WO2012030199A2

WO2012030199A2 - Electrophoretic particles, and display device and image sheet comprising same

Info

Publication number: WO2012030199A2
Application number: PCT/KR2011/006561
Authority: WO
Inventors: 김재환; 조영태; 정민영; 이창빈; 이용의; 김철환
Original assignee: 주식회사 이미지앤머터리얼스
Priority date: 2010-09-03
Filing date: 2011-09-05
Publication date: 2012-03-08
Also published as: WO2012030199A3; KR20120024084A

Abstract

The present invention relates to electrophoretic particles, and to a display device and image sheet comprising same. The circularity of each of the electrophoretic particles for an electrophoretic display device according to one embodiment of the present invention is determined by the following FIG. 1A, wherein the circularity is no less than 0.930 and less than 1. The particle size distribution of the particles is 10% to 40%, and is determined by the following mathematical formula 2 (where A represents a projected area of a two-dimensionally projected particle, and P represents the perimeter of the two-dimensionally projected particle): [Mathematical formula 2] particle size distribution = (â/á) × 100 (where, á is an arithmetic mean diameter of particle sizes, and â is a standard deviation of the particle sizes).

Description

Electrophoretic particles, display device and image sheet comprising the same

The present invention relates to display technology, and more particularly, to electrophoretic particles, a display device and an image sheet comprising the same.

As an information display device for replacing a liquid crystal display device, a display device using an electrophoresis method, an electro-chromic method, and a dichroic particles rotary method has been proposed. These techniques have been extensively studied as next generation display devices that can replace liquid crystal display devices due to advantages such as wide viewing angle, low power consumption, and memory effect in proximity to conventional print media such as paper.

Among these display devices, an electrophoretic display device uses a phenomenon in which charged particles move by an electric field applied between two electrodes. The particles may have one kind of color or two or more kinds of colors. In the case of using two or more kinds of colored particles, the polarities of these particles are generally opposite to each other, but can be independently controlled by the difference in electrophoretic mobility even if they have the same polarity.

As such, in the electrophoretic display device, image information is implemented by particles, so design parameters such as image quality and driving voltage, such as contrast ratio and color reproducibility, depend on the characteristics of the particles.

The technical problem to be achieved by the present invention is to provide electrophoretic particles that can not only improve image quality such as contrast ratio and color reproducibility, but can also reduce driving voltage.

In addition, another technical object of the present invention is to provide a display device using the particles having the above-described advantages.

In addition, another technical problem to be achieved by the present invention is to provide an image sheet using particles having the aforementioned advantages.

Particles according to an embodiment of the present invention for achieving the above technical problem, the particles for the electrophoretic display device, the circularity of the particles is defined by Figure 1a below, the circularity is 0.930 or more and less than 1 size Has 1A is the projection area of the two-dimensionally projected particles, and P is the circumferential length of the two-dimensionally projected particles.

In addition, the particles according to another embodiment of the present invention, the particles for the electrophoretic display device, the particle size distribution of the particles is determined by the following equation 2, the particle size distribution may have a size of 10% to 40%. have.

[Equation 2]

Particle size distribution = (β / α) × 100 (where α is the arithmetic mean diameter of particle size and β is the standard deviation of the particle size)

In addition, the particles according to another embodiment of the present invention may have all the features of the circularity and the particle size distribution described above. In some embodiments, the size of the particles may have a size of 0.02 μm to 50 μm.

In addition, the particles may have a color. In some embodiments, the particles may comprise any one or a mixture of pigments, dyes, metal particles, metal oxide particles, and resins.

Electrophoretic display device according to an embodiment of the present invention for achieving the above another technical problem, the substrate facing each other; At least one cavity disposed between the substrates; And particles dispersed in the cavities and having at least one of the foregoing features. In some embodiments, the particles in the cavities may include two or more kinds of particles in which at least one of color and electrophoretic mobility is different. In this case, only particles corresponding to any one of the two or more kinds of particles may satisfy at least one of the circularity and the particle size distribution.

According to another aspect of the present invention, there is provided an image sheet including support substrates facing each other; At least one cavity disposed between the support substrates; And dispersed in the cavities and having at least one of the foregoing features. In some embodiments, the particles in the cavities may include two or more kinds of particles in which at least one of color and electrophoretic mobility is different, and in this case, any one of the two or more kinds of particles Only the corresponding particles may satisfy at least one of the circularity and the particle size distribution.

Electrophoretic particles according to the embodiments of the present invention may improve the shielding power to the external light transmitted by the light reflective sub-particles while ensuring excellent light reflectivity, thereby improving the color reproducibility of the electrophoretic display device. In addition, according to an embodiment of the present invention, by having an optimized circularity to have excellent filling and light shielding power, it is possible to improve the contrast and color reproducibility of the electrophoretic display device.

In addition, according to an embodiment of the present invention, by ensuring the light shielding power by the optimized particle size distribution, it is possible to further improve the contrast and color reproducibility of the electrophoretic display device, it is possible to reduce or omit a separate classification process In addition, manufacturing costs can be reduced.

1 illustrates various forms of electrophoretic particles.

2A and 2B respectively show aggregates of particles having different particle size distributions, and FIG. 2C is an electron scanning microscope image of particles manufactured to have a particle size distribution according to an embodiment of the present invention.

3A is a cross-sectional view of an electrophoretic display apparatus using particles according to an embodiment of the present invention, and FIG. 3B is a cross-sectional view of an electrophoretic display apparatus using particles having the same spherical shape and the same size as a comparative example.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art, and the following examples can be modified in various other forms, and the scope of the present invention is It is not limited to an Example. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept to those skilled in the art.

In addition, the thickness or size of each layer in the drawings is exaggerated for convenience and clarity, the same reference numerals in the drawings refer to the same elements. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" may include the plural forms as well, unless the context clearly indicates otherwise. Also, as used herein, "comprise" and / or "comprising" specifies the presence of the mentioned shapes, numbers, steps, actions, members, elements and / or groups of these. It is not intended to exclude the presence or the addition of one or more other shapes, numbers, acts, members, elements and / or groups.

Although the terms first, second, etc. are used herein to describe various members, parts, regions, and / or parts, these members, parts, regions, and / or parts should not be limited by these terms. Is self-explanatory. These terms are only used to distinguish one member, part, region or part from another region or part. Thus, the first member, part, region, or portion, which will be described below, may refer to the second member, component, region, or portion without departing from the teachings of the present invention.

Embodiments of the present invention will now be described with reference to the drawings, which schematically illustrate ideal embodiments of the present invention. In the drawings, for example, the size and shape of the members may be exaggerated for convenience and clarity of description, and in actual implementation, variations of the illustrated shape may be expected. Accordingly, embodiments of the present invention should not be construed as limited to the specific shapes of the regions shown herein.

The inventors have observed that the particle shape and particle size distribution of the electrophoretic particles affect the response speed, display ratio and color reproduction of the electrophoretic display device. The following examples improve the performance of the electrophoretic display device such as response speed, contrast ratio and color reproduction of the electrophoretic display device by controlling the particle shape and particle size distribution of the particles, and using the same for various image sheets and electrophoretic display devices. It is about.

1A is a characteristic equation relating to the circularity of particles, and FIG. 1B shows various forms of electrophoretic particles. Particles used in the electrophoretic display device may have a variety of shapes, such as spherical (10A), elliptical (10B) and amorphous potato (10C) shown in Figure 1b, the particles having a variety of these forms Used as

The extent to which the shape of these particles is spherical can be assessed by the circularity shown in FIG. 1A. The circularity is determined by the ratio of the projected area of the particle to the circumferential depth of the particle. In FIG. 1A, A is the projection area of the two-dimensionally projected particles, and P is the circumferential length of the two-dimensionally projected particles. The circularity of the particles can be measured using commercial software such as ImageJ ^(R) from an image obtained from a scanning electron microscope. Alternatively, the circularity can also be measured by a flow particle image analyzer with a FPIA-3000 ^(R) manufactured by SYSMEX (Kobe, Japan).

In reflective electrophoretic display devices, when the particles are close to a perfect sphere, the contact between the particles and the contact between the particles and the control electrode surface are almost point contact. As a result, the shielding force of the incident light by the particles may be lowered, thereby lowering the quality of the display image. In addition, the point contact may cause a decrease in Van der Walls force between the electrode and the particles, thereby reducing the bistable stability of the particles when the power is removed.

According to an embodiment of the invention, the particles preferably have a circularity of 0.93 to less than 1, which is not a perfect sphere. Within the above circularity range, the light shielding power of the particles is increased, so that display quality such as contrast ratio and color reproducibility can be improved, and a suitable driving voltage can be ensured. These advantages of the present invention will become more apparent from the description of the embodiments of the display device described below. If the particles have a roundness of less than 0.93, the sticking phenomenon due to electrical attraction between particles having different polarities is increased, and the van der Waals force between the particles and the control electrode surface is increased. As a result, not only the image density is reduced under the same driving voltage, but also the driving voltage required to obtain an equivalent level of image density can be rapidly increased, for example, to 100 V or more.

2A and 2B show aggregates 11 and 12 of particles having different particle size distributions, respectively, and FIG. 2C is an electron scanning microscope image of an aggregate of particles having a particle size distribution according to an embodiment of the present invention.

The particle size distribution of the particles is defined by equation (2).

[Equation 2]

Particle Size Distribution = (β / α) × 100

Where α is the arithmetic mean diameter of particle size and β is the standard deviation of the particle size. The particle size distribution of the particles, from the images obtained from the scanning electron microscope as shown in the circular diagram, can be measured using commercial software such as ImageJ ^(R) . The small value of the particle size distribution indicates that the particle size is almost similar, and the large value of the particle size distribution indicates that the particle size varies widely.

In general, when the size of the particles is uniform, the charging and cohesiveness of the particles may be improved. However, as the particle size becomes uniform, in the reflective mode display, the light shielding power of the particle layer by the particles is weakened, thereby reducing the business card ratio and color reproducibility. In addition, when the size of the particles used is several micro to sub micro size, the weakening of the light shielding force causes a drastic deterioration of the image quality.

According to an embodiment of the present invention, the particle size distribution of the particles may preferably be 10% to 40%. Within this range, the light shielding power of the particle layer (refering to the aggregate of particles distributed over the control electrode) is significantly increased, thereby improving the contrast ratio and color reproducibility. In the particle size distribution of less than 10%, not only the filling of the particle layer is low, sufficient light shielding cannot be obtained, but also a separate classification process is required to obtain a small particle size distribution, which increases the particle manufacturing cost. If the particle size distribution exceeds 40%, there is a problem that the interchargeability between particles is deteriorated, and the life of the display device is shortened due to the aggregation of particles having different polarities. The aggregate of particles according to the embodiment of the present invention shown in FIG. 2C has a particle size distribution of about 0.2 μm to about 0.8 μm and a particle size distribution of about 20%. These particles not only had excellent color reproducibility, but also exhibited excellent contrast ratio of about 10 degrees. However, this is exemplary and the particles may have a size of 0.02 μm to 50 μm or less. If desired, in the case of a wet drive, the size of the particles may be within a relatively small range of 0.02 μm to 10 μm, and in the case of a dry drive, the size of the particles may be in the range of 0.02 μm to 50 μm. .

3A is a cross-sectional view of an electrophoretic display apparatus 1000 using particles according to an embodiment of the present invention, and FIG. 3B is a cross-sectional view of an electrophoretic display apparatus 1000R using particles having the same spherical shape and the same size as a comparative example. .

3A and 3B, at least particles are to be dispersed between a first substrate 21 (which may be a lower substrate in this figure) and a second substrate 22 (which may be an upper substrate in this figure) facing each other. A light conversion layer 70 may be provided that includes one or more cavities V1, V2, V3. At least one of the lower substrate 20 and the upper substrate 21, for example, the upper substrate 21 on the observer 1 side may be formed of a transparent material such as glass and transparent resin.

The cavities V1, V2, V3 may be defined by the partition 30 as a separating member, as shown. However, this is exemplary and the cavities V1, V2, V3 may be defined by other separating members, such as microcup structures or microcapsule shells, as is well known in the art. The cavities V1, V2, V3, alone or in combination with one or more other adjacent cavities, may constitute one subpixel or pixel.

The electrophoretic display apparatus 1000R may include

electrodes

41 and 42 for driving the

particles

100R, 100G, 100B, and 100K; PR, PG, PB, and PK. The

electrodes

41 and 42 may be configured to face each other so as to generate an electric field perpendicular to the main surfaces of the substrates 21 and 22, as shown. The electrodes 22 disposed on the lower substrate 21 are

individual electrodes

42R, 42G, 42B that can be independently addressed for each pixel by a suitable switching element such as a transistor, and the electrodes on the upper substrate 22 ( 41 may be a common electrode opposite the individual electrodes 42.

At least one of these

electrodes

41, 42, for example the common electrode, may be a transparent electrode. The transparent electrode may include, for example, Indium-Tin-Oxide (ITO), Fluorinated Tin Oxide (FTO), Indium Oxide (IO), and Tin Oxide; It may be formed of any one or a combination of a transparent metal oxide such as SnO ₂ ), a transparent conductive resin such as polyacetylene, or a conductive resin containing conductive metal fine particles. However, the above-described electrode configuration is exemplary and the present invention is not limited thereto. For example, it may have a known in-plane configuration or a combination thereof.

Individual electrodes 42 may be driven by an active matrix comprising transistors 50 as switching elements. However, this is only illustrative, and those skilled in the art will appreciate that a passive matrix type electrode configuration, or a segment type electrode configuration and wiring structure for static driving are also included in the embodiments of the present invention.

In the cavities (V1, V2, V3) has a high resistance and low viscosity fluid (U) and at least one kind of electrophoretic particles (100R, 100G, 100B, 100K; PR, PG, PB) dispersed in the fluid , PK) is dispersed. Fluid U may be a solution or gas of one or more dielectric liquids. Fluid U may be colored with dyes and / or pigments.

Electrophoretic particles (100R, 100G, 100B, 100K; PR, PG, PB, PK) have a positive or negative charge, any one of pigments, dyes, metal particles, metal oxide particles and resins or these It can be formed into a mixture of. For example, a mixture particle of a pigment and a polymer may be used, and the mixture particle may be a pigment coated on the surface of the polymer particle or a composition in which the pigment is dispersed in the polymer. Preferably, the particles disclosed in the applicant's Korean application No. 10-2010-0086456 can be used, the matters disclosed in these patent documents are hereby incorporated by reference in their entirety.

The

particles

100R, 100G, 100B, 100K; PR, PG, PB, PK may have a size of several tens of micro to submicron levels to have suitable electrophoretic mobility. For example, the particles may have a size of 0.02 μm to 50 μm or less. If desired, in the case of a wet drive, the size of the particles may be in a relatively small range of 0.02 μm to 10 μm, and in the case of a dry drive, the size of the particles may be in the range of 0.02 μm to 50 μm.

In addition, two types of particles having different colors and / or electrophoretic mobility may be dispersed in each of the cavities V1, V2, and V3 to implement a multi-color display device. However, this is exemplary, and each cavity may be filled with particles having one kind of color and electrophoretic mobility, or three or more kinds of particles having different color and / or electrophoretic mobility.

The

particles

100R, 100G, 100B (PR, PG, PB) dispersed in the cavities V1, V2, and V3 may have red, green, and blue colors, respectively, in order to realize multi colors by the RGB color system. have. Alternatively, the

particles

100R, 100G, 100B (PR, PG, PB) may implement a multi color by the CMY color system, and in this case, may have cyan, magenta, and yellow colors, respectively. The other particles 100K (PK) may have white or black depending on the color system.

The

particles

100R, 100G, 100B of FIG. 3A have a circularity of less than 0.930 to 1 and a particle size distribution of 10% to 40%, according to an embodiment of the present invention, and the particles of FIG. PR, PG, PB) have a perfect sphere with a circularity of 1 and a particle size distribution of 0%. For convenience of description, the

particles

100R, 100G, 100B; PR, PG, PB have red, green and blue, respectively, charged with +, other particles 100K (PK) are black,-polarity Assume that we have

When the scan signal is received through the gate electrode 50G of the transistors 50 and the data signal is received through the source electrode 50S, between the

individual electrodes

42R, 42G, 42B and the common electrode 41. Any electric field may be applied. For example, a negative potential is applied to the individual electrodes 42R of the first cavity V1, a positive potential is provided to the

individual electrodes

42G and 42B of the second and third cavities V2 and V3, and common. The ground potential may be applied to the electrode 41. In this case, each

particle

100R, 100G, 100B, 100K; PR, PG, PB, PK will be distributed as shown in Figs. 2A and 2B, respectively.

In the first and second cavities V1, V2, the incident light i is reflected by the particles 100R, 100G (PR, PG), and as a result, wavelengths of red and green color to the observer 1, respectively. Light with will be delivered. In contrast, in the third cavity V3, the incident light i is absorbed and turned off by the black particles 100K and PK, and no light is transmitted to the observer 1. By the color additive mixing method, the observer 1 observes the color in which the red light (iR; iR ') and the green light (iG; iG') which are reflected light are mixed.

In the embodiment of FIG. 3A using the

particles

100R, 100K, and 100G according to the embodiment of the present invention, the filling state of the particle layer PL distributed on the common electrode side is good, so that only a few layers may provide excellent light shielding power. You can get it. Accordingly, the black particles 100K, which should not be visible to the observer 1, are sufficiently covered by the particle layer PL so that they are not reflected to the observer 1. In particular, even if the dielectric fluid U is transparent without being colored with a dye or pigment that may mask the black particles 100K, such as gray, since the black particles behind it may be covered by the color particles 100R and 100G. Contrast can be significantly improved, and color reproducibility can be improved.

On the contrary, in FIG. 3B according to the comparative example, the particle layer PL distributed on the common electrode side has a poor filling state due to the point contact and the uniform size, thereby providing sufficient light shielding force by the empty space in the particle layer PL. Can not get Thus, the intensity of the reflected light is reduced, and the contrast and color reproducibility of the display information are reduced. If the dielectric fluid U is transparent, black particles PK may be illuminated which should not be visible to the observer 1 by transmitted light iT. This immersion phenomenon causes a reduction in color reproducibility in a display device including particles having two or more different colors in a pixel or subpixel.

In Figures 3A and 3B, optionally only the colored

particles

100R, 100G, 100B are disclosed with respect to having a certain circularity and particle size distribution according to an embodiment of the present invention, but those skilled in the art will appreciate that these colored particles in the same cavity It will be appreciated that other black or white particles 100K dispersed with the

fields

100R, 100G, and 100B may also have a predetermined circularity and particle size distribution. However, in a two- or three-particle or more system in which two or more kinds of particles are dispersed in a cavity, it is polarity that only particles of any one type, for example color particles, have a certain circularity and particle size distribution. It may be desirable to prevent or reduce agglomeration between these different dissimilar particles, thereby preventing an increase in driving voltage.

Although the color particles have been described above, those skilled in the art can realize that the same advantages can be obtained by designing the black and / or white particles to have a predetermined circularity and / or particle size distribution even in a monochrome monochrome display device. have. In addition, although the above embodiments relate to an electrophoretic display device having a partition structure, the same advantages can be obtained in an electrophoretic display device having a microcapsule structure, a microcup structure, or other various types of cavity structures and polymer dispersed structures. It can be obvious.

The above-described embodiments disclose an electrophoretic display device as a finished product, but form cavities defined by suitable separating members between supporting substrates that do not include a drive element, so that the layer indicated by 70 in FIG. 3A (light conversion layer). May comprise an image media layer (or image sheet). After the image media layer is completed, the electrophoretic display apparatus 1000 as illustrated in FIG. 3A may be provided by bonding the image media layer to the substrate on which the driving element is formed by using an adhesive layer.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and alterations are possible within the scope without departing from the technical spirit of the present invention, which are common in the art. It will be apparent to those who have knowledge.

Claims

Particles for an electrophoretic display device, the circularity of the particles is determined by the following equation 1, the circularity is a particle having a size of more than 0.930 and less than 1.

A is the projection area of the two-dimensionally projected particle, and P is the circumferential length of the two-dimensionally projected particle)
As particles for an electrophoretic display device, the particle size distribution of the particles is defined by Equation 2 below, wherein the particle size distribution has a size of 10% to 40%.

[Equation 2]

Particle size distribution = (β / α) × 100 (where α is the arithmetic mean diameter of particle size and β is the standard deviation of the particle size)
As particles for an electrophoretic display device, the circularity of the particles is determined by Equation 1, the circularity is 0.930 or more and less than 1, the particle size distribution of the particles is determined by Equation 2, Particle size distribution has particles having a size of 10% to 40%.
The method according to any one of claims 1 to 3,

The particles are particles, characterized in that having a size of 0.02 ㎛ to 50 ㎛ or less.
The method according to any one of claims 1 to 3,

Particles, wherein the particles have a color.
The method according to any one of claims 1 to 3,

Said particles comprising any one or a mixture of pigments, dyes, metal particles, metal oxide particles and resins.
Substrates facing each other;

At least one cavity disposed between the substrates; And

An electrophoretic display device dispersed in said cavities and comprising the particles of any one of claims 1 to 3.
The method of claim 7, wherein

And the particles in the cavities include two or more kinds of particles in which at least one of color and electrophoretic mobility is different from each other.
The method of claim 8,

Only particles corresponding to any one of the two or more types of particles satisfy at least one of the circularity and the particle size distribution.
Support substrates facing each other;

At least one cavity disposed between the support substrates; And

An image sheet dispersed in said cavities and comprising the particles of any one of claims 1 to 3.
The method of claim 10,

And said particles in said cavities comprise two or more kinds of particles in which at least one of color and electrophoretic mobility is different.
The method of claim 10,

Only particles corresponding to any one of the two or more kinds of particles satisfy at least one of the circularity and the particle size distribution.