condition described above in terms of the barrier-rib structure has both physical dimension restriction and panel gap uniformity insured electrophoretic display manufacturing process condition specifically for non-self-sustaining display media.

Second step

The second step is particles’ injection process in the formed barrier-rib structure. This particle injection process is used both dried particles and wet process. Selection of dry or wet process is dependent on particle size and number of sub-pixels. Figure 8 illustrates a wet process case. Dispersed particles are mixed with a volatile liquid such as ethyl alcohol. The mixed particle with ethyl alcohol is put into pressure-controlled injection syringe as illustrated in Figure 8. The injection amount at each separated sub-pixel surrounded by the barrier-rib structure is pre-calculated and injected with pressure control of the injector. Depending on dispersed particle size, instead of using pressurized injection system, ink-jet pushing out system is also available. For injection process itself, a known injection process is available and not limited above described method. In particular, sub-pixel pitch is relatively large, screen printing method is also available for the particle injection to a specific portion of sub-pixel. Since, this Invention is under premise of using different colored dispersed particles, selective sub-pixel particle injection is required. Use of pressurized injection system, ink-jet injection system, and screen printing method, all of these methods enable selective particle injection.

As a dry particle injection method, Figure 9 illustrates an example of the dry injection process. Dried particles are charged by externally equipped electron gun before the particles are put on a certain sub-pixel on the barrier-rib substrate. The pre-fabricated barrier-rib substrate is covered by a metal mask which is connected to DC bias voltage to adjust charged dry particle bombardment energy at the barrier-rib sub-pixel surface. For each primary colored particle, using specific metal mask with bias voltage control, at each primary colored sub-pixel is filled with the specific colored particle. For different colored particle, same process is repeated to fill all of sub-pixels with specific colored particles.

Third step

The third step is lamination process. Figure 10 illustrates this step. At wet particles injection method is deployed, the used liquid should be evaporated by elevated temperature. After wet or dry process of particle injection, top surface of the barrier-rib is coated with adhesive materials. This process is applicable with well-known process such as a screen printing, dispensing, and so on. Then, a counter electrode patterned substrate is registered its position and laminated. After the lamination, using well-known process, the adhesive materials is cured such as heat press method, vacuum bag press method, and so on. Depending on single panel size and sub-pixel pitch, and so on, not only thermoset glue, but also UV curable glue is applicable at this step of process. At this process and consecutive process, this Invention provides specific seal pattern as shown in Figure 11. The outer wall barrier-rib structure is specifically for the fourth step that is sustaining fluid filling process and completion of the panel fabrication process. An adhesive material is also placed on the top of the outer wall barrier-ribs using above well-known process. The outer wall barrier-rib enables complete separation between inner and outer panel for consecutive sustaining fluid filling process as well as protection of the display medium from external environment. The material of the outer wall barrier-rib is preferable with inorganic materials such as low melting glass powder slurry widely used for PDPs. However, it is not limited to such materials, and depending on the height of the outer wall barrier-ribs, some polymer materials such as epoxy resin is also applicable.

Fourth step

The final step is filling process of sustaining fluid in the laminated panel. Thanks to open slit and/or lower height wall separation area, this process is applicable of well-known non-self-sustainable fluid media such as liquid crystal materials. Similar to use of pressure difference filling method of liquid crystal material to a liquid crystal panel, the open area after the lamination process shown in Figure 11, is filled in a display medium reservoir in a vacuum chamber.

Both completely laminated panel with dried particles and sustaining fluid reservoir are placed in the vacuum chamber. After vacuum chamber’s pressure is reduced enough, the laminate panel is soaked its open area shown in Figure 11. Then, the vacuum chamber’s pressure is gradually increased with dried nitrogen gas. Due to vacuum chamber’s pressure increase, sustaining fluid is absorbed into the laminated panel. After confirmation of full injection of sustaining fluid, the panel is lifted up and the filling open area of barrier-rib is cleaned up, sealed by adhesive.

One of the most intrinsic inventions of this Invention is self-adjustment of sustaining fluid for all of separated barrier-rib wall areas. Preventing from electrophoretic particles invasion from pre-located barrier-rib wall area to other barrier-rib wall areas, only sustaining fluid enables to travel freely beyond all of separated barrier-rib wall areas. Therefore, the most intrinsic innovative concept of this Invention is self-adjustment of sustaining fluid and restriction of particle travel along with separated barrier-rib structure.

Example 1 (Invention)

Following glass substrates were prepared to confirm this Invention’s performance. Silicate glass substrate having its thickness of 1.1 mm and 60 nm thickness indium oxide layer prepared by low temperature magnetron sputtering was cleaned using high PH (PH 11) alkaline cleaner with 40 kHz ultrasonic application. After the alkaline cleaning, the substrate was rinsed by DI water followed by iso-propyl alcohol cleaning with ultrasonic application. Finally, the substrate was rinsed and dried under 110 °C, 60 minutes in a clean oven.

A green sheet with barrier-rib structure was prepared as the following method. In order to confirm this Invention’s performance, a barrier-rib structure was prepared here. High polymerization density of polyethylene film having its thickness of 200 micron was used as a base film. This film was made with several places of slit structures using lazar blade as shown in Figure 12. Thanks to sharp lazar blade, a hand crafted cutting line was up to 50 micron size. The slit width of up to 50 micron was measured and confirmed with microscope observation. This slit structured film was lifted on to the cleaned glass substrate as shown in Figure 13. After the sheet and glass substrate was set, then, average size of 100 micron diameter particles made of polystyrene (Phosphorex, Inc.) were dispersed as dry method as illustrated in Figure 9. In order to disperse dry particles, height of four feet of metal coated plastic hood was prepared. As illustrated in Figure 9, an electron gun, particle reservoir, and ground voltage potential board were set. After the air inside the hood was dried using de-humiliate one hour, the substrate with slit structure was set on the ground voltage board. About 0.3 gram of polystyrene particles was supplied to the electron gun path with compressed air as shown in Figure 9. The polystyrene particles were charged negative by the electron gun, and the charged particles were separated each other due to negative charge of each particle. The isolated particles fell on to the glass substrate with gravity help. Some of polystyrene particles were stacked on the top surface of the barrier-rib wall. Those particles were effectively brown away by low pressurized dried nitrogen flow. Some of particles located in each surrounded area of barrier-rib were also brown away; however, such loss was not so much.

A counter glass substrate having non-patterned indium oxide layer (60 nm thickness) with the same cleaning method was prepared. The counter glass substrate was laminated on the particle located substrate using epoxy thermoset glue with room temperature hardening type as shown in both Figures 11 and 14 using a vacuum bag. The glue line had couple of open area for sustaining fluid filling purpose. After the glue was completely harden, 5 centi-stroke viscosity of silicon oil was filled using vacuum chamber with same method of liquid crystal display material filling. After confirmed full filling of the fluid, excess amount of fluid around filling open area was cleaned up by cotton-puff with acetone. During the fluid filling process, no located particles were observed to invade next or neighbouring barrier-rib wall area. The fluid was successfully filled through the slit of the barrier-rib structure.

The electronics setting shown its block diagram in Figure 15 was prepared to drive the particles in the laminated panel. The original waveform was 2Hz of rectangular waveform using function generator (Tektronix Model AFG3011C). This signal was amplified with voltage amplifier (Stanford Research Model PS310). The panel was set on the stage of microscope (Nikon Model LVI 50N), and connected electronics with digital oscilloscope (Tektronix Model TDS 1,). Optical illumination was set as illustrated in Figure 15 using battery driven LED white light. Thanks to reflective index difference between silicon oil and polystyrene as well as Mie-scattering nature, even actual light scattering strength was not strong, with wide field of view using X 20 objective lens, the particle rotation was confirmed as shown in Figure 16. Figure 16 was used +/- 300 V, 2Hz rectangular waveform voltage.

Example 2 (Invention)

Following glass substrates were prepared to confirm this Invention’s performance. Silicate glass substrate having its thickness of 1.8 mm and 60 nm thickness indium oxide layer prepared by low temperature magnetron sputtering was cleaned using high PH (PH 11) alkaline cleaner with 40 kHz ultrasonic application. After the alkaline cleaning, the substrate was rinsed by DI water followed by iso-propyl alcohol cleaning with ultrasonic application. Finally, the substrate was rinsed and dried under 110 °C, 60 minutes in a clean oven.

A green sheet with barrier-rib structure was prepared as the following method. In order to confirm this Invention’s performance, a barrier-rib structure was prepared here. Middle polymerization density of polyethylene film having its thickness of 300 micron was used as a base film. This film was made with several places of dent structures using pressing relief. Thanks to the soft base film nature and the hard relief pressing surface, a hand crafted dent structure was formed. The dent portion of size is about 20 micron depth. This dent structure was confirmed with microscope. This dent structured sheet was put on the cleaned glass substrate. After the sheet and glass substrate was set, then, average size of 100 micron diameter particles made of polystyrene (Phosphorex, Inc.) were dispersed as dry method as illustrated in Figure 9. In order to disperse dry particles, height of four feet of metal coated plastic hood was prepared. As illustrated in Figure 9, an electron gun, particle reservoir, and ground voltage potential board were set. After the air inside the hood was dried using de-humidifier one hour, the substrate with slit structure was set on the ground voltage board. About 0.3 gram of polystyrene particles was supplied to the electron gun path with compressed air as shown in Figure 9. The polystyrene particles were charged negative by the electron gun, and the charged particles were separated each other due to negative charge of each particle. The isolated particles fall on to the glass substrate with gravity help. Some of polystyrene particles were stacked on the top surface of the barrier-rib wall. Those particles were effectively brown away by low pressurized dried nitrogen flow. Some of the particles located in each surrounded area of the barrier-rib were also brown away; however, such loss was not so much.

A counter glass substrate having non-patterned indium oxide layer (60 nm thickness) with the same cleaning method was prepared. The counter glass substrate was laminated on the particle located substrate using epoxy thermoset glue with room temperature hardening type as shown in Figure 14 using a vacuum bag. The glue line had couple of open area for sustaining fluid filling purpose. After the glue was completely harden, 5 centi-stroke viscosity of silicon oil was filled using vacuum chamber with same method of liquid crystal display material filling. After confirmed full filling of the fluid, excess amount of fluid around filling open area was cleaned up by cotton-puff with acetone. During the fluid filling process, no located particles were observed to invade next or neighbouring barrier-rib wall area. The fluid was successfully filled through the slit of the barrier-rib structure.

Using electronics setting shown its block diagram in Figure 15 was prepared to drive the particles in the laminated panel. The original waveform was 2 Hz of rectangular waveform using function generator (Tektronix Model AFG3011C).This signal was amplified with voltage amplifier (Stanford Research Model PS310). The panel was set on the stage of microscope (Nikon Model LVI 50N), and connected electronics with digital oscilloscope (Tektronix Model TDS 1,). Optical illumination was set as illustrated in Figure 15 using battery driven LED white light. Thanks to reflective index difference between silicon oil and polystyrene as well as Mie-scattering nature, even actual light scattering strength was not strong, with wide field of view using X 20 objective lens, the particle rotation was confirmed as shown in Figure 17. Figure 17 was used +/- 300 V, 2 Hz rectangular waveform voltage.

Example 3 (Invention)

Following glass substrates were prepared to confirm this Invention’s performance. Silicate glass substrate having its thickness of 0.7 mm and 60 nm thickness indium oxide layer prepared by low temperature magnetron sputtering was cleaned using high PH (PH 11) alkaline cleaner with 40 kHz ultrasonic application. After the alkaline cleaning, the substrate was rinsed by DI water followed by iso-propyl alcohol cleaning with ultrasonic application. Finally, the substrate was rinsed and dried under 110 °C, 60 minutes in a clean oven.

A green sheet with barrier-rib structure was prepared as the following method. In order to confirm this Invention’s performance, a barrier-rib structure was prepared here. High polymerization density of polyethylene film having its thickness of 200 micron was used as a base film. This film was made with several places of slit structures using lazar blade as shown in Figure 12. Thanks to sharp lazar blade, a hand crafted cutting line was up to 50 micron size. The slit width of up to 50 micron was measured and confirmed with microscope observation. This slit structured film was lifted on to the cleaned glass substrate as shown in Figure 13. After the sheet and glass substrate was set, then, average size of 100 micron diameter particles made of polystyrene (Phosphorex, Inc.) were dispersed as wet method as illustrated in Figure 18. In order to disperse wet particles, the 0.1 gram of polystyrene particles was dispersed with 500 gram of methyl alcohol. After the mixture was stirred by magnetic stirrer, the dispersed solution was sprayed by a spray gun with 0.3 atm. of dried air pressure. After the dispersed fluid was sprayed, the barrier-rib equipped glass substrate was heated its temperature at 80 °C. half-hour. Some of the polystyrene particles were stacked on the top surface of the barrier-rib wall. Those particles were effectively brown away by low pressurized dried nitrogen flow. Some of the particles located in each surrounded area of barrier-rib were also brown away; however, such loss was not so much.

A counter glass substrate having non-patterned indium oxide layer (60 nm thickness) with the same cleaning method was prepared. The counter glass substrate was laminated on the particle located substrate using epoxy thermoset glue with room temperature hardening type as shown in Figure 14 using a vacuum bag. The glue line had couple of open area for sustaining fluid filling purpose. After the glue was completely harden, 5 centi-stroke viscosity of silicon oil was filled using vacuum chamber with the same method of liquid crystal display material filling. After confirmed full filling of the fluid, excess amount of fluid around filling open area was cleaned up by cotton-puff with acetone. During the fluid filling process, no located particles were observed to invade next or neighbouring barrier-rib wall area. The fluid was successfully filled through the slit of the barrier-rib structure.

Using electronics setting shown its block diagram in Figure 15 was prepared to drive the particles in the laminated panel. The original waveform was 2 Hz of rectangular waveform using function generator (Tektronix Model AFG3011C). This signal was amplified with voltage amplifier (Stanford Research Model PS310). The panel was set on the stage of microscope (Nikon Model LVI 50N), and the connected electronics with digital oscilloscope (Tektronix Model TDS 1). Optical illumination was set as illustrated in Figure 15 using battery driven LED white light. Thanks to the reflective index difference between silicon oil and polystyrene as well as Mie-scattering nature, even actual light scattering strength was not strong, with wide field of view using X 20 objective lens, the particle rotation was confirmed as shown in Figure 19. Figure 19 was used +/- 300 V, 2 Hz rectangular waveform voltage.

Example 4 (Invention)

Using exactly same glass substrates and open slit barrier-rib structure described above Example 1, the following structure of lamination panel was prepared.

Instead of using the peripheral glue sealing pattern shown in Figure 13 for the Example 1, non-open area peripheral sealing pattern was used as illustrated in Figure 20. This non-open peripheral seal pattern was formed by a commercially available dispensing machine (Mushahi Engineering, Co., Ltd. Model Image Maste 350 PC) both equipped with syringe and X-Y stage. Used perimeter seal glue was UV-curable epoxy-acrylic glue (Sanritsu Chemicals, Co., Ltd. World-rock UV curable glue). After the non-open area glue seal pattern shown in Figure 20 was formed, using the same dry particle dispersing system illustrated in Figure 14, average size of 100 micron diameter particles made of polystyrene (Phosphorex, Inc.) were dispersed in each separated area of the barrier-rib wall. At this process, over the perimeter seal pattern area was covered by mask to prevent from particles stacking on the top surface of the perimeter seal pattern. Some of polystyrene particles were stacked on the top surface of the barrier-rib wall. Those particles were effectively brown away by low pressurized dried nitrogen flow. Some of particles located in each surrounded area of barrier-rib were also brown away; however, such loss was not so much.

As the next step, using micro-amount dispensing nozzle system which is widely used for liquid crystal materials injection to a liquid crystal display panel, 5 centi-stroke viscosity silicon oil was injected to each separated area of barrier-rib wall. Then, the same counter substrate used for the Example 1 was covered to make a lamination. After the lamination, the stacked panel was put into a vacuum bag, and exposed i-line of UV light for curing of UV-curable glue seal.

The electronics setting shown its block diagram in Figure 15 was prepared to drive the particles in the laminated panel. The original waveform was 2 Hz of rectangular waveform using function generator (Tektronix Model AFG3011C). This signal was amplified with voltage amplifier (Stanford Research Model PS310). The panel was set on the stage of microscope (Nikon Model LVI 50N), and connected electronics with digital oscilloscope (Tektronix Model TDS 1). Optical illumination was set as illustrated in Figure 15 using battery driven LED white light. Thanks to reflective index difference between silicon oil and polystyrene as well as Mie-scattering nature, even actual light scattering strength was not strong, with wide field of view using X 20 objective lens, the particle rotation was confirmed as shown in Figure 21. Figure 21 was used +/- 300 V, 2 Hz rectangular waveform voltage.

Example 5 (Control)

Using exactly the same glass substrates described above Example 1, but using without any open slit area, nor dent structure in the barrier-rib structure as illustrated in Figure 22, following lamination panel was prepared.

After no-open area, no dent area type of barrier-rib structure as illustrated in Figure 22, this barrier-rib sheet was put on the ITO patterned glass substrate. On this barrier-rib stacked glass substrate, non-open area of UV-curable perimeter seal pattern same with the patter used with the Example 4 was formed with the same process applied with Example 4.

After the non-open area glue seal pattern shown in Figure 20 was formed, using the same dry particle dispersing system illustrated in Figure 14, average size of 100 micron diameter particles made of polystyrene (Phosphorex, Inc.) were dispersed in each separated area of the barrier-rib wall. At this process, over the perimeter seal pattern area was covered by mask to prevent from particles stacking on the top surface of the perimeter seal pattern. Some of polystyrene particles were stacked on the top surface of the barrier-rib wall. Those particles were effectively brown away by low pressurized dried nitrogen flow. Some of particles located in each surrounded area of barrier-rib were also brown away; however, such loss was not so much.

As the next step, using micro-amount dispensing nozzle system which is widely used for liquid crystal materials injection to a liquid crystal display panel, 5 centi-stroke viscosity silicon oil was injected to each separated area of barrier-rib wall. Then, the same counter substrate used for the Example 1 was covered to make a lamination. After the lamination, the stacked panel was put into a vacuum bag, and exposed i-line of UV light for curing of UV-curable glue seal.

Above process, however, could not provide good enough panel gap uniformity due to slight but critical difference of sustaining silicon oil fluid amount at each separated barrier-rib wall area. Due to slight, but critical difference of the amount of fluid, this difference was not adjusted at the panel lamination process. Unlike self-adjustment effect using open slit and/or dent structure in the barrier-rib walls, this Example case has no self-adjustment effect of excess/lack amount of sustaining fluid at each separated barrier-rib wall structure. Due to variation of fluid amount at each separated barrier-rib structure, uniform panel gap was not obtained.

This Invention provides an innovative barrier-rib structure for non-self-sustaining display media based electrophoretic displays both in terms of uniform panel gap realization and its higher manufacturability. Moreover, this Invention enables reduction of display panel manufacturing process based on open slit and/or dent barrier-rib wall structure. By enabling self-adjustment capability of sustaining fluid at non-self-sustaining fluid electrophoretic display system, both display performance in uniformity and productivity of the display panel are reasonably expected to show dramatic improvement.

Claims (12)

1. An electrophoretic display device for effecting a display by moving electrophoretic particles, comprising:

   - a specific physical barrier-rib wall structure enabling sustaining fluid passing through beyond each separated barrier-rib wall structure and preventing from electrophoretic particles travel beyond pre-selected barrier-rib wall area.
2. The specific physical barrier-rib wall structure according to claim 1, characterised by that the barrier-rib wall has different height in their structure enabling fluid transfer beyond the wall and preventing from particles travelling.
3. The specific physical barrier-rib wall structure according to claim 2, characterised by that the barrier-rib wall has slit open area having its open area size that is defined as following:

   h > a > d, where

   a is an average size of electrophoretic particles, d is slit open area size, and h is height of barrier-rib wall.
4. The specific physical barrier-rib wall structure according to claim 2, characterised by that the barrier-rib wall has different height portion from base height that is defined as following:

   h > c, a > d, a > c, where

   c is height of lower area of the barrier-rib wall.
5. The specific physical barrier-rib wall structure according to claim 2, characterised by that the barrier-rib wall has lower height than that of averaged particle size and has spacer portion of structure having its height, width, and distance of neighbouring spacer portions on the barrier-rib wall structure as defined bellow:

   n + m > a, p > a, a > l, where

   n is base height of barrier-rib wall, m is height of spacer portion of barrier-rib wall, a is an average size of electrophoretic particles, p is distance between the spacer portion of barrier-rib wall, and l is width of spacer portion of barrier-rib wall.
6. The specific physical barrier-rib wall structure according to claim 2, characterised by that the barrier-rib wall consists of polymer materials, low melting temperature glass materials.
7. An electrophoretic display device for effecting a display by moving electrophoretic particles, comprising:

   - a specific physical barrier-rib wall structure enabling sustaining fluid passing through beyond each separated barrier-rib wall structure and preventing from electrophoretic particles travel beyond pre-selected barrier-rib wall area and perimeter seal patterning having at least one open area.
8. A electrophoretic display device for effecting a display by moving electrophoretic particles, with panel fabrication process where:

   - electrophoretic particles are dispersed to pre-fabricated barrier-rib wall structure according to claim 1,

   - then, counter substrate having counter electrodes is laminated with perimeter glue pattern seal,

   - consequently, the laminated panel is filled sustaining fluid.
9. The panel fabrication process according to claim 8, characterised by that electrophoretic particles are dispersed in the separated barrier-rib wall structure with dry particles dispersion method.
10. The particle fabrication process according to claim 8, characterised by that electrophoretic particles are dispersed in the separated barrier-rib structure with wet particles dispersion method.
11. An electrophoretic display panel production process according to claim 7, characterised by that sustaining fluid is filled with vacuum pressure difference method.
12. The electrophoretic display panel production process according to claim 7, characterised by that sustaining fluid is filled with injection method prior to counter substrate lamination process using injection nozzle head means.

Images