JP4586943B2 - Visibility evaluation method for electronic paper - Google Patents

Description

The present invention also relates to visibility valuation method of electronic paper.

  In recent years, with the increase in the operating speed of personal computers, the spread of network infrastructure, the increase in capacity and price of data storage, information such as documents and images that have been conventionally printed on paper and provided as printed matter The opportunity to obtain electronic information more easily and browse the electronic information is increasing.

  In order to browse such electronic information, a light-emitting display such as a liquid crystal display, a CRT (CRT) display, or an organic EL display is mainly used.

  However, in particular, when the electronic information is a document, it is necessary to watch the screen for a relatively long time. Therefore, it is difficult to say that a light-emitting display is friendly to human eyes. That is, as a defect of the light emitting display, there is a point that eyes are fatigued by flicker (flickering phenomenon).

  As a solution to this drawback, a reflection type display using outside light, so-called electronic paper, which can rewrite an image, is known. For example, Patent Document 1 discloses an electrophoretic electronic paper that performs light modulation by moving charged particles according to an electric field.

  Electronic paper is generally considered to have better visibility than a light-emitting display.

  As a method for evaluating the visibility of electronic paper, Patent Document 2 proposes a method for inspecting image unevenness by calculating the luminance value (Y value) and obtaining a difference image from the maximum luminance and the minimum luminance. ing.

JP 2008-242495 A JP 2006-17571 A

  The electronic paper has the same feature as a printed matter that there is no eye fatigue due to the flicker phenomenon, and has the feature that it can be rewritten repeatedly on the same display screen.

  Therefore, usually, when reading a document by electronic paper, for example, one image page is displayed and read, and then rewritten to the information of the next image page and read, for example, a plurality of image pages are displayed on the same display screen. You will stare continuously.

  However, when a plurality of electronic papers having the same evaluation by the method of Patent Document 2 are subjected to sensory evaluation that is actually observed with the eyes while continuously displaying different image pages, the results differ depending on each electronic paper. is the current situation. Note that different image pages are pages with different types of images such as document images with different font sizes and font types, and image images with different colors and image contents.

  Electronic paper has the demerit that the texture of the display surface derived from the configuration of the electronic paper device is directly transferred to the next page in exchange for the merit that the image can be rewritten. Specifically, when a page with an image with a noticeable texture and a page with an inconspicuous image are continuously displayed for a certain texture, the difference in the texture is large and it is felt that the visibility is inferior. Evaluation becomes low.

  As a result of repeated studies by the present inventors, it has been found that a texture that particularly affects visibility is a rough feeling. Roughness derived from the configuration of this device is, for example, due to malfunction of charged particles in electrophoretic electronic paper, or in the case of a configuration in which charged particles are further enclosed in microcapsules. It is presumed to be caused by the influence.

The present invention has been made on the basis of the circumstances as described above, and the purpose of the visibility of electronic paper is to obtain visibility that matches the scale of sensory evaluation as a numerical value. It is to provide visibility valuation method of electronic paper that can be objectively evaluated.

  The object of the present invention can be achieved by the following constitution.

1. (1) A step of photographing the target electronic paper in a state where an image is displayed to obtain a digital image;
(2) calculating a luminance value (Y value) of each area obtained by dividing the digital image into a plurality of areas, and obtaining a standard deviation value thereof;
(3) Based on the standard deviation value ,
Image quality (Rw) when the image is a white image,
Quality level (Rgr) when the image is a gray image, and
A step of obtaining a degree of image quality (Rbl) when the image is a black image ,
Visibility evaluation of electronic paper characterized by obtaining different color visibility evaluation value (X value) calculated by calculation f (Rw, Rgr, Rbl) and evaluating the target electronic paper by the different color visibility evaluation value Method.

  2. 2. The electronic paper visibility evaluation method according to item 1, wherein the digital image is obtained by photographing the entire image displayable area of the target electronic paper.

  3. 2. The electronic paper visibility evaluation method according to 1 above, wherein the digital image is an image of a part of an image displayable area of the target electronic paper.

  4). 4. The electronic paper visibility evaluation method according to any one of 1 to 3, wherein the image quality is an RMS granularity obtained by the standard deviation value × 1,000.

5). The calculation 1 is characterized in that the calculation f (Rw, Rgr, Rbl) is a differential calculation represented by a calculation formula (1): Max (Rw, Rgr, Rbl) −Min (Rw, Rgr, Rbl). To 4. The electronic paper visibility evaluation method according to any one of 4 above:
However, in the above equation (1), Max (Rw, Rgr, Rbl) is the maximum value of Rw, Rgr, Rbl, and Min (Rw, Rgr, Rbl) is the minimum value of Rw, Rgr, Rbl. is there.

6). The arithmetic f (Rw, Rgr, Rbl) is, Rw / Yw, Rgr / Yw and Rbl / Yw from the 1, characterized in that to have a process of obtaining an electronic paper according to any one of the 4 Visibility evaluation method :
Yw is a luminance value (Y value) related to the white image .

7). The calculation f (Rw, Rgr, Rbl) is expressed by a calculation formula (2): Max (Rw / Yw, Rgr / Yw, Rbl / Yw) −Min (Rw / Yw, Rgr / Yw, Rbl / Yw). electronic paper visibility evaluation method as set forth in the 1 in any one of the 4, which is a that computation:
However, in the above equation ( 2 ), Max (Rw / Yw, Rgr / Yw, Rbl / Yw) is the maximum value of Rw / Yw, Rgr / Yw, Rbl / Yw , and Min (Rw / Yw, Rgr) / Yw, Rbl / Yw) is the minimum value of Rw / Yw, Rgr / Yw, Rbl / Yw .

8). The target electronic paper has a black matrix,
8. The method for evaluating the visibility of electronic paper according to any one of 1 to 7 , wherein the black image is removed from the digital image by the black matrix .

9. Visibility Evaluation how the electronic paper according to any one of the 8 above, wherein the said target electronic paper, and performs display of the image by moving the charged particles in accordance with the electric field.

  According to the visibility evaluation method for electronic paper of the present invention, the visibility that is digitized for the electronic paper is shown, and thus the visibility that matches the scale of sensory evaluation can be evaluated.

It is a schematic diagram showing a specific configuration of an example of electrophoretic electronic paper that performs light modulation by moving charged particles encapsulated in microcapsules according to an electric field. It is a figure which shows schematic structure of the evaluation system of the electronic paper in embodiment of this invention. It is a flowchart which shows the procedure of the visibility evaluation method of the electronic paper in embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail.
[Electronic paper visibility evaluation method]
The visibility evaluation method of electronic paper in the embodiment of the present invention is as follows.
(1) The target electronic paper is photographed in a state where an image is displayed to obtain a digital image,
(2) After image processing of the digital image, the luminance value (Y value) of each region obtained by dividing the digital image into a plurality of regions, for example, pixels is calculated to obtain the standard deviation value thereof,
(3) The obtained standard deviation value is calculated to determine the image quality of the image,
The method includes a step of evaluating the electronic paper based on the image quality level.

  Specifically, the image quality can be the RMS granularity obtained by (standard deviation value × 1,000), for example.

  When shooting a digital image for calculating the image quality level, the entire image displayable area of the target electronic paper may be shot, or a part of the image displayable area of the target electronic paper may be shot. Good. In addition, the area where the captured digital image is processed may be the entire image displayable area of the electronic paper, or may be a partial area thereof.

  When a part of the image displayable area is photographed or when an area for image processing is selected from the photographed digital image, an arbitrary area of the target area can be selected. For example, EIAJ ED- 4.43 Standard measurement screen position of 2523 (Electronic Information Technology Industry Association Standard Established in March 2001) The area of C3 in FIG. 6 and the area of B2, B3, B4, C2, C3, C4, D2, D3, and D4 as a whole You can choose. Moreover, it is good also as what combined the arbitrary partial area | region of the image displayable area | region of object electronic paper, for example, the area | region of A3, C1, C3, C5, and E3 prescribed | regulated in the said FIG.

  The digital image preferably has a resolution of, for example, 72 to 4000 dpi.

  Image processing of a digital image and calculation of a luminance value (Y value) are performed as follows.

That is, by using a digital microscope “VHX-900” (manufactured by Keyence Corporation), the shooting magnification, the size of the field of view and the number of shooting pixels are set to the size of one pixel of the digital image on the electronic paper. Image processing is performed to capture a digital image and obtain RGB (24 bit) information of digital data of each pixel of the captured digital image. And from each RGB information obtained by image processing,
Luminance (Y) = 0.22989 × R + 0.586611 × G + 0.114478 × B
The luminance value (Y value) of each pixel is calculated by the following formula.

  When the target electronic paper is of a display format having a black matrix, it is preferable to include a black portion removal process using a black matrix during the image processing of the digital image.

  The black portion removal process using the black matrix is performed by, for example, not using a pixel including the black matrix in a digital image that has been photographed and processed to be used for calculating the visibility evaluation value.

  It is preferable to perform visibility evaluation over a plurality of image pages for one target electronic paper using such a method for evaluating the visibility of electronic paper based on the image quality level for one image page.

  Specifically, for one target electronic paper, the image quality (Rw) when the image is a white image, the image quality (Rgr) when the image is a gray image, and the image quality when the image is a black image The image quality (Rbl) is obtained, and the different color visibility evaluation value (X1 value) calculated by the following calculation formula (1) or the different color visibility evaluation value (X2 value) calculated by the following calculation formula (2) is obtained. This can be evaluated.

  Here, the “gray image” refers to an image having a contrast ratio (CR) of 2 represented by {the luminance value of the gray image (Ygr value) / the luminance value of the white image (Yw value)}. .

  The contrast ratio of “black image” (CR = {luminance value of the black image (Ybl value) / luminance value of the white image (Yw value)}) is 8.

Arithmetic Formula (1): Max (Rw, Rgr, Rbl) −Min (Rw, Rgr, Rbl)
[In the above equation (1), Max (Rw, Rgr, Rbl) is the maximum value of Rw, Rgr, Rbl, and Min (Rw, Rgr, Rbl) is the minimum value of Rw, Rgr, Rbl. . ]
Arithmetic formula (2): Max (Rw / Yw, Rgr / Yw, Rbl / Yw) −Min (Rw / Yw, Rgr / Yw, Rbl / Yw)
[In the above equation (2), Max (Rw / Yw, Rgr / Yw, Rbl / Yw) is the maximum value of Rw / Yw, Rgr / Yw, Rbl / Yw, and Min (Rw / Yw, Rgr / Yw, Rbl / Yw) is the minimum value of Rw / Yw, Rgr / Yw, Rbl / Yw. ]
The smaller the different color visibility evaluation value (X1 value) or the different color visibility evaluation value (X2 value), that is, the smaller the variation in roughness between image pages, the better. The reason is that the smaller the variation in the feeling of roughness between image pages, the less likely it is to feel the roughness even when the user continuously stares at a series of different image pages that are displayed continuously. It is.

According to the above-described electronic paper visibility evaluation method, digitalized numerical visibility is shown, and thereby visibility evaluation that matches the sensory evaluation scale can be performed.
[Electronic paper]
The electronic paper according to the embodiment of the present invention has an image quality level (Rw) related to a white image represented by RMS granularity, an image quality level (Rgr) related to a gray image, and an image quality level (Rbl) related to a black image. The values divided by the average values (Ywm, Ygrm, Yblm) of the luminance values (Yw, Ygr, Ybl) of the pixels are 0 or more and 1.0 or less, respectively. More preferably, they are each 0 or more and 0.4 or less.

  Further, the electronic paper according to the present embodiment uses the image quality level (Rw) related to the white image, the image quality level (Rgr) related to the gray image, and the image quality level (Rbl) related to the black image, and the above equation (1) ) Is preferably a dissimilar color visibility evaluation value (X1 value) calculated using 2.3) or less.

  Furthermore, the electronic paper according to the present embodiment uses the image quality level (Rw) related to the white image, the image quality level (Rgr) related to the gray image, and the image quality level (Rbl) related to the black image, and the above equation (2) ) Is preferably 0.15 or less.

  According to the above electronic paper, since the image quality and / or the different color visibility evaluation value evaluated by the above-described electronic paper visibility evaluation method is equal to or less than a specific value, the user is continuously displayed. Even when a series of different image pages are continuously stared, good visibility with no roughness is reliably obtained.

  The electronic paper of this embodiment is not particularly limited as long as it satisfies the above-described image quality and / or different color visibility evaluation value, and is not particularly limited. Various known configurations such as an electrophoretic method can be adopted, but those related to the reflective liquid crystal method have a reflectance of 35% or less, have a low contrast ratio, and are difficult to display bright white. In view of the above, it is preferable to employ an electrochemical or electrophoretic configuration.

  Electrophoretic electronic paper is disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-333743, and further, in Japanese Patent Application Laid-Open No. 2002-287177, charged particles encapsulated in microcapsules are moved according to an electric field. Thus, an electrophoretic electronic paper that performs light modulation is disclosed.

  Hereinafter, an electrophoretic electronic paper that performs light modulation by moving charged particles enclosed in microcapsules according to an electric field will be described.

  FIG. 1 is a schematic diagram illustrating a configuration of an example of electrophoretic electronic paper that performs light modulation by moving charged particles encapsulated in microcapsules according to an electric field.

  In the electronic paper 10 of this example, a microcapsule 16 in which charged particles 13 and a solvent 14 are sealed in a space formed between a front substrate 11 and a back substrate 12 provided to face each other through a binder 17. It is arranged in a fixed manner, and is further provided with an electrode pair consisting of a first electrode 18 and a second electrode 19.

  In FIG. 1, the specific installation positions of the first electrode 18 and the second electrode 19 are a position in contact with the microcapsule 16 and the front substrate 11, and a position in contact with the microcapsule 16 and the rear substrate 12, respectively. However, the present invention is not limited to this. For example, the electrodes 18 and 19 may be arranged so as not to contact the substrates 11 and 12.

  In addition, an insulating layer, an electrode protective layer, or the like may be formed on these electrodes 18 and 19 as necessary.

  The first electrode 18 and the second electrode 19 are configured so that the potential difference can be controlled independently for each pixel corresponding to each microcapsule 16. Specifically, one of the first electrode 18 and the second electrode 19 (the first electrode 18 in the example of FIG. 1) is used as a common electrode, for example, in a ground state, and the other electrode (in the example of FIG. 1). The second electrode 19) is partitioned so as to correspond to each pixel, and a voltage having an arbitrary polarity is applied to each region corresponding to each pixel. The first electrode and the second electrode may be partitioned so as to correspond to each pixel, and a voltage having an arbitrary polarity may be applied to each region corresponding to each pixel.

  The magnitude and application time of the voltage applied to the first electrode 18 and / or the second electrode 19 depend on the charge amount of the charged particles 13 and the pitch between the electrodes, and to a desired gradation in the formed image. It can be adjusted accordingly, for example, usually about several tens of volts.

  The charged particles 13 may be a plurality of types of particles, and the charged particles 13 and the solvent 14 may be visible light-transmitting or colored (visible light-impermeable). As a combination of the charged particles 13 and the solvent 14, (charged particles 13, solvent 14) are (white particles + black particles, visible light transmitting substance), (white particles, black), (white particles, yellow color). + Magenta color + cyan color).

  The charged particles 13 are positively or negatively charged. As a material constituting the charged particles 13, for example, a resin such as polystyrene resin or polyethylene resin is a main component, and a colorant such as carbon is mixed therewith. A combination thereof can be suitably used. A charge control agent or the like may be added to the charged particles 13 as necessary.

  The particle diameter of the charged particles 13 can be set to, for example, 0.1 to 100 μm, and preferably has a small diameter.

  The solvent 14 can charge the charged particles 13 satisfactorily and has fluidity. As the solvent 14, it is particularly preferable to use a low-viscosity liquid. What dissolved the dye which develops a desired color in paraffin, silicone oil, xylene, toluene, an isopar, etc. can be used.

  The solvent 14 is preferably made of a solvent having a specific gravity substantially equal to that of the charged particles 13.

  Examples of the capsule base material constituting the wall of the microcapsule 16 include gelatin and gum arabic.

  The average particle size of the microcapsules 16 can be set to 2 to 500 μm, for example. The average particle diameter of the microcapsules is obtained by photographing 100 or more microcapsules using an optical microscope, obtaining the equivalent circle diameter of each microcapsule from the photographed image, and calculating the number average of these. It is.

  The front substrate 11 is not particularly limited as long as it has translucency, and various known materials such as glass can be used. In order to make electronic paper flexible, polyethylene is used. A plastic film such as terephthalate (PET) or polyethersulfone (PES) may be used.

  Further, as the back substrate 12, various known ones can be used without particular limitation.

  As the 1st electrode 18 and the 2nd electrode 19, it is preferable to use a transparent electrode with high light transmittance, such as Indium Tin Oxide (ITO), for example.

  As the material constituting the binder 17, various known materials can be used without any particular limitation. For example, a silicone binder, an acrylic binder, a urethane binder having a dielectric constant of 3.3 F / m or less, and the like. Can be preferably used.

  In such an electronic paper 10, the black matrix may be formed in a state where pixels adjacent in the planar direction are disconnected when viewed from the observation direction. The black matrix is preferably formed between the front substrate 11 and the second electrode 19 or between the second electrode 19 and the binder 17.

  According to the electronic paper 10 of the display format in which the black matrix is formed, a good contrast ratio can be obtained without causing color mixing between adjacent pixels.

  The electronic paper 10 described above is operated as follows, for example. That is, when displaying the color (for example, white) of the charged particles 13 in the microcapsule 16, the electric field between the electrodes 18 and 19 is controlled so that the charged particles 13 are on the front side in the space in the microcapsule 16 ( 1 is collected in the region above, and the color of the charged particles 13 is thereby reflected, and when viewed from the direction from the outside toward the front substrate 11 (the arrow direction in FIG. 1), white display is performed.

  On the other hand, when displaying the color of the solvent 14 (for example, blue), the electric field between the electrodes 18 and 19 is controlled so that the charged particles 13 are in the back side (lower side in FIG. 1) in the space inside the microcapsule 16. As a result, the color of the solvent 14 is reflected and a blue display is performed.

  In this white / blue display, the gradation is determined based on the reflection density that is changed by the mobility of the charged particles 13.

The above electronic paper 10 can be configured to perform full color display. Specifically, for example, three microcapsules 16 are configured to selectively display white and red, blue, or green, and a plurality of unit cells of these three microcapsules 16 are arranged in a plane direction. By controlling one unit cell as one pixel, full color display is performed.
[Method for producing electronic paper]
The electronic paper 10 as described above is
(1) A microcapsule 16 filled with charged particles 13 and a solvent 14 inside is prepared.
(2) A coating liquid containing the microcapsule 16 is prepared,
(3) The coating solution is applied and dried on the surface side of the front substrate 11 provided with the second electrode 19 on the surface thereof to form a coating film,
(4) Affixed so that the surface side of the back substrate 12 having the first electrode 18 attached to the surface thereof is in contact with the coating film,
(5) The electronic component is assembled by connecting it to the electrodes 18 and 19.

The microcapsule 16 dissolves or disperses a capsule base material for forming the charged particles 13, the solvent 14, and the microcapsule 16 in an aqueous medium at a temperature of, for example, about 40 ° C. It is formed by performing pH change treatment and temperature change treatment.
[Evaluation system for electronic paper]
FIG. 2 shows a schematic configuration of an electronic paper evaluation system in the embodiment of the present invention.

  As shown in FIG. 2, the evaluation system 100 generally includes a computer 1 and a digital micro slope 2 connected to the computer 1. The computer 1 is connected to the scanning-side electrode terminal 6a and the signal-side electrode terminal 6b of the electronic paper display panel 5 through the DA boards 3a and 3b and the amplifiers 4a and 4b.

  In this configuration, the computer 1 includes a CPU, a memory, and the like, and implements various functions for executing the visibility evaluation method described above by executing installed software.

  Specifically, in order to display a predetermined image on the display panel 5, the scanning side driving waveform and the signal side driving waveform are respectively generated by the waveform forming unit and output to the DA boards 3a and 3b. These drive waveforms are DA-converted by the DA boards 3a and 3b, respectively, amplified by the amplifiers 4a and 4b, and input to the scanning-side electrode terminal 6a and the signal-side electrode terminal 6b of the display panel 5. The display density of the image on the display panel 5 can be changed to an arbitrary value by changing conditions such as the amplitude and time of the scanning side driving waveform and the signal side driving waveform.

  The digital microscope 2 captures an electronic paper display panel 5 displaying a predetermined image, and outputs the digital image data to the computer 1.

  The computer 1 receives the digital image from the digital micro slope 2 and executes image processing by the image processing unit, thereby obtaining RGB digital data of each pixel. Based on the RGB digital data, a luminance value (Y value) of each pixel, its standard deviation value, image quality, and different color visibility evaluation value are obtained by the arithmetic unit. These obtained values can be displayed on a display unit provided in the computer 1.

  FIG. 3 is a flowchart showing the procedure of the electronic paper visibility evaluation method, which is realized by executing software on the computer 1 based on a digital image obtained from the digital micro slope 2.

  Specifically, a digital image is obtained from the digital micro slope 2 (S1), and the digital image data is processed (S2) to calculate RGB digital data (24 bits) for each pixel (S3). . Based on this digital data, the luminance value (Y value) and its standard deviation value for each pixel are calculated by performing the above-described arithmetic processing (S4). Based on this standard deviation value, an image quality level (or a different color visibility evaluation value) as an RMS granularity is obtained (S5). The visibility of electronic paper can be evaluated by the above procedure.

  In the electronic paper manufacturing process as described above, the electronic paper evaluation system according to the embodiment of the present invention has one lot obtained in step (1) between step (1) and step (2). Using the microcapsules, test electronic paper is prepared, the electronic paper for testing is evaluated by the above-described electronic paper visibility evaluation method, and the microcapsules of the lot are obtained based on the evaluation results. A process of selecting whether or not to use for the manufacture (mass production) of electronic paper is performed. In addition, what is necessary is just to perform the process similar to the said process (2)-(5) for preparation of the electronic paper for a test.

Specifically, when the test electronic paper satisfies any of the following conditions (a) to (c), the microcapsules of the lot are used for the production of the electronic paper, and the conditions (a) to (c) If none of them is satisfied, the microcapsules of the lot are not used for manufacturing electronic paper, but are used for applications that do not require high visibility, such as a remaining amount display mark such as a USB memory.
(A) The image quality level (Rw) related to the white image, the image quality level (Rgr) related to the gray image, and the image quality level (Rbl) related to the black image are average values of the luminance values (Yw, Ygr, Ybl) of the pixels. The values divided by (Ywm, Ygrm, Yblm) are 0 or more and 1.0 or less, respectively.
(A) Different colors calculated using the above equation (1) using the image quality level (Rw) related to the white image, the image quality level (Rgr) related to the gray image, and the image quality level (Rbl) related to the black image The visibility evaluation value (X1 value) is 2.3 or less.
(C) Different colors calculated using the above equation (2) using the image quality level (Rw) related to the white image, the image quality level (Rgr) related to the gray image, and the image quality level (Rbl) related to the black image The visibility evaluation value (X2 value) is 0.15 or less.

Examples of practical means for improving the visibility evaluation value of the target electronic paper include the following methods.
(1) A method of increasing the drive voltage. This makes it easier for the charged particles 13 that are difficult to move due to the electric field to move.
(2) A method of increasing the charged particles 13 to be contained by expanding the interval between the first and second electrodes 18 and 19.
(3) A method of increasing the adsorption amount of the external additive externally added to the charged particles 13.
(4) A method of thinning the wall of the microcapsule 16.
(5) A method of reducing the dielectric constant and viscosity of the solvent 14 in which the charged particles 13 are dispersed.
(6) A method for improving the uniformity of the particle size distribution of the microcapsules 16.

  According to the above-described electronic paper evaluation system, since the evaluation by the above-described electronic paper visibility evaluation method is performed within the manufacturing process, a high yield can be obtained in the manufacture of electronic paper.

  Although the embodiment of the present invention has been specifically described above, the present embodiment is not limited to the above example, and various modifications can be added.

  For example, in the electronic paper evaluation system, the electronic paper visibility evaluation method is not limited to being applied to the selection of each lot with respect to microcapsules. For example, the evaluation is performed on the obtained electronic paper to quantify the evaluation. You may apply to an aspect.

Hereinafter, although the specific Example in the embodiment of this invention is demonstrated, this invention is not limited to these. In the following, “part” means part by mass.
<Electronic Paper Production Example 1 (EPID11)>
48 parts of liquid paraffin with a chlorination rate of 40%, 0.2 parts of carbon black “TB # 75550F” (manufactured by Tokai Carbon Co., Ltd.), 1.2 parts of titanium oxide surface-treated with a coupling agent containing an ammonium salt, and an interface After adding 0.6 parts of an activator “Span80” (manufactured by Tokyo Chemical Industry Co., Ltd.) and crushing the aggregation of titanium oxide using a homogenizer, the temperature was raised to 40 ° C. and water was added to 180 parts of gelatin and 6 parts of Arabic. A solution in which 6 parts of gum was dissolved was added, the number of rotations of the homogenizer was changed, and an oil-in-water dispersion [1] having an average particle diameter corresponding to a circle of 50 μm was prepared.

  This oil-in-water dispersion [1] was cooled to 10 ° C. to confirm that coacervation occurred, and then 1.3 parts of formalin was added, and the pH was adjusted to 3.5 and stirred. Thereafter, the pH is raised to 11.5, the temperature is raised to 40 ° C. at a rate of 1 ° C./1 minute, and a microcapsule containing microcapsules containing gelatin and gum arabic as a wall material and containing a colored solvent and white pigment fine particles is included. A capsule solution [1] was obtained. The average particle size of the microcapsules was 51.5 μm. The average particle size of the microcapsules was measured by the same method as described above.

  A liquid mixed at a ratio of 2 parts of a silicone-based binder solution to 1 part of this microcapsule solution [1] was applied to a polyethylene terephthalate (PET) substrate with an ITO film using an applicator coating machine at 60 ° C. The water of the silicone binder solution was dried, and further, the ITO film-coated PET substrate was superposed with the ITO film surface facing each other, and adhered at a laminating temperature of 80 ° C. to obtain an electronic paper [1].

  In this electronic paper [1], it was confirmed that when a DC voltage of 15 V was applied between the ITO films, a contrast difference between black and white was generated, and movement of titanium oxide white fine particles was observed.

This electronic paper [1] is 11 inches (diagonal) and 180 ppi.
<Electronic Paper Production Example 2 (EPID12)>
11 inch (diagonal) in the same manner as in the electronic paper production example 1 except that microcapsules having an average particle size of 100 μm obtained by shortening the stirring time of the homogenizer after addition of gelatin / gum arabic were used. , 180 ppi of electronic paper [2] was obtained.

In this electronic paper [2], it was confirmed that when a DC voltage of 30 V was applied between the ITO films, a contrast difference between black and white was generated, and movement of titanium oxide white fine particles was observed.
<Production Example 3 of Electronic Paper (EPID13)>
An electronic paper [3] of 11 inches (diagonal) and 180 ppi was obtained in the same manner except that the amount of titanium oxide and carbon black added was doubled in the electronic paper production example 1.

In this electronic paper [3], it was confirmed that when a DC voltage of 30 V was applied between the ITO films, a contrast difference between black and white was generated, and movement of titanium oxide white fine particles was observed.
<Example 4 of Electronic Paper Production (EPID14)>
In the electronic paper production example 1, microcapsules having an average particle size of 100 μm obtained by changing the addition amount of titanium oxide and carbon black to 2 times and shortening the stirring time of the homogenizer after addition of gelatin / gum arabic 11 inch (diagonal), 180 ppi electronic paper [4] was obtained in the same manner except that it was used.

In this electronic paper [4], it was confirmed that when a DC voltage of 50 V was applied between the ITO films, a contrast difference between black and white was generated, and movement of titanium oxide white fine particles was observed.
<Production Example 5 of Electronic Paper (EPID21)>
In the electronic paper production example 1, microcapsules having an average particle size of 25 μm obtained by changing the addition amount of titanium oxide and carbon black to 3 times and extending the stirring time of the homogenizer after addition of gelatin / gum arabic 11 inch (diagonal), 180 ppi electronic paper [5] was obtained in the same manner except that it was used.

In this electronic paper [5], it was confirmed that when a DC voltage of 30 V was applied between the ITO films, a contrast difference between black and white was generated, and movement of titanium oxide white fine particles was observed.
<Electronic Paper Production Example 6 (EPID22)>
An electronic paper [6] of 11 inches (diagonal) and 180 ppi was obtained in the same manner except that the addition amount of titanium oxide and carbon black was changed to 0.75 times in the electronic paper production example 1.

In this electronic paper [6], it was confirmed that when a DC voltage of 30 V was applied between the ITO films, a contrast difference between black and white was generated, and movement of titanium oxide white fine particles was observed.
<Preparation Example 7 of Electronic Paper (EPID23)>
An electronic paper [7] of 11 inches (diagonal) and 180 ppi was obtained in the same manner except that the addition amount of titanium oxide and carbon black was changed to 1.2 times in the electronic paper production example 1.

In this electronic paper [7], it was confirmed that when a DC voltage of 15 V was applied between the ITO films, a contrast difference between black and white was generated, and the movement of the titanium oxide white fine particles was observed.
<Electronic Paper Production Example 8 (EPID24)>
An electronic paper [8] of 11 inches (diagonal) and 180 ppi was obtained in the same manner as in Electronic Paper Production Example 1 except that the addition amounts of titanium oxide and carbon black were changed to 0.5 times.

In this electronic paper [8], it was confirmed that when a DC voltage of 15 V was applied between the ITO films, a contrast difference between black and white was generated, and movement of titanium oxide white fine particles was observed.
<Examples 1-4>
A white image was displayed using the above electronic papers [1] to [4].

  The display area is divided into a total of 25 image areas of 4.4 standard measurement screen positions (A1 to E5) of EIAJ ED-2523, and using “Digital Microscope VH Series VHX900” (manufactured by Keyence Corporation), A1 The center part of the image area was photographed (imaging condition: 2.11 million pixels, RGB each 16 bits, photographing area 2.4 mm × 3.2 mm) to obtain a digital photographed image. A digital image of an area of 20 × 20 pixels (one pixel is 20 μm square) is cut out from the center of the digital photographed image, and the luminance value (Yw) of each pixel in the digital image is measured. The standard deviation value of the luminance value (Yw) was obtained, and the RMS granularity was calculated from (standard deviation value × 1,000). Similar operations were repeated in the image areas A2 to E5, and an average value (Rw) of 25 points A1 to E5 was calculated.

  The gray image (contrast ratio CR = 2) and the black image (CR = 8) were similarly calculated. The average RMS granularity is (Rgr) and (Rbl), respectively.

  Using this average RMS granularity (Rw), (Rgr), and (Rbl), a different color visibility evaluation value (X1 value) was calculated according to the above equation (1). The results are shown in Table 1.

In addition, the following document data including alphanumeric characters, hiragana and kanji were prepared.
First page: Black image with a pixel rate of 10%, Font type: MS Mincho, Font size: 12
Second page: Imaging Society of Japan test chart No. 6G 1995R
Third page: Black image with a pixel rate of 15%, Font type: MS Gothic, Font size: 8
4th page: Imaging Society of Japan test chart No. 6G 1995R
5th page: Black image with a pixel rate of 10%, Font type: MS Mincho, Font size: 12
6th page: black image with a pixel rate of 20%, font type: Century, font size: 10
7th page: JIS X6933 & ISO / IEC 15775: 1999 compliant chart 8th page: Imaging Society of Japan test chart No. 6G 1995R
9th page: Black image with a pixel rate of 15%, Font type: MS Gothic, Font size: 8
Page 10: Imaging Society of Japan Test Chart No. 10 6G 1995R
The document data of each page is converted into an electronic paper display format, and each page is displayed for 1 minute using electronic papers [1] to [4] on 30 monitors, for a total of 10 minutes. Gaze at the electronic paper [1] to [4], and with respect to the rough texture of the image, 0 points when the rough texture is not felt, 0.5 points when the rough texture is hardly felt, and the rough texture is too worrisome Perform a sensory evaluation that is classified into 5 grades, with 1.0 points for cases that do not become necessary, 1.5 points for cases where the feeling of roughness is slightly worrisome, and 2 points for cases where the feeling of roughness is greatly concerned. The total score was evaluated according to the following evaluation criteria. The results are shown in Table 1.
-Evaluation criteria-
○: 0 to 10 points Δ: 11 to 40 points ×: 41 to 60 points

<Examples 5 to 8>
A white image was displayed using the above electronic papers [5] to [8].

  The display area is divided into a total of 25 image areas of 4.4 standard measurement screen positions (A1 to E5) of EIAJ ED-2523, and using “Digital Microscope VH Series VHX900” (manufactured by Keyence Corporation), A1 The center part of the image area was photographed (imaging condition: 2.1 million pixels, RGB each 16 bits, photographing area 2.4 mm × 3.2 mm) to obtain a digital photographed image. A digital image of an area of 20 × 20 pixels (one pixel is 20 μm square) is cut out from the center of the digital photographed image, and the luminance value (Yw) of each pixel in the digital image is measured. The standard deviation value of the luminance value (Yw) was obtained, and the RMS granularity was calculated from (standard deviation value × 1,000). Similar operations were repeated in the image areas A2 to E5, and an average value (Rw) of 25 points A1 to E5 was calculated.

  In addition, an average value (Ywm) of luminance values (Yw) of each pixel (for a total of 10,000 pixels) of each digital image according to (20 × 20 pixel region) × A1 to E5 was calculated.

  The gray image (contrast ratio CR = 2) and the black image (CR = 8) were similarly calculated. The average RMS granularity is (Rgr) and (Rbl), respectively.

  Using this average RMS granularity (Rw), (Rgr), (Rbl), a different color visibility evaluation value (X2 value) was calculated according to the above equation (2). The results are shown in Table 2.

In addition, the following document data including alphanumeric characters, hiragana and kanji were prepared.
First page: Black image with a pixel rate of 10%, Font type: MS Mincho, Font size: 12
Second page: Imaging Society of Japan test chart No. 6G 1995R
Third page: Black image with a pixel rate of 15%, Font type: MS Gothic, Font size: 8
4th page: Imaging Society of Japan test chart No. 6G 1995R
5th page: Black image with a pixel rate of 10%, Font type: MS Mincho, Font size: 12
6th page: black image with a pixel rate of 20%, font type: Century, font size: 10
7th page: JIS X6933 & ISO / IEC 15775: 1999 compliant chart 8th page: Imaging Society of Japan test chart No. 6G 1995R
9th page: Black image with a pixel rate of 15%, Font type: MS Gothic, Font size: 8
Page 10: Imaging Society of Japan Test Chart No. 10 6G 1995R
The document data of each page is converted into an electronic paper display format, and each page is displayed for one minute on 30 monitors using electronic paper [5] to [8], for a total of 10 minutes. Gaze at the electronic paper [5] to [8], and for the feeling of roughness of the image, 0 points if you do not feel the roughness, 0.5 points if you feel almost no roughness, Perform a sensory evaluation that is classified into 5 grades, with 1.0 points for cases that do not become necessary, 1.5 points for cases where the feeling of roughness is slightly worrisome, and 2 points for cases where the feeling of roughness is greatly concerned. The total score was evaluated according to the following evaluation criteria. The results are shown in Table 2.
-Evaluation criteria-
○: 0 to 10 points Δ: 11 to 40 points ×: 41 to 60 points

  As is apparent from Table 1 and Table 2 above, according to the visibility evaluation method of the electronic paper of the present embodiment, it was confirmed that a different color visibility evaluation value that matches the scale of sensory evaluation can be obtained. Thereby, it was confirmed that the visibility of electronic paper can be expressed numerically and objectively evaluated.

DESCRIPTION OF SYMBOLS 10 Electronic paper 11 Front substrate 12 Back substrate 13 Charged particle 14 Solvent 16 Microcapsule 17 Binder 18 1st electrode 19 2nd electrode

Claims (9)

(1) A step of photographing the target electronic paper in a state where an image is displayed to obtain a digital image;
(2) calculating a luminance value (Y value) of each area obtained by dividing the digital image into a plurality of areas, and obtaining a standard deviation value thereof;
(3) Based on the standard deviation value ,
Image quality (Rw) when the image is a white image,
Quality level (Rgr) when the image is a gray image, and
A step of obtaining a degree of image quality (Rbl) when the image is a black image ,
Visibility evaluation of electronic paper characterized by obtaining different color visibility evaluation value (X value) calculated by calculation f (Rw, Rgr, Rbl) and evaluating the target electronic paper by the different color visibility evaluation value Method.   2. The electronic paper visibility evaluation method according to claim 1, wherein the digital image is obtained by photographing the entire image displayable area of the target electronic paper.   2. The electronic paper visibility evaluation method according to claim 1, wherein the digital image is obtained by photographing a part of an image displayable area of the target electronic paper.   The method for evaluating the visibility of electronic paper according to any one of claims 1 to 3, wherein the image quality is an RMS granularity obtained by the standard deviation value x 1,000. The calculation f (Rw, Rgr, Rbl) is a difference calculation represented by an arithmetic expression (1): Max (Rw, Rgr, Rbl) −Min (Rw, Rgr, Rbl). The visibility evaluation method for electronic paper according to any one of claims 1 to 4:
However, in the above equation (1), Max (Rw, Rgr, Rbl) is the maximum value of Rw, Rgr, Rbl, and Min (Rw, Rgr, Rbl) is the minimum value of Rw, Rgr, Rbl. is there. The arithmetic f (Rw, Rgr, Rbl) is, Rw / Yw, electrons according to claims 1, characterized in that to have a process of obtaining a Rgr / Yw and Rbl / Yw to any one of claims 4 Paper visibility evaluation method :
Yw is a luminance value (Y value) related to the white image . The calculation f (Rw, Rgr, Rbl) is expressed by a calculation formula (2): Max (Rw / Yw, Rgr / Yw, Rbl / Yw) −Min (Rw / Yw, Rgr / Yw, Rbl / Yw). that computation in visibility evaluation method of electronic paper as claimed in any one of claims 4, characterized in that:
However, in the above equation ( 2 ), Max (Rw / Yw, Rgr / Yw, Rbl / Yw) is the maximum value of Rw / Yw, Rgr / Yw, Rbl / Yw , and Min (Rw / Yw, Rgr) / Yw, Rbl / Yw) is the minimum value of Rw / Yw, Rgr / Yw, Rbl / Yw . The target electronic paper has a black matrix,
The electronic paper visibility evaluation method according to any one of claims 1 to 7 , wherein a black portion is removed from the digital image by the black matrix . The target electronic paper, the visibility evaluation method of an electronic paper as claimed in any one of claims 8, characterized in that the charged particles is intended for displaying an image by moving in accordance with an electric field .