JPH0368919A - Color image forming medium - Google Patents

Abstract

PURPOSE:To form a satisfactory color image by allowing display image element regions having different colors to cause transition from a transparent state to a scattering state due to heat at different temps. and reducing the heat capacity of image elements in accordance with the reduction of the transition temp. CONSTITUTION:A color image forming medium 3 has a mosaic pattern dyed red R, green G and blue B and a thermal head 8 acts as a thermal signal means to the medium 3. The medium 3 is made of a heat-sensitive material reversibly brought into an optical transparent state and an optical scattering state by thermal control and having two or more display image element regions having different colors in the plane direction. The regions cause transition from a transparent state to a scattering state due to heat at different temps. and the heat capacity of image elements is reduced in accordance with the reduction of the transition temp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a color image forming medium, and more particularly to a color image forming medium using a polymeric liquid crystal whose optical or physical state changes with temperature.

[Prior Art] Traditionally, video output from a television or VTR, or output from interaction with a computer, is displayed on a display monitor such as a CRT (cathode ray tube) or TN (twisted nematic) liquid crystal display, or is displayed on a display monitor such as a WP (word processor). ), facsimiles, and other high-definition images of documents, graphics, etc. have been output and displayed on vapor as printed hard copies.

Furthermore, in recent years, displays using polymer liquid crystals have been proposed for outputting still images, for example, in Japanese Patent Laid-Open No. 10930/1983. Polymer liquid crystals can be made thinner and larger in area, and can be easily fabricated into flat displays, as well as being able to produce clear and stable memory images comparable to vapor output.

Furthermore, since the optical properties of polymer liquid crystals can be changed reversibly using heat, electric fields, etc., images can be repeatedly displayed and erased. In particular, when light scattering in the polydomain state of polymer liquid crystal is used, a display image with less viewing angle dependence can be obtained.

[Problems to be Solved by the Invention] On the other hand, as a method for displaying a color image using an image forming medium using a polymer liquid crystal, for example, a method in combination with a color filter filed by the present applicant (Japanese Patent Application No. 62-3121
No. 48), or a method of adding a coloring material to a polymeric liquid crystal and patterning it in an array or random array in the plane direction of the medium to select a color (Patent Application No. 6:1-31861)
No. 0) etc. have been proposed.

An image forming medium in which a dye for color display is added to the polymeric liquid crystal and displays a color image using light scattering is superior in viewing angle characteristics and the like as compared to one using the color filter. However, in order to form a desired color image, there are problems such as the need for precise color separation selection, and it is not sufficient to form a good color image.

It is an object of the present invention to solve the problems of the prior art and to provide a color image forming medium that can form good color images.

[Means for Solving the Problems] That is, one aspect of the present invention is to provide an image made of a heat-sensitive material that reversibly assumes a transparent-scattering optical state through thermal control and has display pixel areas of two or more different colors in the plane direction. The forming medium is characterized in that the display pixel regions of the respective colors have different transition temperatures between transparent and scattering states due to heat, and are formed so that the lower the transition temperature of the pixel, the smaller the heat capacity thereof. It is a color image forming medium.

The present invention will be explained in detail below.

FIG. 1 is a schematic diagram of the configuration of an image forming apparatus using the color image forming medium of the present invention. In the drawing, 3 is a color image forming medium, which includes red (R), green (G),
A mosaic pattern dyed blue (B) is formed. 8 is a thermal signal means for the above-mentioned medium, such as a thermal head or a laser, and 8a is a medium holding means for the above-mentioned thermal means, such as a platen or a platen roller.

The most suitable material for forming the color image forming medium is a polymer liquid crystal material exhibiting thermotropic liquid crystal properties. Specific examples of this include so-called side-chain polymer liquid crystals, which have methacrylic acid polymers, siloxane polymers, etc. as the main chain and low-molecular liquid crystals are added in pendant shapes, and are used in the fields of high-strength, high-elasticity, heat-resistant fibers and resins. Examples include main chain polymer liquid crystals such as polyester-based or polyamide-based liquid crystals. Further, as the phases that can be taken in the liquid crystal state, there are smectic, nematic, cholesteric and other phases, and discotic liquid crystal and the like can also be used. Furthermore, by introducing asymmetric carbon into the polymer liquid crystal, S
A polymer liquid crystal having a phase exhibiting "ac" and exhibiting ferroelectricity can also be preferably used.

Specific examples of polymeric liquid crystals that can be used in the color image forming medium of the present invention are illustrated below.

The present invention is not limited to these.

Note that the transition temperature Tg of the glass-liquid crystal phase shown below is generally expressed as a value measured by DSC, and refers to the inflection point of the generally-called DSC curve.
The transition temperature Ti5o of 1sotropic (Iso) refers to the peak value appearing in the DSC.

〈w　　　　18,000 (1) 1ass 75℃ One liquid crystal layer (N) 110℃ Iso.

(■〉 1ass 47°C -Liquid crystal layer (N) 77℃ -Is o.

(m) 1ass 120°C -Liquid crystal layer (N) 152°C Iso.

Also included is a polymer liquid crystal formed by copolymerizing 113 1 . As an example, the following two types of copolymer material (V) 1ass 55''C - liquid crystal layer 88°C Iso.

or The following three types of copolymer materials or Two or more side chains or main chains C,H.

(Vl) C311? X/y/Z = 3/6/1X/y/Z
=4/4/2 (IX) 98°C (X) Tg=35°C Ti5o=108°C, etc.

In addition, as solvents for coating and forming these films, in addition to dichloroethane, DMF, cyclohexane, etc., tetrahydrofuran (THF), acetone, ethanol, other polar or non-polar solvents, or mixed solvents thereof are used. The material can be 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.

These polymer liquid crystals have the characteristic of being able to maintain their structural state at temperatures below the glass transition point, so that, for example, the following recording modes are possible.

Liquid crystal phase polydomain state ←→ Isotropic phase state (light scattering state) (first non-scattering state to transparent state 8) This recording mode first records a polymer liquid crystal in a polydomain state where the liquid crystal phase consists of many domains (domains). Keep it in domain state. Next, after heating the polymer liquid crystal to a temperature that shows the equal labor phase,
By rapidly cooling the polymer liquid crystal, it is possible to maintain the polymer liquid crystal in a stable state, and recording can be performed.

The recording area can be returned to the initial polydomain state by heating the polymeric liquid crystal to a temperature close to the isolaboratory phase and then slowly cooling it. Furthermore, it is also possible to reverse each state of first non-scattering and light scattering to create a recording mode.

Next, the above-mentioned recording or scattering recovery (erasing) process will be explained in more detail using FIG.

In FIG. 3, the scattering state is as shown in the figure. When this is heated to Ti5o or higher as shown in PO in the figure using a heating means such as a thermal head or a laser, and then rapidly cooled, it is fixed in a light transmitting state similar to the equi-blade state as shown in P4 in the figure. .

On the other hand, as shown in PO in the figure, if the temperature is Ti5o or higher (after heating, the liquid crystal temperature is maintained between Tg and Ti5o, especially between ΔTx on the high temperature side for a relatively long time (one second to several seconds as one example)) As shown by PI in the figure, the scattering state returns to its original state again, and this state is stably maintained below 7 g.

Also, in the figure, P2. As shown in P3, if the ΔTx is controlled to be maintained for a relatively short period of time (for example, 10 milliseconds to several hundred milliseconds) and maintained slowly, depending on the degree of slow cooling, an intermediate transmission state or scattering state will occur. It is possible to realize various states, and it is also possible to use it as a gradation expression.

In other words, in the above example, once heated to a uniform blade state, the liquid crystal temperature, especially the time period ΔTx, is maintained depending on the
The transmittance or scattering intensity can be controlled, and the state can be stably maintained at 7 g or less.

Here, in the temperature range of the high temperature side ΔTx of the liquid crystal temperature shown above, a large change in scattering behavior occurs (because the retention time in this temperature range has a large effect that determines the resulting scattering state (or transparent state)). In the present invention, the polymer liquid crystal used in °C falls within this temperature range.
It is preferable to use a material that has a temperature of at most ±500 °C, at most ±10 °C, and when the medium is kept in this temperature range for a long time,
Even if the medium is left in the air after this, a sufficient scattering state can be obtained. On the other hand, after maintaining the recording state for -1 days, ΔTx
Even if heated to a temperature below this range, the change in state is small; the ΔTx reaches a temperature near the rise or fall of the Ti5o observation peak at a constant value of DSC1tA.

Figure 4 shows the temperature application waveform to obtain the transmittance state shown in Figure 3, and in the figure, Ti5o, ΔTx, and PO~P4 correspond to the temperature, temperature range, and corresponding process temperature shown in Figure 3, respectively. However, in PI-P4, the medium holding time within the ΔTx temperature range is controlled. With such a waveform, recording with gradation can be performed in one line signal section of the thermal means.

The polymer liquid crystal substrate that exhibits the above-mentioned scattering behavior may be non-oriented or may be subjected to extraction treatment in multiple directions using ethyl alcohol, etc., but in either case, dirt on the surface is sufficiently removed. It is preferable to form the film by coating it on a coated substrate.

As the solvent for the polymeric liquid crystal, it is possible to add a mixed solvent of a plurality of solvents, a mixture other than the polymeric liquid crystal material, a pigment material, and the like to the extent that it does not adversely affect the coating.

Next, the layer structure of the color image forming medium according to the present invention shown in FIG.
ii A dye having optical absorption at least in the visible range, such as blue (B), green (G), red (R
) dichroic or axis-free dyes or pigments mixed into polymer liquid crystals can be used to create color patterns such as color mosaics or stripes using halftone printing or other printing or coating methods. A color polymer liquid crystal layer 4 is formed.

In order to obtain a desired color, it is necessary to add yellow (for example, LSY-1 manufactured by Mitsubishi Chemical Corporation) to the various polymer liquid crystals mentioned above.
16), magenta (LSR-401), cyan (LSB-335), green (LSY-1)
16 and LSB-:l:Is), red (mixture of
LSR-405 or LSR-401 and LSY-116
It is sufficient to mix a small amount of various dyes such as (mixtures with) in a solvent. A mixture of these dyes exhibits coloring properties. The coating layer thickness of the polymeric liquid crystal is 0.5 #Lm or more, preferably 2 to 15 #Lm.

In addition, in order for the formed color polymer liquid crystal layer 4 to exhibit strong optical scattering properties at the liquid crystal temperature, the amount of the dye mixed with the polymer liquid crystal should be 10% by weight or less, preferably 5% by weight or less, and more preferably 1% by weight or less. 4% by weight, and preferably 1% by weight or less based on the solvent used.

Further, in another configuration of the color image forming medium according to the present invention, a dye, for example, blue (B),
Red (R), green (G) dichroic or axes-free dyes or pigments are mixed into polymer liquid crystals with different scattering or transparent state change temperatures, especially Ti5O, for each color. The object is formed into a color pixel pattern (PLC, PLCR, PLC, etc.) such as an array or random array color mosaic or stripe shape by halftone printing, other printing, coating methods, etc.

Specifically, a colored polymer liquid crystal film is created as follows.

First, polymer liquid crystal solids corresponding to each of R, G, and B are pulverized at a temperature below the glass transition point. As an example,
The particles are sorted according to the particle size of 20 fiLm±10 pm, and the particles corresponding to each color are mixed and coated uniformly in a layer using an electrostatic coating machine.

After this, the entire surface is the most Ti5 of the PLCs that support three colors.
It is formed into a film by baking at a high temperature of Ti5o or higher.

In this case, in the color image forming medium of the present invention, R
The Ti5o of the polymer liquid crystal corresponding to each of , G, and B is different, and an example of its design is, for example, PLC, /Tg = 60°C Ti5o = 120°C
PLCa/Tg=50℃ Ti5o=105
℃PLCG/Tg= 40℃ Ti5o= 9
0°C.

In order to realize the above design example in terms of materials, it is possible to adjust the basic material by changing the degree of polymerization of the polymer compound or the chemical structure connecting the main chain and mesogen.

Furthermore, in the color image forming medium of the present invention, Ti
The heat capacity of a pixel made of a color polymer liquid crystal with Ti5o on the low temperature side is made smaller than that of a pixel made of a color polymer liquid crystal with Ti5o on the high temperature side. By doing so, it is possible to select desired color pixels for recording when recording a color image.

That is, for a color image forming medium consisting of a mosaic pattern of the above-mentioned PLCs, PLCs, and PLCs having a smaller heat capacity than these, PL(:.

When only the PLC is changed from a scattering state to a transparent state, the temperature of the PLC can be increased most rapidly with respect to the amount of heat supplied in the negative direction. Therefore, other Pl, C,, PL
C, or PL before being heated above each Tiso.
Only C, is heated to a temperature higher than Tiso, and the above state change can be obtained, and changes in polymer liquid crystals of other colors due to crosstalk can be suppressed.

As mentioned above, specific means for reducing the heat capacity of each color pixel include fine particles with a small heat capacity (for example, ultrafine particles of silica, aluminum oxide, and titanium oxide).
By mixing such as in the pixel, it is possible to increase the thermal conductivity of the pixel and speed up the temperature rise.

[Example] Hereinafter, the present invention will be explained in more detail according to Examples.

Example 1 Table 1 shows examples of combinations of polymer liquid crystals and dyes having different state change temperatures.

The above polymer liquid crystal (■) and (LSR-405) (as red polymer liquid crystal (R)), polymer liquid crystal (IK) and (
Obtain a display medium by combining LSY-116) + (LSB-335) (as green polymer liquid crystal (G)), polymer liquid crystal (Vl) and (LSB-278) (as blue polymer liquid crystal (B)) At this time, the red polymer liquid crystal contains silica (for example,
2wt% of AERO3IL■300 or AERO3IL■380)
In addition, 0.5 wt% of the same silica was mixed into the green polymer liquid crystal (IX).

Note that the blue polymer liquid crystal (VI) did not contain the above-mentioned fine particles.

The following image formation was performed on the color image forming medium of the present invention in which a mosaic pattern was formed on these color pixels. (Refer to FIG. 5. Reference numeral 15 in FIG. 2 is a halogen lamp. 16 is a heat insulating member for slow cooling, 17 is a contact member for applying heat, and 18 is a thermal head. Note that the color image forming medium 11 is abbreviated as medium.) (a) A previous image is formed. The shaded areas have high transparency, and the dotted areas have high scattering.

(b) After heating the entire surface to a uniform temperature at a temperature T□ (>114° C.), the entire surface is gradually cooled to erase the scattered state. (In this case, a halogen lamp 15 is irradiated, and a contact member 17 made of aluminum or the like that is heated by the irradiation is brought into contact with the medium and heated. A heat insulating member 16 such as a surface heater is provided near the medium to keep the medium at a constant temperature. (C) Thermal head 1 follows the B (blue) signal.
The actual heating temperature for the medium in step 8 is THH (instantaneous temperature of the medium) 1
The applied voltage (or current) is adjusted so that the temperature is 14° C.) to apply a write scan to the medium. As a result, R, G of the heating section,
Color pixels corresponding to all B (polymer liquid crystal (■), (IK)
(VI)) is made transparent.

(d) Erasing temperature T, (98℃<T, <about 104℃(
By heating the entire surface with Tiso (approximately VI〉-10°C) and then slowly cooling it, the color pixels (polymer liquid crystals (■), (IX)) corresponding to R and G are erased to a scattering state, 8 images are formed.

(e) According to the G (green) signal, the actual heating temperature of the medium of the thermal head is THM (the instantaneous temperature of the medium is 98°C < TIIM < 109°C (114°CTi
5o (VT) (approximately -5°C)), and write scanning is applied to the medium. As a result, the G of the heating part
The color pixel (polymer liquid crystal (■)) corresponding to is made transparent. (8 images remain displayed without being affected by THM heating.) (f) Erasing temperature TL (81'C < TL < approx. 88°C
(98°(:Tis.

(IX) By heating the entire surface at about -10°C) and then slowly cooling it, the color pixel corresponding to R (polymer liquid crystal (II)) is erased to a scattering state, and the 0 image becomes the 8 image mentioned above. Additionally formed.

(g) According to the R (red) signal, the actual heating temperature of the medium of the thermal head is THL (the instantaneous temperature of the medium is 8
1'C<THL<about 93℃ (98℃Tg(IX)-
5'c)) and apply write scanning to the medium. As a result, the color pixel (polymer liquid crystal (■)) corresponding to R in the heating section is made transparent, and a color image (h) is formed.

Complaining about the image forming processes in (b) to (g) above, (
The entire surface erasing in b) may be performed when image formation is repeated.

Furthermore, the operations (a) to (g) above may be performed independently or in combination as appropriate.

For example, if you want to display B and 0 images at the same time,
(b) (c) Just perform the operations in 0). If you want to display only the G image, perform the operations in (b), (e), and (f), and if you want to display the B and R images, perform the operations in (b) and (c).
(d) Just perform the operation in (g).

According to the above embodiment, there is no need to control precise alignment between the color pixels and the writing means, and a good image can be formed relatively easily. When this was displayed in scattered colors using an apparatus as shown in FIG. 6, a good color display image was obtained.

Example 2 For the same group 1 combination as in Example 1, an average particle size of 20 mμ (7) was added to the red and green polymer liquid crystals.
2 shows waveforms of temperature application to color image forming media containing 2 wt% and 0.5 wt% of titanium oxide (AERO3IL@P25), respectively.

In FIG. 2, a represents the area covered by one line of heating scanning of the thermal signal means 8 in FIG. 1, PLCa, P
LOD, PL (: This is an initialization signal section in which all of a are made to be equal to or higher than Ti5o and are temporarily in a transparent state.Next,
The area in the figure indicates the section of the temperature application waveform shown in FIG. 4 that affects PLC:B, and determines the recording state of PLC. At this time, the PLC, , PLC, remains at the isotonic temperature, and both remain in a transparent state.

Next, at C in the figure, the waveform of FIG. 4 is similarly applied to PLO. The maximum temperature at this time is B15 in the diagram.
By setting the temperature lower than o-Δ'r+ (ΔT is the temperature range that causes a large state change for the PLC, similar to ΔT and l described above), the states of pt and ca to which signals have already been applied are almost unaffected. You can prevent it from being affected. Therefore, in this interval C, only the recording state of PLC, is determined, while PLO, remains in the transparent state.

In the next section d, the recording state of the PLCR is determined by applying the waveform of FIG. 4 to the PLC. At this time, G
By setting the recording temperature of the PLO to a temperature below 15o-ΔT2 (ΔT2 is the temperature range where the state change is large with respect to ptca as described above), there is no strong influence on the recording state of the PLCB and PLC.

The last section e is a cooling section for the thermal signal means, in which the temperature is lowered to around room temperature.

By operating as described above, if a thermal head is used as the thermal signal means, erasing of the previous image and formation of a desired color image can be performed at the same time, typically by one line signal application section of the thermal head of one line. Especially can be done.

[Effects of the Invention] As explained above, according to the color image forming medium of the present invention, it is possible to easily obtain a good color image.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the configuration of an image forming apparatus using the color image forming medium of the present invention, FIG. 2 is a graph showing the waveform of temperature applied to the color image forming medium in Example 2, and FIG. 3 is a polymer liquid crystal An explanatory diagram showing the process of recording or scattering recovery (erasing) of the layer, FIG. 4 is a graph showing the temperature application waveform to obtain the transmittance state shown in FIG. 3, and FIGS. 5(a) to (h)
) is an explanatory diagram showing an image forming method on a color image forming medium in Example 1, and FIG. 6 is a schematic configuration diagram showing a color image forming apparatus. l, 13...Transparent substrate 2...Colored polymer liquid crystal 3.11...Color image forming medium 4.12...Color polymer liquid crystal layer 5...Scattering section 6...Transparent section 7 ... Fresnel lens 8 ... Thermal signal means 8a ... Medium holding means 15 ... Halogen lamp 16 ... Heat retention member for slow cooling 17 ... Contact member 18 ... Thermal spatula

Claims (1)

[Claims] An image forming medium made of a heat-sensitive material that reversibly assumes a transparent-scattering optical state through thermal control and has display pixel areas of two or more different colors in the plane direction, and that A color image forming medium characterized in that the transition temperatures between transparent and scattering states are different from each other, and pixels having lower transition temperatures have smaller heat capacities.