JPH06171226A - Method for decoloring recording of reversible thermosensible recording medium - Google Patents

Abstract

PURPOSE:To erase a recording quickly and completely by a method wherein when a colored recording which is formed on a recording layer of a reversible thermosensible recording medium is erased, after holding the recording layer which is under a colored and recorded condition at a temperature zone being higher than a high speed decoloring temperature zone once, the recording layer is held at the high speed decoloring temperature zone. CONSTITUTION:The reversible thermosensible recording medium is equipped with a recording layer containing an electron donative coloring compound and an electron acceptable compound. Then, a coloring recorded condition is formed by heat-melting, and in the meantime, the coloring recorded condition is erased by being heated to a temperature which is lower than the color-recording temperature. In this case, in order to erase a color-recording, the recording layer which is under a color-recorded condition is once held at a temperature zone which is higher than a high speed decoloring temperature zone first, and then, the recording layer is held at the high speed decoloring temperature zone. For this reason, e.g. a heating roll 1 and pressing roll 2 are arranged to a reversible thermosensible recording medium 3, and at the same time, a two-step heating record-erasing is performed by changing a nip width (d) of these rolls to adjust the heating time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording method utilizing a color reaction between an electron-donating color-forming compound and an electron-accepting compound.

[0002]

2. Description of the Related Art Conventionally, heat-sensitive recording utilizing a color-forming reaction between an electron-donating color-forming compound (hereinafter also referred to as a color-developing agent) and an electron-accepting compound (hereinafter also referred to as a color-developing agent). The medium is widely known, and the output of electronic calculators, facsimiles, vending machines, printers of scientific measuring machines, C
Widely used in RT medical measurement printers. However, all of the conventional products are irreversible in color development, and it is not possible to alternately repeat color development and color erasing.

On the other hand, according to the patent publication, a reversible color developing and decoloring method is also proposed. For example, a combination of gallic acid and phloroglucinol is used as a color developer. No. 193,691; JP-A-61-237684, in which a compound such as phenolphthalein or thymolphthalein is used as a developer, and a recording layer contains a homogenous solution of a color former, a developer and a carboxylic acid ester. JP 62-138556 A, JP 62-13
No. 8568 and JP-A-62-140881, JP-A-2-188294 in which a salt of gallic acid and a higher aliphatic amine is used as a color developer, and bis (hydroxyphenyl) acetic acid or butyric acid and a higher color are used as color developers. JP-A-2-188293, which uses a salt with an aliphatic amine, is disclosed. However, various problems remain in the conventional reversible thermosensitive recording medium described above, and it is not yet satisfactory.

The applicant of the present invention previously used a compound such as an organic phosphoric acid having a long-chain aliphatic group, a carboxyl compound, a phenol compound, or a hydroxyphosphonic acid as a color developer, and used it as a fluoran compound or the like as a color developing agent. By combining them, the coloring and decoloring can be easily performed only by heating, and the coloring and decoloring states can be maintained at room temperature, and the decoloring temperature is lower than the coloring temperature. In addition, a reversible thermochromic composition capable of repeatedly forming and erasing an image by changing temperature, and a reversible thermosensitive recording medium containing the same in a recording layer have been proposed (Japanese Patent Application No. 3- 355078). This reversible thermosensitive recording medium does not cause a problem such as a decrease in color density even when it is repeatedly used many times, and it can be used many times which is unthinkable from the prior art. However, there are some problems in the recording and erasing of the recording medium, and it is often found that if the erasing conditions such as the erasing temperature are not proper, sufficient erasing of the recording cannot be performed even if the erasing time is lengthened. It was In this case, the defective erasing is not such that it is difficult to read a new print,
Although it is a slight colorless decoloring defect, it is a serious problem from the viewpoint of maintaining confidentiality and is not preferable from the viewpoint of sharpness.

[0005]

DISCLOSURE OF THE INVENTION According to the present invention, when erasing the record of the reversible thermosensitive recording medium in the color-developed / recorded state, the color is sufficiently erased so as not to cause any problem from the viewpoint of keeping confidentiality. It is an object of the present invention to provide a recording / erasing method by which a recording medium can be obtained.

[0006]

The inventors of the present invention have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, a reversible recording layer containing a color former and a color developer, which forms a color recording state by heating and melting, and forms a decolored state in which recording disappears when heated below the color recording temperature. In a method for erasing a color-developed recording formed on a thermal recording medium, the recording layer in the color-recorded recording state is maintained in a temperature range just higher than the high-speed decolorized temperature range, and then the high-speed decolorized temperature range is maintained. A method for erasing a record of a reversible thermosensitive recording medium, characterized in that

The reversible thermosensitive recording medium used in the present invention instantly develops color upon heating, and the color development state thereof is stable even at room temperature. However, the recording layer in the color development state is decolored by heating below the color development temperature, The decolored state is stable even at room temperature. The principle of coloring and erasing of the reversible thermosensitive recording medium used in the present invention, that is, the principle of image formation and image erasure will be described with reference to the graph shown in FIG. The vertical axis of the graph represents the color density, the horizontal axis represents the temperature, and the solid line 1
Shows the image forming process by heating, and the broken line 3 shows the image erasing process by heating. A is the density in the completely erased state, B is the density in the saturated coloring state when heated to a temperature of T ₁ or higher, and C is T _{0 in the} saturated coloring state.
It is the density at the following temperatures, and D shows the density when the material is erased by heating at the temperature between T _{0 and} T ₁ .

The reversible thermosensitive recording medium of the present invention is in a colorless state (A) at a temperature of T ₀ or lower. To record
It may be heated to a temperature of T ₁ or higher with a thermal head or the like,
Color development (B) is performed to form a recorded image. Even if the recorded image is returned to the temperature of T ₀ or less according to the solid line 2, the state (C) is maintained as it is, and the recording memory property is not lost. Next, in order to erase the recorded image, the formed recorded image may be heated to a temperature between T _{0 and} T _{1, which} is lower than the coloring temperature, and the state becomes colorless (D). This state is maintained as it is even if the temperature is returned to T ₀ or lower (A). That is, the process of forming the recorded image reaches C by the path of the solid line ABC and the recording is held. During the process of erasing the recorded image, the erased state is maintained up to A by the path of the broken line CDA. The behavioral characteristics of formation and erasure of the recorded image are reversible and can be repeated many times.

FIG. 2 is an explanatory view showing an example of image formation and image erasure. S is a support and L is a reversible thermosensitive recording layer. The image forming steps (A) → (B) are achieved by recording and printing at a temperature of T ₁ or higher in FIG. 1 by an image forming heat source, for example, a thermal head H. Next, the image erasing step (B) → (A) is achieved by heating the image erasing heat source, for example, a heating roll R to a temperature between T _{0 and} T ₁ . In FIG. 2, P indicates a color image. The reversible thermosensitive recording medium of the present invention contains a color former and a developer as essential components. Then, the color development of the reversible thermosensitive recording medium of the present invention, a color former composition formed by the eutectic reaction of the developer and the color developer constituting the reversible thermosensitive recording layer by heating,
It is obtained by cooling to room temperature. Since this color-forming material composition has a decoloring temperature region on the lower temperature side than the melting temperature, it is generally preferable to perform rapid cooling in order to cool from the melt-colored state to room temperature while maintaining the color development. When gradually cooled, some color disappears when passing through the color-erasing temperature range, and the density often decreases.

It is considered that in the color former composition, the molecules of the color former and the developer interact with each other to open the lactone ring of the color former to develop a color. The composition rapidly cooled from the molten state contains color former molecules and color developer molecules that are not directly involved in the formation of the color former. In the reversible thermosensitive recording medium of the present invention, the color former composition at room temperature is in a solidified state due to the cohesive force between these molecules. Further, although the aggregate structure of the color former composition shows some regularity, it may be very regular or not very regular. This depends on the combination of the color developer and the color developer, the amount ratio, and the cooling conditions. The main reason for forming such an aggregate structure is
There is some binding force between the alkyl chain structure part of the developer molecule forming the color former and the excess alkyl chain structure part of the developer molecule not forming the color former. It is estimated to be. The formation of such an aggregated structure is related to the decoloring phenomenon of the color former composition.

The color-forming material composition can be decolored by heating its color-developed state to a specific temperature range.
In this decoloring process, the aggregate structure of the color-developing state changes, and finally the developer molecules are separated and crystallized from the color-forming composition to form crystals of the developer alone, resulting in a stable decolorized state. Is confirmed by X-ray. As described above, in the reversible thermosensitive recording medium of the present invention, it is clear that the alkyl chain portion of the color developer plays a large role in the formation of the color-developed state and the decoloring process thereof. This is a characteristic of the color former composition formed on the thermosensitive recording medium. Therefore, the decoloring temperature can be controlled by the length of the alkyl chain portion of the color developing agent, and the longer the chain length, the more often the coloring and decoloring temperatures shift to the high temperature side. This is because the aggregation and motility of the developer molecules change depending on the length of the portion.

The reversible thermochromic composition formed in the recording layer of the recording medium used in the present invention is basically a composition obtained by combining the color developer and the color developer having an alkyl chain structure portion. There are preferred color formers for each individual developer. The combination of the color-developing agent and the color-developing agent used in the reversible thermochromic composition is a color-developing state composition obtained by heating both of them to a melting temperature or higher, and decoloring that occurs when the composition is heated to a temperature lower than the melting temperature. It is appropriately selected depending on the ease of decolorization (erasability) and the characteristics such as the color tone of the coloring state. Among these, the decoloring property is the differential thermal analysis (DT) of the color-developed state composition obtained by the combination.
A) or the presence or absence of an exothermic peak appearing in the temperature rising process in differential scanning calorimetry (DSC). This exothermic peak corresponds to the decoloring phenomenon that characterizes the composition, and serves as a criterion for selecting a combination having a good decoloring property. In the reversible thermosensitive recording medium used in the present invention, the third substance may be present in the reversible thermosensitive recording layer, for example, the reversible decoloring / coloring behavior should be maintained even if a polymer compound is present. You can

In the reversible thermosensitive recording medium used in the present invention, the color developing agent used in combination with the color developing agent basically has a structure showing a color developing ability capable of developing the color developing agent in the molecule and a molecule. It is a compound that also has an alkyl chain structure part that controls the cohesive force between the compounds, and is an organic phosphoric acid compound, an aliphatic carboxylic acid compound, or a phenol compound having an aliphatic group having 12 or more carbon atoms, or an aliphatic compound having 10 to 18 carbon atoms. Metal salt of mercaptoacetic acid having a group or carbon number of 5-8
It is an alkyl ester of caffeic acid having an alkyl group of. The aliphatic group includes a linear or branched alkyl group and alkenyl group, and may have a substituent such as halogen, an alkoxy group and an ester group. The reversible thermochromic composition constituting the recording medium used in the present invention is basically composed of a combination of the color developer and the color developer. The color former is a colorless or light-colored dye precursor exhibiting an electron donating property, and is not particularly limited, and conventionally known triphenylmethanephthalide compounds, fluoran compounds, phenothiazine compounds, leukoauramine compounds, indolinofta. Lido compounds and the like are used. Specific examples of the color developer and the color former used in the present invention are described in Japanese Patent Application No. 3-3.
55078, Japanese Patent Application No. 4-191643 and Japanese Patent Application No. 4-2.
07604.

In the reversible thermosensitive recording medium used in the present invention, the ratio of the color former to the developer in the reversible thermosensitive recording layer needs to be appropriately selected depending on the physical properties of the compound used. The range is generally in a molar ratio of 1 to 20 for the color developer and 1 to 20 for the color developer, and preferably 2 to 10. If the amount of the developer is more than the above range, or the amount of the developer is more than the above range, the density of the color-developed state becomes low, which is a practical problem. Further, even in the above preferable range, the decoloring property changes depending on the ratio of the color developing agent and the color developing agent, and when the amount of the color developing agent is relatively large, the decoloring start temperature becomes low, and when the amount of the color developing agent is relatively small, Decolorization becomes sharp with respect to temperature. Therefore, this ratio must be appropriately selected according to the application and purpose. The reversible thermochromic composition is basically composed of the color developer and the color developer, but for the purpose of improving various properties such as decoloring property and storability,
Additives and the like having an effect of controlling crystallization of the color developer can be contained.

The reversible thermosensitive recording medium used in the present invention is one in which a recording layer containing the above-mentioned reversible thermochromic composition is provided on a support, and the basic constitution of the recording medium is the bottom layer. Is provided with a support, on which a recording layer and a protective layer are sequentially laminated. The support used here is paper, synthetic paper, plastic film, or a composite of these, as long as it can hold the recording layer. The recording layer may be in any form as long as the above-mentioned reversible thermochromic composition is present, but normally, the developer and the color former are sufficiently well dispersed in the binder resin to form the recording layer. It is good and a long-life reversible thermosensitive recording medium can be obtained by this method. The color-developing agent and the color-developing agent can be used as they are or by being encapsulated in microcapsules. Color developer,
The microencapsulation of the color former can be performed by a known method such as a coacervation method, an interfacial polymerization method, an in situ polymerization method. The developer and the color former may be used alone or in combination of two or more.

The recording layer may be formed by a known method in which a color former and a color developer are uniformly dispersed or dissolved in water or an organic solvent together with a binder resin, and this is coated on a support and dried. The main role of the binder resin in the recording layer is to prevent the reversible thermochromic composition from aggregating due to repeated coloring and decoloring, and to keep the composition uniformly dispersed. Since the composition often agglomerates when heat is applied during color development, it is preferable to use a binder resin having high heat resistance. In the reversible thermosensitive recording medium used in the present invention, if necessary, for the purpose of improving coating properties or recording properties, various additives used in ordinary thermosensitive recording paper, such as a dispersant and a surfactant, Polymeric cationic conductive agent, filler, color image stabilizer,
Antioxidants, light stabilizers, lubricants and the like can be added to the recording layer.

Since the protective layer prevents deformation and discoloration of the surface due to heat and pressure when heat is applied, installation of the protective layer is extremely effective for many uses. The protective layer also has a role of improving chemical resistance, water resistance, abrasion resistance, head matching property, and the like. Therefore, the material for forming the protective layer is preferably one that has high heat resistance and high strength.
Silicone resin, polysiloxane graft polymer, UV curable resin, electron beam curable resin and the like are used. By forming such a protective layer, heat resistance is improved, and resistance to contact with organic solvent, plasticizer, oil, sweat, water, etc. is also increased, and image formation / erasure can be repeated without problems even in a bad environment. A recording medium is obtained. Further, when a light stabilizer is contained in the protective layer, the light resistance of the image and the background is remarkably improved, and the addition of the polymeric cationic conductive agent enables antistatic property. Furthermore, it is possible to significantly reduce sticking development by adding organic or inorganic fillers and lubricants to the protective layer. As with the recording layer formation method, the protective layer component may be formed by uniformly dispersing or dissolving the components of the protective layer in water or an organic solvent, and uniformly coating and drying this on the recording layer. 0.5 to 10 μm
The degree is good.

The reversible thermosensitive recording medium used in the present invention may be provided with an undercoat layer or an intermediate layer having various functions. The undercoat layer is provided for the purpose of improving heat insulation, improving the adhesiveness between the support and the recording layer, and improving the resistance of the support to the solvent when forming the recording layer. The important role of the undercoat layer is to improve the heat insulating property, but this is to make the applied thermal energy useful for forming and erasing recording without waste. Therefore, by installing the heat insulating layer, coloring and decoloring can be performed sharply, and high-speed recording can be supported. The heat insulating undercoat layer may be formed by coating organic or inorganic fine hollow body particles on a support, and specifically, a fine hollow body having a particle size of 10 to 50 μm formed of glass, ceramics, plastic, or the like. And the binder resin may be well dispersed in a solvent, and uniformly coated and dried on the support. Instead of providing the heat insulating layer, a heat insulating support can be used to effectively utilize the applied heat energy.

For forming a recorded image, a hot pen, a thermal head, laser heating or the like is used depending on the purpose of use and is not particularly limited. Similarly, the erasing of the recorded image is not particularly limited as long as the erasing temperature condition is given, such as a heating roll or a sheet heating element. In the present invention, it is possible to form a recorded image by another thermal head set at the recording temperature while erasing the recorded image by the thermal head set at the erasing temperature. Next, a method for erasing a color image and an apparatus for implementing the same according to the present invention will be described in detail with reference to the drawings.

FIG. 3 is a diagram showing the relationship between the optical density of the recording layer after heating the recording layer having a color-developed image having an optical density of 1.8 for 1 second and the heating temperature. In this figure, the vertical axis represents the optical density of the recording layer and the horizontal axis represents the heating temperature. Figure 3
As you can see, the speed of erasing the colored image (erasing speed)
Is related to the heating temperature, and the erasing temperature range (62 to 62 in FIG.
High-speed decoloring temperature range A (85 ° C.) (70 to 70 in FIG. 3)
75 ° C.) is present. The temperature in this high speed erasing temperature range is the erasing temperature that is actually used, and this temperature range includes the temperature that gives the maximum erasing speed, and gives an erasing speed of 90% or more of the maximum erasing speed. It is defined as the temperature range. Next, the time-dependent change in the image density when the color image was held at 73 ° C., which is the maximum erasing speed, was obtained and FIG. 4 was obtained. The vertical axis of FIG. 4 represents the image density, and the horizontal axis represents the elapsed time (seconds). From FIG.
In this experiment, the optical density of the image decreases from 1.8 to 0.4 within 1 second after the start of the recording erasing operation, but thereafter, the optical density may decrease to only about 0.27 even after 20 seconds or more. I understand. This experiment was continued until the erasing time of the recording was 10 minutes or more, but the optical density of the image still decreased only to 0.24, and the background optical density of the recording medium was 0.20. In this experiment, the optical density of 0.04 is left unerased.

From the above experimental data, when the colored image of the reversible thermosensitive recording medium is erased, if it is erased in the above-mentioned high speed erasing temperature range ((A) of FIG. 3), some erasure remains. It is clear that it will occur. The present inventors have acknowledged that this phenomenon poses a problem in terms of confidentiality protection and image sharpness, and have conducted trial and error studies to solve this problem, raising the temperature to a temperature higher than the high-speed erasing temperature range. It has been found that the above problems can be solved by heating and then heating in the high speed erasing temperature range. It is considered that heating to a high temperature at the time of decoloring weakens the cohesive force of the color former composition, thereby promoting decoloring by heating in the next high speed decoloring temperature range. The relationship between the image density and the elapsed time in the method of the present invention is shown in FIG. The vertical axis and the horizontal axis of this figure are the same as those of FIG. 4, and the ranges of (B) and (C) on the horizontal axis are the high temperature holding process (5 seconds in FIG. 5) and the erasing process (2 in FIG. 5, respectively).
0 seconds). The former is the above-mentioned initial high temperature process, and the latter is the process of maintaining the temperature in the high speed erasing temperature range (73 ° C. in FIG. 5). The curve (F) in FIG. 5 shows the relationship between the image density and the elapsed time when there is no high temperature holding process (B) (comparative example), and the curves (D) and (F).
The temperature of the high temperature holding process (B) is 120 ° C and 8
This is the case at 5 ° C.

As can be seen from FIG. 5, 1
Comparing the image densities at the time of 0 second, in the case of the curve (D) in which the temperature of the high temperature holding process (B) was 120 ° C., the image density was 0.22, which was the lowest, and then the high temperature holding process was changed to 85 ° C. The curve (E) was (image density 0.24). Further, in the curve (D), the completely decolored density reaches 0.20 after 15 seconds. This result shows that the best decoloring state is obtained when the temperature is raised to the color development temperature in the initial process, and the temperature in the high temperature holding process (B) is raised only to a temperature below the color development temperature. The curved line (E) is superior to the curved line (F) without the high temperature holding process, but is inferior to the curved line (D) in terms of decoloring speed and attainable decoloring density. Further, when the temperature in the high temperature holding step (B) is set to the coloring temperature, the recording layer of the recording medium is entirely colored in this step, so that the previous image completely disappears at this point and Even if the erasing is insufficient due to an accident, there is no problem with confidentiality.

Regarding the relationship between the holding temperature in the high temperature holding process and the decoloring density and the decoloring speed, detailed experiments were tried in many experiments other than FIG. 5, but even if the temperature was kept below the coloring temperature, it was high. The difference in the erasing speed with the absence of the holding process is not so large. However, the effect of holding at the coloring temperature is extremely large, and in the method of holding at the coloring temperature for several seconds and then at the high speed erasing temperature range, complete erasing can be performed within 10 to 15 seconds after the start of erasing operation. Admitted. It was confirmed that the time required for keeping at high temperature is often 5 seconds or less in many cases, and that it is often possible to reduce the erasing time of the record sufficient for keeping confidentiality by 10 seconds or more by introducing the high temperature keeping process. . Therefore, in consideration of the fact that the above-mentioned holding at a high temperature often allows complete erasing, the two-step heat recording and erasing method of the present invention can be said to be an extremely advantageous recording and erasing method. In particular, it can be said that this is a recording / erasing method which has many advantages when it comes to practical devices that often require recording / erasing in a short time and where confidentiality is required.

The decoloring heating device used in the present invention is a heating roll, a linear heating element, a planar heating element, hot air, a constant temperature bath, a thermal head, etc., and the temperature at which the two-step heating of the present invention is possible. The heating mechanism is not particularly limited as long as the conditions are satisfied, and any heating mechanism can be used. Further, the initial stage and the latter stage of the two-stage heating may be performed by the heating element having the same structure or may be different. For example, the initial stage may be performed with a heating roll and the latter stage may be performed with a planar heating element or a linear heating element, or vice versa. An example of the heating roll used in the present invention is shown in FIG. In this figure, 1 is a heating roll, 2
Is a pressure roll, and 3 is a reversible thermosensitive recording medium in which color is developed. The heating roll 1 is a hollow roll made of aluminum having an outer diameter of 30 mm and an inner diameter of 20 mm, the surface of which is coated with a silicone rubber having a thickness of 0.1 mm, and a halogen lamp having a length of 250 mm and a length of 150 w inserted in the roll. By blinking, the roll surface is kept at a constant temperature. The pressure roll 2 is a SUS304 stainless steel roll having an outer diameter of 18 mm, and the surface thereof is covered with silicone rubber having a thickness of 4 mm. Since the pressure roller is pressed against the heating roller as described above, since the pressure roller is pressed against the heating roller, the circumferential length d of the contact portion (this is called the nip width) becomes about 9 mm.

The two-step heating and recording erasing method of the present invention can be achieved by providing two sets of heating rolls and pressure rolls as shown in FIG. 6, but the adjustment of the heating time in this case can be achieved by adjusting the nip width. It is achieved by changing d. That is, FIG.
In addition to the pair of the heating roll and the pressure roll described in 1., the pressure roll covered with hard rubber (4 in FIG. 7) is used. The contact time is 1/3 to 1 / of that in FIG.
It will be 4.5. A schematic diagram of such a two-stage heating device is shown in FIG.
Shown in. Further, the heating time can be controlled by using an endless belt, and an example thereof is shown in FIG. In FIG. 8, 1 and 1'are heating rolls, 2 and 2'are pressure rolls,
Reference numeral 5 represents a tension roll, and 6 represents an endless belt.
In addition to the above, a method in which two-stage sheet heating elements maintained at the temperatures of the high temperature holding process and the erasing process are passed through the erasing device arranged above and below (Fig. 9), heating in the high temperature holding process A wide variety of erasing methods are possible, such as a method of performing heating with a sheet heating element and performing heating in the erasing process with a heating roll (Fig. 10), and a erasing method using a constant temperature chamber type heating box (Figs. 11 and 12). However, specific examples of these will be described in Examples.

[0026]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Moreover, Examples 1 to 11 and Comparative Example 1
The reversible thermosensitive recording media used in ~ 8 were prepared as follows. The coloring density and the erasing density are R by Macbeth
It was measured with a D-914 densitometer. (Recording Layer) A 100 μm thick transparent polyester film was coated with a coating liquid prepared by pulverizing and dispersing the liquid having the following formulation for 24 hours in a ball mill, followed by drying to form a recording layer having a thickness of 10 μm. 2- ( o-chloranilino) -6-dibutylaminofluorane 14 parts by weight hexadecylphosphonic acid 42 〃 vinyl chloride-vinyl acetate copolymer resin 42 〃 (manufactured by Union Carbide Co., VYHH) methyl ethyl ketone 210 〃 toluene 210 〃

(Intermediate Layer) A liquid having the following formulation was applied onto the recording layer and dried to form an intermediate layer having a thickness of 1 μm. In addition,
The intermediate layer is intended to improve the adhesiveness of the protective layer. Ethyl cellulose (reagent) 10 parts by weight Isopropyl alcohol 45 〃 Ethyl acetate 45 〃 (Protective layer) After coating and drying the liquid of the following formulation on the above-mentioned intermediate layer, it is cured by an 80 w / cm ultraviolet lamp to 3 μm.
A reversible thermosensitive recording medium having a thick protective layer was prepared. Urethane acrylate UV curable resin butyl acetate 7
5 wt% solution (Dainippon Ink and Chemicals, Unidec C7-157) (Coloring temperature, high speed decoloring temperature range, background density and color density) Coloring temperature: about 110 ° C or higher High speed decoloring temperature range: 70 to 75 ℃ Background density: 0.2 Color density: 1.8

Example 1 and Comparative Example 1 A heating device for recording and erasing was produced by combining the same heating roll and pressure roll as the device shown in FIG. Using two sets of this device as shown in FIG. 7, the same pressure roll 4 as the device of FIG. 6 was used in the former stage except that the rubber for pressure roll coating was changed to hard rubber, and the latter was used in the device of FIG. The same pressure roll 2 as that used above was used, and the nip width d was 3 mm in the former stage and 9 mm in the latter stage. Further, the surface temperature of the heating roll 1 was controlled to 85 ° C. and that of the heating roll 1 ′ was controlled to 73 ° C. by blinking the halogen lamp. A reversible thermosensitive recording medium having a color density of 1.8 was fed into the recording / erasing apparatus at a linear velocity of 3 mm / sec. In this experiment, it took about 7 seconds for the recording medium to move from the heating roll 1 to the heating roll 1 ', and the surface temperature of the recording medium immediately before contacting the heating roll 1'was 79 ° C. Considering these,
In this embodiment, the recording medium that has developed color is held for 1 second at 85 ° C. and for 3 seconds during the erasing process. The image density of the recording medium discharged from the heating roll 1'was 0.21 and was almost completely decolored (Example 1). However, for comparison, when the surface temperature of the heating roll 1 is set to 73 ° C., which is equal to that of the heating roll 1 ′, the image density of the recording medium discharged from the heating roll 1 ′ becomes 0.28, and in this case, the background density. The color could not be erased until (0.20) (Comparative Example 1).

Example 2 and Comparative Example 2 Recording and erasing were performed by the recording and erasing device shown in FIG. 1 of FIG.
And 1'are the same heating rolls as the apparatus of FIG. Further, 2 and 2'are the same pressure rolls as in the apparatus of FIG. 5 is a tension roll, which has an outer diameter of 15 mm
This is an aluminum roll. An endless belt 6 made of polyethersulfone resin is applied between the pressure roll 2 ′ and the tension roll 5 with a tensile force of 500 gf / cm ² . Therefore, heating roll 1 and pressure roll 2
The recording medium 3 inserted between the heating roller 1 ′ and the pressure roller 2 ′ is fed into the endless belt 6 and is discharged after contacting the heating roller 1 ′. In this embodiment, the length of the color recording medium 3 in contact with the heating roll 1'is 30 mm in the circumferential direction. The moving speed of the colored recording medium 3 is 6 mm / linear speed.
When the surface temperature of the heating roll 1 is kept at 120 ° C. and that of the heating roll 1 ′ is kept at 73 ° C., the experiment is conducted until the recording medium comes into contact with the heating roll 1 until it comes into contact with the heating roll 1 ′. It took about 4 seconds, and the surface temperature of the recording medium was 113 ° C. immediately before contact with the heating roll 1 ′. therefore,
In this embodiment, the recording medium in the colored state was held for 0.5 seconds at 120 ° C. and for 5 seconds during the erasing process. When the recorded image erasing apparatus described above was used to erase the color image developed to an image density of 1.8, the image density after erasing was 0.21 and it was confirmed that the image was almost completely erased ( Example 2).
On the other hand, when the surface temperature of the heating roll 1 was set to 73 ° C., which is the same as that of the heating roll 1 ′, the decoloring density was 0.29 (Comparative Example 2).

Example 3 and Comparative Example 3 A recording and erasing experiment was conducted using the apparatus shown in FIG. Reference numerals 8 and 8'in FIG. 9 denote sheet heating elements for carrying out a high temperature holding process.
Reference numerals 9'and 9'denominate sheet heating elements for carrying out the erasing process. Also, 7
Reference numerals 1 and 72 are transport rolls for feeding the color-developed recording medium 3 to the recording / erasing apparatus, and 73 and 74 are transport rolls for removing the erased recording medium. Each of these conveying rolls is an aluminum roll having an outer diameter of 15 mm, the surface of which is coated with silicone rubber having a thickness of 0.1 mm. Sheet heating elements 8, 8 ', 9, 9'at 2 ℃ at 2
An electric heater showing a resistance value of 2.4Ω, which can be maintained at a constant temperature by voltage control. The distance between the sheet heating elements 8 and 8'and 9 and 9'are both 2 mm. Further, the length of the sheet heating elements 8 and 8'in the recording medium advancing direction is set to 20 mm, and that of the sheet heating elements 9 and 9'is set to 20 mm.
The temperature was 0 mm, and the set temperatures were 120 ° C. and 73 ° C., respectively. Using the recording / erasing apparatus described in detail above, a reversible thermosensitive recording medium having a color density of 1.8 was formed on the recording / erasing apparatus at a linear velocity of 1
When fed at 0 mm / sec, a recording medium with an image density of 0.21 and almost completely decolored was obtained (Example 3). On the other hand, when the set temperature of the sheet heating elements 8 and 8'is set to 73 ° C., which is the same as that of the sheet heating elements 9 and 9 ', the image density after discharging the recording and erasing apparatus is 0.24, which indicates complete erasing. It was not possible to obtain a reversible thermosensitive recording medium in a state (Comparative Example 3).
The color image retention time in this embodiment is 120.
2 seconds at ℃, 10 seconds for the erasing process.

Example 4 and Comparative Example 4 A recording and erasing experiment was conducted using the apparatus shown in FIG. In this figure, 8 and 8'are the same sheet heating elements as those used in the apparatus of FIG. 9, and the distance between 8 and 8'is also the same as in the case of FIG. In addition, 7 and 7'are transport rolls, which are the same products as the transport rolls used in the apparatus of FIG. In FIG. 10, 1'is a heating roll, 2'is a pressure roll, 5 is a tension roll, and 6 is an endless belt. These are the same as those used in the apparatus of FIG. The force and the contact length between the heating roller 1'and the color-developed recording medium 3 were also the same as those in the apparatus shown in FIG. The length of the sheet heating elements 8 and 8'in the recording medium advancing direction is 20 mm, the set temperature is 110 ° C, and the surface temperature of the heating roll 1'is 7 mm.
Along with 3 ℃, the feeding speed of the recording medium is 3m in linear velocity.
The time from when the recording medium 3 that has developed color comes out of the heated portion composed of 8 and 8'to when it contacts the heating roll 1'is 2 seconds. When a color-developed image with an image density of 1.8 was sent to such a recording / erasing apparatus, the image density after the recording / erasing was 0.21 (Example 4). On the other hand, when the temperature of the heating portion constituted by the planar heating elements 8 and 8'was 73 ° C., the image density after the recording and erasing was 0.24, and the unerased image was observed (Comparative Example). 4). In addition,
The holding time of the color image in this embodiment is 3.3 seconds at 110 ° C. and 10 seconds for the erasing process.

Example 5 and Comparative Example 5 A recording and erasing experiment was conducted using the apparatus shown in FIG. In this figure, 10 and 11 are box type thermostats, which are provided with heaters 13 on the upper and lower wall surfaces through which the recording medium passes, and a space between the heater and the recording medium is partitioned by a wire mesh 12 of 10 mesh. ing. Therefore, the recording medium 3 is heated in the box-shaped constant temperature bath 10 without contacting the heater 13 and then sent to the box-shaped constant temperature bath 11 and stored therein. Further, 7 and 7'in FIG. 11 are the same transport rolls as those used in the apparatus of FIG. The recording medium passage width of the box-shaped constant temperature chamber 10 is 5 mm, and the length in the recording medium traveling direction is 20 m.
m, and the set temperature was 125 ° C. Also, the box-shaped constant temperature bath 11
Then, the width of the recording medium storage part is 15 mm, and the set temperature is 75 ° C.
And Into this recording / erasing apparatus, 50 sheets of A-4 size reversible heat-sensitive recording medium colored at an image density of 1.8 at a linear velocity of 10 mm / sec were continuously fed, and the box type constant temperature bath 11 was charged with 5 sheets.
After all 0 sheets were stored and left for 10 minutes, the lid of the thermostat was opened and the decolorized recording medium was taken out. These 5
When the color densities of the zero-erased recording media were examined, the highest density was 0.21, but most of them was 0.20.
Was observed and it was confirmed that the color was completely erased (Example 5). In this case, the color-developed recording medium was held at 125 ° C. for 2 seconds and then at 75 ° C. for 10 minutes or more. On the other hand, when the set temperature of the box-type constant temperature bath 10 was set to 75 ° C., all 50 recording media showed a color density of 0.24 and the decoloring was not sufficient (Comparative Example 5).

Example 6 and Comparative Example 6 A recording and erasing experiment was conducted using the apparatus shown in FIG. In this figure, 1 and 2 are the same heating roll and pressure roll as those used in the apparatus of FIG. Further, 11 is the same storage type box type thermostat as the one used in the apparatus of FIG. The surface temperature of the heating roll 1 is 120 ° C., the temperature of the storage box type constant temperature bath 11 is 75 ° C., and the reversible thermosensitive recording medium of A-4 plate colored at an image density of 1.8 has a linear velocity of 3 mm / sec. When 50 sheets were continuously fed and a recording and erasing experiment was conducted in the same manner as in Example 5, the average density of the 50 erased recording media was 0.21 and the maximum density was 0.22. (Example 6). In this case, the color-developed recording medium was held at 120 ° C. for 1 second and then at 75 ° C. for 10 minutes or more. On the other hand, when the surface temperature of the heating roll 1 is set to 75 ° C., which is the same as the temperature of the constant temperature bath, the decolored recording medium 50
The average density of the sheets was 0.24 and the maximum density was 0.26 (Comparative Example 6).

Example 7, Comparative Example 7 A recording and erasing experiment was conducted with the apparatus shown in FIG. This apparatus uses the same planar heating elements 8 and 8'as in the apparatus of FIGS. 9 and 10 in place of the heating roll 1 and the pressure roll 2 used in FIG. Recording medium 3
For transporting the same is provided with the same transport rolls 7 and 7'used in the apparatus of FIGS. The temperature of the sheet heaters 8 and 8'is set to 125 ° C, and the storage box type constant temperature bath 11
And the image density was 1.8.
Fifty sheets of A-4 size reversible heat-sensitive recording medium that had been colored in Example 2 were continuously fed into this apparatus at a linear velocity of 10 mm / sec, and recording and erasing experiments were conducted in the same manner as in Examples 5 and 6. As a result, all the 50 recording media were erased to a density of 0.21 (Example 7). In this case, the color-developed recording medium was held at 125 ° C. for 2 seconds and then at 75 ° C. for 10 minutes or more. On the other hand, when the temperature of the sheet heaters 8 and 8 ′ is set to 75 ° C., the decolored recording medium 5
The average image density of 0 sheets was 0.24 and the maximum image density was 0.26 (Comparative Example 7).

Examples 8 to 10 and Comparative Example 8 The same reversible thermosensitive recording medium as in Examples 1 to 8 (unused product)
With a thermal head having a printing energy of 0.50 mJ / dot at 8 dots / mm, a line width of 0.25 m
m, 0.5 mm, 1.0 mm and 2.0 mm lines and a character Ricoh having the same line width were printed. The color-developed image having an image density of 1.8 thus obtained was held in a constant temperature bath kept at 120 ° C. for 5 seconds so that the whole was in a color-developed state.
It was kept for 10 minutes in a constant temperature bath at 0 ° C. to visually inspect whether or not the characters could be read. In addition, in this experiment, when heated to 73 ° C. immediately after heating to 120 ° C. (Example 8), when heated to 120 ° C. and left at room temperature for 24 hours and then heated to 73 ° C. (Example 9), 120 ° C. In addition to the case of heating to 73 ° C. after standing at room temperature for 5 days (Example 10), a method of heating to 73 ° C. for 10 minutes to erase the color (Comparative Example 8) was also tried for comparison. The results of these experiments are shown in Table 1.

[0036]

[Table 1]

Example 11 On the colored images described in Examples 8 to 10, printing with a triple width was performed using the same thermal head as that used in Examples 8 to 10. That is, line width 0.25 mm, 0.50
A line having a triple width was printed on the lines of mm, 1.0 mm, and 2.0 mm, and the Ricoh character portion was black solid printed in a quadrangle so that the character portion was covered. When the same recording and erasing method as in Examples 8 to 10 was tried on these color-developed images, lines and characters were read from the decolorized image with or without leaving time between 120 ° C. heating and 73 ° C. heating. I couldn't.

Examples 12 to 19 and Comparative Examples 9 to 16 Reversible thermosensitive recording media identical to the recording media used in Examples 1 to 11 were prepared except that the types and amounts of the color developer and color developer were changed. Then, the reversible thermosensitive recording medium is made to develop color, and then the recording medium is fed to the recording / erasing apparatus (the apparatus shown in FIG. 8) described in Example 2 at various feeding rates to erase the color. Then, the decolorization density was compared with that of the comparative example, and Table 2 was obtained.

[Table 2]

[0039]

According to the recording and erasing method of the present invention, the recording and erasing are completed and sufficient erasing is achieved by heating to a temperature higher than the high speed erasing temperature range and then heating in the high speed erasing temperature range. The heating time until the color condition is obtained is shortened. Therefore, the reversible thermosensitive recording medium targeted by the present invention can be used for copying confidential documents. In addition, when it is necessary to increase the recording / erasing speed, for example, when an image is recorded and erased at the same time by using an endless belt-shaped transparent recording medium and the image is used for projection display of news, etc. The use range of the thermal recording medium is increased as compared with the case of using the conventional recording / erasing method. The effect of using the recording / erasing method of the present invention described above can be further increased by setting the holding temperature in the initial high temperature holding process to the color recording temperature of the recording medium.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between color density and temperature of a reversible thermosensitive recording medium of the present invention, and is an explanatory view of the principle of color development and color erasing.

FIG. 2 is an explanatory diagram of an image forming process and an image erasing process.

FIG. 3 is a graph showing the relationship between the holding temperature and the image density when a color image is held in the erasing temperature range for 1 second.

FIG. 4 is a graph showing a relationship between holding time and image density when the same color image as in FIG. 3 is held at 73 ° C.

FIG. 5 shows the same color image as in FIG. 3 at 73 ° C., 85 ° C. and 1
6 is a graph showing the relationship between the holding time and the image density when the temperature is held at 73 ° C. after being held at 20 ° C. for 5 seconds.

FIG. 6 is an explanatory diagram showing the concept of recording and erasing by a heating roll.

FIG. 7 is a schematic view showing an example of a case where the two-step heating record erasing method of the present invention is performed with a two-step heating roll.

FIG. 8 is a schematic view showing a method different from that of FIG. 7 in which the two-step heating recording and erasing method of the present invention is performed with a two-step heating roll.

FIG. 9 is a schematic diagram showing an example in which the two-step heating recording and erasing method of the present invention is performed by a two-step planar heater.

FIG. 10 is a schematic diagram showing an example of the case where the heating of the first stage is performed by a sheet heater and the heating of the second stage is performed by a heating roll in the two-step heating recording / erasing method of the present invention.

FIG. 11 is a schematic view showing an example in which the two-step heating and recording erasing method of the present invention is performed in a two-stage box-type thermostatic chamber, and the latter-stage box-type thermostatic chamber also serves as a storage tank.

FIG. 12 is a schematic diagram showing an example of the two-stage heating recording method of the present invention, in which the latter heating is performed in the same box-shaped constant temperature chamber also serving as the storage tank in the case of FIG. 11, but the first heating is performed. In the case of (a), the heating roll is used, and in the case of (b), the sheet heater is used.

[Explanation of symbols]

S support 1,1 'heating roll L reversible thermosensitive recording layer 2,2' pressure roll P color development image 3 reversible thermosensitive recording medium in color recording state H thermal head 4 pressure roll R heating roll 5 tension roll 6 endless Belts 71, 72, 73, 74 Conveying rolls 8, 8 ', 9, 9'Sheet heating elements 10 Box-type thermostat 11 Storage box-type thermostat 12, 14 Wire mesh 13 Heater

Claims (2)

[Claims] 1. A recording layer containing an electron-donating color-forming compound and an electron-accepting compound is provided, and a color-recorded state is formed by heating and melting, and when the temperature is lower than the color-recording temperature, the state where the record disappears is formed. In the method for erasing the color-developed recording formed on the reversible thermosensitive recording medium, the recording layer in the color-developed recording state is maintained in a temperature range just higher than the high-speed decolorized temperature range, and then the high-speed decolorized A method for erasing a record on a reversible recording medium, which is characterized by holding in a temperature range. 2. The recording of the reversible thermosensitive recording medium according to claim 1, wherein the recording layer in the color-developed state is held in the color-developing temperature range only once and then in the high-speed decoloring temperature range. Erase method.