JPH0240618A - Color image forming method - Google Patents

Abstract

PURPOSE:To prevent the crosstalk of colors which are not display colors and to obtain desired color contrast by arranging dots formed on the transparent part of a pattern so as to be smaller than the dots of a corresponding color pattern. CONSTITUTION:A color filter 12 and an image carrier 10 which are aligned to each other are irradiated with the use of an optical system projecting the light of back lights having directivity. A scatterer 31 such as paper of frosted glass is provided on the side of a viewpoint. As a result, a color (indicated by R in the figure) which passes almost linearly through the transparent parts of the image carrier 10 is scattered by the scatterer 31 and viewed, whereas light scattered on the scatterer of the image carrier 10 is not made incident intensely on the scatterer 31, which is viewed as being dark in such parts. The crosstalk can be prevented by forming the dots of the image carrier 10 so as to be smaller than those of the color pattern 12. However, when the dots are too small, an image is darkened and a sharp color contrast cannot be obtained. Therefore, it is desireble to be as large as possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention outputs and displays an image in response to an image signal output from a floppy disk, an optical disk, a magneto-optical memory medium, a computer, or a facsimile signal or other image signal. The present invention relates to image display methods, particularly to image display methods for outputting increasingly diverse color images.

(Conventional technology) Conventionally, video output from TVs and VTRs, and output for interaction with computers, have been done using CRTs (cathode ray tubes) and T.
High-definition images such as documents and graphics have been output and displayed on paper as printed hard copies on N (twisted nematic) liquid crystal display monitors, WP (word processors), facsimiles, and the like.

Here, although a CRT outputs a beautiful image when outputting a moving image, the visibility of an image that remains stationary for a long period of time is reduced due to flicker and scan results due to insufficient resolution. Further, although conventional liquid crystal displays such as the above-mentioned TN liquid crystal have achieved flatness, they have problems in manufacturing such as sandwiching the liquid crystal between glass substrates, and the screen is dark. Furthermore, CRTs and TN liquid crystals have drawbacks such as having to constantly access the beam, pixel type, and pressure because they do not have a stable image memory even while outputting the above-mentioned static image.

On the other hand, images output on paper can be obtained as high-definition and stable memory images, but if you use a large number of them, it takes space to organize them, and it is also a waste of resources to discard large quantities. do not become.

Therefore, an image display method has been studied to construct a display device that can express high-definition images, which were previously only available as hard copies, with the same clarity as hard copies, and can be repeatedly displayed and erased. Various display systems using belt-like image carriers using methods such as electrophotographic recording and thermosensitive recording have been proposed. For example, JP-A-5
No. 7-171380 proposes a method for forming color images using a thermal method.

[Problem to be solved by the invention]

However, in the image display method of the prior art, it is necessary to arrange the color paint in a staggered manner, and to select the color paint parts closely with a heat-sensitive head, and a means for keeping warm during display is required. It has been difficult to put it into practical use due to these drawbacks. Therefore, in order to solve the above problems, the present inventors formed an image on an image carrier using differences in optical scattering states, prepared a color pattern separately from this, and combined the two into one unit. An application has already been filed for an image forming apparatus (Japanese Patent Application No. 62-338125). According to this, since the image carrier and the color pattern are separate, it is possible to easily obtain a flicker-free, high-definition color image. The image display principle of this device is as shown in FIG. 11, and the image is formed by the difference in the optical scattering state by the polymer liquid crystal 21 of the image carrier 10, that is, the transparent state and the opaque state, and the image is When irradiated with light, the light passes through the image portion formed on the image carrier and further passes through the color pattern 12, so that a color image is displayed.

The present invention further improves the color display method that can be widely applied in the color display method having the above structure, and specifically, prevents crosstalk between display colors and easily enables clearer color display. This provides a method to do this.

[Means to solve the problem]

According to the present invention, a color image is converted into position information and formed as a transparent-opaque pattern on an image carrier, and the stiffness is combined with the color pattern to create a color image mainly composed of color light transmitted through the transparent portion. A color image is formed in a state where each dot formed in the transparent part of the pattern is smaller than each dot of the corresponding color pattern, thereby preventing crosstalk of colors other than the displayed color, A clear desired color contrast can be obtained, and the alignment between the image carrier and the color pattern can be made to have a certain attitude.

The basic configuration of color image display according to the present invention will be explained in detail below.

In the present invention, a material exhibiting thermotropic liquid crystal properties is suitable as a material for forming a transparent-opaque pattern on a sheet. Examples of this include so-called side-chain type polymer liquid crystals in which low-molecular liquid crystals with main chains of methacrylic acid polymers, siloxane polymers, etc. Main chain type polymer liquid crystal such as polyester or polyamide.

In addition, liquid crystal phases include smectic, nematic,
Those with cholesteric properties, those with other phases, and discotic liquid crystals are also used.

Furthermore, Sn+C″, which has asymmetric carbon introduced into the polymer liquid crystal.
Polymer liquid crystals having a phase exhibiting ferroelectricity are also preferably used.

Specific examples of polymer liquid crystals will be illustrated below, but the present invention is not limited thereto.

Mve = 18,000 75℃ 110℃ Glass□ Liquid crystal phase □Iso.

(N) fCH2- to Hen CH3 (CH2-(:]-n r (IV) The optical anisotropy of the liquid crystal shown above changes depending on the temperature, temperature rise, and cooling rate, and the light transmission rate changes. The image forming principle in the present invention utilizes this property of liquid crystal, but next we will explain the principle for the case where a polymer liquid crystal layer is provided on a transparent substrate using the 1θ diagram. Describe the process.

In FIG. 1O, ▪ in the figure indicates a state of light scattering. If this is heated to T2 (Tiso = isotropic state transition temperature) or higher as shown in ■a using a heating means such as a thermal head or a laser, and then rapidly cooled, the light transmission becomes almost the same as in the isotropic state, as shown in ■ in the figure. The state is fixed. In this rapid cooling state, it is sufficient to naturally dissipate heat from the substrate into the air without using any particular cooling means. This isotropic state is T+
It is stable at room temperature or room temperature below (Tg=glass transition temperature), and is also stable as an image memory.

On the other hand, after heating to 12 or more as in ■a, the liquid crystal temperature T,
When held for one to several seconds between ~T2, for example, the scattering intensity increases again during this holding time, as shown in (b), and returns to the original scattering state (■) again at room temperature.
This state is stably maintained below T.

In addition, as shown by ■ in the figure, if the liquid crystal temperature is held between T and T2 for a period of about 10 milliseconds to 1 second, the intermediate transmission state can be maintained at room temperature in that part. It is also possible to use it as a gradation expression.

In other words, in this example, after heating to an isotropic state, the transmittance or scattering intensity can be controlled by how long it is held at the liquid crystal temperature before reaching room temperature, and this is T, which is Can be held stably. Furthermore, the temperature when returning to the scattering state in the above is
It is faster if it is closer to T2 within the liquid crystal temperature, and if it is left at the liquid crystal temperature for a relatively long time, it will return to the scattering state of ■ regardless of the previous state, even if it is not heated to the isotropic state. It is possible.

Using a liquid crystal having the above-mentioned properties, a transparent part and a scattering part are formed according to a desired image by adjusting the heating conditions, and a color image is displayed by combining this with a color pattern and irradiating light. be able to.

Next, each component for actually displaying a color image will be described. First, the above-mentioned liquid crystal is coated on a substrate to create an image carrier. At this time, a solvent is used to coat the liquid crystal onto a transparent substrate such as glass or polyester that has been washed with alcohol. The coating properties can be adjusted, and the solvent used is dichloroethane, DMF, cyclohexane, etc., as well as tetrahydrofuran (THF), acetone, ethanol, other polar or non-polar solvents, or a mixture of these solvents. The material is selected depending on factors such as solubility with the polymeric liquid crystal used, the material of the substrate to which it is coated, wettability with the surface layer provided on the surface of the substrate, and film-forming properties.

In order to obtain a more beautiful image, the weight percent of liquid crystal to solvent should be such that after addition and stirring, a clear solution or viscous state is obtained. For example, when the polymeric liquid crystals represented by the structural formulas (I) to (IV) are dissolved alone in dichloroethane, the wt% concentration of the polymeric liquid crystals is 1.
At 0%, the solution is cloudy and micellar, but at a relatively high concentration of about 15% to 25%, a stable, transparent, viscous solution is obtained. This tendency is also observed in combinations with several other types of polymeric liquid crystals and solvents. After applying this transparent viscous solution to a well-cleaned substrate such as glass or polyester using an applicator, wire bar, or dipping, and maintaining it at the liquid crystal temperature, when similarly applied in the micellar form, In comparison, an optical scattering film with extremely high uniformity can be obtained.

That is, a stable optical scattering film can be obtained by dissolving liquid crystal in a solvent and applying it onto a substrate, and then maintaining the substrate at the liquid crystal temperature (75°C to 110°C) for a certain period of time during or after volatilizing the backfilling solvent. can be formed.

Among the liquid crystals, polymer liquid crystals as shown in the structural formulas (I) to (TV) are preferable, and the solvent used for coating may be a mixed solvent of a plurality of solvents or a mixture other than polymer liquid crystal materials. It is also possible to add pigment materials and other substances within a range that does not adversely affect the coating. The resulting film thickness is 20% by weight based on the weight of the polymer liquid crystal solvent in the coating agent.
%, it is about 10 μm, and generally 3 to 15 μm
It is.

By scanning the thus obtained image carrier with a thermal head, a desired pattern of 9 characters can be fixed as a transparent portion. If this image carrier is placed on a black background with an optical density of 1.2, a clear display of black on a white background will be obtained.

Moreover, the above image can also be deleted. In other words, if the entire surface of the image carrier on which the above image is recorded is heated to about 120°C and then kept at about 105°C for a few seconds, the entire surface will return to its original white scattering state, and it will remain stable even if returned to room temperature. can be,
Record 1 can be displayed again. This phenomenon is caused by the first O
It can be controlled by changing the state of the liquid crystal shown in the figure. On the other hand, if the image carrier on which the above-described image is recorded is guided over the color pattern and irradiated with a backlight or front light source, the color display image can be viewed depending on the alignment of the color pattern and the image carrier.

The color pattern is generally used, for example, R (red), G (green), B at a pitch of 125 μm.
(Blue) can be used. The principle behind color display is as follows. The image portion fixed as a transparent portion of the image carrier is composed of dots having the same pitch as the pitch of the color pattern (in the present invention, smaller than the dots of the color pattern), and these dots form the R of the color pattern. When aligned with G, red light is transmitted; when aligned with G, green light is transmitted; however, the colored light that has passed through the transparent portion of the image carrier is (a) , frosted glass, etc.), it is clearly visible, and since the light scattered by the scattering part of the machine carrier does not strongly enter the scatterer, it is seen darkly on the scatterer.

(b) When projected onto a separately provided screen, it is clearly projected and visible; - Light scattered by the scattering portion of the machine carrier is hardly projected, resulting in a dark portion.

(C) If you look directly at the light that has been scattered by a scattering plate at the illumination light stage, it will be visible as it is, and -
The light further scattered by the scattering part of the machine carrier is visually visible.

For example, if only R (red) passes through the transparent portion of the image carrier, the color that can be clearly seen is R (red) in all of (a) to (C). As a result, in any of the above three modes, one color display image can be formed as a whole. Note that in the above description, the light that is transmitted through the image carrier without being scattered is referred to as substantially straight-line transmitted light.

In the structure for color display described above, the color pattern and the image carrier are separate, so a normal thermal blink, FAX, etc. can be used to draw the image on the image carrier, and positioning can also be done at the recording pitch. However, if the incident angle of the illumination light is not constant and the light is not very directional, it is difficult to create a color pattern and image. Due to the thickness of the cap, color pattern, and liquid crystal layer on the image carrier that inevitably occur between the image carrier and the carrier, the incident light hits unnecessary dots of the color pattern or dots of the image on the image carrier, resulting in a sharp image. It is also possible that a good color contrast cannot be obtained.

In other words, if the light passing through the color pattern and image carrier is incident perpendicularly to both, and the dot positions of both are perfectly matched, a beautiful color image will be displayed, but if the angle of incidence of light is perpendicular, If it deviates from the line, the pitch of the image dots and the color pattern will not align with the incident light due to the thickness of the color pattern, the thickness of the image carrier, and the gap between them, and the light will fall onto the scattering part of the image carrier. The scattered lights overlap at the boundary, causing so-called crosstalk and making it impossible to obtain clear color contrast.

It is difficult to make the beam directivity of the illumination light completely vertical, and it is also not easy to make the color pattern and the dots of the image perfectly match each other.

In the present invention, the above-mentioned crosstalk is solved by the relationship between the sizes of the image dots on the image carrier and the color pattern dots. This will be explained in detail below with reference to the drawings.

Figure 1 shows a system that uses an optical system that projects backlight as directional light to illuminate the aligned color filter and image carrier, with a scatterer (paper, frosted glass, etc.) provided on the viewpoint side. .

In this way, the color (R red in the figure) that passes through the transparent part of the image carrier in a substantially straight line is scattered by the scatterer and is visually recognized, whereas the light scattered by the scatterer of the image carrier is reflected by the scatterer. The light is not strongly incident on the area, and the scatterer in that area appears dark.

This also applies to the arrangement shown in FIG. In Figure 1, a mirror image is formed, and in Figure 2, a normal image is formed.
This is because the surfaces of the liquid crystal layer on the image carrier are exactly opposite.

In the above structure, in order to prevent color light other than the display color from entering the scatterer in order to prevent crosstalk, in the case of Figure 1, unnecessary color light should be directed toward the transparent part of the image carrier. It is necessary to prevent the light from being transmitted in a straight line, or in the case of FIG. 2, to prevent unnecessary substantially straight-line transmitted light from passing through the dots of the color pattern. The degree of crosstalk is affected by the gap between the image carrier and the color pattern, the thickness of the two, the directivity of the illumination light, and the like. Naturally, crosstalk can be prevented if the dots on the image carrier are sufficiently small compared to the dots in the color pattern, but if they are too small, the image will be dark and clear color contrast will not be obtained, so make them as large as possible. is preferred. To this end, since the thickness of the color pattern and the liquid crystal layer of the image carrier are usually about 0.1 to 5 μm and 3 to 15 μm, respectively, first, the gap between the image carrier and the color pattern is set to about 500 μm or less, and the illumination light is The incident angle of 0° to 1
Set it so that it is within the range of 0 degrees, and then set the dot size of the image to 30 degrees of the color pattern dot size.
% to about 95%.

If the gap between the image carrier and the color pattern is too large, it will be undesirably influenced by the ray directivity of the illumination light.

Also, as a light source, a Fresnel lens, etc., which can be used as both a backlight and a frontlight, can be used to make the omnidirectional light from the light source directional, and it is effective within the above range. to prevent crosstalk.

If the dots in the image are smaller than the above range, the displayed image will be slightly darker, but if the dots are as large as the color pattern dots, crosstalk cannot be effectively prevented. On the other hand, within the above range, it is possible to prevent crosstalk even if the positions of the color pattern and the image carrier are deviated to some extent, so that alignment can be performed relatively easily.

The gap between the image carrier and the color pattern can be adjusted to some extent by adjusting the thickness of the protective layer of the liquid crystal layer on the image carrier.
The gap can be adjusted as appropriate depending on the structure of the color display device.

The above configuration is particularly suitable for the above (a), (b), and (c).
), it is possible to extract only the desired color as substantially linearly transmitted light, and a sufficiently bright image can be obtained.

In the modes (b) and (C), the situation is as follows.

In FIG. 3, the same optical system as in FIG. 1 is used to irradiate the same color pattern and image carrier and project it onto a separately provided screen.

The color of the color pattern (R red in the figure) corresponding to the transparent portion of the image carrier is clearly projected onto the screen.

The same applies to the arrangement shown in FIG. A mirror image is formed in FIG. 3, and a normal image is formed in FIG.

In the case of a projected image, an enlarged image can be easily obtained.

In FIG. 5, a backlight is used as scattered light by a scattering plate provided in the figure to illuminate the aligned color filter and image carrier, and an image is directly viewed as scattered light of illumination light. The color (R, red in the figure) that passes through the dots of the color pattern corresponding to the transparent part of the image carrier is visible, but
The color that has passed through the dots of the color pattern corresponding to the scattering portions of the image carrier is scattered again at the scattering portions of the image carrier and appears dark.

Similar visibility can be obtained with the arrangement shown in FIG.

In FIG. 5, a mirror image is formed, and in FIG. 6, a normal image is formed.

Incidentally, as a method of forming an image on the image carrier, a normal thermal printer, FAX, etc. can be used. For example, when passing an image carrier through a thermal printer having a thermal head with a density of 8 dots per millimeter to form an image, one dot out of three is continuously turned on to the thermal printer with a gap of two dots. Print a striped pattern that looks like this. This is R (red) at a pitch of 125 μm.
, G (green), and B (blue) are combined with a stripe color pattern or a mosaic color pattern formed in sequence, and if R is transmitted, the G and B lights will enter the scattering part, and the G and B will become dark and R can be clearly seen.

Note that the polymer liquid crystal shown above has sufficient heat resistance and strong film strength, so even if the polymer layer is directly rubbed and scanned with a thermal head, it is basically impossible to repeat image writing and erasing. Although there is no problem in image formation, if necessary, in order to further increase the strength, the surface may be laminated with a protective layer of polyimide, aramid, etc., or coated with fluororesin.

In addition, polymer liquid crystals have a large contrast between transparent parts and opaque parts (scattering parts), and the liquid crystal state changes quickly depending on temperature.
When this material is used as an image carrier, it is possible to form a clear image, and by shifting the alignment between the image carrier and the color pattern described above, the crosstalk prevention effect is further enhanced, and the desired excellent color can be obtained. It becomes possible to obtain contrast.

Furthermore, it is also possible to obtain gradation display by changing the strength of the voltage applied to each dot by a thermal head or the like during drawing, as well as the applied voltage pulse width.

As explained above, various display formats can be obtained by using the difference between the transparent part and the scattering part. Therefore, if various color images corresponding to the desired colors are recorded on the image carrier using a thermal head or laser heat, etc., as the difference between the transparent part and the scattering part whose colors are changed in position, this can be done. By combining this with a color pattern, it is possible to form a clear, full-color image.

Furthermore, as shown in the display mode above, a wide latitude can prevent the color to be hidden (the color corresponding to the scattering part) from being transmitted as leakage light with respect to the incident light, resulting in color crosstalk. It is possible to prevent this.

(Example〕 Example 1 Hereinafter, the present invention will be explained in further detail along with Examples.

FIG. 7 is a block diagram of a display device for implementing the color image display method according to the present invention. The display device includes a recording section consisting of a thermal head 11, a scattering plate image carrier belt, a color filter (color pattern), a Fresnel lens, a display section 1 side heater consisting of a backlight, an image erasing section consisting of a temperature sensor, a roller, and an image. It is composed of a conveyance section consisting of a carrier belt.

The image carrier belt 10 has a polymer liquid crystal Glass□ liquid crystal phase □1so represented by the following structural formula on a polyethylene terephthalate transparent substrate having a thickness of 50 μm.

was dissolved in dichloroethane to make a 20% solution, applied with a wire bar, and left in an oven at 90° C. for 15 minutes to form an endless white scattering layer. The thickness of the obtained liquid crystal layer was 7 μm.

The drive roller 17 is driven by a motor (not shown), and
All other means were operated by mechanical components or electrical or electronic components (not shown).

First, when writing an image, the drive roller 17 is driven in the direction of the arrow and an image signal is output to the thermal head (multi-head) 11 using a facsimile signal from another facsimile machine.
An image-shaped transparent pattern is formed in the heated portion on the 0. Through this operation, the image-like transparent pattern for one page of A4 size is sequentially formed and then stopped at the display section 20.

Here, the dots of the thermal head have a density of 8 dots per 1 mm, and the diameter of the dots formed on the belt is 75 μm, and the pitch of the color filter is 12
Since the dot diameter was 5 μm, the dot diameter of the image was about 60% of the pitch of the color filter.

In this example, as a protective layer for the liquid crystal layer, 3.
A 5 μm aramid sheet was laminated, the average gap between the color filter and the image carrier was 10 μF, and the range of the average incident angle of light was about 10° or less.

The display uses a striped color filter,
A scattering plate was placed above it, and as a result, a beautiful color image without crosstalk was displayed on the scattering plate.

There was no change in this image even if it was left as it was for 100 days.

Next, the image is erased using a halogen lamp 14 and a roller 15.
a halogen roller 32 and a surface heater 13
After displaying a predetermined image, the driving roller 17 was again started to be driven in the direction of the arrow. At this time, the temperature of the halogen roller 32 is controlled to approximately 115° C., and the surface heater 13 is controlled to approximately 95° C. from the detection output of the temperature sensor 16. When the state of the image carrier belt 10 was observed in this way, when it passed through the halogen roller 32, almost the entire surface became transparent, and when it passed through the area heater 13, the entire surface became scattered white again. With this operation, the displayed image was completely erased, and a white scattered state was obtained again. Here, the width of the surface heater 13 used in the above-mentioned present configuration in the belt movement direction was approximately 40 ma+, and the entire surface was set to be at least 74 DEG C. or higher.

Example 2 FIG. 8 shows a projection type display device using the same components as in Example 1, and as in Example 1, a clear image without crosstalk was projected onto the screen.

Embodiment 3 FIG. 9 shows a device in which the scattering plate of Embodiment 1 is installed below the image carrier belt, that is, on the light source side. As in Embodiment 1, a clear image without crosstalk can be obtained using the color filter. displayed above.

〔Effect of the invention〕

As explained above, by making the dots forming the image smaller than the dots of the color pattern, crosstalk other than display colors can be prevented and clear desired color contrast can be obtained. Furthermore, according to this method, an image can be formed not only by direct viewing but also by projection, and a considerable latitude can be provided in positioning to form a clear image.

The method of the present invention can also be applied to a conventional sheet in which a color filter and an image carrier are integrated.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a color display unit for explaining the color image display method of the present invention, and FIG. 2 is a schematic diagram of the unit shown in FIG. 1 in which the positions of the color pattern and the image carrier are reversed. Figure 3 is a schematic diagram of the unit shown in Figure 1 that projects an image without using a scattering plate;
The figure is a schematic diagram of the unit shown in Figure 3, with the color pattern and image carrier in reversed positions, and Figure 5 is a schematic diagram of the unit shown in Figure 1, with the scattering plate located on the light source side. FIG. 6 is a schematic diagram of the unit shown in FIG. 5 in which the positions of the color pattern and the image carrier are reversed, and FIG. 7 is a configuration diagram of the color display device used in Example 1 of the present invention. FIG. 8 is a configuration diagram of a color display device used in Embodiment 2 of the present invention, and FIG. 9 is Embodiment 3 of the present invention.
FIG. 1O is a diagram showing the relationship between temperature and light transmittance in the liquid crystal according to the present invention, and FIG. 11 is a diagram showing the principle of the color display method. 10 Image forming medium 11 Thermal head 12 Color pattern (color filter) 13 Surface heater 14 Halogen lamp 15 Roller 16 Temperature sensor 17 Drive roller 18 Fresnel lens 19 Background substrate Display section Liquid crystal layer Transparent substrate Photocabra cutout Light emitting element Light receiving element Transparent Part scattering part Backlight Incident light Halogen roller Scattering plate Holding plate Lens screen Patent applicant Canon Corporation

Claims (1)

[Claims] 1. Converting a color image into positional information and forming it as a transparent-opaque pattern on an image carrier, and combining this with a color pattern to create a color image mainly based on color light transmitted through the transparent part. 1. A color image forming method for displaying an image, characterized in that each dot formed in a transparent portion of the pattern is smaller than each dot of a corresponding color pattern. 2. The method according to claim 1, wherein the image carrier is made of polymeric liquid crystal.